By John Grandfield, Grandfield Technology.
Climate change has brought the greenhouse gas (GHG) emissions of aluminum smelting into sharp focus. Other important sustainability issues include bauxite residue dam integrity, waste disposal (spent potling, dross, etc.), water consumption, working conditions, biodiversity, etc. In this article, past work to reduce GHG emissions is examined together with latest trends within the industry around “green” low CO2e aluminum marketing and certification. The prospects for renewable energy replacement of fossil fuel power by solar generated water splitting to obtain hydrogen are discussed in the context of the Australian energy policy.
Lifecycle analysis (LCA) is an important tool in sustainability assessments applied across many industries. The aluminum industry has been assessing its GHG emissions for more than 30 years and many cradle-to-gate lifecycle studies and calculations of emissions for individual smelters and technologies have been made by companies, industry associations, and universities. See for example Keniry;1 the IAI;2-3 Mahadevan who examines Indian industry emissions;4 Zhang, et al., on Chinese smelters;5 the 2019 study by Macquarie University;6 and the extensive 2018 review by Kvande and Welch7 on steps to minimizing CO2e. The Aluminum Association has carried out LCA studies of aluminum production and cradle-to-grave studies of final applications (automobiles, beverage containers, etc.) from 1993 to the present. Their most recent analysis of the primary industry was in 2013, when they updated their lifecycle inventory (LCI) database. LCI is part of LCA and involves tallying up the unit inputs and outputs of a product including primary resource extraction, manufacturing, distribution, use, and ultimate disposal or recycling.
Emissions are generally divided into three areas, as follows:
- Scope 1 – Those occurring directly at the site of operations.
- Scope 2 – Indirect GHG emissions from the consumption of purchased electricity, heat, or steam.
- Scope 3 – Other indirect emissions, such as the extraction and production of purchased materials and fuels, transport-related activities in vehicles not owned or controlled by the company, electricity-related activities (e.g. transmission and distribution losses) not covered in Scope 2, outsourced activities, waste disposal, etc.
Sometimes LCA is done for individual plants and sometimes for regions with similar energy profiles. Despite difficulties of accounting for differing emission scopes, especially over time as the Intergovernmental Panel on Climate Change (IPCC) assessment reports modify the greenhouse warming potentials (GWPs) for use in the determination of CO2e per activity, there is a reasonable consensus of the results obtained. ISO standards 14040 and 14044 specify such methodologies. LCA methodology has converged on the GHG protocols of the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD).
Generally, direct on-site emissions (Scope 1) and offsite emissions (Scope 2, in particular from electricity generation) are included. Other offsite emissions (Scope 3) include those from material inputs, i.e., alumina, bauxite, petroleum coke, and pitch production. It is not always clear which items have been included in quoted CO2e numbers. By far the biggest emissions are due to electricity production (Figure 1). Smelters running on power from coal are around 15-20 CO2e t/t, while regions with 100% hydropower are less than 4 CO2e t/t (Scope 1, 2, and 3). Many of the coal-fired smelters are in China (Figure 2), and consequently nearly 70% of the industry’s emissions originate in China (Figure 3).
Casthouse emissions are often ignored in smelter LCAs. However, they do make a contribution to the overall load, particularly for highly alloyed product with magnesium and silicon, which have a high carbon footprint, around >20 t CO2e t/t of metal.8
Emissions during alumina production vary. One study reported 1.2 t CO2e per tonne of alumina or 2.3 t CO2e per tonne of aluminum.4 Kvande and Welch put the average emission at 1.5 tonnes per tonne of aluminum produced based on Aluminum Association numbers. The Australian Aluminium Council estimates 0.7 t CO2e per t alumina (1.3 t/t Al) for the Australian smelters. GHG emissions from bauxite mining are very small compared to the other inputs. Green coke emissions from calcination are ~0.4 t/t Al depending on technology and practice.
How to Reduce Emissions
The Kvande and Welch paper looks at where the emissions come from and how to reduce them. This includes lowering the kWh/kg, lowering the net carbon, lowering the voltage drop, improving the casting furnace energy efficiency, using higher current cells, implementing better cell MHD and bus design, and improving the cell controls to reduce anode effects. Addressing these issues has resulted in a good improvement in energy efficiency across the industry (Figure 4). Some pilot technology is running at <12 kWh/kg.
