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Minerals, Volume 10, Issue 9 (September 2020) – 109 articles

Cover Story (view full-size image): 226Ra is an important contributor to naturally occurring radioactive materials (NORM) and also relevant in some safety cases related to the disposal of spent nuclear fuel in a deep geological repository. Recrystallization and solid solution formation with sulfates are regarded as an important retention mechanism for 226Ra. Here, we have investigated the (Ba,Sr)SO4 solid solution at the Ba-rich end with regard to the 226Ra uptake kinetics and solubility. It is remarkable how already low amounts of Sr have an impact on the 226Ra solubility and the recrystallization kinetics of the solid solution–aqueous solution system (Ba,Sr,Ra)SO4 + H2O. The experimental findings confirm a theoretically predicted minimum of the 226Ra solubility in this system that is lower than that in the (Ba,Ra)SO4 binary solid solution. View this paper
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Open AccessArticle
Geochemistry and Zircon U-Pb-Hf Isotopes of Metamorphic Rocks from the Kaiyuan and Hulan Tectonic Mélanges, NE China: Implications for the Tectonic Evolution of the Paleo-Asian and Mudanjiang Oceans
Minerals 2020, 10(9), 836; https://doi.org/10.3390/min10090836 - 22 Sep 2020
Cited by 1 | Viewed by 563
Abstract
The Late Paleozoic–Early Mesozoic tectonic evolution of the Changchun-Yanji suture (CYS) was mainly associated with the Paleo-Asian and Mudanjiang tectonic regimes. However, the spatial and temporal overprinting and variations of these two regimes remains are still dispute. In order to evaluate this issue, [...] Read more.
The Late Paleozoic–Early Mesozoic tectonic evolution of the Changchun-Yanji suture (CYS) was mainly associated with the Paleo-Asian and Mudanjiang tectonic regimes. However, the spatial and temporal overprinting and variations of these two regimes remains are still dispute. In order to evaluate this issue, in this contribution, we present new zircon U-Pb ages and a whole-rock geochemical and zircon Hf isotopic dataset on a suite of metamorphic rocks, including gneisses, actinolite schist, leptynites, and biotite schists, from tectonic mélanges in northern Liaoning and central Jilin provinces, NE China. Based on zircon LA-ICP-MS U-Pb dating results, protoliths show wide ranges of aging spectrum, including Paleoproterozoic (2441 Ma), Early Permian (281 Ma), Late Permian (254 Ma), and Late Triassic (230 Ma). The Permian protoliths of leptynites from the Hulan Tectonic Mélange (HLTM) and gneisses from the Kaiyuan Tectonic Mélange (KYTM) exhibit arc-related geochemical signatures, implying that the Paleo-Asian Ocean (PAO) did not close prior to the Late Permian. The Late Triassic protoliths of gneisses from the KYTM, in combination with previously reported coeval igneous rocks along the CYS, comprises a typical bimodal igneous suite in an E–W-trending belt, suggesting a post-orogenic extensional environment. Consequently, we infer that the final closure of the PAO took place during the Early–Middle Triassic. The Early Permian protoliths of biotite schists from the HLTM are alkali basaltic rocks and contain multiple older inherited zircons, which, in conjunction with the geochemical features of the rocks, indicate that they were generated in a continental rift related to the initial opening of the Mudanjiang Ocean (MO). Data from this contribution and previous studies lead us to conclude that the MO probably opened during the Middle Triassic, due to the north–south trending compression caused by the final closure of the PAO. Full article
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Open AccessArticle
Impact of Fly Ash as a Raw Material on the Properties of Refractory Forsterite–Spinel Ceramics
Minerals 2020, 10(9), 835; https://doi.org/10.3390/min10090835 - 22 Sep 2020
Viewed by 594
Abstract
This article examines the process for the synthesis of forsterite–spinel (2MgO·SiO2/MgO·Al2O3) refractory ceramics from fly ash and alumina as sources of aluminum oxide. Raw materials were milled, mixed in different ratios and sintered at 1500 °C for [...] Read more.
This article examines the process for the synthesis of forsterite–spinel (2MgO·SiO2/MgO·Al2O3) refractory ceramics from fly ash and alumina as sources of aluminum oxide. Raw materials were milled, mixed in different ratios and sintered at 1500 °C for 2 h. Sintered samples were characterized by XRD, thermal analyses and SEM. Porosity, water absorption, bulk density, refractoriness, refractoriness under load and thermal shock resistance were also investigated. The impact of fly ash as a raw material was investigated in accordance with the resulting properties and microstructure of samples with fly ash and alumina as the raw materials. Due to the positive effect of flux oxides (iron oxides and alkalis) on sintering, the mullite contained in fly ash completely decomposed into silica and alumina, which, together with magnesium oxide, formed spinel. This led to improved microstructural and mechanical properties and thermal shock resistance. In particular, mixtures with 10 wt.% and 20 wt.% of fly ash had the most promising results compared to alumina mixtures. Both modulus of rupture and thermal shock resistance were improved, while the impact on refractory properties was minimal. The novelty of this research lies in the recycling of fly ash, a by-product from coal-burning power plants, into a raw material for the production of forsterite–spinel refractory ceramics. Full article
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Open AccessArticle
The History of Transgressions during the Late Paleocene-Early Eocene in the Kuqa Depression, Tarim Basin: Constraints from C-O-S-Sr Isotopic Geochemistry
Minerals 2020, 10(9), 834; https://doi.org/10.3390/min10090834 - 22 Sep 2020
Cited by 1 | Viewed by 553
Abstract
The Tethys Sea extended into the Kuqa Depression from the Paleocene to the late Eocene and provided an abundant provenance for the deposition of evaporite sequences. Until now, detailed research on the history of transgressions during the late Paleocene-early Eocene in the Kuqa [...] Read more.
The Tethys Sea extended into the Kuqa Depression from the Paleocene to the late Eocene and provided an abundant provenance for the deposition of evaporite sequences. Until now, detailed research on the history of transgressions during the late Paleocene-early Eocene in the Kuqa Depression has been limited. Therefore, in this study, we took the upper Paleocene Talak section and the lower Eocene Xiaokuzibai section in the western part of the Depression as the research objects and analyzed the petrology, the carbon and oxygen isotopes of carbonate rocks, and the sulfur and strontium isotopes of gypsum rocks to systematically study the above issues. The δ13C, δ18O and δ34S values of the upper Paleocene evaporite sequences were determined to be between 4.2‰ and 5.7‰, between −5.2‰ and 2.4‰, and between 16.5‰ and 17.9‰, respectively. The δ13C, δ18O, δ34S, and 87Sr/86Sr values of the lower Eocene evaporite sequences were determined to be between −6.9‰ and −2.0‰, between −9.0‰ and −4.5‰, between 10.5‰ and 17.0‰, and between 0.708642 and 0.709883, respectively. The analysis results show that the evaporite sequence of the upper Paleocene was formed by transgression. The deposition of the evaporite sequence changed from continental to marine deposition, and then gradually transitioned to continental during the Early Eocene. This paper is of great significance for reconstructing the history of transgressions in the Tethys tectonic realm during this period. Full article
(This article belongs to the Special Issue Mineralogy, Petrology and Geochemistry of Evaporites)
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Open AccessArticle
Rare Earth Elements and Sr Isotope Ratios of Large Apatite Crystals in Ghareh Bagh Mica Mine, NW Iran: Tracing for Petrogenesis and Mineralization
Minerals 2020, 10(9), 833; https://doi.org/10.3390/min10090833 - 22 Sep 2020
Viewed by 630
Abstract
The 320 Ma Ghareh Bagh mica mine is the only active mica mine in northwest Iran, and hosts Mg-bearing biotite (phlogopite) with apatite, epidote, and calcite. Chemical investigation of apatite infers the high abundances of the rare earth elements (REEs up to 5619 [...] Read more.
