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By Pan Gu, Zhen Zhang, Jiang Diao, Bing Xie, Hongyi Li

Viscosities of FeO-SiO2-V2O3-CaO-P2O5 slags have been measured at the temperature range of 1673 K to 1773 K (1400°C to 1500°C). This investigated system represents the major components of basic vanadium slag that is an important intermediate product of a novel vanadium extracting process, in which removal of phosphorus and extraction of vanadium can be achieved from the vanadium-containing hot metal simultaneously. It was found that higher CaO/SiO2 ratio resulted in lower viscosity in the composition range of interest. Also, the viscosities increase with the increasing P2O5 concentration. The varying viscosities can be attributed to the modification in complexity and polymerization of the slag network. The variation of apparent activation energies are in tune with the viscosity measurements. The results of this work revealed the effect of CaO/SiO2 and P2O5 on the viscous properties of FeO-SiO2- V2O3-CaO-P2O5 slags and therefore provide the theoretical foundation for the control of the coupling de-P and V-extraction process.

Jan 1, 2016

By Yang Hong-ying, Yu Juan

Electrochemical behavior of natural chalcopyrite in electrolyte solution at pH value of 6.97 was studied by cyclic voltammetry, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The results showed that the electrochemical processes occurred on electrode surface were controlled mainly by the growth of sulfur species at lower applied potentials (<0.35Vvs.SHE), and the oxidative dissolution of sulfur species and the hydroxylation of iron at higher applied potential (>0.45V). The EIS spectra of oxide product layers could be illustrated by the equivalent circuit of Re(QdlRct(QfRf)), and the degree of hydrophilicity for chalcopyrite was higher when the value of charge transfer resistance Rct. was greater. The optimum potential range for the floatation of chalcopyrite in collectorless solution at pH value of 6.97 was between OCP (0.165V) and 0.35V.`

Jan 1, 2015

By Eltefat Ahmadi

Iron-free titanium oxycarbonitride (TiOxCyNz) is a promising feedstock for production of titanium tetrachloride (TiCl4) at low temperatures. In this study, the effects of leaching variables such as temperature, time, particle size of staring material and concentration of the leaching solutions were evaluated on iron removal from nitrided Malaysian ilmenite by Becher process. The nitrided ilmenite was prepared by isothermal reduction with graphite at 1200 °C for 3 h in H2-N2 atmosphere. The aerated leaching experiments were conducted at 50–90 °C with addition of 0.3–2.0 wt% of NH4Cl catalyst. The highest extent of iron removal (XFe) was obtained at about 96.2% for the sample leached at 90 °C for 7 h with 2.0 wt% NH4Cl. The iron concentrate and titanium oxycarbonitride product were characterized by ICP-OES, XRD, XRF and SEM-EDX analyses. The results indicated that the aeration leaching process was a successful route to prepare low-iron titanium oxycarbonitride.

