WO2006046800A1

WO2006046800A1 - Method for manufacturing high purity indium and apparatus therefor

Info

Publication number: WO2006046800A1
Application number: PCT/KR2005/002387
Authority: WO
Inventors: Sang Mo Woo; Chong Ho Sonu; Kyu Young Song
Original assignee: 9Digit Company Limited
Priority date: 2004-10-26
Filing date: 2005-07-22
Publication date: 2006-05-04
Also published as: KR100614890B1; KR20060036629A

Abstract

The present invention relates to a method for producing high-purity indium wherein indium is refined with high-purity for use as a starting material of a target material ITO (Indium Tin Oxide) used for the conductive film of liquid crystal display and apparatus therefore. The present invention relates to a molten salt electrorefining, wherein assistant indium including tin as the main impurity is refined with high-purity, and thus, as compared with a conventional aqueous electrolysis, removal efficiency of tin and productivity are raised at least by three times, which is an art regarding a method for refining indium and an apparatus therefore, characterized in that electrorefining is carried out at a temperature no less than a melting point of the electrolyte using assistant indium as an anode and using InCl or a composite compound of InCl and ZnCl asan electrolyte. Indium, Molten salt electrolysis, InCl, Zncl

Description

METHOD FOR MANUFACTURING HIGH PURITY INDIUM AND APPARATUS THEREFOR

Technical Field

[1] The present invention relates to a method for producing high-purity indium wherein indium is refined with high-purity for use as a starting material of a target material ITO (Indium Tin Oxide) used for the conductive film of liquid crystal display and apparatus therefore. Background Art

[2] Conventionally, indium is refined by electrowinning using an insoluble anode or by electrorefining using assistant indium including impurities as an anode.

[3] The combination of conventional wet refining processes such as an acid dissolution method, ion-exchange method and solvent extraction method is used: for example a method that cleanses and pulverizes ITO scrap, dissolves with nitric acid, precipitates and gets rid of impurities such as tin, lead and copper as sulfide by blowing hydrogen sulfide into the solution, neutralizes with ammonia, and recovers as indium hydroxide.

[4] In Japanese Patent Laid-Open No. 2001-240992 a method for recovering indium by electrolytic refining by regulating the conditions of an electrolytic in such a manner that the dendrite deposits to be the cause for shorting may be prevented, and by regulating the chlorine ion concentration in an electrolytic refining liquid to 10 to 40 g/ L using alkali metal salt compounds of hydrochloric acid, sodium chloride, potassium chloride and indium hydroxide and indium trichloride thereby preventing the dropping of current efficiency and the formation of the dendritic electrodeposits.

[5] In U.S. Patent No. 4,287,030 a method is described in which the metal is vacuum melted in the first stage at a temperature of from 850 to 94O⁰C for 1 to 5 hours; in the second stage at a temperature of from 950 to 1,100⁰C for 0.5 to 2 hours. Thereafter, the metal is subjected to an electrochemical refinement in a hydrochloric acid solution, while the residue of indium evolved on the cathode is remelted by introducing into molten indium at a temperature of from 16O⁰C to 400⁰C.

[6] Further, in U.S. Patent No. 5,543,031 a channel purification method is described, comprising: using sulfuric acid solution as an anolyte for an anode compartment, using an indium-containing hydrochloric acid solution as a catholyte for a cathode compartment, separating said cathode compartment and said anode compartment with a cation exchange membrane. Disclosure of Invention Technical Problem [7] The above-mentioned methods use an aqueous solution wherein indium exists as ionic status (In ⁺) as an electrolyte, and obtain indium which is electrodeposited on the cathode by current sent through a rectifying device.

[8] Plenty of studies regarding aqueous electrolysis have been made, and it is a com¬ mercially verified method. However, too many electrolytic cells are required for mass production because of its low productivity resulted from the low-density range of producing high-purity indium of 0.1-2.0 A/dm .

