Pre-removal and kinetic analysis of copper from anode slime by oxidation at atmospheric pressure

Copper anode slime, rich in precious metals (gold, silver, platinum and palladium) and rare metals (selenium and tellurium), is an important raw material for the extraction of rare precious metals. However, a certain anode slime contains more than 10% of Cu, and the excessive copper may increase the consumption of leaching agents in the subsequent precious metal recovery and thus seriously affect the recovery ratio of gold and silver, which needs to be removed in advance. Based on thermodynamic analysis, XRD, SEM-EDS and other characterization methods, pre-removal of copper from anode slime was carried out at normal pressure in a sulfuric acid medium with MnO₂ as the oxidant. The effects of H₂SO₄ concentration, MnO₂ addition, leaching time, liquid-solid ratio, reaction temperature and other factors on the copper leaching ratio of anode slime were investigated, respectively. Furthermore, the kinetics of the copper leaching process were analyzed according to shrinking unreacted core model. The results show that the reaction rate of copper leaching process is controlled by diffusion, with an apparent activation energy of 4.1 kJ/mol. Under the conditions of initial H₂SO₄ concentration of 100 g/L, MnO₂ concentration of 10 g/L, leaching time of 120 min, liquid-solid ratio of 4:1, reaction temperature of 80 °C, the leaching ratio of Cu can reach 92.19%. Under the same conditions, part of arsenic and selenium are also leached, and the leaching ratios are maintained at about 28% and 13%, respectively.