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By Anand Kumar, Pradeep kumar Jha, Suman Kant, Pradeep Kumar

"It has been a major challenge to reduce the intermixed grade formation during ladle change-over operation in continuous casting process of tundish steelmaking. The F-curve generated by step input of the tracer (new grade steel) tells about the intermixed grade amount for different grade specifications. Use of flow modifiers is beneficial in reducing the intermixed grade because of the change in slope (in different time zones) and position of the F-curve due to their placement at tundish bottom. Present study aims at investigating the role of dam placed before the outlet in a multi-strand tundish with reference to the slope behavior of F-curve in different time zones during the teeming operation plays an important role in determining the intermixed amount.Introduction In Continuous casting process, the old grade steel remaining in the tundish (reservoir between ladle and mould) from the old ladle gets mixed with new grade steel from new ladle and leads to intermixed grade which is considered to be of inferior quality. Although formation of intermixed grade is inevitable with the sequential method of casting, its amount can be controlled by changing the flow behavior of steel inside the steel. Intermixing in a slab caster tundish was simulated using 3-D numerical model based on k-å turbulence equation and compared their result with that of water model experiment Yeh and Hwang [1]. Huang and Thomas [2] reported that quantity of residual fluid in tundish affects the composition distribution in the transitional slab and thus the intermixed length. Huang and Thomas [3] developed three sub models to predict mixing in tundish, liquid core of strand and solidification. Thomas [4] developed a one dimensional model to simulate the final composition distributions in slab caster of continuous casting and investigated the effect of process variables on the intermixing. Alizadeh mehdi et al., [5] simulated of the intermixing phenomenon for slab casting for three different sub models. Goldschmidt et al. [6] developed a numerical model that predicted the location of the intermixed steel in a four line round caster. Lan and Khodadadi [7] studied for the transient fluid flow of liquid steel, heat transfer and solidification during the flying tundish change process. Cho and Kim [8] developed a mixing model to predict the outlet concentration of the tundish during grade transition. Most of the work reported in the literature has dealt with intermixing in slab caster tundish. Billet caster units are more often being used by steel industries due to growing demand of billets. The multiple outlets lead to varying degree of intermixing with time owing to their different distance (location) from the inlet. Use of flow modifier to minimize the intermixed amount, however has also not been discussed in detail so far. Further no work has been reported regarding effect of slope of F-curves obtained through different outlets on intermixing. Hence keeping these objectives in mind attempt has been made by authors to analyze the slope of Fcurves after dividing them into three different time zones and the effect of these time zones on intermixing."

Jan 1, 2012

By Katragadda Sarveswara Rao

"In view of the increasing importance of processing lean ores as potential future resources, efforts are being made worldwide to develop suitable technologies for the recovery of both nonferrous, base and precious metals. There are various types of low grade ores present in many countries. Gradually, the mineral reserves for production of metals have undergone complex changes with regards to their grades and particularly the physical and chemical properties of the minerals to be separated from each other. So, there is a need for new processing routes or the upgrading of existing technologies to recover metal values that are otherwise unutilized. Accordingly, an overview of the different types of mineral resources and economical processes, based on ore horizons, consumption of energy and reagents and environmental concerns, is made in this paper. In addition, the paper provides a summary of metallurgical and engineering challenges to be overcome when implementing new technologies and concepts with regard to base metal extraction and sulphur removal efficiency.IntroductionLow grade multimetal complex sulfide ores are likely to become an importance source for nonferrous as well as precious metals in the near future. The principle metallic minerals are chalcopyrite, sphalerite, galena, pyrite, pyrrhotite, arsenopyrite, tetrahedrite, boulangerite and cassiterite. Such ores are located throughout the world as multi-pocketed reserves which have present complex challenges with regard to their grades and particularly the physical and chemical properties of the minerals to be separated from each other. Their compositions can vary widely from one deposit to another and even from one location to another in the same deposit, and this poses a problem for the recovering metals present therein. Successful aqueous processing of complex sulphide ores depends on the composition and mineralogy of the raw materials and on their leaching behaviour."

