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By P. K. Narasimhargahavan

This paper discusses briefly the major reasons associated with the growth and its impact on the energy requirement and Environmental imbalance. A projection based on the present global Alumina and Al requirement indicate a substantial further growth of at least 30% over the next 10 years. It is indicated that the main factors which are likely to influence investments are the environmental factors such as the Climate Change and global response to the growing energy prices and sustainable development. Each of the developed / developing nations must find response to the GHG emissions which will encourage the Al Industry to make an effective contribution to global warming while preserving the international competitiveness of the industry - a challenging task. The efforts shall concentrate on improving energy efficiency in the industry possibly of the order of 25% over the next 10 to 20 years. The developments in this line are discussed.

Jan 1, 2010

By Margarete Kalin

Mine abandonment is associated with the securing of access to underground workings, shafts, raises and adits. Waste rock piles and tailings are generally contoured and revegetated. When the waste materials contain pyritic material seepages can often emerge long after the physical reclamation work has been carried out. Their extent and origin has to be delineated to facilitate remedial measures. The depth to which the seepages extended can be determined with an electromagnetic (EM) survey. This paper reports on the experience gained using a winter and a summer EM survey correlated with measurements of specific conductivity at the sediment water interface. Lake sediments and ponds which represent a homogenous background material are good media, where specific conductivity and electromagnetic conductivity can be correlated. The origin of the seepage within the recontoured mine site requires detailed site knowledge, as many anomalies in heterogenous materials such as represented by a mine site are evident.

Jan 1, 1994

By Luciano B. Oliveira, Luis G. C. Marques, Sergio N. Monteiro, Marcos V. M. Fagundes

"Biodiesel production is normally associated with large plantations of oily vegetables such as soybean and colza, in large rural areas. However, in the municipal limits of the city of Rio de Janeiro, southeast of Brazil, biodiesel is being produced from wastes commonly generated by typical urban activities such as sewage sludge, discarded fat from meat markets and post-used cooking oils. In the present work, the experience of producing biodiesel from urban wastes in Rio de Janeiro is assessed. The type of precursor materials, equipments and logistics are presented. The environmental and economical advantages as well as the drawbacks are discussed.IntroductionThe interest for a liquid fuel that could substitute those obtained from petroleum started more than one hundred years ago when Rudolph Diesel tested his no-spark internal combustion engine, impelled by compression, with peanut oil. By that time, petroleum was beginning to be extracted in large scale and no one was concerned with the future environmental problems and its eventual depletion. In the last century, the successful association of petroleum based fuels with the automotive industry was an almost insurmountable obstacle to any attempt to use nonmineral oils [1]. In addition to the greater efficiency and, by then, lower price of the diesel from petroleum, the use of plain vegetable oils introduced undesirable carbon deposits and reduced the engine lifetime. Today, the situation is reverse. The continuous increase in the price of petroleum and, above all, its contribution to climate changes are strongly motivating the use of biofuels to replace those obtained from fossil fuels such as petroleum, natural gas and coal [2].In the case of the common petroleum derived diesel, many countries are now engaged in large scale substitution programs. The USA should produce more than 700 million litters of biodiesel, while the European Community is expected too produce around 6.5 billion litters in 2008. In Brazil, the federal biodiesel program imposed a minimum of 2% addition to the common diesel. This would demand a production of 800 million litters in 2008 [3]. The Brazilian biodiesel is made from a diversified source of vegetables mainly castor bean, African palm and soybean. The main producers are agrobusiness firms located in large rural areas of the Brazilian hinterland [4]."

