A method for comprehensive recovery of zinc, copper, and cadmium from copper-cadmium slag

Abstract

This invention discloses a comprehensive recovery method for zinc, copper, and cadmium from copper-cadmium slag. First, chromium slag undergoes oxidative alkaline leaching. After solid-liquid separation, copper-cadmium slag is added to the acidified leachate. Zinc in the slag is oxidized by dichromate to form zinc sulfate. Cadmium and copper do not react with dichromate and accumulate in the slag phase, forming copper-cadmium-rich slag. Solid-liquid separation is then performed. Ammonia is added to the acid leaching solution to adjust the pH, causing chromium to precipitate as chromium hydroxide and zinc to form [Zn(NH3)4](OH)2. Solid-liquid separation is then performed. The slag phase undergoes oxidative acid leaching to convert Cr(III) to Cr(VI), which is then recycled. Sulfuric acid is added to the liquid phase to adjust the pH, converting [Zn(NH3)4](OH)2 to zinc sulfate, which then enters the electrowinning process. Sulfuric acid is added to copper-cadmium slag for acid leaching, and sodium sulfite is added to the leachate to precipitate cadmium. This process utilizes chromium slag produced in the chromate production process, which is oxidized and alkali-leached. After the alkali leaching solution is acidified, it interacts with the copper-cadmium slag, which not only enables the wet separation of zinc, copper, and cadmium in the copper-cadmium slag, but also realizes the resource utilization and harmless treatment of the slag.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, and in particular to a method for the comprehensive recovery of zinc, copper and cadmium from copper-cadmium slag. Background Technology

[0002] The refining of metallic chromium and the production of industrial chromium salts generate a large amount of chromium slag. For every ton of metallic chromium and chromium salt produced, 8 tons and 3 tons of chromium slag are generated, respectively. Currently, my country has accumulated 4 million tons of chromium slag awaiting treatment. Most of this slag is stockpiled without effective treatment. The highly toxic Cr(VI) is soluble in water and easily enters rivers and soil, polluting the environment. In addition, the diversified industrial uses of chromium have led to the discharge of large amounts of chromium-containing waste liquids, solid wastes, and exhaust gases into the environment, increasing the threat of Cr(VI) to the environment.

[0003] Copper-cadmium slag is a leaching residue produced in the purification process of hydrometallurgical zinc smelting. For every 10,000 tons of cathode zinc produced, 300 tons of copper-cadmium slag are generated, with high zinc, cadmium, and copper content. Currently, the main processes for copper-cadmium slag recycling and treatment are pyrometallurgical and hydrometallurgical processes. Pyrometallurgical processes are mature but energy-intensive and require demanding equipment. Hydrometallurgical processes are simple and energy-efficient. Industrially, copper-cadmium slag treatment mainly focuses on cadmium recovery. The grade of sponge cadmium obtained from the replacement process is controlled only by adjusting the zinc powder addition ratio during the two-stage replacement process. This method cannot effectively remove impurities or improve the grade of sponge cadmium, and its economic efficiency is low.

[0004] Therefore, there is an urgent need to develop a comprehensive copper-cadmium slag recycling technology that is simpler and faster to operate, has lower investment and production costs, higher economic benefits, and is more environmentally friendly. This technology utilizes the harmless treatment of chromium slag followed by liquid leaching to extract copper-cadmium slag, achieving the separation of zinc from cadmium and copper. Then, copper and cadmium are separated through acid leaching, ultimately achieving the dual goal of comprehensive utilization of chromium slag and copper-cadmium slag. Summary of the Invention

[0005] The purpose of this invention is to address the technical problems of traditional chromium slag and copper-cadmium slag recycling and treatment methods, which are limited in scope, cannot effectively remove impurities, and have low economic efficiency. This invention provides a method that can achieve the harmless treatment of chromium slag and the efficient recovery of valuable metals such as zinc, cadmium, and copper from copper-cadmium slag. It features a short process, simple operation, low investment, and no secondary pollution.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for the comprehensive recovery of zinc, copper, and cadmium from copper-cadmium slag includes the following steps:

