RU2840987C1 - Improved plasma-induced fuming furnace - Google Patents

Abstract

FIELD: furnaces.

SUBSTANCE: group of inventions relates to the field of pyrometallurgical extraction of non-ferrous metals, such as copper, lead, tin and zinc, from primary and/or secondary raw materials by means of fuming. Furnace for fuming comprises bath furnace and is equipped with at least one plasma burner of indirect action for generation of first hot gases, at least one first submersible injector for injection thereof, at least one second submersible injector, different from said at least one first submersible injector, for injection of additional gas into furnace and at least one source of compressed gas and/or compressor for supply of additional gas in form of compressed gas into said at least one second submersible injector. Furnace also includes an afterburning zone, a cooling zone and a zone for extracting the oxidised form of said at least one evaporated metal or metal compound. Furnace is used for fuming of at least one evaporated metal or metal compound from metallurgical charge selected from copper-smelting slag and copper refining slag, as well as their combinations.

EFFECT: higher efficiency, accelerated fuming and stable operation of furnace.

59 cl, 4 tbl, 2 ex

Description

FIELD OF INVENTION

The present invention relates to the field of pyrometallurgical recovery of non-ferrous metals such as copper, lead, tin and zinc from primary and/or secondary raw materials, also known as recycled materials, or from combinations thereof. More specifically, the invention relates to the recovery of volatile metals such as zinc and lead from a molten slag bath and/or metal, using a process step commonly referred to as fuming, fuming or slag sublimation.

BACKGROUND OF THE INVENTION

The processes for the production of non-ferrous metals such as copper, nickel, lead, tin and zinc typically involve at least one and typically multiple pyrometallurgical process steps in which the metals and metal oxides are in a liquid molten state, and whereby the metal oxides can be separated by gravity as a separate lower-density liquid slag phase from the higher-density molten metallic phase. If the slag phase is poor in valuable metals, it is typically withdrawn from the process as a separate stream, and this separation can result in the production of a slag as a by-product of metallurgical production, which may also be referred to as a "final slag" or "final slag".

WO 2013/133748 A1 and US 2015/0040722 A1 disclose a two-stage smelting reduction process for producing molten iron from raw materials containing iron oxide. The raw materials are treated first in a smelting reactor and then in a smelting-reduction reactor. The atmospheres in the two reactors are kept strictly separate, so that strongly reducing conditions can be maintained in the smelting-reduction reactor to increase the reduction yield to molten iron, while more neutral conditions can be maintained in the smelting reactor so that the combustion energy from the combustion of carbonaceous substances can be better utilized. The smelting-reduction reactor is heated by means of immersion plasma generators, and the reducing atmosphere is created by adding a reducing agent such as coal or petroleum coke. The reaction produces a combustible gas mixture containing CO and/or _H2 and usually also small amounts of _CO2 and _H2O . This gas mixture, after purification from impurities, contains mainly CO and/or _H2 and is partly returned to the plasma generator heating the smelting-reduction reactor. The remainder of the gas mixture is used to heat the smelting reactor by further combustion using another submerged plasma generator and/or by feeding oxygen-containing gas and a mixture of combustible gases into a tuyere below the surface of the smelting furnace contents. Any sulphur in the iron-bearing feedstock is usually removed in the smelting reactor either in the reactor gases or as part of the matte phase. Copper present in the feedstock is usually removed as metallic and/or matte copper at the bottom of the smelting reactor. This process can have much lower _CO2 emissions than the traditional blast furnace process. WO 2013/133748 A1 and US 2015/0040722 A1 do not mention any purification or fuming of the evaporated metal or metal compound, and the equipment described is not intended for their recovery as a separate product. Thus, the furnace described is not suitable for fuming the evaporated metal or metal compound from the metallurgical charge.

US 4,601,752 discloses a less complex method for producing metals and/or obtaining slag, illustrated for the production of ferrochrome from chromite ore. Finely ground oxide ore, possibly together with slag formers, is processed in a single-chamber reactor consisting of three zones: an upper oxidation zone in which the material is preheated and possibly melted by burning carbon monoxide and hydrogen gas rising from the middle zone with an oxygen-containing gas, a middle zone consisting of a slag bath in which the preheated and possibly melted oxide material is at least partially reduced by the simultaneous introduction of carbonaceous material and/or hydrocarbon-containing material and thermal energy supplied mainly through plasma generators, and a lower zone in the lower part of the reactor into which the metal formed during the reduction process drops and from which the metal product and the by-product slag can be discharged. The oxygen-containing gas supplied to the middle zone is 99.5 wt.% pure oxygen. The oxygen addition is controlled to provide sufficient energy to preheat and melt the ore and additives added to the chamber, and this occurs in the more oxidizing atmosphere found in the middle and upper zones of the single chamber reactor. The energy supplied through the plasma generators is controlled to drive endothermic reactions between the slag and carbon in the reducing atmosphere of the lower portion of the single chamber reactor. Most of the furnace off-gas is treated to remove _H2O and _CO2 and returned to the furnace as feed gas for the plasma generator. The remainder of the off-gas is removed from the process for use as fuel. US 4,601,752 makes no mention of any purification or fuming of the vaporized metal or metal compound, and the equipment described is not intended to recover it as a separate product. The material balance in Figure 2 shows that no other gas is supplied to the furnace except plasma gas and oxygen gas. Therefore, this furnace is also not suitable for fuming the evaporated metal or joining the metal from the metallurgical charge.

WO 2016/078959 A1 describes a single-bath furnace for melting metallurgical batch and separating metals under flexible oxidation-reduction conditions. The furnace was equipped with a plasma torch with a power of 3 MW, as well as a conventional, so-called "oxygen-gas" torch with a power of 1.5 MW. This device allows for the oxidation and reduction steps to be carried out in the same furnace. This document proposes to use the oxy-gas mode for melting and/or for operating under mild reduction conditions or any oxidizing conditions in the melting furnace, and to use the plasma mode for operating under strong reduction conditions. If very high energy is required, the two heating technologies can also be operated simultaneously.

The final slags that are recovered from pyrometallurgical processes producing non-ferrous metals are usually cooled, granulated and crushed/screened, and they can be used in the production of concrete as a substitute for rocks and gravel or as aggregate in road construction. In crushed form, the slags may also be of interest for use as sand or abrasive for sandblasting.

Some of the substances that may be found in slag products known in the art are considered to be potentially hazardous to the environment. Lead in particular, but also zinc to some extent, are prominent examples of such undesirable substances. Zinc and lead are metals that may be at least partially present in forms that are leached from the slag, and their presence in significant quantities hinders many uses of the slag product, especially in more economically attractive applications, and can make the disposal of such slags difficult, since they usually must be treated as "hazardous waste". Acceptability of use in specific applications is often determined by testing the leaching behavior of the slags. In general, elements such as Pb and Zn are more prone to leaching and may cause a particular slag to fail such acceptance tests.

In addition, the applicants have found that zinc levels in slags of the order of 5% by weight or higher significantly retard the hardening of concrete and other building compositions such as cements when the slags are used in such building compositions. This effect on the rate of hardening constitutes an obstacle to the use of slags containing significant amounts of zinc as a binder and/or as a filler in concrete or cements.

For at least some of the above reasons, non-ferrous metal producers have attempted to reduce the zinc content, and also lead if present, in their slag by-products, often through a step known as "fuming".

In Michael Borell, “Slag - a resource in the sustainable society,” proceedings of the International Conference on Mining and the Environmental Metals and Energy Recovery “Securing the Future,” Sweden, 2005, pp 130-138, describes how, already since the 1960s, liquid slag from electric smelting furnaces producing copper matte can be treated with reducing gases in a slag fuming furnace, also known as a "Box Fumer", in a batch process step in which the zinc content of the copper smelting slag as well as additional zinc recycled material is reduced to 1.2 wt%. The evaporated slag is further purified in a settling furnace where the remaining droplets of copper alloy and copper sulphide are held for some time so that they separate into a heavier liquid phase before the slag is crushed, dewatered and can be sold for road construction purposes and for sandblasting. The reducing gases for the fumer are obtained by thoroughly mixing pulverised coal with the primary air fed to the furnace. The problem with this type of fuming is that the reaction of the coal with air must be limited to producing primarily carbon monoxide to maintain reducing conditions, and thus much of the heat of reaction, that is, the portion produced by the subsequent oxidation reaction of carbon monoxide to carbon dioxide, remains unavailable in the furnace core to carry out endothermic reactions such as the reduction of metal oxides such as zinc oxide to the elemental metal that can be removed from the molten bath. Another disadvantage of the box fuming system is the large volume of gases produced and exiting the furnace, which must be cooled, filtered, and treated to recover the sublimed metals and to clean them before being released to the atmosphere.

US 4,588,436 discloses a method for recovering metals from a batch of liquid slag in metallic or sulphide form by reduction with a carbonaceous reducing agent, wherein the thermal energy required to maintain the temperature and to carry out the reduction and sulphiding is provided by blowing gas preheated in a plasma generator below the surface of the slag bath. The volatile metal vapours are condensed in a condenser and recovered as liquid metal. The resulting non-volatile metals and sulphides are collected as molten droplets which are allowed to settle out of the slag. Reducing conditions must necessarily be maintained throughout the process as described, right up to the outlet after the condenser, to allow the volatile metals to condense in the condenser as a liquid metal product. The vapours from the furnace containing volatile metals also pose a significant safety risk. They are highly reactive and have a high temperature. Any air ingress, no matter how small, will result in spontaneous combustion of the vapors and possibly even an explosion.

In a paper entitled "ScanArc's Development of Plasma Based Processes for Recovery of Metals and Heat Energy from Waste and Hazardous Waste Materials" presented at the International Workshop on Plasma Technologies for Hazardous Waste Destruction, Como, Italy, September 12-15, 1992, ScanArc Plasma Technologies AB proposed an indirect immersion plasma generator for the reduction of metallurgical slags by fuming, whereby heavy metals could be reduced, metals recovered, and a vitrified non-leachable slag obtained. The plasma generator can operate with most gases at any chosen oxygen potential, generating very high useful enthalpy at relatively low gas flow rates, including lean gas mixtures, and thus offering a significant advantage in flexibility. SO presented a very similar story at the 21st McMaster Iron and Steel Symposium, "Pretreatment and Recovery of Dust, Sludge and Scale," held at McMaster University, Hamilton, Ontario, Canada, May 11-13, 1993. This technology has been commercially applied, among others, in Norway by Energy Recycling AS (ERAS) at Sink Gjenvinning AS, as evidenced by the Environmental Permit Request "Recovery of Valuable Metals from EAF Dust Using the Arc Fuming Process", submitted on 10 October 2002 and made public approximately two weeks before the public hearing on the matter held on 31 October 2002. This request also describes in great detail the process itself, the compositions of the raw materials and products, including flux components, also known as slag formers, the operating parameters and the design of the equipment.

WO 2005/031014 A1 also describes such a fuming reactor for treating zinc-containing residues using a submerged plasma lance connected to a plasma torch as a source of heat and gas. WO 2008/052661 A1 describes a method for fuming Zn using a submerged plasma torch generating an oxidizing gas mixture, in which a solid reducing agent is fed into the melt.

WO 2016/046593 A1 describes the melting and fuming of a metallurgical batch using a hot gas jet from a submerged plasma torch, whereby the resulting hot gas (more correctly "plasma") has an enthalpy of at least 200 MJ/kmol. WO 2016/156394 A1 describes a process for the fuming of zinc from a metallurgical slag using a submerged plasma torch, whereby the zinc content of the resulting slag was at most 1.00 wt.%, and the clean slag had the advantage of rapid solidification when the slag was finely ground and used as an active binder in a 50/50 mixture with sodium silicate for the manufacture of tiles.

The plasma fuming furnaces described in the above documents used exclusively plasma generators as a heat source, i.e. burners that produce heat at very high temperatures by consuming electricity, an energy source that is quite expensive in many countries.

However, the applicants have found that the gas flow that can be produced by an industrial scale plasma generator remains limited in order to maintain the electric arc in working order and stable, and also in order to keep the enthalpy content of the hot gas from the plasma generator high enough to form the desired plasma. This is explained in more detail later in this document. Thus, there is a limit to the amount of stripping gas that can be provided by the plasma generator to strip the evaporative substances from the liquid bath in the furnace. This also limits the mixing that the gas blown from the plasma generators can cause in the liquid bath contained in the furnace.

In slag fuming, strongly reducing conditions are preferred because zinc oxide and other vaporizable metals may need to be reduced to their respective elemental forms in order for the metals to become vaporizable. Strongly reducing conditions may be achieved by adding at least one reducing agent, which may be a gas, liquid, solid, or a combination thereof, preferably a solid reducing agent, preferably carbon, and may be added to the hot plasma gas that is injected into the furnace. Due to the small amount of plasma gas available per plasma generator, this method of introducing additional reducing agent remains limited, however. Additional reducing agent may then be added to the furnace by pouring preferably a solid reducing agent onto the surface of the bath through the furnace feed opening.

However, this additional method of introducing an additional reducing agent leaves much to be desired.

A gaseous reducing agent such as natural gas cannot be introduced by this method of addition through the furnace feed opening, since it will not enter the liquid bath in which it is to exert its reducing activity, because this would require the gaseous reducing agent to move against the flow of the furnace outlet gases. The injection of a liquid reducing agent such as fuel oil is also less preferable, since its evaporation causes a large volumetric expansion leading to foaming and splashing in the furnace, and some of the reducing agent may be carried away with the exhaust gases before it can perform its intended function. The choice of suitable reducing agents is therefore very limited.

The additional reducing agent, which is usually added through the feed and outlet openings at the top of the furnace, must pass downwards through the gas space at the top of the furnace before it can reach the surface of the liquid. Just before the furnace gases enter, additional air is usually introduced into the outlet duct to oxidize the vaporized elemental metals or metal compounds to the corresponding metal oxides. The oxides have much higher boiling and melting points than the corresponding metals. The resulting oxides readily appear in the flue gases as entrained dust, and as such can be recovered further downstream in the furnace off-gas handling system. Thus, during its passage through the top of the furnace, the additional reducing agent comes into contact with air, and at the high temperatures in the furnace, at least some of the reducing agent can be readily oxidized before the remainder can reach the surface of the liquid bath. The heat generated by this oxidation also does not reach the liquid bath, but remains with the off-gases. Instead of being useful, this heat becomes an additional load on the exhaust gas treatment system.

The additional reducing agent that can reach the surface of the liquid bath will not be able to perform its function properly if it is not well mixed in the liquid bath. However, the gas flow coming from the plasma generators does not cause very intensive mixing of the bath.

The additional reducing agent must also be able to move downwards through the furnace gas space against the upward flow of the stripping gas before it can reach the surface of the liquid bath. Therefore, the particle or droplet size of the solid or liquid reducing agent must be large enough to avoid excessive entrainment of particles and/or droplets by the stripping gas into the off-gas handling system. However, large particles have a limited surface area per unit mass and are therefore less reactive when mixed with the liquid bath. Most reducing agents, such as solid carbon, have a much lower density than the liquid bath in the furnace. Larger particles have a higher buoyancy and therefore have a higher tendency to float on top of the liquid bath, which further reduces the contact surface between the solid reducing agent and the liquid bath.

