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By Neng-Wen Yu, Shau-Jun Zhu, Ji-He Wei

The desulfurization process by powder injection and blowing in the RH refining of molten steel and its mechanism have been considered and analyzed. Based on the two-resistance mass transfer theory and the mass balance of sulfur in the system, a kinetic model for the process has been developed. The related parameters of the model, including the mass transfer coefficients and the effective amount of powder in the molten steel being treated for desulfurization, have been more reasonably determined. Modeling and predictions of the process of injecting and blowing the lime-based powder flux under assumed operating modes with the different initial contents of sulfur and amounts of powder injected and blown in a RH degasser of 300 t capacity have been carried out using the model. The relevant circulation rate of the liquid steel and the powder injection and blowing rate were taken to be 100 t/min and 150 kg/min, respectively. The initial contents of sulfur in the liquid steel to be treated and the amounts of powder injection and blowing were respectively assumed to be 0.007, 0.006, 0.005, 0.004, 0.003, 0.002 mass-% and 10, 8, 6, 5, 4, 3 kg/t-steel. The total treatment time for desulfurization under each mode was set up at 24 min, equivalent to eight circulation cycles of the liquid steel to be treated. The results indicated that the predictions made with this model are in good agreement with some data of the industrial experiments and practice. Injecting and blowing the lime-based powder flux with the composition of 85 mass-% lime (CaO) + 15 mass-% fluorspar (CaF2) of 3-5 kg/t-steel, it is possible to decrease the sulfur content in the molten steel to ultralow level below (5-10)x10·4 mass-% from (60-80)x 10·4 mass-%. The total treatment time needed will appropriately be 12-20 min. Intensifying the powder injection and blowing operation and increasing the circulation rate of the liquid steel may effectively' raise the rate of the process in RH refining. The model may be expected to offer some useful information and a reliable basis for determining the reasonable process parameters and help in optimizing the technology of desulfurization by powder injection and blowing in the RH refining of molten steel.

Jan 1, 2000

By Michael J. Nicol

Growing environmental and occupational safety concerns about the use of cyanide in gold processing has increased the interest in more acceptable alternatives. The most likely of these is thiosulfate. However, the thiosulfate process lacks a proven in-pulp method of recovering the dissolved gold, because activated carbon is not effective for the absorption of the gold thiosulfate complex .. Anion exchange resins do offer a possible route for in-pulp recovery. This paper describes work aimed at the evaluation of the effectiveness of commercially available anion exchange resins for the recovery of gold from thiosulfate leach liquors? and pulps. It has been found that strong-base resins are superior to weak-base resins in that they have a larger capacity, which assists in reducing the competition from other anions within a leach solution. Further studies with a selected commercial strong-base resin have shown that competing polythionateanions (particularly tri-and tetrathionate). Lower the maximum possible gold loading but that gold is selectively recovered over other base metal anions in solution. Kinetic experiments found that while? competilig anibns did not affect the initial rate? of gold loading it was important to minimise the contact time of the resin in solution so to prevent displacement of loaded gold by competing anions over longer times. A small-scale resin-in-pulp plant investigation showed gold can be recovered from a leach pulp by a strong-base resin to yield gold loadings of 3000 mg/L, barren pulp containing less than 0.05 mg/L of dissolved gold and. copper loadings of 500 mg/L. Loaded copper was displaced gold and at a loading of 2000 mg/L gold the copper loading was minimal «500 mg/L). The resin was found to recover gold adsorbed on the solids that would, otherwise have. reported to tails if a solid/liquid separation method were used. A patented two-step elution process in which copper and then gold are separately eluted from the resin is also discussed.

