Adsorption of Ca(II) and K(I) on the kaolinite surface: a DFT study with an experimental verification

Abstract

The clay minerals have a negative influence on the settlement of coal tailings, and the addition of metal cations has a positive effect on treating coal tailings water. Microscopic adsorption mechanism of Ca(II) and K(I) on kaolinite surface was investigated by means of density functional theory (DFT) calculations and Monte Carlo method. The structures of Ca(II) and K(I) adsorption on kaolinite (001) and (00−1) was obtained, with Mulliken bond populations and binding energies calculated. Ca(II) adsorbed on kaolinite (001) surface and K(I) adsorbed on (00−1) surface are their main products, respectively, and the binding energies of all the adsorption products of Ca(II) are higher than those of K(I). Partial density of states projections combining with Mulliken bond charge and populations indicate that Ca−O and K−O bonds of the adsorption products are dominated by ionic interaction. Cation hydration can make the adsorption occurs more easily and enhance the covalent interaction of the bonds. The adsorption experiment verifies that Ca(II) is easier to adsorb on kaolinite than K(I).