Search Documents

By V. A. Luganov

During the treatment of raw materials containing arsenic and antimony, problems in the distribution of these elements in the process products occur. In a number of cases in processing of copper-bearing materials, it is possible (or necessary) to obtain speiss. The purpose of the present research is to study the theoretical aspects and analyze the technological possibilities of producing copper-bearing speiss and the subsequent electrometallurgical processing with copper extraction as well as arsenic and antimony utilization. Copper arsenide (Cu3As) and copper antimonide (Cu3Sb) are the main components of the speiss. A thermodynamic analysis of the electrochemical oxidation of Cu3As and Cu3Sb, carried out using Pourbaix diagrams, showed that in a pH range from 0 to 2, oxidation potential 0.45-0.55V, ions of copper and arsenic and antimony trioxide are in the equilibrium. The kinetic study has shown, that with an increase in the polarization potential, the dissolution process changes from chemical to diffbsion control. An increase in temperature stabilizes the electrolysis process due to dissolution of arsenic trioxide forming on the anode. Electrolysis of speiss using a cathode diaphragm with the solution pH = 1-2, current density 150-200 A/m2 and temperature 60-70°C makes it possible to obtain cathode copper with a current efficiency of 95-96% and to remove the arsenic from the process during the electrolyte cleaning process. The arsenic content in the cathode copper did not surpass 0.002%. As the result of the research, a technological flowsheet for copper-lead speiss processing was developed. At the present time this technology is undergoing pilot testing.

Jan 1, 1999

By Farouk Tedjar

The growth of miniaturization in one hand and energy density need lead to rapid development of new chemistry for batteries as observed during last decade particularly in secondary systems. However dark side of the progress is always in environment impact and scarcity of resources. In the lithium segment a jump from six electrochemical series (all non rechargeable systems) before 1990 to more than 15 systems including new rechargeable systems has been observe during last decade. Lithium battery chemistry was enriched with new electrolytes, conductive salts and new oxide composition. In the same time, lithium ion battery safety was strongly improved during last period. The progress of these technologies was strongly boosted by the substantial growth of the mobile telephone market in the mid 1990's (+ 1% a month in 2000, and a 71% penetration rate in Europe in 2005 compared to just a few percent in 1996). This market is constantly in search of higher electrochemical performance (mainly energy density in front of increasing miniaturization. Recycling of end of life product could be managed not only in environment aspect, but also under resource conservation and economic aspect of arising technology (mainly on the effect of re-injection recovered materials) The Li-ion segment is a new branch in the cobalt market and impact of LiCoOx will be fitted with the actual increase of the demand for this battery. For this reason all the processes aim to valorize active and packaging material. RECUPYL process project was conducted in this direction to offer a new solution for recycling those lithium systems. The process has been developed at pilot industrial scales using synergy between new equipment (for mechanical pre-treatment step) and existing line at RECUPYL facility (for chemical treatment) and should lead to high valorization rate with a minimum hazardous co-products. The process was also developed in order to be able to recover news cathode materials introduced in electrode like LiFEPO4, LiMxCoyO2 and new anode composition in substitution with former carbon anode.

Jan 1, 2006

By Camila Martini Matos, Maria das Graças da Silva Valenzuela, Francisco Rolando Valenzuela Diaz, Lucy Gomes de Sant' Anna, Orley de Oliveira Magalhães, Flavio M. S. Carvalho, Isaac Jamil Sayeg

