Groundwater remediation by anionic surfactant micelles - An innovative double layer model applied to Na+ and Mg2+ association with dodecylsulfate micelles

The association reactions involving counterions, Na+ and Mg2+, and micelles composed of the anionic surfactant, dodecylsulfate (DS-), were investigate d in ultrafiltration experiments. To access the data, an innovative model w as developed that considered specific counterion binding within a Stern lay er, with binding constant dependent upon the electrical potential as derive d by the Poisson-Boltzmann equation and with calculation of the cmc as a fu nction of counterion binding (or association). The experimental and model r esults both show that magnitude of counterion binding is greater for divale nt species, Mg2+, than that for the monovalent species, Na2+. However, high concentration of Na+ compete for surface area diminishing the ability of t he DS- to bind either divalent species. At experimental conditions from 0 t o 100 mM NaCl addition, the binding ratio (BR) varied only from 0.58 to 0.6 3. The optimum binding constants, K-Mg and K-Na were determined to be 0.4 a nd 1.0 L mol(-1), respectively, for the model. The experimental data and mo del calculated results were generally in good agreement. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.