Examination of the effect of alpha radiolysis on plutonium(V) sorption to quartz using multiple plutonium isotopes

Hixon, Amy E.; Arai, Yuji; Powell, Brian A.

doi:10.1016/j.jcis.2013.04.007

Cited by 30 publications

(44 citation statements)

References 37 publications

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“…Remarkably, although the study of Hixon et al (2013) involves another actinide and another mineral than in this study, these independent estimations are in very good agreement. pe-pH data plotted for all experiments in Fig.…”

Section: Np(v)/np(iv) Redox Speciation In Presence Of Illitesupporting

confidence: 66%

“…Consequently, reduction to Np(IV) at the illite surface becomes less favorable and the redox boundary surface species is only approximately 3 pe units (0.18 V) higher as compared to the respective solute species at pH = 10. Hixon et al (2013) observed surface mediated reduction of Pu(V) to Pu(IV) in the presence of quartz. Based on the thermodynamic favorability of Pu(IV) at the quartz surface, the authors calculated that the redox potential of the Pu(V)/Pu(IV) couple would need to be raised by 0.28 V for pH = 7.…”

Section: Np(v)/np(iv) Redox Speciation In Presence Of Illitementioning

confidence: 89%

“…Spectroscopic and microscopic examination very often reveal that reduced Pu(IV) species are predominantly found at the mineral surface, thus implying surface mediated reduction being the relevant reaction mechanism. Reduction is, however, also found at mineral surfaces where a specific reducing partner is absent (Hixon et al, 2013), suggesting that Pu(IV) under given conditions simply is the thermodynamically favored species. Zaravin et al (2012) studied Np(V) sorption onto montmorillonite under the same conditions as for Pu(V), but did not observe Np(V) reduction.…”

Section: Introductionmentioning

confidence: 99%

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Neptunium redox speciation at the illite surface

Marsac

Banik

Lützenkirchen

et al. 2015

Geochimica et Cosmochimica Acta

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Neptunium (Np(V)) sorption onto a purified illite is investigated as a function of pH (3-10) and [Np V O 2 + ] tot (3 Â 10 À8 -3 Â 10 À4 M) in 0.1 M NaCl under Ar atmosphere. After about one week reaction time, only insignificant variation of Np sorption is observed and the establishment of reaction equilibrium can be assumed. Surprisingly, solid-liquid distribution ratios (R d ) are clearly higher than those measured for Np(V) sorption onto illite under aerobic conditions. The observation that R d increases with decreasing pe (pe = Àlog a eÀ ) suggests partial reduction to Np(IV), although measured redox potentials (pe values) at a first glance suggest the predominance of Np(V). Reduction to Np(IV) at the illite surface could indeed be confirmed by X-ray absorption near-edge spectroscopy (XANES). Np speciation in presence of the purified Na-illite under given conditions is consistently described by applying the 2 sites protolysis non-electrostatic surface complexation and cation exchange model. Measured pe data are taken to calculate Np redox state and surface complexation constants for Np(IV) are derived by applying a data fitting procedure. Constants are very consistent with results obtained by applying an existing linear free energy relationship (LFER). Taking Np(IV) surface complexation constants into account shifts the calculated Np(V)/ Np(IV) redox borderline in presence of illite surfaces by 3-5 pe units (0.2-0.3 V) towards redox neutral conditions. Our study suggests that Np(V) reduction in presence of a sorbing mineral phase is thermodynamically favored.

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Section: Np(v)/np(iv) Redox Speciation In Presence Of Illitesupporting

confidence: 66%

Section: Np(v)/np(iv) Redox Speciation In Presence Of Illitementioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

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Neptunium redox speciation at the illite surface

Marsac

Banik

Lützenkirchen

et al. 2015

Geochimica et Cosmochimica Acta

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“…Several studies have shown that minerals may facilitate surface-mediated reduction of Pu(V/VI) to Pu(IV/III) even on minerals that are considered oxidizing or non-reactive [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Theories proposed to describe the surface-mediated reduction of Pu are shown below [14], however disproportionation and self-reduction have been previously proven negligible at environmentally relevant pH values and concentrations of Pu [17,19]: -Thermodynamic favorability of Pu(IV) hydroxide complexes [14,18,19,24].…”

Section: Introductionmentioning

confidence: 99%

“…Theories proposed to describe the surface-mediated reduction of Pu are shown below [14], however disproportionation and self-reduction have been previously proven negligible at environmentally relevant pH values and concentrations of Pu [17,19]: -Thermodynamic favorability of Pu(IV) hydroxide complexes [14,18,19,24]. -Self-reduction via radiolysis byproducts [5,11,19].…”

Section: Introductionmentioning

confidence: 99%

Observations of surface-mediated reduction of Pu(VI) to Pu(IV) on hematite nanoparticles by ATR FT-IR

Emerson

Powell

2015

Radiochimica Acta

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Previous studies have shown that mineral surfaces may facilitate the reduction of plutonium though the mechanisms of the reduction are still unknown. The objective of this study is to use batch sorption and attenuated total reflectance Fourier transform infrared spectroscopy experiments to observe the surface-mediated reduction of plutonium on hematite nanoparticles. These techniques allow for in situ measurement of reduction of plutonium with time and may lead to a better understanding of the mechanisms of surface mediated reduction of plutonium. For the first time, ATR FT-IR peaks for Pu(VI) sorbed to hematite are measured at ∼ 916 cm −1 , respectively. The decrease in peak intensity with time provides a real-time, direct measurement of Pu(VI) reduction on the hematite surface. In this work pseudo first order rate constants estimated at the high loadings (22 mg Pu /g hematite , 1.34 × 10 −6 M Pu /m 2 ) for ATR FT-IR are approximately 10× slower than at trace concentrations based on previous work. It is proposed that the reduced rate constant at higher Pu loadings occurs after the reduction capacity due to trace Fe(II) has been exhausted and is dependent on the oxidation of water and possibly electron shuttling based on the semiconducting nature of hematite. Therefore, the reduction rate at higher loadings is possibly due to the thermodynamic favorability of Pu(IV)-hydroxide complexes.

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