An exploratory study of the solar thermal electrolytic production of Mg from MgO

The electrolytic production of Mg from MgO was experimentally and theoretically investigated near 1550 K. The experimental work was carried out in a SiC electrolytic cell housed in a 10 kW solar receiver that was located at the focal point of a concentrating solar furnace. The oxide was dissolved in either CaF2 or MgF2. The cathode was Mo and the anode was either Pt or Cgraphite. Mg evolved as a gas, was quenched on cooling coils at the exit of the reactor and was collected for analysis. A thermodynamic cycle study indicates that the ideal thermal efficiency for the solar process is 35 percent for an inert anode and 39 percent for a carbon anode. Experimental results from both current-cell potential traces and X-ray diffraction verify the successful electrolysis of MgO and the production of Mg. The experimental decomposition potential of the oxide was near the expected thermodynamic value. As expected, the experimental decomposition potential was reduced when carbon replaced the inert anode. In the experiment with Pt as the anode and MgF2 as the solvent, a current efficiency of 14 percent was measured.

► We present for the first time theoretical and experimental work that explores the solar thermal electrolysis of MgO.
► The measured decomposition potentials at 1550 K were within 10% of the theoretical values.
► To our knowledge we are the first to report that we recovered Mg from MgO with any solar energy process.