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Minerals, Volume 7, Issue 11 (November 2017)

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Cover Story High-sulfidation epithermal Au ± Ag–Cu deposits occur in volcanic arcs around the world. In this [...] Read more.
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Research

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Open AccessArticle REE Incorporation into Calcite Individual Crystals as One Time Spike Addition
Minerals 2017, 7(11), 204; doi:10.3390/min7110204
Received: 15 September 2017 / Revised: 21 October 2017 / Accepted: 22 October 2017 / Published: 26 October 2017
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Abstract
Experiments on the incorporation of trace elements into calcite were performed, and rare earth elements (REE) were used to mark the growth zones of individual crystals. Experiments were conducted at different pH (7.7 to 8.8) and temperatures (2 °C to 24.6 °C) in
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Experiments on the incorporation of trace elements into calcite were performed, and rare earth elements (REE) were used to mark the growth zones of individual crystals. Experiments were conducted at different pH (7.7 to 8.8) and temperatures (2 °C to 24.6 °C) in NH4Cl + CaCl2 solutions, where REE were rapidly consumed by growing calcite. LA-ICP-MS line-scans yielded the distribution of (REE/Ca)calcite within individual crystals in a manner consistent with the addition of REE into fluid. A sharp decrease of (REE/Ca)calcite toward the crystal edge suggests the fast depletion of (REE/Ca)fluid due to strong REE consumption by growing calcite. An attempt was made to estimate the lower limit of the partition coefficients between calcite and fluid using selected REE/Ca data within individual calcite crystals and the amount of REE added into fluid. Full article
(This article belongs to the Special Issue Rare-Earth Carbonates)
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Open AccessArticle Investigation of Enhanced Leaching of Lithium from α-Spodumene Using Hydrofluoric and Sulfuric Acid
Minerals 2017, 7(11), 205; doi:10.3390/min7110205
Received: 21 August 2017 / Revised: 11 October 2017 / Accepted: 25 October 2017 / Published: 27 October 2017
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Abstract
An effective method using hydrofluoric and sulfuric acid was proposed to enhance the leaching of lithium from α-spodumene, without calcination that is subjected to 1000 °C for phase transformation. The thermodynamic feasibility of the reactions was firstly verified. Dissolution conditions were tested to
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An effective method using hydrofluoric and sulfuric acid was proposed to enhance the leaching of lithium from α-spodumene, without calcination that is subjected to 1000 °C for phase transformation. The thermodynamic feasibility of the reactions was firstly verified. Dissolution conditions were tested to maximize the leaching efficiency of lithium and with efficient utilization of hydrofluoric acid (HF) served as evaluation criteria. The results showed that 96% of lithium could be transferred into lixivium with an ore/HF/H2SO4 ratio of 1:3:2 (g/mL/mL), at 100 °C for 3 h. Due to the fact that HF molecules were the main reaction form, the dissolution behaviors were theoretically represented and investigated by dissolution in HF/H2SO4. When combined with chemical elements analyses and characterizations, the results of the dissolution behaviors revealed that α-spodumene and albite were preferentially dissolved over quartz. Insoluble fluoroaluminates, such as AlF3, cryolite (Na3AlF6) and cryolithionite (Na3Li3Al2F12), were generated and might be further partially dissolved by H2SO4. Fluorosilicates, such as K2SiF6, Na2SiF6, or KNaSiF6, were also generated as a part of the insoluble residues. This work provides fundamental insight into the role of HF/H2SO4 played in the dissolution of α-spodumene, and sheds light on a novel and promising process to efficiently extract lithium. Full article
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Open AccessArticle Preparation of Silica-Alumina Nanoparticles via Blast-Furnace Slag Dissolution in Low-Concentration Acetic Acid for Carbonation
Minerals 2017, 7(11), 206; doi:10.3390/min7110206
Received: 4 September 2017 / Revised: 24 October 2017 / Accepted: 25 October 2017 / Published: 28 October 2017
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Abstract
Blast-furnace slag (BFS) has been used as a feedstock for CO2 sequestration by indirect mineral carbonation to produce calcium carbonate precipitates and solid residues. The most-abundant elements in these residues, Si and Al, are usually considered to be impurities that need to
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Blast-furnace slag (BFS) has been used as a feedstock for CO2 sequestration by indirect mineral carbonation to produce calcium carbonate precipitates and solid residues. The most-abundant elements in these residues, Si and Al, are usually considered to be impurities that need to be removed in acid-dissolution processes involving BFS. The co-production of value-added materials from these residues is an attractive option for strengthening the economic competitiveness of mineral carbonation methods. In view of this, we separated the Si and Al, as their hydrated forms, during the dissolution of BFS in acetic acid prior to carbonation. During the sol-gel processing of Si-Al nanoparticles, a catalyst is usually required during the hydrolysis and subsequent condensation processes. In this study, only condensation occurs because the low-concentrations of acetic acid used facilitate in-situ hydrolysis during the dissolution process. Aging was carried out not only to structurally arrange the Si and Al but also to oxidize the marginal Fe(II) to reddish Fe(III). Silica-alumina nanoparticles (78% Si and 22% Al) were prepared by a simple sol-gel route at ambient pressure. These nanoparticles were amorphous and below 20 nm in size. Fourier-transform infrared (FT-IR) studies reveal that the nanoparticles consist of Si–O–Si and Si–O–Al bonds. 27Al nuclear magnetic resonance (NMR) spectroscopy reveals a significant resonance corresponding to tetra-coordinated Al inside the particle framework. Full article
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Open AccessArticle CO2 Mineralization Using Brine Discharged from a Seawater Desalination Plant
Minerals 2017, 7(11), 207; doi:10.3390/min7110207
Received: 12 September 2017 / Revised: 16 October 2017 / Accepted: 27 October 2017 / Published: 30 October 2017
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Abstract
CO2 mineralization is a method of sequestering CO2 in the form of carbonated minerals. Brine discharged from seawater desalination is a potential source of Mg and Ca, which can precipitate CO2 as forms of their carbonate minerals. The concentration of
