Aluminium
Global aluminium production is responsible for around 2% of global human-caused greenhouse gas emissions when indirect emissions from electricity are accounted for (Source: Climate TRACE).
Aluminium is produced from bauxite, which is first refined into alumina through the Bayer process. The alumina is then converted into unwrought aluminium using the Hall-Héroult process, an electrolytic reduction method. The unwrought aluminium is subsequently processed into finished aluminium products.
Aluminium can also be produced from recycled aluminium (secondary aluminium), which requires significantly less energy and helps reduce greenhouse gas (GHG) emissions compared to primary production.
In addition to carbon dioxide (CO2) emissions, the production of aluminium is responsible for the release of perfluorocarbons (PFCs), such as tetrafluoromethane (CF4) and hexafluoroethane (C2F6), which have higher global warming potentials than CO2.
EU CBAM Reminder: Neither alumina nor carbon anodes are CBAM goods. As such, they are treated as raw materials with zero embedded emissions.
EU CBAM Reminder: Greenhouse gas (GHG) emissions to be monitored in the aluminium sector include carbon dioxide (CO₂) and perfluorocarbon (PFC) emissions.
Unwrought aluminium can be produced either from primary aluminium, which is made via electrolysis, or from aluminium scrap, also known as secondary aluminium.
Primary aluminium (primary smelting) is produced via the electrolytic reduction (Hall-Héroult process) of alumina, which is purified aluminium oxide obtained from bauxite through the Bayer process. Approximately 100 tonnes of bauxite yields 40-50 tonnes of alumina (aluminium oxide), which can then produce 20-25 tonnes of aluminium. The production of alumina usually takes place at a separate site from primary aluminium production, primarily due to logistical considerations and the need for substantial electricity supply.
The electrolytic reduction process occurs in electrolytic cells (also known as "pots"), where alumina is dissolved in a molten bath primarily composed of sodium aluminium fluoride (cryolite) at a temperature of around 960°C.
Each electrolytic cell consists of a carbon cathode and carbon anodes suspended from an electrically conductive anode beam. A direct current is passed from the carbon anodes through the bath and a layer of molten metal to the cathode, and then, via a set of current conductors, to the next cell. Liquid aluminium is deposited on the cathode at the bottom of the cell. Molten aluminium is periodically withdrawn from the cells using vacuum siphons into crucibles. During this process, aluminium is reduced, and oxygen from the alumina is liberated, combining with the carbon anode to form carbon dioxide and carbon monoxide. The molten aluminium is transported to the casting plant, where it is held in holding furnaces for further processing prior to casting metal ingots, blocks, billets, slabs or similar.
Fluoride compounds are also added to lower the bath's melting point, allowing the cells to operate at a lower temperature. Aluminium fluoride (AlF3) is the most common additive. However, fluoride emissions increase as the excess AlF3 in the bath is raised.
Alumina is added to the cells to maintain an alumina content of 2-6% in the molten bath. If the alumina content of the electrolyte falls below 1-2%, the so-called anode effect occurs. During an anode effect, instead of decomposing alumina, the cryolite bath decomposes into metal and fluoride ions, which react with the carbon anode to form gaseous PFC emissions.
Primary aluminium cell systems vary based on the type of anode used:
- Søderberg cells: Søderberg technology uses a continuous anode made from a paste of calcined petroleum coke and coal tar pitch. The anode is baked in situ within the cell by the heat generated from the molten bath and the electric current passing through it. This process does not require the anodes to be replaced.
- Prebaked cells: Prebake technology uses multiple anodes manufactured from a mixture of calcined petroleum coke, clean and recycled anode butts, and coal tar pitch. The anodes are formed into blocks and baked in a separate anode plant, which is often integrated with the primary aluminium plant. Prebaked cells typically have 12 to 40 individual anodes, which are replaced at regular intervals.
The EU CBAM covers the following production steps for primary aluminium:
- Raw material preparation - including storage of various additive constituents;
- Electrolytic cell system for aluminium production process - all steps;
- Casting plant - all steps including holding furnaces, conveying systems, further metal processing (metal treatment, alloying and homogenisation) and casting;
- Emissions control - for treating releases to air, water or ground.
The diagram below shows the example of an installation producing 500,000 tonnes of primary aluminium (Prebake technology).
