Kinetics of microwave roasting of zinc slag oxidation dust with concentrated sulfuric acid and water leaching

The microwave irradiation is used to roast zinc slag oxidation dust in the presence of concentrated sulfuric acid with the aim of accelerating roasting process. The roasted material is leached with tap water for the recovery of zinc and indium. The influence of roasting temperature, particle size, and the ratio of acid to ZSOD mass on the rate of roasting reactions were investigated. The results show that the extraction rate of zinc and indium increases with increasing the roasting temperature and the ratio of acid to ZSOD mass, while decreases with increase in the particle size. The samples were characterized using XRD and SEM. Under the conditions employed in the present work a maximum recovery of 94% and 90% of zinc and indium could be achieved. Shrinking core model was used to describe the kinetic parameters and to identify the rate controlling step. Both zinc and indium extraction were controlled by the internal diffusion in the solid product layer, with the apparent activation energy of the roasting reaction were 15.94 kJ/mol and 12.68 kJ/mol respectively. The reaction order with respect to concentrated sulphuric acid was 1.75 and 1.59 for zinc and indium, respectively.