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By Halvor Dalaker, Pål Tetlie

The decomposition of methane has been studied experimentally in contact with various oxides at elevated temperatures. For each oxide, the temperature at which the cracking starts has been determined. No correlation was found to exist between the temperature for the onset of cracking for a given oxide and the affinity for carbon of the oxide's metallic component. In terms of potential for using methane as a reducing agent, calculations are presented that indicate that the suitability of an oxide for such reduction depends on the desired methane+oxide reaction being more energetically favourable than the methane+methane=ethylene/acetylene reactions.

Jan 1, 2014

By C. Lupi

Electric arc furnace dust generated during the production of steels is regarded as hazardous waste because of the presence of leachable elements such as Cr, Pb, Cd .... Different processes are available according to the management policy chosen by the steelmaker: disposal. recycle and/or recovery. The feasibility of an hydrometallurgical Zn recovery process on fumes generated during the pyrometallurgical treatment of EAF dust has been investigated. The recovery of metallic iron, chromium and nickel as molten metal provides fumes very rich in zinc oxide ( 63.1% ) and poor in zinc ferrite. This secondary dust is still an hazardous waste and represents the raw material for the recovery of Zn and Pb. The waste material is first leached in 1.5 M sulphuric acid at 30°C to provide a Zn, Fe and Mn rich aqueous solution and a Pb and Ca sulphate rich sludge. The iron is eliminated by precipitation because is harmful to the following electrowinning process. The ftltered and purified leached solution is acidified in order to obtain good electrowinning conditions. A pure cathodic deposit of zinc is then produced in an electrolytic cell at laboratory scale.

Jan 1, 1996

By C. Koopman

During the production of phosphoric acid from phosphate ore and sulfuric acid, large amounts of calcium sulfate are formed, in which impurities from the feedstock are incorporated. To use the calcium sulfate in, for example, the building industry, a lower concentration of impurities is desired. Mercury, copper, lead, and cadmium were extracted from clear industrial recrystallization acid (0.8-3.9 mol/kg H3PO4, 0.2-0:5 mol/kg H2SO4) by supported solvent extraction with the extracting agent Cyanex 302 in kerosene in a transverse flow hollow fiber module. The permeability for the mercury ion was 1.4.10-6 m/s, whereas that for the copper ion was calculated to be 1.5.10 m/s. Cadmium, lead, and copper were extracted during the recrystallization of calcium sulfate hemihydrate to dihydrate, an existing step within the ,phosphoric acid production process, by solvent extraction with the same extracting agent. The concentrations of cadmium and zinc in the newly formed calcium sulfate were proven to be decreased. Unfortunately, concentrations of mercury and lead were too low for analysis.

Jan 1, 1999

By Lin Yang, Yuanbo Zhang, Zhuoxuan Li, Guanghui Li, Jinghua Zeng, Tao Jiang

A technique has been proposed for recovering iron from hematite-rich diasporic-type bauxite ore in this study. Direct reduction roasting followed by low intensity wet magnetic separation process was carried out. The parameters including reduction temperature and time, sodium salts, grinding conditions and magnetic field intensity for separation of iron were determined. The optimum process parameters as follows: roasting temperature of 1050 oC, time of 60 min, sodium salts involving sodium sulfate, borax, sodium carbonate with dosages of 10 wt%, 2 wt%, 35 wt% respectively, and magnetic field intensity of 1000 Gs with fineness of pulp reached 92.75% passing -0.074mm. Under the optimal conditions, an iron concentrate containing 88.17% total iron grade and iron recovery of 92.51% was obtained, 4.55% total iron grade in tailings. This novel technique provide a potential route for utilizing hematiterich diasporic bauxite ore, recovering iron resource firstly, and extracting alumina from magnetic separation tailings further.

Jan 1, 2015

By S. C. Dhara

The recovery of Platinum Group Elements from various industrial scraps and spent materials in the form of high and low grade, such as, impure metals, matte, catalysts and other ceramic substrates, etc., has .been described by using high pressure reaction method. Nickel, Stainless Steel, Titanium and glass lined reaction vessels? are used in the reaction process. Primarily, the method involves either direct leaching of the substrates from the metal value or dissolving the precious metal from the substrate. Both acids and alkalies are used along with other reagents in the reaction process. The temperature and pressure of the leaching process are the main criteria for the reaction kinetics.