[0008] Step 1, Oxidative Alkali Leaching: Place the chromium slag in a reactor equipped with a stirrer, maintaining a liquid-to-solid ratio of 3-6:1 (L / kg). Add 30% (wt) hydrogen peroxide dropwise to the chromium slag (diluted 5-10 times), controlling the hydrogen peroxide concentration to 1.5-5 times the theoretical reaction value of Cr(III) in the chromium slag (the Cr(III) content in the chromium slag is 3-10%, the total Cr content is 5-15%, and the Cr(VI) content is 2-5%), controlling the dropping rate at 5 mL / min. Then, maintaining a solid-to-liquid ratio of 3-6:1 (L / kg), add 25% (wt) hydrogen peroxide... The solution pH was adjusted to 8-14 using -28% (wt) ammonia water. The reaction was maintained at 30°C and a stirring speed of 120 r / min for 35-80 min. Solid-liquid separation was then performed to obtain alkali leaching residue and alkali leaching solution. The alkali leaching residue, determined by ICP and chemical titration, contained 0.6-0.8% Cr, 10-25% Fe, 10-20% Si, 45-50% Ca, 20-25% Mg, and 0.2-0.4% other components. This residue is used in building materials. The alkali leaching solution, determined by chemical titration, contained 20-50 g / L Cr and was used as a strong oxidizing agent.

[0009] Step 2: Reduction of copper-cadmium slag:

[0010] Add 30-40% (wt) sulfuric acid solution to the alkaline leaching solution prepared in step one for acidification to obtain an acidified solution. Then add copper-cadmium slag and maintain the reaction temperature at 25-90℃, the solid-to-liquid ratio at 3-6:1 (L / kg), and the stirring speed at 200 r / min for 40-90 min. After solid-liquid separation, zinc leaching solution and copper-cadmium-rich slag can be obtained. The copper-cadmium-rich slag contains 20-34% copper by mass and 18-36% cadmium by mass.

[0011] Step 3: Zinc-chromium separation:

[0012] Add 25-28% (wt) ammonia water to the zinc leaching solution prepared in step two to adjust the pH of the solution to 8-12, so that chromium forms a mixed precipitate of chromium hydroxide and cadmium oxysulfate, and zinc forms [Zn(NH3)4](OH)2. After solid-liquid separation, add 30% (wt) hydrogen peroxide to the slag phase for oxidative alkaline leaching, so that Cr(III) is converted into Cr(VI) for recycling. Add 30% (wt) sulfuric acid solution to the liquid phase to adjust the pH of the solution to 5-5.2, so that [Zn(NH3)4](OH)2 is converted into zinc sulfate solution and then enters the electrowinning process.

[0013] Step 4: Copper-cadmium separation:

[0014] Add a 40-50% (wt) sulfuric acid solution to the copper-rich cadmium slag prepared in step two. React for 60-180 minutes at a reaction temperature of 30-90℃, a liquid-to-solid mass ratio of 3-6:1 L / kg, and a stirring speed of 120 r / min. Separate the solid and liquid to obtain a cadmium leaching solution and copper-rich slag. The cadmium leaching solution is a cadmium sulfate solution with a cadmium content of 30-140 g / L. Add a 99% (wt) sodium sulfite solid to the cadmium leaching solution to convert the cadmium sulfate into cadmium sulfite precipitate, which can be sold as a product or used as a raw material for cadmium smelting. The copper-rich slag has a copper mass percentage content greater than 98% and is used for copper refining and recovery.

[0015] The zinc content of the zinc sulfate solution prepared in step three was determined to be 60-160 g / L by chemical titration; the cadmium content of the cadmium sulfite precipitate prepared in step four was greater than 57%; and the copper content of the copper-rich slag was greater than 98% by mass.

