ADSORPTION OF ZEARALENONE BY ORGANOPHILIC MONTMORILLONITE CLAY

Acidic montmorillonite clay was chemically modified via exchange with various ammonium- and pyridinium-based organic cations. These organo c lays were then shown to adsorb zearalenone (ZEN) with an efficacy rela ted to the exchanged cation hydrophobicity, as gauged by estimated cri tical micelle concentration values (cmc) and length of the alkyl chain . ZEN adsorption was greatest for clay samples that had been modified by interlayer exchange with cations possessing 16-carbon alkyl chains: hexadecyltrimethylammonium (HDTMA) and cetylpyridinium (CP). Isotherm al analysis of ZEN adsorption (at 37 degrees C, pH 6.5) indicated that the clay exchanged with CP at a level of less than or equivalent to t he cation exchange capacity (CEC) binds ZEN primarily by a partition p rocess. In contrast, clay exchanged at the 1.5 CEC level gave an S-sha ped curve with at least two plateaus, suggesting additional mechanisms of adsorption. A capacity (Q(max)) and distribution coefficient (K-d) for the first site were estimated. At acid pH, the adsorption capacit y for 1.5 CEC CP clay decreased and the isotherm shape predicted a sim ple partition process. Conversely, the shape remained curved at alkali ne pH, suggesting an adsorption site. These data imply an adsorption m echanism at neutral pH that involves hydrophobic attraction of ZEN int o the interlayer in addition to multisite binding of the anionic form to hydroxyl groups on the edge of the clay via ion-dipole interactions and electrostatic attraction to excess exchanged surfactant cations.