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By Honggang Zhong, Xin Cao, Qijie Zhai, Hongmei Song, Congsen Wu, Cheng Zhang, Jingzheng Ye

"The influence of superheat on the solidification structure and ferrite/austenite phase transformation of a novel lean duplex stainless steel (DSS) was investigated on a setup, which designed to thermally simulate the continuous casting process. The results showed that the macrostructure of the samples all exhibited chill zone, columnar zone and equiaxed zone. The distance from chill zone to position of columnar to equiaxed transition (CET) moved from 51.0 mm to 39.8 mm with an decrease of superheat from 70 °C to 10 °C, and that the grains in the chill zone tended to be finer. In equiaxed zone, the fme and uniform grains were observed when superheat higher than 40 °C; while, coarse grains were found in samples poured at low superheat. Generally, the volume fraction of ferrite increased along the dendritic growth direction, and stabilized in equiaxed zone. The high superheat decreased the volume fraction of ferrite in equiaxed zone, while it had indistinctive influence on chill zone and columnar zone.IntroductionDuplex stainless steel with approximately equal volume of ferrite and austenite, offering an attractive combination of corrosion resistance and mechanical properties. [ l]. The production of DSS, worldwide application in structural engineering[2] and petrochemical industry[3], have increase by more than 100% in the latest decade[4]. But due to the sharp prices increase of nickel and chromium, lean duplex stainless steels which have lower contents of alloy elements were developed. They perform well in both mechanical and corrosion resistance[S, 6] and even have TRlP(Transformation Induced Plasticity) effect[?]. Nonetheless , the mechanical properties of DSS was affected greatly by the solidification structure, such as columnar to equiaxed transition (CET), grain size and phase content[8]. So, the solidification behavior of stainless steel was investigated widely"

Jan 1, 2014

By Kazuyoshi Sato, Keizo Uematsu, Nozomu Uchida

"Confocal fluorescence scanning laser microscope was applied to characterize the surface flaw of ceramics in great detail. A high potential -of the characterization technique is presented first. Then the technique was applied to clarify the relationship between the flexural strength of ceramics and the surface flaw. This kind of direct information of surface flaw should be essential for the fundamental study in this area, but has been lacking. The examination revealed that large defects are present on the machined surface of ceramics. Their size is consistent to the flexural strength measured on the material. The characterization tool was also applied to examine the formation of surface flaw in machining of ceramics.IntroductionClarification of fracture origin should be the starting point in the study on strength in ceramics. However, this task has been extremely difficult in some ceramics, such as an alumina ceramics. It may break from both internal and surface flaws. The former should reflect the quality of production process and the latter the machining. Examination of surface flaws should be very important for developing a better machining method for ceramics. The knowledge may valuable for establishing a better production process also.ExperimentAlumina Referceram (JFCC) was used as samples. They are cut to size of 3x4x40mm, and the surfaces were ground to meet the requirements of testing method for flexural strength of fine ceramics, JIS R 1601. They were soaked in an aqueous solution of fluorescence dye and evacuated with an aspirator for an hour to allow the solution penetrate into surface flaws. After excessive solution remained on the surface was removed by gentle washing, the specimens were dried at 120°C for 48 hours. The 4 point bending mode was applied to measure the fracture strength."

Jan 1, 2000

By Tiffany Brown

In the thiosulfate gold leaching process, thiosulfate is used to complex gold following electrocatalytic oxidation of the native metal by Cu(II)-ammines. Unfortunately, Cu(II) complexes also catalyse the undesirable conversion of thiosulfate to polythionates. We have been seeking alternatives to ammonia, which fulfil the role of ammonia but minimize thiosulfate decomposition. One aspect of these studies has involved the determination of the rate of thiosulfate oxidation by the Cu(II) complexes from UV-Visible spectral changes. Various ligand classes, including pyridyls, polyamines, aminocarboxylates and picolinates, have been tested and the majority found to inhibit thiosulfate decomposition. Interesting variations in reactivity with the nature and denticity of the ligand and L/M ratio have been observed. In the case of open chain polyamine ligands with 2 to 5 nitrogen donors, the rate of thiosulfate oxidation was generally found to decrease with the denticity and the concentration of each ligand. Saturation of the Cu(II) coordination sphere appears to inhibit the oxidation of thiosulfate when excess thiosulfate is present. The Cu(II) complex of the branched polyamine ligand, tris(2-aminoethyl)amine (tren) exhibits this behaviour in excess thiosulfate. Interestingly, when the [Cu(tren)(OH2)]2+ complex is in excess oxidation of thiosulfate was observed. This unexpected finding prompted a spectrophotometric study of this reaction which has revealed that the oxidation of thiosulfate involves several processes, two of which involve the formation and decay of a tetrathionate radical.

