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Pyrometallmurgical reactors constitute a key processing component in the total primary and secondary resource cycle, being involved both in primary smelting, converting and extraction, as well as the reprocessing of scrap, from aluminum cans to end-of-life automobiles. To effectively control the overall resource cycle, one needs to take a systems modeling approach of the whole cycle, seeking to also understand the dynamic process behavior of the individual components of the cycle, and then especially the part that contributes most to the chemical conversion, namely the pyrometallurgical reactor. This paper highlights the role of pyrometallurgical thermodynamics, in the whole resource cycle and specifically places equilibrium thermochemistry in the context of process dynamics where large variable inventories are recycled or maintained within the system. This paper will therefore review the semi-empirical dynamic modeling tools, which are used to model complex systems with the specific goal of developing dynamic predictive models, which also include slag-alloy chemistry, towards controlling the recycling in a feed forward manner. To illustrate the primary processing side, high carbon ferrochrome will be presented as a brief case study. It also will show how the distributed nature of the chemistry of melts in the case of primary extraction, and secondary materials such as recycled end-of-life vehicles, have a significant impact on the process outcomes and model predictions. It is therefore argued that the fundamental thermodynamics and kinetics in metallurgical reactors playa final crucial role in modeling the closed material cycle, but only when it is used in conjunction with process systems theory based on reconciled data for parameter estimation and model calibration.

Jan 1, 2003

By A. Siegmund, R. D. Prengaman

Lead anodes used in zinc electrowinning generally contain 0.5 - 1.0 % silver to reduce the rate of corrosion over the service life. For good quality zinc, the cathodes must contain less than 10 ppm lead. In order to reduce the lead contamination of the cathode, the lead anode must become coated with a protective layer of Pb02/Mn02. The formation of this layer may take as long as 30 - 60 days, during which time zinc production is substantially reduced and the cathodes are contaminated with lead. To improve the mechanical properties of Pb-Ag-anodes alloying elements such as calcium, strontium, barium and others are added. The production of cast lead-silver or lead-silver-calcium anodes often results in the formation of numerous holes, voids or laps in the anode surface that can initiate localized internal corrosion. Based on the experience as the major supplier of rolled anodes for copper electrowinning, RSR Technologies has developed an improved anode for zinc electrowinning. The anode consists of a rolled Pb- Ag-Ca-alloy with a controlled surface grain structure. It forms an adherent protective oxide coating within 2 - 3 days when placed in an electrowinning cell. The preferred calcium and silver contents of the alloy are 0.03 - 0.08 % and 0.3 - 0.4%, respectively. Rolling sheets significantly reduces the presence of internal porosity or laps. The lack of defects results in long anode life. The rolling also produces a uniform grain structure to which the corrosion product readily adheres, thus significantly reducing the conditioning period.

Jan 1, 2000

By T. S. Piwonka

Modeling the solidification of shaped castings has progressed beyond the initial problem of determining the correct heat and fluid flow relationships which describe the solidifying castings. Today the challenge is to describe second order effects which determine the ultimate quality of the casting. The challenges to the modeling community posed by the needs of today's foundries for models that work are discussed, with some examples of current modeling problems.

Jan 1, 1992

By Lei Wang, Xiancong Zhao, Hongxu Li, Lifeng Zhang

Recovery of Fe from red mud has been studied using statistically designed experiments. The effects of three factors, namely: reduction temperature, reduction time and proportion of additive on recovery of Fe have been investigated. Experiments have been carried out using orthogonal central composite design and factorial design methods. A model has been obtained through variance analysis at 92.5% confidence level.

Jan 1, 2015

By Cong Wang, Kexin Jiao, Yongan Zhao, Haibin Zuo, Jianliang Zhang

The carbon composite brick is a new refractory used in blast furnace hearth and bottom. It caused wide attention due to its high thermal conductivity and low erosion by molten iron. In this paper, chemical constituents, SEM-EDS and X-ray diffraction were carried out in order to understand reaction mechanisms. A series of experiments of oxidation resistance characteristics were made. The oxidation mechanisms of carbon composite bricks in the presence of air were analyzed. According to the analysis on many experimental results, the oxidation process of carbon composite bricks under different temperatures were controlled by different mechanisms. In the condition of high temperature, SiO2 as oxidation product hindered the diffusion of O2, and reduced the oxidation loss of graphite in the internal.

