Study On The Removal Of Heavy Metal Pollution In Aged Refuse Humus Soil By EDTA/Humic Acid And Citric Acid/Humic Acid

The humus soil of aged refuse usually refers to the undersized fraction from aged municipal solid waste.It often encounters the phenomenon of excessive heavy metals in its resource utilization,and it cannot reach the standard of greening soil.This study took the sieved humus from a landfill in Wuhan City as the research object.Aiming at the problem of excessive Cu,Zn,and Mn,this paper studied the extraction performance of single leaching of EDTA,citric acid（CA）,humic acid（HA）and mixed leaching of EDTA/HA,CA/HA,optimized washing parameters by response surface methodology,carried out a greening experiment and selected MnO₂@kaolin with PMS to treat the subsequent leaching solution.The main conclusions are as follows:（1）Single EDTA and CA leaching have 36.53%,33.75%and 38.24%,29.66%removal on Zn and Mn respectively,which were better than 25.46%,21.45%of HA.The removal of Cu by single HA leaching reached 40.23%,which was better than 29.63%and35.72%of EDTA and CA.Leaching has little effect on the p H of the humus soil.After leaching,the organic matter content and available nitrogen increased,but the ability of humus soils to retain fertilizer after leaching decreased.After leaching,the four components of the three heavy metals are all reduced.The removal rate of the exchangeable and reducible states of Cu,Zn,and Mn by HA is higher,reaching 73.13%and 39.11%,62.22%and 22.39%,55.33%and 49.41%respectively,which reduced the toxicity of heavy metals and the harm to the environment.Increasing the concentration of the washing solutions,prolonging the washing time,reducing the solid-liquid ratio,and maintaining acidic conditions were conducive to the removal of heavy metals.（2）The response surface method was used to optimize the parameter conditions.The results showed that for the EDTA/HA system,the concentration of the elution agent of0.15mmol·L^-1/1.5g·L^-1,the p H of 3.03,leaching time of 286.3 minutes leading to the highest removal of Cu,Zn and Mn for 48.68%,46.12%,and 30.63%respectively.For the CA/HA system,the concentration of the eluent of 0.15mmol·L^-1/1.5 g·L^-1,p H of 3.06,leaching time of 292.5 minutes leading to the highest removal of Cu,Zn,and Mn for42.36%,39.67%,and 28.49%respectively.Comparing the planting experiments of adding different proportions of leaching humus soil as a greening substrate,it was found that when humus soil proportion was 25%,the growth of the plants was better and the content of the heavy metals in the three plants could reach the greening requirements.The leaching experiment of the humus soil after leaching showed that the leaching rate was below 20%,indicating that leaching effectively reduces environmental risk.（3）This study selected MnO₂@kaolin/PMS system and Cu-EDTA as the target pollutant.When[Cu-EDTA]₀=50 mg/L,[MnO₂@kaolin]=0.2 g/L,[PMS]₀/[Cu-EDTA]₀=30,the initial p H=2.0,and the reaction time=50 min,the removal rate of Cu-EDTA reached 81.15%.As the concentration of MnO₂@kaolin and PMS increased,the removal rate of Cu-EDTA increased,but when the catalyst concentration was higher than 0.2 g/L or[PMS]₀/[Cu-EDTA]₀ was higher than 30,the removal rate had no more significant increase.The removal rate of Cu-EDTA decreased first and then increased with the increase of p H,and the removal effect was the worst when p H was close to 7.The MnO₂@kaolin/PMS system was applied to the washing solution of EDTA/HA leaching humus soil,and it was found that the metal complex had been mostly removed.