Interfacial Interaction of Clay and Saturates in Petroleum-Contaminated Soil: Effect of Clay Surface Heterogeneity.

Abstract

Petroleum-contaminated soil (PCS) exhibits a variety of oil-soil interfacial properties. Surface heterogeneity of soil particles is one of the most critical influencing aspects. The interaction energies of the heterogeneous surfaces of montmorillonite (Mnt) and kaolinite (Kln) for saturates adsorption were determined by molecular simulation to be -1698.88 ± 0.67 (001 surface of Mnt), -73.81 ± 0.51 (010 edge of Mnt), -3086.33 ± 0.46 (001 surface of Kln), and -850.17 ± 0.74 (010 edge of Kln) kJ/mol, respectively. The adsorption of both clays with saturates relied on van der Waals forces, and the edges of Mnt were hardly adsorbed with saturates. According to adhesive force measurements, the oil-clay interaction forces of Mnt and Kln were 111.18 ± 0.01 and 122.65 ± 0.03 μN, respectively. In agreement with the simulations, Kln adsorbed saturates more strongly. Dynamic interfacial rheology and liquid viscoelasticity also revealed differences in adsorption behaviors between Mnt-saturates and Kln-saturates. It demonstrated that in the case of relatively low clay concentrations, the impact of particle surface heterogeneity on the adsorption process was stronger than that of structure even though Mnt had multilayer structures. Moreover, in thermodynamic adsorption experiments, it was evident that Kln adsorbed more oil than Mnt at the adsorption equilibrium states even though both were multilayer adsorptions and the adsorption amounts declined with increasing temperature. Simultaneously, the characteristics of the thermal adsorption of clay and saturates with different proportions were consistent with clay dispersion in saturates, and Kln released more heat being combined with oil. Overall, the heterogeneity of clay particles strongly affects the oil-clay interfacial chemical behaviors, causing more difficulty in treating PCS containing Kln than those containing Mnt. These results provide a theoretical basis for PCS treatment technology.