Supercritical fluid process for removal of polychlorodibenzodioxin and dibenzofuran from fly ash

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Abstract
A process is proposed for the decontamination of fly ash from an urban solid‐waste incineration facility (USWI), where the target contaminants are polychlorodibenzodioxins (PCDDs) and dibenzofurans (PCDFs), a class of highly toxic tricyclo‐polychlorinated organics. In general, the ash waste requires inertization and disposal into a controlled landfill. Here, we propose an inertization process based on the reduction of the PCDDs and PCDFs content before dumping. Inertization is brought about by extraction with a solvent consisting of supercritical carbon dioxide modified with a co‐solvent (10% toluene). The plant would run in semibatch mode, with continuous flow of fluid through a packed bed of fly ash. Then, carbon dioxide and the co‐solvent would be separated and recycled. Favorable extraction conditions were found in the laboratory at 300 bar and 60°C. Under these conditions, the removal efficiency of native PCDDs and PCDFs is around 50% refereed to the extraction of the same sample using the EPA method 1613 (Soxhlet extraction with toluene). A techno‐economic appraisal of a treatment facility is presented for a medium sized incineration plant (50,000 ton urban waste yearly) producing 1,500 ton of fly ash/y. The ash production would be inertised in a specially designed supercritical fluid (SCF) extraction unit, located on‐site at the incineration facility.