Recovery of zinc from wastewater and zinc ash of zinc hot galvanizing plants
热镀锌厂酸洗废水及锌灰中锌回收

Steamed acid process, ammonia complexation process and sulphide precipitation process were conducted to investigate separation and recovery of zinc and iron from wastewater and zinc ash of zinc hot galvanizing plants. Different HCl evaporation characterization, zinc extracting effect with ammonia leaching process, and using the acidity of wastewater to leach out zinc ash and then separating zinc and iron from acid leaching solution by ammonia complexation were performed, respectively. Selective precipitation of zinc with Na2S from acid leaching solution based on product solubility was employed under different conditions of Na2S dosage, aeration time, pH value and reaction time. It is found that addition of sulphuric acid can slightly promote the evaporation of HCl. Ammonia complexation could hardly separate zinc from iron. On the contrary, sulphide precipitation can isolate zinc and iron effectively. Under the optimal conditions, the recovery rate of iron, the precipitation rate of zinc and the purity of ZnS can reach 97.12%, 99.99% and 68.51%, respectively.