Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/04—Working-up slag
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B3/00—General features in the manufacture of pig-iron
  • C21B3/04—Recovery of by-products, e.g. slag
  • C21B3/06—Treatment of liquid slag
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B2400/00—Treatment of slags originating from iron or steel processes
  • C21B2400/02—Physical or chemical treatment of slags

Definitions

• the invention relates to a method for processing slag.
• EAF slags electric arc furnace slags
• desulfurization slags slags from iron desulfurization
• converter slags steerelworks slags
• secondary metallurgical slags slags from secondary metallurgy, such as ladle furnace slags or deoxidation slags
• JP 3667346 B2 An example of a steelworks slag that can be adjusted to an iron content below 6% and thus reused is shown in the JP 3667346 B2 revealed. All the aforementioned types of slag are known to the expert.
• the task is to provide a process for processing slags which can have a positive impact on reducing CO2 emissions and/or improving the quality and/or further processing of slags.
• Slags comprising or consisting of electric arc furnace slags, converter slags, desulfurization slags, and/or secondary metallurgical slags with a total oxide iron content of at least 10 wt.% are provided, wherein the oxide iron may be in the form of FeO, Fe2O3 , Fe3O4 , or a mixture thereof.
• the total oxide iron content (in wt.%) may, in particular, be at least 11%, 12%, or 13%.
• the slag content may be, preferably at least 14%, 15%, 16%, preferably at least 17%, 18%, 19%, and at most 50%.
• the slag may consist solely of electric arc furnace slag, converter slag, desulfurization slag, secondary metallurgical slag, or mixtures thereof, for example, electric arc furnace slag and converter slag, in particular with a mixing ratio between 2:98 and 98:2, preferably with a mixing ratio between 20:80 and 80:20, more preferably with a mixing ratio between 30:70 and 70:30, and most preferably with a mixing ratio between 40:60 and 60:40.
• the slag can be introduced, for example, with a particle size fraction of up to 180 mm, particularly between 46 and 180 mm. It can preferably be introduced in ground form, i.e., with a particle size fraction of up to 45 mm, particularly preferably either between 0 and 10 mm or between 11 and 45 mm. Grinding increases the surface area of the slag, allowing the reducing gas in the rotary kiln to flow around it more effectively and thus promoting the reduction process.
• the rotary kiln preferably has an inlet section and an outlet section, as well as a rotary tube arranged between the inlet and outlet sections, which is rotatably mounted relative to the inlet and outlet sections.
• the rotary kiln can be, or is, designed as a gas-tight rotary kiln.
• Rotary kilns have long been known in many fields of application. In many cases, the inlet section is designed as an inlet casing and/or the outlet section as an outlet casing. An example of a rotary kiln of this type is shown in the EP 4 361 545 A1 described.
• the mixture is conveyed along a conveying direction through the rotary kiln as the kiln rotates.
• a reducing gas which flows counter-currently through the rotary kiln against the conveying direction to induce reduction reactions in the mixture.
• a reducing gas is introduced that is not produced in situ by introduced solid, fossil materials.
• Reducing agent in the form of coal is introduced into the rotary kiln and, as a result of thermal exposure, is converted into a carbon-containing and therefore reducing gas phase.
• the mixture is thus exposed to a reducing atmosphere, which is provided by introducing a reducing gas into the rotary kiln.
• a reducing gas therefore flows through the rotary kiln, specifically through the rotary tube of the rotary kiln.
• Carbon monoxide, hydrocarbons, hydrogen, or a mixture thereof are used as the reducing gas.
• a process gas from a steelworks, particularly an integrated steelworks can be used, such as coke oven gas, converter gas, blast furnace gas, or gas from an electric melting unit, or mixtures thereof.
• the slag contained in the mixture is removed from the rotary kiln with a total oxide iron content of a maximum of 6.0 wt.%.
• the total oxide iron content (in wt.%) can be, in particular, a maximum of 5.5%, 5.0%, 4.5%, preferably a maximum of 4.0%, 3.5%, 3.0%, and preferably a maximum of 2.5%, 2.0%, or 1.5%.
• a total content of 0% would be possible, but this is not practically relevant, as the total oxide iron content will generally always be > 0%, and in particular > 0.25%.
• the conveyed mixture is heated to a temperature between 750 °C and 1250 °C, preferably by indirect heating.
• the mixture can be heated to a temperature of at least 800 °C, preferably at least 850 °C, preferably at least 900 °C, and particularly to a maximum of 1250 °C, preferably a maximum of 1200 °C, preferably a maximum of 1150 °C, most preferably a maximum of 1100 °C, and more preferably a maximum of 1050 °C. Determining the temperature is a familiar procedure for those skilled in the art and standard practice in rotary kilns.