"Kaolin clays are widely used in various industry segments. Its main properties are fine granulometry, chemical inertness and whiteness. In general, kaolins are not easily organophiilized as a result of its 1: 1 structure. The aim of this paper is to describe the modification of a Brazilian kaolin sample, in order to obtain an organophilic kaolin of high performance. The clay as received was identified by X-ray diffraction and characterized by optical microscopy, cation exchange capacity and swelling tests for observation of their performance in water and organic solvents. Then, the sample was treated with a 10% sodium carbonate solution and with ammonium quaternary, washed several times with distilled water, dried at 60°C, and characterized by XRD and swelling assays. Our results show that the clay was organophiilized and its ability to swell in organic solvents has increased.IntroductionThe kaolin clay, also known as ""china clay"" is chemically a hydrated aluminum silicate characterized as a very fine powder and lamellar structure (1:1), being constituted mainly by kaolinite [l]. Kaolin is a mineral extremely used as raw material. Its properties such as color, softness, small particle size and chemical inertness make it a suitable material for several industrial applications. The desired properties of kaolin varies widely for each application, beginning with its largest use in the paper industry until minor uses in the sectors of cosmetics and pharmaceutics. These two last applications require purified kaolin with defined functionality [2]. To find improvements in the functionality of kaolin for specific applications is important for many industrial uses. Sometimes the way to find these improvements might be modification of the kaolin clay by treatment with a chemical substance as ammonium quaternary, causing surface modifications [3,4]. In this work is described the modification of a Brazilian kaolin sample by treatment with cetyl trimethylammonium chloride (CTAC). The properties of the modified kaolin are being assessed by characterization and essays to understand its functionality and industrial application."

Jan 1, 2013

By Ning Wang, Bing Xie, Hong-Yi Li

"Compared to traditional sodium roasting, calcified roast inhibits chlorine pollution. A vanadium extraction technique based on a calcified roast is especially suitable for vanadium slag with high calcium content. In this report, V205was extracted from vanadium slag by calcified roast followed by acid leaching and hydrolysis precipitation. In optimized conditions, the high silicon low vanadium slag was roasted at 850'C for 2 hours without CaO addition. The roasted materials were leached with 35 % H2SO4 in liquid/solid ratio of 5:1 (mL/g) at 95OC for 4 hours. The extraction of vanadium was as high as 97.66 %. These results are instructive to V2O5 production in industry.IntroductionVanadium slag is produced in converter, sodium salt roasting is the commonly used technique to extract vanadium. In sodium salt roasting, vanadium slag is roasted with sodium salts including sodium chloride and soda as additives, followed by leaching with acidic or basic solution [1]. However, in this process chloride reacts to produce corrosive gases including HC1 andCl2- SO2 and SO3 can also corrode equipment severely and are also an environmental contaminant. The low melting point of sodium salts leads to fusion agglomeration, which blocks vanadium oxidation and thus decreases the extraction rate of vanadium. A large amount of sodium salts consumed as roasting additives increases the production cost. Moreover, sodium salt roasting requires low CaO content in vanadium slag. When the CaO content increases to 1%, V2O5 extraction can amount to 4.7%-9% [2]. For vanadium slag with high CaO content, the sodium salt roasting technique leads to low vanadium extraction rate."

Jan 1, 2012

By Z. Zak Fang, P. Fan, S. Middlemas

"Titanium dioxide (T1O2) has been widely used as pigment in paints, paper and cosmetic products, as well as high-tech applications such as PV Cells, semiconductors, biomedical devices and air purification. T1O2 pigment is primarily produced by the high temperature chloride process, resulting in considerable CO2 emissions. A novel hydrometallurgical process for making T1O2 pigment without direct CO2 emission is investigated. The new method promises to eliminate direct CO2 emissions, consume significantly less energy, and produce minimal environmental waste. The novel process involves molten salt roasting of titania slag, with subsequent washing, leaching, solution purification, hydrolysis, calcination and post-treatment stages, resulting in high-purity anatase or rutile pigments while realizing significantly reduced environmental impacts. Pigment whiteness is critically sensitive to trace amounts of discoloring impurities such as iron and chromium. Several methods for reducing the levels of these impurities are investigated. Energy consumption and emission models are also developed.IntroductionTitanium dioxide (T1O2) is one of the most commonly used minerals in the chemical manufacturing industry. It has been commercially processed since the early 1900's, and has a wide variety of applications. Pigment is used in paints [1], plastics and paper [2], sunscreen [3], cosmetics and even as a food additive [4]. T1O2 has also been used in photovoltaic cells [5], biomedical devices [6], and in air purification [7]. T1O2 pigment has a refractive index of 2.7, which imparts a high level of opacity (and hence whiteness) to whatever material it is added [8]."

