Search Documents

By Eric J. Grimsey

Nickel smelting and converting can be viewed as processes in which iron is either partitioned or transported between matte and slag. Metal recovery depends on the mass of iron transported to slag, the thermodynamic environment in which the transport is made, and the extent to which the slag, once formed, is left in contact with the matte. The importance of these effects is discussed with reference to a new equation which describes metal recovery in terms of a mass balance and a thermodynamically related parameter which is easily measured in practice.

Jan 1, 1993

By R. Singh, C. Gong, J. Chaudhry

"Metalorganic chemical vapor deposition (MOCVD) is an ideal technique for the deposition of conducting and non-conducting oxide based thin film materials. In this paper we have presented a study of photo assisted MOCVD for the low temperature deposition of a number of oxide based advanced materials. We have used incoherent light sources as the source of optical and thermal energy in our MOCVD system. The vacuum ultraviolet (VUV) and ultraviolet (UV) photons can enhance the surface reaction of the absorbed molecules through the perturbation of the electronic state of binding between the absorbed molecules and the solid surface. Unlike plasma process, no surface damage is expected and high quality materials have been deposited. At a given substrate temperature, the performance of deposited film depends on the lamp configuration.INTRODUCTIONMetalorganic chemical vapor deposition (MOCVD) has become the standard manufacturing technique for the deposition of large area thin films of compound semiconductors. l.(.w-cost, high crystalline quality, atomically clean and sharp interfaces, atomic layer epitaxy, high throughput rates and potential for direct writing are some attractive features of MOCVD. Due to a number of potential advantages mentioned above, MOCVD is considered as an ideal technique for the deposition of various electronic and optical materials for a wide variety of applications. Rapid isothermal processing based on incoherent radiation as the source of optical and thermal energy is emerging as the key low thermal budget (integral of processing time and temperature) processing technique for the fabrication of current and next generation of microelectronic and optoelectronic devices and circuits [1]. In this paper we have demonstrated that the design of the lamp assembly plays an important role in determining the properties of the materials deposited by RIP assisted MOCVD. We have studied the growth rates, structural properties and electrical properties of Y2O3/Si structure. At a given substrate temperature, best results are obtained for the lamp assembly that provides maximum number of VUV and UV photons."

Jan 1, 1994

By Irshad A. Rana

In a modern copper smelter, the capital cost of a sulfuric acid plant constitutes the largest single cost item of the total investment. It is thus essential to properly size the acid plant in order to reduce its capital cost and enhance the economic viability of a new smelter project. Whereas the off-gas from a smelting furnace is continuous and generally uniform, the gas flow from the Peirce-Smith converters is intermittent with significant fluctuations. The converters off-gas volume is dependent upon a number of interrelating factors. The most significant factors are the matte feed grade, the system air infiltration, the converter's size and blowing rate, the maximum number of converters simultaneously blowing and the gas cooling system employed. The acid plant size, therefore, is heavily influenced by the converter off-gases. Several of these factors are discussed, and their impact in determining the acid plant size is explored.

Jan 1, 1993

By Nagy El-Kaddah

One of the emerging technologies for the production of ultra-clean metals is electromagnetic filtration. The theory and the mechanism of electromagnetic separation of inclusions from molten metal are briefly reviewed along with basic electromagnetic separation systems. This paper focuses on inclusion removal in the induced current separators, with specific reference to a new separator developed at the University of Alabama. A simple analytical model is presented for the analysis of particle separation in such a system. The role of the applied magnetic field on inclusion removal will be discussed. It is shown that particle velocity increases exponentially with increasing magnetic field strength. At moderate field strengths, the velocity of 50 to 100µ inclusions are an order of magnitude larger than those achieved by buoyancy. The separator developed at the University of Alabama is described together with experimental results of laboratory and large scale experiments on purification of molten aluminum. These results demonstrate ?the capability of the system for producing super-clean metals.