[9] Further, owing to the development of liquid crystal industry, waste ITO target scrap used for liquid crystal conductive film is often used as a raw material of indium refining, in which case replacement of tin, the main impurity is necessary. Tin has very similar chemical features with indium so that if tin exists at an electrolyte or anode indium, it causes the degree of purity of indium to decrease, which makes the process of replacing tin necessary before carrying out aqueous electrolysis, which complicates the process. Technical Solution

[10] In order to solve the previously described problems of aqueous electrolysis, the inventors of the present invention produced a novel method after a long period of study, aiming at raising productivity, and at providing a method for directly refining indium whose tin content is high and apparatus therefore.

[11] To achieve the above technical subject matter, the present invention provides a method for producing high-purity indium wherein indium is refined with high-purity by molten salt electrolysis in which InCl is used as the molten salt electrolyte.

[12] Additionally, the present invention provides a method for producing high-purity indium, wherein the electrolyte of InCl also contains ZnCl .

[13] Additionally, the present invention provides a method for producing high-purity indium, wherein the content of ZnCl 2 is 33-50% wt% of InCl.

[14] Additionally, the present invention provides a method for producing high-purity indium, wherein a temperature of the molten salt electrolyte is 200~350°C.

[15] Additionally, the present invention provides a method for producing high-purity indium, wherein current density in the molten salt electrolysis is 10-30 A/dm².

[16] Additionally, the present invention provides an apparatus for producing high-purity indium, characterized in that a cathode electrolysis cell consists of conductive material, a upper part of a inner wall of the cell is electrically isolated while a lower part of the inner wall is not electrically isolated, and a top of the cell is closed with a non- conductive cover having anode inlet through which anode indium and the electrolyte are charged into the cell; an anode crucible is arranged in the cathode electrolysis cell and containing anode indium; an indium outlet is arranged at a lower part of the cathode electrolysis cell through which refined indium is continuously discharged; a rectifying device causes current to flow between the anode crucible and the carhode of electrolysis cell, and a heater controls a temperature of the cathode electrolysis cell.

[17] Additionally, the present invention provides an apparatus for producing high-purity indium, characterized in that an anode connector is used at the anode.

[18] Additionally, the present invention provides an apparatus, characterized in that the anode connector is made of graphite or metals from family IV ~ VI of the periodic table.

Advantageous Effects

[19] As previously mentioned, the present invention has a remarkable effect in producing 99.999% of high-purity indium from low quality indium containing a large amount of impurities including tin with high tin removed efficiency and high pro¬ ductivity.

[20] Molten salt electrolysis is different from aqueous electrolysis in that molten salt electrolysis has the advantages that large volumes of electrolyte or pH regulation are not required.

[21] Especially, the above-described electrolysis apparatus has the effect that continuous operation can be carried out through an anode inlet and an indium outlet. Brief Description of the Drawings

[22] Fig.1 describes an apparatus for molten salt electrolysis of the present invention.

[23] - Explanation of the numerals of the main portions of the figure-

[24] 1: Electrolysis cell 2: Anode crucible 3: Anode connector 4: Anode indium

[25] 5: Cathode indium 6: Electrolyte 7: Inner wall 8: Heater

[26] 9: Cover 10: Anode inlet 11: Cover of anode inlet

[27] 12: Gas outlet 13: Indium outlet 14: Rectifying device

Best Mode for Carrying Out the Invention

[28] Hereinafter, a detailed description about the constitution of producing method of the present invention follows.

[29] Chloride is the most preferable composition of an electrolyte among indium compounds, and among indium chlorides, InCl, InCl and InCl InCl is the most preferable to raise productivity. Indium in InCl exists as a univalent ion (In⁺), and therefore productivity increases at least three times than that of aqueous electrolysis using In ⁺ under the same current condition.

[30] InCl alone can be used as an electrolyte, however more than two types of electrolytes are used by adding the second compound, that is, chloride when it is necessary to maintain the content of tin in the refined indium less than 2ppm in case that the tin content of the impurities are over 0.01% or although the content of tin in impurities are no more than 0.01%. The second chloride excluding InCl can be NaCl, KCI PbCl MgCl and ZnCl ; however, ZnCl is the most suitable considering working convenience because the melting temperature of the chloride composite of InCl and ZnCl 2 is the lowest.

[31] Chloride composites consisting of more than two types of chloride are not preferable because refining efficiency is not remarkably higher than that consisting of two types of chlorides such as InCl+ZnCl .

