WO2006080742A1

WO2006080742A1 - Method for recovering high purity indium

Info

Publication number: WO2006080742A1
Application number: PCT/KR2005/003365
Authority: WO
Inventors: Sang Mo Woo; Chong Ho Sonu; Kyu Young Song
Original assignee: 9Digit Company Limited
Priority date: 2004-10-26
Filing date: 2005-10-10
Publication date: 2006-08-03
Also published as: KR20060036631A; KR100614891B1

Abstract

The present invention relates to a method for recovering indium, comprising a first electrolysis of removing tin through a dry reduction to an indium-tin alloy under the atmosphere of inert gas from the indium scrap such as ITO waste target; a second electrolysis for highly purifying indium; and vacuum refining in which inflowed zinc is removed when electrolyzing. The present invention provides a method for recovering high-purity indium, comprising a reduction step where scraps containing indium oxide are reduced into alloy; molten salt- electrolyzing step where the alloy is used as an anode and InCl and ZnCl as electrolyte; and vacuum refining step where the refined indium melts obtained from the molten salt-electrolyzing step is treated in a vacuum cell to remove impurities having high vapor pressure. Since the recovering process of the present invention is only consisted of three different types of a simple dry process of recovering-electrolysis-vacuum refining, there is an advantage that it produces no waste water and 95% of recovery yield of indium can be attained with high productivity and low cost.

Description

METHOD FOR RECOVERING HIGH-PURITY INDIUM

Technical Field

[1] The present invention relates to a method for recovering high purity indium from a scrap containing indium such as an ITO (Indium Tin Oxide) waste target used for transparent conductive film of liquid crystal display.

[2] An ITO waste target is consisted of indium oxide (In O ) and tin oxide (SnO ), and, the main impurities in recovering indium are tin. Generally, a method for recovering indium from an ITO waste target, as shown in fig. 2, goes through the processes of pulverizing waste target and leaching it with acid, neutralizing the leached acid solution, removing tin by precipitating it to hydroxide tin (Sn(OH )), and additionally removing impurities such as copper (Cu) and lead (Pb) by blowing gas such as H S. A method for recovering refined indium is used wherein the refined solution uses aluminium (Al) or zinc (Zn) to recover a first indium through cementation, and then the recovered first indium is electro-refined as an anode or a method for recovering refined indium is used wherein electrolytes are extracted by using insoluble anode directly in the refined solution.

[3] Japanese Patent Laid-Open No. 2002-69544 discloses a method for obtaining an

Sn-free solution by making an indium chloride solution by dissolving a scrap containing ITO indium in a hydrochloride acid solution, adding sodium hydroxide solution to said solution, removing the tin contained in the scrap to hydroxide tin, and substituting indium with zinc.

[4] In addition, Japanese Patent Laid-Open No. 2000-169991 discloses a method of dissolving an ITO target scrap, material containing indium, in the hydrochloride acid solution, neutralizing the pH to 0.5-4 by adding alkali in order to precipitate specific metals, blowing hydrogen sulfide gas into it, and sending it to the electrolytic process by precipitating and removing metal ions hazardous to the electrolytic process, the later process, as sulfide.

[5] In addition, Korean Patent No. 142933 discloses a method for recovering indium from indium-tin oxide waste target, comprising: a first step of pulverizing a target composed of an indium-tin oxide, a second step of obtaining leached solutions containing indium by leaching a resulting pulverized materials with an acid, and a third step of electrowinning using said leached solutions as an electrolyte.

[6]

Background Art

[7] However, since hydroxide of tin generated during said process is precipitated in a form of gel, it is difficult for it to be filtrated and to perform a complete solid- liquid separation. In addition, indium recovered after cementation, which is a form of sponge, has problems such that the surface becomes oxidized if it is not cast within a short period of time.

[8] Since an aqueous solution electrolysis refining indium ultimately should be performed at a low current density in order to refine to an indium with high purity, and a filtration step should be gone through in every process, it has a problem that it should go through a number of processes until the final product is released, and thus the productivity is low. Also, since losses of indium are inevitable as it goes through many processes, it is difficult to anticipate a final recovery yield higher than 95%.

[9] Particularly, said processes are all a wet process handling a great deal of solutions, and thus a problem of a wet process such as producing waste water after the process is inevitable, and produced waste water should be taken care of. Therefore, it is a cause of increasing the cost. Disclosure of Invention Technical Problem

[10] In order to solve the above-mentioned problems, the present invention is invented after a long period of studies by the inventors of the present invention, and with regard to processes of recovering and refining indium from indium scrap as well as ITO, the present invention aims at providing methods of recovering and refining indium composed only in a dry process where the number of processes are reduced epochally which used to be problems of the conventional wet process, which produces no waste water and has a high productivity and a final recovery yield higher than 95%. Technical Solution

[11] In order to solve the above-mentioned problems, the present invention provides a method for recovering high-purity indium, comprising a reduction step where scraps containing indium oxide are reduced into alloy; molten salt-electrolyzing step where the alloy is used as an anode and InCl and ZnCl a electrolyte; and vacuum refining step where the refined indium melts obtained from the molten salt-electrolyzing step is treated in a vacuum cell to remove impurities having high vapor pressure.

