Sorption of the ionizable organic compound, dicamba (3,6-dichloro-2-methoxy benzoic acid), by organo-clays

The sorption of 3,6-dichloro-2-methoxy benzoic acid (dicamba) by hexadecyltrimethyl-ammonium (HDTMA) and dioctadecyldimethylammonium (DODMA) exchanged smectites was studied at different concentrations and pH levels to evaluate the capability of organo-clays to sorb an ionizable hydrophobic compound. Dicamba-organo-clay complexes were also prepared and characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Results indicated that organo-clays were effective sorbents for dicamba, a water-soluble, ionizable, and potentially mobile organic compound. Organo-clays with higher organic carbon contents usually resulted in greater dicamba sorption. Solution pH significantly affected the sorption of dicamba by organo-clays, with the isotherm inflection point near the dicamba pKa value. Nearly twice as much dicamba could be sorbed in the molecular form as compared to its anionic, deprotonated form. Excessive DODMA contributed to dicamba sorption at pH levels greater than its pKa. Hydrophobic interactions and ionic attractions were responsible for the retention of dicamba by organo-clays.