Efficient removal of hexavalent chromium in a wide pH range by composite of SiO2 supported nano ferrous oxalate

The reduction of Cr(VI) by iron-based materials was inhibited under neutral and alkaline conditions due to the production of precipitates. In this work, a novel composite with a wide pH range application in the remediation of Cr(VI) contamination, SiO2/nano-FeC2O4 composite (SNFC), was prepared from natural biotite-containing minerals. Transmission electron microscope (TEM) analysis indicated that nano-FeC2O4 with average particle size of 10.08 nm was uniformly coated on the surface of layered minerals. Batch experiments results showed that Cr(VI) was completely removed in the pH range of 2-10 within 60 min at an initial Cr(VI) concentration of 20 mg/L. The removal rate of Cr(VI) was decreased when the initial pH value increased from 2 to 6 and then kept at constant when the initial pH value increased from 6 to 10. Furthermore, continuous fixed bed column studies showed that simulated permeable reactive barriers (PRB) with SNFC was considerably effective for in situ removal of Cr(VI) from groundwater under alkaline conditions. Characterizations of X-ray diffraction (XRD) and scanning electron microscope (SEM) suggested that the reactive component in the composite for Cr(VI) removal was nano-FeC2O4 rather than biotite itself. The Cr(VI) removal mechanisms of SNFC involved reduction, precipitation and surface complexation. These results plus the preliminary cost analysis indicated that the composite was an efficient, economical, and easy for mass production material with application for remediation of Cr (VI) polluted groundwater in a wide pH range.