Search Documents

By S. -H. Jeon, Y. -S. Choi

"The three dimensional current distribution on the rectangular cathode is predicted using a boundary element method with a linear element of trigonal type. The effect of cell geometry and anode shape on current distribution is simulated. Calculated results compare well with experimental results. The proper combination of anode size and distance between electrodes increase the current uniformity.The importance of electrodeposition as a fabrication technology in the electronics industry is large and growing. The main advantages of this wet processing method, in comparison to other dry processing methods, lie in its high yield, rapid processing and low cost. In nearly every application of electrodeposition the pursuit of deposit uniformity, especially thickness uniformity, has been technically imperative. The thickness uniformity of the deposit depends largely on the current distribution over the cathode. The current distribution is primarily determined by the geometrical characteristics of the electrodes and the cell. Also the polarization at the electrode surface and the mass transfer affect the current distribution.The current distribution is an important consideration for those involved in designing electrochemical systems and electroplating systems in particular. Although it is important, the common practice in industry is to use trial and error method to design the cell that optimize the uniformity of current distributions in electroplating. The purpose of this paper is to illustrate the useof boundary element method to predict three-dimensional current distribution in rectangular cell.The calculation of the current distribution is possible by various numerical techniques, which include the finite difference method (FDM)1, the finite element method (FEM)2, and the boundary element method (BEM)3,4. These methods of the numerical calculation have various problems, respectively, but the BEM is considered to be the most efficient. This is due to the fact that the BEM has the advantage of solving field equations only on the surface of a calculation domain. A good comparison between the BEM and the FEM for the secondary current distribution in a Hull cell was made by Matlosz et al.5The fundamentals on the theory of current distribution in electroplating are well-established in the literature by a number of authors.6, 7, 8 However, a small fraction of these works have been specially addressed to three-dimensional analysis, and, mostly thel·10 have focused on the problem qualitatively rather than quantitatively.Extending the previous work to three-dimension, we developed the program for the quantitative calculation of 3-dimensional current distribution using a boundary element method with a linear element of trigonal type. Integrals with singularity from the fundamental solution have been analytically computed and it is shown in detail in the Iiterature11. This paper deals with the three dimensional current distribution for the electrode position of copper in a cubic type cell and the effect of anode shape, size and the distance between electrodes on current distribution is studied."

Jan 1, 1997

By Nobuyuki Higashiyama, Ikuo Yonezu

"Hydrogen-absorbing alloys containing rare-earth elements are used in high capacity nickel-metal hydride secondary batteries,' hydrogen storage systems for portable fuel cells, and refrigeration systems. New hydrogen-absorbing alloys containing rare-earth elements have also been developed and introduced into these applications. High performance in nickel-metal hydride secondary batteries is strongly demanded because of the remarkable advancements in portable electric appliances. A large hydrogen absorption capacity, high electrochemical reactivity and superior corrosion resistance in an alkaline solution are required for hydrogen-absorbing alloys used in nickel-metal hydride batteries. The aim of this investigation is to improve the performance of conventional LaNi5 type hydrogen-absorbing alloys. For example, Mm(Ni-Co-Al-Mn)„ type hydrogen-absorbing alloys with various non-stoichiometric compositions were developed. In addition, a new process of rapid quenching process was applied for preparing these hydrogen-absorbing alloys in order to improve their performance.IntroductionRecently, the trend in electronic appliances toward portability has increased the demand for high capacity of secondary batteries as power sources. Since nickel-metal hydride batteries were first commercialized in 1990 in Japan, they have become increasingly popular as power sources for cellular phones, portable computers, electric shavers, and other, products.The performance of a nickel-metal hydride battery, such as its discharge capacity, high rate capability, and charge-discharge cycle life, strongly depends on the characteristics of the hydrogen-absorbing alloy negative electrode. Many types of hydrogen-absorbing alloys have been developed so far. For a hydrogen absorbing alloy to be used as the negative electrode material, (1) it must allow a large amount of hydrogen to be absorbed and desorbed in an alkaline solution, (2) its reaction rate should be high, and. (3) it must have long term durability under repeated charge-discharge cycling. However, LaNi5, a typical rare earth-nickel type alloy, shows significant capacity deterioration during repeated charge-discharge cycling. Therefore the first step in its development was to obtain sufficient corrosion resistance of the LaNi5 alloy for its use as an electrode material. A partial replacement of nickel with cobalt and a substitution of the lanthanum- content with misch metal (Mm), a mixture of rare earth elements such as lanthanum, cerium, praseodymium and neodymium, were very useful in improving the charge-discharge cycle life. However, the discharge capacity of the alloy was still not sufficient for a practical battery. A study of the effect of the partial substitution of aluminum and manganese showed that the best alloy composition was Mm(Ni-Co-Al-Mn)x, as follows.The stoichiometry x of Mm(Ni-Co-Al-Mn)x largely affects the discharge capacity and cycle life. Theose alloys with non-stoichiometric alloys with the compositions of [Mm(Ni-Co-AMn)x: 4.7<x<4.8] have a large capacity and a long cycle life. Nogami' et al. reported that 'a non-stoichiometric alloy with a Mm(Ni-Co-Al-Mn)x (x=4.76) composition showed approximately 10% higher discharge capacity than the stoichiometric alloy (x=5) [1] and greater influence of x on the electrochemical properties of multi-component AB„ type hydrogen-absorbing alloys for batteries."