Jan 1, 2003

By Varadajan Seshadri

The increase in production of continuous casting machines requires long ladle sequences without interruption. Very often the production schedule has to accommodate a variety of steel grades. In such cases downgrading may be inevitable. Models must be made available to study the alternatives that would make possible mixing of steels in the tundish but minimizing the losses due to downgrading the slabs. Physical modeling was used to evaluate the influence of variables such as internal geometry of the tundish, presence of turbulence inhibitors, depth of ladle long nozzle, weight of steel in the tundish, steel throughput upon the tundish transition curve. Expressions for minimum residence time and transition period have been determined. Mixing-transition is allowed to continue inside the liquid pool in the mold and the final solute distribution in a given cross section is captured by a solidification model. The result is a map of the transition in the final product.

Jan 1, 2006

By W. L. Cornell

Ore microscopy was used in support of both bench-and large-scale continuous beneficiation testing programs. Reflected light microscopy and Vickers hardness measurements were utilized to help identify problems relating to mineral identification, mineral association, mineral liberation, mineral distribution in product streams, and froth entrainment. Specimens studied were size fractions of concentrates and tailings resulting from Bureau of Mines research to recover a siegenite-enriched product by beneficiating chalcopyrite concentrates. Other specimens were size fractions of bulk sulfide concentrates recovered during the enhanced amine scavenging of final tailings by froth flotation. The findings from studies directly affected flowsheet development.

Jan 1, 1987

By Peter Bauer, Klaus Gamweger

"Gas purging systems are well established in nonferrous metallurgy at multiple steps during metal production, including melting, converting, alloying, and metal cleaning. Since the kinetics of all of these stages are positively influenced by using gas purging systems the overall process benefits are substantial. In the aluminum industry, inert or reaction gases are blown into the melt using porous plugs to achieve improved metal grades, higher productivity, and more efficient energy utilization. To enable the most effective application of the process gases a complete package, termed AL KIN, was developed by RHI that includes porous plugs, refractory expertise, gas supply technology, and gas control equipment. This paper discusses the technological and economic advantages of this system and the specific benefits of fuel reduction, production time savings, decreased process gas consumption, and improved refractory service life and maintenance are illustrated using an aluminum slug plant in Austria.IntroductionIn addition to high quality production, increasing productivity is the main goal in many aluminum cast houses to maintain or even strengthen their market position. The Neuman Aluminium Group, based in Austria, North America, and based in Austria, North America, and China, is the largest slugproducer for tubes, cans, and automotive parts worldwide. Recently, a comprehensive improvement program was initiated at the Neuman Aluminium Austria slug plant in Marktl - the main factory and technological centre of the group. The principal goal of the optimization project was to increase the productivity of the strip-casting production. The investment included a gas purging system, ingot preheating equipment, a new insulated launder system, and optimized melting cycles. However, the introduction of the gas purging system was pivotal to the project and has accounted for approximately 50% of the benefits achieved. This paper describes the AL KIN gas purging technology and details the process benefits resulting from the improvements at Neuman Aluminium Austria."

Jan 1, 2009

By John J. Mazza

Treatability studies were performed to determine the effectiveness of two commercially available treatment methods (solvent extraction and thermal desorption) for the removal of PCBs and PAHs from contaminated dredged riverbed sediments. The solvent extraction method evaluated was the B.E.S.T. process which extracts the contaminants with triethylamine. The thermal desorption method utilized was the ATP process which desorbs the contaminants at elevated temperature in an anaerobic atmosphere. A description of both methods and. an evaluation of the treatability study results is provided. Each treatment method was used to treat two separate samples (high and low concentration) from the site. Overall, both methods proved to be very effective with solvent extraction achieving 98% removal of both PCBs and PAHs and thermal desorption achieving better than 99% removal of both the PCBs and PAHs from the high concentration sample. Both solvent extraction and thermal desorption achieved greater than 99% removals of PCBs and PAHs from the low concentration sample. Vendor cost estimates for full scale treatment were roughly equivalent. The primary differences between the two methods lies in the realm of permitting, operational requirements, and emission concerns.

