Effect of adsorption site potential on adsorption of sodium dodecylbenzenesulfonate in highly humic volcanic ash soil
2015
Ahmed, Farook | Ishiguro, Munehide
Sodium dodecylbenzenesulfonate (DBS) is a very useful and widely used anionic surfactant. This surfactant sometimes creates environmental problems when it is released into the water environment. However, the factors influencing the adsorption of DBS in soil have not been studied well. In this study, the influence of the potential at the adsorption site on the adsorption of DBS in a soil was first elucidated using a theoretical adsorption equation. The soil was a highly humic soil with a negative charge. The amount of DBS adsorbed was measured with a batch method for different electrolyte concentrations of sodium chloride (NaCl) at pH 4.5 and 6.5. The adsorption site potential of the soil was obtained with the modified Langmuir adsorption equation. The adsorption of DBS decreased as the electrolyte concentration decreased and as the pH increased because the repulsive electric potential between DBS and the soil increased. These results were confirmed by the obtained adsorption site potential and the measured electrophoretic mobility. The difference between the adsorption of DBS with a linear and with a branched carbon chain was also detected, and this difference was related to the free energy of micellization. Because DBS adsorption is strongly affected by electrolyte concentration and pH, these two factors must be carefully considered to predict the fate of DBS in soil and water environments.
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