MAGNESITE PRECIPITATION AT LOW TEMPERATURE: IMPLICATIONS FOR MICROBIALLY MEDIATED CARBON SEQUESTRATION

Anthropogenic greenhouse gas emissions, primarily carbon dioxide (CO₂), remain a global climate concern. The sequestration of CO₂ as solid and benign carbonates is the most effective long-term storage solution with respect to capacity and stability. While there are numerous metastable hydrated Mg-carbonates, magnesite [MgCO₃] is the most stable and has the highest carbon capacity as a function of volume¹. This makes the preferential precipitation of magnesite of keen interest. Similarly to dolomite, magnesite precipitation is kinetically inhibited at low temperatures (<50°C) making it notoriously difficult to precipitate. Previous studies on microbially mediated dolomite precipitation have yielded numerous insights to the mechanisms of low temperature carbonate precipitation^2,3&4. Tightly bound hydration spheres around Mg²⁺ in solution are a significant barrier to both dolomite and magnesite precipitation. Carboxyl functional groups (R-COOH), found on microbial surfaces, were shown to bind hydrated Mg²⁺, eject a molecule of water and weaken these hydration spheres to facilitate dolomite formation⁴. The dehydration of Mg²⁺ and formation of MgCO₃ has long been considered the rate-limiting step in the formation of dolomite⁵. Using bench-top geochemical microcosm experiments, containing functionalized microspheres as a representation of reactive microbial surfaces, we were able to precipitate magnesite at room temperature. Numerous industrial and natural waters are saturated with respect to magnesite and have the potential to serve as feedstock for sequestering CO₂ as magnesite if the low temperature kinetic barriers are overcome. Microbial biomass naturally produces surfaces containing carboxyl functional groups and elucidating the controls on this process may allow for future large scale magnesite precipitation as part of a strategy for sequestering anthropogenic CO₂.

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