Precipitation treatment of spent electroless nickel plating baths

Electroless nickel plating (EN) has become popular because of its many advantages over the conventional electroplating process. A wide variety of technologies is available for treating spent EN baths containing high concentrations of nickel salt, reducing reagents, organic acids and other compounds. Considering capital investment and the operating-maintenance cost, precipitation as nickel hydroxide resulting from pH adjustment alone, using caustic soda or lime, and/or as elemental nickel with further addition of sodium borohydride are often the preferred methods for treating spent EN baths. Chemical principles governing the nickel removal processes are presented. Limitations of the two precipitation methods and the necesssary modifications are illustrated with experimental results on nickel removals from eight nickel chloride-organic acid solutions, six typical sodium hypophosphite-reduced EN baths, and three actual spent EN baths. For most spent EN baths, on-site precipitation treatment can be implemented to meet the effluent limits at a cost much less than off-site disposal alternatives.