Minerals

8358 KiB

Open AccessArticle

Raman Investigations to Identify Corallium rubrum in Iron Age Jewelry and Ornaments

by Sebastian Fürst, Katharina Müller, Liliana Gianni, Céline Paris, Ludovic Bellot-Gurlet, Christopher F.E. Pare and Ina Reiche

Minerals 2016, 6(2), 56; https://doi.org/10.3390/min6020056 - 15 Jun 2016

Cited by 12 | Viewed by 7123

Abstract

During the Central European Iron Age, more specifically between 600 and 100 BC, red precious corals (Corallium rubrum) became very popular in many regions, often associated with the so-called (early) Celts. Red corals are ideally suited to investigate several key questions [...] Read more.

During the Central European Iron Age, more specifically between 600 and 100 BC, red precious corals (Corallium rubrum) became very popular in many regions, often associated with the so-called (early) Celts. Red corals are ideally suited to investigate several key questions of Iron Age research, like trade patterns or social and economic structures. While it is fairly easy to distinguish modern C. rubrum from bone, ivory or shells, archaeologists are confronted with ancient, hence altered, artifacts. Due to ageing processes, archaeological corals lose their intensive red color and shiny surface and can easily be confused with these other light colored materials. We propose a non-destructive multi-stage approach to identify archaeological corals amongst other biominerals used as ornament during the central European Iron Age with emphasis on optical examination and mobile Raman spectroscopy. Our investigations suggest that the noticeably high amount of misidentifications or at least uncertain material declarations existing in museums or even in the literature (around 15%) could be overcome by the proposed approach. Furthermore, the range of different materials is higher than previously expected in archaeological research. This finding has implications for contemporary concepts of social structures and distribution networks during the Iron Age. Full article

(This article belongs to the Special Issue Biomineralization: Towards a Unification of Concepts in Chemistry, Physics, Earth Sciences and Biology)

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6820 KiB

Open AccessArticle

Reflectance Spectral Characteristics of Minerals in the Mboukoumassi Sylvite Deposit, Kouilou Province, Congo

by Xian-Fu Zhao, Zong-Qi Wang, Jun-Ting Qiu and Yang Song

Minerals 2016, 6(2), 55; https://doi.org/10.3390/min6020055 - 14 Jun 2016

Cited by 2 | Viewed by 6793

Abstract

This study presents reflectance spectra, determined with an ASD Inc. TerraSpec^® spectrometer, of five types of ore and gangue minerals from the Mboukoumassi sylvite deposit, Democratic Republic of the Congo. The spectral absorption features, with peaks at 999, 1077, 1206, 1237, 1524, [...] Read more.

This study presents reflectance spectra, determined with an ASD Inc. TerraSpec^® spectrometer, of five types of ore and gangue minerals from the Mboukoumassi sylvite deposit, Democratic Republic of the Congo. The spectral absorption features, with peaks at 999, 1077, 1206, 1237, 1524, and 1765 nm, of the ore mineral carnallite were found to be different from those of gangue minerals. Spectral comparison among carnallite samples from different sylvite deposits suggests that, in contrast to spectral shapes, the absorption features of carnallite are highly reproducible. Heating of carnallite to 400 and 750°C, and comparing the spectra of heated and non-heated samples, indicates that spectral absorption is related to lattice hydration or addition of hydroxyl. Since carnallite undergoes deliquescence easily, the absorption features of carnallite in the 350–2500 nm spectrum could serve as a robust tool for carnallite identification and separation. Full article

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707 KiB

Open AccessReview

Novel Biotechnological Approaches for the Recovery of Metals from Primary and Secondary Resources

by Katrin Pollmann, Sabine Kutschke, Sabine Matys, Sophias Kostudis, Stefanie Hopfe and Johannes Raff

Minerals 2016, 6(2), 54; https://doi.org/10.3390/min6020054 - 13 Jun 2016

Cited by 35 | Viewed by 7002

Abstract

Microorganisms have developed various mechanisms to deal with metals, thus providing numerous tools that can be used in biohydrometallurgical processes. “Biomining” processes—including bioleaching and biooxidation processes—facilitate the degradation of minerals, accompanied by a release of metals. These processes are especially attractive for low-grade [...] Read more.

Microorganisms have developed various mechanisms to deal with metals, thus providing numerous tools that can be used in biohydrometallurgical processes. “Biomining” processes—including bioleaching and biooxidation processes—facilitate the degradation of minerals, accompanied by a release of metals. These processes are especially attractive for low-grade ores and are used on an industrial scale mainly for sulfidic ores. In biosorption processes, biomass or certain biomolecules are used to bind and concentrate selected ions or other molecules from aqueous solutions. Biosorptive materials can be an environmentally friendly and efficient alternative to conventional materials, such as ion exchange resins. Other interesting mechanisms are bioaccumulation, bioflotation, bioprecipitation, and biomineralisation. Although these processes are well-known and have been studied in detail during the last decades, the recent strong progress of biotechnologies (e.g., genetic engineering and molecule design), as well as their combination with novel developments in material sciences (e.g., nanotechnologies) facilitate new strategies for the application of biotechnologies in mineral processing. The article gives a summary of current activities in this field that are being performed in our group. Full article

(This article belongs to the Special Issue Biotechnologies and Mining)

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7459 KiB

Open AccessArticle

The Influence of Roasting Temperature on the Flotation Properties of Muscovite

by Jiayan Tang, Yimin Zhang and Shenxu Bao

Minerals 2016, 6(2), 53; https://doi.org/10.3390/min6020053 - 3 Jun 2016

Cited by 19 | Viewed by 5091

Abstract

Roasting and flotation are common techniques used in mineral processing, and they have increasingly been combined for the pre-concentration of muscovite from stone coal. The research was mainly to study flotation properties of muscovite after roasting at 200, 400, 600, 800 and 1000 [...] Read more.

Roasting and flotation are common techniques used in mineral processing, and they have increasingly been combined for the pre-concentration of muscovite from stone coal. The research was mainly to study flotation properties of muscovite after roasting at 200, 400, 600, 800 and 1000 °C, respectively. The changes of chemical and physical properties of muscovite during the roasting process were investigated by thermogravimetric analysis (TGA), Fourier transform infrared spectrum (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Zeta potential measurements, particle size analysis, and the BET surface area measurements. The results indicated that the dehydroxylation of crystal structure took place at temperatures over 600 °C. A large number of hydroxyl groups were removed from the crystal structure of muscovite at 600–1000 °C. The layer structure, surface element distribution, and electrical properties of muscovite remained after roasting. The flotation recovery of roasted muscovite samples increased with the increase in roasting temperature in the same flotation system, because the specific surface and the adsorption capacity of dodecylamine (DDA) were reduced when roasting temperature was over 600 °C. A suitable roasting temperature and dosage of reagents can be provided for the roasting-flotation of muscovite. Full article

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4494 KiB

Open AccessArticle

Geoenvironmental Characterisation of Heap Leach Materials at Abandoned Mines: Croydon Au-Mines, QLD, Australia

by Anita Parbhakar-Fox

Minerals 2016, 6(2), 52; https://doi.org/10.3390/min6020052 - 31 May 2016

Cited by 10 | Viewed by 6308

Abstract

Heap leaching is a well-established metallurgical technology which allows metal recovery (e.g., Au, Cu, U) from low-grade ores. However, spent heap leach materials remaining at abandoned or historic mine sites may represent a potential source of contamination. At the Croydon Au-mines, heap leaching [...] Read more.

Heap leaching is a well-established metallurgical technology which allows metal recovery (e.g., Au, Cu, U) from low-grade ores. However, spent heap leach materials remaining at abandoned or historic mine sites may represent a potential source of contamination. At the Croydon Au-mines, heap leaching operations (1984–1985) were performed on mineralized rhyolites hosting sulphides including pyrite, galena, arsenopyrite and minor sphalerite. Characterization of spent heap leach materials (n = 14) was performed using established geochemical and mineralogical techniques, supplemented by automated mineralogical evaluations. Whilst these materials contained low sulphide-sulphur (0.08 to 0.41 wt %) and returned innocuous paste pH values (pH 5.1 to 8.6), they were classified uncertain by net acid producing potential/net acid generating criteria. This was likely due to the reaction of secondary mineral phases (i.e., beudantite, hidalgoite, kintoreite and Fe-As-Pb oxides) during these tests. It is hypothesised that during heap leaching, gangue sulphides have differentially reacted with the cyanide lixiviant, pre-conditioning the formation of these complex secondary phases during surficial oxidation, after heap leaching termination. These materials are considered to represent a moderate geoenvironmental risk as dissolved Pb in basal leachates is in excess of the World Health Organization (WHO 2006) guideline values. Considering this, these materials should be included in ongoing rehabilitation works at the site. Full article

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Figure 1
(A) Map of Australia with the location of the Croydon mining district shown in the inset; (B) Croydon mine workings, showing the abandoned Federation/La Perouse site (image from Google Earth); (C) Heap leach piles with seepage observed at the base; (D) Heap leach sample locations (220 to 233). Full article ">Figure 2
Bulk mineralogy (measured by XRD) results for samples selected from heap leach Piles 1 and 2 (n = 5; samples: 222, 225, 227, 231 and 233; detection limit: ~1 wt %). Full article ">Figure 3
(A) Weathered pyrite grain associated with muscovite, with internal striations displayed but no visible reaction products, with a secondary Pb-As-Fe oxide phase also observed; (B) Pb-As-Fe oxide phase associated with Fe-oxide, both displaying porous texture; (C) Pb-As-Fe oxide phase rimmed by Fe-oxide; (D) Fibrous habit Fe-As oxide with diffuse grain boundary; (E) Cubic arsenolite; (F) Cubic Pb-Fe-As oxides intergrown with fibrous Fe-oxides. Full article ">Figure 4
Classified mineralogy images showing: (A) anhedral pyrite with complex mineral associations (including surite, kaolinite, quartz and an unknown phase, likely iron oxide); (B) fine grained pyrite encapsulated in quartz; (C) fine grained arsenopyrite encapsulated in quartz and (D) fine grained galena encapsulated in quartz. Full article ">Figure 5
Box and whisker plot showing heap leach trace element chemistry (n = 14) with select environmentally significant elements shown. (NB. The box covers the interquartile range, the line is the median and the circle the mean. The whiskers are drawn at the threshold to identify near and far outliers based on the Tukey statistic). Full article ">Figure 6
Net acid producing potential vs. net acid generation (NAG) pH plot showing the acid forming characteristics of the heap leach materials (n = 14). Full article ">Figure 7
Proposed risk assessment framework for geoenvironmental characterisation of spent heap leach materials. If dealing with an abandoned site, Step 1 is mandatory, however, if characterising materials and an operational site, then it can be omitted. NB. This framework does not include an evaluation of the spent material’s physical properties. Full article ">

2006 KiB

Open AccessArticle

Preventive Replacement Decisions for Dragline Components Using Reliability Analysis

by Nuray Demirel and Onur Gölbaşı

Minerals 2016, 6(2), 51; https://doi.org/10.3390/min6020051 - 30 May 2016

Cited by 25 | Viewed by 7021

Abstract

Reliability-based maintenance policies allow qualitative and quantitative evaluation of system downtimes via revealing main causes of breakdowns and discussing required preventive activities against failures. Application of preventive maintenance is especially important for mining machineries since production is highly affected from machinery breakdowns. Overburden [...] Read more.