Jan 1, 1994

By Robert R. Beebe

On the night of August 1'9-20, 1995, seepage was seen at the toe of the Omai tailings dam in Guyana. The mill was immediately shut down, and within two hours the flow, then mostly water, was diverted into an inactive mining pit nearby. At about the same time a second more serious break occurred at a point where water and solids could flow directly into the Omai River. By the time Ii coffer dam could be completed in the early morning of August 24, some 4.2 million cubic meters of tailings water and solids had escaped from the dam, of which nearly2.9 million cubic meters had reached the Omai River. This paper outlines some initial Process considerations and operational decisions which might have contributed to the dam's failure, describes how the Government of Guyana and the operator, Omai Gold Mines Limited, cooperated in dealing with immediate problems and shows how the Government set about investigating the accident. In particular, the paper details the work of a Process Review Committee comprising Guyanese and foreign experts convened to assess the gold processing and effluent management systems at Omai, and to recommend actions where appropriate.

Jan 1, 1998

By G. Gomathi, K. Asokan, K. Subramanian

An electrochemical reactor with anode and cathode chambers separated by a composite perfluoro polymer cation exchange membrane was designed, fabricated and used for the reduction of dissolved carbon dioxide under ambient conditions to formate. The flow reactor enhanced the mass transfer of carbon dioxide compared to the batch reactor. Experiments were conducted using two different perfluoro polymer membranes - Nafion 961. Efficacy of CO2 reduction on various cathode materials (Cd, Pb, Sn and Zn plated stainless steel woven mesh) were determined. Optimum values of flow rate and current density were evaluated for the energy efficient formation of formate in aqueous KHCO3 (pH 7.5-8.5) buffer solutions.

Jan 1, 2008

By H. Y. Sohn, Haitao Wang, Moo Eob Choi

"A novel ironmaking technology is under development at the University of Utah. This technology produces iron directly from iron ore concentrate by gas-solid suspension reduction. Hydrogen is the main reducing agent for high reactivity and for the elimination of carbon dioxide release in this ironmaking process. The direct use of concentrates allows bypassing the problematic pelletization/sintering and cokemaking steps in the steel industry.Intrinsic kinetics of the suspension reduction of magnetite concentrate particles by hydrogen has been measured. Experiments were carried out in the temperature range of 1423-1673 K, other experimental variable being hydrogen partial pressure, the amount of excess hydrogen and particle size. Under most experimental conditions, 95% reduction was attained within several seconds, which presents sufficiently rapid kinetics for a suspension reduction process. The reaction kinetics followed the nucleation-and-growth equation, and a rate equation that contains all the effects of the experimental parameters has been obtained.IntroductionWith the rapid increase in steel production, it is critical to control CO2 emissions which is the main greenhouse gas. It is inevitable to release a huge amount of CO2 when coke and/or coal are used as the main reducing agent in producing iron. As one of the methods to reduce the CO2 emission from ironmaking, the utilization of the gaseous reducing agents and fuels, including hydrogen, has been investigated [1-6]. The use of such gases forms the basis for a new ironmaking technology under development for producing iron directly from fine concentrates by a gas-solid suspension technology. This technology would reduce energy consumption by about 40% of the amount required by the blast furnace and drastically lower environmental pollution, especially CO2 emission, from the steel industry [4]. This is accomplished by adopting H2-based reductant and bypassing pelletization/sintering and cokemaking steps. Unlike other gas-based alternative ironmaking processes using shaft furnaces or fluidized-bed reactors, the suspension reduction technology is a high-intensity process because it will not suffer from the problems that other processes do when operated at high temperatures mainly from the sticking and fusion of particles."

Jan 1, 2011

By C. Palacios

The Plant, which was started up in April 1970, was originally designed for a capacity of 40.000 ton of cathodes per annum, using 12 sections, containing 408 cells. Since then the addition of another 8 sections containing 280 cells and using the Reverse Current System has made possible the increased output of 109.000 ton. The quality of the cathodes produced is excellent. The extension of the Electrolytic Refinery, by the introduction of the Reverse Current System, has been a great success and no problem has arisen in the new equipment or in the modifications carried out in the plant. The operation of the plant has improved due to better control procedures.

Jan 1, 1976

Microstructural investigation has shown that grain splitting or deformation banding ( DB ) develops progressively with increasing strains during cold rolling. Of particular significance to simulating texture development in cold rolled BCC polycrystals is the operation of higher order slip systems other than 110 and, the occurrence of DB in the rolling plane since the latter allows a new relaxation of the shears. Deformation banding ( DB ) model includes grain subdivision in the rolling plane and applies the Relaxed Constraints ( RC ) mechanism for the other shears. An energy criterion for deciding whether deformation banding occurs or not has been postulated, referred to as Deformation Banding Criterion ( DBC ). This paper reports the results of the investigations into the effects of different slip systems, i.e., those based on 110, 112 and 123 slip planes and their combinations using RC, DB and DBC models, in developing simulated BCC rolling textures.

