Search Documents

By Godwin M. Beene

Large scale mining operations started in Zambia in 1913 and rapidly expanded during the post 1930 period with the opening of several mining and processing plants on the present Zambian Copperbelt. As a consequence of poor tailings dumps design methods at the start of the mines, and in view of stringent Government Legislation pertaining to environment in the recent years, Nkana Mine has developed a unique method of dump construction at its current tailings depository, Tailings Dam 15A. This method has enabled the revegetation of the dump retaining walls while construction is still in progress, a situation which was not possible on the older dumps. Cowdung has proved to be a superior fertilizer for providing plant nutrients on the tailings. The new method of dump walls construction and walls rainwater runoff drainage system has almost eliminated tendency of gully formation which is common on older dumps, as rainfall on the Zambian Copperbelt comes in intense thunderstorms. The decanted water from the dump is discharged to the natural environment in a controlled fashion after ensuring that it meets the Zambian Government Statutory requirements.

Jan 1, 1999

By Suman Das, Justin J. Gambone, Rohan Bansal, Ranadip Acharya, Paul Cilino

"This paper focuses on generating a quantitative microstructure prediction model for Scanning Laser Epitaxy (SLE) process based on coupled flow-thermal modeling using Finite Volume method. SLE is a laser-based additive manufacturing process for the deposition of equiaxed, directionally solidified and single-crystal nickel superalloys through the melting of alloy powders onto superalloy substrates. In the current work, the detailed effects of natural and Marangoni convection on the flow field are studied and the results are analyzed in terms of the temperature gradient, vorticity parameter, melt pool dimensions and mushy region extent. The detailed property data of the processed superalloy and the laser scan path are incorporated in the model to predict the microstructure in realistic scenario. An optimization study is carried out to evaluate the critical parameter values at which the columnar-to-equiaxed and the oriented-tomisoriented transition take place. This work is sponsored by the Office of Naval Research through grant N00014-11-1-0670.IntroductionSLE is a laser-based additive manufacturing process for the creation of structures in equiaxed, directionally solidified and single-crystal nickel superalloys through the selective melting and resolidification of superalloy powders. In SLE, a tightly focused laser beam is guided by a highspeed galvanometer scanners allowing for tight control of the amount of energy being applied to the top of the powder bed, as well as the speed at which the melt pool moves across the substrate. Under the proper operating conditions and with sufficient substrate meltback, the solidification microstructure follows the morphology of the underlying substrate, allowing for directional and even SX growth.Several reports on the modeling aspects of laser cladding-based additive manufacturing approaches can be found in the literature. Approaches based on Finite Element Methods (FEM) and Finite Volume Methods (FVM) are employed for the thermal modeling of the system [1, 2]. Gaumann coupled the Columnar to Equiaxed Transition (CET) modeling with the Rosenthal solution in earlier work based on laser cladding [3]. Rappaz et. al. provided a detailed modeling of the microstructure/columnar orientation based on the solidification velocity and crystalline orientation [4]. This approach is based on the selection of the growth direction that closely follows the melt pool normal direction. Later on, substrate orientation is also taken into account [5, 6]."

Jan 1, 2013

By Kenneth G. Thomas

This paper reviews the alkaline and acid gold autoclaving experiences gained at Barrick Gold Corporation. Alkaline autoclaving was operational at Barrick Mercur, Utah, U.S.A., on carbonaceous/sulphide refractory ore for eight years commencing in 1988. Acid autoclaves have been operational at Barrick Goldstrike, Nevada, U.S.A., on sulphide refractory ore since 1990 and now process 17,500 stpd of ore through six large autoclaves. Information is presented on operating costs, materials of construction, reagent requirements and flow sheet developments that reduced capital and operating costs.

Jan 1, 2000

By Norihiko Fukatsu

In order to use effectively the previously reported new sensing system for hydrogen and oxygen potentials in molten copper, the criteria of the potentials for getting sound castings have been determined in the laboratory experiment. The copper melt equilibrated with a given hydrogen and an oxygen potential was rapidly quenched in the crucible. The relations between the holding potentials and the gas porosity in the solidified sample were investigated by measuring the density of the sample and microscopic observations. It was found that the defects of the gas porosity became the maximum at the potentials where the dissolved amount of hydrogen and oxygen was in the mole ratio 2: I. The samples having the density more than 99% of the theoretical value were obtained in the higher oxygen and lower hydrogen potential region or in the lower oxygen and higher hydrogen potential region. The criteria thus determined were examined by comparing with the measured potentials in the practical easting machine. In tough-pitch copper casting, the problem due to gas porosity was found to be serious when the hydrogen potential increased. In the oxygen-free copper casting, the evolution of hydrogen was found not avoided. The gas porosity in the casting, however, was found eliminated when the oxygen potential was kept at a low value.

