Apparatus and method for preparing high-purity gallium and indium by low-temperature molten salt electrolysis

Abstract

The application relates to a device and a method for preparing high-purity gallium and indium by low-temperature molten salt electrolysis, and belongs to the technical field of rare metal smelting. The device and the method solve the problems of long existing process flow, rising energy consumption and cost, low direct yield of high-purity metal, poor stability of purity of batch products and the like. The device comprises a tank body and a temperature control jacket arranged outside the tank body. An inner chamber of the tank body is sequentially provided with a first end electrode, at least one bipolar electrode unit and a second end electrode in an axial direction. The bipolar electrode unit is composed of a liquid metal chamber and porous ceramic membranes on two sides of the liquid metal chamber. The two sides of the liquid metal chamber are separated from adjacent molten salt chambers through the porous ceramic membranes. A coarse liquid metal chamber is arranged between the first end electrode and the liquid metal chamber adjacent to the first end electrode. The device and the method have high current efficiency, can directly obtain high-purity gallium and indium of 6N and above under low-temperature electrolysis of coarse metal, and are simple in process flow, low in equipment cost, low in energy consumption and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of rare metal smelting technology, and in particular to an apparatus and method for preparing high-purity gallium and indium by low-temperature molten salt electrolysis. Background Technology

[0002] Gallium (Ga) and indium (In) are indispensable key raw materials in high-tech fields such as semiconductors, next-generation communications, precision instruments and new energy. Due to their special physicochemical properties and concentrated supply, they have been included in the "critical minerals" list by many countries. Moreover, there are still severe challenges in the preparation technology of high-purity metals (≥6N) for high-end semiconductors, optoelectronics and other fields. Therefore, it is of great significance to develop purification technologies for high-purity gallium and indium that are efficient, low-cost and can be mass-produced.

[0003] Currently, the preparation of 5-6N grade high-purity gallium is mainly carried out by electrolysis, while 6N-8N grade relies on crystallization for purification. Industrially, electrolysis and crystallization are often combined in series to produce 7N grade products. Gallium electrolytic refining is generally carried out in NaOH solution, and 4N crude gallium can usually be reduced to 5N-6N after two electrolysis processes. However, since the electrode potential of gallium (EGaO2- / Ga=-1.22V) is lower than the hydrogen evolution potential (EH2O / H2=-0.828V), the gallium deposition process is accompanied by severe H2 precipitation, resulting in a simultaneous decrease in product quality and current efficiency. Although industrial methods increase the hydrogen evolution overpotential (to -1.40V) to achieve stable gallium deposition by increasing the current density and using stainless steel cathodes, uneven current distribution and concentration polarization are unavoidable, making it difficult to effectively suppress the hydrogen evolution reaction. Crystallization utilizes the supercooling properties of gallium to induce the precipitation of higher purity crystals through seed crystals, enriching impurities in the liquid (partial crystallization, directional crystallization, and zone melting are all examples of this method). This method is simple to operate, but its efficiency is low, requiring multiple crystallization cycles and producing numerous intermediate products. In addition, vacuum distillation is also used for gallium purification, but the crucible container is prone to contaminating the product at high temperatures, so it is only used as an auxiliary method.

[0004] In terms of technology, the high-purity preparation of indium is similar to that of gallium, primarily relying on electrolytic refining. Commonly used systems include In2(SO4)3-H2SO4 and InCl3-HCl solutions. Crude indium can be electrolyzed two or more times to obtain 5N-grade products, but the removal of impurities such as Cd and Tl remains insufficient. The refined indium obtained through electrolysis, combined with zone melting, can further improve the purity to 6N or higher, but the separation efficiency for Pb, Sn, Tl, and Cd remains limited. Therefore, industrially, combined process flows are often used to prepare 7N-grade products.

[0005] CN111455405A reports that 4N indium can be refined to 5N through primary electrolysis, purified to 6N through vacuum distillation, and further refined to 7N through secondary electrolysis. Unlike gallium, monovalent indium compounds are also ubiquitous and possess unique reactivity. InCl readily disproportionates to In and InCl3 in aqueous solution; therefore, high-purity sponge indium can be prepared by purifying InCl through distillation followed by disproportionation in aqueous solution, but the yield is less than 30%. InCl is sufficiently stable in molten salt, thus an indium electrolytic refining technology based on InCl molten salt has been developed. Compared to trivalent indium electrolysis in aqueous solution, the DC power consumption of the molten salt system can theoretically be reduced by 2 / 3; however, under current technological conditions, the refining level generally remains around 5N after multiple refining processes.

[0006] In summary, the preparation of gallium and indium at the 6N level and above often relies on a combination of multiple processes: the series connection of multiple processes makes the process links complicated, increases energy consumption and cost, and results in low direct recovery rate of high-purity metals, leading to poor stability of batch products and serious limitations on large-scale production. Summary of the Invention

[0007] In view of the above analysis, the present invention aims to provide an apparatus and method for preparing high-purity gallium and indium by low-temperature molten salt electrolysis, which is used to solve at least one of the following technical problems: (1) the existing aqueous solution electrolysis method is accompanied by serious hydrogen evolution side reaction, which leads to a decrease in current efficiency and product quality, making it difficult to achieve deep purification; (2) the existing high purification process (such as crystallization method, vacuum distillation, etc.) is complex, energy-intensive and has a high operating temperature, making it difficult to achieve low-cost, efficient and large-scale stable production of high-purity metals.

