Dezincification method of galvanized steel waste

Abstract

The present invention relates to waste treatment and provides a method of depleting zinc from Zn coated Fe by subjecting Zn coated Fe to a leaching step in an acidic solution comprising Fe < 3 + > to provide an acidic solution comprising Zn < 2 + > and Fe < 2 + >; a zinc-depleted metal Fe base material is obtained; and separating Fe < 2 + > from Zn < 2 + > to provide a Zn < 2 + >-containing product and a Fe < 2 + > salt.

Description

Background Art

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

[0002] Generally, the term galvanized steel or galvanized steel scrap as used herein should be understood in a broad sense: galvanized steel or galvanized steel scrap includes any steel sheet or substrate covered with a zinc layer. The zinc layer may be deposited by electroplating or electrolytic deposition, or may be applied by hot dipping the steel substrate into molten zinc, or by zinc vapor deposition or by any other method of coating the steel substrate with a zinc layer.

[0003] Additionally, the term galvanized steel or galvanized steel scrap as used herein includes any material resulting from subsequent processing, such as subsequent annealing of the 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 a large amount of Zn in the flue gas. Therefore, scrap containing Zn coating (galvanized steel scrap or galvanized scrap) has a lower value than scrap without Zn, and there are many attempts in the art to dezincify galvanized steel scrap.

[0005] There are different options for depleting Zn from galvanized steel scrap:

[0006] ·Pyrometallurgy

[0007] Alkali Wetting Metallurgy

[0008] Acid Wet Metallurgy

[0009] Although acid leaching generally performs better than alkaline leaching, it brings with it the significant disadvantage that the acidic solution not only leaches Zn, but also Fe. Therefore, the resulting material is not suitable for electrowinning (pure) Zn metal unless an additional separation step is performed to purify the Zn. This additional separation step is required even if methods are adopted to minimize Fe leaching, such as monitoring the potential by placing a reference electrode in the leaching solution, measuring the corrosion potential and stopping the reaction when the measured potential reaches a plateau, as taught in US2015 / 0259766.

[0010] Therefore, it is considered in the art that acid dezincification of galvanized steel scrap for electrowinning of metallic zinc is economically disadvantageous (see, for example, DEZINCING OF GALVANIZED STEEL by J. Grogan, Colorado Scholl of Mines: http: / / pdfcoffee.com / qdownload / dezincinc-of-galvanized-steel-pdf-pdf-free.html, p. 75, lines 15-16).

[0011] WO 2023 / 089234 relates to a method for recovering zinc and iron products from zinc-containing waste materials. Summary of the invention

[0012] In view of this prior art, the present invention addresses the need to provide an efficient and economical method for recycling Zn coated iron such as galvanized steel scrap.

[0013] The present inventors have found that the use of Fe 3+ The acidic solution used for leaching combines technical and economic advantages in a way that surprisingly overcomes the disadvantages of previously known acid leaching: Fe 3+ Not only is it an oxidant that results in accelerated Zn leaching, but it also generates Fe from otherwise useless waste materials during the leaching step. 2+ , making the separation step suitable for producing Fe 2+ salt, and therefore industrially viable.

[0014] Thus, the present invention provides a method for depleting metallic Zn from Zn-coated Fe (e.g. zinc-coated scrap or galvanized steel scrap, respectively), comprising the following steps:

[0015] a) In the presence of Fe 3+ The Zn-coated Fe is subjected to a leaching step in an acidic solution of 2+ and Fe 2+ Acidic solution;

[0016] b) obtaining a metallic Fe substrate depleted of zinc; and

[0017] c) Fe 2+ With Zn 2+ Separation to provide Zn 2+ The product and Fe 2+ Salt.

[0018] At the beginning of the leaching step, the acid solution preferably contains a concentration of 1.5-60 g Fe 3+ / kg solution Fe 3+Such an acidic solution can be obtained, for example, from treating a material comprising ferric iron with an acid. In a preferred embodiment, the acidic solution used in step a) is obtained by acid treatment of electric arc furnace dust (EAFD).

[0019] In addition, during the leaching process, Fe 3+ Relative to the excess of metallic Zn, the atomic ratio of Fe 3+ / Zn 0 >2.

[0020] Step c) provides two different products, containing Zn 2+ The product and Fe 2+ Salt.

[0021] The Zn-containing 2+ The product is ZnS obtained from the precipitation, which is used to produce metallic Zn by electrolytic extraction after conversion to ZnSO4. 2+ The product is a ZnSO4 or ZnCl2 solution obtained by solvent extraction. 2+ The salt is preferably FeCl2 or FeSO4, which after optional purification can be sold for wastewater treatment, as a chromate reducing agent for cement or as an animal food additive. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A bar graph depicting the residual Zn on the steel surface obtained in Example 4 is provided.

