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By Randall M. Gennan

Generally sintering is focused on the bonding of particles at high temperatures; possibly with simultaneous densification. However, an important aspect of sintering occurs during heating at relatively low temperatures where polymer processing aids are removed via control of the atmosphere, heating rate, or hold time at intennediate temperatures. New insights into burnout processes show impact from the polymenype, particle size, amount of polymer, atmosphere, part geometry, and thermal profile. This presentation focuses on the key parameters to demonstrate improved mechanical property levels are available in traditional powder metallurgy alloys by proper selection of the processing polymer and proper care in its thermal extraction. The focus is on mechanical property, where gains up to 40% are demonstrated due 10 changes in the processing polymer. Further, atmosphere control during polymer burnout provides a benefit by allowing formation of desirable carbonitrides, giving strength levels over 3 GPa (over 400 kpsi). Insight is? gleaned from powder injection molding, where high polymer contents mandate proper processing control.

Jan 1, 1996

By Richard D. Hagni

Polished sections of pyrometallurgical intermediate products from a simulated commercial flash furnace were examined by reflected light microscopy, scanning electron microscopy-energy dispersive spectrometry and electron backscatter analysis, and microprobe analysis for phase and textural relationships. The smelter feed is a copper concentrate from a porphyry copper deposit. The concentrate consists primarily of chalcopyrite, bornite and pyrite with smaller amounts of covellite, chalcocite, molybdenite, magnetite, galena, and sphalerite. The flash furnace reactions for pyrite and chalcopyrite can be observed by reflected light microscopy. Reacted angular particles of pyrite exhibit successive rims of fibrous pyrrhotite and hematite or magnetite. Reacted angular chalcopyrite particles show successive rims of bornite, digenite, and chalcocite. Spherical particles, formed by the complete melting of former pyrite particles, consist of variable amounts of granular pyrrhotite with magnetite rims and minor hematite. Spherical particles, formed by the complete melting of former chalcopyrite particles, exhibit exsolution intergrowths with varying proportions of intermediate solid solution, bornite, digenite, and chalcocite and have rims of hematite, magnetite, and copper-iron spinel. Sphalerite and molybdenite do not show evident mineralogical reactions.

Jan 1, 1987

By E. Maziar Sauber

In order to prepare a more desirable feedstock for a rare earth elements separation refinery, cerium, a penalty element in the refinery feedstock, should be removed from the mixed rare earth elements oxide or carbonate feedstock. In this study, cerium (III) to cerium (IV) oxidation by calcium hypochlorite and subsequent precipitation was used to remove cerium from a mixed rare earth elements chloride solution. A factorial design of experiments was used to determine the effect of process variables such as temperature, pH, and oxidizer addition on the oxidation of cerium (III) using synthetic solutions. Under certain test conditions, all of the cerium was successfully removed from the chloride solution, and some REE accompanied cerium and reported to the precipitate. This proposed technology can allow for low cost removal of cerium from mixed rare earth elements chlorides.

By V. Montenegro

Smelting of copper concentrates in Teniente Converter produces highly oxidized slag, containing from 4 to 10 % Cu and from 15 to 25 % of Fe304. Copper recovery requires magnetite reduction at a level of 5%, determining the degree of cuprous oxide co-reduction and the liberation of copper matte inclusions. The rate of slag reduction is controlled by the mass transfer to the reaction interface. Slag stirring affects the rate of reduction and enhances coalescence of mechanically entrained copper matte inclusions. Slag reduction and sedimentation in the AC electric furnace is a commonly used method of slag cleaning. Utilization of DC electric furnace creates beneficial conditions introducing slag electrolysis additionally to chemical reductions with carbon of coke and electrodes. Application of external magnetic field, interacting with a direct current in an electric furnace, induces magnetohydrodynamic phenomena, such as intensive stirring and electromagnetic buoyancy force acting on inclusions. Laboratory scale research in simulated DC electric furnace with a superimposed magnetic field showed a significant acceleration of the rate of slag reduction and copper removal. Continuous measurement of gas flow and composition allowed for determination of the reduction rate along the time. Application of external magnetic field in the reduction of the industrial slag in a crucible simulated DC electric furnace results such as the increase of the reduction rate from 2 to 3 times, compared with the identical conditions in the AC electric furnace. Interaction of non- homogeneous electric field with crossed permanent magnetic field induces vigorous slag stirring, enhance mass transfer and accelerate the rate of the slag reduction. Additional participations of the slag electrolysis in the magnetite and cuprous oxide reduction as well as the acceleration of the settling of the inclusions by the electromagnetic buoyancy force affect the slag cleaning intensification.

