| METALLURGICAL AND MATERIALS TRANSACTIONS B | |
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Volume 26B, No. 6, December 1995 This Month Featuring: The 1994 Edward DeMille Campbell Memorial Lecture; Hydrometallurgy; Pyrometallurgy; Transport Phenomena; Process Control; Physical Chemistry; Mechanical Working; Welding and Joining; Mathematical Modeling. View December 1995 Table of Contents.
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THE 1994 EDWARD DEMILLE CAMPBELL MEMORIAL LECTURE
Materials, Bicycles, and Design
M.F. ASHBY
If the selection of materials is to be integrated into engineering design, a procedure is needed to identify, from among the enormous range of materials, the subset which most closely meets the design requirements. The elements of such a procedure are here described and illustrated by using it to select materials for bicycle frames.
THE 1995 EXTRACTION AND PROCESSING LECTURE
Importance of Fundamental Study in Hydrometallurgy
HIROSHI MAJIMA
Recent developments in modeling and optimization studies using computer technology have had a remarkable effect on all areas of extractive metallurgy. However, a lack of fundamental data regarding, for instance, activities, diffusion coefficients, limiting current densities, etc. obstructs the reliable use of this method. In studying hydrometallurgy, I recognized the importance of fundamental analysis and continued such works throughout my university life. For example, activities of water and solutes of the solution systems H2SO4-Mx(SO4)y-H2O and HCl-MClx-H2O were determined, and the results were employed to analyze the dissolution mechanism of metal oxides as well as metal sulfides in those solutions. In this article, fundamental studies mainly made in my laboratory to understand hydrometallurgical phenomena will be discussed.
HYDROMETALLURGY
Particulates in Hydrometallurgy: Part I. Characterization of Laterite Acid Leach Residues
A. BRICENO and K. OSSEO-ASARE
Two different laterite samples, designated as Ore No. 1 and Ore. No. 2, respectively, were leached with sulfuric acid in the temperature range of 25 °C to 275 °C, in order to evaluate the effects of ore type and leaching conditions (e.g., temperature and solid/liquid ratio) on the settling behavior of the leach residues. The initial solids, as well as the leach residues, were characterized by chemical and physical techniques such as X-ray diffraction, electrophoretic mobility, particle size, and chemical analyses. Spectrochemical and X-ray analyses determined that Ore No. 1 was a limonitic-type (iron oxide-rich ore) material, whereas Ore No. 2 was a transitional laterite ore (silicate-rich, iron oxide-containing material). By means of X-ray diffraction analysis, it was found that the conversion of goethite to hematite was enhanced as the temperature and/or leaching time was increased. Moreover, it was determined by chemical analysis that as the leaching temperature increased, the concentrations of Ni and Co progressively increased in solution, whereas the impurities (Fe and Al) rose through a maximum and then decreased. This behavior is attributed to the reprecipitation of iron and aluminum from solution as hydrolysis products of hematite and aluminum sulfates. The particle size studies revealed a particle size growth with temperature increase, which is attributed to the deposition of reprecipitation products onto the surface of the solid residues. Investigations of the surface chemistry of the coated particles via the electrophoretic mobility technique revealed that the 275 °C leach residues (Ore No. 2, pzc ~2) exhibited a point of zero charge (pzc) near pH 2, which is probably due to the redeposition of the dissolved silica. In contrast, the 250 °C leach residues (Ore No. 1, iron oxide-rich ore, pzc ~2) had a pzc value of about 3.8. This shift in mobility to less acidic values suggests that in this case, the insoluble iron and aluminum oxide products on the particles dominate the surface chemistry.
