Editor’s Choice Articles

At the nanoscale, particle size affects the surface reactivity of anatase–water interfaces. Here, we investigate the effect of electrolyte media and particle size on the primary charging behavior of anatase nanoparticles. Macroscopic experiments, potentiometric titrations, were used to quantitatively evaluate surface charge of a suite of monodisperse nanometer sized (4, 20, and 40 nm) anatase samples in five aqueous electrolyte solutions. The electrolyte media included alkaline chloride solutions (LiCl, NaCl, KCl, and RCl) and Na-Trifluoromethanesulfonate (NaTr). Titrations were completed at 25 °C, as a function of pH (3–11) and ionic strength (from 0.005 to 0.3 m). At the molecular scale, density functional theory (DFT) simulations were used to evaluate the most stable cation surface species on the predominant (101) anatase surface. In all electrolyte media, primary charging increased with increasing particle size. At high ionic strength, the development of negative surface charge followed reverse lyotropic behavior: charge density increased in the order RbCl < KCl < NaCl < LiCl. Positive surface charge was greater in NaCl than in NaTr media. From the DFT simulations, all cations formed inner-sphere surface species, but the most stable coordination geometry varied. The specific inner-sphere adsorption geometries are dependent on the ionic radius. The experimental data were described using surface complexation modeling (SCM), constrained by the DFT results. The SCM used the charge distribution (CD) and multisite (MUSIC) models, with a two-layer (inner- and outer-Helmholtz planes) description of the electric double layer. Subtle charging differences between the smallest and larger anatase particles were the same in each electrolyte media. These results further our understanding of solid–aqueous solution interface reactivity of nanoparticles. Full article

For a long time, particular attention was paid to glauconitization in the surficial sediments lying on the outer continental shelves of present oceans. Subsequently, the processes observed and analyzed may have served as models for studies of glauconite in Cenozoic or even Mesozoic shelf deposits. Access to the sedimentary domains of deep oceans, particularly those of contouritic accumulation fields, has made it possible to discover unexpected processes of glauconitization. Thus, the long-term prevalence of control using fairly high-temperature water has become obsolete, and the prerequisite influence of continental flows has come to be considered on a new scale. Frequently, sediments from contouritic accumulation provide a condensed and undisturbed sedimentary record without periods of sediment erosion. Glauconitic grains could possibly integrate the signatures of bottom-water masses over prolonged periods of time, which, while preventing their use in high-resolution studies, would provide an effective means of yielding reliable average estimates on past εNd signatures of bottom-water masses. In this regard, glauconitic grains are probably better-suited to paleoceanographic reconstructions than foraminifera and leached Fe-oxyhydroxide fractions, which appear to be influenced by sediment redistribution and the presence of terrestrial continental Fe-oxides, respectively. Direct methodological access to the compositions of the semi-confined microenvironments of neoformation has largely renewed the information, chemical or crystallographic, that was previously, and for a long time, restricted to macromeasurements. The various granular supports (mudclasts, fecal pellets, and foraminifera infillings) include inherited 1:1 clays (or Te-Oc; i.e., clay minerals consisting of one tetrahedral sheet and one octahedral sheet, such as kaolinite) that are gradually replaced by 2:1 clays (Te-Oc-Te) dominated first by smectite, and then by glauconite. In small pores, the water’s activity is diminished; as a consequence, the precipitation of a great number of mineral species is thereby made easier, and their stability domains are changed. A specific methodological approach allows the study of the mineralogy and chemistry of the fine-scale mineral phases and to avoid the global aspect of the analytical methods previously used in the initial studies. Wide-field micrographs taken at a mean direct magnification of 100.000 show the intimate and characteristic organization of the main phases that occur in a single grain. One or several “fine” (about 10 nanometers in scale) microchemical analyses can be recorded, and directly coupled with each interesting and well-identified structure image observed in HRTEM. Full article

The construction of a repository for the geological disposal of radioactive waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository, and the extensive use of cement will result in the development of a highly alkaline porewater, pH > 12.5; this fluid will migrate into and react with the host rock. The chemistry of the fluid will evolve over time, initially with high Na and K concentrations, evolving to a Ca-rich fluid, and finally returning to the natural background groundwater composition. This evolving chemistry will affect the long-term performance of the repository, altering the physical and chemical properties, including radionuclide behaviour. Understanding these changes forms the basis for predicting the long-term evolution of the repository. This study focused on the determination of the nature and extent of the chemical reaction, as well as the formation and persistence of secondary mineral phases within a granite, comparing data from sequential flow experiments with the results of reactive transport modelling. The reaction of the granite with the cement leachates resulted in small changes in pH and the precipitation of calcium aluminium silicate hydrate (C-(A-)S-H) phases of varying compositions, of greatest abundance with the Ca-rich fluid. As the system evolved, secondary C-(A-)S-H phases redissolved, partly replaced by zeolites. This general sequence was successfully simulated using reactive transport modelling. Full article

The geochemistry of rare earth elements and yttrium (REY) in phosphorite has been widely studied. However, the effect of organic matter on REY enrichment has not been well determined. We utilized paired inorganic (δ¹³C_carb) and organic (δ¹³C_carb) carbon isotopes, total organic carbon (TOC), and REY content (∑REY) of the Zhijin Motianchong (MTC) phosphorite and compared them with those of Meishucun (MSC) phosphorite to reveal the effect of organic matter on REY. The δ¹³C_carb of the MTC area (≈0‰) is heavier than that of the MSC area (−5.23‰ to −1.13‰), whereas δ¹³C_org is lighter (−33.85‰ to −26.34‰) in MTC than in MSC (−32.95‰ to −25.50‰). Decoupled δ¹³C_carb and δ¹³C_org in MTC indicate the contribution of chemoautotrophic organisms or methanotrophic bacteria. Compared to the MSC phosphorite, the MTC phosphorite has higher ∑REY and TOC, and these parameters have a positive relationship. MTC phosphorite has REY patterns resembling those of contemporary organic matter. Furthermore, dolomite cement has a higher ∑REY than dolomite in the phosphorus-bearing dolostone. Additionally, pyrites are located on the surface of fluorapatite in the Zhijin phosphorites. It is reasonable to suggest that the REY was released into the pore water owing to the anaerobic oxidation of organic matter at the interface between seawater and sediment, resulting in the REY enrichment of Zhijin phosphorites. Full article

Fe(III)–chitosan microbeads (Fe–CTB) were prepared using a chemical coprecipitation method. SEM–EDX, FTIR, XRD, TGA, BET, and pH _pzc were performed for the characterization of the adsorbent. Various parameters were optimized as pH, adsorption time, adsorbent dose, initial Cr(VI), and PO₄³⁻ ion concentration and the effect of assorted ions for adsorption studies. Fe–CTB microbeads revealed more than 80% detoxification for a 100 mg L⁻¹ initial concentration at pH 3 with 60 min stirring of Cr(VI) and PO₄³⁻ ion having adsorption capacities of 34.15 and 32.27 mg g⁻¹, respectively. The adsorption process for Cr(VI) and PO₄³⁻ ion followed the monolayer adsorption as they favored the Langmuir isotherm model. Kinetic and thermodynamic studies’ emphasis on the adsorption process was spontaneous and exothermic with pseudo-second-order kinetics for both adsorbates. The microbeads were found to be reusable in multiple cycles. Full article

