| The remediation of heavy metal contaminated soil has always been the focus of attention and research in the field of global environment.The in-situ passivation remediation technology has the advantages of rapidity,convenience and not changing the original planting mode,the key of which is to select different efficient passivation materials according to different heavy metal pollution.Titanium gypsum is an industrial waste product,which mainly contains CaSO4 and Fe2O3.At present,it is rare in domestic to use titanium gypsum to repair soil polluted by heavy metal in farmland,as the main target is cadmium polluted soil.In this article,the original soil which is contaminated with arsenic and lead is adopted as the research object,with the added Titanium gypsum(TG),dihydrate gypsum(G),dihydrate gypsum+ferric oxide(STG9:1,STG7:3),dihydrate gypsum+reduced iron powder(CTG9:1,CTG7:3)of different amount being taken as restoration materials,and through indoor soil flooding cultivation experiment and flood-drought rotation plants experiment,the passivation effect of the gypsum materials on arsenic and lead in farmland soil under different farming patterns are studied.The main research results are as follows:(1)In the soil flood culture test,gypsum materials both have certain passivation effects on arsenic and lead in the soil.On the 30th day,when it is in equilibrium,the content of soil available As was decreased by 3.57-16.08%compared with the blank control,and the soil available Pb content was decreased by 10.20～35.23%compared with the blank control.And,the passivation effects on As and Pb in contaminated soil are:titanium gypsum(TG)>single dihydrate gypsum(G);dihydrate gypsum-ferric oxide composite material(STG)>dihydrate gypsum-reduced iron powder composite material(CTG).(2)In the simulated dryland pot experiment,gypsum materials had a great influence on the pH of soil,compared with the blank control,it was significantly reduced by 0.11 to 0.49 units,and decreased with the increase of the amount of addition.The effect of gypsum materials on soil available As content is not significant,but it can effectively reduce the absorption of As by pakchoi.The As content of aboveground and belowground pakchoi was 13.73～56.93%and 5.77～32.09%lower than that of blank control,respectively.Gypsum materials can effectively reduce the soil available Pb content,which is lower than that of the blank control 9.54～16.35%.They also can make the Pb content in the aboveground and belowground parts of the pakchoi lower than those in the blank control by 18.25～43.89%and 6.56～43.81%,respectively.Among them,0.3STG(7:3)treatment had the best passivation effect.(3)In the simulated paddy field pot experiment,gypsum materials can significantly reduce soil pH,which is 0.27～0.69 units lower than the blank control.Compared with the blank control,gypsum materials decreased the available As content in the soil by 6.85～32.23%,and the As content in rice roots,stems,leaves,and brown rice decreased by 80.16～89.26%,30.90～62.64%,29.44～66.59%,14.17～40.23%;the available Pb content in the soil decreased significantly by 6.64～18.32%,and the Pb content in rice roots,stems,leaves,and brown rice decreased by 75.44～84.95%,9.37～45.63%,21.54～64.27%,7.73%～31.99%.Among them,the most significant passivation effect was 0.3STG(7:3)treatment.(4)In the process of simulating flood and drought rotation,soil pH increases gradually with all treatments,and the available As and Pb content in the soil will also increase.The addition of gypsum materials can inhibit the increase of soil pH and the further release of available As and Pb in the soil to a certain extent.The repair effect of gypsum materials on As and Pb under simulated paddy field conditions is stronger than under simulated dry field conditions.And the remediation effect of 0.3%added passivation material on soil As and Pb pollution is better than 0.15%. |
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