Jan 1, 2012

By D. M. Hausen

A refractory siliceous low-grade silver ore (265 g/t Ag) from a prospect in Sonora, Mexico was investigated mineralogically and metallurgically to evaluate extraction of the silver by conventional methods. Approximately half of the silver was recoverable, occurring as coarsely crystalline acanthite (70-300 Am) that was liberated in material crushed to minus 10 mesh. The remaining silver is refractory and occurs mostly as finely locked (-2 to 0.2 Am) acanthite in cherty quartz, and as minor amounts of finely disseminated stylotypite or freibergite in fluorite. The mineralogic data have thus served to explain the 50-60% recovery of silver by flotation and cyanidation.

Jan 1, 1991

By K. Rajani Kanth

Environmental problem is the major concern for any industry and there is a great need to that along green lines. Sangam Dairy being one of the most famous and wide spread Dairies in India, produces wide spectrum of milk products. The BOD levels of effluent water of this industry with MIF treatment were found to be around 100 ppm. Lot of research has been expended in the past to bring down the BOD levels to bare minimum. The main objective of the present study is to minimize the BOD level to the required level stipulated by environmental standards by employing various seeding materials. For this purpose microbes like Bacillus Subtiles, Pseudomonas, Aspergillas, Staphylococcus, and Pencilium have been employed and BOD levels were analyzed. Various Reagents, solutions with different dilution levels have been successfully prepared. Initial and final Dissolved Oxygen levels were determined before and after incubation. From the DO data, BOD was evaluated for all samples and comparison analysis of various seeding material was carried to suggest the efficient seeding material for the ETP plant. In the process, solutions of different dilutions have been prepared using difficult reagents. These samples are treated with above mentioned microbes and BOD levels are estimated. It has been observed that staphylococcus and Pseudomonas proved to be the best seeding materials. When there microbes have employed BOD levels fall to less than 10 and 20 ppm respectively

Jan 1, 2006

By Nathaniel Arbiter

The first ammonia leaching plants, applied to copper carbonate and native copper tailings in 19 15, were followed more recently by research and development of flowsheets for ammonia leaching of sulfide concentrates. These were applied to two commercial plants. Anaconda's Arbiter Plant started up in 1974 with a design capacity of 36,000 tons/year of cathodes, to be produced by ammonia leaching with oxygen, followed by solvent extraction and electrowinning. The plant shutdown in late 1977 as a result of high maintenance and operating costs, partly due to harsh winters; to complications associated with sulfate disposal; and to changes in mineralogy. BHP's Coloso plant in Chile was designed to produce 80,000 tons/year of cathodes by leaching part of Escondida's concentrate production. Using a similar flowsheet but with air and low temperatures to avoid sulfate production, it started up in late 1994 and shutdown in mid-1998, after failing to reach cathode design capacity, and experiencing problems with its technology. The paper reviews the technologies and also alternative methods for overcoming the problems.

Jan 1, 1999

By K. Tozwa

The electrical conductivity of electrolytes for copper electrorefining and electrowinning processes has been reported by many researchers since 1911. The experimental results show that the conductivity increases with an increase in sulfuric acid concentration and decreascs with an increase in copper concentration. In pure copper sulfate solution, however, the conductivity increases with an increase in the copper concentration. After confirming the conductivity of pure and acidified copper sulfate solutions experimentally, the concentrations of hydrogen ion and free (not hydrated) water in the electrolytes were estimated and it was found that the relation between the conductivity of acidified copper sulfate electrolytes and the products of concentration of hydrogen ion and free water is linear. Accordingly, the conductivity of acidified copper sulfate electrolytes increases with an increase in sulfuric acid concentration and decreases with an increase in copper concentration.

Jan 1, 2003

By William Petruk

The Kidd Creek base metal deposit near Timmins, Ontario contains around 0.15 wt% Sn, mainly as cassiterite. The cassiterite occurs largely as inclusions in sphalerite, with 85% being in grains smaller than 18.5 micrometres in diameter. Concentrates and tails from the company's Cu, Pb and Zn circuits were studied to determine the liberations and recoveries of cassiterite in the products. The ore had been ground to about 65.% minus 44 micranetres in diameter (-325 mesh); 55% of the cassiterite was liberated. About 92% of the liberated cassiterite and 70% of the unliberated cassiterite were in the concentrator tails, and 20% of the unliberated cassiterite in the zinc concentrate. The company had attempted to recover the cassiterite from the concentrator tails by gravitational methods but recoveries were low. The grain size of the cassiterite in the gravity Sn concentrate was similar to the grain size of the liberated cassiterite in the concentrator tails. Research on flotation of the fine grained cassiterite from Kidd Creek ore has been conducted,