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CO2 mineralization is a method of sequestering CO2 in the form of carbonated minerals. Brine discharged from seawater desalination is a potential source of Mg and Ca, which can precipitate CO2 as forms of their carbonate minerals. The concentration of Mg and Ca in brine are twice those in the seawater influent to desalination process. This study used a cycle for CO2 mineralization that involves an increase in the pH of the brine, followed by CO2 bubbling, and, finally, filtration. To the best of our knowledge, this is the first time that non-synthesized brine from a seawater desalination plant has been used for CO2 mineralization. The resulting precipitates were CaCO3 (calcite), Mg5(CO3)4(OH)2·4H2O (hydromagnesite), and NaCl (halite) with these materials being identified by X-ray Diffraction (XRD), Fourier transform infrared (FTIR) and thermo gravimetric-differentail thermal Analysis (TGA)-DTA. Despite the presence of Ca with Mg in brine being unfavorable for the precipitation of Mg carbonate, Mg reacted with CO2 to form hydromagnesite at a yield of 86%. Most of the Ca formed calcite, at 99% yield. This study empirically demonstrates that brine from seawater desalination plants can be used for CO2 mineralization. Full article
(This article belongs to the Special Issue Carbon Capture and Storage via Mineral Carbonation)
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Open AccessArticle Increasing the Fine Flaky Graphite Recovery in Flotation via a Combined MultipleTreatments Technique of Middlings
Minerals 2017, 7(11), 208; doi:10.3390/min7110208
Received: 9 October 2017 / Revised: 19 October 2017 / Accepted: 19 October 2017 / Published: 1 November 2017
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Abstract
As the residual flaky graphite ores become miscellaneous and fine, a single treatment technique for the middlings from the flotation process of graphite ore cannot efficiently recover the valuable graphite in the multistage grinding-flotation technology. In the study, the existence form of graphite
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As the residual flaky graphite ores become miscellaneous and fine, a single treatment technique for the middlings from the flotation process of graphite ore cannot efficiently recover the valuable graphite in the multistage grinding-flotation technology. In the study, the existence form of graphite and relationship of graphite with the associated gangue minerals were estimated by optical microscope analysis. The results indicated that the fine flaky graphite particles embedded with gangue minerals like a honeycomb, making it difficult to be beneficiated using the typical flotation technique. A combination technique of individual process and concentrated returning for the treatment of middlings was used to increase the graphite recovery based on the co-existing relationship between graphite and gangue minerals in the middlings. The graphite recovery of the final concentrate upgraded from 51.81% to 91.14% at a fixed carbon (FC) content of 92.01% by a beneficiation process consisted of once coarse (94.41% passing 74 μm) and rougher, five stages regrinding and six stages cleaning. The proposed treatment technique for middlings is of great significance to increase the recovery of fine flaky graphite. Full article
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Open AccessArticle Mechanism and Kinetics of the Reduction of Hematite to Magnetite with CO–CO2 in a Micro-Fluidized Bed
Minerals 2017, 7(11), 209; doi:10.3390/min7110209
Received: 28 August 2017 / Revised: 30 October 2017 / Accepted: 31 October 2017 / Published: 1 November 2017
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Abstract
The mechanism and kinetics of the reduction of hematite to magnetite in a laboratory-scale, micro-fluidized bed reactor were isothermally investigated. The procedure consisted of the isothermal heating in a flow of a 20%CO–80%CO2 mixture at temperatures from 500 °C to 600 °C.
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The mechanism and kinetics of the reduction of hematite to magnetite in a laboratory-scale, micro-fluidized bed reactor were isothermally investigated. The procedure consisted of the isothermal heating in a flow of a 20%CO–80%CO2 mixture at temperatures from 500 °C to 600 °C. It was found that the Avrami–Erofe’ev model of nucleation and 1D growth (n = 1.58) successfully described the phase transition of hematite to magnetite, and the value of activation energy ΔEa of the reaction was estimated to be 48.70 kJ/mol. The microstructure properties for specimens with different conversion degrees were analyzed using the Brunauer, Emmett and Teller (BET) method and scanning electron microscopy (SEM). The results showed that the magnetite nuclei were needle-like, and the hematite specimens became thoroughly porous after complete reduction to magnetite. The physical and chemical processes of the reaction were also discussed. Full article
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Open AccessArticle Effects of Dolomite on Mineral Compositions and Metallurgical Properties of Chromium-Bearing Vanadium–Titanium Magnetite Sinter
Minerals 2017, 7(11), 210; doi:10.3390/min7110210
Received: 22 July 2017 / Revised: 28 October 2017 / Accepted: 30 October 2017 / Published: 2 November 2017
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Abstract
Chengde chromium-bearing vanadium–titanium magnetite (CCVTM) has been used as an important mineral resource in sinter making. The MgO content of this sinter can be enhanced by adding dolomite, which improved operation of the blast furnace. The effects of MgO in the form of
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Chengde chromium-bearing vanadium–titanium magnetite (CCVTM) has been used as an important mineral resource in sinter making. The MgO content of this sinter can be enhanced by adding dolomite, which improved operation of the blast furnace. The effects of MgO in the form of dolomite on metallurgical properties, microstructure and mineral compositions of CCVTM sinter were studied by a sinter pot test, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), and mineral phase microanalysis. The results were as follows: The flame front speed and sinter coefficient decreased with an increase in MgO content from 2.66 to 3.86% by adding dolomite. With an increase in MgO content from 2.66 to 3.86%, the flame front speed, sintering utilization factor, and the value of RI decreased, while RDI and the softening–melting properties improved. In addition, the value of sinter strength (TI) reached a maximum value at MgO = 3.56%. In addition, an increase in the abundance of magnetite, magnesium ferrite, and silicate phase, as well as a decrease in hematite, was found with an increase in MgO content. We concluded that the most appropriate MgO content in the sinter is 3.56%. Full article
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Open AccessArticle Effect of Heating Rate on Pyrolysis Behavior and Kinetic Characteristics of Siderite
Minerals 2017, 7(11), 211; doi:10.3390/min7110211
Received: 10 October 2017 / Revised: 29 October 2017 / Accepted: 1 November 2017 / Published: 3 November 2017
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Abstract
The pyrolysis characteristics of siderite at different heating rates under the neutral atmosphere were investigated using various tools, including comprehensive thermal analyzer, tube furnace, X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and vibrating specimen magnetometer (VSM) measurements. The reaction of
