Increased thermal stability of nesquehonite (MgCO3•3H2O) in the presence of humidity and CO2: Implications for low-temperature CO2 storage

Nesquehonite (MgCO3 center dot 3H(2)O) has in the past been proposed as a low-cost, long-term mineral host for CO2. Here, stability of the phase was investigated under low temperatures (50 degrees C, 100 degrees C), moderate water vapour pressures (pH(2)O = 0.02-0.04 atm) and in both open and closed experimental systems. Specifically, this study explores CO2 storage security in nesquehonite exposed to (1) atmospheric humidity, (2) self-generated humidity, and (3) humidity in simulated flue gases during ex situ carbonation. Both CO2 and N-2 were used as carrier gases for H2O vapour to establish the influence of CO2 on nesquehonite decomposition under humid conditions. Nesquehonite thermal stability was clearly enhanced under humid conditions for short-term (<20 h) in situ X-ray diffraction and thermogravimetric experiments. Formation of hydrous surface layers may impede structural H2O release from nesquehonite; delaying dehydration and preventing subsequent decomposition. Enhanced stability of nesquehonite was also observed under a CO2 atmosphere. This study presents novel insights into the importance of temperature, pH(2)O and pCO(2) when considering the suitability of nesquehonite as a long-term CO2 store. Additionally, it establishes basic, previously overlooked conditions that are essential considerations when tailoring disposal, storage and ex situ carbonation to enhance CO2 stability in metastable Mg-carbonate phases. (C) 2015 Elsevier Ltd. All rights reserved.