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By F. Sanchez, A. Mejias, C. Frias, G. Diaz

"Crude zinc oxides are the major source of secondary zinc and are produced from fuming processes like Waelz kilns. The impurities of crude zinc oxides make difficult their processing in primary zinc refineries due to mainly high chloride tenor. Washing with sodium carbonate is a costly operation and chloride removal efficiency is not good enough, so further purification steps are required. The crude zinc oxides are easily treated using ZINCEX™ technology based on leaching, solvent extraction, and electrowinning. The ZINCEX™ process is commercially available and is designed to be a perfect barrier for metallic impurities and halogens, allowing selective zinc extraction in mixed chloride and sulfate leaching solutions. Other valuable components as lead and silver can be efficiently recovered from the leaching residue using PLINT technology in chloride media. Silver is recovered as silver cement and lead is precipitated as pure lead oxide or carbonate, which can be smelted at low temperature.IntroductionZinc is a fully recyclable metal and at present approximately 70% of the zinc produced worldwide comes from primary zinc while 30% originates from secondary materials. Nowadays, the zinc recycling rate is continuously increasing mainly through galvanized steel scrap processing, and crude zinc oxides are the major source of secondary zinc [1]. Secondary zinc oxides are obtained from fuming processes like W aelz Kiln, Rotary Hearth Furnace or Primus Furnace. Waelz is the dominant technology accounting for 80% of total crude zinc oxides production worldwide. In the Waelz process, steel dust is mixed with solid fuel reductant (coke breeze) and pelletized. It is then fed to the kiln and heated to a reaction temperature of l ,200°C. In such conditions, zinc, lead, and other non-ferrous metals are vaporized into the flue gas together with chlorides and alkaline metals. Mixed oxides are drawn from the kiln with the process gases and separated to produce typical crude zinc oxides [2]."

Jan 1, 2011

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 Aurelian Buzaianu, Cristian-Aurelian Popescu, Gabriela Popescu, Petru Moldovan

"A lot of scraps result in processing of composite materials which contain metallic phases that can be recovered and used again in different field. Considering this point of view the aim of the paper was to separate and recover aluminum from aluminum matrix/graphite composites. The separation and recovery of aluminum alloy from aluminum alloy/graphite composites was done by treatment with halide molten salts. As halide salts were used flux tablets that collect the ceramic particles in dross. After dross separation, was used filtration in order to separate the aluminum matrix from the other impurities.Samples from the recovered alloy were analyzed using chemical analysis, optical and electron microscopy, as well as X-ray diffraction. The desired composition of the aluminum alloy obtained from scraps could be reached by some addition of metals to the metallic phase. From optical microscopy it was obvious that the structure of the aluminum alloy obtained after composite reclamation consists large particle of silicon, eutectic, a-Al solid solution and other phases like Fe, Si, Mg and Ni, or some compounds like CuAl2. 1. IntroductionThe research on the recycling and reclamation of metal-matrix composites (MMCs) becomes active to preserve the natural environment, as environmental requirements become stricter, to save energy, and to reduce garbage. In case of recycled aluminum alloy ingot the production energy is about 3 pct of that of the new ingot. This evidence strongly supports the necessity to recycling of aluminum alloys. Among aluminum alloys, metal matrix composites have high strength and elastic modulus, and also good were resistance. These materials have been developed to meet the demand properties which exceeds that of the ordinary materials, and to save energy."

Jan 1, 2008

By Larry G. Twidwell, Jannette L. Chorney, Bryce D. Ruffier, Katelyn M. Lyons, Daniel W. Gaede, Ryan J. Foy, Jerome P. Downey

The Army Research Laboratory (ARL) has an interest in the recovery and processing of rare earth elements. At Montana Tech, elevated temperature chlorination of rare earth oxides is presently being investigated as a potential methods leading to the selective separation and recovery of rare earth elements from mineral ores and concentrates. After preliminary evaluation, ytterbium oxide was selected as a representative surrogate material for more extensive chlorination studies. Methods used to determine the conversion and recovery include X-ray diffraction (XRD) and inductively coupled plasma (ICP) analysis. These data have been used to establish and confirm process conditions that consistently yield high conversion efficiencies. Based on the promising results, further experimentation is underway to ascertain the metallurgical response of other rare earth oxides and carbonates to the roasting process. The end goal is to create a robust process for industrial application that has greater efficiency and reduced costs as compared to current practice.

