Method for extracting metal indium and tin through molten salt electrolysis of ITO

Abstract

The invention belongs to the technical field of rare metal separation and extraction, and particularly relates to a method for extracting metal indium and tin by molten salt electrolysis of ITO (indium tin oxide), which comprises the following steps of: filling pretreated ITO into a graphite crucible, connecting with a metal tungsten rod to prepare an anode, and directly electrolyzing in chloride molten salt, and enabling indium and tin ions dissociated from the oxide to enter the fused salt, and migrating to a cathode to be reduced into metal indium and tin. The method for extracting the metal indium and tin from the ITO has the advantages of being wide in raw material adaptability, short in technological process, low in treatment cost, high in metal recovery rate and purity and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of separation and extraction of rare metals, and in particular relates to a method for extracting metallic indium and tin by electrolyzing ITO with molten salt. Background Art

[0002] Indium is widely used in high-tech fields such as the electronics industry, aerospace, alloy manufacturing, and new materials. It is an indispensable strategic key metal for the development of modern industry, national defense, and cutting-edge technology. As a rare metal, the content of indium in the earth's crust is very low and its distribution is extremely dispersed. No independent indium mine has been found so far, and it is mostly associated with heavy non-ferrous metal minerals such as zinc, lead, and copper. In recent years, with the rapid development of the electronic information industry, the demand for indium has risen sharply, making the supply of primary indium in short supply. Therefore, extracting and recovering metallic indium from indium-containing secondary resources is of great significance to alleviating the shortage of primary indium supply.

[0003] At present, about 70% of the world's indium is used to produce ITO targets (used in electronic displays, liquid crystal displays, photovoltaic cells, smart phones and other fields). ITO is indium tin oxide, in which the indium oxide content is as high as 90%. Therefore, ITO waste targets, scraps generated during the production of ITO targets, and waste ITO separated from discarded electronic products have become an important secondary resource of indium. In this context, the development of economical and efficient ITO indium extraction technology is particularly important to ensure the stable and sustainable development of my country's indium industry.

[0004] At present, the main method for separating and extracting metallic indium and tin from waste ITO is high-temperature thermal reduction.

[0005] In the technologies disclosed in the Chinese patent documents with publication numbers CN112359243B, CN109957655A, CN104032133A, and CN104711426B, non-metals such as carbon monoxide, hydrogen, carbon powder, or starch are used as reducing agents to deoxidize and reduce ITO waste targets at high temperatures above 1000°C to obtain high-quality indium tin alloys. However, the above reduction reaction can only occur under high temperature conditions, and the energy consumption and equipment maintenance costs are high. In addition, the Chinese patent document with publication number CN110042229A discloses a method for recovering metallic indium from ITO waste targets, using active metals such as lithium, magnesium, aluminum, calcium, and titanium as reducing agents to recover indium tin alloys from ITO waste targets. The metal thermal reduction process needs to be carried out under high temperature and vacuum conditions, which not only has high energy consumption and strict equipment requirements, but also the metal reducing agent is expensive, which increases the recovery cost.

[0006] A Chinese patent document with publication number CN101701340A discloses a method for preparing indium tin alloy by electrolysis in an aqueous solution using an ITO waste target as the cathode. However, the electrochemical window of the aqueous solution system is narrow, and hydrogen and oxygen evolution side reactions are prone to occur, making it difficult to achieve efficient cathode electro-deoxidation reduction of the ITO waste target. A Chinese patent document with publication number CN111809050A also discloses a method for recovering ITO waste targets by electrolysis of an aqueous solution, in which the ITO waste targets are treated in a split electrolytic cell connected by a salt bridge, and indium is recovered through a two-stage electrolysis process. However, the ion composition and pH value of the cathode and anode regions need to be strictly controlled during the electrolysis process, and ultrasonic assistance is required. Not only is the process complicated, but it also places high demands on the equipment.

