Promoting azo dye decomposition in natural molybdenite activated peroxymonosulfate process by low concentration of ferrous ions

In this study, low concentration of ferrous ions (Fe 2+ ) was added into natural molybdenite (MDN) activated peroxymonosulfate (PMS) process to degrade a typical azo dye, orange G (OG). It was found that the addition of Fe 2+ promoted OG degradation and simultaneously reduced the leaching of toxic Mo ions significantly. Further, the utilization efficiency of MDN was improved immensely, which was estimated from reuse experiment. MDN mainly acted as the reductant to promote cycling of Fe 3+ /Fe 2+ redox couple through reducible sulfur and Mo(IV) on its surface. Sulfate radicals (SO 4 •- ), hydroxyl radical (•OH) and singlet oxygen ( 1 O 2 ) were verified as the main reactive oxygen species responsible for OG degradation by scavenging tests and electron paramagnetic resonance. Some experiment parameters, such as MDN dosage, Fe 2+ concentration, PMS concentration, initial solution pH and coexisting anion, all affected OG degradation efficiency. In a word, this work provides a new method of enhancing PMS activation by MDN using low concentration of Fe 2+ for degradation of organic pollutants in water. MDN was applied as an efficient co-catalyst for permonosulfate activation. The sulfur element on MDN surface was able to reduce generated Fe 3+ . ⁠ , ⁠ , and were responsible for the removal of OG in MDN/Fe 2+ /PMS system. The Fe 2+ was demonstrated to promote the reusability of MDN.