INFLUENCE OF ANODE MATERIAL ON CURRENT YIELDS DURING FERRATE(VI) PRODUCTION BY ANODIC IRON DISSOLUTION .2. CURRENT EFFICIENCY DURING ANODIC-DISSOLUTION OF WHITE CAST-IRON TO FERRATE(VI) IN CONCENTRATED ALKALI HYDROXIDE SOLUTIONS

The dependence of the current efficiency for the oxidation of a white cast iron anode to ferrate(VI) ions in 14 M NaOH was measured in the r egion of bubble induced convection for the temperature range 10 to 50 degrees C. Using a white cast iron anode the highest current yield obt ained after 3 h of electrolysis was 55% at a current density of 8 mA c m(-2) and a temperature of 20 degrees C. The anode was activated by ca thodic prepolarization. The iron concentration in low oxidation states contained in the post electrolysis solution increased with temperatur e over the whole temperature range studied. This concentration was alm ost 10 times higher than in the case of grey cast iron reported earlie r. The dependence of ferrate(VI) current yield on the hydroxide concen tration was studied in the range 5 to 16 M. The optimum concentration was found to be 14 M. The quasisteady state anodic polarization curve of white cast iron anode in the transpassive potential region was meas ured. This shows the start of oxygen evolution occurring at higher pot entials compared to grey cast iron.