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Minerals, Volume 8, Issue 4 (April 2018)

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Open AccessArticle Insights into the Surface Transformation and Electrochemical Dissolution Process of Bornite in Bioleaching
Minerals 2018, 8(4), 173; https://doi.org/10.3390/min8040173
Received: 23 March 2018 / Revised: 16 April 2018 / Accepted: 20 April 2018 / Published: 23 April 2018
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Abstract
In this work, density functional theory (DFT) calculations, X-ray photoelectron spectroscopy (XPS) and electrochemistry analysis were combined to analyze the electrochemical dissolution process of bornite during bioleaching. DFT calculations showed that bornite was a conductor with metallic conductivity. The formula of bornite may
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In this work, density functional theory (DFT) calculations, X-ray photoelectron spectroscopy (XPS) and electrochemistry analysis were combined to analyze the electrochemical dissolution process of bornite during bioleaching. DFT calculations showed that bornite was a conductor with metallic conductivity. The formula of bornite may be (Cu+)5Fe3+(S2−)4 and the surface reconstruction of (111)-S surface was discussed. Electrochemistry and XPS analysis showed that bornite tended to be directly oxidized with high conductivity when the potential was higher than 0.3 V vs. Ag/AgCl. Elemental sulfur (S0), FeOOH and CuS were the main intermediate species on the bornite surface during the oxidation process. The production of S0 and FeOOH on bornite surface can be significantly accelerated with increased redox potential, but no insoluble sulfate (SO42−) formed on bornite surface in 0.3–0.65 V vs. Ag/AgCl. The oxidative dissolution of bornite was significantly accelerated with increasing redox potential, which was one important reason why mixed culture was more effective than single strains of A. caldus and L. ferriphilum in bornite bioleaching. The insoluble SO42− was formed mainly through the chemical reactions in solution and then covered the bornite surface in bioleaching. Based on the obtained results, a model for interpreting the dissolution process of bornite in bioleaching was proposed. Full article
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Open AccessArticle Effect of Sodium Sulfite on Floatability of Chalcopyrite and Molybdenite
Minerals 2018, 8(4), 172; https://doi.org/10.3390/min8040172
Received: 14 March 2018 / Revised: 15 April 2018 / Accepted: 16 April 2018 / Published: 22 April 2018
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Abstract
Sodium hydrogen sulfide (NaHS) is commonly used as a copper depressant in the selective flotation of copper and molybdenum ores. However, the process is facing health and safety issues because NaHS readily yields toxic hydrogen sulfide gas (H2S) under acidic conditions.
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Sodium hydrogen sulfide (NaHS) is commonly used as a copper depressant in the selective flotation of copper and molybdenum ores. However, the process is facing health and safety issues because NaHS readily yields toxic hydrogen sulfide gas (H2S) under acidic conditions. In this study, Na2SO3 was proposed as an alternative copper depressant. The effect of Na2SO3 on the surface wettability and floatability of chalcopyrite and molybdenite—typical copper and molybdenum minerals, respectively—was intensively studied using contact angle measurements and flotation tests. Contact angle readings show that the chalcopyrite surface became hydrophilic after the Na2SO3 treatment. Meanwhile, the molybdenite surface was relatively more hydrophobic compared with that of chalcopyrite after the treatment. Flotation tests using pure minerals of chalcopyrite and molybdenite demonstrate that the floatability of chalcopyrite decreased with increasing concentration of Na2SO3. On the other hand, the floatability of molybdenite gradually increased under similar conditions, suggesting that Na2SO3 might have the potential to be used for selective flotation of chalcopyrite and molybdenite. A possible mechanism is proposed in this study to explain the phenomenon using X-ray photoelectron spectroscopy analysis. Full article
(This article belongs to the Special Issue Flotation Chemistry)
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Open AccessArticle Archaean Gold Mineralization in an Extensional Setting: The Structural History of the Kukuluma and Matandani Deposits, Geita Greenstone Belt, Tanzania
Minerals 2018, 8(4), 171; https://doi.org/10.3390/min8040171
Received: 22 March 2018 / Accepted: 22 March 2018 / Published: 21 April 2018
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Abstract
Three major gold deposits, Matandani, Kukuluma, and Area 3, host several million ouncez (Moz) of gold, along a ~5 km long, WNW trend in the E part of the Geita Greenstone Belt, NW Tanzania. The deposits are hosted in Archaean volcanoclastic sediment and
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Three major gold deposits, Matandani, Kukuluma, and Area 3, host several million ouncez (Moz) of gold, along a ~5 km long, WNW trend in the E part of the Geita Greenstone Belt, NW Tanzania. The deposits are hosted in Archaean volcanoclastic sediment and intrusive diorite. The geological evolution of the deposits involved three separate stages: (1) an early stage of syn-sedimentary extensional deformation (D1) around 2715 Ma; (2) a second stage involving overprinting ductile folding (D2–4) and shearing (D5–6) events during N-S compression between 2700 and 2665 Ma, coeval with the emplacement of the Kukuluma Intrusive Complex; and (3) a final stage of extensional deformation (D7) accommodated by minor, broadly east-trending normal faults, preceded by the intrusion of felsic porphyritic dykes at ~2650 Ma. The geometry of the ore bodies at Kukuluma and Matandani is controlled by the distribution of magnetite-rich meta-ironstone, near the margins of monzonite-diorite bodies of the Kukuluma Intrusive Complex. The lithological contacts acted as redox boundaries, where high-grade mineralization was enhanced in damage zones with higher permeability, including syn-D3 hydrothermal breccia, D2–D3 fold hinges, and D6 shears. The actual mineralizing event was syn-D7, and occurred in an extensional setting that facilitated the infiltration of mineralizing fluids. Thus, whilst gold mineralization is late-tectonic, ore zone geometries are linked to older structures and lithological boundaries that formed before gold was introduced. The deformation-intrusive history of the Kukuluma and Matandani deposits is near identical to the geological history of the world-class Nyankanga and Geita Hill deposits in the central part of the Geita Greenstone Belt. This similarity suggests that the geological history of much of the greenstone belt is similar. All major gold deposits in the Geita Greenstone Belt lack close proximity to crustal-scale shear zones; they are associated with intrusive complexes and volcanics that formed in an oceanic plateau rather than subduction setting, and formed late-tectonically during an extensional phase. They are not characteristic of typical orogenic gold deposits. Full article
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Open AccessArticle Breakage Function for HPGR: Mineral and Mechanical Characterization of Tantalum and Tungsten Ores
Minerals 2018, 8(4), 170; https://doi.org/10.3390/min8040170
Received: 1 March 2018 / Revised: 13 April 2018 / Accepted: 17 April 2018 / Published: 20 April 2018
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Abstract
The modelling of high pressure grinding rolls is described by the population balance model, a mass balance which includes several functions that are related to the mineral characteristics, material kinetics and operative conditions of the device. The breakage distribution function is one of
