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Minerals, Volume 8, Issue 5 (May 2018)

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Cover Story (view full-size image) We identify the new mineral species oyonite, ideally Ag3Mn2Pb4Sb7As4S24, in the Uchucchacua [...] Read more.
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Open AccessArticle Automatic Parameter Tuning of Multiple-Point Statistical Simulations for Lateritic Bauxite Deposits
Minerals 2018, 8(5), 220; https://doi.org/10.3390/min8050220
Received: 25 April 2018 / Revised: 18 May 2018 / Accepted: 18 May 2018 / Published: 22 May 2018
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Abstract
The application of multiple-point statistics (MPS) in the mining industry is not yet widespread and there are very few applications so far. In this paper, we focus on the problem of algorithmic input parameter selection, which is required to perform MPS simulations. The
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The application of multiple-point statistics (MPS) in the mining industry is not yet widespread and there are very few applications so far. In this paper, we focus on the problem of algorithmic input parameter selection, which is required to perform MPS simulations. The usual approach for selecting the parameters is to conduct a manual sensitivity analysis by testing a set of parameters and evaluating the resulting simulation qualities. However, carrying out such a sensitivity analysis may require significant time and effort. The purpose of this paper is to propose a novel approach to automate the parameter tuning process. The primary criterion used to select the parameters is the reproduction of the conditioning data patterns in the simulated image. The parameters of the MPS algorithm are obtained by iteratively optimising an objective function with simulated annealing. The objective function quantifies the dissimilarity between the pattern statistics of the conditioning data and the simulation image in two steps: the pattern statistics are first obtained using a smooth histogram method; then, the difference between the histograms is evaluated by computing the Jensen–Shanon divergence. The proposed approach is applied for the simulation of the geological interface (footwall contact) within a laterite-type bauxite mine deposit using the Direct Sampling MPS algorithm. The results point out two main advantages: (1) a faster parameter tuning process and (2) more objective determination of the parameters. Full article
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Open AccessArticle Preparation of Mullite-Silica Composites Using Silica-Rich Monophasic Precursor Obtained as a Byproduct of Mineral Carbonation of Blast-Furnace Slag
Minerals 2018, 8(5), 219; https://doi.org/10.3390/min8050219
Received: 25 April 2018 / Revised: 19 May 2018 / Accepted: 20 May 2018 / Published: 22 May 2018
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Abstract
Previously, mineral carbonation of blast-furnace slag was carried out to sequestrate CO2 and attain pure CaCO3 crystals. In this process, amorphous silica-alumina nanoparticles were obtained as a byproduct. In this study, the crystallization of these nanoparticles on calcination at various temperatures
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Previously, mineral carbonation of blast-furnace slag was carried out to sequestrate CO2 and attain pure CaCO3 crystals. In this process, amorphous silica-alumina nanoparticles were obtained as a byproduct. In this study, the crystallization of these nanoparticles on calcination at various temperatures in air was examined using TGA-DTA, XRD, MAS-NMR spectroscopy, and FT-IR spectroscopy. The precursor nanoparticles (Si:Al = 78:22 mol %) were prepared using the solution extracted from blast-furnace slag (BFS) with acetic acid at room temperature. The XRD analysis showed that the initial amorphous state was retained up to 800 °C, and decomposition to amorphous silica and mullite started after calcination at 950 °C. At temperatures between 1150 °C and 1250 °C, amorphous silica crystalized to cristobalite, which eventually melted to glassy silica at 1500 °C. The mullite crystals initially adopted a metastable tetragonal phase and transformed to a stable, needle-like orthorhombic phase at higher temperatures. 27Al MAS-NMR spectroscopy revealed that octahedrally coordinated Al was favored up to a temperature of 800 °C as a result of the dehydration process and transformed into tetrahedrally coordinated Al at higher temperatures. A microstructural examination revealed that the initially randomly-oriented mullite developed into stable, needle-like grains owing to anisotropic grain growth in the presence of a glass phase at high temperatures. This study suggests that the recycling of BFS can be exploited for the procurement of a mullite-type ceramic material. Full article
