Rejuvenation Of Electroless Nickel Plating Bath By Electrodialysis

Electroless nickel plating can obtain the membrane with excellent characteristic. In characteristic, this coating have some advantages which electroplate layer can't hold, so that, electroless nickel plating technology is developing at full speed and widely used. But as the developing of electroless nickel plating technology. The problem of how to deal with spent electroless nickel plating baths outstanding day by day. Many researchers both at home and abroad overseas attracted in it.Concerning characteristics of spent electroless nickel plating baths. This thesis, which targets on the typical spent electroless nickel plating baths with hypophosphite as its reducing agent, in order to prolong the bath life of electroless nickel planting and decrease the production cost, electrodialysis can be used to decontaminate and regenerate the bath.Former result showed the feasibility of electrodialysis, the contaminants (orthophosphite, and sulfate) in a spent electroless nickel plating bath were removed while the losses of valuable bath ions (nickel, hypophosphite) were also great.Refrigeration can remove sodium sulfate in the EN bath availably, and the total salinity of the EN bath can also be reduced, it is advantageous in the process of ED.Two different types of CEM is select, and the CMS is batter, it can reduce the losing of Ni²⁺ evidently.Studies on the effects of four different operating conditions (current density, pH, flow rate, and temperature) on ion permselectivity revealed both pH and current density to be critical operating parameters. The conditions of one way process operation were optimized in trial. The beset condition was as follows: current density:60 mA/cm², pH:4.5, flow rate:100L/h, temperature:15℃. Under the conditions of this process, the results showed that removal rate of ions:Ni²⁺1.7%, H₂PO₂^- 17%, HPO₃^2- 38%.After 6h treatment of electrodialysis with the optimum operating conditions, the bath was purified, the reform solutions were added into the purified spent bath for regeneration. The service life of planting bath were prolonged 3 MTOs by electrodialysis one time. By testing the hardness and corrosion, the performances of the coatings produced by the purified and regenerated bath completely met the production standard.