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By R. D. Irwin, W. M. Mullins, E. A. Medina

"Various stability criteria are introduced and thermo-kinetic models for metallurgical processes are used as concrete examples for evaluation. Kinetic criteria for the process of dynamic recrystallization are proposed. These criteria are compared to the non-equilibrium thermodynamic approaches discussed in the literature. The application of macroscopic stability criteria to materials processing is then discussed.IntroductionThe mechanical behavior of metals at elevated temperature is very well predicted by any of several empirical constitutive relations. Typical is the power-law (or Swift's) form,Equationwhere r-is the stress, y is the strain and m, n , t0, y0 and Q are material constants. This form has been used with some success in the metals processing area [1]. In general, though, all of the empirical constitutive equations are static, failing to account for any dynamical properties of the system they seek to describe.The physics of warm deformation is qualitatively well understood. An example is power-law creep, where the dominant mechanism is assumed to be lattice diffusion limited climb of dislocations, which allows the strain-rate to be determined by the applied stress through"

Jan 1, 1997

By Jiayan Li, Yi Tan, Yao Liu, Yaqiong Li, Shenrui Wu

"A metallurgical grade silicon (MG-Si) refining concept process was presented. Under vacuum conditions, silicon was selectively oxidized by high purity silicon dioxide to form gaseous silicon monoxide while impurities with low vapor pressure in MG-Si were rejected in residue; Then high purity silicon was obtained from the disproportionation of condensed silicon monoxide; and by-produced silicon dioxide was recycled for the oxidation step. Thermodynamics on boron rejection during the oxidation were studied in this work. In the temperature range of 1200-1800K, the saturated vapor pressure of boron, and the Gibbs free energy changes, the equilibrium partial pressures of silicon monoxide and boron oxides of potential reactions were calculated. And the effect of boron activity in MG-Si was also discussed. The results indicated that boron in MG-Si can be rejected during the oxidation and it showed the potential for the further development of the new refining process.IntroductionAs global energy consumption growing dramatically, higher prices of energy and global warming problem have attracted more and more attention [1]. As a clean and renewable energy industry, the photovoltaic (PV) industry converts solar energy to electricity using solar cell device and has a growth rate of about 30% in recent years. It has caused a shortage of silicon feedstock due to that about 90% of solar cells are made of crystalline silicon. And high energy consumption during the production of silicon material, i.e. solar grade silicon (SoG-Si), is main obstacle for its mass production."

Jan 1, 2012

By H. Ipek

In this study the effects of interstitial ratios on k-feldspar samples were investigated. The k-feldspar samples were taken from Egypt using dry batch grinding conditions and a kinetic model. Three different mono size fractions (-3350+2360, -850+600 and -300+212 µm) were ground separately for 0.5, 1, 4, and 8 minutes and at four different interstitial ratios (125%, 100%, 75% and 50%) using a Bond mill with a mixture of five ball sizes. The mill used was at a size of 30.5 cm diameters, with 30.5 cm length, providing a total mill volume of 22272 cm3. The mill has a total mass consisting of 22648 g. steel ball mixtures of 38.10, 31.75, 25.40, 19.05 and 12.70mm diameters, occupying 22% of mill volume. The mill rotates at a speed of 70 rpm. The weights of the feed charges were 3000, 2000, 1000, and 500 g for 125%, 100%, 75% and 50% filling of the interstices of the balls respectively. The specific rate of breakage (Si) was determined from the top size fractions at different grinding times that were mentioned above and the model parameters were compared for the four different powder filling ratios (U). In many investigations, it has been found that an interstitial filling ratio of U = 0.6-1.1 is a good powder ball loading ratio to give an efficient breakage in a ball mill. In this study, it was found that U=1.25 is a good ratio for K-Feldspar.

