Adsorption experiments were performed under batch process, using Th(IV) initial concentration, pH of solution, contact time and temperature as variables. Th(IV) uptake by calcined (C-D) and flux calcined diatomite (FC-D) was pH dependent (pH range, 3.0-6.0) and maximum sorption was observed at pH 4.0. Sorption capacities for Th(IV) were found to be 0.52 (121.22 mg Th/g) and 0.50 mmol/g (116.69 mg Th/g) for calcined diatomite (C-D) and flux calcined diatomite (FC-D), respectively. Adsorption process is well described by Freundlich and Dubinin-Radushkevich (D-R) isotherms in comparison with Langmuir, Temkin and Flory-Huggins isotherms. Thermodynamic data (Delta H degrees, Delta S degrees, Delta G degrees) were calculated from the temperature-dependent sorption isotherms. Results suggested that the adsorption of Th(IV) on calcined and flux calcined diatomite was a spontaneous and endothermic process. A comparison of kinetic models applied to the adsorption of Th(IV) onto C-D and FC-D was evaluated for the pseudo-first-order, pseudo-second-order, intraparticle diffusion and film diffusion kinetic models. The experimental data fitted very well the pseudosecond-order kinetic model and also followed by intra-particle diffusion model, whereas intraparticle diffusion and film diffusion are both the rate limiting steps for Th(IV) onto calcined and flux calcined diatomite. (C) 2012 Elsevier B.V. All rights reserved.