Sorption properties of Th(IV) on the raw diatomite - Effects of contact time, pH, ionic strength and temperature

Diatomite has a number of unique physicochemical properties and has diversified industrial uses. Natural diatomite has been tested as a potential sorbent for the removal of Th(IV) from aqueous Solutions. The results indicate that sorption of Th(IV) is strongly dependent on ionic strength at pH < 3, and is independent of ionic strength at pH > 3. Outer-sphere complexation or ion exchange may be the main sorption mechanism of Th(IV) to diatomite at low pH values, whereas the sorption of Th(IV) at pH > 3 is mainly dominated by innersphere complexation or precipitation. The competition for Th(IV) between aqueous or surface adsorbed anions (e.g., herein ClO4-, NOT and Cl-) and surface functional groups of diatomite is important for Th(IV) sorption. The thermodynamic data (Delta H-0, Delta S-0, Delta G(0)) a re calculated from the temperature-dependent sorption isotherms. The results suggest that sorption process of Th(IV) on diatomite is spontaneous and endothermic. (c) 2008 Elsevier Ltd. All rights reserved.