A green process for simultaneously efficient base metals removal and precious metals enrichment from copper anode slime

Abstract

In this study, a green process consisting of NaOH roasting - water leaching - synergistic acid leaching with only low-concentration and green reagents employed, was developed for simultaneously efficient base metals removal and precious metals enrichment from copper anode slime. Results showed that: (1) phases prepared by the first NaOH roasting under the NaOH/slime ratio of 1.0, roasted at 700 °C for 2.0 h, was easier to remove base metals but harder to extraction PMs; (2) 76.39% Pb, 79.29% Sn, 87.72% S and 95.20% As were dissolved by the second water leaching; (3) main base metals including 99.68% Cu, 81.99% Ni and 99.94% Sb were removed by the final synergistic acid leaching under H2SO4 of 2.00 mol/L, tartaric acid of 0.33 mol/L, H2O2 of 0.44 mol/L, the solid-liquid ratio of 25 g/L and 80 °C. As a result, 99.98% Ag, 99.50% Au and 91.00% Pd were retained with their contents enriched by 517.08%, 330.77%, and 400.00%, respectively. The calculated negative Gibbs Free Energy Changes indicated that the roasting reactions can proceed spontaneously. Moreover, electric potential-pH analysis of the acid leaching unit suggested that the effective removal of Sb and high retention of Ag was attributed to the complexation of tartaric acid and its interaction with H2O2. In addition, the valuable base metals in the leachates were successfully recovered. Therefore, the process could be a novel green technology for simultaneously efficient base metals removal and precious metals enrichment from copper anode slime.