10 Search Results

Subsurface injection of carbon dioxide (CO₂) into mafic-ultramafic rocks for permanent storage via mineralization is being studied to reduce emissions. Here, we investigated the carbonation products of enstatite (MgSiO₃) to assess its efficiency in sequestering CO₂ for safe and permanent storage as carbonate minerals. This was accomplished by conducting variable temperature carbonation reactions with samples of differing crystallinities and surface chemistries. Reaction progress was monitored utilizing in situ X-ray diffraction, and the presence of carbonate products was confirmed using additional techniques, such as thermogravimetric analysis coupled with mass spectrometry and scanning electron microscopy with energy dispersive spectrometry. Our results showmore » that crystalline enstatite produces small amounts of the anhydrous form of MgCO₃ (magnesite), while amorphous MgSiO₃, which was used to simulate mafic glass, more readily converts to the hydrated/hydroxylated hydromagnesite [Mg₅(CO₃)₄(OH)₂·4H₂O]. These results, supplemented with dynamic vapor sorption experiments, suggest that surface properties play a significant role in the pathway and degree of carbonation. These developments concerning the reactivity of CO₂ with reactive mafic phases will help further our understanding of the reactivity of these mafic-ultramafic minerals with implications for permanent carbon storage and other subsurface engineering scenarios involving reactive reservoirs.« less

Algal biochar, as the solid residue of biofuel production from algal biomass, is reported to explore disposition options, aiming to lessen the liability or obstacles to biofuel production processes. However, landfills and open combustion lead to adverse environmental impacts. One way to add value to such wastes is to use them as admixtures in cementitious construction materials. This study aims to investigate the feasibility of algae-derived biochar as supplementary cementitious materials (SCM) at different water contents and mixture ratios. Algal biochar-cement composites were prepared with different algal biochar content as well as different water-to-cement (w/c) ratios, and the surface area,more » morphology, elemental, and mineralogical composition were characterized. To compensate for the high-water absorption of algal biochar, a small concentration of a superplasticizer was used since higher w/c ratios negatively impact strength. The mechanical performance of algal biochar-cement composites is compared with control composites using commercial silica fume as a typical commercial SCM. The findings suggest that algal biochar is a promising candidate to replace commercial SCM, like silica fume, since algal biochar-cement composites can reach comparable compressive strength and Young’s modulus to commercial pozzolan-cement materials with the same w/c ratio, though at later curing times, 33 days. Although the tensile strength of algal biochar-cement composites is statistically similar at 7 days, it is significantly lower at later curing times, and further investigation is required to improve this property. Algal biochar-based cement binders showed comparable embodied carbon to silica fume-based cement binders based on a cradle-to-gate lifecycle analysis. However, the ability of algal biochar to absorb large volumes of CO₂ over short periods of time, as measured in this study, makes this novel SCM an excellent alternative to reduce the embodied carbon of concrete structures cradle-to-grave at 1/10 of the cost. In conclusion, valorization of algae-derived solid waste provides great potential to reduce embodied carbon and brings credit to biofuel production and concrete-based construction.« less

Geologic carbon sequestration in mafic and ultramafic reservoirs is a scalable strategy for carbon dioxide removal, offering permanent storage via mineralization as stable carbonates. However, there is limited information on the structure and composition of key mineralization endpoints during sequestration. Here, we unravel the atomic structure, composition, and nanoscale morphology of carbonates recovered from a field-scale demonstration of CO₂ mineralization in basalt. Using transmission electron microscopy, we mapped mineralogical variations from the initial to later stages of subsurface carbonate growth and identified a previously unknown cation-ordered ankerite phase that exerts a primary control over carbonation processes. This study has providedmore » a new understanding of subsurface carbonation pathways which will impact the parameterization of predictive geochemical models for future sequestration efforts in basalt formations.« less

