A method for synchronously extracting metals and tellurium by molten salt electrolysis of solid semiconductor telluride

Abstract

The present invention discloses a method for simultaneously extracting metal and tellurium by molten salt electrolysis of solid semiconductor telluride, belonging to the field of electrochemistry metallurgy. The present invention uses semiconductor sulfide as a raw material, melts it into a rod-shaped electrode under vacuum conditions, and then uses this electrode as the cathode to carry out electrolysis in a molten chloride salt, so that a metal can be obtained at the cathode, and elemental tellurium can be obtained at the anode at the same time. The method for simultaneously extracting metal and tellurium by molten salt electrolysis of solid semiconductor telluride provided by the present invention has a simple process flow, no consumption of any other raw materials during the process, no pollution of waste residue, waste water and waste gas, and the obtained products have high purity.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical metallurgy, and more specifically, relates to a method for simultaneously extracting metal and tellurium from solid semiconductor telluride by molten salt electrolysis. Background Art

[0002] With the continuous development of science and technology, the consumption of tellurium has shifted to the emerging semiconductor industry. Today, the use of tellurium in semiconductor materials has reached about 80% of its total use. According to the current situation of the tellurium industry, the demand for tellurium in China and even the world will continue to grow in the future. The content of tellurium in the earth's crust is extremely low, and it is mostly associated with metal mines such as copper, lead, and zinc. Therefore, the recycling and treatment of waste semiconductor tellurides is an important way to ensure the sustainable use of tellurium resources.

[0003] At present, there are few technical reports on the recovery and treatment of waste semiconductor tellurides, and the wet process is the main one. For example, the Chinese patent with application number CN201210205184.6 discloses a method for comprehensive extraction of valuable metals from tellurium-containing multi-metal materials, in which tellurium enters the solution through nitric acid oxidation leaching, and then reduction separation is performed to obtain crude tellurium powder. The Chinese patent with application number CN201910391872.8 discloses a method for recovering tellurium from bismuth telluride-based semiconductor refrigeration sheet waste, and recovers metallic tellurium from bismuth telluride-based semiconductor refrigeration sheet waste through oxidative acid leaching, reduction precipitation and electrodeposition. The Chinese patent with application number CN201711441063.0 discloses a method for recovering tellurium and zinc from zinc telluride waste, and the selective separation and recovery of tellurium and zinc in zinc telluride waste is achieved through an alkaline leaching-oxidation process. A Chinese patent with application number CN202111669611.1 discloses a method for recovering cadmium telluride waste, in which tellurium is first obtained by oxidative acid leaching and sulfurous acid reduction, and then cadmium sulfide is obtained by hydrogen sulfide reduction.

[0004] However, the main problems with the wet recovery process are that the process flow is complicated, the consumption of other auxiliary chemical reagents is large, it is easy to produce wastewater and waste residue pollution, and it can only gradually separate and recover the valuable elements in the waste.

[0005] For example, Chinese patent ZL201811629555.7 discloses a method for simultaneously recovering bismuth and tellurium from bismuth telluride-based semiconductor waste. First, the bismuth telluride-based semiconductor waste is dissolved in a mixed molten salt containing BiCl3, and then electrolysis is performed to simultaneously recover metallic bismuth and tellurium on the surface of the cathode and anode for electrolysis. The basic principle of this method is: first, the bismuth telluride-based semiconductor is dissolved in a mixed molten salt containing BiCl3 to dissociate it into Bi 3+ and Te 2-ions; then electrolysis is carried out in molten salt, and under the action of an electric field, Bi 3+ ions migrate to the cathode and are reduced to metallic bismuth, while Te 2- ions migrate to the anode and are oxidized to elemental tellurium. The electrode reactions can be expressed as follows:

[0006] Anode: Te 2- - 2e = Te

[0007] Cathode: Be 3+ + 3e = Bi

[0008] Although two products, bismuth and tellurium, can be obtained simultaneously through a one-step process of molten salt electrolysis in this application, BiCl3 is prone to deliquescence and volatilization, and the electrolysis system is unstable, thus affecting the recovery effect. Summary of the Invention

[0009] 1. Problems to be Solved

[0010] The purpose of the present invention is to overcome the above defects existing in the existing semiconductor telluride waste recycling technology, and to provide a method for simultaneously extracting metal and tellurium from solid semiconductor telluride by molten salt electrolysis. By using the method of the present invention, not only can two electrolysis products with high purity, metal and tellurium, be recovered simultaneously, but also the process flow is simple, and there is no pollution from waste residue, waste water and waste gas.

