RU2824636C2 - Use of improved slag from production of non-ferrous metals - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to processing of by-products obtained during production of non-ferrous metals, in particular to use of slag in construction industry. Slag used contains, in terms of dry substance and when expressing the presence of metal through the aggregate value for metal present in the form of metal in elementary form, and metal present in oxidized state, wt.%: iron: at least 7 and not more than 49, copper: not more than 1.3, silicon dioxide: at least 24 and not more than 44, calcium oxide: at least 1.0 and not more than 20, zinc: at least 0.10 and not more than 1.50, magnesium oxide: at least 0.10 and not more than 2.5 and lead not more than 0.100. Slag is used as an ingredient of a composition selected from concrete or cement, wherein said ingredient is selected from a group consisting of a filler or aggregate, a binding substance and combinations thereof.

EFFECT: said slag is characterized by an average particle diameter of at least 10 mcm and not more than 5,0 mm, and an amorphous substance content of at least 30 wt.%, according to determination using X-ray diffraction analysis.

38 cl, 2 tbl, 3 ex

Description

Field of technology to which the invention relates

The present invention relates to the production of non-ferrous metals, such as copper, from primary sources, meaning fresh ore, from secondary feedstock, also known as recycled materials, or from combinations thereof. Recycled materials may be, for example, by-products, waste materials, and materials that have reached the end of their life. More specifically, the invention relates to improved slag as a by-product from such non-ferrous metal production.

The slag by-product from copper (Cu) production is particularly special in terms of composition. The operating temperatures of a copper smelting furnace are usually significantly lower than those of certain other smelting furnaces. In order to ensure sufficient fluidity of the slag at lower temperatures, specific ingredients are required or desirable, since they can tend, sometimes in specific concentration ranges, to suppress the melting point of the slag and thus make the process operable without exposure to excessively high temperatures, which are very costly in terms of energy consumption and thus in terms of operating costs.

State of the art

The materials available as feedstock for the production of non-ferrous metals typically contain a variety of metals. Because of the high purity requirements for non-ferrous metals in most of their high-volume applications, the various metals must be separated from each other in the production process. Non-ferrous metal production processes typically involve at least one, and typically multiple, pyrometallurgical process steps in which both metals and metal oxides exist in a liquid molten state, and where the metal oxides can be separated by gravity from the molten metal phase as a separate liquid slag phase. The slag phase is typically withdrawn from the process as a separate stream, and this separation can result in the production of slag as a by-product of metal production.

Non-ferrous metals can be produced from fresh ore as feedstock, also called primary sources, or from recycled materials, also known as secondary feedstock, or from a combination of both.

The recovery of non-ferrous metals from secondary feedstock has become an activity of prime importance over the years. Recycling of non-ferrous metals after use has become a key contributor to the industry due to the continuing urgent need for such metals and the decreasing availability of high-quality fresh metal ores. Also, recycling of secondary feedstocks typically involves the use of pyrometallurgical process steps, such as in the case of smelters that produce slag as a by-product.

The slag mainly contains metal oxides, which are liquid at high temperatures. In non-ferrous metal smelting furnaces, such as copper, lead or zinc smelting furnaces, the metal oxides are present in a liquid state and have a lower density compared to the liquid molten metals. The metal oxides can then be separated from the metals by gravity. The slags are usually cooled and crushed/sized, and can be used in the production of concrete, as a substitute for cobblestones and gravel, as an aggregate in road construction, and when ground, due to their unusual hardness, they are also of interest for use as blasting sand or blasting grit.

Some of the substances that may be found in slag products known in the art are considered to be potentially harmful to the environment. The main examples of such undesirable substances are mainly lead, but also to some extent zinc. Both zinc and lead are metals that are usually present in forms that are leachable from the slag, and their presence at significant levels will preclude many uses of the slag product, particularly in more economically attractive applications, and may make disposal of such slags in waste disposal sites much more difficult and problematic, usually requiring them to be treated as "hazardous waste". Acceptability of use in certain applications is often determined by testing the leaching behaviour of the slags. Typically, elements such as Pb and Zn are susceptible to leaching and may cause a particular slag to fail such acceptance tests.

In addition, the level of Pb in a product or composition may impose restrictions on its use, as lead has raised concerns as a possible reproductive toxin. Classification limit studies are currently underway in some jurisdictions for the relevant CLP (Classification, Labelling, Packaging) regulations, with the aim of establishing a specific classification limit (SCL) for Pb and Pb-containing compounds. The limit could potentially be as low as 0.03 wt% Pb. Commercially available slags from non-ferrous metal production are characterized by Pb levels that are typically well above the even higher 0.3% level. If the CLP regulation comes into force, these modern non-ferrous metal slags will be subject to additional labelling requirements, which will make the commercial use and acceptability of these slags in many modern applications more difficult, if not impossible, and which may also increase the burden on selected disposal routes, such as landfill. In this context, it is important to note that certain end-use options, such as the use of slag as blasting sand, mean that the waste by-product from the blasting operation, which includes the slag, is typically disposed of as landfill. Therefore, the level of lead in the slag may seriously impair the use of the slag in some modern high-value end-use applications, such as some forms of sand blasting.

In the publication by S. Monosi et al., “Non Ferrous Slag as Cementitious Material and Fine Aggregate for Concrete”, presented at the 3 ^rd CANMET/ACI International Symposium on Sustainable Development of Cement and Concrete, 2001, a slag containing 4.77 wt% Zn and 2.03 wt% Pb was tested as an ingredient in concrete replacing Portland cement and/or natural sand. The slag also contained 14.65 wt% SiO ₂ . Leaching tests showed the release of zinc and lead, but at values that remained below the 1998 Italian legal standard.

However, as the inventors have discovered, the presence of zinc in the slag at the levels used in the work of the author Monosi results in a significant retardation of the hardening of concrete and other building material compositions such as cements. This effect on the rate of hardening constitutes an obstacle to the use of slags containing significant amounts of Zn as a cementitious material and/or as an aggregate in concrete or cements.

There remains a need, therefore, for a slag from non-ferrous metal production that has a reduced risk of metal leaching, in particular a slag that has a lead content and/or a zinc content that is low enough not to pose any leaching problems, so that the slag can be suitable for use in economically attractive end-use applications and can be upgraded as a result of that use.

In addition, there remains a need for slag from non-ferrous metal production that has a Pb content of less than 0.03% (w/w) and would therefore offer the benefit of being exempt from additional labelling requirements under the potential upcoming CLP regulations in certain jurisdictions.

In addition, there remains a need for slag from the production of non-ferrous metals which does not introduce the disadvantage of reducing the rate of hardening of concrete or cement containing such slag as a cementitious material or as a filler.

Publication US 5749962 describes a slag by-product from the production of nickel from nickel ore, the slag being described as being "essentially FeO⋅SiO ₂ ", and its use after milling as a binder in a mixture with rapid-hardening portland cement of type 3 to produce a cement mixture, such as for the production of concrete. The slag is free of Zn and Pb, since the ore for the production of nickel is also free of these substances.

Publication US 4,571,260 discloses a process for recovering valuable metal particles from tin and/or zinc containing materials, particularly lead containing materials, by heating and melting the feedstock in a Cal-Do converter together with coke as a reducing agent and a large amount of limestone and iron oxide as a flux, all in a series of successive batch processes starting with an oxidation step. In at least one subsequent reduction step, zinc and, if present, tin can be sublimated and recovered from the flue gas effluent. A large amount of flux is required to give the slag a viscous consistency at the selected reduction temperatures so that the coke can be maintained as a suspension in the slag under vigorous agitation or stirring, particularly during the later part of the reduction period. The 8 tons of slag remaining as residue in the single example in US 4571260 contained 1.5% Pb and 1.0% Zn. This slag still contains amounts of zinc and lead that may pose problems with respect to metal leaching. The final slag in US 4571260 is dumped.

In the publication by E. Hecker, B. Friedrich and J. Böhlke – «Treatment of lead and zinc slabs in hollow electrode DC-EAF in consideration of calculated phase equilibria and thermodynamics», in VII International Conference on Molten Slag Fluxes and Salts, 2004, The South African Institute of Mining and Metallurgy, pp. 377-384 the treatment of slags from the lead or zinc industry is disclosed, more specifically slags from the Keno-Schumann-Lergy (KSHL) process for lead recovery and slags from the Imperial Smelting (IS) process for zinc recovery. Pyrometallurgical processes for lead and zinc recovery are known to require higher operating temperatures compared to copper recovery processes. The paper proposes an improved slag treatment compared to conventional slag fuming or its variant known as the Ausmelt or Isaacmelt process. The authors worked using a pilot-scale direct current electric arc furnace (EAF-DC) employing a gas-tight hollow graphite cathode system to feed brown coal coke into the slag. Only a gentle flow of nitrogen gas is used to counteract capillary forces between the slag and the inner surface of the electrode. Thus, the off-gas is enriched in CO ₂ , a gas that is formed by the reduction reaction of the metal oxide in exchange for the oxidation of the injected carbon. A certain amount of tertiary air is introduced to supply sufficient oxygen above the bath to oxidize the vaporized Zn metal in the off-gas to form ZnO and to burn off any remaining CO to form additional CO ₂ . The external heat input to the EAF-DC furnace is direct heating caused by an electric arc running in the slag bath between the two electrodes. Tables I and II in the publication provide information on the slag compositions before and after treatment. In the absence of post-processing information, the grades can be calculated from the enrichment factor for the total Fe concentrations. All slags are free of any copper content. In addition, the slag from the KShL process contains 0.11 wt% Pb after processing and therefore may still pose a problem of unacceptable Pb leaching. The slag from the IS process contains 5.0 wt% MgO after processing. According to the explanation above in this document, the high MgO concentration brings the disadvantage of higher slag melting point, which increases the additional load in terms of processing temperature, requiring additional investment and energy input.

