Alkalinity production and carbon capture from dunite weathering: Individual effects of oxalate, citrate, and EDTA salts

Carbon dioxide mitigation and capture technologies are crucial to keeping global warming within safe limits. Silicate weathering offers a nature-based approach for stable, long-term carbon sequestration through technologies like Carbon Capture and Storage, Enhanced Silicate Weathering (ESW), and Ocean Alkalinity Enhancement. Dunite, a well-studied silicate mineral with a high dissolution rate, shows strong potential for these applications. However, despite its high dissolution rate, natural rates fall short of the speed needed for timely carbon sequestration. Consequently, enhancing silicate dissolution rates through methods like organic additives, which promote element mobilization and reduce saturation levels, has become a key area of research. Our flowthrough column study examined the impact of oxalate, citrate, and EDTA on carbon capture through dunite weathering. Their sodium salts were used to minimize pH effects and focus on ligand-driven dissolution. Citrate significantly improved carbon capture by 1.7 to 2.5 mol-C/mol-citrate per g of dunite by potentially delaying the formation of Fe passivation layers through element mobilization and reducing Mg saturation by facilitating its release from the solid to the liquid phase. Oxalate had a smaller (1 to 1.9 mol-C/mol-oxalate) but still notable effect, likely due to Na ion release caused by binding with Fe, Si, and Ni. In contrast, EDTA significantly reduced carbon capture, likely because its high binding capacity neutralized base cations and lowered the leachate pH. This study highlights the potential of citrate-driven ESW for carbon capture and offers insights into the role of organic ligands in this process, which could be valuable in both industrial and nature-based ESW applications.