[0008] The first aspect of the present invention provides an apparatus for preparing high-purity gallium and indium by low-temperature molten salt electrolysis, comprising a tank 1 and a temperature control jacket 2 disposed outside the tank 1. In the internal cavity of the tank 1, a first end electrode 3, at least one bipolar electrode unit and a second end electrode 4 are arranged sequentially along the axial direction. The bipolar electrode unit is composed of a liquid metal chamber 6 and porous ceramic membranes 5 on both sides. The two sides of the liquid metal chamber 6 are separated from the adjacent molten salt chamber 7 by the porous ceramic membranes 5. A coarse liquid metal chamber 11 is provided between the first end electrode 3 and the adjacent molten salt chamber 7.

[0009] Furthermore, the first end electrode 3 and the second end electrode 4 are configured to be connected to the positive and negative terminals of an external power source, respectively.

[0010] Furthermore, the molten salt chamber 7 and the liquid metal chamber 6 are arranged alternately along the axial direction of the tank 1 to form multiple electrolysis units connected in series; each of the molten salt chambers 7 is provided with an independent feeding pipe 8.

[0011] Furthermore, the temperature control jacket 2 is a closed medium circulation channel with a spiral semi-tube structure.

[0012] Furthermore, the temperature control jacket 2 is fixedly connected to the outer wall of the tank 1.

[0013] Furthermore, it also includes a temperature control system connected to the temperature control jacket 2, the temperature control system including a heating unit, a cooling unit, a circulating pump, and a valve group for switching between heating and cooling modes.

[0014] Furthermore, a heat insulation layer 9 is provided between the tank 1 and the temperature control jacket 2, and a metal protective shell 10 is provided on the outer layer of the temperature control jacket 2.

[0015] A second aspect of the present invention provides a method for preparing high-purity gallium or indium, the method being carried out in the apparatus described in the first aspect, and the steps comprising: S1. Liquid metal is placed in the liquid metal chamber 6, and molten salt electrolyte is placed in the molten salt chamber 7. The liquid metal and molten salt electrolyte are heated to a first temperature to ensure that all components remain liquid. S2. Add the crude gallium or crude indium to be purified into the crude liquid metal chamber 11; S3. Apply direct current to the first end electrode 3 and the second end electrode 4 to perform electrolysis, and obtain high-purity gallium or indium in the cathode chamber.

[0016] Furthermore, when preparing high-purity gallium, the liquid metal is Ga or a mixture of Ga and at least one metal selected from Bi, Sn, In, and Sb.

[0017] Furthermore, the molten salt electrolyte is a mixture of GaCl3 and at least one chloride selected from AlCl3, NaCl, KCl, LiCl, CsCl, ZnCl2 and CaCl2.

[0018] Furthermore, when preparing high-purity indium, the liquid metal is In or a mixture of In and at least one metal selected from Bi, Sn, and Sb.

[0019] Furthermore, the molten salt electrolyte is selected from the first chloride, or a mixture containing the first chloride and the second chloride.

[0020] Furthermore, the first chloride is selected from at least one of InCl and InCl3, and the second chloride is selected from at least one of ZnCl2, AlCl3, CsCl, NaCl, KCl, LiCl and NH4Cl.

[0021] Furthermore, the electrolysis conditions include: an anode current density of 0.1~2 A / cm². 2 The cathode current density is 0.1~2 A / cm². 2 .

[0022] Furthermore, in step S1, the first temperature is 40~300℃.

[0023] Furthermore, it also includes a step of regenerating the liquid metal in the bipolar electrode unit, the regeneration step including: connecting the liquid metal chamber 6 of the bipolar electrode unit to be regenerated to the positive terminal of an external power source as an anode, and performing electrolysis.

[0024] This invention can achieve at least one of the following beneficial effects: 1. This invention employs a low-temperature molten salt system and a multi-stage bipolar electrode series structure, based on the spontaneous separation mechanism of electrochemical potential differences, to achieve a step-by-step purification process of "interface reduction-bulk diffusion-interface oxidation" under low-temperature conditions of 40~300℃. This effectively avoids the severe hydrogen evolution side reaction in traditional aqueous solution electrolysis, significantly improves current efficiency and product purity, and can directly and stably prepare ≥6N grade high-purity gallium or indium from crude metal raw materials, breaking through the bottleneck of existing technologies that depend on multi-process coupling.

[0025] 2. This invention can operate at low temperatures of 40~300℃. Compared with traditional molten salt electrolysis (usually >500℃), it greatly reduces the stringent requirements for the high temperature resistance and corrosion resistance of the equipment, and allows the use of lower-cost structural materials. At the same time, the low temperature makes the operation simpler and safer, with less heat loss, significantly improving the economy and operability of the process.

[0026] 3. The bipolar electrode design of this invention enables multiple electrolysis units to work collaboratively under a single power supply, eliminating the need for an independent power supply and control system for each stage. This significantly simplifies the equipment structure, reduces manufacturing costs and operating energy consumption, and facilitates continuous and automated process control, thus possessing promising prospects for industrial application.

[0027] 4. Each molten salt chamber in this invention is equipped with an independent feeding pipeline, which enables real-time control of the molten salt composition and continuous addition of raw materials during the electrolysis process. At the same time, it supports switching the intermediate liquid metal chamber to the anode for online regeneration and impurity removal, which enhances the flexibility and stability of the process, extends the service life of the liquid metal, and further reduces operating costs and the risk of impurity accumulation.

