Method and device for preparing high-purity indium by multi-unit series multi-stage electrolytic refining

Abstract

The present invention relates to the field of rare metal smelting, and specifically discloses a method and device for preparing high-purity indium through multi-unit series multi-stage electrolytic refining, comprising a pre-electrolysis liquid storage tank, an electrolytic tank, a post-electrolysis liquid storage tank, and a first circulation pump connected through a pipeline and a U-shaped groove to form an electrolytic refining circulation system, and the electrolytic tank is used to perform the four steps of primary electrolysis, vacuum distillation, secondary electrolysis, and single crystal growth to prepare high-purity indium with good quality consistency and a purity of 8N, thereby providing a technical basis and material basis for the preparation of high-end indium phosphide material products in my country.

Description

Technical Field

[0001] The present invention relates to the field of rare metal smelting, and in particular to a method and device for preparing high-purity indium through multi-unit series multi-stage electrolytic refining. Background Art

[0002] In order to actively integrate into the construction of national strategic emerging industries and industrial base strengthening projects, realize the localization of high-purity indium for indium phosphide production in my country, and ultimately realize the localization of ultra-low dislocation indium phosphide for microelectronics defense and military industry, electronic lasers, and 5G communications, realize independent supply of raw materials, make up for the shortcomings of the industrial chain, reduce production costs, and achieve domestic substitution and independent control (now 90% of 8N high-purity indium for domestic preparation of high-quality indium phosphide needs to be imported from abroad). At present, the purity of high-purity indium products prepared by joint multi-units in China can basically only reach 5-6N. Although there are some manufacturers of 7-8 high-purity indium, due to their low product output and poor quality consistency, it is difficult to meet the requirements of high-quality indium phosphide. In the process of preparing ultra-low dislocation indium phosphide semiconductor substrates, affected by the quality of raw material high-purity indium, the prepared indium phosphide is difficult to meet the product quality requirements in terms of dislocation density, carrier concentration, etc., and the preparation process is affected by the raw materials, resulting in poor process stability, which increases the difficulty of large-scale preparation of high-quality indium phosphide. Gu needs a process method and production equipment for preparing high-purity indium through multi-unit series multi-stage electrolytic refining that is easier to realize industrial production and can better ensure product quality consistency, so as to solve the technical and equipment-related problems of 8N high-purity indium for large-scale preparation of high-quality semiconductor material indium phosphide products. Summary of the invention

[0003] The purpose of the present invention is to provide a method and equipment for preparing 8N high-purity indium for preparing high-quality indium phosphide substrate sheets, so as to realize industrial and large-scale production. The high-purity indium obtained has good quality consistency and a purity of 8N, providing a technical basis and material basis for the preparation of high-end indium phosphide material products in my country.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is:

[0005] A multi-unit series multi-stage electrolytic refining device comprises a pre-electrolysis liquid storage tank, an electrolytic tank, and a post-electrolysis liquid storage tank. The pre-electrolysis liquid storage tank is connected to the upper part of the electrolytic tank, and the post-electrolysis liquid storage tank is connected to the lower part of the electrolytic tank, forming a height difference between them. The outlet of the pre-electrolysis liquid storage tank and the inlet of the electrolytic tank are in the same plane and are connected by a U-shaped groove. At least three outlet pipes are arranged at the outlet of the bottom of the pre-electrolysis liquid storage tank, and a first flow stabilizer is installed in the outlet pipe. The electrolyte flows to the U-shaped trough through the liquid outlet pipe, and then enters the electrolytic cell from the U-shaped trough. At least three liquid outlet pipes are installed at the lower part of the electrolytic cell, which are connected with the post-electrolysis liquid storage tank through pipelines. A second flow stabilizer is installed between the pipelines. The post-electrolysis liquid storage tank and the pre-electrolysis liquid storage tank are connected through pipelines. A first circulation pump is installed between the pipelines of the two liquid storage tanks. The pre-electrolysis liquid storage tank, the electrolytic cell, the post-electrolysis liquid storage tank, and the first circulation pump are connected with the U-shaped trough through pipelines to form an electrolytic refining circulation system.

