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By Liu Chunpeng

Under an inert atmosphere, the temperature enhancement of nickel bearing pyrrhotite irradiated by microwave was measured with a special metal-sheathed thermocouple and the non-isothermal rate equations were obtained. Under the controlled oxygen potential of the reacting gas in the microwave field, over 90% sulfur contained in the pyrrhotite is converted into elemental sulfur directly, the iron and the nickel are transformed into FeO,, NiO, NiFe,O, and FeSiO,. According to the experimental data the rate of the elemental sulfur produced is in diffusional control and the non-isothermal equation derived is

Jan 1, 1993

By David G. Dixon

From its first implementation for the recovery of gold from low-grade ores by cyanidation in the early 1970s, heap leaching has developed into a key hydrometallurgical technology, in conjunction with solvent extraction and electrowinning, for the recovery of base metals, including most notably copper from both oxides and secondary sulphides, and more recently, nickel and zinc. And, given recent advances in bioleaching with thermophilic microbes, the successful application of heap leaching technology to low-grade primary copper ores seems only a matter of time. However, with each new development, it becomes increasingly apparent that the successful application of heap leaching technology will ultimately depend on our having an ever more complete understanding of the fundamental processes underlying it. Much work has been done toward the development of this understanding, on many different fronts. In this paper, a critical overview of heap leach modeling work to date is presented in terms of the most important phenomena which occur during heap leaching, and potential directions for future work are discussed.

Jan 1, 2003

By S. Niyomwas, R. G. Reddy

"A mathematical model was developed to describe the plasma gas and particle dynamics and conversion yields. The velocity and temperature fields in the plasma were calculated by solving 1 the Navier-Stokes equations and the thermal energy balance equations. Conservation equations for the system species consider the multi-component diffusion and chemical reactions. Through the application of this model, temperature distribution, flow fields, and production rates were computed. The model was used to study the thermal decomposition of ilmenite in the non-transferred arc plasma reactor. The computed production rates of TiN from ilmenite using nitrogen and methane gas mixtures, are in the range of 5 to 100 x 104 kg/m3/s at 2500 KIntroductionThe widespread interest in thermal plasma processing has stimulated a great deal of research effort into the various aspects of this process, including plasma' spraying, thermal plasma chemical vapor deposition, plasma synthesis of fine powders, thermal plasma decomposition, plasma melting, and plasma extractive metallurgy.In the plasma synthesis of fine powders, the earlier experimental and theoretical studies aimed at predicting the final products1-5. Then it was followed by more recent investigation concerning the profile of plasma gas velocity, plasma temperature and concentration. In this regard, useful plasma processing models have been reported by numerous investigation6 -11 which were increased by both theoretical analysis and measurement.As a result of this work a reasonable plasma-processing model is proposed. It is to be noted that all the thermal analysis that has been made neglected the fluid -flow effects. Also, in the analysis aimed at the quantitative description of the fluid-flow field, the effect of heat transfer was not taken into account."

Jan 1, 2000

By Osamu Takai, Yoshiki Sato, Nobuhiro Tajima, Hiroyuki Sugimura

"Amorphous carbon thin films doped with nitrogen ( a-C:N) have been synthesized by means of shielded arc ion plating (SAIP). Their electron field emission properties, that is, threshold field strengths for electron emission and maximum emission current densities, were evaluated and compared with those of pure amorphous carbon (a-C) films prepared by the same SAIP apparatus. Among all of the fabricated a-C:N films, the a-C:N films with a N concentration of 23 %, which prepared using Nz arc plasm at a pressure of 1 Pa with applying a sample bias voltage of -100 V, showed the lowest threshold filed of 13.4 V/µm and the highest emission current density of 1.87 µAfcm2 at a field of20 V/µm. These field emission properties of the a-C:N film were much better than those of the a-C films. The best results obtained on the a-C film in this study were the lowest threshold filed of 15.5 V/µm and the highest emission current density of 0.052 µA/cm2 at a field of 20 V /µm. Nitrogen doping to aC was found to be effective for lowering threshold voltage for field emission and for increasing emission current density. The electron field emission characteristics of the a-C:N films depended not only on N concentration but also on chemical bonding state of nitrogen in the a-C:N films. The presence of the ~-C3N4-like phase, which contributes to improve wear resistance of a-C:N as well, distinguished by the NlsXPS peak at 400.5 eV is proved to be crucial in order to enhance field emission properties of a-C:N.IntroductionThere has been much interest in electron field emission from a cold cathode due to its potential applications in vacuum microelectronic devices including field emission displays which are expected as flat panel displays in next generation [l]. It is well known that efficient emission can be rather readily realized using tip-like shape cathodes, e.g., microfabricated three-dimensional electrodes [2], carbon nanotubes [3-5], etc. However, electron emission from planar surfaces is of particular importance since such a type of cathode is· simply fabricated and assembled into microelectronic circuits. Currently, amorphous carbon thin films doped with nitrogen (a-C:N) prepared by plasma processes have attracted attention because their threshold voltages of field emission are relatively low [6]. Among various methods for preparing a-C:N films, the process using arc plasma is of special interest since, in arc plasma, nitrogen is highly activated and new types of carbon nitride phase are expected to be synthesized. However, field emission properties of a-C:N prepared by arc plasma have been studied in less detail compared with that prepared by the other methods such as sputtering."

