Additive impact on early-stage magnesium carbonate mineralisation

Carbon capture and utilisation has attracted significant interest due to increasing
\nconcerns about global warming. Mineral trapping viaMgCO3 precipitation is a promising
\nstrategy, though restricted by the slow rate of magnesite (MgCO3) formation
\nand high temperatures needed to avoid the formation of hydrated minerals.
\nAmorphous magnesium carbonate (AMC) is a transient phase, determining the characteristics
\nof the final crystalline MgCO3 phase(s). Research has focused on accelerating
\nMgCO3 formation using additives, but their modus operandi is not completely
\nunderstood. Here, AMC titration experiments were conducted at constant pH, monitoring
\nsolution transmittance, conductivity, and species size evolution to clarify the
\neffect of citrate on the initial steps of MgCO3 precipitation. We demonstrate that citrate,
\nsimilar to more complex additives, alters the hydration of free ions relative to ion associates, thereby destabilising prenucleation
\nion associates and delaying AMC nucleation. The system is thus forced to go through liquid–liquid separation before the
\nformation of the solid, resulting in amorphous and crystalline phases with lower water content, which are more stable and efficient
\nfor C storage, having a positive impact on the cost of CO2 mineralisation.