Publication No. US 8,088,192 discloses the processing of a cold-fed Cu-Fe-Ni based slag in an AC electric arc furnace. The original slag was still copper rich at 8 wt.% and contained 5 wt.% MgO. Prior to processing, highly concentrated copper (97.7 wt.%) was also charged into the furnace. Thereafter, heating to 1450°C, stirring with N ₂ , further addition of slag and quicklime, CaO, resulted in a homogeneous slag. Subsequent reduction was accomplished by injection of finely dispersed anthracite. Settling of the phases resulted in separation of a slag phase containing 3% MgO. The slag of publication US 8,088,192 was reported to be free of any alkali metal oxides.

In the publication by K. Koch and D. Janke, "Schlacken in der Metallurgie", ISBN 3-514-00254-1 on page 157, "dezincified" slag is disclosed. The slag is the result of fuming under reducing conditions of copper-containing slag, during which lead and zinc are reduced and evaporate immediately after leaving the reactor, being oxidized and deposited as dust. The document is silent on any presence of magnesium oxide in the slag.

JP 2001 040431 A discloses how the mobility of a slag by-product from copper production can be improved by adding CaO, _SiO2 and Fe to the slag. According to the disclosure in Table 1, a wide range of slags were considered as starting materials, all of which were enriched in ZnO at least 2.4 wt.%, corresponding to 1.9 wt.% Zn, and in copper at least 6.8 wt.% when expressed as _Cu2O , corresponding to at least 6.04 wt.% copper. Selected slags from Table 1 were subjected to an additional reduction step by adding iron and optionally air in order to reduce their content as _Cu2O and recover more copper. This step resulted in the slag compositions disclosed in Table 2, which contained significantly higher amounts of FeO and in which the _SiO2 content was diluted to at most 20.8 wt.% SiO2. In one working example from JP 2001 040431 A, where subsequent amounts of _SiO2 were added to slag 15 from Table 1 during an iron reduction step with simultaneous air injection, _three intermediate slag compositions were disclosed, one of which contained 0.7 wt.% _Cu2O , 0.9 wt.% ZnO and only 21.5 wt.% _SiO2 .

Publication WO 2014/046593 A1 discloses a method for extracting vaporizable metals and/or metal compounds from molten slag using a submerged jet of high-energy hot plasma gas. The advantage is that high fuming rates can be achieved well below the previously required average slag temperatures. This brings the advantage of reduced energy requirements, reduced requirements for slag formers or fluxes and therefore also a reduced final slag quantity and reduced equipment wear. In the examples, mixtures of 1000 kg of electric arc furnace (EAF) dust, 100 kg of coke and 100 kg of sand are processed to produce slags containing only 1.3 wt.% ZnO, corresponding to 1.04 wt.% Zn, and at most 26.0 wt.% SiO ₂ . The slags produced in WO 2014/046593 A1 still contain sufficient zinc to pose a problem with respect to metal leaching. WO 2014/046593 A1 also provides no information on the possible beneficial effects of its slags when used in specific end-use applications.

A. F. S. Schoukens, L. R. Nelson and N. A. Barcza, "Plasma-Arc Treatment of Steel-Plant Dust and Zinc-Containing Slag – Theoretical and Practical Considerations", Mintek Paper 8128, at The International Lead and Zinc Study Group Conference in Rome, June 11-13, 1991, disclosed a plasma-arc process from Mintek for treating steel-plant dust and lead-furnace slag. The lead-furnace slag contained 14 wt.% ZnO and 2.8 wt.% PbO. The reducing agent was charcoal, which was dosed to selectively reduce lead and zinc oxides while simultaneously preserving iron as oxide in the slag. The slag discharged from the processing of lead smelting furnace slag had a temperature of 1500°C, which is said to be necessary for the reduction of zinc and lead oxides in the dust (Item 4, 2nd paragraph). The slag produced from the lead smelting furnace slag contained only 20% FeO, but up to 26% (mass) CaO and 8% (mass) MgO. The slag has a relatively high melting point, which brings with it the disadvantage of requiring a high amount of energy to process it in a liquid state.

Publication WO 2013/156676 A1 discloses a method for processing slags from non-ferrous metallurgy to convert them into a powder material suitable for uses other than dumping. The method includes a reduction step, wherein the iron in the slag is to be reduced to such an extent that the metal phase contains a sufficient amount of iron to impart magnetic properties to the metal phase. The method includes sufficient mixing in order to retain the metal droplets in the molten slag and to prevent the droplets from settling and settling to the bottom of the furnace. The method further includes evaporating zinc, lead, arsenic and cadmium from the mixture. The slag-metal mixture formed and remaining in the reduction furnace is tapped and cooled. The cooled mixture is crushed and ground to a grain size in the range of 20 μm - 15 μm. Metals and possible sulphides are separated from the slag, for example, as a result of magnetic separation. An example is provided for the processing of slags containing either 4% Zn or 2.4% Zn. The starting slags were treated using silicon carbide (Examples 1 and 2) or carbon (Example 3) as reducing agents. In Example 3, nitrogen was bubbled through the mixture after reduction. The resulting metal alloy and slag mixtures had high levels of Fe with less than 1.00 wt.% Zn, only up to 0.08 wt.% Pb, and either at least 45 wt.% SiO ₂ or at most 1.3 wt.% CaO. The slags were reported to contain metallic inclusions containing both copper and iron. The slag-metal mixtures of Examples 1 and 3 were converted to a powder and subjected to magnetic separation to separate the metals. Only for Example 3, the composition of the residual non-magnetic final slag was reported, and this composition was surprisingly similar to that reported for the mixture of metal alloy and slag before separation of the metal phase. The final slag was enriched in _SiO2 and contained no more than 1.4% CaO. WO 2013/156676 suggests the use of the residual slag in road construction, in landfill applications or as a component of concrete and cement. Nothing is known from WO 2013/156676 about any potential active function of its slag in the construction industry and/or for inorganic polymers.

There remains a need to upgrade the slag by-product from non-ferrous metal production, produced as a by-product in the processing of primary and/or secondary feedstock, using a light and simple process to a quality that is acceptable from the point of view of possible metal leaching and, in addition, capable of providing an active, technical and therefore economic contribution to the downstream use of the slag without the disadvantages explained above.

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

Disclosure of invention

According to the invention, there is proposed a slag, a method for producing slag and variants of using slag in accordance with the definition of the invention in any of the claims of the appended invention.

In one embodiment, the invention provides a slag by-product from the production of non-ferrous metals, containing, on a dry matter basis and wherein the presence of metal is expressed as a combined value for metal present as elemental metal and metal present in an oxidized state, preferably as a metal oxide, in pure form and/or in combination with other metals:

a) at least 7% (mass) and not more than 49% (mass) of iron, Fe,

b) no more than 1.3% (mass.) copper, Cu,

c) at least 24% (wt.) and not more than 44% (wt.) silicon dioxide, SiO ₂ , and

d) at least 2.0% (wt.) and not more than 20% (wt.) calcium oxide, CaO,

and the slag contains the same calculation

e) at least 0.10% (wt.) and not more than 1.00% (wt.) zinc, Zn,

f) at least 0.10% (wt.) and not more than 2.5% (wt.) magnesium oxide, MgO, and

g) not more than 0.100% (mass.) lead, Pb.

In one embodiment, the present invention provides an object comprising, as a binder and/or as a filler, a slag according to the present invention, wherein the slag contains no more than 1.50% (by weight) zinc, Zn.

As the inventors have found, the slag according to the present invention is capable of performing the function of a binder in a geopolymer system. As the inventors have further found, the slag according to the present invention can also be a very suitable filler for use in such a geopolymer system, and its use as a filler also contributes to the extremely good properties of the products produced using such a geopolymer system.

In comparison with the publication US 5,749,962, the present invention brings the advantage of being able to process zinc-containing feedstock in a smelter. The method for producing slag according to the present invention is able to ensure the removal of Zn, which is present in the feedstock, the content of which in the slag is reduced to a level that is acceptable and creates little or no problems from the point of view of health, industrial hygiene and the environment, but is still sufficient to be detected using an appropriate analytical technique, such as at least 0.10% (wt.).

The slag according to the present invention has both a minimum and a maximum MgO content according to the teaching of the invention. Magnesium may enter the slag due to its presence in the raw material of the process, but it may also be leached out. As the applicants have found, the presence of a minimum amount of MgO in the slag is capable of providing a significant reduction in the melting point of the slag. However, as the applicants have also found, higher amounts of MgO, on the other hand, may again lead to a significant increase in the viscosity of the slag and thus weaken or eliminate the observed effect and may even ultimately lead to a slag having a viscosity that is greater in comparison with the viscosity in the absence of any MgO. It is believed by the applicants, without wishing to be bound by this theory, that this effect is due to the release of MgO from solution, possibly during the formation of the spinel form, which gives the slag a thick and oily appearance. The relatively small presence of MgO oxide coming from the solution is believed to lead to a slight and significant increase in the viscosity of the slag, which makes the processing in the liquid state very difficult. Therefore, the slag according to the present invention, as indicated, also contains no more than an upper limit of MgO. Due to the presence of MgO in the indicated range, the slag is more fluid at relatively low temperatures in the furnace where the slag is formed, before its plasma treatment. This brings the advantage of being able to achieve a better separation between the components in the slag and the components in the liquid metal phase so that a more concentrated metal phase and at the same time a more concentrated slag phase can be obtained, in both cases in terms of the desired components for these two phases. This leads, on the one hand, to a higher degree of extraction of the desired metals in the metal phase, a higher concentration of the desired metals in the metal phase, and, on the other hand, to a lower concentration of the contents of valuable metals in the slag phase. The presence of MgO according to the teaching of the invention also brings the advantage of reducing the requirements of the downstream processes, in the case of the present invention, for the processing step by plasma treatment of the slag in order to produce the final slag. The plasma treatment step can be carried out at a lower temperature and still show at least the desired fuming activity, but, more importantly, an improved separation between the different phases, liquid-liquid as well as vapor-liquid, due to better slag flowability, such as lower viscosity, and thus achieving at least the desired processing rates in terms of fuming zinc and/or lead from the slag and producing a slag according to the present invention. Therefore, the level of MgO in the slag according to the present invention is an important element of the present invention.

