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By P. F. Stratton, M Huggahalli, N Saxena

"Several studies have been carried out to determine how the optimum atmosphere conditions in the heat treatment of metals can be established for a given product by using different gas injectors and varying atmosphere flow rate and composition. The most common approach taken to gain insight into furnace atmospheres has been to use commercial computational fluid dynamics codes and examples of their use are shown. However, the complexity of these codes, the difficulty in establishing boundary conditions, their cost and computational demands limit their usability in solving day-to-day production problems.A simplified, web-based model of a furnace atmosphere is described where the conservation equations are solved to determine the composition profiles of the atmosphere in the furnace. Although the model is restricted in scope to certain types of furnace, it is shown to give better results than CFD when boundary conditions are uncertain. The application of the model to the understanding of existing furnace conditions and to determining ways of optimising the use of gases are discussed. IntroductionThe important role of protective atmospheres during heat treatment of metals, furnace brazing of assemblies and soldering of printed circuit boards is well established. The atmosphere in the furnace prevents air ingress and oxidation of the parts, helps flush away any flux or binder from braze and solder pastes and provides an important mode of heat transfer [1]. In a batch furnace having typically one or two gas injectors, the gas utilisation and process can be optimised by minimising air leaks and mantaining atmosphere homogeneity with fans or other atmosphere circulation techniques. In a continuous furnace, however, atmosphere optimisation is more difficult as furnace inlets and exits can also let in air. The atmosphere requirements of different stages of heat treatment, brazing or soldering vary [2]. Achieving these atmospheres in different sections of the open-ended furnace is a relatively complex task. Methods such as atmosphere zoning and the use of physical curtains and gas injectors have evolved with time, though it is hard to predict how effective these techniques will be for a given furnace and process. Experts in the field tend to rely on experience and rules-of-thumb rather than scientific method to achieve the required results."

Jan 1, 2001

By Alex Luyima, Honglan Shi, Lifeng Zhang, Yongqing Jiang

"Leaching process has been suggested to recover most metals from waste PWBs. In this study, the leaching behavior of most metals present in waste PWBs is evaluated before and thermal treatment. Different leaching acids: hydrochloric acid (HCl), nitric acid (HNO3) and aqua regia are compared. The effects of acid concentration, particle size of sample, leaching time and temperature are examined. Results revealed that most metals are present in small particle size and sequential leaching of PWBs with a combination of HCl acid and aqua regia is capable of dissolving most of the metals content of PWBs. Leaching of thermally treated PWBs produced the highest leaching percentages for similar leaching conditions.IntroductionApproximately 20–50 million tonnes of electronic waste (e-waste) is produced globally per year. Waste Electrical and Electronic Equipment (WEEE) or E-waste is one of the fastest growing waste streams in the world. In developed countries, it equals 1% of total solid waste on an average [1]. The growing stockpile of used and obsolete consumer electronics has been called the “largest toxic waste problem of the 21st century [2]. Printed wiring boards (PWBs) is an essential part of almost all WEEE, and accounts approximately 3% of all WEEE by weight [3]. PWBs are a platform upon which microelectronic components are mounted. PWBs contain metals (~40 wt. %), ceramics (~30 wt. %) and plastics (~30 wt. %) [4]. The metallic part includes; Cu, Pb, Zn, Fe, Cd, Be, Cr, Au, Pt, Pd, Ag, etc. The plastic part of the PWBs is mostly epoxy resins. These plastic resins also contain very toxic halogenated flame retardants (HFRs) [5]."

Jan 1, 2012

By T. R. A. Davey

A simple model for metal solution behaviour may be derived, on the basis of dilute solution solubilities (where? log concentration of solute varies linearly with reciprocal temperature) and not-so-dilute region solubilities (where the log of the alpha-function at saturation frequently varies linearly with reciprocal temperature) and assuming activity to vary according to the quadratic formalism in between. Matte binary systems usually exhibit regular .solution behaviour when the constituent species are chosen appropriately. In many recent papers, metal solubilities in .slags are expressed as the sum of several different and supposedly independant molecular species (e.g. oxides, sulfides, chlorides), Such a view is untenable because of the now proven ionic nature of slags. Some possible reasons for the great effect of sulfur on copper solubilities in slags are discussed.