• the Fe x O y in the slag can be reduced by the reducing gas in a gas-solid reaction. Furthermore, other undesirable byproducts such as lead and/or zinc oxide can also be reduced and transferred into the gas phase, which can then be better processed and/or further utilized.
• Fe x O y is representative of FeO, Fe 2 O 3 , Fe 3 O 4 or a mixture thereof.
• Temperatures within this range have the advantage that, on the one hand, they are sufficiently high to significantly accelerate the reduction processes and ensure that any resulting and undesired reaction products, such as zinc/zinc oxides and/or lead/lead oxides and/or lead chlorides, are present in the gas phase, while on the other hand, they are still sufficiently low to prevent an undesired transition of Fe ⁇ sub>x ⁇ /sub>O ⁇ sub> y ⁇ /sub> into the liquid phase.
• the heating be carried out indirectly. This means that, unlike direct heating, in which combustion processes are induced within the rotary kiln, the heating is achieved using heat generated outside the rotary kiln and introduced into it. Preferably, heating elements attached to the outer shell of the rotary kiln or rotary tube are used for heat generation.
• These elements preferably operate electrically, for example via electrical resistance heating, microwave heating, or induction.
• the heat emitted by these elements is conducted through the metallic shell of the rotary kiln or rotary tube, which can be made of stainless steel, for example, into the interior of the rotary kiln or rotary tube.
• This indirect heating of the interior of the rotary kiln or rotary tube has the advantage of preventing reoxidation of the reduced components.
• cooling can be carried out before the mixture is removed from the rotary kiln.
• This cooling system can be designed to convey the mixture after it has passed through the rotary kiln to a cooling station located on the rotary kiln. This cooling station can, for example, be coupled to or integrated into the outlet section of the rotary kiln.
• a separation station for separating the mixture passing through the rotary kiln is coupled to the system.
• the separation station can utilize suitable magnetic separation, e.g., a magnetic separator, or separation based on density differences, e.g., a sedimenter, a centrifuge, a decanter, or a separator, or a combination thereof.
• the separation process separates the processed slag from the unwanted components in the mixture.
• the methods and operating principles for material separation are familiar to those skilled in the art. Through this separation, unwanted components, such as...
• Iron components are separated from the mixture, which can then be fed as melt material to an agglomeration plant (such as a sintering or pelletizing plant), an electric arc furnace/melter, a shaft furnace (such as a direct reduction plant, blast furnace, cupola furnace, etc.), and/or a converter, or within secondary metallurgy up to casting (e.g., as cooling chips when starting up a continuous or ingot casting).
• an agglomeration plant such as a sintering or pelletizing plant
• an electric arc furnace/melter such as a direct reduction plant, blast furnace, cupola furnace, etc.
• a shaft furnace such as a direct reduction plant, blast furnace, cupola furnace, etc.
• a converter such as a direct reduction plant, blast furnace, cupola furnace, etc.
• Other unwanted non-ferrous metals and their oxides such as zinc, lead, chromium, manganese, titanium, vanadium, phosphorus, sulfur, and lime, can also be separated from
• a process gas is conveyed from the rotary kiln, comprising or consisting of components from unreacted reducing gas and gases generated during the reduction of the mixture, as well as optionally a transport gas.
• a gas discharge system is preferably coupled to an inlet section of the rotary kiln, which, due to the countercurrent flow of the reducing gas, is located at the end of the reduction gas flow path. This discharge system removes the gases generated during the reduction of the mixture from the rotary kiln.
• This approach has the advantage of maintaining a largely consistent, highly reducing atmosphere within the rotary kiln.
• the conveyance of the generated gases which may consist in particular of zinc/zinc oxides and/or lead/lead oxides and/or lead chlorides, is carried out, in particular, with the reaction gas.
• a transport gas can additionally be introduced in the same flow direction, i.e., against the direction of flow of the mixture due to the countercurrent principle.
• the transport gas is preferably a protective gas, which, due to its lower properties compared to other protective gases, is particularly suitable.
• nitrogen (N2 ) is preferably used.
• the use of one or more noble gases, such as argon is also possible.
• a gas discharge system for the removal of the process gas, through which, among other things, gaseous reaction products are discharged from the rotary kiln.
• a gas conditioning system coupled to the rotary kiln for conditioning the process gas discharged from the rotary kiln.
• the gas conditioning system can be coupled to the gas piping system in such a way that the gas is fed into the gas conditioning system via the gas discharge system.
