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By T. R. A. Davey

The technologies of lead, zinc and tin extraction have made varying degrees of progress over the past twenty years. Producers of all metals have faced increasing demands for reduction of pollution and environmental degradation, and the level of public concern is rising rather than abating. New processing techniques must therefore be not only economically feasible, but politically acceptable, even when the demands of "conservationists" and ?environmentalists? are unreasonable. A new generation of processing techniques has come into being, which do not rely on an expensive sintering stage, nor use metallurgical coke, which is difficult to make without serious pollution. They utilise intense reactors, conveying materials from one stage to the next preferably within an enclosed space, obviating fume emissions, and avoiding heat losses as far as possible. The acceptability of the new techniques? is increased if lowgrade or complex materials can be treated, along with a variety of returns and wastes. In addition, a good selling and servicing organisation seems to be as important as good process technology in determining the spread of the new processes. In the field of pyrometallurgical refining the need is for more general application of several recently developed techniques rather than a search for alternatives to the existing process technologies. However, there is a need for fundamental work investigating the phenomenon of oxygen anode overvoltage in the electrolytic zinc process, in order to make progress in the further reduction of energy consumption. There is also scope for further development and application of vacuum distillation to up-grade thermally produced zinc. This paper presents a personal view of processes which should be developed to overcome existing problems, as we approach the turn of the century,

Jan 1, 1990

By Tetsuya Uda

Our recent achievements of rare earth separation technique[1,2] and new process idea for rare earth magnet recycling[3] are reviewed, (1) Binary chloride mixtures of rare earths were separated by a new selective reduction-vacuum distillation process. According to our experimental results, apparent separation factors were 8.1 for the Pr-Nd chloride mixture and 570 for the Nd-Sm chloride mixture. These values are much higher than conventional solvent extraction methods. (2) A study of recycling process of magnet sludge was carried out. The rare earths in the neodymium magnet sludge were extracted by chlorination with FeCI2, An activated carbon was used as a de-oxidation reagent Metallic iron in the sludge was not chlorinated because the iron monochloride is not stable, The extracted rare earth chlorides were easily separated from Fe-alloy and the excess of FeCh by vacuum distillation, 96 % of neodymium and 94 % of dysprosium in the sludge were extraeted into chloride phase, By the vacuum distillation, a mixture of neodymium and dysprosium trichlorides of 99.2 % purity was recovered, On the other hand, the rare earth chlorides can be converted to the corresponding oxides by a pyrohydrolysis reaction accompanied by a formation of HCl gas, The HCI gas can chlorinate metallic iron to FeCh, Therefore, a new recycling process for rare earth magnet waste can be realized as a chlorine circulation type process. During the process, only carbon and water are consumed and there are no toxic pollutants, Moreover, the obtained rare earth oxide can be directly used as raw material in the conventional oxide electrolysis process,

Jan 1, 2003

By Chikabumi Yamauchi, Mitsuru Tanahashi, Jutaro Miura, Takaharu Iwadachi, Toshiharu Fujisawa

"Tue oxidation behavior of molten Cu-Be alloys was investigated by exposing· the molten Cu-Be alloys to various Ar-O2 atmospheres to control the oxygen partial pressure, PO2 = 10 ~105 Pa at 1423 K. The following results were obtained:• The oxygen · partial pressure in gas phase affects the morphology of the oxide formed on the surface of the alloy and · the oxidation rate of beryllium.• At lower oxygen partial pressure, a molten Cu-Be alloy is covered with a homogeneous and compact internal layer of BeO. Thus, the beryllium oxidation rate can be minimized.• By adding a small amount of calcium or zirconium into the molten Cu-0.5 mass% Be alloy, a protective BeO layer is formed even at higher oxygen partial pressure. Thus, the beryllium oxidation rate can be reduced.IntroductionCopper-beryllium (Cu-Be) alloys are well recognized for their unique properties, such as high electrical conductivity, high strength, high fatigue strength, excellent properties at elevated temperatures, good formability and good corrosion resistance. .This extraordinary collection of properties are the reasons why Cu-Be alloys are expected to be ""Key-materials"", which are necessary to further advance science and technology and to be applied in.various fields such as electronic devices, machine parts, repeater housings of undersea optical fiber communication cables, etc.However, a large amount of beryllium is oxidized to BeO in melting stage of the current Cu-Be alloy production process, because beryllium is a highly reactive element. This is one of the ·main factors that negatively affect the production yield and th_e product quality."

