Hard Mineral Research Articles

Marine sulfate‐reducing bacteria cause serious corrosion of iron under electroconductive biogenic mineral crust

Iron (Fe0) corrosion in anoxic environments (e.g. inside pipelines), a process entailing considerable economic costs, is largely influenced by microorganisms, in particular sulfate-reducing bacteria (SRB). The process is characterized by formation of black crusts and metal pitting. The mechanism is usually explained by the corrosiveness of formed H2S, and scavenge of ‘cathodic’ H2 from chemical reaction of Fe0 with H2O. Here we studied peculiar marine SRB that grew lithotrophically with metallic iron as the only electron donor. They degraded up to 72% of iron coupons (10 mm × 10 mm × 1 mm) within five months, which is a technologically highly relevant corrosion rate (0.7 mm Fe0 year−1), while conventional H2-scavenging control strains were not corrosive. The black, hard mineral crust (FeS, FeCO3, Mg/CaCO3) deposited on the corroding metal exhibited electrical conductivity (50 S m−1). This was sufficient to explain the corrosion rate by electron flow from the metal (4Fe0 → 4Fe2+ + 8e−) through semiconductive sulfides to the crust-colonizing cells reducing sulfate (8e− + SO42− + 9H+ → HS− + 4H2O). Hence, anaerobic microbial iron corrosion obviously bypasses H2 rather than depends on it. SRB with such corrosive potential were revealed at naturally high numbers at a coastal marine sediment site. Iron coupons buried there were corroded and covered by the characteristic mineral crust. It is speculated that anaerobic biocorrosion is due to the promiscuous use of an ecophysiologically relevant catabolic trait for uptake of external electrons from abiotic or biotic sources in sediments.

Old laws for new risks at sea: mineral resources, climate change, sea lanes, and cables

Maritime security in a broad sense means more than piracy and terrorism. This paper concentrates on the risk potential of current and future resource-related activities on the seabed. The seabed mining of hard mineral resources—in addition to hydrocarbons—leads to new controversial maritime boundary claims of states in their effort to expand national access rights to raw materials. Outer continental shelf claims in the Arctic Ocean are today's test bench for law of the sea conflicts. Fiber-optic cables running through regional seas, straits, and land bridges may become another risky issue, while the pattern of maritime transport routes is moving from Northern to Southern waters. Under a medium-term perspective, the sea level rise will endanger ports and coasts. Borderlines of maritime zones will move and thus generate more injustice and conflicts among states. The tools to solve borderline conflicts and options for dispute settlement are available in UNCLOS. Some other legal gaps are covered by the 2005 SUA Convention and by bilateral agreements, while resolutions by the UN Security Council begin to broaden rights of intervention and interdiction. The need for new laws remains.

Long Memory in German Energy Price Indices

This study examines the long-memory properties of German energy price indices (specifically, import and export prices, as well as producer and consumer prices) for hard coal, lignite, mineral oil and natural gas adopting a fractional integration modelling framework. The analysis is undertaken using monthly data from January 2000 to August 2011. The results suggest nonstationary long memory in the series (with orders of integration equal to or higher than 1) when breaks are not allowed for. However, endogenous break tests indicate a single break in all series except for producer prices for lignite for which two breaks are detected. When such breaks are taken into account, and with autocorrelated disturbances, evidence of mean reversion is found in practically all cases.

Cyborg cells: functionalisation of living cells with polymers and nanomaterials

Living cells interfaced with a range of polyelectrolyte coatings, magnetic and noble metal nanoparticles, hard mineral shells and other complex nanomaterials can perform functions often completely different from their original specialisation. Such "cyborg cells" are already finding a range of novel applications in areas like whole cell biosensors, bioelectronics, toxicity microscreening, tissue engineering, cell implant protection and bioanalytical chemistry. In this tutorial review, we describe the development of novel methods for functionalisation of cells with polymers and nanoparticles and comment on future advances in this technology in the light of other literature approaches. We review recent studies on the cell viability and function upon direct deposition of nanoparticles, coating with polyelectrolytes, polymer assisted assembly of nanomaterials and hard shells on the cell surface. The cell toxicity issues are considered for many practical applications in terms of possible adverse effects of the deposited polymers, polyelectrolytes and nanoparticles on the cell surface.

