Influence of additives, temperature, and pressure on the morphology of nesquehonite: results from three synthesis routes

Carbon mineralization is expected to play a key role in the mitigation of climate change, as viable and efficient carbon capture and utilization (CCU) pathway. Indeed, the process has the advantage of enabling the recycling of waste-streams such as mine tailings or desalination brine, as well as the prospect of large-scale uptake of carbon dioxide emissions. However, the applications of the produced carbonates still hinder the commercial feasibility of the existing CCU routes, especially when hydrated Mg carbonates (HMCs) are obtained. HMCs are thermodynamically unstable, which poses potential risks in long-term stability. Nesquehonite (NQ, MgCO₃·3H₂O) is the major product of Mg carbonation in most aqueous reaction settings at moderate temperatures (15–50 °C), which has demonstrated suitable properties for producing construction materials. At somewhat higher temperatures (50–100 °C) hydromagnesite is obtained (4MgCO₃·Mg(OH)₂·4H₂O). Yet, the final applications are not feasible as NQ often converts to hydromagnesite or other HMCs over time causing liberation of CO₂ and volume instability. A key scientific gap remains on the relationship between the morphology of NQ with the operational settings of the carbonation reaction. In turn, such understanding is needed to enable tuning NQ applications in construction materials. Therefore, the current work reports the observed features of NQ via three different synthetic routes, showing the effect of two additives (Mg acetate, and sodium dodecyl sulphate), and overpressure CO₂ on the physico-chemical features of NQ formed from magnesium chloride or sulphate solutions and from brucite-water system and sCO₂ conditions.