無電解ニッケルめっき廃液処理への溶媒抽出法の適用

Abstract

Electroless plating is widely used in electronics, semiconductor and automobile industries as a surface treatment technique, because uniform thickness metal can be deposited on plastics, ceramics or polymers with intricately shaped surfaces. Above all, electroless nickel plating using hypophosphite as a reducing agent is very popular and has been studied a lot, since it gives excellent plated metal surfaces with corrosion resistance, lubricity and magnetic properties. As metal deposition progresses in this process, however, phosphorous acid increases in the plating bath, which causes degradation of the bath solution. Therefore, the bath itself must be disposed after a certain number of turnovers before the degradation occurs. The waste solution from electroless nickel plating bath contains a large quantity of nickel, hypophosphite, phosphite and organic compounds such as citrate, malate or succinate. It is quite harmful to the environment and at the same time, these hazardous wastes can be viewed as resources if properly handled. Therefore, it is very important to develop an effective extraction technique removing these chemical substances separately.In the present study, the application of solvent extraction to the treatment of electroless nickel plating waste water was investigated. In the treatment of caustic alkaline plating waste water, TOMAC is favorable to the extraction of nickel and citrate, and the separation from hypophosphite and phosphite. It is difficult to apply TOMAC to the treatment of ammoniacal alkaline plating waste water, while the use of chelating extractants such as LIX 26 is favorable to extraction of nickel. Meanwhile, the application of solvent extraction to the treatment of acidic plating waste water is difficult.