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Microorganisms inhabiting uranium (U)-rich environments have specific physiological and biochemical coping mechanisms to deal with U toxicity, and thereby play a crucial role in the U biogeochemical cycling as well as associated heavy metals. We investigated the diversity and functional capabilities of indigenous bacterial communities inhabiting historic U- and Rare-Earth-Elements-rich polymetallic tailings from the Mount Painter Inlier, Northern Flinders Ranges, South Australia. Bacterial diversity profiling identified Actinobacteria as the predominant phylum in all samples. GeoChip analyses revealed the presence of diverse functional genes associated with biogenic element cycling, metal homeostasis/resistance, stress response, and secondary metabolism. The high abundance of metal-resistance and stress-tolerance genes indicates the adaptation of bacterial communities to the "harsh" environmental (metal-rich and semi-arid) conditions of the Northern Flinders Ranges. Additionally, a viable bacterial consortium was enriched from polymetallic tailings. Laboratory experiments demonstrated that the consortium scrubbed uranyl from solution by precipitating a uranyl phosphate biomineral (chernikovite), thus contributing to U biogeochemical cycling. These specialised microbial communities reflect the high specificity of the mineralogy/geochemistry, and biogeography of these U-rich settings. This study provides the fundamental knowledge to develop future applications in securing long-term stability of polymetallic mine waste, and for reprocessing this "waste" to further extract critical minerals., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

The presence of organic matter (OM) has a profound impact on uranium (U) redox cycling, either limiting or promoting the mobility of U via binding, reduction, or complexation. To understand the interactions between OM and U, we characterised U oxidation state and speciation in nine OM-rich sediment cores (18 samples), plus a lignite sample from the Mulga Rock polymetallic deposit in Western Australia. Uranium was unevenly dispersed within the analysed samples with 84% of the total U occurring in samples containing >21 wt % OM. Analyses of U speciation, including x-ray absorption spectroscopy and bicarbonate extractions, revealed that U existed predominately (∼71%) as U(VI), despite the low pH (4.5) and nominally reducing conditions within the sediments. Furthermore, low extractability by water, but high extractability by a bi-carbonate solution, indicated a strong association of U with particulate OM. The unexpectedly high proportion of U(VI) relative to U(IV) within the OM-rich sediments implies that OM itself does not readily reduce U, and the reduction of U is not a requirement for immobilizing uranium in OM-rich deposits. The fact that OM can play a significant role in limiting the mobility and reduction of U(VI) in sediments is important for both U-mining and remediation., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Aluminum-phosphate-sulfate (APS) minerals of the alunite supergroup are minor components of uranium-bearing copper ores from the Olympic Dam deposit, South Australia. They typically represent a family of paragenetically late replacement phases after pre-existing REE-bearing phosphates (fluorapatite, monazite, and xenotime). Characterization with respect to textures and composition allows two groups to be distinguished: Ca-Sr-dominant APS minerals that fall within the woodhouseite and svanbergite compositional fields; and a second REE- and phosphate-dominant group closer to florencite in composition. All phases nevertheless display extensive solid solution among end-members in the broader APS clan and show extensive compositional zoning at the grain-scale. Samples representative of the deposit (flotation concentrate and tailings), as well as those that have been chemically altered during the processing cycle (acid leached concentrate), were studied for comparison. NanoSIMS isotope mapping provides evidence that the APS minerals preferentially scavenge and incorporate daughter radionuclides of the 238U decay chain, notably 226Ra and 210Pb, both over geological time within the deposit and during ore processing. These data highlight the role played by minor phases as hosts for geologically mobile deleterious components in ores as well as during mineral processing. Moreover, Sr-Ca-dominant APS minerals exhibit preferential sorption of Pb from fluid sources, in the form of both common Pb and 210Pb, for the first time revealing potential pathways for 210Pb elimination and reduction from ore processing streams. [ABSTRACT FROM AUTHOR]

