PNNL

Abstract

Induced temperature gradients within a high-pressure reactor were used to assess how the thickness of surface-adsorbed water films affect the carbonation of forsterite, Mg2SiO4, in water-saturated supercritical carbon dioxide (scCO2). Water monolayer (ML) coverages on the mineral surface were estimated by in situ infrared spectroscopy and were shown to increase nearly exponentially from approximately 5 to 170 when the forsterite region was cooled from +0.5 to -0.3 °C relative to a nearby pool of excess water. Carbonation rates and extents were strongly dependent on the water film thickness, with the highest rates and complete mineral conversion occurring within 40 hr under bulk-like water coverages. Reaction passivation, possibly due to a reduction in reactive surface area, was observed for thinner water films ranging from 5-53 ML. Temperature modulation can be an effective technique for investigating basalt reactivity over a range of water coverages in humidified scCO2.