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By G. Kugler, M. Tercelj

"The use of the up-to date light alloys and their development are in the sharp ascent especially in transportation industry. In the last years the use of the magnesium alloys for the various purposes was strongly increased. The aim of present research was to study the influence of solidification rate on hot workability and on obtained mechanical properties of AM60 magnesium alloy. The study was also focused on possibility to omit prior homogenisation process which would result in cost reduction. The solidification of gravity cast alloy has been investigated with various methods of the thermal analysis: in situ simple thermal analysis and simultaneous thermal analysis. In order to reveal optimal hot working conditions the deformation behaviour was studied in the temperature range 200-450°C and strain rates between 0.001-lOs-1. Mechanical properties have been studied with tensile and impact toughness testing.IntroductionIn recent years, the increased demand for magnesium alloys has been mainly driven by the need of automotive and transportation industry to reduce the weight, as this is the most important parameter to reduce the energy consumption. Beside their very low weight in comparison to other metals, the magnesium alloys are characterized by good machinability, corrosion resistance and good mechanical properties, and can thus compete with aluminium alloys and for some applications even with steels. Due their decreased workabilty they are typically used as cast alloys, but in recent years also the research of their wrought state has become more extensive [1-7]. Decreased hot workability of magnesium alloys originates from their hexagonal close-packed structure. One of the most popular magnesium alloys with great potential for many applications is AM60 (MgA16Mn), which is predominately used for casting. But its application could be increased if the mechanical properties, could be improved. This can be done by hot working. Namely it is well known that wrought microstructure is characterized by better mechanical properties in comparison to as-cast state. On the other hand due to its low hot workability the homogenization process is required prior hot deformation, which results in increased production costs. Thus the aim of the present research was to study the influence of solidification rate on hot workability of AM60 alloy in order to improve its mechanical properties and to check the possibility of producing near-net-shape casting products omitting homogenisation process by employing small additional deformations after casting. Within the framework of this research the solidification of gravity cast AM60 alloy has been investigated with various methods of the thermal analysis."

Jan 1, 2011

By M. J. Collins

Direct pressure leaching of zinc sulphide concentrates was started? commercially in October 1980. Continuing research and development studies at Sherritt and feasibility studies for a number of clients have defined various pressure leach configurations for integrattons with existing roast- 1 each operations and for grass roots plants. Existing and potential applications of zinc pressure leaching are discussed.

Jan 1, 1990

By Dumitru Mitrica, Vasile Soare, Elvira Alexandrescu, Mihai Ghita, Marian Burada, Petru Moldovan, Raluca Maria Florea

"Aluminum metal matrix composite Al-Si /SiCp was prepared by reactive gas injection and subsequent remelting. The influence of the remelting process on the microstructure and physicalmechanical properties of the resulted material was investigated. Samples resulted from the synthesis process contained silicon carbide agglomerations in the vicinity of primary silicon and large pore concentrations. In-situ formed silicon carbide presented mostly a polymorphic structure with particle sizes varying from 1 to lOµm. Physical and mechanical properties were largely influenced by the porosity distribution. The remelting process provided a decrease in the composite material porosity and pore size, with significant improvements in the particle distribution and physical-mechanical properties of the composite material. Additions of up to lwt.%Mg in the starting alloy improved the in-situ carbide formation and particles distribution in the solidified material. However, stable and large particle agglomerations were detected in the material in absence of conventional stirring or controlled solidification techniques.IntroductionThe remarkable properties of composite materials (yield strength, stiffuess, hardness and resilience at a reduced specific weight) make them attractive for applications in automotive, aerospace and military industries. Particle reinforced aluminum metal matrix composites (PAMMC) are known for their high strength to weight ratio. The recent development of P AMMC created the possibility to obtain large particles concentrations, exceeding 10% by volume ofreinforcement (SiC, AIN, Al203, etc.). The improvement ofhigh temperature strength and wear resistance made them appropriate for the use in automotive applications, such as the pistons, rotors, disc brakes, and propeller shafts [ 1]. The present main disadvantage of the P AMMCs is their high costs for obtaining and processing related to the final product performance. In order to benefit from the advantages that offer composite materials properties a reasonable production cost - performance ratio must be obtained [2]. Recent innovations in the manufacturing of aluminum-based metal matrix composites provided notable performance improvements but no feasible solutions were found for lowering their present high prices."