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The modelling of high pressure grinding rolls is described by the population balance model, a mass balance which includes several functions that are related to the mineral characteristics, material kinetics and operative conditions of the device. The breakage distribution function is one of these functions and refers to the way in which the daughter particles are generated by the process of comminution. The piston-die press is presented as a methodology to determine the breakage distribution function of two different materials, from the mechanical response point of view: altered granite and a cal-silicate material. The aim is to determine the relation between the operative conditions and the mineral characteristics in order to explain and predict the breakage function parameters. The materials were characterised using XRD and single compression strength tests. The altered granite is a brittle material, which generates more fines under single compression conditions compared to bed compression conditions, mainly due to the mineral composition and the response of the material to the breakage action. The cal-silicate material shows a normal trend in its breakage behaviour. As is expected, the mineralogical characterisation is a useful tool to predict the values of the parameters of the breakage distribution function. Full article
(This article belongs to the Special Issue Process Mineralogy of Critical Metals)
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Open AccessArticle Carbonation-Induced Mineralogical Changes in Coal Mining Waste Blended Cement Pastes and Their Influence on Mechanical and Microporosity Properties
Minerals 2018, 8(4), 169; https://doi.org/10.3390/min8040169
Received: 12 February 2018 / Revised: 16 April 2018 / Accepted: 17 April 2018 / Published: 20 April 2018
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Abstract
The worldwide pursuit of new eco-efficient pozzolans is ongoing. Kaolinite-based waste is an eco-friendly source of recycled metakaolinite, a highly pozzolanic product. In this study, a blended cement paste containing 20% activated coal waste (ACW) was exposed to a 100% CO2 atmosphere
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The worldwide pursuit of new eco-efficient pozzolans is ongoing. Kaolinite-based waste is an eco-friendly source of recycled metakaolinite, a highly pozzolanic product. In this study, a blended cement paste containing 20% activated coal waste (ACW) was exposed to a 100% CO2 atmosphere at 65% RH for 7 days. The variations in its phase composition and strength were studied and compared to an OPC control. Both pastes were cured for 28 days prior to the carbonation test. Reaction kinetics were assessed using XRD, SEM/EDX, TG/DTG, FT-IR, Micro-Raman spectroscopy, pore solution pH and the cumulative carbonated fraction. The blended cement carbonated 68% faster than the control. While portlandite carbonation was the main reaction in both cements, decalcification was also observed (more intensely in the 20% ACW paste) in other hydraulic calcium phases (C-S-H gel, monocarboaluminate (C4AcH12), ettringite and tetracalcium aluminate (C4AH13). The end product of this reaction was calcium carbonate, mainly in the form of calcite, although traces of aragonite and amorphous carbonate were also detected. Compressive strength values rose with accelerated carbonation time and pore size reduction in both cement pastes. Full article
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Open AccessArticle Effect of Chain Length Compatibility of Alcohols on Muscovite Flotation by Dodecyl Amine
Minerals 2018, 8(4), 168; https://doi.org/10.3390/min8040168
Received: 15 March 2018 / Revised: 11 April 2018 / Accepted: 15 April 2018 / Published: 19 April 2018
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Abstract
A portion of dodecyl amine (DDA) in a muscovite flotation system was replaced with alcohols with different carbon-chain lengths. These alcohols included octanol (OCT); decanol (DEC); dodecanol (DOD); and tetradecanol (TER). The muscovite adsorption behavior of the mixed DDA and alcohol systems were
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A portion of dodecyl amine (DDA) in a muscovite flotation system was replaced with alcohols with different carbon-chain lengths. These alcohols included octanol (OCT); decanol (DEC); dodecanol (DOD); and tetradecanol (TER). The muscovite adsorption behavior of the mixed DDA and alcohol systems were investigated through zeta potential; contact angle; and adsorption quantity tests. Single-mineral flotation tests showed that the muscovite-collecting power of the mixed DDA/alcohol (OCT, DEC, or DOD) system was stronger than that of the pure DDA system. The muscovite-collecting power of the collector systems decreased in the following order: DDA/DEC > DDA/OCT > DDA/DEC > DDA > DDA/TER. Zeta potential and contact angle analysis indicated that when combined with DDA; alcohols physically adsorbed on the surfaces of muscovite. This behavior improved the hydrophobicity of muscovite. Furthermore, adsorption analysis revealed that synergy between DDA and alcohol enhanced the adsorption of alcohol on muscovite. DDA has a dominant role in synergistic adsorption; whereas alcohol has a supporting role. Among all tested alcohols; DDA and DOD exhibit the highest synergetic adsorption effect because of their similar carbon-chain lengths. This similarity promotes the formation of a compact adsorption layer on the muscovite surface. Full article
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Open AccessArticle Strength Development and Microstructure Evolution of Cemented Tailings Backfill Containing Different Binder Types and Contents
Minerals 2018, 8(4), 167; https://doi.org/10.3390/min8040167
Received: 20 March 2018 / Revised: 16 April 2018 / Accepted: 17 April 2018 / Published: 19 April 2018
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Abstract
The microstructure evolution and strength development of cemented tailings backfill (CTB), mixed with plant tailings and cement, is critical to a more thorough and complete understanding of its functionality as a support structure in underground mining operations. Here, an experimental study is conducted
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The microstructure evolution and strength development of cemented tailings backfill (CTB), mixed with plant tailings and cement, is critical to a more thorough and complete understanding of its functionality as a support structure in underground mining operations. Here, an experimental study is conducted to investigate the effect of the solid contents of tailings, binder proportion, and type of cement reagent on unconfined compressive strength (UCS) and microstructure evolution with respect to a 90-day curing time. The results indicate that the mechanical strength gain is proportionally associated with increased binder and solid content. Besides, the samples prepared with 70 wt % solid content and a 25 wt % binder/tailings ratio have a maximum UCS of 6.26 MPa at a curing time of 90 days. In addition, it is also concluded that the binder proportion promotes the strength acquisition of CTB samples. Specifically, the 90-day UCS of the CTB with solid content of 68 wt % and binder content of 25 wt % is approximately twice that of the CTB with a 12.5 wt % binder proportion. Slag cement (Binder B1) and slag cement with 5 wt % NaOH (Binder B2) are used as admixture to replace the cement reagent; the results show that Binder B2 has more advantages than Binder B1 and Portland cement, and is a suitable cementing material for the CTB technology in the Daye Iron Mine. The microstructure is dominated by the network of hydration products and distribution of the pore, and hydrated material is significantly influenced by the curing time. The tailings particles are enclosed by the hydration products, and randomly disperse within their matrix at curing time of 90 days. Finally, the UCSs of CTB samples are observed to significantly increase with the increase in the curing time. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle An Insight into Flotation Chemistry of Pyrite with Isomeric Xanthates: A Combined Experimental and Computational Study
Minerals 2018, 8(4), 166; https://doi.org/10.3390/min8040166
Received: 26 March 2018 / Revised: 12 April 2018 / Accepted: 16 April 2018 / Published: 19 April 2018
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Abstract
The flotation chemistry between pyrite and isomeric xanthates (butyl xanthate and isobutyl xanthate) was investigated by means of adsorption experiments, surface tension tests, and molecular dynamic simulations in this work. The flotation chemical results were confirmed and further interpreted by quantum chemical calculations.