Jan 1, 2012

By Viktor Ashikhin, Pavel Arkhipov, Yurii Zaikov

"Lead alloys electro-winning from chloride melts was under investigation. Impurities concentration in cathode lead is strongly depended on temperature, electrolyte composition, anode current density. The equilibrium electrode potentials of lead-antimony alloys with the various content of electropositive metal in the alloy were investigated in the wide temperature interval. Thermodynamic properties of Pb-Sb alloys containing 20-95 mol% of Pb were studied by EMF method in temperature interval 723-873K in molten mixture of potassium and lead chlorides. Partial and integral thermodynamic characteristics were calculated. Small negative deviations from Raul’s law were found. Anode processes were investigated. The lead dissolution was found to be the only process in certain interval of current densities and electropositive metal content in alloy.IntroductionAt present human race is facing the problem of pollution by lead and its compounds and also the pollution influence on population health all over the world. One of the solution ways is the recycling lead containing technical wastes by ecologically clean technologies.World scientific community pays much attention to the electrolysis of molten salts. The usage of salt mixtures, as electrolytes, discovers new possibilities in the production of metals, metal compounds and alloys. ?????????? of the electrolysis at the temperature 50 - 200 °? above the melting temperature of chosen salt mixture allow to unbreaks processes, that undergo in the pre-electrode layer. The rate of the electrodepositing of elements are much higher than in the water electrolytes. At present there are technologies developed for production of metals (Ta, Nb, Ti, Zr, Hf, Ca, Al, Mg, Be, Li and others) by the electrolysis of the melts. Electrolysis of melts might be used in order to convert different technological formations containing lead and other nonferrous metals, that produced by different enterprises. According to the level of the influence on the living organisms lead is in the group of highly dangerous substances alongside with arsenic, cadmium, mercury, selenium, zinc, etc. Toxity and ability to accumulate in the human organism are two main sources of danger for the human being."

Jan 1, 2008

By E. Yegan Erdem, Fiona M. Doyle, Alyssa A. Maich

"There is an expanding interest in synthesizing high quality magnetic nanoparticles, most notably for biomedical applications. Different processing routes have been reported for the synthesis of magnetite and maghemite. However, some ambiguity remains on their precise chemistry, intermediates, and final products, due to the structural similarity of maghemite and magnetite, and the relative ease of redox transitions during synthesis. Here we present the results of TEM, x-ray and electron diffraction, and SQUID studies aimed at characterizing the products from two different reaction systems, thereby clarifying the reaction chemistry. The first system hydrolyzed aqueous FeCh and FeCb chlorides with ammonia in a micro fluidic reactor at ambient temperature; although the reaction product displayed a uniform distribution, it included non-magnetic goethite and lepidocrocite. If the aqueous solutions contained dissolved oxygen, there appeared to be extensive oxidation of Fe(II). The second system thermally decomposed iron (III) acetylacetonate in ether. In prior studies, oleylamine has been reported to serve as both a reducing agent and capping ligand to control particle characteristics; however, our studies revealed little reduction, with maghemite dominating the reaction products.IntroductionMagnetite and maghemite nanoparticles are co=only used in ferrofluids, in medical applications, and in drug delivery. Superparamagnetic properties, along with low cytotoxicity, colloid stability and bioactive molecule conjugation capability, make these nanomagnets ideal for both in-vitro and in-vivo biomedical applications [1]. One of the major constraints on widespread adoption of nanoparticles for these applications is the amount needed. Typical batch synthesis methods produce polydispersed nanoparticles, which require further size selection procedures to isolate the mono disperse nanoparticle population needed for many applications. In order to maximize the yield of usable particles from a synthesis operation, the reaction conditions must be closely controlled. This requires full knowledge of how the reaction conditions control the various aspects of nanoparticle growth. Many methods have been used to synthesize iron oxides, including sonochemical reactions, mechanochemical synthesis, hydrolysis and thermal decomposition. This work examines the latter two methods, focusing on oxidation and reduction of iron."

