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By Shamil Shaikhutdinov

CO adsorption on gold particles deposited on well-ordered alumina and various iron oxide films has been studied with temperature programmed desorption (TPD) and infrared reflection adsorption spectroscopy (IRAS). Structural characterization has been performed with scanning tunneling microscopy. Data show that the CO adsorption exhibits a size effect in that small particles adsorb CO more strongly. The effect generally vanishes after annealing to 500 K. For annealed samples, CO TPD and IRAS spectra are nearly independent of the particle size and supports studied. The results indicate that the CO interaction with gold surfaces is essentially similar and involves low coordinated atoms.

Oct 1, 2003

By A Murphy, D Lauder, J Miranda

Minera Alumbrera Limited operates the Alumbrera concentrator, treating a nominal 80 000 tpd of porphyry gold/copper ore. It is located in Argentina, 1200 km north-west of Buenos Aires in Catamarca Province, at an elevation of 2550 m above sea level. Treatment facilities consist of crushing, SAG and primary ball mill grinding circuits, rougher flotation, ball mill regrinding, gravity recovery and cleaner flotation. It is one of only a small number of concentrators in the world, which uses Jameson Cells alone for cleaner circuit flotation. Plant design was started in June 1995, with commissioning commencing in July 1997. Following a successful ramping up to design tonnages and recoveries, a number of options were reviewed to improve gold and copper recoveries. This paper concentrates on a detailed size by size flotation recovery project, commenced in May 1999. Utilising optical microscopy, scanning electron microscopy and analysis of surface chemistry it has allowed losses by size fraction to be quantified and options for enhanced recoveries to be developed. Coupled with extensive circuit surveys it has also provided an insight into previously unknown properties of Jameson Cell operation. Among these are unique residence time and bubble formation reactions to reagent and pulp flow variations, which has permitted a number of novel changes to the operation to maximise capacity and recovery.

Jan 1, 2000

By Groves J

The sizing and classification circuits at the Mt. Newman Beneficiation Plant have performed satisfactorily. Investigations have been aimed at solving minor problems and achieving small' improvements. Emphasis has been placed on cost reduction rather than metallurgical performance. It has been found that some circuits will give better performance with the sieve bends removed. 1.0 BACKGROUND Mt. Newman. Mining operates a major iron ore mine in the Pilbara region of Western Australia. Rainfall is sparse (average 250 mm/year). Current mining is all above the water table. What rain there is tends to run off quickly instead of soaking in. The total operation produces about 30 Mt/ year of saleable product. Most of this product comes from high grade crushing plants where ore from the quarries is simply crushed and conveyed to product stockpiles. About 3 Mt/ year comes from the Beneficiation Plant.

Jan 1, 1984

By T. H. Patching, M. W. Mikhail

"Data from a standardized procedure for measuring methane desorption rates from samples of Western Canadian coals gave a good correlation (0.994) with the percentage of fines (-0.6 mm) found in the corresponding run-of-mine coal. The correlation was independent of the mining method and the top size of the samples. It is suggested that both methane desorption rate and the production of fine coal sizes are functions of the fissuration of the coal being mined.This relationship, in conjunction with established data of degradation by unit process equipment, may be useful in predicting the amount of fines that will be produced from new seams of coal and by planned new washeries. It also could be a valuable guide in modifying existing washery processes to minimize production of fines."

Jan 1, 1980

Plant survey data has shown that gold recovery through a specific copper concentrator was significantly lower than copper recovery. Size-by-size analysis revealed that this was due to poor recovery of+75 µm and ?23 µm gold containing particles. In order to further investigate the nature of the gold losses, experiments were conducted at laboratory scale. Gold deportment studies on the laboratory flotation products revealed that coarse gold (+75 µm) reporting to the rougher tailing was predominantly associated with non-sulphide gangue. Further grinding of the plant rougher tailing improved recovery of gold and copper, while not affecting iron recovery, due to improved liberation of gold from non-sulphide gangue in coarse size fractions. EDTA extraction to remove surface contaminants showed a similar improvement for fine, liberated gold flotation.