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The flotation chemistry between pyrite and isomeric xanthates (butyl xanthate and isobutyl xanthate) was investigated by means of adsorption experiments, surface tension tests, and molecular dynamic simulations in this work. The flotation chemical results were confirmed and further interpreted by quantum chemical calculations. The experiment results demonstrated that the isobutyl xanthate exhibited superior adsorption capacity and surface activity than those of butyl xanthate in flotation chemistry. In addition, molecular dynamic simulations were simultaneously performed in constant number, constant volume and temperature (NVT), and constant number, constant volume, and pressure (NPT) ensemble, indicating that the NPT ensemble was more suitable to the flotation system and the isobutyl xanthate was easier to be adsorbed on pyrite surface compared with butyl xanthate during an appropriate range of concentrations. Furthermore, the quantum chemical calculations elucidated that the isobutyl xanthate presented higher reactivity than that of the corresponding butyl xanthate based on the frontier molecular orbital theory of chemical reactivity, which was consistent with experimental and simulation results obtained. This work can provide theoretical guidance for an in-depth study of the flotation chemistry of pyrite with isomeric xanthates. Full article
(This article belongs to the Special Issue Flotation Chemistry)
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Open AccessArticle Response Surface Methodology for Optimization of Copper Leaching from Refractory Flotation Tailings
Minerals 2018, 8(4), 165; https://doi.org/10.3390/min8040165
Received: 5 March 2018 / Revised: 27 March 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
Response surface methodology is used to optimize the leaching process for refractory flotation copper tailings. The proportion of the refractory combination oxide copper (chrysocolla) is 64.84%. At present, few studies have examined the leaching of chrysocolla. In this study, we examine the effects
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Response surface methodology is used to optimize the leaching process for refractory flotation copper tailings. The proportion of the refractory combination oxide copper (chrysocolla) is 64.84%. At present, few studies have examined the leaching of chrysocolla. In this study, we examine the effects of several variables, including the amount of concentrated sulfuric acid, leaching temperature, and leaching time, on leaching efficiency. Using a response surface methodology, we develop a quadratic model relanbting all the above experimental variables with leaching efficiency. The resulting model is highly consistent with experimental data. According to the model, the factor with the greatest influence on leaching efficiency is the amount of concentrated sulfuric acid. According to the model, the optimal leaching conditions are 85 kg/t concentrated sulfuric acid, a leaching temperature of 68.51 °C, and a leaching time of 4.36 h. The actual measured leaching efficiency under these conditions is 85.86%, which is close to the value of 86.79% predicted by the model. We study the leaching processes using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) surface scan analyses. Both methods allow us to explore the content of the main element and visually observe its distribution, allowing us to develop effective methods for treating low-grade oxide ores. Full article
(This article belongs to the Special Issue Sustainable Mineral Processing Technologies)
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Open AccessArticle Source and Enrichment of Toxic Elements in Coal Seams around Mafic Intrusions: Constraints from Pyrites in the Yuandian Coal Mine in Anhui, Eastern China
Minerals 2018, 8(4), 164; https://doi.org/10.3390/min8040164
Received: 7 March 2018 / Revised: 8 April 2018 / Accepted: 8 April 2018 / Published: 17 April 2018
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Abstract
Pyrite, a mineral that can cause potential environmental issues in coal mining, is commonly found in coal seams around intrusions. In this paper, pyrites from the Yuandian Coal Mine (Huaibei Coalfield, Anhui, Eastern China) were studied using SEM, Raman and LA-ICP-MS. The pyrite
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Pyrite, a mineral that can cause potential environmental issues in coal mining, is commonly found in coal seams around intrusions. In this paper, pyrites from the Yuandian Coal Mine (Huaibei Coalfield, Anhui, Eastern China) were studied using SEM, Raman and LA-ICP-MS. The pyrite morphologic and geochemical data suggest that (1) four pyrite generations are present (framboidal sedimentary pyrites (Py I) in the original coal, coarse-grained magmatic pyrites (Py II) in the intruding diabase, fine-grained metamorphic pyrites (Py III) in the intrusive contact aureole, and spheroid/vein hydrothermal pyrites (Py IV) in the cokeite); and (2) concentrations of cobalt, nickel, arsenic, selenium, lead and copper in the metamorphic pyrites are much higher than the other pyrite generations. We propose that mafic magmatism is the main contributor of the toxic elements to the intrusion-related cokeite at Yuandian. Full article
(This article belongs to the Special Issue Toxic Mineral Matter in Coal and Coal Combustion Products)
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Open AccessArticle Pore Structure and Fractal Characteristics of Niutitang Shale from China
Minerals 2018, 8(4), 163; https://doi.org/10.3390/min8040163
Received: 14 March 2018 / Revised: 9 April 2018 / Accepted: 12 April 2018 / Published: 17 April 2018
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Abstract
A suite of shale samples from the Lower Cambrian Niutitang Formation in northwestern Hunan Province, China, were investigated to better understand the pore structure and fractal characteristics of marine shale. Organic geochemistry, mineralogy by X-ray diffraction, porosity, permeability, mercury intrusion and nitrogen adsorption
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A suite of shale samples from the Lower Cambrian Niutitang Formation in northwestern Hunan Province, China, were investigated to better understand the pore structure and fractal characteristics of marine shale. Organic geochemistry, mineralogy by X-ray diffraction, porosity, permeability, mercury intrusion and nitrogen adsorption and methane adsorption experiments were conducted for each sample. Fractal dimension D was obtained from the nitrogen adsorption data using the fractal Frenkel-Halsey-Hill (FHH) model. The relationships between total organic carbon (TOC) content, mineral compositions, pore structure parameters and fractal dimension are discussed, along with the contributions of fractal dimension to shale gas reservoir evaluation. Analysis of the results showed that Niutitang shale samples featured high TOC content (2.51% on average), high thermal maturity (3.0% on average), low permeability and complex pore structures, which are highly fractal. TOC content and mineral compositions are two major factors affecting pore structure but they have different impacts on the fractal dimension. Shale samples with higher TOC content had a larger specific surface area (SSA), pore volume (PV) and fractal dimension, which enhanced the heterogeneity of the pore structure. Quartz content had a relatively weak influence on shale pore structure, whereas SSA, PV and fractal dimension decreased with increasing clay mineral content. Shale with a higher clay content weakened pore structure heterogeneity. The permeability and Langmuir volume of methane adsorption were affected by fractal dimension. Shale samples with higher fractal dimension had higher adsorption capacity but lower permeability, which is favorable for shale gas adsorption but adverse to shale gas seepage and diffusion. Full article
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Open AccessArticle Property and Microstructure of Waterborne Self-Setting Geopolymer Coating: Optimization Effect of SiO2/Na2O Molar Ratio