Jan 1, 1990

By Kenji Monden

A simple technique is presented to evaluate optical property of biomimetic microlens array (BMA) as an antireflective surface on a polydimethylsiloxane (PDMS) sheet. The integration of these structures is done by a thermoforming process. We have only UV-VIS spectrophotometer for optical evaluation apparatus. The transmittance of the sheet is measured with angled sample holder. The 50 deg. transmittance of 270nm pitch BMA on PDMS sheet increases from 87 to 92% after the moth-eye structure is introduced. The transmittance of 350nm pitch BMA on PDMS sheet increases from 87 to 96% after the moth-eye structure is introduced. The transmittance increases with increasing pitch of BMA. The results obtained using UV-VIS spectrophotometer with handmade sample holder.

Jan 1, 2015

By He Zhi-jun, Ning Zhe, Pang Qing-hai, Zhang Jun-hong, Zhan Wen-long

The effect of microwave irradiation on grinding property of coal was studied by using Hardgrove grindability index tester. Superior grindability of coal was obtained to varying extent after microwave irradiation treatment. The variation in microstructure of pulverized coal during microwave irradiation was observed by utilizing scanning electronic microscope (SEM). The results indicated that the different microwave absorbance of minerals and carbon matrix led to cracks on their interface, by which coal particles were further pulverized and therefore the granularity of coal powder was reduced. Due to the different formation process of various coals, bituminite and anthracite are very different in physical and chemical properties. According to the content of coal pulverization, it can found that microwave irradiation has a stronger pulverizing effect on bituminite in comparison to anthracite.

Jan 1, 2016

By Ana E. Bohé, Georgina De Micco, Gastón G. Fouga

"In this work the reaction between several manganese oxides and chlorine is investigated in the range of temperatures between 650 and 950ºC. The reaction path for the chlorination of MnO is established, which involves recrystallization of high valence manganese oxides (Mn3O4 and Mn2O3) followed by its chlorination. For this reason, to understand the reaction of MnO, the chlorination of Mn3O4 and Mn2O3 has also been studied. The starting temperature for the reaction of these oxides is determined by non isothermal thermogravimetric measurements. The effect of temperature is analyzed, under our experimental conditions the rate of reaction is mass transfer controlled. The activation energy for the volatilization of manganese chloride is obtained which is in good agreement with volatilization enthalpy of MnCl2.IntroductionMany oxide ores which have manganese in their composition undergo chlorination processes during the extraction of refractory metals such as Ti, Hf and Nb. Although several works related with chlorination of manganese oxides were reported, there is no information about the kinetics or mechanism of the manganese oxide chlorination reactions. Okahara et al. studied the chlorination of manganese oxides and established that they react easily above 250ºC. Furthermore, they observed that chlorination of high order oxides is more difficult when there is not a reducing agent [1]. Ivashentsev studied the chlorination of manganese oxides using Cl2(g), CO(g) + Cl2(g) and COCl2(g). He established that the reaction of MnO started at 130ºC with formation of MnCl2(s), he also observed recrystallization of manganese sexquioxide [2]. Finally, the chlorination of manganese nodules from the ocean was studied by Murthy and Reddy [3] with the aim of obtaining valuable metals such as Mn, Co, Ni and Cu. They studied the influence of several parameters like temperature, carbon percentage, particle size and chlorine flow rate in the extraction process."

Jan 1, 2008

By Karl A. Gschneidner

Magnetic refrigeration was first used in the mid-1920's and new developments seem to have taken place about every 20 years, and this is especially true for the mid-1990's. The active magnetic regenerator magnetic refrigerator has the promise to become the first practical machine utilizing the magnetocaloric effect for cooling (and also heating). The basic principles are briefly discussed. Since the temperature lift for the magnetocaloric effect spans about 50 K, one will need to utilize several ferromagnets with different magnetic ordering temperatures in order to reach temperatures below ~250 K. The basic properties, behaviors, limitations, and new phenomena and knowledge are discussed.