[0023] Figure 2 A bar graph depicting the residual Zn on the steel surface obtained in Example 5 is provided. DETAILED DESCRIPTION

[0024] Acidic solution and leaching steps

[0025] The acidic solution may be obtained by reacting a waste product with fresh or waste acid and is therefore preferably a waste derived solution. The waste product or waste acid may be any waste H2SO4 (or spent H2SO4 or dilute H2SO4), for example from the production of TiO2 using the sulfate process, waste acidic solutions from zinc production, any waste HCl, steel pickling solutions containing FeCl2 or FeSO4, waste metal chlorides from chlorination of TiO2 from the production of TiO2 using the chloride process, ferric chloride solutions from synthetic rutile production, or iron chloride solutions containing FeCl2 or FeSO4. 3+ Any waste acid used to dissolve Fe oxides or hydroxides, or a combination of the above waste products. The pH of the acidic solution is preferably 1.5 or less.

[0026] Preferably, the following industrial residues containing Fe can be dissolved in acid or leached with acid:

[0027] EAFD (typically 20-50% Fe; 10-40% Zn)

[0028] EAFD from stainless steel production (containing Cr and Ni)

[0029] Slag from the lead industry

[0030] Jarosite or geothite as waste from the zinc industry; Jarosite = MFe3(OH)6(SO4)2, M = Na, K or NH4

[0031] Mill scale (preferably after removing adhering oil)

[0032] ·Dust from cupola furnace

[0033] Dust from stainless steel production

[0034] Blast furnace dust and sludge (typically 30-40% Fe; 1-8% Zn)

[0035] Basic oxygen furnace (BOF) dust and sludge (up to 70% Fe, <5% Zn)

[0036] Spent H2S absorbent containing EAFD or ZnO as absorbent

[0037] Furthermore, the following Zn-containing industrial residues can be dissolved in acid or leached with acid, assuming that Fe is incorporated into the acidic solution by using an Fe-containing acid or by combining with one of the residues listed above:

[0038] Zinc ash

[0039] Zinc skimming

[0040] Brass Gray

[0041] Jarrosite is obtained in primary zinc production by precipitation at 95°C and pH 3.5. Since jarosite is mainly landfilled, any use of jarosite generates additional value due to the avoidance of landfill costs. The same applies to goethite obtained as waste in primary zinc production. See WO2018 / 109283 for the properties and hydrometallurgical processing of jarosite.

[0042] A further option is the leaching of iron oxides or compositions comprising iron oxides and / or metallic iron. 2+ and / or Fe 3+Any of these options can be combined, resulting in a high degree of freedom in choosing the best solution from a technical, economic and logistic point of view.

[0043] Preferably, Fe 3+ The acidic solution is based on H2SO4 or HCl. Depending on the waste material used, the acid and base can be selected accordingly. For example, recycling steel pickling solutions containing FeCl2 should preferably have an HCl-based matrix. Solutions containing FeSO4 should preferably have an H2SO4-based matrix. If there is a free choice, such as when dissolving EAFD in acid, a sulfate-based matrix is ​​most preferred because the FeSO4*7H2O crystals absorb a lot of water from the system.

[0044] Preferably, the acidic solution used in the process of the present invention contains 1.5-60 g, preferably 4-50 g, more preferably 10-40 g, and most preferably 14-28 g Fe 3+ / kg solution. Total dissolved Fe was analyzed by ICP and Fe was titrated with permanganate 2+ Fe 3 + Determination of Fe 3+ is the total dissolved Fe and Fe 2+ The difference between.

[0045] Preferably, the acidic solution used in the process of the present invention comprises Zn obtained by leaching 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 Metal lurgy - ERZMETALL 75 (2022) No. 1, 28-35).

[0046] Preferably, the reaction of EAFD with sulfuric acid is carried out using sulfuric acid with >90% H2SO4.

[0047] In a preferred embodiment, EAFD and sulfuric acid are simultaneously fed into the mixing zone and then removed from the mixing zone. Thus, the reaction of 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 transported to the other end within 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 heat generated by the reaction. Thus, the temperature of the mixture can be maintained at a temperature of >200°C for a longer period of time.

[0048] Preferably, Fe 3+ The acidic solution has an oxidation state of Fe greater than 25%, more preferably greater than 50%, and most preferably greater than 75%. 3+Fe.

