Method for removing zinc from galvanized steel scrap

Abstract

The present invention relates to waste treatment and is directed to a method for reducing zinc from Zn-coated Fe, comprising: 3+ Zn 2+ and Fe 2+ obtaining an acidic solution containing Fe; obtaining a zinc-reduced metallic Fe substrate; and 2+ Zn 2+ Zn 2+ Containing products and Fe 2+ and obtaining a salt.

Description

[Background technology]

[0001] Galvanizing is the process of coating steel with a thin layer of zinc for improved corrosion resistance. Zn coating is a thin layer of metallic zinc that may contain some dopants, such as Al, Sn, Ni, Co, or Fe. Galvanizing can be done by electrolytic deposition (electrogalvanizing) or by immersing the steel body in a liquid of molten zinc. Since galvanizing generally improves the properties of the steel, for example, in terms of corrosion resistance, galvanized steel with a zinc layer comprising 3 to up to 40 kg per ton of steel is a common industrial product.

[0002] In general, the term galvanized steel or galvanized steel scrap as used herein will be understood in a broad sense: galvanized steel or galvanized steel scrap includes any sheet or substrate of steel covered with a zinc layer. The zinc layer may be applied by galvanic or electrolytic deposition, or the zinc layer may be applied by high-temperature dipping of the steel substrate in molten zinc or by zinc vapor deposition or by any other method of coating a steel substrate with a zinc layer.

[0003] Furthermore, the term galvanized steel or galvanized steel scrap as used herein includes any material resulting from subsequent processing, such as subsequent annealing of a zinc-coated steel substrate for better adhesion or performance of the zinc layer.

[0004] However, for steel recycling, Zn coating is undesirable because the Zn coating evaporates at higher temperatures, resulting in significant amounts of Zn in the flue gases. Therefore, scrap containing a Zn coating (galvanized steel scrap or galvanized scrap) has a lower value compared to scrap without Zn, and there have been many attempts in the art to remove zinc from galvanized steel scrap.

[0005] There are various options for reducing Zn from galvanized steel scrap: ·Pyrometallurgy Hydrometallurgy by alkaline leaching Hydrometallurgy by acid leaching

[0006] While acid leaching generally performs better than alkaline leaching, it also has a significant drawback: acid solutions not only leach Zn, but also Fe. As a result, the resulting material is not suitable for electrowinning (pure) Zn metal unless an additional separation step is performed to purify the Zn. Such an additional separation step is required even when measures are implemented to minimize Fe leaching, such as by monitoring the potential by placing a reference electrode in the leach solution, measuring the corrosion potential, and terminating the reaction when the measured potential reaches a plateau, as taught in US 2015 / 0259766.

[0007] As a result, acidic zinc removal of galvanized steel scrap for electrowinning of metallic zinc is considered economically unfavorable in the art (see, e.g., DEZINCING OF GALVANIZED STEEL, by J. Grogan, Colorado School of Mines: https: / / pdfcoffee.com / qdownload / dezincinc-of-galvanized-steel-pdf-pdf-free.html, page 75, lines 15-16).

[0008] WO2023 / 089234 relates to a method for recovering zinc and iron products from zinc-containing waste materials. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2015 / 0259766 [Patent Document 2] International Publication No. 2023 / 089234 [Patent Document 3] International Publication No. 2018 / 109283 [Patent Document 4] German patent number 102007032418 [Non-patent literature]

[0010] [Non-Patent Document 1] J. Grogan, DEZINCING OF GALVANIZED STEEL, Colorado Scholl of Mines: https: / / pdfcoffee.com / qdownload / dezincinc-of-galvanized-steel-pdf-pdf-free.html, page 75, lines 15-16. [Non-patent document 2] World of Metallurgy - ERZMETALL 75 (2022) No.1, 28~35 [Non-patent document 3] Energy Fuels 2022, 36, 3695~3703 [Non-patent document 4] J. Grogan, DEZINCING OF GALVANIZED STEEL, Colorado Scholl of Mines: https: / / pdfcoffee.com / qdownload / dezincinc-of-galvanized-steel-pdf-pdf-free.html, 25 pages Summary of the Invention [Problem to be solved by the invention]

[0011] In view of this prior art, the present invention addresses the need to provide an efficient and economical method for recycling Zn-coated Fe, such as galvanized steel scrap. [Means for solving the problem]

[0012] The inventors have investigated the Fe 3+The use of an acidic solution containing Fe surprisingly combines technical and economic advantages in such a way as to overcome the already known drawbacks of acid leaching: 3+ is not only an oxidizing agent that accelerates Zn leaching, but also promotes Fe leaching during the leaching process. 2+ is generated from waste materials that would otherwise be useless, and the separation process is carried out using Fe 2+ It has been found to be suitable for salt production and therefore also industrially feasible.

