Effect of activated persulfate on the properties of contaminated soil and degradation behavior of PAHs

Sulfate radical-based advanced oxidation processes have been applied in the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated soil, during which sulfate can be activated in different ways. In this work, effects of four different ways (FeSO4, NaOH, H2O2, and Heat) activated sodium persulfate (PS) on PAHs removal and soil physicochemical properties (pH, organic matter, functional groups, surface morphology, and partial heavy metal elements) were compared, and the influencing factors and mechanism of soil PAHs removal by thermally activated PS were also studied. The results showed that at the dosage of 3% of persulfate, the removal efficiency of PAHs followed the sequences of Heat (91.4%) > FeSO4 (86.6%) > H2O2 (86.2%) > NaOH (72.9%). However, thermal activation decreased the soil pH and organic matter content more significantly than other treatments. The reaction tended to reach equilibrium at 6 h when the dosage of persulfate was 3% and the activation temperature was 60 °C, and the reaction obeyed pseudo-first-order kinetics. Through quenching experiments, it was found that the free radicals playing a dominant role in the oxidation process were sulfate radicals. Compared with pH, liquid to soil (L/S ratio) and the temperature had more significant impacts on the degradation efficiency of PAHs.