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The pyrolysis characteristics of siderite at different heating rates under the neutral atmosphere were investigated using various tools, including comprehensive thermal analyzer, tube furnace, X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and vibrating specimen magnetometer (VSM) measurements. The reaction of siderite pyrolysis followed the one-step reaction under the neutral atmosphere: FeCO3 → Fe3O4 + CO2 + CO. As the increasing of heating rate, the start and end pyrolysis temperatures and temperate where maximum weight loss rate occurred increased, while the total mass loss were essentially the same. Increasing heating rate within a certain range was in favor of shortening the time of each reaction stage, and the maximum conversion rate could be reached with a short time. The most probable mechanism function for non-isothermal pyrolysis of siderite at different heating rates was A1/2 reaction model (nucleation and growth reaction). With increasing heating rate, the corresponding activation energies and the pre-exponential factors increased, from 446.13 to 505.19 kJ∙mol−1, and from 6.67 × 10−18 to 2.40 × 10−21, respectively. All siderite was transformed into magnetite with a porous structure after pyrolysis, and some micro-cracks were formed into the particles. The magnetization intensity and specific susceptibility increased significantly, which created favorable conditions for the further effective concentration of iron ore. Full article
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Open AccessArticle The Use of Univariate and Multivariate Analyses in the Geochemical Exploration, Ravanj Lead Mine, Delijan, Iran
Minerals 2017, 7(11), 212; doi:10.3390/min7110212
Received: 31 August 2017 / Revised: 21 October 2017 / Accepted: 27 October 2017 / Published: 3 November 2017
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Abstract
A geochemical exploration program was applied to recognize the anomalous geochemical haloes at the Ravanj lead mine, Delijan, Iran. Sampling of unweathered rocks were undertaken across rock exposures on a 10 × 10 meter grid (n = 302) as well as the accessible
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A geochemical exploration program was applied to recognize the anomalous geochemical haloes at the Ravanj lead mine, Delijan, Iran. Sampling of unweathered rocks were undertaken across rock exposures on a 10 × 10 meter grid (n = 302) as well as the accessible parts of underground mine A (n = 42). First, the threshold values of all elements were determined using the cut-off values used in the exploratory data analysis (EDA) method. Then, for further studies, elements with lognormal distributions (Pb, Zn, Ag, As, Cd, Co, Cu, Sb, S, Sr, Th, Ba, Bi, Fe, Ni and Mn) were selected. Robustness against outliers is achieved by application of central log ratio transformation to address the closure problems with compositional data prior to principle components analysis (PCA). Results of these analyses show that, in the Ravanj deposit, Pb mineralization is characterized by a Pb-Ba-Ag-Sb ± Zn ± Cd association. The supra-mineralization haloes are characterized by barite and tetrahedrite in a Ba- Th- Ag- Cu- Sb- As- Sr association and sub-mineralization haloes are comprised of pyrite and tetrahedrite, probably reflecting a Fe-Cu-As-Bi-Ni-Co-Mo-Mn association. Using univariate and multivariate geostatistical analyses (e.g., EDA and robust PCA), four anomalies were detected and mapped in Block A of the Ravanj deposit. Anomalies 1 and 2 are around the ancient orebodies. Anomaly 3 is located in a thin bedded limestone-shale intercalation unit that does not show significant mineralization. Drilling of the fourth anomaly suggested a low grade, non-economic Pb mineralization. Full article
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Open AccessArticle Mineralogical Distribution of Germanium, Gallium and Indium at the Mt Carlton High-Sulfidation Epithermal Deposit, NE Australia, and Comparison with Similar Deposits Worldwide
Minerals 2017, 7(11), 213; doi:10.3390/min7110213
Received: 13 October 2017 / Revised: 27 October 2017 / Accepted: 31 October 2017 / Published: 5 November 2017
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Abstract
Germanium, gallium and indium are in high demand due to their growing usage in high-tech and green-tech applications. However, the mineralogy and the mechanisms of concentration of these critical elements in different types of hydrothermal ore deposits remain poorly constrained. We investigated the
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Germanium, gallium and indium are in high demand due to their growing usage in high-tech and green-tech applications. However, the mineralogy and the mechanisms of concentration of these critical elements in different types of hydrothermal ore deposits remain poorly constrained. We investigated the mineralogical distribution of Ge, Ga and In at the Mt Carlton high-sulfidation epithermal deposit in NE Australia, using electron probe microanalysis and laser ablation inductively-coupled plasma mass spectrometry. Parageneses from which selected minerals were analyzed include: Stage 1 acid sulfate alteration (alunite), Stage 2A high-sulfidation enargite mineralization (enargite, argyrodite, sphalerite, pyrite, barite), Stage 2B intermediate-sulfidation sphalerite mineralization (sphalerite, pyrite, galena) and Stage 3 hydrothermal void fill (dickite). Moderate to locally high concentrations of Ga were measured in Stage 1 alunite (up to 339 ppm) and in Stage 3 dickite (up to 150 ppm). The Stage 2A ores show enrichment in Ge, which is primarily associated with argyrodite (up to 6.95 wt % Ge) and Ge-bearing enargite (up to 2189 ppm Ge). Co-existing sphalerite has comparatively low Ge content (up to 143 ppm), while Ga (up to 1181 ppm) and In (up to 571 ppm) are higher. Sphalerite in Stage 2B contains up to 611 ppm Ge, 2829 ppm Ga and 2169 ppm In, and locally exhibits fine colloform bands of an uncharacterized Zn-In mineral with compositions close to CuZn2(In,Ga)S4. Barite, pyrite and galena which occur in association with Stage 2 mineralization were found to play negligible roles as carriers of Ge, Ga and In at Mt Carlton. Analyzed reference samples of enargite from seven similar deposits worldwide have average Ge concentrations ranging from 12 to 717 ppm (maximum 2679 ppm). The deposits from which samples showed high enrichment in critical elements in this study are all hosted in stratigraphic sequences that locally contain carbonaceous sedimentary rocks. In addition to magmatic-hydrothermal processes, such rocks could potentially be important for the concentration of critical elements in high-sulfidation epithermal deposits. Full article
(This article belongs to the Special Issue Mineral Deposits of Critical Elements)
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Open AccessArticle Identification of Zn-Bearing Micas and Clays from the Cristal and Mina Grande Zinc Deposits (Bongará Province, Amazonas Region, Northern Peru)
Minerals 2017, 7(11), 214; doi:10.3390/min7110214
Received: 11 October 2017 / Revised: 3 November 2017 / Accepted: 3 November 2017 / Published: 7 November 2017
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Abstract
Zn-bearing phyllosilicates are common minerals in nonsulfide Zn deposits, but they seldom represent the prevailing economic species. However, even though the presence of Zn-bearing clays is considered as a disadvantage in mineral processing, their characteristics can give crucial information on the genesis of
