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By Riyad N. Ahmad-Bita, Shadia J. Ikhmayies

"SnO2:F/CdS:In structures were prepared by the spray pyrolysis technique on glass substrates at a substrate temperature Ts = 450°C. NH4F and HF were both tried as the sources of fluorine in the precursor solution of SnO2:F. A comparison between the properties of structures obtained by using the two doping compounds was performed. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmittance measurements were used to characterize the films. The structures prepared by using HF as a fluorine source were found to have more ordered crystal growth, larger grain size and sharper absorption edge. From the inspection of the first derivative of the absorbance it is expected that more interdiffusion on the SnO2:F/CdS:In interface takes place in the structures made by using HF. These results confirm that these films are better as forecontacts for CdS/CdTe solar cells.IntroductionThin film CdS/CdTe solar cells built in the superstrate geometry rely on transparent conducting oxides (TCOs) to make the front contact The investigation of combined CdS-TCO films has recently been developed owing to the great interest of better understanding the effect of these bilayers on the absorbers [1]. Usually SnO2 is utilized as a front contact for these solar cells. Optimizing the properties of the SnO2/CdS structures is an important step on the way to get high performance CdS/CdTe solar cells.There are different methods to prepare SnOz thin films, such as reactive sputtering [2], evaporation [3], chemical vapour deposition [3, 4], dip coating [5] and spray pyrolysis [6-9]. At the same time CdS thin films can be prepared by different techniques such as chemical bath deposition [10], thermal evaporation [11], screen printing [12] and spray pyrolysis [7, 13]. However, the spray pyrolysis technique is a very low cost and simple technique that enables intentional doping and getting large area and uniform thin films [14]. For these reasons it is choused to prepare SnOz and CdS thin films in this work. To improve the properties of these compound semiconductors, SnOz was doped with fluorine and CdS was doped with indium where such doping is well known for these compounds."

Jan 1, 2012

By Shadia J. Ikhmayies

"Nanocrystalline fluorine doped tin oxide (Sn02:F) thin films were produced by the spray pyrolysis technique (SP) on glass substrates at a substrate temperature T, = 450 ° C. The hydrated stannous chloride (SnClz.2H20) was used as a precursor and ammonium fluoride (NH4F) and hydrofluoric acid (HF) were used as the doping compounds. A comparison between the compositional, morphological and optical properties of the films obtained by using the two doping compounds was performed by using scanning electron microscope (SEM) observations, energy dispersive spectroscopy by X-rays (EDAX) and transmittance measurements. It is found that the films prepared by using HF have larger grain size, and higher fluorine content than the films prepared by using ~- In addition these films have higher transmittance and higher direct optical bandgap energy. These results are interesting for the use of Sn02:F as a forecontact in CdS/CdTe solar cells.IntroductionTin dioxide is an n-type, wide bandgap semiconductor (about 3.5 eV) and in the form of thin films, it is a transparent conducting material, characterized by high optical transmission (80- 90%) [l]. Sn02:F is the most widely used transparent-conducting oxide material. The transparent-conducting thin films of this oxide are used as electrodes in a variety of optoelectronic devices, as heat mirror coatings in 'smart windows' for buildings, in automobile and airplane windshields, in incandescent light bulbs, in flat-plate and concentrating solar collectors. Tin oxide and zinc oxide, in thin film configuration are technologically important materials because of their applications in photovoltaic cells [2].Among various dopants for Sn02, fluorine is often preferred, because fluorine doping results in films with high transparency and good conductivity [3]. By exploring the literatures, it was found that different sources of fluorine were used to produce Sn02:F thin fihns, among which are ammonium fluoride (NH4F) and hydrofluoric acid (HF) are the most used. Some researchers used~ [2, 4-7] and others used HF [3, 6-8] for doping Sn02 films. Gordillo et al.[7] used both of NH4F and HF and showed that the resistivity of thin films obtained by using HF was lower than that of similar films obtained by using NH4F by a factor of 2.2. They also found that the films obtained by using HF have more random orientations."

Jan 1, 2013

By Jari Aromaa, Antti Kekki, Olof Forsén

"The deposition of copper on inert substrate depends on the number of active sites that will react at certain overpotential. The critical overpotential depends on surface morphology, surface film resistance and additives on cathode surface. The effects of surface properties on copper nucleation and growth rates were studied for used stainless steel blanks from several tankhouses. The surfaces of the blanks were characterized with electrochemical and mechanical methods. Electrochemical deposition tests were done at current density of 300 A/m2 for 10, 30 and 60 seconds. The nucleation density and copper coverage were estimated using image analysis. The surface film resistance did not correlate with copper growth. Increasing surface roughness correlated with lower copper growth.IntroductionStainless steel cathode blanks in copper electrorefming are usually made of AISI 3 I6L type steel. They have a typical lifetime over 10 years. During use the surface will collect deposits and become rough due to wear and corrosion. These factors can affect the nucleation and growth of copper. The nucleation and deposition of copper on inert substrate depends on the number of active sites that will react at certain overpotential. The critical overpotential can depend on surface film resistance, surface morphology, and additives adsorbed on cathode surface.The deposition potential of metallic ions on a foreign substrate is usually higher than the deposition potential on the electrode made of the same metal due to crystallographic substrate/metal misfit [I]. If the substrate has traces of the depositing metal they will be preferential growth sites. For a smooth deposit a large number of simultaneous nuclei is necessary. However, excessive nucleation density can lead to porous deposits [2]. Surface films of good conductivity are needed for dense nucleation and small nuclei. On cathode blanks the number of active sites increases with increasing surface film conductivity [3-5] and/or surface film porosity [6]. On AISI 3 I6 L stainless steel a more resistive oxide has been found to limit favourable sites for copper nucleation and more conductive film promoted high-density copper nucleation [7]. Also Urda-Kiel et al. have concluded that thicker oxide layers on AISI 304 stainless steel resulted in lower nucleation [8]. Increase in overpotential or current density activates more and more of the potential nucleation sites and this can be seen as higher number of nuclei [9] or smaller average distance between nuclei [10]."

