Comparative Removal of Polycyclic Aromatic Hydrocarbons Using Iron Oxide and Hydrogen Peroxide in Soil Slurries

Three polycyclic aromatic hydrocarbons (PAHs), phenanthrene, anthracene, and pyrene in sand slurries, were subjected to a heterogeneous catalytic oxidation process using goethite catalyzed by hydrogen peroxide. Specifically, we studied the effects of different concentrations of goethite, H₂O₂, bicarbonate, and pH. The kinetics of the degradation of PAHs followed pseudo first-order kinetics. Determined rate constants varied between 2.0 × 10^–4 to 1.1 × 10^–3, 1.5 × 10^–4 to 9 × 10^–4, and 1.1 × 10^–4 to 7 × 10^–4 min^–1, for phenanthrene, anthracene, and pyrene, respectively. The highest rate of PAHs degradation was observed in 5 M H₂O₂ with 33.5 g/kg of goethite. The intermediate product formed during the degradation of phenanthrene was salicyclic acid, and was shown to degrade to CO₂ and H₂O. Intermediate products of anthracene and pyrene oxidation were not detected, but their final products were CO₂ and H₂O. More than 80% of the 5 M H₂O₂ was consumed within 30 min, and the reaction was almost complete after 3 h. The degradation of phenanthrene, anthracene, and pyrene was 73, 60, and 55%, respectively, after 3 h. It is of significant advantage that this method produces optimal PAHs removal at neutral pH. PAHs degradation was also dependent on the bicarbonate concentration, suggesting that it may act as an OH radical scavenger. Our experimental results may suggest the potential use of goethite catalyzed by H₂O₂ for the remediation of soils contaminated with PAHs.