Modeling the two stages of surfactant-aided soil washing

This paper provides new insights into modelling the distribution of hydroph obic compounds between soil and water phases in the presence of nonionic su rfactant micelles. Experimental measurements were made of various systems c omprising a non-ionic surfactant, five soils of different fractional organi c carbon contents, and a hydrophobic (disperse) dye. Soil-washing performan ce was quantified using reciprocal surfactant-soil solubilization coefficie nts (1/K-d). Two stages of partitioning were identified. In stage 1, the dy e concentration increased slightly with increasing surfactant dose until su rfactant monomers saturated the bulk solution at the critical micelle conce ntration (cmc). The washing performance was 1:1 proportional to the surfact ant monomer concentration, Most of the surfactant in this stage is sorbed. In stage 2, above the cmc, soil-washing performance increased linearly with increasing available surfactant micelles in the bulk solution. Reciprocal surfactant-soil solubilization coefficients (1/Kd), octanol-water partition coefficients (K-ow), fractional organic carbon content of the soil (f(oc)) and surfactant concentration were correlated for each stage in the soil-wa shing process using two simple equations. (C) 2001 Elsevier Science Ltd. Al l rights reserved.