Liquid-metal-electrode-assisted electrolysis for the production of sodium and magnesium
Lei Guo, Huayi Yin, Wenmiao Li, Shiyu Wang, Kaifa Du, Hao Shi, Xu Wang, Dihua Wang
Abstract
Sodium (Na) and magnesium (Mg) are becoming important for making energy-storage batteries and structural materials. Herein, we develop a liquid-metal-electrode-assisted electrolysis route to producing Na and Mg with low-carbon emissions and no chlorine gas evolution. The clean production stems from the choice of a molten NaCl-Na2CO3 electrolyte to prevent chlorine gas evolution, an inert nickel-based anode to produce oxygen, and a liquid metal cathode to make the cathodic product sit at the bottom of the electrolytic cell. We achieve a current efficiency of >90% for the electrolytic production of liquid Na-Sn alloy. Later, Mg-Sn alloy is prepared using the obtained Na-Sn alloy to displace Mg from molten NaCl-MgCl2 with a displacement efficiency of >96%. Further, Na and Mg are separated from the electrolytic Na-Sn and displaced Mg-Sn alloys by vacuum distillation with a recovery rate of >92% and Sn can be reused. Using this electrolysis-displacement-distillation (EDD) approach, we prepare Mg from seawater. The CO2 emission of the EDD approach is ∼20.6 kg CO2 per kg Mg, which is less than that of the Australian Magnesium (AM) electrolysis process (∼25.0 kg CO2 per kg Mg) and less than half that of the Pidgeon process (∼45.2 kg CO2 per kg Mg).