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Minerals, Volume 7, Issue 4 (April 2017)

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Cover Story By using first-principles simulation techniques, we found that arsenic species can enter the [...] Read more.
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Open AccessArticle A New Procedure for Deep Sea Mining Tailings Disposal
Minerals 2017, 7(4), 47; doi:10.3390/min7040047
Received: 3 February 2017 / Revised: 13 March 2017 / Accepted: 18 March 2017 / Published: 23 March 2017
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Abstract
Deep sea mining tailings disposal is a new environmental challenge related to water pollution, mineral crust waste handling, and ocean biology. The objective of this paper is to propose a new tailings disposal procedure for the deep sea mining industry. Through comparisons of
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Deep sea mining tailings disposal is a new environmental challenge related to water pollution, mineral crust waste handling, and ocean biology. The objective of this paper is to propose a new tailings disposal procedure for the deep sea mining industry. Through comparisons of the tailings disposal methods which exist in on-land mining and the coastal mining fields, a new tailings disposal procedure, i.e., the submarine–backfill–dam–reuse (SBDR) tailings disposal procedure, is proposed. It combines deep sea submarine tailings disposal, backfill disposal, tailings dam disposal, and tailings reuse disposal for the deep sea mining industry. Then, the analytic network process (ANP) method is utilized to evaluate the performances of different tailings disposal methods. The evaluation results of the ANP show that the new proposed tailings disposal procedure is the most suitable for the deep sea mining industry. Full article
(This article belongs to the Special Issue Minerals in Mine Wastes: Contributions to the Circular Economy)
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Open AccessArticle Rational Utilization of Fine Unclassified Tailings and Activated Blast Furnace Slag with High Calcium
Minerals 2017, 7(4), 48; doi:10.3390/min7040048
Received: 27 February 2017 / Revised: 20 March 2017 / Accepted: 22 March 2017 / Published: 24 March 2017
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Abstract
The utilization of cemented tailings/paste backfill (CPB) by the mining industry is becoming increasingly important. However, it has been difficult to analyze the economic usage of CPB for fine unclassified tailings. Therefore, the physical and chemical properties of fine unclassified tailings, sampled from
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The utilization of cemented tailings/paste backfill (CPB) by the mining industry is becoming increasingly important. However, it has been difficult to analyze the economic usage of CPB for fine unclassified tailings. Therefore, the physical and chemical properties of fine unclassified tailings, sampled from the Sijiaying Mine, were first analyzed in this study. After this, active excitation of blast furnace slag was examined, with a cement mixture made up of slag, lime, plaster and cement being used to conduct the physicochemical evaluations and proportioning tests. These results were compared with those from ordinary cement. It was revealed that the cement mixture can effectively harden the unclassified tailings. The cement mixture specimens have good performance in early strength, with the seven-day strength being about twice as high as ordinary cement, which meets the requirements for efficient continuous mining. This strength was reduced after 10 days due to expansion and complicated reactions, with an average reduction of 11.8% after 28 days under recommended and better conditions. In addition, analysis of the microstructures was carried out to observe the hydration products and the change in strength. Furthermore, fluidity characteristics of the slurry were measured, with the slurry found to have a mass fraction of 70%–72% in addition to containing an ideal fluidity and a paste-like flow state. Considering the mining conditions, the aggregates with a tailings-cement ratio of 6:1 and a mass fraction of 70%–72% are recommended as high-strength CPB, which should be used for the surface layer and safety pillars. In addition, backfilling materials with a tailings-cement ratio of 15:1 and a mass fraction of 70%–72% are recommended as low-strength CPB, which should be used as ordinary CPB to achieve economic benefits. The application cases showed that the cement mixture is suitable for utilization of unclassified tailings with regards to safety, economics and efficiency. Full article
