Carbon footprint of Aluminium Alloys

You probably already know that Aluminium requires a lot of energy to melt. Today’s topic is how much energy is needed to produce Aluminium and how that impacts the alloy’s carbon footprint.

Primary Aluminium is made from the ore bauxite. The largest producers of this ore are Australia, China, Guinea, and Brazil. In 2020, these five countries mined 314 million tons of bauxite, which is 80% of the world’s production this year.

The first step is to mix the Bauxit with caustic soda. After cleaning off iron and silicon oxides, aluminium oxide can be burned. This is the Bayer process. In the next step, most of the energy is needed. The Hall–Héroult process uses molten cryolite and the aluminium oxide at 950 to 1000°C. With graphite electrodes the aluminium oxides are reduced to pure aluminium. At the graphite electrode carbon dioxide is formed. So it takes about 17 kWh of energy per kilogram Aluminium.

That is a lot of energy. If you would use that energy in a hair dryer you could use it for more than 8 hours with the same energy of 1kg of Aluminium.

The origin of the energy used defines the carbon footprint of the later Aluminium product. If you use water power the contribution of the electrical power is 0.0 kg CO2 per kg Al. But there are other sources of CO2. The aluminium oxide production, the carbon emissions from the electrodes, the silicon addition to make an AlSi7 or AlSi10 alloy are the largest factors besides the energy.

Secondary alloys are made from scraps. So they do not need the go through the mining process. Therefore, they save a lot of energy. I compare several primary and secondary alloys in the video regarding their carbon footprint.

There will be an update on the cost effects of carbon emissions on the whole car body and a calculation of the CO2 tax differences for different alloys.

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