The slag according to the present invention contains a minimum amount of MgO according to the teaching of the invention. The advantages and benefits of this in comparison with the disclosure in the publication by K. Koch and D. Janke, "Schlacken in der Metallurgie", ISBN 3-514-00254-1 in accordance with the disclosure on page 157 and cited above in this document have already been discussed elsewhere in this document.

The slag according to the present invention, in comparison with the slag treated using the KSL process from the article by E. Hecker, B. Friedrich and J. Böhlke cited above in this document, brings the advantage of having less of a problem with respect to Pb leaching in its application area and thus creates little or no problems from the standpoint of health, industrial hygiene and the environment.

The slag according to the present invention, in comparison with the slag treated using the SI process of the article by E. Hecker, B. Friedrich and J. Böhlke cited above in this document, brings the advantage of a small amount of MgO. This brings the advantage of reducing the melting point of the slag and as a result of this improving the fluidity of the slag at the same temperature. This makes it possible to reduce the operating temperature and thus the energy requirement and/or an improved separation between the liquid slag phase and the liquid metal phases in the stage of the process where the slag and the metal are separated from each other by gravity, preferably a combination of both advantages. Due to the small presence of MgO, the slag is more fluid at relatively low temperatures in the furnace where the slag is formed, before its plasma treatment. This brings the advantage of being able to achieve a better separation between the components in the slag and the components in the liquid metal phase so that a more concentrated metal phase and at the same time a more concentrated slag phase can be obtained, in both cases in terms of the desired components for these two phases. This leads, on the one hand, to a higher degree of extraction of the desired metals in the metal phase, a higher concentration of the desired metals in the metal phase and, on the other hand, to a lower concentration of the valuable metal contents in the slag phase. The low presence of MgO also brings the advantage of reducing the requirements for the downstream process, in the case of the present invention, the processing step by plasma treatment of the slag for the production of the final slag. The plasma treatment step can be carried out at a lower temperature and still exhibit at least the desired fuming activity due to better slag flowability, such as lower viscosity, and thus achieving at least the desired processing rates in terms of fuming zinc and/or lead from the slag and producing a slag according to the present invention. Therefore, the low MgO content in the slag according to the present invention also represents an important element of the present invention.

As the inventors have furthermore discovered, slags containing rather high concentrations of iron, usually in its oxide form, are characterized by excellent fluidity in themselves and therefore require less calcium in order to achieve the same desirable performance characteristics for separation between the slag and the metal phase and thus the desirable low level of Pb and/or Zn in the slag, but also a reduction in the level of other valuable metals in the slag, such as Cu and/or Sn. Therefore, the inventors prefer to produce a slag containing at least 8% by weight of Fe, preferably at least 10% by weight, more preferably at least 15% by weight, even more preferably at least 20% by weight, furthermore more preferably at least 25% by weight, preferably at least 30% by weight, more preferably at least 35% by weight, even more preferably at least 37% by weight of Fe. Therefore, when converted to FeO, the inventors prefer to produce a slag containing at least 9% (w/w) of iron oxide when expressed in terms of FeO and calculated in accordance with the explanation elsewhere herein. Preferably, the slag contains at least 10% (w/w) of FeO, preferably at least 12% (w/w), more preferably at least 15% (w/w), even more preferably at least 20% (w/w), further more preferably at least 30% (w/w), preferably at least 40% (w/w), more preferably at least 45% (w/w), even more preferably at least 50% (w/w) of iron oxides when expressed in terms of FeO. As the applicants have found, this feature makes it possible to produce a slag which is less enriched in CaO and which therefore requires the addition of smaller amounts of CaCO ₃ in order to obtain the desired good fluidity, low melting point and thus good workability and separation at lower temperatures. Therefore, the inventors prefer that the slag contain no more than 18% by weight of CaO, preferably no more than 15% by weight, more preferably no more than 12% by weight, still more preferably no more than 10% by weight, furthermore more preferably no more than 8.0% by weight.

In another embodiment of the invention, a method for producing a second slag according to the present invention is provided, wherein the slag contains no more than 1.50% (wt.) zinc, Zn, and at least 1.0% (wt.) CaO, wherein the method comprises the steps of

• providing a first slag containing at least one metal selected from zinc, lead and combinations thereof,

• introduction of the first slag into the fuming furnace,

• fuming at least one metal selected from zinc, lead and combinations thereof from a first slag using at least one plasma torch to produce a second slag and

• removal of the second slag from the fuming furnace.

As the inventors have found, the slag according to the present invention can be easily produced using the method according to the present invention, in particular the method is capable of easily achieving the desired low levels of Pb and Zn in a single and relatively simple process step. As the inventors believe, this method brings significant advantages over the methods known in the art, such as the method of publication WO 2013/156676 A1, which includes first a reduction step in an electric furnace, followed by fine grinding of the material plus magnetic separation of metal particles from the remaining slag. As the inventors have further found, the method according to the present invention does not require the large amounts of flux required by other methods known in the art, where these materials would dilute and perhaps even suppress the technical contribution that the slag would otherwise be able to make in its use as a binder in the construction industry.

As the inventors have further discovered, the slag according to the present invention has a sufficiently low zinc and/or lead content such that the slag does not present metal leaching problems and thus can be considered acceptable in more economically attractive end-use applications.

As the inventors have furthermore also discovered, using the process according to the present invention, a slag could be produced which has a very low Pb content, which could therefore be able to avoid additional labelling requirements possibly imposed by the CLP regulations when produced in certain jurisdictions. Therefore, the slag could also remain quite acceptable for use in a variety of modern applications where conventional slags may run the risk of being shown to be unacceptable or undesirable. In addition, in the event of excess availability of slag in comparison to the commercial need for it, the burden and cost of establishing waste disposal sites for such excess slag according to the present invention would remain limited.

As the inventors have also discovered, the slag according to the present invention, in particular obtained by using the method according to the present invention, is characterized by a particularly low zinc content. As the inventors have discovered, when using the slag according to the present invention in concrete and/or cement, the rate of hardening of the composition is no longer significantly reduced, as is the case with slags containing higher amounts of Zn.

In yet another embodiment of the invention, a wide range of uses for the slag of the present invention is provided, as set forth in several claims relating to the use.

As the inventors have found, the slag according to the present invention, which contains not more than 1.50% by weight of zinc, Zn, and at least 1.0% by weight of CaO, can be used as an active binder in the construction industry. The slag can be used as a partial substitute for Portland cement. Such activity can be called "pozzolanic activity", which is defined as a measure of the degree of reaction over time or the rate of reaction between the pozzolan and Ca ^{2 +} or Ca(OH) ₂ in the presence of water. The rate of the pozzolanic reaction depends on the intrinsic characteristics of the pozzolan, such as the specific surface area, the chemical composition and the content of the active phase. Physical adsorption on the surface is not considered as part of the pozzolanic activity, since no irreversible molecular bonds are formed in this process. As the inventors have discovered, for example, by adding the slag of the present invention in an amount of approximately 30% of the Portland cement substitute, 30% less Portland cement can be used while still being able to produce from the mixture a concrete product exhibiting a compressive strength that is only 6% less than the compressive strength of the same product produced using 100% cement. As the inventors believe, without wishing to be bound by this theory, this ability is made possible by the low presence of zinc, below the level at which it can act as a poison or pollutant, interfering with the activity of the slag. As the inventors have discovered, a similar slag containing approximately 8% by weight of zinc was unable to exhibit this activity.

Therefore, in yet another embodiment of the invention, there is provided the use of slag according to the present invention as an ingredient selected from the group consisting of a filler, a binder and combinations thereof, in the construction industry.

As it was found by the inventors, the slag according to the present invention, in particular when ground, in the case of using this second slag as a partial substitute for Portland cement as a binder in the composition, showed performance characteristics significantly better in comparison with the equivalent produced from the first slag from which the slag according to the present invention was produced using the method according to the present invention and which contained approximately 8% (wt.) zinc, Zn, and in the range of 0.3-0.5% (wt.) lead, Pb. As it is believed by the inventors, this difference in performance characteristics can be due to the lower level of zinc content based on the observation that zinc retards the activity of conventional cement. As it was found by the inventors, this difference in performance characteristics is already significant for a slag containing not more than 1.50% (wt.) zinc, Zn, and at least 1.0% (wt.) CaO.

As the inventors have discovered, the slag according to the present invention can also be used to bring about several other technical effects.

In one embodiment, the slag of the present invention, wherein the slag comprises no more than 1.50% by weight of zinc, Zn, and at least 1.0% by weight of CaO, can be used in an end use selected from the preparation of a wearing layer and/or coating for roofing tiles or roofing shingles, as a component of blast sand or blast chips, as a component of foam tiles, as a black colorant, preferably in building products, more preferably in black tiles, as black hard chunks, preferably for decorative purposes, and as high-density ballast, preferably for underwater applications, more preferably for hydraulic engineering, and combinations thereof.

In yet another embodiment, wherein the slag comprises no more than 1.50% (wt.) zinc, Zn, and at least 1.0% (wt.) CaO, the invention provides an effect selected from reducing the sintering temperature of brick or unfired brick, sound insulation, protection from x-ray radiation, and combinations thereof.

As the inventors have discovered, the slag is characterized by a high material density, in the range of 2.9-4.0 tons/ ^m3 . In addition, the slag has been found to be non-porous. Thus, the slag can provide a good sound insulation effect. As the inventors have also discovered, in particular, the high material density makes the slag suitable for use and of exceptional interest for X-ray protection.