Reliability-based maintenance policies allow qualitative and quantitative evaluation of system downtimes via revealing main causes of breakdowns and discussing required preventive activities against failures. Application of preventive maintenance is especially important for mining machineries since production is highly affected from machinery breakdowns. Overburden stripping operations are one of the integral parts in surface coal mine productions. Draglines are extensively utilized in overburden stripping operations and they achieve earthmoving activities with bucket capacities up to 168 m³. The massive structure and operational severity of these machines increase the importance of performance awareness for individual working components. Research on draglines is rarely observed in the literature and maintenance studies for these earthmovers have been generally ignored. On this basis, this paper offered a comprehensive reliability assessment for two draglines currently operating in the Tunçbilek coal mine and discussed preventive replacement for wear-out components of the draglines considering cost factors. Full article

(This article belongs to the Special Issue Frontiers of Surface Mining Research)

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3400 KiB

Open AccessArticle

Leaching Behavior and Potential Environmental Effects of Trace Elements in Coal Gangue of an Open-Cast Coal Mine Area, Inner Mongolia, China

by Liu Yang, Jianfei Song, Xue Bai, Bo Song, Ruduo Wang, Tianhao Zhou, Jianli Jia and Haixia Pu

Minerals 2016, 6(2), 50; https://doi.org/10.3390/min6020050 - 27 May 2016

Cited by 26 | Viewed by 5454

Abstract

In order to better understand the role of coal gangue in potential environmental and ecological risks, the leaching behavior of trace elements from coal gangue has been investigated in an open-cast coal mine, Inner Mongolia, China. Four comparative column leaching experiments were conducted [...] Read more.

In order to better understand the role of coal gangue in potential environmental and ecological risks, the leaching behavior of trace elements from coal gangue has been investigated in an open-cast coal mine, Inner Mongolia, China. Four comparative column leaching experiments were conducted to investigate the impacts of leaching time, pH values and sample amount on the leaching behavior of trace elements. Enrichment factors (EF), maximum leached amount (L_am), maximum leachability (L_rm), effects range low (ERL) and effects range median (ERM) were employed to evaluate potential environmental and ecological hazards resulting from the leaching behavior of environment-sensitive trace elements from coal gangue. Leaching time and sample amount display important effects on trace element concentrations, leached amounts and leachability. The pH values exhibit a weak influence on the leaching behavior of the selected trace elements (e.g., As, V, Cr, Co, Ni, Cu, Zn, Se, Cd, Sn, Pb and Hg). The coal gangue are enriched in As, Co, Se and Pb and, in particular, show higher environmental pollution levels of As and Se (EF > 2). L_am values suggest that all of the elements investigated do not show potential risk to soils and vegetation, but have a high hazard risk for ground water. Elements including Ni, As, Cr and Zn are inclined to show high or moderate biological toxicity. Full article

(This article belongs to the Special Issue Minerals in Coal)

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1520 KiB

Open AccessReview

Microbiological Advances in Biohydrometallurgy

by Helen Watling

Minerals 2016, 6(2), 49; https://doi.org/10.3390/min6020049 - 25 May 2016

Cited by 64 | Viewed by 8592

Abstract

The most exciting advances in biohydrometallurgy are occurring in the field of microbiology. The two main technologies employed in biohydrometallurgy, agitated tanks for the processing of refractory concentrates and heaps and dumps for the processing of low-grade ores, are technologically sound and widely [...] Read more.

The most exciting advances in biohydrometallurgy are occurring in the field of microbiology. The two main technologies employed in biohydrometallurgy, agitated tanks for the processing of refractory concentrates and heaps and dumps for the processing of low-grade ores, are technologically sound and widely practised at commercial scale, but their development began at a time when very little was known of the microorganisms that assisted metals extraction from sulfide ores. During and subsequent to those developments it has been shown that microbial communities in metals extraction are more diverse than originally thought, and extremely robust and adaptable to different and variable environments. Recent advances in genomics and proteomics, exploiting hugely increased computing power and speed, have made it possible to describe not only which microorganisms are present in bioleaching systems, but also what physiological functions are being exercised. The body of knowledge being acquired through the application of molecular biology methods will be used increasingly to monitor microbial behaviour, optimise conditions for more appropriate microbiological activity and/or infer the “microbiological health” of bioreactors (tanks and heaps). Full article

(This article belongs to the Special Issue Biotechnologies and Mining)

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Figure 1
Trend with time of the numbers of acidophilic microorganisms (Bacteria and Archaea) isolated from environments relevant to biohydrometallurgy since the discovery of At. thiooxidans. They are grouped according to whether they are chemolithotrophs or mixotrophs that utilise iron(II) (Fe OX), both iron(II) and sulfur (Fe + S OX), sulfur but not iron(II) (S OX) or are heterotrophs (HET). Data to February 2016. Full article ">Figure 2
Heat generation profiles (solid lines) for (a) a 5000 tonne test heap of Ni-Cu-FeS ore and (b) the same ore, acid-agglomerated, inoculated and leached in an aerated, dynamically-controlled, insulated column; (c) estimates of cell numbers (broken line) in column effluent representing the microbial response to increased ore temperature. Full article ">Figure 3
Preferred solution pH of microorganisms associated with AMD sites, geothermal regions and managed leaching heap or tank bioreactors, referenced against their preferred growth temperatures. Data obtained from their descriptions or from the recommended growth conditions obtained from commercial culture-collection database. Full article ">Figure 4
Bioleaching of chalcopyrite concentrate by isolates of S. thermosulfidooxidans exhibiting different copper tolerances. Tests were conducted with 3 wt % concentrate in basal salts medium (initial pH 1.8) in a shaking incubator (45 °C, 165 rpm). Initial cell density 5 × 106 cells·mL−1. Full article ">Figure 5
Maximum salt tolerance of acidophiles referenced against their preferred solution pH. The dotted line represents the concentration of chloride salts in seawater. (Data obtained from published descriptions of species or from the recommended growth conditions obtained from the DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH database). Full article ">Figure 6
Microbiological diversity to genus level in heaps (H), and agitated tanks (T); A, attached; P, planktonic cells; % solids loading. Data collated from [<a href="#B97-minerals-06-00049" class="html-bibr">97</a>,<a href="#B98-minerals-06-00049" class="html-bibr">98</a>,<a href="#B99-minerals-06-00049" class="html-bibr">99</a>,<a href="#B100-minerals-06-00049" class="html-bibr">100</a>,<a href="#B101-minerals-06-00049" class="html-bibr">101</a>,<a href="#B102-minerals-06-00049" class="html-bibr">102</a>]. Full article ">

3255 KiB

Open AccessArticle

A Study of Digging Productivity of an Electric Rope Shovel for Different Operators

by Mohammad Babaei Khorzoughi and Robert Hall

Minerals 2016, 6(2), 48; https://doi.org/10.3390/min6020048 - 25 May 2016

Cited by 10 | Viewed by 7110

Abstract

A performance monitoring study of an electric rope shovel operating in an open pit coal mine was conducted. As the mining industry moves toward higher productivity, profitability and predictability, the need for more reliable, productive and efficient mining shovels increases. Consequently, it is [...] Read more.

A performance monitoring study of an electric rope shovel operating in an open pit coal mine was conducted. As the mining industry moves toward higher productivity, profitability and predictability, the need for more reliable, productive and efficient mining shovels increases. Consequently, it is critical to study the productivity of these machines and to understand the effect of different operational parameters on that. In this paper a clustering analysis is performed to classify shovel digging effort and behaviour based on digging energy, dig time and payload per pass. Then the influence of the operator on the digging efficiency and productivity of the machine is analyzed with a focus on operator technique during digging. A statistical analysis is conducted on different cycle time components (dig time, swing time, return time) for different operators. In addition to time components, swing and return angles as well as loading rate and mucking rate are observed and analyzed. The results of this study help to understand the effect of different operators on the digging productivity of the shovel and then to set the best operator practice. Full article

(This article belongs to the Special Issue Frontiers of Surface Mining Research)

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5449 KiB

Open AccessArticle

Geochemistry and Mineralogy of Tuff in Zhongliangshan Mine, Chongqing, Southwestern China

by Jianhua Zou, Heming Tian and Tian Li

Minerals 2016, 6(2), 47; https://doi.org/10.3390/min6020047 - 20 May 2016

Cited by 25 | Viewed by 6421

Abstract

Coal-bearing strata that host rare metal deposits are currently a hot issue in the field of coal geology. The purpose of this paper is to illustrate the mineralogy, geochemistry, and potential economic significance of rare metals in the late Permian tuff in Zhongliangshan [...] Read more.

