Mechanism(s) Controlling Sorption of Neutral Organic Contaminants by Surfactant-Derived and Natural Organic Matter

Layer silicate clays modified with cationic surfactants (organoclays) such as hexadecyltrimethylammonium (HDTMA) are effective sorbents for neutral organic contaminants (NOCs) and may be useful for in-situ and ex-situ remediation of contaminated soils and waters. In this study, the sorptive characteristics of organoclays were compared in terms of magnitude and mechanism to those of natural soil organic matter. The data presented here support multiple mechanisms controlling the sorption of aqueous-phase NOCs on organoclays including solvation of the cationic ammonium centers, the alkyl chains of HDTMA, and the mineral surfaces and solute partitioning. In contrast, solute partitioning appears to be the singular mechanism for the sorption of aqueous-phase NOCs by natural soil organic matter. Organic contaminant sorption by the surfactant-derived organic matter of organoclays is substantially higher than by natural soil organic matter due to the existence of multiple sorptive mechanisms for organoclays and the greater solvency of their organic phases.