[0013] The present invention therefore provides a method for reducing metallic Zn from Zn-coated Fe (such as zinc-coated scrap or galvanized steel scrap, respectively), comprising the steps of: a) Zn 2+ and Fe 2+ The Zn-coated Fe is then added to provide an acidic solution containing Fe 3+ and subjecting the mixture to a leaching step in an acidic solution containing b) obtaining a zinc-depleted metallic Fe substrate; c) Zn 2+ Containing products and Fe 2+ To provide salt, Zn 2+ From Fe 2+ and separating the The present invention provides a method comprising:

[0014] The acidic solution preferably contains at least 100% Fe per kg of solution at the start of the leaching process. 3+ Fe at concentrations from 1.5 to 60g 3+ Such an acidic solution may, for example, be obtained from the treatment of a material containing ferric iron (Fe) with an acid. In a preferred embodiment, the acidic solution used in step a) is obtained by subjecting electric arc furnace dust (EAFD) to an acid treatment.

[0015] Furthermore, during leaching, it is preferable to use an excess of Fe relative to the Zn metal. 3+ There is an atomic ratio of Fe 3+ / Zn 0 is more than 2.

[0016] Step c) produces two different products, Zn2+ Containing products and Fe 2+ Provide salt.

[0017] Zn obtained in step c) 2+ The product is ZnS obtained from the precipitation, which is used after conversion to ZnSO4 to produce metallic Zn by electrowinning. 2+ The containing product is a ZnSO4 or ZnCl2 solution obtained by solvent extraction. 2+ The salt is preferably FeCl2 or FeSO4 which can be sold, after optional purification, for wastewater treatment, as a chromate reducing agent for cement or as an additive for animal feed. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a bar graph showing residual Zn on the steel surface obtained in Example 4. [Figure 2] 1 is a bar graph showing residual Zn on the steel surface obtained in Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0019] Acidic solution and leaching process The acid solution can be obtained by reacting a waste product with fresh or spent acid, and is therefore preferably a waste-derived solution. The waste product or spent acid can be, for example, any waste H2SO4 (or used H2SO4 or dilute H2SO4) from TiO2 production using the sulfate process, waste acid solutions from zinc production, any waste HCl, steel pickling solutions containing FeCl2 or FeSO4, waste metal chlorides from TiO2 chlorination for TiO2 production using the chloride process, iron chloride solutions from the production of synthetic rutile, or Fe 3+ The acidic solution may be any waste acid containing, or a waste acid used to dissolve Fe oxides or hydroxides, or a combination of the waste products listed above. The pH of the acidic solution is preferably 1.5 or less.

[0020] Preferably, the following industrial residues containing Fe can be dissolved or leached in acid: EAFD (typically 20-50% Fe; 10-40% Zn) EAFD from stainless steel production (containing Cr and Ni) Slag from the lead industry Jarosite or goethite as a waste product from the zinc industry; jarosite = MFe3(OH)6(SO4)2 (where M = Na, K, or NH4) Mill scale (preferably after removal of adhered oil) Dust from cupola furnaces Stainless steel generated dust Blast furnace dust and sludge (typically 30-40% Fe; 1-8% Zn) Basic oxygen furnace (BOF) dust and sludge (max. 70% Fe; <5% Zn) Spent H2S absorber containing EAFD or ZnO as absorbent

[0021] The following industrial residues containing Zn can also be dissolved or leached in acid by using an acid containing Fe or by combining it with one of the residues listed above, provided that the Fe is in contact with the acidic solution: Zinc ash Zinc skimming Brass ash

[0022] Jarosite is obtained in primary zinc production by precipitation at 95°C and pH 3.5. Since jarosite is mainly disposed of in landfills, any use of jarosite generates additional value due to the avoidance of landfill costs. The same applies to goethite, which is obtained as waste in primary zinc production. For the properties and hydrometallurgical processing of jarosite, see WO2018 / 109283.

[0023] A further option is the leaching of Fe oxide or compositions containing Fe oxide and / or metallic Fe. 2+ and / or Fe3+ It is also possible to use waste acids containing: Any of these options can be combined, providing a high degree of freedom to choose the best scenario from a technical, economic and logistical point of view.

[0024] Preferably, Fe 3+ Acidic solutions containing FeCl2 are based on H2SO4 or HCl. Depending on the waste material used, the acid-base can be selected accordingly. For example, to recycle a steel pickling solution containing FeCl2, an HCl-based matrix should be selected. For solutions containing FeSO4, an H2SO4-based matrix should be selected. When there is a choice, for example, when dissolving EAFD in acid, a sulfate-based matrix is most preferred, since the FeSO4·7H2O crystals will remove a significant amount of water from the system.

[0025] Preferably, the acidic solution used in the method of the present invention contains 1.5 to 60 g, preferably 4 to 50 g, more preferably 10 to 40 g, most preferably 14 to 28 g of Fe per kg of solution. 3+ Contains Fe 3+ Determination of total dissolved Fe by ICP and Fe by permanganate titration 2+ This is done by analyzing Fe 3+ is the total dissolved Fe and Fe 2+ It is the difference between

[0026] Preferably, the acidic solution used in the process of the present invention is Zn obtained from the leaching of Zn-containing industrial waste material (see above) with an acid, most preferably H2SO4. 2+ Most preferably, the acidic solution is prepared by leaching electric arc furnace dust (EAFD) with sulfuric acid (World of Metallurgy-ERZMETALL 75 (2022) No. 1, 28-35).

