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By Carlos Eduardo Gomes de Souza, Luis G. S. Sobral, Paulo A. Medeiros da Silva, Selma G. F. Leite, Renata de B. Lima

"The use of mixed cultures of acidophilus microorganisms that act in different temperature ranges, aims at speeding up the digestion of chalcopyrite, highly refractory sulphide mineral, the major mineral in the flotation concentrate of Caraíba Mining Co., with an attractive processing cost. The concentrate under consideration contains mainly chalcopyrite (CuFeS2) and bornite (Cu5FeS4) with contents of, approximately, 70 and 30%, respectively. It was observed in this study, the performance of consortium of mesophiles, moderate and extreme thermophile microorganisms, in the oxidation of the aforementioned sulphides minerals, evaluating operational parameters such as pH of the leaching solution, the reaction temperature and redox potential, with consequent extraction of 80% of the concentrate copper content within 60 days of bioleaching. Such high copper extraction was achieved in column bioleaching tests.INTRODUCTIONThe solubilization of metals by the application of microorganisms from the mineral ores and the subsequent recovery of metals from solution are referred to as bioleaching (Rohwerder, T et al, 2003). This is an economical method for the recovery of metals from minerals; especially lowgrade ores, overburden, and waste from current mining operations which requires moderate capital investment with operating cost (Watling, 2006).Furthermore, bioleaching is generally more environmentally friendly than conventional metal recovery processes such as concentration and smelting. Those physicochemical metal extraction processes generate sulphur dioxide, a toxic emission that is increasingly the target of regulatory legislation (Stott et al., 2000; Olson et al., 2003). Bioleaching of chalcopyrite is the key industry target. The main problem hindering commercial application of chalcopyrite bioleaching is the slow dissolution rate (Fu et al, 2008).Dissolution of acid-soluble sulphide minerals such as sphalerite, and to a lesser extent chalcopyrite, occurs by a combination of ferric iron and proton attack via the polysulphide pathway (Rohwerder et al., 2003)."

Jan 1, 2008

By Henry Hu, Alfred Yu

"A numerical model has been developed to simulate heat and mass transfer phenomena occurring during a novel magnesium reduction process-the vertical retort technology. The model was based on the control - volume finite difference approach. Simulations were run to determine the effect of various processing parameters on magnesium reduction cycle time. The model predicted temperature distributions, heating curves, recovery ratio of magnesium, and total process times. The predictions were used to optimize the magnesium reduction process including dimensions of the retort, geometries of the reactant compounds, and productivities. The results indicate that the implementation of the optimized processing parameters significantly decreases the reduction time, and consequently increases the production rate as well as lowers the energy consumption.IntroductionMagnesium consumption has been growing considerably in the past decade [1]. Of the total magnesium production, 30% is produced by the thermal reduction (Pidgeon) process, and it is anticipated to be still the main technology for producing magnesium in future [2]. One of the advantages of the Pidgeon process is that it is capable of producing high purity magnesium demanded by both the automotive and aerospace industries. However, the inefficiency of heat and mass transfer taking place in the horizontal Pidgeon reduction process results in low productivity, high energy consumption, labor-intensive operation, large floor space and high capital investment. This limits the production scale of a horizontal Pidgeon reduction process [3].Vertical reduction processTo overcome the shortcomings of the horizontal magnesium reduction process, a novel vertical magnesium reduction process [3] for large-scale production has been developed, in which heat and mass transfer in the retort is enhanced. The new process shortens reduction time, reduces energy consumption and increases productivity. The vertical reduction system is comprised of a vertically-placed retort, a heating furnace and a vacuum system. A section of the vertical retort is illustrated in Figure 1. Since the retort is set vertically, instead of horizontally, the entire procedure of loading the reactants material in the new process is different from the one for the horizontal reduction process."

