The studied materials are zeolite-rich rocks (>70 wt% analcime, named analcimolite) forming a laterally continuous aquitard within the southern of the Tim Merso & iuml; Basin (Niger). This unit, commonly referred to as the Abinky Formation, occurs as three mineralogical facies: a reduced facies containing Fe-chlorite, an oxidized facies with hematite, and an intermediate 'transition' facies. This analcimolite unit acts as an aquitard, separating the overlying and underlying sandstone aquifers, the latter locally providing potable water. Due to the low permeability of these analcime-rich rocks, diffusion is expected to be the dominant transport mechanism. However, no data on transport properties in zeolite-rich formations have been reported, and the mobility of water and ionic solutes remains unknown. This study aims to characterize diffusion in the three facies of the Abinky formation, identifying key controls on water and ion transport prior to any anthropogenic perturbation. Through-diffusion experiments using water tracers (HDO and HTO) showed that water diffusion (effective diffusion coefficient from 1.3 to 2 x 10(-11) m(2)/s) is primarily controlled by pore throat size rather than total porosity. A dual-porosity model was required, distinguishing a fast-transport network (open, low-tortuous zones) from a slow one (confined, tortuous zones). Despite variations in diffusion coefficients, all data are interpreted with capacity factors equal to total external porosity measured by water impregnation (excluding crystal water located in zeolite micropores). This confirms that water behaves as an inert tracer and that micropores contribute negligibly to water migration. For ionic tracers in reduced facies, Cl-36(-) is partially excluded from external pores (anionic exclusion) and slightly adsorbed, with an extent of about 0.1 meq/100 g, a very small value compared to the cation exchange capacities of such rocks (up to similar to 40 meq/100 g for H+ and NH4+). In contrast, Na-22(+) exhibits strong adsorption due to isotopic exchange with Na-23(+) in the analcime framework, leading to a diffusivity similar to 4 times higher than that of water. This dataset is a first step in constraining reactive transport models of water and solutes in zeolite-rich porous media under environmental conditions and prior to anthropogenic disturbance.

Hydrogeochemical management of mine effluents is essential to ensure a responsible and sustainable mining industry. These effluents can be heavily affected by acid mine drainage (AMD) over time spans that often extend over decades, during which continuous monitoring and treatment are required. However, significant uncertainties typically remain regarding the duration and evolution of AMD, as the source terms are often poorly characterized—particularly in the case of old or legacy mines. For mining operators, reducing these uncertainties represents a key advantage for optimizing long-term treatment and operational strategies, both technically and economically. In this study, we use reactive transport (RT) modeling to interpret 30 years of monitoring data from the former Bertholène uranium mine in France. Our results show that metal loadings have steadily decreased (Al, Fe, Mn, and U) to reach levels below regulatory limits for U (<1.8 mg/L), in parallel with a general decline in sulfide oxidation rates. This improved understanding will contribute to the development of a treatment strategy. In the coming decades, treatment will focus on addressing the remaining acidity, rather than on metals or radionuclides whose pre-treatment concentrations should comply with regulatory requirements.

In-situ recovery (ISR) is the most widely used uranium mining technique worldwide due to its cost-effectiveness, accounting for 55 % of global uranium production as of 2022. However, acidic ISR operations affect groundwater quality by increasing the concentrations of dissolved elements (such as SO4) and decreasing its pH. This study firstly demonstrates natural attenuation within the '3y' unit at the Kanzhugan deposit (Kazakhstan), where uranium was mined using ISR in the 1980s, using 30 years of monitoring data over a kilometric scale. Secondly, it aims to predict the environmental footprint of any such ISR production thanks to a reactive transport (RT) modeling approach using HYTEC, based on the monitoring data. The model, which assumes a homogeneous medium but incorporates key geochemical reactions, successfully reproduced the natural attenuation data over a 10-year period, previously published by Kayukov (2005). It was extended to the present day with validation points to enhance long-term prediction reliability. The geochemical model developed in this study shows that cationic exchange on clay surfaces and the precipitation of secondary minerals like gypsum regulate the behavior of contaminants (pH and SO4) over extended periods and distances. Parameter calibration reveals the geochemical changes across broad temporal and spatial scales. In addition, this research is the first to validate an RT model over a long period for such applications. Consequently, RT simulations can now be utilized to predict uranium production and evaluate the long-term environmental footprint.