Perflurocarbon compounds (PFCs) in particular CF4 and C2F2 are emitted during anode effects in the cells. These gases have very high global warming potential. Work to reduce anode effects resulted in major reductions in PFC emissions intensity across the industry, going from 5 t CO2e/t to 0.6 (90% reduction since 1990). For further detail on PFC emissions, see the review by A. Tabereaux9 and update by Wong and Welch.10 The IAI published results of its survey on 2018 anode effects this year. The absolute emissions have dropped from 100 million tonnes per annum to 36 million in 2018. Best practice is now at 0.06 t CO2e/t.6
Much activity and investment has been made into inert anodes, an idea first proposed 131 years ago. Major programs have been undertaken in Russia, Norway, China, North America, and other countries (see international patents).11 Elysis is the joint venture between Rio Tinto and Alcoa to develop inert anode technology. In December 2019, they shipped the first metal produced with this process to partner Apple. The press release describes it as carbon free smelting technology eliminating all direct GHGs. It seems there is no allowance in this figure for the Scope 3 emissions like alumina. The assumption is also that the power comes from hydroelectricity. However, even though Apple is a high profile customer, the actual tonnage of metal going to the electronics sector is a small proportion <1% of global aluminum demand.
Questions still remain as to whether inert anodes are a viable solution. For example, it has been pointed out that inert anodes have higher theoretical energy requirements than carbon anodes,12 because they do not make use of the chemical energy stored in the carbon. For coal plants, this means the GHG emissions are greater than just using a carbon anode. If the smelter is running off hydropower as part of an overall energy grid that utilizes coal generation, then the smelter is essentially taking away the availability of hydropower that the grid might otherwise have been used elsewhere.
While inert anodes are a welcome improvement, many other questions about inert anodes remain to be answered such as availability of the material of the anode. The use of charcoal has been examined as a carbon neutral alternative to petroleum coke, but further work is needed.
Carbon capture and sequestration (CCS) is also a possibility to reduce the GHG emissions from a Hall-Heroult cell. The main downside is that about 0.5kWh/kg in energy is required to separate the CO2. Even so, CCS looks on paper to be more beneficial than inert anodes when taking into account the CO2 emissions associated with the higher energy requirements. CCS may have a role in reducing coal-fired power emissions as an interim solution.
Alternatives to Hall-Heroult
Alternatives and variants to the traditional Hall-Heroult process—like drain cathode cells, carbothermal reduction, and aluminum chloride electrolysis—have been investigated over the years. In terms of GHG, they could potentially be better than standard Hall-Heroult.13 Anyone contemplating the chloride route should look carefully at the history of magnesium chloride electrolysis for magnesium production and the difficulties experienced in that sector.
The biggest potential impact on emissions is converting the industry to renewables and since the global economic hydroelectric resources have mostly been exploited we must look to the sun as the main source of renewable power.
Renewable Energy Sources
A big question for the aluminum industry is how to use renewable energy sources to power smelters when the variability of energy supply is extreme. Solar power is a major focus in this regard, although wind and geothermal power could also be part of the renewable mix. Nuclear power is demonstrably an option, too. Rio Tinto is currently installing small demonstrator renewable plants across 20 locations although none are for smelters.14 The switch to solar would reduce operating costs, since the cost of solar and battery technology is falling rapidly. BloombergNEF forecasts wind and solar will be cheaper than coal or gas in most jurisdictions by 2030.15
One approach to addressing the variability of renewable energy would be to use solar power for water splitting and using the hydrogen in fuel cells on the night cycle. A first step could be to feed solar generated hydrogen into natural gas power stations. Commercial hydrogen-fed gas turbine generators are available now. Emissions from solar generated hydrogen electricity would be close to those from hydroelectric.
Another opportunity is to modulate smelter power consumption so the smelter performs essentially as a battery in the grid with quick response to renewable energy variation. EnPot technology, developed by Energia Potior Ltd in New Zealand is an enabling technology to improve the smelters modulating ability. Far greater impact to the grid stability is possible than with current battery systems.
Hydrogen generated from renewable energy presents an opportunity for the aluminium industry to become zero carbon. Hydrogen gas turbine generators are available off the shelf, and the variability challenge of renewable energy supply is solved by storing hydrogen. Hydrogen is getting a lot of press and activity is accelerating. Both a recent World Economic Forum (WEF) article and a Hydrogen Council report point to the expectation that costs of green hydrogen will fall by 60% by 2030 — primarily from scale up alone. The report points to tangible government policies to develop hydrogen. Eighteen governments representing 70% of global GDP moving ahead on hydrogen. This includes “recent announcements from the coalition of governments forming the Energy Ministerial to target the global deployment of 10 million fuel cell electric vehicles (FCEVs) by 2030 – a fourfold increase of the target over the last two years – and projects across China, Japan, the US, and South Korea to build 10,000 hydrogen refuelling stations by 2030.” (This paragraph was added on February 21, 2020.)