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Zn-bearing phyllosilicates are common minerals in nonsulfide Zn deposits, but they seldom represent the prevailing economic species. However, even though the presence of Zn-bearing clays is considered as a disadvantage in mineral processing, their characteristics can give crucial information on the genesis of the oxidized mineralization. This research has been carried out on the Mina Grande and Cristal Zn-sulfide/nonsulfide deposits, which occur in the Bongará district (Northern Peru). In both of the deposits, Zn-bearing micas and clays occur as an accessory to the ore minerals. The XRD analyses and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) investigations revealed that the Zn-bearing micas that are occurring in both deposits mostly consist of I/S mixed layers of detrital origin, which have been partly altered or overprinted by sauconite during the supergene alteration of sulfides. Sporadic hendricksite was also identified in the Cristal nonsulfide mineral assemblage, whereas at Mina Grande, the fraipontite-zaccagnaite (3R-polytype) association was detected. The identified zaccagnaite polytype suggests that both fraipontite and zaccagnaite are genetically related to weathering processes. The hendricksite detected at Cristal is a product of hydrothermal alteration, which is formed during the emplacement of sulfides. The complex nature of the identified phyllosilicates may be considered as evidence of the multiple processes (hydrothermal and supergene) that occurred in the Bongará district. Full article
(This article belongs to the Special Issue Geology and Mineralogy of Zn-Pb Nonsulfide Deposits)
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Open AccessArticle Subsolidus Evolution of the Magnetite-Spinel-UlvöSpinel Solid Solutions in the Kovdor Phoscorite-Carbonatite Complex, NW Russia
Minerals 2017, 7(11), 215; doi:10.3390/min7110215
Received: 19 September 2017 / Revised: 31 October 2017 / Accepted: 3 November 2017 / Published: 9 November 2017
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Abstract
The Kovdor phoscorite-carbonatite ore-pipe rocks form a natural series, where apatite and magnetite first gradually increase due to the presence of earlier crystallizing forsterite in the pipe marginal zone and then decrease as a result of carbonate development in the axial zone. In
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The Kovdor phoscorite-carbonatite ore-pipe rocks form a natural series, where apatite and magnetite first gradually increase due to the presence of earlier crystallizing forsterite in the pipe marginal zone and then decrease as a result of carbonate development in the axial zone. In all lithologies, magnetite grains contain (oxy)exsolution inclusions of comparatively earlier ilmenite group minerals and/or later spinel, and their relationship reflects the concentric zonation of the pipe. The temperature and oxygen fugacity of titanomagnetite oxy-exsolution decreases in the natural rock sequence from about 500 °C to about 300 °C and from NNO + 1 to NNO − 3 (NNO is Ni-NiO oxygen fugacity buffer), with a secondary positive maximum for vein calcite carbonatite. Exsolution spinel forms spherical grains, octahedral crystals, six-beam and eight-beam skeletal crystals co-oriented with host magnetite. The ilmenite group minerals occur as lamellae oriented along {111} and {100} planes of oxy-exsolved magnetite. The kinetics of inclusion growth depends mainly on the diffusivity of cations in magnetite: their comparatively low diffusivities in phoscorite and carbonatites of the ore-pipe internal part cause size-independent growth of exsolution inclusions; while higher diffusivities of cations in surrounding rocks, marginal forsterite-rich phoscorite and vein calcite carbonatite result in size-dependent growth of inclusions. Full article
(This article belongs to the Special Issue Fundamentals and Frontiers in Mineralogy)
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Open AccessArticle Use of Cemented Super-Fine Unclassified Tailings Backfill for Control of Subsidence
Minerals 2017, 7(11), 216; doi:10.3390/min7110216
Received: 11 October 2017 / Revised: 30 October 2017 / Accepted: 6 November 2017 / Published: 9 November 2017
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Abstract
Known for its advantages in preventing geological and environmental hazards, cemented paste backfill (CPB) has become a topic of interest for scientists and mining engineers in recent decades. This paper presents the results of a study on the use of cemented super-fine tailings
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Known for its advantages in preventing geological and environmental hazards, cemented paste backfill (CPB) has become a topic of interest for scientists and mining engineers in recent decades. This paper presents the results of a study on the use of cemented super-fine tailings backfill (CSUTB) in an underground mine for control of surface subsidence. An analytical solution is developed based on the available model to calculate the required strength of backfill when in contact with non-cemented tailings (NCT). The effect of solid contents on the rheological properties of CSUTB is investigated. A reasonable mix proportion (RMP) of CSUTB is determined for Zhongguan Iron Mine (ZGIM) based on laboratory experiments. The validity of RMP in surface subsidence control is verified by a 3D numerical model. The obtained results show that CSUTB requires higher strength when in contact with NCT than when in contact with orebody. Rheological characteristics, e.g., slump, fluidity, and bleeding rate of fresh CSUTB, decrease with higher solids content, of which values with a certain solids content can be determined by quadratic polynomial regression equations. RMP with a cement to tailings (c/t) ratio of 1:10 and a solids content of 70% is recommended for ZGIM, as it shows favorable mechanical and rheological abilities. The deformation parameters (curvature, inclination, and horizontal deformation rate) obtained from numerical modeling are acceptable and lower than critical values, meaning CSUTB can feasibly be used with RMP in subsidence control. Full article
(This article belongs to the Special Issue Minerals in Mine Wastes: Contributions to the Circular Economy)
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Open AccessArticle Biogeochemical Cycling of Silver in Acidic, Weathering Environments
Minerals 2017, 7(11), 218; doi:10.3390/min7110218
Received: 15 September 2017 / Revised: 1 November 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
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Abstract
Under acidic, weathering conditions, silver (Ag) is considered to be highly mobile and can be dispersed within near-surface environments. In this study, a range of regolith materials were sampled from three abandoned open pit mines located in the Iberian Pyrite Belt, Spain. Samples
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Under acidic, weathering conditions, silver (Ag) is considered to be highly mobile and can be dispersed within near-surface environments. In this study, a range of regolith materials were sampled from three abandoned open pit mines located in the Iberian Pyrite Belt, Spain. Samples were analyzed for Ag mineralogy, content, and distribution using micro-analytical techniques and high-resolution electron microscopy. While Ag concentrations were variable within these materials, elevated Ag concentrations occurred in gossans. The detection of Ag within younger regolith materials, i.e., terrace iron formations and mine soils, indicated that Ag cycling was a continuous process. Microbial microfossils were observed within crevices of gossan and their presence highlights the preservation of mineralized cells and the potential for biogeochemical processes contributing to metal mobility in the rock record. An acidophilic, iron-oxidizing microbial consortium was enriched from terrace iron formations. When the microbial consortium was exposed to dissolved Ag, more than 90% of Ag precipitated out of solution as argentojarosite. In terms of biogeochemical Ag cycling, this demonstrates that Ag re-precipitation processes may occur rapidly in comparison to Ag dissolution processes. The kinetics of Ag mobility was estimated for each type of regolith material. Gossans represented 0.6–146.7 years of biogeochemical Ag cycling while terrace iron formation and mine soils represented 1.9–42.7 years and 0.7–1.6 years of Ag biogeochemical cycling, respectively. Biogeochemical processes were interpreted from the chemical and structural characterization of regolith material and demonstrated that Ag can be highly dispersed throughout an acidic, weathering environment. Full article