Minerals 2018, 8(4), 162; https://doi.org/10.3390/min8040162
Received: 12 February 2018 / Revised: 31 March 2018 / Accepted: 13 April 2018 / Published: 17 April 2018
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Abstract
As a kind of coating material, the inorganic coating of alkali-activated metakaolin geopolymer cured at high temperature has been studied a lot for special applications. To our best knowledge, however, not much attention has been given to investigate the influence of SiO2
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As a kind of coating material, the inorganic coating of alkali-activated metakaolin geopolymer cured at high temperature has been studied a lot for special applications. To our best knowledge, however, not much attention has been given to investigate the influence of SiO2/Na2O molar ratio on property of the geopolymer coating. This paper is, thus, dedicated to investigate the role of SiO2/Na2O molar ratio on property and microstructure of metakaolin-based geopolymer coating at ambient temperature. The effects on setting behavior, adhesive strength, shrinkage deformation and permeability are discussed. Multiple experiments were used to reveal microstructure changes of the geopolymer coating with different ratios of SiO2/Na2O, including Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The results indicated that the optimal ratio of SiO2/Na2O was 1.0 for good properties of adhesive strength, shrinkage and impermeability. In addition, it has been found that the setting time of geopolymer coating increased with SiO2/Na2O ratio which increased from 0.8 to 1.5. That agrees well with the other property and results of exothermal rate of alkali-activated metakaolin. As for the microstructural changes, the SiO2/Na2O ratio of 1.0 reduced pore size and porosity of the geopolymer coating and particularly increased volume percentage of pores with a size lower than 20 nm. Besides, FTIR results suggested that geopolymer prepared by the ratio of 1.0 was likely to produce more heterogeneous geopolymer due to a greater silicate structural reorganization. Full article
(This article belongs to the Special Issue Geopolymers)
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Open AccessArticle Lauric Acid Hybridizing Fly Ash Composite for Thermal Energy Storage
Minerals 2018, 8(4), 161; https://doi.org/10.3390/min8040161
Received: 27 February 2018 / Revised: 8 April 2018 / Accepted: 11 April 2018 / Published: 16 April 2018
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Abstract
Fly ash includes different mineral phases. This paper reported on the preparation of a novel lauric acid (LA)/fly ash (FA) composite by vacuum impregnation as a form-stable phase change material (PCM) for thermal energy, and especially investigated the effect of the hydrochloric acid-treated
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Fly ash includes different mineral phases. This paper reported on the preparation of a novel lauric acid (LA)/fly ash (FA) composite by vacuum impregnation as a form-stable phase change material (PCM) for thermal energy, and especially investigated the effect of the hydrochloric acid-treated fly ash (FAh) on the thermal energy storage performance of the composites. The morphology, crystalline structure, and porous textures of the samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), X-ray fluorescence (XRF), and differential scanning calorimetry (DSC). The results indicated that hydrochloric acid treatment was beneficial to the increase of loading capacity and crystallinity of LA in the LA/FAh composite, which caused an enhanced thermal storage capacity with latent heats for melting and freezing of LA/FAh (80.94 and 77.39 J/g), higher than those of LA/FA (34.09 and 32.97 J/g), respectively. Furthermore, the mechanism of enhanced thermal storage properties was investigated in detail. Full article
(This article belongs to the Special Issue Mineral Materials)
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Open AccessArticle Experimental Evaluation of Efficient Si Dissolution from Perlite at Low Level Activator’s Concentration
Minerals 2018, 8(4), 160; https://doi.org/10.3390/min8040160
Received: 20 March 2018 / Revised: 29 March 2018 / Accepted: 30 March 2018 / Published: 14 April 2018
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Abstract
This paper deals with the Si dissolution of fine perlite in alkaline solutions for the determination of the SiO2/Na2O mass ratio in the aqueous phase of geopolymer slurries. In the present work, the effect of the main synthesis parameters
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This paper deals with the Si dissolution of fine perlite in alkaline solutions for the determination of the SiO2/Na2O mass ratio in the aqueous phase of geopolymer slurries. In the present work, the effect of the main synthesis parameters such as NaOH concentration and curing temperature on the setting time of the paste were studied. The obtained results showed that the inorganic polymer pastes present fast hardening at low concentrations of NaOH solutions for both 70 and 90 °C. This observation was also identified by the Si dissolution study of perlite pastes as a function of different concentrations of NaOH solutions and different solid to liquid ratios of the slurries, under a constant temperature. The optimum synthesis conditions for geopolymer pastes proved to be a low initial NaOH concentration in the alkaline phase (2–4 M NaOH), where the fast hardening of the paste was attributed to the high SiO2/Na2O mass ratio, enhancing the polycondensation phenomena and promoting the geopolymerization process. Full article
(This article belongs to the Special Issue Geopolymers)
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Open AccessArticle The Evidence of Decisive Effect of Both Surface Microstructure and Speciation of Chalcopyrite on Attachment Behaviors of Extreme Thermoacidophile Sulfolobus metallicus
Minerals 2018, 8(4), 159; https://doi.org/10.3390/min8040159
Received: 25 January 2018 / Revised: 4 April 2018 / Accepted: 9 April 2018 / Published: 13 April 2018
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Abstract
The effect of the surface microstructure and chemical speciation of chalcopyrite on the attachment behaviors of thermoacidophilic archaeon Sulfolobus metallicus was evaluated for the first time by using integrated techniques including epifluorescence microscopy (EFM) and sulfur K-edge X-ray absorption near edge structure (S
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The effect of the surface microstructure and chemical speciation of chalcopyrite on the attachment behaviors of thermoacidophilic archaeon Sulfolobus metallicus was evaluated for the first time by using integrated techniques including epifluorescence microscopy (EFM) and sulfur K-edge X-ray absorption near edge structure (S K-edge XANES) spectroscopy, as well as scanning electron microscopy with energy dispersive spectrometry (SEM/EDS) and Fourier transform infrared (FT-IR) spectroscopy. In order to obtain the specific surface, the chalcopyrite slices were electrochemically oxidized at 0.87 V and reduced at −0.54 V, respectively. The EFM analysis showed that the quantity of cells attaching on the mineral surface increased with time, and the biofilm formed faster on the electrochemically treated slices than on the untreated ones. The SEM-EDS analysis indicated that the deficiency in energy substrate elemental sulfur (S0) in the specific microsize of local defect sites was disadvantageous to the initial attachment of cells. The XANES and FT-IR data suggested that the elemental sulfur (S0) could be in favor of initial attachment, and surface jarosites inhibited the adsorption and growth of S. metallicus. These results demonstrated that not only the surface microstructure but also the chemical speciation defined the initial attachment behaviors and biofilm growth of the extreme thermophilic archaeon S. metallicus. Full article
(This article belongs to the collection Bioleaching)
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Open AccessReview Tracing Mineral Reactions Using Confocal Raman Spectroscopy
