and energy consumption about 15 kWh/kg (7.0 kWh/lb) of magnesium metal. Chlorine is also produced free from HC1 and water vapor. Depending upon the process used to produce anhydrous MgCL, some of the chlorine may be marketable and be a credit against the magnesium production cost. Recent developments have made possible the elimination of the semi wall; a current efficiency of 90%; and energy consumption of only 13 kWh/kg (6 kWh/lb) of magnesium metal. Silicothermic Magnesium Process Processes that can use magnesium oxide as a feed material avoid some of the complexities of preparing magnesium chloride feed where this is required. With silicon as a reducing agent MgO or calcined dolomite can be used. The batch process developed by Pidgeon involved charging ferrosilicon and calcined dolomite to a retort with cold and hot ends. Magnesium is distilled off and collected in the cold end. Only 20 to 25 kg (44 to 55 lb) were produced in each run. The modern adaptation of this process is the Magnetherm process (4). Figure 4 is a flow diagram of this process and Fig. 5 is a drawing of the production equipment. Heating is by means of electrical conduction through the slag resistance. The slag is composed of a mixture of CaO/SiO2/Al2O3. The system is evacuated and magnesium distills over into a condenser and collector.
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