Browsing by Author "Boland, DD"
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- ItemEffect of amorphous Fe(III) oxide transformation on the Fe(II)-mediated reduction of U(VI).(American Chemical Society, 2011-02-15) Boland, DD; Collins, RN; Payne, TE; Waite, TDIt has recently been reported that the Fe(II)-catalyzed crystallization of 2-line ferrihydrite to goethite and magnetite can result in the immobilization of uranium. Although it might be expected that interference of the crystallization process (for example, by the presence of silicate) would prevent uranium immobilization, this has not yet been demonstrated. Here we present results of an X-ray absorption spectroscopy study on the fate of hexavalent uranium (U(VI)) during the Fe(II)-catalyzed transformations of 2-line ferrihydrite and ferrihydrite coprecipitated with silicate (silicate−ferrihydrite). Two-line ferrihydrite transformed monotonically to goethite, whereas silicate−ferrihydrite transformed into a form similar to ferrihydrite synthesized in the absence of silicate. Modeling of U L(III)-edge EXAFS data indicated that both coprecipitated and adsorbed U(VI) were initially associated with ferrihydrite and silicate−ferrihydrite as a mononuclear bidentate surface complex. During the Fe(II)-catalyzed transformation process, U(VI) associated with 2-line ferrihydrite was reduced and partially incorporated into the newly formed goethite mineral structure, most likely as U(V), whereas U(VI) associated with silicate−ferrihydrite was not reduced and remained in a form similar to its initially adsorbed state. Uranium(VI) that was initially adsorbed to silicate−ferrihydrite did, however, become more resistant to reductive dissolution indicating at least a partial reduction in mobility. These results suggest that when the Fe(II)-catalyzed transformation of ferrihydrite-like iron oxyhydroxides is inhibited, at least under conditions similar to those used in these experiments, uranium reduction will not occur. © 2011, American Chemical Society
- ItemFerric iron geometry and coordination during hydrolysis and ferrihydrite precipitation(Mineralogical Society of Great Britain & Ireland, 2011-10-01) Collins, RN; Rose, AL; Glover, CJ; Boland, DD; Payne, TE; Waite, TDDefinitive structural characterisation of ferrihydrite has challenged scientists primarily due to its nanosized particles and inherent long-range structural disorder which challenges analytical methodology (and modelling) typically employed to determine the structure of minerals. Here we report on the application of a synchrotron quick-scanning X-ray absorption spectroscopy (XAS) approach, which allows the collection of Extended X-ray Absorption Fine Structure (EXAFS) spectral data to k = 15 Å-1 in < 1 minute, to obtain unparalleled iron Kedge data on the hydrolysis of FeIII(H2O)6 and ferrihydrite precipitation. Modelling of the pre-edge and EXAFS data: 1) supports theoretical studies which have suggested the existence of a monomeric penta-coordinated FeIII hydrolysis species and; 2) corroborates recently proposed structural models of ferrihydrite that contain tetrahedral FeIII. Modelling results indicate that ferrihydrite consists of 15 to 25 % tetrahedral FeIII and suggest that this geometry must be included in any comprehensive structural model of ferrihydrite and, furthermore, should be considered when evaluating the reactivity, stability and other structure-property relationships of this mineral. © 2011 The Authors.
- ItemInhibitory effect of silicate on the Fe(II)-catalysed sequestration of U by Fe(III) oxides(Elsevier; Cambridge Publications, 2010-06-17) Boland, DD; Collins, RN; Payne, TE; Waite, TDIt has recently been reported that the natural Fe (II)- catalysed transformation of Fe (III) minerals to more crystalline forms can result in the sequestration of uranium [1], thus potentially leading toward a solution to the universal and emotive problem of uranium contamination. While this process may reduce uranium migration, there is no clear knowledge of its viability in conditions which inhibit the transformation of iron oxides. Here we present XAS results of Fe (II)-catalysed transformations in systems containing 2-line ferrihydrite, silicate and uranium as U (VI). The chemical environment of both co-precipitated and adsorbed U (VI) bound by 2-line ferrihydrite was initiallyidentical, in both cases being associated with the iron oxides as a surface complex. Upon addition of aqueous Fe (II) in anoxic conditions, 2-line ferrihydrite with associated U (VI) transformed to goethite. Ab initio modelling of EXAFS data indicated that U (VI) associated with 2-line ferrihydrite was incorporated into the newly formed goethite mineral structure. In contrast, silicate-ferrihydrite only transformed to ferrihydrite with the associated U (VI) remaining in a form similar to its initial state. The adsorbed U (VI) did however become more resistant to reductive dissolution indicating at least a partial reduction in mobility. These results demonstrate that the Fe (II)-catalysed crystallisation of iron oxides may not always induce uranium reduction or immobilisation in relevant environmental conditions. The precise mechanism of the inhibitory effect of silicate, with a focus on how to control conditions to reduce this effect, must be resolved before this process may be considered a reliable means of preventing sub-surface uranium transport. © 2020 Elsevier B.V.
