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By K. Krishnapisharody

The phenomenon of slag droplet formation under the action of gas-stirring in steel ladles has been analyzed with experiments conducted in a thin-slice room-temperature model using water and mineral oils as the working fluids. Visual and video investigations have been performed on the interface behaviour along with measurements of liquid velocities in both phases, using the Particle Image Velocimetry (PIV) technique. The measured velocity data and observations on the interface break-up establish that the droplet formation results primarily from an instability mechanism at the interface.

Jan 1, 2008

By G. Gao

Flyash from municipal solid waste (MSW) incinerators is frequently classified as a characteristic hazardous waste due to its lead and cadmium content. Extensive investigation has therefore been carried out to detoxity the flyash by leaching and to recover lead, cadmium and zinc. Detoxification can be accomplished by leaching in HCI/NaCI solutions. Optimization of leaching conditions for effective detoxification and subsequent metal recovery can be achieved by controlling the acidity of the lixiviant and flyash to lixivaint ratio. Lead and cadmium In the leaching solution is recovered by cementation with zinc dust. Leaching and cementation experiments have shown that zinc concentrations suitable for electrowinning, > 15 g/liter, can be achieved. Experiments have also been performed to determine the effects of pH, particle size of the zinc dust used, quantity of zinc added and dissolved impurities on the cementation kinetics. After recovery of lead and cadmium, electrowinning or electrowinning coupled with solvent extraction can be used to recover zinc. A process flowsheet is presented.

Jan 1, 1991

By J. L. Jambor

Previous crystal-structure determination of magnesian annabergite (Ni,MgMAsO4)2 8H2O indicated that ordering of Ni and Mg occurs in non-equivalent octahedral sites; such ordering supports the possibility of miscibility gaps on the Ni3(AsO4)2 8H2O -MgiAs04)2 8H2O. (annabergite-hornesite) join. In a predecessor study based on analyses of natural specimens, it was proposed that solid solution is incomplete both for annabergite-hornesite and annabergite-erythrite [Co, (AsO4)2 8H2O]. In the current study, syntheses by use of a slow-addition technique and aging of the precipitates indicated that the annabergite-erythrite solid solution is complete, and that no miscibility gap is present on the annabergite-hornesite join to at least 58 mol % Mg. Thus, interpretation of the compositions of these phases in oxidized mill-tailings impoundments can be done with the normal precautions for homogeneity, and without the added concern of the possible presence of miscibility gaps in the ternary system.

Jan 1, 1995

By Thomas M. Harris

To avoid the escalating cost of disposal of metals-containing wastewater and residues, new wastewater treatments will focus on the recovery of the metals. A combination of ion exchange and electrowinning can produce water suitable for discharge and relatively pure metals. The use of a chelating resin can enhance the selectivity of both the removal process and the elution of metals from the resin. A new, simple method of preparing a variety of chelating resins is being developed. The materials produced by this method exhibit interesting, as well as potentially useful, elution behavior. The performance of one test resin is described.

Jan 1, 1992

By Vaughan R. Voller

"Over the last ten years an increasing number of heat and mass transfer models of solidification processes have been presented in the literature. A key component in these models is the coupling between thermal and solute fields. This is achieved by developing relationships based on the behavior at the microscopic scale in the casting (typically a secondary dendrite arm space). An important class of models in this respect are models that describe the local scale redistribution of solute alloy components-collectively referred to as microsegregation models. This paper explores this class of models.IntroductionModeling takes a key role in processing materials for properties. This is particularly time in solidification processes where current computer techniques allow for a detailed treatment of the critical macroscopic phenomena. Typically these macro scale models consist ·of three main coupled components.1. A model of flow in the melt and solid + liquid mushy region.2. A model of heat transfer.3. A model of solute transport.The focus of this paper is the solute transport component, in particular the manner in which process scale transport is coupled to transport ·at the local scale of the solid-liquid interface. This step requires a modeling of the redistribution of solutes at the scale of the secondary arm spaces in the dendritic mushy region-a process referred to as microsegregation. Basic microsegregation models use the limit assumptions of no mass diffusion in the solid (Gulliver-Scheil [l]) or complete diffusion in the solid (equilibrium lever rule) in a fixed and space. Recently, however, more sophisticated microsegregation models that account for finite mass diffusion and coarsening of the arm space have been developed [2-19]. In this paper governing equations for a general microsegregation model for a multi-component alloy in a coarsening and spacing _are introduced. From these general equations various models for a binary system are developed and tested"