Jan 1, 2003

By Mridul Gautam, Alex Bugarski

Size Distribution and Deposition in Human Respiratory Tract: Particle Mass and Number Aleksandar Bugarski and Mridul Gautam National Research Center for Alternative Transportation Fuels, Engines and Emissions Department of Mechanical and Aerospace Engineering West Virginia University TOXICITY OF ULTRAFINES (MAUDERLY et al.) ? FINER PARTICLES PENETRATE MORE READILY INTO CELLS AND TIXROUGH TISSUE BARRIERS ? FINER PARTICLES HAVE GREATER SURFACE AREA PER UNIT MASS, AND A LARGE NUMBER OF TOXIC REACTIONS OCCUR AT THE SURFACE ? FINER PARTICLES DISSOLVE MORE READILY THAN LARGER PARTICLES THUS ENHANCING THE BIO- AVAILABILITY OF SOLUBILIZED COMPOUNDS EPIDEMIOLOGICAL STUDIES INDICATE THAT THE IMPORTANCE OF ULTRAFINES REMAINS SPECULATIVE

By C. Dinis da Gama

In mining, all unit operations are closely interrelated, and the results of blasting are probably the key factor within that sequence. The drilling program prior to blasting is just as dependent upon the desired rock fragmentation as are the loading, hauling, and mechanical crushing operations which are economically and technically influenced by the results of blasting, namely, the size and scatter of the product. What is known today as optimum blasting is the process of designing a blast in order to obtain a certain degree of fragmentation so that overall mining costs are minimized. Applying this criterion often results in a different program than when an individual blasting pattern is chosen only on the basis of the lowest operational cost for that pattern, disregarding what comes before or after the blast. [Fig. 1] shows the characteristic variation of mining unit costs with the degree of fragmentation, or the maximum size of blocks obtained from blasting. From the figure, it can be seen that optimum breakage must correspond to the lowest total costs, but reducing drilling-blasting costs only does not achieve such an optimum solution. Methods of designing surface or underground blasting operations should comply with the optimization criterion, but this compliance is feasible only if a detailed mining system analysis is available. Therefore, predictions of costs of loading, transporting, and mechanical breakage of ore as a function of its size will define a narrow range of variation for drilling and blasting parameters in order to get the minimum total costs.

Jan 1, 1972

By M. Brozek

The constant of flotation velocity is the value characterizing the kinetics of cyclic flotation. In the statistical theory of flotation its value is the function of probabilities of collision, adhesion and tearing off the grain from the air bubble. The grain ? air bubble collision plays a key role since there must be a prior collision before the grain ? air bubble adhesion happens. The probability of such an event to occur is proportional to the relation of the grain diameter to the bubble diameter. When the grain sizes are given, it is possible to control the value of collision probability by means of the size of air bubbles. Consequently, it is significant to find the effect of physical and physicochemical factors upon the diameter of air bubbles in the form of a mathematical dependence. In the pneumo-mechanical flotation machine the air bubbles are generated by the blades of the rotor. The dispergation rate is affected by, among others, the rotor rotational speed, the amount of air transported to the flotation chamber an time and the liquid surface tension, depending on the type and number of applied flotation reagents. In the proposed paper the authors will present the distribution of air bubble diameters on the grounds of the above factors, according to the laws of thermodynamics. The correctness of the de-rived dependences will be verified empirically.

