Search Documents

By T. Mulpeter, G. Deschênes

Sadiola Gold Mine is an open pit operation located in Mali and owned by Anglogold Ashanti Ltd, Iamgold Corporation and the State of Mali. A conventional cyanidation process (cyanidation/CIP) treats 15,000 tpd (of a mixture of oxide and sulphide ores) at an average grade of 3 g/t Au. In 2002, the increasing tonnage of sulphides caused an increase in production costs and a decrease in gold extraction (from 95% to 70-76%). Because of the short retention time of the leach circuit (18 hours) and the refractory nature of the sulphides, gold leaching kinetics are critical. A laboratory investigation was initiated to evaluate actual plant practice and identify a means of improving the gold leaching rate. The study was conducted on a "soft" sulphide gold sample containing 4.96 g/t Au, 0.4 g/t Ag, 2.5% pyrite, 1.2% arsenopyrite, and 0.2% pyrrhotite with a P80 of 74microns. Pre-leaching significantly influenced the gold leaching rate. A short pre-leach (2 hours) performed at pH 8, a DO of 8 ppm, and with 300 g/t lead nitrate added at the start or the end, produced the preferred conditions. Pre-leaching for more than 2 hours was detrimental to gold extraction. The cyanide concentration had to be maintained at 450 ppm NaCN to reach a maximum gold extraction within the retention time of the circuit. A maximum extraction of 81.3% Au was obtained in 20 hours (leach residue at 0.97 g/t Au). A high level of dissolved oxygen in the pre-leach was not of any benefit. Extension of gold leaching beyond 20 hours indicated that all leachable gold had been extracted by that time. Plant modifications were made to allow leaching of oxides and sulphides in separate circuits. Treatment of oxide ores is now performed at a higher rate. Sulphides are processed at a lower throughput, with 300 g/t lead nitrate, to allow a retention time of 22 hours. Combined throughput remains the same, and total gold recovery has increased from 76% to 80% for an additional gold production of 16,000 ounces per year.

Jan 1, 2005

"The Waite-Amulet, an important copper-zinc mine, lies astride the Duprat-Dufresnoy township boundary about 8 miles northwest of Noranda, Quebec. It is an amalgamation of two properties, that of the former WaiteAckerman- Montgomery Mines to the north and that of Amulet Mines, Limited, to the south. This amalgamation took place in 1933. The description that follows is confined to the Amulet section.Ore was first discovered on the Amulet property in the autumn of 1924. The C Shaft and Upper A orebodies were found in 1925 and the F orebody in 1929, the latter by diamond drilling under a swamp. Under the present management, Lower A ore body was discovered by diamond drilling at a depth of 700 to 1,200 feet in 1938, and new ore was found from the old C Shaft workings between 1943 and 1945.From April 15th to October 20th, 1930, 60,291 tons of ore was produced from the Amulet. During the second half of this period, the ore averaged 4.2 per cent copper, 16.3 per cent zinc, and 0.02 oz. gold and 3.35 oz. silver per ton. Due to the prevailing low prices of metals, there was no further production until July, 1937. Output was greatly accelerated in 1940 when the newly found Lower A orebody assumed the main burden of production. Up to January 1st, 1946, mill reports indicate the treatment of the following ore: GENERAL GEOLOGYFig. 1 shows the geology of the entire property. To the east is the Lake Dufault granodiorite stock and to the west the Flavrian Lake granite mass. Around the granodiorite and separating the Waite from: the Amulet section is an older diorite intrusion. The ore occurs in a series of lavas that form a broad anticline pitching eastward at a relatively low angle into the Lake Dufault intrusives. There are several steep east-west faults. The late Powell diabase dyke is shown, also the general areas of strong dalmatianite alteration, a type closely associated with the sulphide mineralization."

