Search Documents

By A. S. Usrnani

Due to both turbulence and the highly variable geometry of castings, a realistic numerical simulation of the metal flow is prohibitvely expensive with current technology. However, when the chief purpose is to achieve realistic thermal fields a precise How simulation is not necessarily required. In this paper we assume a laminar flow regime and obtain the flow field by solving the incompressible Navier-Stokes Equations using a velocity-pressure segregated semi-implicit finite element method. The free metal surface is predicted by advecting a pseudo-concentration function via the computed How field. This involves an explicit finite element solution of a pure advection equation. The thermal field is calculated by solving the convective-diffusive energy equation by an explicit finite element method using the computed flow field and the location of the free surface. All the advection terms are discretized using a Taylor-Galerkin method. The interface between the metal and mould is modelled using special interface elements. The model is demonstrated by solving practical example problems. The results show that a sharp thermal front is maintained during the course of filling without excessive diffusion. The heat diffusion in the mould can be controlled by varying the metal mould heat transfer coefficient.

Jan 1, 1994

By Vianey Garcia-Osorio

One of the problems in the carbothermic aluminum process is the substantial loss of aluminum compounds as vapors due to the high temperatures in the process. In order to solve this problem a Vapor Recovery Unit (VRU) is proposed. In this unit operation the aluminum vapor undergoes a series of heterogeneous non-catalytic reactions forming solid, liquid and gas products. In this work a model for the simulation of this unit was developed which includes heat and material balances as well as heterogeneous non-catalytic reactions. The model leads to a system of differential equations; its solution was implemented in Matlab giving as a result a stage-by- stage solid-fluid reaction model.

Jan 1, 2001

By Saskia Duyvesteyn

Small ion-exchange resin particles provide faster mass transport than conventional-sized beads. Unfortunately, high pressures are needed to pump solutions through columns containing small resin particles. It is preferable to disperse fine resins in the solution being treated. Screens have been used to separate the resin from the solution, but screens do not retain fines created by attrition of the resin particles. We have developed a separation process based on flotation, which relies on the surface characteristics of the resin, instead of size. The resin is conditioned with a surfactant before dispersing it in the solution to be treated; this increases the hydrophobicity of the resin sufficiently for froth flotation, without introducing surfactant directly into the solution. The surfactant adsorbed on the resin surface does not appear to impair the kinetics of metal ion removal. A flowsheet for an effluent treatment process is proposed; other applications are clearly possible.

Jan 1, 1998

Novel techniques were developed to obtain samples from and make measurements in the shaft of the flash furnace at the Kalgoorlie Nickel Smelter. The data obtained was used to validate mathematical models of the burners and the reaction shaft. Particle, gas and wall temperatures were measured along with the oxygen potential of the molten particles. Collected particles were characterised by sizing, chemical analysis and optical microscopy. The region of the shaft immediately beneath the burner where the rate of change was most rapid received special attention.

Jan 1, 1993

By D. J. Chaiko

Certain radionuclide ions (e.g., TcO4) exhibit unusually strong Affinities toward the polymer-rich phase in aqueous biphase systems generated by combinations of salt solutions with polymers such as poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). Thus, aqueous. polymer ,phases could potentially be used to selectively extract these ions during pretreatment of radioactive tank wastes at Hanford. To help develop a fundamental understanding of the interactions between various ions and polymers in aqueous solution, interaction enthalpies between sodium -perrhenate and a random copolymer of PEG and PPG (UCON-50) were measured by microcalorimetric titration. An entropy compensation effect was observed in this system in which changes in enthalpic interactions were balanced by entropy changes such that the interaction free energy remained constant and approximately equal to zero.

Jan 1, 1999

By P. R. Taylor

Laboratory experiments have been performed to evaluate the kinetics of roasting pyrite and arsenopyrite in air at elevated temperatures, in the presence of lime. The effects of temperature, time, air flow rate, particle size, lime type, and mineral/lime weight ratio on the rates of oxidation, lime sulfation, and lime arsenation were studied. The reaction products were identified using chemical analysis, x-ray diffraction, SEM analysis, and optical microscopy. The results are discussed in terms of the utilization of lime to capture sulfur and arsenic during the roasting of refractory precious metal concentrates. More than 99.9% of the arsenic and 98% of the sulfur are contained when roasting pyrite and arsenopyrite with hydrated lime under typical roasting conditions.

Jan 1, 1991

By I. Iwasaki

Flotation characteristics of pyrrhotite by itself and in complex sulfide ores are reviewed with respect to the effects of oxidation, grinding media and other electroactive minerals.

