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By Shengqi Chen

The reduction smelting of nickel laterites produces slag, consisting principally of the chemical components MgO, "FeO", SiO2, and A12O3, and ferro-nickel alloy. Despite the fact that the phase equilibria for the ternary MgO-"FeO"-SiO2 up to 1500°C is well established limited experimental data are available in the MgO-"FeO"-SiO2-Al2O3 system, which is relevant to commercial operation of the process. A methodology has been developed for the experimental investigation of the liquidus temperatures for the multi-component system MgO-"FeO"-SiO2-Al2O3-Cr2O3 in equilibrium with metallic iron. Experiments have been carried out using high temperature equilibration, quenching, followed by electron probe X-ray microanalysis (EPMA). Liquidus temperatures have been determined in the silica primary phase field in the composition ranges directly relevant to the Cerro Matoso S.A. ferro-nickel smelting slag. Liquidus isotherms have been determined for temperatures between 1450 to 1600°C. The study enables the liquidus to be described for a range of MgO/FeO ratios. It was found that liquidus temperatures in the silica primary phase field decrease significantly with the addition of AI2O3. Keywords: Liquidus temperature, ferro-nickel, pyrometallurgy, smelting

Jan 1, 2004

By Y. Fautrelle, F. Felten, O. Metais, Y. Du Terrail

"We deal with the prediction of electromagnetically-driven turbulent flows by means of a Large-Eddy- Simulation method (LES). The model is applied in the case of a liquid metal pool submitted to a polyphase linear electromagnetic stirrer. We investigate two cases: (i) the frequency of the magnetic field is equal to 50 Hz; in that case the effects of the pulsating part of the Lorentz forces may be neglected; (ii) the frequency of the magnetic field is low (f= 1 Hz), then the oscillating part of the electromagnetic forces is taken into account. The LES predictions agree well with the mean velocity measurements, as does the standard k-a model. However, as for the turbulent kinetic energy predictions, there is a large discrepancy between the two models. When the oscillating part of the Lorentz forces is taken into account, the computations show that the fluid flow is sensitive to the unsteady part of the forces. We find that the mean velocity is not affected by the fluctuating component of the force. As for the turbulence parameters, the presence of the pulsating part leads to a significant reduction of the turbulent kinetic energy, whilst the turbulence length scale decreases.IntroductionElectromagnetic stirring is commonly used in various metallurgical processes. In continuous casting for example, it may improve the structure of the solidified metal products. Fluid flows generated by electromagnetic stirrers have been extensively investigated (1 ). As for numerical predictions, many works have been published on the subject. In most of the previous works, onepoint closure models have been used. The most used model is the well-known k-i:: model. Those models yield fairly good results as for the mean velocity prediction. However, it has two main drawbacks:(i) the turbulence is not predicted accurately,(ii) it is not well fitted for unstationary flows as well as transitional turbulent motions, where theReynolds number is moderate."

Jan 1, 1999

By R. Mehta, M. Misra, X. Su

"The conventional methods to assess Acid Mine Drainage (AMD) potential of the waste rocks and tailings are based on wet chemistry and leachability tests. These methods are time consuming and expensive. There is a growing interest to develop alternate techniques to establish the reactivity of acid mine tailings and stability of treated waste forms. The Electrochemical Impedance Spectroscopy (EIS) is a reliable non-invasive technique which can be used for quick estimation of reactivity of the potential acid generating tailings. In this paper the utilization of the EIS technique for the estimation of reactivity of tailings is discussed. EIS can also be used to predict the long term stability of different stabilized waste forms.IntroductionMetal contaminated mine drainage is one of the most persistent environmental problems facing the mining and mineral processing industries today. Of all the mine drainage pollutants, acid mine drainage has become a substantial concern because of the potential long-term environmental implications and the accompanying liabilities. The main source of acid mine drainage is the tailings containing sulfide-ores which are generated during the ore processing. When these sulfide minerals, particularly pyrite and pyrrhotite, are exposed to oxygen and water they begin to oxidize. The initial chemical reactions produce acid and the acid dissolves heavy metals present in the tailings. Rainfall and snow-melt flush the toxic solutions from the waste sites into the downstream environment [1-2]. In addition to mining tailings, several Department of Energy (DOE) sites contain wastes which are contaminated with radionuclides and heavy metals."

