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By S. Moussa

The formation of boron-doped nickel aluminides Ni3AI, (76 at. % Ni) from elemental powders by reaction synthesis using reactive sintering was studied. The process involves the mixing of elemental powders of nickel and aluminium with various wt % of boron up to 1 wt % boron. Nickel and Aluminium powders were mixed in the correct proportion to form the intended boron-doped nickel aluminide intermetallic. XRD, SEMI EDS, Image analysis and Archimedes principle; were used to study the effect of Boron addition on the final microstructure, bulk density, average grain size of as reactively-sintered nickel aluminides (boron-doped), compared with no boron addition. The results showed that at greater boron content than 0.3 wt %, a two-phase non-equilibrium microstructure of consisting of NiAI phase in NiJAI matrix was formed that have been primarily retained even after heat treatment for 5 hours at 1000 °C. Boron was present in solid-solution within both the NiAI and the Ni3AI (in greater amounts) phases.

Jan 1, 2001

By Warren J. Bruckard, Mark I. Pownceby, Sazzad Ahmad, M. Akbar Rhamdhani

Rutile is the preferred feedstock for producing high-grade TiO2 pigment but due to decreasing resources, alternative materials such as ilmenite is now used to produce a synthetic rutile (SR) feedstock. This requires removal of impurities (e.g. Fe, Mg, Mn) which, for a primary ilmenite is straightforward process. Processing of weathered ilmenite however, is complex, especially when chrome-bearing impurities are present since minor chromium downgrades the SR market value as it imparts color to the final TiO2 pigment, Chrome-bearing spinels are a problem in weathered ilmenites from the Murray Basin, Australia as their physical and chemical properties overlap with ilmenite making separation difficult. In this paper, different sulfidation process routes for weathered ilmenites are analyzed for their applicability to Murray Basin deposits as a mean of remove chrome spinel impurities. Thermodynamic and experimental studies indicated that selective sulfidation of chrome-bearing spinel can be achieved under controlled pO2 and pS2 processing conditions thereby making them amenable to separation.

Jan 1, 2015

By Kafui Nyavor

The indirect, and the direct contact mechanisms of bacteria oxidation of sulfides were studied using Thiobacillus ferrooxidans and pyrite. The aim was to determine which of the two generally aeeepted mechanisms played a dominant role, if any, during acid mine drainage (AMD) formation from the oxidation of sulfide minerals. The results show that at a pH of 4.5 where T. ferrooxidans are quite active, but where initial chemical oxidation of pyrite to Fe2+ is limited, the bacteria were unable to directly oxidize pyrite to any significant extent. Whereas, in the presence of Fe2+, T. ferrooxidallS assisted oxidation of pyrite by the indirect mechanism was observed and sustained over the pH and Eb range where the bacteria is active. The results lead to the conclusion that the direct contactmechanism of pyrite oxidition by T. ferrooxidans is insignificant. The predominant, and possibly the only, pathway involves the indirect bacteria oxidation of available Fe2+ to Fe3+, which in turn oxidizes FeS2 to generate additional Fe2+ and acidity in a cyclic process.

Jan 1, 1996

By Paul S. Korinko, Simona E. Hunyadi Murph

To address a radiological contamination event, a materials and process project was initiated. During the course of this project, processes and materials were developed that successfully captured zinc vapors physically and chemically, respectively. However, the physical traps were placed in an undesirable area and it was determined that the chemically captured zinc reactions was reversible. Consequently, advanced nanomaterials are being developed to capture zinc vapors. The current state of the art of the science and engineering of these materials and their efficacy for zinc capture and retention is discussed in this paper.

Jan 1, 2015

By W. -D. Schneider, B. Schwab

Like all metals, zinc can be recycled theoretically without end. To demonstrate environmentally friendly use of zinc, it is necessary to increase the recycling rate. In this regard, the Imperial Smelting Process developed in the forties and fifties in the United Kingdom has become more and more important. This unique process combined with a sinter plant, hot briquetting, and direct injection through the ISP furnace tuyeres offers ideal possibilities to recycle all kinds of zinc and lead bearing materials. Possible secondary materials include Electric Arc Furnace (EAF) dust, zinc-containing sludges and even zinc/carbon batteries. This high temperature process also destroys all organic materials, like dioxin, and can be seen as a sink for many harmful substances.

