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By Brad Wahlquist

An ex-situ biological treatment system was implemented at a gold mine site in South Dakota. The system removes selenium and nitrate from a mixture of groundwater and surface water runoff at ambient water temperatures. The Applied Biosciences? system replaced a denitrification system that did not perform consistently, did not treat for selenium and required heating of the influent water. Installation was completed in phases starting with the selenium circuit being brought into operation in February, 2002 and the nitrate circuit in March, 2002. System design can accommodate average flows of 380 L/min (100 gallons/minute) and a maximum flow of 1,136 L/min (300 gallons/min). Four cells were designed to remove nitrate from approximately 30 mg/L to below 10 mg/L and two cells were designed to remove selenium from 0.01 mg/L and higher, to below 0.005 mg/L. No pretreatment is required to operate the system at ambient temperatures, which can fall as low as -12C in the winter, and treat water at temperatures ranging between 8C to 16C. Nutrient requirements are met using a sugar based nutrient mixture that includes a balanced C:N:P:S ratio, trace elements and vitamins. Since start up, the system has consistently been in compliance for nitrate and selenium, treating water to below detection limits for both contaminants. This paper discusses laboratory biotreatability testing of a system designed to remove selenium, arsenic, and nitrate and full-scale implementation and optimization of a system to remove nitrate and selenium.

Jan 1, 2003

By David Forrest

In 1981, K. E. Drexler proposed using massively parallel nanomechanical systems to manufacture large atomically exact structures. As in macroscopic mechanical systems, they would contain components that serve traditional functions such as trusses for support, gears to transmit power, bearings for low-friction support of rotating surfaces, motors to supply torque, pipes and conveyor belts for material transport, and channels for coolant. Many of these components would only contain a few thousand atoms. Specific designs for these devices became available in the early 1990s, and a few working devices appeared in laboratories by the early 2000s. As advances continue, a thorough understanding of the operative transport phenomena will guide the intelligent design and construction of nanomechanical structures, devices, and systems. The familiar equations of continuum mechanics are generally inadequate to describe the flow of heat and mass in the proposed nanosystems. Boundary conditions often need to be described in terms of potential surfaces. Surfaces are not geometrically smooth, but periodic according to the locations of atomic nuclei. Friction occurs not due to the plastic deformation of asperities on mating surfaces, but to phenomena such as thermoelastic damping and phonon viscosity when atoms slide past each other. Electrostatic forces dominate over gravitational forces by orders of magnitude; there is no role here for natural convection. Structural components, no matter how stiff and strong, are in constant motion due to the thermal noise in the system. The fluids are described in terms of individual molecules in constant motion.

Jan 1, 2006

By Rachel De Lucas

Current methods of hydrogen storage are an impediment to the transition of our energy infrastructure from a hydrocarbon to a hydrogen base. The transportation, handling, and storage costs of hydrogen gas account for a majority of its selling price. Magnesium hydride slurry is a safe, environmentally friendly alternative for hydrogen storage. If this form of storage is to be adopted on a large scale, a cost-effective method for recycling the enormous amounts of magnesium hydroxide byproduct must be identified. The solid oxide membrane (SOM) process can be used to recycle the magnesium hydroxide byproduct into magnesium metal, which can be reformed into magnesium hydride and reused for fuel storage. Conventional magnesium extraction/recycling technologies require a great deal of energy and create byproducts that are harmful to the environment and human health. The SOM process poses none of these detrimental effects and requires less energy and feed preparation. The economic viability of a facility that utilizes the solid oxide membrane process for the direct reduction of magnesium must be examined in more detail if industry is to consider it. Cost analysis data related to the commercial viability of a scale-up will be compared to two standard industrial processes: current magnesium production techniques including electrolytic and metallo-thermic processes. We have shown in our cost comparison that the SOM process is cheaper than these traditional techniques and that it is also comparable to aluminum's Hall-Héroult process in cost but with none of the environmentally harmful byproducts.

