WO2011071151A1 - Method for producing indium metal, molten salt electrolytic cell, and method for purifying low melting point metal - Google Patents

Abstract

Disclosed is a method for producing indium metal, wherein an indium metal-containing alloy is used as the positive electrode, indium metal is used as the negative electrode and indium chloride-zinc chloride molten salt that is mainly composed of indium chloride is used as the electrolyte, so that indium is released from the positive electrode in the form of positive ions and indium metal is electrodeposited on the negative electrode by molten salt electrolysis. In the indium chloride-zinc chloride molten salt, the indium chloride content is not less than 68% by weight and the water content is not more than 0.5% by weight.

Description

Method for producing metal indium, molten salt electrolytic cell, and method for purifying low melting point metal

The present invention relates to a method for producing metal indium from a metal indium-containing alloy, a molten salt electrolytic cell, and a method for purifying a low melting point metal.

Indium is a rare metal that is not contained in a specific ore at a high concentration and is contained as a trace component in zinc ore. In recent years, indium-tin oxide (ITO) containing indium as a main component has been used for a transparent conductive film of a liquid crystal display device, and its demand has been rapidly increased. Therefore, it is expensive by refining and recovering metal indium from scraps containing indium generated from within the ITO manufacturing process and scrap after using ITO as a target (collectively referred to as “ITO scrap”). Various methods for recycling metal indium have been studied.

As one of these methods, a method for producing metal indium by a molten salt electrolysis method is known. For example, a method is known in which metallic indium is collected at the cathode by molten salt electrolysis using mercury (indium-tin amalgam) containing metallic indium-tin as an anode and a molten salt electrolyte as a medium (for example, Patent Documents). 1). In this method, since the standard precipitation potentials of metal indium and tin are close, in ordinary molten salt electrolysis, tin is mixed in metal indium. Therefore, by using amalgam, indium is selectively oxidized and dissolved. It has been.

In addition, as a method for recovering metallic indium from an alloy containing indium, a method is also known in which an indium-containing alloy is used as an anode, electrolytic purification is performed using a molten salt electrolyte containing indium monochloride, and metallic indium is deposited on the cathode. (For example, refer to Patent Document 2).

Further, in a method of electrolytic purification using a mixed molten salt containing indium chloride and zinc chloride using an alloy containing indium metal as an anode, a method of adding ammonium chloride for the purpose of improving the oxidation resistance of the mixed molten salt is also known. (For example, see Patent Document 3).

On the other hand, an aluminum chloride-based molten salt electrolyte bath mainly composed of aluminum chloride and containing at least one kind of chloride is used for electroplating aluminum or aluminum alloy. When the amount of impurities such as moisture contained in the electrolyte bath increases, it becomes difficult to form a smooth plating film. Therefore, in order to remove this impurity, the composition of the electrolyte bath is adjusted so that the aluminum chloride content is 50 mol% or less. There is known a method of purifying an electrolyte bath by adjusting so that the precipitated impurities are separated from the bath (see, for example, Patent Document 4).

Moreover, as an electrolytic cell used for the molten salt electrolysis method, there is an electrolytic cell in which a cathode is arranged at the bottom, a layer of a molten salt bath is held on the cathode, and an anode is held in a container made of a porous body on the cathode. It is disclosed (for example, see Patent Document 5).

Japanese Patent Publication No.46-2734 WO 2006-046800 Soviet Patent No. 531380 JP 04-254600 A JP-A-57-207185

Although it is possible to recover purified metal indium containing almost no impurities such as tin by the method described in the cited document 1, molten salt electrolysis is performed at a temperature of 160 ° C. or higher using mercury for the anode. For this reason, it is a method that requires consideration for health and the environment, for example, when mercury partially vaporizes as vapor. In addition, the metal indium deposited on the cathode contains a small amount of mercury, and it was necessary to combine further advanced purification techniques to remove the mercury.

Moreover, when the molten salt containing indium chloride described in the cited document 2 comes into contact with air having a normal gas composition, that is, a high water vapor concentration, the moisture content of the molten salt becomes high, and the molten salt is denatured by a chemical reaction. In addition, the cell voltage is increased and the quality of metallic indium deposited on the cathode is decreased. Moreover, it is necessary to exchange part or all of the molten salt deteriorated by moisture absorption.

In Patent Document 2, the content of indium chloride is preferably 50 to 67% by weight. The reason is that when the content is lower than 50% by weight, zinc is mixed in the precipitated indium, which is not preferable. If it is higher, tin is mixed in the deposited indium, which is not preferable.

In addition, the addition of ammonium chloride described in the cited document 3 increases the melting point of the molten salt, so that the electric resistance of the molten salt is increased, the electrolytic cell voltage is increased, the impurity content is increased, and the decomposition of ammonium chloride is increased. Since the odor of ammonia as a product deteriorates the working environment, there are many problems such as the need for an exhaust gas treatment facility as a countermeasure.

Although the electrochemical operation such as electroplating can be performed by the method described in the cited document 4, the molten salt is mainly composed of aluminum chloride, so that the hygroscopic property is remarkable and the hydrolyzability is remarkable. The molten salt may be altered by moisture slightly leaking into the phase part. In addition, since aluminum chloride has a high vapor pressure, a part of the aluminum chloride evaporates, the composition changes, and industrially long-term stable operation is difficult. In addition, the present inventors made this aluminum chloride as a molten salt and produced metal indium from a metal indium-containing alloy. As a result, it has been found that there are many problems such as a part of metal aluminum being electrodeposited in metal indium and reducing the purity of indium.

And indeed, useful components such as metal indium can be electrolytically deposited from the alloy by the electrolytic cell described in the cited document 5. However, since a special porous body that is not used in an ordinary electrolytic cell is required, the equipment cost is high, and it was necessary to pay close attention so that the porous body was not damaged even during operation.

The present invention has been made in view of the above problems, and is highly purified from an effective and efficient method for producing metal indium that can solve various problems of conventional methods, that is, a metal indium-containing alloy. It is an object to provide a method for producing high-recovery metal indium over a long period of time, a molten salt electrolytic cell for producing a low-melting-point metal containing metal indium, and a method for purifying a low-melting-point metal using the same. And

As a result of intensive studies on the technology for producing metal indium from an alloy containing metal indium, the present inventors have optimized the type and composition of the electrolyte used for molten salt electrorefining and optimized the water content in the molten salt. Thus, it has been found that the purity of metallic indium deposited on the cathode can be increased, the electrolyte of the molten salt is stabilized, and the metallic indium can be efficiently electrodeposited and recovered. In addition, the inventors have found a molten salt electrolysis tank and a molten salt electrolysis apparatus for producing a low melting point metal containing metal indium, and have completed the present invention.

That is, the present invention uses a metal indium-containing alloy as an anode, metal indium as a cathode, and indium chloride-zinc chloride molten salt containing indium chloride as a main component as an electrolyte, and eluting indium from the anode as a cation by molten salt electrolysis. Indium chloride is electrodeposited on the cathode, and the indium chloride content in the indium chloride-zinc chloride molten salt is 68% by weight or more, and the water content is 0.5% by weight. A method for producing metal indium is provided as follows.

In the present invention, indium chloride is preferably indium monochloride.

