Minerals

23 pages, 13657 KiB

Open AccessArticle

Micrometric Inclusions in Platinum-Group Minerals from Gornaya Shoria, Southern Siberia, Russia: Problems and Genetic Significance

by Gleb V. Nesterenko, Sergey M. Zhmodik, Dmitriy K. Belyanin, Evgeniya V. Airiyants and Nikolay S. Karmanov

Minerals 2019, 9(5), 327; https://doi.org/10.3390/min9050327 - 27 May 2019

Cited by 4 | Viewed by 5245

Abstract

Micrometric inclusions in platinum-group minerals (PGMs) from alluvial placers carry considerable information about types of primary rocks and ores, as well as conditions of their formation and alteration. In the present contribution, we attempt to show, with concrete examples, the significance of the [...] Read more.

Micrometric inclusions in platinum-group minerals (PGMs) from alluvial placers carry considerable information about types of primary rocks and ores, as well as conditions of their formation and alteration. In the present contribution, we attempt to show, with concrete examples, the significance of the data on the composition and morphology of micrometric inclusions to genetic interpretations. The PGM grains from alluvial placers of the Gornaya Shoria region (Siberia, Russia) were used as the subject of our investigation. In order to determine the chemical composition of such ultrafine inclusions, high-resolution analytical methods are needed. We compare the results acquired by wavelength-dispersive spectrometry (WDS; electron microprobe) and energy-dispersive spectrometry (EDS) and scanning electron microscopy (SEM) methods. The results obtained have good convergence. The EDS method is multi-elemental and more effective for mineral diagnostics in comparison with WDS, which is its certain advantage. The possible conditions for the formation of inclusions and layers of gold, sulfoarsenides and arsenides in Pt₃Fe grains, which have an original sub-graphic and layered texture pattern, are discussed. They are the result of solid solution and eutectic decompositions and are associated with the magmatic stages of grain transformation, including the result of the interaction of Pt₃Fe with a sulfide melt enriched with Te and As. Full article

(This article belongs to the Special Issue Platinum-Group Minerals: New Results and Advances in PGE Mineralogy in Various Ni-Cu-Cr-PGE Ore Systems)

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(a) Location of the study area; (b) the Kuznetsk Alatau–Gornaya Ghoria–Altai platinum-bearing belt is indicated by black color in the inset (modified from [<a href="#B20-minerals-09-00327" class="html-bibr">20</a>]): 1, Kaigadat massif; 2, Srednyaya Ters’ massif; 3, Seglebir massif and placers of Gornaya Shoria; (c) geological map showing the location of PGM and gold placers in the western Altai-Sayan folded area (Gornaya Shoria); (d,e) geological maps of catchment areas r. Kaurchak (d) and r. Koura (e). Full article ">Figure 2
Back-scattered electron (BSE) image showing multiphase Grain No. 1 (a) A placer grain of Pt3(Fe,Cu) consists of a rim of Cu-enriched alloy phase (hongshiite PtCu) with inclusions of rhodarsenide (Rh,Pd)2As. (b,c) The exsolution micro-lamellae of rutheniridosmine (the decomposition of a solid solution) in isoferroplatinum and platarsite (PtAsS). The composition of measurement points is listed in <a href="#minerals-09-00327-t004" class="html-table">Table 4</a>. White—isoferroplatinum (Pt,Fe) and osmium (Os); light gray and gray—platarsite (PtAsS), cooperite (PtS), and sperrylite (PtAs); rectangular contours—the position of the microsites “b” and “c”. Explanation in the text. Full article ">Figure 3
BSE image showing multiphase Grain No. 2. (a) A placer grain of Pt3(Fe,Cu) consists of a rim of Cu-enriched alloy phase (hongshiite PtCu) with inclusions of rhodarsenide (Rh,Pd)2As. (b,c) The exsolution micro-lamellae of rutheniridosmine (the decomposition of a solid solution) in isoferroplatinum and platarsite (PtAsS). For the composition of measurement points see <a href="#minerals-09-00327-t005" class="html-table">Table 5</a>. White—isoferroplatinum (Pt3Fe) and osmium (Os); light gray and gray—platarsite (PtAsS), cooperite (PtS), and sperrylite (PtAs); rectangular contours—the position of the microsites “b” and “c”. Full article ">Figure 4
Grain No. 3 was derived from the placer of Kaurchak River (dredge 138). (a) Reflected light micrograph of grain No. 3 of the Pt-Fe alloy with alteration sperrylite composition rim (gray) and inclusions and overgrowths of native gold (reddish). (b–f) BSE images showing the structure and morphology of the local areas. Light gray background—matrix Pt4Fe; gray and dark gray rim—sperrylite and platarsite; white inclusions and overgrowths—native gold; the compositions of the Pt-Fe alloy and inclusions at these points are given in <a href="#minerals-09-00327-t007" class="html-table">Table 7</a> and <a href="#minerals-09-00327-t008" class="html-table">Table 8</a>. Full article ">Figure 5
Backscattered-electron image (BSE) (a) and element distribution maps (b—polyelement; c—Pt; d—Fe; e—Ru; f— Au; g—S; h—As) in the grain No. 3 (see <a href="#minerals-09-00327-f004" class="html-fig">Figure 4</a>) platinum nugget. Full article ">Figure 6
The areas of detail 4d of grain No. 3. Distribution patterns obtained in the mapping mode: Au, Ag, Rh, Ru, As, S, Pt. Full article ">Figure 7
Backscattered-electron (BSE) image (top) and the graphs of changes of the main elements content (at.%) in the Core, Rim-I, Rim-II, with micro-layers in grain No. 3 (see also <a href="#minerals-09-00327-f004" class="html-fig">Figure 4</a>e). Full article ">

17 pages, 4701 KiB

Open AccessArticle

Trace Element Geochemistry in Quartz in the Jinqingding Gold Deposit, Jiaodong Peninsula, China: Implications for the Gold Precipitation Mechanism

by Binghan Chen, Jun Deng, Hantao Wei and Xingzhong Ji

Minerals 2019, 9(5), 326; https://doi.org/10.3390/min9050326 - 27 May 2019

Cited by 12 | Viewed by 5227

Abstract

Lots of studies on gold precipitation mechanisms have focused on fluid inclusions within quartz. However, the trace elements in quartz reflect the properties of the ore fluid, and a comparison of the trace element content in different types of quartz can reveal the [...] Read more.

Lots of studies on gold precipitation mechanisms have focused on fluid inclusions within quartz. However, the trace elements in quartz reflect the properties of the ore fluid, and a comparison of the trace element content in different types of quartz can reveal the precipitation mechanism. The Jinqingding gold deposit is the largest gold deposit in the Muping–Rushan gold belt and contains the largest single sulfide–quartz vein type orebody in the gold belt. This study distinguished four types of quartz in this orebody through field work and investigations of the mineralogy and cathodoluminescence (CL) of the quartz and crosscutting relationships as seen under a microscope. In situ studies via electron probe micro-analyzer (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were used to determine the trace element content of the different quartz types. Type Qa displayed a comb structure in the field and zoning under the microscope and in CL. Milky white and smoke grey Qb was the most common quartz type and hosted the most sulfide and gold. Qc was Qa and Qb quartz that recrystallized around pyrite or overgrew and appeared different from Qa and Qb in CL images. Qd occurred within fractures in pyrite. Qa formed prior to the mineralization of gold, and Qd formed post-mineralization. Qb and Qc provided information regarding the ore fluid during mineralization. Sericites occurred with pyrite in fractures in the quartz, and some, along with free gold, filled in fractures in pyrite. Free gold occurred within Qa, Qb, Qc, and in brittle fractures in pyrite. Qc had the lowest Al content of all of the quartz types. As Al content is related to the acidity of the ore fluid in previous study, this indicated an acidity decrease during mineralization, which could be attributed to the sericitization. Sericitization could indicate a potential gold occurrence. The Ti content decreased from Qb to Qc, indicating a decrease in temperature during quartz overgrowth formation. Change in acidity and cooling can therefore be identified as possible causes of gold precipitation in the sulfide–quartz vein type in the Jinqingding gold deposit. Full article

(This article belongs to the Special Issue Polymetallic Metallogenic System)

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Regional geological map: (a) Geological map of the Eastern Jiaodong Peninsula; (b) geological map of the Muping–Rushan gold belt (modified from [<a href="#B15-minerals-09-00326" class="html-bibr">15</a>]; ages are from [<a href="#B20-minerals-09-00326" class="html-bibr">20</a>,<a href="#B21-minerals-09-00326" class="html-bibr">21</a>]). HQF—Haiyang–Qingdao fault; HSF—Haiyang–Shidao fault; MRF—Muping–Rushan fault; TCF—Taocun fault; WQYF—Wulian–Qingdao–Yantai fault; WHF—Weihai fault; RCF—Rongcheng fault. Full article ">Figure 2
Geological maps of the Jinqingding gold deposit: (a) plan view; (b) section (modified from [<a href="#B20-minerals-09-00326" class="html-bibr">20</a>]). Full article ">Figure 3
Alteration and mineralization types in the Jinqingding gold deposit: (a) A quartz–sulfide vein with unaltered wallrock; (b) K-feldspar alteration in the wallrock; (c) sericitization in the wallrock of a quartz–sulfide vein; (d) milky and smoke grey quartz (Qb + Qc + Qd) plus massive, disseminated pyrites in a hand sample of quartz–sulfide vein; (e) smoke grey quartz (Qb + Qc + Qd) in a hand sample of quartz–sulfide vein in which pyrites occur as veins (Py); (f) The earliest quartz (Qa) has a comb structure. Py—pyrite; Q—quartz. Full article ">Figure 4
Features of different types of quartz: (a) Qa is zoned and is crosscut by pyrite; (b) cathodoluminescence (CL) shows zoning in Qa and gold grains within it; (c) gold occurs in Qb; (d) quartz outside and inside the pyrite goes extinct at the same angle; (e) quartz inside and outside pyrite has similar CL features; (f) recrystallized (Qc) quartz contains free gold and has darker CL features than other quartz types; (g) recrystallized quartz around a crosscutting pyrite vein; (h) quartz (Qd) in fractures in pyrite shows different CL features from Qb. Py—Pyrite; Q—Quartz; Au—Gold; Gn—Galena. See <a href="#sec4-minerals-09-00326" class="html-sec">Section 4</a> for description of red circles. Full article ">Figure 5
Sericite occurrence in the Jinqingding gold deposit: (a) Feldspar altered to sericite; (b) a QEMSCAN mineral map showing sericite coexisting with gold in pyrite fractures; (c) a QEMSCAN map showing the coexistence of sericite and pyrite in Qb. White color part is the glue on the thin section. Full article ">Figure 6
Paragenesis of quartz and other minerals. The thickness of the line indicates scale and intensity of mineral occurrence. Full article ">Figure 7
EPMA-derived Al content in different types of quartz. Full article ">Figure 8
Trace element content in quartz as obtained via LA-ICP-MS. (a) CL shows differences between quartz cores and rims; (b) Al content in the quartz; (c) Ti content in the quartz; (d) estimated formation temperature of quartz under lithostatic and hydrostatic pressure. Full article ">

