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By N. Can

Kinetics and mechanism of the chemical interactions between Si3N4 and TiC were investigated by isothermally reacting samples under nitrogen and argon atmospheres at temperatures between 1600°C and 1700°C? The initial composition of the powder compact contained 20, 30 and 40 volume per cent TiC? Kinetic analysis were performed by measuring mass losses and composition of the titanium carbonitride (TiC1-xNx) at predetermined time intervals? It was found that in the Si3N4-TiC system the degree and rate of the reactions increased with increasing temperature and content of TiC in both nitrogen and argon atmospheres? Si3N4 in the presence of TiC was stable in nitrogen atmosphere and the reactions were confined to Si3N4/TiC and TiC/N2 interfaces? At both interfaces interchange reaction occurs by simultaneous diffusion of nitrogen towards the centre of the particle and desoprtion of carbon in the opposite direction resulting in formation of titanium carbonitrides with various compositions? Reaction products under nitrogen atmosphere were B-SiC, TiCl1-xNx and N2? The maximum "x" value in TiC1-xNx was found to be 0?67 under nitrogen atmosphere? Si3N4 was found to be unstable in argon atmosphere in the presence of TiC and dissociated into liquid silicon and nitrogen gas within approximately four hours of reaction time, depending on temperature? The reaction mechanism in the initial stages of the interaction between Si3N4 and TiC under argon atmosphere proceeds similar to reactions under nitrogen atmosphere? However, considerable amount of Si3N4 dissociates within the first half hour? Liquid silicon aggressively attack both TiC1-xNx and unreacted or partially reacted TiC particles through cracks and pores and diffuses into interier part of the particle forming liquid solutions? After this stage, reactions under argon atmosphere proceeded according to Si-Ti-C ternary system?

Jan 1, 1999

By J. Boitano

This paper discusses the study, design and implementation of the new gas handling system for the Caletones Smelter of Cbdelco..Chile. A discussion on design conditions for a Mure Sulphuric Acid Plant using Teniente Converter.gases.is also included. The old system which started to be modified in 1985 and relied on natural draft and used balloon flues, resulted in a limited .gas handling capacity for operation under Mure process conditions. This system also caused excessive fugitive gases in the smelter working areas. The new system permits handling of process gases from the higher capacity Teniente converters installed in 1987-1989 Improving the gas handling of the reverberatory furnaces and Peirce-Smith converters as well as the environmental conditions of the smelter. This system utilises improved converter gas hoods, evaporative cooling and electrostatic precipitators gas cleaning, and is based on natural draft.

Jan 1, 1992

By M. J. King

The Chino Smelter embarked on a program to reduce smelter emissions. Fugitive sulfur dioxide and particulate emissions were reduced by (i) removing the flash furnace settling chamber and (ii) installing a baghouse, to treat converter secondary emissions. Neutralization plant capacity was increased, to accommodate increased flow from the flash furnace off-gas cleaning system and to reduce costs.

Jan 1, 1998

By Kathryn Hindmarsh

The most common method for the concentration of cyanide in gold leach circuits is based on the titration of cyanide ions with silver ions. This can either be done manually as a titration with a visual end-point or by using one of several commercial cyanide analysers which are 'based on the same titration but use a potentiometric end point This method has 'its limitations in the case of some ores such as those containing high amounts of soluble copper and those that are treated at low (less than pH 9) pH values in that the titration results do not accurately reflect the concentration of cyanide which is available for the dissolution of gold. This paper will present the results of the development of a novel "active" cyanide analyser which is based on the rate, of the reaction between gold colloids and cyanide. Gold colloids have a deep red colour and can be very simply prepared and stored for extended periods of time when stabilized. t has been shown that colloidal gold behaves similarly to metallic gold, dissolving in aerated sodium cyanide solutions to give the colourless Au(CNh-ion, This allows the reaction between the colloids and cyanide to be monitored spectrophotometrically at 520 nm. An automated instrument has been developed around this concept which can analyse a filtered pulp stream every few minutes with periodic calibration using standard cyanide solutions, Results of test work on synthetic solutions and solutions derived from several Australian gold plants will be presented as will the results of a comparative evaluation with a commercial titration analyser on a local gold plant

Jan 1, 1998

This paper describes developments in ferro-nickel furnace technology, specifically improvements to cooling methods, furnace controls, and high voltage furnace operating regime. The evolution of these technologies is briefly presented, as context for describing the current state of the art that has enabled ferro-nickel furnace operation at over 75 MW and specific energy consumption of less than 400 kWh/t dry ore. Examples from existing operations are used to illustrate present best practices, and potential future trends are discussed: The paper begins with an overview of the fundamental aspects of pyrometallurgical treatment of lateritic ores that drive ferro-nickel furnace design. Furnace wall cooling methods are related to the requirements resulting from specific furnace process conditions, including slag and metal compositions, as well as arc and bath power. The benefits of high productivity and low specific energy consumption resulting from high voltage (shielded-arc) operating practice are discussed, along with the furnace controls and electrical power train that enable such operation even with captive power generation. This paper is an update of that which the authors prepared for the Infacon X ferro-alloys conference.

