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By John Pilling

The concept of microstructure, its evolution through materials processing and its effect on the properties of the material is, perhaps, the foundation upon which the science of materials is built. PHAUST, a computer aided learning program, attempts to provide instruction in establishing the relationships between phase diagrams, thermal processing and microstructure. Using phase diagrams derived from a database or created by the user, the evolution of microstructure during processing is quantified using the lever rule and/or the Scheil equation and tracked through a doubly linked list (a form of binary tree). Microstructures, in the form of full colour cartoons are then drawn using the quantitative and logical information contained within the linked list using bitmapped templates and logigal operators such as NOT. AND, OR and XOR, giving the student a view of the structure as it would be seen under the optical microscope. The software provides complete diagnostics of student answers, locates errors and misconceptions as well as providing tutoring towards the correct solution method and answer.

Jan 1, 1991

By Batric Pesic

The interactions of mineral-pyrite with T. ferrooxidans were studied by using a cyclic voltametry technique. The interactions with bacteria were examined during the entire growth stage of bacteria (fermentation), The pyrite ?surface invariably drastically changed ' its. properties at the second day of fermentation. Beyond two .. days of fermentation, the cyclic voltamograms were insensitive to convective diffusion produced by stirring. The product layer was examined by SEM,. X-ray diffraction and chemical analysis. The SEM study revealed that bacteria populated the pyrite surface at an extremely high density levels. The high density of bacteria, and the solid reaction products formed on the pyrite surface created conditions for pore diffusion which explained why the CVs became .insensitive to convective diffusion in solution (stirring). The x-r:ay diffraction study confirmed jarosite as a product layer. A mechanism of T. ferrooxidans cells serving as nucleation sites for jiarosite formation is proposed.

Jan 1, 1991

By Rivera Jose Antonio Ore

Top Submerged Lance (TSL) smelting technology is currently used in a wide range of applications in the non ferrous and waste product treatment industries. The use of TSL technology for tin concentrates smelting has been successfully applied at the Minsur Tin Smelter and Refinery at Pisco, Perú. The process is based on the air-cooled top entry submerged Sirosmelt lance, developed by Dr. John Floyd at the CSIRO division of Mineral and Process Engineering in the 1970?s. Advantages of the process include flexibility to operate the lance, main burner of the Sirosmelt furnace, with different levels of combustion stoichiometry which allows us to get from highly reducing to highly oxydising atmospheres in the smelting reactor according to the type of feed we are processing, ability to utilize cheap energy sources such as natural gas, low capital cost and an environmentally friendly operation. This presentation summarises the application of the Submerged Sirosmelt technology for smelting tin concentrates and a variety of tin containing materials like iron dross, copper dross, tin residues, low tin/antimony slags by applying recent metallurgical developments at the Minsur smelter. The impact of new feed conditions and level of impurities on reactor performance with features of process and operation control are described. As a result of these recent advances in tin smelting using TSL technology, the Minsur Tin Smelter and Refinery improved its overall tin recovery, substantially reduced tin inventories and became the second largest tin smelter in the world, currently producing more than 40,000 metric tones of refined tin per year.

Jan 1, 2006

By Gustavo Díaz, Miguel A. García, Carlos Frías

"Under the auspices of the Commission of the European Union, a consortium composed of six European organi~ations has conducted a project to scale up the PLACID electrowinning cell to industrial size within the Placid process development. This paper is concerning the results and achievement of the industrial cell prototype after more than 1,000 hours operating time and about 10,000 Kg electrolytic lead production. In general, results have been very satisfactory, demonstrating the ability ofthe PLACID electrowinning cell to produce top quality electrolytic lead (> 99.99 %) with high current efficiency and low energy consumption.IntroductionThis paper is concerning the development of an industrial size PLACID electrowinning cell within the PLACID process development. This project began on January 1993 and was finished on April 1996.Lead metal production and manufacturing industries produce large amounts of dusts and also lead bearing slags. Spent lead-acid battery recycling also produces lead oxides from the battery pastes rather similar to those mentioned above. Those lead secondary materials are hazardous and difficult to handle by usual procedures.Existing processes to treat-lead oxides may inflict considerable damage on the environment, incur high operating costs and have limitations to produce top quality lead.The main aim of this project has been to develop a novel hydrometallurgical process able to deal with different lead bearing materials, mainly lead oxide secondaries: lead-acid battery pastes, lead fumes, furnace slags, oxide residues, etc., producing ""four nines"" pure lead in an efficient manner with a benign influence on the environment; it is called the PLACID process."

