A COMPARATIVE-STUDY OF THE ADSORPTION OF LINEAR ALKYL SULFATES AND ALKYLBENZENE SULFONATES ON RIVER SEDIMENTS

The adsorption of linear alkyl sulphates, (AS, C8 to C14 homologues) on two river sediments was measured at 25-degrees-C in 0.01 M NaHCO3 at pH 7.6. The results were compared with the adsorption of linear alkylbenzene sulphonates, LAS, (C10 to C13 homologue mixture) on the same sediments under identical conditions. Both AS and LAS exhibited fast adsorption phases (< 20 min), with the AS demonstrating an additional slow disappearance from the solution over several hours. Extensive oxidative treatment of the sediment greatly reduced the adsorption capacity for AS and altered the kinetics. Henry's law adsorption constants (partition coefficients) were evaluated for each of the homologues in each surfactant series. The results are interpreted in terms of a hydrophobic bonding mechanism. The increase in the free energy of adsorption for the addition of successive methylene groups to the alkyl chain were estimated as 1.13 and 3.80 kJ mol-1 for AS and LAS, respectively.