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By A. P. Pavia

Investigation on profitable ways to recover significant quantities of silver remaining dissolved in highly concentrated chloride solutions frequently pass through the development of solvent extraction (SX) routes. In this work, the general pathways involving Ag(I) extraction by dibutylthiourea (DBT) or tetraethylthiuram disulfide (disulfiram, DSF), from concentrated acidic chloride solutions, are investigated. With this purpose, the dependence of Ag(I) distribution coefficient on ligand and chloride concentrations has been analysed. Furthermore, in order to check whether there is some protonation at any site of DBT or DSF after contact with adequate chloride phases, lH NMR has also been used. The collected spectroscopic data suggest that anionic Ag(I) extraction reactions are not likely to occur. Based on the overall results achieved, proposals for the most probable Ag(I) extraction reactions are made.

Jan 1, 2001

By Zhongning Shi, Ramana G. Reddy

"By cyclic voltammetry and potentiostat electrodeposition using Potentiostat/Galvanstat, electrochemical behavior on Ag electrode in electrolyte 0.2M NaOH+0.01MPb(NO3)2-0.01M TeO2 -0.01M TlNO3 solution were also carried out at 298K. The processes of electrodeposition of Tl2Te3 and PbTl4Te3, a thermoelectric material, are reported along with analysis of the composition of the obtained deposits. The results showed that two different underlying processes are occurring depending on deposition potential. One process involves the reduction of TeO3 2- and Tl+ to Tl2Te3 in a potential interval of -0.70V < E < - 0.89V (vs. Hg/HgO). A second process at more negative reduction potentials involves reduction of TeO3 2-, Pb2+ and Tl+ to PbTl4Te3 in a potential interval of -1.02V < E < - 1.19V. The crystalline Tl2Te3 and PbTl2Te3 were deposited electrochemically on Ag substrates at -0.84V and -1.10V respectively. Thermoelectric (TE) material can form a temperature gradient across the material to make electric voltage, which is popular in waste heat utilization and recovery industry. Lead telluride, PbTe, is a small band gap semiconductor of 0.32eV at 300K. PbTe can change its n-type semiconductors with Pb-rich to p-type semiconductors with Te-rich[1]. And it is one of the best TE materials used in thermoelectric generators working between 500K and 600K, or even at a higher temperature of 800K.Three facto,rs play a role in the performance of a thermoelectric material: electrical conductivity (s), thermal conductivity(?), and the Seebeck coefficient (S). These can be combined with absolute temperature (T) to give a figure of merit (ZT) for the material, ZT = s2sT/?. By increasing the electrical conductivity and decreasing the thermal conductivity, which can enhance the ZT value, many efforts, such as alloying with other elements and making the materials nano-sized, have been done to improve its properties recently. Hsu et al. reported that the ZT value of Cubic AgPbmSbTe2+m is increased to 2.2 by doping Ag-Sb to PbTe.[2]."

Jan 1, 2011

By Rodney L. Williamson

Optimal estimation theory has been applied to the problem of estimating process variables during vacuum arc remelting (V AR), a process widely used in the specialty metals industry to cast large ingots of segregation sensitive and/or reactive metal alloys. Four state variables were used to develop a simple state-space model of the V AR process: electrode gap (G), electrode mass (M), electrode position (X) and electrode melting rate (R). The optimal estimator consists of a Kalman filter that incorporates the model and uses electrode feed rate and measurement based estimates of G, M and X to produce optimal estimates of all four state variables. Simulations show that the filter provides estimates that have error variances between one and three orders-of-magnitude less than estimates based solely on measurements. Examples are presented that verify this for electrode gap, an extremely important control parameter for the process.