Jan 1, 2006

By Migen Dibra

Antitrust and competition laws are designed to protect the free markets and promote competition in order to assure a dynamic and efficient economy and to provide competitive prices for quality products and services. They apply to mergers and acquisitions as well as to joint ventures especially among competitor companies who possess market power and these include collaborations on research and development. If it is determined that these actions are likely to substantially prevent or lessen competition the courts might dissolve, stop, alternate them, etc. Two new factors affect this process today: The role of new technologies and the markets globalization. They both have a considerable effect on the way these laws are interpreted by the courts and on their eventual amendments in order to reflect the new reality. A new applied technology and the globalization separately or together may change the factors that determine how anticompetitive a merger or acquisition between competitors may be and may also serve as a basis for amending the antitrust and competition laws. In this paper, a short review of the recent mergers and acquisitions of various companies has been carried out along with an abridged analysis of the current antitrust and competition laws in USA, Canada and European Union in the view of their capacity to handle the new reality. Some related court decisions are also examined and several examples are given in order to illustrate the influence of new technologies and globalization in interpreting the existing laws and on their amendment possibilities.

Jan 1, 2006

By Jonathan A. Paul

The most profitable companies in the world recognize that a huge competitive and financial power lies in their intangible assets. The competition to be in command of raw materials and markets is now waged more and more over the exclusive rights to new technology and ideas. The value gained from mining the innovation in your organization and protecting your intellectual property can be enormous. This paper will address the following topics: ? Understanding the connection between your competitive position and intellectual property ? Determining the value of your current portfolio and strengthening protection ? Converting knowledge into assets and adding value to the operation ? Litigation strategies to enforce your position and achieve your business objectives The presentation is designed for company executives and government managers who need to know how to identify and address core intellectual property issues that arise in the minerals, metals and materials extraction and processing industries.

Jan 1, 2006

By M. M. Sadawy

"The increased rate of exploitation of iron ores has resulted in a rapid depletion of high-grade iron ore deposits in Egypt. New iron reserves have to be discovered to secure the iron ore for steel production. This paper aims to study the characterization and magnetic separation of low grade Aswan iron ore. The results showed that Aswan iron ore is composed of oolitic hematite, goethite, quartz and kaolinite. The screen analysis indicated that Aswan iron ore had a uniform distribution of iron and silica in the different particle size fractions and there is no any particle size has high amount of iron or low content of silica. On the other hand the results of dry high intensity magnetic separation illustrated that this technique is not suitable for upgrading this ore.IntroductionIron is one of the common metals used in industry, as well as being the fundamental raw material used in iron-steel industry; products are wide spread even in daily uses. The total iron ore reserves of the world have been estimated as 3 70 billion tones; 160 billion tones is classified as economical, while 210 billion tones as potentially economical [1]. An estimated 98% of the iron ore exploited in the world is used in the manufacture of pig iron and steel, which are non-substitutable backbones of modem society. The rapid increase of world steel production over the last few years have required an equal increase in iron ore production, from 876.8 Mt in 2006 to 948.1 Mt in 2007 [2]. The increased rate of exploitation of iron ores has resulted in a rapid depletion of known high-grade iron ore deposits. This, in turn, has led to a dramatic increase of prices. In the absence of any major new discoveries of high-grade iron ore deposits, mining companies have turned to lower-grade materials to assess their beneficiation potential to expand their production base and beneficiation capacity, in order to satisfy future demand. Egypt is going to face shortage in iron production, consequently new iron reserves have to be discovered to secure the iron needed for the country [3]. Exploitation of low grade ores requires special equipments and techniques for recovery of minerals values. High gradient magnetic separators offer promise and great potential of application both technologically and economically in the processing of fine particles containing weakly or feebly paramagnetic components [4-6]. Within this existing framework, this research was initiated to assess the beneficiation potential of low-grade Aswan iron ore by high intensity magnetic separation."

