Systematic study on dynamic pyrolysis behaviors, products, and mechanisms of weathered petroleum-contaminated soil with Fe₂O₃

Weathered petroleum-contaminated soil (WPCS) with a high proportion of heavy hydrocarbons is difficult to remediate. Our previous research demonstrated that Fe₂O₃-assisted pyrolysis was a cost-effective technology for the remediation of WPCS. However, the pyrolysis behaviors, products, and mechanisms of the WPCS with Fe₂O₃ are still unclear. In this study, a combination of Thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) techniques were used to explore these pyrolysis characteristics. The thermal desorption/degradation of light and heavy hydrocarbons in the WPCS mainly occurred at 200-400 °C and 400-550 °C, respectively. The activation energy of thermal reaction of heavy hydrocarbons was decreased in the presence of Fe₂O₃ during the WPCS pyrolysis processes. In the process, the released inorganic gaseous products were mainly H₂O and CO₂, while the released organic gaseous compounds were primarily cycloalkanes, alkanes, acids/esters, alcohols, and aldehydes. Compared with the WPCS pyrolysis without Fe₂O₃, the yields of gaseous products released during the WPCS pyrolysis with Fe₂O₃ were reduced significantly, and some gaseous products were even not detected. This phenomenon was contributed by the following two reasons: 1) heavy hydrocarbons in the WPCS were more easily transformed into coke in the presence of Fe₂O₃ during pyrolysis; 2) some released gaseous products were reacted with Fe₂O₃ and fixed on the soil particles. Therefore, the WPCS pyrolysis with Fe₂O₃ can effectively reduce the burden of tail gas treatment. Criado method analysis results suggested that the reaction mechanism of heavy hydrocarbons during the WPCS pyrolysis with Fe₂O₃ was rendered as the synergic effects of diffusion, order-based, and random nucleation and growth reactions.