Jan 1, 1988

By Md. Maniruzzaman

The quenching performance of a liquid quenchant can be controlled by controlling the agitation in the quench tank. Without agitation, a vapor layer or bubbles form at the hot part surface and the natural convention of the quenchant limit the heat extraction rate at the quenched part surface. Resistance to the heat extraction rate can be reduced by breaking the vapor layer or by inducing a turbulent convection at the part surface through agitation (Le. forced circulation of the quenchant). To determine the effects of agitation on the quench performance of a mineral oil based quenchant, the CHTE quench probe system was used with AISI4140 steel probe tip. Quenching performance of the oil is evaluated by computing the effective heat transfer coefficients of the steel probe as a function of surface temperature using Lumped Parameter Analysis. In addition, computational fluid dynamics (CFO) simulation of the quench tank with an impeller type agitator has been done to understand and predict the fluid flow pattern in the tank. CFO simulation also provides insights for determination of optimal location of the impeller and the quench probe tip. Keywords: CHTE Quench Probe, agitation, CFD simulation, liquid quenchant, 4140 steel

Jan 1, 2003

By Kimura. E.

Continuous estimation of phosphorus content of molten copper is required to produce phosphorus deoxidized copper in a continuous casting operation. The phosphorus content of molten copper was related to its electric resistivity, which was measured by the four-probed technique with a specially-shaped cell. In a laboratory scale, the linear relationship between the above factors was confirmed in the temperature range of 1083OC through 1200°C. The phosphorus concentration range measured was from 40 to 500 ppm. The phosphorus content was monitored successfully by measuring the electric resistivity of the molten copper in the distributor of a continuous caster in an industrial scale.

Jan 1, 1992

By Peter G. Mason

Over the last 15 years numerous Pressure Oxidation and Pressure Leach plants have been installed throughout the world. The technology is no longer regarded with awe and trepidation as plants designed to treat a wide range of feedstocks continue to be successfully brought on line. Important aspects of the design of such plants include feed preparation, slurry pumping, heating and heat recovery, pressure control and let-down, vessel design, safety and provision of associated services.

Jan 1, 1999

By G.A Subagyo

The condition of slag in a pyrometallurgical reactor is vital to ensuring control of the process. A new technique based on multivariate image analysis (MIA) of digital images has been developed to provide an online measurement of important slag characteristics, such as the presence of exposed metal, the presence of solid phases, and temperature. This paper shall describe the technique and provide some results from analysis using industrial plant data.

Jan 1, 2003

By D. E. Woolley

The rate of reduction of iron oxide from calcia-silica-alumina slag by carbon in liquid iron has been measured over the temperature range 1400-1600°C by monitoring the rate of carbon monoxide (CO) evolution. Slags containing ferric iron have been used in order to study the reduction of both ferric and ferrous cations. Results show that ferric iron is reduced before ferrous iron, so that the ferrous iron concentration increases initially. It is also shown that the rate constant, k, decreases at low reaction rates, or, equivalently, at low concentrations. The authors conclude that the reaction occurs in two periods. During the first period, ferric iron is reduced to ferrous iron. During the second period, ferrous iron is reduced to metallic iron, and the rate-limiting step during the second period is the mass transfer of ferrous cations in the slag phase to the slag-metal interface.

Jan 1, 1998

By Michael L. Sorokin

The various methods of converter slag cleaning operation are analysed from the thermodynamk point of view: cleaning using coal, cleaning using combustion products of natural gas and cleaning in presence of matte. All calculations were done, applying the developing computer procedure based on the free energy minimisation algorithm. Three-suffix Margules equations were used to calculate thermodynamic properties of melts; The calculations resulted in recommendations for the practical appliance.

Jan 1, 1995

By K. G. Wang, M. E. Glicksman, P. Crawford

"We formulate the mathematical solution to late-stage multi particle diffusion in finite systems. The transition from finite system behavior to that for an infinite system is established. Large-scale simulations are reported regarding the dynamics of phase coarsening. Even in the case of a small volume fraction (Vv = 10-4), the particle size distribution is broader than that for the well-known Lifshitz-Slyozov limit at zero volume fraction. We also report the first simulation studies of extremely low volume fraction, for which corresponding experiments, as well as other simulations, do not exist at present for comparison. However, in the case of moderate volume fractions (Vv = 0.1), the fiucutations in the volumetric growth rate of particles are extracted from our simulations. These simulations provide additional insight into the statistical nature of diffusion interactions, including multiparticle stochastics during microstructural evolution.IntroductionPredicting microstructure evolution in alloys remains one of the cornerstones of materials science. Phase coarsening is a common process in microstrucural evolution that leads to a decrease in the excess total interfacial energy of the system. The system typically consists of separate and identifiable units, or domains, such as second-phase particles distributed in a matrix. During phase coarsening, larger particles grow at the expense of small particles. Over time, this ""competition"" results in an increase in the average size of the particle population, and in a concomitant decrease in the number of particles.Particle size and microstructure of many cast alloys depend on similar coarsening processes. Indeed, properties of these materials, such as strength, toughness, ductility, and electrical conductivity, depend on the material's average particle size and particle size distribution (PSD). Understanding and controlling microstructures in two-phase systems are clearly of widespread technological importance."