[12] In addition, the present invention provides a method for recovering high-purity indium, characterized by in the reduction step the reduction is occurred using active charcoal.

[13] In addition, the present invention provides a method for recovering high-purity indium characterized by in the reduction step is carried out under inert gas atmosphere.

[14] In addition, the present invention provides a method for recovering high-purity indium, characterized by in the reduction step the rejection is occurred adding Na CO , K CO , NaOH or KOH alone or combination thereof.

2 3

[15] In addition, the present invention provides a method for recovering high-purity indium, characterized by the step of electrolyzing molten salt comprising a first electr olysis for separating and removing Sn and a second electrolysis for highly purifying indium from which Sn is separated.

[16] In addition, the present invention provides a method for recovering high-purity indium, characterized by the vacuum refining step is carried out in a degree of vacuum of 10³~10^~4 torr and at temperature of 800~900°C.

Advantageous Effects

[17] Since the recovering process of the present invention is consisted of three different types of a simple dry process of reduction-electrolysis-vacuum refining, there is an advantage that it produces no waste water and that indium can be recovered with high productivity and low cost. Brief Description of the Drawings

[18] Fig. 1 describes a process drawing for indium recovery of the present invention.

[19] Fig. 2 describes a process drawing for indium recovery of the conventional method.

Best Mode for Carrying Out the Invention

[20] Hereinafter, a detailed description about the present invention referring to the drawing follows.

[21] Fig. 1 is a recovery process of the present invention, comprising a reduction step where the powder of crushed ITO oxidized substance is made into an alloy of indium and tin, a first molten salt electrolysis in which tin is removed from the reduced indium-tin alloy, a second molten salt electrolysis in which indium firstly removed with tin is made to have high purity, and a vacuum refining step of eradicating Zn wherein a small amount is mixed when molten salt is electrolyzed.

[22] Hereinafter, each process is more specifically explained.

[23] <Reduction step>

[24] A reduction process is a process necessary for reducing ITO, an oxidized substance of indium and tin to a metal and using it as an anode for an electrolysis process. If alloy of indium-tin is made by reducing ITO, theoretically, it results in an alloy of 90.4% of indium and 9.6% of tin.

[25] In order to reduce an oxidized substance, a reducing agent that can remove oxygen from the oxidized substance under a condition heated above a fixed temperature is required, and as a reducing agent, hydrogen gas or activated charcoal can be used. If hydrogen gas is used, the necessary temperature is between 700~900°C, and as for the temperature of activated charcoal, 900- 1200⁰C is required. A reduction by hydrogen gas can be operated at a temperature lower than the case of using activated charcoal. [26] However, since the melting points of indium and tin are as low as 157⁰C and 232⁰C respectively, there is a problem that the reduction reaction might not be further progressed because it becomes a molten condition at the same time of reduction, and the molten alloy contacts the surface of ITO powder where a reduction is not yet progressed.

[27] Accordingly, as for a reduction of ITO, it is appropriate to use activated charcoal powder. At this moment, a mixture ratio of activated charcoal, theoreticlaly, is 6.25 wt% of raw materials. However, in an actual operation, the contact between activated charcoal and materials is not achieved uniformly, and some charcoals react with oxygen in the atmosphere, and thus about 7-10 wt% compared to the raw materials is required.

[28] If activated charcoal is used for reduction, the appropriate reaction temperature is

900- 1200⁰C as seen above. If it is lower than 900⁰C, the reaction rate decreases so dramatically that even if it reacts more for than 24 hours, it is not possible to anticipate a reduction rate higher than 50%. Also, at a temperature higher than 1200⁰C, the reaction rate is satisfactory; however, the price of the heating parts in the reactor furnace will increase and subsequently the price of investment will increase.

[29] In addition, reduced indium is oxidized rapidly at a temperature of higher than

25O⁰C, and thus it is necessary to prevent reduced molten indium from being oxidized by rejecting inert gas such as nitrogen or argon into a reaction cell or adding alkali compounds such as Na CO , K CO , KOH or NaOH to a reaction receptacle during the reduction reaction.

[30] If inert gas is injected, the amount and speed of injection do not affect the reaction, and a small amount of injection can prevent the oxidization. If an alkali compound is used, the injection amount is also required to be a small amount to the extent that the alkali compound can cover the surface of the reaction receptacle, and whether the amount is large or small does not affect the reaction.

