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Detoxification of Hazardous Waste Incineration Fly Ash by Using Microwave Pyrolysis and Stabilization

Author: SiMaZuoZuo
Tutor: LuoQiShi
School: East China University of Science and Technology
Course: Environmental Science and Engineering
Keywords: Hazardous waste fly ash microwave pyrolysis PCDD/Fs heavy metals
CLC: X705
Type: Master's thesis
Year: 2012
Downloads: 129
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Abstract


Hazardous waste incineration fly ash contains a large amount of heavy metals and PCDD/Fs. The un-treated fly ash will cause the potential and long-term pollution to the soil and aqueous environment. This study applies the microwave pyrolysis and heavy metals stabilization to the treatment of hazardous waste incineration fly ash, in order to discover an economical and effient technology for the treatment and disposal of fly ash.The following aspects were investigated in this dissertation:(1) the characteristics of fly ash, (2) the pyrolysis of PCDD/Fs in fly ash using microwave technology, (3) the chemical stabilization of heavy metals in fly ash and the optimization of reaction factors, and (4) the preliminary study on the feasibility of the reclamation of the detoxified fly ash.The results of the characteristics of fly ash demonstrated that the content of both heavy metals and PCDD/Fs in fly ash is significant high. In addition, the leaching concentration of heavy metals is closely related to the conent and distributions of heavy metals.The results of microwave pyrolysis of fly ash in low temperature showed that the dechlorination/hydrogenation reaction occured in appropriate atmosphere. A 45.7% of PCDD/Fs removal rate was observed under the optimal reaction condition, i.e., reaction for 60 minutes at 300℃in nitrogen atmosphere.The results of stabilization of fly ash indicated that:the best stabilization effect on heavy metals was achieved by using organic chelating agent TMT, comparing with that of the other three inorganic agents i.e., Na2S, FeSO4 and Na3PO4. The leaching toxicities of Cr, Pb and Zn reduced by 97.2%,85.0% and 93.5% for alkaline fly ash at an addition of 0.9% TMT. The leaching toxicities of Cu, Zn, Pb, Cr and Cd reduced over 99% at an addition of 12% TMT for acidic fly ash. The treated fly ash can keep stabilization within wide pH values. The analysis results show that surface structure become stable, and the structure of the product was amorphous under atmospheric conditions. The speciation analysis revealed that the distributions of heavy metals changed after treatment significantly.The proportion of exchangeable phase decreased and that of oxidizable phase increased. Therefore the leaching toxicities of fly ash could be gradually reduced.Finally, the economic, technical feasibility and the environmental acceptance of the re-use process of fly ash were analyzed. With 40% fly ash addition at curing 28 days, the unconfined compressive strength of unburned brick was 25.3MPa, the absorption rate was 9.8%, and the strength loss was 24.1%. The above results indicated that the unburned bricks made by fly ash could be considered as an economic and environmental friendly way to re-use the fly ash and attract more detailed researches.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Solid waste disposal and utilization
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