Sorption of Linear Alkylbenzenesulfonates on Sediment Materials

Linear alkylbenzenesulfonates (LAS) are anionic surfactants that are used in large quantities in industrial and consumer products. They enter the environment primarily through wastewater and sludge. In this study, the sorption of LAS to the surfaces of sediment particles was investigated as a function of LAS homologue, H+ concentration in solution, Ca2+ concentration in solution, sediment properties, and concentration of solids. Evidence for both hydrophobic and specific or electrostatic interactions was seen. Isotherms were generally nonlinear and were represented well by the Freundlich and the virial (electrostatic) equations. Comparisons of apparent distribution ratios, D (L/kg), for linear portions of the isotherms showed Δ log D/Δ log nCH2 ≈ 0.4, Δ log D/Δ log H+ ≈ 0.17, and Δ log D/Δ log Ca2+ ≈ 0.23. The value of D for different sediments seemed to correlate most closely with the organic carbon content (foc) of the sediments. The value of the distribution ratio increased with the concentration of solids in the system; this effect could be explained partially by the concomitant increase in Ca2+ concentration in solution.