Multilayer Sorption Model for the Interactions Between Crude Oil and Clay in Patagonian Soils

Abstract

Since characteristic Patagonian soils have low amounts of organic matter (usually less than 1%) and high clay contents, the relative contribution of minerals to sorption of hydrophobic organic solutes may become significant. The purpose of the present study was to examine the interactions between oil and soil for an extended range of concentrations (1 to 400 mg L⁻¹). The prediction of isotherms by a multilayer sorption model was examined by studying the behavior of pure compounds and mixtures of known chemical composition. It was found that the extent of sorption is strongly dependent on the nature of the different interactions between sorbent and sorbates. The difference between the predicted and experimental oil isotherms was calculated to be only 13%, which indicates the reliability of the model. Not a simple dependence with the interaction forces was found to be responsible for the applicability of the model. Other factors such as 3‐D arrangements and molecular sizes should be considered. The estimations of the surface area of the soil with pyridine and phenanthrene are consistent with the sorption behavior of the polar and nonpolar sorbates in vapor phase. It was found that that crude oil is more sorbed than the sum of its fractions (aliphatic, aromatic, and polar), and this could be likely due to the asphaltenes present in the crude oil that have a stronger sorption behavior. The results observed for the different oil fractions, compared with those of the pure compounds studied in this article, are consistent with competitive interactions of the different chemical species for accessing to active sites. The determined parameters could be useful for the design of remediation techniques.

Acknowledgments

Financial support from the University of La Patagonia San Juan Bosco and from the National Research Council of Argentina (CONICET) are gratefully acknowledged.