Therefore, this method of adding additional reducing agent suffers from a significant drawback in both efficiency and effectiveness.

Therefore, the plasma fuming processes and furnaces known in the art leave much to be desired. There remains a need for an improved plasma fuming process and apparatus that provides increased fuming speed, in particular due to greater bath agitation and/or a larger amount of fuming gas, as well as the ability to introduce additional reducing agent in a more effective and efficient manner.

The present invention aims to eliminate or at least alleviate the above-described problem and/or to provide improvements.

ESSENCE OF THE INVENTION

In accordance with the present invention, a device and a method are proposed, characterized in the attached claims.

In one embodiment, the present invention provides a single-chamber furnace or single-chamber device for fuming at least one vaporizable metal or metal compound from a metallurgical batch, comprising a tank furnace capable of containing the molten batch up to a certain level, wherein the furnace is equipped with at least one indirect plasma torch for generating first hot gases of plasma quality and at least one first submersible injector for injecting first hot gases from the plasma torch below said certain level, wherein the furnace further comprises an afterburning zone for oxidizing said at least one vaporizable metal or metal compound in the fuming gas to form an oxidized form of said at least one vaporizable metal or metal compound and an extraction zone for extracting the oxidized form of said at least one vaporizable metal or metal compound from the gas formed in the afterburning zone, wherein the furnace is characterized in that it is further equipped with at least one second submersible injector characterized in that from the first immersion injector, for injecting additional gas into the furnace below the said specified level.

In another embodiment, the present invention provides a method for fuming at least one vaporizable metal or metal compound from a metallurgical charge using a furnace or apparatus according to the present invention, comprising the steps of:

- introducing into the furnace a metallurgical charge containing the said at least one evaporated metal or metal compound, and forming a bath of molten charge to a certain level;

- fuming a quantity of at least one vaporizable metal or metal compound from a bath using hot plasma quality gases from said at least one plasma torch and at least one reducing agent, resulting in a fuming gas containing the vaporizable metal or metal compound;

- afterburning in the afterburning zone of the fuming gas to oxidize the said at least one vaporized metal or metal compound into an oxidized form of the said at least one vaporized metal or metal compound,

- removing the gas formed in the furnace from the furnace and extracting the oxidized form of the at least one evaporated metal or metal compound from the gas formed during the afterburning stage;

characterized in that during at least part of the fuming step, additional gas is injected by said at least one second injector into the bath below said defined level, thereby increasing the amount of vapor containing the evaporated metal or metal compound.

The term "metallurgical charge" in the context of the present invention represents a broad family of compositions that may occur as or part of the furnace contents or furnace charge at any time during a pyrometallurgical process step, preferably a step that is part of a non-ferrous metal production process.

Preferably, the metallurgical charge is a first slag, and the product obtained as a result of the method according to the present invention is a second slag, which has a content of said at least one vaporizable metal or metal compound reduced compared to the content of the same vaporizable metal or metal compound in the first slag.

In another embodiment, the present invention provides the use of a furnace according to the present invention for fuming at least one vaporizable metal or metal compound from a metallurgical charge.

The applicants have found that the fuming of a vaporised metal or metal compound from a metallurgical batch, in which the fuming step uses first hot plasma quality gases from a plasma torch injected into a liquid molten bath by a first immersion injector, can be significantly improved by injecting an additional amount of gas into the liquid molten bath through at least one second immersion injector.

The applicants have found that the additional gas introduced through the additional submerged injector provides an additional injection point and additional gas volume for the removal of vaporized metal or metal compound from the molten metallurgical charge. The applicants have found that with only the volume of plasma or hot gases from plasma torches available for stripping zinc from copper smelter slag, the zinc concentration in the gas bubbles that rise up through the molten slag bath can reach values of up to 40 mol%. Since at best the equilibrium of reaction (I) for the fuming of zinc can be achieved,

ZnO + C → Zn(g) + CO(g) (I)

Despite the favorable equilibrium constant that the process has at very high temperatures of hot plasma-quality gases from the plasma torch, the high level of Zn in the gas bubbles results in a significant amount of zinc oxide still remaining in the liquid bath. The applicants have found that this concentration in the gas phase can be significantly reduced by the present invention due to the additional gas supplied for stripping through the additional injector, and further due to the increased presence of reducing agent in the entire liquid bath that can thereby be achieved. Since the amount of hot gases that can be produced by the plasma torch is limited, the applicants have found that it is advantageous to inject additional gas into the liquid melt bath, and it is particularly advantageous to do so through at least one second immersion injector that is different from the first immersion injector.

Thus, another advantage of the present invention also lies in the fact that the invention provides at least one more immersion point for injecting gas into the liquid molten bath. This gives the advantage of additional mixing of the liquid molten bath in the furnace, which improves the mixing in the bath, leads to a more uniform distribution of the temperature and any reducing agent that may be introduced into the furnace, and therefore also promotes the chemical reactions, as well as obtaining a more uniform distribution of the reduced metal or metal compound formed as a result of the reaction with the reducing agent. Thus, the additional immersion point of injecting gas by means of these mechanisms also brings an improvement to the fuming operation.

Another advantage of the present invention is that it provides at least one additional means for additionally introducing reducing agent into the liquid molten bath inside the furnace. Since at least one second injector is also a submerged injector, this additional means simultaneously offers a wider choice of suitable reducing agent compared to adding a solid substance in the form of large particles and/or a liquid reducing agent through the feed and outlet openings in the upper part of the furnace. While using conventional means any coke particles entering the furnace through the feed opening should preferably have an average particle size in the range of at least 6 mm, so that most of the particles can fall into the furnace and their entrainment by gases leaving the furnace through the same opening remains limited, the second submerged injector offers a much wider choice of suitable reducing agent. The reducing agent introduced through the second immersion injector may be a gas, liquid, solid or combinations thereof, and in the solid state the reducing agent may have a much finer particle size distribution, which provides the additional advantages of a high surface/volume ratio and a higher contact area, and hence higher reactivity, when it comes into contact with the liquid molten bath inside the furnace. The immersion introduction of the reducing agent also provides for closer contact between the reducing agent and the liquid bath. This advantage applies to all aggregate states of the reducing agent, but is particularly noticeable when the reducing agent is a solid, in particular a finely divided solid.

Thus, the present invention achieves more than simply providing more stripping gas to strip the evaporated metal or metal compound from the metallurgical charge. An additional effect is additional mixing of the bath, resulting in greater homogeneity of the bath inside the furnace, and yet another additional advantage is the ability to inject more and optionally also a different and more effective reducing agent in a more efficient manner. These additional effects contribute to further improvements in fuming due to improved conditions that favor the intended chemical reactions.

DETAILED DESCRIPTION

The present invention will be further described in the form of specific embodiments and with possible reference to specific drawings, but the invention is not limited by them, but only by the claims. Any drawings described are schematic and non-limiting. In the drawings, the size of some elements may be exaggerated and not shown to scale for illustrative purposes. The dimensions and relative sizes in them do not necessarily correspond to the actual ones.

In addition, the terms "first," "second," "third," and the like in the description and claims are used to distinguish between like elements and not necessarily to describe a sequential or chronological order. These terms are interchangeable under appropriate circumstances, and embodiments of the invention may operate in other sequences than those described and/or illustrated herein.

In addition, the terms "top," "bottom," "above," "below," and the like in the description and claims are used for descriptive purposes and not necessarily to describe relative positions. These terms are interchangeable under appropriate circumstances, and the embodiments of the invention described herein may operate in orientations other than those described or illustrated herein.

The term "comprising" as used in the claims shall not be considered as being limited to the elements that are listed in context with it. It does not exclude the presence of other elements or steps. Thus, it shall be interpreted as specifying the presence of the claimed features, objects, steps or components as specified, but does not exclude the presence or addition of one or more other features, objects, steps or components, or groups thereof. Thus, the scope of the term "article comprising means A and B" cannot be limited to an object that consists exclusively of means A and B. This only means that A and B are the only elements essential to the object related to the present invention. Accordingly, the terms "comprising" and "including" also cover the more restrictive terms "consisting essentially of" and "consisting of". Therefore, by replacing the phrases “comprising” and “including” with “consisting of,” these terms form the basis of preferred but limited embodiments that are also provided as part of the content of this document with respect to the present invention.

Unless otherwise expressly stated, all ranges given herein include the end points of the stated ranges, and the contents of constituents or components of the compositions are expressed as weight percent or wt.% of each ingredient in the composition.

As used herein, the terms "weight percent", "wt%", "percent by weight", " ^ppm " (mass parts per million), " ^ppm by weight" or " ^ppm " and variations thereof refer to the concentration of a substance as the mass of that substance divided by the total mass of the composition and multiplied by 100 or 1,000,000, as the case may be, unless explicitly stated otherwise. As used herein, "percent", "%" is intended to be synonymous with "mass percent", "wt%", etc.

It should be noted that the grammatical forms of the singular used in this description and in the appended claims also include the plural, unless the context clearly indicates otherwise. Thus, for example, a reference to a composition comprising a "compound" includes a composition comprising two or more compounds. It should also be noted that the term "or" is generally used in the meaning of "and/or", unless the context clearly indicates otherwise.

Additionally, each compound used herein may be referred to interchangeably by its chemical formula, chemical name, abbreviation, etc.

Plasma is considered the fourth state of matter, completing the series formed by solid, liquid, and gas, on the high-energy side. As the temperature of a gas increases, at least some of the atoms disintegrate into ions and electrons, forming an ionized gas, which is a "plasma," but may be called hot plasma gas or, according to other sources, even just "hot gas." The ionization of the atoms may be partial or complete, so the transition from gas to plasma is fairly smooth. One of the defining characteristics of a plasma is that ionization must be maintained, which implies high temperature.

In an indirect plasma arc torch, the plasma arc is generated between two electrodes inside the torch body, through which gas flows, which is converted into plasma by the energy dissipated by the electric arc. An indirect plasma torch differs from a direct plasma torch, where the workpiece is placed in an electrically grounded metal vessel and acts as an anode, so the reacting material must be an electrically conductive material. In a direct plasma torch, the anode can also be made of carbon. However, the disadvantage of a carbon electrode is that it fixes the reducing conditions, which greatly reduces the versatility of the equipment in relation to the fuming process.

In order to produce plasma, the enthalpy content of the plasma-forming gas produced by the plasma generator must be at least 1 kWh/ ^Nm3 . Thus, the plasma-quality hot gases have an enthalpy content of at least 1 kWh/ ^Nm3 . Plasma torches known in the art can have a power of up to 5 or even 7 MW. A more typical plasma torch produces about 3 MW, which means that it cannot generate more than 3000 ^Nm3 of plasma-quality hot gases. A more typical operating mode provides plasma having an enthalpy content in the range of 3.5-5.5 kWh/ ^Nm3 , which means that a 3 MW plasma torch typically produces 600-800 ^Nm3 /hour of plasma-quality hot gases. Thus, a plasma torch with a given electrical power is not capable of producing more than the volume of hot gases of plasma quality corresponding to this power.

In the context of a plasma torch, the stated gas volumes only take into account the gas volumes that are fed to the plasma torch and are under standard/normal conditions. The volumes stated in the context of the present invention for the volumes of hot gases of plasma quality produced by the plasma generator (PG) include only the gas that has passed through the PG itself, i.e. what is called the "primary gas" or "primary gas volume". They therefore do not take into account any additional gas that may additionally be fed directly to the downstream lance, the so-called "secondary gas volumes" in the context of the present invention and which are usually mixed with the hot gases of plasma quality coming from the plasma generator and injected together with them into the bath. After this mixing, it is quite possible that the mixed gas no longer meets the criterion of "plasma quality", because the enthalpy content per unit volume may no longer correspond to the lower limit specified elsewhere in this document for such gases. All these gas volumes are expressed for "normal" conditions. Thus, they also do not take into account any change in volume that may occur as a result of changes in temperature, pressure, chemical reaction or phase change that may occur in the plasma generator or in the lance downstream of it.

A submerged injector is a connecting pipe or tuyere between the gas source and the injection point, located below the bath level or a certain liquid level in the furnace, i.e. in a submerged position or in a position intended to be submerged during operation. This ensures a more direct and intense contact between the gas and the molten mass.

Preferably, the tuyeres or injectors should be short so as to be subject to minimum wear. This also ensures low heat losses. The tuyeres may be cooled to reduce their wear in severe temperature conditions. The tuyeres may be mounted horizontally, penetrating the furnace wall below the bath level. The torches or flares, whether plasma or oxy-gas, which may feed the tuyeres are then positioned outside the furnace in a submerged (also known as "immersed") position. Preferably, when a liquid bath of metallurgical charge is present in the furnace, they are continuously supplied with gas to prevent molten matter from flowing back into the tuyeres, which would otherwise cause the tuyeres to submerge, causing serious damage to it, and possibly also damaging the torch or burner feeding the tuyeres. Alternatively, the tuyeres may be mounted at an angle, still blowing into the bath, but allowing the torches or flares to be above the bath level and outside the furnace. This arrangement results in somewhat longer tuyeres, but it can also ensure that molten material does not flow back into the burners or flares. Although it may be less advisable in larger furnaces, tuyeres can also be positioned vertically. Similarly, tuyeres for additional gas injection can be positioned, i.e. submerged and penetrating the furnace wall, perpendicular or at another angle to the furnace wall.

An indirect plasma torch is a thermogas generator that uses a plasma torch in which an electric arc is maintained between electrodes inside the torch block. Gas is introduced through an inlet into a flow chamber in which an electric arc is maintained. The gas is heated to extreme temperatures and ejected through an outlet as hot plasma-quality gases, at least partially as plasma.

Between the plasma torch and the injection point into the furnace, additional substances such as a shielding gas or a diluting gas may be added to the flow from the torch to the injection point. In the context of the present invention, the amount of hot gases generated by the plasma torch should include only the primary gas passing through the plasma generator and exclude the addition of secondary gas, such as any additional gas or other substance that may be added between the plasma torch itself and the injection point or tuyere through which the first hot gases of plasma quality are introduced into the furnace from the plasma torch.

An oxy-gas burner is a thermogas generator that mixes and burns a carbonaceous fuel and an oxygen-containing gas. In order to easily achieve the high temperatures required for proper operation of an oxy-gas burner, the oxygen-containing gas should preferably be rich in oxygen, more preferably virtually pure oxygen with low levels of inert components. This not only results in higher flame temperatures, but also reduces the amount of inert gases that enter and must be processed by the furnace exhaust gas treatment system. The mixing zone of an oxy-gas burner is located inside the burner block, and the combustion zone of an oxy-gas burner can be internal or external to the burner block.

The metallurgical charge in the context of the present invention may be any composition that can be in a liquid molten state at a stage of the pyrometallurgical process for the production of non-ferrous metal. Thus, the metallurgical charge may be, for example, a molten metal composition containing at least one non-ferrous metal, but may also be a molten slag phase formed at such a stage of the process. The metallurgical charge may be in the form of a molten liquid, but may alternatively have a solid form of any kind, for example, the charge may have the form of aggregates obtained by cooling or granulating the liquid molten phase from the furnace in which the pyrometallurgical process stage was carried out.

