Increasing awareness and activity relating to greenhouse gas emissions have seen companies start to burnish their green/environmental responsibility credentials.
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.