The knowledge of aqueous speciation of uranium and radium in mining context is important for the modelling strategies based on reactive transport. The use of thermochemical databases allows accessing to theoretical speciation when the water compositions are known. If the usual concentration of radium in natural or anthropized waters is too low to have access to speciation experimentally, this can be achieved for uranium(VI), e.g. using time-resolved laser-induced fluorescence spectroscopy (TRLFS). In this work, theoretical radium and uranium inorganic and organic speciation were calculated using the water compositions collected in the legacymine site of Le Cellier (Loze`re, France) currently under monitoring after its closure and decommissioning, and database file extracted from the Prodata database for the PhreeqC and Orchestra codes. We also have measured TRLFS uranium spectra, which allows monitoring the uranium(VI) evolution from sulphate-like UO2(SO4)n2-2n complexes, at the beginning of the treatment, to characteristic CanUO2(CO3)3(4-2n)- complexes towards the end of the treatment, with an expected decrease of the total uranium concentration. Inorganic thermodynamic calculations are in excellent agreement with the spectroscopic attributions all along the treatment, whatever the speciation code used. The influence of natural organic matter, as part of the dissolved organic carbon outside of the legacy-mine perimeter, cannot be ruled out but is not straightforward to ascertain. The effluent seems only to disturb slightly the uranium speciation in the local stream from UO2CO3(aq) to CanUO2(CO3)3(4-2n)- due to calcium increase.

The BeaQuant gas detector is a real-time digital autoradiography system that sequentially acquires alpha and beta emissions from natural decay chains. Each emission is identified according to the type of particle emitted (alpha or beta), and the time and position of emergence in two dimensions. The experimental data generated were interpreted using an algorithm to identify Time and Space Coincidences (TSCs). Three different TSCs were detected on a thin section of uranium ore at secular equilibrium. These alpha/alpha, alpha/alpha/alpha and beta/alpha coincidences come from three short-lived radionuclides: 215Po and 219Rn in the 235U chain, and 214Po in the 238U chain. The distribution of the differences in arrival times of the particles forming a coincidence was analysed in terms of halflife. This analysis confirmed that these three coincidences originated from these three radionuclides, the periods having been found experimentally. The theoretical calculations of the number of coincidences confirm those obtained by the algorithm for analysing the experimental autoradiographic data.

Sandstone-hosted uranium is mined in the Sahel regions of Niger. The Teloua aquifer is located beneath the ore- processing facilities of one such former mine, COMINAK. The pores of the sandstone bedrock are partially filled by tosudite, a clay with sorption capacities. The local groundwater presents a strong oxidizing signature and very low water recharge. This study aims to determine the geochemical baseline of anthropogenic activity for uranium under such extreme conditions. The major and trace elements of both the contaminated and the pristine local groundwaters were sampled and analyzed to develop geochemical and reactive transport models. Kd distribution coefficients were calculated a posteriori from the mechanistic simulations. The entire water chemistry, with large variations in calcium, carbonate and sulfate concentrations, had to be taken into account to properly simulate the speciation and migration of U(VI) in the aquifer locally affected by the mining activities. U(VI) sorption significantly decreases during the propagation of the contaminant plume, due to the formation of CanUO2(CO3)3(4- 2n)- complexes that were clearly demonstrated by TRLFS acquisition. The sorption of UO2(CO3)n(2-2n) can play a key role in the immobilization of U(VI). The mitigating factors for U(VI) are sorption on clay and the dispersion/ dilution of the contaminated source terms within the groundwater, in which the strong ternary complexes are less important. There should be an efficient immobilization of fixed anthropic uranium by natural attenuation once the contaminant source terms have become depleted.