Metallurgical slag is usually not a pure substance but a mixture of many different components. Consequently, metallurgical slag does not have a clear melting point. In this field of technology, it has become common to use the term "liquidus temperature", which means the temperature at which the slag becomes completely liquid.

As mentioned in the section "Background of the invention", "fuming" is an operation that has already been used commercially in the field of pyrometallurgy as early as the 1960s. It is well known to those skilled in the art that certain metals or metal compounds can be vaporized from a metallurgical batch by gas stripping, also called "fuming", which can occur at near atmospheric pressure and therefore does not require a high vacuum, as in the distillation of lead from tin. This is possible because the vapor pressure of the metal or metal compound being vaporized is much higher than that of most other compounds in the batch. Therefore, such a compound is considered and referred to in the art as "fuming" from the metallurgical batch.

Well known examples are the fuming of zinc from other pyrometallurgical compositions. This fuming of zinc may even be carried out as part of another pyrometallurgical step, such as the removal of (usually part of) the zinc via the fumes formed during the copper smelting step or the copper refining step. Less commonly, fuming may be carried out as a separate process step, i.e. as the "box fumer" described by Michael Borrell or ScanArc, as discussed above. As also discussed above, when the metallurgical feedstock is a slag, zinc may be present in the feedstock primarily as its non-volatile oxide ZnO, so that fuming may need to be enabled by first reducing the oxide to the elemental metal, which can be stripped by fuming. Another example is the recovery of lead and tin in the form of their oxides by evaporation during the recovery of copper from copper-containing waste, as described in the Background section of US 3,682,623. It is also known that elements such as bismuth, indium and/or germanium are evaporable metals or have metal compounds that are evaporable in the context of the present invention. The evaporable metal compounds may be the corresponding oxides, chlorides and/or sulfides.

In this document, unless expressly stated otherwise, the amounts of metals and oxides are expressed in accordance with common practice in pyrometallurgy. The presence of each metal is usually expressed in its total presence, regardless of whether the metal is present in its elemental form (oxidation state = 0) or in any chemically combined form, usually in an oxidized form (oxidation state > 0). For metals that can be relatively easily reduced to their elemental forms and which can often occur as molten metal in a pyrometallurgical process, it is quite common to express their presence in terms of their elemental metallic form, even when the composition of a slag is given in which most of such metals may actually be present in oxidized form. Therefore, the composition of a slag, such as the slag according to the present invention, indicates the content of Fe, Zn, Pb, Cu, Sb, Bi as elemental metals. Less noble metals are more difficult to reduce under the conditions of non-ferrous metal pyrometallurgy and occur mainly in oxidized form. These metals are usually expressed as their most common oxide form. Consequently, slag compositions usually give the contents of Si, Ca, Al and Na, respectively expressed as SiO ₂ , CaO, Al ₂ O ₃ , Na ₂ O.

Since the oxygen in the slag, which is associated with the more noble metals, is not reflected in the composition, which only shows the elemental metal content, the slag composition reported according to this method often does not add up to 100 wt%.

In one embodiment of the device or furnace according to the present invention, the device is arranged to inject through said at least one second injector a total amount of additional gas that is at least 10%, preferably at least 15%, more preferably at least 20%, 25%, 30%, 35%, 40%, 45%, 50% or 55%, more preferably at least 60%, preferably at least 70%, more preferably at least 75%, 80%, 90%, 100%, 110%, 120%, 125%, 130%, 140%, 150%, 175%, 200%, 225%, and even more preferably at least 230% of the amount of hot plasma-quality gases, expressed in volume units under normal conditions, that can be generated by a single element said at least one plasma torch having the highest rated power, when this torch supplies plasma having an enthalpy content of at least 3.5 kW⋅h/ ^Nm3 . Optionally, the device is equipped to inject through said at least one second injector an amount of additional gas equal to no more than 500%, preferably no more than 450%, more preferably no more than 400%, 350%, 325%, 300%, 290%, 280%, 275%, 270%, 265%, 260%, 250%, 240%, 230%, 220%, 210%, 200%, 180%, 165%, 150%, 135%, 120%, 110%, 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30% and even more preferably no more than 20% of the volumetric value at under normal conditions, the amount of plasma that can be generated by one element of said at least one plasma torch having the highest rated power, when this torch delivers plasma having an enthalpy content of at least 3.5 kW⋅h/ ^Nm3 . The applicants have found that the main advantage of the present invention can already be achieved by injecting through the second injector an amount of additional gas flow that is closer to the said lower limit, especially when the additional gas flow is used as a carrier for the additional reducing agent, in particular when a fine powder such as coal powder or petroleum coke dust is used as the additional reducing agent. The applicants have found that the advantages of the present invention, generally explained above in the "Summary of the Invention" section, can be further enhanced by further increasing the amount of additional gas. However, applicants also prefer to comply with the specified upper limit in order to reduce the risk of splashing and foaming of the liquid bath, to reduce vibrations and other types of dynamic loading on the tuyeres as well as on the rest of the furnace structure, and to reduce the volumes of gases that need to be processed after the top of the furnace, i.e. in the afterburning zone and the extraction zone.

In the afterburning zone of the furnace or device according to the present invention, at least one vaporized metal or metal compound in the fuming gas is oxidized to form an oxidized form of said at least one vaporized metal or metal compound. The purpose of this step is to reduce the safety hazard posed by the fuming gas and to make it possible to more easily extract the metal from the fuming gas.

The fuming gas formed in the top of the furnace is a safety hazard. It is very hot. The vaporized metal or metal compound contained in this gas is usually a reduced form of the metal and thus also exhibits high reactivity when exposed to oxidizing conditions, such as when in contact with oxygen. Therefore, the fuming gas formed in the top of the furnace is a significant safety hazard. Any oxygen that enters the equipment in an uncontrolled manner and comes into contact with the fuming gas from the furnace, such as part of the ambient air that may be sucked into the top of the furnace or downstream in the exhaust gas handling section of the device, will readily react and oxidize the vaporized metal or metal compound, and this reaction is highly exothermic. Under poorly controlled conditions, i.e., with poor mixing and/or especially in relatively stagnant zones, such a combination of hot gases with oxygen can almost inevitably lead to an uncontrolled combustion and possibly even an explosion of the gas cloud.

In a steady and relatively fast flowing gas stream and with good mixing, such a combination of gas with a known supply of air or other source of gaseous oxygen is capable of creating a flame front which can be maintained in a steady and well controlled manner. Accordingly, the applicants provide as part of the present invention an afterburning zone in which hot gases from the top of the fuming furnace are controlled by suction, brought into a steady and relatively fast flow and intensively mixed with oxygen so that the conditions in the gas mixture are changed from reducing to oxidizing. The result of good mixing and high temperature is that a flame front develops and establishes itself in the gas stream withdrawn from the top of the furnace and that this flame front can be easily maintained in a steady state. The applicants prefer to provide this flame front in the space above the fuming furnace, anticipating the advantage that radiation from the established flame front can still reach the molten bath in the furnace and return some of the heat from the flame front to the molten bath.

Another result of the afterburning stage or zone is that the safety hazard posed by the hot and highly reactive gas at the top of the furnace remains limited to the volume of gas ahead of the flame front.

The oxidized form of said at least one vaporizable metal or metal compound is most often a metal oxide. Oxide forms of a metal or metal compound are typically non-volatile and typically form a dust of fine particles entrained in the gas stream, making them more easily extracted therefrom.

The furnace according to the present invention further comprises a zone for extracting the oxidized form of said at least one evaporated metal or metal compound from the gas formed in the afterburning zone. The method according to the present invention also comprises a corresponding stage for extracting the oxidized form of said at least one evaporated metal or metal compound from the gas formed in the furnace and subjected to the afterburning stage.

In one embodiment of the device or furnace according to the present invention, the device comprises a plurality of second injectors, and each injector is arranged to inject through each second injector a quantity of additional gas that is at least 10%, preferably at least 15%, more preferably at least 20%, 25%, 30%, 35%, 40%, 45% or 50%, more preferably at least 55%, preferably at least 60%, more preferably at least 65%, even more preferably at least 70%, even more preferably at least 75%, preferably at least 80% of the quantity, expressed in volume units under normal conditions, of first hot gases of plasma quality that can be generated by one element of said at least one plasma torch having the highest rated power, when this torch delivers first hot gases having an enthalpy content of at least 3.5 kW⋅h/Nm ³ . Optionally, each second injector is equipped for blowing through it a quantity of additional gas which is not more than 200%, preferably not more than 190%, more preferably not more than 180%, 170%, 160%, 150%, 140%, 130%, 125%, 120%, 115%, 110%, 105%, 100%, 95%, and even more preferably not more than 90% of the quantity, expressed in volume units under normal conditions, of hot gases of plasma quality which can be generated by one element of said at least one plasma torch having the highest rated power, when this torch supplies plasma having an enthalpy content of at least 3.5 kW⋅h/Nm ³ .

In one embodiment of the furnace or device according to the present invention, the device is connected to at least one source of compressed gas and/or is equipped with a compressor for supplying compressed gas to said at least one second injector. The applicants have found that this provides a very convenient way of supplying additional gas to the furnace. The term "compressor" can be interpreted in its very broad sense and can, for example, include a gas turbine from which combustion gases can be supplied at a pressure higher than atmospheric.

In one embodiment of the furnace or device according to the present invention, the source of supplying additional gas to the device comprises a source of gas selected from the group consisting of hydrogen, nitrogen, air, carbon dioxide, argon, neon, helium, methane, ethane, propane, butane and combinations thereof, preferably nitrogen or air, more preferably air, and even more preferably compressed air. The applicants have found that nitrogen and air, preferably compressed air, are very convenient gases as a basis for the additional gas blown into the furnace.

In one embodiment of the furnace or device according to the present invention, the device comprises means for thermally treating the additional gas before said at least one second injector to change its enthalpy content, preferably means for thermally treating the additional gas comprising at least one heat exchanger. If during operation the gas is fed into the furnace at a temperature below the temperature of the liquid bath inside the furnace, then the applicants prefer to heat the gas before it is introduced by said at least one second injector. This reduces the cooling effect that the injection of additional gas may have on the furnace and simplifies the maintenance of a thermal balance throughout the furnace. Preferably, such heating at least partially uses the heat available in the furnace exhaust gas treatment system.

In one embodiment of the furnace or device according to the present invention, the device is further equipped with means for introducing a reducing agent into the additional gas before said at least one second injector. As explained above in the section "Summary of the invention", blowing additional gas into the furnace through said at least one second injector represents an additional entry point for adding reducing agent to the furnace. In addition, since said at least one second injector is submersible, the choice of a suitable reducing agent is very wide.

In one embodiment of the furnace or device according to the present invention, the introduced reducing agent can be selected from a gas, a liquid, a solid and combinations thereof. The applicants have found that the injection of additional gas according to the present invention is a suitable carrier for a wide range of reducing agents in terms of the volume or weight of the reducing agent, which can be conveniently introduced not only if the reducing agent is a gas or liquid, but also if the reducing agent is a solid. In addition, the solid reducing agent can have a very fine particle size distribution, offering a high surface to mass ratio and, therefore, high reactivity to participate in the target chemical reactions.

In one embodiment of the furnace or device according to the invention, the device comprises means for controlling the lambda of the additional gas injected into the bath by the second injector. Lambda ("λ") is a very convenient parameter that is commonly used in relation to burners and combustible fuels, in particular in the case of internal combustion engines, and which is a ratio in the numerator of which is the actual ratio of air and fuel, and in the denominator - their stoichiometric ratio. If the air-fuel mixture corresponds to the stoichiometry for complete combustion, then its lambda is equal to 1.0. The applicants apply this lambda parameter to each gaseous mixture in which oxygen is present, as well as another substance that can easily react with oxygen, such as a combustible substance, wherein this other substance can be a gas, a liquid, a solid, or a combination thereof. The applicants have found that the regulation of the lambda of the additional gas, which is injected through the at least one second injector, is a very convenient means for controlling the atmosphere in the furnace, thereby establishing whether the atmosphere is neutral, oxidizing or reducing, as well as establishing the degree of oxidation or reduction. The applicants have found that the additional point of addition of the reducing agent in the device according to the present invention is very versatile, and the control of the lambda parameter in the injected additional gas provides a very convenient way of controlling the oxidation-reduction conditions inside the furnace, and therefore controlling the chemical reactions occurring inside the furnace. The applicants have found that the combination of injecting additional gas with injecting hot gases from the plasma generator(s) makes it possible to provide a wide range of oxidation-reduction conditions, wherein the oxidation-reduction conditions can be established practically independently of the heat input to the furnace, in contrast to more traditional heating means, such as the use of burners operating on natural gas.

In one embodiment of the furnace or device according to the present invention, the device is equipped for injecting oxygen and gaseous or liquid fuel as part of the additional gas, and for providing a higher velocity of the additional gas in said at least one second injector or in another place before it than the flame propagation velocity of the fuel as part of the additional gas. The applicants have found that an additional heat supply to the furnace can be provided by injecting gaseous or liquid fuel as part of the additional gas, preferably when the additional gas also additionally contains oxygen, even in the case when the additional gas has not been heated or ignited, and therefore the fuel and oxygen have not reacted before they reach the liquid bath. Typically, the temperature of the liquid bath inside the furnace is significantly higher than the temperature at which the fuel and oxygen in the additional gas begin to react, even without an ignition source, and they can easily react after they have been introduced into the liquid bath. The applicants prefer this embodiment, since they have found that otherwise such a reaction may go against the direction of flow of the additional gas in the gas ducts before said at least one second injector, as well as in the second injector itself. Such a "flame back" phenomenon may lead to the release of heat in this gas duct or injector and, thus, to an increase in temperature and, consequently, to wear and rupture, or even to an explosion of the additional gas upstream of and/or inside the injector. The applicants have found that the risk of damage to equipment as a result of such heating inside or before the injector may be reduced if the device is equipped to allow the additional gas in the second injector or elsewhere before it to achieve a higher speed than the flame propagation speed in the additional gas. A further advantage is that the additional gases are injected at a lower temperature, which further reduces the wear and rupture of the second injector.

In one embodiment of the furnace or device according to the present invention, the device is equipped to limit the amount of fuel injected in such a way that the combustion of the injected fuel under the assumed operating conditions of the furnace leads to such an increase in the enthalpy of the additional gas that the additional gas at the point of injection into the bath is at a temperature not exceeding the temperature of the molten charge assumed to be in the furnace during operation. This also contributes to less wear and tear of the second injector.

In one embodiment of the furnace or device according to the present invention, said at least one second injector directs its additional gas into a second volume as a part of the interior of the furnace below a predetermined (specified) level, which is different from the first volume into which said at least one first injector directs its first hot gases. The applicants have found that this feature enhances the advantages associated with the present invention and explained above in the section "Summary of the invention", i.e. improved mixing of the bath, a more uniform composition of the liquid bath, improved chemical reactions and, of course, improved stripping of the evaporated metal or metal compound from the liquid bath.

