Search Documents

By A. Singh

Deformation structures after tensile and compression tests on Mg926Zn64Y alloy extruded at 250°C and 400°C are studied, in as-extruded and heat treated conditions. The icosahedral phase particles stimulate recrystallization during extrusion, resulting in fine grain size. Tensile and compression tests at room temperature show comparable yield strength, with a yield asymmetry ratio up to 0.98. c-type dislocations are observed in the grains near the submicron size icosahedral phase particles. The source of these dislocations is believed to be dissociation of <c+a> type non-basal dislocations. No dislocation pile-ups on icosahedral phase particles are found. {10 1 2} type twinning occurs in compression.

Jan 1, 2006

By Sun Y. L, Jiang J. J, Lu S. L

A distinguishing feature of tunnels in squeezing rocks is that a large deformation of the surrounding rocks takes place slowly and gradually, often called squeezing phenomenon. It is different from the rocksbursting phenomenon during which the deformation of tunnels occurs instantaneously when the resulting stresses exceed the strength of the surrounding rocks. The squeezing phenomenon has received great attention in the field of rock mechanics and tunnelling recently. The mechanism and various factors related to the large deformation and failure of tunnels in squeezing rocks are discussed in this paper on the basis of field investigations and laboratory model tests. The relationship between the deformation of surrounding rocks and support of the tunnels in squeezing rocks is presented in the form of numerical modelling.

Jan 1, 1995

By S. M. Brisbane

The life of refractory linings in rotary cement kilns can be shortened by uneven or inadequate support of the kiln and its shell and by variations in the conditions of operation. Alteration of these factors may, according to their nature, bring about mechanical deterioration of the lining or promote chemical attack. Chemical attack has been described elsewhere. The distortion of cement kilns has been discussed in a general manner by Rochow, who indicates the amount of distortion which may occur in an unlined shell, and by Rosenblad; who states that the deformations of the shell are greatest above the trunnions. The present article indicates the extent of the distortion of a kiln to an oval shape in certain selected positions and the deviation from a straight line of the kiln along its length between two supports. The cement kiln is a long, hollow, rotating cylinder consisting of steel plates which may be either welded or riveted together. This shell is supported on tires, frequently 60 ft apart, which roll on trunnions. The large mass of the kiln causes distortion of its cross-section; it becomes slightly oval, i.e., diameters lengthen as they become horizontal and shorten as they become vertical. There is also a tendency for the shell to bow between supporting tires; this bowing may be upwards or downwards depending on the position of the weight forces and the supports. The extent of the deviations from the ideal kiln shape was investigated.

Feb 1, 1956

By J Robinson, L D’Uva

"The Gold Fields group and Gekko Systems have successfully worked together on multiple projects, including at the St Ives, Agnew and Granny Smith operations in Western Australia, and the Damang operations in Ghana, with gravity recovery design, technology installation and optimisation the key driver on each occasion.In 2014, Gold Fields Australia identified an opportunity to challenge the historical thinking at Granny Smith and reassessed the benefit of upfront gravity gold recovery. The historical approach had been to employ gravity on the tailings stream of the carbon-in-pulp (CIP) circuit, recovering sulfide minerals into a concentrate from spiral concentrators for further liberation of gold via a regrind circuit.Gekko was engaged to assess the implementation of a gravity circuit within the grinding area, and to perform a comprehensive gravity recoverable gold test program. Test data was fed into the AMIRA P420 BCC Gravity Model to confirm the gravity recovery potential of the ore, and for process design basis generation. Height, space and capital limitations proved to be a design challenge. However, collaborative learnings throughout the project ensured the design and operation of a reliable and economic gravity gold circuit. Ultimately, the Granny Smith gravity circuit was a success, satisfying all the project objectives and yielding consistent, measurable benefits. On average, the gravity circuit recovers 33 per cent of total gold, resulting in an increase to overall gold recovery by 0.7 per cent.This paper highlights the key project drivers for Gold Fields, and the development of the Granny Smith free gold gravity circuit. It details application of test work and modelling, and the challenges and learnings encountered during the design, installation and commissioning stages. This paper seeks to demonstrate that continuous improvement in a long standing operation can be beneficial to overall circuit flexibility and increased ounce production.Citation:D'Uva, L, Robinson, J and Bell, T, 2016. Defying Gravity - Brownfield Continuous Improvement, in Proceedings 13th AusIMM Mill Operators’ Conference 2016, pp 135–144 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Oct 10, 2016