Jan 1, 2004

By Tam Tran

Most new gold mines in Australia are required to treat tailings to reduce cyanide levels before they are discharged to storage ponds to meet the stringent environmental management guidelines set by government statutory authorities. In New South Wales, the average level of weak acid dissociable cyanide allowed in open tailings dams is now limited to 20 ppm, As stringent environmental guidelines continue to be enforced in Australia as well as in other parts of the world, the management of cyanide wastes has emerged as a key issue for the gold mining industry. This paper provides a critical evaluation on technical aspects related to the use of ion exchange resins and affiliated processes in cyanide management and tailing treatment. Particular attention is given to the use of ion exchange resin technologies in the processing of mixed gold-copper ores, where cyanide usage is the highest. Information presented in this paper is heavily drawn from the experience on the application of ion exchange resin processes at May Day mine, in New South Wales, Australia and associated pilot plant test programs. Issues related to the management of thiocyanate, especially with respect to the recovery of cyanide from thiocyanate are also discussed.

Jan 1, 1998

By P. Meyers, F. DeSilva, L. Gottlieb

A number of tests looking at lead removal using ion exchange resins of various types from various aqueous streams have been undertaken. The tests focused on strong acid cation (SAC) and weak acid cation 0N AC) resins. It was found that the mechanism of lead removal is partly by lead filtration rather than solely by ion exchange in a large portion of the applications studied. This is not surprising since lead carbonate is essentially insoluble and almost all water supplies contain at least some carbonate alkalinity. Regeneration of lead from exhausted resins containing significant amounts of lead may not be practical in some cases because of the large chemical and waste volumes involved. Since lead, .·along with many other very insoluble metals, is often present as a suspended solid rather than in ionic form, ion exchange is probably not always the best technology for bulk lead removal.

Jan 1, 2000

By Jan G. H. du Preez, C. Viviers, B. J. A. M. van Brecht, H. E. Rohwer, Nicole M. Sumter

"At the basis of metal ion separation lies some particularly metal ion specific chemical property which lends itself towards exploitation. This could be in the form of an anionic complex or a neutral chelate complex. In the former a cationic centre with a particularly high affinity for the complex will have to be designed. In the latter case a stereospecific chelate ligand containing the correct symmetry and type of donor atoms will have to be designed. In both above cases the ""active centre"" can be entered in a from that it can function in different media of hydrophobicity, eg a precipitant, a resin or a solvent extractant. Recent results obtained in this laboratory will be used to illustrate how the above variables can be exploited to develop improved processes for the separation of base metal and platinum group metals.IntroductionThe separation of metal ions in hydrometallurgy can be performed broadly speaking with two major aims. Firstly the separation/removal of a certain group of metal ions, either as a means of preconcentration or as a removal from effluent as part of a purification process and, secondly the removal of a specific metal ion from an industrial stream in order to produce a specific metal in a pure form. This latter operation is by far the most difficult of the two and is becoming more so in the light of the fact that the world is moving in the direction of lower grade ores and increasing pollution. Such a process can be divided into three essential parts, firstly the molecular one in which an active centre is required to obtain specificity, secondly a matrix within which this active centre must function, i.e. as part of a resin or solvent extractant and thirdly the design of the total system to optimize the realization of the operation."