Jan 1, 2015

By M. D. Crites

As part of a multi-year program for assessing the viability of chrome-free refractories in copper smelting, converting and refining furnaces, dynamic corrosion tests have been conducted on a series of refractories from the magnesia-alumina system, using a ferrous silicate slag. The corrosion rates of the test refractories are compared with those of a reference mag-chrome brick, and recommendations are made for more in-depth evaluations of the more corrosion-resistant materials.

Jan 1, 1999

Direct electrowinning is an electrochemical process which has been developed for the extractive recovery of copper from dilute, acidic leach solutions. In passing through a thin particulate coke cathode. copper is reduced and electrodeposited in a thin layer forming a solid copper-coke sheet. The product is melted in a furnace to separate the coke, then the molten copper is fire refined to produce a salable product. A description is given of a prototype unit which is designed to treat 20 gpm leach liquor and recover over 100 pounds of copper per day. Economic analyses show that in a commercial facility producing about 25.000 TPY copper.*the direct electrowinning process has lower overall cost than either conventional iron-cementation or the newer liquid ion exchange-electrowinning when the leach liquors contain less than 2 grams per liter of copper.

Jan 1, 1976

By Edmundo Manilla, Merete Tangstad, Daniel Davila, Eli Ringdalen

FeMn alloys are typically produced with lumpy ore or sinters. Minara Autlan, the Mexican FeMn producer, is however making Mn-nodules as a raw material for Mn-alloy production. The Mn nodules have been characterized by XRF, XRD, by wet chemical methods and by EPMA. The Mn/Fe ratio is somewhat lower compared to commercial Mn ore on the marked. The basicity of the ore is however close to 1, and additional fluxes may not be used. The Mn-nodules will be in a state of manganosite (MnO), tephroite ((Mn, Ca)2SiO4) and galaxite ((Mn,Mg)Al2O4). This leads to a low melting temperature area. A low porosity and low amount of higher Mn-oxides gives a high thermal strength to the nodules.

Jan 1, 2016

By L. A. Neumeier

The Bureau of Mines, U.S. Department of the Interior, is investigating the feasibility of partitioning complex sulfide minerals to simpler sulfide .phases by sulfldation reactions. Such partitioning can afford opportunity to improve selective extraction of mineral constituents of value. This report describes initial research involving sulfidation partitioning of chalcopyrite concentrates. Small chalcopyrite samples were sulfidized with elemental sulfur in glass capsules sealed after evacuating and backfilling with helium, by heating for 1 to 24 h at specific temperatures in the range of 250° to 500° C. which extends from below to above the boiling point of sulfur (-445° C). Above the boiling point of sulfur, the overall reaction with adequate sulfur (13.9 wt pct of CuFeS2) is 5CuFeS2 + 4S g ? Cu5FeS6 + 4FeS2.

Jan 1, 1989

By John Petersen

Heap bioleaching technology has become well established for the exploitation of copper sulfide ores. Still, in many operations the rate of copper extraction is rather slow, often taking two years or more to recover 80% of the copper. Chalcocite, the most common secondary copper sulfide, leaches by a two-stage mechanism. The first stage is rapid, whereas the second stage has a high activation energy and proceeds slowly at ambient temperatures. Nonetheless, this rate is still considerably faster than what is typically realized in a full-scale heap. A comprehensive column bioleaching study of a chalcocite ore has shown that the chalcocite columns are leached in a zone-wise fashion. The first zone corresponds to the first stage of chalcocite leaching, where all ferric produced by the bacteria is immediately consumed and all acid entering with the feed solution is consumed within a relatively narrow band. The second stage of chalcocite leaching proceeds much more slowly in the wake of the first stage, within a zone that grows gradually over the entire length of the column. The overall rate of leaching is thus determined by the rate of acid supply into the column rather than by mineral or bacterial kinetics, at least until the entire column is engaged in second-stage chalcocite leaching. In full scale heaps, there is evidence to suggest that solution distribution favours channelling between relatively large clusters of material which are exposed only to stagnant solution. Reagents have to migrate into such clusters by diffusion, which retards the delivery of acid dramatically. Thus, we believe that the rate of chalcocite oxidation in heaps is governed by sideways diffusion rather than downward migration. Column experimental results have been reproduced with a comprehensive heap-modelling tool. The model predicts that by simply changing the length of the average diffusion channel from column conditions (a few cm) to heap conditions (tens of cm), extraction times can change from weeks to years under otherwise identical conditions.

