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By Laurentiu Nastac

"An advanced casting simulation-based optimization approach was applied in this study to assist in the improvement of the mold design of aerospace components made of A3 56 alloy. By using this approach, mold filling and solidification related defects (including macro-shrinkage and shrinkage porosity) were significantly minimized and hence it helped in cost reduction, performance enhancement and quality assurance of complex A3 56 cast parts.An experimental validation and detailed calibration procedures of the models for prediction of macro-shrinkage and shrinkage porosities were performed using A3 5 6 plates cast in fiiran-silica sand molds using the Prometal's Rapid Casting Technology (RCT) - mold printing technology. Correlations between Niyama values and the pore percentage were also developed. Thus, the severity level of shrinkage porosity can be determined via the Niyama criterion. Predictions were then compared with the macro-shrinkage and porosity measurements in plates of various plate thicknesses and in other commercial A3 56 casting components.IntroductionThis paper describes the process modeling approach used in the development of the mold design technology used to produce assist in the improvement of the mold design of aerospace components made of A356 alloy. Nova Flow&Solid™ software [3] was applied in this study. This casting simulation software was previously validated for several alloys including Ti, steel and superalloys [1-4]. The objective of this paper is to calibrate and validate the simulation software for A356 alloy sand mold castings. For this purpose, an experimental validation and detailed calibration procedures of the models for prediction of macro-shrinkage and microshrinkage (e.g., shrinkage porosities) were performed using A356 plates cast in fiiran-silica sand molds using the Prometal Rapid Casting Technology (RCT) mold printing technology. The details of the RCT technology are shown in Fig. 1 [5]. Prometal's RCT technology is used for rapid production of sand molds and cores directly from CAD files. The RCT technology relies upon ink jet printer technology to selectively bind the grains of sand to create three-dimensional sand molds and cores. Mold filling and solidification modeling as well as stress analysis are typically performed to properly design the casting and the rig system of each prototype component."

Jan 1, 2012

By Juan H. Rojas C.

The Chuquicamata mining and metallurgical complex is the main Division belonging to Corporation Nacional del Cobre de Chile (CODELCO-CHILE) and it accounts for 50% of the 1.4 Mt of fine copper output of the Corporation. It has been producing copper since 1915. The paper refers to the challenges that Chuquicamata has to solve in the near future. These challenges are: the increasing operation costs associated to a 800 m depth pit with low prices in an overstocked copper market; the increasing people's sensitivity to environmental preservation; and, the transformation needed for achieving high levels of organizational effectiveness. According to Corporate policy, Chuquicamata is making efforts to switch from a management style focused on supply to a management style focused on demand side of the industry. In this direction is tempting to establish strategic alliances to develop both new copper products and uses, to rise the metal demand. In more than 80 years of operation, Chuquicamata had exploited just one third of its geological resources. The exploitation of the remaining two third is a huge engineering challenge, taking into account the depth of the deposit, the impurities content, the decreasing ore grades and the transportation distances for waste dumping. All those factors are relevant in the economical process of transforming geological resources into ore reserves. Chuquicamata has other limitations. First, a 20,000 people town just aside the pit that limits the mining rates because of dust generation; second the scarceness of water in the desert area where Chuquicamata deposit is located; and, finally, the new tailing pond is a problem which solution will demand huge engineering efforts and investments. People are the principal factor associated to a company success. In this field, Chuquicamata have been progressing, but much more efforts from people will be necessary to reduce production costs for being successful as any other price-taker within the copper industry. Chuquicamata must develop the skills of its Supervisors to transform them into leaders and entrepreneurs, who additionally have the challenge of passing on their knowledge to non-professional workers. It is an ethic commitment to assure personal and professional growth of workers, as the only sustainable way to get real and integral success.

