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By Luiz A. Teixeira

This paper reports the results of kinetic studies involving the precipitation of arsenic from aqueous solutions as FeAs041 Fe(OH)3' using FeS04 as source of Fe ions, and Air or H202 as oxidizing agents. Both systems lead to an efficient removal of arsenic. The differences in oxidants performances are in the precipitation reaction rate -much faster using hydrogen peroxide. Mechanisms of reactions were suggested based on the following main steps:

Jan 1, 1996

By James W. Evans, Dong Xu, Jr. Jones

A physical (water) model based on particle image velocimetry (PIV) has been constructed at UC Berkeley. The PIV technique enables the use of water modeling to quantitatively characterize the fluid flow behavior in the mold during the continuous casting of steel, in a whole field sense, i.e., section by section. A method to obtain e\e time-averagevelocity (TA V) vector maps was developed by averaging 40 instant aneous vectc -r plots revealing the time average features of the flow. Another benefit of TAV vector maps is the ability to compare with present mathematical models, which are mostly based on the time-average technique. Bifurcated submerged entry nozzles (SEN) with ports inclined at various angles to the horizontal were used in the modeling to study their effects on the flow inside the caster. Argon was also introduced into the model to simulate the influence of argon injection on the metal delivery from the tundish into the caster. The bubble sizes and distribution (in specific sections) of argon were characterized, at the same time, by the imaging system of the PIV. This will allow for validation of current mathematical models that were developed to simulate argon injection in casters. Comparison with results calculated by the commercial finite element package FIDAP is also presented.

Jan 1, 1998

By Zhou Shu-cai

"A method has been proposed for the pre-treatment of high phosphorus iron ore by carbothermic reduction assisted with microwave irradiation and magnetic separation on a laboratory scale. Chemical analysis of the reduced ore sample, the metal sample and the slag sample were conducted. Based on the above research, the influences of carbon addition, microwave power and microwave irradiation time on the recovery of Fe and dephosphorization were discussed. It indicated that the increase of microwave irradiation time and power had substantial effect on the recovery of Fe while the influence of carbon addition was not obvious and the highest iron recovery ratio reaches some 95.5% when the dephosphorization ratio was 37.68%. A high iron recovery ratio and a reasonable dephosphorization rate were incompatible under the conditions investigated in this study due to the reduced iron and because unreduced P-contained gangues were not efficiently separated. This method may provide a reference for the future utilisation of high-phosphorus iron ore.IntroductionWith the rapid growth of crude steel production in China, the source of iron ore tends to become increasingly strained and is facing the risks of raw material shortage for the iron and steel industry. In order to decrease the production cost, China has to focus on the utilization of its domestic low grade iron ores for the iron and steel plants [1-2]. China has a large deposit of high phosphorous iron ore with a reserve of 7.45 billion tons which is unused in any large scale [3]. Therefore, the development of a successful and economically viable technology for high phosphorus iron ore is of profound importance. To remove phosphorus from the high phosphorus iron ore, several mineral and metallurgical processes have been proposed, such as bio-leaching [4], roasting reduction plus melting separation [5], pre-reduction and screening methods combined with mechanical crushing or air jet milling[6] selective agglomeration plus reverse flotation [7]. However these processes are not cost effective or are time consuming. The traditional pyrometallurgical process( BF+ BOF) refuse this kind of ore mainly because that molten iron is saturated with carbon or high carbon content and thus all phosphor us in the burden goes to the molten iron[8]. Therefore, it is important to exploit the cheap and abundant high phosphorus iron ore as a resource in ironmaking. In recent years, the microwave was widely introduced as a heat resource for extractive metallurgy of iron ore or other minerals. For example, microwave assisted ore milling, microwave assisted carbothermic reduction of metal oxides and microwave assisted mineral leaching issues[9-10]"

Jan 1, 2014

By M. Giralico

Optimized mixer settler designs will now handle flows of over 25,000 GPM. The size and expense of the equipment hamper experimental settler optimization efforts. Computational Fluid Dynamics (CFD) is a timely and predictable tool for settler design development. In the past, CFD has been used to evaluate only the flow field in pumped and auxiliary tanks. A similar numerical analysis is used to evaluate settler flow and phase separation. Phase separation is analyzed using multiple species for the aqueous and organic phase. Experimental validation shows good agreement between the computational and experimental solutions in both flow field and phase separation. The computational model is used to show performance differences between various choices of settler geometry, liquid depth, with variable flow rates. Understanding the differences allows the development of optimized settler designs. System improvements are predicted to lower entrainment levels further and/or allow new smaller footprint designs. This paper focuses on the major design components of the settler and how future technological advances will lead to further improvements in their design. LIGHTNIN?s new designs will handle tomorrow?s production requirements, while maximizing profits.

