Search Documents

By V. V. Pankov, W. R. Chen, L. R. Zhao

Diffusion nickel aluminide and overlay NiCrAlY coatings were deposited on single crystal Ni-base superalloy CMSX-4 substrate using the chemical vapour deposition and cathodic arc evaporation techniques, respectively. The NiCrAlY coating underwent a post-deposition heat treatment in an argon atmosphere at 1100°C for 2 hours. All the coated specimens were subjected to furnace cyclic oxidation testing at 1000°C up to 1500 one-hour cycles. The morphology, elemental composition and phase constituents of the oxide scales formed on the coating surface were analyzed using scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. It was observed that the diffusion aluminide coating experienced accelerated weight gain at an early stage of the test (150-400 cycles), whereas the overlay NiCrAlY coating fabricated by cathodic arc evaporation maintained steady-state weight gain throughout the entire 1500 cycle test duration. This difference in oxidation behaviour between the two types of coatings is attributed to the early development of nickel-aluminum spinel on the surface of the diffusion aluminide coating, in contrast to the stable aluminum oxide scale formed on the overlay NiCrAlY coating during cyclic oxidation testing.

Jan 1, 2015

Stellite-6 coatings were formulated on two Ni-base superalloys, namely Superni 75 and Superni 600, by a shrouded plasma-spray process, and the oxidation behaviour of these coatings has been investigated in air and in an aggressive environment of Na2SO4- 60%V2O5. Accelerated oxidation tests were conducted in a silicon-carbide tube furnace under cyclic conditions at an elevated temperature of 900°C for 50 cycles. Each cycle consisted of 1 h heating and 20 min cooling in air. A thermogravimetric technique was used to approximate the oxidation kinetics. The corrosion scales were characterised by XRD, SEM/EDAX and EPMA analysis. It has been observed that the coatings nearly followed the parabolic rate law of oxidation. Overall weight gain conceived in air was just 51% of that in the aggressive environment in the case of coated Superni 75, whereas in case of coated Superni 600, the cumulative weight gain in air was found to be one-third of that in the Na2SO4-60% V2O5 atmosphere. Furthermore, the coating showed very good adherence to both of the substrates during the course of air oxidation, whereas some superficial cracks were observed near the edges of the specimens during the molten salt induced oxidation. XRD analysis revealed the presence of phase-like CoO, CoCr2O4 and Cr2O3 in the oxide scales, which are reported be protective against high-temperature oxidation. The XRD results were further supported by SEM/EDAX and EPMA.

Jan 1, 2005

By W. Choi

The present study revealed that the bioleachability of a chalcopyrite flotation concentrate is influenced by the semiconductor properties of CuFeS2. The overall reaction of biooxidation,

Jan 1, 1991

By C. -S. Jiang

In most copper refineries, addition agents are added at predetermined rates with no further monitoring of their activity or concentration in the electrolyte. Increasingly stringent cathode quality requirements, and a desire for better process control in tankhouse operations, have recently directed a number of refineries to search for a better addition agent control strategy. Extensive development work has been carried out at the Noranda Technology Centre for the monitor in of glue and thiourea in copper refinery electrolyte using cyclic voltammetry (cv~. Data from both synthetrc and commercial electrolytes are presented, showing the ability of CV to produce reliable and easily identifiable fingerprints of addition agent concentrations in copper refinery electrolyte.

Jan 1, 1991

By Roy A. Grancher

CYCLING WITH CEMENT "THE WHEEL IS COME FULL CIRCLE" Shakespeare's King Lear Act V, Scene 3, Line 176 The time clock of the cement industry has been turned back to the early 1950s. After the trials and tribulations of the decade of the Sixties, the hands now stand where they did just over twenty years ago. Cement shipments have steadily increased, with a record 419 million barrel level (78.8 million tons) being reached last year. Plants are operating at average utilization rates in excess of 85 percent of rated capacity. The spread between supply and demand has narrowed to where a definite shortage of cement now exists within the industry. The notable and unfortunate difference between the two periods however is that, back then, cement's returns were a respectable 14 to 18 percent, whereas today they stand at less than half those levels. Insufficient return forms the present foundation of the U.S. cement industry. This lack is destined to have a cumulative effect. Just as the industry's balance between supply and demand is returning to favorable proportions, promising a period that has historically and now should generate those profit levels required to modernize and provide for capacity addition, cement instead finds itself frozen by federal price controls into the semi-depressed condition that has existed for over a decade and from which it was just starting to emerge. Capital is not attracted to continued low returns, and increasingly restrictive pollution control measures are necessitating great non-productive expenditures be made as definite costs to stay in business. Even a clouded crystal ball would reveal that additional cement plant closings can be expected.