(This article belongs to the Special Issue Mineral Materials)
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Open AccessArticle Tsygankoite, Mn8Tl8Hg2(Sb21Pb2Tl)Σ24S48, a New Sulfosalt from the Vorontsovskoe Gold Deposit, Northern Urals, Russia
Minerals 2018, 8(5), 218; https://doi.org/10.3390/min8050218
Received: 2 May 2018 / Revised: 18 May 2018 / Accepted: 19 May 2018 / Published: 21 May 2018
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Abstract
Tsygankoite, ideally Mn8Tl8Hg2(Sb21Pb2Tl)Σ24S48, is a new sulfosalt discovered at the Vorontsovskoe gold deposit, Northern Urals, Russia. It occurs as lath-like elongated crystals up to 0.2 mm embedded in calcite–dolomite–clinochlore
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Tsygankoite, ideally Mn8Tl8Hg2(Sb21Pb2Tl)Σ24S48, is a new sulfosalt discovered at the Vorontsovskoe gold deposit, Northern Urals, Russia. It occurs as lath-like elongated crystals up to 0.2 mm embedded in calcite–dolomite–clinochlore matrix. The associated minerals also include aktashite, alabandite, arsenopyrite, barite, cinnabar, fluorapatite, orpiment, pyrite, realgar, routhierite, sphalerite, tilasite, and titanite. The new mineral is non-fluorescent, black, and opaque with a metallic lustre and black streak. It is brittle with an uneven fracture and no obvious parting and cleavage. Its Vickers hardness (VHN10) is 144 kg/mm2 (range 131–167 kg/mm2) and its calculated density is 5.450 g cm. In reflected light, tsygankoite is white; between crossed polars it is dark grey to black. It is strongly anisotropic: rotation tints vary from light grey to dark grey to black. Pleochroism and internal reflections are not observed. The chemical composition of tsygankoite (wt %, electron-microprobe data) is: Mn 6.29, Hg 5.42, Tl 26.05, Pb 5.84, As 3.39, Sb 30.89, S 21.87, total 99.75. The empirical formula, calculated on the basis of 90 atoms pfu, is: Mn8.06Tl8.00Hg1.90(Sb17.87As3.19Pb1.99Tl0.97)Σ24.02S48.03. Tsygankoite is monoclinic, space group C2/m, a = 21.362(4) Å, b = 3.8579(10) Å, c = 27.135(4) Å, β = 106.944(14)°, V = 2139.19(17) Å3 and Z = 1. The five strongest diffraction peaks from X-ray powder pattern (listed as (d,Å(I)(hkl)) are: 3.587(100)(112), 3.353(70)(−114), 3.204(88)(405), 2.841(72)(−513), and 2.786(99)(−514). The crystal structure of tsygankoite was refined from single-crystal X-ray diffraction data to R = 0.0607 and consists of an alternation of two thick layer-like arrays, one based on PbS-archetype and the second on SnS-archetype. Tsygankoite has been approved by the IMA-CNMNC under the number 2017-088. It is named for Mikhail V. Tsyganko, a mineral collector from Severouralsk, Northern Urals, Russia, who collected the samples where the new mineral was discovered. Full article
(This article belongs to the Special Issue Thallium: Mineralogy, Geochemistry and Ore Processes)
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Open AccessArticle Surface-Modified Garnet Particles for Reinforcing Epoxy Composites
Minerals 2018, 8(5), 217; https://doi.org/10.3390/min8050217
Received: 6 March 2018 / Revised: 14 May 2018 / Accepted: 17 May 2018 / Published: 19 May 2018
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Abstract
The present study investigated the tribological performance of epoxy (EP) matrix composites enhanced with natural garnet. The garnet was surface-modified with sodium stearate for optimal performance. Composites comprising different contents and particle sizes of modified garnet (MG) were prepared with a mixture of
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The present study investigated the tribological performance of epoxy (EP) matrix composites enhanced with natural garnet. The garnet was surface-modified with sodium stearate for optimal performance. Composites comprising different contents and particle sizes of modified garnet (MG) were prepared with a mixture of EP and MG. The sodium stearate-bonded garnet and EP formed a stable structure. Tribological performance was measured by a ball-on-plate apparatus under permanent dry sliding conditions and a wear track was obtained by an optical profilometer. The wear mechanism was explored by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) images. Wear test results showed that the coefficient of friction for all EP/MG composites decreased compared with that for neat epoxy. The results also indicated that the addition of MG can evidently improve the tribological properties of EP matrix composites. Full article
