Remediation of soil contaminated with ibuprofen by persulfate activated with gallic acid and ferric iron

This study investigated the ibuprofen (IBP) degradation by persulfate (PS) activated with Fe(III) and gallic acid (GA) in the soil system. This study aimed to find an environmentally friendly method for the purification of soil organic pollutants. Results showed that the addition of GA could greatly improve the IBP oxidation efficiency due to the GA reduction effect of Fe(III) to Fe(II). The optimum dosage of each reagent was obtained with Fe(III):GA:PS = 1:1:10 to achieve 80.7% deterioration of IBP in 2 h when the initial IBP concentration was 48.4 μmol kg⁻¹. Quenching experiments suggested that hydroxyl radical (HO^[rad]), sulfate radical (SO₄^[rad]−), and superoxide anion radicals (O₂^[rad]−) played important roles in the oxidation of IBP, and the contribution ratios were 28.5%, 25.5% and 44.4% respectively. The reaction started from the complexing between Fe(III) and GA. The Fe(III)-GA complex was transferred to quinone substance and Fe(II). PS was efficiently activated by Fe(II), and radicals were produced. The second order rate constants of the reactions between HO^[rad]/SO₄^[rad]−and GA/IBP were determined with laser flash photolysis experiments (k_{HO[rad], GA} = 2.80 × 10¹⁰ M⁻¹ s⁻¹, k_{SO4[rad]−, GA} = 2.01 × 10⁹ M⁻¹ s⁻¹, and k_HO[rad],IBP = 3.11 × 10⁹ M⁻¹ s⁻¹, k_{SO4[rad]−,IBP} = 1.97 × 10⁹ M⁻¹ s⁻¹). The soil organic matter (SOM) slightly decreased by 4.46%, and pH was changed from 7.8 to 6.2 after 240 min of reaction. The introduction of GA significantly increased the dissolved organic carbon (DOC), while the oxidation of the Fe(III)/GA/PS system decreased by 5.85% of the DOC content. Four chief byproducts were identified with GC–MS, and a potential degradation mechanism of IBP was proposed.