10 Search Results

Mineral carbonation simulates a natural weathering phenomena by breaking down silicates and oxides to form Ca & Mg carbonates. Various mineralization methods have been demonstrated as a potential technique to improve the quality of slags and tailings through neutralization and stabilization of problematic species to yield a product better suited for use in concrete. This study aims to characterize, quantify and analyze carbonates in various carbonated products such as mineralized CaCO₃, CO₂ mineralized Steel Slags and Mine Tailings. More than 10 samples were analyzed for carbonate measurement and verification from industrial and academic partners that pioneer commercial CO₂ mineralization technologies.more » The samples were characterized primarily by using X-ray diffraction (XRD), Thermogravimetric Analyses (TGA), and Scanning Electron Microscopy (SEM) to gain insights into CaCO₃ content. A baseline characterization of lab-grade CaCO₃ and MgCO₃ also revealed important considerations for CaCO₃ measurement using TGA alone. The experiments using synthetic lab-grade samples also revealed that the presence of MgCO₃/MgO can accelerate the decomposition of CaCO₃ and thus can affect measurement parameters. Lab-grade CaCO₃ samples dosed into steel slag and mine tailing also showed significant deviation in their decomposition behavior. These insights are used to inform the development of a standardized protocol for the measurement and verification of carbonate-bearing products.« less

Widespread implementation of portland limestone cements (PLC) in industry has raised new questions about their carbonation resistance due to higher initial limestone content than ordinary portland cement. While carbonation of portland cement and each of its hydrate phases has been studied at a fundamental level, the integral role of how limestone fillers interact chemically or physically during carbonation necessitates further study. In this study, a C-S-H binder comprised of a highly reactive zeolite pozzolan and lime was used to evaluate the effect of varying calcite additions on carbonation behavior at a microstructural level. Fundamental insight into hydration kinetics and carbonationmore » mechanisms of hydraulic binders was obtained via analysis of the C-S-H and calcite microstructure. X-ray microcomputed tomography (X-ray CT) was used to quantify microstructural changes, and the results showed a decrease in shrinkage for increased calcite dosages, with a ∼50% reduction observed for a 45% wt. calcite replacement level. Crystallographic and thermal analyses measured compositional changes in the binder and confirmed that shrinkage was related to the decalcification of C-S-H. Furthermore, the addition of calcite to the C-S-H binder effectively reduced the liquid-to-solid ratio, porosity, and amount of C-S-H present in these binders. Ultimately, these results help elucidate how the carbonation risks of PLC can be mitigated by proportioning the mixture water only to the reactive component of the binder.« less

Carbonation of alkaline earth metals (e.g., magnesium (Mg)) and sulfidation of nickel (Ni) are promising methods to achieve concurrent carbon mineralization and selective Ni recovery. However, the coexistence of alkaline earth metals and Ni from silicate ores or mining wastewater complicates the carbonation and sulfidation owing to cation coprecipitation. To better understand simultaneous metal carbonation and Ni-sulfide formation, we used Mg- and Ni-containing solutions and systematically investigated the Mg and Ni coprecipitates’ phase transformation during sequential/concurrent carbonation and sulfidation. During a single carbonation process, hydromagnesite dehydrated and formed magnesite over time. Nickel bicarbonate formed and became a Mg–Ni carbonate solidmore » solution because of their similar ionic radii. During a single sulfidation process, the pH did not affect Ni-sulfide formation, but it controlled Mg behavior. Specifically, at pH 9.6, brucite formed, while at pH 7.8, Mg²⁺ remained in the solution. For the sequential carbonation–sulfidation process, Ni-carbonate formed during carbonation converted to Ni-sulfide because of the low Ni-sulfide K_sp. For the sulfidation–carbonation process, Ni-sulfide remained the same even after carbonation and Mg-carbonate precipitates. For the concurrent carbonation and sulfidation process, Mg-carbonate and Ni-sulfide formed simultaneously. Finally, this study develops a scientific foundation of carbonation and sulfidation processes, benefiting coupled CO₂ storage and sulfide-enabled resource recovery.« less

A synthesis method for nanosized forsterite (Mg₂SiO₄) doped with varying concentrations of Ni and Co has been developed to support studies of carbonation-based extraction and separation of Ni and Co from mafic and ultramafic rocks. The protocol expands upon an existing sol–gel/surfactant method and is demonstrated for doping levels of 5% and 25% of Ni or Co. Variables such as metal reagents, surfactant ratios, and calcination procedures were optimized to achieve high specific surface areas and small particle sizes while minimizing secondary phase formation. Particle sizes ranged from 29 to 83 nm, and specific surface areas were between 11 andmore » 32 m² g⁻¹. Metal oxide impurities were minimal, appearing only in undoped and 25% Ni-doped samples at 0.6 wt% or less. Ni and Co were only detected in the +II oxidation state and partitioned predominantly in the M1 cation site of the forsterite crystal structure. Doped nanosized forsterites prepared with this method will enable in situ experiments that can track, at the molecular scale, the fate of Ni and Co during carbonation reactions and thus provide a knowledge base for improving metal extraction and separation technologies.« less