Jan 1, 1998

By G. A. Bala

As part of ongoing research to define mechanisms of microbial enhanced oil recovery (MEOR), this work describes the activity of Bacillus l1chen1formis JF-2 (ATCC 39307) Mosurfactant against crude oils with varying compositions. Surfactant based MEOR improves oil recovery by lowering the oil/brine interfactal tension (IFT) therefore permitting oil to be displaced or solub1lized into the aqueous phase.? MEOR is an Enhanced Oil Recovery (EOR) process which allows for the introduction of chemical and miscible fluids, in the form of microbial metabolic end-products, through the injection of microorganisms into the reservoir or stimulation of indigenous reservoir microbial populations. These microorganisms represent a replenishable in situ source of acid, gas, biopolymer, solvent, or surfactant products which can be. supported and manipulated by the addition of simple and inexpensive nutrients to enhance the recovery of oil. Microbially mediated surfactant production represents one mechanism of MEOR. Bacillus licheniformis JF-2. has been used in a mode 1 MEOR system based on Berea sandstone cores (permeabilly .85 to 400 md) to examine surfactant based MEOR of medium to heavy crude oils (API gravity 38.1° to 17.5°). Enhanced oil recovery was achieved with all oils tested using either cell free culture supernatants or microbial suspensions as injectants with no detrimental effect to the oil. Spatial distribution of cells following mf?crobtal flooding was analyzed with scanning electron microscopy. Data indkate complete distribution of cells with a predominance of organisms located distal to the point of injection. There appears to be no sign:if1cant recovery trend with respect to oil composition.. The biosurfactant produced by Bacillus lichen1form1s JF-2 lowers the interfacial tension of all oils tested equally well.

Jan 1, 1991

By Hylton McWhinney, Doanh Tran, Jewel Andrew Gomes, George Irwin, Sameer Pallavkar, Md Islam, David Cocke, Mohammad Rafiqul Islam

"High-performance nickel-based nanocrystalline zinc oxide adsorbents have been prepared adjusting Ni/Zn mol ratio of 1 :5 by thermal decomposition, coprecipitation and sol-gel method for selective adsorption of thiophene in liquid hydrocarbon fuels at ambient temperature and pressure. To understand the nature of reactive adsorption of thiophene (C4H4S) on Ni/ZnO, the effect of preparation techniques, morphological and textural structure on the desulfurization activity was investigated. A model fuel (20 mL) consisting of pentane (C5H12) and thiophene was prepared and adsorption experiments were performed by a batch method under ambient conditions. The physicochemical behaviors of the fresh adsorbents were obtained using X-ray diffraction (XRD) with EDAX, scanning electron microscopy (SEM). The sulfur concentration in the mixture was monitored by UV-vis spectrophotometry. The adsorption reaction confirmed that ZnO played a crucial role in taking up S element to convert it into ZnS. The deposition of nickel on ZnO is an innovative approach which takes advantage of the selectivity of Ni towards S-species and the high adsorptive capacity of ZnO support.IntroductionLow temperature deep desulfurization of fuels via selective adsorption of sulfur compounds keeping coexisting aromatic hydrocarbons and olefins intact is receiving increasing attention in the research community worldwide in order to satisfy the upcoming environmental regulations and fuel specifications. The sulfur compounds in the transportation fuels is a matter of concern when global crude oil slate is becoming heavier and sourer and environmental restrictions on both the refining process and the refined products are becoming more stringent. According to the current refinery technologies, the sulfur content in refinery fuel is typically around 300-500 ppm by weight (ppmw) [1-3]. Starting in 2006, sulfur limits in highway diesel and gasoline were set to 15 ppm and 30 ppm, respectively. During combustion sulfur in the fuel are converted to toxic sulfur oxide (SOx) and contributes to air pollution and acid rains [ 4]."