Jan 1, 2015

By Judy Che, Steven Ceccio, Gretar Tryggvason

"A detailed understanding of drop deformation and solidification is essential for quantitative predictions of geometry and properties of parts made by ballistic particle manufacturing processes. Axisymmetric results of towers built by the deposition of multiple drops are presented. In these computations, fluid flow, heat transfer, and phase change are fully coupled throughout the drop deformation and solidification process. The solution method is based on a single set of conservation equations written for all phases simultaneously. The phase boundaries are treated as imbedded interfaces by adding the appropriate source terms to the conservation equations. A parameter study demonstrates the effect of Weber number, Peclet number, and drop deposition frequency on the final shape of the structure. Numerical results show that most successful method of building uniform towers is when two conditions are met. First, each drop solidifies at the same time in the deformation cycle. Second, the cooling rate is slow enough to allow for good adhesion between drops. The ability to predict the final shape of deposited drops will greatly reduce the amount of experimentation necessary to select the desired set parameters for any artifact.IntroductionMaterial deposition techniques based on layering small molten metal drops holds the promise to build small, coherent three-dimensional structures. In this process, numerous 20-100 µm diameter drops are deposited onto a substrate with a low impact velocity (on the order of 5 mis). Both the momentum and trajectory of each drop are controlled precisely to build up complex parts. This material layering technique differs from processes such as spray forming and splat quenching which involve high impact velocities (on the order of 100 mis) and high frequency deposition with little control over individual drop placement. This process of layering small drops can produce parts with near net shape accuracy, while spray forming produces slabs of material which must then be worked to make a usable part. The ability to computationally predict final drop shape and cooling rate has the advantage of allowing the user to select parameters to produce parts with desired shape and mechanical properties. However, the development of such predictive methods requires a thorough understanding of both drop deformation and solidification"

Jan 1, 1999

By E. Gutierrez-Miravete

Hot pressing processes are widely used to shape metallic, ceramic, and glass components. The process is an essential step in manufacturing ceramic fibre-glass matrix composites. The paper describes the use of computer simulation by the particle method, to the analysis of the deformation and flow of glass during hot pressing. The hot glass is represented by an assembly of interacting particles which deform in response to the applied pressure. The results, which should be regarded as complementary to continuum-based studies, provide useful insight about the hot pressing process.

Jan 1, 1990

By Bo Zhou

During secondary aluminum recovery, complex aluminum scraps are melted and refined often in a rotary melting furnace and the aluminum metal has to pass through a molten salt layer and melt down in a bottom aluminum bath. Previous experimental study and industrial observations have indicated that salt shell formation and re-melting on the metal solids in the early stage plays a critical role in the overall melting process of the scrap. In the present paper, mathematical models are developed to simulate the process of salt shell formation and its re-melting, as well as aluminum melting in the molten melt. Influence of the salt layer properties, the residence time of the metal particles in the salt layer, the particle size, the temperature of bulk melt were investigated. Reasonable agreement with the measurement data was reached. The developed melting model will be used to construct a population balance model of the scrap melting behavior for a rotary melting furnace, taking into account the distributed characteristics of the scrap. Finally, an overall process model based on Computational Fluid Dynamics (CFD) for the rotary furnace will be constructed, coupling with the population balance model for the scrap melting.

Jan 1, 2003

By Shan He, Qiang Wang, Xuling Chen, Min Gan, Lishun Yuan, Xiaohui Fan

"The sintering properties of vanadium-titanium magnetite concentrate(VTC) was studied in this paper. Through the optimizing the sintering process of VTC, the suitable granulation moisture and coke proportion were determined. The sintering velocity decreased from 23.05 mm/min to 18.22 mm/min. With the increase of VTC proportion from 0 to 46%, the specific productivity and tumbler index were respectively decreased from 1.55 t/(m2·h) to 1.21 t/(m2·h), and 62.93% to 57.73%. The temperature of liquid phase formations of mixtures increased, the amount of liquid lowered, and the content and sharp of sintering mineral gradually changed with the increase of VTC ,these lead that sinter quality became worse.IntroductionIn recent years, the steel industry of China is developing rapidly. And the steel production was 627 million tons in 2010. At present, the resources of vanadium-titanium magnetite concentrate(VTC) was about 14.4% of the total national iron reserves of China[1]. VTC has been used as sintering material by Magang, Chenggang and Pangang. The amount of VTC in Pangang is maximum. However, there exist many problems in VTC sintering, which involve in high specific productivity, bad sintering tumbler strength and high energy consumption[2~5]. That’s why the proportion of VTC is limited in sintering.The high quality of iron ore resources is worse in China. Therefore, it’s necessary to study the properties of VTC sintering, and to find out the reason how the VTC ratio affect the sinter performance. Purpose and significance of the research is to get high-quality sinter with the proportion of VTC greatly raised."