[0049] A preferred embodiment of the present invention is

[0050] Leaching of Zn-containing waste materials with H2SO4, preferably EAFD

[0051] · Separate the undissolved material and obtain the + 、Zn 2+ and Fe 3+ Acidic solution

[0052] Use of an acidic solution for depleting zinc from galvanized steel waste or a composition comprising galvanized steel waste

[0053] Obtaining zinc-depleted waste and a solution containing ZnSO4 and FeSO4

[0054] ·Fe 2+ With Zn 2+ Separation to provide Zn 2+ The product and Fe 2+ Salt.

[0055] The dissolution of EAFD in H2SO4 can be accomplished in a single step using concentrated H2SO4, or in two steps: using dilute H2SO4 in step 1 and concentrated H2SO4 in step 2. The dilute H2SO4 can be any waste H2SO4, or a solution obtained after crystallization and separation of FeSO4*7H2O according to the method of the present invention. The acidic solution produced by the dissolution of EAFD contains H + , Fe 3+ and Zn 2+ and may contain Fe 2+ .

[0056] After the waste material reacts with the acid, dissolution in water or dilute acid can be performed using a reducing agent. Preferably, metallic Zn or Fe from the waste or H2 generated during Zn leaching can be used.

[0057] In the prior art, acid leaching Zn is + Oxidation, known H + Due to the overpotential associated with H2 production, kinetic problems arise. In contrast, according to the present invention, Fe 3+ is an oxidant for metallic Zn. This avoids or at least reduces the kinetic problem of overpotential for H2 production, thus leading to accelerated Zn leaching. Moreover, H2 production can be reduced or even avoided completely, and the reducing power of Zn is not useless, but is useful for Fe 3+ The reduction is very valuable, rather than blowing off the H2.

[0058] Preferably, there is more than one leaching step (at least one leaching step with a relative amount of Fe 3+ The leaching step is carried out with a stoichiometric excess of metallic Zn, and at least one leaching step is carried out with a stoichiometric excess of H relative to the metallic Zn. + and Fe 3+ For the Fe 3+ In the leaching step of the stoichiometric excess of metallic Zn, the concentration of H2SO4 is preferably <10%, most preferably <4%. Thus, it is possible to obtain a steel scrap with residual Zn <0.5%, preferably <0.2%, most preferably <0.1% and a Fe-free steel scrap with <2%, preferably <1.5%, most preferably <1% H2SO4. 3+ Any H2SO4 concentration herein refers to free H2SO4.

[0059] The subject of the present invention is also Zn-coated Fe (or galvanized steel), which contains 1.5-60 g, preferably 4-50 g, most preferably 10-40 g Fe 3+ / kg solution is covered with acidic solution.

[0060] Preferably, Fe 3+ The amount of acidic solution used is such that relative to the metal Zn, Fe 3+ Temporary excess. Preferably, this excess is present at the beginning of the process. However, it can also be present at the end of the leaching step. More preferably, Fe 3+ / Zn 0 The atomic ratio of Fe is > 2, even more preferably > 4, and most preferably > 10. Thus, some metallic Fe can be consumed for Fe 3+ of restoration.

[0061] This allows for a more thorough leaching for better Zn removal. If the waste is in the form of compacted inclusions, some Zn-coated surface areas cannot be directly reached by the leachant. Therefore, a certain degree of "overleaching" can help approach (close to) 100% Zn depletion; the "hot-dipped" Zn layer contains a Zn-Fe intermediate layer, which can result in co-leaching of metallic Fe. This "overleaching" (meaning dissolving some metallic Fe from the waste) can be done to varying degrees depending on chemical and economic conditions:

[0062] Slight "overleaching" saves metallic Fe for further use (e.g. in steelmaking), moderate "overleaching" may be justified or necessary for maximum Zn depletion (particularly in the case of galvanized Zn layers), and more thorough "overleaching" may be desirable for maximizing the yield of Fe salts, particularly if an otherwise waste stream containing Fe(III) can be converted into valuable products (e.g. 1 metallic Fe will convert 2 Fe from jarosite or goethite). 3+Converted into 3 valuable Fe 2+ substance).

[0063] Preferably, the leaching rate of metallic Zn (or Zn removal rate) is >90% or >98% or >99%, more preferably >99.5%; most preferably >99.8%.

[0064] In the case of polymers, paints or varnishes on Zn coated steel substrates, accepting some "overleaching" of Fe may also contribute to more efficient Zn removal.

[0065] Another embodiment is to dissolve an Fe(III) compound such as Fe oxide, goethite or jarosite in sulfuric acid or in a solution containing H + 、Zn 2+ and Fe 3+ In an acidic solution. 3+ In the subsequent reaction with galvanized steel scrap, it is reduced to Fe 2+ .

