title: Incorporation of Uranium into Hematite during crystallization from ferrihydrite.
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(VI) (≈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(VI) 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 Å, 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(VI) by incorporation into hematite has clear and important implications for limiting uranium migration in natural and engineered environments.
authors.affiliation: Research Centre for Radwaste Disposal and Williamson Research Centre for Molecular Environmental Science, School of Earth, Atmospheric and Environmental Sciences, The University of Manchester , Manchester, M13 9PL, United Kingdom.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Marshall
authors.forename: Katherine
authors.initials: K
authors.lastname: Morris
authors.forename: Gareth T W
authors.initials: GT
authors.lastname: Law
authors.forename: Francis R
authors.initials: FR
authors.lastname: Livens
authors.forename: J Frederick W
authors.initials: JF
authors.lastname: Mosselmans
authors.forename: Pieter
authors.initials: P
authors.lastname: Bots
authors.forename: Samuel
authors.initials: S
authors.lastname: Shaw
mesh_terms: D000327:Adsorption; D003460:Crystallization; D004787:Environmental Pollution / Q000032:analysis; D005290:Ferric Compounds / Q000737:chemistry*; D005583:Fourier Analysis; D013052:Spectrometry, X-Ray Emission; D013696:Temperature; D014501:Uranium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide; D014501:Uranium; C092844:ferric oxyhydroxide