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By H. J. Thevik, A. K. Dahle

"A mathematical model that calculates the stress development in a coherent and stationary dendritic network due to interdendritic flow is proposed. The fluid flow is assumed to be related to the solidification shrinkage, and under the assumption of no porosity formation and unidirectional solidification, the shrinkage-induced flow within the mushy zone is calculated analytically. The interdendritic melt flow exerts a force on the solid network and an analytical expression for the stress build-up in the network is developed. Parameter studies illustrating the influence of cooling conditions, mushy zone length, dendrite coherency, fraction solid, volume fraction of eutectic, and solidification shrinkage upon the stress development within the solid network are presented. Comparing the magnitude of the calculated stresses to measurements of the strength in equiaxed mushy zones shows that it is possible for the stresses to exceed the strength, thereby resulting in reorientation or collapse of the dendritic network.IntroductionInterdendritic fluid flow is at present regarded as a very important mechanism for feeding of shrinkage during solidification of metal alloys. Solidification of many alloys is often characterised by heterogeneous nucleation of the primary phase on substrates in the melt with subsequent evolution of equiaxed dendrites. These equiaxed dendrites can initially grow freely, but impinge on each other and form a continuous dendritic network, ie. dendrite coherency, quite early in the solidification process. Measurements of the dendrite coherency point have shown that the dendritic network is established at solid fractions ranging between 0.1 and 0.5, and most often around about 0.2 [l]. Depending on the alloy composition this means that as much as 70 to 80% of the volumetric shrinkage has to be compensated by flow of liquid through the interdendritic network. Interdendritic flow occurs with a much larger resistance compared to free flow of the liquid and flow of a liquid with dispersed crystals. The pressure drop associated with the interdendritic flow increases rapidly with decreasing fraction ofliquid."

Jan 1, 1999

By Francis Vanbellen

Umicore Precious Metals Refining operates an integrated precious metals smelting and refining plant in Hoboken, Belgium. Once a smelter and refiner of complex concentrates, the plant today?s feed consists exclusively of industrial and consumer recycled products, making it the world?s largest recycling facility for precious metals. Unlike the fairy tale of the Frog Prince, it took much more than a princess? kiss to successfully realize this makeover. A completely renewed plant has been built over the past decade. The most visible technological innovation was the commissioning of the Pb-Cu smelter. Its flexibility towards very different types of feed makes it perfectly suited as main entry to the Hoboken flow sheet. A new Cu-leaching & electro winning plant and precious metals refinery make up the Precious Metals Operations (PMO) whose targets are fast throughput and maximized yields for gold, silver and the platinum group metals. The Base Metals Operations (BMO), flexibly process the by-products from the PMO, valorizing ?impurities? like indium, tellurium, selenium and others. Off gas and waste water treatments ensure compliance with strict environmental standards. Precious metals recycling is an art that goes beyond mastering a unique flow sheet. Umicore Precious Metals Refining offers a complete recycling service, taking care of sampling and assaying, metals management and logistics. The quality of this integral service is recognized through the attribution of ISO certifications for our operational activities, sampling and the environmental care. And it?s an art that follows Michelangelo?s experience: ?Art is 5% of inspiration and 95% of transpiration.?