[0066] The Zn in galvanized steel scrap is used as the Fe 3+ The reducing agent saves the life of Fe as a metal; Fe as a metal in waste is smaller than Fe 2+ Have higher value.

[0067] Preferably, the reaction of the acidic solution with the galvanized steel scrap is continued until all or substantially all of the Zn is dissolved (reaction A) and (subsequently) all of the Fe 3+ Both are reduced (reaction B):

[0068] Reaction A: Zn + 2Fe 3+ =>Zn 2+ +2Fe 2+

[0069] Reaction B: 2Fe 3+ +Fe=>3Fe 2+

[0070] Leaching of metallic Zn can be carried out in a 2-step or multi-step process: the new galvanized steel scrap can be subjected to a first leaching step with an acidic solution obtained from a previous leaching step or with a solution recycled from another process step, e.g. a solution obtained from the first ZnS precipitation step. And subsequently, a solution with a higher acidity or a higher Fe 3+ The leaching steps are carried out with other solutions of different concentrations to improve the leaching of the last part of the metallic Zn. This can be done, for example, by immersing a basket with the galvanized steel scrap in the corresponding solution or by passing the different leaching solutions one by one through a reactor filled with steel scrap.

[0071] Partial recycling of the solution can help optimize the acidity of the leaching step and adjust the Fe 3+ The pH can be adjusted to optimize Zn leaching, increase ion concentration for a more efficient separation step, or fine-tune pH to precipitate ZnS. For example, the solution obtained after crystallization and separation of FeSO4*7H2O can be used to make Fe-containing 3+ The process steps of the acidic solution.

[0072] If for ZnS precipitation or Zn 2+ If a subsequent step of solvent extraction requires, the pH can be raised. This can be achieved by providing new Zn-coated material (reaction C) or continuing to leach metallic Fe (overleaching; reaction D), or by alkaline material (reaction E) or by reaction with new waste material (reaction F):

[0073] Reaction C: Zn + H2SO4 = > ZnSO4 + H2

[0074] Reaction D: Fe+H2SO4=>FeSO4+H2

[0075] Reaction E: 2NaOH+H2SO4=>Na2SO4+H2O

[0076] Reaction F: Fe2O3+3H2SO4=>Fe2(SO4)3+3H2O

[0077] Reaction E is the least favorable because Na2SO4 is produced which must be terminated or separated in the wastewater stream. Reactions C and D have the disadvantage of producing hydrogen but the advantage of simply continuing with the leaching step and not requiring additional processing steps. Reaction C has the advantage over reaction D that there is no loss of metallic Fe.

[0078] The preferred choice is reaction F. Raising the pH can be achieved by dissolving iron oxide (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 reaction A or B, but after a portion of the ZnS is precipitated and separated. However, reaction F requires another treatment according to reaction A or B to remove Fe 3+ Reduction to Fe 2+ .

[0079] The overall setting of process parameters is heavily influenced by the acid consumption used to dissolve the waste material to produce the acid solution. A high acid ratio means better dissolution rates for Zn and Fe from the waste material, but also means more effort to maintain the acid balance to completely and selectively precipitate ZnS. The process can be adjusted quite freely depending on the relative volumes of waste material and galvanized steel scrap, the Fe and Zn content of each material, the price of Zn and FeSO4*7H2O, or logistic or quality constraints.

[0080] Process control of the Zn leaching step can be performed by monitoring the redox potential. 3+ The reduction of each is indicated by the characteristics of the redox potential (see US2015 / 0259766). Any acidic solution from the process of the present invention can be partially recycled back to the previous process steps, such as the solution obtained after Zn leaching, the solution obtained after ZnS precipitation and separation, or the solution obtained after FeSO4*7H2O crystallization. This can help improve the acid balance of the process of the present invention. Preferably, the acid required to produce the acidic solution by dissolving the waste product can be partially derived from the recycling from the subsequent process steps.

[0081] Due to the negative price of some waste products (e.g. EAFD or jarosite or goethite with low Zn content), the use of waste materials as Fe 3+ This is particularly applicable to waste products with low zinc content, for which there are no satisfactory methods for recovering those materials.

[0082] Containing Fe 3+ The acidic solution covers the Zn-coated Fe

[0083] Consistent with the above description of the acidic solution and the leaching step, the present invention also provides the product present at the beginning of the leaching step. Thus, the present invention also provides Zn-coated Fe, which is comprised of 1.5-60g, preferably 4-50g, most preferably 10-40g Fe 3+ The Zn-coated Fe and acidic solutions are described in detail in the previous section.