Jan 1, 2000

By David G. Dixon

A general, unsteady-state model for leaching of one or more solid reactant species from a non- reactive, porous, spherical pellet is derived in dimensionless form for the interpretation of leaching data, and for use in the design of coarse-ore leaching processes. The effects of diffusion rate, chemical reaction rate, variable reaction order, and competition between multiple solid reactants are examined using the concept of the effectiveness factor. It is shown that the model is capable of simulating both "reaction-zone" and "heterogeneous" kinetics, depending on the choice of three dimensionless parameters. Results of batch leaching tests of artificial ore pellets are presented, and their relationship to the model is discussed.

Jan 1, 1993

By Basant L. Tiwari

An electrolytic process, based on a three-layer concentration cell, to extract magnesium from commercial aluminum alloy scrap has been examined. The process was repeatedly tested at 1025 K with two cells of d1fferent sizes, 0.6 kg and 5 kg feed aluminum, to have a better understanding of the opera ting parameters and evaluate the scale-up potential. In both cells, the magnesium content of the scrap was selectively reduced ?from 1. 1 to less than 0.1 wt.% at anodic current dens-Hy as high as 1. 1 A/cm2 with current efficiency exceeding 85%. Magnesium was recovered in the form of salt coated globules. Comparison of performances for the two cells suggests that the process can be scaled up. With further development, this process could become a viable alternative for demagging secondary aluminum.

Jan 1, 1985

By John Norton

"This presentation will cover the physical properties of waste heat recovery. It is a two part presentation. The first deals with actually recovering the heat with new state of the art heat exchangers and applying that heat to the furnace combustion and the second part will cover what other processes you can enhance with this ""free"" heat. It will also talk about converting it to steam, hot air or electricity to be used or sold back to the utility company. The economics of various schemes will be reviewed. A brief discussion on State and Federal grants and subsidies will be presented.IntroductionThere are large quantities of wasted heat in the usual aluminum melting process. And, there are several techniques for reducing and/or using some of that wasted heat as you have seen. Any technique that can make use of wasted heat is a form of recovery. This can range from simply preheating aluminum billets prior to melting, to more complicated processes like air-to-air heat exchangers using the boiling and condensing characteristics of special fluids in “heat pipes.” The objective of this type energy recovery process is to move the wasted heat from the hot and dirty exhaust gas stream into some useful process.Waste Heat Recovery in the Aluminum Melting Furnace.There are considerations, of course:1) What might the value be of the recovered energy?2) Can the recovered energy be used within the process? Within the plant? Or by theneighbors?3) What is the capital cost?4) Is the recovery process complicated?5) Will it take additional staff?6) Will it cause additional downtime on the melting line?7) Will the operations staff need to be licensed?Ideally, the process will be simple and inexpensive, the recovered energy will be very valuable, and the whole effort will cause little distraction to the aluminum melting process itself. These would be ideal."

Jan 1, 2011

By Chikabumi Yamauchi, Mitsuru Tanahashi, Tsuyoshi Taniguchi, Nobuo Furuta, Toshiharu Fujisawa