Jan 1, 1985

By Zhenglong Li

A process has been developed to recover titanium from a blast-furnace slag which contains about 20-25% Ti02 and 12% Fe. In this process. "hot" slag from the blast furnace is directed to a separate furnace where it is reheated with additives to form two simple slag phases: one is titanium enriched anosovite (Ti3O5) and the other is a titanium lean non-crystal glass phase. The modified slag is then processed by conventional beneficiation techniques to produce a marketable titanium concentrate and a usable slag material. This paper focus on separating anosovite from glass by electrostatic separation and froth flotation.

Jan 1, 1996

By Deming Wang, R. A. Overfelt

"The oscillating cup viscometer has become a dominant technique to measure the viscosities of high temperature molten metals. Unfortunately, the viscosity estimation model from the observed logarithmic decrement and period of the oscillation is very complicated. There are still large discrepancies of viscosity estimation values between using different measurement facilities and using different viscosity estimation models for a same molten metal. The purpose of the paper is to evaluate the accuracy of an oscillating cup viscometer in Auburn University. Two well known viscosity estimation models, Roscoe's and Torklep's equations, are compared and discussed. The theoretical literature for the fluid flow inside an oscillating cup is reviewed and a more accurate working equation for the Auburn oscillating cup viscometer is developed. Some design parameters of the oscillating cup viscometer, which directly affect the accuracy of viscosity estimation by using the working equation, are discussed. In addition, applications and experimental measuring data are presented in the paper for several different commercial alloys, such as aluminum alloys: A319, A356 and A201, nickel-base super alloys: In713 and In718, and casting irons, C40 Gray Iron and Ductile Iron.1 IntroductionThe oscillating cup viscometer is the most important and has been most frequently used in viscosity measurement for high temperature liquids [1-4]. The principal advantages of this technique over others are its mechanical simplicity and the ability to measure the time period and amplitude decay with great precision. In the viscometer, a high temperature liquid (such as a molten metal) is contained within a crucible suspended by a wire to form a torsional pendulum, which induces torsional oscillation motion. This motion is damped primarily by viscous dissipation within the viscous liquid inside the cup. The viscosity of the liquid can be calculated by an analytical or numerical solution ofthe equations of motion of the oscillating cup system."

Jan 1, 2001

By Kexin Jiao, Zhijia Zhang, Jianliang Zhang, Zhengjian Liu

Carburization behavior of molten iron in blast furnace is an essential part of BF long campaign technology. Maintaining carbon content stable is an important prerequisite to ensure the high production of the blast furnace. In this paper, the important aspects of the research progress which mainly including the study of iron carburization at the upper and the lower parts of the blast furnace was reviewed. Indirect carburizing is the main way at the top of the blast furnace. The content of carbon in metallic iron increases with the reducibility of iron ore improved. The thermodynamics and kinetics conditions are good for carburization reaction to take place at the bottom of the blast furnace. Carbon content of molten iron increased by coke carburizing. Meanwhile, the drawbacks of the existing literature on iron carburization behavior were analyzed and new research directions of iron carburization were proposed in the future.

Jan 1, 2015

By Zeljka Pokrajcic

Crushing and grinding, or comminution, circuits are the most energy intensive process of a mineral processing plant. Comminution involves the physical size reduction of an orebody to a particle size sufficient for recovery of the mineral values. However, the comminution process remains inherently inefficient. The inefficiency is a result of the operating nature of comminution devices such as grinding mills, where transfer of energy between grinding media and particles in unconstrained and completely random. New comminution circuit design strategies are presented in this paper. The aim of the new strategies is to improve the overall efficiency of the comminution process and reduce the total energy consumption of a comminution circuit. The energy efficient strategies include the: ? rejection of coarse size liberated gangue from the comminution circuit and further downstream size reduction ? use of more efficient grinding and crushing equipment ? the selection of coarser particle product sizes to alleviate the increased energy intensity required to achieve finer product sizes Singularly and when combined, these energy efficient strategies can significantly decrease the overall energy consumption of a comminution circuit. This paper also explores the financial impact of certain energy efficient strategies using an analysis tool called EcoNomics?. It shows that substantial financial gains can be made by including more efficient technologies and methods in comminution circuit design.

