Research On Regenation Of Spent Electroless Nickel Plating Bath By Synthesis Method

Electroless nickel plating is widely used as a surface treatment. But the service life of the electroless nickel plating bath is so limited because of the accumulation of by-products such as HPO32- ions. The main purpose of this research is to find an effective and environmentally friendly regeneration methods to extend the life of electroless nickel plating bath. In this paper, we demonstrated the whole regeneration process, which was a combination of electrodialysis, precipitation, reverse osmosis.Electrodialysis process is to remove HPO32-, which is the main factor leading to scrap the electroless nickel plating bath. In the electroless experiments, the influence of ion-selective removal performance such as processing time, pH value of the bath, concentration of concentrated chamber, concentration of polarity chamber was studied. It showed that, under the condition of 5.5h processing time, bath pH4.78, concentration in concentrated chamber 0.1 mol/L, concentration in polarity chamber 0.15mol/L, the best purification was achieved. In that case, the removal rate of HPO32- came up to 59.2%, while the removal rate of H2PO2-was 38.9%, the loss of Ni2+was only 0.8%. Aftet electrodialysis processing, there were large amount of HPO32- and part of H2PO2- in the concentrated chamber.The purpose of precipitation was to separate HPO32- and H2PO2- based on their differences on solubility with metal ions. Firstly, the feasibility of metal salts as precipitant was investigated, then Ca2+and Fe3+were chosen. Then the affects of dosage, temperature, pH value, aging time were studied, after all the investigation, CaO was chosen as the best precipitant. The result was that 93.1% of HPO32-were precipitated, the precipitant could be reused as phosphorus fertilizer or architectual coatings. And H2PO2- didn't loss in the precipitation. The filtrate after precipitation contained not only H2PO2- but also a small part of Ca2+.If Ca2+was added to the plating bath, the coating quality would be affected largely. So, the last part is to use reverse osmosis to separate H2PO2- and Ca2+. The results of treatment was the outlet of RO which did not contain any Ca2+, was used as solution of concentrated chamber in electrodialysis process, and the retention water of RO process was recycled as precipitant. The results of polarization curves of coatings test showed that the performance of regenerated bath would be significantly enhanced than spent bath:Finally, the concentration of overall regeneration process was verified, and the economic benefit was estimated. After preliminary calculations, regeneration of spent electroless nickel plating bath based on this application of the whole regeneration process could obtain a benefit as 1626 yuan/m3.