| Summary: | 碩士 === 國立聯合大學 === 環境與安全衛生工程學系碩士班 === 101 === Almost of municipal solid waste incineration (MSWI) fly ash in Taiwan was treated by cement solidification/stabilization and final disposed in isolated landfill sites; however, which does not match the principles of waste treatment and resource reuse. In this research, two domestic A and B large incineration plants fly ashes were studied to explore the feasibility of detoxification and reutilization.
Water extraction experiments were carried out first and the results show that the higher L/S, the lower ion concentration release in low-speed water extraction processes was found; in addition, with the increases in the L/S ratio and the water extraction time, some of the ions release had slowed down. Also, all of TCLP-Cd and -Pb passed the regulatory standard. In medium-speed water extraction processes, ions were rapidly released from fly ash and significant removals of much Pb and parts of Cd ions were detected; moreover, TCLP-Cd and -Pb also passed the regulatory standard. Thereafter, an optimal water extraction process was summarized and achieved that the water soluble chloride ion contents were at the range of 6.6–11.3% and the A and B fly ashes passed the TCLP test and became non-hazardous fly ashes (NHFA).
Some advanced experiments for reducing water soluble chlorides was conducted after the previous water extraction experiments. The results show that the thermal treatment of fly ash does not benefit the stabilization of heavy metals and the reduction of water soluble chlorides; however, adding phosphates might slightly reduce the water soluble chlorides of fly ash. Twice water extraction for fly ash could significantly reduced the water soluble chlorides to 1.08%, verifying that more water extraction and increasing the L/S ratio could decrease the water soluble chlorides. Furthermore, an optimal water extraction at 50 °C could notably reduce the dioxin content of fly ash.
Finally, the NHFA was reused for producing cement mortar and brick. The results of cement mortar show that the addition of 10% NHFA as pozzolanic fine aggregate filling the micro-pores of cement mortar not only dramatically reduce the dissolutions of heavy metal and water soluble chlorides but also enhance the compressive strength about 20–150 kgf/cm2. In the reuse for producing brick, increase of NHFA ratio would increase the water absorption and decrease the bulk density and volume shrinkage. The produced brick fired at 1,100 °C could meet the CNS first brick standard, and the compressive strengths of all of 10% NHFA bricks could also meet the CNS first brick standard. Moreover, the heavy metal concentrations in TCLP test for all bricks were far below the regulatory limits. In summary, the feasibility of detoxification of MSWI fly ash and reusing NHFA for producing concrete and brick was verified.
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