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By K. A. Lewandowski

Heap leaching efficiency is reduced by poor solution flow characteristics (channeling and ponding), which result from compaction and fines migration. Agglomeration of the ore can prevent compaction and immobilize fines, but copper leaching requires an acid-resistant binder to stabilize the agglomerates. Until now, there has not been a satisfactory way to evaluate whether a binder was effective, other than squeezing a handful to see if it ?feels right.? Procedures have been developed to quantitatively determine whether a binder produces agglomerates that can withstand compaction in an acidic solution, and have identified several binders that will provide sufficiently compaction-resistant agglomerates for copper heap leaching. Keywords: Copper heap leaching, Binder performance, Compaction

Jan 1, 2010

By R. L. Levens

Researchers at the U. S. Bureau of Mines conducted investigations to evaluate the potential for ground water contamination by mine waste used as backfill. Samples of cemented waste backfill and water discharging from drillholes and seeps were collected to use in chemical analyses and laboratory tests to determine the physical and chemical factors that control release of heavy metals to ground water. Greater water retention by cemented backfill (as compared to uncemented sandfill) reduces the surface area exposed to oxidation, which in turn reduces the amount of acid produced. The acid is neutralized by the cement and minerals contained in the backfill. The grain-size distribution of tailings used for backfill affects the structural integrity of cemented backfill under attack by acidic water; breakdown of the backfill structure releases neutralizing materials faster. Backfilled stopes in rock with low hydraulic conductivities will constitute preferential flow paths after mine flooding; however, the rate of flow through backfill will be much slower than when the stope is partially saturated during mine operation. Considering all factors, acid generation and release of metal ions from cemented backfill should be less than in uncemented sandfill.

Jan 1, 2010

By B. Seymour

The National Institute for Occupational Safety and Health (NIOSH) is conducting research to develop safe practices for the use of shotcrete as ground support in underground mines, particularly mines operating in weak host rock. As part of this research, tests were conducted with a commercial poly-fiber reinforced shotcrete mix to develop a practical means of measuring shotcrete adhesion strength. Full-scale tests were conducted in a test frame equipped with concrete panels having three distinct surface roughness profiles. Adhesion test fixtures either embedded or epoxied in the shotcrete were overcored into the underlying concrete, and direct tensile tests were conducted to determine the bond strength of the shotcrete cores to the substrate after a selected shotcrete curing interval (1, 3, 7, 14, 28, or 90 days). Measured adhesion strengths typically ranged from 0.5 to 2.0 MPa depending on the curing age of the shotcrete samples. This paper presents the results of these tests, describes the portable test system components, and addresses some of the design issues encountered in the development of a rugged and reliable method for determining shotcrete adhesion strength in underground mines.

Jan 1, 2010

By P. L. Sibrell

Previous research by the U.S. Bureau of Mines has shown that autoclave cyanide leaching of used automobile exhaust catalysts for recovery of platinum-group metals (PGM) is technically feasible. The purpose of this work was to investigate the chemistry of the dissolution of PGM in cyanide solutions in more detail. Where possible, samples of pure, elemental PGM powders or foils were used instead of automobile exhaust catalysts, because of their greater purity. Ultraviolet spectra revealed that Pt and Pd were solubilized as the square planar tetracyanometallate (II) complexes, while Rh was solubilized as the octahedral hexacyanorhodate (III) complex. This explained the poor recovery of Rh from solution by carbon adsorption, solvent extraction, and ion exchange observed in earlier research, because of the higher anionic charge and size of the octahedral complex. Leaching rate studies showed that the rate of solubilization was greatest for Pd, followed by Pt and Rh. Although the rate of chemical reaction was the controlling step for the dissolution of elemental Pt and Rh samples, the rate of pore diffusion was rate limiting for PGM in catalyst samples.