In one embodiment of the furnace or device according to the present invention, said at least one first injector is arranged in a side wall of the furnace, wherein said at least one second injector is arranged in the wall of the furnace opposite said at least one first injector, preferably along the horizontal perimeter of the furnace, passing at substantially the same height as said at least one first injector. The applicants have found that such an arrangement is very convenient and effective for obtaining the desired effects of the present invention, explained above in the section "Summary of the invention". Said at least one first injector can inject its additional gas in a direction approximately perpendicular to the side wall of the furnace. The applicants, however, prefer to inject the additional gas at an angle to the horizontal plane, either downwards or upwards, because the additional gas gives an additional stimulus for vertical circulation in the liquid bath, which improves the mixing of the bath, and also draws more reducing agent into the volume of the liquid bath, which can float on top of the liquid bath. The applicants prefer the upward direction because it may be better for creating a torus-shaped circulation path in the liquid bath.

In one embodiment of the furnace or device according to the present invention, the device comprises at least two, and preferably at least three first injectors distributed along the horizontal perimeter of the side wall of the furnace, wherein said at least one second submersible injector directs its additional gas to that part of the internal volume of the furnace below a predetermined level, which is close to the vertical axis of the furnace, and/or said at least one second submersible injector is located along the side wall of the furnace at an approximately equal distance between the positions of the two closest of these at least two first injectors. In the embodiment with said at least one second submersible injector located along the side wall of the furnace, said at least one second injector preferably directs its blown additional gas to that part of the internal volume of the furnace below a predetermined level, which is different from the volumes to which the first injectors direct their first hot gases. The applicants have found that this enhances the beneficial effects achieved by the present invention and described in detail above in the Summary of the Invention section.

In one embodiment of the furnace or device according to the present invention, the device is additionally equipped for introducing a reducing agent into the first hot gases before said at least one first injector. This has the advantage that an even larger amount of reducing agent can be introduced into the furnace compared to the amount that can be introduced in other ways, for example together with an additional gas and/or through an inlet. The amount of additional reducing agent that can be introduced through said at least one first injector is independent of the enthalpy supplied to the furnace. Thus, this method of introducing the reducing agent is very convenient for controlling the oxidation-reduction properties of the atmosphere in the furnace. An additional advantage is that the reducing agent introduced through the first injector is introduced together with the enthalpy of the highest temperature introduced into the furnace. At a higher temperature, the equilibrium constant of the desired reaction (I) of zinc fuming promotes the formation of metallic zinc, which is an evaporating substance. Thus, the efficiency of the reducing agent introduced with the first hot gases is higher, and since this injection is also carried out through an immersion injector, it is also highly efficient due to the very close contact of the first hot gases with the liquid in the liquid bath, which means that a small amount of this reducing agent can reach the surface of the liquid bath without coming into contact with the liquid from the bath.

In one embodiment of the furnace or device according to the present invention, the reducing agent introduced before said at least one first injector may be selected from a gas, a liquid, a solid and combinations thereof. The applicants have found that the supply of the first hot gases from the plasma torch through the first injector provides a very versatile option for introducing an additional reducing agent, since it is very tolerant with respect to the choice of reducing agent, in particular with respect to its aggregate state, as well as with respect to the amount that can be introduced.

In one embodiment of the furnace or device according to the present invention, the device is additionally equipped with at least one oxygen-gas torch for generating additional first hot gases in addition to the amount of first hot gases of plasma quality from said at least one plasma torch. This provides the advantage that an additional enthalpy input can be provided to the furnace compared to the enthalpy input provided by the plasma generators. This can facilitate maintaining an advantageous heat balance in the entire furnace, in the entire device and in the entire process.

In one embodiment of the furnace or device according to the invention, the device is equipped with at least one third submersible injector for injecting additional first hot gases below a certain level. This gives the advantage of a very close contact between the additional first hot gases and the liquid bath, which is favorable for heat transfer from the additional first hot gases to the liquid bath inside the furnace. This makes the heat transfer very efficient.

In one embodiment of a furnace or device according to the present invention, comprising at least one oxygen-gas burner, the at least one oxygen-gas burner is located below a certain level.

In one embodiment of the apparatus according to the present invention, the plasma torch is located below a certain level.

The indications of the location of the hot gas and/or plasma generator below a certain level allow the use of very short connecting pipes, while the hot gas or plasma generator can be located at the injection point level, on the outside of the furnace. However, measures must be taken to avoid flooding the generator with molten mass inside the furnace. Therefore, a continuous flow of protective gas through the injector can be used.

In one embodiment of the furnace or device according to the invention, the afterburning zone is provided above said certain level as part of a single-chamber furnace. Preferably, the afterburning zone is provided above the molten bath due to the radiation heat that can return from the afterburning zone to the molten bath in the furnace. As explained elsewhere in this document, oxidizing conditions are established in the afterburning zone in order to oxidize the vaporized metal or metal compound to the corresponding oxidized form. One of the main effects achieved by the complete oxidation conversion of the reduced form formed in the fuming step is that the gas containing the oxidized form is no longer flammable, and therefore the safety hazard posed by the gas from the fuming step is present and removed after the afterburning zone or stage. A secondary purpose of the afterburning stage is also to oxidize most of the carbon monoxide that may have been formed during the fuming stage by reacting the carbon in the reducing agent, for example with oxygen available in the slag as a metal oxide, to carbon dioxide, and/or oxidizing hydrogen to water. This further reduces the safety hazard and also makes further treatment of the furnace off-gases, including any possible release to the atmosphere, simpler, safer and more environmentally acceptable.

Preferably, the applicants carry out the afterburning by introducing an oxidizer into the fuming gas, wherein the oxidizer is preferably oxygen.

In one embodiment of the furnace or device according to the present invention, the afterburning zone comprises a connection to a supply source of oxygen-containing gas, preferably selected from air, oxygen-enriched air and purified oxygen gas. Applicants prefer to use air due to its availability. Preferably, applicants introduce oxygen by blowing the oxygen-containing gas into the fuming gas stream leaving the top of the furnace. Typically, the fuming gas leaving the top of the furnace is at a pressure below atmospheric pressure due to the draft that is created by the subsequent treatment of the exhaust gases, which typically includes at least a stack and, optionally, an exhaust fan in front of the stack. Thus, the oxygen-containing gas can be supplied at atmospheric pressure. Applicants prefer to supply the oxygen-containing gas at a pressure above atmospheric pressure, since this provides a higher pressure difference between the source of oxygen-containing gas and the fuming gas supplied to the equipment for treating the exhaust gases from the furnace due to natural or artificial draft. The advantage of a higher pressure difference is that the flow of oxygen-containing gas into the fuming gas can be controlled more precisely.

In a simpler embodiment, the applicants provide at least one opening to the atmosphere in the duct connecting the furnace to the subsequent exhaust gas treatment equipment, through which air from the environment can be sucked. Preferably, the size of the opening in the duct is controllable. A plurality of openings can be provided, which provides the advantage of faster and better mixing of the oxygen-containing gas with the fuming gas.

The applicants have found that a stable flame front can be formed in the afterburning zone in which oxidation reactions occur. The applicants have found that the flame front becomes more stable as the fuming gas is made to move faster and as mixing with the oxygen-containing gas occurs faster and/or more intensely.

Applicants prefer to feed a significant excess of oxidizer to the afterburning zone or stage so that the oxidation reactions in the afterburning zone are virtually complete. This ensures that the safety hazard is completely contained in and before the afterburning zone or stage. It also ensures that the final exhaust gas is virtually free of carbon monoxide, which is a toxic gas, and hydrogen.

In one embodiment of the furnace or device according to the present invention, the device further comprises a cooling zone for cooling the gas that is formed or was formed in the afterburning zone before the extraction zone. The cooling can be carried out in various suitable ways.

One suitable method is to provide a so-called waste heat boiler, i.e. a heat exchanger in which the heat of the gas from the afterburning stage is used to produce steam. The advantage is that the heat is used to produce steam, and this steam can be used elsewhere to produce electricity or heat, where it can be used. Thus, the high capital costs of the waste heat boiler compared to other alternatives can be offset by the cost of the steam produced. However, a steam consumer of a suitable size is not always available in the vicinity of the furnace according to the invention.

Another suitable cooling method is to use a radiant water cooler, in which the water on the coolant side is circulated quickly enough to avoid the formation of steam, so that only hot water is produced. Preferably, the water is returned to the radiant water cooler after most of the heat has been removed from it. This hot water can also advantageously be used economically in a heating system, for example for heating a plurality of residential buildings, and more preferably it is reused after it has been used for heating. In addition to this and/or as an alternative, the hot water can be cooled in a conventional cooling tower. The amount of water evaporated in the cooling tower must be replenished before the remaining water is returned to the radiant water cooler. Since salts accumulate in such a water cycle, water must be withdrawn, and the amount of water withdrawn must also be replenished. The radiant water cooler also has the advantage that it does not change the amount of gas that must be processed further downstream on the gas side of the cooling stage. Another advantage of the radiant water cooler is that this cooling stage can be combined with the afterburning zone, which means that the afterburning stage can be performed inside the radiant water cooler. This embodiment provides a further simplification of the equipment and therefore a reduction in capital costs.

Another cooling method is spray cooling or "evaporative cooling". This method involves injecting water into the hot gas stream, with the injected water taking its heat of evaporation from the gas stream. This method is very efficient and fast, requiring little equipment and therefore low capital costs. The disadvantage is that this method increases the volume of gas that must be processed after the cooling stage.

Another suitable method is to use a gas/gas heat exchanger with the gas from the afterburning stage on one side and, for example, ambient air on the other side of the heat exchanger. This has the advantage of being compact in volume and does not increase the gas flow that needs to be processed after the cooling stage.

The preferred cooling step may comprise a number of similar or different cooling methods selected from those listed above. A suitable combination may be, for example, to provide on the hot inlet side first a radiation water cooler to bring the temperature of the gas from the afterburning step, for example, from about 1500°C to about 1000°C, followed by a spray cooler to further reduce the gas temperature to about 200°C, which may be low enough for the equipment used in the subsequent extraction zone.

In one embodiment of the furnace or device according to the present invention, the extraction zone comprises a gas filtration zone, preferably comprising at least one gas filter fabric. Applicants prefer to use filter bags made of polytetrafluoroethylene (PTFE) fabric, since they are capable of withstanding processing temperatures of up to about 260°C.

Typically the last piece of equipment in the gas handling sequence is a blower or fan to push the gas from the extraction zone into the stack and to increase the upstream draft by sucking the gas through a sequence of post-combustion, optional cooling and extraction zones. The use of a blower or fan has the advantage that the natural draft requirements of the stack are reduced so that the stack can be built less high.

In one embodiment of the furnace or device according to the present invention, the furnace has a generally cylindrical shape, and preferably also has a conical lower section tapering to a smaller circular bottom, wherein the cylindrical shape of the furnace has a largest internal diameter d and a total internal height h from the bottom to the top, wherein the ratio of h to d is at least 0.75, preferably at least 0.80, more preferably at least 0.85, even more preferably at least 0.90, even more preferably at least 0.95, preferably at least 1.00, more preferably at least 1.05, even more preferably at least 1.10, even more preferably at least 1.15, preferably at least 1.20, more preferably at least 1.25, and even more preferably at least 1.30. In the context of the present invention, the internal diameter of the furnace is the distance between two opposite surfaces of the furnace wall and, if there is a refractory lining, the surfaces of the refractory lining in the furnace during construction. The internal diameter is considered to be such as to exclude the possible accumulation of solidified slag on these surfaces, a layer that can be called a "scum". The applicants have found that this feature gives the advantage of less splashing of molten material in the furnace bath during operation. Such splashing molten material can solidify on any hard and colder surface, such as the furnace inlet and/or the furnace outlet pipe, where this can cause problems due to its high temperature and where such growth of material can cause other operational problems, such as deterioration of gas flow and/or feed input capabilities.

In one embodiment of the furnace or device according to the present invention, the furnace comprises a conical lower section, wherein the determined level is approximately at the height at which the cylindrical shape passes into the conical lower section. The applicants have found that the conical lower section provides a very convenient installation in which most of the immersion injectors and preferably also the corresponding power supplies for these immersion injectors can be located with the possibility of very efficient injection into the liquid bath inside the furnace with a minimum of connecting piping, and also limits the area of the site that the device can occupy. This arrangement provides the advantage of bringing the first injectors closer to the central vertical axis of the furnace, which is beneficial for mixing the bath. This arrangement also provides a stronger mixing in the lower section, where the first hot gases are injected, and also, in those embodiments in which the device is provided with tuyeres in the furnace wall of the smaller lower section, where additional gas is injected, while in the upper section the splashing is reduced due to the larger diameter. An additional benefit is that a torus-shaped liquid flow can be formed in the upper section, which is useful for drawing in any solid reducing agent particles that may be floating on top of the liquid level inside the bath.

In one embodiment of the furnace or device according to the invention, the furnace is provided with an internal refractory lining, in particular where contact with molten metal and/or matte may occur. This provides the advantage that metallurgical charges with high melting points and/or high liquidus temperatures can be processed or treated. The refractory lining is preferably provided in the lower section, where a free phase of molten metal and/or matte may be located, providing increased resistance to the chemical and/or mechanical effects of these liquids.

In one embodiment of the furnace or device according to the present invention, the peripheral walls of the furnace are water-cooled. The applicants have found that this contributes to a longer resistance of the equipment to possibly very high temperatures that may occur inside the furnace during operation. An additional advantage is that a build-up can be formed inside the furnace at its side walls. Such a build-up can provide additional thermal insulation from possibly very high temperatures inside the furnace during operation and provide additional protection for the refractory material that may be applied to the walls of the furnace.

In one embodiment of the method according to the present invention, the amount of additional gas injected through said at least one second injector is at least 10%, preferably at least 15%, more preferably at least 20%, 25%, 30%, 35%, 40%, 45%, 50% or 55%, more preferably at least 60%, preferably at least 70%, more preferably at least 75%, 80%, 90%, 100%, 110%, 120%, 125%, 130%, 140%, 150%, 175%, 200%, 225%, and even more preferably at least 230% of the amount, expressed in volume units under normal conditions, of hot gases of plasma quality that can be generated by a single element of said at least one plasma burner having the highest rated power, when this burner delivers first hot gases having an enthalpy content of at least 3.5 kW⋅h/ ^Nm3 . Optionally, the amount of additional gas injected through said at least one second injector is no more than 500%, preferably no more than 450%, more preferably no more than 400%, 350%, 325%, 300%, 290%, 280%, 275%, 270%, 265%, 260%, 250%, 240%, 230%, 220%, 210%, 200%, 180%, 165%, 150%, 135%, 120%, 110%, 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, and even more preferably no more than 20% of the amount expressed in volume units under normal conditions plasma which can be generated by one element of said at least one plasma torch having the highest rated power, when this torch delivers plasma having an enthalpy content of at least 3.5 kW⋅h/ ^Nm3 . The applicants have found that the main advantage of the present invention can be achieved already by injecting through the second injector an amount of additional gas flow which is closer to the said lower limit, especially when the additional gas flow is used as a carrier for an additional reducing agent, in particular when a fine powder such as coal powder or petroleum coke dust is used as an additional reducing agent.

