Silicate Phases Research Articles

Effectiveness and mechanism of uranium adsorption on size-graded red mud

As a type of useful solid waste, red mud (RM) should be reused to achieve waste-to-resource strategies. Additionally, the fast development of nuclear industry requires effective and reliable materials for treating uranium (U)-containing wastewater. This study attempted to remove uranyl ions [U(VI)] from mimic radioactive wastewater by various RM particles with different size fractions (e.g., >75, 45–75, 20–45, 10–20, 5–10, and <5-μm). Sorption data confirmed that the RM with a size fraction of <5-μm exhibited the largest adsorption capacity. The U removal behavior was favorably described by the pseudo-second-order model and Langmuir model. The mineral phases in the RM remarkably influenced U(VI) removal. Cancrinite, katoite, grossular, calcite, and calcium aluminum silicate phases made contributions to U(VI) adsorption. In addition, redox precipitation with iron-bearing minerals on RM surface also led to U(VI) adsorption. The findings of this work offer fundamental knowledge on the potential application of RM for clean-up of U(VI) from contaminated sites.

Chemical analysis of trace elements at the nanoscale in samples recovered from laser-heated diamond anvil cell experiments

High pressure and high temperature experiments performed with laser-heated diamond anvil cells (LH-DAC) are being extensively used in geosciences to study matter at conditions prevailing in planetary interiors. Due to the size of the apparatus itself, the samples that are produced are extremely small, on the order of few tens of micrometers. There are several ways to analyze the samples and extract physical, chemical or structural information, using either in situ or ex situ methods. In this paper, we compare two nanoprobe techniques, namely nano-XRF and NanoSIMS, that can be used to analyze recovered samples synthetized in a LH-DAC. With these techniques, it is possible to extract the spatial distribution of chemical elements in the samples. We show the results for several standards and discuss the importance of proper calibration for the acquisition of quantifiable results. We used these two nanoprobe techniques to retrieve elemental ratios of dilute species (few tens of ppm) in quenched experimental molten samples relevant for the formation of the iron-rich core of the Earth. We finally discuss the applications of such probes to constrain the partitioning of trace elements between metal and silicate phases, with a focus on moderately siderophile elements, tungsten and molybdenum.

PCL/Si-Doped Multi-Phase Calcium Phosphate Scaffolds Derived from Cuttlefish Bone.

Increasing attention is focused on developing biomaterials as temporary scaffolds that provide a specific environment and microstructure for bone tissue regeneration. The aim of the present work was to synthesize silicon-doped biomimetic multi-phase composite scaffolds based on bioactive inorganic phases and biocompatible polymers (poly(ε-caprolactone), PCL) using simple and inexpensive methods. Porous multi-phase composite scaffolds from cuttlefish bone were synthesized using a hydrothermal method and were further impregnated with (3-aminopropyl)triethoxysilane 1–4 times, heat-treated (1000 °C) and coated with PCL. The effect of silicon doping and the PCL coating on the microstructure and mechanical and biological properties of the scaffolds has been investigated. Multi-phase scaffolds based on calcium phosphate (hydroxyapatite, α-tricalcium phosphate, β-tricalcium phosphate) and calcium silicate (wollastonite, larnite, dicalcium silicate) phases were obtained. Elemental mapping revealed homogeneously dispersed silicon throughout the scaffolds, whereas silicon doping increased bovine serum albumin protein adsorption. The highly porous structure of cuttlefish bone was preserved with a composite scaffold porosity of ~78%. A compressive strength of ~1.4 MPa makes the obtained composite scaffolds appropriate for non-load-bearing applications. Cytocompatibility assessment by an MTT assay of human mesenchymal stem cells revealed the non-cytotoxicity of the obtained scaffolds.

