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Minerals, Volume 3, Issue 3 (September 2013), Pages 258-336

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Research

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Open AccessArticle Geology and Mineralogy of Uranium Deposits from Mount Isa, Australia: Implications for Albitite Uranium Deposit Models
Minerals 2013, 3(3), 258-283; doi:10.3390/min3030258
Received: 1 March 2013 / Revised: 14 June 2013 / Accepted: 14 June 2013 / Published: 26 June 2013
Cited by 5 | PDF Full-text (3146 KB) | HTML Full-text | XML Full-text
Abstract
New geological, bulk chemical and mineralogical (QEMSCAN and FEG-EPMA) data are presented for albitite-type uranium deposits of the Mount Isa region of Queensland, Australia. Early albitisation of interbedded metabasalt and metasiltstone predated intense deformation along D2 high strain (mylonite) zones. The early
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New geological, bulk chemical and mineralogical (QEMSCAN and FEG-EPMA) data are presented for albitite-type uranium deposits of the Mount Isa region of Queensland, Australia. Early albitisation of interbedded metabasalt and metasiltstone predated intense deformation along D2 high strain (mylonite) zones. The early sodic alteration paragenetic stage includes albite, riebeckite, aegirine, apatite, zircon and magnetite. This paragenetic stage was overprinted by potassic microveins, containing K-feldspar, biotite, coffinite, brannerite, rare uraninite, ilmenite and rutile. An unusual U-Zr phase has also been identified which exhibits continuous solid solution with a uranium silicate possibly coffinite or nenadkevite. Calcite, epidote and sulphide veinlets represent the latest stage of mineralisation. This transition from ductile deformation and sodic alteration to vein-controlled uranium is mirrored in other examples of the deposit type. The association of uranium with F-rich minerals and a suite of high field strength elements; phosphorous and zirconium is interpreted to be indicative of a magmatic rather than metamorphic or basinal fluid source. No large intrusions of appropriate age outcrop near the deposits; but we suggest a relationship with B- and Be-rich pegmatites and quartz-tourmaline veins. Full article
Open AccessArticle Numerical Simulations of Two-Phase Flow in a Dorr-Oliver Flotation Cell Model
Minerals 2013, 3(3), 284-303; doi:10.3390/min3030284
Received: 18 May 2013 / Revised: 5 July 2013 / Accepted: 2 August 2013 / Published: 9 August 2013
Cited by 2 | PDF Full-text (3557 KB) | HTML Full-text | XML Full-text
Abstract
Two-phase (water and air) flow in the forced-air mechanically-stirred Dorr-Oliver machine has been investigated using computational fluid dynamics (CFD). A 6 m3 model is considered. The flow is modeled by the Euler-Euler approach, and transport equations are solved using software ANSYS-CFX5. Unsteady
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Two-phase (water and air) flow in the forced-air mechanically-stirred Dorr-Oliver machine has been investigated using computational fluid dynamics (CFD). A 6 m3 model is considered. The flow is modeled by the Euler-Euler approach, and transport equations are solved using software ANSYS-CFX5. Unsteady simulations are conducted in a 180-degree sector with periodic boundary conditions. Air is injected into the rotor at the rate of 2.63 m3/min, and a uniform bubble diameter is specified. The effects of bubble diameter on velocity field and air volume fraction are determined by conducting simulations for three diameters of 0.5, 1.0, and 2.0 mm. Air volume fraction contours, velocity profiles, and turbulent kinetic energy profiles in different parts of the machine are presented and discussed. Results have been compared to experimental data, and good agreement is obtained for the mean velocity and turbulent kinetic energy profiles in the rotor-stator gap and in the jet region outside stator blades. Full article
Open AccessArticle Potentiostatically Poised Electrodes Mimic Iron Oxide and Interact with Soil Microbial Communities to Alter the Biogeochemistry of Arctic Peat Soils
Minerals 2013, 3(3), 318-336; doi:10.3390/min3030318
Received: 16 August 2013 / Revised: 11 September 2013 / Accepted: 13 September 2013 / Published: 23 September 2013
Cited by 4 | PDF Full-text (1324 KB) | HTML Full-text | XML Full-text
Abstract
Dissimilatory metal-reducing bacteria are ubiquitous in soils worldwide, possess the ability to transfer electrons outside of their cell membranes, and are capable of respiring with various metal oxides. Reduction of iron oxides is one of the more energetically favorable forms of anaerobic respiration,
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Dissimilatory metal-reducing bacteria are ubiquitous in soils worldwide, possess the ability to transfer electrons outside of their cell membranes, and are capable of respiring with various metal oxides. Reduction of iron oxides is one of the more energetically favorable forms of anaerobic respiration, with a higher energy yield than both sulfate reduction and methanogenesis. As such, this process has significant implications for soil carbon balances, especially in the saturated, carbon-rich soils of the northern latitudes. However, the dynamics of these microbial processes within the context of the greater soil microbiome remain largely unstudied. Previously, we have demonstrated the capability of potentiostatically poised electrodes to mimic the redox potential of iron(III)- and humic acid-compounds and obtain a measure of metal-reducing respiration. Here, we extend this work by utilizing poised electrodes to provide an inexaustable electron acceptor for iron- and humic acid-reducing microbes, and by measuring the effects on both microbial community structure and greenhouse gas emissions. The application of both nonpoised and poised graphite electrodes in peat soils stimulated methane emissions by 15%–43% compared to soils without electrodes. Poised electrodes resulted in higher (13%–24%) methane emissions than the nonpoised electrodes. The stimulation of methane emissions for both nonpoised and poised electrodes correlated with the enrichment of proteobacteria, verrucomicrobia, and bacteroidetes. Here, we demonstrate a tool for precisely manipulating localized redox conditions in situ (via poised electrodes) and for connecting microbial community dynamics with larger ecosystem processes. This work provides a foundation for further studies examining the role of dissimilatory metal-reducing bacteria in global biogeochemical cycles. Full article
(This article belongs to the Special Issue Interactions between Microbes and Minerals)
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Review

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Open AccessReview Sustainability of Rare Earths—An Overview of the State of Knowledge
Minerals 2013, 3(3), 304-317; doi:10.3390/min3030304
Received: 7 July 2013 / Revised: 16 August 2013 / Accepted: 3 September 2013 / Published: 10 September 2013
Cited by 18 | PDF Full-text (567 KB) | HTML Full-text | XML Full-text
Abstract
Rare Earths (RE) have been the focus of much attention in recent years as a consequence of a number of converging factors, prominent among which are: centralization of supply (in China), unique applications in high-end technologies particularly in the low-carbon energy industry, and
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Rare Earths (RE) have been the focus of much attention in recent years as a consequence of a number of converging factors, prominent among which are: centralization of supply (in China), unique applications in high-end technologies particularly in the low-carbon energy industry, and global demand outstripping availability. Despite this focus, RE supply chain sustainability has not been examined in depth or in any systematic manner. This paper provides an initial review of RE sustainability considerations at present, including current initiatives to understand the research and development needs. The analysis highlights a broad range of areas needing consolidation with future research and calls for collaboration between industry and academia to understand the sustainability considerations of these critical elements in more depth. Full article

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