There is a big push on hydrogen in Australia.18 The Australian federal government has already committed over A$146 million. The Australian research organization CSIRO has a major project on technology to use ammonia for hydrogen transport. Projects include the Hydrogen Energy Supply Chain (HESC) supported by Australian and Japanese companies, as part of the Japanese government’s strategy to decarbonize its industry. In this case, brown coal is used but the process includes CCS. Other projects include building a 220 kW electrolyzer using solar or grid renewables to support a fleet of fuel cell electric vehicles for the Queensland state government.
Another thing to consider is that emissions associated with alumina refining also need to be dealt with to get to zero carbon aluminum. At the moment, there seems to be no electric calciners that would enable the use of renewable energy.
Sustainability Organizations and Certification
There are many organizations involved in sustainability. For example, the CDP (formerly Carbon Disclosure Project) has GHG data on 3,600 companies, which is available for purchase. Others include World Resources Institute (WRI) and World Business Council for Sustainable Development (WBCSD).
Companies with low CO2e emission power sources like hydroelectric are seeking to differentiate their metal in the market as low carbon output “green” aluminum. It is one thing to say you have low carbon sustainable operations, but not all of these claims are independently assessed or verified. To support their claims, companies are joining the Aluminium Stewardship Initiative (ASI) and obtaining certification of their processes. ASI is a global, multi-stakeholder organization working to set standards and certifications in order to foster the responsible production, sourcing, and material stewardship of aluminum throughout the supply chain (from mine to downstream users of aluminum). ASI has two standards, the ASI Performance Standard, which outlines governance, environmental and social requirements, and the ASI Chain of Custody, which sets out the requirements to control the sourcing and production of ASI aluminum throughout the aluminum value chain using a mass balance model. ASI became an associate member of ISEAL, a global membership organization for credible sustainability standards, in December 2018 and full member in December 2019.
Companies that produce bauxite, alumina, or aluminum metal (whether primary or secondary) or companies that use aluminum in their products (such as for packaging, automotive, etc.) must have at least one of its facilities certified to the ASI Performance Standard within two years of joining ASI to maintain membership.
Certification to ASI standards independently verifies a level of sustainable practice. These types of certification processes have been applied in other commodities, e.g., forestry, conflict-free diamonds, tungsten, coltan etc. The LME is in the process of implementing a chain of custody standard for the LME metals based on the OECD sourcing standards.
The ASI Performance Standard includes several requirements for existing smelters with respect to GHG emissions, as follows:
- Publicly disclose material GHG emissions and energy use by source on an annual basis.
- Publish time-bound GHG emissions reduction targets and implement a plan to achieve these targets. The targets shall cover the material sources of direct and indirect GHG emissions.
- Demonstrate management systems, evaluation procedures, and operating controls to limit direct GHG emissions.
- Demonstrate that the Scope 1 and Scope 2 GHG emissions from the production of aluminum will be at a level below 8 t CO2e/t Al by 2030.
The ASI Performance Standard does not prescribe methodologies for determining GHG emissions or how to set reduction targets but the supporting guidance documentation refers to existing methodologies such as the GHG protocols of the WRI and WBCSD. Note that Scope 3 emissions, notably from alumina and bauxite production, are not included in the 8 t CO2e/t figure.
The 8 t CO2e/t aluminum target is about half the total global average figure and represents a stretch target for smelters using natural gas. It implies that no existing smelters using electricity sourced from coal-fired plants will be able to be certified after 2030, since it would be extremely difficult to get coal GHG emissions to that level. However, coal-fired electricity supply smelters are now 60% of all smelters. In particular, the rapid growth in Chinese smelting capacity has predominantly been coal based. Chinese smelters are 90% coal-fired and 10% hydropowered.17 Likewise, Indian smelters are solely based on coal-fired power.
Companies that exceed the 8 t CO2e/t aluminum target can still be certified if they claim and can demonstrate to their independent ASI auditors that they will emit less than 8 t/t by 2030. However, the Performance Standard does not require companies to publicly disclose how they will meet this requirement. Companies are required to publish time-bound GHG emission reduction targets and implement a plan to achieve these targets, but reporting of progress is not mandatory.
