Fayalite dissolution and siderite formation in water-saturated supercritical CO2

Olivines, significant constituents of basaltic rocks, have the potential to immobilize permanently CO2 after it is injected in the deep subsurface, due to carbonation reactions occurring between CO2 and the host rock. To investigate the reactions of fayalitic olivine with supercritical CO2 (scCO(2)) and formation of mineral carbonates, experiments were conducted at temperatures of 35 degrees C to 80 degrees C, 90 atm pressure and anoxic conditions. For every temperature, the dissolution of fayalite was examined both in the presence of liquid water and H2O-saturated scCO(2). The experiments were conducted in a high pressure batch reactor at reaction time extending up to 85 days. The newly formed products were characterized using a comprehensive suite of bulk and surface characterization techniques: X-ray diffraction, Transmission/Emission MOssbauer Spectroscopy, Scanning Electron Microscopy coupled with Focused Ion Beam, and High Resolution Transmission Electron Microscopy. Siderite with rhombohedral morphology was formed at 35 degrees C, 50 degrees C, and 80 degrees C in the presence of liquid water and scCO(2). In H2O-saturated scCO(2), the formation of siderite was confirmed only at high temperature (80 degrees C). Characterization of reacted samples in H2O-saturated scCO(2) with high resolution TEM indicated that siderite formation initiated inside voids created during the initial steps of fayalite dissolution. Later stages of fayalite dissolution result in formation of siderite in layered vertical structures, columns or pyramids with a rhombus base morphology. (c) 2012 Elsevier B.V. All rights reserved.