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Abstract: Glauconite is an authigenic, iron-rich clay mineral that is abundant in greensands formations worldwide. Evidence from these formations suggests that glauconite is commonly diagenetically converted to carbonate minerals such as siderite, ankerite, and ferroan dolomite. This process represents a natural CO2 sink that may provide an effective mechanism for the engineered mineralization of anthropogenic CO2. To evaluate glauconite carbonation reactions and improve our understanding of glauconite diagenesis, we performed a detailed evaluation of the mechanisms through which carbonate minerals naturally replace glauconite during diagenesis of glauconitic sandstones from the Lower Cretaceous Upper Mannville Group in western Alberta, Canada. Using a combination of optical microscopy and scanning electron imaging, electron microprobe and bulk geochemical analyses, and X-ray fluorescence mapping, we show glauconite carbonation in the Mannville group is an reduction-facilitated, coupled glauconite recrystallization and siderite precipitation reaction. X-ray absorption near-edge spectroscopic mapping and spot analyses demonstrate that this reaction is accompanied by a significant shift in the oxidation state of Fe, from dominantly oxidized in glauconite to reduced in carbonate reaction products. Together, these results suggest that geochemical conditions - most importantly, temperature, partial pressure of CO2, and fluid redox state - were thermodynamically favorable for glauconite carbonation during burial diagenesis of Mannville Group sandstones. Results of thermodynamic models illustrate that, although K-feldspar is favored to precipitate during reductive glauconite dissolution and accompanying Fe-carbonate precipitation, its precipitation is likely kinetically limited, and that an Fe-impoverished glauconite is expected to recrystallize instead. Our findings show that glauconite carbonation is likely a common phenomenon in the subsurface, and thus that glauconite is potentially a significant cation source for mineralizing anthropogenic CO2.

Open Access

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Abstract: The high-energy release of plutonium (Pu) and uranium (U) during the Maralinga nuclear trials (1955–1963) in Australia, designed to simulate high temperature, non-critical nuclear accidents, resulted in wide dispersion µm-sized, radioactive, Pu–U-bearing ‘hot’ particles that persist in soils. By combining non-destructive, multi-technique synchrotron-based micro-characterization with the first nano-scale imagining of the composition and textures of six Maralinga particles, we find that all particles display intricate physical and chemical make-ups consistent with formation via condensation and cooling of polymetallic melts (immiscible Fe–Al–Pu–U; and Pb ± Pu–U) within the detonation plumes. Plutonium and U are present predominantly in micro- to nano-particulate forms, and most hot particles contain low valence Pu–U–C compounds; these chemically reactive phases are protected by their inclusion in metallic alloys. Plutonium reworking was observed within an oxidised rim in a Pb-rich particle; however overall Pu remained immobile in the studied particles, while small-scale oxidation and mobility of U is widespread. It is notoriously difficult to predict the long-term environmental behaviour of hot particles. Nano-scale characterization of the hot particles suggests that long-term, slow release of Pu from the hot particles may take place via a range of chemical and physical processes, likely contributing to on-going Pu uptake by wildlife at Maralinga.

Open Access

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Abstract: Objective: Malformations of cortical development (MCD), including focal cortical dysplasia (FCD), are the most common cause of drug-resistant focal epilepsy in children. Histopathological lesion characterisation demonstrates abnormal cell types and lamination, alterations in myelin (typically co-localised with iron), and sometimes calcification. Quantitative susceptibility mapping (QSM) is an emerging MRI technique that measures tissue magnetic susceptibility (χ) reflecting it's mineral composition. We used QSM to investigate abnormal tissue composition in a group of children with focal epilepsy with comparison to effective transverse relaxation rate (R2*) and Synchrotron radiation X-ray fluorescence (SRXRF) elemental maps. Our primary hypothesis was that reductions in χ would be found in FCD lesions, resulting from alterations in their iron and calcium content. We also evaluated deep grey matter nuclei for changes in χ with age. Methods: QSM and R2* maps were calculated for 40 paediatric patients with suspected MCD (18 histologically confirmed) and 17 age-matched controls. Patients’ sub-groups were defined based on concordant electro-clinical or histopathology data. Quantitative investigation of QSM and R2* was performed within lesions, using a surface-based approach with comparison to homologous regions, and within deep brain regions using a voxel-based approach with regional values modelled with age and epilepsy as covariates. Synchrotron radiation X-ray fluorescence (SRXRF) was performed on brain tissue resected from 4 patients to map changes in iron, calcium and zinc and relate them to MRI parameters. Results: Compared to fluid‐attenuated inversion recovery (FLAIR) or T1‐weighted imaging, QSM improved lesion conspicuity in 5% of patients. In patients with well-localised lesions, quantitative profiling demonstrated decreased χ, but not R2*, across cortical depth with respect to the homologous regions. Contra-lateral homologous regions additionally exhibited increased χ at 2-3mm cortical depth that was absent in lesions. The iron decrease measured by the SRXRF in FCDIIb lesions was in agreement with myelin reduction observed by Luxol Fast Blue histochemical staining. SRXRF analysis in two FCDIIb tissue samples showed increased zinc and calcium in one patient, and decreased iron in the brain region exhibiting low χ and high R2* in both patients. QSM revealed expected age-related changes in the striatum nuclei, substantia nigra, sub-thalamic and red nucleus. Conclusion: QSM non-invasively revealed cortical/sub-cortical tissue alterations in MCD lesions and in particular that χ changes in FCDIIb lesions were consistent with reduced iron, co-localised with low myelin and increased calcium and zinc content. These findings suggest that measurements of cortical χ could be used to characterise tissue properties non-invasively in epilepsy lesions.