Jan 1, 2014

By Beate Ina Jenssen

Ferric iron removal from the nickel electrolyte at Glencore Nikkelverk AS in Kristiansand, Norway, is achieved by precipitation of iron hydroxide followed by filtration, and it is desirable to improve filtration properties of the precipitated iron hydroxide in order to decrease the filtration time. The effect of increasing the residence time from the current 45 min to 75 min and temperature from 65 °C to 90 °C on the filtration properties of the precipitated iron hydroxide (akaganéite) was studied by simulating the industrial process conditions in a continuous reactor setup operating at steady state, using ferrous-containing process solution as feed material. It was possible to decrease the filter cake resistance by both increasing residence time and temperature, but temperature gave the most pronounced effect and reduced the filter cake resistance by one order of magnitude.

By Rudolf Keller

"EMEC Consultants is developing a process to extract oxygen, aluminum and silicon from lunar anorthositic soil. The process will provide oxygen in space for propulsion, aluminum as a structural material, and possibly silicon for the construction of solar cells.The evolution of the process concept in the course of our present NASA-sponsored SBIR effort is discussed. A molten salt electrolysis producing aluminum and oxygen is the central step; inert anode technology is to be employed. Silicon will be produced by reducing the anorthite, CaAI2Si20S' with aluminum. In a steady-state operation, all components of the ore added have to be removed from the process, and the removal of calcium is a major topic of our experimental studies.Utilization of Lunar ResourcesUtilization of lunar resources may play an essential role in the exploration of the solar system and the conquest of space. High costs are involved in overcoming Earth's gravity to supply missions in space. Even at a low projected cost of $ 300 for transporting a pound of payload into Earth orbit -- today's costs are many times higher -- it appears attractive to use resources in space to produce needed materials. Processing of lunar resources on the lunar surface is an obvious possibility.Oxygen is a product of major interest. It is required for support of human life in space. Even greater quantities may be needed for propulsion, to conduct further missions into space. To satisfy this demand for oxygen through lunar processing requires a quite different solution than to supply oxygen on Earth, where oxygen gas is abundant and easy to extract from air or water. On the lunar surface, solid oxide materials have to be used. Hydrogen reduction of ilmenite and subsequent electrolysis of the resulting water is being studied [1]. Other suggestions include fluorination of lunar soil [2], reduction with lithium and electrolytic decomposition of the resulting lithium oxide [3], and aqueous HF leaching [4]."

Jan 1, 1988

By Miguel Barron

Recently, a new lance design for BOF steelmaking has been proposed in the literature. This lance, in addition to six peripheral inclined supersonic nozzles, contains a vertical centered nozzle whose oxygen flow is independent from the main oxygen supply. The above authors affirm that their lance maximizes the droplet generation without causing spitting. In this work, the performance of a lance with four peripheral nozzles and one vertical centered nozzle is numerically modeled by means of Computational Fluid Dynamics software. Transient two dimensional computer simulations were carried out considering two phases, namely molten steel and gaseous oxygen. Numerical results confirm that bath agitation and droplet generation are enhanced as a result of the vertical centered nozzle, however a proper performance of this lance, related to a conventional one, strongly depends on the Mach number of the oxygen jets and the lance height.

Jan 1, 2008

By Annette Revet

Aluminum fluxes have been used for the remelting of secondary aluminum since the beginning of the recycling industry. During the last sixty years, a number of fluxes have been designed, researched and tested at the laboratory and plant scale. Fluxes are primarily a mixture of potassium chloride and sodium chloride with the addition of some other chloride and fluoride containing salts. The conventional Mining methods of potassium chloride and sodium chloride yield products that are not high in purity without costly reprocessing or additional refining. In 1993, Kalium Chemicals, Ltd. began supplying flux mixtures to the aluminum industry. Kalium produces potassium chloride and sodium chloride which are mined and refined by a patented solution-mining process. The salts produced by this process are high in purity with lower concentrations of iron oxide, sulfates, and other impurities. This paper will present the different mining methods used in the production of sodium chloride and potassium chloride. The paper Will address how these mining methods affect the purity of the final product as well as the effect of purity on the performance of the fluxing salt.

