A Concept for Electrowinning of Aluminium Using Depolarized Gas Anodes

Aluminium is today commercially produced by the Hall-Heroult process using consumable carbon anodes. Consumable anodes have some concerns such as CO2 emission, continuous anodecathode distance adjustments and replacements of anodes. Replacing the consumable anodes with inert anodes has been a topic for many decades without commercial success so far. Using porous inert anodes where natural gas or hydrogen take place in the anode reaction has been shown in laboratory tests to reduce the anode potential and reduce the CO2 emission. However, formation of water results in evolution hydrogen fluorides which must be solved. Laboratory experiments using porous depolarized SnO2-based anodes with CH4 and H2-gases have been performed with off-gas analysis and with special attention to hydrogen fluoride evolution. Some ideas of how to deal with the additional HF evolution are presented.