Jan 1, 2001

By Moo Eob Choi

A new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and calcium sulfate without generating secondary pollutants was developed at the University of Utah. In this process, sulfur dioxide is reacted with calcium sulfide to produce elemental sulfur and calcium sulfate. The latter is reduced by hydrogen to regenerate calcium sulfide. In the present work, the effects of different pelletization conditions for the initial reactant calcium sulfate on the strength and reactivity of the pellets were determined. These conditions include the type, amount, and impregnation method of catalyst, binder amount, and sintering. Experiments were also performed to determine the effects of temperature in the range of 973-1173 K, pellet size, cycle repetition, and water vapor or carbon dioxide content in sulfur dioxide stream on the reaction rates of the cyclic process. Nickel-catalyzed fired pellets produced by the use of molasses or cement as a binder showed good reactivity as well as high compressive strength during the cyclic tests. The binder amount did not significantly affect the reaction rate.

Jan 1, 2006

This report presents overview of the authors' results of thermodynamical investigation of some important metallurgical processes and phenomena. Among them: carbo thermal reduction of silica, and boron oxide, silicon carbide obtaining from different precursors, investigations on copper and manganese ores processing, investigations on pollution from different sources. Special attention is paid-to thermodynamical approach to investigation and estimation of multi component multi element compositions stability, developed by the authors. Also are discussed some auxiliary but' important for the thermodynamical investigations issues.

Jan 1, 1997

By Sergio N. Monteiro

The interface between the matrix and the reinforcing fiber plays an important role in the efficiency by which an applied load is transmitted through the composite structure. The shear stress at the fiber/matrix interface can be associated with this load transference and,consequently,affects the composite strength. In the present work, pullout tests were used to evaluate the interfacial shear stress of curaua fiber in epoxy matrix composites. A small critical length was found for the curaua fiber embedded in epoxy, which corresponds to a relatively weak fiber/matrix bond and lower interfacial strength.

Jan 1, 2009

By R. M. Westcott

A two-electrode, direct current, slag resistance furnace (SRF) has been constructed and operated to selectively reduce the zinc and lead contents of non-ferrous slags. The experimental SRF is equipped with multiple methods of gas/solids injection for both mixing and reaction. A computer is used to position the electrodes and for data acquisition. A geometric factor correlation was previously developed at Columbia University for calculating the electrical resistance on the basis of furnace geometry and slag conductivity. The experimental SRF was used to test this correlation.

Jan 1, 1994

By Wenbin Liu

A novel route for rapid synthesis of ultrafine WC-Co cemented carbides with homogeneous binder phase distribution is reported. The composite powder is produced by in situ reduction-carbonization reactions by using WO2.9, Co3O4 and carbon black as raw powders. The reaction equilibrium and phase stability are studied by thermodynamic calculations. The WC-Co composite powder is condensed by spark plasma sintering (SPS) to obtain the cemented carbides bulk. The sintering temperature is lower than that in the conventional sintering methods by 1500C, while the sintering time is remarkably reduced by 3-5 times. The high performances of the hardness and the fracture toughness are obtained. The experimental results confirm that the present processing scheme of in situ reduction-carbonization reactions and subsequent SPS sintering is an efficient way to prepare WC-Co cemented carbides, and is apparently superior to the conventional long-period techniques of preparing composite powder and cemented carbides bulk.

