Some studies on sulfuric acid leaching of anode slime with additives

The most effective hydrometallurgical processing of anode slime is based on a chlorination route. However, it requires special attention with respect to pollution problems and construction materials. To minimize the problems, a new hydrometallurgical approach was pursued for the recovery of valuable metals and metalloids from copper electrorefining anode slime. The process involved the leaching of anode slime in sulfuric acid medium. At room temperature, sulfuric acid leaching without any additive resulted in poor recoveries of metals other than copper. With the addition of MnO2 to the leaching system at room temperature, an increase in the recovery values of copper, selenium, and tellurium was found. The recovery was further increased to 90% Cu, 37% Se, and 66% Te with an increase in temperature to 80 degreesC. However, the recoveries of Ni (13%), Au (trace), and Ag (9.5%) were poor. Satisfactory amounts of copper, selenium, tellurium, and gold were leached when both manganese dioxide and sodium chloride were added during leaching. The maximum recoveries were 90% Cu, 80% Se, 79% Te, and 77% Au at 50 degreesC after 40 min of leaching. The effects of various parameters such as time, temperature, solid/liquid ratio, amount of additives, and acid concentration on the recoveries of metals were studied. The kinetics of leaching was also examined at different temperatures. The dissolution of metals was observed to be very fast with both manganese dioxide and sodium chloride addition even at room temperature. The leaching kinetics of selenium, tellurium, and gold with manganese dioxide and sodium chloride additives followed the ash diffusion control model, whereas copper leaching followed the mixed control (chemical and ash diffusion control) model. These leaching mechanisms were further corroborated with SEM findings.