• Zinc/zinc oxide present in the gas conditioning system is preferably deposited; for this purpose, the gas conditioning system can, for example, have a zinc trap, which is designed, for example, as cooled metal plates, such as copper, providing condensation surfaces for zinc condensation.
• the gas processing system may, for example, have a metal vapor trap, which may be designed as cooled metal plates, for example made of copper, which provide condensation surfaces for metal condensation, in particular for lead condensation.
• slag formers comprising or consisting of at least one component from the group SiO2 , CaO, MgO, Al2O3 , in iron melts to ensure the purity of the iron melt and to promote slag control in electric arc furnaces, blast furnaces, converters, and within secondary metallurgy. Thus, they also serve to condition slag in the liquid phase.
• Typical electric arc furnace slags can have the following compositions (in wt.%): CaO: 35 - 45% SiO2 : 10 - 18% Al 2 O 3 : 3 - 8% MgO: 7 - 15% Total Fe: 10 - 30% where Fe is essentially in oxide form and Fe met can amount to up to 1%, the remainder being impurities such as MnO, P2O5 , Cr2O3 , CaO free , S in total up to 5 wt%, see paragraph 2.8.2.1 in conjunction with Table 2.8-2 in the "Publication".
• Converter slag Approximately 120–180 kg of converter slag is produced per ton of crude steel. Additives influence the chemical composition of the converter slag.
• Typical converter slags can have the following compositions (in wt.%): CaO: 36 - 50%, SiO2 : 10 - 15% Al 2 O 3 : 1 - 4% MgO: 4 - 8%, Total Fe: 18 - 24% where Fe is essentially in oxide form and Fe met can amount to up to 1%, the remainder being impurities such as MnO, P 2 O 5 , Cr 2 O 3 , CaO free , S in total up to 10 wt%, cf. paragraph 2.7.2.1 in conjunction with Table 2.7-2 in "Publication”.
• the mixture preferably comprises a slag former comprising or consisting of at least one component from the group consisting of SiO2 , CaO, MgO, Al2O3 .
• the slag former can either be added separately or pre-mixed with the slag before being fed into the rotary kiln.
• the slag formers can be added in ground form, for example with a particle size of up to 180 mm. Slag formers are preferably added such that a basicity B4 in the processed slag is between 0.7 and 4.5.
• the basicity B4 can be at least 0.8, preferably at least 0.9, and particularly at most 3.7, preferably at most 2.6, preferably 1.8.
• the basicity B4 corresponds to the ratio (CaO + MgO) to ( SiO2 + Al2O3 ) , whereby the determination of the characteristic values is generally familiar to those skilled in the art in solid-state slag.
• a target composition could, for example, correspond to that of blast furnace slag, which is predominantly used in the cement industry. Since, as part of decarbonization, blast furnaces for the production of pig iron are to be successively replaced by so-called direct reduction plants for reducing iron ore and electric arc furnaces for melting the reduced iron ore, the sources of raw materials for the cement industry that have been standard for decades will no longer be available for much longer, and alternative sources must be found.
• This document describes how slag can be conditioned in an electric melter, which can be used for the production of mineral building materials. Slag with an iron content of less than 10 wt% is advantageous for use in the cement industry.
• the slags resulting from the melting of gangue from iron ore carriers have a CaO + MgO content of between 10 and 30%, while the SiO2 content varies between 30 and 70% , and the Fe2O3 and Al2O3 content varies between 5 and 55%.
• Conditioning aims to achieve a composition similar to granulated blast furnace slag or Portland cement (see Figure 4), which is ideally suited as a raw material for the cement industry.
• the chemical adjustment takes place downstream in the rotary kiln.
• An initial target composition of the processed slag can be exemplified by the following components in wt.%: CaO: 30 to 60% SiO2 : 25 to 50% Al 2 O 3 : 4 to 18% MgO: 3 to 15% and impurities totaling 100% by weight.
• a second target composition of the processed slag can be exemplified by the following components in wt.%: CaO: 50 to 70% SiO2 : 15 to 30% Al 2 O 3 : 3 to 17% Fe x O y : > 0 to 5% and impurities totaling 100% by weight.
• composition of the (processed) slags can be carried out, for example, according to DIN EN ISO 12677:2013-02 "Chemical analysis of refractory products using X-ray fluorescence (XRF) - Fused Cast-Bead method".
• XRF X-ray fluorescence
• the slag or parts thereof can first be converted into an amorphous structure by rapid cooling, such as by wet or dry granulation according to the prior art, given a specific chemical composition.
• rapid cooling such as by wet or dry granulation according to the prior art, given a specific chemical composition.
