Search Documents

By Hongmin Zhu, Guihua Wang, Xiangsheng Wang

"The anode process of carbon electrode in fluoride melt was studied by voltammetry and chronoamperometry. Anode gases were analyzed by gas chromatography on-line during controlled-potential electrolysis. Two peaks were observed on the cyclic voltammograms. According to the results of gas chromatography, the first peak was corresponded to the discharge of residual oxide ions, with the formation of CO and CO2. Discharge of fluoride ions occurred at 4.1 V vs. Li+/Li, and leading to the anode effect. With the occurrence of anode effect, small amount of CF4 was detected. As the potential reached 4.5 V, CF4 and C2F6 gas evolution occurred, and the current increased to form the second peak.1.IntroductionIn the primary production of Aluminum and some rare earth metals like neodymium, a departure from normal cell operation known as anode effect results in the generation of perfluorocarbons (PFCs), which have high global warming potentials [1]. Owing to the pressure of environmental protection, considerable research has been carried out to clarify the mechanism of anode effect and PFC generation of industry and laboratory cells in the aluminum electrolysis system [2-9]. The common result on PFC generation is that the PFCs are emitted from Hall-Heroult cells only when they are on anode effect. In this article, we selected LiF, the main electrolyte for the neodymium electrolysis [10-11], to perform further investigation on the underlying kinetics of PFC generation and the nature of the reactions at the electrode.2. ExperimentalAll experiments were carried out in an alumina tube reactor, which was filled with high purity helium atmosphere. Spectrographic graphite crucibles were used, which played the dual role of molten fluoride container and the counter electrode. Lithium fluoride was analytical grade. The experiments were carried out at 900 °C."

Jan 1, 2011

By G. A. Brooks, R. W. Matusewicz, Nazmul Huda

"A computational fluid dynamic (CFD) model of a conventional tuyere blown slag fuming furnace has been developed in Eulerian multiphase flow approach. The model was developed by coupling CFD with kinetics equations developed by Richards et al. for zinc fuming furnaces. The model integrates submerged coal combustion and chemical reactions with the heat, mass and momentum interfacial interaction between the phases in the system. The model predicts the velocity, temperature field of the molten slag bath, generated turbulence, vortex and coal utilization behavior from the slag bath. The highest coal penetration distance was found to be at l/L = 0.2, where / is the distance from the tuyere tip and L is the total length (2.44m) of the modeled furnace. The model also predicts that 10% of the injected coal bypasses the tuyere gas stream un-combusted and carried to the free surface, which contributes to ZnO reduction near the free surface.IntroductionSignificant metal values are often discarded with slag in the form of metal oxide produced by the smelting industries. These metal values can be recovered from the slag by proper treatment. Zinc slag fuming is such a process, where a reductant source (usually coal) is injected in the molten slag bath to reduce dissolved ZnO from the bath into metallic zinc vapour. The process can be carried out in either conventional tuyere blown furnace or top submerged lance (TSL) smelting furnace. Conventional slag fuming processes are carried out on batch basis in a rectangular tuyere blown furnace. Approximately 50 tonnes of charge (either molten slag or solid slag) is fed to the furnace at the beginning of each fuming cycle. Two opposing sets of submerged tuyeres are employed to inject air and pulverized coal into the molten slag bath to carry out combustion and reducing reactions."

Jan 1, 2012

By Mari Naess, Jan Erik Olsen, Gabriella Tranell

"Fume, also known as dust, is produced during metal refining. Exposure to fume is damaging to the health of plant operators. A mathematical model has been developed to study the different factors governing the fuming mechanism. It is shown that natural convection is the main driving force of the phenomenon, and that the fuming rate is highly sensitive to the area of the exposed metal surface. A new feature introduced in the modeling concept is the ability to include a gas flux of unconsumed process gas flowing up through the metal surface. This reduces the fuming rate, and should normally not be neglected.IntroductionFormation of fume from the ladle in which metal is refined into its final specifications is an environmental issue of importance for the working environment in the production plant. In layman-term fume is often known as dust. It is formed when metal reacts with oxygen. As an example of a fuming process, we will focus on ladle refining of silicon. Note that many of the principles and conclusions will apply to other metal refining processes. For silicon production, silica fume (S1O2) is produced when silicon metal (Si) reacts with oxygen (O2).Silicon is produced in a submerged arc furnace. The metal is tapped from the furnace into a ladle for refining. The refining is conducted by injecting a mixture of air and pure oxygen at the bottom of the ladle. The oxygen reacts with the metal and the impurities, and the amount of impurities is reduced according to product specification. At the ladle surface, metal also reacts with oxygen present in the air surrounding the ladle. This reaction produces silica fume as illustrated in Figure 1."

