E.C. La Plante, J. Wang, A. Alturki, D. Simonetti, D. Jassby, G. Sant
University of California, Los Angeles,
Keywords: single-step, mineralization, electrolytic, alkalinity
Summary:Limiting the increase in the global average temperature to 1.5 °C requires removal of 10–20 Gt of CO2 annually from the atmosphere over the next century. The injection of CO2 captured from point sources or the atmosphere into geological formations could sequester up to 22,000 Gt of CO2 in North America. While the conceivable capacity of geological sequestration sites is more than sufficient to accommodate current (and future) levels of CO2 emissions, the risk of CO2 migration and leakage, and the management and verification of the injection process necessitate significant monitoring of the wells, the subsurface, and the ground surface over time. In this perspective, we present a single-step carbon sequestration and storage strategy based on the synthetic precipitation of solid calcium carbonate (CaCO3), magnesium carbonate (MgCO3), and their variants by combining dissolved CO2 gas with Ca2+ and Mg2+ species within an aqueous reaction medium. Thermodynamic and kinetic analyses show the amounts of reactants and the processes which facilitate carbonation. We examine a typical approach of addition of a strong base such as NaOH to a circumneutral Ca- and Mg-containing solution, likening CO2 mineralization to water treatment processes, and then propose an alternative electrochemical pathway conceptualized around metallic (i.e., conductive) membranes that induce pH shifts near the electrode-solution interface. The respective energy demands were estimated and compared with those for a geological carbon capture and storage (CCS) strategy. Unlike geological CCS, mineralization-based CO2 abatement does not require a CO2 capture step. Thus, the energy requirements of the process are based around the needs of: water handling and processing, and NaOH production. The proposed scheme can be applied without cost escalation over a wide range of CO2 concentrations (i.e., atmospheric concentrations to 100% CO2) and temperatures (i.e., ambient to ~90°C), and is insensitive to the impurities found in post-combustion CO2 streams. The mineralized carbonate solids can be disposed of on the Earth’s surface, either terrestrially or in shallow ocean regions in proximity of the continental shelf where they will remain inert, requiring minimal monitoring unlike geological storage. The process, which is conditioned around handling large quantities of water and producing hydrogen as a co-product, is well-suited for integration into desalination plants. Most significantly, the approach results in reduced process complexity with fewer unit operations which eases process intensification and enables complete renewable energy integration. The large and durable carbon storage capacity, the benign, environmentally compatible nature of the process, and the elimination of the risk of CO2 release warrant the viability of the process for long-term gigaton-scale CO2 waste management.