Study On Fly Ash Passivation Remediation Technology Of Cadmium-Contaminated Soil In Ningdong Energy And Chemical Base

Aiming at the heavy metal pollution of soil in some parts of Ningdong Energy and Chemical Base,as well as soil desertification and vegetation degradation caused by the local natural environment of drought and little rain,Based on the findings of the heavy metal pollution investigation and evaluation,several amendments,including fine particles fly ash and fly ash compound organic fertilizer,were added to the Cd-contaminated sandy soil in accordance with the principle of "waste disposal with waste" to address the issues of vegetation degradation and soil desertification in Ningdong Energy and Chemical Base.Taking perennial ryegrass as the test plant,the physical and chemical properties of soil,the content and form of Cd and the enrichment of Cd in different parts of the plant were determined and analyzed.The ideal application pattern was chosen on the basis of the low-cost,high-effect approach,and in situ soil restoration was proven.In order to provide a theoretical foundation for ecological remediation in regions of heavy metal pollution at Ningdong Energy Chemical Base,this study suggests a remediation technique that may both reduce soil heavy metal pollution and enhance soil qualities.The study’s findings indicate that:(1)Although the average concentrations of Pb,Cd,Cr,and As in the surface soil of the Ningdong Energy Chemical Base study area did not exceed the risk screening value(pH>7.5)in the "Risk Control Standard for Soil Pollution on Agricultural Land(Trial)"(GB 15618-2018),the average concentrations of Cd,Cr,were higher than the background value of the soil environment in the Ningxia region.The examination of the integrated contamination level in Nemero revealed that the research area overall was at a mild contamination level,despite the combined potential ecological risk result for soil ecological risk being low.The fact that the single element potential ecological hazard index of Cd surpasses 40,indicating a moderate ecological hazard,and that the effective state of Cd accounts for a significant percentage,necessitating targeted treatment,is particularly concerning.(2)A total of 13 treatments were set up in the pot experiment,which were CK(without adding the modifier),F1,F2,F4(only adding 100%fly ash,the mass ratio of the modifier/soil was 1%,2%,4%,respectively),FP1,FP2,FP4(adding 80%fly ash,20%hydroxyapatite compound modifier,the mass ratio of the modifier/soil,Were 1%,2%,4%,respectively),FY1,FY2,FY4(adding 80%fly ash and 20%organic fertilizer compound improvers,and the mass ratio of improvers/soil was 1%,2%,4%,respectively),FS1,FS2,FS4(adding 80%fly ash and 20%humic acid compound improvers,and the mass ratio of improvers/soil,1%,2%and 4%,respectively).The pot test demonstrated that amendments are added to contaminated sandy aeolian soil,to varying degrees,enhance the soil’s saturated water content and field water holding capacity.As comparison to the CK treatment,the FS4 treatment enhanced the field’s water retention capacity by 26.40%,while the FY2 treatment raised the saturated water content by 20.85%.There was no significant difference between the soil alkali-hydrolyzed nitrogen content of fine particle fly ash and CK;however,the Three compound amendments have a positive impact.The addition of amendments also resulted in an increase in the quantity of organic matter,fast-acting potassium,and effective phosphorus in the soil.The addition of amendments decreased the Cd content of the ryegrass,while the dry weight of the ryegrass rose as a result of the enhanced soil characteristics.Eventually,all treatments enhanced the ryegrass’ Cd enrichment,with the exception of F1,which had a lower enrichment than CK.After the remediation of the modifier and ryegrass,the overall soil Cd level was decreased;however,the three FP treatment groups showed the largest reduction in soil Cd content and the lowest percentage of effective state Cd.The ecological restoration benefits were sorted from greatest to lowest:FY4>FY2>FS4>FP4>FP2>FS2>FP1>FS1>FY1>F4>F2>F1>CK,among them,FY4 treatment,i.e.adding fly ash organic fertilizer combined with 4%amendments,had the best ecological restoration effect.(3)Five treatments were set up in the field experiment,which were CK(no amendment added)、F(100%fly ash added,modifier/soil mass ratio 2%)、FP(80%fly ash added,20%hydroxyapatite compound modifier added,modifier/soil mass ratio 2%)、FY(Add 80%fly ash,20%organic fertilizer compound modifier,mass ratio of modifier/soil 2%)、FS(add 80%fly ash,20%humic acid compound modifier,mass ratio of modifier/soil 2%).In-situ ecological restoration of Ningdong Base was tested in the field to determine the efficacy of fly ash and its compound improver.The findings demonstrated that the amendment’s addition greatly raised the soil’s saturation water content and field water retention capacity.The relevant indices to soil agglomerates were measured in order to better explore the mechanism of soil property change.The addition of the amendment enhanced the fraction of big agglomerates with particle size more than 0.25 mm in soil mechanical and water stability compared to CK,as well as the MWD and PAD of agglomerates.The inclusion of the amendment decreased the ryegrass’s above-ground Cd concentration.As compared to CK,the FS treatment demonstrated a 31.58%reduction in above-ground Cd concentration.However,as a result of the improvement in the aboveground dry weight of plants following the application of the improver,there was ultimately an increase in aboveground Cd enrichment as compared to CK,with the FY treatment showing the greatest increase in Cd enrichment at 117.06%.Principal component analysis was used to comprehensively evaluate the ecological restoration effect.It was found that adding three kinds of fly ash compound amendments significantly improved the ecological restoration effect,among them,FS treatment,that is,application of fly ash humic acid compound modifier,has the best ecological restoration effect,and the ecological restoration effect of FP and FY treatment is similar to FS treatment.In conclusion,fly ash and fly ash compound amendments can significantly promote the growth of ryegrass,and have good ecological restoration effect on Cd polluted soil in Ningdong Energy and Chemical Base.It is clear from the pot test and field test findings that the combination of fly ash humic acid amendment FS and fly ash organic fertilizer amendment FY generates the optimum ecological remediation effect.