Characterization and lab-scale carbonation of wood biomass ashes: Exploring links between ash properties and CO2 capture

Biogas from anaerobic digestion typically contains 30%–50% CO 2 , which must be removed to obtain grid-quality biomethane. Simultaneously, woody biomass combustion generates large amounts of alkaline ash (rich in Ca/Mg oxides) that remain poorly valorized despite their carbonation potential. This study provides a novel, systematic analysis of wood ash properties governing CO 2 capture, using ashes from commercial boilers differing in combustion technology ( e.g. , moving grate vs. volcanic grate) and type (fly/bottom). Ashes were characterized (mineralogy, bulk and surface composition, basicity, particle size, morphology, Total Organic Carbon (TOC)/Total Inorganic Carbon (TIC)), and carbonated in a novel gas-liquid contactor (pure CO 2 , 6 bar, 100 g L -1 suspensions). The best-performing ashes reached 328 g CO 2 /kg ash. Surface Ca content (Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS)) and basic site density (Temperature-Programmed Desorption (TPD)) correlated more strongly (R 2 = 0.81 for TPD) with carbonation performance than bulk Ca content, establishing quantitative selection criteria for efficient ash valorization. These findings support coupling wood ash carbonation with biogas upgrading to simultaneously valorize biomethane and ash residues. Pilot-scale validation is needed.