Jan 1, 2010

By Jim Sadowski, Steve Stewart, Bob McMurdy, Martin Nevens

"Mohawk Garnet has been operating a small pilot plant near Sudbury, Ontario for several years attempting to produce commercially viable garnet. The challenges of operating a pilot scale mining, processing, and product handling operation as a full time plant have led Mohawk Garnet to seek a better way. In co-operation with Mohawk Garnet, Outotec (USA) Inc. has taken on the technical and design challenges of increasing garnet product from twenty tonnes per day to two hundred tonnes per day.Outotec performed a comprehensive test and flowsheet development program applying Outotec’s density separators, spirals, flotation, and other technologies to design a successful process for the separation and recovery of the valuable garnet for Mohawk.This paper explores the test program, the process flowsheet development work, plant design and preliminary engineering of a new garnet processing. The various technical challenges, process technologies involved, and design concepts will be discussed.INTRODUCTIONMohawk garnet has been operating a small-scale garnet mine and process plant in Wahnapitae, Ontario near Sudbury.The current operation was intended to be a pilot plant and so only produces 20-25 tonnes of garnet concentrate per day. The garnet is bagged and sold for use as abrasive. The process is inefficient with low yields, poor material handling and very high cost per tonne. Mohawk garnet approached Outotec to help them improve their garnet process and transform themselves into a larger scale and more efficient operation."

Jan 1, 2010

By P. C. McWilliams

Researchers at the U.S. Bureau of Mines investigated the use of close-range photogrammetry and subsequent stereo digitizing to obtain data from rock fracture roughness profiles. The photogrammetric process yielded results that were acceptable but somewhat inferior to those obtained by a mechanical profilometer. On the basis of this study, further pursuit of photogrammetry as a data collection method in mining is proposed. Fractal geometry was investigated as a means of measuring the roughness of rock fracture profiles. Four fractal algorithms were used: divider method, modified divider method, box method, and spectral method. A comparison of the methods gave ambiguous results. Brown's modified divider method provided the best means of obtaining the fractal dimension. Shear strength estimates were obtained using the parameters of the modified divider method and Myers' Z2 measure. Because of differences in results when comparing the different ways of obtaining the fractal dimension, future users of fractals in studies of rock fractures are advised to cross-check their results carefully.

Jan 1, 2010

By Charles Vaught

The U.S. Bureau of Mines evaluated the self-contained self-rescuer (SCSR) donning proficiency of 243 miners. These workers were from eight underground coal mines in the eastern United States. The objectives of the study were (1) to gather information on skill levels, since all miners in the study had prior instruction and opportunity to practice donning the apparatus, and (2) to summarize a quality control procedure useful in conducting periodic evaluations of donning proficiency. The sampling procedure used proved to be both reasonable and efficient in gathering information on training effectiveness. It also provided a good statistical base for making informed site-specific decisions regarding SCSR training needs. Results from the observed samples at each of the eight mines indicate a wide variability across sites. The rate at which miners failed to isolate their lungs varied from 3.3 to 40.0 pet. Concomitantly, proficiency rates (miners either performing adequately or demonstrating a perfect 3 + 3 sequence) ranged from 13.3 to 63.3 pet.

Jan 1, 2010

By Raj Thamburaj

"Over the last few decades, the emphasis on affordability and reduced cost of ownership has necessitated the development of innovative processes to carry out repairs in aero engine components. Conventional weld and braze repairs have evolved into advanced, sophisticated processes using state of the art knowledge in lasers, robotics and materials technology. This paper illustrates past and present scenarios in an attempt to illustrate progress that has been made in this area. The problems encountered in the past have been detailed along with the solutions that have been developed and commercially implemented to address these issues. Apart from technical progress, this presentation also addresses the progress made in business approaches and in Certification/Regulatory issues surrounding aero engine repair. Progress in Technology Repair technologies have also been the embryo from which new and revolutionary manufacturing technologies have evolved as well. Electron Beam Free Forming and LENS are examples of how a completely new manufacturing concept can evolve what was originally only a process to join metals. The current and future potential of these spin offs is discussed providing examples of application. While several problems have been solved over time with the implementation of advanced repair technologies, the demands of the industry have created new challenges. The paper describes these issues, outlines potential solutions and discusses the future of repair technologies in terms of the far reaching influence it is sure to have in design, manufacturing, maintenance management and life extension. Progress in Business Trends.Business approaches to repair and maintenance have also gone through considerable change with the introduction of ""Power by the Hour"" and other similar arrangements between the companies responsible for engine overhaul and the end-users. Program Based Logistics (PBL) is yet another innovation to provide a win-win situation for the repair service provider and the end user. This paper traces the development of these business initiatives and highlights successful applications. Progress in Repair Certification, Regulatory Issues.Understanding of the issues surrounding certification of repairs has also evolved with time and regulatory issues have been clarified considerably. Procedures for analysis and testing are much clearer and ""Check Lists"" are being drafted for certifying repairs on various engine components. The PMA phenomenon has added yet another dimension to the issues regarding certification and these are discussed as well."