[0084] Galvanized steel scrap

[0085] Galvanized steel scrap contains or consists of an Fe substrate coated with a zinc layer. Fe substrates coated with zinc 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.

[0086] Galvanized steel scrap can be comminuted or compacted into inclusions that are easy to handle, for example by immersing the inclusions in a leaching solution (i.e., containing Fe 3+Another option is to fill a container or column with 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 frame and immerse the frame in the leaching solution, i.e., the Fe-containing 3+ Yet another option is to shred the galvanized steel scrap and convey the material onto a moving belt and pass through an area sprayed with an acid solution and a subsequent area sprayed with water.

[0087] After leaching of Zn is complete, the zinc-depleted metallic Fe substrate may be washed with dilute acid and / or water to remove adhering solution comprising Zn and anions such as sulfate or chloride ions.

[0088] The zinc-depleted Fe substrate can be used as a high-quality raw material for ironmaking processes, such as for steelmaking using electric arc furnaces, for oxygen furnaces or for foundries.

[0089] Separation steps

[0090] Dissolved Zn 2+ and Fe 2+ The separation can be performed by bubbling H2S into the solution to precipitate ZnS.

[0091] The preferred choices are:

[0092] ·Zn 2+ Precipitate as ZnS in solution

[0093] · From the inclusion of dissolved Fe 2+ Separation of ZnS from the solution

[0094] Crystallization of Fe compounds by evaporating water and / or lowering the temperature

[0095] Separation of crystals of Fe compounds and recycling of the resulting liquid phase back into one of the previous process steps

[0096] During the precipitation of ZnS with H2S, the pH drops. In a preferred embodiment of the invention, the precipitation of ZnS is carried out in a (at least) 2-step process. In the first step, part of the ZnS is precipitated using H2S waste gas from the second step or H2S obtained by stripping the solution obtained after precipitation and separation of ZnS in the second step. 2+ Precipitate as ZnS. In the second step, high concentration of H2S is used to shift the equilibrium towards ZnS precipitation. Another option is to use Na2S or (NH4)2S to precipitate ZnS.

[0097] A preferred embodiment is to react the precipitated ZnS with H2SO4 to obtain a ZnSO4 solution and gaseous H2S, and to recycle the obtained H2S for the precipitation of ZnS. Preferably, the moist ZnS filter cake reacts with diluted H2SO4. It may be necessary to remove the stripping H2S by N2 or air to shift the equilibrium in the desired direction. Alternatively, H2S reacts with NH4OH or NaOH to obtain Na2S or (NH4)2S.

[0098] However, where long distance transport to a zinc production site is required, ZnS may be the preferred material.

[0099] If purified to produce higher value Zn 2+ solution, there is a synergistic effect of dissolving EAFD with H2SO4 and dezincification of galvanized steel scrap in purification (e.g. Cu, Cd, Mn, Ni from Zn-Ni coating).

[0100] H2S can be produced from H2 and S, or can be obtained as a by-product of coke production. H2S can also be obtained from a spent H2S absorbent, such as EAFD (Energy Fuels 2022, 36, 3695-3703) as an H2S absorbent.

[0101] Metal oxides have a wide range of industrial applications as adsorbents for the removal of H2S from industrial gases such as synthesis gas, coke oven gas from steel production, fuel cell hydrogen, sulfur recovery unit tail gas, and bio / natural gas. These materials can be used for H2S generation and can also be used in the preparation of Fe-containing 3+ The acidic solution is used as a source of Fe and / or Zn.

[0102] Separation of dissolved Zn 2+ and Fe 2+ Another option is solvent or membrane extraction. Zn is preferred 2+ Transfer to an organic phase, most preferably D2EHPA, di-(2-ethylhexyl)phosphoric acid. D2EHPA is an inexpensive and widely available reagent.

[0103] Zn 2+ The extraction process steps are:

[0104] D2EHPA is dissolved in an organic solvent, usually an inert hydrocarbon such as kerosene or naphtha. 2+ The organic phase containing D2EHPA is immiscible with the aqueous solution containing Zn 2+ Aqueous solution contact:

[0105]

[0106] The Zn(D2EHPA)2 complex is more soluble in the organic phase than in the aqueous phase. As a result, the complex is transferred from the aqueous phase to the organic phase.

[0107] The loaded organic phase containing the extracted Zn(D2EHPA)2 complex is then separated from the aqueous phase by sedimentation, centrifugation or decantation.

[0108] To recover the extracted zinc from the organic phase, H2SO4 is used as a stripping agent. After stripping the zinc from the organic phase, the D2EHPA can be regenerated and reused in the extraction process.

