AN INVESTIGATION OF ANODES FOR THE OXIDATION OF MANGANATE (VI) TO MANGANATE (VII)

The mechanism and kinetics of the MnO4-/MnO4(2-) couple at vitreous carbon and nickel electrodes in 2.5 mol dm-3 potassium hydroxide has been investigated with a view to defining improved conditions for the oxidation of manganate (VI) to manganate (VII). It is shown that at a vitreous carbon electrode, the couple is essentially reversible while at nickel the mechanism is more complex, involving reactions of the surface nickel oxides. With 0.5 mol dm-3 manganate (VI) at 323 K, the limiting current densities for the oxidation were 190 and 90 mA cm-2 at rotating carbon and nickel disc anodes respectively. Good current efficiencies for the formation of manganate (VII) could be achieved at both anodes using current densities well above those currently used in the industrial process. It was, however, found that at least the grade of vitreous carbon used in this work, underwent corrosion during the electrolyses.