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By Thomas Schemmel, Bertram Kesseiheim, Helge Jansen, Uwe Kreme

"During the last decades the refractory life time of the different aggregates of the secondary aluminium production was improved significantly. However, each repair and installation of refractory material affects the operating schedule and can cause costs in the million range. The downtime of just one melting furnace generate costs of 100.000 to 400.000 $ per day. Besides cooling down of the furnace and its repair, the heating-up procedure accounts for the longest time of the shutdown. Usually, heating-up of low cement or ultra low cement castables takes 120 to 150 hours. In order to reduce such expensive downtimes Refratechnik developed a unique and novel product series: Nanobond. These materials can be heated-up in only a third of the usual time. This paper talks about the theoretical aspects, as well as the mechanical and physical properties and especially practical experience of using Nanobond.Theoretical Aspects and Laboratory ResultsCement containing castables such as RCC, MCC, LCC or ULCC are considered standard in many refractory applications. Over the years a wide range of possible raw materials and practical installation methods were developed. However, all of these cement bonded refractory mixes possess one main important drawback. Such materials are characterized by the hydration of the cement bonding. As a result the physical bonded and the hydraulic water has to be removed in a relatively complicated drying procedure. The hydraulic water specifically demands a very careful and cautious heating up procedure. Most of the dreaded steam explosions can occur at a furnace temperature of approx. 250 oC. [1] To avoid such destructions, the heating-up of a new lined or repaired furnace can be very complex and slow. Depending on the furnace or the casted part a drying time of several days with long curing times are common."

Jan 1, 2012

By K. Pagalthivarthi, P. V. Desai

"During solidification of alloys, many inter-related physical processes, such as melt convection, mass diffusion, heat transport, macrosegregation and melt-undercooling occur. Several research workers have studied one or more of these effects separately. To answer important questions on solidification behavior, an overall approach interrelating the processes is necessaryAs a first step toward accomplishing the overall modeling, the freezing of a binary liquid metal is examined. The various stages during freezing of the alloy are critically described to build a continuum model for the entire process. Diffusive mixture theory is used to write the conservation equations for the liquid and the mushy zones. The concept of local thermodynamic equilibrium in the presence of curvature effects is used to restrict the number of degrees of freedom within the mushy zone. Constitutive equations relating flux quantities and affinities, the governing differential equations and boundary conditions are discussed briefly for the freezing process.IntroductionA solidification study encompasses such facets as solifidication time, microstructure, macrosegregation of the solute, shrinkage effects and soundness of the casting. Influence of one or more of the coupled heat and mass transfer phenomena such as local solute redistribution, thermosolutal convection, melt undercooling at dendrite tips and heat dissipation to the ambient have all been previously examined [1-3J. Several studies have examined the individual facets of alloy solidification as isolated processses. In fact, the transport processes occur simultaneously and a comprehensive model should include their inter-relationships. In particular, some of the existing studies of the mushy zone [4-6J do not emphasize thermodynamic completeness. This work represents an attempt to develop a thermodynamically consistent model of the entire solidification process on physical grounds."

Jan 1, 1986

A series of electron beam, cold hearth, single melt Ti-6Al-4V plates (nominally 2.5 cm thick) impacted by 2cm diameter, 4340 steel projectiles (with 54g nominal mass) at velocities ranging from 0.633 to 1.027 km/s were sectioned along the impact axis and examined by optical metallography to characterize the formation, growth, and microstructure of adiabatic shear bands. Near ballistic limit velocities, the shear bands propagate towards the rear of the target where they coalesce and grow to provide a cylindrical solid state flow regime for the plug volume.

