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By Djalma Souza, Rubén Sánchez, Regina Maria Pinheiro, Carlos Maurício Fontes Vieira, Sergio Neves Monteiro

"This work has for objectives to characterize a waste generated in the form of sludge during the treatment of the effluent of a paper making industry and to evaluate the effect of its incorporation up to 10 wt.% on the properties of a clayey body used for brick production. For the characterization of the waste the following techniques were used: X-ray diffraction, X-ray fluorescence, differential thermal analysis and termogravimetric analysis with mass spectrometry. Specimens were prepared by uniaxial pressing at 20 MPa before firing at 750 °C. The physical and mechanical properties evaluated were: linear shrinkage, water absorption and flexural rupture strength. The results showed that, in agreement with the characteristics of the waste, its recycling into red ceramic can contribute to decrease the consumption of fuel during the firing stage. However, the waste changes the physical and mechanical properties, generating a deleterious effect on the water absorption and flexural rupture strength of the ceramic.IntroductionAccording to the Brazilian Association of Pulp and Paper, in the last 10 years, the global production of paper grew 35%. Brazil produced 8,2 million tons of paper in 2004 and held the position of the seventh largest world manufacturer of pulp, with about 9,4 million tons per year [1]. The pulp and paper industry generates effluents that present problems related to their disposal, even after the treatment. Among the solid wastes generated by this industry, the main waste is the primary sludge from the effluent treatment plant (ETP).After the initial treatment the decanted solids go through a dewatering stage, generating the solid form denominated primary sludge. This sludge resembles a paper paste of dark gray color when humid, and clear gray color when dry. This primary waste is composed basically of kaolin, pulp, traces of chemical substances and water. This waste generated in the pulp and paper industry depends on the characteristics of the process and of the employed techniques. It can vary significantly from one industrial unit to another, even in the case that the final products are similar. Its composition is approximately 60% of kaolin and 40% of pulp, and these percentages can vary in some moments as a function of the process [2,3]."

Jan 1, 2008

By G. T. Lapidus, O. J. Solis-Marcial

"The oxidative dissolution of copper from refractory minerals, such as chalcopynte, represents a technological challenge that has occupied hydrometallurgists for more than half a century. Innumerable processes have been suggested, but the majority operates at high temperatures or employs corrosive media. The origin of this refractory nature is the formation of passivating phases of iron(III) or copper. One option is to add non-corrosive ligands that complex these metal ions, thereby facilitating their dissolution. In the present work, the effect of acetone in sulfuric acid solutions was studied. The initial experiments were on chalcopynte carbon paste electrodes using cyclic voltammetry, where greater reactivity was observed. Later, leaching tests with hydrogen peroxide, cupric sulfate and ozone and, as oxidants, were performed. High extractions were achieved in three hours at 50°C. The solid residues contained the iron in the form of Fe203 and FeOOH.IntroductionChalcopyrite is the most important mineral of polysulfide copper ores [1] and accounts for approximately 70% of the world's copper reserves [2]. Currently, the copper present in chalcopyrite is extracted mainly by pyrometallurgical processes, which generate environmental concerns because of the formation of SO2 gas and submicron particulates [3]. The development of a less aggressive hydrometallurgical process for the extraction of copper would constitute a possible solution to these problems. For that reason, studies of the dissolution behavior of chalcopyrite are of great technological importance [4], However, the proposed oxidative leaching routes for chalcopyrite, generally at high pressures and temperatures, have not been implemented on an industrial scale, because of the elevated costs required to equal the high copper extractions obtained in thermal processes. These extreme leaching conditions are required because of the refractory nature of chalcopyrite. Passivation has been used to explain this phenomenon, although researchers have disagreed on the composition of the layer, which is various have assumed to be sulfur, copper sulfides, and iron-bearing jarosites or hydroxides [5]. If the latter compounds are the cause, an alternative solution would be the use of polar organic solvents in the oxidative leach to decrease the formation of the passivating iron layer. In this work, the influence of acetone on the oxidative leaching of a chalcopyrite concentrate at room conditions is explored."