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Open AccessArticle Experimental Study of Montmorillonite Structure and Transformation of Its Properties under Treatment with Inorganic Acid Solutions
Minerals 2017, 7(4), 49; doi:10.3390/min7040049
Received: 17 December 2016 / Revised: 2 March 2017 / Accepted: 19 March 2017 / Published: 23 March 2017
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Abstract
This paper discusses the mechanism of montmorillonite structural alteration and modification of bentonites’ properties (based on samples from clay deposits Taganskoye, Kazakhstan and Mukhortala, Buriatia) under thermochemical treatment (treatment with inorganic acid solutions at different temperatures, concentrations and reaction times). Treatment conditions were
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This paper discusses the mechanism of montmorillonite structural alteration and modification of bentonites’ properties (based on samples from clay deposits Taganskoye, Kazakhstan and Mukhortala, Buriatia) under thermochemical treatment (treatment with inorganic acid solutions at different temperatures, concentrations and reaction times). Treatment conditions were chosen according to those accepted in chemical industry for obtaining acid modified clays as catalysts or sorbents. Also, more intense treatment was carried out to simulate possible influence at the liquid radioactive site repositories. A series of methods was used: XRD, FTIR, ICP-AES, TEM, nitrogen adsorption, and particle size analysis. It allowed revealing certain processes: transformation of montmorillonite structure which appears in the leaching of interlayer and octahedral cations and protonation of the interlayer and –OH groups at octahedral sheets. In turn, changes in the structure of the 2:1 layer of montmorillonite and its interlayer result in significant alterations in the properties: reduction of cation exchange capacity and an increase of specific surface area. Acid treatment also leads to a redistribution of particle sizes and changes the pore system. The results of the work showed that bentonite clays retain a significant portion of their adsorption properties even after a prolonged and intense thermochemical treatment (1 M HNO3, 60 °C, 108 h). Full article
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Open AccessArticle Uraninite, Coffinite and Brannerite from Shear-Zone Hosted Uranium Deposits of the Bohemian Massif (Central European Variscan Belt)
Minerals 2017, 7(4), 50; doi:10.3390/min7040050
Received: 31 January 2017 / Revised: 7 March 2017 / Accepted: 22 March 2017 / Published: 29 March 2017
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Abstract
New mineralogical data are presented for shear-zone hosted uranium mineralisation from selected uranium deposits that occur in the Bohemian Massif. The uranium mineralisation is in high-grade metamorphic rocks of the Moldanubian Zone and/or in granitic rocks of the Moldanubian batholith and Bor pluton
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New mineralogical data are presented for shear-zone hosted uranium mineralisation from selected uranium deposits that occur in the Bohemian Massif. The uranium mineralisation is in high-grade metamorphic rocks of the Moldanubian Zone and/or in granitic rocks of the Moldanubian batholith and Bor pluton as complex uraninite–coffinite and uraninite–coffinite–brannerite assemblages. For analysed coffinites and brannerites, anomalous enrichment of Y (up to 3.4 wt % Y2O3) and Zr (up to 13.8 wt % ZrO2) is significant. The microprobe data indicate that coffinites from the Rožná and Okrouhlá Radouň uranium deposits contain variable PbO (0–4.3 wt %), FeO (0–2.5 wt %), Al2O3 (0–3.5 wt %), P2O5 (0–1.8 wt %), and CaO (0.7–3.5 wt %). Brannerite is present in unaltered and altered grains with variable concentrations of U4+ (0–0.5 apfu), U6+ (0.06–0.49 apfu), Ti (0.90–2.63 apfu), Ca (0.09–0.41 apfu), and low concentrations of Al (0–0.19 apfu), Th (0–0.04 apfu), Y (0–0.08 apfu), Zr (0–0.13 apfu) and REE (0–0.14 apfu). Full article
(This article belongs to the Special Issue Geochemistry and Corrosion of Uranium-based Waste Materials)
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Open AccessArticle Study of the Effect of Sodium Sulfide as a Selective Depressor in the Separation of Chalcopyrite and Molybdenite
Minerals 2017, 7(4), 51; doi:10.3390/min7040051
Received: 19 December 2016 / Revised: 21 March 2017 / Accepted: 27 March 2017 / Published: 30 March 2017
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Abstract
Two kinds of collectors, sodium butyl xanthate and kerosene, and a depressor, sodium sulfide, were used in this research. The study applied flotation tests, pulp potential measurements, contact angle measurements, adsorption calculations, and Fourier Transform Infrared Spectroscopy (FTIR) analyses to demonstrate the correlation