Jan 1, 1997

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 P. Louis

Gécamines is the world largest cobalt producer with about 60 % of the Western World production. During the last ten years, its annual production varied from 5,400 to 14,600 t/year. The actual cobalt production capacity of Gécarnines is 18,000 t/year and could be increased in the near future if necessary. Cobalt is presently produced at the Shituru plant by an old in-pulp electrolysis process and in Luilu, by electrolysis of a clear weakly acidic solution. The Shituru Cobalt quality is lower than the Luilu one. For that reason, part of the Shituru Cobalt is fire refined and cast into granules. Large efforts have been succesfully accomplished to improve the cobalt quality. This has been made possible by a better knowledge of the purification processes and of the electrolysis parameters.

Jan 1, 1988

By F. Michael Hosking

Modeling of a furnace brazing process is described. The computational tools predict the thermal response of loaded hardware in a hydrogen brazing furnace to programmed furnace profiles. Experiments were conducted to validate the model and resolve computational uncertainties. The results from selected furnace simulations and measured thermal events were compared. Critical boundary conditions that affect materials and processing response to the furnace environment were determined. "Global" and local issues (i.e., at the furnace/hardware and joint levels, respectively) are discussed. The ability to accurately simulate and control furnace conditions is examined.

Jan 1, 1998

By A. P. Paiva

Although the advantages of Solvent Extraction for separation/purification of relatively concentrated solutions are well known in Extractive Metallurgy, its use for the recovery of elements present in low levels only recently has been discussed, with particular attention devoted to precious metals. In this work, the extraction behaviour of Cyanex 471X towards silver, from an acidic chloride medium is reported, the extraction and stripping isotherms and related kinetic features analysed. Results on the selectivity of silver extraction against high contents of iron, copper and lead are discussed. Phosphine sulphide extractants are generally associated with solvation mechanisms: analysis of the extraction pathways along with the possibility of reaching a suitable loading in the organic phase are also presented.

Jan 1, 1993

By Alain Jardy, Valerio De Felice, Jean-Pierre Bellot, Ismael Lis Alves Daoud, Stephane Hans

"Gas-stirring ladle treatment of liquid metal has been pointed out for a long time as the processing stage mainly responsible for the inclusion population of specialty steels. A steel ladle is a complex three-phase reactor, where strongly dispersed inclusions are transported by the turbulent liquid metal / bubbles flow. We have coupled a population balance model with CFD in order to simulate the mechanisms of transport, aggregation, flotation and surface entrapment of inclusions. The simulation results, when applied to an industrial gas-stirring ladle operation, show the efficiency of this modelling approach and allow us to compare the respective roles of these mechanisms on the inclusion removal rate.IntroductionThe reduction of the weight of high performance materials together with the improvement of mechanical properties and the increase of the recycling of used metal are new challenges which emphasize the importance of metal cleanliness. Ladle treatment of specialty steels has long been described as the secondary metallurgical process mainly responsible for the non-metallic inclusion derived from the deoxidation process. The treatment is accomplished by blowing argon through one or more porous plugs for the purposes of desulphurization, minor composition adjustments, and inclusion removal. Gas injection is applied on routine basis to achieve both the stirring of the liquid bath (thermal and chemical homogenization) and the entrapment of the inclusions by the bubbles (flotation). Furthermore, the turbulence produced in bubble swarms enhances the probability of inclusion collisions and makes aggregation the first mechanism for particle removal. The physical processes involved in gas stirred ladles are numerous and complex owing to the three dimensional and multiphase (metal-gas and inclusions) nature of the reactor. Despite these difficulties, the population balance equations can be implemented in CFD code11'21 and combined CFD-PBM (computational fluid dynamics - population balance method) models are investigated for steel ladle processes13'41 and produce very promising results in terms of inclusion removal efficiency."