Jan 1, 2011

By Ken-ichi Machida

"Surface modification of R-Fe-N intermetallic compounds was made to improve their magnetic property and nitrogenabsorbing ability, arid high-performance resin-bonded magnets and nitrogen storage materials were developed: Surface coating for Sm2Fe11Nx by the zinc metal produced via photodecomposition of Zn(C2Hs)2 was effective to avoid the further oxidation in the molding process of the fine powders for bonded magnets and the resulting (BH)max values were improved to -186 kJm-3. Meanwhile, R2Fe17 as the mother compounds for RzFe11Nx was highly active for decomposition of NH3 molecule and subsequent nitrogen absorption as metal nitrides. Furthermore, even inert Nz molecule was dissociated on them by impregnating Ru metal and the resulting nitrogen atoms were absorbed in the crystal lattice of R2Fe17. These results demonstrated that the nitrogen storage system was established by cycling the nitrogenation and hydrogenation of RzFe11/R2Fe11Nx materials.IntroductionProcessing for rare earth metals and intermetallic compounds requires well-controlled conditions in order to avoid the oxygen contamination involved in it due to their high reactivity, as causes the serious damage for materials such as magnets, metal hydride for hydrogen storage, and so on. Rare earth-iron intermetallic compounds, R2Fe17, provide the corresponding metal nitrides (R2Fe11Nx) by heating in N2 or a mixed gas stream ofNH3-H2 [l] and, among them, Sm2Fe11N3 has been particularly noted as one of the promising materials for high-performance permanent magnets such as bonded ones [2- 6]. Usually, the nitrogenation for Sm2Fe17 is made in Nz, but it needs the much more hard conditions of reaction pressure (-10 MPa), temperature (-550°C) and time (-72 h) than the nitrogenation in the NH3-H2 mixture [l]. In the latter case, a significant amount of nitrogen can be interstitial introduced in· the R2Fe17 crystal lattice (x=-7) under the more moderate conditions than in N2 (at 0.1 MPa and -450°C for -3 h) [3-6] and then, in a similar manner as metal hydride systems [7], the excess nitrogen in RzFe1 7Nx (x>3) is reversibly desorbed by heating at a temperature around 500°C in Ar to form the RzFe11N3 compounds. This behavior of nitrogen absorption and desorption has a close relation to the sites for nitrogen in the crystal lattices."

Jan 1, 2000

By Stephen Chryssoulis, Stamen Dimov

Detection and quantification of precious metals (Au, Pd, Pt, and Rh) in spinels and silicate minerals is important for establishing the maximum attainable recovery by sulphide flotation. To achieve this goal subpart per billion (ppb) detection limits are required plus the ability to quantify results. Existing quantitative microbeam techniques (EPMA, PIXE, SIMS, TOFLIMS) have limits of detection in the O. l-200ppm range. Time-of-flight resonance ionization mass spectrometry (TOF-RIMS) is a microbeam analytical technique that allows for the identification and quantification of atomic species in very small quantities. It utilizes a tunable laser source for resonant excitation and ionization of a particular element of interest and has some unique features: elemental selectivity, linear response over a large dynamic range and very high sensitivity. The analysis consist of three steps: (i) the solid sample is vaporized by laser ablation to form a plume containing neutral atoms, (ii) the neutral atoms of a specific atomic element in the plume are resonantly excited and ionized by another tunable laser, and finally (iii) the ions created are mass analyzed in a time-of-flight mass spectrometer. A TOF-RIMS mass spectrometer was developed at AMTEL for trace element analysis of Au, Pd, and Rh in minerals. The spectrometer was calibrated using homogeneous CANMET and NIST reference samples covering three orders of magnitude in concentration. Attained minimum detection limits (MDL=2cr of the background) are in the low ppb range.

Jan 1, 1999

By Vianey Garcia-Osorio

One of the problems in the carbothermic aluminum process is the substantial loss of aluminum compounds as vapors due to the high temperatures in the process. In order to solve this problem a Vapor Recovery Unit (VRU) is proposed. In this unit operation the aluminum vapor undergoes a series of heterogeneous non-catalytic reactions forming solid, liquid and gas products. In this work a model for the simulation of this unit was developed which includes heat and material balances as well as heterogeneous non-catalytic reactions. The model leads to a system of differential equations; its solution was implemented in Matlab giving as a result a stage-by- stage solid-fluid reaction model.

Jan 1, 2001

By Bora Derin

The partial pressure ratios of sulfur and oxygen for several copper flash smelting plants were derived using the Reddy-Blander (RB) model and predicted dissolved sulfur contents available in the literature. The sulfide capacities (Cs) of six different flash smelting plants (FeO-CuO0.5- CaO-MgO-FeOwAIOl.s?SiO2) slags were calculated. The log (Po2/PS2) versus matte grades of various industrial processes was determined. The PoiPS2 ratio increased with an increase of copper grade. The calculated partial pressure ratios for the copper flash smelting are in good agreement with those of the experimental data.