Abrasivity Assessment of Granitic Building Stones in Relation to Diamond Tool Wear Rate Using Mineralogy-Based Rock Hardness Indexes

The objective of the present study was to determine the abrasive wear potential of granites in circular sawing using some mineralogy-based rock hardness indexes. A literature study indicated that little or no attention has been given to assessing this kind of relationship in the field of stone processing. To accomplish this objective, sawing experiments were performed on nine different granites used widely as building and decorative stone materials. The measured sawblade-specific wear rates were correlated with three different rock hardness indexes attained by combining the percentage content of hard mineral constituents with their known hardness values. Statistical analysis of the experimental data revealed that rock hardness indexes that are based on both Vickers hardness number and Rosiwal hardness could be accepted as reliable indicators of granite abrasivity. These two indexes were also found to correlate well with the average power drawn during the process. However, the rock abrasivity index based on Mohs relative scratch hardness did not show statistically significant correlations with sawblade wear rate and power drawn. Although quartz percentage content is regarded as an important abrasivity parameter by practitioners, the observations made here indicate that consideration of quartz percentage content alone is not sufficient to describe the abrasive potential of granites, and thus incorporation of other hard mineral constituents could be more suitable.

Comparison of Topsoil Magnetic Properties Between the Loess Region in Tianshan Mountains and Loess Plateau, China, and Its Environmental Significance

AbstractThe topsoils of the loess region of Tianshan Mountains and Loess Plateau in northwestern China are systematically collected and analysed on their rock magnetism and grain size. Their magnetic characteristics indicate that high magnetic minerals are magnetite and maghemite, and the weakly magnetic minerals are hematite, goethite or lepidocrocite. There are at least parts of maghemite deposited in the Loess Plateau that was originally from aeolian source area. The grain size of magnetic minerals (and particle size) in Tianshan topsoil samples is generally much coarser; mostly within range of multi‐domain (MD). Hard magnetic minerals in Tianshan topsoils are in higher percentage than that in Loess Plateau. The magnetic susceptibility of topsoils from Loess Plateau shows a good positive relation with frequency dependent susceptibility. Climatic condition, such as temperature and precipitation, especially the latter one, is explained as a major factor effecting susceptibility enhancement in the Loess Plateau. Tianshan topsoil samples contain a very small amount of ultrafine magnetic grains produced during pedogenic process, such ultrafine magnetic grains have very limited contribution to the susceptibility enhancement. Tianshan topsoils generally show a characteristic of less weathering or weak pedogenesis, aeolian coarser grains therefore play an important role in mechanism of magnetic susceptibility. Frequency dependent susceptibility shows a close relation with mean annual precipitation (MAP) in all studied areas, However, the relations between magnetic susceptibility and MAP are different in various regions: showing positive correlation in the central Loess Plateau (study area), but negative in Tianshan regions. The precondition of ‘wind vigor' model is discussed, ‘wind vigor' theory is debated as not suitable for interpretation of Alaskan and Siberian loess, but suitable for Xinjiang loess.

Magnetic property of loess strata recorded by Kansu profile in Tianshan Mountains

Kansu (KS) profile is located in the east of Yili basin, western Xinjiang, where typical loess sediments are distributed. The magnetic parameters (such as IRM, SIRM SOFT, and M) and grain size in the KS profile were analyzed in the study. The results showed that the magnetic property of KS loess is dominated by ferrimagnetic minerals, such as magnetite and maghemite. Antiferromagnetic and superparamagnetic minerals also exist in the profile, but had less impact on magnetic susceptibility. Compared with the typical loess sediments of the central Loess Plateau in China, the strata of Kansu profile contained more magnetic minerals and hard magnetic minerals. The analysis of grain size for magnetic minerals indicated that the properties of loess and paleosol were respectively dominated by PSD/MD and coarse SSD magnetite. The research found that the contents of magnetic minerals in loess and paleosol sequences in Kansu profile were similar, but the proportion of fine grained magnetite and soft magnetic minerals were varying, which implies a positive relationship between the value of magnetic susceptibility and intensity of pedogenesis.

The morphology and mineralization of dental hard tissue in the offspring of passive smoking rats

ObjectiveTo study the effects of maternal passive smoking on the morphology and mineralization of dental hard tissue in offspring rats. DesignWe have established a maternal passive smoking model. Offspring rats were sacrificed on the 20th day of gestation (E20) or the 3rd (D3) or 10th day (D10) after birth. We observed hard tissue morphology using Haematoxylin–Eosin (H&E) staining sections, used micro computer tomography (Micro-CT) to measure hard tissue thickness and volume on the mandibular first molars of the offspring rats, and used Micro-CT and energy dispersive X-ray spectroscopy with scanning electron microscopy (SEM/EDS) to determine the hard tissue mineral density and the ratio of calcium atom number/calcium atom+phosphorus atom number (Ca2+/P3−+Ca2+). ResultsOverall, the development of dental hard tissue was delayed in the offspring of passive smoking rats. The thickness and volume of hard tissue were lower in the offspring of the maternal passive smoking group than in the offspring of the control group. Mineral density of the hard tissue and the ratio of (Ca2+/P3−+Ca2+) were also reduced in the offspring of the maternal passive smoking group. ConclusionMaternal passive smoking inhibits the morphological development and mineralization level of hard tissue on the mandibular first molars of offspring rats.

