Conversion of CO2 into mineral carbonates using a regenerable buffer to control solution pH

Dissolution of Mg from serpentine has been found to be favourable with a solids to solution volume of more than 50 g/L to enable a low pH, and with temperatures close to the boiling point of the solution. The pH needed for magnesium carbonate precipitation was found to be approximately 8.2. Both triethylamine and tripropylamine were found to be capable of achieving this at 18 °C. Yields of around 20-40 wt.% carbonate were achieved using residence times of approximately 1 h. The pH swing for the tertiary amines was found to be approximately 2.5 pH units between 5 and 85 °C, suggesting that an amine capable of achieving a pH of 8.2 at low temperature generates a pH of 5.7 in solution when heated to 85 °C. Further work will examine whether the lower pH values needed for serpentine dissolution can be achieved by heating the protonated amine to higher temperatures.