Role of goethite during air-oxidation of PAH-contaminated soils

The impact of goethite on air-oxidation of PAH-contaminated soils was studied through two sets of experiments. (i) Soil extractable organic matter (EOM) and (ii) whole coking plant soils were oxidized at 60 and 100 °C for 160 d, with/without goethite. Organic matter (OM) mineralization was monitored via CO2 production and polycyclic aromatic compounds (PACs) oxidation was investigated by GC-MS analyses. The decrease in EOM and PAH contents, and the oxygenated-PAC production observed during EOM oxidation, were enhanced by the presence of goethite. PACs were likely transformed at the goethite surface through electron transfer process. Mass carbon balance revealed a transfer from EOM to the insoluble organic fraction indicating condensation/polymerization of organics. Soil oxidation induced a decrease in EOM, PAH but also in oxygenated-PAC contents, underscoring different oxidation or polymerization behavior in soil. The goethite addition had a lesser impact suggesting that indigenous minerals played an important role in PAC oxidation.