This paper deals with adsorption regularities and mechanisms of nonradioactive Cs(I) and Sr(II) analogs on bentonites of different chemical and mineral composition from solutions of Cs and Sr nitrates with pH 3, 7, and 10 units at constant ionic strength. The bentonites were taken from the deposits Taganskoe (T), Dash-Salakhlinskoe (DS), Zyryanskoe (Z), and 10th Khutor (10H). The pH of bentonite aqueous suspensions, T and DS, exceeded 9 units. A less alkaline reaction was observed in bentonite suspensions Z and T with pH 8.94 and 7.70, respectively. Bentonites T and DS contained significant amounts of nonsilicate iron compounds, 1.0 and 0.5%, respectively. The recovery rate of the studied clays from aqueous solutions of Cs(I) and Sr(II) ions in concentrations from 0.25 to 5 mmol/L varied from 50% to 90% and decreased in the following order: “Ta-ganskoe” > “Dash-Salakhlinskoe” > “Zyryanskoe” > “10th Khutor” in the studied pH range. The main mechanism of Cs(I) and Sr(II) sorption in the studied pH range was cation fixation in the form of outer-sphere complexes on planar surfaces resulting from ion exchange. Increasing pH (pH > 6) enhanced pH-dependent positions, which allowed Cs(I) and especially Sr(II) ions to fix on them more firmly as inner-sphere complexes. At pH 9–10, Sr(II) could precipitate in the form of carbonates. The sorption of Cs(I) + and Sr(II) was accompanied by competitive interactions with proton at pH < 6 and Na⁺, Ca²⁺, Mg²⁺, and K⁺ cations at higher pH values. This competition was more apparent at concentrations of Cs(I)and Sr(II) in initial solutions < 0.5 mmol/L. The ability of bentonite T to sorb Cs(I) and Sr(II) in large amounts compared to the other bentonites was determined by high CEC values and charge of smectite T. Full article

Historic tailings dams and their associated mine waste can pose a significant risk to human and environmental health. The Wheal Maid mine site, Cornwall, UK, serves as an example of the temporal evolution of a tailings storage facility after mining has ceased and the acid-generating waste subjected to surficial processes. This paper discusses its designation as a contaminated land site and reviews our current understanding of the geochemistry, mineralogy, and microbiology of the Wheal Maid tailings, from both peer-reviewed journal articles and unpublished literature. We also present new data on waste characterisation and detailed mineral chemistry and data from laboratory oxidation experiments. Particularly of interest at Wheal Maid is the presence of pyrite-bearing “Grey Tailings”, which, under typical environmental conditions at the Earth’s surface, would be expected to have undergone oxidation and subsequently formed acidic and metalliferous mine drainage (AMD). The results identified a number of mechanisms that could explain the lack of pyrite oxidation in the Grey Tailings, including a lack of nutrients inhibiting microbial Fe(II) oxidation, passivation of pyrite mineral surfaces with tailings processing chemicals, and an abundance of euhedral pyrite grains. Such research areas need further scrutiny in order to inform the design of future tailings facilities and associated AMD management protocols. Full article

Solid-phase mineral inclusions in diamond (1–3 mm in diameter) from the No. 50 kimberlite diatreme of Liaoning Province, China, were exposed by polishing. A variety of silicate, carbonate and sulfide inclusions were recovered in the diamond. The common solid-phase inclusions are olivine, chromite, garnet and orthopyroxene; the rare phases include Ca carbonate, magnesite, dolomite, norsethite, pyrrhotite, pentlandite, troilite, a member of the linnaeite group, an unknown hydrous magnesium silicate and an Fe-rich phase. Abundance and composition of the solid-phase inclusions in diamond indicate that they belong to the peridotitic suite and are mainly harzburgitic. No eclogitic mineral inclusions were found in the diamond. The slightly lower Mg # of the olivine inclusions (peak at 93) than that of harzburgitic olivine inclusions worldwide (Mg # peak at 94), the higher Ni content (0.25–0.45 wt. %) of the olivine inclusions than those of olivine inclusions worldwide (0.30–0.40 wt. %), the higher Ti contents (up to 0.79 wt. %) in some chromite inclusions in diamond than those in chromite inclusions worldwide, the existence of carbonate inclusions in diamond, and the possible presence of hydrous silicate phases in diamond all indicate a metasomatic enrichment event in the source region of diamond beneath the North China craton, suggesting that the diamond probably formed by solid-state growth under metasomatic conditions with the presence of a fluid. Solid-state growth of diamond is also supported by abundant graphite inclusions in the diamond. Sulfide inclusions in diamond often coexist with chromite and olivine or are rich in Ni content, indicating that the sulfide inclusions belong to the peridotitic suite. From the chemical compositions, most sulfide inclusions in diamond from the No. 50 kimberlite were probably trapped as monosulfide crystals, although some may have been entrapped as melts. Full article

The Clapeyron slope is the slope of a phase boundary in P–T space and is essential for understanding mantle dynamics and evolution. The phase boundary is delineating instead of balancing a phase transition’s normal and reverse reactions. Many previous high pressure–temperature experiments determining the phase boundaries of major mantle minerals experienced severe problems due to instantaneous pressure increase by thermal pressure, pressure drop during heating, and sluggish transition kinetics. These complex pressure changes underestimate the transition pressure, while the sluggish kinetics require excess pressures to initiate or proceed with the transition, misinterpreting the phase stability and preventing tight bracketing of the phase boundary. Our recent study developed a novel approach to strictly determine phase stability based on the phase equilibrium definition. Here, we explain the details of this technique, using the post-spinel transition in Mg₂SiO₄ determined by our recent work as an example. An essential technique is to observe the change in X-ray diffraction intensity between ringwoodite and bridgmanite + periclase during the spontaneous pressure drop at a constant temperature and press load with the coexistence of both phases. This observation removes the complicated pressure change upon heating and kinetic problem, providing an accurate and precise phase boundary. Full article

The vulnerability of the rare earth element (REE) supply in a global context of increasing demands entails important economic and political issues, and has encouraged several countries to develop their own REE production projects. This study comparatively evaluated the production of REEs from primary and secondary resources in terms of their sustainability and contribution to the achievement of the Geoethics concept as responsibility towards oneself, colleagues, society, and the Earth system. Twelve categories of potential environmental and social impacts were selected: human health toxicity, global warming or climate change, terrestrial and aquatic eutrophication, acidification potential, particulate matter, resource depletion, water consumption, fresh water ecotoxicity, ionizing radiation, fossil fuel consumption, and ozone depletion. The results showed that the environmental impact of REE production from secondary sources is much lower relative to primary sources. A comparison of conventional and non-conventional REE resources showed that significant impact categories were related to particulate matter formation, abiotic resource depletion, and fossil fuel depletion, which could result from avoiding the tailings disposal before reuse. Based on these findings, governments and stakeholders should be encouraged to increase the recycling of secondary REE sources with Geoethics in mind, in order to balance the high demand of REEs while minimizing the overexploitation of non-renewable resources. Full article

The Black Angel Zn-Pb ore deposit is hosted in folded Paleoproterozoic marbles of the Mârmorilik Formation. It is exposed in the southern part of the steep and inaccessible alpine terrain of the Rinkian Orogen, in central West Greenland. Drill-core data integrated with 3D-photogeology and hyperspectral imagery of the rock face allow us to identify stratigraphic units and extract structural information that contains the geological setting of this important deposit. The integrated stratigraphy distinguishes chemical/mineralogical contrast within lithologies dominated by minerals that are difficult to distinguish with the naked eye, with a similar color of dolomitic and scapolite-rich marbles and calcitic, graphite-rich marbles. These results strengthen our understanding of the deformation style in the marbles and allow a subdivision between evaporite-carbonate platform facies and carbonate slope facies. Ore formation appears to have been mainly controlled by stratigraphy, with mineralizing fluids accumulating within permeable carbonate platform facies underneath carbonate slope facies and shales as cap rock. Later, folding and shearing were responsible for the remobilization and improvement of ore grades along the axial planes of shear folds. The contact between dolomitic scapolite-rich and calcitic graphite-rich marbles probably represents a direct stratigraphic marker, recognizable in the drill-cores, to be addressed for further 3D-modeling and exploration in this area. Full article

Geoenvironmental models were formulated by the U.S. Geological Survey in the 1990s to describe potential environmental effects of extracting different types of ore deposits in different geologic and climatic regions. This paper presents a geoenvironmental model for roll-front (roll-type) uranium deposits in the Texas Coastal Plain. The model reviews descriptive and quantitative information derived from environmental studies and existing databases to depict existing conditions and potential environmental concerns associated with mining this deposit type. This geoenvironmental model describes how features of the deposits including host rock; ore and gangue mineralogy; geologic, hydrologic, and climatic settings; and mining methods (legacy open-pit and in situ recovery [ISR]) influence potential environmental effects from mining. Element concentrations in soil and water are compared to regulatory thresholds to depict ambient surface water and groundwater conditions. Although most open-pit operations in this region have been reclaimed, concerns remain about groundwater quality at three of the four former mills that supported former open-pit mines and are undergoing closure activities. The primary environmental concerns with ISR mining are (1) radon gas at active ISR operations, (2) radiation or contaminant leakage during production and transport of ISR resin or yellowcake, (3) uranium excursions into groundwater surrounding active ISR operations, and (4) contamination of groundwater after ISR mining. Although existing regulations attempt to address these concerns, some problems remain. Researchers suggest that reactive transport modeling and a better understanding of geology, stratigraphy, and geochemistry of ISR production areas could minimize excursions into surrounding aquifers and improve results of groundwater restoration. Full article

