Direct XAS evidence for heterogeneous redox at the aqueous chromium/magnetite interface

Conference · Fri Dec 01 04:00:00 EST 1995

OSTI ID:126341

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

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1. Stanford Univ., CA (United States)

Hexavalent chromium is a highly toxic, carcinogenic, and mobile contaminant present in wastewaters from mining and industrial operations. Its reduction to trivalent chromium, both less toxic and more insoluble over the pH range of most natural waters, has previously been observed in solutions in contact with the redoxsensitive iron oxide magnetite (Fe{sup 2+}Fe{sup 3+}{sub 2}O{sub 4}) via electron transfer from Fe{sup 2+} in the magnetite structure. This study presents direct, in-situ XAS evidence for the presence of Cr(III) at the surface of synthetic magnetite which had been reacted with Cr(VI) in solution at near-neutral pH. Cr(VI) reacted with freshly-synthesized magnetite at surface coverages of 1-4.5 {mu}mol/m{sup 2} is entirely reduced to Cr(III), as evidenced by the Cr absorption edge position and by the absence of a 1s{r_arrow}3d pre-edge peak. Cr on progressively oxidized magnetite surfaces, however, show increasing pre-edge peak areas indicating the presence of Cr(VI), hence a reduction in the Cr-reducing capacity of altered (maghemite-coated) magnetite grains. As expected, Cr(VI) sorbed to a ferric oxide, synthetic maghemite ({gamma}-Fe{sup 3+}{sub 2}O{sub 3}), is not significantly reduced. The Cr pre-edge peak area for Cr(VI) reacted with maghemite is comparable to pre-edge peak areas of Cr(VI) model compounds. Fit parameters derived from FEFF 6 models of Cr(III) and Cr(VI)-containing compounds were used to determine the coordination environment (number and chemical identity of neighboring shells of atoms and their interatomic distances) of Cr sorbed to magnetite and maghemite samples.

• OSTI ID: 126341
• Report Number(s): CONF-950402--
• Country of Publication: United States
• Language: English

Related Subjects

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
40 CHEMISTRY
ABSORPTION
CHROMIUM
ELECTRON TRANSFER
ELECTRONIC STRUCTURE
INDUSTRIAL WASTES
INTERATOMIC DISTANCES
MAGNETITE
PH VALUE
REDUCTION
SORPTIVE PROPERTIES
SPECTRA
WASTE MANAGEMENT
WASTE WATER