Thermodynamic study of Th(IV) sorption on attapulgite.

Sorption of Th(IV) on attapulgite was studied as a function of pH and temperature under ambient conditions using batch technique. The results indicated that sorption of Th(IV) on attapulgite was strongly affected by pH values and temperature. The kinetic sorption of Th(IV) can be described by pseudo-second-order rate very well. Sorption isotherms of Th(IV) at 293.15, 308.15 and 323.15K were modeled by Langmuir and Dubinin-Radushkevich models very well, and the parameters indicated that the sorption of Th(IV) on attapulgite was strongly dependent on temperature and the sorption of Th(IV) increased with increasing temperature of the system. Enthalpy (DeltaH(0)), entropy (DeltaS(0)) and Gibbs free energy (DeltaG(0)) were calculated from the temperature dependent sorption data, and the results indicated that the sorption of Th(IV) on attapulgite was a spontaneous process, and the sorption was endothermic.