Jan 1, 1972

By Liugen Sun, Xingming Jiang, Weijiao Yang, Yihang Hu, Yongqiang Yang, Hua Wang

During the past decades, cyclone electrowinning (CE) has been regarded as a novel separation technology, which can be used for direct electrowinning of metals from low concentration solution. Recently, CE was proven effective for the treatment of antimonic gold concentrates. The experimental results of cyclone electrowinning of antimony show the current efficiency increases from 43.8 to 72.2% with the increasing current density (from 254.8 to 647.3 A/m2), and on the other hand, power consumption per ton antimony decreases from 6100 to 4200 kWh with the aforementioned increasing current density. The grade of the obtained cathode antimony could reach 98.6%. Compared with the traditional electrowinning using parallel-board electrodes, the economic profit of CE was 33.1% higher attributed to the high current efficiency of CE. In addition, CE could adapt to high current density. All these characteristics indicate the CE method can be implemented commercially for processing antimonic gold concentrates.

Mar 1, 2018

By R. N. Murarka

"Hydrocyclone modelling and selection procedure is illustrated. Computerized procedure for hydrocyclone cut size determination for grinding and non-grinding applications is described.A standard procedure for evaluating operating hydrocyclones is described in detail. Many case studies are illustrated comparing actual plant performance with the computer simulation output in terms of overflow product size distributions.INTRODUCTION Cyclones are widely used for applications such as: close circuit grinding, backfill, tailings and dewatering. Normally, cyclones are used for very fine separations where screens are not suitable or too expensive. Figure 1 shows the separation size range of various classifying devices. Cyclones are popular because of their low capital and operating cost. Cyclone selection procedure for different applications depends on the amount of information available on the cyclone feed slurry characteristics. Closed circuit grinding applications will be discussed in detail in this paper. The Cut Size:The size of the material in the feed which reports 50% to each product stream (i.e. underflow and overflow), after correcting for the feed solids by-passing with the underflow liquid, is termed the cut size or ""d50c"". This is often used as the criterion and the basis for cyclone design.When the corrected recovery to underflow of each mesh size in the feed is plotted against the geometric mean size in microns on a log scale, the micron size corresponding to 50% recovery is the d50c size."

Jan 1, 1992

By D. A. Dahlstrom

Although the liquid-solid cyclone is a relatively recent innovation in the field of coal preparation, various authors have already indicated three distinct applications to operations encountered in the modern tipple. Driessen's articles and work at the Dutch State Mines exhibited its possibilities in the beneficiation of fine coal with apparently high efficiencies down to the 200-mesh fraction. 1 2 3 4 Other publications point out its use as a recoverer, thickener, and preliminary dewatering agent of fine coal which in too many cases is being wasted due largely to former high operating cost limitations 5 6. Finally, certain authors have emphasized the practicability of applying the cyclone to the elimination of coarse and fine solids from water slurries in the tipple in order to produce a water suitable for recycle purposes containing only minute particles far below the 200-mesh size.6 This would result in a closed water system for many cases, with its accompanying economic and operating advantages to locations where water quantity and quality problems are severe; better operation of washing equipment using a consistent water devoid of injurious fine particles; lowered maintenance costs due to the lesser abrasion resulting when the fine abraiding particles are removed; and the greater ease of disposing of refuse streams of reduced volume containing greater percentages of solids.

Jan 1, 1949

By P. R. Taylor

Recent research by the investigators has evaluated the oxidation roasting of refractory gold concentrates in the presence of hydrated lime. (Taylor, 1990, 1991, 1992, 1993). These results have indicated that it may be possible to roast concentrates in such a way as to contain nearly all of the sulfur and arsenic in the roaster calcine and that cyanidation may be possible. To further evaluate the behavior of this type of roasting system a laboratory cyclone reactor was built and operated using pyrite and hydrated lime as a .model system. Approximately 50 years ago, the principle of cyclone firing entered practical boiler construction. The appeal of the cyclone configuration was that it afforded the flash combustion process greater efficiency due to turbulence-induced increased mass transfer, heat exchange, and combustion rates.

