| With superiority in harmless, reduction of volume and recovery of energy,incineration has been the main method during the disposal of Municipal Solid Wastes(MSWs) in many developed countries. In2011,16.1%of MSWs were disposaled byincineration and the proportions is increasing year by year, which will lead to producemore and more Municipal Solid Wastes Incineration (MSWI) fly ash as byproducts ofwaste incineration. The fly ash was determined to be hazardous waste, and a lot of heavymetals and dioxin were obtained in fly ash, which were the risk source of environmentand health riskFly ash could cause serious harm to the ecological environment and humanhealth. For the management ideas of MSWI fly ash, a safe landfill site of hazardous wastechanges into life safety landfill, and in order to transfer the safety landfill todetoxification resource utilization of MSWI fly ash with the purpose of zero landfill. Weneed to research and develop low cost, safe and reliable, and easy to manage the MSWIfly ash during the disposal and recycling use of new methods and new technologies. Andbadly need to establish domestic waste incineration disposal process of environmentalrisk management of new technology policy and management system.The project studied the typical regions MSWI fly ash, collected from15differentcities and regions throughout the country. Firstly, we analyzed the pollutioncharacteristics of heavy metal in raw fly ash, including total content of metals, chemicalspeciation, and leaching toxicity, and preliminarily indicated the relationships of totalcontent, speciations and TCLP leaching. Based on the demand of detoxicate, resource andreuse of MSWI fly ash, then conducted a series of washing and pickling pre-treatmentand explored the impact of the pre-treatment of the elution on the pollution characteristicsof heavy metals in fly ash. Finally, we assessed risk of the main heavy metals in the flyash from risk assessment methodology. The main conclusions as follows:(1) Fly ash contains large amounts of hazardous heavy metals (Zn, Pb, Cu, Cr, Cdand Ni), and the total concentrations of these metals range from2088to14129,782.6to9901,728.0to2162,232.0to716.23,83.67to525.0and140.7to378.63mg/kg. Forwater-washed and acid-washed fly ash, the extent of washing out for soluble salts was greater than that of heavy metals, resulting in zinc and Cr presented the enrichment trendin most of the samples. In contrast, Pb and Cd of the raw ash in the fraction F1wererelatively high, and the total concentrations of Pb and Cd in the washed ash presentedcertain degree of reduction, and the total concentrations of Cu and Ni were nearlyunchanged.(2) leaching toxicity of heavy metals in most raw ash samples (73.3%) was excessive,and the excessive elements were Cd, Pb and Zn. Compared with the over standard rate ofleaching toxicity for raw fly ash,46.7%of the water-washed ash samples was excessive,indicating that water-washing pretreatment effectively reduced the leaching toxicity ofheavy metals in fly ash. Contraryly, the leaching toxicity in13acid-washed samplesexceeded standard limits, and the leaching of Zn, Pb, Cd exceeded the1~4,1~7,1~18times, respectively.(3) Speciation results found Cd in fly ash was mainly in the form of F1and F2,rangeing from0%to78.1%and12.0%to99.7%, respectively. Cd could easily migrate inthe environment, and was the most unstableelement. In most samples, the sum of fractionF1and F2for Pb and Zn ranged from40%to60%, and other metals mainly in therelatively stable form. Water-washing and pickling pretreatment reducted the propotionsof F1in different degrees, and ultimately the chemical form of heavy metals in fly ashconverted the unstable form into the stable form, especially for Pb, Cr and Cd. Thewater-washing presented effective stabilization.(4) Principal component analysis study found that leaching toxicity Zn, Pb, Cr, Cdand Ni in fly ash was mainly affected by the fraction F1, but no significant relationshipfor Cu.(5) To track the consecutive samples of fly ash, and analysis total content of metals,chemical speciation, and leaching toxicity of the samples. The results indicated that nosignificant difference was found for the total content of heavy metals. So the metalscontent was nearly stable for the different sampling time, especially for Cr, Cd, Ni. TCLPresults in individual samples showed some differences, but in general showed nosignificant difference.(6) The RAC results of raw ash showed that risk degree of heavy metals in fly ash onthe environment from high to low was: Cd, Pb, Zn, Cu, Ni and Cr, and high risk or high risk (37.5%<RAC <78.1%) in samples (S1, S2, S5, S9, S10, S12and S14) of werecaused by Cd and Pb; Zn, Cu and Ni is mainly the low risk and the media risk metals, andCr with low risk. Pre-treatment results showed that the water could significantly reducethe risk level of all the heavy metals, especially for Pb (after washing grey RAC <10%);But the acid-washing only significantly reduce the risk level of Pb (after acid-washingexcept for the S1and S9in the fly ash, the rest of the samples for low risk).(7) The risk of non-cancer in raw ash for children was significantly higher than thatof adults, and its HI value ranged0.35~17.48,0.07~0.35respectively; At the same time,the cancer risk of all the samples was small. The HI values of washing pre-treatment offly ashes for children and adults ranged0.25~8.77, and0.70~4.52, the correspondingthe HI values acid-washing pretreatment ranged0.05~1.88,0.15~0.05, respectively,showed that water and acid washing pretreatment significantly reduced the risk of cancerin fly ash, especially for children; The TCR values of water and acid washingpretreatment of samples were below <10-4, which indicated that smaller effects on cancerrisk of fly ash. |
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