Method for preparing metal zinc through molten salt electrolysis

Abstract

The invention discloses a method for preparing metal zinc through molten salt electrolysis in the technical field of molten salt electrolysis, and aims to solve the technical problems of high energy consumption, serious pollution, complex zinc hydrometallurgy process and heavy environmental load of traditional pyrometallurgical zinc. The method comprises the following steps: by taking mixed molten salt consisting of two or three of zinc sulfide and zinc sulfide as an electrolyte, taking zinc sulfide as a raw material, adding flaky sodium sulfide and 1 # lead to optimize an electrolysis system, carrying out constant-voltage electrolysis at 600-720 DEG C and 3.2-4.0 V by taking a graphite crucible as a cathode and a graphite rod as an anode under the protection of inert gas, and separating by utilizing density difference to obtain metal zinc. The method is short in process and high in efficiency, does not need complicated steps such as roasting, leaching and purifying, obviously reduces energy consumption, does not generate a large amount of waste liquid and residues, is outstanding in environmental protection property, and provides a green and efficient new scheme for the zinc smelting industry.

Description

Technical Field

[0001] This invention relates to the field of molten salt electrolysis, specifically a method for preparing metallic zinc by molten salt electrolysis. Background Technology

[0002] Currently, the most widely used zinc smelting processes in industry are pyrometallurgical zinc smelting and hydrometallurgical zinc smelting, but both have obvious drawbacks:

[0003] 1) Pyrometallurgical zinc smelting: In the pyrometallurgical zinc smelting process, zinc concentrate is first oxidatively roasted to convert it into zinc oxide. Then, it is reduced at high temperatures using a carbonaceous reducing agent (such as coke or carbon monoxide) to produce zinc vapor, which is then condensed to obtain crude zinc. Finally, high-purity metallic zinc is obtained through distillation. However, this method suffers from problems such as high energy consumption, large consumption of reducing agents, and severe environmental pollution.

[0004] 2) Hydrometallurgical Zinc Refining: Hydrometallurgical zinc refining mainly includes roasting, leaching, purification, and electrolysis. In the leaching process, the zinc component in the zinc-containing material dissolves into the sulfuric acid solution. However, impurities inevitably enter the solution partially or completely during leaching, necessitating purification of the zinc sulfate solution to remove harmful impurities and prevent side effects on the subsequent electrolysis process. This process generates a large amount of waste liquid and residue, resulting in a heavy environmental burden, and is complex with a long processing cycle.

[0005] Molten salts, as stable reaction media at high temperatures, contain a large number of freely migrating ions, resulting in high mass transfer efficiency. They can maintain a liquid state within the melting to boiling point range. Due to the eutectic effect, multi-component mixed salt systems can achieve a minimum eutectic temperature below the melting point of a single component, offering a wide applicable temperature range. Molten salts exhibit excellent electrical conductivity, with superior thermal and ionic conduction compared to aqueous solutions and ionic liquids. Viscosity decreases with increasing temperature, reducing ion migration resistance and further enhancing conductivity. Furthermore, molten salts maintain stable physicochemical properties at high temperatures, allowing for separation and recovery through simple post-processing after cooling to room temperature, reducing production costs and providing a green and efficient new approach for metal extraction. Based on these superior properties, molten salt electrolysis demonstrates significant advantages in metal separation and extraction; however, current technologies have not yet developed a mature industrial-scale solution for the electrolytic preparation of metallic zinc using molten salts.

[0006] Therefore, those skilled in the art have provided a method for preparing metallic zinc by molten salt electrolysis to solve the problems mentioned in the background art. Summary of the Invention

[0007] This invention aims to solve the technical problems of high energy consumption, serious pollution, complex process and heavy environmental impact of traditional zinc smelting technology, and provides a method for preparing metallic zinc by molten salt electrolysis, realizing short process, high efficiency and green environmental protection zinc smelting, and providing a new idea for the zinc smelting industry.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for preparing metallic zinc by molten salt electrolysis includes the following steps:

[0010] S1: Raw material pretreatment: Zinc sulfide is ball-milled and then dried at 100°C for 8 hours; chloride salts are vacuum-dried at 200°C for at least 12 hours, wherein the chloride salts are NaCl, KCl, and... A mixture of two or three of the ingredients;

[0011] S2: Mixing configuration: Mix the dried chloride salts evenly according to the set ratio to obtain a mixed molten salt;

[0012] S3: Equipment assembly: Place the raw materials and mixed molten salt in a graphite crucible, place the graphite crucible on the cathode support assembly, cover the furnace lid and lift the graphite anode;

[0013] S4: Atmosphere and Temperature Rise: After the system is evacuated, inert gas is introduced. After the pressure inside the furnace stabilizes, the circulating cooling water is turned on and the electrolysis furnace is started.

