Search Documents

By N. Krishna

The utilization of Electrochemical Impedance Spectroscopy (EIS) in conjunction with Atomic Force Microscopy (AFM) is a powerful surface characterization technique to study the role of sulfur formation during acidic oxidation of chalcopyrite. It has been established that the chalcopyrite dissolution kinetics is controlled by the formation of passive sulfur layer during leaching. The objective of the study was to characterize the intermediate sulfur layer formation at different oxidation conditions in acidic solution. The chalcopyrite samples were subjected to anodic oxidation and the oxidation process was analyzed using impedance spectroscopy. The sulfur growth on the chalcopyrite surface during oxidation was further analyzed using Atomic Force Microscope for sulfur roughness and grain size, peak height and sulfur growth.

Jan 1, 1999

By K. Tozwa

The electrical conductivity of electrolytes for copper electrorefining and electrowinning processes has been reported by many researchers since 1911. The experimental results show that the conductivity increases with an increase in sulfuric acid concentration and decreascs with an increase in copper concentration. In pure copper sulfate solution, however, the conductivity increases with an increase in the copper concentration. After confirming the conductivity of pure and acidified copper sulfate solutions experimentally, the concentrations of hydrogen ion and free (not hydrated) water in the electrolytes were estimated and it was found that the relation between the conductivity of acidified copper sulfate electrolytes and the products of concentration of hydrogen ion and free water is linear. Accordingly, the conductivity of acidified copper sulfate electrolytes increases with an increase in sulfuric acid concentration and decreases with an increase in copper concentration.

Jan 1, 2003

A study was undertaken to remove the Se from waste solutions using a raw form of the biomass called Iota Chips derived from the seaweed, Eucheuma spinosum. Removal of Se from solutions was investigated as a function of time, pH, conc. of Se in solution (0.1 to 100 ppm) and lota Chips to liquid ratios of 10-2 to 10-5. For solutions containing initial conc. of 0.1 ppm Se, with the addition of Iota Chips at a solid to liquid ratio of 10-3, the Se conc. decreased to 0.03 ppm in about 3 hours. Iota Chips absorption capacity to the Se and its application to the treatment of the metallurgical processing effluents are discussed.

Jan 1, 1992

By Laurence Whitty-Léveillé

Proper handling of the radioactive fraction associated with the production of rare earth elements (REEs) in the mining industry is essential for a sustainable environment and human health. Actinides, such as uranium and thorium, have similar chemical properties to REEs, and are often co-dissolved in current hydrometallurgical processes. This causes radioactive contamination of the infrastructure through the extraction cycle. The present study optimizes, through experimental design, a sequential leaching procedure with Na2CO3/NaHCO3 and HCl for the rapid and selective dissolution of REEs and actinides. Optimization focuses on the main operating parameters (time, temperature, and concentration); different types of minerals, REE composites, and ores; on achieving maximal leaching yield; and on minimizing dissolution of the gangue metals (Fe, Si, and Ca). The final sequential procedure was rapid (1 h), effective, and led to the segregation of Th, U, and REEs with limited dissolution of the gangue metals.

