Search Documents

By Thomas E. P. Wechsler

The limiting factor for most pyro-metallurgical processes in secondary cop- per melting is the time required to heat and melt the product. American Combustion's proprietary PYRETRON variable £uel/air/oxygen combustion system improves the throughput of existing scrap melting and heating furnaces for copper and copper alloy production by increasing the rate of heat transfer from the flame to the product. The increased productivity and energy savings obtained from this technology can result in sizable reductions in operating costs for smelting operations.

Jan 1, 1991

By S. C. Sharma, M. Krishna, N. Sanmukha

"The oxidation behavior of an aluminium composite with 0, 2, 4, and 6% by weight of hematite at 200 to 500 °C has been investigated. Within the experimental temperature ranges a parabolic weight gain was observed. The, weight gain as a function of oxidation time becomes linear after an initial period on oxidation formation, an oxide scale was found whose morphology depends on temperature, cooling rate and sub-scale formation at the interface between the matrix and reinforcement. The presence of hematite particulate reinforcement has very little effect on the oxidation behavior. The interface oxidization rate was found to be higher than that of other regions. The, oxidation products were either metallic oxides or ceramic oxides. The exposure time of specimens to oxidation was 1000 minutes at various temperatures. In the present work key principles of alloy oxidation were discussed. Also the paper emphasizes various reactions taking ' place and the activation energies involved in the oxidation reactions.IntroductionMetal matrix composites (MMCs) reinforced with ceramic particulate, whiskers, or fibers have received increasing attention due to their potentially high fracture toughness and strength 1-5. Particle reinforced Aluminium MMCs find potential application in several thermal environment, especially in the automobile engine parts, space applications, such as drive shafts, cylinders, pistons, and brake rotors6.With the exception of gold, no metal or alloy is stable at room temperature, they tend to form their respective oxides. Most of the metals in the solid or liquid state are morphologically unstable when exposed to air at higher temperatures. An investigation relating to the temperature profiles of the piston area in a diesel engine has shown that the temperature can reach as high as 500¬800 K in certain regions of the piston. As the piston and cylinder areas are exposed to high temperature environment, the MMCs should have sufficient stability on both mechanical and chemical strength (oxidation). Oxidation occurs at grain boundaries in alloys and at the interface of the particulate and matrix in MMCs, which usually enhances intergranular fracture, resulting in premature failure and severe brittleness 8-10. Therefore for high-temperature applications, it is essential to have a thorough understanding of the oxidation behavior of aluminium MMCs."

Jan 1, 2000

By G. A. Brooks

Reactive ball milling has been proposed as a new route for producing carbides from oxides through carbothcrmic reduction. It is claimed that through milling oxide and graphite powders to the nanoscale, amorphous materials with very high reactivity are formed, that allows for easy transformation of the starting material to another in a subsequent thermal process. Thermodynamic analysis of this proposed process suggests that unless particle sizes are reduced to below 10nm, then reduction in size alone cannot explain a change in the stability of oxides. Even with nanometer scale powders, the products formed need to have a lower total surface energy than the reactants before a chemical change will occur. A model developed by Bhattacharya and Arzt for predicting localized temperature changes based on milling conditions suggest that temperarure rises less than 400 K will be achieved in laboratory conditions. The present calculations suggest that nanometer scale powders formed through high speed ball milling (>10 mls) may have undergone a process analogous to melting and quenching. Further work is required to fully distinguish these features.

