Critical micellar concentrations for three surfactants and their diesel-removal efficiencies in petroleum-contaminated soils

Abstract

In this work, the critical micellar concentration (CMC) for three anionic and nonionic surfactants was measured. The commercial products employed were Texapon 5 (sodium lauryl ether sulfate), Surfacpol 906 (ethoxylated nonylphenol), and Canarcel TW80 (ethoxylated sorbitan monooleate), and the CMC measured values were 0.941, 0.0934, and 0.05 mM, respectively. The diesel adsorption on sandy and clayey soils was characterized by means of the partition coefficients Kd, resulting in values of 0.5 and 1.4 mL/g for sandy and clayey soil, respectively. There are a few reports of Kd values for complex mixtures of organic compounds such as diesel. Retardation factors for every system were calculated, resulting in 2.6 and 2.9 for the sandy and the clayey soil, respectively. Interestingly, the retardation factors for both soils are quite similar, even when the diesel-soil partition coefficient for clayey soil is threefold the value for the sandy soil. Finally, diesel-removal efficiencies for the three surfactants from an aged contaminated sandy soil were evaluated at the sub-CMC and supra-CMC levels, at concentrations of 0.5, 5, 100 and 300 times the CMC for every surfactant. The results of the soil's washing as a removal percentage were 46.474.2, 41.983.3, and 52.588.2% for Texapon 5, Canarcel TW80, and Surfacpol 906, respectively. Experimental data were recalculated according to an equation where foc/Kd is a function of the total surfactant dose [D]. The experimental behavior for concentrations between 0.47 and 47 mM for Texapon, 0.025 and 2.5 mM for Canarcel, and 0.046 and 4.66 mM for Surfacpol was predicted by the mentioned equation. After these values, the foc/Kd values increased at a very accelerated rate, especially for the case of Surfacpol.