[0027] Preferably, the reaction of EAFD with sulfuric acid is carried out using sulfuric acid that is >90% H2SO4.

[0028] In a preferred embodiment, EAFD and sulfuric acid are simultaneously fed into the mixing zone and then discharged from the mixing zone. Thus, the reaction between EAFD and sulfuric acid can be carried out in a continuous process. For example, EAFD and sulfuric acid are simultaneously fed into a screw reactor and conveyed to opposite ends inside the screw reactor. Preferably, the screw reactor is double-walled and can be heated or cooled depending on the residence time in the reactor and the amount of heat generated by the reaction. Thus, the temperature of the mixture can be maintained at temperatures above 200°C for longer periods.

[0029] Preferably, Fe 3+ Acidic solutions containing Fe 3+ Fe in an amount of more than 25%, more preferably more than 50%, and most preferably more than 75%.

[0030] A preferred embodiment of the present invention comprises: Leaching of Zn-containing waste materials, preferably EAFD, with H2SO4 Separation of non-dissolved materials and H + , Zn 2+ , and Fe 3+ to obtain an acidic solution containing Use of an acidic solution to reduce zinc from galvanized steel scrap or compositions containing galvanized steel scrap Obtaining zinc-depleted scrap and solutions containing ZnSO4 and FeSO4 Zn 2+ Containing products and Fe 2+ Zn, to provide salt 2+ Fe from 2+ Separation of is.

[0031] The dissolution of EAFD in H2SO4 can be carried out in a single step reaction with concentrated H2SO4, or in a two-step dissolution with dilute H2SO4 in step 1 and concentrated H2SO4 in step 2. The dilute H2SO4 can be any waste H2SO4 or the solution obtained after crystallization and separation of FeSO4·7H2O by the method of the present invention. The acidic solution obtained from the dissolution of EAFD can be diluted with H2SO4.+ , Fe 3+ , and Zn 2+ Contains Fe 2+ may include:

[0032] After reaction of the waste material with acid, dissolution in water or dilute acid can be carried out using a reducing agent, preferably metallic Zn or Fe from scrap, or H2 generated during Zn leaching.

[0033] In the prior art, acid leaching Zn was + This is known to lead to kinetic problems due to the overpotential associated with H evolution. In contrast, according to the present invention, Fe 3+ is an oxidizing agent for metallic Zn. This avoids or at least reduces the kinetic problems due to overpotential for H2 evolution, thus resulting in accelerated Zn leaching. Furthermore, H2 evolution can be reduced or even completely avoided, and the reducing power of Zn is not wasted, as H2 is blown away instead of being oxidized by Fe. 3+ It is very valuable to get a return on your investment.

[0034] Preferably, there is more than one leaching step (at least one leaching step is Fe 3+ and at least one leaching step is carried out with a stoichiometric excess of Zn metal relative to Zn metal. + and Fe 3+ (This is done in Fe 3+ Regarding leaching with a stoichiometric excess of metallic Zn, the concentration of H2SO4 is preferably less than 10%, most preferably less than 4%. Thus, for steel scrap with residual Zn less than 0.5%, preferably less than 0.2%, most preferably less than 0.1%, and H2SO4 less than 2%, preferably less than 1.5%, most preferably less than 1%, Fe 3+ It is possible to obtain a solution free of H2SO4. Any H2SO4 concentration herein means free of H2SO4.

[0035] The subject of the present invention is a solution containing 1.5 to 60 g, preferably 4 to 50 g, most preferably 10 to 40 g of Fe per kg of solution. 3+ It is also Zn-coated Fe (or galvanized steel) that has been covered with an acidic solution containing

[0036] Preferably, Fe 3+ The acidic solution containing Fe temporarily in excess of the metallic Zn provided as a coating. 3+ Preferably, this excess is present at the beginning of the process, but it can also be present at the end of the leaching step. More preferably, the atomic ratio Fe 3+ / Zn 0 is greater than 2, even more preferably greater than 4, and most preferably greater than 10. This follows from the fact that some metallic Fe is Fe 3+ This means that it can be consumed for the reduction of

[0037] This allows for more complete leaching for better Zn removal. When the scrap is in the form of a pressurized package, some of the surface area coated with Zn is not directly accessible to the leaching agent. As a result, a certain degree of "over-leaching" can help approach (near) 100% Zn depletion; the "hot-soaked" Zn layer contains a Zn-Fe interlayer that can result in the co-leaching of metallic Fe. This "over-leaching" (meaning the dissolution of some metallic Fe from the scrap) can be carried out to various degrees depending on chemical and economic conditions.

[0038] A slight "over-leaching" reserves metallic Fe for further use (e.g., in steelmaking), a moderate "over-leaching" may be reasonable or necessary for maximum Zn reduction (especially galvannealed Zn layers), and a more complete "over-leaching" may be desirable, especially when additional waste streams containing Fe(III) can be converted into valuable products (e.g., converting one metallic Fe to two Fe(III) from jarosite or goethite). 3+ Three valuable Fe 2+species), which may be promising for maximizing the output of Fe salts.