Jan 1, 2010

By Rafael Colás

Computer visualization can be employed in industry as an aid to the understanding of the complex interactions between variables encountered in production. The examples of ingot casting of rimming steel and that of hot rolling of low carbon steel strip are presented. Both processes are mathematically modeled, and their results are presented in a graphical way. Such models have been proven to be an asset in quality improvements and increase of productivity as the personnel involved get a better understanding of their job.

Jan 1, 1993

By N. V. . Panishev

The Bakal (South Ural, Russia) deposit of iron ore bearing iron carbonate (siderite) with the capacity of more than 1 billion tones belongs to the MMK. This ore cannot be fully processed via blast furnace technology because of high content of MgO. According to the investigations carried out in the USA and Japan in 1999-2004 the ITmk3 (Ironmaking Technology mark three) RHF technology is a breakthrough in Ironmaking. Four iron ore types (hematite, magnetite, high and low Al2O3/SiO2) were tested. Reduction, melting and slag removal can be achieved in just 10 min. The main objective of the investigation is to establish optimum operation conditions for the production of iron nuggets from iron carbonate bearing ore via the ITmk3 by means of the lab scale testing. Samples of iron ore and carbon reductant were chemically and physically analyzed. Green pellets were processed via a lab tube furnace to simulate RHF conditions. The nuggets and slag were chemically analyzed. This preliminary test work provides valuable information which may be used for large-scale testing in a commercially sized RHF.

Jan 1, 2010

By Chris P. Pistorius

Over the past few decades the carbon intensity of ironmaking and steelmaking has been reduced considerably through improved efficiency in blast furnace ironmaking, partial replacement of coke with less carbon-intensive fuels, and increased use of scrap and direct-reduced iron in steelmaking. To evaluate possible further reductions in carbon intensity accurate process information is needed. A preliminary test of the fidelity of publicly reported data as a source of process information is reported here. The sources are industry roundups of electric furnace furnace steelmaking and blast furnace ironmaking (published by the Association for Iron and Steelmaking Technology), and data recorded by the Environmental Protection Agency under the US Greenhouse Gas Reporting Program. From a comparison for an integrated steelmaking plant and an electric furnace furnace plant, it appears that the values from the two data sources are consistent. The comparison does rely on process details such as the quantitative relationship between injected oxygen and carbon emissions in electric furnace steelmaking.

By D. Doungdeethaveeratana

The extraction kinetics in a novel solvent extraction process have been investigated. In this process, the liquid-liquid emulsion is generated by bottom gas injection into countercurrently flowing aqueous and organic phases. This process has a number of advantages over the mixer-settler unit or the spray column in terms of simple equipment configuration, without any mechanical moving parts, and the ease of cleaning and process control, while providing a sufficiently large interfacial area for rapid mass transfer. The overall rate increased with increasing gas injection rate and height of the aqueous phase but decreased with increasing injector diameter at the same gas injection rate. The variation of the overall rate constant was correlated against a set of dimensionless numbers, representing the operating conditions. Extraction rates and efficiencies comparable to those in a mechanically generated emulsion were attained in this new process.

Jan 1, 1998

By Khandaker M. Anwar Hossain

This paper presents the development of lightweight concrete (LWC) incorporating pumice aggregate and volcanic ash (VA) based ASTM Type I blended cement (PVAC). Fresh and mechanical properties of LWC mixtures such as slump, air content, compressive strength, tensile strength, density and modulus of elasticity are described. The durability characteristics are investigated by drying shrinkage (DS) and water permeability. The investigation suggests the production of LWCs incorporating blended PVAC and VPA having satisfactory strength/durability characteristics for structural applications. The use of PVAC induces the beneficial effect of reducing drying shrinkage and water permeability. Development of such non- expensive and environmentally friendly LWCs with acceptable strength and durability characteristics is extremely helpful for the sustainable development and rehabilitation of volcanic disaster areas around the world.

Jan 1, 2010

By Timothy W. Ellis

This paper presents the basic theory of operation, physical chemistry and phase equilibria which allow the development of liquid-liquid extraction circuits based on metallic solvents. The incorporation of reduction and reduction/diffusion processes into the process 'scheme is discussed and a detailed description of ,several liquid-liquid extraction schemes are developed. A synopsis of experimental results obtained using this: method to separate rare earth and other metal based materials will be given.

