What process emission factor does the UK CBAM give for limestone and dolomite?
HMRC's UK CBAM guidance gives stoichiometric factors for carbonates: 0.440 tonnes of CO2 per tonne of calcium carbonate (limestone), 0.522 per tonne of magnesium carbonate, 0.415 for soda ash and 0.380 for iron carbonate. Dolomite is a mix of calcium and magnesium carbonate, so use each part's share.
Standard factors, Annex VI Table 3 (method A)
- CaCO3: 0.440 tCO2 per tonne of carbonate.
- MgCO3: 0.522.
- Na2CO3 (soda ash): 0.415.
- FeCO3: 0.380.
- NaHCO3: 0.524; K2CO3: 0.318; BaCO3: 0.223.
Where carbonates show up
- Sponge iron kilns using dolomite or limestone as desulphuriser.
- Clinker making, from limestone in the raw meal.
- Flue gas cleaning with limestone or soda ash, which the UK boundaries for DRI and secondary aluminium include.
Use the actual carbonate content
These factors apply to the pure carbonate. Use lab analysis of your limestone or dolomite to find how much of each tonne is carbonate before multiplying.
Worked example: dolomite in a sponge iron kiln
- Dolomite used: 3,000 t a year; lab analysis: 54% CaCO3 and 40% MgCO3.
- CaCO3: 3,000 x 0.54 x 0.440 = 712.8 tCO2.
- MgCO3: 3,000 x 0.40 x 0.522 = 626.4 tCO2.
- Process CO2 from dolomite: 1,339.2 tCO2.
What Senseible does here
Senseible reads dolomite and limestone purchase invoices into tonnes per month for this calculation. We build the figure from your records and check every figure in-house; for the UK it must then be verified by a verifier accredited for UK CBAM. Have your own verifier? Send it to them.
Sources: HMRC, UK CBAM monitoring, reporting and verification technical guidance (October 2026)
Last reviewed 2026-11-02.