(This article belongs to the Special Issue Mineral Materials)
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Open AccessArticle Effect of Ethylene Diamine Phosphate on the Sulfidization Flotation of Chrysocolla
Minerals 2018, 8(5), 216; https://doi.org/10.3390/min8050216
Received: 29 April 2018 / Revised: 16 May 2018 / Accepted: 16 May 2018 / Published: 18 May 2018
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Abstract
In this study, ethylene diamine phosphate (EDP) was employed as an activator to improve the sulfidization and flotation of chrysocolla. The micro-flotation experiment results indicated that EDP could greatly increase the flotation recovery of chrysocolla. BET and TEM measurements confirmed that the porous
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In this study, ethylene diamine phosphate (EDP) was employed as an activator to improve the sulfidization and flotation of chrysocolla. The micro-flotation experiment results indicated that EDP could greatly increase the flotation recovery of chrysocolla. BET and TEM measurements confirmed that the porous structure of the chrysocolla’s surface would lead to large amounts of the reagents. ICP-AES analysis revealed that the addition of EDP caused more active Cu sites formed on the chrysocolla’s surface, enhancing the adsorption of S2− on its surface. Meanwhile, a redox reaction occurred between the S2− and [Cu(en)2]2+ ions causing the Cu, S, and N in the solution to counter-adsorb onto the chrysocolla’s surface by forming new complexes. During this reaction, the Cu(II) species reduced to Cu(I) species and the sulfide ions in the form of S2−, S22−, Sn2−, and SO42− appeared on the mineral surface. The zeta potential measurements further revealed that the EDP-activated chrysocolla surfaces adsorbed more sulfide species and xanthate species, thereby improving the floatability of the chrysocolla. Full article
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Open AccessReview Bioleaching of Arsenic-Bearing Copper Ores
Minerals 2018, 8(5), 215; https://doi.org/10.3390/min8050215
Received: 10 February 2018 / Revised: 6 May 2018 / Accepted: 9 May 2018 / Published: 17 May 2018
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Abstract
World copper (Cu) production has been strongly affected by arsenic (As) content, because As-rich Cu concentrates are not desirable in the metal foundries. When As-rich Cu concentrates are processed by smelting they release As as volatile compounds into the atmosphere and inside furnaces,
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World copper (Cu) production has been strongly affected by arsenic (As) content, because As-rich Cu concentrates are not desirable in the metal foundries. When As-rich Cu concentrates are processed by smelting they release As as volatile compounds into the atmosphere and inside furnaces, generating serious risks to human health. In recent years, exports of Cu concentrates are being penalized for the increasingly high As content of the ores, causing economies that depend on the Cu market to be seriously harmed by this impurity. In the last few decades, biohydrometallurgy has begun to replace the traditional Cu sulfide processing, however bioleaching processes for As-bearing Cu ores which contain enargite are still in the development stage. Researchers have not yet made successful progress in enargite bioleaching using typical mesophilic and thermophilic bacteria that oxidize sulfide. New approaches based on direct oxidative/reductive dissolution of As from enargite could result in significant contributions to Cu biohydrometallurgy. Thus, As-rich Cu concentrates could be pre-treated by bioleaching, replacing current technologies like roasting, pressure leaching and alkaline leaching by selective biological arsenite oxidation or arsenate reduction. In this article, we review the As problem in Cu mining, conventional technologies, the biohydrometallurgy approach, and As bioleaching as a treatment alternative. Full article
(This article belongs to the collection Bioleaching)
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Open AccessArticle Metasomatic Replacement of Albite in Nature and Experiments
Minerals 2018, 8(5), 214; https://doi.org/10.3390/min8050214
Received: 1 April 2018 / Revised: 4 May 2018 / Accepted: 12 May 2018 / Published: 17 May 2018