(This article belongs to the Special Issue Geomicrobiology and Biogeochemistry of Precious Metals)
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Open AccessArticle Preparation of Direct Reduced Iron and Titanium Nitride from Panzhihua Titanomagnetite Concentrate Through Carbothermic Reduction-Magnetic Separation
Minerals 2017, 7(11), 220; doi:10.3390/min7110220
Received: 30 August 2017 / Revised: 31 October 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
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Abstract
A novel process for preparing direct reduction iron (DRI) and titanium nitride (TiN) from Panzhihua titanomagnetite concentrate is proposed. This process involves pelletizing, direct reduction roasting and magnetic separation. The effects of reduction temperature, coal dosage and reduction time on the phase transformation
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A novel process for preparing direct reduction iron (DRI) and titanium nitride (TiN) from Panzhihua titanomagnetite concentrate is proposed. This process involves pelletizing, direct reduction roasting and magnetic separation. The effects of reduction temperature, coal dosage and reduction time on the phase transformation of composite pellets were investigated by X-ray diffraction. Results show that TiN formation proceeds less easily than metallic iron formation. Increasing the reduction temperature, reduction time and coal dosage can promote the transformation of titanium to TiN. Titanium was almost completely transformed into TiN under the conditions of 1300 °C reduction temperature, 26 wt % coal dosage and 90 min reduction time. The scanning electron microscopy (SEM) analysis showed that near-spherical metallic iron particles with diameters from dozens of microns to about 300 μm were formed in the reduced pellets, whereas the TiN particles generally measured less than 10 μm. The energy dispersive spectroscopy (EDS) results revealed that the TiN phase contains a certain amount of vanadium and carbon, and traces of other impurities. The reduced composite pellets under the optimum conditions were processed by grinding and subsequent magnetic separation. As a result, a DRI with 92.88 wt % Fe, 1.00 wt % Ti, and 0.13 wt % V was obtained, and the recoveries of Fe, Ti, and V were 92.85 wt %, 9.00 wt %, and 19.40 wt %, respectively. 91.00 wt % Ti and 80.60 wt % V were concentrated in the rough TiN concentrate. Full article
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Open AccessArticle Study on the Dispersion Mechanism of Citric Acid on Chlorite in Hematite Reverse Flotation System
Minerals 2017, 7(11), 221; doi:10.3390/min7110221
Received: 29 September 2017 / Revised: 31 October 2017 / Accepted: 9 November 2017 / Published: 13 November 2017
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Abstract
The adhesion behavior between particles in the pulp will seriously affect the index of concentrate. In this paper, the effect of citric acid on chlorite in hematite reverse flotation system was studied. The flotation test and settlement test of artificial mixed ore showed
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The adhesion behavior between particles in the pulp will seriously affect the index of concentrate. In this paper, the effect of citric acid on chlorite in hematite reverse flotation system was studied. The flotation test and settlement test of artificial mixed ore showed that a lower dosage of citric acid could significantly improve the removal rate of chlorite. The mineral contact angle measurement and zeta potential analysis, combined with the extended DLVO theory showed that chlorite is easily adsorbed on the surface of hematite, results in a lower removal rate, and the phenomenon was analyzed by a laser particle size analyzer and optical microscope. The results showed that citric acid can reduce the apparent grain size of artificial mixed ore and improve the dispersion degree of pulp by changing the wettability and surface potential of the minerals, thus increased the removal rate of chlorite. Full article
(This article belongs to the Special Issue Flotation Chemistry)
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Open AccessArticle Comparison of Seven Texture Analysis Indices for Their Applicability to Stereological Correction of Mineral Liberation Assessment in Binary Particle Systems
Minerals 2017, 7(11), 222; doi:10.3390/min7110222
Received: 27 October 2017 / Revised: 10 November 2017 / Accepted: 14 November 2017 / Published: 16 November 2017
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Abstract
An effective correction method for stereological bias is required because of the importance of accurate assessment of mineral liberation of ore particles. Stereological bias is error caused by the estimation of a three-dimensional liberation state based on two-dimensional sectional measurements. Recent studies have
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An effective correction method for stereological bias is required because of the importance of accurate assessment of mineral liberation of ore particles. Stereological bias is error caused by the estimation of a three-dimensional liberation state based on two-dimensional sectional measurements. Recent studies have proposed a stereological correction method based on sectional particle texture analysis, which employs numerical particle models. However, the applicability of this method to unfamiliar particle systems, with different shape and texture characteristics from the numerical particle model, has not been thoroughly investigated. In this study, the viability of the method for examination of the internal structure and shape of unfamiliar particles, was assessed using four types of particle systems, based on combinations of two types of internal structures (Boolean and Voronoi) and two types of particle shapes (spherical and irregular). Seven different texture analysis indices were utilized for composition distribution correction with regard to each of the four types of particle systems. The results suggested that a model based on the angular second moment and/or entropy, employed by the spatial gray level dependence method, showed the greatest viability for assessment of unfamiliar particle internal structure and/or shape. Full article
(This article belongs to the Special Issue Process Mineralogy of Critical Metals)
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Open AccessArticle Role of Collectors and Depressants in Mineral Flotation: A Theoretical Analysis Based on Extended DLVO Theory
Minerals 2017, 7(11), 223; doi:10.3390/min7110223
Received: 23 October 2017 / Revised: 12 November 2017 / Accepted: 13 November 2017 / Published: 16 November 2017
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Abstract
