Metal ions sorption can be significantly affected by the presence of other sorbates, especially of complexing ligands. In
this study, the effect of Se(IV) on Eu(III) sorption onto TiO2 at different pH and Eu(III) concentration was investigated. Se(IV) was found to enhance Eu(III) sorption as a function of
Se(IV) concentration. Constant capacitance model was successfully used to interpret the sorption experimental data. The solubility
product of Eu2(SeO3)3 at ambient temperature was investigated to highlight the sorption mechanism of ternary sorption system. The pKsp value of Eu2(SeO3)3 was found to be 31.51 ± 0.95.