Process optimization of modified sodium persulfate for the remediation of total petroleum hydrocarbon contaminated soil.

Petroleum hydrocarbon (TPH) contamination at industrial sites poses severe ecological and health risks to humans. However, conventional persulfate oxidation suffers from low efficiency and high oxidant demand requirements. To address this limitation, we employed citric acid-FeSO₄-modified sodium persulfate (FNS) for soil remediation.In this study, the petroleum hydrocarbon (TPH)-contaminated soil of a chemically contaminated site was used as the test object, and sodium persulfate modified by citric acid-FeSO4 (FNS) was selected as the oxidant. Based on laboratory tests, quantifying TPH degradation efficiency, soil pH variation, and sulfate leaching concentrations, the effects of oxidant dosage, oxidant dosage times, and CaO dosage on the remediation effect of petroleum hydrocarbon-contaminated soil were systematically investigated. The results demonstrated that citric acicd-FeSO4 significantly enhanced sodium persulfate activation (p < 0.01), achieving within 28 days a 36% higher TPH degradation efficiency than unmodified persulfate at 2% dosage. This modification amplified oxidation intensity and efficiency by up to 2.3-fold over the remediation period.For the contaminated soil with a petroleum hydrocarbon content of 16524 mg/kg, after a 28-day remediation period,FNS amendment achieved significant TPH reductions of 76.9% (to 3820 mg/kg) at 4% dosage-below Class II construction land in China's soil environmental quality standard (4500 mg/kg). At a 6% dosage, after the same 28-day remediation period,reduction efficiency reached 95.5% (to 750 mg/kg) lower than the screening value of soil contamination risk for Class I construction land in China's Soil Environmental Quality Standard (826 mg/kg). The FNS agent can significantly improve the oxidation strength and efficiency of sodium persulfate, but it causes soil acidification and exceeds the SO42- leaching concentration standard, among other things. The restored soil needs to be conditioned with CaO neutralization. In addition, FNS must be applied at one time and cannot be applied separately.