Jan 1, 2012

By Peter K. Liaw, Charlie R. Brooks, David C. Joy, Wei Zhao

In this paper, effects of oxidation, porosity and fiber-fabric stacking sequence on flexural strength of a continuous silicon carbide fiber (SiCr) fabric-reinforced SiC ceramic-matrix composite (CFCC) were studied. The failure mechanisms were correlated with flexural strengths of CFCC samples, both before and after oxidation. Microstructures and fractography were investigated using scanning electron microscopy (SEM). The chemical change after oxidation, such as Si, C, and 0, and their distributions, were detected by the SEM energy-dispersive X-ray spectroscopy (EDXS) line-scan chemical analysis technique. These effects on the strength of the CFCC can be attributed to following reasons: (i) The decrease in the flexural strength after oxidation is mainly due to degradation of the strength of Nicalon fibers and the damage of fiber/matrix interface both caused by high-temperature chemical reactions, (ii) Porosity is not too important in affecting the strength of the CFCC, when the bonding of the forced flow chemical vapor infiltration (FCVI)-SiC matrix is stronger than that of the fiber/matrix interface. However, a higher porosity content will be harmful, because higher porosity will both decrease the effective elastic modulus of the FCVI-SiC and make pore-linkage easier to occur, which is more likely to cause premature failure, (iii) The variation in the lamina stacking sequence of the CFCC changes the elastic stress distributions along the thickness direction of specimens, the magnitude of ceramic matrix-cracking stress, the effective elastic moduli of the laminate, and different crack initiation sites as well as different failure modes, and thus, leading to the scatter in the flexural strength of the CFCC.

Jan 1, 1998

By William A. Hockings

Methods for the measurement of liberation of finely ground iron ores are described. The general method consists of separating a sample of the ground ore into a number of size fractions, followed by measuring the liberation of each fraction. The size separation has been done using electro-formed screens of 20-, 10-and 5-micrometer apertures, and also by air elutriation. Liberation (i.e., the distribution of compositions of individual particles) has been measured by optical microscopy. A computer pro-gram was used to adjust the raw count data so that it agrees with the chemical analyses of the size fractions. Various ways of presenting the results are given, and Some applications of the results to flotation processing are discussed.

Jan 1, 1981

By David E. Hardt

"One of the critical variables to be controlled during arc welding is the size or geometry of the weld pool. The measurement of pool geometry has become an increasingly important problem with the advance of welding automation and control, and this paper addresses that problem. The basic concept of pool size estimation via measurement of pool dynamics is presented. The theory underlying this concept is discussed and is followed by a review of the current work in this area. It is concluded that pool dynamics can be characterized by natural frequencies of oscillation, for stationary welds, and that these can be measured by appropriate signal processing performed on the arc voltage. However, it appears that only full penetration welds show a strong correlation between weld size and natural frequency. Also, the extension of these results to the realistic case of moving welds has yet to be considered in detail. Nonetheless, this method of in-process measurement for real-time weld process control is still quite attractive where applicable since it can be accomplished simply by modifying the arc current schedule and by signal processing of the arc voltage.INTRODUCTUIONThe study of welding process control has been dominated by research into methods of in processing sensing of the weld pool geometry. While it has been shown feasible to measure the topside pool geometry using video methods [1,2], the penetration or backside bead width have remained elusive quantities. This is particularly true if a topside sensor location is required.The concept of using weld pool motion as a pool geometry sensing method was proposed by Hardt et al. [3] and later demonstrated by Hardt and Zacksenhouse [5] and Richardson and Renwick [6]. The concept is based on the fluid dynamics of a pool constrained by a solid container and by significant surface tension forces (i.e. a small shallow pool, not a ""pond"" or ""lake""). Such a pool, if subjected to external forces, will exhibit a surface motion is a function of that force, the properties of the fluid, the surface tension, and the shape of the container. Thus, if this motion can be excited and measured, and the relationship to the pool geometry determined, a means of sensing pool shape will exist."

