Selenium Leaching from Copper Anode Slimes Using a Nitric Acid–Sulfuric Acid Mixture

Abstract

Based on the Eh–pH diagram for the Se–H₂O system, a new method is proposed for leaching selenium from copper anode slimes using a nitric acid–sulfuric acid mixture. The effects of solid/liquid ratio, HNO₃ and H₂SO₄ concentrations, leaching temperature, and reaction time on the leaching efficiency of selenium were investigated. Samples were mineralogically characterized by x-ray diffraction and scanning electron microscopy with energy-dispersive spectroscopy to study the transformation of selenium-containing phases during the leaching process. The results showed that the optimal conditions comprised a solid/liquid ratio of 0.25 g/ml, HNO₃ concentration of 0.5 M, H₂SO₄ concentration of 2 M, leaching temperature of 363 K, and reaction time of 3 h. A selenium leaching efficiency of 97.79% was obtained under these conditions. Mineralogical characterization indicated that selenium occurred as Cu–Ag selenide in the raw copper anode slimes. This was first converted to elemental selenium and then to selenite ions in solution.