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Minerals, Volume 8, Issue 2 (February 2018)

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Cover Story (view full-size image) We show that the Fe-Mn-Cu ore deposit of Jbel Rhals (Morocco) has a polyphased metallogenic [...] Read more.
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Open AccessArticle Rare Earth Element Phases in Bauxite Residue
Minerals 2018, 8(2), 77; https://doi.org/10.3390/min8020077
Received: 30 January 2018 / Revised: 13 February 2018 / Accepted: 15 February 2018 / Published: 24 February 2018
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Abstract
The purpose of present work was to provide mineralogical insight into the rare earth element (REE) phases in bauxite residue to improve REE recovering technologies. Experimental work was performed by electron probe microanalysis with energy dispersive as well as wavelength dispersive spectroscopy and
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The purpose of present work was to provide mineralogical insight into the rare earth element (REE) phases in bauxite residue to improve REE recovering technologies. Experimental work was performed by electron probe microanalysis with energy dispersive as well as wavelength dispersive spectroscopy and transmission electron microscopy. REEs are found as discrete mineral particles in bauxite residue. Their sizes range from <1 μm to about 40 μm. In bauxite residue, the most abundant REE bearing phases are light REE (LREE) ferrotitanates that form a solid solution between the phases with major compositions (REE,Ca,Na)(Ti,Fe)O3 and (Ca,Na)(Ti,Fe)O3. These are secondary phases formed during the Bayer process by an in-situ transformation of the precursor bauxite LREE phases. Compared to natural systems, the indicated solid solution resembles loparite-perovskite series. LREE particles often have a calcium ferrotitanate shell surrounding them that probably hinders their solubility. Minor amount of LREE carbonate and phosphate minerals as well as manganese-associated LREE phases are also present in bauxite residue. Heavy REEs occur in the same form as in bauxites, namely as yttrium phosphates. These results show that the Bayer process has an impact on the initial REE mineralogy contained in bauxite. Bauxite residue as well as selected bauxites are potentially good sources of REEs. Full article
(This article belongs to the Special Issue Bauxite Deposits)
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Open AccessArticle Effect of Dissolved Silica on Immobilization of Boron by Magnesium Oxide
Minerals 2018, 8(2), 76; https://doi.org/10.3390/min8020076
Received: 1 February 2018 / Revised: 16 February 2018 / Accepted: 22 February 2018 / Published: 24 February 2018
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Abstract
The effect of silica on the immobilization reaction of boron by magnesium oxide was investigated by laboratory experiments. In the absence of silica, due to dissolution of the magnesium oxide, boron was removed from solutions by the precipitation of multiple magnesium borates. In
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The effect of silica on the immobilization reaction of boron by magnesium oxide was investigated by laboratory experiments. In the absence of silica, due to dissolution of the magnesium oxide, boron was removed from solutions by the precipitation of multiple magnesium borates. In the presence of silica, magnesium silica hydrate (M-S-H) was formed as a secondary mineral, which takes up boron. Here 11B magic-angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared spectrometer (FT-IR) data show that a part of the boron would be incorporated into M-S-H structures by isomorphic substitution of silicon. Another experiment where magnesium oxide and amorphous silica were reacted beforehand and boron was added later showed that the shorter the reaction time of the preceding reaction, the higher the sorption ratio of boron. That is, boron was incorporated into the M-S-H mainly by coprecipitation. The experiments in the study here show that the sorption of boron in the presence of silica is mainly due to the incorporation of boron during the formation of the M-S-H structure, which suggests that boron would not readily leach out, and that stable immobilization of boron can be expected. Full article
(This article belongs to the Special Issue Environmental Mineralogy)
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Open AccessArticle Structural Transition of Inorganic Silica–Carbonate Composites Towards Curved Lifelike Morphologies
Minerals 2018, 8(2), 75; https://doi.org/10.3390/min8020075
Received: 2 February 2018 / Revised: 14 February 2018 / Accepted: 16 February 2018 / Published: 18 February 2018
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Abstract
The self-assembly of alkaline earth carbonates in the presence of silica at high pH leads to a unique class of composite materials displaying a broad variety of self-assembled superstructures with complex morphologies. A detailed understanding of the formation process of these purely inorganic
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The self-assembly of alkaline earth carbonates in the presence of silica at high pH leads to a unique class of composite materials displaying a broad variety of self-assembled superstructures with complex morphologies. A detailed understanding of the formation process of these purely inorganic architectures is crucial for their implications in the context of primitive life detection as well as for their use in the synthesis of advanced biomimetic materials. Recently, great efforts have been made to gain insight into the molecular mechanisms driving self-assembly in these systems, resulting in a consistent model for morphogenesis at ambient conditions. In the present work, we build on this knowledge and investigate the influence of temperature, supersaturation, and an added multivalent cation as parameters by which the shape of the forming superstructures can be controlled. In particular, we focus on trumpet- and coral-like structures which quantitatively replace the well-characterised sheets and worm-like braids at elevated temperature and in the presence of additional ions, respectively. The observed morphological changes are discussed in light of the recently proposed formation mechanism with the aim to ultimately understand and control the major physicochemical factors governing the self-assembly process. Full article
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Open AccessArticle Analysis of Dynamic Surface Subsidence at the Underground Coal Mining Site in Velenje, Slovenia through Modified Sigmoidal Function
Minerals 2018, 8(2), 74; https://doi.org/10.3390/min8020074
Received: 30 December 2017 / Revised: 26 January 2018 / Accepted: 5 February 2018 / Published: 17 February 2018
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Abstract
In underground coal mining engineering, one of the most important tasks is to monitor, predict and manage the surface subsidence due to underground coal excavation. The impact of underground mining excavation reflects as subsidence of the overlying strata and the formation of surface
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In underground coal mining engineering, one of the most important tasks is to monitor, predict and manage the surface subsidence due to underground coal excavation. The impact of underground mining excavation reflects as subsidence of the overlying strata and the formation of surface depressions soon after excavation. The surface subsidence is one of many natural processes that exhibit a progression from small beginnings that accelerate and approach a climax over time. When detailed data is lacking, a logistic function is often used. In this paper, the analysis of the surface subsidence above underground mining sites in the Velenje Coal Mine by using a modified sigmoid function (surrogate of logistic function), with the common “S” shape, is introduced. Furthermore, the time estimation of the next and the final epoch measurement is considered. Full article
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Open AccessArticle Role of Volcano-Sedimentary Basins in the Formation of Greenstone-Granitoid Belts in the West African Craton: A Numerical Model
Minerals 2018, 8(2), 73; https://doi.org/10.3390/min8020073
Received: 20 December 2017 / Revised: 11 February 2018 / Accepted: 12 February 2018 / Published: 17 February 2018
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Abstract
Greenstone belts in the West African Craton (WAC) are separated by several generations of granitoids intruded at ca. 2.18–1.98 Ga. Simultaneous folding and exhumation play an important role in the formation of greenstone-granitoid belts. However, the overall tectonic regime and origin of granitoids