"It is essential to clarify the equilibrium relations among nonmetallic inclusions of the Mn0-SiO2-CrOx system and molten stainless steel in order to control non-metallic inclusions formed by the deoxidation of stainless steel with silicon. In the present study, the phase equilibria of the MnO-SiO2-CrOx system were measured by conducting the following experiments under controlled oxygen partial pressure, Po2, at 1873 K:1) Phase equilibria of the MnO-Cr20 3 binary system were measured for Po2 = 2 x 10-6 ~2 x 102 Pa.2) Phase equilibria of the MnO-SiO2-CrOx ternary system were measured for Po2 = 2 X 10-6 Pa.Based on the results, the phase diagram of this ternary system was established under the condition of the Si-deoxidation process of stainless steel (Po2 = 2 x 10-6 Pa and T = 1873 K).IntroductionAt the deoxidation stage in steelmaking process, generally multiple deoxidizers participate in deoxidation reactions, and the composition of deoxidation products ""non-metallic inclusions"" greatly varies depending on deoxidizing efoments and their contents. In order to control non-metallic inclusions formed by the refining process of steel, it is essential to clarify the equilibrium relations among non-metallic inclusions and molten steel.Especially, during the refining process of stainless steel, nonmetallic inclusions in molten steel seem to- change as follows. After the oxidation refining, Mn-chromite is formed in molten steel as non-metallic inclusion. By the deoxidation with silicon addition (mainly less than 1 mass%), Mn-chromite inclusions are changed their compositions to Mn-silicate. Segawa et al.[l] have reported the effect of amount of silicon addition on composition and mass ratio· of non-metallic inclusions during the Sideoxidation process of 18Cr-8Ni stainless steel at 1873 K, as shown in Figuri; L At higher silicon content than 0.5 mass%, only Mn-silicate was identified as non-metallic inclusion. On the other hand, at lower silicon content, both of Mn-chromite (MnO Cr2O 3) and Mn-silicate were identified. However, the thermodynamic and the kinetic analyses of the above-mentioned Sicdeoxidation process have not been made due to lack in the thermodynamic data for the non-metallic inclusions· of the MnO-SiO2-CrOx system, such as the phase diagrams, the activities of the components, and the free energy of intermediate compounds. In relation to the phase diagram of this system, those of the MnO-SiO2 [2] and the SiO2-Cr2O 3 [3] binary systems have been only reported"

Jan 1, 2000

By Xinhua Wang, Qiangqiang Wang, Yubin Li, Shusen Li, Lifeng Zhang

"Numerical simulation on the fluid flow in a Flow-Control Mold (FC-Mold) were performed. The motion of inclusions were calculated. With FC-Mold, the flow pattern and surface velocity become more symmetrical, and at higher casting speed the velocity of liquid steel in the top region of the mold was largely reduced with the highest velocity of the meniscus reducing from 0.65 mis to 0.4 mis, and the meniscus shape became flatter. With FC-Mold, more inclusions approached to the surface of the slab and the amount of inclusion in the center of mold became fewer. Larger inclusions were easier to remove, however, the EM filed of the FC-Mold could hardly improve the removal of inclusions from the molten steel.IntroductionElectromagnetic brake technology is an effective method to control the flow pattern within continuous casting mold, together with other casting parameters, nozzle design and mold geometry [1-5]. Due to the interaction between the applied magnetic flux and the conductive molten steel inside the mold cavity, a force is generated in the direction opposite to the jet flow, which can decelerate the high speed steel jet from the SEN ports. The potential benefits include fewer surface and internal defects, fewer inclusion especially at higher casting speed. However if used imperfectly, electromagnetic forces can have opposite effect [6]. Numerical models are the best tool to optimize electromagnetic flow control. In the current study, numerical simulation was performed to investigate the flow field in a continuous casting FC-Mold, and the effect of different operation parameters on the flow, surface level and velocity in FC-Mold were discussed."

