Search Documents

By Shivendra Sinha

Total pressure oxidation (TPOX) is widely outreached leaching practice for base metals from sulfide minerals, wherein high temperature (T ∼ 200 °C) and oxygen pressure (pO2 ∼ 25 bar) are required. These aggressive conditions intensify the oxygen mass transfer, and therefore facilitate metal dissolution. However, challenging-cum-negative aspects of such practice are energy and material intensive requirements and high oxygen demand. Thus, the present study explores the novel emulsified medium for enhancement of oxygen mass transfer, which assists faster metal dissolution at significantly lower temperature and pressure condition. It is possible to achieve quantitative dissolution (>95%) of Cu, Ni and Co from mixed sulfide minerals at T ∼ 95 °C and pO2 ∼ 2 bar using an emulsion of 2.5% (v/v) n-Hexadecane in dilute sulfuric acid. In addition, n-Hexadecane was found to be inert, stable and immiscible in a pressurized leaching system, thus can be easily separated and recycled in subsequent leaching stages. Thus, this study offers an energy efficient route for low temperature-pressure leaching of sulfides.

By Andreas Weber

Batrec operates a plant for the recycling of used dry batteries with a capacity of 3000 tons per year. The plant Is situated In a tourist area of Switzerland and has complied with all the strict emission restrictions. The process yields four products: FeMn. Zn, Hg and slag. No hazardous waste Is produced. All types of batteries can be treated.

Jan 1, 1995

By Berndt Moeller

Mercury-cell chlor-alkali production plants generate mercury contaminated wastewater streams from which mercury must be precipitated and filtered, resulting in a sludge containing 2% mercury (designated KI06) that cannot be landfilled in the United States without treatment. REMERC is a chemical treatment process used to recover 99% of the mercury from wastewater sludge generated at these plants. The process uses leaching to oxidize mercury compounds to mercuric chloride, washing and filtration to separate mercuric chloride from the treated sludge, and cementation to reduce the mercuric chloride to metallic mercury. Mercury not recovered in cementation is recycled to the wastewater process for precipitation and filtration. Treated sludge contains less than 260 ppm total mercury and 0.2 ppm TCLP, meeting the USEPA low mercury subcategory specifications that allow landfill disposal. REMERC uses readily available chemicals, is straightforward to control and inexpensive to operate, has no mercury emissions to air, and recovers metallic mercury. REMERC enabled significant cost savings including lower solids disposal costs, recovery and reuse of metallic mercury in the chlor-alkali process, and ability to treat non-wastewater sludge. No new EPA permits were required. REMERC was shown to be a viable process for recovery of metallic mercury from K106 designated sludge.

Jan 1, 2003

By Patrick R. Taylor

The synthesis of high-purity ultra-fine barium strontium titanate powders (BST: BaO6Sro.4TiO3) has been performed in a non-transferred are D.C. thermal plasma reactor. Slurries of aqueous solutions of dissolved barium and strontium nitrates and solid titanium dioxide powders were used as precursors. Oxygen and argon were used as carrier gases, and pure argon and combinations of argon and nitrogen were used as plasma gases. The plasma torch power was varied, as well as the oxygen flow rate and the total molar concentration of the precursors. A graphite plate was designed to protect the torch electrode and lower the level of impurities in the product. A thermochemical analysis of the Ba(NO3)2-Sr(NO3)2-TiO2-H2O-O2 system was performed to predict the conditions for the formation of BST and the feasibility of the reaction, The powders collected from the different sections of the reactor were characterized using Transmission and Scanning Electron Microscopy, X-Ray Diffraction, and ICP chemical analysis. The powders produced showed high conversion to BST, ultra-fine particle size (< 30 rim) and high purity, which makes this a potential process to produce ceramic materials for electronic devices.