Jan 1, 2000

By Zhigan Deng

Cooling crystallization was used to separate iron (III) and nickel (II) from acidic sulfate solution produced by leaching of molybdenum-nickel black shale. The effect of K2SO4 concentration, crystallization temperature, solution pH and crystallization time on recovery of nickel (II) and precipitation of iron (III) was investigated, in order to obtain effective separation of nickel and iron. The optimum parameters determined were as follows: 200 g/L K2SO4, 10 °C crystallization temperature, solution pH of 0.5 and 24 h crystallization. Under these conditions, 97.6% nickel (II) was recovered as K2Ni(SO4)2, 6H2O crystals and only 2.0% of the total iron (III) was precipitated. Recrystallization yielded K2Ni(SO4)2, 6H2O crystals with a purity of 98.4%.

By Xuling Chen, Yi Wang, Xiaohui Fan

"The current control method of grate-kiln iron ore oxide pellet production is lack of accuracy and normalization due to the limited detection conditions. Therefore, mathematical models of grate-kiln temperature field are presented. With calculation of gas-particle heat transfer as well as enthalpy changes of moisture evaporation and magnetite oxidation, the thermal history of pellets throughout grate-kiln process can be acquired and used for production status estimation. Taking the calculated results as well as detected data in production as inputs, process parameters such as running speed, fan opening and coal injection rate as adjusting objects, expert system for grate-kiln pellet production is outlined. And the preheating section dominated control strategy is explained. Results of production application show that the stability rate of gas temperature in gas hood of preheating section is increased from 91.0% to 94.2%, compressive strength and first grade rate of pellet are increased by 3.62% and 2.36%, respectively, while FeO content is 18.18% lower. Control guidance of this expert system can solve production anomalies effectively, stabilize grate-kiln iron ore oxide pellet production and improve pellet quality.IntroductionSteel industry in China has developed rapidly in recent years. China’s crude steel production in 2010 is nearly 627 million, which is 44.2% of the world total production. Burden with higher quality is demanded by enlargement and modernization of blast furnaces. And oxide pellet production has become a growing concern. In 2010, the total production of pellet in China is 110 million, and about 60% is produced by grate-kiln process."

Jan 1, 2012

By Evan Jamieson

The conditions under which various iron(III) oxy-hydroxides phases precipitate from iron(III) chloride and sulfate solutions at ambient temperatures (<60°C) are reviewed. Many of these precipitates are slow settling and gelatinous but ultimately transform into other more stable or crystalline phases. The phase that forms depends upon the rate of precipitation and pH. A comparison has been made of the iron(III) oxides formed upon the neutralisation of various iron(III) solutions with caustic, slaked lime or slaked magnesia which provide different rates of neutralisation and slowly dissolving solids with localised high pH. Mössbauer spectra of ferrihydrites precipitated under these different conditions are compared and interpreted. Particular attention is paid to the settling rate and settled volume which is likely to relate to industrial thickener and filter performance. It is shown that in pure chloride solutions, poorly settling ferrihydrite is usually produced at 20oC regardless of the choice of base. However in sulfate solutions fast settling precipitates are produced using lime and magnesia but not with caustic. In mixed chloride/sulfate solutions, optimum settling rates occur when the molar ratio of [SO4]2to Fe3+ is about 1:1 and when the sulfate concentration is <0.20 M. It is proposed that ?dense amorphous basic iron sulfate? or well-ordered ferrihydrite is formed on slowly dissolving lime or magnesia surfaces. Implications for industrial liquors are considered.

Jan 1, 2003

By K. R. Robilliard

Ausmelt Technology has been developed to process copper concentrates containing significant levels of lead, arsenic and antimony. A process was developed aimed at smelting these concentrate materials to remove the contaminants to fume and produce a clean copper product. The production of clean copper and the potential economic benefits of this process step over the sale of impure concentrates is discussed.

