First principles study of structural stability against the distribution of Mg and Al atoms and adsorption behaviors of heavy metals of attapulgite

First principles calculations are carried out to study the occupation properties of heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd, Sb, Hg and Pb) in attapulgite. The stability of attapulgite with different distributions of Al and Mg ions and the influence of aluminum contents was evaluated by calculating of cohesive energy. The most stable attapulgite owns equal Mg and Al contents. The influence of Al contents and occupation on the adsorption properties of heavy metals in attapulgite is studied. The heavy metals tend to occupy in the interstitial site comparing to the substitution of metal (Mg and Al) sites. Mg-rich attapulgite is a good adsorbent for Pb and Cd, but unable to adsorb Sb and Hg in term of the thermodynamic stability. Electronic structure analysis indicates that Al content is a key factor to determine the adsorption ability of attapulgite for heavy metals, and the interaction between heavy metal and O atoms is the dominate force to hold heavy metal atom in attapulgite.