Jan 1, 2003

By Malti Goel

"The cost-effective capture of carbon dioxide (CO2) from the point sources for its reduction the atmosphere offers many challenges in materials science. Novel CO2 capturing approaches using chemical, physical and biological methods are in the research stage and are aimed to minimize the cost. Appropriate materials development , which can withstand required temperature or pressure as the case may be for CO2 emanating from coal gas or industrial waste gases form the minimum condition. Other requirements are reclyclability of material and cost of separation. Nano-material composites can be more effective in selective capture of CO2 and can offer solutions for large-scale separation process. Nano-porous material catalysis can enhance the reaction rate of CO2 with other chemicals and thus help in capture of CO2 and convert it into value added products. This paper reviews recent industrial scale developments. In the Indian context, R&D priority areas in CO2 capture process development with a focus on energy industry are presented.IntroductionScience of Climate Change is growing at an enormous pace. With the ultimate goal of stabilization of greenhouse gases in the atmosphere, new scientific approaches are being researched worldwide. A shift in policies from low carbon and no carbon energy sources to fossil fuel sources with capture of carbon and its permanent storage is taking place. The process of carbon capture is both energy and materials intensive and the cost of power generation may increase up to 40% when carbon capture and storage (CCS) technology is implemented. Development of cost effective R&D technology therefore remains the greatest challenge before the scientific community."

Jan 1, 2009

By K. Morsi, S. K. Kassegne, K. S. Moon, A. Numula

"Current Activated Tip-based Sintering (CATS) is a new process for the powder-based manufacturing of macro, micro and possibly nano-scale features and shapes. CATS enables the selective sintering of powders by localizing current activation conditions through an electrically conducting small tip (either in the stationary or moving mode). This paper presents preliminary experimental results on the CATS of reactive mixtures of Ni/Al powder to form nickel aluminide intermetallics. Preliminary investigations on the effect of current on the reaction characteristics are discussed.IntroductionSpark Plasma Sintering (SPS) has been the subject of intense research over the past decade [1,2, 3,4,5,6]. The process boasts remarkable advantages which include ultra fast heating rates (hence by-passing low temperature non-densifying sintering mechanisms), considerably lower sintering temperatures and shorter sintering times than achieved in conventional sintering. The process is however limited to the generation of simple geometries on the macro-scale. Recently three of the authors conducted work on a novel process ""Current-activated tip-based sintering (CATS)"" [7], where electric current is passed through a conducting tip that is placed or allowed to travel over a powder bed/compact to locally sinter powders. lD, 2D and 3D micro-scale sintered shapes can be generated with the possibility of 3D rapid prototyping on the macro/micro or nano-scale. Although CA TS of single phase powders has been conducted, the CATS of reactive powders has not yet been investigated.The Ni-Al phase diagram contains five intermetallic compounds, AhNi, AhNh, AlNi, AhNi5 and NhAl. Out of these intermetallics, NiAl and NhAl have received the vast majority of scientific and industrial interest [8]. NhAl can be formed by reaction synthesis, where nickel and aluminum reactant powders are heated to a reaction ignition temperature at which the reactant powders are converted to the intended intermetallic product. The reaction is exothermic which gives rise to considerable compact self heating, thus instantaneously raising the compact temperature by several hundred degrees which facilitates sintering [8]. Applying and electric current locally would not only provide for a rapid local reactive sintering, but would generate a number of intriguing scientific investigations. For example, of interest would be, how would the reaction propagation and microstructural/phase evolution be affected by the temporal and spatial temperature and current distributions."