• the granulation achieves a glass content of at least 40%, particularly at least 70%, preferably at least 90%, and at most 100%, particularly up to 99%.
• the material is then considered granulated slag.
• the glass content can be determined by X-ray diffraction analysis, see DIN EN 13925-1:2003-07, "Non-destructive testing - X-ray diffractometry of polycrystalline and amorphous materials" - Part 1: General principles. This structure is more reactive than a crystalline structure, which forms upon slow cooling.
• the still high iron oxide content in the slag particularly prevents its use as a cement substitute. Therefore, further processing in a rotary kiln is carried out as described (reduction of Fe x O y , etc.) to obtain the appropriate chemical composition.
• This product in granular form, can then ideally be used as a cement clinker substitute; that is, it has latent hydraulic properties, meaning it reacts upon the addition of water. This would not be possible with a crystalline product, as its structure is too stable, whereas an amorphous one is not.
• a preferred combination of granulation and chemical treatment/post-reduction in a rotary kiln can create a product similar to blast furnace slag.
• the mixture can also include carbon-containing feedstocks in the form of waste plastics, biomass, plastics, or mixtures thereof. Due to the temperatures prevailing in the rotary kiln, combined with a reducing atmosphere, the components of the carbon-containing feedstocks decompose into, among other things, a carbon-rich gas, which can act as a reducing agent and thus contribute to the efficiency of the process, and other components. These components, if gaseous, are separated via a gas discharge or gas treatment system, and/or, if solid, via a separation station, for further processing and/or recycling.
• each rotary kiln has an optimal operating point or range specific to its system, and any addition of carbon-containing feedstocks should be directed towards this optimum.
• the carbon-containing feedstocks can be mixed either separately or in advance with the slag and optional slag formers before being fed into the rotary kiln.
• the carbon-containing feedstocks can be added in milled form, for example with a particle size of up to 25 mm, preferably up to 10 mm. This would also allow for the recycling of materials from the non-ferrous/non-steel industry.
• the mixture can include, in addition to slags, optional slag formers, and optional carbon-containing feedstocks, iron-containing metallurgical residues and/or recycled metallurgical materials.
• iron-containing metallurgical residues and/or recycled metallurgical materials containing or consisting of oxygen compounds are present in oxide form.
• These include, for example, iron-containing agglomerates or oxide recycled metallurgical materials generated in a complex of metallurgical plants, particularly dusts. Dusts are defined as substances with a diameter of less than 10 mm, particularly less than 6 mm. Dusts can originate from steelworks, sintering and pelletizing plants, direct reduction plants, electric arc furnaces, coking plants, and blast furnaces.
• metallurgical residues can include scale (rolling scale), slag from secondary metallurgy, or desulfurization. Due to the temperatures prevailing in the rotary kiln, in conjunction with a reducing atmosphere, the metallurgical residues and/or metallurgical recycling materials are reduced, among other things to iron, which can be used for iron recovery and separated via a separation station.
• the processed slag can be separated, and any other components, which, if gaseous, are routed via a gas discharge or gas treatment system and/or, if solid, via a separation station, are separated for further processing and/or recycling.
• Such metallurgical residues and/or recycled materials can be reduced very efficiently in a rotary kiln by applying a reducing gas in a countercurrent flow, so that after passing through the rotary kiln, completely or almost completely reduced materials are present. Determining the appropriate levels of iron-containing residues and/or recycled materials does not pose any particular difficulties for those skilled in the art, as every rotary kiln has an optimal operating point or range, and any addition of iron-containing metallurgical residues and/or recycled materials should be directed towards this optimum.
• the iron-containing blast furnace residues and/or recycled materials can be mixed either separately or in advance with the slags, optional slag formers, and optional carbon-containing feedstocks before being fed into the rotary kiln.
• the carbon-containing feedstocks can be added in milled form, for example, with a particle size of up to 25 mm, preferably up to 10 mm.
• Figure 1 shows an exemplary embodiment of a rotary kiln 100 for processing slag.
• a rotary kiln 1 is provided with an inlet section 2 and an outlet section 3.
• Slag comprising or consisting of electric arc furnace slag, converter slag, desulfurization slag, and/or secondary metallurgical slag with a total oxide iron content of at least 10 wt.%, wherein the oxide iron may be in the form of FeO, Fe2O3 , Fe3O4 , or a mixture thereof, is provided.
• the slag is preferably ground to a particle size of up to 180 mm, preferably up to 45 mm, and particularly preferably up to 10 mm.
