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In this study, the kinetics of arsenite (As(III)) removal in a ferrihydrite/oxalate system under irradiation was investigated, and the effects of pH, ferrihydrite dosage, As(III) initial concentration, and oxalate concentration...

The decolorization of azo dye Orange II using a UVA-Fe3+-PMS-oxalate system was studied. A series of experiments was performed to investigate the effects of several variables, including the pH, PMS dosage, Fe3+ concentration, oxalate concentration, and coexisting anions. The results revealed that a lower pH facilitated the decolorization, and relatively high decolorization efficiency (97.5%) could be achieved within 5 min at pH 3.0. The electron paramagnetic resonance (ESR) and radical quenching experiments revealed that SO4•− played a crucial role in the decolorization of Orange II (85.8%), •OH was of secondary importance (9%), and 1O2 made a small contribution to the decolorization (5.2%). Furthermore, the formation of •OH in the experimental system strongly depended on HO2•/O2•−. These reactive oxidants were able to directly attack the azo bond of the luminescent group in Orange II and initiate the decolorization process. The efficient UVA-Fe3+-PMS-oxalate system showed great application potential in the treatment of wastewater contaminated by azo dyes.