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By Srinath Viswanathan, Adrian Sabau

"In general, the occurrence of microporosity during metal casting is due to the combined effects of solidification shrinkage and gas precipitation. The governing equations for fluid flow and hydrogen evolution indicate that porosity formation and fluid flow are strongly coupled. However, in most studies on microporosity, it is considered that the porosity formation does not influence the fluid flow in the mushy zone. In this study, a computational methodology is presented for the numerical simulation of interdendritic fluid flow and microporosity evolution. The solution algorithm presented includes a fully coupled, implicit treatment of microporosity and local pressure in the mushy zone. The effects of microporosity evolution due to the local pressure drop in the mushy zone, and pore expansion in casting regions where liquid feeding alone cannot compensate for the solidification shrinkage are also considered. It is shown that neglecting the effect of porosity formation on the pressure in the mushy zone yields higher pressure drops. By its growth, microporosity partially compensates for the solidification shrinkage, reducing the feeding demand. A reduced feeding demand requires less fluid flow to compensate for solidification shrinkage, and results in smaller pressure drops in the mushy zone. Therefore, in order to accurately describe casting defects, comprehensive models of fluid flow, heat transfer, and solidification must include the effect of microporosity as well.IntroductionIn the terminology commonly used by foundrymen, porosity is usually considered to be either ""hydrogen"" or ""shrinkage"" porosity. Hydrogen porosity is the term given to porosity that is generally rounded, isolated, and well distributed. Porosity that is interconnected or clustered, and of an irregular shape corresponding to the shape of the interdendritic region, is usually termed shrinkage. In general, the occurrence of microporosity in aluminum alloys is due to the combined effects of solidification shrinkage and gas precipitation [1]. Continuum models [1, 2- 7] have been used to predict the level of porosity in castings. A number of other studies have also attempted to understand the phenomena of porosity formation and pore growth [8-10] and pore morphology [11].The governing equations for fluid flow and hydrogen evolution indicate that porosity formation and fluid flow are strongly coupled. However, in most studies [4, 9, 10], it is considered that the porosity formation does not influence the fluid flow in the mushy zone. Kubo and Pehlke [3] presented a methodology for the prediction of microporosity distribution in shaped castings by considering the effects of both the hydrogen precipitation during solidification and the pressure drop in the mushy zone. In their approach, the local pressure and porosity were computed in an uncoupled manner based on a ""flux of interdendritic liquid"" criterion, i.e., either pressure or porosity was first computed using the other variable at the previous time step. Their approach has been used with little change in numerous studies [6, 12, 13]. Recently, Kuznetsov and Vafai [14] presented a fully coupled, one-dimensional model for the computation of pressure and porosity. They showed that neglecting the effect of porosity formation on the pressure in the mushy zone yields higher pressure drops and an over-prediction of final porosity. They also showed that the influence of porosity formation on the pressure is larger at lower pressures in the mushy zone."

Jan 1, 2001

By G. Upadhya

Of late, solidification modeling has progressed considerably to emerge as a viable simulation tool for the foundry engineer. A wide variety of tools exist in the commercial market to cater to the various needs of the design/ foundry engineer. In fact, recent developments in the area of solidification modeling have been so rapid that a comprehensive review of the state-of-the-art is very much needed. In this paper, an attempt is made to summarize the various issues of solidification modeling, at the same time addressing the historical evolution of the subject. The various phenomenological issues covered in this paper include: heat transfer, fluid flow during mold-filling, solidification kinetics and microstructural evolution, quick-analysis schemes for approximations, porosity prediction models, and the phenomena of fluid flow in the mushy zone. Modeling issues related to the development of solidification stresses which lead to defects such as hot tears and the development of artificial intelligence concepts in the area of rigging design are also discussed. Due emphasis is given to the various phenomena which add to the complexity of the whole subject, and the various alternatives available for solving a particular problem. For example, the heat transfer problem can be approached by the use of simple modulus schemes or by solving the conduction equation to obtain a more accurate temperature distribution. Similarly the microstructural evolution can be handled in a deterministic way by use of nucleation and growth models, or in a probabilistic way by use of empirical models. The main goal of this paper is to put the multi-faceted problem of solidification modeling in proper perspective so that it can serve as a guide for future developments in this area.

Jan 1, 1994

By R. L. Nyirenda

An investigation of the reducibility of a cassiterite concentrate with charcoal was made in the temperature range of 1123-1373 K. The course of the reaction was monitored by a combination of sample weight loss measurements, product gas analysis, and chemical analysis of the reaction product. It was found that the cassiterite could be best reduced by a combination? of high temperature, reasonably high charcoal proportions, high charge poroslty, and the addition of a small percentage of lime. Analysis of kinetic data obtained from isothermal experiments using theory from the oxidation of carbon by carbon dioxide gave an activation energy value of 255 lci/mole for the consumption of carbon by reaction with cassiterite.