Jan 1, 2003

By Brian G. Thomas

Quality problems in continuous casting of steel can be identified as they occur by monitoring mold signals (level sensor, thermocouples in the mold walls, friction etc.) and taking appropriate action (such as slowing casting speed, changing taper, changing a clogged nozzle, or later visual inspection of the surface for possible downgrading. Surface depressions and groups of deep oscillation marks form at meniscus and reduce local heat transfer as they move down the mold at the casting speed. This slows shell growth, increases shell surface temperature, and causes characteristic dips in mold thermocouple signals. More importantly, they are also associated with longitudinal cracks. Characteristic thermocouple signatures have been identified for many defects, including sticker breakouts, transverse depressions and deep oscillation marks, narrow-face bleeds, transverse comer cracks, longitudinal cracks, mold level fluctuation defects, and other problems. With the help of computational models, these mold signals should be used to troubleshoot defects, and to take appropriate corrective action. Keywords: Continuous casting, defect detection, thermocouple signals, on-line control

Jan 1, 2003

By Huanmei Yuan, Yuanyuan Wang, Hao Bai

Composite phase change materials are widely used in energy-saving and energy efficient process. Nano-encapsulated phase change materials are especially significant for making advanced working fluid applicable to waste heat recovery or storage. In this study, silica-coated stearic acid (SA) Nano composite phase change materials were prepared from tetraethyl orthosilicate (TEOS) and stearic acid (SA) via sol-gel process. The materials were investigated by Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy(FT-IR) and Differential scanning calorimeter (DSC).The FE-SEM and TEM results show that monodisperse microspheres with stable core– shell structure were formed and SA was encapsulated in the silicon dioxide shell. The FT-IR results show that there were no chemical reaction between silicon dioxide and SA, which is the chemical property of the composite material, is stable. The DSC results show that the composite phase change material has favorable heat capacity.

Jan 1, 2016

By Chikabumi Yamauchi, Mitsuru Tanahashi, Jutaro Miura, Takaharu Iwadachi, Toshiharu Fujisawa

"Tue oxidation behavior of molten Cu-Be alloys was investigated by exposing· the molten Cu-Be alloys to various Ar-O2 atmospheres to control the oxygen partial pressure, PO2 = 10 ~105 Pa at 1423 K. The following results were obtained:• The oxygen · partial pressure in gas phase affects the morphology of the oxide formed on the surface of the alloy and · the oxidation rate of beryllium.• At lower oxygen partial pressure, a molten Cu-Be alloy is covered with a homogeneous and compact internal layer of BeO. Thus, the beryllium oxidation rate can be minimized.• By adding a small amount of calcium or zirconium into the molten Cu-0.5 mass% Be alloy, a protective BeO layer is formed even at higher oxygen partial pressure. Thus, the beryllium oxidation rate can be reduced.IntroductionCopper-beryllium (Cu-Be) alloys are well recognized for their unique properties, such as high electrical conductivity, high strength, high fatigue strength, excellent properties at elevated temperatures, good formability and good corrosion resistance. .This extraordinary collection of properties are the reasons why Cu-Be alloys are expected to be ""Key-materials"", which are necessary to further advance science and technology and to be applied in.various fields such as electronic devices, machine parts, repeater housings of undersea optical fiber communication cables, etc.However, a large amount of beryllium is oxidized to BeO in melting stage of the current Cu-Be alloy production process, because beryllium is a highly reactive element. This is one of the ·main factors that negatively affect the production yield and th_e product quality."

Jan 1, 2000

By M. Huang

A conductivity-based sensor for on-line measurement of free acid was recently built. This sensor is suitable for high ionic strength solutions and its corrosion-free operation is based on induction currents. It has been tested against literature data and measurements made using a previous developed contact-type conductivity cell, with an average difference within 1%. The electrical conductivities of H2SO4?H2O, H2SO4?MgSO4?H2O and NaCl?Laterite-H2Osolutions at temperatures up to 250 °C were discussed. It was found that the solution conductivity depends on various factors, such as the electrolyte concentrations, the type of electrolytes, temperature and the amount of dispersions. A semi-empirical model was developed to account for all the factors discussed. This model was further tested on actual process solutions from the hydrometallurgy of nickel where sulphuric acid solutions containing a variety of metal sulphates and solids. The average difference between the estimated acid concentration from this model and the one from titration was generally less than 5%, which is excellent for industrial applications.