Jan 1, 2012

By S. Malinov, J. J. McKeown, W. Sha, S. McShane

"A model is developed for prediction of fatigue stress life S-N diagrams for Ti-6Al-4V alloy at different conditions, using Artificial Neural Network (ANN). Different factors which have influence on the S-N diagram are involved as input parameters of the NN, namely microstructure, environment, texture, test/work temperature, surface treatment and stress amplitude. As the output the S-N fatigue diagram is simulated and plotted.The model is based on standard multilayer feedforward neural network. The NN is trained with a comprehensive data set collected from the literature, using Levenberg-Marquardt training algorithm in combination with Bayesian regularisation. A very good performance of the trained Neural Network is achieved. Good correspondence between ANN"" prediction and experimental S-N diagrams is observed. Using the model S-N diagrams for different conditions are predicted and analysed. Graphical User Interface is developed for use of the model. We believe that the model will be important for practical applications in solving various problems on fatigue behaviour of the titanium alloy.IntroductionTitanium and its alloys have an increasing range of applications due to their very good combination of mechanical properties, corrosion and erosion resistance. They are currently finding widespread applications in many industries due to their desirable and versatile properties. Most important among the alloys is Ti-6AI-4Y. Jet aircraft manufacturers are the principal 'consumers of Ti-6Al-4V and it is often specified for critical parts, the failure of which could result in the loss of an entire system. A generic class of Ti-6AI-4V has been developed over the past years and it has become the best understood of all the titanium alloys. The advantages of titanium alloys include: (i) low densities, giving very attractive strength to weight ratios allowing lighter and stronger structures; (ii) superior corrosion and erosion resistance in many environments; (iii) high temperature capability. Although the titanium materials are still considered as expensive materials, for many applications the cost of titanium alloys can be justified on the basis of their desirable properties."

Jan 1, 2001

By W. F. Drinkard

Many in the environmental movement have focused on this element. But, nothing they or anyone does will change the amount of arsenic in the world. This report is on actual commercial plants that we developed and operated to recover or stabilize arsenic values from metallurgical dusts from gold and copper pyro operations and arsenical gold bearing ores. When they were available gold and copper values were recovered. Our experience in arsenic extends over thirty years. My first corporation, Mineral Research & Development Corporation was the first in North America to manufacture the then new CCA (copper-chrome-arsenic) wood preservatives. This class of wood preservatives proved to be so effective that it made wood into an entirely new material of construction. It is not uncommon for wood properly treated with arsenical CCA preservatives to last for thirty; forty, and sixty years. Over a hundred years have been projected in some field tests. Hundreds of thousands of trees have been saved. Millions more trees would have been saved had environmentalists not decided that their arsenic phobia was more important than trees. There are several variations of CCA. The most popular is CCA-C. Its formula is: CrO3 . . . . . . . . . . . . . . . . . . . 47.5% CuO . . . . . . . . . . . . . . . . . . . 18.5% As2O5 . . . . . . . . . . . . . . . . . 34.0% Until recent restrictions were placed on the consumption of arsenical wood preservatives, annual consumption in North America was about 150,000,000 lbs./yr. About 64,500,000 of arsenic as the pentoxide was safely consumed this way. World CCA consumption has been about double the above figures or 300,000,000 lbs. as 100% CCA and 129,000,000 lbs/yr as As2O5. Close to 100% of all the arsenic used in wood preservatives is derived from gold or copper processing. The valence of arsenic required for CCA wood preservatives and many other markets is the same valence that is required for stabilization. The economic challenge is how to get there. We have built and operated eleven plants to oxidize arsenic trioxide to its pentavalent form. Most of these have been classic in that they used a common oxidants such as hydrogen peroxide or nitric acid to achieve this.