Jan 1, 2012

By Xuyang Liu, Xuewei Lv, Chenguang Bai, Meilong Hu

"The electro-deoxidation process for ilmenite concentrate in molten salt was studied by cyclic voltammetry and AC impedance spectroscopy. The results from cyclic voltammetry are consistent with those of AC impedance spectroscopy. The results showed that the electro-deoxidation process for ilmenite concentrate consists of two steps. In the first step, Fe is reduced from the ilmenite concentrate. The second reaction is the decomposition of TiCh. CaTiCh is an intermediate product. At low voltage, the electrochemical reaction is the main step. With the increasing potential, the diffusion of ion is the main rate controlling step for the electro-deoxidation of FeTiO3.IntroductionTitania and titanium-rich products are mainly prepared from ilmenite concentrates (FeTi03), which contain about 40%-60% T1O2 after ore dressing and other physical or chemical processes [1]. At present, the main methods to prepare titania are the sulfuric acid process and the chloride process, but the sulfuric acid process consumes a large amount of sulfuric acid and the materials requirements for the chloride process are strict [2], Since the Electro-Deoxidization in Molten Salt (FFC) method was put forward in 2000, many researchers have successfully extracted the metal and alloys by this method, such as Ti, Cr, Tb, Si, Al-Si, TiV, FeTi, etc. [3-7], FeTi alloy is a typical hydrogen storage material, and because of its favorable properties, the preparation of FeTi alloy has become a hot research topic [7-9]. However, the mechanism of electro-deoxidization has not been studied thoroughly [10-11]. Therefore, in this study, the electro-deoxidation process for titanium concentrate was investigated by electrochemical methods, and the study makes a contribution to improving the current efficiency of the electrolysis."

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 Gerhard Meyer

A new instrument for the determination of iron., zinc, calcium, and other metals independently directly in the fumes emitted from steelmaking processes is described. Based on the well- accepted method of X-ray fluorescence, the instrument can detect numerous metals simultaneously in the fume as well as report their concentration on a mass per unit time basis real time to a control room computer. The instrument mounts on the wall of the fume duct and can., via a small opening, directly view the hot exhaust plum inside the duct. The concentration of metal in the fume over time has been shown to change dramatically depending on process variables. Variables such as oxygen flow rate, lance height and nozzle configuration., slag condition., and episodic scrap addition can affect the presence of metal particles and fume in the exhaust. An analysis response time of 6 seconds enables better control of the steelmaking process thereby conserving primary resources and reducing environmental impact.

Jan 1, 2001

By Leonard A. Duval

This concept employs a viable energy saving method that uses a solvent to separate oil from particle matter; it can be used in metal forming industries to deoil sludges, oxides, and particle matter that is presently committed to landfill. If oily particles are used in their oily state, severe consequences to environmental control systems such as explosions or filter blinding, occur in the air handling equipment. This is due to the presence of hydrocarbons in the stack gases resulting from the oily particles. After deoiling, the particles can be recycled and the separated oil can be used as a fuel. The process does not produce a waste of it's own and does not harm air or water. It demonstrates the dual benefits of being commercially viable and in the national interest of conserving resources.