Jan 1, 1996

By Peter K. Liaw, Charlie R. Brooks, David C. Joy, Wei Zhao

In this paper, effects of oxidation, porosity and fiber-fabric stacking sequence on flexural strength of a continuous silicon carbide fiber (SiCr) fabric-reinforced SiC ceramic-matrix composite (CFCC) were studied. The failure mechanisms were correlated with flexural strengths of CFCC samples, both before and after oxidation. Microstructures and fractography were investigated using scanning electron microscopy (SEM). The chemical change after oxidation, such as Si, C, and 0, and their distributions, were detected by the SEM energy-dispersive X-ray spectroscopy (EDXS) line-scan chemical analysis technique. These effects on the strength of the CFCC can be attributed to following reasons: (i) The decrease in the flexural strength after oxidation is mainly due to degradation of the strength of Nicalon fibers and the damage of fiber/matrix interface both caused by high-temperature chemical reactions, (ii) Porosity is not too important in affecting the strength of the CFCC, when the bonding of the forced flow chemical vapor infiltration (FCVI)-SiC matrix is stronger than that of the fiber/matrix interface. However, a higher porosity content will be harmful, because higher porosity will both decrease the effective elastic modulus of the FCVI-SiC and make pore-linkage easier to occur, which is more likely to cause premature failure, (iii) The variation in the lamina stacking sequence of the CFCC changes the elastic stress distributions along the thickness direction of specimens, the magnitude of ceramic matrix-cracking stress, the effective elastic moduli of the laminate, and different crack initiation sites as well as different failure modes, and thus, leading to the scatter in the flexural strength of the CFCC.

Jan 1, 1998

By Shoji Taniguchi, Lifeng Zhang, Kaike Cai

"In the present paper, based on the two-phase (Eulerian-Eulerian) model, the 3D fluid flows in gas-stirred systems, i.e., air-stirred water vessel and argon-stirred liquid steel ladle, are simulated. In the Eulerian-Eulerian two-phase model, gas and liquid are considered to be two different continuous fields. The phases are assumed to share space in proportion to their volume fractions. The exchange between the phases is represented by source terms in conversation equations. Turbulence simulated by the k- e model is assumed to be the property of the liquid phase. The following effects of mathematical treatments and operational factors on the fluid flow are discussed, such as interphase drag force, turbulent model, the size of bubble, and gas injection mode.Some interesting results are derived. Except the interphase drag force, the interphase lift force should be taken into accounted in order to exactly simulate the fluid flow in gas-stirred systems. Suitable turbulent model and drag coefficient have effect on the mathematical simulation. Injecting small bubbles can realize a well mixing flow condition. The distance between the two gas-injection nozzles has effect on the fluid flow."

Jan 1, 2000

By S. Sundarraj

The morphological transition between columnar and equiaxed structures is an important solidification phenomenon frequently observed in castings, especially complex parts with varying cross-section, The mechanical properties and the occurrence of defects such as hot tears are strongly dependent on the structure formed in the casting. Hence, it is important to understand the conditions leading to columnar or equiaxed structures. Although extensive work has been done in modeling solidification systems, almost all of the existing models are based on the assumption that the structure formed in the casting is either purely columnar or purely equiaxed. Prediction of the columnar-equiaxed transition (CET) requires a solidification model which accounts for the formation of both columnar and equiaxed structures, along with related microscopic and macroscopic solidification phenomena. In this paper a CET model is presented which: (i) takes account of both columnar and equiaxed structures, (ii) accounts for macroscopic heat transfer coupled with microscopic phenomena such as nucleation, growth and microsegregation, (iii) satisfies solute conservation, and (iv) is easy to implement in commercial finite element and finite difference software. The proposed model predictions of CET have been validated with available experimental results for a uni-directional solidification of an aluminum-copper alloy. A sensitivity analysis has also been carried out to determine the effects of various parameters on the CET model predictions. The model is being extended to other alloy systems and more complex geometries. This work will be published in due course.

Jan 1, 1996

By C. Gasparrini

Mineralogy may be applied to the selection of appropriate separation techniques, as well as to assist in the evaluation of problems causing loss of metals and other economically important elements during plant processing. Mineralogic studies may thus help develop techniques to optimize metal recoveries. The present paper describes how such factors as the minerals in which the elements of interest are concentrated, their chemistry, the chemistry of the associated minerals, grain size and textural associations with other minerals in the ore, may affect decisions on separation techniques for the recovery of economic elements. A number of case studies are described in which the mineralogical observation of ore samples has revealed the cause of problems experienced in the extraction of select precious and base metals, or has been decisive in the choice of appropriate techniques for recovery.

Jan 1, 1981

By Akio Ohta

The Hyuga smelter has been producing ferronickel by a rotary kiln-electric furnace process in Miyazaki, Japan. Several approaches to improve our operation have decreased the electrical energy consumption. A new process was developed to decrease the cost of energy even further. Oil and technical oxygen are injected through lances to heat up the calcined ores (calcine) instead of the electric power. Main problems during the development of the process were the short life of the water-cooled lances, the check on security of the safety system and the eruption of combustion gases through the calcine bed. These problems have now been overcome successfully, and stable operation can be maintained. The addition of 1 Litre of heavy oil per tonne of ore can save the electrical energy requirement by 8.6 kwh per tonne of ore. The new process has resulted in a reduction of the electrical energy consumption by more than 10 percent