[0011] 2. Technical Solutions

[0012] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0013] A method for simultaneously extracting metal and tellurium from solid semiconductor telluride by molten salt electrolysis according to the present invention uses semiconductor telluride as a raw material, which is melted and cast into a rod-shaped electrode under vacuum conditions, and then directly uses this electrode as a solid cathode to carry out electrolysis in a molten chloride salt, so that a metal can be obtained at the cathode and elemental tellurium can be obtained at the anode simultaneously.

[0014] The present invention directly uses solid semiconductor telluride as the cathode, and through molten salt electrolysis, metal and tellurium can be simultaneously extracted from it. Compared with other existing technologies, it mainly has the following four advantages: (1) The technology provided by the present invention mainly includes two steps: melting and casting the electrode and molten salt electrolysis, and the process flow is simple; (2) By using the technical solution provided by the present invention, a metal can be obtained at the cathode and elemental tellurium can be obtained at the anode simultaneously; (3) The electrolyte used has high stability, and no other raw materials are consumed during the extraction of metal and tellurium, and there is no pollution from waste residue, waste water and waste gas; (4) The purity of the metal and elemental tellurium obtained by molten salt electrolysis is high.

[0015] Furthermore, the method of the present invention includes the following steps:

[0016] (1) Fusible cast electrode: The semiconductor telluride is fusibly cast into a rod-shaped electrode under vacuum conditions;

[0017] (2) Preparation of fused salt: Take the dried metal chloride and heat it to melt under argon protection to obtain the chloride fused salt;

[0018] (3) Fused salt electrolysis: Using the fusibly cast rod-shaped electrode as the cathode and a graphite rod as the anode, perform fused salt electrolysis in an argon atmosphere. After the electrolysis is completed, remove the fused salt on the surfaces of the electrolysis products of the cathode and anode respectively, and then two products, namely metal and elemental tellurium, can be obtained.

[0019] Furthermore, the temperature of the fused salt electrolysis is 500 - 900 °C, the cell voltage is 2.0 - 3.2 V, and the electrolysis time is 3 - 15 h.

[0020] Furthermore, the chloride fused salt uses alkali metal or alkaline earth metal chlorides. Specifically, the alkali metal or alkaline earth metal chlorides are at least one of LiCl, NaCl, KCl, MgCl₂, CaCl₂, BaCl₂, and the purity is further preferably above 99.8%.

[0021] Furthermore, the semiconductor telluride is selected from but not limited to bismuth telluride, zinc telluride, cadmium telluride, lead telluride, tin telluride, indium telluride, and gallium telluride, and its purity is above 99.5%.

[0022] Furthermore, the diameter of the rod-shaped electrode is 0.5 - 4 cm.

[0023] Furthermore, a corundum crucible is placed directly below each of the cathode and anode to collect the electrolysis products. The chloride is dried at 220 - 250 °C for more than 48 h before use to remove the adsorbed water therein.

[0024] 3. Beneficial effects

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) For the method of synchronously extracting metal and tellurium by fused salt electrolysis of solid-state semiconductor telluride of the present invention, after the semiconductor telluride is fusibly cast into a rod-shaped electrode under vacuum conditions, it is used as the cathode for electrolysis in the chloride fused salt, so that metal and elemental tellurium can be obtained synchronously. Compared with the prior art, the present invention mainly includes two steps of fusible casting electrolysis and fused salt electrolysis, thus greatly simplifying the process flow of extracting valuable metals from telluride and being beneficial to reducing production costs.

[0027] (2) The method for synchronously extracting metal and tellurium from solid semiconductor telluride by molten salt electrolysis according to the present invention directly uses solid semiconductor telluride as the cathode, and through molten salt electrolysis, two products, namely a certain metal and elemental tellurium, can be obtained simultaneously, which is completely different from the technical route of gradually separating and extracting valuable metals in the existing hydrometallurgy technology, improving the production efficiency. And at the same time, by controlling the electrolysis process, metals and elemental tellurium with higher purity can be obtained.

[0028] (3) The method for synchronously extracting metal and tellurium from solid semiconductor telluride by molten salt electrolysis according to the present invention uses molten salts of alkali metals or alkaline earth metal chlorides as electrolytes, which have high electrolyte stability, and there is no consumption of any other raw materials during the process, and no waste residue, waste water and waste gas pollution are generated, with good economic and environmental benefits; in addition, the extraction technology of the present application can be applied to semiconductor tellurides including but not limited to bismuth telluride, zinc telluride, cadmium telluride, lead telluride, tin telluride, indium telluride, and gallium telluride, with strong universality. Detailed implementation mode

[0029] Waste semiconductor telluride is a secondary resource with high value. Its recycling and treatment can not only generate good economic value, but also be a strong guarantee for the sustainable development of scarce metal resources. However, in the existing technology, wet processes are mainly used to recycle waste semiconductor telluride, and the process flow is relatively complex, and usually different metal elements in it need to be extracted separately. Therefore, it is of great practical significance to develop a new short-process technology with universality that can directly and efficiently extract metals and elemental tellurium from semiconductor telluride synchronously.