A theoretical analysis was conducted to study the role of collectors and depressants in flotation, based on the extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, where the hydrophobic force is considered. The collector-coated hydrophilic particle and the depressant-coated hydrophobic particle are simplified to a sphere uniformly
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A theoretical analysis was conducted to study the role of collectors and depressants in flotation, based on the extended Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, where the hydrophobic force is considered. The collector-coated hydrophilic particle and the depressant-coated hydrophobic particle are simplified to a sphere uniformly covered with respectively hydrophobic and hydrophilic nanometer-sized hemispherical asperities of identical radius. Results show that the role of a collector in bubble–particle attachment is to create an attractive hydrophobic force and thus overcome the repulsive van der Waals and electrostatic forces. Moreover, increasing the length of the hydrophobic part of the collector molecule is a more effective way to enhance flotation recovery, compared to increasing the collector concentration. For a depressant, however, its function mechanism is to create a strong electrostatic double-layer force, while the suppression of the hydrophobic force plays a secondary role in decreasing the bubble–particle attachment barrier. The depressant molecule length is also a dominant parameter in designing a powerful depressant. Full article
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Open AccessArticle PGE Production in Southern Africa, Part I: Production and Market Trends
Minerals 2017, 7(11), 224; doi:10.3390/min7110224
Received: 24 July 2017 / Revised: 13 October 2017 / Accepted: 14 November 2017 / Published: 18 November 2017
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Abstract
Platinum group elements (PGEs) are an important resource for many applications, such as automotive catalytic converters for vehicles, jewelry, electrical devices and as catalysts in the chemical and petroleum industries. At present, the greatest share of global PGE supply is extracted from the
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Platinum group elements (PGEs) are an important resource for many applications, such as automotive catalytic converters for vehicles, jewelry, electrical devices and as catalysts in the chemical and petroleum industries. At present, the greatest share of global PGE supply is extracted from the South African Bushveld Complex and from the Zimbabwean Great Dyke. In this context, this article provides a comprehensive summary of detailed mining data between 2010 and 2015 and discusses these in regard to the global PGE market. On the supply side, the data reveal that the production volumes as well as the ore grades fluctuated in recent years, while the mining and processing of economically less favorable Upper Group 2 (UG2) ore increased. The average head grade from 2010 to 2015 was 3.58 g 6E/t. In the long term, the ore grades decreased. On the market side, PGE prices and increasing (primary) production costs can be observed. On the market side, the demand for vehicles is expected to grow globally resulting in an increase in PGE demand. At the same time, secondary production is expected to increase and will eventually compete with primary production. These findings indicate challenging conditions for the Southern African PGE industry. Full article
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Open AccessArticle PGE Production in Southern Africa, Part II: Environmental Aspects
Minerals 2017, 7(11), 225; doi:10.3390/min7110225
Received: 24 July 2017 / Revised: 8 November 2017 / Accepted: 14 November 2017 / Published: 18 November 2017
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Abstract
Platinum group elements (PGEs, 6E PGE = Pt + Pd + Rh + Ru + Ir + Au) are used in numerous applications that seek to reduce environmental impacts of mobility and energy generation. Consequently, the future demand for PGEs is predicted to
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Platinum group elements (PGEs, 6E PGE = Pt + Pd + Rh + Ru + Ir + Au) are used in numerous applications that seek to reduce environmental impacts of mobility and energy generation. Consequently, the future demand for PGEs is predicted to increase. Previous studies indicate that environmental impacts of PGE production change over time emphasizing the need of up-to-date data and assessments. In this context, an analysis of environmental aspects of PGE production is needed to support the environmental assessment of technologies using PGEs, to reveal environmental hotspots within the production chain and to identify optimization potential. Therefore, this paper assesses greenhouse gas (GHG) emissions, cumulative fossil energy demand (CEDfossil), sulfur dioxide (SO2) emissions and water use of primary PGE production in Southern Africa, where most of today’s supply originates from. The analysis shows that in 2015, emissions amounted to 45 t CO2-eq. and 502 kg SO2 per kg 6E PGE in the case GHG and SO2 emissions, respectively. GHG emissions are dominated by emissions from electricity provision contributing more than 90% to the overall GHG emissions. The CEDfossil amounted to 0.60 TJ per kg 6E PGE. A detailed analysis of the CEDfossil reveals that electricity provision based on coal power consumes the most fossil energy carriers among all energy forms. Results show that the emissions are directly related to the electricity demand. Thus, the reduction in the electricity demand presents the major lever to reduce the consumption of fossil energy resources and the emission of GHGs and SO2. In 2015, the water withdrawal amounted to 0.272 million L per kg 6E PGE. Additionally, 0.402 million L of recycled water were used per kg 6E PGE. All assessed indicators except ore grades and production volumes reveal increasing trends in the period from 2010 to 2015. It can be concluded that difficult market conditions (see part I of this paper series) and increasing environmental impacts present a challenging situation for the Southern African PGE mining industry. Full article
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Open AccessArticle Quantification and Prediction of Bulk Gold Fineness at Placer Gold Mines: A New Zealand Example
Minerals 2017, 7(11), 226; doi:10.3390/min7110226
Received: 15 October 2017 / Revised: 5 November 2017 / Accepted: 16 November 2017 / Published: 19 November 2017
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Abstract
This study documents the bulk Au fineness (Au parts per thousand) of the bullion from a placer gold mine in southern New Zealand. The compositions of doré bars produced approximately every 10 days over nearly three years is compared to the range of
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This study documents the bulk Au fineness (Au parts per thousand) of the bullion from a placer gold mine in southern New Zealand. The compositions of doré bars produced approximately every 10 days over nearly three years is compared to the range of compositions of gold particles which have been extracted. Silver is the principal impurity in the gold, and the doré bars contained 2–3 wt % Ag over the period examined. At the scale of a typical individual 0.5 mm gold particle, there are three different types of gold: an Ag-bearing core (2–9 wt % Ag), a 10–50 µm wide Ag-poor rim (typically <1 wt % Ag), and micron scale overgrowth gold (0% Ag). The overgrowths are volumetrically negligible, and the average Ag content of a gold particle is controlled principally by the proportions of core and rim gold. The rims have been formed by recrystallisation of deformed core gold, with associated leaching of the Ag from the recrystallised gold. The volumetric proportion of cores has decreased with increasing flattening of gold particles, and highly flattened and folded flakes have little or no remnant cores. The bulk Au fineness of doré bars from the mine has decreased from ~980 to ~970 as the mine progressed upstream in a Pleistocene paleochannel because the upstream gold has been less flattened than the downstream gold. Full article