Jan 1, 2006

By William A. Hockings

Methods for the measurement of liberation of finely ground iron ores are described. The general method consists of separating a sample of the ground ore into a number of size fractions, followed by measuring the liberation of each fraction. The size separation has been done using electro-formed screens of 20-, 10-and 5-micrometer apertures, and also by air elutriation. Liberation (i.e., the distribution of compositions of individual particles) has been measured by optical microscopy. A computer pro-gram was used to adjust the raw count data so that it agrees with the chemical analyses of the size fractions. Various ways of presenting the results are given, and Some applications of the results to flotation processing are discussed.

Jan 1, 1981

By K. Watling

Vibrational spectra of surface and solution compounds formed during cyclic voltammetry of a gold electrode in a deoxygenated 0.01 mol dm-3 NaCN solution have been examined using surface-enhanced Raman scattering (SERS) spectroscopy. The presence of cyanide at the electrode surface was indicated by Raman bands characteristic of the carbon-nitrogen stretch, CN.. Chemisorption of cyanide on the gold surface was evidenced by the presence of vibrational modes due to gold-carbon stretching, AuC, and gold-carbon-nitrogen bending, AuCN. Prior to the disappearance of the surface cyanide stretch band, a limiting value of the CN was obtained, the same as the value reported for adsorbed cyanide. Effects upon the voltammetry and vibrational modes of surface species due to additions of silver and lead to the gold-cyanide system have been observed.

Jan 1, 2003

"An experimental study has been performed to investigate the dispersed phase holdup induced by a high-strength submerged gas injection in a bottom blown air-stirred one-seventh water model of CLU (Creusot-Loire Uddeholm) reactor using two different tuyere configurations. The air flow rates varied from 0.00599 m3/sec to 0.01312 m3/sec. In these series of experiments, water height and kerosene height were kept constant at 0.23m and 0.02m respectively. The dispersed phase holdup was determined at various gas flow rates, and tuyere orientations by using water and kerosene.The dispersed phase holdup increased with gas injection rate and decreased with vertical distance from the original interface. At constant gas flow rate, as the vertical distance increased in the centerline, off-center configuration of nozzles displayed higher values of the dispersed phase holdup than those of the center configuration. The variation of the dispersed phase holdup with the dimensionless axial distance and the gas injection rate was correlated by using the Modified Froude Number. The experimental values of the dispersed phase holdup were found to be in good agreement with the calculated values obtained from the correlation equations."

Jan 1, 1999

By Peng ZANG, Qihang Liu

Experimental work was conducted to determine the relationships of coal char conversion with temperature and heat absorption. The results show that at an earlier stage of the coke forming process, lump coal would absorb large amounts of heat but the increase of high temperature strength of lump coal was not significant. Contrarily, the lump coal’s high temperature strength was greatly improved at later stage of coke forming process. A number of residual coal was found in most tuyere coke samples illustrating that the lump coals added in the melter gasifier were not completely transformed into coke when they arrived at the tuyere region. The results indicate that the improvement of lump coal’s high temperature performance is limited in the melting gasifier by the low coke forming rate which could become the core factor of fines generation of lump coal in the melting gasifier.

Jan 1, 2016

By Thomas Frost

In this time of market globalization, many industrial companies are including detailed arbitration clauses in their international contracts, in order to avoid the potential costs, delays, and uncertainties of litigation in foreign courts. Arbitration is less expensive and more flexible, procedurally, than court proceedings, and arbitral awards enjoy much greater international recognition than judgments of national courts. More than 134 countries have signed the 1958 United Nations Convention on the Recognition and Enforcement of Foreign Arbitral Awards, known as the "New York Convention", which facilitates the enforcement of arbitral awards internationally. There are several other similar arbitration conventions that provide for the enforcement of cross-border arbitral awards. Additionally, arbitral awards are not subject to appeal, whereas judgments of national courts are routinely subjected to a lengthy appeals process, and there are very few viable bases to challenge arbitral awards. This discussion will review key considerations in drafting arbitration clauses, including choice of law and choice of forum considerations; issues surrounding the selection of arbitrators; the discovery process; presentation of evidence; and enforcement of arbitral awards.

Jan 1, 2006

By D. Zhao

High temperature deformation characteristics of austenitic 304L, and martensitic 410 and 416 stainless steels were investigated by conducting compression tests over a wide range of temperatures and strain rates (950-1250 C and 0.001-20 s-1). Flow behaviors of the three alloys were characterized. Optical metallography was performed to determine the as-deformed microstructures. The flow behaviors were related to microstructural phenomena during high temperature deformation. Dynamic recrystallization was responsible for the flow softening. Both dynamic and static recrystallization were operating, and the recrystallized grain size increased with increasing temperature and decreasing strain rate. Strain rate sensitivity was found to increased with increasing temperature and decreasing strain rate. No defects such as cracking and shear bands were observed at those test conditions. Preferred processing conditions can be selected by considering as-deformed microstructure and strain rate sensitivity.