Jan 1, 2008

By G. T. Lapidus, O. J. Solis-Marcial

"The oxidative dissolution of copper from refractory minerals, such as chalcopynte, represents a technological challenge that has occupied hydrometallurgists for more than half a century. Innumerable processes have been suggested, but the majority operates at high temperatures or employs corrosive media. The origin of this refractory nature is the formation of passivating phases of iron(III) or copper. One option is to add non-corrosive ligands that complex these metal ions, thereby facilitating their dissolution. In the present work, the effect of acetone in sulfuric acid solutions was studied. The initial experiments were on chalcopynte carbon paste electrodes using cyclic voltammetry, where greater reactivity was observed. Later, leaching tests with hydrogen peroxide, cupric sulfate and ozone and, as oxidants, were performed. High extractions were achieved in three hours at 50°C. The solid residues contained the iron in the form of Fe203 and FeOOH.IntroductionChalcopyrite is the most important mineral of polysulfide copper ores [1] and accounts for approximately 70% of the world's copper reserves [2]. Currently, the copper present in chalcopyrite is extracted mainly by pyrometallurgical processes, which generate environmental concerns because of the formation of SO2 gas and submicron particulates [3]. The development of a less aggressive hydrometallurgical process for the extraction of copper would constitute a possible solution to these problems. For that reason, studies of the dissolution behavior of chalcopyrite are of great technological importance [4], However, the proposed oxidative leaching routes for chalcopyrite, generally at high pressures and temperatures, have not been implemented on an industrial scale, because of the elevated costs required to equal the high copper extractions obtained in thermal processes. These extreme leaching conditions are required because of the refractory nature of chalcopyrite. Passivation has been used to explain this phenomenon, although researchers have disagreed on the composition of the layer, which is various have assumed to be sulfur, copper sulfides, and iron-bearing jarosites or hydroxides [5]. If the latter compounds are the cause, an alternative solution would be the use of polar organic solvents in the oxidative leach to decrease the formation of the passivating iron layer. In this work, the influence of acetone on the oxidative leaching of a chalcopyrite concentrate at room conditions is explored."

Jan 1, 2012

By Jhon Cuya

Titanium dioxide is the well-known catalyst for the photodecomposition of water in UV region and its nanoparticles show better performance than its bulk materials. Furthermore, partially sulfurized TiO2 is expected to be chemically stable and have an enhanced photocatalytic activity compared with TiO2. For this purpose, the sulfurization behavior ofTiO2 nanopartic1es was thermogravimetrically (TG) studied by a thermo-balance with a quartz spring using CS2. From the TG curve of TiO2 nanopartic1es, first, the weight decrease appeared down to around 8 wt% and then sulfurization reaction started at around 500°C at a heating rate of 1 C°/min. The weight increase curve showed a maximum of ca 30 wt% at around 750°?C and then gradually decreased to ca 12 wt% at 1000°C. This would be caused by the formation of TiS2 followed by the decomposition ofTiS2 to lower sulfides, such as Tit.0.8S2 and Ti3S4. From the comparison of the sulfurization of TiO2 nanoparticles with that of anatase, rutile and Ti(OH)4, it was found that TiO2 nanoparticles showed a similar behavior to that of Ti(OH)4.

Jan 1, 2003

By Chai Li-yuan

Anodizing behaviors of magnesium alloys AZ31 at constant applied current, based on the electrolyte solution free of chromate or fluoride, were investigated. The anodizing process was influenced by constituents of electrolyte greatly. Therein, the oxylate salts, which led to the occurrence of the two totally different processes, played a determinant role in anodizing. They were stable and sparking process respectively. The morphology of anodizing film was observed by SEM and the structure of film was analyzed by XRD. During the stable process, a brown thin film was formed, however the sparking process led to the formation of white hard thick film. The functions of some kinds of additives, such as ammonia, glyceryl alcohol and PVP etc were also studied. Some of them had great effect on surface morphology of anodic film and some of them affected stability of anodizing process significantly.

Jan 1, 2006

By C. Dresen

This paper discussed the reaction kinetics of the reduction of industrial phosphate pellets for P4 production. In the reduction process of various phosphate ores, the following parameters were investigated: Diffusion of the phosphorus oxide and other gaseous products from the reaction mixture after having been reduced on the reductant (coke) surface. Influence of silica on reaction kinetics. Temperature influence. Influence of mineralogy and morphology (different ores). Particle size influence of silica and coke. Experiments were carried out in a vertical tube furnace with 2 ores, 2 types of silica and one type of coke. Selected experimental conditions simulated furnace conditions. The following conclusions could be made: Reaction rate increases with the addition of SiO2 into the pellet. The reaction rate increases above 1350°C (melting temperature of the slag). Mixing different ore types in the pellets leads to differences in reduction kinetics. Particle size of the coke particles influence reduction kinetics. The amount of slag formation is influenced by silica addition, coke size and temperature.