Jan 1, 1994

By James K. Kindig

Solvent extraction as a method of purifying and concentrating metal values from solution has become a standard hydrometallurgical operation for recovery of both uranium and vanadium, and within the past two years it has been put into operation in a commercial plant for recovery of copper from leach solutions. In this first full scale solvent extraction plant for recovery of copper operated by Ranchers Exploration and Development Corporation near Miami, Arizona, a kerosene solution of an organic compound, LIX-64® is used to selectively extract the copper from the dilute acidic copper sulfate leach liquor obtained from heap leach operations. The copper is back extracted from the solvent into a stripping solution which is fed to an electrolysis circuit producing cathode copper for sale.

Jan 1, 1970

By Norman A. Jull

"IntroductionThe scope of this paper is intended to deal mainly with cyclones in grinding circuits. However, the section on Cyclone Equipment, contains more general descriptions, to cover most of the cyclones used in mineral separation plants.Cyclones as heavy media separation vessels are discussed by Mark Freberg (this volume). Their use in tailings deslirning is discussed by P.C. Lighthall, eta/. (this volume).Cyclone EquipmentCyclone TerminologyApexObviously, the apex of a cone is the smallest end. However, with cyclones the term is usually used for the fitting which is attached there to control discharge of the underflow stream.Note that the cyclone need not be so mounted that the apex is the lowest point, although that is the most common method. Keeping the apex below the rest of the cyclone helps avoid plugging when the underflow contains very large particles and the tonnage of underflow solids can fluctuate.Various devices for adjusting apex diameter or otherwise controlling the underflow are discussed later under ""Cyclone Construction"".BypassingThe transport of a portion of feed slurry directly to underflow so that classification is bypassed by that portion of feed.This action is fundamental in any hydraulic classification, whether gravity or centrifugal, because the large particles going to underflow have some void volume between them, which remains filled with feed slurry.D50By definition, D50 is that particle size which has an equal probability of going to overflow or to underflow.It is calculated by drawing a curve of recovery vs particle size and noting the size at which 500Jo recovery occurs.This may be done equally with corrected or with gross recovery (see below) and the resulting value should therefore be identified as d50c (corrected d50) or as d500 (gross d50).Note also that it is common in industry practice to plot size analysis data on the retained size rather than on the average of passing and retained (the middle of the size band). To portray sizing alone it makes no difference, but to read a D50 value off a curve of corrected or gross recoveries, it is essential to plot those values on the average size of each band."

Jan 1, 1989

By E. S. Allen, P. R. Kruesi, J. L. Lake

An electrochemical process is described for converting concentrates of base-metal sulphides to the corresponding pure metals and elemental sulphur. The application of the process to chalcopyrite is discussed. The process is also of potential interest in processing copper-nickel sulphides, and laboratory data concerning this potential are presented. The process creates neither air nor water pollution.

Jan 1, 1973

By Ross R. Bhappu

Anticipating a major power cost increase in 1990, Cyprus Copper Company decided to modernize the Miami Smelter at a cost of $92.5 million. The modernization project included the addition of an Isasmelt vessel for use as the primary copper smelter and the modification of the existing electric furnace to a slaglmatte separating vessel. The project was completed in June of 1992 and is currently operating at close to its design capacity. This paper provides a summary of the decision making process, a description of the project, a summary of start-up problems and solutions and the current status of the smelter operation.

Jan 1, 1994

By Jack E. Bailey

From a start in 1957, milling 3,000 TPD of copper ore, the Cyprus Pima Mining Company, which is located 20 miles south of Tucson, has expanded its operations four times, and is currently treating over 55,000 TPD of ore.1 The most recent expansion added a 14,000 TPD semi-autogenous concentrator to the operation. Shortly after startup in January, 1972, the semi -autogenous plant exceeded the designed tonnage rate.2 Ore from the mine is delivered to a 54 inch gyratory crusher and is reduced to a minus 8 inch product. From the crusher the ore is stacked on a surge pile and then reclaimed and fed to the two parallel grinding circuits. A 28 ft. diameter by 12 ft. long semi-autogenous mill and a 16.5 ft. diameter by 19 ft. long ball mill make up each grinding circuit. The semi-autogenous mills are in closed circuit with screens and the ball mill circuits are closed with hydro- cyclones. Rougher flotation follows the grinding operation. Concentrate regrinding and cleaner flotation is performed in Mill I, the older mill. The generalized flowsheet is shown in Figure 1.

