Search Documents

By Bart Blanpain, Muxing Guo, Zhuangzhuang Liu

In order to stabilize free lime in the basic oxygen furnace (BOF) slag to achieve high value products, quartz sand and other additives are injected into slag. However, the current hot stage slag stabilization does not work in case of slag (before treatment) with a liquid fraction lower than 90%, where the slag containing solid particles is too viscous. Therefore, it is essential to understand how solid phases affect the viscosity of the slag system. In this study, the industrial BOF slags were investigated with respect to the correlation between volume fraction of solid phases and its viscosity. Slag viscosity was measured with a rotating type viscometer at temperatures below the liquidus. The volume fraction of solid phases was quantitatively calculated with FactSage. The Einstein-Roscoe equation was employed to predict the viscosity of BOF slag.

Jan 1, 2016

By Patrick R. Taylor

This investigation studied the inflight calcination kinetics of nuclear waste simulant using a thermal plasma reactor. A series of experiments were performed to determine the conversion of insoluble aluminum compounds to the soluble compounds and the decomposition of complex organic and nitrite compounds present in the simulant waste. Thermodynamic calculations based on free energy minimization were performed to establish a theoretical basis for this investigation. A kinetic model to describe the conversion of gibsite to sodium aluminate has been proposed. The products of the calcination were characterized using XRD, Gas Chromatography, and chemical analysis by ICP. The results of this investigation indicated 85% gibsite conversion to sodium aluminate, 90% of nitrate decomposition, 52% TOC decomposition and 90% conversion of chromium to soluble compounds. A process is identified for inflight calcination of wastes. Key words: Plasma, waste, simulant, calcination

Jan 1, 1996

By Dariusz Kopyci ski, Józef Dorula

The study proves that by introducing the iron powder and disintegrated steel scrap to low-sulphur cast iron still before the inoculation carried out with a conventional graphitising inoculant, the mechanical properties similar to those obtained during the inoculation treatment carried out on cast iron with the recommended high sulphur content are achieved. The said operation increases the number of crystallisation nuclei for dendrites of the primary austenite. In this case, the iron particles act as substrates for the nucleation of primary austenite, due to a similar crystallographic behaviour of the regular face centred cubic lattice The more numerous are the dendrites of primary austenite, the less free space is available in the interdendritic spaces for the formation of graphite eutectic grains, which makes the structure more refined (more eutectic grains) and the mechanical properties higher.

Jan 1, 2016

By S. Eckert, G. Gerbeth, K. Timmel, B. Willers, T. Wondrak, N. Shevchenko, M. Röder

The quality of the produced steel in the continuous casting process is significantly governed by the melt flow in the mold. However, direct flow measurements in liquid metals are still rather scarce. In order to investigate these flow phenomena, three experimental facilities operating with low melting liquid metals were installed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The melt flow in the models is measured by the Ultrasonic Doppler Velocimetry (UDV) or the Contactless Inductive Flow Tomography (CIFT), multi-phase flows can be visualized by X-ray imaging. The obtained measurement results are primarily used for validation of numerical models. In this paper we will investigate the fluid flow in the mold and the behavior of the surface of the liquid metal using flow measurements by UDV and surface profile measurement by a laser scanner, respectively. Strong fluctuations and deviations of the free surface were observed in case of a static magnetic field

Jan 1, 2016

By Katerina Kryst

Antimony and bismuth are two of the elements that need to be removed from copper electrolyte to ensure a trouble free operation as well as to maintain copper cathode purity. One method to control these impurities is the use of aminophosphonic ion exchange resins. Antimony is present as both Sb(III) and Sb (V). Sb(V) is very difficult to remove from these resins, requiring excess amounts of highly concentrated hydrochloric acid. In industry this affinity of Sb(V) for the resin causes a buildup of Sb(V) and degrading resin performance due to continual reduction of resin capacity. A new method for regeneration of aminophosphonic resins loaded with Sb(V) has been developed, which utilizes catalytic regeneration of the resin. Ion exchange can then be utilized for continual control of Sb and Bi in copper electrolyte.