Jan 1, 1999

By Changqing Su

A batch incubation experiment has been carried out to investigate the optimal condition for the microbial remediation of hexavalent chromium (Cr(VI)) in soils contaminated by chromate ore processing residue at Hunan Iron-Alloy Factory in China. The optimal condition was obtained by comparing the remediation efficiency of Cr (VI) by indigenous bacteria under different culture media, the quantity of nutrient sources, the pH and the temperature. The results indicated that glucose and yeast extract was the optimal component of culture medium and the quantities of the above components were 8 g L-1 and 13 g L-1, respectively. The optimal temperature and pH value were 30_ and 10.0, respectively. A bioreactor was operated under the optimal condition to evaluate the efficiency of Cr(VI) remediation in the contaminated soil. The result showed that water soluble Cr(VI) in soils was reduced from 320 mg kg-1 Cr(VI) of the initial concentration to below detection limit after 30 h in a bioreactor. Thus, there is a large potential to make bioremediation for the reduction of Cr(VI) to Cr(III) by the addition of optimal culture medium under aerobic condition.

Jan 1, 2010

By Kenneth C. Mills

Interfacial phenomena can have a dramatic effect on the separation of phases. Furthermore, since they involve surface-active materials, concentrations at ppm levels are enough to cause dramatic effects on separation processes. The effects of (i) emulsification, (ii) contact angle and wettability and (iii) Marangoni flows on phase separation are reviewed.

Jan 1, 1999

By K. Nona C. Liddell

There is a significant amount of early work that has been largely forgotten that deals with the validity of the pseudo-steady approximation for liquid-solid reactions. Much of this was originally published in the chemical engineering literature but is highly relevant to hydrometallurgical processes. The purpose of this paper is to summarize some criteria that were been developed by various authors for determining the error associated with use of shrinking core models for liquid-solid systems.

Jan 1, 2002

By Steven C. Torma

The present article reviews some of the technologies available for recycling high-energy yield explosives loaded projectiles. These activities lead to reduction of military ammunition stockpiles and their conversion into commercial and industrial applications. The recycling technologies involve dismantling and separation of ammunition components into recyclable metals, plastics, paper and explosive materials. The metal 1 ic components will be sent to smelters, where they will be converted to products that can be used in a variety of industries, such as construction, automotive, housing and so on. Plastics and paper will be recycled and reused. Explosives will be recycled to be used for industrial purposes in the mining industry. Propellants (ammonium nitrate and ammonium perchlorate) can be ground to small particle size and treated to be used in the agricultural industry as fertilizer. In addition, some of the excess explosive material recovered in the demilitarization process may be incinerated to produce energy for steam production for heating purposes, or for production of electricity. Furthermore, this article reviews the developments in the bioremediation of explosive contaminated soils and industrial effluents.

Jan 1, 1994

By Jing Zhong, Yugang Li, Chen Yan, Shaoda Zhang, Qian Wang

Online surface quenching technology has been developed for the hot charging process to prevent the surface cracks in high strength low-alloy steel slabs. In this paper, a two-dimensional heat transfer model of surface quenching process was presented. This finite element model includes nonlinear thermodynamic properties, by which the slab temperature distributions were computed. The model predicted temperatures show reasonable agreement with the measurements. The effects of the water flow rate and slab movement velocity on temperature variation during the quenching and subsequent tempering process were investigated. The result shows that the temperature drop increases but the tempering temperature changes slightly with increasing water flow rate and decreasing slab velocity. Keeping the slab movement velocity at 1.2-2.1m/min and the water flow rate at 55-70m3/h, the slab surface experiences a temperature drop of 400-600 firstly, then recovers above 650, the quenching and energy-saving effect are remarkable.