Jan 1, 2002

By Soumitro Nagpal

Bacterial oxidation of a pyrite-arsenopyrite-gold ore concentrate was carried out in .14-liter continuous-flow stirred-tank reactors (CSTR). Oxygen and carbondioxide consumption rates mineral dissolution rates, and bacterial concentrations were measured at various steady-state residence times and with 6, 11, and 16 wt.% solids in the feed slurry. A sharp optimum in biooxidation rate .was found at a residence time of approximately 40 hours for operation at each of the three pulp-densities. Biooxidation rates increased consistently. with increasing pulp density. Cell washout accompanied by negligible biooxidation rates was found to occur at a residence time of approximately 20 hours. Mineral' oxidation was found to be strongly dependent on bacterial activity. Arsenopyrite was found to be preferentially oxidized? at the higher Pulp densities.

Jan 1, 1991

By Xavier Kleber, Aude Lamontagne, Veronique Massardier, Daniele Mari

"The thermoelectric power (TEP) technique was used to determine with high accuracy the strain ageing kinetics in heavily cold drawn pearlitic steel. Because of the very high sensitivity of the TEP to solute atoms, this technique allowed the strain ageing to be followed from the very first moments. The kinetics were followed during isothermal ageings performed between 20°C and 200°C for different strains. In order to avoid any ageing at room temperature, the samples were kept at -80°C immediately after cold drawing. TEP evolution versus strain highlights cementite decomposition occurring during cold drawing. During the ageing, a redistribution of the dissolved carbon atoms in ferrite occurred. The TEP increase with the ageing time was attributed to the departure of carbon atoms from ferrite (segregation to dislocations and/or carbide precipitation). The kinetics were analysed using the Johnson-Mehl-Avrami-Kolmogorov approach which enabled to determine activation energies associated with carbon atoms redistribution.IntroductionHeavily cold drawn pearlitic steel wires are commonly used as structural materials for their high strength and their acceptable ductility. However, several previous studies highlight the microstructural destabilization of pearlite mainly due to cementite decomposition during the drawing process, which induces changes of mechanical properties [1, 2]. This phenomenon was detected by several experimental techniques such as Mossbauer spectroscopy [3, 4, 5], themomagnetic analyses [6, 7], TEM [8, 9, 10] or atom probe tomography [9, 10, 11]. Nevertheless, the mechanism of cementite decomposition is still unclear. Several hypotheses were proposed in the literature. The first hypothesis relies on a strong interaction energy between carbon atoms and dislocations involving higher binding energy than that between carbon atoms and iron atoms in cementite [3]. The second hypothesis is the increase of the free energy of the interface between cementite and ferrite due to the fragmentation of cementite during deformation (Gibbs-Thomson effect) [8]. Some authors even suggest that the dissolution of cementite occur during a post-deformation ageing [12, 13]. It is worth"

Jan 1, 2013

By R. W. Smith

A microorganism will function as a mineral flocculant if it is to some degree hydrophobic and can attach itself in some manner, such as through electrostatic interaction, to the fine mineral particles to be flocculated. The present paper concerns the use of a hydrophobic bacterium, Mycobacterium phlei, as flocculating agent for phosphate slimes. Experimental work on the flocculation of phosphate slimes and of dolomite and clay mineral suspensions was performed. It was found that M. phlei functions as an excellent flocculant for a dolomitic slime but does not function as well for mineral suspensions where large quantities of the solids are finer in size than the approximately 1 µm size of the bacterium.

Jan 1, 1992

By J. Tang, B. Q. Li, R. Akarapu

"An integrated model is developed to represent the three-dimensional electromagnetic wave propagation and thermal phenomena during microwave heating of ceramics and dielectric/biological materials. The model development is based on the edge finite element formulation for electromagnetic fields and the node fmite element formulation for thermal phenomena. Results are presented and compared well with available analytical solutions and experimental measurements. With the model, the effect of sample positions on the electromagnetic and thermal field distributions is studied.IntroductionMicrowave, as an electro-heating source, has been widely used in the processing industries for packaged foods and other materials. The commonly used household microwave oven is a typical example of microwave heating processes. Other industrial microwave processing systems include large-scale microwave guides and cavities, which are used for the sintering operations as required for making ceramic components or for sterilizing the packaged foods."

