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By Jose F. Hevia

This study is part of a broader project on the hydrothermal conversion of copper concentrates to metallic copper by solid state reactions in which the copper remains localized in the solid phases. The kinetics of the solid/solid hydrothermal hydrogen reduction of tenorite (CuO) and cuprite (Cu,O) to metallic copper are presented. After an induction period, the process is governed initially by a nucleation step followed by rapid solid state reduction. Nucleation promoter agents decrease the induction period and control the particle morphology. Separate nucleation and reduction rate processes have been identified. Following nucleation, reduction follows a shrinking core process.

Jan 1, 1994

By Jintao Gao, Zhancheng Guo, Chong Li

A new approach to enrich MFe and RO phase from the converter slag by super gravity was investigated. The samples obtained by the gravity coefficient G=600 and cooling rate V=5K/min from 1623K to 1373K appeared significant stratification and the MFe gathered at the bottom of sample. With the help of metallographic microscopy and X-ray diffraction, it is found that large quantity of white RO phase gathered at the lower part of the sample as the concentrate, with volume fraction appearing gradient distribution along the direction of super gravity, while the upper part was mainly composed of dicalcium silicate as the tailing. The mass fractions of the FeO, MgO and MnO in the concentrate are up to 40.46%, 6.9% and 3.91%, while that in the tailing are just 11.65%, 2.15% and 1.55%. The recovery ratios of FeO, MgO and MnO in the concentrate are 60.35%, 58.45% and 72.24%, respectively.

Jan 1, 2016

By N. Gopalakrishnana, R. Beccard, S. Lourdudoss, R. Holz, M. Deschler

"Rapid growth of conducting and/or insulating InP, GaAs, Gao.47In0.53As, and GaAs0.6Po.4 on one or more of (001), (110), (111)A, (3ll)A and (3ll)B surfaces by Hydride Vapour Phase Epitaxy (HYPE) is demonstrated. The maximum growth rate of the binaries lies between 12 and 300 µm/hr and of the ternaries between 7 and 170 µm/hr. A simple model is developed to describe the influence of crystallographic orientation on temperature dependent growth rates. The growth rates predicted by the model is compared with the experimental values. Room temperature resistivity of insulating InP:Fe can be as high as 5xl09 ohm cm. Temperature dependent differential resistivity is also analysed. This feasibility of growing conducting and insulating layers rapidly on different orientations is very useful for electronic and optoelectronic devices.IntroductionRecently there is a renewed demand for very thick layers of III-V compound semiconductors for high performance electronic and optoelectronic devices [1]-[2]. Long wavelength high speed lasers that can be modulated up to 30 GHz necessitate epitaxial growth of semi-insulating (SI) layers [3]. There is also an increased interest on the growth of epitaxial layers on surfaces other than (001) surface. Epitaxial growth of these materials on such surfaces is of theoretical importance besides being technologically relevant. These demands led us to focus on the growth of conducting and insulating III-V compounds by Hydride Vapour Phase Epitaxy (HYPE). lnP, GaAs, Gao.471no.s3As on lnP and GaAso.6Po.4 on GaAs were grown as conducting materials using Low Pressure HYPE (LP-HYPE) on (001) 2° off substrates. Gao511no.49P on (001) GaAs substrate and lnP on lnP substrates of (001), (110), (l 11)A, (31l)A and (3 ll)B orientations were grown as semi-insulating materials using Atmospheric Pressure HYPE (AP-HYPE). In this report we present the growth aspects of these materials. We also present a simple model on the growth of InP on substrates of various orientations. The theoretically obtained temperature dependent growth rates are compared with the experimental values. Differential resistivities of semi-insulating lnP grown on substrates of various orientations as a function of temperature are also summarised."

Jan 1, 1998

By Olexandr Gydin

The evolution of grain and dislocation structures during cold deformation of the new steel LH800 of Salzgitter AG is investigated in the frame of this work. The main feature of this material is its ability to air-harden by carbon content of about 0.1%. The initial ferrite structure of the metal provides high plasticity at cold deformation and subsequent heat treatment increases tensile strength approximately two times. Described are results of in-situ tensile tests in the SEM. SEM and TEM analysis of grain and dislocation structures evolution in samples, which have been uniaxially deformed to certain strains, are carried out. After statistical evaluation of results the grain elongation against strain is determined. A microstructure of a deep drawn cup is analyzed by means of SEM. A quantitative evaluation of grain elongation on the different cup zones and comparison of these data with prediction results based on tensile tests are carried out.