Jan 1, 2003

By Renaud Metz

The DOPA process (Direct Oxidation of a Precursor Alloy) was used to prepare ceramic powders based on doped SnO2 and ZnO. The DOPA process consists essentially in the direct oxidation of a homogeneous precursor alloy. A unique advantage of this process is its rather benign environmental impact since no dangerous reactants are used and no harmful by-products are generated. Only oxygen and the alloy metals participate on the chemical reaction to produce the multi-component oxide. Homogeneous alloys of niobium, cobalt and chromium doped tin have been prepared. The molten metal alloy is atomised in air using a double fluid nozzle to produce metallic powders. A subsequent thermal treatment is carried out to fully oxidise the sprayed metal alloy powders. These raw powders are used to prepare a ceramic powder through a mill homogenisation and atomisation process. The ceramic powder is then uniaxially compacted in disc shape and sintered in an oxidising atmosphere. The resulting sintered bodies are metallised on their flat faces and the cylindrical surface is passivated using lead free glass enamel. These ceramics present excellent semiconducting properties with non-linear (non-ohmic) characteristics. The DOPA process is found to be an attractive procedure to obtain ceramic powders for the preparation of SnO2 varistors.

Jan 1, 2006

By R. Padilla

In most of the Chilean copper and gold concentrates, arsenic is present mainly as enargite, Cu3AsS4, which at the conventional roasting or smelting temperatures decomposes liberating arsenic as gaseous compounds. The objective of this investigation was to study the decomposition reaction of enargite in an inert atmosphere in the range of 500 °C - 750°C. The results obtained indicated that the decomposition begins at about 525 °C. Two distinct regions in the temperature dependence of the decomposition rate were observed: a low temperature region between 525 °C to 650°C and a high temperature region between 650 °C to 725 °C. The X-ray diffraction analysis suggests that the decomposition of enargite occurs through the formation of intermediate tenantite, according to the following sequential reactions: 4Cu3AsS4(s) ? Cu12 As4S13(s)+ 3/2S2(g) Cu12 AS4S13(s) ? 6Cu2S(s) + 2As2S3(g) + 1/2S2(g) The decomposition kinetics was analyzed by using the model for a topochemical reaction of spherical particles: 1-(1-X) 1/3 = kt, which represented well the data. Apparent activation energies of 113 kJ/mol and 60.5 kJ/mol were found for the low and high temperature regions, respectively.

Jan 1, 1999

By Rikiya Kamezawa, Rudiono, Manabu Takeuchi

"Schottky type solar cells based on phthalocyanine (Pc) thin films were fabricated, and their photovoltaic performance was investigated in various ambient atmospheres. Most of cells prepared in this study showed a good rectification and photovoltaic effects in the visible wavelength region. The introduction ofN02 gas into the measuring chamber was confirmed to increase the current both in dark and under light illumination. However, chemical reaction between the Al electrode and N02 formed some oxide and deteriorated the Schottky barrier, resulting in an increase in cell resistivity. SF 6 gas also showed similar effects on the cell performance.IntroductionPhthalocyanine is one of the typical organic semiconductors, which shows high photoconductive sensitivity in the visible to infrared region. Today, several kinds of metal phthalocyanines are used in electrophotographic photoreceptors. In addition, application of phthalocyanines to solar cells have also been trying by many workers [1, 2]. Many efforts have been made for improving performance of phthalocyanine solar cells by modification of device structure [3, 4], doping by dye or pigment [5, 6] and incorporation of metal clusters [7]. It is known that electrical conductivity in phthalocyanine is increased by adsorption ofNO2 [8, 9]. We tried to improve photovoltaic performance ofphthalocyanine solar cell by adsorption ofNO2. This paper describes the influence of N02 adsorption on the photovoltaic behavior of phthalocyanine solar cells."