[0109] Preferably, the solvent extraction process comprises multiple extraction and stripping stages to increase the overall efficiency of zinc recovery.

[0110] Preferably, the pH of the solution to be treated by extraction is > 0.5, more preferably > 1.0, most preferably > 1.5.

[0111] Due to Mn 2+ With Zn 2+ are extracted together, so Mn needs to be separated. This can be done by replacing the precipitate with fine Zn powder: Zn + Mn 2+ =>Zn 2+ + Mn. Mn can be separated from the unreacted Zn by sedimentation, filtration or centrifugation. Another option is to 2+ Oxidation to MnO2. Preferably, this can be carried out by O2, O3, H2O2 or H2SO5, followed by separation of the MnO2 by sedimentation, filtration or centrifugation.

[0112] Preparation of iron salts

[0113] ZnS precipitation and precipitate separation or Zn removal by solvent or membrane extraction 2+ The solution obtained after the extraction is used for the recovery of Fe compounds. The residual H2S in the solution can be stripped by N2. Crystallization is the preferred option for obtaining solid Fe compounds from a solution containing FeSO4. It is preferred to extract Fe from the solution by vacuum evaporation and heat supply. 2+ Water is removed from the solution to prevent the temperature from dropping too quickly. The preferred option is to reduce the temperature to +5°C and then separate the FeSO4*7H2O crystals by filtration or centrifugation. Methods for crystallizing and separating FeSO4*7H2O from acidic solutions are state of the art in TiO2 production. The specific parameters depend on the composition of the solution. General principles and considerations can be found in DE102007032418.

[0114] Preferably, the FeSO4 concentration in the solution is > 100 g / l. This is because a large amount of crystal water bound to the FeSO4*7H2O water is effectively removed from the solution, resulting in a significant drop in pH. The final concentration of the saturated solution at +5°C is about 35-40 g / lFe 2+ .

[0115] Due to evaporation of water from the FeSO4 solution and water capture of the heptahydrate, the acidity of the solution becomes even significantly higher (pH << 0.5). Therefore, this solution or a portion of this solution can be used to close the loop and recycled back to one of the previous steps: for reaction with EAFD or for leaching Zn from galvanized steel scrap.

[0116] It was found that the crystallization of FeCl2 was similar to that of FeCl2*4H2O.

[0117] At least part of this solution leaves the process as wastewater and serves as a sink for some ions such as Na or K. Preferably, Fe is precipitated by alkaline treatment, separated and recycled to one of the preceding steps, e.g. for producing an Fe-containing 3+ of an acidic solution or for raising the pH according to reaction F.

[0118] Electrolytic extraction

[0119] Careful precipitation of ZnS and washing of the precipitate with dilute H2SO4 (pH ~ 2) can achieve almost complete separation of Fe and other impurities. This ZnS can be fed into the primary Zn production process.

[0120] After ZnS is converted into ZnSO4 solution by reaction with H2SO4, the resulting solution can be used for electrowinning of metallic zinc; further purification by displacement precipitation step with metallic zinc powder can further remove impurities such as Ni, Cd, Cu and Fe. Since only low concentrations of these impurities are present, the demand for zinc powder is low.

[0121] More details on displacement precipitation from other references can be found in: DEZINCING OF GALVANIZED STEEL by J. Grogan, Colorado School Mines: http: / / pdfcoffee.com / qdownload / dezincinc-of-galvanized-steel-pdf-pdf-free.html, p.25

[0122] In summary, the method of the present invention provides some significant advantages:

[0123] No major waste streams from EAFD for recycling

[0124] Hydrometallurgical processes generally have less energy consumption and a lower CO2 footprint compared to thermal processes (e.g. Waelz process)

[0125] Leaching step has maximum efficiency of Zn depletion (implies some co-leaching of Fe)

[0126] High flexibility

[0127] Possibility to transfer the method to more H2 production for further use

[0128] Separation step: If cheap H2S is available, use H2S to precipitate ZnS; if no H2S or no cheap H2S is available, use solvent extraction

[0129] The present invention also provides a method comprising Fe 3+ Use of an acidic solution of EAFD as an oxidizing agent, preferably for dezincification of galvanized steel, wherein the waste acidic solution is obtained by reacting EAFD with sulfuric acid.

[0130] Example 1: Recycling of Electric Arc Furnace Dust (EAFD) and Dezincification of Galvanized Steel Scrap

[0131] 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, a Fe 3+ and Zn 2+ of acidic solution.

