Investigation of the sorption behavior of Cd(II) on GMZ bentonite as affected by solution chemistry

Clay minerals have been studied extensively due to their strong sorption and complexation ability towards various environmental pollutants. In this study, the removal of cadmium from wastewaters by GMZ bentonite was studied as a function of various solution chemistry conditions such as pH, ionic strength, coexisting electrolyte ions, humic substances and temperature under ambient conditions. The results indicated that the sorption of Cd(II) on GMZ bentonite was strongly dependent on pH and ionic strength. Langmuir and Freundlich models were used to simulate the sorption isotherms of Cd(II) at three different temperatures of 298,318 and 338 K. The thermodynamic parameters (Delta H degrees, Delta S degrees and Delta G degrees) calculated from the temperature dependent sorption isotherms indicated that the sorption process of Cd(II) on GMZ bentonite was endothermic and spontaneous. At low pH, the sorption of Cd(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on GMZ bentonite surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, one can conclude that GMZ bentonite may have good potentialities for the disposal of cadmium bearing wastewaters. (C) 2010 Elsevier B.V. All rights reserved.