Comparative study of Rhodamine B degradation by the systems pyrite/H 2 O 2 and pyrite/persulfate: Reactivity, stability, products and mechanism

This study makes a comparison between the pyrite/H2O2 and pyrite/persulfate (PS) Fenton systems to investigate the degradation of Rhodamine B (RhB). The most relevant findings revealed that a significantly negative effect of carbonate and a narrow pH range of 2–4 were found in the pyrite/H2O2 system, whereas a relatively less negative effect of carbonate and a broad pH range of 2–11 were observed in the pyrite/PS system. It was demonstrated that the pyrite catalyst in the pyrite/PS system exhibited better structural stability and showed a relatively limited loss in performance upon reuse as compared to pyrite in the pyrite/H2O2 system. Experiments with different scavengers indicated that HO radicals were the major reactive species responsible for RhB degradation by pyrite/H2O2. In this case the contribution of radical was in the order of HOHO >O2 −, whereas the SO4− radicals prevailed over HO in the pyrite/PS system. The role of O2− in the recycling of Fe(III) to Fe(II) was very important. The possible mechanism for RhB degradation by pyrite/H2O2 mainly involves the reaction of the dissolved Fe2+ released by the surface of the pyrite with added H2O2, whereas the reaction of the dissolved Fe2+ formed in the pyrite with PS triggers degradation in the pyrite/PS system. The degradation of RhB is initiated in both cases by N-de-ethylation, chromophore cleavage and ring opening processes, which leads to the production of a series of oxidation products with smaller molecular sizes. The pyrite/PS system is here proven to be a superior heterogeneous Fenton-like oxidant process for the removal of dyes from wastewater.