Jan 1, 1995

By S. K. Utimurd, D. C. R. Espinosa, J. A. S. Tenório

"Waste Electrical and Electronic Equipment (WEEE) has become an environmental issue due to technological advance and waste plastic is one of the main polluters. The excessive discard of these plastics result in a difficult to dispose it to landfill and need further separation with technique in order to produce high added value plastics. There are many kinds of plastics in extensive use at the present time and the co=on are the acrylonitrile-butadiene-styrene (ABS) and high impact polystyrene (HIPS) used in the production of electric appliances. These plastics are difficult to separate because they have similar densities. Flotation of plastics is one possible separation technique and using selective wetting agents. The separation may be possible given close control at particle size and the concentration of the reagent. The process was able to produce a concentrate of HIPS with at least of 93% purity and a concentrate of ABS with 99% purity.IntroductionThe current situation of municipal solid waste (MSW) management especially in emerging economies like Brazil, the growing population and economic activity will result in a significant increase in the generation of waste in the coming decades. It is worthwhile to review and update the sources, amounts and recovery technologies of specific materials from waste, particularly from municipal solid waste (MSW).The growing impact of the current waste management practices stresses the need for a change in how waste is handled. The 2012 survey and the Brazilian Association of Public Cleaning and Special Waste Disposal Companies (ABRELPE) reports the generation of 62 Mt urban MSW in that year, which is an increase of 13% compared to 2011. It has been reported that in Brazil about 90.17% of the generated MSW is currently collected, which indicates an increase in the coverage of collection services compared to 2011 [ l]."

Jan 1, 2014

By Huimin Lu, Min Li, Jinghua Zou

"Zeolitic imidazolate frameworks (ZIFs) are new type of porous materials, form inerratic polyhedral in three-dimensional with large cages and small apertures, and appear structural diversity. Their hole size can be adjusted. These materials have high selective adsorption capacity to carbon dioxide. In this paper, zeolitic imidazolate frameworks were synthesized by solvothermal synthesis method with dimethylformamide (DMF) as solvent and structuredirecting agent, divalent metallic ions as cation, and imidazole as ligand. The crystals were characterized with XRD, SEM for their crystal structures and physical properties, the adsorption of the crystals for carbon dioxide was also tested, and the result suggests that these porous materials have a capacity of 1.35ml/g for storing carbon dioxide at 273 Kelvin under ambient pressure.IntroductionGlobal warming caused by the increase of carbon dioxide in the atmosphere has become one of the main environment problems, contemporary research has focused on ways to slow or stop this trend. CO2 capture has attracted attention due to the potential to trap and sequester large amounts of CO2 from concentrated sources such as power plants [1]. Traditional technologies in capturing CO2 include absorption by aqueous amines [2]. However, utilization of this process is energy intensive and expensive. Carbon dioxide storage materials investigated so far can be divided into two categories: chemical storage adsorbents and physical storage media [3]. The first kind of materials can chemically adsorb carbon dioxide within their structures and need thermal energy to release the adsorbed carbon dioxide. The examples of the chemical adsorbents include aqueous amines, gas-hyperbranched aminosilicas [4]. The physical adsorbents store carbon dioxide by physical adsorption of carbon dioxide at elevated pressure and release the adsorbed carbon dioxide at low pressure. The physical adsorbents that have been investigated for carbon dioxide storage include zeolites, carbonaceous materials and other porous materials. Until recently, a new type of microporous material, known as zeolitic imidazolate frameworks (ZIFs), has been reported as promising adsorbents for carbon dioxide storage [5 ~ 10]."

Jan 1, 2010

By Alexander Burns

Electrolytic salt splitting is a technology where acid and/or base is regenerated from a neutral salt using membrane electrolysis. Recent advances in the understanding of brine treatment, membrane stability, and cell design have made electrolytic salt splitting feasible on certain hydrometallurgical solutions. Meanwhile, environmental regulations have made the bulk disposal of salt solutions more difficult. In this paper, sodium sulfate salt splitting is examined from a cost perspective, compared to purchasing the reagents directly. Relative costs are estimated for several regions based on published electricity and reagent prices. The results show that salt splitting is economically favourable in some regions, and can be made more favourable by applying modifications to the traditional three-compartment desig

By Dominik Hofer

A broad spectrum of tantalum containing input materials can be processed for the production of synthetic tantalum concentrate (“SynCon”). The use of these low grade substances offers a secure alternative to mining of coltan in Central Africa. SynCon is produced in a multi-stage pyrometallurgical process, wherefore the melting behaviour of slags presents an important factor especially regarding the energy consumption and its optimisation. The characteristics of a slag comprising mostly Al2O3, CaO, SiO2 and MgO are influenced by the amount of other oxidic constituents which enfolds the main focus of this study. A hot stage microscope serves for the investigation of the slag behaviour in a temperature range from 1000 to 1600 °C under reducing atmosphere (CO/CO2 gas). The experimental results are compared with thermodynamic calculations (FactSage) to get a better understanding of the process.

