Adsorption and desorption of Ni2+ on Na-montmorillonite:: Effect of pH, ionic strength, fulvic acid, humic acid and addition sequences

Humic substances and clay minerals have been studied intensively because of their strong complexation and adsorption capacities. In this work, adsorption of Ni2+ on Na-montmorillonite was studied using batch technique under ambient conditions. Effect of pH, ionic strength, solid content, humic acid (HA), fulvic acid (FA) and the addition sequences of fulvic acid/Ni2+/montmorillonite on Ni2+ adsorption was also investigated. The results indicate that adsorption of Ni2+ on montmorillonite are strongly dependent on pH and ionic strength. The adsorption of Ni2+ is mainly dominated by surface complexation and ion exchange. The adsorption-desorption hysteresis suggests that the adsorption of Ni2+ is irreversible. The thermodynamic parameters (Delta H, Delta S, and Delta G) are calculated from the temperature dependence, and the results suggest that the adsorption reaction is endothermic and spontaneous. The presence of FA and the addition sequences of FA/Ni2+/montmorillonite do not influence the adsorption of Ni2+ on FA bound montmorillonite hybrids. Montmorillonite is a suitable candidate for pre-concentration and solidification of Ni2+ from large volume of solutions. (C) 2007 Elsevier B.V. All rights reserved.