The current yield during the electrochemical production of ferrate(VI) in a batch cell was measured using grey and white cast iron as working electrode materials. Sinusoidal alternating current superimposed on the direct current with a frequency varying in the range 0.1 mHz to 5 kHz was used. The amplitude (peak to peak) of the alternating current component varied from 39.8 to 91.1 mA cm(-2) in the case of grey cast iron and 37.0 to 86.0 mA cm(-2) in the case of white cast iron. The direct current density was maintained at a constant value of 16.0 mA cm(-2) in both cases. A 14 M NaOH solution was used as electrolyte and the temperature range of 10-50 degrees C was studied. The current yield for ferrate(VI) synthesis exhibited a maximum at frequencies varying from 0.5 mHz to 0.5 Hz and 0.5 to 5 Hz depending on the alternating current amplitude for the grey and white cast iron electrode, respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.