[0039] Preferably, the leaching rate of metallic Zn (or Zn removal rate) is greater than 90% or 98% or greater than 99%, more preferably greater than 99.5%; most preferably greater than 99.8%.

[0040] Accepting some "over-leaching" of Fe can also aid in more efficient Zn removal in the case of polymers, paints, or lacquers on top of Zn coated steel substrates.

[0041] Another embodiment involves the oxidation of Fe(III) compounds such as Fe oxides, goethite, or jarosite with sulfuric acid or H + , Zn 2+ , and Fe 3+ Dissolution in an acidic solution containing Fe 3+ is converted to Fe in the subsequent reaction with galvanized steel scrap. 2+ is reduced to.

[0042] Fe obtained after dissolution of EAFD 3+ Obtaining Zn from galvanized steel scrap as a reducing agent for Fe preserves the life of the metal; Fe 2+ It is more valuable as a metal in scrap than as a metal.

[0043] Preferably, the reaction of the acidic solution with the galvanized steel scrap dissolves all or nearly all of the Zn (reaction A) and (then) all of the Fe 3+ is reduced (reaction B): Reaction A: Zn + 2Fe 3+ →Zn 2+ +2Fe 2+ Reaction B: 2Fe 3+ +Fe → 3Fe 2+

[0044] The leaching of Zn metal can be carried out in a two-step or multi-step process: virgin galvanized steel scrap can be subjected to a first leaching step with an acidic solution obtained from a previous leaching step or with a recycled solution from another process step, e.g., a solution obtained from the ZnS precipitation of the first step. Further leaching steps can be carried out with higher acidity or higher Fe content for improved leaching of the very last fraction of Zn metal. 3+ It is possible to continue using other solutions with different concentrations, for example by immersing a basket containing galvanized steel scrap in the corresponding solution, or by passing various leach solutions one after the other through a reactor filled with scrap.

[0045] Partial recycling of the solution optimizes the acidity for the leaching process and the Fe content for optimized Zn leaching. 3+ This can help adjust the level, increase the ion concentration for a more efficient separation process, or fine-tune the pH for ZnS precipitation. For example, the solution obtained after crystallization and separation of FeSO4 7H2O contains Fe 3+ Due to its acidity in the process step of producing an acidic solution containing

[0046] ZnS precipitate or Zn 2+ If required for subsequent solvent extraction steps, the pH can be raised by feeding fresh Zn coating material (reaction C), continuing the leaching of metallic Fe (over-leaching; reaction D), or by alkaline material (reaction E), or by reaction with fresh waste material (reaction F): Reaction C: Zn + H2SO4 → ZnSO4 + H2 Reaction D: Fe + H2SO4 → FeSO4 + H2 Reaction E: 2NaOH + H2SO4 → Na2SO4 + H2O Reaction F: Fe2O3 + 3H2SO4 → Fe2(SO4)3 + 3H2O

[0047] Reaction E is least preferred due to the generation of Na2SO4 which must be separated or terminated in the wastewater stream. Reactions C and D have the disadvantage of generating hydrogen but the advantage that the leaching process simply continues and no additional treatment steps are required. Reaction C has the advantage over reaction D that no metallic Fe is lost.

[0048] A preferred option is reaction F. The increase in pH can be achieved by dissolving iron oxides (e.g., from wastewater treatment after crystallization of FeSO4·7H2O), dissolving EAFD, or other waste materials. In a preferred embodiment, reaction F is not carried out after reactions A or B, but after a portion of the ZnS has precipitated and been separated. However, reaction F does not involve the addition of Fe 3+ From Fe 2+ requires further treatment by reaction A or B to reduce it to

[0049] The overall setting of process parameters is highly influenced by the consumption of acid to dissolve the waste material to generate an acidic solution. A higher acid ratio means a better dissolution rate of Zn and Fe from the waste material, but also requires more effort to maintain the acid equilibrium for complete and selective precipitation of ZnS. Depending on the relative volumes of waste material and galvanized steel scrap, the Fe and Zn content of each material, the price for Zn and FeSO4·7H2O, or logistical or quality constraints, the process can be adjusted with a considerable degree of flexibility.

[0050] Process control of the Zn leaching step can be achieved by monitoring the redox potential. Complete dissolution of Zn and Fe 3+The reduction of each is exhibited by a characteristic feature of the redox potential (see US 2015 / 0259766). Any acidic solution from the method of the present invention can be partially recycled back to the previous process step, for example, the solution obtained after Zn leaching, the solution obtained after precipitation and separation of ZnS, or the solution obtained after crystallization of FeSO4·7H2O. This can help improve the acid balance of the method of the present invention. Preferably, the acid required to generate the acidic solution by dissolving waste products can be partially derived from a recycle from a later process step.