Jan 1, 2008

By W. E. Wallace, J. A. Warren, D. Josell, D. Wheeler

"We present the results of experiments and modeling of flip-chip geometry solder joint shapes under shear loading. Modeling, using Surface Evolver, included development of techniques that use an applied vector force (normal and shear loading) as input to determine a vector displacement of the pads connected by the solder joint (standoff height and misalignment). Previous solutions solved the converse problem: fixed displacements used to determine required applied force. Such solutions were inconvenient for applications, where the applied force (chip weight) is known. Also, for geometric and materials studies of solder joint shapes involving multiple parameters, determining the equilibrium displacement from applied force by bracketing solutions could become computationally expensive. Measurements of solder joint standoff height and misalignment as functions of the applied force (normal and shear), solder volume and pad diameter are presented. Experiments were carried out for solder ball diameters from 0.38 mm (0.029 mm3 volume) to 0.15 mm (0.0019 mm3 volume) on pads of diameter 0.64 mm and 0.35 mm. Fitting of simulation to experimental results gave optimized values for the contact angle and surface tension of the solder which were consistent with measured and literature values. IntroductionIn packaging technology flip-chip has become an important method for attaching semiconductor devices to substrates. Generally, the chip and substrate are bumped with solder and then the chip is flipped onto the substrate and the solder reflowed to form conductive interconnects. An epoxy underfill is normally flowed between the substrate and chip to reduce the thermal fatigue on the solder joints. A flip-chip assembly is illustrated in Figure 1.In flip-chip applications, the use of an integrated underfill/solder bump system [1, 2) removes an extra process step, namely infiltration of the underfill. However, the presence of an underfill will retard the self-alignment of the flip-chip. A first step in understanding and predicting this retardation is to develop a model to describe normal and lateral force-displacements curves when underfill material is not present. At this stage it is unclear whether static surface tension theory is sufficient to describe a complete model for flip-chip realignment even without underfill."

Jan 1, 2001

By Jiann-Yang Hwang

A study on microwave assisted chalcocite leaching was carried out with a microwave hydrothermal reactor. The leaching was conducted with thick mineral slurries (50-100 g/l). The leaching media is a mixed solution of CuCL2 and NaCL The investigation included the effect of leaching temperature, quantities of the minerals per unit slurry volume as well as the initial concentration of cupric ions were investigated. The results were discussed and compared with that using conventional leaching method.

Jan 1, 2003

By M. A. Cocquerel

The future economic necessity of mining copper ores with a high impurity content and increased environmental awareness will require closer examination of the distribution of arsenic within copper smelting processes. A generalized approach is developed which can be adapted to specific projects for the determination of an overall process configuration to satisfy all requirements in a cost effective manner.

Jan 1, 1983

By W. G. Davenport

Changes in copper extraction from 1960 till today are documented. The top ten changes have been: (a) replacement of reverberatory smelting by high intensity oxygen rich smelting (b) growth of the Outokumpu flash smelting to over 50% of the world's smelting capacity (c) successful development of single furnace coppermaking but only for low slag fall concentrates (d) replacement of the batch Peirce-Smith converter by continuous converting, but only in a few cases (e) increased SO2 capture throughout the industry, mainly-as sulfuric acid (f) development of low initiation temperature `big bight' Cs catalysts for treating the continuous high-SO2 strength gases from continuous smelting/converting (g) complete replacement of reverberatory anode scrap and cathode melting furnaces by the Asarco shaft furnace (h) adoption of stainless steel permanent cathodes and automated stripping technology for electrorefining and electrowinning (i) complete elimination of wire bar casting by continuous bar casting/rod rolling (j) development and adoption of extractants for turning weak impure leach solutions into strong pure electrolytes. It is postulated that the biggest possible change over the next 20 years would be complete replacement of smelting/converting by hydrometallurgical processing. However, this seems unlikely due to copper purity, precious metal recovery, and economic concerns. The increasing value of sulfuric acid to many copper companies gives chalcopyrite smelting/oxide-supergene leaching a nice synergy especially with the energy credits now coming from continuous smelters, and their acid plants.

