| In recent years,with the rapid development of my country’s urbanization and industrialization,industrial and agricultural activities(such as metal smelting,mining,farmland fertilization and industrial sewage irrigation,etc.)have led to the accumulation of toxic and harmful heavy metals in farmland soil in many areas of our country.Background values.Therefore,it is necessary to remediate farmland soil polluted by heavy metals to ensure that farmland soil can provide healthy crops.Therefore,it is necessary to remediate heavy metal contaminated soil in farmland to ensure that the farmland soil can provide healthy crops.By reducing the bioavailability of heavy metals in farmland soil,it is a better method to reduce the entry of heavy metals into humans and animals through crops and food chains.The use of phosphate in phosphorus materials to reduce the available content of heavy metals in soil is currently widely used.At present,the use of phosphorus materials to stabilize and remediate heavy metals in soil mainly focuses on single heavy metal pollution such as lead,cadmium,copper,and zinc.There are few studies on remediation and composite heavy metal remediation in different soil particle sizes,and little attention has been paid to the problem of phosphorus migration and loss after the application of phosphorus materials.In this study,soil culture and soil column leaching experiments were conducted to explore the passivation effect of different phosphorus materials and dosages on composite heavy metal polluted soil,and screened for better passivation effects on lead,cadmium,copper,and zinc composite polluted soil in farmland polluted soil.Phosphorus materials,and study the passivation effect of phosphorus materials on heavy metals in soils with different particle sizes and the characteristics of phosphorus materials migration and loss in the lower soil layer.The main findings are as follows:(1)Diammonium hydrogen phosphate(DAP),potassium dihydrogen phosphate(MPP),tricalcium phosphate(TCP)and calcium magnesium phosphate fertilizer(CMP)have good passivation effects on soil heavy metals Pb and Cd,mainly making that extracted state and reducible state of the main weak acid transform into the residue state;however,the stabilization effect of different phosphorus materials on Cu and Zn is poor,and even leads to the risk of activation.Each phosphorus treatment increased soil p H,and the magnitude of the increase was in the order of DAP > CMP > TCP > MPP.With the increase of p H,the contents of available Cd and Pb decreased,and there was a very significant negative correlation between the two.Therefore,the increase of p H is also one of the important mechanisms for the stabilization and remediation of Cd and Pb contaminated soils by phosphorus materials.(2)In the comparison of different particle sizes of soil,the content of available state and total amount of heavy metals Pb,Cd and Zn all showed: 100 mesh or more > 60 mesh > 20 mesh,and the content of soil heavy metal Cu available state and total amount showed: 60 mesh > 100 mesh and above > 20 mesh.The passivation effect of phosphorus materials on heavy metals Pb and Cd in soils with different particle sizes increased with the decrease of particle size,and the activation risk of heavy metals Cu and Zn in soils with different particle sizes decreased with the decrease in particle size.(3)The passivation effect of water-soluble phosphorus material(MPP)on Pb and Cd is better than that of citric acid-soluble phosphorus material(CMP),but water-soluble phosphorus material is more likely to cause phosphorus leaching loss.In order to achieve a good passivation effect on the Pb,Cd,Cu,Zn composite polluted soil as much as possible and reduce the secondary pollution of phosphorus caused by the application of phosphorus materials,it is recommended that the molar ratio of water-soluble phosphorus materials(MPP)to heavy metals be 1.And it is more appropriate to control the amount of phosphorus application below 2 g/kg,the molar ratio of citrate soluble phosphorus material(CMP)to heavy metals is 0.5 and the amount of phosphorus application to be controlled below 8 g/kg. |
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