Jan 1, 1995

By S. Mattlgod

Self-assembled monolayers on mesoporous supports (SAMMS) have been developed for the removal of heavy metals and some transition metals. The thiol functional groups were assembled on the internal and external surfaces of mesoporous silica with a uniform pore size of about 55 A. The mesoporous supports provide high surface area (>900 m2/g) needed for high metal loading in chemical separation. Self-assembled monolayers of organic molecules bond to the ceramic substrate with prescribed densities, and with terminal functional groups for excellent molecular selectivity. The unique characteristics include: (1) High metal absorption capacity, up to 3.2 mmol/g of SAMMS. (2) Fast Hg-binding kinetics (reducing mercury concentration from 0.5 ppm to 0.5 ppb in less than 5 minutes). (3) High selectivity in the presence of a range of cations, anions, and organic species. (4) Applicability in both aqueous and non-aqueous solvents. (5) Flexibility in surface chemistry. The materials can be designed to adsorb heavy metals, transitional metals, and radionuclides. (6) Chemical stability, and potential for regeneration or waste storage. This paper discusses the results on mercury adsorption.

Jan 1, 1999

By Adele Garkida

Compacts of crushed waste window glass, fluorescent tubes, drinking glasses and laboratory glass wares were made at various proportions from 106 microns and minus 75 microns powders in combination with 5% bentonite as binder for each glass type, after several trials to determine compatibility of particle sizes. They were made using the uniaxial press at 10,000 psi and sintered at a temperature range of 700- 750oC. The results showed anisotropic shrinkage behavior for all the samples, exhibiting an axial shrinkage lower than the radial shrinkage. Sintered compact from waste drinking glass which comprised of 60% 106 microns and 40% minus 75 microns powders showed the least sintering shrinkage factor of 1.125, fused at 700oC and the highest shrinkage factor of 1.286 obtained at 750oC. This shrinkage behaviour connotes that sintering can be employed to utilize these waste glasses up to the maximum of 95% recycled glass content in ceramic tile production.

Jan 1, 2008

By Elsa Agante

Recycling of solid wastes, a common practice nowadays, requires the separation of the different materials in order to increase the products added value. The separation of one plastic from mixtures of different types of plastics is not easy due to their similar physical properties, but different techniques are available, from automatic sorting systems based on optical sensors to techniques adapted from mineral processing, namely gravity, froth flotation and electrostatic processes. In the last decade, many researchers have addressed the separation?s problem of different polymers, like Polyethylene Terephthalate (PET) and Polyvinyl Chloride (PVC), two polymers commonly used in packaging which have similar density. One proposed technique is the classical froth flotation performed in agitated cells. Froth flotation is a versatile and relatively cheap process widely used in mineral separation. It is based on the different behaviour of particles in the presence of an inter-phase air-water, which depends on the materials surfaces properties. Froth flotation can be affected by some variables such as impeller speed and air flow rate. Agitated cells, when used with low density materials, like plastics, can produce overstated turbulence that prevents the adhesion and collection of particles in the froths. In this case, separation is favoured by column flotation smoother hydrodynamics. This paper proposes the separation of PET from PVC by column flotation. The experimental work was carried out in a column of 9cm diameter and 1m high. The effects of some operating conditions, such as depressor and frother concentration, air flow rate and feed grain size on products grade and recovery were evaluated and the best flotation conditions for the separation of these plastics were established.

Jan 1, 2006

By Lifeng Zhang

The transport of fluid, heat ,and particles (bubbles and solid inclusions) in flowing molten steel is investigated in steel refining ladles, the continuous casting tundish, continuous casting mold and strand, and steel ingot casting processes. The two-equation k-?? model is used to simulate the turbulence. Multiphase fluid flow is numerically simulated with a Lagrangian-Eulerian approach, an Eularian-Eulerian approach and the Volume Of Fluid (VOF) method. The simulation can predict inclusion trajectories, inclusion removal fraction, free surface waves and other phenomena, which can be used to optimize these important metallurgical operations.