As the inventors have found, the slag has a very dark black color. Despite the fairly widespread black coloration of fayalite slag, as the inventors have found, this coloration of the slag according to the present invention is extremely stable, in particular in comparison with many alternative colorants. Therefore, due to the low zinc content and the low lead content, the slag according to the present invention can be used as a suitable colorant for use in the production of black building products, such as black floor tiles, which are currently extremely popular and for which iron oxide, FeO, is currently used, but which is a more scarce and rather expensive raw material.

Implementation of the invention

The present invention will be described in the following with respect to specific embodiments, but the invention is not limited by them, but only by the claims.

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

In addition, the terms "upper," "lower," "above," "below," and the like in the description of the invention and in the claims are used for descriptive purposes and not necessarily to describe relative positions. Thus, the terms used are interchangeable in appropriate circumstances, and embodiments of the invention described herein may be suitable for operation in orientations other than those described or illustrated herein.

The term "comprising" used in the claims shall not be interpreted as being limited to the means listed after it; it does not exclude other elements or steps. It must be interpreted as indicating the presence of the claimed features, integers, steps or components according to the reference thereto, but does not exclude in advance the presence or addition of one or more other features, integers, steps or components or groups thereof. Thus, the scope of the expression "a device comprising means A and B" shall not be limited to devices consisting only of components A and B. This means that, with respect to the present invention, the only significant components of the device are A and B. Accordingly, the terms "comprising" and "including" cover to a greater extent the limiting terms "consisting essentially of" and "consisting of".

In this document, unless otherwise indicated, the amounts of metals and oxides are expressed in accordance with the usual practice in pyrometallurgy. The presence of each metal is usually expressed in terms of 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 reduced relatively easily to their elemental forms and that can exist as molten metal in a pyrometallurgical process, it is quite common to express their presence in terms of their elemental metal form even when giving a slag composition where the main part of such metals may actually be present in an oxidized form. This is why for a slag composition such as the slag according to the present invention, the level of Fe, Zn, Pb, Cu, Sb, Bi as metals in elemental form is indicated. Less noble metals are more difficult to reduce under non-ferrous pyrometallurgical conditions and mainly exist in an oxidized form. These metals are usually expressed in terms of their most common oxide form. Therefore, for slag compositions, the content level of Si, Ca, Al, Na is usually given, respectively, when expressed as SiO ₂ , CaO, Al ₂ O ₃ , Na ₂ O.

The Cal-Do process as used in US 4,571,260 and WO 2013/156676 A1 is a conventional pyrometallurgical process using a top-blown rotary converter (TBRC - Cal-Do furnace or Cal-Do converter) in which molten metal as a heavier phase and a molten slag phase as a lighter phase can exist simultaneously. Heat is provided in this process by means of an oxy-fuel flame and subsequently by introducing coke or some other suitable reducing agent into the already molten liquid(s). The plasma method according to the present invention uses a plasma torch to fume some metals from the slag. The method according to the present invention exhibits higher performance characteristics due to the ability of the very high temperature plasma stream at temperatures significantly greater than 1500°C and easily at least 3000°C and even 5000°C to cause local temperatures that are much higher than the average temperature in the melt, and is more flexible in comparison with conventional torch systems since it makes it possible to regulate the oxygen potential practically independently of the amount of heat generated.

In one embodiment, the slag according to the present invention comprises at least 8% by weight of Fe, preferably at least 10% by weight, more preferably at least 15% by weight, even more preferably at least 20% by weight, furthermore more preferably at least 25% by weight, preferably at least 30% by weight, more preferably at least 35% by weight, even more preferably at least 37% by weight. In a further embodiment, the slag according to the present invention comprises at most 48% by weight of Fe, preferably at most 47% by weight, more preferably at most 45% by weight, even more preferably at most 43% by weight, furthermore more preferably at most 41% by weight. The Fe content of the slag from non-ferrous metal production is preferably determined according to the method described in DIN EN ISO 11885.

In one embodiment, the slag according to the present invention comprises at least 22% by weight of SiO ₂ , preferably at least 24% by weight, more preferably at least 25% by weight, even more preferably at least 26% by weight, furthermore more preferably at least 27% by weight, preferably at least 28% by weight, more preferably at least 29% by weight, even more preferably at least 30.0% by weight. In another embodiment, the slag according to the present invention comprises no more than 42% by weight of SiO ₂ , preferably no more than 40% by weight, more preferably no more than 37% by weight, even more preferably no more than 33% by weight, furthermore more preferably no more than 32% by weight. The SiO ₂ content of slag from non-ferrous metal production is preferably determined in accordance with the method described in DIN EN ISO 12677. The SiO ₂ content can also be determined indirectly by first determining the silicon content, Si, using the method in accordance with DIN EN ISO 11885 and then converting this result to the oxide SiO ₂ .

As the inventors have found, the presence of significant amounts of SiO ₂ in the slag according to the present invention, as indicated in the claims, is a significant factor in terms of avoiding explosions during the slag quenching when using water during the pouring of the molten slag from its container. The slag is inevitably enriched in iron in the form of FeO. At sufficiently high temperatures, FeO can act as a catalyst for the reaction of decomposition of water into gaseous O ₂ and gaseous H ₂ . Hydrogen gas in a mixture with air and certainly with oxygen has a very wide flammability range and thus readily explodes in a mixture with air or oxygen in the presence of an ignition source. As the applicants have found, the presence of a sufficient amount of SiO ₂ in the slag is capable of suppressing the catalytic activity of the iron present in the slag in relation to the decomposition of water during the quenching stage with the formation of explosive mixtures. One additional benefit of the presence of more _SiO2 is that it improves the fluidity of the slag such that lower temperatures are sufficient to achieve the same degree and ease of separation between the molten slag and molten metal phases and thus to achieve the desired good separation in terms of the desired level of metal content in the two phases.

On the other hand, maintaining the SiO ₂ content of the slag below the upper limit in accordance with the teaching of the invention brings the advantage of maintaining a lower melting point of the slag. At higher SiO ₂ levels, as discovered by the inventors, the melting point of the slag increases. The melting point of the slag is often also referred to as the "liquidus temperature" of the slag. As it is believed by the applicants, without wishing to be bound by this theory, at high concentrations, some of the SiO ₂ may precipitate as a separate phase, which may have a high viscosity. It is this separate, highly viscous phase that may be responsible for the processing problems at high SiO ₂ levels. Maintaining the SiO ₂ content of the slag below the said upper limit brings the additional advantage of reducing the amount of slag by-product for the same amount of parent metal produced. This reduces the processing load for upgrading a given slag in a manner similar to that achieved by using the method of the present invention.

In one embodiment, the slag according to the present invention comprises at least 1.0% by weight of CaO, preferably at least 1.2% by weight, more preferably at least 1.4% by weight, even more preferably at least 1.75% by weight, furthermore more preferably at least 2.0% by weight, preferably at least 2.25% by weight, more preferably at least 2.50% by weight, even more preferably at least 3.00% by weight. In another embodiment, the slag according to the present invention comprises no more than 18% by weight of CaO, preferably no more than 15% by weight, more preferably no more than 12% by weight, even more preferably no more than 10% by weight, furthermore more preferably no more than 8.0% by weight. The CaO content of slag from non-ferrous metal production is preferably determined in accordance with the method described in DIN EN ISO 11885.

As the applicants have found, the CaO levels in accordance with the invention provide, on the one hand, with respect to the lower level, the advantage of improving the fluidity of the slag and reducing the melting point (or "liquidus temperature") of the slag. This provides advantages in terms of the ease of handling the slag in molten form and allows for improved separation from the molten metal phase at a lower temperature. The CaO level in the slag comes primarily from the added flux, such as CaCO ₃ . As the applicants have found, the addition of CaO to the process, such as by adding CaCO ₃ material which is then converted to CaO, improves the recovery of metal from the slag in the upstream metal recovery stages of the process, facilitates the achievement of low Pb levels and improves the fluidity of the slag. As the applicants have also found, the CaO material also provides advantages in the use of the slag product in geopolymers. Therefore, the prescribed grade levels, in particular the upper limit value, also bring the advantage of not requiring the production and introduction of any excess quantities of such added flux. In addition, these grade levels also result in a reduction in the amount of slag by-product that is produced, which reduces the slag processing load, including the associated waste stream disposal load.

As the applicants have furthermore discovered, the desire to achieve specific levels of CaO in the slag makes it possible to rationally and partially accept, at the upstream stage of the metal recovery process, feedstocks which contain various types of metals of interest but which may be enriched in interfering Ca compounds. These feedstocks are typically waste streams from other processes and typically represent a high disposal load for their operators. Examples of such materials are wastewater treatment sludges containing gypsum (CaSO ₄ ).

The inclusion of an upper limit on the CaO content brings the advantage that less _SiO2 may be needed to maintain CaO in solution and that the slag amount can be kept lower. The lower CaO requirement in the slag brings the additional advantage that less _CaCO3 and/or _CaSO4 may need to be added, which significantly reduces the energy requirement of the process since the melting and decomposition of these calcium sources are extremely energy intensive.

In one embodiment, the slag according to the present invention comprises no more than 1.50% by weight of Zn, preferably no more than 1.40% by weight, more preferably no more than 1.30% by weight, even more preferably no more than 1.20% by weight, furthermore more preferably no more than 1.10% by weight, preferably no more than 1.00% by weight, more preferably no more than 0.90% by weight, still more preferably no more than 0.80% by weight, furthermore more preferably no more than 0.70% by weight. The Zn content of the slag from non-ferrous metal production is preferably determined in accordance with the method described in DIN EN ISO 11885. In a further embodiment, the slag contains at least 0.10% by weight of Zn, preferably at least 0.15% by weight, more preferably at least 0.20% by weight, even more preferably at least 0.25% by weight, furthermore more preferably at least 0.30% by weight, preferably at least 0.35% by weight, more preferably at least 0.40% by weight, and even more preferably at least 0.50% by weight. While on the one hand the applicants prefer to lower the zinc content below the upper limit value according to the indication of the invention, in order to obtain the advantage of a reduced risk of leaching and no risk of classifying the slag as an item of hazardous classification, on the other hand the applicants also prefer to maintain the zinc content above a certain lower limit value, since in this case the burden and costs of removing zinc from the slag remain acceptable.