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Two kinds of collectors, sodium butyl xanthate and kerosene, and a depressor, sodium sulfide, were used in this research. The study applied flotation tests, pulp potential measurements, contact angle measurements, adsorption calculations, and Fourier Transform Infrared Spectroscopy (FTIR) analyses to demonstrate the correlation between reagents and minerals. For xanthate collectors, the best flotation responses of chalcopyrite and molybdenite were obtained at pH = 8, and, for kerosene, these were obtained at pH = 4. The flotation of molybdenite seemed to be less influenced by xanthate than by kerosene, while that of chalcopyrite showed the opposite. The optimum concentration of sodium sulfide for separation was 0.03 mol/L, which rejected 83% chalcopyrite and recovered 82% molybdenite in the single mineral flotation. Pulp potential measurements revealed that the dixanthogen and xanthate were decomposed and desorbed, respectively, from the mineral surface in a reducing environment. The contact angle measurement and adsorption calculation conformed to the flotation response, indicating that few functions of the xanthate and sodium sulfide on the molybdenite flotation were due to their low adsorption densities. The FTIR results further clarified that the xanthate ion was adsorbed on chalcopyrite by forming cuprous xanthate and dixanthogen; however, on molybdenite the adsorption product was only dixanthogen. After conditioning with sodium sulfide, the chalcopyrite surface became clean, but the molybdenite surface still retained slight peaks of dixanthogen. Meanwhile, the possible mechanism was expounded in this research. Full article
(This article belongs to the Special Issue Flotation in Mineral Processing)
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Open AccessArticle The Effect of Polystyrene on the Carrier Flotation of Fine Smithsonite
Minerals 2017, 7(4), 52; doi:10.3390/min7040052
Received: 8 February 2017 / Revised: 27 March 2017 / Accepted: 28 March 2017 / Published: 29 March 2017
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Abstract
Carrier flotation is a common technique used to improve flotation recovery of ultrafine ores. In this study, we used coarse polystyrene as the carrier material to enhance flotation recovery of fine smithsonite (ZnCO3) particles. Sodium oleate was used as the collector
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Carrier flotation is a common technique used to improve flotation recovery of ultrafine ores. In this study, we used coarse polystyrene as the carrier material to enhance flotation recovery of fine smithsonite (ZnCO3) particles. Sodium oleate was used as the collector and played a role in the adhesion of fine smithsonite to polystyrene due to its amphipathic properties. The carrier feature of polystyrene was demonstrated using particle size analysis, total organic carbon, and scanning electron microscopy. The fine smithsonite particles coated the polystyrene particles through a reaction between the active zinc sites and the carboxyl head groups of the oleate adsorbed on smithsonite and through a hydrophobic interaction between polystyrene and the hydrocarbon chains of the oleate. Newly enlarged particle aggregates with smithsonite shells enhanced collision and attachment of the hydrophobized aggregates with bubbles, which accelerated smithsonite flotation recovery. Full article
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Open AccessArticle Interlayer Structures and Dynamics of Arsenate and Arsenite Intercalated Layered Double Hydroxides: A First Principles Study
Minerals 2017, 7(4), 53; doi:10.3390/min7040053
Received: 26 January 2017 / Revised: 13 March 2017 / Accepted: 23 March 2017 / Published: 30 March 2017
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Abstract
In this study, by using first principles simulation techniques, we explored the basal spacings, interlayer structures, and dynamics of arsenite and arsenate intercalated Layered double hydroxides (LDHs). Our results confirm that the basal spacings of NO3-LDHs increase with layer charge