Coal-bearing strata that host rare metal deposits are currently a hot issue in the field of coal geology. The purpose of this paper is to illustrate the mineralogy, geochemistry, and potential economic significance of rare metals in the late Permian tuff in Zhongliangshan mine, Chongqing, southwestern China. The methods applied in this study are X-ray fluorescence spectrometry (XRF), inductively coupled mass spectrometry (ICP-MS), X-ray diffraction analysis (XRD) plus Siroquant, and scanning electron microscopy in conjunction with an energy-dispersive X-ray spectrometry (SEM-EDX). The results indicate that some trace elements including Li, Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Zr, Nb, Cd, Sb, REE, Hf, Ta, Re, Th, and U are enriched in the tuff from Zhongliangshan mine. The minerals in the tuff mainly include kaolinite, illite, pyrite, anatase, calcite, gypsum, quartz, and traces of minerals such as zircon, florencite, jarosite, and barite. The tuff is of mafic volcanic origin with features of alkali basalt. Some minerals including florencite, gypsum, barite and a portion of anatase and zircon have been derived from hydrothermal solutions. It is suggested that Zhongliangshan tuff is a potential polymetallic ore and the recovery of these valuable elements needs to be further investigated. Full article

(This article belongs to the Special Issue Minerals in Coal)

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8792 KiB

Open AccessArticle

Chromite Composition and Accessory Minerals in Chromitites from Sulawesi, Indonesia: Their Genetic Significance

by Federica Zaccarini, Arifudin Idrus and Giorgio Garuti

Minerals 2016, 6(2), 46; https://doi.org/10.3390/min6020046 - 20 May 2016

Cited by 13 | Viewed by 8992

Abstract

Several chromite deposits located in the in the South and Southeast Arms of Sulawesi, Indonesia, have been investigated by electron microprobe. According to the variation of the Cr# = Cr/(Cr + Fe³⁺), the chromite composition varies from Cr-rich to Al-rich. Small [...] Read more.

Several chromite deposits located in the in the South and Southeast Arms of Sulawesi, Indonesia, have been investigated by electron microprobe. According to the variation of the Cr# = Cr/(Cr + Fe³⁺), the chromite composition varies from Cr-rich to Al-rich. Small platinum-group minerals (PGM), 1–10 μm in size, occur in the chromitites. The most abundant PGM is laurite, which has been found included in fresh chromite or in contact with chlorite along cracks in the chromite. Laurite forms polygonal crystals, and it occurs as a single phase or in association with amphibole, chlorite, Co-pentlandite and apatite. Small blebs of irarsite (less than 2 μm across) have been found associated with grains of awaruite and Co-pentlandite in the chlorite gangue of the chromitites. Grains of olivine, occurring in the silicate matrix or included in fresh chromite, have been analyzed. They show a composition typical of mantle-hosted olivine. The bimodal composition and the slight enrichment in TiO₂ observed in some chromitites suggest a vertical zonation due to the fractionation of a single batch magma with an initial boninitic composition during its ascent, in a supra-subduction zone. This observation implies the accumulation of Cr-rich chromitites at deep mantle levels and the formation of the Al-rich chromitites close or above the Moho-transition zone. All of the laurites are considered to be magmatic in origin, i.e., entrapped as solid phases during the crystallization of chromite at temperature of around 1200 °C and a sulfur fugacity below the sulfur saturation. Irarsite possibly represents a low temperature, less than 400 °C, exsolution product. Full article

(This article belongs to the Special Issue Advanced Research on Accessory Minerals)

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4191 KiB

Open AccessArticle

Clay Mineralogy of Coal-Hosted Nb-Zr-REE-Ga Mineralized Beds from Late Permian Strata, Eastern Yunnan, SW China: Implications for Paleotemperature and Origin of the Micro-Quartz

by Lixin Zhao, Shifeng Dai, Ian T. Graham and Peipei Wang

Minerals 2016, 6(2), 45; https://doi.org/10.3390/min6020045 - 17 May 2016

Cited by 42 | Viewed by 8069

Abstract

The clay mineralogy of pyroclastic Nb(Ta)-Zr(Hf)-REE-Ga mineralization in Late Permian coal-bearing strata from eastern Yunnan Province; southwest China was investigated in this study. Samples from XW and LK drill holes in this area were analyzed using XRD (X-ray diffraction) and SEM (scanning electronic [...] Read more.

The clay mineralogy of pyroclastic Nb(Ta)-Zr(Hf)-REE-Ga mineralization in Late Permian coal-bearing strata from eastern Yunnan Province; southwest China was investigated in this study. Samples from XW and LK drill holes in this area were analyzed using XRD (X-ray diffraction) and SEM (scanning electronic microscope). Results show that clay minerals in the Nb-Zr-REE-Ga mineralized samples are composed of mixed layer illite/smectite (I/S); kaolinite and berthierine. I/S is the major component among the clay assemblages. The source volcanic ashes controlled the modes of occurrence of the clay minerals. Volcanic ash-originated kaolinite and berthierine occur as vermicular and angular particles, respectively. I/S is confined to the matrix and is derived from illitization of smectite which was derived from the original volcanic ashes. Other types of clay minerals including I/S and berthierine precipitated from hydrothermal solutions were found within plant cells; and coexisting with angular berthierine and vermicular kaolinite. Inferred from the fact that most of the I/S is R1 ordered with one case of the R3 I/S; the paleo-diagenetic temperature could be up to 180 °C but mostly 100–160 °C. The micro-crystalline quartz grains (<10 µm) closely associated with I/S were observed under SEM and were most likely the product of desiliconization during illitization of smectite. Full article

(This article belongs to the Special Issue Minerals in Coal)

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Figure 1
Geological setting during Late Permian in southwest China, showing the location of Nb-Zr-REE-Ga mineralization. (A) Schematic map showing the inner, intermediate and outer zones of the Emeishan Large Igneous Province. (B) Paleogeography map showing the distribution of terrestrial Xuanwei Formation and transitional Longtan Formation during the Wuchiapingian in SW China. The red spots indicate the localities of the two studied drill holes (XW and LK). <a href="#minerals-06-00045-f001" class="html-fig">Figure 1</a> is modified from [<a href="#B20-minerals-06-00045" class="html-bibr">20</a>]. Full article ">Figure 2
Stratigraphic sections of the XW and LK drill holes. The red areas indicate the sampling locations. Full article ">Figure 3
XRD of a selected sample (X-16). Abbreviations in the figure indicate the minerals identified, such as I/S: mixed layer illite/smectite; K: kaolinite; B: berthierine; Q: quartz; A: anatase; Ca: calcite; and S: siderite. Full article ">Figure 4
XRD patterns for air-dried, EG-solvation, and heated clay fractions of selected samples (A) X-2 and (B) L-19. Abbreviations are same as in <a href="#minerals-06-00045-f003" class="html-fig">Figure 3</a>. AD: air-dried; EG: ethylene glycol saturated; H: heated. Full article ">Figure 5
Microscopic observations of the studied samples (cross-polarized light). (A) Volcanic shard-like berthierine particles (X-17); (B) Vermicular kaolinite (L-11). Full article ">Figure 6
Back-scattered electron images of clay minerals. (A) Authigenic lath-like I/S (X-2); (B) Berthierine and I/S within plant cell (black areas), and micro-quartz particles (X-1); (C) Berthierine particles (X-2); (D) I/S surrounding berthierine (L-18); (E) Quartz coexisting with berthierine within plant cells (L-5); (F) berthierine within fractures of vermicular kaolinite (X-10). Full article ">Figure 7
XRD patterns for EG-solvation slides with S (%) = 15, 20, 25, 30, 35, respectively. Blue bars indicate the synthetic peaks at 7, 3.5 and 3.3 Å. Abbreviations are the same as <a href="#minerals-06-00045-f003" class="html-fig">Figure 3</a>. Full article ">

2638 KiB

Open AccessArticle

Molecularly-Limited Fractal Surface Area of Mineral Powders

by Petr Jandacka, Jaromir Pistora, Jan Valicek and Vilem Madr

Minerals 2016, 6(2), 44; https://doi.org/10.3390/min6020044 - 13 May 2016

Viewed by 4276

Abstract

The topic of the specific surface area (SSA) of powders is not sufficiently described in the literature in spite of its nontrivial contribution to adsorption and dissolution processes. Fractal geometry provides a way to determine this parameter via relation SSA ~ x⁽ [...] Read more.

The topic of the specific surface area (SSA) of powders is not sufficiently described in the literature in spite of its nontrivial contribution to adsorption and dissolution processes. Fractal geometry provides a way to determine this parameter via relation SSA ~ x^{(D − 3)}s^{(2 − D)}, where x (m) is the particle size and s (m) is a scale. Such a relation respects nano-, micro-, or macro-topography on the surface. Within this theory, the fractal dimension 2 ≤ D < 3 and scale parameter s plays a significant role. The parameter D may be determined from BET or dissolution measurements on several samples, changing the powder particle sizes or sizes of adsorbate molecules. If the fractality of the surface is high, the SSA does not depend on the particle size distribution and vice versa. In this paper, the SSA parameter is analyzed from the point of view of adsorption and dissolution processes. In the case of adsorption, a new equation for the SSA, depending on the term (2 − D)∙(s₂ − s_BET)/s_BET, is derived, where s_BET and s₂ are effective cross-sectional diameters for BET and new adsorbates. Determination of the SSA for the dissolution process appears to be very complicated, since the fractality of the surface may change in the process. Nevertheless, the presented equations have good application potential. Full article

(This article belongs to the Special Issue Mineral Surface Science and Nanogeoscience)

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Figure 1
Examples of powder particles with high SSA: fractal-like topography of montmorillonite (a) with SSA ≈ 1000 m2·g−1 (nanometric pores) and activate black coal (b) with surface area around 1100 m2·g−1 and pore size of approximately 5 μm (maximum)—its surface seems to be non-homogenous, i.e., non-fractal. Scale bars 0.1 mm. Full article ">Figure 2
Relatively smooth surface topography of olivine, SSA ≈ 1 m2·g−1 (a) and bio-sample of rapeseed oil having bio-topography (b)—where the surface area was not measured. Scale bars: (a) 0.1 mm, (b) 1 mm. Full article ">Figure 3
Linear approximation of particle size distribution within a narrow interval of log-normal particle size distribution. Full article ">Figure 4
Simulation of hypothetic time-dependence of DR on the time in the case of adsorption processes—influence of diffusion of adsorbate on fractal surface topography. Full article ">Figure 5
Simulation of hypothetic time-dependence of DR on the time in the case of specific dissolution process—influence of diffusion and “dissolution of fractality.” Full article ">

8351 KiB

Open AccessArticle

Experimental Study on the Microstructure Evolution of Mixed Disposal Paste in Surface Subsidence Areas

by Wei Sun, Aixiang Wu, Kepeng Hou, Yi Yang, Lei Liu and Yiming Wen

Minerals 2016, 6(2), 43; https://doi.org/10.3390/min6020043 - 9 May 2016

Cited by 20 | Viewed by 4610

Abstract

The integrated disposal of surface subsidence pits and surface solid waste can be realized by backfilling a surface subsidence area with a paste made from the solid wastes of mines, such as tailings and waste rock. The microstructures of these wastes determine the [...] Read more.