[0006] Furthermore, a movable cover is installed on the electrolytic cell, and the movable cover fits tightly with the U-shaped groove and the edge of the electrolytic cell. Two rows of tooth grooves are symmetrically arranged on the edge of the movable cover, and the size of the tooth groove is not less than the size of the plate hanging ear placed therein.

[0007] Furthermore, a plurality of holes are arranged on the movable cover plate.

[0008] Furthermore, a bottom plate is installed on the top of the outlet of the electrolytic cell, and the bottom plate is sloped with an inclination angle of 0. 。 -15 。 An independent space is formed between the bottom plate and the bottom of the electrolytic cell, and holes are arranged on the bottom plate, and the arrangement of holes is consistent with that of the movable cover plate.

[0009] Furthermore, the bottom plate holes are in an inverted trapezoidal shape.

[0010] Furthermore, the number and size of the liquid outlet pipe openings at the bottom of the liquid storage tank before electrolysis and the liquid outlet pipe openings at the bottom of the electrolytic tank are the same.

[0011] Furthermore, a second circulation pump is installed at intervals on the liquid outlet pipe at the bottom of the electrolytic cell.

[0012] Furthermore, a liquid inlet pipe disposed inside the post-electrolysis liquid storage tank extends to the bottom of the post-electrolysis liquid storage tank.

[0013] The present invention also provides a method for preparing high-purity indium, which is used to prepare 8N-grade high-purity indium and comprises the following steps:

[0014] (1) Primary electrolytic refining: 4N refined indium ingots are cut into granules and cleaned, and then cast into anode plates using a mold. The cathode is a titanium plate. The anode and cathode are arranged in an electrolytic cell with a positive and negative pole distance of 20 mm to 25 mm. High-grade pure NaCl and high-grade pure gelatin are added, and In is prepared in the post-electrolysis liquid storage tank. 3+The electrolyte concentration is 100g / L-120g / L, the NaCl concentration is 70g / L-80g / L, the pH value is 2-2.5, and the current density is 50A / m 2 -60A / m 2 Indium is deposited at the cathode to obtain 5N grade refined indium;

[0015] (2) Vacuum distillation: The 5N grade refined indium obtained by the primary electrolytic refining is cleaned and placed in a cleaned vacuum furnace using a high-purity quartz crucible; 6N high-purity hydrogen is passed and vacuum is drawn, and the pressure in the vacuum furnace is maintained at 1-5 Pa for distillation. The distillation temperature is 850°C-950°C, and the current is adjusted to maintain a constant temperature for 60-150 minutes. After the constant temperature time is reached, the power is cut off, and the temperature drops below 100°C, the cooling water supply and vacuum drawing are stopped, and the vacuum furnace is opened to take out the obtained 6N grade refined indium and low-boiling-point substances;

[0016] (3) Secondary electrolytic refining: The 6N grade refined indium obtained by vacuum distillation is sheared into granules in the same manner as in step (1), cleaned and cast, and In is prepared in the post-electrolysis liquid storage tank using high-grade pure sulfuric acid, cleaned refined indium, high-grade pure NaCl and high-grade pure gelatin. 3+ The electrolyte concentration is 80g / L-100g / L, the NaCl concentration is 60g / L-70g / L, the pH value is 1.5-2.5, and the current density is 80-100A / m 2 Indium is deposited at the cathode to obtain 7N grade refined indium;

[0017] (4) Single crystal growth: The 7N grade refined indium obtained by secondary refining is cleaned and placed in a cleaned single crystal furnace. The single crystal furnace uses a high-purity quartz crucible, a sealed single crystal furnace, and 6N high-purity hydrogen and vacuum to grow single crystals to obtain 8N grade refined indium;

[0018] The electrolytic cell used for electrolytic refining in the steps (1) and (3) is any one of the multi-unit series-connected multi-stage electrolytic refining devices provided by the present invention.

