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By Yves Fautrelle, Kader Zaidat, Hervé Combeau, Miha Zaloznik, Mohammed M'Hamdi, Bachir Saadi, Xiaodong Wang, Knut Omdal Tveito

"Numerical simulations of macrosegregation formation during horizontal solidification of a hypoeutectic Sn-Pb alloy in a rectangular cavity is presented and compared to experimental results. The experiment involves a melting phase, a holding stage at constant temperature with/without application of electromagnetic stirring, and finally solidification. We simulate all stages of the experiment and study the segregation of Pb throughout the experiment. A twophase volume averaged model is used for the numerical simulations, accounting for thermosolutal convection and assuming perfect microscopic mixing (lever rule). The influence of the melting phase and the electromagnetic stirring is studied with different cases to illustrate the consequences on the flow pattern and Pb segregation. The numerical simulations are compared to the experimental data and the impact of chemical inhomogeneities prior to solidification on macrosegregation formation is discussed.IntroductionMany extensive investigations have been performed so far on the solidification of metallic alloys. However, the melting process of metallic alloy has not attracted attention in a same manner. Nevertheless, melting of alloy may put forth peculiar effects as described in the present paper. It has been observed from a benchmark experiment [1, 2] that significant stratification might arise during the melting process of Sn-Pb alloy. That effect was put forth thanks to the analysis of the experimental temperature distribution which indicated that the convective fluid flow was almost zero. The effect was enhanced when the lead composition was higher (above 6wt.%). The present paper is aimed at confirming that the melting of an alloy containing a heavier solute may be accompanied with a stratification of the solute which exerts a stabilizing effect on the convective fluid flow. Results obtained from numerical modeling are compared with experimental data obtained from the benchmark facility."

Jan 1, 2012

By James A. Sommers

Combustion of niobium nitride powder in a stream of oxygen results in several niobium oxide phases, depending upon reaction parameters. Under rapid oxygen flow, the oxidation produces a molten mass which coalesces into droplets of ca. 2 mm dimension and effectively quenches to leave NbO2 and other lower oxides of niobium, despite the ambient atmosphere of oxygen. A preliminary survey of reaction parameters which govern the split between reduced and oxidized products is presented. This technique offers novel synthesis means for binary oxides when mixtures of NbN and other materials are combusted together, since the niobium moiety is generated in a molten state.

Jan 1, 1995

By Corby G. Anderson

Today, with a stringent economic and environmental climate prevailing in the copper business, there is increased interest in evaluating new processing alternatives for production. Hydrometallurgical pressure oxidation of copper concentrates is one of the more viable approaches and several technological candidates have emerged. Of these, an overlooked but industrially proven methodology utilizing nitrogen species catalyzation in the oxidizing pressure leach system may prove to be a feasible process alternative for the future. In this paper, the history of the system and its application to chalcopyrite concentrates will be outlined. In particular, a methodology for effective treatment of precious metals bearing chalcopyrite concentrates via partial oxidation at low temperatures and pressures will be discussed. Finally, the perceived economics of this unique industrially proven process will be delineated.

Jan 1, 1999

By V. T. Taniguchi

A process for large scale chromatographic separations using a continuous chromatography technique is described. The process combines the advantages of large scale batch fixed column displacement chromatography with conventional analytical or elution continuous annular chromatography (CAC) to enable large scale displacement chromatography to be performed on a continuous basis (CDC). Such large scale, continuous displacement chromatography separations have not been reported in the literature. The process is demonstrated with the ion exchange separation of a binary lanthanide (Nd/Pr) mixture. The process is, however, applicable to any displacement chromatography separation that can be performed using conventional batch, fixed column chromatography.

