The Study On The Stabilization Of Heavy Metals Of Cd & Pb In The Soil Amended With Coal Fly Ash And Its Mechanism

As China's soil is contaminated by heavy metals and food security as well as green agricultural products demand strict standards of soil quality,the paper aims to observe the change of heavy metals'--Cd and Pb--absorption morphology and biological effectiveness before and after adding fly ash by simulating Cd and Pb's pollution.Besides,it will analyze its theoretical foundation of fly ash's passivation effect for soil heavy metal Pb and provide improvement measures for soil pollution and agricultural products safety.(1)As a type of powder particle,fly ash is porous,scaly and rich in ash elements,which make it possible for improving soli quality and providing nutrients.The physicochemical properties of soil and nutrient status have changed after adding fly ash.So when adding fly ash,it is necessary to know about its physicochemical properties and to determine its quantity and adding methods in order to avoid bad effects on plants.The p H and conductivity of soil both strengthened after adding fly ash into three kinds of soil.In the experiment,the strength of soil p H and conductivity is within the scope of plant growth after testing.As a result,it wouldn't lead to alkaline and salt damage for plant growth.(2)The fly ash,mainly used in the stabilization of soil heavy metals,could stabilize Cd and Pb in the soil,which is more effective than the inorganic passivator and organic fertilizer.Putting fly ash into the soil could lower the Cd and Pb content in the wheat.If the amount of the fly ash is controlled as 8%,the effect will be optimal.According to the previous researches on the proportion of Cd and Pb in roots and leaves of the wheat,it is reasonable to infer that four kinds of soil could reduce the content of wheat heavy metals that accords with the national safety standards.Those are the treatments for 8% coal fly ash on the cinnamon soil in low Cd pollution,for 4% coal fly ash on the cinnamon soil and black soil in low Pb pollution,for 8% coal fly ash on the three kinds of soil,and for 8% coal fly ash on the black ash in high Pb pollution,And has no effect on wheat biomass.(3)Heavy metals morphological distribution in the soil is affected by types of soil,kinds of heavy metals and its content.Among them,Pb in the soil mainly takes bound form of the carbonate and the second form is Fe-Mn oxides.Meanwhile,Cd mainly exists as organic combination state in the low-pollution oil and another form is the exchange state.As the contaminative degree of heavy metals in the soil is increasing,the proportion of Cd exchange state grows evidently as well as the pollution damage.However,comparing to Cd,Ph,mainly taking the form of carbonate bound and having low proportion of exchange state,has low risks in pollution.(4)The stabilization of fly ash is that the occurrence state of soil heavy metals is transformed.If fly ash is added,the proportion of soil heavy metal Cd's available contents and carbonate bound form will be decreased and it will be transformed into its Fe-Mn oxide bound form,organic-bound form and residual bound form.If the fly ash is added,the proportion of soil heavy metal Pb's available contents,carbonate bound form and Fe-Mn oxide bound form will be dropped,and it will be changed into its organic bound form and residual bound form.It is that heavy metals' main ingredients are stabilized by the Mullite of fly ash.If the amount of fly ash is increased,the stabilization of soil heavy metals will be enhanced while its amount is added;the stabilization of soil heavy metals will be reduced.It is obvious that the effect of stabilization of coal fly ash is the adsorption.Meanwhile,the effect of stabilization and the amount of coal fly ash are related with the density of the pollution of heavy metals.