Jan 1, 2006

By M. Fafard, R. Ahmed, O. Dion-Martin

"The optimization of aluminum sheet and tube forming needs the use of large strain finite elements software. The precision of the predicted results from those simulations depends mainly on the quality of constitutive law of the material used. In order to improve quality of these simulations, Barlat has suggested a new yield function named YLD2000-2d. This criterion describes the anisotropic behavior of the rolled aluminum plates. This work consists of characterizing the AA5754 alloy and estimating the material parameters needed for the YLD2000-2d criterion in LS-DYNA. In order to get these parameters, various mechanical testing were performed such as bulge and tensile tests. Moreover, the bulge test was also used to obtain an estimation of work hardening curve in large strain condition, up to 50%. The objective of this paper is to share the experimental results of the characterization of AA5754 aluminum alloy.IntroductionResearchers from National Research Council Canada's Aluminium Technology Center (NRCATC) and Aluminium Research Centre - REGAL, are working on aluminium tube hydroforming processes of AA-5754-0 alloy, used in automotive industries. Hydroforming process presents several difficulties such as wall thinning and section changes. In order to control them, some parameters can be set during the process like pressure rate and end feed level [1]. Given the complexity of the parts and the variability of the control parameters, the use of finite element method (FEA), like LS-DYNA, based on large strain theory is thus necessary. The accuracy of predicted results depends mainly on the quality of the constitutive law used to model the behavior of material. FEA results seem to be valid with the von Mises yield criterion used in some cases. But, given the anisotropic properties of the AA-5754 alloy, a more appropriate criterion could be used. The *MAT_ BARLAT YLD2000 shell material criterion, developed by Barlat [2], who's taking into account the anisotropic behaviour, was chosen due to its large flexibility and its good adaptation to particular elastoplastic behavior of aluminum. However, the use of this criterion needs to determine some material parameters by experimental way."

Jan 1, 2013

By David K. Melgaard

Electroslag Remelting (ESR) is a complex process used to produce high quality specialty alloy materials. The quality can be directly correlated to variances in melt rate and immersion depth. Conventional ESR furnaces control these quantities using two independent control loops using proportional changes in current for melt rate and driving the electrode up and down to match a voltage set point for immersion depth. However it is well known that the control loops are highly coupled, i.e. changing the current to account for melt rate deviations changes the voltage depth relationship and vice verse. In addition the noise in measurements of the ESR process can be considerable, forcing conventional controllers to use highly damped responses. A new model-based controller has been developed to embody the coupling and improve responsiveness by using estimates from a reduced-order linear ESR model and the typical process measurements to control melt rate and immersion depth simultaneously. Kalman filtering is used to optimally combine the model estimates of eight process states and the measurements of voltage, current, position and mass to estimate the instantaneous melt rate and immersion depth. Several ESR melts under steady state and transient conditions were conducted to evaluate the performance of the new controller. This paper will discuss the design of the new ESR model and controller and will present experimental results demonstrating its much improved control and responsiveness. While this controller was developed for the ESR process, the effectiveness of model-based control in managing such a complex process with relatively simple equations suggests the approach could be employed for many other processes as well.

Jan 1, 2006

By Kandipati Sreenivasarao

A promising method for removing heavy metal ions from dilute effluents is ion- or precipitate- flotation, in which a suitable collector is added to form hydrophobic metal-collector complexes or compounds that can be collected as foams. We have successfully removed Cu(II), Cd(II), and Pb(ll) from dilute solutions using sodium dodecylsulfate and ethanol as collector and frother respectively. However the process would not be economically viable unless the collector could be recycled, and the heavy metals recovered in a concentrated, preferably marketable, form from the foams. We investigated four different methods to decompose heavy metal-dodecylsulfate complexes, namely precipitation of hydroxides, precipitation of sulfides, chemical stripping, and electrolysis. We compare the performance of these methods. In each case the observed behavior is related to known thermodynamic data, and potential applications are discussed.

Jan 1, 1995

By Raymond F. Dalton

Despite the ready availability of numerous zinc sources, the process of solvent extraction- electrowinning (SX-EW) has as yet found little favour in the zinc industry. It is suggested that this is largely due to the previous lack of availability of suitable selective reagents having the particular features required to enable them to fit in to a solvent extraction-electrowinning based process for zinc, particularly with regard to strength and selectivity for zinc over iron. This paper describes work on the development of new selective extractants for the recovery of zinc from both sulfate and chloride aqueous solutions and suggests how they might be integrated into new zinc processes.

