Understanding and controlling the key phase transformation for selective extracting Ni and Cu from Cr-containing electroplating sludge

Abstract

Electroplating sludge containing abundant toxic heavy metals is a metal mine. However, selective separation of Ni and Cu from Cr-containing electroplating sludge is a huge challenge for the recovery of electroplating sludge resource. Herein, we proposed a chlorination phase transformation and water leaching method for selectively extracting Ni and Cu. Metal hydroxides were converted into chlorides by chlorination, and the dissociation of the agglomerate released heavy metals. Under the regulation of temperature, CrCl3 converted into Cr2O3 while Ni and Cu still existed in chlorides. Finally, soluble NiCl2 and CuCl2 were recovered by water leaching. Under the optimal conditions (T = 350 °C, L/S = 1.2, t = 0.5 h), 96.3% of Ni and 90.7% of Cu were extracted. And water leaching is more moderate and environmentally friendly than acid leaching. The simulated natural aging test showed that the residue could stay safe and stable for a year. This work would provide a new idea for the selective extraction of heavy metals from hazardous solid wastes.