Zero-valent iron and iron oxide-coated sand as a combination for removal of co-present chromate and arsenate from groundwater with humic acid

The combination of zero-valent iron (Fe0) and iron oxide-coated sand (IOCS) was used to remove Cr(VI) and As(V) from groundwater in this study. The efficiency and the removal mechanism of Cr(VI) and As(V) by using this combination, with the influence of humic acid (HA), were investigated using batch experiments. Results showed that, compared to using Fe0 or IOCS alone, the Fe0-IOCS can perform better on the removal of both Cr(VI) and As(V). Metal extraction studies showed that As(V) was mainly removed by IOCS and iron corrosion products while Cr(VI) was mainly removed by Fe0 and its corrosion products. Competition was found between Cr(VI) and As(V) for the adsorption sites on the iron corrosion products. HA had shown insignificant effects on Cr(VI) removal but some effects on As(V) removal kinetics. As(V) was adsorbed on IOCS at the earlier stage, but adsorbed/coprecipitated with the iron corrosion products at the later stage.

Research Highlights► Fe0-IOCS is better reactive media for removing Cr(VI) and As(V) from groundwater. ► As(V) was mainly removed by the IOCS and the iron corrosion products. ► Cr(VI) was mainly removed by Fe0 and its corrosion products. ► As(V) adsorption was inhibited in the presence of HA, when using Fe0 alone. ► IOCS can provide the adsorption sites for As(V) that complement the weakness of Fe0