Jan 1, 2012

By Shun Fujieda, Shigeru Suzuki, Kozo Shinoda, Tetsuo Fujita

"Dowa's scorodite, synthesized by oxidation of Fe(II) ions in the presence of As(V) ions at atmospheric pressure, was characterized. The scorodite was well crystallized and had a very low solubility. To examine the conditions for stable storage of the scorodite for long periods, experiments with various synthesis and leaching conditions were done. The scorodite had a very low arsenic solubility in sea water. It was estimated in consecutive leaching tests that the arsenic concentration would eventually converge to zero. The prevention of arsenic leaching by adding goethite or ferrihydrite was limited in some cases. Very low toxicity was confirmed by toxicity tests. The investigation results suggest that disposal at a specifically designed well-controlled storage place is preferable for the scorodite whose toxicity had been made sufficiently low. Disposal to an isolated final disposal site with more stringent prevention for the outflow of toxic substances was thought another option.IntroductionArsenic is a considerable environmental concern. A system of technologies for the effective immobilization, storage and final disposal has been sought. Dowa Metals & Mining Co. Ltd. has developed a unique scorodite synthesis method (DMSP®) which works at ambient pressure [1]. The scorodite is precipitated by oxidizing Fe(II) ions in a high-concentration As(V) solution. The scorodite produced in this way does not readily release arsenic because of its high crystallinity. Final disposal is necessary because scorodite currently has no commercial value. A standard method for the final disposal of scorodite has not been established because its long-term stability under various conditions has not been fully examined."

Jan 1, 2012

By Bernd Kopacek

"Nowadays more and more consumers substitute their conventional TV-sets and computer monitors by LCD panels. In the near future huge amounts of LCDs will start coming back to recycling. As LCDs with hazardous mercury backlight lamps are used an appropriate recycling technology has to be implemented.IntroductionLiquid Crystal Displays (LCDs) are widely used in notebooks, organizers, mobile phones, pocket calculators, measuring and control instruments, electronic games, hand-held miniature TVs, audio-video equipment, large signboards, automotive displays and more and more also for PC monitors and TVs.According to a study from Stanford Resources (San Jose, California) the annual value of LCDproducts reached 35 billion EUR in 2002, about 30% of this within the European Union, representing a total area of 2,1 million m2 Liquid Crystal Displays. An annual increase rate of about 15% is estimated for the next years (up to 4,1 million m2 in 2005).As LCDs are already on the market for several years, larger quantities of the more than 2,5 billion LCDs are coming into their End-of-Life stage for treatment. In 2005 this figure will become even more dramatic - 40.000 tons of LCD-modules contained in 2 million tons of waste electrical and electronic equipment (WEEE) or about 30% of total WEEE within EU. An amount which is representing 400 million EUR costs for incineration.Currently the only method used to deal with redundant LCD units is incineration or landfill. Both are expensive and causes emissions into the atmosphere (global warming) respectively water contamination (Class II) and difficulties in biodegradation. Up to now there is no recycling solution for LC-Displays available.As a consequence European Commission requests the disassembly of LCDs with an area bigger than 100 cm2 in the Directive 2002/96/EC of the European Parliament and of the Council on Waste Electrical and Electronic Equipment (WEEE Directive) of February 13, 2003."

Jan 1, 2008

By Tracy Morris, Weldon Read, Luis Navarro

"During the leaching of anodic slimes, tellurium dissolves into the leach liquor together with copper and must be removed before the solution is sent to liberator cells for copper recovery. Prior to the installation of autoclaves, tellurium was precipitated using raw slimes that caused a recirculation of tellurium in the leaching circuit. After autoclaves were installed the old leach tanks were converted into tellurium reactors utilizing copper chips, steam and agitation to form a copper telluride precipitate. Tellurium levels of less than 10 rng/L are achieved in a timely manner.IntroductionThe electrolytic refining of copper consists of an electrolytic cell provided with an anode of impure copper, a cathode of substantially pure copper (starter sheet) and an electrolyte made of copper sulfate and sulfuric acid [1]. When a direct electrical current is passed between the anode and cathode inside the cell, the impure copper anode dissolves in the electrolyte and pure copper is plated onto the cathode. During this operation, many of the impurities are deposited on the bottom of the cell as an anodic slime residue composed of insoluble chemical compounds. Slimes are a major source of rare and precious metals in the copper industry [2-5],In the Amarillo Copper Refinery (ACR), the anodic copper slimes are sent to the Precious Metals department in order to extract and then refine the gold, silver, platinum and palladium from them. The remaining impurities, in the form of a soda slag or copper slag are sent to the Hayden smelter for further processing. Copper telluride is sent to the Selenium/Tellurium department inside the plant for selenium and tellurium recovery. During the leaching process of the anodic slimes, copper, tellurium, and other metal species in the slimes are dissolved into leach liquor that cannot be returned to the tankhouse unless the tellurium concentration is below 10 mg/L."