[0019] Preferably, during the electrolytic refining process, the refined indium ingot is sheared into 1 cm particles, the refined indium is heated and cast in a mold, the anode is wrapped with a filter paper bag and then a polyester cloth bag, the vacuum distillation and single crystal growth are held in a high-purity quartz crucible for holding the refined indium, the inner wall of the quartz crucible is treated with a silicon-carbon film, and heating is performed by electromagnetic induction; the silicon-carbon film coating process uses a three-channel high-temperature resistant nozzle to spray argon protection, oxygen and silane combustion, and the silicon-carbon material produced by the combustion is directly sprayed on the inner wall of the crucible.

[0020] The beneficial effects of the present invention are:

[0021] 1. The loaded materials and equipment components that come into contact with the materials involved in the operation process are physically and chemically cleaned with high-purity cleaning fluids according to strict operating procedures. The operation of each unit in the work process is carried out in an ultra-clean work area, creating excellent prerequisites for the preparation of high-purity indium;

[0022] 2. According to the different characteristics of impurity types and contents of refined indium, a more scientific and reasonable process flow is adopted to remove the corresponding impurities as much as possible in each production unit in a targeted manner, and the materials used for each component, heat transfer method and various parameters in the control process are strictly optimized;

[0023] 3. Self-made electrolytic refining equipment is used to improve the material transmission from the equipment structure design to the greatest extent, so that the fluid transmission in the electrolytic refining liquid exchange process tends to flow regularly, forming a fast and stable transmission system, ensuring that the electrolytic refining unit plays the role of purification as much as possible;

[0024] 4. Two-stage electrolytic refining uses different process control parameters, which is more flexible and targeted in impurity removal;

[0025] 5. Compared with the currently widely used process of purifying indium by first low-temperature distillation and then high-temperature distillation, the present invention preferably uses and only uses low-temperature distillation in the vacuum distillation unit. The purpose is to reduce the pollution caused by the volatilization and re-condensation process of indium due to high-temperature distillation, especially to reduce the difficulty in removing indium caused by the adhesion of indium in the vacuum furnace hearth and the condensation chamber. A further effect is that it is easier to realize industrial process operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of electrolytic refining device from top view;

[0027] Figure 2 A schematic side view of an electrolytic refining unit;

[0028] Figure 3 Schematic diagram of the bottom plate holes;

[0029] Figure 4 8N high purity indium preparation process flow chart;

[0030] Among them: 1. liquid storage tank before electrolysis; 2. U-shaped trough; 3. liquid storage tank after electrolysis; 4. electrolytic cell; 5. first flow stabilizer; 51. second flow stabilizer; 6. first circulation pump; 61. second circulation pump; 7. movable cover plate; 8. tooth groove; 9. hole; 10. bottom plate; 11. independent space; 12. bottom plate hole; 13. pipeline; 131. liquid outlet pipe of liquid storage tank before electrolysis; 132. liquid outlet pipe of electrolytic cell; 133. liquid outlet pipe of liquid storage tank after electrolysis; 134. liquid inlet pipe of liquid storage tank after electrolysis. DETAILED DESCRIPTION

[0031] In each process of the present invention, the refined indium is strictly cleaned physically and chemically before entering the electrolytic refining, vacuum distillation, and single crystal growth unit. The specific operations are: cleaning with high-grade pure dilute nitric acid, high-grade pure dilute hydrochloric acid, ultra-clean water with a purity of 18 mega resistivity, high-grade pure methanol for dehydration, and high-purity nitrogen with a purity greater than 5N for drying (unless otherwise specified, the materials and equipment cleaning involved in the present invention are all cleaned in this manner, hereinafter referred to as cleaning);

[0032] The components of the vacuum furnace high-purity quartz crucible, furnace inner wall, electrolytic cell, single crystal growth crucible, quartz tube and the like that are in contact with indium are strictly cleaned; the electrolytic refining adopts the self-made specific electrolytic cell of the present invention, and each operation in the work flow is carried out in an ultra-clean working area.

