Method for collecting gold from zinc leaching residues through chloridizing volatilization

Abstract

The invention discloses a method for chloridizing, volatilizing and collecting gold from zinc leaching residues, which comprises the following steps: drying and grinding the zinc leaching residues into powder, mixing the zinc leaching residues with a composite chlorinating agent, heating in a rotary kiln, carrying out chlorination reaction to generate volatile chloride, collecting the volatile chloride, and carrying out two-stage condensation to obtain liquid gold chloride, and then the liquid gold chloride compound is introduced into reducing gas for reduction, and sponge gold is obtained. According to the method, the composite chlorinating agent is used for regulating and controlling the slag type, Au in the slag is effectively volatilized and recycled through a chlorination volatilization method, inert gas protection and a condensation collection technology, meanwhile, no secondary pollutant is generated, gold is efficiently recycled from the zinc leaching slag, the temperature needed in the reaction process is low, the reagent cost is low, the technology is simple, and operation is easy.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal smelting technology, specifically a method for collecting gold from zinc leaching residue by chlorination volatilization. Background Technology

[0002] In the hydrometallurgical zinc smelting process, most of the rare and precious metals in the zinc concentrate are concentrated in the hydrometallurgical slag. This slag is acidic and characterized by high toxicity, severe environmental pollution, and difficulty in microbial degradation. It is classified as a toxic and harmful industrial solid waste, and its storage can cause environmental pollution and pose safety hazards. Reusing the rare and precious metals in the hydrometallurgical slag as a secondary resource can not only effectively solve the environmental problems caused by hydrometallurgical zinc smelting but also significantly improve the economic benefits of enterprises, which is of great significance for achieving sustainable development.

[0003] The main metallic elements in zinc leaching residue are Zn, Fe, and Pb. The leaching residue produced by zinc hydrometallurgy often contains 0.5–10 g / t of gold. However, because the gold is encased in minerals such as iron oxide and silicates, traditional methods for collecting gold include cyanidation and pyrometallurgical smelting. Cyanidation typically yields less than 30% gold from zinc leaching residue and produces highly toxic waste. Pyrometallurgical smelting requires temperatures above 1200℃, resulting in high energy consumption and a gold recovery rate of only 40-50%. Traditional zinc leaching residue treatment methods have low gold recovery efficiency and are complex and costly. Summary of the Invention

[0004] The purpose of this invention is to provide a method for collecting gold from zinc leaching residue by chlorination volatilization. Under a low-temperature nitrogen protection environment, zinc leaching residue is mixed with a chlorinating agent to carry out a chlorination volatilization reaction. The gas phase is collected, condensed, and reduced to obtain gold.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for collecting gold from zinc leaching residue by chlorination volatilization includes the following steps: Step 1: Raw material pretreatment: After drying the zinc leaching residue to a moisture content of ≤5% by mass, grind it to a particle size of <200 mesh, and remove ferromagnetic impurities from the zinc leaching residue by magnetic separation; Step 2, Chlorination Volatilization Reaction: The zinc leaching residue treated in Step 1 is mixed with the composite chlorinating agent at a mass ratio of 1:0.03-0.05, placed in a rotary kiln, and inert gas is introduced. The mixture is heated to 400-800℃ at a heating rate of 5-8℃ / min and reacted for 2.0-3.0 hours. The metals in the zinc leaching residue undergo a chlorination reaction, generating volatile gases containing ZnCl2, AuCl3, PbCl2, and FeCl3. Step 3: Gas phase collection and condensation: Collect the volatile gas containing AuCl3 produced in Step 2 and introduce it into a two-stage condensation system for condensation to obtain liquid gold chloride; Step 4: Reduction and recovery: Hydrogen or hydrogen sulfide gas is introduced into the liquid AuCl3 collected in step 3 as a reducing agent and kept at 350±10℃ for 1.5h to carry out reduction treatment to obtain sponge gold; the purity of the obtained sponge gold is ≥99.5% after testing.

[0006] The chemical formula for the chlorination reaction in step two is: ZnO(s)+ CaCl2=ZnCl2(g)+CaO (1) PbO(s)+ CaCl2=PbCl2(g)+CaO (2) 2Au(s)+ 3Cl2=2AuCl3(g) (3) Preferably, step one uses zirconia ductile iron media for grinding, which can avoid iron contamination of the raw materials.

[0007] Preferably, the composite chlorinating agent is a mixture of CaCl2 and NaCl in a mass ratio of 3:1.