Jan 1, 2015

By Sergio N. Monteiro

Polymeric matrix composites reinforced with coir fibers are being used in many industrial applications such as automobile interior panels and cushions. These composites have relatively low mechanical strength due to the weak fiber/matrix interface. The objective of the present work was to investigate the effect of a surface alkali treatment of the curaua fiber on the mechanical behavior of polyester composites with different amounts of these fibers. The treatment, also known as mercerization, was performed with distinct concentrations, 0.1 and 10% of NaOH at 1 min and 1 hour, before incorporation of the coir fibers into the polyester composite. The results showed no significant change in comparison to similar untreated coir fiber composites. A microstructure analysis revealed that, in addition to reducing the hydrophilic characteristic of the fiber,the treatment also affects the surface morphology and impairs the fiber/matrix interfacial strength.

Jan 1, 2009

By R. Y. Wan

Low grade sulfidic-carbonaceous refractory ore from Newmont Gold Company's Carlin deposit was microbially pretreated. The biological pretreatment process gave partial oxidation of the sulfidic components of the refractory ore but the preg-robbing carbon continued to be active resulting in approximately zero cyanide gold extraction. A 495 ton pilot plant test heap was conducted using acidic thiourea leach following biooxidation. Activated carbon and cation exchange resin adsorption were tested for gold recovery from the thiourea pregnant solution. The results obtained from the test heap were not satisfactory. Gold extraction was low due to slow reaction kinetics which was caused by relatively large particles and very low winter temperatures. Problems existed in the thiourea-test heap and are discussed in this paper. An alternative heap leach process using thiosulfate has been successfUl at the pilot scale for gold extraction following biooxidation pretreatment of refractory sulfidic-carbonaceous ores.

Jan 1, 1995

By Shirleny Fontes Santos

Muscovite mica crystals lower than 15 mm diameter are discarded as waste in the mining area of Borborema-Seridó (BRAZIL). The objective of this work was the ore dressing and purification of this waste to be used in the preparation of pearlescent pigment. Muscovite was dry ground using knife mills and an ultrasound treatment. It was possible to achieve 67% of mica with particle size lower than 100 µm. This product was used in the preparation of brilliant pigments based on muscovite flakes covered with rare earth oxides (CeO2, PrO2, Ce0,95Pr0,05O2). The pigments were characterized by X-ray diffraction, thermal analysis and scanning electronic microscopy. The color of the resulting pigments was analyzed using the CIELAB method and it showed the following colors: muscovite-CeO2 ? yellow, muscovite-PrO2? black and muscovite-Ce0,95Pr0,05O2 ? orange. Those results have shown that ?trash mica? is suitable for use in pigment preparation.

Jan 1, 2010

By F. F. Aplan, G. Simkovich

"A review is given of the effects of solid state point imperfections upon a number of mineral benefication processes and a metal extraction process. It has been found in numerous flotation studies that small amounts of aliovalent impurities (dopants) in binary compounds may show major effects upon flotation behavior. Both semiconducting and ionic conducting compounds are affected. These effects are also seen in hydrometallurgical studies as well as in electrostatic operations. Additionally, de-copperization of lead melts appears to be strongly influenced by similar defects. It is hypothesized that the effects observed in these studies are present in actual operations and should be considered in designing processes. A few speculations concerning future efforts are advanced. IntroductionImperfections [point (e.g., vacancies, interstials, quasi-free electrons, electron holes, impurity ions), line (e.g., dislocations), two dimensional (e.g., grain boundaries) and three dimensional (e.g., 2nd phases) defects] are generally present in solid materials and these imperfections may, and often do, have important effects upon a variety of properties and processes. In general, one may, in most cases, attain elimination of three dimensional defects by a separation process of one type or another (e.g., gravity, electrostatic, magnetic, flotation, hydrometallurgical etc.,). Thus, this type of defect has rarely been investigated in a systematic fashion. Two dimensional defects are always present in non-single crystal materials but have also escaped systematic studies in processes primarily because the control of such defects is not easily attained. Line defects are non-equilibrium entities which are present in ill-defined quantities so that they present a variable that cannot be easily controlled although through careful systematic experiments one can attain some reproducible relations pertaining to this type of defect.Contrary to the lack of studies concerned with the effects of 1, 2 and 3 dimensional types of defects there has been some activity concerned with point defects and their effects upon a number of mineral/metallurgical processes, especially flotation processes. Thus, this article will present a review primarily of point defects in relation to their effects upon flotation although other processes and defects will also be mentioned."