Jan 1, 2006

By John J. Jonas, Sang-Hyun Cho, Ki-Bong Kang

"The recrystallization behavior of Nb micro alloyed steels containing Cr, Mo, Ni and Ti. was studied using hot torsion testing with the aim of modeling the recrystallization processes and the mean flow stress taking into account the microstructural behavior during hot rolling. The kinetics of static and metadynamic recrystallization were characterized and appropriate expressions were formulated for the recrystallization kinetics. These are shown that the recrystallization kinetics depend on steel composition and the processing conditions. The stress-strain curves were determined in order to derive new equations for the peak stress, peak strain, mean flow stress and softening kinetics. The peak strain is influenced by the presence of alloying elements; their addition, which has a solute drag effect, retards the rate of grain boundary motion, shifting the peak to the right. The addition of Nb to the steel results in a significant increment in the activation energy for hot deformation, and Mo has smaller effect than Nb, but Cr has the opposite effect. It was also found that the deformation activation energy in these steels was not altered by the addition of Ni. The rate of metadynamic recrystallization increases with strain rate and temperature and is observed to be independent of strain, in contrast to the observations for static recrystallization.The mean flow stress (MFS) calculations, based on the Sims analysis, are then compared with the predictions of a model based on an improved Misaka mean flow stress equation in which solute effects, strain accumulation, as well as the kinetics of static and metadynamic recrystallization are accounted for. Good agreement between the measured mean flow stresses, which is obtained from the mill logs of POSCO Kwangyang #3 HSM (hot strip mill), and 'predicted ones is obtained over the whole range of rolling temperatures. The results demonstrate that dynamic recrystallization followed by metadynamic recrystallization, supported by the unexpected load drops, sometimes occurs for the rolling schedules studied in the present analysis."

Jan 1, 2001

By Jennifer Mager, G. P. Martins, Dean Mussatti

"The role of lead, at low concentrations in high pH cyanide-electrolytes, on the dissolution behavior of gold, has been a topic of scientific and industrial concern for well over a century. The recent paper by Kondos et al [1] at CANMET (1995) this continuing interest and apparent importance. Nevertheless, the mechanism(s) by which this (and other heavy metal) component influences the electrodics of this electrochemical system has still not been unequivocally demonstrated. Instead, several plausible hypotheses, by pioneering researchers in this field, have been advanced and reiterated OVer the ensuing years. While it is generally accepted, based on equilibrium elctrode-potential calculations, that reduction (or co-reduction when oxygen is present in the electrolyte) of lead on the gold surface may occur due to cementation (contact reduction), the cemented lead has never been characterized. The work presented has reexamined the role of lead in this system, by delineating the species distribution of these system components and by interpreting the results of potentiodynamic studies in conjunction with SEM analyses of a gold electrode.1. INTRODUCTIONThe leaching of gold ores in cyanide electrolytes has been practiced for well over a 100 years. Research conducted on this topic has been primarily focused on the effects of operating parameters such as concentrations of oxygen and cyanide, and the pH of the electrolyte; or the leaching behavior of carbonaceous and sulfitic gold-bearing materials.Mechanisms by which pure gold is leached in alkaline cyanide media, with oxygen serving as the oxidant, have been subjected to continual examination and re-examination in the published technical literature during this century. Recently, it has been speculated that without the presence in the electrolyte of trace heavy metals, such as lead or mercury, that gold would not be leachable. Researchers who have tackled this topic, have either considered heavy metals to be a natural occurrence in these systems and ignored the role they may serve in the leaching process, or they have deliberately focussed on controlling their concentrations in the system to undetectable limits. As a result, conflicting findings have been reported for what would appear - depending on the details provided in these reports - to be identical systems."

Jan 1, 1997

By Alex I. Kociubczyk, Wilky Desrosin, Lucía Mabel Boycho, Alicia E. Ares, Carlos E. Schvezov

In the present research, commercially pure Sn and Zn, and Sn-Zn alloys (Sn-1wt.%Zn, Sn- 2wt.%Zn, Sn-4wt.%Zn, Sn-8wt.%Zn and Sn-8.9wt.%Zn, weight percent) were obtained by a horizontal directional solidification process with two opposite senses and heat extraction. The solidification process was realized using a horizontal furnace with two heat extraction systems at both ends. The temperature was measured using eight K-type thermocouples and an electronic recorder of temperature data. The resulting structures were analyzed using optical microscopy. From the solidification process the thermal and metallographic parameters were determined in all samples. The presence of defects in the solidified pieces was observed. Internal defects pretended to be dependent not only on the composition of the alloys under consideration but also on the size of the structures formed, also, on the velocities and accelerations of interphases, and on the variation of thermal gradients. A model of the phenomenon from the first principles is presented.