[0132] The galvanized steel scrap is leached with the acid solution until the Zn coating is dissolved to >99% and the Fe 3+ Reduction to Fe 2+ This can be done by immersing a basket filled with waste into an acidic solution or by passing an acidic solution through a column filled with waste. The resulting zinc-free metallic Fe substrate can be washed, dried, and used as a Fe source for steelmaking or casting.

[0133] The typical mass ratio of EAFD to galvanized steel scrap is 1:8.

[0134] The Zn-containing 2+ and Fe 2+ The solution is used to precipitate ZnS. ZnS is separated by filtration or centrifugation and washed with dilute H2SO4 (pH ~ 2) to remove FeSO4. ZnS can be used as a raw material for primary zinc production or converted into ZnSO4 solution by dissolving in H2SO4 for electrolytic extraction of zinc.

[0135] The FeSO4 solution obtained after the separation of ZnS precipitation is used for crystallization of FeSO4*7H2O (green vitriol) by evaporating the water in vacuo and cooling the system to 5°C. The FeSO4 solution obtained after the separation of green vitriol can be recycled (in whole or in part) to one of the above process steps.

[0136] Products obtained: Zn-depleted waste, ZnS (or ZnSO4), and FeSO4*7H2O (green vitriol)

[0137] Example 2: Recycling of jarosite and dezincification of galvanized steel waste

[0138] Jarrosite is dissolved in dilute H2SO4 (preferably waste H2SO4 from TiO2 production).

[0139] The galvanized steel scrap is leached with the acid solution until the Zn coating is dissolved to >99% and the Fe 3+ Reduction to Fe 2+ This can be done by immersing a basket filled with waste into an acidic solution or passing an acidic solution through a column filled with waste. The resulting Zn-free metallic Fe substrate can be washed, dried, and used as a Fe source for steelmaking or casting.

[0140] The Zn-containing 2+ and Fe 2+ The solution is used to precipitate ZnS. ZnS is separated by filtration or centrifugation and washed with dilute H2SO4 (pH ~ 2) to remove FeSO4. ZnS can be used as a raw material for primary zinc production or converted into ZnSO4 solution by dissolving in H2SO4 for electrolytic extraction of zinc.

[0141] The FeSO4 solution obtained after the separation of ZnS precipitation is used for crystallization of FeSO4*7H2O (green vitriol) by evaporating the water in vacuo and cooling the system to 5°C. The FeSO4 solution obtained after the separation of green vitriol can be recycled (in whole or in part) to one of the above process steps.

[0142] The products obtained are: Zn-depleted scrap, ZnS (or ZnSO4), and FeSO4*7H2O (green vitriol); thus three low-cost waste materials are recycled and converted into valuable products: jarosite, diluted H2SO4, and galvanized steel scrap.

[0143] Example 3: Recycling of Electric Arc Furnace Dust (EAFD) and Dezincification of Galvanized Steel Scrap

[0144] 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, a Fe 3+and Zn 2+ of acidic solution.

[0145] The galvanized steel scrap is leached with the acid solution until the Zn coating is dissolved to >99% and the Fe 3+ Reduction to Fe 2+ This can be done by immersing the compacted scrap elements or baskets filled with scrap in an acidic solution or by passing an acidic solution through a container filled with scrap. The resulting zinc-free metallic Fe substrate is washed, dried, and used as a Fe source for steelmaking or casting.

[0146] The Zn-containing precipitate obtained from the Zn leaching step was treated by solvent extraction with D2EHPA in kerosene. 2+ and Fe 2+ The loaded organic phase containing the extracted Zn(D2EHPA)2 complex is then separated from the aqueous phase by sedimentation. The organic phase is mixed with H2SO4 as a stripping agent. After stripping zinc from the organic phase, the D2EHPA is reused in the extraction process.

[0147] By oxidizing Mn with O3 2+ It is converted into MnO2 and subsequently separated by filtration.

[0148] Extract Zn with solvent 2+ The FeSO4 solution obtained is used for crystallization of FeSO4*7H2O (green vitriol) by vacuum evaporation of water and cooling the system to 5°C. The FeSO4 solution obtained after separation and crystallization of green vitriol can be recycled (in whole or in part) back to one of the above process steps.

[0149] Products obtained: Zn-depleted waste, ZnSO4, MnO2 and FeSO4*7H2O green vitriol

[0150] Example 4: Dezincification of galvanized steel scrap

[0151] use

[0152] (a) Acidic solution containing 150 g / l H2SO4

[0153] (b) Contains 150 g / l H2SO4 and 10 g / l Fe 3+ Galvanized steel scrap containing 0.9% Zn was leached with an acidic solution of 2% Zn (in the form of Fe2(SO4)3) for 10, 20 and 30 seconds. After the leaching step, the scrap samples were washed with deionized water and dried before XRF characterization. Results with a bar graph showing the surface Zn concentration determined by XRF ( Figure 1 ) clearly shows that in Fe 3+ The dissolution of Zn is accelerated in the presence of .

