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By Jafar Safarian

A new kinetic modelling technique has been applied to study the rate of MnO reduction from slags by dissolved carbon in liquid iron. Based on a consideration of the fundamental reaction kinetics, a general differential equation for the slag reduction process has been formulated, which then is solved analytically for certain special cases. By re-writing the solutions in a dimensionless form the poorly known kinetic constants are eliminated, which makes the model both flexible and applicable to a wide range of experimental conditions. For example, changes in process parameters such as temperature, metal composition, slag composition, gas composition can readily be captured along with variations in the crucible geometry. Based on a comparison with a series of experimental reduction curves being reported in the literature, it is concluded that the predictive power of the model is surprisingly good, yielding outputs that are both reliable and physically reasonable. An attractive feature of the model is that it provides an alternative way of calculating the activation energies from experimental reductions curves. For example, it suggests that the activation energy for the reduction of MnO by dissolved carbon in liquid iron is about 90 kJ/mol, which is different from the previously reported activation energies. The model also suggests that the crucible geometry, which affects both slag the volume and the resulting slag/metal interfacial area, has a significant influence on the overall reduction kinetics. This design parameter is a key to further optimisation of the process on an industrial scale.

Jan 1, 2006

By Jannie S. J. van Deventer

Geopolymers are novel engineering materials with the potential to play a highly significant role in the transformation of the construction materials and building products industry in the push towards sustainable development. These materials are formed by activation of industrial aluminosilicate waste materials such as coal ash or blast furnace slag with alkaline solutions. Geopolymers derived from coal ash can exhibit superior mechanical properties and chemical stability when compared to ordinary Portland cement (OPC). The use of waste-based geopolymers can also result in significant (up to 90%) reduction in carbon dioxide emissions when used in cement replacement applications. In addition to the formation of conventional pre-cast products, these high performance mineral binders are ideally suited to use in the encapsulation of mine tailings, immobilization of heavy metals and back-filling of mines due to their chemical stability and resistance to acid attack. A key attribute of geopolymer technology is the robustness and versatility of the manufacturing process; it enables products to be tailor-made from a range of raw material sources (waste and/or virgin) with specific properties for a given application at a competitive cost. Despite these key technical and environmental attributes, it is the ability to add significant value to coal ash or and/ or metallurgical slag waste streams which drives the commercial development and uptake of the technology.

Jan 1, 2006

By Jonathan M. Berkoe

Design engineers and metallurgists have long recognized the need for better methods to calculate a wide range of fluid dynamic effects in smelters and hydro- metallurgical facilities. Examples can range from the capture of fume in the secondary hoods of a copper converter, to controlling the thermal effects of heat transfer resulting from metal and slag flows within a furnace. With the advent of relatively low-cost, high- speed computers and user-friendly, commercially available computerized fluid dynamic (CFD) programs, these calculations can now be made. Use of CFD increased the understanding of both hot gas and molten flows in smelter facilities and has already led to design improvements in converter fume control hoods as well as improved management of heat transfer in electric furnaces. This paper will present two representative CFD applications to metals industry facilities. To date, Bechtel has implemented CFD results on four continents.

Jan 1, 1999

By Xi Dai

The LiFe1-xNixPO4(x=0, 0.05, 0.10) cathode materials for Li-ion battery were synthesized with Fe1xNixC2O4?2H2O(x=0, 0.05, 0.10) as Fe sources by high temperature solid-state reaction method. The Fe1xNixC2O4?2H2O(x=0, 0.05, 0.10) materials were produced by liquid co-precipitation method and crystal structure and morphology of cathode materials were characterized by X-ray diffraction and scanning electron microscopy. The composition contents and charge-discharge performances were measured by chemistry analysis and charge-discharge apparatus. The XRD patterns showed that LiFe1-xNixPO4(x=0, 0.05, 0.10) cathode material samples were well-crystallized homogeneous olivine-type phase, with only tiny trivalent iron impurities according to chemistry analysis results. Charge-discharge test showed that cathode materials possessed excellent charge/discharge capacities, about 150mAh/g at 0.1C rate and more than 120mAh/g at 0.4C rate. The polarization of cathode in charge-discharge process can be restrained effectively, for the potential offset between oxidative peak and reductive peak of doped LiFePO4 material was only 0.079V, lower than pure LiFePO4 markedly.