Jan 1, 2003

By Edita Vircikova

The best demonstrated available technology (BOAT) for the removal of dissolved arsenic and some heavy metals as reported by USEPA (Contaminants and Remedial Options at Metal Sites, Draft Report, August 1993) (1) is still the chemical precipitation. Coprecipitation with the excess of iron is usually practised because of the availability of iron at low/no cost and also in order to meet the stringent regulatory discharge limits. The arsenic is usually removed with iron because of its common occurence in the mined orebodies and the excellent adsorptive property of the precipitated hydrous ferric oxide compounds. There has been controversy, however, over the long-term stability of the arsenic-bearing ferrihydrite which is produced.

Jan 1, 1995

By Tomás Vargas

The catalytic influence of a pure strain of Thiobacillus ferrooxidans (ATCC 19859) on the dissolution of natural pyrite crystals was studied using electrochemical techniques. The results showed that this microorganism catalyze the leaching of pyrite by both, oxidizing ferrous iron in solution and depolarizing the reduction of ferric ion on this sulfide. In addition, studies of bacterial corrosion under applied potential showed that pitting on the pyrite surface centers on weak sites of the sulfide structure in which bacteria has attached, but occurs only when the ferric iron in solution induces an adequate level of anodic polarization on the mineral.

Jan 1, 1992

By Gopalakrishna B. Prabhu, David L. Bourell

"Three mol% Yttria-Stabilized Tetragonal Zirconia (YSTZ) was prepared by a sol-gel synthesis technique using zirconium tetrachloride and hydrated yttrium chloride precursors. After drying and annealing at 823K, the particle size was in the range 10 to 20 nm. The zirconia powder was sintered using a uniaxial hot press at an applied stress of 20 to 40 MPa. One hour, isothermal sintering was performed in air after initial heating at 50K/min. Theoretical density was obtained at densification temperatures above 1498K. After sintering, grain coarsening characteristics were studied using constant heating rate anneals followed by quenching, based on a model for grain coarsening in a linear heating rate cycle. The microstructural change was studied using SEM and TEM and the phases were determined using x-ray diffraction.IntroductionThe ability to sinter nanocrystalline materials to full density several hundred degrees below the normal sintering temperatures is one reason for their current interest. [1-5] Yttria Stabilized Tetragonal Zirconia (YSTZ) of grain size of about 300 nm has exhibited superplasticity, with elongations as large as 800%.[6-7] Fine grain size is critical for superplasticity. Retention of the fine grain size during sintering of nanocrystalline powder is important if a material is to exhibit superplasticity or to exhibit physical or mechanical properties associated with the ultra fine structure. This paper investigates the sintering behavior and the grain coarsening characteristics ofnanocrystalline YSTZ.Techniques for synthesizing nanocrystalline materials have been studied in great detail earlier. [8-12] The techniques used to synthesize nanocrystalline zirconia include alkoxide synthesis [9], the chloride method [11], the peroxide method [13] and the acetone-toluene method. [13] In this paper the method used in the synthesis of zirconia is the chloride technique. With this precipitation technique, either zirconium chloride or oxychloride and a corresponding yttrium salt or even pure yttria are used."

Jan 1, 1994

By V. P. Bystrov

Vanyukov process has been developed and investigated in Russia over the last 25 years. It has been established that various kind of material could be treated in Vanyukov process. The results of the pilot plant trials as well as industrial experience are presented in this paper.

Jan 1, 1993

By Shijie Wang

In pressure oxidation leaching of copper anode slimes, than 65% of the tellurium is m' cxtraoted during decopperizing. About l0- 15% of the selenium is also dissolved simultane¬ously by severe leach conditions. Current operation for the treatment of the leachate is to constantly recirculate the leach solution through a bed of copper turnings. The tellurium and sele¬nium are precipitated from the leach liquor as copper telluride and copper selenide and sepa¬rated from the solution by filtration. In order to improve the reaction efficiency and reduce the process cost, viz, minimize the copper addition, cut retention time, and reduce the energy consumption; a chemical reducing agent is studied and the cementation process tested in the laboratory. In this paper, the test results are presented and the process chemistry is discussed.