Jan 1, 1999

By Florian Aurelian, Mihai Popescu

"It will be tested four types of “geochemical barriers”. All those mixtures were contacted with mine waters containing uranium, radium and heavy metals. The loading capacity was determined. The optimum mixture was determined and its efficiency was tested within an uranium areal, where the activity was stopped. It was determined the possibility to recover the radioactive elements and the heavy metals from the investigated barriers.IntroductionThe paper presents the results concerning the performances of some “geochemical barriers” used for the decontamination of mine waters from uranium mining sites, which were tested in lab and in situ.ExperimentalThe research activity was carried out in lab and on the site.In the lab a module was constructed in order to follow up the uptake capacity of the “permeable reactive geochemical barriers” used to remove the radiolelements from the contaminated waters originated from the uranium mining industry. The barriers, which were used, are made of cheap natural materials, which can be easily got (wood chips, peat coal, sawdust, iron span, steel and zeolitic tuff). The following types of barriers were tested:•, 1st barrier: peat coal, sawdust, zeolite on weight ratio of 1/1/1;•, 2nd barrier: bentonite, sand, wood chips, peat coal on weight ratio of 1/1/1/1;•, 3rd barrier: iron span, steel, sawdust, peat coal on weight ratio of 2/1/1;•, 4th barrier: iron span, steel, sand, firry wood chips on weight ratio of 1/1/1.Lab researches concerning the uranium uptake capacity of the above described “reactive barriers” pointed out that the 3rd mixture (iron span, steel, sawdust, peat coal on a ratio of 2/1/1) didn’t reach the maximum uranium uptake capacity not even after eleven contact stages (the uptake capacity being of 70.6 mg U/ kg of mixture) and the mixture of peat coal, sawdust and zeolite has an uranium uptake capacity of 26.6 mg U/kg of mixture and becomes saturated after four contact stages.Each one of the components involved in physical-chemical processes of sorption, reduction and precipitation, will determine the diminution of uranium and other metals contents upstream the permeable reactive barrier."

Jan 1, 2008

By Wankun Wang, Shixing Wang, Jinhui Peng, Zebiao Zhang

"Germanium leaching from germanium dust and fume was carried out using sulphuric acid. Response surface methodology (RSM), based on a five level, four variable central composite design (CCD), was employed to obtain the best possible combination of liquid/solid ratio (Xi: 2-10), leaching time (X2: 1-5 h), sulphuric acid concentration (X3:3.15-15.75mol/L) and leaching temperature (X4:50-90 *C) for germanium leaching. The obtained experimental data were fit to a one-order polynomial equation using multiple regression analysis and also analyzed by analysis of variance (ANOVA). The 3-D response surface plot and the contour plot derived from the mathematical models were applied to determine the optimal conditions. The optimum extraction conditions were: liquid/solid ratio of 10, leaching time of 1 h, sulphuric acid concentration of 15.75 mol/L, and leaching temperature of 87.8 'C. Under these conditions, the germanium leaching extent was 65.14%, which is in close agreement with the value predicted by the model. The samples were characterized before and after leaching using X-ray diffraction (XRD).IntroductionResponse surface methodology (RSM) is one of the relevant multivariate techniques which can deal with multivariant experimental design strategy, statistical modeling and process optimization [1-15]. It is used to examine the relationship between one or more response variables and a set of quantitative experimental variables or factors. This method is often employed after the vital controllable factors are identified. It is also used to find the factor settings that optimize the response. Designs of this type are usually chosen when a curvature in the response surface is suspected [6], The process optimization of the sulphuric acid leaching of germanium from germanium dust and fume has not been reported in the literature. Hence the present work intends to assess the effects of variables such as liquid/solid ratio, leaching time, sulphuric acid concentration and leaching temperature and to identify the optimum conditions using RSM. The characteristics of sample before and after leaching are assessed using the advanced analytical instruments such as X-ray diffraction (XRD)."

Jan 1, 2012

By Bo Jiang, Lianyun Liu, Hongmin Zhu, Kai Huang

"Watermelon peel is selected as a novel adsorbent to remove Pb(II) from aqueous solution. A simple saponification process is proposed to modify the peel and the adsorbent is characterized by SEM and FTIR. The effects of pH, contact time, initial concentration of Pb(ll), biosorbent dosage and temperature on adsorption of Pb(II) are investigated. Different models are used to fit experimental data. These models indicate that the adsorption process follows the Langmuir model and pseudo-second-order model. The maximum adsorption capacity obtained from Langmuir model is 1.05mol kg-1 for the prepared sorbent. Equilibrium time is attained in 5-10 min for the studied concentrations. The watermelon peel can be used as an effective and low-cost biosorbent for removal of Pb(ll) from aqueous solution.IntroductionRecently, removal of heavy metal ions from industrial effluents by biosorption has become a very attractive topic, since the more serious pollution issues caused by heavy metals emerge frequently, and more strict requirements for its control are called upon by society [1,2]. In this case, most conventional purification technologies are not suitable due to poor cost-effectiveness [3]. For example, chemical precipitation by alkaline reagents usually can not decrease the metal ion concentration below the permissive levels, and also it will produce a large amount of sludge containing toxic metals. Membrane separation techniques can realize deep purification of wastewater easily, although its operating cost is usually high. Thus, considering the high effectiveness, low cost and free-sludge operation, bisorption has become a promising technique in water treatment [4]. The most important thing for this technology is the synthesis of a suitable biosorbent, whose adsorption properties will determine the removal efficiency and economic cost for the whole process. Watermelon is one of the most popular fruits for mankind for its delicious flavor. Usually, the watermelon is consumed mainly for its edible pulp, and its peel is discarded or only used as feed for livestock. Considering the pectin contained in the watermelon peel, just like that in orange wastes in the reported literatures [3], the idea of using it as the raw material to prepare the biosorbents for heavy metal ions removal from the aqueous solution was evaluated in this study."