Jan 1, 2014

By H. S. Chiang, Y. Luo, S. S. Peng

"IntroductionThe way in which the particle sizes distribute in the airborne coal dust plays an important role in the transportation of the dust in the mine air and human respiratory systems. Though the particles of a size less than 10 microns could be inhaled, the real distractive portion of the dust is that the sizes range from 1 to 5 microns since only they can reach the lungs and be retained there. Those with an equivalent diameter larger than 5 microns will settle on the membranes of the branchial tubes(1) while those with diameter less than 1 micron can either be exhaled out of the lungs or the settled quantity is so insignificant that does very little harm to the lungs. In the transportation process, the finer dust will fly farther away from the sources than the coarser ones. Thus once the fine dust is generated and becomes airborne, it will spread out to a larger area.In this paper, the coal samples collected from two longwall faces were analyzed statistically for size distribu¬tion. A mathematical model is proposed and the effects of different conditions on the dust size distribution were analyzed using the mathematical model.Sampling and Statistical AnalysesSampling Instrument and ProcedureThe instrument used in the sampling were Mine Safety Appliance (MSA) personal sampling units equipped with 10-mm nylon cyclones, pre-weighed MSA PVC filters and constant-flow pumps.Two longwall operating faces were selected for the dust sampling. The two faces were located in two coal mines ex-tracting Pittsburgh seam. The double-ended ranging-drum shearer applying the unidirectional cutting sequence was employed. The two-leg shield supports were used for face support. The width of the two faces was about 215 meters.In each of the two faces, four sampling stations were set up. The stations were located at the cross-cut immediately outby the headentry side, the 15th support (25 m), 65th support (107 m) and 111th support (182 m) from headentry T-junction, and numbered as #1, #2, #3, and #4 station, respectively (Figure 1). At each sampling station, a group of three sampling units was hung at proper position. At cross¬cut (#1) station, the units were hung about one foot under the roofline in the center of the cut (Figure 2a), and at the stations in the face, the units were position near the hydraulic legs and one foot below the support canopy (Figure 2b).One complete set of 12 samples was collected for each day. The sampling were performed for five consecutive days. All the samplings were conducted in the morning shifts. The time duration of the sampling for each day was about five hours. During that time, the shearer might complete 5 to 7 mining cycles."

Mar 1, 1989

By M. Kataoka, Y. Obara

It is known that compressive strength and tensile strength of rocks vary significantly with specimen size. Rocks are composed of crystals and grains in a fabric that includes flaws such as microcracks, grain boundaries and pores. As the likelihood of including severer flaws becomes greater for a larger specimen, the strengths are small. On the other hand, the size effect in the fracture toughness of rocks has not been made clear until now because there are few studies focused on it. In this paper, Semi- Circular Bend (SCB) test was performed using Kimachi sandstone with various specimen sizes. A shape of the specimen is a semi-circular disc with an artificial notch. The specimens were prepared with various thickness t and radius r as the following two groups; t was changed from 10 to 37.5 mm with r = 37.5 mm in the specimen of group (a), and r was changed from 12.5 to 150 mm with t/r = 0.8 in the specimen of group (b). As a result, there was no significant change in the fracture toughness with different t. On the other hand, the fracture toughness increased with increasing r and converged on a certain constant value in a range larger than approximately 70 mm of r. Consequently it was clear that the size effect in the fracture toughness of the sandstone exists.

