The Influence Of Different Freezing Conditions On Redistribution Of Benzene In Ice-water Phases

In our country,the permafrost area is large,widely distributed and exists for a long time.There are serious petroleum pollutions in many regions,and the laws of the migration and redistribution of water-soluble petroleum pollutants in the process of freeze-thaw are not yet clear.In this dissertation,benzene,a typical petroleum pollutant,is selected as the study object.The study inspects the distribution law of benzene solution whose initial concentrations are 1.096mg/L,10.97mg/L and 43.83mg/L with constant temperature-7°C,-10°C,and-15°C.The distribution of benzene in the ice-water phase during the static icing process is discussed.The effects of freezing conditions such as freezing temperature,initial solution concentration and freezing direction on the distribution of benzene are also inspected.Get the following conclusions:(1)During the process of solution freezing,the solute benzene is released by the ice phase and undergoes “freezing separation”,and it is redistributed in the ice-water phases.As a whole,the solute tends to pool in the liquid phase as the solution freezes.The distribution of benzene in the final ice phase is not uniform,with the lowest concentration in the ice phase formed earlier,followed by the formation of evenly distributed solute fractions in next phase,and more than half of the solute concentration in the final formed 20% volume of ice phase.As the freezing progresses,the "rate" of benzene entering the ice phase differs in different freezing stages,and it follows the law of "decrease first,then rise,remain stable within a certain interval,and rise again when the freezing approaches the end".(2)Differences in temperature conditions effect the migration behavior of ice-water two phases of benzene.And it is mainly reflected in the interval for freezing rate of 0.3<N<0.95.This range includes the gradual entry of benzene into the ice phase,the re-entry of ice phase to the unfrozen solution,and the solute enters the ice phase at a stable “rate” in the following step.The lower the temperature,the higher the concentration of ice phase formed during the early freezing phase,and the greater the discharge rate of benzene from the ice phase,the higher the uniform concentration of ice will come out.(3)Differences in the initial concentration of the solution effect the migration behavior of ice-water two phases of benzene.The influence is mainly reflected in the interval for freezing rate of 0.45<N<1.When the freezing rate is between 0.5 and 0.88,the experimental group with initial concentration of 1.096 mg/L does not reflect the phase in which benzene is re-entered into the unfrozen solution from the ice phase;comparing the other two groups,the higher the initial concentration is,the lower the benzene removal rate is,and the concentration of benzene in the ice phase after the formation of a uniform concentration is higher.After the freezing rate is higher than 0.88,the difference in solute distribution under each condition becomes more significant.The higher the initial concentration of the solution,the lower the concentration ratio of the unfrozen solution,the greater the proportion of benzene entering the ice phase and the poorer the solute separation effect.(4)Under the conditions of three-dimensional freezing and unidirectional freezing,the redistribution patterns of benzene in the ice-water two phases are similar.The latter has a slow freezing rate,and the ice phase concentration is slightly lower than the former.