Removal of malathion and butachlor from aqueous solution by clays and organoclays

Adsorption of malathion and butachlor onto kaolin. montmorillonite. bentonite clays and respective organoclays were studied, Organoclays were prepared by the exchange of quaternary ammonium type surfactants such as tetradecyltrimethyl ammonium bromide (TTAB), dodecyltrimethylammonium bromide (DTAB), and cetylpyridinium chloride (CPC) for inorganic cations like Na+ and Ca2+ on internal and external surface of the clays. This modification produces a change of surface property of clay from hydrophilic to hydrophobic. The adsorption equilibrium data points were fitted to Freundlich isotherm equations. The adsorption of malathion and butachlor were significantly enhanced by surfactant treatment of the clays. The amount of both pesticides adsorbed per unit mass of organoclay followed the order of TTA-kaolin < TTA-montmorillonite < TTA-bentonite, which is inconsistent with the organic carbon content of the clays. The removal efficiency of organomontmorillonite to treat malathion is in the order of CP(C-16)-montmorillonite > TTA(C-14)-montmorillonite > DTA(C-12)-montmorillonite. Butachlor is adsorbed to greater extent than malathion by each adsorbent. which may be due to the higher hydrophobicity of butachlor, indicating considerable hydrophobic interaction between adsorbent/radsorbate system. These findings may find applications in the removal of sparingly water soluble pesticides from aquifers. (C) 2001 Elsevier Science B.V. All rights reserved.