Jan 1, 1954

By Nathan C. Rockwood

BASIC mineral commodities may be divided into two general classifications in their market or price characteristics. In one class are commodities sold on a world-wide basis, as gold, silver, nickel, asbestos and petroleum, and in the second are those produced and sold locally. Of course, no precise line of demarcation exists between the two; coal, for instance, belongs more or less in both. If there are enough producers of any commodity to prevent control of production by any one person or group, a free market then exists and the price in a buyer's market is determined by the most favored producer-meaning the producer, with the lowest production cost or the lowest cost of transportation, or both, to the particular market, or place of use. With minerals in the first classification, their high intrinsic value far outweighs the transportation cost and a uniform market price is accepted as an essential element in the economy of distribution. But with common minerals of small. intrinsic value and relatively high transportation costs, economists are reluctant to admit that a uniform price may also be an essential element in distribution.

Jan 1, 1940

By C. Musingwini, A. S. Nhleko

"Since the Global Financial Crisis (GFC) in mid-2008, capital has been more difficult to access. Mining projects must contend with projects from other industries for scarce capital. A decision to invest available capital in mineral projects requires that valuation be conducted to assess the expected return on the projects. The discounted cash flow (DCF) analysis is generally applied for the valuation of mining projects, whereby future cash flows are discounted to present value using an appropriate discount rate. The discount rate significantly affects the outcome of a valuation. Economic and finance theory provides tools to calculate discount rates. The discount rate must account for factors such as the risk and stage of development of the mineral project; hence the appropriate discount rate to utilize in a project is often a subject of debate.The discount rate is the weighted sum of the cost of debt and equity. There are several methods for determining the cost of equity. This study considers the commonly applied Capital Asset Pricing Model (CAPM) and Gordon’s Wealth Growth Model because of their simplicity and availability of parameters required to estimate the cost of equity. This study explores how differences in the cost of equity obtained by these two methods can be explained for a mining environment. Data for empirical analysis were collected from the I-Net Bridge, McGregor BFA, and Bloomberg databases. It was found that Gordon’s Wealth Growth Model provides better estimates of the cost of equity compared to the CAPM under depressed market conditions. Therefore, this research recommends that Gordon’s Wealth Growth Model be used to estimate the discount rates for mining projects during periods of depressed market conditions."

Jan 1, 2016

By G E. Smith, G N. Lye

Wall control blasting practices are necessary to reduce the impact of blasting on mine faces but can also have a significant negative impact on mine productivity and operating costs. The conventional practice in deep open pit mines is to use so-called trim blasts adjacent to pit walls. To provide burden relief these trim blasts have fewer rows than full production blasts and are fired to a cleared free-face; hence they are termed æunchokedÆ. This practice leads to scheduling constraints on the pit operations and can cause ore dilution due to excessive muckpile movement. The use of such trim blasts stems from the perception that increased wall damage results from æchokedÆ blasts. These concerns are based on the unproven assumptions that blast vibration levels and explosive gas penetration increase with increased blast burden and face confinement. This paper describes work undertaken as part of a major investigation into wall control blasting at the KCGM Fimiston Mine, Kalgoorlie, Western Australia. It details a study to assess damage effects due to blast burden. Borehole air pressure measurements and borehole video camera inspections were done behind a series of single blastholes drilled with varying burden distances, as well as behind a dedicated trim blast and a full production blast. It was found that the measured damage effects, including visible rock cracking, dilation, and the limited extent of gas penetration behind the blastholes, did not vary significantly with burden or blast type for the cases tested. This result was in complete agreement with detailed vibration measurements conducted by Blair and Armstrong (2001) during the study, which found that vibration was independent of blast burden. As a result of these investigations, changes to the blasting practices at the mine were implemented. Dedicated trim blasts and free-face blasting have been replaced by modified production blasts and the practice of æchokingÆ blasts has been introduced. This has resulted in a significant improvement in productivity and cost savings without compromising pit wall integrity.

Jan 1, 2001

By G. W. Luxbacher

This volume describes the use of the Penn State Mine Ventilation Simulator (PSU/MVS) to model existing mine ventilation systems and, in addition, to evaluate the effect of system modifications. Ventilation survey methods designed to insure computer input data of sufficient accuracy for simulation purposes are covered in comprehensive detail, including quantity and pressure measurement and fan performance testing. The development of input data from ventilation survey results is discussed and illustrated by the use of an actual field survey. Two programs, written in FORTRAN IV with WATFIV, are presented to calculate airway head losses from altimeter pressure measurements. An existing coal mine ventilation system is analyzed and modifications to the system are simulated and evaluated. In addition the application of the PSU/MVS to non-coal mines is briefly discussed. An extensive bibliography on ventilation surveying and simulation is included.