Jan 1, 1994

By Hee Dong Jang, Hong Yong Sohn, Miguel Olivas-Martinez

"Tetramethylorthosilicate (TMOS), a precursor of silica nanoparticles, is prepared from the waste silicon sludge, followed by the synthesis of silica nanoparticles from the TMOS by flame spray pyrolysis. A two-dimensional multiphase computational fluid dynamics (CFD) model for the flame spray pyrolysis process (FSP) for the synthesis of silica nanoparticles has been developed. The model incorporates the governing turbulent equations of overall continuity, momentum, energy and species mass transport to represent the gas phase and the population balance model (PBM) to account for the silica nanoparticles. The model has been validated with experimental data in terms of gas temperature and average particle size. Introduction Silica (SiO2) nanoparticles are used in various industrial applications, such as catalyst, pigments, thin film substrates, electronic and thermal insulators, and humidity sensors [1]. They are also used as additives in plastics and rubbers to improve the mechanical properties of elastomers, and in liquid systems to improve their suspension behavior. These applications rely on the particle morphology, average particle size, particle size distribution, and phase composition [2]. Silica nanoparticles can be synthesized by wet chemical processes such as sol-gel methods and high-temperature processes such as flame spray pyrolysis (FSP). The FSP process provides a unique control of particle size and crystalline structure and it can also produce high-purity, thermally stable particles continuously with minimal further treatments. The sizes of the flame- made particles range from a few to several hundred nanometers, depending on the operating conditions [1]. The synthesis of silica nanoparticles from organic compounds that contain silicon by the FSP process is of interest because it generates no harmful by-products [1, 3]. Several compounds such as tetraethylorthosilicate (TEOS) and tetramethylorthosilicate (TMOS) can be used to synthesize silica nanoparticles, but most such compounds are expensive. Thus, it is desirable to prepare the precursor compounds from waste materials. In the present study, TEOS and TMOS synthesized from silicon sludge were used as precursors of silica nanoparticles [4]."

Jan 1, 2008

By Gus Van Weert

This paper describes the results of autoclave testwork where ferric nitrate was hydrolysed in the presence of certain cations and anions and the resulting hematite analyzed for foreign constituents. For the cations Zn++, Ni++, Cu++, and AI+++, selectivity factors of over 107 were found. Magnesium gave 3.106. These factors are calculated as Me/Fe in solution over Me/Fe in the hematite; Me representing the metal in ion added. As-a result of the testwork at Delft University of Technology, BUDELCO (the Netherlands electrolytic zinc producer) ran a series of ferric nitrate hydrolysis tests in the presence of 10 additional trace elements. Impurity levels were prejudiced on Me2 EPHA extraction of iron from their zinc circuit, followed by HNO3 stripping. Good selectivity against base metals was confirmed, but trace elements forming anions (As. Sb) and sulphate were incorporated in the hematite. These BUDELCO results are also presented.

