title: Reoxidation of Chromium(III) Products Formed under Different Biogeochemical Regimes.
abstract: Hexavalent chromium, Cr(VI), is a widespread and toxic groundwater contaminant. Reductive immobilization to Cr(III) is a treatment option, but its success depends on the long-term potential for reduced chromium precipitates to remain immobilized under oxidizing conditions. In this unique long-term study, aquifer sediments subjected to reductive Cr(VI) immobilization under different biogeochemical regimes were tested for their susceptibility to reoxidation. After reductive treatment for 1 year, sediments were exposed to oxygenated conditions for another 2 years in flow-through, laboratory columns. Under oxidizing conditions, immobilized chromium reduced under predominantly denitrifying conditions was mobilized at low concentrations (≪1 μM Cr(VI); ∼ 3% of Cr(III) deposited) that declined over time. A conceptual model of a limited pool of more soluble Cr(III), and a larger pool of relatively insoluble Cr(III), is proposed. In contrast, almost no chromium was mobilized from columns reduced under predominantly fermentative conditions, and where reducing conditions persisted for several months after introduction of oxidizing conditions, presumably due to the presence of a reservoir of reduced species generated during reductive treatment. The results from this 3-year study demonstrate that biogeochemical conditions present during reductive treatment, and the potential for buildup of reducing species, will impact the long-term sustainability of the remediation effort.
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Charuleka
authors.identifier: http://orcid.org/0000-0002-4142-3224
authors.initials: C
authors.lastname: Varadharajan
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Harry R
authors.initials: HR
authors.lastname: Beller
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Markus
authors.initials: M
authors.lastname: Bill
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Eoin L
authors.initials: EL
authors.lastname: Brodie
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Conrad
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Ruyang
authors.initials: R
authors.lastname: Han
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Courtney
authors.initials: C
authors.lastname: Irwin
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Joern T
authors.initials: JT
authors.lastname: Larsen
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Hsiao-Chien
authors.initials: HC
authors.lastname: Lim
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Sergi
authors.initials: S
authors.lastname: Molins
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Carl I
authors.initials: CI
authors.lastname: Steefel
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: April
authors.initials: A
authors.lastname: van Hise
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Li
authors.initials: L
authors.lastname: Yang
authors.affiliation: Earth and Environmental Sciences, Lawrence Berkeley National Laboratory , One Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Nico
mesh_terms: D002857:Chromium; D060587:Groundwater; D010084:Oxidation-Reduction
chemical_list: D002857:Chromium