[0008] Preferably, in step two, the volatile gas containing AuCl3 is introduced into a two-stage condensation system. The first-stage condensation system uses -20°C ethylene glycol coolant for pre-cooling, causing AuCl3 to completely solidify, while ZnCl2 and PbCl2 remain in a gaseous state. The second-stage condensation system uses liquid nitrogen for deep cooling to -50°C, targeting the capture of AuCl3. However, due to their extremely low saturated vapor pressure, ZnCl2 and PbCl2 will not solidify in the two-stage condensation system and will continue to enter the subsequent system with the exhaust gas.

[0009] Preferably, the gold volatilization rate in step two reaches 55-65%.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Au in zinc leaching residue is characterized by extremely low content and complex occurrence state. This invention uses a composite chlorinating agent to control the residue type, so that Au can be effectively volatilized and recovered without the generation of secondary pollutants, which can provide technical support for reducing the cost of industrial applications. (2) The present invention uses a grinding and magnetic separation process to pretreat the raw materials, thereby reducing the influence of ferromagnetic impurities in the zinc leaching residue; (3) This invention uses chlorination volatilization, inert gas protection and condensation collection technology to efficiently recover gold from zinc leaching residue. The reaction process requires a low temperature, low reagent cost, simple process and easy operation. (4) During the chlorination volatilization reaction, chlorine gas can be prevented from escaping, and the waste gas is discharged in compliance with standards after being absorbed by alkaline solution, thus meeting environmental protection requirements; (5) The method described in this invention increases the gold volatilization rate by more than 2 times compared with the traditional cyanide method, and reduces the reaction temperature by more than 40% compared with the pyrometallurgical method; (6) The present invention employs a two-stage condensation system, which can capture 100% of AuCl3 and ensure zero penetration loss. Attached Figure Description

[0011] Figure 1 This is a flowchart of the method described in this invention. Detailed Implementation

[0012] The present invention will now be described in further detail with reference to the accompanying drawings.

[0013] In the following examples, the content of metal elements in the zinc leaching residue is: Zn 5-10%, Fe 17-23%, Pb 4-7%, Au 0.5–3 g / t.

[0014] Example 1 A method for collecting gold from zinc leaching residue by chlorination volatilization includes the following steps: Step 1: Raw material pretreatment: After drying the zinc leaching residue to a moisture content of ≤4.8% by mass, add it to a grinder and grind it to a particle size of <200 mesh using zirconia ball milling media. Then, use magnetic separation to remove ferromagnetic impurities from the zinc leaching residue. Step 2, Chlorination Volatilization Reaction: The zinc leaching residue treated in Step 1 is mixed with a composite chlorinating agent at a mass ratio of 1:0.03 and placed in a rotary kiln. The composite chlorinating agent is a mixture of CaCl2 and NaCl at a mass ratio of 3:1. Under a nitrogen protective atmosphere, the temperature is increased to 500℃ at a heating rate of 5℃ / min, and the reaction is carried out for 2.0h. After the metal in the zinc leaching residue undergoes the chlorination reaction, ZnCl2, AuCl3, PbCl2, and FeCl3 are generated. Step 3: Gas phase collection and condensation: Collect the volatile gas containing AuCl3 produced by chlorination in step 2 and introduce it into a two-stage condensation system. The first stage condensation system uses -20℃ ethylene glycol coolant for pre-cooling, and AuCl3 is completely solidified, while ZnCl2 and PbCl2 remain in a gaseous state. The second stage uses liquid nitrogen for deep cooling to -50℃, targeting the capture of AuCl3. However, ZnCl2 and PbCl2, due to their extremely low saturated vapor pressure, will not solidify during the two-stage condensation process and will continue to enter the subsequent system with the tail gas. Step 4: Reduction and recovery: Hydrogen gas was introduced into the liquid AuCl3 collected in step 3 as a reducing agent at a flow rate of 200 mL / min. The temperature was raised to 350℃ and the reduction was carried out for 1.0 h to obtain sponge gold. The purity of the obtained sponge gold was tested to be 99.6%.

