| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 96 === Fly ash generated from incinerator contains high contents of alkali chlorides and trace amounts of heavy metals and toxic organics, and it belongs to hazardous wastes. This work studies the feasibility of producing artificial aggregates from fly ash by using a process in which the raw fly ash is washed by deionized water or phosphoric acid and then calcined at high temperatures to remove the alkali chlorides and stabilize the heavy metals.
Fly ash, collected from the air pollution control unit, was washed with deionized water and H3PO4 solutions(1wt%~10wt%), respectively, with a liquid/ solid weight ratio of 10. The dry washed samples were pelletized with a pressure of 5000psi, and the pellets were sintered at 900℃ and 1000℃ for 1 hour.
After washing the fly ash, the chlorine content of the fly ash decreased markedly. Leaching tests for the fly ash treated by washing and/or sintering showed that the amounts of heavy metals leached were far less than the regulatory limits in Taiwan. The amount of Pb leached decreased markedly after the fly ash was treated, but the amounts of Cr leached decreased only a little. The amount of of Cd leached increased if the fly ash was washed with H3PO4 solutions, and that of Cu leached increased if the acid-washed ash was sintered.
The sintered cylinders of the fly ash washed with deionized water or with 5 and 10 wt%H3PO4 solutions had initial compressive strengths (112-760Kgf/cm2) comparable to those of bricks and marble. However, the sintered cylinders disintegrated due to weathering.
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