To potentially enable CO₂ sequestration, reactive MgO carbonate cement is emerging as an alternative binder to Portland cement. Understanding the mechanical properties of its binding phase is critical for understanding the strength development and performing materials design for reactive MgO cement systems; however, the intrinsic mechanical properties of hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O), a key binding phase, remain unexplored. Here the present study utilized synchrotron-based high-pressure X-ray diffraction to determine the unit cell-scale, intrinsic mechanical properties of hydromagnesite for the first time. Up to hydrostatic loading of 7.7 GPa, the bulk modulus of hydromagnesite was determined as 59 GPa or 71 GPa fittedmore » using the second-order or third-order Birch-Murnaghan equation of state, which we contextualize with binding phases in various cement systems. The experiment results are applicable in materials design of low-carbon concrete and valuable for the validation and calibration of atomistic models.« less

Iron plays a vital role in natural processes such as water, mineral, iron, and nutrient cycles. Iron undergoes reduction-oxidation and catalytic reactions to produce various corrosion films depending on its chemical environment. Near ambient pressure X-ray photoelectron spectroscopy, polarized modulated infrared reflection absorption spectroscopy, and Auger electron spectroscopy were used to study the key reactants, from O₂(g), H₂O vapor, Na⁺ and Cl^– on the initial stages of iron surface corrosion. Here, with increasing the ratio of O₂ and H₂O, surface hydrocarbons were shown to oxidize into carbonates, while the Cl^– was found to migrate into the interface. The effect ofmore » each individual reactant was measured separately and water was shown to have a first order rate dependence on the carbonate growth at low pressures, with little dependence for O₂. Near ambient pressures, both H₂O and O₂ were found to increase the carbonate growth, which was estimated using the Langmuir isotherm model, yielding Gibbs energies between –9.8 to –8.5 kJ/mol. A mechanism is suggested to explain the oxidation is catalyzed by NaCl on iron surfaces and the adventitious hydrocarbons served as the source for surface carbonation. These findings have implications for understanding other surface catalytic and redox interface chemistry in complex environments.« less

Cast Stone is a cementitious waste form being considered for the solidification of low activity waste at the DOE Hanford Site. Under near-surface disposal conditions in an arid environment, Cast Stone is subject to drying and carbonation which may impact retention of waste constituents. Here this study investigates the effects of environmental CO₂ concentration and relative humidity (RH) on the carbonation of Cast Stone. The rate of carbonation front ingress and the extent of carbonation reaction were characterized for samples aged up to 48 weeks at three RH levels and two CO₂ concentrations. While the 68% RH environment allowed themore » greatest reaction extent, the 15% RH environment yielded the deepest carbonation front ingress. At 68% RH, there was a linear relationship between the ingress rate and CO₂ concentration. Carbonation reactions increased the drying rate of Cast Stone. Redistribution of sodium toward the wetting front was observed under drying and carbonation conditions.« less

Silicon (Si) is the most naturally abundant element possessing 10-fold greater theoretical capacity compared to that of graphite-based anodes. The practicality of implementing Si anodes is, however, limited by the unstable solid/electrolyte interphase (SEI) and anode fracturing during continuous lithiation/delithiation. We demonstrate that glyme-based electrolytes (GlyEls) ensure a conformal SEI on Si and keep the Si “fracture-free”. Benchmarking against the optimal, commonly used carbonate electrolyte with the fluoroethylene carbonate additive, the Si anode cycled in a GlyEl exhibits a reduced early parasitic current (by 62.5%) and interfacial resistance (by 72.8%), while cell capacity retention is promoted by >7% over themore » course of 110 cycles. A mechanistic investigation by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy indicates GlyEl enriches Si SEI with elastic polyether but diminishes its carbonate species. Glyme-based electrolytes proved to be viable in stabilizing the SEI on Si for future high energy density lithium-ion batteries.« less

Wellbore cement is subjected to a number of mechanical, thermal and chemical stress regimes over its lifetime. Therefore, next-generation wellbore cement formulations need to be evaluated in conditions relevant to these environments. In this work, we investigate the mechanism of the alteration of a novel self-healing polymer-cement composite after exposure to a CO₂-rich environment by using synchrotron-based X-ray Fluorescence (XRF), X-ray absorption near edge structure (XANES), and scanning electron microscopy coupled with energy dispersive spectroscopy. Results showed that a chemical alteration of the polymer-cement follows the rim carbonation mechanism, similar to conventional cement, although carbonation takes place to a lessermore » extent in polymer-cements despite the higher porosity. Along with detailed mechanistic insights on carbonation in polymer-cement composite, the performance of these in CO₂-rich environment is further studied using standard compressive strength analysis.« less

Exposing operating AEMFCs to CO ₂ leads to performance-robbing overpotentials, linked to fundamental thermodynamics, transport and kinetics – the impact of which can be reduced through careful systems design and selection of operating conditions.