Jan 1, 2001

By Y. Fautrelle, F. Felten, O. Metais, Y. Du Terrail

"We deal with the prediction of electromagnetically-driven turbulent flows by means of a Large-Eddy- Simulation method (LES). The model is applied in the case of a liquid metal pool submitted to a polyphase linear electromagnetic stirrer. We investigate two cases: (i) the frequency of the magnetic field is equal to 50 Hz; in that case the effects of the pulsating part of the Lorentz forces may be neglected; (ii) the frequency of the magnetic field is low (f= 1 Hz), then the oscillating part of the electromagnetic forces is taken into account. The LES predictions agree well with the mean velocity measurements, as does the standard k-a model. However, as for the turbulent kinetic energy predictions, there is a large discrepancy between the two models. When the oscillating part of the Lorentz forces is taken into account, the computations show that the fluid flow is sensitive to the unsteady part of the forces. We find that the mean velocity is not affected by the fluctuating component of the force. As for the turbulence parameters, the presence of the pulsating part leads to a significant reduction of the turbulent kinetic energy, whilst the turbulence length scale decreases.IntroductionElectromagnetic stirring is commonly used in various metallurgical processes. In continuous casting for example, it may improve the structure of the solidified metal products. Fluid flows generated by electromagnetic stirrers have been extensively investigated (1 ). As for numerical predictions, many works have been published on the subject. In most of the previous works, onepoint closure models have been used. The most used model is the well-known k-i:: model. Those models yield fairly good results as for the mean velocity prediction. However, it has two main drawbacks:(i) the turbulence is not predicted accurately,(ii) it is not well fitted for unstationary flows as well as transitional turbulent motions, where theReynolds number is moderate."

Jan 1, 1999

By Xuerong Wen

The oxidation behavior of TiAl3 intermetallics was investigated as a hnction of time at 1273K in pure dry oxygen. The oxidation experiments were carried out using TGA method. The oxidation scales were analyzed using SEM, EDS and X-ray diffraction methods. The structures of oxides formed at the different oxidation times were analyzed. The mechanism of oxidation of TiAl3 intermetallics was discussed.

Jan 1, 1998

By Gopalakrishna M. Rao

"Several industrial and government laboratories are of the opinion that solar--cell technology will grow into a billion-dollar industry by the year 2000, especially if oil prices rise again. Of the variety of materials that have been investigated as the major component of photovoltaic systems, silicon appears to have an outstanding advantage. The cost factor is the primary importance in photovoltaic development, since the technology to make silicon cells of acceptable efficiency and life time has existed since the early stage of the space program. Electrometallurgy is one of the low--cost processes for the production of silicon, since it allows direct, single-stage production from some abundant, inexpensive source materials such as silica and fluorosilicates. Among several systems, two are given particular attention, using inorganic baths with Si0 2 or K2SiF6 as the source of silicon respectively. They appear capable of development to commercial production. Conceptual designs of a commercial--scale cell for silicon production at temperatures above its melting point, and of a pilot' plant for plating silicon from an all-fluoride bath are presented. Energy ProspectsThe major changes in the world energy since the first energy crisis in 1970 have impacted on our community. When oil was $40 a barrel in the mid-1970s, we became obsessed with the energy conservation and a search for alternate energies. Even though the crude oil fell below $15 a barrel during the last several years, our energy security fears continue to haunt us. This time it is not the scarcity, but the abundance of foreign oil and the decline in the domestic production.The prospects of energy depends on the demand and supply of energy. These, in turn, depend on future energy prices, which are linked to economic factors, political events, and unforeseen circumstances. Although no one can predict the future with certainty, three energy consumption patterns used by the Ford Foundation are as shown in Fig. 1."

Jan 1, 1988

By D. J. Murdock

Cominco Ltd. has developed a number of innovative technologies for electrowinning. The paper discusses the application of these technologies to the copper industry. Tankhouse and cell design will be discussed in addition to anode cleaning and cathode handling. Specific examples of the application of this technology to the copper industry are cited.

Jan 1, 1987

By Hitoshi Iijima, Fumitaka Tsukihashi

"Fine powder of tantalum is used as materials of electric condenser. It is important to control the distribution of particle diameter of tantalum fine powders for the commercial use. In this study, fine powders of tantalum were produced by reducing tantalum chloride vapor with hydrogen gas at 1673 and 1773K. The tantalum chloride vapor was reduced with hydrogen and the produced fine particles of tantalum were collected to observe the distribution of particle diameter. The effects of reaction temperature, partial pressure of hydrogen gas and vaporization temperature of tantalum chloride on the distribution of particle diameter and reaction efficiency of reduction were determined. The mechanism of reduction reaction of tantalum was discussed.IntroductionThe ultra fine powder shows various different physical properties from that of bulk materials. Therefore, the application of ultra fine powder to various fields such as magnetic material, electric material, catalyst, etc is anticipated. The control of shape of powder, size distribution, property of agglomeration, purity is required for the practical use of ultra fine powder. Although the ultra fine powders of ceramics are produced by various methods, the ultra fine powder of metals are produced by the evaporation in gas atmosphere, plasma evaporation process, chemical vapor deposition process, and reduction and precipitation in liquid phase depending on the metal and productivity. The chemical vapor deposition process has features that pure metal powder can be obtained and the control of the distribution of powder size is easy. [1,2,3,4,5]"

