Trends and Challenges for Electrowinning of Aluminium and Magnesium from Molten Salt Electrolytes

Abstract

Modern aluminium producing cells are operating at ~955–965 °C. The current efficiency with respect to aluminium can be as high as 96% and the corresponding energy consumption may be ~13 kWh/kg Al and higher in cells running at ~300 kA or higher. The current density is ~0.9 A/cm2. Developing inert anodes for oxygen evolution and measures to eliminate PFC emissions are important research topics. The role of impurities is also an important issue. Today, magnesium is mainly produced by the Pidgeon process, which involves the reduction of MgO by silicon in the form of ferrosilicon. The thermal process is presently more economic but electrowinning in molten chlorides with MgCl2 feedstock may be more sustainable and may make a comeback. However, electrolysis is still important for producing magnesium in the Kroll process for titanium production. The presence of moisture will affect the collection of produced Mg droplets and the consumption of graphite anodes.