Jan 1, 2006

By Go-Gi Lee, Jae-Young Jung, Myung-Duk Seo, Hyun-Na Bae, Seon-Hyo Kim

"Bubbles form at the anode during the electrowinning of magnesium and cause hydrodynamic acceleration and electrical field disturbance. A three-dimensional computational model was developed to investigate the effects of the geometry of the electrochemical chamber and the size distribution of bubbles on the fluid flow in the pilot plant. The results are validated by measurements of the surface characteristics of molten salt and the bubbles formed. Fluid flow at the surface was recorded with a high speed camera, and the distribution of bubble size is determined by inspecting the video images frame by frame. The measured size distribution of the bubbles is entered into the computer simulation of a multi-phase flow. A sloped roof is installed above the electrodes, to enhance the flow of the molten salt, thus resulting in higher current efficiency, lower energy consumption, and higher quality of magnesium metal.IntroductionTitanium's excellent properties of low density, high specific strength, high temperature strength, and exceptional resistance to corrosion are highly beneficial to diverse applications including aerospace, automotive, construction, and medical implants. Although the Kroll process[l] and Hunter process have been used for the extraction of titanium in the 20th century, their complicated engineering stages and high production cost, have led to further research into new processes such as FCC Cambridge, Armstrong and TiRO. Despite these intense research efforts, no process has yet been developed that is more economical than the Kroll process, by which most of the global commercial titanium is still being produced."

Jan 1, 2011

By James D. Navratil

Advances in hydrometallurgy require the introduction of new separation and purification processes, but they can be complex, costly and energy intensive. Chromatographic processes have low energy requirements and possess very high separation efficiencies. However, they have not yet made the great industrial impact that might be expected from their benefits. The large-scale and difficult separation of rare earths would greatly benefit from an improved continuous chromatographic operational device. Truly continuous, multicomponent chromatographic separations may be achieved by means of the continuous annular chromatograph. Work has been Initiated at The University of New South Wales involving the improvement and development of such equipment for the separation and purification of rare earths.

Jan 1, 1990

By M. I. Novgorodova

An overview of the systems Au-Ag and Au-Cu is given. The nature and levels of concentration of various elements occurring with native gold is reviewed. The examples cited are mainly from the USSR. The lack of homogeneity within naturally occurring Au-Ag solid solutions is examined.

Jan 1, 1991

By T. A. Edison

A distinct hydrocarbon maturation anomaly coincides with the Gold Acres open pit, Nevada (Figure 1). Both atomic hydrogen to carbon (H-C) ratios and reflectance measurements of contained organic matter indicate significantly higher maturity in samples collected within the confines of the open pit than in samples from the surrounding region (not shown in Figure 1).

Jan 1, 1987

By W. Petruk

The behaviour of galena, chalcopyrite and tetrahedrite during floration of a fine-grained base metal ore from New Brunswick was investigated by image analysis study of the mill concentrates and tailings. The minerals were analyzed to determine the grades and recoveries as related to free and unliberated mineral grains and their size distributions. The results show that only 37 wt % of the galena was liberated but 88 wt % of the free galena was recovered, indicating good mill performance for the lead. The lead recovery was 65 wt %, with the main loss due to unliberated galena. Most of the unliberated galena lost to mill tailings is so fine-grained that galena liberation and Pb recovery would not improve significantly by re-grinding. Chalcopyrite liberation was 56 wt % but only 75 wt % of the free chalcopyrite was recovered. Copper recovery was 45 wt %, with the chalco-pyrite loss in the mill tailings being both as large free grains, and as small and large unliberated grains. It was calculated that copper recoveries could be improved about 8 to 10 wt % by changing the concentrator operations and by regrinding. Concentrator operations hive already been modified and copper recoveries have improved about 5 wt %. About 29 wt % of the silver was lost to tailings mainly as both free and unliberated, large and very small, Silver-bearing tetrahedrite grains. It was calculated that about 25 wt % of the silver in the tailings might be recovered by improved milling conditions and by regrinding.