Permanent hard water softening using carbon nanotube sheets

Permanent hard water softening using oxidized carbon nanotube (CNT) sheets was performed. CNT sheets were synthesized by chemical vapor deposition of cyclohexanol and ferrocene in nitrogen atmosphere at 750 °C, and oxidized with concentrated nitric acid at room temperature and then employed as adsorbent for permanent hard water softening. Various isotherms and kinetic models were applied to fit the experimental data. It was found out that the adsorption behavior of hard mineral ions by oxidized CNT sheets match well with the Freundlich isotherm and the pseudo-second-order kinetic model. The results demonstrated that the oxidized CNT sheets can be used as an effective adsorbent for hard water softening due to their high adsorption capacity. Also, using the oxidized CNT sheets, hard water softening without CNT leakage into water is economically feasible.

Precision Grindability of Granite in Relation to Discrete Distribution Parameters of Microhardness and Microbrittleness

The natural granite includes various hard and brittle minerals with different material behaviors. In this paper, the discrete distribution parameters of microhardness and microbrittleness are proposed to describe its micron-scale material behavior. The objective is to evaluate and predict the precision grindability of various granites by using its microhardness and microbrittleness. First, the relative values of microhardness and microbrittleness were defined by measuring diagonal length and crack spreading length of micron-scale indentation in a micro-indentation experiment; then the microhardness, the microbrittleness, and their average deviations were introduced as discrete distribution parameters with regard to the weighted coefficients of various minerals in granite; finally, a precision grinding experiment was carried out to investigate the grinding force and surface roughness with regard to different grinding variables. It is found that grinding force and surface roughness have good and very good correlations with the microhardness and its average deviation, respectively, but they have no obvious relations with the microbrittleness. The ground surface can be improved when grinding the granite with high microhardness and its uniform distribution even if leading to large grinding force. For grinding variables, the grinding force increases with the decrease in the depth of cut and the work speed in brittle-mode grinding, but it has little correlation with work speed when approaching ductile-mode grinding. It is concluded that the precision grindability of granite may be evaluated and predicated by the relative microhardness and its average deviation.

Location Depending Textures of the Human Dental Enamel

Dental enamel is the most highly mineralised and hardest biological tissue in human body [1]. Dental enamel is made of hydroxylapatite (HAP) - Ca5(PO4)3(OH), which is hexagonal (6/m). The lattice parameters are a = b = 0.9418 nm und c = 0.6875 nm [1]. Although HAP is a very hard mineral, it can be dissolved easily in a process which is known as enamel demineralization by lactic acid produced by bacteria. Also the direct consumption of acid (e.g. citric, lactic or phosphoric acid in soft drinks) can harm the dental enamel in a similar way. These processes can damage the dental enamel. It will be dissolved completely and a cavity occurs. The cavity must then be cleaned and filled. It exists a lot of dental fillings, like gold, amalgam, ceramics or polymeric materials. After filling other dangers can occur: The mechanical properties of the materials used to fill cavities can differ strongly from the ones of the dental enamel itself. In the worst case, the filling of a tooth can damage the enamel of the opposite tooth by chewing if the interaction of enamel and filling is not equivalent, so that the harder fillings can abrade the softer enamel of the healthy tooth at the opposite side. This could be avoided if the anisotropic mechanical properties of dental enamel would be known in detail, hence then another filling could be searched or fabricated as an equivalent opponent for the dental enamel with equal properties. To find such a material, one has to characterise the properties of dental enamel first in detail for the different types of teeth (incisor, canine, premolar and molar). This is here exemplary done for a human incisor tooth by texture analysis with the program MAUD from 2D synchrotron transmission images [2,3,4].

The effect of plant cover on the mechanical composition of eroded soil

The effect of plant cover on the mechanical composition of eroded soil Water erosion causes migration of the finest soil particles and chemical compounds. The paper attempts to compare the mechanical composition of sediments susceptible to water erosion on the hillslopes with different cover crops. The research was conducted on the experimental plots in Puczniew. Its results showed that the composition of the sediment washed out from the fallow land significantly differed from that washed out from the plots with grass and barley crops. In the case of fallow land, soil particles were markedly larger. This might indicate the existence of a very hard mineral fraction.

