Degradation of Azo Dyes Using Natural Pyrite as Fenton-Like Reaction Catalyst

Abstract

The degradation of azo dyes by pyrite-Fenton system was studied in this work. In the pyrite-Fenton system, Fe²⁺ comes from the reaction of H₂O with pyrite, and then Fe²⁺ reacts with H₂O₂ in the solution. The decolorization of the dye was significantly inhibited by the addition of hydroxyl radical scavenger (ethanol), but not by the addition of superoxide ion scavenger (chloroform), indicating that the presence of hydroxyl radical was the main reason for the decolorization of dye. Three azo dyes (acid red G [ARG], methyl orange, and congo red) were degraded by pyrite-Fenton system and showed good decolorization and mineralization efficiency, which proved that the pyrite-Fenton system has a good effect in degradation of azo dyes. The degradation kinetics of the above three dyes in the pyrite-Fenton system are highly consistent with the pseudo-first-order reaction kinetic. This work explored the effects of pH, initial dye concentration, inorganic salt, pyrite, and H₂O₂ dosage on the degradation efficiency of pyrite-Fenton. The dosage of pyrite and H₂O₂ was studied by central composite design in response surface method. Under optimized conditions, the ARG decolorization rate reached 99.07% after 60 min. To explore the reusability of pyrite as Fenton reaction catalyst, five cycles of experiments were carried out, which proved that pyrite has high reusability.