Jan 1, 2005

By Antonio de Lucas, Juan Francisco Rodríguez, Ignacio Gracia, Mª Teresa García

"The amount of waste of Polystyrene (PS) foams is increasing in last years due to their use in insulation, protecting and, storing many different food products. Conventional methods of recycling such as crushing and shrinking by heated air or frictional heat have the disadvantages of molecular degradation, resulting in a reduction of the quality of the recycled polymer. Dissolution and shrinking with suitable solvents is one of the cheapest and more efficient ways of polystyrene recycling but in the process of the solvent recovery by distillation a certain degree of molecular degradation is produced. In this way, CO2 supercritical technology appears as an interesting alternative for the elimination of solvent. This work proposes a global process to polystyrene recycling in two steps: a polystyrene dissolution with a suitable “green” solvent followed by its elimination by supercritical tecnologhy. In order to develop a “green process” the constituents of essential oils, limonene, terpinene, cymene, and phellandrene, are selected as the most appropriated solvents. Introduction In the last years, disposal of the non-biodegradable plastic wastes has been recognized as a serious environmental problem. Recycling these wastes has great interest in order to prevent the environmental pollution and to preserve natural sources (1, 2, 3). Since the Polystyrene foams (PS) is one of the most used foam in isolation, protecting and food storage most of recycling work is concerned with this polyolefin (4). The two main alternatives for treating polymer wastes are energy recycling, where wastes are incinerated, and mechanical recycling (5). Environmental argumentations such as toxic emissions are building up a public resistance against incineration process (6). Mechanical recycling is a popular recovery path for manufacturers and is carried out on single-polymer waste streams. Any way, the market for recycled products can only be found if the quality is close to that of the original. Unfortunately the process of classification and further recovery of these wastes makes them often more expensive than virgin plastic (7, 8). Solvent extraction is one of the cheapest and more efficient ways for PS recycling. If it is done in house of waste producers the separation between plastics could be easy and effective and the transport costs would be eliminated."

Jan 1, 2008

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 Ronald C. Askin

Dredging is a common method of remediating ponds containing contaminated wastes. However, dewatering of the dredged solids is usually not well integrated with the dredging phase. As a result, overall project efficiency can be poor. Specifically, since dredges deliver material in a widely varying slurry form and since dewatering presses require the delivered material to be uniform, union of the two systems often results in inconsistent operation of the overall process. In an effort to enhance overall dredging and dewatering process production rates as well as minimize the return of suspended solids in the decant water, a new process was developed to provide a consistent dredged sludge for delivery to the press. This paper discusses modifications made to a conventional dredging and dewatering process to improve production rates and dewatering capabilities. These modifications are applicable to any project where efficient solids dewatering is required and where returning decant water must be visually free of suspended solids.

Jan 1, 1996

By Meifeng Zhi

Separation of uranium and molybdenum in the alkaline leach solution of a U–Mo ore was studied. A process of acidification-solvent extraction-precipitation uranium and molybdenum was determined. The influences of solution acidity and phase ratio of acidic scrubbing on separation of uranium and molybdenum were examined. The molybdenum extraction equilibrium isotherm was drawn. The results show that the separation of molybdenum and uranium can be achieved by acidifying the alkaline leach solution, solvent extracting molybdenum using trialkylamine at equilibrium pH 2.5, and scrubbing the loaded organic phase using sulfuric acid solution. The strip solution can directly precipitate ammonium molybdate. Uranium can be directly precipitated from the raffinat