Jan 1, 2010

By A. E. Petersen

To reduce U.S. dependence on imports of titanium, the U.S. Bureau of Mines has investigated the recovery of titanium from perovskite (CaTi03). Domestic perovskite deposits represent a significant, but untapped, titanium resource. An acid sulfation method was developed that will extract about 97 pct of the titanium and the columbium and 70 to 90 pct of the rare-earth byproducts from perovskite concentrates. A flow-sheet for recovering titanium as pigment-grade titanium dioxide (Ti02) is discussed. Test work performed in developing each unit operation is described. The first three unit operations have been demonstrated using laboratory-scale continuous methods of operation: acid sulfation of perovskite concentrates, leaching sulfation residue to dissolve metal values, and precipitation of titanium oxysulfate monohydrate (TiOS04?HP) from the resulting leach flltrate. Batch testing of other unit operations was performed: TiOS04?H20 redissolution and iron reduction, precipitation of Ti02 by hydrolysis, and regenerating recoverable acid with rare-earth byproduct recovery. Cost evaluation results are provided, indicating that processing perovskite concentrates by acid sulfation may be an economically viable means of producing Ti02.

Jan 1, 2010

By Tad Crowie, Victor Delgado, Nick Katsikaros, Tim Hughes

"A number of silver producers have identified a need for a system to recover silver and gold from base metal flotation concentrates on site rather than sending the concentrate to third party smelters to improve mine economics. Historically intensive cyanidation has only been used for coarse gold gravity concentrates in batch machines but Gekko have applied the InLine Leach Reactor (ILR) to these difficult to leach concentrates.The ILR’s unique ability to operate at various solid to solution ratios, high mass capacity, the ability to handle fines, the use of peroxide to aid silver leach kinetics and simple operation has resulted in significant economic benefits to Hochschild PLC’s Selene and Arcata operations. This paper describes the commissioning phase of the ILR5000BA intensive cyanidation reactors on concentrates from the Selene mine at the Ares Concentrator.INTRODUCTIONIntensive leaching of high grade concentrates in gold ore treatment is now commonplace and is considered an essential feature of most gold circuits (Lane, Fountain and LeBrooy, 2008). The devices commonly used for intensive leaching (InLine Leach Reactor, Acacia Reactor, etc) are specifically designed for the typical coarse nature of the concentrate.In some of these intensive leach applications, significant amounts of silver are co-recovered with the gold. In fact, the intensive leaching conditions of 1 to 2% NaCN in solution and high dissolved oxygen levels, overcome the issue with silver’s slow dissolution rate in traditional CIL/CIP circuits and avoids the formation of insoluble silver sulphide minerals on the surface of the gold (Marsden, 2006).There are a significant number of mine operators producing silver in the form of mixed base metal sulphides flotation concentrates. Typically the mine operators are paid for the silver after processing of the concentrate by the base metal smelter whom recovers the silver during the refining process."

Jan 1, 2010

By A. L. Martikainen

Booster fans increase air pressure to overcome resistance, the objective being to force adequate amounts of air through distant workings. They are used in areas that are difficult or uneconomic to ventilate with main fans alone. Booster fans are currently permitted in underground coal mines in some countries; the United Kingdom, South Africa, Australia and Canada have been defined as major users. Booster fans are not allowed in the US bituminous and lignite coal mining operations at the present time due to safety concerns. This paper presents the history of booster fan use in coal mines of the United States during the last 90 years. Changes in regulations, as well as advantages and disadvantages of booster fan use, are discussed. Research and petitions for booster fan use are highlighted in order to bring the debate into focus.

