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By S. P. Marsh, M. E. Glicksman

"The effect of capillarity-driven diffusion on the recalescence of mushy zones is studied in pure materials. The solid-liquid mixture is formed by rapid partial solidification of an initially undercooled melt, and the ratio of the two phases is subsequently maintained constant by an externally imposed adiabatic constraint. A novel technique has been developed that permits tracking of the kinetics of the diffusion-controlled evolution process in situ using precision temperature measurements averaged on a length scale larger than that of the microstructure.The mean ""temperature of a mushy zone is slightly below the bulk equilibrium melting point, and is related to a characteristic length scale of the microstructure through an appropriate statistical average of the GibbsThomson equation. Theoretical considerations indicate that the diffusion controlled recalescence will progress as t- l / 3, where t is time. This behavior is experimentally verified for both succinonitrile (SCN) and ethylene carbonate (ETC), which have markedly different morphologies. The kinetic rate constant is observed to increase monotonically with increasing volume fraction of solid in the two-phase mixtures, although a firm theoretical foundation for this result has not been developed.INTRODUCTIONA dispersed multiphase system seeking equilibrium will generally contain variations in the local .free energy density. These density variations arise from such factors as variations in the bulk free energies of the phases and the distribution of interfacial energies. In this study, we examine the kinetics of diffusion-controlled recalescence in 1 solid-liquid mixture of a pure substance at its melting point. This type of two-phase system is particularly convenient to analyze because of the well-characterized physical properties of pure phases (crystals and their melts) and their interfacial energies, and the absence of any solutal effects."

Jan 1, 1986

By J. R. Budden

The growth and oxidation characteristics of any bacterial culture are ultimately determined by the nature of the sample being treated. The most important parameters in the application of bio-oxidation are bacterial cell number, growth rates, oxygen uptake and rate of oxidation. Cells present in the solution of an established culture were counted directly using a microscope, related to a protein value, and then used to determine the total cell number (in solution and on the solids). Protein determination of total cells enabled the growth rates on slurry to be calculated. The cell number and culture growth is related to the iron and sulphide contents of the sample. To illustrate these considerations a moderately thermophilic culture was used to treat ore and concentrate samples obtained from Australian mines.

Jan 1, 1990

The oxidation of ferrous ions by oxygen in sulphate solutions is a very slow process, but it tills long been known that the addition of sulphur dioxide increases the rate of reaction very significantly. The kinetics and mechanism of the process were investigated in the laboratory and the results confirmed the advantage of adding small amounts of sulphur dioxide to the oxygen stream for the removal of iron from solutions. The effect of various parameters on the overall rate of iron oxidation and precipitation was studied. In particular, temperature, acidity and composition of the gas mixture were considered and the optimum conditions for the precipitation of goethite were determined.

Jan 1, 1991

By Jie Ma, Bo Wang, Jieyu Zhang, Jian Zhao, Guangxin Wu, Shunli Zhao

"Nucleation and growth model based on a 3D CAFE model, which was incorporated with macro heat transfer calculation within ProCAST software was used to predict the solidification microstructure of austenitic stainless steel in twin-roll strip casting. The simulation results of solidification microstructure agreed well with experimental results of austenitic stainless steel. The effect of different casting process parameters on the solidification microstructure was simulated. The predicted results show that solidification microstructure is obviously sensitive to superheat and convection heat transfer coefficient. With the increase of superheat, the grain density decrease and the proportion of columnar crystal increase. In addition, the proportion of columnar grains increases when convection heat transfer coefficient increases. Thus, it was demonstrated that the solidification microstructure evolution of twin-roll strip casting could be predicted reasonably by using this model.IntroductionNear-net-shape casting technology is an important research area in the iron and steel industry today. Twin-roll strip casting represents a major area of concentration of near-net-shape casting technology. It has been widely used for its outstanding advantages, such as extended solubility of alloying elements, refined solidification microstructure and reduced microsegregation [1]. Furthermore, it is the most environmentally friendly, energy saving, and C02-sensitive way to produce steel strips [2]. Therefore, much attention remains to be paid to this aspect. A lot of published works indicated that the solidification microstructure of twin-roll thin strip has obvious effect on the thin strip properties [3, 4]. For the accurate control of parameters of the process are made difficult due to the complicated process and the multi-fold factors, great attentions have been paid to numerical simulations to provide insight into the solidification behaviors of the thin strip formed by twin-roll strip casting [5, 6].Simulations of casting solidification can provide a method to predict microstructure and to improving strip quality by controlling the process parameters."

