Effect of pH, ionic strength and temperature on the sorption of radionickel on Na-montmorillonite

Sorption of Ni(II) on Na-montmorillonite was studied under ambient conditions using the batch technique. The effects of pH, solid content, ionic strength and temperature on Ni(II) sorption was also investigated. The kinetic sorption process was well described by a pseudo-second-order rate model. The sorption thermodynamics of Ni(II) on montmorillonite were carried out at 20 +/- 2 degrees C, 37 +/- 2 degrees C, and 67 +/- 2 degrees C, respectively. The thermodynamic parameters, such as standard free energy changes (Delta G(0)), standard enthalpy change (Delta H-0) and standard entropy change (Delta S-0), were obtained. The sorption of Ni(II) is an endothermic process. The sorption of Ni(II) on montmorillonite was strongly dependent on pH values and temperature, and independent of ionic strength. At acidic pH, sorption of Ni(II) is dominated by cation exchange and outer-sphere surface complexation, but at alkaline pH the sorption is dominated by inner-sphere surface complexation. (C) 2009 Elsevier Ltd. All rights reserved,