The present study is concerned with the sulfidation treatment of copper-containing plating sludge towards copper resource recovery by flotation of copper sulfide from treated sludge. The sulfidation treatment was carried out by contacting simulated or real copper plating sludge with Na2S solution for a period of 5 min to 24 h. The initial molar ratio of S2- to Cu2+ (S2- to Me2+ in the case of real sludge) was adjusted to 1.00, 1.25 or 1.50, while the solid to liquid ratio was set at 1:50. As a result, it was found that copper compounds were converted to various copper sulfides within the first 5 min. In the case of simulated copper sludge, CuS was identified as the main sulfidation product at the molar ratio of S2- to Cu2+ Of 1.00, while Cu7S4 (Roxbyite) was mainly found at the molar ratios of S2- to Cu2+ of 1.50 and 1.25. Based on the measurements of oxidation-reduction potential, the formation of either CuS or Cu7S4 at different S2- to Cu2+ molar ratios was attributed to the changes in the oxidation-reduction potential. By contrast, in the case of sulfidation treatment of real copper sludge, CuS was predominantly formed, irrespective of S2- to Me 21 molar ratio. (c) 2006 Elsevier B.V. All rights reserved.