Jan 1, 2003

By H. Bai, B. G. Thomas

"A three-dimensional finite difference model has been developed to study the liquid steel-argon bubble two-phase turbulent flow in continuous casting tundish nozzles. Experiments have been performed on a 0.4-scale water model to verify the computational model by comparing its prediction with velocity measurements using PIV (Particle Image Velocimetry) technology. The computational model was developed using CFX and then employed to investigate the effects of various casting process variables. A fast, simple inverse model to quantify relationships between those process variables was developed, based on interpolation of the numerical model results, using Bernoulli's Equation and advanced multivariable curve fitting methods. Predictions using this model compare well with plant measurements. The model has been applied to present trends and observations on the relationship between casting speed, tundish depth, slide gate opening, and argon gas injection rate. The results can also be used to predict .the theoretical steel flow rate through the nozzle, so that clogging conditions can be identified in the plant.IntroductionTundish nozzle geometry is one of the few variables that are both very influential on the casting process and relatively inexpensive to change. Designing an effective nozzle requires quantitative knowledge of the relationship between nozzle geometry and other process variables on the influential characteristics of the flow exiting the nozzle. This relationship depends on the flow pattern within the nozzle components. Most previous modeling studies of flow in the nozzle have focused on single-phase flow [1-4]. Argon injection into nozzle is an efficient and widely employed method to reduce nozzle clogging, even though the real working mechanism(s) are still not fully understood [5]. Argon injection may greatly affect the flow pattern in the nozzle, and subsequently in the mold. Therefore, two-phase flow modeling is needed to improve understanding of fluid flow in the nozzle."

Jan 1, 2000

By Y. Z. Zhang

Cyanide has generated environmental concerns because of its toxicity, and it may not respond to the treatment of complex and refractory gold ores. Gold leaching by thiourea is one of the most promising substitutes of cyanide. However, the high reagent consumption has hindered thiourea from its commercial application in gold extraction. The process chemistry and mechanism of thiourea degradation has been discussed on the basis of chemical bonding theory, thermodynamics and electrochemistry in this paper. Progresses on the decreasing of thiourea consumption have been summarised. The potential application of thiourea in gold extraction has been evaluated.

Jan 1, 1996

By N. Kanari

The kinetics of oxychlorination of MgO by Cl2+O2 was studied in the temperature range of 850 °C - 1025 °C, using thermogravimetric analysis. The effects of C12/02 ratio, gas velocity, temperature and partial pressure of reactive gases on the reaction rate were investigated. The oxychlorination process was characterized by an apparent activation energy of about 214 kJ/mol. The reaction orders with respect to C12+O2. C12 and O2 at 950 °C were about 0.65.0.98, and -0.37, respectively. Some data about oxychlorination kinetics of MgO, Cr2O3, and MgCr2O4 contained in chromite were compared. Efficiency of using oxychlorination for the removal of iron oxides contained in magnesia was demonstrated.

Jan 1, 1999

By Songsong Wang

Recently, replacing Pierce-Smith converting process with the oxygen bottom-blowing continuous converting technology has become a new research focus. Based on the principle of Gibbs free energy minimization, the thermodynamic model of oxygen bottom-blowing continuous converting multiphase equilibrium system has been established. The elements distribution behavior is calculated at the same burden composition and operation parameters as the industrial production. The results show that the absolute errors of the mass fraction (wt%) of Cu, Fe, S, Pb, Zn, As, Sb, Bi in crude copper are 0.06, 0.0030, 0.070, 0.38, 0.39, 0.020, 0.017, 0.034, 0.010, respectively, and the absolute errors of the mass fraction (wt%) of Cu, Fe, S, Pb, Zn, As, Sb, Bi in slag are 0.53, 0.81, 0.020, 0.23, 2.5, 0.0048, 0.0010, 0.0030, 1.49, respectively. The calculated results agree well with the actual industrial production data, indicating that the model can be well applied in the oxygen bottom-blowing continuous converting practice.