Jan 1, 2012

By Reuben John Mathew

"Oxygen evolution is the main anode reaction in industrial copper electrowinning. The oxygen bubbles do not conduct electricity, thus increasing the electrolyte resistance. The oxygen bubbles formed at the anode rise to the surface, occupying a larger volume of the electrolyte at the top of the cell than at the bottom. This oxygen bubble concentration gradient contributes to a gradient in electrolyte resistance and consequently a tendency toward uneven current distribution. This phenomenon increases the chance for uneven growth on the cathode and/or short-circuits, particularly on the lower portions of the cathode. This issue may be ameliorated by increasing the charge transfer resistance for oxygen evolution down the height of the anode. This concept was studied by solving the current distribution for a 2-D model of a copper electrowinning cell using COMSOL.IntroductionA copper electrowinning tankhouse aims to operate at the highest current density that will deposit on the cathode a layer of copper metal possessing the desired physical and chemical characteristics. The operating current density is directly related to the physical nature of the copper deposit on the cathode (Figure 1), limiting a copper electrowinning tankhouse to some operating current density that produces acceptable copper deposits.[!] The ratio of the operating current density to the limiting current density is typically around 0.3.[2] If the limiting current density for a cell could be raised, the operating current density could also be raised and thus result in savings in capital cost for a tankhouse. [3]The average operating current density in a copper electrowinning plant is 270A·m- 2 .[4] The value for average current density, however, obscures the fact that the face of a cathode does not experience this value equally. Indeed, the current density varies along the height of an electrode and is independent of the height of the electrode.[5] This phenomenon partly explains why the lower portions of a cathode tend to display a rougher copper deposit.In order to utilize a higher operating current density but still remain at 30% of the limiting current density, the limiting current density must be raised, but it is affected by the mass transfer regime at the electrodes. The mass transfer regime is currently poorest at the lower portions of the cathode and this is part of the reason for the tendency for poor cathode deposits to occur at the lower portion of the cathode.[6]"

Jan 1, 2012

By Jorge Alberto Soares Tenório, Denise Crocce Romano Espinosa, Viviane Tavares Moraes

"The development of mobile phone technology has increased the replacement of outdated equipments for more modern models, transforming disposal of such devices into a serious environmental problem. Recycling appears as an attractive alternative to minimize the environmental impact of disposing such large quantities. Recycling can be accomplished by treating the printed circuit boards of used mobile phones by using the same techniques used in ore treatments with hammer mill; magnetic separation, electrostatic separation and grain size range. Before performing the recycling process a PCB characterization was performed to identify the fraction with the higher metals concentration/content. This study demonstrated that the electrostatic separation was not the best metals concentration of PCB aiming the recycling, while the non-magnetic residue had presented a more significant metal concentration. Furthermore, after the magnetic separation was possible to separate the following metals: iron and nickel.IntroductionPortable electronic devices have gained increasing acceptance over the last decades. Mobile phones sales in Brazil, for instance, have reached 104 million in 2007, and 128 million in 2008. It is estimated that, around the world, 100 million mobiles are thrown away every year, either because of loss of functionality or because newer models are launched in the market [1,2, 3]. Printed circuit boards in mobile phones are made of many materials, with approximately 83% in weight being metals and fiber-glass, and the balance being plastics pl. Several metals can be recovered from the electronics waste, such as copper, tin, iron, lead, nickel, titanium, aluminium as well as some precious metals such as gold, silver and palladium [4, 5, 6, 7, 8]. Concurrent with the increasing world demand for copper, there average metal content in ores has been decreasing. Economically interesting copper mines used to have 4% metal content, whereas presently, such content is around 1%, i.e., for every 1 ton of ore extracted, only 10 kg are copper [9, 10]. Approximately 33% of printed circuit boards (PCBs) composition is copper, that is, for every 1 ton of PCBs waste, 330 kg are copper [1]. Research in recycling PCB waste focuses on mechanical, electrometallurgy, pyrometallurgical and hydrometallurgical processes [3, 8]. Collecting and recycling obsoletes electro-electronic equipments is very important these days, in order to, not just preserve the non renewable natural resources but also to keep the environment and the population safe from the pollution caused by the toxic materials and heavy metals present in this kind of waste."

Jan 1, 2011

By Carla Lupi, Mauro Pasquali

"Photographic technology is based on light sensitivity of silver halides that, because of silver properties, are capable of forming photographic images. Photographic laboratories and hospital departments because of digital photographic systems less use this technology today. Nevertheless recovery of silver is still advantageous because environmental problems related to Ag ions danger to biological system. Many processes have been studied to treat silver containing photographic bath: cementation, chemical precipitation and electrowinning. In this work, after preliminary voltammetric tests, a batch electrometallurgical process has been studied to completely deplete the silver containing photographic fixing baths. The effect, of silver concentration in the electrolyte, varying over the range 0,2-1 g/L, bath stirring and current density ranging from 10 to 500 A/m2 on process yield and deposit quality, has been investigated. Introduction Photographic wastes, electronic scrap and spent catalysts constitute the main sources of materials for silver recycling. Among those silver secondary sources, the photographic discharged material could be still important and useful, even if photographic laboratories and hospital departments, because of digital photographic systems, less use photographic technology. Several processes have been developped in order to recover silver used in the field of photography from both photographic solutions and scrap film paper[1-5]. Fixing solutions are very complex baths but, because of silver position in the electromotive series, electrolysis could represent an advantageous method for silver recovery. Electrolysis produces high purity silver without generating new pollutants, while the fixer can be reused: obviously it is necessary to purge off a portion of this solution in order to avoid the excessive build up of other deleterious compounds into solution. A tested recovery method was constituted by the dissolution of silver from X-ray films with concentrated nitric acid. Internal electrolysis and external electrolysis methods were carried out using a steel electrode as cathode and a copper electrode as anode [6]. Silver recovery from photographic chemical solutions has been also performed in a special cell [7]: the solution is supplied to the bottom of a non-agitated cell having a vertically elongated form and including a central anode enclosed by a cathode. An other study discloses the use of an electrolytic cell comprising at least one anodic compartment and one cathodic compartment: the solution is treated in the cathodic compartment and then recycled in the anodic one [8]. A more recent work proposes the use of zirconium cathode for the recovery of silver from photographic fixing solution [9]: studies carried out by cyclic voltammetry showed that about 98% of total Ag can be recovered with an electrical efficiency close to 92%."

