Study On Stabilization Of Heavy Metals In Fly Ash By Landfill Leachate Coupling Chemicals

Due to the high concentration of heavy metals,soluble salts and dioxin compounds,fly ash is regarded as hazardous waste.In order to fully understand the potential toxicity of heavy metals in fly ash,this paper uses the incineration of fly ash by a renewable energy company in Anhui Province as an example.The research object,based on the analysis of the physicochemical characteristics of fly ash,used a variety of stabilization schemes to study the leaching toxicity of fly ash.The main conclusions are as follows:(1)The total amount of Fe,Pb,Zn,Cu,Ni,and Cd in the raw ash is 2066.6mg/kg±37.70,548.72mg/kg±14.59,510mg/kg±18.84,172.28±3.38,132.52±1.87,113.56±2.45,of which the leaching toxicity of heavy metals of Pb,Ni,and Cd exceeds the "Pollution Control Standard for Domestic Waste Landfill Sites"(GB16889-2008),Pb and Cu mainly exist in reducible and oxidizable states,and iron mainly exists in the residue state Medium(accounting for 76%),Zn,Cd,and Ni mainly exist in the form of reducible state and residue state,and the total proportion exceeds 71%.(2)A single reagent stable and stable heavy metal experiment was carried out for the original fly ash sample.The results showed that the concentration of heavy metals decreased with the increase of the dosage of NaH2PO4,Na2S,and DDTC,which confirmed the combination of inorganic and organic reagents selected in the experiment.Fly ash heavy metals have a good stabilizing effect.Compared with inorganic reagents,DDTC has a better stability test effect when the dosage is less.However,the stabilizing effect of copper did not improve significantly with the increase of Na2S dosage,but showed a slow decline.The stabilization effect of landfill leachate on heavy metals is not good.With the increase of the dilution ratio of landfill leachate,the leaching concentration of heavy metals shows an overall upward trend,and the leaching concentration of Cd and Pb in the chelate product exceeds the standard limit.(3)The results of the orthogonal test of DDTC+landfill leachate+Na2S composite reagent stabilizing heavy metals show that:in this study,the composite reagent can effectively combine the heavy metals Ni,Cd and Fe,and the leaching concentration is reduced by 90%-96%compared with the original ash.,88%-94%,93%97%,0.8%DDTC,5 times diluted landfill leachate,3%sodium sulfide chemical combination has a better chelating effect than other stabilization schemes,and can be reduced after reaction The state decreased significantly,the residual state increased,and the weak acid extraction state and the oxidizable state changed slightly,indicating that the chemical combination can effectively convert the unstable form of heavy metals into stable oxidizable state and residual state.(4)The heat treatment temperature has an important influence on the stabilization effect of heavy metals in fly ash.When the heat treatment temperature is 800℃,the main crystalline materials of fly ash include apatite minerals Ca10(SiO4)3(SO4)3F2,kaolin Al2Si2O5(OH)4,etc.The loose structure of the fly ash surface has undergone obvious densification,which makes the heavy metals in the fly ash change from a relatively unstable state to a relatively stable state.As the heat treatment temperature rises from 300℃ to 800℃,the leaching concentration of heavy metals in the original ash increases with The increase in temperature generally shows a trend of increasing first and then decreasing.(5)After mid-temperature sintering by adding landfill leachate to chelate fly ash,the heavy metals in fly ash can be stabilized.At a temperature of 600℃,adding a 20fold dilution of landfill leachate for heat treatment will significantly reduce the porosity of fly ash.Some irregular layered structures are attached to the surface of fly ash.Combined with XRD pattern analysis,it is speculated that on the surface of fly ash,the landfill leachate reacts with fly ash to form carbonate minerals.Compared with the heattreated sample of raw ash,the leaching concentration of heavy metals is significant.Decrease,the form of the chelated product BCR changes from a weak acid extraction state and a reducible state to a stable oxidizable state.Figure[61]Table[14]Ref.[116]...