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Greenstone belts in the West African Craton (WAC) are separated by several generations of granitoids intruded at ca. 2.18–1.98 Ga. Simultaneous folding and exhumation play an important role in the formation of greenstone-granitoid belts. However, the overall tectonic regime and origin of granitoids remain controversial. In this study, we present the estimates of the mantle potential temperature (Tp) for the WAC, which yields values of about 1500–1600 °C, pressure estimates of initial and final melting yield values of about 3.7–5.2 GPa and 1–1.3 GPa, respectively. Subsequently, 2D thermo-mechanical models have been constructed to explore the width of volcano-sedimentary basin on spatial-temporal evolution of diapirs that emplaced in the lower-middle crust during compression. The models show that the width of the volcano-sediment layer plays an important role in the formation mechanisms of greenstone-granitoid belts. The lower crust beneath sedimentary sequences is deformed into a buckle fold during the first compressional stage, through which relief uplifts slowly. Subsequently, the buckle fold is further deformed into several individual folds. Diapirs made of lower crust rocks ascend and emplace in the middle-upper crust resulting from instability. Benefitting from the mantle temperature, the pressure estimates and the numerical modelling results, a new geodynamic model was constructed. This model indicates that a series of sheet-like granitoids possibly derived from either subducted mélanges, lower crust and/or mantle melting that are accumulated at depths of the subcontinental mantle would channel along diapirs before feeding the upper crust. When the granitoids arrive at the solidified lids of the diapirs, they would favour migrating horizontally and intrude into the upper crust through weakening zones between the diapirs. Our geodynamic model also suggests an asymmetry of structures between the upper and middle-lower crust, with the dome-like granitoids overlying high-grade sedimentary synforms and high-grade diapirs underlying low-grade greenstone belts. Full article
(This article belongs to the Special Issue Geological Modelling)
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Open AccessArticle Investigation of Fluids in Macrocrystalline and Microcrystalline Quartz in Agate Using Thermogravimetry-Mass-Spectrometry
Minerals 2018, 8(2), 72; https://doi.org/10.3390/min8020072
Received: 3 November 2017 / Revised: 12 February 2018 / Accepted: 14 February 2018 / Published: 17 February 2018
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Abstract
Gaseous and liquid fluids in agates (banded chalcedony—SiO2) of different localities were investigated systematically by thermogravimetry-mass-spectrometry within a temperature range from 25 to 1450 °C, for the first time. Chalcedony and macrocrystalline quartz from twelve agate samples were investigated, from Germany
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Gaseous and liquid fluids in agates (banded chalcedony—SiO2) of different localities were investigated systematically by thermogravimetry-mass-spectrometry within a temperature range from 25 to 1450 °C, for the first time. Chalcedony and macrocrystalline quartz from twelve agate samples were investigated, from Germany (Schlottwitz, St. Egidien, Chemnitz and Zwickau), Brazil (Rio Grande do Sul), Scotland (Ayrshire) and the USA (Montana). They originate from mafic and felsic volcanic rocks as well as hydrothermal and sedimentary environments. The results were evaluated regarding compounds of hydrogen with fluorine, chlorine, nitrogen, carbon and sulphur. Additionally, oxygen compounds were recognized with hydrogen, fluorine, nitrogen, sulphur and carbon. The nature of the compounds was identified based on their mass-charge-ratio and the intensity ratios of the associated fragments. Due to interferences of different compounds with the same mass-charge-ratio, only H2O, HF, NO, S, SO, CO3—as well as several hydrocarbon compounds (for example CO32− or CO)—could be properly identified. The main degassing temperatures were detected at around 500 and 1000 °C. Generally, a difference between quartz and chalcedony regarding the composition of their fluids could not be found. The results indicate a silica source for the agate formation from aqueous solutions but also a possible role of fluorine compounds. Additionally, CO2 and other fluids were involved in the alteration of volcanic rocks and the mobilization and transport of SiO2. Full article
(This article belongs to the Special Issue Mineralogy of Quartz and Silica Minerals)
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Open AccessArticle Determination of Seismic Safety Zones during the Surface Mining Operation Development in the Case of the “Buvač” Open Pit
Minerals 2018, 8(2), 71; https://doi.org/10.3390/min8020071
Received: 14 December 2017 / Revised: 29 January 2018 / Accepted: 12 February 2018 / Published: 16 February 2018
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Abstract
Determination of the blasting safety area is a very important step in the process of drilling and blasting works, and the preparation of solid rock materials for loading. Through monitoring and analysis of the negative seismic effects to the objects and infrastructures around
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Determination of the blasting safety area is a very important step in the process of drilling and blasting works, and the preparation of solid rock materials for loading. Through monitoring and analysis of the negative seismic effects to the objects and infrastructures around and at the mine area, we were able to adapt the drilling and blasting parameters and organization of drilling and blasting operation according to the mining progress so that the affected infrastructures could be protected. This paper analyses the safety distances and model safety zones of drilling and blasting for the period 2013–2018 at the open pit at “Buvač”, Omarska. This mathematical calculation procedure can be used during the whole life of the mine. By monitoring of the blasting seismic influence in first years of the mine's work, as well as by using recorded vibration velocities, mathematical dependence of the important parameters can be defined. Additionally, the level and laws of distribution and intensity of the seismic activity can be defined. On one hand, those are known quantities of the explosive and the distances between blasting location and endangered objects. On the other hand, those are coefficients of the manner of blasting and the environment where blasting is done, K, as well as the coefficient of the weakening of seismic waves as they spread, n. With the usage of the allowed vibration velocities, based on certain safety criteria and mathematical formulas of laws of spreading and intensity of seismic influence for a concrete case, it is possible to calculate explosive quantities and distances, with numerically-defined values of parameter K and n. Minimum distances are calculated based on defined or projected explosive quantities. Additionally, we calculate the maximum allowed explosive quantities based on known distances which can be used based on projected drilling-blasting parameters. For the purpose of the planning of drilling and blasting it is possible to define the allowed explosive quantities or minimum allowed distances in any area of the surface pit from the aspect of seismic safety. In the indicated case, and based on the analysis results, it is shown that in some areas of mining works in the case of the “Buvač”, Omarska open pit, projected explosive quantities cannot be used. In some cases, it is even necessary to divide the explosive charge in blasting holes with additional delayers. Full article
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Open AccessArticle Models of Determining the Parameters of Rock Mass Oscillation Equation with Experimental and Mass Blastings
Minerals 2018, 8(2), 70; https://doi.org/10.3390/min8020070
Received: 21 December 2017 / Revised: 1 February 2018 / Accepted: 7 February 2018 / Published: 16 February 2018
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Abstract
The explosion caused by detonation of explosive materials is followed by release of a large amount of energy. Whereby, a greater part of energy is used for rock destruction, and part of energy, in the form of seismic wave, is lost in the
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The explosion caused by detonation of explosive materials is followed by release of a large amount of energy. Whereby, a greater part of energy is used for rock destruction, and part of energy, in the form of seismic wave, is lost in the rock mass causing rock mass oscillation. Investigations of the character and behavior of the pattern of seismic wave indicate that the intensity and nature of the seismic wave are influenced by rock mass properties, and by blasting conditions. For evaluation and control of the seismic effect of blasting operations, the most commonly used equation is that of M.A. Sadovskii. Sadovskii’s equation defines the alteration in the velocity of rock mass oscillation depending on the distance, the quantity of explosives, blasting conditions and geological characteristics of the rock mass, and it is determined based on trial blasting for a specific work environment. Thus, this paper offers analysis of the method for determination of parameters of the rock mass oscillation equation, which are conditioned by rock mass properties and blasting conditions. Practical part of this paper includes the experimental research carried out at Majdanpek open pit, located in the northern part of eastern Serbia and the investigations carried out during mass blasting at Nepričava open pit, located in central Serbia. In this paper, parameters n and K from Sadovskii’s equation were determined in three ways—models in the given work environment. It was noted that, in practice, all three models can be successfully used to calculate the oscillation velocity of the rock masses. Full article
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Open AccessArticle Prismatic to Asbestiform Offretite from Northern Italy: Occurrence, Morphology and Crystal-Chemistry of a New Potentially Hazardous Zeolite
Minerals 2018, 8(2), 69; https://doi.org/10.3390/min8020069
Received: 21 January 2018 / Revised: 10 February 2018 / Accepted: 12 February 2018 / Published: 14 February 2018
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Abstract
A multi-methodological approach, based upon field investigation, morphological characterization, chemical analysis and structure refinement was applied to different samples of fibrous offretite, a new potentially hazardous zeolite recently discovered in northern Italy. Their morphology ranges from stocky-prismatic to asbestiform. All the investigated fibers