Jan 1, 2013

By Srinath Viswanathan, Adrian Sabau

"In general, the occurrence of microporosity during metal casting is due to the combined effects of solidification shrinkage and gas precipitation. The governing equations for fluid flow and hydrogen evolution indicate that porosity formation and fluid flow are strongly coupled. However, in most studies on microporosity, it is considered that the porosity formation does not influence the fluid flow in the mushy zone. In this study, a computational methodology is presented for the numerical simulation of interdendritic fluid flow and microporosity evolution. The solution algorithm presented includes a fully coupled, implicit treatment of microporosity and local pressure in the mushy zone. The effects of microporosity evolution due to the local pressure drop in the mushy zone, and pore expansion in casting regions where liquid feeding alone cannot compensate for the solidification shrinkage are also considered. It is shown that neglecting the effect of porosity formation on the pressure in the mushy zone yields higher pressure drops. By its growth, microporosity partially compensates for the solidification shrinkage, reducing the feeding demand. A reduced feeding demand requires less fluid flow to compensate for solidification shrinkage, and results in smaller pressure drops in the mushy zone. Therefore, in order to accurately describe casting defects, comprehensive models of fluid flow, heat transfer, and solidification must include the effect of microporosity as well.IntroductionIn the terminology commonly used by foundrymen, porosity is usually considered to be either ""hydrogen"" or ""shrinkage"" porosity. Hydrogen porosity is the term given to porosity that is generally rounded, isolated, and well distributed. Porosity that is interconnected or clustered, and of an irregular shape corresponding to the shape of the interdendritic region, is usually termed shrinkage. In general, the occurrence of microporosity in aluminum alloys is due to the combined effects of solidification shrinkage and gas precipitation [1]. Continuum models [1, 2- 7] have been used to predict the level of porosity in castings. A number of other studies have also attempted to understand the phenomena of porosity formation and pore growth [8-10] and pore morphology [11].The governing equations for fluid flow and hydrogen evolution indicate that porosity formation and fluid flow are strongly coupled. However, in most studies [4, 9, 10], it is considered that the porosity formation does not influence the fluid flow in the mushy zone. Kubo and Pehlke [3] presented a methodology for the prediction of microporosity distribution in shaped castings by considering the effects of both the hydrogen precipitation during solidification and the pressure drop in the mushy zone. In their approach, the local pressure and porosity were computed in an uncoupled manner based on a ""flux of interdendritic liquid"" criterion, i.e., either pressure or porosity was first computed using the other variable at the previous time step. Their approach has been used with little change in numerous studies [6, 12, 13]. Recently, Kuznetsov and Vafai [14] presented a fully coupled, one-dimensional model for the computation of pressure and porosity. They showed that neglecting the effect of porosity formation on the pressure in the mushy zone yields higher pressure drops and an over-prediction of final porosity. They also showed that the influence of porosity formation on the pressure is larger at lower pressures in the mushy zone."

Jan 1, 2001

By Clara María Lamus Molina

The following minerals found in the residual black sands from gold mining in El Bagre Antioquia (Colombia) were identified as having major economic interest: Ilmenite (FeTiO3), with an average of 49% of TiO2, frequently altered presenting crowns; lamellaes of rutile and alteration textures; titanomagnetite with up to 25% of TiO2; magnetite (Fe3O4) in individual grains or associated with others minerals as hematite and ferromagnesian silicates rutile (TiO2) with considerable quantities of Nb2O5(0.1-3.7%Wt); zircon (ZrSiO4) with 66%Wt of ZrO2 and monazite with an average of 63.43%Wt of REE, this frequently associated to xenotime and thorite forming textures as little drops. Analysis in EPMA and SEM/EDS showed percentages of minor elements and traces, thereby clearly establishing the applications of these minerals in diverse industries. Furthermore, a detailed granumetric study of the different minerals and textural relationships among them also allowed for establishing the basis for possible processing and exploitation.

Jan 1, 2006

By Paul-Dominique Oudenne

For many years, CMI NESA has gained considerable experience in the field of alternative thermal processing processes by which useful by products result in addition to the destruction of the raw wastes. The CMI NESA pyrolysis process has been extensively applied to a wide range of sewage, industrial sludge and residues. This paper describes in details the development works carried out at the pilot stage as well as the key parameters of the process. Some of the industrial realisations are briefly described, the most recent one being the erection of a sludge pyrolyser on predried sludge at 90% dryness of a capacity of 100 tons of dry matter per day for the Valenton plant of the SIAAP (city of Paris).

