Pre-treatment with extraction solvent yields higher recovery: Method optimization for efficient determination of polycyclic aromatic hydrocarbons in organic-rich fine-textured wastes

Abstract

Fluid fine tailings (FFT) contain numerous organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Growing concerns of PAH toxicity warrants monitoring for environmental consequences and natural attenuation. Conventional Soxhlet extraction yields low (∼50%–60%) recovery of PAHs (naphthalene, phenanthrene, pyrene, dibenzofuran, fluorene, and dibenzothiophene) from FFT, which impedes accurate PAH determination. Therefore, an optimized method was developed in this study that included (1) selection of a suitable solvent, (2) enhancement of PAH recovery by pretreatment, (3) determination of optimal extraction time, and (4) optimization of sample cleanup procedure. Results showed that (1) dichloromethane (DCM) recovered significantly higher masses of PAHs from FFT than hexane (HEX), cyclohexane, or their mixtures with DCM; (2) pretreatment of FFT with DCM significantly improved PAHs recovery using either Soxhlet or mechanical shaking methods; (3) a 24-h Soxhlet extraction with pretreatment yielded the highest and the most consistent PAH recoveries; (4) DCM proved to be an efficient eluent for sample cleanup in silica gel column; and (5) consecutive cleanups with additional silica gel column removed excessive impurities without PAH losses. Therefore, this study developed an optimized method for PAH recoveries from FFT, achieving a pooled mean recovery of ∼94%. This method is applicable to other organic-rich fine-textured wastes such as sludge and clay sediments.