Inert Anodes-the Blind Alley to Environmental Friendliness?

The introduction of inert anodes in alumina reduction cells may bring about some advantages, but also a number of serious drawbacks. In view of the developments in the Hall-Heroult process during the last decades, it was considered desirable to make a critical evaluation of the inert anode concept as compared to state-of-the-art electrolysis cells. It was found that the DC energy consumption will be about 3 kWh/kg Al higher with inert anodes, partly because the 1 V higher isothermal cell voltage cannot be fully compensated, but mainly because a cell with inert anodes requires similar heat loss as a cell with carbon anodes. Consequently; the total carbon dioxide footprint will be higher with inert anodes when the power is generated in a coal fired plant, while there is not much difference if the power comes from a gas fired plant. The full carbon dioxide reduction potential with inert anodes can only be realized when using renewable energy sources. However, a Hall-Heroult plant with carbon capture and sequestration will still require less electric power than a plant with inert anodes.