Jan 1, 1994

By Wayne Bell, Shivanand A. Borkar, Anish Upadhyaya, Matthew D. Andriese, Jiann-Yang Hwang, Zhiwei Peng

"A refractory ore body located in Michigan’s Upper Peninsula contains high concentrations of nickel and copper chiefly occurring in the minerals pyrrhotite, chalcopyrite, and pentlandite. Refractory ore bodies are difficult to treat by conventional mineral processing methods so microwave pre-treatment of the ore is employed to increase metallic-particle/host rock liberation by making use the differential thermal expansion properties of the mineral phases that absorb microwave energy. The Curie temperature measurement of metallic-bearing particles is in agreement with the known value for pyrrhotite occurring at 325°C. A nickel-rich iron sulfide mineral is found to be in occurrence and also appears to be magnetic under BSE imaging. It is shown the ore particles heat rapidly when exposed to microwave radiation for short durations of time mainly due to the high concentration of ferromagnetic mineral phases. Rapid heating causes thermal expansion of constituent mineral phases that produce cracks within ore particles. SEM imaging shows fracture occurring along grain boundaries and throughout host rock matrix. Ball milling experiments show an increased grindability of the ore resulting in a decrease in work index values.IntroductionCrushing and grinding operations consume 50-70% amount of energy used in mineral processing operations [1]. All these processes involve high energy impact of surfaces to develop compressive stresses that produce cracks to initiate breakage of particles. Microwave pre-treatment of certain types of ore might provide an energy savings to these type grinding processes by taking advantage of the tensional forces produced by selectively heating microwave absorbing type mineral phases. The heating of ore particles produces cracking by thermal expansion of the constituent mineral phases. Conventional heating has been investigated and shown to positively aid in grinding processes but determined energy inefficient to be used commercially."

Jan 1, 2011

By Ian Masters

Rotary furnaces are widely used throughout the metals industry. These furnaces vary in size and geometry, but are fundamentally the same from a thermodynamic viewpoint. A generic method is proposed that can be used to model all furnaces of this type, provided that the correct material and process parameters are known. Various approaches have been attempted in the past based on a continuum (FEA or CFD) approach. However, the complex fluidlsolid interactions present in a rotary vessel are not easily solved using these methods, which work best where the material boundaries are well defined. In this paper a lumped parameter model is proposed. Variations within a section of the model are ignored, but to ensure thermodynamic correctness, the heat transfer between sections is carefully considered. For example, it is reasonable to assume that the whole of the melt pool is at the same temperature, due to rotary mixing. This may then be modeled with a single set of parameters, and the detail is contained in obtaining the correct heat transfer mechanisms from the rest of the furnace.

Jan 1, 2002

By James J. Komadina, Robert R. Beebe

"Heap leaching of gold ores has enjoyed wide acceptance in the arid and semi-arid regions of the western U.S., Australia and South America. There are areas, however, where cold weather or excessive precipitation can limit the usefulness of heap leaching. Even in Nevada difficulties can be encountered which call for special operating procedures.The paper discusses the general climatological limitations and some of the techniques used to extend heap leaching into colder conditions. A case history of the Cripple Creek and Victor Gold Mining Company operation in Colorado examines 'valley-fill"" technology as an ideal cold-climate solution, where topographical conditions permit.AcknowledgementsThe authors gratefully acknowledge the management of Independence Mining Company for their permission to present this paper. The contributions of Golder Associates; Pikes Peak Mining Company Environmental Affairs Department staff, and the Colorado Department of Mines and Geology were all invaluable in successfully concluding this project.BackgroundWhen heap leaching of oxidized gold ores was introduced in the rnid-1970s it was aimed at large tonnages of low-grade material which could not, in general, be developed via conventional milling. Normally, the reasons for this were economic rather than technical: capital and operating costs for milling were simply too high. At first, grade was almost the only criterion, but deposits too small to justify milling were also potential targets for heap leaching.Renewed interest in gold was centered in the western United States and Australia, where exploration for milling-grade deposits had never really died. When heap leaching came along, it was in these areas that the first developments took place. Coincidentally, these same areas were favorable for heap leaching: climates were temperate for most of the year and competing land uses were limited. Even so, in the western United States in particular, winter temperatures were low enough to complicate operations. Precipitation was less a problem, although heavy snowfalls could periodically interfere as well."

