Fixed-bed flow experiments with supported green nZVI for the remediation of contaminated waters: Effect of pH and...

Aim of this study is to evaluate the performance of a nanocomposite material (R-nFe), consisting of nano zero valent iron (nZVI) and a cation exchange resin, for Cr(VI) reduction and heavy metals removal from contaminated water streams. The effect of pH and the background solution composition was investigated by conducting three columns tests. In Column I, the experiments were carried out using NaCl as background electrolyte while in Column II and III the background solution consisted of 50% tertiary effluents of a waste water treatment plant and 50% deionized water. The kinetics of Cr(VI) removal was found to be much faster at acidic pHs. Based on the experimental results it was calculated that the required contact time of the permeating solution with the RnFe beads for Cr(VI) removal at pH 7 is 6.5 times longer than at pH 4. The results also revealed the role of competing ions on the performance of RnFe. During the operation of the column with an inert electrolyte, such as NaCl, the RnFe bed removed an amount of Cr(VI) equivalent to 4200 mg/kg. When the column was fed with a water stream containing relatively high levels of nitrates, the RnFe removed efficiently only 190 mg/kg Cr(VI), due to the competitive consumption of nanoiron for the reduction of nitrates. The nanocomposite was found to be very efficient for the simultaneous removal of tested heavy metals, i.e. Cu, Zn, Ni, Cd and Pb, which were selectively retained in the cation exchange sites of the supporting resin matrix.