Rejuvenation Of Spent Electroless Nickel Plating Bath Recovered By Electrochemical Method Combined With Chemical Method

The electroless nickel planting is widely concerned for its potential properties,such as corrosion resistance,fretting-resistance and uniformity.But the service life of the electroless nickel planting bath is so limited,which lead to high cost of process.There are both a number of contaminants(sodium,orthophosphite,and sulfate) and many valuable ions(nickel, hypophosphite,and organicacids) in spent bath.This paper aims to seek an effective method to recover the electroless nickel plating bath and to further improve the result of regeneration.In this paper,we demonstrated the regeneration process,which was a combination of sequential electrodialysis,precipitation,membrane electrolysis and ion exchange.The factors affecting the selective removal operations were discussed in electrodialysis process,and the optium operation parameters were gained.The precipitation effect between calcium, magnesium salt and six complexing agents were investigated in details.The factor that affect the recovery performance of hypophosphite were discussed in membrane electrolysis process, and the optium conditions were gained as well.The adsorption properties of 732 exchange resin with calcium were investigated.Studies of the effects of operating conditions(current density,pH,flow rate,and temperature) on phosphate removal rate were carded out.The optimized parameters are: current density of 60mA/cm²,pH of 4.5,flow rate of 400L/h,and temperature of 20℃.The membrane electrolysis experiment revealed that bath pH and current density were to be critical operating parameters.Meanwhile,recovery of hydrophophite is affected by homonymy ion migration process and diffusion process.The static adsorption capacity to Ca²⁺ is 73.83mg/g resin,and dynamic adsorption capacities are 7.12mg/g resin.It shows the exchange capacity of 732 type cation exchange resin is affected by pH value of solution,and the flow velocity obviously affect the exchange speed and utilization ratio of ion exchange resin.