Particulates in Hydrometallurgy: Part II. Dewatering Behavior of Unflocculated Laterite Acid Leach Residues
A. BRICENO and K. OSSEO-ASARE
The effects of ore type and leaching conditions (e.g., temperature and solid/liquid ratio) on the settling behavior of laterite acid leach residues were investigated. Settling rate, supernatant turbidity, and filtrability of the slurry were used in evaluating the settling behavior. The slurries showed three different regimes of sedimentation, involving free, hindered, and compression settling behavior. An improvement in the dewatering characteristics of the leach residues was observed as the leaching temperature was increased. Furthermore, the leach residues showed markedly different settling behaviors depending on the temperature. Below 175 °C, the settling rate for both 2.5 and 25 pct solids increased steadily with temperature. However, the results indicated clearly that at higher temperatures (>175 °C), there is a steep increase in settling rate. These pronounced differences in settling behavior with temperature increase are believed to be due to the sharp increase in particle size above 175 °C. The mineral content in the ore has a great effect on the settling behavior of the leach residues. It was found that the oxide-silicate material (Ore No. 2 leach residues) showed a lower settling rate than the iron-rich material (Ore No. 1 leach residues). This behavior is attributable to the presence of a gelatinous, siliceous product in the Ore No. 2 leached pulp.
Particulates in Hydrometallurgy: Part III. Dewatering Behavior of Flocculated Laterite Acid Leach Residues
A. BRICENO and K. OSSEO-ASARE
Three polyacrylamide-based polymers of different chemical properties (polymer A, 34 pct anionic, 11 X 106 mol wt; polymer B, 7 pct anionic, 7.5 X 106 mol wt; polymer C, nonionic, 13.5 X 106 mol wt) were used to evaluate the flocculation behavior of laterite acid leach residues. The solid-liquid separation characteristics of the leach residues were investigated with the aid of settling rate, supernatant turbidity, and slurry filtrability measurements. The polymeric flocculants were found to be effective in improving the dewatering properties of the acid leach residues. Polymer effectiveness increased with increasing polymer dosage for all the polymers, but an optimum polymer dose was only found for polymer A (34 pct anionic, 11 X 106 mol wt) in the studied range of polymer addition. Similarly, the dewatering behavior was improved at higher polymer molecular weight. In addition, it was found that the flocculation performance was adversely affected by an increase in the degree of polymer hydrolysis which, in turn, increases the ratio of carboxylic to amide functional groups in the polymer chain. Polymer C (nonionic ~0 pct hydrolysis, 13.5 X 106 mol wt) was found to be the most efficient flocculant in terms of all the performance criteria investigated. The preceding results were rationalized in terms of bridging flocculation, the ionization and molecular configuration of the polymers, hydrogen bonding, and the solid/aqueous interfacial charge.
PYROMETALLURGY
Bubble Overlap in Multipoint Gas-Injection Systems
M. NILMANI and A.K. DAS
Factors affecting bubble overlap (interaction) in multipoint (multituyere/lance) gas-injection systems such as the Pierce-Smith converter and the zinc-fuming furnace have been investigated in laboratory room-temperature modeling experiments and at the industrial scale. Pressure changes have been recorded simultaneously from adjacent tuyeres both in the laboratory and in plant trials. It has been found that the factors which influence bubble overlap include the tuyere separation to tuyere diameter ratio, gas injection velocity, gas and liquid properties, and position and orientation of the tuyeres.
The Activities of Sulfide and Oxide Components and the Solubility of Oxygen in Copper-Iron-Sulfur-Oxygen Mattes at 1300 °C
C. SOMSIRI and D.R. GASKELL
The activities of iron and copper and the solubilities of oxygen in copper-iron-sulfur-oxygen mattes have been determined by equilibrating mattes with CO-CO2-SO2 gas mixtures of fixed partial pressures of oxygen and sulfur and equilibrating a small mass of platinum with the melt. Iron and copper transferred from the matte to form a platinum-iron-copper alloy in which the activities of iron and copper are the same as in the matte. The activities of iron and copper in the matte were then determined from knowledge of the activities of iron and copper in the system platinum-iron-copper. Sulfides of WFe = 0.1, 0.3, and 0.5 were studied, where WFe = wt pct Fe/(wt pct Fe + wt pct Cu), and sulfur pressures of 0.005, 0.0158, and 0.025 atm and oxygen pressures of 3.16 X 10-10, 7.94 X 10-10, 2.00 X 10-9, and 3.16 X 10-9 were used. The activity of copper, which varied in the range 0.06 to 0.165, decreases with increasing po2 at constant WFe and ps2 and decreases with increasing ps2 at constant WFe and constant po2. The activity of iron, which varied in the range 0.002 to 0.06, increases with increasing po2 at constant WFe and ps2 and decreases with increasing ps2 at constant WFe and po2. The activities of the components Cu2S, FeS, Cu2O, FeO, and Fe3O4 were calculated from the activities of iron and copper, the partial pressures of oxygen and sulfur, and the appropriate equilibrium constants. The variations of the activities of these components with matte grade, oxygen pressure, and sulfur pressure are presented and discussed. Within the range of experimental conditions studied, the solubility of oxygen in the melts is given by wt pct O = 2.59p0.225o2 p-0.18s2 (1 + 9.0WFe)1.86.