Worldwide, In situ recovery (ISR) is the most widely used uranium mining technique. As of 2022, it accounted for 55% of global uranium production. Uranium ISR consists in dissolving the ore minerals using an acidic leaching solution directly within the deposit through a series of injection and extraction wells. The U-enriched solution is then pumped to the surface in order to separate the dissolved uranium from the acid solution. Reagents are then recycled before being reinjected into the deposit. The key advantage of ISR over conventional underground and open-pit mining lies in its significantlyreduced costs and environmental footprint since it generates no tailings or solid waste and does not require excavation of the rock. It is by far the most cost effective extraction technique. However, an ISR exploitation impacts the groundwater quality by increasing the concentration of dissolved elements (SO4, ...) and decreasing the pH. Subsequently, groundwater impacted by acid ISR mining is typically remediated using various rehabilitation strategies. This study aims to forecast uranium production and predict the long-term environmental footprint of such exploitation using a reactive transport modeling approach. To do so, we will use HYTEC, an investigative tool to assess both production and the environmental footprint of an ISR mining site. HYTEC includes the three-dimensional hydrogeochemical simulation of the relevant chemical reactions which govern uranium production and the long-term evolution of the aquifer. The model is applied to an uranium deposit of the KATCO mine in Kazakhstan that has not been exploited yet. This model can simulate the 3D evolution of the aquifer geochemistry during and after the production phase. We will study how operating parameters (well design, injection-production rates, acidity and oxidation levels, …) impact both the uranium production and the environmental footprint of the ISR exploitation. The environmental footprint can be described in terms of distance and time. The distance is generally controlled by the migration of sulfate ions resulting from the injection of sulfuric acid, which have low reactivity and hence an important mobility. Acidity or pH is the parameter which influences the duration of the impact, as H+ has a very important reactivity and can also be stored locally by adsorption on clay mineral surfaces. The geochemical model, previously developed in a separate study, suggests that cationic sorption on clay surfaces and the precipitation of secondary minerals like gypsum regulate the behavior of contaminants (SO4, pH) over extended durations and distances.

The three natural decay chains have short-lived daughter elements, and the existence of these radioelements makes it possible for alpha and beta particle emissions to be generated at the same place and the same time. We show theoretically that such time and space coincidences (TSCs) can be detected efficiently by suitable autoradiographic systems using an algorithm that is six times more efficient than an approach based on the classical slicing of space-time. Two types of TSC coexist: true TSCs, resulting from the decay of short-lived daughter elements, and random TSCs. True TSCs are predictable and their numbers vary linearly with activity; the prediction of true alpha/alpha and alpha/alpha/alpha TSCs of the 235U chain is presented. Random coincidences are also predictable using Poisson's law. They vary quadratically as a function of activity. Examination of the case of an uranium ore at secular equilibrium shows that the observed alpha/alpha coincidences result from the sum of random and true TSCs. For high uranium contents, random coincidences predominate. For uranium at secular equilibrium, the theoretical calculation shows that true TSCs predominate for contents below similar to 5000 ppm.

The Abinky formation, composed of analcimolites (i.e., rocks with <70 wt% analcime), underlies Tchirezrine II, which hosts the Imouraren (Niger) uranium deposit. A potential mining project is under consideration to recover U by in situ acid leaching. Analcimolites are uncommon rocks, and assessing their ion-exchange properties is the first step to understand and predict the mobility of aqueous species in these formations. The objective of this study is then to understand the link between the Cation Exchange Capacities (CEC) of analcimolites as a function of their analcime content and associated crystal chemistry. Mineral quantification was performed by Rietveld refinement constrained by local chemical analysis with scanning electron microscopy coupled with Energy Dispersive Spectrometry. CEC were obtained at neutral pH by performing NH4+-for-Na+ exchange (CECNa/NH4), and Na+/H+ ion exchange experiments were performed with 4 analcimolites.Results showed that the analcime crystal chemistry deduced from Rietveld refinement was in good agreement with that obtained from SEM analysis (1.99 < Si/Al < 2.53). The results showed that all samples had a positive correlation between CECNa/NH4 and analcime content until ~30 meq/100 g for a sample containing ~85wt%Riet. of analcime, and that ~6 % of the total amounts of Na+ present in the analcime could be exchanged by NH4+ and H+. Based on Si and Al aqueous measurements, results showed that exchange with Na+ is the main process consuming H+ during Na+/H+ exchange when pH > 3.5. These experimental data were then interpreted by considering a single site equal to the CECNa/NH4 value, specific for each analcimolite, and a selectivity coefficient equal to log KNa/H = 1.3 (Gaines Thomas convention) being equal for all samples investigated. Finally, these data were used to assess the role played by Na+/H+ exchange in the pH evolution of the pore water of an analcime-rich rock subjected to dynamic acidification.