By L. Katgerman, R. Van Toi, H. E. A. Van den Akker

"Mould filling simulations are powerful tools for optimizing the characteristics of castings. The robustness of calculational methods for mould filling simulations is generally tested in simple geometries. While a vertical plate has been used often for validation studies, this paper aims at mould filling simulations of a horizontal thin wall casting. Such castings exhibit a strong interaction between heat transfer (solidification), surface tension and gravitational force.The results are presented of a study to validate numerical simulations of mould filling phenomena in a thin wall horizontal casting. Solidification during mould filling is studied computationally. Velocities are measured using Particle Image Velocimetry.INTRODUCTIONIn foundry practice Computational Fluid Dynamics (CFD) is being considered a promising tool to arrive at a better understanding of casting defects introduced during the mould filling period of a casting. The use of CFD is believed to be advantageous in predicting possible defect locations, pouring times, and the lowest possible casting temperature without the risk of cold shuts. In addition, CFD may be used to optimize pouring system geometries [1,2]. As opposed to experimental studies in, e.g., cold water models, CFD allows for the flexible modification of the casting geometry and the pouring system, and for the inclusion of physical effects such as solidification and heat transfer. Thus, a proper use of CFD may lead to a reduction of the casting rejection rate without expensive trial-and-error procedures, and to a decrease of production costs in foundries. Mould filling simulations take a special place in CFD, because a free surface tracking algorithm is required. Over the past decade methods, MAC [3] and SOLAVOF [4], have been extended to 3-D. The robustness of computational methods for mould filling simulations is generally tested in simple geometries [5,6]. While a vertical plate has been used often for validation studies, this paper concentrates at mould filling simulations of a horizontal thin wall casting. Thin wall horizontal castings exhibit a strong interaction between heat transfer (solidification), surfaces tension and gravitational force. The gravitational force in this setting is orthogonal to the plane of flow and has therefore no influence on the shape of the free surface in the plane of flow. Mould filling numerical methods and algorithms have been recently reviewed by Chen et al.[7]."

Jan 1, 1999

By Bing Hu, Zhu-Cheng Huang, Guang-Bin Xia, Hu Peng, Hua Wang

"The temperature rising characteristics and reaction of the reduction of iron oxide pellets with anthracite fines were studied using a MW-L0316V microwave oven and Leica-DM-RXP polarizing microscope. The results show that iron oxide pellets and anthracite fines have good microwave absorbing properties, and high temperature and reducing atmosphere in a relatively short time for reduction of iron oxide pellets can be achieved. The reduction reaction, which follows the unreacted core model, is rapid and the metallization increases from 13.41% to 56.57% as the reduction end point temperature increases from 850oC to 950oC. The iron is formed, fine grain crystals of iron are transferred and the contraction of metal phase occurs firstly at the surface of pellets, which hinders the reduction reaction at the center of pellets. The rate of reduction reaction increases slowly as the reduction end point temperature increases from 950oC to 1050oC.IntroductionIron ore direct reduction can be divided into gas-based reduction and coal-based reduction. Owing to the effect of the resource and the related economic benefits [1, 2, 3, and 4], the development of gas-based direct reduction technology is restricted, but the development of coal-based direct reduction supported by the relevant industrial policy has very good prospects for application.As a source of clean energy, in China microwaves have been applied in many fields [5, 6, and 7]. Chen Jin studied the reduction of carbon pellets under microwaves, and has made some progress on reduction kinetics and reaction mechanisms. Other countries also have related research in this field [8 - 15], for example, Kotaro Ishizaki and Kazuhiro Nagata have done research on the reduction reaction of carbon magnetite heated by microwaves. The research shows that Fe3O4 is deoxidized to FeO at about 800oC, and FeO is deoxidized to Fe at 1000oC-1025oC. Due to the very good heat absorbing properties of iron oxide pellets and anthracite fines, the selective and rapid heating of microwaves can rapidly raise the temperature of pellets and anthracite, and the iron oxide pellets can be rapidly reduced. In order to provide enough theoretical basis for direct reduction by microwave heating, this paper studies the temperature rising characteristics, behavior of the reduction reaction and the changes of the iron oxide pellets and anthracite in the microwave field."