By Leo Ranney

ANY years ago a prospector came to a Nevada town and built himself a shack. Day after day he searched the hills for gold -but he found none. He closed his shack and hurried north, where a strike had been made. Next he tried to trap the flour gold that floats down the Snake River. He panned the black sands along the Oregon coast. He ranged over the mountains and up the gulches of far-off Alaska. At last, broken in health, six years ago he came back to his old home in Nevada. There his shack still stood-nobody wanted it. One day he started a garden in the rocky soil that he owned. His spade turned up a chunk of quartz, and in that quartz were stringers of gold. He had found a rich gold vein, running right under his own house. You gas producers who have hurried to Oklahoma, Louisiana, East Texas, South Texas, West Texas, even to California to drill wildcat holes a mile or two miles deep-why not, like the old gold prospector, have a look in your own back yard? Some of your coal seams contain 20,000,000 cu. ft. of natural gas per acre.

Jan 1, 1943

By C. Özgen Karacan

Methane emissions from the active face areas and from the fractured formations overlying the mined coalbed can affect safety and productivity in longwall mines. Since ventilation alone may not be sufficient to control the methane levels on a longwall operation, gob vent boreholes (GVB), horizontal and vertical drainage boreholes, and their combinations are drilled and used as supplementary methane control measures in many mines. However, in most cases, the types of degasification wellbores chosen are decided based on previous experiences without analyzing the different factors that may affect this decision. This study describes the development of an expert classification system used as a decision tool. It was built using a multilayer perceptron (MLP) type artificial neural network (ANN) structure. The ANN was trained using different geographical locations, longwall operation parameters, and coalbed characteristics as input and was tested to classify the output into four different selections, which are actual degasification designs that US longwall mines utilize. The ANN network selected no degasification, GVB, horizontal and GVB, and horizontal, vertical and GVB options with high accuracy. The results suggest that the model can be used as a decision tool for degasification system selection using site- and mine-specific conditions. Such a model can also be used as a screening tool to decide which degasification design should be investigated in detail with more complex numerical techniques.