Jan 1, 2000

By Kazuyuki Kakegawa

"Sintered body of lead zirconate titanate (PZT) was prepared through the spark plasma sintering (SPS) technique. When the mixture of raw materials was calcined at 800°C and sintered at 900°C for 10 min. with SPS technique, the sintered body had almost theoretical density but was a mixture of lead titanate (PT) and PZT. When a calcining temperature of 1100°C was employed, sintered body had a single PZT phase but a lower density. High dielectric constant was obtained for a sample calcined at 800°C, sintered with SPS tecbriique and fired again in the air at 1100°C.IntroductionSpark plasma sintering (SPS) is a recently developed technique for sintering metals and ceramics1. The scheme of SPS is shown in Fig. 1. Sample is put in a graphite die in a vacuum chamber. It is pressed and pulse voltage is applied. The electric current heats the die. It is said that the pulse causes a spark-plasma between particles in the sample. Because of the spark- plasma, sample can be sintered at temperatures lower than that in the ordinary sintering by several hundred degrees of Celsius. The sintering period is also very short2Low sintering temperature and short sintering period in SPS technique cause low reaction rate. It is both disadvantage and advantage. In some cases, the reaction cannot be completed under the SPS conditions. If a mixture of several compositions having different properties can be sintered without a compositional change by the diffusion during the sintering, combination of properties, and therefore a design of property will be possible3. The low reaction rate of SPS may enable such combination."

Jan 1, 2000

By Susan Fredholm, Randolph Kirchain, Jeremy Gregory

"Jurisdictions across the world have struggled to create and finance systems that can effectively collect and process electronics waste (e-waste). Many different system architectures have been proposed and implemented, but it is difficult for policy-makers and system architects to compare the costs and benefits of different systems, particularly when the systems operate in different contexts. This paper presents a systematic methodology that seeks to address this challenge and uses data from several existing electronics recycling systems across the world to illustrate its implementation. The methodology characterizes three main system characteristics: architecture (e.g., financing and collection methods), context (e.g., jurisdiction population, density, and wages), and performance, both economic and materials collection. A comparison of systems in Europe and North America with different system architectures and contexts illuminates the importance of using the methodology to discern the extent to which architecture and context drive system performance.IntroductionElectronic waste (e-waste) recycling offers several environmental benefits when processing is done responsibly. The controversy around e-waste recycling systems rarely debates such benefits; rather, it focuses on the characteristics of an effective system and whether benefits outweigh costs. Historically, the costs of recycling most electronics have outweighed the value of the scrap recovered. Thus, in the absence of legislation, e-waste recycling systems have been limited to private recycling of high-value waste with minimal consumer participation. E-waste recycling systems now exist in many locations worldwide including Asia, the European Union, Canada and the United States and the amount of related legislation continues to increase. Numerous approaches have been proposed including landfill bans, extended producer responsibility (EPR) and consumer advance recovery fee (ARF) funded recycling systems."

Jan 1, 2008

By Heng Yi

The salt lake brines that lithium is extracted from have high chloride levels making the brine very corrosive to stainless steel extraction column internals. This is a significant problem in column scale-up to industrial production. Two types of corrosion-resistant ceramic internals, the hybrid ceramic internal and ceramic plate, were designed and tested under pilot conditions for future industrial application in this field. The hydrodynamic results (Yi et al. Ind Eng Chem Res 56 (4):999–1007 (2016), [1]) show that holdup of hybrid ceramic internal is higher than that of ceramic plate by around 50%, while Sauter mean diameter when using the hybrid ceramic internal is smaller than when using the ceramic plate by around 30%. This results in a larger mass transfer area, hence better mass transfer efficiency for the hybrid ceramic internal. Axial dispersion and mass transfer parameters are also examined (Yi et al. Ind Eng Chem Res 56(11):2049–3058 (2017), [2]). The results show that the column with hybrid ceramic internals has 50% lower axial dispersion coefficient and 50% higher mass transfer coefficient, leading to higher mass transfer efficiency. The transfer unit height of the column using hybrid ceramic internals can be as low as 0.2 m, showing very good efficiency. This is promising for near-future applications. Two-phase computational fluid dynamics (CFD) models have been developed for the two columns with ANSYS FLUENT commercial software. CFD successfully predicts the higher holdup and lower axial dispersion coefficients for the hybrid sieve plate pulsed column as measured in the experiments, and the cause for the difference in performance has been explained with information from CFD.

