Degradation of azo dye active brilliant red X-3B by composite ferrate solution

Composite ferrate(VI) solution (CFS) with improved stability was successfully prepared in this study. The stability of Fe(VI) increased from hours for potassium ferrate at pH 9-10 to 16 d for 1 mmol L−1 Fe(VI) in CFS at 25 °C, decomposing 24%. The Fe(VI) was more stable at low concentration (1 mmol L−1) than that at high concentration (10 mmol L−1). The degradation of the azo dye reactive brilliant red X-3B (X-3B) by CFS was investigated. The results showed that pH, initial dye concentration and CFS dosage affected the degradation efficiency. For 0.08 mmol L−1 X-3B simulate wastewater, the optimal pH and CFS dosage were 8.4 and 25 mg L−1 (as K2FeO4), and about 99% X-3B was decolorized after 20 min under this conditions. The color decay was considerably faster than the decrease in COD and TOC, which was attributed to the ease of chromophore destruction. Compared with the decolorization, the removal percentage of COD and TOC were 42% and 9% after 60 min, respectively. The Fe(VI) and ClO− were contained in CFS, which have synergetic effect for the degradation of X-3B. Additionally, phthalic acid and muconic acid were identified as intermediates by GC/MS, which was in accordance with the lowered pH with the reaction time. The complete mineralization of X-3B cannot be achieved under the oxidation by CFS. And a tentative pathway for the oxidative degradation of X-3B was postulated.