By J. Grogan

Leaching of galvanized steel coatings allows the steel substrate to be used as a zinc-free scrap source to steel and iron furnaces. In this study the behaviors of sulfuric acid leaching solutions are investigated. The ranked significance of the variables are shown to be acid concentration > temperature > zinc concentration. Examination of the leaching mechanism finds the rate-limiting step to be the cathodic hydrogen reduction reaction. This rate is not only influenced by acid concentration, but also by the hydrogen reduction exchange current density. Dezincing leaching rates are improved by taking advantage of the higher exchange current density of the iron substrate versus the zinc coating. This is accomplished in practice by increasing the exposed interfacial zinc:iron surface area through shredding. Also, a leach control mechanism is proposed through online monitoring of the zinc-iron couple mixed potential.

Although anion exchange resins are widely used for gold recovery in Russia and the former CIS, accounting for almost 50 percent of gold recovery in that part of the world, the technology has not been adopted in the West, apart from one small operation in South Africa. This situation is likely to change as the gold industry heads into the twenty first century. With gold prices having declined steadily through the 1990's, mining companies are under great pressure to reduce costs and improve gold recovery. Most studies on the use of resins for gold recovery from cyanide solution or pulp have shown that this technology has the ability to achieve both these goals. Resins can also be used to recover and recycle free and complexed cyanide in gold plant tailings, which has the potential to significantly lower operating costs, and latest developments in this area of technology are discussed. Finally, recent studies on thiosulphate leaching of gold have'shown that this process is very well suited to the treatment of carbonaceous, preg-robbing ores from the Carlin trend (Nevada, USA), and elsewhere in the world, because the gold thiosulphate complex does not load on to carbon. Whilst this obviously benefits the leaching process, it means CIP and CIL are ineffective in this situation, and the use of ion-exchange resins for gold recovery from thiosulphate leach solution are discussed.

Jan 1, 1998

By Animesh Jha, Chris Dometakis

"Without the use of a flux, only a poor dispersion of ceramic phase can be achieved. A molten-flux-assisted ceramic phase dispersion technique for producing aluminium alloy metalmatrix composites has been developed. In this paper, we report the physical chemistry for the dispersion of TiB2 in molten aluminium. In particular, aspects of the interfacial energy and the thermodynamics of the dispersion reactions are briefly discussed for enhancing the volume of dispersion phase in the molten metal and for controlling their morphology. This investigation also addresses the role of molten flux in the fabrication of AI-alloy mmc using a casting technique. The morphological aspects of the dispersion are explained on the basis of the classical theory· of nucleation.IntroductionMetal matrix composites (MMCs), have long been recognised as an important class of material due to their greater wear resistance, specific stiffness and temperature capability when compared to conventional monolithic alloys. Particulate reinforced composites produced by melt casting techniques have been amongst the first MMCs to achieve commercial market viability. The advent of melt mixing techniques such as the Duralcan™ process have enabled low cost, easily fabricated composites based on the AI-SiC and AIAlz0 3 systems to be produced. In this process, uncoated ceramic particles with diameters 10ltm and larger, are incorporated into conventional monolithic alloys with reinforcement levels up to 25 volume percent. The AI-7Si-SiC metal-matrix composites have good wear resistance, high strength, low density and high thermal conductivity. The combination of these physical and mechanical properties has become a major attraction for the fabrication of light-alloy composite disc rotor brakes for the automotive sector2. However, in silicon-free alloys, SiC is thermodynamically unstable above the composite melting point and is extensively attacked by the melt to form aluminium carbide3 :"

Jan 1, 1996

By Milton Blander

A review of concepts and theories for predicting thermodynamic solution properties of multi- component high temperature liquid solutions is reviewed. During the last 50 years the ability to predict :such properties for molten salts, silicates and metals based on the generally known properties of the lower order (often binary) systems has been developed and shown to provide predictions which are quite useful in science and technology. There are many gaps in our understanding of these high temperature solutions, especially for metals, and considerably more work is needed.

Jan 1, 1996

By Chai Li-yuan

Anodizing behaviors of magnesium alloys AZ31 at constant applied current, based on the electrolyte solution free of chromate or fluoride, were investigated. The anodizing process was influenced by constituents of electrolyte greatly. Therein, the oxylate salts, which led to the occurrence of the two totally different processes, played a determinant role in anodizing. They were stable and sparking process respectively. The morphology of anodizing film was observed by SEM and the structure of film was analyzed by XRD. During the stable process, a brown thin film was formed, however the sparking process led to the formation of white hard thick film. The functions of some kinds of additives, such as ammonia, glyceryl alcohol and PVP etc were also studied. Some of them had great effect on surface morphology of anodic film and some of them affected stability of anodizing process significantly.

