Comparison of the Life Cycle Analysis of inert electrodes and the Hall-Heroult process in aluminum production

Comparison of the Life Cycle Analysis of inert electrodes and the Hall-Heroult process in aluminum production

 

Bethany Bronkema bethanyb@ru.is Guðrún Arnbjörg Sævarsdóttir gudrunsa@ru.is

David C. Finger davidf@ru.is

 

To be presented orally at EGU2023 – April 23^rd-28^th.

• Reykjavik University, School of Science and Engineering, Department of Engineering, Reykjavik, Iceland

 

The global production of pure aluminum consumes substantial amounts of energy and alone produces around 1.1 billion metric tonnes of carbon dioxide emissions (CO_{2, eq}) each year, or around two percent of global emissions. The Hall-Heroult process is currently the only industrial process for primary aluminum production, producing up to two tonnes of CO₂ per tonne of pure aluminum by electrolysis in a molten salt electrolyte using carbon anodes. However, the use of inert electrodes represents a low-carbon alternative to the Hall-Heroult process as direct emissions can be significantly reduced, lowering the CO_{2, eq} footprint and the ecotoxicity of aluminum production. However, a transition to inert anodes implies a redesign of current electrolysis cells to optimize the energy requirement of the new process. In this study, we performed a life cycle analysis to compare the ecological footprint of the aluminum production process with inert electrodes and the Hall-Heroult process. The life cycle assessment was conducted using GaBi software linked to the ecoinvent database and complemented with primary data. We calculated the ecological footprint for five scenarios: i) using inert electrodes with a 13.5 kWh per kilogram of aluminum energy requirement, ii) using a 17 kWh per kilogram of aluminum energy requirement, iii) using Icelandic grid electricity (primarily renewable hydropower), iv) using a global energy mix (primarily based on fossil energy), and v) and “best case scenario” in which a renewable source of energy is assumed for the refinement stage preceding the smelting stage. Each of these scenarios were then compared with the ecological footprint for the Hall-Heroult process using carbon anodes. The preliminary results reveal that the energy mix always has the highest impact on the ecological footprint in the earlier refinement and electrolysis stages. However, using inert electrodes in smelters powered with renewable electricity can significantly lower the carbon footprint and ecotoxicity of aluminum production.