Abstract:The exploitation, transportation, storage and use of petroleum can lead to soil contamination by petroleum hydrocarbons (PHCs), which may cause potential risk to ecological safety and human health, so it is necessary to conduct soil remediation. In this study, PHCs in contaminated soil were oxidized by thermally activated sodium persulfate, and the effects of oxidant dosage and ultrasound combined with thermal activation on the removal efficiency of petroleum hydrocarbons were tested. Oxidation products from petroleum hydrocarbon and soil physiochemical properties after oxidation were investigated. The results showed that when the amount of sodium persulfate was 2.4 mmol/g soil, the concentration of petroleum hydrocarbons decreased from 3 800 mg/kg to 1 175 mg/kg, and the removal efficiency of petroleum hydrocarbons could reach 69%. The removal efficiency of petroleum hydrocarbons showed an upward trend with the increase of oxidant dosage. However, when the dosage of oxidant exceeded 2.4 mmol/g, the removal efficiency of petroleum hydrocarbons no longer increased. Using ultrasound combined with thermal activation, the removal efficiency of petroleum hydrocarbons could be further increased. Persulfate oxidation significantly decreased soil pH, causing soil acidification. Gas chromatography mass spectrometry (GC/MS) and fourier transform infrared spectroscopy (FTIR) analysis indicated that some alcohols and carboxylic acid compounds might be generated after the oxidation of petroleum hydrocarbons. Petroleum hydrocarbons and soil organic matter were oxidized into small polar molecules, which tended to enter the water phase, causing the total organic carbon (TOC) content in water to increase from 52.4 mg/kg to 79.8 mg/kg. In addition, scanning electron microscopy and particle size analysis showed that oxidation treatment changed soil morphology, and decreased soil particle size. Oxidation decreased soil carbon and hydrogen contents, and increased soil sulfur content. The findings of this study can provide reference for the remediation of petroleum hydrocarbon contaminated soil.