Open Access

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Abstract: Thallium (Tl) is a highly toxic trace metal. It occurs mostly as soluble monovalent Tl(I) and less frequently as poorly soluble trivalent Tl(III). Laboratory studies have shown that vacancy-containing hexagonal birnessites can sorb Tl with a very high affinity via a mechanism that involves the oxidation of Tl(I) to Tl(III) and strong complexation of Tl(III), whereas other manganese (Mn) oxides bind Tl(I) non-oxidatively and with lower sorption affinity. Information on the mode of Tl uptake by natural Mn oxides in soils, on the other hand, is still limited. In this study, we characterized the association of Tl with Mn oxides and Tl (redox) speciation in a naturally Tl-rich soil using micro-focused synchrotron X-ray absorption near edge structure (XANES) spectroscopy and X-ray fluorescence (XRF) chemical imaging. The results show that most soil Tl was Tl(I) associated with micaceous clay minerals in the soil matrix. High levels of Tl in soil Mn concretions, on the other hand, were mostly identified as Tl(III), suggesting that oxidative Tl uptake by vacancy-containing hexagonal birnessite was the main process of Tl accumulation in soil Mn concretions. The spectroscopic results in combination with chemical extractions and published sorption isotherms for Tl on synthetic Mn oxides suggest that the formation and transformation of natural Mn oxides in soils and sorption competition of Tl with major and trace metal cations determine the extent and mode of Tl uptake by soil Mn oxides. Methodologically, this study compares classical micro-XRF element mapping combined with point XANES analyses for spatially-resolved element speciation with high-resolution chemical imaging of entire sample areas, which is of great interest for the geochemical community in light of diffraction-limited storage ring upgrades to many synchrotron lightsources.

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Abstract: Carbon steel is a universally used material in various transportation and construction industries. Research related to CO2 corrosion environments agrees on the occurrence of siderite (FeCO3) as a main product conforming corrosion films, suggested to impart protection to carbon steel. Identifying and understanding the presence of all corrosion products under certain conditions is of greatest importance to elucidate the behavior of corrosion films under operation conditions (e.g., flow, pH, temperature), but information regarding the nature and formation of other Fe corrosion products apart from FeCO3 is lacking. Corrosion products in CO2 environments typically consist of common Fe minerals that in nature have been demonstrated to undergo transformations, forming other Fe phases. This fact of nature has not been yet explored in the corrosion science field, which can help us to describe mechanisms associated with industrial processes. In this work, we present a multiscale and multidisciplinary approach to understand the mechanisms occurring on corrosion films under the key factors of flow and pH through the combination of molecular techniques with imaging. We report that certainly siderite (FeCO3, cylindrical with trigonal-pyramidal caps) is the main product identified under the conditions used (representative of brine transport at 80 °C), but wustite (FeO) and magnetite (Fe3O4) minerals also form, likely from the de-carbonation of FeCO3 → FeO → Fe3O4, depending on pH under the action of flow. These minerals exist across the corrosion films evidencing a more complex nature of the three-dimensional layer not currently accounted for in the mechanistic models. A relatively low flow velocity (1 m/s), as recognized for industrial operations, is enough to produce chemo-mechanical damage to the FeCO3 crystals, causing breakage at low pH where dissolution of FeCO3 occurs with a rapid crystal size reduction of the cylindrical FeCO3 geometry of ∼80% in just 8 h, changing also the local chemical structure of Fe3C under the film. Similarly, a flow velocity of 1 m/s is capable of inducing crystal removal at neutral pH, promoting further degradation of the steel, compromising the protectiveness assumption of FeCO3 corrosion films. The chemo-mechanical damage and Fe phase transformations will affect the critical localized corrosion, and therefore, they need to be accounted for in mechanistic models aiming to find new avenues for control and mitigation of carbon steel corrosion.