Thermochemical Remediation of Petroleum-Contaminated Soil: TG-FTIR-MS Analysis and Residue Characteristics

Thermochemical remediation of petroleum-contaminated soil (PCS) has attracted increased attention. Pyrolysis is one of an important thermochemical treatment technology. The pyrolysis behavior of PCS and the main gaseous products evolved were investigated by means of a simultaneous thermogravimetric analyzer (TG) coupled with Fourier transform infrared spectrometry (FTIR) and mass spectrometry (MS). Pyrolysis residue characteristics were determined by X-ray photoelectron spectrometry (XPS), FTIR, and X-ray diffraction (XRD). The results revealed that the pyrolysis process of PCS was divided into water evaporation, volatilization of light volatile, degradation of low/high boiling point organic matters, and decomposition of inorganic mineral. The increase of heating rate would lead to the shift of thermal profiles to a higher temperature region and the increase of mass loss rate, without changing the patterns of thermal degradation of PCS. In addition, CO2, the most important gaseous product, was released in two temperature regions of 700–1090 K and 1090–1220 K. The trace pollution gaseous product SO2 was discharged above 1100 K. After pyrolysis, the organic matters were significantly reduced, and the inorganic minerals such as CaCO3 and BaSO4 were decomposed. The sulfur in PCS mainly existed in the form of sulfate-S, sulfonic acid-S or sulfone-S, sulfoxide-S, aromatic-S, and aliphatic-S. During pyrolysis, sulfate-S was continuously decreased, while the other four forms of organic-S may be transformed into each other and finally partially stabilized in the pyrolysis residue.