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A multi-methodological approach, based upon field investigation, morphological characterization, chemical analysis and structure refinement was applied to different samples of fibrous offretite, a new potentially hazardous zeolite recently discovered in northern Italy. Their morphology ranges from stocky-prismatic to asbestiform. All the investigated fibers may be considered as “inhalable”, and they are well within the range of the “more carcinogenic fibers” regarding diameter. As regards the length, the main mode observed in the asbestiform samples is 20–25 μm, and ~93% of the measured fibers are >5 μm and may be significantly associated with carcinogenesis also in terms of lengths. The chemical-structural features of the investigated fibers are comparable: the extra-framework cations K+, Mg2+ and Ca2+ are present in all samples in similar proportions, and refined cell parameters are similar among the samples. Offretite occurs in 60% of the investigated sites, with an estimated amount up to 75 vol % of the associated minerals. The presence of this mineral could be of concern for risk to human health, especially if one considers the vast number of quarries and mining-related activities that are operating in the zeolite host rocks. Full article
(This article belongs to the Special Issue Occurrence, Crystal-Chemistry and Properties of Fibrous Minerals)
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Open AccessArticle Effective-Medium Inversion of Induced Polarization Data for Mineral Exploration and Mineral Discrimination: Case Study for the Copper Deposit in Mongolia
Minerals 2018, 8(2), 68; https://doi.org/10.3390/min8020068
Received: 30 November 2017 / Revised: 29 January 2018 / Accepted: 7 February 2018 / Published: 14 February 2018
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Abstract
This paper develops a novel method of 3D inversion of induced polarization (IP) survey data, based on a generalized effective-medium model of the IP effect (GEMTIP). The electrical parameters of the effective-conductivity model are determined by the intrinsic petrophysical and geometrical characteristics of
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This paper develops a novel method of 3D inversion of induced polarization (IP) survey data, based on a generalized effective-medium model of the IP effect (GEMTIP). The electrical parameters of the effective-conductivity model are determined by the intrinsic petrophysical and geometrical characteristics of composite media, such as the mineralization and/or fluid content of rocks and the matrix composition, porosity, anisotropy, and polarizability of formations. The GEMTIP model of multiphase conductive media provides a quantitative tool for evaluation of the type of mineralization, and the volume content of different minerals using electromagnetic (EM) data. The developed method takes into account the nonlinear nature of both electromagnetic induction and IP phenomena and inverts the EM data in the parameters of the GEMTIP model. The goal of the inversion is to determine the electrical conductivity and the intrinsic chargeability distributions, as well as the other parameters of the relaxation model simultaneously. The recovered parameters of the relaxation model can be used for the discrimination of different rocks, and in this way may provide an ability to distinguish between uneconomic mineral deposits and zones of economic mineralization using geophysical remote sensing technology. Full article
(This article belongs to the Special Issue Mining and Mineral Exploration Geophysics)
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Open AccessArticle Nanoscale Study of Clausthalite-Bearing Symplectites in Cu-Au-(U) Ores: Implications for Ore Genesis
Minerals 2018, 8(2), 67; https://doi.org/10.3390/min8020067
Received: 19 January 2018 / Revised: 9 February 2018 / Accepted: 9 February 2018 / Published: 13 February 2018
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Abstract
Symplectites comprising clausthalite (PbSe) and host Cu-(Fe)-sulphides (chalcocite, bornite, and chalcopyrite) are instructive for constraining the genesis of Cu-Au-(U) ores if adequately addressed at the nanoscale. The present study is carried out on samples representative of all three Cu-(Fe)-sulphides displaying clausthalite inclusions that
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Symplectites comprising clausthalite (PbSe) and host Cu-(Fe)-sulphides (chalcocite, bornite, and chalcopyrite) are instructive for constraining the genesis of Cu-Au-(U) ores if adequately addressed at the nanoscale. The present study is carried out on samples representative of all three Cu-(Fe)-sulphides displaying clausthalite inclusions that vary in size, from a few µm down to the nm-scale (<5 nm), as well as in morphology and inclusion density. A Transmission Electron Microscopy (TEM) study was undertaken on foils prepared by Focussed Ion Beam and included atom-scale High-Angle Annular Dark-Field Scanning TEM (HAADF-STEM) imaging. Emphasis is placed on phase relationships and their changes in speciation during cooling, as well as on boundaries between inclusions and host sulphide. Three species from the chalcocite group (Cu2–xS) are identified as 6a digenite superstructure, monoclinic chalcocite, and djurleite. Bornite is represented by superstructures, of which 2a and 4a are discussed here, placing constraints for ore formation at T > 265 °C. A minimum temperature of 165 °C is considered for clausthalite-bearing symplectites from the relationships with antiphase boundaries in 6a digenite. The results show that alongside rods, blebs, and needle-like grains of clausthalite within the chalcocite that likely formed via exsolution, a second, overprinting set of replacement textures, extending down to the nanoscale, occurs and affects the primary symplectites. In addition, other reactions between pre-existing Se, present in solid solution within the Cu-(Fe)-sulphides, and Pb, transported within a fluid phase, account for the formation of composite, commonly pore-attached PbSe and Bi-bearing nanoparticles within the chalcopyrite. The inferred reorganisation of PbSe nanoparticles into larger tetragonal superlattices represents a link between the solid solution and the symplectite formation and represents the first such example in natural materials. Epitaxial growth between clausthalite and monazite is further evidence for the interaction between pre-existing Cu ores and fluids carrying REE, P, and most likely Pb. In U-bearing ores, such Pb can form via decay of uranium within the ore, implying hydrothermal activity after the initial ore deposition. The U-Pb ages obtained for such ores therefore need to be carefully assessed as to whether they represent primary ore deposition or, more likely, an overprinting event. A latest phase of fluid infiltration is the recognised formation of Cu-selenide bellidoite (Cu2Se), as well as Fe oxides. Full article
(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)
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Open AccessArticle Depression Mechanism of Strontium Ions in Bastnaesite Flotation with Salicylhydroxamic Acid as Collector
Minerals 2018, 8(2), 66; https://doi.org/10.3390/min8020066
Received: 3 January 2018 / Revised: 3 February 2018 / Accepted: 5 February 2018 / Published: 13 February 2018
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Abstract
Metal ions are widely present in flotation pulp. Metal ions change solution chemistry and mineral surface properties, consequently affecting mineral flotation. In this work, the effect of strontium ions on bastnaesite flotation with salicylhydroxamic acid (SHA) was investigated by microflotation tests, contact angle
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Metal ions are widely present in flotation pulp. Metal ions change solution chemistry and mineral surface properties, consequently affecting mineral flotation. In this work, the effect of strontium ions on bastnaesite flotation with salicylhydroxamic acid (SHA) was investigated by microflotation tests, contact angle measurements, zeta-potential measurements, and X-ray photoelectron spectroscopy (XPS) analysis. Microflotation tests confirmed that the addition of strontium ions decreased bastnaesite floatability, compared with that in the absence of strontium ions. Contact angle measurements suggested that the pretreatment of strontium ions decreased SHA adsorption. Zeta potential measurements confirmed that the bastnaesite was depressed by the adsorption of positively charged strontium species, and the lower adsorption capacity of SHA onto the bastnaesite surfaces was obtained after modifying with strontium ions. XPS analysis demonstrated that strontium ions adsorbed onto the bastnaesite surfaces through the interaction between strontium ions and oxygen atoms of surface CeOH 0 groups. This occurrence hindered surface Ce sites which chelated with SHA and therefore, decreased bastnaesite floatability. Full article
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Open AccessArticle Pyrophosphate-Inhibition of Apatite Formation Studied by In Situ X-Ray Diffraction
Minerals 2018, 8(2), 65; https://doi.org/10.3390/min8020065
Received: 28 August 2017 / Revised: 10 February 2018 / Accepted: 12 February 2018 / Published: 13 February 2018
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Abstract
The pathways to crystals are still under debate, especially for materials relevant to biomineralization, such as calcium phosphate apatite known from bone and teeth. Pyrophosphate is widely used in biology to control apatite formation since it is a potent inhibitor of apatite crystallization.
