Mineral carbon dioxide sequestration: Enhancing process kinetics and a resource base assessment for minerals suitable for use in enhanced carbonation processes

Mineral carbon dioxide sequestration binds CO2 by reacting it with calcium or magnesium silicate minerals to form solid magnesium or calcium carbonate products that are ready for disposal. The development of a cost effective process would provide a powerful tool in carbon management. Research on mineral sequestration has focused on enhancing process kinetics in aqueous processing schemes. High costs of these processes are associated with mineral processing, such as ultrafine grinding steps, or the consumption of acids and bases, required to speed up silicate mineral dissolution kinetics. Through experimental work neutral organic salts such as sodium oxalate, and sodium citrate, are identified as potential catalysts for use in enhancing dissolution kinetics without being consumed in the reaction. Neutral salts NaCl, NH4Cl, and sodium acetate are shown to be ineffective. The dissolution rate of antigorite serpentine is shown to have concentration dependence of order 0.52 and activation energy of dissolution of 38.3 kJ/mol in the presence of the citrate ion under weakly acidic conditions. Rates are shown to be several orders of magnitude higher in the presence of citrate than in the weakly acidic solution alone. The 2005 Intergovernmental Panel on Climate Change report on Carbon Dioxide Capture and Storage suggested that a major gap in mineral CO2 sequestration is locating the magnesium-silicate bedrock available to sequester the carbon dioxide. Researchers at Columbia University and the U.S. Geological Survey have developed a digital geologic database of ultramafic rocks in the conterminous United States. Data were compiled from varied-scale geologic maps of magnesium-silicate ultramafic rocks. The focus of our national-scale map is entirely on ultramafic rock types, which typically consist primarily of olivine- and serpentine-rich rocks. These rock types are potentially suitable as source material for mineral CO2 sequestration. Simple estimates are made on the potential for CO2 storage capacity. Using simplifying assumptions on the depth of mines, the efficiency of conversion, and the magnesium concentration of the rock, it is shown that a conservative surface area specific sequestration capacity range for ultramafic rocks is 50-80 Mt CO2 per km2 of ultramafic rock exposure. There is over 16,000 km2 of ultramafic rock exposure in the conterminous United States, about 4,000 km2 of which lies in urban areas and federal lands such as national parks that exclude the possibility of mining. Thus the sequestration capacity of ultramafic rocks in the conterminous United States can reasonably believed to be at least 600-960 Gt CO2

Pore Scale Observations of Trapped CO₂ in Mixed-Wet Carbonate Rock: Applications to Storage in Oil Fields

Geologic CO₂ storage has been identified as a key to avoiding dangerous climate change. Storage in oil reservoirs dominates the portfolio of existing projects due to favorable economics. However, in an earlier related work (Al-Menhali and Krevor Environ. Sci. Technol. 2016, 50, 2727−2734), it was identified that an important trapping mechanism, residual trapping, is weakened in rocks with a mixed wetting state typical of oil reservoirs. We investigated the physical basis of this weakened trapping using pore scale observations of supercritical CO₂ in mixed-wet carbonates. The wetting alteration induced by oil provided CO₂-wet surfaces that served as conduits to flow. <i>In situ</i> measurements of contact angles showed that CO₂ varied from nonwetting to wetting throughout the pore space, with contact angles ranging 25° < θ < 127°; in contrast, an inert gas, N₂, was nonwetting with a smaller range of contact angle 24° < θ < 68°. Observations of trapped ganglia morphology showed that this wettability allowed CO₂ to create large, connected, ganglia by inhabiting small pores in mixed-wet rocks. The connected ganglia persisted after three pore volumes of brine injection, facilitating the desaturation that leads to decreased trapping relative to water-wet systems

Pore Scale Observations of Trapped CO2 in Mixed-Wet Carbonate Rock: Applications to Storage in Oil Fields

Geologic CO2 storage has been identified as a key to avoiding dangerous climate change. Storage in oil reservoirs dominates the portfolio of existing projects due to favorable economics. However, in an earlier related work (Al-Menhali and Krevor Environ. Sci. Technol. 2016, 50, 2727−2734), it was identified that an important trapping mechanism, residual trapping, is weakened in rocks with a mixed wetting state typical of oil reservoirs. We investigated the physical basis of this weakened trapping using pore scale observations of supercritical CO2 in mixed-wet carbonates. The wetting alteration induced by oil provided CO2-wet surfaces that served as conduits to flow. In situ measurements of contact angles showed that CO2 varied from nonwetting to wetting throughout the pore space, with contact angles ranging 25° < θ < 127°; in contrast, an inert gas, N2, was nonwetting with a smaller range of contact angle 24° < θ < 68°. Observations of trapped ganglia morphology showed that this wettability allowed CO2 to create large, connected, ganglia by inhabiting small pores in mixed-wet rocks. The connected ganglia persisted after three pore volumes of brine injection, facilitating the desaturation that leads to decreased trapping relative to water-wet systems