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In this study, by using first principles simulation techniques, we explored the basal spacings, interlayer structures, and dynamics of arsenite and arsenate intercalated Layered double hydroxides (LDHs). Our results confirm that the basal spacings of NO3-LDHs increase with layer charge densities. It is found that Arsenic (As) species can enter the gallery spaces of LDHs with a Mg/Al ratio of 2:1 but they cannot enter those with lower charge densities. Interlayer species show layering distributions. All anions form a single layer distribution while water molecules form a single layer distribution at low layer charge density and a double layer distribution at high layer charge densities. H2AsO4 has two orientations in the interlayer regions (i.e., one with its three folds axis normal to the layer sheets and another with its two folds axis normal to the layer sheets), and only the latter is observed for HAsO42−. H2AsO3 orientates in a tilt-lying way. The mobility of water and NO3 increases with the layer charge densities while As species have very low mobility. Our simulations provide microscopic information of As intercalated LDHs, which can be used for further understanding of the structures of oxy-anion intercalated LDHs. Full article
(This article belongs to the Special Issue Computational Geochemistry)
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Open AccessArticle Feasibility of Recycling Ultrafine Leaching Residue by Backfill: Experimental and CFD Approaches
Minerals 2017, 7(4), 54; doi:10.3390/min7040054
Received: 3 March 2017 / Revised: 24 March 2017 / Accepted: 2 April 2017 / Published: 5 April 2017
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Abstract
Large amounts of leaching residue are released into tailings dams from mines, and their acid content can cause environmental pollution. The aim of this study was to research the feasibility and value of a leaching residue backfill recycling method. The combination of property
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Large amounts of leaching residue are released into tailings dams from mines, and their acid content can cause environmental pollution. The aim of this study was to research the feasibility and value of a leaching residue backfill recycling method. The combination of property detection, laboratory tests (the neutralization method, strength test and diffusivity test) and numerical simulation methods (3D computational fluid dynamics (CFD) simulations of pipeline transportation properties) were used to assess the performance of the leaching residue backfill. The results show that backfill body with the cement:sand mass ratio of 1:3, the leaching residue:classified tailings ratio of 1:6, and slurry mass concentration of 71 wt % can meet the strength and pipeline self-flowing transportation requirements of mine backfill. The leaching residue is a good backfill aggregate, and its recovery ratio can reach 19.5 wt %. In addition, the recycling of leaching residue effectively alleviates the problem of mine waste emissions and protects the ecological environment surrounding the mining area. This study serves as a guide for the recycling of fine tailings and the environmental governance of the mining area. Full article
(This article belongs to the Special Issue Minerals in Mine Wastes: Contributions to the Circular Economy)
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Open AccessArticle Predicting the Risk of Fault-Induced Water Inrush Using the Adaptive Neuro-Fuzzy Inference System
Minerals 2017, 7(4), 55; doi:10.3390/min7040055
Received: 4 February 2017 / Revised: 23 March 2017 / Accepted: 5 April 2017 / Published: 7 April 2017
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Abstract
Sudden water inrush has been a deadly killer in underground engineering for decades. Currently, especially in developing countries, frequent water inrush accidents still kill a large number of miners every year. In this study, an approach for predicting the probability of fault-induced water
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Sudden water inrush has been a deadly killer in underground engineering for decades. Currently, especially in developing countries, frequent water inrush accidents still kill a large number of miners every year. In this study, an approach for predicting the probability of fault-induced water inrush in underground engineering using the adaptive neuro-fuzzy inference system (ANFIS) was developed. Six parameters related to the aquifer, the water-resisting properties of the aquifuge and the mining-induced stresses were extracted as the major parameters to construct the ANFIS model. The constructed ANFIS was trained with twenty reported real fault-induced water inrush cases, and another five new cases were used to test the prediction performance of the trained ANFIS. The final results showed that the prediction results of the five cases were completely consistent with the actual situations. This indicates that the ANFIS is highly accurate in the prediction of fault-induced water inrush and suggests that quantitative assessment of fault-induced water inrush using the ANFIS is possible. Full article
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Open AccessArticle Numerical Investigation of Caved Rock Mass Friction and Fragmentation Change Influence on Gravity Flow Formation in Sublevel Caving
