Partition of a mixture of chlorinated organic compounds in real contaminated soils between soil and aqueous phase using surfactants: Influence of pH and surfactant type

The equilibrium between surfactant adsorption and contaminants desorption was studied. Two soil samples from a polluted site with residues from lindane production, compounded of a complex mixture of 28 chlorinated organic compounds (COCs) and different concentration of COCs in soil (2.27 and 34.69 mmolCOCs⋅kg− 1 soil), were used. Soil was in contact with aqueous surfactant solutions (1–15 g⋅L− 1) of nonionic (E-Mulse® 3, and Tween® 80) and anionic (sodium dodecylsulfate) surfactants. Due to alkaline pH promoting the dehydrochlorination of COCs, neutral pH and strongly alkaline pH (pH > 12) were studied. It was found that the higher the COCs concentration adsorbed in soil, the higher the adsorption of the surfactants, finding an irreversible adsorption in the case of nonionic surfactants. The desorption of COCs increased with the surfactant concentration in the aqueous phase and was not selective towards any contaminant. Although at neutral pH, higher COC desorption was found with nonionic surfactants, at alkaline pH surfactant the anionic surfactant improved its COCs desorption capacity significantly. Finally, the adsorption of the surfactants was well adjusted to Langmuir, and the apparent partition coefficient predicted the partitioning of COCs between the soil and aqueous phases, which changes with the surfactant concentration in the aqueous solution