Jan 1, 2006

By Seong-Jong Kim

The formation behavior and corrosion characteristics of anodic oxide films on pure Mg and Mg-AI alloys were investigated focusing on the effects of anodizing potential, Al content, temperature and NaOH concentration. Pure Mg and Mg-AI alloys were anodized for 10 min at 3, 10, 40, and 80 V in NaOH solutions. Mg(OH)2 was generated by an active dissolution reaction at the surface of the specimen and the product was affected by temperature while MgO generation increased with NaOH concentration. Moreover, the current density after anodizing for 10 min at a constant potential decreased with increasing AI content in Mg-AI alloys,

Jan 1, 2003

By Ryan Walton

The Flash Converting Furnace at Kennecott Utah Copper converted over 465kmt of high-grade matte in 2002 but was restricted due to low matte production to 395kmt in 2003. This paper presents updated operational performance data and describes improvements implemented since the mid 2001 rebuild. Matte burner feed distribution, silica and arsenic impacts on settler lime-based slag operability, blister laundering, uptake/boiler accretion control, and dust sulfation will be discussed, as well as current development requirements dictated by operational imperatives and furnace modification plans.

Jan 1, 2005

By Pragna Bhakta

The use of microbes for sulfide oxidation was investigated as a potential treatment option for low-grade refractory gold ores at Newmont Mining Corporation. The resulting patented technology for heap biooxidation maximizes oxidation rate by distributing the microbial population on the ore before placement on a heap. This paper presents data on global oxidation rates based on oxygen uptake in a 50-kg column for sulfidic refractory ores from the Gold Quarry mine. The oxygen uptake data was converted to a global oxidation rate. The calculated global oxidation rate was used to determine heap cycling times for Newmont?s commercial heap biooxidation facility.

Jan 1, 2003

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 Anthony C. Mulligan

Metals have historically been used in mining since they offer an excellent combination of hardness, toughness and cost and can be fabricated to form a variety of shapes. However, for many applications the metals used today have limited performance in the environments in which they are needed. This is particularly true for geothermal environments where the brines are highly siliceous causing corrosion and accelerated wear of many components. Geothermal sources are increasingly being explored for their high thermal value as well as possible sources for future minerals. While advanced ceramics have historically been expensive to produce in comparison with metals, they offer significantly greater corrosion resistance and hardness and can improve the overall performance when used in selected ?problem? areas. One of the major drawbacks in the use of ceramics in high impact areas has been their brittle nature and propensity to fracture and spall (fail) when loaded. Recent advances in the fabrication of ceramics have combined hard (strong) ceramics with more ductile ceramics in a architecturally designed microstructure, thus allowing ceramics to perform well in these high impact regions. Additionally, ceramics are significantly more inert to corrosion from either alkaline or acidic environments and can typically be used for significantly longer periods in these environments than their metallic counterparts.

Jan 1, 2006

By A. V. Tarasov

The nonferrous metals industry has been a sector with one of the highest growth rates during the recent years. The prospects for the Russian metals industry during the period until 2010 are associated first of all with a growing domestic demand for its products. The technological level of the metallurgical operations in Russia is relatively low in comparison with industrially developed countries: the average energy requirement is higher by 20% to 30%; the amount of generated waste in the process of rolled products manufacture is twice as high; the average labor productivity is lower by 2.5 to 3.0 times; the overall negative environmental impact is twice as high. Improvement of the technological level of the nonferrous metals production under the conditions of market economy is possible by application of innovative technologies for the development of this sector. The main trends for development of the nonferrous metals sector are: - meeting of more stringent requirements to the quality of concentrates; - more complete recovery of associated elements as commercial-grade products; - development of continuous process lines based on autogenous, resource-saving and environmentally safe processes; - use of combined technologies, including pyrometallurgical, hydrometallurgical and upgrading processes; - expansion of the fields of application for nonferrous metals and their alloys.

Jan 1, 2006

By Kaspar Tall, Dmitri Goljandin, Kristiina Vilsaar, Jaan Kers, Valdek Mikli, Lifeng Zhang, Riho Tarbe, Viktor Laurmaa, Mart Saarna, Priidu Peetsalu

In this paper, the mechanical milling of the Printed Circuit Boards (PCB) was carried out. First goal of the work was to examine the management of the WEEE, in particular the re-use of PCB. Firstly, recycling methods of PCBs were summarized. During the study mechanical separation methods (magnetic-, density- and air separaten), electrical, and chemical methods were examined. Secondly the optimal particle size for air-classification was determined. Several tests were carried out to find the most effective separation method for separation of different material groups from PCB scrap. The new air classification stand was developed for testing the separation of lightweight particles like tinfoil stripes and plastics. The test results showed sufficiently good separation of heavier Al and Cu. For milled materials characterization the SA, IA, laser diffraction analysis and SEM were used. The chemical composition of the PCB powders was studied by means of energy dispersive X-ray microanalysis (EDS).