Jan 1, 2011

"Mineral flotation processes are often characterized by long dead times and slow process dynamics. The process dynamics change due to different ore types, feed grades and circulating loads. These are some of the factors that can make control of flotation processes difficult. Implementation of adaptive control algorithms at Brunswick Mining has made controlling these processes feasible. The role of adaptive controllers in plant optimization and the overall control philosophy is discussed.IntroductionBrunswick Mining is located just outside of Bathurst, New Brunswick, Canada. The concentrator processes approximately 10,250 tonnes per day of ore that assays at approximately 8.9 %Zn, 3.6 %Pb, 0.3 %Cu and 100 gram/tonne of Ag. The four products produced are zinc concentrate assaying 51 %Zn, lead concentrate assaying 36 %Pb, copper concentrate assaying 21 %Cu, and a bulk concentrate assaying 32 %Zn and 18 %Pb.The original flotation process control system, supplied by Outokompu Oy of Finland, was replaced in the summer of 1988 by a Provox system supplied by Fisher Controls Inc. The Provox system consists of two redundant integrated function controllers (IFC's), two operator console stations with two screens each and a Digital Equipment Co. microVax II computer running Fisher's Computer Highway Interface Package (CHIP).In January 1989 a boiler management package, which includes the boiler control hardware and another operator's console, will be added to the Provox system. In late spring of 1989, a Vax 3200 computer running G2 artificial intelligence software from Gensym Corporation will be installed. These devices are all connected using a redundant data highway that runs around the plant.The primary measurement devices in the flotation circuit are two Courier on-stream X-ray analyzers. The Courier systems each have 14 sample cells with two streams multiplexed into each cell. Each pass of the on-stream head takes approximately 6 minutes yielding a nominal sampling interval of 12 minutes. The Courier passes its assays to its respective IFC. The IFC handles the digital and analog I/O, DDC and cascade loop control, some low level calculations and sequencing. The CHIP microVax has 9MB of memory and 220MB of mass storage running under the VMS operating system. The CHIP microVax is a central database for the Provox system. It is used for data trending, metallurgical modelling and balancing, instrumentation database, long term storage, and on-line adaptive assay control."

Jan 1, 1989

By Xie Zhang, Jiang Diao, Xiaojun Li, Bing Xie

"Vanadium is widely utilized as an important element to improve the quality of alloyed steels in iron and steel industry. Moreover, the crystallization process of V-containing spinels plays a significant role due to the aim of achieving a fairly larger size of spinel crystals in vanadium extraction. Thus, a comprehensive exploration and discussion on the competitive precipitation and growth of vanadium, chromium and titanium spinel crystals in vanadium slag during a cooling process were carried out in the present study on the basis of a crystallization kinetic model. To be more specific, the abilities of forming crystal, precipitation order and suitable temperature range for crystallization of the three kinds of spinels were discussed with both theoretical and experimental methods.IntroductionVanadium is an important element which is used almost exclusively in ferrous and non-ferrous alloys due to its excellent physical properties such as high tensile strength, hardness, and fatigue resistance [1]. Various kinds of processes of vanadium extraction from V-containing hot metal are available at present. However, only four processes which are the Highveld process (South Africa), the Pan-steel process (China), the NTMK duplex process (Russia) and the New Zealand steel process (New Zealand) take the dominant positions [2, 3]. Although the type of reactor and the initial vanadium content in hot metal are different in these techniques, they share the same principle that vanadium is oxidized by oxygen into vanadium slag."

Jan 1, 2012

By J. A. S. Tenorio, A. B. Botelho Junior, I. A. Anes, D. C. R. Espinosa, M. A. Caralho

Recovery of metals from reserves with low grade and from waste with high presence of contamination is a challenge to be overcome. Metals like nickel, cobalt and copper could be recovery from nickel laterite leach waste by many different processes. Among recovery processes that could be applied are ion exchange, solvent extraction and precipitation. The aim of this work was recover copper from liquor of nickel laterite by precipitation using chemical reduction. Copper concentration in liquor was 146 mg L −1 and reducing agent used was sodium dithionite 1 mol L −1. Influence of stirring speed was studied between 0–200 rpm. Results indicated a selective precipitation of copper on solution with others metals at 240 mV. The analyzes were conducted in SEM, energy-dispersive X-ray spectroscopy and XRD, that indicated presence of copper and sulfur.

