Chemical and electrochemical behaviour in molten alkali hydroxides .6. Electrochemistry of Mn(V) in acidic NaOH-KOH (49 mol%) eutectic mixture

The use of voltammetric, chronopotentiometric and chronoamperometric techniques has been discussed for the electrochemical investigation of the Mn(V) species in low (10(-2)M H2O) and high (7.3M H2O) acidic NaOH-KOH eutectic mixture. The Mn(V) solutions were prepared by dissolution of MnO2 or KMnO4. This last compound was finally chosen because the coformed O-2(-) ions were eliminated after a few hours. Most measurements were carried out at 483K. The reduction of MnO43- at a platinum electrode leads to the formation of MnO44- that is unstable because of its disproportionation into Mn2O3 and MnO43-. The formation of Mn(OH)(6)(3-). species was suggested as the dissolution of the Mn(III) oxide is improved by increase of the acidity of the melt. The diffusion coefficients of Mn(V) were determined within the temperature range 483-598K.