Jan 1, 1994

By V. B. Telles, D. C. R. Espinosa, J. A. S. Tenório

"The purpose of this work was to study the reutilization of the steelmaking dust, derived from steel production in the electric arc furnace (EAF), in iron ore sintering process aiming zinc elimination. In each sintering process were collected sintered samples, these materials were analyzed by chemical analysis using atomic absorption spectrophotometry in order to determine the zinc content. Samples of not sintered mixtures were also characterized by chemical analysis aiming to determine the initial amounts of zinc, i.e. in order to check the zinc amounts present in the mixture before the sintering process. The comparation among the zinc contents of samples sintered and not sintered allowed to determine the elimination of zinc during the experiments. Results showed that the zinc elimination in the process is proportional to the ratio reducer/waste. The zinc removal was lower when the reducer/waste ratio was decreased.IntroductionThe electric arc furnace dust (EAFD) is a residue generated in the steelmaking process using electric arc furnace. Aproximately 30% of all steel produced (in the year 2009) was obtained through electric arc furance (EAF). In the United States of America the percentage of this process in the total crude steel production was about 62% in 2009, while in 2000 this percentage was only 47% [1].The iron ore sintering is a process that reuses wastes generated in metallurgical industries. However, the materials used must be physical and chemical characteristics compatible with the blast furnaces.The quantity of zinc, cadmium, chrome and other metals present in the EAFD depends on the quality of the scrap used to feed the EAF and the type of steel that it is been made [2,3]. The reuse of EAFD waste is interesting to steelmaking processes because of its iron content. However the presence of zinc inside a blast furnace is undesirable since the zinc oxide can be deposited on the blast furnace walls and in the drivers of gas output, interrupting the flow. Another part of the zinc oxide can form deposits on the refractory lining of the blast furnace [4,5]."

Jan 1, 2012

By Sumantra Mandal

The hot deformed microstructure of the 15Cr-15Ni-2.2Mo-Ti modified austenitic stainless steel (commonly known as alloy D9) was investigated employing electron backscatter diffraction (EBSD). Hot compression tests were conducted in a Gleeble thermo-mechanical simulator at temperatures of 1173K-1373K (in steps of 100K) with a strain rate of 10 and 100 s-1 to different strains. Various kinds of deformation patterns were observed inside the deformed grains. These were inferred as the development of geometrically necessary boundaries or formation of parallel set of micro-bands. Recrystallized grains were partitioned from the deformed grains employing grain orientation spread approach. Extent of dynamic recrystallization (DRX) was found to be minimal at 1173K. DRX was predominantly found to happen at and above 1273K which increases with increase in strain. DRX nucleation and development mechanisms were discussed with respect to bulging of the parent grains and sub-grain rotation. Special emphasize is given on the role of annealing twins on DRX nucleation and subsequent expansion.

Jan 1, 2009

"In this paper, a mobile heat treatment furnace from Akkermans Gloeitechniek, a Dutch company, was simulated with Computational Fluid Dynamics (CFD). The furnace is cylindrical with four oil burners, and large metal products such as dredging pumps and impellers can be flexibly heat treated to obtain required microstructure and mechanical properties through stress relief, annealing, hardening and tempering. The furnaces are exposed to the open air, and thus the heat loss becomes significant and varies from day to day and from season to season. Since the temperature of the metal products to be heat treated can only be measured on the surface, the temperature evolution inside the metal could not be tracked in practice. CFD simulation provides a useful tool to predict the temperature evolution within the metal pieces and within the combustion space of the furnace. Energy distribution and heat loss can be subsequently estimated. An overall energy balance through temperature measurement indicted relatively low energy efficiency. Especially during the soaking period, the high energy supplied is barely used to compensate the heat loss of the furnace to maintain a constant temperature of the metal piece. The current CFD modeling aims to give advice on how to modify the design and optimize the operation to reach higher energy efficiency and low heat loss. The CFD model consists of turbulent combustion model, radiation model in participating media, and conjugate heat transfer between the combustion space and solid metal. Temperature measurement was carried out to provide thermal boundary conditions and overall energy balance of the operation. After the model validation with temperature measurement within the combustion space and metal surfaces, furnace optimization will be conducted.IntroductionHeat treatment is a common practice in metal production and manufacturing industries. Through heat treatment at certain temperatures with special patterns, unique mechanical properties of the metals and the metallic products could be obtained. ""Akkermans Gloeitechniek"" is a company situated in K.inderdijk, at location of LHC-Holland (www.ihccaland.com), the Netherlands. Heat treatment of metals is its core business. Various type of heat treatment are applied, such as stress relieving, soft annealing and hardening (quenching), tempering, transformation and precipitation. At the company 6 furnaces are in operation and the 7th is being built"

Jan 1, 2004

By Hideki Yamamoto

A new technology to convert fluoride gas (C2H2F4 : R-134a) contained in the exhaust gases from semiconductor manufacturing plants and refrigerators directly into a harmless substance have been established, thus, presenting a new concept for the disposal of fluoride gases such as CFCs that are associated with the global warming. Experimental results verify that chemical reactions with metal compounds can take place at substantially lower temperatures of 700- 800K as compared with combustion treatment temperatures of 1200-1500K. The reaction product is mainly metal fluoride, which chemically is a harmless material. Furthermore, this process is compact, easily controlled, safe and has low running costs. This paper deals with a new chemical reaction method for the harmless disposal of gases effecting the global warming.

