Study On Regeneration Of Spent Electroless Nickel Plating Bath By Electrodialysis

The electroless nickel plating technology that use hypophosphite as reducing agent obtained widespread application in various industrial fields because of its excellent performance. However, when the nickel plating liquid has been used six or seven periods, the by-product HPO32- will be accumulated to a high concentration and produced precipitate of nickel phosphate, which hinder the deposition of Ni-P alloy coatings and made the deposition rate significantly slowly as well as coating rough and appear pinholes, or even the plating bath could spontaneous decomposition and scrapped, all which resulted that the costs of electroless nickel plating increased, affected the application and development. Meanwhile, with the application scope and production scale of electroless nickel plating technology expanded inceasingly, if the nickel plating liquid was directly discharged without treatment, it will not only damage the ecological balance, pollute the environment and seriously endanger human health, but also cause great waste of resources. Therefore, the study of electroless nickel plating wastewater treatment technology attracted increasingly wide attention at home and abroad.At present, there are two main ways to deal with the electroless nickel plating wastewater, one is to discharge the waste liquor after treatment or recycle part of nickel and phosphorus before discharged; the other is to implement purification and regeneration of electroless nickel plating waste.In view of protecting environment and saving resources, and according to the characteristics of spent electroless nickel plating bath, using electrodialysis technology not only the harmful substance HPO32- can be removed, the excess substances Na+ and SO42- also can be removed, in theory the life of bath can achieve the unlimited extension. On the one hand the pollution to the environment and the destruction to the ecological can be reduced, on the other hand the abundant nickel, phosphate resources can be obtained resource utilization, thus the purification treatment and resource utilization for spent electroless nickel plating bath to explore a feasible way.According to domestic research, use electrodialysis method handle spent bath of electroless nickel plating existing some problems, such as the removal rate of HPO32- is too low; the loss of useful components, cause secondary pollution and waste; the bath that handle by electrodialysis can only achieve the fourth cycle; according to domestic reported that the bath only prolongs 17 cycles or so after electrodialysis, and a far gap with foreign; and so on.The research that used electrodialysis device made-by-self for electroless nickel plating wastewater was purified to regeneration within the range of laboratory. Three different types of ion-exchange membrane were used on regeneration treatment of electroless nickel plating waste from a Guangdong factory, the removal rate of HPO32- and the loss rate of Ni2+ and H2PO2- be measured to determine one of ion-exchange membranes in desalination rate and the selectivity aspects on HPO32-, H2PO2- are both better.The results showed that the heterogeneous membrane is better for ion selectivity of spent electroless nickel plating bath than homogeneous membrane. And this good performance membrane is used to experiment, several technical conditions for influence of various ions removal rate were emphasis studied, and obtained the appropriate operating conditions. The optimal process conditions are:current density is 65mA/cm2, pH is 4.5, and flow rate is 1L/45s, and the results showed that the selectivity of HPO32- and H2PO2- is not obvious, thus caused the useful material of H2PO2- losses mass. Meanwhile the regeneration cost of plating may be more expensive in this condition, and could increase the difficulty of handling concentration.Meanwhile the performances of regeneration plating were tested and the results showed that:deposition rate is 10.56μm/h, hardness is 480HV, phosphorus content is 12%, and the surface morphology of coating is similar to the third period plating of morphology with new open cylinder, the resistant color degeneration and salt spray tested are also comply with its production requirements.