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The pathways to crystals are still under debate, especially for materials relevant to biomineralization, such as calcium phosphate apatite known from bone and teeth. Pyrophosphate is widely used in biology to control apatite formation since it is a potent inhibitor of apatite crystallization. The impacts of pyrophosphate on apatite formation and crystallization kinetics are, however, not fully understood. Therefore, we studied apatite crystallization in water by synchrotron in situ X-ray diffraction. Crystallization was conducted from calcium chloride (0.2 M) and sodium phosphate (0.12 M) at pH 12 where hydrogen phosphate is the dominant phosphate species and at 60 °C to allow the synchrotron measurements to be conducted in a timely fashion. Following the formation of an initial amorphous phase, needle shaped crystals formed that had an octacalcium phosphate-like composition, but were too small to display the full 3D periodic structure of octacalcium phosphate. At later growth stages the crystals became apatitic, as revealed by changes in the lattice constant and calcium content. Pyrophosphate strongly inhibited nucleation of apatite and increased the onset of crystallization from minute to hour time scales. Pyrophosphate also reduced the rate of growth. Furthermore, when the pyrophosphate concentration exceeded ~1% of the calcium concentration, the resultant crystals had reduced size anisotropy suggesting that pyrophosphate interacts in a site-specific manner with the formation of apatite crystals. Full article
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Open AccessArticle Mobility and Attenuation Dynamics of Potentially Toxic Chemical Species at an Abandoned Copper Mine Tailings Dump
Minerals 2018, 8(2), 64; https://doi.org/10.3390/min8020064
Received: 18 December 2017 / Revised: 24 January 2018 / Accepted: 5 February 2018 / Published: 12 February 2018
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Abstract
Large volumes of disposed mine tailings abound in several regions of South Africa, as a consequence of unregulated, unsustainable long years of mining activities. Tailings dumps occupy a large volume of valuable land, and present a potential risk for aquatic systems, through leaching
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Large volumes of disposed mine tailings abound in several regions of South Africa, as a consequence of unregulated, unsustainable long years of mining activities. Tailings dumps occupy a large volume of valuable land, and present a potential risk for aquatic systems, through leaching of potentially toxic chemical species. This paper reports on the evaluation of the geochemical processes controlling the mobility of potentially toxic chemical species within the tailings profile, and their potential risk with regard to surface and groundwater systems. Combination of X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) techniques, show that the tailing profiles are uniform, weakly altered, and vary slightly with depth in both physical and geochemical properties, as well as mineralogical composition. Mineralogical analysis showed the following order of abundance: quartz > epidote > chlorite > muscovite > calcite > hematite within the tailings profiles. The neutralization of the dominant alumino-silicate minerals and the absence of sulfidic minerals, have produced medium alkaline pH conditions (7.97–8.37) at all depths and low concentrations of dissolved Cu (20.21–47.9 µg/L), Zn (0.88–1.80 µg/L), Pb (0.27–0.34 µg/L), and SO42− (15.71–55.94 mg/L) in the tailings profile leachates. The relative percentage leach for the potentially toxic chemical species was low in the aqueous phase (Ni 0.081%, Cu 0.006%, and Zn 0.05%). This indicates that the transport load of potentially toxic chemical species from tailings to the aqueous phase is very low. The precipitation of secondary hematite has an important known ability to trap and attenuate the mobility of potentially toxic chemical species (Cu, Zn, and Pb) by adsorption on the surface area. Geochemical modelling MINTEQA2 showed that the tailings leachates were below saturation regarding oxyhydroxide minerals, but oversaturated with Cu bearing mineral (i.e., cuprite). Most of the potentially toxic chemical species occur as free ions in the tailings leachates. The precipitation of secondary hematite and cuprite, and geochemical condition such as pH of the tailings were the main solubility and mobility controls for the potentially toxic chemical species, and their potential transfer from tailings to the aqueous phase. Full article
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Open AccessArticle Vanadium Transitions during Roasting-Leaching Process of Vanadium Extraction from Stone Coal
Minerals 2018, 8(2), 63; https://doi.org/10.3390/min8020063
Received: 12 January 2018 / Revised: 7 February 2018 / Accepted: 9 February 2018 / Published: 12 February 2018
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Abstract
The vanadium occurrence in stone coal, water leaching, and acid leaching residue was investigated by energy dispersive spectrometer (EDS) mapping and point analysis, and the vanadium transitions during roasting-leaching of stone coal were revealed. In the roasting process, vanadium-bearing muscovite is converted to
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The vanadium occurrence in stone coal, water leaching, and acid leaching residue was investigated by energy dispersive spectrometer (EDS) mapping and point analysis, and the vanadium transitions during roasting-leaching of stone coal were revealed. In the roasting process, vanadium-bearing muscovite is converted to K-Na-feldspar, accompanying the liberation of vanadium. Most liberated vanadium reacts with sodium salt to generate water-soluble sodium vanadate, some reacts with calcite in stone coal to form water-insoluble calcium vanadate, and other liberated vanadium exists as free vanadium oxide. However, for coarse muscovite grains, the reaction of muscovite converted to K-Na-feldspar only occurs at the outer margin of muscovite grains, and the vanadium in the interior of muscovite grains is not liberated. During water leaching, the sodium vanadate is leached out. The calcium vanadate and free vanadium oxide are dissolved out in the process of acid leaching, and the vanadium, presenting in muscovite grains surrounded by K-Na-feldspar, still remains in the acid leaching residue. Two suggestions, including optimization of grinding-classification process and adopting microwave roasting, were proposed for improving vanadium recovery according to the vanadium transition rules. Full article
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Open AccessArticle Origin of Reverse Zoned Cr-Spinels from the Paleoproterozoic Yanmenguan Mafic–Ultramafic Complex in the North China Craton
Minerals 2018, 8(2), 62; https://doi.org/10.3390/min8020062
Received: 20 December 2017 / Revised: 7 February 2018 / Accepted: 8 February 2018 / Published: 12 February 2018
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Abstract
We conducted petrological and mineral chemistry investigations of Cr-spinel in ultramafic rocks of the Yanmenguan mafic–ultramafic complex in the North China Craton. The Cr-spinel grains occur as inclusions in enstatite, tschermakite, phlogopite, and olivine, or as interstitial grains among the aforementioned silicate minerals,