Jan 1, 1999

By C. Hennesmann, D. Maijer, S. L. Cockcroft, P. Yo

"Die cast aluminum wheels are one of the most difficult automotive castings to produce because of stringent cast surface and internal quality requirements. As part of a collaborative research agreement between researchers at the University of British Columbia and Canadian Auto Parts Toyota Incorporated, work has been underway to predict heat transport and porosity formation in die cast A356 wheels. The basic heat transfer equations have been solved using the commercial finite element package ABAQUS to which specialized routines have been added to predict porosity. Preliminary work on predicting porosity formation focused on using the Niyama parameter as a measure of the probability of porosity. The latest version of the model incorporates a new fundamentally based porosity criterion, which takes into account the effect of hydrogen concentration. The development of this model together with its application to a series of cylindrical test castings as well as a production cast wheel are presented.I. IntroductionDie cast aluminum wheels are one of the most difficult automotive castings to produce because of stringent cast surface and internal quality requirements. Microporosity, in particular, is a common defect that can adversely affect wheel quality. The mechanism of microporosity formation in aluminum alloys is complex owing to its dependence on the interaction of a number of phenomena occurring during solidification including the decrease in hydrogen solubility, the decrease in volume, the development of the solidification structure, and the increase in difficulty in interdendritic feeding [1]. As a result, the amount, size, and distribution of microporosity is affected by a large number of casting parameters including thermal variables, melt composition, grain structure, modification, and inclusion content, making optimization by trial-and-error methodologies difficult.The use of criteria functions, based on thermal conditions during casting, offers a relatively simple approach to predicting microporosity. In practical terms, they are useful because they provide a straightforward method of assessing the impact of varying casting parameters on porosity through various thermal parametersl21 such as thermal gradient, cooling rate, solidification time, and solidus velocity. Drawbacks of criteria functions include insensitivity to varying hydrogen concentration and the limitation to qualitative predictions. Consequently, in aluminum alloys, attempts have been made to develop models incorporating the effects of hydrogen gas and microstructure evolution. However, these types of models represent a significant increase in complexity and sacrifice the simplicity and ease of application of the thermally based criteria functions."

Jan 1, 2001

During electrowinning of nickel chloride, hydrochloric acid was regenerated instead of chlorine in a two membrane cell, by segregating the chloride catholyte with an anion exchange membrane, and the sulphate anolyte with a cation exchange membrane from the middle electrolyte (ampholyte) compartment. Successful operation of such a cell depends on controlling chloride leakage through the cation exchange membrane to the anolyte. Small amounts of chlorine gas could be detected in the oxygen evolved at the anode. In this paper, the chloride. leakage as a function of various types of cation exchange membrane and different composition of the anolyte is reported and discussed. Ag+ was added to the anolyte to eliminate chloride leakage to the anode. The cell voltage, electrode potential and voltage drop over the membrane as a function of current density has also been investigated.

Jan 1, 1996

By R. Colás, A. Salas, M. P. Guerrero Mata, R. Garza

"The use of the finite element method (FEM) for studying the plastic behavior of metals has become a common practice over the past few years, because it has been proved to be a good means of evaluating processes parameters, and predicting and improving processes, avoiding the traditional trail and error technique. FEM was used via a commercial package (Abaqus) to create two dimensional models to simulate uniaxial tensile tests for a galvanized low carbon steel. The aim of the work was to analyse the plastic behaviour of a distribution of grains on the zinc cover of a set of galvanized low carbon steel samples. A mesh with lines 2 mm apart was drawn on one of the faces of the samples that were deformed at room temperature, at constant crosshead speed, stopping the deformation at different times. Before and during the stops the deformation measurements were recorded for further calculations in an image analyser in order to compare these with computational predictions, as well as validate the numerical model. The results of this study can be extended to other testing conditions, besides the model can be used for obtaining constitutive equations of the materials.INTRODUCTIONThe use of the finite element method has been widely spread during the last two decades in most engineering areas, it is a good means of obtaining approach values at a first try [1-4]. Thanks to the software and hardware developments it is now possible to run huge problems within hours or minutes, making the technique more accessible and useful for the industry.The aim of this work is to create a finite element model for the uniaxial simple tension test, and compare the results with some experimental results, and asses the validity of the model.The plastic behaviour of the materials with FEM has been studied for a long time [5] and there is always something new to learn about this behaviour of the metals in particular, as well as to characterized new materials and alloys [6,7]. The tension test has been used since XIX century to get knowledge of the materials [5,8], it is the test that has been used the most and the only that is fully standardized, although it has the limiting of low strains, it is still the most widely used, especially in the industry.Two different finite element models in two dimensions (2D) have been developed, one called the mesh model and the other one the grain model, attention was focused on the geometry and strain prediction. The model is validated with experimental test, by using the data and directly comparing it with the numerical predictions. All the tests were carried out at the same constant crosshead speed at room temperature. An analysis of the grid distortion using FEM and analytical methods has been carried out."