Jan 1, 1989

By Metehan Erdogan, Ishak Karakaya, Fuat Erden, Emre Ergül

"The FFC Cambridge process was suggested as a promising Si production technique for the expanding solar energy industry. Direct electrochemical reduction of bulk SiO2 plates and porous SiO2 pellets in molten CaCl2-NaCl salt mixture were investigated at 750°C by applying 2.8 V potential difference. The produced Si powder was brown and found to be contaminated by the Ni and stainless steel plates used as the cathode contacting materials. The reduction rates of the bulk SiO2 plates and porous SiO2 pellets were compared from variations of current and accumulative electrical charge that passed through the cell during the electrochemical reduction. The amorphous bulk SiO2 plates were reduced slightly faster than porous pellets of crystalline SiO2. The overall reduction potential of SiO2 pellets against the graphite anode at 750°C in molten CaCl2-NaCl salt mixture was determined as 2.3 V by cyclic voltammetry. This potential was supported by calculations.IntroductionMetallurgical grade Si cannot be directly used in electronic industry and some intermediate steps are required to produce industrial solar grade silicon (SOG-Si). A promising alternative solar grade silicon production technique is the FFC Cambridge Process [1]. Production of Si by electrochemical reduction of SiO2 at 850oC in molten CaCl2 electrolyte was first studied by Nohira et.al. [2]. In their study; Si formation was observed on bulk SiO2 cathodes after 1 hour of electrolysis. Complete electrochemical reduction of porous SiO2 pellets was first reported by Jin and his coworkers [3]. The mechanism of electrochemical reduction of SiO2 to Si in molten CaCl2 was explained in another study [4]. Reduction rates of bulk SiO2 and porous SiO2 pellets were also compared previously and it was found that reduction rates for bulk plates were higher [5]. Furthermore, it was reported that mixing Si into porous SiO2 pellet increased the reduction rate [5]. Mo [2, 4-7], Ni [3, 8, 9] or Si [6] were used as cathode contacting materials in various studies. Yasuda et. al. [6] produced Si with 99.80 % purity using Si plates as cathode contacting material to reduce metal contamination."

Jan 1, 2012

By Y. H. Su, C. Y. A. Tsao

"The solidification behaviors and velocity of atomized droplets during flight is formulated by a mathematical model, in which the concept of transient nucleation is applied. During the flight, the droplet velocity shows a maximum, followed by an inflection phenomenon. The velocity of large droplet is lower than that of small droplet at shorter flight distance, and higher than that of small droplet at longer flight distance. The effect of the gas flow pattern is more significant at longer flight distance than at shorter flight distance at a given flight distance, large droplet has higher temperature than small droplets prior to nucleation. Large droplet has higher nucleation temperature than small droplet. Medium size droplet flies over the shortest flight distance before the nucleation starts. At the end of recalescence, large droplet has less solid fraction than small droplet has.IntroductionTraditional concept of steady state nucleation was used in all the previous models describing the solidification of molten droplets. [1-5] However, during atomization, the solidification rate of the molten metal droplets is very high, and therefore there is very little time for the nucleation event to occur. In the present work, the concept of transient nucleation [6] is considered to model such short nucleation event during solidification of the atomized droplets. The solidification behaviors and velocity of atomized droplets are modeled and the effects of the atomization gas flow pattern are also presented."

Jan 1, 1997

By Annette Revet

Aluminum fluxes have been used for the remelting of secondary aluminum since the beginning of the recycling industry. During the last sixty years, a number of fluxes have been designed, researched and tested at the laboratory and plant scale. Fluxes are primarily a mixture of potassium chloride and sodium chloride with the addition of some other chloride and fluoride containing salts. The conventional Mining methods of potassium chloride and sodium chloride yield products that are not high in purity without costly reprocessing or additional refining. In 1993, Kalium Chemicals, Ltd. began supplying flux mixtures to the aluminum industry. Kalium produces potassium chloride and sodium chloride which are mined and refined by a patented solution-mining process. The salts produced by this process are high in purity with lower concentrations of iron oxide, sulfates, and other impurities. This paper will present the different mining methods used in the production of sodium chloride and potassium chloride. The paper Will address how these mining methods affect the purity of the final product as well as the effect of purity on the performance of the fluxing salt.