Jan 1, 2010

By Tatiana Ravani von Ow, Leandro Bomvisinho

"The size of mills driven by ring-gear or by a gearless solution has significantly increased in the last years. This has created additional challenges for the driven equipment. The requirements for the mechanical devices and the power grid have become more demanding. Controlled soft starting and operation, especially in dual pinion mills, as well as the protection of the equipment has gained importance. The selection of the drive solution for the mill therefore becomes more critical. Besides the classical criteria such as performance, efficiency and capital costs other factors come in the evaluation of the system such as flexibility and optimization of operation, reliability and the ageing of the grinding equipment.Variable speed solutions offer significant advantages over conventional fixed speed drives due to their application specific features and process optimization capabilities, even for ball mills where these are not seen yet as a must.The initial capital costs are higher than some of the direct on-line solutions however the benefits for the operation during the lifetime of the mill generated by the use of converter solutions justify the additional higher investment.INTRODUCTIONThe method of powering mills such as AG, SAG and Ball has a long and technically interesting history. It can be said; almost every decade in the last half century had its own trend. The trend was dominated by the market demand, by the process development and requirement of the mechanical and the electrical technology but mostly by the price of the applied technology.All has started about 50 years ago with mill diameters less than 20 feet driven by fix speed synchronous or wound rotor motors with the power of about 2 MW. Around 10 years later, the mill sizes increased, but the necessary torque could not be transmitted by one pinion therefore dual pinion solutions were developed to power the mills. However, realization of the dual pinion solution was only possible when load could be evenly shared between the two pinions."

Jan 1, 2010

By Meghan McGrath

Third generation advance high strength steels with microstructures of acicular ferrite and retained austenite were investigated and meet mechanical property goals. A good combination of strength and ductility were achieved with duplex ferrite and austenite microstructures where cementite formation was suppressed. Transformation induced plasticity (TRIP) behavior produced rapid work hardening. The mechanical properties of two hot-rolled steels with duplex microstructures were compared and had the following compositions: (1) Fe-0.14C-13.87Mn-1.42Si-3.51Al; and (2) Fe-0.06C-14.2Mn-1.85Si-2.38Al. These steels were cast, homogenized, and hot rolled at 900ºC to obtain a refined microstructure with ultimate tensile strengths and elongations to failure of 865 MPa and 39% and 1,217 MPa and 28%, respectively. The amount of metastable austenite in both compositions decreased after tensile testing from 58% and 28% to 6% and 0%, respectively. Microstructures were characterized using optical microscopy, scanning electron microscopy (SEM), and x-ray diffraction.

Jan 1, 2010

By H. W. Kilau

The U.S. Bureau of Mines is evaluating water spray additives for the purpose of improving respirable dust control during coal mining operations, with particular emphasis on the longwall shearer. Recent field tests of surfactant-polymer reagents at two production longwall operations have shown favorable respirable dust reductions compared with water sprays containing no additive. Gravimetric dust samples obtained by a technician downwind of the shearer while following or preceding the machine showed dust reductions in the range of about 40% to 60% for some of the reagent formulations compared with using water alone. Three polymers were tested: two polyethylene oxide compounds of different molecular weight and hydroxypropyl methylcellulose (HPMC). All were effective for dust reduction, and two were cost effective when used in combination with sodium di(2-ethylhexyl) sulfosuccinate surfactant. How-ever, the use of these reagents requires the longwall operator to be more aware of headgate dust control. Experimental evidence indicates that dust captured by reagent-treated sprays at the shearer can be reemitted in the headgate area if stagcloader-crusher sprays and other dust controls are inadequate.

Jan 1, 2010

When science and the human spirit come together amazing things can happen. This was perhaps never more evident than through the events that unfolded during August and October in a remote desert in northern Chile. On Aug. 5, the main shaft of the San José copper and gold mine near Copiapó in Chile?s Atacama Region collapsed, leaving 33 miners trapped more than 624 m (2,000 ft) beneath the earth?s surface.

