Aluminium’s production process is very energy intensive and therefore, contributes greatly to climate change: in 2018, the sector was responsible for 1.1 billion tonnes of greenhouse gas emissions.
As we are moving towards a low carbon economy, aluminium is playing a key role in driving societal and economical transformations. Why? Because of its numerous properties. Among others: its recyclability.
As regulations on carbon emissions are getting stricter, it is paramount that all players understand the logic behind carbon accounting to avoid any greenwashing. Companies need to apprehend the structure of their carbon emissions across the entire value chain and within their products. In addition to carbon corporate management, companies need to assess their product lifecycle. Aluminium is a widely used material in the food industry, in the transport industry, in construction and more. It has a high value as well as complexity, it is not well-known and a high emitting material. For these reasons, Cozero wanted to dive into the topic of aluminium decarbonization and understand what is at stake.
Aluminium is the second most used metal on earth (after iron) and it is profusely used in our everyday life - from foil to beverage cans to airplanes or automobiles. In Europe, the largest application of aluminium is transport (39%) according to the European Aluminium Association in 2014.
Aluminium has a broad range of unique properties that may contribute to the development of low carbon products such as lighter cars and energy efficient buildings. Its properties can be summarised as follows:
How to create aluminium
The production process of primary aluminium (creation of new aluminium) starts with the mining of bauxite, a clay-like soil type found around the equator. The bauxite is then transported to a plant where the clay is washed off and the bauxite passes through a grinder. This process produces a thick paste that is collected in special containers and heated with steam to extract alumina or aluminum oxide. After refining and filtering, the remaining alumina is dried to a white powder.
Next stop is the metal plant: where the refined alumina is transformed into aluminium. Aluminium smelting is the process of extracting aluminium from the alumina, generally made with the Hall-Héroult process, an electrolytic process using huge amounts of electric power.
Sustainable consequences and carbon footprint
Mined from a few meters below the ground, the extraction of bauxite can cause air, water and soil pollution because of the dust created. Additionally, the extraction of raw materials and the production process of aluminium can affect human health: lung and kidney disease have been reported as well as bone disease for children.
The carbon footprint of primary aluminium is highly dependent on the source of electricity used: it varies between 4 tCO2e/t of aluminium with hydropower-based electricity to more and 20 tCO2e/t of aluminium when using coal power-based electricity.
Recyclability of aluminium and carbon accounting
The property of aluminium that interests us the most is its recyclability. Indeed, aluminium can be reused infinitely without losing its other properties when being recycled. The recycled product can become the same as the original product or become completely different.
On average, recycling aluminium emits 0.5 tCO2e/t of aluminium. The process requires less energy than primary aluminium production (only 5% of the energy used).
According to ISO 14021, there are two types of materials in general:
Pre-consumer material: Material diverted from the waste stream during a manufacturing process. Excluded is reutilization of materials such as rework, regrind or scrap generated in a process and capable of being reclaimed within the same process that generated it.
Post-consumer material: Material generated by households or by commercial, industrial and institutional facilities in their role as end-users of the product which can no longer be used for its intended purpose. This includes returns of material from the distribution chain.
Therefore, applied to the case of aluminium, on the one hand we have pre-consumer scrap (or process scrap) which comes from the production process and hasn’t been used yet as a product, e.g. rolled foil. It is worth noting that when processing aluminium, 20 to 30% of the material ends up as processed scrap which has a recycling rate close to 100%. On the other hand, we have post-consumer scrap which is aluminium scrap coming from products which have been used already by end-consumers and have fulfilled the purpose for which they were produced.
Let’s take an aluminium can as an example. Once the can is produced, it is transported to a supermarket where a consumer will buy it, eventually drink it and finally throw it away. If the can is properly sorted out, it should go back into the waste stream and will enter a recycling process. When this post-consumer scrap is recycled, it starts a second lifecycle with no carbon footprint attached to it because it reached its end-of-life during its first lifecycle: the can was consumed, its footprint is reset. The carbon footprint of recycled post-consumer scrap is on average 0.5 tCO2e/t of aluminium (including scrap collection, transport, sorting and remelting).
Going back to our example, during the production process of the can, some aluminium is lost in the waste stream from refining and cutting stages. This process scrap can still be recycled into another product. However, this pre-consumer scrap has a quite different carbon footprint compared to post-consumer scrap as it has not yet fulfilled its purpose as a product. Indeed, the aluminium wasted during the production process is not a product per se. Therefore, it carries the carbon footprint of the original primary aluminium from which it was produced. As a result, after being recycled, its carbon footprint is higher than the primary aluminium’s footprint.
Is aluminium able to become a sustainable material?
There is no straightforward answer although there is no doubting the wide range of uses of aluminium. However, the negative consequences of aluminium primary production and the low recycling rate still make it a difficult material to use without some degree of consideration.
Here are a few examples of solutions to implement:
- Implementing technology elements in order to optimize productivity, energy efficiency and emissions in aluminium smelters
- Developing recycling technology and improve end-of-life scrap collection and sorting
- Learn to design for recycling
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