Sorption of Nonionic Surfactants on Sediment Materials

The distribution of a series of nonionic surfactants between sediments and water was studied as a function of surfactant structure, ionic strength, pH value, Ca 2+ concentration in solution, sediment composition, and concentration of suspended solids. The surfactants were monotridecyl ethers of poly(ethylene glycol), also known as alcohol ethoxylates, A n E x = CH 3 (CH 2 ) n - 1 (OCH 2 CH 2 ) x OH), with n = 13 and x = 3, 6, and 9. Isotherms were nonlinear, with the degree of nonlinearity and the extent of sorption increasing with the number of oxyethylene (-OCH 2 CH 2 -) groups. Freundlich isotherms represented the data well. The pH and ionic strength of the solution had a small effect on sorption, but the effect increased with the number of oxyethylene groups. These observations suggest that the oxyethylene chain is specifically adsorbed, presumably through a hydrogen-bond mechanism. Addition of Ca 2+ did not affect the distribution of AEs. The distribution ratios of the AEs did not correlate well with the fraction organic carbon of the sediments; the amount of swelling clay in the sediment may affect distribution ratios. The concentration of solids had no effect on the extent of sorption.