Jan 1, 2012

By Elsa Olivetti, Randolph Kirchain, Gabrielle Gaustad

"As scrap usage increases, it is often necessary to “dilute” the melt with primary aluminum to ensure the finished product meets compositional specifications. Secondary raw materials, particularly postconsumer scraps, often include high levels of unwanted or “tramp” elements, such as iron and silicon in the case of aluminum. Recent literature on this issue cites several causes including inherent contamination during processing as well as ineffective segmentation at end-of-life. To address this accumulation problem, “upgrading” solutions have been developed including: dismantling of end-of-life products, spectrographic or magnetic sorting of shredded scrap, and “filtration” technologies that remove tramp elements in the melt. Although it is clear that upgrading strategies enable increased usage of scrap, it is not clear that they would be economic or efficient. This work presents a set of analytical methods, based on chance constrained optimization, to quantify the potential environmental and economic value of several scrap upgrading technologies.IntroductionAluminum recycling has a number of key environmental and economic benefits. Compared to other materials, aluminum production has one of the largest energy differences between primary and secondary production: 175 MJ/kg for primary compared to 10-20 MJ/kg for secondary[1]. With energy and cost savings in mind, many producers now have targets of increasing their usage of secondary materials[2, 3]. However, the accumulation of impurities in these recycled material streams provides a significant compositional barrier to these goals[4].A growing number of studies and literature would suggest that accumulation of unwanted elements is a growing problem, in all recycled material streams. In the case of aluminum, the list of problematic impurities is quite large, including but not limited to: Si[5, 6], Mg, Ni, Zn, Pb, Cr[7], Fe[5-7], Cu[6, 7], V, and Mn[6]. Metals recycling is a metallurgical process and is therefore governed by the laws of thermodynamics. The removal of unwanted elements in the scrap stream is dictated by the energy considerations of the melt process. Compared to many metals, aluminum has a high degree of difficulty in the removal of tramp elements, due to thermodynamic barriers. Therefore, with no simple thermodynamic solution, producers must identify strategies through-out the production process to mitigate this elemental accumulation."

Jan 1, 2008

By Antonio de Lucas, Juan Francisco Rodríguez, Ignacio Gracia, Mª Teresa García

"The amount of waste of Polystyrene (PS) foams is increasing in last years due to their use in insulation, protecting and, storing many different food products. Conventional methods of recycling such as crushing and shrinking by heated air or frictional heat have the disadvantages of molecular degradation, resulting in a reduction of the quality of the recycled polymer. Dissolution and shrinking with suitable solvents is one of the cheapest and more efficient ways of polystyrene recycling but in the process of the solvent recovery by distillation a certain degree of molecular degradation is produced. In this way, CO2 supercritical technology appears as an interesting alternative for the elimination of solvent. This work proposes a global process to polystyrene recycling in two steps: a polystyrene dissolution with a suitable “green” solvent followed by its elimination by supercritical tecnologhy. In order to develop a “green process” the constituents of essential oils, limonene, terpinene, cymene, and phellandrene, are selected as the most appropriated solvents. Introduction In the last years, disposal of the non-biodegradable plastic wastes has been recognized as a serious environmental problem. Recycling these wastes has great interest in order to prevent the environmental pollution and to preserve natural sources (1, 2, 3). Since the Polystyrene foams (PS) is one of the most used foam in isolation, protecting and food storage most of recycling work is concerned with this polyolefin (4). The two main alternatives for treating polymer wastes are energy recycling, where wastes are incinerated, and mechanical recycling (5). Environmental argumentations such as toxic emissions are building up a public resistance against incineration process (6). Mechanical recycling is a popular recovery path for manufacturers and is carried out on single-polymer waste streams. Any way, the market for recycled products can only be found if the quality is close to that of the original. Unfortunately the process of classification and further recovery of these wastes makes them often more expensive than virgin plastic (7, 8). Solvent extraction is one of the cheapest and more efficient ways for PS recycling. If it is done in house of waste producers the separation between plastics could be easy and effective and the transport costs would be eliminated."