[0014] S5: Electrolysis preparation: After the temperature reaches 600-720℃, keep it at the temperature to allow the molten salt to fully form a molten salt electrolyte state, and then lower the graphite anode;

[0015] S6: Constant voltage electrolysis: Apply a DC power supply and perform constant voltage electrolysis for 1 to 2 hours at a voltage of 3.2 to 4.0V until the current stabilizes;

[0016] S7: Product separation: After the electrolysis reaction is completed, the graphite crucible is allowed to cool naturally inside the furnace, then removed and treated with deionized water to separate the zinc product.

[0017] As a further aspect of the present invention: in step S1, the particle size of the zinc sulfide after ball milling is 100 mesh.

[0018] As a further aspect of the present invention: In step S2, the set ratio is determined by a binary phase diagram or a ternary phase diagram at the corresponding temperature. The lowest eutectic point of the NaCl-KCl binary system is 657℃, and the molar ratio of NaCl to KCl at this temperature is 50.6:49.4.

[0019] As a further aspect of the present invention: in step S3, the raw materials include zinc sulfide, flake sodium sulfide and lead No. 1, where flake sodium sulfide is used to increase the ion migration ability of the system and lead No. 1 is used to improve conductivity.

[0020] As a further embodiment of the present invention: in step S4, the inert gas is nitrogen or argon, and the electrolytic furnace is a pit-type resistance furnace.

[0021] As a further aspect of the present invention: in step S5, the heat preservation time is 30 minutes to ensure that the mixed molten salt is completely melted to form a uniform and stable electrolyte.

[0022] As a further aspect of the present invention: in step S6, the graphite crucible is the cathode and the graphite rod is the anode. The graphite anode only serves to connect the circuit and does not change the composition and microstructure of the cathode product.

[0023] As a further aspect of the present invention: in step S7, the separation is based on density difference: when lead #1 is added, metallic zinc floats on top of the bottom lead; when lead #1 is not added, metallic zinc is deposited at the bottom of the crucible.

[0024] As a further embodiment of the present invention: in the mixed molten salt, NaCl and KCl are the basic components. To adjust the composition, it is used to increase the conductivity of the electrolyte and reduce its own hygroscopicity and volatility.

[0025] As a further aspect of the present invention: the amount of sodium sulfide flakes added does not exceed 1.5% of the mass of zinc sulfide, so as to avoid the current efficiency from decreasing due to excessively rapid sodium ion circulation. During the electrolysis process, the behavior of anode bubbles is regulated by controlling the electrolysis temperature and optimizing the electrolyte composition to reduce anode overvoltage. In step S4, the circulating cooling water is used to cool the electrodes and prevent the power cord from aging at high temperatures.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] This invention, through the design and optimization of a mixed molten salt electrolyte, directly prepares metallic zinc via molten salt electrolysis using zinc sulfide as raw material. It completely eliminates the cumbersome steps of traditional processes such as roasting, leaching, and purification, significantly shortening the process, reducing energy consumption, and enhancing environmental friendliness. The electrolysis process is stable and controllable; electrolysis efficiency can be improved by adding auxiliary raw materials and adjusting process parameters. Product separation is simple, and the purity of metallic zinc meets industrial requirements. This provides reliable technical support for the green and efficient development of the zinc smelting industry and has broad prospects for industrial application. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1

[0030] (1) Crush and grind the zinc sulfide raw material to a particle size of 100 mesh, and then dry it at 100°C for 8 hours; place different types of chloride salts in a vacuum drying oven at 200°C for more than 12 hours to fully remove moisture; weigh a total of 500g of NaCl-KCl mixed chloride salts according to the set molar ratio and mix them evenly.

[0031] (2) Lay a layer of lead (No. 1 lead) about 3-4 mm thick at the bottom of the graphite crucible, and add 20 g of pretreated ZnS powder, 3 g of Na2S and 500 g of dried NaCl-KCl mixed chloride salt in sequence.