The integrated disposal of surface subsidence pits and surface solid waste can be realized by backfilling a surface subsidence area with a paste made from the solid wastes of mines, such as tailings and waste rock. The microstructures of these wastes determine the macroscopic properties of a paste backfill. This paper presents an experimental study on the internal structure evolution of pasty fluid mixed with different waste rock concentrations (10%, 30%, and 50%) and cement dosages (1% and 2%) under damage. To this end, a real-time computed tomography (CT) scan is conducted using medical CT and a small loading device. Results show that UCS (uniaxial compressive strength) increases when the amount of cement increases. Given a constant amount of cement, UCS increases first and then decreases as waste rock content increases. UCS is maximized at 551 kPa when the waste rock content is 30%. The paste body is a typical medium used to investigate initial damage, which mainly consists of microholes, pores, and microcracks. The initial damages also exhibit a high degree of random inhomogeneity. After loading, cracks are initiated and expand gradually from the original damage location until the overall damages are generated. The mesostructure evolution model of the paste body is divided into six categories, and this mesostructure is reasonable when the waste rock content is 30%. Full article

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3582 KiB

Open AccessArticle

Sn-Bearing Minerals and Associated Sphalerite from Lead-Zinc Deposits, Kosovo: An Electron Microprobe and LA-ICP-MS Study

by Joanna Kołodziejczyk, Jaroslav Pršek, Panagiotis Voudouris, Vasilios Melfos and Burim Asllani

Minerals 2016, 6(2), 42; https://doi.org/10.3390/min6020042 - 6 May 2016

Cited by 15 | Viewed by 8413

Abstract

Stannite group minerals (ferrokësterite and stannite) occur in small amounts in association with sulfides in hydrothermal Pb-Zn deposits in Kosovo. The chemical composition of sphalerite co-existing with Sn-bearing minerals has been investigated using laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). Flat Sn-spectra suggest [...] Read more.

Stannite group minerals (ferrokësterite and stannite) occur in small amounts in association with sulfides in hydrothermal Pb-Zn deposits in Kosovo. The chemical composition of sphalerite co-existing with Sn-bearing minerals has been investigated using laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). Flat Sn-spectra suggest that Sn is bound in the sphalerite lattice or as nanoincluions. Sphalerite from Stan Terg, overgrown by ferrokësterite, contains the lowest Sn content (few ppm) and have been precipitated before Sn-enrichment in the fluids. The highest value of Sn (520 ppm) of Stan Terg sphalerite was obtained directly close to the ferrokësterite rim, and indicates a rapid increase of Sn in the hydrothermal fluids. Significantly higher values of Sn in sphalerite were obtained from other deposits: 1600 ppm (Artana), up to 663 ppm (Kizhnica), up to 2800 ppm (Drazhnje). Stannite-sphalerite geothermometry revealed the following ore-forming temperatures for the Kosovo mineralization: 240–390 °C for Stan Terg, 240–370 °C for Artana, >340 °C for Kizhnica, and 245–295 °C for Drazhnje. Sphalerite and stannite group minerals precipitated simultaneously during cooling from reduced hydrothermal fluids and under low-sulfidation fluid states. Fluctuations in physico-chemical fluid conditions are evidenced by the presence of stannite group minerals along growth zones in sphalerite and may be related to short interval of magmatic pulses during ore deposition. Full article

(This article belongs to the Special Issue Advanced Research on Accessory Minerals)

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(A) Position of the Trepça Mineral Belt, (B) is marked in rectangle. (B) Simplified geological map of the Trepça Mineral Belt with marked mines, occurrences of Pb-Zn mineralization and three mineralized zones (thick grey lines), modified from Hyseni et al. [<a href="#B27-minerals-06-00042" class="html-bibr">27</a>]. Full article ">Figure 2
Examples of LA-ICP-MS time-resolved depth profiles for sphalerite from Kosovo deposits. CPS—counts per second. Numbers indicate concentration of selected elements (in ppm). (A) Stan Terg sphalerite with some Sn-In-Cu-Ag-Sb inclusion. Flat spectra in the first part was used to calculate concentration in sphalerite; (B) flat spectra of sphalerite from Artana; (C) flat spectra of sphalerite from Kizhnica; (D) spectrum of sphalerite from Drazhnje with two parts with elevated Sn and In content, possible two tiny indium-enriched SGM minerals in sphalerite. Full article ">Figure 3
Microphotographs demonstrating textures of Sn-minerals in the investigated ore samples (A,B)—Stan Terg; (C,D)—Artana; (E,F)—Kizhnica; (G,H)—Drazhnje. (A) Fine inclusions of stannite (st) intergrown with chalcopyrite (cpy) within chalcopyrite and carbonates (crb); (B) stannite (st) filling up cracks in pyrite (py) grain. ttd—tetrahedrite, cpy—chalcopyrite; (C) ferrokësterite (fks) and galena (gn) filling cracks and veinlets in sphalerite (sph); (D) ferrokësterite (fks) grown zones in sphalerite (sph); (E) ferrokësterite (fks) exsolution marking growth zone within sphalerite (sph) accompanied by chalcopyrite inclusions (cpy); (F) ferrokësterite (fks) inclusion in sphalerite in association with chalcopyrite; (G) ferrokësterite (fks) overgrowing sphalerite grains (sph) in the carbonate matrix (crb). White needles are boulangerite (blg); (H) ferrokësterite (fks) overgrowing sphalerite (sph) in the zone enriched in boulangerite (blg). (A–C, E–H) — BSE images, (D)—reflected light crossed polaroids. Full article ">Figure 4
Binary plots showing chemical composition (at. %) of stannite group minerals from Kosovo Pb-Zn deposits: (A) Zn vs. Fe at. %; (B) Sn vs. Zn at. %; (C) Sn vs. Fe at. %; and (D) Sn + In + Ga vs. Cu + Ag at. %. Full article ">Figure 5
Comparison of sphalerite composition from Artana, Kizhnica, Drazhnje, and Stan Terg. Values obtained by LA-ICP-MS (in ppm). Full article ">Figure 6
Binary plots showing chemical composition (ppm) of sphalerite from Kosovo Pb-Zn deposits: (A) Fe vs. Mn; (B) Fe vs. In; (C) Cu vs. In; (D) Fe vs. Cd; (E) In/Fe vs. Cd/Fe; (F) Sn vs. Cu; (G) Sn vs. In; (H) Sn vs. Ag; and (I) Cu + Ag vs. Ga + Sn + In. Full article ">Figure 7
Chemical composition of stannite group minerals from Kosovo deposits as a function of (A) Cu vs. Fe/(Fe + Zn); and (B) Cu/(Cu + Zn) vs. Fe/(Fe + Zn). Grey boxes indicate the approximate fields of stability for stannite-kësterite solid solution regarding Fe/(Fe + Zn). Full article ">Figure 8
Log (XFeS/XZnS)sphalerite–log (XCu2FeSnS4/XCu2ZnSnS4) stannite diagram showing results for sphalerite and stannite from Kosovo deposits. Temperature lines are based on data by Nakamura and Shima [<a href="#B17-minerals-06-00042" class="html-bibr">17</a>]. Full article ">

9840 KiB

Open AccessReview

Role of Fungi in the Biomineralization of Calcite

by Saskia Bindschedler, Guillaume Cailleau and Eric Verrecchia

Minerals 2016, 6(2), 41; https://doi.org/10.3390/min6020041 - 5 May 2016

Cited by 114 | Viewed by 18632

Abstract

In the field of microbial biomineralization, much of the scientific attention is focused on processes carried out by prokaryotes, in particular bacteria, even though fungi are also known to be involved in biogeochemical cycles in numerous ways. They are traditionally recognized as key [...] Read more.