The hydrolysis of uranium(VI) has been investigated by solubility experiments conducted on sodium uranate (Na 2 U 2 O 7) over a pH T range of 4.5–8 at 200 and 250 °C. Equilibrium constants for the U O 2 O H + , U O 2 OH 2 0 , U O 2 OH 3 - and U O 2 OH 4 2- complexes have all been derived at both temperatures. Alongside this investigation a comprehensive literature review has been conducted to document previous investigations into U(VI) hydrolysis at temperatures above 25 °C. Using the new data reported here alongside those available in the literature, modified Ryzhenko-Bryzgalin equation of state parameters have been generated for the U O 2 O H + , U O 2 OH 2 0 , U O 2 OH 3 - and U O 2 OH 4 2- complexes along with the polynuclear U O 2 2 OH 2 2+ and U O 2 3 OH 5 + complexes. This permits future works to extrapolate thermodynamic properties for these complexes to pressure–temperature conditions beyond those for which experimental data are available. Results reported here highlight the potential inadequacies of using the Ryzhenko-Bryzgalin and revised Helgeson-Kirkham-Flowers equations of state to extrapolate thermodynamic properties solely from room temperature data, with discrepancies ranging over 2–6 orders of magnitude being observed between extrapolations and the equilibrium constants experimentally derived at 200/250 °C. Using the newly derived properties, we report the results of thermodynamic calculations of uranium solubility and aqueous speciation under hydrothermal conditions relevant to a range of geological systems. These calculations suggest that uranyl hydroxide complexes may be responsible for uranium transport in a wide range of crustal fluids potentially obviating the need for high ligand concentrations. [ABSTRACT FROM AUTHOR]

Interface coupled dissolution-reprecipitation reactions (ICDR) are a common feature of fluid-rock interaction during crustal fluid flow. We tested the hypothesis that ICDR reactions can play a key role in scavenging minor elements by exploring the fate of U during the experimental sulfidation of hematite to chalcopyrite under hydrothermal conditions (220-300 °C). The experiments where U was added, either as solid UO2+x(s) or as a soluble uranyl complex, differed from the U-free experiments in that pyrite precipitated initially, before the onset of chalcopyrite precipitation. In addition, in UO2+x(s)- bearing experiments, enhanced hematite dissolution led to increased porosity and precipitation of pyrite+magnetite within the hematite core, whereas in uranyl nitrate-bearing experiments, abundant pyrite formed initially, before being replaced by chalcopyrite. Uranium scavenging was mainly associated with the early reaction stage (pyrite precipitation), resulting in a thin U-rich line marking the original hematite grain surface. This 'line' consists of nanocrystals of UO2+x(s), based on chemical mapping and XANES spectroscopy. This study shows that the presence of minor components can affect the pathway of ICDR reactions. Reactions between U- and Cu-bearing fluids and hematite can explain the Cu-U association prominent in some iron oxide-copper-gold (IOCG) deposits. [ABSTRACT FROM AUTHOR]

In situ recovery (ISR) has become an increasingly utilized technology worldwide for the economical extraction of uranium (U). Microorganisms play a significant role in U mobilization/immobilization and have therefore been used for the bioremediation of U contaminated sites. In natural environments a wide range of microorganisms has the ability to oxidize or reduce U compounds as part of their metabolism. Hence, microbiota is very likely to play an important role at all stages of U ISR; however the effect of resident microbial communities subject to ISR has not been investigated. Therefore, this review focuses on the interactions between microorganisms and U and the possible effects this could have on ISR operations. Microorganisms may affect ISR in either a positive or negative way, e.g. assisting in U mobilization via the oxidation of U or immobilizing U by reducing it into an insoluble form. The use of native microbial communities to influence the mobilization/immobilization of U during ISR could help to increase U recovery rates or speed-up post-mining remediation. [ABSTRACT FROM AUTHOR]