[0007] Indium and tin from waste ITO can also be recovered by molten salt electrochemical methods. A Chinese patent document with publication number CN108754544A discloses a method for recovering crude indium from waste ITO powder using molten salt electrochemical methods. In this application, graphite is used as an anode and molten metal indium or tin is used as a liquid cathode. The ITO sintered sheet obtained by high-temperature sintering is suspended in a mixed electrolyte of lithium chloride and potassium chloride for molten salt electrolysis, and an indium-tin alloy is obtained inside the liquid metal cathode. However, the solubility and dissolution rate of ITO in chloride molten salt are both low, which limits the efficiency of the electrolysis process. A Chinese patent document with publication number CN115261930A provides a method for efficiently separating and recovering indium and tin from ITO waste targets based on molten salt electrochemistry. The indium-tin alloy is prepared in one step by molten salt electrolysis directly using ITO waste target blocks as cathodes, and in situ electrochemical separation of indium and tin is carried out in the same system, and high-purity metal indium and tin are obtained at the cathode and anode, respectively. The technology provided by this invention has the characteristics of simple process, low energy consumption, low reagent consumption, and high indium tin recovery rate. It is suitable for recovering indium and tin from bulk ITO (such as ITO waste targets); if it is scraps in the production of ITO targets or waste powder separated from discarded electronic products, it needs to be burned into blocks before it can be recycled through this method. Summary of the invention

[0008] The present invention provides a method for extracting metallic indium and tin by molten salt electrolysis of ITO, aiming to overcome the problems of high energy consumption and high cost in the existing high-temperature thermal reduction technology, overcome the problems of long process flow, high equipment requirements, low electrolysis efficiency, etc. in the aqueous solution electrolysis technology, and solve the problem of low efficiency caused by the solubility and dissolution rate of ITO in traditional molten salt electrolysis, as well as the problem that solid cathode molten salt electrolysis has poor adaptability to raw materials.

[0009] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0010] A method for extracting metallic indium and tin by molten salt electrolysis of ITO, wherein pretreated ITO is placed in a graphite crucible, connected to a tungsten rod to form an anode, and then electrolyzed directly in a chloride molten salt, so that indium and tin ions dissociated from the oxide enter the molten salt and migrate to the cathode to be reduced to metallic indium and tin.

[0011] Furthermore, the method for extracting metallic indium and tin by molten salt electrolysis of ITO as described above specifically comprises the following steps:

[0012] 1) ITO pretreatment: Take powdered ITO with a particle size of less than 0.5 mm, and then heat it to above 200°C to remove moisture and volatile impurities;

[0013] 2) Preparation of molten salt: taking dried alkali metal or alkaline earth metal mixed chloride in proportion, mixing well and placing in a corundum crucible, heating to melt to obtain chloride molten salt;

[0014] 3) Molten salt electrolysis: The pretreated ITO obtained in step 1) is placed in a small graphite crucible, which is connected to a tungsten rod to form an anode, and a metal rod is used as a cathode. Electrolysis is performed in the chloride molten salt obtained in step 2), and finally metal indium and tin are obtained at the cathode.

[0015] Furthermore, in step 1), the sources of powdered ITO include but are not limited to analytically pure indium tin oxide, ITO waste targets, and ITO waste powder recovered from electronic products, and the purity thereof is above 98%.

[0016] Furthermore, in step 2), the mixed chlorides are any two chlorides selected from anhydrous LiCl, NaCl, KCl, MgCl2, CaCl2, and BaCl2, and their purity is above 99.9%.

[0017] Furthermore, in step 2), the ratio of the mixed chlorides is the eutectic ratio of the two chlorides.

[0018] Furthermore, in step 2), the alkali metal or alkaline earth metal chloride needs to be vacuum dried at 200° C. for more than 24 hours before use to remove adsorbed water therein.

[0019] Furthermore, in step 3), the graphite crucible is made of high-purity graphite, and the material of the cathode metal rod is tungsten, molybdenum or iron.

[0020] Furthermore, both step 2) and step 3) are carried out under the protection of high-purity argon, and the heating temperature in step 2) is consistent with the electrolysis temperature in step 3), which is 50 to 100° C. above the eutectic point of the binary chloride mixed system.

[0021] Furthermore, in step 3), the cell voltage of the molten salt electrolysis is 2.2 to 3.5V.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention provides a method for extracting metallic indium and tin by molten salt electrolysis of ITO, which directly uses ITO powder as a raw material for molten salt electrolysis, so that indium ions and tin ions are dissociated at the anode and migrate to the cathode for reduction to metallic indium and tin. It avoids the shortcomings of traditional high-temperature thermal reduction process in terms of energy consumption and high equipment requirements, as well as the long process flow and low efficiency of wet leaching process, and has the remarkable characteristics of simple operation and low cost.