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Abstract
Replacement of albite by sodium-rich, secondary phases is a common phenomenon, observed in different geological settings and commonly attributed to alkaline metasomatism. We investigated growth of nepheline and sodalite on albite in time series experiments between two and 14 days. A total of
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Replacement of albite by sodium-rich, secondary phases is a common phenomenon, observed in different geological settings and commonly attributed to alkaline metasomatism. We investigated growth of nepheline and sodalite on albite in time series experiments between two and 14 days. A total of 42 hydrothermal experiments were performed in cold-seal hydrothermal vessels at a constant pressure of 4 kbar and 200–800 °C in the system SiO2–Al2O3–NaCl–H2O. To allow for fluid flow and material transport, a double-capsule technique was used; hereby, a perforated inner Pt capsule was filled with cleavage fragments of natural albite, whereas the shut outer Au capsule was filled with γ-Al2O3 and the NaCl–H2O solution. Complete overgrowth of albite by sodalite and nepheline occurred after just two days of experiments. At high salinity (≥17 wt % NaCl) sodalite is the stable reaction product over the whole temperature range whereas nepheline occurs at a lower relative bulk salinity than sodalite and is restricted to a high temperature of ≥700 °C. The transformation of albite starts along its grain margins, cracks or twin lamellae. Along the reaction front sodalite crystallizes as small euhedral and highly porous grains forming polycrystalline aggregates. Coarse sodalite dominates in the outermost domains of the reaction zones, suggesting recrystallization. Sodalite may contain fluid inclusions with trapped NaCl-rich brine, demonstrating that the interconnected microporosity provides excellent pathways for fluid-assisted material transport. Highly porous nepheline forms large, euhedral crystals with rectangular outline. Sodalite and nepheline in natural rock samples display only minor porosity but fluid and secondary mineral inclusions, pointing to coarsening of a previously present microporosity. The reaction interface between sodalite and albite in natural rock samples is marked by open channels in transmission electron microscopy. In many of the experiments, a zone of Si–H-rich, amorphous material is developed at the reaction front, which occurs at a temperature of up to of 750 °C as nanometer to 350 µm wide reaction zone around albite. This change in composition corresponds with the abrupt termination of the crystalline feldspar structure. The presence of sodalite as micro- to nanometer-sized, euhedral crystals within the amorphous zone demonstrates, that both the sodalite reaction rim and the amorphous material allow for fluid-assisted material transport between the crystalline albite (release of Si, Al) and the bulk fluid (H2O, Na, Cl). This texture, moreover, suggests that the amorphous phase represents a metastable interstage reaction product, which is progressively replaced by sodalite and nepheline. Remarkably, product sodalite, nepheline, and the amorphous material largely inherit the trace element budget of the respective ancestor albite, indicating that at least part of the trace elements remained fixed during the reaction process. The observed reaction textures in both natural and experimental samples indicate an interfacial dissolution–reprecipitation mechanism. Results of our study bear important implications with respect to mineral replacement in the presence of a fluid phase, especially regarding the interpretation of trace element patterns of the product phases. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
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Open AccessArticle Geochronology, Petrology, and Genesis of Two Granitic Plutons of the Xianghualing Ore Field in South Hunan Province: Constraints from Zircon U–Pb Dating, Geochemistry, and Lu–Hf Isotopic Compositions
Minerals 2018, 8(5), 213; https://doi.org/10.3390/min8050213
Received: 21 April 2018 / Revised: 11 May 2018 / Accepted: 12 May 2018 / Published: 15 May 2018
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Abstract
Two small-sized granitic plutons, outcropped in Xianghualing ore field, South Hunan (South China), have a close relationship with the super large-scale Sn–W polymetallic mineralization in this ore field. The Laiziling and Jianfengling plutons are composed of medium- to coarse-grained two-mica and coarse-grained biotite
