Study on wet air oxidation of aqueous ferrous cyanide solution catalyzed by three metal salts

The catalytic wet oxidation (CWO) process with Cu²⁺, Mn²⁺, and Ce²⁺ as catalysts, respectively, was applied to investigate the degradation of ferrocyanide (Fe(CN)64-) solution. For the conversions of Fe(CN)_-6^4- during the noncatalytic wet oxidation (WO) process up to 99.9% was attained after a reaction time of 70 min. The COD removal efficiency was observed as only 38% in a noncatalytic oxidation; however, it could be enhanced to 75%, 61%, and 50% in the presence of Cu²⁺, Mn²⁺, and Ce²⁺, respectively. Both noncatalytic and catalytic wet oxidation processes of Fe(CN)_-6^4- solution were considered to be a two-step reaction at pH 9.0 and temperatures of 433-473 K. The oxidation rate was initially fast, followed by a slow step, which did obey first-order kinetics with respect to chemical oxygen demand (COD). Both the ²⁺ and Ce²⁺ catalyzed oxidation showed a significant effect on the reduction of activation energy during the first reaction of the WO runs.