Search Documents

By O. E. Omotoso

This study is part of an ongoing investigation to understand the mechanism of stabilization/solidification of hazardous chromium wastes in ordinary Portland cement (OPC). Tricalcium silicate (C3S*),a major component of OPC is mixed with reagent grade Cr(lll) and Cr(VI) solutions, to simulate complex cementiCr waste systems. Scanning electron microscopy (SEM) and energy disperse spectrometry (EDS) were employed to provide microstructural and chemical information. Transmission electron microscopy (TEMlEDS), apart from complimenting the SEM, was used to probe the distribution of Cr in the hydration products of C3S and to provide crystallographic information. 29Si MAS NMR (magic angle spinning - nuclear magnetic resonance) Was used to characterize the influence of Cr on the hydrated silicate structure.

Jan 1, 1995

By Katsukiyo Marukawa, Manabu Iguchi, Sigeta Hara, Shinichiro Yokoya, Sigeo Takagi

"A numerical analysis and water model study of the mold region of a continuous casting apparatus was performed with a novel injection concept using swirling flow in the pouring tube, to control the heat and mass transfer in the continuous casting mold.As a result, the following results were found:1) By changing swirl strength, it is easy to control the flow pattern as well as the direction of the flow.2) Uniform velocity distribution can be obtained within a very short distance from the outlet of the nozzle.3) Heat and mass transfer near the meniscus can be remarkably activated compared with a conventional straight type immersion nozzle without swirl.4) Swirl helps the superheat in the melt dissipate.S) Penetration depth of nozzle outlet flow is decreased remarkably by the application of swirling.6) For the case without swirl, the peak of the flow moves near the mold-wall with flowing down from the outlet of the nozzle due to the Coanda-effect. On the other hand, peak of the flow moves near the mold axis with flowing down from the nozzle-outlet within considerable short distance, namely axi-symmetric velocity distribution can be obtained within very short distance from the nozzle-outlet.Those findings mentioned above are very useful to control the flow pattern in the billet and bloom continuous casters."

Jan 1, 2001

By F. J. Tavera

Recently Jameson cell technology has gained acceptance in both mineral and non-mineral applications, mainly because of the high degree of contact between the involved phases in the downcomer, fact that leads to an efficient collection performance. The key for an acceptable performance of the downcomer operation depends on the stability of the jet zone, the mixing zone, and the plug flow zone. in this work the behaviour of the downcomer of a laboratory Jameson cell is reported, as a function of gas hold-up, superficial gas velocity, superficial liquid (or slurry) velocity, and length of the operating zones. The presence of carbon is evaluated in terms of its effect on the gas hold-up and bubble surface area flux. The influence of the downcomer operating conditions on the gas-liquid disengaging cell is presented. Keywords: Jameson cell, downcomer, gas hold-up, mixing, plug flow, conductivity.

Jan 1, 2003

By Yuzo Hiroshige, Kiyotaka Tahara, Hiroki Hatayama, Masaharu Motoshita, Tomohiko Akahori

Large amount of rare earth metals is stored in the used electric products. Hitachi has started to develop the environment-friendly process for rare earth metals recovery from used magnets. We report here the environmental impact of our process, in comparison with the conventional recycle process utilizing solvent extraction. As an evaluation method, Life-cycle Impact assessment Method based on Endpoint modeling ver.2 (LIME2) developed by the National Institute of Advanced Industrial Science and Technology (AIST) in Japan is applied. It was found that the environmental impact of the new process was more than that of the conventional process. For further reduction of its environmental impact, minimization of energy consumption to operate the equipment was most effective. Decreasing the amount of magnesium, used as an extractant, and the improvement of the extraction rate of rare earth metals were also considered as specific options for reducing energy consumption in the plant development.

Jan 1, 2014

By Sacha Neven

Submerged lance technologies combine high intensity processing characterized by rapid mixing and reaction rates using a simple reactor design. The Isasmelt technology uses a central submerged lance to inject oxygen-enriched air and fuel into a bath thus creating large gas bubbles and intensive turbulence and splash. The lance is equipped with swirlers to increase gas velocity and heat transfer. This enables the formation of a frozen slag layer on the lance which protects it from the aggressive environment. Water models as well as high temperature reactors were used to validate the Davidson-Schiiler model on bubbling. Frequencies and pressure amplitudes were measured in a wide range of gas flow rates: from m3/sec using a water model to more than 30 m3/sec in an industrial process. Agreement with the model was satisfactory. The experiments however also clearly showed that cross-flow and bubble wake induce slightly higher frequencies. No influence of the use of swirlers on the bubbling frequency was observed in the water models.