Jan 1, 2008

By Erich Hovestädt, Hans-Jürgen Odenthal, Christian Wuppermann, Herbert Pfeifer, Antje Rückert

"During the argon oxygen decarburization (AOD) process high-chromium steel melts are decarburized by oxygen and inert gas injection through sidewall nozzles and a top-lance. Due to the large amount of the injected processing gas, low frequency oscillations of the vessel can be observed. It is suspected that these oscillations can influence the converter's structure. The exchange of forces between fluid and the surrounding vessel is the focus of this study. An oscillation model was developed and tested, one objective being to limit the computational effort which is necessary for fully coupled and time resolved CFD and FEM simulations. Experimental results obtained from water-model studies as well as from on-sight measurements are available and were used in order to validate the numerical results. The authors' intention is a contribution towards a more in depth understanding of the factors influencing vessel vibration during the AOD process.IntroductionDuring the last four decades the AOD process has been established as a reliable and efficient refining process in stainless steel making. The injection of process gases (O2, N2, Ar) through sidewall nozzles shows advantages in mixing effectiveness compared to other injection geometries e.g. bottom blowing [1]. Stainless steel grades contain usually more than 10% chromium. With decreasing carbon content during the decarburization periods the tendency of chromium oxidation increases according to the varying chemical equilibrium which depends on the partial pressure of carbon-monoxide (CO) in the gas phase. That's why oxygen is gradually replaced by inert gases, usually argon or nitrogen, in order to lower the CO partial pressure and thus to minimize chromium oxidation. Despite the high injection velocity of approximately Ma = 1, the kinetic energy of the gas jets is consumed within a short distance from the nozzle exits due to the large density ratio between gas and melt of approximately 1:8000. With increasing distance to the nozzle exit, the initial horizontal velocity of the gas jet decreases and due to buoyancy force motion of the detached bubbles turns into a vertical direction. Subsequently a gas plume develops with its typical conical shape described by various authors [1-4]. Due to the drag force between gas bubbles and melt also the liquid phase is forced into a vertical motion. Near the free surface and the wall regions the melt flow is deflected in different directions. Subsequently, the typical flow pattern in the AOD vessel arises, as sketched in Figure 1 and described in literature [5-9]."

Jan 1, 2012

By A. Dell’Era, M. Pasquali, C. Lupi

"An electrochemical cell has been designed to treat very diluted cobalt solutions, i.e. those deriving from recycling processes of lithium-ion batteries. A reticulated vitreous carbon sponge was used as cathode and a Pt-coated Ti net as anode. A controlled potential electrolysis has been carried out in a solution flowing in the cell and maintained at a constant pH of 6.5. Considering the cathode dimensions (10.0 cm * 10.0 cm * 1.25 cm), rather high volumes of solution (>1 litre) can be treated with flow rates up to 1.6 l/min. The process yield is obviously related to the solution concentration; it has been observed that, starting with a solution containing 200 ppm of Co2+, the yield is initially ~35-40%, but it decreases to ~20% when 80% of the initial cobalt content has been electrowon. The yield increases up to ~50% if the carbon electrode is coated by cobalt. The conditions allowing a fast and complete removal of cobalt are outlined. Introduction Industrial liquid effluents containing heavy metal ions arise not only during hydrometallurgical processing, but also in many sector of chemical industries utilizing metal catalysts and process reagents. These waste solutions containing low quantities of metallic ions can be treated by chemical precipitation, solvent extraction, ion exchange, etc. before final discharge. All these techniques could be efficient for complying the aqueous effluents with the severe rules related to the environmental impact, but they can not directly produce metals. Particularly the chemical precipitation presents two main drawbacks, huge amount of sludge prodction and reagent costs to produce this useless and sometime dangerous sludge that have to be considered. Electrochemical technologies can be used for the treatment of effluents polluted by metal ions, showing the following advantages in comparison with other processes: 1. recovering of the polluting substances in metallic forms, with subsequent reusing; 2. absence of process slag, which should be subsequently disposed of. In this work an electrochemical reactor with a reticulated vitreous carbon cathode and a platinated titanium net anode has been designed and utilized for removal Co from waste aqueous solutions. Porous materials have been used as electrodes for this cell, as their high specific surface area favours the treatment of these low metal content solutions (1-7). This kind of electrodic material presents very interesting chemical-physical characteristics such as: low density, low thermal expansion and high electrical and thermal conductivities; particularly the reticulated vitreous carbon (RVC) presents a very elevated void volume, rigid structure, good resistance to temperatures in non-oxidizing environments and very low resistance to fluid flow."