Settling of Copper Drops in Molten Slags
A. WARCZOK and T.A. UTIGARD
The settling of suspended metal and sulfide droplets in liquid metallurgical slags can be affected by electric fields. The migration of droplets due to electrocapillary motion phenomena may be used to enhance the recovery of suspended matte/metal droplets and thereby to increase the recovery of pay metals. An experimental technique was developed for the purpose of measuring the effect of electric fields on the settling rate of metallic drops in liquid slags. Copper drops suspended in CaO-SiO2-Al2O3-Cu2O slags were found to migrate toward the cathode. Electric fields can increase the settling rate of 5-mm-diameter copper drops 3 times or decrease the settling until levitation by reversal of the electric field. The enhanced settling due to electric fields decreases with increasing Cu2O contents in the slag.
ELECTROMETALLURGY
Electrolytic Reduction of Eu(III) to Eu(II) in Acidic Chloride Solutions with Titanium Cathode
TETSUJI HIRATO, HIROSHI KAJIYAMA, HIROSHI MAJIMA, and YASUHIRO AWAKURA
The feasibility of a rare earth separation process by electrolytic reduction of Eu(III) with a titanium cathode was examined by cathodic polarization characteristics of Eu(III) on a titanium electrode and batch-type electrolytic reduction of Eu(III) using a bipolar electrolytic cell in acidic aqueous solutions of EuCl3. The reduction of Eu(III) started at a cathode potential of about -0.6 V vs standard hydrogen electrode (SHE). The plateau current for the reduction of Eu(III) was observed at around -1.2 V vs SHE, but a further decrease in cathodic potential resulted in a decrease in the reduction current, which was caused by the hydrolysis of Eu(III). The plateau current is a diffusion-limiting current in the reduction of Eu(III). In the batch-type electrolytic reduction of Eu(III) using a bipolar electrolytic cell, complete reduction of aqueous 0.1 kmol m-3 EuCl3 solution with a current efficiency of over 0.6 could be achieved by keeping the catholyte pH at 2, to avoid hydrolysis of Eu(III). The final percent Eu(III) reduction of the solution from an industrial europium purification process, which contained other rare earths, was lower than that of a synthetic EuCl3 single electrolyte solution probably because of a more significant hydrolysis of rare earth ions. However, the final percent reduction increased with decreasing reduction current, the concentration of rare earths, and the viscosity of solution.
Levitation of Liquid Sodium Droplets
S.S. ROY, A.W. CRAMB, J.F. HOBURG, and B. LALLY
Droplets of liquid sodium ranging from 1.2 to 2.1 g, immersed in mineral oil, were levitated in an electromagnetic field. The experimental setup was designed and constructed to levitate small metal droplets at audio frequencies. The levitated droplet was found to be very stable inside the inductor, and the equilibrium shape attained by the droplet in the electromagnetic field was measured during the experiment. A surface coupled mathematical model was used to calculate the self-consistent equilibrium droplet shape of liquid sodium under the influence of an electromagnetic field. The predicted shapes of the metal droplet and the position of the droplet inside the inductor compare well with the experimental data.
Magnetic Shaping of Columns of Liquid Sodium
S.S. ROY, A.W. CRAMB, and J.F. HOBURG
The meniscus of a cylindrical column of liquid sodium in mineral oil was shaped under an electromagnetic field. The electromagnetic field was generated by an alternating current flowing through a coil surrounding the liquid metal column. The equilibrium shape of the meniscus, under the influence of electromagnetic field, was experimentally measured and compared with the predicted results from the mathematical model. The experimental technique used to measure the meniscus shape of the liquid metal column and the development of the mathematical model are presented. The validity of the mathematical model to predict the meniscus shapes is also discussed.
