A method for improving the electrolysis efficiency of molten salt electrolysis to prepare refractory metals and molten salt purification

Abstract

The present invention relates to a method for improving the electrolysis efficiency of refractory metals prepared by molten salt electrolysis and molten salt purification. In the process of preparing refractory metals such as titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), tungsten (W), tantalum (Ta), and molybdenum (Mo) by molten salt electrolysis, refractory metal oxides such as TiO2, ZrO2, Nb2O5, Ta2O5, and Cr2O3 are added to the molten salt without being connected to the cathode to absorb excess O released by the cathode during the electrolysis process. 2‑ On the one hand, it reduces the calcium thermal reduction ratio, reduces the background current, and improves the current efficiency; on the other hand, it purifies the molten salt so that it can be recycled, effectively improving the economy of molten salt electrolysis for preparing refractory metals and avoiding the pollution of the environment by waste molten salt.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and in particular to a method for improving the electrolysis efficiency of preparing refractory metals by molten salt electrolysis and purifying molten salt. Background Art

[0002] Refractory metals usually have a melting point higher than 1650°C, and mainly include titanium (Ti), vanadium (V), chromium (Cr), niobium (Nb), tungsten (W), tantalum (Ta), molybdenum (Mo), etc. Refractory metals are widely used in key fields such as aerospace, nuclear industry, and medical equipment due to their excellent heat resistance, wear resistance, and corrosion resistance.

[0003] The preparation of refractory metals generally involves multiple steps such as leaching, precipitation, calcination, chlorination, and vapor deposition, which have problems such as complex process, long process, and high production cost. Taking the production of titanium metal as an example, titanium ore is first prepared into high-titanium slag through redox pretreatment and pickling to remove impurities, and then titanium metal is prepared through chlorination, distillation, reduction and other operations. The University of Cambridge has achieved a short-process preparation of titanium metal by directly electrolyzing TiO2 in CaCl2 molten salt. Since then, the preparation of refractory metals such as vanadium, chromium, niobium, tungsten, tantalum, and molybdenum has been successively achieved through molten salt electrolysis. However, in the process of preparing refractory metals by molten salt electrolysis using refractory metal oxides as raw materials, due to the O 2- Slow diffusion often leads to problems such as slow reduction rate, low current efficiency and high oxygen content in the product.

[0004] Using refractory metal oxyacid salts instead of refractory metal oxides as raw materials can create more O in the electrolysis process. 2- Diffusion channel, thus can effectively improve the reduction rate and shorten the preparation time of refractory metals. For example: Chinese patent CN201410724949 uses refractory metal oxygenates such as V, Cr, Ti as raw materials to directly prepare metal vanadium, titanium and chromium products through molten salt electrolysis. Chinese patent CN102230194B uses CaWO4 as raw material to prepare metal tungsten products through molten salt electrolysis. In the process of preparing metals by making refractory metal oxides into cathode electrolysis, O 2- It dissociates from the cathode oxide and then diffuses to the anode, generating carbon monoxide or carbon dioxide after receiving electrons at the anode. During the whole process, no O is accumulated in the molten salt. 2- However, unlike the direct electrolysis of refractory metal oxides, the use of refractory metal oxyacids as raw materials in molten salt electrolysis will lead to the accumulation of oxygen ions in the molten salt system. 2- Too high a concentration will cause thermal reduction of calcium, and the dissolved metallic calcium will trigger electronic conduction, thereby increasing the background current and reducing the current efficiency. 2-Too high a concentration will also pollute the molten salt medium, making it impossible to recycle the molten salt. The reduced current efficiency and the inability to recycle the molten salt medium in the process of preparing refractory metals by molten salt electrolysis are important factors limiting its industrial application. Therefore, how to improve the current efficiency and purify the molten salt medium in the process of refractory metal molten salt electrolysis is a problem that we urgently need to solve. Summary of the invention

[0005] Aiming at the problem of reduced electrolysis efficiency in the process of preparing refractory metals by molten salt electrolysis and the inability to recycle the molten salt medium due to contamination, the present invention provides a method for reducing O online without affecting the process of preparing refractory metals by molten salt electrolysis based on a large amount of molten salt reaction thermodynamic data and solubility data. 2- concentration, reducing electronic conductivity and purifying the molten salt medium at the same time.

[0006] In order to achieve the above object, the present invention is implemented by the following specific scheme:

[0007] The present invention provides a method for improving the electrolysis efficiency of refractory metals prepared by molten salt electrolysis and molten salt purification, comprising the following steps: in the process of preparing refractory metal products by molten salt electrolysis in a molten salt system mainly containing chlorides, refractory metal oxides are immersed in the molten salt for purifying the molten salt, and the refractory metal oxides are taken out from the molten salt before the end of the electrolysis, and the refractory metal product is obtained at the cathode, and the molten salt is the purified molten salt, which can be recycled.

