Strategy of periodic reverse current electrolysis to synthesize Ferrate(VI): Enhanced yield and removal of sulfachloropyridazine

A strategy of periodic reverse current (PRC) electrolysis in the electrochemical synthesis of ferrate(VI) (FeVIO42-) was developed to alleviate the problem of anode passivation to increase the yield. The use of a cyclic reverse controller in the PRC electrolysis improved the space–time yield of ferrate(VI), demonstrated by carrying out experiments under different polarity switching frequencies (23.1 – 163.6 times per hour), electrolyte flow rates (20–60 rad), and electrolyte concentrations (8–16 mol/L NaOH). At a switching frequency of 112.5 times per hour in 12 mol/L NaOH at an electrolyte flow rate of 60 rad, the available current density increased from 56.6 mA/cm2 (DC electrolysis alone) to 73.2 mA/cm2 (cyclic reverse current electrolysis), and the concentration of ferrate(VI) increased from 0.16 mol/L to 0.28 mol/L. The formation rate of ferrate(VI) under the non-passivated state of the electrode was established. The comparison of the experimentally obtained ferrate(VI) concentrations with the expected levels from the rate equation allows the estimation of the degree of passivation of the electrode which aids in minimizing passivation of the anode in the long-term production of high yield ferrate(VI). The prepared ferrate(VI) successfully removed sulfachloropyridazine (SCP), a sulfonamide antibiotic, in water.