The adsorption of gemini and conventional surfactants onto some soil solids and the removal of 2-naphthol by the soil surfaces

The adsorption of two cationic gemini surfactants, [CnH2n+1 N+(CH3)(2)-CH2C H2](2). 2Br(-), where n=12 and 14, on limestone, sand, and clay (Na-montmor illonite) from their aqueous solution in double-distilled water and the eff ect of this adsorption on the removal of 2-naphthol have been studied. Comp ared to those of conventional cationic surfactants with similar single hydr ophilic and hydrophobic groups (CnH2n+1N+(CH3)(3). Br-, where n=12 and 14), the molar adsorptions of the gemini and the conventional surfactants on Na -montmorillonite are almost identical and very close to their cation exchan ge capacities. On sand and limestone, the molar adsorption of the cationic gemini surfactants is much larger than that of their corresponding conventi onal surfactants. Adsorption studies of the pollutants onto the three kinds of solids treated by either the gemini or the conventional surfactants sho w that the former are both more efficient and more effective at removing 2- naphthol from the aqueous phase. On all three soil solids, the addition of KBr increases the efficiency of the adsorption of both types of cationics a nd for most cases increases also the maximum amount adsorbed, but decreases slightly the efficiency of removal of 2-naphthol. On limestone, the anioni c gemini adsorbs with one hydrophilic group oriented toward the Ca2+ sites on the surface and its second hydrophilic group oriented toward the aqueous phase. The conventional anionic surfactant forms a double layer. The gemin i anionic is more efficient and more effective than the conventional anioni c in the removal of 2-naphathol from the aqueous phase. Both anionic conven tional and gemini surfactants have no adsorption on sand. The adsorption me chanisms for all the surfactants on the three soil solid surfaces are discu ssed. (C) 2001 Academic Press.