Decarbonizing Aluminum

Heat decarbonization can address emissions from refining

While refining only produces about a sixth of the total primary aluminum production emissions, we should not ignore this step when it comes to decarbonization. Refining requires first extracting aluminum hydroxide through the Bayer process and then turning that into alumina through calcination. For the lower-temperature Bayer process, fossil fuel combustion for steam production can be replaced with mechanical vapor recompression (MVR) or electric boilers . MVR uses electricity to power a series of compressors to efficiently increase the temperature and pressure of waste steam. For the higher-temperature Bayer process (325 to 400 degrees Celsius), electric boilers can be used. Neither MVR nor electric boilers for the Bayer process have been proven at commercial scale but are expected for commercial scale operation around 2030. The second step, calcination, which requires 1,000 degrees Celsius heat, can be decarbonized through electrification or green hydrogen combustion.

Improved secondary aluminum circularity can contribute to overall aluminum decarbonization

Secondary, or recycled, aluminum requires just 5 percent of the energy needed for primary aluminum production, so fulfilling some future demand with secondary aluminum will support overall aluminum decarbonization. However, a large amount of secondary aluminum ends up in landfills rather than being recycled. Increasing the amount of aluminum that is recycled and recirculated is key to leveraging secondary aluminum as a decarbonization solution.

Expanding recycling infrastructure and increasing monetary incentives for recycling can improve postconsumer aluminum scrap collection rates. Better sorting and purification methods will be needed to yield higher-quality secondary aluminum that can be used in a wider range of applications.

Additionally, centralizing secondary aluminum production can drive efficiency and quality gains. Mini mills are small aluminum mills that take aluminum scraps to be sorted, melted, and made into products, all in one place. With all processes occurring in one facility, the multiple heating and cooling steps required in the typically decentralized process can be eliminated, resulting in energy, cost, and emissions savings. More control over each step of the process can also lead to better-quality secondary aluminum.

Decarbonizing aluminum is necessary to meet climate targets, and supportive domestic policies will be needed

Aluminum is, ironically, a carbon-intensive material whose increased production is necessary for the clean energy transition. To maximize aluminum's climate benefit, primary aluminum production must be decarbonized by addressing electricity, process, and heating emissions. Simultaneously, secondary aluminum recycling must be improved by diverting more of this material away from landfills, alongside better sorting and purification techniques. The U.S. Department of Energy estimates that decarbonizing U.S. aluminum could require $10 to $15 billion in capital investment through 2050. However, this investment is necessary to ensure we reach our clean energy goals. With the right investments and policies, aluminum decarbonization is achievable.

This white paper provides policymakers and advocates with options and pathways for aluminum decarbonization.