Modeling interactions of Hg(II) and bauxitic soils Original Research Article

The adsorptive interactions of Hg(II) with gibbsite-rich soils (hereafter SOIL-g) were modeled by 1-pK surface complexation theory using charge distribution multi-site ion competition model (CD MUSIC) incorporating basic Stern layer model (BSM) to account for electrostatic effects. The model calibrations were performed for the experimental data of synthetic gibbsite–Hg(II) adsorption. When [NaNO3] less-than-or-equals, slant 0.01 M, the Hg(II) adsorption density values, of gibbsite, ΓHg(II), showed a negligible variation with ionic strength. However, ΓHg(II) values show a marked variation with the [Cl−]. When [Cl−] greater-or-equal, slanted 0.01 M, the ΓHg(II) values showed a significant reduction with the pH. The Hg(II) adsorption behavior in NaNO3 was modeled assuming homogeneous solid surface. The introduction of high affinity sites, i.e., >AlsOH at a low concentration (typically about 0.045 sites nm−2) is required to model Hg(II) adsorption in NaCl. According to IR spectroscopic data, the bauxitic soil (SOIL-g) is characterized by gibbsite and bayerite. These mineral phases were not treated discretely in modeling of Hg(II) and soil interactions. The CD MUSIC/BSM model combination can be used to model Hg(II) adsorption on bauxitic soil. The role of organic matter seems to play a role on Hg(II) binding when pH > 8. The Hg(II) adsorption in the presence of excess Cl− ions required the selection of high affinity sites in modeling.