How low can you go? - Extending downwards the limits of plastic deformation in pyrite

AbstractUnderstanding the deformation mechanisms that may operate in pyrite (FeS2) across a range of P-Tconditions is important in deciphering the history of deformed ore deposits. Pyrite has frequently been considered a hard mineral, which deforms by cataclastic flow or diffusive processes, if at all, at temperatures <425°C. However, utilizing SEM-based orientation-contrast (OC) imaging and electron-backscatter diffraction (EBSD) techniques, plastic deformation can now be readily identified within pyrite grains. In this study, a series of pyrite-rich polymetallic ore deposits, deformed at low temperature metamorphic conditions (∼200—420°C), have been investigated. Results indicate that pyrite grains in all the ore deposits preserve internal lattice ‘distortion’ or ‘bending’ and therefore plastic deformation mechanisms have operated. Many pyrite grains in the ore deposits also contain low-angle (∼2°) sub-grain boundaries or ‘dislocation walls', indicating that both dislocation glide and creep have been the dominant deformation mechanisms at peak metamorphic conditions within the pyrite grains. These results suggest that the brittle-ductile transition in pyrite occurs at temperatures potentially as low as ∼200°C, far lower than implied from previous studies or the current pyrite deformation-mechanism map.

Magnetic characterisation and correlation of a Younger Dryas tephra in North Atlantic marine sediments

AbstractA technique for identifying non‐visible basaltic tephra‐rich horizons of Younger Dryas (YD)/Greenland Stadial (GS) 1 age in northeast Atlantic sediments using rapid, non‐destructive magnetic measurements is presented. Three high‐resolution marine sediment cores have been studied in an E–W transect across the Hebridean margin: St Kilda Basin (MD95‐2007), Barra Fan (MD95‐2006) and Rockall Trough (MD04‐2822). Magnetic susceptibilities and remanent magnetisations were measured at contiguous 1 cm resolution on bulk sediments. In all three cores, an interval with higher proportions of hard magnetic minerals coincides with a clearly defined peak in basaltic tephra shard (>250 µm) counts, which can be constrained to the early part of the YD/GS1 based on faunal climate proxies. Electron microprobe analyses of the magnetically distinct basaltic tephra interval, in all three cores, displays the same major element geochemistry as published for the Vedde basaltic (I Tab. 1), i.e. sourced from the Icelandic volcano Katla. The identification of transitional alkalic basaltic tephras within marine sediments could potentially be facilitated by magnetic analysis as a useful chronostratigraphic screening tool. Copyright © 2009 John Wiley & Sons, Ltd.

Abrasivity by bentonite dispersions

Bentonites are used for various industrial applications. Their physicochemical properties depend on the mineralogical and chemical composition, the type of smectite, the grain size distribution, the cation exchange capacity (CEC), the dominant interlayer cation (Na +, Ca 2+, Mg 2+), and the layer charge density. All these parameters can be measured with acceptable precision. Nevertheless, the performance of a bentonite in a given application is often unpredictable. An additional relevant parameter is the “microfabric” describing the arrangement of minerals and/or the intergrowth of the minerals with glass. The microfabric is supposed to affect different bentonite properties such as swelling capacity and rheology. The present study focuses on the influence of different microfabrics on the abrasivity by bentonite dispersions. The abrasivity of bentonite dispersions mainly depended on two factors: 1) on the amount of hard and sharp accessory minerals and volcanic glass and 2) the grain size distribution, which was produced by different grinding techniques. The abrasivity increased with decreasing grain size, which was caused by breaking the hard components (minerals and glass) leading to an increased number of sharp edges. In addition, there was evidence for a subordinate influence of the type of exchangeable cations. This influence is explained by the different relative arrangements of smectite particles towards the surfaces of hard and sharp minerals. Na + exchanged glass rich samples showed higher abrasion values than the Ca 2+ exchanged samples.

Magnetic characteristics of topsoil from Xinjiang, Northwestern China, and their implications

In this study, a set of environmental magnetic parameters (χlf, χfd%, χARM, SIRM, HIRM, SOFT and SIRM/χlf, χARM/SIRM and χARM/χlf) of 331 top-soil samples from Xinjiang Uygur Autonomous Region of China were systematically measured and the magnetic characteristics and its environmental significance were discussed. Our results indicate that the main magnetic minerals of these top-soils are single-domain magnetite. The content of magnetic minerals in top-soils from north Xinjiang is higher than that from south Xinjiang; however, the content of hard magnetic minerals is higher in the top- soils from south Xinjiang. The top-soils from Yili region contain similar magnetic minerals as that from south Xinjiang, but with much stronger magnetic SP content due to higher pedogenic processes. The differences in magnetic characteristics among top-soils from different regions of Xinjiang might reflect the differences of regional climatic factors, especially the precipitation.