The 320 Ma Ghareh Bagh mica mine is the only active mica mine in northwest Iran, and hosts Mg-bearing biotite (phlogopite) with apatite, epidote, and calcite. Chemical investigation of apatite infers the high abundances of the rare earth elements (REEs up to 5619 ppm), higher ratios of the LREE/HREE ((La/Yb)N = 28.5–36.7)) and high content of Y (236–497 ppm). REE pattern in the apatite and host A-type granite is almost the same. Ghareh Bagh apatite formed from the early magmatic-hydrothermal exsolved fluids at the high temperature from the Ghushchi alkali feldspar granite. The apatite crystals came up as suspension grains and precipitated in the brecciated zone. The early magmatic-hydrothermal fluids settle phlogopite, epidote, chlorite, K-feldspar and albite down in the brecciation zone. Due to the precipitation of these minerals, the late-stage fluids with low contents of Na+, Ca2+ and REE affected the early stage of alteration minerals. The high ratios of 87Sr/86Sr (0.70917 to 0.70950) are more consistent with crustal sources for the apatite large crystals. The same ages (320 Ma) for both brecciated mica veins and host alkali feldspar granites infer the apatite and paragenesis minerals were related to host granite A-type granite in the Ghareh Bagh area. Full article
(This article belongs to the Special Issue Rare Earth Elements and Their Isotope Geochemistry)
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Open AccessArticle
Characterization of Slag Reprocessing Tailings-Based Geopolymers in Marine Environment
Minerals 2020, 10(9), 832; https://doi.org/10.3390/min10090832 - 22 Sep 2020
Cited by 2 | Viewed by 561
Abstract
In this study, copper slag reprocessing tailings (CSRT) were synthesized into geopolymers with 40%, 50% and 60% metakaolin. The evolution of compressive strength and microstructures of CSRT-based geopolymers in a marine environment was investigated. Except for compressive strength measurement, the characterizations of X-ray [...] Read more.
In this study, copper slag reprocessing tailings (CSRT) were synthesized into geopolymers with 40%, 50% and 60% metakaolin. The evolution of compressive strength and microstructures of CSRT-based geopolymers in a marine environment was investigated. Except for compressive strength measurement, the characterizations of X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) were included. It was found that marine conditions changed the Si/Al ratio in the sodium-aluminosilicate-hydrate (N-A-S-H) gel backbone, promoted the geopolymerization process, led to more Q4(3Al), Q4(2Al) and Q4(1Al) gel formation and a higher compressive strength of the geopolymers. This provided a basis for the preparation of CSRT-based geopolymers into marine concrete. Full article
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Open AccessArticle
Evolution of Deformation Fabrics Related to Petrogenesis of Upper Mantle Xenoliths Beneath the Baekdusan Volcano
Minerals 2020, 10(9), 831; https://doi.org/10.3390/min10090831 - 21 Sep 2020
Cited by 1 | Viewed by 948
Abstract
Knowledge of the formation and evolution of cratonic subcontinental lithospheric mantle is critical to our understanding of the processes responsible for continental development. Here, we report the deformation microstructures and lattice preferred orientations (LPOs) of olivine and pyroxenes alongside petrological data from spinel [...] Read more.
Knowledge of the formation and evolution of cratonic subcontinental lithospheric mantle is critical to our understanding of the processes responsible for continental development. Here, we report the deformation microstructures and lattice preferred orientations (LPOs) of olivine and pyroxenes alongside petrological data from spinel peridotite xenoliths beneath the Baekdusan volcano. We have used these datasets to constrain the evolution of deformation fabrics related to petrogenesis from the Baekdusan peridotites. Based on petrographic features and deformation microstructures, we have identified two textural categories for these peridotites: coarse- and fine-granular harzburgites (CG and FG Hzb). We found that mineral composition, equilibrium temperature, olivine LPO, stress, and extraction depth vary considerably with the texture. We suggest that the A-type olivine LPO in the CG Hzb may be related to the preexisting Archean cratonic mantle fabric (i.e., old frozen LPO) formed under high-temperature, low-stress, and dry conditions. Conversely, we suggest that the D-type olivine LPOs in the FG Hzb samples likely originated from later localized deformation events under low-temperature, high-stress, and dry conditions after a high degree of partial melting. Moreover, we consider the Baekdusan peridotite xenoliths to have been derived from a compositionally and texturally heterogeneous vertical mantle section beneath the Baekdusan volcano. Full article
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Open AccessArticle
The Origin of Hydrocarbon Gases in the Lovozero Nepheline-Syenite Massif (Kola Peninsula, NW Russia), as Revealed from He and Ar Isotope Evidence
Minerals 2020, 10(9), 830; https://doi.org/10.3390/min10090830 - 21 Sep 2020
Viewed by 733
Abstract
The occurrence of hydrocarbon gases (HCG) in unusually high concentrations for magmatic complexes, in the Lovozero and some other alkaline massifs, is of both geochemical and practical interest. The nature of these gases, despite the long history of research, remains the subject of [...] Read more.
The occurrence of hydrocarbon gases (HCG) in unusually high concentrations for magmatic complexes, in the Lovozero and some other alkaline massifs, is of both geochemical and practical interest. The nature of these gases, despite the long history of research, remains the subject of debate. As an approach to solving this problem, we studied the coupled distribution of occluded HCG and the recognized tracers of various geological processes, such as helium and argon isotopes. The extraction of the gas components trapped in fluid micro-inclusions was carried out by the mechanical crushing of rock and mineral samples. A positive correlation was found between the 3He/4He and CH4/C2H6 ratios, whereas a negative correlation of the latter was found with the 36Ar concentration, which in turn was directly related, in varying degrees, to the content of HCG and most strongly with pentanes. Conjugacy of the processes of the heavier gaseous hydrocarbons, a loss of the deep component of the fluid phase and dilution of it with the atmogenic component was established. In the absence of a correlation between CH4 and 3He, the value of the CH4/3He ratio in the Lovozero gas substantially exceeded the estimates of it in gases of a mantle origin, and mainly corresponded to the crustal values. However, in some samples, a small fraction of mantle methane was allowed. The peculiarities of the relationships between hydrocarbon gases and the isotopes of noble gases indicate a sequential process of abiogenic generation and transformation of HCG at the magmatic and post-magmatic stages during the formation of the Lovozero massif. The obtained results confirm the usefulness of this approach in solving the origin of reduced gases in alkaline igneous systems. Full article
(This article belongs to the Section Mineral Deposits)
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Open AccessArticle
Magma Mingling in Kimberlites: Evidence from the Groundmass Cocrystallization of Two Spinel-Group Minerals
Minerals 2020, 10(9), 829; https://doi.org/10.3390/min10090829 - 20 Sep 2020
Viewed by 548
Abstract
We present the results of a detailed petrographic study of fresh coherent samples of the Menominee kimberlite sampled at site 73, located in Menominee County, MI, USA. Our objective is to account for its unusual and complex paragenetic sequence. Several generations of olivine, [...] Read more.