Jan 1, 1997

By Jari Aromaa, Antti Kekki, Olof Forsén

"The deposition of copper on inert substrate depends on the number of active sites that will react at certain overpotential. The critical overpotential depends on surface morphology, surface film resistance and additives on cathode surface. The effects of surface properties on copper nucleation and growth rates were studied for used stainless steel blanks from several tankhouses. The surfaces of the blanks were characterized with electrochemical and mechanical methods. Electrochemical deposition tests were done at current density of 300 A/m2 for 10, 30 and 60 seconds. The nucleation density and copper coverage were estimated using image analysis. The surface film resistance did not correlate with copper growth. Increasing surface roughness correlated with lower copper growth.IntroductionStainless steel cathode blanks in copper electrorefming are usually made of AISI 3 I6L type steel. They have a typical lifetime over 10 years. During use the surface will collect deposits and become rough due to wear and corrosion. These factors can affect the nucleation and growth of copper. The nucleation and deposition of copper on inert substrate depends on the number of active sites that will react at certain overpotential. The critical overpotential can depend on surface film resistance, surface morphology, and additives adsorbed on cathode surface.The deposition potential of metallic ions on a foreign substrate is usually higher than the deposition potential on the electrode made of the same metal due to crystallographic substrate/metal misfit [I]. If the substrate has traces of the depositing metal they will be preferential growth sites. For a smooth deposit a large number of simultaneous nuclei is necessary. However, excessive nucleation density can lead to porous deposits [2]. Surface films of good conductivity are needed for dense nucleation and small nuclei. On cathode blanks the number of active sites increases with increasing surface film conductivity [3-5] and/or surface film porosity [6]. On AISI 3 I6 L stainless steel a more resistive oxide has been found to limit favourable sites for copper nucleation and more conductive film promoted high-density copper nucleation [7]. Also Urda-Kiel et al. have concluded that thicker oxide layers on AISI 304 stainless steel resulted in lower nucleation [8]. Increase in overpotential or current density activates more and more of the potential nucleation sites and this can be seen as higher number of nuclei [9] or smaller average distance between nuclei [10]."

Jan 1, 2012

By Masahiro Sasaki, Wu Kepeng, Chang-Yong. Kang, Kohji Okada, Naohiro Igata, Kazuya Miyahara

"The damping capacity of the Fe-12 mass % Cr-6 to 30 mass % Mn alloys has been investigated. Particularly the effects of microstrucutre composed of the phases of a , a ' , y , and e on the damping capacity have been clarified. Various fraction of these phases were formed depending on the Mn content and cold work degree. The combination of 22 mass % Mn and 50% cold rolling formed the largest volume fraction of e martensite and showed the highest damping capacity. The other phases of a, a' and y had very small effect on the increasing of damping capacity.IntroductionFe-Mn alloys are known to be one of the high damping capacity materials [l-3]. In the present research, the damping capacity of the Fe-12 mass % Cr-6 to 30 mass % Mn alloys, in which 12% Cr is added for the improvement of corrosion resistance of the Fe-Mn alloys, has been investigated. Particularly the effects of microstrucutre composed of various phases of a (bee), a ' (bet martensite), y (fee), and e (hcp martensite) on the damping capacity have been clarified. The results of preliminary research on Fe-Cr-Mn alloys are reported by Igata et al. [4] Various volume fraction of these phases were formed depending on the Mn content and cold work degree. The combination of 22 % Mn and 50% cold rolling formed the largest fraction of e martensite and the measurement indicated clearly that e martensite had the largest effect on the damping capacity. The other phases of a ' y and a I had very small effect on the increasing of damping capacity."

