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32 Xiao Y. Yan and Derek J. Fray 3.4.1.Electrolytic Removal of Magnesium from Scrap Aluminium Tiwari and Sharma examined an experimental process designed to electrolytically remove magnesium from scrap charges in secondary aluminium industry using the three-layer cell configuration consisting of scrap Al-Mg as the anode on a bottom layer, 10 wt%MgCl2- 45 wt%CaCl2-30 wt%NaCl-15 wt%KCl electrolyte as the middle layer, and deposited liquid magnesium on the top layer [14]. The graphite disk was used as the cathode for depositing the liquid magnesium. The refined aluminium contained 90 ppm Mg after the fused salt electrolysis at the current density of 0.1 A/cm2 with the cell voltage of 0.8 V. Another example is the use of the packed bed cell to remove magnesium from aluminium to produce magnesium metal, as studied by Cleland and Fray [117]. Their laboratory results show that electrochemical separation gives the same aluminium product as chlorination but, at the same time, produces magnesium of commercial value. The process is also free from pollution. The second application is to upgrade low grade secondary aluminium to pure aluminium. Overall, electrorefining would give the necessary smelter access to the wrought aluminium market. 3.4.2. Processing of Dross Yan recently studied a novel molten salt process, where Al as metal or contained in Al2O3 and AlN was recovered from Al from Al2O3 and AlN present in Al dross by electrolysis in molten salts [118]. Electrolysis experiments were carried out under argon at temperatures from 850-970 °C. In order to better understand the reduction behaviour, the as-received Al dross was simulated using simplified systems including pure Al2O3, pure AlN, an Al2O3/AlN binary mixture, and an Al2O3/AlN/Al ternary mixture. The reduction of the as-received dross was also studied experimentally. It was concluded that the value of aluminium was readily recovered from the Al2O3 present in the drosses during the electrolytic reduction processes. However, it was difficult to directly recover the aluminium from AlN in the dross. It was suggested to apply the AlN-to-Al2O3 conversion techniques to recover indirectly the aluminium value from the AlN. The reduction mechanisms are discussed based upon the present experimental observations. Flow sheets for recovering the metallic aluminium and the aluminium in the Al2O3 and AlN from aluminium dross are finally proposed. 3.4.3. Electrometallurgical Treatment of Spent Nuclear Fuels Fresh metal oxide fuel rods for the generation of electricity from nuclear energy contain uranium dioxide. After use the uranium oxides have transmuted into a large number of other oxides and these need to be separated in order to reprocess the uranium. Oxides are very difficult to refine so that the oxides are usually reduced to the metals using calcium or lithium, with the calcium or lithium oxide dissolving in their respective chlorides which also need to be treated. Electrometallurgical treatment of spent nuclear fuels using molten salts has been studied in several countries. These fuels exhibit a wide variety in their physical conditions, chemical stability, burnup, and environment, complicating their long-term storage and disposal. Such a molten salt process was initially developed by Argonne National Laboratory (ANL) suitable for conditioning U.S. Department of Energy (DOE) oxide spent fuel for long-term storage or disposal [119-122]. The ANL’s process consists of an initial reduction of oxide compounds of the actinides to a metallic form. The actinide oxides are reduced using lithium dissolved in molten LiCl at 650 °C, yielding the corresponding metals and Li2O. The metallic product from the reduction step becomes the feed material for the second stage of the process, knownPDF Image | Molten salt electrolysis for sustainable metals extraction
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