Abstract
Clay minerals have been studied extensively due to their strong sorption and complexation ability toward various environmental pollutants. In this study, the sorption of Sr-90(II) on Na-montmorillonite was studied as a function of various environmental conditions such as pH, ionic strength, humic acid (HA) and temperature. The results indicated that the sorption of Sr-90(II) on Na-montmorillonite was strongly dependent on pH and ionic strength. The experimental data of Sr-90(II) sorption was simulated by the diffuse-layer model (DLM) well with the aid of Visual Minteq 3.0. At low pH, the sorption of Sr-90(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on Na-montmorillonite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of HA enhanced Sr-90(II) sorption at pH <7.0 but decreased Sr-90(II) sorption at pH >7.0. Langmuir and Freundlich models were used to simulate the sorption isotherms of Sr-90(II) at three different temperatures of 303, 318 and 333 K. The thermodynamic parameters (Delta H, Delta S and Delta G) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Sr-90(II) on Na-montmorillonite was an endothermic and spontaneous process. The thermodynamic parameters calculated from temperature-dependent sorption data were crucial to understand the interaction behavior of Sr-90(II) with Na-montmorillonite. (C) 2015 Elsevier B.V. All rights reserved.