Jan 1, 2011

By R. D. Osmanson

A series of batch roasting tests was performed on minus 1/2 inch gold bearing refractory samples from the Gold Acres deposit, and 67 select particles were polished and the sulfide alterations were examined microscopically. The suite of specimens represents two hour batch roast treatments at 600°C, 700°C, 725°C, 750°c, 800°C, and 900°C. Auriferous pyrites were found to alter sequencially to pyrrhotite, magnetite and finally to hematite. It was found that the decrease in cyanidation extraction with high temperature roasting is likely due to the increas ing stability of magnetite and more crystalline hematite, and the decrease in porosity with these phases which occlude the gold. Gold has been noted to occur very early in the mineralizing sequence, with gold being found in quartz and in clay/carbonate rock matrix. No gold was found in the two pyrite phases, but numerous gold grains were found in pyrrhotite after pyrite and in subsequent iron oxides. Gold mineralization had apparently ended by the time base metals were introduced into the deposit.

Jan 1, 1987

By Wang Zhi

High-Mg-content concentrates are usually treated in Jinchuan flash smelting Furnace. Because the viscosities of high-Mg-content slag is very high, the operation of flash smelting becomes very difficult. To solve this problem, the viscosities of the semi-synthesized FeO-MgO-SiO2 slag of different compositions were measured. The results showed that when in the slag the weight percentage of MgO [w(MgO)] is 6-10%, the ratio of the weight percentage of iron to that of Si02, w(Fe)/w(Si02) is 1.1-1.4 and the temperatures are within 1473-1773K, the slag viscosities increased with the increase of W(MgO) and w(Fe)/w(SiO,). When w(Mgo)<6%, the smelting temperature should be controlled at I 300°C in order to to keep the smooth operation. When w(MgO)>10%, the temperature should be kept above I 633K. When the content of MgO is higher, a lower viscosity slag can be produced by decreasing the ratio of w(Fe)/w(SiO,). The appropriate ratio of w(Fe)/w(SiO,) for Jinchuan flash smelting furnace is about 1.2.

Jan 1, 2003

By Wang Zhi

High-Mg-content concentrates are usually treated in Jinchuan flash smelting Furnace. Because the viscosities of high-Mg-content slag is very high, the operation of flash smelting becomes very difficult. To solve this problem, the viscosities of the semi-synthesized FeO-MgO-Si02 slag of different compositions were measured. The results showed that when in the slag the weight percentage of MgO [m(Mgo)] is 6-10%, the ratio of the weight percentage of iron to that of Si02, m(Fe)/m(SiO2) is 1.1-1.4 and the temperatures are within 1473?1773K, the slag viscosities increased with the increase of m(Mgo) and m(Fe)/m(sio,). When m(Mgo)<6%, the smelting temperature should be controlled at I 300°C in order to to keep the smooth operation. When m(Mgo» 10%, the temperature should be kept above 1633K. When the content of MgO is higher, a lower viscosity slag ean be produced by decreasing the ratio of m(Fe)/m(sio,). The appropriate ratio of m(Fe)/m(sio,) for Jinchuan flash smelting furnace is about 1.2.

Jan 1, 2003

By Kazue Moriya

At the 1980 TMS-AIME world symposium, Dr. Davey mentioned that the traditional lead blast furnace is now being challenged by direct smelting processes. In the copper smelting field both the blast furnace and reverberatory furnace are also disappearing in favour of direct smelting processes such as Outokumpu flash smelting, Mitsubishi continuous smelting, Noranda furnace, Inco furnace and so on. Those new processes all have the following in common: (1) High degree of mechanization (2) Metallurgical reactions carried out in closed vessels (3) Application of oxygen and/or oxygen enriched air (4) Minimization of handling materials and gaseous volume (5) Minimum energy requirements (6) Removal of workers from near the furnace (7) Reduction of emissions of harmful gas to meet environmental regulations. (8) Improvement to the work place environment to avoid occupational hygiene hazards. Direct and continuous smelting of powdered concentrate in one vessel was a romance of the metallurgist since early times. However as mentioned above, in the copper field this objective is being achieved in practice. The industry however can&apos;t deny that the serious and severe regulation of environmental pollution in every country was the prime motive for the modernization of smelters. In early days, to meet regulations, it was anticipated that many economic difficulties such as higher capital and energy costs and extravagant use of resources and waste disposal would be the result. "Turn a misfortune into a blessing" is an old saying which reveals the current thinking and reacent developments in the nonferrous industries. In the last ten years in the lead smelting field, about two decades later than copper, commercial scale smelting using new furnance technology has started. The KIVCET process and QSL process, which is flash smelting and bath smelting respectively, are becoming major competitors. They will be sure to upgrade their processes to remain economically and environmentally viable in the comming decade.