We present the results of a detailed petrographic study of fresh coherent samples of the Menominee kimberlite sampled at site 73, located in Menominee County, MI, USA. Our objective is to account for its unusual and complex paragenetic sequence. Several generations of olivine, ilmenite, and spinel-group minerals are described. Early olivine and ilmenite are xenocrystic and were replaced or overgrown by primary minerals. Zoned microcrysts of olivine have a xenocrystic core mantled by a first rim in which rutile, geikielite, and spinel s.s. (spinel sensu stricto) cocrystallized. The in situ U–Pb dating of a microcryst of primary rutile yielded 168.9 ± 4.4 Ma, which was interpreted as the age of emplacement. The groundmass consists of olivine, spinel s.s., a magnesian ulvöspinel–ulvöspinel–magnetite (MUM) spinel, calcite, and dolomite. An extremely low activity of Si is suggested by the crystallization of spinel s.s. instead of phlogopite in the groundmass. The presence of djerfisherite microcrysts indicates high activities of Cl and S during the late stages of melt crystallization. The occurrence of two distinct spinel-group minerals (spinel s.s. and qandilite-rich MUM) in the groundmass is interpreted as clear evidence of the mingling of a magnesiocarbonatitic melt with a dominant kimberlitic melt. Full article
(This article belongs to the Special Issue Spinel Group Minerals, Volume II)
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Open AccessArticle
Fluid Infiltration and Mass Transfer along a Lamprophyre Dyke–Marble Contact: An Example from the South-Western Korean Peninsula
Minerals 2020, 10(9), 828; https://doi.org/10.3390/min10090828 - 20 Sep 2020
Viewed by 667
Abstract
In this contribution, we report the metasomatic characteristics of a lamprophyre dyke–marble contact zone from the Hongseong–Imjingang belt along the western Gyeonggi Massif, South Korea. The lamprophyre dyke intruded into the dolomitic marble, forming a serpentinized contact zone. The zone consists of olivine, [...] Read more.
In this contribution, we report the metasomatic characteristics of a lamprophyre dyke–marble contact zone from the Hongseong–Imjingang belt along the western Gyeonggi Massif, South Korea. The lamprophyre dyke intruded into the dolomitic marble, forming a serpentinized contact zone. The zone consists of olivine, serpentine, calcite, dolomite, biotite, spinel, and hematite. Minor F and Cl contents in the serpentine and biotite indicate the composition of the infiltrating H2O-CO2 fluid. SiO2 (12.42 wt %), FeO (1.83 wt %), K2O (0.03 wt %), Sr (89 ppm), U (0.7 ppm), Th (1.44 ppm), and rare earth elements (REEs) are highly mobile, while Zr, Cr, and Ba are moderately mobile in the fluid. Phase equilibria modelling suggests that the olivine, spinel, biotite, and calcite assemblage might be formed by the dissolution of dolomite at ~700 °C, 130 MPa. Such modelling requires stable diopside in the observed conditions in the presence of silica-saturated fluid. The lack of diopside in the metasomatized region is due to the high K activity of the fluid. Our log activity K2O (aK2O)–temperature pseudosection shows that at aK2O~−40, the olivine, spinel, biotite, and calcite assemblage is stable without diopside. Subsequently, at ~450 °C, 130 MPa, serpentine is formed due to the infiltration of H2O during the cooling of the lamprophyre dyke. This suggests that hot H2O-CO2 fluids with dissolved major and trace elements infiltrated through fractures, grain boundaries, and micron-scale porosity, which dissolved dolomite in the marble and precipitated the observed olivine-bearing peak metasomatic assemblage. During cooling, exsolved CO2 could increase the water activity to stabilize the serpentine. Our example implies that dissolution-reprecipitation is an important process, locally and regionally, that could impart important textural and geochemical variations in metasomatized rocks. Full article
(This article belongs to the Special Issue Microtexture Characterization of Rocks and Minerals)
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Open AccessArticle
Synthesis of Fly Ash-Based Geopolymers: Effect of Calcite Addition and Mechanical Activation
Minerals 2020, 10(9), 827; https://doi.org/10.3390/min10090827 - 20 Sep 2020
Cited by 3 | Viewed by 550
Abstract
Blends of fly ash and natural calcite, mechanically activated for 0–400 s in a planetary mill, were used to synthesize geopolymers at ambient temperature. The calcite content in the blends was 0–10 wt.%. Sodium hydroxide solution was used as an alkaline agent. Mechanical [...] Read more.
Blends of fly ash and natural calcite, mechanically activated for 0–400 s in a planetary mill, were used to synthesize geopolymers at ambient temperature. The calcite content in the blends was 0–10 wt.%. Sodium hydroxide solution was used as an alkaline agent. Mechanical activation of the raw material considerably enhanced its reactivity with respect to the alkaline agent, as was observed using Fourier-transform infrared spectroscopy, isothermal conduction calorimetry, thermogravimetry coupled with mass spectrometry analysis of the evolved gas, and SEM/EDS. The addition of calcite to the fly ash improved the compressive strength of the geopolymers, especially during the early age of curing. For 7 d aged geopolymers based on the 90% fly ash + 10% calcite blend, the strength was 8.0-, 3.5- and 2.9-fold higher than that for the geopolymers based on the unblended fly ash for 30 s, 180 s and 400 s mechanical activation time, respectively. Using Mössbauer spectroscopy, it was revealed that iron present in the fly ash did not play a significant part in the geopolymerization process. The dominant reaction product was sodium containing aluminosilicate hydrogel (N-A-S-H gel). Calcite was found to transform, to a small extent, to vaterite and Ca(OH)2 in the course of the geopolymerization. Full article
(This article belongs to the Special Issue Alkali Activated Materials: Advances, Innovations, Future Trends)
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Open AccessFeature PaperArticle
Environmental Assessment of Trace Metals in San Simon Bay Sediments (NW Iberian Peninsula)
Minerals 2020, 10(9), 826; https://doi.org/10.3390/min10090826 - 19 Sep 2020
Cited by 1 | Viewed by 926
Abstract
A gravity core (220 cm depth) was collected to investigate the geochemistry, enrichment, and pollution of trace metals in anoxic sediments from San Simon Bay, an ecosystem of high biological productivity in the northwest of Spain. A five-step sequential extraction procedure was used. [...] Read more.
