Removal of Hypophosphite and Phosphite from Electroless Nickel Plating Baths

Electroless nickel plating (EN) is a popular commercial technique for depositing nickel coating on a suitably treated surface by controlled chemical reduction of nickel ions. The nickel coating catalyzes the reduction reaction, and the deposition of nickel continues as long as the substrate remains in contact with the EN solution. The major types of wastewater resulting from EN process are spent EN baths, stripping solutions, and rinse waters. This chapter discusses the experimental results for removing hypophosphite and phosphite species from various solutions, including three spent EN baths. It demonstrates the effects of complexing agents and reducing agents on removing Ni(II) and phosphorus. Data for a wide variety of reaction conditions, i.e., pH, reagent type and dose, reaction time and temperature, were obtained to illustrate chemical principles governing the precipitation and oxidation reactions and to allow estimation of the chemical cost for treating typical spent EN baths.