Jan 1, 1995

By Gabriel Plascencia

Copper was oxidized in the temperature range from 300 to 1000 °C under different pressures of oxygen, In the range from 300 to 500 °C, copper oxidizes following the logarithmic rate law; while in the range from 600 to 1000°C oxidation follows the parabolic rate law. Transition from logarithmic to parabolic growth occurs at about 525°C. X-ray diffraction was performed on oxide scales to account for the CuO/Cu2O ratio at different temperatures. Activation energies found in this work are in good agreement with reported values.

Jan 1, 2003

By Gabriel Plascencia

Copper was oxidized in the temperature range from 300 to 1000 GC under different pressures of oxygen. In the range from 300 to 500°C, copper oxidizes following the logarithmic rate law; while in the range from 600 to 1000°C oxidation follows the parabolic rate law. Transition from logarithmic to parabolic growth occurs at about 525°C. X-ray diffraction was performed on oxide scales to account for the CuO/Cu2O ratio at different temperatures. Activation energies found in this work are in good agreement with reported values.

Jan 1, 2003

By R. C. Chaturvedi, S. B. Padwal

"Padwal and Chaturvedi have developed the model based on M-K theory, considering Hosford's yield criterion and critical thickness strain criterion"" to predict the sheet metal forming limits under simple (constant) strain ratio paths. This analysis has been extended in this paper to predict the sheet metal forming limits under complex strain paths. The effects of exponent ""a"" in Hosford's yield criterion and strain paths on the forming limits under complex strain paths are studied using this analysis. The predictions of the present analysis are compared, both for simple and complex strain paths, with experimental results of Ishigaki for A.K. steel and also with the predictions of Rao and Chaturvedi's model. The quantitative analysis of the error in predicting the forming limits has also been carried out using a method suggested by the authors earlier.1. INTRODUCTIONThe constant strain ratio condition has been assumed in the theories developed for prediction of forming limit diagrams (FLO). In actual forming operation, this condition is seldom satisfied. Even in the case of simple single stage press formed components, the strain path becomes curved and non-linear. In the case of pressings with complex shapes, or multiple stages of forming, the changes in strain path are more pronounced and even abrupt.Experimental study of the forming limits, under two stage strain paths, by Ishigaki [1], has shown that the forming limits are path dependent. It has been observed that the forming limits lower than that under simple strain paths, may be obtained under certain strain paths (when the first stage strain path is either equibiaxial tension or uniaxial tension, followed by the second stage strain path as plane strain). Rasmussen's work [2J, on the theoretical study of forming limits under curvilinear strains paths, has shown that a large drop in formability can result from very small changes in strain path. Thus if a deformation process gives rise to failures due to plastic instability, the failure is not necessarily due to insufficient formability of the material. In such cases, FLOs based on constant strain ratio path should not be used directly in predicting the success or failure of the forming operation. Thus the knowledge of forming limits under complex strain paths is of great importance to the interpretation of press-shop problems."

Jan 1, 1994

By Juan B. Cabezas

"The favorable characteristics and workability of plastics as a replacement of wood, lead, stainless steel, asphalt and other materials are described. Various types of plastic have proven to be the most favorable choice for handling a variety of acidic, alkaline and organic solutions, as well as pulps, chemical wastes, slurries or tailings for impoundments. The material origin of various plastics, methods of manufacturing and specifications applied to leaching solutions are discussed, including availability and costs. Examples of select plastics are considered for use as alternatives of other materials under severe environmental requirements.IntroductionHydrometallurgical processes applied to gold recovery, as well as other metals, require the use of strong solutions of alkaline, acidic or organic nature, and may also include a variety of materials with extraneous characteristics and complications for handling in storage.The technology of leaching has been in use for more than 100 years, but the applications of leaching processes in metallurgy have become more commonly used in the last 15 years. Suitable materials for the construction of containers, launders, piping, and various accessories, to be used in the handling of leach solutions or slurries, have become a serious problem. Various metals such as brass, lead, stainless steel, etc., and non metallics including wood, clays, glass, rubber, ooncrete, tars or miscellaneous compounds have been tried in the past with serious limitations in workability and resistance to wear and corrosion. For example, the use of metallic, wooden or glass piping systems would require extraordinary shop maintenance to keep such systems in operation"

