Method of selective recovery of valuable metals from mixed metal oxides

Abstract

The present invention relates to a process for recovering metals from indium tin oxide (ITO) scrap. It allows the selective recovery of indium and tin from waste ITO by means of a simple and environmentally benign dissolution-deposition method, with no requirement of using strong corrosive acid/alkaline chemicals (e.g. hydrochloric acid, nitric acid, sulfuric acid and sodium hydroxide) for dissolution and complicated procedures/operation. The dissolution baths can be reused without observable recovery deterioration. It significantly reduces the cost requirement in the recovery process.

What is claimed is: 
     
         1 . A method for sequentially recovering indium and tin from ITO-containing waste comprising:
 a) reducing the size of ITO-containing materials by shredding and crushing so as to form finely-divided particles;   b) subjecting the finely-divided particles to chemical and physical cleaning for pre-treatment to substantially avoid the interference in dissolution step;   c) transferring the pre-treated particles to a first dissolution bath comprising a first bath formulation at a bath temperature ranging from 60° C. to 120° C. with continuous stirring for 30-180 minutes to dissolve the pre-treated particles;   d) adding 50-300% by volume of water into the solution containing the dissolved particles from step (c) to form a first mixture and filtering the first mixture so as to collect an indium-rich filtrate and a tin-rich filtrand;   e) putting an indium plate in the indium-rich filtrate for 1-10 hours to remove the tin residue by a displacement reaction;   f) recovering indium with purity not less than 99.9% from the indium-rich filtrate by a first deposition process;   g) reusing the dissolution bath in step (c) for the next recovery cycle after water evaporation.   
     
     
         2 . The method of  claim 1 , further comprising:
 h) transferring the tin-rich filtrand obtained from step (d) to a second dissolution bath comprising a second bath formulation at a bath temperature ranging from 60° C. to 120° C. with continuous stirring for 30-180 minutes to dissolve the tin-rich filtrand;   i) adding 50-300% by volume of water into the solution containing the dissolved tin-rich filtrand to form a second mixture and filtering the second mixture so as to collect tin-rich filtrate and non-dissolved substrates;   j) recovering tin from the tin-rich filtrate obtained in step (i) by a second deposition process;   k) reusing the second dissolution bath in step (h) for the next recovery cycle after water evaporation.   
     
     
         3 . The method of  claim 1 , wherein the first bath formulation comprises the following components:
 one or more than one kind of organic halide salts, wherein cation of the organic halide salts comprise tetraalkylammonium, (di-, tri- and tetra alkyl)imidazolium, alkylpyridinium, dialkylpyrrolidinum, dialkylpiperidinium, tetraalkylphosphonium, tetralkylsulfonium, dialkylpyrazolium, and N-alkylthiazolium; and   20-80 mol % of dicarboxylic acid, said dicarboxylic acid comprising oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid.   
     
     
         4 . The method of  claim 3 , wherein the cation of the organic halide salts is tetraalkylammonium and the dicarboxylic acid is oxalic acid; said organic halide salts and dicarboxylic acids are in a molar ratio of 1:1. 
     
     
         5 . The method of  claim 1 , wherein the first deposition process is an electrodepsition process of indium comprising the following operation conditions and/or components:
 a pH of not higher than 1.5;   current density from 0.6 to 4 mA/cm 2  or voltage from 2V to 4V;   electrodeposition time from 10 to 60 minutes;   temperature from 20° C. to 70° C.;   a substrate for electrodepositing indium from the indium-rich filtrate comprising titanium, stainless steel and graphite; and   a counter electrode comprising titanium, platinum and graphite.   
     
     
         6 . The method of  claim 2 , wherein the second bath formulation comprises the following components:
 one or more than one kind of organic halide salts, wherein cation of the organic halide salts comprise tetraalkylammonium, (di-, tri- and tetra alkyl)imidazolium, alkylpyridinium, dialkylpyrrolidinum, dialkylpiperidinium, tetraalkylphosphonium, tetralkylsulfonium, dialkylpyrazolium, and N-alkylthiazolium; and   20-80 mol % of carboxylic acid, said carboxylic acid comprising trifluoroacetic acid, trichloroacetic acid, dichloroacetic acid, chloroacetic acid, propanoic acid, butyric acid, and valeric acid.   
     
     
         7 . The method of  claim 6 , wherein the cation of the organic halide salts is tetraalkylammonium and the carboxylic acid is trichloroacetic acid; said organic halide salts and carboxylic acids are in a molar ratio of 1:2. 
     
     
         8 . The method of  claim 2 , wherein the second deposition process is an electrodeposition process of tin comprising the following operation conditions and/or components:
 a pH of not higher than 1;   current density from 0.8 to 5 mA/cm 2  or voltage from 2.2V to 4.5V;   electrodeposition time from 10 to 60 minutes;   temperature from 20° C. to 70° C.;   a substrate for electrodepositing tin from the tin-rich filtrate comprising titanium, stainless steel and graphite; and   a counter electrode comprising titanium, platinum and graphite.   
     
     
         9 . The method of  claim 1 , wherein the displacement reaction comprises a galvanic displacement process by an indium plate for removing tin residues from the indium-rich filtrate after said first deposition process. 
     
     
         10 . The method of  claim 1 , wherein the ITO-containing materials comprises ITO-containing scraps and ITO-containing powders from display panel, solar cell panel, or consumer electronic by-products. 
     
     
         11 . A bath formulation for dissolving indium to form an indium-rich solution, said formulation comprising:
 one or more than one kind of organic halide salts, wherein cation of the organic halide salts comprise tetraalkylammonium, (di-, tri- and tetra alkyl)imidazolium, alkylpyridinium, dialkylpyrrolidinum, dialkylpiperidinium, tetraalkylphosphonium, tetralkylsulfonium, dialkylpyrazolium, and N-alkylthiazolium; and   20-80 mol % of dicarboxylic acid, said dicarboxylic acid comprising oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid.   
     
     
         12 . The bath formulation of  claim 11 , wherein the cation of the organic halide salts is tetraalkylammonium and the dicarboxylic acid is oxalic acid; said organic halide salts and dicarboxylic acids are in a molar ratio of 1:1. 
     
     
         13 . A bath formulation for dissolving tin to form a tin-rich solution, said formulation comprising:
 one or more than one kind of organic halide salts, wherein cation of the organic halide salts comprise tetraalkylammonium, (di-, tri- and tetra alkyl)imidazolium, alkylpyridinium, dialkylpyrrolidinum, dialkylpiperidinium, tetraalkylphosphonium, tetralkylsulfonium, dialkylpyrazolium, and N-alkylthiazolium; and   20-80 mol % of carboxylic acid, said carboxylic acid comprising trifluoroacetic acid, trichloroacetic acid, dichloroacetic acid, chloroacetic acid, propanoic acid, butyric acid, and valeric acid.   
     
     
         14 . The bath formulation of  claim 13 , wherein the cation of the organic halide salts is tetraalkylammonium and the carboxylic acid is trichloroacetic acid; said organic halide salts and carboxylic acids are in a molar ratio of 1:2.