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We conducted petrological and mineral chemistry investigations of Cr-spinel in ultramafic rocks of the Yanmenguan mafic–ultramafic complex in the North China Craton. The Cr-spinel grains occur as inclusions in enstatite, tschermakite, phlogopite, and olivine, or as interstitial grains among the aforementioned silicate minerals, and show concentric or asymmetrical textures. Back-scattered electron and elemental images and compositional profiles of the spinel grains indicate the presence of Cr- and Fe-rich cores and Al- and Mg-rich rims. The host silicate minerals display a decrease in Al and Mg contents accompanied by an increase in Cr and Fe away from the spinel. These textures and compositional variations suggest that subsolidus elemental exchange more likely gave rise to the compositional zonation, resulting in the transfer of Al and Mg from the silicate minerals to the spinel. The Mn, Ni, and Ti contents in spinel and the major elements of olivine-hosted spinel are relatively stable during subsolidus elemental diffusion and thus are more reliable tracers of primary high-temperature processes. The temperature estimates reveal that the subsolidus diffusion might have occurred at 600–720 °C, which could be linked to the regional metamorphic event. Full article
(This article belongs to the Special Issue Spinel Group Minerals)
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Open AccessArticle Molecular Modeling of Adsorption of 5-Aminosalicylic Acid in the Halloysite Nanotube
Minerals 2018, 8(2), 61; https://doi.org/10.3390/min8020061
Received: 29 December 2017 / Revised: 25 January 2018 / Accepted: 31 January 2018 / Published: 11 February 2018
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Abstract
Halloysite nanotubes are becoming interesting materials for drug delivery. The knowledge of surface interactions is important for optimizing this application. The aim of this work is to perform a computational study of the interaction between 5-aminosalicylic acid (5-ASA) drug and halloysite nanotubes for
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Halloysite nanotubes are becoming interesting materials for drug delivery. The knowledge of surface interactions is important for optimizing this application. The aim of this work is to perform a computational study of the interaction between 5-aminosalicylic acid (5-ASA) drug and halloysite nanotubes for the development of modified drug delivery systems. The optimization of this nanotube and the adsorption of different conformers of the 5-ASA drug on the internal surface of halloysite in the presence and absence of water were performed using quantum mechanical calculations by using Density Functional Theory (DFT) and methods based on atomistic force fields for molecular modeling, respectively. Full article
(This article belongs to the Special Issue Molecular Simulation of Mineral-Solution Interfaces)
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Open AccessArticle Dissolution Behaviors of Trace Muscovite during Pressure Leaching of Hydrothermal Vein Quartz Using H2SO4 and NH4Cl as Leaching Agents
Minerals 2018, 8(2), 60; https://doi.org/10.3390/min8020060
Received: 26 December 2017 / Revised: 2 February 2018 / Accepted: 7 February 2018 / Published: 11 February 2018
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Abstract
Dissolution behaviors of trace muscovite during pressure leaching of hydrothermal vein quartz using H2SO4 and NH4Cl as leaching agents have been studied by means of optical and electronic microscopes. Phase transformations of pure muscovite during calcination and the
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Dissolution behaviors of trace muscovite during pressure leaching of hydrothermal vein quartz using H2SO4 and NH4Cl as leaching agents have been studied by means of optical and electronic microscopes. Phase transformations of pure muscovite during calcination and the pressure leaching were analyzed by powder X-ray diffraction (XRD) and thermal analysis (TG-DSC), which are used for indirectly discussing dissolution mechanisms of the trace muscovite. Structure damages of trace muscovite are caused by calcination, and further developed during pressure leaching of the quartz sand using H2SO4 and NH4Cl as leaching agents. The trace muscovite is dissolved, and then efficiently separated from quartz sand by coupling effects of calcination and fluorine-free pressure leaching. Full article
(This article belongs to the Special Issue Mineralogy of Quartz and Silica Minerals)
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Open AccessArticle Washability and Distribution Behaviors of Trace Elements of a High-Sulfur Coal, SW Guizhou, China
Minerals 2018, 8(2), 59; https://doi.org/10.3390/min8020059
Received: 27 December 2017 / Revised: 2 February 2018 / Accepted: 5 February 2018 / Published: 11 February 2018
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Abstract
The float-sink test is a commonly used technology for the study of coal washability, which determines optimal separation density for coal washing based on the desired sulfur and ash yield of the cleaned coal. In this study, the float-sink test is adopted for
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The float-sink test is a commonly used technology for the study of coal washability, which determines optimal separation density for coal washing based on the desired sulfur and ash yield of the cleaned coal. In this study, the float-sink test is adopted for a high-sulfur Late Permian coal from Hongfa coalmine (No.26), southwestern Guizhou, China, to investigate its washability, and to analyze the organic affinities and distribution behaviors of some toxic and valuable trace elements. Results show that the coal is difficult to separate in terms of desulfurization. A cleaned coal could theoretically be obtained with a yield of 75.50%, sulfur 2.50%, and ash yield 11.33% when the separation density is 1.57 g/cm3. Trace elements’ distribution behaviors during the gravity separation were evaluated by correlation analysis and calculation. It was found that Cs, Ga, Ta, Th, Rb, Sb, Nb, Hf, Ba, Pb, In, Cu, and Zr are of significant inorganic affinity; while Sn, Co, Re, U, Mo, V, Cr, Ni, and Be are of relatively strong organic affinity. LREE (Light rare earth elements), however, seem to have weaker organic affinity than HREE (Heavy rare earth elements), which can probably be attributed to lanthanide contraction. When the separation density is 1.60 g/cm3, a large proportion of Sn, Be, Cr, U, V, Mo, Ni, Cd, Pb, and Cu migrate to the cleaned coal, but most of Mn, Sb and Th stay in the gangue. Coal preparation provides alternativity for either toxic elements removal or valuable elements preconcentration in addition to desulfurization and deashing. The enrichment of trace elements in the cleaned coal depends on the predetermined separation density which will influence the yields and ash yields of the cleaned coal. Full article
(This article belongs to the Special Issue Toxic Mineral Matter in Coal and Coal Combustion Products)
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Open AccessArticle Structural and Electronic Properties of Different Terminations for Quartz (001) Surfaces as Well as Water Molecule Adsorption on It: A First-Principles Study
Minerals 2018, 8(2), 58; https://doi.org/10.3390/min8020058
Received: 6 December 2017 / Revised: 4 February 2018 / Accepted: 5 February 2018 / Published: 9 February 2018
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Abstract
Structural and electronic properties of Si termination, O-middle termination, and O-rich terminations of a quartz (001) surface as well as water molecule adsorption on it were simulated by means of density functional theory (DFT). Calculated results show that the O-middle termination exposing a
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Structural and electronic properties of Si termination, O-middle termination, and O-rich terminations of a quartz (001) surface as well as water molecule adsorption on it were simulated by means of density functional theory (DFT). Calculated results show that the O-middle termination exposing a single oxygen atom on the surface is the most stable model of quartz (001) surface, with the lowest surface energy at 1.969 J·m−2, followed by the O-rich termination and Si termination at 2.892 J·m−2 and 2.896 J·m−2, respectively. The surface properties of different terminations mainly depend on the surface-exposed silicon and oxygen atoms, as almost all the contributions to the Fermi level (EF) in density of states (DOS) are offered by the surface-exposed atoms, especially the O2p state. In the molecular adsorption model, H2O prefers to adsorb on the surface Si and O atoms, mainly via O1–H1 bond at 1.259 Å and Si1–Ow at 1.970 Å by Van der Waals force and weak hydrogen bond with an adsorption energy of −57.89 kJ·mol−1. In the dissociative adsorption model, the O-middle termination is hydroxylated after adsorption, generating two new Si–OH silanol groups on the surface and forming the OwH2···O4 hydrogen bond at a length of 2.690 Å, along with a large adsorption energy of −99.37 kJ·mol−1. These variations in the presence of H2O may have a great influence on the subsequent interfacial reactions on the quartz surface. Full article