Minerals 2018, 8(4), 158; https://doi.org/10.3390/min8040158
Received: 7 March 2018 / Revised: 6 April 2018 / Accepted: 9 April 2018 / Published: 13 April 2018
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Abstract
Raman spectroscopy is a powerful tool used to identify mineral phases, study aqueous solutions and gas inclusions as well as providing crystallinity, crystallographic orientation and chemistry of mineral phases. When united with isotopic tracers, the information gained from Raman spectroscopy can be expanded
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Raman spectroscopy is a powerful tool used to identify mineral phases, study aqueous solutions and gas inclusions as well as providing crystallinity, crystallographic orientation and chemistry of mineral phases. When united with isotopic tracers, the information gained from Raman spectroscopy can be expanded and includes kinetic information on isotope substitution and replacement mechanisms. This review will examine the research to date that utilizes Raman spectroscopy and isotopic tracers. Beginning with the Raman effect and its use in mineralogy, the review will show how the kinetics of isotope exchange between an oxyanion and isotopically enriched water can be determined in situ. Moreover, we show how isotope tracers can help to unravel the mechanisms of mineral replacement that occur at the nanoscale and how they lead to the formation of pseudomorphs. Finally, the use of isotopic tracers as an in situ clock for mineral replacement processes will be discussed as well as where this area of research can potentially be applied in the future. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
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Open AccessArticle Characteristic and Geological Implications of Major Elements and Rare Earth Elements of Triassic Chang 7 Oil Shale in Tongchuan City, Southern Ordos Basin (China)
Minerals 2018, 8(4), 157; https://doi.org/10.3390/min8040157
Received: 19 February 2018 / Revised: 17 March 2018 / Accepted: 9 April 2018 / Published: 12 April 2018
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Abstract
The study of the oil shale from Triassic Chang 7 oil layer in Ordos Basin is of great importance to oil and gas resources investigation. Based on systematic analyses of major elements and rare earth elements of twelve oil shale samples and grain
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The study of the oil shale from Triassic Chang 7 oil layer in Ordos Basin is of great importance to oil and gas resources investigation. Based on systematic analyses of major elements and rare earth elements of twelve oil shale samples and grain size analyses of four sandstone samples from the Yishicun Profile in southern Ordos Basin, the elements characteristics and corresponding geological implications are discussed. The Al/Si and Si/(Si + Al + Fe) of oil shale samples are in small range, with the averages of 0.29 and 0.67, indicating that quartz is the main mineral and the oil shale deposits near terrigenous provenance. Rare earth elements of the oil shale illustrate the enrichment of light rare earth elements (LREEs) and deficit of heavy rare earth elements (HREEs). The Chondrite- and North American shale composite (NASC)-normalized distributing patterns manifested that the oil shale have been derived from the same terrigenous source and controlled by a similar sedimentary environment. The vertical variation of major elements and REEs show that the heterogeneity of oil shale samples is relatively low. By grain size analysis, the interlayer sandstone is the typical turbidite. The Chemical index of alteration (CIA) and (Fe + Mn)/Ti of the oil shale samples ranges in 65.02–78.09 and 6.60–25.82, respectively, indicating that during oil shale sedimentation, the paloeclimate is warm and humid with moderate chemical weathering and that there are obviously hydrothermal fliud activities. The correlation between δCeN and δEuN, total rare earth elements (ΣREE) and (Dy/Sm)N, implying that the diagenesis of oil shale is relatively low with middle diagenetic stage A period. The Ceanom of oil shale samples ranges from −0.094 to −0.049, suggesting that the redox condition of oil shale sedimentation is dominated by strong reducing condition, and the (La/Yb)n is from 1.3 to 2.1, manifesting the whole sedimentary rate of oil shale is relatively low. By the comparison with REEs distribution characteristics from surrounding potential provenance, the main provenances of Chang 7 sedimentation in southern Ordos Basin are from Yinshan Mountain and Qinling-Dabie Mountain. Full article
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Open AccessArticle Analysis of Potential for Critical Metal Resource Constraints in the International Energy Agency’s Long-Term Low-Carbon Energy Scenarios
Minerals 2018, 8(4), 156; https://doi.org/10.3390/min8040156
Received: 27 December 2017 / Revised: 28 March 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
As environmental problems associated with energy systems become more serious, it is necessary to address them with consideration of their interconnections—for example, the energy-mineral nexus. Specifically, it is unclear whether long-term energy scenarios assuming the expansion of low carbon energy technology are sustainable
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As environmental problems associated with energy systems become more serious, it is necessary to address them with consideration of their interconnections—for example, the energy-mineral nexus. Specifically, it is unclear whether long-term energy scenarios assuming the expansion of low carbon energy technology are sustainable in terms of resource constraints. However, there are few studies that comprehensively analyze the possibility of resource constraints in the process of introducing low carbon energy technology from a long-term perspective. Hence, to provide guidelines for technological development and policy-making toward realizing the low carbon society, this paper undertakes the following: (1) Estimation of the impact of the expansion of low carbon energy technology on future metal demand based, on the International Energy Agency (IEA)’s scenarios; (2) estimation of the potential effects of low carbon energy technology recycling on the future supply-demand balance; (3) identification of critical metals that require priority measures. Results indicated that the introduction of solar power and next-generation vehicles may be hindered by resource depletion. Among the metals examined, indium, tellurium, silver, lithium, nickel and platinum were identified as critical metals that require specific measures. As recycling can reduce primary demand by 20%~70% for low carbon energy technology, countermeasures including recycling need to be considered. Full article
(This article belongs to the Special Issue Critical Minerals: Methodologies and Case Studies)
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Open AccessArticle Formation of Fe- and Mg-Rich Smectite under Hyperalkaline Conditions at Narra in Palawan, the Philippines
Minerals 2018, 8(4), 155; https://doi.org/10.3390/min8040155
Received: 5 February 2018 / Revised: 30 March 2018 / Accepted: 8 April 2018 / Published: 12 April 2018
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Abstract
The formation of Fe- and Mg-rich smectite and zeolite under alkaline conditions, as secondary minerals after the alkaline alteration of bentonite in repositories for radioactive waste, is of major concern. It is crucial for safety assessments to know whether smectite is formed as