[0028] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0029] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 This is a cross-sectional structural schematic diagram of the apparatus for preparing high-purity gallium and indium by low-temperature molten salt electrolysis according to the present invention; Figure 2 This is a cross-sectional structural schematic diagram of the axial front view of the three-stage bipolar electrode series structure in Embodiment 1 of the present invention.

[0030] Figure Labels

[0031] 1-Tank body; 2-Temperature control jacket; 3-First end electrode; 4-Second end electrode; 5-Porous ceramic membrane; 6-Liquid metal chamber; 7-Molten salt chamber; 8-Feeding pipe; 9-Heat insulation layer; 10-Metal protective shell; 11-Rough liquid metal chamber; 12-High-purity liquid metal; 13-Discharge pipe. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, exemplary embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. For clarity and brevity, not all features of actual embodiments are described in the specification.

[0033] Existing technologies typically employ aqueous solution electrolysis to prepare high-purity gallium or indium. However, this method is accompanied by severe hydrogen evolution side reactions, leading to a decrease in current efficiency and product quality, making it difficult to achieve deep purification (i.e., ≥5N). Crystallization and vacuum distillation, on the other hand, involve complex processes, high energy consumption, high operating temperatures, or are susceptible to contamination, making it difficult to achieve efficient, continuous, and stable batch production of high-purity metals. To overcome the above-mentioned technical defects, the first aspect of this invention provides an apparatus for preparing high-purity gallium and indium by low-temperature molten salt electrolysis, comprising a tank 1 and a temperature control jacket 2 disposed outside the tank 1. In the internal cavity of the tank 1, along the direction of material flow, a first end electrode 3, at least one bipolar electrode unit, and a second end electrode 4 are sequentially arranged axially. The bipolar electrode unit is composed of a liquid metal chamber 6 and porous ceramic membranes 5 on both sides. The two sides of the liquid metal chamber 6 are separated from the adjacent molten salt chamber 7 by the porous ceramic membranes 5. A coarse liquid metal chamber 11 is provided between the first end electrode 3 and the adjacent liquid metal chamber 7.

[0034] This invention utilizes a multi-stage bipolar electrode series structure and a spontaneous separation mechanism based on electrochemical potential differences to achieve a stepwise purification process of "interface reduction-bulk diffusion-interface oxidation" at low temperatures. This effectively avoids the severe hydrogen evolution side reaction in traditional aqueous solution electrolysis, significantly improves current efficiency and product purity, and can directly and stably prepare ≥6N grade high-purity gallium or indium from crude metal raw materials, breaking through the bottleneck of existing technologies that rely on multi-process coupling.

[0035] It is understood that the apparatus for preparing high-purity gallium and indium by low-temperature molten salt electrolysis is a multi-chamber electrolytic cell.

[0036] In this invention, taking crude gallium as an example, after the electrolytic cell is energized, the gallium in the crude metal is oxidized into gallium ions at the first end electrode and enters the molten salt chamber. The gallium ions migrate to the liquid metal / molten salt interface of the adjacent first bipolar electrode unit and are reduced into gallium atoms, which then enter the liquid metal chamber. The gallium atoms diffuse to the interface between the liquid metal chamber and the next-level molten salt chamber by means of the concentration gradient, are oxidized into ions, and enter the next-level molten salt. The liquid metal bipolar electrode can physically isolate the two-stage molten salt chambers and undertake the role of transferring electrons and target metal atoms, thereby realizing the circuit series connection of the multi-stage molten salt electrolytic chambers.

[0037] The metal sequentially passes through all the aforementioned bipolar electrode units, repeating the "interface reduction-bulk diffusion-interface oxidation" transfer process. During this process, impurities in the crude gallium with electrode potentials positive than the target gallium are trapped in the preceding liquid metal and gradually enriched, while the target metal is continuously purified, ultimately yielding high-purity gallium or high-purity indium with a purity ≥6N in the cathode molten salt chamber adjacent to the second end electrode. Impurities in the crude gallium, particularly elements more reactive than gallium (e.g., Ti, Al, Li, Na, K, Ca, Mg), are preferentially oxidized without reduction and ultimately enriched in the electrolyte, while more inert elements (e.g., Fe, Ni, Cu, Mn) are enriched in the bipolar liquid electrode. These elements are difficult to enter the gallium product at the second end electrode (cathode), ensuring the gallium product has a purity ≥6N.

[0038] In this invention, the trough 1 is a horizontal cylindrical structure.

[0039] According to some embodiments of the present invention, the first end electrode 3 and the second end electrode 4 are configured to be connected to the positive and negative terminals of an external power source, respectively. The molten salt chamber 7 and the liquid metal chamber 6 are arranged alternately along the axial direction of the tank 1 to form a plurality of electrolysis units connected in series. Each of the molten salt chambers 7 is provided with an independent feeding pipe 8.

[0040] In this invention, the bipolar electrode unit comprises a liquid metal chamber 6 and porous ceramic membranes 5 and molten salt chambers 7 on both sides thereof, the porous ceramic membranes 5 forming the sidewalls of the molten salt chambers 7. The molten salt chambers and liquid metal chambers are arranged alternately along the axial direction of the tank, thereby dividing the electrolysis region into multiple series-connected electrolysis units. Each molten salt chamber is provided with an independent feed pipe for adding raw materials or adjusting the electrolyte composition.

