| Seasonal frozen soil are mainly distributed in the northern areas in China,and most of these areas developed petrochemical industry,in the process of oil production,transportation,refining would inevitably cause oil pollution,benzene content is an important part of oil-the main ingredient in aromatic hydrocarbon,its high toxicity,not easily soluble in water,the characteristics of refractory,frozen-melt-frozen circulation is a typical process in seasonal frozen soil experience,it will affect the benzene content in the process of occurrence and adsorption-in soil,and to a certain extent determine pollutants migration process.This study is an indoor soil column experiment.The operation of freezing-thawing cycle-freezing-thawing cycle is carried out on the soil column in the freezing-thawing experimental group by means of human temperature control.The temperature change is realized by the low-temperature circulating pump,and the height of the liquid level in the pump is the height of the freezing-thawing interface of the soil column.The soil column of the non-freeze-thaw experimental group was always placed in the low-temperature refrigerator,and the location of the soil column sampling mouth was the same as that of the freeze-thaw experimental group,so the soil column was also divided by the freeze-thaw interface.According to the changes of benzene series contents in soil samples at the freeze-thaw interface,the upper part of the freeze-thaw interface and the lower part of the freeze-thaw interface,the longitudinal migration and transformation process and mechanism of benzene series in the soil column under freeze-thaw conditions were investigated.The results show that when the soil in the soil column is homogeneous and water-bearing soil,the gravity of benzene series has no effect on its migration in the soil column under non-freeze-thaw 5℃condition,and the strong volatility of benzene series itself is the main reason for its migration in the soil column.The migration of benzene series components in soil column at 5～-5 ℃,5～-10 ℃ and 5～-15 ℃showed that each benzene series component migrated to the freeze-thaw interface under freeze-thaw conditions.Freeze-thaw treatment also enhanced the soil adsorption capacity of benzene series,and the freeze-thaw condition at5～-10℃ enhanced the soil adsorption capacity of benzene series most significantly.Finally,the total content of benzene series in the soil below the freeze-thaw interface of the soil column was 5～-5℃: 62.05μg/g;5～-10℃: 104.36μg/g;5～-15℃: 85.59μg/g.Decreased by57.13%,23.11% and 35.47% respectively compared with the initial content.Comparing the longitudinal migration of benzene series in soil column under non-freezing-thawing condition and freezing-thawing condition,the hydrothermal migration under freezing-thawing condition and the strong volatility of benzene series themselves are the main mechanism of longitudinal migration in soil column.Based on the basic properties of porous media and fluid,according to the dynamics equation of fluid in porous media and thermodynamic equation under the condition of freezing and thawing is established in the benzene content in the soil column vertical migration,the mathematical model according to contain benzene content the initial content of the benzene content in the soil,after many iterations calculated 5～-5℃,5～-10℃,5～-15℃group upper freezing and thawing interface of benzene series pollution in soil of soil column 7days freeze-thaw interface benzene content in the soil after freezing and thawing cycle is8.47μg/g,76.90μg/g and 18.31μg/g.The toluene content was 3.23μg/g,2.14μg/g and 1.78μg/g.The error of each result is less than 2%.Through soil column simulation experiment,the longitudinal migration mechanism of benzene series under freezing-thawing conditions was explored,and the migration and transformation of benzene series in soil column under freezing-thawing conditions were numerically simulated,which provided a theoretical basis for predicting the migration and diffusion of volatile organic compounds pollution in permafrost regions and improving the efficiency of pollution remediation. |