[0033] The electrolytic refining of the present invention adopts a self-made specific electrolytic cell, the electrolytic cell adopts a liquid replacement method of upper liquid inlet and lower liquid outlet, and the front electrolytic pre-liquid storage tank is raised to increase the potential energy of the front liquid storage. When the electrolyte is inlet and transmitted, the potential energy is converted into kinetic energy to realize self-flow conduction; specifically, Figure 2 As shown, a multi-unit series multi-stage electrolytic refining device includes a pre-electrolysis liquid storage tank 1, an electrolytic cell 4, and a post-electrolysis liquid storage tank 3. The pre-electrolysis liquid storage tank 1 is connected to the upper part of the electrolytic cell 4, and the post-electrolysis liquid storage tank 3 is connected to the lower part of the electrolytic cell 4, forming a height difference between them. The outlet pipe 131 of the pre-electrolysis liquid storage tank is in the same plane as the liquid inlet of the electrolytic cell, and is connected by a U-shaped groove 2. At least three outlet pipes 131 are arranged at the outlet pipe opening at the bottom of the pre-electrolysis liquid storage tank, and a first flow stabilizer 5 is installed in the outlet pipe. The electrolyte flows to the U-shaped groove 2 through the outlet pipe 131, and then enters the electrolytic cell 4 from the U-shaped groove 2. The electrolyte flows out by itself through the flow transmission of the flat plate at the bottom of the U-shaped groove to gradually form a steady flow and enter the electrolytic cell, which reduces the acid volatilization caused by turbulence and the disordered stirring of the electrolyte in the electrolytic cell, and creates a more stable solution system for the electrolytic deposition of indium.

[0034] At least three liquid outlet pipes 132 are installed at the lower part of the electrolytic cell 4, which are connected to the post-electrolysis liquid storage tank 3 through pipelines, and a second flow stabilizer 51 is installed between the pipelines. The post-electrolysis liquid storage tank 3 and the pre-electrolysis liquid storage tank 1 are connected through pipelines, and a first circulation pump 6 is installed between the pipelines of the two liquid storage tanks. The pre-electrolysis liquid storage tank 1, the electrolytic cell 4, the post-electrolysis liquid storage tank 3, and the first circulation pump 6 are connected through pipelines and U-shaped grooves to form an electrolytic refining circulation system.

[0035] like Figure 1As shown, the electrolytic cell is equipped with a flow-stabilizing movable cover plate 7, which fits tightly with the edges of the U-shaped groove 2 and the electrolytic cell 4. The ideal state is seamless connection, so anti-corrosion rubber or silicone can be used to wrap the movable cover plate. The edge of the flow-stabilizing movable cover plate 7 has regularly arranged tooth grooves 8, and the size of the tooth grooves 8 is preferably such that the plate hanging ears are completely inserted. The function is to regulate the arrangement of the positive and negative plates so that the same pole distance and the positive and negative pole distance are controlled at the specified value. There are several holes regularly arranged on the flow-stabilizing movable cover plate, and the holes are arranged in a straight line between the positive and negative plates. The function is to regulate the flow direction of the electrolyte entering the electrolytic cell. The regularized electrolyte fluid flows evenly from top to bottom between the positive and negative plates.

[0036] like Figure 2 As shown, the electrolytic cell is equipped with a bottom plate 10, and the bottom plate 10 is sloped (0 。 -15 。 ) is inclined toward the liquid outlet and installed above the liquid outlet at the bottom of the electrolytic cell 4. The bottom plate holes 12 are arranged on the plate, and the arrangement is consistent with the holes 9 on the movable cover plate 7. The role of installing the bottom plate: First, the electrolyte fluid coming out of the liquid storage tank through the flow stabilization device before electrolysis is regarded as laminar flow motion. The fluid doing laminar flow motion separates a layer each time it flows through a row of holes, until the top layer of fluid flows out through the last row of holes. The holes in the bottom plate correspond to the holes in the cover plate, which ensures the smooth progress of the laminar flow. Second, an independent space 11 is separated in the lower part of the electrolytic cell, so that the independent space becomes an extension of the liquid inlet of the circulating pump. The electrolyte in the independent space is subjected to the force generated by the suction of the circulating pump to promote fluid transmission. The suction force on the laminar flow close to the pump end is stronger than the suction force on the laminar flow far away from the pump end. The suction overcomes the friction force, further prompting each layer of fluid to move at a uniform speed.