A gravity core (220 cm depth) was collected to investigate the geochemistry, enrichment, and pollution of trace metals in anoxic sediments from San Simon Bay, an ecosystem of high biological productivity in the northwest of Spain. A five-step sequential extraction procedure was used. The Cu, Pb, and Zn contents decreased with depth, with maximum values in the top layers. Ni and Zn were bound to pyrite fractions, while Cd and Pb were associated with the most mobile fractions. The analyzed metals were associated with the fractions bound to organic matter, mainly with the strongly bound to organic matter fraction. High Cd and Cu values were observed. The fractionation showed a high mobility for Cd (28.3–100%) and Pb (54.0–70.2%). Moreover, the pollution factor and the geoaccumulation index reflected a high contamination for Pb and a moderate contamination for Cu and Zn in the superficial layers, pointing to a possible ecotoxicological risk to organisms in San Simon Bay. Full article
(This article belongs to the Special Issue Elemental Concentration and Pollution in Soil, Water, and Sediment)
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Open AccessArticle
KIMERA: A Kinetic Montecarlo Code for Mineral Dissolution
Minerals 2020, 10(9), 825; https://doi.org/10.3390/min10090825 - 18 Sep 2020
Cited by 2 | Viewed by 855
Abstract
KIMERA is a scientific tool for the study of mineral dissolution. It implements a reversible Kinetic Monte Carlo (KMC) method to study the time evolution of a dissolving system, obtaining the dissolution rate and information about the atomic scale dissolution mechanisms. KIMERA allows [...] Read more.
KIMERA is a scientific tool for the study of mineral dissolution. It implements a reversible Kinetic Monte Carlo (KMC) method to study the time evolution of a dissolving system, obtaining the dissolution rate and information about the atomic scale dissolution mechanisms. KIMERA allows to define the dissolution process in multiple ways, using a wide diversity of event types to mimic the dissolution reactions, and define the mineral structure in great detail, including topographic defects, dislocations, and point defects. Therefore, KIMERA ensures to perform numerous studies with great versatility. In addition, it offers a good performance thanks to its parallelization and efficient algorithms within the KMC method. In this manuscript, we present the code features and show some examples of its capabilities. KIMERA is controllable via user commands, it is written in object-oriented C++, and it is distributed as open-source software. Full article
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Open AccessArticle
Application of Evolved Gas Analysis Technique for Speciation of Minor Minerals in Clays
Minerals 2020, 10(9), 824; https://doi.org/10.3390/min10090824 - 18 Sep 2020
Viewed by 594
Abstract
Mineralogical characterization of clays used in manufacturing of traditional ceramic products is critical for guarantee the quality of the final product, but also for assessing the environmental impact of the industrial process in terms of atmospheric emissions. In fact, the presence of impurities [...] Read more.
Mineralogical characterization of clays used in manufacturing of traditional ceramic products is critical for guarantee the quality of the final product, but also for assessing the environmental impact of the industrial process in terms of atmospheric emissions. In fact, the presence of impurities even in low-level concentrations can have a big impact. So, it is very important to carry out an accurate mineral quantification of those minerals which are related to carbon dioxide and acid emissions (hydrogen fluoride, hydrogen chloride or sulfur dioxide). The development of hyphenated techniques coupling thermal analysis equipment with mass spectrometry and Fourier-transform infrared spectroscopy provides more valuable information and lower limit quantification than other primary techniques, such as X-ray diffraction or infrared spectroscopy. The main objective of this work is to develop an analytical procedure using evolved gas analysis to identify and quantify minerals such as chlorides, sulfides, carbonaceous materials and minor clay minerals. In addition to this, the study includes the analysis of acid emissions during the ceramic firing treatment even if they are present at low quantitative levels. This methodology was applied to reference materials so that it allows the identification of sulfur, chlorine, fluorine and carbonaceous compounds in concentrations lower than 1%. Full article
(This article belongs to the Collection Clays and Other Industrial Mineral Materials)
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Open AccessArticle
The Ultramicrochemical Analyses (UMCA) of Fluid Inclusions in Halite and Experimental Research to Improve the Accuracy of Measurement
Minerals 2020, 10(9), 823; https://doi.org/10.3390/min10090823 - 17 Sep 2020
Cited by 1 | Viewed by 610
Abstract
Fluid inclusions in halite are widely used in research to determine the conditions of sedimentation in salt basins and reconstruct the chemical composition of seawater during a specific geological period. However, previous preliminary studies of the genetic types of inclusions, considered in the [...] Read more.
Fluid inclusions in halite are widely used in research to determine the conditions of sedimentation in salt basins and reconstruct the chemical composition of seawater during a specific geological period. However, previous preliminary studies of the genetic types of inclusions, considered in the present research project, have not received due attention. Consequently, we decided to take into account the main distinguishing features of fluid inclusions in halite, belonging to various genetic types. The ultramicrochemical analysis (UMCA) method is one of the several methods that are used for the quantitative determination of the chemical composition of the primary fluid inclusions in halite. We have upgraded that technique, and that allowed us to reduce the analytical error rates of each component determination. The error rates were calculated in the study of Ca-rich and SO4-rich types of natural sedimentary brines. Full article
(This article belongs to the Special Issue Mineralogy, Petrology and Geochemistry of Evaporites)
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Open AccessArticle
Ultrahigh-Temperature Sphalerite from Zn-Cd-Se-Rich Combustion Metamorphic Marbles, Daba Complex, Central Jordan: Paragenesis, Chemistry, and Structure
Minerals 2020, 10(9), 822; https://doi.org/10.3390/min10090822 - 17 Sep 2020
Cited by 1 | Viewed by 697
Abstract
Minerals of the Zn-Cd-S-Se system that formed by moderately reduced ~800–850 °C combustion metamorphic (CM) alteration of marly sediments were found in marbles from central Jordan. Their precursor sediments contain Se- and Ni-enriched authigenic pyrite and ZnS modifications with high Cd enrichment (up [...] Read more.
