Abstract
The significant complexity of the chemical forms and reactions of HgCl2 in clay-water systems make elucidating the corresponding interaction mechanisms and activities challenging. The specific ion effect and its mechanisms for HgCl2 adsorption at charged clay surfaces were investigated in this study. Experimental results showed that (1) at a fixed background concentration, the adsorption capacity and adsorption energy of HgCl2 on montmorillonite surface decreased in the order Li+> > Na+ > K+, and HgCl2 adsorption exhibited a strong specific cation effect. (2) For the same background cation (Li+, Na+ or K+), the adsorption capacity and energy of HgCl2 decreased as the cation concentration increased. An analysis of the origin of the adsorption energy for HgCl2 showed that this energy linearly increased with the surface electric field strength of montmorillonite. On the basis of orbital asymmetric hybridization theory, we speculated that specific adsorption of the HgCl2 molecule occurs via “polarization-induced covalent bonding” adsorption between O (clay surface) and Hg (HgCl2) atoms. The adsorption energy linearly increased with the surface electric field strength in the clay-water system. These findings provide useful information on modifying the physical, chemical and biological activities of HgCl2 in clay-water systems.
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