Pyrolysis of heavy hydrocarbons in weathered petroleum-contaminated soil enhanced with inexpensive additives at low temperatures

Abstract Pyrolysis is a promising technology for the remediation of soil contaminated with petroleum hydrocarbons. However, for weathered petroleum-contaminated soil (WPCS) with massive recalcitrant heavy hydrocarbons, pyrolysis still has the drawback of high energy consumption. To reduce energy consumption, commonly used inexpensive additives, including Fe2O3, Al2O3, K2CO3, CaO, HZSM-5, and red mud, were selected to strengthen the pyrolysis of heavy hydrocarbons in WPCS. The removal of the total petroleum hydrocarbon (TPH) content from WPCS increased as the dosage of additives increased from 1% to 5% at 400 °C for 30 min, and increased slightly or even decreased when the additive dosage was further increased to 10%. The reduction rates of the TPH content in soil treated with 5% additives of K2CO3, CaO, Fe2O3, red mud, HZSM-5, and Al2O3 increased by 26.16%, 25.65%, 25.53%, 23.93%, 23.15%, and 20.75%, respectively. Among these additives, CaO exhibited the best performance for the removal of aromatics (73.00%) and asphaltenes (72.44%), while Fe2O3 exhibited the best performance for the removal of resins (52.25%). The removal mechanisms of heavy hydrocarbons using additives during WPCS pyrolysis were proposed based on a combination of thermogravimetric analysis and the iso-conversional Flynn–Wall–Ozawa method. The reduction in the activation energy when additives were included during WPCS pyrolysis was closely related to whether the additives participated in the reaction and to the type of pyrolysis product. The soil characterization results demonstrated that the investigated additives would not severely impact further soil cultivation. The additive-assisted pyrolysis of WPCS is expected to reduce the required energy input by 34.71% compared to the traditional pyrolysis method, thus providing an energy-efficient and cost-effective method for treating petroleum-contaminated soil in future engineering applications.