Jan 1, 1990

By KNona C. Liddell

Goethite is an important naturally occurring sorbent for divalent heavy metals and has often been used as a model compound in studies of adsorption on oxide mineral surfaces. Surface complexation modeling, surface spectroscopy, and electrochemical techniques have all been applied to goethite adsorption. Modeling studies have shown that usually several different sets of fitted parameters are equally successful in representing surface charging and adsorption data. Surface spectroscopic data are proving valuable in determining the nature of the surface sites, and refined models now incorporate structural information on interatomic distances and coordination numbers. Multisite surface complexation models can give very good fits to surface charging and adsorption data, but further improvements are needed to better represent surface reactions involving exchange of protons and divalent cations. Recent experimental and modeling studies on adsorption of divalent transition metals on goethite are described and the present status of the field is assessed.

Jan 1, 1999

By Anette Mueller, Thomas Schnellert, Sérgio C. Angulo

"The use of automatically sorting technique, to separate gypsum components from recycled material of processed construction and demolition waste (C&DW), is motivated by environmental and economical aspects. Only if the gypsum can be separated the aggregates can fulfill the environmental requirements and also the structural characteristics according to the standards. Furthermore, the separation of red brick can also improve the quality of the aggregates.This paper aims at analyzing the separation of gypsum components and red brick by using the color sorting technique. The impacts on the composition and the envelope density of recycled aggregates are described. Depending on the gypsum content the application of two processing stages (rougher-cleaner) can be necessary to produce aggregates with sufficiently low gypsum content. Additionally, the separation of red brick and concrete is successful. So, the color sorting may be a promising technique to upgrade the quality of mixed C&DW aggregates.IntroductionConstruction and demolition waste (C&DW) is a mixture of different materials. Such mixtures can be used only in low grade applications. If the material is used as certified material for road construction or as aggregate in concrete the concrete particles must be separated from the other building materials. This paper aims at analyzing the separation of gypsum components and red brick by optical sorting. The needed stages of sorting for getting a product quality according to the German Standards are deduced.Gypsum is a building material that is increasingly used for interior works in Germany like it is shown in figure 1 [1]. At present the content of gypsum in C&DW is estimated at about 1 %. Assessments on the basis of material streams of gypsum and concrete and their life spans show that higher gypsum contents of about 3 % must be expected in future [2]. Also in other countries the use of gypsum has grown considerably in the last decades. From the characterization of C&DW available in some cities in Brazil, 4 to 15 % of total amount of C&DW that may arrive at the recycling plant to be processed is excessively contaminated by gypsum. In one of these cities, the average content of gypsum in the C&DW before processing was as high as 2.1 % [3]."

Jan 1, 2008

By E. Fregeau-Wu

The major obstacle in recycling steelmaking slags to the blast furnace is their phosphorus content. Removal of the phosphorus, which is primarily associated with the silicate and phosphate phases, would allow for greater recycle of these slags for their iron, manganese, and lime contents. Calculations show that separation of the silicates from the oxide phases would remove nearly 90% of the phosphorus from the slag. The variable grain size of the as-received slag made liberation by fine grinding difficult. Therefore, slow-cooling experiments were undertaken to improve the grain size distribution. The grain size distributions were determined using in-situ image analysis. The samples were ground to their apparent liberation size and high gradient magnetic separation was used to separate the magnetic oxides from the nonmagnetic silicates and phosphates. Liberation analysis and modeling was performed on selected separation products for discussion of benefication characteristics.

Jan 1, 1995

By Zengjie Wang

Investigation on hydrochloric acid leaching of the ilmenite from Panzhihua, China was carried out to prepare synthetic rutile. The leaching parameters were optimized to obtain high content of TiO2 in the products. The experimental data suggest that an optimum leaching can be realized with 30% acid, a solid/liquid ratio of 1/4 at 95°C for 4h, and ore ground for -400 mesh size. After the acid leaching, an additional alkaline leaching process using hot NaOH solution was performed, and then the products was in grain form followed by heat treated at 900°C for 2h in order to extract Si and increase the particle size of synthetic rutile. The final product has a high content of TiO2 (about 95%), a low content of chlorine consuming elements (total CaO+MgO =0.07%) and a suitable particle size distribution for chlorination process.

