Recovery of valuable metals from waste diamond cutters through ammonia-ammonium sulfate leaching

Copper and zinc were recovered from waste diamond cutters through leaching with an ammonia-ammonium sulfate system and air as an oxidant. The effects of experimental parameters on the leaching process were investigated, and the potential-pH (E-pH) diagrams of Cu-NH₃-SO₄^2--H₂O and Zn-NH₃-SO₄^2--H₂O at 25℃ were drawn. Results showed that the optimal parameters for the leaching reaction are as follows:reaction temperature, 45℃; leaching duration, 3 h; liquid-to-solid ratio, 50:1 (mL/g); stirring speed, 200 r/min; ammonia concentration, 4.0 mol/L; ammonium sulfate concentration, 1.0 mol/L; and air flow rate, 0.2 L/min. The results of the kinetics study indicated that the leaching is controlled by the surface chemical reaction at temperatures below 35℃, and the leaching is controlled by diffusion through the product layer at temperatures above 35℃.