TRANSPORT PHENONEMA
An Experimental Study of Process Behavior in Planar Flow Melt Spinning
THOMAS J. PRAISNER, JIM S.-J. CHEN, and AMPERE A. TSENG
A parametric study concerning the process behavior in planar flow melt spinning (PFMS) of Pb-Sn alloy ribbons is presented in this article. Experiments were conducted to develop correlations between the produced ribbon thickness and process variables, including wheel speed, crucible pressure, nozzle-wheel gap, and melt superheat. The ribbon thickness was found to vary with the wheel speed to the power of -2/3 and the crucible pressure to the power of 1/3. Puddle lengths were found to increase linearly with crucible pressure. The ribbon thickness behaved in a two-term exponential manner in relation to the melt superheat. A processing window for the production of high-quality ribbons was determined using dimensionless parameters. Five distinct ribbon patterns were identified, and their respective surface roughnesses were measured and reported.
The Sublimation of an Electrically Conducting Droplet through the Use of an External Alternating Magnetic Field
VICTOR G. STICKEL, JR. and YILDIZ BAYAZITOGLU
A nondimensionalized mathematical model is developed for a stationary, electrically conducting, spherical droplet undergoing equilibrium sublimation. Sublimation is caused by the presence of an external, alternating magnetic field generated by a current carrying solenoid. The model incorporates the influence of magnetic field parameters, phase change, and radiative heat transfer. Numerical results from the model are compared with sublimation rates obtained from experimentation.
PHYSICAL CHEMISTRY
Viscosity of Copper Slags from Chalcocite Concentrate Smelting
J. KOWALCZYK, W. MROZ, A. WARCZOK, and T.A. UTIGARD
The viscosity of smelting slags from the Glogow copper plant in Poland was measured using a concentric cylinder viscometer. These slags contain typically 45 pct SiO2, 16 pct CaO, 8 pct MgO, 11 pct Al2O3, and only 5 to 7 pct total iron. The viscosity was measured as a function of the CaO, MgO, SiO2, Cu2O, Cr2O3, and Fe3O4 contents in the temperature range from 1473 to 1623 K. Silica and chromium oxide additions increased the viscosity, while small additions of the other oxides decreased the viscosity. However, at large additions of CaO or MgO, cooling resulted in a rapid increase in the viscosity upon reaching the transition temperature. This critical transition temperature increased with increasing additions of CaO and MgO. This was explained by the precipitation of solid particles upon reaching the saturation limit. Depending on the slag composition, the activation energy for viscous flow was found to be in the range from 200 to 370 kJ/mol.
Communication: Solid Electrolyte Sensor for Measuring Magnesium in Molten Aluminum
JEFFREY W. FERGUS and SHIQIANG HUI
SOLIDIFICATION
An Asymptotic Model of the Mold Region in a Continuous Steel Caster
J.A. DiLELLIO and G.W. YOUNG
A model is developed to simulate the solidification of the steel shell in the mold region of the continuous casting process. Conduction-dominated temperature fields in the mold, mold flux, steel shell, and molten steel regions are determined through the development of an evolution equation for the solidifying front. This equation is derived in the limit of small aspect ratio, mold width to height, using asymptotic methods. These results are coupled with a lubrication-theory model for the mold flux region. This model assumes a temperature-dependent viscosity for the mold flux and allows for solidification of the flux at temperatures below a critical value. System response to changing casting speeds, superheat, mold wall temperatures, and mold flux properties is investigated.