The structure of the uranyl aqua ion (U O 2 2 + ) and a number of its inorganic complexes (specifically, U O 2 C l + , U O 2 C l 2 0 , U O 2 S O 4 0 , U O 2 S O 4 2 2 − , U O 2 C O 3 3 4 − and U O 2 OH 4 2 − ) have been characterised using X-Ray absorption spectroscopy/extended X-Ray absorption fine structure (XAS/EXAFS) at temperatures ranging from 25 to 326 ºC. Results of ab initio molecular dynamics (MD) calculations are also reported for uranyl in chloride and sulfate-bearing fluids from 25 to 400 ºC and 600 bar to 20 kilobar (kb). These results are reported alongside a comprehensive review of prior structural characterisation work with particular focus given to EXAFS works to provide a consistent and up-to-date view of the structure of these complexes under conditions relevant to U mobility in ore-forming systems and around high-grade nuclear waste repositories. Regarding reported EXAFS results, average equatorial coordination was found to decrease in uranyl and its sulfate and chloride complexes as temperature rose – the extent of this decrease differed between species and solution compositions but typically resulted in an equatorial coordination number of ∼3–4 at temperatures above 200 ºC. The U O 2 C O 3 3 4 − complex was observed at temperatures from 25 to 247 ºC and exhibited no major structural changes over this temperature range. U O 2 OH 4 2 − exhibited only minor structural changes over a temperature range from 88 to 326 ºC and was suggested to manifest fivefold coordination with four hydroxyl molecules and one water molecule around its equator. Average coordination values derived from fits of the reported EXAFS data were compared to average coordination values calculated using the experimentally derived thermodynamic data for chloride complexes reported by Dargent et al. (2013) and Migdisov et al. (2018b), and for sulfate complexes reported by Alcorn et al. (2019) and Kalintsev et al. (2019). Sulfate EXAFS data were well described by available thermodynamic data, and chloride EXAFS data were described well by the thermodynamic data of Migdisov et al. (2018b), but not by the data of Dargent et al. (2013). The ab initio molecular dynamics calculations confirmed the trends in equatorial coordination observed with EXAFS and were also able to provide an insight into the effect of pressure in equatorial water coordination – for a given temperature, higher pressures appear to lead to a greater number of equatorially bound waters counteracting the temperature effect. [Display omitted] • The first detailed review of uranium complex structure work has been conducted. • Up to now, very little work has been conducted at temperatures above 25 ºC. • Overall coordination systematically decreases with temperature. • Uranyl complexes exhibit no major structural changes up to 400 ºC. • We have verified recently derived thermodynamic data for uranyl complexes. [ABSTRACT FROM AUTHOR]

The new mineral françoisite-(Ce), (Ce,Nd,Ca)[(UO2)3O(OH)(PO4)2]·6H 2O is the Ce-analog of françoisite-(Nd). It has been discovered simultaneously at the La Creusaz uranium deposit near Les Marécottes in Valais, Switzerland, and at the Number 2 uranium Workings, Radium Ridge near Mt. Painter, Arkaroola area, Northern Flinders Ranges in South Australia. Françoisite-(Ce) is a uranyl-bearing supergene mineral that results from the alteration under oxidative conditions of REE- and U4+-bearing hypogene minerals: allanite-(Ce), monazite-(Ce), μuraninite at Les Marécottes; monazite-(Ce), ishikawaite-samarskite, and an unknown primary U-mineral at Radium Ridge. The REE composition of françoisite-(Ce) results from a short aqueous transport of REE leached out of primary minerals [most likely monazite-(Ce) at Radium Ridge and allanite-(Ce) at La Creusaz], with fractionation among REE resulting mainly from aqueous transport, with only limited Ce loss due to oxidation to Ce4+ during transport. [ABSTRACT FROM AUTHOR]

Pseudojohannite is a hydrated copper(II) uranyl sulfate described from Jáchymov, Northern Bohemia, Czech Republic (type locality). Pseudojohannite also occurs at the Musonoï quarry near Kolwezi, Shaba, Congo, and the La Creusaz prospect, Western Swiss Alps. At all three localities, pseudojohannite formed through the interaction of acid sulfate mine drainage waters with uraninite (Jáchymov and La Creusaz) or uranyl silicates (Musonoï). Pseudojohannite forms moss green, non UV-fluorescent aggregates consisting of irregularly shaped crystals measuring up to 25 µm in length and displaying an excellent cleavage parallel to (1̄01). dmeas is 4.31 g/cm³, dcalc 4.38 g/cm³, and the refractive indices are nmin = 1.725 and nmax = 1.740. A high-resolution synchrotron powder diffraction pattern on the material from Musonoï shows that pseudojohannite is triclinic (P1 or P1̄), with a = 10.027(1) Å, b = 10.822(1) Å, c = 13.396(1) Å, a = 87.97(1)°, ß = 109.20(1)°, γ = 90.89(1)°, V = 1371.9(5) ų. The location of the uranium and sulfur atoms in the cell was obtained by direct methods using 1807 reß ections extracted from the powder diffractogram. Pseudojohannite contains zippeite-type layers oriented parallel to (1̄01). The empirical chemical formula calculated for a total of 70 O atoms is Cu6.52U7.85S4.02O70H55.74, leading to the simplified chemical formula Cu6.5 [(UO2)4O4 (SO4)2]2 (OH) 5·25H2O. The distance of 9.16 Å between the uranyl-sulfate sheets in pseudojohannite shows that neighboring layers do not share O atoms with the same CuΦ6 [F = (O,OH)] distorted octahedrons, such as in magnesium-zippeite. Rather, it is expected that CuΦ6 forms a layer bound to the zippeite-type layers by hydrogen bonding, as in marécottite, or one apex of the CuΦ6 polyhedron only is shared with a zippeite-type layer, as in synthetic SZIPPMg. The higher number of cations in the interlayer of pseudojohannite (Cu:S = 1.6:1) compared to marécottite (3:4) and SZIPPMg (1:1) indicates that pseudojohannite has a unique interlayer topology. Ab-initio powder structure solution techniques can be used to obtain important structural information on complex micro-crystalline minerals such as those found in the weathering environment. Pseudojohannite represents a new member of the zippeite group of minerals, and further illustrates the structural complexity of zippeite-group minerals containing divalent cations, which have diverse arrangements in the interlayer. Peudojohannite and other divalent zippeites are common, easily overlooked minerals in acid drainage environments around uranium deposits and wastes. [ABSTRACT FROM AUTHOR]