Jan 1, 2008

By M. Furuta, M. Hasimoto, Y. Komoda, K. Haiki

"Tamano Smelter & Refinery started its operation in 1972 with high current density electrolysis (350Nm2 of maximum) applying PRC technology. After the start up, four times of expansion have been done, the cathode production capacity has increased from- 84,000 t/y to 191,000 t/y. However, recent refining technology with permanent stainless steel cathode enabled to increase current density up to 300 Nm2 or more without PRC method. In order to increase current density more than 350 A/m2 , experimental work using commercial size cell has been carried out at several conditions, such as current density, PRC conditions, electrolyte composition and electrode condition. As a result, it was found that high quality (LME A grade) cathode can be produced at such a high current density as 405 A/m2•IntroductionWhen considering the production increase of electrolytic copper, what becomes important is the improvement of productivity per unit of production facility. Conventionally, production had been expanded by increasing the number of cells but a huge investment required for this had a influence to the business profitability. Because of this, increase of current density, which is one of the methods to improve unit productivity, 'was expected and this method at the same time has another advantage of shortening the retention time of copper and other precious metals in the cells. At present, the average current density at Tamano during full capacity production is around 350 A/m2 and this used to be the limit throughout the world (1)."

Jan 1, 2000

By Peter C. Hayes

"The high temperature reduction of solids through the use of reactive gas atmospheres has application in a wide range of industrially important processes. Whilst significant advances have been made in understanding and describing these processes, some key aspects of the chemical reactions and reaction mechanisms operating in these systems, for example, the transformation from metal oxide to metal, remain poorly understood. A number of different product morphologies have been identified in these reaction systems and the reaction rates have been shown to be critically dependent on the product structure.Theoretical examination of the elementary process steps taking place in the region of the gas/metal/metal oxide interface, combined with electron microscope studies of the resultant product microstructures, have enabled the key process and material variables responsible for the development of the various product morphologies to be identified. By considering i) established criteria for the stability of moving interfaces in a thermodynamic potential gradient, ii) the relative rates of chemical reactions on the oxide and metal surfaces, and iii) key process phenomena and physico-chemical properties of the solid phases, the mechanisms and conditions for the formation of various product morphologies are identified. Interestingly the analysis points to direct analogies between these phase transformations and, the phenomena and microstructures observed in metal solidification, and the potential to develop generic models of these fluid/solid reaction systems."

Jan 1, 2013

By Joachim Ulrich

The spreading and splashing behaviour of single tin, lead, copper, aluminium and steel droplets impacting on a solid surface were experimentally examined. The droplet impact was observed using a high speed video imaging technique. The onset of splashing and the mass of the secondary droplets of impacting tin and lead droplets was quantified by the weight difference of the droplets before melting and the splat after the impact. The spread factor and the mass of the secondary droplets in dependence of the impact velocity is shown for different droplet materials, initial droplet diameters, target temperatures in ambient air and inert gas atmosphere. An empirical found correlation predicting the transition from spreading to splashing is presented by means of dimensionless numbers.

Jan 1, 1999

By Norbert Steiner

For the desulfurization of weak SO2 gas streams, Degussa developed a process using dilute H2SO4 solution containing H2O, instead of conventional gas scrubbing with all solid absorbent medium (limestone, MgO). The process is based on fast reaction of H2O, with SO2 yielding H2SO4 up to 70% strength, depending on off-gas temperature. Compared to the conventional systems with typically < 95% efficiency, independent on the raw gas SO2 concentration, residual SO2 concentrations of less than 20 mg/Nm3 can be easily achieved, corresponding to nearly 100% removal. These features render the H2O, process a very attractive, low capital cost technology to retrofit existing conventional desulfurization plants.

Jan 1, 1996

By H. Y. Sohn, M. Pérez-Tello, P. J. Smith, K. M. Riihilahti

A three-dimensional computer model for the Kennecott-Outokumpu flash converting process for copper matte is presented. The model incorporates the transport of momentum, heat and mass, and reaction kinetics between the gas and particles in a particle-laden turbulent gas jet. The k-E model is used to describe gas-phase turbulence in an Eulerian framework. The particlephase is treated from a Lagrangian viewpoint which is coupled to the gas phase through the source terms in the Eulerian gas-phase governing equations. Matte particles were represented as Cu2S·yFeSx. Based on experimental observation, the oxidation products were assumed to be Cu2O, CuO, Fe3O4, and SO2. A reaction mechanism involving the external mass transfer of oxygen to the particle surface and diffusion of the oxygen through the oxide layers of CuzO/Fe304 and CuO/Fe3O4 is proposed. Predictions of the mathematical model were compared with the experimental data collected in a large laboratory furnace. A reasonable agreement between the model predictions and the measurements was obtained in terms of fractional conversion of the oxidation reactions and of sulfur remaining in the reacted particles. The simulation of an industrial flash converting furnace was also performed. Higher oxidation rates, more even distribution of particles, and thus a more efficient use of the reactor volume are predicted with a burner having a distributor cone, than with a single-entry burner.

