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By S. E. Maddigan, B. R. Zimmerman

MOST metallurgists are well acquainted with the contributions already made to the study of metals by the use of X-rays. On the one hand, the radiographic method is constantly becoming of increasing importance as a nondestructive testing procedure, while on the other hand the techniques of X-ray diffraction have made important contributions to the fundamental knowledge in studies of phase diagrams, stress conditions, and so forth. A new, and as yet insufficiently appreciated, tool exists in the application of microradiography to alloy structures. This new procedure in many respects bears the same relation to microscopic investigations as does macroradiography to the gross inspection of metal surfaces. However, where macroradiography is used ordinarily to determine the soundness of the metal structure, this new method can be used not only to investigate micro-un- soundness but also to examine the distribution of the constituent elements within the body of the alloy. When combined with the normal procedures of microscopy, this offers a technique of great potential power. It is intended in this paper to present a few examples of copper-base alloys demonstrating the additional knowledge obtained from the microradiographic method. The detection of micro-unsoundness is demonstrated in Fig. I for a sample of cartridge brass as cast. The sample appeared quite sound when viewed under the microscope, but in reality was thickly populated with minute voids. This application of the method conforms in every way to conventional large-scale radiography and has been used to facilitate production of metal for vacuum devices.1 The true potentialities of the technique are revealed by comparison of Figs. 2a and 2b, which are respectively a- photomicrograph and a microradiograph of a cast alloy of 80 per cent Cu, 10 per cent Sn, 10 per cent Pb. The remarkable difference in appearance provides some concept of the additional information this method may yield when used as an auxiliary to microscopic studies. Fig. 2a shows two phases of the copper-tin system plus segregated lumps of lead. Fig. ab, on the other hand, shows with exceptional clarity the actual dendritic growth of the metal crystals during solidification. The practice of microradiography depends upon the laws of absorption of X-rays. This subject has been reviewed thoroughly in recent papers,1,2,3 but for clarity a brief resumé will be given here. As is well known, when a beam of X-rays is transmitted through a layer of homogeneous material, the intensity is reduced according to the relation:[ ]

Jan 1, 1944

By M I. Pownceby, A Torpy, C Johnson, N C. Wilson

To extract uranium from low-grade, calcrete-hosted uranium (CHU) ore is challenging owing to the presence of carbonate and swelling clay gangue minerals that require an alkaline lixiviant to be used. Western Australia possesses ~75 000 U3O8 t in CHU resources. Improvements to alkaline leach extraction practices would improve the economic potential of these deposits.A column leach study of CHU ore was run for 105 days using an alkaline carbonate-bicarbonate lixiviant. The uranium content of the liquor plateaued after 75 days at ~275 mg U/L; the calculated maximum solution capacity was 800 mg U/L. Spiked peaks and troughs were seen in the data set beyond the 60th day, where concentrations ranged from 220 - 290 mg U/L, indicating possible cyclic uptake and loss of uranium from the solution.Pristine and leached ore samples were geochemically analysed and mineralogically characterised at high resolution using a field emission gun-electron probe micro-analyser (FEG-EPMA). Results showed that leached ore samples from the top of the column contained less carnotite than pristine ore. In contrast, leached ore samples from the column base contained regions with more carnotite than pristine ore, indicating precipitation. Three carnotite grain micro-structures were identified in the leached ore; fan-spherulite, granular and core-shell cubes, with evidence for multiple growth phases.Evidence of carnotite precipitation was seen at the edge of and in pore spaces within montmorillonite and dolomite grains. The point of zero charge of both minerals is lower than the pH of the lixiviant (pH 10.8), thus the mineral surfaces are negatively charged and would not attract UO2(CO3)34- ions out of solution. Similarly, the decrease in the uranium content of the lixiviant is not attributed to super-saturation, as this was unlikely to have been achieved. Work is ongoing to understand the reason for carnotite precipitation and the fluctuations in the lixiviant uranium concentration that are seen.CITATION:Johnson, C, Pownceby, M I, Wilson, N C and Torpy, A, 2013. Microscale characterisation of pristine and processed ore - implications for leaching calcrete-hosted uranium ore, in Proceedings The Second AusIMM International Geometallurgy Conference (GeoMet) 2013 , pp 303-316 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 29, 2013

