Long-term efficiency and kinetic evaluation of ZVI barriers during clean-up of copper containing solutions

Sixteen continuous column experiments were carried out under dynamic flow conditions in order to study the efficiency of zero-valent iron (ZVI) permeable reactive barriers (PRBs) to remove copper from solutions. The effect of various operational parameters, such as pH of the feed solution (2.5 and 4.5), initial copper concentration (5 and 50 mg/L), pore water velocity (30.48 and 152.40 cm/day) and residence time on iron corrosion and degree of copper removal was evaluated. Breakthrough curves showed that higher initial copper concentration and pore water velocity accelerated iron corrosion and slowed down the rate of copper removal due to the formation of mineral precipitates. The maximum removal rates recorded for initial copper concentrations of 5 and 50 mg/L were 2.68 and 13.33 mg/g of ZVI/sand mixture, after 440 and 227 pore volumes, respectively. The reduction of copper follows a pseudo-first-order kinetics while the rate constants (kobs) decrease over time from 0.60 to 0.10 h−1, indicating thus progressive passivation of the ZVI/sand reactive bed. Mineralogical studies of the exhausted reactive mixture, using XRD and SEM/EDX, confirmed the deposition of copper on the ZVI surface and the formation of iron (oxy)hydroxides.