An-Najah Staff

Understanding the chemical/geochemical mechanisms and phenomena that occur during above-ground mineral sequestration and below-ground geological sequestration under the pressure, temperature and activities present during sequestration are central to process understanding and development. We have developed two novel reaction cells that are being utilized to investigate the associated phenomena and mechanisms under in situ sequestration conditions in the laboratory. These observations are being synergistically integrated with advanced atomistic modeling (e.g., carbonate phase formation, fluid/solution behavior) to better understand the associated processes and phenomena. Our microreactor (X-ray synchrotron diffraction, Raman Spectroscopy, etc.) and nuclear magnetic resonance (NMR) probe provide sequestration process environments with controlled temperature, pressure, and reactant activity. We have recently enhanced the capabilities of the NMR probe to enable direct observation of fluid/solution diffusivities, as well as speciation and activities, for the associated 13 C and 1 H containing species under sequestration conditions. Enhancing the mechanistic understanding of aqueous serpentine and olivine mineral carbonation is of substantial interest for reducing above-ground sequestration process costs and in exploring the potential that Mg-bearing mineral additives offer to engineer enhanced reservoir seals (e.g., well-bore seals) for geological sequestration. To this end, aqueous mineral carbonation of a variety of activated serpentine and olivine feedstock materials has been investigated in situ to better understand (i) the mechanisms that enhance above-ground carbonation reactivity and (ii) the hydrothermal phase space that controls the hydrous/hydroxyhydrous/anhydrous carbonates that form during above-and below-ground sequestration (e.g., nesquehonite, hydromagnesite and magnesite). As solution/fluid behavior is critical to both above and below-ground sequestration process understanding, the associated fluid speciation, activity and diffusion behavior is being explored in parallel. Initial speciation, activity and diffusivity observations using the NMR probe indicate it offers an important tool for investigating solution/fluid behavior central to sequestration process development. The above experimental observations are being integrated with advanced atomistic modeling to deepen process understanding. Current results and their implication for furthering process understanding are discussed.