Importance of dissolution and precipitation kinetics for mineral carbonation

Abstract

Studies of olivine carbonation are relevant for ex-situ CO2 storage, and the main results can be transferrable to geological storage of CO2. The total reaction rate of mineral and CO2 is always dependent on the slowest partial reaction, and with olivine the obtained conversion values were not correlated to dissolution rates. These direct carbonation results indicate that the precipitation rate of magnesite and not the dissolution rate of olivine was rate limiting for the reaction between olivine, CO2 and H2O at 185 °C and 115 bar. In industrial carbonation scenarios where the dissolution rate is not limiting, process optimization has to focus on the maximizing the precipitation kinetics. In industrial processes were precipitation is rate limiting, a conventional ball mill is probably the best alternative due to the low energy consumption, while in processes where the dissolution is rate limiting, more energy intensive pre-treatment methods may have potential. In the context of geological CO2 storage, the precipitation rate of carbonate will influence CO2 mineral trapping, and it is possible that precipitation kinetics is not equal to dissolution kinetics. Injection of CO2 into reservoir will lower the pH and thereby dissolve several minerals. The balance between dissolution and precipitation is dependent on the kinetics and solubility of the present minerals and possible products, where silica and carbonates probably are the most important. Mineral precipitation is unwanted in the storage formation due to lowering of porosity and possibly the permeability, but with time carbonate precipitation is positive due to mineral trapping of CO2.