Jan 1, 1995

By Kuniaki Murase, Tetsuji Hirato, Koji Nitta, Yasuhiro Awakura

"The redox behavior of copper species in an ""ammonium imide"" room temperature molten salt was examined in order to clarify the applicability of the salt to the electroplating media of various metals. Trimethyl-n-hexylammonium bis(trifluoromethanesulfonyl)- amide (TMHA-Tf2N), having an electrochemical window of 5.6 V (50 °C), and corresponding copper(II) salt were synthesized. In TMHA-Tf2N media monovalent copper ion, Cu(I), was stable and Cu metal was oxidized, or corroded, in the presence of Cu(II) species. Cathodic electrodeposition of copper metal and anodic dissolution of it were, thus, one-electron reaction and their current efficiencies were almost 100%.IntroductionElectrodeposition of metals from aqueous solutions is an important soft process for manufacturing thin-film materials, surface finishing, and extractive metallurgy. However, the electrodeposition of base metals, such as zinc, chromium, and nickel, from aqueous media inevitably accompanies hydrogen evolution, which lowers the cathodic current efficiency of metal deposition. Since the electrodeposition of aluminium, titanium, and rare earths from aqueous media is actually impossible due to their largely negative redox potentials, nonaqueous media such as aprotic organic solvent and high-temperature molten salts have been employed for the electrodeposition of these metals. Room temperature molten salts (RTMS),1, 2) or room temperature ionic liquids, have also been developed as a promising electrolytes for the electrodeposition of base metals. In this field, chloroaluminates of alkylpyridinium or alkylimidazolium cation have been well investigated for aluminium3) or alluminium-alloy4-5) electroplating media. On the other hand, in order to avoid high hygroscopicity arising from the use of aluminium chloride, attempts have been made to combine the alkylimidazolium cations with fluorine-containing hydrophobic anions, e.g. BF4-,6) CF3SO3- (TfO-),7) (CF3SO2)2N- (Tf2N-),8) and H(HF)n-ions,9) and investigated for electrodeposition media.'°) Recently, a new series of RTMS consisting of tetraalkylammonium cations and Tf2N- anion, sometimes abbreviated as TFSI- anion, was found independently by MacFarlane et al.11, 12) and Matsumoto et al. 13) This type of RTMS, which is commonly named ""ammoniumimide"" salt, has a wide electrochemical window of ca. 5 V and, thus, the RTMS seems to be suited for practical application as a solvent for the electrodeposition process. In this paper, we report the electrochemical behavior of copper species in an ammoniumimide RTMS, trimethyl-n-hexylammonium bis(trifluoromethanesulfonyl)amide (TMHA-Tf2N)."

Jan 1, 2000

By Zhi Yang, Ahmad Ghahreman, Farzaneh Sadri

Impurity removal is a very important stage of the hydrometallurgical treatment of rare earth elements (REE) processing circuit, which is performed after water leaching of the acid baked REE concentrate. Lime neutralization has a high efficiency in removal of impurities and is the preferred process due to its economic advantage; however, the process has its own problems, such as the production of large volumes of gypsum and co-precipitation of REE with gypsum, i.e. REE loss. This work deals with the effect of several additives (cetryltrimethylammonium bromide (CTAB), polyvinylsulfonic acid (PVS) and polyacrylic acid (PAA)) on the uptake of REE by gypsum from synthesized acidic solutions. The main purpose of this study is to investigate the changes in the crystalline morphology of gypsum precipitated by the addition of crystal habit modifiers and to determine the crystal changes’ effects on the uptake of REE by gypsum. In this regard, different concentrations (0.2, 2 and 5 g L−1) of above-mentioned additives were studied at room temperature.

Mar 1, 2018

By Z. M. Zheng

Cyclic voltammetry, potential step, and ac impedance techniques were applied to study the electrochemical reaction of arsenopyrite in chloride solutions. The relationship between anodic current density and time in potential step measurements indicates that the oxidation of arsenopyrite is irreversible. The results of the constant potential coulometry show that the stoichiometric factor of the total electron involved in the overall reaction is 14. It is proposed that the dissolution of arsenopyrite is retarded by coverage of sulfur produced in the reaction as an intermediate product. The measured results of ac impedance strongly support the proposition. The proposed reaction mechanism also explains satisfactorily the charging current density and Tafel slopes measured in potential step measurements.

Jan 1, 1995

By Eiichi Kuzuno, Atsushi Shibayama, Toyohisa Fujita, Kazuo Koike, Toshio Miyazaki, Hitoshi Masuda

"A solid sulfur is more useful to recover and store than a sulfuric acid as a by-product in the zinc hydrometallurgy. In this experiment a zin concentrate (sphalerite) was leached with ferric sulfate at about 373 K for 3 to 6 hours. Zinc was leached more than 95%. After a solid-liquid separation, the leached residue contained solid sulfur was obtained. The particles in the residue were dispersed by lignin and the solid sulfur of approximately 85% was recovered as float product by a flotation with frother in the pH 4. The dried float product was heated at 413K for 2 hours. The pure solid sulfur was recovered. On the other hand in the leached liquid a zinc oxide was ·added and ferrous .iron was oxidized to ferric iron by blowing oxygen. This ferric iron was returned to the zinc leached process after solid-liquid separation.IntroductionZinc concentrate is usually roasted as pretreatment in zinc hydrometallurgy and the produced S02 is changed to sulfuric acid. However, recently in Japan the utilization of sulfuric acid has been limited and it is more costly to store. Instead of producing sulfutic acid the solid sulfur recovery has been examined by direct leaching of zinc_ concentrate in this experiment.In the direct leaching, several kinds of effects have been studied for leaching of sphalerite in ferric sulfate solution. The addition of lignine siilfonate1 • 2) and fine· grinding3) increases the · speed arid leaching fraction of sphalerite. The leaching ratio depends on impurities in sphalerite ores4 • 5). Here, the zinc concentrate is leached ferric sulfate solution under atmospheric pressure at 373K. The solid sulfur in leached residue is separated as float products from other solids by sink-float separation and flotation. The sulfur in float products is purified by evaporation at 413K and recovered."