Jan 1, 1996

By Jose R. Parga

In mining operations, cyanidation is the ,predominant method by which gold and silver are recovered from their ores and it is recognized that cyanide consumption can be a major factor that contributes to the operating costs for such operations. Also after extraction and recovery of precious metals a certain amount of cyanide is delivered to the tailings pond and must be considered with respect is environmental problems due to the toxicity of cyanides. In this regard, the Air-Sparged Hydrocyclone (ASH) has been used as a reactor for the treatment of cyanide solutions in two ways; first for cyanide recovery by acidulation using the Mexican modification of the Mills-Crowe process and second for cyanide destruction by oxidation with the use of chlorine dioxide (ClO2). In both cases, excellent performance can be achieved using the high capacity ASH system.

Jan 1, 1998

By Masatoshi Ogasawara

Saganoseki smelter & refinery operated two flash smelting furnaces, producing a combined 330,000 metric tons per year (hereinafter mtpy) of copper. In 1996, however, it successfully shifted to a single furnace operation while maintaining production at the same level. Since then, the production capacity has been further increased to the present 470,000 mtpy by technological improvements. Also, in order to reduce the converter load which represents a bottleneck in efforts to increase production, the matte grade was gradually increased and currently runs at 65 to 66% attaining the low copper content in the slag (hereinafter slag loss) of 0.7 to 0.8%. This paper introduces some improvements, recent operation results and thermodynamic analyses.

Jan 1, 2003

By Shekhar Bhansali, Shyam Aravamudhan

"This paper reports on the design and simulation results of a silicon bulk-micromachined diaphragm-type piezoresistive pressure sensor capable of operating linearly over a wide dynamic range (0-1000 meters of water). The piezoresistor elements of the sensor are arranged in a wheat stone bridge configuration to achieve a higher output response. Simulation results (output voltage and sensitivity analysis) obtained using coupled MemPZR-MemMech module of the CoventorWare2003 Finite Element tool are presented. The effect of diaphragm size, diaphragm thickness and thickness of the piezos on output sensitivity were analyzed and optimized to get a linear response over the wide dynamic range.IntroductionThe physical and biological processes in the ocean are critically influenced by ocean parameters (pressure, salinity and temperature). Thus there is a need to develop inexpensive and reliable sensors to continuously measure large volumes of sea-space over long time spans. A key component in any such system will be a pressure/depth sensor. This sensor is routinely employed in marine applications such as wave and tide gauges, tsunami detection, platform leveling etc. More significantly, pressure measurement is needed for depth determination. Depth sensors are vital for remote operated vehicles (ROVs), profiling instruments and towed arrays.Several techniques have been routinely used in the past to measure pressure in the marine environment [1-3]. In general, the pressure sensor design is based on a flexible membrane as the spring element for the sensing pressure [4]. The deflection of the membrane, induced by the applied pressure, is converted into an electrical output through a component that is sensitive to diaphragm deflection (capacitive coupling) or associated stresses (piezoresistors, strain gauges). The temperature compensated pressure measurement can be readily converted to depth using"

Jan 1, 2004

By Geoffrey A. Brooks, M Akbar Rhamdhani, Md Saiful Islam

A novel electrically-enhanced metal purification using slag has been developed. This was achieved by applying DC potential between liquid metal and slag phases. The concept was demonstrated through small-scale experiments at temperatures of 1500-1600oC for the removal of boron from Si-B melt using CaO-SiO2-16wt%Al2O3. Silicon (containing B) and slag were reacted in an alumina crucible in a resistance tube furnace. A circuit was produced by immersing graphite rods into the silicon bath and the slag layer. Electrical potential differences of up to 3.5 V were applied during the reactions. The reaction rates, the opencircuit voltages and short-circuit currents (in the case when the potential was applied) were then measured and determined for various slag to silicon ratio. It has been shown from this study that both the apparent rate and the boron partition ratio were increased by a factor of approximately 1.6.