Jan 1, 2013

By F. L. Meng, C. S. Henkel, R. M. Alchalabi

For secondary aluminum producers to maintain a profitable melting operation, five technical factors have to be taken into account from the initial furnace building decision to the final operation and production. These factors are furnace design, furnace equipment selection, furnace control, furnace charge selection and inventory, and furnace operation. Any of these five factors, if not chosen or performed wisely, will likely result in sub-optimal melting operation. As a result the MeltSim melting optimization package has been developed by the collaborative effort of Chinook Sciences and AMCS Corporation to take into account these five factors. The package is a mixture of hardware, software, science and experience. The package incorporates years of reverb furnace operational observations, start-up installations, furnace operator experience and furnace physiochemical mathematical model development. The optimization package enables aluminum producers to design new furnaces, select and place proper equipment, optimize existing furnace operations, and convert air-fuel installations to oxy-fuel. The package provides furnace operation monitoring and advisory signals, and furnace automatic optimal control to furnace operators, shift supervisors and plant managers, all customized, based on plant and melter need and ease of information management.

Jan 1, 2000

By A. V. Tarasov

Regeneration of carbide waste from hard-alloy (sintered carbide) manufacture is an important scientific and technical objective aimed at improving the degree of recycling of rare metals (W, Co, Ta, Ti, Nb). Currently, the degree of recycling of those metals does not exceed 25% to 35% of their total production even in industrially developed countries. This is attributed to a significant extent to the substantial drawbacks of the technologies applied for their processing (environmental pollution, limitations to the use of regenerated products for important applications, sophisticated equipment to be used). An innovative environmentally sound technology has been developed in the Institute of Metallurgy of the Russian Academy of Sciences (IMET RAN) for processing of carbide waste of WC, TiC, TTC and other carbides using asymmetric alternating current of industrial frequency (the electrolyte used for this purpose is nitric acid solution). The current efficiency under optimal conditions is as high as 96% to 98%. The process has been tested on bench scale. The following commercial-grade products are obtained: pure ammonium paratungstate, tungstic acid, cobalt oxide, titanium dioxide and tantalum-niobium concentrate. The total metals recovery is 98% to 99%.

Jan 1, 2006

By Dan Adams

A number of gas-liquid processes require high intensity agitation systems to provide uniform blending and dispersion of reactants in order to achieve desired end products. Processes such as hydrogenation, fermentation, and minerals processing have used conventional down pumping or radial agitation systems with some success. In 1996, LIGHTNIN introduced the concept of Up-Pumping to the industrial marketplace as an improved mixing technology for these applications. For processes requiring gas-liquid mass transfer, such as those listed above, conventional mixing technology requires the use of gas introduction devices (sparges) below impellers. These devices can be a maintenance concern due to plugging and erosion in the presence of solids. Up-Pumping impeller systems are able to draw in a significant amount of gas from the headspace, much more so than conventional vortexing impellers designed for headspace gas incorporation. This paper will demonstrate the effectiveness of Up-Pumping impeller systems that have the potential to eliminate need for sparge devices entirely. It demonstrates the ability of Up-Pumpers to re-entrain gas for higher utilization compared with conventional impeller technology. This is significant in applications using costly gases such as enriched oxygen or hydrogen, reducing overall operating costs of production.

Jan 1, 2003

By A. V. Tarasov

In order to improve technical, economic and environmental performance of hydrometallurgical processing of intermediate products containing copper and nickel, the Gintsvetmet Institute and the IMET Institute of the Russian Academy of Sciences have conducted studies into the efficiency of the use of alternating current of industrial frequency on processes applied for hydrochemical leaching of various copper- and nickel-containing materials. It has been found that: 1.Imposition of alternating current over the process of leaching of softly reduced nickel oxide with recycled copper sulfate solutions resulted in an increase by 20 to 30% of the rate of the copper cementation process and reduced by 20% its activation energy. At the same time, the recoveries of nickel, cobalt and iron to the leach solution increased up to 82.2%, 78.5% and 57.1%, respectively, and that of copper to the cement precipitate up to 74%. Optimal process conditions have been identified with respect to the current density, electrode material, copper concentration in solutions and the process temperature. 2.In the process of hydroelectrochemical sulfuric acid leaching of nickel and copper sulfides, the grain size, the phase form of sulfides, the solution composition (H2SO4, Cl?, Cu2+, Fe3+)and the current amperage had an effect on the nickel recovery to the solution, which reached 90%, while the degree of copper transfer to solution did not exceed 20%. The process of hydroelectrochemical sulfuric acid leaching of nickel and copper sulfides with an addition of Cl? made it possible to selectively recover nickel into the leach solution along with concentrating copper in the leach residue. 3.When subjecting samples of commercial-grade magnetic fractions of converter matte to sulfuric acid leaching, the imposition of electric current, the concentrations of sulfuric acid and chloride ion in the solution and the duration of the reaction process had an effect on the process. The nickel recovery was 85% and that of cobalt and iron was 95% and the recoveries reached 97.5%, 98.3% and 99.8% as a result of repeated treatment of the primary residue under similar process conditions. Up to 75% of copper, 75% of sulfur and 99.0-99.5% of palladium was concentrated in the solid reach residues. The experimental data obtained indicates that the use of AC for hydroelectrochemical sulfuric acid leaching for separation of copper- and nickel-containing intermediate products has favorable prospects.

