Oxidation of Azo Dyes by H2O2 in Presence of Natural Pyrite

Pyrite, FeS2, is the most common sulfide mineral. The aim of this work was to assess the oxidative ability of H2O2 in presence of natural pyrite by employing reactive black 5, acid red GR, and cationic red X-GRL as model pollutants. The effects of H2O2 dosage, pyrite loading, and initial pH on reaction were investigated. The results reveal that natural pyrite-promoted H2O2 has a great activity in the decoloration of azo dyes. About 85 % of reactive black 5 and acid red GR can be removed within 10 min when 0.3 mM H2O2 and 0.3 g/L pyrite are used with initial pH values ranging from 6.32 to 6.96. The discoloration efficiencies are demonstrated to be less sensitive to the initial solution pH value. Approximately 90 % of discoloration for reactive black 5 and acid red GR can be achieved when initial pH value ranges from 2 to 10. Ion leaching experiments show that high levels of ferrous iron and sulfate can be detected when natural pyrite is added to dye solution alone. To gain an understanding of the reaction mechanism and the role of natural pyrite takes in these processes, techniques including scanning electron microscope, X-ray diffraction, and X-ray photoelectron were employed to characterize the solid sample and ion leaching experiments were also carried out. Results indicate that the determined high levels of ions have resulted from the dissolution of FeSO4 center dot H2O formed on the surface of pyrite and the homogeneous Fenton reaction initiated by ferrous iron in presence of H2O2 is mainly responsible for the observed fast color removal rate.