In the present invention, molten salt electrolysis is preferably performed in a gas atmosphere having a water vapor concentration of 1% by volume or less. Moreover, it is preferable to carry out molten salt electrolysis in a gas atmosphere having an oxygen concentration of 10% by volume or less. Here, the gas in the gas atmosphere is more preferably at least one selected from nitrogen, argon, and helium.

In the present invention, the operating temperature of the molten salt electrolysis is preferably 140 to 500 ° C.

In the present invention, an alloy obtained by reducing an indium compound can also be used as the metal indium-containing alloy. The indium compound is more preferably an indium oxide-containing material, and the indium oxide-containing material is more preferably ITO scrap.

The present invention also provides a molten salt electrolytic cell for purifying a low-melting point metal, containing a liquid material of an alloy containing the low-melting point metal, and an anode chamber having an opening into which an anode lead wire can be inserted. An inner cylinder for holding a molten salt layer of a low-melting-point metal halide on the liquid material and allowing the liquid material to communicate in the anode chamber without causing the molten salt layer to flow outside, and a refined low-melting-point metal A cathode chamber having an introduction port and a discharge port, the introduction port being disposed so as to be located in the molten salt layer, and having a cathode lead wire capable of being inserted therein and filled with a low melting point metal; A molten salt electrolyzer is provided.

Here, in the molten salt electrolyzer according to the present invention, the inner cylinder is preferably composed of one or more selected from glass, ceramics and fluororesin.

The molten salt electrolyzer according to the present invention preferably includes an inert gas inlet and an exhaust gas outlet in the inner cylinder.

In the present invention, the cathode chamber is preferably made of glass. More preferably, the cathode chamber has a plurality of inlets.

In the present invention, the anode chamber may be composed of one or more selected from stainless steel, iron, titanium, and graphite. Among these, it is more preferable to be made of stainless steel.

In the present invention, the anode chamber preferably further has a lead-out port for leading out the alloy containing the low-melting-point metal after purification, and more preferably a nozzle is formed at the lead-out port.

In the molten salt electrolytic cell, the present invention further accommodates an alloy containing at least one metal selected from indium, tin and gallium in the anode chamber, and corresponds to the metal on the liquid material of the alloy in the inner cylinder. The molten salt of the metal halide to be retained is retained, and a voltage is applied with the anode lead wire and the cathode lead wire inserted to cause molten salt electrolysis, and purified indium, tin and gallium are discharged from the outlet of the cathode chamber. The present invention provides a method for purifying a low melting point metal, wherein one or more metals selected from the group consisting of:

Here, it is preferable to carry out molten salt electrolysis at 50 ° C. to 400 ° C.

Further, it is preferable to carry out molten salt electrolysis at 1 to 200 A / dm ² .

According to the present invention, from a metal indium-containing alloy, a method for producing highly purified metal indium over a long period of time with a high recovery rate, and a molten salt electrolytic cell for producing a low melting point metal containing metal indium, And a method for purifying a low-melting-point metal using the same.

It is a longitudinal section showing one embodiment of a molten salt electrolysis tank concerning the present invention. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 2 is a schematic cross-sectional view of an H-type electrolytic cell used in Examples 1 and 2 and Comparative Example 1. FIG. 2 is a schematic cross-sectional view of an H-type continuous electrolytic cell used in Example 3 and Comparative Examples 2, 3, and 4. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as the case may be. In addition, the dimensional ratio of drawing is not restricted to the ratio of illustration.

The method for producing metal indium according to the present invention uses a metal indium-containing alloy as an anode, metal indium as a cathode, and indium chloride-zinc chloride molten salt containing indium chloride as a main component as an electrolyte. A method for producing metal indium by eluting indium as a cation and electrodepositing metal indium on a cathode, wherein the indium chloride content in the indium chloride-zinc chloride molten salt is 68% by weight or more, and the water content Is 0.5% by weight or less.

“Metal indium-containing alloy” as an anode refers to a metal-like substance composed of metal indium and one or more other metal elements and / or non-metal elements, and the bonding state thereof is not particularly limited. The content of metal indium is not particularly limited. That is, it can be suitably used regardless of whether metal indium is a main component or a trace amount. The metal indium content in the metal indium-containing alloy is preferably 100 ppm by weight to 99.999% by weight, more preferably 1% by weight to 99.99, from the degree of metal indium purification, indium recovery, and indium productivity. % By weight, more preferably 60% by weight to 99.9% by weight.

The type of metal other than metal indium in the metal indium-containing alloy is not particularly limited. For example, Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co , Ni, Cu, Zn, Ga, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Sb, Te, Cs, Ba, Ta, W, Re , Os, Ir, Pt, Au, Tl, Pb, Bi.

Among these, metals having good separation and purification from indium in molten salt electrolysis are Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu. , Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Sn, Cs, Ba, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb Bi, especially Sn, Cu, Fe, Si, Ni, Pb, Na, Ca and Mg are preferable because they can be easily separated and purified from indium.

In addition, as the metal indium-containing alloy, used indium solder after using metal indium as solder, metal indium-containing alloy obtained by reducing the indium compound, and the like can also be used. The indium compound is not particularly limited as long as it is a compound containing indium, and specific examples include indium oxide-containing materials such as indium oxide, indium hydroxide, indium chloride, indium sulfate, indium nitrate, and ITO scrap. it can.

For example, as a method of obtaining an alloy containing indium metal from ITO scrap, a method of reducing the ITO scrap with a reducing agent, dissolving the ITO scrap in an acidic aqueous solution such as hydrochloric acid, nitric acid, sulfuric acid, or a mixed acid thereof, After obtaining indium chloride, indium sulfate, indium nitrate or the like, and then adding an alkali to form a compound containing indium hydroxide, and further converting the compound containing indium hydroxide into indium oxide by heat treatment, a reducing agent Or a solution containing indium chloride, indium sulfate or indium nitrate, and then adding a base metal rather than indium, specifically metallic aluminum or metallic zinc. Metal-indium-containing alloy Obtaining method, and the like.

The “metal indium” as the cathode preferably has a metal indium content of 95% by weight or more.

As a molten salt, first, a salt containing indium is naturally essential. As the type, indium chloride is used because it has a low melting point, excellent oxidation resistance, and low electrical resistance. However, using indium chloride alone is not economical because indium is a rare metal and expensive.

Therefore, although it is used as a mixed molten salt containing a salt other than indium chloride, zinc chloride is used in combination, considering that the salt has characteristics of low hygroscopicity and hydrolyzability and relatively low melting point.

In the method for producing metal indium according to the present invention, the content of indium chloride in the molten salt is 68% by weight or more based on the total amount of the molten salt, and the moisture content of the molten salt is based on the total amount of the molten salt. As 0.5% by weight or less is essential. When the content of indium chloride is less than 68% by weight, that is, when the zinc chloride content is 32% by weight or more, zinc is considerably electrodeposited on the cathode, and the purity of metallic indium is lowered. Furthermore, zinc chloride has a low electrical conductivity in the molten salt, and if it is contained at 32% by weight or more, the liquid resistance increases, the electrolytic cell voltage increases, and the running cost increases, which is not economical. By containing 68% by weight or more of indium chloride, the electrolytic cell voltage can be lowered, the melting point can be lowered, and the operating temperature can be lowered. Accordingly, the content of indium chloride in the molten salt is preferably 70% by weight or more, and more preferably 75% by weight or more.