[0016] The working principle of this invention is as follows:

[0017] Hydrogen peroxide and ammonia are added to the chromium slag produced from the refining of metallic chromium and the production of industrial chromium salts for oxidative alkaline leaching, converting Cr(III) to Cr(VI). The alkaline leaching solution is then acidified and copper-cadmium slag is added. Zinc in the slag is oxidized by dichromate to form zinc sulfate, while cadmium and copper do not react with dichromate and accumulate in the slag phase, forming copper-cadmium-rich slag. Ammonia is added to the zinc leaching solution to adjust the pH to 8-12, causing chromium to form a mixed precipitate of chromium hydroxide and cadmium oxysulfate, and zinc to form [Zn(NH3)4](OH)2. Solid-liquid separation occurs, and the slag phase undergoes oxidative alkaline leaching to convert Cr(III) to Cr(VI), which is then recycled. Sulfuric acid is added to the liquid phase to adjust the pH to 5-5.2, converting [Zn(NH3)4](OH)2 to zinc sulfate, which is then used in the electrowinning process. Sulfuric acid is added to the copper-cadmium-rich slag to leach cadmium, and sodium sulfite is added to the leachate to precipitate cadmium. The filter residue has a copper content greater than 98% and is used for copper refining and recovery.

[0018] The chemical reaction equations in the above steps are as follows:

[0019] 3Zn+Na2Cr2O7+7H2SO4=7H2O+3ZnSO4+Cr2(SO4)3+Na2SO4

[0020] 2NH3+ZnSO4+2H2O=Zn(OH)2↓+(NH4)2SO4

[0021] Zn(OH)₂ + 4NH₃ = [Zn(NH)₄](OH)₂

[0022] [Zn(NH3)4](OH)2+3H2SO4=ZnSO4+2(NH4)2SO4+2H2O

[0023] Cr2(SO4)3+6NH3+6H2O=2Cr(OH)3↓+3(NH4)2SO4

[0024] 2Cr2(SO4)3+3H2O=Cr4(OSO4)3↓+3H2SO4

[0025] 2Cr(OH)3+3H2O2+4NH3+4H2O=2(NH4)2CrO4+8H2O

[0026] 2(NH4)2CrO4+H2SO4=(NH4)2Cr2O7+(NH4)2SO4+H2O

[0027] Cd + H₂SO₄ = CdSO₄ + H₂↑

[0028] Zn + CdSO4 = Cd + ZnSO4

[0029] CdSO4+Na2SO3=Na2SO4+CdSO3↓

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (1) This invention uses the steps of oxidation and alkaline leaching, copper-cadmium slag reduction, and zinc-chromium separation and zinc recovery to separate zinc from cadmium and copper, enrich copper and cadmium, and harmlessly treat chromium slag. The copper and cadmium grades in the leaching residue reach 20-34% and 18-36%, respectively. The treated chromium slag can be reused as building material.

[0032] (2) The present invention uses the leachate of chromium slag as an oxidant to oxidize copper-cadmium slag, which can efficiently separate zinc and cadmium. The copper content in the slag phase after copper-cadmium separation is greater than 98%, which has higher economic benefits.

[0033] (3) This invention recycles copper-cadmium slag produced in the wet zinc smelting process in a high-value manner, and solves the environmental pollution problem caused by the stockpiling of chromium slag produced in the production of chromium and chromium salts. The process is short, simple to operate, and pollution-free. Attached Figure Description

[0034] Figure 1 This is a flowchart of the comprehensive recovery method for zinc, copper, and cadmium from chromium slag according to the present invention. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments.

[0036] Example 1

[0037] A method for the comprehensive recovery of zinc, copper, and cadmium from copper-cadmium slag includes the following steps:

[0038] Step 1, Oxidation-Alkali Leaching: Weigh 1 kg of the chromium slag and place it in a reactor equipped with a stirrer. Maintain a solid-to-liquid ratio of 3:1 (L / kg). Add 30% (wt) hydrogen peroxide dropwise to the chromium slag (diluted 5-10 times), controlling the reaction between the hydrogen peroxide and Cr(III) in the chromium slag to 1.5 times the theoretical value. The chromium slag contains 10% Cr(III), 15% total Cr, and 5% Cr(VI). Control the dropping rate at 5 mL / min. Then add a 25-28% (wt) solution. The solution pH was adjusted to 14 with ammonia water, and the solid-to-liquid ratio was maintained at 3:1 (L / kg). The reaction was carried out at 30℃ and a stirring speed of 120 r / min for 80 min. After solid-liquid separation, alkali leaching residue and alkali leaching solution were obtained. The alkali leaching residue contained 0.6% Cr, 10% Fe, 49% Ca, 19% Si, 21% Mg, and 0.4% other components, as determined by ICP and chemical titration. It is used for building materials. The alkali leaching solution contained 32 g / L Cr, as determined by chemical titration. It is used as a strong oxidizing agent.