Jan 1, 2008

By Maria Salazar-Villalpando, Todd H. Gardner

"Efficient utilization of CO2 can help to decrease global warming. Methane reforming using carbon dioxide has been of interest for many years, but recently that interest has experienced a rapid increase for both environmental and commercial reasons. The use of CO2 provides a source of clean oxygen, which eliminates the need for costly oxygen separation plants. The product of dry reforming is useful syn-gas, which can be used to generate electrical power in a SOFC or in the production of synthetic fuels (hydrocarbons and alcohols). Hexaaluminate catalysts prepared at NETL may represent a product that can be utilized for the conversion of CO2 to syn-gas. In this work, transition metals dispersed in barium hexaaluminate have shown to be promising new catalysts for dry methane reforming. In this investigation, a series of BaNixAl12-yO19-d catalysts with varying Ni content were prepared by co-precipitation followed by calcination at 1400°C. CO2 reduction by dry methane reforming was carried out to determine catalyst performance as a function of temperature and carbon formation was also quantified after the reforming tests. Results of catalysts characterization, dispersion and surface area, were correlated to catalytic performance.IntroductionEfficient utilization of CO2 can help to decrease global warming. Methane reforming using carbon dioxide has been of interest for many years, but recently that interest has experienced a rapid increase for both environmental and commercial reasons. The use of CO2 provides a source of clean oxygen, which eliminates the need for costly oxygen separation plants. The product of dry reforming is useful syn-gas, which can be used to generate electrical power in a SOFC or in the production of synthetic fuels (hydrocarbons and alcohols). The dry reforming reaction has been known for a long time. Recent publications have reported studies over several catalysts. For example, the CO2 reforming of CH4 over mesoporous nanocrystalline zirconium powders (ZrO2–3%M2Ox; M: Ce, La and K) at 700ºC have shown methane conversion up to 60% (1). Similarly, the effect of Ni content (1–12 wt%) on the surface and catalytic behavior of bimetallic PtNi catalysts supported on ZSM-5 for reforming of methane with CO2 has been studied and report shows a maximum conversion of 16% and catalyst deactivation was observed during the first hour of time on stream (2). In another report, (3) Ni/a-Al2O3 catalyst was tested for syn-gas generation at 750ºC. The maximum methane conversion was 25%."

Jan 1, 2008

By Edouard Asselin, Guikuan Yue

"In the present study, electrochemical measurements, especially cathodic potentiodynamic polarization (CPC) and cyclic potentiodynamic polarization (CPP), have been employed to study the kinetics of ferric reduction on chalcopyrite in aqueous Fe( II )-Fe(III)-H2S04 solution at 25°C and 70 °C. Results from the calculation ofspeciation in the above solution reveal that, at both 25 °C and 70 °C, the real Fe3+/Fe2+ ratio is much lower than the nominal ratio, which leads to smaller values for the reversible potential of the ferric/ferrous couple based on the Nemst equation. Exchange current densities of the ferric/ferrous couple were obtained by extrapolating the cathodic linear Tafel line to the reversible potential and are on the order of 10-7·10-6 A/cm2 at 25°C and 10·6-10-5 A/cm2 at 70 °C, respectively. The transfer coefficients were about 0.35-0.38 at 25°C and 0.35-0.45 at 70 °C. Polarization plots of CPC and CPP under different nominal Fe3+/Fe2+ ratios are in good agreement at 25 ·c and at 70 °C. Based on the obtained exchange current densities, the rate constant k, was calculated and is on the order of 10-1 cm/s at 25 °C and 10 1 cm/s at 70 °C.IntroductionChalcopyrite is the most abundant copper mineral in nature, accounting for about 70% of copper reserves in the world [I]. In recent years, the metallurgical industry has been searching for a hydrometallurgical process as an alternative to pyrometallurgical treatment due to high emissions of S02 and capital costs associated with smelting. Activity in this area has increased recently due to some inherent advantages associated with hydrometallurgical processing, such as the possibility of treating low-grade ores (increasingly more abundant in the case of copper) and easier control of waste, with the attendant benefits to the environment [I]. Chalcopyrite is highly refractory under most hydrometallurgical conditions, owing to the formation of an anodic passivation layer on the chalcopyrite surface which renders the process kinetics very slow. Most of the currently proposed processes are based on sulfuric acid with ferric ions and/or dissolved oxygen as oxidants. Sulfuric acid is preferred over all other leaching reagents in terms of cost, environmental friendliness, and ease of its regeneration during electro-winning. Some of these processes have been piloted in attempts to implement these technologies on an industrial scale,"

Jan 1, 2012

By Jian Li, S. Penttilä, P. Liu, W. Zheng, C. Bibby

"The materials selection for Gen IV supercritical water reactor in-core components faces major challenges due to severe operating condition. The current Canadian pressure-tube supercritical water (SCW) concept design requires core outlet temperature of 650 °C at 25 MPa with peak cladding temperature reaching as high as 850 °C. Aside from oilier challenges, there is currently very limited data on candidate stainless steels' corrosion resistance under this operating condition. Austenite stainless steels that include 316L, 304H, AL6XN and 3 l0S that cover a wide range of Cr contents are promising candidates for either direct in core applications or as base coating materials. However, their corrosion resistance has not been tested systematically under this stringent condition. In this study, these types of stainless steels are tested, and their corrosion resistances are compared.IntroductionThe Canadian pressure-tube supercritical water (SCW) concept will operate at a core outlet temperature of 650 °C at a pressure of 25 MPa, with potential peak cladding temperature reaching as high as 850 °C. High-temperature corrosion resistance is one of the key design requirements for fuel cladding components. As summarized by Allen [1 ], most testing to date has been carried out at temperatures below 730 °C. To date, SCW corrosion data above 600 °C is very limited. Even at relatively low temperature exposure to SCW (e.g. 500 °C), F/M steels develop a thick oxide layer rapidly, while some austenitic stainless steels develop thinner surface oxide. Ni based alloys appear to form very thin surface oxide, however pitting was observed in the vicinity of intermetallic precipitates [2-5]. Dissolution of major alloying components from all of these alloys could also pose significant problems for downstream piping [6]. Kaneda et al. [7] suggested some modified stainless steels provide better SCW general corrosion resistance, with no sign of SCC under the slow-strain rate test.Cho [8] suggested that as the Cr content increase, general corrosion resistance improved at 510 °C and 25 MPa. However, similar to Cho's work, most of the SCW corrosion resistance assessments were based on weight change measurement. This can be unreliable due to potential exfoliation of thick oxide film. Besides, there have been no systematic SCW corrosion resistance tests for candidate stainless steels under higher temperatures. SCW corrosion rate increase dramatically for alloys tested at 600 °C [1]. It is also important to understand the role of major alloying elements under this stringent operating condition, not only for fuel cladding components' materials selection, but also for coating materials development."