Jan 1, 1992

By Mingming Zhang, Ramana G. Reddy

"Carbon dioxide (CO2) is one of the most common by-products produced during light metals production. It is considered to be the cause of greenhouse effects. Efficient reduction of CO2 can help minimize the rate of global warming and improving energy sufficiency. In this paper, a novel light metal production process was developed using ionic liquid electrolytes. This process has significant advantages compared to the traditional high temperature processes such as zero CO2 and CF4 emission, low energy consumption due to the low temperature operation and nonconsumable electrodes. Two types of anode materials (graphite, extruded carbon) were tested in electrolysis experiment. The results showed that both anode materials were stable (negligible weight loss). However, the extruded carbon was found to be superior to graphite in terms of current density and current efficiency. The calculated energy consumption for aluminum production was less than 10 kWh/kg at current densities up to 300 A/m2.IntroductionGlobal demand for ultra-light, ultra-strong, recyclable metals is growing as the world switches to low-emission vehicles, energy-saving devices and sustainable products. Aluminum demand is forecast to climb by 30 percent; magnesium demand by 200 percent, while for the emerging industrial light metal, titanium, the demand is expected to be at least double in the next decade. However smelting of light metals is the most energy intensive among all the steps of light metals production. For example, on an average it takes about 15.7 kWh of electricity to produce one kilogram of aluminum from alumina [1, 2, 3]. Advancements in energy efficiency have been steady, but slow, and most U.S. aluminum smelting production operates at 95% current efficiency. Besides high energy consumption, another major concern of the light metals smelting process is the emissions of greenhouse gases (GHG). Electrolysis green house gas emissions in the Hall-Héroult process can be split into three groups: 1) reduction reaction emissions, carbon dioxide (CO2) and carbon monoxide (CO); 2) process upset perfluorocarbons emissions; and 3) hydrogen fluoride (HF) formed from the moisture (H2O) present in the raw materials [2, 3]. Hydrogen fluoride gas can be captured and returned to the cells by the alumina dry scrubbing system used in modern facilities. A total of 5.31 kilograms of CO2 is generated from the reduction process for each kilogram of aluminum produced in the average U.S. primary facility. The perfluorocarbon emissions are related to the “anode effect.” If the concentration of alumina in the bath becomes too low, other reactions between the carbon anode and the bath occur and tetrafluoromethane (CF4) and hexafluoroethane (C2F6) are generated. These gases have high global warming potentials (GWP), which is a ratio developed to compare the ability of each greenhouse gas to trap heat in the atmosphere relative to carbon dioxide"

Jan 1, 2008

By Ma Ying

The continuous directional solidification technique of five kinds of special ZA alloys with eutectic, peritectic and eutectoid transformation under the condition of continuous casting by heated mold was studied. The mechanism of surface defects appearing in ZA alloy line was discussed and the structure of some defects were analyzed by SEM. The results show that only when the fitting of various technique factors, pressure head, outlet temperature, pulling speed and cooling condition are reasonable under a certain range, can the ZA alloy smooth line be continuously pulled out. Unreasonable techniques will result in hot tear, rough surface, mush outlet, leaking and other defects. The shape and location of solid-liquid zone have an important influence on the formation of the above defects. When the solid-liquid zone is located in the mould outlet or inner mould, the surface of solidification will protrude into the inner mould. If the remaining liquid cannot counteract the solidification contraction, a rough surface will appear. If the solidification surface further into the mould, the ingot in the mould will have a great friction force when pulling and will form a hot tear. When the solid-liquid zone is moved out of mould, the solidification surface will turn into a plane, which easily results in leaking. A vibration or unstable operation will cause an ingot winding during pulling

Jan 1, 2003

A comprehensive numerical capability for the analysis of Thermal Spray (TS) systems consisting of a three-dimensional compressible, turbulent flow Navier-Stokes model and a multi-phase particle flow model in Lagrangian formulation, was developed. This capability is validated for a set of flow conditions typical for TS. The developed methodology is used for analysis of the JP-5000 TS gun gas and coating powder flow conditions. Modeling and analysis of particle/turbulent eddies interaction is performed. Details of gas flow field, particle temperature, and particle velocity histories, and particle temperature, velocity profiles in the system are presented. For the validation of numerical analysis, the computed results are compared with available experimental measurements. The flow phenomena for different flow parameters are analyzed and explained as the results of gas dynamics and heat and momentum transfer between the gas and particle phases. This methodology can be used for process control and reliability improvement, and has the potential to significantly improve TS gun performance through control of its parameters.