Jan 1, 1986

By Daniel Kim, Justin McAllister, Shijie Wang

"At the Kennecott Utah Copper Refinery, impurities in the electrolyte are being precipitated in the circulation system and form a hard scale in the piping. This scale must be removed periodically for proper electrolyte flow. Distinct layers of differing composition form as the operating conditions of the tank house change. Scale samples from the inlet and outlet pipes were analyzed to discover the nature of the precipitates. Each sample was sectioned and examined under optical microscopy and SEM. The composition of the scale was analyzed using ICP, XRD, and SEM/EDX mapping. The rate of deposition was determined by measuring the amount deposited on new pipes after elapsed time intervals. In order to determine how to minimize the formation of the scale, the mechanism was studied and the results are presented in this paper.IntroductionIn copper electrorefining, impure copper anodes are refined into pure copper cathodes. The impurities from the anodes are either insoluble and report to the slimes or soluble and dissolve concentrating in the electrolyte. These impurities are controlled by bleeding electrolyte from the system. Over time, the impurities combine to precipitate a hard scale on the surfaces contacted by the electrolyte. The scale causes problems with tank house circulation systems. In order for the refinery to operate properly, the scale must be removed periodically from the walls of the pipes. The first step to control the buildup of scale on the pipes is to understand the composition and the phases that are present in the scale."

Jan 1, 2012

By L. Petitnicolas

The experimental study of nitrogen absorption and its removal from a liquid Ni-20%Cr alloy at 1873 K has been undertaken, using an experimental, apparatus based on the Sieverts technique in order to determine the solubility of nitrogen in the alloy. as well as the kinetics of nitrogen transfer across the gas/melt interface. Experiments show that nitrogen solute equilibrium content can be calculated using the Sievens law. Measurements point out the nitrogen absorption reaction rate to be well described by first order kinetics, whereas experiments on nitrogen removal reveal that the rate is better expressed using a second order equation.

Jan 1, 1996

By Yang Hong-ying, Yu Juan

Electrochemical behavior of natural chalcopyrite in electrolyte solution at pH value of 6.97 was studied by cyclic voltammetry, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The results showed that the electrochemical processes occurred on electrode surface were controlled mainly by the growth of sulfur species at lower applied potentials (<0.35Vvs.SHE), and the oxidative dissolution of sulfur species and the hydroxylation of iron at higher applied potential (>0.45V). The EIS spectra of oxide product layers could be illustrated by the equivalent circuit of Re(QdlRct(QfRf)), and the degree of hydrophilicity for chalcopyrite was higher when the value of charge transfer resistance Rct. was greater. The optimum potential range for the floatation of chalcopyrite in collectorless solution at pH value of 6.97 was between OCP (0.165V) and 0.35V.`

Jan 1, 2015

By Hwa-Soo Park, J. K. Yoon, Hoseok Nam

In a thin slab casting process, control of fluid flow in mold is particularly difficult due to the high casting speed and large aspect ratio of the mold and the understanding of the fluid flow motion as well as heat transfer in mold is regarded as the most important information because the melt delivery is directly related to the problems of shell growth nonuniformity, surface turbulence and mold powder entrapment. A mathematical model has been developed for the coupled analysis of fluid flow, heat transfer and solidification in funnel type mold using finite volume method based on a body fitted coordinate and the characteristics of the transport phenomena in the mold of thin slab caster were analyzed by numerical simulation. As a result of simulation, the basic flow pattern is characterized as four large recirculations and two small eddies near the narrow faces of mold, which is somewhat different from that of parallel type mold or other conventional slab caster. The heat transfer model accurately predicted the mold positions susceptible to cracking as a result of thermal stress and the predicted shell thickness shows good agreements with the measured shell thickness on breakout products. We also investigated the influences of some operation parameters such as casting speed, nozzle type, submerging depth and mold material on fluid flow, heat transfer and distribution of solidifying shell and various information for the determination of optimal operating conditions were obtained.