(This article belongs to the Special Issue Molecular Simulation of Mineral-Solution Interfaces)
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Open AccessArticle Evaluation of Sulfonate-Based Collectors with Different Hydrophobic Tails for Flotation of Fluorite
Minerals 2018, 8(2), 57; https://doi.org/10.3390/min8020057
Received: 28 December 2017 / Revised: 3 February 2018 / Accepted: 5 February 2018 / Published: 9 February 2018
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Abstract
This investigation aims to demonstrate the effects of hydrophobic tails on the affinity and relevant flotation response of sulfonate-based collectors for fluorite. For this purpose, a series of alkyl sulfonates with different hydrophobic tails, namely sodium decanesulfonate (C10), sodium dodecylsulfate (C12), sodium hexadecanesulfonate
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This investigation aims to demonstrate the effects of hydrophobic tails on the affinity and relevant flotation response of sulfonate-based collectors for fluorite. For this purpose, a series of alkyl sulfonates with different hydrophobic tails, namely sodium decanesulfonate (C10), sodium dodecylsulfate (C12), sodium hexadecanesulfonate (C16), and sodium dodecylbenzenesulfonate (C12B) were applied. The flotation tests showed that C12 and C12B had a better collecting performance than C10 and C16 at pH < 10, and the flotation recovery of fluorite was higher when adopting C12B as a collector compared with C12 with a strong base. The adsorption behaviors of collectors on the fluorite surface were studied through zeta potential, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses. It was found that the affinity of alkyl sulfonates for fluorite was enhanced with the increase of the alkyl chain length from C10 to C16. The existence of phenyl in the hydrophobic tail of sulfonates could improve its activity for fluorite by reducing its surface tension. The abnormal phenomenon C16 with a high affinity for fluorite had a low collecting performance for fluorite mainly due to its overlong alkyl chain, resulting in low solubility in pulp, which restrained its interaction with fluorite. We concluded that C12B was the most applicable collector for fluorite among these reagents due to its high activity, high solubility, and low cost, which was further substantiated by calculating their molecular frontier orbital energy. Full article
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Open AccessArticle Biological and Geochemical Development of Placer Gold Deposits at Rich Hill, Arizona, USA
Minerals 2018, 8(2), 56; https://doi.org/10.3390/min8020056
Received: 18 January 2018 / Revised: 2 February 2018 / Accepted: 5 February 2018 / Published: 8 February 2018
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Abstract
Placer gold from the Devils Nest deposits at Rich Hill, Arizona, USA, was studied using a range of micro-analytical and microbiological techniques to assess if differences in (paleo)-environmental conditions of three stratigraphically-adjacent placer units are recorded by the gold particles themselves. High-angle basin
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Placer gold from the Devils Nest deposits at Rich Hill, Arizona, USA, was studied using a range of micro-analytical and microbiological techniques to assess if differences in (paleo)-environmental conditions of three stratigraphically-adjacent placer units are recorded by the gold particles themselves. High-angle basin and range faulting at 5–17 Ma produced a shallow basin that preserved three placer units. The stratigraphically-oldest unit is thin gold-rich gravel within bedrock gravity traps, hosting elongated and flattened placer gold particles coated with manganese-, iron-, barium- (Mn-Fe-Ba) oxide crusts. These crusts host abundant nano-particulate and microcrystalline secondary gold, as well as thick biomats. Gold surfaces display unusual plumate-dendritic structures of putative secondary gold. A new micro-aerophilic Betaproteobacterium, identified as a strain of Comamonas testosteroni, was isolated from these biomats. Significantly, this ‘black’ placer gold is the radiogenically youngest of the gold from the three placer units. The middle unit has well-rounded gold nuggets with deep chemical weathering rims, which likely recorded chemical weathering during a wetter period in Arizona’s history. Biomats, nano-particulate gold and secondary gold growths were not observed here. The uppermost unit is a pulse placer deposited by debris flows during a recent drier period. Deep cracks and pits in the rough and angular gold from this unit host biomats and nano-particulate gold. During this late arid period, and continuing to the present, microbial communities established within the wet, oxygen-poor bedrock traps of the lowermost placer unit, which resulted in biological modification of placer gold chemistry, and production of Mn-Fe-Ba oxide biomats, which have coated and cemented both gold and sediments. Similarly, deep cracks and pits in gold from the uppermost unit provided a moist and sheltered micro-environment for additional gold-tolerant biological communities. In conclusion, placer gold from the Devils Nest deposits at Rich Hill, Arizona, USA, preserves a detailed record of physical, chemical and biological modifications. Full article
(This article belongs to the Special Issue Geomicrobiology and Biogeochemistry of Precious Metals)
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Open AccessArticle Rare Earth Elements (La, Ce, Pr, Nd, and Sm) from a Carbonatite Deposit: Mineralogical Characterization and Geochemical Behavior
Minerals 2018, 8(2), 55; https://doi.org/10.3390/min8020055
Received: 5 December 2017 / Revised: 2 February 2018 / Accepted: 2 February 2018 / Published: 8 February 2018
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Abstract
Geochemical characterization including mineralogical measurements and kinetic testing was completed on samples from the Montviel carbonatite deposit, located in Quebec (Canada). Three main lithological units representing both waste and ore grades were sampled from drill core. A rare earth element (REE) concentrate was
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Geochemical characterization including mineralogical measurements and kinetic testing was completed on samples from the Montviel carbonatite deposit, located in Quebec (Canada). Three main lithological units representing both waste and ore grades were sampled from drill core. A rare earth element (REE) concentrate was produced through a combination of gravity and magnetic separation. All samples were characterized using different mineralogical techniques (i.e., quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), X-ray diffraction (XRD), and scanning electron microscopy with X-ray microanalysis (SEM-EDS)) in order to quantify modal mineralogy, liberation, REE deportment and composition of REE-bearing phases. The REE concentrate was then submitted for kinetic testing (weathering cell) in order to investigate the REE leaching potential. The mineralogical results indicate that: (i) the main REE-bearing minerals in all samples are burbankite, kukharenkoite-Ce, monazite, and apatite; (ii) the samples are dominated by REE-free carbonates (i.e., calcite, ankerite, and siderite); and (iii) LREE is more abundant than HREE. Grades of REE minerals, sulfides and oxides are richer in the concentrate than in the host lithologies. The geochemical test results show that low concentrations of light REE are leached under kinetic testing conditions (8.8–139.6 µg/L total light REE). These results are explained by a low reactivity of the REE-bearing carbonates in the kinetic testing conditions, low amounts of REE in solids, and by precipitation of secondary REE minerals. Full article