Jan 1, 2006

By Vladyslav M. Sokolov

The cost effective and environmentally friendly recycling technology was developed and tested. It enables utilization of the fine nickel-base superalloy scrap in a form of heavily oxidized scarfing granulates. The process of granulates generation was discussed in details. Their properties were investigated. The results of literature search showed anticipated sufficient improvement of the properties of cast iron by its alloying with the elements from the scarfing granulates. The novel alloying approach is based on the two stage reduction operation. Firstly thegranulates were partially reduced in a solid state by their exposure with powdery carbon at the range of 1550 ? 1700°C. Then the gotten product was efficiently introduced into liquid iron since it has a form of fine natural agglomerates for arranging the optimal conditions for reduction of the granulates. The thermodynamic evaluation demonstrates higher reduction efficiency of carbon and silicon dissolved in iron than of the same elements in a form of the separate phases. The considered process partially provides itself by energy since the reaction of reduction of the chromium oxide by silicon dissolved in liquid iron has exothermal character. The mostly complete extraction of Ni was received. The sufficient reclamation of Cr was gotten at the same time.

Jan 1, 2006

By Zhong Juya, Wang Yong, Guo Xueyi, Song Yu, Tian qinghua

"In this work, the flow of zinc in China, 2004, was traced within the STAF model, and the situation of production, consumption and recycling of zinc resources in China were introduced. The SFA is performed on zinc flows during its one year life cycle in detail. The result reveals that China produces and utilizes a large amount of zinc, while the efficiency of renewable zinc resources is still relatively lower. As one of the biggest producer and consumer of zinc in the world, China is facing a severe depletion of zinc resources. How to increase the resource efficiency is a significant issue for zinc industry of China. Based on the result, several advices were proposed in the paper, aiming to contribute important reference information for the industrial metabolism and resource management and recycling of zinc industry in China. IntroductionZinc is one of the important metals in national economic development in China; it has good conductivity and corrosion resistance, with high scalability when heated to 100 ~105_. Zinc is mainly used for galvanized zinc industry, as the coating of steel and various parts, and it has also been applied to the manufacture of brass, bronze and corrosion-resistant alloys, which are widely used in machinery manufacturing, printing, national defense and so on. In addition, zinc compounds are utilized in various fields, for example, ZnO is used for infiltration wood, paper, rubber, paints, etc.; ZnSO4 for leather, ceramics, textiles, medicine, etc.; ZnCl2 for infiltration wood; ZnS2O4 and Zn (HSO2 • CH2O) 2 for the paper and textile bleaching, etc. [1]. The extensive use and consumption of zinc in industrial production and social life promot the rapid development of zinc industry, which made zinc the third largest non-ferrous metals in the world."

Jan 1, 2008

By A. Filzwieser

The highest current density suitable for the electrowinning process is between 50 to 60 % of its limiting current density. One of the most important influences on the limiting current density is the thickness of the hydrodynamic boundary layer near the electrode surface. Therefore, the fluid flow in a copper electrowinning cell is calculated. The numerical simulation - using the CFD-software package FIRE® - considers all three different types of the fluid flow, namely, the natural convection, the forced convection by electrolyte circulation and the forced convection by electrochemically induced gas stirring. The simulation of natural convection is based on the different density values in the boundary layer at the electrode surface given by a density/concentration correlation. The copper concentration - linked with the current density by Faraday law - is solved by an additional transport equation. The simulation of the forced convection by the electrochemically-induced gas stirring is done by using a real two-phase calculation. That means that all differential equations are solved again for the second phase. The numerical solution of the fluid flow field is compared with the results of LDA- measurements, which were done in a special cell. The software for the LDA enabled a calculation of the void fraction possible and therefore a rough estimate of the mass transfer coefficient through the prevailing gas bubble induced convection can be made by assuming the influence of relative bubble volume.

Jan 1, 1999

By J. E. Murphy

Neodymium was electrowon into a Mg-Cd molten cathode at 650 °C from NdC1,-KC1 electrolyte. With the chloride system, neodymium was deposited into the molten alloy cathode until the neodymium concentration reached 20 wt pct. The alloy was then vacuum melted to remove the Mg and Cd. The current efficiency exceeded 80 pct under optimum conditions and the purity of the metal was 99.9 pct after vacuum melting. As an alternative approach, neodymium was electrowon at 1,030 °C from Nd,O, dissolved in a molten fluoride eleotrolyte. With the oxide-fluoride electrolyte, the metal was electrowon in a molten state with current efficiencies up to 60 pct. The purity of the metal was 99.8 pct with oxygen and carbon as major impurities. A number of problems were encountered including anode effect, low oxide solubility in the electrolyte, high neodymium metal solubility in the electrolyte, and reactivity of the metal with the cell materials. Approaches to improved cell, operation and prospects for commercial adoption of the electrolytic production of neodymium metal are discussed.