The long-term management of tailings from former uranium (U) mines requires an in-depth understanding of the hydrogeological processes and water flow paths. In France, most of the legacy U mines are located in fractured crystalline (plutonic) rocks, where the intrinsic subsurface heterogeneity adds to the uncertainties about the former extraction and milling activities and the state of the mine when production was ceased. U ores were mainly processed by sulfuric acid leaching, leading to high-sulfate-content mill tailings now contained in several tailing storage facilities (TSFs). The La Ribière site, located in western central France, is a former open-pit and underground U mine, closed in 1992 and used to store mill tailings. This site is being used as a test case to establish a workflow in order to explain and predict water flow and subsurface contaminant transport. A conceptual model of water flow and sulfate transport, at the scale of the La Ribière watershed, is first developed based on available information and hydrogeochemical monitoring. Recent geophysical investigations allows refining this model. Electrical Resistivity Tomography (ERT) proves to be efficient at localizing the extent of the highly conductive sulfate plume inherited from the U-mill tailings, but also at imaging the weathering profile. Magnetic Resonance Sounding (MRS), despite the limited signal intensity due to the low porosity in crystalline rocks, gives some insight into the porosity values, the depth of the fractured layer and the location of the low-porosity ore-processing muds. Based on this conceptual model, a 3D flow and non-reactive transport model with the METIS code is developed and calibrated. This model allows predicting the evolution of the sulfate plume, but will also be used in future investigations, to build reactive transport models with simplified hydrogeology for U and other reactive contaminants.

A series of laboratory experiments are conducted to simulate the acidification and subsequent recovery of a sand aquifer exploited by in situ recovery (ISR) mining. A sulfuric acid solution (pH 2) is first injected into a column packed with sand from the Zoovch Ovoo uranium roll front deposit (Mongolia). Solutions representative of local groundwater or enriched in cations (Na+, Mg2+) are then circulated through the column to simulate the inflow of aquifer water. pH and major ion concentrations (Na+, Cl-, SO42- , Ca2+, Mg2+, K+) measured at the column outlet reproduce the overall evolution of porewater chemistry observed in the field. The presence of minor quantities of swelling clay minerals (approximate to 6 wt% smectite) is shown to exert an important influence on the behavior of inorganic cations, particularly H+, via ion-exchange reactions. Numerical models that consider ion-exchange on smectite as the sole solid-solution interaction are able to reproduce variations in pH and cation concentrations in the column experiments. This highlights the importance of clay minerals in controlling H+ mobility and demonstrates that sand from the studied aquifer can be described to a first order as an ion-exchanger. The present study confirms the key role of clay minerals in controlling water chemistry in acidic environments through ion-exchange processes. In a context of managing the long-term environmental footprint of industrial and mining activities (ISR, acid mine drainage ...), this work will bring insights for modeling choices and identification of key parameters to help operators to define their production and/or remediation strategies.

