Scientists from the Swiss Federal Institute of Technology in Lausanne (EPFL) together with their colleagues from Net Zero Lab are tackling a task that just recently was considered virtually impossible to achieve: completely eliminating CO₂ emissions from primary aluminum production without disrupting the existing process chain in its entirety. Aluminum production is one of the most energy- and carbon-intensive industries in the world. On average, each ton of aluminum produces 12–15 tons of CO₂ taking into account the entire production life cycle, including emissions from the operation of electrolysis cells. The process emissions from electrolysis account for a smaller portion of those: roughly 1.5 tons of CO₂ are generated during the combustion of the carbon anode, and up to 0.8 tons of CO₂ equivalent come from perfluorocarbon emissions. The primary source is the electrolysis of alumina in molten cryolite. This process chemistry has remained virtually the same since the late 19th century, making aluminum one of the most difficult materials to decarbonize.
However, the Swiss researchers have shown that the solution lies not in targeted modernization but in reconfiguring the entire energy system of an aluminum plant. In their study, they proposed redesigning the energy architecture of production facilities, from biomass gasification to CO₂ capture to integration into the municipal heating grid. Aluminum production causes emissions of up to 6–7 MWh of low- and medium-temperature heat per ton of metal, from the cooling of electrolysis cells to biomass gasification and CO₂ mineralization. In conventional practice, this heat is dissipated, but the proposed model has it being collected and forwarded to the municipal heating system or used for on-site power generation.
The researchers posit that the first technological element of this reconfiguration is the replacement of the anode in the electrolysis cell with an alternative reducing agent, such as biochar or hydrogen. Biochar is obtained through the gasification of wood waste. While its chemical properties are completely identical to those of carbon in a traditional anode, its origin is biogenic. For each ton of aluminum, roughly 0.42 tons of biochar are required, and the resulting CO₂ can be converted into stable magnesium carbonates instead of being discarded. Instead of 1.5 tons of fossil CO₂, the atmosphere receives a stream that can be reliably bound in a mineral.
The second option is hydrogen reduction of alumina, during which only water vapor is produced as a by-product. However, the effectiveness of this solution depends on the source of hydrogen. Electrolytic H₂ is too expensive and is tied to the carbon footprint of the electric industry. This is why the scientists are considering the option of producing hydrogen in the same gasification units that, under certain conditions, deliver a high proportion of H₂, completely eliminating the need for fossil fuels.
As a result, biomass gasification becomes a central element of the entire architecture. It converts waste into synthesis gas, biochar and CO₂ concentrate. Synthesis gas can replace natural gas in recycling furnaces, which typically produce a significant portion of emissions. The CO₂ stream is sent to mineralization, while biochar or hydrogen is sent to the electrolysis process.
The simulation has shown that the combination of these elements (biomass use, hydrogen reduction, CO₂ mineralization and heat recovery) can drastically alter the overall carbon balance of production. In the most efficient scenario, where hydrogen is produced from biomass and all CO₂ emissions are mineralized, the carbon footprint is negative, reaching minus 0.4–0.5 tons of CO₂ per ton of aluminum produced. This means that, in addition to emitting no carbon dioxide, the plant essentially removes some of the biogenic carbon from the atmosphere, preventing it from coming back.