Jan 1, 2004

By J. Sofra

The quantity of copper produced by secondary material processing is increasing as metal producers look to cleaner and cheaper sources of copper. The need to smelt secondary copper more economically, to process a wide range of materials with large fluctuations in size and composition and to cope with the increasingly stringent environmental constraints have put considerable pressure on existing conventional secondary copper smelters. The Top Submerged Lance process, developed and commercialized by Ausmelt Ltd offers a low cost technology, which is particularly adapt at processing copper-bearing scrap and residues. The application of Ausmelt Technology to replace conventional secondary copper processing operations introduces potential for significant advantages in environmental performance, and improved process efficiencies through the use of cheaper hels and reductants, the high rate of metal recovery and the flexibility inherent in the technology to process various feed material types. The economical, process and environmental benefits of its application are highlighted for both the smelting and converting stages of copper production.

Jan 1, 1997

The entrainment of copper matte in the slag during the slag skimming stage of a Peirce-Smith converter was studied with a dam break model. Experiments were carried out with a range of fluid pairs where the lighter fluid was allowed to overflow a weir and the amount of entrained heavier fluid measured. The resulting entrainment is measured as the ratio of the heavy to light fluid withdrawn. The fluids include oil-water, water- glycerol and salt solutions-water pairs to cover a wide range of densities and viscosities. It was found that the Richardson number, Ri, correlates the entrainment well. For the case of the liquid-liquid interface initially at the same height as the weir, the entrainment was found to vary with Ri-1/3. The transient flow was simulated with a volume of fluid (VOF) code written in-house and used a stairstep approach to represent flow obstacles. The code was validated against the experimental results with good agreement for the variation of the heights of the two fluid with time. The simulation showed that the prevailing mechanism for entrainment is due to a pressure differential created across the liquid in the converter during pouring resulting in the heavier liquid being rotated upwards and over the weir.

Jan 1, 1999

By Carlos Maurício Fontes Vieira, Sergio Neves Monteiro

"A ceramic body traditionally used to produce bricks and roofing tiles with kaolinitic clays was reformulated by the addition of sand and illitic clay. The objective was to obtain a ceramic product with better technological properties. Specimens were made by uniaxial press-molding at 20 MPa and then fired at 850, 900 and 950°C. The determined technological properties were: linear shrinkage, water absorption and flexural rupture strength. The results showed that both sand and illitic clay contribute to reduce the water absorption of the industrial clayey body. With respect to the flexural behavior, it was observed that the incorporation of sand decreased the mechanical strength. On the other hand, the illitic, incorporated in an amounts of 30 wt.% contributed to increase the mechanical strength of the clayey ceramic.IntroductionCeramic bodies industrially fabricated in the county of Campos, north of the State of Rio de Janeiro, in Brazil, are still empirically elaborated using a mixture of local clays. These clays are predominantly kaolinitic mineral in nature, associated with high plasticity and elevated weight loss during the firing stage. Due to the excessive plasticity of the ceramic bodies, dimensional defects, which occur after drying and firing are usually obtained. Moreover, the kaolinitic nature and the presence of aluminum hydroxide (gibbsite) confer a refractory behavior to the local clays, which impairs sintering during the firing operation. In the case of clay ceramic products for civil construction, this results in greater porosity associated with elevated values of water absorption and low mechanical strength [1,2]. To avoid these problems, it is necessary to reformulate the ceramic body composition. The addition of both non-plastic materials to reduce plasticity and fluxes to condition the refractoriness is a possible alternative.As an alternative to reduce the plasticity of clayey ceramics sand, which is predominantly constituted of silica, can be used. The incorporation of sand in amounts of up to 25 wt.% to a clayey ceramic body used for roofing tiles fabrication was studied by Vieira et al. [3]. In that work specimens were prepared by extrusion and fired at 850°C. The results indicated that in the pre-firing stages the sand improved the workability of the investigated clayey ceramic body and facilitates the drying stage. It was also observed that the incorporated sand significantly improved the physical and mechanical properties of the clayey ceramic after firing. On the other hand, the apport of flux oxides could be done by the use of illitic clays that have a higher amount of alkaline oxides in comparison with the kaolinitics clays."