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 Anurag Tripathi, J. K. Saha, S. K. Ajmani, J. B. Singh

"The quality of steel is a major concern in the metallurgical industry. The control of liquid steel temperature can enhance the level of cleanliness in steel. Ladle is one of the major vessels used to transfer liquid steel between different stations. The heat transfer phenomenon taking place in this vessel needs to be monitored for controlling the liquid steel temperature. A CFD model was developed for prediction of liquid steel temperature during complete process cycle of ladles in direct heats. The model was validated with liquid steel temperature measured at on-line purging station and tundish during teeming from one of the actual steel plant. The accuracy of model was 96 %. The results obtained show insignificant effect of slag thickness, tapping temperature and ladle life on liquid steel temperature in the ladle. However, the importance of initial refractory temperature was noticed. The CFD model developed in present work can generate the thermal history of liquid steel and refractory walls of any ladle at any stage.1. IntroductionThe control of liquid steel temperature is desired to achieve required steel quality. The low casting temperature is detrimental and may result in nozzle blockages due to premature solidification in the tundish. The phenomenon of heat losses taking place in ladles needs to be understood for prediction of liquid steel temperature. The assessment of thermal profile of liquid steel from BOF converter to caster can be done through consideration of heat losses at all points. Hlinka and Miller [1] showed that the ladle pouring temperature varies due to heat losses from molten steel into surrounding refractory layers. The phenomenon of thermal stratification was numerically simulated by Ilegbusi and Szekeley [2]. The effects of slag cover on heat loss and liquid steel flow in ladle before and during teeming to a continuous casting tundish was numerically simulated by Chakraborty and Sahai [3]. Investigators also developed some simple models to predict the steel temperature for some of the processes taking place in ladles [4-9].The present work is an effort to generate the full information about the temperature drop taking place in any ladle throughout its process cycle. This information can be used to predict liquid steel temperature and to take decisions to minimize heat losses."

Jan 1, 2012

By Djalma Souza, Rubén Sánchez, Regina Maria Pinheiro, Carlos Maurício Fontes Vieira, Sergio Neves Monteiro

"This work has for objectives to characterize a waste generated in the form of sludge during the treatment of the effluent of a paper making industry and to evaluate the effect of its incorporation up to 10 wt.% on the properties of a clayey body used for brick production. For the characterization of the waste the following techniques were used: X-ray diffraction, X-ray fluorescence, differential thermal analysis and termogravimetric analysis with mass spectrometry. Specimens were prepared by uniaxial pressing at 20 MPa before firing at 750 °C. The physical and mechanical properties evaluated were: linear shrinkage, water absorption and flexural rupture strength. The results showed that, in agreement with the characteristics of the waste, its recycling into red ceramic can contribute to decrease the consumption of fuel during the firing stage. However, the waste changes the physical and mechanical properties, generating a deleterious effect on the water absorption and flexural rupture strength of the ceramic.IntroductionAccording to the Brazilian Association of Pulp and Paper, in the last 10 years, the global production of paper grew 35%. Brazil produced 8,2 million tons of paper in 2004 and held the position of the seventh largest world manufacturer of pulp, with about 9,4 million tons per year [1]. The pulp and paper industry generates effluents that present problems related to their disposal, even after the treatment. Among the solid wastes generated by this industry, the main waste is the primary sludge from the effluent treatment plant (ETP).After the initial treatment the decanted solids go through a dewatering stage, generating the solid form denominated primary sludge. This sludge resembles a paper paste of dark gray color when humid, and clear gray color when dry. This primary waste is composed basically of kaolin, pulp, traces of chemical substances and water. This waste generated in the pulp and paper industry depends on the characteristics of the process and of the employed techniques. It can vary significantly from one industrial unit to another, even in the case that the final products are similar. Its composition is approximately 60% of kaolin and 40% of pulp, and these percentages can vary in some moments as a function of the process [2,3]."

Jan 1, 2008

By Dmitri Goljandin, Jaan Kers, Xiangjun Zuo, Lifeng Zhang, Priidu Peetsalu

"In this paper, the mechanical milling of the electronic wastes was carried out. The metal parts and plastic parts were roughly separated. The final plastic powder size could be as small as ~100 µm. Then the pyrometallurgical recycling Printed Circuit Boards (PCB) was executed. The mechanisms of thermal degradation and combustion are investigated using TG/DTA and MS. Some chemical powders, such as Na2CO3, NaHCO3, NaOH and CaCO3 are used to control the exhausted toxic gas such as Br2. Introduction Waste electric and electronic equipment (WEEE), or electronic wastes (E-wastes), has been taken into consideration not only by the government but also by the public due to their hazardous material components [1-3]. From the point of material composition, electronic wastes can be defined as a mixture of various metals, particularly copper, aluminum, and steel, attached to, covered with, or mixed with various types of plastics and ceramics [4]. Precious metals have a wide application in the manufacture of electronic appliances, serving as contact materials due to their high chemical stability and their good conducting properties. Platinum group metals are used among other things in switching contacts (relays, switches) or as sensors to ascertain the electrical measurand as a function of the temperature [5]. Table 1 [6] gives examples of the metal composition of different electronic scraps from literatures. Additionally, non-ferrous metals and precious metals content have gradually decreased in concentration in scraps. The value distributions for different electronic scrap samples are shown in Table 2 [6], where the metal price data are from London Metal Exchange (LME) (Octoebr 2007). It can be seen that for cell phones, calculators, and printed circuit board scraps, the precious metals make up more than 70% of the value, for TV boards and the DVD player they still contribute to about 40%. This indicates that the major economic driver for recycling of electronic waste in industry is from the recovery of precious metals. Behind the precious metals come copper and zinc, while Al, Pb, and Fe are less value. Recycling of electronic waste is an important subject not only from the point of waste treatment but also from the recovery aspect of valuable materials."