[0037] like Figure 3 As shown, the bottom plate 10 has a certain thickness, and the bottom plate hole 12 is in the shape of an inverted trapezoid with a larger upper part and a smaller lower part. The purpose of adopting this design is to form a force expansion for the pump suction force, and to target and solve the problem of transferring the flocs formed during the electrolysis process, so that it can be better transmitted to the rear section along with the fluid, further avoiding the deposition of flocs on the anode and cathode plates, reducing the purity reduction caused by the increased indium inclusions deposited on the cathode plate, and avoiding the anode passivation caused by the increase of the anode plate potential.

[0038] The outlet of the electrolytic cell 4 is combined with the industrial operation site of electrolytic refining of indium, and two liquid discharge methods are set. One is the gravity outlet. The number of gravity outlet pipes 132 is equal to the number of gravity outlet pipes 131 at the bottom of the liquid storage tank before electrolysis (i.e., the number of gravity inlet ports). In order to achieve the equal amount of liquid inflow and liquid outflow during the stable electrolysis, and to ensure the smooth liquid replacement of the electrolysis system, their sizes are equal; the second is the installation of the outlet pipe of the second circulating pump 61. The number of the outlet pipes of the second circulating pump 61 is arranged at intervals between the gravity outlet pipes 132. The function is to suck the floccules and other impurities generated during the electrolysis process that are not easy to be removed by gravity, improve the environment of the electrolytic system, and make the electrolytic deposition of indium tend to be stable and benign. The electrolyte flowing out of the two liquid discharge methods is connected to the liquid storage tank after electrolysis through a liquid infusion pipeline.

[0039] The post-electrolysis liquid storage tank adopts the bottom-in-top-out method, that is, the liquid inlet pipe 134 placed inside the post-electrolysis liquid storage tank extends to the bottom of the tank below the liquid surface, and the liquid outlet pipe 133 of the post-electrolysis liquid storage tank is placed on the upper part of the tank body. The bottom-in-top-out method reduces the contact area between the electrolyte and the air during conduction, reduces the acid volatilization caused by the generation of bubbles in the electrolyte, and improves the working environment of the operator. The post-electrolysis liquid storage tank also has the function of a liquid preparation tank, that is, according to the changes in the electrolysis process, the electrolyte composition is adjusted within the specified operating parameters, such as In 3+ The concentration, NaCl concentration, pH value, gelatin content and other indicators are adjusted to make the electrolysis process stable.

[0040] The electrolytic cell prepared above is used for the electrolytic refining step in the 8N high-purity indium preparation process. The specific preparation steps are as follows:

[0041] 1. As shown in the process flow chart, 4N refined indium is used to prepare high-purity indium, including electrolytic refining, vacuum distillation, and single crystal growth operation procedures;

[0042] 2. Use diluted hydrochloric acid prepared with analytical grade hydrochloric acid to rinse the purchased refined indium. The cleaning equipment is a high-pressure water jet cleaning machine. After rinsing, use high-grade pure methanol to dehydrate and high-purity nitrogen with a purity greater than 5N to blow dry for later use;

[0043] 3. Cut the refined indium ingot into particles with a diameter of about 1 cm and clean them;

[0044] 4. Clean the mold for casting the anode plate and the titanium plate used as the cathode;

[0045] 5. The cleaned refined indium is heated and cast in the mold, and the anode is first wrapped with a filter paper bag and then with a polyester cloth bag;

[0046] 6. Clean the inside of the electrolytic cell first and then the outside of the cell, and then arrange the anode and cathode in the electrolytic cell (3) with a positive and negative pole distance of 20 mm to 25 mm, preferably 22 mm;