In one embodiment, the slag according to the present invention contains no more than 0.30% by weight of Pb, preferably no more than 0.25% by weight, more preferably no more than 0.20% by weight, even more preferably no more than 0.15% by weight, furthermore more preferably no more than 0.100% by weight, preferably no more than 0.050% by weight, more preferably no more than 0.040% by weight, still more preferably no more than 0.030% by weight, furthermore more preferably no more than 0.026% by weight. The Pb content of the slag from non-ferrous metal production is preferably determined in accordance with the method described in DIN EN ISO 11885. In a further embodiment, the slag contains at least 0.005% (wt) Pb, preferably at least 0.010% (wt), more preferably at least 0.015% (wt), even more preferably at least 0.020% (wt), furthermore more preferably at least 0.025% (wt), preferably at least 0.030% (wt), more preferably at least 0.035% (wt), and even more preferably at least 0.040% (wt). While on the one hand the applicants prefer to lower the lead content level below the upper limit value according to the indication of the invention, in order to obtain the advantage of a reduced risk of leaching and no risk of classifying the slag as an item of hazardous classification, on the other hand the applicants also prefer to maintain the lead content level above a certain lower limit value, since in this case the burden and costs of removing lead from the slag remain acceptable.

In one embodiment, the slag according to the present invention comprises at most 1.30% by weight of copper, Cu, preferably at most 1.10% by weight, more preferably at most 1.00% by weight, even more preferably at most 0.90% by weight, furthermore more preferably at most 0.80% by weight, preferably at most 0.75% by weight, more preferably at most 0.70% by weight, still more preferably at most 0.60% by weight, furthermore more preferably at most 0.40% by weight. The Cu content of the slag from non-ferrous metal production is preferably determined according to the method described in DIN EN ISO 11885. In another embodiment, the slag comprises at least 100 ppm. (wt.) Cu, preferably at least 0.05% (wt.), more preferably at least 0.10% (wt.), even more preferably at least 0.15% (wt.), even more preferably at least 0.20% (wt.), Cu. Preferably, the slag contains at least 0.30% (wt.), more preferably at least 0.35% (wt.), even more preferably at least 0.40% (wt.) Cu.

The presence of a small but measurable amount of copper, as may be indicated in the claims, makes it possible to process copper-containing raw materials in the production of the slag according to the present invention. Applicants prefer to maintain the copper content of the slag below the upper limit in order to extract as much copper as possible from the raw materials in a more valuable metallic form. In addition, copper is a metal that often exists in a form that can be leached from the slag. Copper has an adverse effect on algal life in aquatic environments. Therefore, leaching of copper may create ecotoxicity problems in some of the potential applications for the slag according to the present invention. On the other hand, applicants prefer to maintain the copper content of the slag above the lower limit since the effort and associated costs of removing additional amounts of copper from the slag increase to an ever-increasing extent. Therefore, maintaining the copper content level in accordance with the invention above the lower limit value reduces the load on processing the feedstock and the corresponding operating costs.

In one embodiment, the slag according to the present invention comprises at most 2.5% by weight of magnesium oxide, MgO, preferably at most 2.00% by weight, more preferably at most 1.50% by weight, even more preferably at most 1.3% by weight, furthermore more preferably at most 1.20% by weight, preferably at most 1.10% by weight, more preferably at most 1.00% by weight. The MgO content of the slag from non-ferrous metal production can be determined by converting the analytical result for magnesium, Mg, to MgO. The magnesium content of such a slag is preferably determined according to the method described in DIN EN ISO 11885. In another embodiment, the slag comprises at least 0.10% by weight of MgO, preferably at least 0.20% by weight, more preferably at least 0.30% by weight. Preferably, the slag contains at least 0.40% (wt.) MgO, preferably at least 0.50% (wt.), more preferably at least 0.60% (wt.), even more preferably at least 0.70% (wt.), furthermore more preferably at least 0.75% (wt.).

The advantages of the stated levels of MgO content in the slag according to the present invention are explained to a large extent elsewhere in this document.

The method described in DIN EN ISO 11885 uses inductively coupled plasma atomic emission spectroscopy (ICP-AES), also called inductively coupled plasma optical emission spectrometry (ICP-OES).

In one embodiment, the slag according to the present invention contains at most 2.0% by weight of sulfur, S, preferably at most 2.00% by weight, more preferably at most 1.50% by weight, even more preferably at most 1.25% by weight, furthermore more preferably at most 1.00% by weight, preferably at most 0.50% by weight, more preferably at most 0.40% by weight, still more preferably at most 0.30% by weight, furthermore more preferably at most 0.20% by weight. The S content of the slag from non-ferrous metal production is preferably determined essentially following the method described in ISO 15350. In another embodiment, the slag contains at least 0.05% by weight of S.

In one embodiment, the slag according to the present invention further comprises at least 9% by weight and no more than 63% by weight of iron oxide when expressed as FeO. This content level is again expressed on the same basis as in claim 1, i.e. on a dry basis. The FeO content level can easily be obtained by converting the content level of Fe in elemental form to FeO. In this context, the Fe content level is expressed as the combined value for the metal present as elemental metal and the metal present in an oxidized state. In one embodiment, the slag according to the present invention comprises at least 10% by weight of FeO, preferably at least 12% by weight, more preferably at least 15% by weight, even more preferably at least 20% by weight, furthermore more preferably at least 30% by weight, preferably at least 40% by weight, more preferably at least 45% by weight, even more preferably at least 50% by weight. In another embodiment, the slag according to the present invention comprises no more than 60% by weight of FeO, preferably no more than 58% by weight, more preferably no more than 56% by weight, even more preferably no more than 54% by weight, furthermore more preferably no more than 53% by weight.

In one embodiment, the slag of the present invention comprises no more than 5.0% by weight of sodium oxide, _Na2O , preferably no more than 4.50% by weight, more preferably no more than 4.00% by weight, even more preferably no more than 3.75% by weight, further more preferably no more than 3.50% by weight, preferably no more than 3.25% by weight, more preferably no more than 3.10% by weight, still more preferably no more than 3.00% by weight, further more preferably no more than 2.90% by weight. The _Na2O content of the slag from non-ferrous metal production can be determined by converting the analytical result for sodium, Na, to _Na2O . The sodium content of such a slag is preferably determined in accordance with the method described in DIN EN ISO 11885. In another embodiment, the slag contains at least 1.00% (wt.) _Na2O .

As the applicants have found, the presence of sodium in the feedstock of the slag producing process is at least partly responsible for the level of _Na2O in the slag according to the invention. As the applicants have further found, the presence of _Na2O is capable of providing a significant reduction in the melting point of the slag. Due to the presence of _Na2O , the slag is more fluid at the relatively low temperatures in the furnace where the slag is formed, before it is plasma treated. This brings the advantage of being able to achieve a better separation between the components in the slag and the components in the liquid metal phase, so that a more concentrated metal phase and at the same time a more concentrated slag phase can be obtained, in both cases in terms of the desired components for these two phases. This leads, on the one hand, to a higher degree of extraction of the desired metals in the metal phase, a higher concentration of the desired metals in the metal phase, and, on the other hand, to a lower concentration of the valuable metal contents in the slag phase. The presence of _Na2O also brings the advantage of reducing the downstream process requirements in the case of the present invention to the processing step by plasma treatment of the slag to produce the final slag. The plasma treatment step can be carried out at a lower temperature and still exhibit at least the desired fuming activity and phase separation rate due to better slag flowability, such as lower viscosity, and thus achieving at least the desired processing rates in terms of fuming zinc and/or lead from the slag and producing a slag according to the present invention. Therefore, the _Na2O content in the slag according to the present invention represents an additional significant element in the context of the present invention.

In one embodiment, the slag according to the present invention further comprises, in the same calculation, at least 3% by weight and not more than 12% by weight of aluminum oxide, Al ₂ O ₃ . Preferably, the slag comprises at least 3.0% by weight of Al ₂ O ₃ , more preferably at least 4.0% by weight, even more preferably at least 5.0% by weight, furthermore more preferably at least 6.0% by weight, preferably at least 7.0% by weight, more preferably at least 7.5% by weight, even more preferably at least 8.0% by weight. In another embodiment, the slag according to the present invention contains at most 11.5% by weight of Al ₂ O ₃ , preferably at most 11.0% by weight, more preferably at most 11.0% by weight, still more preferably at most 10.5% by weight, furthermore more preferably at most 10.0% by weight. The Al ₂ O ₃ content of the slag from non-ferrous metal production is preferably determined in accordance with the method described in DIN EN ISO 11885 for determining the aluminum content and converting the result to aluminum oxide Al ₂ O ₃ .

As has been discovered by the applicants, the raw materials of the process according to the present invention can introduce Al into the process in such a way as by introducing bronze. The element Al can also be introduced as a metal intentionally, for example as a reducing agent, i.e. when oxidized to form Al ₂ O ₃ , the aluminum can assist in reducing, for example, an oxide of a more noble metal to form its elemental metal form. As has been discovered by the applicants, metallic aluminum as a reducing agent can contribute a relatively large amount of energy to the process. As has been discovered by the applicants, the presence of said amounts of aluminum can bring the advantage of reducing the melting point of the slag, all of which have already been discussed elsewhere in this document. As it is further believed by the applicants, the presence of said amounts of Al ₂ O ₃ has a positive effect on the performance of the slag as a geopolymer.