[0015] Example 2 A method for collecting gold from zinc leaching residue by chlorination volatilization includes the following steps: Step 1: Raw material pretreatment: After drying the zinc leaching residue to a moisture content of ≤5% by mass, add it to a grinder and grind it to a particle size of <200 mesh using zirconia ball milling media. Then, use magnetic separation to remove ferromagnetic impurities from the zinc leaching residue. Step 2, Chlorination Volatilization Reaction: The zinc leaching residue treated in Step 1 is mixed with a composite chlorinating agent at a mass ratio of 1:0.04 and placed in a rotary kiln. The composite chlorinating agent is a mixture of CaCl2 and NaCl at a mass ratio of 3:1. Under a helium protective atmosphere, the mixture is heated to 600℃ at a heating rate of 6℃ / min to carry out the chlorination volatilization reaction for 2.5 hours. After the metals in the zinc leaching residue undergo chlorination, ZnCl2, AuCl3, PbCl2, and FeCl3 are generated. Step 3: Gas phase collection and condensation: Collect the volatile gas containing AuCl3 produced by chlorination in step 2 and introduce it into a two-stage condensation system. The first stage condensation system uses -20℃ ethylene glycol coolant for pre-cooling, and AuCl3 is completely solidified, while ZnCl2 and PbCl2 remain in a gaseous state. The second stage uses liquid nitrogen for deep cooling to -50℃, targeting the capture of AuCl3. However, ZnCl2 and PbCl2, due to their extremely low saturated vapor pressure, will not solidify during the two-stage condensation process and will continue to enter the subsequent system with the tail gas. Step 4: Reduction and recovery: Hydrogen sulfide gas was added to the liquid gold chloride collected in step 3 as a reducing agent. The flow rate of hydrogen sulfide gas was 200 mL / min. The mixture was heated to 380℃ for reduction treatment for 1.5 h to obtain sponge gold. The purity of the obtained sponge gold was tested to be 99.8%.

[0016] Example 3 A method for collecting gold from zinc leaching residue by chlorination volatilization includes the following steps: Step 1: Raw material pretreatment: After drying the zinc leaching residue to a moisture content of ≤5% by mass, grind it to a particle size of <200 mesh, and remove ferromagnetic impurities from the zinc leaching residue by magnetic separation; Step 2, Chlorination Volatilization Reaction: The zinc leaching residue treated in Step 1 is mixed with a composite chlorinating agent at a mass ratio of 1:0.05 and placed in a rotary kiln. The composite chlorinating agent is a mixture of CaCl2 and NaCl at a mass ratio of 3:1. Under a nitrogen protective atmosphere, the mixture is heated to 600℃ at a heating rate of 7℃ / min to carry out the chlorination volatilization reaction for 3.0h. After the metals in the zinc leaching residue undergo chlorination, ZnCl2, AuCl3, PbCl2, and FeCl3 are generated. Step 3: Gas phase collection and condensation: Collect the volatile gas containing AuCl3 produced by chlorination in step 2 and introduce it into a two-stage condensation system. The first stage condensation system uses -20℃ ethylene glycol coolant for pre-cooling, and AuCl3 is completely solidified, while ZnCl2 and PbCl2 remain in a gaseous state. The second stage uses liquid nitrogen for deep cooling to -50℃, targeting the capture of AuCl3. However, ZnCl2 and PbCl2, due to their extremely low saturated vapor pressure, will not solidify during the two-stage condensation process and will continue to enter the subsequent system with the tail gas. Step 4: Reduction and recovery: Hydrogen gas was added to the liquid gold chloride collected in step 3 for reduction treatment. The flow rate of hydrogen gas was 200 mL / min, and the reduction was carried out at 370℃ for 1.5 h to obtain sponge gold. The purity of the obtained sponge gold was tested to be 99.65%.

[0017] Example 4 A method for collecting gold from zinc leaching residue by chlorination volatilization includes the following steps: Step 1: Raw material pretreatment: After drying the zinc leaching residue to a moisture content of ≤5% by mass, grind it to a particle size of <200 mesh, and remove ferromagnetic impurities from the zinc leaching residue by magnetic separation; Step 2, Chlorination Volatilization Reaction: The zinc leaching residue treated in Step 1 is mixed with a composite chlorinating agent at a mass ratio of 1:0.05 and placed in a rotary kiln. The composite chlorinating agent is a mixture of CaCl2 and NaCl at a mass ratio of 3:1. Under a nitrogen protective atmosphere, the mixture is heated to 700℃ at a heating rate of 8℃ / min to carry out the chlorination volatilization reaction for 2.5 hours. After the metals in the zinc leaching residue undergo chlorination, ZnCl2, AuCl3, PbCl2, and FeCl3 are generated. Step 3: Gas phase collection and condensation: Collect the volatile gas containing AuCl3 produced by chlorination in step 2 and introduce it into a two-stage condensation system. The first stage condensation system uses -20℃ ethylene glycol coolant for pre-cooling, and AuCl3 is completely solidified, while ZnCl2 and PbCl2 remain in a gaseous state. The second stage uses liquid nitrogen for deep cooling to -50℃, targeting the capture of AuCl3. However, ZnCl2 and PbCl2, due to their extremely low saturated vapor pressure, will not solidify during the two-stage condensation process and will continue to enter the subsequent system with the tail gas. Step 4: Reduction and recovery: Hydrogen gas was introduced into the liquid gold chloride collected in Step 3 as a reducing agent for reduction treatment. The flow rate of hydrogen gas was 200 mL / min, and the reduction was carried out at 380℃ for 2.0 h to obtain sponge gold. The purity of the obtained gold was tested to be 99.5%.

