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By Xiaoming Huaa

The effect of the anodic polarization on the composition and morphology of the surface layer formed on chalcopyrite during ammonia–ammonium chloride leaching was investigated. The anodic polarization on the chalcopyrite electrode was used for oxidation and dissolution of chalcopyrite, and the resulting oxidized layers were characterized by XPS, SEM and optical microscopy. The results show that oxide layers exist on the chalcopyrite surface with or without any anodic polarization in the leaching solution at ambient atmosphere. However, the composition and morphology of the layers are strongly depended on the extent of polarization. The distribution of FeOOH and Fe2O3 within the oxidized layer was inhomogeneous for the sample at the open circuit potential (OCP). The composition and morphology of the oxidized layers which were formed at anodic potentials lower than 0.3 V versus SCE were similar to those of the chalcopyrite at the OCP. At anodic potentials above 0.4 V, the oxidized layers contained many cracks, and they were fragile and exfoliated. Furthermore, the sulfide had been oxidized to sulfur species with higher oxidation states. The oxidation of the chalcopyrite seemed to undergo a cyclically oxidative process that suggested growth and spallation of oxidation layers on chalcopyrite in a layer-by-layer sequence.

By George Nekoksa

The biofilm activity monitoring probes measure applied current during intermittent short-term polarization of the probe electrodes and current or potential between the electrodes after removal of the polarization. The probe polarization mimics conditions at crevices, welds and inclusions where the biofilm activity and microbially influenced corrosion usually concentrate. Monitoring of AC resistance between the probe electrodes can provide infornation about the thickness of deposits.

Jan 1, 1994

By Christian Redl

"The Lattice Boltzmann Method (LBM) solves fluid dynamics problems based on a discrete mesoscopic approach. It is based on the Lattice Boltzmann equation which is a special discretisation of the continuous Boltzmann equation. Its principle advantage is that it can handle complex physical phenomena (like interaction between different components and surface effects), complicated boundary and initial conditions very well, free from many gridding and stability constraints that plague conventional numerical methods used for fluid flow simulations. Complex structures like porous media can be resolved directly. The LBM algorithm has a simple structure and acts locally, which is favourable for parallel computing. Its potential for metallurgical process simulation is demonstrated in the present study which is concerned with the simulation of the fluid flow in a copper winning electrolysis cell. The electrolyte is modelled as the carrier fluid and the oxygen is considered via a so called active scalar equation. The modelling of buoancy, momentum exchange and the free surface requires special effort. The results of the simulation are validated against experimental data obtained by Laser-Doppler-Anemometry. Despite the simplifications made, good agreement between the simulation and the experiments was found.IntroductionThe hydrodynamics in an electrometallurgical cell is a complex, highly non-linear phenomenon. It includes the simulation of a two component system with high density ratio, gravity driven flow and a free surface. A general solution to this problem is currently unknown.The flow field is a result of the combination of various hydrodynamic effects [18]. Metal deposition at the cathode yields in a decrease in the ion concentration, which reduces the density of the electrolyte. At the anode molecular oxygen is formed as a consequence of the oxidation of water molecules. The oxygen is solved in the electrolyte and again the electrolyte density is decreased. Both effects lead to a free upwards directed convective flow, refered to as natural convection."

Jan 1, 2001

By Varadarajan Seshadri

The performance of mould fluxes in satisfying its quality requirements can have a significant effect on the efficiency of the continuous casting process and on the surface quality of the products. This performance is affected by various parameters including the characteristics of the mould fluxes, the quality of the steel being cast and the operational conditions of the caster. The extremely complex relationships involving the parameters mentioned above make it very difficult to have simple criteria for selecting mould fluxes for casting a certain grade of steel in a continuous casting machine. These difficulties led steelmakers and mould flux suppliers to select mould fluxes based mainly on plant trials. In the present work, a software to help in the analysis and development of mould fluxes for continuous casting was developed_ This software includes several models for prediction of mould flux viscosity and consumption. A mathematical model was also used to predict the heat flux through the mould flux. The proposed methodology was applied to continuous casting of crack sensitive steels_ Some of the results given by this software are presented, discussed and compared to plant data.