By Donna Post Guillen

"Cyclopentane, a flammable hydrocarbon, is being considered as a working fluid for waste heat recovery applications using Organic Rankine Cycles with Direct Evaporators. A postulated failure mode consisting of a pinhole leak in a heat exchanger tube raises safety concerns due to autoignition of the working fluid. Experiments were conducted to determine the ignition delay time (IDT) of cyclopentane using an Ignition Quality Test™ (IQT™) device. Two sets of experiments were conducted per ASTM D6890 (with exception to charge pressure and temperature) to determine ignition delay of the fuel at atmospheric pressure for standard air (-20.95% oxygen) and vitiated air (13.3% oxygen) at a temperature of 803 K. Operation of the IQT device at a much lower pressure (1 bar) than normal operation (21.4 bar) with a standard injector led to very rich conditions and wetting of the stainless steel chamber walls. Catalytic effects are postulated to produce the small IDTs observed. Experiments were repeated with a modified injector to prevent wall wetting, resulting in average IDTs that are substantially longer.IntroductionCyclopentane is being considered for use as a working fluid in a Direct Evaporator of an Organic Rankine Cycle (ORC). In this configuration, the heat exchanger is placed directly in the flow of the hot exhaust gas, rather than using a secondary heat transfer loop to isolate the flammable working fluid from the heat source. This configuration offers the advantages of approximately 15% lower cost and improved efficiency over a standard ORC. However, placing a heat exchanger operating with a flammable hydrocarbon in the hot exhaust gas stream presents potential safety risks. If a pinhole leak were to occur in the heat exchanger, working fluid could leak into the hot exhaust stream. Gas turbine exhaust is provided to the Direct Evaporator at a temperature of approximately 803 K, whereas the autoignition temperature of cyclopentane is 634 K (Gallant and Yaws, 1993). Autoignition of the working fluid has been identified as the key risk for this type of system.Autoignition occurs when sufficient self-heating by chemical reactions takes place to accelerate reaction rates to produce full-scale combustion. This is in contrast to forced ignition, in which an external source (e.g., spark) is employed to initiate the combustion process. For combustion to occur, the fuel to oxidizer concentration must be between the lower (lean) and upper (rich) flammable limits. The reaction rate depends on the species concentration of the fuel and oxidant, the local temperature and pressure. Ignition processes are comprised of steps that take a fmite amount of time. This latent period prior to the start of combustion is referred to as ignition delay time (IDT)."

Jan 1, 2012

By Ping-Ping Fan, Yong-Quan Wu

The polarized Brillouin scattering spectra were systematically measured to study the elastic properties of bulk hexagonal close-packed (hcp) ZnO single crystal in this paper. The peak polarizations of all modes in spectra were analyzed firstly. The elastic properties, such as the whole set of Elastic constants were accordingly calculated and compared with the previous literatures. Also investigated were the effects of the rotation of the sample in the (0001) plane perpendicular to the z axis on different acoustic modes. The results show that the quasi-longitudinal and quasi-transverse modes perpendicular to the (0001) plane act as the expected trigonometric function of the rotation angle,while the longitudinal and transverse modes on the (0001) plane remain constant.

Mar 1, 2017

By Leizhang Gao, Zhengfeng Qu, Pingsheng Lai, Chenguang Bai, Meilong Hu

Since Fray-Farthing-Chen (FFC) Cambridge process was proposed in 2000 for electrochemical extraction of titanium from titanium oxide, a great quantity of research has been carried out to investigate the mechanism of the electro-reduction of the process. Results show that the intermediate products of perovskite phases are inevitable during the electro-deoxidation process. In this paper, a new perspective focus on the anodic behavior was applied. The behavior of the graphite anode with different times has been investigated. Although the main anodic process in the electrolysis is the oxygen evolution by means of the CO2. The interphases of calcium species appeared on the cathode are closely related with chlorine ions in the molten CaCl2. In addition, the released CO2 from the anode is related with the formation of CaCO3 which floated on the surface of the molten salt.

Mar 1, 2018

By Siyuan Zhang, Lu Lin, Yanping Bao, Wei Xiao, Chaojie Zhang

In order to decrease high aluminum consumption in Interstitial-Free (IF) steel production in a steel plant, Ruhrstahl Heraeus (RH) process data from 2428 heats were analyzed by statistical methods. The results showed that the blowing oxygen quantity and oxygen activity, before the RH and before deoxidization, have positive correlations with aluminum consumption, especially the blowing oxygen quantity. Waiting time before refining also has a positive correlation with aluminum consumption when it exceeds 7 min. On the contrary, steel temperature before RH has a significant negative correlation with aluminum con sumption, when it is between 1600 and 1630 °C. According to the statistical results, the RH refining process was optimized when the steel temperature before RH was controlled between 1630 and 1645 °C, waiting time was controlled at less than 7 min, blowing oxygen quantity was controlled to less than 100 m3, and the oxygen activity before RH was controlled between 0.050–0.075%. After optimization, the reduction of aluminum consumption was remarkable. Average aluminum consumption decreased from 1.45 to 1.17 kg/t steel.