Jan 1, 2000

By Boxun Lu, Juan Wei, Kun Chen, Wanlin Wang, Lejun Zhou

"Slag system is an indispensable part during the continuous casting process, and playing various important roles like absorbing inclusions, modifying heat transfer rate, preventing oxidation of molten steel, etc. to ensure the smooth process and excellent slab quality. However most slags contains more than 8% fluorides which tend to introduce a series of environmental and health problems. This study involves the research of the removal of fluorine through the chemical composition optimization. Through the studies of CCT, DHTT, XRD and SEM, it has been successfully founded that the crystalline phase of Ca11Si4B2O22 discovered in this study shows very similar crystallization property as Cuspidine (Ca4Si2O7F2), which is the most important crystalline phase in the current fluorine bearing slags. Moreover, the optimized free/low fluorine slag shows the opportunity to replace conventional high-fluorine mold slag for casting medium carbon steels that is regarded as the bottleneck of green slag development for continuous casting.IntroductionMold flux has been widely used in continuous casting to control heat transfer, lubricate the strand, absorb inclusions, provide insulation and prevent oxidation of the molten steel[1-3]. It usually contains fluorides, like CaF2, NaF etc., which are used to control the viscosity and solidification temperature of mold fluxes [4-5]. However, the presence of fluoride leads to corrosion of equipment, serious environmental pollution (toxic volatiles and water pollution), and high processing cost of cooling water[6-7]. Therefore, the study of low or free fluorine mold flux is of interest and attracts worldwide attention.S. Y. Choi et al. [4] used B2O3 as a substitute for cuspidine in steel B2PB2) however, B2O3 content was extremely high (up to 30 w%). Other studies have investigated F-free mold flux by adding or optimizing components as MgO, Li2O, B2O3 et al[8-11]. However, most of these focused on the melting and viscosity issues or for low or ultra-low carbon steels, where crystallization tendency is not significantly strong. Very few studies regarding to the development of low/free Fluorine mold flux for casting medium carbon (MC) steels have been conducted, due to the difficulty of the crystallization and heat transfer control without the formation of cuspidine."

Jan 1, 2014

By Harovel G. Wheat

It has been shown that the incorporation of fly ash into concrete as a replacement for part of the cement can be beneficial. In some cases, the strength of the concrete can be increased and the permeability can be decreased. This latter property can lead to a reduction in the migration and/or penetration of aggressive species into reinforced concrete. Some of these species, such as chlorides from deicing salts or marine environments, can subsequently result in accelerated corrosion of the steel reinforcement, a loss of the protection provided by the passive film on steel, and a loss of structural integrity of the concrete. Care has to be taken so that the appropriate compositions of the components of the fly ash are utilized in order to ensure maximum benefit to the concrete structures. This will be discussed as it relates to fly ash generation and treatment.

