Interfacial Properties And Interaction Mechanisms Of Soil Minerals-Crude Oil Components

The complex and diverse compositions and structures of petroleum-contaminated soil are the main reasons limiting efficient oil-soil separation.In this thesis,analytical characterization,molecular simulations,and experimental tests were combined to examine the interaction energy and force,wetting and spreading behavior,and adsorption properties of four crude oil components on the surface of four typical soil minerals.Meanwhile,the migration pattern of crude oil within the soil medium was studied,thereby providing a preliminary insight into the formation mechanism of petroleum site contamination and an important physical cognitive theoretical basis for the development of efficient oil-soil separation technology for petroleum-contaminated soil.The interfacial interaction energies and forces between montmorillonite（Mnt）,kaolinite（Kln）,illite（Kit）,quartz sand（Qs）and saturated hydrocarbon（S）,aromatic hydrocarbon（Ar）,resins（R）and asphaltenes（As）were investigated,respectively.The sources of interfacial forces were analyzed in conjunction with EDLVO theory.The results showed that the order of the interaction energies between different single component of crude oil and the same mineral was As>R>Ar>S.Meanwhile,the order of interaction energies between different kinds of minerals and the same component of crude oil was Mnt>Kln>Kit>Qs.The mineral-crude oil interaction energies were determined by van der Waals interaction.Mineral species determined the van der Waals interaction between crude oil and minerals,with clay minerals and crude oil having a greater van der Waals interaction than that of sand minerals.In the case of the same mineral species,the number of benzene rings,along with the type and number of polar groups（-S,-N,-O）in crude oil resulted in a greater van der Waals interaction.The mineral-crude oil interfacial adhesive forces were tested in 1m M Na Cl and 1 m M Mg Cl₂solution systems,respectively,and the same pattern as the interaction energies conclusions were obtained.According to the EDLVO theory,the mineral-crude oil interfacial forces in the 1 m M Na Cl solution system were mainly provided by the van der Waals force,the electrostatic double layer force hindered the adhesion between the single component of crude oil and minerals.Simultaneously,the hydrophobic force promoted the adhesion of mineral-crude oil below 5 nm.In the presence of Mg²⁺,the electrostatic double layer inhibiting effect was greatly reduced,whereas van der Waals and hydrophobic forces were not affected.The wetting and spreading behaviors and adsorption characteristics of single component of crude oil on soil mineral surfaces and the migration of crude oil in soil minerals were studied.Based on the results,the wetting activation free energy determined the spreading rate and degree of spreading of single component of crude oil on mineral surfaces.A small wetting activation free energy resulted in easy spreading.The order of the free energy of wetting activation required for the same component oil spreading on mineral surfaces was Mnt>Kln>Kit>Qs.When different crude oil components were spread on the same mineral surface,saturated hydrocarbon required large free energies for wetting and activation.However,asphaltene required low free energy of wetting activation when spreading on mineral surfaces.The single component of crude oil adsorbed on the surfaces of all four minerals were multilayer adsorptions,and its adsorption quantity decreased as temperature increased.The migration law of crude oil indicated that the depth of crude oil migration increased with the increasing saturated hydrocarbon.The difficulty of oil-soil separation is due to the high content of montmorillonite,which has a high adsorption capacity.As a consequence of the molecular dynamics simulation of the mineral-oil-water system,the equilibrium conformation of the single component of crude oil adsorption on the mineral surface was determined by the mineral-crude oil interaction energy.The simulation results were consistent with the experimental results.According to the concentration distribution curves of the the single component of crude oil molecules,asphaltene molecules were more tightly adsorbed on their surfaces because the interaction energies between asphaltene and montmorillonite,kaolinite and illite were large.The asphaltene molecules had a low interaction energy with the Qs surface,and the diffusion rate of asphaltene molecules in the mineral-oil-water system decreased with the increase of interaction energy.The treatment of petroleum-contaminated soil simulated samples by thermal desorption technology verified that petroleum-contaminated soil containing more Mnt and asphaltenes required high activation energy to desorb the single component of crude oil from the mineral surface,which was not conducive to mineral-oil separation treatment.Meanwhile,the activation energy of mineral-crude oil separation was calculated by the thermal desorption technology to treat petroleum-contaminated soil with different mineral species or oil component distribution ratios.Combined with the separation efficiency obtained by the treatment of the leaching method,the separation degree of oil and soil in petroleum-contaminated soil was preliminarily divided,which laid the foundation for the development of oil-soil separation technology standard of petroleum-contaminated soil.This thesis contains 88 figures,40 tables and 195 pieces of references.