(This article belongs to the Special Issue Geometallurgy)
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Open AccessArticle Short-Range Stacking Disorder in Mixed-Layer Compounds: A HAADF STEM Study of Bastnäsite-Parisite Intergrowths
Minerals 2017, 7(11), 227; doi:10.3390/min7110227
Received: 3 October 2017 / Revised: 11 November 2017 / Accepted: 13 November 2017 / Published: 20 November 2017
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Abstract
Atomic-scale high angle annular dark field scanning transmission electron microscopy (HAADF STEM) imaging and electron diffractions are used to address the complexity of lattice-scale intergrowths of REE-fluorocarbonates from an occurrence adjacent to the Olympic Dam deposit, South Australia. The aims are to define
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Atomic-scale high angle annular dark field scanning transmission electron microscopy (HAADF STEM) imaging and electron diffractions are used to address the complexity of lattice-scale intergrowths of REE-fluorocarbonates from an occurrence adjacent to the Olympic Dam deposit, South Australia. The aims are to define the species present within the intergrowths and also assess the value of the HAADF STEM technique in resolving stacking sequences within mixed-layer compounds. Results provide insights into the definition of species and crystal-structural modularity. Lattice-scale intergrowths account for the compositional range between bastnäsite and parasite, as measured by electron probe microanalysis (at the µm-scale throughout the entire area of the intergrowths). These comprise rhythmic intervals of parisite and bastnäsite, or stacking sequences with gradational changes in the slab stacking between B, BBS and BS types (B—bastnäsite, S—synchysite). An additional occurrence of an unnamed B2S phase [CaCe3(CO3)4F3], up to 11 unit cells in width, is identified among sequences of parisite and bastnäsite within the studied lamellar intergrowths. Both B2S and associated parisite show hexagonal lattices, interpreted as 2H polytypes with c = 28 and 38 Å, respectively. 2H parisite is a new, short hexagonal polytype that can be added to the 14 previously reported polytypes (both hexagonal and rhombohedral) for this mineral. The correlation between satellite reflections and the number of layers along the stacking direction (c*) can be written empirically as: Nsat = [(m × 2) + (n × 4)] − 1 for all BmSn compounds with S ≠ 0. The present study shows intergrowths characterised by short-range stacking disorder and coherent changes in stacking along perpendicular directions. Knowing that the same compositional range can be expressed as long-period stacking compounds in the group, the present intergrowths are interpreted as being related to disequilibrium crystallisation followed by replacement. HAADF STEM imaging is found to be efficient for depiction of stacking sequences and their changes in mixed-layer compounds, particularly those in which heavy atoms, such as rare-earth elements, are essential components. Full article
(This article belongs to the Special Issue Rare-Earth Carbonates)
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Open AccessArticle BBUNS: Bluetooth Beacon-Based Underground Navigation System to Support Mine Haulage Operations
Minerals 2017, 7(11), 228; doi:10.3390/min7110228
Received: 28 September 2017 / Revised: 2 November 2017 / Accepted: 18 November 2017 / Published: 21 November 2017
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Abstract
A Bluetooth beacon-based underground navigation system (BBUNS) was developed to identify the optimal haul road in an underground mine, track the locations of dump trucks, and display this information on mobile devices. A three-dimensional (3-D) geographic information system (GIS) database of the haul
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A Bluetooth beacon-based underground navigation system (BBUNS) was developed to identify the optimal haul road in an underground mine, track the locations of dump trucks, and display this information on mobile devices. A three-dimensional (3-D) geographic information system (GIS) database of the haul roads in an underground mine was constructed, and the travel time for each section was calculated. A GIS database was also constructed for 50 Bluetooth beacons that were installed along the haul roads. An Android-based BBUNS application was developed to visualize the current location of each dump truck and the optimal haul road to the destination on mobile devices, using the Bluetooth beacon system that was installed in the underground mine. Whenever the BBUNS recognized all of the Bluetooth beacons installed in the underground mine, it could provide the dump truck drivers with information on the current location and the two-dimensional (2-D) and 3-D haul road properties. The operating time of each dump truck and the time spent on each unit task could be analyzed using recorded data on the times when Bluetooth beacon signals were recognized by the BBUNS. The underground mine navigation system that was developed in this study can contribute to the improvement of haul operation efficiency and productivity. Full article
(This article belongs to the Special Issue Geological Modelling)
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Open AccessArticle Selenium and Other Trace Element Mobility in Waste Products and Weathered Sediments at Parys Mountain Copper Mine, Anglesey, UK
Minerals 2017, 7(11), 229; doi:10.3390/min7110229
Received: 16 October 2017 / Revised: 20 November 2017 / Accepted: 20 November 2017 / Published: 22 November 2017
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Abstract
The Parys Mountain copper mining district (Anglesey, North Wales) hosts exposed pyritic bedrock, solid mine waste spoil heaps, and acid drainage (ochre sediment) deposits. Both natural and waste deposits show elevated trace element concentrations, including selenium (Se), at abundances of both economic and
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The Parys Mountain copper mining district (Anglesey, North Wales) hosts exposed pyritic bedrock, solid mine waste spoil heaps, and acid drainage (ochre sediment) deposits. Both natural and waste deposits show elevated trace element concentrations, including selenium (Se), at abundances of both economic and environmental consideration. Elevated concentrations of semi-metals such as Se in waste smelts highlight the potential for economic reserves in this and similar base metal mining sites. Selenium is sourced from the pyritic bedrock and concentrations are retained in red weathering smelt soils, but lost in bedrock-weathered soils and clays. Selenium correlates with Te, Au, Bi, Cd, Hg, Pb, S, and Sb across bedrock and weathered deposits. Man-made mine waste deposits show enrichment of As, Bi, Cu, Sb, and Te, with Fe oxide-rich smelt materials containing high Pb, up to 1.5 wt %, and Au contents, up to 1.2 ppm. The trace elements As, Co, Cu, and Pb are retained from bedrock to all sediments, including high Cu content in Fe oxide-rich ochre sediments. The high abundance and mobility of trace elements in sediments and waters should be considered as potential pollutants to the area, and also as a source for economic reserves of previously extracted and new strategic commodities. Full article