Minerals of the Zn-Cd-S-Se system that formed by moderately reduced ~800–850 °C combustion metamorphic (CM) alteration of marly sediments were found in marbles from central Jordan. Their precursor sediments contain Se- and Ni-enriched authigenic pyrite and ZnS modifications with high Cd enrichment (up to ~10 wt%) and elevated concentrations of Cu, Sb, Ag, Mo, and Pb. The marbles are composed of calcite, carbonate-fluorapatite, spurrite, and brownmillerite and characterized by high P, Zn, Cd, U, and elevated Se, Ni, V, and Mo contents. Main accessories are either Zn-bearing oxides or sphalerite, greenockite, and Ca-Fe-Ni-Cu-O-S-Se oxychalcogenides. CM alteration lead to compositional homogenization of metamorphic sphalerite, for which trace-element suites become less diverse than in the authigenic ZnS. The CM sphalerites contain up to ~14 wt% Cd and ~6.7 wt% Se but are poor in Fe (means 1.4–2.2 wt%), and bear 100–250 ppm Co, Ni, and Hg. Sphalerite (Zn,Cd,Fe)(S,O,Se)cub is a homogeneous solid solution with a unit cell smaller than in ZnScub as a result of S2− → O2− substitution (a = 5.40852(12) Å, V = 158.211(6) Å3). The amount of lattice-bound oxygen in the CM sphalerite is within the range for synthetic ZnS1−xOx crystals (0 < x ≤ 0.05) growing at 900 °C. Full article
(This article belongs to the Special Issue Mineral Formation in Pyrometamorphic Process)
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Open AccessArticle
Alteration of Granitoids and Uranium Mineralization in the Blatná Suite of the Central Bohemian Plutonic Complex, Czech Republic
Minerals 2020, 10(9), 821; https://doi.org/10.3390/min10090821 - 17 Sep 2020
Viewed by 522
Abstract
The Bohemian magmatic complex belongs to granitoid plutons of the Central European Variscides. Hydrothermal uranium mineralization evolved in the small uranium deposits Nahošín and Mečichov is associated with N–S shear zones occurring on the SW margin of the Central Bohemian plutonic complex formed [...] Read more.
The Bohemian magmatic complex belongs to granitoid plutons of the Central European Variscides. Hydrothermal uranium mineralization evolved in the small uranium deposits Nahošín and Mečichov is associated with N–S shear zones occurring on the SW margin of the Central Bohemian plutonic complex formed by amphibole-bearing biotite granodiorites of the Blatná suite. The purpose of presented study is description of uranium mineralization bounded on brittle shear zones, which is coupled with intense low-temperature hydrothermal alteration of granitic rocks. Uranium mineralization, formed predominantly of coffinite, rare uraninite, and thorite, is accompanied by intense hematitization, albitization, chloritization, and carbonatization of original granitic rocks that could be described as aceites. These alterations are accompanied by the enrichment in U, Ti, Mg, Ca, Na, K, Y, and Zr and depletion in Si, Ba, and Sr. The analyzed coffinite is enriched in Y (up to 3.1 wt % Y2O3). Uraninite is enriched in Th (up to 9.8 wt % ThO2) and thorite is enriched in Zr (up to 5.7 wt % ZrO2). The REE-elements are concentrated in the REE-fluorcarbonate synchysite-(Ce). Full article
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Open AccessArticle
Optimizing the Crystalline State of Cu Slag by Na2CO3 to Improve Cu Recovery by Flotation
Minerals 2020, 10(9), 820; https://doi.org/10.3390/min10090820 - 17 Sep 2020
Viewed by 538
Abstract
Cu is the most important component in Cu slag, which is usually recovered by flotation. However, the crystalline state of Cu slag is not conducive to flotation, which limits the recovery of Cu. This study investigated the effect of Na2CO3 [...] Read more.
Cu is the most important component in Cu slag, which is usually recovered by flotation. However, the crystalline state of Cu slag is not conducive to flotation, which limits the recovery of Cu. This study investigated the effect of Na2CO3 on the crystalline state of Cu slag and the recovery of Cu by flotation. The mechanism was investigated by thermodynamic, viscosity, X-ray diffraction (XRD) analyses and scanning electron microscopy (SEM). The results of thermodynamic, viscosity and XRD analysis demonstrate that Na2CO3 is beneficial for the transformation of fayalite to low-melting point materials, such as Na2SiO3, Na4SiO4 and NaFeSi3O6, thereby reducing the viscosity of Cu slag. Moreover, SEM results indicate that the addition of Na2CO3 during the melting modification process can promote the aggregation of Cu-bearing minerals and simplify its intercalation relationship with gangue minerals. The flotation results verify the above conclusions that at 10% Na2CO3, the Cu flotation recovery index is the best. Compared with that without Na2CO3, the use of Na2CO3 has resulted in increased Cu grade and recovery by 3.544% and 28.94%, respectively. Full article
(This article belongs to the Section Mineral Processing and Extractive Metallurgy)
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Open AccessArticle
The Use of Tailings to Make Glass as an Alternative for Sustainable Environmental Remediation: The Case of Osor, Catalonia, Spain
Minerals 2020, 10(9), 819; https://doi.org/10.3390/min10090819 - 16 Sep 2020
Cited by 2 | Viewed by 557
Abstract
Tailings from the Osor fluorite mines release large amounts of potentially toxic elements into the environment. This work is a proposal to remove these waste materials and use them as a raw material in the manufacture of glass. The chemical composition of the [...] Read more.
Tailings from the Osor fluorite mines release large amounts of potentially toxic elements into the environment. This work is a proposal to remove these waste materials and use them as a raw material in the manufacture of glass. The chemical composition of the tailings was determined by X-ray fluorescence and the mineralogy by X-ray diffraction. Waste materials have SiO2, Al2O3 and CaO contents suitable for a glass production, but Na as NaCO3 has to be added. Two glass formulations, with 80–90% of the residue and 10–20% Na2CO3, have been produced. The crystallization temperatures, obtained by differential thermal analysis, were 875 and 901 °C, and the melting temperatures were 1220 and 1215 °C for the G80-20 and G90-10 glasses, respectively. The transition temperatures of glass were 637 and 628 °C. The crystalline phases formed in the thermal treatment to produce devitrification were nepheline, plagioclase and diopside in the G80-20 glass, and plagioclase and akermanite-gehlenite in the G90-10 glass. The temperatures for the fixed viscosity points, the working temperatures and the coefficient of expansion were obtained. The chemical stability of the glass was tested and results indicate that the potentially toxic elements of the tailings were incorporated into the glass structure. Full article
(This article belongs to the Special Issue Industrial Minerals)
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Open AccessFeature PaperArticle
Biogenic Fe(II-III) Hydroxycarbonate Green Rust Enhances Nitrate Removal and Decreases Ammonium Selectivity during Heterotrophic Denitrification
Minerals 2020, 10(9), 818; https://doi.org/10.3390/min10090818 - 16 Sep 2020
Viewed by 567
Abstract
Nitrification-denitrification is the most widely used nitrogen removal process in wastewater treatment. However, this process can lead to undesirable nitrite accumulation and subsequent ammonium production. Biogenic Fe(II-III) hydroxycarbonate green rust has recently emerged as a candidate to reduce nitrite without ammonium production under [...] Read more.