Jan 1, 1977

By Dale Berner, Michael O’Sullivan

"This paper focuses on lessons learned from the innovative designs, in-the-wet construction methodology and modified foundation conditions, for two United States Army Corps of Engineers, USACE, Megaprojects:(a) The over $2 Billion Olmsted Dam across the Ohio River for the Louisville District; and(b) The $1.75 Billion Inner Harbor Navigation Canal, IHNC, Lake Borgne Hurricane Barrier in New Orleans for the Hurricane Protection Office, and the New Orleans District.Design innovations for the 24-inch dia. pipe pile foundation for the Olmsted Dam project include: (i) the use of controlled-fixity moment connections to the dam monoliths in order to tune the response of the dam under the 8.3 Richter scale seismic Maximum Credible Event, MCE; (ii) soil densification to inhibit liquefaction potential and (iii) design to facilitate underwater construction in a river with a highly moveable sand bed.Design innovations for 66-inch dia. concrete cylinder piles for the IHNC floodwall include: (i) the use of soil structure interaction, SSI, analyses to verify capacity to resist deep-seated failure plane in soft soil, while limiting lateral deflections to acceptable limits; (ii) the use of geo-fabric and scour stone for enhanced foundation response and (iii) design for ""in-the-wet"" construction on a fast-track basis.LESSONS LEARNED FROM THE INNOVATIVE OLMSTED DAM FOUNDATIONThe over $2Billion Olmsted Dam on the Ohio River is currently under construction 16 miles upstream from the confluence with the Mississippi River. It will consist of an 800-foot-long tainter gate section, a 1,400-foot navigable pass, two boat abutment sections, a fixed weir section, and upstream and downstream scour protection. The Olmsted Dam and its two, 1,200-foot locks, which were built in 2002, will eventually replace both Locks and Dam #52 and #53, both built in 1929, and thereby bring significant benefits to the Ohio River navigation system.In 2002, the Jacobs/COWI JV completed the design of the dam; which was an engineering challenge for several reasons, including:(a) Its proximity to the New Madrid Fault, could impose an 8.4 Richter Scale seismic event on the structure, which is located in an area of potentially liquefiable alluvium. The extensive seismic analysis performed by COWI included a response spectra analyses; lateral pushover analyses of pile foundations; hydrodynamic added masses; pile group effects; and the development of kinematic motions as a result of the soil-pile-structure interaction.(b) Maintaining vessel traffic along the river and accommodating fluctuating river elevations between 30-40 ft annually, and as much as 60 ft in a 100-year period.(c) Designing for the scour and uplift forces of artesian ground water and preserving a wildlife sanctuary on the Southern shore at the dam site."

Jan 1, 2017

By Nicholas Bonderoff, Amily Xu

The evaluation of battery electric vehicles (BEVs) in underground mines involves comprehensive business case analysis beyond just the capital and operating costs of the equipment itself. BEVs demonstrate benefits from an EHS perspective, reduced mine ventilation costs, lower energy operating costs, reduced overall GHG emissions (dependent on the source of electricity), elimination of DPM, lower equipment maintenance costs, and reduced cooling requirements in deep mines. When including batteries and supporting infrastructure, BEV capital costs are approx. 80% greater than that of diesel equipment. The project economics are highly dependent on the cost of electricity and diesel fuel, and these can vary widely depending on the location of the mining operation. Battery charging and swapping methodologies must be evaluated as there are a variety of approaches that can be employed which vary by manufacturer and type of equipment. Careful consideration of the cycle times, charging methodologies, and location of the battery charging infrastructure is necessary. Specific operating conditions must also be taken into consideration. For example, the time for blast gases to clear will be increased by reducing ventilation flow, and the potential impact on production needs to be evaluated. Similarly, the electrical distribution system needs to be evaluated for peak loading conditions when BEVs are charging. Criteria including maintainability, reliability, commercial availability, and performance need to be evaluated. BEVs have fewer components than diesel equipment and this correlates to lower overall maintenance costs, however, BEVs require maintenance personnel with specific skill sets in order to maintain the equipment. Battery lifecycle costs need to be considered as battery replacement incurs significant capital expense. Some manufacturers offer services to offset these capital costs through usage agreements. Recycling and disposal of batteries at the end of their lifecycles also need to be considered. With the increased selection of BEV equipment that will be available in the next 2-4 years, 100% BEV adoption is also possible. We recommend a holistic approach when evaluating BEVs for underground mines. This will ensure that everything is considered in order to evaluate the full impact of BEV implementation.

