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Direct iron production at molten metal state from iron oxides by the sole application of electrical energy represents a possible route to decarbonize steel industry. Although chemically simple, this reaction is difficult to implement due to the problem of the multiple valence states of iron and to an operating temperature above 1811 K. Thermal, chemical, and electrical conditions have been identified based on thermodynamic considerations to carry out this reaction in a laboratory device. Experiments were undertaken to determine the contribution of the thermal level to the decomposition of iron oxide and to estimate the electronic current resulting from iron multiple valence states. The production of liquid iron was obtained resulting in recoverable samples produced at liquid state and from a faradaic process checked in real time by its accompanying anodic oxygen evolution. Graphical AbstractKeywords Molten oxide electrolysis · Metal extraction · Oxide melts · Electrochemical engineering · High-temperature processing

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Chromium oxide solubility was measured in soda-lime-silicate melts using a thermochemical reactor allowing an independent control of temperature, glass composition, and oxygen fugacity in a closed system. This investigation performed in the ternary Na 2 O-CaO-xSiO 2 (NCS) system showed that the physicochemical and thermochemical models used for chromium chemistry description in binary melts are applicable in the ternary system. The presence of Cr(II), Cr(III), and Cr(VI) has been evidenced and their respective contributions in the total chromium content dissolved in the melt were determined. A new approach based on optical basicity allowed the quantification of the basicity of the melt and consequently the free oxygen ions activity (aO 2À ). The treatment of the obtained results led to the determination of thermodynamical properties of the system. The standard enthalpies and entropies corresponding to the oxidation and reduction reactions were determined. J. Smialek-contributing editorThis work was financially supported by the ANR through the Actimelt project.

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