Jan 1, 2006

By Upali Siriwardane, Tushar V. Kudale, Naidu V. Seetala

"Cellulose acetate (CA) membranes with 25% triethyl citrate (TEC) as plasticizer were prepared with varying thickness for CO2 gas separation from water-gas-shift (WGS) reaction products. The AFM analysis of the CA membrane showed that the uniform coating had fewer and smaller pores as the film thickness increased, and corroborated by gas permeability studies. The CO2 permeability has decreased faster than CO permeability with the CA/TEC membrane thickness, and findings support that the CA membrane could be used to entrap CO2. Several CA/TEC membranes were also staked to increase the separation efficiency. Positron Annihilation Lifetime Spectroscopy (PALS) was used to estimate the nano-porosity (pore size and concentration) changes of CA/TEC films. PALS results show a decrease in pore size with increasing CA-TEC concentration in acetone, while the pore concentration increases. The PALS results are correlated with the CO2/CO permeability variations as the CA-TEC concentration change.IntroductionHydrogen is one of the main energy sources available for the future advancement of clean fuel technologies especially for fuel cells. Generation of hydrogen and CO2 from Water Gas Shift (WGS) reaction mixtures of CO and H2O is of interest to many researchers since it allows a large scale production of hydrogen [1, 2]. Once hydrogen is produced using the WGS reaction, the output products contain mixture of CO, CO2, H2, and water vapor. Metallic membranes have been used as hydrogen separation membranes [3-6]. As H2 is separated from the mixture using the metal membranes, we need to separate CO2, and find ways of sequestration of CO2 to avoid environmental problems by greenhouse gasses. Polymeric Membranes have been used for CO2 separation [7]. Plasticizer can control the micro-structural properties such as pore size and concentration of polymer membranes [8], which influence the size/molecular weight dependent diffusion rates of the gas molecules. We have used cellulose acetate with triethyl citrate as plasticizer to separate CO2 from the WGS reaction products. Positron annihilation lifetime spectroscopy (PALS) is very sensitive and able to identify different kinds of defects and their agglomerates such as vacancies, vacancy loops, and voids [9, 10]. PALS has been successful in determining the free volume in polymers that influence the properties of the polymers [11, 12]. Microscopic properties of the free volume obtained from PALS have been correlated to macroscopic properties [13, 14]. We used PALS to study the nanoporosity (pore size and concentration) and fractional free volume changes of CA/TEC films, and used to understand the variations observed in the CO2/CO permeability as the CA-TEC concentration in the membranes change."

Jan 1, 2014

By Hu Meilong, Liu Lu, Bai Chenguang

Extracting perovskite from high titanium-bearing blast furnace (BF) slag is a green and potential method to recover the second titanium resource. The non-isothermal crystallization process of perovskite in synthesized high titanium-bearing slag was studied in situ by confocal scanning laser microscope (CSLM) with cooling rate of 20 K/min. The results showed that perovskite was the primary phase formed during cooling process in the titanium-bearing synthesized slag (TiO2=23%). Perovskite started to precipitate at 1719 K and finally presented an orthogonal straight lines morphology.

Jan 1, 2014

By A. D. Damodaran

Batch scale and continuous rotary kiln carbothermic metallisation of ilmenite followed by different down-stream treatments such as catalytic rusting, acidic chloride leaching, oxidation-leaching etc. has given rise to a high grade synthetic rutile (98% TiO2). Rotary reactor metallisation experiments had concurrently given important information with respect to mean residence time, dispersion number, hold-up and axial velocity profiles of the solids bed. A mathematical model based on law of additive reaction times has indicated that Boudouard reaction becomes faster than reduction reaction at higher conversions. A possible use of high grade synthetic rutile in paint industry and metallised ilmenite as welding electrode flux material are discussed.