Jan 1, 2013

By R. W. Hammack

Results for the treatment of a problematic mining wastewater using bacterial sulfate reduction (BSR) are presented. Specifically, a BSR pilot treatment plant (250 L per day) was used to treat Berkeley Pit simulant to discharge standards with the selective recovery of separate Cu- and Zn-sulfide concentrates. Concentrates recovered in these tests contained greater than 50 % of the target metal and met specifications for sale to existing smelters. The biological component of the treatment was found to be surprisingly robust. Scaling and solid/liquid separation problems were encountered but considered normal for sulfide treatment. For Berkeley Pit water, capital costs for BSR treatment was found to be comparable to high-density sludge lime treatment. The value received from the sale of recovered copper ands zinc concentrates paid for all the operating costs.

Jan 1, 1999

By Di Yang

The influence of high density (104 -105 A/cm2) electric current pulses (70 us duration) and continuous DC (~103 A/cm2) on the flow stress and ductility in tension of a high carbon steel wire were determined at 204°, 427° and 649°C. Electropulsing (100 pulses per second) with an effective current density of 100-200 A/cm2 gave a 10% enhancement in the uniform elongation of the wire at 204°C, but had no effect at 427°C and 649°C. In contrast, continuous DC either had no significant effect on the ductility or gave a decrease. The electropulsing per se decreased the flow stress only slightly at 204° and 427°C, but gave a significant decrease at 649°C. Continuous DC increased the flow stress at all three temperatures. The present results along with those by others suggest that the enhanced ductility by electropulsing and the reduction in flow stress may be further increased by raising the effective current density through increases in either the pulsing frequency, maximum current density of each pulse or pulse duration. This could conceivably increase the reduction per pass during wire drawing or the number of passes between anneals.

Jan 1, 2001

By G Hope, C Young, R. N. Gow

"The presence of enargite (Cu3AsS4) is problematic in gold processing as it is refractory, increasing cyanide and oxygen consumption, and enviromnentally hazardous. Selective leaching and treatment of the arsenic would prove advantageous to conventional gold leaching methods. The reactivity of enargite samples from Montana, US and Quiruvilca, Peru were studied under alkaline conditions, pH range of 8-13, using a cyclic voltammetry corrosion cell setup. Raman spectra of the surface were taken during and after cycling to compare surface species against theoretical predominance diagrams. Under slightly oxidizing conditions, covellite (CuS) peaks were found on the surface in a short matter of time, above - 200m V vs SHE for pH 9-13, suggesting arsenic leaching, but for longer conditioning times, elemental sulfur peaks were also found, which created a passivating surface layer. By operating above pH 12, under reducing conditions, ~-500mV vs SHE, arsenic can be leached as a thioarsenate (AsS4-xOx3-), without sulfur formation.IntroductionEnviromnental limitations on pyrometallurgical processing of arsenic has pushed the desire to process enargite-, Cu3AsS4, bearing concentrates towards a hydrometallurgical solution. Attempts to process can be broken down into two categories - the co-dissolution of arsenic and copper under acidic conditions or the selective leaching of arsenic under basic conditions. The selective leaching of arsenic would preferably leave behind a chalcocite, Cu2S, or covellite, CuS, phase that would be more amenable to conventional processing methods of the copper and gold industries. These methods employ bi- or poly-sulfides to leach arsenic as Assl· [1-4], hypochlorite leaching [5-7], ammoniacal leaching [8] or fine grinding to mechanically activate the enargite surface and increase normally slow reaction kinetics[9]. This study looked into the surface formations of an enargite electrode under alkaline conditions, in a pH range from 8-13, as it cycled from -1000 mV to 1000 mV vs SHE. The understanding of the formations and under what conditions they form will be helpful in further development of any of the aforementioned processes."