[0030] The inventors of the present application have been committed to the research of recycling technologies for waste resources and have achieved certain research results. For example, in Chinese Patent ZL201811629555.7, two products, namely bismuth and tellurium, can be obtained simultaneously through one-step molten salt electrolysis. However, BiCl3 is prone to deliquescence and volatilization, and the electrolysis system is unstable, thus affecting the recovery effect.

[0031] Based on the above situation, the present invention proposes a method for synchronously extracting metal and tellurium from solid semiconductor telluride by molten salt electrolysis. The semiconductor sulfide is melted and cast into a rod-shaped electrode under vacuum conditions, and then this electrode is used as the cathode for electrolysis in molten chloride salts. A metal can be obtained at the cathode, and elemental tellurium can be obtained at the anode simultaneously. Taking bismuth telluride as an example, the reaction principle for extracting bismuth and tellurium from it using the technology of the present invention is as follows:

[0032] Cathode: Bi2Te3 + 6e = Bi + 3Te 2-

[0033] Anode: Te 2- - 2e = Te

[0034] This is significantly different from the reaction principle in Patent ZL201811629555.7.

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

[0036] Example 1

[0037] A method for simultaneously extracting metal and tellurium from molten salt electrolysis of solid semiconductor telluride in this example specifically includes the following steps:

[0038] (1) Melting and casting the electrode: Using semiconductor bismuth telluride as the raw material, melting it into a rod-shaped electrode with a diameter of 0.5 cm under vacuum conditions.

[0039] (2) Preparing the molten salt: Weighing lithium chloride, potassium chloride, and calcium chloride powders according to the molar ratio of 1:1:1, drying them at 250 °C for 48 h, mixing them evenly, placing them in a corundum crucible, and heating them to 500 °C under argon protection to melt them to obtain a LiCl-KCl-CaCl2 mixed molten salt;

[0040] (3) Molten salt electrolysis: Using the rod-shaped electrode obtained in step (1) as the cathode and a graphite rod as the anode, using the LiCl-KCl-CaCl2 mixed molten salt prepared in step (2) as the electrolyte, controlling the cell voltage to 2.4 V, and electrolyzing at 500 °C for 8 h. The electrolysis process is carried out in an argon atmosphere. A corundum crucible is placed directly below each of the anode and cathode to collect the electrolysis products. After the electrolysis is completed, take out the products and remove the molten salt on the surface of the products to obtain metallic bismuth and elemental tellurium respectively.

[0041] Using the method of this example, the purity of metallic bismuth measured by chemical analysis is 99.55% and the purity of tellurium is 99.75%.

[0042] Example 2

[0043] A method for simultaneously extracting metal and tellurium from molten salt electrolysis of solid semiconductor telluride in this example specifically includes the following steps:

[0044] (1) Melting and casting the electrode: Using semiconductor zinc telluride as the raw material, melting it into a rod-shaped electrode with a diameter of 2.5 cm under vacuum conditions.

[0045] (2) Preparing the molten salt: Weighing calcium chloride powder, drying it at 250 °C for 55 h and then placing it in a corundum crucible, heating it to 900 °C under argon protection to melt it to obtain CaCl2 molten salt;

[0046] (3) Molten salt electrolysis: Using the rod-shaped electrode obtained in step (1) as the cathode and the graphite rod as the anode, and using the CaCl2 molten salt prepared in step (2) as the electrolyte, controlling the cell voltage to 3.2 V, electrolyzing at 900 °C for 10 h. The electrolysis process is carried out in an argon atmosphere. A corundum crucible is placed directly below each of the anode and cathode to collect the electrolysis products. After the electrolysis is completed, the products are taken out and the molten salt on the surface of the products is removed, and metallic zinc and elemental tellurium can be obtained respectively.

[0047] Using the method of this example, the purity of metallic zinc was measured to be 99.50% and the purity of tellurium was 99.65% by chemical analysis.

[0048] Example 3

[0049] A method for simultaneously extracting metal and tellurium from solid-state semiconductor telluride by molten salt electrolysis in this example specifically includes the following steps:

[0050] (1) Melting and casting the electrode: Using cadmium telluride semiconductor as the raw material, melting it into a rod-shaped electrode with a diameter of 3.0 cm under vacuum conditions.