Jan 1, 2000

By Barry Welch, Kai Grjotheim

"The capital intensive nature of the present process for aluminium smelting, the low productivity per unit reactor, and pressure to reduce the electdcal energy demand have motivated the search for an alternative process. Optional routes include carbo-thennal reduction of alumina (using an alloy phase immediate), chlorination followed by electrolysis of aluminium chloride, and electrolytic decomposition of alumina using inert electrodes. Materials performance and reactor design constraints have been a major limitation for alternatives. However parallel research has led to considerable advances in the process efficiencies and scale of both the Bayer process and the Hall-Heroult cells.Future development of alternatives is dependent on breakthroughs in Materials Science such as the development of stable conducting anodes and stable wettable cathode materials. However if successful it is probable that some spin-offs will be retrofitted to existing cells. Therefore the basic Hall-Heroult technology will continue as the dominant process for at least the next half century.IntroductionThe present Bayer/Hall-Heroult process for production of aluminium is just over 100 years old. Frequently, during the century of its technological development questions have been raised as to whether it is the ideal route for metal production. The questioning was particularly intense in the period between the mid-1950s and the mid-1060s when the limitations of the Hall-Heroult electrolytic stage were evident. Then the cells were only 30 to 35 % efficient with respect to the utilisation of the hydro-electricity (requiring 16 18 kWh/kg, thus making it strongly dependent on cheap electrical energy), while the size of cells being installed were 80 to 130 kA. Hence the process was capital intensive, the productivity per reactor volume low, and the process was labour intensive (requiring about 15 man hours per tonne of aluminium). In addition, the use of pitches for Soderberg anodes and the fluoride electrolyte were creating problems through emission. At that time material science had paid little attention to the manufacture and use of carbonaceous materials or the development of alternatives that were corrosion resistant to cryolite or liquid aluminium. Hence cell lives were short - typically 600 to 1000 days - thus adding to operating costs. Thus the grass over the fence, as foreseen in 1960s vintage crystal balls appeared much greener for alternative processes."

Jan 1, 1988

By M. J. Adam

The U.S. Bureau of Mines is investigating the partitioning of selected complex minerals into simple phases using sulfidation reactions. Successful partitioning of complex mineralogy to simple phases may afford an opportunity to improve selective extraction of mineral constituents of economic value. The research has shown that complex minerals, such as chalcopyrite (CuFeS2) and pentlandite [(Fe,Ni)9Se]&apos; may be partitioned to the simpler phases covellite (CuS) plus pyrite (FeS2) and vaesite (NiS2) plus pyrite (FeS2), respectively. Demonstrations of these reactions were verified through long-react ion-time (24 h or more) experiments, but basic rate investigations and modeling were not included in the previous research. This report describes research aimed at determining the rate at which the complex mineral CuFeS2 converts to the simple sulfides CuS plus FeS2. Small samples of CuFeS2 were blended with elemental S prior to thermal treating under an He atmosphere for time periods up to 4 h. Products from each treatment period were characterized using metallography, chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results of the investigation revealed a rapid conversion of CuFeS2 to CuS plus FeS2 early in thermal treatment periods. As the reaction occurred, a CuS rimming of particles was observed which separated the reacting species (CuFeS2 and S) and caused a considerable decrease in transformation rate.