16 pages, 2706 KiB

Open AccessArticle

LKZ-1: A New Zircon Working Standard for the In Situ Determination of U–Pb Age, O–Hf Isotopes, and Trace Element Composition

by Albert Chang-sik Cheong, Youn-Joong Jeong, Shinae Lee, Keewook Yi, Hui Je Jo, Ho-Sun Lee, Changkun Park, Nak Kyu Kim, Xian-Hua Li and Sandra L. Kamo

Minerals 2019, 9(5), 325; https://doi.org/10.3390/min9050325 - 27 May 2019

Cited by 18 | Viewed by 5319

Abstract

This study introduces a new zircon reference material, LKZ-1, for the in situ U–Pb dating and O–Hf isotopic and trace element analyses. The secondary ion mass spectrometric analyses for this gem-quality single-crystal zircon yielded a weighted mean ²⁰⁶Pb/²³⁸U age of [...] Read more.

This study introduces a new zircon reference material, LKZ-1, for the in situ U–Pb dating and O–Hf isotopic and trace element analyses. The secondary ion mass spectrometric analyses for this gem-quality single-crystal zircon yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 572.6 ± 2.0 Ma (2σ, n = 22, MSWD = 0.90), with moderately high U concentrations (619 ± 21 ppm, 1 SD), restricted Th/U ratios (0.146 ± 0.002, 1 SD), and negligible common Pb content (²⁰⁶Pb_c < 0.2%). A comparable ²⁰⁶Pb/²³⁸U age (570.0 ± 2.5 Ma, 2σ) was produced by the isotope dilution-thermal ionization mass spectrometry. The secondary ion mass spectrometric and laser ablation-assisted multiple collector inductively coupled plasma mass spectrometer analyses respectively showed that LKZ-1 had little variation in O (δ¹⁸O_V-SMOW = 10.65 ± 0.14‰; laser fluorination value = 10.72 ± 0.02‰; 1 SD) and Hf (¹⁷⁶Hf/¹⁷⁷Hf = 0.281794 ± 0.000016, 1 SD) isotopic compositions. LKZ-1 was also fairly homogeneous in its chemical composition (RSD of laser ablation ICPMS data ≤ 10%), displaying a relatively uniform chondrite-normalized rare earth element pattern ((Lu/Gd)_N = 31 ± 3, Eu/Eu^* = 0.43 ± 0.17, Ce/Ce^* = 44 ± 32; 1 SD). These consistencies suggest that the LKZ-1 zircon is a suitable working standard for geochronological and geochemical analyses. Full article

(This article belongs to the Section Mineral Geochemistry and Geochronology)

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A photograph of the LKZ-1 zircon (inset) and representative backscattered electron (upper) and cathodoluminescence (lower) images. The grain and spot numbers are the same as in Table 2. Full article ">Figure 2
206Pb/238U-207Pb/235U concordia diagram showing the SHRIMP results for the LKZ-1 zircon with ±1σ error ellipses. The plotted data are uncorrected for common Pb. Full article ">Figure 3
206Pb/238U–207Pb/235U concordia diagram showing LA-MC-ICPMS results for the LKZ-1 zircon with ±2σ error ellipses. Full article ">Figure 4
Concordia diagram showing U–Pb data obtained by ID-TIMS analysis of LKZ-1 zircon with ±2σ error ellipses. The concordia curve is depicted as a band, which incorporates the uncertainty of the U decay constants. Full article ">Figure 5
O isotopic variation in the LKZ-1 zircon based on HR-SIMS analyses. Vertical error bars denote 2 standard errors. Solid and dashed lines represent the average (10.65‰) and standard deviation (±0.14‰), respectively. Full article ">Figure 6
Hafnium isotopic variation in the LKZ-1 zircon. Vertical error bars denote 2 standard errors. Solid and dashed lines represent the average (0.281794) and standard deviation (±0.000016), respectively. Full article ">Figure 7
Chondrite-normalized REE patterns of 91500 (a) and LKZ-1 (b) zircons. Chondrite values were taken from McDonough and Sun (1995) [<a href="#B52-minerals-09-00325" class="html-bibr">52</a>]. Vertical error bars denote 1 standard deviation of our data, or uncertainties reported in previous works. (c–f) U vs. Th and Yb vs. Y variations for 91500 and LKZ-1 zircons. Full article ">

14 pages, 4153 KiB

Open AccessArticle

Investigations of MgO on Sintering Performance and Metallurgical Property of High-Chromium Vanadium-Titanium Magnetite

by Liheng Zhang, Songtao Yang, Weidong Tang and Xiangxin Xue

Minerals 2019, 9(5), 324; https://doi.org/10.3390/min9050324 - 27 May 2019

Cited by 15 | Viewed by 3299

Abstract

High-chromium vanadium-titanium magnetite (HCVTM) in the Hongge region has been used as an essential mineral resource in ironmaking. The effects of MgO on sintering performance and metallurgical properties were investigated by sintering pot tests, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy [...] Read more.

High-chromium vanadium-titanium magnetite (HCVTM) in the Hongge region has been used as an essential mineral resource in ironmaking. The effects of MgO on sintering performance and metallurgical properties were investigated by sintering pot tests, X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). HCVTM sinters with varying MgO contents (2.7–3.5%), which was achieved by adding dolomite, were tested for yield, strength, reduction degradation index (RDI), reduction index (RI), and softening-melting properties. The productivity and the comprehensive index were evaluated. The results show that yield and productivity increased, while the vertical sintering speed and the tumbler index (TI) initially increased then decreased with the increase of MgO content. The mineral structure of HCVTM sinter changed from a non-uniform state to a uniform state with increased MgO content. Most of the Mg²⁺ entered the magnetite lattice, while a small amount entered the perovskite and the calcium silicate. The increase of MgO content improved RDI and softening-melting properties while reducing RI. The best recommended amount of MgO was 3.3% from the comprehensive index. Full article

(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)

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17 pages, 5930 KiB

Open AccessArticle

Perovskites of the Tazheran Massif (Baikal, Russia)

by Eugene V. Sklyarov, Nikolai S. Karmanov, Andrey V. Lavrenchuk and Anastasia E. Starikova

Minerals 2019, 9(5), 323; https://doi.org/10.3390/min9050323 - 27 May 2019

Cited by 6 | Viewed by 3414

Abstract

The paper provides details of local geology and mineralogy of the Tazheran Massif, which was the sampling site of perovskite used as an external standard in perovskite U-Pb dating by sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively-coupled plasma (LA–ICP–MS) mass spectrometry. [...] Read more.

The paper provides details of local geology and mineralogy of the Tazheran Massif, which was the sampling site of perovskite used as an external standard in perovskite U-Pb dating by sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively-coupled plasma (LA–ICP–MS) mass spectrometry. The Tazheran Massif is a complex of igneous (mafic dikes, syenite, nepheline syenite), metamorphic (marble), and metasomatic (skarn, calc–silicate veins) rocks. Metasomatites are thin and restricted to the complex interior being absent from the margins. Perovskite has been studied at four sites of metasomatic rocks of three different types: forsterite–spinel calc–silicate veins in brucite marble (1); skarn at contacts between nepheline syenite and brucite marble (2), and skarn-related forsterite–spinel (Fo-Spl) calc–silicate veins (3). Pervoskite from Fo-Spl calc–silicate veins (type 1) is almost free from impurities (<1 wt.% in total: 0.06%–0.4% REE₂O₃, 0.10%–0.22% Nb₂O₅, ≤0.1% ThO₂). The U contents are from 0.1 to 1.9 wt.% UO₂ and are relatively uniform in perovskites from the same vein but differ from vein to vein of this type. Perovskite from the contact skarn (type 2) contains 1.5 to 4.5 wt.% REE₂O₃ but is poor in other impurities. Perovskite grains from skarn-related Fo-Spl calc–silicate rocks (type 3) belong to two generations that differ in REE, Nb, Th, Fe, and Na concentrations. Early-generation perovskites occurs as compositionally homogeneous octahedral or cubic-octahedral crystals with contents of impurities higher than in other varieties (3.6 wt.% REE₂O₃, 1.6 wt.% Fe₂O₃, 1.3 wt.% Nb₂O₅, 0.7 wt.% ThO₂, 0.6 wt.% UO₂, and 0.6 wt.% Na₂O) but the lowest is at the respective site. Late-generation varieties show highly variable impurity concentrations of 1.5 to 22.7 wt.% REE₂O₃, 0.4 to 8.4 wt.% Nb₂O₅, and 0.8 to 4.5% ThO₂, while the perovskite component may be as low as 65%. In addition to the lueshite and loparite, components, they contain REEFeO₃ and Th_0.5TiO₃ endmembers which have no natural analogs. Full article

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14 pages, 3668 KiB

Open AccessEditor’s ChoiceArticle

Elemental Compositions of Smectites Reveal Detailed Sediment Provenance Changes during Glacial and Interglacial Periods: The Southern Drake Passage and Bellingshausen Sea, Antarctica

by Young Kyu Park, Jae Il Lee, Jaewoo Jung, Claus-Dieter Hillenbrand, Kyu-Cheul Yoo and Jinwook Kim

Minerals 2019, 9(5), 322; https://doi.org/10.3390/min9050322 - 26 May 2019

Cited by 11 | Viewed by 5515

Abstract

Variations in clay mineral assemblages have been widely used to understand changes in sediment provenance during glacial and interglacial periods. Smectite clay minerals, however, have a range of various elemental compositions that possibly originated from multiple different sources. Therefore, it might be crucial [...] Read more.

