Carbonation of calcium-magnesium pyroxenes: Physical-chemical controls and effects of reaction-driven fracturing

The weathering of primary silicates, and their carbonation in particular, is key for the geochemical cycling elements, strongly affecting C cycle long-term regulation Earth's climate. knowledge on controlling factors mechanisms aqueous silicates however still far from complete. This precludes a better understanding chemical nature strong handicap to implement effective Carbon Capture Storage (CCS) strategies. Here, dissolution-carbonation reactions two abundant Ca-Mg pyroxenes, augite diopside, have been investigated experiments conducted at hydrothermal conditions, presence/absence different carbonate sources (NaHCO3 Na2CO3). We show that main reaction products are low-magnesium calcite amorphous silica. A higher conversion (?38 wt%) than diopside (?15 was achieved. presence Fe Al (and minor Na) former pyroxene enhances release cations solution, contributes formation secondary crystalline as well carbonates (Na-phillipsite magnesium silicate hydrate, MSH, calcite). In Na-phillipsite nucleates etch pits exerting crystallization pressure ?100 MPa exceeding tensile strength (i.e, failure under tension due breaking inter-atomic bonds opening propagation subcritical fractures or flaws) causing extensive fracturing. takes place via an interface-coupled dissolution-precipitation mechanism, despite bulk system being undersaturated with respect this phase. Limited reaction-induced fracturing also observed following MSH precipitation within crystals. Reaction-induced increases exposed reactive surface area creates channels solution flow, thereby contributing progress positive feedback loop. Ultimately, our results help understand differences kinetics these rock forming inosilicates relevant CCS strategies, showing phase (other carbonates) fostered by moderately alkaline pH alkali metals, resulting reaction-driven enables effective, safe, permanent CO2 mineral storage. experimental conditions silica cannot generate sufficient create fracturing, effect limits Mg-Ca-Fe pyroxenes.