Mar 1, 2017

By K. Itagaki, H. Henao

"The experimental study on the phase equilibrium and distribution of minor elements such as chromium and copper between magnesia saturated FeOx-MgO-SiO2 slag and Fe-Ni alloy were carried out under controlled oxygen partial pressure between 10-6-5 and 10-10 using CO and CO2 mixed gas at 1773 and 1873 K.The effect of slag additives such as lime (CaO/SiO2 molar ratio: 1) and alumina (AlO1.5/SiO2 molar ratio: 0.1) on the distribution behavior of the minor elements was also investigated.The value of distribution ratio for chromium, defined by (%Cr in slag)/[%Cr in alloy], is larger than 70 at the pO2 region conducted in the present study for the MgO saturated FeOx-MgO-SiO2 slag at 1773K. These value are almost 4-order higher then that of nickel though the distribution ratio of copper shows similar values with nickel. Analysis of the data indicates that addition of lime in the slag and the increase of temperature reduce the dissolution of chromium into the slag and the addition of aluminum increases the dissolution of chromium into the slag while reduces the dissolution of copper and nickel.IntroductionChromium. is a minor element in a nickel oxide ore but a Japan major component in the secondary material of stainless steel and is also introduced in the Fe-Ni production process due to dissolving bricks of a furnace. Chromium is a concerned matter for the beneficial utilization and disposition of ·slag because Cr6+ is a harmful element. Considering Fe-Ni as an alloy component in steel making, and the demand of high purity nickel, chromium is an -undesirable element that has to be eliminated into slag prior to the steel making, or the production of high temperature refractory alloys. On · the other ·hand chromium is an element of steel alloy for many applications, thus Fe-Ni containing chromium in minor element is desirable in some stainless steel making."

Jan 1, 2000

By Sergio Sanchez-Segado, Yuan Zhang, Animesh Jha, Ahmad Fahmi Ruzaidi

Niobium and tantalum are considered critical materials because the increasing demand in the energy sector which is reliant on limited abundance of these two metals in minerals. Traditionally, niobium and tantalum mineralsare digested using hydrofluoric acid at moderate temperatures, producing oxy-fluorides which are separated by solvent extraction, involving the use ofhazardous chemicals. The increasing environmental pressures are forcing the industry to search for alternative low carbon processing methods. In this paper alkali roasting based separation and beneficiation, which is not well understood in the literature, is proposed, for which the kinetics and thermodynamic equilibria for the formation of sodium tantalate and niobate with sodium hydroxide are analyzedat the temperature range of 400ºC to 700ºC. The apparent activation energy of formation,changes from 31.0±0.8 to 22.3±1.2 kJ mol-1 and from 23.8±1.2 to110.2±12.8 kJ mol-1, for tantalate and niobate, respectively. The reaction mechanism is examined on the basis of the analysis of reaction products using X-ray powder diffraction (XRPD) and X-ray fluorescence (XRF).

Jan 1, 2015

By Xingming Zhang, Huawei Zhang, Yanxiang Li

"A hybrid porous metal with nano-micro double scale pore size and regular-random bimodal porous structure has been fabricated by unidirectional solidification of a lotus-type alloy followed by dealloying treatment to the base alloy. The base alloy selected is a Cu-Mn binary alloy. The lotus-type porous Cu-Mn alloy with straight pores of several hundred micrometers in diameter was manufactured by unidirectional solidification with a mould casting process. Dealloying treatment was then done to the lotus-type porous structure of Cu-Mn alloy. The solid Cu-Mn alloy wall of the lotus-type porous structure was transformed to random porous structure of dozens to hundreds nanometers. The influence of corrosion parameters, such as the current and time in electrochemical corrosion, temperature and corrosion agent in chemical corrosion, on the nano-porous structure formed has been studied systematically.1. IntroductionA hybrid porous metal is a kind of cellular structure with different porous or cellular forms inside, which possesses special properties and can be applied in many fields as fuel cells, catalysis, sensors, etc. Several means have been developed to fabricate this kind of porous material [1-2]. In this paper, a novel process of Gasar plus dealloying is introduced to fabricate a new form of hybrid porous metal with nano-micro double size and regular-random bimodal structure.The Gasar process, also called the metal-gas eutectic directional solidification, that invented by Shapovalov [3] in Ukraine and now in USA some twenty years ago, is used to fabricate porous metals with regularly aligned pores basing on the solubility difference of a gaseous element in solid and liquid metal. Nakajima and his colleagues [4] in Japan studied this process further and called this kind of structure a lotus-type porous metal. They put more attention to various fabrication techniques and properties of lotus-type porous metals. Li heading a group [5-6] in P.R. China studied the mechanism of Gasar process and process controlling techniques. The Gasar pore structure and porosity can be controlled by processing parameters, and a regular Gasar structure with oriented pores distributing uniformly in the solid matrix can be obtained under optimized processing parameters."

