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

A process is proposed for the decontamination of fly ash from an urban soli d-waste incineration facility (USWI), where the target contaminants are pol ychlorodibenzodioxins (PCDDs) and dibenzofurans (PCDFs), a class of highly toxic tricyclopolychlorinated organics. In general, the ash waste requires inertization and disposal into a controlled landfill. here, we propose an i nertization process based on the reduction of the PCDDs and PCDFs content b efore dumping. Inertization is brought about by extraction with a solvent c onsisting of supercritical carbon dioxide modified with a co-solvent (10% t oluene). The plant would run in semibatch mode, with continuous flow of flu id through a packed bed of fly ash. Then, carbon dioxide and the co-solvent would be separated and recycled. Favorable extraction conditions were foun d in the laboratory at 300 bar and 60 degrees C. Under these conditions, th e removal efficiency of native PCDDs and PCDFs is around 50% refereed to th e extraction of the same sample using the EPA method 1613 (Soxhlet extracti on with toluene). A techno-economic appraisal of a treatment facility is pr esented for a medium sized incineration plant (50, 000 ton urban waste year ly) 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.