Sorption of Th(IV) on Na-bentonite: Effects of pH, ionic strength, humic substances and temperature

The sorption of Th(IV) on bentonite as a function of pH, ionic strength and humic substances (HSs) was investigated in detail using batch experiments. The results showed that K+, Mg2+ and Ca2+obviously restrained Th(IV) sorption on bentonite. In the whole pH range, anions (i.e., NO3−, ClO4− and Br−) made unobvious difference, while F− and PO43−dramatically enhanced Th(IV) sorption on bentonite. It was very interesting to find that SO42− had a negative effect on Th(IV) sorption. The positive effects of humic acid (HA) and fulvic acid (FA) at low pH were mainly attributed to the strong complex ability of Th(IV)-HA/FA, whereas the sorption of Th(IV) decreased quickly from ∼90% to ∼40% in high pH range. The notable influence of temperature suggested that high temperature was advantageous for Th(IV) sorption to bentonite. Isotherms of Th(IV) sorption on bentonite could be described by Langmuir model better than Freundlich model. The thermodynamic data indicated that the sorption of Th(IV) on bentonite was a spontaneous and endothermic process.

► The influence of pH, ionic strength and humic substances on the sorption of Th(IV) onto Gaomiaozi-bentonite (GMZ-bentonite) was studied in detail using batch experiments.
► The sorption of Th(IV) on GMZ-bentonite was significantly influenced by both cations and anions.
► The thermodynamic parameters of Th(IV) sorption on GMZ-benonite were achieved from the sorption isotherm at various temperatures.