Jan 1, 2015

By C. Liliane Carvalho

In the current study, bio-oxidation tests were carried out in shaking flasks with a flotation concentrate containing the sulphides pyrite, arsenopyrite and gudmidite. The tests were performed with mesophilic microorganisms (At. ferrooxidans) at 30 °C and also with the moderate thermophile S. thermosulfidooxidans, at 50 °C. The effects of (i) previous adaptation of the microorganisms to the concentrate, (ii) ferrous iron concentration and (iii) pulp density (2%, 4% and 6% (w/v)) on the dissolution of the sulphide were studied through arsenic extractions. S. thermosulfidooxidans was more sensitive to the pulp density in comparison to At. ferrooxidans as a reduction in sulphide oxidation was observed with the increase in the solid content to 6%. Therefore, the mesophilic strain was selected for further work, which comprised a rolling bottle experiment at 10% solids. After 40 days of bio-oxidation, the solid material was subjected to cyanidation, which revealed 85% gold extraction as compared to 21% from the original concentrate. The antimony sulphide grains in the bio-oxidized product showed similarity to what was observed in the original sample, suggesting such particles were not susceptible to the bio-oxidation process.

By M. Z. Mubarok

Effect of single addition of a lignin-based biopolymer additive, DP 2782, at various dosages as well as in combination with thiourea on cathode polarization during copper deposition was investigated by performing potentiodynamic and galvanostatic measurements using a potentiostat. The result of electrochemical measurements was compared with the behaviour of cathode deposition with glue and thiourea additives. Surface micro-appearance of the copper deposit after 1 h galvanostatic scan under current density of 330 A/m2 and various additive type and dosage was evaluated by scanning electron microscopy (SEM) examination. It was found that the addition of 2.5 mg/l biopolymer gave sufficiently polarizing effect of copper deposition. SEM examination of the cathode surface after galvanostatic scan revealed that the combination of the biopolymer with thiourea (2.5 and 3.5 mg/l) resulted in a compact deposit which is comparable with that resulted from the test with glue and thiourea.

By Gabriel A. Torma

This paper provides infonnation on selected technologies available for remediation of metal contaminated soils and industrial effluent solutions. Because some of the industrial sites are contaminated with organics (solvents, gasolines and oils), an effort has been made to introduce the most frequently used cost-effective cleanup methods, such as "bioventing" and "composting." The microorganisms involved in these processes are capable of degrading organic soil contaminants to environmentally harmless compounds: water and carbon dioxide. Heavy metals and radionuclides contaminated mining and industrial sites can be remediated by using adapted heap and dump leaching technologies, which can be chemical in nature or bio-assisted. The importance of volume reduction by physical separation is discussed. A special attention is devoted to the remediation of soils by leaching (soil washing) to remove heavy metal contaminants, such as chromium, lead, nickel and cadmium. Furthermore, the applicability of biosorption technology in the remediation of heavy metals and radionuclides contaminated industrial waste waters and acidic mining effluent solutions was indicated.

Jan 1, 1996

By Armin D. Ebner

A hetero-f1occulation model is developed to calculate the net force exerted on a paramagnetic nanoparticle that is moving in the proximity of a magnetite particle that is fixed or supported within an open flow and magnetically energized packed bed. Important variables investigated include the size and surface charge of the particles, the magnetic field, the ,flow velocity, the electrolyte concentration and the magnetic susceptibility of ,the nanoparticle. The ?influence: of other naturally occurring forces, such as hydrodynamic and DLVO(Le., van der Waals and electrostatic) forces on the magnetic attractive forces between the magnetite particle and the nanoparticle are also examined. This model reveals the feasibility of using magnetite particles instead, of stainless steel as the energizable element for high gradient magnetic separation.

Jan 1, 1999

By Stephen M. Testa

Several methodologies are available for the remediation of contaminated soils including bioremediation, vapor extraction, chemical fixation, incineration and direct disposal. A proven innovative and cost effective alternative for the fixation of contaminated soils is via cold-mix Environmentally Processed Asphaltm (EPA"'). EPAm methodology utilizes contaminated soil as an ingredient in an industrial process to produce a commercially viable product. Petroleum hydrocarbon and metal affected soil is incorporated with a water-based asphalt emulsion and varying amounts of aggregate to produce a range of cold-mix asphaltic products that fulfills the requirements of a variety of end uses. This viable and creative use which is within the intent and spirit of current regulations in producing, in lieu of a landfill waste, an end product for use as a berm, road base, liner, or other site specific application. Consideration of certain engineering and environmental factors including durability, stability, chemical resistance and ageing, biological resistance, permeability, leachability and geochemical aspects suggests that cold-mix asphalt incorporation of affected soil will perform more than adequately under normal conditions for a long period of time.

