Efficient transformation of diethyl phthalate using calcium peroxide activated by pyrite

Abstract

In this study, pyrite (FeS₂) was used as a novel activator of calcium peroxide (CaO₂) for the degradation of diethyl phthalate (DEP) in both aqueous solution and soil. DEP (10 mg/L) in aqueous solution was completely degraded within 5.0 min by the FeS₂ (0.30 g/L)/CaO₂ (1.0 mM) system at pH 3.5. X-ray diffraction (XRD), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), free radical quenching, and X-ray photoelectron spectroscopy (XPS) were used to elucidate the mechanism of the catalytic decomposition of CaO₂, radical formation and DEP degradation in the presence of by pyrite. The results show that hydroxyl radicals (OH) are the dominant active species responsible for DEP degradation. Surface or lattice Fe(II) of FeS₂ readily activates H₂O₂ generated by CaO₂ decomposition to produce OH, while the reducing sulfur species of FeS₂ promotes the regeneration of surface of Fe(II) that catalyzes the production of additional OH, leading to the efficiently oxidative degradation of DEP. Although high concentration of common anions, such as Cl^-, NO₃^-, SO₄^2-, and HCO₃^-, exert inhibitory effects on DEP degradation by pyrite/CaO₂, the reaction system can still efficiently degrade DEP in realistic soil. It was observed that 78% of DEP (25 mg kg^-1) was degraded by 2.5% CaO₂ (w/w) and 0.5% FeS₂ (w/w) within 24 h. These results provide new insight into the mechanistic processes of CaO₂ activation and OH formation by the novel FeS₂ catalyst, demonstrating a promising alternative to the traditional H₂O₂-base Fenton process for contaminated soil remediation.

Keywords: Activation; Calcium peroxide; Hydroxyl radicals; Pyrite.