Studies On Migration, Transformation And Leaching Technique Of Oil Pollutants In Unsaturated Aquifer Media

With the large-scale oil exploration, mining, development of petroleum chemical industry and widely use of its products, oil pollution to environment cannot be ignored. After entering into environment, oil contaminants undergo a series of acts, such as volatilization, leaching, adsorption and biological degradation, which determine the ultimate fate of oil contaminants in environment. Therefore, it has important scientific significance and application value for assessment, control and remediation of oil-contaminated fields to research the migration, transformation and the final fate of oil contaminants deeply.In this paper, loam and sand were taken as representative aquifer media, and diesel oil and gasoline were chosen as the pollutants. The oil volatilization, leaching and residual behaviors were studied. Different solution conditions caused the change of oil-water interfacial tension, which affected the chemical leaching efficiency at the same time. On the basis of these investigation and experimental tests, some conclusions can be summarized as follows:(1) The volatilization rates of oil on aquifer media are relevant to oil content, wind speed, vessel diameter, volatilization thickness and particle size. Elovich equation and parabolic model can express the volatilization process of gasoline and diesel oil in aquifer media respectively. The wind can accelerate the volatilization rate of oils. The wind can speed up the volatilization of nC9～nC15of diesel oil significantly, but has little effect on the volatilization of nC16. Linear equations can describe the increment of diesel oil volatilization coefficients with the increasing of volatilization thickness and vessel diameter. But vessel diameter has no significant effect on gasoline volatilization, and the increasing volatilization thickness makes gasoline volatilization rate slow down. The finer is the aquifer media particle size, the faster diesel oil volatizes. But aquifer media block the gasoline volatilization, and gasoline in fine grained aquifer media volatilizes slower. The water in coarse sand can speed up the diesel oil volatilization, while which in fine sand and loam reduce the diesel oil volatilization rate. In the oil volatilization process, the low-carbon components disappear gradually, the relative contents of high-carbon components increase.(2) The particle size and bulk density of aquifer media affect oil volatilization and washing process. When the oil volatilization in aquifer media reaches equilibrium, the oil volatilization losses in coarse sand, fine sand and loam increase in turn. In the same aquifer media, oils in coarse sand and loam under lower bulk density volatilize faster and slower respectively, and the bulk density has little effect on the oil volatilization in fine sand. The oil releases fastest in coarse sand with water leaching. The minimum oil content of loam is20times than that of coarse sand under the water washing repeatedly.(3) The oil content and oil components in vadose zone soil distribute differently because of the different aquifer media characteristic and soil depth. The oil content of top and bottom layers is higher for coarse sand column, and the oil content of central layer is relatively lower. For loam column, the oil content of top layer is lowest, and the oil content of the layer under top layer is highest. The relative contents of nC2o, nC21, nC18and nC17are relatively higher in different depth of coarse sand column, but the relative contents of nC16and nC15are highest for loam column.(4) The particle size, organic matter content and specific surface area of aquifer media affect the maximum residual oil saturation, stable residual oil saturation and minimum oil content. The maximum residual oil saturation, stable residual oil saturation and minimum oil content of homogeneous aquifer media decrease with the increase of mean grain size. Mean grain size of heterogeneous aquifer media is the main factor affectting maximum residual oil saturation, while the stable residual oil saturation is related to organic matter content and specific surface area. Bulk density of homogeneous aquifer media affects the maximum residual oil saturation, but its effect on stable residual oil saturation is little.(5) The residual oil saturation is related to the initial water saturation of aquifer media. The increasing of initial water saturation can result in residual oil saturation in aquifer media reducing, but which has little effect on the residual oil saturation of homogeneous aquifer media. When the initial water saturation is greater than the critical water saturation, the total saturation of oil and water is a constant value, but when the initial water saturation is less than the critical water saturation, the total saturation increases with increasing of initial water saturation.(5) The change of solution properties, the adding of inorganic salt and organic solvent affect the oil-water interfical tension. The intruduction of inorganic salt, organic solvent and anionic surfactant can improve the oil removal efficiency of sole surfactant. The chemical leaching experiments show that the oil removal rates of mixed solvent are higher than the single Triton X-100. The improvement effects of CaCl2, SDS and organic increase in turn. The composite effect of the three factors on the oil removal rate of Triton X-100is Acetone>SDS> CaCl2in orthogonal test. While the effect of the four factors on the oil removal rate of water is CaCl2＞temperature＞flow velocity＞pH.