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Due to the small size of uranium minerals, the occupations of U4+ and U6+, Th and Pb in uraninite is little studied. The coarse giant uraninite (CGU) from Miyi with size up to 1 cm is one of the best samples for studying uraninite mineralogical property. CGU mainly composed of UO2, ThO2, PbO, CaO. There are three forms of occurrence of U, namely UO2, UO3, and UO2+x; and impurity such as ThO2, PbO, CaO may entering the mineral lattice, which can affect mineral properties and facilitate the chemical reactions during mineralization and leaching processes. [ABSTRACT FROM AUTHOR]

Sandstone-type deposits have emerged as the primary uranium deposits being mined in China, utilizing in-situ leaching technology. However, the leaching of uranium resources within sandstone formations faces significant constraints due to their extremely low permeability, accounting for approximately seventy percent of the total. This paper aims to present recent advancements in the field in enhancing seepage-leaching mass-transfer properties in in-situ leaching of uranium from low-permeability sandstone. We will provide an overview of the main factors influencing the in-situ leaching process in low-permeability ore layers, discussing the technical characteristics of applicable methods designed to enhance permeability in low-permeability uranium-bearing sandstone based on the existing research. Additionally, we will also explore the suitability of various approaches from other fields in the in-situ leaching of uranium process. Finally, we will outline the prospects regarding process methodologies, leaching agents, and enhancing permeability methods. [ABSTRACT FROM AUTHOR]

Uranium exploration plays a pivotal role in meeting global energy demands and advancing nuclear technology. This study presents a comprehensive approach to uranium exploration in the Gebel Duwi area of the Central Eastern Desert of Egypt, utilizing remote sensing and airborne gamma-ray spectrometric data. Multispectral remote sensing techniques, including Principal Component Analysis (PCA), Minimum Noise Fraction (MNF), and Band Ratioing (BR), are employed to identify lithological units and hydrothermal alteration zones associated with uranium deposition, such as iron oxides, argillic, propylitic, and phyllic alterations. Additionally, airborne gamma-ray spectrometry data provide insights into the spatial distribution of radioelements, including uranium (eU), thorium (eTh), and potassium (K), as well as radioelement ratios (eU/eTh, eU/K, and eTh/K). The uranium migration index map (eU-(eTh/3.5)) and the F-parameter map (K*(eU/eTh)) have been generated to investigate the movement of uranium within various geological zones and characterize anomalous uranium concentrations. Statistical analyses, including mean (X), standard deviation (S), and coefficient of variability (C.V.), are conducted to identify uranium-rich zones. The integration of these datasets enables the generation of a uranium potential map highlighting areas of elevated concentrations indicative of uranium mineralization. Field observations and mineralogical analyses of collected samples validate our findings, confirming the presence of minerals associated with uranium mineralization in mapped high-potential areas. The significance of minerals like Fe-Chlorite, Fe-Mg-Chlorite, ferrihydrite, goethite, calcite, muscovite, dolomite, actinolite, vermiculite, and gypsum in indicating potential uranium mineralization processes underscores the importance of our results. [ABSTRACT FROM AUTHOR]

The objective of this study was to evaluate the extent of radon contamination in twenty-six drinking water samples from natural springs were collected from Dhirkot Azad Kashmir, along with four bottled mineral water samples. Radon gas escapes from the earth's crust due to uranium ores and diffuses into the atmosphere. This study assessed the levels of radon concentration, the yearly effective radiation dose, and carcinogenic risk from radon exposure in drinking water samples. The radon concentration varied from 0.28 to 30.25 Bq/L. The mean radon concentration of all samples was found to be 7.86 ± 2.3 Bq/L. The radon concentrations in bottled drinking water were found to be lower than those in natural springs. The statistical and GIS analyses included the use of interpolation and Pearson's correlation matrix. Seven samples had radon concentration that surpassed the standard limit established by the US-EPA, which is 11 Bq/L. The average annual effective dose from inhalation and ingestion was found to be lower than the value (0.1 mSv/y) provided by the WHO, but for some natural spring water samples, it exceeded the risk limit. The cancer risk revealed that 40% of the samples had an elevated lifetime cancer risk from radon exposure. Overall, the majority of the results obtained aligned with the worldwide guidelines established by the US-EPA. However, there were a few instances where the limits were exceeded, and constant monitoring is recommended. This study establishes a baseline for radon concentration in the area and provides a basis for future studies. [ABSTRACT FROM AUTHOR]

Based on the study of local volumes of minerals using the classical methods of isotope dilution and thermal ionization mass spectrometry (U–Pb ID TIMS), an isotopic study of pitchblende and galena is carried out at the Natali uranium ore occurrence (Northern Transbaikalia). For the first time, it was shown that the pitchblende mineralization at the ore occurrence has a Late Silurian (422 ± 4 Ma) age. Its formation is related to the Early–Middle Paleozoic collisional tectogenesis in the area of the Tonod uplift, accompanied by increased fluid activity. The Pb isotopic composition analysis in galena associated with pitchblende show that galena is enriched in radiogenic isotopes 206Pb and 207Pb, a source of which was ancient (Precambrian) concentrations of uranium. [ABSTRACT FROM AUTHOR]

Heap bioleaching is considered to be a less energy-intensive metal-extraction technique compared to other methods, making it particularly attractive for low-grade sulfide ores. It has been successfully applied to recovery of copper, gold, and uranium from ores over decades. Despite its seemingly straightforward nature, heap bioleaching can experience failures if the ore is unsuitable or the heap leach process is not thoroughly investigated and well-developed. Therefore, multidisciplinary approaches are essential for research and development in heap bioleaching, as its performance depends on numerous processes operating across a wide range of length scales. This review focused on the current state of knowledge regarding the understanding of multi-scale mechanisms in heap bioleaching and the use of multidisciplinary approaches at different scales to develop the process. The investigation covered various scales, such as atomic and molecular, mineralogy and microbes, reaction particles, heap bioleaching units and full-scale factory production. Different approaches were employed to gain a comprehensive understanding of the microbial molecular structure and metabolism, the structure and reaction of minerals, microbial–mineral interaction, particles and aggregation states, and multiphase flow transfer, as well as laboratory experiments, modeling, industrialization, and operation optimization. We emphasized the need for collaboration among researchers from different disciplines and stress the importance of considering the coupling effects of physical, chemical, and microbiological factors when running heap bioleaching plants. Such collaboration and coupling are vital for successful implementation and optimization of heap bioleaching processes. This paper aimed to provide a comprehensive overview of current research related to heap bioleaching at different scales and disciplines, and gave implications to heap bioleaching technology development. [ABSTRACT FROM AUTHOR]