Variations in clay mineral assemblages have been widely used to understand changes in sediment provenance during glacial and interglacial periods. Smectite clay minerals, however, have a range of various elemental compositions that possibly originated from multiple different sources. Therefore, it might be crucial to distinguish the various types of smectites by analyzing their elemental composition in order to verify the sediment provenances with certainty. This hypothesis was tested for the clay mineral characteristics in a marine sediment core from the southern Drake Passage (GC05-DP02). Rare earth elements and

ε_{N d}

data had previously indicated that fine grained detritus was supplied from the Weddell Sea to the core site during interglacial periods, when the sediments contained more Al-rich smectite (montmorillonite). Indeed, marine sediments collected close to the Larsen Ice Shelf on the eastern Antarctic Peninsula continental shelf, western Weddell Sea embayment, show more Al-rich smectite components as compared with other possible West Antarctic sources, such as the Ross Sea embayment or King George Island, South Shetland Islands. Furthermore, two types of smectite (Al-rich and Al-poor) were identified in core GC360 from the Bellingshausen Sea shelf, suggesting that during glacial periods some sediment is derived from subglacial erosion of underlying pre-Oligocene sedimentary strata containing predominantly Al-rich montmorillonite. This finding reveals different sources for smectites in sediments deposited at site GC360 during the last glacial period and during the present interglacial that show only minor differences in smectite contents. For the interglacial period, two groups of smectite with a wide range of Al-rich and Mg–Fe-rich were identified, which indicate delivery from two different sources: (1) the detritus with high contents of Mg–Fe-rich smectite supplied from Beethoven Peninsula, southwestern Alexander island and (2) the detritus with higher contents of Al-rich smectite (montmorillonite) possibly derived from the subglacial reworking of pre-Oligocene sedimentary strata. These results demonstrate that the elemental compositions of smectites can be used to differentiate the sources of smectites in marine sediments, which is an important tool to define sediment provenance in detail, when down-core changes observed in clay mineral assemblages are interpreted. Full article

(This article belongs to the Special Issue Clays and Micro-Organisms: From Nature to Industry)

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13 pages, 3846 KiB

Open AccessArticle

Durability Evaluation of Phosphogypsum-Based Cemented Backfill Through Drying-Wetting Cycles

by Xibing Li, Shitong Zhou, Yanan Zhou, Chendi Min, Zhiwei Cao, Jing Du, Lin Luo and Ying Shi

Minerals 2019, 9(5), 321; https://doi.org/10.3390/min9050321 - 26 May 2019

Cited by 25 | Viewed by 3835

Abstract

In this study, the durability of phosphogypsum (PG)-based cemented backfill was investigated by drying-wetting cycles to explore deterioration of its strength and the release of impurities. The leachates in this test were composed of deionized water, 5% Na₂SO₄ solution, 5% [...] Read more.

In this study, the durability of phosphogypsum (PG)-based cemented backfill was investigated by drying-wetting cycles to explore deterioration of its strength and the release of impurities. The leachates in this test were composed of deionized water, 5% Na₂SO₄ solution, 5% NaCl solution, and a range of sulfuric acid solutions with pH values of 1.5, 3, and 5. After drying-wetting cycles, unconfined compressive strength (UCS), visual deterioration, porosity, microstructure and concentrations of phosphate and fluoride in the leachates were measured. The results showed that both saline and acidic solutions could lead to strength reduction of PG-based cemented backfill under different deterioration mechanisms. The mechanical damage of salinity was caused by micro-cracking and degradation of C–S–H. However, the H⁺ broke the backfill by dissolving hydration products, leaving the conjunctures between PG particles weakened. Furthermore, the environmental impact was investigated by measuring the concentration of phosphate and fluoride in the leachates. In acidic solutions, the release of phosphate and fluoride was greatly enhanced by H⁺. Compared to the great strength deterioration in saline leachates, the concentration of phosphate and fluoride were similar to that of deionized water, indicating that saline solutions had little impact on the release of hazardous impurities. Full article

(This article belongs to the Special Issue Recent Trends in Phosphate Mining and Beneficiation and Related Waste Management)

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Full article ">Figure 1
Particle size distributions of the phosphogypsum and binder. Full article ">Figure 2
The development of unconfined compressive strength of the phosphogypsum (PG)-based backfill specimens within 120 days. Full article ">Figure 3
Visual inspection of the PG-based backfill specimens with different exposure solutions after 30 drying-wetting cycles. Full article ">Figure 4
Scanning electron microscope (SEM) images of the PG-based backfill specimens with 120 d curing age and different exposure solutions after 30 drying-wetting cycles. Magnification factor: 2500×; accelerating voltage: 10.00 kV; and working distance: 6.0 mm. Full article ">Figure 5
Energy dispersive spectrometry (EDS) analysis of specimens exposed to NaCl. Magnification factor: 2500×; accelerating voltage: 10.00 kV; and working distance: 6.0 mm. Full article ">Figure 6
Variation of the porosity of hardened backfill samples with different drying-wetting cycles. Full article ">Figure 7
Unconfined compressive strength of the PG-based backfill specimens at different drying-wetting cycles and exposure solutions. Full article ">Figure 8
Visual inspection of the PG-based backfill specimens with different exposure solutions after 30 drying-wetting cycles. Full article ">Figure 9
pH values in 30 drying-wetting cycles; the dotted lines indicate the initial values for each solution. Full article ">Figure 10
The cumulative leaching quantities of hazardous impurities in leachates: (a) The cumulative leaching quantities of fluoride and (b) the cumulative leaching quantities of dissolved phosphate. Full article ">

13 pages, 17346 KiB

Open AccessArticle

Magnetite and Carbon Extraction from Coal Fly Ash Using Magnetic Separation and Flotation Methods

by Dmitry Valeev, Irina Kunilova, Alexander Alpatov, Alika Varnavskaya and Dianchun Ju

Minerals 2019, 9(5), 320; https://doi.org/10.3390/min9050320 - 25 May 2019

Cited by 38 | Viewed by 8200

Abstract

In this study, enrichment methods for coal fly ash (CFA) from Omsk thermal power station No. 4 (TPS-4) were investigated. The magnetite and unburned carbon concentrates were obtained by magnetic separation and flotation methods. The wet magnetic separation used in the study increased [...] Read more.

In this study, enrichment methods for coal fly ash (CFA) from Omsk thermal power station No. 4 (TPS-4) were investigated. The magnetite and unburned carbon concentrates were obtained by magnetic separation and flotation methods. The wet magnetic separation used in the study increased the magnetite content in the magnetic fraction from 10.48 to 12.72 wt % compared to dry magnetic separation. The XRD analysis showed that the magnetic fraction primarily consists of magnetite, mullite, and quartz. The SEM analysis demonstrated that magnetite is located primarily on the surface of alumosilicate spheres and has three types of shape: dendritic structures, hexagonal bulk agglomerates, and star-like structures. For the flotation tests, a low-price diesel was used as the collector. It was found that, if CFA particles of 40–71 µm are used, ~99% of unburned carbon can be recovered. It was also found by SEM that, if CFA particles of 71–100 µm are used, alumosilicates on a carbon surface prevent complete interaction of diesel with carbon particles and decrease thereby carbon recovery to 83%. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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12 pages, 3608 KiB

Open AccessFeature PaperArticle

Leaching of White Metal in a NaCl-H₂SO₄ System under Environmental Conditions

by Jonathan Castillo, Rossana Sepúlveda, Giselle Araya, Danny Guzmán, Norman Toro, Kevin Pérez, Marcelo Rodríguez and Alessandro Navarra

Minerals 2019, 9(5), 319; https://doi.org/10.3390/min9050319 - 24 May 2019

Cited by 15 | Viewed by 5012

Abstract

The effect of NaCl on the leaching of white metal from a Teniente Converter was investigated in NaCl-H₂SO₄ media under environmental conditions. The copper dissolution from white metal was studied using ferric ions in the range of 1–10 g/L, NaCl [...] Read more.

The effect of NaCl on the leaching of white metal from a Teniente Converter was investigated in NaCl-H₂SO₄ media under environmental conditions. The copper dissolution from white metal was studied using ferric ions in the range of 1–10 g/L, NaCl in the range of 30–210 g/L, and sulfuric acid in the range of 10–50 g/L. The test without NaCl produced a dissolution of 55%; through the addition of NaCl, the dissolution increased to nearly 90%. The effect of sulfuric acid on the copper dissolution was not significant in the studied range, as the excess sulfuric acid simply increased the iron precipitation. The positive effect of NaCl seems to be related to the action of chloro-complex oxidizing agents in relation to the Cu⁺²/Cu⁺ couple. A simplified two-stage mechanism is proposed for the leaching of white metal. In the first stage, the white metal produces covellite and Cu²⁺, and in the second stage it produces elemental sulfur and Cu²⁺. The first stage is very rapidly compared to the second stage. Full article

(This article belongs to the Special Issue Recent Advances in Hydro- and Biohydrometallurgy)

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18 pages, 6486 KiB

Open AccessArticle

Phosphate Mine Tailing Recycling in Membrane Filter Manufacturing: Microstructure and Filtration Suitability

by Mohamed Loutou, Wafa Misrar, Mohammed Koudad, Mohammed Mansori, Liga Grase, Claude Favotto, Yassine Taha and Rachid Hakkou

Minerals 2019, 9(5), 318; https://doi.org/10.3390/min9050318 - 24 May 2019

Cited by 29 | Viewed by 4089

Abstract

Ceramic membrane filters based on industrial by-products can be considered to be a valorization alternative of phosphate mine tailings, even more so if these ceramic membranes are used in the industrial wastewater treatment due to their good mechanical, chemical, and thermal resistance. The [...] Read more.