Jan 1, 2000

By Aline Maria dos Santos Teixeira, Francisco Manoel dos Santos Garrido, Joao Alves Sampaio, Marta Eloisa Medeiros

"Rocks for crops is a natural practice for soils fertilization which consists on adding rocks to the soil while water decomposes the rock, through chemical weathering, and gradually releases nutrients to the soil solution. This practice can be considered an alternative to the low production of potassium fertilizers in Brazil. In this context, the phonolite rock was characterized in order to evaluate its application as an alternative source of nutrients to the Brazilian agriculture. The phonolite studied is an igneous, volcanic rock with alkaline character that is chemically composed of a high grade of potassium due to the presence of feldspar minerals. In order to quantify the minerals present in the sample, characterization was carried out using several techniques such as X-ray diffraction, X-ray fluorescence and scanning electron microscopy.IntroductionBrazilian soils are generally acidic and nutrient poor due to the tropical climate in which high temperatures and intense rainfall favor a rapid decomposition of the rocks that from the soil. And as agriculture is one of the main bases of the country's economy, large amounts of fertilizer are used to make the soil productive.Although Brazil has large reserves of potassium, the demand for potash fertilizer is higher than the national supply, which makes the country dependent on fertilizer imports, especially in the form of potassium chloride. Thus, we must look for economic alternatives to traditional fertilizer [1].Stonemeal is a natural practice for soil fertilization that consists in adding basic or ultrabasic rocks to the soil so that water, through chemical weathering, decomposes the rock while it gradually releases nutrients."

Jan 1, 2011

By I. Gaballah

High and low grade concentrates of tantalum and niobium oxides were obtained by leaching a medium grade tin slag. Chlorination and carbochlorinalion of these concentrates were studied between 200 and 1000 "C. Chlorination or carbochlorination of the low grade concentrate led, at 1000 OC, to the extraction of about 95 % of the tantalum and niobium oxides. However, the tantalum and niobium chlorinated compounds were contaminated by iron and manganese chlorides. Complete extraction of the niobium and tantalum pentoxide was achieved during the carbochlorination of the high grade concentrate at 300 and 500 "C, respectively. While chlorination of this concentrate at 1000 "C, allowed to the volatilization of about 60 and 80 % of Ta205 and Nb205. In both cases, condensates were composed of almost pure tantalum and niobium chlorinated compounds. The results demonstrate the advantages of the lixivialion based on the "pseudo- structure" of the raw tin slag to obtain the high grade concentrate. The conclusions of this work suggest that the carbochlorination of the high grade concentrate is an efficient process for the extraction of refractory elements from tin slag.

Jan 1, 1993

By Claudia Gasparrini

Uranium occurs in a variety of minerals, the more common primary ones of which are uraninite-pitchblende, coffinite and a group known as the complex multiple oxides. Identification and description of the uranium-bearing and associated minerals in ore samples may give a preliminary indication of the potential economic importance of the deposit and may also suggest initial approaches to metal extraction. The present paper reviews the common uranium minerals, describes their manner of occurrence and compares the types of deposits with which they are associated. Methods and techniques for their identification are described and their leaching characteristics discussed.

Jan 1, 1981

By Thomas Havlik

It is proposed to realise the direct leaching, during which will be generated elemental sulfur and not sulfate or sulfuric acid as end product, under conditions that sulfur will not cover the leaching surface and Hot hinder the leaching course. The following improvements have been considered: -use of organic sulfur solvents -ultra high-frequency leaching -ultrasonic leaching -use of surface detergents or surfactants in leaching processes -simultaneously crushing and leaching These proposals are under investigation and preliminary results are promising

Jan 1, 1996