Effect and mechanisms of red mud catalyst on pyrolysis remediation of heavy hydrocarbons in weathered petroleum-contaminated soil

Abstract In this study, industrial waste red mud (RM)-assisted pyrolysis of weathered petroleum-contaminated soil (WPCS) was developed based on the principle of “Treating the wastes with wastes”. In contrast with WPCS treated without RM at 400 °C for 30 min, the total petroleum hydrocarbons content reduced by 23.93% in the WPCS treated with 5% RM, and the contents of saturates, aromatics, resins, and asphaltenes decreased by 6.39%, 66.79%, 37.78%, and 64.95%, respectively. X-ray photoelectron spectroscopy results showed that the percentages of pyridinic−N and thiophene compounds on the surface of soil treated with 5% RM decreased significantly. The binding of metal oxides in RM with oxygen-containing groups and deposition of graphitic C increased the C O and O−C O groups. The activation energy at petroleum hydrocarbon thermal degradation stages of WPCS pyrolyzed with 5% RM reduced by 13.53% (lighter petroleum) and 16.40% (heavier petroleum), suggesting the strong catalytic action between RM and petroleum hydrocarbons. The catalytic mechanisms of RM for the removal of heavy hydrocarbons include (1) producing Bronsted/protonic acid in the absence of water vapor; (2) producing lattice oxygen [O] in the presence of water vapor; and (3) transforming metal oxides in RM into more active forms with a higher specific surface area. Our results suggest that the RM-assisted pyrolysis of WPCS is a cost-effective and energy-saving method that can not only promote heavy hydrocarbon removal but also relieve the environmental burden by converting industrial waste to a value-added product.