You are here:
LONG-TERM GEOCHEMICAL BEHAVIOR OF A ZEROVALENT IRON PERMEABLE REACTIVE BARRIER FOR THE TREATMENT OF HEXAVALENT CHROMIUM IN GROUNDWATER
Citation:
WILKIN, R. T., C. SU, R. G. FORD, AND C. J. PAUL. LONG-TERM GEOCHEMICAL BEHAVIOR OF A ZEROVALENT IRON PERMEABLE REACTIVE BARRIER FOR THE TREATMENT OF HEXAVALENT CHROMIUM IN GROUNDWATER. GEOCHIMICA ET COSMOCHIMICA ACTA. Elsevier Science Ltd, New York, NY, 69(10):Suppl 1, A264, (2005).
Impact/Purpose:
To share information
Description:
Passive, in-situ reactive barriers have proven to be viable, cost-effective systems for the remediation of Cr-contaminated groundwater at some sites. Permeable reactive barriers (PRBs) are installed in the flow-path of groundwater, most typically as vertical treatment walls. Redox-active solids used in PRBs, such as zerovalent iron (ZVI), promote rapid removal of redox-sensitive contaminants, such as Cr, by various mechanisms including adsorption and reductive precipitation. Further development of PRB technology to improve long-term performance, reduce operation and maintenance costs, and to plan post-remediation activities requires a better understanding of the mechanisms responsible for contaminant removal in and around reactive barriers. Long-term trends in groundwater geochemistry and solid-phase characteristics were examined in a full-scale, zerovalent iron, PRB installed in 1996 to treat groundwater contaminated with hexavalent chromium. After 8 years of operation, the PRB remains effective at reducing concentrations of Cr from average values >1500 mg L-1 in groundwater hydraulically upgradient of the PRB to values <1 mg L-1 in groundwater within and hydraulically downgradient of the PRB. Chromium removal from groundwater occurs at the leading edge of the PRB and also in the aquifer immediately upgradient of the PRB. These regions also witness the greatest amount of secondary mineral formation due to steep geochemical gradients that result from the corrosion of zerovalent iron. X-ray absorption near-edge structure (XANES) spectroscopy indicated that chromium is predominantly in the trivalent oxidation state within and around the PRB, confirming that reductive processes are responsible for Cr sequestration. XANES spectra and microscopy results suggest that Cr is, in part, associated with iron sulfide grains formed as a consequence of microbially-mediated sulfate reduction. Results of this study provide evidence that secondary iron-bearing mineral products may enhance the capacity of zerovalent iron systems to remediate Cr in groundwater. [Abstract from 15th Annual Goldschmidt Conference published by journal as A264 in abstract volume.]
