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, Ca2+ 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)=CH3(CH2)(n-1)(OCH2CH2)(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 (-OCH2CH2-) 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 Ca2+ 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.