[0051] Fe 3+ The use of waste materials as a source of feedstock for can generate another source of income due to the negative prices for some waste products (e.g., EAFD or jarosite or goethite with low Zn content). This applies in particular to waste products with low zinc content, for which no satisfactory methods for recycling exist for such materials.

[0052] Fe 3+ Zn-coated Fe covered with acidic solution containing In line with the above description of the acidic solution and the leaching process, the present invention also provides the product present at the beginning of the leaching process. Thus, the present invention provides a leaching solution of 1.5 to 60 g, preferably 4 to 50 g, and most preferably 10 to 40 g of Fe per kg of solution. 3+ Also provided is a Zn-coated Fe that is covered with an acidic solution comprising: The Zn-coated Fe and the acidic solution are described in detail in the previous sections.

[0053] Galvanized Steel Scrap Galvanized steel scrap consists of or contains an Fe substrate coated with a zinc layer. Zinc-coated Fe substrates are often used for corrosion-resistant products, for example in the automotive industry. Sometimes the protective layer is not pure zinc but may contain other elements such as Sn, Al, or Ni.

[0054] Galvanized steel scrap, for example, is packaged in a leachable liquid (i.e., Fe 3+ The scrap can be shredded or pressed into easy-to-handle packages by immersing it in an acidic solution containing Zn (an acidic solution containing Fe) and removing it again after the Zn leaching process. Another option is to fill a tank or column with the galvanized steel scrap and subject it to the acidic solution in a continuous or discontinuous manner. Another option is to place the galvanized steel scrap in a basket and then immerse the basket in the leachate, i.e., Fe 3+ Yet another option is to shred the galvanized steel scrap and transport the material on a moving belt through an area where it is sprayed with an acid solution and a subsequent area where it is sprayed with water.

[0055] After leaching of the Zn is complete, the zinc-depleted metallic Fe substrate is washed with dilute acid and / or water to remove any adhering solution containing Zn and anions such as sulfates or chlorides.

[0056] The zinc-reduced Fe substrate can be used as a high-quality raw material for iron smelting processes, for example for steelmaking using electric arc furnaces, for blast oxygen furnaces or for casting.

[0057] Separation process Dissolved Zn 2+ and Fe 2+ Separation can be achieved by precipitation of ZnS by bubbling H2S into the solution.

[0058] The preferred options are: Obtained Zn 2+ Precipitation of ZnS in solution Dissolved Fe 2+ Separation of ZnS from solutions containing Crystallization of Fe compounds due to evaporation of water and / or decrease in temperature Separation of the crystals of the Fe compound and recycling of the resulting liquid phase back into one of the previous process steps

[0059] During the precipitation of ZnS with H2S, the pH drops. In a preferred embodiment of the present invention, the precipitation of ZnS is carried out in a (at least) two-step process. In the first step, Zn 2+ A portion of the ZnS is precipitated as ZnS using H2S off-gas from the second step or H2S obtained from stripping the solution obtained after precipitation and separation of ZnS in the second step. Also, high concentrations of H2S are used in the second step to shift the equilibrium towards ZnS precipitation. Another option is the precipitation of ZnS using Na2S or (NH4)2S.

[0060] A preferred embodiment is to react the precipitated ZnS with H2SO4 to obtain a ZnSO4 solution and gaseous H2S, which is then recycled for precipitation of ZnS again. Preferably, the wet ZnS filter cake is reacted with dilute H2SO4. It may be necessary to remove residual H2S with N2 or air to shift the equilibrium in the desired direction. Alternatively, the H2S can be reacted with NH4OH or NaOH to obtain Na2S or (NH4)2S.

[0061] However, ZnS may be the preferred material if it must be transported long distances to the zinc manufacturing site.

[0062] Higher value Zn 2+ When refining to create a solution, there is a synergistic effect between dissolving EAFD with H2SO4 and removing zinc from galvanized steel scrap during refining (e.g., Cu, Cd, Mn, Ni from the Zn-Ni coating).

[0063] H2S can be produced from H2 and S or obtained as a by-product from the production of coke. H2S may also be obtained from spent absorbents for H2S, such as EAFD as absorbents for H2S (Energy Fuels 2022, 36, 3695-3703).

[0064] There are widespread industrial applications of metal oxides as sorbents for H2S removal from industrial gases such as synthesis gas, coke gas from steel production, hydrogen in fuel cells, tail gas from sulfur recovery units, and bio / natural gas. These materials can be used for H2S generation and at the same time, Fe 3+ It can be used as a source of Fe and / or Zn in the production of an acidic solution containing

[0065] Dissolved Zn 2+ and Fe 2+ Another option for separating Zn is solvent or membrane extraction. 2+ is transferred to an organic phase, most preferably D2EHPA, di-(2-ethylhexyl)phosphoric acid. D2EHPA is an inexpensive and widely available reagent.

