Screening Of Passivating Agent For Cadmium Contamination In Acid Soil And Its Remediation Effect On Chinese Cabbage

Current our country south of farmland soil polluted by cadmium pollution and mostly mild-to-moderate,for acidic cadmium pollution of farmland soil in south China passivation repair to provide theoretical basis and data support,this topic to exogenous cadmium pollution soil as the research material,adding sepiolite,bentonite,calcium magnesium phosphate fertilizer,and passivation of ground phosphate rock,choose passivation effect is good at repairing the several kinds of materials are combined,In order to determine the optimal application mode of passivating materials,combined materials with passivating rate of more than 40% were screened,and the remediation effect was tested through cabbage pot experiment and actual cadmium contaminated farmland soil remediation experiment.The main research results are as follows:(1)The single passivation material remediation test results show that the passivation effect of each passivation material is not significant in 0.3mg /kg Cd contaminated soil,so the use of passivation remediation materials is not recommended;In 1.0 mg/kg cadmium contaminated soil,sepiolite(2%)and calcium-magnesium phosphate(1%)had better effects.After 30 days of passivation,soil p H increased by 2.01 and 1.66 units,respectively,and the available cadmium decreased by 50%.Single application of sepiolite(1.5%)and calcium magnesium phosphate fertilizer(1%)in 1.5 mg/kg Cd contaminated soil had better effects.After passivation for 30 days,soil p H increased by 1.66 and 1.68 units,respectively,and effective Cd decreased by 40.00% and 56.67%,respectively.(2)The results of composite passivation material remediation experiment showed that,in1.0 mg/kg Cd-contaminated soil,the treatment of noziolite(2%),calcium-magnesium phosphate(1%),sepiolite + calcium-magnesium phosphate(2% : 1%),1.5 mg/kg Cd-contaminated soil,the treatment of sepiolite(1.5%),calcium-magnesium phosphate(1%),sepiolite + bentonite(1.5% : 3%),sepiolite + calcium magnesium phosphate fertilizer(1.5% :1%),bentonite + calcium magnesium phosphate fertilizer(3% : 1%),sepiolite + bentonite +calcium magnesium phosphate fertilizer(1.5% : 3% : 1%),the passivation effect is good and the passivation rate is more than 40%,and the effect of passivation material restoration is evaluated.(3)The pot experiment results showed that the application of sepiolite and calcium magnesium phosphate fertilizer(2% : 1%)in the soil with 1.0 mg/kg exogenous Cd increased the soil p H by 3.27 units,and the available Cd in the soil decreased by 49.44%,78.82% and90.95% respectively in the underground and aboveground parts of the plant.When adding 1.5mg/kg exogenous Cd in soil and applying sepiolite + calcium magnesium phosphate fertilizer(1.5% : 1%),soil p H increased by 3.30 units,soil available Cd decreased by 51.39%,plant underground Cd content decreased by 92.55%,plant aboveground Cd content decreased by95.33%.The combination of sepiolite and calcium-magnesium phosphate can passivate the soil heavy metals and improve the acidic environment of the southern soil.(4)In the undisturbed Cd contaminated soil(Cd content was 9.86 mg/kg),sepiolite + calcium magnesium phosphate fertilizer(1.5% :1%),soil p H increased by 0.28 unit,soil available Cd decreased by 37.24%,Cd in underground and aboveground parts of plants decreased by65.28% and 29.94%,respectively.Leaf area,plant height,root length,root hair number,fresh weight of underground part,fresh weight of aboveground part,dry weight of underground part and dry weight of aboveground part increased by-9.63%,6.07%,21.32%,28.88%,4.05%,3.74%,2.70% and 0.66% compared with the control.The combination of sepiolite and calcium magnesium phosphate fertilizer increased plant biomass.In conclusion,the combined application of sepiolite and calcium-magnesium phosphate fertilizer not only reduces the available cadmium content in soil and in plants,but also increases the biomass of plants and promotes plant growth.The passivation effect is stable,and the combined application in proportion can be used as the preferred remediation material for cadmium polluted farmland.