In one embodiment of the method according to the present invention, wherein the device comprises a plurality of second injectors, the amount of additional gas injected through each second injector is at least 10%, preferably at least 15%, more preferably at least 20%, 25%, 30%, 35%, 40%, 45% or 50%, more preferably at least 55%, preferably at least 60%, more preferably at least 65%, even more preferably at least 70%, even more preferably at least 75%, preferably at least 80% of the amount, expressed in volume units under normal conditions, of first hot gases of plasma quality that can be generated by one element of said at least one plasma torch having the highest rated power, when this torch delivers first hot gases having an enthalpy content of at least 3.5 kW⋅h/ ^Nm3 . Optionally, each second injector injects a quantity of additional gas that is no more than 200%, preferably no more than 190%, more preferably no more than 180%, 170%, 160%, 150%, 140%, 130%, 125%, 120%, 115%, 110%, 105%, 100%, 95%, and even more preferably no more than 90% of the quantity, expressed in volume units under normal conditions, of first hot gases of plasma quality that can be generated by one element of said at least one plasma torch having the highest rated power, when this torch supplies first hot gases having an enthalpy content of at least 3.5 kW⋅h/ ^Nm3 .

In one embodiment of the method according to the present invention, the additional gas injected through said at least one second injector comprises at least one gas selected from the group consisting of hydrogen, nitrogen, air, carbon dioxide, argon, neon, helium, methane, ethane, propane, butane and combinations thereof, preferably nitrogen or air, more preferably air, and even more preferably compressed air. The applicants have found that nitrogen and air, preferably compressed air, are very convenient gases as a basis for the additional gas injected into the furnace.

In one embodiment of the method according to the present invention, the additional gas introduced through said at least one second injector is thermally treated before said at least one second injector in order to change its enthalpy content, and preferably the thermal treatment of the additional gas is carried out using at least one heat exchanger. If the gas is fed into the furnace at a temperature below the temperature of the liquid bath inside the furnace, then the applicants prefer to heat the gas before it is introduced by said at least one second injector. This reduces the cooling effect that the injection of additional gas may have on the furnace and makes it easier to maintain a thermal balance in the entire furnace. Preferably, such heating at least partially uses the heat available in the furnace exhaust gas treatment system.

In one embodiment of the method according to the present invention, the temperature of the additional gas entering said at least one second injector is at most equal to the temperature of the bath in the furnace, preferably lower than the temperature of the bath by at least 20 degrees Celsius, more preferably by at least 50, even more preferably by at least 100, and even more preferably by at least 200 degrees Celsius lower than the temperature of the bath in the furnace. The advantage of this is less wear and tear of the injection point, or tuyere. Optionally, the temperature of the additional gas entering said at least one second injector is not more than 400 degrees Celsius below the temperature of the bath in the furnace, preferably not more than 350, more preferably not more than 300, even more preferably not more than 250, preferably not more than 200, more preferably not more than 150, even more preferably not more than 100, preferably not more than 75, more preferably not more than 50, and even more preferably not more than 25 degrees Celsius below the temperature of the bath in the furnace. The advantage of this is a lower risk of accumulation of solidified slag on the throat of the injection point or the tuyere mouth, which can be caused by the cooling effect of the additional gas passing through the injection point or tuyere and entering the furnace.

In one embodiment of the method according to the present invention, the additional gas injected through said at least one second injector comprises at least one first reducing agent, preferably at least one reducing agent selected from the group consisting of any substances that contain elements other than oxygen and inert gases and that are capable of reacting with oxygen under the conditions inside the furnace, preferably any substances containing carbon and/or hydrogen in a chemically bound form capable of oxidation, more preferably the reducing agent is selected from the group consisting of natural gas, gaseous and/or liquid hydrocarbon, fuel oil, rubber, plastic, preferably plastic made from at least one polyolefin, more preferably waste rubber and/or plastic, charcoal or coke and combinations thereof, even more preferably coke, even more preferably petroleum coke, which is a high-carbon by-product of crude oil refining. As explained above in the section "Essence of the invention", the injection of additional gas into the furnace through said at least one second injector represents an additional entry point for adding a reducing agent to the furnace. In addition, since said at least one second injector is submersible, the choice of a suitable reducing agent is very wide.

In one embodiment of the method according to the present invention using a first reducing agent, the first reducing agent is a solid, preferably in the form of particles, more preferably particles having an average diameter of at most 6 mm, even more preferably at most 5, 4, 3, 2 or 1 mm, preferably at most 500 μm, more preferably at most 250, 200, 150, 100 or even 50 μm. The applicants have found that suitable solid reducing agents are available in a wide variety and quality and from a variety of sources. In addition, some of these suitable solid reducing agents have virtually no alternative uses in which they would be of any significant economic value. These solid reducing agents are therefore a very interesting source for use according to the present invention. As explained elsewhere in this document, the smaller particle size offers the advantage of a higher surface to weight ratio as well as lower buoyancy and hence a more efficient use of the reducing agent.

In one embodiment of the method according to the invention, the additional gas injected through the at least one second injector further comprises oxygen and a quantity of fuel suitable for introducing into the furnace, when combusted under the operating conditions in the furnace, such an enthalpy that compensates for at least 50% of the cooling effect that the additional gas may have on the furnace in the event that it has a temperature lower than the temperature of the molten charge in the furnace at the injection point. The applicants prefer to add such a quantity of fuel that compensates for at least 75%, and preferably at least 100%, of the described cooling effect. The applicants have found that an additional heat input into the furnace can be achieved by injecting gaseous or liquid fuel as part of the additional gas, preferably when the additional gas also further comprises oxygen, more preferably at least enough oxygen to achieve the desired lambda value in the additional gases. Typically, the temperature of the liquid bath inside the furnace is higher than the temperature at which the fuel and oxygen in the additional gas begin to react, even without an ignition source. Thus, if there is sufficient oxygen in the additional gas, the added fuel is easily ignited as soon as the additional gas comes into contact with the molten charge in the furnace. The applicants have found that the gas flows can easily be set high enough so that the combustion reaction does not proceed against the direction of flow of the additional gas in the second injector and/or in the gas ducts leading to the at least one second injector. Thus, the risk of such a "flame back" phenomenon becomes very low. The applicants have found that the risk of equipment damage due to such heating in or before the injector can be easily eliminated if the additional gas reaches a higher velocity in or before the second injector than the flame propagation velocity in the additional gas. The applicants have found that this condition can be satisfied quite well.

In one embodiment of the method according to the present invention, the additional gas injected through said at least one second injector has a first lambda value, taking into account only gaseous and liquid combustible substances, of less than 1.0, preferably no more than 0.9, more preferably no more than 0.8, even more preferably no more than 0.7, and most preferably no more than 0.6. Lambda ("λ") is understood to be a very convenient parameter, which is usually used in relation to burners and combustible fuels, in particular in the case of internal combustion engines, and which is a ratio, in the numerator of which is the actual ratio of air and fuel, and in the denominator - their stoichiometric ratio. If the air-fuel mixture corresponds to stoichiometry, then its lambda is equal to 1.0. The applicants apply this first lambda parameter to each gaseous mixture in which oxygen is present, as well as another substance that can readily react with oxygen, such as a combustible substance, wherein this other substance can be a gas, a liquid or a combination thereof. The applicants have found that if no solid reducing agent is used in the process, adjusting the first lambda value of the additional gas that is injected through said at least one second injector is a very convenient means for controlling the atmosphere inside the furnace, thereby establishing whether the atmosphere is neutral, oxidizing or reducing, as well as establishing the degree of oxidation or reduction. The applicants have found that the additional point of addition of the reducing agent in the device according to the present invention is very versatile, and controlling the first lambda parameter and/or the second lambda parameter, further described below, for the injected additional gas provides a very convenient way of controlling the oxidation-reduction conditions inside the furnace, and therefore controlling the chemical reactions occurring inside the furnace. The applicants have found that the combination of additional gas injection with the injection of the first hot gases from the plasma generator(s) allows a wide range of oxidation-reduction conditions to be achieved, wherein the oxidation-reduction conditions can be established virtually independently of the heat input to the furnace, in contrast to more traditional heating means such as the use of natural gas fired burners.

The applicants also contemplate a second lambda value that takes into account all combustibles that are used in the method and added to the additional gas, i.e. including any solid combustibles such as most of the reducing agents described above in this document. In one embodiment of the method according to the present invention, the additional gas injected through said at least one second injector has a second lambda value of less than 0.6, preferably no more than 0.5, more preferably no more than 0.4, even more preferably no more than 0.3, and most preferably no more than 0.2. The applicants have found that such low values of the second lambda parameter are very useful for fuming metals such as zinc from metallurgical slag.

In one embodiment of the method according to the present invention, the additional gas injected through said at least one second injector is combustible, and the additional gas in said at least one second injector reaches a higher velocity than the flame propagation velocity in the additional gas. The applicants have found that an additional heat supply to the furnace can be provided by injecting gaseous or liquid fuel as part of the additional gas, preferably when the additional gas also additionally contains oxygen. Typically, the temperature of the liquid bath inside the furnace is higher than the temperature at which the fuel and oxygen in the additional gas begin to react, even without an ignition source. The applicants have found that such a reaction can go against the direction of flow of the additional gas in the gas ducts leading to said at least one second injector, as well as in the second injector itself. Such a "flame back" phenomenon can lead to the release of heat in this injector gas duct and thus to an increase in the temperature of the additional gas upstream and/or inside the injector. The applicants have found that the risk of equipment damage due to such heating within or before the injector can be easily reduced or even eliminated if the additional gas reaches a higher velocity within or before the injector than the flame propagation velocity of the additional gas.

In one embodiment of the method according to the present invention, said at least one vaporized metal or metal compound is a metal in its elemental form or a vaporized metal-containing compound, preferably a metal selected from the group consisting of zinc, lead, tin, bismuth, cadmium, indium, germanium and combinations thereof, wherein the vaporized compound can be, for example, an oxide, sulfide, chloride or a combination thereof. The applicants have found that the method according to the present invention is very suitable for removing by evaporation a metal or a metal-containing compound selected from a prescribed list. The applicants have found that this method provides a highly competitive alternative to the recovery of one of said metals from a metallurgical charge.

In one embodiment of the method according to the present invention, wherein a less noble metal than the metal in the evaporated metal or metal compound, preferably iron and/or aluminium, is added to the furnace, wherein preferably the less noble metal is added in the form of particles, more preferably particles having an average diameter of not more than 5, 4, 3, 2 or 1 mm, preferably not more than 500 μm, more preferably not more than 250, 200, 150, 100 or even 50 μm, wherein the concentration of the less noble metal in the slag is preferably maintained below its solubility limit in the slag under the process conditions. The applicants have found that this has the advantage of improving the fluidity of the slag phase that may be present within the furnace as part of the molten bath. The applicants have found, however, that it is preferable to maintain the concentration of these compounds below the solubility limit of the compound in the molten bath, since exceeding the solubility may cause a separate phase of the particular compound to form in the furnace. Such a separate phase may impair the contact between the other liquid phase in the liquid bath with the injected additional gas and/or the first hot gas generated by the plasma torch and/or the additional first hot gases generated by the oxygen-gas torch, if any, and may therefore impair the chemical reactions that are desired in the furnace, in particular leading to impairing the evaporation of the evaporated metal or metal compound.

In one embodiment of the method according to the invention, the second reducing agent is added to the first hot gases of plasma quality before the at least one first injector. This has the advantage that an even larger amount of reducing agent is introduced into the furnace compared to the amount that can be introduced together with the additional gas. The amount of additional reducing agent that can be introduced through the at least one first injector is independent of the enthalpy supplied to the furnace. Thus, this method of introducing the reducing agent is very convenient for controlling the oxidation-reduction properties of the atmosphere in the furnace. An additional advantage is that the reducing agent introduced through the first injector is introduced together with the enthalpy of the highest temperature introduced into the furnace. At a higher temperature, the equilibrium constant of the desired reaction (I) of zinc fuming promotes the formation of metallic zinc, which is an evaporated metal or metal compound. Thus, the efficiency of the reducing agent introduced with the first hot gases from the plasma torch is higher, and since this injection is also carried out through a submerged injector, it is also highly efficient due to the very close contact of the first hot gases with the liquid in the liquid bath, which means that a small amount of this reducing agent can reach the surface of the liquid bath without coming into contact with the liquid from the bath.

In one embodiment of the method according to the present invention using a second reducing agent, the second reducing agent is selected from a gas, a liquid and a solid and combinations thereof, preferably the second reducing agent is selected from the group consisting of natural gas, a gaseous and/or liquid hydrocarbon, fuel oil, charcoal or coke and combinations thereof, even more preferably it is coke, yet more preferably the second reducing agent is petroleum coke, preferably in the form of solid particles, more preferably particles having an average diameter of no more than 6 mm, even more preferably no more than 5, 4, 3, 2 or 1 mm, even more preferably no more than 500 μm, no more than 250, 200, 150, 100 or even 50 μm. The applicants have found that introducing plasma through the first injector provides a very versatile option for introducing additional reducing agent, since it is very tolerant with respect to the choice of reducing agent, in particular with respect to its state of aggregation, as well as with respect to the amount that can be introduced.

In one embodiment, the method according to the present invention comprises the step of adjusting the oxygen potential in the slag within the range from 10 to 10 ^-9 Pa (i.e. from 10 ^-4 to 10 ^-14 atm). Preferably, the oxygen potential in the slag is adjusted by adding the first and/or second reducing agent. Due to the use of a plasma torch, virtually any oxygen potential can be combined with any amount of heat release. In combination with the extraction of one or more vaporized metals or metal compounds from the feedstock fed into the furnace, other metals can also be extracted. In one embodiment, the oxygen potential in the slag can be made suitable for selectively reducing the metal compounds in the slag to a molten metal phase. Typical examples of such metals that can be reduced from the slag are Cu, Ni, Sn, Pb, Ag, Au, Pt and Pd. The molten metal phase can then be collected at the bottom of the furnace. The molten metal phase can then be continuously or intermittently removed through a tap. For this purpose, the furnace can be provided with a refractory lining at the bottom. In another embodiment, where the material introduced into the furnace, and thus the slag, contains sulfur or sulfur compounds, a matte phase can also be obtained. The oxygen potential in the slag can then be made suitable to prevent oxidation of the sulfur. The metals can then be extracted in the molten matte phase. Examples of metals that can be extracted from the slag in the matte phase are Fe, Cu, Ni, Sn, Pb, Ag, Au, Pt and Pd. The molten matte phase can also be collected at the bottom of the furnace. The molten matte phase can be removed, continuously or intermittently, through a tap. In yet another embodiment, both the metal phase and the matte phase can be obtained by appropriately adjusting the oxygen potential and the sulfur content. As a non-limiting example, Au, Pt and Pd can be reduced to the metallic phase, while Cu and Ni can be converted to the matte phase. The matte phase usually appears on top of the metallic phase because it usually has a lower density than the metallic phase and because the two phases remain more or less undissolved in each other. The matte phase and the metallic phase can be discharged from the furnace through separate outlets or through a common outlet.

