Greeshma Gadikota

Chemical and morphological changes during olivine carbonation for CO2 storage in the presence of NaCl and NaHCO3

The increasing concentrations of CO2 in the atmosphere are attributed to the rising consumption of fossil fuels for energy generation around the world. One of the most stable and environmentally benign methods of reducing atmospheric CO2 is by storing it as thermodynamically stable carbonate minerals. Olivine ((Mg,Fe)2SiO4) is an abundant mineral that reacts with CO2 to form Mg-carbonate. The carbonation of olivine can be enhanced by injecting solutions containing CO2 at high partial pressure into olivine-rich formations at high temperatures, or by performing ex situ mineral carbonation in a reactor system with temperature and pressure control. In this study, the effects of NaHCO3 and NaCl, whose roles in enhanced mineral carbonation have been debated, were investigated in detail along with the effects of temperature, CO2 partial pressure and reaction time for determining the extent of olivine carbonation and its associated chemical and morphological changes. At high temperature and high CO2 pressure conditions, more than 70% olivine carbonation was achieved in 3 hours in the presence of 0.64 M NaHCO3. In contrast, NaCl did not significantly affect olivine carbonation. As olivine was dissolved and carbonated, its pore volume, surface area and particle size were significantly changed and these changes influenced subsequent reactivity of olivine. Thus, for both long-term simulation of olivine carbonation in geologic formations and the ex situ reactor design, the morphological changes of olivine during its reaction with CO2 should be carefully considered in order to accurately estimate the CO2 storage capacity and understand the mechanisms for CO2 trapping by olivine.

Morphological changes during enhanced carbonation of asbestos containing material and its comparison to magnesium silicate minerals.

The disintegration of asbestos containing materials (ACM) over time can result in the mobilization of toxic chrysotile ((Mg, Fe)3Si2O5(OH)4)) fibers. Therefore, carbonation of these materials can be used to alter the fibrous morphology of asbestos and help mitigate anthropogenic CO2 emissions, depending on the amount of available alkaline metal in the materials. A series of high pressure carbonation experiments were performed in a batch reactor at PCO2 of 139atm using solvents containing different ligands (i.e., oxalate and acetate). The results of ACM carbonation were compared to those of magnesium silicate minerals which have been proposed to permanently store CO2 via mineral carbonation. The study revealed that oxalate even at a low concentration of 0.1M was effective in enhancing the extent of ACM carbonation and higher reaction temperatures also resulted in increased ACM carbonation. Formation of phases such as dolomite ((Ca, Mg)(CO3)2), whewellite (CaC2O4·H2O) and glushinskite (MgC2O4·2H2O) and a reduction in the chrysotile content was noted. Significant changes in the particle size and surface morphologies of ACM and magnesium silicate minerals toward non-fibrous structures were observed after their carbonation.

The Grand Challenges in Carbon Capture, Utilization, and Storage

1 Department of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, CA, USA 2 Energy Center and Laboratory of Molecular Simulation, Institut des Sciences et Ingenierie Chimiques, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne, Switzerland 3 Department of Earth and Environmental Engineering, Lenfest Center for Sustainable Energy, Columbia University, New York, NY, USA 4 Department of Chemical Engineering, Lenfest Center for Sustainable Energy, Columbia University, New York, NY, USA *Correspondence: berend-smit@berkeley.edu

Chapter 8 – Accelerated Carbonation of Ca- and Mg-Bearing Minerals and Industrial Wastes Using CO2

Abstract This chapter introduces the concept of carbon mineralization that involves the conversion of CO 2 into solid inorganic carbonates. It starts by presenting an overall scheme of CO 2 reactions with alkaline-rich materials such as minerals and industrial wastes containing calcium and magnesium. The engineered weathering of silicate minerals including olivine ((Mg,Fe) 2 SiO 4 ), serpentine ((Mg,Fe) 3 (OH) 4 (Si 3 O 5 )) and wollastonite (CaSiO 3 ) are discussed as one of the most safe and permanent carbon storage solutions. The method of using CO 2 to treat industrial wastes such as fly ash, cement kiln dust, stainless steel slag and red mud is also presented in detail. The carbonated materials can be readily landfilled without the concern of contaminant leaching, or utilized in various applications such as in construction. Environmental implications and potential benefits of CO 2 utilization via various carbon mineralization schemes are summarized.

The Effect of Hydration on the Structure and Transport Properties of Confined Carbon Dioxide and Methane in Calcite Nanopores

The effect of hydration on the structure and transport properties of confined carbon dioxide (CO2) and methane (CH4) in 2 nm slit-shaped calcite nanopore was studied using molecular dynamics simulations. The effect of no confined water, one layer of confined water composed of 150 water molecules, 500 water molecules, and 1,296 water molecules that correspond to the density of bulk water of 1 g/cm3 on the structural arrangement and diffusivity of confined CO2 and CH4 were investigated. Higher number of water molecules in confinement influenced the anisotropic distribution of the confined gases by displacing the adsorbed gas molecules away from the pore surface toward the pore center. The diffusivities of CO2 and CH4 were influenced by the density of confined water and were found to vary anisotropically in the calcite nanopores. In the absence of confined water, the enhanced affinity of CO2 for the calcite interface is influenced by van der Waals and electrostatic interactions. In the case of CH4, van der Waals energetic interactions contribute to the affinity to the calcite interface. In the presence of interfacial water with a density similar to that of bulk water, the van der Waals contributions arising from gas interactions with the calcite interface are much smaller compared to the van der Waals contributions arising from interactions with the water. In case of CO2, the van der Waals and electrostatic interactions arising from interactions with water contribute to CO2 solvation. However, the van der Waals interactions are the primary contributors to CH4 solvation in confined water.