"Mechanical alloying (MA) synthesizing technology and thennohydrogen processing (THP) were utilized to produce nanocrystalline Ti-MMC's reinforced by TiB intermetallic compound by using TiH2-B powder mixtures. Powders MA'ed up to 8 hours were examined by X-ray diffraction and SEM study. All MA'ed powders afterwards were HIP'ed at 700, 800 and 950EC for 1 hour. Detailed XRD, SEM and TEM study of the samples were carried out to determine the structure and micrography of the Ti-TiB MMC material processed by MA+THP approach followed by HIP'ing at high temperatures.IntroductionThe fiber reinforced titanium base composites [1,2] which possess a great resistance to high temperature have been investigated. In these studies fibers of C and SiC were used as reinforcing materials. However, these fibers react with Ti-matrix at elevated temperature resulting in product formation at the interface between the matrix and the fiber. Because of the chemical reactions, strength of the product MMC material diminishes.In conventional techniques of whisker reinforced composite material production, the mixtures of matrix metal powders and dispersed fibers are consolidated by hot pressing, HIP and/or hot extrusion. These techniques, however, have some shortcomings. Hard and brittle fibers could be broken during mixing cycle of the processing. Consolidation techniques could also be the cause for fiber breakdown. Attaining of the uniform dispersion of fibers into the metal matrix is not an easy process. The chemical reactions at elevated temperature exposures in the interface between the matrix material and fiber reinforcement cause product formations leading to poor mechanical properties."

Jan 1, 1998

By Mark C. Bronson

The feasibility of several pyrochemical approaches-for separating non-radioactive constituents from ICPP HLW calcine were examined. The removal of aluminum as AICI3 from aluminia calcine was successfully demonstrated. The examination of pyrochemical processes to remove non-radioactive constituents, primarily aluminium, zirconium, calcium and fluorine, from zirconia calcine showed that fluorine removal was required in order to chlorinate the calcine. A molten calcium chloride wash, a calcium reduction, and. a sulfuric acid treatment were examined as possible zirconia calcine pretreatment options for fluorine removal. Fluorine removal from simulated ICPP zirconia calcine was demonstrated by both a CaCl2 wash method and a sulfuric acid treatment method. X-ray fluorescence analysis indicated that greater than 97% of the fluorine can be removed by either method. Fluorine removal by a calcium reduction using an alloying agent, zinc, or a calcium reduction using, a filtration separation were also demonstrated, but the efficiencies of fluorine removal were considerably less ranging from 50 to 90%. Regeneration of CaCl2 from the salt and oxide residues of the CaCl2 wash experiments was also demonstrated 'by an aqueous dissolution method. From the salt residue, 85% or more of the CaCl2 was recovered and contained little if any CaF2 or CaO. From the oxide residue close to 100% of the CaC12 was recovered. Because of the overall success of the CaCI2 wash, it was determined to be the preferred fluorine removal process. The sulfuric acid treatment to remove fluorine is effective, but the proposed overall flowsheet has not' been adequately demonstrated.

Jan 1, 1995

By Lijuan Li, Xin Xia, Junjun Huang, Qijie Zhai, Xiang Jiang

"Some experiments with different temperatures (1173, 1223, and l273K) and different annealing times (3, 4, 5, 6min) were carried out on cold-rolled plate of Fe-36Ni invar alloy. The microstructure and the mechanical properties were observed and tested respectively, and the fracture morphology was observed by SEM. The results show that with increasing of the temperature and the annealing time, the austenite grains gradually grow up accompanied by a small amount of annealing twin crystals, meanwhile, its plasticity and toughness are improved, and it is typical ductile fracture under the condition of tensile failure. After annealed at l223K, the invar alloy has better comprehensive properties than that at the other annealing temperatures, and the grains size is more uniform. Furthermore, when the annealing time is 4min, the invar alloy has the best comprehensive properties.IntroductionAs we known, most metals and alloys expand with increasing temperature. More than one hundred years ago (in 1897), Guillaume observed that Fe-Ni alloy with face-centered cubic (fcc) crystal structure, consisting of36%Ni, showing a very small thermal expansion coefficient below the ferro-to-paramagnetic transition, the thermal expansion coefficient around room temperature( <2 X 1O-6K-1 compared to most metallic materials which have a thermal expansion coefficient of 10-20 X 1O-6K-1) [1,2]. Since then, the subject has attracted many researchers, and various alloys with low thermal expansion coefficients have been developed. These alloys, generally known as ""invar alloys"", are in demand where dimensional changes due to variation in temperature must be minimized and where high stability is required [3, 4]."