Jan 1, 2009

In 1981, North American Degerstrom Contracting began gold mining on the Little Rocky Mountain Range, near Zortman, MT. In the past four years, the price of gold has fluctuated from a high of $16/g ($500 per oz) to a low of $9.60/g ($300 per oz). With that kind of a moving target, profitability presents a management challenge. Based in Spokane, WA, Degerstrom employs 85 people at the mine. It is one of the largest heap leach operations in the nation. Last year, 8 Mt (9 million st) of low-grade ore was moved to the leach pads in a two-shift, five-day operation. The current pit being worked produces 218 kt/m (240,000 stpm) of leaching ore. Ore fragmentation critical The gold bearing ore has no defined patterns or seams. It is an igneous intrusion resulting from volcanic activity. It occurs spontaneously throughout the range. To recover the gold, areas are staked out and core samples are taken and analyzed. These data determine if the ore is rich enough to mine. Once mining begins, an average of 150 holes are drilled and blasted on a two-day rotation. Five Ingersoll-Rand T4s drill on a 4- x 4.5-m (14- x 15-ft) spacing to a 7.6-m (25-ft) depth. "When we first came to this site, we drilled on a 3.6- x 3.6-m (12- x 12-ft) pattern," said Paul Baker, superintendent for N.A. Degerstrom Contracting. "We did some experimenting using a high density emulsion in the bottom of the hole and filling the rest with regular Anfo." The high density emulsion saved the company on overall drilling and blasting costs since the holes could be spaced on a wider pattern and still achieve the high degree of fragmentation needed for leaching. Blasting is important because the gold lays in the natural strata of the rock. Also, the ore is not crushed before it goes to the leach pads. So complete fragmentation is critical. Terrain dictates loading/hauling system The shot ore is worked in 6 m (20 ft) benches by two Caterpillar 245 front shovels equipped with 3 m3 (4 cu yd) buckets, a 992C wheel loader with a 12.6-m3 (16.5-cu yd) bucket, and a 988E high lift fed by a D9H. A Caterpillar D10 tractor trap dozes to the loader. According to Baker, the 6 m (20 ft) bench is an efficient lift for the front shovel and the wheel loader. In tight quarters or in a pocket of ore, Degerstrom uses the 245s. For high production areas, the wheel loader is used. The hauling fleet includes 28 Cat 773 off highway trucks. The 45 t (50 st) trucks are seven pass loaded by the 245s with a 25-second cycle time per bucket load. The 992C loads the trucks in two passes in less than 30 seconds. The cycle time is four to five minutes for a 1.2-km (4000-ft) haul on grades that average 10%. Grades, in some places, exceed 16%. "We use the 773s because they have a low weight-to-horsepower ratio - that&apos;s what you need in steep country," Baker said. The trucks haul the shot ore to the leach pad. Currently, Degerstrom is working a pad that has a capacity for 5 Mt (5.5 million st) of ore. Building the leach pads The base of the pads resemble a large drainage basin. They take about one month to construct. A 0.3-m (1-ft) layer of impervious bentonite clay is hauled in and leveled by a Cat D9H tractor. A 30-mm (1.2-in.) PVC liner is then laid in place on top of the clay base. It, in turn, is covered with tailings from an old on-site mill. Degerstrom uses the tailings to protect the liner from tears when the ore is dumped. The ore is leveled and built up in 9 m (30 ft) lifts by the D9H. The tractor rips the top layer. Then, a network of plastic irrigation pipe is put in place to distribute a cyanide solution over the surface. The leaching solution percolates through the ore and dissolves the gold. The solution drains from the pads and is pumped to a 22.7-ML (6-million gal) pregnant solution holding pond. The liquid then goes through two separate filtration units. One unit removes entrained solids and the other side adds a zinc dust to precipitate the gold. This is collected on filters. The affluent then returns to a solution holding pond for redistribution through the pipeline network. Typically, 80% of the pad&apos;s potential recovery takes place in the first 30 days of leaching. The process stops when the ambient temperature falls below the cyanide&apos;s freezing level. And each pad has a leach cycle of four to five years before recovery values decline to a point where further leaching becomes uneconomical. At Zortman, it takes 9 t (10 st) of ore to produce 31 g (1 oz) of gold. It is therefore critical to keep total production costs down and efficiency high.

Jan 1, 1986

By L. Bichler, A. Siebert-Timmer

In this research, novel YSZ ceramics doped with 5 mol% Nd2O3 were manufactured via Spark Plasma Sintering (SPS) process. The sintered Nd2O3-YSZ ceramics were subjected to a static supercritical water environment at a temperature and pressure of 400 °C and 31 MPa, respectively. The weight loss and microstructure development of the sintered ceramic before and after exposure to supercritical water was studied. The results suggested that Nd2O3 addition significantly improved the degradation resistance of the YSZ ceramics. This was attributed to the improved phase stability of the 5 mol% Nd2O3-YSZ ceramics, since X-ray Diffraction (XRD) studies showed that the cubic stabilized matrix in these ceramics was retained after exposure to supercritical water. In comparison, pure YSZ ceramics exhibited a rapid degradation behavior as well as a phase change.

