Thus, an electrolyte composition close to alumina saturation is necessary to avoid the refractory’s chemical dissolution. Other constituents of the electrolyte must be less reducible than the iron oxides.Īlumina was chosen as the refractory material for the crucible, since it is known to withstand high temperatures and a large range of P(O 2). The electrolyte must be in the liquid state in order that oxygen gas separates as bubbles by buoyancy from the electrolyte. The electrolyte composition must be compatible with the refractory material chosen for the crucible to avoid or to minimize its chemical dissolution. Thus, a silica-based electrolyte is selected to continue the formulation of an electrolyte composition.įor practical implementation of the MIDEIO route, additional properties of the electrolyte are required: It becomes apparent that the choice of a silica-based electrolyte with a low concentration of iron oxide can achieve a very low ferric ratio in the reducing conditions of the cathode. 2, showing the incorporation of the different cations in the electrolyte structure. This effect is illustrated by the two sketches in Fig. Conversely, basic conditions depolymerize the network, allowing thereby the stabilization of ferric iron by incorporation in higher proportions. Acidic conditions lower the ferric ratio due to the increasing polymerization of the network of the molten oxide. 2 in dependence of oxygen partial pressure P(O 2). To this respect, the effects of acidity by dilution of iron oxides in silica and of basicity by dilution in lime are represented on Fig. Hence, the chemical environment must be changed to decrease the ferric ratio to vanishing low values. Clearly, the thermal conditions during MIDEIO are too high to consider a ferric ratio close to unity.

Both equilibria define the electrodes reaction. It shows also that liquid iron is in equilibrium with wüstite and oxygen with magnetite at high temperatures.

The general trend is toward lowering the oxidation state of iron with lower oxygen partial pressure and with higher temperature. The phase diagram showing the domains of stability of iron oxides according to temperature and oxygen partial pressure is presented in Fig. Where Fe 2+ and Fe 3+ denote in this formula the molar concentrations. Accordingly, an experimental device is proposed to carry out the reaction at laboratory scale at temperature above 1811 K. In the present study, these shortcomings are addressed following thermodynamic considerations to identify suitable solutions for MIDEIO development. The first constraint requires highly demanding properties for the cell materials and the second causes a low faradaic yield. Indeed, iron has a significantly higher liquidus temperature and is considered unsuitable to electrochemical treatments due to the multiple valence states of its ions. However, straightforward application of the underlying concepts in terms of electrolyte composition and electrode materials can hardly be considered for iron production. Today, massive metal production following this route represents a substantial part in metal industry, e.g., the Hall–Héroult technology for aluminum metal. Recently, a comprehensive review on the prospects of electrolytic metal production was published, highlighting the process’s perspective and industrial potential. It offers attractive advantages, such as the production of liquid, chemically pure iron, and without direct emission of CO 2. The concept is inspired from developments on the production of oxygen gas on the moon and was later reconsidered for metal production. One of the possible routes is molten iron by direct electrolysis of iron ore (MIDEIO). To reduce these emissions, the ULCOS research program (2004–2012) was launched to evaluate alternative techniques to cut down this vast amount of emission of greenhouse gases. World steel industry is responsible for emissions of more than 2 billion tons of carbon dioxide per year. Climate change represents one of the biggest problems faced by carbon dioxide emitting industrial activities.

Iron cathode reaction