Adsorption of Aniline on Layer Silicate Clays and an Organic Soil

Abstract

AbstractAdsorption isotherms of organic pollutants such as aniline on soil colloidal materials have generally not been described for a wide range of solution concentrations. The characteristics of isotherms for aniline adsorption on Ca‐saturated kaolinite, montmorillonite, vermiculite, and an organic soil were determined for a wide range of aqueous concentrations at acid and neutral pH. Aniline adsorption was greater at acid than neutral pH for all adsorbents, an indication of preferred adsorption of anilinium. Adsorption on montmorillonite, vermiculite, and kaolinite across the aniline concentration range of 1 × 10−4 to 2 × 10−2 M was best described by a sigmoid (S‐type) isotherm, an equation for which was derived from a model of cooperative adsorption, in which aniline was assumed to adsorb in molecular “clusters”. Adsorption on the organic soil across the same wide range of aqueous concentration was not described adequately by the S‐type isotherm, but rather by the Brunauer‐Emmett‐Teller (BET) function. Within the restricted range of low aniline adsorption, the adsorption isotherms were linear for all adsorbents. At somewhat higher (intermediate) aniline adsorption, the isotherms remained linear for kaolinite and vermiculite, but curvilinear (L‐type) isotherms were obtained for montmorillonite and the organic soil. Generally, the equation best describing adsorption data was different in form for each range of adsorption being considered. Fourier‐transform infrared (FTIR) spectroscopy indicated that, at least at low pH and high adsorption levels, aniline‐anilinium complexes adsorbed on all of the adsorbents. Adsorption on clay and organic matter had characteristics of both electrostatic and weak physical bonding.