Jan 1, 2015

By Y. -H. Chang, Y. -J. Jou, T. -S. Ueng, I. -H. Peng

In order to systematically study the size effect on the shear strength of rock joints, this study used the computer-aided-manufacturing system to reproduce the artificial rock joints for saw-toothed joints, Barton's standard joint profiles of JRC = 4~6 and 18~20, and natural rock joint profiles. We divided, enlarged, reduced, and assembled these joint profiles to obtain joint specimens of various sizes ranging from 75 mm to 300 mm in length. The shear strengths of these joint specimens were tested under different normal stresses using a direct shear test apparatus. The surface conditions of the joints at failure were also examined. The size and geometry effects on the shear strengths of these joints of various sizes and configurations were evaluated based on the test results. Um die künstlichen Trennflächen für reguläre dreieckige Trennflächen, Bartonsche standardmäßige Querschnitte der Trennflächen von JRC = 4~6 und 18~20 und natürliche Querschnitte von Trennflächen wiederherzustellen, benutzt diese Forschungsarbeit das Computergestützte-Erstellungssystem, damit die Maßstabswirkung auf die Scherfestigkeit von Trennflächen systematisch untersucht werden kann. Die Querschnitte werden geteilt, vergrößert, verkleinert und zusammengesetzt, um Trennflächenproben in Längen variierend von 75 mm bis 300 mm zu erhalten. Die Scherfestigkeit dieser Trennflächenproben wird unter unterschiedlichen Normalspannungen mit einem Direktscherversuchsgerät getestet. Die Querschnittszustände der Trennflächen bei Versagen werden ebenfalls untersucht. Nach den Untersuchungsergebnissen werden die Maßstabs- und Geometriewirkung auf die Scherfestigkeit dieser Trennflächen verschiedener Größen und Konfigurationen ausgewertet. Pour étudier systématiquement l’effet de la dimension des fractures des roches sur leur résistance au cisaillement un système de creation de fractures artificielles à l’ordinateur a été employé. Des fractures artificielles triangulaires, profils de fractures de Barton avec JRC = 4~6 et 18~20, et profils de fractures naturelles ont été reproduits. Les profils des fractures ont été arrangés de manière à obtenir des échantillons de longueur entre 75 et 300 mm. Une boîte de cisaillement a été utilisée pour étudier la résistance des fractures au cisaillement, sous plusieurs conditions de contraintes normales. Les conditions superficielles des fractures après rupture ont été étudiées. Les résultats de ces essais, effectués sur plusieurs échantillons de dimensions et configurations variées, ont contribué à établir l’influence des dimensions et de la géométrie des fractures sur leur résistance au cisaillement.

Jan 1, 2003

By B. Andreaus

In spite of tremendous efforts in research and development of polymer electrolyte fuel cells (PEFCs), essential properties of the actual catalyst material, supported Pt or Pt-alloy nanoparticles, are not yet well understood. Fundamental understanding of the catalyst structure and the prevailing kinetic mechanisms is, however, of utmost importance for further progress. In the present study, we investigate catalyst activity for CO oxidation from a theoretical point of view. Electrochemical CO oxidation serves as an important test reaction for the study of the fundamental properties of supported Pt nanoparticles. Recent experiments have revealed strong effects of catalyst particle size and supporting material on catalytic activity. It was found, that the activity towards CO oxidation decreases significantly when the particle diameter drops below 2.5 nm. We perform kinetic Monte Carlo simulations of CO oxidation on supported catalyst particles to elucidate this particle-size effect. The simulations are based on the active site concept, highlighting the role of active site formation and finite surface mobility of adsorbed electroactive species for catalyst activity. For comparison with experimental results, potential step experiments were simulated. The Monte Carlo simulations consistently reproduce effects of particle size and electrode potential found experimentally. In comparison with our simulations, analytical mean field models and nucleation and growth models exhibit inferior agreement with experimental data. In summary, our findings support an oxidation mechanism via active site formation. The reason for the slow reaction kinetics on catalyst particles with diameters below 2.5 nm is a rather low CO surface diffusivity. The rates of active site formation, diffusion and CO oxidation via recombination with adsorbed OH can be determined from the simulations.

Jan 1, 2005

By W. Pietsch

For a number of reasons, solids entering and leaving facilities for the treatment of minerals are becoming increasingly finer. Such materials pose problems throughout processing. Solids featuring small particle sizes tend to dusting, result in losses and segregation, exhibit various storage, transportation, and metering problems, and fine particulate effluents can not be easily captured, used and/or recycled. Sustainable mineral processing must minimize the exploitation of natural resources and avoid the need for disposal of wastes. The first requires the use of lower quality raw materials and upgrading, which typically results in the production of fine grained concentrates, and the latter encourages the recycling of wastes and byproducts or efforts to investigate them as sources for secondary raw materials or other beneficial applications. To overcome the difficulties associated with fine particulate solids, size enlargement by agglomeration is necessary. The resulting products have free flow characteristics, do no longer dust or segregate, and are sized and shaped as required for optimum processing. In addition, agglomerated materials may be engineered to feature desirable structure, composition, and a number of related, improved properties. Such engineering may be applied for the modification of fine run-of-mine and up-graded minerals as well as the production of secondary raw materials from by-products or wastes. By the interdisciplinary application of size enlargement by agglomeration waste-free processing of minerals becomes feasible.