Jan 1, 1981

By Jin Yu, Fang-Qiu Zu, Yun Xi, Li-Na Mao

"According to the behaviors of resistivity-temperature of Cu-Sb70 melt, which suggests a partly reversible temperature-induced liquid structure transitions (LST) could occur in this alloy, in this paper, we investigated the dependence of solidification on the liquid state. Both resistivity and temperature were measured to track solidification process. The results show that the nucleating undercooling of the melt which experienced the LST increased and the solidified time decreased. Meanwhile, the solidified microstructures refined evidently, with the microscopic pattern of primary phase changes from disordered pillarlike dendrites into homotaxic ones. Moreover, it is verified that the microstructures would be different if the reversible part of the LST was restrained. The new phenomena and results reflected in this paper suggest that grasping the rules of melt structure change with temperature before material processing will give help for controlling the solidification more effectively and finally resulting in more ideal microstructures.IntroductionThe structure and quality of liquid alloys have a direct and important influence on the structure, performance and quality of the solidified ones. In recent years with in-depth study of liquid structure, researchers have found that some liquid structure transitions (LST) could occur on dependence of the temperature or pressure [1-5]. And the article [6] reported that a pressure-induced reversible LST was found in liquid triphenyl phosphite, which further confirmed the authenticity of the existence of the LST. Furthermore, in our earlier studies of Sn-based melts using resistivity method, some abnormal structure changes induced by temperature have been found at hundreds of degrees above liqiudus, and these LSTs are partly reversible[7]. This phenomenon has been discussed and it is suggested that the reversible LST in Sn-based melts are related to the short-range ordering (SRO) structures of Sn, which are tetrahedron structure with covalent bonding. However, does this reversible LST exist in other melts too?"

Jan 1, 2012

By S. R. Hutchins

Several refractory sulfide and carbonaceous gold ores were examined to determine whether microbial pretreatment could be used to enhance gold recovery. Test samples were biologically leached using unique. thermophilic microorganisms to solubilize iron sulfide minerals. Gold recovery from sulfide ores and concentrates was enhanced following pretreatment with the thermophiles; responses varied widely for the individual materials. Although bioleaching had little effect on the preg-robbing characteristics of the carbonaceous gold ores, cyanidation of the bioleached residues yielded higher gold recoveries than cyanidation of the native ore. By combining bioleaching with abiotic processes designed to inhibit preg robbing, gold recoveries of 83-98% were obtained from carbonaceous ores yielding 10-50% gold recovery by direct cyanidation.

Jan 1, 1987

By Minh H. Pham

This paper presents a technique for imaging the extent of solidification of molten metal flowing in a cooled pipe based on the concept of eddy currents. A 3D mathematical model, which relates the geometry of solidification to the scattered field induced in a solenoid external to the pipe, is derived. The model is described by a set of integral equations which are solved numerically using the moments method. An iterative algorithm is developed to reconstruct the solidification distribution image. Experimental measurements have shown that the eddy current technique is sufficiently sensitive for practical purposes.

Jan 1, 2001

By Youn-Bae Kang

In order to overcome weak points of steel for its engineering applications, in particular, for environmentally benign, energy-efficient, lightweight engineering systems, a number of new steels have been proposed, especially to improve strength-to-weight ratio (specific strength). Mass production of these steels, however, has encountered a serious roadblock particularly in the steel refining and casting processes. This is because their chemistries and cleanliness requirements are vastly different from those of the conventional steels, and thus an incremental improvement of the prevailing process technologies is found hard to meet the requirements. In this study, a new process is proposed, which employs inert gas bubbles in the shroud nozzle, liquid steel drops in the degassing chamber, and the siphon transport for continuous casting. The proposed process which integrates the final refining and cleaning steps prior to casting is expected to be a technologically disruptive innovation on the conventional counterpart. The effectiveness of the individual steps is discussed with experimental results.