Jan 1, 2012

By Steve Johnston, Mowafak Al-Jassim, Fei Yan, Omar Sidelkheir, Alain Blosse, Katherine Zaunbrecher

"Imaging techniques are applied to multi-crystalline silicon wafers and solar cells throughout the production process. Photoluminescence imaging, both band-to-band and defect-band, is used to characterize defects and wafer quality at all process steps. These steps include bricks sawn from ingots, wafer sawing, cleaning and texturing, emitter diffusion, edge isolation and glass removal, anti-reflective coating/passivation, and metallization of finished cells. Bricks, wafers, and cells can be imaged at a rate commensurate with in-line measurement, giving spatial information to characterize quality and defect content. Photoluminescence images on silicon bricks can be correlated to lifetime measured by photoconductive decay and could be used for high-resolution characterization of material before wafers are cut. The defect areas in as-cut wafers are compared to imaging results from electroluminescence and lock-in thermography, and cell parameters of near-neighbor finished cells, showing correlations to efficiency, open-circuit voltage, and short-circuit current.IntroductionImaging techniques can rapidly characterize material quality and defect density. Photoluminescence (PL) imaging can be applied to silicon from the brick level to all wafer process steps [1-8]. At the brick level, material thickness allows for measurement and correlation to lifetime where surface recombination effects are minimized [6, 7]. At the as-cut wafer level where thin unpassivated wafers prevent accurate lifetime assessment due to surfaces, defects can still be categorized and quantified to predict finished cell performance [3-5]. Defect regions can be identified by recombination-limited band-to-band PL or by defect-band emission [9-12]."

Jan 1, 2012

By Jhon Cuya

Titanium dioxide is the well-known catalyst for the photodecomposition of water in UV region and its nanoparticles show better performance than its bulk materials. Furthermore, partially sulfurized TiO2 is expected to be chemically stable and have an enhanced photocatalytic activity compared with TiO2. For this purpose, the sulfurization behavior of TiO2 nanoparticles was thermogravimetically (TG) studied by a thermo-balance with a quartz spring using CS2. From the TG curve of TiO2 nanoparticles, first, the weight decrease appeared down to around 8 wt% and then sulfurization reaction started at around 500 °C at heating rate of 1O 'Cumin. The weight increase curve showed a maximum of ca 30 wt% at around 750 T and then gradually decreased to ca 12w% at 1000OC. This would be caused by the formation of TiS2 followed by the decomposition of TiS2 to lower sulfides, such as Til.08S2 and Ti3S4. From the comparison of the sulfurization of TiO2 nanpparticles with that of anatase, rutile and Ti(OH)4, it was found that TiO2 nanoparticles showed a similar behavior to that of Ti(OH)4.

Jan 1, 2003

By Juan B. Cabezas

"The favorable characteristics and workability of plastics as a replacement of wood, lead, stainless steel, asphalt and other materials are described. Various types of plastic have proven to be the most favorable choice for handling a variety of acidic, alkaline and organic solutions, as well as pulps, chemical wastes, slurries or tailings for impoundments. The material origin of various plastics, methods of manufacturing and specifications applied to leaching solutions are discussed, including availability and costs. Examples of select plastics are considered for use as alternatives of other materials under severe environmental requirements.IntroductionHydrometallurgical processes applied to gold recovery, as well as other metals, require the use of strong solutions of alkaline, acidic or organic nature, and may also include a variety of materials with extraneous characteristics and complications for handling in storage.The technology of leaching has been in use for more than 100 years, but the applications of leaching processes in metallurgy have become more commonly used in the last 15 years. Suitable materials for the construction of containers, launders, piping, and various accessories, to be used in the handling of leach solutions or slurries, have become a serious problem. Various metals such as brass, lead, stainless steel, etc., and non metallics including wood, clays, glass, rubber, ooncrete, tars or miscellaneous compounds have been tried in the past with serious limitations in workability and resistance to wear and corrosion. For example, the use of metallic, wooden or glass piping systems would require extraordinary shop maintenance to keep such systems in operation"

Jan 1, 1997