Nitrification-denitrification is the most widely used nitrogen removal process in wastewater treatment. However, this process can lead to undesirable nitrite accumulation and subsequent ammonium production. Biogenic Fe(II-III) hydroxycarbonate green rust has recently emerged as a candidate to reduce nitrite without ammonium production under abiotic conditions. The present study investigated whether biogenic iron(II-III) hydroxycarbonate green rust could also reduce nitrite to gaseous nitrogen during bacterial nitrate reduction. Our results showed that biogenic iron(II-III) hydroxycarbonate green rust could efficiently decrease the selectivity of the reaction towards ammonium during heterotrophic nitrate reduction by native wastewater-denitrifying bacteria and by three different species of Shewanella: S. putrefaciens ATCC 12099, S. putrefaciens ATCC 8071 and S. oneidensis MR-1. Indeed, in the absence of biogenic hydroxycarbonate green rust, bacterial reduction of nitrate converted 11–42% of the initial nitrate into ammonium, but this value dropped to 1–28% in the presence of biogenic hydroxycarbonate green rust. Additionally, nitrite accumulation did not exceed the 2–13% in the presence of biogenic hydroxycarbonate green rust, versus 0–28% in its absence. Based on those results that enhance the extent of denitrification of about 60%, the study proposes a water treatment process that couples the bacterial nitrite production with the abiotic nitrite reduction by biogenic green rust. Full article
(This article belongs to the Special Issue Redox Reactivity of Iron Minerals in the Geosphere)
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Open AccessArticle
Potential Benefits in Copper Sulphides Liberation through Application of HRC Device in Ore Comminution Circuits
Minerals 2020, 10(9), 817; https://doi.org/10.3390/min10090817 - 16 Sep 2020
Cited by 1 | Viewed by 456
Abstract
The article presents results of investigations on a high-pressure comminution process carried out in the roller press device, aiming at potential improvement of effectiveness of downstream beneficiation operations. The major point of interest of the paper concerned an assessment of the useful mineral [...] Read more.
The article presents results of investigations on a high-pressure comminution process carried out in the roller press device, aiming at potential improvement of effectiveness of downstream beneficiation operations. The major point of interest of the paper concerned an assessment of the useful mineral liberation in relation to the volume of operating pressing force in the press device. Obtained results of mineral liberation were compared to flotation effects and downstream grinding process in a ball mill. Environmental influence in terms of dust emission was also analysed. The feed material was crushed in the high-pressure roller crusher (HRC) device under four different values of pressing force (Fsp): 3.0, 3.5, 4.0 and 4.5 N/mm2. Each product then underwent the liberation analysis, together with determination the energy savings through calculation of Bond’s working index, flotation recoveries and grinding kinetics. Results of investigations showed that both the most favourable crushing results and mineral liberation level were achieved for the highest values of operational pressing force. Nevertheless, the observed effects were less than linear together with further increasing of Fsp in HRC device. However, the obtained results of investigation unambiguously showed that pressing force affects the obtained crushing results: comminution degrees and flotation recoveries were higher while the duration of downstream grinding operation and grinding energy consumption were lower. Full article
(This article belongs to the Special Issue Mineral Liberation)
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Open AccessArticle
Geochemical Constraints on Mantle Melting and Magma Genesis at Pohnpei Island, Micronesia
Minerals 2020, 10(9), 816; https://doi.org/10.3390/min10090816 - 16 Sep 2020
Viewed by 433
Abstract
The lithospheric mantle is of paramount importance in controlling the chemical composition of ocean island basalts (OIBs), influencing partial melting and magma evolution processes. To improve the understanding of these processes, the pressure–temperature conditions of mantle melting were investigated, and liquid lines of [...] Read more.
The lithospheric mantle is of paramount importance in controlling the chemical composition of ocean island basalts (OIBs), influencing partial melting and magma evolution processes. To improve the understanding of these processes, the pressure–temperature conditions of mantle melting were investigated, and liquid lines of descent were modelled for OIBs on Pohnpei Island. The studied basaltic samples are alkalic, and can be classified as SiO2-undersaturated or SiO2-saturated series rocks, with the former having higher TiO2 and FeOT contents but with no distinct trace-element composition, suggesting melting of a compositionally homogenous mantle source at varying depths. Both series underwent sequential crystallization of olivine, clinopyroxene, Fe–Ti oxides, and minor plagioclase and alkali feldspar. Early magnetite crystallization resulted from initially high FeOT contents and oxygen fugacity, and late feldspar crystallization was due to initially low Al2O3 contents and alkali enrichment of the evolved magma. The Pohnpei lavas formed at estimated mantle-melting temperatures of 1486–1626 °C (average 1557 ± 43 °C, 1σ), and pressures of 2.9–5.1 GPa (average 3.8 ± 0.7 GPa), with the SiO2-undersaturated series forming at higher melting temperatures and pressures. Trace-element compositions further suggest that garnet rather than spinel was a residual phase in the mantle source during the melting process. Compared with the Hawaiian and Louisville seamount chains, Pohnpei Island underwent much lower degrees of mantle melting at greater depth, possibly due to a thicker lithosphere. Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Open AccessArticle
The Effect of Carbon Defects in the Coal–Pyrite Vacancy on the Electronic Structure and Optical Properties: A DFT + U Study
Minerals 2020, 10(9), 815; https://doi.org/10.3390/min10090815 - 15 Sep 2020
Viewed by 524
Abstract
Pyrite is a mineral often associated with coal in coal seams and is a major source of sulfur in coal. Coal–pyrite is widely distributed, easily available, low-cost, and non-toxic, and has high light absorption coefficient. So, it shows potential for various applications. In [...] Read more.
Pyrite is a mineral often associated with coal in coal seams and is a major source of sulfur in coal. Coal–pyrite is widely distributed, easily available, low-cost, and non-toxic, and has high light absorption coefficient. So, it shows potential for various applications. In this paper, the density-functional theory (DFT + U) is used to construct coal–pyrite with carbon doped in the sulfur and iron vacancies of pyrite. The effects of different carbon defects, different carbon doping concentrations, and different doping distributions in the same concentration on the electronic structure and optical properties of coal–pyrite were studied. The results show that the absorption coefficient and reflectivity of coal–pyrite, when its carbon atom substitutes the iron and sulfur atoms in the sulfur and iron vacancies, are significantly higher than those of the perfect pyrite, indicating that coal–pyrite has potential for application in the field of photovoltaic materials. When carbon is doped in the sulfur vacancy, this impurity state reduces the width of the forbidden band; with the increase in the doping concentration, the width of the forbidden band decreases and the visible-light absorption coefficient increases. The distribution of carbon impurities impacts the band gap but has almost no effect on the light absorption coefficient, complex dielectric function, and reflectivity, indicating that the application of coal–pyrite to photovoltaic materials should mainly consider the carbon doping concentration instead of the distribution of carbon impurities. The research results provide a theoretical reference for the application of coal–pyrite in the field of photoelectric materials. Full article
(This article belongs to the Special Issue First Principles Calculations of Minerals and Related Materials)
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Open AccessArticle
Metal Mobility in a Mine-Affected Floodplain
Minerals 2020, 10(9), 814; https://doi.org/10.3390/min10090814 - 15 Sep 2020
Viewed by 504
Abstract
The study attempted to map and predict the remobilization of metals in a floodplain which had been heavily affected by long-term Zn–Pb mining. This research, based on Zn, Cd, Pb, Ca and Fe speciation, mineralogy and the stratigraphy of sediments which had accumulated [...] Read more.