Jan 1, 2012

By Gervais Soucy

During mineral and industrial processing, contaminated wastewater can be generated such as cyanide liquors (free species or in complex form). This paper presents the treatment of cyanide solution derived from the aluminum industry, by direct contact of the solution with thermal plasma in a novel reactor. The reacation energy is provided by a plasma submerged in solution which allows direct contact between the plasma and the solution to be treated. The scope of this' study was to determine the feasibility of treating free and complex cyanides in solution through mini-pilot scale operations. An innovative reactor was designed and fabricated to provide stable: process operating conditions. Many parameters were studied. These experiments permitted the evaluation of the kinetics of complex cyanides decomposition under thermal plasma conditions. At atmospheric pressure (temperature about 100°C), the rate of cyanide decomposition by thermal plasma was 12 times greater than that of thermal hydrolysis in a plug flow reactor et the same temperature. The improvements in the decomposition rates are attributed to high thermal gradients at the plasma liquid interface and photocatalysis induced by the plasma UV radiation.

Jan 1, 1998

By Orion Ciftja, Arjan Ciftja

"The directional solidification method is routinely used to produce polycrystalline silicon, an important material for the photovoltaic (PV) industry. The form of the solid-liquid interface during solidification has considerable influence on the material quality. The dissolved impurities and the solid inclusions above the solidification front affect the interface and may cause interface breakdown. We investigate the effects of pushing and engulfment of silicon carbide (SiC) particles by the solidification front during directional solidification of silicon. We employ a 12kg directional-crystallization furnace to cast the molten silicon. We use upgraded metallurgical grade silicon with low concentrations of metallic impurities (< 5ppm) and a high content of carbon (700 ppm) present as SiC particles. Samples from the cast polycrystalline silicon ingots are investigated by light microscope. The expected interaction of impurities with the solidification front is investigated theoretically using empirical models. The data obtained from the models are in good agreement with the experimental results.IntroductionDirectional solidification is a well-known method for producing multi-crystalline silicon for the PV industry. In this method a planar front, achieved during solidification, results in a clearly defined interface between the solid and the liquid phase. The solubility of major impurities is higher in the liquid than in the solid phase. Therefore, directional solidification will work as a purification process where the impurities are retained in the liquid phase [1]. Apart from the process of removing the dissolved elements in molten silicon, the directional solidification plays also another role. It will interact with the solid particles that may be present in the melt. When a liquid containing an insoluble particle is solidified, three distinct interaction phenomena are observed: engulfment of particles, continuous pushing, and entrapment [2]. The term “engulfment” is used to describe incorporation of a particle by a planar interface, and the term “entrapment” is used for particle incorporation by a cellular or dendritic interface (see Figure 1) [3]."

Jan 1, 2014

By I. Kim, J. C. Choi, W. D. Cho

"The effect of yttrium addition on the oxidation behavior of Fe3Al intermetallic compound was investigated in the range of temperature 800 to 1100 °C in 0.2 atm 02 in terms of oxidation rate and oxide adhesion. The oxidation rate of alloys, Fe-14.3 wt% Al and Fe-14.1 wt% Al-0.3 wt% Y, was nearly identical and the parabolic rate constant calculated as a function of temperature is Kp=5128 exp[-39506(cal/mol)/RT] mg2/cm4 hr.Rapid cooling and ultrasonic stress tests were carried out to test adhesion of scale formed on the alloys. While the oxide layer formed on the Fe-Al alloy without Y was found to be fragile and detached easily during the tests, the oxide layer formed on the Fe-Al alloy containing Y was protective, dense, and adhesive. The following two mechanisms were proposed to explain the adhesion improvement of Ah03 formed on the Fe3Al containing yttrium : (1) the addition of yttrium decrease generation of growth stress in alumina scale because the preferential diffusion of yttrium through grain boundary in alumina scale prevent internal oxidation of Al, one of main causes of growth stress, and (2) the second phase formed on the oxide scales prevents crack propagation through the scales, leading to better mechanical stability of the oxide scales.IntroductionIron aluminides have attracted the attention of many researchers as a candidate for use at high temperature because of their excellent oxidation resistance due to the formation of protective alumina scale. In order to resist aggressive environments at elevated temperatures, oxide scale formed on iron-uluminum alloy must satisfy the following three requirements : (1) thermodynamic stability (2) slow growth rate (3) adherence on substrate. According to Wallwork and Hed [l], the most suitable alloys for high temperature application are Fe, Ni, and Co alloys with the protection of Si02, Cr203, and Ah03 scales. While chromium oxide can vaporize as Cr03 above 1000 °C and silicon oxide may form low melting silicate [2,3], Alz03 has a high melting point and is the most stable among the three oxides thermodynamically [6]. In this respect, iron aluminides forming alumina seem to be most suitable for use at high temperature. However, alumina scale formed on the iron aluminum alloys tends to be easily spalled during oxidation due to the combination of growth stress and thermal stress."