Jan 1, 2014

By Premil Agarwal, Alok R. Patnaik, Pulak Dhar, Prakash C. Patnaik

In this study, a physics based model has been presented, considering the growth of the thermally grown oxide (TGO) layer on the bond coating of a thermal barrier coating. Using diffusion equations, a model has been developed to physically describe the oxidation process. The mathematical equations representing the diffusion formulations have been solved numerically. The computed results show the depletion of Al in the bond coating as it diffuses both towards the super-alloy substrate and towards the TGO produced in between the bond coating and the ceramic TBC top layer.

Jan 1, 2004

By G. Kordosky

The experience of one plant regarding degradation of copper solvent extraction reagents in the presence of 20 to 30 g/1 nitrate in the leach solution was described at Cobre 2003. However, little information is available about the degradation of copper solvent extraction reagents where the nitrate concentration of leach solution is much lower. Analysis of plant organic samples taken from an operating copper SX plant over a long period of time shows that small amounts of nitrate in the leach liquor can be a significant contributor to reagent degradation provided certain other conditions are present. These conditions are discussed and cautionary suggestions on copper SX plant operations in the presence of even low levels of nitrate in the pregnant leach are made based on industry experience with copper solvent extraction plants and copper solvent extraction reagents.

Jan 1, 2007

By Muir D

A review of the various methods of degrad- ing cyanide either from gold processing liquors or electroplating baths is presented with some discussion on their relative merits or problems. Whilst alkaline chlorination is common practice in many U.S. and Canadian plants it poses particular problems for certain plants. Alter- native methods include electrolysis, hydrolysis and air oxidation with activated carbon as catalyst which are also integral steps in the carbon-in-pulp process. A basic study of the degradation of cyanide ion has been carried out therefore to determine the effect of temperature, oxygen and carbon. It is shown that carbon is an excellent catalyst for degradation by air and likely to lead to higher losses of cyanide in a C.I.L. circuit. Degradation by hydrolysis is important at high temperatures and high pH such as employed in the Pressure Zadra or Anglo elution processes. Carbon catalysed degradation of cyanide by oxygen in effluent streams may be an environmentally acceptable alternative to conventional chlorine degradation.

Jan 1, 1987

By Garth James

Bacterial consortia capable of degrading cyanide and metal-cyanide complexes were obtained from gold mine process waters using enrichment cultures. The cultures contained either cyanide, tetracyanonickelate, or ferrocyanide as a sole nitrogen source. Several bacteria were isolated from the consortia, but none of these organisms were capable of degrading cyanide or cyanide-metal complexes at rates equivalent to those of the intact consortia. The consortium from the cyanide enrichment was capable of completely degrading cyanide from an initial concentration of over 100 ppm in less than one day, when cultured using a fed-batch method. Tetracyanonickelate and ferrocyanide were degraded more slowly. Overall, these results demonstrate that bacteria capable of degrading cyanide and cyanide-metal complexes can be isolated from mine process solutions and are capable of significantly reducing cyanide concentrations under appropriate conditions.

Jan 1, 1998

By Donna M. Noel

Bacterial strains have been cultivated from solids previously exposed to cyanide that will tolerate 300 ppm sodium cyanide under anaerobic conditions. In selected solid samples, these bacteria have been shown to reduce the level of cyanide from approximately 300 ppm to essentially zero in about 50 days under anaerobic conditions. Various media were investigated, and the nutrients providing maximal growth were ?established .. Degradation of cyanide in sterilized solids was determined for comparison with degradation obtained in bioactive solids. All experiments were conducted at ambient temperature and initial pH of approximately 10.5.