In the field of microbial biomineralization, much of the scientific attention is focused on processes carried out by prokaryotes, in particular bacteria, even though fungi are also known to be involved in biogeochemical cycles in numerous ways. They are traditionally recognized as key players in organic matter recycling, as nutrient suppliers via mineral weathering, as well as large producers of organic acids such as oxalic acid for instance, an activity leading to the genesis of various metal complexes such as metal-oxalate. Their implications in the transformation of various mineral and metallic compounds has been widely acknowledged during the last decade, however, currently, their contribution to the genesis of a common biomineral, calcite, needs to be more thoroughly documented. Calcite is observed in many ecosystems and plays an essential role in the biogeochemical cycles of both carbon (C) and calcium (Ca). It may be physicochemical or biogenic in origin and numerous organisms have been recognized to control or induce its biomineralization. While fungi have often been suspected of being involved in this process in terrestrial environments, only scarce information supports this hypothesis in natural settings. As a result, calcite biomineralization by microbes is still largely attributed to bacteria at present. However, in some terrestrial environments there are particular calcitic habits that have been described as being fungal in origin. In addition to this, several studies dealing with axenic cultures of fungi have demonstrated the ability of fungi to produce calcite. Examples of fungal biomineralization range from induced to organomineralization processes. More examples of calcite biomineralization related to direct fungal activity, or at least to their presence, have been described within the last decade. However, the peculiar mechanisms leading to calcite biomineralization by fungi remain incompletely understood and more research is necessary, posing new exciting questions linked to microbial biomineralization processes. Full article

(This article belongs to the Special Issue Biomineralization: Towards a Unification of Concepts in Chemistry, Physics, Earth Sciences and Biology)

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(A) Hyphal filamentous structure showing cells arranged one after the other, with the formation of ramification by cell branching; (B) Typical two-dimensional morphology of a mycelium as a result of the hyphal branched pattern. Full article ">Figure 2
Simplified phylogenetic tree of Fungi showing the five main phyla currently defined. For each phylum, one typical morphological example is shown. Full article ">Figure 3
Sketch showing the involvement of fungi in global some biogeochemical cycles; (a) Fungi contribute substantially to mineral weathering, leading to the release of bioavailable metals or nutrients, which eventually may be uptaken by living organisms or precipitated as secondary minerals; (b) Fungi as heterotrophs, recycle organic matter (OM). While doing so, they produce metabolites such as organic acids that can also precipitate as secondary minerals (salts). OM recycling eventually releases constitutive elements such as C, N, P and S; (c) CO2 produced by heterotrophic fungal respiration can dissolve into H2O and depending on the physicochemical conditions precipitate as CaCO3 leading to the formation of a secondary mineral. Full article ">Figure 4
Scanning Electron Microscope (SEM) images of fungal hyphae (white arrow) coated with calcium oxalate crystals (probably wheddelite). Both images (A) and (B) are from a sample of plant root associated to fungal hyphae (possibly mycorrhizal fungi) in a secondary CaCO3 deposit of a calcic Cambisol humic calcaric skeletic soil (WRB 2006) in Villiers, Switzerland. Detailed procedure of sample treatment prior to electron microscopy and operation of SEM can be found in [<a href="#B14-minerals-06-00041" class="html-bibr">14</a>]. Full article ">Figure 5
Processes potentially leading to fungal CaCO3 biomineralization at the fungal microenvironment scale. These processes are mainly linked to both Ca2+ sequestration and metabolic control of carbonate alkalinity within cell compartments (cell wall (cw), cytoplasm (cy), and organelles) of fluids translocated inside the hypha. (i) Carbonate alkalinity levels in the fungal microenvironment influence Ca2+ and CO32− bioavailability; (ii) Ca2+ sequestration rate by fungi in the different cellular compartments influences Ca2+ bioavailability. Ca2+ can be present within the cell-wall (Ca2+-cw) as free cytoplasmic Ca2+ bounded to proteins (Ca2+-B) or stored in organelles. Finally, fungi may exert a metabolic control on intra-hyphal alkalinity levels (represented as CO32−), through pH regulation for instance (e.g., H+ excretion). Full article ">Figure 6
Scanning Electron Microscope (SEM) images of natural samples of secondary CaCO3 deposit composed of needle fibre calcite (NFC; white arrows) and nanofibres (black stars) from a calcic Cambisol humic calcaric skeletic soil (WRB 2006) in Villiers, Switzerland. Both images (A) and (B) are from a fungal rhizomorph (fungal hyphae are shown in A by a black arrow) associated to a limestone fragment from deep mineral layers of a soil covered with secondary CaCO3 deposits. Full article ">Figure 7
Transmission electron microscopy (TEM) images of fungal rhizomorphs and associated EDS spectra. Analysed zones are indicated with a star. Cu is from the TEM grid. Fungal rhizomorphs sampled in a calcic Cambisol humic calcaric skeletic soil (WRB 2006) in Villiers, Switzerland at the interface between the B and C horizons, showing the presence of calcium in both their cell wall (left-hand side) and in intrahyphal inclusions (right-hand side). Os peak indicates that inclusions also contain organic material (see [<a href="#B91-minerals-06-00041" class="html-bibr">91</a>] for further details). Full article ">

4118 KiB

Open AccessArticle

Modes of Occurrence and Abundance of Trace Elements in Pennsylvanian Coals from the Pingshuo Mine, Ningwu Coalfield, Shanxi Province, China

by Ning Yang, Shuheng Tang, Songhang Zhang and Yunyun Chen

Minerals 2016, 6(2), 40; https://doi.org/10.3390/min6020040 - 27 Apr 2016

Cited by 21 | Viewed by 4936

Abstract

The Pingshuo Mine is an important coal mine of the Ningwu coalfield in northern Shanxi Province, China. To investigate the mineralogy and geochemistry of Pingshuo coals, core samples from the mineable No. 4 coals were collected. The minerals, major element oxides, and trace [...] Read more.

The Pingshuo Mine is an important coal mine of the Ningwu coalfield in northern Shanxi Province, China. To investigate the mineralogy and geochemistry of Pingshuo coals, core samples from the mineable No. 4 coals were collected. The minerals, major element oxides, and trace elements were analyzed by scanning electron microscopy (SEM), LTA-XRD in combination with Siroquant software, X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS) and ICP-CCT-MS (As and Se). The minerals in the Pennsylvanian coals from the Pingshuo Mine dominantly consist of kaolinite and boehmite, with minor amounts of siderite, anatase, goyazite, calcite, apatite and florencite. Major-element oxides including SiO₂ (9.54 wt %), Al₂O₃ (9.68 wt %), and TiO₂ (0.63 wt %), as well as trace elements including Hg (449.63 ng/g), Zr (285.95 μg/g), Cu (36.72 μg/g), Ga (18.47 μg/g), Se (5.99 μg/g), Cd (0.43 μg/g), Hf (7.14 μg/g), and Pb (40.63 μg/g) are enriched in the coal. Lithium and Hg present strong positive correlations with ash yield and SiO₂, indicating an inorganic affinity. Elements Sr, Ba, Be, As and Ga have strong positive correlations with CaO and P₂O₅, indicating that most of these elements may be either associated with phosphates and carbonates or have an inorganic–organic affinity. Some of the Zr and Hf may occur in anatase due to their strong positive correlations with TiO₂. Full article

(This article belongs to the Special Issue Minerals in Coal)

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2239 KiB

Open AccessArticle

Study on the Selection of Comminution Circuits for a Magnetite Ore in Eastern Hebei, China

by Guangquan Liang, Dezhou Wei, Xinyang Xu, Xiwen Xia and Yubiao Li

Minerals 2016, 6(2), 39; https://doi.org/10.3390/min6020039 - 26 Apr 2016

Cited by 4 | Viewed by 5279

Abstract

Standard drop weight, SMC, and Bond ball work index tests have been conducted to investigate the comminution circuit of a magnetite ore located in Eastern Hebei, China. In addition, simulations based on JKSimMet and Morrell models have been performed to compare the specific [...] Read more.

Standard drop weight, SMC, and Bond ball work index tests have been conducted to investigate the comminution circuit of a magnetite ore located in Eastern Hebei, China. In addition, simulations based on JKSimMet and Morrell models have been performed to compare the specific energy consumption of various comminution circuits. According to the desired capacity and the ore communition characteristics observed, a simulation was conducted to determine the size and driving power of the grinding mills. The SMC and Bond ball work index experiments as well as the Morrell model indicated that the order of the specific energy consumption of comminution was “Jaw crusher + HPGR mill + ball mill” < “Jaw crusher + ball mill”< “SAG mill + ball mill”. Full article

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3589 KiB

Open AccessTechnical Note

Beneficiation of a Sedimentary Phosphate Ore by a Combination of Spiral Gravity and Direct-Reverse Flotation

by Xin Liu, Yimin Zhang, Tao Liu, Zhenlei Cai, Tiejun Chen and Kun Sun

Minerals 2016, 6(2), 38; https://doi.org/10.3390/min6020038 - 20 Apr 2016

Cited by 25 | Viewed by 6358

Abstract

In China, direct-reverse flotation is proved to be applicable to most phosphate ores. However, because the ratio of froth product is generally high, current direct-reverse technology faces challenges in terms of high reagent consumptions and cost. A new gravity and flotation combined process [...] Read more.

In China, direct-reverse flotation is proved to be applicable to most phosphate ores. However, because the ratio of froth product is generally high, current direct-reverse technology faces challenges in terms of high reagent consumptions and cost. A new gravity and flotation combined process has been developed for the recovery of collophanite from sedimentary phosphate ore from the beneficiation plant of Hubei, China. In this process, 53% of the collophanite was firstly recovered by gravity separation, reducing the mass flow to direct flotation. The gravity tailing was the feed for the direct flotation. The flotation concentrate, mixed with gravity concentrate, was then subjected to reverse flotation. A final concentrate with a grade of 30.41% P₂O₅ at a recovery of 91.5% was produced from the feed analyzing 21.55% P₂O₅. Compared to the conventional direct-reverse flotation 86.1% recovery at 31.69% P₂O₅, it was found that pre-recovery of collophanite by spiral separation could significantly reduce the flotation reagent consumption and lead to improved overall collophanite recovery. The benefits of the new process in terms of cost savings were also discussed. Full article

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4221 KiB

Open AccessArticle

Fungal Iron Biomineralization in Río Tinto

by Monike Oggerin, Fernando Tornos, Nuria Rodriguez, Laura Pascual and Ricardo Amils

Minerals 2016, 6(2), 37; https://doi.org/10.3390/min6020037 - 18 Apr 2016

Cited by 18 | Viewed by 6068

Abstract

Although there are many studies on biomineralization processes, most of them focus on the role of prokaryotes. As fungi play an important role in different geological and biogeochemical processes, it was considered of interest to evaluate their role in a natural extreme acidic [...] Read more.

