Aluminium

Aluminium production is highly energy-intensive, with electricity making up a large share of the energy consumed. Improving the energy efficiency of production will be important to get on track with the Sustainable Development Scenario (SDS).

Material efficiency efforts that would reduce the amount of metal used while delivering the same services would also be beneficial, as would innovative alternative production methods that reduce primary production process emissions.

Given the high level of electricity consumed in the aluminium subsector, power sector decarbonisation is a key complement to reduction efforts in aluminium.

Energy intensity and secondary production

Global energy intensity of overall aluminium production fell by 1.1% in 2017, compared with annual reductions of 1.7% in 2010‑16.

This energy intensity includes both primary production from bauxite ore and secondary production from scrap. Primary production is approximately ten times more energy intensive than secondary production.

Primary aluminium production involves two key steps: alumina refining, to refine bauxite ore into alumina (aluminium oxide), and aluminium smelting, to convert alumina to pure aluminium.

The energy intensity of alumina refining decreased less in 2017 (‑2.8%) than in 2010‑16 (‑3.8% on average), while that of aluminium smelting declined more in 2017 (‑1.1%) than the 2010‑16 average (‑0.5%).

The downward trend in both is the result of new capacity additions equipped with the best available energy-efficient technologies. Reductions in primary production energy intensity are thus the main reason for declining overall aluminium energy intensity in recent years.

Falling global energy intensity of aluminium smelting from 2010 to 2017 resulted largely from developments in China.

Capacity grew significantly in recent years, such that China accounted for more than half of global primary production in 2017 (USGS, 2019). This enabled robust energy intensity declines and put China’s average energy intensity at the best-available-technology performance level in 2014.

The proportion of aluminium produced by secondary methods also affects the overall average energy intensity of aluminium production.

In 2017, 32% of aluminium was produced from new and old scrap, of which 60% was from old scrap (new and old scrap includes product manufacturing and end-of-life scrap; it does not include internal scrap produced in aluminium fabrication facilities).

The share of secondary production has remained relatively constant at close to 32% since 2000, except for a small temporary decline around 2007.

Scrap-based production tends to cost less than primary production, so the key constraint is scrap availability. In 2017, collections rates for aluminium were over 95% for new scrap and 70% for old. While these rates are high, there is potential to improve old-scrap collection.

For alignment with the SDS, it will be important to continue reducing the energy intensities of primary and secondary aluminium production, and to expand secondary production by improving old-scrap collection and sorting as well as reducing losses within the recycling system.

The global intensity of overall aluminium production (primary and secondary combined) needs to fall at least at 1.2% annually to 2030. This is a more moderate reduction rate than during 2010‑17, since half of primary aluminium is already produced with the best available technologies.

An increasing share of secondary production will be the primary catalyst of energy intensity improvements. The combined share of aluminium produced from recycled new and old scrap needs to reach nearly 40% (at least 70% of which from old scrap) by 2030 to attain the SDS pathway.

Achieving this share will require better scrap collection and sorting, particularly for old scrap, since stronger material efficiency efforts under the SDS will reduce the availability of new scrap.

Although energy efficiency and scrap-based production are important for alignment with the SDS, on their own they cannot decarbonise the subsector. Transformational change is required, particularly to deal with process emissions from primary production, and the groundwork for breakthrough technologies needs to be laid before 2030.

Decarbonisation of the power sector is also crucial because of the high electricity intensity of aluminium production. 

Demand trends

Global aluminium production grew an estimated 5.2% in 2017, an increase from the 2.4% climb in 2016 but less than the 7.1% per year registered from 2010 to 2015.

Production is expected to continue expanding, driven by population and GDP growth. Clean energy transitions will also impact aluminium demand, with potential for upward pressure from technology shifts that require greater use of aluminium, e.g. for lightweight vehicles and solar energy  (which uses aluminium for various components).

Adopting material efficiency measures can help curb demand growth, however.

Examples include reducing scrap generation during fabrication and manufacturing, reusing old scrap, and designing products with recycling in mind.

In the SDS, demand growth slows to an average annual rate of 3%, but this still represents over 40% growth in total demand from the current level. Measures will therefore be needed to curb growth in energy and emissions intensities.

Accelerate energy and material efficiency

Expanding secondary production through better scrap collection and sorting will be important to raise energy efficiency and decarbonise the aluminium subsector.

Stakeholders should work to increase scrap collection and recovery by improving recycling channels and sorting methods, and by better connecting participants along supply chains. Focusing on end uses that currently have low collection rates will be important.

The aluminium industry, aluminium product manufacturers and waste collectors can work together to ensure that manufacturing and end-of-life scrap is channelled back to aluminium producers.

Engineers should consider reusability and recyclability in product designs, and governments can assist by setting requirements and co‑ordinating channels for end-of-life material reuse and recycling.

Participants all along the value chain (aluminium producers, engineers, construction companies and product manufacturers) can also adopt material efficiency strategies to reduce overall aluminium demand.

Furthermore, ensuring efficient equipment operation and maintenance will help guarantee optimal energy performance. This can be reinforced by implementing energy management systems.

Accelerate innovation and deployment of low-carbon primary production technologies

Reducing emissions from primary production is important, as scrap availability will put an upper limit on the potential for secondary production.