Ceramic membrane filters based on industrial by-products can be considered to be a valorization alternative of phosphate mine tailings, even more so if these ceramic membranes are used in the industrial wastewater treatment due to their good mechanical, chemical, and thermal resistance. The depollution of textile industry rejections with this method has not been studied in detail previously. In this work, ceramic membrane filters have been manufactured from natural clay and phosphate mine tailings (phosphate sludge). Blends of the abovementioned materials with a pore-forming agent (sawdust, up to 20 wt. %) were investigated in the range 900–1100 °C using thermal analysis, X-ray diffraction, scanning electron microscopy, and mercury porosimetry. Ceramic properties were measured as a function of firing temperature and sawdust addition. Filtration tests were carried out on samples with advantageous properties. The results showed that gehlenite together with diopside neoformed from lime decomposed carbonates and breakdown products of clay minerals, while calcium phosphate derived from partial decomposition of fluorapatite. Both quartz and fluorapatite resisted heating. The results of the experimental design showed that the variations of physical properties versus processing factors were well described by the polynomial model. Filtration results are quite interesting, allowing these membranes to be used in industrial effluent treatment. Full article

(This article belongs to the Special Issue Recent Trends in Phosphate Mining and Beneficiation and Related Waste Management)

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23 pages, 7679 KiB

Open AccessEditor’s ChoiceArticle

A Bat-Optimized One-Class Support Vector Machine for Mineral Prospectivity Mapping

by Yongliang Chen, Wei Wu and Qingying Zhao

Minerals 2019, 9(5), 317; https://doi.org/10.3390/min9050317 - 23 May 2019

Cited by 33 | Viewed by 3651

Abstract

One-class support vector machine (OCSVM) is an efficient data-driven mineral prospectivity mapping model. Since the parameters of OCSVM directly affect the performance of the model, it is necessary to optimize the parameters of OCSVM in mineral prospectivity mapping. Trial and error method is [...] Read more.

One-class support vector machine (OCSVM) is an efficient data-driven mineral prospectivity mapping model. Since the parameters of OCSVM directly affect the performance of the model, it is necessary to optimize the parameters of OCSVM in mineral prospectivity mapping. Trial and error method is usually used to determine the “optimal” parameters of OCSVM. However, it is difficult to find the globally optimal parameters by the trial and error method. By combining OCSVM with the bat algorithm, the intialization parameters of the OCSVM can be automatically optimized. The combined model is called bat-optimized OCSVM. In this model, the area under the curve (AUC) of OCSVM is taken as the fitness value of the objective function optimized by the bat algorithm, the value ranges of the initialization parameters of OCSVM are used to specify the search space of bat population, and the optimal parameters of OCSVM are automatically determined through the iterative search process of the bat algorithm. The bat-optimized OCSVMs were used to map mineral prospectivity of the Helong district, Jilin Province, China, and compared with the OCSVM initialized by the default parameters (i.e., common OCSVM) and the OCSVM optimized by trial and error. The results show that (a) the receiver operating characteristic (ROC) curve of the trial and error-optimized OCSVM is intersected with those of the bat-optimized OCSVMs and (b) the ROC curves of the optimized OCSVMs slightly dominate that of the common OCSVM in the ROC space. The area under the curves (AUCs) of the common and trial and error-optimized OCSVMs (0.8268 and 0.8566) are smaller than those of the bat-optimized ones (0.8649 and 0.8644). The optimal threshold for extracting mineral targets was determined by using the Youden index. The mineral targets predicted by the common and trial and error-optimized OCSVMs account for 29.61% and 18.66% of the study area respectively, and contain 93% and 86% of the known mineral deposits. The mineral targets predicted by the bat-optimized OCSVMs account for 19.84% and 14.22% of the study area respectively, and also contain 93% and 86% of the known mineral deposits. Therefore, we have 0.93/0.2961 = 3.1408 < 0.86/0.1866 = 4.6088 < 0.93/0.1984 = 4.6875 < 0.86/0.1422 = 6.0478, indicating that the bat-optimized OCSVMs perform slightly better than the common and trial and error-optimized OCSVMs in mineral prospectivity mapping. Full article

(This article belongs to the Special Issue Novel Methods and Applications for Mineral Exploration)

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17 pages, 3731 KiB

Open AccessArticle

Characterization of Microbial Communities Associated with Ceramic Raw Materials as Potential Contributors for the Improvement of Ceramic Rheological Properties

by Angela M. Garcia-Sanchez, Bernardino Machado-Moreira, Mário Freire, Ricardo Santos, Sílvia Monteiro, Diamantino Dias, Orquídia Neves, Amélia Dionísio and Ana Z. Miller

Minerals 2019, 9(5), 316; https://doi.org/10.3390/min9050316 - 23 May 2019

Cited by 4 | Viewed by 4205

Abstract

Technical ceramics are being widely employed in the electric power, medical and engineering industries because of their thermal and mechanical properties, as well as their high resistance qualities. The manufacture of technical ceramic components involves complex processes, including milling and stirring of raw [...] Read more.

Technical ceramics are being widely employed in the electric power, medical and engineering industries because of their thermal and mechanical properties, as well as their high resistance qualities. The manufacture of technical ceramic components involves complex processes, including milling and stirring of raw materials in aqueous solutions, spray drying and dry pressing. In general, the spray-dried powders exhibit an important degree of variability in their performance when subjected to dry-pressing, which affects the efficiency of the manufacturing process. Commercial additives, such as deflocculants, biocides, antifoam agents, binders, lubricants and plasticizers are thus applied to ceramic slips. Several bacterial and fungal species naturally occurring in ceramic raw materials, such as Sphingomonas, Aspergillus and Aureobasidium, are known to produce exopolysaccharides. These extracellular polymeric substances (EPS) may confer unique and potentially interesting properties on ceramic slips, including viscosity control, gelation, and flocculation. In this study, the microbial communities present in clay raw materials were identified by both culture methods and DNA-based analyses to select potential EPS producers based on the scientific literature for further assays based on the use of EPS for enhancing the performance of technical ceramics. Potential exopolysaccharide producers were identified in all samples, such as Sphingomonas sp., Pseudomonas xanthomarina, P. stutzeri, P. koreensis, Acinetobacter lwoffi, Bacillus altitudinis and Micrococcus luteus, among bacteria. Five fungi (Penicillium citrinum, Aspergillus niger, Fusarium oxysporum, Acremonium persicinum and Rhodotorula mucilaginosa) were also identified as potential EPS producers. Full article

(This article belongs to the Special Issue Clays and Micro-Organisms: From Nature to Industry)

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Sampling at Rauschert Portuguesa of ceramic raw materials and slips: (A) sampling of talc into sterile containers; (B) clay minerals collection from transportation bag; (C) replicates collected from each raw material; (D) ceramic slip from the mixing tank was collected directly into sterile containers. Full article ">Figure 2
Fourier Transform Infrared spectra of the ceramic raw materials (<a href="#minerals-09-00316-t001" class="html-table">Table 1</a>) used by Rauschert Portuguesa. Full article ">Figure 3
Distribution of bacterial phyla retrieved from samples 1A (mill ceramic suspension), 2B (talc 1), 4D (clay), 6F (barium carbonate), 7G (talc 3) and 8H (tank ceramic slip). Full article ">Figure 4
Distribution of bacterial genera retrieved from samples 1A (mill ceramic suspension), 2B (talc 1), 4D (clay), 6F (barium carbonate), 7G (talc 3) and 8H (tank ceramic slip). Full article ">Figure 5
Phylogenetic affiliations (order level) of the ITS sequences obtained from sample 7G–F (talc 3). Full article ">Figure 6
Identification of fungal strains isolated from samples 1A, 2B, 3C and 7G. Full article ">Figure 7
Conceptual model of the effect of adding EPS to ceramic materials and their potential impact on the rheological properties. Full article ">

10 pages, 2126 KiB

Open AccessArticle

Hydrochloric Acidic Processing of Titanite Ore to Produce a Synthetic Analogue of Korobitsynite

by Lidia G. Gerasimova, Anatoly I. Nikolaev, Ekaterina S. Shchukina, Marina V. Maslova, Galina O. Kalashnikova, Gleb O. Samburov and Gregory Yu. Ivanyuk

Minerals 2019, 9(5), 315; https://doi.org/10.3390/min9050315 - 22 May 2019

Cited by 3 | Viewed by 3237

Abstract

The modal composition of (apatite)-nepheline-titanite ore and its geological setting within apatite deposits of the Khibiny Massif allow selective mining of titanite ore and its hydrochloric acidic processing. The reaction of titanite with concentrated hydrochloric acid produces hydrated titanosilicate precipitate (TSP) which, in [...] Read more.