Although there are many studies on biomineralization processes, most of them focus on the role of prokaryotes. As fungi play an important role in different geological and biogeochemical processes, it was considered of interest to evaluate their role in a natural extreme acidic environment, Río Tinto, which has a high level of fungal diversity and a high concentration of metals. In this work we report, for the first time, the generation of iron oxyhydroxide minerals by the fungal community in a specific location of the Tinto basin. Using Transmission Electron Microscopy (TEM) and High Angle Angular Dark Field coupled with Scanning Transmission Electron Microscopy (HAADF-STEM) and Energy-Dispersive X-ray Spectroscopy (EDX), we observed fungal structures involved in the formation of iron oxyhydroxide minerals in mineralized sediment samples from the Río Tinto basin. Although Río Tinto waters are supersaturated in these minerals, they do not precipitate due to their slow precipitation kinetics. The presence of fungi, which simply provide charged surfaces for metal binding, favors the precipitation of Fe oxyhydroxides by overcoming these kinetic barriers. These results prove that the fungal community of Río Tinto participates very actively in the geochemical processes that take place there. Full article

(This article belongs to the Special Issue Biomineralization: Towards a Unification of Concepts in Chemistry, Physics, Earth Sciences and Biology)

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1268 KiB

Open AccessArticle

Seasonal Microbial Population Shifts in a Bioremediation System Treating Metal and Sulfate-Rich Seepage

by Susan A. Baldwin, Al Mattes, Maryam Rezadehbashi and Jon Taylor

Minerals 2016, 6(2), 36; https://doi.org/10.3390/min6020036 - 12 Apr 2016

Cited by 18 | Viewed by 5384

Abstract

Biochemical reactors (BCRs) using complex organics for bioremediation of mine-influenced water must operate successfully year round. In cold climates, where many mines in Canada are located, survival of the important microorganisms through the winter months is a concern. In this work, broad phylogenetic [...] Read more.

Biochemical reactors (BCRs) using complex organics for bioremediation of mine-influenced water must operate successfully year round. In cold climates, where many mines in Canada are located, survival of the important microorganisms through the winter months is a concern. In this work, broad phylogenetic surveys, using metagenomics, of the microbial populations in pulp mill biosolids used to remediate metal leachate containing As, Zn, Cd and sulfate were performed to see if the types of microorganisms present changed over the seasons of one year (August 2008 to July 2009). Despite temperature variations between 0 and 17 °C the overall structure of the microbial population was fairly consistent. A cyclical pattern in relative abundance was detected in certain taxa. These included fermenter-related groups, which were out of phase with other taxa such as Desulfobulbus that represented potential consumers of fermentation byproducts. Sulfate-reducers in the BCR biosolids were closely related to psychrotolerant species. Temperature was not a factor that shaped the microbial population structure within the BCR biosolids. Kinetics of organic matter degradation by these microbes and the rate of supply of organic carbon to sulfate-reducers would likely affect the metal removal rates at different temperatures. Full article

(This article belongs to the Special Issue Biotechnologies and Mining)

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Graphical abstract
Full article ">Figure 1
Relative abundance of the major Orders in the biochemical reactor (BCR) biosolids over the study period. Full article ">Figure 2
Principle co-ordinate plot comparing the microbial population compositions in the various months. Full article ">Figure 3
Plots of relative (to the total read count for that OTU) prevalence of co-occurring taxa in the two negatively correlated clusters (a) and (b). Full article ">Figure 4
Percentage of bacterial SSU rRNA amplicon sequences assigned to known sulfate-reducing bacteria taxonomic groups in each month (orange bars and left-hand side y-axis). Number of bacterial SSU rRNA gene copies ascribed to sulfate-reducing bacteria (blue diamonds and right-hand side y-axis). Full article ">Figure 5
Number of bacterial SSU rRNA gene copies per 0.5 g of biosolids mixture in each of the monthly samples measured using qPCR. Full article ">Figure 6
Schematic of the main steps speculated to take place in the microbial degradation of biosolids in the BCR. Prevalent genus-level taxa found in this study potentially involved in each step are listed in italics. Full article ">

806 KiB

Open AccessArticle

The Fate of Trace Elements in Yanshan Coal during Fast Pyrolysis

by Jiatao Dang, Qiang Xie, Dingcheng Liang, Xin Wang, He Dong and Junya Cao

Minerals 2016, 6(2), 35; https://doi.org/10.3390/min6020035 - 6 Apr 2016

Cited by 10 | Viewed by 5513

Abstract

In this study, a high-sulfur and high-ash yield coal sample obtained from the Yanshan coalfield in Yunnan, China was analyzed. A series of char samples was obtained by pyrolysis at various temperatures (300, 400, 500, 600, 700, 800, and 900 °C) and at [...] Read more.

In this study, a high-sulfur and high-ash yield coal sample obtained from the Yanshan coalfield in Yunnan, China was analyzed. A series of char samples was obtained by pyrolysis at various temperatures (300, 400, 500, 600, 700, 800, and 900 °C) and at a fast heating rate (1000 °C/min). A comprehensive investigation using inductively coupled plasma mass spectrometry (ICP-MS), a mercury analyzer, ion-selective electrode (ISE) measurements, X-ray diffraction (XRD) analysis, and Fourier transform infrared (FTIR) spectroscopy was performed to reveal the effects of the pyrolysis temperature on the transformation behavior of trace elements (TEs) and the change in the mineralogical characteristics and functional groups in the samples. The results show that the TE concentrations in the raw coal are higher than the average contents of Chinese coal. The concentrations of Be, Li, and U in the char samples are higher than those in raw coal, while the opposite was observed for As, Ga, Hg, and Rb. The F and Se concentrations are initially higher but decrease with pyrolysis temperature, which is likely caused by associated fracturing with fluoride and selenide minerals. Uranium shows the highest enrichment degree, and Hg shows the highest volatilization degree compared to the other studied TEs. As the temperature increases, the number of OH groups decreases, and the mineral composition changes; for example, pyrite decomposes, while oldhamite and hematite occur in the chars. It is suggested that the behavior and fate of TEs in coal during fast pyrolysis are synergistically influenced by self-characteristic modes of occurrence and mineralogical characteristics. Full article

(This article belongs to the Special Issue Minerals in Coal)

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2777 KiB

Open AccessReview

Apatite Biominerals

by Christèle Combes, Sophie Cazalbou and Christian Rey

Minerals 2016, 6(2), 34; https://doi.org/10.3390/min6020034 - 5 Apr 2016

Cited by 175 | Viewed by 15753

Abstract

Calcium phosphate apatites offer outstanding biological adaptability that can be attributed to their specific physico-chemical and structural properties. The aim of this review is to summarize and discuss the specific characteristics of calcium phosphate apatite biominerals in vertebrate hard tissues (bone, dentine and [...] Read more.

Calcium phosphate apatites offer outstanding biological adaptability that can be attributed to their specific physico-chemical and structural properties. The aim of this review is to summarize and discuss the specific characteristics of calcium phosphate apatite biominerals in vertebrate hard tissues (bone, dentine and enamel). Firstly, the structural, elemental and chemical compositions of apatite biominerals will be summarized, followed by the presentation of the actual conception of the fine structure of synthetic and biological apatites, which is essentially based on the existence of a hydrated layer at the surface of the nanocrystals. The conditions of the formation of these biominerals and the hypothesis of the existence of apatite precursors will be discussed. Then, we will examine the evolution of apatite biominerals, especially during bone and enamel aging and also focus on the adaptability of apatite biominerals to the biological function of their related hard tissues. Finally, the diagenetic evolution of apatite fossils will be analyzed. Full article

(This article belongs to the Special Issue Biomineralization: Towards a Unification of Concepts in Chemistry, Physics, Earth Sciences and Biology)

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Schematic representation of the surface hydrated layer model for poorly crystalline apatite nanocrystals (Reprinted from Nanocrystalline apatite based biomaterials: synthesis, processing and characterization; Copyright (2009), Eichert D., Drouet C., Sfihi H., Rey C. and Combes C. [<a href="#B43-minerals-06-00034" class="html-bibr">43</a>] with permission from Nova Science Publishers Inc.). Full article ">Figure 2
Maturation pathways of nanocrystalline apatites depending on the composition of the medium (the arrows, after the ions, represent an increase (or decrease) of the species considered during maturation). Full article ">Figure 3
Example of the effect of adsorbed molecules on crystal growth [<a href="#B102-minerals-06-00034" class="html-bibr">102</a>,<a href="#B103-minerals-06-00034" class="html-bibr">103</a>]. (A) Effect of bovine serum albumin (BSA) on octacalcium phosphate crystal growth: kinetics results (relative rate of crystal growth of octacalcium phosphate (OCP) in %) and SEM micrographs of OCP crystal growth on collagen in the presence of various concentrations of bovine serum albumin (BSA) using the constant composition crystal growth technique (adapted from [<a href="#B102-minerals-06-00034" class="html-bibr">102</a>,<a href="#B103-minerals-06-00034" class="html-bibr">103</a>]). At low albumin concentrations, when the solution reaches depletion due to nucleation and adsorption, a burst rate of crystal growth occurs exceeding that observed in the absence of albumin. At high albumin concentrations, however, there is never depletion of free BSA molecules in solution and only the well-known crystal growth inhibitory effect of the molecule on OCP crystals is evidenced. SEM micrographs showed smaller but more numerous OCP crystals in the presence of BSA. (B) Schematization of the effect of nucleation and growth without (a) or with (b) the presence of adsorbing molecules/ions on crystal growth depending on their solution concentration. Adsorbing species may have positive effect on crystal nucleation by stabilizing nuclei with a critical radius smaller than the critical radius in the absence of adsorbing species, due to a decrease of interfacial energy. As a result a multiplication of nuclei is observed in the presence of such adsorbing species. Nuclei grow together slowly and new nuclei form until depletion is reached, a ‘‘burst’’ of growth is then observed when a multitude of nuclei have formed and no crystal growth inhibitory species remains in solution: this leads to small but numerous crystals and provides a relatively homogeneous population of crystals. With larger amounts of adsorbing species, only an inhibiting crystal growth effect dominates. Full article ">Figure 4
Schematic representation of classical and non-classical theory of crystallization: classical nucleation and crystal growth pathway (a); iso-oriented crystal pathway (b); mesoscale assembly pathway in the presence of polymer or additive (c); and transformation of amorphous precursor particles pathway (d) (from [<a href="#B108-minerals-06-00034" class="html-bibr">108</a>]. Copyright 2008 John Wiley & Sons. Reproduced with permission). Full article ">Figure 5
Gibbs free energy of activation associated with nucleation (n), growth (g) and phase transformation (T) through two main pathways: with (B) and without (A) intermediate phase(s) (adapted from Gower’s review paper for the calcium phosphate system [<a href="#B107-minerals-06-00034" class="html-bibr">107</a>]). Full article ">Figure 6
The various phenomena involved in the diagenetic evolution of biological apatites (adapted from [<a href="#B145-minerals-06-00034" class="html-bibr">145</a>]). Full article ">

6990 KiB

Open AccessArticle

Petříčekite, CuSe₂, a New Member of the Marcasite Group from the Předbořice Deposit, Central Bohemia Region, Czech Republic

by Luca Bindi, Hans-Jürgen Förster, Günter Grundmann, Frank N. Keutsch and Chris J. Stanley

Minerals 2016, 6(2), 33; https://doi.org/10.3390/min6020033 - 1 Apr 2016

Cited by 12 | Viewed by 6703

Abstract

Petříčekite, ideally CuSe₂, is a new mineral from the Předbořice deposit, Central Bohemia Region, Czech Republic. It occurs as rare inclusions, up to 150 μm across, in large eucairite grains closely associated with athabascaite/klockmannite and unknown selenide phases. Petříčekite is opaque [...] Read more.

