Synergistic effect of coupling zero-valent iron with iron oxide-coated sand in columns for chromate and arsenate removal from groundwater: Influences of humic acid and the reactive media configuration

A column study was conducted using a combination of zero-valent iron (Fe⁰) and iron oxide-coated sand (IOCS) for removing Cr(VI) and As(V) from groundwater. The removal efficiency and mechanism of Cr(VI) and As(V), the effects of humic acid (HA), and the various configurations of Fe⁰ and IOCS were investigated. The results showed that the use of an Fe⁰ and IOCS mixture in a completely mixed configuration can achieve the highest removal of both Cr(VI) and As(V), whilst the effects of HA were marginal in using these reactive materials. The solid phase analysis revealed the occurrence of the synergistic effect in these reactive materials as Fe²⁺ can be adsorbed onto the IOCS and transform the iron oxides to magnetite, providing more reactive surface area for Cr(VI) reduction and reducing the passivation on the Fe⁰. As(V) can then be removed by adsorption onto these iron corrosion products. HA can be adsorbed onto the IOCS so that the impacts of the deposition of HA aggregates on the Fe⁰ surface can be reduced, thus enhancing the Fe⁰ corrosion.