Studies of Eu(III) sorption on TiO2: Effects of pH, humic acid and poly(acrylic acid)

The influences of pH, ionic strength, initial Eu(III) concentration, humic acid (HA) and ploy(acrylic acid) (PAA) on Eu(III) sorption onto TiO2 were carried out using batch technique. The results indicated that the presence of HA and PAA strongly enhanced Eu(III) sorption onto TiO2 surface in low pH range, which suggested that PAA and HA played an important role as “bridge” between Eu(III) and TiO2 to provoke Eu(III) sorption. Furthermore, the negative effects were observed above pH 4.0 in the presence of organic matters, because the residual PAA or HA in aqueous solution could form soluble Eu–HA/PAA complexes easily. The batch analysis showed that Eu(III) sorption on TiO2 was significantly dependent on pH and independent of ionic strength, suggesting that the sorption of Eu(III) was mainly attributed to inner-sphere complexes. Three inner-sphere complexes, namely, SOEu2+ (logK = 3.80), SOEu(OH)+ (logK = −2.55) and SOEu(OH)20 (logK = −8.33), predominated for Eu(III) on TiO2 surface.

► The sorption of Eu(III) on TiO2 was investigated in detail.
► The influences of HA and PAA on Eu(III) sorption were studied at different pH values.
► Surface complexation model and MINTEQ 3.0 code were applied to discuss the sorption mechanism of Eu(III) on TiO2 surface.