HR: 0830h
AN: V51H-0387 [PDF]
TI: Oxidative promoted dissolution of chromite by manganese dioxide and concurrent production of
chromate
AU: * Oze, C
EM: oze@dartmouth.edu
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115
AU: Bird, D K
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115
AU: Fendorf, S
AF: Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115
AB:
Chromium release and oxidation from chromite is a potential environmental hazard in sediments and soils and a pathway for
soil development (weathering of primary minerals) related to ultramafic rocks and their metamorphic derivatives
(serpentinites). Birnessite is a common pedologic mineral in these sediments and soils capable of oxidizing aqueous Cr(III).
In this study, the interaction between chromite and birnessite is investigated, with an interest in the potential generation
of Cr(VI). Specifically, the effects of chromite suspension density, birnessite suspension density, and pH at a temperature
of 25 C in relation to the reaction kinetics were examined. The rate of Cr(VI) in solution increases with increasing
chromite suspension densities and decreasing pH, but is independent of birnessite suspension densities at values greater than
20 m$^{2}$ L$^{-1}$. The overall rate expression of Cr released and oxidized in solution from chromite can be expressed as
d[Cr(VI))]/dt = kÝ,¦{Chromite}$^{0.69}$
where kÝ is 0.0016,¦pH$^{2}$ V 0.025pH + 0.097 uM L m$^{2}$ L$^{-1}$, {Chromite} is the chromite suspension density in
m$^{2}$ L$^{-1}$, birnessite suspension densities are greater than 20 m$^{2}$ L$^{-1}$ and pH values are between 3 to 8.
Experiments involving serpentine soils containing chromite and birnessite produce Cr(VI) rates consistent with those
predicted by the overall rate expression with Cr(VI) rates ranging from 9E-4 to 4.4E-3 uM h$^{-1}$. Additionally, these
experiments demonstrate that serpentine soils are a source of non-anthropogenic Cr(VI).
DE: 0317 Chemical kinetic and photochemical properties
DE: 0330 Geochemical cycles
DE: 1045 Low-temperature geochemistry
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting