Sorption of Th(IV) ions onto TiO2: Effects of contact time, ionic strength, thorium concentration and phosphate

Summary The sorption of Th(IV) onto TiO₂ was studied by the batch technique as a function of pH and ionic strength at moderate concentration (10^-4-10^-5 mol/l) and in the presence and absence of phosphate. It was found that the sorption rate of Th(IV) was relatively slow, the sorption percent was abruptly increased from pH 2 to 4, and the sorption was decreased with increasing ionic strength as a whole. In the concentration range of Th(IV) from trace concentration to 1.4 ^. 10^-4 mol/l and in the absence of phosphate, the sorption isotherms were roughly fitted the Freundlich equation at different ionic strengths and approximately constant pH. These sorption characteristics of Th(IV) onto TiO₂ were compared with those of uranyl on the same sorbent. In addition, the positive effect of phosphate on the sorption of Th(IV) onto TiO₂ was demonstrated obviously and can be attributed to strong surface binding of phosphate, and the subsequent formation of ternary surface complexes of Th(IV). The difference between the sorption characteristics of Th(IV) ions and uranyl ions onto TiO₂ is discussed.