Modified bauxite refinery residues for immobilizing U(VI)
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Date
2012-10-16
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Nuclear Science and Technology Organisation
Abstract
Bauxite refinery residues (BRR) are a waste from the production of alumina using the Bayer process, which has high pH and soluble alkalinity. However, a modified BRR (MBRR) can be made using Mg and Ca to precipitate alkalinity as acid neutralizing capacity (ANC), which lowers pH from ≈13 to ≈8.5. The combined
effects of a fine-grained mineral mix providing high surface area across a range of minerals for metal removal, and an ANC (3-5 mol/kg), gives MBRR potential for many environmental remediation and wastewater-treatment applications. We conducted several laboratory experiments that investigate and assess the application potential of MBRR for the environmental remediation U(VI). Isotopic exchange data show that U(IV) is, in part, irreversibly bound and that irreversibility increases with increased surface loading; it is also age- and temperature-sensitive. Synchrotron X-ray absorption techniques (EXAFS and XANES) suggest that a
limited number of minerals bind U(VI), and the mechanisms and minerals involved are U(VI) concentration dependent. Data indicate that U(VI) binding is initiated by adsorption, largely to the hematite, but precipitation dominates as U(VI) concentration increases. This in turn suggests that irreversibility in the U(VI) binding
is driven by precipitate re-crystallization rather than intra-particulate diffusion into adsorbing minerals. Moreover, the results of this work suggest that MBRR may well be useful in the environmental remediation of U(VI) contaminated soils and waters.
Description
Keywords
Bauxite, Residues, Magnesium, Acid neutralizing capacity, Calcium, Minerals, Adsorption, Soils, Water, Uranium
Citation
Clark, M. W., Payne, T. E., Harrison, J. J., Comarmond, M. J., Dore, M. J. & Collins, R. (2012). Modified bauxite refinery residues for immobilizing U(VI). Paper presented to the 12th South Pacific Environmental Radioactivity Association Conference (SPERA 2012), Sydney, Australia, 16 October – 19 October 2012 . Lucas Heights, NSW: Australian Nuclear Science and Technology Organisation. (pp. 23).