Jan 1, 2010

By Dennis Dolinar

"Tailgate entries in U.S. longwalls can be subjected to high loads and deformations. Therefore, tailgate entries are generally supported with varying types and amounts of standing support. However, even with standing support, roof falls and blockages can occur in the tailgate when the support system is not properly designed. Safe and efficient operation of a longwall face requires the selection of the appropriate type and amount of standing support. Because of the importance of maintaining a safe and functional tailgate entry, the National Institute for Occupational Safety and Health (NIOSH) is currently developing a standing support design methodology based on the ground reaction curve. Using the ground reaction curve for design requires that the ground and support interaction be quantified. This can be accomplished by the installation and analysis of data from instrumented field sites. Although necessary, the field results cannot develop the complete ground reaction curve. Numerical models, calibrated to the field results, are used to establish the complete ground reaction curve. In the present study, data was obtained and evaluated to establish points for calibration of the ground reaction curve for two western longwall operations.One test site, Mine A, was located at a depth of 1,550 ft. At this site, the floor consisted of siltstone, while the roof was an interbedded siltstone and sandstone. Because of the depth, a double row of22-in diameter CANs1 were installed to support the tailgate. Both the first and second longwall panels have mined past the instrumented site.The second site in Mine B is at a depth of only 760 ft. The floor at this mine consists of a weak shale/mudstone and the roof consists of thick, top coal overlain by weak shales. At this site, a double row of pumpable cementitious cribs was installed. The second test site has only been subjected to side abutment loading from first panel longwall mining.The measurements indicate that the support at both mines was heavily loaded when subjected to the side abutment loading from first panel mining. At the deeper site, the support began to yield when the face was more than 300 ft outby during second panel mining. In comparison to results from previous test sites in the Pittsburgh Seam and Illinois Basin, the amount of support loading and roof-to-floor convergence was an order of magnitude higher at the western sites. This has resulted in a significant difference in the position and shape of the ground reaction curves."

Jan 1, 2010

By Dale Preece, Joergen Pilz, Zavis Zavodni

An overland conveyor was constructed at a surface coal mine to reduce the truck haul distance and make the operation more efficient. An important element in this system is a truck dump facility to transfer coal from truck to conveyor. Mechanically stabilized earth retaining walls were employed to accommodate the coal processing equipment, including the crusher, in this facility. These retaining walls are close enough to the pits being mined that blasting induced vibrations must be considered in analyses of the wall structural stability.

Jan 1, 2010

By S. F. Diehl

Suites of monomineralic sulfide and carbonate minerals, as well as mine-waste composite samples, were analyzed using chemical and microanalytical techniques to understand behavior and bioavailability of mine waste elements such as Cu, Fe, Pb, or Zn. Petrographic, scanning electron microscopy (SEM), and laser-ablation inductively-coupled mass spectrometry (LA-ICP-MS) studies of mineralogical residence sites of trace elements are important because trace elements affect the chemical and physical behavior of minerals. Leachate solutions show that chalcopyrite, bornite, azurite, malachite, and galena are host to the trace elements Ag, Al, As, Cd, Co, Cr, Mn, Ni, Pb, and Zn. SEM studies reveal whether these trace elements occur within mineral inclusions or are substituted within lattice structures. SEM analysis reveals mineral phases not identified by X-ray diffraction (XRD), such as inclusions of sphalerite and cobaltite(?) within chalcopyrite.

Jan 1, 2010

By B. W. Moore

The U.S. Bureau of Mines investigated the separation of heavy rare-earth elements (REE) in an ion-exchange process. An ion-exchange column consisting of two sections, a loading section and a separation section, provides high levels of REE loading and good REE separation with an expected processing cycle of less than a month, while current ion-exchange technology requires more than 5 months. A different resin is used in each section: sulfonic resin in the loading section and iminodiacetic resin in the separation section. The separation section is further divided into two segments: the first conditioned with NH4 and the second with acid. Erbium is loaded onto both segments of the separation column as a retaining ion. Bands of mixed REB eluting between separated bands of pure REB were recycled directly to the column. Without mixed-band recycle, over 80% of the REE eluted from the column was separated into fractions with 99% purity of each element; with such recycle, the percentage of separated elements can be increased to around 90%.

Jan 1, 2010

By E. T. Pecina

Bioleaching is a viable option for the processing of auriargentiferous refractory ores with high arsenic content. The application of mesophilic (A. ferrooxidans and ?L. ferrooxidans?) and thermophilic bacteria of the genus Sulfolobus (S. solfataricus and S. acidocaldarius) as oxidant treatment before the cyanidation of an industrial arsenical pyrite concentrate is presented. The results show that extraction of gold and silver increases due to bio-oxidation caused by mesophilic bacteria and results in a maximum gold recovery of 68%. In all strains studied, biooxidation resulted in an average silver recovery of 50%. The results showed that all evaluated strains were sensitive to solids content (5 to 20%) and average particle size (75 and 38 µm) of the concentrate.

Jan 1, 2010