Abstract
H2O2- and PDS-based reactions are two typical advanced oxidation processes (AOPs). In this paper, a comparative study of H2O2/PDS-based AOPs employing natural pyrite as a catalyst to degrade methylene blue (MB) was reported. The adaptive pH range in pyrite/PDS extended from 3 to 11, in contrast to the narrow effective pH range of 3–7 in pyrite/H2O2. As a result of the iron leaching, a synergistic effect of both homogeneous and heterogeneous catalysis was observed in pyrite/PDS, whereas heterogeneous catalytic oxidation dominated pyrite/H2O2. Furthermore, the batch results showed that the MB removal by pyrite/PDS was highly dependent on chemical conditions (e.g., pH, pyrite and PDS concentration, temperature). Powerful SO4•− was generated by pyrite rapidly under acidic or weakly acidic conditions, while SO4•− and PDS were assumed by OH− under alkaline condition. The lower pyrite loading (from 0.1 to 0.5 g/L) was affected the removal efficiency obviously, while the scavenging of SO4•− did not seem to be remarkable with the excessive amounts of pyrite (>0.5 g/L). Excessive amounts of PDS (>2 mmol/L) might negatively affect the pyrite/PDS system. The reaction temperature that increased from 20 to 40 °C had a positive effect on the degradation of MB. SEM and XRD showed that the passivation of catalyst did not occur due to the strong acid-production ability of pyrite/PDS, inhibiting the formation of Fe-oxide covering the pyrite surface.
Highlights
Many industries discharge organic dyes into the natural environment during synthesis and processing [1,2,3]
Performance of methylene blue (MB) degradation in pyrite/H2O2 and pyrite/PDS system were both obtained under 0.5 g/L pyrite, 2 mmol/L oxidant and different desired initial pH
The results showed that the removal efficiency between the pyrite/PDS and the pyrite/H2O2 (Figure 1a)
Summary
Many industries discharge organic dyes into the natural environment during synthesis and processing [1,2,3]. As one kind of dyes, methylene blue (MB) is widely used in industrial processes, such as textiles, printing, paper, pharmaceuticals, and cosmetics processing [4]. MB is toxic, carcinogenic, and non-biodegradable, which can cause a serious threat to environmental safety and human health [5]. This kind of pollutant has remarkable antibiotic effects on microorganisms in traditional biological treatment processes. Among them, advanced oxidation processes (AOPs) have shown great potential in advanced treatment due to the high removal efficiency of refractory compounds [10,11,12]. As one kind of AOP, the Fenton process has been proved to be feasible because of its high efficiency, simple operation, and low cost [13,14,15]
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