Electrowinning of Aluminum —Challenges and Possibilities for Reducing the Carbon Footprint—

Abstract

Primary aluminum is produced by the Hall-Heroult process which is based on electrolysis in molten fluoride electrolyte, Na3AlF6-AlF3, at ∼960 °C in which the raw material alumina is dissolved and decomposed into pure aluminum and CO2 gas due to the use of carbon anodes. Direct CO2 emissions are due to the anode process including perfluoro carbon (PFC) formation during anode effect. An inert anode to produce oxygen may eliminate direct CO2 emissions including PFC gases and give possibilities to improve the cell design. CO2 emissions from generation of electricity are the most important issue globally. Also the use of pure metals to produce alloys may significantly increase the carbon footprint due to the primary production of alloying elements. A new approach to produce alloys directly during electrolysis is proposed, and results from lab experiments show that this method may give significant reduction of carbon footprint for the production of aluminum alloys. Other sources of CO2 emissions are production and manufacture of alumina and carbon anodes as well as loss in current efficiency for aluminum. A new process based on aluminum chloride electrolysis and recycling of CO2 may eliminate CO2 emissions from the production process.

Keywords

• aluminum
• electrolysis
• molten salts
• carbon footprint