The aim of this study is to improve and simplify the measurement of radon exhalation rate using the closed-loop accumulation method. Based on the 222Rn concentration data obtained from reference the standard module of uranium ore sands and cement, this work simplifies the 222Rn concentration growth model for calculating radon exhalation rate using the least squares method and proves its accuracy. Through fitting residual analysis, anomalies are screened at the significance level of α = 0.05 to enhance fitting precision. Herein, the influence of the starting point on the fitting effect and the calculation of radon exhalation rate is explored. The results indicate that after screening anomalous data, the fitting effects of the two sets of experimental data are further improved, and the relative errors in radon exhalation rate measurements are reduced from 1.77 to 1.41% and 13.08 to less than 10% respectively. [ABSTRACT FROM AUTHOR]

Aiming at the problems such as low settling speed and poor solid-liquid separation effect of a uranium ore high-calcium slurry, static flocculation method was used to settle high-calcium pulp of a uranium ore, and the effects of flocculant type, dosage, mixed flocculant ratio and adding method on the settling effect were investigated. The results show that the settling rate of high calcium pulp can be significantly increased by the mixed flocculant prepared by WZ944 flocculant and 5330 flocculant. The optimal mass ratio of the two flocculants is 1:1, and the minimum dosage of the mixed flocculant is 35 g/t. The research results can provide reference for the optimization design of the uranium ore solid-liquid separation process. [ABSTRACT FROM AUTHOR]

Leaching of uranium, thorium and rare earth from the monazite selective solution residue were studied by conventional leaching--two-stage countercurrent leaching was studied. The effects of various factors on the leaching was investigated. The results show that the leaching rates of uranium, thorium and rare earth are 98.66 %, 95.37 % and 64.23%, respectively under suitable conditions using conventional leaching method. Using the two-stage countercurrent leaching method, the leaching rates of uranium, thorium and rare earth can be increased by 0.5%~1.0%, the residual acid of the leaching solution can be reduced by more than 50%, and the solid-liquid separation performance of the slurry can be improved to a certain extent. [ABSTRACT FROM AUTHOR]

The article discusses the use of tiny crystals found in volcanic rocks to estimate the timing of volcanic eruptions. These crystals, known as "crystal clocks," resemble tree rings and can be used to determine how long magma remains underground before erupting. However, there is ongoing debate about the accuracy of these crystal clocks, as different laboratories have found varying rates of ticking. Researchers are working to improve the technique and better understand the behavior of magma underground to provide early warning for volcanic activity. While crystal clocks can provide valuable insights, they should not be relied upon as the sole forecasting tool, and efforts are being made to refine the models and improve predictions. [Extracted from the article]

In recent years, there have been important breakthroughs in the exploration for sandstone-hosted uranium (U) deposits in the Louzhuangzi district of the southern Junggar Basin. Between 2020 and 2023, a medium-sized sandstone-hosted uranium deposit production area was identified in the region. Only a few investigations have been conducted at the Louzhuangzi U deposit, including those analyzing its geological–tectonic evolution, basic geological features, hydrogeology, and ore-controlling factors. It is generally believed that uranium mineralization at the Louzhuangzi U deposit is controlled by a redox zone. Organic matter (referred to as OM hereafter) consisting of bitumen and carbonaceous debris is very common in the uranium ores (especially in high-grade ores) at the Louzhuangzi U deposit. However, the characteristics of the OM and its contribution to uranium's mineralization have not been studied in detail. In this study, OM-rich U-ores, altered sandstone, and barren sandstone samples were collected for petrography, mineralogical, micro-spectroscopy, carbon, and sulfur isotope studies. The results of this study show that the distribution of U minerals and metal sulfides (pyrite, sphalerite, etc.) was strictly controlled by bitumen at the Louzhuangzi U deposit. The bitumen may have been formed by hydrocarbon-rich and U-rich ore-forming fluids, which were formed after hydrocarbon generation and expulsion in the underlying Jurassic coal-bearing source rocks. The fluids contained U, Zn, Fe, and other metal elements, which migrated together and then precipitated into the oxidized Toutunhe Formation sandstone through cracking and differentiation processes. Therefore, the results indicate that migrated hydrocarbons were involved in U mineralization, in addition to oxidation–reduction processes, in the Louzhuangzi district, south of the Junggar Basin (China). [ABSTRACT FROM AUTHOR]

The Kunduleng granite hosts one of several significant uranium anomalies within the southern Great Xing'an Range, NE China. Whole-rock geochemistry and mineral chemistry data, along with the zircon U-Pb-Hf isotope have been used to constrain the petrogenesis of this granitic intrusion and the origin of the uranium anomaly. Microscopically, quartz, alkali-feldspar, and plagioclase are the essential mineral constituents of the granite, with minor biotite, while monazite, apatite, xenotime, and zircon are accessory minerals. Geochemically, the silica- and alkali-rich granites show a highly fractionated character with "seagull-shaped" REE patterns and significant negative anomalies of Ba and Sr, along with low Zr/Hf and Nb/Ta ratios. The granite has positive zircon εHf(t) values ranging from +12.7 to +14.5 and crustal model ages (TDM2) of 259–376 Ma, indicating a Paleozoic juvenile crustal source. Uraninite and brannerite are the main radioactive minerals responsible for the uranium anomaly within the Kunduleng granite. Uraninite presents well-developed cubic crystals and occurs as tiny inclusions in quartz and K-feldspar with magmatic characteristics (e.g., elevated ThO2, Y2O3, and REE2O3 contents and low CaO, FeO, and SiO2 concentrations). The calculated U-Th-Pb chemical ages (135.4 Ma) are contemporaneous with the U-Pb zircon age (135.4–135.6 Ma) of the granite, indicating a magmatic genesis for uraninite. The granites are highly differentiated, and extreme magmatic fractionation might be the main mechanism for the initial uranium enrichment. Brannerite is relatively less abundant and typically forms crusts on ilmenite and rutile or it cements them, representing the local redistribution and accumulation of uranium. [ABSTRACT FROM AUTHOR]

The current study aims to develop mathematical techniques to predict the impact of uranium radioactivity on humans using five minerals; namely, Urbanite, Craniate, Austenite, Samarskite, and Brannerite, using the graph method. We use this technique for calculating uranium radioactivity concentration in these minerals, and obtain different sets of results. [ABSTRACT FROM AUTHOR]

