Adsorption behaviors of heavy metal Pb(II) on clay

Adsorption of lead on clay is studied by batch experiments. The effect of soil-water content, reaction time, solution pH and temperature on the removal of Pb(II) by clay, and the kinetic process and adsorption equilibrium are investigated. Adsorption capacity of clay decreases with the increase of soil-water content, while the Pb(II) removal efficiency increases sharply. The adsorption of Pb(II) on clay is a fast process and can reach equilibrium within 120 min. The removal of Pb(II) from aqueous solutions onto clay is strongly dependent on the value of pH. At low value of pH0, the removal of Pb(II) is dominated by ion-exchange on clay surfaces, whereas surface complexation is the main adsorption mechanism at high value of pH0. The kinetic data fit the pseudo-second order kinetics very well and the rate of film diffusion is obviously higher than that of the diffusion into clay particles. The adsorption isotherms are best-fit with the Langmuir isotherm. The saturated adsorption capacity of Pb(II) on clay is 18.86 mg/g and low temperature favors the adsorption process.