Influence of iron redox transformations on plutonium sorption to sediments
-
Amy E. Hixon
Abstract
Plutonium subsurface mobility is primarily controlled by its oxidation state, which in turn is loosely coupled to the oxidation state of iron in the system. Experiments were conducted to examine the effect of sediment iron mineral composition and oxidation state on plutonium sorption and reduction. A pH 6.3 vadose zone sediment containing iron oxides and iron-containing phyllosilicates was treated with various complexants (ammonium oxalate) and reductants (hydroxylamine hydrochloride and dithionite-citrate-bicarbonate (DCB)) to selectively leach and/or reduce iron oxide and phyllosilicate/clay Fe(III). 57Fe-Mössbauer spectroscopy was used to identify initial iron mineral composition of the sediment and monitor dissolution and reduction of iron oxides and reduction of phyllosilicate Fe(III). 57Fe-Mössbauer spectroscopy showed that the Fe-mineral composition of the untreated sediment is: 25–30% hematite, 60–65% small-particle/Al-goethite, and <10% Fe(III) in phyllosilicate; there was no detectable Fe(II). Upon reduction with a strong chemical reductant (dithionite-citrate-bicarbonate buffer), much of the hematite and goethite was removed. Partial reduction of phyllosilicate Fe(III) was evident in the sediments subjected to DCB treatment. Sorption of Pu(V) was monitored over one week for the untreated and each of five treated sediment fractions. Plutonium oxidation state speciation in the aqueous and solid phases was monitored using solvent extraction, coprecipitation, and XANES. The rate of sorption appears to correlate with the fraction of Fe(II) in the sediment (untreated or treated). Pu(V) was the only oxidation state measured in the aqueous phase, irrespective of treatment, whereas Pu(IV) and much smaller amounts of Pu(V) and Pu(VI) were measured in the solid phase. Surface-mediated reduction of Pu(V) to Pu(IV) occurred in treated and untreated sediment samples; Pu(V) remained on untreated sediment surface for two days before reducing to Pu(IV). Similar to the sorption kinetics, the reduction rate appears to be correlated with sediment Fe(II) concentration. The correlation between Fe(II) concentrations and Pu(V) reduction demonstrates the potential impact of changing iron mineralogy on plutonium subsurface transport through redox transition areas. These findings should influence the conceptual models of long-term stewardship of Pu contaminated sites that have fluctuating redox conditions, such as vadose zones or riparian zones.
© by Oldenbourg Wissenschaftsverlag, Richland, Germany
Articles in the same Issue
- Preface
- Solubility of tetravalent actinides in alkaline CaCl2 solutions and formation of Ca4[An(OH)8]4+ complexes: A study of Np(IV) and Pu(IV) under reducing conditions and the systematic trend in the An(IV) series
- Solubility of triuranyl diphosphate tetrahydrate (TDT) and Na autunite at 23 and 50 °C
- Effect of reduction on the stability of Pu(VI) hydrolysis species
- Retention and redox behaviour of uranium(VI) by siderite (FeCO3)
- Neptunium(V) complexation by natural pyoverdins and related model compounds
- Complexation of Nd(III) with tetraborate ion and its effect on actinide(III) solubility in WIPP brine
- Complexation of Tc(IV) with acetate at varying ionic strengths
- Uranyl photochemistry: decarboxylation of gluconic acid
- Influence of Boom Clay organic matter on the adsorption of Eu3+ by illite – geochemical modelling using the component additivity approach
- The role of green rust in the migration of radionuclides: An overview of processes that can control mobility of radioactive elements in the environment using as examples Np, Se and Cr
- A comparative batch sorption and time-resolved laser fluorescence spectroscopy study on the sorption of Eu(III) and Cm(III) on synthetic and natural kaolinite
- U(VI) sorption on granite: prediction and experiments
- Quantum chemical study of inner-sphere complexes of trivalent lanthanide and actinide ions on the corundum (0001) surface
- Quantum chemical modeling of uranyl adsorption on mineral surfaces
- Interaction of PuO2 thin films with water
- Molecular interactions of plutonium(VI) with synthetic manganese-substituted goethite
- Chlorine speciation in nuclear graphite: consequences on temperature release and on leaching
- Chemical status of U(VI) in cemented waste forms under saline conditions
- Influence of iron redox transformations on plutonium sorption to sediments
- Modelling of a large-scale in-situ migration experiment with 14C-labelled natural organic matter in Boom Clay
- Sorption and diffusion of Eu in sedimentary rock in the presence of humic substance
- Diffusion and sorption of neptunium(V) in compacted montmorillonite: effects of carbonate and salinity
- Uranium(VI) diffusion in low-permeability subsurface materials
- Distribution of Cs and Am in the solution-bentonite colloids-granite ternary system: effect of addition order and sorption reversibility
- Mechanisms of plutonium sorption to mineral oxide surfaces: new insights with implications for colloid-enhanced migration
- Understanding uranium behaviour at the Askola uranium mineralization
Articles in the same Issue
- Preface
- Solubility of tetravalent actinides in alkaline CaCl2 solutions and formation of Ca4[An(OH)8]4+ complexes: A study of Np(IV) and Pu(IV) under reducing conditions and the systematic trend in the An(IV) series
- Solubility of triuranyl diphosphate tetrahydrate (TDT) and Na autunite at 23 and 50 °C
- Effect of reduction on the stability of Pu(VI) hydrolysis species
- Retention and redox behaviour of uranium(VI) by siderite (FeCO3)
- Neptunium(V) complexation by natural pyoverdins and related model compounds
- Complexation of Nd(III) with tetraborate ion and its effect on actinide(III) solubility in WIPP brine
- Complexation of Tc(IV) with acetate at varying ionic strengths
- Uranyl photochemistry: decarboxylation of gluconic acid
- Influence of Boom Clay organic matter on the adsorption of Eu3+ by illite – geochemical modelling using the component additivity approach
- The role of green rust in the migration of radionuclides: An overview of processes that can control mobility of radioactive elements in the environment using as examples Np, Se and Cr
- A comparative batch sorption and time-resolved laser fluorescence spectroscopy study on the sorption of Eu(III) and Cm(III) on synthetic and natural kaolinite
- U(VI) sorption on granite: prediction and experiments
- Quantum chemical study of inner-sphere complexes of trivalent lanthanide and actinide ions on the corundum (0001) surface
- Quantum chemical modeling of uranyl adsorption on mineral surfaces
- Interaction of PuO2 thin films with water
- Molecular interactions of plutonium(VI) with synthetic manganese-substituted goethite
- Chlorine speciation in nuclear graphite: consequences on temperature release and on leaching
- Chemical status of U(VI) in cemented waste forms under saline conditions
- Influence of iron redox transformations on plutonium sorption to sediments
- Modelling of a large-scale in-situ migration experiment with 14C-labelled natural organic matter in Boom Clay
- Sorption and diffusion of Eu in sedimentary rock in the presence of humic substance
- Diffusion and sorption of neptunium(V) in compacted montmorillonite: effects of carbonate and salinity
- Uranium(VI) diffusion in low-permeability subsurface materials
- Distribution of Cs and Am in the solution-bentonite colloids-granite ternary system: effect of addition order and sorption reversibility
- Mechanisms of plutonium sorption to mineral oxide surfaces: new insights with implications for colloid-enhanced migration
- Understanding uranium behaviour at the Askola uranium mineralization