[0039] Step 2: Reduction of copper-cadmium slag:

[0040] Acidification is achieved by adding 30% sulfuric acid solution to the alkaline leaching solution prepared in step one, resulting in an acidified solution. Then, copper-cadmium slag ground to -120 mesh (containing 50% Zn, 15% Cd, 11% Cu, 5% S, and 20% O) is added. The liquid-to-solid ratio is maintained at 8:1, and the reaction is carried out for 90 minutes at a reaction temperature of 90°C and a stirring speed of 200 r / min. After filtration, zinc leaching solution and copper-cadmium-rich slag are obtained. The copper-cadmium-rich slag contains 27% copper and 36% cadmium by mass.

[0041] Step 3: Zinc-chromium separation:

[0042] Add 25-28% (wt) ammonia to the zinc leaching solution prepared in step two to adjust the pH of the solution to 12. This causes chromium to form a mixed precipitate of chromium hydroxide and cadmium oxysulfate, and zinc to form [Zn(NH3)4](OH)2. After solid-liquid separation, add 30% (wt) hydrogen peroxide and 25-28% (wt) ammonia to the slag phase for oxidative alkaline leaching, which converts Cr(III) into Cr(VI) for recycling. Add 30% (wt) sulfuric acid solution to the liquid phase to adjust the pH of the solution to 5-5.2, which converts [Zn(NH3)4](OH)2 into zinc sulfate solution before entering the electrowinning process. The zinc recovery rate reached 92%.

[0043] Step 4: Copper-cadmium separation:

[0044] A 30% (wt) sulfuric acid solution was added to the copper-rich cadmium slag prepared in step two. The reaction was carried out at a reaction temperature of 90℃, a liquid-to-solid ratio of 3:1 (L / kg), and a stirring speed of 120 r / min for 180 min. Solid-liquid separation was then performed to obtain a cadmium leaching solution and copper-rich slag. The cadmium leaching solution was a cadmium sulfate solution with a cadmium content of 140 g / L. A 99% (wt) sodium sulfite solid was added to the cadmium leaching solution to convert the cadmium sulfate into cadmium sulfite precipitate, which was then sold as a product or used as a raw material for cadmium smelting. The copper-rich slag had a copper content of more than 98% by mass and was used for copper refining. The copper and cadmium recovery rates reached 95% and 96%, respectively.

[0045] The zinc content of the zinc sulfate solution prepared in step three was determined to be 160 g / L by chemical titration; the cadmium content of the cadmium sulfite precipitate prepared in step four was 57%; and the copper content of the copper-rich slag was greater than 98% by mass.

[0046] Example 2

[0047] A method for the comprehensive recovery of zinc, copper, and cadmium from copper-cadmium slag includes the following steps:

[0048] Step 1, Oxidative Alkali Leaching: Weigh 1 kg of the chromium slag and place it in a reactor equipped with a stirrer, maintaining a liquid-to-solid ratio of 4:1 (L / kg). Add 30% (wt) hydrogen peroxide dropwise to the chromium slag (diluted 5-10 times), controlling the reaction between the hydrogen peroxide and Cr(III) in the chromium slag to twice the theoretical value. The chromium slag contains 8% Cr(III), 10% total Cr, and 2% Cr(VI), with a dropping rate of 5 mL / min. Then add 25-28% (wt) alkali leaching solution. Ammonia water was used to adjust the pH of the solution to 12, maintaining a liquid-to-solid ratio of 3:1 (L / kg). The reaction was carried out at a temperature of 90℃ and a stirring speed of 120 r / min for 50 min. Solid-liquid separation was then performed to obtain alkali leaching residue and alkali leaching solution. The alkali leaching residue, as determined by ICP and chemical titration, contained 0.8% Cr, 23% Fe, 45% Ca, 10% Si, 21% Mg, and 0.2% other components, and is used for building materials. The alkali leaching solution, as determined by chemical titration, contained 25 g / L Cr and is used as a strong oxidizing agent.