Jan 1, 1996

By Elsa Olivetti

Life cycle assessment (LCA) is used increasingly as a tool to provide quantitative metrics of environmental impact and inform early stage materials selection decisions. One common challenge in LCA stems from allocation of burden when multiple adjacent products share some of the same processes. A critical example of this is the partitioning of benefit or burden at product disposition in open-loop recycling scenarios. This work reviews the challenge of allocation and investigates the various methods proposed for allocating end-of-life (EOL) burden. Specifically this work examines whether these methods lead to different results and explores the trends in allocation method bias for or against particular materials classes.

Jan 1, 2010

By Matthew John M. Krane

"The macrosegregation patterns and convective behavior of a Pb-5wt%Sb-35wt%Sn alloy are studied using new numerical treatments of solid particle motion and of transport phenomena occurring during the solidification of ternary metal systems. At this composition, the solidification which occurs while the local liquid composition is in the (Pb)-(SbSn) binary eutectic trough has a significant effect on these phenomena. The effects of this solidification path on fluid flow and macrosegregation are compared to the more familiar binary alloy patterns and the effect of solid particle transport is evaluated. The final predictions of macrosegregation are compared to measured composition profiles. IntroductionThe macroscopic maldistribution of alloy constituents during solidification, commonly called macrosegregation, is a defect which occurs in real metal processing systems. This nonuniformity of species distribution, especially when it forms a high composition gradient or a poor distribution of secondary phases, can lead to areas of high stress concentration, which contribute to cracking during extrusion or forging of wrought alloys or when an as-cast piece is severely loaded in service [1, 2]. Macrosegregation studies in binary systems have become quite common since the introduction of single-domain numerical models which feature one set of conservation equations and boundary conditions for an entire, fixed computational domain containing solid, liquid and multiphase regions. A complete review up to 1995 has been presented by Prescott and Incropera [3]. However, most commercial alloys generally have more than two species in amounts significant enough to affect the convective flows which lead to macrosegregation and other defects. The formation of secondary solid phases, including eutectic and peritectic reactions, also may occur in commercial metal alloys and should be treated using appropriate thermodynamic models."

Jan 1, 1999

By Corby G. Anderson

In the majority of industrial operations recovering gold and silver by hydrometallurgical means, cyanide is the predominant lixiviant. However, as an economic alternative, production of massive quantifies of silver chloride was done on an industrial scale in the nitrous-sulfuric acid pressure leaching of a refractory precious metals concentrate. This proven process required no cyanide. Thus, because of the large volumes encountered during day-to-day plant operation, the need for efficient and low cost methods of silver chloride precipitation, reduction and materials handling was mandatory. As such, this paper covers the evolution of plant scale precipitation, filtration, washing, reduction and control of silver chloride processing. As well, an in-depth description of the unique leaching system is included.

Jan 1, 1998

By Rainer Schmid-Fetzer

"Isothermal solidification can be used to form strong bonds at low temperature which remain solid at much higher temperatures. The exploitation of this principally known technique for new high temperature processing steps and applications in electronic assemblies is the aim of this study. Three basically different variants of this bonding process are given. A comprehensive metallurgical screening is performed and the feasibility of binary material systems is given on a quantitative scale. Very attractive systems are spotted that have never been studied before. Detailed examples for the realization of bonding with complex ternary and multilayer systems are given. A highly innovative example is the chip stack or wafer to wafer bonding of unmetallized Si or SiC at 250°C. The proposed bond remains stable above the melting point of Si and enables entirely new semiconductor manufacturing steps. An improved die bonding process was proposed and verified experimentally.1. IntroductionIsothermal solidification can be applied to form strong bonds at relatively low temperature which remain solid at higher temperatures. The general principle of this type of joining processes is illustrated in Fig. 1. An interlayer of a low melting component, Lo, is provided as a foil or a thin film coating between the high melting joint components, Hi. The assembly is heated under moderate pressure to the bonding temperature, T 8 , and a liquid filler forms, either because the melting point of Lo is exceeded or due to a eutectic reaction between Lo and Hi. This molten filler initiates a rapid interdiffusion or reaction diffusion between Lo and Hi and the subsequent approach to an equilibrium state results in isothermal solidification. The solid phases formed at T 8 in the joint region exhibit a remelt temperature above T8 •"