Jan 1, 2002

By Mark Cross, Hadi Abou-Chakra, Nicholas Christakis, Mayur K. Patel, John Baxter, Ugur Tiizful

"In recent years significant effort has been put into using continuum mechanics for the description of granular flows. Although these models are partially successful in capturing some flow characteristics, they lack essential information on material properties, which are needed to account for the interactions between different particles. Thus, they are incomplete and can not be used to describe processes such as hopper filling/emptying and pneumatic conveying, where particle-particle interactions can lead to phenomena such as segregation, degradation and agglomeration. In this paper, a 3-D unstructured finite-volume framework is presented, which employs interface tracking techniques to solve for the individual material components of the granular mixture in the bulk and thus, determine the material-air interface. Various transport processes, arising from the micro-mechanical properties of the different particle species in the granular mixture, can be obtained through kinetic theory. The transport coefficients of each of the individual species can be determined and analysed in a micro-mechanical framework and the transport process parametrised in the form of constitutive models. These models provide the continuum theory with information on the micro-mechanics.This work describes the continuum framework and the micro-mechanical parametrisations, which are used to describe the processes and interactions at the microscopic level. Numerical simulations and comparisons with experimental data are then presented for the case of binary granular mixtures and conclusions are drawn on the capability of the model to realistically predict and quantify the main characteristics of granular flows."

Jan 1, 2001

By B. M. Satish

The aim of the present work is to study the effect of annealing on the vibration damping capacity of high-chromium (16%) ferromagnetic steel. The alloys were prepared from raw materials of 99.9% purity melted in a high frequency induction furnace under high vacuum. The samples were heat-treated in vacuum at various temperatures (800 to 1200°C) for 1 hour followed by slow cooling (120°C/h). The inverted torsional pendulum method was used to evaluate the vibration damping capacity. The results indicated that the vibration damping capacity of the alloys is influenced by annealing and there exists a critical annealing temperature after 1000°C. The damping capacity increases quickly below the critical temperature since the magnetic domains move more easily.

Jan 1, 2009

By J. W. Matousek

In the flash smelting of copper sulfide concentrates, the course of reactions from the burner tip, through flame "burn-out" (the point of oxygen depletion), to settled matte and slag is of particular interest in understanding the mechanisms of the process. Numerous reaction sets can be proposed to describe the chemical changes that might be taking place, but from outside the furnace no one set offers an obvious advantage in explaining the actual processes involved. Only a combination of mathematical modeling and flame and bath sampling can achieve this result. This paper shows that flash smelting, while still reasonably orderly, is a more complex process than suggested by the technical literature.

Jan 1, 1993

By Robert Vidal

A model of the homogeneous chemistry and transport processes within the separator of a chrome-alum electrowinning cell is introduced, discussed, and compared to experiment. The influence of diffusion, electromigration, and convection are included; it is found that convection was the dominant mode of transport for the experimental conditions. Simulation results explain experimental observations concerning an apparent disappearance of dichromate ions produced at the cell anode. The relation between potential drop across the diaphragm and the current and fluid flow is also illustrated. The model is used to recommend future experimental and theoretical work.

