FUEL 87-Injection of CO2-SO2 mixtures in geological formations as a potential approach for CO2 storage

Carbon dioxide (CO2) injection into saline aquifer formations is one of the most promising geologic CO2 storage options because of their large capacity and worldwide distribution. Amongst the different mechanisms by which CO2 can be trapped underground, mineral trapping is the safest, most permanent and most desirable one since CO2 is converted into stable mineral carbonates. Underground injection of CO2-SO2 mixtures into specific rock formations has been suggested lately and, aimed formations would include widespread ferric-iron bearing sediments, i.e. red beds. Thermodynamic modelling studies have shown that ferric iron can be reduced by sulphur dioxide (SO2) to ferrous iron, making this available for further siderite (FeCO3) precipitation. An additional benefit would be the oxidation of the SO2 to sulphate and because SO2 is already a component of flue gas, the CO2 capture process would be more efficient. Accordingly, this work aims to experimentally assess and identify the conditions under which mineral trapping would take place in ferric-iron bearing sediments, provided that the injected stream is a CO2-SO2 mixture. Thermodynamic simulations have been computed to predict the different gas, solid and fluid composition at equilibrium; the output given by the model could be then validated with the experimental work. The modelling and experimental results conducted thus far show that this approach could play an important role in the storage of CO2 underground.