Bentonite is a claystone formed by a complex mineralogical mixture, composed of montmorillonite, illite, and accessory minerals like quartz, cristobalite, feldspars, carbonates, and minor amounts of iron oxy-hydroxides. Bentonite presents complexity at various scales: (1): a single mineral may present different chemical composition within the same quarry (e.g., feldspars solid solutions); (2): montmorillonite presents variability in the cation-exchange distribution while illite may be presented as mixed-layer with smectite sheets; and (3): hardness and crystal size are larger in accessory minerals than in clay minerals, preventing uniform grinding of bentonite. The FEBEX bentonite used is originally from Almería (Spain), and it is a predominantly calcium, magnesium, and sodium bentonite. This Spanish FEBEX bentonite has been hydrothermally altered at laboratory scale for 7–14 years. A thermal gradient was generated by heating a disk of pressed iron powder, simulating the metal waste canister, in contact with the compacted bentonite sample. Hydration was forced from the opposite direction. XRD recorded patterns were very similar. In order to minimize the bias of XRD semi-quantitative determination methods, Rietveld refinement was performed using BGMN software and different structural models. Confidence in the quantification of the main phases allows us to convincingly detect other subtle changes such as the presence of calcite in the hydration front, right at the interface between the saturated and unsaturated bentonite, or the presence of goethite, and not hematite, in the saturated bentonite, near the source of hydration. Smectite component was 72 ± 3% and the refinement was consistent with the presence of ~10% illite, comparable with previous characterizations. Full article

As it descends into the Earth’s mantle, the olivine that constitutes the lithosphere of subducting slabs transforms to its high-pressure polymorphs, wadsleyite and ringwoodite, in the so-called transition zone. These transformations have important rheological consequences, since they may induce weakening, strain localization, and, in some cases, earthquakes. In this study, germanium olivine (Ge-olivine) was used as an analogue material to investigate the rheology of samples undergoing the olivine–ringwoodite transformation. Ge-olivine adopts a ringwoodite structure at pressures ~14 GPa lower than its silicate counterpart does, making the transformation accessible with a Griggs rig. Deformation experiments were carried out in a new-generation Griggs apparatus, where micro-seismicity was recorded in the form of acoustic emissions. A careful analysis of the obtained acoustic signal, combined with an extensive microstructure analysis of the recovered samples, provided major insights into the interplay between transformation and deformation mechanisms. The results show that significant reaction rates cause a weakening via the implementation of ductile shear zones that can be preceded by small brittle precursors. When kinetics are more sluggish, mechanical instabilities lead to transformational faulting, which stems from the unstable propagation of shear bands localizing both strain and transformation. The growth of these shear bands is self-sustained thanks to the negative volume change and the exothermic nature of the reaction, and leads to dynamic rupture, as attested by the acoustic emissions recorded. These micro-earthquakes share striking similarities with deep focus earthquakes, which may explain several seismological observations such as magnitude frequency relations and the occurrence of deep repeating earthquakes and foreshocks. Full article

Mining uranium by in situ recovery (ISR) typically involves injecting an oxidant and a complexing agent to mobilize and extract uranium in a saturated ore zone. This strategy involves less infrastructure and invasive techniques than traditional mining, but ISR often results in persistently elevated concentrations of U and other contaminants of concern in groundwater after mining. These concentrations may remain elevated for an extended period without remediation. Here, we describe a field experiment at an ISR facility in which both a chemical reductant (sodium dithionite) and a biostimulant (sodium acetate) were sequentially introduced into a previously mined ore zone in an attempt to establish reducing geochemical conditions that, in principle, should decrease and stabilize aqueous U concentrations. While several lines of evidence indicated that reducing conditions were established, U concentrations did not decrease, and in fact increased after the amendment deployments. We discuss likely reasons for this behavior, and we also discuss how the results provide insights into improvements that could be made to the restoration process to benefit from the seemingly detrimental behavior. Full article

Barite (Ba[SO₄]) is one of the promising candidates for sequestration of radioactive waste. Barite can incorporate radium (Ra) and form ideal solid solutions, i.e., (Ba,Ra)[SO₄]. Together with isostructural celestite (Sr[SO₄]), ternary solid solutions, (Ba,Sr,Ra)[SO₄], may exist in natural conditions. Our fundamental understanding of the dissolution kinetics of isostructural sulfates is critically important for a better risk assessment of nuclear waste repositories utilizing this mineral for sequestration. So far, the barite-water interface has been studied with experimental methods and atomistic computer simulations. The direct connection between the molecular scale details of the interface structure and experimental observations at the microscopic scale is not yet well understood. Here, we began to investigate this connection by using a kinetic Monte Carlo approach to simulate the barite dissolution process. We constructed a microkinetic model for the dissolution process and identified the reactive sites. Identification of these sites is important for an improved understanding of the dissolution, adsorption, and crystal growth mechanisms at the barite–water interface. We parameterized the molecular detachment rates by using the experimentally observed etch pit morphologies and atomic step velocities. Our parameterization attempts demonstrated that local lattice coordination is not sufficient to differentiate between the kinetically important sites and estimate their detachment rates. We suggest that the water structure and dynamics at identified sites should substantially influence the detachment rates. However, it will require more work to improve the parameterization of the model by means of Molecular Dynamics and ab initio calculations. Full article

In the age of big data, the prediction and evaluation of geological mineral resources have gradually entered a new stage, intelligent prospecting. This review briefly summarizes the research development of textual data mining and spatial data mining. It is considered that the current research on mineral resource prediction has integrated logical reasoning, theoretical models, computational simulations, and other scientific research models, and has gradually advanced toward a new model. This type of new model has tried to mine unknown and effective knowledge from big data by intelligent analysis methods. However, many challenges have come forward, including four aspects: (i) discovery of prospecting big data based on geological knowledge system; (ii) construction of the conceptual prospecting model by intelligent text mining; (iii) mineral prediction by intelligent spatial big data mining; (iv) sharing and visualization of the mineral prediction data. By extending the geological analysis in the process of prospecting prediction to the logical rules associated with expert knowledge points, the theory and methods of intelligent mineral prediction were preliminarily established based on geological big data. The core of the theory is to promote the flow, invocation, circulation, and optimization of the three key factors of “knowledge”, “model”, and “data”, and to preliminarily constitute the prototype of intelligent linkage mechanisms. It could be divided into four parts: intelligent datamation, intelligent informatization, intelligent knowledgeization, and intelligent servitization. Full article

This study presents the novel idea of a cyanide-free leaching method, i.e., glycine-ammonia leaching in the presence of permanganate, to treat a low-grade and copper-bearing gold tailing. Ammonia played a key role as a pH modifier, lixiviant and potential catalyst (as cupric ammine) in this study. Replacing ammonia with other pH modifiers (i.e., sodium hydroxide or lime) made the extractions infeasibly low (<30%). The increased additions of glycine (23–93 kg/t), ammonia (30–157 kg/t) and permanganate (5–20 kg/t) enhanced gold and copper extractions considerably. Increasing the solids content from 20 to 40% did not make any obvious changes to copper extraction. However, gold leaching kinetics was slightly better at lower solids content. It was indicated that the staged addition of permanganate was unnecessary under the leaching conditions. Recovery of gold by CIL was shown to be feasible, and it improved gold extraction by 15%, but no effect was observed for copper extraction. Percentages of 76.5% gold and 64.5% copper were extracted in 48 h at 20 g/L glycine, 10 kg/t permanganate, 20 g/L carbon, pH 10.5 and 30% solids. Higher extractions could be potentially achieved by further optimization, such as by increasing permanganate addition, extending leaching time and ultra-fine grinding. Full article