Jan 1, 2003

By N. Verbaan, E. Bourricaudy, M. Dry

"Starfield Resources is developing a novel circuit for the recovery of nickel, copper, cobalt, iron oxide, sulphuric acid and precious metals from the Ferguson Lake deposit in Nunavut, Canada. In this deposit, pentlandite is too finely disseminated in pyrrhotite for the production of a smelter-grade nickel concentrate at an acceptable nickel recovery, so established technology is not applicable and a novel chloride-based circuit is under development. The enabling aspect of this circuit is the hydrolysis of ferric chloride to hematite, releasing gaseous hydrochloric acid that is recycled. Conventional steps are used for separating and recovering the valuable metals from the chloride solution generated. This paper briefly outlines the circuit and presents the results of experimental work on the enabling steps, viz. the oxidation and hydrolysis of iron chloride to hematite and gaseous hydrochloric acid.IntroductionThe Ferguson Lake bulk sulphide ore body in Nunavut, Canada, owned by Starfield Resources Inc., contains significant amounts of base and precious metals but its mineralogy is such that it is not amenable to conventional processing. Pentlandite, for example, is too finely disseminated in pyrhhotite for even modem techniques such as fine grinding and improved flotation reagents to be effective [ 1] and extracting the value requires processing the entire bulk sulphide, including the pyrrhotite. To give the project a total green footprint, in terms of both carbon emissions and acid rock drainage, Starfield imposed the following requirements:• No reactive tailings to generate acid rock drainage.• No gaseous emissions other than normal atmospheric constituents.• No liquid effluents.• No regular consumption of fossil fuel.• High recoveries of all the valuable metals."

Jan 1, 2011

By W. D. Judge, Z. W. Xiao, G. J. Kipouros

Rare earths have taken a prominent position in the Hi-Tech field after the discovery of the NdFeB permanent magnets. Their use in the magnets sparked miniaturization of the communication devices such as computers and mobile phones and are being considered in many more applications. Potential applications of rare earth elements in energy conversion technologies including wind turbines, photovoltaics, and other renewable energy systems are reviewed, along with sustainability considerations and production processes.

Mar 1, 2017

By J. van Driel

NOx is a growing concern for acid plant operators due to recent legislation reducing the allowable stack limits, as well as continually more stringent requirements for product acid quality. NOx also causes a major problem during maintenance as NOx rich acid residues fume following exposure to moisture in the air. Until recently, the solution for NOx related issues was to treat the symptom, rather than the cause. NOx in product acid was treated using chemicals and the NOx in the plant stack was generally left untreated. As part of an environmentally driven change in concentrates, Budel Zink installed the first gas phase NOx destruction process to be incorporated into a commercial scale acid plant. Nitrogen oxides contained in the process gas are reduced selectively with ammonia over a catalyst to form nitrogen and water. As a result, the NOx reduction is in agreement with the permit requirements.

Jan 1, 2002

By C. A. Young, J. D. Miller

Adsorption isotherms previously determined by in-situ Fourier transform infrared/internal reflection spectroscopy (FT-IR/IRS) for oleate adsorption at calcite and fluorite surfaces near pH 9 and at various temperatures are compared. Results indicate that, at both mineral surfaces, chemisorption occurs at equilibrium concentrations below approximately l x l0-5 M oleate while calcium dioleate surface precipitation occurs at higher equilibrium oleate concentrations. The extent of chemisorption at the calcite surface is 3 to 5 times less than that at the fluorite surface while the extent of calcium dioleate surface precipitation on calcite is nearly a magnitude larger than that on fluorite. However, for both minerals, surface precipitation decreases with increasing chemisorption. Contact angle measurements and flotation recoveries show the hydrophobicity of fluorite to be greater than that of calcite at each of the temperatures and oleate concentrations studied. Significant differences are noted only in the chemisorption region. Unlike calcite, the hydrophobicity of fluorite was sensitive to the presence of oxygen in the system. Multichannel Laser Raman Spectroscopy (MLRS) showed this behavior was caused by the double-bond reactivity of adjacent chemisorbed oleate molecules and subsequent formation of an epoxide/polyether complex at the fluorite surface. Such a reaction product could not be detected at the calcite surface. These differences in adsorption density, hydrophobicity, and polymerization behavior are discussed in terms of the intrinsic surface properties of the minerals.

Jan 1, 1999

By P. N. Anyalebechi

A comparative study of the mechanical properties of automotive steering knuckles produced by three different shape-casting related processes has been conducted. It involved the characterization of the tensile and fatigue properties of aluminum alloy A356 knuckles produced by the vacuum/pressure riserless casting (VRC/PRC), pressure counter pressure casting (PCPC), and the hybrid Cobapress (a casting-forging) processes, in accordance with the appropriate ASTM standards. Surprisingly, the knuckles produced by the hybrid Cobapress process exhibited the lowest strength. For example, the average 0.2% yield strength of the Cobapress knuckles was 31 MPa and 40 MPa less than that of the VRC/PRC and PCPC knuckles, respectively. However, between stresses of 150-200 MPa, the fatigue lives of the VRC/PRC, PCPC, and Cobapress knuckles were comparable. But above 200 MPa, the Cobapress knuckles exhibited the lowest fatigue life. The observed differences in the mechanical properties are attributed to the inherently different microstructures of the different knuckles.