Jan 1, 1991

By R. Fedel-Moen, R. W. L. Kimber, B. D. Williams, S. R. Ragusa

The use o f cyanide to extract gold from ores is widespread. In the process of extracting gold, cyanide may form metal cyanide complexes with a variety of other metals present in the ore. This study was carried out to investigate the biodegradation of the Cu(I)-cyanide complex and tetracyanonickelate under varying pH and nutrient additions. Detailed studies using shake flask cultures and bioreactors showed that naturally occurring bacteria residing on gold-leach-pad ore uti¬lized the Cu(I)-cyanide complex (CuCN) and tetracyano-nickelate, Na2(NiCN4), as carbon and/or nitrogen sources. Ammonium-nitrogen (NH4+-N) and/or cyanate (CNO-) accumulated in solution as the metal cyanide complexes were degraded. The accumulation of cyanate as a product is a concern due to its toxicity. Degradation rates were increased if a growth substrate (peptone, 0.1%) was added to the medium or if bioreactors were primed with peptone before addition of the metal-cyanide complex. Tetracyanonickelate was degraded at pH 8 without added peptone, but it was not degraded at pH 10. The addition of peptone was required for degradation of the Cu(I)-cyanide complex at pH 8 and pH 10. At pH 8, the addition of peptone resulted in the accumulation of cyanate, whereas, at pH 10, cyanate was not detected in the cultures. Biodegradation of metal-cyanide complexes was faster (approximately 1.5 to ten times faster) in bioreactors than in shake flask cultures. The addition of peptone was not required for degradation of metal-cyanide complexes in bioreactors. However, priming the bioreaetor with peptone resulted in higher metal-cyanide degradation rates over multiple cycles.

Jan 1, 2000

By Anne Kvithydl

Printed circuited boards contain considerable quantities of valuable metal, while also containing many environmental pollutants making them unsuitable for landfill. In this study the decomposition of common plastics used in printed circuit boards were studied. Polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC) and polyethylene (PE) were heated in both CO, and argon atmospheres using a thermo-gravimetric furnace (TG) coupled to a mass spectrometer (MS). Soda ash Na,C03 and baking soda NaHC03 were used as reactants. The degradation temperatures and evolved gases are presented for single plastics and mixtures. Mixed plastics are shown to behave as a sum of the individual plastics. The mass loss temperature is the same in CO, and argon. However, less residue is formed when heated in CO,.

Jan 1, 2008

By M. G. Ayat, B. C. Scott

Coal degradation is the breakage of coal particles to finer sizes due to the continuous forces of attrition and gravity to which coal is subjected during mining, handling, and preparation. The objective of this paper is to determine the extent of degradation that a coal slurry experiences when transported through pumps and pipelines. The examination of degradation results for a number of different coal slurries have indicated that the extent of breakage is dependent on the physical properties of coal and the time span of circulation. These results have also indicated that certain size fractions of coal are more susceptible to breakage than others.

Jan 1, 1987

By M. G. Ayat, J. Dasher

Having an interest in coal slurry pipelines from a decade of arguments with Ed Wasp and crew at Bechtel about pumping thicker slurries slower, I immediately read this article and found nothing in it pertinant to the title. Ayat and Scott pumped five unidentified coals at 9% solids (50%-60% is the area of interest) in a 25-mm (1-in.) pipe around two square elbows through a 76-mm (3-in.) cyclone for up to 60 minutes and sized a large number of samples of unstated size on an unidentified wet screening device. They did not measure power consumption, discharge pressure, flow rate, or give pump tip speed or impeller diameter. They siad the cyclone had a "high" pressure drop (unmeasured) and did much of the degradation (measured) but more or less per unit of energy expended? Hargrove was not measured, so there are no data as to whether it would correlate with degradation. The authors conclude, with no attempt, correlation is "hard to establish." Please experiment before concluding. I am at a loss to know what "increasingly smaller size" means, much less what theory says such particles take "exponentially larger quantities of energy," which the authors neglected to measure. If such experiments without pertinent data or justified conclusions must be published, please attach a pertinant title.

