Adsorption of anionic and nonionic surfactant mixtures from synthetic detergents on soils

Abstract

Adsorption of anionic surfactant (sodium dodecylbenzenesulfonate, SDBS) and nonionic surfactant (an alcohol ethoxylates with 12 carbons and 9 oxyethyl groups, A 12E 9) mixtures, widely used as the major constituents of synthetic detergents in China and become the most common pollutants in the environment, on soils was conducted to investigate the behavior of mixed surfactants in soils. The effects of addition order and mixing ratios of two surfactants, associated with pH and ion strength in solutions, on adsorptions were considered. The results show that saturated adsorption amount of SDBS and A 12E 9 on soils decreased respectively when A 12E 9 was added into soils firstly compared with that secondly, possibly resulting from the screening of A 12E 9 to part adsorption sites on soils and the hydrocarbon chain–chain interactions between SDBS and A 12E 9. The adsorption of SDBS and A 12E 9 on soils was enhanced each other at pre-plateau region of isotherms. At plateau region of isotherms, the adsorption of SDBS on soils decreased with the increase of molar fraction of A 12E 9 in mixed surfactant solutions, while that of A 12E 9 increased except the molar ratio of SDBS to A 12E 9 0.0:1.0. With the increase of pH in mixed surfactant solutions, adsorption amount of SDBS and A 12E 9 on soils decreased, respectively. The reduction of ion strength in soils resulted in the decrease of adsorption amount of SDBS and A 12E 9 on soils, respectively.