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Lartigue, J. E., Charrasse, B., Reile, B., & Descostes, M. (2020). Aqueous inorganic uranium speciation in European stream waters from the FOREGS dataset using geochemical modelling and determination of a U bioavailability baseline. Chemosphere, 251, 126302.
Abstract: The concentration of the bioavailable uranium fraction (Ubio) at the European scale was deduced by geochemical modelling considering several definitions found in the literature and the FOREGS European stream waters geochemical atlas dataset to produce a Ubio baseline. A sensitivity analysis was performed using three thermodynamic databases. We also investigated the link between total dissolved uranium (Uaq) concentrations, speciation and global stream water chemistry on the one hand, and the lithology and ages of the surrounding rocks on the other. The more U-enriched the stream sediments or rock type contexts are, which tends to be the case with rocks containing silicates (4.1 mg/kg), the less U-concentrated the stream waters are (0.15 μg/L). Sedimentary rocks lead to slightly higher Uaq concentrations (0.34 μg/L) even if the concentration in sediment (Used) is relatively low (1.6 mg/kg). This trend is reversed for Ubio, with higher concentrations in a crystalline context. The mean estimated Ubio value ranges from 1.5.10−3 to 65.3 ng/L and can fluctuate by 3 orders of magnitude depending on the considered definition as opposed to by 2 orders of magnitude accountable to differences between thermodynamic databases. The classification of the water in relation to the two surrounding rock lithologies makes it possible to reduce the mean variability for the Ubio concentrations. Irrespective of the definition of Ubio considered, in 59% of cases the Ubio fraction represents less than 1% of Uaq. Several threshold values relating to Ubio were proposed, assuming knowledge only of the aqueous concentrations of the major elements and Uaq.
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Ammar, F. H., Deschamps, P., Chkir, N., Zouari, K., Agoune, A., & Hamelin, B. (2020). Uranium isotopes as tracers of groundwater evolution in the Complexe Terminal aquifer of southern Tunisia. Quaternary International, 547, 33–49.
Abstract: The Complexe Terminal (CT) multi-layer aquifer is formed by Neogene/Paleogene sand deposits, Upper Senonian (Campanian-Maastrichtian limestones) and Turonian carbonates. The chemical composition and isotopes of carbon and uranium were investigated in groundwater sampled from the main hydrogeological units of the (CT) aquifer in southern Tunisia. We paid special attention to the variability of uranium contents and isotopes ratio (234U/238U) to provide a better understanding of the evolution of the groundwater system. Uranium concentrations range from 1.5 to 19.5 ppb, typical of oxic or mildly reducing conditions in groundwaters. The lowest concentrations are found southeast of the study area, where active recharge is supposed to take place. When looking at the isotope composition, it appears that all the samples, including those from carbonate levels, are in radioactive disequilibrium with significant 234U excess. A clear-cut distinction is observed between Turonian and Senonian carbonate aquifers on the one hand, with 234U/238U activity ratios between 1.1 and 1.8, and the sandy aquifer on the other hand, showing higher ratios from 1.8 to 3.2. The distribution of uranium in this complex aquifer system seems to be in agreement with the lithological variability and are ultimately a function of a number of physical and chemical factors including the uranium content of the hosting geological formation, water-rock interaction and mixing between waters having different isotopic signatures. Significant relationships also appear when comparing the uranium distribution with the major ions composition. It is noticeable that uranium is better correlated with sulfate, calcium and magnesium than with other major ions as chloride or bicarbonate. The 14C activities and δ13C values of DIC cover a wide range of values, from 1.1 pmc to 30.2 pmc and from −3.6‰ to −10.7‰, respectively. 14C model ages estimated by the Fontes and Garnier model are all younger than 22 Ka and indicate that the recharge of CT groundwater occurred mainly during the end of the last Glacial and throughout the Holocene.
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Qiu, W., Yang, Y., Song, J., Que, W., Liu, Z., Weng, H., et al. (2023). What chemical reaction dominates the CO2 and O2 in-situ uranium leaching?: Insights from a three-dimensional multicomponent reactive transport model at the field scale. Applied Geochemistry, 148, 105522.
