X-RAY AND VIBRATIONAL SPECTROSCOPIC TOOLS FOR INVESTIGATING Cr(VI) REDUCTION BY Fe(II) AND Fe(0) MATERIALS

摘要

Chromate (Cr(VI)) is a soluble groundwater contaminant of environmental concern and is a known human carcinogen. Remediation of Cr(VI) using zero-valent iron (Fe~0)-containing permeable reactive barriers has been extensively investigated and is an effective means of immobilizing Cr(VI). Zero-valent iron is an efficient in situ remediation material due to its ability to facilitate chemical reduction and form high surface area Fe~0 corrosion products such as Fe(III) hydroxides and oxyhydroxides that bind pollutants. The Cr(VI) removal mechanism involves reduction of dissolved chromate (CrO_4~(2-)) to insoluble Cr(III) by Fe~0 followed by precipitation of Cr(OH)3 or co-precipitation of Cr(III) with Fe(III) oxides/hydroxides. In addition to Fe~0-induced reduction it is also well understood that Fe(II), an intermediate in the Fe~0 corrosion reaction, is an effective reducing agent for Cr(VI). In this paper we focus on the application of X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (EXAFS and XANES) to determine the oxidation state and surface complexation chemistry of Cr(VI)-treated Fe(II)-zeolite and nano-Fe~0. In addition, preliminary work using Raman scattering will be presented.