Sorption studies of Pb(II) onto montmorillonite clay

In this research, the lead (Pb(II)) removal rate of montmorillonite (Mt) was studied in aqueous solution. The adsorption conditions (contact time, pH, and temperature) were adjusted to study the effect of those factors on the removal rate of Pb(II) adsorption by Mt. The results indicated that the effect of temperature on the Pb(II) removal rate of Mt was not significant. The Pb(II) removal rate was found to be pH-dependent, improving with increasing pH in the range of 3 to 7. The equilibrium time of adsorption was attained after around 1 hour. The adsorption kinetics were analyzed by fitting to three models (pseudo-first-order (PFO) kinetic model, pseudo-second-order (PSO) kinetic model and intraparticle diffusion model. In comparison, R² value (0.9952) of PSO kinetic model is better than PFO (0.9718), supposing that the adsorption process of Pb(II) onto Mt was chemisorption. The intraparticle diffusion model fitting showed that the Pb(II) adsorption process by Mt was controlled by three steps. Langmuir, Freundlich, Redlich-Peterson and Sips isotherm models were used to describe the adsorption mechanism of Pb(II) adsorbed onto Mt. The experiment results showed the adsorption isotherms are a perfect fit to the Sips model, indicating both homogeneous monolayer adsorption and heterogeneous multilayer adsorption were occurred in the Pb(II) adsorption process by Mt, and the adsorption was mainly controlled by heterogeneous multilayer adsorption.