Industry should prioritise RD&D of alternative production methods that reduce process emissions from primary production, such as the use of inert anodes. R&D will be needed within the next decade to enable widespread deployment post-2030.

Increased support for RD&D is needed from governments and financial investors, particularly to advance the large-scale demonstration and deployment of technologies that have already shown promise.

Private-public partnerships can help, as can green public procurement, which generates early demand and can enable producers to gain experience and bring down costs. Government co‑ordination of stakeholder efforts can also direct focus to priority areas and avoid overlap.

Integrating variable renewables

Given the high electricity requirements of aluminium production, efforts to decarbonise the grid will be necessary to reduce the indirect emissions of aluminium production.

The aluminium sector can in turn assist with grid decarbonisation by providing flexibility services that would help integrate a higher portion of variable renewables. Electricity producers can assist by offering electricity pricing incentives to aluminium producers using demand management systems.

Adopt mandatory CO2 emissions policies and expand international co‑operation

Policy makers can promote CO₂ emissions reduction efforts by adopting mandatory reduction policies, such as a gradually increasing carbon price or tradeable industry performance standards that require average CO₂ intensity for production of each key material to decline across the economy and permit regulated entities to trade compliance credits.

Adopting these policies at lower stringencies within the next three to five years will provide an early market signal, enabling industry to prepare and adapt as stringency increases over time. It can also help reduce the costs of low-carbon production methods, softening the impact on aluminium prices in the long term.

Complementary measures may be useful in the short to medium term, such as differentiated market requirements, that is, a government-mandated minimum proportion of low carbon aluminium in targeted products.

Ideally, these policies would be applied globally at similar strengths. Since aluminium is traded extensively internationally, measures may be needed to help ensure the competitiveness of domestic industries and prevent carbon leakage if the strength of policy efforts differs from one region to another.

Examples include time-limited measures to ease transition, such as declining free allocation of permits, or novel measures to apply emissions regulations on the lifecycle emissions of end-products rather than directly on materials production. The latter could potentially be used to apply border carbon adjustments, provided that they are implemented in line with international trade rules.

Governments can extend the reach of their efforts by partaking in multilateral forums to facilitate low-carbon technology transfer and to encourage other countries to also adopt mandatory CO₂ emissions policies.

Improve data collection

Improving collection, transparency and accessibility of energy performance and CO₂ emissions statistics on the aluminium subsector would facilitate research, regulatory and monitoring efforts (including, for example, multi-country performance benchmarking assessments).

Better data on recycled production levels, recycled energy intensities and scrap availability are particularly needed. Industry participation and government co‑ordination will both be important to improved data collection and reporting.

Innovation in the aluminium subsector is essential to reduce emissions from primary production, given that the Hall-Héroult cells currently used produce process emissions during electrolysis. Although it is important to expand secondary production to reduce emissions, decarbonising primary production is also necessary because scrap availability will put a limit on secondary production.

Inert anodes are a key innovation to reduce primary production process emissions, and otherwise, any innovations that improve energy efficiency can also reduce electricity consumption – and thus indirect electricity emissions.

Several technologies (multipolar cells, novel physical designs for anodes, wetted cathodes, carbothermic reduction of alumina, and kaolinite reduction) offer energy efficiency potential, but many are still in relatively early stages of development.

Other areas for innovation are electrolysis demand-response, which could help with integrating variable renewable energy by providing flexibility services to the grid, and new physical recycling techniques that could increase scrap availability for secondary production.

Inert anodes for primary aluminium production

Using inert anodes would substantially reduce process emissions from primary aluminium production.

Technology principles: Primary aluminium smelting currently relies largely on carbon anodes, which produce CO₂ as they degrade. Inert anodes made from alternative materials instead produce pure oxygen and do not degrade.

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Multipolar cells

While conventional Hall-Héroult cells have a single-pole arrangement, multipolar cells could be produced with bipolar electrodes or with multiple anode-cathode pairs in the same cell. They could reduce energy consumption by 40%, owing to lower operating temperatures and higher current densities. Since the cells require inert anodes, process emissions from the use of carbon anodes would also decrease.

Technology principles: The Hall-Héroult method is currently the main commercial process for primary aluminium smelting. It uses electrolysis to separate aluminium from aluminium oxide (alumina) within a cell. The carbon-lined cell acts as a cathode, and an anode is dipped into the electrolyte bath contained within the cell. A current is passed from the anode to the cathode to separate the aluminium.

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Novel physical designs for anodes

The physical design of anodes can be altered to improve the energy efficiency of Hall-Héroult cells. For example, sloped and perforated anodes make electrolysis more efficient by allowing better circulation within the electrolyte bath, while vertical electrode cells save energy by reducing heat loss and improving electrical conductivity. Energy savings can be considerable, with one source estimating that slotted anodes can reduce energy consumption by 2 kWh to 2.5 kWh per kg of aluminium.

Technology principles: The Hall-Héroult method is currently the main commercial process for primary aluminium smelting. It uses electrolysis to separate aluminium from aluminium oxide (alumina) within a cell. The carbon-lined cell acts as a cathode, and an anode is dipped into the electrolyte bath contained within the cell. A current is passed from the anode to the cathode to separate the aluminium.

Read more about this innovation gap →

Chris Bayliss (International Aluminium Institute), Hugo Salamanca (IEA), Joe Ritchie (IEA), Marlen Bertram (International Aluminium Institute)