ENERGY CONSUMED IN MAGNESIUM PRODUCTION The standard free energy of formation of MgO is -136.17 kcal/mole (20.1 x 10fi Btu/Ston Mg)* corresponding to 2.95 V. Standard enthalpy of formation is —143.84 kcal/mole (21.3 x IO6 Btu/Ston Mg). Thus, the reduction of MgO carried out at the theoretical potential is endothermic and 7.67 kcal/mole of thermal energy must be supplied to maintain a constant temperature. The standard free energy of formation of MgCl2 is —143.77 kcal/mole or 5.92 x 106 kcal/Mton* (21.3 x 10“ Btu/Ston) Mg corresponding to 3.12 V. If power conversion losses are 10% and the fossil energy requirement for electrical production is 2646 kcal (10,500 Btu)/kWh, the minimum electrical power for reduction at 100% current efficiency is 7639 kWh/Mton (6930 kWh/Ston) Mg or 20.21 x 106 kcal/Mton (72.76 x 106 Btu/Ston) Mg. The commerial production of primary magnesium by current technology is an energy-intensive operation. Energy uses for the processes discussed are compared in Table 1. The high energy use for the Dow process is due to the additive effects of [1] the need for external heating of the cells, [2] the high energy needed for dehydrating *Ston=standard ton; Mton=metric ton.
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