Jan 1, 2014

By Saskia Duyvesteyn

Ion flotation is a technique applicable to the removal of metal ions from dilute solutions, using ionic surfactants.- While there are a number of physical and chemical parameters that influence the ion flotation process, this paper focuses on two of the important chemical ones, namely frother concentration and ionic strength. The effect of several frothers, including ethanol, iso-propanol and MIBC at concentrations ranging from 0% to 0.4%, was studied for the model Cd-dodecylsulfate and Cu-dodecylsulfate systems. The ionic strength, as well as the effect of monovalent and multivalent counter ions, was also studied in the range of 1@3 - 1 M, at constant pH. The results are discussed in terms of applicability to a range of effluents from minerals and materials processing operations.

Jan 1, 1994

By M. S. Lee

A cold model study on the effects of various operating conditions on the dispersed-phase holdup in a liquid-liquid emulsion generated by bottom gas injection has been performed using water and kerosene. Dimensional analysis was used to correlate the holdup with the operating conditions and the sampling locations. The holdup increased with gas velocity, and decreased with axial and radial distances. The radial distribution of holdup follows a Gaussian function. The holdup increased with increasing ratio of the heavy phase to light phase volumes and decreased with the total height of the heavy phase. The combined effects of various operating conditions can be represented by the Froude number. The variation of the holdup within the plume was correlated by a single equation involving a set of dimensionless numbers.

Jan 1, 1995

By G. R. Adams, N. Y. Tang, N. Qiang

"Aluminum is the most important alloy addition to Zn baths for controlling the reaction kinetics between the steel substrate and molten Zn in continuous galvanizing operations. Due to the complexity of the Zn-Fe-Al ternary system, the measurement and control of effective bath Al remains a challenge for modem galvanizers. The successful development of Al sensors has made the real-time measurements of bath Al contents possible. To facilitate their application, a computer interface and a palm-size data logger have been developed by Cominco. Plant applications indicated that the sensor possessed sufficient accuracy for process monitoring and control. The working mechanism of the Al sensors and Cominco's development work is described, and the results of sensor applications are presented.IntroductionControl of bath Al content is critical in modem continuous galvanizing because it has a strong influence on coating structure and properties and the overall product quality. The control of effective bath Al content (Al in liquid solution) is particularly critical for galvannealing where a high bath Al content may lead to incomplete alloying during post annealing, and a low bath Al content may result in other operation problems, such as excessive bottom dross accumulation and difficulties in coating thickness control. The desirable accuracy of the Al control is within ±50 ppm of target levels. In principle, such an accuracy is achievable for modem chemical analysis facilities, such as atomic absorption photospectrometer (AAS) and induction-coupled plasma (ICP). However, a recent study carried out by the International Lead and Zinc Research Organization (ILZRO) indicated that such an accuracy is rarely achieved in the zinc and steel industries.(1)"

Jan 1, 1997

By Ping-Ping Fan, Yong-Quan Wu

The polarized Brillouin scattering spectra were systematically measured to study the elastic properties of bulk hexagonal close-packed (hcp) ZnO single crystal in this paper. The peak polarizations of all modes in spectra were analyzed firstly. The elastic properties, such as the whole set of Elastic constants were accordingly calculated and compared with the previous literatures. Also investigated were the effects of the rotation of the sample in the (0001) plane perpendicular to the z axis on different acoustic modes. The results show that the quasi-longitudinal and quasi-transverse modes perpendicular to the (0001) plane act as the expected trigonometric function of the rotation angle,while the longitudinal and transverse modes on the (0001) plane remain constant.

Mar 1, 2017

By Jun Li

Several metal sulfides were examined in-situ by Raman spectroscopy before and after anodic oxidation. Results obtained for chalcocite, chalcopyrite, covellite, galena, pyrrhotite and pyrite electrodes are presented. Under appropriate conditions, sulfur was detected after a potential was applied to the mineral electrodes for a threshold period of time. For all the minerals, application of a negative potential on the oxidized mineral reduced the surface product and the sulfur peaks disappeared from the observed spectra. For those minerals containing sulfur as S< in the crystal lattice, polysulfides were identified as oxidation intennediates.

Jan 1, 1993

By Gabriel Riveros

Fire refining of copper consists of two stages copper oxidation and copper reduction. Very frequently the capacity of the anode furnace is determined by the rate of copper reduction, The analysis of factors affecting the rate of the oxygen reduction from a liquid copper with solid carbon or injected hydrocarbons pointed out the role of the mass transfer in a liquid copper in final stage of the reduction. Experimental results of copper reduction with graphite and injected natural gas in laboratory-scale crucibles showed two stages of the reduction process with a sharp change of the controlling mechanism. The estimated dynamic surface area of gas bubbles based on the measured bubble frequency and the gas flowrate allowed for the determination of the reaction constant as a degree of the partial pre-combustion of the air/natural gas mix. The variation of the used reductant as a function of the oxygen concentration and temperature has been evaluated based on the determined kinetic model. The intensification of copper reduction in fire refining has been discusses on the basis of obtained kinetic data and analysis of various factors determining the time of reduction.