The modal composition of (apatite)-nepheline-titanite ore and its geological setting within apatite deposits of the Khibiny Massif allow selective mining of titanite ore and its hydrochloric acidic processing. The reaction of titanite with concentrated hydrochloric acid produces hydrated titanosilicate precipitate (TSP) which, in turn, can be a precursor in titanosilicate synthesis. It is particularly noteworthy that a synthetic analogue of korobitsynite, Na₅(Ti₃Nb)[Si₄O₁₂]₂O₂(OH)₂·7H₂O, was synthesized by means of TSP alteration by alkaline hydrothermal solution at 200 °C within three days. The titanosilicate obtained this way has comparatively weak cation-exchange properties regarding Cs⁺ and Sr²⁺ cations and considerable photocatalytic activity occurring under visible light, which allows the use of a synthetic korobitsynite analogue (SKR) for production of self-cleaning, sterilizing, and anti-fouling building materials. Full article

(This article belongs to the Special Issue Kola Alkaline Province: Ores, Rocks and Minerals—In Memory of Dr. Gregory Yu. Ivanyuk)

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Schema of photocatalytic decomposition of organic pollutants, CxHyOz, where hv is the light energy, Ebg—the band gap energy; h+ is positive hole; e–—electron, O2–•—superoxide radical; HO•—hydroxyl radical. Full article ">Figure 2
Radiated aggregates and long prismatic crystals (a) and crystal structure of korobitsynite ((b), after [<a href="#B21-minerals-09-00315" class="html-bibr">21</a>]). 1—korobitsynite, 2—quartz, 3—albite, 4—aegirine. Full article ">Figure 3
A principal scheme of apatite-nepheline-titanite ore processing for SKR synthesis. Full article ">Figure 4
Change in Ti and Ca contents in concentrated hydrochloric acidic solution with time. Full article ">Figure 5
Powder X-Ray diffraction profile (a) and TG/DSC curves of TSP (b). Indexed peaks correspond to rutile. Full article ">Figure 6
SE image of sample 3 (a) and powder X-Ray diffraction patterns of samples 1–4 in comparison with the patterns of natural korobitsynite and TR01 after [<a href="#B24-minerals-09-00315" class="html-bibr">24</a>] (b). L—lorenzenite. Full article ">

20 pages, 3259 KiB

Open AccessArticle

In Situ Effectiveness of Alkaline and Cementitious Amendments to Stabilize Oxidized Acid-Generating Tailings

by Abdellatif Elghali, Mostafa Benzaazoua, Bruno Bussière and Thomas Genty

Minerals 2019, 9(5), 314; https://doi.org/10.3390/min9050314 - 22 May 2019

Cited by 34 | Viewed by 4686

Abstract

This study investigates the effectiveness of alkaline and cementitious additives in the in situ stabilization of localized acid-generating tailings from a closed gold mine in Abitibi–Témiscamingue, Québec (Eagle/Telbel mine site). Five field cells (including one control) were constructed and equipped with mechanisms for [...] Read more.

This study investigates the effectiveness of alkaline and cementitious additives in the in situ stabilization of localized acid-generating tailings from a closed gold mine in Abitibi–Témiscamingue, Québec (Eagle/Telbel mine site). Five field cells (including one control) were constructed and equipped with mechanisms for collecting vertical water infiltration and surface runoff. The five cells included: (C1) Control cell; (C2) 5 wt % limestone amendment; (C3) 10 wt % limestone amendment; (C4) 5 wt % half ordinary Portland cement and half fly ash amendment; and (C5) 5 wt % ordinary Portland cement amendment. The control cell showed an acidic behavior (pH < 4.5) with variable concentrations of Fe, Al, Zn, and Cu. The amendments were used to neutralize the acidic leachates and decrease dissolved metal concentrations. Leachates from surface runoff samples of amended cells were less loaded with metals compared to samples of vertical infiltration. All amendment formulations increased the pH of the leachates from approximately 4 to circumneutral values. Furthermore, metal and metalloid concentrations were greatly limited, except for Cr and As for the carbonate-based amendments. Metal(-oid) stabilization was successfully achieved using the different amendment formulations, with the exception of C2, which still released As. Full article

(This article belongs to the Special Issue Towards a Sustainable Management of Mine Wastes: Reprocessing, Reuse, Revalorization and Repository)

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23 pages, 2490 KiB

Open AccessArticle

Non-Metamict Aeschynite-(Y), Polycrase-(Y), and Samarskite-(Y) in NYF Pegmatites from Arvogno, Vigezzo Valley (Central Alps, Italy)

by Alessandro Guastoni, Luciano Secco, Radek Škoda, Fabrizio Nestola, Mariangela Schiazza, Milan Novák and Giorgio Pennacchioni

Minerals 2019, 9(5), 313; https://doi.org/10.3390/min9050313 - 21 May 2019

Cited by 9 | Viewed by 4373

Abstract

At Arvogno, Vigezzo valley in the Central Alps, Italy, pegmatite dikes are unique in the scenario of a tertiary alpine pegmatite field because they show marked geochemical and mineralogical niobium–yttrium–fluorine features. These pegmatites contain AB₂O₆ aeschynite group minerals and ABX [...] Read more.

At Arvogno, Vigezzo valley in the Central Alps, Italy, pegmatite dikes are unique in the scenario of a tertiary alpine pegmatite field because they show marked geochemical and mineralogical niobium–yttrium–fluorine features. These pegmatites contain AB₂O₆ aeschynite group minerals and ABX₂O₈ euxenite group minerals as typical accessory minerals including aeschynite-(Y), polycrase-(Y), and samarskite-(Y). They are associated with additional typical minerals such as fluorite, Y-dominant silicates, and xenotime-(Y). The Y–Nb–Ti–Ta AB₂O₆ and ABX₂O₈ oxides at the Arvogno pegmatites did not exhibit any textural and compositional features of oxidation or weathering. They are characterized by low self-radiation-induced structural damage, leading to the acquisition of unit-cell data for aeschynite-(Y), polycrase-(Y), and samarskite-(Y) by single-crystal X-ray diffraction. Aeschynite-(Y) and polycrase-(Y) crystals allowed for both to provide space groups whereas samarskite-(Y) was the first crystal from pegmatites for which cell-data were obtained at room temperature but did not allow for the accurate determination of the space group. According to the chemical compositions defined by Ti-dominant content at the B-site, the cell parameters, respectively, corresponded to polycrase-(Y), aeschynite-(Y), and the monoclinic cell of samarskite-(Y). Emplacement of Alpine pegmatites can be related to the progressive regional metamorphic rejuvenation from east to west in the Central Alps, considering the progressive cooling of the thermal Lepontine Barrovian metamorphic dome. Previous studies considered magmatic pulses that led to emplace the pegmatite field in the Central Alps. As an example, the pegmatites that intruded the Bergell massif were aged at 28–25 millions of years or younger, around 20–22 m.y. Full article

(This article belongs to the Special Issue Rare Earth Deposits and Challenges of World REE Demand for High-Tech and Green-Tech at the Beginning of the 3^rd Millennium)

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Simplified structural map of the Central Alps with the field of the Alpine pegmatites showing the locations of the Vigezzo, Codera, and the Bodengo areas. The thick black lines represent the Periadriatic Fault (PF), the Giudicarie Fault (GF), and the Engadine Fault (EF). The light-grey areas represent quaternary deposits along major valleys. The tertiary batholith of Bergell (Br) is in dark-grey, and the smaller, younger Novate stockwork intrusion (No) is in black. A detailed sketched map of the geographical location of the Vigezzo valley between Domodossola in Italy (IT) towards the west and Locarno in Switzerland (CH) is shown in the upper left of the figure. The location of the Arvogno pegmatites are shown with stars. Full article ">Figure 2
The composition of aeschynite-(Y), polycrase-(Y), and samarskite-(Y), plotted in terms of the Ti–Nb–Ta and (REE + Sc + Y)-Ca-(Th + U) apfu ternary plots are shown in (a) and (b). The quadrilateral plot of Ta/(Nb + Ta) and U/(Th + U) showing compositional variations of aeschynite-(Y), polycrase-(Y), and samarskite-(Y) are shown in (c). The CV2 versus CV1 Ercit [<a href="#B13-minerals-09-00313" class="html-bibr">13</a>] statistical diagram is shown in (d) and the chondrite versus normalized REE pattern of aeschynite-(Y), polycrase-(Y), and samarskite-(Y) from Arvogno is shown in (e). For all plots, aeschynite-(Y) and polycrase-(Y) are plotted in white and samarskite-(Y) in grey. Raman spectra of aeschynite-(Y) from Bosco1, samarskite-(Y) from Bosco3, and polycrase-(Y) from Fiume1 are shown in (f). Full article ">Figure 3
Back-scattered electron images of aeschynite-(Y) in (a) and (b) (Bosco1 and Bosco2), samarskite-(Y) in (c) (Bosco3), in (d) the polished section of intergrowth polycrase-(Y) (grey) with samarskite-(Y) (light gray), in (e) the detailed sample section (Bosco4), and polycrase-(Y) in (f) (Fiume1). Full article ">Figure 4
The quadrilateral plots showing compositional variations of aeschynite-(Y), polycrase-(Y), and samarskite-(Y) from (a) to (f). For all plots, the symbols plotted in white are aeschynite-(Y) and polycrase-(Y), and in grey samarskite-(Y). Full article ">

18 pages, 3079 KiB

Open AccessArticle

The Role of Mineral Matter in Concentrating Uranium and Thorium in Coal and Combustion Residues from Power Plants in Poland

by Henryk R. Parzentny and Leokadia Róg

Minerals 2019, 9(5), 312; https://doi.org/10.3390/min9050312 - 20 May 2019

Cited by 16 | Viewed by 5175

Abstract

Based on the results of tests on feed coal from the Lublin Coal and Upper Silesian Coal Basin and its fly ash and slag carried out using X-ray diffraction and X-ray fluorescence analysis, atomic emission spectroscopy, and scanning electron microscopy, it was found [...] Read more.

Based on the results of tests on feed coal from the Lublin Coal and Upper Silesian Coal Basin and its fly ash and slag carried out using X-ray diffraction and X-ray fluorescence analysis, atomic emission spectroscopy, and scanning electron microscopy, it was found that in feeds, coal Th is associated with phosphates and U with mineral matter. The highest Th content was found in anhedral grains of monazite and in Al-Si porous particles of fly ash of <0.05 mm size; whereas in the slag, Th is concentrated in the massive Al-Si grains and in ferrospheres. U is mainly concentrated in the Al-Si surface of porous grains, which form a part of fly ash of <0.05 mm size. In the slag, U is to be found in the Al-Si massive grains or in a dispersed form in non-magnetic and magnetic grains. Groups of mineral phase particles have been identified that have the greatest impact on the content of Th and U in whole fly ash and slag. The research results contained in this article may be important for predicting the efficiency of Th and U leaching from furnace waste storage sites and from falling dusts to soils and waters. Full article

(This article belongs to the Collection Critical Metals and Minerals in Coal and Coal Combustion Products)

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35 pages, 18227 KiB

Open AccessArticle

Silician Magnetite: Si–Fe-Nanoprecipitates and Other Mineral Inclusions in Magnetite from the Olympic Dam Deposit, South Australia

by Cristiana L. Ciobanu, Max R. Verdugo-Ihl, Ashley Slattery, Nigel J. Cook, Kathy Ehrig, Liam Courtney-Davies and Benjamin P. Wade

Minerals 2019, 9(5), 311; https://doi.org/10.3390/min9050311 - 20 May 2019

Cited by 34 | Viewed by 6666

Abstract

A comprehensive nanoscale study on magnetite from samples from the outer, weakly mineralized shell at Olympic Dam, South Australia, has been undertaken using atom-scale resolution High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF STEM) imaging and STEM energy-dispersive X-ray spectrometry mapping [...] Read more.