[0047] 7. Use high-grade pure sulfuric acid to dissolve the cleaned refined indium, add high-grade pure NaCl and high-grade pure gelatin, and prepare In in the post-electrolysis liquid storage tank (16). 3+ The electrolyte has a concentration of 100g / L-120g / L, a NaCl concentration of 70g / L-80g / L, and a pH value of 2-2.5. At this time, the electrolyte contains a lot of metal impurities such as Pb, Sn, Sb, Cu, Ni, Ag, etc. whose electrode potential is higher than that of indium, and the current density is 50A / m 2 -60A / m 2 Indium is deposited at the cathode, preferably fixed at 56A / m 2 . The pH of the electrolyte is prepared at a lower level in this operation in order to promote some insoluble metals and oxides in the anode plate to enter the electrolyte. Furthermore, a weak electric field is formed by a low-density current. A large part of the metal impurities with a more positive electrode potential than indium sink into the anode mud near the anode, and another small part of the impurities are deposited on the cathode with indium due to the weak electric field. The electrolyte is purified and deposited on the cathode together with indium. The impurities deposited on the cathode are easier to remove in the next step of vacuum distillation. In this process, since refined indium contains relatively more impurities, it is easy to form flocs between the anode and cathode plates. The flocs will absorb impurities in the electrolyte and adhere to the anode and cathode plates, affecting the smooth progress of electrolysis. Therefore, once some abnormal conditions such as increased cell voltage or (and) the indium deposited on the cathode is found, on the basis of rigorous analysis, the second circulation pump in front of the liquid outlet of the electrolytic cell can be opened to promote the discharge of the electrolyte faster than gravity, and acid adjustment or current density adjustment can be performed in the liquid storage tank after electrolysis.

[0048] 8. Clean the refined indium obtained after the first-level electrolytic refining.

[0049] 9. After the refined indium is cleaned, it is placed in a vacuum furnace. The vacuum furnace uses a high-purity quartz crucible to coat the inner wall of the crucible with a silicon-carbon film and complete the cleaning in an ultra-clean working area. The silicon-carbon film coating process uses a three-channel high-temperature resistant nozzle to spray argon protection, oxygen and silane combustion. The silicon-carbon material produced by the combustion is directly sprayed on the inner wall of the crucible, and the heating is carried out by electromagnetic induction.

[0050] 10. Load the materials, seal the vacuum furnace, and then start to pass 6N high-purity hydrogen and evacuate. When the vacuum degree reaches the process requirements, turn on the cooling circulating water, close the heating power switch, adjust the electrical control equipment, and gradually raise the furnace temperature to the distillation temperature (850℃-950℃). The pressure in the vacuum furnace is maintained at 1-5Pa, and the current is adjusted to keep the constant temperature for 60-150 minutes, preferably 100 minutes. Passing 6N high-purity hydrogen keeps the vacuum furnace in a reducing atmosphere to prevent indium from being oxidized by oxygen in the air under high temperature conditions. It can also reduce the oxidized indium. At the same time, it can also react with impurities such as As in indium that are easily reactive with H2 to generate volatile substances such as AsH3, which plays a role in further purifying indium. This operation belongs to the common low-temperature distillation for vacuum distillation purification of indium. The present invention only selects this distillation section. The purpose is to achieve the impurity removal effect while reducing the pollution caused by the volatilization and re-condensation process of indium using the high-temperature section (1050°C-1075°C) distillation, especially reducing the difficulty in removing indium caused by the adhesion of indium in the vacuum furnace hearth and the condensation chamber. A further effect is to shorten the indium travel and distillation time, shorten or avoid the contact between indium and other substances, and make it easier to realize industrial process operation.

[0051] 11. After the constant temperature time is reached, adjust the current and voltage to zero, turn off the power switch, cool down, and let the vacuum pump continue to work. When the temperature drops below 100°C, stop supplying cooling water and vacuuming, open the vacuum furnace and take out the refined indium and low-boiling-point substances;

[0052] 12. The obtained refined indium is cut into particles with a diameter of about 1 cm and cleaned;

[0053] 13. The cleaned refined indium is heated and cast in the cleaned mold, and the anode is first wrapped with a filter paper bag and then with a polyester cloth bag;