In addition, as described above, in Patent Document 2, when the content of indium chloride is higher than 67% by weight, it is described that tin is mixed in the precipitated indium, which is not preferable. Not only the content of indium chloride is set to 68% by weight or more, but also the water content of the molten salt is set to 0.5% by weight or less, so that tin is not mixed in indium, and further the conductivity in the molten salt is increased. The liquid resistance is reduced, the electrolytic cell voltage is lowered, and the running cost is reduced, so that it is economical and the present invention has been completed. If the water content exceeds 0.5% by weight, solids are deposited in the molten salt, inhibiting the deposition of indium metal on the cathode, leading to a decrease in current efficiency. However, the impurity content in the metal indium deposited on the cathode becomes high, and sufficient purification may not be possible.

At the time of melting in the above-mentioned Patent Document 4, it is described that the water content in the molten salt is 0.5% by weight or less. The molten salt in this prior document is a chloride mainly composed of aluminum chloride. The aluminum-based molten salt has an indium chloride content of 50 mol% or less (= 53 wt% or less), and the indium chloride content and its action are completely different from those of the present invention.

Indium chloride contained in the molten salt includes InCl, InCl ₂ , and InCl ₃ whose indium valences are monovalent, divalent, and trivalent, and it is essential to include at least one of them. More preferred is InCl that has a low melting point and enables molten salt electrolysis at a lower temperature. The molten salt electrolyte bath containing InCl, since indium move univalent preferable from the fact that compared to InCl ₃ is trivalent, it triples the production rate of In in the same amount of electricity.

The moisture content in the present invention is a value based on the moisture content of the molten salt, and the moisture content indicates the moisture content per unit weight of the molten salt containing moisture (edited by the Powder Engineering Society). , "Handbook of Powder Engineering", page 588 (1986)). And the “water content” in the present invention refers to dehydrating methanol to a water content of 20 ppm by weight or less, dissolving a molten salt therein, sampling a part thereof, Karl Fischer reagent (manufactured by Sigma Aldrich, This is a value calculated by titration with the product name “Hydranal Composite 5”).

The “water content” in the molten salt in the present invention indicates the water content at any time during the operation from the beginning of molten salt electrolysis to the end of molten salt electrolysis. The most preferred embodiment is to dehydrate the water in the molten salt before the start of operation, reduce the water content in the molten salt to 0.5 wt% or less, prevent water absorption of the molten salt even during operation, It is to keep the weight percent or less. Furthermore, the water content of a preferable molten salt is 0.4% by weight or less.

The water vapor concentration in the gas phase part in contact with the molten salt is not particularly limited, but when the water vapor concentration is low, the water content of the molten salt evaporates, but when it is high, the molten salt absorbs moisture and the water content increases. Sometimes. Therefore, as one method for keeping the water content low, there is a method for keeping the water vapor concentration in the gas phase part (gas atmosphere) in the electrolytic cell low. Specifically, the water vapor concentration in the gas phase part is preferably 1% by volume or less, more preferably 0.5% by volume or less. Moreover, the component of the gaseous phase part which is contacting with molten salt is not specifically limited, For example, air, nitrogen, argon, helium, hydrogen, carbon monoxide, a carbon dioxide etc. can be used. Preferably, the oxygen concentration in the gas phase is 10% by volume or less, whereby the dissolved oxygen concentration in the molten salt can be kept low, and oxidation of the molten salt and electrodeposited indium can be prevented. More preferably, the main component of the gas phase part is at least one selected from nitrogen, argon and helium. Here, the “main component” means a component contained by 50% by volume or more with respect to the total volume of the gas phase part.

The shape of the electrolytic cell used for molten salt electrolysis is not particularly limited as long as the anode chamber and the cathode chamber are not in contact with each other and electricity does not flow directly. In other words, the anode chamber and the cathode chamber need only be separated from each other. For example, the normal use introduced in the book "Molten salt technology is a key technology of the 21st century: Application of molten salt (IPC Publishing)" A molten salt electrolyzer can be applied. The appropriate electrolytic cell shape differs depending on the operation method such as whether the anode and the cathode are solid or liquid, and whether the operation is a continuous type or a batch type, and may be appropriately selected.

Specifically, when the metal indium-containing alloy in the anode chamber is melted and the metal indium in the cathode chamber is also melted, the cathode chamber and the anode chamber are partitioned by a partition, and the upper part of both electrodes is a molten salt electrolyte bath. Examples include an electrolytic cell in which a salt bridge structure or an electrolytic cell shape is cylindrical, and an anode is placed in an insulating container in the center of a molten salt electrolyte bath, and a cathode is disposed so as to surround the anode. be able to. As described above, the gas atmosphere in the molten salt electrolyzer may sometimes improve the stability of the molten salt by lowering the water vapor concentration and the oxygen concentration. Furthermore, depending on the structure of the molten salt electrolysis tank, the area where the molten salt comes into contact with the gas phase part may be reduced, and moisture absorption of the molten salt may be suppressed. Preferably, the contact area with the gas phase part is 0.1 to 100 m ² / m ³ per unit molten salt volume, more preferably 0.2 to 80 m ² / m ³ .

In such a molten salt electrolysis method, a One of the features that can increase the current density, the current density is preferably 1 ~ 200A / dm ^2. When operating at less than 1 A / dm ² , the production rate per unit electrode area may decrease. From the viewpoint of productivity, the higher the current density, the better. However, at a current density exceeding 200 A / dm ² , when metal indium is deposited on the cathode, impurities may be taken in and it may be difficult to obtain high-purity indium. The current density is more preferably 2 to 100 A / dm ² and further 3 to 50 A / dm ² .

Also, the operating temperature of the molten salt electrolysis is not particularly limited as long as it is equal to or higher than the melting point of the molten salt electrolyte. 90 to 500 ° C. is preferable, and 100 to 450 ° C. is more preferable from the viewpoint of corrosion of the apparatus material and operation of molten salt electrolysis.

Furthermore, the time required for the molten salt electrolysis is sufficient if it can be electrolyzed for 50 to 100% of indium contained in the alloy in order to avoid a sufficient recovery rate and contamination with impurities.

By electrolyzing under the proper operating conditions described above, high-purity metal indium can be deposited on the cathode, but if the metal indium has not achieved the target purity, the same operation is performed. Molten salt electrolysis may be further performed one or more times, and purification may be performed until the target purity is reached. Or depending on the kind of impurity, you may implement combining the purification method of the metal indium known conventionally. Specifically, alkali casting methods using alkali metal hydroxides and chlorination methods using chlorinating agents such as ammonium chloride can be adopted, and by combining these purification techniques as appropriate, more effective and efficient Indium metal can be manufactured.

Subsequently, the molten salt electrolyzer according to this embodiment will be described with reference to FIGS. The molten salt electrolytic cell described below is only one aspect of the present invention, and the present invention is naturally not limited to the following contents.