Four promising iodine “getter” materials (Ag, Cu, Bi, and Sn) for radioiodine capture were assessed in their pure metal-iodide (MI_x) pelletized forms to compare relative chemical durabilities. To study chemical durability, commercial MI_x compounds of AgI, BiI₃, BiOI, CuI, and SnI₄ were converted to dense monolithic pellets using spark plasma sintering. Semidynamic leach testing in the form of modified ASTM C1308 tests was then performed on the pellets in two different forms including unmounted (as-pressed) specimens (i.e., “U”) and epoxy-mounted specimens (i.e., “M”) with polished surfaces. The chemical durability results and sample characterizations showed that three of the five MI_xmore » compounds tested (i.e., AgI, CuI, and BiOI) displayed moderate to high leach resistances. Further, the remaining two MI_x compounds (i.e., BiI₃ and SnI₄), which are both desirable iodine waste forms due to their high iodine loading capacities, readily decomposed during leach testing, indicated by crystallographic changes in the specimens as well as large amounts of iodine detected in the leachate solutions. The instabilities of BiI₃ and SnI₄ raise uncertainties for using the base metals/cations (i.e., Bi⁰/Bi³⁺ and Sn⁰/Sn⁴⁺, respectively) as viable getters for radioiodine capture due to likely poor waste form chemical durabilities after capture and consolidation into waste forms.« less

This Review summarizes a range of analytical techniques that can be used to detect, quantify, and/or distinguish between isotopes of iodine (e.g., long-lived ¹²⁹I, short-lived ¹³¹I, stable ¹²⁷I). One reason this is of interest is that understanding potential radioiodine release from nuclear processes is crucial to prevent environmental contamination and to protect human health as it can incorporate into the thyroid leading to cancer. It is also of interest for evaluating iodine retention performances of next-generation iodine off-gas capture materials and long-term waste forms for immobilizing radioiodine for disposal in geologic repositories. Depending upon the form of iodine (e.g., molecules,more » elemental, and ionic) and the matter state (i.e., solid, liquid, and gaseous), the available options can vary. In addition, several other key parameters vary between the methods discussed herein, including the destructive vs nondestructive nature of the measurement process (including in situ vs ex situ measurement options), the analytical data collection times, and the amount of sample required for analysis.« less

Here, borosilicate waste glasses were successfully developed to immobilize two high-level waste raffinate streams via an in-can melter process with an Inconel 601 canister at 1050 °C. Measured viscosity and crystallinity thermal profiles were within the targeted processing constraints for the in-can melter process. Measured chemical durability of the glass by ASTM C1285–21 (Method A), ranged from normalized loss of boron, NL(B) = 1.44 – 2.65 g•m^-2, and NL(B) decreased with increased waste loading, accompanied by increased SnO₂ crystallinity. Measured corrosion of the in-can melter canister by a glass melt showed that Inconel 601 performed well at 1100 °C formore » up to 500 hr. Resistance polarization measurements versus time revealed that Inconel 601 corrosion rates in (and by) glass melts decreased from an initial rate of 63 mm•y^-1 down to 10.2 mm•y^-1 after 137 h with increased duration, which was attributed to formation of an oxide passivation layer (mainly Cr₂O₃) at the alloy-glass interface.« less

The ongoing use of fossil fuels to supply modern energy demands has necessitated research on combating carbon dioxide (CO₂) emissions and climate change. Carbon storage via mineral trapping in basalt and related rocks is a promising strategy. However, mineralization rates depend on the variable minerology that makes up these rock formations. Diopside (CaMgSi₂O₆) is a common pyroxene mineral in ultramafic and mafic rocks including basalt, but relatively little work has been done to understand its carbon mineralization kinetics using hydrated supercritical CO₂, which induces the formation of reactive nanoscale interfacial water films. Here, in situ XRD experiments at 50–110 °Cmore » and 90 bar indicate that diopside transforms into a myriad of Mg/Ca carbonates, including huntite [Mg₃Ca(CO₃)₄] and very high magnesium calcite (VHMC, i.e., protodolomite). Through ex situ characterization, we were able to constrain reaction pathways for the dissolution–precipitation transformation process including metastable intermediate precipitates. Experiments performed at variable temperatures enabled Avrami-derived rate constants and an apparent activation energy of 97 ± 16 kJ mol^–1, implying the dissolution of diopside is the rate-limiting step. Density functional theory (DFT) calculations, used to gain molecular insight into the surface stability of the diopside during dissolution, suggest that exposed calcium cations are susceptible to dissolution when put in contact with water given their coordination environment. The collective results point to the high CO₂ mineralization potential of diopside in basalts, which could help guide parameterization of reactive transport models needed to design and permit commercial-scale subsurface carbon storage operations.« less