Jan 1, 1989

By P. H. Scaife

The pyrometallurgy industry faces a series of environmental challenges, based on local, national and global issues. While local impacts continue to be important, national and global concerns with Sustainable Development, Greenhouse emissions, Acid Rain and water resources are key strategic drivers for the industry. The environmental problems of the industry are well known: emissions of sulphur dioxides and carbon dioxide, disposal of arsenic wastes, consumption of fresh water, fate and impact of minor components/trace elements in raw materials (whether conventional or complex, or wastes). Solutions to these problems require the application of Cleaner Production principles (waste minimisation, energy conservation, product design to enable ease of post consumer recycling), new technology and scientific studies to assess impacts of discharges. A number of opportunities, driven by environmental concerns, have also been identified

Jan 1, 1994

By A. D. Besser

The world production of lead has been growing continuously and reached over 7 million tonnes in 2005. At the same time, the structure of lead consumption has changed: the use of lead compounds to liquid fuel has been virtually terminated; the proportion of lead for manufacture of lead-acid batteries has been growing and reached 76.7% of the overall world production of this metal. This has taken place against the background of increasingly stringent environmental norms and environmental legislation. This is due to the lack of an alternative for lead in manufacture of local power sources. A solution to the problem of meeting the industrial demand for lead with simultaneous reduction in the primary lead production is in recycling. A large amount of batteries manufactured worldwide and their short life cycle, as well as the positive economics and a possibility to comply with the environmental requirements encourage the development of secondary lead production. Currently, over 60% of the world demand for lead is met due to recycling. The current situation with collection, transportation, storage and processing of spent lead-acid batteries has been analyzed in this paper. Examples are given to illustrate technological and equipment solutions and trends for improvement of secondary lead production discussed.

Jan 1, 2006

By Thomas Schuman, Jaan Kers, Lucas N. W. Damoah, Xiangjun Zuo, Lifeng Zhang

"Rapid technological innovation has propelled the use of electronic equipment leading to the generation of more and more waste electrical and electronic equipments (WEEE). Printed wiring board (PWB) is a component made of one or more layers of insulating material with electrical conductors. To investigate an environmentally friendly process to recycle PWBs, PWB samples with and without additives were pyrolyzed. Liquid, gas and solid products were achieved with different conversion fraction. Analysis of the exhaust gases from the experiments using GC-MS and MS showed that without CaCO3 additives poisonous gases such as C6H6 and HBr were produced which were adequately controlled if CaCO3 was added.IntroductionPyrolysis is one of the best methods for treating complex mixtures of waste polymers and to recover the material and energy content. The process consists of thermal decomposition at moderate temperatures in total absence or small amount of oxygen in which the structures of polymers break down into smaller intermediate products "". The decomposition temperature of a substance is the temperature at which the substance breaks up into smaller substances or into its constituent atoms 2). Thermal treatment of PWBs were reported using DC Arc Plasma furnace 3), and fixed bed reactor 4). One drawback in dealing with thermal treatment of PWB scraps is the likely production of super-toxic halogenated dibenzodioxins and dibenzofurans from the bromine containing structures. Pyrolysis of organic materials contained in waste PWBs leads to the formation of gases, oils, and chars which can be used as chemical feedstock or fuels ""'. Dehalogenation of the pyrolysis product of electronic scraps is essential to make it commercially acceptable. It would be obviously the most advantageous solution as pyrolysis and dehalogenation are carried out simultaneously. Reported pyrolysis investigations are at experimental stage and have been carried out in vacuum, molten salt, fluidized bed, rotary kiln, entrained, stationary, and moving bed reactors 7). Comparing to the incineration and combustion of PWBs, the pyrolysis process has several characteristics: 8'"">) 1). Converting the organic solid substance into fuel gas, fuel oil and carbon-black as storage energy; 2) Emitting toxic substances such as sulfur, bromine and heavy metals in wastes; and 3) Keeping metals from being oxidized. Although many researches into the pyrolysis of PWB wastes have been reported, most of the works have been carried out using analytical pyrolysis techniques or very small batch reactors ""~'5). Also, most of the works for the pyrolysis of PWBs haves concentrated on the composition of the organic products, particularly the brominated organics. The current study is to investigate the pyrolysis of PWB powders in a small TG-DTA scale and a 50-gram tube furnace scale."