Jan 1, 1990

By P. S. Dunn, A. D. Rollett, H. D. Lewis

"The results of preliminary work on the modeling and measurement of the heat transfer coefficients of metal/mold interfaces is reported. The system investigated is the casting of uranium in graphite molds. The motivation for the work is primarily to improve the accuracy of process modeling of prototype mold designs at the Los Alamos Foundry. The evolution in design of a suitable mold for unidirectional solidification is described, illustrating the value of simulating mold designs prior to use. Experiment indicated a heat transfer coefficient of 2 kW/m /K both with and without superheat. It was possible to distinguish between solidification due to the mold and that due to radiative heat loss. This permitted an experimental estimate of the emissivity, ~ = 0.2, of the solidified metal.IntroductionA feature that distinguishes casting processes from welding processes is the presence of an interface with a low heat transfer coefficient between the mold and the casting. Especially when chill casting, the interface delays the start of solidification and increases freezing times significantly. By comparison welds can be assumed to have a very high heat transfer coefficient. The heat transfer coefficient controls such phenomena as folds and laps on the surface of castings which can be crucial to the acceptability of a casting. The time delay for the start of solidification influences the occurrence of cold shut defects. The standard mold material for uranium casting is high quality graphite which is an excellent refractory when used in vacuum and coated with a refractory wash. Graphite is an effective chill material and has a thermal diffusivity approximately twice that of uranium. Experience has shown that practicable superheat without mold pre-heat is not sufficient for avoiding cold shut defects when casting in graphite molds.TheoryIt is possible to calculate the position of the freeze front s, as a function of time, t, the superheat and interface heat transfer coefficient, h, [1]. However, the value of h cannot be obtained explicitly. The Virtual Adjunct Method (VAM) [2] offers a method for extending the standard equation for an insulating mold where s is proportional to the square root of time. By considering the effect of the interface to be equivalent to finite thicknesses of mold and metal, the following quadratic equation is obtained,"

Jan 1, 1986

By J. A. Eisele

There is currently much interest in how extraction of gold and silver from ores with acidic thiourea solution compares with extraction using alkaline cyanide solution. Agitation leaching tests were performed by the Bureau of Mines on 14 precious metal ores using sodium cyanide (?NaCN) and thiourea [(NH2)2CS) as extractants. The objective was to compare the results of the two extractants. NaCN was used at a concentration of 2 g/L with and without H202 as an oxidant. (NH2)2CS was used at concentrations of 2 and 20 gjL, and the solution potential was controlled at 390 to 420 mV standard hydrogen electrode (Eh) with Fe2(S04)3. With both reagents a.t 2 g/L extractant levels, NaCN extracted more gold and silver than (NH2liCS from all of the ores. At 20 g/L (NH2)2CS compared with 2 g/L NaCN, (NH2)2CS extracted more gold than NaCN from two ores, the same amount from one ore, and more silver from one ore. NaCN extracted more gold than (NH2 )2CS from 10 ores and more silver from 4 ores.

Jan 1, 1989

By Yuanbo Zhang, Mingjun Rao, Guanghui Li, Chongzhong Ouyang, Shuhui Zhang

Oolitic hematite ore with high-phosphorus content is currently recognized as one of the most refractory iron ore resources in the world. The high-phosphorus content and unique structure of the oolitic hematite ore make it difficult to be beneficiated. The process of direct reduction followed by magnetic separation has significance to the utilization of oolitic hematite ore, and sodium salts can improve the dephosphorization. However, the behavior of phosphorus during reduction roasting, and the intensified dephosphorization mechanism of sodium salts are not clear. In this study, by using chemical analysis, chemical phase analysis, XRD analysis, optical microscopy, and scanning electron microscopy analyses, the behavior of phosphorus during reduction roasting of high-phosphorus content oolitic hematite ore and the effect of sodium salts on behavior of phosphorus were studied.