By R. Boom, B. Kraaijveld, H. Kuntzel, Y. Meteleva-Fischer

"Alloying refining with rare earth elements followed by acid leaching was examined for the potential of upgrading of metallurgical grade silicon. Microstructure study of silicon alloyed with small additions of rare earths showed behavior relatively similar to the influence of calcium addition. After alloying with neodymium the phosphorus content was detected in various intermetallic silicides containing neodymium and iron. The content of lanthanum and neodymium in refined silicon was by several times lower than that of aluminium and calcium. Alloying with lanthanum and neodymium at smaller additions than calcium reduced the phosphorus content down to the same level. The efficiency of lanthanum and neodymium in removal of boron and phosphorus at the 1-2 wt% of their additions and their low solubility in silicon make the alloying with these metals followed by acid leaching an attractive option for the refining route of metallurgical grade silicon up to solar grade.IntroductionA striving for a cheap ""green"" energy directs the research interests in silicon solar cells towards new efficient refining routes for metallurgical grade silicon (MG-Si, -98% purity). The silicon price determines up to high extent the solar module's price, so that cheap and efficient metallurgical process is awaited. The research challenge is to fulfil the purity requirements of solar grade silicon (SoG-Si, 6N) by competing with the energy-consuming and environmentally unfriendly Siemens process. Most difficult impurities to remove are boron and phosphorus, so technologies dedicated to their efficient removal attract an attention of industry and academia.Alloying refining (also known as solvent refining) is one of the most promising refining options, which is based on a principle of solid-liquid extraction using limited solubility of impurity elements in solid silicon [ 1]. Various elements were proposed for alloying refining: aluminium [2], calcium [3], tin [4], iron [5], copper [6] etc. The attractiveness of the alloying refining is in decreasing a melting point of the metal mixture and an affinity of the alloying element to the most harmful impurities, especially to boron and phosphorus. However, the difficulties are still faced due to self-solubility of the alloying elements, their low affinity to boron and/or phosphorus, silicon losses and necessity of removal of the silicide impurity phases in an additional step, using acid leaching [7], fractional melting [ 8] etc."

Jan 1, 2013

By W. K. Choi

Stainless steel exposed to wet environments at ambient temperature is subject to the formation of a surface biofilm. Depending upon the prevailing environmental conditions (dissolved oxygen, pH, Eh, concentration of cationic/anionic species), the biofilm may stimulate corrosion through formation of differential aeration zones and concentration cells. Corrosion significantly impacts the United States economy, since on a yearly basis, corrosion induced losses are estimated to be over $200 billion. A large portion of this corrosion is imputable to bacterial activity, and basic information is needed for a better understanding and control of the biocorrosion phenomenon. The present study has investigated the influence of Thiobacillus ferrooxidans in the corrosion of American Iron and Steel Institute (AISI) 304, 316 and 416 stainless steel samples. The formation of biofilm and microstructural changes on the surface of stainless steel samples and their weldments were assessed by microscopic examination, and the changes in the mechanical properties by stress-strain measurements. The significance of the results will be discussed.

Jan 1, 1993

By Ann E. Visser

Aqueous Biphasic Systems (ABS) form upon the admixture of certain water-soluble polymers or polymers and salts above critical concentrations, and thus represent liquid/liquid extraction systems whose nature is entirely aqueous. We are currently investigating the utility of ABS (and its solid phase analogs) as "green" alternatives to the use of volatile organic diluents in separations of metal ions. Chaotropic (water-destructuring) metal ions with small negative AGhyd (e.g., Tc04) tend to partition quantitatively to the PEG-rich phase of an ABS, but even hydrated metal cations can be partitioned to the PEG-rich phase if a suitable extractant (e.g., halide, dye, crown ether, etc.) is used to produce a more chaotropic ion-complex.

Jan 1, 1999

By P. N. Anyalebechi

The effects of application of steady and pulsed electric current on the cast microstructures of ingots of a 7050 type aluminum alloy have been experimentally investigated over a solidification rate range of 0.1-10 K/s. This involved the application of an electric current of 465-930 mA/cm2 of melt surface area to laboratory-size ingots solidified in a unidirectional manner. Within the ranges of electric current density and solidification rate investigated, the applied electric current reduced the average dendrite, grain, and second-phase particle size. It also made the size distribution of the second-phase particles more uniform. The mechanism for the observed refinement of the cast microstructure by the applied electric current is not well understood. The potential effects of heat-induced local convections, shear stress-induced fragmentation of dendrites, increased temperature gradient due to Joule heating and the thermal and constitutional supercooling engendered by Peltier, Thompson, and Joule heating are discussed.

