Recarbonation of lime-based systems: new quantitative evidence for permanent mineral carbon dioxide removal (CDR).

Lime is an essential industrial material used in more than 200 applications across the European value chain, including steelmaking, water treatment, flue gas cleaning, construction, and emerging uses related to critical raw materials and marine environments. In downstream applications, lime reacts with CO₂ to form calcium carbonate through recarbonation. Recarbonation has been recognised by the IPCC since 2006 as a mechanism for CO₂ uptake and permanent storage, yet recarbonation of lime-based materials remains largely excluded from current carbon dioxide removal (CDR) assessments and accounting frameworks.

This contribution presents new academic results on carbonation of lime-based materials, complemented by emerging evidence from marine systems, with a focus on quantification, permanence, and relevance for CDR accounting. New results are reported for lime-based systems used in soil stabilisation and water treatment, alongside established construction and environmental applications. The analysis builds on the methodological framework developed by Politecnico di Milano (PoliMI) and applies mass-balance and life cycle–based approaches to quantify CO₂ uptake under real-use conditions.

High carbonation rates are observed in specific applications, notably drinking water and wastewater treatment (up to 100% within months), air-lime mortars (up to ~80–90% over their service life), and pulp and paper applications (up to ~93%, instantaneous). Soil stabilisation and other civil engineering applications exhibit lower but non-negligible CO₂ uptake over longer time horizons, depending on exposure conditions and material properties. These results confirm that recarbonation is highly application-dependent and that time-resolved modelling is essential for robust quantification.

These findings are placed in the context of broader PoliMI conclusions, which show that across major European lime applications, representing around 80% of the EU market, recarbonation reabsorbs on average approximately 33% of process CO₂ emissions, largely within the first year of use. The PoliMI work further demonstrates that recarbonation constitutes permanent carbon storage and that both spontaneous and enhanced pathways can be consistently addressed within life cycle and mass-balance frameworks.

For marine systems, the contribution discusses emerging research on ocean alkalinity enhancement using lime-based materials, indicating potential for additional atmospheric CO₂ uptake while highlighting remaining uncertainties related to environmental impacts, monitoring, and governance.

By combining new terrestrial results with established academic evidence and emerging marine research, this contribution positions lime recarbonation as a scientifically validated and permanent mineral-based CDR pathway rooted in well-understood chemistry and long-standing industrial practice.