Jan 1, 2009

By Varadarajan Seshadri

The performance of mould fluxes in satisfying its quality requirements can have a significant effect on the efficiency of the continuous casting process and on the surface quality of the products. This performance is affected by various parameters including the characteristics of the mould fluxes, the quality of the steel being cast and the operational conditions of the caster. The extremely complex relationships involving the parameters mentioned above make it very difficult to have simple criteria for selecting mould fluxes for casting a certain grade of steel in a continuous casting machine. These difficulties led steelmakers and mould flux suppliers to select mould fluxes based mainly on plant trials. In the present work, a software to help in the analysis and development of mould fluxes for continuous casting was developed_ This software includes several models for prediction of mould flux viscosity and consumption. A mathematical model was also used to predict the heat flux through the mould flux. The proposed methodology was applied to continuous casting of crack sensitive steels_ Some of the results given by this software are presented, discussed and compared to plant data.

Jan 1, 2003

By G. L. Peralta

Geothermal energy is an important source of power in more than 12 countries and is a potential source in 50 countries. However, the exploration and use of geothermal resources generate residues such as scale and sludge. The scale is from the steam distribution pipes while the sludge is from cooling ponds. These solids contain significant levels of elements which are of environmental importance notably, arsenic, sulfur, copper, zinc and lead that require safe treatment and disposal. The compositions, phases, textures, morphologies and size of scale and sludge particles have been studied by laser particle size analysis, light microscopy, scanning electron microscopy, X-ray microanalysis, and X-ray diffraction. In addition, their leachability was tested with protocol leaching procedures and sequential extractions. The detailed spatial relationships and speciation of the environmentally significant constituents have received particular emphasis. The information obtained is useful in understanding how the scale and sludge are formed, their leaching behavior if disposed of in a landfill and in developing appropriate treatment strategies.

Jan 1, 1994

By E. vanHuyssteen

A method of establishing the relationship between the mineralogy of a sinter and its subsequent processing behaviour in a lead blast furnace is demonstrated. It involves: 1) analyzing the Zn-spinels, hardystonite, larsenite, Pb-silicates, Pb-arsenates, Pb-(Ca)-sulphates and other femtes with an electron microprobe; 2) determining the extent of elemental substitutions in various mineral structures; 3) establishing a sequence in which the various phases formed during sintering. In this manner the relationship between the bulk chemistry of a sinter formulation and the speciation of elements into various phases in the sinter can be established. Specifically, the-substitution of Mg for Zn in hardystonite significantly influences sinter production. Mg substitution releases Zn into the surrounding matrix. This Zn reacts with the Pb-silicate to form larsenite thereby reducing the amount of Pb-silicate available for anhydrite digestion. Excessive amounts of residual anhydrite thus result if the sinter formulation is based solely on the CaO/Si& ratio.

Jan 1, 1993

By Peng Lv, Shiqian Liu, Bin Xu, Qian Li, Yongbin Yang, Tao Jiang

The treatment process of a low-grade refractory gold ore containing sulfide minerals and carbonaceous matters was studied in this work. The gold extraction of this ore by all-sliming cyanidation was only 11.75%. Hence, a pretreatment was necessary. In this paper, a flotation-preoxidation-cyanide leaching process was developed. The concentrate from the flotation procedure was processed using different preoxidation methods. A concentrate containing 34.08g/t of gold with the gold recovery ratio of 81.20% was obtained by flotation. After roasting, microwave heating or alkaline pressure oxidation, the gold cyanidation ratio reached 82.37%, 81.26% and 71.09% respectively. Roasting was an effective, reliable and mature technique to oxidize sulfide minerals and carbonaceous matters. Roasting and microwave heating both produced dangerous environmental pollutants while alkaline pressure oxidation was eco-friendly.

