Study On The Ecological Health Risks Of Heavy Metals In Fly Ash And Its Resource Utilization Process

Northern region,as an important energy base of our country,produces a large number of fly ash every year.Due to the problems of economic development and technology,the region has a low utilization rate of fly ash,resulting in large piles of fly ash that not only occupy a large amount of land but also pose a grave threat to the local ecological environment.Fly ash has the dual characteristics of pollution and resource,and can be utilized as a resource in various ways.Even so,secondary pollution is inevitably generated in the process of resource utilization.Heavy metals are the toxic components that need to be paid attention to in the process of resource utilization,so it is necessary to study the migration rule of heavy metals and the environmental risks.In this study,the generation,storage and utilization of fly ash in key areas of northern China are analyzed,and the future generation trend of fly ash is predicted by using grey prediction model.Simultaneously,the resource utilization of high-aluminum coal ash is taken as an example,and the migration rule of heavy metals is studied through material flow analysis and element flow analysis.On this basis,Nemerow pollution index method is adopted.The potential ecological pollution index method is used to quantitatively evaluate the environmental risks arising from the process of high alumina coal ash resources.In order to provide reference for environmental management of fly ash in key provinces in northern China,formulation of relevant policies and control of heavy metal secondary pollution in the process of resource utilization of high aluminum coal ash.The main research contents and conclusions are as follows:(1)In the past 20 years,the annual production of fly ash in the five northern provinces has maintained a continuous growth,among which the annual production of fly ash in Inner Mongolia ranks the first among the five northern provinces,and the annual production of fly ash in the five provinces has increased by 728.6%in the past 20years,and the gray prediction model predicts that the fly ash production in the five provinces will continue to maintain a rapid growth in the next ten years.Nonetheless,the comprehensive utilization rate of fly ash is only 30%,resulting in a large amount of fly ash accumulation in the five northern provinces.In the past 20 years,about 1.986 billion tons of fly ash was deposited in the five provinces,occupying 1.42×10~5km~2 of land.(2)Based on material flow analysis,the migration and transformation law of heavy metals in the recycling process of the typical high-alumina coal ash in Inner Mongolia is studied.The results show that the activation process of physical ball milling generally increases the release of various heavy metals in the high-alumina coal ash,especially the release of Cr increased by 82%;More than 80%of the iron group elements represented by Cr and Mn migrated to the poly aluminum residue generated by acid activation,while the metal ore-forming elements represented by Zn,Pb and Cu migrated during acid activation and alkali desilication.The final amount of Cr,Mn,Zn,Pb and Cu in Mullite products is 20%,9%,24%,22%and 24%,respectively.(3)The potential ecological risk model is used to carry out environmental risk assessment of heavy metals in the recycling process.The results show that the potential comprehensive ecological risk index of solid waste polyaluminum residue generated from the recycling process is 527,6.6 times higher than the standard of extremely strong ecological risk level.The potential ecological risk of Cr is the most prominent,13 times higher than the standard of extremely strong ecological risk level;The toxic leaching test shows that the toxicity of calcium silicate products is Zn>Mn>Cu>Pb>Cr,and that of mullite products is Mn>Cu>Zn>Pb>Cr,but all of them are far below the quality standard limit of groundwater.(4)Through human health risk model,human health risk assessment is carried out on adults and children living around fly ash dumps and workers working in factories.The evaluation results showed that the non-carcinogenic health risks and carcinogenic health risks of children were greater than those of adults.For workers,the health risk from polyaluminum residue is greater than that from high aluminum coal ash,and the health risk from heavy metal Cr is the highest.