On the other hand, the applicants prefer to take into account the upper limit amount in accordance with the indication of the invention for Al ₂ O ₃ , since, as they have found, excessive levels of Al ₂ O ₃ can increase the viscosity of the slag and thus impair processing.

In one embodiment, the slag according to the present invention contains no more than 1.50% by weight of zinc oxide, ZnO, preferably no more than 1.40% by weight, more preferably no more than 1.30% by weight, even more preferably no more than 1.20% by weight, further more preferably no more than 1.10% by weight, preferably no more than 1.05% by weight, more preferably no more than 1.00% by weight, still more preferably no more than 0.95% by weight, further more preferably no more than 0.90% by weight. The level of ZnO in the slag from the production of non-ferrous metals can be determined by converting the analytical result for zinc, Zn, to ZnO. The zinc content of such slag is preferably determined in accordance with the method described in DIN EN ISO 11885. In another embodiment, the slag contains at least 0.25% (wt.) ZnO.

In one embodiment, the slag of the present invention comprises no more than 0.323% by weight of lead oxide, PbO, preferably no more than 0.300% by weight, more preferably no more than 0.250% by weight, even more preferably no more than 0.200% by weight, further more preferably no more than 0.100% by weight, preferably no more than 0.050% by weight, more preferably no more than 0.030% by weight, still more preferably no more than 0.028% by weight, further more preferably no more than 0.020% by weight. The level of PbO in the slag from non-ferrous metal production can be determined by converting the analytical result for lead, Pb, to PbO. The lead content of such slag is preferably determined in accordance with the method described in DIN EN ISO 11885. In another embodiment, the slag contains at least 0.005% (wt.) PbO.

In one embodiment of the slag according to the present invention, the iron present in the slag is primarily present in the fayalite structure Fe ₂ SiO ₄ , also called ferruginous chrysolite.

In one embodiment of the slag according to the present invention, the slag is characterized by an amorphous content of at least 30% by weight, as determined using quantitative X-ray diffraction (XRD) analysis using Topas Academic Software V5 and using Al ₂ O ₃ as an internal standard, preferably at least 50% by weight, more preferably at least 70% by weight, even more preferably at least 80% by weight, furthermore more preferably at least 85% by weight, for the amorphous content. A higher amorphous content in the slag brings the advantage to the slag of better grindability of the slag. This property is of particular interest when small particles are desired, for example when the slag is to be used as a binder. In another embodiment, the slag is at least substantially crystalline, such as at least 30% crystalline, preferably at least 50%, more preferably at least 70%. The high degree of crystallinity brings the advantage of high hardness and high strength, as well as a high intensity dark black color, which is of particular interest in other end uses, such as quarry stone, and for other decorative purposes.

In one embodiment, the slag according to the present invention has a granular form characterized by an average particle diameter (d50 as calculated on a weight basis and obtainable by sieving) of at least 0.5 mm and at most 5.0 mm, preferably at least 0.7 mm, more preferably at least 0.9 mm, and optionally at most 3.0 mm, preferably at most 2.0 mm. The grinding fineness of the slag can also be expressed by its "Blaine grinding fineness", which is a number widely used to indicate the grinding fineness (specific surface area) of cement. The grinding fineness is determined by measuring the air permeability [ ^cm2 /g] in accordance with DIN 1164 part 4. The Blaine grinding fineness of the slag in one embodiment according to the invention should be in the range of 1800-6000, preferably at least 2000, more preferably at least 2200, even more preferably at least 2500, furthermore more preferably at least 3000. In one embodiment, the Blaine grinding fineness of the slag is at most 5500, preferably at most 5000, more preferably at most 4500, and even more preferably at most 4000. These Blaine grinding finenesses are particularly advantageous when using slag as a binder.

In one embodiment, the slag according to the present invention is in powder form, characterized by an average particle diameter (d50), as determined by wet sieve analysis and therefore an average value calculated on a mass basis, of at least 10 μm and not more than 500 μm, preferably at least 20 μm, more preferably at least 30 μm, and optionally not more than 200 μm, preferably not more than 100 μm, more preferably not more than 50 μm. This brings advantages, in particular, when it is necessary to use the slag as a binder.

In one embodiment of the slag according to the present invention, at least 90% (by weight) of the particles (d90) have a diameter of at most 200 μm, as determined by wet sieve analysis, preferably at most 150 μm, more preferably at most 100 μm. This brings the advantage that the amount of particles is very limited, so that the slag is very easy to handle and results in a homogeneous paste when using the slag as a binder.

In one embodiment, the slag according to the present invention has the form of large pieces having an average particle diameter (d50 as calculated on a weight basis) of at least 4 mm and no more than 200 mm. In one particular embodiment, the slag has an average particle diameter in the range of 4-20 mm. This form of slag is very suitable for use in other applications, such as in the case of filler. In another particular embodiment, the slag has an average particle diameter in the range of 50-200 mm. This form of slag may be suitable for use, for example, as decorative elements, such as quarry stone.

In one embodiment of the object according to the present invention, the object further comprises an aggregate, said aggregate preferably comprising sand and/or slag according to the present invention, which contains no more than 1.50% (by weight) of zinc, Zn. As the applicants have found, said slag is also extremely well suited for use as an aggregate in the construction industry, alone or in combination with other aggregates, such as sand. The slag according to the invention can bring about improvements in strength, as well as improve the aesthetic characteristics of the final product.

In one embodiment of the object according to the present invention, the slag comprises at least 1.0% (w/w) CaO and is present as a binder, wherein the object further comprises an activator. As it has been found by the applicants, the slag according to the present invention can function as an active binder, capable of reacting with a suitable activator and thus exhibiting a strong binding capacity for aggregates. Therefore, the slag can be used as a substitute for 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 resistance properties to coatings, adhesives, composites and the like.

Geopolymers are typically amorphous materials with framework structures containing repeating unit units, which in this case contain Fe and Si atoms linked by common oxygen atoms. Geopolymer applications range widely, many of which are determined by the fire and heat resistance of the materials.

In one embodiment comprising an activator, the activator is selected from the group consisting of sodium hydroxide, _NaOH , potassium hydroxide, KOH, sodium silicate, _Na2SiO3 , potassium silicate _{, K2SiO3} , and combinations thereof, wherein preferably the activator is NaOH.

In one embodiment, the object according to the present invention is a building element, preferably an element selected from the group consisting of a tile, a paving stone, a block, a concrete block and combinations thereof.

The object according to the present invention may possibly be subjected to sintering, which may bring the advantage of changing the color, such as obtaining a reddish color as a result. Also, a curing step at a lower temperature compared to sintering, but for example at a temperature in the range of 120-250 °C, may be used, which may easily contribute to the mechanical properties of the object, as well as to aesthetic aspects.

In one embodiment, the object according to the present invention has a foamed structure. This brings the advantage of reducing the conductivity of heat and sound so that the object can demonstrate heat and/or sound insulation properties and find increased acceptability in applications where these properties are desired or required.

The method of the present invention uses a plasma torch. In the plasma torch, an electric arc is generated between two electrodes, in the space between which a gas stream, such as air or an inert gas, passes. The electric arc heats the gas stream to very high temperatures, and after optional mixing with a reducing agent, such as natural gas, the hot gas stream is then injected into the molten slag bath. It is the hot gas stream passing through the slag bath that heats the slag bath. On its way to the surface, the gas stream picks up fumigable metals, such as Zn and/or Pb. Alternatively, a reducing agent, such as a form of solid carbon or carbonaceous material, preferably petroleum coke, can be added to the slag bath. In this case, the plasma torch provides the energy, and it is the reducing agent in the bath that makes the reduction possible.

One important advantage of the plasma torch fusion process over the EAF-DC process discussed earlier in this document is that the capital investment and ongoing maintenance costs for the processing equipment are much lower. In particular, the electrical and arc generating equipment are much simpler and the furnace containing the slag bath is not part of the electrical circuit for generating the electric arc. One additional advantage is that the plasma torch process is much better suited for use in fusion because the process by its very nature involves passing a significant amount of gas through the slag bath, resulting in vigorous mixing of the bath. In the EAF-DC process, the anode is formed by the molten metal phase beneath the molten slag. The method requires maintaining the two liquid phases clearly separate and continuous and therefore cannot provide the same degree of mixing in the liquid bath as the plasma torch method. Therefore, the plasma torch method is much more efficient in fumigating zinc and/or lead from slag compared to the EAF-PT method.

Thus, the EAF-PT method described in the article by E. Hecker, B. Friedrich and J. Böhlke cited above in this document, as well as the plasma arc treatment method disclosed in the publication by A. F. S. Schoukens, L. R. Nelson and N. A. Barcza, “Plasma-Arc treatment of steel-plant dust and zinc-containing slag – Theoretical and Practical Considerations”, are much less suitable for use in fuming zinc and/or lead in accordance with the present invention.

One suitable method for use in the present invention is discussed in K. Verschuere et al., “Continuous Fuming of Zinc-Bearing Residues: Part II, The Submerged-Plasma Zinc-Fuming Process,” Metallurgical and Materials Transactions B, Vol. 38B, February 2007, pp. 21-33. The authors used a model to investigate the potential effects of a variety of operating parameters on bath temperature, heat loss, slag Zn concentration and grade, and matte Cu concentration and grade. The slag produced in the base case contains 3.25 wt.% ZnO in addition to 0.78 wt.% ZnS, which together represents a Zn level of 3.13 wt.% in the slag. In all simulations, the Zn concentration in the remaining slag is at least 1.3 wt.% Zn. With regard to the amount of MgO in the feed material, according to the presentation in the document in Figure 12, in order to reduce the level of Zn content in the slag, actions are carried out with the supply of MgO/feed material (% (mass)) amounting to at least 3%.