Jan 1, 2003

By B. Mishra

Calcium and lithium gallides have been synthesized by powder metallurgy techniques in the stoichiometries that can be used as reduction alloys for the Rocky Flats Plant Salt-Scrub (SS) process. The SS process is performed to recover valuable metals from salts generated in the electrorefining and the molten salt extraction processes. Combustion synthesis has been optimized for variable heating rates up to the reaction ignition temperature and for green densities of the powder compacts in terms of the ignition temperature and the exothermic heating of the product in an effort to develop LiGa and CaGaz alloys. The problems arising from the melting point and density differences of calcium, lithium and gallium have also been studied. The SS alloy compositions were produced by mixing, pressing and sintering the metal-powders. The efficiency of the intermetallic alloy, Ca-17 wt. pct. Ga, as a reductant and the effect of gallium on salt clean- up has been discussed. Measurement of actinide recovery has been studied with cerium as the surrogate for the actinide metal. The development of an alloy for SS reduces a major contaminated waste disposal problem besides recovering the valuable reactive metal.

Jan 1, 1993

By S. V. Subramanian

The tool material and the machine design for high speed machining are well advanced over the last decade but the steel design has lagged behind. The paper examines the design of steel in order to control the sliding tribology for high speed machining under dry machining conditions. In high speed machining of steel, accelerated chemical wear of the tool occurs once atomic contact is established at the tool-chip interface, resulting in poor tool life even with high performance tools such as cubic boron nitride. Recent research has confirmed the occurrence of nanocrystalline grains in the interfacial layer of the chip at the tool-chip contact. The volume percentage of grain boundary is increased significantly (10 to 30%) as the nanocrystalline grain size is decreased well below 30 nm. The solubility of tool material into the nanocrystalline grain boundary is two or three orders of magnitude greater than in the crystal lattice. Further the kinetics of diffusion in the grain boundary is seven or eight orders of magnitude greater than in the crystal lattice. Enhanced nanocrystalline grain boundary diffusion occurring in the interfacial layer at the tool-chip contact causes the accelerated chemical wear. Significant improvement in tool life could be achieved by engineering glassy oxide inclusions in steel, designed to self-lubricate the tool-chip interface in-situ at higher cutting speeds. Thus the control of sliding tribological condition at the tool-chip interface is key to suppress nanocrystalline layer formation at the tool-chip contact and hence prevent accelerated chemical tool wear. Sulfide inclusions are designed essentially to promote chip fracture. In addition, sulfide inclusions are designed to act as a diffusion barrier at the tool-chip interface. The application of inclusion engineering concepts to enhance the tool life in high speed machining will be demonstrated with a suitable case history.

Jan 1, 2006

By Thomas Niehoff

Many industrial processes require energy. Energy is required for melting or heating purposes. The heat can be generated by electrical heating or combustion/oxidation of hydrocarbons. Oxygen supports the combustion process. Oxygen is naturally contained in air with about 21 vol.-percent. The use of technical oxygen will allow an increase to the natural oxygen concentration of combustion air. Altering the combustion process by increasing the oxygen content has various effects. These effects are described and analyzed with regard to heat transfer, emissions and energy consumption. Industrial processes requiring oxyfuel are described and discussed regarding energy aspects.

Jan 1, 2008

By V. I. Lakshmanan

Whilst the prices of metals in nominal terms have largely remained static over the past forty years, in real terms, the primary metals industry receives very much less today for its products than in the past. Yet, it has largely managed to remain competitive, despite the fact that ore reserves are not only diminishing, but are of lower grade and higher complexity, and that there are much greater pressures on companies to be good environmental stewards. This paper examines how hydrometallurgical processing has shown itself to be highly innovative in order to remain viable both economically and environmentally. Aspects of process chemistry are discussed, and the lessons to be learned from having a good understanding of this chemistry are highlighted with reference to a number of case histories such as HPAL for nickel laterites, the Avmin/Chambishi Cosac Project, use of chloride chemistry for titanium extraction, and plant effluent treatment and recycle.

