Adsorption Behaviors Of Heavy Metal Pb(Ⅱ) On Clay Minerals

Widely distributed soil and water pollution by heavy metals from the industrial "three wastes" requires the study and development of adsorbents in China. Therefore, low cost and high efficient adsorbents remain important theory and engineering value to remove heavy metals in aquatic environment. The adsorption behaviors and mechanisms of Pb(II) on clay and bentonite, and the effect of various factors are studied by batch experiments. The conclusions are obtained through test results analysis.(1) The adsorption of Pb(II) on clay and bentonite is significantly influenced by different test conditions. Kaolinite is the most important components of the clay and adsorption results show that adsorption capacity of clay decreases with the increasing of soil-water ratio, while Pb(II) removal efficiency increases gradually; adsorption capacity rapidly increases, whereas removal efficiency decreases with the increase in initial Pb(II) concentration; both adsorption capacity and removal efficiency decrease with the rise of temperature; the removal of Pb(II) from aqueous solutions by clay is strongly dependent on pH and the optimum pH is2.91-6.0. For bentonite contained abundant montmorillonite, adsorption capacity increases up to the peak with the initial increasing of soil-water ratio, followed decreases in adsorption capacity with the increasing further; pH and ionic strength have greatly effect on the removal of Pb(II) from aqueous solutions. About100%Pb(II) is removed by bentonite at the pH range of8.0～12.0. The minimum removal efficiency is found at ionic strength of0.1mol/L.(2) The adsorption of Pb(II) on clay and bentonite is a fast process and can reach equilibrium within120min. The kinetic data fit the pseudo-second order kinetics very well and coefficients of determination are greater than0.999. The overall rates of Pb(II) adsorption on clay and bentonite are controlled by film diffusion and diffusion into soil particles.(3) The adsorption isotherms are best-fit with the Langmuir model. The clay and bentonite have much greater affinity for lower Pb(II) concentration. The thermodynamic parameters of Pb(II) adsorption on clay indicate the spontaneous, exothermic and decreased randomness nature, and lower temperature favors the adsoption process; adsorption capacity of bentonite is higher than that of clay, adsorption reaction is the spontaneous, endothermic and increased randomness process, and the adsorption is in favor of higher temperature.