Selective recovery method of metals from mixed metal waste water by sulfuration treatment is proposed. Sulfuration treatment is characterized by low solubility of metal sulfides; metal sulfides are, in general, lower in solubility than that of metal hydroxides. Separation of metal like copper, zinc and nickel which are commonly use from mixed solution in various pH ranges was conducted by employing three sulfurating agents; sodium sulfide (Na2S), sodium disulfide (Na2S2) and sodium tetrasulfide (Na2S4). Aqueous solution of CuSO4, ZnSO4 and NiSO4 and those of real plating wastewater, of which the initial concentrations were adjusted to 100-300 mg dm3 were employed.
By sulfuration treatment of the solution using sulfurating agent without adjusting pH, CuS was first precipitated, but ZnS and NiS were also precipitated at the same time. The result saw from the formation behavior of metal prcipitates depended on pH value of the solution. For the sulfuration with three kinds of sulfurating agent, copper was first separated from the solution as CuS in pH = 1.4 – 1.5, then ZnS was separated in pH = 2.4 – 2.5, followed by the precipitation of nickel sulfide, NiS in the residual solution as pH = 5.5 – 6.0. The effective agent to make selective precipitation of sulfides use Na2S, Na2S2 and Na2S4. The selective of CuS in the filtrated cake obtained by the sulfuration treatment in pH = 1.4 – 1.5 was about 94%. The sequence selectivity of ZnS and NiS in the cake after the sulfuration treatment in pH = 2.4-2.5 were 75-77 % and about 20%, respectively. The selective of NiS and ZnS in the cake after sulfuration treatment in pH = 5.5 – 6.0 was 64% and 33 – 35 % respectively.