Flotation is a common mineral processing method used to upgrade copper sulfide ores; in this method, copper sulfide mineral particles are concentrated in froth, and associated gangue minerals are separated as tailings. However, a significant amount of copper is lost into tailings during the processing; therefore, tailings can be considered secondary resources or future deposits of copper. Particle–bubble collision efficiency and particle–bubble aggregate stability determines the recovery of target particles; this attachment efficiency plays a vital role in the selectivity process. The presence of fine particles in the flotation circuit is because of excessive grinding, which is to achieve a higher degree of liberation. Complex sulfide ores of markedly low grade further necessitate excessive grinding to achieve the maximum degree of liberation. In the flotation process, fine particles due to their small mass and momentum are unable to collide with rising bubbles, and their rate of flotation is very slow, further lowering the recovery of target minerals. This collision efficiency mainly depends on the particle–bubble size ratio and the concentration of particles present in the pulp. To overcome this problem and to maintain a favorable particle–bubble size ratio, different techniques have been employed by researchers to enhance particle–bubble collision efficiency either by increasing particle size or by decreasing bubble size. In this article, the mechanism of tailing loss is discussed in detail. In addition, flotation methods for fine particles recovery such as microbubble flotation, column flotation, nanobubble flotation, polymer flocculation, shear flocculation, oil agglomeration, and carrier flotation are reviewed, and their applications and limitations are discussed in detail. Full article

Antigorite is the main carrier of water in Earth’s subduction zones. The dehydration processes of antigorite were investigated by carrying out in situ phase transition experiments using a dynamic diamond anvil cell, with a time-resolved Raman scattering system, at 0.3–10 GPa and 396–1100 K. Three typical phase transformation reactions occurred within the P–T range of this study, corresponding to three reaction products. At low pressures (<0.7 GPa), antigorite transfers to talc and forsterite; as the temperature increases, the talc disappears and a combination of forsterite and clinoenstatite occurs. At moderate pressures (1.8–7.5 GPa), antigorite dehydrates into forsterite and clinoenstatite as temperatures increase; with the continuous increase in pressure, the dehydration products become clinoenstatite and phase A. At high pressures (>8.6 GPa), the products of the dehydration phase transition of antigorite are consistently clinoenstatite and phase A. Compared with the previous studies carried out by large-volume presses (such as a multi anvil press and a piston-cylinder press), the reaction to produce phase A occurs at higher P–T conditions, and the stable temperature region for talc as a dehydration product is narrower. Moreover, large quantities of pores with 5–10 μm in diameter formed in dehydration products, supporting the hypothesis that intermediate-depth earthquakes may result from dehydration embrittlement. The precise phase boundary determined by this in situ study provides a better understanding of the dehydration phase transition behavior and geological phenomena exhibited by antigorite under different pressure and temperature conditions. Full article

Rare earth, with the reputation of “industrial vitamins”, has become a strategic key metal for industrial powers with increasingly significant industrial application value. As a unique rare earth resource, ionic rare earth ore (IREO) has the outstanding advantages of complete composition, rich resource reserves, low radioactivity, and high comprehensive utilization value. IREO is the main source of medium and heavy rare earth raw materials, which are in great demand all over the world. Since the discovery of IREO, it has attracted extensive attention. Scientists in China and the around world have carried out a lot of research and practical work and achieved a series of important breakthroughs. This paper introduces the discovery process, metallogenic causes, deposit characteristics, and the prospecting research progress of IREO, so as to deepen the understanding of the global distribution of ionic rare earth resources and the prospecting direction of ionic rare earth deposits. The leaching principle of IREO, the innovation of leaching process, the influencing factors and technological development of in situ leaching process, and the technical adaptability of in situ leaching process are reviewed. The development of leachate purification and rare earth extraction technology is summarized. We aim to provide guidance for the industrial development of IREO through the above review analysis. Additionally, the problems existing in the development of IREO are pointed out from the aspects of technology, economy, and the environment. Ultimately, a series of suggestions are put forward, such as the development of ammonium free extraction technology in the whole exploitation process of in situ leaching and leachate purification and rare earth precipitation, research on enhancing of seepage and mass transfer process, and research on the development of new technologies for impurity removal of leachate and extraction of rare earth, so as to promote the development of green and efficient exploitation new technologies and sustainable development of ionic rare earth ore. Full article

The aim of this paper is to present a chemical composition and quantities of mining and processing waste landfills material developed during historical mining and smelting. After detailed inspection, it was found that approximately 2.6 gigatons of the waste had been deposited at 1650 sites, covering almost 65 km². More than half of this material, 55%, is characterized as conventional mining waste, 37% belongs to the processing tailings, and 8% to metallurgical waste. Most of these tailing sites are unclaimed, presenting a source of contamination for nearby communities. According to the literature data collected and additional chemical analyses, in accordance with zero-waste philosophy, about 42 promising locations (c. 270 million tons) could be selected, where various advanced eco-innovative methods of recovery could possibly apply. The areas with the highest prospective recovery are Serbia and Kosovo. In accordance with the metal prices achieved in March 2022, it is estimated that the recovery of tailings could bring up to 18,100 million USD, which is much more compared to the prices of March 2020—10,600 million USD—when the commodity market was governed by the COVID-19 restrictions. In addition to the commercial value of the metals, the environmental aspect should not be forgotten after the application of reuse and recycling concepts. Full article

Thirty-three samples from natural apatite (Ap) solid solutions, ideal structural formula ^[9]Ca1₂^[7]Ca2₃(^[4]PO₄)₃^[3](F,OH,Cl), (Z = 2) were examined with electron-probe microanalysis, synchrotron high-resolution powder X-ray diffraction (HRPXRD), and Rietveld refinements. Apatite has space group P6₃/m for the general chemical formula above. In Ap, the two different Ca sites are generally occupied by Ca, Mn, Sr, Na, or REE³⁺ cations; the P site is occupied by P, Si, or S, and the X is occupied by F, OH, Cl, O²⁻, or (CO₃)²⁻ anions. However, it may be possible for CO₃²⁻ + F⁻ anions to partially replace PO₄³⁻ groups. In this study, the unit-cell parameters a, c, and c/a ratio, vary smoothly and non-linearly with the unit-cell volume, V. The data falls on two distinct trend lines. The average <P-O>[4] distance is nearly constant across the Ap series, whereas the average <O-P-O>[6] angle decreases linearly. The coordination numbers for the atoms are given in square brackets in the general chemical formula above. The average <Ca1-O>[9], <Ca2-O>[6], <Ca2-O,X>[7], and Ca2-X distances change non-linearly with increasing V. Although Cl⁻ anion is larger than OH⁻ and F⁻ anions, the c unit-cell parameter in F-Ap is larger than that in Cl-Ap. In Cl-Ap, the Ca2 polyhedra are larger than in F-Ap, so the O and Cl anions are under-bonded, which cause the Ca1 polyhedra to contract and charge balance the anions. Alternatively, the Ca1 polyhedra are smaller in Cl-Ap than in F-Ap, so the Ca1 polyhedra in Cl-Ap cause the c axis to contract compared to that in F-Ap. Full article

Mining has advanced primarily through the use of two strategies: pyrometallurgy and hydrometallurgy. Both have been used successfully to extract valuable metals from ore deposits. These strategies, without a doubt, harm the environment. Furthermore, due to decades of excessive mining, there has been a global decline in high-grade ores. This has resulted in a decrease in valuable metal supply, which has prompted a reconsideration of these traditional strategies, as the industry faces the current challenge of accessing the highly sought-after valuable metals from low-grade ores. This review outlines these challenges in detail, provides insights into metal recovery issues, and describes technological advances being made to address the issues associated with dealing with low-grade metals. It also discusses the pragmatic paradigm shift that necessitates the use of biotechnological solutions provided by bioleaching, particularly its environmental friendliness. However, it goes on to criticize the shortcomings of bioleaching while highlighting the potential solutions provided by a bespoke approach that integrates research applications from omics technologies and their applications in the adaptation of bioleaching microorganisms and their interaction with the harsh environments associated with metal ore degradation. Full article