Jan 1, 1996

By F. Sanchez, A. Mejias, C. Frias, G. Diaz

"Crude zinc oxides are the major source of secondary zinc and are produced from fuming processes like Waelz kilns. The impurities of crude zinc oxides make difficult their processing in primary zinc refineries due to mainly high chloride tenor. Washing with sodium carbonate is a costly operation and chloride removal efficiency is not good enough, so further purification steps are required. The crude zinc oxides are easily treated using ZINCEX™ technology based on leaching, solvent extraction, and electrowinning. The ZINCEX™ process is commercially available and is designed to be a perfect barrier for metallic impurities and halogens, allowing selective zinc extraction in mixed chloride and sulfate leaching solutions. Other valuable components as lead and silver can be efficiently recovered from the leaching residue using PLINT technology in chloride media. Silver is recovered as silver cement and lead is precipitated as pure lead oxide or carbonate, which can be smelted at low temperature.IntroductionZinc is a fully recyclable metal and at present approximately 70% of the zinc produced worldwide comes from primary zinc while 30% originates from secondary materials. Nowadays, the zinc recycling rate is continuously increasing mainly through galvanized steel scrap processing, and crude zinc oxides are the major source of secondary zinc [1]. Secondary zinc oxides are obtained from fuming processes like W aelz Kiln, Rotary Hearth Furnace or Primus Furnace. Waelz is the dominant technology accounting for 80% of total crude zinc oxides production worldwide. In the Waelz process, steel dust is mixed with solid fuel reductant (coke breeze) and pelletized. It is then fed to the kiln and heated to a reaction temperature of l ,200°C. In such conditions, zinc, lead, and other non-ferrous metals are vaporized into the flue gas together with chlorides and alkaline metals. Mixed oxides are drawn from the kiln with the process gases and separated to produce typical crude zinc oxides [2]."

Jan 1, 2011

By Ruiling DU, Xiao YUAN, Keng Wu, Daan XU, Changyao CHAO

To utilize low grade coals to produce high quality semi-coke which can be used in blast furnaces, the pyrolysis of low grade coals was studied in this paper. According to the characteristics of coal pyrolysis process, the temperature range was divided into three parts. The interfacial chemical reaction model, random pore model and the internal diffusion model with the shrinking volume of resultant were established to describe the different ranges of pyrolysis process respectively. The results showed that the experimental data was fitted well, and all the correlation coefficients (r2) exceeded 0.97. Finally, the kinetic parameters for each temperature range have been calculated, which laid a necessary foundation for the simulation and expanded production.

Jan 1, 2016

By G. Upadhya

Of late, solidification modeling has progressed considerably to emerge as a viable simulation tool for the foundry engineer. A wide variety of tools exist in the commercial market to cater to the various needs of the design/ foundry engineer. In fact, recent developments in the area of solidification modeling have been so rapid that a comprehensive review of the state-of-the-art is very much needed. In this paper, an attempt is made to summarize the various issues of solidification modeling, at the same time addressing the historical evolution of the subject. The various phenomenological issues covered in this paper include: heat transfer, fluid flow during mold-filling, solidification kinetics and microstructural evolution, quick-analysis schemes for approximations, porosity prediction models, and the phenomena of fluid flow in the mushy zone. Modeling issues related to the development of solidification stresses which lead to defects such as hot tears and the development of artificial intelligence concepts in the area of rigging design are also discussed. Due emphasis is given to the various phenomena which add to the complexity of the whole subject, and the various alternatives available for solving a particular problem. For example, the heat transfer problem can be approached by the use of simple modulus schemes or by solving the conduction equation to obtain a more accurate temperature distribution. Similarly the microstructural evolution can be handled in a deterministic way by use of nucleation and growth models, or in a probabilistic way by use of empirical models. The main goal of this paper is to put the multi-faceted problem of solidification modeling in proper perspective so that it can serve as a guide for future developments in this area.

Jan 1, 1994