Jan 1, 2023

By B. Wasmund, M. Y. Solar, I. Candy

The nickel laterite industry is divided into two camps when it comes to the grade of the ferronickels produced. One group, led by Falcondo and Cerro Matoso, markets high-grade ferronickels in the range of 35 to 40% nickel, while another group, led by SLN and the Japanese smelters, favour lower grades in the range of 20 to 25%. Because the ores processed by these smelters vary widely in terms of nickel content and iron to nickel ratios, it is probably more accurate to classify these smelters in terms of their iron recovery: Falcondo and Cerro Matoso smelt at lower reduction potentials and thus recover only 15 to 30% of the iron in their ores, while SLN and the Japanese smelters are very reducing and recover 45 to 65% of their iron. Low reductions generally imply higher slag losses and lower nickel recoveries, but also lower power and reductant requirements; higher reductions, the reverse. The question is, therefore, whether an economically optimum ferronickel grade exists for processing any given ore. This paper proposes a methodology for determining this optimum grade and concludes that nickel laterite smelters should favour low reductions and production of high-grade ferronickels.

Jan 1, 2008

By James Coull, Brian Wilson, David Siddle

"In 2012, Golder Construction Inc. was awarded a Design-Build contract for the design and construction of an extensive, deep ground improvement scheme to support up to 20 metres (66 ft) high Mechanically Stabilized Earth walls and bulk earthworks required for the development of the proposed Kitimat Liquefied Natural Gas (LNG) facility at Bish Cove, British Columbia (BC). Utilizing Cutter Soil Mixing (CSM) to construct barrettes consisting of overlapping rectangular panels of in-situ cement-treated soils, a deep mixing scheme, covering an area of approximately 12,900 m2 (15,430 yd2) and comprising some 1645 CSM panels to depths of up to 30.7 m (101 ft), was developed to provide the required static and seismic stability for the LNG structures, and meet the project-specific performance criteria.CSM panels were constructed through varying thicknesses and discontinuous layers of fine-grained, very soft to soft marine deposits, and loose to compact sands, with occasional interbeds of dense sands and gravels. Panel completion criteria was based on soil response factors, as measured by the CSM equipment, with the design requiring a typical embedment of about 2 m (7 ft) into dense silty sand to sand and gravel to provide the required bearing. A total volume of approximately 73,900 m3 (96,660 yd3) of soil was treated with cement to consistently yield average unconfined compressive strengths exceeding 2.5 MPa (363 psi).This paper outlines the challenges associated with the construction and quality control of this large deep mixing scheme in highly variable geotechnical conditions at a remote location with barge-only access, and limited communication facilities. Specifically the paper will discuss the logistical challenges faced and solutions adopted for the project; equipment redundancy requirements for a 24/7 operation; the impacts of wear and tear, as well as variability in subsurface conditions on productivity; quality control processes adopted for the project, including the value of provision of an on-site laboratory; and materials handling issues, and their impacts on mix design and quality control."