Jan 1, 1995

By Sergei A. Degterov

A thermodynamic database for the slag, matte and liquid copper phases in the Cu-Ca-Fe-Pb-Zn-Si-O-S system has been developed for the ranges of compositions of importance to the production of copper. When used with the Gibbs energy minimization software and other databases of the F*A*C*T thermodynamic computing system, this database will permit the calculation of matte-slag-copper-gas phase equilibria that take place during copper smelting and converting. The calculations reproduce within experimental error limits all available experimental data on phase diagrams, activities of components, enthalpies of mixing, matte - alloy miscibility gap and tie-lines. The calculated solubilities of Cu in both S-free slag and slag equilibrated with matte are also in good agreement with experiment under all studied conditions, such as at SiO2 saturation, in equilibrium with Fe, Cu or Cu-Au alloys, at fixed oxygen or SO2 partial pressures and at different contents of Pb, Zn and CaO in the slag. Sulfide contents (sulfide capacities) of the slags are predicted within experimental error limits. The distribution of Pb and Zn among matte, slag, copper and gas has been calculated. The calculations are in good agreement with experimental data and predict the distributions under conditions which are difficult to study experimentally, such as at magnetite saturation or under various oxygen partial pressures and iron to silica ratios in the slag.

Jan 1, 1999

By Florian Kongoli

The liquidus surface of multicomponent slags is an important parameter in various smelting and converting processes. It helps not only to optimize the slag, chemistry of current processes and their fluxing strategies, but also to determine the availability of new slags for more advanced technologies. In a series of our previous publications, the liquidus surface of some multicomponent iron oxide slags has been quantified at several constant oxygen potentials and the effect of the latter, ignored until that moment, was quantified along with the effect of some minor components. In this work, the liquidus surface of some iron oxide slags is quantified at constant CO2/CO ratios. This is a new convenient way for the quantitative description of the slag liquidus surface and the effect of several fluxes, especially in those processes such as slag solidification, where oxygen potential changes continuously. This type of diagram also describes more dynamically the effect of oxygen potential, clarifies the relation between CO2/CO ratio and oxygen potential in terms of the liquidus surface, which is not widely understood by metallurgist today, and reduces the gap between laboratory work and industrial experience.

Jan 1, 2002

By I. S. Escobar

Copper, particularly the oxygen-free grade Cu-OFP, is a candidate material for containers for the long-term isolation and disposal of high-level radioactive waste (HLW) in underground repositories. After having been buried for a few hundred years, all oxygen will have been consumed in the repository, and corrosion of the copper will be caused entirely by contact with dissolved sulfides. Chloride is another potential corrodant, but in deep repositories where groundwater is neutral or slightly alkaline, the effect of chlorides can be ignored on thermodynamic grounds. Thus, the corrosion of copper in the presence of sulfide ion and under reducing conditions has been studied using cyclic voltammetry and Tafel slope measurements. It is possible to determine the effect of sulphide ion on copper corrosion resistance which is minimized at low temperature and also at low sulphide concentration. The presence of anions such as HCO3 under environmental conditions produces a beneficial effect because these ions are inhibitors.

Jan 1, 1999

By Manolete Mena

WC-Co nanocomposite powder is among the first group of materials with a promising potential for nanocrystalline-materials application. A chemical vapor synthesis (CVS) process that has previously been used for preparing the aluminides of titanium and nickel, and other metallic and intermetallic powders has been applied to the preparation of WC-Co nanocomposite powder. This CVS system was designed so that a tungsten precursor (WCl6 powder) and a cobalt precursor (CoCl2 powder) were separately fed into each evaporator in a reactor by means of specially designed powder feeders. The reduction and carburization of the vaporized chlorides by methane-hydrogen mixtures produced nanosized WC and Co composite powder. The product is a very uniform mixture of the constituent powders, which is important to ensure a high quality of the bulk cemented tungsten carbide product after consolidation. In the present work, the effects of reaction temperature, CH4 to WCl6 ratio, CH4 to H2 ratio, residence time, and Co content on the powder composition and particle size were determined. The products were characterized using XRD, carbon analyzer, and TEM.

