# Mineralization of alkaline materials (ex situ) | **Methodology name** | Mineralization of alkaline materials (ex situ) | | -------------------- | ---------------------------------------------- | | **Version** | 1.0 | | **Methodology ID** | RBW-CDR-MIN-V1.0 | | **Release date** | September 10, 2025 | | **Status** | In use | ## Introduction It is widely acknowledged that in addition to reducing global greenhouse gas (GHG) emissions, [carbon dioxide must be removed from the atmosphere](#user-content-fn-1)[^1] and permanently sequestered. One way to do this is through [mineral carbonation](#user-content-fn-2)[^2]/mineralization of concrete and alkaline wastes that contain metal ions, destined for permanent incorporation into permanent products. In this process, captured CO₂ is exposed to and reacts with alkaline materials, generating stable carbonates that can [permanently ](#user-content-fn-3)[^3]store the CO₂. This methodology document outlines the general requirements for mineral carbonation of materials projects certified under the [Rainbow Standard Rules](https://docs.rainbowstandard.io/~/changes/113/rainbow-standard-documents/rainbow-standard-rules).

Acknowledgements 🤝

*This methodology was developed by Rainbow with valuable input and support from the Rainbow Mineralization Working Group members and other expert contributors.* *We would like to thank Christina Stavridi, Bernardo Martinez, and Gabriel Carrero (Carbon Limit), Colin Hills (University of Greenwich), Jamie Rogers (CarbonCure), Paula Carey and Aaron Lyons (Carbon8), Stephen Roscoe (O.C.O), and Roxby Hartley (EcoEngineers) for their insights and contributions throughout the development process.*

## Modules **Modules are like mini-methodologies** that only cover a part of the project life-cycle. Combining the relevant modules for a project results in a complete picture of eligibility criteria, GHG reduction quantification requirements, required data, monitoring plans, and other instructions for Rainbow certification. This methodology shall be used in conjunction with the following Rainbow modules:

		Cover image
Processing and energy use	processing-and-energy-use	processing and energy use_new.jpg
Transportation	transportation	transportation module.jpg
Infrastructure and machinery	infrastructure-and-machinery	infrastructure and equipment module.jpg

## Glossary


Mineralization, Mineral Carbonation	A chemical process where CO₂ reacts with alkaline materials (e.g., concrete, cement, industrial residues) to form stable carbonates (e.g. CaCO₃), permanently storing CO₂. Mineralization and carbonation are used interchangeably in the present methodology.
Ex situ	Processes that occur in controlled, engineered environments, such as reactors or industrial facilities, rather than in situ approaches that take place in the natural environment (e.g. enhanced rock weathering).
Carbonated Material	The solid product resulting from mineral carbonation, containing CO₂ locked in stable carbonate form (e.g., carbonated concrete or aggregate).
Carbonation curing	A process where CO₂ is introduced to concrete or cement-based materials during the curing stage, to accelerate strength development and chemically bind CO₂ into the material.
Carbonation batch	The carbonated material produced using the same input materials (alkaline feedstock and CO₂) and operating conditions. It is assumed that all carbonated material from the same carbonation batch has similar characteristics.
Alkaline Feedstock	Materials that contain metal oxides (e.g., calcium, magnesium, iron) that react with CO₂ to form carbonates.
Biogenic CO₂	CO₂ originating from biomass sources. Its carbonation leads to net carbon removals, and is eligible for removal carbon credits.
Atmospheric CO₂	CO₂ captured directly from the atmosphere, typically from Direct Air Capture (DAC) or ambient air. Its carbonation leads to net carbon removals, and is eligible for removal carbon credits.
Fossil CO₂	CO₂ originating from fossil fuels. Its carbonation leads to carbon storage, and is eligible for avoidance carbon credits.
Calcination CO₂	CO₂ originating from lime that is calcinated in cement production, from breaking up CaCO₃ into CO₂ and calcium silicates. Its carbonation leads to carbon storage, and is eligible for avoidance carbon credits.
Fugitive CO₂ Emissions	Unintended leaks of CO₂ from equipment (e.g., reactors, pipelines, trucks). Not to be confused with the Leakage eligibility criteria.
Ordinary Portland Cement (OPC)	The most common type of cement, produced by heating limestone and other materials to form clinker, which is then ground into a fine powder.
Supplementary cementitious materials (SCM)	Industrial by-products (e.g. fly ash, slag) or natural pozzolans used to partially replace OPC in concrete. They can both replace and reduce clinker-related emissions, and serve as reactive alkaline materials that bind CO₂ into stable carbonates.

{% content-ref url="../glossary" %} [glossary](https://docs.rainbowstandard.io/~/changes/113/glossary) {% endcontent-ref %} [^1]: IPCC, 2022: Summary for Policymakers. In: Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi: 10.1017/9781009157926.001 [^2]: Baciocchi R and Costa G (2021) CO₂ Utilization and Long-Term Storage in Useful Mineral Products by Carbonation of Alkaline Feedstocks. *Front. Energy Res.* 9:592600. DOI: 10.3389/fenrg.2021.592600. URL. [^3]: Baciocchi, R., Costa, G., 2021. CO2 Utilization and Long-Term Storage in Useful Mineral Products by Carbonation of Alkaline Feedstocks. Front. Energy Res. 9. [URL](https://doi.org/10.3389/fenrg.2021.592600).