Jan 1, 2006

By B. Q. Li

A numerical study of the developing fluid flow and thermal aspects during the staning phase of aluminum continuous casting processes is presented. The deforming finite element method, coupled with a quasi-Lagrangian formulation, is used to represent the growth of an ingot and the dynamic fluid flow and thermal behavior that evolves in the growing ingot. The mathematical formulation of the problem and the numerical treatment are discussed. The algorithm solves the free moving nodes as part of total unknowns with an automatic time step control for time integration. This permits an optimal computing efficiency while still keeping the computational errors under control. A selection of the results obtained using the algorithm is presented. The results are concerned with the evolution of fluid flow, temperature and solidification phenomena during a DC round ingot casting process, as it evolves from the beginning of casting operation to a steady state. These results show that the time-varying, complex fluid flow and thermal phenomena during continuous casting processes can be very well represented by the computational algorithm. The results also illustrate that, during the casting process, ~e fluid flow and temperature fields change drastically at the initial stage but evolve slowly afterwards

Jan 1, 1993

By R. P. Tavares, M. Isac, R. I. L. Guthrie

"The configuration of the metal delivery system used in twin-roll casting can play a significant role in determining both internal and surface quality of the strips produced by this process.In the present work, a mathematical model for coupled turbulent fluid flow, heat transfer and solidification was developed and used in the study of metal delivery systems for twin-roll casting of low-carbon steels. This study was applied to a pilot twin-roll caster being investigated in Canada, with a roll radius of 0.3 m, producing strips of thicknesses from 4 to 7 mm, at roll speeds ranging between 4 and 12 m/min. Various configurations of metal delivery systems were simulated and their effects on the advance of the interdendritic solidification front and levels of turbulence and temperature within the caster investigated. According to the predictions of the model, an extended nozzle with inlet flow towards the surface of the rolls seems to be the best alternative for feeding liquid steel into twin-roll casters.A full scale water model of a pilot twin-roll caster was also built and used to qualitatively validate the predictions of the mathematical model.Various techniques for fluid flowvisualization were applied. In general, the predictions of the mathematical model were in reasonable agreement with the experiments with the water model."

Jan 1, 1999

By K. H. Bech, S. T. Johansen

"The mass transfer at fluid-fluid interfaces due to turbulent agitation is investigated theoretically. In particular a theory is derived for interface stresses due to interface energy and surface renewal. This theory indicates that surface renewal may take place if the geometry is sufficiently large and if surface tension is sufficiently low.By using a model for a typical turbulent structure we compute the interface mass transfer for a stressless interface and a fully interface. Results for the general situation is not presently available. The computed results are used to derive analytical expressions for the mass transfer based on turbulent kinetic energy and free stream turbulent length scales.One important application of the theory is the mass transfer at the electrolyte side of the bath-metal interface in the Hall-Heroult process. For this process we show that mass transfer should be expected to be of the rigid surface type."

Jan 1, 1999

By William Petruk

The Kidd Creek base metal deposit near Timmins, Ontario contains around 0.15 wt% Sn, mainly as cassiterite. The cassiterite occurs largely as inclusions in sphalerite, with 85% being in grains smaller than 18.5 micrometres in diameter. Concentrates and tails from the company's Cu, Pb and Zn circuits were studied to determine the liberations and recoveries of cassiterite in the products. The ore had been ground to about 65.% minus 44 micranetres in diameter (-325 mesh); 55% of the cassiterite was liberated. About 92% of the liberated cassiterite and 70% of the unliberated cassiterite were in the concentrator tails, and 20% of the unliberated cassiterite in the zinc concentrate. The company had attempted to recover the cassiterite from the concentrator tails by gravitational methods but recoveries were low. The grain size of the cassiterite in the gravity Sn concentrate was similar to the grain size of the liberated cassiterite in the concentrator tails. Research on flotation of the fine grained cassiterite from Kidd Creek ore has been conducted,

Jan 1, 1990

By Ljiljana Solujic

The need for the removal of mercury from the precious metals extraction circuits may be influenced by process, environmental, as well as by occupational hazard reasons. In these circuits mercury is mainly present as cyanide complexes. The effectiveness of any stabilization method will be influenced by the high thermodynamic stability mercury-cyano species exhibit in an aqueous solution. In this study, we have investigated the utility of the trisodium salt of trimmercapto-s-triazine (TMT) for precipitation of mercury from the corresponding cyano-complexes. The influence of pH molar ratio of TMT to Hg, coagulant and flocculant additions, excess of free cyanide, as well as the presence of other metal-cyano species on the effectiveness of mercury precipitation were investigated in detail. Also, a "teal world" precious metals mill effluent initially containing ~7 ug/mL (ppm) of Hg was treated and A was found that greater than 99.8% of the mercury was removed from the solution as am insoluble Hg/TMT complex.