Jan 1, 1991

By S. P. Rivers

The stainless steel industry re1ies on nitric-hydrofluoric acid (HNO,/HF) pickling solutions to remove surface contaminants and maintain the corrosion resistance of the steel. More stringent environmental guide1ines are expected to be placed on the disposal of these solutions which could significantly increase processing costs. The U.S. Bureau of Mines has been conducting research to develop a process for recycling depleted pickling solutions, thus reducing the quantity of by product acids generated. Research has shown that F- can be liberated from the predominant iron fluoride species (FeF,&apos;) by using oxalic acid in an electrodialysis cell. Ion selective membranes allow dissolved metals in the depleted solution to be replaced with hydronium ions by metathesis, thereby regenerating the HF. The regenerated HN03/HF is then retained in the pick1ing solution. This paper reports on the research effort at the U.S. Bureau of Mines Rolla Research Center to apply electrodialytic recycling to HN03/HF pickling solutions.

Jan 1, 1993

By V. P. Keran

The lead and copper smelting processes employed by Mount Isa Mines Limited, Mount Isa, Australia, are used to illustrate an operating viewpoint of some problems and solutions encountered in existing commercial sulphide smelters. The smelting processes discussed; include updraught sintering, blast furnace and reverberatory smelting, and converting. Selected examples are given of methods implemented, and options available, to improve the productivity and efficiency of conventional smelting processes.

Jan 1, 1983

By J. R. Rendón

Cylinders of commercial aluminium alloy 6063 were homogenized under different conditions. The experimental results indicated that the general mechanical behaviour as related to curves of 0.2% yield strength, ultimate tensile strength and Brunnell hardness versus homogeneizing process is the same in both cases. The mechanical properties as compared to those required by plant specifications, tend to be better with increasing values of % Mg2Si in the alloy, as expected. The electron microscopy investigations revealed that in both homogeneizing processes the resulting microstructure consist of significant spheroidizing of the alpha phase (AlFeSi) and fine-needle type structure of beta phase. The alpha phase was also present in a Chinese type scripture. Furthermore, the slow cooling within the furnace resulted in the nucleation and growth of Mg2Si precipitates generally along the grain boundaries.

Jan 1, 1997

By Axel Hoppe

Although Tantalum is not usually regarded as a precious metal, its pricing structure is very similar to that of Silver. Different from precious metals, Tantalum has only industrial applications and its use is about 1000 metric tons per year. The intrinsic value of Tantalum already in .the past was a driving force for its recycling. Based on these facts the Tantalum industry world-wide is approaching the closed-loop concept of its recycling. A detailed material flow of Tantalum processing as well as recovery of residues and used products will be discussed.

Jan 1, 1995

By Do-Hyeong Kim, Tae-Jung Kim, Seung-Yeon Won, Jong-Jin Pak, Min-Kyu Paek

Liquid iron alloys containing V, Mo, and Ni can be produced by the carbothermic reduction of spent catalysts used in petrochemical industry. Thermodynamics of carbon in these alloy melts is important for refining these alloys. In the present study, the carbon solubility in Fe-V, Fe-Mo, Fe-Ni, Fe-V-Mo, Fe-V-Ni, Fe-Mo-Ni and Fe-V-Mo-Ni alloy melts of various compositions was measured at 1873 K. The temperature dependency of vanadium effect on carbon solubility in liquid iron was also measured in the temperature range from 1823K to 1923K. The additions of vanadium and molybdenum significantly increased the carbon solubility in liquid iron alloys while nickel decreased the solubility. The experimental results were thermodynamically analyzed using Lupis’ relation at constant activity to determine the first- and the second-order interaction parameters of vanadium, nickel and molybdenum on carbon at carbon saturated condition. Using thermodynamic parameters determined in the present study, the carbon solubility in Fe-V-Mo-Ni alloy melts of various composition were accurately predicted and verified experimentally at 1873 K.

Jan 1, 2014

By Christopher B. Vierrether

Reflected light microscopy, scanning electron microscopy, and electron microprobe analysis have been used to determine the mineralogy, phase percentages, grain sizes, textures, and partitioning of cobalt and nickel in two cobalt-nickel rich mattes. These mattes were prepared by submerged bath smelting from a flotation cobalt-nickel concentrate containing 4.8% cobalt and 5.1% nickel. The concentrate was derived from lead-zinc-copper ores of the Viburnum Trend, southeast Missouri. Eleven discrete phases have been distinguished in the matte samples, three of which contain significant cobalt and nickel. The phases are cobaltpentlandite ((Co,Ni,Fe)9S8), cobalt-bearing marmatite ((Co,Fe,Zn)S), shandite (Ni3Pb2S2), bornite (Cu5FeS4), galena (PbS), magnetite (Fe3O4), pyrrhotite ((Co,Ni,Cu,Fe)1_xS), chalcocite (Cu2S), CuPbS phase, metallic copper, and metallic silver. Cobaltpentlandite and cobalt-bearing marmatite- occur in coarse grains (50 µm) that would separate readily during grinding, but shandite contains small (5 - 10um), abundant inclusions of pyrrhotite and bornite.. Some mineralogical variations between the two matte samples were due to differing degrees of oxidation during smelting,