Jan 1, 2004

By Thomas Palangio, Lyall Workman, Jack Eloranta, Tom C. Palangio

The fragmentation distribution of the blasted ore is an important descriptor of blasting results. Traditionally it has been hard to measure quantitatively. Developments in image analysis over several years makes it more feasible to measure fragmentation before crushing on a continuous basis. Post crushing, mill feed distributions can also be measured.

Jan 1, 2007

This paper presents an analysis of the production data for the period 1861 - 1953 from hydrothermal gold-silver deposits of the Hauraki Goldfield. To directly compare the metal content of the deposits a figure of ounces of gold equivalents (oz gold equivalent) is calculated from the value of the gold-silver bullion produced from each deposit. Frequency distributions for ore tonnage and oz gold equiv. appear to be lognormal and show a high proportion of very small deposits, with 90 per cent less than 100 000 tonnes. The deposits when plotted in order of size fall roughly on a smooth curve which suggests that the size distribution is not random. A large proportion (68 per cent) of the total gold-silver extracted from the Hauraki district was contained in the largest deposit û Waihi. A technique used for predicting undiscovered mineral resources is ZipfÆs law, which relates the size of an item to its rank order. The figures for ounce gold equivalents from the major Hauraki deposits fit ZipfÆs law remarkably well. Taking Waihi at 6.8 million oz gold equivalent as the rank one deposit, Thames is number five and Karangahake number seven. A Zipf plot indicates that down to rank 100 (68 000 oz gold equivalent) only 28 per cent of the total gold-silver resource in the Hauraki Goldfield has been extracted. A further 72 per cent or 25.4 million oz gold equivalent, including the deposits of rank 2, 3, 4, 6, 8, 9 and 10, are undiscovered. However, since some deposits will be deeply buried under younger rocks and others will be under the sea only a proportion of the total resource will be discoverable.

Jan 1, 1981

By A. Kar, J. Mazumder

"Laser ablation is a process that can be used to synthesize novel nanoscale particles as well as to deposit thin films of various materials. Usually, nanoscale particles and thin films are formed at relatively high and low pressures, respectively, inside the ablation chamber. This paper presents a mathematical model to predict the particle size distribution in the plasma generated during laser ablation. The model is developed by considering the effects of the laser-matter and laser-plasma interactions, the Stefan condition, and the discontinuity across the Knudsen layer. The nanoscale particles are found to be located at the central region of the plasma near the target. The particles have very high velocity and temperature. A good qualitative agreement is observed between the results of this model and experimental data. IntroductionRapid solidification produces novel microstructures whose atomic arrangements and/or chemical compositions are different from those of conventional materials. The conventional materials are either crystalline or amorphous. The crystalline materials have both short- and long-range orders, whereas the amorphous materials have only the shortrange order. The nanocrystalline materials have neither short- nor long-range orders, and for this reason, they exhibit novel properties which are important for synthesizing new materials. The atoms of a nanocrystal can be classified as ""crystal atoms"" and ""boundary atoms"", where the ""crystal atoms"" have the nearest-neighbor configurations similar to the lattice configuration, whereas the nearest-neighbor configurations of the ""boundary atoms"" differ from the lattice configurations 1. Various aspects of the nanoscale materials have been discussed in Refs. [1-7]."

Jan 1, 1994

By J. P. Matoney

In recent years, the diminishing supply of natural gas has led energy suppliers and consumers to consider making synthetic natural gas from coal. A number of processes have been devised to produce gas from coal; many of these have been operated at the pilot stage and some have been operated commercially. Each process has specific coal feed stock requirements with respect to size consist and moisture content. The purpose of this presentation is to compare the estimated costs for coal handling, live storage, size reduction and drying facilities that would be required for delivery of coal feedstock to different gasification processes.

