Adsorption of dodecylbenzenesulfonates by soil colloids and influence of soil colloids on their degradation

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Abstract
In order to elucidate the behavior of surfactants in soil ecosystems, the mechanism involved in the reaction of dodecylbenzenesulfonates (ABS and LAS) with soil colloids was studied in 19 soils. Soil colloids, especially sesquioxides, were capable of adsorbing considerable quantities of dodecylbenzenesulfonates. ABS adsorption on soils was strongly affected by pH, and was scarecely affected by Cl- but appreciably by SO4 2- and H2PO4 -. ABS was adsorbed by the ligand exchange on soil colloids. ABS adsorption on clay surfaces follows the Langmuir isotherm. However, “intermolecular associations” occurred with increasing ABS concentration. Within certain levels of adsorption, ABS-c1ay complex became hydrophobic and floated to the liquid surface. The degradation of ABS was depressed by the addition of soil, while a difference among soils was slight. On the other hand, LAS degradation rate differed from one another depending upon the soil. LAS adsorbed on soils containing large amounts of allophane and/or sesquioxides was partially protected from microbial degradation.

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