Jan 1, 2003

By W. C. Hellyer

The papers in this section provide several examples of the application of Process Mineralogy to metallurgical problems. Any experienced metallurgist could cite numerous other examples when process mineralogy has, or could have, provided data of value in his understanding of metallurgical processes. The data developed by mineralogic techniques may supplement conventional chemical analyses, but cannot be replaced by assays. Mineralogic and chemical analyses each provide different types of information. In order for the process mineralogist to interpret his results in the most useful manner, it is desirable that he should have some knowledge of metallurgical processes. Conversely, the metallurgist should have some knowledge of mineralogic techniques to understand the scope and limitations. Mineralogic examinations are time-consuming and expensive. To ensure the effort is not wasted, and indeed does not generate misleading information, the utmost care must be taken at every stage of sampling and sample preparation. The mineralogist may examine microscopically or by x-ray diffraction a one-gram sample representing a flow of possibly thousands of tons per day through a concentrator. Conditions in a concentrator change continually in response to changes in feed rate, feed characteristics, grind, reagent additions, temperature, circulating loads, etc. Lengthy sampling periods are required to ensure the samples examined are representative of average conditions. The sampling program should be drawn up jointly by the metallurgist and mineralogist. Sampling points should be selected with a view to ease of sample cutting. The sampler should be instructed in the method of cutting the samples, the weight or volume of sample to be taken at each cut, the sampling frequency, and sampling period. The sampling period required depends on the scope of the investigation. For example, if a complete survey is to be made of all final and intermediate products of a flotation concentrator, samples should be cut at not more than two-hour intervals, twenty-four hours per day, for not less than one week. For a more limited investigation of one circuit or one section of a concentrator, 'the sampling frequency could be increased to every hour and the sampling period reduced to one or two days.

Jan 1, 1981

By Shuo Wang, Yu Wang, Bing Xie, Rui Tang, Hong-Yi Li, Kun Wen

"During present converter vanadium extraction process, phosphorus could not be removed from hot metal due to absence of CaO in slag though it is an efficient way for vanadium extraction. In order to improve the phosphorus remove and produce CaO-containing vanadium slag, which could be directly used in subsequent roasting process, during the converter vanadium extraction process, lime dissolution in FeOx-Si02-V203-Ti02 slag was investigated by using a rotating cylinder technique and the slag-lime interface was characterized by SEM/EDS. Results showed that changes in the slag chemistry and phase compositions during the lime dissolution process were similar to that in CaO-Si02-FeOx based slag during the BOF process. The V and Ti in the slag were expected to diffuse into the lattice of2CaO·Si02 solid solution, which formed a rather thinner layer in thickness at the slag-lime interface than that in BOF process, leading to improvement of lime dissolution in the slag.IntroductionVanadium is important material that widely applied in industries. The traditional technique to extract vanadium was to leach vanadium after sodium salt roasting. However, the sodium salt roasting process has several problems including lower yielding rate[!] and environmental pollution[2]. Therefore, the more environment-friendly technique of calcium roasting[3-4] was proposed. In order to increase roasting efficiency of vanadium slag, it is essential to study the dissolution/reaction mechanism between lime and vanadium slag. Many investigations about the dissolution reaction of lime in molten slag have been carried out from the standpoints of rapid slagging to De-Pin steelmaking process[5-6]. However, their studies were focused on BOF slag and the reaction mechanism between solid lime and slag containing vanadium has not been reported yet. In present work, the dissolution process was studied with rotating cylinder technique and the reaction interfaces were observed and analyzed by SEM/EDS to elucidate the dissolution mechanism of lime in vanadium slag. This work was supported by National Natural Science Foundation of China No. 51090382."

