Temperature-dependence of CO2 drawdown into Mg-bearing minerals.

Mg-bearing minerals, including brucite [Mg(OH)₂], lizardite [Mg₃(Si₂O₅)(OH)₄] and iowaite [Mg₆Fe³⁺₂(OH)₁₆Cl₂·4H₂O] are variably reactive with carbon dioxide (CO₂) at Earth’s surface conditions and can be used to mineralize and sequester this greenhouse gas. Here, we assess the impact of temperature (5, 20 and 40 °C) on the rate of CO₂ mineralization of these minerals. At each temperature, mineral powders (~100 mg ) were placed in a 7.5-litre flow-through reactor that was supplied with humidified laboratory air (0.042% CO₂; 100% RH) at ~200 mL/min. Subsamples (n = 54) of each mineral were collected over 3 months and analyzed (XRD, TIC, BET) to ascertain the amount and rate of carbonation as a function of time, temperature, and mineral feedstock.

Preliminary X-ray diffraction (XRD) results show the formation of dypingite [Mg₅(CO₃)₄(OH)₂·5H₂O] and a decrease in the abundance of brucite over time. The 003 peak of iowaite shifted to smaller d-spacings, indicating replacement of chloride by carbonate ions and a transition to a more pyroaurite-rich [Mg₆Fe³⁺₂(CO₃)(OH)₁₆·4H₂O] composition. Total Inorganic Carbon (TIC) measurements were used to determine the amount and rate of carbonation as a function of time, temperature, and mineralogy.

The results of this study will help us estimate the carbonation kinetics of these minerals in ultramafic ores and mine tailings under different temperature conditions relevant to large-scale deployment of CO₂ mineralization at mines across the globe.