[0018] Example 5 A method for collecting gold from zinc leaching residue by chlorination volatilization includes the following steps: Step 1: Raw material pretreatment: After drying the zinc leaching residue to a moisture content of ≤4.7% by mass, grind it to a particle size of <200 mesh, and remove ferromagnetic impurities from the zinc leaching residue by magnetic separation. Step 2, Chlorination Volatilization Reaction: The zinc leaching residue treated in Step 1 is mixed with a composite chlorinating agent at a mass ratio of 1:0.04 and placed in a rotary kiln. The composite chlorinating agent is a mixture of CaCl2 and NaCl at a mass ratio of 3:1. Under a nitrogen protective atmosphere, the mixture is heated to 800℃ at a heating rate of 6℃ / min to carry out the chlorination volatilization reaction for 2.0h. After the metals in the zinc leaching residue undergo chlorination, ZnCl2, AuCl3, PbCl2, and FeCl3 are generated. Step 3: Gas phase collection and condensation: Collect the volatile gas containing AuCl3 produced by chlorination in step 2 and introduce it into a two-stage condensation system. The first stage condensation system uses -20℃ ethylene glycol coolant for pre-cooling, and AuCl3 is completely solidified, while ZnCl2 and PbCl2 remain in a gaseous state. The second stage uses liquid nitrogen for deep cooling to -50℃, targeting the capture of AuCl3. However, ZnCl2 and PbCl2, due to their extremely low saturated vapor pressure, will not solidify during the two-stage condensation process and will continue to enter the subsequent system with the tail gas. Step 4: Reduction and recovery: Hydrogen sulfide gas was added to the liquid gold chloride collected in step 3 for reduction treatment. The flow rate of hydrogen sulfide gas was 200 mL / min, and the reduction was carried out at 360℃ for 2.0 h to obtain sponge gold. The purity of the obtained gold was tested to be 99.92%.

[0019] The above are merely preferred embodiments of the present invention. It should be noted that, for those skilled in the art, other equivalent modifications and improvements can be made based on the technical teachings provided by the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for collecting gold from zinc leaching residue by chlorination volatilization, characterized in that: Includes the following steps: Step 1: Raw material pretreatment: After drying the zinc leaching residue to a moisture content of ≤5% by mass, grind it to a particle size of <200 mesh, and remove ferromagnetic impurities from the zinc leaching residue by magnetic separation; Step 2, Chlorination Volatilization Reaction: The zinc leaching residue treated in Step 1 is mixed with the composite chlorinating agent at a mass ratio of 1:0.03-0.05, placed in a rotary kiln, and inert gas is introduced. The mixture is heated to 400-800℃ at a heating rate of 5-8℃ / min and reacted for 2.0-3.0 hours. The metals in the zinc leaching residue undergo a chlorination reaction, generating volatile gases containing ZnCl2, AuCl3, PbCl2, and FeCl3. Step 3: Gas phase collection and condensation: Collect the volatile gas containing AuCl3 produced in Step 2 and introduce it into a two-stage condensation system for condensation to obtain liquid gold chloride; Step 4: Reduction and recovery: Hydrogen or hydrogen sulfide gas is introduced into the liquid AuCl3 collected in step 3 as a reducing agent and kept at 350±10℃ for 1.5h to carry out reduction treatment to obtain sponge gold; the purity of the obtained sponge gold is ≥99.5% after testing.

2. The method for collecting gold from zinc leaching residue by chlorination volatilization according to claim 1, characterized in that: Step one involves grinding with zirconia spherical ink media.

3. The method for collecting gold from zinc leaching residue by chlorination volatilization according to claim 1, characterized in that: The composite chlorinating agent is A mixture of NaCl and NaCl at a mass ratio of 3:

1.

4. The method for collecting gold from zinc leaching residue by chlorination volatilization according to claim 1, characterized in that: In step two, the volatile gas containing AuCl3 is introduced into a two-stage condensation system. The first-stage condensation system uses -20°C ethylene glycol coolant for pre-cooling, causing AuCl3 to completely solidify, while ZnCl2 and PbCl2 remain in a gaseous state. The second-stage condensation system uses liquid nitrogen for deep cooling to -50°C, targeting the capture of AuCl3. However, due to their extremely low saturated vapor pressure, ZnCl2 and PbCl2 will not solidify in the two-stage condensation system and will continue to enter the subsequent system with the exhaust gas.

5. The method for collecting gold from zinc leaching residue by chlorination volatilization according to claim 1, characterized in that: In step two, the gold volatilization rate reaches 55-65%.

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