Jan 1, 2012

By Laurentiu Nastac

"Two advanced control solidification technologies were studied in this article to improve the quality of the cast ingots as well as to control the solidification structure evolution during the plasma arc melting (PAM) processing of Ti-6-4 ingots: (i) electromagnetic stirring (EMS), and (ii) ultrasonic treatment (UST). The developed EMS modeling approach is based on the numerical solution of Maxwell's equations, fluid flow, and heat transfer equations, and mesoscopic modeling of the grain structure. The UST analysis tool is capable to model acoustic streaming and cavitation. It is used in this work to study ingot solidification under the presence of ultrasound. Predictions of the macrostructure, GET formation and primary dendrite arm spacing for PAM Ti-6-4 ingots processed with and without EMS or UST were discussed.1. IntroductionTitanium (Ti) alloys are melted, refined and cast into ingots through plasma arc cold hearth melting (PAM), electron beam cold hearth melting (EBM) and vacuum arc remelting (VAR) for jet engine applications. Process modeling has become a viable tool to optimize the PAM, EBM, and VAR processes. A comprehensive modeling approach to simulate ingot solidification phenomena in primary melting and secondary remelting processes of Ti alloys would include models for macroscopic mass transfer, heat transfer, fluid flow, acoustic, electromagnetic and species transport. The approach should also include microscopic models to predict the evolution of grain structure in solidifying ingots in conjunction with electromagnetic stirring (EMS) and ultrasonic stirring (UST)."

Jan 1, 2012

By Hideyuki Takahashi, Taro Aichi, Kazuyuki Tohji, Makoto Muramatsu, Rie Sato

"There are several ways to condition lead-based alloy anodes for zinc electrowinning: electrochemical treatment, chemical treatment and physical treatment. Two advantages of physical treatments are their productivity and variety. In this report, physical treatments, including blasting with silica, alumina, steel grit and cut zinc wire, were tested. The laboratory tests confirmed there were differences in the formation of anode scales during electrowinning and in the suppression of lead dissolution from the anodes. With an increase in the surface roughness, the misfit between the PbC""2 and the MnC>2 was mitigated and the anchor effect was promoted; these effects resulted in dense Mn oxide scales on the anode.IntroductionZinc is widely used for hot-dip zinc plating and for die casting alloys. As a supplier of materials, we have endeavored to produce zinc that is economical and contains as little impurity as possible. As a result of our efforts, a technology for consistently providing special high-grade (SHG) zinc has been established. However, as seen in the issuance of the Restriction of Hazardous Substances (RoHS) Directive, public awareness of the industrial impact of heavy metals on the environment has been heightened. Increasing efforts to control environmentally sensitive substances will be necessary for our production processes.Electrolytic SHG zinc is produced by electrodeposition in an acidic solution with a Pb-Ag or Pb-Ag-Ca alloy for the anode and an Al alloy for the cathode. Pb alloy anodes are widely used because of their excellent durability; however, they are a source of Pb, which is the main impurity of the product."

Jan 1, 2012

By Aly M. Abdel-Rehim

The present work deals with a study of the mechanical activation of processing of Egyptian monazite by its simultaneous ball-milling and pressure leaching in order to improve the recovery of thorium and lanthanides from monazite. Experiments of simultaneous ball-milling and alkaline leaching of monazite contrary to autoclave leaching were carried out in stainless steel ball-mills of cylindrical shape under different conditions of temperature, pressure, time and alkali amount and strength. The ball-mills were heated and mechanically rotated in an electric furnace by means of roll mechanism. The effective rotation speed was fixed at 130 rpm in all tests. The charge of steel balls of different diameters was equivalent to 45% of the total mill volume. Monazite was charged in ball-mill without preliminary grinding. It is found that high rate of monazite leaching by ball-milling leaching method is achieved at lower temperature, shorter time and lower expense of alkali than in autoclaves. The results obtained show that complete recovery of thorium and lanthanides from monazite (99.8%) by simultaneous ball milling and alkaline leaching is attained at 140°C within 2 h. It is concluded that processing of monazite by its simultaneous ball-milling and leaching is mechanically activated and accelerated as a result of grinding action of steel balls that caused the continuous removal of the hydroxide product from reacting particle surfaces. This leads to the exposing of fresh and activated monazite particles surfaces to alkali leach solution and consequently the acceleration of the reaction of monazite processing.