<Molten salt electrolytic cell>
As shown in FIGS. 1 and 2, the molten salt electrolysis cell 100 in this embodiment includes an anode chamber 1, an inner cylinder 2, and a cathode chamber 8. The anode chamber 1 is an open container for containing an alloy liquid material 9 containing a low melting point metal. The inner cylinder 2 is disposed in the container so that an end surface having an opening faces the bottom surface inside the anode chamber 1. The wall surface of the inner cylinder 2 and the surface opposite to the end surface having the opening cover part of the liquid material 9 of the alloy containing the low melting point metal accommodated in the anode chamber 1. The cathode chamber 8 has an inlet 3 for introducing a low-melting point metal and an outlet 7 for leading out the low-melting point metal. The inlet 3 is arranged inside the inner cylinder 2 and leads out the low-melting point metal. The outlet 7 is disposed outside the inner cylinder 2. The inside of the cathode chamber 8 is filled with a low melting point metal 11. The molten salt electrolyzer may be disposed on the heater 12 and may be electrolyzed while being heated by the heater 12 from the lower part of the anode chamber 1.

(Anode chamber 1)
The anode chamber 1 is a container for holding a liquid material (anolyte 9) of an alloy containing a low-melting-point metal, and the anolyte 9 is charged into the space formed by the anode chamber 1 and the inner cylinder 2 from the opening side. It is possible to insert the lead wire 14 for the anode. Further, if the electrolysis operation is continued for a long time, the components that have not been electrolyzed constituting the alloy are concentrated in the anode chamber 1, so that the composition of the anolyte 9 can be kept constant after purification from the opening. The anolyte 9 used, that is, the used anolyte 9 can also be derived. In order to derive the refined alloy, the anode chamber 1 may be provided with a separate outlet. The lead-out port may be disposed in a gap between the anode chamber 1 and the inner cylinder 2. An extraction nozzle 4 may be formed at the outlet, and it is more preferable to extract the refined alloy intermittently or continuously. When the extraction nozzle 4 is opened when the content of the low melting point metal contained in the anolyte 9 is 30% by weight or less, and preferably 50% by weight or less, the purity of the low melting point metal is obtained. Can do. The supply of the anolyte 9 may be continuous or intermittent, and the supply location of the alloy may be from the gap between the anode chamber 1 and the inner cylinder 2 or a separate supply unit may be provided.

The material of the anode chamber 1 is not particularly limited as long as it does not react with the held alloy. Preferable is graphite or a metal material that is hardly damaged, and specific examples of the metal material include stainless steel, nickel-base alloy, iron, iron-base alloy, titanium, and titanium-base alloy. Especially, the material comprised from 1 or more types chosen from stainless steel, iron, titanium, and graphite is preferable, and stainless steel is more preferable from the surface of corrosion resistance and economical efficiency.

The shape of the anode chamber 1 is not particularly limited, such as a cylindrical shape, a square shape, or a polygonal shape. Preferably, it is a cylindrical type or a square type that is easy to manufacture and has high mechanical strength.

(Inner cylinder 2)
The inner cylinder 2 is open at the bottom, and has, for example, an inert gas inlet 5 and an exhaust gas outlet 6 that can be opened and closed at the top. Since the upper part of the inner cylinder 2 is closed, the contact between the surface of the molten salt 10 and the outside air can be cut off, so that the mixing of moisture in the atmosphere, which is a cause of deterioration of the molten salt 10, can be prevented, and stable operation for a long time Is possible. Examples of the inert gas introduced into the gas phase portion in contact with the molten salt 10 include nitrogen gas and argon gas.
The inner cylinder 2 accommodates a liquid material 9 of an alloy containing a low-melting-point metal inside, and a molten salt layer 10 of a low-melting-point metal halide is held on the liquid material. In order to form the molten salt layer 10 in a floating state on the top of the anolyte 9, specifically, the anolyte 9 is stored at the bottom of the inner cylinder 2, and the molten salt is supplied from the inert gas inlet 5 and the exhaust gas outlet 6. Examples include a method of pouring, or putting a powdered metal salt in the inner cylinder, turning the inner cylinder 2 over the anolyte 9 and heating to melt the metal salt.
Further, in order to allow the anolyte 9 to move between the inside and outside of the inner cylinder 2 without causing the molten salt layer 10 to flow outside, for example, a part of the lower side surface of the inner cylinder 2 is slit-shaped. It is cut out. Thereby, the anolyte 9 can go back and forth between the inside and the outside of the inner cylinder 2, and the composition of the anolyte 9 can be made uniform.

The material of the inner cylinder 2 is not particularly limited as long as it does not react with an alloy containing a molten salt and a low melting point metal held inside. From the viewpoint of price and ease of production, it is preferably composed of one or more selected from glass, ceramics and fluororesin, more preferably quartz glass and ceramics.

(Cathode chamber 8)
The cathode chamber 8 is filled with a low melting point metal 11, and a cathode lead wire 15 can be inserted into a portion disposed outside the inner cylinder 2. The purity of the low melting point metal 11 preliminarily filled in the cathode chamber 8 before electrodeposition is preferably such that the content of the low melting point metal is 90% by weight or more.

The inlet 3 in the cathode chamber 8 is composed of one or a plurality of containers depending on the size of the equipment. When the inlet 3 is composed of a plurality of containers, the purified low-melting-point metal liquid (catholyte 11) that is electrolytically deposited on the surface of the inlet 3 is gathered by the connected pipes, and from the outlet 7. Discharged and collected continuously or intermittently. Further, the arrangement of the introduction port 3 is not particularly limited, but as shown in FIG. 2, the oxidative dissolution of the low melting point metal from the anode alloy becomes more uniform as the introduction port 3 is uniformly dispersed in the molten salt layer 10, that is, This is preferable because the current density distribution can be reduced. The larger the cross-sectional area of the inlet 3, that is, the area of the interface between the catholyte 11 and the molten salt 10, the larger the area that can be electrolytically deposited and the lower the electrical resistance. The cross-sectional area (the area of the molten salt 10 in FIG. 2) is reduced, so that the electrical resistance of the molten salt 10 is increased. Preferably, the cross-sectional area of the inlet 3 is 30 to 70%, more preferably 40 to 60% of the inner cylinder cross-sectional area.

It is essential that the cathode chamber 8 be formed of an insulator. Among insulators, glass, ceramics, and fluororesins that are highly corrosion resistant to molten salts and low-melting metals are preferable, and glass that is easy to manufacture, has high heat resistance, is inexpensive, and is also quartz. Glass is preferred.
The shape of the cathode chamber 8 is not particularly limited as long as the low melting point metal can be electrolytically deposited. A cube, a rectangular parallelepiped, and a cylinder are preferable.

<Purification of low melting point metal>
Subsequently, a method for purifying a low melting point metal according to the present embodiment will be described. In the method for refining the low melting point metal, in the molten salt electrolytic cell 100, the anode chamber 1 contains an alloy containing one or more metals selected from indium, tin and gallium, and the alloy in the inner cylinder 2 A molten metal halide corresponding to the metal is held on the liquid. Then, by applying a voltage with the anode lead wire 14 and the cathode lead wire 15 inserted, molten salt electrolysis is performed, and one kind selected from purified indium, tin and gallium from the outlet 7 of the cathode chamber 8. The above metals are derived.