Jan 1, 2013

By Laurence G. Dyer, David G. Dixon, John Rumball, Maziar Eghbalnia, Edouard Asselin

"Linear scan voltarnmetry was used to determine the reactions that occur during the cyanidation of petzite (Ag3AuTe2). Gold oxidation in petzite requires more oxidising conditions than are required for pure gold, it also does not achieve the same current (related to reaction rate). Tellurium oxidation occurs at a similar potential in water and cyanide, but as a component of petzite is impeded somewhat in water, likely due to the stability of the precious metals. Pre-treatment of petzite to oxidise tellurium in the absence of cyanide prior to gold recovery appears to be at least moderately successful.IntroductionWhile gold occurs most prevalently in its native form, many other gold bearing phases appear throughout natural systems [I]. Tellurides are a common group of such minerals, many of which also contain silver, often existing in association with native gold deposits. The six major gold-bearing tellurides are calaverite (AuTe2), sylvanite [(Au, Ag)2Te4], montbrayite [(AuSb)zTe3], krennerite [(Au1-x, Ag,)Te2], petzite (Ag3AuTe2) and muthmannite (AuAgTe2) [2]. While several other phases exist they are much more complex (i .e. buckhornite), which dilutes and confuses the influence of each specific component. Studies of gold tellurides have predominantly focussed on calaverite as it is the simplest and most common phase, however petzite, commonly found in Australia and North America, is the focus of this investigation.Gold processing via cyanidation has been operated for more than a century and is a highly effective hydrometallurgical treatment of native gold deposits. However, some gold alloys such as tellurides have proven to be somewhat less responsive under the same conditions. Several groups have shown that gold/silver tellurides are amenable to cyanidation, but are significantly more refractory than native gold [3]. Pre-oxidation steps have been tested to remove constituents that would consume cyanide such as sulfides. Such species are also linked to the precipitation of oxidised telluriwn, forming a passive layer, further inhibiting gold recovery [2]. It is uncertain to the definite reasons underpinning the refractory nature of precious metal tellurides in conventional cyanidation."

Jan 1, 2012

By M. Fafard, R. Ahmed, O. Dion-Martin

"The optimization of aluminum sheet and tube forming needs the use of large strain finite elements software. The precision of the predicted results from those simulations depends mainly on the quality of constitutive law of the material used. In order to improve quality of these simulations, Barlat has suggested a new yield function named YLD2000-2d. This criterion describes the anisotropic behavior of the rolled aluminum plates. This work consists of characterizing the AA5754 alloy and estimating the material parameters needed for the YLD2000-2d criterion in LS-DYNA. In order to get these parameters, various mechanical testing were performed such as bulge and tensile tests. Moreover, the bulge test was also used to obtain an estimation of work hardening curve in large strain condition, up to 50%. The objective of this paper is to share the experimental results of the characterization of AA5754 aluminum alloy.IntroductionResearchers from National Research Council Canada's Aluminium Technology Center (NRCATC) and Aluminium Research Centre - REGAL, are working on aluminium tube hydroforming processes of AA-5754-0 alloy, used in automotive industries. Hydroforming process presents several difficulties such as wall thinning and section changes. In order to control them, some parameters can be set during the process like pressure rate and end feed level [1]. Given the complexity of the parts and the variability of the control parameters, the use of finite element method (FEA), like LS-DYNA, based on large strain theory is thus necessary. The accuracy of predicted results depends mainly on the quality of the constitutive law used to model the behavior of material. FEA results seem to be valid with the von Mises yield criterion used in some cases. But, given the anisotropic properties of the AA-5754 alloy, a more appropriate criterion could be used. The *MAT_ BARLAT YLD2000 shell material criterion, developed by Barlat [2], who's taking into account the anisotropic behaviour, was chosen due to its large flexibility and its good adaptation to particular elastoplastic behavior of aluminum. However, the use of this criterion needs to determine some material parameters by experimental way."