Jan 1, 2012

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 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 B. J. Jody

This paper describes a one-step thennal-treatment process, developed at Argonne National Laboratory, to remove all organic contaminants from the glass-fiber waste that is generated during the glass-fonning process. The recovcred glass fibers can then be recycled into new glass fibers or new glass products without adversely impacting the operations of the glass industry or the quality of its products. Our process involves shredding the waste to a manageable size and then processing it at temperatures below its melting point to remove the polymeric-coating layer. The glass industry generates more than 60,000 tons of glass-manufacturing waste annually in the glass-forming process alone. Recycling of this waste stream can keep this non-biodegradable waste out of the landfills. In addition, use of recycled glass lowers energy costs, by an average of about $5 per ton as compared to using virgin raw materials to make virgin glass fibers. This process will also reduce the emission of C02 by 17,400 tons a year and it will also reduce the emission of nitrogen oxides. Economic analysis of our process shows a potential payback of less than 2 years.

Jan 1, 2003

By Denis Shishin

The pyrometallurgical production and recycling of non-ferrous metals involves the use of complex feed stocks, having awide range of chemical compositions from sources that include mineral sulphide concentrates, high value obsolete materials and process wastes. The commercial viabilities of these operations hinge on the ability to extract value from these materials. Increasingly, modern computer-based tools are used to describe and predict process outcomes, including mass and heat balances, the partitioning of elements and phase equilibria. At the heart of these predictive tools are thermodynamic databases that describe the fundamental chemical properties of a system and all the components present. A comprehensive research program has been established to develop an accurate, self-consistent thermodynamic database describing all gas-slag-matte-metal-speiss-solid phases in the system Cu2O-PbO-ZnO-Al2O3- CaO-MgO-FeO-Fe2O3-SiO2-S-(As-Bi-Sb-Sn-Ag-Au). The database can be used in conjunction with the FactSage computer platform. The accuracy of the database and its application to industrial practice is demonstrated.

By Wilson Pascheto

This paper presents results of investigations performed as part of a Root-Cause-Failure-Analysis (RCFA) of a DC smelting furnace that was brick lined with MgO-based refractories. An unusual continuous contraction of the furnace hearth was identified during operation. Cracks in the refractories were envisaged after a major shutdown of the furnace. To determine the mechanism and causes of the unusual contraction behaviour of the furnace hearth, refractory samples were taken from the furnace at different locations and subjected to different analysis including Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), QEMSCAN and Electron Probe Micro Analysis (EPMA). Creep testing of refractories under different loads (ASTM C832) was also employed to evaluate the mechanical integrity of the used bricks in comparison with the new ones. Results of the various characterisation analyses revealed that there was an interaction between refractory bricks and molten material during furnace operation, which resulted in reduced creep resistance of the MgO-based refractories. This was verified by comparing creep performance of the used brick samples and new brick samples at different temperatures and applied stresses.

By Joel Anderson

Allvac 718Plus is a newly developed superalloy with a good potential for use in fabricated aircraft engine structures when service temperatures exceed 650°C; the limit for standard alloy 718. Fabrication involves welding, where cracking usually is a prohibitive factor. Comparison of the solidification cracking behavior between these two alloys was made by Transvarestraint testing. It was shown that the total amount of cracking was significantly lower for 718Plus alloy, which was associated with a lower amount of ?/Laves or ?/NbC eutectic-type constituents. This in turn is believed to be due to the lower iron content of the Allvac 718Plus material. The analysis of alloying element segregation both within primary dendrite and interdendritic constituents clearly indicates that the segregation of Nb is the controlling factor in determining the final solidification microstructure in these alloys. The Nb concentrations of these constituents are significantly higher compared to the bulk alloy concentration. This was confirmed by the SEM-EDS analysis and calculations assessed with JMatPro, the latter also indicated that alloy 718 is more prone to form Laves and NbC eutectic-type constituents compared to Allvac 718Plus material.

Jan 1, 2008

By R. H. Rubisov

Sulphuric acid pressure leaching of nickeliferous laterites has attracted considerable attention from the nickel industry during the past five years. The process is especially advantageous for limonitic laterites that mostly contain goethite, because iron precipitates releasing acid and thus rendering low acid consumption. It is also applicable to mixtures of limonites and saprolites, although at higher acid consumption due to magnesium. Effective process design requires the solubility of metals that precipitate during the process to be known. In the present work, determination of metal solubilities is based on a simple speciation program that assumes the presence of only one dominant complex for each metal. The thermodynamic data for the precipitation reactions are extracted from high-temperature experiments with monometallic systems published previously. The validity of the approach is then tested against mixed bimetallic systems, and finally applied to calculate the solubility of aluminium, iron and magnesium in laterite leaching effluents "at temperature". In both cases of limonitic feed and limoniticfsaprolitic blends, the prediction closely follows metal solubilities measured experimentally at temperatures from 230 to 270°C and at terminal he acidities ranging from 10 to 75 g/L.