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Two small-sized granitic plutons, outcropped in Xianghualing ore field, South Hunan (South China), have a close relationship with the super large-scale Sn–W polymetallic mineralization in this ore field. The Laiziling and Jianfengling plutons are composed of medium- to coarse-grained two-mica and coarse-grained biotite granites, respectively, and have zircon U–Pb ages of 156.4 ± 1.4 Ma and 165.2 ± 1.4 Ma, respectively. Both of the Laiziling and Jianfengling granites are characterized by extremely similar elemental and Lu–Hf isotopic compositions with high contents of SiO2, Al2O3, Na2O, K2O, high A/CNK ratios, negative εHf(t) values (ranging from −3.86 to −1.38 and from −5.44 to −3.71, respectively), and old TDMC ages (ranging from 1.30 to 1.47 Ga and from 1.32 to 1.56 Ga, respectively). These features indicate that they both belong to highly fractionated A-type granites, and were formed in an extensional setting and from the same magma chamber originated from the Paleoproterozoic metamorphic basement of South China with a certain amount of mantle-derived magma involved with temperatures of ca. 730 °C and low oxygen fugacity. Full article
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Open AccessArticle Effects of Microbial Growth Conditions on Synthesis of Magnetite Nanoparticles using Indigenous Fe(III)-Reducing Bacteria
Minerals 2018, 8(5), 212; https://doi.org/10.3390/min8050212
Received: 2 March 2018 / Revised: 10 May 2018 / Accepted: 11 May 2018 / Published: 14 May 2018
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Abstract
Recent researches have shown that microbe–metal interactions play an important role in metal cycling and biomineralization in subsurface environments. The objective of this research was to study the effects of microbial growth conditions for size control on the synthesis of magnetite nanoparticles using
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Recent researches have shown that microbe–metal interactions play an important role in metal cycling and biomineralization in subsurface environments. The objective of this research was to study the effects of microbial growth conditions for size control on the synthesis of magnetite nanoparticles using Fe(III)-reducing bacteria enriched from intertidal flat sediments in Korea. The microbial formation of the magnetite nanoparticles was examined under various incubation temperatures (8–35 °C), concentrations (20–60 mM) of magnetite precursor, medium pHs (6.5–8.5), and incubation times (0–3 weeks). The Fe(III)-reducing bacteria formed 2~10 nm-sized magnetite (Fe3O4) by reduction of 40 mM akaganeite, especially under the conditions at 25 °C and medium pH = 8.5 within a 1-week incubation time. The magnetite nanoparticles formed by microbial processes exhibited superparamagnetic behavior. Full article
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Open AccessReview 210Pb and 210Po in Geological and Related Anthropogenic Materials: Implications for Their Mineralogical Distribution in Base Metal Ores
Minerals 2018, 8(5), 211; https://doi.org/10.3390/min8050211
Received: 19 April 2018 / Revised: 8 May 2018 / Accepted: 10 May 2018 / Published: 13 May 2018
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Abstract
The distributions of 210Pb and 210Po, short half-life products of 238U decay, in geological and related anthropogenic materials are reviewed, with emphasis on their geochemical behaviours and likely mineral hosts. Concentrations of natural 210Pb and 210Po in igneous
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The distributions of 210Pb and 210Po, short half-life products of 238U decay, in geological and related anthropogenic materials are reviewed, with emphasis on their geochemical behaviours and likely mineral hosts. Concentrations of natural 210Pb and 210Po in igneous and related hydrothermal environments are governed by release from crustal reservoirs. 