Jan 1, 2013

By Alessandra Bonoli, Garfìm Marianna

"Construction and demolition waste (CDW) is no dangerous material resulting from construction, and demolition of houses, large building structures, roads, bridges, piers, and dams. It is possible to recycle these materials, to reduce environmental impacts, and to reuse them in construction sector. To evaluate in a correct way the possibility to reuse this material it is important to lead laboratory tests to assess the proprieties and quality characteristics. European, Italian and British ad hoc Committees had elaborated specific Standards, to evaluate Geometrical, Physical, and Chemical requirements of recycled materials. A research was carried on to define the guidelines for laboratory tests, their suggested values and quality standards. The Construction and Demolition Waste Construction and demolition waste (CDW) is no dangerous, uncontaminated material resulting from construction, renovation, repair, and demolition of houses, large building structures, roads, bridges, piers, and dams. CDW waste is made up of wood, steel, concrete, gypsum, masonry, railway ties, roofing materials, carpeting, insulation, plaster, metal, and asphalt, and all waste included in CER Code 17. In particular Demolition wastes are defined as materials resulting from the demolition, instead Construction wastes are defined as waste materials resulting during construction process or in pre-manufacturing construction industry. Environmental problems In a lot of cases Construction and Demolition Waste materials were discharged in landfills, these are filling up with CDW and others, and some of them will close in the near future. In addition, illegal dumping of CDW debris can result in future health risks, decreased property values, cleanup costs and enviromental problems. The typical environmental impacts generated by CDW dumps are: 1- Dust problem, which causes air pollution, as will as forming dirty areas. 2- Uncontrolled locations, that will encourage the disposal of other waste types with the usual construction wastes leading to an environmental disaster. 3- The degradation and deterioration of the coastal lands and the natural protectorates. 4- The loss of aesthetic features. 5- Occupation of large areas, causing extra hauling costs. Therefore, it is wise to find other alternatives, like reuse or recycling, other than landfilling CDW debris or illegal dumps, because a proper management and the reduction of CDW amount can save money, conserve resources, and preserve the environment."

Jan 1, 2008

By Robert T. Oxnard

"EXECUTIVE SUMMARYThe history of Refractory Recycling indicates there was little recycling until the 1950s. Energy incentives were the primary reason for the beginnings of a recycling effort by the refractory brick manufacturers. Quality benefits quickly became evident and fewer rejects were the result. Today, economic factors including higher valued raw materials and increased competition are the driving forces of refractory recycling.There are some success stories in refractory recycling but we have a long way to go. Few incentives, quality concerns, relatively cheap energy, comparatively lax government regulations, inexpensive landfills and inexpensive substitutes make recycling a difficult choice for many companies. Marketing advantages such as ISO 14000, eliminating multiple audits and reduced liability exposure can tip the scales toward recycling viability. Increasingly, the ideological philosophy of a company, a desire to minimize environmental impact and develop favorable public and other interested party perceptions can drive recycling and waste minimization efforts.Recycled materials can be more trouble ""up front"" and harder to ""manage"" due to their suspect quality. However, due to their nearly inexhaustible supply and the fact that once developed, they constantly contribute to the bottom line, they are certain to be the materials of the future. Waste refractory materials will likely see the same bright future as the steel scrap yards and slag piles of yesterday. In hindsight, we will realize that now was the perfect time to prepare and plan for the bright future of refractory recycling."