Minerals 2017, 7(4), 56; doi:10.3390/min7040056
Received: 13 February 2017 / Revised: 5 April 2017 / Accepted: 5 April 2017 / Published: 11 April 2017
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Abstract
Metal grade dilution is the main production disadvantage of the sublevel caving method, and overcoming this problem has been investigated over the years using different methodologies. Herein, numerical simulation using the discrete element method is used to analyze the influence of friction and
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Metal grade dilution is the main production disadvantage of the sublevel caving method, and overcoming this problem has been investigated over the years using different methodologies. Herein, numerical simulation using the discrete element method is used to analyze the influence of friction and fragmentation change in caved rock mass on ore dilution and recovery. The individual and mutual change of each parameter is analyzed. It is considered that at the beginning, the friction angle can be lower or higher than the basic friction angle, and after a certain moment, it will come close to the basic friction value, while fragmentation always decreases. The results showed that both friction and fragmentation, when decreasing, are influencing the higher dilution due to smaller kinematic resistance in the caved mass. If lower friction than the basic one is considered, with the drop of fragmentation, the decrease of dilution occurs. Once the basic friction angle is reached, the fragmentation of the caved mass becomes the dominant influencing factor, and its decrease will continuously increase the dilution until the end of production. However, identifying periods when these changes occur, the possibility for better production planning opens at the design stage, as well as the application of different sublevel designs. Full article
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Open AccessArticle Migration Behavior of Lithium during Brine Evaporation and KCl Production Plants in Qarhan Salt Lake
Minerals 2017, 7(4), 57; doi:10.3390/min7040057
Received: 8 January 2017 / Revised: 28 March 2017 / Accepted: 2 April 2017 / Published: 11 April 2017
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Abstract
Lithium-brine is an important potential source of lithium. Much research and investigation has been carried out aimed at lithium recovery from brine. Although the distribution and occurrence status of lithium in brine have important implications for lithium recovery, few reports had correlated to
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Lithium-brine is an important potential source of lithium. Much research and investigation has been carried out aimed at lithium recovery from brine. Although the distribution and occurrence status of lithium in brine have important implications for lithium recovery, few reports had correlated to this issue. In this article, a study was carried out to explore the lithium migration behavior during brine evaporation and KCl production process at Qarhan Salt Lake. The occurrence status of lithium both in fresh mined brine and residual brine after evaporation were also speculated by means of lithium concentration evaluation and theoretical calculation based on the Pitzer electrolyte solution theory. Results showed that, for Qarhan brine mined from the Bieletan region, most lithium was enriched in the residual brine during the brine evaporation process. The concentration of lithium in the residual brine could be more than 400 mg/L. More than 99.93% lithium ions in residual brine exist in free ions state and lithium does not precipitate from brine with a density of 1.3649 g/mL. The results also revealed that lithium concentration in wastewater discharged from KCl plants can reach a level of 243.8 mg/L. The investigation results provide a theoretical basis for comprehensive development and utilization of lithium resources in Qarhan Salt Lake. Full article
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Open AccessArticle Strength Characteristics and Failure Mechanism of Cemented Super-Fine Unclassified Tailings Backfill
Minerals 2017, 7(4), 58; doi:10.3390/min7040058
Received: 7 March 2017 / Revised: 5 April 2017 / Accepted: 10 April 2017 / Published: 12 April 2017
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Abstract
This experimental study investigates the strength characteristics of cemented super-fine unclassified tailings backfill (CSUTB) and its failure mechanism. Physical and chemical properties of tailings from the Zhongguan Iron Mine (ZGIM) were tested. A series of uniaxial compressive strength (UCS) tests was conducted to