Jan 1, 2014

By Jr. Foot

The Bureau of Mines, U.S. Department of the Interior, investigated flotation methods for recovering fluorite and byproduct beryllium from the Fish Creek deposit of Nevada. The preferred method includes (l) fluorite rougher and cleaner flotation, (2) de sliming at 20 micrometers, (3) muscovite flotation, (4) silicate flotation, (5) hypochlorite wash of silicate concentrate, and (6) beryllium rougher and cleaner flotation from the silicate concentrate, Laboratory results showed that over 94 pct of. the fluorite was recovered in a concentrate containing 96 pct CaFz. Beryllium flotation produced .concentrates .containing in excess of 5 pct BeO with recoveries over 70 pct. A 1.00-lb/h continuous flotation unit was constructed to demonstrate this procedure,

Jan 1, 1985

By Mathilde Guilpain

A wide variety of plants are able to extract nickel (Ni) from soils and accumulate this metal in their foliage. Hydrometallurgical processes have been developed to recover Ni in the form of metal or salts, starting from the plant A. murale. They include: (1) a combustion step, to obtain ash containing 15–20% Ni; (2) a leaching step; and (3) purification. That whole flowsheet has been thoroughly investigated, and the processes scaled up to the pilot scale. Another strategy is presented here, consisting of recovering Ni without burning the plant. Ni can be extracted from the dry plant by water leaching, but the leachate is a multi-element solution from which Ni has to be separated. Selective precipitation of Ni hydroxide is not possible since Ni is bound to organic ligands. In this work, the plant leachate is processed by adsorption on the chelating resin DOWEXTM M4195. The results showed that Ni was selectively retained whereas the other main cations were not. Nickel could be recovered at the elution step. This methodology needs to be further investigated but these initial results are very encouraging and open the possibility of Ni recovery by agromining.

By E. A. Thiers

The causes of structural changes in the markets for high technology alloying metals are discussed in terms of technological, economic, and financial trends. Recent market imbalances have affected producers in developed and developing countries differently. Possible response strategies for suppliers in the two types of countries are examined that may alleviate future market imbalances.

Jan 1, 1988

By M. Kobashi, T. Choh, N. Kanetake

"A new processing route, which enables the cost-effective and energy- saving fabrication of metal matrix composites, have been proposed. The pressureless infiltration of the reactive powder blend with molten aluminum was investigated in this work. The molten aluminum infiltrated into the [Ti + C] powder blend spontaneously, whereas the spontaneous infiltration into the TIC powder phase did not occur under the same experimental condition. The processing time was shortened and· the processing temperature was .lowered by adding the aluminum powder in the [Ti + C] powder. The differential thermal analysis revealed that the aluminum powder in the powder blend melted at 933K and then ignited the reaction between titanium and ·carbon. However there was an .optimum additional amount of aluminum in the powder blend. The TiC formed in situ had three-dimensionally continuous morphologyIntroductionThe squeeze casting process has been used as one of the processing routes for aluminum matrix composites. [1, 2]. Non-reactive metal-ceramic systems have been, generally, used in this technique in order to prevent the degradation of the ceramic phase. Materials obtained by this process basically consist of a continuous metal matrix and discontinuously dispersed ceramic particles. Reactive systems have begun to be introduced into the infiltration process· recently [3A]. Since the ceramics are synthesized in-situ, this process can provide a continuous ceramic matrix [5]. This is one of the outstanding features of this technique in that a bulk ceramic-can be synthesized at relatively lower temperatures in a short time. Another advantage is that the highly reactive combination of a ceramic with a molten metal is in many cases wettable [6], which enables a spontaneous infiltration."

Jan 1, 2000

By T. H. Jeffers

The U.S. Bureau of Mines' Salt Lake City Research Center. has developed porous polymeric beads containing immobilized non-living biological materials for extracting metal contaminants? from wastewater&. Immobilized biological materials include peat moss, algae, biological polymers, and other materials that demonstrate high .affinities for heavy metals. The beads, designated as BIO-FIX beads, have distinct advantages over traditional methods of utilizing biological materials in that they have excellent handling characteristics . and can be used in conventional processing equipment or low-maintenance systems.. Toxic metals such as copper, cadmium, zinc, lead, and mercury are several of the many heavy metals effectively removed from mine wastewater& using B'IO"FIX beads. Continuous cyclic testing indicated that the beads continued to produce treated effluents which met National Drinking Water Standards (NDIJS) after 175 loading-elution cycles, Adsorbed metals were removed from the beads using dilute ?mineral .acids. In many cases" the extracted metals were further concentrated to enable processors to reclaim the metals, thus minimizing the generation of a hazardous sludge. Tests indicated that use of the beads in a low-maintenance system was particularly effective for treating remote acid mine drainage waters? and small toxic seeps from hardrock mining districts ..

