Theoretical study of adsorption mechanism of heavy metals As and Pb on the calcite (104) surface

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Heavy metal pollution has attracted much attention because it has long-term serious impact on the environment. Arsenic (As) and lead (Pb) are two kinds of heavy metals that are widely existing and highly toxic. Adsorption method has been proved to be an economical and efficient treatment to remove or reduce their toxicity. The adsorption of As and Pb atoms on the calcite (104) surface has been studied by density functional theory. The coverage dependence of the adsorption energetics and structures were comprehensively discussed at different adsorption sites for a wide range of coverage Θ from 0 to 1.0 monolayers (ML). Among all the adsorption sites, the one-fold top site cannot be adsorbed, and the three-fold hollow site was the most stable, followed by the two-fold bridge site. For the adsorption of As atom, the adsorption energy increased first and then decreased in the coverage range of 0–1.0 ML, indicating that the interaction between As atoms leaded to the decrease of adsorption energy. However, the adsorption energy of adsorbed Pb atom increased with the increase of coverage, implying that the Pb atoms tended to form clusters on calcite surface, thus improving adsorption stability. The calculation results showed that calcite minerals could be used to remove heavy metal atoms, which had high removal ability to As and Pb atoms. Besides, the lattice relaxation, different charge distribution and electron density of states for As or Pb / calcite (104) system were also investigated in depth.