title: Pu(V)O2+ adsorption and reduction by synthetic hematite and goethite.
abstract: Changes in aqueous- and solid-phase plutonium oxidation state were monitored over time in hematite (alpha-Fe2O3) and goethite (alpha-FeOOH) suspensions containing 239Pu(V)-amended 0.01 M NaCl. Solid-phase oxidation state distribution was quantified by leaching plutonium into the aqueous phase and applying an ultrafiltration/solvent extraction technique. The technique was verified using oxidation state analogues of plutonium and sediment-free controls of known Pu oxidation state. Batch kinetic experiments were conducted at hematite and goethite concentrations between 10 and 500 m2 L(-1) in the pH range of 3-8. Surface-mediated reduction of Pu(V) was observed for both minerals at pH values of 4.5 and greater. At pH 3 no adsorption of Pu(V) was observed on either goethite or hematite; consequently, no reduction was observed. For hematite, adsorption of Pu(V) was the rate-limiting step in the adsorption/reduction process. In the pH range of 5-8, the overall removal of Pu(V) from the system (solid and aqueous phases) was found to be approximately second order with respect to hematite concentration and of order -0.39 with respect to the hydrogen ion concentration. The overall reaction rate constant (k(rxn)), including both adsorption and reduction of Pu(V), was 1.75+/-2.05 x 10(-10) (m(-2) L)(-2.08) (mol(-1) L)(-0.39) (s(-1)). In contrast to hematite, Pu(V) adsorption to goethite occurred rapidly relative to reduction. At a given pH,the reduction rate was approximately independent of the goethite concentration, although the hydrogen ion concentration (pH) had only a slight effect on the overall reaction rate. For goethite, the overall reaction rates at pH 5 and pH 8 were 6.0 x 10(-5) and 1.5 x 10(-4) s(-1), respectively. For hematite, the reaction rate increased by 3 orders of magnitude across the same pH range.
authors.affiliation: Department of Environmental Engineering and Science, Clemson University, Anderson, South Carolina 29625, USA. BAPowell@lbl.gov
authors.forename: Brian A
authors.initials: BA
authors.lastname: Powell
authors.forename: Robert A
authors.initials: RA
authors.lastname: Fjeld
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Kaplan
authors.forename: John T
authors.initials: JT
authors.lastname: Coates
authors.forename: Steven M
authors.initials: SM
authors.lastname: Serkiz
mesh_terms: D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D008027:Light; D008903:Minerals; D010084:Oxidation-Reduction; D011005:Plutonium / Q000737:chemistry*; D014462:Ultrafiltration
chemical_list: D005290:Ferric Compounds; D058085:Iron Compounds; D008903:Minerals; C026885:plutonium dioxide; C094886:goethite; C000499:ferric oxide; D011005:Plutonium