Microwave Stabilization of Heavy Metal in MSWI Fly Ash and Quantification of Fugitive Heavy Metal Emissions during Treatment
Date Issued
2012
Date
2012
Author(s)
Fan, Ming-Je
Abstract
Municipal Solid Waste Incinerators (MSWI) in Taiwan generates 230,000 tons of fly ash annually. Many heavy metals in the waste will not be degraded or oxidized and they may end up in ashes. The ashes may need to be stabilized before reuse or disposal because heavy metal concentrations in the leading solution of Toxicity Characteristic Leaching Procedure (TCLP) may exceed the regulatory limits. Stabilization of MSWI fly ash can be divided into two common methods: solidification and thermal treatment. Solidification has a disadvantage of increasing waste volume, which would shorten the service life of landfills. On the other hand, thermal treatment consumes a lot of energy. In this study, microwave was used to stabilize MSWI fly ash. Gas samples were collected and analyzed during microwave radiation to determine the extent of fugitive the emission of heavy metals.
Experiments were conducted to determine the optimal operating parameter conditions in terms of microwave power and reaction time. The decision was made based on the extent of stabilization as well as the amount of all emission. The energy consumption of the microwave irradiation was compared with that of conventional heating.
The results showed at a power setting of 500 watts, microwave irradiation, can effectively reduce the leaching concentrations of cadmium, copper and lead, and the performance improved with reaction time. Chromium leaching concentration increased with reaction time, but still below the regulatory limit of 5 mg/L. Time of 30 minutes, the leaching concentrations of cadmium, copper and lead decreased with microwave power, but there was no obvious trend for chromium. For all the conditions tested, the optimum operating parameters were found to be microwave power of 500 watts and reaction time of 10 minutes. The lead leaching concentration was 3.5 mg/L, gaseous emission of 4.3%, and solid-phase stability of 101.5%. When compared to conventional heating, microwave irradiation consumed less energy and required 1/6 of the reaction time.
Subjects
fly ash
microwave process
thermal treatment
sinter
emission
Type
thesis
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