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Incorporation of Uranium into Hematite during Crystallization from Ferrihydrite.

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Title: Incorporation of Uranium into Hematite during Crystallization from Ferrihydrite.
Authors: Marshall, Timothy A.1, Morris, Katherine1, Law, Gareth T. W.2, Livens, Francis R.2, Mosselmans, J. Frederick W.3, Bots, Pieter1, Shaw, Samuel1 sam.shaw@manchester.ac.uk
Source: Environmental Science & Technology. 4/1/2014, Vol. 48 Issue 7, p3724-3731. 8p.
Subject Terms: Ferric hydroxides, Crystallization kinetics, Uranium absorption & adsorption, Hematite, Clustering of particles, Extended X-ray absorption fine structure, X-ray absorption near edge structure, Migration of uranium
Abstract: Ferrihydrite was exposed to U(VI)-containing cement leachate (pH 10.5) and aged to induce crystallization of hematite, A combination of chemical extractions, TEM, and XAS techniques provided the first evidence that adsorbed U(V1) (≈3000 ppm) was incorporated into hematite during ferrihydrite aggregation and the early stages of crystallization, with continued uptake occurring during hematite ripening-Analysis of EXAFS and XANES data indicated that the U(V1) was incorporated into a distorted, octahedrally coordinated site replacing Fe(III). Fitting of the EXAFS showed the uranyl bonds lengthened from 1.81 to 1.87 A, in contrast to previous studies that have suggested that the uranyl bond is lost altogether upon incorporation into hematite. The results of this study both provide a new mechanistic understanding of uranium incorporation into hematite and define the nature of the bonding environment of uranium within the mineral structure. Immobilization of U(Vl) by incorporation into hematite has clear and important implications for limiting uranium migration in natural and engineered environments. [ABSTRACT FROM AUTHOR]
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Abstract:Ferrihydrite was exposed to U(VI)-containing cement leachate (pH 10.5) and aged to induce crystallization of hematite, A combination of chemical extractions, TEM, and XAS techniques provided the first evidence that adsorbed U(V1) (≈3000 ppm) was incorporated into hematite during ferrihydrite aggregation and the early stages of crystallization, with continued uptake occurring during hematite ripening-Analysis of EXAFS and XANES data indicated that the U(V1) was incorporated into a distorted, octahedrally coordinated site replacing Fe(III). Fitting of the EXAFS showed the uranyl bonds lengthened from 1.81 to 1.87 A, in contrast to previous studies that have suggested that the uranyl bond is lost altogether upon incorporation into hematite. The results of this study both provide a new mechanistic understanding of uranium incorporation into hematite and define the nature of the bonding environment of uranium within the mineral structure. Immobilization of U(Vl) by incorporation into hematite has clear and important implications for limiting uranium migration in natural and engineered environments. [ABSTRACT FROM AUTHOR]
ISSN:0013936X
DOI:10.1021/es500212a