A perspective of stepwise utilization of hazardous zinc plant purification residue based on selective alkaline leaching of zinc

A new route for selective recovery of zinc from hazardous zinc plant purification residue was proposed by alkaline leaching process. The thermodynamic analysis revealed that by controlling solution pH in the range from 14.30 to 16.78 at 25 °C, basic zinc sulfate can be converted to ZnO 2 2− instead of Zn(OH) 2 , while Cd will enter into alkaline leaching residue as a hydroxide. It is feasible to leach selectively Zn and to separate it with Cd by alkaline leaching, and the experimental results confirm that. Under the conditions of NaOH concentration of 3 mol/L, L/S of 20 ml/g, temperature of 40 °C, and time of 50 min, LR of Zn reached 96.14% while them of Pb and Cd were only 0.66% and 2.83% respectively. ZnO with hexagonal wurtzite structure and Cd(OH) 2 were the main phases of leaching residue. They crystallized and adhered to the surface of leaching residue particles, which result in the loose and random particle morphology. The findings confirm that alkaline leaching is efficient in separation of Zn and Cd in ZPPR. In addition, nano-ZnO with flowerlike was synthesized with the zinc-rich leaching solution by precipitation method and the its photocatalytic property was similar to that of nano-ZnO purchased.