The 1 km thick evaporitic Permian Zechstein group in the Netherlands is subdivided into 5 halite rich evaporitic sequences including K–Mg salts (polyhalite, kieserite, sylvite, carnallite and bischofite) for which the position in the Zechstein stratigraphy is still poorly constrained. Understanding the repartition of K–Mg salts is especially important for the development of salt caverns which require a salt as pure as possible in halite. By compiling well log and seismic data in the offshore and onshore domains of the Netherlands, regional cross-sections and isopach maps were performed in order to update the lithostratigraphy of the Zechstein group by including the K–Mg salts. Results enable (i) to propose paleogeographic maps representing the spatial repartition and the thickness variations of one to two K–Mg rich intervals in each evaporite cycle, (ii) to constrain the depositional setting of the different type of salts and the hydrological conditions which influenced the Zechstein stratigraphic architecture and (iii) to develop over the Netherlands risking maps assessing the risk of encountering K–Mg salts in salt pillows or salt diapirs eligible in term of depth and thickness for the development of salt caverns. Full article

Structural properties of the anionic surfactant dioctyl sodium sulfosuccinate (AOT or Aerosol-OT) adsorbed on the mica surface were investigated by molecular dynamics simulation, including the effect of surface loading in the presence of monovalent and divalent cations. The simulations confirmed recent neutron reflectivity experiments that revealed the binding of anionic surfactant to the negatively charged surface via adsorbed cations. At low loading, cylindrical micelles formed on the surface, with sulfate head groups bound to the surface by water molecules or adsorbed cations. Cation bridging was observed in the presence of weakly hydrating monovalent cations, while sulfate groups interacted with strongly hydrating divalent cations through water bridges. The adsorbed micelle structure was confirmed experimentally with cryogenic electronic microscopy, which revealed micelles approximately 2 nm in diameter at the basal surface. At higher AOT loading, the simulations reveal adsorbed bilayers with similar surface binding mechanisms. Adsorbed micelles were slightly thicker (2.2–3.0 nm) than the corresponding bilayers (2.0–2.4 nm). Upon heating the low loading systems from 300 K to 350 K, the adsorbed micelles transformed to a more planar configuration resembling bilayers. The driving force for this transition is an increase in the number of sulfate head groups interacting directly with adsorbed cations. Full article

Reconstruction of the mechanisms of carbonatitic melt evolution is extremely important for understanding metasomatic processes at the base of the continental lithospheric mantle (CLM). We have studied the interaction between garnet lherzolite and a carbonatitic melt rich in molecular CO₂ and H₂O in experiments at 6.3 GPa and 1200–1450 °C. The interaction with garnet lherzolite and H₂O-bearing carbonatite melt leads to wehrlitization of lherzolite, without its carbonation. Introduction of molecular CO₂ and H₂O initiates carbonation of olivine and clinopyroxene with the formation of orthopyroxene and magnesite. Partial carbonation leads to the formation of carbonate–silicate melts that are multiphase saturated with garnet harzburgite. Upon complete carbonation of olivine already at 1200 °C, melts with 27–31 wt% SiO₂ and MgO/CaO ≈ 1 are formed. At 1350–1450 °C, the interaction leads to an increase in the melt fraction and the MgO/CaO ratio to 2–4 and a decrease in the SiO₂ concentration. Thus, at conditions of a thermally undisturbed CLM base, molecular CO₂ and H₂O dissolved in metasomatic agents, due to local carbonation of peridotite, can provide the evolution of agent composition from carbonatitic to hydrous silicic, i.e., similar to the trends reconstructed for diamond-forming high density fluids (HDFs) and genetically related proto-kimberlite melts. Full article

In this paper, mixed metal hydroxide (MMH) was prepared via MgCl₂ and AlCl₃ by the co-precipitation method and characterized by XRD, TGA laser and particle size analysis. The inhibitory effect of MMH on the swelling of clay was evaluated by linear expansion, mud ball, laser particle size analysis, X-ray diffraction analysis and TGA. The linear expansion experiment showed that MMH with a ratio of Mg:Al = 3:1 displayed a strong inhibitory effect on bentonite expansion when 0.3% MMH was added to the drilling fluid, demonstrating better inhibition than 4.0% KCl. Within 48 h, only a few cracks were visible on the mud ball surface in the 0.3% MMH suspension, which indicates that MMH can inhibit wet bentonite for deep hydration. X-ray diffraction and particle size analyses of bentonite were conducted before and after MMH was added to illustrate the inhibition. MMH also displayed high temperature resistance in water-based drilling fluid as a shear strength-improving agent, and its dynamic plastic ratio and shear force were stable after aging at 200 °C for 16 h. Full article

Ferruginous clay minerals in saturated soils and within hydrocarbon deposits often exist in a reduced state. Upon introduction of dissolved oxygen, or other oxidants, the clay minerals oxidise and changes in mineral surface charge and sorption capacity occur, resulting in changes in hydration as well as flux of intercalated species. Here we examine the sorption of water to the Fe-containing clay minerals nontronite NAu-2 (23 wt% Fe) and illite IMt-2 (7 wt% Fe) as a function of Fe oxidation state and exchangeable cations by means of water vapour volumetry and N₂ surface area analysis. The clay minerals were chemically reduced using sodium dithionite. Sorption isotherms of water vapour and nitrogen, controlled relative humidity diffractograms, and chemical analyses were recorded. The results show that, after reduction using sodium dithionite, increased amounts of water vapour and nitrogen were adsorbed to the high Fe content nontronite, despite decreased interlayer separation. Little change was observed for the non-swelling and low Fe content illite. Sodium from the reducing agent was found to exchange with calcium present in the starting clay minerals, and sodium balanced the additional mineral charge generated during reduction. The findings presented in this study deliver improved understanding of sorption at the surface of the reduced clay minerals, which aid constrain the role of clay mineral interfaces in subsurface environments. Full article

A multitude of applications in engineering, ore processing, mineral exploration, and environmental science require grain recognition and the counting of minerals. Typically, this task is performed manually with the drawback of monopolizing both time and resources. Moreover, it requires highly trained personnel with a wealth of knowledge and equipment, such as scanning electron microscopes and optical microscopes. Advances in machine learning and deep learning make it possible to envision the automation of many complex tasks in various fields of science at an accuracy equal to human performance, thereby, avoiding placing human resources into tedious and repetitive tasks, improving time efficiency, and lowering costs. Here, we develop deep-learning algorithms to automate the recognition of minerals directly from the grains captured from optical microscopes. Building upon our previous work and applying state-of-the-art technology, we modify a superpixel segmentation method to prepare data for the deep-learning algorithms. We compare two residual network architectures (ResNet 1 and ResNet 2) for the classification and identification processes. We achieve a validation accuracy of 90.5% using the ResNet 2 architecture with 47 layers. Our approach produces an effective application of deep learning to automate mineral recognition and counting from grains while also achieving a better recognition rate than reported thus far in the literature for this process and other well-known, deep-learning-based models, including AlexNet, GoogleNet, and LeNet. Full article

Rare earth elements (REEs) are considered critical elements in modern society due to their irreplaceable role in new innovative and energy technologies. The giant carbonatite-related Bayan Obo deposit contributes most REE resources in the world’s market, while its origin is still unclear because of the complicated and diverse REE ore mineralogy and texture. Thescanning electron mircroscopy SEM)-based automated mineralogy allows for the numeric assessment of rocks and ores’ compositional and textural properties. Here, we use TIMA (TESCAN Integrated Mineral Analyzer) to quantitatively characterize REE ore mineralogy from the deep drill core within the H8 unit (“dolomite marble”) to better understand the deposit. The mineral composition, occurrence, and Ce elemental deportment of the borehole ores at different depths (i.e., 1107 m, 1246 m, 1406 m, 1546 m, and 1682 m) were obtained. The results show that the main types of ores in the investigated samples can be divided into banded REE-Fe ores, banded REE ores, disseminated REE-Fe ores, and veined REE ores. REE and gangue minerals vary significantly in abundance and occurrence. Monazite-(Ce) and bastnäsite-(Ce) are the primary REE host minerals, and both contribute the most to the REE budget. Other REE minerals, such as parisite-(Ce)/synchysite-(Ce), cerite-(Ce), huanghoite-(Ce)/cebaite-(Ce), and aeschynite-(Ce), are significant contributors. The gangue minerals generally include fluorite, barite, magnetite, pyrite, quartz, magnesio-arfvedsonite, and minerals of the biotite and apatite groups, among others. Combined with the newly published mineral-scale chronological and isotopic geochemical analyses, it is reasonable to conclude that the later hydrothermal fluids remobilized and redistributed the original Mesoproterozoic carbonatitic REE minerals and formed a high variable ore mineral assemblage. Furthermore, it is demonstrated that the mineralogical study using TIMA can provide accurate and reliable mineralogy data for the comprehensive interpretation of the complex REE ores, and extend our understanding of the deposit. Full article