Jan 1, 2003

By P. Klut, D. Groult, R. Marechalle, B. T. H. Bonnema

In the past 5 years, Compagnie Europeenne de Dezingage (CED) has developed a successful dezincing process and the St. Saulve pilot plant has evolved into a commercially successful production plant. Currently the plant meets all the required standards for scrap and zinc quality, output capacity, availability, and meets the prescribed environmental emissions standards. The initial process problems relating to zinc recovery, uncontrollable explosions and sodium hydroxide aerosol emissions have all been solved. Presntly, the yearly production of dezinced scrap is around 50.000 tonnes/year; this capacity is enough to supply the local market. This capacity can be increased easily to 65.000 tonnes/year or more. The market for dezinced material is growing due to the increased consumption of galvanized material on one hand and on the other hand the higher demand for high quality scrap. The proven technology of CED is currently patented worldwide, but CED is inviting licensees to implement the dezincing technology in other parts of the world.

Jan 1, 2000

By Batric Pesic

Dissolution of gold with sodium bromate solutions of various compositions was studied by using a rotating disc technique. The role of bromide ion, acid and externally added bromine was examined. It was found that sodium bromate could not dissolve gold in the absence of either acid or bromide ion, or both. When acid was absent, no bromine necessary for gold dissolution could be produced. When bromide ion was absent, formation of soluble gold bromide species, AuBr,-, was not possible. Bromate concentration had a complex effect, and it was dependant on bromide ion concentration. For fixed initial bromide ion concentration, gold dissolution rate increased with sodium bramate concentration increase until certain level, beyond which further increase of bromate concentration decreased the gold dissolution rate. The negative effect of bromate was explained by the depletion of necessary bromide ion. Sulfuric acid concentration effect was a function of initially present bromine.

Jan 1, 1992

By V. M. Sokolov, Jr. DuPlessis

The technology for recycling fine wastes, grinding sludges or swarf, and solids such as slag that contain a high content of metallic material needed improving. The objective was to produce a master alloy that met the tight requirements of the Western manufacturers and achieve improved yields of the valuable elements, nickel and cobalt, to over 90%. The alloys from the production of Alnico. magnets were chosen for this work. A process is proposed .that is able to recycle all kinds of Alnico wastes. This process is able to reduce all detrimental elements, which are contained in the wastes, to within acceptable levels. Molybdenum, if present, is an exception. Depending on the levels of contamination of undesirable elements different recycling strategies are proposed. The majority of the wastes can be recycled by melting and refining with a liquid slag layer using unique melting furnaces that are relatively unknown in Western nations. The proposed technologies allow the reelamation of over 95% of the cobalt and nickel from any kind of Alnico waste, and there are no limitations on the proportion of different kinds of wastes in the charge. The proposed processes and technologies could also be applied to the recycling of grindings, turnin

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 M. Suzuki, M. Dobashi, M. Kahata, T. Yoshida

Almost 30% of steel in Japan is produced by electric arc furnace (EAF) treatment of iron scrap. EAF dust includes approximately 20 wt % of Zn and 3- 5 wt % of CI and is treated by the pyrometallurgical processes to recover Zn as Zn oxide. Direct hydrometallurgical processing is one of the most effective methods to recover high purity Zn. In this case, CI in the EAF dust is dissolved in the liquid phase by leaching, and the CI anion in electrolyte attacks anodes which are commonly made of a lead base alloy. Several processes have been proposed to remove CI anions from acidic sulfate solution. In this study, an electrolytic process was examined to eliminate CI anions from Zn sulfate electrolyte. From our study it can be said that the elimination rate of CI anion depends on the anode material ( i.e., the elimination rate is Pb-Ag alloy == Pb > DSE== Pt). In industrial Zn electrowinning process, the electrolyte contains Mn, which means the influence of Mn should be considered in the elimination of Cl. Mn dioxide deposition on an anode plate reduces the efficiency of CI removal. A periodical reverse current electrolytic system was examined to prevent this efficiency decrease, and deposited Mn dioxide could be removed very rapidly when the current is reversed. More than 95% of CI anion could be removed by this method in a shorter period than direct current method.

Jan 1, 1997

By C. E. Dodson

Conventionally hydrometallurgical recovery processes from sulphide concentrates include roasting, leaching, precipitation, impurity removal and zinc electrowinning. The use of the novel (yet commercially proven in other mineral and metallurgical industries) TORBED process reactor for the flash roasting of sulphides will be proposed. The potential advantages in its application will be discussed including very fine particle processing capability, lower cost smaller roasters, waste minimization, improved leaching efficiency and overall process simplification.