[0041] In this invention, the multi-stage bipolar electrode series structure can be a two-stage bipolar electrode series structure, a three-stage bipolar electrode series structure, a four-stage bipolar electrode series structure, etc. For example, a three-stage bipolar electrode series structure is used as an example. Figure 2 As shown, the three-stage bipolar electrode series structure includes, from left to right, a first porous ceramic membrane 501, a first molten salt chamber 701, a second porous ceramic membrane 502, a first liquid metal chamber 601, a third porous ceramic membrane 503, a second molten salt chamber 702, a fourth porous ceramic membrane 504, a second liquid metal chamber 602, a fifth porous ceramic membrane 505, a third molten salt chamber 703, a sixth porous ceramic membrane 506, a third liquid metal chamber 603, a seventh porous ceramic membrane 507, and a fourth molten salt chamber 704.

[0042] In this invention, each molten salt chamber 7 is provided with a discharge pipe 13 at its lower part.

[0043] In this invention, the porous ceramic membrane is made of zirconium oxide, alumina, silicon carbide or boron nitride, and has excellent molten salt wettability and metal barrier properties, which can effectively isolate liquid metal and molten salt while ensuring efficient ion migration.

[0044] In this invention, considering the collection of high-purity gallium or indium products, the electrolytic cell also includes a cathode chamber adjacent to the second end electrode 4.

[0045] According to some embodiments of the present invention, in order to improve the pressure-bearing capacity and heat transfer efficiency of the process equipment, the temperature control jacket 2 is a closed medium circulation channel with a spiral semi-pipe structure.

[0046] According to some embodiments of the present invention, the temperature control jacket 2 is fixedly connected to the outer wall of the tank 1.

[0047] Specifically, the temperature control jacket 2 can be welded to the outer wall of the tank 1.

[0048] According to some embodiments of the present invention, a temperature control system connected to the temperature control jacket 2 is also included, the temperature control system including a heating unit, a cooling unit, a circulating pump, and a valve group for switching heating and cooling modes.

[0049] In this invention, the temperature control system is connected to the temperature control jacket 2, and precise, rapid and uniform temperature control of the tank is achieved by circulating heat transfer oil in the jacket.

[0050] In this invention, a heat insulation layer 9 is provided between the tank 1 and the temperature control jacket 2, and a metal protective shell 10 is provided on the outer layer of the temperature control jacket 2 to reduce heat loss and protect the internal structure.

[0051] For example, the heat insulation layer 9 may be selected from ceramic fiber, and the metal protective shell 10 may be a carbon steel protective shell.

[0052] According to some embodiments of the present invention, the second end electrode 4 is made of high-purity platinum or high-purity titanium.

[0053] In this invention, the second end electrode is preferably made of high-purity platinum or high-purity titanium. High-purity platinum has excellent chemical inertness and conductivity, can withstand molten salt corrosion, and ensures stable current transmission; high-purity titanium, on the other hand, has good mechanical strength and low cost while maintaining conductivity, making it suitable for long-term industrial operation.

[0054] Furthermore, the material of the first end electrode 3 can be graphite.

[0055] A second aspect of the present invention provides a method for preparing high-purity gallium or indium, the method being carried out in the apparatus described in the first aspect, and the steps comprising: S1. Liquid metal is placed in the liquid metal chamber 6, and molten salt electrolyte is placed in the molten salt chamber 7. The liquid metal and molten salt electrolyte are heated to a first temperature. S2. Add the crude gallium or crude indium to be purified into the crude liquid metal chamber 11; S3. Apply direct current to the first end electrode 3 and the second end electrode 4 to perform electrolysis, and obtain high-purity gallium or indium in the cathode chamber.

[0056] In this invention, a direct current is applied to the first end electrode 3 and the second end electrode 4, so that the first end electrode 3 serves as the anode and the second end electrode 4 serves as the cathode, and the liquid metal in the middle liquid metal chamber 6 forms a bipolar electrode due to the electric field.

[0057] It should be noted that, by utilizing the electrolytic cell of this invention, multiple-stage series electrolysis can be driven by a single power source, eliminating the need for independent power supplies for each unit. This significantly simplifies the equipment structure and reduces manufacturing costs and system energy consumption. Simultaneously, this design results in more uniform current distribution, more stable control, and easier automation. Combined with a porous ceramic membrane, gallium or indium ions are efficiently transferred between stages via "interface reduction-diffusion-interface oxidation," with impurities being progressively retained at each stage. This enables continuous and deep purification from crude gallium or indium to high-purity gallium / indium at levels above 6N at low temperatures (40~300℃).

[0058] Specifically, the crude metal to be purified (crude gallium or crude indium) is added from the feed pipe 8 to the crude liquid metal chamber 11 adjacent to the first end electrode 3. After electrolysis, the crude metal is oxidized into metal ions in the molten salt chamber 7 (i.e., the anode chamber) and enters the molten salt. The metal ions migrate to the liquid metal / molten salt interface of the adjacent first bipolar electrode unit and are reduced into metal atoms and enter the liquid metal. The metal atoms diffuse to the interface between the liquid metal chamber 6 and the next stage molten salt chamber 7 by means of the concentration gradient, are oxidized into ions and enter the molten salt of that stage molten salt chamber 7. The metal passes through all the bipolar electrode units in sequence, repeating the above reduction, diffusion and oxidation transfer process. Impurities are gradually separated and enriched in the previous stage liquid metal. Finally, high-purity gallium or high-purity indium with a purity higher than 6N is obtained in the cathode chamber adjacent to the second end electrode 4. The high-purity liquid metal 12 generated by the cathode is precipitated at the second end electrode 4 and enriched at the bottom of the last stage molten salt chamber, and discharged through the discharge pipe 13.

