Carbon sequestration via carbonic anhydrase facilitated magnesium carbonate precipitation

• Carbonic anhydrase (CA) facilitates CO2 hydration and Mg–carbonate precipitation.
• Rates of atmospheric CO2 uptake and Mg–carbonate precipitation were determined.
• Solutions amended with CA approach chemical and isotopic equilibrium more rapidly.
• CA increases CO2 uptake rates by up to 600% in comparison to controls.
• CO2 sequestration is enhanced by 360% with CO2 stored in Mg–carbonate minerals.

Strategies for sequestering CO2 directly from the atmosphere are likely required to achieve the desired reduction in CO2 concentration. This study examined the effect of bovine carbonic anhydrase (BCA) on the rate of atmospheric CO2 uptake into solution and Mg–carbonate precipitation as a means of sequestering CO2. Alkaline Mg-rich solutions, prepared using either NaOH or natural brucite [Mg(OH)2], were amended with BCA and supplied with laboratory air (~470 ppm CO2). BCA catalyzed the hydration of aqueous CO2, thereby minimizing the rate-limiting step for Mg–carbonate precipitation. Geochemical modelling of solution chemistry and the δ13C values of the dissolved inorganic carbon indicated that solutions amended with BCA approached equilibrium more rapidly. Rates of CO2 uptake were accelerated by up to 600% and 150% in systems using NaOH and brucite in comparison to controls, respectively. CO2 sequestration was enhanced by up to 360% with CO2 stored in a Mg–carbonate mineral that is mineralogically similar to dypingite [Mg5(CO3)4(OH)2·5H2O]. CO2 uptake and sequestration rates increased non-linearly with BCA concentration, suggesting that BCA concentration could be better optimized to achieve maximum efficiency. Given the global abundance of available cation sources (e.g., saline waste waters), carbonic anhydrase facilitated Mg–carbonate precipitation is a promising means of sequestering CO2.

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