Degradation of methyl orange by the Fenton-like reaction of pyrite-activated hydrogen peroxide forming the Fe(III)/Fe(II) cycle

Abstract

In this study, the typical azo dye methyl orange (MO) was degraded by pyrite (FeS₂) activated by hydrogen peroxide (H₂O₂). When [MO] = 0.1 mM, [FeS₂] = 2.0 g/L and [H₂O₂] = 22 mM, 96.4% MO was removed in 120 min and the TOC removal rate was higher than 50%. HO^• was the primary radical responsible for MO degradation. In addition, the acid condition promoted the degradation of MO in the FeS₂/H₂O₂ system. MO in tap water and river water was not effectively degraded, whereas acidification could weaken the inhibitory effect on the FeS₂/H₂O₂ system to enable the degradation of MO in tap and river water. The OD₆₀₀ indicated that the solution was environmentally friendly after the reaction, and three degradation pathways of MO were discussed. In summary, Fe(II) could be dissolved from FeS₂, which activated H₂O₂ to generate Fe(III) and HO^•. FeS₂ could reduce Fe(III) into Fe(II), thus realizing the Fe(III)/(II) cycle and efficiently activating H₂O₂ to degrade MO.