In one embodiment of the method according to the present invention, the first slag is introduced into the fusion furnace in the form of a liquid. This brings the advantage of not requiring the feed material to be melted in the fusion furnace, so that the amount of heat input into the fusion furnace remains limited. It is extremely advantageous to combine the method according to the present invention with other pyrometallurgical processes in the same production facility, which can result in the first slag being in liquid form, which can be easily fed as such into the fusion furnace according to the present invention.

In one embodiment of the method according to the present invention, the first slag is heated in a fusion furnace, preferably using a plasma torch.

In one embodiment of the method according to the present invention, at least part of the first slag is melted using a plasma torch in a fuming furnace. This brings the advantage of being able to process also the solid first slag in the method according to the present invention.

In one embodiment of the method according to the present invention, during fuming, the plasma torch is immersed in the molten slag present in the fuming furnace. This brings the advantages of intensive mixing of the molten slag using the hot plasma fluid flow, intensive contact of the slag with the high-temperature plasma fluid, and very effective fuming of metals that are susceptible to fuming, such as zinc and lead.

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 brings the advantage of being able to further optimize and stabilize the final composition of the second slag after fuming and to make the slag more suitable for specific end uses as a result of the possible effect on the mineralogical composition as well. As has been found by the applicants, addition at high temperature, such as that described in the invention, and in the molten state, is more effective in obtaining the desired effects.

In one embodiment of the method according to the present invention, the second slag is cooled to convert into a solid, wherein the second slag is preferably removed from the fuming furnace as a liquid. The advantage is that the fuming furnace can be freed for further processing of the slag while simultaneously cooling the second slag. The slag can be cooled and/or solidified by contacting the slag with a cooling medium, such as air, possibly ambient air.

In one embodiment of the method of the present invention, cooling of the slag is accomplished by contacting the liquid second slag with water. As the applicants have found, cooling using water is very effective and can be used in a wide variety of ways, resulting in relatively well-controlled cooling rates.

In one embodiment of the method according to the present invention, the second slag is cooled at a rate of at least 40 degrees Celsius per second, preferably at least 50 degrees Celsius per second, more preferably at least 60 degrees Celsius per second. As the applicants have found, by using a higher cooling rate in accordance with the teaching of the invention, a higher level of amorphous matter in the slag can be obtained, which is of interest for certain end uses, such as when the slag is intended for use as a binder.

In one embodiment of the method according to the present invention, the method further comprises the step of grinding the solid second slag, preferably grinding the slag to form a powder.

In one embodiment of the method according to the present invention, the second slag is cooled at a rate of no more than 30 degrees Celsius per second, preferably less than 30 degrees Celsius per second, more preferably no more than 20 degrees Celsius per second. As the applicants have found, by using a slower cooling rate in accordance with the teaching of the invention, a lower level of amorphous matter in the slag and thus a higher degree of crystallinity can be obtained, which is of interest for certain end uses, such as when the slag is intended for use as a filler or for decorative purposes.

In one embodiment of the present invention, the slag comprises no more than 1.50% by weight of zinc, Zn, and at least 1.0% by weight of CaO and is used as a binder for aggregates, preferably as an active binder, preferably as a binder exhibiting pozzolanic activity. As the applicants have found, the slag can function as a binder as a cement substitute, such as a partial replacement of cement such as Portland cement, but also as a binder for the production of geopolymer compositions.

In one embodiment of the present invention, where slag is used as a binder for aggregates, the slag is used as a substitute for Portland cement, preferably as a partial substitute for Portland cement.

In one embodiment of the present invention, where the slag is used as a binder for aggregates, the slag contains no more than 1.50% (wt.) zinc, Zn, and at least 1.0% (wt.) CaO and is used as a binder in an inorganic polymer composition, preferably in combination with a base, more preferably as a main binder in the inorganic polymer composition, even more preferably as the only binder in the inorganic polymer composition.

In one embodiment of the present invention, the use further comprises the step of foaming the inorganic polymer composition. The result is a foamed composition that may be desirable for its insulating properties with respect to heat and/or sound.

In one embodiment involving foaming, the slag may be used to improve thermal and/or acoustic insulation.

In one embodiment of any one of the uses according to the present invention, wherein the slag comprises no more than 1.50% (wt.) zinc, Zn, and at least 1.0% (wt.) CaO, it is used in combination with an additional oxide or precursor thereof selected from calcium oxide, CaO, aluminum oxide, Al ₂ O ₃ , calcium hydroxide, Ca(OH) ₂ , calcium carbonate, CaCO ₃ , calcium sulfate, CaSO ₄ , wherein preferably the slag and the additional oxide or precursor are mixed with each other prior to use.

As the applicants have found, the additional oxide or its precursor can be introduced as blast furnace slag, as suitable slag from non-ferrous metal production, as gypsum-containing residues, thus containing CaSO ₄ ⋅2H ₂ O, as lime-containing compositions, such as suitable filtered fine lime (Ca(OH) ₂ ), or as limestone (CaCO ₃ ). As the applicants have further found, the additional oxide or its precursor can be introduced into the liquid molten slag before it solidifies. The advantage of this introduction into the liquid is the possibility of thoroughly mixing the additional oxide or its precursor with the slag according to the present invention.

The plasma treatment of materials is known in the art. Publication WO 2011/136727 A1 discloses a method for plasma treatment of waste material that is fluid at room temperature, such as liquids and suspensions, and in particular evaporator concentrate from nuclear power plants. The purpose of the treatment is to minimize the volume of waste subjected to such treatment. An oxidizing gas is supplied to a plasma generator, and then a highly heated, high-enthalpy plasma gas is mixed with the waste material in a mixing zone. The feedstock contains approximately 15% organic and inorganic material and approximately 25% salts. During the treatment, water evaporates and the organic components as a whole decompose and partially burn, while the inorganic materials melt and oxidize. After the mixing zone, a separator is provided in which the liquid inorganic materials are separated from the gas flow. The resulting glass matrix/slag product contains metals and oxides and is preferably bound in the anti-leaching silicate slag, and suitable slag-forming materials such as cullet, sand/quartz, etc. may be added to the mixing zone or flowable waste in order to improve the formation of the anti-leaching glass matrix/slag. The glass/slag may then be transported to final storage, possibly without any further processing.

Also, WO 2014/046593, discussed above, describes the use of a plasma torch to produce hot gas having a temperature of more than 3000°C or even more than 4000°C for the purpose of treating slag. Publications GB 2448556 and GB 2445420 disclose a plasma method for vitrifying nuclear waste.

EXAMPLE 1: Slag production by plasma fuming

Pilot tests were conducted at 3 metric ton scale demonstrating the feasibility of producing a second slag from a first slag using a submerged plasma system.

The experiments were carried out using equipment from Scanarc Plasma Technologies. The reactor was fed using a 1 MW plasma torch submerged below the liquid slag level. Slag fuming was achieved by injecting natural gas through the torch and/or petroleum coke through a feed port at the top of the reactor. Slag composition was monitored at regular intervals by taking samples through a sampling port. Slag composition evolved over time as shown in Table 1, where data are expressed as wt% relative to the total slag composition.

Table 1

Sample collection time (min) 15 104 151 207 Fe 40.0 40.9 41.2 40.5 _SiO2 28.2 30.2 30.6 31.9 Zn 7.5 4.1 2.7 0.7 Pb 0.25 0.064 0.029 0.024

The final slag was analyzed more exhaustively and also showed the concentrations shown in Table 2.

Table 2

Component % (mass.) CaO 3.0 FeO 52.1 _Na2O 2.7 _{Al2O3 ​} 9.0 ZnO 0.9 PbO 0.026

The final slag was rapidly cooled by cold water granulation, resulting in an amorphous content of 72 wt% as determined by XRD. A portion of the same slag was slowly cooled by pouring it over a metal plate, resulting in an amorphous content of 44 wt% as determined by XRD. The XRD technique used was quantitative X _- ray diffraction analysis using Topas Academic Software V5 and using _Al2O3 as an internal standard.

The Zn content in the slag was clearly reduced during the plasma treatment. Also, during the treatment, the Pb content was also reduced. After about 200 minutes, the Zn content was less than 1% and the Pb content was less than 0.03% (mass).

EXAMPLE 2: Production of slag tiles

A compacted inorganic polymer sample was produced using the rapidly cooled slag of Example 1 as a binder and using the slowly cooled slag of Example 1 as an aggregate. For the binder, a portion of the slag was finely ground and the resulting powdered slag had a particle size distribution where 90% (wt%) of the particles had a particle diameter in the range of 50 to 70 μm. The slag was ground in a centrifugal mill (Retsch ZM100) using a sieve opening of 80 μm. The particle size distribution (PSD) was measured using wet mode analysis using laser scattering (Malvern Mastersizer S) and was found to have a ratio of d90 ≤ 70 μm. As a filler, another part of the slag was ground and, from the result of sieving through sieves and re-mixing, a mixture was produced with a particle size distribution that corresponded well to the particle size distribution of the product Normsand or Norm Sand, which complies with the industrial standard EN 196-1. In order to achieve a particle size of the slag filler comparable to that of the product CEN Norm sand (EN 196-1), the slowly cooled slag was gradually ground in a disc mill (Retsch® DM 200). The crushed particles were then separated into fractions of 0.08 mm - 0.16 mm, 0.16 mm - 0.5 mm, 0.5 mm - 1 mm, 1 mm - 1.6 mm and 1.6 mm - 2 mm. This was carried out using a sieve column (Retsch® type) with the above-mentioned sieve mesh sizes on a vibrating sieve shaker (Retsch® AS 200 basic). By mixing the obtained fractions at percentage levels in accordance with the specification in EN 196-1, batches of slag filler were produced at the desired quantities of the individual fractions. In addition, an activating solution was used, produced by mixing at a ratio of 50/50 (w/w) commercial water glass (Na ₂ SiO ₃ ), obtained from abcr GmbH, Karlsruhe (DE) as sodium silicate, soluble glass at 39-40% silicates in water, with a solution of NaOH in water at 6 N. (6 mol/liter). The following mixing ratios were used:

• Activating solution/binder: 0.48/1.0,

• Filler/binder: 4.7/1.0.