Jan 1, 2000

By Terence Makanyire, Animesh Jha

The dissolution and chemical properties of vanadium, zirconium, and niobium in rutile lattice are analyzed by comparing the octahedral site preference energies, with respect to Ti4+ ion in the solvent phase. The oxides are often present in rutile lattice and interfere in achieving the quality of pigment grade TiO2 due to favourable Gibbs energy for dissolution in the solvent rutile matrix. Binary mixtures of V2O5 { TiO2; Nb2O5 { TiO2 and ZrO2 { TiO2 with compositions of 80, 85, 90, 95 and 97 wt% TiO2 were made, pelletized and sintered at 1100 °C for 24 hours. The solidsolution mixtures were then cooled and leached in 2M NaOH for 3 hours at 60 °C. Phase and lattice parameter characterizations, and microstructural and compositional analyses were then carried out using X-ray diraction and SEM/EDX, respectively. The leachates were analysed by Atomic Absorption Spectroscopy (AAS), using which the solute dissolution model for oxides were investigated.

Jan 1, 2014

By Isadora Dias Perez, Denise C. Romano Espinosa, Flávia P. Cianga Silvas, Jorge A. Soares Tenório, Mónica M. Jiménez Correa

In view of the rising generation of wastewater containing metals, sustainable and clean techniques to recover them are being researched. This study investigated the adsorption of aluminum, cobalt, chromium, copper, iron (III), magnesium, manganese, nickel and zinc presents in a synthetic ef fluent by chelating ion exchange resin Dowex XUS43605. The resin was tested in columns experiments and was analyzed the flow rate (0.45, 0.66 and 1.11 BV/h), at pH 1.5 and 20 °C. After loading the column, the elution experiments occurred with 1 M of H2SO4 and 4 M of NH4O. The concentration of the metals in solution was obtained by X-ray fluorescence spectrometry energy dispersive (EDX). The results showed that the breakthrough experimental curves demonstrated that the main metals (aluminum, cobalt, manganese and zinc) were immediately broken through just after the initiation of the feeding, while the breakthrough of copper began later. Therefore, the study showed that the chelating resin could be used to treat contaminated effluents with metals.

Mar 1, 2017

By Timothy W. Skszek, Adrian S. Sabau, Hebi Yin, Xiaoping Niu

The microstructure evolution during solution treatment plays an important role in mechanical properties of heat-treated aluminum alloys. In this paper, models were reviewed that can predict the microstructure evolution during the solutionizing process of the aging heat treatment of aluminum alloys. The dissolution ofMg2Si particles has been modeled as a diffusion process of Mg in the a-Al matrix. The evolution of volumetric fraction of fragmented silicon as a function of time and temperature was also considered. The growth and coarsening of silicon particles during the heat treatment was considered. It was found that constitutive equations and required property data for most of the phenomena that need to be considered are available. Several model parameters that need to be obtained from material characterization were identified. Pending the availability of these model parameters, this comprehensive model can be used to describe the microstructure evolution of aluminum alloys in order to optimize the solutionizing heat treatment for energy savings.

