The isotherms shown in Figure indicate that the kaolinite sorption of a longer-chain compound was always stronger than that of a shorter-chain analogue; e.g., the isotherm for C12-BAC is to the upper left of that for C10-BAC. The isotherms for C10-BAC and C8-C8-DADMAC are close to each other, as are the isotherms for C14-BAC and C10-C10-DADMAC, the respective compounds with Section 3.2 below. The type and concentration of inorganic salt dissolved in water affected the sorption isotherms of C12-BAC on kaolinite (Figure ). An NaCl concentration of 150 mM In contrast to our results, Droge and Goss 29 reported that a 10-fold increase in NaCl concentration resulted in a 10-fold decrease in Kkao/w for organic cations, consistent with the 1:1 exchange hypothesis. It is likely that the kaolinite sample used in the literature had a different property than that used in this work. Differences in sorption properties between kaolinite samples have been reported previously for nonionic surfactants. The data in Figure demonstrate that 5 mM CaCl2 is equivalent to 150 mM NaCl as a cation exchange competitor to C12-BAC. The stronger suppression of sorption by divalent Ca 2+ than by monovalent Na + has been reported, and the comparative competitive effects of 5 mM CaCl2 and 150 mM NaCl are consistent with results for illite and bentonite in the literature. Figure . Salt-dependence of C12-BAC sorption on kaolinite (pH 7, 25°C).