[0154] Example 5: Dezincification of galvanized steel scrap

[0155] use

[0156] (a) Acidic solution containing 20 g / l H2SO4

[0157] (b) Contains 20 g / l H2SO4 and 28 g / l Fe 3+ Acidic solution (Fe2(SO4)3 form)

[0158] (c) Contains 55 g / l Fe 3+ Galvanized steel scrap containing 0.9% Zn was leached with a solution of (Fe2(SO4)3 form) (pH of the solution < 4) for 300 seconds. After the leaching step, the scrap sample was washed with deionized water and dried before XRF characterization. Results with a bar graph showing the surface Zn concentration determined by XRF ( Figure 2 ) clearly shows that in Fe 3+ The dissolution of Zn is accelerated in the presence of .

[0159] After 300s, for the Fe 3+ The residual Zn on the steel surface is 0.1% and 1.1%, for the solution without Fe 3 + The H2SO4 solution is 17%.

Claims

1. Method for depleting zinc from Zn-coated Fe by a) In the presence of Fe 3+ The Zn-coated Fe is subjected to a leaching step in an acidic solution of 2+ and Fe 2+ of acidic solution, in which Fe 3+ Relative to the excess of metallic Zn, the atomic ratio of Fe 3+ / Zn 0 >2, and / or wherein the acidic solution comprises a concentration of 1.5 to 60 g Fe at the beginning of the leaching step 3+ / kg solution Fe 3+ , b) obtaining a metallic Fe substrate depleted of zinc; and c) Fe 2+ With Zn 2+ Separation to provide Zn 2+ The product and Fe 2+ Salt.

2. The method according to claim 1, characterized in that Contains Fe 3+ The acid solution is made from the dissolution of arc furnace dust, jarosite, mill scale or goethite, or from waste H2SO4 from the production of TiO2 using the sulfate process, acidic solutions from zinc manufacturing, steel pickling solutions containing FeCl2 or FeSO4, waste metal chlorides from the chlorination of TiO2 from the production of TiO2 using the chloride process, ferric chloride solutions from synthetic rutile production, or any combination of the waste products listed above.

3. The method according to claim 1 or 2, characterized in that The acidic solution contains Zn 2+ .

4. A method according to any one of claims 1 to 3, characterised in that There are more than one leaching step, at least one of which is carried out with a relative amount of Fe 3+ The leaching step is carried out with a stoichiometric excess of metallic Zn, and at least one leaching step is carried out with a stoichiometric excess of H relative to the metallic Zn. + and Fe 3+ conduct.

5. The method according to one or more of claims 1 to 4, characterized in that During the leaching process of step a), Fe 3+ Relative to the excess of metallic Zn, the atomic ratio of Fe 3+ / Zn 0 >4, preferably >10.

6. The method according to one or more of claims 1 to 5, wherein the Fe 2+ With Zn 2+ The acid obtained after separation is used to treat the waste material to produce 3+ of acid.

7. The method according to one or more of claims 1 to 6, comprising the following steps i. Leaching Zn-containing waste materials with H2SO4, preferably EAFD ii. Separate the residue of undissolved material and obtain a + 、Zn 2+ and Fe 3+ Acidic solution iii. using the resulting acidic solution for depleting zinc from galvanized steel scrap or a composition comprising galvanized steel scrap iv. obtaining a zinc-depleted waste and a solution comprising ZnSO4 and FeSO4, and v.Fe 2+ With Zn 2+ Separation to provide Zn 2+ The product and Fe 2+ Salt.

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

9. Method according to one or more of claims 1 to 8, characterised in that The obtained Zn was precipitated as ZnS 2+ With the obtained Fe 2+ Separation.

10. Method according to one or more of claims 1 to 8, characterised in that The obtained Zn 2+ With the obtained Fe 2+ Separation.

11. The method according to one or more of claims 1 to 9, comprising the following additional steps: ·Zn precipitated as ZnS 2+ · From the inclusion of dissolved Fe 2+ Separation of ZnS from the solution Crystallization of Fe compounds by evaporating water and / or lowering the temperature - Separation of the crystals of the Fe compound and recycling of the resulting liquid phase into one of the preceding process steps.

12. The method according to claim 11, characterized in that The precipitated ZnS is reacted with H2SO4 to obtain ZnSO4 and H2S, and the obtained H2S is recycled for precipitation of ZnS.

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

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