Jan 1, 1994

By R. C. Chaturvedi, S. B. Padwal

"Padwal and Chaturvedi have developed the model based on M-K theory, considering Hosford's yield criterion and critical thickness strain criterion"" to predict the sheet metal forming limits under simple (constant) strain ratio paths. This analysis has been extended in this paper to predict the sheet metal forming limits under complex strain paths. The effects of exponent ""a"" in Hosford's yield criterion and strain paths on the forming limits under complex strain paths are studied using this analysis. The predictions of the present analysis are compared, both for simple and complex strain paths, with experimental results of Ishigaki for A.K. steel and also with the predictions of Rao and Chaturvedi's model. The quantitative analysis of the error in predicting the forming limits has also been carried out using a method suggested by the authors earlier.1. INTRODUCTIONThe constant strain ratio condition has been assumed in the theories developed for prediction of forming limit diagrams (FLO). In actual forming operation, this condition is seldom satisfied. Even in the case of simple single stage press formed components, the strain path becomes curved and non-linear. In the case of pressings with complex shapes, or multiple stages of forming, the changes in strain path are more pronounced and even abrupt.Experimental study of the forming limits, under two stage strain paths, by Ishigaki [1], has shown that the forming limits are path dependent. It has been observed that the forming limits lower than that under simple strain paths, may be obtained under certain strain paths (when the first stage strain path is either equibiaxial tension or uniaxial tension, followed by the second stage strain path as plane strain). Rasmussen's work [2J, on the theoretical study of forming limits under curvilinear strains paths, has shown that a large drop in formability can result from very small changes in strain path. Thus if a deformation process gives rise to failures due to plastic instability, the failure is not necessarily due to insufficient formability of the material. In such cases, FLOs based on constant strain ratio path should not be used directly in predicting the success or failure of the forming operation. Thus the knowledge of forming limits under complex strain paths is of great importance to the interpretation of press-shop problems."

Jan 1, 1994

By Kouji Mimura, Tamas Kekesi, Yongfu Zhu, Masahito Uchikoshi, Minoru Isshiki

"The formation and anion exchange sorption of chloro complex ions can offer a great potential to be utilized for the separation and purification of metals in aqueous solutions. Available stability data were primarily used to estimate the predominance of chloro complex species, indicating the feasibility of such separations. Anion-exchange sorption functions, describing the equilibrium distribution of a number of important elements have been determined by the batch equilibrating method in the practical HC1 concentration range. Various oxidation states were stabilized by the addition of appropriate agents. Tendencies in oxidation, complex formation and anion exchange sorption were confirmed by spectrophotometric investigations. Based on the fundamental results, anion exchange processes have been developed for the purification of iron, cobalt, copper and zinc. The efficiency of separation was assessed and the procedure optimized by the analysis of experimental elution curves. Results have demonstrated that by properly controlling the oxidation states and HC1 concentrations, practically all the impurities can be eliminated. Computer programs have been developed to estimate complex formation and redox equilibria, to screen and correct analytical data, to determine distribution coefficients and to evaluate efficiencies of separation.IntroductionBase transition metals have long been used as the staple materials in various fields of industry. In general, there has been an increasing tendency in purity requirements but recent advances have created a rapidly increasing demand for ultra-high purity metals. To give a few examples, ultra high purity copper can be used as bonding wire and interconnection in integrated circuits, or as material for superconductor stabilizing, high-field magnets, beside its use in cryogenics and ultra high vacuum technology [1]. Iron holds promises as a constituent element in the ß-FeSi2 material to be applied in new opto-electronic devices [2] and it is currently used, together with chromium and manganese, in the production of special magneto-optical materials for digital recording. The use of ultra high purity manganese and chromium in semiconductor technology is evolving. Although not considered a transition metal, zinc is also treated here because of the major significance in compound ZnSe semiconductors [3], and the possibility to purify it by the anion exchange method."

