T207 Environmental and Engineering Geology Student Research Competition (Posters)

Tuesday, 3 November 2015
9:00 AM - 6:30 PM
Exhibit Hall

IN SITU INFRARED SPECTROSCOPIC STUDY OF NANOCRYSTALLINE FAYALITE CARBONATION IN WET SUPERCRITICAL CO2

Paper number: T207-9
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Mineral trapping, the most permanent CO2 storage option, is a process where metal silicate minerals are reacted with CO2 to form solid metal carbonates. Reservoirs that are best suited for mineral trapping are those in volcanic flood basalts. Olivine is a major basalt component with high reactive potential for mineral trapping because it dissolves to release divalent metal cations that readily precipitate as carbonates. Olivine has complete solid solution between magnesium-rich forsterite, Mg2SiO4, and iron-rich fayalite, Fe2SiO4. Carbon dioxide injected into basalt reservoirs will initially reside as a supercritical fluid (scCO2) containing varying amounts of dissolved water. While many previous studies have focused on forsterite carbonation in wet scCO2, few have examined the fayalite reactivity in this low-water high-pressure fluid.

In this current study, the reaction of nanocrystalline fayalite with variably wet scCO2 was investigated at 50 degrees C and 90 bar using a combination of in situ probes, including IR spectroscopic titrations and high pressure XRD, and ex situ analyses, including TGA-MS and SEM. While no reaction occurred in anhydrous CO2, reaction products varied depending on the adsorbed H2O concentration. At lowest adsorbed H2O concentrations, water was consumed by reacting with CO2 to ultimately form adsorbed bicarbonate and a protonated fayalite surface. At moderate concentrations, either surface complexed carbonate or (sub)nanocrystalline siderite formed, but the reaction was not continuous. Above a threshold adsorbed H2O concentration, siderite precipitated continuously. These results are discussed in comparison with those from similar studies of forsterite, with the differences attributed to siderite versus magnesite solubility.