Jan 1, 1999

By Chang-Young Choi

Korea Zinc commenced zinc production in 1978 with a capacity of 50,000 tpa. Since then, continuous investments have been made and resulted in Korea Zinc now being the biggest zinc and lead producer in the world. In the course of increasing zinc production capacity, the company management realized that the company needed a lead smelter to prevent the solid waste disposal problems by treating the lead containing solid waste. This paper begins by briefly stating the objectives and the roles of the lead smelter at Onsan. It describes the QSL process and the TSL process, and further extends the description of the TSL process, through which harmless inert solid waste could be produced for secure final disposal. It is also mentioned that the TSL process plays an important role in the integration of zinc and lead production. Throughout the paper, a positive attitude in handling the environmental issues in the non-ferrous smelting industry is emphasized. Finally, a solution for the solid waste disposal problem in the zinc and lead industry is proposed, with which the environmental issues can be an opportunity rather than a crisis. The current operation at Onsan suggests the future direction of the non-ferrous smelting technology that all of the zinc and lead producers should pursue.

Jan 1, 2003

By Nobuhiro Oguma, Yuji Mizuta, Hideya Sato, Shigehiko Iwahori

"Recyclable materials containing copper and precious metals have been treated at the Mitsubishi Process in Naoshima. In 2003, a new incinerating and melting plant (pre-treatment plant) for waste materials, such as shredder residue of automobile and scrapped appliance, was constructed. All of produced slag/metal mixture is treated at the Mitsubishi Process, and which results in the significant increase of recyclable materials treatment. The combination of two processes has realized a highly efficient and environmentally friendly system for recycling valuable metals in the waste which used to be sent to a landfill. Naoshima continues to make efforts to achieve the highly efficient operations of the two processes, and plans to increase the treatment of recyclable materials further. This paper summarizes the recent operations and the various improvements implemented in the pre-treatment plant.IntroductionRecyclable materials containing valuable metals such as copper and precious metals have been treated at the Mitsubishi Continuous Copper Smelting and Converting Process (Mitsubishi Process) since the start-up in 1991. In the early stages, recyclable materials consisting mainly of metal scrap were charged into the process and the treatment had been increased steadily. In order to promote the recycling business, treatment of various kinds of materials including printed circuit boards was started. However, the treatment hit the ceiling due to a limitation of furnace boiler capacity, since they contained large amounts of combustible materials. In addition, severe corrosion of boiler tubes was caused by halogen contained in recyclable materials."

Jan 1, 2012

By Tim B. Vander Wood

Standard methods of determining clay mineral powder aspect ratios involve manual scanning electron microscopy analyses of shadowed particles in order to measure both platelet thickness and diameter. We present a method whereby the diameters of platelets are quickly determined by automated scanning electron microscopy and their images are recorded and digitally transferred to a transmission electron microscope equipped for parallel electron energy loss spectroscopy. Thickness&apos; of platelets whose diameters are known from the previous analyses are determined by measurement of the ratio of scattered and unscattered electrons in the beam after it has been transmitted through the platelet.

Jan 1, 1995

By Giuseppe Bonifazi

Minerographic and petrochemical research was carried out on crude ore samples from the complex polymetallic Zn-Cu-Pb sulfide ores of , Sotiel in Huelva province west of Seville, Spain. A computerized image analysis system was used to define the structural and textural characteristics of the ore to obtain information on the degree of liberation of the different minerals (i.e. pyrite, sphalerite, galena, chalcopyrite). Techniques of digital multispectral image processing of reflected light microscopy images were used. Particular structures were identified by means of mineral associations and numerically quantified to obtain useful information for designing beneficiation processes.

