Simultaneous Removal of Cd(II), Cu(II), Pb(II), and Zn(II) from Aqueous Solution Using Nano Zero-valent Iron: Effect of Contact Time, Fe(0) Loading, and pH

In this study, stabilised nano zero-valent iron (nZVI) was used to investigate the simultaneous removal of Cd(II), Cu(II), Pb(II), and Zn(II) from their aqueous solution over a 32-day period. The concentration of each metal used in the solution was 50 mg/L, and the applied nZVI doses were 0.25, 0.50, 1.0, and 2 g/L. The experiments were carried out using multi-metal solutions with initial pH values of 3 and 5. The results of the study showed that the overall metal removal efficiency followed the sequence: Pb > Cu > Zn > Cd. When 2.0 g/L of nZVI was applied to the multi-metal solutions, a high level of Pb(II) removal efficiency was achieved over a 32-day period, i.e. Pb(II) removal from the solutions with an initial pH of 3.0 and 5.0 was in the range 94.6-99.5% and 97.9-99.6%, respectively. Meanwhile, at the same dose of nZVI and both the initial solution pH values, high removal efficiencies of Cu (99.6-99.9%), Zn (62.8-82.2%), and Cd (52.2-67.1%) were achieved only over 2.5 h of contact time, and later substantially decreased. The initial pH of the multi-metal solutions did not have a considerable effect on the removal of metals at the initial contact time (0.5 h). However, the impact of pH on metal removal increased with an increase in contact time. Lower nZVI corrosion and therefore superior long-term treatment efficiency was achieved for solutions with an initial pH of 5 compared to that in solutions with an initial pH of 3.