Jan 1, 1975

By N. S. Dalal, B. Jafari, F. H. Y. Green, V. Vallyathan

"INTRODUCTIONThe mechanistic details of the biological events leading to coal workers pneumoconiosis (CWP) are not yet fully understood, despite several decades of extensive epidemiologic1.2 and laboratory studies.2-6 Epidemiologic studies1.2 have shown, for example, that the incidence and severity of CWP differ markedly in the different regions and mines at comparable exposures, but laboratory investigations2-6 have demonstrated only partial correlation of the epidemiologic data with the differences in the mineral composition and the rank of coal mined. In particular, while epidemiologic data indicate1.2 direct correlation of the· prevalence and severity of CWP with the rank (i.e., % carbon content) of coal, this correlation has not been established by laboratory4'6 and animal exposure3 studies. In order to explain these results, in 1980 Artemov and Reznik' suggested that perhaps they arise from the fundamental differences in the surface properties of the coal. dusts inhaled by the coal miners and those used in the laboratory studies: while the miners inhale freshly fractured coal particles, henceforth called the 'fresh' coal dust, the laboratory studies generally utilize 'aged' coal dusts (i.e., dusts that have been stored for many days or even longer). Reznik and Artemov' used electron spin resonance (ESR) spectroscopy to show that the mechanical crushing of some Soviet Union coals generated organic free radicals and that the concentration and the decay times (hence the reactivity) of these radicals were higher for the coals of higher ranks. Since some of the radicals decayed within a few minutes in air, the authors surmised that while these radical species could lead to certain specific pathogenic reactions at the sites of mining operations, this might not be the case in the laboratory studies, due to the conventional use of 'stored' dusts which would be expected to contain significantly smaller free radical concentrations. This is consistent with the recent findings that, standardized, aged coal dusts exhibit minimal cytotoxicity. 8While the above mentioned work of Artemov and Reznik7 did suggest a possible new clue to the pathogenesis of CWP (i.e., the role of the coal based free radical species), no direct biological/cytotoxicity data were provided to show that 'fresh' coal dusts were, indeed, more pathogenic than the 'stale' ones. Because of the rather significant implications of the Artcmov-Reznik hypothesis to the understanding of 1hc biochemical mechanism and, hence, the strategies for the eventual containment of CWP, we have initiated a comparative study of the free radical formation and cytotoxicity properties of freshly crushed coal ·particles. As done by Artemov and Reznik, 7 we have used the ESR technique as the direct method of measuring the concentration and decay kinetics of the coal based free radicals. Our preliminary ESR studies on two Pennsylvania coals, a bituminous (carbon content 72 % ) and an anthracite (95 % carbon) coal, have confirmed the Artemov-Reznik finding that the crushing-induced free radical sites are higher on the coals with higher carbon content (i.e., higher rank).9-11 In the present work we describe our more recent results of a parallel study of the time dependence of the decrease in the free radical content of a freshly made anthracite dust (as measured via ESR) and that of the dust's cytotoxicity potential as measured by the extent of hemolysis of (sheep) erythrocytes. We have also investigated the effects of free radical scavengers on the cytotoxicity potential of the dust and deduce that indeed the free radicals could play a significant role in the initial events in the mechanism of the cytotoxic effects due to the inhalation of coal dust inhalation."

Jan 1, 1990

By Gabriel Braga Regattieri Sampaio

Neste trabalho, determinou-se o calor latente de fusão da liga A356.0 através da Curva Zero, calculada pelo método Newtoniano de análise térmica linear. Para tanto, foram feitos experimentos com dois Copos de Análise Térmica (CAT) em moldes cerâmicos. Utilizou-se um sistema de aquisição de dados configurado para obtenção das curvas de resfriamento experimental (CR). Para o processamento matemático da curva de resfriamento e a determinação da Curva Zero Newtoniana (CZN) utilizou-se um programa comercial com planilha de cálculo. Obteve-se os valores de 321J/g e 345J/g para cada copo de análise térmica. Comparando com a bibliografia cujo valor do calor latente é 403J/g, a precisão foi de 82%.

