Application of Fered-Fenton and chemical precipitation process for the treatment of electroless nickel plating wastewater

Electroless nickel plating wastewaters commonly contain the citrate chelating complex and the coexisting hypophosphite, which is a scavenger of hydroxyl radicals, typically lowers the catalytic efficiency of H2O2 by Fe2+ in Fenton reaction. Hence, in this work, the Fered-Fenton method was adopted to remediate the citrate, and then alkaline precipitation was utilized to remove the freed nickel ions. The chemical oxidation demand (COD) of citric acid could be efficiently reduced by approximately 95% using 1080 mM H2O2 (dosed in continual mode) and 20 mM ferrous ions at a current density of 190 A m(-2) ([citric acid] = 100 mM and [Ni] = 100 mM). Meanwhile, 99.9% of the nickel that was liberated from the chelation of citric acid was removed by the cathodic deposition and the sequential precipitation. The hypophosphite did not significantly influence the COD or nickel removal efficiency. Finally, those optimal conditions for the successful management of simulated electroless plating wastewater consisted of citric acid and nickel ions coexisting with hypophosphite were then used to demonstrate the treatment of real wastewater (45,000 ppm COD and 8000 ppm nickel ions). The high COD removal, 93%, from the effluents of the electroless nickel plating process verified that the Feted-Fenton process can be practically applied. (c) 2012 Elsevier B.V. All rights reserved.