Jan 1, 2003

By David M. Davidson

Seven intrusive phases have been mapped to date in the 1 b.y. Red Bluff Granite Complex (RBGC) near El Paso, Texas. This batholith is 20 km2 in area and intrudes older supracrustal units as well as a trachyte ignimbrite cap. Two early microgranite sills are spatially separated 6 km from a porphyritic, three-phase "ring complex" by a tin-bearing, biotite granite which cores the RBGC. These units are intruded, in turn, by a riebeckite granite which locally exhibits lineated and pegmatitic textures as well as exceptionally high light REE and Zr values (800 ppm La; 3,000 ppm Zr). The riebeckite granite is exposed in three separate occurrences within the Franklin Mountains. REE values in the RBGC are depleted in HREE and show distinct negative Eu anomalies. Typical La/Yb ratios are 5:1-2:1 with Eu values ranging from 10-80 ppm. The mineral source of the high REE values in the riebeckite granite has not yet been specifically identified, but is believed to be zircon.

Jan 1, 1988

By Vaughan R. Voller

"Solidification systems from conduction controlled freezing of a pure material through to alloy phase change that include flow and segregation processes are described. The components in a general solidification model-variables, governing transport equations, and local scale relationship-are outlined. A central focus is the presentation of an explicit procedure for coupling between macroscopic and local scale variables.IntroductionSince the seminal work of Byres et al.[!] in the 1940's there has been a steady progress in modeling solidification systems with increasing levels of complexity. The object of this paper is to track the evolution of these solidification models and present a general modeling approach that applicable to a wide range of the solidification systems of current interest.Solidification SystemsIn a broad sense the underlying physics in a solidification process occur at two distinct length scales:1. The macroscopic scale of the process over which the governing transport equations of heat, mass and momentum hold.2. The local scale at the solid-liquid interface where the solidification phenomena are operative."

Jan 1, 1999

By J. D. Scott

The counter-current jarosite acid wash circuit presently in operation in the zinc plant produces a combined jarosite plus Pb/Ag residue which is discarded. Extensive pilot-scale testwork, and some past in-plant operational experience, has shown that the zinc plant can be easily reconfigured to produce two residues during periods of high silver feeds and/or prices. Plant.optimized circuit configurations are available for silver recovery to a Pb/Ag residue and are in use for the prevention of Pb/Ag-jarosite formation in both the neutral and high-acid leaching circuits. Silver in the zinc plant undergoes several changes in state as it proceeds through these circuits. The roaster calcine is ~3:1 silver sulfate: silver metal, with metallic silver mainly as micro-Inclusions In an aluminosilicate phase. In neutral leach residue, the majority is as silver sulfide or Pb/Ag/Zn-sulfide coatings on unroasted sphalerite grains, with minor Pb/Ag-jarosite and some residual metallic silver in unreacted alumina-silicate grains. In high-acid leach residue, silver occurs as Se-rich silver sulfide particles in sulfur/jarosite ball aggregates, as silver sulfate impregnations in silica-gel masses and in solid solution in Pb/K/Zn~jarosite. Silver concentrations in solution range from 20 to 60 ppb.

Jan 1, 1990

By T. Innmi

The potential of the nickel matte anode was measured during the matte electrolysis in the commercial cell. The slime layer consists of elemental sulfur and was found to greatly influence the potential of anode. The measurements of porosity and permeability of the slime suggest that the voltage drop of the slime layer dominates the potential. Furthermore, the diffusion of the electrolyte through the slime layer is also one of the factors to determine the potential. In addition, the copper content of the nickel matte anode was found to affect the change in the anode potential during the electrolysis. The role of copper on the anodic dissolution of nickel matte is discussed in this work.

Jan 1, 1988

By Vitalij K. Pecharsky

Recent interest in complex aluminohydrides as potential near ambient, ultra-high capacity, solid-state sources of hydrogen (e.g., for fuel cells) calls for an improved understanding of the processes occumng in these hydrogen-containing materials during both the release and the uptake of hydrogen. Lithium aluminohydride (LiAlH4) rapidly releases 5.2 wt. % of hydrogen (i.e., nearly four times more than LaNis-based alloys) during mechanochemical processing at ambient conditions in the presence of transition metal catalysts. Using a variety of solid-state characterization techniques, the mechanochemical transformations in a series of LiAlH4 - metal catalyst systems have been examined and preliminary insights on the mechanism have been obtained. Surprisingly, the well-known hydrogenating-dehydrogenating catalysts, such as Ni and Pt, are practically inactive in the mechanochemical dehydrogenation of LiAlH4.