Jan 1, 2003

By Kinya Atsumi, Kanjana Khunathai, Hisaya Kato, Hidetka Kawakita, Keisuke Ohto, Katsutoshi Inoue

"Crosslinked microalgae were prepared from the residue generated in the production of biofuel, by crosslinking-condensation in concentrated sulfuric acid. These microalgae were tested for adsorption of various metal ions in hydrochloric acid medium. The crosslinked microalgae exhibited high selectivity for Au(III) over other precious and base metal ions. From an isotherm experiment, the maximum adsorption capacity was evaluated to be 3.25 mol/kg of dry gel for Au(III) which was many times higher than that of the original microalgae residue. SEM and X-ray diffraction confirmed the formation of metallic gold particles, suggesting the occurrence of a redox reaction between surface functional groups on the gel surface and trivalent gold ion.IntroductionSubstantial quantities of precious metals are being used by the electronic industry because of their excellent electrical conductivity and resistance to corrosion. In recent years, recovery of precious metals from secondary sources such as electronic scrap [1,2 ], and leach liquors is being favored because of environmental concerns. Of course, recovery is only practical, if its cost is lower than the value of the metals (gold, platinum and palladium) recovered.Traditional methods of separation and refining do not fulfill this requirement. In order to overcome this problem, attempts have been made in recent years to develop new processes including total leaching in hydrochloric acid containing chlorine gas or hypochlorite, followed by solvent extraction and ion exchange [3]. In the new processes, new solvent extraction reagents or ion exchange resins with high selectivity and high loading capacity are used to simplify the process and to reduce the operating costs."

Jan 1, 2011

By Jong Hyeon Lee, Go-Gi Lee, Chang-Kyu Lee, Hong Youl Ryu, Sung-Koo Jo

This study deals with research on the reduction process of neodymium oxide by molten salt electrowinning. Neodymium fluoride and lithium fluoride electrolyte were used for feed stock of electrolyte and neodymium oxide was added as precursor. Cell current was confirmed that cell potential was applied as constant potential of 4.5V. Argon gas injection into the electrolyte was carried out to confirm convection effect on current efficiency. Applied current was gradually decreased without argon flow, but applied current was kept within a certain range with argon flow in electrolyte.

Jan 1, 2015

By M. Cassir

"The unique properties of molten carbonates offer a large scope of applications in the field of energy. In effect, these molten salts are in the center of chemical and electrochemical reactions involving carbon and carbonaceous species, carbon dioxide and carbon monoxide, significant for energy generation or even for the production of fuels. Moreover, such media have also an oxidative character; they dissolve molecular oxygen and oxygen reduced species, O 2-, O22- and hypothetically o-, which may have an important role in waste treatments, homogeneous catalysis and synthesis of oxides. In this presentation, an overview will be given on the principal physicochemical properties of molten carbonates, before focusing on their main known application, the molten carbonate fuel cell (MCFC). Progress in other new fuel cells applications will also be analyzed, such as direct carbon fuel cell (DCFC), hybrid carbon fuel cell (HDCFC) and composite high-temperature fuel cells combining the features of MCFC and solid oxide fuel cell (SOFC). Afterwards, membranes for the separation and capture of C02 will be reviewed. Finally, other topics, as the oxidative coupling of methane in molten carbonates, will be briefly mentioned.IntroductionIn the thirty past years, the molten carbonate science and advances have been mainly dedicated to the understanding and optimization of the molten carbonate fuel cell (MCFC), which is still a major issue in the heart of a new vision of energy development. More recently, new topics related to other kinds of fuel cells (DCFC, composite SOFC/MCFC systems) and C02 capture have emerged and are concentrating important research and technological efforts. Moreover, new fields of implementation, related to molten carbonates, are also present: geology, glasses, production of nanocarbon particles etc. Considering other areas where this molten phase plays a major role, such as catalysis, waste destruction, surface treatment, it can be confirmed that the field of molten carbonates is very rich and offers many opportunities for fundamental science and competitive applications. Whatever their specific application, molten carbonates activity is associated to more efficient energy systems with low production of C02 and, in a prospective sense, to non-polluting energy using the value of C02. A recent event, the International Workshop on Molten Carbonates & Related Topics, IWMC201 I, held in Paris in 2011 , have put in evidence the importance to improve and exploit this investigation and technological domain."