There are understandably some sensitivities about the public disclosure requirement of the ASI. Companies may be reluctant to share all their details as some information is related to competitive advantage, e.g., energy used per tonne or net carbon consumption. On the ASI website, audit reports and public summaries are available describing the scope, etc. Within these reports are links to company documents, such as sustainability reports, which provide headline numbers. For example, the report from Emirates Global Aluminium (who is ASI certified) stated, “In 2018 the greenhouse gas intensity of our smelting, casting and power production was the lowest in our history at 7.93 t CO2e/t Al (exceeding our 2018 target of 7.97 t CO2e/t Al).”
Downstream companies looking to be certified have to use certified primary metal as input. Chinese production and transformation companies that have been and want to be certified may need to import ASI-certified metal in order to meet the standard—as no Chinese primary producer is yet certified (although an announcement is in the wings).
The hydropowered smelters in China will be able to meet the 8 t/t target easily, and there are some signs that China is beginning to switch from coal to hydropowered smelters. Hongqiao Group, Chalco, Weiqiao Group, Heqing Yixin Aluminum, and Henan Shenhuo are building and operating smelters in the hydropower rich region, Yunnan. Altogether, seven smelters in Yunnan are running off hydroelectricity. Three other smelters—Hanjiang Danjiangkou Aluminum, Huanghe Hydropower (CPI Qinghai), and Aba Al Smelter (Bosai)—are operating outside Yunnan on 100% hydroelectric power. Total hydroelectric smelter capacity in China is around 2.8 million tpy. The main driver to switch to hydro is to reduce costs.
The IAI estimates Yunnan’s power mix results in 0.24 kg CO2e/kWh of power (about 3.24 kg CO2e/kg of aluminum) compared to 0.92 kg CO2e/kWh (12.4 kg CO2e/kg) for the Chinese average. Since there are limited capacity quotas, most Chinese producers cannot build more aluminum production capacity without closing plants, thus new plants in Yunnan displace old coal-powered smelters in provinces such as Shandong. This trend will likely continue and result in GHG reductions.
Currently, the ASI is planning a comprehensive revision of its standards and certification program. The review will take place over a two-year period, commencing in 2020, and will include the ASI Performance Standard and Chain of Custody Standard and the supporting Guidance, Assurance Manual and Claims Guide. The scope of the review with regard to GHG emissions has not yet been defined.
Are customers preferring to take material that comes from certified sustainable sources? Will they pay more for it? At this stage, there is no direct evidence freely available that companies will pay extra for green metal. However, it is reasonable to expect that green material would be preferred, if available at the same price as uncertified material. Green brands of primary metal in the market include ALLOW by UC Rusal, REDUXA by Norsk Hydro, RenewAl by Rio Tinto, and Sustana by Alcoa. Secondary rich ~75% secondary material brands such as Hydro 75R are also in the market. Some of these green brands are ASI certified. Some are certified by other agencies, e.g., DNV GL. Marketing to high profile customers like Apple is also part of this green image. The amount of low carbon and ASI certified material is still a small portion of total production. Therefore, by necessity, customers will have to use non-certified material for some time.
Automotive is a high profile market sector for aluminum, but as yet, no signs of strong bias to sustainable material are apparent. The aluminum industry associations’ studies point to the focus being on fuel savings from using aluminum in transport, which offsets the emissions during aluminum smelting.
There have been suggestions by EN+ (Rusal) that all producers should report their CO2e figures and energy efficiency.18 Many companies already produce sustainability reports which include CO2e data. For those that don’t, it is relatively easy to estimate their emissions, since the source of power is known, and assume typical industry performance on anodes, etc. Thus, buyers can make their own assessment of the green credentials of a particular supplier.
The global response to climate change at this point has been disorganized, but is nonetheless having some positive impact in terms of flat growth in coal emissions, growth in renewable energy, a focus on lightweighting in transport, and an increased interest in electric vehicles (EVs). The EU and North America have been reducing emissions in absolute and per capita terms in recent years (Figure 5). However, China and India have increased their emissions in amounts greater than these reductions.
Like all materials, aluminum must be of net benefit to society. Aluminum is certainly able to provide a green solution for the transport industry, offering fuel savings and reducing CO2e. Even the use of high-carbon, coal-fired aluminum is able to reduce more emissions after 100,000 km of travel in ICE vehicles than is emitted from the primary production process. For EVs, aluminum also increases range and improves energy efficiency.
Furthermore, the industry will continue to make improvements around pot control, MHD design, net carbon, and specific energy consumption, but if aluminum is to make a positive contribution to the target of keeping climate change warming to less than 2°C, the aluminum industry needs to do more. It is critical that the industry start pilot projects to examine how to run smelters on renewable power.