Jan 1, 2000

By H. Kung, T. R. Jervis, M. Nastasi, T. E. Mitchell

"A systematic study of the structure-mechanical properties relationship is reported for nanolayered composites of MoSh-SiC, Mo-MoSh, Mo-MoShNx, MoSi2-MoSi2Nx, and Mo-MoShMoSi2Nx (x=3-4) synthesised by sputtering techniques. These composites have been studied by nano-indentation and cross-sectional TEM as a function of annealing temperature. As-deposited layers are amorphous except for Mo. With increasing annealing temperature, first MoSh and then SiC crystallize, while the hardness progressively increases until the layers start to spheroidize and grain growth sets in at 900ºC. For the case of Mo-MoSi2, the layers react and the composite deteriorates rapidly. However, MoSi2Nx remains amorphous up to 1000ºC, suggesting that it could act as a diffusion barrier between Mo and MoSi2. In fact the Mo. MoSi2Nx, MoSi2-MoSi2Nx and Mo-MoSi2-MoSi2Nx nanolayers are found to remain stable up to such temperatures. IntroductionMolybdenum dislicide, MoSh, is a potential matrix material for high temperature structural composites due to its high melting point and good oxidation resistance at elevated temperature [1]. The two major drawbacks for structural applications are inadequate high temperature strength and poor low temperature ductility. Silicon Carbide (SiC) being hard and thermally compatible with most ceramics and intermetallic compounds, has been found to be suitable for second phase reinforcement in various structural applications and, in particular, the addition of SiC whiskers improves the high temperature yield strength of MoSi2 [2]. While most of the research in MoSb-SiC composites has been on the particulate form of SiC, laminated composites may offer unique properties. It has been shown that synthetic multilayers with alternating layers of metal and/or compounds may exhibit interesting mechanical properties [3]. Enhancement in mechanical properties by decreasing the wavelength of multilayer spacing has been studied extensively. In general, two types of strengthening have been proposed: (1) Hall-Petch strengthening [4,5], where the strength increase is inversely proportional to the square root of the layer thickness; (2) Koehler modulus strengthening [6], which increases with modulus difference and decreasing layer thickness. In the present study, we have performed a systematic study of the relationship between strength and structure in a number of different nanolayered systems based on MoSh. Layer thicknesses have been varied and their nanostructures have been varied by heat treatment. Previous work on MoSi2-SiC is summarized [7]. In an attempt to improve fracture toughness, MoSh-Mo nanolayered materials have been prepared but are found to react and deteriorate. Previous work has shown that nitrided MoSi2 (MoSi2Nx with x=3-4) is highly stable [8] and so nanolayered composites of MoSi2-MoSi2Nx and Mo-MoSi2-MoSi2Nx have been prepared to assess the' stability and mechanical properties of these composites. Preliminary results are presented."

