Adsorption of micelle forming and non-micelle forming surfactants on the adsorbents of different nature

Abstract

Wastewater treatment is considered to be a part of mineralization processes of man-caused substance. The mineralization of substance, in turn, is an inclusion of vital functions products, waste and metabolites into the continual natural cycles of substance and energy exchange. Study of water-soluble organic substances adsorption in order to find effective and cheap adsorbents both natural and artificially created is an important problem of the XXI century. Due to the increasing use and global scale of production of surfactant detergents being pollutants of water bodies, grounds and soils, adsorption of both micelle forming surfactant detergents (anionic sodium dodecylsulfate SDS, cationic cetyltrimethylammonium bromide CTAB and non-ionic Triton X-100) and non-micelle forming surfactants—aliphatic alcohols ( n-butanol, n-pentanol and n-hexanol) on aluminum oxide (of analytical grade) and natural mineral shungite was studied in this paper. Isotherms of adsorption were found according to the data of surface tension obtained. The Gibbs–Langmuir adsorption model constant values were determined for surfactants at both the air/water interface and at the water/adsorbent interface studied. Critical micellization concentrations of the solutions of surfactants also were determined by the tensiometric and the conductometric methods. The most effective hydrophilic and hydrophobic adsorbents are revealed for alcohols and micelle forming surfactants. The given results on surfactant adsorption, in particular, on aluminum oxide, are interpreted on the basis for Nechaev's conceptions (1989) about the connection of adsorption ability of organic molecules with resonance potential of adsorbents. For thermodynamic estimation of adsorbents efficiency the standard Gibbs free energy change of adsorption and the standard Gibbs free energy change of micellization were calculated. Comparison of the Gibbs free energies values for micelle forming surfactants shows that wastewater treatment from cationic CTAB is effective using both powders of shungite and aluminum oxide. Another case is wastewater treatment from SDS and Triton X-100 for which aluminum oxide is non-effective while shungite is still efficient. Data obtained are considered to be a component part of colloido-chemical base of purification of sewage polluted with surfactants.