Recovery and purification of indium from waste sputtering target by selective solvent extraction of Sn

Abstract

A large volume of indium is being discarded from electronics factories in the forms of waste sputtering targets, polishing slurry, and etching slurry. Of these, waste sputtering targets consist mainly of indium together with tin (∼10 wt%) and a small amount of impurities of other metals. As such, it is more advantageous and environmentally benign to extract tin rather than indium for removal in terms of the purification process since much smaller amount of raffinate (∼1/25) and lead time (∼1/9) are required compared to conventional processes such as cementation and In-extraction. This study examined the process of removing Sn impurities from waste sputtering targets through a solvent extraction method. Among PC88A, D2EHPA, Alamin 336 and versatic acid, PC88A was selected as the most suitable solvent for the purpose of this study, and acid concentration (M_H⁺) = 2 M, the volume ratio of organic to aqueous phase (O/A) = 3, and retention time = 10–15 min were determined as the optimal conditions to extract Sn impurities only, not indium. Acid concentration (M_H⁺) = 3.0 M was the suitable condition to scrub indium containing small amounts in the organic phase from which Sn was extracted. Meanwhile, acid concentration (M_H⁺) = 12.0 M was the appropriate condition for stripping the extracted Sn. When the Sn was removed in a pilot-scale continuous apparatus under the aforementioned conditions, it was confirmed that indium was purified with In concentration = 180 g L⁻¹, Sn = 4–11 ppm. Indium in the purified solution was reduced, and then electrorefining was performed. As a result, 99.9976% pure indium ingots could be obtained.