A previously completed mineral resources assessment of the Texas Coastal Plain indicated the potential for the future discovery of uranium resources. Geoenvironmental assessments that include the hydrogeologic framework can be used as a tool to understand the potential effects of mining operations. The hydrogeologic framework for this study focused on the composite hydrogeologic unit of the tract permissive for the occurrence of uranium consisting of the upper part of the Miocene-age Fleming Formation/Lagarto Clay, Pliocene-age Goliad and Pleistocene-age Willis Sands, Pleistocene-age Lissie and Beaumont Formations, and Holocene-age alluvial sediments (fluvial alluvium and eolian sand deposits). This composite hydrogeologic unit, which contains the Chicot and Evangeline aquifers of the Gulf Coast aquifer system, is intended for inclusion in a regional-scale geoenvironmental assessment of as yet undiscovered uranium resources. This article provides (1) a brief literature review describing the geologic and hydrogeologic settings, (2) the methodology used to develop a composite hydrogeologic framework, and (3) descriptions and maps of the land-surface altitude, composite hydrogeologic unit base and midpoint depth, water-level altitude, depth of water, unsaturated and saturated zone thickness, and transmissivity and hydraulic conductivity. A composite hydrogeologic unit, created by combining geologic and hydrogeologic data and maps for individual geologic and hydrogeologic units, is intended for use as a tool in a geoenvironmental assessment to evaluate potential contaminant migration through various avenues. Potential applications include using the hydrogeologic framework as an input into a geoenvironmental assessment to help estimate the potential for (1) runoff of contaminants into surface water, (2) infiltration of contaminants into the groundwater (aquifers), or (3) movement of contaminants from the mining area through wind, groundwater-flow, or streamflow in a given permissive tract. The procedures outlined in this paper also provide a method for developing hydrogeologic frameworks that can be applied in other areas where mining may occur. Full article

Dynamically recrystallizing quartz is believed to approach a steady-state microstructure, which reflects flow stress in dislocation creep. In a classic experimental study performed by Masuda and Fujimura in 1981 using a solid-medium deformation apparatus, two types of steady-state microstructures of quartz, denoted as S and P, were found under varying temperature and strain rate conditions. However, the differential stresses did not systematically change with the deformation conditions, and unexpectedly high flow stresses (over 700 MPa) were recorded on some experimental runs compared with the applied confining pressure (400 MPa). Internal friction in the sample assembly is a possible cause of reported high differential stresses. Using a pyrophyllite assembly similar to that used in the previous work and setting up paired load cells above and below the sample assembly, we quantified the frictional stress acting on the sample and corrected the axial stress. The internal friction changed in a complicated manner during pressurization, heating, and axial deformation at a constant strain rate. Our results suggest that Masuda and Fujimura overestimated the differential stress by about 200 MPa in their 800 °C runs. Crystallographic fabrics in the previous experimental sample indicated that the development of elongated quartz grains, which are characteristics of Type-S microstructures, was associated with preferential growth of unfavorably oriented grains during dynamic recrystallization. Full article

Microbial mats represented the earliest complex ecosystems on Earth, since fossil mineralized examples (i.e., microbialites) date back to the Archean Eon. Some microbialites contain putative remains of organic matter (OM), however the processes and pathways that lead to the preservation of OM within microbialite minerals are still poorly understood. Here, a multidisciplinary study is presented (including petrographic, mineralogical and organic geochemical analyses), focusing on a modern calcifying mat from a hypersaline lake in the Kiritimati atoll (Central Pacific). The results show that this mat has a complex history, with two main growth phases under hypersaline conditions, separated by an interruption caused by desiccation and/or freshening of the lake. The mineral precipitates of the mat are predominantly aragonitic and two contrasting precipitation modes are observed: the main growth phases of the mat were characterized by the slow formation of irregular micritic particles with micropeloidal textures and subspherical particles, linked to the degradation of the exopolymer (EPS) matrix of the mat; whereas the interruption period was characterized by the rapid development of a thin but laterally continuous crust composed of superposed fibrous aragonite botryoids that entombed their contemporaneous benthic microbial community. These two precipitation modes triggered different preservation pathways for the OM of the mat as the thin crust shows a particular lipid biomarker signature, different from that of other layers and the relatively rapid precipitation of the crust protecting the underlying lipids from degradation, causing them to show a preservation equivalent to that of a modern active microbial community, despite them being >1100 years old. Equivalent thin mineral crusts occur in other microbialite examples and, thus, this study highlights them as excellent targets for the search of well-preserved biomarker signatures in fossil microbialites. Nevertheless, the results of this work warn for extreme caution when interpreting complex microbialite biomarker signatures, advising combined petrographic, mineralogical and geochemical investigations for the different microbialite layers and mineral microfabrics. Full article

Combined sandstone petrography and heavy mineral analysis allow to decipher different sediment routing systems that could not be resolved by one method alone in the South Pyrenean foreland basin. We apply this approach to deltaic and alluvial deposits of the southern part of the Jaca basin, and in the time equivalent systems of the nearby Ainsa and Ebro basins, in order to unravel the evolution of source areas and the fluvial drainage from the Eocene to the Miocene. Our study allows the identification of four petrofacies and five heavy-mineral suites, which evidence the interplay of distinct routing systems, controlled by the emergence of tectonic structures. Two distinct axially-fed systems from the east coexisted in the fluvial Campodarbe Formation of the southern Jaca basin that were progressively replaced from east to west by transverse-fed systems sourced from northern source areas. In the late stages of evolution, the Ebro autochthonous basin and the Jaca piggy-back basin received detritus from source areas directly north of the basin from the Axial Zone and from the Basque Pyrenees. Coupling sandstone petrography with heavy mineral provenance analysis allows challenging the existing model of the South Pyrenean sediment dispersal, highlighting the relevance of this approach in source-to-sink studies. Full article

The paper shows the preparation of the numerical models necessary for the simulation mapping of industrial-scale crushers of problematic material, such as copper ore with complex lithology. The crushers investigated in this work are located in the KGHM Polska Miedz S.A. copper ore processing plant. The complex ore consisting of sandstone, dolomite and shale is modeled using the Discrete Element Method (DEM) with Particle Replacement Model (PRM) that was chosen to simulate the crushing process. The article discusses the tests and calibration of material parameters and proceeds to test a breakage model in a laboratory-scale jaw crusher. The results are finally validated with the data from actual industrial-scale crushers and compared with the simulations. As an optimization option, the new shape of hammers is proposed and tested in a numerical environment. The performance of the newly designed hammers was examined using numerical methods. The numerical tests showed that the new design performed worse than the current solution. As a result, time and money were saved by avoiding industrial tests. In conclusion, the work shows how complex processes can be characterized in the numerical environment and used for further analysis. Full article

This paper deals with the “modern” plaster mortars based on air lime, hydraulic lime, and cement used between the 1950s and 1990s of the last century, taking, as a case study, a historical building of the Cagliari city whose foundations and ground floor are cut into in-situ limestone. Different plaster layers (i.e., arriccio and intonachino, paint), applied on the excavated limestone walls, were collected from cave-room. All samples were analysed by optical and electron (SEM-EDS) microscopy and X-ray diffractometry (XRD) in order to define their microstructures, textures and compositional features. In addition, real and bulk density, water and helium open porosity, water absorption kinetic, and saturation index were measured. By microscopic imaging analyses, the binder/aggregate ratio as vol.% was determined. Results revealed that cement mortars, composed mainly of C-S-H, C-A-H, and C-F-H phases, given their high hydraulicity, low open porosity, and a rigid behaviour, showed a good chemical but not physical–mechanical adherence, as they were often found detached from the substrate and frequently loaded with salt efflorescence. On the contrary, the hydraulic lime-based mortars, characterised by a binder composed of C-S-H and C-A-H phases and calcite derived from the portlandite carbonation, showed a greater affinity with limestone substrate and other plasters. Thus, they are more suitable to be used as a repair mortar, showing a long durability on the time. The thin air lime-based plasters (intonachino) showed a good adhesion to the substrate, exerting their coating function better than the harder, cement-based mortars. Lime-based wall paints have a good chemical adhesion and adaptability to the irregular surface of the substrate, due to low thickness of lime paint layers (<1 mm) that confers an elastic physical behaviour. Full article

