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  1. Carbon Mineralization of Sulfate Wastes Containing Pb: Synchrotron Pb M3-Edge XANES Analysis of Simultaneous Heavy Metal and Carbon Sequestration

    Hu, Jun ; Pincus, Lauren N. ; Wierzbicki, Dominik ; ... - Environmental Science and Technology
    Sulfate wastes are produced in large quantities and contain toxic heavy metals such as lead (Pb), posing environmental risks. Because of favorable solubility differences, these wastes can be repurposed for engineered carbon dioxide (CO2) sequestration. Understanding the fate and mobility of heavy metals during this process is important. This study focuses on Pb and the effect of zinc (Zn) on Pb in carbon mineralization. Synthesized gypsum was treated with a carbonate-rich solution at pH 11.5 to convert the sulfates to carbonates. Aqueous solutions and mineral solids were analyzed. Synchrotron-based micro-X-ray fluorescence and a novel application of Pb M3-edge X-ray absorptionmore » near-edge structure provided detailed insights into Pb distribution and mineral forms. Results showed significant reductions in aqueous Pb and Zn concentrations, indicating effective metal sequestration. Carbon mineralization transformed Pb from soluble anglesite (PbSO4) into insoluble cerussite (PbCO3) and hydrocerussite (Pb3(CO3)2(OH)2). Pb primarily precipitated onto calcium carbonate surfaces through surface-mediated precipitation reactions. While the presence of Zn modified crystallization dynamics, it did not impede Pb sequestration and potentially enhanced surface reactivity, facilitating greater Pb immobilization. These findings highlight carbon mineralization as a sustainable approach to immobilize toxic metals in sulfate wastes while advancing CO2 sequestration efforts.« less

  2. In Situ Monitoring the Nucleation and Growth of Nanoscale CaCO3 at the Oil–Water Interface

    Zhu, Yaguang ; Wang, Ying ; Gao, Zhenwei ; ... - ACS Nano
    Interfaces can actively control the nucleation kinetics, orientations, and polymorphs of calcium carbonate (CaCO3). Prior studies have revealed that CaCO3 formation can be affected by the interplay between chemical functional moieties on solid–liquid or air–liquid interfaces as well as CaCO3’s precursors and facets. Yet little is known about the roles of a liquid–liquid interface, specifically an oil–liquid interface, in directing CaCO3 mineralization which are common in natural and engineered systems. Here, in this study, by using in situ X-ray scattering techniques to locate a meniscus formed between water and a representative oil, isooctane, we successfully monitored CaCO3 formation at themore » pliable isooctane–water interface and systematically investigated the pivotal roles of the interface in the formation of CaCO3 (i.e., particle size, its spatial distribution with respect to the interface, and its mineral phase). Different from bulk solution, ∼5 nm CaCO3 nanoparticles form at the isooctane–water interface. They stably exist for a long time (36 h), which can result from interface-stabilized dehydrated prenucleation clusters of CaCO3. There is a clear tendency for enhanced amounts and faster crystallization of CaCO3 at locations closer to isooctane, which is attributed to a higher pH and an easier dehydration environment created by the interface and oil. Our study provides insights into CaCO3 nucleation at an oil–water interface, which can deepen our understanding of pliable interfaces interacting with CaCO3 and benefit mineral scaling control during energy-related subsurface operation.« less

  3. Vaterite Optical Petrography in Lake Sturgeon Otoliths

    Chakoumakos, Bryan C. ; Pracheil, Brenda M. - Canadian Journal of Mineralogy and Petrology
    Vaterite occurring in fish otoliths exhibits plumose and spherulitic habits, the latter being like those grown from aqueous solutions. Vaterite spherulites are known to have sheaf-like texture and can be up to 100 μm in size. In thin section, the spherulites typically show uniaxial positive interference figures between cross-polarizers using a polarizing light microscope but without conoscopic or Bertrand lenses because the spherulites mimic the effect of these lenses. Plumose vaterite can show both uniaxial (+) and biaxial (+) interference figures with a small 2V, which suggests that crystal structural models for vaterite should have the plane of the carbonatemore » group parallel to the optic axis or acute bisectrix. Finally, vaterite spherulites grown from aqueous solution exhibit similar structure and growth habits.« less

  4. Replacement of Calcium Carbonate Polymorphs by Cerussite

    Kim, YoungJae ; Abdilla, Bektur ; Yuan, Ke ; ... - ACS Earth and Space Chemistry
    Calcium carbonate (CaCO3) polymorphs, calcite, aragonite, and vaterite, serve as a major sink to retain various metal ions in natural and engineered systems. Here, we visualize the systematic trends in reactivities of calcite, vaterite, and aragonite to Pb2+ dissolved in acidic aqueous solutions using in situ optical microscopy combined with ex situ scanning electron and transmission X-ray microscopies. All three polymorphs undergo pseudomorphic replacement by cerussite (PbCO3) but with distinct differences in the evolution of their morphologies. The replacement of calcite and aragonite occurs through the formation of a pseudomorphic cerussite shell (typically 5–10 μm thick) followed by a slowermore » inward propagation of reaction fronts through a thin solution gap (~0.1 μm wide) between the shell and the CaCO3 substrate. The replacement of vaterite is characterized by the formation of a thinner cerussite shell (≤1 μm thick) and a larger cavity between the shell and the host mineral. These systematic differences in cerussite morphology for different CaCO3 polymorphs are explained by the relative dissolution and precipitation rates of the reactant and product minerals, coupled with the role of ion transport through the cerussite shells. We also find that the replacement of calcite by cerussite is the slowest when all three polymorphs coexisted. Furthermore, our results provide mechanistic insights into the growth mode of cerussite on dissolving calcium carbonate and demonstrate these CaCO3 polymorphs as promising substrate materials for removal and recycling of Pb from acidic polluted water and industrial effluents.« less