• Ore-stage pyrite from roll front deposits across the world have similar signature evolution. • Ore-stage pyrite signatures reflect the dynamic evolution of biogeochemical processes. • Roll front activity cycle is characterized by transitional open to closed system behavior. • Roll front activity cycle results in large S isotope and trace element fractionation in pyrite. • Changes in roll front pyrite signatures derived from a single fluid and a single source of sulfur. Complex pyrite textures associated with large changes in isotopic and trace element compositions are routinely assumed to be indicative of multi-faceted processes involving multiple fluid and sulfur sources. We propose that the features of ore-stage pyrite from roll front deposits across the world, revealed in exquisite detail via high-resolution trace element mapping by LA-ICP-MS, reflect the dynamic internal evolution of the biogeochemical processes responsible for sulfate reduction, rather than externally driven changes in fluid or sulfur sources through time. Upon percolation of oxidizing fluids into the reduced host-sandstones, roll front systems become self-organized, with a systematic reset of their activity cycle after each translation stage of the redox interface down dip of the aquifer. Dominantly reducing conditions at the redox interface favor the formation of biogenic framboidal pyrite (δ34S from −30.5 to −12.5‰) by bacterial sulfate reduction and the genesis of the U mineralization. As the oxidation front advances, oxidation of reduced sulfur minerals induces an increased supply of sulfate and metals in solution to the bacterial sulfate reduction zone that has similarly advanced down the flow gradient. Hence, this stage is marked by increased rates of the bacterial sulfate reduction associated with the crystallization of variably As-Co-Ni-Mo-enriched concentric pyrite (up to 10,000′s of ppm total trace contents) with moderately negative δ34S values (from −13.7 to −7.5‰). A final stage of pyrite cement with low trace element contents and heavier δ34S signature (from −6.9 to +18.8‰) marks the end of the roll front activity cycle and the transition from an open to a predominantly closed system behavior (negligible advection of fresh sulfate). Blocky pyrite cement is formed using the remaining sulfate, which now becomes quickly heavy according to a Rayleigh isotope fractionation process. This ends the cycle by depleting the nutrient supplies for the sulfate-reducing bacteria and cementing pore spaces within the host sandstone, effectively restricting fluid infiltration. This internally-driven roll front activity cycle results in systematic, large S isotope and trace element fractionation. Ultimately, the long-time evolution of the basin and fluid sources control the metal endowment and evolution of the system; these events, however, are unlikely to be preserved by the roll front, as a direct result of its hydrodynamic nature. [ABSTRACT FROM AUTHOR]

The speciation of uranyl in sulfate-bearing solutions at temperatures up to 250 °C has been investigated using in situ UV–Visible spectrophotometry. Formation constants for the reactions U O 2 2 + + S O 4 2 - ⟺ U O 2 S O 4 0 (l o g β 1 = 3.38, 4.40, 5.44, 6.33, 7.74) and U O 2 2 + + 2 S O 4 2 - ⟺ U O 2 S O 4 2 2 - (l o g β 2 = 4.10, 5.26, 6.83, 8.00, 9.70) were derived at 25, 100, 150, 200 and 250 °C respectively. These formation constants were fitted to the modified Ryzhenko–Bryzgalin (MRB) model to derive pK(298), A(zz/a) and B(zz/a) values for both complexes: 3.262, 2.212, −197.96 (U O 2 S O 4 0) and 4.189, 3.21, −473.14 U O 2 S O 4 2 2 - respectively. Compared with values extrapolated using previously available data for 25, 70 and 75 °C, our new data suggest higher stability of U O 2 S O 4 0 at temperatures above 150 °C and significantly lower stability of U O 2 S O 4 2 2- at all temperatures above 25 °C. Molar absorbances of both sulfate species were also derived. At 25 °C we found our molar absorbance for U O 2 S O 4 0 agreed well with those reported previously in the literature, however we report lower peak amplitudes for U O 2 S O 4 2 2 - . We also noted significant temperature-dependent red shifts in the molar absorbance of U O 2 S O 4 0. We suggest that these shifts could be explained by changes in sulfate bonding behaviour around the uranyl ion – namely shifts in the distribution of complexes with sulfate bound in either a monodentate or bidentate configuration. Simple models calculated with our new data suggest that sulfate complexes may readily predominate over chloride complexes even in solutions containing upwards of 20 wt% chloride and only 100 ppm sulfate. In addition, moderate concentrations of sulfate (∼1 wt%) can increase the solubility of uranium by an order of magnitude. Thus we suggest that sulfate could play an important role in mobilising uranium in hydrothermal systems, and that the removal of sulfate via precipitation of sulfate minerals may act as a means of depositing uranium under oxidizing conditions. This in turn might explain the associations between sulfate minerals and uranium mineralisation occasionally seen in large uranium ore deposits such as Olympic Dam and MacArthur River. [ABSTRACT FROM AUTHOR]