By C. Garcia, C. L. Lin

Characterization and analysis of multiphase particles and/or particulate systems (such as the packed particle bed) are of great technological importance for mineral processing applications. In general the performance of these applications depends on the statistical characteristics of particle microstructures, such as composition distribution, surface exposure of mineral grains, pore network structure, etc. For continued technological progress in the field of multiphase particulate processes, the need for quantitative spatial analysis of multiphase particles in three dimensions has increased sign6cantly. Such quantitative information must be accurate enough that the measured values can be used as parameters for simulation models, process design procedures, and control strategies. Modern 3D image-acquisition techniques, such as X-ray microtomography (XMT), offer a unique imaging capability that can produce high-resolution (a few micrometers) three-dimensional images of the internal structure of multiphase particulate samples. These three-dimensional image data present new challenges for image analysis, image processing, and visualization. Furthermore, important issues should focus on how to use the 3D information and derive new insights into the improvement, design, and operation of mineral processing processes. In this paper, utilization of XMT for characterization and analysis of leaching process involving multiphase particulate system is discussed.

Jan 1, 2005

By J. A. Herbst, Y. C. Lo

An attempt has been made to parameterize the population balance model for a ball mill based on measurements of the elementary breakage process obtained using an ultrafast load cell device. Detailed insight obtained concerning the fragmentation of particle assemblies with the ultrafast load cell leads to a better understanding of ball mill grinding. The ball mill breakage function and specific selection function are derived from an average single event representing the multiple breakage events which occur in ball mill grinding. Since both the breakage function and the specific selection function depend on the loading mode in the mill, predictions of breakage mechanisms in ball mills are possible by using data obtained in various elementary loading modes. The application of this model to the description of batch ball milling behavior has resulted in reasonably accurate predictions of product size distributions for various energy inputs.

Jan 1, 1992

By R. P. King

Thermal pretreatment can significantly improve industrial comminution operations by reducing energy requirements and increasing mineral liberation. The effect of pretreatment using conventional and dielectric heating followed by quenching on the fracture characteristics of a number of single and multiphase brittle materials has been investigated using the Ultrafast Load Cell. It has been observed that very significant reductions in both fracture energies and the material integrity (damage) were achieved by heating followed by water quenching.

Jan 1, 1995

By José Fernandes De Oliveira

El presente texto aborda los resultados de tres estudios realizados por Microscopía Electrónica de Barrido con Energía Dispersiva (SEM/EDS) en el Laboratorio de Caracterización Mineralógica, donde destaca la importancia de la técnica en el sector de minería y materiales. El primer estudio comprende el análisis de los contenidos de fierro y manganeso en concentrado de zinc, donde se verifica que la esfalerita contiene fierro cerca del límite aceptable de 5%. El segundo estudio realiza una caracterización mineralógica de muestras con minerales de plata, para conocer el estado de la plata (inclusión, solución sólida, encapsulada), con qué minerales está asociada y si puede ser liberada. Finalmente, el tercer estudio refiere el análisis de secciones fracturadas de tornillos de latón para evaluar las causas del rompimiento prematuro de los tornillos.

Sep 12, 2011

By Alei Leite Alcantara Domingues

A microscopia óptica é uma ferramenta importante para o entendimento dos processos envolvidos na produção do minério de ferro e seus aglomerados. Nos laboratórios em que esse tipo de análise é feita, tem-se geralmente um microscópio de luz refletida e um operador treinado que leva diversas horas para concluir uma única amostra. Nesse trabalho serão mostrados exemplos de resultados de minérios de ferro, sínter e pelotas obtidos em um sistema de microscopia óptica automática com análise de imagens. No estudo do minério de ferro foram determinados a composição mineralógica quantitativa, morfologia das partículas e tamanho dos cristais. Na microscopia de sínter foram determinados a quantificação de fases, porosidade, textura, recristalização de hematita e morfologia das ferritas. Nas pelotas produzidas com minério de ferro foram feitas análises de quantificação de fases, distribuição e quantificação dos poros e evolução microestrutural dos grãos. A implantação de um sistema de microscopia óptica automática com análise de imagens permite que análises sejam feitas em menor tempo, com maior reprodutibilidade possibilitando que a técnica seja implantada em áreas de produção que exijam respostas mais rápidas.

