The Removal of Tin from ITO-scrap Using Molten NaOH

Abstract

Indium demand has grown abruptly in the last few years at an average of ten percent per year. Consumption of indium is expected to increase throughout the next decade, especially by dint of growth for liquid crystal displays, high-definition television, semiconductor materials, batteries, low-temperature solders, and electronic application. Indium is used in various forms such as indium oxide/indium-tin oxide, indium metal and alloy, and indium compounds. 1,2 Indium-tin oxide (ITO) formed by doping indium oxide with approximately 10% of tin oxide, increases both electrical conductivity without significantly affecting transparency. Flat panel display applications for indium in the form of ITO are the most important end uses, more than onehalf of the world , s indium consumption. ITO, which has a high optical transparency and a high electrical conductivity, has been used as transparent electrodes for flat panel displays. ITO films are generally fabricated by DC magnetron sputtering using ITO ceramic target. Magnetron sputtering is favoured because it is easily applied to large area with good uniformity. However, ITO targets should be replaced before a large portion of ITO material (60-70%) has been used because of race track formation. 3-5 So, it might be said that the recycling of unused ITO target is indispensable as indium is a trace element and very expensive. As shown in In1.82Sn0.18O3 obtained by doping indium oxide with approximately 10% of tin oxide, tin is the major impurity in recovery process of indium metal from ITO target-scrap. Indium and tin are chemically very similar and separation one from the other in solution is a knotty problem. Tin has been removed from residue of acetate leaching by chemical replacement with zinc in 5-20% HCl. 6 Another method concerns neutralization of solutions containing tin to pH 1 followed by cementation with indium 7,8 or by treating with NaOH to a pH value of 2.8. 9,10 In this paper, I demonstrate a new method to remove tin and purify indium metal from ITO target scrap using molten NaOH.