Jan 1, 2009

By Shengli Wu, Jinming Zhu, Wei Huang, Xinliang Liu

The sinter of high basicity would interact with lump ores or acid pellets in the cohesive zone of blast furnace due to the difference of chemical composition and micro structures. The results of this work showed that the softening-melting properties of lump ores and acid pellet would be obviously improved by the high temperature interaction. However, the high temperature interaction index (INI) would be influenced by many factors, such as chemical composition, porosity, interaction interface and so on. The INI between sinter and porous limonite lump ore (L-2) was much higher than that of dense hematite lump ore (L-1) and acid pellet (P-1). In addition, though the softening and melting properties of L-2 were poorest in respective iron ores, the softening and melting properties of integrated burden B (consist of sinter and L-2) were not worse than other integrated burdens due to the strong high temperature interaction.

Jan 1, 2015

By Niloy K. Nath

Two layer sintering by charging green sinter mix with normal coke rate in the upper layer and reduced coke rate in the lower layer, can substantially reduce the coke rate and also improve the sinter quality by producing more uniform thermal profile through out the bed height. The two-layer sintering process have been analyzed by numerical simulation of the process by a detailed CFD based model, considering all the important phenomena like gas-solid reaction, melting and solidification, flow through porous bed, heat and mass transfer etc. Optimization techniques like genetic algorithm, differential evolution is then applied to evaluate the optimum coke rate in the two layers of the bed to produce the ideal thermal profile and melting fraction in the sinter bed for optimum sinter quality. Through this optimization method both high quality sinter with minimum return fines can be achieved along with reduced coke rate. Application of a genetic algorithm for this type of process optimization has several advantages over the traditional optimization techniques since it can identify global optimum condition and perform multi-objective optimization much easily for complex industrial process like iron ore sintering. Keywords: Two-layer Sintering, Iron Ore Sinter Quality, Ergun's Equation, Gas-solid reaction, Melting Fraction, Multi Objective Optimization, Pareto Set, Genetic Algorithm

Jan 1, 2003

By K. Nona C. Liddell

There is a significant amount of early work that has been largely forgotten that deals with the validity of the pseudo-steady approximation for liquid-solid reactions. Much of this was originally published in the chemical engineering literature but is highly relevant to hydrometallurgical processes. The purpose of this paper is to summarize some criteria that were been developed by various authors for determining the error associated with use of shrinking core models for liquid-solid systems.

Jan 1, 2002

By Xuefeng She, Qingguo Xue, Jingsong Wang, Guang Wang

Iron nugget could be got at high temperature using carbon composite pellet, which were made by the mixture of ludwigite and reducing agent. In order to reduce sulfur content in the nugget, effects of additives on the desulfurization was investigated. The sulfur content could be dramatically reduced if the CaO was introduced into the pellet and the sulfur content was as low as 0.046wt.% when the addition amount of CaO was 5wt.%. However, the melting separation of pellet became increasingly difficult and the yield of iron decreased when CaO content in the pellet gradually increased. Na2CO3 could also reduce the sulfur content in the iron nugget and made the iron and slag separate difficultly as well. When 6wt.% Na2CO3 was added into the pellet, the pellet was too difficult to melt separation and the sulfur content in the nugget was 0.084wt.%, which didn’t meet the need of steel making.

Jan 1, 2015

By Tengfei Qi, Liqiang Fan, Huiqing Tang

A new method to process the oolitic high phosphorus iron ore for phosphorus removal has been proposed in this research. It is an integration of direct reduction and melting separation with carbon-containing pellets prepared using biomass char. Experiments of direct reduction were preceded using a tubular furnace and three parameters were investigated and they were reduction temperature, biomass char adding ratio(molar ratio of carbon to oxygen） and atmosphere. Results show that the optimum condition is of reduction temperature is 1373 K, biomass adding ratio 0.9, PCO2/PCO 1.0 and reduction time 15~25 min. Under this condition, the reduced briquettes with a metallization of 75.0~80.0 % and a residual carbon content of 0.69~0.11 wt% could be obtained. Subsequent melting separation experiments were conducted using a Si-Mo high temperature furnace. Results show metal with phosphorus content of about 0.4 mass% could be obtained from the reduced sample.

Jan 1, 2015

By J. S. Lee

A new high performance adsorbent is synthesized by the sol-gel method and applied to the removal of cadmium and mercury ions from aqueous solutions. Adsorbents based on metal oxides have been developed by immobilizing chelating molecules on the surface of the existing metal oxide networks and show ability for selective metal extraction from aqueous solutions. However, efficiencies of such adsorbents are limited due to low ligand density, and difficulty in pore accessibility. These difficulties are circumvented by synthesizing adsorbents using the sol-gel technique. In one example to be discussed, the sol-precursor possesses an organic moiety that binds cadmium, mercury, and copper ions. The capacities of 1.98mmol Cd(II-/gm and 6.40 mmol Hg/gm of this adsorbent are considerably higher than those of adsorbents prepared by the ligand immobilization technique. The scope of this paper is to discuss the development of the new adsorbent and its applications for cadmium and mercury removal from aqueous solutions.