210Po may undergo volatilisation, inducing disequilibrium in magmatic systems. In sedimentary environments (marine, lacustrine, deltaic and fluvial), as in soils, concentrations of 210Pb and 210Po are commonly derived from a combination of natural and anthropogenic sources. Enhanced concentrations of both radionuclides are reported in media from a variety of industrial operations, including uranium mill tailings, waste from phosphoric acid production, oil and gas exploitation and energy production from coals, as well as in residues from the mining and smelting of uranium-bearing copper ores. Although the mineral hosts of the two radionuclides in most solid media are readily defined as those containing parent 238U and 226Ra, their distributions in some hydrothermal U-bearing ores and the products of processing those ores are much less well constrained. Much of the present understanding of these radionuclides is based on indirect data rather than direct observation and potential hosts are likely to be diverse, with deportments depending on the local geochemical environment. Some predictions can nevertheless be made based on the geochemical properties of 210Pb and 210Po and those of the intermediate products of 238U decay, including isotopes of Ra and Rn. Alongside all U-bearing minerals, the potential hosts of 210Pb and 210Po may include Pb-bearing chalcogenides such as galena, as well as a range of sulphates, carbonates, and Fe-oxides. 210Pb and 210Po are also likely to occur as nanoparticles adsorbed onto the surface of other minerals, such as clays, Fe-(hydr)oxides and possibly also carbonates. In rocks, unsupported 210Pb- and/or 210Po-bearing nanoparticles may also be present within micro-fractures in minerals and at the interfaces of mineral grains. Despite forming under very limited and special conditions, the local-scale isotopic disequilibrium they infer is highly relevant for understanding their distributions in mineralized rocks and processing products. Full article
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Open AccessArticle Si-Disordering in MgAl2O4-Spinel under High P-T Conditions, with Implications for Si-Mg Disorder in Mg2SiO4-Ringwoodite
Minerals 2018, 8(5), 210; https://doi.org/10.3390/min8050210
Received: 20 April 2018 / Revised: 8 May 2018 / Accepted: 8 May 2018 / Published: 12 May 2018
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Abstract
A series of Si-bearing MgAl2O4-spinels were synthesized at 1500–1650 °C and 3–6 GPa. These spinels had SiO2 contents of up to ~1.03 wt % and showed a substitution mechanism of Si4+ + Mg2+ = 2Al3+
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A series of Si-bearing MgAl2O4-spinels were synthesized at 1500–1650 °C and 3–6 GPa. These spinels had SiO2 contents of up to ~1.03 wt % and showed a substitution mechanism of Si4+ + Mg2+ = 2Al3+. Unpolarized Raman spectra were collected from polished single grains, and displayed a set of well-defined Raman peaks at ~610, 823, 856 and 968 cm−1 that had not been observed before. Aided by the Raman features of natural Si-free MgAl2O4-spinel, synthetic Si-free MgAl2O4-spinel, natural low quartz, synthetic coesite, synthetic stishovite and synthetic forsterite, we infer that these Raman peaks should belong to the SiO4 groups. The relations between the Raman intensities and SiO2 contents of the Si-bearing MgAl2O4-spinels suggest that under some P-T conditions, some Si must adopt the M-site. Unlike the SiO4 groups with very intense Raman signals, the SiO6 groups are largely Raman-inactive. We further found that the Si cations primarily appear on the T-site at P-T conditions ≤~3–4 GPa and 1500 °C, but attain a random distribution between the T-site and M-site at P-T conditions ≥~5–6 GPa and 1630–1650 °C. This Si-disordering process observed for the Si-bearing MgAl2O4-spinels suggests that similar Si-disordering might happen to the (Mg,Fe)2SiO4-spinels (ringwoodite), the major phase in the lower part of the mantle transition zone of the Earth and the benchmark mineral for the very strong shock stage experienced by extraterrestrial materials. The likely consequences have been explored. Full article
(This article belongs to the Special Issue Spinel Group Minerals)
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Open AccessArticle The Carbonation of Wollastonite: A Model Reaction to Test Natural and Biomimetic Catalysts for Enhanced CO2 Sequestration
Minerals 2018, 8(5), 209; https://doi.org/10.3390/min8050209
Received: 13 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 11 May 2018
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Abstract
One of the most promising strategies for the safe and permanent disposal of anthropogenic CO2 is its conversion into carbonate minerals via the carbonation of calcium and magnesium silicates. However, the mechanism of such a reaction is not well constrained, and its
