Comparison of XANES analyses and extractions to determine chromium speciation in contaminated soils

Chromium-contaminated soils from three sites in Wisconsin were analyzed for the total concentration of chromium with neutron activation analysis, extractable Cr(VI) with a typical phosphate buffer and exchangeable Cr(VI) with isotope dilution analysis. X-ray absorption near-edge structure (XANES) spectroscopy provided a physical method for determining the ratio of Cr(VI):Cr(III) in the contaminated soils. In most samples, less than 10% of the total Cr was present as Cr(VI). Of the total Cr(VI) measured with XANES analysis, only a fraction was isotopically exchangeable, and an even smaller fraction of the total Cr(VI) was extracted with a phosphate buffer. The speciation and extraction of chromium in actual contaminated soils are apparently more complex than traditional chemical methods can show.