(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)
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Open AccessReview Global Potential of Rare Earth Resources and Rare Earth Demand from Clean Technologies
Minerals 2017, 7(11), 203; doi:10.3390/min7110203
Received: 10 August 2017 / Revised: 16 October 2017 / Accepted: 18 October 2017 / Published: 25 October 2017
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Abstract
Rare earth elements (REE) are widely used in high technologies, medical devices, and military defense systems, and are especially indispensable in emerging clean energy. Along with the growing market of green energy in the next decades, global demand for REE will increase continuously,
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Rare earth elements (REE) are widely used in high technologies, medical devices, and military defense systems, and are especially indispensable in emerging clean energy. Along with the growing market of green energy in the next decades, global demand for REE will increase continuously, which will put great pressure on the current REE supply chain. The global REE production is currently mainly concentrated in China and Australia; they respectively contributed 85% and 10% in 2016. However, there are 178 deposits widely distributed in the world, and reported REE resources as of 2017 totaled 478 megaton (Mt) rare earth oxides (REO); 58% of these deposits contained exceed 0.1 Mt REO; 59 deposits have been technically assessed. These resources could sustain the global REE production at the current pace for more than a hundred years. It is noted that REE demand from clean technologies will reach 51.9 thousand metric tons (kt) REO in 2030, Nd and Dy, respectively, comprising 75% and 9%, while these two elements comprise 15% and 0.52% of the global REE resources, respectively. This indicates that Nd and Dy will strongly influence the development of exploring new REE projects and clean technologies in the next decades. Full article
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Open AccessReview C–O Stable Isotope Geochemistry of Carbonate Minerals in the Nonsulfide Zinc Deposits of the Middle East: A Review
Minerals 2017, 7(11), 217; doi:10.3390/min7110217
Received: 3 October 2017 / Revised: 30 October 2017 / Accepted: 6 November 2017 / Published: 10 November 2017
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Abstract
Zinc nonsulfides are well represented in the Middle East, with occurrences in Turkey, Iran, and Yemen. Their genesis can be constrained by using carbon and oxygen isotope systematics applied to carbonate minerals. The δ13C ratios of smithsonite and hydrozincite in Iran
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Zinc nonsulfides are well represented in the Middle East, with occurrences in Turkey, Iran, and Yemen. Their genesis can be constrained by using carbon and oxygen isotope systematics applied to carbonate minerals. The δ13C ratios of smithsonite and hydrozincite in Iran and Turkey are comprised in the typical interval of supergene Zn carbonates (−0.4 and −7.1‰ V-PDB). The oxygen isotope geochemistry is more complex. Oxygen isotope compositions of smithsonite of the Hakkari deposit (Turkey) (δ18O from 24.2 to 25.6‰ V-SMOW) point to precipitation temperatures between ~4 and ~18 °C, corresponding to a normal weathering environment at these latitudes, whereas δ18O of smithsonite from other Middle East deposits (Angouran in Iran, Jabali in Yemen) point to the precipitation from low- to medium-temperature hydrothermal fluids. The C–O isotopic compositions of hydrozincite from the Mehdi Abad, Irankuh, and Chah-Talkh deposits can be only partially compared with those of smithsonite, because the oxygen isotopes fractionation equation for hydrozincite-water is not known. A comparison between the geochemical characteristics of all Zn-nonsulfide ores in the Middle East indicates that, even though several mineral deposits are derived from supergene weathering processes, other ones have been deposited from fluids associated with magmatic activity (Angouran, Iran) or with hydrothermal systems (Jabali, Yemen). This suggests that it is not possible to apply a common interpretative model to the genesis of all nonsulfide deposits in the Middle East. Full article
(This article belongs to the Special Issue Geology and Mineralogy of Zn-Pb Nonsulfide Deposits)
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Open AccessReview Fluorine in Chinese Coal: A Review of Distribution, Abundance, Modes of Occurrence, Genetic Factors and Environmental Effects
Minerals 2017, 7(11), 219; doi:10.3390/min7110219
Received: 30 August 2017 / Revised: 29 October 2017 / Accepted: 2 November 2017 / Published: 10 November 2017
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Abstract
Fluorine, a hazard that is associated with coal, has resulted in serious environmental issues during the production and utilization of coal. In this paper, we provide a detailed review of fluorine in Chinese coal, including the distribution, concentration, modes of occurrence, genetic factors,
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Fluorine, a hazard that is associated with coal, has resulted in serious environmental issues during the production and utilization of coal. In this paper, we provide a detailed review of fluorine in Chinese coal, including the distribution, concentration, modes of occurrence, genetic factors, and environmental effects. The average concentration of fluorine in Chinese coal is 130.0 mg/kg, which is slightly higher than coal worldwide (88.0 mg/kg). The enrichment of fluorine in Chinese coal varies across different coal deposit regions, and it is especially high in Inner Mongolia (Junger coalfield, Daqingshan coalfield) and southwest China (coal mining regions in Yunnan, Guizhou province). The fluorine distribution is uneven, with a relatively high content in southwest coal (including Yunnan, Guizhou, Chongqing, and Sichuan provinces), very high content in the coal of North China (Inner Mongolia) and South China (Guangxi), and is occasionally found in the northwest (Qinghai). Fluorine occurs in various forms in coal, such as independent minerals (fluorine exists as fluorapatite or fluorite in coal from Muli of Qinghai, Taoshuping of Yunnan, Guiding of Guizhou, and Daqingshan of Inner Mongolia), adsorption on minerals (fluorine in coal from Nantong, Songzao of Chongqing, Guxu of Sichuan, and Shengli, Daqingshan, and Junger from Inner Mongolia), substitution in minerals (Wuda coal, Inner Mongolia), and a water-soluble form (Haerwusu coal, Inner Mongolia). The enrichment of fluorine is mainly attributed to the weathering of source rock and hydrothermal fluids; in addition to that, volcanic ash, marine water influence, and groundwater affect the fluorine enrichment in some cases. Some environmental and human health problems are related to fluorine in coal, such as damage to the surrounding environment and husbandry (poisoning of livestock) during the coal combustion process, and many people have suffered from fluorosis due to the burning of coal (endemic fluorosis in southwest China). Full article
(This article belongs to the Special Issue Toxic Mineral Matter in Coal and Coal Combustion Products)
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