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This experimental study investigates the strength characteristics of cemented super-fine unclassified tailings backfill (CSUTB) and its failure mechanism. Physical and chemical properties of tailings from the Zhongguan Iron Mine (ZGIM) were tested. A series of uniaxial compressive strength (UCS) tests was conducted to determine the relationships between UCS of CSUTB and three factors of cement-tailings ratio (CTR), solid content and curing time. Gray relational analysis (GRA) method was then used to study the sensitivity of UCS to these three factors. Results indicate that ZGIM unclassified tailings is a kind of alkaline super-fine tailings with high activity and quality. UCS of CSUTB increases exponentially with the increase of CTR and solid content, and increases linearly with curing time. The curing time is the most important factor for the UCS of CSUTB, followed by CTR and solid content. The stress-strain curves obtained from UCS tests show the failure process of CSUTB, including four stages of initial deformation, linear elastic, yield deformation and complete failure. It is the result of damage evolution. Full article
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Open AccessArticle A Time Varying Ventilation and Dust Control Strategy Based on the Temporospatial Characteristics of Dust Dispersion
Minerals 2017, 7(4), 59; doi:10.3390/min7040059
Received: 20 November 2016 / Revised: 5 April 2017 / Accepted: 7 April 2017 / Published: 14 April 2017
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Abstract
Generally, an effective ventilation system is essential to reduce coal dust disaster. However, with the implementation of carbon tax and increase of energy and operating costs, it is urgent to design a cost-effective ventilation and dust control system. In this paper, a real
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Generally, an effective ventilation system is essential to reduce coal dust disaster. However, with the implementation of carbon tax and increase of energy and operating costs, it is urgent to design a cost-effective ventilation and dust control system. In this paper, a real driving face in an excavation laneway of coal mine in China was taken as the physical model, and the temporospatial characteristics of airflow and dust dispersion is investigated for the first time to design an original conception of time-varying ventilation and dust control strategy. Specifically, computational fluid dynamic (CFD) approaches are utilized to investigate the dynamic regularity of airflow behavior and dust dispersion, and parametric studies are conducted to select the appropriate ventilation pattern, which is validated to be potential in energy saving as well as dust removal efficiency. In addition, based on the selection of key time point according to the regularity of dust concentration changed over time, the most effective type of speed function is brought out for this novel ventilation system, which reduces energy usage up to 15.11% in a ventilation period. Furthermore, the accuracy of simulation result is verified by field measurements, which demonstrates that adjusting the ventilation velocity at the appropriate time point (case 7) can effectively control the dust concentration, which performs as well as the steady flow. The research results suggest that the further understanding of temporospatial characteristics of dust dispersion is helpful for ventilation design, and significant energy savings and dust removal requirements are verified to be possible in the proposed scheme. Full article
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Open AccessArticle A Novel Longwall Mining Layout Approach for Extraction of Deep Coal Deposits
Minerals 2017, 7(4), 60; doi:10.3390/min7040060
Received: 19 March 2017 / Revised: 9 April 2017 / Accepted: 12 April 2017 / Published: 18 April 2017
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Abstract
As more easily mined deposits are depleted, the reserves are becoming more limited and less favorable. Deposits of coal or trona that are being longwall mined are deep and are getting deeper. Coal bursts and bumps frequently occur within development entries in longwall