Jan 1, 2000

By Hiroshi Nakajima, Kotobu Nagai, Toshihiro Hanamura

"Low carbon ferritic steel bars with ultra-fine grain structure was developed through a warm rolling for the first time by the present authors. They show better low temperature toughness than conventionally hot-rolled plates. Hence, the brittle fracture surfaces in Charpy tests were examined in terms of the effective grain size of fracture, compared with those of conventional QT steels. The ductile-to-brittle transition temperatures were in good accordance with those for the QT steels if referred to the effective grain size of fracture: · However, the size was a few times that of the ferrite grain. This means the grain refining is not yet fully utilized from the viewpoint of low temperature toughness. The anisotropy of· the impact properties and the annealing effect of highly dislocated structure on the toughness are also discussed in the present paper.IntroductionFor structural materials, both high strength and good toughness are required. Well-known approaches for obtaining better toughness for steels are as follows:1) Grain refining2) Addition of Ni3) Thin plate effect by cracking parallel to the rolling direction prior to crack propagation4) Contribution of metastable austenite.Among them, only the grain refining can raise the strength and improve the toughness. And it is well known that the finer the ferrite grain size, the lower the ductile-to-brittle transition temperature. For example, in the case of 0.11 carbon steel, the transition temperature decreases linearly to in d 1/2 [1 ]. However, these have been told in the regime of coarse grain size that is larger than 10 µm in diameter. There ~as .been no study dealing with the low temperature toughness in the regime of ultra-fine grain size with a diameter in the order of 1 µm."

Jan 1, 2000

By Kenneth L. Reid

The Mineral Resources Research Center at the University of Minnesota has recently installed a QEM*SEM system (Quantitative E.valuation of Materials using Scanning Electron Microscopy) to aid in detailed mineralogical evaluation of potential mineral resource developments in Minnesota and to provide services to the North American mineral industry. A primary application for the unit is to serve the Minnesota taconite industry by providing mineralogical analysis of ores and concentrator products. Minnesota taconite ores contain fine-grained magnetite in a quartz matrix. The ores undergo several size-reduction/magnetic-separation steps to produce a final concentrate with approximately 75% passing 325 mesh and containing about 5% gangue. The paper describes a typical taconite concentrator flowsheet and reports some preliminary results of the applications of QEM*SEM particle image maps and cumulative yield liberation data to samples from selected points in the concentrator circuit.

Jan 1, 1988

By M. F. Hochella

Transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) analysis have been used to study the mode of occurrence and mineral associations of gold in partially oxidized high grade gold ore from the Carlin sediment-hosted deposit. Rounded.gold particles have been observed that range in size from 0.03 to 0.1 p.m (300 to 1000 A) in diameter. The gold is associated with maghemite h-Fep3l and a K-Al-Si-bearing phase that is suspected to be illite. Detailed descriptions of gold and its mineral associations in 'Carlin-type' gold deposits are critical not only to understanding the mechanism of fluid transport and precipitation of gold, but also to developing improved metallurgical techniques for the recovery of gold from refractory ore. Direct observation of gold in unoxidized ore is rare due to its relatively high degree of dissemination and low average bulk concentration which averages 9 ppm according to Radtke (1). Hausen and Kerr (2) observed 1 to 5 p.m grains of gold directly in oxidized ore but these microscopically visible particles account for only a small percentage of gold present in the ore. The samples used in this study were selected from individual beds of high grade, partially oxidized ore (4.55 oz/ton or 156 ppm gold) that were collected in the Main pit of the Carlin mine. The samples were collected from several thinly laminated carbonate micrite beds within the top 50 meters of the Roberts Mountains Formation. The carbonate micrite has been altered by hydrothermal fluids to a calcite-absent, moderately silicified rock referred to as alteration zone #3 by Bakken and Einaudi (3). Based on petrographic and SEM studies, the samples contain carbonaceous matter, and both pyrite and iron oxide pseudomorphs after pyrite. The oxidation of pyrite may be a pro-duct of deep weathering, in which case limited remobilization of gold may have occurred. TEM sections of the rock were prepared by first embedding small chips in low viscosity epoxy. The epoxy blocks were cut with a Reichert Ultracut E ultramicrotome, producing thin sections less than 0.1 p.m thick. The sections were examined with a Phil-lips 400ST TEM at 120 keV in both imaging and selected area diffraction modes. Native golci*was easily detected in TEM bright field images due to the large electron density contrast between gold and all other phases that are present (Figs. 1 and 2), Gold was positively identified with high spatial resolution EDX analysis in the transmission electron microscope, although selected area diffraction of individual grains was not successful EDX analyses of the platy and massive minerals immediately surrounding the gold particles typically indicate the presence of Si, AI, K, and Fe, However, the d-spacings derived from selected area diffraction of these polycrystalline masses (as, for example, in Fig. 2) give an exact match for maghemite. As a result, there is no diffraction information to identify the K-AI-Si-bearing phase(s). The lack of a diffraction pattern could be due to either electron beam damage or to a poorly crystalline phase(s).