Jan 1, 1988

By Timothy W. Ellis

"This paper presents the basic theory of operation, physical chemistry and phase equilibria which allow the development of liquid-liquid extraction circuits based on metallic solvents. The incorporation of reduction and reduction/diffusion processes into the process scheme is discussed and a detailed description of several liquid-liquid extraction schemes are developed. A synopsis of experimental results obtained using this method to separate rare earth and other metal based materials will be given.IntroductionConcerns over the effects of waste materials in the environment has been one of the significant social hallmarks of the late 20th century. Essentially every industrialized country has had to incorporate the cost of waste material into the equation of production. Legislative initiatives have led to the passing of very tough laws, by historical standards, which govern the environmental impact of materials processing.Liquid-Liquid extraction is a very common unit operation normally using aqueous and/or organic based solvents. Early work at the Ames Laboratory focused on the use of this technique for the reprocessing of spent fuel from liquid metal breeder reactors by the use of metallic solvents. Recently, we have revisited this area as a means to recycle/reprocess several emerging rare earth based materials, although this method has a much wider range of application. The reinvestigation of this technology is particularly timely as hydrometallurgical based processes are coming under increasing scrutiny in the U.S.A. by the Environmental Protection Agency (EPA). Although technology currently exists to remove contaminants from aqueous based waste streams, often the application of such methods is expensive. With proper design and judicious selection of reagents liquid metal extraction can achieve a high recovery along with a benign waste stream.This process has several possible advantages over other technologies. First is the elimination of aqueous solvents. Therefore, problems associated with disposal or reprocessing of the aqueous carrier are eliminated. Second, with proper system design, very high separation coefficients can be obtained thus limiting the number of stages required. Third, metals are extracted from metals with a metallic product, thereby eliminating the need to re-reduce metal for oxides or other compounds which are the common output for aqueous based extraction procedures."

Jan 1, 1996

By W. Murray Small

Nickel plays an important role in determining the properties of many stainless steels and superalloys. Cobalt also contributes significantly to the performance of certain grades of superalloys. A major technical aspect, in which both of these metallic elements are involved, concerns the solubility of nitrogen in these classes of alloys. Beyond certain content limits, dissolved nitrogen may contribute to the deleterious mechanical behavior by these alloys. It is therefore essential to control the level of this element during alloy processing. In this paper, results from several experimental studies have been assembled and are analyzed to describe phenomena related to the individual effects of nickel and cobalt on the solution of nitrogen in several groups of alloys. Both solid and liquid alloy systems are considered. This information may be used as a guide to limit or control the presence of this interstitial element in alloys.

Jan 1, 1993

By Xinghui Meng

The leaching behavior of platinum powder in .iodide solutions under oxygen pressure in an autoclave was investigated. Ammonium salts were added to the leaching solution at neutral pH as a key lixiviant for platinum. The effect of temperature, partial pressure of oxygen, concentration of iodide and of arttmonium salts on the dissolution rate of platinum was examined. Under experimental conditions, the leaching behavior of platinum powder exhibited a complex reaction mechanism. A precipitate was found during the leaching process and was identified to be platinum ammine iodide, Pt(NH3hI4. The dissolution rate was controlled by a series of chemical reactions, the equilibrium concentration of the platinum ammine iodide being responsible for the ultimate limit to the recovery.