[0024] 2. The present invention provides a method for extracting metallic indium and tin by molten salt electrolysis of ITO, wherein ITO is subjected to anodic electrolysis in a chloride molten salt, so that indium and tin enter the molten salt in the form of ions and migrate to the cathode for reduction into metal precipitation. The method of the present invention not only avoids the problem of slow reaction caused by the low solubility of ITO in chloride in the traditional molten salt electrolysis process, but also overcomes the problem of incomplete deoxidation reaction caused by metal covering the oxide surface in solid cathode electrolysis, and has the advantages of fast electrolysis rate and high efficiency.

[0025] 3. The present invention provides a method for extracting metal indium and tin from ITO by molten salt electrolysis. Not only can metal indium and tin be extracted from powdered ITO (such as ITO waste powder separated from discarded electronic devices), but also blocky ITO (such as ITO waste targets and scraps generated during ITO target material processing) can be recycled by this method after simple crushing. Therefore, the technology for extracting metal indium and tin from ITO provided by the present invention has strong adaptability to raw materials.

[0026] 4. The present invention provides a method for extracting metallic indium and tin from ITO by molten salt electrolysis, which makes full use of the good conductivity of ITO and can extract metallic indium and tin through one-step electrolysis. The entire electrolysis process does not consume other chemical reagents, does not introduce new impurities, does not generate waste residue, wastewater and waste pollution, and has high product recovery rate and purity.

[0027] Of course, any product implementing the present invention does not necessarily need to achieve all of the above advantages at the same time. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The present invention provides a method for extracting metallic indium and tin by electrolyzing ITO in molten salt, wherein the pretreated ITO powder is loaded into a graphite crucible, connected to a tungsten rod to form an anode, and then electrolyzed directly in a chloride molten salt, so that the indium and tin ions dissociated from the oxide enter the molten salt, migrate to the cathode and are reduced to metallic indium and tin. The technical solution of the present invention makes full use of the good electrical conductivity of ITO, so that indium ions and tin ions are dissociated at the anode, and migrate to the cathode to be reduced to metallic indium and tin, and has the characteristics of short process, strong raw material adaptability, low cost, high metal recovery rate and purity, clean and environmentally friendly, etc.

[0030] The processing technology of the present invention specifically comprises the following steps:

[0031] 1) ITO pretreatment: Take powdered ITO with a particle size of less than 0.5 mm, and then heat it to above 200°C to remove moisture and volatile impurities;

[0032] 2) preparing molten salt: taking binary mixed chlorides of alkali metals or alkaline earth metals dried at 200° C. in vacuum for more than 24 hours in proportion, mixing them evenly and placing them in a corundum crucible, and heating them in a high-purity argon atmosphere to 50 to 100° C. above the eutectic point of the binary chloride system to obtain a chloride mixed molten salt;

[0033] 3) Molten salt electrolysis: The pretreated ITO obtained in step 1) is placed in a small graphite crucible, which is connected to a tungsten rod to form an anode, and metal tungsten, molybdenum or iron rod is used as a cathode. The cell voltage is controlled at 2.2 to 3.5 V in the chloride mixed molten salt obtained in step 2), and constant voltage electrolysis is performed to finally obtain metal indium and tin at the cathode.

[0034] The present invention is further described below in conjunction with specific embodiments.

[0035] Example 1

[0036] This embodiment provides a method for extracting metal indium and tin by molten salt electrolysis of ITO, which specifically includes the following steps:

[0037] 1) ITO pretreatment: Take analytical pure ITO reagent with a purity of 99.5% and a particle size of about 0.1 mm, and heat it to 300°C to remove moisture and volatile impurities;

[0038] 2) Preparation of molten salt: weigh 70.1 g of powdered NaCl and 89.4 g of KCl which had been vacuum dried at 200° C. for 48 h, mix them well and place them in a corundum crucible, and heat them to 740° C. in a high-purity argon atmosphere to obtain a chloride mixed molten salt;

[0039] 3) Molten salt electrolysis: 3.4 g of the pretreated ITO powder obtained in step 1) is placed in a small graphite crucible, the graphite crucible is connected to a tungsten rod to form an anode, and a metal molybdenum rod is used as a cathode. The cell voltage is controlled to be 3.0 V in the chloride mixed molten salt obtained in step 2), and constant voltage electrolysis is performed at 740°C to finally obtain metal indium and tin at the cathode.