Systematic boron isotope analysis on a Quaternary deep SG-1 core from the Qaidam Basin, NE Tibetan Plateau and its paleoclimate implication

Boron (B) isotope has been widely used in marine sediments to reconstruct paleoclimate evolution history. However, due to the relatively complex continental deposition environment, complicated fractionation process and controls of multi-processes on the δ11B variations of terrestrial sediments, the application of B isotope in terrestrial sediments and its indicative significance are limited and controversial. Here we conducted systematic B isotope and chemical composition studies on extracted evaporite, carbonate and silicate phases of sediments from a well-studied Quaternary deep drilling core (SG-1) from the Qaidam Basin, NE Tibetan Plateau, to explore the respective geochemical behavior of the B isotope in different phases of sediments and their respective implications. The results indicate that B in the evaporite phase of the SG-1 sediments is primarily derived from ion co-precipitated minerals instead of fluid inclusions. The δ11B variations in the carbonate and silicate phases possess different implications. The δ11Bcarbonate could serve as a potential paleo-salinity indicator, and the δ11Bsilicate could be a possible indicator to reflect the chemical weathering history of the catchment. Our systematic B isotope analysis explores the influences of different processes on the B isotope components of terrestrial sediments and decomposes the respective implication of B isotope in different phases of sediments. It can therefore provide important reference significance for future B isotope in terrestrial sediments and its application in paleoclimate study.

Silica Zinc Titanate Wide Bandgap Semiconductor Nanocrystallites: Synthesis and Characterization

AbstractSiO2x:ZnO: (1-x)TiO2 nanocrystallites were made via sol-gel route, and co-firing at a lower temperature (600oC). The synthesized nanocrystallites were characterized using several analytical techniques including XRD, SEM/TEM, FT IR, THz, and UV–visible spectroscopy analysis. The results appear that the silicate phase was used to promote the density of the nanocrystalline ceramic during calcination. The lower temperature calcined (∼600oC) nanocrystallites consist of ZnTiO3, Zn2SiO4, and TiO2 phases, with ZnTiO3 dominant rhombohedral phase, showing various electronic transitions. The obvious electronic properties give 2.8 eV as indirect bandgap transition and 3.35 ± 0.01 eV as direct bandgap transition with the increase of silica content. The dielectric constant is in the range 8 at a frequency higher than 104 Hz due to the formation of Zn2SiO4, and the ac conductivity is in the range 10− 10 to 10− 7 S/cm.

Revealing the co-doping effects of fluorine and copper on the formation and hydration of cement clinker

Fluorine in fluorite mineralizer and copper were easily doped together into cement clinker during cement kiln co-disposing wastes bearing Cu, yet that co-doping effects on the formation and hydration of cement clinker get few attention. The findings in this work revealed that the co-doping CaF2 (fluorine source) and CuO (copper source) into cement clinker showed a synergistic effect on the burnability, the immobilization rates of fluorine and copper in clinker phased were promoted. Compared with doping CaF2 into cement clinker, Co-doping CaF2 and CuO further enhanced the formation of alite and brownmillerite, while hindered the formation of tricalcium aluminate, and also triggered the right shift of characteristic diffraction peaks for C3S polymorphisms. It co-doping not only changed the microstructures, but also induced the visible defects on the surfaces of clinker mineral grains. In addition, most of fluorine would likely enter into the alite structure by replacing O2– of silicate phases, while most of copper would possibly enter into the brownmillerite structure by replacing Fe3+. Compared with the hydration process of cement clinker doped with CaF2, Co-doping CaF2 and CuO further accelerated the initial hydration process, obviously prolonged the induction period, but promoted the later hydration of co-doped clinker. Although the mechanisms about co-doping on the hydration process of co-doped clinker need more investigation, the above findings could extend the value-added utilization of wastes bearing Cu to reduce the large CO2 emission and energy/resource consumption in cement industry.

