A Laboratory Investigation of the Reduction of Chromium Oxide by a Reverse-Polarity DC Plasma-Driven Molten Oxide Electrolysis Process

A method for producing chromium metal/chromium alloys using a reverse-polarity DC plasma-driven molten oxide electrolysis process was investigated. A laboratory-scale 50 kW DC plasma-crucible system was designed and built to investigate the feasibility of this process. Experiments on molten oxide electrolysis were successfully conducted to produce chromium metal from chromic oxide. Two starting slag systems, SiO₂–CaO–Al₂O₃–Cr₂O₃–Na₂O and SiO₂–CaO–Cr₂O₃–Na₂O, were used in this study. It was found that in each case chromic oxide was successfully reduced to metallic chromium. Aluminum was also reduced with the presence of alumina in the starting slag. Small amounts of carbon monoxide gas were introduced to the electrolysis system to study oxygen evolution rates from the plasma/slag interface. For the SiO₂–CaO–Al₂O₃–Cr₂O₃–Na₂O system, the oxygen evolution rate showed a maximum during the electrolysis process. For the SiO₂–CaO–Cr₂O₃–Na₂O system, the oxygen evolution rates displayed a declining trend with processing time. These two reduction behaviors were apparently controlled by different mechanisms. The significance of this process is that it might be used to produce carbon-free chromium metal/chromium alloys without carbon containing reducing agent and since no carbon based reactants are used for heating or reduction there are no carbon dioxide emissions.