[0066] Zn 2+ The extraction process steps are as follows: D2EHPA is dissolved in an organic solvent, typically an inert hydrocarbon such as kerosene or naphtha. This organic phase contains Zn 2+ This D2EHPA-containing organic phase is immiscible with an aqueous solution containing Zn. 2+ contacting the mixture with an aqueous solution containing:

[0067] [ka]

[0068] The Zn(D2EHPA)2 complex is more soluble in the organic phase than in the aqueous phase, so the complex is transferred from the aqueous phase into the organic phase.

[0069] The loaded organic phase, containing the extracted Zn(D2EHPA)2 complex, is then separated from the aqueous phase by settling, centrifugation, or decantation.

[0070] To recover the extracted zinc from the organic phase, H2SO4 is used as a scavenger. After removing the zinc from the organic phase, the D2EHPA can be regenerated and reused in the extraction process.

[0071] Preferably, the solvent extraction process involves multiple extraction and removal steps to increase the overall efficiency of zinc recovery.

[0072] Preferably, the pH of the solution to be treated by extraction is above 0.5, more preferably above 1.0, and most preferably above 1.5.

[0073] Mn 2+ is Zn 2+ Since Mn is extracted together with Zn, it must be separated. This can be done by cementation with fine Zn powder: Zn + Mn 2+ →Zn 2+ + Mn. Mn can be separated along with the unreacted Zn by sedimentation, filtration, or centrifugation. Another option is to 2+ to MnO. Preferably, this can be done with O, O, H0, or HSO, with subsequent separation of the MnO by sedimentation, filtration, or centrifugation.

[0074] Formation of Fe salts ZnS precipitation and separation of the precipitate or Zn by solvent or membrane extraction 2+ The solution obtained after the removal of H2S is used for the regeneration of the Fe compound. Removal of residual H2S in the solution can be carried out with N2. Crystallization is the preferred option for obtaining solid Fe compounds from solutions containing FeSO4. Preferably, water is evaporated in vacuo and by providing heat so that the temperature does not drop too quickly. 2+ The FeSO4·7H2O crystals are removed from the solution. A preferred option is to lower the temperature to +5°C and then separate the FeSO4·7H2O crystals by filtration or centrifugation. The process of crystallization and separation of FeSO4·7H2O from acidic solutions is prior art in TiO2 production. The specific parameters depend on the composition of the solution. General principles and considerations can be found in DE 10 2007 032 418.

[0075] Preferably, the FeSO4 concentration in the solution is greater than 100 g / L. Due to the large amount of crystals, the bound water in the FeSO4·7H2O solution is efficiently removed from the solution, resulting in a significant drop in pH. The final concentration of the saturated solution at +5°C is approximately 35-40 g / L FeSO4. 2+ is.

[0076] Due to the evaporation of water from the FeSO4 solution and water trapping the heptahydrate, the acidity of the solution becomes significantly higher (pH<<0.5). This solution or parts of this solution can therefore be used to close the loop and recycle back to one of the previous steps: for reaction with EAFD or for Zn leaching from galvanized steel scrap.

[0077] A similar situation is found in the crystallization of FeCl2 as FeCl2·4H2O.

[0078] At least a portion of this solution leaves the process as wastewater and a sink for some ions, e.g., Na or K. Preferably, Fe is precipitated and separated by alkaline treatment and added to one of the preceding steps, e.g., Fe 3+ It is recycled to generate an acidic solution containing or to raise the pH by reaction F.

[0079] electrowinning Careful precipitation of ZnS and washing of the precipitate with dilute H2SO4 (pH about 2) can achieve nearly complete separation of Fe and other impurities. This ZnS can be fed into the primary Zn production process.

[0080] After conversion of ZnS to ZnSO solution by reaction with H2SO4, the resulting solution can be used for electrowinning of metallic zinc; further purification by a cementation step with metallic zinc powder is possible to remove many more impurities, such as Ni, Cd, Cu, and Fe. Since these impurities are present in very small concentrations, the demand for zinc powder is very low.

[0081] Further details and further references to cementation can be found in DEZINCING OF GALVANIZED STEEL, by J. Grogan, Colorado School of Mines: https: / / pdfcoffee.com / qdownload / dezincinc-of-galvanized-steel-pdf-pdf-free.html, page 25.

[0082] In summary, the method of the present invention offers several impressive advantages: No significant waste stream from EAFD recycling Hydrometallurgical processes generally have lower energy consumption and a lower CO2 footprint compared to thermal processes (e.g., the Waelz process) Maximum efficiency of the leaching process in terms of Zn reduction (implies some co-leaching of Fe) High flexibility Possible shift in process to generate more H2 for further use Separation step: Use H2S for precipitation of ZnS if cheap H2S is available; or use solvent extraction if no H2S or cheap H2S is available.

[0083] The present invention relates to a process for the removal of zinc from galvanized steel, preferably using Fe as an oxidizing agent. 3+ The present invention also provides the use of an acidic solution comprising:

[0084] [Example 1] Recycling of Electric Arc Furnace Dust (EAFD) and Dezincing of Galvanized Steel Scrap The acidic solution is prepared by reacting electric arc furnace dust (EAFD) with concentrated sulfuric acid and dissolving the resulting reaction product in water. After separation of the solid residue, Fe 3+ and Zn 2+ An acidic solution containing

[0085] The Zn coating is dissolved to over 99% and the Fe 3+ Fe 2+ Galvanized steel scrap is leached with this acidic solution until it is reduced to Zn. This can be done by immersing a basket filled with the scrap in the acidic solution or by passing the acidic solution through a column filled with the scrap. The resulting Zn-free metallic Fe substrate can be washed with water, dried, and used as an Fe source for steelmaking or foundries.