Oct 30, 2017

By G. O. Oniyide, H. Yilmaz

The South African platinum mines in the Bushveld Complex (BC) have unique features that distinguish them from the gold mines. They have a higher horizontal stress closer to the surface, lower occurrence of seismic activity (caused mainly by pillar failure), and are sited in an area of high geothermal gradient. One of the future challenges of platinum mining is the increasing temperatures as the mining depth increases. High temperatures invariably bring about higher ventilation costs and require different approaches to human factors and ergonomics. Excavation stability would also be another area of concern due to increasing stresses. In this investigation, the effect of temperature on the physical and chemical properties of selected Bushveld rocks (chromitite, pyroxenite, norite, leuconorite, gabbronorite, mottled anorthosite, varitextured anorthosite, granite, and granofels) was studied by means of optical microscopy and scanning electron microscopy using energy-dispersive Xray spectrometry (SEM-EDX). The rock specimens were heated in a temperature-controlled oven a rate of 2°C /min to 50°C, 100°C, and 140°C and kept at temperature for five consecutive days. Samples were allowed to cool to ambient temperature (approximately 20°C) before image capturing. Micrographs of the specimens were taken before and after heat treatment. All the SEM samples were also subjected to heating and cooling on alternate days for ten days in order to observe the effect of repeated heating and cooling on the rocks. The results of the optical microscopy analyses showed minor physical changes in the rocks. The SEM images revealed that cracks initiating at lower temperatures extend with increasing temperature. The chemical analyses showed that the temperature range considered in this research is not high enough to induce changes in the chemical composition of rock samples.

Jan 1, 2016

By A. Röttger, W. Theisen, J. Küpferle, M. Alber

"Wear of TBM tools significantly affects tunneling advance rates. Wear-prediction models are based (amongst others) on the abrasivity of the present geology, which is determined via laboratory tests. To evaluate the results from such tests in context, this work considers the tribological system TBM tool from a materials technology perspective. In so doing, the microstructures of different application-oriented materials are presented and discussed in terms of their wear behavior and wear resistance. The significant influence of tool materials on the abrasivity of the geology and thus wear prediction models has already be identified. LCPC, Cerchar and nano-scratch experiments have been performed as confirmation. Material-dependent wear mechanisms and their correlation in terms of tunneling have shown that it is mandatory to consider the complete tribological system to estimate the wear of TBM tools. 1 INTRODUCTION Mechanized tunneling is vital to ensure necessary infrastructure development in megacities like Tokyo (Bay Tunnel), Istanbul (Eurasia Tunnel) and Mexico City (Tunnel Emisor Oriente). The use of Tunnel Boring Machines (TBMs) has been established for many years. In contrast to other methods such as boring and blasting or excavation using dredgers, tunneling with TBMs allows simultaneous excavation and removal of both the mineral and tunnel lining by tubbing segments or shotcrete. This makes tunneling more efficient, allowing for faster development of the tunnel in both hard rock and soil [1]. When budgeting such tunneling projects, precise planning and coordination in terms of tunneling technique choice (e.g. EPB or Slurry-shield), the relevant geology, and the associated penetration rates and tool wear are required. In particular, wear to TBM tools has a significant impact on tunneling progress. Due to wear, tools become dulled or lose their functionality because of brittle material behavior, thus reducing penetration rates and therefore tunneling efficiency [1]. As a result, additional tool changes are necessary, leading to higher overall costs due to down times and maintenance costs. Therefore, there is strong interest in a reliable and precise wear prediction model for TBMs. As already mentioned, the geology and associated wear of the tunneling tools define the maintenance times."