Jan 1, 1994

By Y. Houbaert, L. Kestens, R. Decocker

"A magneto-elastic model is presented to calculate the orientation dependence of the magnetostrictive strain, observed at saturated magnetisation in ferromagnetic materials with a cubic crystal structure and an arbitrary crystallographic texture. The formula of Becker and Doring is used to express the anisotropy of magnetostriction for a single crystal. In order to simulate the macroscopic average magnetostriction of a polycrystalline aggregate (with an arbitrary texture) the Reuss assumption of the elasticity theory was applied. According to this assumption the various orientations of the polycrystal can defonn without constraints, producing local strain incompatibilities in the microstructure but observing total stress equilibrium. The macroscopic strain is calculated as the weighted average of the individual strains of all orientations composing the polycrystal. The weight factors are determined by the volume fractions of the corresponding orientations of the given texture, which can be measured by standard X-ray diffraction techniques. The model is applied to simulate the variation of magnetostriction (at saturation) with respect to the rolling direction for a standard grade of Goss-oriented electrical steel. A brief comparison with experimental data allows validating the basic model assumptions. IntroductionBecause of tougher environmental constraints, the noise reduction in transformer cores has become increasingly important. It is generally accepted that the main source of noise is magnetostriction, which is known to be caused during the magnetisation process by the movement of 90° magnetic domain walls and the rotation of the magnetisation vector out of the easy directions. Therefore, it is obvious that when a ferromagnetic body is magnetised to saturation, the resulting magnetostriction will be dependent on the distribution of magnetic domains in the initial state.In the literature two coefficients are used to describe the resulting magnetostriction at a saturating magnetic field. The total strain, measured from an arbitrary demagnetised state to technical saturation, is called the saturation magnetostriction, and is denoted by (~)s. The tenn magnetostriction coefficient will be employed to designate the strain measured from the ideal demagnetised state (i.e. one in which no preferred orientation of domains exists) to technical saturation. Failure to recognise the difference between these two quantities has led to considerable confusion in the literature.The magnetostriction coefficient for a single crystal is a well-known property for ferromagnetic cubic materials. In 1939 Becker and Doring [1] have derived the following relation, describing the magnetostriction coefficient for single crystals with a cubic symmetry:"

Jan 1, 2001

By Mark Jolly

"Over the last ten years or so many man hours have been dedicated to developing methods for simulating shape casting processes. The majority of the methods developed have been devised by a combination of computer, mathematics and materials specialists often with limited knowledge of foundries and foundrymen. As a result of this it would appear that although there are many software packages for the foundryman to use there still exist fundamental misunderstandings as to their usefulness and suitability within the foundry.The paper aims to identify how well current software packages perform. The relationships between physical phenomena, practical defects and software capabilities are presented. Some discussion of the use of criteria functions is also presented. Finally issues arising from the postprocessing of results are discussed as the presentation of the results to the lay-person in simulation techniques is possibly one of the most important aspects in influencing the adoption of this type of software in the foundry community."

Jan 1, 1999

By C. F. Ferron

A process has been developed to treat the copper gold ores from the Guelb Moghrein mine in Mauritania. The process consists of pressure leaching the sulphide concentrate, neutralising with the oxide ore, recovery of copper by SX/EW and of gold by cyanidation of the autoclave residue. This paper focuses on the pressure leaching step, and presents data from bench and pilot plant test programs. In particular, attention is drawn to the effects of temperature, grind size, neutralisation, retention time and solution recycle on the kinetics of copper dissolution from various flotation concentrates. Likely leach mechanisms are briefly discussed.

Jan 1, 2000

By P. Balachandran

The paper outlines the existing facilities and working practices at the Khetri electro-refinery of Hindustan Copper Limited. Plans have been drawn up to mechanize some key operations to improve the quality of cathodes and the working environment as well as economize the refinery operations. The economic analysis for determining various optimum operational parameters under conditions existing in India have also been outlined. The impact of capacity utilization and mechanization under different sets of conditions on operational costs have been highlighted.

Jan 1, 1987

By Halvor Dalaker, Pål Tetlie

The decomposition of methane has been studied experimentally in contact with various oxides at elevated temperatures. For each oxide, the temperature at which the cracking starts has been determined. No correlation was found to exist between the temperature for the onset of cracking for a given oxide and the affinity for carbon of the oxide's metallic component. In terms of potential for using methane as a reducing agent, calculations are presented that indicate that the suitability of an oxide for such reduction depends on the desired methane+oxide reaction being more energetically favourable than the methane+methane=ethylene/acetylene reactions.

Jan 1, 2014

By Lincoln McCrabb

Correct measurement and interpretation of viscosity data is critical for design of any thickening and pumping process that involves a non Newtonian slurry. The nickel laterite pressure acid leach (PAL) process relies on producing a slurry of maximum achievable solids concentration. Small variations of 1-2% solids concentration can alter economics significantly. For the Ravensthorpe Nickel Project, a rheology protocol has been developed which optimizes the solids concentration across a range of ore types. The vane yield stress technique has been utilized to accurately quantify the flow of thickened slurry in the lower shear range. A yield stress of 100Pa has been used as a benchmark to determine the optimum solids concentration achievable utilizing deep cone thickening. Statistical analysis of the data shows critical rheology distinctions between ore type, particle size, lithology and geochemistry. Linear and power law models have been applied to rheology flow curves to reconcile the material transport properties with the anticipated thickener underflow solids concentration. Keywords: Vane Yield Stress, Thickening, Rheograms

Jan 1, 2004

By Joseph C. Milbourne

Tetra Technologies CCIX? (continuous countercurrent ion exchange) system has been involved in a wide range of uranium concentration, separation and purification applications over the past 40 years. Uranium ion exchange applications have ranged from the treatment of copper heap leach solution containing 5 parts per million of uranium to the treatment of high strength sulfuric acid solutions containing several thousand parts per million of uranium. The flexibility and the countercurrent mode of operation and other unique features of the CCIX? have resulted in successful uranium recovery from these solutions and many others.