Jan 1, 2015

By L. Z. Villanueva

An investigation and evaluation has been performed to determine the potential utilization of electron beam irradiation technology for sulfur oxides removal from reduced-S02-strength metallurgical gases from copper smelters. These off-gases, though too weak to be converted to usable, concentrated: sulfuric acid by conventional means, are characterized by SO2 content higher than 2,000 ppm and a complex chemical composition, including high oxygen content and its generation occurring in a cyclical, fluctuating pattern. This work was based on information supplied by principal smelter companies in Chile. A laboratory facility with flow rate of 20 Nm3/h and equipped with an electron accelerator of beam energy 8.00 keV, has been used for testing. Influence on SO2 removal efficiency of operational parameters such as gas temperature, water vapor content, ammonia feed ratio and irradiation dose was established. The main conclusion of this work, from experimental laboratory tests as well as engineering studies, is that the Electron Beam Process (EBDS) is a cost-effective, simple and appropriate chemical process means for emission abatement. EBDS can, on a site-specific basis, adequately augment SO2 removal to upgrade overall abatement as required and in an optimal manner.

Jan 1, 1999

By M. J. Perpich

Electrochemical and chemical leaching tests were carried out on chalcocite, covellite and chalcopyrite in acidified iron sulfate solutions sparged with a mixture of O2 - SO2. The gas mixture catalyzed the ferrous to ferric oxidation reaction in situ and, therefore, increased the redox potential and oxidizing strength of the solution. Anodic polarization curves in dilute sulfuric acid on copper sulfide electrodes showed that chalcopyrite passivates and dissolves at current densities orders of magnitude less than chalcocite and covellite. The addition of a depassivating agent (Ag+) increased the passive current density of chalcopyrite and caused breakdown near 0.625 V (SCE). The depassivating effect was also observed during the leaching of chalcopyrite particulate samples as small amounts of Ag+ added to acidified iron sulfate solutions in the presence of O2 - SO2 mixtures greatly increased the leaching rate and the total amount of Cu oxidized (> 90%). Passivation was prevented in the absence of Ag+ by decreasing the initial oxidizing power of the solution and by pretreating the sample in a reductive leach. Both of these methods resulted in transformation of the chalcopyrite surface from its characteristic greenish-gold into deep black. Increased concentrations of Fe+++ due to 02 - S02 sparging were then able to oxidize the transformation product.

Jan 1, 1999

By Sung Wng Kim

The binary antimonide compounds with the skutterudite structure have a potential for thermoelectric applications because of the high carrier mobility, high thermoelectric power, and relatively low thermal conductivity due to the complex crystal structure. However, the room temperature thermal conductivity of these skutterudite materials is as high as about IOW/mK with an estimated 80-90% contribution from the lattice thermal conductivity. Because the lattice thermal conductivity of related ternary skutterudite compounds can be substantially reduced due to the additional phonon scattering, a study of thermoelectric properties of these compounds is of interest. The binary IrSb3, ternary Ir1.xRuxSb3 and Ir(MxSb1.x)3(M=Ge, Sn) compounds were prepared by hot pressing of pre-reacted powders. We have measured the electrical resistivity, thermoelectric power, and thermal conductivity, in a temperature range from room temperature to 973K. The binary IrSb3 compound is found to have P-type electrical properties exhibiting a good Seebeck coefficient (up to 225µV/K around 773K), electrical resistivity(5x10-5Ohm M around 933K), and relatively low thermal conductivity(6W/mK around 950K). The lattice thermal conductivity, K[2] was calculated from the Wiedemann-Franz relationship.

Jan 1, 2002

By Cynthia K. Belt

Improved energy efficiency has grown in importance within industry as energy costs have escalated. The analysis of trends and changes to a process is critical in making the best business decision in energy management. Frequently, energy use per day (Kilowatt-Hour or British Thermal Units) is used to track energy efficiency. Sometimes, the somewhat more complex method of energy per processed weight (Kilowatt-Hour per Metric Ton or BTU per Pound) is used to make this evaluation. Yet both methods ignore the effects due to throughput and weather. In this paper, different thermal processes and systems will be evaluated using statistical methods to highlight alternative methods to evaluate energy efficiency. Examples and potential problems will be discussed for both a single process and a collection of processes within a plant or corporation.