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Groundwater is in direct contact with the soil and rocks that dissolve many compounds and minerals including uranium and its daughter products. 210Po is one of the decay products of 238U series that cause internal radiation dose in humans when consumed in the form of water and food, including sea food. Therefore, activities of 210Po have been studied in ground and surface water, and in food samples that are commonly used in Chamarajanagar region of Karnataka, India. The average 210Po concentration in bore well water samples and surface water samples are 3.21 and 1.85 mBq L−1, respectively. In raw rice and wheat, the average values of 210Po are 96 and 41 mBq kg−1, respectively. In millets and pulses, the average activity of 210Po is 157 and 79 mBq kg−1, respectively. Among food items, the highest activity of 1.3 kBq kg−1 is observed in marine crabs and the lowest activity of 2.6 mBq kg−1 is found in milk samples. The average ingestion dose due to 210Po in ground and surface water are 2.8 and 1.62 μSv y−1, respectively. The ingestion dose due to various food samples to the population is also calculated. Total ingestion dose due to 210Po to pure vegetarian population and general population are 38.09 and 590.80 μSv y−1, respectively. The concentration of 210Po in water samples and food samples of this region are in a comparable range with the world and Indian average values and lies well below the recommended guideline level. [ABSTRACT FROM AUTHOR]

Overlapping uranium and coal resources are widely distributed in the basins of China. The current uranium–coal coordinated mining model, mining interaction, and multi-phase and multi-field coupling mechanisms remain unclear, thereby substantially restricting the mining of overlapping uranium and coal resources. This article reviews the overlapping uranium–coal mining technology and conditions, summarizes the main problems faced by the coordinated mining of coexisting uranium–coal resources, proposes a dynamic coordinated mining technology system for the entire life cycle of coexisting uranium–coal resources, and describes the multiphase and multifield coordinated mining of co-associated uranium–coal resources. The multifield coupling mechanism clarifies the solid–liquid–gas three-phase spatiotemporal coupling effects of the stress, fracture, seepage, geochemical, pressure, and microbial fields, and explains the safe and efficient mining technology of uranium and coal resources, and the coordinated mining and isolation technology of uranium and coal. "Trinity" pollution prevention and control technology and other key research directions are discussed to promote green, efficient, joint, and coordinated mining of uranium and coal. [ABSTRACT FROM AUTHOR]

A geochemical study of rare earth elements (REEs), uranium (U), thorium (Th) and major elements was conducted in mylonitic rocks found in north Abu Rusheid, south eastern desert, Egypt, a well-known uranium ore deposit area. The concentrations of REEs, U, and Th were measured using inductively coupled plasma mass spectrometry. ∑REEs varied from 38 to 183 µg/g with a mean value of 90 µg/g. U and Th concentrations varied from 67 to 171 and 98 to 454 µg/g, respectively. The mean value of the U/Th ratio was higher than the upper continental crust value and the mylonitic rocks were concluded to have high U content. [ABSTRACT FROM AUTHOR]

Extraction of molybdenum (Mo) from jordisite is difficult due to the amorphous state of MoS2. In this study, mechanical activation was employed to pretreat this type of ore with a low Mo content of 0.26%, and then molybdenum and uranium were both extracted from the milled ore using sulfuric acid. The effects of milling time, oxidant, and optimal leaching conditions were investigated in the laboratory. The results show that the mechanical activation will reduce the particle size and increase the specific surface area of the ore under certain milling conditions. Mechanical activation without oxidants in a hypoxia environment is not conductive to the recovery of molybdenum. When the oxidant of MnO2 is added during the milling process, the Mo recovery will increase greatly. The effect of mechanical activation on U recovery is not so obvious. The phenomenon of agglomerate will occur during the milling process, which will reduce Mo recovery seriously, especially when the milling time is more than 120 min. The Mo and U recovery can reach 84.52% and 61.39%, respectively, after optimization of sulfuric acid leaching process conditions. [ABSTRACT FROM AUTHOR]

The content of uranium 238 (238U) in naturally evolved soils with a meta-morphic and poorly developed profile, later technogenically contaminated by the activity of the former "Kremikovtsi" metallurgical plant, located at the foot of the Buhov uranium ore field, was investigated. A total of six soil profiles were analyzed, incl. five from the industrial site of the combine and one control. Data on uranium content were obtained by two methods - Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), simultaneously with results for over 50 chemical elements, as well as measured by its daughter product - thorium 234 (234Th), determined by gamma spectrometric analysis via multichannel analyzer with high purity germanium detector (HPGe). The results demonstrate that the uranium content of the investigated profiles in single cases exceeds the background norms of 11-173 Bq/kg and is within the range of 50±5 - 180±40 Bq/kg. The maximum values of the studied element are obtained from the coarsest profiles, with the maximum content of coarse sand, which suggests a primary state of uranium in the form of ore minerals or isomorphically included in primary insoluble accessory minerals in the soil of the studied profiles. From the research, the characteristic relationship of the heavy metal with the soil organic matter was not established. Still, an accumulation was observed in the cambic horizons of the metamorphic profiles. A factor for the upward migration and accumulation of uranium is the change of the water-air soil regime and establishment of periodic reducing conditions; as a general conclusion, the natural radionuclide undergoes migration from the surface horizons of the studied Technosols. [ABSTRACT FROM AUTHOR]

This study presents findings regarding the kinetics of ferrous iron oxidation in solution mediated by Acidithiobacillus ferrooxidans bacteria within a continuous-flow bioreactor employing diverse types of immobilizers. The objective is to augment the rate of ferrous iron oxidation in solutions utilizing an immobilizer for Acidithiobacillus ferrooxidans strains. Immobilization represents a promising avenue for enhancing the efficiency of Fe2⁺ oxidation via acidophilic ferrooxidizing bacteria, leading to a several-fold increase in oxidation rate. A comparative analysis was conducted to evaluate the efficacy of different types of immobilizer in facilitating iron oxidation within a continuous-flow bioreactor, including the application of wood chips coated with Fe(OH)3. The results indicate that wood chips coated with iron hydroxide serve as effective type of immobilizer, facilitating the robust attachment of Acidithiobacillus ferrooxidans via electrostatic interactions between negatively charged bacteria and positively charged surfaces. Experimental investigations were conducted using novel immobilization matrices in pilot-scale tests simulating the underground borehole leaching (UBL) of uranium. The bioactivation of leaching solutions enhances the efficiency and environmental compatibility of UBL compared to conventional chemical oxidation methods. The relationships between redox potential and ferric iron content in bioactivated solutions during the UBL of uranium were delineated. The significance of this study lies in its elucidating the pivotal role of Fe2⁺ oxidation in uranium extraction processes, particularly in the context of UBL. By employing bioactivation mediated by Acidithiobacillus ferrooxidans, the study demonstrates not only enhanced uranium extraction efficiency, but also markedly improved environmental sustainability compared to traditional chemical oxidation methods. The findings reveal crucial correlations between redox potential and ferric iron concentration in bioactivated solutions. [ABSTRACT FROM AUTHOR]