A comprehensive nanoscale study on magnetite from samples from the outer, weakly mineralized shell at Olympic Dam, South Australia, has been undertaken using atom-scale resolution High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF STEM) imaging and STEM energy-dispersive X-ray spectrometry mapping and spot analysis, supported by STEM simulations. Silician magnetite within these samples is characterized and the significance of nanoscale inclusions in hydrothermal and magmatic magnetite addressed. Silician magnetite, here containing Si–Fe-nanoprecipitates and a diverse range of nanomineral inclusions [(ferro)actinolite, diopside and epidote but also U-, W-(Mo), Y-As- and As-S-nanoparticles] appears typical for these samples. We observe both silician magnetite nanoprecipitates with spinel-type structures and a γ-Fe_1.5SiO₄ phase with maghemite structure. These are distinct from one another and occur as bleb-like and nm-wide strips along d₁₁₁ in magnetite, respectively. Overprinting of silician magnetite during transition from K-feldspar to sericite is also expressed as abundant lattice-scale defects (twinning, faults) associated with the transformation of nanoprecipitates with spinel structure into maghemite via Fe-vacancy ordering. Such mineral associations are characteristic of early, alkali-calcic alteration in the iron-oxide copper gold (IOCG) system at Olympic Dam. Magmatic magnetite from granite hosting the deposit is quite distinct from silician magnetite and features nanomineral associations of hercynite-ulvöspinel-ilmenite. Silician magnetite has petrogenetic value in defining stages of ore deposit evolution at Olympic Dam and for IOCG systems elsewhere. The new data also add new perspectives into the definition of silician magnetite and its occurrence in ore deposits. Full article

(This article belongs to the Special Issue Minerals Down to the Nanoscale: A Glimpse at Ore-Forming Processes)

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23 pages, 6886 KiB

Open AccessArticle

The Role of Organic Matter on Uranium Precipitation in Zoovch Ovoo, Mongolia

by Dimitrios Rallakis, Raymond Michels, Marc Brouand, Olivier Parize and Michel Cathelineau

Minerals 2019, 9(5), 310; https://doi.org/10.3390/min9050310 - 18 May 2019

Cited by 36 | Viewed by 5502

Abstract

The Zoovch Ovoo uranium deposit is located in East Gobi Basin in Mongolia. It is hosted in the Sainshand Formation, a Late Cretaceous siliciclastic reservoir, in the lower part of the post-rift infilling of the Mesozoic East Gobi Basin. The Sainshand Formation corresponds [...] Read more.

The Zoovch Ovoo uranium deposit is located in East Gobi Basin in Mongolia. It is hosted in the Sainshand Formation, a Late Cretaceous siliciclastic reservoir, in the lower part of the post-rift infilling of the Mesozoic East Gobi Basin. The Sainshand Formation corresponds to poorly consolidated medium-grained sandy intervals and clay layers deposited in fluvial-lacustrine settings. The uranium deposit is confined within a 60- to 80-m-thick siliciclastic reservoir inside aquifer driven systems, assimilated to roll-fronts. As assessed by vitrinite reflectance (%Rr < 0.4) and molecular geochemistry, the formation has never experienced significant thermal maturation. Detrital organic matter (type III and IV kerogens) is abundant in the Zoovch Ovoo depocenter. In this framework, uranium occurs as: (i) U-rich macerals without any distinguishable U-phase under SEM observation, containing up to 40 wt % U; (ii) U expressed as UO₂ at the rims of large (several millimeters) macerals and (iii) U oxides partially to entirely replacing macerals, while preserving the inherited plant texture. Thus, uranium is accumulated gradually in the macerals through an organic carbon–uranium epigenization process, in respect to the maceral’s chemistry and permeability. Most macerals are rich in S and, to a lesser extent, in Fe. Frequently, Fe and S contents do not fit the stoichiometry of pyrite, although pyrite also occurs as small inclusions within the macerals. The organic matter appears thus as a major redox trap for uranium in this kind of geological setting. Full article

(This article belongs to the Special Issue Sedimentary Ore Deposits: Origin, Exploitation, Paleoenvironmental Significance)

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26 pages, 5419 KiB

Open AccessArticle

Geochemical Characteristics of A-Type Granite near the Hongyan Cu-Polymetallic Deposit in the Eastern Hegenshan-Heihe Suture Zone, NE China: Implications for Petrogenesis, Mineralization and Tectonic Setting

by Chen Mao, Xinbiao Lü and Chao Chen

Minerals 2019, 9(5), 309; https://doi.org/10.3390/min9050309 - 18 May 2019

Cited by 8 | Viewed by 5984

Abstract

In the eastern Hegenshan-Heihe suture zone (HHSZ) of NE China, Cu-Au hydrothermal mineralization at the newly discovered Hongyan deposit is associated with the Shanshenfu alkali-feldspar granite (SAFG). Zircon U-Pb dating showed that the inner phase and outer phase of the SAFG were formed [...] Read more.

In the eastern Hegenshan-Heihe suture zone (HHSZ) of NE China, Cu-Au hydrothermal mineralization at the newly discovered Hongyan deposit is associated with the Shanshenfu alkali-feldspar granite (SAFG). Zircon U-Pb dating showed that the inner phase and outer phase of the SAFG were formed at 298.8 ± 1.0 Ma and 298.5 ± 1.0 Ma, respectively. Whole rock geochemistry suggests that the SAFG can be classified as an A-type granite. Halfnium isotopes and trace elements in zircon suggest that the SAFG has high Ti-in-zircon crystallization temperature (721–990 °C), high magmatic oxygen fugacity and largely positive ε_Hf(t) (from +6.0 to +9.9). We proposed that the SAFG was derived from crustal assimilation and fractional crystallization of juvenile crust metasomatized by subducting oceanic crust. The high oxygen fugacity of the SAFG suggests the chalcophile elements (e.g., Cu, Au) remained in the magma as opposed to the magma source. An arc-related juvenile source favors enrichment of Cu and Au in the resulting magma. Combined, these magmatic characteristics suggest Cu ± Au exploration potential for magmatic-hydrothermal mineralization related to the SAFG, and similar bodies along the HHSZ. The results obtained combined with regional geological background suggest that the Permian A-type granites and related mineralization along the HHSZ were formed in a post-collisional slab break-off process. Full article

(This article belongs to the Special Issue Polymetallic Metallogenic System)

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17 pages, 4396 KiB

Open AccessArticle

Selective Separation of Arsenic from Lead Smelter Flue Dust by Alkaline Pressure Oxidative Leaching

by Wei Liu, Zihan Li, Junwei Han, Wenhua Li, Xun Wang, Na Wang and Wenqing Qin

Minerals 2019, 9(5), 308; https://doi.org/10.3390/min9050308 - 18 May 2019

Cited by 18 | Viewed by 4699

Abstract

This study investigated the feasibility of using an alkaline pressure oxidative leaching process to treat lead smelter flue dust containing extremely high levels of arsenic with the aim of achieving the selective separation of arsenic. The effects of different parameters including NaOH concentration, [...] Read more.

This study investigated the feasibility of using an alkaline pressure oxidative leaching process to treat lead smelter flue dust containing extremely high levels of arsenic with the aim of achieving the selective separation of arsenic. The effects of different parameters including NaOH concentration, oxygen partial pressure, liquid-to-solid ratio, temperature, and time for the extraction of arsenic were investigated based on thermodynamic calculation. The results indicated that the leaching efficiency of arsenic reached 95.6% under the optimized leaching conditions: 80 g/L of NaOH concentration, 1.0 MPa of oxygen partial pressure, 8 mL/g of liquid-to-solid ratio, 120 °C of temperature, 2.0 h of time. Meanwhile, the leaching efficiencies of antimony, cadmium, indium and lead were less than 4.0%, basically achieving the selective separation of arsenic from lead smelter flue dust. More than 99.0% of arsenic was converted into calcium arsenate product and thus separated from the leach solution by a causticization process with CaO after other metal impurities were removed from the solution with the addition of Na₂S. The optimized causticization conditions were established as: 4.0 of the mole ratio of calcium to arsenic, temperature of 80 °C, reaction time of 2.0 h. The resulting product of calcium arsenate may be used for producing metallic arsenic. Full article

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22 pages, 2389 KiB

Open AccessFeature PaperArticle

A NanoSIMS 50 L Investigation into Improving the Precision and Accuracy of the ²³⁵U/²³⁸U Ratio Determination by Using the Molecular ²³⁵U¹⁶O and ²³⁸U¹⁶O Secondary Ions

by N. Alex Zirakparvar, Cole R. Hexel, Andrew J. Miskowiec, Julie B. Smith, Michael W. Ambrogio, Douglas C. Duckworth, Roger Kapsimalis and Brian W. Ticknor

Minerals 2019, 9(5), 307; https://doi.org/10.3390/min9050307 - 18 May 2019

Cited by 7 | Viewed by 3709

Abstract

A NanoSIMS 50 L was used to study the relationship between the ²³⁵U/²³⁸U atomic and ²³⁵U¹⁶O/²³⁸U¹⁶O molecular uranium isotope ratios determined from a variety of uranium compounds (UO₂, UO₂F [...] Read more.