Jan 1, 2000

By Saskia Duyvesteyn

For many applications in hydrometallurgy and water treatment it would be advantageous to use ion-exchange resins in stirred reactors. However, attrition of the resin may lead to significant losses of both resin and metal values and prevent water quality goals from being reached. We have studied the recovery of fine resin particles by froth flotation, using the model copper - Dow XFS4195 chelating resin system. As the functional group on the resin is a bis-picolylamine, the resin should be amenable to flotation by anionic collectors, such as sodium dodecylsulfate and sodium dodecylsulfonate. The kinetics of copper loading from dilute aqueous solutions in an agitated vessel were studied as a function of copper concentration, pH and resin bead size. The flotation of unloaded resin was investigated for different types of collector, collector concentration, conditioning time, and resin bead size. Potential applications are discussed.

Jan 1, 1995

By Shinya Otsuka

Activity coefficient of oxygen in sulfide-rich and metal-rich melts in copper-sulfur binary were determined at 1423 and 1523 K by means of a modified coulometric titration technique using the following cell: 0 ( is Cu-S melts) I Zr02 (+Ca0) I air, Pt The activity coefficient values obtained in the present study increase rapidly with sulfur composition in the vicinity of xs = 0.3333. The data obtained for the matte saturated with the metal-rich melts are in good agreement with those obtained by Kuxmann and Benecke, Schmied 1, and Eguchi and Yazawa. Those obtained for the metal-rich melts are in good agreement with the results of Sano and Sakao.

Jan 1, 1983

By Tao Li

The development of DP(Dual Phase) steels and TRIP(Transformation Induced Plasticity) steels has received much attention in recent years due to their high strength and simultaneous good ductility, which provides the potential for weight reduce and resource savings on certain components in automobile or other industries. So a controlled rolling process was simulated in the present study by thermomechanical simulator (Gleeble 1500) for producing DP steels on a kind of low carbon steel containing a small amount of Si and Cr. F+M dual phase microstructures have been obtained during continuous cooling processes of a wide cooling rate range from 10°C /s to 60°C /s. The grain size of the dual phase steel developed can be refined to less than 5 m through the mechanism of deformation induced ferrite (DIF) transformation. The ultrafine ferritic grains are equiaxed with high-angle boundary, and the martensite islands of an average size less than 5m disperse uniformly in the ferrite matrix. The ultrafine martensite islands not only inhibit the growth of ultrafine ferritic grains and improve the bonding of F/M interface, but also increase remarkably the strain hardening rate in the processing of the present Dual-Phase steel. As a result, the tensile strength of ultrafine grained Dual-Phase steel reaches higher than 1000 MPa. The result shows that an ultrafine grained Dual-Phase steel of low carbon and low alloy is promised to exhibit desired F+M microstructure by means of this new TMCP process.

Jan 1, 2006

By Gunnar Eriksson

Computer simulation has become an everyday practice in thennodynamic and materials research. Advanced thennochemical algorithms take into account heat transfer effects and salient reaction kinetics when applied for process models. In particular, the combination of mass transfer or overall reaction rates with multi-component Gibbs energy minimisation provides an effective tool for simulation of industrial thennochemical processes and processing of materials. In this work the combination of rate factors with the Gibbs energy technique was studied by using the novel program ChemSheet, which operates through Microsoft's Excel® spreadsheets. Such processes as, for example, CVD of pure silicon production, titania pigment manufacturing, vapour pressure of Mercury in amalgams (in Hg-Iamp manufacturing) and melting behaviour of low-temperature alloys have been modelled. Provided that the thennochemical data is available simulations can be performed with any thennodynamic system. The calculation can be performed as an affinity study without a particular reactor model or with a specific reactor scheme.