• further additives in the form of slag formers, carbon-containing feedstocks, and/or iron-containing metallurgical residues and/or metallurgical recycling materials can optionally be introduced as a mixture into the rotary kiln 100.
• the mixture is introduced into the inlet section 2, preferably via a sluice gate.
• the rotary kiln 1 rotates, the mixture is conveyed through the rotary kiln 100 along a conveying direction A.
• the mixture is exposed to a reducing gas, which flows countercurrently in the opposite direction to the conveying direction A.
• B is conveyed flowing through the rotary kiln 1.
• the processed slag has a basicity B4 between 0.7 and 4.5, particularly up to 3.7, and more preferably up to 2.6.
• the temperature is selected such that the reduction processes occur sufficiently quickly, and the temperatures are not so high as to prevent an undesired transition to a liquid phase, but are high enough to prevent condensation of initially gaseous metals or metal compounds of other metals, for example, zinc oxides and/or lead oxides/chlorides.
• the slags processed in the mixture are chemically and structurally modified and, as secondary building materials such as common granulated blast furnace slag, Portland cement, or concrete, are removed from a discharge sluice in the discharge section 3 and then further processed, particularly as raw materials for the cement and concrete industries. It is particularly advantageous to granulate the slags in the liquid phase to achieve an amorphous structure, i.e., with a glass content of at least 40%.
• the chemical modification then takes place in the described rotary kiln process.
• a cooling station 8 for cooling the mixture that has passed through the rotary kiln 100 is integrated in the discharge section 3.
• the mixture can be cooled, for example, to a temperature below 150 °C.
• a separation station 7 is coupled for separating the mixture that has passed through the rotary kiln 100.
• the separation station 7 can employ suitable magnetic separation, separation based on density differences, or a combination thereof. Magnetic separation is preferred in order to effectively separate iron content from the mixture, which can then be used for iron production. In at least one or more separation steps, unwanted components, such as the aforementioned iron and other metals, can be separated from the processed slag.
• a gas recirculation system 23 Downstream of the gas processing system 20 is a gas recirculation system 23 coupled for the return of processed reducing gas to the rotary kiln 100, whereby the recirculation can be optional or is.
• the mixture was fed into rotary kiln 100 and conveyed through it along a conveying direction A while the rotary tube 1 rotated.
• the mixture was exposed to a reducing gas, which flowed countercurrently through rotary kiln 100 and rotary tube 1, respectively, in the opposite direction to conveying direction A.
• Pure H2 was used as the reducing gas, and this occurred as the mixture of converter slag and slag former passed through it.
• the rotary kiln 100 was heated to 950 °C by indirect electrical heating of the interior of the rotary tube 1.
• the throughput time of the mixture through the rotary kiln 100 was 30 minutes.
• the experiment was carried out with an exemplary flow rate of the reducing gas of 5 Nm3 /h, where Nm3 denotes a standard cubic meter and h denotes a period of one hour.
• the exact flow rates are not essential to the nature of the invention, as they depend in particular on the specific plant parameters, for example, the volume of the rotary kiln 100 and the upstream and downstream components. Due to this dependence on the specific circumstances, such as the specific plant parameters, the person skilled in the art carrying out the process must empirically adjust the reducing gas flow, in particular the H2 gas flow, such that the processed slags have the desired composition and preferably the desired basicity B4. This empirical determination of a sufficiently high gas flow does not present any particular difficulties for the person skilled in the art.
• a mixture was obtained, and from it a processed slag with a low iron content was separated, exhibiting the following composition in wt.%: 42.6 CaO, 37.8 SiO2, 11.3 Al2O3 , 6.5 MgO , ⁇ 2 FexO5 , ⁇ 1 Fe metallic .
• the basicity B4 was 1.0.
• the processed slag obtained was very similar to blast furnace slag.
• Large proportions of the zinc and lead contained in the mixture of reactants could be removed; both of these elements escaped as gas or as part of a gas compound and could be separated in the gas processing system.
• Other metals, such as iron and chromium, could be selectively separated from the mixture by further separation.
• the invention can be understood as a type of "upcycling" of slags (electric arc furnace slags/converter slags/desulfurization slags/secondary metallurgical slags), the quality of which can be improved and/or increased in a rotary kiln, thus enabling previously inaccessible applications for this type of slag.
• the slags can be granulated prior to the rotary kiln process.
• the processed slags can be used as feedstock in the cement industry, for example, similar to the standard granulated blast furnace slag (blast furnace slag) currently used in blast furnaces.

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Citations (5)

• 2024
  • 2024-05-13 EP EP24175372.2A patent/EP4650461A1/fr active Pending

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