In one embodiment of the method according to the present invention, the afterburning is carried out inside a single-chamber furnace. This has the advantage of a much more compact design of the equipment and, therefore, a reduction in capital costs.

In one embodiment of the method according to the present invention, the afterburning comprises introducing into the afterburning zone an oxygen-containing gas, preferably selected from air, oxygen-enriched air and purified oxygen gas. Applicants have found that this choice is a relatively simple, low capital cost option for performing the function of the afterburning zone. Applicants prefer to use simply air, as explained above.

In one embodiment of the method according to the present invention, the oxidized form of said at least one vaporizable metal or metal compound is recovered from the gas in the form of dust. The applicants have found that this embodiment is much safer compared to the alternative embodiment in which the metal is condensed to form a liquid metal phase, for example as explained in US 4,588,436, since the risk of spontaneous combustion and/or explosion of the furnace exhaust gas essentially ends at the outlet of the afterburning zone. The applicants have also found that this embodiment also requires relatively low capital costs, for example compared to the alternative embodiment described in US 4,588,436.

In one embodiment of the method according to the present invention, the extraction of the oxidized form of said at least one vaporizable metal or metal compound from the gas comprises filtering the gas containing the oxidized form of said at least one vaporizable metal or metal compound using a filter, preferably a filter cloth. As explained above, the applicants prefer to use filter bags made of polytetrafluoroethylene (PTFE) fabric. In such a gas filter, the gas velocities can be locally very low. However, the presence of oxygen is expected. Therefore, for the method according to the present invention, it is important that substantially all of the reduced form of the metal or metal compound is oxidized to its oxidized form, so that the risk of spontaneous combustion and/or explosion is acceptably low.

In one embodiment of the method according to the present invention, the method further comprises a cooling step before extracting the oxidized form of said at least one vaporizable metal or metal compound from the gas. A variety of suitable cooling methods can be used, as explained above.

Typically the last stage in the gas processing sequence is a blower or fan which pushes the gas from the extraction zone into the stack and also increases the upstream draft by drawing the gas through a sequence of an afterburning zone, an optional cooling zone and an extraction zone.

In one embodiment of the method according to the present invention, the method comprises forming a molten metallic phase, and the method further comprises the step of removing the molten metallic phase from the furnace. The applicants have found that the method according to the present invention can result in the formation of a separate liquid phase of the melt caused by the reduction of less volatile metals to their elemental form. This can be a pure metal phase or a molten alloy. In such circumstances, it is very convenient to remove the separate molten metallic phase from the furnace as a separate by-product. In the case of an alloy, it may be preferable to further process the alloy such that at least one of the metals in the alloy is recovered separately from some other metals in the alloy. This further processing can comprise pyrometallurgical stages and/or electrolytic stages.

In one embodiment of the method according to the present invention, in which the metal charge comprises slag and in which the slag comprises sulfur and/or sulfur compounds, the method further comprises a step of forming a molten matte phase and a further step of removing the molten matte phase from the furnace. This is an optional option, in addition to extracting liquid molten metal or alloy from the process.

In one embodiment of the method according to the present invention, the metallurgical charge is introduced into the furnace in liquid form. This has the advantage that the metallurgical charge does not have to be melted and/or smelted as part of the process carried out in the device and/or furnace, which is beneficial for the heat balance of the furnace and therefore for the productivity of the process and its equipment, i.e. the furnace itself.

In one embodiment of the method according to the present invention, the metallurgical charge is a metallurgical slag, preferably a metallurgical slag selected from copper smelter slag, copper refining slag and combinations thereof, and the method produces a second slag. The applicants have found that the method (and apparatus) according to the present invention is very suitable for treating the feedstock in this manner.

In one embodiment of the method according to the present invention, the molten slag has an average temperature which is less than 50 degrees Celsius above the liquidus temperature of the slag. This has the advantage that the hard slag crust formed on the inner surfaces of the furnace wall and providing protection for the refractory lining easily maintains a sufficient thickness to provide adequate protection and thermal insulation. Such a crust is very advantageous from the point of view of the thermal balance of the furnace, since it acts as thermal insulation between the hot liquid slag in the furnace and the furnace wall, which is preferably cooled to protect its mechanical integrity. The crust thus reduces heat loss from the furnace to the cooled wall.

In one embodiment of the method according to the present invention, an oxide selected from CaO, Al ₂ O ₃ and combinations thereof is added to the slag in the fuming furnace, preferably at a temperature of at least 1000 °C, preferably at least 1050 °C, more preferably about 1150 °C. This feature provides the additional advantage that the final composition of the second slag after the fuming step can be further optimized and stabilized, making this slag more suitable for specific end uses due to the possible influence on the mineralogy. The applicants have found that addition at a high temperature, such as indicated, and in a molten state is more effective in obtaining the desired effects.

In one embodiment of the method according to the invention, the temperature of the slag in the furnace is at least equal to the temperature specified in the previous paragraph, more preferably even higher, for example at least 1200 or 1250 or 1300°C, and more preferably about 1350°C. This gives the advantage of a more favorable equilibrium constant between the evaporated metal or metal compound and its precursor in the liquid slag. A further advantage of the higher temperature is that it facilitates the removal of the evaporated slag from the furnace, the so-called "tapping", regardless of whether this is carried out by overflow or by tapping from a bottom taphole at a suitable location in the furnace wall.

In one embodiment of the method according to the present invention, the method further comprises the step of cooling the second slag so that it becomes solid, and preferably the second slag is first removed from the furnace as a liquid. The advantage is that the fuming furnace can be released for further processing of the slag while the second slag cools. The slag can be cooled and/or solidified by contacting the slag with a cooling medium, such as air and/or water, possibly ambient air.

In one embodiment of the method according to the present invention, in which the second slag is cooled, the cooling is accomplished by contacting the liquid second slag with water. Applicants have found that water cooling is very effective and can be applied in a variety of ways, resulting in relatively well-controlled cooling rates.

In one embodiment of the method according to the present invention, in which the second slag is cooled, the second slag is cooled at a rate of at least 30 degrees Celsius per second, preferably at least 40 degrees Celsius per second, and more preferably at least 50 or 60 degrees Celsius per second. The applicants have found that with a higher cooling rate, a higher content of amorphous matter in the slag can be obtained, which is of interest for certain end uses, for example when the slag is intended for use as a binder in the construction industry.

In one embodiment of the method according to the present invention, in which the second slag is cooled, the method further comprises the step of grinding the solid second slag, preferably grinding the second slag into powder.

In one embodiment of the method according to the present invention, in which the second slag is cooled, the second slag is cooled at a rate of less than 40 degrees Celsius per second, preferably no more than 30 degrees Celsius per second, and more preferably no more than 20 degrees Celsius per second. The applicants have found that a lower cooling rate can result in a lower amorphous content in the slag and therefore a higher crystallinity, which is of interest for certain end uses, such as when the slag is intended for use as an aggregate or for decorative purposes.

In one embodiment of the method according to the present invention, wherein the method forms a second slag, the method further comprises the step of adding the second slag as a binder or aggregate during the production of the object for the construction industry. The applicants have found that the second slag can be used as a binder for aggregates, preferably as an active binder, preferably as a binder having pozzolanic activity. The applicants have found that the slag can act as a binder instead of cement, for example in partial replacement of cement, such as Portland cement, and also as a binder for the production of geopolymer compositions.

In one embodiment of the method according to the present invention, in which slag is used as a binder during the production of an object for the construction industry, the object further comprises an aggregate, wherein the aggregate preferably comprises sand and/or a second slag.

In one embodiment of the method according to the present invention, in which the slag is used as a binder during the production of an object for the construction industry, and the object further comprises an aggregate, the method further comprises the step of adding an activator during the production of the object. The applicants have found that the second slag can act as an active binder, capable of reacting with a suitable activator and thereby exhibiting strong binding properties for aggregates. Therefore, the second slag can be used instead of Portland cement or as the only binder in the object, in which case it is considered a "geopolymer", which, for example, imparts fire and heat resistant properties to coatings, adhesives, composites, etc.

In one embodiment of the method according to the present invention using an activator, the activator is selected from the group consisting of sodium hydroxide, NaOH, potassium hydroxide, KOH, sodium silicate, Na ₂ SiO ₃ , potassium silicate, K ₂ SiO ₃ , and combinations thereof, and preferably the activator is NaOH.

In one embodiment of the method according to the present invention, in which an object for the construction industry is formed, the object is a building element.

In one embodiment of the method according to the present invention, in which a building element is formed, the building element is selected from a list consisting of a tile, a paving stone, a block, a concrete block and combinations thereof.

In one embodiment of the method according to the present invention, in which an object for the construction industry is formed, the object has a foamed structure.

In one embodiment of the present invention, the metallurgical charge is selected from copper smelter slag and copper refining slag, as well as combinations thereof.

In one embodiment of use in accordance with the present invention, the vaporized metal or metal compound is selected from zinc, lead, tin, bismuth, cadmium, indium, germanium, and combinations thereof.

In one embodiment of the method according to the present invention, at least part of the method is monitored and/or controlled electronically, preferably by a computer program. The applicants have found that electronic control of the stages of the method according to the present invention, preferably by a computer program, gives the advantage of a much better processing, with much more predictable results, which are closer to the objectives of the method. For example, on the basis of temperature measurements and, if desired, also pressure and/or level measurements, and/or in combination with the results of chemical analyses of samples taken from the process streams and/or with analytical results obtained in real time, the control program can control equipment related to the supply or shutdown of electricity, the supply of heat or cooling medium, the regulation of flow and/or pressure. The applicants have found that such monitoring or control is particularly advantageous with stages that are operated in a continuous mode, but it can also be advantageous with stages that are operated in a batch or semi-continuous mode. In addition and preferably, the results of the monitoring obtained during or after the execution of the steps in the method according to the present invention are also used for monitoring and/or controlling other steps that are part of the method according to the present invention and/or methods that are applied before or after the method according to the present invention, as part of an overall process of which the method according to the present invention is only a part. Preferably, the entire overall process is monitored electronically, more preferably at least one computer program. Preferably, the overall process is controlled electronically to the greatest possible extent.

Applicants prefer that the computer control also provides for the transmission of data and instructions from one computer or computer program to at least one other computer or computer program, or to a module of the same computer program, to monitor and/or control other processes, including, but not limited to, the methods described in this document.

EXAMPLE 1

In this example, the furnace was equipped with 3 plasma generators.

The furnace, also called the "device", "reactor" or "fumer", had an overall height from the bottom to the top feed opening of approximately 7.34 m. The top of the furnace was formed by a dome containing the top feed opening and the exhaust gas duct. Below the 1.09 m high upper dome, the furnace contained an upper section, cylindrical about a vertical axis, approximately 3.00 m high and with an outside diameter of 5.50 m. Below this upper section, the furnace tapered over a vertical distance of approximately 1.66 m, ending in a lower cylindrical section approximately 3.19 m in diameter and 1.00 m high. The lower dome had a height of 0.60 m. The lower cylindrical section had a height of 1.00 m, and the conical section had a height of 1.66 m.

During operation, the furnace is intended to contain a liquid melt bath up to a level at least above the highest opening of the entry points of the first hot gases of plasma quality and of the additional hot gases. The applicants prefer for this purpose to maintain a liquid level in the furnace that is at least at the level of the bottom of the conical section. More preferably, the liquid level is maintained somewhat higher, somewhere at the height of the conical section. If necessary, its level may be allowed to rise above the conical section, but it must remain below the level at which the static pressure becomes too great an obstacle to the entry of the first hot gases and/or of the additional gases, so that the mixing of the bath would be impaired.

The furnace shell was a double-walled water-cooled structure made of alloy steel, except for sections that were well protected by a refractory lining, and the space inside the double walls was supplied with running cooling water during operation as part of a circulation loop. This cooling is provided to protect the structural integrity, especially the mechanical strength of the reactor wall. The cooling also causes a portion of the liquid slag inside the furnace near the wall to solidify in the so-called "crust" below the liquid level, and due to splashing, also on most of the furnace wall above the liquid level. This hard crust protects the walls from many types of chemical and mechanical wear. It also provides thermal insulation, thereby reducing heat loss from the furnace contents to the cooling water. Since some molten metal phase may also be formed during the process, the lower cylindrical section and the lower dome were lined with a suitable refractory material, in this case a combination of insulating bricks, wear lining and refractory concrete. Most of these sections were not part of the cooling water system.

In the wall of the lower cylindrical section, and therefore below the liquid level during operation, three (3) plasma generators (PG) were provided along the perimeter at the same height and at approximately equal distances for blowing hot gases into the furnace through tuyeres in a direction perpendicular to the furnace wall.

A plasma generator is a device that produces very hot gas that is at least partially converted into plasma. Typical gas temperatures are 3500-5000°C. This gas is heated by electrical energy. The high voltage difference across two electrodes creates an electric arc between them. In this reactor, air was blown through the arc and heated by the energy of the arc. As the electric current increased, more air could be heated and more energy could be transferred to the air. The power of the PG (W, expressed in watts, W) is defined as voltage (V, expressed in volts, V) × electric current (A, expressed in amperes, A). When operating this type of plasma generator, there is a relationship between the rated power of the PG and the amount of air that can be blown through the PG.

The three plasma generators of the reactor in the example had a nominal power of 3 MW, and during furnace operation, each of them was supplied with a quantity of compressed air in the range of 300-900 ^Nm3 /h. With a reference enthalpy of 3.5 kW⋅h/ ^Nm3 for the produced gas, each of the plasma generators was capable of producing 857 ^Nm3 of such hot gases of plasma quality as "primary gas".

The NGs were not installed directly into the reactor wall. They injected their first hot gases (plasma produced and plasma quality) into the furnace through a lance. The lance is a nozzle that forms an opening in the reactor through which hot gases can be injected into the reactor. This lance may additionally be used to mix secondary volumes of natural gas and/or additional air with the hot gases from the NGs, if necessary. Preferably, the applicants maintain a significant volume of secondary gases through the lance at all times when a hot liquid bath is present in the furnace. The objective is that even if the NGs have to be shut down and/or removed, there will be sufficient gas flowing through the lance to prevent hot liquid from entering the lance and to avoid the risk of some liquid flowing into the lance where it will cool and solidify, which would present a serious problem of removal before the lance is again fully fit for its intended use.

During operation, an additional 90-200 ^Nm3 /h of natural gas was added to the first hot gases from each SG through openings in the corresponding tuyeres. In addition, additional air was typically added through each of these tuyeres at a rate in the range of 100-250 ^Nm3 /h. These volumes are therefore classified as secondary gas volumes.

The natural gas used in this example contained 84.206 vol.% methane, 3.646 vol.% ethane, 0.572 vol.% propane, and 9.966 vol.% nitrogen. The remainder, less than 1 vol.%, consisted of higher alkanes, primarily butanes and pentanes.

Opposite each plasma generator-lance combination, an additional lance was provided for injecting additional gas into the furnace, i.e. also 3 lances for the entire furnace. These additional lances or injectors are the second submersible injectors according to the present invention. They were also arranged to inject their additional gases in a direction perpendicular to the furnace wall, but a change is planned compared to the preferred option for injecting at an angle upwards into the bath.