Jan 1, 2017

By Brian D. Barkauskas, Terence P. Holman

A major combined nuclear and coal-fired power plant, located in on the western coast of Florida has undergone multiple upgrades in recent years to increase power output and enhance environmental controls. Construction of new elements within the existing plant structure required working in highly congested conditions and heavy crane lifts with large picking radii. The largest crane pick involved the use of an 1800 metric tonne capacity Mammoet PTC ring crane for a single long-radius, high altitude lift of a precipitator unit. Original bid tender documents had called for drilled shaft foundation support, but the presence of many critical utilities and unfavorable access for cost effective construction led specialty contractor Moretrench American Corporation to propose an alternate micropile foundation on the basis that high capacities could be achieved in the weak limestone geology and that the smaller size of micropiles would allow for more surgical installation in the utility-congested areas. This case history describes the design and construction of seventy three (73) high capacity micropiles for the value engineering alternative and the crane foundation for this critical lift. Each micropile was founded in a competent dolomitic fossiliferous limestone unit at typical depths of 23 m below existing ground surface. Strain gauge instrumented load testing was used to validate the geotechnical design parameters in the weak limestone bedrock and resulted in the finding that the entire test load was being carried in the upper half of the bond zone. Construction of the production micropiles required numerous relocations due to utility conflicts and local reanalysis and redesign of the 1.2 m thick reinforced concrete ring beam cap. Crane foundation performance was satisfactory and the effective life of this temporary foundation was only 6 months before decommissioning and demolition.

Jan 1, 2017

By Justin Lukens, Di Stasim Jeffrey, Frank Di Salvo

Columbia University’s Manhattanville Campus expansion includes the construction of two new business school buildings. The new buildings require development of an entire city block bound by 12th Avenue, W 131st Street, W 130th Street and Broadway in Upper Manhattan. A support of excavation (SOE) package was first released, followed by a foundation package. The SOE package consisted of approximately 100 soldier piles and 280 anchors, up to 215’ long, to support a cut anywhere from 30’- 50’ below street level. The foundation package alone included approximately 1600 drilled micropiles. Given the breadth of the work scope, Hayward Baker Inc and Moretrench joint ventured on these two projects to bring sufficient knowledge and work resources to complete the work in an efficient and timely manner. This included working with the Owner/Engineer to propose different means and methods for construction to significantly reduce the schedule while meeting the design intent, such as large diameter (36” diameter) augercast piles in place of conventionally drilled soldier piles and large hollow-bar micropiles (103/51 bars) in lieu of pressure-grouted micropiles. The anchors, ranging from 3 to 22 strands, were used for earth retention through both soldier pile and lagging walls and existing slurry walls. These anchors were complicated based not only on their size and length, but also the need to drill some of them under the historic Studebaker building. The overall magnitude of the project with considerations to resource management and material lead times will be addressed, highlighting critical strengths provided by the Contractor to ensure project success. The scope of work discussed in this paper was executed under two separate competitive bid contracts. The first contract included the support of excavation work and the second contract included the foundation package. The support of excavation comprised of drilled soldier piles (performed by Case Foundation as a subcontractor to the JV), driven soldier piles, driven sheet piles, hollow bar tiebacks, multi-strand tieback anchors and micropile soldier piles. The foundation package consisted of drilled micropiles. Due to the large scope of work and critical schedule requirements of the project, the JV had to think outside the box and present value engineered alternates to expedite installation durations.

Jan 1, 2019

By Thomas Varley

"The literature on flotation of oxidized ores except for patents (especially for reagents) is very sparse. The Bureau of Mines in 1936, published a circular on the subject, by Ralston and Allen. The treatment of oxides by flotation was then in its infancy, but several of the most important mining companies in the Western United States and Mexico are now operating flotation plants for treating oxidized ores. The purpose of this present circular is to review the progress made and bring the subject up to date. One of the writers of the 1916 report (Mr. Allen) has been associated with some of the most important mining companies who have put into practical operation the process of flotation of oxidized ores; among these companies are the Shhttuck Arizona Copper Co., Bisbee, Arizona (now the Shattuck Denn Co.) and the San Francisco Mines of Mexico, Ltd., San Francisco Del Oro, Chihuahua, Mexico. His experience and other sources of information have been freely drawn on in pre-paring this paper. Mr. Ralston, assistant chief metallurgist of the Bureau of Mines, contributed many valuable suggestions and criticisms.Sulphidizing Reagents for Oxidize Ores.The various reagents and methods that might possibly be used for sulphidizing were summarized by Ralston and Allen as follows:""Sulphidizing (1) by the use of hydrogen sulphide on either the dry or the wet crushed ore, (2) by the use of solutions of the various sulphides and sulpho-compounds of sodium, (3) by the use of solutions of the various sulphides and sulpho-compounds of calcium, (4) by the use of sulphur vapor, (5) by the use of a sulphureted oil, (6) with colloidal sulphur."