[31] 815g of alloy was recovered after mixing 1000 g of ITO powder with lOOg of activated charcoal, charging it in the box furnace, and reacting them with each other under the atmosphere of nitrogen at a temperature of 1100⁰C for two hours. The results of analyzing the composition of recovered alloy are as provided in Table 1. In said example, the recoverage was 99%.

[32]

[33] Table 1

Impurity contents in indium after reduction of ITO by carbon (nitrogen atmosphere)

[34] 810g of alloy was recovered after mixing lOOOg of ITO powder with lOOg of activated charcoal, and charging it in the reaction receptacle, throwing 1Og of Na CO , and charging it in the box furnace, and reacting it at a temperature of 1100⁰C for one hour. The results of analyzing the composition of recovered alloy are as provided in Table 2. In said example, the recovery yield was 98.4%.

[35] [36] Table 2 Impurity contents in indium after reduction of ITO by carbon (Na CO is added)

[37] <Electrolysis Process> [38] The electrolysis process is divided into a first electrolysis for separating and removing tin from indium- tin alloy containing 10 wt% of reduced tin and a second electrolysis for making indium of high purity from which tin is separated. A first and second electrolysis all can be operated under the same conditions. Said electrolysis is a molten salt electrolysis using InC 1+ZnCl , not a conventional aqueous solution electrolysis, as an electrolyte and carries out an electrolysis using indium as the anode that should be refined at a temperature of 200~350°C and Graphite as the cathode. At this moment, a current density of 10-30 A/dm is appropriate.

[39] After the first electrolysis is carried out under the condition of using 815g of indium-alloy of Table 1 obtained in said reduction process as an anode, and a temperature of 25O⁰C and the current density of 2OA/ dm to obtain 73Og of indium. Indium obtained from the cathode was evaluated by ICP. The results are as provided in Table 3.

[40] [41] Table 3 Indium purity after the first electrolysis

[42] 725g of the refined indium obtained by carrying out the second electrolysis under the same operating condition as that of the indium of Table 3, was evaluated by ICP. The results are as provided in Table 4.

[43] [44] Table 4 Indium purity after the second electrolysis

[45] <Vacuum Refining> [46] Molten salt electrolysis has an excellent effect in separating and removing tin, which is main impurities when recovering indium from ITO; however, it can remain in indium by ZnCl used as an electolyte as shown above table 4.Zinc remaining in indium can be easily removed under the condition of low pressure because vapour pressure is much higher compared to indium. When vacuum refining, the appropriate degree of vacuum is 10 -10 torr and an appropriate temperature is 800~900°C. Zinc is not completely removed at a temperature lower than 800⁰C, and a temperature of higher than 900⁰C causes indium loss, and thus the temperature should not exceed 900⁰C.

[47] Indium of Table 4 is charged in a tubular vacuum furnace and refined at a temperature of 800⁰C and with the degree of vacuum of 10 torr for four hours, and then 725g of the refined indium was evaluated by ICP. As a result, 5N(Five nine) of 99.999% of indium was obtained. The results are as provided in Table 5.

[48] [49] Table 5 Indium purity after vacuum refining

Industrial Applicability

[50] Since the recovering process of the present invention is only consisted of three different types of a simple dry process of recovering- electrolysis-vacuum refining, there is an advantage that it produces no waste water and 95% or more of recovery yield of indium can be attained with high productivity and low cost, and thus the unit cost of production can be lowered remarkably and the economical efficiency can be increased. [51] In addition, the present invention can be applied not only to an oxidized scrap such as ITO waste target but also to a low indium of every type of alloy, and thus high purity indium from various alloys can be supplied. [52]

Claims

[1] Method for recovering high-purity indium, comprising a reduction step where scraps containing indium oxide are reduced into alloy; molten salt-electrolyzing step where the alloy is used as an anode and InCl and

ZnCl as electrolyte; and vacumm refining step where the refined indium melts obtained from the molten salt-electrolyzing step is treated in a vacumm cell to remove impurities having high vapor pressure. [2] The method cited in 1, in the reduction step the reduction is occurred using actived charcoal. [3] The method cited in 1, in the reduction step is performed under inert gas atmosphere. [4] The method cited in 2, in the reduction step the reduction is occurred adding Na

CO , K CO , NaOH or KOH along or combination thereof. [5] The method cited in 1, in the step of electrolyzing molten salt comprising a first electrolysis for seperating and removing Sn and a secod electrolysis for highly purifying indium from which Sn is seperated. [6] The method cited in 1, in the vacumm refining step is performed in a degree of vacumm of 10³~10^~4 torr and at temperature of 800~900°C.