A Multicomponent Analysis of the Sorption of Polydisperse Ethoxylated Nonionic Surfactants to Aquifer Materials: Equilibrium Sorption Behavior

Surfactant-based aquifer remediation methods have been the subject of a substantial amount of research in recent years due to the growing awareness that traditional remediation methods are often inadequate for the restoration of contaminated aquifers, particularly when nonaqueous-phase organic liquid contaminants are present. Ethoxylated nonionic surfactants are often suggested for aquifer remediation applications because many exhibit high solubilization capacities for organic contaminants and are readily biodegradable. A property of ethoxylated nonionic surfactants that is often overlooked when their behavior in the subsurface is considered is the fact that they are nearly always broadly distributed mixtures, often containing as many as 40 separate surfactant components. The work described here examines the influence of the surfactant distribution on the mixed sorption behavior of ethoxylated linear alcohol surfactants. It is found that selective sorption can be significant, particularly for broadly distributed mixtures. The greatest difference between sorbed and solution surfactant distributions is found to occur at solution concentrations near the surfactant critical micelle concentration. At high surfactant concentrations, the sorbed and solution distributions approach the initial distribution. The presence of an organic coating on the aquifer material is found to significantly increase the extent of sorption, but to have little effect on the observed selective sorption behavior. Implications of these trends for the use of ethoxylated nonionic surfactant mixtures for aquifer remediation applications are discussed.