Sorption of non-ionic surfactants onto soil

Abstract

Experiments in batch soil/aqueous systems were conducted to evaluate the sorption onto soil of three micelle-forming non-ionic surfactants and one lamellae-forming non-ionic surfactant. Non-ionic surfactant sorption onto soil was assessed using a surface tension technique for aqueous-phase surfactant concentrations less than surfactant monomer saturation. These sorption data were found to fit a Freundlich isotherm. Non-ionic surfactant sorption onto soil was assessed in the presence of surfactant micelles, or surfactant bilayer lamellae, depending on the type of surfactant, with either a spectrophotometric technique or a chemical oxidation technique. Sorption of the micelle-forming non-ionic surfactants onto soil was found to be constant at a value of the bulk solution surfactant concentration exceeding surfactant monomer saturation, i.e. the critical micelle concentration. Sorption of the lamellae-forming non-ionic surfactant onto soil was found to be an increasing function of the surfactant dose for bulk solution surfactant concentrations exceeding a critical aggregate concentration. Understanding of surfactant sorption onto soil is needed to assess surfactant mobility in soil and surfactant-facilitated transport of organic compounds in soil/aqueous systems.