[0008] As a preferred technical solution of the present invention, the refractory metal product includes an alloy composed of any one or several refractory metals of Ti, Cr, W, Zr, V, Nb and Ta.

[0009] As a preferred technical solution of the present invention, the chloride-based molten salt system includes at least one of LiCl, CaCl2 and BaCl2.

[0010] As a preferred technical solution of the present invention, the refractory metal oxides are TiO2, ZrO2, Nb2O5, Ta2O5, and Cr2O3.

[0011] As a preferred technical solution of the present invention, the refractory metal oxide needs to be immersed in the molten salt 0.5 hours after the start of the electrolysis operation.

[0012] As a preferred technical solution of the present invention, the refractory metal oxide immersed in the molten salt can be in powder, block, porous and honeycomb shapes, preferably porous and honeycomb shapes.

[0013] As a preferred technical solution of the present invention, the refractory metal oxide immersed in the molten salt cannot contact the cathode or the anode.

[0014] The present invention has the following beneficial effects:

[0015] (1) Simple operation, no need to modify the existing electrolysis system

[0016] The refractory metal oxide is placed in the molten salt without contacting the electrodes. The refractory metal oxide can be adjusted according to the size of the molten salt electrolysis cell without the need to modify the molten salt electrolysis equipment.

[0017] (2) The materials used are widely available, cheap, and recyclable

[0018] To absorb O 2- Refractory metal oxides such as TiO2, ZrO2, Nb2O5, Ta2O5, and Cr2O3 are widely available and fully absorb O 2- After that, it will be transformed into refractory metal oxygen salts. Taking TiO2 as an example, it can fully absorb O 2 Afterwards, depending on the different molten salt media, it transforms into CaTiO3, BaTiO3, etc. These substances themselves can be used as raw materials for the preparation of refractory metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 To compare the reduction in background current when TiO2 is added to the CaCl2 molten salt electrolysis system and when TiO2 is not added. DETAILED DESCRIPTION

[0020] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. However, the following embodiments are limited to explaining the present invention, and the protection scope of the present invention should include the entire contents of the claims, not just limited to the present embodiments. Moreover, through the following embodiments, those skilled in the art can fully implement all the contents recorded in the claims of the present invention.

[0021] Example 1

[0022] A method for improving the electrolysis efficiency of molten salt electrolysis to prepare refractory metals and molten salt purification, comprising the following steps:

[0023] (1) Place 200 g of CaCl2 in a corundum crucible, dry it thoroughly, and heat it to 950 °C to completely melt it.

[0024] (2) After 5g of CaTiO3 is pressed into a tablet, it is sintered at 1000℃ for 1 hour, and connected to the cathode with a metal wire and the anode with a graphite rod. The cathode and anode are placed in molten CaCl2 salt and constant voltage electrolysis is started.

[0025] (3) The constant-voltage electrolysis voltage was controlled at 3.2 V. After the current dropped to 0.54 A, it basically did not drop further. The electrolysis was terminated. The electrolysis time was 610 min, and the current efficiency was 26%.

[0026] (4) Repeat steps (1) and (2), control the constant voltage electrolysis voltage at 3.2 V, wait for 2 hours of electrolysis, and then put 1 g of the pressed flake TiO2 into the CaCl2 molten salt.

[0027] (5) After the current drops to 0.48 A, it basically does not drop further. The electrolysis ends. The electrolysis time is 540 min, the current efficiency is 38%, and there is no residual O in the molten salt. 2- .

[0028] Example 2

[0029] (1) Place 500 g of CaCl2-NaCl (1:1) into a corundum crucible, dry it thoroughly, and then heat it to 750 °C to completely melt it.

[0030] (2) After 10g of CaZrO3 is pressed into a tablet, it is sintered at 1200℃ for 1 hour, and connected to the cathode with a metal wire and the anode with a graphite rod. The cathode and anode are placed in the molten CaCl2-NaCl salt and constant voltage electrolysis is started.

[0031] (3) The constant-voltage electrolysis voltage was controlled at 2.8 V. After the current dropped to 0.60 A, it basically did not drop further. The electrolysis was terminated. The electrolysis time was 480 min, and the current efficiency was 42%.

[0032] (4) Repeat steps (1) and (2), control the constant voltage electrolysis voltage at 3.2 V, wait for 1 hour of electrolysis, and then put 2 g of powdered Nb2O5 into the CaCl2-NaCl molten salt.

