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 similar to 90% to similar 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. (C) 2011 Elsevier B.V. All rights reserved.