The alloy containing one or more metals selected from indium, tin and gallium can be purified by the above purification method. Among them, an alloy containing indium is suitably purified by the purification method according to this embodiment because it has a relatively low melting point and high production efficiency in molten salt electrolytic purification. The alloy refers to a metal-like substance composed of a metal element and / or a non-metal element, and the bonding state thereof is not particularly limited. The content of the low melting point metal is not particularly limited. That is, even if the low melting point metal is a main component or a trace amount is contained, it can be suitably used. From the degree of purification, recovery rate, and productivity of the low melting point metal, the content of the low melting point metal in the alloy is preferably 100 wtppm to 99.999 wt%, more preferably 1 wt% to 99.99 wt%, and even more preferably 60 wt%. 99.9 wt%.

The type of metal other than the low melting point metal in the alloy is not particularly limited. For example, Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni , Cu, Zn, Ge, As, Se, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Sb, Te, Cs, Ba, Ta, W, Re, Os, Ir, Pt , Au, Tl, Pb, Bi.

Among these, metals having good separation and purification from low melting point metals in molten salt electrolysis are Li, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni. , Cu, Zn, Ge, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Cs, Ba, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, Bi In particular, Cu, Fe, and Ni are preferable because separation and purification are easy.

The molten salt 10 held in the inner cylinder 2 contains a metal halide corresponding to the metal to be refined, and has a specific gravity smaller than that of an alloy containing a low melting point metal held in the anode chamber 1. There is no particular limitation as long as it is a molten salt electrolyte that can be electrolyzed. For example, a mixed molten salt of a metal halide and a zinc halide corresponding to the metal to be purified, and a mixed molten salt of a metal halide and an aluminum halide corresponding to the metal to be purified can be mentioned. More specifically, when the object to be refined is an alloy containing indium, it is preferable to use a mixed molten salt of zinc chloride and indium monochloride, a mixed molten salt of aluminum bromide and indium monobromide, or the like. it can. In addition, from the viewpoint of the purity of the metal to be purified, the metal halide corresponding to the metal to be purified is preferably more than 50% by weight based on the total amount of the mixed molten salt, and more than 65% by weight. It is preferable that the content be 75% by weight or more. Further, the water content in the molten salt is preferably 0.7% by weight or less, more preferably 0.5% by weight or less, and further preferably 0.4% by weight or less.

By using the molten salt electrolyzer, electrolysis can be performed at a high current density in the purification method according to the present embodiment. The current density is preferably 1 to 200 A / dm ² . When operating at less than 1 A / dm ² , the production rate per unit electrode area may decrease. From the viewpoint of productivity, the higher the current density, the better. However, at a current density exceeding 200 A / dm ² , when a low melting point metal useful for the cathode is electrolytically deposited, impurities may be incorporated and the purity may be lowered. The current density is more preferably 2 to 150 A / dm ² , further 3 to 100 A / dm ² .

Further, the temperature at which the molten salt electrolysis is performed is not particularly limited as long as the electrolyte bath, the alloy containing the low melting point metal, and the low melting point metal are all in a molten state. The temperature of the molten salt 11 is preferably 50 ° C. to 400 ° C., more preferably 90 ° C. to 350 ° C. from the viewpoint of corrosion of the apparatus material and operation of molten salt electrolysis.

Since the molten salt electrolytic cell according to the present embodiment has a structure in which moisture hardly enters, the amount of moisture in the molten salt can be maintained at a low level over a long period of time. Further, according to the purification method according to the present embodiment, the molten salt is supplied to the upper surface of the liquid material (anolyte) of the alloy containing the low melting point metal, and the used anolyte can be appropriately extracted, The concentration of the low melting point metal halide in the molten salt can be kept constant. As a result, the low melting point metal to be purified can be produced from the low melting point metal with a high recovery rate over a long period of time.

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to these examples.

In addition, the measuring method of the water content in the molten salt in the present invention is to dehydrate methanol (manufactured by Kanto Chemical Co., Ltd., reagent special grade) to have a water content of 20 ppm by weight or less, in which the molten salt is dissolved, A part of the sample was sampled and titrated with a Karl Fischer reagent (Sigma Aldrich, trade name “Hydranal Composite 5”).

Example 1
As raw material for the metal indium-containing alloy, 1814 g of ITO scrap (91.1 wt% indium oxide, 8.9 wt% tin oxide) generated during the production of the ITO target was ground to an average particle size of 51 μm with a crusher, and reduced to 1735 g of ground powder. 170.9 g of graphite (product name “KS-75”, manufactured by Lonza) was mixed, and the mixture was placed in a magnetic crucible having an internal volume of 1 L and charged into an electric furnace. After replacing the inside of the electric furnace with nitrogen gas, the temperature of the furnace wall was raised to 1100 ° C. in 6 hours and held at 1100 ° C. for 3 hours. After completion of the reaction, the inside of the electric furnace was cooled and the total weight of the reduction product and the unreacted raw material powder was measured to be 1456.3 g.

When the processed product was analyzed with an X-ray diffractometer, the diffraction peak of indium oxide in the scrap became weak, and instead a strong peak of metal indium was observed, so the reduction of indium oxide in the ground ITO scrap was reduced. Was confirmed to be good. Also, almost all of the tin oxide was converted to metallic tin, and it was confirmed that the reduction product was an indium-tin alloy.

Next, in order to purify and recover metallic indium from the alloy, molten salt electrolysis was performed. As shown in FIG. 3, the electrolytic cell is an H-type electrolytic cell made of Pyrex (registered trademark) glass having an inner diameter of 2 cm and a height of 13 cm, and an anode of 63.2 g of an indium-tin alloy as a reduction product. The cathode was charged with 29.9 g of indium metal having a purity of 99.999% by weight. The weight of the molten salt charged was 70.3 g, and the composition was synthesized by reacting indium trichloride (indium trichloride (manufactured by Rare Metal Co., Ltd., anhydrous)) and metal indium at 350 ° C. ) 73.5 wt% (= 71.5 mol%), zinc chloride (manufactured by Toshin Chemical Industry Co., Ltd., purity 99% or more) 28.5 mol%. The water content at this time was 0.4% by weight.

Next, platinum conducting wires were inserted into the anode and cathode of the electrolytic cell, and the electrolytic cell was placed in an electric muffle furnace, and the temperature of the electrolytic cell was 240 ° C., and molten salt electrolysis was performed. Molten salt electrolysis was carried out for 8 hours using a constant current device (Kikusui Electronics Co., Ltd., trade name “PMC18-5”) at a current value of 0.94 A and a current density of 30 A / dm ² .

As a result, 31.5 g of metal indium was dissolved from the indium-tin alloy charged in the anode chamber, and 61.1 g of metal indium was obtained from the cathode chamber. The water content in the molten salt at the end of electrolysis was 0.3 wt. %Met. Since the amount charged into the cathode chamber was 29.9 g, the amount of electrodeposition was 31.2 g, which was a good recovery rate of 99.0%.

Moreover, the electrolytic cell voltage changed at 4.5V.

A portion of the metal indium on the cathode is taken out, dissolved in hydrochloric acid (manufactured by Kanto Chemical Co., Ltd., reagent grade), the impurity content is obtained with an ICP (inductively coupled plasma) analyzer, and the amount and purity of the charged metal indium The tin content in the indium-deposited metal indium was as low as 95 ppm by weight, and the zinc content was as low as 2 ppm by weight.

Indium oxide was produced using the recovered metal indium as a raw material, an ITO target was produced from the indium oxide and tin oxide, and the sputtering performance as the ITO target was evaluated. As a result, the generation of nodules was hardly observed, and it was reusable as a raw material for producing the ITO target.

