硫化カルシウムを用いた模擬めっき廃液中の銅，亜鉛，ニッケルの不均一系硫化反応特性

Abstract

The present work is concerned with sulfidation of Cu, Zn and Ni containing plating wastewater with CaS. The sulfidation experiments were carried out by adding solid CaS (purity higher than 99%) to a simulated single-metal solution of NiSO4, ZnSO4 and CuSO4 solutions at a room temperature.At first, the experiments were conducted without pH adjustment and it was found that the complete sulfidation of Zn and Ni was achieved at an equimolar ratio of CaS to metal. For Cu, complete copper sulfidation was achieved at a CaS to Cu molar ratio of about 2 : 1. It was considered that CuS was almost instantly precipitated on the surface of un-dissolved CaS particles, which led to CaS being enclosed in CuS particles and it was thereby concluded that a higher CaS to Cu molar ratio was needed. This conclusion was further supported by a subsequent experiment, in which the sulfidation treatment was carried out using CaS solution. In this experiment, it was found that the concentration of Cu in the filtrate fell to below 1 mg/dm3 at an equimolar ratio of CaS to Cu.Finally, to investigate the possibility of selective precipitation, the experiments were conducted at fixed pH values and it was found that Cu was almost completely separated at pH = 1.8−2.0 when the CaS to Cu molar ratio was adjusted to 1 : 5. Further, almost 100% of Zn at pH > 4 and about 91% of Ni at pH = 7.5 was separated when an equimolar ratio of CaS to metal was used.