Jun 1, 1927

By Peter Price

Introduction The Horne mine, the property of Noranda Mines, Limited, has in the last six years become one of Canada's leading gold and copper producers. Since the smelter was blown-in during December, 1927, up to the end of 1933, it has produced approximately 1,200,000 oz. of gold and 35O,OOO,OOO lb. of copper. The property is situated within an area occupied entirely by pre-Cambrian rocks and characterized by the complexity of rock types and structures common in such terrain. But apart from this the mine also presents other features of unusual interest in the size, number, and variety of the ore-bodies, the mineralogical associations, and the rather exceptional values both in gold and copper. It is not surprising, therefore, that a study of the geology of the mine should bring to light many interesting problems. The present paper summarizes, as concisely as possible, the results of such a study. Actually, it is a much abridged version of a more comprehensive and detailed paper completed by the writer a year ago (1), but embodying certain corrections and additional data made possible as a result of further development at the mine and of field work carried out during the summer of 1933. Owing to limitations of space, the paper is, in the main, a presentation of conclusions arrived at in the course of the study. Much of the supporting evidence cited in the thesis referred to has, of necessity, been omitted here.

Jan 1, 1934

By Jörn M. Seitz

Dynamic load testing is employed with ever increasing frequency to estimate the strength and elastic settlement behavior of piles of all types. For dynamic loading ram masses up to 20 Mg have been used and pile resistance forces up to 30 MN have been activated. Strains and accelerations induced by the impact are measured near the pile top and a load-set curve is computed by the so-called CAPWAP method. This paper briefly describes both the necessary equipment and other details of the dynamic tests and the available analytical tools for data interpretation. Furthermore the need for further research and the current status of standardization will be discussed. This paper also presents the results from several static and dynamic correlation tests on cast-in-situ piles of up to 2 m diameter and 64 m length. The results demonstrate the economical and technical feasibility of this test method.

Jan 1, 1987

The rocks of Waihi and the surrounding district are almost entirely rhyolitic and ande5itic in character. Sedimentary rocks, with the exception of some surface deposits of clay loosely compacted conglomerate, etc., and one or two thin and broken beds of a very poor lignite, occasionally changed by igneous agencies into a bituminous coal, are almost absent. In the shafts sunk by the Waihi and Grand Junction companies outside the outcropping andesitic area of the Martha Hill, more than one old surface or lake bottom has been passed through. At these points layers of sand, consolidated volcanic mud and tuff, accompanied by numerous broken fragments of imperfectly silicified wood have been enccuntered, but these occurrences may, for the purpose of this paper, be neglected.The youngest rock of the district are rhyolites, probably of Pliocene age. At least three distinct classes of rhyolitic lava, each possessing features of unusual interest, may be made out. None of these, however, is gold-bearing. The youngest flow, a light-coloured, fine-grained rock, is remarkable owing to its enclosing at times fragments of carbonised wood, varying in size from mere specks up to quite large pieces of almost pure charcoal. Rhyolitic tuff is also met with. The rhyolites cover a large extent of nearly flat country east, south, and west of Waibi, here and there rising into barren, stony hills.Below the rhyolites, geologically speaking, but for the most part. forming hills which bound the rhyolitic plain, or rise out of it as isolated patches, come ahdesites of older...

Jan 1, 1902

Fast Adsorption Phenomena at Air/Liquid Interfaces

Sep 13, 2010

By J. R. Evans

Mining claims must have a discovery of a valuable mineral deposit to be valid. When required, a Federal government mineral examiner makes a determination of validity and recommendations thereof to authorized management officials. The examiner should show whether or not an existing mining operation, or a proposed operation have economic viability. This is accomplished through an analysis of legal entities, land status and use, geologic and mineralogic relationships, and mining, milling and processing techniques considered in an appropriate economic evaluation framework. A framework involves market and market entry studies, reserve analyses, all costs analysis, royalty buyouts, tax structure, discount rate of return, and escalation and risk factors. An income approach to value is then used by means of a simple or complex discounted cash flow (DCF) analysis to certify validity. Whether one claim is owned by a single miner, or hundreds of claims are owned by a large corporation, thorough, fair, consistent, and appropriate economic concepts should be applied by the mineral examiner.