Please note that these values are purely for explanatory and illustrative purposes, as each factory will have its unique design
Inputs
Intermediate Goods:
- Alumina: 967,500 tonnes → no GHG emissions
- Aluminium Fluoride (AlF₃): 10,750 tonnes --> no GHG emissions
- Anodes: 215,000 tonnes --> 384,850 tCO2e (direct emissions)
Electricity:
- Grid: 7,325,000 MWh → 4,274,870 tCO2e (indirect emissions)
Perfluorocarbon (PFC) Emissions:
- Method used: Slope method (anode effect minutes per cell-day are recorded)
- Technology: Legacy point feed pre bake
- Anode Effect Minutes / Cell Day (AEM): 1.5
- CF4 Emission Factor (kg CF4 /t Al produced) / (AE-Mins/cell-day): 0.122
- C2F6 Emission Factor (t C2F6 / t CF4): 0.097
Resulting in the following direct and indirect specific embedded emissions (SEE):
- Direct: 2.1800 tCO2e/tonne
- Indirect: 8.5497 tCO2e/tonne
Aluminium can also be produced from scrap (secondary melting). The scrap can be categorized as either "new scrap", which is generated during the production and fabrication of wrought and cast products, or "old scrap", which is recovered from finished products at the end of their useful life.
Secondary aluminium is produced mainly from post-consumer aluminium scrap collected for recycling (although unwrought aluminium may also be separately added). Scrap is sorted according to type (cast or wrought alloy) and the sort of pre-treatment measures required (e.g., de-coating, de-oiling), and is then re-melted in the appropriate type of furnace (typically rotary or reverberatory, but induction furnaces may also be used) before further processing including: alloying, melt treatment (addition of salt or chlorination) and finally casting metal ingots, block, billets, slabs or similar. Typical fuels used are natural gas, LPG, or fuel oil.
There are no PFC emissions from the secondary aluminium process.
EU CBAM Reminder: Aluminium scrap is treated as a raw material with zero embedded emissions.
The EU CBAM covers the following production steps for secondary aluminium:
- Raw material preparation - including sorting, pre-treatment (de-coating, de-oiling), drying and pre-heating of scrap;
- Furnace system for aluminium production process - all steps, including furnace charging, melting and holding furnaces;
- Casting plant - all steps including holding furnaces, conveying systems, further metal processing (metal treatment, alloying and homogenisation) and casting;
- Emissions control - for treating releases to air, water or ground.
The diagram below shows the example of an installation producing 500,000 tonnes of secondary aluminium.
Please note that these values are purely for explanatory and illustrative purposes, as each factory will have its unique design
Inputs
Intermediate Goods:
- Aluminium Scrap: 526,316 tonnes --> no GHG emissions
Fuels:
- Natural gas: 78,328,000 tonnes --> 159,932.16 tCO2e (direct emissions)
Electricity:
- Grid: 486,150 MWh → 110,988.05 tCO2e (indirect emissions)
Resulting in the following direct and indirect specific embedded emissions (SEE):
- Direct: 0.3199 tCO2e/tonne
- Indirect: 0.2220 tCO2e/tonne
CBAM Reminder: If you produce final aluminium products that contain more than 5% by mass of other materials, only the mass of iron or steel shall be reported as the mass of the goods produced.
CBAM Reminder: If the produced aluminium contains more than 5% alloying elements, the embedded emissions should be calculated as if the mass of these alloying elements were unwrought aluminium from primary smelting.
Aluminium products are produced by the further processing of precursor unwrought aluminium (alloyed or un-alloyed). Aluminium products are produced by a variety of forming processes, including extrusion, casting, hot and cold rolling, forging and drawing.
Extrusion: Common process used to produce aluminium profiles
Hot and cold rolling: May be used to produce plate, sheet and foil
Casting: May be used to produce complex forms
The EU CBAM covers the following production steps for finished aluminium products:
- Raw material preparation - including pre-heating, re-melting and alloying;
- Forming processes - all forming process steps for basic aluminium products, including (but not limited to): extrusion, casting, hot and cold rolling, forging, drawing;
- Finishing activities - including sizing, annealing, surface preparation and treatment and further fabrication;
- Emissions control - for treating releases to air, water or ground.
The diagram below shows the example of an installation producing 100,000 tonnes of finished aluminium products.
Please note that these values are purely for explanatory and illustrative purposes, as each factory will have its unique design
Inputs
CBAM Goods (Relevant Precursors):
- External Precursor:
- Unwrought aluminium: 111,111 tonnes
- Direct embedded emissions: 262,221.96 tCO2e
- Indirect embedded emissions: 904,443.54 tCO2e
Fuels:
- Natural gas: 6,000,000 tonnes --> 12,250.96 tCO2e (direct emissions)
Electricity:
- Grid: 350,000 MWh → 79,905 tCO2e (indirect emissions)
Resulting in the following direct and indirect specific embedded emissions (SEE):
- Direct: 2.7447 tCO2e/tonne
- Indirect: 9.8435 tCO2e/tonne
