Investigation of the adsorption characteristics of Pb(II) onto natural kaolinite and bentonite clays

Abstract

Pb(II) pollution threatens human health and environmental safety, and suitable adsorption materials are important for Pb(II) removal. In this study, the adsorption characteristics of Pb(II) onto natural kaolinite and bentonite in the Dalian and Heishan areas (China) were investigated, and the effects of the solid-to-liquid ratio, pH, temperature, and reaction time on the adsorption performance of Pb(II) were analyzed. The results showed that the adsorption capacity of kaolinite decreases as the solid-to-liquid ratio increases, whereas the adsorption capacity of bentonite first increases to a maximum and then decreases. The processes by which kaolinite and bentonite adsorb Pb(II) are both rapid, in which adsorption equilibrium is reached within 120 min, and the pseudo-second-order kinetic model provides the best fit to the experimental results. The Langmuir model provides the best simulation of the isothermal adsorption characteristics of Pb(II) onto kaolinite and bentonite. The adsorption of Pb(II) onto kaolinite is a spontaneous, exothermic, and entropy-decreasing process, where a lower temperature is beneficial for adsorption. However, the adsorption of Pb(II) onto bentonite is a spontaneous, endothermic, and entropy-increasing process, where high temperature is beneficial for adsorption. The results indicate that both natural kaolinite and bentonite can be used as effective adsorbents for Pb(II) removal.