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One of the most promising strategies for the safe and permanent disposal of anthropogenic CO2 is its conversion into carbonate minerals via the carbonation of calcium and magnesium silicates. However, the mechanism of such a reaction is not well constrained, and its slow kinetics is a handicap for the implementation of silicate mineral carbonation as an effective method for CO2 capture and storage (CCS). Here, we studied the different steps of wollastonite (CaSiO3) carbonation (silicate dissolution → carbonate precipitation) as a model CCS system for the screening of natural and biomimetic catalysts for this reaction. Tested catalysts included carbonic anhydrase (CA), a natural enzyme that catalyzes the reversible hydration of CO2(aq), and biomimetic metal-organic frameworks (MOFs). Our results show that dissolution is the rate-limiting step for wollastonite carbonation. The overall reaction progresses anisotropically along different [hkl] directions via a pseudomorphic interface-coupled dissolution–precipitation mechanism, leading to partial passivation via secondary surface precipitation of amorphous silica and calcite, which in both cases is anisotropic (i.e., (hkl)-specific). CA accelerates the final carbonate precipitation step but hinders the overall carbonation of wollastonite. Remarkably, one of the tested Zr-based MOFs accelerates the dissolution of the silicate. The use of MOFs for enhanced silicate dissolution alone or in combination with other natural or biomimetic catalysts for accelerated carbonation could represent a potentially effective strategy for enhanced mineral CCS. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
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Open AccessArticle Removal Process of Structural Oxygen from Tetrahedrons in Muscovite during Acid Leaching of Vanadium-Bearing Shale
Minerals 2018, 8(5), 208; https://doi.org/10.3390/min8050208
Received: 21 April 2018 / Revised: 4 May 2018 / Accepted: 9 May 2018 / Published: 11 May 2018
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Abstract
Process mineralogy shows that most vanadium in mica-type black shale exists in the octahedral sites of muscovite. The extraction of vanadium mainly occurs in the acid leaching process with participation of H ions. In this work, we firstly analyzed the dissolution rules of
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Process mineralogy shows that most vanadium in mica-type black shale exists in the octahedral sites of muscovite. The extraction of vanadium mainly occurs in the acid leaching process with participation of H ions. In this work, we firstly analyzed the dissolution rules of elements in acid leaching of muscovite, then adopted the density functional theory (DFT) calculation to accurately visualize the primary process of the surface corrosion of muscovite by H ions. The experimental results show that K releases the fastest and the release of Al is consistent with K. The simulation results find that the H preferentially shifts to the unsaturated structured O of the tetrahedron to form a strong 001 surface hydroxyl after replacing K, as well as relaxing the near Al(Si)–O bonds for the further removal of structural oxygen. Then, the 001 surface hydroxyls more likely participate in the dehydroxylation reaction through the reverse-path mechanism to remove the structural oxygen and break the hexagonal rings of the tetrahedral sheets. Remarkably, the formation and removal of structural water are overall endoergic, meaning that the disintegration of muscovite requires a sustained supply of heat. Further, the octahedral sheets where vanadium exists can be exposed to the acid environment for overall destruction. This detailed atomic migration process in acid leaching of black shale is visualized, which not only illuminates the reaction mechanism of H ions with the muscovite, but also provides guidance for vanadium extraction from black shale and a new concept for the destruction of other minerals. Full article
(This article belongs to the Special Issue Process Mineralogy of Critical Metals)
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Open AccessArticle Interfacial Precipitation of Phosphate on Hematite and Goethite
Minerals 2018, 8(5), 207; https://doi.org/10.3390/min8050207
Received: 19 March 2018 / Revised: 30 April 2018 / Accepted: 9 May 2018 / Published: 10 May 2018
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Abstract
Adsorption and subsequent precipitation of dissolved phosphates on iron oxides, such as hematite and goethite, is of considerable importance in predicting the bioavailability of phosphates. We used in situ atomic force microscopy (AFM) to image the kinetic processes of phosphate-bearing solutions interacting with
