The Research Of Electroless Nickel Plating Wastewater Treatment Technology Using Electrochemical Method

Electroless nickel plating is a kind of surface treatments in modern world which is widely used in industrial production field. But during the production process electroless nickel plating bath decomposed because of the accumulation of by-products such as HPO32- ions and became electroless nickel plating wastewater. The main pollutants in electroless nickel plating wastewater were total nickel, total phosphorus and COD. In this paper, we applied a combination of electrolysis, precipitation and EF to treat the electroless nickel plating wastewater in the purpose of resource recycle and pollutants removal.Electrolysis was applied to treat the wastewater first.The effects of pH, current density, temperature, circulation, electrolysis time on the recovery efficiency of nickel and the removal efficiency of COD was studied. The result showed the purpose of electrolysis should be the recovery of nickel considering the whole treating process of electroless nickel plating wastewater.And the optimal parameters were pH of 9, current density of 8.0 mA·cm-2, temperature of 80℃, circulation, electrolysis time of 2h while the recovery efficiency of nickel was 98.7% and the removal efficiency of COD was 61.91%. The H2PO2- in the wastewater was completely oxidized. Then precipitation was applied for the purpose of the removal of phosphorus. CaO and Fe2(SO4)3 were chosen as the precipitant. Each effect of precipitant's parameters on the removal efficiency of HPO32-, PO43- and total phosphorus were studied. The result of Fe2(SO4)3 was better than CaO, the optimal parameters were pH of 5, Fe/P molar ratio of 1, aging temperature of 20℃, aging time of 6.5h. The removal efficiency of HPO32-, PO43- and total phosphorus were 98.6%,99.99% and 99.48% with a certain degradation of COD. EF was applied to degrade the COD of wastewater. It showed that EF could remove the COD of wastewater effectively. The optimal parameters were continuous dosing, pH of 3, current density of 13.16 mA·cm-2, H2O2 dosage of the oretical value, Fe2+/H2O2 molar ratio of 1/10. The removal efficiency of COD is 97.89%. HPO32- was oxidized to PO43-,then PO43- precipitated with Fe3+.After the whole treating process, total nickel and total phosphorus of electroless nickel plating wastewater achieved the national discharge standard. The residual COD was 305.52mg·L-1 and pH was 3. The quality of the wastewater was greatly improved.