Jan 1, 2015

By Jogre A. S Tenório

he aim of the present investigation was to investigate technological features of the Fe-NbC dissolution in liquid Fe-C alloys. Fe-NbC is a Ferro-niobium alloy with 7%C, has a particle size smaller than 150 pm and its micro constituents are polygonal niobium carbides and an iron matrix. The obtained dissolution time was less than one-minute and the yields were in the range of 80-90% at 1873 K. In the Fe-NbC dissolution process, the dissolution occurs at first, and as a consequence the niobium carbides become free to dissolve. These carbides will dissolve until the melt reaches a saturation point. The non-dissolved carbides remain trapped in the liquid or will form a dross. The addition yields decreases when the niobium concentration reaches this limit value, that depends on the carbon concentration. These define a saturation curve.

Jan 1, 1994

By Andreas Siegmund

During the decade of the nineties the conventional method of primary lead smelting (sinter machine/blast furnace) was successfully challenged by the introduction of novel direct and continuous smelting processes. In combination with a significant shift in market structure, as well as more stringent government regulations these modem technological innovations like the QSL, Kivcet, and Isa/Ausmelt processes became more than major competitors. They have proven to be economically and environmentally viable. The intensification of the metallurgical reaction by applying oxygen enriched or pure oxygen bath or flash smelting principles resulted in cost savings and a higher flexibility with respect to raw materials and additives usage. By synchronizing individual auxiliary plant sections with the smelting process a virtually waste-free production and low-emission mode of operation with nearly optimum energy exploitation is achieved. The primary lead industry will gradually substitute the sinter -blast furnace operation with novel high-energy efficient technologies in the new millennium.

Jan 1, 2003

By C. M. Egert, S. Rajic

"We have developed a monolithic micro-spectrometer suitable for a variety of sensing applications including industrial process monitoring. The device consists of a solid structure with a volume less than 6 cubic centimeters. All optical components of the spectrometer including two aspheric mirrors, a diffraction grating, and entrance and exit surfaces are fabricated onto the surface of the structure. All light paths are internally contained within the structure. The result is a small, rugged spectroscopic sensor ideally suited for use as a process monitor. Due to its monolithic nature the device requires no post-fabrication alignment; nor can it be knocked out of alignment during use. Although many materials and thus wavelength regions were possible, the prototype device discussed here was produced in PMMA by precision diamond turning. However, lower cost manufacturing approaches involving injection molding are under development to produce an affordable sensor.Due to its rugged monolithic design, small footprint, and low cost the monolithic micro-spectrometer is ideally suited for distributed monitoring applications often required for industrial processes. It is expected that modified versions of this sensor designs will be required for specific applications so as to maximize the performance and resolution over the operating range. For example, the prototype device described here operates over a wavelength range of 500 nm to 1000 nm. The performance of this device as a real-time surface monitoring sensor will be discussed in detail. Our approach of using wavelength dependant scattering resulted in the reduction to practice of a miniature, monolithic, rugged, low-cost, micro-instrument in a sensor sized package. The process sensor applications community has been faced by the cost versus performance issue. Simple go/no-go sensors are typically inexpensive but they provide very limited and sometimes dubious data. Scaled down traditional instruments offer very good measurand information but are typically cost prohibitive, fragile, and still relatively large. This work will bridge the gap between these two extreme sensing alternatives."

Jan 1, 1997

By Jesus Gonzalez

Peirce-Smith converters (PSC) are long cylindrical chemical reactors where copper matte reacts with air. Traditionally, air is injected laterally through submerged tuyeres at different subsonic velocities. However, the accumulated experience in steelmaking, particularly in the basic oxygen furnace (BOF) process, shows that the gas bottom injection may improve the mixing efficiency of a liquid pool. The aim of bottom injection is to maximize the copper kinetic energy meanwhile avoiding excessive reactor splashing. When gas is injected from a single orifice at the bottom of a liquid pool, two main gas flow regimes can be identified, bubbling and jetting. In this work, a PSC with bottom air injection is studied by means of multiphase 3D CFD numerical simulations considering multiple air velocities. Special attention is paid to the bubbles and jet formation mechanism. The mixing efficiency is measured by calculating the turbulent kinetic energy of the copper matte.