Jan 1, 1996

By Masayoshi Matswnoto

The Kosaka Smelter and Refinery produces copper and lead, and has a history of more than 100 years as a metallurgical department of Dowa?s Kosaka Mine. The Smelter treats complex sulfide concentrates which are difficult to smelt. Valuable metals are recovered using various processes developed by Kosaka Smelter and Refinery. Effluent waters from the smelter contain large quantities of heavy metals. This paper describes how Kosaka Smelter and Refinery recovers valuable metals from various effluent waters and handles overall waste waters in order to meet strict environmental standards.

Jan 1, 1993

By Jafar Safarian

A new kinetic modelling technique has been applied to study the rate of MnO reduction from slags by dissolved carbon in liquid iron. Based on a consideration of the fundamental reaction kinetics, a general differential equation for the slag reduction process has been formulated, which then is solved analytically for certain special cases. By re-writing the solutions in a dimensionless form the poorly known kinetic constants are eliminated, which makes the model both flexible and applicable to a wide range of experimental conditions. For example, changes in process parameters such as temperature, metal composition, slag composition, gas composition can readily be captured along with variations in the crucible geometry. Based on a comparison with a series of experimental reduction curves being reported in the literature, it is concluded that the predictive power of the model is surprisingly good, yielding outputs that are both reliable and physically reasonable. An attractive feature of the model is that it provides an alternative way of calculating the activation energies from experimental reductions curves. For example, it suggests that the activation energy for the reduction of MnO by dissolved carbon in liquid iron is about 90 kJ/mol, which is different from the previously reported activation energies. The model also suggests that the crucible geometry, which affects both slag the volume and the resulting slag/metal interfacial area, has a significant influence on the overall reduction kinetics. This design parameter is a key to further optimisation of the process on an industrial scale.

Jan 1, 2006

By Yan Wen

For the impurities in the copper smelting waste acid, SO3, Cu, As, Pb, Zn, Re and other elements enter the waste acid and generate a lot of arsenic residue, gypsum and neutralized residue, in which Cu, Zn and Re metals have not been recycled. Cu, Re and As are separated by step-wise vulcanization. The valuable metals of Cu, Zn and Re are recovered by separating zinc through pH adjustment. Calcium injection is conducted for boiler for reducing the amount of SO3. The residues generated in the form of arsenate and hydroxide will be returned together with arsenic filter cake for smelting treatment so as to achieve the purpose of valuable metal recycling and solid waste reduction and harmless treatment.

By Emil B. Milosavljevic

The photochemical reactions of cyanide ion induced by light were investigated in the presence or absence of a titanium(IV) oxide semiconductor photocatalyst. The light sources employed were the sun and arrays of either mercury or fluorescent (cool white) lamps. The results obtained verify that cyanide decomposes much faster when TiO2 is present in the solution and that it is first oxidized to cyanate. However, contrary to the previous studies, it is established that cyanide is subsequently further oxidized via nitrite all the way to nitrate irrespective of the light source. As expected, the rates of the oxidation processes decrease with the illumination source utilized in the following order: Hg-lamps > sunlight > fluorescent lamps. As nitrate is a significantly less hazardous contaminant than cyanide, complete photocatalytic oxidation of cyanide to nitrate may be a viable method for decontamination of cyanide wastes. Contrary to previous claims, we find that cyanide is slowly photochemically decomposed even in the absence of TiO2. For example, with the mercury lamps as the light source, in two hours, cyanide concentration decreases to essentially zero; up to 7% was converted to cyanate and the remainder to unidentified products.

Jan 1, 1992

By Ma Lijuan, Zhang Yubing, Wang Bo, Sun Huilan

The effect of lime ratio on phase composition and alumina leaching property of MgO-contained calcium aluminate clinker were investigated by analytical reagent, the XRD analysis of its mechanism was discussed. The results showed that: when the sintering temperature was 1350 ℃, C/A was 1.4, A/S was 1.3 and the content of MgO was 4%, the increase of the C/A promoted the formation of C12A7 and restrained the formation of Q-phase. The alumina-leaching ratio of the clinker (A/S was 1.3) was increased from 74.33% to 91.34% when the content of CaO was 5.21%.

Jan 1, 2015