The study attempted to map and predict the remobilization of metals in a floodplain which had been heavily affected by long-term Zn–Pb mining. This research, based on Zn, Cd, Pb, Ca and Fe speciation, mineralogy and the stratigraphy of sediments which had accumulated over the distance of a dozen or so km from the mine, revealed variable potential for metal mobilization. The results suggest that a drop in the water table, something to be expected after the closure of a mine, would be accompanied by a decrease in the pH of the river water and can induce the remobilization of metals associated with carbonates and exchangeable cations over the short-reach downstream of the mine. However, the mobilization of contaminants may be impeded by the alkaline, impermeable stratum of loams, which play a pivotal role in maintaining anaerobic conditions and buffering the acidity resulting from the partial degradation of sulfides. Based on the findings of the study, it can be expected that the intrinsic attenuation will limit the need for remediation works, although monitoring river water quality is recommended to determine the need for any intervention in cases where permissible quality values have been exceeded over a longer period. Results of this research can be useful as a reference for remediation works planned in other contaminated river systems experiencing water table lowering, where the mobilization of contaminants as a consequence of sediment oxidization can be expected. Full article
(This article belongs to the Section Environmental Mineralogy and Biogeochemistry)
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Open AccessArticle
Geochemistry of Recent Brahmaputra River Sediments: Provenance, Tectonics, Source Area Weathering and Depositional Environment
Minerals 2020, 10(9), 813; https://doi.org/10.3390/min10090813 - 15 Sep 2020
Viewed by 822
Abstract
Sediments from stable sand bars along a 40 km section of the Brahmaputra River in northern Bangladesh were analyzed for their major, trace and rare earth element contents to determine their provenance, compositional maturity, source area weathering and tectonic setting. Geochemically, the sediments [...] Read more.
Sediments from stable sand bars along a 40 km section of the Brahmaputra River in northern Bangladesh were analyzed for their major, trace and rare earth element contents to determine their provenance, compositional maturity, source area weathering and tectonic setting. Geochemically, the sediments were classified as litharenites and the Index of Compositional Variability (ICV) varied between 1.4 and 2.0, indicating low compositional and mineralogical maturity. A high mean SiO2 concentration (72.9 wt.%) and low Al2O3 (11.1 wt.%) were consistent with a low abundance of shale and clay components. The depletion of the oxide components Na2O, CaO and K2O relative to average upper crustal compositions (UCC) reflected loss of feldspar during chemical weathering in the source region. Average TiO2 values for most samples were higher than average crustal levels, consistent with the northern section of the Brahmaputra River being a potential resource for valuable Fe-Ti oxide heavy minerals. Major and trace element ratios indicated the sediments represented erosional products from typical felsic upper continental crustal materials with contamination (30%–40%) from more intermediate/mafic compositions. The rare earth element patterns showed negative Eu anomalies (0.57–0.71), indicating they were derived mainly from fractionated felsic rocks. Resemblance of the sediment compositions to mean compositions from Higher Himalaya crystalline rocks pointed to these being potential source rocks but with components from a mafic source also present. Major element chemistries and low to intermediate weathering indices for all sediments indicated a lack of substantial chemical weathering. Evidence from tectonic discrimination diagrams suggested the Brahmaputra River sediments were derived from rock types that formed in a transitional tectonic setting ranging from an ancient passive margin to an active continental margin. Deposition occurred under cool to semi-arid climatic conditions in an oxic environment. Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Open AccessArticle
Recrystallization and Uptake of 226Ra into Ba-Rich (Ba,Sr)SO4 Solid Solutions
Minerals 2020, 10(9), 812; https://doi.org/10.3390/min10090812 - 15 Sep 2020
Viewed by 601
Abstract
226Ra is an important contributor to naturally occurring radioactive materials (NORM) and also considered in safety cases related to the disposal of spent nuclear fuel in a deep geological repository. Recrystallization and solid solution formation with sulfates is regarded as an important [...] Read more.
226Ra is an important contributor to naturally occurring radioactive materials (NORM) and also considered in safety cases related to the disposal of spent nuclear fuel in a deep geological repository. Recrystallization and solid solution formation with sulfates is regarded as an important retention mechanism for 226Ra. In natural systems sulfates often occur as (Ba,Sr)SO4. Therefore, we have chosen this solid solution at the Ba-rich end for investigations of the 226Ra uptake. The resulting 226Ra-solubility in aqueous solution was assessed in comparison with a thermodynamic model of the solid solution-aqueous solution system (Ba,Sr,Ra)SO4 + H2O. The temperature and composition of the initial (Ba,Sr)SO4 solid solution were varied. Measurements of the solution composition were combined with microscopic observations of the solid and thermodynamic modeling. A complex recrystallization behavior of the solid was observed, including the dissolution of significant amounts of the solid and formation of metastable phases. The re-equilibration of Ba-rich (Ba,Sr)SO4 to (Ba,Sr,Ra)SO4 leads to a major reconstruction of the solid. Already trace amounts of Sr in the solid solution can have a significant impact on the 226Ra solubility, depending on the temperature. The experimental findings confirm the thermodynamic model, although not all solids reached equilibrium with respect to all cations. Full article
(This article belongs to the Special Issue Formation of Sulfate Minerals in Natural and Industrial Environments)
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Open AccessArticle
Analysis and Prediction of the Thiourea Gold Leaching Process Using Grey Relational Analysis and Artificial Neural Networks
Minerals 2020, 10(9), 811; https://doi.org/10.3390/min10090811 - 15 Sep 2020
Viewed by 498
Abstract
The thiourea (TU) leaching of gold from refractory ores can be considered an alternative to cyanidation. However, the high reagent consumption causes an increase in cost, which seriously limits its use. In order to effectively reduce the TU consumption, it is necessary to [...] Read more.
The thiourea (TU) leaching of gold from refractory ores can be considered an alternative to cyanidation. However, the high reagent consumption causes an increase in cost, which seriously limits its use. In order to effectively reduce the TU consumption, it is necessary to analyze the influencing parameters of gold recovery and TU consumption and apply them to the prediction of the TU leaching process. This paper investigated six potential influencing parameters and used grey relational analysis (GRA) to analyze the relational degree between each parameter and gold recovery and TU consumption. Then, the artificial neural network (ANN) model was established to simultaneously predict the gold recovery and TU consumption in the TU gold leaching process. The results of the GRA indicated that the leaching time, initial pH, temperature, TU dosage, stirring speed, and ferric iron concentration were all well related to the gold recovery and TU consumption. Therefore, the incorporation of these parameters can significantly improve the ANN model validation. The predictive results noted that the prediction accuracy of gold recovery varied from 94.46% to 98.06%, and the TU consumption varied from 95.15% to 99.20%. Thus, the predicted values corresponded closely to the experimental results, which suggested that the ANN model can accurately reflect the relationship between the operational conditions and the gold recovery and TU consumption. This prediction method can be used as an auxiliary decision-making tool in the TU gold leaching process, and it has broad engineering application prospects in engineering. Full article
(This article belongs to the Section Mineral Processing and Extractive Metallurgy)
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Open AccessArticle
Effect of MgO and K2O on High-Al Silicon–Manganese Alloy Slag Viscosity and Structure
Minerals 2020, 10(9), 810; https://doi.org/10.3390/min10090810 - 14 Sep 2020
Cited by 3 | Viewed by 770
Abstract
The viscosity, melting proprieties, and molten structure of the high-Al silicon–manganese slag of SiO2–CaO–25 mass% Al2O3–MgO–MnO–K2O system with a varying MgO and K2O content were studied. The results show that with the increase [...] Read more.
