Geochemical potentiality of glauconitic shelf sediments for sequestering atmospheric CO2 of anthropogenic origin

Abstract

An experimental analysis was made of the glauconite dissolution rate as a function of pH. The results were used to model the geochemical evolution of glauconitic shelf sediments injected with CO2 and estimate the possibilities and limitations for sequestering CO2 in the form of minerals through carbonation reactions. The experimental results show how, under acidic conditions, glauconite is slightly more soluble than other silicates, producing more insoluble carbonated products. The dissolution mechanism is incongruent at very acidic pH values and tends to be congruent at intermediate and neutral values. The reactive surface decreases during the process as a result of the formation of an amorphous residue. Kinetic data were used to model the reactions of carbonation in marine sediments using reaction/speciation calculations. This study shows that, in the case of glauconite, the efficiency of CO2 sequestration depends primarily on two factors: the dissolution/speciation kinetics of CO2 in sediments and the kinetics of Fe2+ release. The greatest limitation for the implementation of this process is that pH evolves to more acidic values. The results suggest that, in the medium term, this process could be technically optimized by modifying the neutralization response of sediments through the injection of alkalinizing agents and by appropriately selecting the mode of injection as well as the composition of the sediments and of the most favourable diagenetic zones.