Graphene nanoplatelets (GNPs) were functionalized with an organic ligand to prepare materials for selective extraction of uranium from acidic solution. The effects of di-2-ethylhexylcarbamoylethylbutyl phosphonate (DEHCEBP) ligand concentration on the structure of the final solids and the effect on its extraction capacity were investigated in materials with 0.3, 0.5, 0.8, 1.0 and 1.2 mmol of organic ligand per gram of solid. Raman spectroscopy and X-ray diffraction analysis confirm that impregnation does not modify the carbon network and interlayer distance of the GNPs. As shown with nitrogen adsorption–desorption experiments, the amidophosphonate ligand first fills the micropores then the mesopores of the support while the ligand concentration increases. Acidic uranium solutions with high sulfate content were used to simulate the composition of ore treatment leaching solutions. Increasing the ligand concentration inside the graphene leads to an increase of the equilibration time in batch extraction experiments. This suggests that the DEHCEBP molecules form multiple layers in the materials containing the highest ligand contents. The results also suggest that the ligands located inside the micropores remain inaccessible for extraction. Maximum extraction capacities of the material with 1.2 mmol g−1 to 0.3 mmol g−1 DEHCEBP ranged respectively from 108 mg to 18 mg of uranium per gram of solid. This indicates the high potential of these functionalized graphene nanoplatelets for solid phase uranium extraction. [ABSTRACT FROM AUTHOR]

In-situ leaching of uranium is the most predominant method for the current exploitation of sandstone-type uranium deposits. The focus of in-situ leaching of uranium deposits lies in enhancing extraction capacity, and leaching rate, and reducing extraction costs. In order to improve leaching efficiency and reduce costs, the optimization experiments and research on the filter, acidity, and pumping volume were carried out at a uranium in-situ leaching deposit in Inner Mongolia. The research showed that maintaining the length of the filter could be controlled within 4-6 m to ensure its high efficiency and the connection between the upper section of the filter and the rich ore-bearing block with relatively high grade was conducive to the improvement of uranium leaching rate. The leaching efficiency and concentration of uranium in the leaching solution could be improved by controlling the acidity of the solution at about 15 g/L. The pumping volume(single width) was maintained at 0. 75-1.0 mz/h, so that the mining area could maintain a high uranium extraction capacity and a low leaching volume. Through the optimized technical parameters, the optimized peak uranium concentration in the leaching solution was increased from 28.89 mg/L to 59. 72 mg/L. During the initial two years of operation in the mining area, the uranium leaching rate increased from 47.20% to 60. 99%, the average uranium concentration in the leaching solution increased from 17.43 mg/L to 32. 63 mg/L, the acid consumption per ton of uranium decreased by 15. 26%,and the electricity consumption per ton of uranium decreased by 46. 51%. The research had changed the previous "large flow, low concentration" leaching mode, achieving efficient optimization of uranium extraction technology by in-situ leaching. [ABSTRACT FROM AUTHOR]

Purpose: Several studies using life cycle assessment (LCA) have highlighted nuclear electricity's possible role as a low carbon-emitting electricity source. But the variability of results has also been questioned by several published LCA reviews, the latest identified dating back from 2016. This article aims at assessing whether new developments and knowledge confirm this statement. Methods: Meta-analysis is a systematic review approach that allows to assess this variability. It was applied in this study to measure and understand the dynamics behind the greenhouse gases (GHG) emissions of nuclear electricity in a life cycle perspective. From 114 publications identified since 2012, 22 primary studies were selected and analysed to provide a meta-database of 63 estimations of greenhouse gases (GHG) per kWh generated. A descriptive analysis of the meta-database provided a status of the art on the topic in terms of approaches adopted, data sources, etc. Additional data exploitation using boxplot graphs was performed to assess the dispersion and variability of the results around these figures depending on several factors such as extraction mining technique and energy demand, enrichment technology used, reactor's size, and type of LCA practitioners. Results and discussion: The life cycle GHG emissions of nuclear electricity found with the meta-analysis were 3.09 g CO2 eq./kWh (min), 6.36 g CO2 eq./kWh (median), 12.4 g CO2 eq./kWh (average excluding extrema), and 43.2 g CO2 eq./kWh (max), although extremum values were also identified at 53.4, 60.0, and one outlier, based on theoretical scenarios. Using principal component analysis (PCA), the two most influential variables of the environmental performance of nuclear electricity were identified: GHG emissions intensity of the electricity consumed during the enrichment of uranium and energy demand for the extraction of uranium ore. Conclusions: Finally, the contributions of this meta-analysis to current knowledge on the GHG emissions intensity of nuclear electricity generation systems were discussed, including life cycle step breakdown, data gaps, limits, and uncertainties associated to the back end and reactor activities. Among the main areas for improvement for future LCA studies, the study helped identify a need for consolidated industrial data along with harmonised practices regarding system boundary definition. [ABSTRACT FROM AUTHOR]

This paper investigates the implementation of a model-based predictive control (MPC) strategy to improve the performance of a semi-autogenous grinding (SAG) mill in a uranium mineral processing plant. The SAG mill, crucial in crushing and grinding uranium ore to the desired size, is currently managed using conventional proportionalintegral-derivative (PID) controllers. However, to enhance production efficiency and control over the SAG mill's variables, this paper suggests the adoption of MPC. The proposed MPC controller is developed using a neural network (NN) model of the SAG mill, created in MATLAB with data collected over 21 days. The effectiveness of the MPC controller is assessed by contrasting its response with that of the real-time operator control. This comparison utilizes tools like MATLAB and the RSlinx remote server for accessing OPC real-time data. Findings reveal that the MPC controller exhibits a quicker reaction to alterations in the SAG mill's process outputs and proficiently regulates crucial outputs such as Mill mass, ensuring that the manipulated variables stay within their designated limits. Unlike operator control, which is slower and adjusts one variable at a time, the MPC approach can maximize the mill's throughput rate without impacting the ore feed rate. This demonstrates the MPC controller's superior ability to optimize SAG mill operations efficiently. [ABSTRACT FROM AUTHOR]

Margaritasite is a mineral compound discovered in the early 1980s in Chihuahua, Mexico. It is a natural cesium uranyl vanadate found only, so far, in the Margaritas mine of the Peña Blanca highlands. In this work, a thorough characterization of the aforementioned mineral is presented. The portfolio of the techniques employed includes high-resolution X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy, transmission electron microscopy in selected area electron diffraction (SAED) mode, and X-ray absorption spectroscopy (XAS). After extensive data analysis and modeling, new information on the mineral has been retrieved. Its phase composition is margaritasite–carnotite: a solid solution of cesium and potassium uranyl vanadate [(Cs,K)2(UO2)2(VO4)2·nH2O], and margaritasite, which is practically pure cesium uranyl vanadate [Cs2(UO2)2(VO4)2·nH2O]. The crystal structure of both components presents the space group P 1 21/c 1. Yet, each phase has similar, but appreciably different, lattice parameters. The mineral has a lamellar tabular and prismatic morphology. SAED patterns confirm the crystal structure of margaritasite. XAS spectra of Cs, V, and U confirm the elemental composition, oxidation states, and interatomic distances of this structure. These findings are consistent with the presence of cesium in this unique mineral from the paragenesis point of view. [ABSTRACT FROM AUTHOR]