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As more easily mined deposits are depleted, the reserves are becoming more limited and less favorable. Deposits of coal or trona that are being longwall mined are deep and are getting deeper. Coal bursts and bumps frequently occur within development entries in longwall mining of deep mines due to high stresses. This paper presents a novel patented longwall mining layout “Longwall Mining with Split-level Gate roads (LMSG)” that has the potential to mitigate several problems related to deep mining (Patent No. ZL98100544.6). LMSG locates gate roads on either end of a longwall panel at different vertical heights within a coal seam or in a geologically split seam, so that the two adjacent panels can be partially offset horizontally. It is novel in that it incorporates unit operations of different mining methods into the system. By employing multiple slice longwall mining method locally at the face ends, and adjacent panels overlapping end to end, pillar-less longwall mining can be achieved to mine deep deposits. A conventional rectangular gate road pillar is therefore transformed into a small triangular pillar and the gate road of the subsequent panel can be located along or under the gob of the previously mined panel where the stresses are lower. Several mines in China and Russia are currently using the technology with reduced incidence of ground control problems. Through theoretical analysis, and physical and numerical modeling approaches, it is demonstrated that LMSG significantly improves stress environment for development entries, with associated reduction in coal bursts and ground control problems. Full article
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Open AccessArticle Effect of the Structure of Alkyl Salicylaldoxime on Extraction of Copper(II)
Minerals 2017, 7(4), 61; doi:10.3390/min7040061
Received: 18 January 2017 / Revised: 28 March 2017 / Accepted: 29 March 2017 / Published: 20 April 2017
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Abstract
Four kinds of alkyl salicylaldoxime (AS) were investigated to probe the effect of molecular structure on the extraction of Cu(II). With the augment of R groups, tert-octylsalicylaldoxime and nonylsalicylaldoxime have much stronger extraction ability for Cu(II) than salicylaldoxime and tert-butylsalicylaldoxime, which
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Four kinds of alkyl salicylaldoxime (AS) were investigated to probe the effect of molecular structure on the extraction of Cu(II). With the augment of R groups, tert-octylsalicylaldoxime and nonylsalicylaldoxime have much stronger extraction ability for Cu(II) than salicylaldoxime and tert-butylsalicylaldoxime, which is consistent with the rise of hydrophobicity (Log P) of the extractants. The umbrella structure of the R group can endow tert-octylsalicylaldoxime with stronger steric-hindrance effect than nonylsalicylaldoxime, which results in the better separation efficiency of Cu(II) from Fe(III) for tert-octylsalicylaldoxime. The extraction ability of the extractants for Cu(II) is related to the hydrophobicity and molecular size, as predicted from quantum chemistry calculation. Full article
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Open AccessArticle Characteristics of Strata Behavior during Thick Seam Mining by Fully-Mechanized Top Coal Caving in a Loess-Covered Gullied Region
Minerals 2017, 7(4), 63; doi:10.3390/min7040063
Received: 22 March 2017 / Revised: 16 April 2017 / Accepted: 19 April 2017 / Published: 24 April 2017
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Abstract
This study systematically investigates the overburden movement and strata behavior at a fully-mechanized top coal caving (FMTCC) face in a thick coal seam in a loess-covered gullied region by field measurement and theoretical analysis. A comparative analysis was performed to examine how the
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This study systematically investigates the overburden movement and strata behavior at a fully-mechanized top coal caving (FMTCC) face in a thick coal seam in a loess-covered gullied region by field measurement and theoretical analysis. A comparative analysis was performed to examine how the attitude of surface gullies and the structure of overburden affect face support resistance. The characteristics and evolution mechanism of strata behavior during FMTCC under gully slopes in a loess-covered gullied region were discovered through a mechanical analysis of the roof structure and a comparison to the mining of a typical shallow seam under gully slopes. The study found that as the FMTCC face advanced, the strata behavior initiated in the middle part of the face and then continued to both ends, and its intensity was higher in the middle part than in the upper and lower parts. During mining under gullies, the increases in support resistance were generally less than 5% (except for the maximum increases of 7–9%), indicating that the occurrence of gullies on the surface had little influence on the strata behavior at the FMTCC face. Due to the increased burial depth and the number of key strata, the roof at the FMTCC face under gullies formed a stable load-bearing structure called a voussoir beam, which was the key difference from the strata behavior characteristics in the shallow mine under gullies. Full article
