Supercritical fluid extraction and accelerated solvent extraction of dioxins from high- and low carbon fly ash

This study investigates the replacement of Soxhlet extraction by supercriti cal fluid extraction (SFE) or accelerated solvent extraction (ASE) for the removal of dioxins from municipal waste incinerator fly ash. SFE is very ma trix dependent; higher percent recoveries versus Soxhlet extraction can be obtained for low-carbon-level fly ash, but only a few percent of dioxins ca n be extracted from high-carbon-level fly ash. The addition of large quanti ties of toluene in the extraction cell prior to extraction of high-carbon n y ash improves the recovery of the lowest chlorinated dioxins (similar to 9 0%), but a maximum of 20% of the octachlorodibenzo-p-dioxins can be extract ed. Since large quantities of toluene are needed to improve the recoveries, ASE with toluene was tested. Recoveries similar to Soxhlet extraction can be obtained in 2 h at 80 degrees C. Increasing the temperature to 150 degre es C increases the extraction rate and yields recoveries of similar to 110- 160% compared to 48-h Soxhlet extraction for all congeners for both low- an d high-carbon ny ashes. These results question the choice of Soxhlet extrac tion as a reference method for dioxin determination.