[0086] A typical mass ratio of EAFD to galvanized steel scrap is 1:8.

[0087] Zn 2+ and Fe 2+ The solution resulting from the Zn leaching process, containing FeSO4, is treated with H2S gas to precipitate ZnS. The ZnS is separated by filtration or centrifugation and washed with dilute H2SO4 (about pH 2) to remove FeSO4. The ZnS can be used as a raw material in primary zinc production or can be converted to ZnSO4 solution by dissolving it in H2SO4 for zinc electrowinning.

[0088] The FeSO4 solution obtained after separation of the ZnS precipitate is used for crystallization of FeSO4·7H2O (copperas) by vacuum evaporation of the water, allowing the system to cool to 5 °C. The FeSO4 solution obtained after separation of the copperas can be recycled (fully or partially) to one of the original preceding process steps.

[0089] Obtained products: Zn-depleted scrap, ZnS (or ZnSO4), and FeSO4·7H2O (copalus).

[0090] [Example 2] Recycling of jarosite and dezincing of galvanized steel scrap Jarosite is dissolved in dilute H2SO4 (preferably waste H2SO4 from TiO2 production).

[0091] The Zn coating is dissolved to over 99% and the Fe 3+ Fe 2+ Galvanized steel scrap is leached with this acidic solution until it is reduced to Zn. This can be done by immersing a basket filled with the scrap in the acidic solution or by passing the acidic solution through a column filled with the scrap. The resulting Zn-free metallic Fe substrate can be washed with water, dried, and used as an Fe source for steelmaking or foundries.

[0092] Zn 2+ and Fe 2+ The solution resulting from the Zn leaching process, containing FeSO4, is treated with H2S gas to precipitate ZnS. The ZnS is separated by filtration or centrifugation and washed with dilute H2SO4 (about pH 2) to remove FeSO4. The ZnS can be used as a raw material in primary zinc production or can be converted to ZnSO4 solution by dissolving it in H2SO4 for zinc electrowinning.

[0093] The FeSO4 solution obtained after separation of the ZnS precipitate is obtained for crystallization of FeSO4·7H2O (copalus) by vacuum evaporation of the water, allowing the system to cool to 5 °C. The FeSO4 solution obtained after separation of the copalus can be recycled (fully or partially) to one of the original preceding process steps.

[0094] The resulting products are: Zn-reduced scrap, ZnS (or ZnSO4), FeSO4·7H2O (copallas); this recycles three low-cost waste materials and converts them into valuable products: jarosite, waste diluted H2SO4, and galvanized steel scrap.

[0095] [Example 3] Recycling of Electric Arc Furnace Dust (EAFD) and Dezincing of Galvanized Steel Scrap The acidic solution is prepared by reacting electric arc furnace dust (EAFD) with concentrated sulfuric acid and dissolving the resulting reaction product in water. After separation of the solid residue, Fe 3+ and Zn2+ An acidic solution containing

[0096] The Zn coating is dissolved to over 99% and the Fe 3+ Fe 2+ Galvanized steel scrap is leached with this acidic solution until it is reduced to Zn. This can be done by immersing pressed scrap elements or a basket filled with scrap in the acidic solution, or by passing the acidic solution through a tank filled with scrap. The resulting Zn-free metallic Fe substrate is washed with water, dried, and used as an Fe source for steelmaking or foundries.

[0097] Zn 2+ and Fe 2+ The solution obtained from the Zn leaching process, containing Zn(D2EHPA)2, is treated by solvent extraction with D2EHPA in kerosene. The input organic phase, containing the extracted Zn(D2EHPA)2 complex, is then separated from the aqueous phase by settling. The organic phase is mixed with H2SO4 as a removal agent. After removing zinc from the organic phase, the D2EHPA is reused for the extraction process.

[0098] Mn 2+ is converted to MnO2 by oxidation with O3 and then separated by filtration.

[0099] Zn 2+ The FeSO4 solution obtained after solvent extraction is used for the crystallization of FeSO4·7H2O (copalus) by vacuum evaporation of water, allowing the system to cool to 5 °C. The FeSO4 solution obtained after separation of the crystalline copalus can be recycled (fully or partially) to one of the original preceding process steps.

[0100] Obtained products: Zn-depleted scrap, ZnSO4, MnO2, and FeSO4·7H2O (copalus).