Heat Transport and Solidification in the Electromagnetic Casting of Aluminum Alloys: Part I. Experimental Measurements on a Pilot-Scale Caster
D.C. PRASSO, J.W. EVANS, and I.J. WILSON
While many investigators have examined electromagnetic and magnetohydrodynamics phenomena in electromagnetic casting (EMC) of aluminum, there appears to be no published work on heat transport and solidification in such casters. This two-part series is an attempt to remedy this deficiency. The first part describes two experimental campaigns, carried out on a pilot-scale electromagnetic caster at Reynolds Metals Company, in which sacrificial thermocouples were used to obtain many data on temperature distributions within the aluminum of a pilot-scale caster and thereby to obtain the shape of the liquid metal pool ("sump''). The data reveal a strong dependence of temperature distribution and sump depth on casting speed but a relatively weak dependence on the flow rate of the quenching water striking the outside of the ingot.
WELDING AND JOINING
An Inelastic Analysis of a Welded Aluminum Joint
ROBERT E. VAUGHAN and WILLIAM P. SCHONBERG
Butt weld joints are most commonly designed into pressure vessels by using weld material properties that are determined from a tensile test. These properties are provided to the stress analyst in the form of a stress vs strain diagram. Variations in properties through the thickness of the weld and along the width of the weld have been suspect but not explored because of inaccessibility and cost. The purpose of this study is to investigate analytical and computational methods used for analysis of multiple pass aluminum 2219-T87 butt welds. The weld specimens are analyzed using classical plasticity theory to provide a basis for modeling the inelastic properties in a finite element solution. The results of the analysis are compared to experimental data to determine the weld behavior and the accuracy of currently available numerical prediction methods.
MATHEMATICAL MODELING
A Three-Dimensional Mathematical Model of Electromagnetic Casting and Testing Against a Physical Model: Part I. The Mathematical Model
D.P. COOK and J.W. EVANS
This first of two related articles describes a mathematical model for electromagnetic casting in three dimensions, i.e., where the dependent variables are functions of all three spatial coordinates. It is shown how the method of inductances can be extended to three dimensions in order to solve Maxwell's equations for the electromagnetic field in and around the caster. The principal task here is the calculation of the inductances between loops of irregular shape, and the method by which this is done is described. The computations are self-consistent ones in that the free surface of the molten metal is adjusted in response to the supporting electromagnetic forces which are themselves dependent on the shape of that surface. The computed electromagnetic forces are input into a second phase of the calculations where melt flow is computed in three dimensions using the finite element package FIDAP.
A Three-Dimensional Mathematical Model of Electromagnetic Casting and Testing Against a Physical Model: Part II. Results from a Physical Model and Testing of the Mathematical Model
D.P. COOK, S. NISHIOKA, and J.W. EVANS
A physical model of an electromagnetic caster was constructed. The model was intended to provide measured data for comparison with the predictions of the three-dimensional (3-D) mathematical model described in part I. The physical model consisted of a molten Wood's metal pool (176 X 176 mm seen from above) on the top of an aluminum-bronze block. Probes were used to measure electric and magnetic fields, the deformation of the liquid surface, and the electromagnetically driven flow, at many positions within the melt, as a function of model geometry. Agreement between the measurements and the predictions of the mathematical model was generally good. The melt flow was 3-D and strongly influenced by the position of the electromagnetic screen interposed between the inductor and the metal pool.
Heat Transport and Solidification in the Electromagnetic Casting of Aluminum Alloys: Part II. Development of a Mathematical Model and Comparison with Experimental Results
D.C. PRASSO, J.W. EVANS, and I.J. WILSON
In this second article of a two-part series, a mathematical model for heat transport and solidification of aluminum in electromagnetic casting is developed. The model is a three-dimensional one but involves a simplified treatment of convective heat transport in the liquid metal pool. Heat conduction in the solid was thought to play a dominant role in heat transport, and the thermal properties of the two alloys used in measurements reported in Part I (AA 5182 and 3104) were measured independently for input to the model. Heat transfer into the water sprays impacting the sides of the ingot was approximated using a heat-transfer coefficient from direct chill casting; because this heat-transfer step appears not to be rate determining for solidification and cooling of most of the ingot, there is little inaccuracy involved in this approximation. Joule heating was incorporated into some of the computations, which were carried out using the finite element software FIDAP. There was good agreement between the computed results and extensive thermocouple measurements (reported in Part I) made on a pilot-scale caster at Reynolds Metals Company (Richmond, VA).
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