Jan 1, 1996

By Gerald M. Ellis

Exploration for gold .deposits on Hispaniola has taken place sporadically over the years but has expanded in the past decade. There are veintype, disseminated, alluvial and elluvial deposits. Investigations were previously undertaken in Haiti by combined Haitian, Bureau of Mines, and UN geological teams at Grand Bois Limbe(Milot) and Cap Coq areas. Later studies were conducted at the Miches and Moncion districts. Gold occurrences were reported in quartz, silicic-barite veins and gossans. An important deposit ?at Pueblo Viejo is? a disseminated type where extraction is taking place in the oxidized zone. Exploration by Japanese and West German firms with local geologists are described in this paper together with Pueblo Viejo, Miches, Restauracion, Milot, and Meme ?areas where occurrences are known. Copper deposits with associated gold va1ues are also described. These include vein deposits in Central Cordillera and disseminated deposits at Terrier Rouge and Blondin.

Jan 1, 1989

By A. McLean, S. Dawson, N. D. G. Mountford

"IntroductionIn order to predict the accepted industrial practice for the year 2000, it may be helpful to first consider the rate of development of scientific knowledge. If the speed with which man can travel on commercial vehicles is taken as a criterion for determining the rate of progression, then it can be seen from Figure 1 that advancement in our present century is very rapid. Likewise, if computer technology is used as a criterion for the measurement of scientific advancement, it becomes evident that technological evolution can be highly exponential. These two examples are sufficient to demonstrate that engineers and managers cannot afford to regard scientific development as being linear with respect to time if they are to avoid underestimating the needs of society.Within this framework of overall development, the time required for individual ideas to progress from inception to regular application has decreased considerably. For example, X-rays first discovered by Roentgen in the 1890's and now used widely in medicine and engineering, required a developmental period of some eighty years. The motorcar evolved from early beginnings at the turn of the century to a position of great social impact in sixty years. Rectifier materials used in high frequency radar to the present explosion in communications, required forty years. As illustrated in Figure 2, the period is shortening rapidly.The use of sound waves appears to be following a similar path. There is now a considerable body of knowledge concerning their behaviour and exceptional advances have been made. In medicine and engineering the sonic approach to examination is well established, and acoustic testing forms the basis of several diagnostic and quality control applications. With respect to metals engineering, ultrasonic testing has contributed to the understanding of the relationship between the size and number of internal defects and the probability of premature failure. This has allowed the designer to incorporate appropriate safety factors in his designs; but more importantly, the realization of the deleterious effect of inclusions on the performance of the final product has resulted in a continuous pressure on the material suppliers to reduce the number of defects in their products.It is not only the designer who is demanding defect free material but also the fabricator, as material breakdown during manufacture can be prohibitively expensive. Examples of this can be found in both the aluminum and steel industries where ultra clean sheet is required to ensure that rejections are minimized during beverage can manufacture and other deep drawing operations."

Jan 1, 1988

By Kent D. Peaslee

When supersonic oxygen jetting is used in electric furnace steelmaking, the lance jet axis is typically inclined at larger angles to the vertical than is used in basic oxygen steelmaking. The supersonic jet is important not only for refining the steel, but for sustaining the foamy slag in the electric furnace. Physical modeling was carried out using a room temperature, two-dimensional slice apparatus in which mercury represented the metal and water-glycerol the slag. High speed video photography with image analysis was used to study the effects of the angle of inclination on the slag/metal bath. Mathematical modeling using FLUENT provided a method of predicting flow patterns and the trajectories of drops injected at various points in the flowfield. A one-half scale water model of the system, in which lance heights, angles, and flowrates simulated those encountered in steelmaking operations, was used to provide a better understanding of some aspects of the oxygen blowing process in electric furnace steelmaking.

Jan 1, 1994

By Karl A. Gschneidner

The magnetocaloric effect has been known for 120 years and has been utilized for cooling about 70 years. But in the last four years significant advances have been made to show that magnetic refrigeration is a viable and competitive cooling technology. Most of the work has focused on reciprocating devices, but rotary apparati are being developed. To date the magnetocaloric properties have been characterized for more than 200 materials. The magnetocaloric effect behaviors have been classified into three types of behaviors. The most common one is found in magnetic materials which exhibit a second order magnetic phase transition. Magnetic materials which exhibit a first order magnetic phase transition account for the second group of materials. Materials which exhibit multi-magnetic phase transitions make up the third group. The best candidate materials for magnetic cooling over the range from -4 to -1 350 K are also presented.

Jan 1, 2002