Jan 1, 2003

By Yuzo Hiroshige, Kiyotaka Tahara, Hiroki Hatayama, Masaharu Motoshita, Tomohiko Akahori

Large amount of rare earth metals is stored in the used electric products. Hitachi has started to develop the environment-friendly process for rare earth metals recovery from used magnets. We report here the environmental impact of our process, in comparison with the conventional recycle process utilizing solvent extraction. As an evaluation method, Life-cycle Impact assessment Method based on Endpoint modeling ver.2 (LIME2) developed by the National Institute of Advanced Industrial Science and Technology (AIST) in Japan is applied. It was found that the environmental impact of the new process was more than that of the conventional process. For further reduction of its environmental impact, minimization of energy consumption to operate the equipment was most effective. Decreasing the amount of magnesium, used as an extractant, and the improvement of the extraction rate of rare earth metals were also considered as specific options for reducing energy consumption in the plant development.

Jan 1, 2014

By Paul O. Malan

"The Tusc gold deposit is located along the Carlin Trend approximately 13 kilometers north of Carlin, Nevada and 2.5 kilometers northwest of the Gold Quarry mine. Tusc is one of several structurally controlled oxide gold deposits located along the Good Hope fault within the Maggie Creek subdistrict. Mining commenced in 1994 with an oxide reserve of780,000 troy ounces of gold at an average grade of 1.34 g/t Au. The Good Hope fault forms the southwestern edge of the Schroeder Mountain uplift (also known as the Carlin Window) and juxtaposes carbonate rocks of the Siluro-Devonian Roberts Mountains Formation against siliceous mudstone, siltstone, and silty limestone of the Devonian Rodeo Creek unit. Submicroscopic gold mineralization is disseminated in the Good Hope fault system and in fractured hanging wall carbonate rocks. Wallrock alteration includes silicification, deca!cification, sericitization, and late alunite replacement and veins. All Tusc ore is transported 2.5 kilometers to Gold Quarry for processing. Leach-grade ore (0.2 - 1.7 g/t gold) is placed on the oxide leach pads, and mill-grade ore(> 1.7 g/t gold) is processed through the CIL oxide mill. IntroductionThe Tusc gold deposit is located in Eureka County, Nevada, U.S. A, approximately 13 kilometers north of the town of Carlin and 2.5 kilometers northwest of the Gold Quarry mine (Fig. 1 ). Tusc is one of several open-pit, oxide, gold deposits within the Maggie Creek subdistrict of the Carlin Trend. Tusc is a structurally controlled gold deposit located along the Good Hope fault. Submicroscopic gold mineralization is disseminated in the brecciated and silicified Good Hope fault zone and along intersecting northeast and northwest striking structures."

Jan 1, 1997

By Cui Wang, Qian Li, Kexin Jiao, Haibin Zuo, Jianliang Zhang

Abstract：A rational cooling water system is the assurance for long campaign life of blast furnace．In the paper, the heat transfer of different furnace period and different furnace condition based on the water quality characteristics were analysed, and the reason of the heat flux over the normal from the hydrodynamics was analysed. The results showed that, the vapour-film and scale existence significantly influenced the hearth heat transfer, which accelerated the brick lining erosion. The water dynamic characteristics of the parallel inner pipe or among the pipes were the main reason for the abnormal heat flux and film boiling. As to the reasonable cooling water flow, the gas film and the scale should be controlled and the energy saving should be considered.

Jan 1, 2015

By P. D. Ferro

The direct oxide reduction (DOR) of plutonium oxide generates significant amounts of contaminated waste. This waste primarily consists of calcium oxide-saturated calcium chloride salt. This investigation explores the possibility of recycling the salt, by the electroreduction of the calcium oxide. Fused salt electrolysis of a simulated salt mix (CaC12 + ~10 wt. pct. CaO) is being carried out to electrowin calcium, and the process is being optimized in terms of the calcium solubility, cell temperature, current density and cell design to maximize the current efficiency. This work identifies the major concerns in the development of a process to electrowin calcium from this simulated salt mix.