Jan 1, 2013

By Jeffrey Shepherd, Scott R. Smith, Eduard Guerra

"Electrochemical and spectroscopic evidence for the dissolution of a Au electrode by meso-2,3- dimercaptosuccinic acid (DMSA) from an acidic LiCl04 electrolyte is presented. Near the potential of zero charge, DMSA was determined to form a stable layer on the metal surface but at more anodic polarizations, DMSA was displaced from the metal through an oxidative process. The anodic displacement of the layer from the electrode resulted in a small amount of Au that was detected in the electrolyte using atomic absorption analysis. The extent of Au dissolution, was monitored while holding the potential of the electrode for 24 hours at the thermodynamic Eo/H,O in LiCl04 electrolytes containing 10 mM DMSA. This routine resulted in detectable quantities of a soluble Au-DMSA complex in the electrolyte and the greatest leaching was observed at a pH = 2.0. At room temperature, the leaching rate was stable at 10.9 µg cm·2 hr·' however, upon increasing the temperature to 50.0°C, the rate of Au dissolution increased yielding an average rate of extraction of 40.1 µg cm·2 hr- 1. Interestingly, after the first 12 hours of leaching at 50.0°C, the leaching current decreased dramatically suggesting surface passivation which prevented further Au extraction. The implications of this process in the industrial leaching of Au will be discussed.IntroductionThe use of cyanide in the industrial process of leaching Au from ores has raised concerns regarding both operational safety and environmental issues surrounding the disposal of spent leaching eftluents in tailings ponds. Depending on the chemical nature of the processed ore, the spent solutions that are released into the tailings ponds can contain toxic cyanide, either dissolved or complexed with different metals and may pose serious risk to wildlife as well as freshwater contamination to nearby water systems. Because of these issues, some recent studies have focused on the exploration of more environmentally-friendly molecules to selectively leach Au with appropriate kinetics. However, to effectively leach Au into an aqueous solution, a suitable ligand that reacts to form a stable chemical bond with Au is needed to form soluble Au complexes that can be later recovered [I]. Recently several sulfur bearing alternatives have been shown to leach significant quantities of Au in aqueous solutions. These include thiourea [2], thiocyanate [3], and thiosulphate [4]. However, alkylthiols are also known to quickly form a stable covalent Au-S bond [5], but have been relatively understudied in term of their ability to leach Au in solution, even though some short chain thiols are water soluble and relatively nontoxic."

Jan 1, 2012

By Jie Li, Liangxing Jiang, Yexiang Liu, Junfeng Gui, Bo Hong, Xiaocong Zhong, Yanqing Lai, Xiaoying Yu

"Pb-based alloys with Pr and Ag were prepared in vacuum electromagnetic induction furnace. The tensile strength, corrosion rate and anodic potential in sulfate solution were measured, and the experimental data were analyzed according to the metallographic phases of alloys, the micromorphology and composition of their oxide films. The results show that, with the addition of Pr, the ultimate tensile strength and corrosion rate of pure lead were increased, and the anodic potential decreased. The extra addition of Ag can improve the properties of alloy further. Comparing with Pb-Ag0.8 alloy which is widely used in zinc electrowinning industry, the ultimate tensile strength of Pb-Ag0.6-Pr2.0 alloy was increased by 31.75%, the anodic potential under 50mA/cm2 was decreased by 30m V.IntroductionIn zinc electrowinning industry, the Pb-Ag (0.5-1.0 wt.%, 0.8wt.% normally) anode is widely used as an insoluble anode['l. It can meet the basic requirements, but still has several problems such as high oxygen evolution over-potential (about 860mV), unsatisfactory corrosion resistance, lead contamination of the cathode product and high consumption of Ag etc.In order to reduce the energy consumption, enhance the corrosion resistance, improve the product quality and reduce the consumption of Ag (or even dispense with it), much research has been done, mainly focusing on Pb-based alloy anodes and Ti-based coated anodes. Detailed investigations have already been carried out on binary alloys (Pb-Ca and Pb-Co), ternary alloys (Pb-Ag-Ca, Pb-Ag-Ti, Pb-Ag-Sn, Pb-Sr-Sn, and Pb-Ca-Sn) and quaternary alloys (Pb-Ca-Sr-Ag, Pb-Ca-Ce-Ag, and Pb-Ag-Sn-Co)[Z-4l, Although these anodes can effectively reduce the consumption of Ag, only the Pb-Co and Pb-Ag-Sn-Co anodes perform well with regard to reducing the anodic potential. However, their complicated manufacturing conditions restrict further commercial use.Besides its application in nonferrous metal electro-winning industry, Pb-based alloy is also used as grid alloy for lead-acid battery, serving as active materials supporter and current collector. In order to enhance the corrosion resistance and deep-cycling performance, reduce the impedance of the corrosion film, the addition of appropriate rare earth elements into anodic grid alloys has become a research focus. Studies proved that RE can enhance the mechanical strength of grids, inhibit the formation of anodic Pb(II) film on the surface of grids and then reduce the impedance of the film[ 10-12l."