Jan 1, 2011

By John O. Burckle

For years, the measurement of fugitive emissions from the primary copper converter has defied all attempts based on inferential measurements, It has been concluded by virtually all investigators that the only dependable tech¬nique to measure these emissions would be to completely enclose an operating converter to permit the capture and measurement of all emissions. However, complete enclosure with a metal hood is difficult; many of the most serious fugitive emissions result during periods when the converter must be attended with crane-operated equipment. This approach would require either opening of the enclosure to permit the entry of large items of equipment or completely new methods for charging and tapping converters' The installation of the air curtain hooding system at ASARCO's Tacoma smelter has permitted a quantitative approach to the direct measurement of the fugitive for the first time. In this program, the fugitives captured by the air curtain were measured at a downstream sampling point in the exhaust side of the air curtain system during the various portions of the converter cycle. Emission factors were established for sulfur dioxide, filterable particulate (method 5), inhalable particulate, and selected trace elements.

Jan 1, 1983

By Pradip

The selective adsorption of chemisorbing fatty acids at high temperatures together with the addition of soda ash and lignin sulfonate as depressants is the key to the industrial processing of bastnaesite ores. This paper presents the results of a fundamental investigation that indicate that alkyl hydroxamates can be an alternative collector for the beneficiation of bastnaesite ores that contain barite and calcite as the principal gangue minerals. The primary mechanism for providing sites for the chemisorption of hydroxamate on bastnaesite appears to be through dissolution of cations, formation of the respective hydroxo complexes and readsorption at the interface.

Jan 1, 1989

By Reinhold G. Schulze

Thiourea is being applied as an industrial leaching agent for gold and silver only in a few cases. A GIP technique was developed which eliminates most of the obstacles against its use. Omission of an acid treatment and mild conditions for precious metals stripping from the loaded carbon simplifies process conditions in comparison to cyanide CIP technique. Examples are given.

Jan 1, 1989

By Markus A. Reuter, Antoinette van Schaik

"Product design engineers select from a wide range of materials and combine them into multimaterial product designs. These include various materials (metals and non-metals) which are complexly integrated (e.g. welded, glued, alloyed, layered). The recycling/recovery rate of consumer products are determined by the different materials and alloys used, but also by the particle size and multi-material particle composition after shredding (combination of materials due to design). Eco-design (for recycling) and Design for Recycling (DfR) can only be conducted if the interconnectivity of material/metal in various unliberated materials is accounted for and its effect on material and energy recovery can be linked back to design. This paper will discuss the basic principles of these DfR models and it is shown how these tools (i) are linked Computer Aided Design (CAD) and Life Cycle Assessment (LCA) software, (ii) affect conceptual design specifications of products, (iii) integrate the complex detail of the recycling system and recyclate quality and hence (iv) make recycling an integrated part of the product system. Furthermore, it is shown how these assessment tools and models can be applied for benchmarking of the recyclability and environmental damage created by the recycling of end-oflife consumer goods in order to e.g. (i) provide the (original) equipment manufacturer with knowledge and solutions to support product stewardship and Extended Producer Responsibility; (ii) create awareness of the consequences/benefits of design, products and recycling systems to manufacturer, designer, legislator, recycler etc.; and (iii) assist the consumer in their choice of consumer goods from an end-of-life point of view.IntroductionA first-principles basis is required in order to be able to simulate and predict the recycling/recovery behaviour of products facilitating Design for Recycling (DfR) and Eco- Design. This links recycling technology and the environmental consequences of recycling directly to product design."

Jan 1, 2008

By Shunli Zhang

Metals recovery from electronic scrap by physical separation may provide an alternative to the current recycling approach, through which halogenated flame retardants can result in hazardous dibenzo-p-dioxins and dibenzo-furans. On the basis of a complete sink-float analysis of personal computer and printed circuit board scrap, and in view of the advantages of dry processes for electronic scrap recycling by mechanical separation, air table separation is prioritized in an attempt to separate metals from plastics and glass involved. In the present paper, theoretical and practical considerations of air table separation have been detailed. It has been shown that air table separation is effective for recovering copper and precious metals from this specific waste stream. With the feed rate of 60 kg per hour, the combined grade and recovery of copper, gold, and silver attainable for the two heavy products produced by the air table used in the present study was shown in the following table:

Jan 1, 1998

By Ravinder N. Reddy

Electrochemical capacitors are charge storage devices. They bridge the gap between dielectric capacitors and batteries in terms of energy and power density. Electrochemical capacitors are classified into two types, electrochemical double layer capacitors (EDLCs) and capacitors based on pseudocapacitance. In EDLC, charge is stored at the interface between electrode and electrolyte. Carbon is considered to be prime electrode material for EDLCs due to its many favorable characteristics. In this study carbon materials are derived from thermal decomposition of catechol- formaldehyde polymers and are studied as electrode material for electrochemical double layer capacitors. Carbon electrode surface is characterized using NOVA 1200 gas sorption analyzer. It is also characterized using XRD and SEM. Carbon electrodewaselectrochemically characterized using cyclic voltammetry (CV). A highest capacitance of 110 F/g was observed in 30 wt% H2SO4.

Jan 1, 2006

By Doug Halbe

?Many are called, but few are chosen.? The biblical adage applies not only to life, but also to hydrometallurgical processes. There have been, in the past, many outstanding successes with new processes ? and also some dismal failures. What are the odds of success for a new process? When there have been problems, why? What can you do to make sure these problems don?t occur with your process? What effect will a slow startup have on project economics? How do financial institutions ? the people who loan your company money for the project ? feel about new processes and why? Is it possible to predict or estimate the time required to reach design parameters?and if so, how do you sell this estimate to management ? and financial institutions? Probably most important ? when do you start thinking about the answers to these questions?

Jan 1, 2003

By Bora Derin

The partial pressure ratios of sulfur and oxygen for several copper flash smelting plants were derived using the Reddy-Blander (RB) model and predicted dissolved sulfur contents available in the literature. The sulfide capacities (Cs) of six different flash smelting plants (FeO-CuO0.5- CaO-MgO-FeOwAIOl.s?SiO2) slags were calculated. The log (Po2/PS2) versus matte grades of various industrial processes was determined. The PoiPS2 ratio increased with an increase of copper grade. The calculated partial pressure ratios for the copper flash smelting are in good agreement with those of the experimental data.

Jan 1, 2003

By Alice Barreto Bevitori, Frederico Muylaert Margem, Renan Sopeletto Carreiro, Sergio Neves Monteiro, Isabela Leão Amaral da Silva

"The ramie fiber is one of the strongest lignocellulosic fibers with applications ranging from simple items such as fabrics and ropes to engineering composites for automobile parts and building panels. Characterization of the ramie fiber has recently been conducted for physical and mechanical properties. In principle, thinner ramie fiber could be comparatively stronger and consequently more effective as a composite reinforcement. In this work an attempt to correlate the ramie fiber elastic modulus obtained in tensile test with its corresponding diameter, precisely measured by means of a profile projector, was carried out. Tensile results analyzed by the Weibul1 statistic showed a significant increase in elastic modulus with decreasing the diameter of ramie fiber. Scanning electron microscopy observation of the fracture of selected ruptured fiber revealed possible mechanisms that could justify the elastic modulus/diameter inverse dependence.IntroductionEngineering applications of natural fibers obtained from cellulose-rich plants, also known as lignocellulosic fibers, are currently being the focus of attention. In fact, they are considered an enviromnental1y correct alternative to substitute synthetic fibers such as the glass fiber, associated with an intensive intake of energy during production, as reinforcement of polymer composites [1-4]. In recent years there has been a growing tendency towards the use of lignocellulosic fiber composites in several industrial sectors from civil constructions to car making. In particular, the automotive industry is expanding the number of both interior and exterior components made of natural fiber composites [5]."

Jan 1, 2012

By J. W. A. Morris

To investigate the use of centrifugal fields in fused salt electrowinning cells, a high temperature rig has been designed, constructed and commissioned. Initially, the cell has been applied to the fused salt electrowinning of zinc. Current efficiencies of 93% have been obtained for inter electrode gaps as small as 8mm for 70mm diameter electrodes rotating at 100rpm. The construction of a semi-rigorous physical model has shown the potential exists to extend the use of centrifugal fields to the electrowinning of light metals.

Jan 1, 1994