Taking the broader context, the biggest driver for reduction in CO2e of the aluminum industry is the survival of the industry itself. The industry is at risk of regulations restricting power sources and emission intensity, as well as the implementation of carbon taxes. It is doubtful that any premiums (such as carbon pricing) will be high enough to incentivize aluminum companies to significantly reduce CO2e emissions in the short term. Rather, differentiation in the market and market share appears to be a bigger incentive. Reductions in energy intensity, PFC emissions, net carbon, and so on also have the added benefit of reducing costs in a tangible way, which has a direct impact on the company’s bottom line—also a strong incentive in itself. It’s also important to note that marketing an aluminum product as being “green” only works as a selling point, if the pricing remains the same. If the price of “green” material increases and there remains a limited supply, then it could push customers toward buying high-carbon material. This is not the desired outcome.
Whether or not ASI certification is actually reducing the GHG footprint of the aluminum industry at this stage is difficult to say. However, that may change. Companies with smelters that use natural gas and renewable power will be able to meet the 8 t CO2e/t target and achieve certification—as long as they have a plan to reduce emissions. This is likely, since reducing emissions goes hand in hand with reducing costs, which they will need to do anyway. Arguably, certification is having no impact on the avalanche of new Chinese coal-fired production. This is unfortunate, since the industry’s emissions are critically dependent on what happens in China and India and when, and if, they shut down coal-fired smelters.
Finally, it should be noted that GHG emissions are not just an aluminum industry problem. All industries around the world need to become zero carbon. If we want to have a sustainable future, then we need to do this now.
- Keniry, J., “Aluminum Smelting Greenhouse Footprint and Sustainability,” Light Metals 2008, pp. 369–373.
- International Aluminium Institute, www.world-aluminium.org.
- Nunez, P. and S. Jones, “Cradle to gate: life cycle impact of primary aluminum production,” International Journal of Life Cycle Assessment, 2016, pp. 1,594–1,604.
- Mahadevan, H., “Managing Greenhouse Gas Emission in the Indian Aluminum Industry,” JOM, Vol. 53, Issue 11, 2001, pp. 34-36.
- Zhang, Y., et al., “Environmental footprint of aluminum production in China,” Journal of Cleaner Production, Vol. 133, 2016, pp. 1,242-1,251.
- Farjana, S.H., et al., “Impacts of aluminum production: A cradle to gate investigation using life-cycle assessment,” Science of the Total Environment, Vol. 663, 2019, pp. 958-970.
- Kvande, H. and B.J. Welch, “Impacts of Aluminum Production: A Cradle-to-Gate Investigation Using Lifecycle Assessment,” Light Metal Age, February 2018, pp. 28-41.
- Koltun, P., et al., “Greenhouse Emissions in Primary Aluminum Smelter Cast Houses – A Life Cycle Analysis” Materials Science Forum, V630, 2010, pp. 27-34
- Tabereaux A. T., “ Anode Effects, PFCs, Global Warming, and the Aluminum Industry,” JOM, Vol. 46, Issue 11, 1994, pp. 30–34.
- Wong, D. and B.J. Welch, “PFCs & Anode Products – Myths, Minimisation and IPCC Method Updates to Quantify the Environmental Impact,” 12th Australasian Aluminum Smelting Technology Conference, 2018.
- Tabereaux, A.T., “Innovations Transforming Aluminum Smelting Today,” Light Metal Age, February 2019, p. 43.
- Solheim, A., “Inert Anodes – The Blind Alley to Environmental Friendliness?” Light Metals 2018, pp. 1,253-1,260.
- Sustainability, Vol. 10, Issue 1, January 2018, 1216
- “Our approach to climate change,” Rio Tinto report, 2018.
- “New Energy Outlook2019,” BloombergNEF, 2019, about.bnef.com/new-energy-outlook.
- “Australia’s National Hydrogen Strategy,” Council of Australian Governments (COAG) Energy Council, November 2019, www.industry.gov.au/data-and-publications/australias-national-hydrogen-strategy.
- “A life-cycle model of Chinese grid power and its application to the life cycle impact assessment of primary aluminum,” IAI, 2017.
- “‘Green’ aluminium critical but producers shy, says EN+ chairman,” S&P Global Platts, October 2019
Dr. John Grandfield has 40 years experience in light metals casthouse research and technology, working with company and government laboratories to achieve process improvements and develop and commercialize patented technologies. He is currently director of Grandfield Technology Pty. Ltd. and has been consulting for the industry for 11 years, offering training, industry analysis, and technology development to industry and research groups. Contact via email: firstname.lastname@example.org.