title: In situ chemical reduction of Cr(VI) in groundwater using a combination of ferrous sulfate and sodium dithionite: a field investigation.
abstract: A field study was conducted to evaluate the performance of a ferrous iron based in situ redox zone for the treatment of a dissolved phase Cr(VI) plume at a former industrial site. The ferrous iron based in situ redox zone was created by injecting a blend of 0.2 M ferrous sulfate and 0.2 M sodium dithionite into the path of a dissolved Cr(VI) plume within a shallow medium to fine sand unconfined aquifer formation. Monitoring data collected over a period of 1020 days after more than 100 m of linear groundwater flow through the treatment zone indicated sustained treatment of dissolved phase Cr(VI) from initial concentrations between 4 and 8 mg/L to less than 0.015 mg/L. Sustained treatment is assumed to be primarily due to the reduction of Cr(VI) to Cr(III) by ferrous iron adsorbed to, precipitated on, and/or incorporated into aquifer iron (hydr)oxide solid surfaces within the treatment zone. Precipitated phases likely include FeCO3 and FeS based on saturation index considerations and SEM/EDS analysis. The detection of solid phase sulfites and thiosulfates in aquifer sediments collected from the treatment zone more than 2 years following injection suggests dithionite decomposition products may also play a significant role in the long-term treatment of the dissolved phase Cr(VI).
authors.affiliation: United States Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, 919 Kerr Research Drive, Ada, Oklahoma 74820, USA. ludwig.ralph@epa.gov
authors.forename: Ralph D
authors.initials: RD
authors.lastname: Ludwig
authors.forename: Chunming
authors.initials: C
authors.lastname: Su
authors.forename: Tony R
authors.initials: TR
authors.lastname: Lee
authors.forename: Richard T
authors.initials: RT
authors.lastname: Wilkin
authors.forename: Steven D
authors.initials: SD
authors.lastname: Acree
authors.forename: Randall R
authors.initials: RR
authors.lastname: Ross
authors.forename: Ann
authors.initials: A
authors.lastname: Keeley
mesh_terms: D002857:Chromium / Q000737:chemistry*; D004227:Dithionite / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D005618:Fresh Water / Q000737:chemistry*; D007501:Iron / Q000032:analysis; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D019163:Reducing Agents / Q000737:chemistry; D012987:Soil / Q000032:analysis*