The features of uranium mining on Kazakhstan's enterprises have been examined, and uranium deposits located in the Syrdarya and Shu-Sarysu depressions have been described. Actual and projected data on the development of technological blocks in areas with complex geological structures have been analyzed and compared. Core samples were collected and, using X-ray diffraction analysis, quantitative and qualitative characteristics as well as mineral compositions of ores from various productive horizons of uranium deposits in the Syrdarya and Shu-Sarysu depressions were comparatively analyzed. It was determined that the ores in the Syrdarya depression are relatively homogeneous compared to those in the Shu-Sarysu depression, although in some places, clay minerals and gypsum are present, which hinder the uranium leaching processes. In the ores of the Shu-Sarysu depression, clay minerals that impede the uranium leaching processes are present in certain areas. Microscopic analysis of core material samples using a LEICA DM 2500 P microscope revealed particle sizes and shapes, as well as their distribution within the structure of host rocks in the productive horizon. Using X-ray diffraction analysis, mineral compositions of sediment-forming components during uranium well mining in the considered productive horizons were determined and comparatively analyzed. It was established that in the geotechnological wells of the Syrdarya depression, sediments of predominantly chemical origin, such as gypsum, are formed. However, in the geotechnological wells of the Shu-Sarysu depression, sediments of mechanical origin, consisting predominantly of quartz particles and clay minerals, are formed. Based on the obtained data, a method for intensifying underground uranium leaching in complex geological conditions has been developed, which involves dissolving sediment formations and increasing the oxidative–reductive potential of the leaching solution. The proposed and experimentally substantiated universal methodology for enhancing uranium well production involves the dissolution and prevention of precipitation using hydrofluoric acid solutions, as well as the oxidation of uranium dioxide with hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Currently, a widely accepted solution to reduce gypsum precipitation in acid leaching of low-grade uranium ore has not yet been identified. This study aims to delve into the impact of different flow rates on gypsum precipitation in ore through column leaching experiments. Complementary methods such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize slag samples. The results indicate that as the flow rate surged from 63.69 Lh−1m−2 to a whopping 254.76 Lh−1m−2, the gypsum content and types in the slag decreased gradually. This can be attributed to two factors: (1) the elevation of flow rates maintains the ore heap in a lower pH environment, promoting the conversion of SO42− to HSO4−; (2) higher flow rates contribute to increased ore heap porosity, providing more migration pathways for solutions containing high concentrations of Ca2+, SO42−, and HSO4−, thus facilitating the separation of gypsum from the ore. This study affirms the feasibility of employing high-flow pre-leaching to address gypsum clogging issues, offering a new perspective for acid pre-leaching. [ABSTRACT FROM AUTHOR]

For the leaching process of uranium ore, the leaching rate, leaching efficiency, and energy consumption are hot research topics. In order to meet the industry's demand for natural uranium and ensure the stable supply of uranium products, this article proposes the use of surfactants to improve the leaching efficiency and leaching rate of uranium ore, thereby achieving better leaching results at larger particle sizes and reducing grinding energy consumption. This article focuses on the core samples of a certain mine and adopts a stirring leaching method. Firstly, the acid stirring leaching process conditions were optimized. Based on this, the types and concentrations of surfactants were selected, and the influence of the selected surfactants on the stirring leaching law of the ore was investigated. The results indicate that the addition of cetyltrimethylammonium bromide (CTAB) cationic surfactant has the highest leaching efficiency in the optimal conventional stirring leaching environment for ores. Compared with the stirring leaching effect without CTAB, after adding 50 mg/L CTAB for leaching, the leaching rate of uranium ore increased from 90.79 to 96.34% within the same leaching cycle; By adding 50 mg/L CTAB to leach ore with a particle size of − 60 mesh, the uranium leaching rate increased from 35.09 to 87.79%, achieving effective leaching of uranium ore with coarser particles; Through analysis such as BET and SEM, it was determined that the addition of CTAB promoted the solution to enter the microporous gaps between ores, achieving an increase in leaching rate. Surfactants reduced the thickness of the liquid film formed on the ore surface and the diffusion time of the liquid film, which was the reason for the improvement of uranium leaching effect. [ABSTRACT FROM AUTHOR]

Xiazhuang uranium ore field, located in the southern part of the Nanling Metallogenic Belt, is considered one of the largest granite‐related U regions in South China. In this paper, we contribute new apatite fission track data and thermal history modeling to constrain the exhumation history and evaluate preservation potential of the Xiazhuang Uranium ore field. Nine Triassic outcrop granite samples collected from different locations of Xiazhuang Uranium ore field yield AFT ages ranging from 43 to 24 Ma with similar mean confined fission track lengths ranging from 11.8 ± 2.0 to 12.9 ± 1.9 μm and Dpar values between 1.01 and 1.51 μm. The robustness time‐temperature reconstructions of samples from the hanging wall of Huangpi fault show that the Xiazhuang Uranium ore field experienced a time of monotonous and slow cooling starting from middle Paleocene to middle Miocene (∼60–10 Ma), followed by relatively rapid exhumation in the late Miocene (∼10–5 Ma) and nearly thermal stability in the Pliocene–Quaternary (∼5–0 Ma). The amount of exhumation after U mineralization since the Middle Paleogene was estimated as ∼4.3 ± 1.8 km according to the integrated thermal history model. Previous studies indicate that the ore‐forming ages of U deposits in the Xiazhuang ore field are mainly before Middle Paleocene and the mineralization depths are more than 4.4 ± 1.2 km. Therefore, the exhumation history since middle Paleocene plays important roles in the preservation of the Xiazhuang Uranium ore field. [ABSTRACT FROM AUTHOR]