Jan 1, 1990

By M. G. Ayat

I have been following the discussions on coal degradation started by the article "Degradation process in coal slurry pipe-lines," by M.G. Ayat and B.C. Scott. I agree with Mr. Dasher&apos;s comments in January that the title of the article was perhaps misleading as the information appeared to pertain more to processing the coal than to transportation. Specifically, the authors&apos; conclude that the cyclone had an important impact on the degradation. Dr. Ferri&apos;s comments on degradation in other physical processes was very correct, handling of coal in a turbulent manner has an impact on the size distribution of the coal. This is one reason that when I design a coal system (mine to rail car) I try to minimize the total number of transfer and processing steps consistent with achieving the desired product specifications. Another area, mentioned in passing in the article, the impact of natural causes and the mining step, is of particular interest to me. A mine in West Virginia had a variation of 50% in the -6.35 mm (-0.25 in.) raw coal depending upon the direction of mining. Since it was a single unit mine, this significantly impacted the final product. Two articles on mining&apos;s impact on size distribution are: • Stefanko, R., Chopra, I. K., and Ramani, R. V., 1974, "Mining influence on size consistency and washability char¬acteristics of coal," SME Fall Meeting. September; and • Albrecht, M., and Olsen, D., 1980, "Mining methods impact on coal preparation plant design." 1st International Mine Planning and Development Symposium. September. Both articles presented information on variation of size distribution and cleaning plant performance on a coal depending on the mining method used. Both articles considered a single coal seam at one mining operation. Stefanko&apos;s article considered continuous and conventional mining of coal in Pennsylvania. Albrecht&apos;s article considered surface, underground continuous, and underground hydraulic mining of a coal in British Columbia. Both concluded that mining methods do impact coal characteristics. I agree with Mr. Ayat&apos;s comments in reply to Dr. Ferri&apos;s discussion, "... degradation is a multi-faceted phenomenon involving many natural and man-made factors." As efforts are being made to produce a higher quality (lower sulfur) coal, this topic becomes even more important

Jan 1, 1990

By Fábio de Oliveira Braga

A descoberta de óleo e gás no Pré-Sal transformou o Brasil em um dos grandes possuidores de reservas de petróleo no mundo e aumentou as expectativas de produção em águas profundas. Apesar da euforia, alguns desafios têm o potencial de inviabilizar a exploração do Pré-Sal: a complexa logística offshore, as dificuldades de acesso ao reservatório, as condições físico-químicas do poço e de subsuperfície. As condições impostas pelo ambiente são relevantes, devido aos altos teores de contaminantes, alta temperatura e pressão, que exigem materiais de alto desempenho. O objetivo deste trabalho é revisar os avanços que podem contribuir para superar as condições físico-químicas do Pré-Sal. Verificou-se que a solução deste problema pode envolver três tipos de abordagem: O desenvolvimento de ligas resistentes à corrosão (LRC), a adição de agentes modificadores do meio corrosivo (inibidores) e modificações no projeto dos equipamentos. Espera-se, portanto, que a utilização conjunta das diferentes abordagens proporcione a viabilidade de longo prazo da produção no Pré-Sal.

Aug 17, 2017

By Luís Marcelo Marques Tavares

Pelotas de minério de ferro representam uma parcela significativa do mercado transoceânico de minério de ferro, contando com uma participação importante de empresas brasileiras. Pelotas concorrem favoravelmente com granulados e sínteres de minério de ferro na carga metálica de fornos, em particular devido à sua elevada resistência à degradação durante o manuseio e transporte. Entretanto, pelotas ainda sofrem desse problema, que resulta na geração de finos, removidos previamente à alimentação do forno, ou de cacos, que podem resultar no aparecimento de clusters em fornos de redução direta. Esses efeitos danosos da degradação podem ser minimizados caso uma metodologia adequada de caracterização de pelotas e de simulação do processo de manuseio se encontrasse disponível. O presente trabalho trata do desenvolvimento de metodologia inédita e inovadora para previsão de resultados de degradação de pelotas, desde a usina pelotizadora até o pátio ou forno do cliente, desenvolvido como parte da parceria entre o Laboratório de Tecnologia Mineral da COPPE/UFRJ e a Samarco Mineração. O trabalho mostra ainda uma validação preliminar a partir de um ensaio de quedas múltiplas em laboratório, mostrando ótima aderência. Um simulador do processo foi desenvolvido, o qual permite inserir as características das pelotas produzidas, bem como o fluxograma de manuseio, permitindo prever a intensidade da degradação.

Aug 16, 2017