By Li Ma, Shaoguo Chen, Gele Qing, Qihang Liu, Keng Wu

Olivine contains higher MgO element, which can be added into blast furnace burden to improve slag stability and fluidity. Effect of calcined olivine and untreated olivine on low silicon pellet production process and quality was studied in this paper. The results shows, calcined olivine has no effect on bursting temperature of green pellet, however the bursting temperature of green pellet will decrease with increase of untreated olivine ratio. Untreated olivine has slight effect on green pellet strength than calcined olivine while the ratio is higher than 2%. The compressive strength of low silicon pellet will increase first and decrease afterwards with increases of calcined olivine ratio under firing temperature of 1250°C, whereas, the changing sequence is reverse fired under 1280°C. The result of untreated olivine pellet compressive strength is same as calcined olivine pellet. However, the compressive strength and metallurgical property of calcined olivine pellet is slightly higher than that of untreated olivine pellet under same condition.

Jan 1, 2015

By Lifeng Zhang

Printed circuited boards contain considerable quantities of valuable metal, while also containing many environmental pollutants making them unsuitable for landfill. In this study the decomposition of common plastics used in printed circuit boards were studied. Polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC) and polyethylene (PE) were heated in both C02 and argon atmospheres using a thermo-gravimetric furnace (TG) coupled to a mass spectrometer (MS). Soda ash Na2C03 and baking soda NaHC03 were used as reactants. The degradation temperatures and evolved gases are presented for single plastics and mixtures. Mixed plastics are shown to behave as a sum of the individual plastics. The mass loss temperature is the same in CO2 and argon. However, less residue is formed when heated in CO2.

Jan 1, 2008

By Theodore Ineich

The “BIOMOre” project aims to prove the technical feasibility of indirect in situ bioleaching of sulfide minerals contained in a deep underground deposit, by bringing together the disciplines required to make a success. The underground location in Poland was provided by project partner KGHM inside an operating copper mine. Key components of this project were the design and construction of a pilot plant, and its operation in an underground environment. This project also included a ∼250 t (100 m3) fragmented rock reactor hydraulically connected to the pilot plant. The pilot plant consisted of several tanks and pumps, a fluidised bed ferric iron generating bioreactor containing immobilised acidophilic iron oxidation biomass, and all the required instrumentation and utilities. Before the bioleaching phase could start, the rock reactor had to be flushed continuously firstly with water to remove chloride salts that are corrosive and also harmful for the bacteria used in the bioreactor, and secondly, with sulfuric acid solution to react with the carbonates present in the ore matrix. This paper summarizes the design, construction, commissioning, and operation of the pilot plant.

By Petrus Christiaan Pistorius, Farzin Fatollahi-Fard

The production of synthetic rutile—a common starting material for most titanium production processes—from iron-rich titanium minerals such as pseudorutile and ilmenite is described. The process for “upgrading” the mineral to synthetic rutile is by carbothermal reduction of the mineral while immersed in a molten salt at high temperature, followed by magnetic separation of the reduced iron. A variety of factors are also investigated, such as particle size of the mineral, the type of mineral, and the molten salt used. The solubility of iron(III) oxide in different molten salts is also experimentally determined.