Jan 1, 2011

By María Cristina Ruiz

In the processing of copper concentrates by the conventional smelting-converting technology, complying with the increasingly severity of environmental legislation in some countries has become difficult, mainly due to severe fugitive emissions of gases produced during the batch PS (Peirce-Smith) converting step. In this work, the results of an investigation on the pressure leaching with sulfuric acid and oxygen of white metal (produced in a Teniente Converter reactor) are discussed. The study was carried out at laboratory scale and the main variables studied were temperature, concentration of sulfuric acid and partial pressure of oxygen. The experimental results indicated that most of the sulfur in the white metal was oxidized to sulfate in the whole range of temperature studied (105ºC to 150 ºC). The concentration of sulfuric acid over 0.05 M, and oxygen partial pressure over 6 atm had little effect on the dissolution of copper from the white metal. On the other hand, temperature had the most significant effect on copper dissolution; below 130 ºC copper dissolution was incomplete after 5 hours of leaching while at 150 ºC the dissolution was complete in 90 minutes and 10 atm of partial pressure of oxygen

Jan 1, 2006

By Andreas Siegmund

Cast or rolled lead anodes employed in zinc electrowinning typically contain between 0.5?1.0% silver to decrease the overall corrosion rate. The production of cast lead-silver or lead-silver-calcium anodes often results in the formation of numerous holes, voids or laps in the anode surface that can initiate internal corrosion in localized areas. In rolled anodes the presence of internal porosity is significantly reduced, thus resulting in extended service life. The obtained grain structure of cast or rolled Pb-Ag anodes, however, requires a relatively long period of time to form a stable protective PbO2/MnO2 layer that can evolve oxygen without excessive lead contamination of the cathode. Therefore, these anodes are often mechanically, chemically or electrochemically conditioned prior to being placed in the electrowinning process. RSR Technologies has developed an improved anode for zinc electrowinning. The anode consists of a rolled Pb-Ag-Ca-alloy with controlled surface grain structure. The preferred calcium and silver content of the alloy is 0.05?0.08 % and 0.3?0.4%, respectively. Since May 2001, industrial-scale tests have been carried out at two zinc refineries in North America in industrial electrowinning cells. The controlled grain structure of these anodes allows forming an adherent protective oxide coating within a short period of several days when placed in an electrowinning cell without the necessity of being preconditioned. Anode sludge growth is evenly distributed. The anodes stay dimensionally stable and no short-circuits have been observed. Consequently, low corrosion rates and improved current efficiencies have been achieved.

Jan 1, 2003

By Petr Sulovsky, Jaroslava Ledererova, Miroslav Svoboda, Michaela Suchardova

"The thinning resources of natural raw materials necessitate an increased degree of waste material recycling. The building industry offers a range of technologies enabling incorporation of industrial wastes into building materials for construction purposes in an economically acceptable way. Our research is focused on finding the appropriate technologies for specific groups of industrial waste materials (IWM). The studied IWM involve coal combustion residues (CCR), desulphurization products, sludges, metallurgical slags, and various other wastes. Many of them contain increased amounts of toxic elements that can under certain conditions get released. In order to prevent this, each specific IWM requires finding the technology that best ensures the binding of toxic elements in the building matter are fixed for the long term.Introduction The sustainable development of mankind is more than ever viewed as a matter of resources. Many aspects of the switch from a throw-away to a recycling society concern one of the largest consumers of natural resources and producer of greenhouse gases, the building industry. One of the biggest tasks lying before the researchers in the field of building materials is to find substitute or alternative raw materials that would save the thinning reserves of natural resources. The most promising and natural way is to replace the traditional raw materials with rejected and unwanted products of industrial processes, classified as wastes. These of course are not produced with the primary intention of achieving some desired properties. The usage of industrial wastes therefore involves finding the optimal way of usage their existing positive (from the point of view of utilizations) properties and minimizing the impact of their undesired properties, i.e. from the perspective of the considered application."