[0033] (5) After the current drops to 0.51 A, it basically does not drop further. The electrolysis ends. The electrolysis time is 390 min, the current efficiency is 56%, and there is no residual O in the molten salt. 2- .

[0034] Example 3

[0035] (1) Place 300 g of BaCl2 in a corundum crucible, dry it thoroughly, and heat it to 1050°C to completely melt it.

[0036] (2) After 10g of CaCr2O4 is pressed into a tablet, it is sintered at 900℃ for 1 hour, and connected to the cathode with a metal wire and the anode with a graphite rod. The cathode and anode are placed in molten BaCl2 and constant voltage electrolysis is started.

[0037] (3) The constant-voltage electrolysis voltage was controlled at 3.1 V. After the current dropped to 0.49 A, it basically did not drop further. The electrolysis was terminated. The electrolysis time was 450 min, and the current efficiency was 48%.

[0038] (4) Repeat steps (1) and (2), control the constant voltage electrolysis voltage at 3.2 V, wait for 0.5 hours of electrolysis, and then put 1 g of porous Cr2O3 into the BaCl2 molten salt.

[0039] (5) After the current drops to 0.45 A, it basically does not drop further. The electrolysis ends. The electrolysis time is 410 min, the current efficiency is 54%, and there is no residual O in the molten salt. 2- .

[0040] Example 4

[0041] (1) Place 400 g of CaCl2-KCl (1:1) into a corundum crucible, dry it thoroughly, and heat it to 750 °C to completely melt it.

[0042] (2) After 10g of CaWO4 is pressed into a tablet, it is sintered at 1100℃ for 2 hours, and connected to the cathode with a metal wire and a graphite rod with an anode. The cathode and anode are placed in molten CaCl2-KCl molten salt and constant voltage electrolysis is started.

[0043] (3) The constant-voltage electrolysis voltage was controlled at 3.2 V. After the current dropped to 0.53 A, it basically did not drop further. The electrolysis was terminated. The electrolysis time was 390 min, and the current efficiency was 48%.

[0044] (4) Repeat steps (1) and (2), control the constant voltage electrolysis voltage at 3.2 V, wait for 0.5 hours of electrolysis, and then put 5 g of block Ta2O5 into the CaCl2-KCl molten salt.

[0045] (5) After the current drops to 0.46 A, it basically does not drop further. The electrolysis ends. The electrolysis time is 320 min, the current efficiency is 62%, and there is no residual O in the molten salt. 2- .

[0046] It should be noted that, according to the above-mentioned embodiments of the present invention, those skilled in the art can fully implement the full scope of the independent claims and dependent rights of the present invention, and the implementation process and method are the same as the above-mentioned embodiments; and the parts not elaborated in detail in the present invention belong to the well-known technology in the field.

[0047] The above descriptions are only some specific implementation methods of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any person familiar with the art within the technical scope disclosed in the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for improving the electrolysis efficiency of refractory metals prepared by molten salt electrolysis and molten salt purification, characterized in that: The following steps are involved: In the process of preparing refractory metal products by molten salt electrolysis in a chloride-based molten salt system using refractory metal oxygen acid salts as raw materials, refractory metal oxides are immersed in molten salts for purifying the molten salts, and the refractory metal oxides immersed in the molten salts cannot contact the cathode or the anode. The refractory metal oxides are taken out of the molten salts before the end of the electrolysis, and the refractory metal products are obtained at the cathode and the molten salt is the purified molten salt, which is recycled; The refractory metal oxide is any one of TiO2, ZrO2, Nb2O5, Ta2O5, or Cr2O3; The chloride-based molten salt system includes any one of CaCl2 and BaCl2.

2. A method for improving the electrolysis efficiency of refractory metals prepared by molten salt electrolysis and molten salt purification according to claim 1, characterized in that: The refractory metal product includes any one or an alloy composed of several refractory metals including Ti, Cr, W, Zr, V, Nb or Ta.

3. The method for improving the electrolysis efficiency of refractory metals prepared by molten salt electrolysis and purifying molten salt according to claim 1, characterized in that: The refractory metal oxide needs to be immersed in the molten salt 0.5 hours after the start of the electrolysis operation.

4. A method for improving the electrolysis efficiency of refractory metals prepared by molten salt electrolysis and molten salt purification according to claim 1, characterized in that: The refractory metal oxide immersed in the molten salt is in powder, block, porous or honeycomb shape.

5. A method for improving the electrolysis efficiency of refractory metals prepared by molten salt electrolysis and molten salt purification according to claim 4, characterized in that: The refractory metal oxide immersed in the molten salt is porous or honeycomb-shaped.

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