Adsorption of surfactants from water onto raw and HCl-activated clays in fixed beds

The removal of surfactants from water by adsorption onto raw and HCl-activated montmorillonite in fixed beds was studied. Three surfactants hexadecylpyridinium chloride (cationic), sodium dodecyl sulfate (anionic), and Triton X-102 (non-ionic) were selected in the concentration ranges lower than their critical micelle concentrations in fixed bed experiments. It was shown that the adsorption of anionic surfactant onto Ca-montmorillonite (SAz-1) decreased with increasing pH but that of cationic surfactant increased. The adsorption capacity of non-ionic surfactant was maximized at pH 7.0. For given clay, the adsorption capacities of surfactants were strongly pH-dependent. The adsorption capacity and adsorption rate of non-ionic surfactant onto SAz-1 could be largely improved after acid activation of the clay. Such an improvement was due to the fact that the dissolution of Al³⁺ or Fe²⁺ of montmorillonite occurs in acid solution. The calculated breakthrough curves in fixed bed agreed with the measured ones (standard deviation < 6%). The 50% C/C₀ breakthrough time (τ) decreased with increasing liquid flow rate. The effects of flow rate on the adsorption constant and adsorption capacity were also discussed.