Jan 1, 1999

By Christina V. White

An experimental study was undertaken to investigate the feasibility of utilizing vapor transport for the treatment of heavy metal contaminated smelter soils. The focus of this project was to develop process chemistries that would make incineration a viable process for the treatment these soils. The experimentation concentrated on the elimination of arsenic, cadmium, and lead, and was performed in a laboramry scale rotary kiln setup. Three soil samples from non¬ferrous smelter sites, which contained various concentrations of contaminants, were utilized in the experimentation. Three chemistries were investigated for the volatilization of the heavy metals: Chloridizing volatilization, ferric chloride vapor complex formation, and the use of oxygen potential control. The samples were analyzed for residual heavy metals so that the extractions could be determined. However, the ultimate test was the leachability of the residual arsenic, cadmium, and lead, as determined by the TCLP test. The results firmly establish that incineration is a feasible process for the treatment of metal contaminated soils. It was found that no one process chemistry is suitable for all different soil samples. A two-step process consisting of a reducing step followed by a hydro-chlorination step was required to make Soil Sample-B pass the TCLP tests for all three heavy metals. Soil Sample-A passed the TCLP tests for arsenic, cadmium, and lead using a hydro-chlorination process at a minimum temperature of 700°C. In addition to passing the TCLP mm for Soil Sample-A and Soil Sample-B, 70 to 80 percent removal of the impurities was accomplished. This demonstrates that the leachability of the impurities was decreased primarily due to the removal of a large fraction of the contaminants, Soil Sample-C possessed very high levels of cadmium and lead and only moderate extractions of the impurities were generated from this soil. The arsenic TCLP test was passed at 500&apos;C using a process gas containing ferric chloride and at temperatures of 700°C and above using chlorination of hydro-chlorination.

Jan 1, 1996

By Huanmei Yuan, Yuanyuan Wang, Hao Bai

Composite phase change materials are widely used in energy-saving and energy efficient process. Nano-encapsulated phase change materials are especially significant for making advanced working fluid applicable to waste heat recovery or storage. In this study, silica-coated stearic acid (SA) Nano composite phase change materials were prepared from tetraethyl orthosilicate (TEOS) and stearic acid (SA) via sol-gel process. The materials were investigated by Field emission scanning electron microscopy (FE-SEM), Transmission electron microscope (TEM), Fourier transform infrared spectroscopy(FT-IR) and Differential scanning calorimeter (DSC).The FE-SEM and TEM results show that monodisperse microspheres with stable core– shell structure were formed and SA was encapsulated in the silicon dioxide shell. The FT-IR results show that there were no chemical reaction between silicon dioxide and SA, which is the chemical property of the composite material, is stable. The DSC results show that the composite phase change material has favorable heat capacity.

Jan 1, 2016

By Corby G. Anderson

For over a century, the Sunshine Mine in Idaho has been a major producer of silver. An estimated 335,000,000 troy ounces of silver has been mined. This has established the Sunshine Mine as the largest single source of silver in the world. Because the dominant silver containing mineral is tetrahedrite, a copper and antimony sulfide, normal metallurgical treatments to recover the precious metal are not practical. Thus, over the course of the company&apos;s history, novel, hydrometallurgical technologies have been developed on-site to handle complex, precious metal containing materials. Recently, the use of Sunshine technology has been extended to the recycle of secondary materials. As well, the use of Sunshine technology by other organizations for treatment of both primary and secondary feedstocks containing precious and base metals is an area of growing interest. This paper will provide an overview of Sunshine hydrometallurgical technologies including the applicability of Sunshine technology to the recycling of precious and base metals.

Jan 1, 1995

By Thomas J. Keefe, O&apos

The effects of cobalt, B-naphthol, glue and antimony on the polarization behavior of zinc sulfate electrolyte were investigated. It was found that B-naphthol was beneficial in reducing the detrimental effects of cobalt while antimony and excess glue were each harmful. Since the nu cl eat ion over potential was insensiti1ve to coba1t, other regions of the polarization curve were used to indicate electrolyte balance. The low? current density area occurring in the reverse or anodic sweep direction was? often an indicator when an ?unstable condition existed. The two parameters evaluated were the degree of inflection in the polarization curve in the low current density region during scanning and the rate of current rise observed when the sample was potentiostated at -0.781 Volts (SHE). Using this technique, a two-additive system was shown to be desirable to control cobalt and antimony containing electrolytes. The structure of the deposits was examined using scanning electron microscope techniques.

Jan 1, 1985