CURRENT EFFICIENCY DURING ANODIC-DISSOLUTION OF IRON TO FERRATE(VI) IN CONCENTRATED ALKALI HYDROXIDE SOLUTIONS

The dependence of the current efficiency for oxidation of an iron anod e to ferrate(VI) ions in 14 M NaOH was measured in the region of free convection. The highest current yield of 40% was obtained at a current density of 2.1 mA cm-2 and temperature of 30-degrees-C. The iron anod e was activated by cathodic prepolarization. The iron concentration in low oxidation states in solution was determined as 0.13 +/- 0.1 and 0 .29 +/- 0.25 g Fe dm-3 at 20 and 30-degrees-C, respectively. The stead y state anodic polarization curves of iron in the transpassive potenti al region are shifted to lower potential values with increasing NaOH c oncentration from 11 to 17 m. At 40-degrees-C all the curves show a li miting current density around 660 mV vs Hg/HgO. namely 9 and 23 mA cm- 2 at NaOH concentrations of 11 and 17 M, respectively.