  5. Sulfate-Controlled Heterogeneous CaCO3 Nucleation and Its Non-linear Interfacial Energy Evolution

    Zhu, Yaguang ; Li, Qingyun ; Kim, Doyoon ; ... - Environmental Science and Technology
    Unveiling the effects of an environmental abundant anion “sulfate” on the formation of calcium carbonate (CaCO3) is essential to understand the formation mechanisms of biominerals like corals and brachiopod shells, as well as the scale formation in desalination systems. However, it was experimentally challenging to elucidate the sulfate–CaCO3 interactions at the explicit first step of CaCO3 formation: nucleation. In addition, there is limited quantitative information on the precise control of nucleation kinetics. Here, heterogeneous CaCO3 nucleation is monitored in real time as a function of sulfate concentrations (0–10 mM Na2SO4) using synchrotron-based grazing incidence X-ray scattering techniques. The results showedmore » that sulfate can be incorporated in the nuclei, resulting in a nearly 90% decrease in the CaCO3 nucleation rate, causing a 120% increase in the CaCO3 nucleus size, and inhibiting the vaterite-to-calcite phase transformation. Moreover, this work quantitatively relates sulfate concentrations to the effective interfacial energies of CaCO3 and finds a non-linear trend, suggesting that CaCO3 heterogeneous nucleation is more sensitive at a low sulfate concentration. This study can be readily extended to study other additives and obtain quantitative relationships between additive concentrations and CaCO3 interfacial energies, a key step toward achieving natural and engineered controls on CaCO3 nucleation.« less

  6. Calcium Carbonate Cement: A Carbon Capture, Utilization, and Storage (CCUS) Technique

    Hargis, Craig W. ; Chen, Irvin A. ; Devenney, Martin ; ... - Materials
    A novel calcium carbonate cement system that mimics the naturally occurring mineralization process of carbon dioxide to biogenic or geologic calcium carbonate deposits was developed utilizing carbon dioxide-containing flue gas and high-calcium industrial solid waste as raw materials. The calcium carbonate cement reaction is based on the polymorphic transformation from metastable vaterite to aragonite and can achieve >40 MPa compressive strength. Due to its unique properties, the calcium carbonate cement is well suited for building materials applications with controlled factory manufacturing processes that can take advantage of its rapid curing at elevated temperatures and lower density for competitive advantages. Examplesmore » of suitable applications are lightweight fiber cement board and aerated concrete. The new cement system described is an environmentally sustainable alternative cement that can be carbon negative, meaning more carbon dioxide is captured during its manufacture than is emitted.« less

  7. Empirically testing vaterite structural models using neutron diffraction and thermal analysis

    Chakoumakos, Bryan C. ; Pracheil, Brenda M. ; Koenigs, Ryan ; ... - Scientific Reports
    Otoliths, calcium carbonate (CaCO3) ear bones, are among the most commonly used age and growth structures of fishes. Most fish otoliths are comprised of the most dense CaCO3 polymorph, aragonite. Sturgeon otoliths, in contrast, have been characterized as the rare and structurally enigmatic polymorph, vaterite a metastable polymorph of CaCO3. Vaterite is an important material ranging from biomedical to personal care applications although its crystal structure is highly debated. We characterized the structure of sturgeon otoliths using thermal analysis and neutron powder diffraction, which is used non-destructively. We confirmed that while sturgeon otoliths are primarily composed of vaterite, they alsomore » contain the denser CaCO3 polymorph, calcite. For the vaterite fraction, neutron diffraction data provide enhanced discrimination of the carbonate group compared to x-ray diffraction data, owing to the different relative neutron scattering lengths, and thus offer the opportunity to uniquely test the more than one dozen crystal structural models that have been proposed for vaterite. Of those, space group P6522 model, a = 7.1443(4)Å , c = 25.350(4)Å , V = 1121.5(2)Å3 provides the best fit to the neutron powder diffraction data, and allows for a structure refinement using rigid carbonate groups.« less

  8. Sturgeon and paddlefish (Acipenseridae) saggital otoliths are composed of the calcium carbonate polymorphs vaterite and calcite: acipenseridae otoliths are vaterite and calcite

    Pracheil, Brenda M. ; Chakoumakos, Bryan C. ; Feygenson, Mikhail ; ... - Journal of Fish Biology
    The otoliths of modern fishes are most commonly comprised of the metastable aragonite polymorph of calcium carbonate (CaCO3); however, sturgeons have otoliths reportedly comprised of the least stable of the three most-common polymorphs, vaterite. In this study, we used neutron diffraction to characterize CaCO3 polymorph composition of lake sturgeon and paddlefish otoliths. Based on previous summaries of CaCO3 composition over fish evolutionary history, we hypothesized that sturgeon and paddlefish otoliths would have similar polymorph composition. We found that despite previous reports of sturgeon otoliths being comprised entirely of vaterite, that all otoliths we examined in this study also had amore » calcite fraction that ranged from 17.9+ 6.0 wt. % to 35.9 + 2.9 wt. %. We also conducted a grinding experiment that demonstrated that calcite fractions were due to biological variation and not an artifact of polymorph transformation during preparation. Our study provides the initial characterization of the polymorph composition of the otoliths of lake sturgeon, and paddlefish and also provides the first-ever report of otoliths of Acipenserids as having a calcite fraction.« less
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