[0040] By using the method of this embodiment, it was found that the metal obtained from the cathode was composed of metal In and Sn, and the total content of the two reached 99.52%.

[0041] Example 2

[0042] This embodiment provides a method for extracting metal indium and tin by molten salt electrolysis of ITO, which specifically includes the following steps:

[0043] 1) ITO pretreatment: Take the ITO waste target with a purity of 98.8% and a particle size of about 0.5 mm, and heat it to 450°C to remove the moisture and volatile impurities therein;

[0044] 2) Preparation of molten salt: weigh 71.2 g of powdered LiCl and 83.4 g of KCl which had been vacuum dried at 200° C. for 36 h, mix them well and place them in a corundum crucible, and heat them to 450° C. in a high-purity argon atmosphere to obtain a chloride mixed molten salt;

[0045] 3) Molten salt electrolysis: 3.8 g of the pretreated ITO powder obtained in step 1) is placed in a small graphite crucible, the graphite crucible is connected to a tungsten rod to form an anode, and a metal tungsten rod is used as a cathode. The cell voltage is controlled to be 3.5 V in the chloride mixed molten salt obtained in step 2), and constant voltage electrolysis is performed at 450°C to finally obtain metal indium and tin at the cathode.

[0046] By using the method of this embodiment, it was found that the metal obtained from the cathode was composed of metal In and Sn, and the total content of the two reached 99.36%.

[0047] Example 3

[0048] This embodiment provides a method for extracting metal indium and tin by molten salt electrolysis of ITO, which specifically includes the following steps:

[0049] 1) ITO pretreatment: Take waste ITO powder with a purity of 98% and a particle size of about 0.15 mm, heat it to 600°C to remove moisture and volatile impurities;

[0050] 2) Preparation of molten salt: weigh 108.3 g of powdered BaCl2 and 45.6 g of NaCl that have been vacuum dried at 200°C for 50 h, mix them well and place them in a corundum crucible, and heat them to 710°C in a high-purity argon atmosphere to obtain a chloride mixed molten salt;

[0051] 3) Molten salt electrolysis: 3.5 g of the pretreated ITO powder obtained in step 1) is placed in a small graphite crucible, the graphite crucible is connected to a tungsten rod to form an anode, and a metal iron rod is used as a cathode. The cell voltage is controlled to be 3.2 V in the chloride mixed molten salt obtained in step 2), and constant voltage electrolysis is performed at 710°C to finally obtain metal indium and tin at the cathode.

[0052] By using the method of this embodiment, it was found that the metal obtained from the cathode was composed of metal In and Sn, and the total content of the two reached 99.05%.

[0053] Example 4

[0054] This embodiment provides a method for extracting metal indium and tin by molten salt electrolysis of ITO, which specifically includes the following steps:

[0055] 1) ITO pretreatment: Take the ITO waste target with a purity of 99.1% and a particle size of about 0.4 mm, and heat it to 500°C to remove the moisture and volatile impurities therein;

[0056] 2) Preparation of molten salt: weigh 97.1 g of powdered CaCl2 and 68.9 g of NaCl that have been vacuum dried at 200°C for 45 h, mix them well and place them in a corundum crucible, and heat them to 570°C in a high-purity argon atmosphere to obtain a chloride mixed molten salt;

[0057] 3) Molten salt electrolysis: 3.9 g of the pretreated ITO powder obtained in step 1) is placed in a small graphite crucible, the graphite crucible is connected to a tungsten rod to form an anode, and a metal tungsten rod is used as a cathode. The cell voltage is controlled to be 2.8 V in the chloride mixed molten salt obtained in step 2), and constant voltage electrolysis is performed at 570°C to finally obtain metal indium and tin at the cathode.

[0058] By using the method of this embodiment, it was found that the metal obtained from the cathode was composed of metal In and Sn, and the total content of the two reached 99.28%.

