Sometimes referred to as ‘solidified energy’, primary aluminium is one of the most energy-intensive industrial-scale metals to produce. Australia’s CSIRO has estimated the total embodied energy of aluminium is 211GJ/t (58.6MWh/t)—for comparison, steel was estimated at 22.7GJ/t (6.31MWh/t).

By far the largest proportion of this embodied energy comes from the electricity used in the smelting process. Major producers, in response to the market’s demands for more environmentally responsible materials, are increasingly looking to offer a low-carbon aluminium product and to bank a premium for it.

Low-carbon aluminium encompasses primary aluminium with a CO2 footprint sufficiently below the current industry average as well as material with significant recycled content—recycled aluminium has a production energy intensity ~95% below that of primary metal.

The industry benchmark for low-carbon primary metal appears to be <4t of CO2 per tonne of aluminium—significantly below the industry average of ~11.5t of CO2 per tonne of aluminium (coal-powered sources, prevalent in China and Australia, can typically release 18-20t of CO2 per tonne of aluminium).

Environmental footprint has emerged as a product differentiator. The major producers outside China are now marketing low-carbon aluminium products, or have at least indicated an intention to do so. They highlight the fact that the metal is produced using electricity from low or zero-emission power sources (generally hydropower—some argue the focus on just the emissions benefits of hydropower underplays the environmental impact dams can have when assessing overall CSR).

Size Matters

Almost all existing low-carbon aluminium is produced at smelters associated with zero-emission hydropower electricity. It is currently the only renewable energy source capable of generating the required amount of power.

To get in on the action, producers in the Middle East have looked to other renewable electricity sources—and noticed the size of the challenge. The sheer amount of electricity required has found wind and solar wanting. Emirates Global Aluminium (EGA), to produce its ‘CelestiAL’ low-carbon product, has reached agreement with the Dubai Electricity and Water Authority for the supply of 560MWh of power from the 1,013MW Mohammed bin Rashid Al Maktoum solar park. However, this is sufficient to produce just 40kt of CelestiAL from the company’s 2.6Mt of production capacity—just 1.5%.

Other producers in the region have looked into powering capacity expansion projects with solar. They abandoned the idea after a back-of-the-envelope assessment of the required solar park and storage capacity. As a result, low-carbon production volumes from the region will be limited in the short to medium term.

What the Scope?

CO2 is the primary contributor to a smelter’s GHG emissions. Many countries and companies have adopted the GHG emission standards outlined by the Greenhouse Gas Protocol. The protocol classifies emissions across three scopes:

Scope 1: Direct emissions – emissions directly generated by a company. AME’s carbon methodology includes captive power generation within Scope 1.

Scope 2: Indirect emissions – emissions from (typically) third-party electricity generation consumed by a company.

Scope 3: Additional indirect emissions – value chain emissions – emissions from consumers utilising company output.

Emissions from power generation, either Scope 1 or 2, are the heavy hitters in the aluminium production process. The additional Scope 1 emissions, beyond captive power generation, are often overlooked in broad discussions. They shouldn’t be.

Don’t Mention the Anode

Understandably given its energy intensity, calculations of the carbon emissions of aluminium production typically focus on the source of a smelter’s electricity. As such, low carbon primary aluminium is typically produced with power from a renewable, low-emission source. However, the ubiquitous technology for producing primary aluminium, the Hall-Heroult process, involves a redox chemical reaction between alumina and a carbon anode which produces aluminium metal and its own direct carbon dioxide:

Up to 500kg of carbon anode is consumed per tonne of aluminium metal produced. The carbon dioxide directly produced in this process, a Scope 1 emission, ranges from 1.4-1.8t CO2 equivalent per tonne of aluminium produced and accounts for ~16% of the industry average emissions. These direct emissions cannot currently be viably eliminated from the process.

Anode of the Future

Primary aluminium produced without carbon dioxide production at the anode is the holy grail of low-carbon ‘green’ aluminium. While power can be sourced from renewable or low emission sources, reducing emissions associated with power generation, there is currently no commercially viable replacement for the carbon anode.

Elysis, a JV between Rio Tinto and Alcoa, is developing carbon-free reduction technology with the potential to eliminate direct carbon dioxide emissions from the reduction process. The JV is currently undertaking work to scale up its technology and plans to demonstrate commercial-size and amperage cells in 2023. The fact China hasn’t yet stolen the technology and built full potlines of inert anode reduction cells raises some (potentially cynical) questions as to its operability/viability.

Rusal has also invested heavily in research for an inert-anode—although, in practice, it still operates outdated Soderberg anodes, which are the least carbon-efficient. However, the company has worked to improve this with its eco-Soderberg upgrade programme.

Current aluminium reduction technology is also inefficient with the electricity it does consume, with estimates of up to 50% of incoming energy lost as heat. Improved refractories in cells, capable of withstanding the corrosive conditions, could help insulate the process, keeping more heat in and improving energy efficiency. Alternate anodes, reducing resistance losses, and improved process control are also being investigated with the aim of reducing electricity requirements and therefore carbon emissions per tonne of metal produced.

Implications?

Increasing demand from end-consumers for environmentally friendly and responsibly sourced feedstocks will drive growth in demand for low-carbon aluminium, though consumers may need to expect to pay a premium for it, particularly with the relatively limited hydro-powered capacity.

With many producers along the aluminium value chain looking for certification by the Aluminium Stewardship Initiative (ASI) to flex their CSR credentials, demand for low carbon products is expected to grow. Already—off a small base—primary aluminium producers are anticipating significant increases in demand for ‘green’ or low carbon metal.

Norsk Hydro has previously stated that property developers in Europe, North America and elsewhere are increasingly willing to pay more for metal that can help to lower their carbon footprint.