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 hexad ecyltrimethylammonium (HDTMA) and dioctadecyldimethylammonium (DODMA) exchanged smectites was studied at different concentrations and pH lev els to evaluate the capability of organo-clays to sorb an ionizable hy drophobic compound. Dicamba-organo-clay complexes were also prepared a nd characterized by X-ray diffraction (XRD) and Fourier transform infr ared spectroscopy (FT-IR). Results indicated that organo-clays were ef fective sorbents for dicamba, a water-soluble, ionizable, and potentia lly mobile organic compound. Organo-clays with higher organic carbon c ontents usually resulted in greater dicamba sorption. Solution pH sign ificantly affected the sorption of dicamba by organo-clays, with the i sotherm inflection point near the dicamba pK(a) 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 so rption at pH levels greater than its pK(a). Hydrophobic interactions a nd ionic attractions were responsible for the retention of dicamba by organo-clays. Copyright (C) 1996 Elsevier Science Ltd