[0101] [Example 4] Dezincing galvanized steel scrap Galvanized steel scrap containing 0.9% Zn, (a) Acidic solution containing 150 g / l H2SO4 (b) 150 g / l H2SO4 and 10 g / l Fe 3+ Acidic solution containing (as Fe2(SO4)3) The samples were leached for 10, 20, and 30 seconds at 2000 W. After the leaching process, the scrap samples were washed with deionized water and dried before XRF characterization. The results (in Figure 1) show that the surface Zn concentration as determined by XRF is significantly higher than that of Fe. 3+ The acceleration of Zn dissolution in the presence of Zn is clearly evident.

[0102] [Example 5] Dezincing galvanized steel scrap Galvanized steel scrap containing 0.9% Zn, (a) Acidic solution containing 20 g / l H2SO4 (b) 20 g / l H2SO4 and 28 g / l Fe 3+ Acidic solution containing (as Fe2(SO4)3) (c) 55g / l Fe 3+ (as Fe2(SO4)3) solution (pH of the solution < 4) After the leaching process, the scrap samples were washed with deionized water and dried before XRF characterization. The results (Fig. 2) show that the surface Zn concentration as determined by XRF is higher than that of Fe. 3+ The acceleration of Zn dissolution in the presence of Zn is clearly evident.

[0103] After 300 seconds, the residual Zn on the steel surface was 0.1% and Fe 3+ For solutions containing 1.1%, Fe 3+ For the H2SO4 solution without H2SO4, it is 17%.

Claims

1. 1. A method for reducing zinc from Zn-coated Fe, comprising: a) Zn-coated Fe, ３＋ Zn is extracted by leaching in an acidic solution containing ２＋ and Fe ２＋ and during leaching, providing an acidic solution containing an atomic ratio of Fe ３＋ / Zn ０ >2 and excess Fe relative to metallic Zn ３＋ and / or the acidic solution contains 1.5 to 60 g of Fe per kg of solution at the start of the leaching process. ３＋ At a concentration of Fe ３＋ and b) obtaining a zinc-depleted metallic Fe substrate; c) Fe ２＋ Zn ２＋ Zn ２＋ Containing products and Fe ２＋ A process for obtaining salt; By, method.

2. Fe ３＋ is made from the dissolution of electric arc furnace dust, jarosite, mill scale, or goethite, or from TiO using the sulfate process. ２ Waste H from production ２ SO ４ , acidic solution from the production of zinc, FeCl ２ or FeSO ４ Pickling solutions for steel containing TiO using the chloride process ２ Manufacturing TiO ２ 10. The method of claim 1, characterized in that it is made from waste metal chlorides from chlorination, iron chloride solutions from the production of synthetic rutile, or any combination of the waste products listed above.

3. The acidic solution is Zn ２＋ 3. The method of claim 1 or 2, comprising:

4. There is more than one leaching step, and at least one leaching step is ３＋ and at least one leaching step is carried out with a stoichiometric excess of H relative to the Zn metal. ＋ and Fe ３＋ 4. The method according to claim 1, wherein the method is carried out by

5. During the leaching of step a), an atomic ratio of Fe greater than 4, preferably greater than 10 ３＋ / Zn ０ In this case, excess Fe is present relative to metallic Zn. ３＋ 5. The method according to claim 1, wherein:

6. Zn ２＋ Fe from ２＋ The acid obtained after separation of ３＋ 6. The method of claim 1, wherein the method is used to produce an acid comprising:

7. i. Zn-bearing waste material, preferably EAFD, is treated with H ２ SO ４ and leaching with ii. Separate the residue of undissolved material and ＋ , Zn ２＋ , and Fe ３＋ obtaining an acidic solution comprising iii. using the resulting acidic solution to reduce zinc from galvanized steel scrap or a composition comprising galvanized steel scrap; iv. Zinc-depleted scrap and ZnSO ４ and FeSO ４ obtaining a solution comprising v. Zn ２＋ From Fe ２＋ Separating Zn ２＋ Containing products and Fe ２＋ providing salt; 7. The method of claim 1, comprising:

8. 8. The method according to any one of claims 1 to 7, characterized in that the leaching rate of metallic Zn from the Zn-coated Fe is more than 90%, preferably more than 98%, most preferably more than 99.5%.

9. The Fe obtained by precipitation as ZnS ２＋ Zn obtained from ２＋ 9. The method according to claim 1, wherein the

10. The Fe obtained by solvent extraction ２＋ Zn obtained from ２＋ 9. The method according to claim 1, wherein the

11. The following additional steps: Obtained Zn ２＋ as ZnS; Dissolved Fe ２＋ Separating ZnS from the solution containing Crystallization of the Fe compound by evaporation of water and / or reduction of temperature; Separating the crystals of the Fe compound and recycling the resulting liquid phase into one of the preceding process steps; 10. The method of claim 1, comprising:

12. The precipitated ZnS was ２ SO ４ By reacting with ZnSO ４ and H ２ S is obtained, and the resulting H ２ 12. The method according to claim 11, characterized in that S is recycled for the precipitation of ZnS.

13. 13. The method according to any one of claims 1 to 12, characterized in that the obtained Zn-depleted scrap is used as raw material for an iron smelting process, preferably in an electric arc furnace, a blast furnace, a basic oxygen furnace or for casting.

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