Adsorption performance of bentonite and clay for Zn(II) in landfill leachate

Abstract

Abstract The proportion of zinc in the landfill increased as the popularity of Galvanized industry, dry battery industry, and it bring harm to the environment. Bentonite is a potential candidate for barriers in landfill due to its metal adsorption ability. This work studies the character of adsorption in natural bentonite and shanghai clay for Zn(Ⅱ). Factor influencing the adsorption of Zn(Ⅱ), such as pH, ion strength of Na, contact time, initial concentration of Zn(Ⅱ), adsorption temperature, were examined by batch-type sorption test. The obtained result show that the change of pH value and ion strength of Na has no significant effect on the Zn(Ⅱ) adsorption onto bentonite. This indicates the strong selectivity of bentonite for Zn(Ⅱ). The Zn(Ⅱ) equilibrium sorption capacity onto clay increases with the increase of pH value or the decrease of ion strength. The effect of contact time on the adsorption process was studied within the kinetic models. The pseudo-second-order, intra-particle diffusion and Elovih model could described well the Zn(Ⅱ) adsorption onto bentonite, because its R2༞0.9. The results show that both physical adsorption and chemical adsorption exist in the Zn(Ⅱ) adsorption onto bentonite or clay, but the main factor determining the adsorption rate is chemical adsorption. The effect of Zn(Ⅱ) initial concentration on the adsorption was studied within the adsorption isotherms. The results show that the adsorption process is controlled by chemical mechanism. The effect of the temperature on the adsorption was studied within the adsorption thermodynamics. The Zn(Ⅱ) adsorption onto bentonite is spontaneous, but not onto clay. The result of SEM, XRD-EDS and FT-IR was show that the adsorption mechanism of Zn(Ⅱ) onto bentonite and clay has van der Waals force, ion exchange, and chemical action such as inner-sphere complexation.