Jan 1, 2008

By Shuo Wang, Yu Wang, Bing Xie, Rui Tang, Hong-Yi Li, Kun Wen

"During present converter vanadium extraction process, phosphorus could not be removed from hot metal due to absence of CaO in slag though it is an efficient way for vanadium extraction. In order to improve the phosphorus remove and produce CaO-containing vanadium slag, which could be directly used in subsequent roasting process, during the converter vanadium extraction process, lime dissolution in FeOx-Si02-V203-Ti02 slag was investigated by using a rotating cylinder technique and the slag-lime interface was characterized by SEM/EDS. Results showed that changes in the slag chemistry and phase compositions during the lime dissolution process were similar to that in CaO-Si02-FeOx based slag during the BOF process. The V and Ti in the slag were expected to diffuse into the lattice of2CaO·Si02 solid solution, which formed a rather thinner layer in thickness at the slag-lime interface than that in BOF process, leading to improvement of lime dissolution in the slag.IntroductionVanadium is important material that widely applied in industries. The traditional technique to extract vanadium was to leach vanadium after sodium salt roasting. However, the sodium salt roasting process has several problems including lower yielding rate[!] and environmental pollution[2]. Therefore, the more environment-friendly technique of calcium roasting[3-4] was proposed. In order to increase roasting efficiency of vanadium slag, it is essential to study the dissolution/reaction mechanism between lime and vanadium slag. Many investigations about the dissolution reaction of lime in molten slag have been carried out from the standpoints of rapid slagging to De-Pin steelmaking process[5-6]. However, their studies were focused on BOF slag and the reaction mechanism between solid lime and slag containing vanadium has not been reported yet. In present work, the dissolution process was studied with rotating cylinder technique and the reaction interfaces were observed and analyzed by SEM/EDS to elucidate the dissolution mechanism of lime in vanadium slag. This work was supported by National Natural Science Foundation of China No. 51090382."

Jan 1, 2013

By Chris T. Vild

"ABSTRACT NOT AVAILABLEPRESENTATION SUMMARYIntroductionToday, light gauge aluminum scrap is melted in sidewell furnaces using natural gas reverberatory burners. The scrap is introduced into the sidewell adjacent to the combustion chamber through a submerged archway. Super-heated metal is then pumped into the sidewell where it aids in melting the scrap. From the sidewell, the flow is returned to the combustion chamber through a second submerged archway at some lower temperature. Normally, the burners are set at a designed high fire level and the scrap is introduced at a rate to attempt to mat.ch the burner input. A thermocouple in the bath is programmed to throttle back the burners to low fire if a high temperature limit is exceeded.Jn many cases the thermal efficiencies of these furnaces can be very low. With inadequate circulation, air and natural gas furnaces run at a dismal 18% thermal efficiency. If a circulation system· is added, the efficiency can jump to 28%. For a $100 million lb/yr recycling facility, and natural gas prices reaching $4.50 per million Btu, fuel cost at 18% efficiency can reach $1 million per year. A 10% increase in thermal efficiency saves $350,000 a year in fuel costs.With an increase in thermal efficiency, furnace utilization also increases. A 10% increase in thermal efficiency would result in a 20 million Btu furnace producing 12,000 lb/hr up from 8,000 lb/hr or 35 million lb more produced per year. This is a 33% increase in output.Most current furnace development has focused on burner technology using oxy-fuel, regenerative burners, etc. However, thermal efficiency is also largely effected by the molten metal circulation rate and how well the scrap is mixed into the superheated metal. Therefore, the flow dynamics should be optimized first, before installing of more thermal power.Jn an effort to understand the effect of these variables, a series of computer models were made and the critical factors studied with the goal of demonstrating an increase in thermal efficiency and production. Large-scale graphical representations of these models will be presented."