Jan 1, 2009

By Milton Manrique

The thermal decomposition of zircon concentrates in a non-transferred arc thermal plasma flow reactor was investigated. The plasma torch was operated using argon-helium and argon-nitrogen mixtures as plasma gases. The effect of power, feed rate and zircon particle size was studied. Products were characterized by XRD, SEM, TEM and chemical analytical techniques. The average size of the product was in the submicron range. Free energy minimization plots were used to predict the behavior of the system under different operating conditions. A kinetic model to describe the different stages of the thermal decomposition process is proposed. The results of this investigation showed a significant segregation process where the zirconia-rich product is collected in the reactor while the silica-rich product is collected in the filter. TEM analysis indicated that silica vapor is condensed on the surface of the zirconia particles.

Jan 1, 1996

By P. D. Lee

The effect of strontium on porosity formation in aluminum-silicon alloys is not well understood and there is no consensus upon the cause of the effects observed. This paper describes a series of experiments where the effect of adding strontium on pore formation was observed directly with combination of a traditional temperature gradient stage and real time micro-focus radiography. These in situ observations provide a new insight into the effect of strontium on the nucleation and growth kinetics of porosity. The addition of strontium was found to have a minor effect on the growth of the pores in the mushy zone. However, strontium appeared to alter the nucleation and stability of hydrogen bubbles within the melt. The interaction of strontium with titanium-boride grain refiners produced an even stronger change in the nucleation and stability of the bubbles formed.

Jan 1, 2002

By Yiling Zhang, Paul A. Salvador, Gregory S. Rohrer

"Photocatalysis utilizes solar energy to produce hydrogen by splitting H2O. When a thin film of photocatalyst TiO2 is supported on a ferroelectric BiFeO3 substrate (band gap ~2.5 eV), the TiO2/BiFeO3 heterostructure is capable of photochemically reducing Ag+ to Ag0 in aqueous solutions under blue light with enhanced efficiency. The observation of spatially selective silver patterns on surface of the heterostructure after reaction suggests that photogenerated electrons and holes in ferroelectric BiFeO3 are driven in opposite directions to reduce their chance of recombination. Comparisons of the amounts of reduced silver on TiO2 film grains with distinct phases/orientations show that the reactivity is mildly preferential on anatase TiO2 phase and does not strongly depend on crystallographic orientation of BiFeO3.IntroductionTitania (TiO2) is capable of photocatalytically converting H2O to hydrogen and oxygen under the irradiation of ultraviolet light. [1, 2] One of the limiting factors for titania to be used as an effective photocatalyst is its band gap. Because the absorption edges of rutile and anatase titania are at 3.0 eV and 3.2 eV, respectively, they can only absorb light in the UV portion of the spectrum, which is about 3% of the available solar energy. [3-5] This limitation has motivated attempts to modify the absorption edge of titania so that it can absorb visible light.One strategy is to substitute a portion of the titanium and/or the oxygen with other atoms. There are numerous reports on visible light absorption of titania by doping and co-doping of Cr, V, Mo, Sb, Fe, N, S, C, and F. [6-34] Another strategy is to add an adsorbed molecular species that absorb visible light and donate an electron or hole to the titania, such as organic dyes [33, 35, 36] and Ce3+/Ce4+. [37, 38]The strategy in the present work takes the approach of depositing a pure titania thin film on a visible light absorbing substrate BiFeO3 to induce visible light activity of the heterostructure. BiFeO3 is a semiconductor with a band gap of about 2.5 eV [39-41] and is photocatalytically active in visible light. [42, 43] It is also ferroelectric with spontaneous polarization along pseudo-cubic <111> directions of 6.1 µC cm-2. [44] The spontaneous polarization gives rise to internal electric fields that drive photogenerated charge carriers, namely electrons and holes, in opposite directions to reduce their chance of recombination. [45-47] Additionally, the separation of electrons and holes leads to the spatial separation of reduction and oxidation half reactions so that the back reaction of intermediates is also suppressed. Such charge carrier separation has been reported in TiO2/BaTiO3 heterostructures with UV light illumination. [48-51] The TiO2/BiFeO3 heterostructures in this work combine both advantages of the relatively narrow band gap and the internal fields in BiFeO3 to enhance the overall photocatalytic activity."

