Title

The pH-dependence and reversibility of uranium and thorium binding on a modified bauxite refinery residue using isotopic exchange techniques

Document Type

Article

Publication details

Clark, MW, Harrison, JJ & Payne, TE 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, vol. 356, no. 2, pp. 699-705.

Published version available from:

http://dx.doi.org/10.1016/j.jcis.2011.01.068

Peer Reviewed

Peer-Reviewed

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 238U and 232Th isotopes were contacted with MBRR in an 8 day loading period (equilibrium pH ≈ 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 232U and 229Th. Relative concentrations of the thorium isotope pair (232Th and 229Th) indicate that Th is very strongly bound to MBRR, and although at pH 3, some de-sorption is observed 232Th (≈3%) and 229Th (≈2.5%), released thorium is partially re-adsorbed during an overnight equilibration. During the initial equilibration, approximately 50% of the 238U was adsorbed, and a U adsorption maximum occurs between pH 5 and pH 6, where 232U and 238U 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.