Example 2
The indium-tin alloy recovered by the reduction in Example 1 was used, and molten salt electrolytic purification was performed using the same Pyrex (registered trademark) glass H-type electrolytic cell as in Example 1.
The anode chamber was charged with 61.7 g of the alloy, and the cathode chamber was charged with 30.4 g of 99.999 wt% metallic indium prepared separately. The weight of the molten salt charged was 75.4 g, and its composition was 73.6% by weight of indium monochloride (= 71.6% by mole), 28.4% by mole of zinc chloride, and 0.5% by weight of water content. Platinum lead wires were inserted into the anode and cathode of the electrolytic cell, and the electrolytic cell was placed in an electric muffle furnace, and the temperature of the electrolytic cell was 240 ° C., and molten salt electrolysis was performed.

Molten salt electrolysis was carried out for 14 hours using the constant current device used in Example 1 with a current value of 0.94 A and a current density of 30 A / dm ² .

As a result, 55.8 g was dissolved from the indium-tin alloy charged in the anode chamber, and 86.1 g was obtained from the cathode chamber. The water content in the molten salt at the end of electrolysis was 0.3% by weight. It was. Since the amount charged into the cathode chamber was 30.4 g, the amount of electrodeposition was 55.7 g. A part of the metal indium on the cathode is taken out, dissolved in hydrochloric acid, the impurity content is obtained with an ICP analyzer, and tin in the deposited metal indium corrected from the amount and purity of the charged metal indium is 520 ppm by weight, the zinc content Was also as low as 3 ppm by weight. Further, the weight of indium electrodeposited in the cathode chamber was 55.7 g against the indium weight of 56.5 g charged in the anode chamber, and the recovery rate was 98.6%, which was good.

Moreover, the electrolytic cell voltage changed at 4.8V.

Comparative Example 1
The indium-tin alloy recovered by the reduction in Example 1 was used, and molten salt electrolytic purification was performed using the same Pyrex (registered trademark) glass H-type electrolytic cell as in Example 1. The anode chamber was charged with 63.3 g of the alloy, and the cathode chamber was charged with 30.1 g of indium metal having a purity of 99.999 wt% prepared separately. The weight of the molten salt charged was 70.8 g, and the composition was 73.5% by weight of indium monochloride (= 71.5% by mole) and 28.5% by mole of zinc chloride. The water content was adjusted to 0.9% by weight by adding water to the molten salt.

Platinum lead wires were inserted into the anode and cathode of the electrolytic cell, and the electrolytic cell was placed in an electric muffle furnace, and the temperature of the electrolytic cell was 240 ° C., and molten salt electrolysis was performed. Molten salt electrolysis was carried out for 14 hours in the same manner as in Example 2, using the constant current device used in Example 1 and setting the current value to 0.94 A and the current density to 30 A / dm ² .

As a result, 53.8 g was dissolved from the indium-tin alloy charged in the anode chamber, and 83.7 g was obtained from the cathode chamber. The water content in the molten salt at the end of electrolysis was 0.8% by weight. It was. Since the amount charged into the cathode chamber was 30.1 g, the amount of electrodeposition was 53.6 g. A part of the metal indium on the cathode was taken out, dissolved in hydrochloric acid, the impurity content was determined with an ICP analyzer, and tin in the electrodeposited metal indium corrected from the amount and purity of the charged metal indium was 1860 ppm by weight, the zinc content Was as high as 52 ppm by weight. In addition, the weight of indium electrodeposited in the cathode chamber was 53.7 g, the indium recovery rate was 93.9%, which was lower than 98.6% in Example 2, compared to 57.2 g of indium charged in the anode chamber.

Also, the electrolytic cell voltage was unstable and increased to the initial 5.2V and 6.1V just before the end of the operation.

Example 3
In order to purify and recover metallic indium from used indium solder, molten salt electrolytic purification was performed. The used indium solder contained 99.22 wt% of the main component indium, 4580 wt ppm of tin, which is an impurity, and 3220 wt ppm of copper.
For the molten salt electrolytic purification, an H-type continuous electrolytic cell made of Pyrex (registered trademark) glass shown in FIG. 4 was used. The anode chamber was charged with 143.9 g of the alloy, and the cathode chamber was charged with 49.1 g of 99.999 wt% metallic indium prepared separately. The weight of the molten salt charged was 127.1 g, and the composition was 68.1% by weight of indium monochloride (= 65.9% by mole) and 34.1% by mole of zinc chloride. The water content at this time was 0.4% by weight. Stainless steel wires are inserted into the anode and cathode of the electrolytic cell, the electrolytic cell is placed in an electric muffle furnace, the temperature of the electrolytic cell is set to 290 ° C., and nitrogen gas is continuously introduced into the electrolytic cell at 1.2 L / hr. Molten salt electrolysis was carried out while circulating the product. At this time, the water vapor concentration in the nitrogen gas was 0.1 vol%.

In the molten salt electrolysis, the constant current apparatus used in Example 1 was used, and the current value was set to 0.45 A and the current density was set to 20 A / dm 2, and the current was continuously supplied for 30 days. Since indium in the anode chamber is electrolyzed and the holding amount decreases, 46.3 g of used indium solder is supplied once a day. The metal indium electrodeposited in the cathode chamber was recovered by continuously flowing out from the overflow tube.

As a result, the weight of metal indium recovered from the cathode chamber, the current efficiency of the cathode chamber, and the contents of impurities tin, copper, and zinc are shown in Table 1 below.

From this table, despite the continuous operation for 30 days, metal indium can be recovered from the cathode chamber with a current efficiency of 99% or more, and over 30 days, the content of impurities tin, copper, zinc is small, It was a good result. Further, the water content in the molten salt was measured after the operation was completed, and as a result, it was as low as 0.2% by weight and good.

Moreover, the electrolytic cell voltage was as high as 3.5 V immediately before supplying the indium solder to the anode chamber because the maximum distance between the electrodes was 3.5 V, and immediately after the insertion, the distance between the electrodes was minimum and became 2.5 V. This electrolytic cell voltage remained substantially constant over 30 days.

Comparative Example 2
In order to purify and recover metallic indium from the used indium solder used in Example 3, molten salt electrolytic purification was performed.

As in Example 3, the molten salt electrolytic purification used an H-type continuous electrolytic cell made of Pyrex (registered trademark) glass as shown in FIG. The anode chamber was charged with 140.3 g of the alloy, and the cathode chamber was charged with 50.4 g of metallic indium of 99.999 wt% prepared separately. The weight of the molten salt charged was 125.6 g, and the composition was 63.1% by weight of indium monochloride (= 60.8% by mole) and 39.2% by mole of zinc chloride. The water content at this time was 0.4% by weight. Stainless steel wires are inserted into the anode and cathode of the electrolytic cell, the electrolytic cell is placed in an electric muffle furnace, the temperature of the electrolytic cell is set to 290 ° C., and nitrogen gas is continuously introduced into the gas phase of the electrolytic cell at 1.2 L / hr. Molten salt electrolysis was carried out while circulating. At this time, the water vapor concentration in the nitrogen gas was 0.1 vol%.