Jan 1, 2014

By A. Cullaj

Several industrial sites suffer from the contamination of soils from heavy metals, which are emitted among others by anthropogenic mining and metallurgical activities. Effective and economic physicochemical technologies for remediation of these sites remain complicated and costly. A new alternative remediation technique is the so-called phytoremediation. This is based on the ability of some plants to accumulate very high concentrations of metals from soils and thus providing the basis for a remediation of the contaminated sites. This technique as an emerging branch of natural biotechnology, has several advantages compared to the sophisticated physicochemical techniques of soil remediation. It is not only environmentally friendly but also its costs are quite low since it is solar driven. Furthermore plants can accumulate metals to such levels that the mineral recovery maybe feasible even in conventional Ni refinery or smelting operations. In this work, thc potential of many plants to accumulate nickel has been investigated in order to identify the species which offer the best phytoremedial potential for nickel contaminated soils in Albania. Field surveys have been made in five nickel-containing sites in order to identify the nickel tolerant species that have spontaneously grown in contaminated soils. Atomic Absorption Spectrometry measurements were carried out on 145 different plants collected. 16 of them were identified as having an hyper ability to accumulate nickel since they contained more than 10 000 mg Ni per kg (DW). Seven taxa are of Alyssum genus and one of Bornmuellera genus of Cruciferae. The highest accumulation of nickel was present in aerial parts of Alyssum murale var. chlorocarpum Hausskn (25 500 mglkg or 2.5%) and Alyssum markgrafli O.E. Schulz (23 700 mg/kg or 2.37%). The seeds germinated are more evidenced at A.m.var. chlorocarpum, about 63%. These plants are suggested as the most promising species to be used for phytoremediation purposes in nickel contaminated soils and phytoextraction of nickel.

Jan 1, 2003

By M. C. Esposito

Seven pyrite samples purified from coal sources and one ore source pyrite (for comparative purposes) have been characterized by chemical and mineralogical analyses, inherent floatability, apparent specific gravity, surface area, semiconductor type, optical anisotropy, dissolution and oxidation rate. The data clearly demonstrate that pyrites from various coal sources differ not only from ore pyrite but from each other as well.

Jan 1, 1987

By John Hanna

The University of Alabama Mineral Resources Institute (MRI) has developed a unique process for selective fatty acid flotation of carbonate gangue from sedimentary apatites (francolite) in the pH range of 4-6, without collector conditioning of the pulp. The process, which does not require an apatite depressant, was modified to beneficiate a high MgO siliceous phosphate matrix from South Florida. The modified process includes two flotation stages, one for carbonate removal, as mentioned above, and the other for phosphate recovery from the siliceous gangue. The selective flotation separation of the carbonate and phosphate from siliceous constituents of the matrix at various pH levels and collector dosages are discussed. In the carbonate flotation stage, about 70% of the MgO was rejected in the froth, and the phosphate flotation stage produced concentrates analyzing about 31% P20S&apos; 0.7% MgO and 4% acid insolubles. The overall P20S recovery in the two stages is about 85%.

Jan 1, 1989

By F. Patisson

During exothermic gas-solid reactions, heat generation makes temperature rise and modifies the rate of the various mass transfer processes, namely the chemical reaction itself, the pore diffusion and the external transfer. We have investigated this thermal effect during the oxidation of zinc sulfide porous pellets in a thermo balance furnace, between 550 and 900°C-and under O2-N2 atmosphere. The results have been&apos; analyzed by using, firstly, the law of additive reaction times derived from the isothermal Grainy Pellet Model, and, secondly, a new numerical model taking into account non-isothermal conditions. Both the models can satisfactorily simulate conversion versus time, but the numerical model also depicts the temperature evolution within the pellet. Finally it is shown that owing to the heat generation the zinc sulfide oxidation takes place under diffusion control (3/4 internal, 114 external) in all the cases studied. During the course of reaction, the. pellet undergoes strong temperature variations, with thermal gradients confined to a shell oxide layer.

Jan 1, 1996

First, a classification of the various primary sources of feed materials for the production of cobalt is presented from a mineralogical point of view : sulfides, arsenides, sulfo-arsenides and oxide minerals. Each of these cate- gories will be characterized by its behaviour towards concentration methods, taking account of the presence of the associated minerals of other metals and of the nature of the gangue minerals. Then, for each category of cobalt bea- ring ores, typical flowsheets of treatment will be presented and discussed and the characteristics of the cobalt concentrates produced will be under- lined having in view their subsequent processing by pyro - and (or) hydrome- tallurgical methods.

Jan 1, 1988