A NanoSIMS 50 L was used to study the relationship between the ²³⁵U/²³⁸U atomic and ²³⁵U¹⁶O/²³⁸U¹⁶O molecular uranium isotope ratios determined from a variety of uranium compounds (UO₂, UO₂F₂, UO₃, UO₂(NO₃)₂·6(H₂O), and UF₄) and silicates (NIST-610 glass and the Plesovice zircon reference materials, both containing µg/g uranium). Because there is typically a greater abundance of ²³⁵U¹⁶O⁺ and ²³⁸U¹⁶O⁺ molecular secondary ions than ²³⁵U⁺ and ²³⁸U⁺ atomic ions when uranium-bearing materials are sputtered with an oxygen primary ion beam, the goal was to understand whether use of ²³⁵U¹⁶O/²³⁸U¹⁶O has the potential for improved accuracy and precision when compared to the ²³⁵U/²³⁸U ratio. The UO₂ and silicate reference materials showed the greatest potential for improved accuracy and precision through use of the ²³⁵U¹⁶O/²³⁸U¹⁶O ratio as compared to the ²³⁵U/²³⁸U ratio. For the UO₂, which was investigated at a variety of primary beam currents, and the silicate reference materials, which were only investigated using a single primary beam current, this improvement was especially pronounced at low ²³⁵U⁺ count rates. In contrast, comparison of the ²³⁵U¹⁶O/²³⁸U¹⁶O ratio versus the ²³⁵U/²³⁸U ratio from the other uranium compounds clearly indicates that the ²³⁵U¹⁶O/²³⁸U¹⁶O ratio results in worse precision and accuracy. This behavior is based on the observation that the atomic (²³⁵U⁺ and ²³⁸U⁺) to molecular (²³⁵U¹⁶O⁺ and ²³⁸U¹⁶O⁺) secondary ion production rates remain internally consistent within the UO₂ and silicate reference materials, whereas it is highly variable in the other uranium compounds. Efforts to understand the origin of this behavior suggest that irregular sample surface topography, and/or molecular interferences arising from the manner in which the UO₂F₂, UO₃, UO₂(NO₃)₂·6(H₂O), and UF₄ were prepared, may be a major contributing factor to the inconsistent relationship between the observed atomic and molecular secondary ion yields. Overall, the results suggest that for certain bulk compositions, use of the ²³⁵U¹⁶O/²³⁸U¹⁶O may be a viable approach to improving the precision and accuracy in situations where a relatively low ²³⁵U⁺ count rate is expected. Full article

(This article belongs to the Special Issue Nuclear Forensic Applications in Geoscience and Radiochemistry)

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8 pages, 419 KiB

Open AccessLetter

Study of the Adhesion Mechanism of Acidithiobacillus ferrooxidans to Pyrite in Fresh and Saline Water

by Francisca San Martín and Claudio Aguilar

Minerals 2019, 9(5), 306; https://doi.org/10.3390/min9050306 - 17 May 2019

Cited by 4 | Viewed by 2845

Abstract

In the present work, the streaming potential of A. ferrooxidans and pyrite was measured in two environments: fresh and saline water (water with 35 g/L of NaCl) at different pH values. Also, attachment kinetics of A. ferrooxidans to pyrite was studied in fresh [...] Read more.

In the present work, the streaming potential of A. ferrooxidans and pyrite was measured in two environments: fresh and saline water (water with 35 g/L of NaCl) at different pH values. Also, attachment kinetics of A. ferrooxidans to pyrite was studied in fresh and saline water at pH 4. The results show that A. ferrooxidans and pyrite had lower streaming potentials (comparing absolute values) in saline water than in fresh water, indicating the compression in the electrical double layer caused by Cl⁻ and Na⁺ ions. It was also determined that the bacteria had a higher level of attachment to pyrite in fresh water than in saline water. The high ionic strength of saline water reduced the attractive force between A. ferrooxidans and pyrite, which in turn reduced bacterial attachment. Electrostatic interactions were determined to be mainly repulsive, since the bacteria and mineral had the same charge at pH 4. Despite this, the bacteria adhered to pyrite, indicating that hydrophobic attraction forces and Lifshitz–van der Waals interactions were stronger than electrostatic interactions, which caused the adhesion of A. ferrooxidans to pyrite. Full article

(This article belongs to the Special Issue Microorganisms–Minerals Interactions in Aquatic Environments)

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22 pages, 18862 KiB

Open AccessArticle

Sparse 3D Seismic Imaging in the Kylylahti Mine Area, Eastern Finland: Comparison of Time Versus Depth Approach

by Brij Singh, Michał Malinowski, Felix Hloušek, Emilia Koivisto, Suvi Heinonen, Olaf Hellwig, Stefan Buske, Michał Chamarczuk and Sanna Juurela

Minerals 2019, 9(5), 305; https://doi.org/10.3390/min9050305 - 17 May 2019

Cited by 25 | Viewed by 6028

Abstract

A 10.5 km² 3D seismic survey was acquired over the Kylylahti mine area (Outokumpu mineral district, eastern Finland) as a part of the COGITO-MIN (COst-effective Geophysical Imaging Techniques for supporting Ongoing MINeral exploration in Europe) project, which aimed at the development of [...] Read more.

A 10.5 km² 3D seismic survey was acquired over the Kylylahti mine area (Outokumpu mineral district, eastern Finland) as a part of the COGITO-MIN (COst-effective Geophysical Imaging Techniques for supporting Ongoing MINeral exploration in Europe) project, which aimed at the development of cost-effective geophysical imaging methods for mineral exploration. The cost-effectiveness in our case was related to the fact that an active-source 3D seismic survey was accomplished by using the receiver spread originally designed for a 3D passive survey. The 3D array recorded Vibroseis and dynamite shots from an active-source 2D seismic survey, from a vertical seismic profiling experiment survey, as well as some additional “random” Vibroseis and dynamite shots made to complement the 3D source distribution. The resulting 3D survey was characterized by irregular shooting geometry and relatively large receiver intervals (50 m). Using this dataset, we evaluate the effectiveness of the standard time-imaging approach (post-stack and pre-stack time migration) compared to depth imaging (standard and specialized Kirchhoff pre-stack depth migration, KPreSDM). Standard time-domain processing and imaging failed to convincingly portray the first ~1500 m of the subsurface, which was the primary interest of the survey. With a standard KPreSDM, we managed to obtain a good image of the base of the Kylylahti formation bordering the extent of the mineralization-hosting Outokumpu assemblage rocks, but otherwise the image was very noisy in the shallower section. The specialized KPreSDM approach (i.e., coherency-based Fresnel volume migration) resulted in a much cleaner image of the shallow, steeply dipping events, as well as some additional deeper reflectors, possibly representing repetition of the contact between the Outokumpu assemblage and the surrounding Kalevian metasediments at depth. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

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38 pages, 8289 KiB

Open AccessEditor’s ChoiceArticle

Spatial and Temporal Controls on the Distribution of Indium in Xenothermal Vein-Deposits: The Huari Huari District, Potosí, Bolivia

by Lisard Torró, Joan Carles Melgarejo, Laura Gemmrich, Diva Mollinedo, Malena Cazorla, Álvaro Martínez, Núria Pujol-Solà, Júlia Farré-de-Pablo, Antoni Camprubí, David Artiaga, Belén Torres, Pura Alfonso and Osvaldo Arce

Minerals 2019, 9(5), 304; https://doi.org/10.3390/min9050304 - 17 May 2019

Cited by 25 | Viewed by 6775

Abstract

The Huari Huari deposit, Potosí Department in SW Bolivia, hosts polymetallic stratiform and vein mineralization of Miocene age with significant concentrations of the critical metal indium (In). Vein mineralization records document early crystallization of quartz and cassiterite followed by prominent associations of sulfides [...] Read more.

The Huari Huari deposit, Potosí Department in SW Bolivia, hosts polymetallic stratiform and vein mineralization of Miocene age with significant concentrations of the critical metal indium (In). Vein mineralization records document early crystallization of quartz and cassiterite followed by prominent associations of sulfides and sulfosalts. The earliest sulfide was arsenopyrite, followed by pyrrhotite, and progressively giving way to pyrite as the main iron sulfide, whereas Cu–Ag–Pb sulfosalts constitute late hypogene associations. Sphalerite is the chief ore mineral, and its crystallization is extended during most of the mineralization lifespan as evidenced by its initial cocrystallization with pyrrhotine, then with pyrite, and finally with Ag–Pb sulfosalts. The composition of sphalerite varies from early to late generations with a continuous decrease in FeS that attests to a decrease in temperature, which is constrained to vary from ~450 to <200 °C, and/or an increase in f(S₂), both congruent with the described paragenetic sequence. Indium concentrated mostly in the structure of Fe-rich sphalerite (up to 3.49 wt. %) and stannite (up to 2.64 wt. %) as limited solid solutions with roquesite in the (Zn,Fe)S–Cu₂FeSnS₄–CuInS₂ pseudoternary system. In sphalerite, In shows a strong positive correlation with Cu at Cu/In = 1, suggesting its incorporation via a (Cu⁺ + In³⁺) ↔ 2Zn²⁺ coupled substitution, and it does not correlate with Fe. In stannite, In shows a moderate, negative correlation with Cu and Sn, and an In³⁺ ↔ (Cu⁺ + ½ Sn⁴⁺) coupled substitution is suggested. Coexisting sphalerite and stannite yielded the highest In concentrations and crystallized at temperatures between 350 and 250 °C. Copper activity probably played a major role in the accumulation of In in the structure of sphalerite since In-bearing sphalerite coexisted with the deposition of stannite, shows high concentrations of Cu (up to 0.13 atoms per formula unit (a.p.f.u.)) in its structure, and hosts exsolutions of stannite and chalcopyrite. Distribution on the district scale of In suggests an input of hydrothermal fluids richer in Cu in the central position of the mineralizing system, represented by the Antón Bravo vein. Full article

(This article belongs to the Special Issue Mineral Deposits of Critical Elements)

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25 pages, 13387 KiB

Open AccessArticle

Characterization and Economic Potential of Historic Tailings from Gravity Separation: Implications from a Mine Waste Dump (Pb-Ag) in the Harz Mountains Mining District, Germany

by Kerstin Kuhn and Jeannet A. Meima

Minerals 2019, 9(5), 303; https://doi.org/10.3390/min9050303 - 16 May 2019

Cited by 27 | Viewed by 5141

Abstract

In contrast to modern tailings from froth flotation, little is known about historic tailings from gravity separation. However, they may be of economic interest due to their higher metal grades compared to modern tailings. As an example for these types of historic tailings, [...] Read more.

