Reaction of water-saturated supercritical CO2 with forsterite: Evidence for magnesite formation at low temperatures

Abstract

The nature of the reaction products that form on the surfaces of nanometer-sized forsterite particles during reaction with H 2 O-saturated supercritical CO 2 (scCO 2 ) at 35°C and 50°C were examined under in situ conditions and ex situ following reaction. The in situ analysis was conducted by X-ray diffraction (XRD). Ex situ analysis consisted of scanning electron microscopy (SEM) examination of the surface phases and chemical characterization of precipitates using a combination of confocal Raman spectroscopy, 13 C and 29 Si NMR spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). The results show that the forsterite surface is highly reactive with the primary reaction products being a mixture of nesquehonite (MgCO 3 Á3H 2 O) and magnesite (MgCO 3 ) at short reaction times ($3-4 days) and then magnesite (MgCO 3 ) and a highly porous amorphous silica phase at longer reaction times (14 days). After 14 days of reaction most of the original forsterite transformed to reaction products. Importantly, the formation of magnesite was observed at temperatures much lower (35°C) than previously thought needed to overcome its well-known sluggish precipitation kinetics. The conversion of nesquehonite to magnesite liberates H 2 O which can potentially facilitate further metal carbonation, as postulated by previous investigators, based upon studies at higher temperature (80°C). The observation that magnesite can form at lower temperatures implies that water recycling may also be important in determining the rate and extent of mineral carbonation in a wide range of potential CO 2 storage reservoirs.

Experimental Study of Organic Ligand Transport in Supercritical CO2 Fluids and Impacts to Silicate Reactivity

“…These results indicate that nesquehonite is a metastable precursor to magnesite, exemplified in the reactions: and which illustrates the precipitation of nesquehonite and amorphous silica, followed by the conversion of nesquehonite to magnesite. This is consistent with work that demonstrates magnesite is the most thermodynamically stable magnesium carbonate phase at 50 °C [39,51,52] and hydrated carbonate phases are metastable precursors [25,41,53]. The coupled forsterite dissolution and carbonate precipitation reactions likely occurred in nanometer-sized thin water films on the forsterite surface.…”

“…Additionally, citrate is a suitable example of a multivalent organic ligand that is often used in forsterite reactivity studies [29][30][31][32][33]. Forsterite was chosen as a model silicate mineral in order to compare the results with previous studies [25,[34][35][36][37][38][39].…”

Fundamental study of CO2-H2O-mineral interactions for carbon sequestration, with emphasis on the nature of the supercritical fluid-mineral interface.

“…Several studies have focused on the carbonation reaction of hydrous supercritical CO 2 with forsterite [7,9,86,87]. These studies also investigated the role that water plays in surface reaction by comparing reactivity between mineral/water/scCO 2 and mineral/anhydrous scCO 2 systems, or by characterizing surface reactions and/or reactivity as a function of water saturation in the scCO 2 phase.…”

Field Reaction Experiments of Carbonate Minerals in Spring Waters: Natural Analogue of Geologic CO2 Storage

“…Similarly, strong hydration energy of Mg 2+ inhibits magnesite formation at low temperature [22]. Factors that might overcome this constraint include high temperature and high CO 2 pressure [23][24][25]. Actually, authigenic magnesite precipitation was observed at 10 MPa and 90-150 ∘ C in the presence of supercritical CO 2 [26].…”