Zinc adsorption by lime-treated montmorillonite clay

In this research, lime-treated montmorillonite clay is used to adsorb Zn(II) in a wide range of Zn(II) concentrations. Batch test results show that the adsorption of Zn(II) by montmorillonite appears to be dominated by different adsorption mechanisms. At low Zn(II) concentrations, chemisorption affects the amount of Zn(II) adsorbed by montmorillonite. When lime is added, physisorption becomes increasingly important. At high Zn(II) concentrations, physisorption is the dominant mechanism for Zn(II) adsorption. Lime also enhances the ability of montmorillonite to adsorb Zn(II) at low initial Zn(II) concentrations, and does not significantly affect the ability of montmorillonite to adsorb Zn(II) at high initial Zn(II) concentrations. In chemisorption, montmorillonite provides cation exchange sites for the adsorption of Zn(II). In physisorption, montmorillonite acts as not only nucleation center to adsorb zinc hydroxide-oxides but also helps to coagulate the zinc hydroxide-oxides. Lime-treated clay can therefore be an effectively used to adsorb metals such as zinc even at very high metal concentrations. The significance of these findings is in the design of landfill liner. A mixture of montmorillonite (bentonite) clay and lime is shown to have characteristics that would make this material a superior landfill liner. The lime-treated clay has low hydraulic conductivity, enhanced metal removal capability, and better resistance to penetration by sharp objects.