Jan 1, 2006

By Ledjane Barreto, Tulio Flávio Accioly de Lima e Moura, Wilson Acchar, Antonio Carlos Silva da Costal

"Clays are common ingredients in pharmaceutical products both as exclplents and active substances. Clay minerals are naturally cationic exchangers and they may undergo ion exchange with basic drugs in solution. Smectites, and montmorillonite have been studied due their high cation exchange capacity as compared to other silicates. Recently a patented study reports the use of attapulgite as the encapsulating agents both for the protecting the active substance and modulating release into the body. Some clays such as kaolinite, smectites, talc, etc are also used as dermatological protectors. Sepiolite and smectites have the ability to form complexes with organic compounds with absorb ultra-violet radiation, enabling them to be used in sun screens with protection factors. The objective of this work is to characterize the attapulgite in order to study the potential use of this clay material in the human health.IntroductionSince the begimling of time, nature has served humanity as a source of various raw materials. Among these, clays such as kaolinite and ilitte are common ingredients in the tile production. Recently, special clay materials have been investigated in order to identifY new potential uses of these class of materials. Clay materials are natural raw material and have excellent properties such as low toxicity, good biocompatibility, making them a good material to be used in biological applications. Attapulgite (paligorskite) and sepiolite is so called special clays. These special clay materials are very sin1ilar and have a great potential to be used in some technological areas due their special catalytic, sorptive and colloidal-rheological properties [1-8]. Recently some works have reported the use of these special clays materials for many applications such as drug delivery, wound dressing, oil absorbent, pesticides, fertilizers [9-12]. Brazil has a significant reserve of attapulgite located in Piaui state, making the study of the potential of this mineral in special areas, very attractive. Attapulgite is classified a fibrous alluminous silicate material and shows the presence of micro pores and channels, fine particle size and high surface area making this material a good candidate alternative material to be used in many industrial applications [6,8,9,11,12]. The objective of this work is to characterize the physical and microstructure of attapulgite."

Jan 1, 2012

"Silver is traditionally recovered in base metal smelters (lead and copper), or as a by-product of other precious metals (gold and/or PGM's). This paper presents the results of non-conventional techniques to recover silver from complex materials. The PLATSOL® process has been developed to recover, in one step and without the use of cyanide, base metals (copper, cobalt, nickel) and precious metals (gold, PGM's) from sulphide concentrates too low in grade to enter the mainstream extraction processes. Silver is only partially recovered in solution with gold and the PGM's during the PLATSOL® process. However, the silver minerals are transformed into silver chloride, which can then be recovered from the PLATSOL® residue using conventional techniques. Some South American silver concentrates contain levels of impurity (mostly arsenic) so elevated that the penalties incurred significantly affect the process economics. The present results have shown that a low temperature calcination process transforms the concentrate into a product well suited for traditional recovery treatments. Metallurgical details will be provided, as well as the results of mineralogical studies that helped clarify the process mechanisms.IntroductionSilver occurrences in nature are very diversified, and, therefore, primary silver is produced as a by-product of many base metal and precious metal operations [1], as well as a co-product of most gold ores. However, difficulties can arise when high temperature processes are used for refractory gold ores or copper concentrates, or when the silver concentrate contains impurity elements such as arsenic that trigger high penalties."