Jan 1, 1987

By Peter Forschner

Classical Mixing Theory is based on applying many fundamental correlations to standard baffled dished bottomed vertical cylindrical vessels with high degrees of symmetry. Horizontal autoclaves operating at elevated temperatures and pressures have been used for more than two decades. All compartments and especially the first and last compartments are asymmetrical. To date no comparison of the effects of the asymmetric geometry on mixing system design and scale-up has been published. The results of investigating solids suspension, mixing time, momentum transfer from the impeller to feed slurry and feed inlet location in the first autoclave compartment are presented as influences on residence time distribution. CFD modeling was developed and verified with the test apparatus.

Jan 1, 2003

By Riyad N. Ahmad-Bita, Shadia J. Ikhmayies

"SnO2:F/CdS:In structures were prepared by the spray pyrolysis technique on glass substrates at a substrate temperature Ts = 450°C. NH4F and HF were both tried as the sources of fluorine in the precursor solution of SnO2:F. A comparison between the properties of structures obtained by using the two doping compounds was performed. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmittance measurements were used to characterize the films. The structures prepared by using HF as a fluorine source were found to have more ordered crystal growth, larger grain size and sharper absorption edge. From the inspection of the first derivative of the absorbance it is expected that more interdiffusion on the SnO2:F/CdS:In interface takes place in the structures made by using HF. These results confirm that these films are better as forecontacts for CdS/CdTe solar cells.IntroductionThin film CdS/CdTe solar cells built in the superstrate geometry rely on transparent conducting oxides (TCOs) to make the front contact The investigation of combined CdS-TCO films has recently been developed owing to the great interest of better understanding the effect of these bilayers on the absorbers [1]. Usually SnO2 is utilized as a front contact for these solar cells. Optimizing the properties of the SnO2/CdS structures is an important step on the way to get high performance CdS/CdTe solar cells.There are different methods to prepare SnOz thin films, such as reactive sputtering [2], evaporation [3], chemical vapour deposition [3, 4], dip coating [5] and spray pyrolysis [6-9]. At the same time CdS thin films can be prepared by different techniques such as chemical bath deposition [10], thermal evaporation [11], screen printing [12] and spray pyrolysis [7, 13]. However, the spray pyrolysis technique is a very low cost and simple technique that enables intentional doping and getting large area and uniform thin films [14]. For these reasons it is choused to prepare SnOz and CdS thin films in this work. To improve the properties of these compound semiconductors, SnOz was doped with fluorine and CdS was doped with indium where such doping is well known for these compounds."

Jan 1, 2012

By Cashman R. S. Mason

Removal of halides (fluoride, chloride) from metallurgical solutions can reduce corrosion rates and improve hygiene from decreased anodic chlorine evolution. This is particularly true for zinc sulphate electrowinning solutions. This paper describes the chemistry of a new process for the removal of halides from such solutions by solvent extraction ? the Teck Cominco Halogon? process, for which patents are pending. In this process, the halides are loaded directly from commercial zinc sulphate solutions and are stripped into a form suitable for disposal. Sulphate extraction efficiency is variable while maintaining halide extraction efficiency. The method of optimizing the solvent composition is demonstrated.

Jan 1, 2003

By Steven Wright

The extent and the rate of reduction of slags produced from the smelting of recycled lead batteries were investigated under laboratory conditions using graphite as reductant. Simultaneous reduction of PbO, Fe2O3, Sb2O3 and As2O3 occurred at temperatures of 1180 and 1200°C, with Sb and As reporting to the metal phase while the PbO content of the slag was above 2 wt%. Fuming of As from the metal occurred at lower concentrations of lead in the slag. Discard slags with low levels of As, Pb and Sb were produced. Arsenic levels were reduced to less than accurately measurable by ICP analysis, and Sb levels in the final slags were in the range of 0.1 to 0.2 wt%. The kinetic data obtained were analysed and compared with other measurements on lead oxide containing slags. The results showing a dependence of the reduction rate on the oxidation state and the basicity are consistent with other studies on well characterised industrial and. synthetic lead slags. These results indicate that when carbonaceous reductants are used, the rate of interfacial reactions play an important role in enabling the production of environmentally acceptable discard slags.

Jan 1, 1994