[0049] Step 2: Reduction of copper-cadmium slag:

[0050] Add 25-28% sulfuric acid solution to the alkaline leaching solution prepared in step one for acidification treatment to obtain an acidified solution. Then add copper-cadmium slag ground to -100 mesh (the copper-cadmium slag contains 45% Zn, 9% Cd, 8% Cu, 8% S, and 30% O), maintain a liquid-to-solid ratio of 6:1 (L / kg), and react for 60 minutes at a reaction temperature of 60℃ and a stirring speed of 200 r / min. After filtration, zinc leaching solution and copper-cadmium-rich slag can be obtained. The copper-cadmium-rich slag contains 20% copper and 23% cadmium by mass.

[0051] Step 3: Zinc-chromium separation:

[0052] Add 25-28% (wt) ammonia to the zinc leaching solution prepared in step two to adjust the pH of the solution to 10. This causes chromium to form a mixed precipitate of chromium hydroxide and cadmium oxysulfate, and zinc to form [Zn(NH3)4](OH)2. After solid-liquid separation, add 30% (wt) hydrogen peroxide and 25-28% (wt) ammonia to the slag phase for oxidative alkaline leaching, which converts Cr(III) into Cr(VI) for recycling. Add 30% (wt) sulfuric acid solution to the liquid phase to adjust the pH of the solution to 5-5.2, which converts [Zn(NH3)4](OH)2 into zinc sulfate solution before entering the electrowinning process. The zinc recovery rate reached 93%.

[0053] Step 4: Copper-cadmium separation:

[0054] A 35% (wt) sulfuric acid solution was added to the copper-rich cadmium slag prepared in step two. The reaction was carried out at a reaction temperature of 60℃, a liquid-to-solid ratio of 4:1 (L / kg), and a stirring speed of 120 r / min for 120 min. Solid-liquid separation was then performed to obtain a cadmium leaching solution and copper-rich slag. The cadmium leaching solution was a cadmium sulfate solution with a cadmium content of 59 g / L. Sodium sulfite solid with a purity of 99% (wt) was added to the cadmium leaching solution to convert the cadmium sulfate into cadmium sulfite precipitate, which was then sold as a product or used as a raw material for cadmium smelting. The copper-rich slag had a copper mass percentage content greater than 98% and was used for refining and recovering copper. The copper and cadmium recovery rates reached 95% and 94%, respectively.

[0055] The zinc content of the zinc sulfate solution prepared in step three was determined to be 107 g / L by chemical titration; the cadmium content of the cadmium sulfite precipitate prepared in step four was 57.2%; and the copper content of the copper-rich slag was greater than 98% by mass.

[0056] Example 3

[0057] A method for the comprehensive recovery of zinc, copper, and cadmium from copper-cadmium slag includes the following steps:

[0058] Step 1, Oxidation-Alkali Leaching: Weigh 1 kg of the chromium slag and place it in a reactor equipped with a stirrer. Add 30% (wt) hydrogen peroxide dropwise to the chromium slag (diluted 5-10 times), maintaining a liquid-to-solid ratio of 6:1 (L / kg). Control the reaction between the hydrogen peroxide and Cr(III) in the chromium slag to 5 times the theoretical value. The chromium slag contains 2% Cr(III), 5% total Cr, and 3% Cr(VI). Control the dropping rate to 5 mL / min. Then add 25-28% (wt) alkali leaching solution. Ammonia water was used to adjust the pH of the solution to 8, maintaining a liquid-to-solid ratio of 6:1 (L / kg). The reaction was carried out at 30℃ and a stirring speed of 120 r / min for 35 min. Solid-liquid separation was then performed to obtain alkali leaching residue and alkali leaching solution. The alkali leaching residue, as determined by ICP and chemical titration, contained 0.7% Cr, 11% Fe, 48% Ca, 17% Si, 23% Mg, and 0.3% other components, and is used for building materials. The alkali leaching solution, as determined by chemical titration, contained 32 g / L Cr and is used as a strong oxidizing agent.

