Preparation of 6N high-purity indium by method of physical-chemical purification and electrorefining

Abstract

The increasing demands for indium in recent years require high purity indium as raw materials. Physical-chemical purification and electrorefining have been performed to obtain 6N high purity indium. Indium is smelted by using NaOH, NaCl and NaNO₃ for 20 min at 400°C, the removing rate of Sn, Zn, Al reaches 40, 60 and 37% respectively. The removing rate of Cd is 90–95% and that of Tl reaches 40–60% when indium is smelted for 10 min by 20% glycerin solution of KI and I₂ at 180°C. When indium metal is vacuum refined in two stages: 800–900°C for 2 h and 950–1050°C for 2 h, the major impurity elements, Pb, Zn, and Bi, are effectively removed. When indium is electrolytic refined in In₂(SO₄)₃-H₂SO₄ system, in which indium content is 60–80 g/L, pH 2.0–3.0, current density 50–80 A/m², the content of impurities can be dropped and the product of indium reaches 99.9999%.