Jan 1, 2002

By Gopalakrishna B. Prabhu, David L. Bourell

"Three mol% Yttria-Stabilized Tetragonal Zirconia (YSTZ) was prepared by a sol-gel synthesis technique using zirconium tetrachloride and hydrated yttrium chloride precursors. After drying and annealing at 823K, the particle size was in the range 10 to 20 nm. The zirconia powder was sintered using a uniaxial hot press at an applied stress of 20 to 40 MPa. One hour, isothermal sintering was performed in air after initial heating at 50K/min. Theoretical density was obtained at densification temperatures above 1498K. After sintering, grain coarsening characteristics were studied using constant heating rate anneals followed by quenching, based on a model for grain coarsening in a linear heating rate cycle. The microstructural change was studied using SEM and TEM and the phases were determined using x-ray diffraction.IntroductionThe ability to sinter nanocrystalline materials to full density several hundred degrees below the normal sintering temperatures is one reason for their current interest. [1-5] Yttria Stabilized Tetragonal Zirconia (YSTZ) of grain size of about 300 nm has exhibited superplasticity, with elongations as large as 800%.[6-7] Fine grain size is critical for superplasticity. Retention of the fine grain size during sintering of nanocrystalline powder is important if a material is to exhibit superplasticity or to exhibit physical or mechanical properties associated with the ultra fine structure. This paper investigates the sintering behavior and the grain coarsening characteristics ofnanocrystalline YSTZ.Techniques for synthesizing nanocrystalline materials have been studied in great detail earlier. [8-12] The techniques used to synthesize nanocrystalline zirconia include alkoxide synthesis [9], the chloride method [11], the peroxide method [13] and the acetone-toluene method. [13] In this paper the method used in the synthesis of zirconia is the chloride technique. With this precipitation technique, either zirconium chloride or oxychloride and a corresponding yttrium salt or even pure yttria are used."

Jan 1, 1994

By C. D. Mishra

The recycling potential for any gainful utilisation of the waste products is dictated by their quality, especially the chemical characterisation. The methods commonly used for the analysis of fly ash e.g. wet chemical, AAS, ICP-AES etc are time consuming. The paper describes a rapid XRF-based method for routine analysis of fly ash which involves preparation of local standards, optimisation of sample preparation technique and use of a simple PC-based software to account for interelement effects. The matrix corrected values are found to agree well with the wet chemical data.

Jan 1, 1992

By Akira Yazawa

Experimental results for the distribution ratios of various elements between the slag, matte and/or copper in the silica-saturated copper smelting system were summarized. The experiments were carried out under an oxidative smelting condition with S02 gas flow, and also a reductive smelting condition equilibrating with metallic copper or iron. To evaluate the results thermodynamically, the availability of one atom cation base expression for the constituent compounds is emphasized from both of theoretical and practical standpoints. Both of oxidic and sulfidic dissolutions in slag are postulated for some elements such as copper, nickel and lead., and the experimental results are reasonably explained thermo-dynamically. The results for the mutual solubility between matte and ferrite slag and the distribution of minor elements between liquid copper and ferrite slag are also discussed.

Jan 1, 1983

By D. Lui, B. G. Thomas, B. Ho

"Results from mathematical models and plant experiments are combined to quantify the effect of transverse depressions and oscillation marks on heat transfer in the continuous casting mold. A heat transfer model has been developed to calculate transient heat conduction within the solidifying steel, coupled with the steady-state heat conduction with the continuous casting mold wall. The model features a detailed treatment of the interfacial gap between the shell and mold, including mass and momentum balances on the solid and liquid powder layers. The model predicts the solidified shell thickness down the mold, temperature in the mold and shell, thickness of the resolidified and liquid powder layers, heat flux distribution down the mold, mold water temperature rise, ideal taper of the mold walls, and other related phenomena. The important effect of non-uniform distribution of superheat is incorporated using the results from previous 3-D turbulent fluid flow calculations within the liquid cavity. Results from plant experiments confirm that transverse surface depressions and oscillation marks form at the meniscus and move down the mold. Measurements of mold thermocouple temperatures and breakout shell thickness were used to calibrate the models. The results indicate that the surface depressions and oscillation marks are filled with mold flux, but still have a significant effect on decreasing heat transfer. The predicted mold temperature fluctuations are consistent with measurements. If the depressions become filled with air, their effect is greatly increased. These results should be useful in the difficult task of interpreting transient mold thermocouple signals for on-line quality monitoring.IntroductionMany different types of intermittent surface defects on steel slabs arise during initial solidification in the mold of the. continuous casting machine. These defects include deep oscillation marks, surface depressions, and cracks. They may lead to quality problems, such as slivers, in the final rolled product. In severe cases, breakouts may occur, where liquid steel bursts through a thin section of the shell and drains over the casting machine below the mold."

