January 2021 - written and researched by BEAMZ founder and director Nick Coates

First of all, I would like to say that whatever material is being used, making bikes is a good thing to do, and bikes have a very positive impact on the planet.

Also, I should declare our interest; BEAMZ believes that locally grown hardwood poles are a realistic sustainable alternative to aluminium in structural applications as demanding as bicycle frames.

The Search For Figures

I set out to find a simple authoritative web resource to indicate the CO₂ equivalent of aluminium. I found papers defining protocols of how it could be worked out, and figures relating to particular manufacturers or sectors, but with insufficient detail to validate them.

Figures readily available vary between just over 2 to 20 kg CO₂ / kg Al.

If you are concerned to minimise your carbon footprint you need to think about where the aluminium was made.

In China 88% of the electrical power is generated by burning coal, and 96% in other parts of Asia.

If the metal appears to have been made in ways which reduce the CO₂-e, how fair are the claims.

The problems are that some of the figures take account of only a part of the production process, and it was not always clear which parts had been included and which had been left out.

A further difficulty is that because aluminium smelting inevitably uses a large amount of electrical power, smelting companies, in Europe, America and Canada, who are a big customer of the power companies, buy the available hydro-power.

Smelting is often done close to sites where hydro-power is produced from water turbines, often from a river dam.

It is frequently the cheapest form of power and one which can be claimed to have a zero-carbon impact.

The amount of hydro-power available is limited because it requires suitable geographic conditions, and it often creates other social and environmental impacts.

It changes the flow of rivers altering the river environment and conditions for people and wildlife upstream and down.

Often it results in flooding of land where land-rights or sites of historic, cultural or environmental importance may exist.

Dam building can also require huge amounts of concrete and steel which have significant embodied carbon footprints.

In some cases, the hydro-electric plants have been built specifically for aluminium smelting, while in others they are part of the grid.

27.5% of the total electrical power for smelting aluminium world-wide was from renewable sources in 2019, which is 0.86% of world electrical power.

This begs the key question, is it fair to claim that using renewable electrical power for smelting causes no increase in CO2-e when it consumes limited supplies of low-cost power, causing other power requirements to have to be serviced by higher priced fossil fuels?

It should be noted that hydro-power, which can be turned up and down as required, is of particular value as back-up for other renewables which, due to their dependence on weather conditions, may not match the supply of power to the demand.

Summary of results

The results are calculated and presented in this spreadsheet and based on figures from the International Aluminium Institute. https://www.world-aluminium.org/

• The world average CO₂ Equivalent of aluminium is 12.88 kg CO₂e/kg Al.

• Total Aluminium production for 2019 to 2020 was 63,657,000 Tonnes.

• Multiplying the figures above gives 820,609,012 Tonnes of CO₂ emissions.

• World annual CO₂ emissions are about 33,000,000,000 Tonnes.

Dividing the Aluminium industry CO₂ emissions by the world figure reveals that aluminium production accounts for 2.5% of world CO₂ emissions.

The result is supported by the paper below which gives a slightly higher figure of 14.77 kg CO₂-e / kg Al, because it is based on aluminium production in China, rather than the whole world.

The paper also discloses that 40kWh of energy is required for each kg of aluminium (144,612 MJ/t) .

The paper states that production in the USA can have half the CO₂ value. This is due to the use of hydro-power and the claimed zero carbon output.

It does not make as much difference to the world figure as you might think because Chinese production is nearly ten times that of the USA and Canada.

Life-cycle analysis of energy consumption and GHG emissions of aluminium production in China

Stages of the Aluminium Production Process.

• Bauxite mining

• Refining Bauxite into alumina (Aluminium oxide), The Bayer Process.

• Shipping to smelters

• Making electrodes

• Electricity Production

• Smelting

• Casting ingots

Bayer Process for Refining Bauxite

https://en.wikipedia.org/wiki/Bayer_process

A full explanation of the smelting process, including an emphasis on industry worker health and safety and a look at potential process improvements in an excellent paper, “The Aluminum Smelting Process and Innovative Alternative Technologies”. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4131935/

Anode Consumption

The above paper details possible future non-consumable anodes. At present the anodes are made from carbon.

Aluminium ions are attracted to the cathode by the electric potential where they become molten aluminium and remain in a layer on the bottom of the cell until the metal is tapped off.

Oxygen ions are attracted to the anode where they would form oxygen gas, but as the anode is carbon it reacts to form carbon monoxide which is combusted to become carbon dioxide.

This CO₂ emission is in addition to those resulting from electrical power production. Research is being conducted to find anode materials which will not react, thereby resulting in a process which releases oxygen rather than CO₂.

Note however that as the carbon reaction helps to power the process, a higher electrical potential would be required.