This paper discusses the geochemical constraints on genesis of dispersed mineralized quartz-fluorite veins (QFV) at south west Sinai Peninsula, Egypt. These veins range from colorless to pale to deep violet in color and extend continuously and/or discontinuously in NE-SW, E-W, N-S, and NW-SE trends. They exhibit varying thicknesses ranging from a few centimeters to approximately 0.3 m. The scanning electron microscope (SEM) analysis has revealed the existence of secondary uranium minerals, notably kasolite Pb(UO2)SiO4.(H2O), in association with other minerals such as galena (PbS), atacamite (Cu2Cl(OH)3), and fluorite (CaF2) within the quartz-fluorite veins (QFV). Furthermore, the SEM analysis indicates a significant presence of fluorine incorporated into the biotite lattice of the host granitic rocks. Geochemically, there is a reasonable difference between the host granitic rocks and QFV, especially, silica and alumina contents. Also, some trace elements experienced enrichment in QFV such as Cu, U, Pb and Ag. The chondrite normalized pattern of QFV rare earth elements (REE) shows conspicuous negative Tb anomalies while the host rocks showed negative Eu anomalies. It is noticeable that there is a closed relation between uranium and fluorine in QFV. The Th/U ratios are < 1 in QFV samples indicating that the QFV had not been derived from magmatic origin. Furthermore, the REE and the mineral assemblages of QFV imply to hydrothermal origin (meteoric water) at shallow depth and low temperature < 200 °C under oxidation condition (epithermal genesis). [ABSTRACT FROM AUTHOR]

Based on the mining of deep metal mineral resources and the current in-situ leaching mining process of uranium ore, combined with the technological characteristics of "fluidized mining of metal ore" and "deep geothermal development", an innovative concept of strengthening the fluidized leaching process of deep metal ore - geothermal co mining is proposed, A numerical simulation method was used to analyze the turbulent flow and heat transfer characteristics of a new type of heat transfer enhancement element - a swirl plate as a support between tubes. The renormalization two equation turbulence model was used for numerical simulation, and the SIMPLEC algorithm was used for pressure and velocity coupling, and the enhanced wall treatment method was used for wall treatment. The periodic changes in the cross-sectional flow field and turbulence intensity of the unit flow channel were analyzed, as well as the synergistic relationship between the flow field and temperature field on the cross-section. The corresponding variation trends of the average Nusselt number and the average synergy angle of the cross-section were compared. The experimental results show that the 270-4.25 cyclone sheet can more fully utilize the enhanced heat transfer of the spin flow, and the overall average Nusselt number is higher than 180-2.0, which is consistent with the experimental results. That is, θm is low where high Nub and θm is high where low Nub is low, indicating that the changing trend of the two is fully consistent with the field synergy principle. This paper systematically analyzes the basic theoretical bottleneck, key technical problems and future development trend in the process of geothermal joint mining of deep metal mine, and aims to provide reference for the strengthening of geothermal joint mining and geothermal joint mining of deep metal ore. [ABSTRACT FROM AUTHOR]

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When operating and dismantling a nuclear facility that handles uranium, the surrounding soil may be contaminated, emphasizing the need for appropriate treatment and disposal methods for soil waste. This study assessed high-temperature sintering technology for uranium contaminated soil waste to overcome limitations in existing decontamination methods and the volume increase associated with current solidification technology. The sintering process was found to effectively vitrify and re-mineralize complex chemical components in the soil. Sintered bodies were produced under varying conditions, adjusting molding pressure, heating temperature, and time. Optimized conditions resulted in sintered bodies with a volume reduction rate exceeding 30 % and a compressive strength surpassing 10 MPa, indicating a significant impact on the phase conversion and re-mineralization of silt and clay minerals. The soil sintering mechanism was identified through comprehensive microscopic observations and mineral phase change analysis. Leaching evaluations of sintered bodies, made from simulated uranium-contaminated soil, demonstrated their applicability to contaminated soil wastes. Additionally, it was confirmed that the sintering temperature of the soil could be lowered by incorporating a small amount of B2O3, suggesting a means to enhance the economic feasibility of the treatment process. The findings of this study highlight the applicability of pressureless sintering technology, based on glass composite materials, capable of simultaneously reducing and stabilizing uranium-contaminated soil waste. [ABSTRACT FROM AUTHOR]

The separation and recovery of valuable metals from the Huayangchuan uranium polymetallic ore was investigated based on mineralogical research and mineral processing experiments. The most promising valuable elements in the ore, according to mineralogical studies, are U, Nb, and Pb. 95.75% of U and 93.00% of Nb are found in betafite, 46.85% of Pb is present in galena, 52.01% of Pb occurs in cerussite, and associated Ag exists primarily in galena. The beneficiation process involving gravity concentration, magnetic separation, and flotation was determined based on the mineralogical characteristics of the ore. The U-Nb concentrate with U grade of 3578 ppm and recovery of 83.18 %, Nb2O5 grade of 4391 ppm and recovery of 74.55 % can be obtained, and five elements including U, Nb, Pb, Ag, and Fe are recovered. Compared with the previous beneficiation experimental process, the flowsheet is greatly simplified and the beneficiation recovery efficiency has been improved. The results of this investigation can help to address the gaps in the processing of low-grade uranium deposits with similar mineralogical properties. [ABSTRACT FROM AUTHOR]

This study focuses on the Medical Isotope Production Reactor (MIPR), an aqueous homogeneous reactor utilized for synthesizing medical isotopes like 99Mo. A pivotal aspect of MIPR's functionality involves the fuel solution's complex chemical interactions, particularly during reactor operation. These interactions result in the formation of precipitates, notably water filamentous uranium ore and columnar uranium ore, which can impact reactor performance. The research presented here delves into the reactions between liquid fuel uranyl nitrate and key radiolytic products, employing simulation calculations complemented by experimental validation. This approach facilitates the identification of uranium precipitate types and their formation conditions under operational reactor settings. Additionally, the article explores strategies to mitigate the formation of specific uranium precipitates, thereby contributing to the efficient and stable operation of MIPR. [ABSTRACT FROM AUTHOR]

This work examines cast stone matrices (CSM) fabricated by comelting of basalt with both uranium-bearing perlite (M150 grade) and U3O8 at a temperature of 1623 K in air for 5 h. As a result of comelting of basalt with uranium-free M150 grade perlite, matrices are obtained containing glass and spinel as the major phases. When basalt is comelted with uranium-bearing perlite (M150 grade) CSMs are formed, the major phases of which are two Cr-spinels of different compositions, uranium-bearing glass, and dendritic aluminosilicate crystals. In the case of fusion of basalt and U3O8 taken in the initial weight ratio of 1 : 1, CSM is generated as the major phases containing UO3, CaU3O10, (Al,Cr,Fe)2U2O9, plagioclase, and uranium-bearing glass. The leaching rate of uranium from a basalt melt with uranium-bearing perlite (M150 grade, ~7.2 wt % U) and that of CSM made by comelting of basalt with U3O8, (~42.5 wt % U) after 28 days contact with water at 298 K was investigated. [ABSTRACT FROM AUTHOR]