Jan 1, 1995

By Tomás Vargas

The catalytic influence of a pure strain of Thiobacillus ferrooxidans (ATCC 19859) on the dissolution of natural pyrite crystals was studied using electrochemical techniques. The results showed that this microorganism catalyze the leaching of pyrite by both, oxidizing ferrous iron in solution and depolarizing the reduction of ferric ion on this sulfide. In addition, studies of bacterial corrosion under applied potential showed that pitting on the pyrite surface centers on weak sites of the sulfide structure in which bacteria has attached, but occurs only when the ferric iron in solution induces an adequate level of anodic polarization on the mineral.

Jan 1, 1992

By Yoshihiko Maeda

It is said that the 21st century will be an era of the remedy of the global environment. In order to reserve natural resources for the future and to avoid the dispersion of heavy metals after usage and to avoid pollution problems, it is extremely important to recycle heavy metals as much as possible by reasonable recovery procedures. The nonferrous metal industry is expected to play a important role in the recycling of heavy metals that are originally their products. From the depressed metal price experienced in Japan in 1980'h due to the sudden change in current exchange rate between US dollar and Japanese yen, one of major nonferrous metal company, Dowa Mining, has diversified its business area not only to the so-called down stream, but also to the environmental business including metal recycling, industrial waste treatment and soil remediation by utilizing technologis and facilities once used or still used for mining and smelting of copper, zinc, lead and precious metals. In this paper some of these applications will be presented.

Jan 1, 2003

By M. A. Barakat

Large amounts of zinc ash and flue dust containing more than 80 % zinc are accumulated during galvanization processes at the surface of molten zinc bath and in the chimney respectively. Pyrometallurgical recovery of zinc from both of the ash and dust samples has been carried out. The ash was sieved with the help of an industrial sieve shaker provided with mesh sieve having a pore size 0.9 mm. The oversize fraction cut (+ 0.9 mm) was melted at 550 °C under ambient conditions. The produced ingot (1) was analyzed whereas the coarse fraction of the produced slag (+ 0.9 mm) was treated as the coarse ash or added to it. The dust was enriched with suitable fluxing salt prior to heat treatment at 600 °C for 1 h. The produced ingot (2) was analyzed whereas the resulting slag was mixed with the fines of the ash and treated by hydrometallurgical processing to prepare valuable salts of zinc. Parameters affecting recovery processes such as time, temperature and flux percentage were studied. Results obtained revealed that the two prepared ingots (1&2) were successfully recovered with recovery efficiency amounts to =85 %. The obtained samples meet the standard specifications with relatively low price. Also in the light of the strict environmental regulations of pollution control, reuse of these wastes materials will help in keeping the environment clean.

Jan 1, 2000

By Art Johnston

Gas handling at Magma Copper company's, San Manuel smelter receives process gas from a flash .smelting furnace and four copper converters. The major gas handling equip11lent consists of four electrostatic precipitators and a sulfuric acid plant. Process ,vessels in gas handling are, typically confined, spaces. Lethal gases, mechanical and chemical hazards, and the difficulty of rescue, should an accident occur, makes this area a must in the safety plan. The presence': of hazardous chemicals and explosive gases in process' vessels and piping are of major concern when repairs' are required. Proper job procedures are critical to prevent injury during repairs. This includes plant employees and contractors who are likely to be unfamiliar with the hazards ,involved. The safe operation of a gas handling operation must include the functions of operations employees on a daily basis. This includes a safe working environment and involvement of all employees in the safety program. If an injury does occur quick medical response is critical to prevent serious injury. Medical responders must be adequately trained and prepared to treat the injured person without becoming victims' themselves. The methods used at Magma Copper Company to deal with these safety problems are the focus of this presentation.

Jan 1, 1992