| The shortage of water resources has become a “bottleneck” restricting the development of the society and economy.With the rapid development of urbanization and industrialization,humans have continuously discharged a large amount of waste into the surface water environment in various ways.It has caused a huge load on surface water resources and caused serious environmental pollution problems,which has caused widespread concern in society.A large number of scholars have conducted many studies on this,but most of the studies are carried out on the surface water during the non-icebound period,and there are relatively few studies on the water bodies during the icebound period.And most of the research on the water bodies during the icebound period has focused on the migration law of organic pollutants and nutrient elements in the natural icing process.Studies on the migration law and mechanism of metal elements during the icing process are rarely reported.However,metal substances are difficult to be decomposed by microorganisms,and it is easy to accumulate in the organism to be transformed into more toxic metal-organic compounds by biological metabolism.To this end,we used iron(Fe),manganese(Mn),calcium(Ca)and magnesium(Mg)as the target substances.Through the laboratory simulation experiment,the migration and release rules of the target substances in the process of water icing and melting were investigated.And the influence of different influencing factors(ice thickness,freezing temperature,initial concentration and initial pH)on the migration and release of Fe,Mn,Ca and Mg during icing and thawing was studied,and the following conclusions were drawn:(1)In each group of simulated natural icing single factor influence experiments,the Fe,Mn,Ca,and Mg ion concentrations all exhibited the phenomenon of ice body < pre-freezing water body < under-ice water body.That is,Fe,Mn,Ca,Mg migrated from the ice body to the water body in the process of water icing.Through the comparative study,it is found that the migration ability of the metals to the under-ice water is: Mn > Fe,Ca > Mg.(2)The distribution coefficient K(the ratio of the average concentration of target substance in the ice to that of iron in the under-ice water)decreases with the increase of icing thickness(4 cm?8 cm?12 cm?16 cm?20 cm),freezing temperature(-5??-10??-15??-20??-25?),initial concentration(five concentration gradients)and initial pH(5.5?6.5?7.5?8.5?9.5).That is,the greater the ice thickness,the higher the freezing temperature,the higher the initial concentration and the higher the initial pH,the more efficient the migration of Fe,Mn,Ca and Mg to the under-ice water;(3)The experiment of melting ice in equal volume at room temperature shows that the release rule of Fe,Mn,Ca and Mg from the ice body is basically the same when the ice body melts.That is,a large amount of metal substance is quickly released in the early stage of ice melting,and a small amount is evenly released in the middle and late stages;In addition,freezing temperature,freezing thickness,initial concentration and pH have little influence on the release rules of Fe,Mn,Ca and Mg in the process of ice body melting.According to the data comparison,it was found that the material release ability of the ice body in the early stage of melting(0%-25%)was Fe > Mn,and the material release ability of the middle and late stage of melting(50%-100%)was Mn > Fe.There is no significant difference in Ca and Mg release capacity in the early stage of ice melting(0%-25%),and the Mg release rate in the middle and late stages of melting(50%-100%)was slightly greater than Ca.Since Fe and Mn have similar chemical properties in natural water bodies,and because the redox potential of Fe is lower than that of Mn,it is easier to be oxidized.Therefore,higher Fe concentration in under-ice water body during the melting period is not conducive to the removal of Mn,and higher requirements are put forward for the water treatment process. |
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