The determination of elemental impurities in uranium ore concentrates (UOCs) is of great importance in the fields of nuclear forensics and nuclear safeguards and more generally for the nuclear industry. To avoid the use of chemical reagents, prevent waste generation, and reduce the duration of the analysis, a simple method based on sample preparation involving the conversion of UOCs into glass beads by alkaline fusion followed by direct measurement by laser ablation—sector-field ICP-MS (LA-ICP-MS) is proposed. External calibration was performed with a mix of UOCs and geological standard reference materials. Accurate results were obtained for most of the 48 elements of interest in six UOC materials. The lowest detection limits are in the ng g−1 range. With this method, concentrations of a wide range of elements can be determined within 24 h. [ABSTRACT FROM AUTHOR]

Uranyl sulfates are important constituents of uranium ores and represent a significant fraction of U(VI) minerals discovered in recent years owing to their propensity to form in mine tailings and legacy sites related to uranium exploration. Recently, we surveyed all published Raman spectra for uranium minerals and found significantly less easily accessible data available for uranyl sulfates relative to other groups of uranium minerals (Spano et al. 2023). In that work, we described average spectra for groups of uranyl minerals to understand common vibrational spectroscopic features attributable to similarities in oxyanion chemistry among U(VI) minerals, but only data for three uranyl sulfate minerals were included in the study. The present work reports on Raman spectra collected for 18 additional uranyl sulfate minerals. To better understand underlying structural and chemical features that give rise to spectroscopic observables, we relate differences in structural topology, charge-balancing cations, and locality of origin to features observed in the Raman spectra of selected natural uranyl sulfates. [ABSTRACT FROM AUTHOR]

During the extraction of nuclear raw materials, rare earths and other elements from ores containing uranium and thorium, various types of radioactive waste and some recovery tailings are generated. Mining and ore processing residues, i.e. waste and tailings, present a variety of problems related to waste management. Their bulky structure prevents their disposal underground, and their long radioactive half-life causes various problems with regard to their long-term storage. As a matter of fact, the secondary presence of nuclear raw materials together with other minerals requires compliance with hazardous waste procedures in the storage of waste containing nuclear raw materials after the recovery of these main minerals. It may be possible in the future to recover these nuclear raw materials from stockpiles of stored mine waste. The prospect of imbalances in the global uranium supply and demand increases the importance of secondary sources contributing to the global uranium supply. The increasing importance of secondary sources of nuclear raw materials suggests that more attention should be paid to the recovery of these resources together with primary minerals than in the past. In world literature, there is no review article that describes and discusses the waste management of nuclear raw materials in mining and mineral processing together with the opportunities and obstacles for their recovery. Considering this deficiency in the literature, in this study, the properties of waste and tailings resulting from mining and ore preparation activities of nuclear raw materials are explained, the difficulties encountered are mentioned, and solution suggestions are presented by making use of the literature on the recovery of tailings and waste management. [ABSTRACT FROM AUTHOR]

The mineralogical, fluid inclusion, and stable isotope (C, O) study was conducted on a Late Variscan Zn-Pb vein Bt23C, Příbram uranium and base-metal district, Bohemian Massif, Czech Republic. The vein is hosted by folded Proterozoic clastic sediments in exo-contact of a Devonian-to-Lower-Carboniferous granitic pluton. Siderite, dolomite-ankerite, calcite, quartz, baryte, galena, sphalerite, V-rich mica (roscoelite to an unnamed V-analogue of illite), and chlorite (chamosite) form the studied vein samples. The banded texture of the vein was modified by the episodic dissolution of earlier carbonates and/or sphalerite. Petrographic, microthermometric, and Raman studies of fluid inclusions proved a complicated fluid evolution, related to the activity of aqueous fluids and to an episode involving an aqueous–carbonic fluid mixture. Homogenization temperatures of aqueous inclusions decreased from ~210 to ~50 °C during the evolution of the vein, and salinity varied significantly from pure water up to 27 wt.% NaCl eq. The aqueous–carbonic fluid inclusions hosted by late quartz show highly variable phase compositions caused by the entrapment of accidental mixtures of a carbonic and an aqueous phase. Carbonic fluid is dominated by CO2 with minor CH4 and N2, and the associated aqueous solution has a medium salinity (6–14 wt.% NaCl eq.). The low calculated fluid δ18O values (−4.7 to +3.6‰ V-SMOW) suggest a predominance of surface waters during the crystallization of dolomite-ankerite and calcite, combined with a well-mixed source of carbon with δ13C values ranging between −8.2 and −10.5‰ V-PDB. The participation of three fluid endmembers is probable: (i) early high-temperature high-salinity Na>Ca-Cl fluids from an unspecified "deep" source; (ii) late low-salinity low-temperature waters, likely infiltrating from overlying Permian freshwater partly evaporated piedmont basins; (iii) late high-salinity chloridic solutions with both high and low Ca/Na ratios, which can represent externally derived marine brines, and/or local shield brines. The source of volatiles can be (i) in deep crust, (ii) from interactions of fluids with sedimentary wall rocks and/or (iii) in overlying Permian piedmont basins containing, in places, coal seams. The event dealing with heterogeneous CO2-bearing fluids yielded constraints on pressure conditions of ore formation (100–270 bar) as well as on the clarification of some additional genetic aspects of the Příbram's ores, including the reasons for the widespread dissolution of older vein fill, the possible re-cycling of some ore-forming components, pH changes, and occasionally observed carbon isotope shift due to CO2 degassing. [ABSTRACT FROM AUTHOR]

Rhenium is an extremely rare critical metal element in Earth's continental crust. Owing to its extremely high melting point and heat-stable crystalline structure, rhenium is an essential component of alloy materials used in high-performance aircraft engines. Demand for rhenium resources is therefore growing. Currently, most rhenium is produced as a byproduct of molybdenum mining in porphyry copper–molybdenum deposits. Research has therefore focused on the enrichment characteristics of rhenium in this type of deposit, with little attention paid to rhenium in other types of deposits. This study reports the occurrence state and enrichment mechanism of rhenium in the Qianjiadian sandstone-type uranium deposit in the Songliao Basin, Northeast China. Sequential extraction revealed that the average proportions of different forms of rhenium are as follows: water-soluble (57.86%) > organic-sulfide-bound (13.11%) > residual (12.26%) > Fe/Mn oxide-bound (10.67%) > carbonate-bound (6.10%). Combining mineralogical analysis techniques such as SEM-EDS, EMPA, and XRD, it has been established that rhenium does not occur as a substitute in sulfides (e.g., molybdenite) or uranium minerals in various types of deposits. Instead, it is mainly adsorbed onto clay minerals and Fe-Ti oxides, and in a small number of other minerals (pyrite, organic matter, and pitchblende). Rhenium is similar to redox-sensitive elements such as uranium and vanadium, and it is transported in a water-soluble form by oxidizing groundwater to the redox transition zone for enrichment. However, unlike uranium, which generally forms as uranium minerals, rhenium is mainly adsorbed and enriched onto clay minerals (kaolinite and interlayered illite–smectite). Most of the rhenium in sandstone-type uranium deposits occurs in an ion-adsorption state, and is easily leached and extracted during in-situ leaching mining of uranium ores. This type of deposit demonstrates excellent production potential and will become a crucial recoverable resource for future rhenium supply. [ABSTRACT FROM AUTHOR]