[0059] According to some embodiments of the present invention, when the crude metal is crude gallium, i.e., when preparing high-purity gallium, the liquid metal is Ga or a mixture of Ga and at least one metal selected from Bi, Sn, In, and Sb. In this invention, Bi, Sn, In, and Sb can all form stable eutectic alloys with gallium in the low-temperature range (40~300℃), maintaining good fluidity. Furthermore, their electrochemical properties in chloride molten salts are similar to those of gallium, neither preferentially oxidizing and precipitating to interfere with the purification process, nor hindering the selective retention of impurities through potential differences. Simultaneously, these components exhibit high chemical stability in the system, reducing side reactions.

[0060] According to some embodiments of the present invention, when the crude metal is crude gallium, i.e., when preparing high-purity gallium, the molten salt electrolyte is a mixture of GaCl3 and at least one chloride selected from AlCl3, NaCl, KCl, LiCl, CsCl, ZnCl2 and CaCl2.

[0061] In this invention, the molten salt electrolyte is selected from the above-mentioned types, which can form a low-temperature eutectic system and reduce the operating temperature to the range of 40~300℃. These chlorides can effectively reduce the melting point of the molten salt, increase the ionic conductivity, and maintain chemical stability, ensuring efficient gallium ion migration and stable electrolysis.

[0062] For example, the mixture comprises GaCl3 and at least one chloride selected from AlCl3, NaCl, KCl, LiCl, CsCl, ZnCl2 and CaCl2, wherein the content of GaCl3 in the mixture is not less than 10 mol%, for example, it can be 10 mol%, 15 mol%, 20 mol%, 30 mol%, 40 mol%, 50 mol%, 55 mol%, 60 mol%, 70 mol%, 72 mol%, 75 mol%, 78 mol%, 80 mol%, preferably 60 to 80 mol.

[0063] For example, the molten salt electrolyte is a mixture of GaCl3 and LiCl, wherein the content of GaCl3 in the mixture is 70 mol%, 72 mol%, 73 mol%, 75 mol%, 76 mol%, 78 mol%, 79 mol%, and 80 mol%.

[0064] According to some embodiments of the present invention, when preparing high-purity indium, the liquid metal is In or a mixture of In and at least one metal selected from Bi, Sn, Sb, and Pb, and the molten salt electrolyte is selected from a first chloride or a mixture of a first chloride and a second chloride.

[0065] Specifically, the first chloride is selected from at least one of InCl and InCl3, and the second chloride is selected from at least one of ZnCl2, AlCl3, CsCl, NaCl, KCl, LiCl and NH4Cl.

[0066] For example, when the molten salt electrolyte is a mixture selected from a first chloride and a second chloride, the content of the first chloride in the mixture is not less than 10 mol%, for example, it can be 10 mol%, 15 mol%, 20 mol%, 30 mol%, 40 mol%, 50 mol%, 55 mol%, 60 mol%, 70 mol%, 72 mol%, 75 mol%, 78 mol%, 80 mol%, preferably 10 to 30 mol.

[0067] For example, the second chloride is selected from AlCl3 and KCl among ZnCl2, AlCl3, CsCl, NaCl, KCl, LiCl and NH4Cl, with a molar ratio of AlCl3 to KCl of 2:3.

[0068] In this invention, In or alloys of In with Bi, Sb, Sn, and Pb are selected, which can form low-melting-point eutectic alloys with indium and maintain good fluidity at low temperatures. Meanwhile, the electrochemical properties of metals such as Bi and Sb help to selectively retain impurities in the reduction-diffusion-oxidation cycle, enhancing the separation effect.

[0069] Furthermore, for molten salt electrolytes containing high-purity indium, using InCl and / or InCl3 mixed with one or more of ZnCl2, AlCl3, CsCl, NaCl, KCl, LiCl, and NH4Cl can adjust the melting point, viscosity, and indium ion activity of the molten salt, improve electrolysis efficiency, suppress side reactions, and ensure deep purification of indium.

[0070] For high-purity indium molten salt electrolytes, InCl is mixed with one or more of ZnCl2, AlCl3, CsCl, NaCl, KCl, LiCl, and NH4Cl. For example, a mixture of InCl with AlCl3 and KCl can be selected, wherein the molar ratio of the three is 10~15:59~64:28~33.

[0071] For example, in the mixing scheme of InCl3 with one or more of ZnCl2, AlCl3, CsCl, NaCl, KCl, LiCl, and NH4Cl, a mixture of InCl with AlCl3 and KCl can be selected, wherein the molar ratio of the three is 10~15:59~64:28~33.

[0072] According to some embodiments of the present invention, considering the effective balance between electrolysis efficiency and process stability, the electrolysis conditions include: an anode current density of 0.1~2 A / cm². 2 The cathode current density is 0.1~2 A / cm². 2 If the current density is too low, the reaction rate will be slow and the purification efficiency will be low; if it is too high, concentration polarization will easily occur, increasing the risk of impurity co-deposition or side reactions (such as molten salt decomposition). In a system with multi-stage bipolar electrodes connected in series, an appropriate current density can ensure a uniform electric field distribution, allowing the "interfacial reduction-diffusion-interfacial oxidation" transfer process of each unit to proceed smoothly, thereby maintaining high current efficiency while ensuring that the purity of the final product consistently reaches 6N or higher. In addition, this range is also matched with the ion conductivity of the selected molten salt electrolyte and the mass transfer characteristics of the porous ceramic membrane, avoiding local overheating or equipment overload.