Jan 1, 1994

By R. G. Robins

Metal separations based on the selective precipitation of phosphates have a potential application in many hydrometallurgical processes. This paper reviews the literature on the solubility of a number of both divalent and trivalent metal phosphates and presents the result of some additional experimental measurements. The systems examined have been modelled to obtain free energy of formation data for the various species. Computer generated solubility diagrams which are described can be useful in predicting a variety of metal separations.

Jan 1, 1991

By Hang Goo Kim

A mathematical analysis based on equilibrium modeling has been developed to describe the distribution behavior of minor elements such as Pb, Zn, Bi, Sb, and As among gas, slag and recovered copper phases during the reduction of copper oxide in slag cleaning with CO gas. The results show that large fractions of the impurities transferred to slag during smelting or converting are recycled to the recovered copper metal. It is also shown that there is a limit to the recovery of copper from slag because iron oxides are also reduced to form a copper-iron alloy at low oxygen potentials. The effects of various operating parameters such as temperature, the activity of FeO, the initial amounts of the elements in the slag and CO content in process gas, on the behavior of these minor elements are discussed. The predicted results were compared with the results of a pilot plant operation in which pulverized coal was used as a reductant. Consistent trends between the two cases were obtained.

Jan 1, 1992

By J. Dille

Metallic cobalt exist in two allotropic forms : the hexagonal compact a which is stable at low temperature ( ( 420&apos;) and the cubic form 0 stable at higher temperature. This latest form is the only one which is ductile. During the electrode position of Co, in moderate acidic conditions, we noticed a code position of both a and B forms. The influence of several parameters on the B/a ratio in the deposit was investigated. High acidity and the presence of Fe increased its ratio; on the opposite, high temperature promote the a phase. No significant influence on the material were noticed. The differentiation of a and B forms of Co is rather difficult and the method of J. Scoyer was improved quite successfully.

Jan 1, 1988

By L. W. Beckstead

The use of acid ferric sulfate solution as a lixiviant for chalcopyrite concentrates has been of little interest from a practical standpoint due to the formation of a tenacious layer of elemental sulfur which severely impedes the reaction progress. CuFeS2 + 4Fe+3 ?Cu+2 + 5Fe+2 +2s° For example, an acid ferric sulfate leach of chalcopyrite concentrate results in only 12% copper extraction in a three hour leach at 93°C. Experimental results suggest that particle size is the only controllable variable which has a significant effect on the rate of acid ferric sulfate leaching at ambient pressure. Size reduction of the concentrate prior to leaching was exam¬ined using various methods of grinding. Of the grinding methods considered, attrition grinding was found to be the most effective. Leaching of an attritor-ground product (median particle size 0.5 microns) resulted in approximately 90% copper extraction in a three hour leach at 93°C. Energy measurements suggest that the costs associated with attrition mill¬ing are not unreasonable. Evidence indicates that "activation" or stored strain energy is not responsibile for the enhanced reaction kinetics of the finely ground concentrate, but rather the experimental results can be explained simply in terms of the increased surface area due to size reduction. Leaching reaction mech¬anisms operative in the acid ferric sulfate system are discussed and the application of ultra-fine grinding technology to other systems is considered.

Jan 1, 1976

By B. Yawney

A copper-nickel sulfide concentrate was leached in water at about 2000C under oxygen pressures of about 0.35 MPa. Oxidation of sulfide to sulfate was virtually complete in about 30 minutes, resulting in greater than 95% copper and 98% nickel extractions. Leaching temperature was shown to be the most important factor affecting metal extractions. Measured rates of oxygen consumption were used to develop batch kinetic data. Mini-plant continuous pressure leaching tests agreed with batch leach results. A proposed overall flowsheet is briefly examined.

