Mineral Solubilities in CO2-Saturated NaCl Brine Systems

Experiments on CO2-brine-mineral interactions were designed to provide kinetic data for individual rock-forming minerals. Samples of an illite-smectite mixed layer mineral and a labradorite separate were stored in flexible Ti-cells together with 2 M NaCl brine and pure CO2 at 80 °C and 20 MPa for two and three weeks, respectively. The empirical formulae K0.5-0.7(Mg0.1-0.2Al1.8-1.9)(Al0.4-0.6Si3.4-3.6)O10(OH)2 and Na0.5-0.6Ca0.4-0.5Al1.3-1.6Si2.4-2.6O8 were calculated for illite and labradorite. X-ray diffraction data with Rietveld refinements reveal a pure labradorite separate. The illite separate is composed of 73.5 ± 1.3 wt% illite, 10.8 ± 1.3 wt% Ca-smectite, 11.9 ± 0.4 wt% orthoclase, and 3.9 ± 0.2 wt% quartz. Based on the acquired geochemical data, the experiments on monomineralic separates indicate (i) preferred dissolution of the Ca-smectite component out of the illite-smectite mixed layer mineral, and (ii) dissolution of labradorite.