Jan 1, 2012

By S. H. Castro

The El Teniente molybdenite plant (Chile), with a nominal capacity of 3,200 tpd of bulk Cu-Mo concentrate, produced approximately 3,385 metric tonnes of Mo during 1998 by using the phosphate Nokes process (LR-744 reagent). This is the only Chilean moly plant which traditionally has depressed copper and iron sulfides with LR 744 reagent, which is a hydrolysis product of P2S5 and NaOH. El Teniente's ore Mo grade is 0.02%Mo and is concentrated to 0.45%-0.50% Mo in bulk Cu-Mo flotation. Subsequently, molybdenite is floated by selective flotation to depress Cu and Fe sulfides, such as chalcopyrite, bornite, digenite and pyrite, to produce typically a 49%-50%Mo molybdenite concentrate. An optimisation program during the last two years was undertaken to improve molybdenite recoveries. Current molybdenite plant technology at El Teniente and use of phosphate Nokes in the process process is reported. Use of phosphate Nokes reagent has increased average Mo recovery from 70.5% in 1977 to a mean 74.7% for the first 4 months of 1999. The global Mo recovery, including bulk flotation, incresed from 42.3% in 1997 to 46.8% in 1998, with a projection of 55.5% for 1999. Mo production per year has increased from 3,181 tons in 1997 to 3,385 tons in 1998 and a projected 4,000 tons for 1999.

Jan 1, 1999

By J. Riccardi

Copper refineries use massive copper castings as moulds into which impure molten copper from the reverberatory furnace is poured to form anodes for further electrolytic refining. To facilitate removal of the copper anodes from the mould and to prolong the life of the mould itself, it is traditional to spray the mould surface prior to each use with a slurry of baryte in water. This slurry application leads to poor housekeeping, operating costs are escalated by the cost of the slurry, and additional problems in the subsequent refining process are experienced due to carry-over of excess undesirable baryte powder. A one-time application of a diffused layer of aluminum to the surface of the copper mould prior to putting the mould into service has been found to provide extended mould life and facilitate anode removal, as well as reducing baryte consumption; thereby reducing operating costs at both the anode manufacturing and refining stages.

Jan 1, 1999

By David J. Roha

"The harsh environment of the Carbothermic Aluminum process makes necessary numerical modeling as a means of process visualization and understanding. A brief survey of the various numerical models, with emphasis on CFD, applied in the development of the process is presented.IntroductionThe environment of the Alcoa Carbothermic reactor is necessarily a harsh one, with temperatures approaching 2100 °C and plenty of reactive dust and vapors. As such, it is difficult to directly observe what is actually taking place. Thermocouples can last for a few minutes but are eventually destroyed. The openings to optical pyrometers become occluded with dust and condensation. Graphite sheathing embrittles, reacts away or becomes clogged with condensate. Dip-samples on steel rods are routinely taken, but their interpretation is often unclear.Those measurements that can be reliably taken are invaluable, but often do not provide a complete picture. Therefore from the very inception of the project both physical and computer based models have played an important role. Modeling provides an intuitive understanding of the processes that might be taking place and in very many cases approach quantitative prediction. I will briefly touch upon computer-based modeling performed at Alcoa over 12 years of the Carbothermic project, with special emphasis on CFD. The explanation of physical models is perhaps best left for those with the greatest familiarity with them"