Aug 16, 2017

By Lis Nunes Soares

A Vallourec Tubos do Brasil é uma siderúrgica integrada com produção de tubos de aço sem costura. A qualidade e o acabamento superficial dos tubos estão diretamente relacionados com o processo de laminação pelo qual eles passam. Um fator extremamente importante para um bom processo de laminação é uma boa lubrificação da peça de laminação, o mandril. Durante o processo de laminação, o mandril passa por várias etapas além da lubrificação, incluindo etapas de aquecimento e resfriamento, que se repetem em ciclos de laminação. Um dos principais parâmetros do processo de produção que influenciam a lubrificação do mandril é justamente o perfil térmico e a temperatura superficial do mesmo. O perfil térmico do mandril afeta a aderência do lubrificante em sua superfície. Visando a melhor compreensão do processo, esse trabalho tem como objetivo propor um modelo matemático em diferenças finitas que descreva a evolução do perfil térmico do mandril durante o processo de laminação de tubos sem costura. O mesmo modelo matemático é validado através de engenharia reversa. A proposta do modelo matemático é ser usado na análise de possíveis métodos de pré-aquecimento de mandris antes da lubrificação, diminuindo ou eliminando assim possível sucateamento de peças e paradas da linha de produção por esse motivo.

Jul 31, 2018

By Alexander Blatt, Franz-Werner Gerressen

Diaphragm wall technique is usually used to construct structural elements in the ground, commonly used for retention systems, permanent foundation elements or deep groundwater barriers, named Cut-Off-Walls (COW). Recent developments proof, that the technology also satisfies the demands for using the diaphragm wall technique for bulk sampling purposes. Such kind of new ideas required the adaption of equipment and tools for a depth capability never reached before by a trench cutter in any commercial application worldwide. Compared to the development of increasing depths, especially inner-city applications with limited space, demand a minimization of equipment to accommodate such projects. The paper will focus on the developments and solutions generated to fulfill these requirements and will give an outlook to future developments. Further it describes finalized reference projects and will give a general outlook on future trends and developments. The Paper/The Presentation explains as well the installation process in general.

May 1, 2022

By V. Ushakov, P. Bogdan

Daily production scheduling in a highly dynamic smelter environment has always been a great challenge for the operation management due to a significant amount of uncertainties. Planned and unexpected equipment failures, various energy outages, inaccuracies in flow and mass balancing, manpower availability conflicts and other constraints make the job of daily production planning exceptionally difficult. This paper discusses a general scheduling approach utilized by the production management of the Phelps Dodge Miami Smelter (the Smelter). It also describes logical assumptions and some practical software solutions that have been exploited by the Smelter managers to assist the front line supervisors in dealing with daily planning activities for several years.

Jan 1, 2007

By John Rushton

Surface mining, from ore extraction to processing, requires many types of equipment to obtain the final product. Mine equipment often includes shovels, drills and haul trucks. Ore processing equipment, including plants, mills and concentrators, are also part of surface mining operations. Surface mining operations emphasize production. Production is where the bills are paid and fortunes are made. However, there must be support to keep the equipment operational. To most production people, equipment maintenance is a necessary evil. Maintenance is not glamorous work. It is often neglected when praise is being passed around. It is easy to recognize higher production, greater capacities, faster cycle times or more loads hauled. But who cares if an engine is replaced in 12 hours instead of 48? The answer is, everyone should - from the hourly miner to the mine manager. Surface mining equipment needs constant maintenance work. It must be lubricated, components replaced, electrical problems repaired and other problems addressed. Repair work for any surface equipment takes time away from production. It costs money. Maintenance costs cannot be avoided. However, they can be minimized. Minewide communication should include operations cooperating with maintenance. Traditionally, operations resist surrendering equipment to maintenance if it can continue to produce. The rationale is, every load that can be hauled today is money in the bank. If the unit is taken down, the money is lost. This thinking is prevalent in many surface mining areas, including the mill. "Not on my shift," the operator thinks. "Let the next crew worry about it. The problem with this thinking is in probability and statistics. The longer equipment goes without maintenance work, the higher the probability of equipment failure. When the failure does occur, it is certain to cause the equipment to remain down longer than if the maintenance department had been allowed to take it down. Many mining operations have closed early in their lives because of poor maintenance practices. This has become the industry standard because substandard levels of performance are acceptable. Management believes it gets five to six hours of work from maintenance people during an eight-hour shift. Actually, the industry average is less than two hours of work per shift. Real productivity levels of less than one hour are not unusual. There are few exceptions. However, a daily work schedule (DWS) will increase productivity at many properties by 50% to 100%. A 200% improvement is not unusual. The DWS will work. Maintenance people are among the most intelligent and motivated people on the property. They deserve the chance to be productive. [ ] In preparing a DWS, management needs to understand two productivity principles - the productivity spread and the real maintenance workday.

Jan 1, 1997