title: Reoxidation behavior of technetium, iron, and sulfur in estuarine sediments.
abstract: Technetium is a redox active radionuclide, which is present as a contaminant at a number of sites where nuclear fuel cycle operations have been carried out. Recent studies suggest that Tc(VII), which is soluble under oxic conditions, will be retained in sediments as Fe(III)-reducing conditions develop, due to reductive scavenging as hydrous TcO2. However, the behavior of technetium during subsequent reoxidation of sediments remains poorly characterized. Here, we describe a microcosm-based approach to investigate the reoxidation behavior of reduced, technetium-contaminated sediments. In reoxidation experiments, the behavior of Tc was strongly dependent on the nature of the oxidant. With air, reoxidation of Fe(II) and, in sulfate-reducing sediments, sulfide occurred accompanied by approximately 50% remobilization of Tc to solution as TcO4-. With nitrate, reoxidation of Fe(II) and, in sulfate-reducing sediments, sulfide only occurred in microbially active experiments where Fe(II) and sulfide oxidation coupled to nitrate reduction was occurring. Here, Tc was recalcitrant to remobilization with <10% Tc remobilized to solution even when extensive Fe(II) and sulfide reoxidation had occurred. X-ray absorption spectroscopy on reoxidized sediments suggested that 15-50% of Tc bound to sediments was present as Tc(VII). Overall, these results suggest that Tc reoxidation behavior is not directly coupled to Fe or S oxidation and that the extent of Tc remobilization is dependent on the nature of the oxidant.
authors.affiliation: Institute of Geological Sciences, School of Earth & Environment, University of Leeds, Leeds, LS2 9JT, UK.
authors.forename: Ian T
authors.initials: IT
authors.lastname: Burke
authors.forename: Christopher
authors.initials: C
authors.lastname: Boothman
authors.forename: Jonathan R
authors.initials: JR
authors.lastname: Lloyd
authors.forename: Francis R
authors.initials: FR
authors.lastname: Livens
authors.forename: John M
authors.initials: JM
authors.lastname: Charnock
authors.forename: Joyce M
authors.initials: JM
authors.lastname: McBeth
authors.forename: Robert J G
authors.initials: RJ
authors.lastname: Mortimer
authors.forename: Katherine
authors.initials: K
authors.lastname: Morris
mesh_terms: D005290:Ferric Compounds / Q000032:analysis / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry*; D007501:Iron / Q000032:analysis* / Q000737:chemistry; D009566:Nitrates / Q000032:analysis / Q000737:chemistry; D010084:Oxidation-Reduction; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D013431:Sulfates / Q000032:analysis / Q000737:chemistry; D013455:Sulfur / Q000032:analysis* / Q000737:chemistry; D013667:Technetium / Q000032:analysis* / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D005290:Ferric Compounds; D009566:Nitrates; D013431:Sulfates; D014874:Water Pollutants, Chemical; D013455:Sulfur; D013667:Technetium; D007501:Iron