[0073] According to some embodiments of the present invention, the first temperature is greater than the melting point of the molten salt electrolyte, the liquid metal, and the crude gallium or crude indium to be purified, ensuring that all components remain in a liquid state.

[0074] Further, specifically, the first temperature is 40~300℃, for example, it can be 40℃, 60℃, 80℃, 100℃, 120℃, 150℃, 180℃, 200℃, 250℃, 300℃, preferably 80~170℃, and the electrolysis time can be 20~40h.

[0075] According to some embodiments of the present invention, the method further includes a step of regenerating the liquid metal in the bipolar electrode unit, the regeneration step including: connecting the liquid metal chamber 6 of the bipolar electrode unit to be regenerated to the positive terminal of an external power source as an anode, performing electrolysis to oxidize the impurities in the liquid metal chamber 6 and allow them to enter the adjacent molten salt chamber 7.

[0076] In this invention, as the electrolysis process proceeds, impurities gradually accumulate in the upstream liquid metal, affecting its melting point, viscosity, and mass transfer efficiency. During regeneration, the target liquid metal chamber is connected to the positive terminal of an external power source as the anode via circuit switching. Under energized conditions, the target metal undergoes an oxidation reaction, converting into ions that enter the adjacent molten salt chamber, thereby achieving the separation of impurities from the target metal and the purification of the target metal. This method restores the purification performance without replacing the liquid metal, significantly extends the material's service life, reduces operating costs, and supports continuous production.

[0077] In this invention, gallium in the target liquid metal chamber is oxidized-reduced-oxidized in the last stage to obtain pure metal. Impurities in the liquid metal are retained and enriched in the target liquid metal chamber. After the liquid metal in the target liquid metal chamber is enriched with impurities, it is discharged through the outlet at the bottom of the target liquid metal chamber and used as the first stage crude metal for electrolytic refining.

[0078] The following examples and comparative examples further illustrate the method for preparing high-purity gallium or indium in the apparatus for preparing high-purity gallium and indium by low-temperature molten salt electrolysis according to the present invention.

[0079] In the following examples, the impurities are at least one of Ti, Al, Li, Na, K, Ca, Mg, Fe, Ni, Cu, and Mn, as determined by ICP-MS.

[0080] Example 1 Figure 1 This is a schematic diagram of the axial cross-sectional structure of the apparatus (multi-chamber electrolytic cell) for preparing high-purity gallium by low-temperature molten salt electrolysis according to the present invention, as shown below. Figure 1 and Figure 2As shown, the device has three bipolar electrode units (the device as a whole constitutes a three-stage bipolar electrode series structure). Specifically, the tank 1 is a horizontal cylindrical structure, and a temperature control jacket 2 composed of a spiral half-tube is welded to its outside. Inside the tank 1, along the axial direction, a first end electrode 3 made of graphite, three bipolar electrode units, and a second end electrode 4 made of high-purity titanium are arranged in sequence.

[0081] Each bipolar electrode unit comprises a liquid metal chamber 6 containing Ga metal and porous zirconia ceramic membranes 5 on both sides thereof. The liquid metal chamber 6 is separated from the adjacent molten salt chamber 7 by the porous zirconia ceramic membranes 5. The three-stage bipolar electrode series structure includes, from left to right, a first porous ceramic membrane 501, a first molten salt chamber 701, a second porous ceramic membrane 502, a first liquid metal chamber 601, a third porous ceramic membrane 503, a second molten salt chamber 702, a fourth porous ceramic membrane 504, a second liquid metal chamber 602, a fifth porous ceramic membrane 505, a third molten salt chamber 703, a sixth porous ceramic membrane 506, a third liquid metal chamber 603, a seventh porous ceramic membrane 507, and a fourth molten salt chamber 704. Each molten salt chamber 7 has a feeding pipe 8 at the top and a discharge pipe 13 at the bottom. The tank body 1 and the jacket 2 are covered with a ceramic fiber thermal insulation layer 9, and the outermost layer is a carbon steel protective shell 10.

[0082] When performing purification, follow these steps: S1. First, 100g of metallic Ga is loaded into each liquid metal chamber 6, and a mixed molten salt electrolyte of GaCl3 and LiCl in a molar ratio of 78:22 is loaded into each molten salt chamber 7. Then, crude gallium with a purity of 99.3% is added from the feed pipe 8 into the crude liquid metal chamber 11 adjacent to the first end electrode 3, and the tank system is heated to 80°C and maintained at a constant temperature through an oil bath system connected to the temperature control jacket 2. S2. Apply direct current to the first end electrode 3 and the second end electrode 4, controlling the current density of both the anode and cathode to be 0.5 A / cm². 2 Electrolysis is carried out; S3. After 24 hours of electrolysis, high-purity metallic gallium with a purity of 99.9999997% (exceeding the 7N standard) was obtained in the cathode chamber adjacent to the second end electrode 4, with a current efficiency of 97.2%.

[0083] Compositional analysis of each stage of the liquid metal chamber showed that the impurity content in the first stage liquid metal chamber was 0.1%, which was significantly higher than that in the second stage (0.03%), proving that the impurities were effectively enriched in the first stage during the purification process.

[0084] Example 2 The method is the same as in Example 1, except that the number of series stages is reduced, that is, the number of bipolar electrode units is replaced from 4 to 2.

[0085] Everything else was the same as in Example 1. After 24 hours of electrolysis, ultra-high purity gallium with a purity of 99.999913% (exceeding the 6N standard) was obtained in the final cathode chamber, with a current efficiency of 92%.

