Characterization of Lin'an montmorillonite and its application in the removal of Ni2+ from aqueous solutions

Clay minerals have been studied extensively because of their strong sorption and complexation ability. In this work, Na-montmorillonite was characterized by using acid-base titration, XRD and FTIR in detail. Sorption of Ni(II) on Na-montmorillonite was investigated under ambient conditions as a function of pH, ionic strength, and temperature. The results indicate that sorption of Ni2+ on montmorillonite are strongly dependent on pH and ionic strength. The sorption of Ni2+ is mainly dominated by ion exchange at low pH values and by inner-sphere surface complexation at high pH values. The relationships of pH-C-eq, Q-C-eq and pH-Q are compared and shown clearly in a 3-D plot, and all Q-C-eq data lie in a straight line with slope (-V/m) and intercept (C0V/m). The thermodynamic parameters (Delta H-o, Delta S-o, and Delta G(o)) are calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption reaction of Ni(II) from solution to montmorillonite is endothermic and spontaneous.