Jan 1, 2006

By Michael S. Moats, Daniel Kim, Shijie Wang

"The behavior and deportment of lead, arsenic, antimony and bismuth are critical in producing high quality cathode by copper electrorefining. A critical review of research related to these elements is presented along with a comparison to industrial data, where appropriate. These elements exist predominantly in the anode as complex oxides along die grain boundaries. Upon dissolution, Group 15 elements report both to the electrolyte and slimes while lead essentially enters the slimes. The deportment of the Group 15 elements appears to be influenced by several chemical interactions which are discussed. The effect of these elements on floating slimes and anode passivation is reviewed. Under normal electrorefining conditions, lead, antimony and bismuth are thought to enter the cathode through the encapsulation of slime particles. The literature indicates that arsenic enters the cathode predominately by electrolyte entrainment. Finally, areas for future research regarding these elements are presented.IntroductionControlling lead, arsenic, antimony and bismuth is critically important for the production of high quality cathode in copper electrorefining. The reasons for this are twofold. First, ASTM Grade 1 Cathode specifications [1] for these elements are low, as listed in Table 1. Second, they can affect the efficiency of the electrorefining process (e.g., through passivation, current efficiency, slime processing)."

Jan 1, 2012

By V. Bojarevics, K. Pericleous

"A number of different methods have been developed for noncontact electromagnetic treatment of liquid metal and to investigate the melting/solidification processes. Applying AC magnetic field in terrestrial conditions, along with the buoyancy and thermo-capillary forces, results in turbulent flow. The use of a homogenous DC magnetic field allows damping both of the turbulence and the large scale flow at different rates leading to surprising results at some stages. The dynamic interaction of the turbulent flow with the oscillating interface needs to be accounted if it is required to levitate liquid metal of up to few kilograms without the contact to container walls. At the high values of magnetic field some oscillation modes are damped quickly, while others are modified with a considerable shift of the oscillating droplet frequencies and the damping constants from the non-magnetic case. Numerical models are used to investigate behavior of liquid metal suspended in high DC magnetic fields providing microgravity-like conditions with laminar viscosity and heat transfer to the surroundings.IntroductionSince the early Electro Magnetic (EM) levitation experiments [1] in AC magnetic field it became apparent that the levitated liquid metal is prone to oscillation and instability. The EM and electrostatic levitation experiments with liquid metal droplets show difficulties related to confinement stability and a need for complex correction functions to establish a correlation between the measurements and the droplet material properties [2,3]. Intense internal fluid flow is visually observed, apparently being in the turbulent regime for earthbound conditions."

Jan 1, 2012

By Marko Suput

Titanium is a high-strength, low-density metal nearly immune to corrosion, but limited in use by its high price. The high price is due to the cost of smelting and processing the ore. The research on titanium production using the Solid Oxide Membrane (SOM) process aims to consolidate most of the processing steps required for conventional titanium production into a single step making it an energy-efficient and cost-effective method for producing CP billet and ingot and possibly also powders used to make titanium alloys. In the SOM process experiment, a steel crucible contains MgF2-CaF2-TiO2 flux; an inert metal/carbon rod serves as the cathode; an oxygen-ion-conducting yttrium-stabilized-zirconia (YSZ) membrane in the form of a one-end-closed tube contains either a liquid metal that acts as the anode or liquid MgF2-CaF2 ionic flux that connects the YSZ membrane to an anode. During electrolysis, when the voltage between anode and cathode is higher than the reduction potential of titanium oxide, titanium ions are reduced at the cathode and the oxygen ions pass through the YSZ membrane and are oxidized at the anode. The oxygen ions are oxidized at the anode by a reducing agent, hydrogen gas or carbon, forming steam or CO(g), respectively. To date, a suitable MgF2-CaF2-TiO2 flux has been selected and the operating temperature for the SOM process has been determined. Several electrolysis experiments have been performed. As expected, lower valence deposits of titanium oxides have been witnessed at the cathode prior to depositing pure titanium. Continuing work will aim to extend the electrolysis time in order to pass enough charge to produce a significant amount (100 g) of titanium at the cathode.

