New Perspectives on Carbonate Mineral Behaviour for Carbon Accounting and Carbon Utilization (original) (raw)
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Chemical Geology
Hydrated Mg-carbonate minerals form during the weathering of ultramafic rocks, and 2 can be used to sequester atmospheric CO 2 to help combat greenhouse gas-fueled climate change. Optimization of engineered CO 2 sequestration and prediction of the composition and stability of Mg-carbonate phase assemblages in natural and engineered ultramafic environments requires knowledge of the solubility of hydrated Mg-carbonate phases, and the transformation pathways between these metastable phases. In this study, we evaluate the solubility of nesquehonite [MgCO 3 •3H 2 O] and dypingite [Mg 5 (CO 3) 4 (OH) 2 •(5 or 8)H 2 O] and the transformation from nesquehonite to dypingite between 5°C and 35°C, using constanttemperature, batch-reactor experimentals.. The logarithm of the solubility product of nesquehonite was determined to be:-5.03±0.13,-5.27±0.15, and-5.34±0.04 at 5°C, 25°C, and 35°C, respectively. The logarithm of the solubility product of dypingite, never reported before, was determined to be:-34.95±0.58 and-36.04±0.31 at 25°C and 35°C, respectively, with eight waters of hydration. The transformation from nesquehonite to dypingite was temperature-dependent, and was complete within 57 days at 25°C, and 20 days at 35°C, but did not occur during experiments of 59 days at 5°C. This phase transformation appeared to occur via a dissolution-reprecipitation mechanism; external nesquehonite crystal morphology was partially maintained during the phase transformation at 25°C, but was eradicated at 35°C. Together, our results facilitate the improved evaluation of Mg-carbonate mineral precipitation during natural and engineered ultramafic mineral weathering systems that sequester CO , and 20 for the first time allow assessment of the saturation state of dypingite in aqueous solutions. 21
International Journal of Greenhouse Gas Control, 2015
Nesquehonite (MgCO 3 •3H 2 O) has in the past been proposed as a low-cost, long-term mineral host for CO 2. Here, stability of the phase was investigated under low temperatures (50 • C, 100 • 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 CO 2 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 CO 2 and N 2 were used as carrier gases for H 2 O vapour to establish the influence of CO 2 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 H 2 O release from nesquehonite; delaying dehydration and preventing subsequent decomposition. Enhanced stability of nesquehonite was also observed under a CO 2 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 CO 2 store. Additionally, it establishes basic, previously overlooked conditions that are essential considerations when tailoring disposal, storage and ex situ carbonation to enhance CO 2 stability in metastable Mg-carbonate phases.
Passive Mineral Carbonation of Mg-rich Mine Wastes by Atmospheric CO2
Energy Procedia, 2017
Mg-rich process tailings and waste rocks from mining operations can react spontaneously with atmospheric CO 2 to form stable carbonate minerals by exothermic reactions. Over the last decade, we have conducted a number of laboratory and field experiments and surveys on both mine waste rocks and different types of mine tailings from Ni-Cu, chrysotile, and diamond mines. The experiments and surveys cover a wide range of time (10 3 to 10 8 s) and mass (1-10 8 g) scales. Mine waste rich in brucite or chrysotile enhances the mineral carbonation reactions. Water saturation, but more importantly, watering frequency, are highly important to optimize carbonation. Adjusting the chemical composition of the interstitial water to favour Mg dissolution and to prevent passivation of the reaction surfaces is crucial to ensure the progress of the carbonation reactions. Preservation of the permeability structure is also critical to facilitate water and CO 2 migration in the rock wastes and tailings. In field experiments, CO 2 supply controled by diffusion in the mining waste is slower than the reaction rate which limits the capture of atmospheric CO 2. Industrial implementation of passive mineral carbonation of mine waste by atmospheric CO 2 can be optimized using the above parameters.
