The Influence of Iron Concentration on the Anodic Charge Transfer in Molten Oxide Electrolysis

Abstract

The anodic charge transfer during the production of iron by Molten Oxide Electrolysis in an Al 2 O 3 -MgO-SiO 2 electrolyte has been investigated at 1793 K in dependence of the iron oxide concentration. Experiments were performed at laboratory scale using an asymmetric electrode configuration. The kinetic relation to the cell voltage was analyzed by a stepped linear scan voltammetry at various iron oxide concentrations up to 15 wt%. Complementary gas analysis allowed the derivation of the oxygen production yield. The obtained results show an electronic contribution to the overall conduction. This contribution diminishes in proportion with increasing iron oxide concentration. Charge transfer at the anode is accomplished by the oxidation of ferrous iron ions and of oxide anions. Conditions for the electrochemical charge transfer to occur solely by the oxidation of oxide anions exist for a limited cell voltage range at iron oxide concentrations of less than 10 wt%. For these concentrations a mass transfer limitation of oxide anions was detected with increasing cell voltage. However, a limit of the total current is absent as ferrous iron participates to the anode charge transfer at cell voltages above the mass transfer limitation of oxide ions.

Ultra‐High Temperature Molten Oxide Electrochemistry

“…The same reduction mechanism was also confirmed in molten SiO 2 À CaOÀ MgOÀ Al 2 O 3 À NaF by Zhang et al [119] (Figure 7c). Wiencke et al [120] investigated the reduction kinetics of Fe 3 O 4 . The results indicated that diffusion was not a limiting step, even at a Fe 3 O 4 content below 15 wt %.…”

Implications of Direct Use of Slag from Ironmaking Processes as Molten Oxide Electrolyte

“…Oxide melts are mixed conductors [30,46] so, to maximize metal production, the fraction of charge carried by electrons is also important. On one side, electronic conduction wastes energy as the movement of electrons is not linked to the production of metal and lowers the faradaic efficiency [47]. However, some electronic conduction is beneficial for Joule heating to satisfy the thermal needs of the process [48].…”