Isotope ratios and age dating of uranium ore concentrates (UOCs) are of great significance in nuclear forensic analysis. This paper presents accurate and precise isotopic analysis of uranium and thorium in 15 different UOCs using two types of ICP-MS instruments. 235U/238U, 234U/238U and 230Th/232Th isotope ratios were determined by Multi-Collector Inductively Coupled-Plasma Mass Spectrometry (MC-ICP-MS), while 230Th/234U and 234U/232Th atom ratios were determined by triple quadruple Inductively Coupled-Plasma Mass Spectrometry (ICP-MS/MS). Results show that the relative uncertainties in the determined values of 235U/238U, 234U/238U and 230Th/234U ratios for CRM124-1 are 0.0014%, 0.02% and 3.2%, respectively. It has been proved that an aliquot containing 1.12 μg of 238U was the minimum sample amount to obtain the representative 235U/238U ratios of the UOC samples for bulk analysis by MC-ICP-MS, especially when the sample of UOCs was inhomogeneous or a mixture of several UOCs. No correlation between the measured 238U/235U and 235U/234U ratios is observed in the UOC samples. It is possible to distinguish a single UOC sample from others by synthesizing 235U/238U ratio, 234U/238U ratio and 230Th/234U ratio simultaneously. The 230Th–234U model ages estimated using a 230Th–234U chronometer lie between 3.5 a and 4435 a. However, it is usually not reliable to determine the age over 100 a of UOCs, mainly because the material was not completely purified from relevant decay products during production. To overcome this problem, an alternative approach for age dating is proposed using multiple measurements of the ratios of 230Th/232Th and 232Th/234U at an interval of about 2 a to 5 a. This work demonstrates that multiple parameters obtained from a combination of multiple analytical techniques, including bulk analysis, imaging and microanalysis techniques, can be used to narrow the range of potential origins for nuclear forensic purpose. [ABSTRACT FROM AUTHOR]

Uranium precipitation involves the decomposition of uranyl complexes and the reduction of hexavalent uranium, which can occur sequentially or simultaneously within one redox reaction. The redox condition of hydrothermal fluid plays a vital role in controlling the migration and precipitation of uranium in hydrothermal uranium deposits. However, little attention has been paid to the role of uranyl complex decomposition in uranium precipitation. In this study, chlorite mineralogy and geochemistry were examined to clarify the process of uranium precipitation in the Shazhou deposit, Xiangshan uranium orefield, Southeast China. Based on comprehensive petrographic and mineral chemistry studies of chlorites obtained from altered granite porphyries and uranium ores, five types of chlorites were identified: (1) chlorite present in the form of pseudomorphous biotite, which was produced by the hydrothermal alteration of biotite in rocks that underwent hematitization and chloritization (Chl-I); (2) chlorite filling the cleavage cracks in biotite in rocks that underwent hematitization and chloritization (Chl-II); (3) chlorite occurring in pyrite veins (Chl-III); (4) chlorite intergrown with pitchblende in ore veins (Chl-IV); and (5) chlorite occurring in calcite veins (Chl-V). Chlorite geothermometry revealed that the formation temperatures of the five types of chlorites ranged from 219 °C to 254 °C. Mineral chemistry analyses revealed that the five types of chlorites formed in a reductive fluid environment, where the oxygen fugacity at different stages is similar, with log fO2 values ranging from -41.6 to -39.1. Uranium precipitation started only in stage Chl-IV. The examination of the mineral assemblage revealed that the ore-forming fluid was rich in F-, HPO32-, and CO32-. Comprehensive investigation of chemistry and physicochemical conditions of the ore-forming fluid revealed that oxidized uranium (UO22+) could be complexed with HPO42- and F-, and uranyl phosphate and the uranyl fluoride complexes were the main uranium species when uranium precipitation and the decomposition occurred at stage Chl- IV. However, the assessment of oxygen fugacity of the solution equilibria between the UO2(s) and the uranyl phosphate and uranyl fluoride complexes revealed that the reducibility of the fluid favoring the reduction of uranyl ions (UO22+) to U4+ was insufficient to reduce the uranyl phosphate and uranyl fluoride complexes. This indicates that the breakup of uranyl phosphate and the uranyl fluoride complexes to release uranyl ions should occur first at stage Chl-IV, reducing uranyl ions to U4+, and leading to uranium precipitation. Hence, the decomposition of uranyl complexes played an important role in uranium precipitation. With the increase in pH, uranyl phosphate and the uranyl fluoride complexes gradually decomposed and became reducible. Moreover, the decrease in ligand concentration was conducive to the decomposition of uranyl phosphate and the uranyl fluoride complexes. During the formation of the Shazhou deposit, the fluid boiling process induced the loss of volatiles, such as CO2, CH4, HF, and H2S, leading to an increase in pH and decrease in HPO42-, F-, and CO32- concentrations in the fluid. These factors also led to the decomposition of uranyl fluoride and the uranyl phosphate complexes and the precipitation of fluorapatite and calcite. Uranium was then reduced by the action of Fe2+ and S- (pyrite) from a hexavalent to a tetravalent, and finally, uranium was precipitated to form uranium ores. [ABSTRACT FROM AUTHOR]

In the period from 1955 to 1992, uranium ore was mined and processed in the Mesta River basin around the village of Eleshnitsa, region of Razlog. The ore processing plant was built and a tailings storage facility was built next to it. In the period 2002–2006, the tailings storage was reclaimed, and in 2011–2012 the ore mines were also reclaimed. For the treatment of drainage water, a treatment plant was built in the valley of Valchoto Dere River, a left tributary of the Mesta River. The radiological monitoring carried out by the Basin Directorate "West Aegean Sea Region" reveals a generally good quality of the surface waters in terms of the content of uranium and radium (226Ra) outside the area of the former uranium mining and the tailings storage facility. In this area, in some years a high content of natural uranium was found, with concentrations from 0.54 to 67.40 mg/l on average per year. The values significantly exceed (by 1.8 to 224.6 times) the norm regulated in the regulation for radiation protection and safety from the liquidation of the consequences of uranium mining. The spread of uranium is limited to a small area shortly downstream from the sources of contamination, but the potential risk to the local ecosystem should not be neglected. Radium, in contrast to uranium, has concentrations below the permissible limits in the twelve years studied. Its content varied from 0.025 to 0.11 Bq/l on average annually. The results show that the Mesta River near the border with the Republic of Greece is not contaminated with the studied radionuclides. [ABSTRACT FROM AUTHOR]