Experimental Evaluation of Three Clay Minerals for CO2 Mineralisation: New Pathways for Carbon Sequestration

Mineral carbonation is increasingly recognised as a promising carbon dioxide removal (CDR) strategy due to its ability to permanently immobilise CO2 as stable carbonate minerals. While most research has focused on ultramafic rocks and alkaline industrial residues, clay minerals remain underexplored despite their abundance and reactive surface properties. This study experimentally evaluates three representative pure clay minerals (kaolinite, montmorillonite, and illite) as alternative feedstocks for CO2 sequestration via mineral carbonation pathways. The materials were characterised using X-ray fluorescence, BET surface area analysis, and cation exchange capacity measurements, and their theoretical CO2 sequestration potentials were calculated. Carbonation experiments were conducted under pressurised slurry, atmospheric slurry, and CO2 incubator conditions. Carbonate formation was quantified using calcimeter and thermogravimetric analyses and confirmed by X-ray diffraction. All three clay minerals exhibited measurable CO2 uptake, with the highest carbonate contents achieved under pressurised slurry conditions. Illite showed the greatest carbonation extent, driven by its high CaO content, while montmorillonite displayed moderate performance supported by its high surface area and ion-exchange capacity. Kaolinite exhibited limited reactivity. These results demonstrate that clay minerals, particularly illite- and montmorillonite-rich materials, represent promising and widely available alternatives to conventional alkaline feedstocks for mineral carbonation-based CO2 sequestration.