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Mineralization of gaseous carbon dioxide into solid carbonates using alkaline industrial residues such as coal fly ash has a dual advantage of reducing the carbon dioxide footprint of coal power plants and improving ash utilization. However, the slow mineral carbonation rate under atmospheric conditions is a major challenge, especially when using natural minerals or industrial residues for direct air capture (DAC) of CO₂. In this study, using coal fly ash samples and concentrated alkali carbonate aqueous solutions as a recyclable solvent, we show the feasibility of coupling mineral carbonation with DAC under atmospheric conditions. Findings show that carbonation efficiency ismore » best under alkaline conditions, achieving as high as ~80% conversion to calcium carbonates within 1 h in a 1.9 M sodium carbonate solution. Based on the experimental results, a process coupling DAC and mineral carbonation that operates entirely under ambient conditions is proposed. Here, the techno-economic and life cycle assessments for the proposed process project a levelized cost of $$\$$116$–133/t-CO₂-sequestered (US $$\$$2019$) and process carbon emissions (GWP) in the range of 0.03–0.25 t-CO₂e/t-CO₂-sequestered. Considering the low cost, simplicity, and gigaton-scale sequestration potential, we believe that DAC based on alkaline industrial residue carbonation can be considered a “low-hanging fruit” in the pursuit of negative emissions to combat climate change.« less

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Abstract Phyllosilicate minerals, due to their sheets structure and morphology, are known to cause anisotropy in bulk rock properties and make the bulk rock more compliant. Accurately characterizing the micromechanical behavior of phyllosilicate minerals from laboratory observations, which eventually translates to the bulk rock behavior, is still challenging due to their fine‐grained nature. Recent advances in atomistic simulations open the possibility of theoretically investigating such mineral mechanical behavior. We compare the elastic properties of biotites recovered by spherical nanoindentation with those predicted from density functional theory (DFT) simulations to investigate to what extent theoretical predictions reproduce actual phyllosilicate properties. Sphericalmore » nanoindentation was conducted using schist rocks from Poorman Formation, South Dakota, USA, to recover continuous indentation stress‐strain curves. Loading in the layer‐normal orientation shows an average indentation modulus ( ) of about 35 GPa, while loading in the layer‐parallel orientation gives a higher average of about 95 GPa. To facilitate comparison, the elastic stiffness constants ( c _ij ) determined from DFT were converted to indentation modulus ( ) using solutions proposed in this study. The majority of the nanoindentation modulus results are below the values inferred from the simulation results representing ideal defect‐free minerals. We suggest that crystal defects present at the nano‐scale, potentially ripplocations, are the dominant cause of the lower indentation modulus recovered from nanoindentation compared to those inferred from DFT simulations. Results highlight the importance of acknowledging the defects that exist down to the nano‐scale as it modifies the mechanical properties of phyllosilicates compared to its pure defect‐free form.« less

High-sulfur mixed fly ash residues from semi-dry flue gas desulfurization units in coal-fired power plants are unsuitable for use as supplementary cementitious material (SCM) for concrete production or carbon dioxide utilization. In this work, we explore the potential for upcycling a representative spray dry absorber ash (10.44 wt% SO₃) into concrete-SCM by selective sulfur removal via weak acid dissolution while simultaneously exploring the possibility for CO₂ capture. Towards this effort, parametric studies varying liquid-to-solid ratio, acidity, and CO₂ pressure were conducted in a batch reactor to establish the sulfur removal characteristics in de-ionized water, nitric acid, and carbonic acid, respectively.more » The dissolution studies show that the leaching of sulfur from calcium sulfite hemihydrate, which is the predominant S phase, is rapid and achieves a concentration plateau within 5 min, and subsequently, appears to be controlled by the primary mineral solubility. Here, preferential S removal was sufficient to meet SCM standards (e.g., 5.0 wt% as per ASTM C618) using all three washing solutions with 0.62–0.72 selectivity (S^), defined as the molar ratio of S to Ca in the leachate, for a raw fly ash with bulk S^ = 0.3. Acid dissolution with 1.43 meq/g of ash or under 5 atm CO₂ retained > 18 wt% CaO and other Si-, Al-rich phases in the fly ash. Based on the experimental findings, two sulfur removal schemes were suggested for either integration with CO₂ capture and utilization processes using flue gas or to produce fly ash for use as a SCM.« less

Alkaline industrial wastes (e.g., slags: ordered crystalline solids, and fly ashes: disordered solids) represent abundant reservoirs of elements such as silicon and calcium. Rapid elemental extractions from these wastes, however, have often relied on the use of “stoichiometric additives” (i.e., acids or bases). Herein, we demonstrate that acoustic stimulation enhances the release of network-forming Si species from crystalline blast furnace slags and amorphous fly ashes at reaction temperatures less than 65 °C. These additive-free enhancements are induced by cavitation processes which reduce the apparent activation energy of solute dissolution (E_a, kJ/mol) by up to 40% as compared to unstimulated conditions.more » Because of the reduction in the apparent activation energy, acoustic stimulation features an energy intensity that is up to 80% lower in promoting dissolution, as compared to other additive-free methods such as enhancing the solute’s surface area, introducing heat, or convectively mixing the solvent. Based on atomic topology analysis, we show that the reduction in apparent dissolution activation energy upon acoustic stimulation scales with the number of weak topological constraints per atom in the atomic network of the dissolving solute, independent of their ordered or disordered nature. This suggests that sonication breaks the weakest constraints in the solute’s atomic network, which, in turn, facilitates dissolution. Furthermore, the results suggest the ability of acoustic stimulation to enhance waste utilization and circularity, by enabling efficient resource extraction from industrial wastes.« less

Calcium hydroxide (Ca(OH)₂), a commodity chemical, finds use in diverse industries ranging from food, to environmental remediation and construction. However, the current thermal process of Ca(OH)₂ production via limestone calcination is energy- and CO₂-intensive. Herein, we demonstrate a novel aqueous-phase calcination-free process to precipitate Ca(OH)₂ from saturated solutions at sub-boiling temperatures in three steps. First, calcium was extracted from an archetypal alkaline industrial waste, a steel slag, to produce an alkaline leachate. Second, the leachate was concentrated using reverse osmosis (RO) processing. This elevated the Ca-abundance in the leachate to a level approaching Ca(OH)₂ saturation at ambient temperature. Thereafter, Ca(OH)₂more » was precipitated from the concentrated leachate by forcing a temperature excursion in excess of 65 °C while exploiting the retrograde solubility of Ca(OH)₂. This nature of temperature swing can be forced using low-grade waste heat (≤100 °C) as is often available at power generation, and industrial facilities, or using solar thermal heat. Based on a detailed accounting of the mass and energy balances, this new process offers at least ≈65% lower CO₂ emissions than incumbent methods of Ca(OH)₂, and potentially, cement production.« less

Irradiation and vitrification can both result in the disordering of minerals. However, it remains unclear whether these effects are comparable or if the glassy state represents an upper limit for irradiation-induced disordering. By reactive molecular dynamics simulations, we compare the structure of irradiated quartz to that of glassy silica. We show that although they share some degree of similarity, the structure of irradiated quartz and glassy silica differs from each other, both at the short- (<3 Å) and the medium-range (>3 Å and <10 Å). In particular, the atomic network of irradiated quartz is found to comprise coordination defects, edge-sharingmore » units, and large rings, which are absent from glassy silica. These results highlight the different nature of irradiation- and vitrification-induced disordering.« less