Africa accounts for nearly 30% of the discovered world’s mineral reserves, with half of the world’s platinum group metals deposits, 36% of gold, and 20% of cobalt being in Southern Africa (SA). The intensification of heavy-metal production in the SA region has exacerbated negative human and environmental health impacts. In recent years, mining waste generated from industrial and artisanal mining has significantly affected the ecological integrity of SA aquatic ecosystems due to the accelerated introduction and deposition of heavy metals. However, the extent to which heavy-metal pollution associated with mining has impacted the aquatic ecosystems has not been adequately documented, particularly during bioassessments. This review explores the current aquatic ecological impacts on the heavily mined river basins of SA. It also discusses the approaches to assessing the ecological risks, inherent challenges, and potential for developing an integrated ecological risk assessment protocol for aquatic systems in the region. Progress has been made in developing rapid bioassessment schemes (RBS) for SA aquatic ecosystems. Nevertheless, method integration, which also involves heavy-metal pollution monitoring and molecular technology, is necessary to overcome the current challenges of the standardisation of RBS protocols. Citizenry science will also encourage community and stakeholder involvement in sustainable environmental management in SA. Full article

Eudialyte-group minerals (EGMs) are Na-Ca zirconosilicates typical for peralkaline plutonic rocks. In the zeolite-like crystal structure of these minerals, there are many sites of different volumes and configurations, and therefore EGMs can include up to one-third of the periodic table. Although there are preferred sites for many elements in the crystal structure of eudialyte-group minerals, the same element can appear in several sites. In addition, many sites may be partially or fully vacant. Currently, 30 mineral species are established in the eudialyte group. However, this diversity is, in fact, limited to holotype specimens. To name any mineral from the eudialyte group, you need to solve its crystal structure and compare it with holotypes. Meanwhile, the composition (and, therefore, the name) of any mineral of the eudialyte group is an excellent indicator of the composition of the mineral-forming media, which is very important to petrological and mineralogical studies. In this article, we propose a diagnostic scheme for minerals of the eudialyte group, based only on the chemical composition. The scheme includes five consecutive steps, each of which evaluates the content of a species-forming element (or the sum of such elements). This scheme can be supplemented by new members without changing its hierarchical structure. Full article

Three types of eclogites were identified in the Xiaoxinzhuang area in the northern Sulu ultrahigh pressure (UHP) terrene based on their petrographic, compositional characteristics and locations. They are composed of garnet, omphacite, amphibole, epidote, phengite, quartz/coesite, rutile, apatite, ilmenite and kyanite. Garnet in eclogite exhibits weak compositional zoning, which shows an increase in X_gr and a decrease in X_py from core to mantle, and a decrease in X_gr and a slight increase in X_py from mantle to rim. Phengite inclusions in garnet show higher Si, up to 3.424 p.f.u., than those in the matrix. Pseudosections calculated using THERMOCALC in the NCKFMASHTO system for three representative samples record three stages of metamorphism: (I) prograde stage, (II) post- P_max decompression and heating to the T_max stage and (III) retrograde stage. Stage-I was recorded in garnet cores with mineral assemblage of garnet + omphacite ± amphibole ± lawsonite + phengite + quartz + rutile, and the P-T condition is constrained at 23.5–26.4 kbar and 623–655 °C. The P_max, 41.5 kbar at 801 °C, is revealed from garnet enclosed by coarse-grained garnet with the mineral assemblage of garnet + omphacite + phengite + coesite + rutile. Stage-II produced garnet rim with mineral assemblage of garnet + omphacite + amphibole + quartz + rutile + metabasite melt, which constrained the P-T conditions of 21.4–23.0 kbar and 869–924 °C. Stage-III, recorded by unzoned garnet grain with the mineral assemblage of garnet + omphacite + amphibole + ilmenite + rutile + metabasite melt, constrained P-T conditions of 13.5–16.4 kbar and 813–852 °C. The data suggest that the rocks in the Xiaoxinzhuang area were subducted to a depth of over 135 km and underwent an UHP metamorphism. The P-T-t path revealed by the Xiaoxinzhuang eclogites is different from those in other areas of the Sulu UHP terrane, suggesting that they represent different rock slices during the subduction and exhumations. Full article

The technologies used in mineral process engineering are evolving. The digital mineral processing solutions are based on advances in our ability to instrumentally measure phenomena at several stages of the beneficiation circuit, manage the data in real-time, and to analyze these data using machine learning to develop the next generation of process control. The main purpose of this study is to overview various digital solutions for mineral processing plants and characterization laboratories while emphasizing their utilization in the current state of the digitization process of the GTK Mintec. This study highlights the specialized digital technologies that are particularly relevant for mineral processing and beneficiation. The digital solutions studied in this article include digital twin, machine vision, information management system, sensors, smart equipment, machine learning techniques, process control system, robotic cell, and Internet of Things applied across the whole chain of studying materials from the mineralogical examinations through the bench-scale studies to the pilot test trials. The aim is to provide a clear view on the different aspects of digitizing mineral processing plants based upon the lessons learned from the development plans in GTK Mintec. Full article

X-ray diffraction (XRD) is an important and widely used material characterization technique. With the recent development in material science technology and understanding, various new materials are being developed, which requires upgrading the existing analytical techniques such that emerging intricate problems can be solved. Although XRD is a well-established non-destructive technique, it still requires further improvements in its characterization capabilities, especially when dealing with complex mineral structures. The present review conducts comprehensive discussions on atomic crystal structure, XRD principle, its applications, uncertainty during XRD analysis, and required safety precautions. The future research directions, especially the use of artificial intelligence and machine learning tools, for improving the effectiveness and accuracy of the XRD technique, are discussed for mineral characterization. The topics covered include how XRD patterns can be utilized for a thorough understanding of the crystalline structure, size, and orientation, dislocation density, phase identification, quantification, and transformation, information about lattice parameters, residual stress, and strain, and thermal expansion coefficient of materials. All these important discussions on XRD analysis for mineral characterization are compiled in this comprehensive review, so that it can benefit specialists and engineers in the chemical, mining, iron, metallurgy, and steel industries. Full article

Beryl occurs in the ancient Roman mines at Wadi Nugrus, South Eastern Desert of Egypt. It ranges from small crystals to 10 mm in size, and it varies in color, appearing as bright green, pale green, dark green and brown-green with biotite inclusions. The trace and minor elements were analyzed by the SIMS method. The two rims are richer in Cs, Na, Mg, Fe, Sc, V, Rb and H₂O than cores but are poor in Mn, Ca, Co, Sr and Li. The bright-green rim is richer than the pale-green one in Na, P, K, Ca, Fe, Rb, Cs and F, but poorer in Mg and Li. The alkaline elements (Cs, Na, Rb) and Fe correlate with the color zoning, and where beryl crystals have a maximum of these elements, the green color is strong and bright. The emerald of Wadi Nugrus has similarities with the geological setting of the Canadian emeralds. Emeralds occur along the contact zone between biotite schists, pegmatites and quartz veins. A large-scale interaction between Be-bearing magmatic fluids from granites and related pegmatites took place with hydrothermal fluids enriched in Cr, V, Sc, Mg and Ca after percolation through pre-existing serpentinite and talc carbonates, metagabbros and biotite schists and additional fluids bearing H₂O, NaCl and CO₂. Full article