Jan 1, 1992

By Youngkook Lee

The precipitation kinetics of NbC in ferrite matrix of the Nb microalloyed steel was investigated experimentally and numerically. The mole fractions of NbC precipitates formed at different isothermal temperatures were measured as a function of holding time by electrical resistivity test and were compared with both a mathematical model based on time-dependent nucleation and growth rates and the hardness. There is a good match among the calculated and measured precipitation kinetics of NbC and the hardness. The isothermal precipitation-temperature-time diagram of NbC in ferrite matrix of the Nb microalloyed steel was newly generated. Keywords: Precipitation, Carbide, Ferrite, Nucleation, Growth, etc

Jan 1, 2003

By E. Charles Abbey

Manganese in electrolyte has both beneficial and detrimental effects in Zn electrowinning. Mn oxidizes to form MnO2 on Pb–Ag anodes, cell walls and pipes. MnO2 reduces anode corrosion but also leads to short circuiting and maintenance issues. MnO2 is thought to interact with chloride ions and produce oxidized chlorine species. The interactions between Mn and Cl are not well understood. Therefore, two sets of 45+ day bench scale experiments were conducted to investigate the effects of the manganese to chloride ratio on anode corrosion rate and electrolyte chemistry using rolled Pb–Ag anodes. Daily manganese and chloride losses from the electrolyte appeared to be correlated. Increasing the average Mn/Cl− ratio from ∼7:1 to ∼11:1 reduced the anode corrosion rate. Increasing the ratio above 11 did not reduce the corrosion rate further. Anode scales produced with Mn/Cl− ratios at and above 11:1 contained some γ–MnO2 while scales formed with ratios less than 11:1 did not.

By Wei Luo, Yuanbo Zhang, Zhixiong You, Zijian Su, Guanghui Li, Tao Jiang

"In this study, the appropriate sintering process parameters for low-grade ferromanganese ores were investigated. The results showed that, under the condition of natural basicity (R=0.03), the optimal parameters were obtained as follows: moisture of mixture 9 .1 %, coke powder 9 .9% and sintering negative pressure 7 KPa. And the corresponding yield, ISO tumbling index and utilization coefficient reached at 80.18%, 61.27% and 1.515t·m-2·h-1, respectively. Under the optimal parameters, the emission of harmful gases, such as S02 and NOx, were reduced evidently with 30% of coke powder replaced by biomass charcoal. Moreover, it was found that the basicity had obvious effects on the quality of the sinters when it changed between 0.03 and 2.4. The ISO tumbling index gradually decreased from 61.27% to 55.47% with the basicity increasing from 0.03 to 1.2, then, it began to increase after the basicity further increased to 2.4.IntroductionManganese is mainly consumed by steel and battery industries, particularly in the steel plants and ferroalloy units. The consumption of metal manganese in the ferroalloy industry accounts for 85%-90% of the total Mn [1-2]. Therefore, ensuring sufficient manganese alloys is essential to meet the rapid development of steel industry. Recently, rich-manganese slag containing high grade Mn (>40%), low Fe (1%) and P (<0.03%) is considered as superior raw materials for manganese alloys. While the sinters made from manganese ores are major raw materials for producing rich-manganese slag with the increasing exhaustion of natural rich manganese lump ores [3-5]."

Jan 1, 2013

By Mingmei Zhu, Xin Qiu, Xiaofei Dou, Yu Wang, Tiancheng Lin, Bing Xie

In this study, the slag forming route of the single-slag steel melting when smelting medium phosphorus hot metal was investigated. The CaO-SiO2-FeO-MgO-MnO-P2O5 as hexahydric slag system was adopted in the converter. The effect of slag composition on liquidus was calculated by FactSage, the isogram of phosphorus distribution ratio was calculated by using the regular ion solution model, combining these two tasks, the theoretical slag forming route was obtained. Through experiments, the actual melting point ofthe corresponding components on theoretical slag forming route was obtained, in this way, the theoretical slag forming route was confirmed. Then, the theoretical slag forming route was applied to industrial test in a 210t BOF. After using the new slag formating route, the dephosphorization ratio was increased 3.6% while the auxiliary materials consumption was reduced, and the cost of steelmaking was reduced.

Jan 1, 2015