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Adsorption and subsequent precipitation of dissolved phosphates on iron oxides, such as hematite and goethite, is of considerable importance in predicting the bioavailability of phosphates. We used in situ atomic force microscopy (AFM) to image the kinetic processes of phosphate-bearing solutions interacting with hematite or goethite surfaces. The nucleation of nanoparticles (1.0–4.0 nm in height) of iron phosphate (Fe(III)-P) phases, possibly an amorphous phase at the initial stages, was observed during the dissolution of both hematite and goethite at the earliest crystallization stages. This was followed by a subsequent aggregation stage where larger particles and layered precipitates are formed under different pH values, ionic strengths, and organic additives. Kinetic analysis of the surface nucleation of Fe-P phases in 50 mM NH4H2PO4 at pH 4.5 showed the nucleation rate was greater on goethite than hematite. Enhanced goethite and hematite dissolution in the presence of 10 mM AlCl3 resulted in a rapid increase in Fe-P nucleation rates. A low concentration of citrate promoted the nucleation, whereas nucleation was inhibited at higher concentrations of citrate. By modeling using PHREEQC, calculated saturation indices (SI) showed that the three Fe(III)-P phases of cacoxenite, tinticite, and strengite may be supersaturated in the reacted solutions. Cacoxenite is predicted to be more thermodynamically favorable in all the phosphate solutions if equilibrium is reached with respect to hematite or goethite, although possibly only amorphous precipitates were observed at the earliest stages. These direct observations at the nanoscale may improve our understanding of phosphate immobilization in iron oxide-rich acid soils. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
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Open AccessArticle Synthesis of Di-(2-ethylhexyl) Phosphoric Acid (D2EHPA)-Tributyl Phosphate (TBP) Impregnated Resin and Application in Adsorption of Vanadium(IV)
Minerals 2018, 8(5), 206; https://doi.org/10.3390/min8050206
Received: 4 March 2018 / Revised: 2 May 2018 / Accepted: 5 May 2018 / Published: 10 May 2018
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Abstract
In order to improve the adsorption capability of solvent-impregnated resins (SIRs) for vanadium(IV) (V(IV)), the dual extractant (D2EHPA (Di-(2-ethylhexyl) phosphoric acid) and TBP (Tributyl phosphate)) impregnated resins (D-TIRs) were prepared by impregnating AmberliteTM XAD-16HP macroporous resins with the mixed extractant that is
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In order to improve the adsorption capability of solvent-impregnated resins (SIRs) for vanadium(IV) (V(IV)), the dual extractant (D2EHPA (Di-(2-ethylhexyl) phosphoric acid) and TBP (Tributyl phosphate)) impregnated resins (D-TIRs) were prepared by impregnating AmberliteTM XAD-16HP macroporous resins with the mixed extractant that is composed by different molar ratios of D2EHPA to TBP. The effects of the ratio of D2EHPA to TBP on the performance of D-TIRs were investigated. The results show that the impregnation ratio of the D-TIRs decreases gradually with the increasing proportion of TBP in the mixed extractant. The sole-TBP impregnated resins (TIRs) have no adsorption capability for V(IV), indicating that the adsorption of V(IV) is attributed to D2EHPA. The adsorption capacity of D-TIRs for V(IV) attained the maximum when the ratio of D2EHPA to TBP is 7:3 at pH 1.8, and it can be improved by increasing the extractants concentration during the impregnation process. Adsorption isotherm indicates that the addition of TBP can increase the adsorption capacity of D-TIRs for V(IV) from 24.65 to 29.75 mg/g after 16 h reaction. Adsorption kinetics verifies that the addition of TBP can largely accelerate the adsorption equilibrium of V(IV) onto the D-TIRs and V(IV). Electrospray ionization (ESI) mass spectra and Fourier transform infrared spectra (FT-IR) analysis indicates that the addition of TBP to D2EHPA can make some dimeric D2EHPA change to monomers by breaking the hydrogen bonds of D2EHPA-dimers, leading to the result that the pseudo-second order kinetic for the adsorption of V(IV) onto the D2EHPA impregnated resins (DIRs) converts to the pseudo-first order kinetic for that onto the D-TIRs. Also, D-TIRs have better separation capability of V(IV) from Fe(II) and Al(III) in the vanadium leaching solution than DIRs. Full article
(This article belongs to the Special Issue Towards Sustainability in Extractive Metallurgy)
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