Degradation of methyl orange by pyrite activated persulfate oxidation: mechanism, pathway and influences of water substrates

Degradation mechanism of methyl orange (MO), a typical azo dye, with pyrite (FeS ) activated persulfate (PS) was explored. The results showed that when the initial concentration of MO was 0.1 mM, FeS was 1.6 g/L and PS was 1.0 mM, the removal rate of MO could reach 92.9% in 150 min, and the removal rate of total organic carbon could reach 14.1%. In addition, both pH ≤ 2 and pH ≥ 10 could have an inhibitory effect in the FeS /PS system. Furthermore, Cl and low concentrations of HCO had little effect on the degradation of MO with FeS /PS. However, H PO and high concentrations of HCO could inhibit the degradation of MO in the system. Besides, MO in river water and tap water were not degraded in FeS /PS system, but acidification (pH = 4) would greatly promote the degradation. In addition, the removal rate of MO with FeS /PS could still reach about 90% after five cycles of FeS . Furthermore, the intermediates and possible degradation pathways were speculated by LC-MS, and the degradation mechanism of MO by FeS /PS was that the cycle of Fe(III)/Fe(II) could continuously activate persulfate to produce SO . The results could provide technical support for azo dye degradation in the FeS /PS system.