Jan 1, 1998

By Takashi Miyamoto, Hideo Nakae, Hideki Yamaura, Takeshi Yanagihara

"For the production of partially composed metal matrix composites, namely discontinuous MMCs, using a casting· process, the interpenetrated phase composites with SiC particles were fabricated by pressureless iDfiltration using molten Al-Si alloys. This process is based on a wetting phenomenon, therefore, we discussed the technique based on the reactive wetting. The SiC particles coated by diluted water glass were sintered in a mullite Tammann tube and simultaneously infiltrated with molten Al-Si alloys in air at 1173~1573K. As for the improvement of the wettability between the SiC and the liquid aluminum alloy, Fe3O 4 powder was mixed with the water glass due to the thermit reaction between Fe3O4 and molten aluminum alloy. In some experiments, pure aluminum powder was placed on the sintered SiC to increase the interfacial area and the chemical reaction between the sintered Sic. and the melt. By combining these conditions, we succeeded in the complete infiltration without pressure at 1173K.IntroductionAs is well known, the mechanical properties of metal matrix composites (abbreviated MMCs) are superior than that of ordinary metals. However, their use has not been widely accepted because the production cost is very high due to their poor machinability. Therefore, the production of partially composed, namely discontinuous MMCs, by as the Lanxide process [l,2] has been investigated for many years. The Lanxide process, it takes a long time, sometimes up to 10h, in a nitrogen atmosphere for the infiltration. Therefore, the cost will be higher for common use. On the other hand, a high 'pressure process has been adopted for the production of discontinuous MMCs by the Toyota Motor Corp.[3]."

Jan 1, 2000

By Sung Wng Kim

The binary antimonide compounds with the skutterudite structure have a potential for thermoelectric applications because of the high carrier mobility, high thermoelectric power, and relatively low thermal conductivity due to the complex crystal structure. However, the room temperature thermal conductivity of these skutterudite materials is as high as about IOW/mK with an estimated 80-90% contribution from the lattice thermal conductivity. Because the lattice thermal conductivity of related ternary skutterudite compounds can be substantially reduced due to the additional phonon scattering, a study of thermoelectric properties of these compounds is of interest. The binary IrSb3, ternary Ir1.xRuxSb3 and Ir(MxSb1.x)3(M=Ge, Sn) compounds were prepared by hot pressing of pre-reacted powders. We have measured the electrical resistivity, thermoelectric power, and thermal conductivity, in a temperature range from room temperature to 973K. The binary IrSb3 compound is found to have P-type electrical properties exhibiting a good Seebeck coefficient (up to 225µV/K around 773K), electrical resistivity(5x10-5Ohm M around 933K), and relatively low thermal conductivity(6W/mK around 950K). The lattice thermal conductivity, K[2] was calculated from the Wiedemann-Franz relationship.

Jan 1, 2002

By C. O. Bounds

The performance of AB5-type alloys for hydrogen absorption including the electrochemical absorption as an electrode for rechargeable batteries has been demonstrated&apos; to be a complex function of the composition, microstructure and surface condition. The compositional studies have focused primarily on substitutions for Ni on the B-site (e.g. Co, Al, Mn, etc.). This current study examines the effect of rare earth substitutions for La on the A-site and considers both other "light" rare earths (Ce, Nd, Pr) and "heavy" rare earths (Dy, Sm, etc.).

Jan 1, 1997

By James D. Navratil

Although liquid membranes have several advantages over conventional liquid-liquid extraction, problems such as membrane instability remain. In order to solve these problems, we have combined an electrostatic field with the principle of liquid membranes and developed a novel reactor system for rare earth recovery. Our cylindrical reactor, filled with extractant and diluent, is divided by means of a perforated cylinder into an outer annular extraction cell and an inner stripping cell. Below the extraction and stripping cells are two settlers for the aqueous solutions. The design of the reactor permits the organic solution to flow freely through the special perforated cylinder and the added feed and strip solutions, outside and inside the perforation, respectively, to be completely separated.

