Use of iron nanoparticles for post-treatment of metal finishing wastewater

This study evaluated the efficiency of copper, nickel and zinc removal from industrial metal finishing wastewater using nZVI material in lab and pilot scale conditions. Initial concentrations of Cu, Ni and Zn in raw wastewater were 3.16 mg/L, 0.38 mg/L and 0.56 mg/L, respectively. All metals were presented in residual concentrations and difficult to remove. Copper concentration was lowered by 77.2% in lab scale and 85.2% in pilot scale test for nZVI dose of 400 mg/L after 3 hours of reaction. Removal efficiency of nickel was 51% in the lab scale and 85.2 % at the pilot scale. Decrease of zinc concentration was less significant and reached 35.4% and 40% in lab and pilot scale experiment, respectively. Increase of efficiency in pilot scale testing was caused by the application of nZVI under inert atmosphere which ensured the preservation of high iron reactivity. pH adjustment before the nZVI dosing had also significant influence for efficiency of reaction. No changes and fluctuations of temperature and conductivity were observed. Pilot-scale test with lower dose of nZVI was performed to reveal the surpluses of previous dose of iron. The dose of 300 mg nZVI/L was applied into the reactor under inert atmosphere with pH adjustment before iron dosing. Efficiency of metals removal dropped to the 70% and 70.1% for copper and nickel. Efficiency of zinc removal increased to the 60.5%. nZVI dose of 300 mg/L was sufficient for reaching of limits for wastewater discharge