[0059] Step 2: Reduction of copper-cadmium slag:

[0060] Acidification was carried out by adding a 40% sulfuric acid solution to the alkaline leaching solution prepared in step one to obtain an acidified solution. Then, copper-cadmium slag ground to -80 mesh (the copper-cadmium slag contains 40% Zn, 8% Cd, 15% Cu, 6% S, 8% O2, and 4% other components) was added. The liquid-solid ratio was maintained at 6:1 (L / kg). The reaction was carried out for 20 minutes at a reaction temperature of 25°C and a stirring speed of 200 r / min. After filtration, zinc leaching solution and copper-cadmium-rich slag were obtained. The copper-cadmium-rich slag contained 34% copper and 18% cadmium by mass.

[0061] Step 3: Zinc-chromium separation:

[0062] Add 25-28% (wt) ammonia to the zinc leaching solution prepared in step two to adjust the pH of the solution to 8, so that chromium forms a mixed precipitate of chromium hydroxide and cadmium oxysulfate, and zinc forms [Zn(NH3)4](OH)2. After solid-liquid separation, 30% (wt) hydrogen peroxide and 25-28% (wt) ammonia are used for oxidative alkaline leaching to convert Cr(III) into Cr(VI) for recycling. Add 30% (wt) sulfuric acid solution to the liquid phase to adjust the pH of the solution to 5.2, so that [Zn(NH3)4](OH)2 is converted into zinc sulfate solution and then enters the electrowinning process. The zinc recovery rate reaches 93%.

[0063] Step 4: Copper-cadmium separation:

[0064] A 40% (wt) sulfuric acid solution was added to the copper-rich cadmium slag prepared in step two. The reaction was carried out at a reaction temperature of 30°C, a liquid-to-solid ratio of 6:1 (L / kg), and a stirring speed of 120 r / min for 60 min. After solid-liquid separation, cadmium leaching solution and copper-rich slag were obtained. The cadmium leaching solution was a cadmium sulfate solution with a cadmium content of 30 g / L. Sodium sulfite solid with a purity of 99% (wt) was added to the cadmium leaching solution to convert the cadmium sulfate into cadmium sulfite precipitate, which was then sold as a product or used as a raw material for cadmium smelting. The copper-rich slag had a copper mass percentage content of more than 98% and was used for refining and recovering copper. The copper and cadmium recovery rates reached 95% and 96%, respectively.

[0065] The zinc content of the zinc sulfate solution prepared in step three was determined to be 65 g / L by chemical titration; the cadmium content of the cadmium sulfite precipitate prepared in step four was 57.4%; and the copper content of the copper-rich slag was greater than 98% by mass.

[0066] The product yield and analysis results are shown in Table 1.

[0067] Table 1 Product Yield and Analysis Results

[0068]

[0069] Based on the data in Table 1, it can be concluded that Examples 1-3 utilize the comprehensive recovery method for zinc, copper, and cadmium from copper-cadmium slag provided by this invention. The chromium slag produced during the chromium and chromium salt production process undergoes oxidative alkaline leaching, copper-cadmium slag reduction, and zinc-chromium separation to recover zinc. This achieves the separation of zinc from cadmium and copper, the enrichment of copper and cadmium, and the harmless treatment of the chromium slag. The copper and cadmium grades in the leaching residue reach 20-34% and 18-36%, respectively. The treated chromium slag can be reused as building materials. Using the leaching solution of the chromium slag as an oxidant to oxidize the copper-cadmium slag can efficiently separate zinc and cadmium. The copper content in the slag phase after copper-cadmium separation is greater than 98%, resulting in higher economic benefits.