In contrast to modern tailings from froth flotation, little is known about historic tailings from gravity separation. However, they may be of economic interest due to their higher metal grades compared to modern tailings. As an example for these types of historic tailings, the inner structure, as well as the economic potential (Pb, Zn, Cu, Ag, Sb), of the old Bergwerkswohlfahrt mine waste dump in Germany were studied. The investigations focused on textural, geochemical, and mineralogical properties. For this purpose, an extensive drilling program was undertaken. The drill cores were subsequently analyzed with a laser-induced breakdown spectroscopy (LIBS) core scanner to obtain the detailed spatial distribution of potentially valuable elements. The fine-sized residues could be differentiated into different layers, all of them including valuable metals in varying proportions. The strong variations in stratification and in metal distribution over short distances are caused by the batch-wise deposition of the tailings. This heterogeneity within short distances has to be taken into account for future exploration of these types of deposits. The application of a core scanner using LIBS is very convenient for detailed spatial analysis of drill cores, however, the calibration effort, particularly for heterogeneous sample material, is proportionally large. The valuable metal content for Bergwerkswohlfahrt was estimated to be 8000 metric tons of Pb and 610,000 ounces of Ag. Although of limited economic value, recycling might finance future remediation costs. Furthermore, the occurrence of historic tailings in nearby clusters may present further recycling opportunities. Full article

(This article belongs to the Special Issue Towards a Sustainable Management of Mine Wastes: Reprocessing, Reuse, Revalorization and Repository)

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29 pages, 10565 KiB

Open AccessArticle

Application of Data Analytics Techniques to Establish Geometallurgical Relationships to Bond Work Index at the Paracutu Mine, Minas Gerais, Brazil

by Mahadi Bhuiyan, Kamran Esmaieli and Juan C. Ordóñez-Calderón

Minerals 2019, 9(5), 302; https://doi.org/10.3390/min9050302 - 16 May 2019

Cited by 21 | Viewed by 5197

Abstract

Analysis of geometallurgical data is essential to building geometallurgical models that capture physical variability in the orebody and can be used for the optimization of mine planning and the prediction of milling circuit performance. However, multivariate complexity and compositional data constraints can make [...] Read more.

Analysis of geometallurgical data is essential to building geometallurgical models that capture physical variability in the orebody and can be used for the optimization of mine planning and the prediction of milling circuit performance. However, multivariate complexity and compositional data constraints can make this analysis challenging. This study applies unsupervised and supervised learning to establish relationships between the Bond ball mill work index (BWI) and geomechanical, geophysical and geochemical variables for the Paracatu gold orebody. The regolith and fresh rock geometallurgical domains are established from two cluster sets resulting from K-means clustering of the first three principal component (PC) scores of isometric log-ratio (ilr) coordinates of geochemical data and standardized BWI, geomechanical and geophysical data. The first PC is attributed to weathering and reveals a strong relationship between BWI and rock strength and fracture intensity in the regolith. Random forest (RF) classification of BWI in the fresh rock identifies the greater importance of geochemical ilr balances relative to geomechanical and geophysical variables. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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13 pages, 3208 KiB

Open AccessArticle

Floc-Flotation of Malachite Fines with an Octyl Hydroxamate and Kerosene Mixture

by Zhili Li, Feng Rao, Xiaoming Lou, Shaoxian Song and Alejandro López-Valdivieso

Minerals 2019, 9(5), 301; https://doi.org/10.3390/min9050301 - 16 May 2019

Cited by 13 | Viewed by 3528

Abstract

Malachite fines are easily produced in the grinding process, leading to low malachite flotation recovery. Floc-flotation of malachite fines with an octyl hydroxamate and kerosene mixture was studied to improve the flotation recovery, using microflotation, microscopy image observations, contact angle measurements, and Extended [...] Read more.

Malachite fines are easily produced in the grinding process, leading to low malachite flotation recovery. Floc-flotation of malachite fines with an octyl hydroxamate and kerosene mixture was studied to improve the flotation recovery, using microflotation, microscopy image observations, contact angle measurements, and Extended Derjguin–Landau–Verwey–Overbeek (EDLVO) analysis. The results showed that the addition of octyl hydroxamate as an emulsifier of kerosene enhanced the aggregation of malachite fines and improved malachite flotation recovery. In addition, when kerosene droplets were smaller and of uniform size distribution, the spreading of kerosene droplets on the malachite surface improved. The enhanced spreading of kerosene droplets led to higher coverage of kerosene on the malachite surface, resulting in improved hydrophobic aggregation and flotation recovery. Full article

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14 pages, 3470 KiB

Open AccessEditor’s ChoiceArticle

Numerical Simulation of Flow Field Characteristics and Separation Performance Test of Multi-Product Hydrocyclone

by Yuekan Zhang, Peikun Liu, Lanyue Jiang, Xinghua Yang and Junru Yang

Minerals 2019, 9(5), 300; https://doi.org/10.3390/min9050300 - 16 May 2019

Cited by 5 | Viewed by 3563

Abstract

A traditional hydrocyclone can only generate two products with different size fractions after one classification, which does not meet the fine classification requirements for narrow size fractions. In order to achieve the fine classification, a multi-product hydrocyclone with double-overflow-pipe structure was designed in [...] Read more.

A traditional hydrocyclone can only generate two products with different size fractions after one classification, which does not meet the fine classification requirements for narrow size fractions. In order to achieve the fine classification, a multi-product hydrocyclone with double-overflow-pipe structure was designed in this study. In this work, numerical simulation and experimental test methods were used to study the internal flow field characteristics and distribution characteristics of the product size fraction. The simulation results showed that in contrast with the traditional single overflow pipe, there were two turns in the internal axial velocity direction of the hydrocyclone with the double-overflow-pipe structure. Meanwhile, the influence rule of the diameter of the underflow outlet on the flow field characteristics was obtained through numerical simulation. From the test, five products with different size fractions were obtained after one classification and the influence rule of the diameter of the underflow outlet on the size fraction distribution of multi-products was also obtained. This work provides a feasible research idea for obtaining the fine classification of multiple products. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

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20 pages, 6660 KiB

Open AccessArticle

A Review of the Classification of Opal with Reference to Recent New Localities

by Neville J. Curtis, Jason R. Gascooke, Martin R. Johnston and Allan Pring

Minerals 2019, 9(5), 299; https://doi.org/10.3390/min9050299 - 15 May 2019

Cited by 50 | Viewed by 9397

Abstract

Our examination of over 230 worldwide opal samples shows that X-ray diffraction (XRD) remains the best primary method for delineation and classification of opal-A, opal-CT and opal-C, though we found that mid-range infra-red spectroscopy provides an acceptable alternative. Raman, infra-red and nuclear magnetic [...] Read more.

Our examination of over 230 worldwide opal samples shows that X-ray diffraction (XRD) remains the best primary method for delineation and classification of opal-A, opal-CT and opal-C, though we found that mid-range infra-red spectroscopy provides an acceptable alternative. Raman, infra-red and nuclear magnetic resonance spectroscopy may also provide additional information to assist in classification and provenance. The corpus of results indicated that the opal-CT group covers a range of structural states and will benefit from further multi-technique analysis. At the one end are the opal-CTs that provide a simple XRD pattern (“simple” opal-CT) that includes Ethiopian play-of-colour samples, which are not opal-A. At the other end of the range are those opal-CTs that give a complex XRD pattern (“complex” opal-CT). The majority of opal-CT samples fall at this end of the range, though some show play-of-colour. Raman spectra provide some correlation. Specimens from new opal finds were examined. Those from Ethiopia, Kazakhstan, Madagascar, Peru, Tanzania and Turkey all proved to be opal-CT. Of the three specimens examined from Indonesian localities, one proved to be opal-A, while a second sample and the play-of-colour opal from West Java was a “simple” Opal-CT. Evidence for two transitional types having characteristics of opal-A and opal-CT, and “simple” opal-CT and opal-C are presented. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Gems)

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14 pages, 4100 KiB

Open AccessArticle

Enhanced Potential Toxic Metal Removal Using a Novel Hierarchical SiO₂–Mg(OH)₂ Nanocomposite Derived from Sepiolite

by Qi-Zhi Yao, Sheng-Hui Yu, Tian-Lei Zhao, Fei-Jin Qian, Han Li, Gen-Tao Zhou and Sheng-Quan Fu

Minerals 2019, 9(5), 298; https://doi.org/10.3390/min9050298 - 15 May 2019

Cited by 15 | Viewed by 4145

Abstract

Clays are widely used as sorbents for heavy metals due to their high specific surface areas, low cost, and ubiquitous occurrence in most soil and sediment environments. However, the low loading capacity for heavy metals is one of their inherent limitations. In this [...] Read more.

Clays are widely used as sorbents for heavy metals due to their high specific surface areas, low cost, and ubiquitous occurrence in most soil and sediment environments. However, the low loading capacity for heavy metals is one of their inherent limitations. In this work, a novel SiO₂–Mg(OH)₂ nanocomposite was successfully prepared via sequential acid–base modification of raw sepiolite. The structural characteristics of the resulting modified samples were characterized by a wide range of techniques including field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and nitrogen physisorption analysis. The results show that a hierarchical nanocomposite constructed by loading the Mg(OH)₂ nanosheets onto amorphous SiO₂ nanotubes can be successfully prepared, and the nanocomposite has a high surface area (377.3 m²/g) and pore volume (0.96 cm³/g). Batch removal experiments indicate that the nanocomposite exhibits high removal efficiency toward Gd(III), Pb(II), and Cd(II), and their removal capacities were greatly enhanced in comparison with raw sepiolite, due to the synergistic effect of the different components in the hierarchical nanocomposite. This work can provide a novel route toward a hierarchical nanocomposite by using clay minerals as raw material. Taking into account the simplicity of the fabrication route and the high loading capacities for heavy metals, the developed nanocomposite also has great potential applications in water treatment. Full article

(This article belongs to the Special Issue Nanomineralogy)

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