Jan 1, 1990

By D. Pradhan, R. G. Reddy

"Electrorefining of aluminum scrap was investigated from AlCl3 –1-Ethyl-3-methyl-imidazolium chloride (EMIC) (Molar ratio 1.65) chloroaluminate electrolyte using copper cathodes at temperature of 90±3°C and cell voltage of 1.5 V. The deposits were characterized using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The study was focused to determine the effect of electrode surface modification as well as deposition time on dendritic depositions of aluminum. Their effect on current density was investigated also. It was shown that the surface modification of electrodes reduced the dendritic depositions of aluminum. Pure aluminum (>99%) was deposited for all experiments with the current efficiency of 94-97%. The use of ionic liquids not only reduced the energy consumption but also minimized pollutant emissions (CO, CO2 etc.) compared to the commercial high temperature aluminum production.1. IntroductionAluminum electrorefining/recycling from aluminum scrap using ionic liquid electrolyte is an attractive process today because of the unique chemical and physical properties such as wide temperature range for the liquid phase, high thermal stability, negligible vapor pressure, low melting point and wide electrochemical window. But in conventional practice, melting of aluminum scrap and high temperature molten salt electrolysis makes this process more expensive and less energy intensive (average 13 kWh/ kilogram of aluminum) [1] . Although recycling scrap aluminum requires only 5% of the energy used to make new aluminum [1-2], but the green house emissions like CO2, CO and HF have to be counted for environmental reason. Approximately, 5.31 kilogram of CO2 emitted per kilogram of aluminum production in most of the US industries."

Jan 1, 2009

By J. M. Tourre

Recently, interest in rare earth based oxide powders for electronic applications has risen dramatically. Considerable research has been devoted to the chemical synthesis of these compounds to improve the control of physical and chemical characteristics of the powder. In most cases, a high degree of homogeneity, purity and reproducibility is necessary in order to obtain good application properties. The synthesis parameters can control particle size, surface area, and morphology as well as the degree of homogeneity and application properties. Rhone-Poulenc, a world leader in the production of separated Rare Earth chemicals has developed a flexible process to produce a wide variety of compounds. The different processes for the synthesis of YBa 2Cu 3 O 7 will be discussed and compared to the RP process in term of product quality, cost and flexibility.

Jan 1, 1992

By I. U. Onyenanu, C. E. Ilochonwu, E. I. Nwonye, C. O. Nwajagu

This work shows how pure silica was derived directly from rice husks ash (RHA) in different temperatures for reduction to Silicon (Si). The processes to form Si materials are usually complex, costly and energy-intensive. The silica in the ash undergoes structural transformations depending on the conditions of combustion. A high purity silica was produced at 650oC after burning the rice husk (RH) for up to 7 hours. The purity of the silica was determined by dissolving the RHA with alkali solution to form sodium silicate solution of pH 11.0. This was added to hydrochloric acid of pH 1.5 which lowered the pH of the solution to 4.0 to form silica gels. The silica gels produced were washed and dried to powder and then characterized using XRD and EDX techniques. This study was done to reduce energy waste and environmental pollution in Nigeria as silica is used to develop many materials.

Jan 1, 2015

By Laurentiu Nastac

"This paper describes the development and validation of a comprehensive multiscale modeling approach capable of predicting at the mesoscopic scale level the ingot solidification structure and solidification-related defects commonly occurring during the vacuum arc remelting (VAR) process. The approach consists of a coupling between a fully transient macroscopic code and a mesoscopic solidification structure code. The predictions from the multiscale model, including grain morphology and size, primary and secondary dendrite arm spacings, Laves and NbC phases, tendency for freckling and columnar-to-equiaxed transition, were validated against experimental measurements for a 20-inch diameter VAR alloy 718 ingots. The validated model was then used to investigate the effects of melting rate and ingot diameter on the solidification structure of VAR processed 718 ingots.IntroductionThe objective of this work was to develop a fully transient multiscale modeling approach to get an insight into the effect of processing parameters on the cast micro- and macro-structure during VAR processing. The developed model assists in achieving better control of the ingot solidification structure and to determine trends in the macrosegregation in these ingots. Another objective of this work was to analyze the transient effects of production rate and ingot size on the resultant ingot microstructures. This objective was met by first understanding the effects of the full range of processing parameters typically used in the VAR process. Processing parameters such as power input and heat extraction rate significantly influence the ingot liquid pool size and shape as well as the ingot structure, which in turn will greatly impacts the final ingot quality."

Jan 1, 2012