Jan 1, 1976

By Zhou Jiemin

In order to fully understand the behavior of the rectangular six- electrode electric smelting furnace and improve its design and operation, a three-dimensional mathematical model has been developed which incorporates the electrical and thermal flows into numerical solutions, assuming a steady state regime. The model has been used to simulate the performance of the 16500 kVA nickel matte smelter at Jinchuan in China, and various factors have been investigated. The results of computation are in agreement with the measured data obtained from this furnace and its physical model. Application of this model is described and the calculation on the Jinchuan smelter shows that the operation expenses can be reduced by optimizing the furnace geometry and some operating parameters.

Jan 1, 1991

By Donald I. Bleiwas

World primary nickel production in 1987 is projected to be 770,000 mt, slightly higher than that in 1986. Market economy country (MEC) production in 1987 is projected to be about 524,000 mt, an increase of almost 5 pct over 1986 production. Production cutbacks and closures at Japanese ferronickel plants in 1987 resulted primarily from the strong yen and higher energy prices. Cutbacks also caused reductions in ore production from Indonesia, New Caledonia, and the Philippines. Technical problems affected production, to varying degrees, in Botswana, Indonesia, and Yugoslavia. World primary nickel production for 1988 is projected to be 787,000 mt, of which 536,000 mt will be produced in MECs. Increased production is projected from Botswana, Canada, Cuba, and possibly Greece and Yugoslavia, while slight production decreases are projected for Indonesia, New Caledonia, the Philippines, and Zimbabwe. .. South African nickel production in 1988 could be severly curtailed by social strife. In the early 1990&apos;s Brazil and China could be major economic competitors to Western nickel producers.

Jan 1, 1988

By L. E. Murr

Preliminary studies of bacterial attachment to MoSp (molybdenite) have indicated a low correlation between dislocation density in the (0001) basal plane and the density of attached microbes. In the present investigation, poly- crystalline thin sections of CuFeSp (chalcopyrite) have been ion-etched or carefully comminuted to electron transparency and observed in the transmission electron microscope. The thinned test sections were then immersed in a culture solution in which bacterial attachment occurred. The attached bacteria were biologically stained in a uranyl acetate solution and the entire thin CuFeSp sections or tiny particles containing thin, electron transparent edges with bacteria attached were observed in the transmission electron microscope, allowing the coincidence of bacteria and their density to be directly observed in relation to lattice dislocations and crystallographic orientations of the exposed surfaces. This technique has the advantage of exposing crystallographic orientations where dislocation lines intersect the free mineral surface, and the emergence sites of dislocations could in principle be directly investigated as a possible preferential attachment site for bacteria. Bacteria morphologies were also extensively observed in the scanning electron microscope. The implications of the results are that although a strong correlation between dislocation density and distribution and bacterial attachment, density, and distribution has not been established, systematic multiplication of dislocation densities in crystalline mineral particles to be leached could enhance leaching rates by increasing the reaction rates as well as the density of attached bacteria at crystalline, metal-rich phases. Techniques for dislocation production in mineral and ore bodies and the particular implications in chalcopyrite leaching are discussed in relation to in-situ leaching where comminution is attained by explosives and the generation of strong shock waves in an ore body. The present study demonstrates the use of microanalytical and microscopic techniques in the investigation of fundamental microstructural phenomena in hydrometallurgical processes.