Jan 1, 1997

By Jinrong Zhang

Major components of soil were tested for their ability to attenuate cyanide. Feldspar, kaolinite, plagioclase and bauxite are found to degrade cyanide at an appreciable amount mainly through adsorption. A soil near a mining site in northern Nevada was studied in detail using a tall column. Many species of cyanide were anlyzed to determine the mechanisms of the reactions of cyanide with soil. Volatilization, adsorption, oxidation, precipitation and complexing were quantitatively identified, being 5 to 10, 11.7, 4.2, 7.3 and 4 per cent of the total cyanide added, respectively. It is found that the oxidation of cyanide to cyanate is due to the catalytic effect of nickel and copper leached from the soil. Precipitation of metal-cyanide complexes occurred at low pH values.

Jan 1, 1991

By A. R. Udupa

The reduction roasting behavior of chalcopyrite has been investigated using various combinations of a desulfurizing agent, i.e., CaO or Na2CO3, and a reductant, i.e., CO, H2 or C. Using these, combinations the sulfur is removed from the mineral as CaS or Na2S rather than SO2 as is the case with conventional copper smelting and converting. The laboratory reduction ex¬periments were conducted using thermogravimetric analysis (TGA) and boat tests of mixed combinations of fine particulate reactants subjected to a continuous gas stream. The degrees of metallization were determined by both weight loss and chemical analysis methods and the products examined using optical and scanning electron microscopy and electron probe microanalysis. The percent reduction after one hour at 900°C ranged from 60% to 94%. From these data It was possible to provide postulations as to the controlling reduction mechanisms.

Jan 1, 1983

By Marcos Aurélio S. Costa, Nilton F. Nagem, Andreia B. Henriques, Herman S. Mansur, Alexandra A. P. Mansur, Antonio E. C. Peres, Valeria G. Silva

The superfine material generated in the Bayer process was used in one innovatively way as a precursor to geopolymerization techniques because of the presence of Gibbsite. Gibbsite can play a role in system adjustment because of the SiO2/Al2O3 ratio. Furthermore in the geopolymeric system it was studied the influenceof the additives such as kaolin, metakaolin and sodium trisilicate in an alkaline media. Others conditions to form the geopolymer were also evaluated such as solid/liquid ratio, SiO2/Al2O3 ratio and total alkaline. The raw materials and geopolymeric products were characterized by several techniques e.g. XRD, DSC, FTIR and SEM. Through the FTIR technique it was observed an increase in intensity and bandwidth in the region centered at 1010 cm-1, which is related to the asymmetric vibration Si(Al)-O, this is an indicating of the possible geopolymer formation This broadening of the band promotes a relative disappearance (overlapping) peaks at 965 and 935 cm-1 associated with raw material (ESPDust).

Jan 1, 2015

By J. Grogan

Leaching of galvanized steel coatings allows the steel substrate to be used as a zinc-free scrap source to steel and iron furnaces. In this study the behaviors of sulfuric acid leaching solutions are investigated. The ranked significance of the variables are shown to be acid concentration > temperature > zinc concentration. Examination of the leaching mechanism finds the rate-limiting step to be the cathodic hydrogen reduction reaction. This rate is not only influenced by acid concentration, but also by the hydrogen reduction exchange current density. Dezincing leaching rates are improved by taking advantage of the higher exchange current density of the iron substrate versus the zinc coating. This is accomplished in practice by increasing the exposed interfacial zinc:iron surface area through shredding. Also, a leach control mechanism is proposed through online monitoring of the zinc-iron couple mixed potential.