[0054] 14. Use high-grade pure sulfuric acid, cleaned refined indium, high-grade pure NaCl and high-grade pure gelatin to prepare In in the post-electrolysis liquid storage tank. 3+ The electrolyte concentration is 80g / L-100g / L, the NaCl concentration is 60g / L-70g / L, and the pH value is 1.5-2.5. At this time, the electrolyte contains more metal impurities such as Al, Zn, Ga, Fe, etc. whose electrode potential is lower than that of indium. The current density is 80-100A / m 2 Indium is deposited at the cathode, preferably fixed at 100 A / m 2. This process uses a stronger electric field formed by a higher density current. Metal impurities with an electrode potential more positive than indium sink into the anode mud near the anode, and some metal impurities with an electrode potential more negative than indium enter the electrolyte, while the other part is deposited at the cathode together with indium. Impurities deposited at the cathode are easier to remove in the next step of single crystal growth. This secondary electrolytic refining can also refer to the primary electrolytic refining for rapid liquid replacement and acid adjustment and liquid preparation in the post-electrolysis liquid storage tank, or adjust the current density according to actual conditions to ensure the smooth progress of electrolytic deposition of indium.

[0055] 15. After the refined indium obtained from the secondary electrolytic refining is cleaned and put into the single crystal furnace, the single crystal furnace uses a high-purity quartz crucible to complete silicon-carbon film coating and cleaning in the ultra-clean working area;

[0056] 16. Fill the material, seal the single crystal furnace, and then start to pass 6N high-purity hydrogen and evacuate. When the vacuum degree reaches the process requirements, turn on the cooling circulating water, close the heating power switch, adjust the electrical control equipment, and gradually raise the furnace temperature to the indium single crystal pulling temperature to start pulling the single crystal. Passing 6N high-purity hydrogen keeps the vacuum furnace in a reducing atmosphere to prevent indium from being oxidized by oxygen in the air in a molten state. It can also reduce the oxidized indium. At the same time, it can also generate volatile substances such as AsH3 with impurities such as As in indium that are easily reacted with H2, which plays a role in further purifying indium. This operation belongs to the common operation process of purifying indium using single crystal growth technology. In the process of using this operation as a purification unit, the present invention strictly follows the operation steps to ensure that the growth process is in a protective and reducing atmosphere, and reduces the indium stroke as much as possible and uses silicon-coated carbon barriers to further avoid the introduction of impurities caused by contact with objects.

[0057] 17. After the single crystal is pulled, the crystal rod is tested, and the unqualified section is cut off and returned to the vacuum furnace for refining system for re-refining, or sold as a 6-7N product. The qualified section is 8N and above high-purity indium.