Jan 1, 2016

By E. Berrezueta

Automatic digital phase imaging should yield unbiased and representative characterization of gold ores. However, this is not a simple task due to low gold grades, fine grain size, possible complex mineralogy, nugget effect, etc. A critical test was done by two methods, using the same sections of a gold-rich ore: with an optical (OM) and with an electron microscope (EM). In general, the two methods are consistent and useful for ore processing. There are some minor differences e.g. the detection of very fine gold grains is enhanced by EM.

Jan 1, 2001

By E. Berrezueta

Automatic digital phase imaging should yield unbiased and representative characterizations of gold ores. However, this is not a simple tusk due to low gold grade, fine grain size, possible complex mineralogy, nugget effect, etc. Using the same sections of a gold-rich ore, a critical test was performed using an optical microscope (OM) and an electron microscope (EM). In general, the two methods are consistent and useful for ore processing. There are some minor differences, such as the detection of very fine gold grains is enhanced by EM. Key words: Digital imaging, Gold ores, Mineralogy, Electron microscopy, Optical microscopy

Jan 1, 2003

By D. M. Hausen

It has been demonstrated that microscopic techniques can be applied in a practical manner to the study of spodumene liberation in the processing of pegmatitic ores at the Kings Mountain spodumene plant, Kings Mountain, North Carolina. Spodumene and associated non-opaque gangue minerals are identified and quantified by microscopic point-counting of polished thin sections of heads, concentrates, middlings and tails fractions. Specially prepared polished thin sections? provide uniform thickness of particles for measurement of diagnostic optical properties and the alternate use of incident and transmitted light in distinguishing the various gangue and ore minerals. Spodumene is commonly associated and interlocked with quartz, albite, microcline and muscovite. Concentrate grade depends on the degree of spodumene liberation, which in turn depends on the crystal size and textural association of interlocked minerals. The liberation of spodumene can be measured as a function of screen size by means of microscopic point-count data. Microscopic data also provide useful metallurgical information about the nature of diluent minerals in spodumene concentrates, and the form of lithia losses in the tails. Lithium assays correlate closely with microscopic spodumene analyses in various flotation products from Foote Mineral's Kings Mountain plant, and confirm the applicability of quantitative optical microscopy to the study of liberation and recovery of spodumene from pegmatitic ores. A better understanding of recovery-grade relationships was developed as a result of quantitative microscopy studies.

Jan 1, 1981

By Chang Chia -Fu

The generic structure of our bimesogens is shown in and for a typical blue-phase mixture of the type we describe here. We use mixtures of the ratio 33.4% (n =2.6), 34.1% (n =6.57), 36.6% (n= 11.15) with of the high twisted power (HTP) agent BD H1381(available from Merck Chemicals and described in ref. We then studied the electric-field dependency of the selective reflection in BP I* at 20.7 °C by applying increasing and the decreasing pulsed alternating current (a.c.) electric fields (100 Hz).

Jan 1, 2006

By Ko-ichiro Ohno

It is recently recognized that the iron reduction and melting as well as the slag separation of a composite of granular iron ore and coal are completed in a very short period of about 10 minutes when the composite is rapidly heated up to approximately 1673K. These phenomena are expected to be applied to a new iron-making process. The mechanism of iron ore reduction and iron-slag separation during rapid heating has not yet been revealed and the fundamental research has just started. Carburization of the reduced iron is regarded as one of the most important steps in this process. In the present work, the composite was prepared from four kinds of coal or graphite as a carbon source and electrolytic iron powder as a completely reduced iron ore. The temperature at which the liquid formation and iron carburization occurred was monitored. Direct observation of smelting reduction behavior was made by a confocal laser-scanning microscope combined with the infrared image-heating furnace to clarify the effect of molten ash on iron carburization. It was found that the meltdown temperature of composite became lower as the melting temperature of coal ash decreased. From the observed result, it was presumed that the liquid slag would act as an important media for the carbon transfer from coal to iron. The carburization mechanism during the smelting reduction was estimated as follows. When slag containing iron oxide melted down and contacted carbon, iron oxide in the slag was reduced and the formation of the metallic iron particle as well as the its carburization occurred simultaneously at the slag-carbon interface. Carburized iron particle was carried from slag-carbon to slag-iron interfaces due to the slag convection flow caused by the difference of the interfacial tension between the carbon-slag and iron-slag interfaces. Carburization of reduced iron could proceed with a repeat of the above-mentioned process.

