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Browsing Conference Publications by Subject "Acid neutralizing capacity"

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    Modified bauxite refinery residues for immobilizing U(VI)
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Clark, MW; Payne, TE; Harrison, JJ; Cormarmond, MJ; Dore, MJ; Collins, RN
    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.