Nanoscale control over water-film thickness using temperature modulation: tuning mineral carbonation reactivity

Abstract

Induced temperature gradients within a high-pressure reactor were used to assess how the thickness of nanoscale 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 ML 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 h 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.