(510n) Leaching and Fixation of Heavy Metals in Municipal Solid Waste Incineration Fly Ash (MSWI FA) Based on CO2 Uptake Process
AIChE Annual Meeting
2021
2021 Annual Meeting
Environmental Division
Poster Session: Environmental Division
Wednesday, November 10, 2021 - 3:30pm to 5:00pm
To prevent negative impact on the environment, stabilizing method of MSW ash have been studied and applied. Representative ways are thermal treatment, solidification and washing treatment. In thermal treatment method, MSWI ash is heated to the high temperature in the range of 1500 â 1700 K resulting in the stabilization of the heavy metal and salts whose vapor pressure is relatively high. One of the merit of this method is that the hazardous organic component can be treated in the same time by the thermal oxidation in that temperature range. However, it costs a lot to maintain high temperature condition. For solidification process, some components in MSWI ash are fixed by the reaction with waste cement or the slag. The merit of this method is the prevention of hazardous component leaching by forming the compounds whose binding force is higher than that in the ash. Also, due to the reaction, the mass after the solidification is increased make it harder to transport to the landfill site. In the washing treatment, hazardous materials in soluble phase are dissolved into the solvent, mainly water. However, it requires the further treatment of wastewater containing dissolved components. In this study, we discussed a new ways to treat MSWI fly ashes which contains shows higher heavy metal contents compared to the MSWI bottom ashes.
Among various kinds of methods for the stabilization of heavy metals in municipal solid waste incineration fly ash (MSWI FA), acid leaching is the most prevalent. However, the process of heavy metals leaching in MSWI FA by various acids must be compared. In this study, we extracted the heavy metals in MSWI FA using 0.5 M solutions of strong acids (HCl, H2SO4 and HNO3), as well as weak acids (NH4Cl, (NH4)2SO4 and NH4NO3). Solidification by CO2 injection occurred in all the leaching solutions. The leaching test was performed for solids such as treated MSWI FA and the precipitates produced in the solidification process, compared with untreated MSWI FA. The solids were analyzed by using X-Ray fluorescence spectroscopy, X-Ray diffraction, and scanning electron microscopy. The leaching solutions were analyzed by inductively coupled plasma-optical emission spectroscopy. Using weak acid solutions, Zn, Pb, and Cu were leached 15 - 70 times, two times, and 20 - 150 times, respectively, more than those leached strong acids. Except H2SO4 and (NH4)2SO4 solutions, all the acids reduced the mass of MSWI FA and extracted heavy metals. The crystalline precipitates were the carbonates. HNO3 solution was found to be the most appropriate solvent for the proposed method.