Oxidative acid leaching of indium phosphide waste and recovery of indium metal by cementation with aluminum

Abstract

This study presents a concise and effective method for waste indium phosphide (InP) recycling through hydrometallurgy. The waste InP was initially processed with H2SO4 in the presence of sufficient H2O2, by which phosphorus is oxidized to the valence state of +5 in the form of stable H3PO4 and indium is dissolved as soluble In3+ in the solution. As a result, efficient leaching of waste InP was achieved. Under the optimized conditions of H2SO4 concentration of 3 mol/L, H2O2/InP mole ratio of 4, liquid to solid ratio of 4, temperature of 80 °C, and reaction time of 3 h, the leaching efficiency of indium reached over 99%. Subsequently, indium was recovered from the pregnant leach solution (PLS) in the form of metallic In sponge through cementation with an aluminum plate. At the reaction temperature of 85 °C, the precipitated indium sponge could spontaneously strip from surface of aluminum plate to facilitate the cementation process, eventually achieving an overall indium recovery of over 90%. The reaction mechanisms of both the oxidative acid leaching and cementation processes are elucidated based on the thermodynamic evaluations and experimental findings.