Jan 1, 1999

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

By John W. Lund

The Geo-Heat Center has been investigating the utilization of waste silica from the Cerro Prieto geothermal field for several years. The main objectives of the research were to com-bine silica with various additives to (1) form bricks for low cost housing, and (2) to produce a suitable road surfacing material. The various additives that were tested included hydrated lime, portland cement, plastic fibers, asphalt cement and emulsified asphalt. The silica-cement combination produced the strongest bricks and had the best weather resistance, whereas, the silica-lime combination produced the bricks with the lowest thermal conductivity and specific gravity density. The addition of plastic fibers to the silica-lime mixture improved both strength and weather resistance. The combination of asphalt and silica is not suitable as a road surfacing material, however, silica-cement appears promising.

Jan 1, 2006

By J. W. Matousek

Cobalt behavior in pyrometallurgical processes is traditionally analyzed using slaglmatte distribution coefficients as functions of matte grades or matte iron contents. L(s/m) = (%Co) I [%Co] = f [%CuNi] or f [%Fe] The method is inconvenient to use in predictive mass balance work because of the interdependence of assays and mass quantities. An alternative procedure is proposed based on cobaltliron ratios for slags and mattes: Js = (%Co) / (%Fe), Jm = [%Co] / [%Fe], and J, = b + m [Jm]

Jan 1, 1993

By Nagy El-Kaddah

"One of the emerging technologies for the production of ultra-clean metals is electromagnetic filtration. The theory and the mechanism of electromagnetic separation of inclusions from molten metal are briefly reviewed along with basic electromagnetic separation systems. This paper focuses on inclusion removal in the induced current separators, with specific reference to a new separator developed at the University of Alabama. A simple analytical model is presented for the analysis of particle separation in such a system. The role of the applied magnetic field on inclusion removal will be discussed. It is shown that particle velocity increases exponentially with increasing magnetic field strength. At moderate field strengths, the velocity of 50 to 100 u. inclusions· are an order of magnitude larger than those achieved by buoyancy. The separator developed at the University of Alabama is described together with experimental results of laboratory and large scale experiments on purification of molten aluminum. These results demonstrate the capability of the system for producing super-clean metals.IntroductionThe nature of extraction, refining and processing of metals is such that oxides and other non-metallic particles will always be present. This is due to the highly reactive nature of metals with oxygen and other non-metallic elements. The presence of these type inclusions in metals, even in minute amounts, can seriously flaw the reliability and performance of the final product. They not only reduce the strength and the stiffness of the metal/1/, they are the reason behind many of manufacturing defects such as porosity in castings, surface and internal cracks in continuously cast ingots and rolled products, etc., which act to cause premature failure of manufactured parts. In fact, for critical applications such as turbine blades, there is virtually no tolerance for inclusions above ten microns in size /2/. Therefore, removal of inclusions from the liquid metal is an essential processing step.The demand for cleaner metals has brought major changes in the technology and practice of metal refining and casting. Inclusion removal from the melt is currently achieved by passing the melt through a series of melt treatment systems, including induction stirring furnaces, argon-stirred ladle, and ceramic foam and deep-bed filters /3,4/. These systems are generally capable of removing all inclusion particles above 50 microns in diameter, which meets current cleanliness requirements for most applications. However, they may not be able to meet the projected cleanliness levels for critical applications due to kinetic and operational limitations of these systems in removing smaller particles /5/."

Jan 1, 1996

By S. Yuan

Oxygen ion conducting yttria-stabilized zirconia (YSZ) tube was used to remove oxygen from molten Cu at 1373K. Outer surface of the tube was in contact with the melt and the inner surface containing a thin layer of porous Ni-ZrO2 cermet electrode was in contact with a reducing gas. The migration of oxygen species (O2-) from the Cu melt through the YSZ tube is accompanied by an equal and opposite flux of electrons maintaining electroneutrality. Without applying an external EMF, the fluxes are maximized by short circuiting the melt with the cermet electrode. For efficient oxygen removal, the YSZ tube must be thin, contact resistances should be negligible, and the electrodes must be porous and cover the entire electrolyte surface for charge transfer. This refining process is environmentally sound, can use reducing gases such as H2, CH4 and CO without running the risk of increasing H or C content of the melt.