Jan 1, 2012

By J. S. Lee

A new high performance adsorbent is synthesized by the sol-gel method and applied to the removal of cadmium and mercury ions from aqueous solutions. Adsorbents based on metal oxides have been developed by immobilizing chelating molecules on the surface of the existing metal oxide networks and show ability for selective metal extraction from aqueous solutions. However, efficiencies of such adsorbents are limited due to low ligand density, and difficulty in pore accessibility. These difficulties are circumvented by synthesizing adsorbents using the sol-gel technique. In one example to be discussed, the sol-precursor possesses an organic moiety that binds cadmium, mercury, and copper ions. The capacities of 1.98mmol Cd(II-/gm and 6.40 mmol Hg/gm of this adsorbent are considerably higher than those of adsorbents prepared by the ligand immobilization technique. The scope of this paper is to discuss the development of the new adsorbent and its applications for cadmium and mercury removal from aqueous solutions.

Jan 1, 1999

By Ullrich Kammer

Metaleurop's secondary lead smelter at Oker produces 60.000 mtpy of lead and lead alloys. More than 8O2 % of the raw materials are spent lead acid batteries. The other 2O2 % consists of drosses, ashes, scrap lead, type metal, sludges, etc., and is processed in a short rotary furnace (SRF). Also, industrial batteries not fitting in the battery scrap treatment plant are processed in the SRF provided with gas/oxygen-burner. Till Sept. 199O2, a soda ash slag was used in the SRF-smelting similar to the rotary kiln-smelting at Oker. Facing the future problems of handling and dumping soda ash slag, Harz-Metall GmbH has improved SRF-smelting with a non¬hazardous slag, insoluble in water, easy to dump and cheap in fluxes. This slag is based on a CaO-SiO2 -Fe0-type. Aim of the slag smelting is to be within the temperature range of 2 1100° and 1200°C - the eutectic line of Olivine in the corresponding ternary system. Since Sept. 199O2 Harz-Metall GmbH has operated the SRF with an "Olivine-type slag" with good results. Although the material is a "leady" slag. HMG is optimistic of using it as a filling material for construction purposes.

Jan 1, 1993

By David G. Dixon, Ahmad Ghahremaninezhad, Edouard Asselin

"In this study pertaining to the electrochemistry of chalcopyrite, the active/passive behavior of a chalcopyrite electrode in 0.5M sulfuric acid solution was investigated. Potentiostatic and potentiodynamic polarization and multi-cyclic voltanunetry were conducted to analyze the electrodissolution parameters of the electrode.The potentiodynamic and potentiostatic polarizations of chalcopyrite revealed the formation of a passive film on the surface of chalcopyrite. From the potentiostatic study in the passive potential region, a decrease in the dissolution current density by increasing the potential was observed. From this, it was concluded that the passive film is an n-type semiconductor and cation interstitial defects or anion vacancies are the charge carriers. From multi-cyclic voltammetry studies, four cathodic peaks at - 0.37, 0.30, -0.10 and-0.20 YsHE were detected on the surface of a passivated chalcopyrite electrode. The cathodic peaks at 0.37 and 0.30 V were connected to ferric to ferrous reduction and copper sulfide formation, respectively. The peaks at -0.10 and - 0.20 were related to chalcopyrite reduction. The products of the chalcopyrite reduction reactions were suggested to be Cu2S, Cu9fesS16 and Cu5feS4 and evolution of hydrogen sulfide gas (H2S).IntroductionChalcopyrite is the most abundant copper bearing mineral in the world and its dissolution behavior represents the most important technological consideration in the hydrometallurgical extraction of copper [I]. Since the current pyrometallurgical methods for copper extraction from chalcopyrite have environmental issues, many studies have considered the leaching and dissolution of CuFeS2 in different aqueous media [2-5]. The main problem associated with leaching processes is the slow dissolution rate of the mineral [6]. During the dissolution process, increasing the potential of the chalcopyrite in the anodic direction will cause the formation of surface layers which hinder the dissolution rate of the mineral [7]. The precise composition of the layers is in dispute. Previous studies have concluded that these layers could be sulfur [8-9], precipitated iron compounds [8], a solid electrolyte interphase (SEI) - which slows the rate of electron transfer- [10], a metal deficient sulfide [ll], or polysulfidic in nature [12-13]. In order to increase the leaching kinetics of chalcopyrite, the characterization of the layers formed during dissolution is essential and electrochemical methods are important to this end. Studies by Biegler [14] show nucleation and growth of a thin two-dimensional sulfide phase on the surface of chalcopyrite during the exposure of a polished sample in HzS04 solution or air. More studies by Biegler and Swift [15] have shown evidence for nucleation and growth of a 3-dimensional phase at low anodic potentials (around 200 mV vs. OCP). The current-time behavior of the dissolution process in this potential area has the characteristics of expansion and overlap of localized dissolution centers."