[0032] (3) Place the graphite crucible containing the material into the electrolytic furnace and perform vacuum treatment at room temperature. Then, introduce an inert gas (nitrogen or argon) to maintain the pressure inside the electrolytic furnace. Turn on the circulating cooling water system and start the pit-type heating furnace to raise the temperature to 700°C to completely melt the mixed chloride salt. Hold the temperature for 30 minutes to form a uniform and stable molten salt electrolyte. Then, insert the graphite anode into the molten electrolyte and electrolyze at a constant voltage of 3.4V for 1-2 hours (stop electrolysis when the current stabilizes).

[0033] (4) After electrolysis, turn off the heating system and remove the graphite crucible after the system has cooled to room temperature. Taking advantage of the density difference between zinc and lead (zinc is less dense than lead), zinc floats on top of the lead in small spheres. The product is washed with deionized water, separated, and dried to obtain zinc.

[0034] Example 2

[0035] (1) Crush and grind the zinc sulfide raw material to a particle size of 100 mesh, and then dry it at 100°C for 8 hours; place different types of chloride salts in a vacuum drying oven at 200°C for more than 12 hours to fully remove moisture; weigh a total of 500g of NaCl-KCl-ZnCl2 mixed chloride salt according to the set molar ratio and mix them evenly.

[0036] (2) Lay a base of lead (No. 1 lead) with a thickness of about 3-4 mm at the bottom of the graphite crucible, and then add 20g of pretreated ZnS powder and 3g of lead powder in sequence. And 500g of dried Mixed chloride salts.

[0037] (3) Place the graphite crucible containing the material into the electrolytic furnace and perform vacuum treatment at room temperature. Then, introduce inert gas (nitrogen or argon) to maintain the pressure inside the electrolytic furnace. Turn on the circulating cooling water system and start the pit-type heating furnace to raise the temperature to 600°C to completely melt the mixed chloride salt. Hold the temperature for 30 minutes to form a uniform and stable molten salt electrolyte. Then, insert the graphite anode into the molten electrolyte and electrolyze at a constant voltage of 3.4V for 1-2 hours (stop electrolysis when the current stabilizes).

[0038] (4) After electrolysis, turn off the heating system and remove the graphite crucible after the system has cooled to room temperature. Taking advantage of the density difference between zinc and lead (zinc is less dense than lead), zinc floats on top of the lead in small spheres. The product is washed with deionized water, separated, and dried to obtain zinc.

[0039] Example 3

[0040] (1) Crush and grind the zinc sulfide raw material to a particle size of 100 mesh, and then dry it at 100°C for 8 hours; place different types of chloride salts in a vacuum drying oven at 200°C for more than 12 hours to fully remove moisture; weigh a total of 500g of NaCl-KCl mixed chloride salts according to the set molar ratio and mix them evenly.

[0041] (2) Add 20g of pretreated ZnS powder and 3g of [unclear text] to a graphite crucible in sequence. And 500g of dried Mixed chloride salts.

[0042] (3) Place the graphite crucible containing the material into the electrolytic furnace and perform vacuum treatment at room temperature. Then, introduce inert gas (nitrogen or argon) to maintain the pressure inside the electrolytic furnace. Turn on the circulating cooling water system and start the pit-type heating furnace to raise the temperature to 700°C to completely melt the mixed chloride salt. Hold the temperature for 30 minutes to form a uniform and stable molten salt electrolyte. Then, insert the graphite anode into the molten electrolyte and electrolyze at a constant voltage of 3.8V for 1-2 hours (stop electrolysis when the current stabilizes).

[0043] (4) After electrolysis, turn off the heating system and remove the graphite crucible after the system has cooled to room temperature. Utilize the density difference between metallic zinc and molten salt to collect the metallic zinc product deposited at the bottom of the crucible. After washing with deionized water, separation and drying, metallic zinc is obtained.

[0044] Example 4

[0045] (1) Crush and grind the zinc sulfide raw material to a particle size of 100 mesh, and then dry it at 100°C for 8 hours; place different types of chloride salts in a vacuum drying oven at 200°C for more than 12 hours to fully remove moisture; weigh a total of 500g of NaCl-KCl mixed chloride salts according to the set molar ratio and mix them evenly.

[0046] (2) Add 20g of the pretreated solution to the graphite crucible in sequence. The powder and 500g of dried NaCl-KCl mixed chloride salt.