Petříčekite, ideally CuSe₂, is a new mineral from the Předbořice deposit, Central Bohemia Region, Czech Republic. It occurs as rare inclusions, up to 150 μm across, in large eucairite grains closely associated with athabascaite/klockmannite and unknown selenide phases. Petříčekite is opaque with a metallic luster and shows a black streak. It is brittle; the Vickers hardness (VHN₁₅) is 33 kg/mm² (range: 28–40 kg/mm²) (Mohs hardness of ~2–2½). In reflected light, petříčekite is pale blue grey to pale pinkish, weakly pleochroic and weakly bireflectant from slightly blue-grey to slightly pinkish-grey. Under crossed polars, it is anisotropic with light grey-blue to light pink rotation tints. Internal reflections are absent. Reflectance percentages for the four COM (Commission on Ore Mineralogy) wavelengths (R_min and R_max) are 42.35, 41.8 (470 nm), 42.0, 42.2 (546 nm), 41.9, 42.35 (589 nm) and 42.05, 42.85 (650 nm), respectively. Petříčekite is orthorhombic, space group Pnnm, with a = 4.918(2) Å; b = 6.001(2) Å; c = 3.670(1) Å; V = 108.31(1) Å³; Z = 2. The crystal structure (R1 = 0.0336 for 159 reflections with I > 2σ(I)) belongs to the marcasite-type structure. It consists of edge-sharing chains of CuSe₆ octahedra parallel to [001] linked by sharing Se₂ dimers. The Se–Se bonds are all parallel to (001). The five strongest powder-diffraction lines (d in Å (I/I₀) (hkl)) are: 2.938 (70) (101); 2.639 (100) (111); 2.563 (85) (120); 1.935 (70) (211); 1.834 (30) (002). The mean of nine electron-microprobe analyses on the crystal used for the structural study gave Ag 0.22(13), Cu 15.39(15), Hg 0.01(3), Pb 0.03(2), Fe 12.18(10), Pd 0.11(4), S 0.09(1), Se 71.61(29) and total 99.64(41) wt %, corresponding on the basis of a total of three atoms, to (Cu_0.53Fe_0.48)_Σ1.01(Se_1.98S_0.01)_Σ1.99. Additional crystals exhibiting higher Cu contents (up to 0.74 a.p.f.u.) were also investigated. The new mineral has been approved by the IMA-NMNC Commission (2015-111) and named after Václav Petříček, renowned crystallographer of the Institute of Physics of the Czech Academy of Sciences, Prague. Optical, compositional and structural properties confirm that nearly pure petříčekite also formed as late-stage mineral in the Se mineralization at El Dragón, Bolivia. It has end-member composition, Cu_0.99Se_2.00 (n = 5), and is typically associated with krut’aite of ideal composition, native selenium and goethite. Finally, optical and chemical data indicate that pure petříčekite is likely present also at Sierra de Cacheuta, Argentina. Full article

(This article belongs to the Special Issue Advanced Research on Accessory Minerals)

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Reflected light photograph of the holotype grain of petříčekite (P, included in EU = eucairite) that was used for structure determination. The chemical composition of this grain is (Cu0.53Fe0.48)Σ1.01(Se1.98S0.01)Σ1.99. Full article ">Figure 2
Reflected light images of petříčekite from Předbořice, all images have 200 μm width. Right hand side with partly crossed polarizers, left hand side without. Top and bottom row correspond to different extinction rotations. P = petříčekite, EU = eucairite, PM = permingeatite, A = athabascaite, UK1 corresponds to an unknown selenide currently under investigation. In plane-polarized incident light, petříčekite is pale blue grey to pale pinkish in color, weakly bireflectant and weakly pleochroic from slightly blue-grey to slightly pinkish-grey. With crossed polars, petříčekite is weakly anisotropic with light grey-blue to light pink rotation tints. Full article ">Figure 3
Fragments of krut’aite-penroseite (k-p) cemented by skeletal palisades of subhedral petříčekite crystals (P), end-member krut’aite (k), goethite (g), and covellite (c). The arrow marks a twinned petříčekite grain. (a) Without polarizers; (b) with partly crossed polarizers. Image width = 200 μm. Sample from El Dragón. Full article ">Figure 4
Petříčekite (P), end-member krut’aite (k), native selenium (se), and olsacherite-molybdomenite (o-m) pseudomorph after clausthalite, surrounded by pyrite (py) and goethite (g). Width = 200 μm, without polarizers. Sample from El Dragón. Full article ">Figure 5
Petříčekite (P), krut’aite (k), watkinsonite (w), and klockmannite (kl) filling a small crack in krut’aite-penroseite (k-p). Note the fine-scale intergrowth of P and k and the partial replacement of k-p, P and w by krut’aite. Width = 200 µm, without polarizers. Sample from El Dragón. Full article ">Figure 6
Sample from Sierra de Cacheuta, Argentina: Clausthalite (cl) partly replaced by krut’aite of ideal composition (blue, k), end-member petříčekite (blue-light violet, P), molybdomenite (dark grey, m) and native selenium (light grey, se). (a) Without polarizers; (b) with partly crossed polarizers. Image width = 200 µm. Full article ">Figure 7
The crystal structure of petříčekite down the c-axis. Light-blue and golden circles indicate (Cu,Fe) and Se, respectively. Four unit-cells are depicted. Full article ">Figure 8
Unit-cell parameters (values in Å) of the two petříčekite crystals from Předbořice, plotted together with the two synthetic end-members FeSe2 and CuSe2 [<a href="#B4-minerals-06-00033" class="html-bibr">4</a>], as a function of the Cu content (a.p.f.u.). Full article ">

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Open AccessArticle

Morphology and Composition of Microspheres in Fly Ash from the Luohuang Power Plant, Chongqing, Southwestern China

by Huidong Liu, Qi Sun, Baodong Wang, Peipei Wang and Jianhua Zou

Minerals 2016, 6(2), 30; https://doi.org/10.3390/min6020030 - 1 Apr 2016

Cited by 29 | Viewed by 8468

Abstract

In order to effectively raise both utilization rate and additional value of fly ash, X-Ray diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive X-Ray spectrometer (EDS) were used to investigate the morphology, and chemical and mineral composition of the microspheres in fly ash [...] Read more.

In order to effectively raise both utilization rate and additional value of fly ash, X-Ray diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive X-Ray spectrometer (EDS) were used to investigate the morphology, and chemical and mineral composition of the microspheres in fly ash from the Luohuang coal-fired power plant, Chongqing, southwestern China. The majority of fly ash particles are various types of microspheres, including porous microsphere, plerospheres (hollow microspheres surrounding sub-microspheres or mineral fragments) and magnetic ferrospheres. Maghemite (γ-Fe₂O₃) crystals with spinel octahedron structure regularly distribute on the surfaces of ferrospheres, which explained the source of their strong magnetism that would facilitate the separation and classification of these magnetic ferrospheres from the fly ash. Microspheres in Luohuang fly ash generally are characterized by an elemental transition through their cross-section: the inner layer consists of Si and O; the chemical component of the middle layer is Si, Al, Fe, Ti, Ca and O; and the Fe-O mass (maghemite or hematite) composes the outer layer (ferrosphere). Studies on composition and morphological characteristics of microspheres in fly ash would provide important information on the utilization of fly ash, especially in the field of materials. Full article

(This article belongs to the Special Issue Minerals in Coal)

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Particle size distribution of the Luohuang fly ash. Full article ">Figure 2
The X-Ray diffraction (XRD) pattern of the fly ash sample from the Luohuang power plant. Q, quartz; Mu, mullite; He, hematite; Mh, maghemite; An, anhydrite. Full article ">Figure 3
Scanning electron microscope (SEM) backscattered electron images and energy-dispersive X-Ray spectrometer (EDS) analyses of microspheres in the Luohuang fly ash: (A) Overall view of the Luohuang fly ash; (B) Enlargement of the area marked in (A), magnetic microsphere; (C) Enlargement of the area marked in (B), maghemite (γ-Fe2O3) crystals with spinel structure; (D) Porous microsphere; (E) Plerosphere; and (F) Cracked plerosphere containing a particle of metallic iron. Full article ">Figure 3 Cont.
Scanning electron microscope (SEM) backscattered electron images and energy-dispersive X-Ray spectrometer (EDS) analyses of microspheres in the Luohuang fly ash: (A) Overall view of the Luohuang fly ash; (B) Enlargement of the area marked in (A), magnetic microsphere; (C) Enlargement of the area marked in (B), maghemite (γ-Fe2O3) crystals with spinel structure; (D) Porous microsphere; (E) Plerosphere; and (F) Cracked plerosphere containing a particle of metallic iron. Full article ">

791 KiB

Open AccessCommentary

Notes on Contributions to the Science of Rare Earth Element Enrichment in Coal and Coal Combustion Byproducts

by James C. Hower, Evan J. Granite, David B. Mayfield, Ari S. Lewis and Robert B. Finkelman

Minerals 2016, 6(2), 32; https://doi.org/10.3390/min6020032 - 31 Mar 2016

Cited by 192 | Viewed by 13825

Abstract

Coal and coal combustion byproducts can have significant concentrations of lanthanides (rare earth elements). Rare earths are vital in the production of modern electronics and optics, among other uses. Enrichment in coals may have been a function of a number of processes, with [...] Read more.