Jan 1, 2000

By Freddy Syvertsen

"During the past two years the Association of Norwegian Foundries in Norway has been running a project in evaluation of CAD/CAM systems for foundries.In this work we have had a closer look to the various steps from drawings to the finished castings. On this background we have made a specification of the special needs in the foundry process. The main content of this paper is a presentation of this specification.Some CAD/CAM sytems have been compared with the specification and a summary of the result is presented.In the project we have also had a closer look at some systems where we actually have tried the user interface and some of the possibilities in the systems. In this way we have gained a more detailed knowledge of the systems and we have also got some experience in NC-machining from the systems.IntroductionThe development of CAD/CAM systems has taken place with almost no interaction with the foundry business. This becomes clear when you are having a closer look at the systems. Most of them have not the possibility to describe the complex sculptured surfaces that is often found on castings. The people developing the software, have paid little or no attention to the problems arising when a geometry is going to be transformed for the casting process. Among the problems are the decision of where to place the parting line and to adjust the draft angle. These problems must be solved properly to be able to withdraw the model from the sandmould. In die casting the problems must be solved to be able to get the casting out of the die.In Norway some companies have been developing CAD/CAM systems for several years, with limited interest in foundry problems till 1983. To present the special foundry problems to them a specification of the needs was made that year. Another reason for making this specification, was to compare it with the CAD/CAM systems on the market (1).Design of castingsGeometry transferThe foundries in Norway are small units with almost no design of their own casting products. They are subcontractors receiving paper drawings and limited informations about the product from the mechanical industry both in Norway and in other European countries. This is going to change, and in the future the geometry will be transferred by magnetic tape or by a network of computers."

Jan 1, 1986

By G. Richards

The Trail smelter of Teck Metals Ltd. produces about 90,000 tonnes of lead per year through two stages of refining following KIVCETTM smelting. Bullion from the KIVCET furnace is first treated in a pyro-refining plant in preparation for Betts electrorefining which makes 99.99% pure lead. Pyro-refining consists of number of integrated unit operations to remove primarily copper, arsenic, antimony and tin. The operation of this plant to meet the specifications for electrorefining requires attention to bullion management and selective use of reagents. The processes used for pyro-refining are reviewed in terms of chemistry and control.

By Liya Bochkareva, David Hui, Sergey Eremeev, Maksim Kireitseu, Igor Nedavniy

The principal goal of the present paper is to demonstrate an application of modern software engineering tools for modeling virtual reality and molecular dynamics of novel nanocomposites. The main technical components of presented system are I) software and nanoengineering tools for modeling of virtual reality, molecular dynamic and 30 video images of novel diamcindscontaining nanocomposites and 2) Problem tracking system to be used during modeling of virtual reality. A computational scheme and software, which utilizes neural networks and/or Microsoft. Net technique was developed to predict properties of nano-structured materials and optimization and control of nano-devices. Developed software and IT nanoengineering tools can be used by both industrial and private single users. For commercial companies proposed technology may provide better cost-effective alternative to the existing solutions for nanoengineering and modeling their virtual realit. For private users (students, professors, and engineers) proposed technology and IT tools can provide simple and cost-effective solution for nanoengineering while studying, exploring virtual reality and modeling novel nanostructures and its properties leading to an innovation or a discovery. Because of using novel software and methodologies, users can easily operate proposed technologies by available computers and operating systems (Pentium III or IV). In addition, users can upgrade it by their own self-written models, if necessary. The proposed technologies could replace or be used along with technologies for modeling such as 30 max studio and others.

Jan 1, 2004

By Xiao Yang

Calcium oxide is one of the major fluxing agents used for steel refining. Because unreacted CaO remains in slag in most cases, discharged slag is difficult to be recycled smoothly. With the growth of environmental concerns, improving utilization efficiency of CaO is required to reduce the amount of discharged slag and energy consumption. The authors have reported a resource and energy-saving process by using multi-phase flux for dephosphorization. Reaction behavior of phosphorus in multi-phase CaO–FeOX–SiO2–P2O5 flux system was investigated. Formation mechanism of P2O5-rich phases was clarified at the interface between solid CaO or 2CaO, SiO2 and molten CaO–FeOx–SiO2–P2O5 slag. Phase relationship and thermodynamic properties of 2CaO, SiO2-3CaO, P2O5 solid solution were observed to confirm the condensation of P2O5 in solid phase. Based on these results, reduction of CaO consumption, discharged slag curtailment, and energy-saving effects in the novel refining process by using multi-phase flux were discussed.

By Fathi Habashi

In the past five years Cuba has been attempting to more than double its nickel production by constructing two new ammonia leaching plants. No metals are yet produced on commercial scale but a variety of oxides and sulfides. This report updates the Cuban nickel industry as a result of two visits : one at the invitation of the Cuban Ministry of Basic Industries in 1987 and the other as a consultant to the United Nations for the Cuban Laterite Project in 1989.