Jan 1, 2000

By Laurence G. Dyer, David G. Dixon, John Rumball, Maziar Eghbalnia, Edouard Asselin

"Linear scan voltarnmetry was used to determine the reactions that occur during the cyanidation of petzite (Ag3AuTe2). Gold oxidation in petzite requires more oxidising conditions than are required for pure gold, it also does not achieve the same current (related to reaction rate). Tellurium oxidation occurs at a similar potential in water and cyanide, but as a component of petzite is impeded somewhat in water, likely due to the stability of the precious metals. Pre-treatment of petzite to oxidise tellurium in the absence of cyanide prior to gold recovery appears to be at least moderately successful.IntroductionWhile gold occurs most prevalently in its native form, many other gold bearing phases appear throughout natural systems [I]. Tellurides are a common group of such minerals, many of which also contain silver, often existing in association with native gold deposits. The six major gold-bearing tellurides are calaverite (AuTe2), sylvanite [(Au, Ag)2Te4], montbrayite [(AuSb)zTe3], krennerite [(Au1-x, Ag,)Te2], petzite (Ag3AuTe2) and muthmannite (AuAgTe2) [2]. While several other phases exist they are much more complex (i .e. buckhornite), which dilutes and confuses the influence of each specific component. Studies of gold tellurides have predominantly focussed on calaverite as it is the simplest and most common phase, however petzite, commonly found in Australia and North America, is the focus of this investigation.Gold processing via cyanidation has been operated for more than a century and is a highly effective hydrometallurgical treatment of native gold deposits. However, some gold alloys such as tellurides have proven to be somewhat less responsive under the same conditions. Several groups have shown that gold/silver tellurides are amenable to cyanidation, but are significantly more refractory than native gold [3]. Pre-oxidation steps have been tested to remove constituents that would consume cyanide such as sulfides. Such species are also linked to the precipitation of oxidised telluriwn, forming a passive layer, further inhibiting gold recovery [2]. It is uncertain to the definite reasons underpinning the refractory nature of precious metal tellurides in conventional cyanidation."

Jan 1, 2012

By Jean Igor Margem, Lucas Barbosa de Souza Martins, Frederico Muylaert Margem, Noan Tonini SImonassi, Sérgio Neves Monteiro, Rômulo Leite Loiola

"Fibers of giant bamboo (Dendrocalmus Giganteus) are amongst the strongest lignocellulosic fibers. Although studies have been already performed, limited information exists on the mechanical properties of polymeric composites reinforced with continuous and aligned giant bamboo fibers. This work evaluates the tensile strength of this type of composite. Standard tensile specimens were fabricated with up to 30% of fibers aligned along the specimen's length. The fibers were press molded with a commercial epoxy resin mixed with a hardener and cured for 24 hours at room temperature. The specimens were tested in an Instron machine and the fracture surface analyzed by scanning electron microscopy. The tensile strength increased significantly with the amount of giant bamboo fiber reinforcing the composite. This performance can be associated with the difficult of rupture imposed by the fibers as well as with the type of cracks resulting from the bamboo fiber/epoxy matrix interaction, which prevents rupture to occur.IntroductionDue to growing concern about the ambient impacts from industrial activities, our society is ever more using environmentally friendly materials. In this regard, cellulose-based natural fibers, known as lignocellulosic fibers, become a promising solution. Nowadays, they are being considered as a substitute for synthetic fibers, such as glass fiber, used by the industry on a large scale [1-5]. The application of these natural fibers is also motivated by many advantages like good toughness and less wear of equipment used in the processing of composites. In addition, such composites are environmentally friendly because they are renewable, biodegradable and neutral with respect to C02 emissions, the main responsible for global warming and climate changes. [3,5,6].Lignocellulosic fibers also have some disadvantages in relation to synthetic fibers such as the difficulty of coupling with polymer matrices, due to the hydrophilic character of fiber and the hydrophobic nature of the matrix, as well as dimensional heterogeneity [ 4,5]. This last one is characteristic of the nature of this material and constitutes an obstacle to the use of these fibers in certain projects, especially those that aim high performance. The above mentioned disadvantages are worrisome reasons for the occurrence of reduction in the strengthening capacity, as indicated by the rule of mixtures for composites [7]."