Jan 1, 2014

By Harrison Hodge

In the Bayer process for alumina production, between 2–35% Al2O3 is lost with bauxite residue due primarily to incomplete dissolution of aluminiumbearing minerals during caustic leaching or the precipitation of sodium alumino-silicate solids. The recovery of sodium and aluminium from the residue, and particularly from the contained sodium alumino-silicates, is becoming an increasingly critical issue from both an environmental and economic standpoint. Lime-soda residue sintering followed by selective leaching has been proposed as a method to recover sodium and alumina. The factors influencing the sintering mechanisms and kinetics, and the subsequent leaching have not been well described to date. In this study, the physical and chemical changes taking place during isothermal sintering of bauxite residue in air, particularly at short reaction times are investigated using scanning electron microscope (SEM) and X-ray diffraction (XRD). The impacts of these changes on the recovery of valuable materials are reported.

By Kristine Bruce Wanderley, Denise Crocce Romano Espinosa, Jorge Alberto Soares Tenorio

Magnesium is present in nickels leach liquor and it is often disposed in waste barriers. However, new technologies with the aim of recuperating magnesium and other metals in the liquor have proven that it is possible to reduce the amount of metal lost during nickel ore processing. In this context, high temperature crystallization removes magnesium, with a concentration of 8 g/L, as MgSO4 H2O from the leach liquor. Kinetic studies of this process are needed to evaluate the thermodynamics of the growth of crystals. Thus, this work aims to study the crystallization kinetics of MgSO4 H2O. Temperatures of 230, 210 and 200 °C were investigated in a batch crystallization system in solutions with pH2. Aliquots were taken at each hour up to 5 h of time residence and analysed by ion chromatography for magnesium concentration. The reaction mechanism as well as rate constant and activation energy for each reaction temperature were obtained

Mar 1, 2018

By I. Moscoso, R. Padilla, M. C. Ruiz

Antimony and arsenic are impurities in copper concentrates found normally as stibnite (Sb2S3), tetrahedrite (Cu12Sb4S13) and enargite (Cu3AsS4). When copper concentrates contain appreciable amounts of As and Sb, they must be removed before smelting to avoid environmental pollution. Oxidizing volatilization roasting at 500–700 °C has been used to eliminate these impurities. However, only a fraction of Sb volatilizes in those conditions; thus, a more effective process to eliminate antimony from concentrates is needed. In this study, the chloridizing roasting of Sb2S3 using CaCl2–O2 was investigated to remove the antimony from concentrates. XRD analysis of calcines indicated that the overall reaction could be written as: Sb2S3 þ3CaCl2 þ6O2 ¼ 2SbCl3 þ3CaSO4 Temperature and oxygen partial pressure have a significant effect on the rate of reaction. An estimated conversion of about 90% was obtained at 750 °C, 5.4% oxygen in 20 min. High oxygen concentrations arrest the advance of the reaction forming various antimony oxides including Sb6O13, Ca5Sb5O17 and Sb2O4.