Jan 1, 2013

By Gaifeng Xue, Lei Zhang, Xia Liu, Lina Wang, Pu Liu, Benquan Fu

"Experiments were conducted to investigate the behavior of the integrated process with a three-dimensional electrode reactor combined with Fenton process for coking wastewater treatment. Effects of initial pH value, reaction time, H20 2 dosage, Fe2+ dosage on Total organic carbon (f OC) removal rate were investigated. The kinetics of degradation of TOC from coking wastewater by three-dimensional fluid bed electrode reactor combined with Fenton process was also studied. Experimental results shows that three-dimensional fluid bed electrode reactor combined with Fenton process had better synergic effect, average 17.4% TOC removal rate was improved within an hour. It was found that TOC degradation in coking wastewater followed a pseudo-first-order reaction kinetic model. The optimum degradation efficiencies of TOC were up to 60% as pH3.4, 3.5 mM ofFe2+ andl.2-1.8ml/L H20 2 in 90min reaction period. Furthermore, the integrated process showed a rapid reaction performance at a low temperature within a short reaction time and remained high efficiencies for TOC removal. Overall, the integrated process was proved feasible for coking wastewater treatment in practical applications.IntroductionCoking wastewater is generated from coal coking, coal gas purification, and by-product recovery processes of coking, which is composed of phenolic compounds, heterocyclic compounds, polycyclic aromatic hydrocarbons, ammonia, cyanide, polycyclic nitrogen-containing aromatics, acyclic compounds, etc. Most of these constituents are refractory, poor biodegradability, toxic and carcinogenic['-31. Currently, coking wastewater is usually treated by different forms of A/O biological nitrogen removal process as the primary treatment process, but the aforementioned processes are not efficient enough to meet the requirements from the National Discharge Standard in China (GB13456-1992). According to the continuous requirement on improving environmental protection for coking industry (revised 2008), increasing wastewater utilization ratio and reducing discharge of effluent in the coke industry has to be implemented for cleaner production and sustainable development. Therefore, advanced technologies need to be developed to treat coking wastewater and reutilize the product as industrial cooling water, which would be one of the best choices to achieve zero discharge of wastewater and reduce water consumption per ton of steel [4-51 . In this study, three-dimensional fluidized bed electrode reactor combined with Fenton process was adopted to advanced treatment of coking wastewater, and the effects of operating conditions, including H2O 2 dosage, Fe2+ dosage, initial pH, and reaction time on TOC removal rate, were investigated. Meantime, study of kinetics of reaction was estimated."

Jan 1, 2013

By E. A. Chavarriaga, L. J. Jaramillo, O. J. Restrepo

"This paper presents the results of the manufacturing ceramic pigments with spinel structure, using methods of synthesis of low temperature. In this work we obtained spinel structures type by the methods of Self-combustion, Coprecipitation, Microemulsion, Gel citrate and Pechini. These methods become an attractive alternative to traditional method (ceramic method), since we can work at a lower temperature, reducing manufacturing costs, lower fuel consumption, less wear on equipment and other environmental and economic implications. Also it is possible to have control over features such as stoichiometry, morphology of the products, reaction times and structures. The products obtained by these routes will be used in the manufacture of ceramic pigments and characterized using different techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-VIS spectrophotometry.IntroductionSpinels are ternary oxides AB204, where A and B are cations occupying tetrahedral and octahedral positions respectively. These oxides exhibit interesting electrical, magnetic and catalytic properties [1-4], depending on its nature, charging and intrinsic distribution of ions [5].The most widely used method to prepare spinels has been through solid state reaction, which consists of mixed oxides at high temperatures [6, 7]. In the last years, there have been a strong tendency to use chemical routes for the synthesis of crystalline ceramic particles at low temperatures [8,9]. Unconventional methods currently employed for the synthesis of complex oxides are Gel citrate method, Pechini, Spontaneous combustion, Microemulsion and Coprecipitation. Pechini method [10, 11], based on polymeric precursors, does not require high temperatures and allows stoichiometric control for greater reproducibility. This method involves the formation of a polymeric resin between a metal quelate and polyhydroxy acid of alcohol by polyestirification.Coprecipitation is important for many environmental problems related to water resources, including acid mine drainage, migration of radionuclides in waste repositories dirty, transport of contaminant metals in the industry, metal concentrations in aqueous systems and the technology of wastewater treatment. The coprecipitation process can vary in each case; the partition in the solid phase can be carried out by surface adsorption, ion exchange, surface precipitation, occlusion and formation of solid solution. The formation of solid solution is the result of structural incorporation of the marker in structural support sites resulting in a minor component in the solid solution with the host phase that has a very low solubility of pure solid [12]. Synthesis by gel citrate method allows the use of a route to obtain ceramic pigments from a very simple experimental system in which the stoichiometric control, the size and shape of the particles and the purity of the phases obtained can be controlled more accurately [13]."

