M.S. Thesis: Examination of Chlorides in Municipal Solid Waste to Energy Combustion Residue: Origins, Fate and Potential for Treatment

By Adam Penque

Advisor: Professor Nickolas J. Themelis

Department of Earth and Environmental Engineering
Fu Foundation School of Engineering & Applied Science
Columbia University

September 2007

Fundamentally, the management of fly ash can be classified into two main schools of practice; treatment or stabilization for disposal or processing for reuse and recovery (Derie 1996), (ISWA 2003). In both of these scenarios a treatment step is critical to mitigate chloride and/or other contaminates. Due to the toxic nature of heavy metals concentrated in fly ash, most of the treatment processes currently available focus on the stabilization of heavy metals and fail to address the presence of chlorides. In fact some of the available heavy treatment mechanisms lead to a net increase in the leachability of chloride post treatment. In response to this problem a need for a simple treatment mechanism designed at targeting chloride was identified. Experimental work carried out as part of this masters research project evaluated the potential for such a treatment process.

The experimental work investigated the potential of using a simple batch type water washing system to remove soluble chloride from fly ash. Fly ash samples from two US WTE facilities were used for this analysis. Extractions were done using several liquid to solid (L/S) ratios and at several process temperatures. The removal of chloride was monitored over time. Trials were done originally at high L/S ratios (>30) to build an understanding of this relationship, as well as test the method against similarly published experiments. After positive findings were presented to experienced industry personnel the research group was advised to use lower L/S ratios (≤10) as they would be more feasible to reproduce on an industrial scale. For the second phase of these tests, L/S ratios of 3, 5 and 10 were used for chloride extractions from fly ash.

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