Recovery of indium from the etching solution of indium tin oxide by solvent extraction

The etching waste solution from the indium-consuming fabrication processes is considered as the viable resource for indium recovery. The extraction equilibrium of indium(III) from a hydrochloride acid solution using di-(2-ethylhexyl) phosphoric acid (D2EHPA) as an extractant and dissolved in kerosene by solvent extraction was studied. To optimize the extraction and separation of indium from etching waste solution, the effects of O/A ratio, pH, and extractant concentration on the distribution ratios of In(III) and selective precipitation of alumina, cerium, and iron from indium were also investigated in this work. The experimental results showed that satisfactory separation of alumina, cerium, and iron from indium was achieved with 0.3 M D2EHPA at room temperature and pH values ranging from 1 to 1.5. In this process, 92% of indium could be extracted from 0.74 to 8.62 g/L at an O/A ratio of 1:1. Quantitative stripping experiments of indium by HCl showed that the preferred O/A phase ratio was 1:2 or less at HCl concentration of 2.0 M to attain a high indium recovery and minimum iron coextraction. Where maximum purity is desired, the extraction is desirably carried out in three theoretical extraction stages. Based on these results, the aqueous and organic phase parameters can be easily manipulated to attain a high separation efficiency of indium(III) from commonly associated elements.