Hybrid amorphous-crystalline silicate composites as feasible solid-state electrolytes

Solid-state electrolytes (SSEs) are considered as the most promising materials for enabling the safer, more efficient, and feasible solution to address the market demands for lithium-ion batteries. The current work investigates the production of inorganic SSEs from silicate minerals, which are abundant materials in natural resources (kaolinite) as well as in industrial waste-streams (amorphous silica). The synthesized materials showed high amorphous contents combined with lithium silicate phases at variable proportions, according to the molar proportions of the reacting system. The materials have been characterized with XRD, SEM/EDS, FTIR, TGA-DSC, XPS, EIS, and density measurements. The results showed that hybrid structures of amorphous and crystalline silicates can form an ordered hotchpotch morphology. The best of the hybrid SSEs presented ionic conductivity values of 1.42 × 10-4 and 1.30 × 10-4 Scm−1 for samples with total amorphous contents of 73 and 83 wt%, respectively. The connected structure between amorphous and crystalline phases in a hotchpotch structure is hypothesized to assist the hopping of the Li+ ions via combined mechanisms of segmental motion of the silicates amorphous chains with defects in the crystalline phases. The proposed approach may offer new research paths towards the low-cost scalable production of SSEs.

Study of Synthetic Titania Slags Demonstrating Characteristics Similar to High Titania Ilmenite Slag

The upgradation of the ilmenite ore, using a pyrometallurgy method, is performed using a carbothermic reduction of the ilmenite. A high titania slag is obtained which is used as a feedstock for the TiO2 pigment production. The slag is cooled after tapping in big molds and can take ten days to cool. This cooling method has remained the same since the inception of ilmenite smelting and recently rapid cooling through granulation has been utilized. The work presented in this paper focuses on the microstructural study of the slags that were prepared using different techniques and cooled at different cooling rates. Various analytical techniques, such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS) were used to exhibit the similarity of these synthetic slags to the properties of high titania ilmenite slag. The slag consisted mostly of pseudo-brookite phase with a M3O5 stoichiometry and smaller amounts of silicate and rutile phase. A glassy phase of silica was observed and most of the impurities were found to be present in the silicate phase. These silica phases were observed to be separate from the pseudo-brookite phase and along the phase boundaries. Micro-cracking of the slag surface, which is the characteristic of the M3O5 phase formed in the ilmenite slag, were observed under the SEM analysis. The XPS analysis revealed that faster cooling does result in lower amount of oxidation but the difference in the TiO2 and Ti2O3 composition can have larger impact on oxidation than the cooling speed.

Dating blueschist-facies metamorphism within the Naga ophiolite, Northeast India, using sheared carbonate veins

ABSTRACT The tectonic significance of blueschist-facies rocks associated with the Indo-Myanmar ophiolite belt is uncertain, given the lack of detailed petrological study and the paucity of reliable age data for different stages in their geological evolution. Here, we present new integrated petrological and geochronological data for samples from the Nagaland complex of the Indo-Myanmar ophiolite belt, northeastern India, which constrains the pressure–temperature conditions and absolute ages of peak and retrograde metamorphism. Several samples of blueschist were collected from the region, which have been variably deformed and subjected to shear recrystallization. Based on microstructural constraints and mineral geochemistry, garnet, omphacite, barroisite, chlorite and muscovite are interpreted to represent a high-pressure prograde-to-peak metamorphic assemblage, and omphacite, actinolite, hornblende and albite represent a lower-pressure retrograde metamorphic assemblage that formed during shear-related exhumation. Petrological modelling and thermobarometry indicates that unsheared samples equilibrated at ~1.9 GPa and ~480–520°C at peak metamorphism, indicating subduction to ~60 km depth, whereas sheared and recrystallised samples re-equilibrated at ~0.6 GPa and ~470°C during retrograde metamorphism associated with obduction of the Naga ophiolite onto the Indian foreland. U–Pb in-situ analysis of carbonate grains (aragonite–calcite) and associated silicate phases (epidote, prehnite, amphibole, etc.) at different microstructural positions, including within dynamically recrystallised shear bands that cross-cut older metamorphic fabrics and cogenetic silicate phases, constrains the age of peak metamorphism to be c. 95 Ma and retrograde metamorphism to be c. 90 Ma. Based on the overall progression of ages in the sheared and unsheared samples, we interpret that the area experienced exhumation at a time-averaged rate of ~1 cm/year in the order of Phanerozoic period plate tectonic rate, which is in the order of rates of plate tectonic processes on the Phanerozoic Earth