Jan 1, 2012

By Xuewei Lv, Maojun Zhou, Xiaobo Huang, Rende Zhang

"The characterization of the surface roughness of the mineral particles is of vital importance for the studies of the mineral processing. In this study, an evaluation of the roughness of the iron ore particles, with the measurements of size distribution and the measurements of specific surface area with the liquid nitrogen absorption, was developed. The main theory of this method is the fact that the roughness of the particle influences the specific surface area apparently. The specific surface area of the particles can be measured with the laser diffraction method and the liquid nitrogen absorption method. The influence of the surface roughness of the particle can be measured with the nitrogen absorption and cannot be measured with the laser diffraction. Therefore, the roughness can be got by comparing the specific surface area with two measurement methods.IntroductionThe characterization of the surface roughness of the mineral particles is of vital importance for the studies of the mineral processing. There are three main methods for measuring the size distribution of mineral particles: sieving, laser diffraction, and sedimentationl). Many techniques involve sedimentation such as the Horiba2, 3) and the Cyclo-sizer1). In the mineral industry, size distribution is usually determined by sieving because it can be carried out accurately for all particle sizes larger than 45 . The preferred method to obtain the size distribution of finer particles is laser diffractometry. The technique has several advantages: it produces measurements in a few minutes with considerably less labor compared with the cyclo-sizer and for a range of sizes considerably wider in comparison with the sedigraph4). The equivalent-sphere size distribution reported by laser diffractometry is valid for metallurgical calculations and can be routinely used in mineral processing plants. The surface area of the particles can be measured by the BET method of nitrogen adsorption, or it can be calculated from the size distribution. However, the latter calculation requires the size distribution to be accurately known across the whole size range, and assumptions have to be made about the shapes and surface roughness of the particles and presence or absence of pores (see below). The BET method is based on the physical adsorption of gas over the whole exposed surface area and measures the surface area stemming from the roughness and open pores on the surface of the particle5). The calculation of the surface area from the size distribution is usually based on the assumption that all the particles are smooth spheres, without considering the shape and/or roughness of the particles. Determining the surface roughness of the particle with these methods, is the objective of this study."

Jan 1, 2012

By Thomas Schuman, Jaan Kers, Lucas N. W. Damoah, Xiangjun Zuo, Lifeng Zhang

"Rapid technological innovation has propelled the use of electronic equipment leading to the generation of more and more waste electrical and electronic equipments (WEEE). Printed wiring board (PWB) is a component made of one or more layers of insulating material with electrical conductors. To investigate an environmentally friendly process to recycle PWBs, PWB samples with and without additives were pyrolyzed. Liquid, gas and solid products were achieved with different conversion fraction. Analysis of the exhaust gases from the experiments using GC-MS and MS showed that without CaCO3 additives poisonous gases such as C6H6 and HBr were produced which were adequately controlled if CaCO3 was added.IntroductionPyrolysis is one of the best methods for treating complex mixtures of waste polymers and to recover the material and energy content. The process consists of thermal decomposition at moderate temperatures in total absence or small amount of oxygen in which the structures of polymers break down into smaller intermediate products "". The decomposition temperature of a substance is the temperature at which the substance breaks up into smaller substances or into its constituent atoms 2). Thermal treatment of PWBs were reported using DC Arc Plasma furnace 3), and fixed bed reactor 4). One drawback in dealing with thermal treatment of PWB scraps is the likely production of super-toxic halogenated dibenzodioxins and dibenzofurans from the bromine containing structures. Pyrolysis of organic materials contained in waste PWBs leads to the formation of gases, oils, and chars which can be used as chemical feedstock or fuels ""'. Dehalogenation of the pyrolysis product of electronic scraps is essential to make it commercially acceptable. It would be obviously the most advantageous solution as pyrolysis and dehalogenation are carried out simultaneously. Reported pyrolysis investigations are at experimental stage and have been carried out in vacuum, molten salt, fluidized bed, rotary kiln, entrained, stationary, and moving bed reactors 7). Comparing to the incineration and combustion of PWBs, the pyrolysis process has several characteristics: 8'"">) 1). Converting the organic solid substance into fuel gas, fuel oil and carbon-black as storage energy; 2) Emitting toxic substances such as sulfur, bromine and heavy metals in wastes; and 3) Keeping metals from being oxidized. Although many researches into the pyrolysis of PWB wastes have been reported, most of the works have been carried out using analytical pyrolysis techniques or very small batch reactors ""~'5). Also, most of the works for the pyrolysis of PWBs haves concentrated on the composition of the organic products, particularly the brominated organics. The current study is to investigate the pyrolysis of PWB powders in a small TG-DTA scale and a 50-gram tube furnace scale."

Jan 1, 2011

By William Brinkman, Mark Jolly, Nasim Soleimanian, Karl Dearn, Oliver Brinkman

"Glass manufacturing is a heat intensive process. There is a direct correlation between the batch distribution techniques and the furnace energy consumption, productivity, and quality of the glass manufactured. All four major segments (float, container, fibre, and specialty glasses) would benefit from using an optimised batch distribution technique where possible. Oscillating batch chargers (OBC) have been in use since the early 70s, despite their superior batch shape, coverage, and in turn positive effects on the energy consumption and productivity of the furnace they are almost exclusively used in container glass manufacturing. The OBC’s main difference compared with other charging methods is its ability to directly influence the batch initial velocity. This paper reports on results achieved in CFD models (GFM) used to study effect of the machine on the overall energy consumption in the doghouse and the melt space.IntroductionGlass manufacturing can be divided to four major segments float glass, container glass, fiberglass, and specialty glasses. The financial cost of manufacture, its impact on the environment, lack of standardisation and mounting pressure imposed by the authorities for reduction in emissions means that the industry and its suppliers are utilising CFD modelling in order to tackle these challenges. The need for high temperature to create and maintain the viscous flow, homogenisation of the glass melt, and maintenance of the process to allow continuous output of glass of the right quality are the contributors to the energy intensive activities that are involved in continuous glass manufacturing. This in turn has resulted in design of large container glass furnaces which have high energy consumption, low specific performance, and high CO2 emissions where the most efficient furnaces in the container glass sector have a specific primary energy consumption of 3.8 GJ /tonne of glass at a level of 50% cullet in the batch making even very small improvements in efficiency by operation optimisation a value adding activity [1-14].The theoretical calculated energy required to melt glass is 2 to 3 times less than the energy actually used to melt glass as a result of glass melt passing a zone 5 to 8 times before leaving the tank.[8]. This causes contamination as the result of mixing between the completely molten glass free from bubbles returning to the batch area where there is freshly molten non-homogeneous glass, still containing very large numbers of bubbles and un-molten batch. At high temperature some components are dissolved rather than melted. Given that an un-molten batch is a good thermal insulator, it can be transported a long way into the furnace, increasing the need for homogenization which also increases the glass residence time of glass melt. This is why large unbroken strings of batch should be avoided, as should an overall blanket without gaps."