(This article belongs to the Special Issue Process Mineralogy of Critical Metals)
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Open AccessArticle Research on Power Plant Ash Impact on the Quality of Soil in Kostolac and Gacko Coal Basins
Minerals 2018, 8(2), 54; https://doi.org/10.3390/min8020054
Received: 29 November 2017 / Revised: 25 January 2018 / Accepted: 31 January 2018 / Published: 8 February 2018
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Abstract
Increased concentrations of heavy metals in ash can adversely affect the microbiological and pedogenetic processes in soil. The aim of this paper is to determine the impact of ash from unburned coal generated in the Kostolac and Gacko coal basins on the quality
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Increased concentrations of heavy metals in ash can adversely affect the microbiological and pedogenetic processes in soil. The aim of this paper is to determine the impact of ash from unburned coal generated in the Kostolac and Gacko coal basins on the quality of soil in the surrounding environment. The investigation included the surface soil layer that was sampled and tested during 2016 and 2017. A total of 30 samples of Kostolac soil and 9 samples of Gacko soil were analyzed for the content of 8 heavy metals: Cu, Pb, Cd, Zn, Hg, As, Cr and Ni. The analyses were carried out by inductively coupled plasma mass spectrometry (ICPMS) technique according to the EPA 6020A method and the following conclusions were made: Kostolac coal ash affects the quality of the surrounding soil in terms of Ni, Cu and Cr as evidenced by the moderately strong correlation of the Ni-Cu pair (k = 0.71), as well as the Cu-Cr pair (k = 0.73) and strong correlation of the Ni-Cr pair (k = 0.82), while the high recorded concentration of Pb, Hg, As and Zn is attributed to other sources of pollution, such as the traffic network and intensive farming activities, and in some cases, its impact is only local. All recorded concentrations of heavy metals are within the remediation values. The effect of ash on soil contamination in the surroundings of the Gacko coal basin is limited to Ni and Cd, with a strong correlation coefficient of this pair (k = 0.82). The recorded overrun of maximum allowed concentration of Cr is evidenced in only 2 samples, and in terms of this element the contamination of the Gacko soil can be considered to be local. It is concluded that prevailing winds play a part in soil pollution. Cluster analysis showed that Ni, Cr and Zn have very similar values in analyzed soil samples from both basins, while a cluster composed of only Hg, in the case of Gacko, indicates lower contamination with Hg compared to the other heavy metals. Full article
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Open AccessArticle Classification of Flotation Frothers
Minerals 2018, 8(2), 53; https://doi.org/10.3390/min8020053
Received: 23 November 2017 / Revised: 9 January 2018 / Accepted: 30 January 2018 / Published: 7 February 2018
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Abstract
In this paper, a scheme of flotation frothers classification is presented. The scheme first indicates the physical system in which a frother is present and four of them i.e., pure state, aqueous solution, aqueous solution/gas system and aqueous solution/gas/solid system are distinguished. As
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In this paper, a scheme of flotation frothers classification is presented. The scheme first indicates the physical system in which a frother is present and four of them i.e., pure state, aqueous solution, aqueous solution/gas system and aqueous solution/gas/solid system are distinguished. As a result, there are numerous classifications of flotation frothers. The classifications can be organized into a scheme described in detail in this paper. The frother can be present in one of four physical systems, that is pure state, aqueous solution, aqueous solution/gas and aqueous solution/gas/solid system. It results from the paper that a meaningful classification of frothers relies on choosing the physical system and next feature, trend, parameter or parameters according to which the classification is performed. The proposed classification can play a useful role in characterizing and evaluation of flotation frothers. Full article
(This article belongs to the Special Issue Flotation Chemistry)
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Open AccessArticle Modelling Geotechnical Heterogeneities Using Geostatistical Simulation and Finite Differences Analysis
Minerals 2018, 8(2), 52; https://doi.org/10.3390/min8020052
Received: 30 November 2017 / Revised: 12 January 2018 / Accepted: 30 January 2018 / Published: 7 February 2018
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Abstract
Modelling a rock mass in an accurate and realistic way allows researchers to reduce the uncertainty associated with its characterisation and reproduce the intrinsic spatial variability and heterogeneities present in the rock mass. However, there is often a lack of a structured methodology
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Modelling a rock mass in an accurate and realistic way allows researchers to reduce the uncertainty associated with its characterisation and reproduce the intrinsic spatial variability and heterogeneities present in the rock mass. However, there is often a lack of a structured methodology to characterise heterogeneous rock masses using geotechnical information available from the prospection phase. This paper presents a characterization methodology based on the geostatistical simulation of geotechnical variables and the application of a scenario reduction technique aimed at selecting a reduced number of realisations able to statistically represent a large set of realisations obtained by the geostatistical approach. This type of information is useful for a further rock mass behaviour analysis. The methodology is applied to a gold deposit with the goal of understanding its main differences to traditional approaches based on a deterministic modelling of the rock mass. The obtained results show the suitability of the methodology to characterise heterogeneous rock masses, since there were considerable differences between the results of the proposed methodology, mainly concerning the theoretical tunnel displacements, and the ones obtained with a traditional approach. Full article
(This article belongs to the Special Issue Geological Modelling)
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Open AccessArticle Styles of Alteration of Ti Oxides of the Kimberlite Groundmass: Implications on the Petrogenesis and Classification of Kimberlites and Similar Rocks
Minerals 2018, 8(2), 51; https://doi.org/10.3390/min8020051
Received: 27 November 2017 / Revised: 22 January 2018 / Accepted: 1 February 2018 / Published: 6 February 2018
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The sequence of replacement in groundmass perovskite and spinel from SK-1 and SK-2 kimberlites (Eastern Dharwar craton, India) has been established. Two types of perovskite occur in the studied Indian kimberlites. Type 1 perovskite is found in the groundmass, crystallized directly from the
