Removal of arsenic from “Dirty acid” wastewater via Waelz slag and the recovery of valuable metals

Abstract The use of Waelz slag produced during zinc (Zn) hydrometallurgical processes to treat “dirty acid” wastewater was investigated in this study. As(III) in the wastewater was oxidized by performing a pre-oxidation process, after which oxidation leaching, Fe-As co-precipitation, Cu-As cementation, neutralization-hydrolysis, and hematite precipitation processes were performed. The initial As concentration was 8.56 g/L, and the treatment processes decreased the concentration to 0.5 mg/L, which meets the integrated wastewater discharge standard stipulated by the Ministry of Ecology and Environment, P.R China. Most of the As was removed during the Fe-As co-precipitation process as crystalline scorodite at atmospheric pressure, and most of the copper in the Waelz slag was removed during the Cu-As cementation process as Cu3As and Cu2O, which could be used to remove Co from the zinc sulfate (ZnSO4) leaching solution used during Zn hydrometallurgical processes. Fe was precipitated as hematite, which could be used as a raw material to make iron at high temperatures and pressures. The proposed treatment process can effectively remove As from “dirty acid: wastewater and allow the recycling of valuable metals in Waelz slag. The treatment process is therefore efficient and inexpensive, and offers promise for industrial use.