Chromium Speciation in the Size-Fractions of a Soil Polluted by Weathered Chromate Ore Process Residue Using Synchrotron X-ray Analysis.

The chromate ore process residues (COPR) polluted soil was physically separated into coarse sand (2.000-0.425 mm), fine sand (0.425-0.053 mm) and silt to clay (< 0.053 mm) fractions. The Cr speciation was characterized by synchrotron based micro X-ray fluorescence (µ-XRF) and micro X-ray absorption near-edge spectra (µ-XANES). The results indicated that Cr was bearing both in COPR parent minerals and hydrated products and was dominated by Cr(III) in three size-fractions. The synchrotron results indicated that Cr(III) was dominated by chromite, organic matter bound Cr(III) and particle adsorbed Cr3+ in the selected hotspots from the coarse sand, fine sand and silt to clay sized fraction, respectively. While Cr(VI) occurred in the form of CrO4 2- in the selected hotspots from three size fractions. The difference of Cr(III) species in the size-fractions suggested that higher edaphic effects occurred in the fine size-fractions than in the coarse size-fraction for the weathered COPR.