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The formation of Fe- and Mg-rich smectite and zeolite under alkaline conditions, as secondary minerals after the alkaline alteration of bentonite in repositories for radioactive waste, is of major concern. It is crucial for safety assessments to know whether smectite is formed as a secondary mineral after the alkaline alteration of bentonite. In the present paper, Fe- and Mg-rich smectite, which interacted with the hyperalkaline groundwater at Narra in Palawan, Philippines, was used. Mineralogical and geochemical investigation was conducted to understand the formation process of the smectite and the factors determining the formation of secondary mineral species. The results suggest that a certain amount of smectite may be generated under hyperalkaline conditions, by alteration from amorphous or poorly crystalline components such as M-S-H and F-S-H. Therefore, the controlling factor determining whether smectite or zeolite will be generated as secondary minerals after alkaline alteration of bentonite could be whether nuclei of M-S-H and/or F-S-H are formed. Whether such formation takes place may be determined by the presence of dissolved Mg2+ and Fe2+ in the environment. The formation process of smectite under alkaline conditions, suggested by the results here, is analogous to the generally accepted model of smectite formation as it may have occurred on early Mars. Full article
(This article belongs to the Special Issue Environmental Mineralogy)
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Open AccessArticle Improving the Total Organic Carbon Estimation of the Eagle Ford Shale with Density Logs by Considering the Effect of Pyrite
Minerals 2018, 8(4), 154; https://doi.org/10.3390/min8040154
Received: 20 February 2018 / Revised: 2 April 2018 / Accepted: 8 April 2018 / Published: 12 April 2018
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Abstract
Pyrite is a common mineral with a higher density than most other minerals in the Eagle Ford Shale formation. Hence, if pyrite is not considered in the total organic carbon (TOC) estimation, based on density logs, it may lead to errors. In order
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Pyrite is a common mineral with a higher density than most other minerals in the Eagle Ford Shale formation. Hence, if pyrite is not considered in the total organic carbon (TOC) estimation, based on density logs, it may lead to errors. In order to improve the accuracy of the TOC estimation, we propose an updated TOC estimation method that incorporates the concentration of pyrite and organic porosity. More than 15 m of Eagle Ford Shale samples were analyzed using Rock-Eval pyrolysis, X-ray fluorescence (XRF), and X-ray diffraction (XRD). TOC, elemental concentration, and mineralogical data were analyzed for a better understanding of the relationship between the concentration of TOC and pyrite content in the Eagle Ford formation. An updated petrophysical model—including parameters such as organic pores, solid organic matter, inorganic pores, pyrite, and inorganic rock matrix without pyrite—was built using the sample data from the Eagle Ford. The model was compared with Schmoker’s model and validated with the Eagle Ford field data. The results showed that the updated model had a lower root mean square error (RMSE) than Schmoker’s model. Therefore, it could be used in the future estimation of TOC in pyrite-rich formations. Full article
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Open AccessArticle Application of Scanning Precession Electron Diffraction in the Transmission Electron Microscope to the Characterization of Deformation in Wadsleyite and Ringwoodite
Minerals 2018, 8(4), 153; https://doi.org/10.3390/min8040153
Received: 19 March 2018 / Revised: 7 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
The mantle transition zone represents an important layer in the interior of the Earth that is characterized by phase transformations of olivine polymorphs. Constraining the rheology difference between wadsleyite and ringwoodite is important in determining the viscosity contrast at a depth of 520
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The mantle transition zone represents an important layer in the interior of the Earth that is characterized by phase transformations of olivine polymorphs. Constraining the rheology difference between wadsleyite and ringwoodite is important in determining the viscosity contrast at a depth of 520 km. In this study, we perform a post-mortem by transmission electron microscopy of a wadsleyite + ringwoodite aggregate, deformed at high-pressure and high-temperature, in a deformation-DIA apparatus. From orientation maps acquired by scanning precession electron diffraction, we calculate local misorientations and misorientation-gradients, which are used as a proxy of plastic strain. We show that at 17.3 GPa, 1700 K, the plastic responses of wadsleyite and ringwoodite are comparable, although recovery by subgrain boundary migration is more easily activated in wadsleyite. Full article
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Open AccessArticle Tiberiobardiite, Cu9Al(SiO3OH)2(OH)12(H2O)6(SO4)1.5·10H2O, a New Mineral Related to Chalcophyllite from the Cretaio Cu Prospect, Massa Marittima, Grosseto (Tuscany, Italy): Occurrence and Crystal Structure
Minerals 2018, 8(4), 152; https://doi.org/10.3390/min8040152
Received: 23 March 2018 / Revised: 6 April 2018 / Accepted: 9 April 2018 / Published: 11 April 2018
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Abstract
The new mineral species tiberiobardiite, ideally Cu9Al(SiO3OH)2(OH)12(H2O)6(SO4)1.5·10H2O, has been discovered in the Cretaio Cu prospect, Massa Marittima, Grosseto, Tuscany, Italy, as very rare, light green,
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The new mineral species tiberiobardiite, ideally Cu9Al(SiO3OH)2(OH)12(H2O)6(SO4)1.5·10H2O, has been discovered in the Cretaio Cu prospect, Massa Marittima, Grosseto, Tuscany, Italy, as very rare, light green, vitreous, tabular {0001}, pseudo-hexagonal crystals, up to 200 μm in size and 5 μm in thickness, associated with brochantite. Electron microprobe analysis gave (in wt %, average of 5 spot analyses): SO3 10.37, P2O5 3.41, As2O5 0.05, SiO2 8.13, Al2O3 5.54, Fe2O3 0.74, CuO 62.05, and ZnO 0.03, for a total of 90.32. Based on an idealized O content of 42 atoms per formula unit, assuming the presence of 16 H2O groups and 13.5 cations (without H), the empirical formula of tiberiobardiite is (Cu8.69Al0.21Fe0.10)Σ9.00Al1.00(Si1.51P0.54)Σ2.05S1.44O12.53(OH)13.47·16H2O. The main diffraction lines, corresponding to multiple hkl indices, are [d in Å (relative visual intensity)]: 9.4 (s), 4.67 (s), 2.576 (m), 2.330 (m), and 2.041 (mw). The crystal structure study revealed tiberiobardiite to be trigonal, space group R 3 ¯ , with unit-cell parameters a = 10.6860(4), c = 28.3239(10) Å, V = 2801.0(2) Å3, and Z = 3. The crystal structure was refined to a final R1 = 0.060 for 1747 reflections with Fo > 4σ (Fo) and 99 refined parameters. Tiberiobardiite is the Si-analogue of chalcophyllite, with Si4+ replacing As5+ through the coupled substitution As5+ + O2− = Si4+ + (OH). The name tiberiobardiite honors Tiberio Bardi (b. 1960) for his contribution to the study of the mineralogy of Tuscany. Full article
(This article belongs to the Special Issue New Mineral Species and Their Crystal Structures)
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Open AccessArticle Quantitative Mineralogical Comparison between HPGR and Ball Mill Products of a Sn-Ta Ore
Minerals 2018, 8(4), 151; https://doi.org/10.3390/min8040151
Received: 16 February 2018 / Revised: 4 April 2018 / Accepted: 5 April 2018 / Published: 11 April 2018
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Abstract
The mineralogy and liberation characteristics of the comminuted Penouta leucogranite host of the Sn-Ta ore were determined. Grinding developed by a combination of high-pressure grinding rolls (HPGR) followed by a ball mill (BM) was compared with a single ball mill process. The mineral