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Open AccessArticle Schwertmannite Adherence to the Reactor Wall during the Bio-Synthesis Process and Deterioration of Its Structural Characteristics and Arsenic(III) Removal Efficiency
Minerals 2017, 7(4), 64; doi:10.3390/min7040064
Received: 27 March 2017 / Revised: 15 April 2017 / Accepted: 19 April 2017 / Published: 22 April 2017
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Abstract
Schwertmannite, a kind of iron oxyhydrosulfate mineral, can removal arsenic(III) from arsenic(III)-bearing groundwater by the adsorption process. In this study, schwertmannite was bio-synthesized by Acidithiobacillus ferrooxidans LX5 in shaking flasks (160 rpm) containing a 0.16 mol/L FeSO4 liquid solution. After bio-synthesis, 25.5%
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Schwertmannite, a kind of iron oxyhydrosulfate mineral, can removal arsenic(III) from arsenic(III)-bearing groundwater by the adsorption process. In this study, schwertmannite was bio-synthesized by Acidithiobacillus ferrooxidans LX5 in shaking flasks (160 rpm) containing a 0.16 mol/L FeSO4 liquid solution. After bio-synthesis, 25.5% of the bio-synthesized schwertmannite adhered to the reactor wall (designated as adhered-sch) and the remainder was suspended in the system (designated as suspended-sch). Particles of adhered-sch exhibited a fractured structure with a small specific surface area (4.36 m2/g) and total pore volume (3.13 × 10−2 cm3/g). In contrast, suspended-sch had a spiny structure (similar in appearance to a hedgehog), and a larger specific surface area (9.62 m2/g) and total pore volume (8.01 × 10−2 cm3/g). When 0.25 g/L of adhered-sch was used as an adsorbent for arsenic(III) removal from 1 mg/L arsenic(III)-bearing waters (at pH 7.5), the arsenic(III) removal efficiency was 43.2% after 4 h of adsorption. However, this efficiency could be increased by 50% by using suspended-sch as the adsorbent. Furthermore, by adding 13.3 g/L and 26.7 g/L additional schwertmannite into the reactor system prior to schwertmannite bio-synthesis, all synthesized schwertmannite remained suspended in the bio-synthesis systems, and the ferrous ions’ bio-oxidation efficiency was improved to a certain extent. Due to the friction effect between the introduced schwertmannite and the reactor wall, adhered-sch was eliminated. The outcomes of this study will provide the necessary data for schwertmannite bio-synthesis and arsenic(III) removal from arsenic(III)-bearing groundwater. Full article
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Open AccessCommentary Polymorphs, Proteins, and Nucleation Theory: A Critical Analysis
Minerals 2017, 7(4), 62; doi:10.3390/min7040062
Received: 1 April 2017 / Revised: 15 April 2017 / Accepted: 18 April 2017 / Published: 21 April 2017
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Abstract
Over the last eight years new theories regarding nucleation, crystal growth, and polymorphism have emerged. Many of these theories were developed in response to observations in nature, where classical nucleation theory failed to account for amorphous mineral precursors, phases, and particle assembly processes
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Over the last eight years new theories regarding nucleation, crystal growth, and polymorphism have emerged. Many of these theories were developed in response to observations in nature, where classical nucleation theory failed to account for amorphous mineral precursors, phases, and particle assembly processes that are responsible for the formation of invertebrate mineralized skeletal elements, such as the mollusk shell nacre layer (aragonite polymorph) and the sea urchin spicule (calcite polymorph). Here, we summarize these existing nucleation theories and place them within the context of what we know about biomineralization proteins, which are likely participants in the management of mineral precursor formation, stabilization, and assembly into polymorphs. With few exceptions, much of the protein literature confirms that polymorph-specific proteins, such as those from mollusk shell nacre aragonite, can promote polymorph formation. However, past studies fail to provide important mechanistic insights into this process, owing to variations in techniques, methodologies, and the lack of standardization in mineral assay experimentation. We propose that the way forward past this roadblock is for the protein community to adopt standardized nucleation assays and approaches that are compatible with current and emerging nucleation precursor studies. This will allow cross-comparisons, kinetic observations, and hopefully provide the information that will explain how proteins manage polymorph formation and stabilization. Full article
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