Jan 1, 1993

By Iain B. Mackenzie

In 1997, a thin layer of Microtherm Microporous Insulation was used to replace fireclay brick behind the magnesia/chrome working lining in #5 refining furnace at BHP?s San Manuel AZ smelter. A 23°C reduction in shell temperature was obtained, together with a large increase in the working capacity of the vessel. There was no sign of metal penetration as a result of the increased insulation. Following these highly favorable results, BHP have introduced this product into all of their refining furnaces.

Jan 1, 1999

By Natasa Mitevska

The distribution coefficients of Ag, As, Au, Bi, Co, Cu, Ni, Pb, Sb, Se, Te, and Zn between copper matte and slag from the reverb furnace No.2 at the Copper Smelter and Refinery, RTB BOR (Yugoslavia), are presented in this paper. The influence of the matte grade on the minor elements distribution coefficients between copper matte and slag is analyzed. The minor elements distribution in the slag phase along the slag melt depth and the furnace length is also determined.

Jan 1, 2002

By Sheng-hai Yang

The electrochemical synthesis was conducted in anhydrous ethanol solvent mixed with conductive reagent when tantalum plate was used as anode and stainless steel plate as cathode. The effects of different conductive reagents (such as NH4Br, (CH3)4NCl, (C4H9)4NCl), conductive reagent concentration and the space on the cell voltage and the current density were investigated. The current efficiency of electrosynthesis was more than 95%. The electrolyte, a mixed solution was then undergone air distillation and vacuum distillation to get the final product which was characterized by Fourier Transform Infrared(FTIR) spectroscopy, Raman spectra, 1H-Neclear Magnetic Resonance(1H-NMR) spectroscopy. Carbon and hydrogen contents in the product were determined by elemental analysis instrument. Results consistently show that the product was tantalum penta-ethoxide.

Jan 1, 2006

By Chai Liyuan

This paper focused on the preparation of porous ceramic pellets for microorganism carriers. A new method for the process was developed using simple gel-casting and bubble-in-water-in-oil type of multiphase double emulsion. The globules, consisting of a foamed sepiolite slurry suspension, were dispersed and consolidated in spherical shape in liquid paraffin as gelation progressed. The green pellets were sintered at 1100°C. The influence of surfactants, extension ratio and impeller revolution rate on the process and characteristics of the pellets was investigated. The pellet size was in the range of 1~4mm and determined directly by impeller revolution rate. The fine cell diameter of porous ceramic was in the range of 100~500m and the micropore diameter was less than 5m. The inner macropores were interconnected and extend to the external surface. It is impossible to analyze a result by SEM micrographs and digital camera.

Jan 1, 2006

By Khoo Khyou Pin, Yoshiyuki Funaki, Hirotsugu Takeuchi, Ryoichi Urao, Naotatsu Asahi

"Steel is used to be ion carburized with mixing gas of methane and hydrogen. In carburizing, carbon in the methane decomposes and deposits on the steel by plasma, so methane gas flow may influence on ion carburizing of the steel. An apparatus in which works can transfer preheating, ion-carburizing and diffusion treating zones continuously was made for effective carburizing of steel. The gases were flown into above three zones with three different gas inlets. The hardness and microstructure of the works were investigated after ion carburizing and quenching. The steel is carburized deeper near the carburizing gas flow nozzle of the inlet than far from the nozzle. Hard surface layer fom1ed by quenching of ion-carburized steel.IntroductionGas carburizing is used for a surface hardening treatment which decreases fatigue and wear of the industrial parts used in automobile, machines etc. Ion and vacuum carburizing have been developed recently and applied to some industrial parts of restrictive purposes. The ion carburizing treatment which uses hollow cathode discharge (HCD ion-carburizing) is superior in energy saving, resource saving, environmental cleanness to the other carburizing treatment. Specially, carburizing energy can be saved in HCD ion-carburizing, because highly heated zone can be restricted in the range between work and subsidiary cathode where hollow cathode discharge arises, and the work is carburized in shorter tin1e in HCD ion carburizing method than other carburizing methods. Three treatments of preheating, carburizing methods and carbon potential controlling by hollow cathode discharge tried to be carried out in one continuous transferring series to carburize works more effectively, so the HCD ion-carburizing apparatus with continuous transferring system was made and gears of works were HCD ion-carburized in continuous transferring. The works were rotated themselves to get homogeneous carburizing by continuous transferring in glow of hollow cathode discharge."