Jan 1, 1999

By Peter Olubambi, Babatunde Obadele, Oluwagbenga Johnson

"The microstructure and corrosion behaviour of titanium carbide (TiC) reinforced duplex stainless steel matrix surface composites synthesized by laser melt injection technique was investigated. The surface melting operation was conducted using a 4.4 kW CW Nd:YAG laser with laser power of 1.5 kW, scanning speed of 0.4 to 1.0 m/min, beam size of 3 mm and argon shield gas flow rate of 4 L/min. The morphologies and microstructures of the coatings examined using field emission gun scanning electron microscope (FEGSEM) revealed homogeneous distribution of fine precipitates of TiC in the matrix, while X-ray diffraction (XRD) analysis confirm no phase change. TiC addition to the steels significantly increased hardness value to about 547 Hv0.1 but slightly decreased the corrosion resistance of the steels in 3.5% NaCl possibly due to the intergranular carbide coating that prevented chromium from forming continuous passive oxide layers.IntroductionComposite materials evolve from the idea of combining two basically dissimilar materials with different physical and mechanical properties to arrive at a product whose final properties are superior to those of the individual components [1]. Metal matrix composites (MMCs) are receiving much attention and are the focus of intense research and development worldwide for aerospace, automotive and other applications because of their excellent combination of ductility and toughness of the metallic matrix with high hardness and strength of carbides reinforced in the matrix [2]. Surface modification techniques such as laser, thermal spray, plasma spray, chemical vapour deposition have been use to fabricate MMCs. Laser melt injection (LMI) is a surface modification technique known since the 1980s [3] has been used to improve surface properties of metallic alloys such as aluminium, titanium and steels [4-6]. It involves the lateral injection of carbides, ceramics and cermets blown by a gas stream into a liquid metallic pool, created by laser irradiation of the top surface of the base material."

Jan 1, 2012

By R. L. Nyirenda

An investigation of the reducibility of a cassiterite concentrate with charcoal was made in the temperature range of 1123-1373 K. The course of the reaction was monitored by a combination of sample weight loss measurements, product gas analysis, and chemical analysis of the reaction product. It was found that the cassiterite could be best reduced by a combination? of high temperature, reasonably high charcoal proportions, high charge poroslty, and the addition of a small percentage of lime. Analysis of kinetic data obtained from isothermal experiments using theory from the oxidation of carbon by carbon dioxide gave an activation energy value of 255 lci/mole for the consumption of carbon by reaction with cassiterite.

Jan 1, 1990

By Ikuhiro Sumi

A new steelmaking process, in which manganese ore was intentionally reduced, was developed to achieve a higher manganese Yield using a combined blowing converter. In this study, manganese behavior was discussed through the introduction of a model. Apparent reduction rates of manganese were calculated by the two terms that were determined experimentally, with SOkg and 2S0ton combined blowing converters. The model calculated manganese changes during the operation. We applied the model to the actual operation and found that manganese behavior was predicted fairly well by this model.

Jan 1, 1996

By Roger C. Urquhart

Copper-nickel-sulphide ores mined in the Rustenburg district of South Africa are generally smelted in electric furnaces because of the high-temperature slag produced, the availability of cheap electric power, and the smaller pollution problems. Apart from melting, the functions of the electric furnace are to recover most of the matte content in the converter slag by physical and chemical interaction with the furnace bath and to provide adequate time for the optimum separation of matte and slag. Smooth, efficient operation will denend on fluid slags for settling, balanced by high resistivities to obtain adequate concentration and distribution of power by way of current heating. To obtain a greater understanding of the processes involved, an investigation was undertaken at Rustenburg Platinum Mines on the smelting of copper-nickel concentrates in a 19.5 MVA furnace with six in-line electrodes. The matte- and slag-tapping temperatures, slag temperatures, slag analyses, electrical data, and electrode position were measured. Radioactive tracers were introduced into the slag, and quantitative results relating to the flow pattern within the furnace were obtained. These studies were augmented by scaled laboratory investigations relating to the determination of cell constants and current distribution within the furnace. Instantaneous field and power distribution plots were determined by use of an on-line mini-computer. The applicability of these results to furnace operation is discussed.