Jan 1, 2008

By Toru H. Okabe

As part of a systematic study on the thermodynamic properties of complex nitrides, phase equilibria of the system Li-M-N (M Mg, AI, Ga) at 900 K were investigated. An attempt to determine the thermodynamic properties of complex nitrides was made by using the galvanic cell method, which utilizes LiMgN as an electrolyte under nitrogen atmosphere. The electromotive force (Emf) of the cell at temperatures between 800 and 1100 K was measured. While the Emf of the cell at 900 K was measured to be 0.137 V, data discrepancies of ±0.03 V were found. It was difficult to determine temperature dependence of the Emf. The Gibbs energy change for the reaction, 113 Li3N (s) + 1/3 Mg3N2 (s) = LiMgN (s), at 900 K was determined to be !'J.Go, (LiMgN) = -13.2 (±2.9) kJ/mol. Using thermodynamic information on the binary nitride from literature, the standard Gibbs energy of LiMgN was derived to be !'J.Go f (LiMgN)= - 121 kJ at 900 K. The thermodynamic stability range of nitride was discussed by constructing isothermal chemical potential diagrams that provide a better understanding of the stability region of the LiMgN phase. The diagram was found to be in good agreement with the isothermal phase diagram determined by the alloy equilibration method. Although the obtained data includes large uncertainties, the results provide a better understanding of the thermodynamic stability of nitrides. The potential application of this complex nitride to nitrogen chemical sensors or a medium for controlling nitrogen potential is also shown.

Jan 1, 2003

By B. Zilbergleyt

Current understanding of chemical equilibrium is based exclusively on the probabilistic considerations that are correct for isolated systems with only one chemical reaction to take place. For the systems with multiple chemical interactions, current paradigm of chemical thermodynamics promotes the idea of openness, artificially flavored with coefficients of thermodynamic activity. Recently introduced thermodynamics of chemical systems and the Method of Chemical Dynamics (MCD) offer explicit accounting for the multiple chemical interactions within the system. In the new theory, thermodynamic equilibrium of the j-subsystem obeys the logistic equation derived exclusively from the currently recognized concepts of thermodynamics. Having the only one new parameter -the subsystem's reduced chaotic temperature 'tj to describe external interactions, and reaction extent Ilj as independent variable, this equation covers the whole domain of the system's possible states from true thermodynamic equilibrium through the open equilibrium to bifurcations and chaos depending on the 'tj value. The MCD brings new opportunities to thermodynamic simulation of complex metallurgical and chemical systems, allowing for the analysis of their domains of states and the area limits, and for more accurate calculation of the equilibrium compositions. Its usage is exemplified in this paper by several applications. Keywords: chemical thermodynamics, open systems. complex systems, chemical dynamics.

Jan 1, 2003

By J. David Chapman

There are a variety of choices of materials for mineral extraction processing. Traditionally, end users have used metallic piping for fluid handling and little is known about the advantages (or limitations) of non-metallic piping systems. This presentation will review custom FRP pipe systems and their use in severe corrosive and erosive process streams. These systems can be designed to various pressure and temperature ratings and different components (such as resin and glass type) can be varied to suit the process conditions

By R. W. Bartlett

A two step process for treating platinum group metal flotation concentrates Is described while experimental results. The process was designed to be simple and Inexpensive While yielding a high recovery and fast turnaround. Ii consists of electric furnace smelting of concentrate to remove gangue and produce a homogeneous sulfide matte containing all of the base metals and platinum group metals. Sulfide oxidation Is minimized during smelting to avoid Installing an acid plant In the second step, matte Is pressure-leached with oxygen In an acid sulfate system to dissolve Iron, nickel, ?and copper while leaving a residue highly concentrated In precious metals, and typically about 1% of the flotation concentrate mass, A batch process with oxygen titration against the base metal composition of the feed Is used to control the end point of the leach. Sulfides must be eliminated while minimizing the precipitation of hydrolysis products. The leach residue can be smelled to bullion to facilitate sampling accuracy.

Jan 1, 1989