The efficiency of CO2 sequestration via carbonate mineralization with simulated wastewaters of high salinity

Salinity generally strongly affects the solubility of carbon dioxide in aqueous solution. This would seem to involve a reduction of the efficiency of the carbonate mineralization process with the objective to sequester this greenhouse gas. On the contrary, we demonstrate here that with a more concentrated solution of magnesium chloride, the residence time of CO2 is enhanced in the aqueous medium because of a reduced tendency to produce CO2(g). Experiments intended to simulate more closely the Mg-rich wastewaters that are industrially available have been carried out using solutions differing in Mg concentration (7, 16, 32 g L−1 Mg). A comparison of the efficiency of the CO2 mineralization process among sets of experiments shows that the reduction of the efficiency, to about 65%, was lower than that expected, as the low degree of CO2 degassing results in the enhanced availability of carbonic ions to react with Mg ions to form stable carbonate minerals over a longer time.