Influence of typical electrolytes on electrooxidation of bio-refractory reactive dye

Electrochemical oxidation is a promising alternative for the degradation of reactive dyestuffs in residual dyeing liquid, which contains organic dyes, as well as salts such as sodium chloride and sodium sulfate. In this work, three kinds of salts, Na2SO4, NaCl and FeSO4, were selected to study the influence of electrolytes on the electrochemical oxidation of recalcitrant reactive red X-3B, using graphite cathode and dimensionally stable anode or graphite anode. The removals of color and chemical oxygen demand have been evaluated. Color removals were 99.97% and 99.84% with graphite anode and dimensionally stable anode in Na2SO4 and NaCl electrolyte. The corresponding chemical oxygen demand removals were 93.60% and 100%. In contrast, the maximum color and chemical oxygen demand removals were 97.32% and 68.76% in FeSO4 electrolyte. It was found that a combination of NaCl and FeSO4 achieved complete oxygen demand removal for both graphite anode and dimensionally stable anode. During the electrochemical oxidation process, anode and electrolyte exhibited a great effect on pH variations. Based on the cyclic voltammetry and active oxidative species investigations, the oxidation of reactive red X-3B was attributed to indirect oxidation of active chlorine and reactive oxygen species.