Jan 1, 1991

By Li Qian

Mechanisms of bio-dephosphorization from iron ore was investigated in this Paper. The results show that there are two bio-dephosphorization ways from iron ore, the one is that Acidithiobacillus ferrooxidans directly derive phosphorus from the ore, the other is phosphorus is able to be leached acid produced during metabolizing of Acidithiobacillus ferrooxidans, and the latter is more important than the other. Adding suitable pyrite can enhance the bio- dephosphorization process through providing nourishment and producing acid directly due to S 3oxidized or indirectly due to Fe3 as oxidant. The potential varies in the range of 0.434~0.498V and pH is in the range of 2.5 ~ 1.25 during bio-leaching process. It can be founded that, according 2+to the E-pH graph of Fe-H2O system, Fe wouldn?t be oxidized under sterile system in this potential and pH ranges. It can be obviously concluded that the Acidithiobacillus ferrooxidans are 2+able to reduce the potential for the oxidization of Fe and make the oxidization occur in the above pH and potential zone, so the bio-leaching process can proceed. the investigation of E-pH graph of P-H2O system show that H3PO4 can exist steadily.

Jan 1, 2009

By Fu-Shen Zhang, Mengjun Chen, Jianxin Zhu

"A novel approach for foam glass preparation, namely vacuum-aided powder sintering technique, was preliminarily investigated in the present communication. The key point of which was to prepare foam glass at a negative pressure. Compared to normal powder sintering process, the new approach could benefit the foaming process by shorting the holding time, reducing the amount of foaming agent and especially decreasing relative density of the product. Optimum conditions were 750 °C, 1000 Pa, 5 min and 1 wt.% foaming agent, respectively.IntroductionFoam glass represents a highly valuable solution for thermal and acoustic insulation, since it possesses a generally higher mechanical, chemical and thermal stability than other foams'1'. The first industrial processing for foam glass production, the direct introduction of gases (""blowing"") into the special molten glass, can be dated back to the end of 1930s'2'. At present, almost all foam glasses is prepared by powder sintering technique instead of blowing,3 since it reduces the temperature by several hundred degrees. Moreover, as fine glass powders or similar powders can be used to substitute corresponding glasses by this technique, considerable attention has been focused on the production of foam glass by considering fully recycled glasses, coal fly ash, or other solid wastes as raw materials,4 especially CRT glasses'3' 5', on the point of environmental protection.In a previous report'6', when discussing the lead removal and recovery from CRT funnel glass by a pyrovacuum process, we found that foam glass could be prepared at a negative pressure. Therefore, in this communication, the similarities and differences between the powder sintering process for foam glass at normal and negative pressure was preliminarily discussed."

Jan 1, 2011

By Eric J. Grimsey

Nickel smelting and converting can be viewed as processes in which iron is either partitioned or transported between matte and slag. Metal recovery depends on the mass of iron transported to slag, the thermodynamic environment in which the transport is made, and the extent to which the slag, once formed, is left in contact with the matte. The importance of these effects is discussed with reference to a new equation which describes metal recovery in terms of a mass balance and a thermodynamically related parameter which is easily measured in practice.

Jan 1, 1993

By S. Sugiyama, M. Kiuchi

"New metal working processes, such as the mashy-state mixing, mashy-state forging, mashy-state rolling and mashy-state extrusion are developed and applied to manufacture the so-called particle reinforced metals, fiber reinforced metals, particle reinforced cladding metals and so forth. These metal-ceramics composites are made of metal sheets, metal powders, ceramics particles and ceramics fibers. The mashy-state processes are also used to work those composites into bars, wires, tubes, plates, sheets, machine parts and other products. The working conditions necessary to manufacture sound composite products are clarified and the mechanical properties of the products are investigated. Through the investigation, it becomes clear that the mashy-state processes are useful and effective to manufacture metal-ceramics composites. It is al so known that these processes may be applied in various ways to development of new metal matrix compounds. IntroductionThe so-called metal-ceramics composites and processes to manufacture them are now being widely investigated in order to comply with increasing demands for new materials with novel and excellent mechanical properties and functions. The metal-ceramics composites are expected to have superior characteristics with respect to the elastic modulus, hardness, anti-wear resistance, high temperature strength and other mechanical properties to those of conventional metallic materials.The present authors ha v e been investigating into new metal working processes which are based upon the characteristics of metals and their alloys in the mashy-state. In the mashy-state, the metal (or alloy) includes both of the solid and liquid components. According to the fact that the partial melting takes place and the liquid component usually exists at grain boundaries, the metal in the mashy-state has quite different mechanical properties from those of the metal in the solid-state. Because of that the bonding force among grains is very weak due to the partial melting occurred at grain boundaries, the mashy metal has distinctively low flow-stress and high deformability. The mashy metal splits into grains or particles and sticks to others very easily. It is so soft as to be stirred up just like a lump of sherbet, but it is sufficiently viscous to be mixed up with other materials, such as ceramics particles and ceramics short-cut fibers."

Jan 1, 1988