Stepwise recovery of Ni, Cu, Zn, and Cr: A green route to resourceful disposal of electroplating sludge

Abstract

The recovery of heavy metals from electroplating sludge not only reduces environmental damage, but also avoids the wastage of resources. However, acid leaching of electroplating sludge requires lengthy procedures for purification and separation of metals, which leads to high material consumption. In this study, alkali-leaching dealumination and a two-stage roasting water leaching process were combined to selectively recover Ni, Cu, Zn, and Cr from electroplating sludge. Thermodynamic calculations were used for analyzing the theoretical feasibility of roasting electroplating sludge and determining the factors affecting the recovery of Ni, Cu, Zn, and Cr in the roasting process. First, approximately 100 % Al was recovered as AlO2- after 6 mol/L of NaOH solution was treated at 90 ℃ for 1 h. Second, dealumination residue was mixed with NaOH and roasted at 800 ℃ for 1 h after water leaching, and nearly 99 % Cr was extracted as CrO42-. Third, more than 99 % Ni, Cu, and Zn were extracted as chlorine salts by blending NH4Cl into the dechroming residue and conducting roasting at 400 ℃ for 1 h after water leaching. Overall, this study provides a novel, simple, and efficient approach for the selective recovery of Ni, Cu, Zn, and Cr from electroplating sludge.