Jan 1, 2000

By Rong Yang, Qijie Zhai, Wenbin Xia, Changjiang Song

"Tills paper focus on the influence of carbon content and cooling rate on the microstructure and phase formation of Fe-Mn-C alloys under near-rapid solidification. When manganese content is about 11wt.%, more s-martensite can be obtained with cooling rate increasing when carbon content is 0.14wt.%, the formed phase changed from a phase to y phase when 0.74wt.% carbon is added to the samples, and when carbon content up to 2.1wt.%, carbide can be obtained in the sample. A host of stacking fault, which attributes to the strain-induced martensite, can be observed in the sample. The microhardness increased with cooling rate increasing, and under the same cooling rate, the microhardness of samples with 0.14wt.% carbon is highest.IntroductionTo obtain high performance materials is eternal pursuit of material science research. Material scientists have explored many new ways to obtain high performance materials from long time ago. Rapid solidification is one of most popular ways to produce advanced materials by obtaining metastable phases, because it is widely known that the solidification of metals in metastable phases gives access to a whole range of materials with novel properties [1]. Furthermore, nowadays metastable materials have been extensively used in many fields, for example, many of our modem high performance materials such as steel products or aluminum alloys for aeronautical applications are in the form of metastable rather than stable phases [1]."

Jan 1, 2012

By Ronald J. McGregor

An overview or precious metals project development and start-up, which emphasizes the process decision. Logic which determines process flowsheet, project economics, and training required to train new operators for start-up. The process decision required to successfully develop a precious metals project requires a blending of test data, environmental considerations and operations experience. Decisions to use Merrill-Crowe or carbon adsorption/ electrowinning/replating, fixed pad or multi-use pad {in heap leach) are dependent not only on technology but also on ability to train new operators. The market for experienced operators is acutely depleted and almost all new operators will have to be "home grown". Experience from the Brewer project in South Carolina as well as other projects put together in the West will be discussed.

Jan 1, 1989

By Renaud Metz

The DOPA process (Direct Oxidation of a Precursor Alloy) was used to prepare ceramic powders based on doped SnO2 and ZnO. The DOPA process consists essentially in the direct oxidation of a homogeneous precursor alloy. A unique advantage of this process is its rather benign environmental impact since no dangerous reactants are used and no harmful by-products are generated. Only oxygen and the alloy metals participate on the chemical reaction to produce the multi-component oxide. Homogeneous alloys of niobium, cobalt and chromium doped tin have been prepared. The molten metal alloy is atomised in air using a double fluid nozzle to produce metallic powders. A subsequent thermal treatment is carried out to fully oxidise the sprayed metal alloy powders. These raw powders are used to prepare a ceramic powder through a mill homogenisation and atomisation process. The ceramic powder is then uniaxially compacted in disc shape and sintered in an oxidising atmosphere. The resulting sintered bodies are metallised on their flat faces and the cylindrical surface is passivated using lead free glass enamel. These ceramics present excellent semiconducting properties with non-linear (non-ohmic) characteristics. The DOPA process is found to be an attractive procedure to obtain ceramic powders for the preparation of SnO2 varistors.

Jan 1, 2006

By Justin Karl, Ali Gordon, James DeMarco, Yongho Sohn

"Aluminum metal-matrix composites are lightweight materials that have the potential to supplant steel in many applications. The current work helps to identify the parameters that confer maximal strength and ductility. Torsion tests were performed on the as-cast aluminum metal-matrix composite A359-SiCp-30% at a variety of temperatures and twist rates. Dependence of material properties on temperature and strain rate were identified from equivalent stress-strain curves constructed from the reduced data. Examination of the microstructure was performed on the as-cast material and on fracture surfaces. A temperature-and strain rate-dependent constitutive model was applied to simulation of the mechanical response of the torsion specimen. Trends in material properties corroborate and extend trends identified previously under tensile loading with regard to temperature and strain rate dependence. Shear properties of simulated specimens agree with properties obtained through experimentation.IntroductionAluminum metal-matrix composites (A1-MMCs) have become increasingly popu1ar in recent years. While unreinforced aluminum alloys have low densities and high ductilities, they are not suitable for many applications due to their lack of strength and stiffness. To provide added strength and stiffness while maintaining favorable densities, it has become common to reinforce aluminum alloys with silicon carbide in various forms, although usually the inclusions are in the form of whiskers or particles. The result is a composite material with superior specific strength and stiffness. While whisker-reinforced composites are expensive due to the necessity of processing by nonstandard techniques and have low transverse properties when rolled, particle reinforced Al-MMCs have transverse material property values almost as high as the longitudinal properties and are not as expensive to process as whisker-reinforced Al-MMCs [1]."

Jan 1, 2012