Given the importance of glass materials to society, their durability when exposed to aqueous solutions is a critical area for research, particularly for vitrified radioactive wastes. This spurred an international team to fabricate a standardized composition based on waste immobilization glass called the International Simple Glass (ISG), which has been the subject of numerous experimental and computational studies focused on aqueous corrosion resistance. With the original batch of ISG nearly depleted, the international team designed and fabricated a standard glass material, ISG-2, where half the Ca in the original composition was replaced with Mg by mole. This paper presents informationmore » on both the ISG-2 composition and a new batch with the same nominal composition as the original ISG, designated ISG-1, including their homogeneity, their physical and thermal properties. The results of static alteration experiments are presented as well to provide a baseline for future aqueous corrosion performance investigations.« less

The glass dissolution rate of some glasses accelerates after prolonged time spent at a slow, residual glass dissolution rate. This phenomenon is referred to as Stage III behavior. Here, the acceleration in glass dissolution rate linked to Stage III behavior is significant and may be the most impactful to long-term performance of glass in a repository. This work is aimed at understanding the effect of glass composition on Stage III behavior to add a level of technical defensibility to glass disposal. To this end, a set of twenty-four glass compositions were statistically designed, where eight glass components (SiO₂, B₂O₃, Al₂O₃,more » CaO, Na₂O, SnO₂, ZrO₂, and Others) have been independently varied in order to study the individual effects of each. These glasses have been subjected to static dissolution tests at 90 °C in deionized water and then seeded with zeolite Na-P2 28 days into the testing to induce Stage III behavior. The response of the glasses to the zeolite seeds fell into four primary types: 1) no response to seeds; 2) an immediate linear sustained acceleration in the rate; 3) an immediate linear acceleration in the rate followed by a decrease; and, 4) a progressive acceleration in the rate that is concurrent with the addition of the seeds. The main glass components observed to influence these behaviors were CaO, Al₂O₃, B₂O₃, and ZrO₂, where: 1) CaO influenced which glasses showed a Stage III response to seeds (high CaO: Types 2, 3, and 4) or did not respond to seeds (low CaO: Type 1), 2) Al₂O₃ and B₂O₃ influenced which glasses showed a sustainable Stage III response (high Al₂O₃: Types 2 and 4) versus transitory response (low Al₂O₃ and high B₂O₃: Type 3), and 3) ZrO₂ concentration influenced whether glasses showed a linear (high ZrO₂: Type 2) versus progressive (low ZrO₂: Type 4) response to seeds.« less

Abstract Understanding composition‐structure‐property relationships of high‐alumina nuclear waste glasses are important for vitrification of nuclear waste at the Hanford Site. Two series of glasses were designed, one with varying Al:Si ratios and the other with (Al + Na):Si ratios based on the international simple glass (ISG, a simplified nuclear waste model glass), with Al ₂ O ₃ ranging from 0 to 23 mol% (0 to 32 wt%). The glasses were synthesized and characterized using electron probe microanalysis, X‐ray photoelectron spectroscopy, small angle X‐ray scattering, high‐temperature oxide melt solution calorimetry, and infrared spectroscopy. Glasses were crystal free, and the lowest Na ₂ O andmore » Al ₂ O ₃ glass formed an immiscible glass phase. Evolution of various properties—glass‐transition temperature, percentage of 4‐coordinated B, enthalpy of glass formation—and infrared spectroscopy results indicate that structural effects differ based on the glass series.« less