Sorption study of radionickel on attapulgite as a function of pH, ionic strength and temperature

Sorption of radionickel on attapulgite is studied as a function of contact time, ionic strength, pH and temperature. The results indicate that the sorption of Ni(II) on attapulgite is strongly ionic strength-dependent at pH < 8, and independent of ionic strength at pH > 8. Outer-sphere surface complexation or ion exchange contributes to Ni(II) sorption on attapulgite at pH < 8, whereas the sorption of Ni(II) is mainly dominated by inner-sphere surface complexation at pH > 8. The sorption of Ni(II) on attapulgite increases with increasing temperature, and the thermodynamic parameters (Delta H (0), Delta G (0) and Delta S (0)) calculated from the temperature dependent sorption isotherms suggest that the sorption of Ni(II) on attapulgite is a spontaneous and endothermic process. The high sorption capacity of attapulgite suggests that attapulgite is a suitable material for the preconcentration and solidification of radionickel from large volumes of aqueous solutions.