Jan 1, 1976

By Caisa Samuelsson, Fredrik Engström, Bo Björkman, Margareta Lidström Larsson

"Large amounts of by-products are generated by the Swedish steel industry each year. The EAF-process generates about 400 000 ton of slag, from which 80% is deposit. An alternative to deposit is to use slag as road construction material. However, metal content in the slag can be a problem, due to the leaching. The aim of this work was to investigate how stable these materials are when ageing and kept outside. Five different EAF-slags from domestic steel plants were used in this study. The materials were characterised after 0, 6, 12, 18 and 24 month to evaluate the ageing process. Scanning electron microscope (SEM), x-ray diffraction pattern (XRD) and a standard test for leaching were used. The changes in behaviour differ between the five materials. The total leachability decreases with time for all samples. CaCO3 is formed on slag surfaces as CaO reacts with moister and CO2 in the air. Introduction The slag generation in the Swedish steel industry is about 1.5 million tonnes annually, of which more than 500 000 ton is generated in EAF (Electric Arc Furnace), AOD- (Argon Oxygen Decarburization) converters and during the refining of steel in the ladle metallurgy. Some of the slags are used in different applications, but most of the steelmaking slags produced in Sweden are landfilled today. The chemistry, mineralogy and physical characteristics of slags make it a suitable material in construction, replacing for example, gravel and rock [1]. In some respects, in road construction, it may even be technically superior to virgin material. Slag from scrapbased steelmaking is used for road construction in Europe. The reason for the low utilization in Sweden is mainly due to potential leaching of harmful elements, legislations and competition with easily available natural raw materials. Except the potential leaching, the technical obstacles for not using some slags in construction include:"

Jan 1, 2008

By Brian R. Green

Resin-in-pulp (RIP) technology has been developed for recovery of gold. It is now time to look forward to the potential for application of the technology to other situations. Some cases have been identified and have merited preliminary testwork. Four examples, which illustrate the potential of RIP, are dealt with in this paper. These include removal of metal-cyanides from pulps, recovery of manganese that is difficult to wash from filter cakes, recovery of nickel from low grade pulps, and recovery of zinc from process residues. The discussion includes descriptions of the problems, factors that affect the choice of resin, and factors that will affect the economics of the process.

Jan 1, 1998

By U. Meyer, A. Alonso, P. Banios

The sampling of cathodes has changed with the introduction of the ISA-process in copper refineries. A Jernkontoret joint working group of refineries and rod plants from both primary and recycled copper plants has been investigating whether the actual sampling of cathodes is representative for this type of cathodes. As a first stage, samples were sent to the members of the working group with the objective to find an easy basis for a comparison of the results of the next stages. All samples show the same tendency for nearly all elements. In some cases, there may exist differences in calibration and for some elements the detection limits are too high, especially when Optical Spectrometry is used. In the second stage, discs were compared with melted samples to answer the question whether the punching of discs is sufficient for the quality control of the cathode. The analyses of the discs represent fairly well the cathode quality. There are differences between cathodes from different crops. Three punches are sufficient to determine the cathode quality. Finally, samples from various lots of cathodes were compared with samples from the rod produced from these cathodes. The impurity content of the rod corresponds to the impurity content of the cathode.

Jan 1, 2000

By Mark William Kennedy

"Electric furnaces containing high quantities of slag are applied in many areas of pyrometallurgy, often for smelting or slag cleaning. A variety of ratios or rules of thumb have been employed in the industry for the dimensioning of these vessels, in most cases with no clear technical basis.In this paper, several design guidelines are presented (electrode size, spacing, vessel dimensions, energy intensity, etc.) as an attempt to provide some technical basis for optimal dimensioning.Furnace heat generation is related to side wall copper cooler heat losses, in an attempt to establish a methodical design strategy particularly for minimum electrode to wall spacing for modern furnaces with cooled linings.Issues regarding the true nature of heat production in a slag furnace are discussed with regards to the possible impact on accurate modeling and design.IntroductionSlag furnaces have passed through a number of design 'generations' characterized by increasing energy intensities, improved electrode technologies and advancing development in their physical structure or 'furnace integrity' as shown in Table I f 1]. A 3rd generation furnace using ultra-high-power (UHP) graphite electrodes is shown in Figure 1, as a generic example of the types of physical structures present in modern slag furnace designs [1]."