Mar 1, 2017

By Lu-ming Zhao, Li Zhao, Yu Wang

In this paper, the change of crystallization rate, dendrite arm spacing and dendrite width of mold flux with various magnetic field conditions were studied by experiment. Having found that the crystallization ratio of mold flux increased from 33 to 96.6%, the dendrite arm spacing decreased from 72.47 to 38.02 lm, the dendrite width decreased from 48.47 to 27.02 lm while the magnetic field frequency (f) equaled to 8 Hz and its strength (B) increased from 0 to 30 mT. The crystallization ratio of the mold flux increased from 91.9 to 96.1%, the dendrite arm spacing decreased from 60.53 to 28.08 lm,the dendrite width decreased from 42.53 to 24.08 lm when B equaled to 20 mT and f increased from 6 to 12 Hz. However, the XRD analysis indicated that the phase types of the mold flux under the experimental conditions did not transform. Results showed that an alternating magnetic field can promote the crystallization of mold flux and refine grain structure.

Mar 1, 2018

By Toshiyuki Nohira, Tetsuo Oishi, Hideki Ono, Hirokazu Konishi

The electrochemical formation of Tb-Ni alloys was investigated in a molten LiCl–KCl–TbCl3 (0.50 mol% added) at 723 K. Open-circuit potentiometry was conducted using a Ni electrode after electrodepositing Tb metal at 0.20 V (vs. Li+/Li) for 300 s. There were four potential plateaus at (a) 0.66 V, (b) 0.80 V, (c) 0.95 V and (d) 1.56 V, respectively. Alloy samples were prepared by potentiostatic electrolysis at 0.60 and 0.70 V at 723 K. The alloy phase was identified as only TbNi2. Anodic dissolution of Tb from the formed TbNi2 was conducted at 0.90, 1.20 and 1.60 V, respectively. In the sample obtained at 0.90 V for 3 h, the existence of TbNi3 was identified by the XRD. Phase of the sample obtained at 1.20 V for 3 h was TbNi5. The sample obtained at 1.60 V for 3 h was Ni. Alloy samples were prepared by potentiostatic electrolysis at 0.50–0.80 V for 1 h using Ni plate cathodes in a molten LiCl–KCl containing TbCl3 (0.50 mol%) and NdCl3 (0.50 mol%). The highest mass ratio of Tb/Nd in the alloy sample was 56 at 0.70 V.

Mar 1, 2018

By Peijia Lin

Wheat straw was chemically modified by alkaline treatment followed by succinylation and sodium carbonate treatment for the use of cadmium and nickel adsorbent. The adsorption efficiency was calculated in different conditions. The experimental parameters were solution pH, adsorbent dosage, contact time and initial metal concentrations. The biosorbent was analysed by FTIR (Fourier- Transform Infrared Spectroscopy) to investigate the changes of surface functional group. The maximum adsorption percentages of cadmium (>99%) and nickel (>98%) were achieved using 5 g/L adsorbent with 50 mg/L initial metal concentrations. The adsorption kinetic study showed that the reaction was pseudo-second order kinetics and the adsorption isotherm was well fit by the Langmuir adsorption model. The dynamic column study indicates that modified adsorbent has a better adsorption capacity towards cadmium than nickel.