The second submersible injectors were designed using a lance of the same type as those used after the plasma generators. These lances, and therefore also the lances after the PG, are water cooled, cylindrical, double walled and project through the furnace wall into the furnace space below the level of the liquid bath expected to be present in the furnace during operation. The lances are designed to inject secondary gases into the double wall of the lance. The inner cylinder of the lance is provided with a plurality of holes through which the secondary gases enter the central volume of the lance through which the primary gases pass, which in the case of the PG upstream will be hot plasma quality gases generated in the PG itself. The holes are preferably in the form of nozzles to impart additional velocity to the gas to facilitate mixing of the secondary gases with the primary gases passing through the lance. In the case of the second submerged injectors, the PG has been replaced by a simple tube projecting through the tuyere towards the molten bath and preferably projecting as far as the tuyere extends into the furnace. Through this tube, a primary gas such as compressed air may be forced, optionally supplemented with some natural gas. Some additional reducing agent such as fine powdered coal may be mixed with the primary gas or one of its components.

During operation, each of the three additional injectors was supplied with a quantity of primary and secondary gases in the amount of 300-600 ^Nm3 /h of compressed air, in which 30-60 ^Nm3 /h of natural gas was mixed with, if necessary, approximately 150-200 kg/h of coal dust as an additional reducing agent. The coal dust had an average particle size of 120 μm. The gas gauge pressure before the additional tuyere was 6 bar. The gas velocity in the additional tuyere was usually greater than 330 m/s during operation.

A system with two pressure vessels was used for the injection of pulverized coal. The upper vessel acted as a water seal: it remained at atmospheric pressure while it was filled from a hopper located on top of the pressure vessel, usually through a discharge valve. The hopper was filled by mechanical transport, usually using a belt conveyor or auger, and optionally also by unloading large bags. Once filled, the pressure in this vessel was increased to the blast pressure. The lower vessel, maintained at blast pressure, could then be filled by discharging the contents from the upper vessel into it. From the lower vessel, a metered feed system of pulverized coal was provided into the injected air. Air and pulverized coal were then transported under pressure to additional injectors and into the liquid slag. The advantage of the two-vessel system is that the supply of reducing agent to the reactor can be made uninterrupted.

All tuyeres, plasma generators and injectors were water-cooled.

At the top of the furnace, a radiant water cooler was provided, made in the form of a metal cylinder with double walls, in which the exhaust gases from the furnace pass through the center of the cylinder, and the cooling water is pushed through the wall of the cylinder.

In the space between the top of the furnace and the radiant water cooler, ambient air is allowed to enter and mix with the exhaust gases from the furnace. The evaporating zinc and CO present in the gas come into contact with the oxygen in the air, at a high gas temperature these substances spontaneously ignite and form an afterburning zone. Due to the significant draft inside the furnace and the water cooler, the exhaust gases flow at a high speed. Ambient air can enter through properly designed openings so that it quickly and intensively mixes with the exhaust gases. As a result, a stable flame front is established inside the radiant water cooler, and part of its radiant heat is radiated downwards, back from the afterburning zone into the furnace onto the liquid bath in the furnace. The top of the furnace and the radiant water cooler are also equipped with multiple injection points through which air under pressure can be blown into the exhaust gases from the furnace. This possibility can be used simultaneously with the access of ambient air through the openings. However, it is preferable that the ambient air inlets are substantially closed and that substantially all of the required oxygen is introduced through the injection points. This mode of operation is preferred because the oxygen supply is more stable and better controlled than alternatives that allow air to be introduced by draught.

Inside the afterburning zone, the gas reaches temperatures of up to 1500°C.

The gas leaving the afterburner had a temperature of approximately 1200°C. After the radiation water cooler, approximately 6-7000 liters of water per hour were injected into the gas stream. This spray cooling stage reduces the gas temperature to approximately 220°C.

The wet gas from the spray cooling stage was directed to a gas filter in which porous PTFE sleeves were located over cylindrical nozzles, and the sleeves retained dust, represented by the oxidized form of the evaporated metal or metal compound, formed in the afterburning zone.

After the gas filter, the fan provides suction from the furnace and blows filtered gas into the chimney.

The fuming process and the fuming furnace were operated in a batch mode. The working batches presented below consisted of a clearly defined sequence of distinguishable process steps. At different process steps, greater or lesser amounts of electrical energy, pulverized coal, air, and natural gas were fed into the reactor, depending on the desired effect. The operation of the PG, tuyeres, and additional injectors or tuyeres varied with the process step. The various steps are described in detail below.

The first stage of the method: filling the furnace with liquid:

At the start of the period, 76,900 kg of liquid slag from the preceding copper smelter was fed into 4 slag kettles with a net weight of approximately 19 tonnes each, measured by a weighing instrument on the overhead crane moving the slag kettles between the various furnaces.

In the previous copper smelting process, the slag is thoroughly mixed before it is poured out of the smelting furnace. Therefore, the slag composition can be considered homogeneous. The content of most metals in the slag was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), also called inductively coupled optical emission spectrometry (ICP-OES) and sometimes simply ICP, and for SiO ₂ by X-ray diffraction (XRF). The XRD method used was quantitative X-ray diffraction analysis using Topas Academic Software V5, using Al ₂ O ₃ as an internal standard.

Table I: Composition of the original slag

Element (wt%) Analysis Cu 0.60 Pb 0.46 Sn 0.11 Ni 0.04 Fe 30.63 Si 0,00 Al 0,00 Zn 11.48 Bi 0,00 As 0,00 Sb 0,00 CaO 3.09 _SiO2 25.07 _{Al2O3 ​} 6.88

For this step of the process, the SGs were set to a power level of 1400 kW each and an average air flow rate of approximately 437 ^Nm3 /h per SG as the primary gas. In addition, the following secondary gases were used. The natural gas flow rate through the lance was controlled at 125 ^Nm3 /h. The air flow rate through the lance was controlled at 100 ^Nm3 /h.

The total flow rate of primary and secondary gases through additional injectors as second submersible injectors was set at 380 ^Nm3 /h of air per injector, natural gas was added at a flow rate of 44 ^Nm3 /h. Pulverized coal injection was not yet activated at this stage of the process.

The second stage of the method: the fuming stage

After filling with liquid slag, the fuming stage began. At this stage, the energy and reducing agent supply was increased to accelerate the evaporation of zinc in the form of steam.

The SGs were brought to a power level of 2500 kW each and an average primary air flow rate of 714 ^Nm3 /h per SG. In addition, the following secondary gases were used. Natural gas was fed to each tuyeres after the SG, with a flow rate of 148 ^Nm3 /h. The additional air flow through the tuyeres was set at 100 ^Nm3 /h.

The total flow of primary and secondary gases through additional injectors was supplied with an air flow rate of 380 ^Nm3 /h per injector. Natural gas was added to each injector at a flow rate of 44 ^Nm3 /h. The injection of pulverized coal into each injector was set at 180 kg/h.

The supply of energy and reducing agent caused the fuming of volatile compounds from the liquid slag. The most volatile element was Zn. It was present in the slag as zinc oxide (ZnO). The reactor temperature was maintained in the range of 1180-1250°C, assuming that the slag remained liquid. Due to the various reducing agents, i.e. pulverized coal and various natural gas supplies, ZnO was reduced to metallic zinc (Zn). At atmospheric pressure, Zn can evaporate at temperatures above 906°C. Zn was thus evaporated from the slag bath and transported as part of the process gases from the furnace to the furnace exhaust gas treatment equipment.

In the reactor off-gas duct, large quantities of air were mixed with the process gases, causing complete afterburning of the process gases. Any remaining CO, Zn, _H2 were completely oxidized at this stage. Zinc in the form of vapor was oxidized to ZnO, forming solid particles. This ZnO thus formed dust in the stream of burnt off-gases. This post-combustion or afterburning stage was followed by a cooling stage. At the outlet of the cooling stage, the temperature of the process gases was below 220 °C. The process gases were then filtered in a bag filter with a PTFE fabric. After filtration, the process gases were pumped to the atmosphere through a stack. ZnO dust particles were captured on the filter, cooled and stored in a dust bin. From the bin, the zinc-rich dust product could be unloaded into bulk tank trucks for sale.

Samples were collected during fuming and analyzed using the fast but slightly less accurate XRF method. When the desired Zn level in the furnace slag was reached, fuming was stopped and the stripping stage was started.

The third stage of the method: cleaning

The purpose of this stage was to oxidize the last remaining pulverized coal in the furnace charge and heat the slag to a more suitable tapping temperature. The target temperature was 1220-1250°C.

The SGs were maintained operating at a power level of 2500 kW each and with an average primary air flow rate of 714 ^Nm3 /h per SG. In addition, the following secondary gases were used. The natural gas flow rate through the tuyere was set at 102 ^Nm3 /h. The air flow rate through the tuyere was set at 100 ^Nm3 /h.

As a total flow of primary and secondary gases, 380 ^Nm3 /h of air and 44 ^Nm3 /h of natural gas were fed through additional injectors into each of these second submersible injectors. The injection of pulverized coal was stopped during this stripping stage.

Slag samples were not taken after the cleaning stage was completed. Discharge began immediately.

The fourth stage of the method: slag release and granulation

The purpose of this step is to extract the liquid slag from the reactor. A tap hole was drilled in the side wall of the reactor and the liquid slag was poured out of the reactor into a trough. The slag product from this trough was granulated by means of a water granulation system in which a large volume of water was sprayed onto the falling slag stream, causing the liquid slag to solidify and break into solid particles of ±1 mm in size.

The SGs continued to operate during this tapping and granulation stage at a capacity of 2000 kW each, with an average primary air flow rate of 606 ^Nm3 /h per SG. The secondary gases were set to a natural gas flow to the lance of 128 ^Nm3 /h, and then the air flow directly to the lance was set to 100 ^Nm3 /h.

The additional injectors also continued to operate with an air flow rate of 380 ^Nm3 /h per injector and a natural gas flow rate of 44 ^Nm3 /h in total for primary plus secondary gases. Pulverized coal injection was stopped.

Samples of the final product were taken after granulation. The composition was considered close to the composition of the slag immediately after the fuming stage.

Additional operating parameters for the SG at each stage of the method are shown in Table II, in which the "Enthalpy" is calculated from the power supplied to the SG and the air flow rate supplied to the SG.

Table II: PG operating parameters

Stage Air/natural gas volume ratio Enthalpy, kWh/nm ³ Filling 5.5 3.2 Fuming 5.5 3.5 Cleanup 8 3.5 Granulation 5.5 3.3

The change in slag composition during the working cycle is illustrated in Table III, which shows the results of analyses of slag samples taken after each stage:

Table III: Change in slag composition

Element (wt%) Nutrition After filling After Fuming Granulated Cu 0.60 0.57 0.48 0.42 Pb 0.46 0.44 0.03 0.025 Sn 0.11 0.10 0.08 0.07 Ni 0.04 0.05 0.03 0.03 Fe 30.63 30.80 35.63 35.8 Zn 11.48 11.08 1.64 1.58 CaO 3.09 3.10 3.78 3.75 _SiO2 25.07 25.15 29.64 29.82 _{Al2O3 ​} 6.88 6.95 7.58 7.74

Composition of the output material

This batch yielded approximately 10,500 kg of filter dust with the composition shown in Table IV, which was determined by ICP analysis of a representative sample:

Table IV: Composition of filter dust product

Filter dust Mass.% Cu 0.09 Sn 0.09 Pb 2.98 Zn 73.46 Ni 0,00 Fe 0.91 Bi 0.49 As 0,00 Cl 0.79 Sb 0,00 S 0.05 Al 0.05 Co 0.05 Cd 0,00

For comparison purposes, a second operating cycle was carried out, in which the additional tuyeres had not yet been installed. In order to provide a similar amount of reducing agent during the fuming stage, the same amount of carbon was introduced by introducing coarse petroleum coke with a particle size in the range of 6-10 mm through the feed port.

The amount and composition of the supplied liquid slag were comparable to the first batch, as were the feeding time, stripping time and tapping time. The main difference was the fuming time.

The quantities and compositions of the product after granulation and filter dust were comparable.

The time required in the fuming step to obtain a very close Zn content in the final slag was significantly higher in this comparative batch compared to the batch according to the present invention, which was described above. This means that the comparative batch had a significantly lower zinc evaporation rate compared to the working example, and therefore the present invention significantly increased the zinc evaporation rate during the fuming step.

EXAMPLE 2

In this example 2, the same furnace was used as in example 1, but with a different configuration regarding the injection of gases through the second immersion injectors. The natural gas supply and its quality were the same.

At the same level or height of the three plasma generator-lance combinations, this time only one additional injector-lance combination was provided as a single second submersible injector for injecting additional gas and fine coke into the furnace. The lance was water-cooled and air was injected through the lance and then through holes in the inner wall of the lance at a constant flow rate of 350-400 ^Nm3 /h. Natural gas supply was not used in this example.

An injector located inside the additional injector-lance combination supplied additional gases to the liquid slag bath in a direction perpendicular to the furnace wall. During operation, 100-400 ^Nm3 /h of compressed air were supplied to the additional injector as primary gases, to which approximately 100-700 kg/h of pulverized coal was mixed as an additional reducing agent if necessary. The pulverized coal had an average particle size of 120 μm. The manometric pressure of the compressed gas before assembling the second submersible injector was 6 bar.

The gas velocity in the additional injector-lance combination during operation typically exceeded 150 m/s.

The first stage of the method: filling the furnace with liquid:

At this stage the same procedure, qualities and quantities were used as in Example 1, with the following exceptions.

The secondary gas flow through the single additional lance as part of the single additional injector-lance combination was set to 350 ^Nm3 /h air and no natural gas was added. The primary gas flow through the additional injector as part of the single additional injector-lance combination was set to 200 ^Nm3 /h air. Fine coke injection had not yet been activated at this stage of the process.

The second stage of the method: the fuming stage

The same procedure was used as in Example 1.

The SGs were again set to a power level of 2500 kW each and an average primary air flow rate of 714 ^Nm3 /h per SG. In addition, the following secondary gases were used. Natural gas was fed to each tuyeres after the SG at a flow rate of 148 ^Nm3 /h. The additional air flow through the tuyeres was set to 100 ^Nm3 /h.

The secondary gas flow through the auxiliary lance as part of the single auxiliary injector-lance combination was 350 ^Nm3 /h air and no natural gas was added. As a primary gas, the flow through the auxiliary injector as part of the auxiliary injector-lance combination was set at 200 ^Nm3 /h air. At this stage of the process, fine coke injection was set at 700 kg/h.

The reactor temperature was maintained in the range of 1180-1250°C, assuming that the slag remained liquid. Due to various reducing agents, i.e. pulverized coal and various natural gas supplies, ZnO was reduced to metallic zinc (Zn). In this way, Zn was evaporated from the slag bath and transported as part of the process gases from the furnace to the furnace exhaust gas treatment equipment.

Samples were taken during fuming and analyzed using the fast but slightly less accurate XRF method. When the desired Zn level in the furnace slag was reached, fuming was stopped and the stripping stage was started.

