The performance of three solid iron wastes (SIW-1, SIW-2 and SIW-3) was evaluated as an activator of persulfate (PS) for the degradation of methylene blue (MB). SIW-3 showed the highest performance among the three catalysts. The morphology, chemical composition and chemical structure of the three SIW were investigated using various analyses. Complete degradation of methylene blue (MB) in neutral pH was achieved after 60 min at PS concentration of 4 mM, initial MB concentration of 10 mg/L and catalyst dose of 1.0 g/100 mL using light. The degradation efficiency of MB decreased from 100% to 34.6% by increasing the initial MB concentration from 10 mg/L to 100 mg/L. The degradation of MB followed the second-order model. Scavenging experiments showed the major role of hydroxyl and sulfate radicals in the MB degradation. The performance of iron waste in the retained form was investigated and the degradation efficiencies were 96%, 91.2%, 91%, 89% and 86% in five succeeding cycles at pH 7, catalyst dose of 1 g/100 mL, initial MB concentration of 10 mg/L and PS concentration of 4 mM. Moreover, the reusability of suspended iron waste was investigated. The degradation efficiencies of methylene blue, methyl red, Congo red and acid blue-25 were 100%, 97%, 96% and 97.3%, respectively after 60 min. The degradation pathways of MB were proposed after the identification of intermediates using liquid chromatography-mass spectroscopy analysis. This study revealed that the iron waste can be efficiently employed for PS activation in the suspended and immobilized modes which reduces the total cost of the Fenton process paving the way for the large-scale application of this technique.
Keywords: Degradation; Iron waste; Operating conditions; Persulfate; Sulfate radicals.
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