Reduction of ferric ions in dilute solution in electrochemical batch reactors

The performance of a semitechnical gas diffusion electrode packed bed electrode cell (GBC) for the reduction of metal ions is investigated. Reduction of Fe3+ in sulphuric acid solution is described by first order kinetics and is found to be significantly influenced by temperature, H2SO4 concentration and the inlet concentration of Fe3+. The condition of packing has a major influence on the overall conversion in the cell. It is shown that a slight decrease in the amount of bed particles can cause a significant drop in the overall degree of conversion. The mass transfer coefficient km is found to be proportional to us0.48 at low flow velocities and us0.80 at high flow velocities, where us is the mean flow velocity. Partitioning of the overall reaction rate, ko,av, into an overall mass transfer coefficient km,av and an apparent overall electrochemical rate constant, kr,av, shows that, for H2SO4 concentration less than 1M, kr,av, can be described by an empirical relationship involving the effects of the inlet Fe3+ concentration, the solution conductivity and temperature.