Jan 1, 1996

By C. S. Simons

This paper presents a review of the extractive processes used in the production of nickel, with emphasis on developments since the beginning of the Second World War. Attention is given to the factors, many outside the nickel industry itself, which determined the direction of process research and strongly influenced the ultimate commitments to industrialize the resulting developments. An example of such a factor is the sudden surge in demand, far exceeding the then available nickel production capacity, that was caused by the advent of World War II; the result was the first serious consideration ever given to low- grade laterites as a viable source of primary nickel. Other factors discussed include such items as process development in the extraction of other metals - particularly copper; the availability of increasingly sophisticated materials of const- ruction; the advent of the "environmentalist" and related political developments; the massive escalation in the price of energy - particularly oil. The paper concludes with an attempt to forecast the nature of the most effective nickel process of the future, based on extrapolation from the economic and political situation that exists today.

Jan 1, 1988

By H. J. Roorda

With an increasing need to obtain metals by processing complex fine intergrown ores, the use of electron-optical techniques will become more important as a tool for mineralogical studies. Electron images enable a higher spacial resolution than can be obtained by optical microscopy and thus provide a powerful and necessary aid for the examination of small grains and finely locked particles. In this paper the mineralogy of Meggen ore was investigated. Both light-optical and electron-optical techniques were used to evaluate the mill feed and products of the concentrator. Detailed examination by reflected-light microscopy to assess the comportment of galena in the complex pyritic ore was inconclusive in establishing the cause for low lead recovery of only forty percent of the ore's lead content. Electron microprobe analyses indicated that the majority of the lead lost to the tailings was accounted for by extreme fine (often smaller than one micron) and complex intergrowths of galena in pyrite. The remainder was lost as fine free galena grains.

Jan 1, 1987

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 B. Abedian, L. M. Racz, S. R. Berry, R. W. Hyers

"The presented work represents an effort to improve understanding and prediction of turbulent flow inside electromagnetically-levitated droplets. We show that the flow field in a test case, a nickel droplet levitated under microgravity conditions, is a low Reynolds number turbulent flow, i.e. in the transitional regime between laminar and turbulent. Past research efforts have used laminar, enhanced viscosity, and k - E turbulence models to describe these flows. In our study, we compare the RNG algorithm to laminar and k - E turbulence model results. We show that accurate description of the turbulent eddy viscosity µr is critical in order to obtain realistic velocity fields, and that µr cannot be uniform in levitated droplets. In the RNG method there are no characteristic length or time scales associated with the flow, thus allowing such anisotropic features to be captured. We perform calculations and analyses for two cases (1) a small, non-deforming, spherical nickel droplet and (2) a deforming, oscillating droplet. In addition to flow field calculations, we compare numerically-obtained surface tension and viscosity values to those obtained experimentally by the oscillating drop technique.IntroductionElectromagnetic levitation (EML) is a containerless processing technique for conductive materials. Its advantages are the avoidance of contamination or chemical reaction at container walls and the ability to perform long-term experiments in a metastable state. Because of its current limitation to small sample sizes, its primary use is in the laboratory. One application of interest is the measurement of thermophysical properties of undercooled liquid metals [1, 2, 3, 4]. In EML, a sample weighing approximately 1 gram is positioned inside an electromagnetic field generated by alternating currents flowing through an axisymmetric water-cooled copper coil. The coil must be designed appropriately so that thesample levitates in a stable manner.Traditionally, mathematical modeling has been performed in tandem with both earth-and spacebound electromagnetic levitation experiments, in order to determine the effect of the magnetic field on material and flow characteristics [5, 6, 7, 8]. These calculations are important because they allow design, planning, and correct interpretation of experiments. In addition, the calculations are of fundamental scientific interest, as they can be applied to other electromagnetic materials processing applications [9]."

Jan 1, 1999

By G. A. Brooks

Reactive ball milling has been proposed as a new route for producing carbides from oxides through carbothermic 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 temperature 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 (> I 0 mls) may have undergone a process analogous to melting and quenching. Further work is required to fully distinguish these features.

Jan 1, 2003