Jan 1, 2008

By Ledjane Barreto, Tulio Flávio Accioly de Lima e Moura, Wilson Acchar, Antonio Carlos Silva da Costal

"Clays are common ingredients in pharmaceutical products both as exclplents and active substances. Clay minerals are naturally cationic exchangers and they may undergo ion exchange with basic drugs in solution. Smectites, and montmorillonite have been studied due their high cation exchange capacity as compared to other silicates. Recently a patented study reports the use of attapulgite as the encapsulating agents both for the protecting the active substance and modulating release into the body. Some clays such as kaolinite, smectites, talc, etc are also used as dermatological protectors. Sepiolite and smectites have the ability to form complexes with organic compounds with absorb ultra-violet radiation, enabling them to be used in sun screens with protection factors. The objective of this work is to characterize the attapulgite in order to study the potential use of this clay material in the human health.IntroductionSince the begimling of time, nature has served humanity as a source of various raw materials. Among these, clays such as kaolinite and ilitte are common ingredients in the tile production. Recently, special clay materials have been investigated in order to identifY new potential uses of these class of materials. Clay materials are natural raw material and have excellent properties such as low toxicity, good biocompatibility, making them a good material to be used in biological applications. Attapulgite (paligorskite) and sepiolite is so called special clays. These special clay materials are very sin1ilar and have a great potential to be used in some technological areas due their special catalytic, sorptive and colloidal-rheological properties [1-8]. Recently some works have reported the use of these special clays materials for many applications such as drug delivery, wound dressing, oil absorbent, pesticides, fertilizers [9-12]. Brazil has a significant reserve of attapulgite located in Piaui state, making the study of the potential of this mineral in special areas, very attractive. Attapulgite is classified a fibrous alluminous silicate material and shows the presence of micro pores and channels, fine particle size and high surface area making this material a good candidate alternative material to be used in many industrial applications [6,8,9,11,12]. The objective of this work is to characterize the physical and microstructure of attapulgite."

Jan 1, 2012

By Anita E. Lam

The thiosulfate leaching of gold generally requires the presence of a catalyst such as cupric tetraammine, Cu(NH3)42+, to obtain reasonable leaching rates and gold extractions. Unfortunately, this same catalyst that accelerates gold leaching also tends to accelerate thiosulfate oxidation to tetrathionate and other species. It is therefore imperative that a detailed understanding of the role of this catalyst and the factors affecting it is obtained. It is equally important for plant application that a method of assessing the catalyst be developed. In this work the role of the cupric tetraammine catalyst was studied using geochemical modeling for speciation prediction, thiosulfate leaching of gold ores, and chemical analyses of resulting leach solutions. It was found that the variables of pH, temperature, and the concentrations of ammonia, thiosulfate, and total copper all work in concert to affect the concentration of the cupric tetraammine species. It was also found that the presence of sufficient thiosulfate and cupric tetraammine was critical to the success of the leach.

Jan 1, 2003

By Mineo Hayashi

Gresik plant, PT Smelting, is the first and the only copper smelter and refinery in Indonesia. It had the original design capacity of 200,000 tpy of LME grade A cathode production and treats copper concentrates mainly coming from Grasberg mine in Papua, Indonesia. The smelter that employs the Mitsubishi process was put into operation at the end of 1998. In April 2004 the refining capacity was expanded up to 259,000 tpy in order to meet with soaring demand of copper cathode in South East Asian market. In addition, the construction work for the second refinery expansion project has started and it is scheduled to be completed in July 2006. At the completion of the project an additional 12,000 tpy capacity will be assured and in total it will make 271,000 tpy,. This paper describes the chronology of the expansion and future operational strategy of Gresik plant.