[32] When using both InCl and ZnCl as electrolytes, the content of ZnCl is preferably

33-50 wt%, and the content of InCl 57 wt% and ZnCl 43 wt% are the most preferable. This is because at such content the melting point is lowest, which allows work at a relatively low temperature. Problems occur when the content of ZnCl is lower than 33wt% that removal efficiency of tin decreases, and when higher than 50wt% that the zinc content of refined indium increases sharply.

[33] Even if electrolytic refining can be carried out at a temperature no less than a melting point of the electrolyte (137⁰C), a preferable temperature of electrolyte is 200 to 35O⁰C because a temperature of lower than 200⁰C worsens flowability of the molten electrolyte, and thus lowers refining effect and current efficiency, and because a temperature of higher than 35O⁰C causes loss due to evaporation of electrolyte although refining effect does not decrease.

[34] In case of cathode, an electrolysis cell itself can be used as a cathode.

[35] Current density of electrolysis is preferably 10-30 A/dm². At a current density no more than 10 A/dm² refining effect increases but productivity decreases. At a current density more than 30 A/dm² it is difficult to obtain high-purity indium, specifically more valuable metal elements such as copper (Cu), lead(Pb) and tin(Sn) increase. At the range of current density 5 to 300 times higher productivity than that of the current density of 0. l~2.0A/dm² used for aqueous electrolysis can be expected.

[36] Hereinafter, an explanation of the apparatus of the present invention as a possible embodiment of the invention is provided.

[37] Fig.1 is a diagrammatic view of the apparatus of the present invention.

[38] A electrolysis cell (1) consists of conductive material, and serves as the cathode, and a upper part of a inner wall of the cell is provided with an insulating layer (7) electrically isolated by a insulator such as quartz while a lower part of the inner wall is not electrically isolated, and a top of the cell being closed with a non-conductive cover (9). A heater (8) is equipped at the bottom and side of the electrolysis cell (1) externally.

[39] The non-conductive cover (9) has an anode inlet (10) through which anode indium

(4) to be refined and an electrolyte (6) are charged into the cell; the anode inlet (10) is closed with a cover (11); a gas outlet (12) that discharges generated gas is provided at a certain area of the non-conductive cover (9).

[40] An anode crucible (2) containing anode indium (4) is arranged in the electrolysis cell (1). The anode crucible (2) should not react with anode indium (4) and indium compounds, preferably consisting of Pyrex or quartz, and preferably circular- shaped for even distribution of current.

[41] Additionally, a rectifying device (14) causing current to flow between anode indium

(4) and the cathode electrolysis cell (1) is arranged.

[42] Fig.l describes an electrolysis device where an anode connecter (3) is used.

[43] Molten salt electrolysis basically uses indium to be refined as an anode, but the anode connector (3) can be provided to connect molten indium and a rectifying device. The anode connector (3) should be a conductor that does not react with molten indium, and should feature high corrosion resistance. The anode connector is preferably made of graphite or metals from family IV -VI of the periodic table.

[44] Hereinafter, the operation of molten salt device of the present invention is described.

[45] Through an anode inlet (10) in the electrolysis cell (1), anode indium (4) is charged into an anode crucible (2), and then an electrolyte (6) is charged through the same anode inlet hole. Thereafter, a heater (8) is turned on to control temperature, and a rectifying device (14) between anode and cathode provides current. Here, anode indium (4) can be provided with current directly or through the anode connector (3).

[46] Gas generated during electrolysis is discharged through a gas outlet (12) and passes through a scrubber (not shown), and refined indium (5) selected at the cathode is obtained through an indium outlet (13). Said electrolysis device has the effect that continuous operation can be carried out through the anode inlet (10) and the indium outlet (13).

[47] (Examples)

[48] Hereinafter, the present invention is more specifically explained with the following examples.

[49] (Example 1)

[50] Molten salt electrolysis was carried out using indium of which impurities include

30ppm of tin as an anode and using two types of electrolytes, InCl and InCl-I-ZnCl₂. Electrorefining was carried out at a current density of 10 A/dm and at a temperature of 25O⁰C, and the purity of the refined indium was evaluated by ICP. The results are as provided in Table 1. Removal efficiency of tin was higher when composite electrolyte InCl+ZnCl was used than InCl alone was used, and the degrees of purity in both cases were at least 99.998%.