Jan 1, 2001

By Raymond F. Dalton

Despite the ready availability of numerous zinc sources, the process of solvent extraction- electrowinning (SX-EW) has as yet found little favour in the zinc industry. It is suggested that this is largely due to the previous lack of availability of suitable selective reagents having the particular features required to enable them to fit in to a solvent extraction-electrowinning based process for zinc, particularly with regard to strength and selectivity for zinc over iron. This paper describes work on the development of new selective extractants for the recovery of zinc from both sulfate and chloride aqueous solutions and suggests how they might be integrated into new zinc processes.

Jan 1, 1994

By Tianzu Yang, Weifeng Liu, Shu Bin, Lin Chen, Wanda Bin

"Vanyukov Process has been mainly applied for processing copper and nickel sulfide ore for more than 30 years. Based on the understanding of the Vanyukov Process, researchers from China introduced the technology into the areas of lead, antimony and bismuth extraction by changing the furnace structure and technical flow, which greatly extended the application area and raised the processing efficiency, thus developed the oxygen-rich side-blow bath smelting (OSBS) technology in 2000. This contribution reviews the history of OSBS technology from four respects: the quantity, the furnace structure, the process flow and the application area. Its potential research direction and industrial application are also summarized.IntroductionVanyukov bath smelting furnace and related bath smelting technology were developed by researchers from Soviet Union who devoted comprehensive research on fundamental theory as well as engineering technology [1,5]. Vanyukov process has been applied for large industrial production since the 1970s and it is still one of the major methods in modem pyrometallurgy process. The appearance ofVanyukov double district furnace and joint double furnace in the past ten years, which are applied for copper smelting, is the most valuable advances of the Vanyukov process [7,8,9]. However, the application ofVanyukov process was limited in copper and nickel sulfide ore smelting, and few countries adopted this process except Soviet Union."

Jan 1, 2013

By Manfred K. Walther

"Tests were conducted on instrumented plates cast in the Abex Experimental Foundry to compare recorded solidification histories with results computed for corresponding models simulated with the C.A.S.T. program. The first plate was cast of low alloy steel and the second of carbon steel with a graphite chill at one end. Both were cast in molds of bonded silica sand. Temperature histories were recorded in the castings, molds and chill. Exceptionally good agreement was achieved between computed and experimental data. Other investigators will find the results useful as a benchmark against which they can compare the results of their own calculations.IntroductionSince the early 1970's our foundry engineers have used both two- and three-dimensional versions of the G.A.S.T. program to gain knowledge of the solidification process [1,2,3]. Study of the computed data gave insight as to how the rigging and risering of specific castings might be changed or adjusted to improve quality and yield. New schemes based on such analyses were then recommended for implementation on the foundry floor. The degree of success of the new practice was subsequently evaluated after the part had been poured, shaken out and examined. Similar conditions were noted in the sectioned castings whenever porosity and voids had been predicted by the computations. Appropriate modifications, when found successful in the model, were applied to the process. This led to a reduction, if not complete elimination, of the defects. Such results gave credence to the use of these programs as an aid in the production of better castings.Earlier investigations on simple shapes revealed excellent correlation between output derived with the G.A.S.T. program and exact solutions. Results also compared favorably with data calculated using other codes as reported in the literature [4] and summarized in the Appendix. However, since the computer program had not been verified by direct experiment, it was decided to run instrumented tests to check the theoretical predictions with actual measurements."