Jan 1, 2016

By Ragnhild E. Aune, Mark William Kennedy, Shahid Akhtar, Jon Arne Bakken

"To determine the heating rate of billets using ‘short coils’, an appropriate correction factor must be applied to the theoretical relationship. In 1945, Vaughan and Williamson published a semi-empirically modified Nagaoka coefficient applicable for moderate frequency induction heating processes (10 kHz). Recently it was demonstrated that the method of Vaughan and Williamson gives <10% error in the estimated power when heating aluminum billets at 50 Hz.In the present study, experiments have been conducted on aluminum billets in order to verify an empirical frequency corrected ‘short coil’ equation. Measurements of electrical conductivity (<± 0.5%), current (± 1%), heat (± 1-3%), and magnetic flux density (± 1-2%) have been performed. The results are compared with 1D analytical calculations, and 2D axial symmetric FEM modeling using COMSOL 4.2®. The frequency corrected equation has proven to provide accurate predictions of power (<4% error) within the frequency range 50 Hz to 500 kHz.IntroductionInduction heating is commonly applied to the re-heating of billets before forging or extrusion processes. The resistive heating produced by eddy currents in the solid or semi-solid work piece during this procedure, is driven by the time varying magnetic flux density in the air-gap between the work piece and the coil. The flux in the air-gap is created by the current flowing in the induction coil, i.e. the magneto-motive force. In Figure 1 it can be seen that the currents present in the work piece are concentrated in the outer ‘shell’, or the first electromagnetic penetration depth (dw), and flow in a direction which opposes the magnetic field produced by the induction coil."

Jan 1, 2012

By Marco Antônio Siqueira Rodrigues

The possibilities for treating rinse waters fiom chromating bath by electrodialysis are discussed together with the possibilities of optimizing the treatment process for waste reduction and reuse of water and chemical products. An industrial effluent with 4600 ppm of Cr(VI), besides other metallic contamination, was used as work solution. This solution has been recirculated on an electrodialysis cell of three compartments, using exchange membranes Selemiom AMT and CMT. A migration of dichromate ions into the anodic compartment was obtained, so that an extraction of circa 99.9 % of Cr(VI) present on the solution was observed, resulting in water with a Cr(V[) concentration of 4 rnd. These results show that electrodialysis can be used to treat these effluents, and this water could be reused as rinse water. The solution of the anodic compartment, consisting at the beginning of the experiment of H2S04, 0.1 N, reached 7200 mg/l of Cr(VI). This concentrate could be reused on the chromating bath itself.

Jan 1, 1999

By Niloy K. Nath

Two layer sintering by charging green sinter mix with normal coke rate in the upper layer and reduced coke rate in the lower layer, can substantially reduce the coke rate and also improve the sinter quality by producing more uniform thermal profile through out the bed height. The two-layer sintering process have been analyzed by numerical simulation of the process by a detailed CFD based model, considering all the important phenomena like gas-solid reaction, melting and solidification, flow through porous bed, heat and mass transfer etc. Optimization techniques like genetic algorithm, differential evolution is then applied to evaluate the optimum coke rate in the two layers of the bed to produce the ideal thermal profile and melting fraction in the sinter bed for optimum sinter quality. Through this optimization method both high quality sinter with minimum return fines can be achieved along with reduced coke rate. Application of a genetic algorithm for this type of process optimization has several advantages over the traditional optimization techniques since it can identify global optimum condition and perform multi-objective optimization much easily for complex industrial process like iron ore sintering. Keywords: Two-layer Sintering, Iron Ore Sinter Quality, Ergun&apos;s Equation, Gas-solid reaction, Melting Fraction, Multi Objective Optimization, Pareto Set, Genetic Algorithm

Jan 1, 2003

By W. Song, C. Richards, B. Q. Li

"This paper presents a two-phase flow numerical model for spouting gas-particle flow reactors used in chemical vapor deposition processes for manufacturing heart valves and other biomedical implants. The model is developed based on the Eulerian-Eulerian formulation of gas-particle flows, with the k-e engineering model modified with the presence of particles for the description of turbulent gas flows. In parallel with the numerical model development, physical models are set up, where the particle image velocimetry is used for visualizing the particle flows and spout shapes and heights and optical probes are used to measure the particle velocities. The numerical model predictions are compared reasonably well with the experimental measurements.IntroductionVarious biomedical implant components, such as bone joints, dental components and heart valves, are coated with bio-compatible thin films by chemical vapor deposition in particle-laden chemical reactors [l-5]. In these reactors fine particles are used as packing and supporting media. During the coating operation, these packed particles are fluidized by an upward gas jet from the nozzle, reach a certain height and fall back on the top of an annulus region. These recirculating particles are mainly for levitating the implant components (usually one or two in a reactor at one time) so that every portion of them is equally exposed to the gaseous atmosphere. An equal exposure is critical for forming a uniform, mechanically strong and corrosion-resistant coating on implants. Plant experience shows that the quality of the coating is directly related to a stream of operating parameters such as temperature, particle size and loading, and gas flow rates [6]. Optimization of these operating parameters for improved reactor performance depends crucially upon our fundamental understanding of the physics governing the gas-particle flow, heat, and mass transfer phenomena taking place in these reactors."

Jan 1, 2004