[0059] Example 5

[0060] This embodiment provides a method for extracting metal indium and tin by molten salt electrolysis of ITO, which specifically includes the following steps:

[0061] 1) ITO pretreatment: Take analytical pure ITO reagent with a purity of 99.5% and a particle size of about 0.1 mm, and heat it to 300°C to remove moisture and volatile impurities;

[0062] 2) Preparation of molten salt: weigh 90.1 g of powdered MgCl2 and 73.2 g of NaCl that have been vacuum dried at 200°C for 24 h, mix them well and place them in a corundum crucible, and heat them to 540°C in a high-purity argon atmosphere to obtain a chloride mixed molten salt;

[0063] 3) Molten salt electrolysis: 3.2 g of the pretreated ITO powder obtained in step 1) is placed in a small graphite crucible, the graphite crucible is connected to a tungsten rod to form an anode, and a metal molybdenum rod is used as a cathode. The cell voltage is controlled to be 2.2 V in the chloride mixed molten salt obtained in step 2), and constant voltage electrolysis is performed at 540°C to finally obtain metal indium and tin at the cathode.

[0064] By using the method of this embodiment, it was detected that the composition of the metal obtained from the cathode was metal In and Sn, and the total content of the two reached 99.41%.

[0065] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for extracting metallic indium and tin by molten salt electrolysis of ITO, characterized in that: The pretreated ITO is placed in a graphite crucible, connected to a tungsten rod to form an anode, and then electrolyzed directly in a chloride molten salt, so that the indium and tin ions dissociated from the oxide enter the molten salt and migrate to the cathode to be reduced to metallic indium and tin.

2. The method for extracting metallic indium and tin by molten salt electrolysis of ITO according to claim 1, characterized in that: The specific steps include: 1) ITO pretreatment: Take powdered ITO with a particle size of less than 0.5 mm, and then heat it to above 200°C to remove moisture and volatile impurities; 2) Preparation of molten salt: taking dried alkali metal or alkaline earth metal mixed chloride in proportion, mixing well and placing in a corundum crucible, heating to melt to obtain chloride molten salt; 3) Molten salt electrolysis: The pretreated ITO obtained in step 1) is placed in a small graphite crucible, which is connected to a tungsten rod to form an anode, and a metal rod is used as a cathode. Electrolysis is performed in the chloride molten salt obtained in step 2), and finally metal indium and tin are obtained at the cathode.

3. The method for extracting metallic indium and tin by molten salt electrolysis of ITO according to claim 2, characterized in that: In step 1), the sources of powdered ITO include but are not limited to analytically pure indium tin oxide, ITO waste targets, and ITO waste powder recovered from electronic products, and the purity thereof is above 98%.

4. The method for extracting metallic indium and tin by molten salt electrolysis of ITO according to claim 2, characterized in that: In step 2), the mixed chlorides are any two chlorides selected from anhydrous LiCl, NaCl, KCl, MgCl2, CaCl2, and BaCl2, and the purity of the mixed chlorides is above 99.9%.

5. The method for extracting metallic indium and tin by molten salt electrolysis of ITO according to claim 4, characterized in that: In step 2), the ratio of the mixed chlorides is the eutectic ratio of the two chlorides.

6. The method for extracting metallic indium and tin by molten salt electrolysis of ITO according to claim 2, characterized in that: In step 2), the alkali metal or alkaline earth metal chloride needs to be vacuum dried at 200° C. for more than 24 hours before use to remove adsorbed water therein.

7. The method for extracting metallic indium and tin by molten salt electrolysis of ITO according to claim 2, characterized in that: In step 3), the graphite crucible is made of high-purity graphite, and the material of the cathode metal rod is tungsten, molybdenum or iron.

8. The method for extracting metallic indium and tin by molten salt electrolysis of ITO according to claim 2, characterized in that: Both step 2) and step 3) are carried out under the protection of high-purity argon, and the heating temperature in step 2) is consistent with the electrolysis temperature in step 3), which is 50-100° C. above the eutectic point of the binary chloride mixed system.

9. The method for extracting metallic indium and tin by molten salt electrolysis of ITO according to claim 2, characterized in that: In step 3), the cell voltage of molten salt electrolysis is 2.2-3.5V.