Jan 1, 2012

By Vasil Kopaleishvili

The bainitic Fe-C-Si alloys with optimum content of retained austenite serve as ?containers? for storing of hydrogen. Both the vacancies of fcc lattice and the possibility of forming hydrides of silicon and other alloying elements will be used. The idea is based on our scientific hypothesis. There is the silicon threshold (Si=0,50%) in "Fe-Si" system and Fe-C bainitic alloys, above which it causes self-organized phenomena: sudden increase of hydrogen solubility and amount of retained austenite in the alloy after ??ß transformation, formation of two supersaturated solid solutions <a??r>, "rejuvenation? and its reverse process. Rapprochement of iron atoms when Si=0,50%, causes appearance of new covalent forces where uncompensated electrons of 3d-subshell are involved and it provokes synergetic phenomena. They ?free? silicon atoms from the previous bonds. After that silicon itself becomes a getter of hydrogen using vacancies (14) of 3P2(6)d0(10) subshell and it results in sudden increase of hydrogen solubility in metal. Simultaneously sudden decrease of iron activity takes place. That in its turn ?releases? the carbon. Thus, its redistribution, controlling the bainitic transformation, is hastened. It stipulates for creation of ?brittle bainite" B[a(C,H)+?r(C,H)] after ??ß transformation. While weathering of metal, "rejuvenating", hydrogen diffuses in ?islets? of retained austenite and ?relaxed bainite? (B[(C)+?r(C,H+H)]) is obtained. When heating austenite ?(C,H) is obtained, and after cooling ?brittle bainite? is obtained, etc. Presented scientific hypothesis explains the available experimental facts ("rejuvenation? and its reverse process, graphitization, weldability, forming of flakes, reaching high strength, etc.) in a new manner, as well as, gives real opportunity for creating of new trends in many fields, e.g. iron based HAA. Provisional data having been obtained are encouraging.

Jan 1, 2006

By Cristiän Vargas, Jaime Simpson, Gerardo Cifuentes

"This paper presents a new process for the precipitation of Sb and Bi present in copper refinery electrolytes in the presence of Pb02 (Chilean Patent No. 45,037). To establish the conditions under which the precipitating compounds form, it was necessary to evaluate the amount of PbCh consumed, antimony extraction efficiency, precipitate stability, reaction kinetics, diffraction analysis and X-ray fluorescence, separation of size, plus observation of the precipitates in the electron microscope. Preliminary tests were carried with synthetic copper refinery electrolyte, and then the final testing was done with electrolytes from Chilean refineries. This process provides a real alternative for the treatment of copper refinery electrolytes for the control of Sb and Bi in solution; it is very simple to operate and is low cost compared with competing processes.Introduction.A high quality copper cathode implies a cathode free of impurities. The electrorefining process seeks to eliminate these impurities from the copper anode (99.5% purity) by its dissolution in an acid electrolyte using chemical and electrochemical reactions. As a result of this process, a cathode (99.99% purity) is obtained. If the concentration of impurities in the electrolyte, from the dissolved anodes, begins to increase; particularly if the antimony concentration in the electrolyte increases up 500 ppm, the formation of floating slimes which are a major cause of contamination of the cathode is favoured. The most important impurities from the point of view of their effect on the quality of the cathode copper, are Ag, As, Sb, Bi, Pb, Se and Te. Silver is necessary for the control of Se and Te. To control all of these impurities, it is necessary to establish different methods or parameters of control in copper electrorefining. These parameters are anode composition, additives, purification of the electrolyte, current density, acidity, etc."