To produce the inorganic polymer sample, the binder was first slowly added to the activating solution while stirring and the result was mixed for an additional 30 seconds. The filler was then slowly added over approximately 1 minute while simultaneously continuing to mix. Mixing was then continued for a further total duration of 3 minutes. An automatic mixer (Dispermat AE) was used at a constant mixing speed of 600 rpm.

The resulting dry mixture was pressed using a hydraulic laboratory press (MIGNON SSN/EA) at a pressing force of ~ 75 MPa for about 15 seconds in a mould of 50 × 50 × 27 mm3 (length × width × height). The thus pressed tile was cured first for 24 hours at a temperature of 180°C in a high-pressure autoclave at a gauge pressure of about 10 bar and then for a period of 27 days in a controlled air environment at a temperature of 20°C and 90% relative humidity.

EXAMPLE 3: Performance testing of tiles

During the performance test, the tile from Example 2 gave the following results.

The compressive strength was measured in the direction of the largest dimension of the specimen using a Schenck-RM100 compression testing machine (pressing speed 1 mm/min). Four specimens were tested. The compressive strength for 28 days was found to be 102.4 ± 4.4 MPa. This compressive strength was already reached after 1 day of curing. The compressive strength remained the same after an additional curing period of 27 days.

For comparison purposes, similar tiles were produced using Norm sand, obtained from Normensand GmbH, Germany, as aggregate. The replacement of the slag aggregate with Normsand was carried out on an equal-volume basis to maintain the same dimensions. The tiles based on Normsand achieved a compressive strength of only 35 ± 1 MPa.

The water absorption of the slag-based tiles was measured in accordance with ISO 10545-3:1995 and was found to be approximately 4.8% by weight. Visual inspection of the tiles after a full 28 days of curing showed no discernible efflorescence.

Now that this invention has been fully described, those skilled in the art will appreciate that the invention may be practiced within a wide range of parameters within which, without departing from the scope of the invention, rights are claimed to be within the scope of the claims.

Claims (53)

1. The use of slag containing, on a dry matter basis and when expressing the presence of metal through the combined value for the metal present as elemental metal and the metal present in the oxidized state, a) at least 7 wt.% and not more than 49 wt.% iron, Fe, b) no more than 1.3 wt.% copper, Cu, c) at least 24 wt.% and not more than 44 wt.% silicon dioxide, SiO ₂ , and d) at least 1.0 wt.% and not more than 20 wt.% calcium oxide, CaO, distinguished by the fact that it contains, in the same calculation, e) at least 0.10 wt.% and not more than 1.50 wt.% zinc, Zn, f) at least 0.10 wt.% and not more than 2.5 wt.% magnesium oxide, MgO, and g) not more than 0.100 wt.% lead, Pb, in the construction industry as an ingredient of a composition selected from concrete or cement, wherein said ingredient is selected from the group consisting of a filler or aggregate, a binder and combinations thereof, wherein said slag is characterized by an average particle diameter of at least 10 µm and no more than 5.0 mm, and said slag is characterized by an amorphous content of at least 30 wt.%, as determined using X-ray diffraction analysis (XRD). 2. The use according to claim 1, wherein the slag is used in the concrete and/or cement composition to prevent a decrease in the hardening rate of the composition. 3. The use according to claim 1 or 2, wherein the slag is used as a binder for fillers, preferably as an active binder, preferably as a binder exhibiting pozzolanic activity. 4. The use according to claim 3, wherein the slag is used as a substitute for Portland cement, preferably as a partial substitute for Portland cement. 5. The use according to any one of paragraphs 1-4, in which the slag is used to provide a wear layer and/or a coating for roofing tiles or roofing shingles. 6. The use according to any of paragraphs 1-5, in which slag is used as a component of foam tiles. 7. The use according to any one of claims 1 to 6, wherein the slag is used as a black dye, preferably in a black tile. 8. The use according to any one of claims 1 to 7, wherein the slag is used as a binder in the inorganic polymer composition, preferably in combination with a base, more preferably as the main binder in the inorganic polymer composition, even more preferably as the only binder in the inorganic polymer composition. 9. The use according to claim 8, which includes the step of foaming the inorganic polymer composition. 10. The use according to item 9, in which the slag is used to improve heat and/or sound insulation. 11. The use according to any one of claims 1 to 10, wherein the slag is used to provide an effect selected from reducing the sintering temperature of the brick or unfired brick, sound insulation, protection from X-ray radiation, and combinations thereof. 12. The use according to any one of claims 1 to 11, wherein the slag is used in combination with an additional oxide or its precursor selected from calcium oxide, CaO, aluminum oxide, Al ₂ O ₃ , calcium hydroxide, Ca(OH) ₂ , calcium carbonate, CaCO ₃ , calcium sulfate, CaSO ₄ , wherein preferably the slag and the additional oxide or its precursor are mixed with each other before use. 13. The use according to any one of claims 1 to 12, wherein the slag additionally contains, in the same calculation, at least 9 wt.% and not more than 63 wt.% iron oxide, FeO. 14. The use according to any one of paragraphs 1-13, wherein the slag additionally contains, in the same calculation, no more than 5 wt.% sodium oxide, Na ₂ O. 15. The use according to any one of claims 1 to 14, wherein the slag additionally contains, in the same calculation, at least 3 wt.% and not more than 12 wt.% of aluminum oxide, Al ₂ O ₃ . 16. The use according to any one of paragraphs 1-15, wherein the slag contains, in the same calculation, no more than 1.5 wt.% zinc oxide, ZnO. 17. The use according to any one of paragraphs 1-16, wherein the slag contains, on a dry matter basis, no more than 0.323 wt.% lead oxide, PbO. 18. The use according to any one of claims 1 to 17, wherein the iron present in the slag is mainly present in the fayalite structure Fe ₂ SiO ₄ . 19. The use according to any one of claims 1 to 18, wherein the slag is characterized by an amorphous content level as determined using X-ray diffraction analysis (XRD) of at least 50 wt.%, preferably at least 70 wt.%, more preferably at least 80 wt.%, even more preferably at least 85 wt.%, for the amorphous content level. 20. Use according to any one of claims 1 to 19, wherein the slag has a granular form characterized by an average particle diameter (d50 as calculated on a weight basis) of at least 0.5 mm and no more than 5.0 mm, preferably at least 0.7 mm, more preferably at least 0.9 mm, and optionally no more than 3.0 mm, preferably no more than 2.0 mm. 21. The use according to any one of claims 1 to 20, wherein the slag is in powder form, characterized by an average particle diameter (d50), as determined by wet sieve analysis and therefore an average value calculated on a mass basis, of at least 10 μm and not more than 500 μm, preferably at least 20 μm, more preferably at least 30 μm, and optionally not more than 200 μm, preferably not more than 100 μm, more preferably not more than 50 μm. 22. The use according to claim 21, wherein in the slag at least 90% by weight of the particles (d90) have a diameter of no more than 200 μm, as determined by wet sieve analysis, preferably no more than 150 μm, more preferably no more than 100 μm. 23. The use according to any one of claims 1 to 22, wherein the slag is used to produce an object representing a building element, containing said slag as a binder and/or as a filler, wherein said slag contains at least 2.0 wt.% CaO. 24. The use according to claim 23, wherein the object comprises said slag as a binder and further comprises a filler, wherein said filler preferably comprises sand and/or said slag. 25. The use according to any one of claims 23 or 24, wherein the slag contains at least 1.0 wt.% CaO and is present as a binder, wherein the object additionally contains an activator. 26. The use according to claim 25, wherein the activator is selected from the group consisting of sodium hydroxide, _NaOH , potassium hydroxide, KOH, sodium silicate, _Na2SiO3 , potassium silicate _{, K2SiO3} , and combinations thereof, wherein preferably the activator is NaOH. 27. The use according to any one of paragraphs 23-26, wherein the building element is selected from the group consisting of a tile, a paving stone, a block, a concrete block and combinations thereof. 28. The use according to any of paragraphs 23-27, wherein the object has a foamed structure. 29. The use according to any one of paragraphs 1-28, in which slag obtained as a second slag by a method for producing a second slag is used, which includes the steps of: providing a first slag containing at least one metal selected from zinc, lead and combinations thereof, introduction of the first slag into the fuming furnace, fuming a quantity of at least one metal selected from zinc, lead and combinations thereof from the first slag using at least one plasma torch to produce a second slag and removing the second slag from the fuming furnace. 30. The use according to claim 29, wherein the first slag is introduced into the fuming furnace in the form of a liquid. 31. The use according to any one of claims 29, 30, wherein the first slag is heated in a fuming furnace, preferably using a plasma torch. 32. The use according to any one of paragraphs 29-31, wherein part of the first slag is melted using a plasma torch. 33. The use according to any one of claims 29 to 32, wherein during fuming the plasma torch is immersed in molten slag present in the fuming furnace. 34. The use according to any one of claims 29 to 33, wherein 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 about 1150°C. 35. The use according to any one of claims 29 to 34, wherein the second slag is cooled to convert into a solid, wherein preferably the second slag is removed from the fuming furnace as a liquid. 36. The use according to claim 35, wherein the cooling is carried out by introducing the liquid second slag into contact with water. 37. The use according to any one of claims 35, 36, wherein the second slag is cooled at a rate of at least 40 degrees Celsius per second, preferably at least 50 degrees Celsius per second, more preferably at least 60 degrees Celsius per second. 38. The use according to any one of claims 35 to 37, which further comprises the step of grinding the solid second slag, preferably grinding the slag to form a powder.