Effects of coexisting anions on decolorization of azo dye X-3B by ferrate(VI) and a comparative study between ferrate(VI) and potassium permanganate

In this study, the effects of anions on the decolorization reaction by potassium ferrate(VI) were investigated for the first time and a comparative investigation between potassium ferrate(VI) and potassium permanganate was carried out. Anions such as Cl − , SO 4 2 - ${\text{SO}}_4^{2-}$ , and NO 3 - ${\text{NO}}_3^{-}$ showed favorable effects on color removal, while, CO 3 2 - ${\text{CO}}_3^{2-}$ and PO 4 3 - ${\text{PO}}_4^{3-}$ displayed inhibitory effects. The effects of the oxidant concentration, initial solution pH, dye concentration and temperature on color removal were studied, and the removal efficiencies of chemical oxygen demand (COD) and total organic carbon (TOC) were also examined. The decolorizing capacity of ferrate(VI) was better than potassium permanganate. When dye concentration was 100   mg/L, oxidants were both 150   mg/L, 100% color removal was achieved by K 2 FeO 4 treatment while only 62.04% by KMnO 4 . Ferrate(VI) has stably high decolorizing efficiency up to 85% in a wide pH range from 4.0 to 9.0. However, potassium permanganate only had better efficiency under acidic solution (100% color removal at pH 3.0, while only 78.05% at pH 9.0). At the temperature of 60   °C, approximately 80% decolorizing efficiency was achieved by ferrate(VI) while potassium permanganate only 59.37%. Ferrate(VI) acquired 58.33% COD and 24.15% TOC removal while potassium permanganate only 42.86% and 9.94% respectively. The oxidizing order was that color   >   COD   >   TOC both for K 2 FeO 4 and KMnO 4 .