[0086] Example 3 The method is the same as in Example 2, except that high-purity In is prepared, the material of the second end electrode is high-purity platinum, and the liquid metal chamber 6 of each bipolar electrode unit is filled with an In-Bi alloy (mass ratio of In to B 66:34).

[0087] During the purification process, an alloy of In and Bi prepared at a mass ratio of 66:34 is first loaded into each liquid metal chamber 6, and a mixed molten salt prepared from InCl3, AlCl3, and KCl at a molar ratio of 11:60:29 is loaded into each molten salt chamber 7. Subsequently, crude indium with a purity of 99.6% is added through the feed pipe 8 of the molten salt chamber 7 adjacent to the first end electrode 3.

[0088] The tank system is heated to 170°C and maintained at a constant temperature via an oil bath system connected to the temperature control jacket 2. Then, a direct current is applied to the first end electrode 3 and the second end electrode 4, controlling the current density of both the anode and cathode to be 0.8 A / cm².

[0089] After 28 hours of electrolysis, high-purity metallic indium with a purity of 99.99985% (exceeding the 6N standard) was obtained in the cathode chamber adjacent to the second end electrode 4, with a current efficiency of 98.1%.

[0090] Compositional analysis of each stage of the liquid metal chamber revealed that the impurity content in the first-stage liquid metal chamber (0.06%) was significantly higher than that in the second-stage chamber (0.01%).

[0091] Example 4 The method is the same as in Example 1, except that the number of bipolar electrode units is changed from 3 to 2.

[0092] Everything else was the same as in Example 1. After 24 hours of electrolysis, ultra-high purity gallium with a purity of 99.9999995% (exceeding the 7N standard) was obtained in the final cathode chamber, with a current efficiency of 94.8%.

[0093] Comparative Example 1 A dual-chamber electrolytic cell is used, which is separated into an anode chamber and a cathode chamber by a single porous ceramic membrane. The anode electrode is directly connected to crude gallium metal, and pure gallium is obtained by cathode electrolysis. However, this device does not have the bipolar electrode unit and multi-stage series structure described in this invention.

[0094] To achieve a purification effect similar to that of Example 2, this comparative example underwent two independent electrolysis operations: first, electrolysis was performed using 99.3% crude gallium as the anode to obtain metallic gallium with a purity of 99.95% (3N5); then, this product was used as the anode for a second electrolysis, lasting a total of 48 hours, ultimately yielding metallic gallium with a purity of 99.992% (4N) in the cathode chamber. This result is significantly lower than the 6N-level purity (99.999913%) obtained in Example 2 of this invention after 24 hours of electrolysis.

[0095] Comparative Example 2 An electrolytic cell with the same physical structure as in Example 1 is provided, but each molten salt chamber is equipped with an independent DC power supply and connected to it. Specifically, the first end electrode is connected to the positive terminal of power supply 1, the first liquid metal chamber is connected to the negative terminal of power supply 1 and the positive terminal of power supply 2, the second liquid metal chamber is connected to the negative terminal of power supply 2 and the positive terminal of power supply 3, and the second end electrode is connected to the negative terminal of power supply 3.

[0096] After electrolysis for 24 hours under the exact same materials and process parameters as in Example 1, high-purity gallium (99.9994%) was obtained in the cathode chamber with a current efficiency of 92%.

[0097] The system complexity of Comparative Example 1 is greatly increased, requiring three independent power supplies and control systems, which is three times that of the present invention; energy consumption is significantly increased, and due to the existence of multiple independent circuit loops, the total Joule heat loss is greater. According to measurements, its total energy consumption is 2.2 times that of Embodiment 1 of the present invention; control is extremely cumbersome, requiring precise matching and coordination of the output of multiple power supplies, otherwise it is very easy for a certain unit to fail due to current imbalance.

[0098] Comparative Example 3 The electrolysis was carried out in a multi-chamber electrolytic cell in Example 2. The raw materials and electrolyte composition were the same as in Example 2. The difference was that the electrolysis temperature was increased to 350°C. After electrolysis at this high temperature for 24 hours, the following phenomena were observed: (1) The current efficiency dropped sharply from about 92% in Example 2 to less than 40%; (2) Electrolyte composition imbalance: a large amount of GaCl3 volatilized, resulting in a severe loss of gallium ion concentration in the molten salt, making the electrolysis process unsustainable, and severe polarization occurred at the anode; (3) Product purity decreased: affected by the above factors, the purity of metallic gallium obtained from the cathode chamber decreased instead of increasing, and was only 99.995%.

[0099] Comparative Example 4 Using crude gallium raw material of the same purity as in Example 1 (99.3% purity), electrolysis was carried out in a conventional NaOH aqueous solution electrolytic cell. The electrolytic cell was a single-chamber structure, with the cell body made of polytetrafluoroethylene or alkali-resistant stainless steel, and contained an anode and a cathode. The anode was made of graphite or platinum sheet and was in direct contact with the crude gallium; the cathode was a stainless steel plate or a high-purity graphite plate. The electrolyte was a 6 mol / L NaOH aqueous solution. Specific steps were as follows: S1. Inject the electrolyte into the electrolytic cell, immersing the anode and cathode in the liquid. Place 100g of crude gallium in the anode chamber, ensuring good contact with the anode. S2. The electrolyte temperature is raised to 60°C and maintained at a constant temperature using an external water bath.