Jan 1, 2013

By J. P. Downey, L. G. Twidwell

"The high density sludge process (HDS) is a commercially proven acid rock drainage wastewater treatment process that is based on acid neutralization and metal precipitation. Previous studies have established that metal removal efficiencies in precipitation-based wastewater treatment applications can be improved through metal ion adsorption on ferrihydrite and/or aluminummodified ferrihydrite. This study was conducted specifically to determine whether the metals removal efficiencies at an existing industrial facility could be improved by promoting ferrihydrite and/or aluminum-modified ferrihydrite precipitation during the pH adjustment stages of the HDS process. The metal tenors of the treated wastewater samples are compared with those obtained through baseline experiments, which were designed to simulate the conventional HDS operation. The subject metals were: aluminum, arsenic, cadmium, copper, iron, manganese, nickel, and zinc.IntroductionThe HDS process is commercially proven ARD wastewater treatment technology that involves raising the wastewater pH by adding hydrated lime, caustic soda, or another alkaline substance. In addition to neutralizing the acidity, many dissolved metals precipitate as pH is elevated. Waste volume is minimized by capturing and immobilizing the precipitated solids.However, ARD streams characteristically contain multiple dissolved metal species. The response of various metals to pH adjustment in the HDS process is neither uniform nor quantitative, so minor to trace concentrations typically remain in the treated wastewater following solid-liquid separation. The effectiveness and applicability of the process would be improved if a means were found to further reduce the metal concentrations.Previous research and industrial applications have proven that metal ion adsorption on ferrihydrite (FH) and/or aluminum-modified ferrihydrite (AMF) increase metal removal efficiencies. Ferrihydrite and AMF are considered ideal for cation and anion adsorption from an aqueous solution at the appropriate pH [1]. Ferrihydrate adsorption of dissolved heavy metals is widely practiced throughout the world [2, 3]. It is established that FH and AMF effectively adsorb As contained in aqueous solutions [4]. Arsenic removal by adsorption on FH is the U.S. Environmental Protection Agency’s (EPA) Best Demonstrated Available Technology [5]. Twidwell and Leonhard also demonstrated that heavy metals (Cd, Cu, Ni, and Zn) are effectively removed from solution by coprecipitation/adsorption using AMF and FH [6]."

Jan 1, 2008

By Magdelinka Padenkova-Yaneva, Emilia Christova Kostakeva

"One of the methods for waste treatment is composting during which as a result of controlled biological decomposition of organic waste in aerobic conditions harmless materials are received. Composting takes place in suitably designed premises which ensure the optimal conditions for biochemical decomposition of the waste. A usual way to process composting is the spreading of the waste on a base made from reinforced concrete.In the paper the phases and basic technical features of the process of composting, the requirements and properties of the base and the ways of protection of concrete base against corrosion are revealed. Technical decisions for a specific construction site in Bulgaria are shown and the advantage of achieving durability of the concrete constructions in the plant while achieving simultaneous environment protection from pollution is discussed.IntroductionComposting is the process of controlled biochemical decomposition of vegetable and animal organic waste in aerobic conditions as a result of which harmless materials are obtained. The latter have better stability and are rich in humus substances which are useful for agricultural crops and can be used for restoring the soil fertility [1, 2, 3, 4].In modern waste treatment plants a composting technology is adopted in which the waste is spread on a concrete base as piles with certain dimensions [1, 3]. These piles are periodically stirred or air is blown through them in order to ensure the quantity of oxygen required for the process of aerobic decomposition of the organic matter. The fluids and gases formed in the course of the composting are take away in order not to pollute the environment – air, water, and soils. For this purpose the base on which the waste is spread must satisfy certain requirements, and the gases must be taken away and rendered harmless in order to protect the atmospheric air from pollution. This paper discusses the need for protecting the concrete base from corrosion and characterizes the stages and main parameters of the composting process and the possibilities for primary and secondary protection of the concrete base from corrosion. Specific technical decisions applied in a composting facility in the area of the town of Plovdiv are presented."

Jan 1, 2008

By Alessandra Bonoli, Garfìm Marianna

"Construction and demolition waste (CDW) is no dangerous material resulting from construction, and demolition of houses, large building structures, roads, bridges, piers, and dams. It is possible to recycle these materials, to reduce environmental impacts, and to reuse them in construction sector. To evaluate in a correct way the possibility to reuse this material it is important to lead laboratory tests to assess the proprieties and quality characteristics. European, Italian and British ad hoc Committees had elaborated specific Standards, to evaluate Geometrical, Physical, and Chemical requirements of recycled materials. A research was carried on to define the guidelines for laboratory tests, their suggested values and quality standards. The Construction and Demolition Waste Construction and demolition waste (CDW) is no dangerous, uncontaminated material resulting from construction, renovation, repair, and demolition of houses, large building structures, roads, bridges, piers, and dams. CDW waste is made up of wood, steel, concrete, gypsum, masonry, railway ties, roofing materials, carpeting, insulation, plaster, metal, and asphalt, and all waste included in CER Code 17. In particular Demolition wastes are defined as materials resulting from the demolition, instead Construction wastes are defined as waste materials resulting during construction process or in pre-manufacturing construction industry. Environmental problems In a lot of cases Construction and Demolition Waste materials were discharged in landfills, these are filling up with CDW and others, and some of them will close in the near future. In addition, illegal dumping of CDW debris can result in future health risks, decreased property values, cleanup costs and enviromental problems. The typical environmental impacts generated by CDW dumps are: 1- Dust problem, which causes air pollution, as will as forming dirty areas. 2- Uncontrolled locations, that will encourage the disposal of other waste types with the usual construction wastes leading to an environmental disaster. 3- The degradation and deterioration of the coastal lands and the natural protectorates. 4- The loss of aesthetic features. 5- Occupation of large areas, causing extra hauling costs. Therefore, it is wise to find other alternatives, like reuse or recycling, other than landfilling CDW debris or illegal dumps, because a proper management and the reduction of CDW amount can save money, conserve resources, and preserve the environment."