Jan 1, 1993

By W. G. Pariseau

"BACKGROUND The Crandall Canyon Mine (CCM) is located in the Wasatch coal field in central Utah. Extensive longwall mining at CCM preceded a decision to recover coal left in barrier pillars on each side of a set of main entries extending far into the mine. During mining in March, 2007, a major bump occurred that led to cessation of mining in the barrier pillar on the north side of the mains and to begin mining in the south barrier pillar. Subsequent loss of ground control in August, 2007, through coal pillar bursts had tragic consequences with loss of six miners and shortly afterwards three rescue team members. An MSHA report describes the events in detail (MSHA, 2008). An important lesson to be learned from CCM is the need to select a computer program suitable for pillar design. Computer programs are engineering tools; selecting the right tool for the job is essential. In this regard, a minimum program requirement is capability for computing stress distribution within a pillar and adjacent roof and floor strata. The reason is simple: strength of rock is stress dependent; both vary from point to point in pillars and adjacent strata. Preferably, one should follow the evolution of stress as the mining plan is executed from start to finish to assure safety or to warn of a potentially hazardous situation developing as mining progresses. The approach to the problem posed by barrier pillar mining at CCM is conventional in the sense of applying well known finite element modeling techniques to analysis of a proposed mining plan. The engineering purpose is to evaluate the mining plan with respect to ground control questions including roof, floor and pillar safety. Results of previous two dimensional finite element analysis indicated pillar safety was by no means assured (1, 2, 3). Geometry of barrier pillar mining is limited in two-dimensions, for example, crosscuts are not seen in vertical cross sections. While three dimensional analyses are preferred, even moderately sized regions often lead to very large problem sizes that exceed computer capabilities. However, a recent development in finite element modeling of tabular deposits allows for whole mine analysis in three-dimensions. This technique involves a dual node – dual mesh concept. Both have been used separately in much earlier work, but are only now are used in combination. Estimation of subsidence at a kilometer scale and details of stress, strain and displacement about barrier pillars, main entries and pillars, and so on at a meter scale are possible (4). No compromise involving empirical formulas or similar guess work is required. Indeed, all calculations are based on first principles: physical laws, kinematics, and material laws. Effects of joints and in situ variability or uncertainty in strata properties, elastic moduli and strengths, may be included for greater realism. An important objective of the present study is to assess the role of three-dimensional pillar geometry in arriving at conclusions regarding barrier pillar mining versus two-dimensional results."

Jan 1, 2015

By Gisele Ferreira de Lima

Magnésio e suas ligas são promissores para armazenagem de hidrogênio devido à alta eficiência, boa reversibilidade, baixo custo e segurança. Entretanto, hidretos à base de Mg apresentam cinéticas de ab/dessorção lentas, temperaturas de operação muito altas, e alta reatividade ao ar para aplicação práticas. A moagem de alta energia (HEBM) combinada com o uso de catalisadores têm produzido nanocompósitos à base de Mg com cinéticas mais rápidas. Recentemente, processos termomecânicos e de deformação plástica severa (SPD) têm sido investigados para produzir nanocompósitos em volume com melhor resistência ao ar (processo de ativação) e que podem ser facilmente fabricados em escala industrial. No presente trabalho, amostras 2Mg-Fe foram misturadas com CNT (0-5%p.) por HEBM, e em seguida processadas por extrusão a quente (termomecânico) a 300oC e/ou laminação a frio (SPD) a temperatura ambiente. Pós com 0%p a 5%p. de CNT mostraram padrões de DRX muito similares indicando similares nanoestruturas. Todas as amostras puderam ser laminadas, mas somente amostras com menos que 2,0%p. de CNT puderam ser extrudadas, e submetidas pela combinação de extrusão-laminação. As propriedades cinéticas, medidas pelos métodos Sieverts e DSC, foram piores para as extrudadas, intermediárias para as extrudadas/laminadas e melhores para as somente laminadas. Nessas últimas, os picos de Bragg mostraram baixa intensidade e textura favorável ao longo de (002) no Mg, que possivelmente explicam esses resultados. Quanto maiores foram as quantidades de CNT melhores foram as propriedades (cinética e temperatura de dessorção).

Aug 8, 2018