Effective decolorization of polyazo direct dye Sirius Red F3B using persulfate activated with Fe0 aggregate

Fe-0 aggregate was used to activate persulfate (PS) in an oxidizing PS/Fe-0 system for decolorization of the polyazo dye Sirius Red F3B (SRF3B, Direct red 80). Decolorization was affected by pH, temperature, and persulfate and Fe-0 dosages. Low PS dosages hindered decolorization; a two-stage oxidation process (a slow heterogeneous reaction on the Fe-0 surface and a fast homogeneous reaction in solution) was observed. SRF3B depletion during the slow and fast stages followed zero-order rate law and modified pseudo-first-order kinetics, respectively. A 95% decolorization efficiency was achieved within 10 min of treating 25 mg/L SRF3B (American Dye Manufactures Institute color 8276) with PS/Fe-0; the four azo links of SRF3B were completely broken down. Through the analysis of gas chromatography-mass spectrometry, intermediates were identified and degradation pathways of SRF3B during PS/Fe-0 oxidative process were proposed. Activation energy of the PS/Fe-0 system was 0.636 kJ/mol, confirming decolorization as a fast reaction. Fe aggregate was reusable. Thus, the PS/Fe-0 system is fast and effective for SRF3B decolorization. (C) 2015 Elsevier B.V. All rights reserved.