Hydrothermal oxidative leaching of Cu and Se from copper anode slime in a diluted H2SO4 solution

Abstract

In this work, aiming at solving serious environmental pollution and high energy consumption for pretreating copper anode slime, hydrothermal oxidative leaching of Cu and Se in a diluted H2SO4 solution was researched in detail. The E-pH diagrams of Cu-Se-H2O and Ag-Se-H2O systems demonstrated that the oxidation route of selenide was strongly dependent on the acid concentration. The transformation pathway was expressed as Cu2Se/Ag2Se → Se → H2SeO3 under a strong acidic condition whereas lower acid environment tended to directly form insoluble CuSeO3·2H2O and Ag2SeO3 compounds. The results of leaching experiments demonstrated that CuSeO3·2H2O and elemental Se precipitates were detected in the 0.25, 0.375 and 0.75, 1 mol/L H2SO4 leaching residues. With an optimal H2SO4 concentration of 0.5 mol/L as the leaching agent, above 99% of Cu and Se were leached at 150 °C for 120 min with a liquid solid ratio of 10 mL/g and oxygen partial pressure of 1.0 MPa. The remaining Se in the residue mainly existed in the form of Ag2Se phase. The method could be considered as a green and efficient technology for base metals removal and precious metals enrichment from copper anode slime.