Jan 1, 2012

By Sung-Joo Lee, Gi-Chon Han, Nam-Il Um, Hee-Chan Cho

"In Korea, almost all of bottom ash produced by coal power plants is disposed of in ash ponds. Ash storage areas comprise more than 80% of most coal power plant sites. This disposal method is causing environmental problems and a managerial burden for plant operators. In this study, investigations to develop a beneficiation process for separating coal pond ash into various products were undertaken. To improve efficiency of the separation, coal ash was separated by sizes and each size fraction was subject to various beneficiation processes. The separation process used were flotation (-200 mesh size), hindered settling (16x200) and tabling (16x200 and 8x16 mesh). The results showed that various marketable products, such as lightweight aggregate, sand, high-carbon fuel, could be recovered from coal pond ash using simple physical separation techniques.IntroductionDue to the increased use of coals every year, about fifty million ton of coals were used in 2007 alone. As a result, about 6 million tons of coal ash were generated. In Korea, the coal bottom ash is classified as a general industrial waste and is usually disposed of in ash ponds. The costs for this disposal method continue to increase due to rising costs of site management and development and more strict environmental regulation. Therefore, utilities are constantly looking for ways to increase utilization of coal ash. In this study, various beneficiation processes were evaluated to examine the possibility of separating coal pond ash into various products which can be used as aggregates and high-carbon fuel."

Jan 1, 2008

By A. V. Tarasov

The insufficient scientific and technical level of a number of operations in the nonferrous metals industry encourages development of new processes and equipment, including smelting in liquid bath, flame-type sparged smelting unit for combined processes, electrothermal process with the use of alternating current (PDF furnace), electrothermal processing of complex raw materials and intermediate products at nonferrous metallurgical plants, etc. One of the most important aspects for development of new processes and equipment in the Gintsvetmet Institute is their environmental safety. Special attention is paid to environmental protection measures, which is also of important economic and social significance. This refers also to a complete extent to processing of reserves of man-made raw materials and wastes available at the existing operations with the use of innovative techniques ensuring not only resource conservation and environmental protection, but also abatement of negative impact on the nature due to accumulated industrial and domestic waste, reclamation of the land used for waste disposal and recycling of nonferrous metals. Technologies and equipment developed in the Gintsvetmet Institute and based on electrothermal processes determine the prospects for ensuring more integrated usage of ores and man-made raw materials.

Jan 1, 2006

By Tim Robinson, Georges Houlachi, Michael Moats, Marco Ginatta, Michael Free, David Creber, Neale Neelameggham, George Holywell

"Electrolytic processing is used commercially to recover and/or refine metals such as aluminum, copper, magnesium, nickel, and zinc. There are also new and exciting opportunities to utilize electrometallurgy in the production of titanium, lead, and other metals. This paper reviews some of the main technologies that are used to produce and refine metals as well as some of the recent advances and future directions the electrometallurgy industry may implement to meet the challenges faced now as well as those that are likely to be faced in the future.IntroductionElectrolytic processing is used commercially to recover and/or refine metals that include large scale production for metals such as aluminum, copper, magnesium, nickel, and zinc as well as small scale production for metals such as gold and silver. There are also new and exciting opportunities to utilize electrometallurgy in the production of titanium, lead, and other metals. This paper will focus only on electrometallurgical processing of metals with relatively large production markets."

Jan 1, 2012