A Gram-stain-negative bacterial strain designated Be4T, belonging to the genus Acidovorax, was isolated from mining porewaters sampled in uranium mill tailings repository sites, located in Bellezane, near Bessines-sur-Gartempe (Limousin, France). Cells were facultative anaerobic, rod-shaped, non-endospore-forming and motile with flagella. The mean cell size was 1.25–1.31 μm long and 0.70–0.73 μm wide. Colonies were light yellow, opaque, circular, convex with smooth margins, and 1–2 mm in diameter. Growth occurs at 4–37 °C and between pH 5.5–9.0. It differed from its phylogenetically related strains by phenotypic and physiological characteristics such as growth at 4 °C, presence of acid phosphatase, naphthol-AS-BI-phosphohydrolase and β-glucosidase enzymatic activities, and fermentation of l-xylose and esculin. The major fatty acids were C16:0, C16:1 ω7c/C16:1 ω6c, C17:0 cyclo and C18:1 ω7c. Phylogenetic analysis based on 16S rRNA and 938 core genes, confirmed its placement within the genus Acidovorax as a novel species. Strain Be4T showed highest 16S rRNA sequence similarity to Acidovorax antarcticus (98.2 %), Acidovorax radicis (97.9 %), Acidovorax temperans (97.8 %) and Acidovorax facilis (97.7 %). The genome of strain Be4T is 5,041,667 bp size with a DNA G + C content of 65.15 %. By automatic annotation numerous sequences involved in the interaction with metals/metalloids including some genes related to Se uptake and selenite resistance were detected in its genome. The average nucleotide identity (ANI) values calculated from whole genome sequences between strain Be4T and the most closely related strains A. radicis and A. facilis were below the threshold value of 95 %. Thus, the data from the phylogenetic, physiological, biochemical, and genomic analyses clearly indicates that strain Be4T represents a novel species with the suggested name Acidovorax bellezanensis sp. nov. The type strain is Acidovorax bellezanensis Be4T (=DSM116209T = CECT30865T). This novel species, due to its unique isolation source, genomic analysis, and preliminary laboratory tests where it was able to reduce toxic Se(IV) to less harmful Se(0) in the form of nanoparticles, holds great potential for further investigation in bioremediation, particularly concerning Se.

The measurement of 226Ra and the identification of 226Ra-bearing minerals are important for studying the behavior of radium in the environment. Various instruments for measuring 226Ra are currently used: among the radiometric techniques that measure in bulk (no spatialization), there are gamma spectrometers and alpha spectrometers. Other instruments such as SEM-EDS can map the chemical elements thus providing information on the distribution of 226Ra, but are limited for ultra-trace analyses on natural geomaterials. Finally, autoradiography techniques can locate radioactivity, but are limited to the identification of the contribution of 226Ra when the 238U series is complete. This study focuses on spectroscopic autoradiography, a method for measuring both the energy of the alpha particle emissions and their positions on the autoradiograph. A gas detector based on a parallel ionization multiplier technology was used for this purpose. Alpha particle energy is dependent on the emitting radionuclides. In order to track the 226Ra, the energy spectrum of the 238U series was studied with modeling software. It appears possible to apply a thresholding on the energy spectrum to discriminate the 226Ra from the first alpha emitters of the 238U decay chain (i.e. 238U, 234U and 230Th, all below 5 MeV). The developed method was applied to a U-mill tailing sample prepared as a thin section. The sample was heterogeneous in terms of radioactivity and was not at secular equilibrium with 238U, as expected. The 226Ra was identified and localized, and different regions of interest were also analyzed with SEM-EDS elements cartography. This revealed 226Ra-rich barite (BaSO₄) phases measured at 3 ppmRa on average and containing no uranium; and uranium in siderite (FeCO3), showing a strong 226Ra deficit compared with secular equilibrium. Spectroscopic autoradiography opens up possibilities for the analysis of heterogeneous geological samples containing natural alpha emitters such as 238U and 226Ra: the 226Ra can be localized and quantified at ultra-trace content, and the method developed can also identify newly (young) uranium phases by measuring 238U/226Ra activity disequilibrium.

