Study On Heavy Metal Migration And Phytoextraction After Sedum Plumbizincicola Liquor Returning To Soils

Sedum plumbizincicola,a hyperaccumulator,has been potentially used in the remediation of cadmium?Cd?and zinc?Zn?polluted soil.As a result of containing a lot of heavy metals in the biomass after phytoremediation,it is necessary to dispose the biomass.At present,the most economic and feasible method to dispose S.plumbizincicola biomass is thermal disposal?incineration?after squeezing and dehydration.However,this process would produce plenty of liquor containing a part of heavy metals and organic materials,which is necessary to be treated.Wastewater land treatment is a comprehensive wastewater purification technology,which uses the interaction of soil,microorganisms and plants to degrade organic matter and remove heavy metals.Therefore,this paper refers to the method of wastewater land treatment,pot experiment and soil column experiment were conducted to return the liquor of S.plumbizincicola to soils and grow S.plumbizincicola,in order to investigate the changes of soil heavy metal speciation,plant reabsorption and the migration risk of heavy metals after mixing liquor with soils or adding liqour to soils.The main results are shown as followed:?1?In the pot experiment,planting S.plumbizincicola after mixing soils with the liquor of S.plumbizincicola is to study the dynamic changes of soil properties,the availability of Cd,Zn and the reuptake efficiency of Cd,Zn with S.plumbizincicola under different types of soils and different dosages of liquor.The results showed that the p H increased in acid soil but decreased in neutral soil,and the DOC of both soils increased significantly on 7th day and 30th day after the addition of liquor,while soil p H and DOC were closed to the control in the middle and late growth stages.Ca Cl₂ extractable Cd and Zn in liquor treated acid soil increased gradually with growth time,and reached maximum on 105 d,while those in neutral soil showed a gradual decline.The liquor treatment inhibited the growth of S.plumbizincicola,but increased the concentrations of Cd and Zn in the shoots.On the 100m L/kg liquor treatment of acid soil,Cd and Zn accumulation in S.plumbizincicola shoot was higher than the input by addition of liquor,and the soil Cd and Zn concentrations after remediation were lower than soil initial values.Consequently,suitable dosage of liquor returning to the acid soil and planting S.plumbizincicola again can remove Cd and Zn input by liquor and achieve the dual purpose of liquor treatment and soil remediation.?2?The liquor of S.plumbizincicola is added on the soil surface in the soil column experiment.The aim of the experiment is to study the effect of planting S.plumbizincicola and soil properties on the dynamic changes of soil solution Cd and Zn concentrations,soil Cd and Zn availability,and reuptake efficiency of S.plumbizincicola on Cd and Zn.The results showed that the distributions of Cd and Zn concentrations of the two soils were generally consistent at harvest time,the concentrations of heavy metals Cd and Zn on the P treatment?planting S.plumbizincicola but no liquor?were the lowest in the soil column.The concentrations of Cd and Zn in the soil column at the L treatment?adding S.plumbizincicola liquor but no plant?were the highest.The heavy metals especially accumulated at 0-10 cm,which means the heavy metals added with S.plumbizincicola liquor migrated less in the soil column,and was easily absorbed by soils,and changed from the water-soluble species to other species.The soil concentrations of Cd and Zn on the PL treatment?planting S.plumbizincicola and adding S.plumbizincicola liquor?decreased significantly at 0-10 cm because of the widespread distribution of the root of S.plumbizincicola.It means adding S.plumbizincicola liquor after planting S.plumbizincicola played the role of dealing with S.plumbizincicola liquor.In the two soils,the treatment of planting S.plumbizincicola on acid loamy soil removed heavy metals more than that on sandy soil.Adding liquor to soils would increase the concentration of heavy metals in the soil solution,while adding liquor to soils after planting S.plumbizincicola would reduce the concentration of heavy metals in the soil solution.Totally speaking,planting S.plumbizincicola after adding S.plumbizincicola liquor to soils played the role of dealing with S.plumbizincicola liquor,and could improve the engineering process of hyperaccumulation plant S.plumbizincicola.