Smooth rims in Queen Alexandra Range (QUE) 99177: Fluid–chondrule interactions and clues on the geochemical conditions of the primordial fluid that altered CR carbonaceous chondrites

Queen Alexandra Range (QUE) 99177 is one of the least altered CR carbonaceous chondrite known, with mineralogical and isotopic characteristics that indicate a high level of pristinity. In this study, we have examined the so-called smooth rims that surround many type I chondrules in QUE 99177, using SEM, EPMA, and FIB-TEM techniques. We have characterized their constituent phases to unravel the precursor material(s) of smooth rims, assess their formation mechanisms, and constrain the conditions of the altering fluid. Smooth rims are the most common type of rims around type I chondrules and exclusively occur around chondrules with Silica-rich Igneous Rims (SIRs). Smooth rims consist of an Fe-rich, hydrous silicate material that is Si- and Fe-rich, with minor Mg, Al, Ca, and Mn, and gives low analytical totals measured by EPMA. TEM observations reveal that the Fe-rich silicate phase is an amorphous gel that contains unaltered crystalline phases and igneous glass. Crystalline phases consist of igneous, unaltered, zoned pyroxenes with compositions consistent with pyroxenes in SIRs, as well as albite and chromite. The amorphous gel preserves previous crystal outlines with morphologies consistent with silica (cristobalite) grains in SIRs and has a composition identical to pseudomorphic silica replacements in SIRs. Based on these observations, we conclude that smooth rims derive from low-temperature aqueous alteration of silica in SIRs by an Fe-rich fluid. We suggest that the Fe was derived by leaching of amorphous silicates in the matrix, which reacted rapidly with melted water ice, although alteration of Fe,Ni metal blebs in SIRs could potentially be an additional source of Fe. Silica underwent dissolution and replacement whereas feldspar and glass remained unaltered because (1) the fluid was slightly alkaline, (2) cristobalite has a reaction rate much higher than quartz and feldspar, and (3) the alteration was very limited and fast, indicating that it was due solely to melting of accreted water ice and there was no introduction of additional fluid from external sources.

Aptness of nano alumina (Al2O3) with high range water reducer-incorporated concrete

PurposeThe purpose of this paper is to study the effect of nano alumina (Al2O3) on the properties of fresh concrete, hardened concrete and microstructure of concrete incorporated with high range water reducer (HRWR). This initiative was taken to improve characteristic properties of concrete using nano alumina because nano alumina can be easily be manufactured from a scrap of industrial aluminum products, so its incorporation in concrete will not only reduce industrial aluminum waste but will also change the morphology of concrete at the microstructural level.Design/methodology/approachTo accomplish the objectives of the research, four different concrete mixes with the constant water–cement ratio (W/C) and superplasticizer (SP) content 0.4 and 0.6% by weight of cement, respectively, were prepared, whereas nano alumina content was altered by 0.3% and 0.4% by weight of cement. Fresh property of concrete was analyzed by using slump cone test, whereas hardened properties of concrete were analyzed through compression test and flexural strength test. The interaction of nano alumina with concrete composite was evaluated using an X-ray diffraction test.FindingsIt was observed that 0.6% superplasticizer by weight of cement increased workability by 22% but with the addition of 0.3%, nano alumina by weight of cement workability decreased by 31%. Compressive strength increased by 4.88% with the addition of 0.6% superplasticizer but with the addition of 0.3% nano alumina by weight of cement compressive strength increased by 18.60%. Also, flexural strength increased by 1.21% with the addition of 0.6% superplasticizer by weight of cement but with the addition of 0.3% nano alumina by weight of cement flexural strength increased by 8.76%. With the addition of superplasticizer, alite and belite phases remained un-hydrated but with the addition of nano alumina alite phase was hydrated while belite phase was un-hydrated. The size of belite crystals in mixes having nano alumina was less than that of mix having 0.6% superplasticizer. Also with the addition of nano alumina, a calcium aluminum silicate phase was formed which was responsible for the increment of strength in mixes having nano alumina.Originality/valueIncorporation nano alumina (Al2O3) in concrete will not only reduce industrial aluminum waste but will also reduce CO2 emission. Nano alumina (Al2O3) also changes morphology of concrete at micro structural level.

