Measurement and prediction of the CO2 effective diffusion coefficient in unsaturated media

Akué Sylvette Awoh, Benoît Plante, Bruno Bussière, Mamert Mbonimpa

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Unsaturated Soils

ABSTRACT: The CO2 transport from air to mine wastes that can capture CO2 is controlled by molecular diffusion and carbonation reactions. The CO2 flux captured depends on the effective diffusion (De-CO2) and CO2 consumption rate (Kr-CO2) coefficients. The objective of this study was to present an experimental determination of the De-CO2 of mine wastes at several degrees of saturation (Sr), based on a procedure inspired from oxygen diffusion tests, and the development of a predictive equation of De-CO2 based on existing De-CO2 models and existing CO2 measured. When the material is almost dry, the measured and calculated CO2 concentrations are closer than when the materials Sr increases. The predicted and the measured De-CO2 coefficients fit at lower Sr compared to higher Sr. These results suggest that H+ consumption by the solids moves the equilibrium of CO2 dissolution to higher-than-predicted values, because the numerical predictive model does not account for H+ reactivity. RÉSUMÉ Le transport du CO2 de l'air vers les rejets miniers séquestreurs de CO2, est contrôlé par la diffusion moléculaire et les réactions de carbonatation. Le flux de CO2 capturé dépend des coefficients de diffusion effective (De-CO2) et de carbonatation du CO2 (Kr-CO2). Cette étude s'intéresse à la détermination expérimentale du De-CO2 de rejets miniers à différents dégrées de saturation (Sr), basé sur une procédure inspirée de la méthode de diffusion de l'oxygène, et le développement d'une équation de prédiction de De-CO2 basé sur des modèles et des mesures de De-CO2 de la littérature. Pour des Sr faibles, les courbes de CO2 mesurées et calculées s'ajustent assez bien et les valeurs de De-CO2 prédites correspondent aux valeurs de De-CO2 mesurées, comparativement aux valeurs de De-CO2 à des Sr élevés. Ces résultats s'expliquent par l'augmentation de la dissolution du CO2 causée par la consommation des H+ par le solide, non prise en compte par le modèle numérique utilisé. 1 INTRODUCTION The increasing in anthropogenic greenhouse gases emissions in the atmosphere, particularly carbon dioxide (CO2), has led to the search for solutions on permanent CO2 sequestration. To date, three main atmospheric CO2 capture and storage (CCS) approaches are known: (1) geological storage, (2) ocean storage and (3) CO2 mineralisation, also named mineral carbonation (e.g. Fagerlund and Zevenhoven 2011; Beinlich and Austrheim 2012). Mafic and ultramafic rocks are known for their ability to sequester CO2. Several mineral deposits composed of mafic and ultramafic rocks are found following mining extraction throughout the world, such as those from the Diavik Diamond mine (Wilson et al. 2006, 2009a), the Ekati mine (North-West Territories) (Rollo and Jamieson 2006), the Cassiar mine (North-West Territories), the Clinton Creek mine (Yukon) (Wilson et al. 2009b), and the Dumont project (Québec) (Royal Nickel Corporation, 2012). When these rocks are exposed in large quantities as wastes due to mining operations, the uptake of CO2 can be accelerated, which reduces the carbon footprint of the mining operations (Hitch et al. 2010; Mills et al. 2010). The sequestration of CO2 involves first the transportation of the molecules from air to the waste pore space, then their dissolution in the pore water, and finally contact with the mafic and ultramafic rocks in order to form stable carbonates by the carbonation process. Examples of CO2 sequestration by serpentinite ((Mg,Fe,Ni)3Si2O5(OH)4) and formation of stable carbonates are illustrated by the carbonation of chrysotile [(Mg)3Si2O5(OH)4], as follows (Teir et al. 2009; Fagerlund and Zevenhoven 2011; Bea et al. 2012): Mg3S2O5 (OH) + 3CO2 3MgCO3 + 2SiO2 + 2H2O [1] The transport of carbon dioxide in the pore space of fine grain size mine waste, such as tailings, is controlled by molecular diffusion and carbonation reactions. CO2 molecular diffusion with reactions can be described by Fick's laws, where the CO2 effective diffusion (De-CO2) and consumption rate coefficients (Kr-CO2) are required to obtain the CO2 flux consumed by the tailings. Having De-CO2 and Kr-CO2 provides more flexibility for simulating CO2 uptake scenarios under different boundary conditions. Several studies were conducted to estimate the CO2 uptake by mine tailings (Pronost et al. 2011, Bea et al. 2012; Assima et al. 2013). Pronost et al. (2011) measured the CO2 consumption by mineral carbonation of mine tailings at atmospheric pressure. The flux of CO2 uptake

RÉSUMÉ: rement and prediction of the CO2 effective diffusion coefficient in unsaturated media Akué Sylvette Awoh1, Benoît Plante1, Bruno Bussière1, Mamert Mbonimpa1 1Research Institute on Mines and the Environment, UQAT-polytechnique, Rouyn-Noranda, QC, Canada ABSTRACT

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Akué Sylvette Awoh; Benoît Plante; Bruno Bussière; Mamert Mbonimpa (2014) Measurement and prediction of the CO2 effective diffusion coefficient in unsaturated media in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper219,author = Akué Sylvette Awoh; Benoît Plante; Bruno Bussière; Mamert Mbonimpa,title = Measurement and prediction of the CO2 effective diffusion coefficient in unsaturated media,year = 2014}