Jan 1, 1997

By Hyun Soo Kim, Joon Soo Kim, Myong Jun Kim, Jyothi Rajesh Kumar, Jin-Young Lee

Rare earth materials have an ever growing variety of applications in the modern and hitech technology. They apply to many an industry with crucial materials and they provide numerous a customers with benefits. Rare earth materials utilization increasing day-by-day in the worldwide, at the same time the resources is very limited in many countries like Korea. The present general article divided four sorts such as 1) mineral processing of Korean ore deals the gravity, magnetic separation and froth flotation, 2) decomposition and leaching of concentrates included sodium hydroxide fritting, sodium hydroxide hot digestion, hydrochloric acid leaching, 3) separation and purification of rare earth elements in mixed rare earth chloride solution consists reduction and oxidation method, solvent extraction, 4) preparation of rare earth oxide compound from purified elemental rare earth chloride solution having oxalate salt precipitation by reaction crystallization. The last part consists of a summary of the present study.

Jan 1, 2015

By Ting Lei, Mingjun Rao, Guanghui Li, Tao Jiang

"With the rapid development of iron and steel industry, the supply of iron ores can not meet the present demand for iron and steel industry in China. Large reserves of oolitic hematite have been discovered with low iron grade (30% ~ 45%) and high phosphorus content (0.4% ~ 1.8%). Traditional processes for utilization of this ore are characterized as either high cost or low dephosphorization. In this study, sodium salts-modified paigeite (SSMP) was added to enhance on the dephosphorization of high-phosphorus oolitic hematite by using reduction roasting followed by magnetic separation. Various parameters, including the amount of SSMP, reduction time,reduction temperature, grinding fineness and the magnetic field intensity were investigated. As a consequence, a magnetic concentrate of metallic iron powder with total iron grade of 93.2% and phosphorus content of 0.08% was obtained under the optimal conditions. The results also provide a potential avenue for the comprehensive utilization of paigeite ore.IntroductionOolitic hematite is currently recognized as one of the most refractory iron ore resources in the world. Over 4.0 billion tons of reserves of such resources have been found in China, and more than 10 billion tons in the long-term. This kind of ore is characterized as low iron grade (30%~45% TFe) and high phosphorus content (0.4%~1.8% P), as well as fine particle size distribution of ferrous minerals (the size distribution varies from 5~30 µm, even less than 2 µm) and the complex association between iron and other gangue elements [1~5]. The unique structural characteristics of the high phosphorus oolitic hematite make it difficult to obtain high iron recovery and good dephosphorization efficiency by using the conventional processes [1,2]. Traditional processes are characterized as high cost and low dephosphorization for oolitic hematite beneficiation [9~15]."

Jan 1, 2012

By S. Goto, S. Yamashita, K. Hata

"The average consumption of zinc dust for purification of zinc leaching solution is more than 25 kg per tonne of electrolytic zinc. Authors proposed to remove impurities in zinc leaching solution by electrolysis instead of cementation by zinc dust. The effects of copper and arsenic on electrodeposition of cobalt in zinc sulfate solution were examined fundamentally using a potentiostat. It is observed that cobalt is easily deposited on a cathode at potentials under -480mV with arsenic. Mesh cathodes of stainless steel and lead anodes were used in a small electrolytic cell and the electrolyte was circulated through 'the electrodes during the electrolysis. The effect of electrolyte circulating rate , pH, cell temperature, current density, and concentration of copper and arsenious ions on removal of cobalt were studied. Removal of Cd and Ni are also examined.IntroductionCobalt is difficult to remove from a zinc leaching solution by a simple cementation reaction using zinc dust. However, it is easily precipitated by zinc dust with co-addition of arsenious or stibinous oxide and copper ion in practical operations(I), (2), (3). The consumption of zinc dust for purification is 16-152 kg per tonne of electrolytic zinc and 65% of this zinc dust consumption is used for cobalt purification. The average retention time for purification of cobalt is 4.5 hours (1). A more economical process for purification is desired instead of zinc dust. The mechanism of this acceleration effect of copper and arsenious oxide on removal of cobalt are explained by the authorsas follows; a galvanic cell is formed between zinc dust and copper which is precipitated firstly, and cobalt is reduced on copper as Co-As alloy by this galvanic current(2). This assumption was confirmed in experiments using a galvanic cell with a membrane( 4). The following galvanic reactions occur between zinc dust and copper precipitate; on copper cathode,2H+ + 2e -= Hz(g)2Coz+ + 2HAs02 + 6H ++ 10e -= 2CoAs + 4HzOand on zinc anode,Zn = Zn = 2+ 2e –This galvanic current becomes almost zero in a zinc sulfate solution which includes only cobalt and no arsenious oxide, and cobalt is weakly deposited on a copper cathode. Cobalt deposition requiers a high degree of cathodic polarization. However, the galvanic current flows almost constantly in an electrolyte, which includes arsenious oxide, and the cathode potential is kept at about -500mV. Cobalt is precipitated as Co-As on the cathode.The authors assumed that cobalt may be removed by electrolysis at a very low current density instead of zinc dust and the following experiments were carried out. In the first part of this paper, the fundamental experiments using a potentiostat on the behaviour of cobalt in zinc sulfate solution are described. In the second part, the results of the electrolysis are reported. Cobalt is removed by a new type of an electrolytic cell, which was desigoed to <Iccelerate the rate of deposition of cobalt. The removal of cadmium and nickel in a solution which includes cobalt and arsenic are also examined."