Jan 1, 2006

By K. Osseo-Asare

Rate laws for the hydrogen reduction of metal ions are typically of the form: [r = -d[M(II)]/dt = k[M(II)]xPy2H] where k is an apparent rate constant, [M(II)] and PH2 represent dissolved metal concentration and hydrogen pressure respectively, while x = 0 - 1 and y = 0.5 - 2. Half-order dependences have been reported for some M(II)/H2 systems; however, no satisfactory explanations have been offered. In an effort to bridge this gap in our understanding, the published precipitation rate data (for M(II) = Cu(II), Ni(II), and Co(II)) are reviewed (with emphasis on the reported reaction orders) and compared with the corresponding but limited electrochemical polarization data. Based on the available literature on the electrochemical kinetics of the M/M(II) and H2/H+ systems it is demonstrated theoretically that, under certain conditions (e.g., in the presence of electron-conducting solids), the rate of the M(II)/H2 reaction can be expressed as: [-d[M2+]/dt = k[M2+]2/1P2/12H] It is concluded that electrochemical processes probably play an important role in the hydrogen reduction of metal ions, especially for systems that involve heterogeneous catalysis.

Jan 1, 2003

By Peng Bing

Stainless steelmaking dust is classified as a hazardous waste due to higher than acceptable heavy metal leachabilities such as zinc, lead, cadmium and chromium. In addition to being an environmental hazard, the flue dust is also an economical concern to stainless steelmakers as it contains large amounts of valuable alloying elements, especially for iron, chromium and nickel. A new technology of direct recycling of stainless steelmaking dust has been developed to recover the metals from the dust. But it was found that zinc was accumulated in the dust collection system in practical run of direct recycling. This study focuses on the effect of the operating parameters such as temperature, dust feed rate and the ratio of CO to dust on the reduction of zinc oxides present in the dust. The mathematical model for the reduction process was setup based on the experimental research. According to the mathematical model, the temperature has obvious effect on the reduction of zinc. It is benefit to the process of zinc reduction to increase the temperature. But the temperature will not be the main factor for the reduction process after 1228C. It will promote zinc reduction to decrease the dust feed rate and control the ratio of dust to CO. It was also found from the experiments that ZnFe2O4 in the dust could be decomposed at high temperature. Decomposing ZnFe2O4 in the dust increases the recovery of zinc from the dust distinctly.

Jan 1, 2006

By P. C. Guillaume

Global plant modernizations or expansions cannot be considered in the same light as any other industrial investment project. Relationships between the partners, relationships and communications with the client, structure and organisation of the teamwork, schedule of the work, and a lot of other tasks and missions devoted to external contractors have to be defined considering one fundamental input: an operating plant. For an engineering company expert in processing, like UM Engineering, such a context requires a specific approach as well as specific procedures able to efficiently challenge the generated constraints. First of all, even if a detailed audit had been conducted at the beginning of the conceptual engineering phase, new elements will be discovered during the preparation and realization of the project, and must be continuously integrated. Consequently, a close proximity to the site is necessary. This is one reason why UM Engineering, most often, works in partnership with a local engineering company. The second important point for the client is that the operation must not be interrupted during the realization. In order to make that possible, UM Engineering has defined a specific project structure and organisation, integrating on a permanent basis the operators (the "users") in the project teams. This paper presents the way UM Engineering copes with this type of "multi-constraints" context with reference to the recent copper cellhouse modernization under realization for the CCR Refinery of Noranda Inc. in Canada.

