Effects of phosphate and Cr³⁺ on the sorption and transport of Th(IV) on a silica column

Abstract

Six column experiments were performed, and six breakthrough curves (BTCs) and six displacement (desorption) curves (DPCs) were obtained, which demonstrate the effects of phosphate and Cr³⁺ on the sorption and transport of Th(IV) on a silica column at pH 3.0 and Th(IV) concentration 8·10⁻⁶ mol/l of the influent. It was found that in the presence of phosphate sorbed preliminarily on the silica column, the amount of Th(IV) sorbed on the silica column is significantly increased. The breakthrough is significantly delayed relative to those in the absence of phosphate; the effect of simultaneous injection of Cr³⁺ on Th(IV) breakthrough is not significant and while the maximum concentration of Th(IV) of BTC is significantly decreased and reached about 70% of the input concentration; a minor proportion of Th(IV) sorbed on the silica column in the presence or absence of phosphate is not readily displaced with 0.01 mol/l KNO₃ aqueous solution at pH 3. Transport and sorption studies of Th(IV) are important, since all thorium isotopes are radioactive, and Th(IV) is an analogue of tetravalent actinides. There is a need to understand the potential for migration from radioactive waste storage and mill tilling sites.