Organic matter is increasingly shown to influence the mobility of uranium (U) in the environment. The mobility of U likely depends on whether the organic matter is in dissolved or solid form, with the latter able to retard U mobility. In this work, column experiments were used to reveal that solid organic matter, in the form of well characterized tree bark from Eucalyptus globulus , dramatically reduced the mobility of aqueous U(VI) which was introduced as uranyl nitrate [UO 2 (NO 3 ) 2 ]. Eucalyptus globulus bark contains high levels of carboxylic and phenolic acid groups which are known to bind to U. Admixtures containing 20 wt. % tree bark and sand were compared to columns containing sand only. We show that soluble U is adsorbed onto the tree bark, likely via a cation exchange with calcium, with no change in U oxidation state as confirmed by X-ray Absorption Near Edge Structure (XANES) analyses. Cation concentrations in column outflow solutions indicated that U was retained in the columns containing tree bark but was released from the sand-only columns. These results demonstrate that solid organic matter such as tree bark has potential applications in trapping U, possibly within permeable reactive barriers, without necessitating further engineering to reduce U(VI) to U(IV). Building on previous work on organic sedimentary U-deposits, this study also helps understand processes of U enrichment from groundwater as observed in environments high in organic matter including wetlands and sediment-hosted ore deposits. [ABSTRACT FROM AUTHOR]

The gradual decrease of global copper resources is among the most urgent challenges for the mining industry. Sustainable utilization of copper sulphide flotation concentrate from iron oxide copper gold (IOCG) deposits is often constrained by the impurity elements (e.g. U, Th and F) and high levels of gangue minerals (e.g. iron oxide/hematite, U-bearing minerals and fluorite). Herein, a spontaneous oxidative H 2 SO 4 leach process (<100 °C) is proposed to selectively remove the penalty elements and upgrade copper sulphide concentrate from IOCG deposits. During H 2 SO 4 leach, 87–92% of F element in the fluorite mineral was extracted and the dissolution of iron oxide/hematite minerals were enhanced by the elevated temperature at 60–90 °C. The released Fe3+ ions from iron oxide/hematite minerals worked as the spontaneous oxidant for dissolving U-bearing minerals and upgrading copper minerals. The results reveal that the H 2 SO 4 leach in presence of dissolved Fe3+ effectively removed 88–97% U and 89–90% Th from U-bearing minerals. Meanwhile, the elevated temperature at 60–90 °C plays a critical role in the phase transformation of bornite to covellite in the presence of Fe3+. Another phase transformation of chalcopyrite to bornite was also significant at the higher temperature of 90 °C through the non-oxidative dissolution mechanism. During the spontaneous oxidative H 2 SO 4 leach, the dissolution of gangue minerals and phase transformations of copper minerals successfully upgraded copper concentrate from 41.1 to 50.5 wt% at 90 °C, while copper dissolution was maintained at less than 7.7%. Unlabelled Image • H 2 SO 4 leach of copper concentrate leads to oxidizing Fe3+ ion from gangue minerals. • Uranium-bearing minerals are spontaneous oxidized by Fe3+ ion and dissolved. • Fluorite mineral is selectively dissolved into leach solution. • Mineral phase transformations at 60–90 °C upgrade the quality of copper concentrate. • Copper dissolution during H 2 SO 4 leach is less than 8 wt%. [ABSTRACT FROM AUTHOR]