The removal of polycyclic aromatic hydrocarbons (PAHs) from marine sediments using persulfate over a nano-sized iron composite of magnetite and carbon black activator

The presence of polycyclic aromatic hydrocarbons (PAHs) in sediments is a potential eco-environmental health risk. Fe3O4-carbon black (FCB) nanocomposite was synthesized by a simplified precipitation method and used to activate persulfate (PS) for the degradation of PAHs in contaminated marine sediments. The carbon black was formed by amorphous non-graphite and the Fe3O4 composed of magnetite of cubic crystal structures. FCB exhibited typical ferromagnetic characteristics and high degradation of PAHs in marine sediments via PS oxidation. The pseudo - first - order rate constant of PAHs degradation significantly increased with PS dosage but decreased with increase in pH from 3 to 9. Langmuir-Hinshelwood model described the kinetics of PAHs degradation well. The observed rate constant, k(obs) (1.8 x 10(-2) h(-1)), at Sigma[PAH]: [PS] = 1:10(4) (the optimal condition) was almost 2.7 times that of 1:1 (k(obs) = 6.6 x 10(-3) h(-1)). At the PS concentration of 2 x 10(-4) M (or a Sigma[PAH]: [PS] = 1:10), pH 3, and 3 g/L of FCB, the FCB/PS system exhibited 94, 97, 94, 98, and 93% degradation of total PAH (Sigma[PAH]), PY, FLU, CH, and PH, respectively, while the highest PAH degradation was 99, 98, 97, and 97%, respectively, for 6 -, 5 -, 4 - and 3 - ring PAHs. The presence of Fe2+/Fe3+ redox pairs greatly enhanced the catalytic capacity of FCB leading to an increase in PAH degradation. Electron paramagnetic resonance (EPR) spectroscopy revealed SO4-(center dot) and HO center dot radicals as major reactive species for PAHs degradation in FCB/PS system. Results clearly indicated the great potential of FCB for remediation of PAHs contaminated marine sediments.