Microstructure and carbon storage capacity of hydrated magnesium carbonates synthesized from different sources and conditions

Recently, the mineral carbonation via the reaction of CO2 with saline aquafers received much attention as one of the most promising ways for geologic CO2 storage. This paper reports microstructure and carbon storage capacity of hydrated magnesium carbonates (HMCs) synthesized from different sources, i.e., reject brine and commercial Mg(OH)2 slurry, and under different conditions, i.e., pH (8-14) and Mg(OH)2:CO2 molar ratio (1:1-1:7). Results show that dypingite (Mg5(CO3)4(OH)2·5H2O) is the main phase forming at lower Mg(OH)2:CO2 ratios. An increase in the Mg(OH)2:CO2 ratio and/or pH leads to the precipitation of nesquehonite (MgCO3·3H2O). A unique "house of cards" texture, involving formation of the rosette-like dypingite flakes on the surface of nesquehonite needles, is discovered under elevated pH and Mg(OH)2:CO2 ratios. HMCs synthesized from reject brine exhibit a much higher carbon storage capacity of 82.6% than that produced from the commercial Mg(OH)2 slurry (43.7%). Findings from this study advance understanding of mineral recovery from reject brine and the capture and long-term storage of CO2 in the form of HMCs