Jan 1, 1976

By Ragnhild E. Aune, Shahid Akhtar, Reza Beheshti

"The potential use of Black Dross (BD) as a raw material for the production of refractories, fluxing agents and glasses is the main motivation of the present study. Heat treatment experiments were carried out in Ar, and under reduced pressure (20 Pa), to evaluate the salt removal efficiency. The chemical composition of the BD after heat treatment was investigated by SEM-EDS and XRD analyses. Based on the present results, it is established that the salt starts to evaporate at ˜1273 K in Ar, and under reduced pressure. The salt removal efficiency in a 20 g sample was found to increase in both cases as a function of time and temperature. Moreover, in Ar the chlorine concentration was lowered to 0.3 wt% after heat treatment at 1523 K for 10 hours. Under reduced pressure, however, 0.2 wt% residual chlorine was obtained after 8 hours at 1473 K.IntroductionIt is believed that aluminum recycling in the near future will become the main route of aluminum production [1]. Black dross (BD) that is produced during this process contains, among other things, high amount of salts like NaCl and KCl [2, 3]. Almost 800,000 tons of BD is annually land filled in United States and this number continues to grow with the increase in aluminum recycling [2]. The BD should be dumped in controlled land field and it is costly procedure [4, 5].The water-soluble compounds in BD react with water or environmental humidity and release chlorides into the water and/or generate toxic gases such as H2, CH4, NH3 and H2 S [6-8]. In the Europe, BD is considered as toxic waste and its disposal as landfill is forbidden [8, 9]. After salt removal, the BD is considered to be non-hazardous and can be buried under ground [10].On the other hand, BD do also contains many relatively valuable compounds that may be changed in to useful materials as a result of further treatment [11, 12]"

Jan 1, 2012

By Jochen Petersen

Design and operation of heap leach processes are still largely based on,operator experience and rule of thumb. Although considered a low-cost, low-tech route for mineral extraction, the underlying physical, chemical and biological processes are actually rather complex. Numerous heap leach models have been devised over time, but the majority of these tend to simplify the true process and are of limited use in practise. The modelling approach presented here combines the more conventional reaction-diffusion model with models accounting for equilibrium reactions in solution, bacterial growth kinetics, complex reactions schemes, gas flow, heat conservation, etc. One particular model application is discussed in the context of developing a novel high temperature heap leach processes using thermophile micro-organisms. The complexity of processes such as this can only be appreciated with the aid of a systematic model. For the designing engineer an accessible, personal computer based model should be an indispensable tool for the design and optimisation of efficient heap leach operations.

Jan 1, 2002

By Kimio Itagaki

The distribution ratios of Ag, Pb, As, Sb and Bi for the Cu2S-FeS or Ni3S2-FeS matte / FeOx SiO2, FeOx-SiO2-CaO or FeOx-CaO slag equilibration in a MgO crucible were determined experimentally at 1523~1573K under controlled partial pressures of S2 and O2 at given PSO2 of 10.1, 50.7 and 101.3 kPa (0.1, 0.5 and 1 atm) and be observed dependency of distribution ratio on the matte grade, SO2 pressure and slag basicity were analyzed on the basis of thermodynamics,

Jan 1, 2003

By M. Okido, H. Yamamoto, T. Sakamoto, R. Ichino, K. Kuroda

"Hydrogen absorption alloy films have been produced by molten salt electrolysis. Lanthanum-Nickel alloy film can be formed on a nickel substrate in KCl-NaCl-LaCb molten salts by electrolysis diffusion process. LaNi5 alloy was formed by mutual diffusion between La ·and Ni after La deposition on Ni substrate. Though several kinds of La-Ni compound existed in deposits, the alloy compounds on Ni substrate changed by electrolysis condition. According to the open-circuit potential measurement in molten salts after La electrodeposition, the formed compounds had a relation to the potential. In the case of the substrate electroplated a cobalt thin film on nickel, LaNi4_5Co0.5 was formed by the electrolysis in the molten salts with lanthanum ions. This ternary alloy film showed better hydrogen absorption behavior in cyclic charge/discharge test in alkaline solution.IntroductionHydrogen storage alloys have attracted attention as the active materials for batteries with the charge/discharge property at ambient temperature. The alloy of nickel and misch metal, mainly consisting of La and Ce, has been commercially 'used as a metal hydride with rechargeable property. In recent years, researches have been developed many kind of new alloys with better hydrogen absorption properties. The hydrogen absorbing alloy ingots are commonly produced by melting method of both metals in furnace, otherwise, prepared by mechanical grinding and metallurgical sintering technique with metal powders. The film is also made by vapor-phase techniques such as sputtering method, ion plating method, etc. ·We have proposed a new method to produce hydrogen absorbing alloy films by molten salts electrolysis technique [1-3]. The hydrogen absorbing film, LaNi5, Mg2Ni and CaNi5, were obtained in this process through controlling the electrolytic condition. The active metals, La, Mg and Ca, are electrodeposited on Ni substrate, diffuse into the substrate and form various kinds of intermetallic compounds. This technique provides a direct process using metal chlorides as resources to produce functional films without using active metals such as La, Ca and Mg."

Jan 1, 2000