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The mineralogy and liberation characteristics of the comminuted Penouta leucogranite host of the Sn-Ta ore were determined. Grinding developed by a combination of high-pressure grinding rolls (HPGR) followed by a ball mill (BM) was compared with a single ball mill process. The mineral characteristics of the grinding products were analyzed using a Tescan Integrated Mineralogical Analyzer (TIMA-X) and X-ray powder diffraction (XRD). The ore contains 103 ppm of Ta and is mainly composed of quartz, albite, microcline, muscovite, and kaolinite. Nb, Ta-rich minerals are columbite-(Mn) and tantalite-(Mn), as well as minor microlite and wodginite. The liberation in the product is high in the size fraction of less than 250 µm (51–52 wt % for columbite-group minerals (CGM) and 74–80 wt % for cassiterite) and reduced in larger particles (8.8–17 wt % for CGM and 28–37 wt % for cassiterite). The recovery in the −250 µm fraction was high, while in the larger fraction it is limited, remaining up to 80 ppm in some tailings. The combined use of HPGR and a BM reduces the particle size distribution of the product and, thus, increases the liberation of the ores. Smaller fractions can be treated directly using gravity methods; however, particles of a size greater than +250 µm should be ground more. Full article
(This article belongs to the Special Issue Process Mineralogy of Critical Metals)
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Open AccessArticle The Influencing Mechanisms of Sodium Hexametaphosphate on Chalcopyrite Flotation in the Presence of MgCl2 and CaCl2
Minerals 2018, 8(4), 150; https://doi.org/10.3390/min8040150
Received: 26 March 2018 / Revised: 5 April 2018 / Accepted: 8 April 2018 / Published: 11 April 2018
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Abstract
Sea water has been used in flotation plants, showing a promising way to save fresh water usage. Previous studies indicated that divalent salts in sea water played negative roles in chalcopyrite flotation, but not much work have been conducted to understand the eliminating
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Sea water has been used in flotation plants, showing a promising way to save fresh water usage. Previous studies indicated that divalent salts in sea water played negative roles in chalcopyrite flotation, but not much work have been conducted to understand the eliminating mechanisms. This study systematically investigated the effects of divalent cations of Ca2+ and Mg2+ on natural flotability of chalcopyrite in the absence of collectors and frothers. The reduced recovery was mainly due to the adsorption of Mg and Ca hydroxyl complexes and precipitation on chalcopyrite surfaces, giving rise to a less hydrophobic surface. The addition of sodium hexametaphosphate (SHMP), however, significantly improved chalcopyrite recovery. Species calculation, contact angle, zeta potential, FTIR and XPS analyses were conducted to understand the influencing mechanisms of divalent ions and the beneficial effects of SHMP on chalcopyrite recovery. The primary mechanism was that SHMP prevented the adsorption of positively charged Mg and Ca compounds or precipitation with hydrophilic properties such as Mg(OH)2 on chalcopyrite surfaces, confirmed by the Derjguin-Landau-Verwey-Overbeek (DLVO) theory. Secondly, SHMP reacted with Mg2+ and Ca2+ to form dissolvable complexes, thereby declining the formation of insoluble Mg2+ and Ca2+ compounds or precipitation. Full article
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Open AccessArticle Developing Effective Separation of Feldspar and Quartz While Recycling Tailwater by HF Pretreatment
Minerals 2018, 8(4), 149; https://doi.org/10.3390/min8040149
Received: 23 February 2018 / Revised: 2 April 2018 / Accepted: 5 April 2018 / Published: 11 April 2018
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Abstract
The effect of hydrofluoric acid (HF) pretreatment on flotation of feldspar and quartz using dodecylamine (DDA) as collector was investigated by micro-flotation, zeta potential, pyrene fluorescence spectroscopy, attenuated total reflection flourier transformed infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS)
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The effect of hydrofluoric acid (HF) pretreatment on flotation of feldspar and quartz using dodecylamine (DDA) as collector was investigated by micro-flotation, zeta potential, pyrene fluorescence spectroscopy, attenuated total reflection flourier transformed infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and bench scale flotation. The micro-flotation tests revealed that there was little difference in the flotation of feldspar and quartz at pH 2, using H2SO4 as pH regulator. After HF pretreatment, the floatability of feldspar significantly increased while the floatability of quartz showed no change. HF pretreatment resulted in leaching of SiO2 and enrichment of Na, K and Al on the feldspar surface. Consequently, the negative surface charge of feldspar increased at pH 2, which allowed for the flotation separation of the feasible minerals. This took place via an increased electrostatic adsorption between DDA and Na, K, Al on the feldspar surface, which effectively increased its hydrophobicity and as a result, improved the floatability of feldspar. An alternative process which exhibited effective separation of quartz and feldspar while recycling the tailwater from the flotation was proposed. Full article
(This article belongs to the Special Issue Sustainable Mineral Processing Technologies)
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Open AccessArticle The Shah-Ali-Beiglou Zn-Pb-Cu (-Ag) Deposit, Iran: An Example of Intermediate Sulfidation Epithermal Type Mineralization
Minerals 2018, 8(4), 148; https://doi.org/10.3390/min8040148
Received: 25 December 2017 / Revised: 14 March 2018 / Accepted: 29 March 2018 / Published: 10 April 2018
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Abstract
The Shah-Ali-Beiglou epithermal base metal-silver deposit is located in the Tarom-Hashjin metallogenic province (THMP) in northwestern Iran. This deposit is hosted by quartz monzonite dikes of Oligocene age and surrounded by andesite to trachyandesite volcanic and volcaniclastic rocks of Eocene age. The subvolcanic
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The Shah-Ali-Beiglou epithermal base metal-silver deposit is located in the Tarom-Hashjin metallogenic province (THMP) in northwestern Iran. This deposit is hosted by quartz monzonite dikes of Oligocene age and surrounded by andesite to trachyandesite volcanic and volcaniclastic rocks of Eocene age. The subvolcanic rocks in the study area vary in composition from quartz-monzonite to monzonite and have metaluminous, calc-alkaline to shoshonitic affinity. These rocks have I-type geochemical characteristic and are related to post-collisional tectonic setting. The mineralization occurs as NE-SW and E-W-trending brecciated veins controlled by strike-slip and normal faults, which are associated to the Late Oligocene compressional regime. The mineral paragenesis of the vein mineralization is subdivided into pre-ore stage, ore stage, post-ore stage, and supergene stage. Pre-ore stage is dominated by quartz, sericite, and subhedral to anhedral pyrite as disseminated form. Ore-stage is represented by quartz, sphalerite (from 0.1 mol % to 4 mol % FeS), galena, chalcopyrite, tetrahedrite-tennantite, minor seligmannite and enargite, as vein-veinlet, cement and clast breccias. Post-ore stage is defined by deposition of quartz and carbonate along with minor barite, and supergene stage is characterized by bornite, chalcocite, covellite, hematite, goethite, and jarosite. The ore mineralization is associated with the silicic alteration. The styles of alteration are silicic, carbonate, sericitic, chloritic, and propylitic. Fluid inclusions in sphalerite have a wide range of salinities between 0.35 wt % and 21.4 wt % NaCl equivalent and homogenization temperatures range from 123 to 320 °C. The isotopic values of sulfides vary from 2.8‰ to 6.7‰ suggesting a magmatic source for the sulfur. In the present study, based on geological setting, alteration style of the host and wall rocks, main textures, mineral assemblages, composition of ore minerals, and structural features, it is suggested that the mineralization in the Shah-Ali-Beiglou is similar to intermediate-sulfidation style of epithermal deposits. Full article
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Open AccessReview Integrated Mineral Carbonation of Ultramafic Mine Deposits—A Review
Minerals 2018, 8(4), 147; https://doi.org/10.3390/min8040147
Received: 15 March 2018 / Revised: 29 March 2018 / Accepted: 4 April 2018 / Published: 9 April 2018
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Abstract