Molten salt electrolysis was carried out continuously for 30 days using the constant current apparatus used in Example 1 with a current value of 0.45 A and a current density of 20 A / dm ² . Since indium in the anode chamber is electrolyzed and the holding amount decreases, 45.2 g of used indium solder was supplied once a day. The metal indium electrodeposited in the cathode chamber was recovered by continuously flowing out from the overflow tube.

As a result, the moisture content in the molten salt was measured after the operation was completed, and the result was as low as 0.3% by weight. Table 2 below shows the weight of metal indium recovered from the cathode chamber, the current efficiency of the cathode chamber, and the contents of impurities tin, copper, and zinc.

From this table, during continuous operation for 30 days, the current efficiency was about 97%, lower than 99% or more of Example 3, the productivity was inferior, the impurity zinc content was large, and sufficient purification was not possible.

Comparative Example 3
Using the used indium solder used in Comparative Example 2, electrolytic purification was performed using the same Pyrex (registered trademark) glass H-type continuous electrolytic cell as in Example 3. The anode chamber was charged with 145.7 g of the alloy, and the cathode chamber was charged with 50.4 g of metallic indium with a purity of 99.999 wt% prepared separately. The weight of the molten salt charged was 128.6 g, and the composition was 63.2% by weight of indium monochloride (= 61.5% by mole) and 38.5% by mole of zinc chloride. The water content was 0.7% by weight by adding water to the molten salt. Stainless steel wires are inserted into the anode and cathode of the electrolytic cell, the electrolytic cell is placed in an electric muffle furnace, the temperature of the electrolytic cell is set to 290 ° C., and the gas phase of the electrolytic cell is 1% of water having a water vapor concentration of 1.5 vol%. Molten salt electrolysis was performed while continuously flowing at 2 L / hr.

Molten salt electrolysis was carried out continuously by using the constant current device used in Example 1 with a current value of 0.45 A and a current density of 20 A / dm ² . Since indium in the anode chamber is electrolyzed and the holding amount decreases, used indium solder is supplied once a day. The metal indium electrodeposited in the cathode chamber was recovered by continuously flowing out from the overflow tube.

As a result, a large amount of white solid was generated in the molten salt, and the current efficiency dropped to 76% on the 10th day after the start of operation. Table 3 below shows the operation results during this period, that is, the weight of recovered metal indium, the current efficiency of the cathode chamber, and the contents of impurities tin, copper, and zinc.

From this table, the current efficiency of the cathode chamber rapidly decreased from 95.5% to 76.0%, and the contents of impurities tin and copper were high, and sufficient purification was not possible. As a result of measuring the water content in the molten salt after the continuous operation for 10 days, it was increased to 3.5% by weight.

Comparative Example 4
Using the used indium solder used in Comparative Example 2, electrolytic purification was performed using the same Pyrex (registered trademark) glass H-type continuous electrolytic cell as in Example 3. The anode chamber was charged with 141.7 g of the alloy, and the cathode chamber was charged with 48.5 g of 99.999 wt% metallic indium prepared separately. The weight of the molten salt charged was 135.3 g, and the composition thereof was 46.6% by weight of indium monochloride (= 45.3% by mole), 54.7% by mole of zinc chloride, and 0.4% by weight of water content. . Stainless steel wires are inserted into the anode and cathode of the electrolytic cell, the electrolytic cell is placed in an electric muffle furnace, the temperature of the electrolytic cell is 290 ° C., and nitrogen gas having a water vapor concentration of 0.1 vol% is added to the gas phase of the electrolytic cell. Molten salt electrolysis was performed while continuously flowing at 1.2 L / hr.

Molten salt electrolysis was carried out continuously by using the constant current device used in Example 1 with a current value of 0.45 A and a current density of 20 A / dm ² . Since indium in the anode chamber is electrolyzed and the holding amount decreases, used indium solder is supplied once a day. The metal indium electrodeposited in the cathode chamber was recovered by continuously flowing out from the overflow tube.

The weight of recovered metal indium, the current efficiency of the cathode chamber, and the contents of impurities tin, copper, and zinc are shown in Table 4 below.

　この表から、陰極室から回収したインジウム中には亜鉛含有量が非常に高く、精製が不十分であったため、運転を３日間で停止した。

From this table, the indium recovered from the cathode chamber had a very high zinc content and was not sufficiently purified, so the operation was stopped in 3 days.

Comparative Example 5
Using the used indium solder used in Comparative Example 2, electrolytic purification was performed using the same Pyrex (registered trademark) glass H-type continuous electrolytic cell as in Example 3. The anode chamber was charged with 137.5 g of the alloy, and the cathode chamber was charged with 51.6 g of 99.999% by weight metallic indium prepared separately. The weight of the molten salt charged was 115.4 g, and the composition was 26.2% by weight of indium monochloride (= 25.5 mol%), aluminum chloride (Nippon Light Metal Co., Ltd., anhydrous, purity 99.0% or more) It was 74.5 mol%. The water content at this time was 0.5% by weight. Stainless steel wires were inserted into the anode and cathode of the electrolytic cell, and the electrolytic cell was placed in an electric muffle furnace, and the temperature of the electrolytic cell was 250 ° C. Molten salt electrolysis was conducted by setting the current value to 0.45 A and the current density to 20 A / dm ² . Molten salt electrolysis was performed while continuously flowing nitrogen gas having a water vapor concentration of 0.3 vol% at 1.2 L / hr in the gas phase of the electrolytic cell.

As a result, 13 hours after the start of operation, white solids were scaled in the exhaust gas line, the line was closed, and continuous operation became difficult. Table 5 below shows the impurity content in the indium flowing out of the cathode chamber immediately before the shutdown.

From this table, the indium recovered from the cathode chamber had a very high aluminum content and was not sufficiently purified.

Example 4
Using the molten salt electrolytic cell shown in FIG. 1, an alloy containing metal indium was supplied to the anode chamber with the following apparatus configuration and molten salt composition, and purified metal indium was electrolytically deposited in the cathode chamber.
1. Apparatus configuration 1) Anode chamber size: length 280 mm × width 350 mm × depth 140 mm, thickness 5 mm
Material: Stainless steel (SUS304)
Shape: Square tank (with anolyte extraction nozzle)
2) Inner cylinder size: length 250mm x width 250mm x height 250mm, thickness 3mm
Material: Quartz glass Shape: Square bath (Bottom: Opening, Lower side: 30mm x 30mm slits, 2 on each side, Upper: With 2 nozzles)
3) Size of cathode chamber: length 30 mm × width 200 mm × depth 30 mm, thickness 3 mm, 5 materials: quartz glass shape: 5 square vessels Molten salt bath composition: indium monochloride: zinc chloride = 78: 22 (mol%) (= 80 wt% indium monochloride), water content 0.4 wt%
Electrolysis temperature: 300 ° C

The composition of the metal indium-containing alloy (anolyte 9) supplied to the anode chamber 1 was metal indium 90.3 wt% and metal tin 9.7 wt%, and 80.1 kg was charged at the start of the electrolysis operation. 100 A is energized with a DC power generator 13 (Kikusui Electronics Co., Ltd., trade name “PAS10-105”), the anode current density is 16 A / dm ² , and the cathode current density is 33 A / dm ² continuously. Driving was carried out. The metal indium electrolytically deposited in the cathode chamber 8 averaged 10.2 kg per day and could be continuously recovered from the outlet 7. The anode chamber 1 was supplied with 10.2 kg of the alloy having the above composition per day. On the 14th day from the start of operation, since the tin content of the indium-containing alloy held in the anode chamber 1 has become slightly higher, 40.2 kg of the anolyte 9 is extracted from the extraction nozzle 4 while the electrolytic operation is continued. 40.2 kg of the alloy having the above composition was supplied in a molten state, and electrolysis was continued. At the time of this anolyte exchange, the molten salt 10 can be operated without coming into contact with the atmosphere, and no deterioration such as discoloration or solidification of the molten salt 10 was observed.