- ItemKinetics of coupled Fe(II)-catalysed ferrihydrite transformation and U(VI) reduction(Mineralogical Society of Greate Britian & Ireland, 2011-10-01) Boland, DD; Collins, RN; Glover, CJ; Payne, TE; Waite, TDAntimony is released into the environment in some natural and man-induced processes. [1]. Yet, its impact on the transformation processes of heavy metal-adsorbing minerals remains poorly understood. In acid-mine drainage systems and shooting ranges, the adsorption of antimony by iron oxides such as ferrihydrite can play a major role. The poorly crystalline 2-line ferrihydrite represents one of the most common Fe oxides in these settings and can transform to goethite (,-FeOOH) or hematite (,-Fe2O3) with time [2]. The rate of transformation depends on the pH, temperature, and on the ions and molecules present during the transformation process [3]. This study focuses on the transformation of synthetic ferrihydrite to crystalline iron oxides in the presence of Sb(V). Transformations were carried out for 1-16 days at 70 ºC and at pH 4, 7 and 12, with different concentrations of Sb(V) (0.00, 0.23, 0.75, 2.25 and 6.00 mM Sb). Samples taken from aqueous suspensions were washed, dried, and characterized by X-ray diffraction (XRD) and atomic absorption spectroscopy (AAS). At pH 12, goethite (Sb concentrations up to 3.7 mg Sb/g) is favored and the transformation is completed after one day. Only a concentration of 6 mM Sb retarded the transformation, where even after 8 days only 50 % of the ferrihydrite was transformed into goethite. Transformations at pH 7 led to a mixture of 75 % hematite and 25 % goethite (4.3 mg Sb/g). However, at concentrations of 6 mM Sb, feroxyhyte (!-FeOOH) (9.1 mg Sb/g) was favored instead. At pH 4, hematite (32.3 mg Sb/g) was favored except for concentrations of 6 mM Sb, were again feroxyhyte (141.1 mg Sb/g) occurred. We assume that increased Sb concentrations favor feroxyhyte and indicate the incorporation of Sb into the structure of feroxyhyte. © The Authors
- ItemReduction of U (VI) by Fe (II) during the Fe (II) - accelerated transformation of ferrihydrite(American Chemical Society, 2014-08-19) Boland, DD; Collins, RN; Glover, CJ; Payne, TE; Waite, TDX-ray absorption spectroscopy has been used to study the reduction of adsorbed U(VI) during the Fe(II)-accelerated transformation of ferrihydrite to goethite. The fate of U(VI) was examined across a variety of pH values and Fe(II) concentrations, with results suggesting that, in all cases, it was reduced over the course of the Fe(III) phase transformation to a U(V) species incorporated in goethite. A positive correlation between U(VI) reduction and ferrihydrite transformation rate constants implies that U(VI) reduction was driven by the production of goethite under the conditions used in these studies. This interpretation was supported by additional experimental evidence that demonstrated the (fast) reduction of U(VI) to U(V) by Fe(II) in the presence of goethite only. Theoretical redox potential calculations clearly indicate that the reduction of U(VI) by Fe(II) in the presence of goethite is thermodynamically favorable. In contrast, reduction of U(VI) by Fe(II) in the presence of ferrihydrite is largely thermodynamically unfavorable within the range of conditions examined in this study. © 2014, American Chemical Society.
- ItemSynthesis and characterization of antibacterial silver nanoparticle-impregnated rice husks and rice husk ash(American Chemical Society, 2013-05-09) He, D; Ikeda-Ohno, A; Boland, DD; Waite, TDSilver nanoparticle (AgNP)-impregnated rice husks/rice hush ash (RHs/RHA) were successfully synthesized, and their potential application as antibacterial materials in water disinfection was investigated with particular attention given to the use of both white rice husk ash (WRHA) and black rice husk ash (BRHA) produced by the combustion of RHs as AgNP supports. AgNPs, with diameter of ∼20 nm, were anchored tightly onto RHA, with the emplacement of the AgNPs on these supports increasing the antibacterial activity of the AgNPs through diminution in the extent of nanoparticle aggregation. Ag K-edge XANES analysis revealed that AgNP-impregnated RHs/RHA are composed of both Ag(0) and Ag(I) species with the Ag(I)/Ag(0) ratio following the order WRHA (65:35) > RHs (59:41) > BRHA (7:93). Sodium thioglycolate, a strong Ag(I) ligand, significantly affected the bactericidal activities of AgNP-impregnated RHs/RHA, suggesting that Ag(I) released from AgNP-impregnated RHs/RHA plays an important role in disinfection. The rate constants of oxidative and dissociative dissolution of Ag(0) and Ag(I) species associated with BRHA are 5.0 × 10–4 M–1s–1 and 1.0 × 10–5 s–1, respectively, while those associated with WRHA are 7.0 × 10–2 M–1s–1 and 2.0 × 10–4 s–1 respectively, demonstrating that the rate of dissolution of silver associated with BRHA is particularly slow. As such, the bactericidal “lifetime” of this material is long and exhibits a lower health risk as a result of release of Ag(I) to consumers than does AgNP-impregnated WRHA. © 2013, American Chemical Society.