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Molten Salt Electrolysis for Sustainable Metals Extraction and Materials Processing 29 electronic conductivity are main problems with the composite anode reduction technology for production of aluminium and magnesium. It may be possible to electrowin magnesium in a cell where MgO is actually reacted with carbon and chlorine in the anode section of the cell to form MgCl2 [106]. The evolved chlorine from the anode reacts exothermically with MgO and carbon to give MgCl2: MgO + C + Cl2(g) = MgCl2 + CO(g) (31) 2MgO + C + 2Cl2(g) = 2MgCl2 + CO2(g) (32) The U.S. Bureau of Mines reported on electrowinning magnesium into liquid lead and aluminium cathodes from melts containing a slurry of MgO and carbon particles [107]. They demonstrated that 98-995 of the chlorine reacted giving a gaseous product of 80-90 % CO2, 8- 15 % CO and a few percent chlorine. Cathode efficiencies were around 90 % but a major difficulty was found to be a build up of sludge consisting of MgO and Carbon, on top of the liquid metal cathode. 3.2.2. The Composite Anode Process for Titanium More recently, in 2005, Withers and Loutfy patented thermal and electrochemical process for titanium metal production using partially reduced TixOy/C composite anodes, based on the same reduction technology for aluminium and magnesium as described above [108]. The process for producing titanium metal is recently called “MER process”, which is shown schematically in figure 10 [109]. It utilizes TiO2 as a feed and essentially involves twp steps: (i) carbothermic reduction of TiO2 to suboxides of titanium which is used in a composite anode with stoichiometric carbon and (ii) anodic dissolution of titanium from the titanium suboxides/C composite anodes into a molten salt electrolyte to electrolytically produce titanium metal at 190-1000 °C, with anode gases of CO/CO2. The electrolysis process can be performed on a continuous basis without opening the cell body. TiO2 powders are mixed with carbonaceous material and binder, moulded into electrode form and thermally treated to form a composite anode at 1200-2100 °C. The composite anode contains a partially reduced TiO2 compound as TixOy/C. Anodically ionised Ti3+ or Ti2+ ions are dissolved into the electrolyte and are cathodically deposited as solid titanium metal at the cathode. A gaseous mixture of CO and CO2 is released at the anode. The deposited titanium metal can be in the form of powder, flake or a solid deposit, depending on electrolyte compositions and electrolysis operating conditions. While impurities are reported to be low, analytical confirmation is necessary. Processing cost as well as consistent production of any particular product form remains to be determined. Deposition of solid deposits with density, uniformity and configuration suitable for mill processing needs to be confirmed. The bench scale product has been produced with oxygen levels below 500 mass ppm. More recently, Maity et al. reported their studies on electro-deposition of titanium using TiO2/C composite anode and molten aluminium cathode in an equimolar NaCl-KCl electrolyte at 800 °C [110]. The Faradic current efficiency of their process was 10-30 %.PDF Image | MOLTEN SALT ELECTROLYSIS
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