Author(s): KONDO Hideyuki, FUJITA Takafumi, KUCHAR Dalibor, FUKUTA Tadashi, MATSUDA Hitoki, KUBOTA Mitsuhiro, YAGISHITA Koichi
Experiments were conducted to investigate selective sulfuration of copper, zinc and nickel contained in a simulated plating wastewater using H2S as a sulfurating agent. The sulfuration of single solutions of copper, zinc and nickel, and mixed solutions of these metals with H2S was conducted in a bubble column reactor. As a result, it was found that heavy metals can be selectively precipitated from the mixed-metal plating wastewater at a pH value of 1.5 for copper, 4.5 for zinc and 6.7±0.2 for nickel. The purities of precipitates based on total amount of metal contained were 95.5%, 87.4% and 94.7% in the case of copper, zinc and nickel, respectively. When the results were compared with those obtained for the selective precipitation with Na2S, it was found that higher purities of metal sulfides were achieved with H2S. It was considered that local increases of pH resulting from an addition of alkaline sulfurating agent of Na2S were avoided in the case of H2S. Consequently, an undesirable co-precipitation of zinc and nickel sulfides at a pH value of 1.5 corresponding to copper selective precipitation was reduced. Similarly, the precipitation of nickel sulfide was partially avoided during the precipitation of zinc sulfide at a pH value of 4.5.