[0051] (2) Preparing the molten salt: Weighing lithium chloride and barium chloride powders according to the molar ratio of 2:1, drying at 220 °C for 60 h, mixing evenly and placing them in a corundum crucible, heating to 850 °C under argon protection to melt and obtain the LiCl-BaCl2 mixed molten salt;

[0052] (3) Molten salt electrolysis: Using the rod-shaped electrode obtained in step (1) as the cathode and the graphite rod as the anode, and using the LiCl-BaCl2 mixed molten salt prepared in step (2) as the electrolyte, controlling the cell voltage to 3.0 V, electrolyzing at 850 °C for 9 h. The electrolysis process is carried out in an argon atmosphere. A corundum crucible is placed directly below each of the anode and cathode to collect the electrolysis products. After the electrolysis is completed, the products are taken out and the molten salt on the surface of the products is removed, and metallic cadmium and elemental tellurium can be obtained respectively.

[0053] Using the method of this example, the purity of metallic cadmium was measured to be 99.65% and the purity of tellurium was 99.85% by chemical analysis.

[0054] Example 4

[0055] A method for simultaneously extracting metal and tellurium from solid-state semiconductor telluride by molten salt electrolysis in this example specifically includes the following steps:

[0056] (1) Melting and casting the electrode: Using indium telluride semiconductor as the raw material, melting it into a rod-shaped electrode with a diameter of 1.0 cm under vacuum conditions.

[0057] (2) Preparation of molten salt: Sodium chloride and calcium chloride powders were weighed according to a molar ratio of 1:1, dried at 240 °C for 50 h, mixed evenly, placed in a corundum crucible, and heated to 640 °C under argon protection to melt and obtain a NaCl-CaCl2 mixed molten salt;

[0058] (3) Molten salt electrolysis: Using the rod-shaped electrode obtained in step (1) as the cathode and the graphite rod as the anode, with the NaCl-CaCl2 molten salt prepared in step (2) as the electrolyte, controlling the cell voltage to 2.8 V, electrolyzing at 640 °C for 15 h. The electrolysis process was carried out in an argon atmosphere. A corundum crucible was placed directly below each of the anode and cathode to collect the electrolysis products. After the electrolysis, the products were taken out and the molten salt on the surface of the products was removed to obtain metallic indium and elemental tellurium respectively.

[0059] Using the method of this example, the purity of metallic indium was measured to be 99.60% and the purity of tellurium was 99.85% by chemical analysis.

[0060] Example 5

[0061] A method for synchronously extracting metal and tellurium from solid-state semiconductor telluride by molten salt electrolysis in this example specifically includes the following steps:

[0062] (1) Melting and casting the electrode: Using lead telluride semiconductor as the raw material, melting and casting it into a rod-shaped electrode with a diameter of 1.5 cm under vacuum conditions.

[0063] (2) Preparation of molten salt: Sodium chloride and potassium chloride powders were weighed according to a molar ratio of 1:1, dried at 250 °C for 50 h, mixed evenly, placed in a corundum crucible, and heated to 800 °C under argon protection to melt and obtain a NaCl-KCl mixed molten salt;

[0064] (3) Molten salt electrolysis: Using the rod-shaped electrode obtained in step (1) as the cathode and the graphite rod as the anode, with the NaCl-KCl molten salt prepared in step (2) as the electrolyte, controlling the cell voltage to 2.7 V, electrolyzing at 800 °C for 12 h. The electrolysis process was carried out in an argon atmosphere. A corundum crucible was placed directly below each of the anode and cathode to collect the electrolysis products. After the electrolysis, the products were taken out and the molten salt on the surface of the products was removed to obtain metallic lead and elemental tellurium respectively.

[0065] Using the method of this example, the purity of metallic lead was measured to be 99.65% and the purity of tellurium was 99.85% by chemical analysis.

[0066] Example 6

[0067] A method for synchronously extracting metal and tellurium from solid-state semiconductor telluride by molten salt electrolysis in this example specifically includes the following steps:

[0068] (1) Casting the electrode: Using semiconductor gallium telluride as the raw material, it is cast into a rod-shaped electrode with a diameter of 4.0 cm under vacuum conditions.

[0069] (2) Preparing the molten salt: Weigh potassium chloride and magnesium chloride powders according to the molar ratio of 2:1, dry them at 250 °C for 55 h, mix them evenly and place them in a corundum crucible, and heat them to 700 °C under argon protection to melt them to obtain the KCl-MgCl2 mixed molten salt.

