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 center dot 6H(2)O) and precipitator. The most optimum reaction conditions were explored: 1.57 g/g dry sludge as the dosage of FeCl3 center dot 6H(2)O, pH 8.5 of the slurry adjusted by ammonia, 4 h as the reaction time, and 200 degrees 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 front 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. (C) 2008 Elsevier B.V. All rights reserved.