Jan 1, 2003

By Ko-ichiro Ohno

It is recently recognized that the iron reduction and melting as well as the slag separation of a composite of granular iron ore and coal are completed in a very short period of about IO minutes when the composite is rapidly heated up to approximately 1673K. These phenomena are expected to be applied to a new iron-making process. The mechanism of iron ore reduction and iron-slag separation during rapid heating has not yet been revealed and the fundamental research has just started. Carburization of the reduced iron is regarded as one of the most important steps in this process. In the present work, the composite was prepared from four kinds of coal or graphite as a carbon source and electrolytic iron powder as a completely reduced iron ore. The temperature at which the liquid formation and iron carburization occurred was monitored. Direct observation of smelting reduction behavior was made by a confocal laser-scanning microscope combined with the infrared image-heating furnace to clarify the effect of molten ash on iron carburization. It was found that the meltdown temperature of composite became lower as the melting temperature of coal ash decreased. From the observed result, it was presumed that the liquid slag would act as an important media for the carbon transfer from coal to iron. The carburization mechanism during the smelting reduction was estimated as follows. When slag containing iron oxide melted down and contacted carbon, iron oxide in the slag was reduced and the formation of the metallic iron particle as well as the its carburization occurred simultaneously at the slag-carbon interface. Carburized iron particle was carried from slag- carbon to slag-iron interfaces due to the slag convection flow caused by the difference of the interfacial tension between the carbon-slag and iron-slag interfaces. Carburization of reduced iron could proceed with a repeat of the above-mentioned process.

Jan 1, 2003

By T. A. Edison

A distinct hydrocarbon maturation anomaly coincides with the Gold Acres open pit, Nevada (Figure 1). Both atomic hydrogen to carbon (H-C) ratios and reflectance measurements of contained organic matter indicate significantly higher maturity in samples collected within the confines of the open pit than in samples from the surrounding region (not shown in Figure 1).

Jan 1, 1987

By H. B. Pulsifier

THE following report on the structure of copper is the result of work done in the laboratory of the Rome Wire Co. early in 1925. Previous work had indicated to the author that excellent results might be expected if a suitable technique in surfacing and etching could be developed. The resources of the Rome Wire Co. enabled this metal to be studied more intensively than previously, although none of the materials were investigated exhaustively. The material presented is hardly more than a preliminary summary of the most obvious character of the metal; a much longer research would have been necessary to solve many of the pressing problems connected with the casting and working of copper. The Rome Wire Co. has generously released the paper; to Dr. E. H. Darby, technical supervisor of the company, are due particular thanks for his appreciation of the importance of metallographic study of copper and for his effective support in the prosecution of the work and in making its publication possible.