Jan 1, 2008

By Alberto Oalvez, Lucya Yunus, Pengfii Tan

"Laboratory flotation tests of slow cooled converter slag have showed that 92.5% copper recovery at the copper cut-off grade of 24 - 25 % can be achieved by using a 50:50 ratio of DSP330 and SIBX (sodium isobutyl xanthate) at the natural pH of 7 and with a grinding time of 18.5 minutes. 70ìéç is the P80 achieved at this grinding time. MIBC is the frother and the solid content of the flotation feed was 46%. In the plant trials, two types of collectors at two different feed particle sizes for both the normal and slow cooled slag were operated. The particle size was controlled by the feed rate. The P80 of 75 ìçé at a feed rate between 32 - 36 t/h were tested. The plant trials have demonstrated that the copper recovery in the milling and flotation process of the slow cooled slags was improved by 3%. IntroductionIt is proposed to float the slow cooled converter slag, in the auxiliary circuit of the copper concentrator at Mount Isa, by using the processing conditions identified from several laboratory flotation tests. Among these laboratory tests, one produced a copper recovery of 4 % higher than those achieved from a normal cooled slag with the same slag feed grade and the same copper content (24 - 26 %) in the concentrate. These test conditions were selected for further studies.Laboratory Test Work and Plant TrialsThere has been a lot of work conducted under laboratory and plant conditions [1]. However, the achieved results did not justify their total implementation in the Mount Isa Copper Concentrator. Initially, the lab trials were carried out with slag cooled 100% in air; then it was changed to combined cooling for 12 h with air and 2.5 days with water sprays. The reason for this change was the shortage of space when the slag was cooled 100% in air, as it takes several days to achieve safe temperatures for its removal. The San Manuel Copper Smelter has reported that their slag was left for air cooling in pits for 8 h and then was followed by water cooling for 2-3 days [2]"

Jan 1, 2012

By Rzyman Michal, Nakamura Takashi, Shibata Etsuro, Grabda Mariusz, Oleszek-Kudlak Sylwia

"Tetrabromobisphenol A (TBBPA) and many systems based on the synergistic effect of brominated organic compounds with Sb2O3 are extensively used as effective brominated flame retardants (BFRs) in many materials such as plastics and textiles. Thermal degradation of BFR containing plastics leads to the formation of hydrocarbons and gaseous compounds such as HBr and SbBr3. Our thermodynamic considerations indicate that these gases can act as bromination agents for metallic oxides such as ZnO, Cu2O, CuO, PbO and FeO. Moreover, these metallic oxides have the thermodynamic tendency to brominate easier than does Sb2O3. The aim of this study was to investigate experimentally the reactivity of ZnO with 1) HBr originating from the thermal decomposition of TBBPA and 2) SbBr3, which is formed during thermal degradation of brominated flame retardant plastics. The thermal treatments of the mixture of compounds of interest were investigated by thermogravimetry coupled with mass spectrometry.IntroductionTetrabromobisphenol A (TBBPA) and many systems based on the synergistic effect of brominated organic compounds with Sb2O3 are extensively used as effective brominated flame retardants (BFRs) in materials such as plastics and textiles. For instance, 4.5 million tons of flame retardant plastics containing BFRs are produced in Japan each year. Thus, in thermal treatments such as the incineration and melting of solid wastes, BFR containing plastics are intentionally or unintentionally included in the wastes. Thermal degradation of BFR-containing plastics leads to the formation of hydrocarbons and gaseous compounds such as HBr and SbBr3 [1-5]. Our thermodynamic considerations [6] indicate that heavy metal oxides such as ZnO, Cu2O, CuO, PbO and FeO should easily react with HBr prior to Sb2O3 and also with SbBr3, the main gaseous product in the thermal decomposition of TBBPA, forming low boiling point metallic bromides suitable for the volatile separation of heavy metals. The metal oxides are also expected to qualitatively and quantitatively affect debromination and decomposition of the flame retardant."

Jan 1, 2008