Clinkerisation of copper tailings to replace Portland cement in concrete construction

In this study, copper mine tailings were used as a replacement for Portland cement in concrete construction using sintering process. The applicability of the concrete samples was evaluated through TG, DTA, SEM, FTIR, XRD, and TCLP. The 28-day compressive strength of the concrete sample made of cement-substituted copper tailings was 42 MPa, which was 9% lower than that of the control sample. It was well supported using t-test with the p-value < 0.05. The TG and DTA tests results indicated that despite the presence of different compounds in the cement samples, the peaks of these tests were almost the same. The TCLP test results showed that the amount of studied heavy metals leaching in all concrete samples was lower than the standard limit (p-values less than 0.05). According to XRD and FTIR results, cement hydration process was well performed, and tricalcium silicate (alite) and dicalcium silicate (belite) phases were formed in the manufactured cement samples. In general, cement clinkers produced using Sungun copper mine tailings could be considered as a substitute for Portland cement in concrete construction.

Аналіз структурно–хімічного стану дуплекс–систем силікати–силіциди лужно–земельних металів. Повідомлення 2. Дуплекс–система SiO2–MgO–CaO: Si–Mg–Ca

A polygonal diagram of the state of the CaO-SiO2-MgO ternary system was constructed in the entire range of concentrations of solid and liquid initial components, which increases the informativeness of polygonal diagrams of the state of metallurgical systems. The obtained results of the SCS analysis of the silicate and silicide phases of the duplex system SiO2–MgO–CaO : Si–Mg–Ca are the scientific basis for the optimization of blast furnace iron refining processes with smelting slags and magnesium alloys. Keywords: polygonal diagram, magnesium slag, silicate and silicide phases of calcium, physicochemical, technological and quantum-mechanical parameters.

Preparation and characterization of Portland cement clinker from sulfuric acid leaching residue of coal fly ash

This work reported a process for the preparation of Portland cement clinker from sulfuric acid leaching residue of coal fly ash. Aluminum and iron in fly ash were effectively leached by sulfuric acid leaching, and the silica was all concentrated in the acid leaching residue. The chemical analysis showed that the content of SiO2 in the leaching residue was 79.1% and the leaching residue contained a small amount of Al2O3, CaO and Fe2O3, which could replace clay as the raw material for the preparation of Portland cement clinker. The effects of main process conditions on the quality of prepared cement clinker were studied. The results showed that the burnability of the raw material with clinker rate value KH = 0.92, SM = 2.1, IM = 1.2 and leaching residue content of 26.98% was excellent and good. The mineralogical analysis and microscopic examination showed that the good quality clinker was obtained under the conditions of sintering temperature of 1450 °C and holding time of 60 min, and the tricalcium silicate phase was well developed. Based on this study, acid leaching residue of coal fly ash was viable as an effective, alternative raw material in Portland cement production.

Sorption of Strontium to Uraninite and Uranium(IV)-Silicate Nanoparticles.

