Mechanistic insights into the activation of nano calcium peroxide by pyrite coupled with citric acid for efficient naphthalene degradation: Performance and kinetics.

• nCP/FeS 2 /CA system could degrade over 90% NAP at a wide pH range of 3–9. • Reductive sulfur species and citric acid played a vital role in Fe(II) regeneration. • nCP/FeS 2 /CA system achieved over 90% of NAP removal in various water matrixes. • Mechanisms of NAP degradation in nCP/FeS 2 /CA system were explored in detail. • NAP degradation intermediates were successfully detoxified. In this research, pyrite was applied in synergy with citric acid for the activation of homemade nano-calcium peroxide to degrade naphthalene in aqueous solution. Results showed that over 90% of naphthalene could be removed within 180 min at a pH range of 3–9 due to the proton-releasing ability of pyrite. Hydroxyl radical, alkyl radical, and singlet oxygen were all detected by electron paramagnetic resonance spectra, with hydroxyl radical playing a dominant role in naphthalene degradation. The nano-calcium peroxide was mainly activated by Fe(II) leached from pyrite in homogeneous ways and the vital role of Fe(III) was also revealed. The superior naphthalene degradation in this system was attributed to the excellent electron-donating capacity of reductive sulfur species in Fe(II)/Fe(III) cycle and the increased concentration of available iron species by the chelating effect of citric acid. Meanwhile, the system showed high tolerance to complex water matrixes and excellent degradation performance for other polycyclic aromatic hydrocarbons and chlorinated olefins. In addition, the naphthalene degradation pathways and the toxicity of detected intermediates were investigated. This research revealed the mechanism of nano-calcium peroxide activation by pyrite coupled with citric acid and demonstrated the great application potential of this system in the treatment of polluted groundwater. [ABSTRACT FROM AUTHOR]