Research On Medical Waste Incineration Fly Ash Removal Of Heavy Metals Under Zero-valent Iron

A large amount of heavy metals were accumulated in Medical Waste Incineration?MWI?fly ash,so it is of great significance for the pollution control of heavy metals to realize the harmless and resource utilization of medical fly ash.The application of zero valent iron?ZVI?provide a new way to deal with hazardous waste in the treatment of fly ash.It is mainly regard heavy metals in the MWI fly ash as the removal object,according the effects of different conditions,such as different pH value,the dosage of Fe0 solution,reaction temperature,different reaction time and different particle size of Fe0 on the removal effect of the fly ash tostudy the leaching toxicity of fly ash,then XPS analysis was carried out on the surface of zero valent iron after reaction,and the mechanism of zero valent iron for heavy metals removal was studied.Finally,the medical fly ash was used for the continuous detoxification test,and the toxicity of zero valent iron was analyzed,for this reason to increase the efficiency of resource utilization.The main conclusions of this study are as follow:?1?Medical waste incineration fly ash contains a lot of heavy metals,The contents of heavy metals Zn,Cu,Pb,As,Cr,Ni and Cd were 38852.5,6967.2,2719.7,458.2,360.7,301.6 and 60.3mg/kg,respectively.Compared with the soil background value,it can be seen that there is a strong enrichment of heavy metals in MSWI fly ash.TCLP leaching experiments showed that the leaching concentrations of heavy metals such as Zn,Pb and Cd were much higher than Hazardous waste identification criteria,Therefore MWI fly ash had the potential risk to environment.?2?The treatment effect of zero valent iron was different under different pH values.When the p H value is 4,the content of Cu,Pb,Zn and other elements in medical fly ash were more obvious.While the eluent pH value was 2,the enhancement of Cr,Cd and As in fly ash by zero valent iron.The removal of heavy metals from fly ash was not obvious,Relatively high temperature and relatively low temperature are not conducive to the treatment of fly ash by zero valent iron.The addition of excess zero valent iron contributed little to the removal efficiency of heavy metals.When the zero valent iron reacted with fly ash12 h,fly ash TCLP showed that the leaching of Cu,Zn and Cr was the lowest.The smaller the particle size,the higher the reducibility of zero valent iron,the better the treatment effect of fly ash.?3?Risk assessment of fly ash after detoxification,TCLP experiments showed that the leaching concentration of Zn in medical fly ash decreased from the original 702mg/L to 97mg/L,the leaching of Pb decreased from 19.54mg/L to 0.125mg/L,and the leaching of Cd decreased from 1.43mg/L to 0.287mg/L.The results of PBET simulation in vitro showed that the fly ash residue entered the human body under extreme conditions,and the leaching concentration of heavy metals increased under the action of protein and organic matter.However,the leaching concentration of Cu,Pb and Zn in the fly ash of the traditional Chinese medicine leaching experiment was increased,The cumulative leaching concentration of Zn exceeds that of hazardous waste,Still has a high environmental risk.?4?X ray photoelectron spectroscopy?XPS?was used to characterize the zero valent iron mixture,From the total spectrum of zero valent iron reactant XPS,The characteristic peaks of Zn,Cu,Cr,Cd and Pb appear on the surface of zero valent iron.The results show that these heavy metals are adsorbed on the surface of zero valent iron.Cu₂ p electron binding energy spectra appear in 932.4eV and 952.2e V,two peaks are Cu?0?and Cu???,The removal of Cu???mainly occurred in the form of chemical reduction,Cd mainly exists in the form of Cd???,and there is no Cd?0?peak.?5?In the TCLP experiment,the exchangeable fraction of Pb and Zn was higher,In PBET and MEP experiments,a large number of exchangeable,carbonate bound,Fe Mn oxide bound and organic bound states were leached,The treatment of fly ash should be determined by the characteristics of fly ash and the actual environment.?6?The results showed that the detoxification of fly ash by zero valent iron detoxification device,The elution concentration of Zn,Cu,Pb and Cd in the fly ash TCLP was further reduced after elution of the elution column,far below the hazardous waste leaching standards,And the comprehensive evaluation of fly ash leaching concentration can meet the standard of domestic waste landfill site,indicating that the fly ash harmless effect is obvious.