Jan 1, 1988

By Bora Derin

The partial pressure ratios of sulfur and oxygen for several copper flash smelting plants were derived using the Reddy-Blander (RB) model and predicted dissolved sulfur contents available in the literature. The sulfide capacities (Cs) of six different flash smelting plants (FeO-CuOo.5- CaO-MgO-FeOu-AlO15-SiO2) slags were calculated. The log (PO2/PS2) versus matte grades of various industrial processes was determined. The PO2/PS2 ratio increased with an increase of copper grade. The calculated partial pressure ratios for the copper flash smelting are in good agreement with those of the experimental data.

Jan 1, 2003

By D. Lui, B. G. Thomas, B. Ho

"Results from mathematical models and plant experiments are combined to quantify the effect of transverse depressions and oscillation marks on heat transfer in the continuous casting mold. A heat transfer model has been developed to calculate transient heat conduction within the solidifying steel, coupled with the steady-state heat conduction with the continuous casting mold wall. The model features a detailed treatment of the interfacial gap between the shell and mold, including mass and momentum balances on the solid and liquid powder layers. The model predicts the solidified shell thickness down the mold, temperature in the mold and shell, thickness of the resolidified and liquid powder layers, heat flux distribution down the mold, mold water temperature rise, ideal taper of the mold walls, and other related phenomena. The important effect of non-uniform distribution of superheat is incorporated using the results from previous 3-D turbulent fluid flow calculations within the liquid cavity. Results from plant experiments confirm that transverse surface depressions and oscillation marks form at the meniscus and move down the mold. Measurements of mold thermocouple temperatures and breakout shell thickness were used to calibrate the models. The results indicate that the surface depressions and oscillation marks are filled with mold flux, but still have a significant effect on decreasing heat transfer. The predicted mold temperature fluctuations are consistent with measurements. If the depressions become filled with air, their effect is greatly increased. These results should be useful in the difficult task of interpreting transient mold thermocouple signals for on-line quality monitoring.IntroductionMany different types of intermittent surface defects on steel slabs arise during initial solidification in the mold of the. continuous casting machine. These defects include deep oscillation marks, surface depressions, and cracks. They may lead to quality problems, such as slivers, in the final rolled product. In severe cases, breakouts may occur, where liquid steel bursts through a thin section of the shell and drains over the casting machine below the mold."

Jan 1, 1997

By M. L. Sorokin

The thermodynamic of nickel production from laterite ore and from sulfide concentrate can be analyzed using PO2 - PS2 diagram of the Ni-Fe-S-0-SiO2 system. The procedure of the diagram computation is suggested and the diagrams for various temperature and Fe/Ni ratio are calculated. Three-suffix Margules equations are used for the calculation of the thermodynamic properties of three solutions: liquid matte, liquid slag and solid Fe-Ni alloy. The diagrams are used for the considerations about direct one-stage metallic nickel production.

Jan 1, 1994

By Chuanfu Zhang

Based on Thermogravimetric and Differential thermal analysis (TGA-DTA), porous copper powder is prepared by thermal decomposition of complicated copper oxalate. The effects of various conditions on the morphology, crystalline grain size and specific surface area of copper powder were investigated, including temperature, duration, mixing ratio of nitrogen and hydrogen. Furthermore, composition and morphologies of the products were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) and BET adsorption isotherm. It is found that porous copper powder was produced under optimum conditions. The specific surface area is over 6.74 m2?g-1, and average pore size in particles is about 30.3 nm. After comparison of SEM images, the final product Cu well inherits the morphology of the precursor, thus a mechanism of in-situ decomposition is proposed.

Jan 1, 2009