Mar 1, 2018

By Matsufumi Takaya, Yukihiro Sakamoto

"Electric field emission properties from CVD diamond fabricated using pulse-modulated microwave plasma CVD were studied. Diamond was synthesized by microwave plasma CVD apparatus equipped with a pulse-modulated microwave power supply. Pulse conditions were varied from 1 to 10 seconds for pulse periods and from 0.1 to lHz for pulse frequency either. Surface morphologies of the deposits were differed by pulse frequency and duty cycle. As a result, FE properties prepared by different pulse duty cycle were different from continuous film which synthesized using continuous microwave significantly. Highest current density was obtained from the uneven morphology diamond film prepared at 17.5% pulse duty cycle.FE properties of the CVD diamond were depended on surface morphologies that related to the pulse conditions.1. IntroductionDiamond has excellent physical and chemical properties as an industrial material. Especially, hydrogen terminated diamond had the negative electron affinity (NEA) 1) and CVD diamond has this NEA property either as deposited 2). So the electron emission source to the FED is expected as one of this application of CVD diamond as cold cathode of electric devices. We studied on FE properties of various CVD diamond, pulse microwave plasma CVD diamond showed better property than those of other CVD diamond 3).This report studied on· the effect of the duty-cycle of pulse modulate microwave condition on FE properties of the diamond fabricated by pulse modulated microwave plasma CVD."

Jan 1, 2000

By Abhishek Lahiri

Titanium dioxide is extracted from titaniferous ores by chloride and sulfate processes. These two processes produce wastes in the forms of iron chloride, iron sulfate and rare earth oxides gangue, each of which has to go through a further treatment before it can be disposed safely, which may be expensive. The shortage of high-grade ores is also making the two conventional processes less efficient. In view of the above mentioned problems, an alternate beneficiation process of roasting titaniferous ores with soda ash is discussed. The advantage of this process is that, there is no production of wastes. The impurities present in the ore can be selectively separated after the roasting process. The roasting of titaniferous ores with soda ash was carried out between temperatures of 873K and1173K for several hours. The roasting process resulted in the formation of complex alkali compounds and various sodium titanate compounds, depending on the Na2CO3to ore ratio. The phases formed after roasting were characterized using the X-ray powder diffraction (XRD), X-ray florescence (XRF) and scanning electron microscopy (SEM) techniques. The phase equilibria in the Na-Ti-O system are evaluated and compared with the phases obtained after the roasting process. The effects of temperature and the proportion of sodium carbonate on titaniferous ores are also discussed. From the experimental data, the overall reaction kinetics and phases formed were analyzed to ascertain the mechanism of overall reaction and the rate-limiting steps.

Jan 1, 2006

By Yuhua Pan

Generic mathematical models have been developed for simulating heat transfer in two types of slag resistance heating electric furnaces for sulphide smelting: i) six-electrode-in-line rectangular furnaces and ii) three-electrode circular furnaces. The models are based on three-dimensional steady-state heat transfer of conduction, convection and radiation. Solidification of liquid slag into solid slag by water-cooling units, for use as freeze lining of furnace walls, is also considered in the models. The developed models are capable of providing predictions with reasonable accuracy for electric furnaces on 1) temperatures in slag, matte, cooling water, freeze lining and other solid regions as well as temperatures at various fluid/solid interfaces, 2) freeze lining thickness, 3) furnace smelting rate and 4) furnace heat loss rate. These computer models are built into executable application programs that are very efficient, with execution time less than one second, and can be easily portable to most computing platforms. This paper describes, as an example, the modelling results on heat transfer in six-electrode furnaces. The major modelling results show that in six-electrode furnaces uniform electric power inputs to the electrodes likely lead to low temperature regions close to slag and matte tapping ends of the furnaces, and the power input and the formation of air gaps between freeze lining and cooling units have significant influences on the thickness of freeze lining maintained by the cooling units.