Jan 1, 2002

By Lu Lin, Yanping Bao, Xiang Li, Linzhu Wang, Xiaobai Yan

The results showed the microinclusions were mainly Al2O3 and sulfide inclusions from tapping to the beginning of LF refining. Al2O3 inclusions were modificated into calcium aluminates after calcium treatment. Lots of spherical calcium aluminates composite inclusions containing MgO, TiO2 and MnS were found after soft blowing and during tundish metallurgy and left in the slab which caused the defects of beam plates. Pure Al2O3 inclusions were observed again after soft blowing 8min. Average sulfur content in inclusions decreased because of the high desulfurization ability of refining slag. Average Ca/Al ratio value in inclusions increased during LF refinging because of the reduction of CaO in slag by carbon and it increased obviously during the process of soft blowing 8min because of the dissolusion of calcium wire.

Jan 1, 2015

By Hideyuki Takahashi, Taro Aichi, Kazuyuki Tohji, Makoto Muramatsu, Rie Sato

"There are several ways to condition lead-based alloy anodes for zinc electrowinning: electrochemical treatment, chemical treatment and physical treatment. Two advantages of physical treatments are their productivity and variety. In this report, physical treatments, including blasting with silica, alumina, steel grit and cut zinc wire, were tested. The laboratory tests confirmed there were differences in the formation of anode scales during electrowinning and in the suppression of lead dissolution from the anodes. With an increase in the surface roughness, the misfit between the PbC""2 and the MnC>2 was mitigated and the anchor effect was promoted; these effects resulted in dense Mn oxide scales on the anode.IntroductionZinc is widely used for hot-dip zinc plating and for die casting alloys. As a supplier of materials, we have endeavored to produce zinc that is economical and contains as little impurity as possible. As a result of our efforts, a technology for consistently providing special high-grade (SHG) zinc has been established. However, as seen in the issuance of the Restriction of Hazardous Substances (RoHS) Directive, public awareness of the industrial impact of heavy metals on the environment has been heightened. Increasing efforts to control environmentally sensitive substances will be necessary for our production processes.Electrolytic SHG zinc is produced by electrodeposition in an acidic solution with a Pb-Ag or Pb-Ag-Ca alloy for the anode and an Al alloy for the cathode. Pb alloy anodes are widely used because of their excellent durability; however, they are a source of Pb, which is the main impurity of the product."

Jan 1, 2012

By P. M. Prasad

The last two decades have witnessed the emergence of numerous hydrometallurgical and direct processing techniques for the extraction of some metals from pocketed/lean/complex sulfide ore deposits. A new approach with some inherent technological merits, investigated in recent years, is the lime-enhanced reduction of metal sulfides. Thermodynamic aspects relevant to the lime-enhanced reduction of metal sulfides by H2,C0 and C are discussed. A survey of the researches on the basic features of and factors influencing the lime-scavenged reduction of selected sulfides and sulfide concentrates reveals that lime tremendously enhances the sulfide reduction rates (up to 100 times) and drastically reduces the sulfur emission into off-gas to negligible levels. Further successful practice of lime-enhanced reduction requires only a moderate temperature of reduction (characteristic of each sul¬fide) and, in the case of gaseous reduction, relatively low gas flow rates. Relevant kinetic aspects of the concerned reactions that have a bearing on process development and its understanding are also briefly discussed. A conceptual scheme of general applicability for the processing of sulfide concentrates by the lime-enhanced reduction technique consists of three main steps: (0 lime-enhanced reduction by a suitable reagent (e,g., H,2, CO, gasified coal, water gas), (ii) separation of the product metal from the dry slag (CaS + unused CO) by mechanical separation, magnetic/gravity concentration or flotation and (iii) melting and refining by standard procedures. This novel approach, which is patently less complex, is expected to employ basically simpler flow sheets at comparatively lower operational temperatures and aid in pollution abatement. Potential for developing such a route for the small scale extraction of metals like copper, molybdenum and antimony is indicated. Possibility of utilizing this technique for the production of fibers/ filaments of some metals is also outlined.