Jan 1, 1997

By Li Cheng

The SKS copper smelting process was jointly developed by Shuikoushan Mining Corp. and ENFI (Beijing Central Engineering and Research Institute for Non-ferrous Metallurgical Industries) in China. It is a new bath copper concentrate smelting process with oxygen enriched air. The pilot plant testwork was completed successfully in 1993. SKS has demonstrated to be an advanced bottom blown smelting process. This technology got the First Class Prize of Scientific and Technological Progress awarded by CNNC (China National Non-ferrous Metal Industry Corp.) in 1994. The SKS process has significant capital and operating cost advantages. Its environmental and industrial safety and hygiene performance represents a substantial improvement when compared to conventional technologies. The technology has generated great interest in the Chinese metallurgical industry. Feasibility studies and basic designs have been carried out to incorporate in retrofit and green field smelter projects in China and abroad. This paper describes the history of the pilot plant operating data (50 tonnes dry feed/day), and discusses the features of the SKS technology, its application and possible future trends.

Jan 1, 1999

By Hongfa Hu, Stavros A. Argyropoulos

"This paper describes a mathematical model which simulates numerically reaction driven fluid flow phenomena. The driving force of this reaction is an exothermic heat of mixing. In addition, the model predicts the heat and mass transfer phenomena where both heat source and heat sink co-exist in close proximity. The heat source is generated by an exothermic reaction. The heat sink is formed by a moving boundary such as the melting of a solid. This type of phenomena occur quite often in various metal processing operations in which exothermic additions are immersed in liquid metals. The model is based on the SIMPLER algorithm and uses an enthalpy method to predict the fluid flow, temperature, and concentration fields. The results indicate that the exothermic mixing reaction was responsible for an abrupt rise in temperature around the moving boundary. The intensity of this reaction was also found to be responsible for the enhanced convection of fluid and the acceleration of the moving boundary. The modelling results were also verified by experimental work which included velocity and temperature measurements in a low temperature physical model. IntroductionAlloying additions are used extensively in the treatment of liquid metals during metallurgical processes. The alloying additions introduced into liquid metals can be classified into various classes, each of which follows its own route[l]. As a major group, the exothermic additions follow two different steps during their assimilation into liquid metals. In the first step, upon immersion, a metal shell solidifies around such additions, and then melts back. At this point, the second step commences. During this second step, due to the mixing of the addition with a liquid metal, an exothermic reaction occurs, which liberates large amounts of heat, resulting in an enhanced convection in the liquid metal surrounding the addition."

Jan 1, 1994

By Sergey Komarov, Manuela Diaz, Sano. Masamichi

"Mixing time, bubble behavior and absorption rate of gas injected into a liquid bath through rotary L-shaped lances have been studied by cold models with an effort to improve refining characteristics of metallurgical processes. Two kinds of the rotary lances were tested, namely the single-hole lance and the multi-hole lance. The effects of gas flow rate, bath depth and rotation speed were examined.It is found that when gas is injected through the rotary lances, the mixing intensity and the gas absorption rate are larger than that for the gas injection through stationary lances. The effect of rotation speed decreases as the bath depth and the gas flow rate increase.The multi-hole lance produces much smaller bubbles, which lead to an increase in the volumetric mass transfer coefficient by 3-4 times as compared with the single-hole lance. However, the effect of rotation speed is smaller for the multi-hole lance. The obtained results are explained in terms of the bubble coalescence and fragmentation, the rate of which depends on the departure bubble size and the power supplied to the liquid bath.IntroductionIn recent years, there has been a growing interest in the development of gas injector for metallurgical processes. The majority of the previous work was focused on modification to the injector design to improve mixing and to increase the of chemical reaction rate. These two goals can not be necessarily achieved by the same way. Bottom nozzles and stationary immersed top lances, which have been widely applied to steelmaking processes, are effective for the bath mixing, but have a limit to decrease in the bubble size. This results from a vigorous coalescence occurring between the bubbles when they rise in the molten bath as a bubble swarm.One of the ways to ensure the small bubble size and the effective bath stirring is the gas purging through rotary injectors. A number of studies have been undertaken to improve the refining characteristics by using rotary injectors. All of them are related to aluminum refining. The SNIF equipment (The Spinning Nozzle Inert Flotation) has significantly improved the quality of aluminum products at National Luxemburg Aluminum [1]. Rotary injectors made in the form of a disc have been applied to the Alcoa 622 [2] and the GBF processes [3]. A study of the gas injection by a rotary impeller has been carried out by C. Leroy and G. Pignacelt [4]. All researchers note the significant improvement in removal of sodium, calcium, hydrogen and non-metallic inclusion."

Jan 1, 1996