title: Role of an organic carbon-rich soil and Fe(III) reduction in reducing the toxicity and environmental mobility of chromium(VI) at a COPR disposal site.
abstract: Cr(VI) is an important contaminant found at sites where chromium ore processing residue (COPR) is deposited. No low cost treatment exists for Cr(VI) leaching from such sites. This study investigated the mechanism of interaction of alkaline Cr(VI)-containing leachate with an Fe(II)-containing organic matter rich soil beneath the waste. The soil currently contains 0.8% Cr, shown to be present as Cr(III)(OH)3 in EXAFS analysis. Lab tests confirmed that the reaction of Cr(VI) in site leachate with Fe(II) present in the soil was stoichiometrically correct for a reductive mechanism of Cr accumulation. However, the amount of Fe(II) present in the soil was insufficient to maintain long term Cr(VI) reduction at historic infiltration rates. The soil contains a population of bacteria dominated by a Mangroviflexus-like species, that is closely related to known fermentative bacteria, and a community capable of sustaining Fe(III) reduction in alkaline culture. It is therefore likely that in situ fermentative metabolism supported by organic matter in the soil produces more labile organic substrates (lactate was detected) that support microbial Fe(III) reduction. It is therefore suggested that addition of solid phase organic matter to soils adjacent to COPR may reduce the long term spread of Cr(VI) in the environment.
authors.affiliation: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.
authors.forename: Weixuan
authors.initials: W
authors.lastname: Ding
authors.affiliation: School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK. Electronic address: D.I.Stewart@leeds.ac.uk.
authors.forename: Douglas I
authors.initials: DI
authors.lastname: Stewart
authors.affiliation: Department of Biological Sciences, School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK.
authors.forename: Paul N
authors.initials: PN
authors.lastname: Humphreys
authors.affiliation: Department of Biological Sciences, School of Applied Sciences, University of Huddersfield, Huddersfield HD1 3DH, UK.
authors.forename: Simon P
authors.initials: SP
authors.lastname: Rout
authors.affiliation: School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK. Electronic address: I.T.Burke@leeds.ac.uk.
authors.forename: Ian T
authors.initials: IT
authors.lastname: Burke
mesh_terms: D002244:Carbon / Q000737:chemistry; D002857:Chromium / Q000032:analysis* / Q000737:chemistry / Q000633:toxicity; D005290:Ferric Compounds / Q000737:chemistry*; D007220:Industrial Waste / Q000032:analysis*; D012037:Refuse Disposal; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis* / Q000737:chemistry / Q000633:toxicity
chemical_list: D005290:Ferric Compounds; D007220:Industrial Waste; D012987:Soil; D012989:Soil Pollutants; D002857:Chromium; C074702:chromium hexavalent ion; D002244:Carbon
keywords: Alkaline; Bioremediation; COPR; Chromium; Iron