Jan 1, 2003

By Jonkion M. Font

An expression for the distribution ratio of arsenic between slag and copper matte or liquid copper was developed by both, an extension of the Reddy-Blander model for deriving a priori the arsenic capacity, and by a relationship between the arsenic capacity and the arsenic distribution ratio. In this study, the a priori arsenic capacities in the FeO-SiO2, CaO-SiO2, MgO-SiO2, FeO-CaO-SiO2, FeO-FeO1.5-CuOo.5-MgO-SiO2, FeO-FeO1.5-CuO0.5-CaO-MgO and FeO-FeO1.5-CuO0.5-CaO-MgO-SiO2 slags were calculated at 1573 K. The a priori arsenic distribution ratio between the FeO-FeO1.5-CuO0.5-CaO-MgO-SiO2 slag and copper matte (L s/m as), and between the FeO-FeO1.5-SiO2 or FeO-FeO1.5-CuO0.5-CaO-MgO slag and liquid copper (L s/Cu as) were calculated. The model calculated data are found to be in good agreement with the reported experimental data. The availability of reliable thermodynamic data for slag components and impurities in the slag-matte-metal system is essential for the accurate prediction of impurity capacities and distribution ratio data. The arsenic distribution ratio model developed here, can be extended for prediction in multi-component slags and mattes or liquid metal, and thereby may lead to the development of new slag systems for the efficient removal of arsenic in the copper smelting, converting and refining processes.

Jan 1, 2003

By C. P. Manning

This paper reports recent progress in the development of a unique metal extraction technology utilizing zirconia-based inert anodes for the electrolytic reduction of metals from their oxides. In this process, the target metal oxide is dissolved in an ionically conducting liquid solvent phase. An extended anode consisting of an oxygen-ion-conducting stabilized zirconia membrane in intimate contact with a catalytically active electronic phase and an inert electronically conducting cathode are inserted into the molten flux containing the oxide. When the appropriate electric potential is applied between the electrodes the target metal is reduced at the cathode and oxygen ions are selectively transported across the stabilized zirconia membrane and oxidized at the anode. When the process is conducted at temperatures between 1200-1400°C, the ohmic resistance drop across the stabilized zirconia membrane is low, and high current densities on the order of I A/cm2 or greater can be obtained. In addition, the process efficiency can be increased further by directly reforming hydrocarbon fuel over the anode. Laboratory experiments at Boston University have demonstrated the technical viability of employing zirconia-based inert anodes for environmentally sound production of metals such as magnesium, tantalum, aluminum, etc., directly from their oxides. Significant progress has been made in the application of this concept to the electrolytic reduction of magnesium at 1300°C. The research topics covered include stability of the zirconia membrane in the selected molten solvent (flux), volatility of the flux, electrochemical characterization of the electrolytic cell, and analysis of the metals produced.

Jan 1, 2003

By Yuanyuan Zhang, Patrick J. Masset

"The reduction of FexO in slag is one of the fundamental reactions in iron and steelmaking technology, including the blast furnace process (BF). Experiments on the reduction reaction of iron oxide using CaO-SiO2-Al2O3-FexO-C mixtures were carried out using thermogravimetric analysis (TGA) under reducing conditions at temperatures up to 1100°C. The composition of the primary slag was chosen so that the FexO concentration varied between 0 and 75 wt % and the CaO/SiO2 ratio being kept constant to 0.90. From the TGA curves recorded isothermally at different temperatures the kinetic parameters of the iron oxide reduction were determined.IntroductionIn blast furnace the iron ores and coke are charged in layers from the top. The reduction of iron oxide by coke is one of the fundamental reactions in the blast furnace process. Although a great amount of work has been done on the topic of reduction of composites [1, 2, 3], gasification of carbon [4, 5] and reduction of iron oxides by CO [4, 5, 6], the mechanism of reduction in iron oxide - carbon powder mixtures is not fully understood. Fruehan [1] and Rao [2] studied the reaction rate of the reduction of iron oxide by different types of carbon and concluded that the reaction mechanism is controlled by the oxidation of carbon at temperatures up to 1200°C. Rao [2] studied the reaction of hematite with graphite as carbon source up to 1080°C. An activation energy close to 300 kJ/mol was calculated within the temperature range of 950°C to 1087°C. In his study, Fruehan [1] determined the rate of reduction of Fe2O3 and FeO by coal, coke and coconut charcoal as carbon sources within the 900°C to 1200°C temperature range. He found that the reduction of Fe2O3 by carbon occurs in two stages and that the reduction of Fe2O3 to FeO is faster than that of FeO to Fe. This is due to the fact that the CO2/CO equilibrium ratio is higher, and hence, the rate of oxidation of carbon is faster. Fortini and Fruehan [3] have studied the reduction reaction of wustite by graphite and wood charcoal. They found that the wustite reduction can have a significant effect on the overall rate of reduction in composites at high temperatures or in the presence of a large excess of carbon. The calculated activation energy of the reduction reaction by wood charcoal was close to 368 kJ/mol, while the activation energy of the reduction reaction by graphite was 444 kJ/mol."