Jan 1, 1997

By Felix Wolters, Michael Schütt

In over 40 years of operation, engineers at Aluminium Oxid Stade GmbH (AOS) have acquired a lot of experience whereby they have developed a series of optimizations regarding the specific primary energy consumption. The tube digester technology, invented by VAW in Germany and applied on an industrial scale for the first time in Stade, was brought to perfection by its innovative cleaning methods, which led to a constantly high heat transfer, low pressure loss and excellent availability of the digesters. Further improvements such as the heat recovery from the exhaust gas stream of the salt heater as well as the optimization of one of the fluid bed calciners and the installation of a combined heat and power generator (CHP) led AOS to where it is now—a leading alumina refinery with regard to the lowest energy consumption per ton of alumina.

Mar 1, 2017

By A. P. Paiva

Studies focused on the recovery of precious metals by solvent extraction have recently increased. either to devise suitable solvents or to clarify the involved extraction mechanisms and kinetics. In this work, a comparison of the performance exhibited by triphenylphosphine (TPP), bis-(penty1thio)-ethane (BPTE) and triisobutylphosphine sulfide CI"I&apos;BPS) in the extraction of silver from acidic chloride media is carried out. Extraction and stripping isotherms involving the three extractants are presented together with the results obtained on the selectivity of silver extraction against high contents of iron, copper and lead. Attempts to clarify the mechanism of silver extraction by TIBPS were performed by studying the distribution coefficient dependence on ligand and chloride concentrations. The effect of temperature on extraction and stripping is also considered. The interfacial tension for the system, measured with different concentrations of extractant in the organic phase, is analysed.

Jan 1, 1994

By Shuichiro Okada

Various efforts to reduce energy consumption and smelting cost are made at Tamano Smelter. Production of anode copper has been increased by about 30 % and energy requirement has been decreased about 50 % respectively. Challenges toward more higher goal are being continued. Details about the following are described in this paper. 1 Waste heat recovery Steam recovery at up-take of FSFE Heat recovery from waste gas of anode furnaces 2 Application of tonnage oxygen 3 Application of pulverized carbonaceous fuels to the flash smelting furnace with furnace electrodes ( FSFE ) 4 Application of computer control system to copper smelting 5 Improvement of the fugitive gas collecting system 6 Improvement of the mechanical tuyere puncher for the converter furnace

Jan 1, 1983

By John Fallavollita

Conventional gas atomization produces powders that vary widely in size distributions and microstructures, thus making it very costly to produce powders tailor made in a narrow size distribution and microstructure. Furthermore, it is difficult to determine the relationships between atomizer operating conditions and resulting powder characteristics. The Impulse Atomization Process (IAP) was developed at the Advanced Materials and Processing Laboratory to produce powders with narrow size distributions. Powders produced by the IAP were reproducible and their sizes could be easily controlled by adjusting experimental conditions. Characteristics of Zn, Sn-Pb, AI-Cu, and Cu powders will be described to illustrate the flexibility of the process to tailor-make powders.

Jan 1, 1994

By P. Felix

A discussion on the need of visualization and animation tools in modelling solidification processes is made. An outline of an approach for the production of a video computer animation is provided. A number of examples including, 2 and 3 dimensional melting, filling, and macrosegregation are presented.

Jan 1, 1993