The Research On Recovery Of Spent Electroless Nickel Planting Bath By Electrodialysis

Elelctrodialysis is a kind of membrane separating technology. By the ion exchange membrane's perselectivity , anion and cation from electrolyte will move directionally in the direct current field, and wastewater is treated, useful materials are recovered. The electroless nickel planting had application very widely for its corrosion -resistant and fretting-resistant and homogeneous nickel-plate. But the life of the electroless nickel planting bath was so limit as to only reach to 6-7(MTOS),which leaded to high cost. There was not only large numbers of contaminants (sodium, orthophosphite, and sulfate) but also many valuable bath ions (nickel, hypophosphite, and organic acids) in the spent bath. The destination of this paper was to enhance the quotiety of ion selective removal, as the removal of contaminants it could save the valuable ions to one's best at the same time.In the paper, the separation of spent bath of electroless nickel planting bath was studied in the laboratory and the separation capacities of two kinds of membranes, heterogeneous ion exchange membrane and homogeneous ion exchange membrane, were compared. The factors of affecting the selective removal operations were discussed. The appropriate operation conditions were gained.Two different types of ion-exchange diaphragm were selected and variations of each components concentration in bath was determined in process of electrodialysis. The solution of sodium hydroxide with concentration of 0.1 g/L was used to rinse the membrane , which could reduce the organic contaminants from the surface of the membrane.Experiments results showed that the effects of four different operating conditions (current density, pH, flow rate, and temperature) on ion selectivity removal revealed bath pH and current density to be critical operating parameters. Compared with the current technics, under the optimization condition, the results showed that the removal of contaminants were increased as the lost of valuable ions dropped especially the removal ratio of orthophosphite and hypophosphite increased almost one time.After treatment of electrodialysis with the optimum operating conditions, the bath was purified. Then the reform solutions were added into the purified spent bath for regeneration. The service life of planting solution were prolonged from 7 to 16 MTOs . The performances of the coasts produced by the purified and regenerated bath completely met the productionstandard. This method is successfully not only saving nickel and phosphorus resources but also reducing the pollutants discharged.