Jan 1, 2011

By Nobuhiro Shinihara, Makio Naito, Keizo Uematsu, Tadashi Horta, Hiroya Abe, Masataro Okumiya

"A significant variation of strength was noted in silicon nitride ceramics made through the powder compaction processing with minor processing changes. The relevance of the fracture strength to the microstructure was examined in these ceramics. In the examination of microstructure, the ceramics were made into thinned specimens, and their internal structures were observed with an optical microscope in the transmission mode. This technique can distinguish a difference in microstructure associated with the minor processing changes. The strength of all ceramics examined in this experiment was qualitatively correlated with the -pore size distribution in the specimens. Clearly, the elimination of these detrimental defects will enhance the reliability of ceramics.IntroductionIn ceramics made through powder processing, a variation of properties is often encountered [l ,2]. This brings a major problem on producing reliable and cost-effective ceramics. The variation is often ascribed to the changes in the characteristics of defects. However, there is no clear evidence f\)r this explanation due to the lack of an adequate tool for identifying the defects determining the properties. Details of the origin of the variation have still been poorly understood.A new technique is very promising for clarifying the origin of the variation [3,4]. This has very high potential in detecting minor differences in structure for .engineering ceramics. With this technique, ceramics are made transparent with its thinning down to about 50 µ m and their internal structures are observed with various types of optical microscopes in the transmission mode. The characteristics of the defects determined through this approach were found to be directly related to the strength of the ceramics [4-6].The objective of this study is to clarify the ongm of fracture strength of silicon nitride ceramics. This material is representative of high performance ceramics, and the origin is of great practical interest. For this study, silicon nitride ceramics with minor changes in processing condition were prepared. Specific feature focused in this study is the difference of large pore structure determined with the new technique and its relevance to the strength of the silicon nitride ceramics."

Jan 1, 2000

By Ian Masters

Rotary furnaces are widely used throughout the metals industry. These furnaces vary in size and geometry, but are fundamentally the same from a thermodynamic viewpoint. A generic method is proposed that can be used to model all furnaces of this type, provided that the correct material and process parameters are known. Various approaches have been attempted in the past based on a continuum (FEA or CFD) approach. However, the complex fluidlsolid interactions present in a rotary vessel are not easily solved using these methods, which work best where the material boundaries are well defined. In this paper a lumped parameter model is proposed. Variations within a section of the model are ignored, but to ensure thermodynamic correctness, the heat transfer between sections is carefully considered. For example, it is reasonable to assume that the whole of the melt pool is at the same temperature, due to rotary mixing. This may then be modeled with a single set of parameters, and the detail is contained in obtaining the correct heat transfer mechanisms from the rest of the furnace.

Jan 1, 2002

By Jürgen Antrekowitsch, Thomas Griessacher

The recovery of valuable metals from residues like dusts and sludges is nowadays state of the art. Depending on the complex constitution, a recovery of different metals can – in the majority of cases – only be performed with considerable energy input in high temperature processes together with insufficient yields and newly generated residues. Often, the behavior of the dust or sludge in the process during melting or reduction is unknown. In this work, a detailed characterization of selected residues like steel mill filter dusts, cupola furnace dusts and leaching residues is done. The different steps of getting from solid particles into a homogenous liquid phase were investigated. Although high temperature processing leads to high reaction speeds, the complexity of residues keeps the system away from thermodynamic equilibrium. With this research program, some basics are generated to understand smelting and reduction and the gap between thermodynamical calculations and real behavior can be explained.

Jan 1, 2008