Recently, integrated mineral carbonation for CO2 sequestration has received significant attention due to the high potential for commercialization towards mitigating climate change. This review compiles the work conducted by various researchers over the last few years on integrated mineral carbonation processes in
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Recently, integrated mineral carbonation for CO2 sequestration has received significant attention due to the high potential for commercialization towards mitigating climate change. This review compiles the work conducted by various researchers over the last few years on integrated mineral carbonation processes in the mining industry, which use ultramafic mine wastes as feedstock for mineral carbonation. Here, we introduce the basic concepts of mineral carbonation including a brief description of the process routes and pre-treatment techniques. We discuss the scope of integrated mineral carbonation process application, and critically review the integrated mineral carbonation process in the mining industry including modified passive carbonation techniques in tailing storage facilities, and ex-situ carbonation routes using fresh tailings. The focus of the discussions is the role of reaction condition on the carbonation efficiency of mine waste with various mineralogical compositions, and the benefits and drawbacks of each integrated mineral carbonation process. All discussions lead to suggestions for the technological improvement of integrated mineral carbonation. Finally, we review the techno-economic assessments on existing integrated mineral carbonation technologies. Research to date indicates that value-added by-products will play an important role in the commercialization of an integrated mineral carbonation process. Full article
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Open AccessArticle The Role of Clay Swelling and Mineral Neoformation in the Stabilization of High Plasticity Soils Treated with the Fly Ash- and Metakaolin-Based Geopolymers
Minerals 2018, 8(4), 146; https://doi.org/10.3390/min8040146
Received: 23 February 2018 / Revised: 29 March 2018 / Accepted: 2 April 2018 / Published: 7 April 2018
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Abstract
In the southern U.S. states, expansive soils are frequently encountered, presenting an important hazard in geotechnical engineering. This research relies on mineralogical and geochemical clues to explain the swelling behavior of smectite-rich, high-plasticity soils, documented in a series of geomechanical swelling tests that
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In the southern U.S. states, expansive soils are frequently encountered, presenting an important hazard in geotechnical engineering. This research relies on mineralogical and geochemical clues to explain the swelling behavior of smectite-rich, high-plasticity soils, documented in a series of geomechanical swelling tests that were performed on the soils stabilized with the metakaolin (MKG) and fly ash (FAG) based geopolymers. These geopolymers were mixed with the soil at several concentration levels. The lowest swelling percentage was shown to correspond to the sample stabilized with 12% FAG and was attributed to the neoformation of calcium silicate hydrates that acted as a cementitious material, preventing the soil from expanding by occupying the pore space, thus binding the clay particles together. Conversely, the 12% MKG-stabilized soil exhibited enormous expansion, which was explained by montmorillonite swelling to the point that it gradually began to lose its structural periodicity. The relatively high abundance of the newly formed feldspathoids in MKG-treated samples is believed to have greatly contributed to the overall soil expansion. Finally, the cation exchange capacity tests showed that the percentage of Na+ and Ca2+, as well as the pH value, exercised strong control on the swelling behavior of smectitic soils. Full article
(This article belongs to the Special Issue Geopolymers)
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Open AccessArticle Preparation of Amino Functionalized Hydrophobic Zeolite and Its Adsorption Properties for Chromate and Naphthalene
Minerals 2018, 8(4), 145; https://doi.org/10.3390/min8040145
Received: 24 February 2018 / Revised: 25 March 2018 / Accepted: 2 April 2018 / Published: 5 April 2018
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Abstract
Amino functionalized hydrophobic zeolite was prepared by modification of natural zeolite with 3-aminopropyltrimethoxysilane. X-ray diffraction, Fourier transform infrared analysis, thermal gravimetric analysis, Brunauer-Emmett-Teller surface areas, and element analysis were employed to investigate the structures of the samples. The water vapor adsorption method was
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Amino functionalized hydrophobic zeolite was prepared by modification of natural zeolite with 3-aminopropyltrimethoxysilane. X-ray diffraction, Fourier transform infrared analysis, thermal gravimetric analysis, Brunauer-Emmett-Teller surface areas, and element analysis were employed to investigate the structures of the samples. The water vapor adsorption method was used to determine the hydrophobicity of the samples. The adsorption properties of the samples for chromate and naphthalene were then investigated. The results showed that the silane modification had a negligible effect on the crystalline structure of zeolite while significantly decreasing the specific surface area and increasing the hydrophobicity of the zeolite sample. The functionalized zeolite samples exhibit higher adsorption capacity and removal rate on chromate and naphthalene as compared with the unmodified zeolite sample due to their specific amino functional group and hydrophobicity property. Full article
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Open AccessArticle The Merensky Cyclic Unit, Bushveld Complex, South Africa: Reality or Myth?
Minerals 2018, 8(4), 144; https://doi.org/10.3390/min8040144
Received: 21 February 2018 / Revised: 26 March 2018 / Accepted: 28 March 2018 / Published: 3 April 2018
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Abstract
The Merensky Unit, Bushveld Complex, is commonly described using genetic terms such as “cyclic unit”, typically without careful consideration of the connotations. We suggest that this contributes to the debate on processes forming the unit. This study integrates an extensive field study with
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The Merensky Unit, Bushveld Complex, is commonly described using genetic terms such as “cyclic unit”, typically without careful consideration of the connotations. We suggest that this contributes to the debate on processes forming the unit. This study integrates an extensive field study with detailed petrographic and textural analyses of the Merensky Unit to determine whether it is a “cyclic unit” sensu stricto. The study indicates that the bulk of the platinum-bearing chromitite-feldspathic orthopyroxenite developed through heterogeneous nucleation and in situ growth during multiple replenishment events. The overlying leuconorite developed above a gradational boundary, reflecting mixing following replenishment by a relatively more evolved magma. The bulk of this unit also formed in situ. The uppermost poikilitic anorthosite formed above a distinct boundary through a subsequent injection of a plagioclase-saturated magma, which crystallised in situ. Processes of gravitational settling and local remobilisation of crystals cannot be discounted from contributing to the development of the unit. The final textures throughout the unit developed through pervasive textural equilibration, with extensive fluid-mediated textural equilibration forming the megacrystic feldspathic orthopyroxenite. The evidence for at least five replenishment events indicates that the Merensky Unit is not a cyclic unit; therefore, the genetic term, “Merensky Cyclic Unit”, is misleading and its use should be carefully considered in future work. Full article
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