Spent nuclear fuel contains both uranium (U) and high yield fission products, including strontium-90 (90Sr), a key radioactive contaminant at nuclear facilities. Both U and 90Sr will be present where spent nuclear fuel has been processed, including in storage ponds and tanks. However, the interactions between Sr and U phases under ambient conditions are not well understood. Over a pH range of 4–14, we investigate Sr sorption behavior in contact with two nuclear fuel cycle relevant U(IV) phases: nano-uraninite (UO2) and U(IV)–silicate nanoparticles. Nano-UO2 is a product of the anaerobic corrosion of metallic uranium fuel, and UO2 is also the predominant form of U in ceramic fuels. U(IV)–silicates form stable colloids under the neutral to alkaline pH conditions highly relevant to nuclear fuel storage ponds and geodisposal scenarios. In sorption experiments, Sr had the highest affinity for UO2, although significant Sr sorption also occurred to U(IV)–silicate phases at pH ≥ 6. Extended X-ray absorption fine structure (EXAFS) spectroscopy, transmission electron microscopy, and desorption data for the UO2 system suggested that Sr interacted with UO2 via a near surface, highly coordinated complex at pH ≥ 10. EXAFS measurements for the U(IV)–silicate samples showed outer-sphere Sr sorption dominated at acidic and near-neutral pH with intrinsic Sr-silicates forming at pH ≥ 12. These complex interactions of Sr with important U(IV) phases highlight a largely unrecognized control on 90Sr mobility in environments of relevance to spent nuclear fuel management and storage.

Olivines as probes into assimilation of silicate rocks by carbonatite magmas: Unraveling the genesis of reaction rocks from the Jacupiranga alkaline‑carbonatite complex, southern Brazil

Assimilation of clinopyroxenite xenoliths by carbonatite magma plays an important role in the Jacupiranga complex, a classical mafic-ultramafic alkaline‑carbonatite occurrence outcropping in Southeastern Brazil. In this complex, different batches of dolomite-bearing carbonatites and calcite carbonatites are found, all of them intrusive in the main clinopyroxenite body. Particularly for the calcite-rich carbonatites (with accessory olivine), the contacts with wall-rock clinopyroxenite are marked by xenolith-rich zones, formed by clinopyroxenite blocks embedded in the carbonatite. Banded reaction rocks occur enveloping such xenoliths, presenting conspicuous textures and compositions, with mineral assemblages changing from clinopyroxenite towards the carbonatite from (i) amphibole + phlogopite ± titanite (amphibole-domain) via (ii) phlogopite (phlogopite domain) to (iii) olivine + phlogopite (olivine domain). The contents of Ni, Co and Sc in olivines from reaction rocks suggest that their trace element budget was strongly influenced by clinopyroxenite assimilation. Schematic reactions between clinopyroxenite and carbonatite melt are presented and these suggest that the observed features can be explained by a single magmatic high-T event. The required carbonatite component increases from amphibole- through phlogopite- to olivine-domains, mirroring their distance to the carbonatite front, reinforcing that carbonatite melt activity is a major control for the formation of the reaction rocks. The proposed reactions also imply that initially Mg-rich carbonatite melts consume diopside in the clinopyroxenite to produce the silicate phases (olivine, phlogopite, amphibole, and titanite), while shifting to Ca-rich melt compositions. The lack of xenoliths zones related to the olivine-free dolomite-bearing carbonatites, the absence of dolomite in the carbonatites proximal to the reaction rocks, and the presence of olivine seams in the carbonatite-reaction rock interface reinforce the link between olivine crystallization in the carbonatite and the consumption of dolomite component of the melt. Unlike previous models, we propose that the investigated reaction rocks formed in a magmatic environment, where carbonatite magmas have both assimilated and modified clinopyroxenite xenoliths. These observations may have general implications and further underline the capability of carbonatitic magmas for reactive bulk assimilation of diverse silicate rocks.