Jan 1, 2012

The merging of flash smelting with spray converting in one single furnace is proposed as a continuous copper making process. The proposed process is expected to produce blister copper, clean slag and gas with high sulfur dioxide concentration. Some high grade matte is an intermediate product recycled within the proposed furnace, spray-atomized and converted. The thermodynamic equilibria of the simultaneous oxidations which take place during copper smelting and converting are discussed in order to establish the gradient of oxygen potential along the furnace required for smooth operation. The proposed process is a dynamic system designed to reach equilibrium only close to the slag skimming end of the furnace. The process feasibility is based on the predesigned significant difference between the rates of converting reactions in a finely dispersed system and the rates of deconverting reactions between immiscible liquid phases of restricted interface area. The converting of small stationary droplets of matte, in a silica saturated system, was studied in the laboratory for extremely short oxidation times (10 to 120 seconds). These experiments led to some interesting observations on reaction mechanisms and kinetic trends. The droplet size and the matte grade affected very strongly the oxidation rate and the proportion of the different products obtained.

Jan 1, 1976

By Amy Nelson

In the electrolytic production of zinc, cobalt is removed from the zinc electrolyte by cementation with zinc dust prior to electrowinning. Although the thermodynamics for this reaction are favourable, kinetic barriers to cobalt reduction render the method almost useless in practice unless activators such as copper and antimony or arsenic are added. There is a large body of work studying the effect of these additives, yet the mechanism by which they act is still poorly understood. Even when the target conditions are met, zinc dust consumption is excessively high: satisfactory operation requires up to 300 times the stoichiometric amount of zinc dust. The objective of this work is three-fold: (1) to examine the effects of activators and elucidate the characteristics that make a good activator; (2) to identify new additives that could lead to a more efficient purification process; and (3) to test the new additives with synthetic and real electrolyte solutions. The present paper gives a status report on this project.

Jan 1, 1998

By Yongfeng Jia

Lime neutralization and co-precipitation of As(V) with iron(III) is the most widely used and most economical method for the removal of arsenic from mineral processing solutions and effluents. However, the arsenate fixation mechanism in the coprecipitated solids is not fully understood. It was suggested by various researchers to be a ferrihydrite precipitation process during which arsenate is removed by adsorption on ferrihydrite. In this study, XRD, EXAFS and microprobe were employed for the speciation of arsenic and the effect of various factors on arsenic solubility was also investigated. The results indicate that coprecipitation is a more complicated process than simple adsorption resulting in lower arsenic solubilities. Poorly crystalline ferric arsenate was observed for the first time to be present in the coprecipitated solids. In case of lime as base, there exists some type of Ca-Fe-arsenate association. A general term ?coprecipitate? is suggested to describe the precipitated arsenic-bearing solids instead of those widely used specific terms ?arsenical ferrihydrite? or ?arsenic-bearing ferrihydrite?.

Jan 1, 2005

By Edita Vircikova

The best demonstrated available technology (BOAT) for the removal of dissolved arsenic and some heavy metals as reported by USEPA (Contaminants and Remedial Options at Metal Sites, Draft Report, August 1993) (1) is still the chemical precipitation. Coprecipitation with the excess of iron is usually practised because of the availability of iron at low/no cost and also in order to meet the stringent regulatory discharge limits. The arsenic is usually removed with iron because of its common occurence in the mined orebodies and the excellent adsorptive property of the precipitated hydrous ferric oxide compounds. There has been controversy, however, over the long-term stability of the arsenic-bearing ferrihydrite which is produced.

Jan 1, 1995

By M. P. Bohrer

A closed-loop hydrometallurgical process has been developed for treatment of smelter flue dust generated by copper recycling. The process is a semi-continuous operation in which zinc, iron, and copper are first extracted from the dust with a sulfuric acid solution. The lead and precious metals, initially present in the dust, remain as solids and can be recycled to the copper smelting furnace. Cementation with iron and zinc metal purifies the zinc and iron-rich liquid stream prior to spray drying. The spray-dried product, consisting of a mixture of zinc sulfate monohydrate and iron sulfate monohydrate, is a desirable micronutrient additive for use in animal feeds. Treatment of the smelter flue dust in this manner will generate a positive return on investment, as well as mitigate a potential environmental liability.

Jan 1, 1992