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This paper reviews a clean metals, production technology that utilizes an oxygen-ion-conducting solid oxide membrane (SOM) to directly electrolyze metal oxides dissolved in a non-consumable molten salts. During the SOM electrolysis process, the desired metal such as magnesium, aluminum, silicon, or a rare earth is produced at the cathode while pure oxygen gas evolves at the anode. Compared with current state-of-the-art metal production processes, such as a chloride-based electrolysis process for magnesium production and the Hall-Héroult process for smelting aluminum, the SOM process brings various advantages such as simplified design, lower cost, lower energy use, and zero emissions. It provides a general route for producing various metals and has great potential to replace current metals, production processes. This paper examines the past and present progress of the SOM process, the challenges faced in commercialization, and the directions for future work.

This paper reports a solid oxide membrane (SOM) electrolysis process using an LSM (La 0.8 Sr 0.2 MnO 3-δ )-Inconel inert anode current collector and liquid silver anode for production of aluminum and oxygen from aluminum oxide dissolved in a pre-selected molten oxy-fluoride flux containing Ca, Mg, Al and Y at 1473K (1200 • C). The electrochemical behavior of the SOM cell was characterized by various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scan and potentiostatic electrolysis. Based on the electrochemical measurement results, an equivalent circuit model of the SOM electrolysis process is presented. A polarization model for aluminum and oxygen production was developed and the polarization losses in the cell were analyzed according to the equivalent circuit. Based on the polarization model analysis, potential approaches to improve the cell performance are also discussed. The aluminum produced and the yttria stabilized zirconia (YSZ) membrane were characterized with scanning electron microscope and energy-dispersive X-ray spectroscopy after the electrolysis. Aluminum is the third most abundant element in the earth's crust, and the most abundant metallic element. It is an essential material in modern manufacturing. It is known for its low density, high strength, corrosion resistance, good recyclability and high electrical and thermal conductivities. Aluminum is also often alloyed with other elements such as magnesium, silicon, tin and zinc in order to improve its properties. Aluminum and its alloys have a wide range of applications making them the second most used industrial metal for the past fifty years. Global aluminum production has been growing at a rate of 5% annually for the past five years.1 Demand for aluminum will continue to grow, mainly due to its increasing use in the transportation sector as a light-weight structural material.The aluminum smelting process was invented in 1886 by Charles Martin Hall and Paul L.T. Héroult (i.e. the Hall-Héroult process). It involves electrolysis of cryolite-alumina melt and even to this day the process used has fundamentally remained the same. The average energy intensity of the process is 14.29 kWh/(kg Al), 2 while its theoretical minimum energy requirement is 5.99 kWh/(kg Al).3 The process is energy-intensive and has low energy efficiency. The use of graphite anode, the electricity input, and the anode effect of the process result in an average of 6.9 kg of equivalent CO 2 emission per kg of Al produced.3 The market potential of aluminum and the environmental impact of the current aluminum production process justify research and development of alternative electrolytic processes for aluminum production that can both reduce the cost and eliminate adverse environmental impacts.Solid oxide membrane (SOM) electrolysis is a novel metals extraction technique that is being developed for the production of several energy-intensive metals, semiconductors or alloys, such as Mg, Ti, Ta, Yb, Si, CeNi 5 and Ti-Fe alloy. [4][5][6][7]...

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