Water flow is an essential component of the long-term environmental management of former mine sites. Flow through tailings storage facilities (TSF) often generates chemical reactions and releases acidic water. In the case of static leaching, this acidification can last for multiple decades depending on the acid remaining in the tailings. This mining water is then collected and treated in treatment plants before it is released in the environment in compliance with environmental standards. The understanding of the current hydrogeological functioning of the TSF is essential to properly adapt water management today. Given the potential impact of climate change, simulation of future hydrogeological behaviour is also required to ensure sustainable water management over this century.We developed a daily time step model with HYDRUS 2D to represent the unsaturated hydrogeological functioning of a tailings pile of the former mine of Le Cellier (France). A granulometric analysis over the pile height provided reliable hydraulic properties and showed that the pile heterogeneity can be distributed into three layers. The historical monthly monitoring and the new daily hydrogeological monitoring implemented in 2021 measured the rainfall and discharges from the various drains that collect the water from the pile. As cross-correlations confirmed the fast reaction of drains discharges to rainfall (1 day), we simulated the water flow with the dual porosity package of HYDRUS. We also implemented the vegetation transpiration due to the presence of bushes and coniferous trees over the pile.The model performance was evaluated by comparing the observed (monthly and daily) discharges and the simulated one. The calibrated model reproduces correctly the annual discharges for the period 2014-2022 as well as the pile fast reaction to rainfall. To evaluate the climate change impacts on the hydrogeological functioning of the pile, we used as input of our calibrated model the daily precipitations and temperatures of the Coupled Model Intercomparison Project (CMIP5) for three climatic scenarios (RCP2.6, RCP4.5 and RCP8.5). The calculation of the Mann-Kendall trend test on the predicted water balance components leads to the conclusion that the effective rainfall should remain stable over the next 100 years. At the end of the century, the frequency of extreme events could increase by 50% and their intensity could rise by 9%. With the calibrated model, we simulated the discharges at the pile outlet and studied their annual changes as well as the pile response to extreme events under climate change. These simulations are essential to ensure an accurate water management for this century.

To assess the long-term stability of uranium in mill tailings, the identification of radionuclide (238U and daughters)-bearing minerals is the first step. A combination of sequential extractions and alpha autoradiography (coupled to scanning electron microscopy) seems powerful for this purpose. Tailings coming from uranium mine sites in Gabon are composed mainly of quartz, feldspars, mica/illite, chlorite and kaolinite and many accessory minerals (siderite, Fe and Ti oxides, sulfate- or sulfide-bearing minerals, uraninite, zircon, etc.).Uranium was detected in minerals inherited from the ore, such as uraninite enclosed in quartz or bitumen and zircons (up to 18 wt% of U), and in newly formed minerals, such as siderite (up to 1.7 wt% of U) and Ti and Fe oxides (up to 3.5 wt% U). Sequential extractions indicate that 40% of U is unextractable, which indicates U is trapped in an efficient way in the tailings, probably in zircon and in uraninite enclosed in quartz grains. U was mainly released during the acetate extraction step targeting the Ti and Fe oxides and siderite and during the H2O2 step that attacked the bitumen, allowing the dissolution of enclosed uraninite.Ba/Pb sulfates, which are well known to incorporate 226Ra through solid solution mechanisms, are identified as the main trap of 226Ra in the studied tailings. Barite, the predominant sulfate, occurs in two populations: an inherited one under grain form and a newly formed one under fibrous habits. Some fibrous habits are sometimes observed at the inherited barite grain surface, corresponding to barite recrystallization. Using alpha autoradiography, amounts of 226Ra ranging from 2 to 30 ppm were estimated in these sulfate minerals (corresponding to specific activities from 70 kBq to 1 MBq per gram of sulfate grain). Barite, the predominant and 226Ra richest sulfate mineral (30 ppm), is quite insoluble. Only the strongest leaching steps partially dissolved it; 40% of 226Ra remained unextractable, highlighting its low mobility in environmental conditions.

Worldwide uranium production is based on the In Situ Recovery mining technique. This exploitation mode directly falls within the scope of the applications of reactive transport modelling to optimize uranium production and limit its associated environmental impact. We hereby propose a modelling approach which is able to represent the natural evolution of the aquifer impacted by the exploitation of an ISR test. Model is calibrated on 12 year-long data obtained from 12 monitoring wells surrounding the ISR pilot cell. Through this process based approach, we simulate the impact of several remediation strategies which could be considered in these contexts. In particular, we model the impact of pump and treat combined with reverse osmosis as well as the circulation of non-impacted fluids through the reservoir with different operating strategies. We show that our approach allows to compare the effectiveness of these strategies. We show that, for this small-scale ISR pilot, monitored natural attenuation constitutes an interesting approach due to its faster pH recovery time with respect to Pump & Treat and circulation of unimpacted fluids. Combined with an economical evaluation of their deployment, this approach can help the mining operator select and design the optimal remediation strategies, from an environmental and economical standpoint.