[0100] S3. Apply direct current between the anode and the cathode, and control the current density of both the anode and the cathode to be 0.5A / cm², consistent with Example 1. After electrolysis for 24 hours, stop the current and remove the metallic gallium deposited on the cathode.

[0101] Testing revealed that the purity of the product was far lower than that of the present invention, reaching only 99.91%, with a current efficiency of 42.7%, and a large amount of hydrogen evolution could be detected by gas chromatography.

[0102] Comparative Example 5 The method was followed in Example 1, except that GaCl3 and LaCl3 were used as the molten salt electrolyte (GaCl3 and LaCl3 molar ratio of 78:22). Because the electrolyte had a high melting point, it only became a completely liquid system at 360°C. After holding at this temperature for 1 hour, the GaCl3 in the electrolyte had almost completely evaporated, leaving only 0.5%. Since the molten salt could not melt and had poor ionic conductivity, electrolysis could not proceed effectively.

[0103] As can be seen from the above, the results of Example 1 compared with those of Example 2 fully demonstrate that by increasing the number of cascade stages, the present invention can flexibly and effectively achieve deep purification of metals, and the purity of the final product increases significantly with the increase of the number of stages.

[0104] Compared with Comparative Example 1, Example 1 shows that without the synergistic effect of multi-stage series connection and bipolar electrodes, even with double the time (48h) and energy consumption, the deep purification effect achievable by the present invention cannot be achieved.

[0105] Compared with Comparative Example 2, Example 2 strongly demonstrates that the electrolytic cell of Example 2 of the present invention achieves a fundamental simplification of the power supply system and control logic without sacrificing the purification effect, and brings about significant energy-saving effects.

[0106] Comparing Example 2 with Comparative Example 3, it can be seen that the low-temperature operating window of 80℃~170℃ selected by the present invention is the key to achieving high current efficiency, maintaining the stability of electrolyte components, and thus ensuring the production of high-purity products.

[0107] 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 changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An apparatus for preparing high-purity gallium and indium by low-temperature molten salt electrolysis, characterized in that, It includes a tank (1) and a temperature control jacket (2) disposed outside the tank (1). In the internal cavity of the tank (1), a first end electrode (3), at least two bipolar electrode units and a second end electrode (4) are arranged sequentially along the axial direction. The bipolar electrode unit is composed of a liquid metal chamber (6) and porous ceramic membranes (5) on both sides. The liquid metal chamber (6) is separated from the adjacent molten salt chamber (7) by the porous ceramic membranes (5). A coarse liquid metal chamber (11) is provided between the first end electrode (3) and the adjacent molten salt chamber (7). The first end electrode (3) and the second end electrode (4) are configured to be connected to the positive and negative terminals of an external power source, respectively; The molten salt chamber (7) and the liquid metal chamber (6) are arranged alternately along the axial direction of the tank (1) to form multiple electrolysis units connected in series; each of the molten salt chambers (7) is provided with an independent feeding pipe (8).

2. The apparatus according to claim 1, characterized in that, The temperature control jacket (2) is a closed medium circulation channel with a spiral semi-tube structure; And / or, the temperature control jacket (2) is fixedly connected to the outer wall of the tank (1).

3. The apparatus according to claim 1, characterized in that, It also includes a temperature control system connected to the temperature control jacket (2), the temperature control system including a heating unit, a cooling unit, a circulating pump and a valve group for switching heating and cooling modes.

4. The apparatus according to claim 1, characterized in that, A heat insulation layer (9) is provided between the tank (1) and the temperature control jacket (2), and a metal protective shell (10) is provided on the outer layer of the temperature control jacket (2).

5. A method for preparing high-purity gallium or indium, characterized in that, The method is performed in the apparatus described in any one of claims 1-4, and the steps include: S1. Liquid metal is placed in the liquid metal chamber (6), and molten salt electrolyte is placed in the molten salt chamber (7). The liquid metal and molten salt electrolyte are heated to a first temperature to ensure that all components remain liquid. S2. Add the crude gallium or crude indium to be purified into the crude liquid metal chamber (11). S3. Apply direct current to the first end electrode (3) and the second end electrode (4) to perform electrolysis and obtain high-purity gallium or indium in the cathode chamber.

6. The method according to claim 5, characterized in that, When preparing high-purity gallium, the liquid metal is Ga or a mixture of Ga and at least one metal selected from Bi, Sn, In, and Sb. And / or, the molten salt electrolyte is a mixture of GaCl3 and at least one chloride selected from AlCl3, NaCl, KCl, LiCl, CsCl, ZnCl2 and CaCl2.

7. The method according to claim 5, characterized in that, When preparing high-purity indium, the liquid metal is In or a mixture of In and at least one metal selected from Bi, Sn, Sb, and Pb. And / or, the molten salt electrolyte is selected from a first chloride, or a mixture comprising a first chloride and a second chloride; And / or, the first chloride is selected from at least one of InCl and InCl3, and the second chloride is selected from at least one of ZnCl2, AlCl3, CsCl, NaCl, KCl, LiCl and NH4Cl.

8. The method according to claim 5, characterized in that, The electrolysis conditions include: an anode current density of 0.1~2 A / cm³. 2 The cathode current density is 0.1~2 A / cm². 2 ; And / or, in step S1, the first temperature is 40~300℃.

9. The method according to claim 5, characterized in that, It also includes a step of regenerating the liquid metal in the bipolar electrode unit, the regeneration step including: connecting the liquid metal chamber (6) of the bipolar electrode unit to be regenerated to the positive terminal of an external power source as an anode, and performing electrolysis.

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