Jan 1, 1977

By Leonard G. Austin

INTRODUCTION Run-of-mine (ROM) coal generally falls into two major groups: that from underground mining (continuous mining machines) and that from strip mining. Continuous miners produce a finer product and strip mining a coarser product that is crushed to produce the desired size. Further size reduction depends on the proposed use or uses for the coal. For example, for pulverized coal power plants as a rough general rule, the coal is ground or pulverized to 80% less than 200 mesh (0.075 mm) before it is blown into the boiler furnace as a coal-air suspension. For solvent-refined coal processes, the desired size is about <30 mesh (< 0.60 mm); in fluidized bed uses, the coal is typically < 8, in. (< 1.6 mm); for Lurgi pressure gasifiers, the desired size is 1 to 2% in. (25 to 63 mm). Coal preparation plants typically work with a coarse size fraction of 6X 1/14 in. (150X32 mm). The past decades has shown a steady increase in the tonnage of coal cleaned, 1 but it seems probable that the next decades will produce much wider applica- tion of deep coal cleaning before use and that the stages of crushing and pulverization from ROM coal to end use will be integrated with coal cleaning processes. Since different cleaning processes work better with different ranges of coal size and the degree of cleaning possible is intimately connected with the size of coal, a systems design engineer will need as much information as possible concerning the size distributions produced by different types of machines and how these can be modified by different ways of operating the machines. In general, the following questions will be of concern: 1.What type of crusher or grinder is best, or most satisfactory, for reducing a given feed size and type of coal to a desired product size? Frequently, the desired product is smaller than some nominal size, but with as few fines as possible, or the fraction in some size range has to be as high as possible. 2. How big does the machine have to be for a given throughput rate? 3. How much electrical energy (or its equivalent) is required per ton of product? 4. How does the size distribution vary with change in throughput rate, and is a control scheme necessary or desirable? 5. Can the size distribution be readily varied if desired? 6. What is the optimum way to operate a machine in a given system? This section will emphasize certain general principles which guide us in answering these questions. PARTICLE SIZING Since particle size and size distribution are the raw information with which we work, it is worthwhile to review the terminology used. In this regard, see

Jan 1, 1991

By Alec G. Richardson, S. H. Chiang, Ralph W. Lai, McMahan L. Gray

The potential of coal cleaning by selective agglomeration was examined for a Pittsburgh seam bituminous coal using isooctane as an agglomerating liquid. The effects of particle size, pH, degree of mixing, and dosage of isooctane on the pyrite and mineral matter removal from finely ground coals were investigated. The role of shear-enhanced-hydrophobic-association in the flocculation of fine particles was examined. The degree of liberation of pyrite from coal at different grinds was examined using an automated petrographic image analyzer. The effect of dispersant on slurry rheology during grinding was studied. The results indicate that over 95 percent of the pyritic sulfur can be removed from the coal. Final products containing less than 0.9 percent ash at a combustible recovery in excess of 90 percent have been obtained with multiple stages of cleaning.

Jan 1, 1989

By Joseph D. McClung, L. G. Austin

INTRODUCTION Run-of-mine (ROM) coal generally falls into two major groups, that from underground mining (continuous mining machines) and that from strip mining. Continuous miners produce a finer product and strip mining a coarser product that is crushed to produce the desired size. Further size reduction depends on the proposed use or uses for the coal. For example, for pulverized coal power plants as a rough general rule, the coal is ground or pulverized to 80% less than 200 mesh (0.075 mrn) before it is blown into the boiler furnace as a coal-air suspension. For solvent-refined coal processes, the desired size is about <30 mesh ( <0.60 mm) ; in fluidized bed uses, the coal is typically < in. ( < 1.6 mm); for Lurgi pressure gasifiers, the desired size is 1-2 1/2 in. (25-63 mm). Coal preparation plants typically work with a coarse size fraction of 6x1 1/4 in. (15Ox32mm). It seems probable that the next decades will see much wider application of coal cleaning before use and that the stages of crushing and pulverization from ROM coal to end use will be integrated with coal cleaning processes. Since different cleaning processes work better with different ranges of coal size and the degree of cleaning possible is inti-

Jan 1, 1979