Adsorption of dodecyl trimethylammonium and hexadecyl trimethylammonium onto kaolinite - Competitive adsorption and chain length effect

Adsorption of dodecyl trimethylammonium (DDTMA) and hexadecyl trimethylammonium (HDTMA) from single and mixed surfactant solutions onto kaolinite was investigated in this study. It was found that the surfactant chain length had minimal effects on the amount of cations desorbed. In contrast, the amounts of surfactant and counterion bromide adsorbed were strongly affected by surfactant chain lengths. Compared to DDTMA, HDTMA and counterion bromide adsorption was much higher. This fact further verified that both cation exchange and hydrophobic interaction played an important role in cationic surfactant adsorption on negatively charge mineral surfaces. The results also indicate that chain length has a minimal influence on surfactant adsorption via cation exchange, but a longer chain length promotes stronger hydrophobic interaction and thus, resulted in a higher surfactant adsorption. (C) 2006 Elsevier B.V. All rights reserved.