[0070] The above are merely preferred embodiments of the present invention. It should be noted that, for those skilled in the art, based on the technical teachings provided by the present invention and as common knowledge in the field of chemistry, other equivalent modifications and improvements can be made, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for the comprehensive recovery of zinc, copper, and cadmium from copper-cadmium slag, characterized in that: Comprising the following steps: Step one, oxidation and alkaline leaching: the chromium residue is placed in a reaction kettle with stirring device, the liquid-solid ratio is kept at 3-6:1 (L / kg), 30% (wt) hydrogen peroxide solution is added dropwise in the chromium residue (diluted 5-10 times), the amount of hydrogen peroxide is controlled at 1.5-5 times of the theoretical value of the reaction of hydrogen peroxide with Cr(III) in the chromium residue (the content of Cr(III) in the chromium residue is 3-10%, the total content of Cr in the chromium residue is 5-15%, and the content of Cr(VI) is 2-5%), the drop rate is controlled at 5 mL / min; then the liquid-solid ratio is kept at 3-6:1 (L / kg), 25-28% (wt) ammonia solution is added to make the pH of the solution equal to 8-14, the reaction is carried out at a temperature of 30°C and a stirring speed of 120 r / min for 35-80 min, and then solid-liquid separation is performed to obtain alkaline leaching residue and alkaline leaching solution; the content of Cr in the alkaline leaching residue is 0.6-0.8% as measured by ICP and chemical titration, the content of Fe is 10-25%, the content of Si is 10-20%, the content of Ca is 45-50%, the content of Mg is 20-25%, and the content of other elements is 0.2-0.4%, and the alkaline leaching residue is used for building materials; the content of Cr in the alkaline leaching solution is 20-50 g / L as measured by chemical titration, and the alkaline leaching solution is used as a strong oxidizing agent; Step two, reduction of copper and cadmium residue: 30-40% (wt) sulfuric acid solution is added to the alkaline leaching solution prepared in step one to obtain an acidified solution, and then copper and cadmium residue is added, and the reaction is carried out at a temperature of 25-90°C, a solid ratio of 3-6:1 (L / kg), and a stirring speed of 200 r / min for 40-90 min, and then solid-liquid separation is performed to obtain zinc leaching solution and copper and cadmium-rich residue, and the content of copper in the copper and cadmium-rich residue is 20-34% by mass percentage, and the content of cadmium is 18-36% by mass percentage; Step three, separation of zinc and chromium: 25-28% (wt) ammonia solution is added to the zinc leaching solution prepared in step two to adjust the pH of the solution to 8-12, so that chromium forms a mixed precipitate of chromium hydroxide and cadmium oxysulfate, and zinc forms [Zn(NH3)4](OH)2, and then solid-liquid separation is performed, 30% (wt) hydrogen peroxide is added to the residue phase for oxidation and alkaline leaching to convert Cr(III) to Cr(VI) for recycling, and 30% (wt) sulfuric acid solution is added to the liquid phase to adjust the pH of the solution to 5-5.2 to convert [Zn(NH3)4](OH)2 to zinc sulfate solution, which then enters the electrodeposition process; Step four, separation of copper and cadmium: 40-50% (wt) sulfuric acid solution is added to the copper and cadmium-rich residue prepared in step two, and the reaction is carried out at a temperature of 30-90°C, a liquid-solid mass ratio of 3-6:1 L / kg, and a stirring speed of 120 r / min for 60-180 min, and then solid-liquid separation is performed to obtain cadmium leaching solution and copper-rich residue; the cadmium leaching solution is a cadmium sulfate solution with a cadmium content of 30-140 g / L, and 99% (wt) sodium sulfite solid is added to the cadmium leaching solution to convert cadmium sulfate to cadmium sulfite precipitate, which is sold as a product or used as a raw material for cadmium smelting; the content of copper in the copper-rich residue is greater than 98%, and the copper-rich residue is used for refining and recovering copper; The zinc content of the zinc sulfate solution prepared in the third step is 60-160 g / L, the cadmium content of the cadmium sulfite precipitate prepared in the fourth step is greater than 57%, and the copper content of the copper-rich residue is greater than 98%.

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