Jan 1, 2008

By K. Morsi, S. K. Kassegne, A. El-Desouky, K. S. Moon

"Current Activated Tip-based Sintering (CATS) is a new process for the powder-based fabrication of macro, micro and possibly nano-scale features and shapes. This new and unique process enables selective sintering of powders by localizing electrically activated sintering conditions through a stationary or moving electrically conducting tip. We present preliminary experimental results on the effect of tip size in the CA TS process as well as the effect of initial powder particle size on the sintering behavior of nickel powder.IntroductionSpark Plasma Sintering (SPS) has been the center of attention of numerous researchers due its noticeable advantages over conventional sintering techniques such as rapid heating rates, lower sintering temperature and shorter holding times. Research on SPS has been applied on a wide variety of materials such as pure metals [ 1], ceramics [2], composites [3], nano-materials [ 4], biomaterials [ 5], shape memory alloys [ 6] and many other material systems. However, it has been mostly limited to bulk materials with simple shapes with a few exceptions ofresearch efforts where the effect of electric current was combined with metal forming processes such as spark plasma extrusion [7,8] and electric rolling of powders[9]. In this paper a novel process (Current-Activated Tip-Based Sintering (CATS)) is discussed where electric current and pressure are applied simultaneously through a small conducting tip (stationary or moving) over a conducting powder compact. This process has the potential advantages of sintering complex geometries with minimum energy requirements as unconventionally high current densities can be achieved due to the small contact area between the tip and the powder compact. Furthermore, by controlling the tip size, it can be possible to sinter features on the macro-, micro- and even nanoscales."

Jan 1, 2011

By G. St-Amant, V. Cloutier, E. Ghali, S. Jin, G. Houlachi

During the casting of lead-silver anodes, variations in cooling rates result in the formation of an uneven microstructure. The slowly cooled areas (SCA) have a coarser microstructure than that of the remaining part (called "the general zone"). The effect of anode microstructure on the electrochemical behavior was investigated using galvanostatic, potentiodynamic and electrochemical impedance techniques. The results show that the resistances for the two steps of the oxygen evolution reaction on the slowly cooled areas of Pb- Ag anodes are higher than that on the general zone. The double layer capacitance for the first step of the oxygen evolution reaction (OER) and the pseudocapacitance of the second step of OER on SCA are smaller than those on the general zone. The potentiodynamic results show that the amount of lead dioxide formed on the SCA is greater than that of the general zone of the anode. The potential decay curves after 30 minutes of galvanostatic polarization at 45 mA/cm2 show that the corrosion potential of the SCA is 200 mV lower than that of the general zone. This can lead to perforation because of the formation of a galvanic cell with a small anode and a large cathode.

Jan 1, 2000

By Mansoor Barati, Shaghayegh Esfahani

"The slag from extraction of ferrous and non-ferrous metals is a potential heat source which if treated properly can contribute to recovery of a significant amount of energy. The waste heat of slag may be used to generate steam, synthetic fuel gas, or electricity. Although several technologies have been investigated for this purpose, very little has been achieved in terms implementing the technology in industry. In this article, the development and application of various granulation techniques are reviewed and the methods to recover energy from granulated slag are discussed.IntroductionEvery year, more than 422 million tons of slag is being produced around the world as a by-product of the metal manufacturing at temperatures of up to 1300-1600°C [1, 2]. Currently slags are either disposed of or treated by processes such as granulation. Through the granulation process, most slags can be converted into a material which may be fully used as a cement feedstock. Conventional cement production is an energy intensive process with large emissions of CO2; therefore, the replacement can both be energy saving and environmentally friendly. However, for this purpose, the slag should have what is known as a “glassy” content (i.e. it should be amorphous) which requires rapid cooling rates that are not easily achieved due to the very low thermal conductivity. The main challenge in all these processes is to granulate the slag at a high cooling rate while the heat is also being recovered."

Jan 1, 2012