Jan 1, 2006

By Hitoshi Iijima, Fumitaka Tsukihashi

"Fine powder of tantalum is used as materials of electric condenser. It is important to control the distribution of particle diameter of tantalum fine powders for the commercial use. In this study, fine powders of tantalum were produced by reducing tantalum chloride vapor with hydrogen gas at 1673 and 1773K. The tantalum chloride vapor was reduced with hydrogen and the produced fine particles of tantalum were collected to observe the distribution of particle diameter. The effects of reaction temperature, partial pressure of hydrogen gas and vaporization temperature of tantalum chloride on the distribution of particle diameter and reaction efficiency of reduction were determined. The mechanism of reduction reaction of tantalum was discussed.IntroductionThe ultra fine powder shows various different physical properties from that of bulk materials. Therefore, the application of ultra fine powder to various fields such as magnetic material, electric material, catalyst, etc is anticipated. The control of shape of powder, size distribution, property of agglomeration, purity is required for the practical use of ultra fine powder. Although the ultra fine powders of ceramics are produced by various methods, the ultra fine powder of metals are produced by the evaporation in gas atmosphere, plasma evaporation process, chemical vapor deposition process, and reduction and precipitation in liquid phase depending on the metal and productivity. The chemical vapor deposition process has features that pure metal powder can be obtained and the control of the distribution of powder size is easy. [1,2,3,4,5]"

Jan 1, 2000

By David G. Dixon, Maziar Eghbalnia

"Gold and silver nanoparticles (NPs) were deposited on pyrite at ambient temperature from colloidal solutions prepared by reduction of hydrogen tetrachloroaurate or silver nitrate by sodium sulfide or sodium tetrahydridoborate. The nanoparticles were characterized using Ultraviolet-Visible (UV-Vis) spectroscopy and the experimental spectra were fitted using Mie - Gans modeling. The modified pyrite was investigated using Electrochemical Impedance Spectroscopy (EIS). Electrodes were prepared from both natural and modified pyrite samples and were modeled using an equivalent circuit (EC) based on the EIS data. The comparison of the results revealed a decrease in charge transfer resistance for the ferric ferrous redox couple associated with the modified pyrite. From this behavior it is concluded that the electronic transport between the nanoparticles and the electrode surface over distances in nanometer scale is enhanced. Nanoparticles below a certain size act as quantum dots due to electronic confmement. Decreased charged transfer resistance at the nanometer scale may be caused by electron transport through tunneling mechanism via quantum dots.IntroductionIn recent years, considerable attention has been focused on the synthesis and study of Metal nanoparticles due to their potential applications in the fields of physics, chemistry, biology, medicine, material science and their interdisciplinary fields[!]. When material is nano-sized, the physical properties deviate markedly from those of bulk material, however, this effect is highly dependent on the particle size, interparticle distance, and morphology of the nanoparticles [2].An extremely small region of space defmed in a semiconductor material in order of nanometers is called a quantum dot, a term coined by Reed [3]. The three dimensional confinement of quantum dots can change properties of the excitons in comparison to free excitons in a bulk material [4]. Nanoparticles behave electronically as zero-dimensional (restricted in all three dimensions) quantum dots when the de Broglie wavelength of the valence electrons and the particle are in the same size range.As Reed [3] explains electrons confined in a plane have no freedom to move the third dimension. Those confined in a quantum wire are only free to move in one dimension, and those confined in a quantum dot are not free in to move in any dimension. An electron inside a cube of material IO nm on a side is confined to a point."

Jan 1, 2012

By Ross R. Bhappu

A theoretical and experimental investigation into pyrometallurgical refining of chloride leach/electrowin copper is described. The two techniques investigated were (i) vaporization and (ii) gaseous halogenation. Experiments were carried out with a packed bed of electrowon copper crystals and a boat of melted copper crystals. Nitrogen gas and Freon 12/nitrogen mixtures were used as the carrier and reac.tive gases. Vaporization was found to be effective in removing Bi, Pb and S while halogenation was effective. in removing As, Bi, Pb, S and Sb. Silver resisted all attempts at removal. Iron was removed but less effectively than the other impurities.

Jan 1, 1985

By S. W. Marcuson

Smelting of nickel-copper sulfide ores at Vale Inco’s Sudbury operations commenced in 1888 and the first converting plant went into operation in 1892. As the demand for nickel grew, the smelting operations expanded and by the 1960’s the Copper Cliff Smelter featured the longest converter aisle in the world with space for nineteen Peirce-Smith converters. During this long period, different converting techniques and vessels were employed. The evolution of converting is reviewed with special emphasis on the modifications made to the Peirce-Smith vessel to accommodate the metallurgical and process needs of the changing times.

Jan 1, 2009