Jan 1, 2001

By Victor Zavodinsky, Sergey Rogov

"Pseudo-potential fully relaxed total energy calculations are used to predict a hypothetical Si1-xCxO2 (x<0.5) compound formed from SiO2 ß -cristobalite by substitution of some SiO2 complexes by CO2 molecules. The simulation shows that the Si1-xCxO2 compound can be quasi stable if the CO2 content is less than fifty per cent. It is assumed that six-molecule Si6-nCnO12 (n=3) rings can play a role of nucleuses for formation of the Si1-xCxO2 compound from SiO2 and CO2 molecules. Thus, silicon dioxide can be considered as a possible solid store for gaseous CO2.IntroductionThe problem of increasing of CO2 in the Earth atmosphere is one of the main modern problems of mankind. One of conceivable ways to decrease the harmful value of CO2 is to convert a part of it to solid state. Iota et al. [1] reported a polymeric (quartz-like) phase of CO2 solid synthesized at high pressure (~40 GPa) and at high temperature (~1800 K). Shortly after this experimental work, Serra et al. [2] reported a total energy calculation of several possible phases of CO2 using plane wave pseudo-potential density functional theory. They concluded that there should be a transition from a molecular phase to a phase isostructural to SiO2 -quartz in the range of 35 to 60 GPa. The latest calculations by Dong et al. [3] have shown that the more favored solid CO2 phase is ß -cristobalite. Recently, Kume et al. [4] have demonstrated the polymerization of CO2 even at room temperature at high pressures up to 80 GPa. Transformations of gaseous CO2 to different solid phases were studied recently experimentally and theoretically [5-8]. The main obstacle for using synthesized CO2 solid as a solution for the CO2 problem is its pressure instability. However the SiO2 ß -cristobalite with the same structure is stable.The question is whether a silicon-oxide system in which a part of atoms of silicon is replaced by atoms of carbon will be stable? If the answer is positive, this system can be considered, in our opinion, as a possible store for CO2."

Jan 1, 2009

By K. Moriyamo

Operation improvement efforts at Hyuga Smelting Co., Ltd. have focused on calcining capacity in the reduction rotary kilns ("the kilns"), whose limited feed rate capacity had capped production at around 18,000t-NiN since 1995. To improve the kilns&apos; feed rate capacity of 80 wet t/hr, attempts were made to increase the gas flow in the kilns by increasing the capacity of the off-gas fans. However, as the increased gas flow resulted in only limited improvement of the kilns&apos; feed rate, a scoop feeder was installed on each kiln to add coal to the middle of each kiln&apos;s interior to gain a higher efficiency of thermal supply and conversion. With these gas flow and coal charge addition operations, the kilns&apos; feed rate capacity increased up to 120 wet t/hr, with burner fuel efficiency increasing by approx. 10% (approx. 5% in total with the additional coal included). As a result, production was raised to a level of 22.000t-Ni/Y Keywords: reduction rotary kiln, scoop feeder, additional coal charge.

Jan 1, 2004

By Catherine Cai

A granular sorbent, prepared by gel-coating polyethyleneimine (PEI) on high surface area silica followed by crosslinking with a low-molecular weight diepoxide, has significantly higher uranium capacity, greater salt tolerance, and faster kinetics than the commercial resin Dowex 21K. Though having lower U(VI)/Fe(III) selectivity than Dowex 21K, the gel-coated PEI affords much higher sorptions of both U(VI) and Fe(III) and also their separation by selective stripping with acid.

Jan 1, 1999

By A. E. Clark

Rare earth compounds are widely known as possessing many extraordinary magnetic properties. In this paper, we focus on the huge magnetically induced displacements (magnetostrictions) which characterize the compounds of terbium with iron (Terfenol). Materials prepared commercially by both free-standing-zone (FSZ) and modified Bridgman (MB) techniques have now become available in large sizes and shapes. Prior to the development of the Terfenol alloys, it was possible to achieve giant magnetostrictions only at cryogenic temperatures. In the cubic Laves phase TbFe2 compound, saturation strains exceed 3000 x 10-6 at room temperature and above. Large magnetization &apos;jumps&apos; can occur, causing huge spontaneous magnetostrictions with small triggering magnetic fields.

Jan 1, 1992