In this study, the theoretical design of ionic liquids (ILs) for predicting selective extraction of lithium from brines has been conducted using COSMO-RS. A theoretical model for the solvent extraction (SX) of the metal species present in brines was established considering extraction stoichiometry, the distribution of the extractants between aqueous and IL phases, and IL dissociation in the aqueous phase. Theoretical results were validated using experimental extraction percentages from previous works. Results indicate that, in general, the theoretical results for lithium extraction follow experimental trends, except from magnesium extraction. Finally, based on the model, an IL was proposed that was based on the phosphonium cation as the extractant, along with the phase modifier tributylphosphate (TBP) in an organic diluent in order to improve selectivity for lithium extraction over sodium. These results provide an insight for the application of ILs in lithium processing, avoiding the long purification times reported in the conventional process. Full article

Cu-HyS-urea and Cu-HyS-NaOH, which are hydrotalcite-like copper hydroxyl salts, were prepared by two different methods, urea hydrolysis and precipitation, respectively. Both synthesis methods provided the successful formation of a copper hydroxyl salt, Cu₂(OH)₃NO₃. From XRD and UV-DRS results, the product from the urea hydrolysis methods (Cu-HyS-urea) displayed higher crystallinity, small bandgap energy (Eg), and high light absorption ability because of some intercalated carbonate anions. For the Cr(VI) removal test, the Cu-HyS-NaOH showed superior adsorption of Cr(VI) than Cu-HyS-urea due to a higher specific surface area, confirmed by BET analysis. However, the Cu-HyS-urea presented higher photocatalytic Cr(VI) reduction under light irradiation than Cu-HyS-NaOH, owing to narrow Eg, less recombination, and a high transfer of the photogenerated charge carriers, proven by the results from photoluminescence, photocurrent density, and electrochemical impedance spectroscopy. Thus, this work provides a new function of the hydrotalcite-like copper hydroxyl salts (Cu-HyS-urea and Cu-HyS-NaOH) that can be utilized not only for adsorption of Cr(VI) but also as photocatalysts for Cr(VI) reduction under light irradiation. Full article

As a dominant water carrier, hydrous silicate minerals and rocks are widespread throughout the representative regions of the mid-lower crust, upper mantle, and subduction zone of the deep Earth interior. Owing to the high sensitivity of electrical conductivity on the variation of water content, high-pressure laboratory-based electrical characterizations for hydrous silicate minerals and rocks have been paid more attention to by many researchers. With the improvement and development of experimental technique and measurement method for electrical conductivity, there are many related results to be reported on the electrical conductivity of hydrous silicate minerals and rocks at high-temperature and high-pressure conditions in the last several years. In this review paper, we concentrated on some recently reported electrical conductivity results for four typical hydrous silicate minerals (e.g., hydrous Ti-bearing olivine, epidote, amphibole, and kaolinite) investigated by the multi-anvil press and diamond anvil cell under conditions of high temperatures and pressures. Particularly, four potential influence factors including titanium-bearing content, dehydration effect, oxidation−dehydrogenation effect, and structural phase transition on the high-pressure electrical conductivity of these hydrous silicate minerals are deeply explored. Finally, some comprehensive remarks on the possible future research aspects are discussed in detail. Full article

Biological apatite in enamel, dentin, cementum, and bone is highly individualized hydroxyapatite with high tissue dependency. Often, standard and average textbook values for biological apatite do not apply to actual subjects, and the reported results of analyses differ among investigators. In particular, the term biological apatite is often confusingly and incorrectly used to describe carbonate apatite. The purpose of this review is to prevent further confusion. We believe that apatite should be well understood across disciplines and the terminology clearly defined. According to a definition by the International Mineralogical Association’s Commission on New Minerals Nomenclature and Classification, biological apatite formed by living organisms is a type of hydroxyapatite. More specifically, it is carbonated hydroxyapatite, which is quite different from frequently misnamed carbonate apatite. We hope that this definition will be widely adopted to remove confusion around the naming of apatite in many research and applied fields. Full article

Skarnoid calc-silicate xenoliths composed of anorthite, clinopyroxene and Mg-Al spinel occur in alkali basalts of the Pliocene-Pleistocene intra-plate magmatic province in the northern part of the Pannonian Basin. Randomly oriented and elongated pseudomorphs are tschermakite crystals replaced by olivine, spinel and plagioclase. The relict amphibole within the pseudomorphs is characterized by high ^VIAl, between 1.95 and 2.1, and very low occupancy of the A-site (<0.1 apfu)—these features are rarely found in nature and are thought to be diagnostic of high-pressure metamorphic rocks. Pyroxene compositions plot along continuous mixing line extending from nearly pure diopside-augite towards a Ca(Fe³⁺Al)AlSiO₆ endmember with an equal proportion of ^VIAl³⁺ and Fe³⁺. Concentrations of kushiroite CaAlAlSiO₆ endmember, up to 47.5 mol%, are the highest recorded in terrestrial samples. The AlFe³⁺-rich pyroxenes originated at the expense of diopside-augite during the interaction with carbonate-aluminosilicate melt. Forsterite (Fo_72–83) and hemoilmenite with up to 32 mol% geikielite (9.3 wt% MgO) also crystallized from the melt, leaving behind the residual calcic carbonate with minor MgO (1–3 wt%). Columnar habit of neoformed olivine growing across diopside-augite layers indicates rapid crystallization from eutectic liquid. Euhedral aragonite and apatite embedded in fine-grained calcite or aragonite groundmass indicate slow crystallization of the residual carbonatite around the calcite-aragonite stability boundary. Corundum exsolutions in rock-forming anorthite are products of superimposed low-pressure pyrometamorphic reworking during transport in alkali basalt. Concomitant alkali metasomatism produced neoformed interstitial sodalite, nepheline, sanidine, albite, biotite, Mg-poor ilmenite (10–18 mol% MgTiO₃), Ti-magnetite and fluorapatite. Olivine-ilmenite-aragonite-calcite thermobarometry returned temperatures of 770–860 °C and pressures of 1.8–2.1 GPa, whereas plagioclase-amphibole thermobarometer yielded 781 ± 13 °C and 2.05 ± 0.03 GPa. The calculated pressures correspond to depths of 60–70 km. The calc-silicate xenoliths are most likely metamorphosed marbles; however, a magmatic protolith (metagabbro, metaanorthosite) cannot be ruled out owing to high Cr contents in spinels (up to 30 mol% chromite) and abundant Cu-sulfides. Full article

Cement companies are significant contributors of the planet’s anthropogenic CO₂ emissions. With increased awareness of the substantial volume of CO₂ emissions from cement production, a variety of mitigation strategies are being considered and pursued globally. Hybrid cements are deemed to be technologically viable materials for contemporary construction. They require less clinker than that for ordinary Portland cement, leading to a decrease in CO₂ emissions per tonne of hybrid cement manufactured. The hybrids produced in this study consist of 70% siliceous coal fly ash and 30% Portland cement, and combines chemical (sodium sulphate) and mechanical (milling) activation. The aim of this work was to develop a better understanding of the hydration products formed and the resulting effect of activation on these hydration products, of hybrid coal fly ash cement pastes over an extended curing period of up to one year. The results indicated that chemical activation increases the formation of stable, well crystallised ettringite. Chemical activation as well as mechanical activation increased the rate of the pozzolanic reaction between portlandite contained in cement and coal fly ash. The application of combined chemical and mechanical activation definitely resulted in the fastest rate of portlandite consumption, hence an increased rate of the pozzolanic reaction. Full article

Edge enhancement is a frequently used transformation of potential field data. Its goal is to sharpen the position of the subsurface structures. Here we propose a new method to enhance the edges of the sources causing the potential anomalies called normalized Harris filter (NHF), which is based on the Harris filter and amplitude balance. Three synthetic data sets are used to evaluate the performance of the proposed approach. The presented approach provides a better estimation of the sources’ edges when compared to the other methods. The proposed method is robust to noisy data and can avoid the generation of artificial edges, thereby reducing the ambiguity of interpretation. The testing on real data set from the Yili basin in Northwestern China demonstrates that the new approach highlights several anomalies not shown in the geological map or other methods. The proposed approach also shows the advantages of gradually enhancing the edges of the deep-seated structure. The results demonstrate that the proposed approach may be a better detector in qualitatively determining the edges of sources causing potential field data. Full article