To provide a method for producing Au-Ag-Cu recycle sludge having a value as valuables from cyanide washing water derived from Au-Ag-Cu plating by the existing device and a simple operation in a plating factory.

An area in which a plurality of plating lines are arranged in parallel is provided, and in the same area or adjacently to the same area, an Au-Ag-Cu recycle sludge formation line and an Ni recycle sludge formation line are provided. In the former line, in the final stage of a process where cyanide washing water containing Au, Ag and Cu is subjected to cyanide decomposition treatment by the charge of sodium hydroxide, sulfuric acid and sodium hypochlorite, by pouring activated carbon, Au, Ag and Cu are adsorbed thereon, and, in a pH regulation process, together with the charge of sodium hydroxide, Ni, Cu-concentrated sludge obtained in the latter line is added as a flocculant to improve dewaterability, and a polymer flocculant is added to dewater the sludge sunk in a settling tank.

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