Jan 1, 2014

By Shulan Wang, Xuan Liu, Li Li

"Electrochemistry of Fe(III) in 69CaCl2-12CaF2-19KF and 81CaCl2-19KF (mole percentage, %) was investigated at 827 oC on molybdenum electrode by cyclic voltammetry, chronoamperometry and galvanostatic electrolysis using Fe2O3 as the Fe(III) source. The reduction of Fe(III) to Fe was conducted in one step and controlled by diffusion process. Fe(III) shown greater reduction rate and diffusion coefficient in molten 81CaCl2-19KF than in 69CaCl2- 12CaF2-19KF. Galvanostic electrolysis of Fe was performed in both molten salts with a cylindrical cathode rotating at 200 r/min and dendritic iron deposit was obtained.Keywords: iron; electrolysis; electrochemistry; molten saltIntroductionThe production of iron and steel causes huge emissions of CO2. Iron electrowinning in molten salts with dissolved Fe2O3 using an inert oxygen evolving anode is an alternative process to reduce or eliminate the formation of CO2. Research on novel process of producing metal has been reported recently [1-2] by using CaCl2 as the main electrolyte and dissolving CaO in CaCl2 due to the high solubility of CaO in the melt. This process has been used in preparing many active metals and alloys [3-14]. In the present work, the electrochemical behavior of iron in CaCl2-KF was studied and transport property of iron ion in the melt was discussed.ExperimentalCaCl2,CaF2 and KF (in analytical purity) were dried in air for 48 h. Mixed salts used in experiments were placed in a graphite crucible (??58 mm inner diameter). The graphite crucible together with the salts was heated at 473 K for 12 h in a furnace with flowing Ar (99.99%) before further heating. Temperature inside the furnace was measured by an S type thermocouple. Electrochemical measurements, such as cyclic voltammetry and chronocoulometry, were performed in a three electrode cell by EG&G PAR273A potentiostat/galvanostatand. Galvanostatic electrodepositon of iron was conducted in a two electrode cell. Molybdenum (??2 mm) and iron (??5 mm) were used as the working electrode (WE) and the reference electrode, respectively. A graphite crucible and a magnetite rod (??25 mm ) consisted of 100% magnetite and sintered at 950 oC in argon atmosphere for 2 h with electrical conductivity of 366 O-1m-1 at room temperature were used as the counter electrodes in the galvanostatic electrolysis experiment. Carbon (??10 mm) was used as the counter electrode in electrochemical measurement. The deposits were washed in distilled water bubbled with argon and dried in air before being characterized by X-ray diffraction (PW3040/60 diffractometer) and scanning electron microscope (SEM, SSX-550)."

Jan 1, 2014

By Y. Moriya, Y. Sadayoshi, Y. Nonogaki, Y. Takeda

"Preparation and growth processes of CaF2 on Si(111) and of . InxGa1-x,As islands on CaF2 by molecular beam epitaxy (MBE) are described. It was found that first of all the Si(111) surface treatment process to obtain the 7x7 reconstructed structure was necessary to ensure the cleanness of the surface and to grow a flat and high quality CaF2 on it. Growth of InxGa11-x,As islands on CaF2 was tried by droplet heteroepitaxy using the same MBE reactor. In,GaxGa1-xAs islands were successfully grown epitaxially, and the size and density of the islands dependent on the In composition were investigated.IntroductionThough semiconductor/semiconductor heterostructures are widely used for many device applications, small band off-sets of the conduction bands and the valence bands restrict the utilization of the intra-subband transitions to far-infrared regions. With InAs as the quantum well and fluorides as the barrier layers, we can design three-electronic-level systems in the infrared region, which is the low loss transmission window of the silica optical fibers. To realize those structures, we have grown InxGa1-xAs islands on CaF2 thin films that were epitaxially formed on Si(111) substrates by molecular beam epitaxy. By the droplet heteroepitaxy that we invented, the InxGa1-xAs islands with height of -10 nm have been obtained successfully. Optimum processing to obtain atomically smooth surfaces of Si and CaF2 and high quality InxGa1-xAs islands is reported.ExperimentsMBEMachineCaF2 was grown on Si(111) and InxGa1-xAs islands were grown on CaF2 successively by MBE. The MBE machine consisted of a growth (or reactor) chamber and a loading chamber. The reactor chamber was equipped with Ga, In, As and Er metal source cells and CaF2 and BaF2 source cells. Cell materials were P-BN for Ga, In and As metals, and were graphite for CaF 2, BaF 2 and Er to avoid reaction with BN cells. The electron gun and screen were attached to the reactor to observe the RHEED pattern during the substrate surface treatment and the growth of CaF2 and InxGa1-xAs islands. The substrate manipulator was designed to heat up the Si substrate up to 1,200°C for the surface cleaning. The QMS was also equipped to analyze the residual gas species in the reactor chamber. The base pressure of the reactor chamber was 2-5x10-11 Torr, being pumped by ion pump and the liquid nitrogen shroud"

Jan 1, 2000