The tin content in the metal indium electrodeposited on the cathode by the 14-day molten salt electrolytic purification was 580 wtppm, and the tin content in the anolyte extracted from the extraction nozzle 4 was 25.6 wt%. The water content in the molten salt was 0.3 wt%.

Example 5
In the apparatus configuration shown in Example 4, an alloy containing metal tin (anolyte 9) was supplied to the anode chamber 1, and purified metal tin was electrolytically deposited in the cathode chamber 8. The composition of the molten salt 10 was a mixed molten salt of 76 wt% tin chloride and 24 wt% zinc chloride, and the electrolysis temperature was 350 ° C.

The composition of the metal tin-containing alloy supplied to the anode chamber 1 was 95.3 wt% metal tin and 4.7 wt% metal lead, and 80.3 kg was charged at the start of the electrolysis operation. The DC power generator 13 (manufactured by Kikusui Electronics Co., Ltd., trade name “PAS10-105”) was energized at 100 A for continuous operation. Metal tin electrolytically deposited in the cathode chamber 8 averaged 5.3 kg per day and could be continuously recovered from the outlet 7. The anode chamber 1 was supplied with 5.3 kg of the alloy having the above composition per day. On the 14th day from the start of operation, since the lead content of the tin-containing alloy held in the anode chamber 1 increased, 41.2 kg of the anolyte 9 was extracted from the extraction nozzle 4 while the electrolysis operation was continued. 41.2 kg was supplied and electrolysis was continued.

As a result of the 14-day molten salt electrolytic purification, the lead content in the metal tin electrolytically deposited on the cathode was 12 wtppm, and the lead content in the anolyte extracted from the extraction nozzle 4 was 8.7 wt%.

DESCRIPTION OF SYMBOLS 1 ... Anode chamber, 2 ... Inner cylinder, 3 ... Inlet port, 4 ... Extraction nozzle, 5 ... Inert gas introduction port, 6 ... Exhaust gas discharge port, 7 ... Outlet port, 8 ... Cathode chamber, 9 ... Anolyte, 10 , 18 ... Molten salt, 11 ... Catholyte, 12 ... Heater, 13 ... DC power generator, 14 ... Conductor for anode, 15 ... Conductor for cathode, 16 ... Anode (chamber) crude In alloy, 17 ... Cathode (chamber) Refined In, 19: Conductor for anode (platinum conductor with protective tube), 20: Conductor for cathode (platinum conductor with protective tube), 21 ... Seal plug, 22 ... Anode (chamber) crude In alloy, 23 ... Cathode (chamber) refined In, 24 ... Molten salt, 25 ... Anode lead wire (SUS wire), 26 ... Cathode lead wire (SUS wire), 27 ... Crude In alloy inlet, 28 ... Purified In overflow port, 29 ... Gas inlet port, 30 ... Exhaust gas outlet, 31 ... Gas communication pipe

Claims (21)

Metal indium-containing alloy as anode, metal indium as cathode, indium chloride-zinc chloride molten salt containing indium chloride as main component is used as electrolyte, and indium is eluted from anode as cation by molten salt electrolysis A method for producing metal indium that deposits metal indium,
A method for producing metallic indium, wherein the indium chloride-zinc chloride molten salt has an indium chloride content of 68% by weight or more and a water content of 0.5% by weight or less. The method for producing metal indium according to claim 1, wherein the indium chloride is indium monochloride. The method for producing metal indium according to claim 1 or 2, wherein molten salt electrolysis is performed in a gas atmosphere having a water vapor concentration of 1% by volume or less. The method for producing metal indium according to any one of claims 1 to 3, wherein molten salt electrolysis is performed in a gas atmosphere having an oxygen concentration of 10% by volume or less. The method for producing metal indium according to claim 3 or 4, wherein a main component of the gas in the gas atmosphere is at least one selected from nitrogen, argon, and helium. The method for producing metallic indium according to any one of claims 1 to 5, wherein an operating temperature of the molten salt electrolysis is 140 to 500 ° C. The method for producing metal indium according to any one of claims 1 to 6, wherein the metal indium-containing alloy is an alloy obtained by reducing an indium compound. The method for producing metal indium according to claim 7, wherein the indium compound is an indium oxide-containing substance. The method for producing metal indium according to claim 8, wherein the indium oxide-containing material is ITO scrap. A molten salt electrolytic cell for purifying a low melting point metal,
An anode chamber containing an alloy liquid containing the low-melting-point metal and having an opening into which an anode conductor can be inserted;
An inner cylinder for holding the molten salt layer of the low-melting-point metal halide on the contained liquid material, and allowing the liquid material to communicate in the anode chamber without causing the molten salt layer to flow outside;
It has an inlet and an outlet for the low-melting-point metal after purification, and is arranged so that the inlet is located in the molten salt layer. The lead wire for the cathode can be inserted, and the inside is the low-melting-point metal. A molten salt electrolysis cell comprising: a filled cathode chamber. The molten salt electrolyzer according to claim 10, wherein the inner cylinder is composed of one or more selected from glass, ceramics, and fluororesin. The molten salt electrolytic cell according to claim 10 or 11, wherein the inner cylinder includes an inert gas inlet and an exhaust gas outlet. The molten salt electrolytic cell according to any one of claims 10 to 12, wherein the cathode chamber is made of glass. The molten salt electrolytic cell according to any one of claims 10 to 13, wherein the cathode chamber has a plurality of the inlets. The molten salt electrolytic cell according to any one of claims 10 to 14, wherein the anode chamber is composed of one or more selected from stainless steel, iron, titanium, and graphite. The molten salt electrolytic cell according to any one of claims 10 to 15, wherein the anode chamber is made of stainless steel. The molten salt electrolytic cell according to any one of claims 10 to 16, wherein the anode chamber further has a lead-out port for leading out the refined alloy containing the low melting point metal. The molten salt electrolyzer according to claim 17, wherein a nozzle is formed at the outlet in the anode chamber. The molten salt electrolyzer according to any one of claims 10 to 18,
An alloy containing one or more metals selected from indium, tin and gallium is accommodated in the anode chamber, and a molten metal halide corresponding to the metal is held on the liquid material of the alloy in the inner cylinder. One or more metals selected from purified indium, tin, and gallium from the outlet of the cathode chamber by applying a voltage with the anode conductor and cathode conductor inserted, and performing molten salt electrolysis A method for purifying low melting point metals. The purification method according to claim 19, wherein the molten salt electrolysis is performed at 50 ° C to 400 ° C. The purification method according to claim 19 or 20, wherein the molten salt electrolysis is performed at a current density of 1 to 200 A / dm ² .

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