[0047] (3) Place the graphite crucible containing the material into the electrolytic furnace and perform vacuum treatment at room temperature. Then, introduce inert gas (nitrogen or argon) to maintain the pressure inside the electrolytic furnace. Turn on the circulating cooling water system and start the pit-type heating furnace to raise the temperature to 700°C to completely melt the mixed chloride salt. Hold the temperature for 30 minutes to form a uniform and stable molten salt electrolyte. Then, insert the graphite anode into the molten electrolyte and electrolyze at a constant voltage of 3.8V for 1-2 hours (stop electrolysis when the current stabilizes).

[0048] (4) After electrolysis, turn off the heating system and remove the graphite crucible after the system has cooled to room temperature. Utilize the density difference between metallic zinc and molten salt to collect the metallic zinc product deposited at the bottom of the crucible. After washing with deionized water, separation and drying, metallic zinc is obtained.

[0049] Example 5

[0050] The preparation method of this embodiment is the same as that of Example 1, except that the electrolysis temperature in step (3) is 720°C.

[0051] Example 6

[0052] The preparation method of this embodiment is the same as that of Example 1, except that the electrolysis voltage is 3.6V in step (3).

[0053] Example 7

[0054] The preparation method of this embodiment is the same as that of Example 1, except that the electrolysis voltage is 3.8V in step (3).

[0055] Example 8

[0056] The preparation method of this embodiment is the same as that of Example 2, except that the electrolysis temperature in step (3) is 650°C.

[0057] Example 9

[0058] The preparation method of this embodiment is the same as that of Example 2, except that the electrolysis temperature in step (3) is 700℃.

[0059] Example 10

[0060] The preparation method of this embodiment is the same as that of embodiment 2, except that the electrolysis voltage is 3.6V in step (3).

[0061] Example 11

[0062] The preparation method of this embodiment is the same as that of embodiment 2, except that the electrolysis voltage is 3.8V in step (3).

[0063] Example 12

[0064] The preparation method of this embodiment is the same as that of Example 3, except that the electrolysis temperature in step (3) is 720°C.

[0065] Example 13

[0066] The preparation method of this embodiment is the same as that of Example 3, except that the electrolysis voltage in step (3) is 3.6V.

[0067] Example 14

[0068] The preparation method of this embodiment is the same as that of embodiment 3, except that the electrolysis voltage in step (3) is 4.0V.

[0069] Example 15

[0070] The preparation method of this embodiment is the same as that of Example 4, except that the electrolysis temperature in step (3) is 720°C.

[0071] Example 16

[0072] The preparation method of this embodiment is the same as that of embodiment 4, except that the electrolysis voltage in step (3) is 3.6V.

[0073] Example 17

[0074] The preparation method of this embodiment is the same as that of embodiment 4, except that the electrolysis voltage in step (3) is 4.0V.

[0075] Summary of performance test data from Examples 5-17

[0076]

[0077] Analysis shows that this invention has the following significant advantages over traditional zinc smelting processes:

[0078] 1) Significantly simplified process: Eliminates cumbersome steps such as roasting, leaching, and purification, and directly uses zinc sulfide as raw material to electrolyze and prepare metallic zinc, greatly shortening the production cycle and reducing process complexity by more than 60%.

[0079] 2) Improved energy consumption and environmental friendliness: The mixed molten salt eutectic effect reduces the electrolysis temperature; no large amount of waste gas, waste liquid, or residue is generated, only a small amount of anode gas (mainly chlorine) is generated, which can be treated to meet emission standards, making it significantly more environmentally friendly than traditional processes.

[0080] 3) Excellent product quality: The purity of the metallic zinc product reaches 99.2% to 99.7%, meeting the industrial-grade high-purity zinc standard, and the zinc volatilization loss is controlled at 3.8% to 5.5%, which is lower than that of traditional pyrometallurgical processes.

[0081] 4) Cost reduction: The raw material pretreatment is simple, the molten salt can be recycled and reused (recovery rate ≥95%), the auxiliary raw materials are readily available and the amount used is controllable, and the overall production cost is reduced by 20% to 25% compared with the traditional process.

[0082] 5) Strong applicability: The process is highly controllable and easy to promote industrially, providing reliable technical support for the green upgrading of the zinc smelting industry.