Jan 1, 2013

By Yongfeng Jia

Lime neutralization and co-precipitation of As(V) with iron(III) is the most widely used and most economical method for the removal of arsenic from mineral processing solutions and effluents. However, the arsenate fixation mechanism in the coprecipitated solids is not fully understood. It was suggested by various researchers to be a ferrihydrite precipitation process during which arsenate is removed by adsorption on ferrihydrite. In this study, XRD, EXAFS and microprobe were employed for the speciation of arsenic and the effect of various factors on arsenic solubility was also investigated. The results indicate that coprecipitation is a more complicated process than simple adsorption resulting in lower arsenic solubilities. Poorly crystalline ferric arsenate was observed for the first time to be present in the coprecipitated solids. In case of lime as base, there exists some type of Ca-Fe-arsenate association. A general term ?coprecipitate? is suggested to describe the precipitated arsenic-bearing solids instead of those widely used specific terms ?arsenical ferrihydrite? or ?arsenic-bearing ferrihydrite?.

Jan 1, 2005

By Hongfa Hu, Stavros A. Argyropoulos, Stephan Ferenczy

"Physical as well as mathematical modeling was carried out to investigate the exothermic mass transfer in liquid metal systems. In these systems, the exothermicity induces unique heat, mass and momentum transfer phenomena. Moreover, these phenomena are deeply coupled and they are further complicated by the presence of a moving boundary.In the physical model used, ice cylinders were immersed into sulfuric acid solutions, because the intermixing of ice with sulfuric acid is very exothermic. In this low temperature system, velocity and temperature measurements in the sulfuric acid were made as well as measurements of the ice melting in the sulfuric acid.The mathematical model developed solved simultaneously the heat, mass and momentum equations numerically, utilizing the control-volume finite difference approach. The enthalpy method was adopted to track the moving boundary. Predictions made by the mathematical model were in close agreement with the results obtained by the physical model.The results from the mathematical model were further validated with experiments involving high temperature liquid metals. Specifically, data were obtained in an experimental setup involving (a) dipping silicon cylinders into high carbon liquid iron and (b) dipping nickel cylinders into liquid aluminum. Results from these experimental studies supported the predictions of the mathematical model."

Jan 1, 1999

By Willem P. C. Duyvesteyn

A novel hydrometallurgical process for Escondida copper concentrates has been developed by The Minerals Laboratory of BHP. The Escondida Process consists of concentrate leaching, solution purification, electrowinning and residue flotation. Part of the copper will be sold as high grade concentrate and part as high purity SX-EW copper. Contrary to previous efforts for the development of a hydrometallurgical process for copper concentrates, this patented process does not advocate the total dissolution of copper. It only aims for the copper that is readily soluble in a mildly oxidizing environment with an ammoniacal or acidic lixiviant. Both lixiviants were studied, but ammonia was preferred because of fast kinetics at ambient temperatures and pressures. By controlling the oxidation potential, the formation of sulfate ions and, consequently, of an ammonium sulfate byproduct, is precluded. These mild leaching conditions also prevent the dissolution of unwanted impurities and result in the production of ultra-high purity electrowon copper. Solution purification is carried out by solvent extraction with LIX-54. The very high loading capacity of this organic results in a compact SX circuit, consisting of two loading, one scrubbing, and one stripping stage. As the organic is selective for simple copper ions, the copper amine complex is broken down and free ammonia is regenerated and recycled for leaching. High purity copper cathodes are produced in a conventional sulfuric acid based electrowinning system. One scrubbing step is needed to separate the ammoniacal circuit from the acid circuit. Limiting copper dissolution to less than 50% also provides an opportunity to produce high grade concentrates by residue flotation. Copper recoveries in excess of 98% with precious metal values reporting to the final concentrate can readily be obtained. Complete breakdown of the copper mineral- pyrite middlings results in a final concentrate grade that can be even higher than the original feed material. The Escondida Process also provides an opportunity to accept lower grade copper concentrates producing improved copper recoveries in the mill and yet high quality concentrates for marketing. The Paul E. Queoeau International

Jan 1, 1993

By Batric Pesic

The interactions of mineral-pyrite with T. ferrooxidans were studied by using a cyclic voltametry technique. The interactions with bacteria were carefully examined during the entire growth stage of bacteria (fermentation). Several very important discoveries were made. For example, 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 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).

Jan 1, 1990