Molecular Insights into the CO2 Mineralization Process with Tricalcium Silicate

CO2 mineralization, a pivotal technology in CO2 capture, storage, and utilization, promises to convert industrial waste into valuable industrial products. However, the intricate reaction mechanism and rate-limiting process remain inadequately elucidated. The suitable reaction conditions should be clarified when designing industrial produce. In this study, we comprehensively examined the reaction kinetics and conversion rates of C3S under varying conditions and degrees of dispersion by reactive molecular dynamics simulation. Furthermore, we set up a sophisticated model depicting C3S encased within a water film, mirroring its prevalent configuration in moist environments. The results show that the reaction is fast when the temperature is 328 K. The conversion rate tends to decrease under elevated pressure when it is higher than 1.0 MPa, while the temperature has a minimal impact. Fragmentation of solid waste can increase the degree of dispersion, disrupting the crystal structure and expanding the reaction surface area, thereby accelerating the reaction. The presence of a water film impedes mass transfer, consequently reducing the reaction speed. The present study sheds light on the reaction mechanism of the CO2 mineralization process.

ZeroCAL: Eliminating Carbon Dioxide Emissions from Limestone's Decomposition to Decarbonize Cement Production

Limestone (calcite, CaCO3) is an abundant and cost-effective source of calcium oxide (CaO) for cement and lime production. However, the thermochemical decomposition of limestone (∼800 °C, 1 bar) to produce lime (CaO) results in substantial carbon dioxide (CO2(g)) emissions and energy use, i.e., ∼1 tonne [t] of CO2 and ∼1.4 MWh per t of CaO produced. Here, we describe a new pathway to use CaCO3 as a Ca source to make hydrated lime (portlandite, Ca(OH)2) at ambient conditions (p, T)-while nearly eliminating process CO2(g) emissions (as low as 1.5 mol. % of the CO2 in the precursor CaCO3, equivalent to 9 kg of CO2(g) per t of Ca(OH)2)-within an aqueous flow-electrolysis/pH-swing process that coproduces hydrogen (H2(g)) and oxygen (O2(g)). Because Ca(OH)2 is a zero-carbon precursor for cement and lime production, this approach represents a significant advancement in the production of zero-carbon cement. The Zero CArbon Lime (ZeroCAL) process includes dissolution, separation/recovery, and electrolysis stages according to the following steps: (Step 1) chelator (e.g., ethylenediaminetetraacetic acid, EDTA)-promoted dissolution of CaCO3 and complexation of Ca2+ under basic (>pH 9) conditions, (Step 2a) Ca enrichment and separation using nanofiltration (NF), which allows separation of the Ca-EDTA complex from the accompanying bicarbonate (HCO3 -) species, (Step 2b) acidity-promoted decomplexation of Ca from EDTA, which allows near-complete chelator recovery and the formation of a Ca-enriched stream, and (Step 3) rapid precipitation of Ca(OH)2 from the Ca-enriched stream using electrolytically produced alkalinity. These reactions can be conducted in a seawater matrix yielding coproducts including hydrochloric acid (HCl) and sodium bicarbonate (NaHCO3), resulting from electrolysis and limestone dissolution, respectively. Careful analysis of the reaction stoichiometries and energy balances indicates that approximately 1.35 t of CaCO3, 1.09 t of water, 0.79 t of sodium chloride (NaCl), and ∼2 MWh of electrical energy are required to produce 1 t of Ca(OH)2, with significant opportunity for process intensification. This approach has major implications for decarbonizing cement production within a paradigm that emphasizes the use of existing cement plants and electrification of industrial operations, while also creating approaches for alkalinity production that enable cost-effective and scalable CO2 mineralization via Ca(OH)2 carbonation.

Electrosteric Control of the Aggregation and Yielding Behavior of Concentrated Portlandite Suspensions

Portlandite (calcium hydroxide: CH: Ca(OH)2) suspensions aggregate spontaneously and form percolated fractal aggregate networks when dispersed in water. Consequently, the viscosity and yield stress of portlandite suspensions diverge at low particle loadings, adversely affecting their processability. Even though polycarboxylate ether (PCE)-based comb polyelectrolytes are routinely used to alter the particle dispersion state, water demand, and rheology of similar suspensions (e.g., ordinary portland cement suspensions) that feature a high pH and high ionic strength, their use to control portlandite suspension rheology has not been elucidated. This study combines adsorption isotherms and rheological measurements to elucidate the role of PCE composition (i.e., charge density, side chain length, and grafting density) in controlling the extent of PCE adsorption, particle flocculation, suspension yield stress, and thermal response of portlandite suspensions. We show that longer side-chain PCEs are more effective in affecting suspension viscosity and yield stress, in spite of their lower adsorption saturation limit and fractional adsorption. The superior steric hindrance induced by the longer side chain PCEs results in better efficacy in mitigating particle aggregation even at low dosages. However, when dosed at optimal dosages (i.e., a dosage that induces a dynamically equilibrated dispersion state of particle aggregates), different PCE-dosed portlandite suspensions exhibit identical fractal structuring and rheological behavior regardless of the side chain length. Furthermore, it is shown that the unusual evolution of the rheological response of portlandite suspensions with temperature can be tailored by adjusting the PCE dosage. The ability of PCEs to modulate the rheology of aggregating charged particle suspensions can be generally extended to any colloidal suspension with a strong screening of repulsive electrostatic interactions.

The Global Carbon Footprint and How New Carbon Mineralization Technologies Can Be Used to Reduce CO2 Emissions

Carbon dioxide is a byproduct of our industrial society. It is released into the atmosphere, which has an adverse effect on the environment. Carbon dioxide management is necessary to limit the global average temperature increase to 1.5 degrees Celsius and mitigate the effects of climate change, as outlined in the Paris Agreement. To accomplish this objective realistically, the emissions gap must be closed by 2030. Additionally, 10–20 Gt of CO2 per year must be removed from the atmosphere within the next century, necessitating large-scale carbon management strategies. The present procedures and technologies for CO2 carbonation, including direct and indirect carbonation and certain industrial instances, have been explored in length. This paper highlights novel technologies to capture CO2, convert it to other valuable products, and permanently remove it from the atmosphere. Additionally, the constraints and difficulties associated with carbon mineralization have been discussed. These techniques may permanently remove the CO2 emitted due to industrial society, which has an unfavorable influence on the environment, from the atmosphere. These technologies create solutions for both climate change and economic development.