Jan 1, 1926

By R. Karl Zipf, Z. T. Bieniawski

"A set of fracture profile photomicrographs is presented for fractures generated under mixed mode loading of the Pittsburgh coal. The fractal dimension is used· to characterize the irregularity of these profiles and a tentative relationship is presented between the fractal dimension and the fracture toughness. Surface roughness appears to depend solely on the stress intensity and no other dependence was observed with fracture loading mode, loading rate· or specimen orientation. Observations of crack bifurcations.in fracture profiles can indicate crack growth direction whereas direct surface observations generally cannot in materials such as rock and coal.1 INTRODUCTIONThe production of fine fragments of material as a result of some loading event occurs in many industrial processes. In crushing and grinding, the efficient production of fine fragments is the desired end result; .however, in coal cutting, the production of fine fragments may lead to high levels of respirable dust in the immediate atmosphere with the danger of human lung diseases. Two of the most important sources of fragments in the 1 to 10 micron size range during a cutting process are 1) severe crushing in a zone near the loading tool and 2) subsequent shearing along major crack surfaces that form the larger fragments during material reduction. These and other sources of fine fragments generation are discussed by Roepke (1984) and Zipf and Bieniawski (1986). The physical character of the nearly created major crack surfaces is believed to have a strong influence on the amount of fine fragment generation that occurs during subsequent shearing movement. When the major large fragments initially form, they are ""locked"" in place by the irregular character of the new fracture surface. Only after some relative motion has occurred between fragments are they actually liberated, and the net result is the formation of additional fine fragments. The fine fragmentation is not necessarily limited to the shearing of high points from the macrocrack surf ace since material remaining in the wake of the crack tip is damaged to a substantial depth below the actual crack surface."

Aug 31, 1989

By H. S. Martin

ALTHOUGH it was known some years ago at the- Utah Copper Co. mills that fine grinding improved flotation recoveries, no accurate data were available until recently as to just how far the grinding could be carried economically. In 1923 the ultimate degree of fineness for flotation feed was supposed to be about 10 per cent. on 65 mesh, with approximately 55 per cent. through 200 mesh, which meant that most of the mineral would pass 100 mesh. At this time Garfield and Wilfley tables were used ahead of flotation and a good deal of the coarse mineral removed prior to the ball mill regrind. Shortly afterwards, mill-scale tests developed the fact that on a feed containing not over 10 per cent. +65¬mesh material flotation alone would give a copper recovery equal to that obtained by the combination of tables and flotation, but that on much coarser feed the recovery with flotation alone was lowered. This was at a time when all the sulfide minerals were floated if possible, so that the only requisite was to grind fine enough to free the mineral from gangue. EARLIEST USE op MICROSCOPIC EXAMINATION OF TAILINGS As early as 1921, the writer had attempted to determine by chemical analysis the relative proportions of copper minerals in tailings from an ore that made extremely poor flotation results. Chemical analysis was not satisfactory or conclusive, and samples of these tailings were sent to the U. S. Bureau of Mines Station at the University of Utah for micro-scopic examination. The question at that time was to determine, if possible, which copper minerals had been lost and why, but R. E. Head, in his report, revealed other interesting data. He said in part: Briefly stated, the mineral particles or grains may be classified into separate groups as follows: 1. Free grains of pyrite, chalcopyrite, chalcocite and bornite, respectively, which contain no other included sulfides; 2. Grains in which all three of the copper sulfides are represented (the core may he of chalcopyrite, partially altered to bornite, these two minerals being entirely surrounded by a shell of chalcocite); 3. Grains composed of equal amounts of bornite and chalcocite or chalcopyrite and chalcocite.

Jan 1, 1929

By C. G. Fink

A PART of the material incorporated in this paper was derived from the studies of ancient metal objects examined by the authors from time to time for museums and art collectors, in order to verify the age of the metal. The data thus accumulated during several years was systemati-cally surveyed and supplemented by new material obtained in examina-tion of a set of specimens that had been generously donated by museums for this study. Altogether over 50 pieces were investigated, of which 39 are described in this paper. Every specimen is at least 1500 years old; the majority are considerably older. Exact conditions to which these bronze and copper objects were exposed in the ground are unknown, unfortunately. It is safe to say that exposure conditions did not remain constant during the long period of burial. Although the collection of specimens studied represents a wide variation in location and age of the objects, as well as in the nature and composition of the metals, it was found that fundamental changes in the metal structure were limited to a few typical cases which, therefore, may be considered as more or less general. The authors' chief aim was to study the effect of extremely long periods of corrosion on the structure of bronze and copper.

Jan 1, 1936