The viscosity, melting proprieties, and molten structure of the high-Al silicon–manganese slag of SiO2–CaO–25 mass% Al2O3–MgO–MnO–K2O system with a varying MgO and K2O content were studied. The results show that with the increase in MgO content from 4 to 10 mass%, the measured viscosity and flow activation energy decreases, but K2O has an effect on increasing those of slags. However, the melting temperature increases due to the formation of high-melting-point phase spinel. Meanwhile, Fourier transform infrared (FTIR) and X-ray photoelectron spectra (XPS) were conducted to understand the variation of slag structure. The O2− dissociates from MgO can interact with the O0 within Si–O or Al–O network structures, corresponding to the decrease in the trough depth of [SiO4] tetrahedral and [AlO4] tetrahedral. However, when K2O is added into the molten slag, the K+ can accelerate the formation of [AlO4] tetrahedra, resulting in the increase in O0 and O and the polymerization of the structure. Full article
(This article belongs to the Special Issue Ferroalloy Minerals Processing and Technology)
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Open AccessArticle
Automated Identification of Mineral Types and Grain Size Using Hyperspectral Imaging and Deep Learning for Mineral Processing
Minerals 2020, 10(9), 809; https://doi.org/10.3390/min10090809 - 13 Sep 2020
Cited by 1 | Viewed by 947
Abstract
In mining operations, an ore is separated into its constituents through mineral processing methods, such as flotation. Identifying the type of minerals contained in the ore in advance aids greatly in performing faster and more efficient mineral processing. The human eye can recognize [...] Read more.
In mining operations, an ore is separated into its constituents through mineral processing methods, such as flotation. Identifying the type of minerals contained in the ore in advance aids greatly in performing faster and more efficient mineral processing. The human eye can recognize visual information in three wavelength regions: red, green, and blue. With hyperspectral imaging, high resolution spectral data that contains information from the visible light wavelength region to the near infrared region can be obtained. Using deep learning, the features of the hyperspectral data can be extracted and learned, and the spectral pattern that is unique to each mineral can be identified and analyzed. In this paper, we propose an automatic mineral identification system that can identify mineral types before the mineral processing stage by combining hyperspectral imaging and deep learning. By using this technique, it is possible to quickly identify the types of minerals contained in rocks using a non-destructive method. As a result of experimentation, the identification accuracy of the minerals that underwent deep learning on the red, green, and blue (RGB) image of the mineral was approximately 30%, while the result of the hyperspectral data analysis using deep learning identified the mineral species with a high accuracy of over 90%. Full article
(This article belongs to the Special Issue Novel Advanced Machine Learning Methods in Mineral Processing)
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Open AccessArticle
Microstructure and Pb2+ Adsorption Properties of Blast Furnace Slag and Fly Ash based Geopolymers
Minerals 2020, 10(9), 808; https://doi.org/10.3390/min10090808 - 13 Sep 2020
Cited by 1 | Viewed by 585
Abstract
In this study, a blast furnace slag (BFS) and fly ash (FA) based adsorbent geopolymer to be used for removing Pb2+ from aqueous solutions were synthesized using the hydrothermal method at 60 °C for 24 h, and then cured at 25 °C [...] Read more.
In this study, a blast furnace slag (BFS) and fly ash (FA) based adsorbent geopolymer to be used for removing Pb2+ from aqueous solutions were synthesized using the hydrothermal method at 60 °C for 24 h, and then cured at 25 °C for another six days. The alkali activator applied in this work was a combination of sodium hydroxide and sodium silicate solutions at a mass ratio of 2. The geopolymer slurry was adjusted to a Si/Al molar ratio of 3. A BFS-based geopolymer (GS) having a specific area of 23.56 m2/g and pore size and volume of 7.8 nm and 73 cm3/kg, respectively, surpassed the raw material surface by approximately 13-fold. An FA-based geopolymer (GA) having a specific area of 35.97 m2/g and a size and porous volume of 9 nm and 124 nm, respectively, surpassed the raw material surface by approximately 23-fold. In addition, GS and GA showed a cation exchange capacity (CEC) of 241.30 and 286.96 Meq/100 g, respectively. X-ray diffraction (XRD) determined sample crystallinity and it was proven by scanning electron microscopy (SEM), showing that both geopolymers were constituted of unreacted particles surrounded by amorphous and semi-amorphous products. Through Fourier transform infrared spectroscopy (FTIR), a band that was assigned to the asymmetric stretching vibration of Si-O-M (M = Na+ and/or Ca2+) non-bridging oxygen type was observed, which suggested that Na and Ca could serve as exchangeable ions in the ionic exchange process. Adsorption test data indicated that good adsorption was obtained when a neutral pH was used at room temperature, and the adsorption isotherm showed that GA had more adsorption sites than GS, which meant greater maximum adsorption capacity. Full article
(This article belongs to the Special Issue Alkali Activated Materials: Advances, Innovations, Future Trends)
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Open AccessArticle
Monte Carlo SEM-EDS Nano-Microanalysis Strategy of Historical Mineral Pigments: The Simulation of the Egyptian Blue from Pompeii (Italy) as an Example
Minerals 2020, 10(9), 807; https://doi.org/10.3390/min10090807 - 13 Sep 2020
Cited by 1 | Viewed by 563
Abstract
A correct determination of the mineral and chemical composition of specimens is of the utmost importance to answer questions regarding the Cultural Heritage field. Because of the preciousness and often very low quantity of sample available, with textures and sizes in the nano-to-micrometric [...] Read more.
A correct determination of the mineral and chemical composition of specimens is of the utmost importance to answer questions regarding the Cultural Heritage field. Because of the preciousness and often very low quantity of sample available, with textures and sizes in the nano-to-micrometric range, scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDS) is one of the most suited and exploited nano-microanalytical techniques. In these cases, to avoid severe mistakes and quantification errors in SEM-EDS, it is mandatory to consider several effects related to the transport of electrons and X-rays in the material, which in turn are dependent on the SEM-EDS setup. In the present work, a Monte Carlo SEM-EDS nano-microanalytical simulation strategy is proposed and applied to a practical selected case. The Egyptian blue mineral pigment, which is found in Pompeian murals, is used here as an example and model system to show the effects of real size variations (0.1–10 µm), basic geometrical shapes of the pigment (prismatic and spherical) and typical SEM setups, sample holders and substrates. The simulations showed a great—sometimes not intuitive—dependence of the X-ray intensity on the thickness and shape of the samples and SEM-EDS parameters, thereby influencing the analysis and quantification. The critical overview of the results allowed the determination of the correct procedure and technical SEM-EDS parameters and indicated how to apply the Monte Carlo simulation strategy to other Cultural Heritage cases. Full article
(This article belongs to the Special Issue Historical Mineral Pigments)
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