Jan 1, 1999

By Peng Peng, Ouo Cheng, Guodong Lai, Lijuan Chu, Zebiao Zhang

"The pressure acid leaching residue of zinc concentrate contains a large quantity of sulfur. The present study attempts to leach sulfur using a mixture of ammonium sulfide and water solution at 25°C. Effects of three leaching variables: ammonium sulfide concentration, leaching time, liquid/solid ratio on the sulfur leaching rate were investigated. The process conditions were optimized using response surface methodology based on the central composite design. From the analysis of variance (ANOVA), the significant factors on response were identified. The optimum conditions for leaching elemental sulfur from pressure acid leaching residue of zinc concentrate were obtained using an ammonium sulfide concentration of 2.5 mol/L, leaching liquid-solid ratio of 6.5:1 and leaching time of 7 min. Under the optimum experimental conditions, a maximum of 98.50% of total sulfur was extracted. The experimental results obtained agreed satisfactorily with the model predictions, with a correlation coefficient (R2) of 0.99.IntroductionSulfur is widely used in agriculture, medicine, rubber, building materials, gunpowder, wine and sugar, and other fields [1]. Currently the world sulfur production is 40Mt, out of which more than 90% is recovered from industrial processes, and 10% is natural [2], This highlights the importance of sulfur recovery. As the pressure leaching technologies [3] continue to mature and are increasingly applied to refining, a large quantity of high-sulfur residue is produced [4-5]. It is desirable to recover sulfur from this residue, so that it is economically advantageous, and reduces environmental pollution [6]."

Jan 1, 2012

By W. John Rankin

Professionals, technical and non-technical, working in the mineral and metal commodity industries need to understand the concept of sustainability and its implications for the industry. Undergraduate courses have not done this well in the past. Much has been written in this field, and there have been great advances in understanding. However, much of what has been published is superficial and sometimes misleading, and there is as yet no coherent, single account that can serve as an introduction or overview for mineral industry graduates. This paper presents an outline which can guide readers in developing an understanding of the topic and its relevance to their work. Key references are provided, particularly those accessible on the internet, which will serve to introduce the reader to the important principles and understandings. The guide should also be useful to academics preparing students to work in the minerals and metal production sectors.

Jan 1, 2010

By Guozhu Ye

Hydrometallurgical zinc recovery from EAF dust has several advantages compared to pyrometallurgical alternatives in terms of low temperature operation, lower energy consumption and higher flexibility. Many hydrometallurgical processes have been suggested and tested over the years without success. The main reasons are: -Low leaching yield of zinc due to the fact that a high fraction of ZnO in the EAF dust exists in the zinc ferrite structure which makes selective leaching of ZnO not possible -Many of the proposals could not handle the halide in the EAF dust To eliminate these two disadvantages, two zinc ferrite elimination concepts have been tested and developed in the REZIN project of the EU 5th Framework Programme. The two concepts for zinc ferrite elimination could be shortly described by the following chemical reactions: A. ZnOFe2O3 + 2CaO = Ca2Fe2O5 + ZnOfree B. ZnOFe2O3 + C = Femet + CO/CO2 + ZnOfree These two concepts were investigated in details in combination with a subsequent leaching step using the novel EZINC process for recovery of zinc from EAF dust. Leaching of pretreated samples has shown great increases of a zinc recovery yield. A zinc recovery of over 90 % could be reached, as compared to about 50 % for no-pretreated samples. This paper will describe the two concepts in details.

Jan 1, 2006

By Yu. A. Grinin, Yu. A. Sannikov, M. A. Lyamina, V. A. Shumskij, L. V. Slobodkin, N. N. Ushakov

This manuscript describes the Kivcet treatment of lead-bearing materials having high contents of copper and zinc. The tests were carried out on bulk concentrates from the Zyrianovsk Mining and Concentrating complex, "Kazzinc" JSC (Kazakhstan) with the following composition: Pb 37.6%, Cu 10.4% and Zn 6.8%. Two properties of the concentrate were under investigation: their calorific value and their desulphurization rate. By adding flux, the charge properties were brought close to the properties of high-grade lead sulphide concentrate. The charge was melted with high productivity. To ensure high copper recovery, Waelz residue was added to the charge. The residue contained more than 20% carbon and about 30% iron metal. The residue was partially replaced by coke that facilitates high copper recovery into the matte. The smelting achieved a production rate of 20 t/h with one burner. Lead recovery into the lead bullion was 88.8%; copper recovery into matte was 92.3%; zinc recovery into slag was 75.5%; and zinc recovery into the fume was 5.1%.

Jan 1, 2000