Enhanced degradation of chloramphenicol at alkaline conditions by S(-II) assisted heterogeneous Fenton-like reactions using pyrite

The Fenton-like reactions catalyzed by pyrite can efficiently degrade organic contaminants by oxidation process. When chloramphenicol (CAP) was exposed to the pyrite-H₂O₂ system, the CAP removal rate rapidly reached 100% however slowed to a halt at alkaline conditions. Results indicated that by adding S(-II) in pyrite-H₂O₂ system improved the oxidation efficiency of CAP at alkaline conditions. The transformation of S₂^2- and S_n^2- observed by X-ray photoelectron spectroscopy (XPS), confirmed that amorphous iron polysulfide (FeS_n) was freshly generated on the pyrite surface. The availability of S(-II) promoted the generation of FeS_n. Besides, S(-II) played a role in accelerating the Fe(III)/Fe(II) cycles. The potential of S(-II) activating H₂O₂ to generate hydroxyl radicals (OH), which was confirmed by electron spin resonance (ESR) spectroscopy, quenching experiments, and trapping experiments, have supported the proposed mechanisms. This study came up with an efficient way of enhancing Fenton-like reactions by pyrite catalyzed at alkaline conditions, by adding S(-II) in the system. The new findings have implications for sulfide minerals, their interactions with pollutants, and the transformation products of sulfur in systems where Fe species are also present.