Chromium has served as an exceptional and necessary elemental component of many industrial processes and consumer products. Its prevalence in the global environment as both a dissolved and wind-borne constituent has prompted concern during the last several decades due to the large migration potential and biological toxicity of various Cr chemical species. The objective of this study was to develop an improved understanding and predictive capability of the rates and mechanisms of competing geochemical redox and sorption reactions that govern the fate and transport of Cr(III) and C(VI) in heterogeneous subsurface environments. Batch and miscible displacement experiments, coupled with solid-phase spectroscopy methods, were utilized to quantify the interaction of Cr with subsurface materials acquired from three geographically distinct locations within the continental United States that represented soils from different Department of Energy facilities known to have issues regarding Cr contamination. Soil chemical and mineralogical properties were found to be important factors controlling the mechanisms of Cr–solid phase interactions, with many of the reactive processes being time dependent. Both sorption and redox reactions impacted Cr(III)– and Cr(VI)–solid phase interactions and were modeled as nonlinear, nonequilibrium or equilibrium, reversible or nonreversible reactive processes. The research investigations within this study highlight the environmental significance of Cr speciation and solid-phase reactivity in heterogeneous subsurface soil systems with contrasting geochemical and mineralogical properties.

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