Removal of ions in nickel electroplating rinse water using low-pressure nanofiltration

This study investigated the performance of nanofiltration (NF), which is more economic than reverse osmosis (RO) and requires lower pressure for the removal of cations and anions in simulated nickel electroplating rinse water environments. Removal rates according to changes in basic parameters such as pressure, crossflow velocity, pH, ion types and ion concentrations were observed. In single-salt system experiments NF removed more Ni²⁺ in NiSO₄ solution than in NiCl₂ solution. As concentration increased in single-salt systems, removal rate of sulfate salts and some chloride salts (in the system with cations of +1 valency) decreased, whereas chloride salts with cations of +2 valency increased. In the experiment with multi-salt systems, the removal rate of ions showed a logarithmic increase with pressure until 3 kgf/cm² (0.294MPa), and beyond this value the removal rate stabilized. Change in crossflow velocity did not affect the ion removal, but change in pH was a significant factor for Cl^- removal rate. Furthermore, the removal rate of Cl^- was heavily dependent on the amount of SO₄^2- present in the same system. In experiments using simulated nickel electroplating rinse water below a pressure of 3 kgf/cm², the removal efficiencies of ions increased greatly with increased influent salt concentration and pressure, whereas beyond 3 kgf/cm², the removal efficiency stabilized. This result indicated that 3 kgf/cm² is the optimum pressure for NF application against nickel electroplating rinse water.