Jan 1, 1992

By Huaming Yang

The vanadium-doped SnO2 nanoparticle was synthesized by the co-precipitation reaction and subsequent calcination from the vanadium(III) chloride and tin(IV) chloride. The crystal size, pore size distribution, micrograph and properties of the nanocrystalline powders were examined by differential thermal analysis (DTA). thermogravimetric analysis (TGA). X-ray diffraction (XRD), desorption isotherm (Barrett-Joyner-Halenda method) and transmission electron microscopy (TEM). Thermal treatment of the precipitate powder at 600'C led to the formation of crystal0nmincrystal size. Most of the pores in the narmparticle are about 5~15nm in diameter. Effect of doped vanadium on the crystal size of the nanoparticle was discussed.

Jan 1, 2003

By Shengqin Zhang, Jagannath Pal, Yousef Mohassab, Hong Yong Sohn, Mohamed Elzohiery

The kinetics of magnetite reduction with mixtures of hydrogen and CO of various compositions has been investigated as part of the development of a flash ironmaking process at the University of Utah. This new process bypasses the cokemaking and pelletization or sintering steps required for the blast furnace. The particle kinetics were studied using magnetite concentrate particles of different sizes. Reduction degree of 60% was achieved in a few seconds in at 1350 oC using CO reductant alone and over 90% when H2 + CO gas mixture was used. The effects of reductant partial pressures, temperature, and particle size on the reduction kinetics were studied.

Jan 1, 2016

By Seong-Jong Kim

The formation behavior and corrosion characteristics of anodic oxide films on pure Mg and Mg-AI alloys were investigated focusing on the effects of anodizing potential, Al content, temperature and NaOH concentration. Pure Mg and Mg-AI alloys were anodized for 10 min at 3, 10, 40, and 80 V in NaOH solutions. Mg(OH)2 was generated by an active dissolution reaction at the surface of the specimen and the product was affected by temperature while MgO generation increased with NaOH concentration. Moreover, the current density after anodizing for 10 min at a constant potential decreased with increasing AI content in Mg-AI alloys,

Jan 1, 2003

By Joseph Sofra

It has become increasingly evident that sustainable metals production in the 21st century requires producers to balance the needs of cost effective, high value production with that of responsible plant operation. This is becoming more difficult as lower grade and more complex feed materials, including recycled scrap and residues, are being processed to reduce production costs and decrease exposure to primary metal market fluctuations. One particular facet of the metals industry facing these challenges in the 21st century are copper producers, The recent steady decline in the copper price has seen the industry cut expenditure, tighten control on income streams and focus on high returns on capital investment. For these reasons copper producers are looking towards flexible technologies that can deliver high value products, with minimal environmental impact at low capital and low sustainable operating costs. Ausmelt's Top Submerged Lancing (TSL) technology for copper production is a low cost, proven technology for the processing of both primary and secondary copper materials. Both the smelting and converting operations introduce significant advantages in environmental performance, improved process efficiencies and high rates of metal recovery, Ausmelt has made significant gains in the past 4 years in establishing a strong market position for its copper technology, New installations in China, South Africa and India as well as existing operations in Zimbabwe and China have demonstrated its effectiveness. This paper reviews the application of Ausmelt Technology for both smelting and converting of primary and secondary sources, It discusses Ausmelt's design and implementation philosophy, and how this philosophy meshes with the needs of the end user.

Jan 1, 2003

By James A. Sommers

Combustion of niobium nitride powder in a stream of oxygen results in several niobium oxide phases, depending upon reaction parameters. Under rapid oxygen flow, the oxidation produces a molten mass which coalesces into droplets of ca. 2 mm dimension and effectively quenches to leave NbO2 and other lower oxides of niobium, despite the ambient atmosphere of oxygen. A preliminary survey of reaction parameters which govern the split between reduced and oxidized products is presented. This technique offers novel synthesis means for binary oxides when mixtures of NbN and other materials are combusted together, since the niobium moiety is generated in a molten state.

Jan 1, 1995