[0083] This invention, through the design and optimization of a mixed molten salt electrolyte, directly prepares metallic zinc via molten salt electrolysis using zinc sulfide as raw material. It completely eliminates the cumbersome steps of traditional processes such as roasting, leaching, and purification, significantly shortening the process, reducing energy consumption, and enhancing environmental friendliness. The electrolysis process is stable and controllable; electrolysis efficiency can be improved by adding auxiliary raw materials and adjusting process parameters. Product separation is simple, and the purity of metallic zinc meets industrial requirements. This provides reliable technical support for the green and efficient development of the zinc smelting industry and has broad prospects for industrial application.

[0084] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing metallic zinc by molten salt electrolysis, characterized in that, Includes the following steps: S1: Raw material pretreatment: Zinc sulfide is ball-milled and then dried at 100°C for 8 hours; chloride salts are vacuum-dried at 200°C for at least 12 hours, wherein the chloride salts are NaCl, KCl, and... A mixture of two or three of the ingredients; S2: Mixing configuration: Mix the dried chloride salts evenly according to the set ratio to obtain a mixed molten salt; S3: Equipment assembly: Place the raw materials and mixed molten salt in a graphite crucible, place the graphite crucible on the cathode support assembly, cover the furnace lid and lift the graphite anode; S4: Atmosphere and Temperature Rise: After the system is evacuated, inert gas is introduced. After the pressure inside the furnace stabilizes, the circulating cooling water is turned on and the electrolysis furnace is started. S5: Electrolysis preparation: After the temperature reaches 600-720℃, keep it at the temperature to allow the molten salt to fully form a molten salt electrolyte state, and then lower the graphite anode; S6: Constant voltage electrolysis: Apply a DC power supply and perform constant voltage electrolysis for 1 to 2 hours at a voltage of 3.2 to 4.0V until the current stabilizes; S7: Product separation: After the electrolysis reaction is completed, the graphite crucible is allowed to cool naturally inside the furnace, then removed and treated with deionized water to separate the zinc product.

2. The method for preparing metallic zinc by molten salt electrolysis according to claim 1, characterized in that, In step S1, the particle size of the zinc sulfide after ball milling is 100 mesh.

3. The method for preparing metallic zinc by molten salt electrolysis according to claim 1, characterized in that, In step S2, the set ratio is determined by a binary phase diagram or a ternary phase diagram at the corresponding temperature. The lowest eutectic point of the NaCl-KCl binary system is 657℃, and the molar ratio of NaCl to KCl at this temperature is 50.6:49.

4.

4. The method for preparing metallic zinc by molten salt electrolysis according to claim 1, characterized in that, In step S3, the raw materials include zinc sulfide, flake sodium sulfide, and lead No.

1. The flake sodium sulfide is used to increase the ion migration ability of the system, and lead No. 1 is used to improve conductivity.

5. The method for preparing metallic zinc by molten salt electrolysis according to claim 1, characterized in that, In step S4, the inert gas is nitrogen or argon, and the electrolysis furnace is a pit-type resistance furnace.

6. The method for preparing metallic zinc by molten salt electrolysis according to claim 1, characterized in that, In step S5, the heat preservation time is 30 minutes to ensure that the mixed molten salt is completely melted to form a uniform and stable electrolyte.

7. The method for preparing metallic zinc by molten salt electrolysis according to claim 1, characterized in that, In step S6, the graphite crucible is the cathode and the graphite rod is the anode. The graphite anode only serves to connect the circuit and does not change the composition and microstructure of the cathode product.

8. The method for preparing metallic zinc by molten salt electrolysis according to claim 1, characterized in that, In step S7, the separation is based on density difference: when lead #1 is added, metallic zinc floats on top of the bottom lead; when lead #1 is not added, metallic zinc is deposited at the bottom of the crucible.

9. The method for preparing metallic zinc by molten salt electrolysis according to claim 1, characterized in that, In the mixed molten salt, NaCl and KCl are the basic components. To adjust the composition, it is used to increase the conductivity of the electrolyte and reduce its own hygroscopicity and volatility.

10. The method for preparing metallic zinc by molten salt electrolysis according to claim 4, characterized in that, The amount of sodium sulfide flakes added does not exceed 1.5% of the mass of zinc sulfide to avoid excessively rapid sodium ion circulation leading to a decrease in current efficiency. During electrolysis, the behavior of anode bubbles is regulated by controlling the electrolysis temperature and optimizing the electrolyte composition to reduce anode overvoltage. In step S4, circulating cooling water is used to cool the electrodes and prevent the power cord from aging at high temperatures.

Images