Coal and coal combustion byproducts can have significant concentrations of lanthanides (rare earth elements). Rare earths are vital in the production of modern electronics and optics, among other uses. Enrichment in coals may have been a function of a number of processes, with contributions from volcanic ash falls being among the most significant mechanisms. In this paper, we discuss some of the important coal-based deposits in China and the US and critique classification systems used to evaluate the relative value of the rare earth concentrations and the distribution of the elements within the coals and coal combustion byproducts. Full article

(This article belongs to the Special Issue Minerals in Coal)

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7317 KiB

Open AccessArticle

Restraining Sodium Volatilization in the Ferric Bauxite Direct Reduction System

by Wentao Hu, Huajun Wang, Xinwei Liu, Chuanyao Sun and Xuqin Duan

Minerals 2016, 6(2), 31; https://doi.org/10.3390/min6020031 - 31 Mar 2016

Cited by 6 | Viewed by 4413

Abstract

Direct reduction is an emerging utilization technology of ferric bauxite. However, it requires much more sodium carbonate than ordinary bauxite does. The volatilization is one of the most significant parts of sodium carbonate consumption, as reported in previous studies. Based on the new [...] Read more.

Direct reduction is an emerging utilization technology of ferric bauxite. However, it requires much more sodium carbonate than ordinary bauxite does. The volatilization is one of the most significant parts of sodium carbonate consumption, as reported in previous studies. Based on the new direct reduction method for utilization of ferric bauxite, this paper has systematically investigated factors including heating temperature, heating time, and sodium carbonate dosage influencing sodium volatilization. For the purpose of reducing sodium volatilization, the Box–Benhken design was employed, and the possibility of separating iron and sodium after direct reduction was also investigated. Full article

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15198 KiB

Open AccessArticle

Mineralogical Characteristics of Late Permian Coals from the Yueliangtian Coal Mine, Guizhou, Southwestern China

by Panpan Xie, Hongjian Song, Jianpeng Wei and Qingqian Li

Minerals 2016, 6(2), 29; https://doi.org/10.3390/min6020029 - 31 Mar 2016

Cited by 18 | Viewed by 5635

Abstract

This paper reports the mineralogical compositions of super-low-sulfur (Yueliangtian 6-upper (YLT6U)) and high-sulfur (Yueliangtian 6-lower (YLT6L)) coals of the Late Permian No. 6 coal seam from the Yueliangtian coal mine, Guizhou, southwestern China. The mineral assemblages and morphology were detected and observed by [...] Read more.

This paper reports the mineralogical compositions of super-low-sulfur (Yueliangtian 6-upper (YLT6U)) and high-sulfur (Yueliangtian 6-lower (YLT6L)) coals of the Late Permian No. 6 coal seam from the Yueliangtian coal mine, Guizhou, southwestern China. The mineral assemblages and morphology were detected and observed by X-ray diffractogram (XRD), optical microscopy and field-emission scanning electron microscope (FE-SEM) in conjunction with an energy-dispersive X-ray spectrometer. Major minerals in the coal samples, partings and host rocks (roof and floor strata) include calcite, quartz, kaolinite, mixed-layer illite/smectite, chlorite and pyrite and, to a lesser extent, chamosite, anatase and apatite. The Emeishan basalt and silicic rocks in the Kangdian Upland are the sediment source for the Yueliangtian coals. It was found that there are several modes of chamosite occurrence, and precursor minerals, such as anatase, had been corroded by Ti-rich hydrothermal solutions. The modes of occurrence of minerals present in the coal were controlled by the injection of different types of hydrothermal fluids during different deposition stages. The presence of abundant pyrite and extremely high total sulfur contents in the YLT6L coal are in sharp contrast to those in the YLT6U coal, suggesting that seawater invaded the peat swamp of the YLT6L coal and terminated at the YLT6U-9p sampling interval. High-temperature quartz, vermicular kaolinite and chloritized biotite were observed in the partings and roof strata. The three partings and floor strata of the No. 6 coal seam from the Yueliangtian coal mine appear to have been derived from felsic volcanic ash. Four factors, including sediment-source region, multi-stage injections of hydrothermal fluids, seawater influence and volcanic ash input, were responsible for the mineralogical characteristics of the Yueliangtian coals. Full article

(This article belongs to the Special Issue Minerals in Coal)

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12281 KiB

Open AccessArticle

Geochemical Characteristics of Trace Elements in the No. 6 Coal Seam from the Chuancaogedan Mine, Jungar Coalfield, Inner Mongolia, China

by Lin Xiao, Bin Zhao, Piaopiao Duan, Zhixiang Shi, Jialiang Ma and Mingyue Lin

Minerals 2016, 6(2), 28; https://doi.org/10.3390/min6020028 - 30 Mar 2016

Cited by 22 | Viewed by 5112

Abstract

Fourteen samples of No. 6 coal seam were obtained from the Chuancaogedan Mine, Jungar Coalfield, Inner Mongolia, China. The samples were analyzed by optical microscopic observation, X-ray diffraction (XRD), scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM-EDS), inductively coupled plasma mass [...] Read more.

Fourteen samples of No. 6 coal seam were obtained from the Chuancaogedan Mine, Jungar Coalfield, Inner Mongolia, China. The samples were analyzed by optical microscopic observation, X-ray diffraction (XRD), scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM-EDS), inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF) methods. The minerals mainly consist of kaolinite, pyrite, quartz, and calcite. The results of XRF and ICP-MS analyses indicate that the No. 6 coals from Chuancaogedan Mine are higher in Al₂O₃, P₂O₅, Zn, Sr, Li, Ga, Zr, Gd, Hf, Pb, Th, and U contents, but have a lower SiO₂/Al₂O₃ ratio, compared to common Chinese coals. The contents of Zn, Sr, Li, Ga, Zr, Gd, Hf, Pb, Th, and U are higher than those of world hard coals. The results of cluster analyses show that the most probable carrier of strontium in the coal is gorceixite; Lithium mainly occurs in clay minerals; gallium mainly occurs in inorganic association, including the clay minerals and diaspore; cadmium mainly occurs in sphalerite; and lead in the No. 6 coal may be associated with pyrite. Potentially valuable elements (e.g., Al, Li, and Ga) might be recovered as byproducts from coal ash. Other harmful elements (e.g., P, Pb, and U) may cause environmental impact during coal processing. Full article

(This article belongs to the Special Issue Minerals in Coal)

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Locations of the Chuancaogedan Mine, Guanbanwusu Mine, Heidaigou Opencut Mine, and Haerwusu Opencut Mine in the Jungar Coalfield. Full article ">Figure 2
Lithostratigraphical column of the Jungar Coalfield and lithological column of the sampling profile. Full article ">Figure 3
Identification of minerals in the X-ray diffraction (XRD) pattern of the low temperature ash (LTA) of Sample 6-10. Full article ">Figure 4
Clay minerals in Sample 6-1. (A) Lumpy clay with microgranular texture (reflected light); (B) Cell-filling clay minerals (scanning electron microscopy, SEM); (C) Crystalline kaolinite (SEM) and energy-dispersive X-ray spectrometry (EDS) spectrum from Spot 1 (D). Full article ">Figure 5
Pyrite in the Sample 6-13. (A) Pyritized cell filling (reflected light); (B) Fracture-filling pyrite (reflected light); (C) Crystals of pyrite (SEM) and EDS spectra of it (D). Full article ">Figure 6
Quartz (A) and calcite (B) in the Sample 6-3 (reflected light). Full article ">Figure 7
(A) Concentrations coefficients (CC) of elements in the Chuancaogedan coal vs. world coals; (B) CC of elements in the Chuancaogedan coals vs. Chinese coals. Full article ">Figure 8
Cluster analyses of analytical results on 14 samples. Full article ">

9732 KiB

Open AccessArticle

Minerals in the Ash and Slag from Oxygen-Enriched Underground Coal Gasification

by Shuqin Liu, Chuan Qi, Shangjun Zhang and Yunpeng Deng

Minerals 2016, 6(2), 27; https://doi.org/10.3390/min6020027 - 30 Mar 2016

Cited by 18 | Viewed by 8654

Abstract

Underground coal gasification (UCG) is a promising option for the recovery of low-rank and inaccessible coal resources. Detailed mineralogical information is essential to understand underground reaction conditions far from the surface and optimize the operation parameters during the UCG process. It is also [...] Read more.

Underground coal gasification (UCG) is a promising option for the recovery of low-rank and inaccessible coal resources. Detailed mineralogical information is essential to understand underground reaction conditions far from the surface and optimize the operation parameters during the UCG process. It is also significant in identifying the environmental effects of UCG residue. In this paper, with regard to the underground gasification of lignite, UCG slag was prepared through simulation tests of oxygen-enriched gasification under different atmospheric conditions, and the minerals were identified by X-Ray diffraction (XRD) and a scanning electron microscope coupled to an energy-dispersive spectrometer (SEM-EDS). Thermodynamic calculations performed using FactSage 6.4 were used to help to understand the transformation of minerals. The results indicate that an increased oxygen concentration is beneficial to the reformation of mineral crystal after ash fusion and the resulting crystal structures of minerals also tend to be more orderly. The dominant minerals in 60%-O₂ and 80%-O₂ UCG slag include anorthite, pyroxene, and gehlenite, while amorphous substances almost disappear. In addition, with increasing oxygen content, mullite might react with the calcium oxide existed in the slag to generate anorthite, which could then serve as a calcium source for the formation of gehlenite. In 80%-O₂ UCG slag, the iron-bearing mineral is transformed from sekaninaite to pyroxene. Full article

(This article belongs to the Special Issue Minerals in Coal)

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