Cyclic voltammetric curves were measured using rotating ring-disk (RRDE) and stationary platinum electrodes. A 0.03M FeO22- solution, a 0.007M FeO2- solution and a 0.003M FeO42- solution were all studied separately in a 14M NaOH solution as electrolytes. Also, the cyclic voltammetric curves for the 14M NaOH solution were measured using a platinum electrode with the surface covered by cathodically deposited iron. In the potential region from 600 to 675 mV vs. HgHgO electrode in a 14M NaOH solution, all of the above-mentioned systems exhibit a previously undescribed current plateau during the positive potential scan. Using an RRDE this plateau was identified as the oxidation of FeO2- to FeO42-. It was found that the current density of the plateau was dependent strongly on the electrolyte temperature and almost independent of the rotational speed. This indicates at least one chemical step in the mechanism of ferrate(VI) formation.