Photochemical and supercritical fluid extraction studies of polycyclic aromatic hydrocarbons adsorbed on coal stack ash fractions

Coal stack ash was separated into carbonaceous, ferromagnetic, and two nonmagnetic mineral fractions by the use of solvent density separation, magnetic separation, and elutriation. The efficiency of photolysis of adsorbed pyrene and benz(a)anthracene (BaA) was monitored on the surface of each fraction, with the carbonaceous fraction being primarily responsible for stabilization of adsorbed pyrene and BaA. Supercritical fluid extraction was applied in an effort to improve the recovery of adsorbed pyrene from the carbonaceous coal ash fraction. Supercritical fluid extraction was shown to yield recoveries (approximately 2/3) of adsorbed pyrene, similar to those obtained using traditional extraction methods (Soxhlet and ultrasonic extraction with methanol or toluene). Supercritical fluid extraction, directly coupled to gas chromatography, was utilized for the identification of a photochemically-produced product (benz(a)anthracene-7,12-dione (BaAD)) of BaA adsorbed on surface of a coal stack ash. The primary advantage of this methodology compared to traditional extraction-concentration techniques is the absence of solvent in the extract (giving rise to a lower limit of detection), because the supercritical fluid is converted to a gas upon collection of the extracted compounds. A yield of ca. 20% of BaAD was calculated from the photochemical consumption of adsorbed BaA on silica gel and a mineral fraction of coal stack ash.