Ferrite process of electroplating sludge and enrichment of copper by hydrothermal reaction

In this paper, ferrite process of electroplating sludge and enrichment of copper by hydrothermal reaction was investigated. By the hydrothermal treatment, Zn, Ni, Cu, Cr-bearing electroplating sludge can be transformed into high value-added Ni–Zn–Cr ferrite by adding iron source (FeCl3·6H2O) and precipitator. The most optimum reaction conditions were explored: 1.57 g/g dry sludge as the dosage of FeCl3·6H2O, pH 8.5 of the slurry adjusted by ammonia, 4 h as the reaction time, and 200 °C as the reaction temperature. Under these conditions, the purer Ni–Zn–Cr ferrite could be prepared, and Cu was extracted to the range from 76 wt% to nearly 84 wt%, when ammonia was selected as the precipitator. Leaching toxicity of heavy metals from Ni–Zn–Cr ferrite prepared with additional iron source and precipitator, was much lower than the regulated limit of Toxicity Characteristic Leaching Procedure (TCLP), indicating that Ni–Zn–Cr ferrite synthesized hydrothermally from electroplating sludge had a better chemical stability. Therefore, the ferrite process by hydrothermal reaction is a feasible method with respect to the reuse and self-purification of electroplating sludge.