Claims

1. A method for preparing high-purity indium, characterized in that: The following steps are involved: (1) Primary electrolytic refining: 4N refined indium ingots are cut into granules and cleaned, and then cast into anode plates using a mold. The cathode is a titanium plate. The anode and cathode are arranged in an electrolytic cell with a positive and negative pole distance of 20 mm to 25 mm. High-grade pure NaCl and high-grade pure gelatin are added, and In is prepared in the liquid storage tank after electrolysis. 3+ The electrolyte concentration is 100g / L-120g / L, the NaCl concentration is 70g / L-80g / L, the pH value is 2-2.5, and the current density is 50A / m 2 -60A / m 2 Indium is deposited at the cathode to obtain 5N grade refined indium; (2) Vacuum distillation: The 5N grade refined indium obtained from the primary electrolytic refining is cleaned and placed in a cleaned vacuum furnace using a high-purity quartz crucible; 6N high-purity hydrogen is passed and vacuumed, and the pressure in the vacuum furnace is maintained at 1-5 Pa for distillation. The distillation temperature is 850°C-950°C, and the current is adjusted to maintain a constant temperature for 60-150 minutes. After the constant temperature time is reached, the power is cut off, and the temperature drops below 100°C, the cooling water supply and vacuuming are stopped, and the vacuum furnace is opened to take out the obtained 6N grade refined indium and low-boiling-point substances; (3) Secondary electrolytic refining: The 6N grade refined indium obtained by vacuum distillation is sheared into particles in the same manner as in step (1), cleaned and cast, and In is prepared in the post-electrolysis liquid storage tank using high-grade pure sulfuric acid, cleaned refined indium, high-grade pure NaCl and high-grade pure gelatin. 3+ The electrolyte concentration is 80g / L-100g / L, the NaCl concentration is 60g / L-70g / L, the pH value is 1.5-2.5, and the current density is 80-100A / m 2 Indium is deposited at the cathode to obtain 7N grade refined indium; (4) Single crystal growth: The 7N grade refined indium obtained from the secondary refining is cleaned and placed in a cleaned single crystal furnace. The single crystal furnace uses a high-purity quartz crucible, a sealed single crystal furnace, and 6N high-purity hydrogen and vacuum to grow single crystals to obtain 8N grade refined indium; The electrolytic cell used for electrolytic refining in steps (1) and (3) is a multi-unit series multi-stage electrolytic refining device; The multi-unit series multi-stage electrolytic refining device comprises a pre-electrolysis liquid storage tank, an electrolytic tank, and a post-electrolysis liquid storage tank. The pre-electrolysis liquid storage tank is connected to the upper part of the electrolytic tank, and the post-electrolysis liquid storage tank is connected to the lower part of the electrolytic tank, forming a height difference between them. The outlet of the pre-electrolysis liquid storage tank and the inlet of the electrolytic tank are in the same plane and are connected by a U-shaped groove. At least three outlet pipes are arranged at the outlet of the bottom of the pre-electrolysis liquid storage tank, and a first flow stabilizer is installed in the outlet pipe. The electrolyte flows to the U-shaped trough through the liquid outlet pipe, and then enters the electrolytic cell from the U-shaped trough. At least three liquid outlet pipes are installed at the lower part of the electrolytic cell, which are connected to the post-electrolysis liquid storage tank through pipelines. A second flow stabilizer is installed between the pipelines. The post-electrolysis liquid storage tank and the pre-electrolysis liquid storage tank are connected through pipelines. A first circulation pump is installed between the pipelines of the two liquid storage tanks. The pre-electrolysis liquid storage tank, the electrolytic cell, the post-electrolysis liquid storage tank, and the first circulation pump are connected to the U-shaped trough through pipelines to form an electrolytic refining circulation system; The electrolytic cell is provided with a movable cover, which is tightly fitted with the U-shaped groove and the edge of the electrolytic cell. Two rows of tooth grooves are symmetrically arranged on the edge of the movable cover, and the size of the tooth groove is not less than the size of the plate hanging ears placed therein; A plurality of holes are arranged on the movable cover plate.

2. The method according to claim 1, characterized in that A bottom plate is installed on the top of the liquid outlet pipe of the electrolytic cell. The bottom plate is sloped with an inclination angle of 0 to 15 degrees. An independent space is formed between the bottom plate and the bottom of the electrolytic cell. Holes are arranged on the bottom plate in the same manner as the movable cover.

3. The method according to claim 2, characterized in that The bottom plate hole shape is an inverted trapezoid.

4. The method according to claim 1, characterized in that The number and size of the liquid outlet pipe openings at the bottom of the liquid storage tank before electrolysis and the liquid outlet pipe openings at the bottom of the electrolytic tank are the same.

5. The method according to claim 1, characterized in that A second circulation pump is installed at intervals on the liquid outlet pipe at the bottom of the electrolytic tank.

6. The method according to claim 1, characterized in that The liquid inlet pipe disposed inside the post-electrolysis liquid storage tank extends to the bottom of the post-electrolysis liquid storage tank.

7. The method according to claim 1, characterized in that During the electrolytic refining process, the refined indium ingot is cut into 1 cm particles, the refined indium is heated and cast in a mold, the anode is wrapped with a filter paper bag and then a polyester bag, the vacuum distillation and single crystal growth are held in a high-purity quartz crucible for the refined indium, the inner wall of the quartz crucible is treated with a silicon-carbon film, and the heating is carried out by electromagnetic induction; the silicon-carbon film coating process uses a three-channel high-temperature resistant nozzle to spray argon protection, oxygen and silane combustion, and the silicon-carbon material produced by the combustion is directly sprayed on the inner wall of the crucible.

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