Jan 1, 1993

By Ernt. W. D.

A membrane based mixed extractant process was developed for selective removal of copper from waste acidic cupric chloride etchant solutions found in printed wire board manufacturing. The process uses a mixture of Adogen 381 (tri-isooctylamine), MOC®-45 (ketoxime) and MOC® 55TD (aldoxime) in a kerosene diluent. The mixed extractants recover the copper from a hydrochloric acid medium and transfers it to a sulfuric acid medium. The process also utilizes unique wetted membranes to separate the aqueous and organic phases. The driving force for these membranes is not pressure but the difference in surface tension between the two phases. By using these membranes, complete phase separation results. There is no physical entrainment contamination as found in conventional systems. The only cross contamination is the solubility concentration of one phase in the other. This however is less than 10 mg/l.

Jan 1, 1998

By S. Gopalan, J. D. Milshtein, S. N. Basu

Production of syngas is proposed utilizing the W/W03 redox system and employing a solarpowered two-step thermochemical cycle. Three chemical reactions occur in two chambers. Assisted by a solar concentrator, a high temperature reaction reduces W03 powder to metallic tungsten in both chambers. Subsequently, the temperature in one of the chambers is lowered and H2(g) is produced via re-oxidation of the tungsten powder using steam. The temperature in the other chamber is simultaneously lowered to an intermediate temperature and CO(g) is produced via oxidation of the tungsten powder using C02(g)· The gas streams coming out of the two chambers result in the syngas production. A complete thermodynamic analysis of the system is described. The W/W03 redox cycle offers greater gravimetric fuel productivity compared to previously proposed systems, and the entire cycle can be operated below 1273K.

Jan 1, 2013

By P. Maraboutis

Iron removal by precipitation as jarosite from Fe-Ni-Co sulfate solutions, (synthetic or real, resulting from laterites leaching) has been investigated. Precipitation was carried out at 95 C, and at an initial pH 1.6, which was either kept constant with CaCO3 or Li2CO3 additions, or left to drift with the evolution of the reaction to lower values. The precipitation of K-, NH4- and Na- jarosite was initially examined using synthetic solutions. In all cases, hydronium ions were incorporated into the precipitate as well. Residual iron in solution was lower (0.2-1 g/1) and equilibrium was achieved faster (within 4-8 h) when precipitating K¬jarosite at constant pH, using CaCO3 for neutralization. Nickel and cobalt losses were small. Na- jarosite precipitation was also studied from real solutions with high initial iron content, under constant pH=1.5, controlled with CaCO3 additions, and it was shown that low residual iron concentration in solution (0.3-0.5 g/1) can be achieved again, with relatively small nickel and cobalt losses. The thickening and filtration characteristics of the precipitates were excellent in all cases examined.

Jan 1, 1988

By T. -M. Guo, M. J. Braun

"This paper presents an experimental and numerical study of melt flow near the solid-liquid interface and its effect on the interface curvature in a horizontal unidirectional solidification system with succinonitrile. Melt flow is introduced by increasing the ampoule channel thickness. Visualization techniques are employed to observe the flow field and the solid-liquid interface curvature. A numerical model is also developed to simulate the heat transfer, melt flow and phase change in the system. Quantitative information on the flow and temperature fields is generated. A good agreement is achieved between the experimental observations and model predictions. The results could be used for the study of the effect of the melt flow on interface morphology during solidification.IntroductionClassic unidirectional solidification experiments of transparent alloys are conducted with thin film samples sandwiched between two glass slides to investigate the development of interface morphology during solidification [1]. Samples with small channel thickness are usually used to suppress any melt flow due to natural convection and solidification in the channel would then be in the diffusive regime so that the solidification theory can be significantly simplified [2, 3]. Effects of melt flow, in particular due to natural convection, on solidification have also been studied extensively in those systems with large geometrical dimensions [4-6]. These studies indicate a strong effect of the melt flow on interface curvature during solidification [5, 6]. Only limited efforts were made to address the effect of the melt flow on interface morphology in horizontal unidirectional solidification, in particular for the cases when the channel thickness is not thin enough to suppress completely the natural convection [7]."

Jan 1, 2004

By David B. Dreisinger

Mass and heat balance modeling is a powerful tool for the design and analysis of hydrometallurgical process flowsheets. In this first of two papers, we examine the basic fundamentals of mass and heat balance modeling, and apply these concepts to several flowsheets using a simple spreadsheet model. In this way, we aim to demonstrate how such models are not only easy to construct, but can also be indispensable for comparing various flowsheet alternatives, for making rational economic decisions, and for developing a basic understanding of existing process behaviour.

Jan 1, 2002