Uranium (U) roll-front deposits constitute a valuable source for an economical extraction by in situ recovery (ISR) mining. Such technology may induce changes in the subsurface microbiota, raising questions about the way their activities could build a functional ecosystem in such extreme environments (i.e.: oligotrophy and high SO4 concentration and salinity). Additionally, more information is needed to dissipate the doubts about the microbial role in the genesis of such U orebodies. A U roll-front deposit hosted in an aquifer driven system (in Zoovch Ovoo, Mongolia), intended for mining by acid ISR, was previously explored and showed to be governed by a complex bacterial diversity, linked to the redox zonation and the geochemical conditions. Here for the first time, transcriptional activities of microorganisms living in such U ore deposits are determined and their metabolic capabilities allocated in the three redox-inherited compartments, naturally defined by the roll-front system. Several genes encoding for crucial metabolic pathways demonstrated a strong biological role controlling the subsurface cycling of many elements including nitrate, sulfate, metals and radionuclides (e.g.: uranium), through oxidation-reduction reactions. Interestingly, the discovered transcriptional behaviour gives important insights into the good microbial adaptation to the geochemical conditions and their active contribution to the stabilization of the U ore deposits. Overall, evidences on the importance of these microbial metabolic activities in the aquifer system are discussed that may clarify the doubts on the microbial role in the genesis of low-temperature U roll-front deposits, along the Zoovch Ovoo mine.

We evaluated the potential of time-resolved laser-induced fluorescence spectroscopy (TRLFS) combined with chemometric methods for fast identification of U(VI)-bearing minerals in a mining context. We analyzed a sample set which was representative of several environmental conditions. The set consisted of 80 uranium-bearing samples related to mining operations, including natural minerals, minerals with uranium sorbed on the surface, and synthetic phases prepared and characterized specifically for this study. The TRLF spectra were processed using the Ward algorithm and the K-nearest neighbors (KNN) method to reveal similarities between samples and to rapidly identify the uranium-bearing phase and the associated mineralogical family. The predictive models were validated on an independent dataset, and then applied to test samples mostly taken from U mill tailings. Identification results were found to be in accordance with the available characterization data from X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX). This work shows that TRLFS can be an effective decision-making tool for environmental investigations or geological prospection, considering the large diversity of uranium-bearing mineral phases and their low concentration in environmental samples.

Worldwide, most uranium production relies on the 'in situ recovery' (ISR) extraction technique. This consists of dissolving the ore using a leaching solution (acid or alkaline) directly within the deposit through a series of injection and extraction wells. Due to the nature of the injected ISR solutions, the water quality of the aquifer could be affected. Reactive transport modeling is a powerful tool for predicting fluid flow and geochemical reactions in ISR reservoirs. In this study we present a coupled 3D environmental geochemical model (EGM) (based on the HYTEC reactive transport software), capable of predicting the physico-chemical conditions in an acid-leaching ISR uranium mine and its environmental footprint on the aquifer in the years following the closure of the production block. The model was validated at the KATCO mine (Kazakhstan) on two different and in-dependent production blocks, over 10 years after their closure. The model shows that incorporating two main geochemical processes, (1) cationic sorption on clay surfaces (smectite-beidellite) and (2) precipitation of gyp-sum (CaSO4.2H2O), successfully reproduces the measured well data (pH, acidity and SO4) over short-and long -term time scales. Clay surface sites remain mostly saturated in protons during the production phase. Simulations show that sorbed protons on the clay surfaces maintains the acid conditions for a longer period of time. The environmental impact model was also compared to a pre-existing model specifically developed for production simulation purposes: differences are observed as expected for the uranium production, but also for the impact distances, due to differences in the considered reactive mineralogical paragenesis. Thus, the choice of geochemical model should be made with due regard for the desired objectives. This work will assist the mine operator by providing a tool capable of assessing both the short-and long-term environmental footprints of the ISR production operation conditions and of identifying the best remediation strategy.