By Takamasa Ishigaki, Gervais Soucy, Mohamed Rahmane

"The induction plasma jets employed for the in-flight nitridation of molybdenum disilicide (MoSi2) powders were investigated in terms of their flow characteristics. The present study shows the effect of the operating parameters of the plasma torch, as used for this process, on the plasma jet properties. The enthalpy probe techniques, along with mass spectrometry, were employed for the measurement of the jet temperature, velocity and concentration fields. The measured values were compared to the results of a numerical simulation performed on the plasma flowing inside the torch-reactor system. The process operating conditions studied were the plasma plate power, chamber pressure and sheath gas composition. The optimal conditions for effecting the nitridation process using thermal plasma are obtained at moderate plasma plate power, at around atmospheric pressure and by using a mixture of argon and nitrogen as the plasma torch sheath gas.IntroductionMolybdenum disilicide (MoSi2) based composites are considered to be one of the most promising candidates for high temperature structural material applications [!], especially because of their high melting points, good oxidation resistance and relatively low cost. However, the wide application of these composite materials is still limited by some factors such as their brittleness at room temperature and lower strength at high temperature (> 1500 K). To overcome such limitations, a number of researchers [2-4] have earlier studied various kinds of reinforcements for MoSi2, e.g. oxides, silicides and nitrides. More recently, Fan and coworkers [5-9] have demonstrated the possibility of in-flight nitridation and carburization of MoSi2, using a thermal plasma process. This work has confirmed the plasma synthesis route as one of the most promising methods for creating an in-situ second phase structure. Properties of the plasma flow, such as its temperature, flow velocity and composition, are of crucial importance for the nitridation of MoSi2 powders during their flight in the plasma. Therefore, the optimization of such a process involving plasma· generated reactive species necessitates a thorough understanding of the plasma flow characteristics."

Jan 1, 2000

By Entov Vladimir M., Gilmer R. Burgos, Andreas N. Alexandrou

"Processing of metal alloys in their mushy state represents a new trend in metal processing. As part of this process, known also as thixocasting, a specially prepared slurry at a temperature in the mushy region is injected into a die. Parts produced using this technology offer better mechanical properties than those produced by casting, and comparable to those of forged alloys.In thixocasting, semisolid slurries are highly concentrated suspensions of rounded rosette-like crystals in eutectic liquid. The mechanical behavior of the slurry is determined by the structure and properties of the skeleton formed by the alpha phase particles. The skeleton structure is almost never at equilibrium, and its evolution is, governed by a number of kinetic phenomena of different c11'aracteristic time-scales. Therefore, the skeleton structure depends on the mechanical and thermal history of the material. As a result of these kinetic processes, the rheological properties of the material, such as effective viscosity and yield stress, decrease with structure breakdown, and increase with its development. In the present investigation, the behavior of semisolid slurries during processing is modeled using the conservation equations, and a Herschel-Bulkley fluid model. The rheological parameters are assumed to be functions of the solid volume fraction, and of a structural parameter that changes with processing history. The evolution of the structural parameter is described by a first order kinetic differential equation that relates the rate of build-up and break-down of the solid"

Jan 1, 2000

By Yasumasa Hattori

An extensive study including fluid dynamic calculations, cold model tests, pilot plant tests as well as measurements in a commercial flash furnace was carried out in order to develop a new Sumitomo flash smelting concentrate burner. The pressure measurements in the commercial burner indicated that the premixing of the concentrate and reaction air in a burner was insufficient. Pilot plant tests showed that enhancement of the premixing of the concentrate and reaction air is very effective for improving the burner performance. Using the additional pressure drop of the reaction air as an indicator of the premixing, a new type Sumitomo premixed concentrate burner was developed.

Jan 1, 2003

By C. Liliane Carvalho

In the current study, bio-oxidation tests were carried out in shaking flasks with a flotation concentrate containing the sulphides pyrite, arsenopyrite and gudmidite. The tests were performed with mesophilic microorganisms (At. ferrooxidans) at 30 °C and also with the moderate thermophile S. thermosulfidooxidans, at 50 °C. The effects of (i) previous adaptation of the microorganisms to the concentrate, (ii) ferrous iron concentration and (iii) pulp density (2%, 4% and 6% (w/v)) on the dissolution of the sulphide were studied through arsenic extractions. S. thermosulfidooxidans was more sensitive to the pulp density in comparison to At. ferrooxidans as a reduction in sulphide oxidation was observed with the increase in the solid content to 6%. Therefore, the mesophilic strain was selected for further work, which comprised a rolling bottle experiment at 10% solids. After 40 days of bio-oxidation, the solid material was subjected to cyanidation, which revealed 85% gold extraction as compared to 21% from the original concentrate. The antimony sulphide grains in the bio-oxidized product showed similarity to what was observed in the original sample, suggesting such particles were not susceptible to the bio-oxidation process.