Jan 1, 1991

By Md. Maniruzzaman

The quenching performance of a liquid quenchant can be controlled by controlling the agitation in the quench tank. Without agitation, a vapor layer or bubbles form at the hot part surface and the natural convention of the quenchant limit the heat extraction rate at the quenched part surface. Resistance to the heat extraction rate can be reduced by breaking the vapor layer or by inducing a turbulent convection at the part surface through agitation (Le. forced circulation of the quenchant). To determine the effects of agitation on the quench performance of a mineral oil based quenchant, the CHTE quench probe system was used with AISI4140 steel probe tip. Quenching performance of the oil is evaluated by computing the effective heat transfer coefficients of the steel probe as a function of surface temperature using Lumped Parameter Analysis. In addition, computational fluid dynamics (CFO) simulation of the quench tank with an impeller type agitator has been done to understand and predict the fluid flow pattern in the tank. CFO simulation also provides insights for determination of optimal location of the impeller and the quench probe tip. Keywords: CHTE Quench Probe, agitation, CFD simulation, liquid quenchant, 4140 steel

Jan 1, 2003

By P. G. Mason

The Getchell property was mined for oxidized gold ore by underground and open pit methods from 1936 to 194.5, by which time known oxide ores were mined out. From 1945 until 1967 sulfide ores were mined and roasted to improve gold recovery with varying degrees of success. In J 983 FRM Minerals, Inc. purchased the property. Since then they have carried out extensive geological exploration to define the size and character of the orebody. The sulfide ore is refractory to direct cyanidation, thus considerable metallurgical testing has been necessary to develop a suitable, cost effective process for its treatment. Wright Engineercs Limited have designed and engineered a gold extraction plant, which incorporates pressure oxidation to liberate the gold and? is scheduled to be commissioned early in 1989.

Jan 1, 1989

By Zhijing Zhang

A thermodynamic structure model for alkali borate melts is developed to describe the distribution of structural groups in the alkali borate melts as a function of compositions. Fractions of threefold coordinated boron atoms and fourfold coordinated boron atoms in the potassium borate melt are calculated for the entire composition range and compared with results reported in the literature. The model has been used for structural interpretation for the borate anomaly in viscosity, which regards the borate anomaly as a manifestation of the various antithetical effects caused by the introduction of alkali oxide into boric oxide. It has been found that the viscosities of alkali borate melts increase or decrease according to the changes in rigidity and spatial connectivity of the glass network structure, which is a function of temperature and composition.

Jan 1, 2001

By V. D. Tathavadkar

Natural chromite mineral is a solid solution of spinet end members namely: chromite (FeCr2O4), hercynite (FeA1204), magnetite (Fe3O4), magnesio-chromite (MgCr2O4), (MgA12O4), and magnesio-ferrite (MgFe2O4). A phase transformation in chromite minerals occurs in oxidising conditions during the soda-ash roasting reaction. This phase transformation plays an important role in improving the extraction efficiency of Cr3+ from mineral phase. The extraction efficiency of chromium (Cr3+) from chromite to a water¬soluble sodium chromate (Cr6+) salt depends upon the decomposition kinetics of the spinet phase. An investigation of the phase changes in chromite ores in the absence of sodium carbonate was carried out in air, argon, and in argon +5 % hydrogen gas mixture. The thermodynamics of phase transformation reaction in chromite solid solution phase is discussed using the solution model proposed by Sack and Ghiorso [1]. The microstructural changes and the changes in elemental compositions of different phases were examined by SEM and electron probe microanalysis (EPMA) respectively. The experimental results indicate that the solid solution spinet phase in chromite mineral undergoes spinodal decomposition under the influence of oxygen partial pressure and temperatures. The structure of phases formed and their morphologies suggest that the phase decomposition may be similar to those observed by Burkert et. a]. 121, although the scale of phase separation in chromite appears to be strongly dependent on oxygen partial pressure.