By Jun Chang, Jin-hui Peng, Jing Chen, Li-bo Zhang

The leaching of indium from refractory zinc oxide flue dust(ZOFD) is attempted to utilize microwave sulfating roasting process, followed by water leaching. The ZOFD and roasted product were characterized by XRD and SEM/EDS analysis. The effects of various roasting parameters, such as roasting temperature/duration, the proportion of sulfuric acid, as well as the leaching parameters such as the leaching duration and liquid/solid ratio, were assessed. The results indicate that nearly 97% of indium could be leached under the following conditions: mass ratio of concentrated sulfuric acid to ZOFD to be 0.5, roasting temperature of 150 ℃ and duration of 1.5 hours; while the optimal leaching conditions hold at temperature of 25 ℃ for 1 hour, with 4:1 of liquid/solid ratio. The indium leaching rate by the microwave roasting increased by 8% as compared with the conventional roasting process under identical conditions.

Jan 1, 2015

By Alwin Frei, Aldo Steinfeld, Peter G. Loutzenhiser, Enrico Guglielmini

"Using concentrated solar radiation as the energy source of high-temperature process heat, the carbothermal reductions of Al2O3 to Al and SiO2 to Si were examined thermodynamically and demonstrated experimentally at vacuum pressures. Reducing the system pressure favors Al(g) and Si(g) formation, enabling their vacuum distillation and avoiding contamination by carbides and/or oxycarbides. Exploratory experimentation in a solar reactor was performed with mixtures of charcoal with alumina and silica in the ranges of 1300-2000 K and 1997–2263 K, respectively, at 10-3 bar by direct exposure to concentrated thermal radiation. Distilled samples contained up to 19 wt% of Al in Al-Al2O3 mixtures and 79 wt% of Si in Si-SiO2 mixtures. When the reducing agent is derived from a biomass source, the solar-driven carbothermal processes are CO2 neutral.IntroductionMetallurgical extractive processes for producing Al1-2 from Al2O3 and Si3-6 from SiO2 are characterized by their high specific energy consumption and concomitant emissions. Alternatively, concentrated solar energy can be used as a high-temperature heat source to drive the carbothermal reductions and, thus, avoid greenhouse gas emissions and other pollutants derived from fossil-fuel-based processes7-12. When the reducing agent is biomass charcoal, the solar-driven carbothermal reduction is CO2 neutral. The carbothermal reductions of Al2O3 and SiO2 are represented by the simplified overall stoichiometric reactions:"

Jan 1, 2011

By G. Cifuentes

The kinetics of the electrolytic oxidation of cyanide to cyanate on PbO2-coated stainless steel anodes have been studied by both experimental and theoretical means. The anodes were based on 316 steel and performed in a satisfactory fashion. The pH of the studied KCN solutions exhibited a constant value about 11. Values for all the kinetic parameters have been determined and a mechanism for the studied reaction is proposed.

Jan 1, 1999

By I. Gaballah

The electrochemical behavior of a chalcopyrite concentrate having a high pyrite content was studied in HC1 by potentiodynamic, potentiostatic and galvanostatic experiments using a cell having separate anodic and cathodic compartments. Anodic oxidation of chalcopyrite particles was realized both by their contact with the cunent feeder and by reaction with ferric and cupric ions. An increase of current leads to a more selective dissolution of chalcopyrite. Surface passivation was observed after an electrolysis time related to the cell current. Cathodic reduction of chalcopyrite concentrate seems to be more promising. Almost complete conversion of chalcopyrite to a copper sulfide (Cui.8.S) is observed, whereas no reaction of the pyrite was detected. This confirms the possible selective dissolution of copper from the chalcopyrite concentrate. Copper sulfide obtained by cathodic reduction was leached using a cupric chloride solution.

Jan 1, 1994

By N. Menad

The formation of the dioxins can be dependent on the quantities of carbon, hydrogen, chlorine and oxygen present in a given system, as well as on parameters such as temperature and pressure. Inadequate supply of combustion air ( incomplete oxidation ), low combustion temperatures ( incomplete combustion ), and insufficient turbulence in the combustion are factors which can favour their formation. Dioxins were produced also calatytically from chlorinated phenol precursors, non-chlorinated compounds that were chemically, and reaction of phenol with inorganic chloride. In this paper different precursors such as combination of C, H, 0, Cl, rapid formation/combustion intermediates and routes to PCDFs are reviewed, and the influence of PVC amount on the formation of these isomers is discussed.

Jan 1, 2000