Use of Certain Sodium Salts can increase effectiveness of Carbon sequestration by Mineral Carbonation

Mineral Carbon Dioxide sequestration is a chemical method of sequestering CO2 that produces an environmentally harmless substance with minimal efforts required to monitor or verify the results (Krevor, 2009). The method, which has only been around as a CO2 sequestration technique since the 1990’s consists of adding magnesium silicate or calcium silicate with supercritical carbon dioxide to form a carbonate.  Unfortunately, high amounts of energy are required in the process compared to other methods of carbon sequestration. 75% of the energy is from the process of grinding the particles down to a small enough size. Though the addition of sodium citrate, sodium oxalate and sodium EDTA increase dissolution, the costs and energy use preclude the commercial success of this form of carbon sequestration. — Jake Bauch 
Krevor, Samuel C., Lackner, Klaus S., 2009. Enhancing Process Kinetics for Mineral Carbon Sequestration. Energy Procedia 1, 4867-4871

 Krevor and researchers at Columbia University tested the effect of adding different inorganic salts and sodium salts to the carbonate forming reaction. In all cases the CO2 was supercritical, at 120°C and 20 bars of pressure. Of the salts added, sodium citrate, sodium oxalate and sodium EDTA showed highest initial dissolution, and within 10 to 20 hours, dissolution reached almost 100%. Measurements ended after 24 hours, so the long term dissolution of the other salts was not measured.
The chemical process involves two steps: dissolution and then precipitation.  The dissolution is more efficient in more acidic solutions, but precipitation is impossible in an acidic solution. A complicated process could change the pH balance during the process, but has not been developed. Consequently, researchers typically add sodium bicarbonate to the reaction to create a neutral solution so that both dissolution and precipitation can happen simultaneously. Since neutral solutions yield low amounts of carbonate, the dissolution is the limiting part of the reaction. Hence, the particles are ground into finer particles to increase the dissolution.

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