[0070] (3) Molten salt electrolysis: Using the rod-shaped electrode obtained in step (1) as the cathode and a graphite rod as the anode, using the KCl-MgCl2 molten salt prepared in step (2) as the electrolyte, controlling the cell voltage to 2.6 V, and electrolyzing at 700 °C for 5 h. The electrolysis process is carried out in an argon atmosphere. A corundum crucible is placed directly below each of the anode and cathode to collect the electrolysis products. After the electrolysis is completed, take out the products and remove the molten salt on the surface of the products to obtain metallic gallium and elemental tellurium respectively.

[0071] Using the method of this example, the purity of metallic gallium is measured to be 99.45% and the purity of tellurium is 99.70% by chemical analysis.

[0072] Example 7

[0073] A method for simultaneously extracting metal and tellurium by molten salt electrolysis of solid-state semiconductor telluride in this example specifically includes the following steps:

[0074] (1) Casting the electrode: Using semiconductor tin telluride as the raw material, it is cast into a rod-shaped electrode with a diameter of 2.5 cm under vacuum conditions.

[0075] (2) Preparing the molten salt: Weigh lithium chloride and calcium chloride powders according to the molar ratio of 2:1, dry them at 250 °C for 60 h, mix them evenly and place them in a corundum crucible, and heat them to 680 °C under argon protection to melt them to obtain the LiCl-CaCl2 mixed molten salt.

[0076] (3) Molten salt electrolysis: Using the rod-shaped electrode obtained in step (1) as the cathode and a graphite rod as the anode, using the LiCl-CaCl2 molten salt prepared in step (2) as the electrolyte, controlling the cell voltage to 2.0 V, and electrolyzing at 680 °C for 10 h. The electrolysis process is carried out in an argon atmosphere. A corundum crucible is placed directly below each of the anode and cathode to collect the electrolysis products. After the electrolysis is completed, take out the products and remove the molten salt on the surface of the products to obtain metallic tin and elemental tellurium respectively.

[0077] Using the method of this example, the purity of metallic tin is measured to be 99.60% and the purity of tellurium is 99.85% by chemical analysis.

Claims

1. A method for synchronously extracting metals and tellurium by molten salt electrolysis of solid semiconductor telluride, characterized in that: The semiconductor telluride is cast into a rod-shaped electrode, and then, using this electrode as the cathode, electrolysis is carried out in a molten chloride salt. Elemental tellurium can be obtained at the anode and metal can be obtained at the cathode. The molten chloride salt uses an alkali metal or alkaline earth metal chloride. The electrolysis temperature of the molten salt is 500 - 900 °C, and the cell voltage during electrolysis is 2.0 - 3.2 V. The semiconductor telluride is selected from bismuth telluride, zinc telluride, cadmium telluride, lead telluride, tin telluride, indium telluride, and gallium telluride.

2. The method for synchronously extracting metal and tellurium from molten salt electrolytic solid semiconductor telluride according to claim 1, characterized in that, It includes the following steps: (1) Casting the electrode: The semiconductor telluride is cast into a rod-shaped electrode under vacuum conditions. (2) Preparing the molten salt: The dried metal chloride is taken and heated under argon protection to melt it to obtain the molten chloride salt. (3) Molten salt electrolysis: Using the cast rod-shaped electrode as the cathode and a graphite rod as the anode, molten salt electrolysis is carried out in an argon atmosphere. After electrolysis, the molten salt on the surfaces of the electrolysis products at the cathode and anode is removed respectively, and two products, metal and elemental tellurium, are obtained.

3. A method for synchronously extracting metal and tellurium by molten salt electrolysis of solid semiconductor telluride according to claim 1 or 2, characterized in that: The electrolysis time is 3 - 15 h.

4. A method for synchronously extracting metal and tellurium by molten salt electrolysis of solid semiconductor telluride according to claim 3, characterized in that: The alkali metal or alkaline earth metal chloride is at least one of LiCl, NaCl, KCl, MgCl2, CaCl2, and BaCl2.

5. A method for synchronously extracting metal and tellurium by molten salt electrolysis of solid semiconductor telluride according to claim 1 or 2, characterized in that: The purity of the semiconductor telluride is above 99.5%.

6. A method for synchronously extracting metal and tellurium by molten salt electrolysis of solid semiconductor telluride according to claim 1 or 2, characterized in that: The diameter of the rod-shaped electrode is 0.5 - 4 cm.

7. A method for synchronously extracting metal and tellurium by molten salt electrolysis of solid semiconductor telluride according to claim 1 or 2, characterized in that: A corundum crucible is placed directly below each of the cathode and anode to collect the electrolysis products. The chloride is dried at 220 - 250 °C for more than 48 h before use to remove the adsorbed water therein.