Characterization of GMZ bentonite and its application in the adsorption of Pb(II) from aqueous solutions

Bentonite has been studied extensively because of its strong adsorption and complexation ability. In this work, GMZ bentonite (China) was characterized by using acid–base titration, XRD and FTIR in detail. Removal of Pb(II) from aqueous solution by adsorption onto Na-bentonite was investigated under ambient conditions as a function of shaking time, pH, ionic strength, Na-bentonite content and temperature using batch technique. The kinetic adsorption was described by the pseudo-second-order rate equation well. The adsorption of Pb(II) on Na-bentonite was strongly dependent on pH. The Langmuir model fitted the adsorption isotherm very well. The thermodynamic parameters (ΔH0, ΔS0 and ΔG0) calculated from the temperature dependent adsorption isotherms suggested that the adsorption of Pb(II) was endothermic and spontaneous process. At low pH, the adsorption of Pb(II) was dominated by outer-sphere surface complexation and ion exchange with Na+/H+ on Na-bentonite surfaces, whereas inner-sphere surface complexation was the main adsorption mechanism at high pH.