Jan 1, 2001

By J. P. Gu, C. Beckermann

"Melt convection and macrosegregation in casting of a large steel ingot is numerically simulated. The simulation is based on a previously developed model for multicomponent steel solidification with melt convection, and involves the solution of fully coupled conservation equations for the transport phenomena in the liquid, mush, and solid. Heat transfer in the mold and insulation materials, as well as the formation of a shrinkage cavity at the top are taken into account. The numerical results show the evolution of the temperature, melt velocity, and species concentration fields during solidification. The predicted variation of the macrosegregation of carbon and sulfur along the vertical centerline is compared with measurements from an industrial steel ingot that was sectioned and analyzed. Although generally good agreement is obtained, the neglect of sedimentation of free equiaxed grains prevents the prediction of the zone of negative macrosegregation observed in the lower part of the ingot. It is also shown that the inclusion of the shrinkage cavity at the top is important in obtaining good agreement between the predictions and measurements.IntroductionMacrosegregation in large steel ingots is one of the most well-known and now classical problems in the field of solidification and casting [1]. Commonly found macrosegregation patterns in steel ingots are a positively segregated zone at the top, negative segregation near the bottom in the equiaxed zone, inverse segregation near the ingot surface, V-segregates along the centerline, and A-segregates in the columnar zone [2, 3]. It is well established that the macroscopic transport of species leading to macrosegregation can occur by a variety of mechanisms, including thermally and solutally driven natural convection of the melt in the mushy zone, flow due to solidification contraction, and the sedimentation of free equiaxed crystals. Fredriksson and coworkers [ 4,5] provide recent overviews of the solidification transport phenomena and macrosegregation in ingot casting."

Jan 1, 1999

By Dietmar Eifler, Marcus Klein, Hendrik Kramer

Conventional methods to characterize the fatigue behavior of metallic materials are very time and cost consuming. That is why the new short-time procedure PHYBALCHT was developed at the Institute of Materials Science and Engineering at the University of Kaiserslautern. This innovative method requires only a planar material surface to perform cyclic force-controlled hardness indentation tests. To characterize the cyclic elastic-plastic behavior of the test material the change of the force-indentation-depth-hysteresis is plotted versus the number of indentation cycles. In accordance to the plastic strain amplitude the indentation-depth width of the hysteresis loop is measured at half minimum force and is called plastic indentation-depth amplitude. Its change as a function of the number of cycles of indentation can be described by power-laws. One of these power-laws contains the hardening-exponentCHT eII, which correlates very well with the amount of cyclic hardening in conventional constant amplitude fatigue tests. To identify heat-treatment-parameters and SAE 52100 TRIP-alloys with high hardening rates as well as their damage tolerance the PHYBALCHT- and PHYBALLIT-method were used. One modified SAE 52100 TRIP-alloy was investigated in detail. The fatigue behavior and the cyclic hardening of the selected SAE 52100 TRIP-alloy was investigated and compared with conventional SAE 52100. Conventional stress-controlled fatigue tests were performed on a servo-hydraulic test system with a frequency of 5 Hz and a load ratio of R = -1. Different rates of cyclic hardening were identified. The size of the nonmetallic inclusions leading to crack initiation and the number of cycles to failure were used to evaluate differences in the damage tolerance capability.

Jan 1, 2015

By I. B. Scorzelli

The aim of this paper is to make a detailed mineralogical characterization of a typical brazilian xenotime and zircon from the Pitinga Mine using SEMIEDS techniques, On the other hand, superficial pretreatments with HCI, HN03 and HF were done to evaluate the modifications on surface compositions and the morphology of the particles for flotation purposes, The studies showed that both xenotime and zircon present very small inclusions of thorite; zircon is strongly metamictizated given rise to malacon. The HF pretreatment deeply affected the morphology of the particles as well as the surface properties in relation to flotation.

Jan 1, 1996