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|Title: ||The pH-dependence and reversibility of uranium and thorium binding on a modified bauxite refinery residue using isotopic exchange techniques.|
|Authors: ||Clark, MW|
|Issue Date: ||15-Apr-2011|
|Publisher: ||ACADEMIC PRESS INC ELSEVIER SCIENCE|
|Citation: ||Clark, M. W., Harrison, J. J., Payne, T. E. (2011). The pH-dependence and reversibility of uranium and thorium binding on a modified bauxite refinery residue using isotopic exchange techniques. JOURNAL OF COLLOID AND INTERFACE SCIENCE, 356(2), 699-705.|
|Abstract: ||The pH-dependence and reversibility of uranium and thorium binding onto a modified bauxite refinery residue (MBRR) were studied in laboratory uptake/leaching experiments. Natural (238)U and (232)Th isotopes were contacted with MBRR in an 8 day loading period (equilibrium pH approximate to 8.5) then leached in pH-dependent experiments, where the pH was decreased from 8 to 3 over several hours following addition of exchange isotopes (232)U and (229)Th. Relative concentrations of the thorium isotope pair ((232)Th and (229)Th) indicate that Th is very strongly bound to MBRR, and although at pH 3, some de-sorption is observed (232)Th (approximate to 3%) and (229)Th (approximate to 2.5%), released thorium is partially re-adsorbed during an overnight equilibration. During the initial equilibration, approximately 50% of the (238)U was adsorbed, and a U adsorption maximum occurs between pH 5 and pH 6, where <0.5% of the U remains in solution. However, at a pH between 5 and 3, some 60% of the bound U releases, hence the pH range of maximum U retention on the MBRR is relatively narrow. When equilibrated overnight, the MBRR releases additional U, suggesting a kinetically controlled de-sorption linked to mineral dissolution. Plots of U isotope exchange between (232)U and (238)U are linear, and suggest that U adsorption is mostly reversible. Data for adsorption in mixed systems of U and Th suggest that Th and U compete for similar binding sites. (C) 2011 Elsevier Inc. All rights reserved.|
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