Abstract: The complex behavior of uranium in recovery is mostly driven by water-rock interactions following lixiviant injection into ore-bearing aquifers. Significant challenges exist in exploring the geochemical processes responsible for uranium release and mobilization. Herein this study provides an illustration of a ten-year field scale CO2 and O2 in-situ leaching (ISL) process at a typical sandstone-hosted uranium deposit in northern China. We also conducte a three-dimensional (3-D) multicomponent reactive transport model to assess the effects of potential chemical reactions on uranium recovery, in particular, to focus on the role of sulfide mineral pyrite (FeS2). Numerical simulations are performed considering three potential ISL reaction pathways to determine the relative contributions to uranium release, and the results indicate that bicarbonate promotes the oxidative dissolution of uranium-bearing minerals and further accelerates the uranium leaching in a neutral geochemical system. Moreover, the presence of FeS2 exerts a strong competitive role in the uranium-bearing mineral dissolution by increasing oxygen consumption, favoring the formation of iron oxyhydroxide, and therefore causing an associated decrease in uranium recovery rates. The simulation model demonstrates that dissolution of carbonate neutralizes acidic water generated from pyrite oxidation and aqueous CO2 dissociation. In addition, the cation concentrations (i.e., Ca and Mg) are increasing in the pregnant solutions, showing that the recycling of lixiviants and kinetic dissolution of carbonate generates a larger number of dissolved Ca and Mg and inevitably triggers the secondary dolomite mineral precipitation. The findings improve our fundamental understanding of the geochemical processes in a long-term uranium ISL system and provide important environmental implications for the optimal design of uranium recovery, remediation, and risk exposure assessment.
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Ingham, E. S., Cook, N. J., Cliff, J., Ciobanu, C. L., & Huddleston, A. (2014). A combined chemical, isotopic and microstructural study of pyrite from roll-front uranium deposits, Lake Eyre Basin, South Australia. Geochimica et Cosmochimica Acta, 125, 440–465.
Abstract: The common sulfide mineral pyrite is abundant throughout sedimentary uranium systems at Pepegoona, Pepegoona West and Pannikan, Lake Eyre Basin, South Australia. Combined chemical, isotopic and microstructural analysis of pyrite indicates variation in fluid composition, sulfur source and precipitation conditions during a protracted mineralization event. The results show the significant role played by pyrite as a metal scavenger and monitor of fluid changes in low-temperature hydrothermal systems. In-situ micrometer-scale sulfur isotope analyses of pyrite demonstrated broad-scale isotopic heterogeneity (δ34S=−43.9 to +32.4‰VCDT), indicative of complex, multi-faceted pyrite evolution, and sulfur derived from more than a single source. Preserved textures support this assertion and indicate a genetic model involving more than one phase of pyrite formation. Authigenic pyrite underwent prolonged evolution and recrystallization, evidenced by a genetic relationship between archetypal framboidal aggregates and pyrite euhedra. Secondary hydrothermal pyrite commonly displays hyper-enrichment of several trace elements (Mn, Co, Ni, As, Se, Mo, Sb, W and Tl) in ore-bearing horizons. Hydrothermal fluids of magmatic and meteoric origins supplied metals to the system but the geochemical signature of pyrite suggests a dominantly granitic source and also the influence of mafic rock types. Irregular variation in δ34S, coupled with oscillatory trace element zonation in secondary pyrite, is interpreted in terms of continuous variations in fluid composition and cycles of diagenetic recrystallization. A late-stage oxidizing fluid may have mobilized selenium from pre-existing pyrite. Subsequent restoration of reduced conditions within the aquifer caused ongoing pyrite re-crystallization and precipitation of selenium as native selenium. These results provide the first qualitative constraints on the formation mechanisms of the uranium deposits at Beverley North. Insights into depositional conditions and sources of both sulfide and uranium mineralization and an improved understanding of pyrite geochemistry can also underpin an effective vector for uranium exploration at Beverley North and other sedimentary systems of the Lake Eyre Basin, as well as in comparable geological environments elsewhere.
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Carrión, A., & Fornes, A. (2016). Underground medieval water distribution network in a Spanish town. Tunnelling and Underground Space Technology, 51, 90–97.
Abstract: The city of Alcudia de Crespins, in the centre of the Valencia province (east of Spain), has an exceptional water distribution system that in the past served fresh water to many houses in the town. This system is formed by more than one km of tunnels and underground cisterns, and dates probably in the late medieval times, while it has been in use and suffering modifications until 1955. This paper presents the structure and characteristics of such exceptional system, and explains the functioning parameters of the infrastructure.
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