In-situ synthesizing carbon nanotubes on cement to develop self-sensing cementitious composites for smart high-speed rail infrastructures

Self-sensing cementitious composites (SSCCs) with carbon nanotubes (CNTs) have attracted extensive attention because of their excellent mechanical and durability properties combined with multifunctional benefits. However, their performance modulation, as well as scalable manufacturing and application, are limited by the uniform dispersion of CNTs inside them. Here, a straightforward approach to in-situ synthesizing CNTs on cement (CNT@Cem) toward alleviating the CNTs’ dispersion issue and enhancing their composite efficiency and effectiveness is explored. Due to the inherently containing silicate and ferrite phases, microscale cement particles act as effective substrate-bound catalysts, facilitating high-yield and strongly anchored CNTs growth. The hierarchically structured CNT@Cem integrates the dual functions of reinforcement and conduction, significantly affecting early-age hydration, mechanical, electrical, and self-sensing properties of the final SSCCs with CNT@Cem. The CNT@Cem structure can promote early-age hydration while slowing the later hydration rate and hindering the strength development of the SSCCs. The addition of CNT@Cem can be effective in tailoring the electrical microstructures to enhance the electrical conductivity and self-sensing sensitivity of the SSCCs. The SSCCs with CNT@Cem achieved a maximum stress sensitivity of 2.87%/MPa with a gauge factor of 748. They demonstrated excellent repeatability and stability, outstanding adaptability to various applied conditions, and fast response and recovery. The developed SSCCs-engineered smart track slab is competent in axle counting and speed detection. It opens up a new territory to develop high-performance and versatile SSCCs-engineered smart components/structures for long-term, wide distribution, and low-cost monitoring of high-speed rail (HSR) infrastructures.

A tetrad effect in the glass transition of lanthanide‐doped sodium disilicate glasses

AbstractScanning calorimetric determination of the glass transition temperatures (Tg) of sodium disilicate doped individually with 25 wt.% of the oxides of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu reveals the presence of the so‐called “lanthanide tetrad effect” in their glass transition temperatures. This is to the best of our knowledge the first observation of a tetrad effect in the macroscopic properties of a high‐temperature silicate phase.

Chemical characterisation of degraded nuclear fuel analogues simulating the Fukushima Daiichi nuclear accident

The Fukushima Daiichi accident generated degraded nuclear fuel material, mixed with other reactor components, known as molten core-concrete interaction (MCCI) material. Simulant MCCI material was synthesised, excluding highly radioactive fission products, containing depleted U, and incorporating Ce as a surrogate for Pu. Multi-modal µ-focus X-ray analysis revealed the presence of the expected suite of U-Zr-O containing minerals, in addition to crystalline silicate phases CaSiO3, SiO2-cristobalite and Ce-bearing percleveite, (Ce,Nd)2Si2O7. The formation of perclevite resulted from reaction between the U-Zr-O-depleted Ce-Nd-O melt and the silicate (SiO2) melt. It was determined that the majority of U was present as U4+, whereas Ce was observed to be present as Ce3+, consistent with the highly reducing synthesis conditions. A range of Fe-containing phases characterised by different average oxidation states were identified, and it is hypothesised that their formation induced heterogeneity in the local oxygen potential, influencing the oxidation state of Ce.

The Lithophile Element Budget of Earth's Core

AbstractThe relative composition of Earth's core and mantle were set during core formation. By determining how elements partition between metal and silicate at high pressures and temperatures, measurements of the mantle composition and geophysical observations of the core can be used to understand the mechanisms by which Earth formed. Here we present the results of metal‐silicate partitioning experiments for a range of nominally lithophile elements (Al, Ca, K, Mg, O, Si, Th, and U) and S to 85 GPa and up to 5400 K. With our results and a compilation of literature data, we developed a parameterization for partitioning that accounts for compositional dependencies in both the metal and silicate phases. Using this parameterization in a range of planetary growth models, we find that, in general, lithophile element partitioning into the metallic phase is enhanced at high temperatures. The relative abundances of FeO, SiO2, and MgO in the mantle vary significantly between planetary growth models, and the mantle abundances of these elements can be used to provide important constraints on Earth's accretion. To match Earth's core mass and mantle composition, Earth's building blocks must have been enriched in Fe and depleted in Si compared with CI chondrites. Finally, too little Mg, Si, and O are partitioned into the core for precipitation of oxides to be a major source of energy for the geodynamo. In contrast, several ppb of U can be partitioned into the core at high temperatures, and this energy source must be accounted for in thermal evolution models.