Jan 1, 1983

By R. Upadhyaya

Aluminium alloy matrix cast composites have been synthesised by incorporating fine graphite powders (0.5 - 20 µm size) and chopped carbon fibres (6.5 pm P). 3-6 mm length) by liquid metallurgy technique. Incorporation of these second phase materials exceeding 6-8 wt% invariably resulted in agglomeration of the dispersoids and sometimes leading to even total rejection. It was found that small additions of mischmetal (1-3 wt%) during dispersion resulted in better incorporation without much agglomeration of the dispersoid as evident from the macro and micro structures of the composites. Further, the additions of mischmetal increased the volume of the effective incorporation of the dispersoid even to the extent 50- 60%. The mischmetal addition results in a significant increase in the power factor of the stirrer motor indicating an apparent increase in the viscosity of the system. The higher viscosity of the melt increase the shear transmission conditions within the melt during stirring thereby breaking the agglomerates of the dispersoids. The increased viscosity of the melt seems to be due to the formation rare earth - aluminium inter metallics precipitation, as observed in the metallographic studies, thereby making the process a "pseudorheocasting? technique. A provisional patent has been filed based on this work.

Jan 1, 1989

By Fang-Qui Zu

Understanding the nature of liquid structures and properties remains an open problem for many fundamental and applied fields such as materials sciences and processing. And as well known, there is no other defined phase line above liquidus (TL ) in phase diagrams of ordinary binary systems. However, via different experimental resorts, our research results on over 30 metallic melts including alloys and elements show a novel physical image: temperature induced liquid-liquid structure transition (TI-LLST) can occur hundreds of degrees over TL. On the other hand, the solidification behaviors and structures out of the melts experienced TI-LLST are distinct from those out of the melts before TI-LLST. In this presentation, some characteristic aspects of the TI-LLST and the effects on solidification behaviors and structures are briefly summarized, and the pertinent rules and mechanism are also analyzed.

Jan 1, 2009

By P. Henry

A novel electrochemical cell has been developed for the recovery of MnO2 from residue of pyrolusite ore leading loaded with Fe, Al Ni, Co and Si impurities, This new process can be considered as an alternative to the traditional methods : S02, H2O2 or bioleaching. It has been observed to proceed fairly rapidly and could prove to be a more economically viable process, as well as being more environmentally acceptable. Electrochemical characterization and kinetic studies have shown that MnO2 is effectively leached by electrogenerated ferrous ions at high current density from a pulp containing less than 5 g8 Fe. The chemical reactions are : Cathode (inox) : 2F23+ + 2e ? 2 Fe2+ Bulk: MnO2 + 2 fe2+ 4H+ ? Mn2+ + 2 Fe3+ + 2 H2O Anode (Pb-Ag) : H2O ? ½ O2 + 2H+ + 2e Global: MnO2 +2H+ Fe2+ = Mn2+ + H2O + 1/2 O2 The catholyte (MnO2 pulp) circulates upward in the expanded mesh cathode separated from the sulfuric acid solution anolyte by a separator which shows high mechanical resistance, low porosity, low potential drop, and reasonable cost. Laboratory and mini-pilot tests have led to the construction of an OT crating pilot plant (100 kg/hr) able to leach more than 95% of Mn, Ni, Co at 1000-1200 A/m2, 50°C with high faradic yield (> 95 %) and low power consumption (3.2 kWh/kg kWh/kg &4D). New applications like the treatment of spent Zn-Mn batteries, polluted soils, spent catalysts and oxide ore (cobalt, nickel) with electrogenerated redox species are now investigated at a laboratory and mini-pilot scale.

Jan 1, 2000

By L. J. Davies

Refractories usage in furnaces for the extraction of nickel from both sulphides and lateritic ores is reviewed. Recent changes in raw materials and basic brick qualities developed to meet the increasing demands of existing and new processes are outlined. Examples of used brick examinations to establish mechanisms of wear are given. The importance of physical and chemical properties are discussed. The use of simulative laboratory testing to aid in refractories development and selection is described.

Jan 1, 1988