Jan 1, 1999

By Guy Deschênes

Thiourea solutions can be used as leach liquors to treat gold ores or slimes. It is also efficient to elute resins or strip solvents that were loaded in cyanides solutions. The hydrogen pressure reduction is a practical step to recover gold and silver from leach solutions, and strips and eluates without any destruction of thiourea. It is a critical point because these processes have to consider the recycling of the liquors to be irore economical. The effect of temperature, pressure, acidity, compotation of the solution and the nature of catalysts on pressure reduction by hydrogen were investigated. An electranetallurgical study was? carried out to investigate the mechanism. The composition of the products was studied by different analytical methods. The process shows a good selectivity to precipitate gold and silver in a thiourea solution containing iron and copper. Gold and silver concentrations can be decreased to 0.2 ppm and 0.1 ppm at respectively 70 KPa H2 and 28°C. No decomposition of thiourea was evident during the tests. Metals such as nickel powder or platinum activate the reaction and improve the reduction.

Jan 1, 1989

By Dengfu Chen, Mujun Long, Youguang Ma, Xin Xie, Xing Zhang, Leilei Zhang

"Processing parameters of a submerged entry nozzle (SEN) affect significantly on the patterns of fluid flow and temperature distribution in beam blank continuous casting mold with double SEN s. Effect of the geometry structure and immersion depth of double SEN s on the fluid flow in beam blank continuous casting mold was studied by water modeling. Results showed that, the optimal nozzle inner diameter was 40mm, and immersion depth was 70-90mm. The mold surface fluctuation, slag distribution, impact depth and removing rate of inclusion particles were discussed under different processing parameters of double SENs. As the results indicated, slag distribution was more non-homogeneous with a higher casting speed. The results provided basic data for the design and optimization of SENs used in beam blank continuous casting mold.IntroductionNear-net-shape casting has the distinct advantages of less rolling procedures, higher metal recovery and lower energy cost. Therefore, in the recent decades, one of the recent trends in the steel making process is moving toward near net shape casting. in which beam blank casting is a typical technology. The schematic section of beam blank is shown in Fig 1."

Jan 1, 2014

By Y. Ide, K. Kishitake

It is expected that an Al-Cr-N composite nitride film may have a higher resistance to oxidation at elevated temperatures than the well-known Ti-Al-N films. The formation conditions of Al-Cr-N films by a de reactive sputtering method and their properties were studied in this study. The films characterized with respect to their high temperature properties such as chemical composition, crystal structure, microhardness, wear and· friction. The crystal structure of the Al-Cr-N films changed from hexagonal phase to cubic phase with an increase in Cr content in the films. The resistivity to thermal oxidation of the Al-Cr-N films is superior to that of usual TI-Al-N films. A half of the friction coefficient in the Al-Cr-N film was obtained comparing with that in the ordinary TI-Al-N film at room temperature and the wear rate of Al-Cr-N film was 2 order smaller than that of TI-Al-N film. The Al-Cr-N films show a small friction coefficient at 500°C and then they are recognized to have good tribological characteristics.

Jan 1, 2000

By Hojat Naderi

In this research assisted leaching of chalcopyrite using sodium peroxodisulfate was studied. Electrochemical techniques such as Tafel analysis and electrochemical impedance spectroscopy (EIS) were used to investigate the surface reactions of a chalcopyrite electrode in the presence and absence of Na2S2O8. According to the results, addition of sodium peroxodisulfate increases the current exchange of the corrosion process and prevents the formation of a passive layer on the surface of the electrode. EIS tests show the trans-passive dissolution of the passive layer on the chalcopyrite electrode in presence of Na2S2O8. Equivalent electrochemical circuits were modeled for Na2S2O8-free and -containing solutions and the model parameters were compared to determine the effect of S2O8 2− on chalcopyrite dissolution. Copper dissolution from pure chalcopyrite mineral and chalcopyrite concentrate was carried out using 15 g/L sulfuric acid solution with and without Na2S2O8. Simultaneous presence of 10 g/L ferric ion and 40 g/L peroxodisulfate salt results in about 40 and 18% of Cu extraction from chalcopyrite concentrate and pure chalcopyrite mineral, after 96 h, respectively.