The dependence of current efficiency for ferrate(VI) synthesis on the superimposed electrolyte flow rate was determined using 14 M NaOH solution and a white cast iron electrode. The electrolyte mean velocity in the cell ranged from 0.4 to 2.9 cm s-1 and current density from 1.4 to 35.3 mA cm-2. It was found that current efficiency was influenced by electrolyte velocity only at current densities lower than 7 mA cm-2. This is explained in terms of the removal of intermediate products from the anode surface by the electrolyte convection. This factor becomes negligible at higher current densities in comparison to mass transfer induced by oxygen evolution on the anode surface.

In this paper the results of a study of ferrate(VI) formation by electrochemical oxidation of a pure and white cast iron anode are summarised. Batch - operating mode electrolysis was used to follow the influence of the anode material composition on the electrolysis current yield. The properties of the anode materials used were compared using electrochemical impedance spectroscopy. The composition of the surface oxidic layers was studied using Mossbauer spectroscopy.

In this paper the current distribution along two parallel segmented 3 dimensional solid electrodes is discussed in terms of the influence of the electrolyte flow, electrolyte temperature and electrode to membrane gap. The experimental work was based in a scale model "zero-gap" cell similar to those used in the chlor-alkali industry evolving oxygen at the working electrode and hydrogen at the counter electrode. A significant influence on the current distribution by both the working electrode and the counter electrode to membrane gap was found, the electrolyte temperature and superimposed flow rate had a lesser effect on the current distribution.

The current efficiencies for ferrate(VI) formation under conditions of bubble induced convection with different anolyte compositions were compared. Results using 14 M KOH, 5 M NaOH, 5 M LiOH and a mixture of LiOH and NaOH of constant OH− concentration of 5 M at various temperatures and current densities were compared to previous data for 14 M NaOH solution. NaOH gave the best results under all conditions studied.

The stability of electrochemically-prepared ferrate(VI) solution in 14 M NaOH solution was studied. White cast iron and pure iron were used as anode materials and the anodic current density during the ferrate(VI) preparation was varied in the range 4.4 to 42.8 mA cm(-2). The solution temperature ranged from 20 to 50 degrees C. The ferrate(VI) decomposition rate was found to depend strongly on solution temperature, anodic current density and also on the anode material composition. The decomposition rate was higher for white cast iron ie the anode material with greater iron carbide content. (C) 1999 Society of Chemical Industry.