Jan 1, 2000

By Yeliz Demiraya, Onuralp Yucelb

"Production of strontium metal from its oxide was studied under the pressure of 1-5 mbar by methalothermic process. SrO with 99 % purity was used in the experiments. Effects of Al powder addition (100, 200, 300 % of stoichiometric ratio) and time were investigated on recovering of metallic strontium. Effects of BaO addition (100 %, 200 %, 300 %) was also investigated. The final residues were examined for their chemical composition. XRD, AAS and Flame Photometer were used for chemical analysis. More than 96 % of strontium metal recovery can be obtained.IntroductionStrontium is an element which is used in many advanced technology applications. Barium strontium titanat, strontium bismuth titanat, and strontium bismuth tantalat thin films are promising materials in ferroelectric and Schottky-based microelectronics technologies, especially for memory applications. Physical vapor deposition (PVD) techniques as magnetron sputtering, thermal evaporation and molecular beam epitaxy (MBE) are the most widely used methods for growth of these thin films [1-3]. In these techniques high-purity of Sr metal is used as evaporation sources and sputtering targets. Furthermore, metallic strontium is used as a ""getter"" in electron tubes, and as an alloying elements in aluminum alloys [4].The most used Sr compound is SrCO3 and widespread process used in production of SrCO3 is the hydrometallurgical carbonation of celestite. Although there are considerable amount of Selestite reserves, SrCO3 and strontinum metal are not being produced in Turkey, yet [5].Concentrated celestite (SrSO4) is conversed to SrCO3 in carbonate media. Black ash and direct conversion processes are currently used methods. There are many satisfactory studies about hydrometallurgical carbonation of celestite and decomposition of SrCO3 [6, 7]. Since strontium metal is produced from it’s oxide (SrO), SrCO3 needs to be decomposed to SrO."

Jan 1, 2011

By G. J. Shiflet

This paper will review work done in our laboratory on the formation, thermodynamics and crystallization of aluminum based metallic glass with the addition of rare earth elements. The results demonstrate that the metallic glasses are truly amorphous and not microcrystalline and that they are unusual in their formation because the alloys contain 90 at. % aluminum and there is no deep eutectic present in the phase diagram. Tensile strengths that exceed 900 MPa are obtained for several of the compositions and exceed 1000 MPa after partial crystallization.

Jan 1, 1992

By David Forrest

In 1981, K. E. Drexler proposed using massively parallel nanomechanical systems to manufacture large atomically exact structures. As in macroscopic mechanical systems, they would contain components that serve traditional functions such as trusses for support, gears to transmit power, bearings for low-friction support of rotating surfaces, motors to supply torque, pipes and conveyor belts for material transport, and channels for coolant. Many of these components would only contain a few thousand atoms. Specific designs for these devices became available in the early 1990s, and a few working devices appeared in laboratories by the early 2000s. As advances continue, a thorough understanding of the operative transport phenomena will guide the intelligent design and construction of nanomechanical structures, devices, and systems. The familiar equations of continuum mechanics are generally inadequate to describe the flow of heat and mass in the proposed nanosystems. Boundary conditions often need to be described in terms of potential surfaces. Surfaces are not geometrically smooth, but periodic according to the locations of atomic nuclei. Friction occurs not due to the plastic deformation of asperities on mating surfaces, but to phenomena such as thermoelastic damping and phonon viscosity when atoms slide past each other. Electrostatic forces dominate over gravitational forces by orders of magnitude; there is no role here for natural convection. Structural components, no matter how stiff and strong, are in constant motion due to the thermal noise in the system. The fluids are described in terms of individual molecules in constant motion.

Jan 1, 2006