Jan 1, 2012

By David G. Dixon, Maziar Eghbalnia

"Gold and silver nanoparticles (NPs) were deposited on pyrite at ambient temperature from colloidal solutions prepared by reduction of hydrogen tetrachloroaurate or silver nitrate by sodium sulfide or sodium tetrahydridoborate. The nanoparticles were characterized using Ultraviolet-Visible (UV-Vis) spectroscopy and the experimental spectra were fitted using Mie - Gans modeling. The modified pyrite was investigated using Electrochemical Impedance Spectroscopy (EIS). Electrodes were prepared from both natural and modified pyrite samples and were modeled using an equivalent circuit (EC) based on the EIS data. The comparison of the results revealed a decrease in charge transfer resistance for the ferric ferrous redox couple associated with the modified pyrite. From this behavior it is concluded that the electronic transport between the nanoparticles and the electrode surface over distances in nanometer scale is enhanced. Nanoparticles below a certain size act as quantum dots due to electronic confmement. Decreased charged transfer resistance at the nanometer scale may be caused by electron transport through tunneling mechanism via quantum dots.IntroductionIn recent years, considerable attention has been focused on the synthesis and study of Metal nanoparticles due to their potential applications in the fields of physics, chemistry, biology, medicine, material science and their interdisciplinary fields[!]. When material is nano-sized, the physical properties deviate markedly from those of bulk material, however, this effect is highly dependent on the particle size, interparticle distance, and morphology of the nanoparticles [2].An extremely small region of space defmed in a semiconductor material in order of nanometers is called a quantum dot, a term coined by Reed [3]. The three dimensional confinement of quantum dots can change properties of the excitons in comparison to free excitons in a bulk material [4]. Nanoparticles behave electronically as zero-dimensional (restricted in all three dimensions) quantum dots when the de Broglie wavelength of the valence electrons and the particle are in the same size range.As Reed [3] explains electrons confined in a plane have no freedom to move the third dimension. Those confined in a quantum wire are only free to move in one dimension, and those confined in a quantum dot are not free in to move in any dimension. An electron inside a cube of material IO nm on a side is confined to a point."

Jan 1, 2012

By Toshiki Kabutomori

In fuel cell powered automobiles, hydrogen is required to be stored in materials that have a hydrogen storage density of over 4 mass%; further, these materials should be capable of supplying hydrogen by using the waste heat from a fuel cell, which is at a temperature of 373 K, in order to match the mileage of gasoline-powered vehicles. A Ti-Cr-V alloy, which exhibits a BCC structure and forms a solid solution, is a promising candidate for onboard hydrogen storage materials. Although it has a large hydrogen storage capacity of over 3.9 mass%, the rechargeable hydrogen capacity is limited to approximately 2.6 mass%. In this study, the effects of fine pulverization of the alloy on PCT (hydrogen pressure-composition-isotherm) characteristics were investigated in order to improve the rechargeable hydrogen storage capacity of the alloy. From the PCT measurements of the finely pulverized samples of the alloy, a plateau in the absorption curve was observed to begin at a hydrogen concentration of 0.5 mass%; further, a rechargeable hydrogen storage capacity of 3.3 mass% was obtained. This was greater than that obtained from the sample that was not finely pulverized, i.e., 2.5 mass%. However, the plateau width in the desorption curve was 2.5 mass%, which was the same as that observed for the sample that was not finely pulverized. The increase in the rechargeable hydrogen capacity during absorption is attributed to the precipitation of the -hydride phase (MH~2) directly from the metal phase (phase). The precipitation of the phase (MH~0.5), which should be formed in low hydrogen concentrations, is suppressed as a result of a possible reduction in the internal defects such as dislocations, vacancies, and grain boundaries by fine pulverization and annealing of the alloy.

Jan 1, 2006

By Kurt Svens

"As zinc consumption is gradually increasing all the time in the world, many zinc plants are looking for possible expansions. As the sulphuric acid market as well as the fertilizer market in many areas is saturated, the costs for the roasting-acid plant section of the zinc plant will create problems when making feasibility calculations for possible expansions. For solving the customers' situation, two proven zinc concentrate direct leaching technologies are available. A third one, which is possible, does not have any industrially proven applications in the zinc area.IntroductionTime to time, the zinc plants in the world scrutinize their operations with respect to their cost efficiency, the total zinc recovery and the near-by or far-away consumer markets, especially the for zinc and sulphuric acid. Their preliminary profitability calculations can show that a possible total expansion is not economical, when they are looking to expand the whole roasting/acid plant - leaching - solution purification - electrowinning - casting route, as the possible market price for the sulphuric acid is low or the sulphuric acid market is too far away. Based on these facts, their economical study often indicates that implementing a zinc concentrate direct leaching option could be more favourable. Regarding this situation, several aspects concerning three alternative direct leaching methods will be discussed, of which pressure leaching and the atmospheric leaching processes have several industrial applications in the zinc industry, as the ultrafine grinding - conventional leaching process at present has none. As iron is also dissolved during zinc concentrate direct leaching, iron removal processes generally used in the zinc industry are additionally discussed below."

Jan 1, 2012