[51] Table 1

Impurity contents of refined indium depending on the type of electrolytes

[52] (Example 2)

[53] Molten Salt electrolysis was carried out using assistant indium of which impurities include 10% of tin as an anode and using InCl+ZnCl as an electrolyte. [54] Electrorefining was carried out at a current density of 10A/dm and at a temperature of 32O⁰C, and purity of refined indium was evaluated by ICP. The results are as provided in Table 2. [55] Electrorefining was carried out for assistant indium containing tin in large amount of 10%, and exhibiting the purity of 90% or less, and as a result 4N(99.99%) grade of refined indium was obtained, and it was found that the composite electrolyte of

InCl+ZnCl was efficient in removing tin. [56] Table 2

Impurity contens of refined indium

[57] (Example 3)

[58] Molten salt electrolysis was carried out using as an anode 99.9 % pure 3N(Three nine) assistant indium which was recovered generally from indium scrap and exhibited the purity of 99.9% and using InCl+ZnCl as an electrolyte. [59] Electrorefining was carried out at a current density of 15 A/dm and at a temperature of 28O⁰C, and purity of refined indium was evaluated by ICP. The results are as provided in Table 3. [60] The purity of the refined 3N indium satisfies 99.998% of the purity which is required for use as ITO. [61] Table 3

Impurity contents of refined indium

[62] (Comparison Example) [63] Electrolysis was carried out at a temperature of 3O⁰C and at a current density of 2 A/dm in aqueous indium electrolyte having the indium concentration of 40 g/1 and of the chlorine concentration of 100 g/1 using the anode used in Example 3, and the refined indium was evaluated by ICP. The results are as provided in Table 4.

[64] As can be seen in the following table, although aqueous electrolysis also has the refining effect, the concentration of impurities is higher than that of molten salt electrolysis, specifically the content of the major impurity tin was no less than 5ppm.

[65] Table 4 Impurity contents of refined indium after aqueous electrolysis

[66] As can be seen in Examples 1 to 3 of the present invention, the present invention can obtain higher-purity indium than the above-mentioned Comparison Example. Industrial Applicability

[67] According to the present invention, an apparatus for producing high-purity indium can be made in a small version, and the process is simple so that a user can easily produce high-purity indium by oneself, and the process can continuously isolate high- purity indium from indium with high content of tin. Thus, the present invention can provide the industry with high-purity indium sufficiently.

Claims

[1] Method for producing high-purity indium wherein indium is refined with high- purity by molten salt electrolysis in which InCl is used as the molten salt electrolyte.

[2] The method for producing high-purity indium according to Claim 1, wherein the electrolyte of InCl also contains ZnCl .

[3] The method for producing high-purity indium according to Claim 2, wherein the content of ZnCl 2 is 33-50% wt% of InCl.

[4] The method for producing high-purity indium according to one of Claims 1 to 3, wherein a temperature of the molten salt electrolyte is 200~350°C.

[5] The method for producing high-purity indium according to one of Claims 1 to 3, wherein current density in the molten salt electrolysis is 10-30 A/dm².

[6] Apparatus for producing high-purity indium comprising: a cathode electrolysis cell consisting of conductive material, a upper part of a inner wall of the cell being electrically isolated while a lower part of the inner wall is not electrically isolated, and a top of the cell being closed with a non- conductive cover having anode inlet through which anode indium and the electrolyte are charged into the cell; an anode crucible arranged in the cathode electrolysis cell and containing anode indium; an indium outlet arranged at a lower part of the cathode electrolysis cell through which refined indium is continuously discharged; a rectifying device causing current to flow between the anode crucible and the cathode electrolysis cell; a heater controlling a temperature of the cathode electrolysis cell.

[7] The apparatus according to Claim 6, an anode connector is used at the anode.

[8] The apparatus according to Claim 7, the anode connector is made of graphite or metals from family IV ~ VI of the periodic table.