Minimizing losses of nonionic and anionic surfactants to a montmorillonite saturated with calcium using their mixtures.

Losses of surfactants through sorption to soils/sediments, especially to clay minerals, by various chemical interactions such as sorption and precipitation threaten the success of surfactant in enhancing remediation of contaminated soil and groundwater. In this study, the behavior of mixtures of a nonionic surfactant (TX-100) and an anionic surfactant (SDBS) sorbed to a montmorillonite saturated with calcium (Ca-montmorillonite) was investigated, and compared with that of individual surfactants. It is shown that the amounts of both TX-100 and SDBS sorbed to Ca-montmorillonite are significant. However, the amount of either TX-100 or SDBS sorbed can be decreased and minimized when they are mixed with each other. Mixed micelle formation, which causes negative deviation of critical micelle concentrations (CMCs) from the ideal, is responsible for the decrease in sorbed TX-100 and sorbed SDBS in their mixtures. Because of their ability to minimize their amounts sorbed and thus enhance their active concentrations, as observed in mixed TX-100 and SDBS systems, mixed anionic-nonionic surfactants exhibit potential advantages in the area of enhanced soil and groundwater remediation.