Jan 1, 2006

By Lanre Oshinowo

The trend in process engineering is to design compact, more efficient processes, there is the paramount requirement to get the job done right the first time going from the drawing board to full-scale commercial operation. To accomplish this goal, there is also the need for tools beyond the traditional engineering toolkit to evaluate designs through virtual prototyping, thereby reducing the risks associated with making design decisions. One of the most important tools that has recently come to the forefront of process design and development is Computational Fluid Dynamics (CFD). CFD has been used at HATCH to address the key process parameters that drive the design of hydrometallurgical unit operations. This paper will detail the role of CFD at HATCH in achieving a superior level of confidence in the process design of autoclave circuits. Specifically, the optimum application of multiphase modeling including hydrodynamic, heat and mass transfer to hydrometallurgy operations, the impact of non-Newtonian slurry rheology on autoclave performance, and the challenges of optimizing the mixing of key reactants into slurries in autoclave reactors, is discussed.

Jan 1, 2003

By Anestis Vlyssides, Elli Maria Barampouti, Sofia Mai, ?postolos Vlyssides

"A new anaerobic reactor variation, the UASB/CO2-stripper reactor was conceived. It consisted of a conventional UASB reactor that recirculated the biogas produced. The sludge characteristics of this system were examined when treating high strength wastewater. From the data collected, it was obvious that the UASB/CO2-stripper system can satisfactorily operate at higher loading rates (25 g COD·L-1·d-1). A pronounced effect on the quality of the granular sludge was observed. The VSS/TSS ratio decreased sharply. A considerable decrease in the mean granule diameter was observed, while the specific gravity of the granules increased. The sludge bed porosity increased significantly leading to a considerable expansion of the sludge bed. These changes in the sludge properties led to a gradual shift of the system towards a fluidized bed process as far as its hydraulic characteristics were concerned.IntroductionIn recent years energy considerations and environmental concerns have increased the interest in direct anaerobic treatment of industrial wastes. The anaerobic method of waste treatment offers, under the present circumstances, a number of significant advantages with trivial or more serious drawbacks over other treatment methods. The major obstacle to the application of the process for this specific purpose is perhaps the difficulty of extending it to a stable and simple operational form. A number of reactor configurations has been developed leading to high biomass concentrations, e.g. the contact process, the filter reactor, the UASB reactor, and the fluidized bed systems, but the process stability problem still remains [1].A prime objective in the operation of anaerobic waste treatment process is the maintenance of a proper pH range. Thus, a possible solution to the process stability problem could be obtained by increasing alkalinity in the anaerobic systems. Therefore, the main objective of this paper is to present and evaluate the results of a system (UASB/ CO2-stripper) with increased alkalinity concentrations."

Jan 1, 2008

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 N. Solak

CrN, TiN and Ti-B-N coatings were deposited onto H13 hot-working tool steel and alumina substrates by arc-PVD. The coatings were characterized with respect to their mechanical and structural properties. Oxidation behavior of the coatings on alumina substrates was investigated by TG/DTA. Samples coated on H13 substrates were oxidized in a tube furnace under atmospheric conditions at specific temperatures determined from TG/DTA tests of the same coatings deposited on alumina substrates. The oxide scale morphology was characterized by scanning electron microscopy and X-ray diffraction. Oxide scale thickness change and TG data were used to calculate oxidation reaction activation energies. It was determined that boron addition into TiN coating improves not only mechanical properties but also oxidation resistance. Depending on the substrate material different oxidation activation energy values for the TiN and Ti-B-N coatings were determined revealing the importance of film morphology on oxidation resistance.

Jan 1, 2006

By A. C. Wadhawan

In the present context of rapid industrialization, production of Lead-Zinc metals from low grade materials, residues and wastes can make substantial contribution to the supply of these metals in India. Recovery from secondary sources also plays an important role in conservation of mineral resources and lower power consumption. Conscious effort is therefore, required to increase the secondary metals which, besides saving in energy cost will also help in waste material management and keeping environment clean. The major thrust is, therefore, needed in this direction. During all these years, the Indian Lead- Zinc industry has made sustained efforts for recovery of metals from low grade ores and from metallurgical wastes and residues. The paper identifies the treatment of low grade ores by various technologies and techniques and the treatment of metallurgical residues and wastes generated during primary Lead and Zinc smelting in India. Some of the major achievements in past decade have also been elaborated in the paper. The strategies to be followed for continuing treatment of low grade ores and waste materials by adopting newer, environmental friendly technologies, in consonance with the rigid standards being adopted by most of the countries including India. have also been dealt with in the paper.

Jan 1, 1994