Jan 1, 2001

By Ramiro Escudero G.

Since the introduction of column flotation almost forty years ago the column technology has grown into several non-mineral applications such as among others the effluent treatment, soils recovery and de-inking of recycled paper. Recent studies have demonstrated that particular characteristics of the dispersion (bubble size, gas holdup, bubble surface area flux) are needed for a given flotation column duty. In this work, two kind of spargers were tested (i.e., internal and external) using a 4 inch column lab in a two phase system. Results show that the external sparger provides a dispersion with characteristics that include those produced by the two internal spargers.

Jan 1, 2003

By Dimitrios Fillippou

Magnesium hydroxide is used in a number of industrial applications, from the neutralisation of acid effluents to the production of pharmaceuticals. High-quality magnesium hydroxide powders can be produced by hydrating slow-reacting magnesia in dilute magnesium acetate solutions. The process of magnesia hydration shows many similarities with a typical hydrometallurgical leaching operation; however, its kinetics are crucial not only for process design and control, but also for the production of powders with a desirable particle morphology. This article shows the results of an experimental work whereby industrial heavily-burned magnesia powders were hydrated in 0.01 to 0.1 mol/L magnesium acetate solutions at temperatures ranging between 333 and 363 K. Examination of the magnesium hydroxide produced and the analysis of the kinetic data suggest that the hydration of heavily-burned magnesia in magnesium acetate solutions is a dissolution-precipitation process controlled by the dissolution of magnesia particles. The activation energy was estimated to be 60 kJ/mol, while the reaction order with respect to magnesium acetate concentration was found to be about one.

Jan 1, 1999

By Fumitaka Tsukihashi

Increasing amounts of steel scrap are being used as resources for steelmaking. Therefore, there has been a growing interest in the removal of harmful tramp elements such as antimony, zinc, tin, arsenic, bismuth, lead and copper from the molten steel. The problem that should be solved is the economic removal treatment of residual tramp elements in the steelmaking processes and the production of high quality steel by reducing the effect of the contaminated tramp elements and satisfying the environmental regulations. In this paper, the available thermodynamic data of the residual tramp elements in the molten steel arc summarized and the possibility of the removal of residual tramp elements from the molten steel is thermodynamically estimated.

Jan 1, 2003

By Toshihiko Emi

The quest for cleaner steel is driven by increasingly stringent requirements from the manufacturing and construction industries. Key issues are the occurrence and removal of inclusions; These are discussed in the context of the unit processes of deoxidation, refining, transfer and casting of molten steel. Process thermodynamics and kinetics are also discussed. Recent progresses achieved and problems yet to be solved are elaborated, and an integration of the unit processes into a system to produce extra clean, steels with better performance is presented.

Jan 1, 1999

By F. M. Nakla

Various methods of Applied Mineralogy were used for determining the nature and composition of products yielded by flotation tests for Maghara coal beneficiation. Coal samples obtained from the Sa fa mine in Northern Sinai, Egypt, were crushed, sieved, &apos;and <32 mesh size fraction was cleaned by froth flotation. Experiments were conducted to determine the effect of certain parameters on beneficiation of Maghara coal by flotation. The investigated factors included nature of frothing and/or collecting reagents, pH value of the medium, particle size distribution in the head sample, and pulp density of the coal slurry. The quality of head samples, coal concentrates, and tailing products were determined by chemical analysis, microscopic study, x-ray diffraction analysis, and occasionally by infrared (IR) absorption spectroscopy.

Jan 1, 1989

By Paykan Safe

Computational Fluid Dynamic (CFD) modeling provides a powerful tool to assist with the design of ventilation and fume control systems in smelters and other high temperature metallurgical facilities. For this paper, this tool has been used to analyze the off-gas flow patterns exiting the mouth of a Peirce-Smith converter into a water-cooled hood and drop out box. The effects of various process and physical plant design parameters on process gas and fume capture and potential build up on the converter hoods was examined, and the optimum design and operating parameters were determined.

Jan 1, 2000