Effect of Pore Size on the Growth of Hydroxyapatite from Mesoporous CaO−SiO2 Substrate

In this work, a new approach for controlling the formation rate of hard tissue mineral hydroxypapatite (HAP) through the control of inner pore sizes of CaO−SiO2 bioactive material is proposed. Highly ordered mesoporous CaO−SiO2 (MCS) bioactive material with different pore sizes were synthesized through two types of surfactants, cetyltrimethyl-ammonium bromide (CTAB) and triblock copolymer EO106PO70EO106 (Pluronic F127). These two surfactants were selected for their different pore size formation tendencies, about 2.7 nm for CTAB template and 4.9 nm for F127 template. These two types of MCS materials have identical chemical composition but differ only in their pore sizes. Their bioactivities were evaluated by the incubation of the MCS in phosphate buffer solution at 37 °C for different periods of time. SEM showed that incubated MCS with 2.7-nm pore size could rapidly form a dense layer of HAP crystallites on its surfaces within a few hours, while incubated MCS with 4.9-nm pore size just formed a sparse laye...

Mineralogical Characterization of Sasol Feed Coals and Corresponding Gasification Ash Constituents

Feed coal and coarse ash particles (heated rock fragments and clinkers), produced from Sasol-Lurgi gasifier tests under different operating conditions, have been characterized by quantitative X-ray diffraction, electron microprobe analysis, and associated chemical techniques, as a basis for better understanding of the relations between the mineralogical and physical properties of the ash particles. Crystalline phases in the ashes include quartz particles inherited directly from the feed coal, as well as anorthite, mullite, and diopside, derived from solid-state reactions or crystallization of a silicate melt during the gasification process. Glass, cooled from the melt, is also abundant in the ash materials. The abundance of large particles of hard minerals in the coal or the ash, such as quartz, anorthite, pyrite, and diopside, has been correlated with a laboratory-determined abrasion index and may contribute significantly to wear on mechanical equipment during coal- or ash-handling operations.

Improvement in Grade of Sericite Ore by Dry Beneficiation

A study on the dry beneficiation of sericite occurring in the Daehyun Mine of the Republic of Korea region as performed by applying selective grinding and air classification techniques. Quartz and sericite occurred in the raw ore as major components. The results of liberation using a ball mill and an impact mill showed that the contents of <TEX>$R_2O$</TEX> were increased while <TEX>$SiO_2$</TEX> was decreased in proportion to decreasing particle size. According to the XRD, XRF analysis and the EDS of SEM analysis, the ball mill gave a better grade product in <TEX>$R_2O$</TEX> content than the impact mill when the particle size was the same. When the raw ore was ground by the impact mill with arotor speed 57.6 m/sec and then followed by 15,000rpm classification using an air classifier, the chemical composition of the over flowed product was 49.65wt% <TEX>$SiO_2$</TEX>, 32.15wt% <TEX>$Al_2O_3$</TEX>, 0.13wt% <TEX>$Fe_2O_3$</TEX>, 10.37wt% <TEX>$K_2O$</TEX>, and 0.14wt% <TEX>$Na_2O$</TEX>. This result indicates that the <TEX>$R_2O$</TEX> contents were increased by 49.5% compared to that of the raw ore. From these results described above, it is suggested that hard mineral such as Quartz little ground by selective grinding using impact mill whereas soft mineral such as sericite easily ground to small size. As a result of that hard minerals can be easily removed from the finely ground sericite by air classification and the <TEX>$R_2O$</TEX> grade of thus obtained concentrate was improved to higher than 10wt% which can be used for ceramics raw materials.

Imaging organic and mineral phases in a biomineral using novel contrast techniques

Chitons are marine molluscs that mineralize their teeth by the process of matrix-mediated biomineralization. The teeth develop in a continuous manner forming hard minerals, including magnetite, making analysis of the matrix within these mineralized regions difficult. This article describes the use of charge contrast imaging techniques, rarely applied to biological samples, to simultaneously image the organic and mineral phases within the teeth of these animals. Resulting evidence demonstrates the power of this technique in delivering architectural information concerning both the matrix and mineral phases, without the need for removal of the hard mineralized material.