Chemical Geology, 2019
Coupled gypsum dissolution-calcium carbonate precipitation experiments were performed in closed system reactors and in the presence of either aqueous 0.1 M Na2CO3, 0.1 M NaHCO3 or 0.1 M Na2CO3 + 0.2 M NaOH solutions. Gypsum dissolved immediately at the start of each experiment provoking the precipitation sequentially of vaterite, calcite and trace aragonite. Fine-grained amorphous carbon carbonate may also be present shortly after each experiment began. Each experiment approached equilibrium within 119 h leading to the maximum possible transformation of gypsum to calcite over this time frame. The rapid transformation of gypsum to calcite in these experiments suggests a similar rapid transformation of gypsum or anhydrite into calcite could occur during subsurface carbon storage efforts where evaporites are present. Evaporite deposits could thus potentially be used for carbonation if sufficient alkalinity is available to neutralize the acid liberated by the gypsum carbonation reaction. Due to a negative volume of the gypsum or anhydrite to calcite transformation, however, the carbonation of these minerals will potentially damage the integrity of evaporite caprocks.
Carbonate geochemistry and its role in geologic carbon storage
2021
Massive quantities of CO 2 need to be captured and stored to address the potential consequences of global warming. Geologic storage of CO 2 may be the only realistic option available to store the bulk of this CO 2 due to the required storage volumes. Geologic storage involves the injection of CO 2 into the subsurface. This injection will lead to the acidification of the formation fluids and provoke a large number of fluid-mineral reactions in the subsurface. Of these reactions, those among CO 2-rich fluids and carbonate minerals may be the most significant as these reactions are relatively rapid and have the potential to alter the integrity of caprocks and well bore cements. This review provides a detailed summary of field, laboratory and modeling results illuminating the potential impacts of the injection of large quantities of CO 2 into the subsurface as part of geologic storage efforts
International Journal of Mining, Reclamation and Environment, 2011
The ability to sequester CO 2 under elevated temperature and pressure has been shown to be successful using MgO-rich rocks. This is achieved by mineral carbonation. Two predominant sources of substrate material are considered, namely ultramafic mine waste rock and process tailings. Each material has specific sequestration potential benefits for select mining operations to source additional revenue from the offset of anthropogenic carbon and sales of carbonate industrial products. Laboratory scale tests can determine the CO 2 fixation capacity of the proposed rocks; however, a more practical repeatable method of determining the carbonation potential is needed. Data generation from autoclave testing of applicable mining waste material facilitates the understanding of carbonation determining parameters. The development of a sequestration potential algorithm that can be applied to drill hole geochemical data is preferred. The generation of non-destructive sequestration potential values from geostatistical interpretation will facilitate their inclusion into applicable mining block models and the determination of bulk carbon sequestration capacity.
Experimental Study of Carbonate Reactivity in the Context of CO2 Geological Storage
ABM Proceedings
CO2 geological storage is one of the current technologies developed worldwide to reduce industrial emissions of carbon dioxide to the atmosphere. Two main mineral types of deep geological reservoir could be contemplated for CO2 storage: sandstone reservoirs and carbonaceous reservoirs. Geochemical reactivity of a dolomite-calcite mineral compound and magnesite pure mineral was studied with a set of nine experiments per crushed mineral phase with two saline solution and with mQ water and three temperatures: 50°C, 90°C and 150°C. Experiments were performed in batch reactors with 250 bar of CO2 partial pressure during 24h to assess the effect of temperature and salinity in constant CO2 pressure. Solid characterization was performed by XRD and solution analysis by ICP-OES. Acidification of solutions due to CO2 dissolution in water is the main source of reactivity in the system. Proton concentration increases and causes partial dissolution of initial dolomite, calcite and magnesite and release of Ca 2+ and Mg 2+ cations in solution. Bicarbonate anion (HCO3) concentration also increases due to CO2 dissolution in water and carbonate minerals dissolution. Temperatures of 90°C and 150ºC increase the kinetic of reaction and the dissolution of minerals and cations release in solution. New carbonate crystalline phase precipitates as a Ca, Mg solid solution between dolomite and calcite pure poles.