Differential redox and sorption of Cr (III/VI) on natural silicate and oxide minerals: EXAFS and XANES results

Journal Article · Fri Aug 01 04:00:00 EDT 1997 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(97)00165-8· OSTI ID:585470

Peterson, M L; Parks, G A ^[1]; Brown, Jr, G E ^[1]; Stein, C L ^[2]

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1. Stanford Univ., CA (United States)
2. Univ. of Washington, Seattle, WA (United States)

Synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy was used to investigate the reduction of aqueous Cr(VI) to Cr(III) in magnetite-bearing soils from Cr-contaminated sites. Soils from two field sites were examined, showing that mixed-valence Cr(III/VI) effluent is reduced to Cr(III) when associated with the magnetite fraction of the soil, whereas the Cr effluent associated with non-Fe(II)-bearing minerals results in mixed Cr(III/VI) adsorbates or precipitated phases. The Fe{sup 2+} in magnetite, Fe{sup 2+}Fe{sub 2}{sup 3+}O{sub 4}, may act as an electron source for heterogeneous Cr(VI)-to-Cr(III) reduction, converting magnetite topotactically to maghemite, {gamma}-Fe{sub 2}{sup 3+}. The ratio of Cr(VI)/total Cr was determined by the height of the Cr(VI) XAFS pre-edge feature, which is due to a Is to 3d electronic transition. This pre-edge feature was calibrated as a function of Cr(VI)/Cr(III) using mixtures of Cr(III) and Cr(VI) model compounds. Environmental remediation of Cr-contaminated sites requires knowledge of chromium oxidation and speciation, and XAFS spectroscopy may be used to supply both types of information with minimal sample processing or data analysis. 36 refs., 9 figs., 2 tabs.

• OSTI ID: 585470
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 16 Vol. 61; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
CHROMIUM
ECOLOGICAL CONCENTRATION
ENVIRONMENTAL TRANSPORT
REDOX POTENTIAL
REMEDIAL ACTION
SOILS
SORPTIVE PROPERTIES
X-RAY SPECTROSCOPY