Extraction of copper, zinc and cadmium from copper-cadmium-bearing slag by oxidative acid leaching process

An intensified oxidative acid leaching of copper-cadmium-bearing slag featuring using high-efficient oxygen carrier, such as activated carbon, was investigated to achieve high leaching rate of valuable metals. The effects of leaching variables, including agitation rate, sulfuric acid concentration, temperature, slag particle size, activated carbon and cupric ion concentration, were examined. It is found that leaching rates of cadmium and zinc both exceed 99 % in a very short time, but for copper, leaching rate of 99 % is achieved under the optimized leaching parameters, which are agitation rate of 100 r.min(-1), sulfuric acid concentration of 15 wt%, leaching temperature of 80 degrees C, slag particle size of 48-75 mu m, activated carbon concentration of 3 g.L-1, liquid-to-solid ratio of 4:1, oxygen flow rate of 0.16 L.min(-1), and leaching time of 60 min. The macro-leaching kinetics of copper metal was analyzed, and it is concluded that the inner diffusion is the controlling step, with apparent activation energy of 18.6 kJ.mol(-1). The leaching solution with pH value of 2-4 can be designed to selectively extract valuable metals without neutralization, and the leaching residue can be treated by prevailing Pb smelting process.