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The sequence of replacement in groundmass perovskite and spinel from SK-1 and SK-2 kimberlites (Eastern Dharwar craton, India) has been established. Two types of perovskite occur in the studied Indian kimberlites. Type 1 perovskite is found in the groundmass, crystallized directly from the kimberlite magma, it is light rare-earth elements (LREE)-rich and Fe-poor and its ΔNNO calculated value is from −3.82 to −0.73. The second generation of perovskite (type 2 perovskite) is found replacing groundmass atoll spinel, it was formed from hydrothermal fluids, it is LREE-free and Fe-rich and has very high ΔNNO value (from 1.03 to 10.52). Type 1 groundmass perovskite may be either replaced by anatase or kassite along with aeschynite-(Ce). These differences in the alteration are related to different f(CO2) and f(H2O) conditions. Furthermore, primary perovskite may be strongly altered to secondary minerals, resulting in redistribution of rare-earth elements (REE) and, potentially, U, Pb and Th. Therefore, accurate petrographic and chemical analyses are necessary in order to demonstrate that perovskite is magmatic before proceeding to sort geochronological data by using perovskite. Ti-rich hydrogarnets (12.9 wt %–26.3 wt % TiO2) were produced during spinel replacement by late hydrothermal processes. Therefore, attention must be paid to the position of Ca-Ti-garnets in the mineral sequence and their water content before using them to classify the rock based on their occurrence. Full article
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Open AccessCase Report Characterization of the Lime Mortars of the Rui Barbosa House Museum in Rio De Janeiro, Brazil
Minerals 2018, 8(2), 50; https://doi.org/10.3390/min8020050
Received: 18 September 2017 / Revised: 8 January 2018 / Accepted: 10 January 2018 / Published: 3 February 2018
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Abstract
The aim of this research is to characterize the mortars of the Rui Barbosa House Museum, built in 1850, in the city of Rio de Janeiro, Brazil, using X-ray diffraction (XRD), gel-CSH determination, Fourier Transform Infrared spectrometry (FTIR), Wavelength-Dispersive X-ray Fluorescence spectrometry (WDXRF),
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The aim of this research is to characterize the mortars of the Rui Barbosa House Museum, built in 1850, in the city of Rio de Janeiro, Brazil, using X-ray diffraction (XRD), gel-CSH determination, Fourier Transform Infrared spectrometry (FTIR), Wavelength-Dispersive X-ray Fluorescence spectrometry (WDXRF), Thermo gravimetric analysis (TG-DTG), and granulometric analysis. Also, petrographic and physical characteristics such as porosity, water absorption, and apparent density of the mortars were used to identify the raw materials employed in their preparation. Mineralogical associations found are similar (quartz, calcite, kaolinite, microcline, muscovite, and albite) for the majority of samples and only vary in their proportions; the most prominent phases are quartz and calcite. The collected data, indicating that the binder is hydrated lime, lead us to conclude that the analyzed samples are lime mortars, discarding the possibility of cement as the binder material. Two samples, located on the corner of the building, which underwent repairs, present a differentiated behavior, with high levels of dolomite and the presence of pozzolanic material, with greater water absorption and higher density, indicating the use of a different mortar type. In addition, it was verified that the WDXRF and XRD methods are able to determine the trace element composition with comparable precision with respect to the methodological approach proposed by Teutonico (1988). In addition, it has been verified that the major pollutant causing degradation of building are sulfur emitted by the vehicles and saline spray. Full article
(This article belongs to the Special Issue Mineralogical Applications for Cultural Heritage)
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Open AccessArticle 13C-NMR Study on Structure Evolution Characteristics of High-Organic-Sulfur Coals from Typical Chinese Areas
Minerals 2018, 8(2), 49; https://doi.org/10.3390/min8020049
Received: 8 January 2018 / Revised: 26 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
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Abstract
The structure evolution characteristics of high-organic-sulfur (HOS) coals with a wide range of ranks from typical Chinese areas were investigated using 13C-CP/MAS NMR. The results indicate that the structure parameters that are relevant to coal rank include CH3 carbon (f
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The structure evolution characteristics of high-organic-sulfur (HOS) coals with a wide range of ranks from typical Chinese areas were investigated using 13C-CP/MAS NMR. The results indicate that the structure parameters that are relevant to coal rank include CH3 carbon (fal*), quaternary carbon, CH/CH2 carbon + quaternary carbon (falH), aliphatic carbon (falC), protonated aromatic carbon (faH), protonated aromatic carbon + aromatic bridgehead carbon (faH+B), aromaticity (faCP), and aromatic carbon (farC). The coal structure changed dramatically in the first two coalification jumps, especially the first one. A large number of aromatic structures condensed, and aliphatic structures rapidly developed at the initial stage of bituminous coal accompanied by remarkable decarboxylation. Compared to ordinary coals, the structure evolution characteristics of HOS coals manifest in three ways: First, the aromatic CH3 carbon, alkylated aromatic carbon (faS), aromatic bridgehead carbon (faB), and phenolic ether (faP) are barely relevant to rank, and abundant organic sulfur has an impact on the normal evolution process of coal. Second, the average aromatic cluster sizes of some super-high-organic-sulfur (SHOS) coals are not large, and the extensive development of cross bonds and/or bridged bonds form closer connections among the aromatic fringes. Moreover, sulfur-containing functional groups are probably significant components in these linkages. Third, a considerable portion of “oxygen-containing functional groups” in SHOS coals determined by 13C-NMR are actually sulfur-containing groups, which results in the anomaly that the oxygen-containing structures increase with coal rank. Full article
(This article belongs to the Special Issue Toxic Mineral Matter in Coal and Coal Combustion Products)
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Open AccessReview Concentration and Distribution of Cadmium in Coals of China
Minerals 2018, 8(2), 48; https://doi.org/10.3390/min8020048
Received: 25 October 2017 / Revised: 25 January 2018 / Accepted: 29 January 2018 / Published: 1 February 2018
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Abstract
Cadmium is considered an important toxicant of major environmental and occupational concern. It can contaminate water, soil, and the atmosphere through coal mining, beneficiation, combustion, etc. This paper is based on the published literature, especially those data reported during the recent 10 years,
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Cadmium is considered an important toxicant of major environmental and occupational concern. It can contaminate water, soil, and the atmosphere through coal mining, beneficiation, combustion, etc. This paper is based on the published literature, especially those data reported during the recent 10 years, including 2999 individual samples from 116 coalfields or mines in 26 provinces in China. The arithmetic mean of cadmium in Chinese coals is 0.43 μg/g. Taking the coal reserves into consideration, the average value of cadmium in coal is estimated as 0.28 μg/g. Cadmium is mostly enriched in the Southern coal-distribution area during the Late Permian. Furthermore, cadmium is highly enriched in Hunan and Chongqing. The modes of occurrence of cadmium in Chinese coals are quite complex. Cadmium in Chinese coals has been found in sulfides, organic matter, silicate minerals, and other minerals. A marine environment may be the most significant factor that influences the cadmium accumulation in coal from the Southern coal-distribution area during the Late Permian. In addition, hydrothermal fluids, source rocks, and volcanic ash have also influenced the content of cadmium in some coalfields in China. Full article
(This article belongs to the Special Issue Toxic Mineral Matter in Coal and Coal Combustion Products)
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