The third stage of the method: cleaning

The target temperature was again 1220-1250°C.

The SGs continued to operate at a power level of 2500 kW each and with an average air flow rate of 714 ^Nm3 /h per SG. In addition, the following secondary gases were used. The natural gas flow rate through the tuyere was set at 102 ^Nm3 /h. The air flow rate through the tuyere was set at 100 ^Nm3 /h.

The secondary gas flow through the additional lance as part of the single additional injector-lance combination was set to 350 ^Nm3 /h air and no natural gas was added. For the primary gas, the air flow through the additional injector as part of the single additional injector-lance combination was set to 200 ^Nm3 /h air. Fine coke injection had not yet been activated at this stage of the process.

Slag samples were not taken after the cleaning stage was completed. Production began immediately.

The fourth stage of the method: slag release and granulation

The same procedure was used as in Example 1.

The SGs were again kept running during this tapping and granulation stage at a capacity of 2000 kW each, with an average primary air flow rate of 606 ^Nm3 /h per SG. The secondary gases used were a natural gas flow into the lance at a flow rate of 128 ^Nm3 /h and an air flow directly into the lance at a flow rate of 100 ^Nm3 /h.

The secondary gas flow through the additional lance as part of the single additional injector-lance combination was 350 ^Nm3 /h air and no natural gas was added. As a primary gas, the air flow through the additional injector as part of the single additional injector-lance combination was set to 200 ^Nm3 /h air. Fine coke injection had not yet been activated at this stage of the process.

Samples of the final product were taken after granulation. The composition was considered close to the composition of the slag immediately after the fuming stage.

The additional operating parameters for the PG at each stage of the process were the same as those shown in Table II as part of Example 1.

The final results of this example were very similar to the results of Example 1, except that they were again obtained in a shorter time than for the batch run for comparison purposes in Example 1.

The applicants have found that with the embodiments according to the present invention, as well as with Example 2, a significant increase in productivity can be obtained. The applicants believe that this effect is due to a combination of (i) more vigorous agitation of the bath, (ii) a larger amount of stripping gas, (iii) a larger amount of reducing agent and, perhaps most importantly, (iv) the use of a solid reducing agent with a much smaller particle size, so that the reducing agent is much more reactive. This effect allows the desired fuming conditions to be reached much more quickly compared to coarse petroleum coke. This combination of beneficial effects has made it possible to significantly speed up the fuming stage at full operation, as evidenced by the much faster increase in the heat that needs to be removed from the afterburning zone, and also by the fact that the stripping stage has been reduced very significantly in time, almost by an order of magnitude, since the required time has been reduced from about a quarter of an hour to only 2-3 minutes. A fuming furnace with a second immersion injector(s) can operate more stably, with greater productivity and closer to its maximum capabilities.

Now that this invention has been fully described, it should be clear to those skilled in the art that the invention can be implemented in a wide range of parameters stated in the claims without going beyond the scope of protection of the invention as defined by the claims.

Claims (64)

1. A single-chamber furnace for fuming at least one vaporizable metal or metal compound from a metallurgical batch, comprising a tank furnace capable of containing the molten batch up to a certain level, wherein the furnace is equipped with at least one indirect plasma torch for generating first hot gases of plasma quality and at least one first submersible injector for injecting first hot gases from said at least one plasma torch below said certain level, wherein the furnace further comprises an afterburning zone for oxidizing said at least one vaporizable metal or metal compound in the fuming gas to form an oxidized form of said at least one vaporizable metal or metal compound, a cooling zone for cooling the gas formed in the afterburning zone, and an extraction zone located downstream of the cooling zone for extracting the oxidized form of said at least one vaporizable metal or metal compound from the gas formed in the afterburning zone and cooled in the cooling zone, characterized in that the furnace is further equipped with at least one second immersion injector, different from said at least one first immersion injector, for injecting additional gas into the furnace below said certain level in addition to the first hot gases from said at least one plasma torch, wherein the furnace is further equipped with at least one source of compressed gas and/or a compressor for supplying additional gas in the form of compressed gas to said at least one second immersion injector. 2. The furnace according to claim 1, which further comprises a plurality of second immersion injectors. 3. The furnace according to claim 1 or 2, wherein said at least one second immersion injector directs its additional gas into a second volume as part of the interior space of the furnace below a predetermined level that is different from the first volume into which said at least one first immersion injector directs its first hot gases of plasma quality. 4. A furnace according to any one of claims 1 to 3, wherein said at least one first immersion injector is located in a side wall of the furnace, and said at least one second immersion injector is located in a wall of the furnace opposite said at least one first immersion injector, preferably along a horizontal perimeter of the furnace, passing at substantially the same height as said at least one first immersion injector. 5. A furnace according to any one of claims 1 to 4, comprising at least two, and preferably at least three first immersion injectors distributed along the horizontal perimeter of a side wall of the furnace, wherein said at least one second immersion injector directs its additional gas to that part of the internal volume of the furnace below a predetermined level that is close to the vertical axis of the furnace, and/or said at least one second immersion injector is located along the side wall of the furnace at an approximately equal distance between the positions of the two closest of the at least two first immersion injectors. 6. A furnace according to any one of claims 1-5, further equipped with at least one oxygen-gas torch for generating additional first hot gases in addition to the amount of first hot gases of plasma quality from said at least one plasma torch. 7. The furnace according to claim 6, further equipped with at least one third submersible injector for injecting additional first hot gases below said determined level. 8. The furnace according to claim 7, wherein said at least one oxygen-gas burner is located below said specific level. 9. A furnace according to any one of claims 1 to 8, wherein the plasma torch is located below said defined level. 10. A furnace according to any one of paragraphs 1-9, in which the afterburning zone is provided above the said specified level as part of a single-chamber furnace. 11. A furnace according to any one of claims 1 to 10, wherein the afterburning zone comprises a connection to a supply source of oxygen-containing gas, preferably selected from air, oxygen-enriched air and purified oxygen gas. 12. A furnace according to any one of claims 1 to 11, wherein the cooling zone comprises a radiant water cooler followed by a spray cooler. 13. A furnace according to any one of paragraphs. 1-12, in which the extraction zone comprises a gas filtration zone. 14. A furnace according to any one of claims 1 to 13, wherein the furnace has a generally cylindrical shape, preferably the furnace also has a conical lower section tapering to a cylindrical lower section of smaller diameter, wherein the cylindrical shape of the furnace has a largest internal diameter d, and the furnace has a total internal height h from bottom to top, wherein the ratio of h to d is at least 0.75. 15. The furnace of claim 14, wherein the furnace comprises a conical lower section and wherein the determined level is approximately at the height where the cylindrical shape transitions into the conical lower section. 16. A furnace according to any one of paragraphs 1-15, wherein the furnace is provided with an internal refractory lining. 17. A furnace according to any one of paragraphs 1-16, in which the peripheral walls of the furnace are water-cooled. 18. A method for fuming at least one evaporated metal or metal compound from a metallurgical charge using a single-chamber furnace according to any one of paragraphs 1-17, comprising the steps of: - introducing into the furnace a metallurgical charge containing the said at least one evaporated metal or metal compound, and forming a bath of molten charge to a certain level; - fuming a quantity of at least one vaporizable metal or metal compound from a bath using hot plasma quality gases from said at least one plasma torch and at least one reducing agent, resulting in a fuming gas containing the vaporizable metal or metal compound; - afterburning in the afterburning zone of the fuming gas to oxidize the said at least one vaporized metal or metal compound into an oxidized form of the said at least one vaporized metal or metal compound, - removing the gas formed in the furnace from the furnace and extracting in the extraction zone the oxidized form of the said at least one evaporated metal or metal compound from the gas formed during the afterburning stage; wherein during at least part of the fuming step additional gas is injected by said at least one second immersion injector into the bath below said determined level, thereby increasing the amount of vapour containing the evaporated metal or metal compound. 19. The method according to claim 18, wherein the amount of additional gas injected through said at least one second immersion injector is at least 10% of the amount of first hot gases, expressed in volume units under normal conditions, that can be produced by one element of said at least one plasma torch having the highest rated power, when this torch delivers first hot gases having an enthalpy content of at least 3.5 kW⋅h/ ^Nm3 . 20. The method according to claim 18 or 19, wherein the furnace comprises a plurality of second immersion injectors, and wherein the amount of additional gas injected through each second immersion injector is at least 10% of the amount of first hot gases, expressed in volume units under normal conditions, that can be produced by one element of said at least one plasma torch having the highest rated power, when this torch delivers first hot gases having an enthalpy content of at least 3.5 kW⋅h/ ^Nm3 . 21. The method according to any one of claims 18 to 20, wherein the additional gas injected through said at least one second submersible injector comprises at least one gas selected from the group consisting of hydrogen, nitrogen, air, carbon dioxide, argon, neon, helium, methane, ethane, propane, butane and combinations thereof, preferably nitrogen or air, more preferably air, and even more preferably compressed air. 22. The method according to any one of claims 18 to 21, wherein the additional gas injected through said at least one second immersion injector is thermally treated before said at least one second immersion injector in order to change its enthalpy content, and preferably the thermal treatment of the additional gas is carried out using at least one heat exchanger. 23. The method according to any one of claims 18 to 22, wherein the temperature of the additional gas entering said at least one second immersion injector is at most equal to the temperature of the bath in the furnace, and preferably at least 100 degrees Celsius lower than the temperature of the bath. 24. The method according to any one of claims 18 to 23, wherein the additional gas injected through said at least one second submersible injector comprises at least one first reducing agent. 25. The method according to claim 24, wherein the first reducing agent is a solid substance. 26. The method according to any one of claims 18 to 25, in which the additional gas injected through said at least one second submerged injector further comprises oxygen and a quantity of fuel suitable for its combustion under operating conditions in the furnace to introduce into the furnace such an enthalpy that compensates for at least 50% of the cooling effect that the additional gas may have on the furnace in the event that the additional gas is at the injection point at a temperature that is lower than the temperature of the molten charge in the furnace. 27. The method according to any one of claims 18 to 26, wherein the additional gas injected through said at least one second submersible injector has a lambda value of less than 1.0. 28. The method according to any one of claims 18-27, wherein the additional gas injected through said at least one second immersion injector is combustible and the additional gas in said at least one second immersion injector reaches a higher velocity than the flame propagation velocity in the additional gas. 29. The method according to any one of claims 18 to 28, wherein said at least one vaporized metal or metal compound is a metal in its elemental form or a vaporized metal-containing compound, wherein preferably the metal is selected from the group consisting of zinc, lead, tin, bismuth, cadmium, indium, germanium and combinations thereof, and also preferably the metal-containing compound is selected from a chloride, an oxide, a sulfide and combinations thereof. 30. The method of claim 29, wherein a less noble metal is added to the furnace than the metal in the evaporated metal or metal compound, wherein the less noble metal is a metal that is less easily reduced and therefore more readily forms an oxidized form under furnace operating conditions, preferably iron and/or aluminum. 31. The method according to any one of claims 18 to 30, wherein a second reducing agent is added to the first hot gases of plasma quality before said at least one first immersion injector. 32. The method of claim 31, wherein the second reducing agent is selected from a gas, a liquid, a solid, and combinations thereof. 33. The method according to any one of paragraphs 18-32, comprising the step of regulating the oxygen potential in the slag within the range from 10 to 10 ^-9 Pa. 34. The method according to any one of paragraphs 18-33, in which the afterburning is carried out inside a single-chamber furnace. 35. The method according to any one of claims 18 to 34, wherein the afterburning comprises introducing into the afterburning zone an oxygen-containing gas, preferably selected from air, oxygen-enriched air and purified oxygen gas. 36. The method according to any one of claims 18 to 35, wherein the oxidized form of said at least one evaporated metal or metal compound is recovered from the gas in the form of dust. 37. The method according to any one of claims 18 to 36, wherein extracting from the gas the oxidized form of said at least one vaporizable metal or metal compound comprises filtering the gas containing the oxidized form of said at least one vaporizable metal or metal compound using a filter, preferably a filter cloth. 38. The method according to any one of paragraphs. 18-37, further comprising the step of cooling before extracting from the gas the oxidized form of said at least one vaporizable metal or metal compound. 39. The method according to any one of claims 18-38, comprising forming a molten metallic phase and further comprising the step of removing the molten metallic phase from the furnace. 40. The method according to any one of paragraphs. 18-39, in which the metal charge contains slag, and wherein the slag contains sulfur and/or sulfur compounds, and the method further comprises the step of forming a molten matte phase and the additional step of removing the molten matte phase from the furnace. 41. The method according to any one of paragraphs 18-40, in which the metallurgical charge is introduced into the furnace in the form of a liquid. 42. The method according to any one of paragraphs. 18-41, in which the metallurgical charge is a metallurgical slag, and wherein the method produces a second slag. 43. The method according to claim 42, wherein the molten slag has an average temperature less than 50 degrees Celsius above the liquidus temperature of the slag. 44. The method according to claim 42 or 43, wherein an oxide selected from CaO, Al ₂ O ₃ and combinations thereof is added to the bath in the furnace, preferably at a temperature in the bath of at least 1000°C, preferably about 1150°C. 45. The method according to any one of claims 42-44, further comprising the step of cooling the second slag to convert it into a solid, wherein the second slag is preferably first removed from the furnace as a liquid. 46. The method according to claim 45, wherein cooling is carried out by contacting the liquid second slag with water. 47. The method according to claim 45 or 46, wherein the second slag is cooled at a rate of at least 30 degrees Celsius per second. 48. The method according to any one of claims 45-47, further comprising the step of grinding the solid second slag, preferably grinding the second slag into powder. 49. The method according to any one of paragraphs. 45-48, in which the second slag is cooled at a rate of less than 40 degrees Celsius per second. 50. The method according to any one of paragraphs 45-49, further comprising the step of adding a second slag as a binder or aggregate during the production of the object for the construction industry. 51. The method according to claim 50, wherein slag is used as a binder and the object further comprises an aggregate, which preferably comprises sand and/or a second slag. 52. The method of claim 51, further comprising adding an activator during production of the object. 53. The method of claim 52, wherein the activator is selected from the group consisting of sodium hydroxide, NaOH, potassium hydroxide, KOH, sodium silicate, Na ₂ SiO ₃ , potassium silicate, K ₂ SiO ₃ and combinations thereof. 54. The method according to any one of paragraphs 50-53, wherein the object for the construction industry is a construction element. 55. The method according to claim 54, wherein the construction element is selected from the list of tiles, paving stones, blocks, concrete blocks and combinations thereof. 56. The method according to any one of paragraphs 50-55, wherein the object for the construction industry has a foamed structure. 57. The method according to any one of claims 18 to 56, wherein at least part of the method is monitored and/or controlled electronically, preferably by means of a computer program. 58. The use of a single-chamber furnace according to any one of paragraphs 1-17 as an apparatus for fuming at least one evaporated metal or metal compound from a metallurgical charge selected from copper smelting slag and copper refining slag, as well as combinations thereof. 59. The use according to claim 58, wherein the evaporated metal or metal compound is selected from zinc, lead, tin, bismuth, cadmium, indium, germanium and combinations thereof.