Jan 1, 1986

By Chai Liyuan

Chromium-containing slag was detoxified by the method of microbial treatment using Ch-1bacteria isolated from nature by our research group, belonging to achromobacter sp. and with the characteristic of reducing high concentration of Cr(VI) in alkaline solution. The detoxifying process of Ch-1 to chromium-containing slag was studied by column-leaching techniques respectively. The results indicate that Cr(VI) in leachate can not be detected when chromium-containing slag has been column-leached for 7 days, and Cr(OH)3 content in precipitate is up to 32.8% with great value of resource recycling. Flowchart of engineering experimentation was ascertained based on the parameters of column-leaching experiments. Using the technique of pelletization of chromium-containing slag heap-leaching by Ch-1,the leaching rate of water-soluble Cr(VI) existing in chromium-containing slag reaches up to 100%, while the leaching rate of full chromium is up to 90%, when the process has been operated for 7-10 days under the conditions of 25-40C and consecutive spray by circular leachate. The content of Cr(VI) in chromium-containing slag after detoxified meet the national identification standard for extraction procedure inxicity for hazardous wastes(GB5085-1996) in China, moreover approximately 90% of Cr(VI) existing in chromium-containing slag has been recycled.

Jan 1, 2006

By Lucas Lopes da Costa, Sergio Neves Monteiro, Rômulo Leite Loiola

"Composites with DGEBA/TETA epoxy matrix reinforced with thinner and continuous bamboo fibers stripped from culms were mechanically characterized by tensile tests. Specimens with up to 30% in volume fraction of aligned fibers were tensile ruptured at room temperature. The results showed a steady increase in both the ultimate strength and the elastic modulus of the composites with the amount of incorporated bamboo fibers. The fractographic analysis by scanning electron microscopy showed evidence of moderate adhesion between the bamboo fiber and the epoxy matrix. This fiber/matrix adhesion by interaction mechanism apparently justifies the improved tensile properties of the composites.IntroductionIn recent years polymer composites reinforced with natural fibers, mainly those lignocellulosic obtained from plants, have been subject to extensive research works [1-5]. Environmental, economical, societal and technical advantages of these composites are motivating their substitution for similar polymer composites reinforced with synthetic fibers. In particular, R & D efforts have been conducted aiming to replace glass fibers composites that are comparatively more abrasive to equipments, non-recyclable, more expensive, heavier and toxic [6]. Among the many lignocellulosic fiber composites being investigated, those fabricated with bamboo stripped fibers, i.e., fibers longitudinally cut from the culm, still need information to support possible industrial applications. Several works, however, have been dedicated to bamboo stripped fibers as possible reinforcement of polymer composites [7-17]. These works reported mechanical properties that could markedly vary with the type of polymer matrix, the fiber disposition (if continuous, aligned, short-cut, mat interlayered, etc) and the test condition."

Jan 1, 2011

By J. D. McCain

Magma's San Manuel smelter has adopted new operating techniques resulting in 21% increased productivity and 87% reduction in lost time accidents. Reverberatory furnaces were converted to coal firing from expensive natural gas and fuel oil. Slag and matte flow problems and safety were improved by implementing hydraulic slag stopping and matte tapping machines. Coordination of furnaces, converters and acid plant was improved by using a computer-aided converter controller/scheduler function. Manual mudding of converter lips after each collar pull was replaced with a gunning system for coating the mouth castings. One converter punch car was automated using robotic technology. An automatic anode take-off was installed with fewer moving parts and a mechanism for ear twisting one cell contact. Anode copper refining was improved by replacing propane/hydrogen mixtures with high pressure/velocity natural gas tuyeres. Improved converter scheduling increased acid plant production 43% with more autothermal operation time. Six dedicated computers/microprocessors are utilized for automation, data acquisition, process monitoring and on-line air quality information for the Supplementary Control System.

Jan 1, 1983