By Toshio Suzuki, Machiko Ode, Won Tae Kim, Seong Gyoon Kim

"The Ostwald ripening and growth and coarsening of the secondary dendrite arm are studied using a phase-field model. The phase-field parameters are obtained at a thin interface limit proposed by Kim et al. In Ostwald ripening analysis, the difference of the concentration due ·to· the curvature effect is shown. The third power of the average particle radius Rav is proportional to time and the ripening constant shows a good agreement with the value by Deppers et al. The particle radii distribution shows the transition behavior to attain a self-similar stationary shape. The growth and coarsening behavior of the secondary dendrite arm is also analyzed using a phase-field model. The estimated arm spacing and its dependence on time are in good agreements with experimental data.IntroductionThe ripening or coarsening process controls the microstructure during the late stage of solidification. The ripening phenomena are recognized firstly by the Ostwald [1]. The first quantitative analysis for the Ostwald ripening in the limit of vanishing solid fraction was provided by Lifshitz, Slyozov and Wagner (LSW) [2,3]. In their study, that the mean radius grows proportional to the cubic root of time and the size distribution of precipitations shows a ""self-similar"" shape are shown. Most of the studies for the Ostwald ripening confirm or predict these two general rules above. In case of finite solid fraction, the general rules are observed but the ripening constant is larger and the self-similar shape is wider than the LSW prediction respectively [4-6]. To analyze· the high solid fraction system, the theories that consider the solute field correlation are proposed [4,7-8]. In the theory, however, since the particle is treated as the point, the effect of the concentration field deviation from the monopole field should be taken into account. Recently the numerical simulation, in which not only diffusive transportation of solute but also convection effect is considered, has been done using a phase-field model [9]."

Jan 1, 2000

By Zhang Libo, Li Wei, Peng Jinhui, Guo Shenghui, L. Jing

Partially stabilized zirconia ceramics (PSZ) were prepared by microwave sintering using natural baddeleyite which was obtained by flotation of baddeleyite ore as starting materials. Because of using natural baddeleyite as raw and the process producing no waste, it realized shorter process, energy savmg, environmentally-friendly and non-damage processing. In this work natural baddeleyite stabilized with 3.8wt.% CaO were sintered at 1300°C for 60min in a multi-mode 2.45GHz microwave furnace. Microwave sintering could fast heating and sintering. Besides that, microwave sintering could heat materials wholly, low the sintering temperature, improve the materials properties and save energy. X-ray spectrum displayed the product composed by the tetragonal phase and monoclinic phase that also showed the product was PSZ. Fine and uniform microstructures were observed in the product through scanning electron microscopy. PSZ which was with high density was confirmed by the method of the Archimedes technique.

Jan 1, 2011

By Toshiyuki Nohira, Eiichi Takeuchi, Tetsuo Oishi, Hideki Ono, Hirokazu Konishi

The Dy-Nd-Pr-Ni alloy sample was prepared by cathodic potentiostatic electrolysis at 0.65 V (vs. Li+/Li) for 1 h using a Ni plate in a molten LiCl-KCl-DyCl3-NdCl3-PrCl3 system at 723 K. The highest mass ratio (Dy/Nd+Pr) in the alloy sample was observed to be 50 at 0.65 V. Anodic potentiostatic electrolysis at 2.20 V for 12 h was conducted using the Nd-Fe-B magnet electrode in a molten LiCl-KCl system. All elements were almost dissolved from the magnet, and the original form of the magnet disintegrated. After anodic potentiostatic electrolysis at 2.20 V, cathodic potentiostatic electrolysis was conducted at 1.00 V for 5 h using a Mo plate in order to remove the dissolved Fe from the bath. Finally, cathodic potentiostatic electrolysis was conducted at 0.65 V for 12 h using a Ni plate. The mass ratio of Dy/Nd in the alloy sample was determined to be about 18.

Jan 1, 2015

By N. Coone

By exploiting the results of solidification modelling foundries can enhance the quality and reduce the cost of their casting processes. However not enough information exists on the thermal boundary conditions, which control the transfer of thermal energy stored in liquid metal to the mould via the metal/mould interface during solidification. This is quantified by the heat transfer coefficient (h.t.c.). An experimental and numerical study was carried out to find the magnitude and variation of the h.t.c. in cylindrical castings during the solidification of grey cast iron in green sand moulds. The h.t.c. values were calculated using a time marching solution to the inverse heat conduction problem. The variation of h.t.c. with metallostatic head was analysed. There is a wide scatter in green sand thermal properties due to the large number of variables involved in mould manufacture including green sand compaction and water content. The sensitivity of the calculation to uncertainties in the thermophysical properties of the green sand was evaluated. Keywords: Heat transfer coefficient, grey cast iron, sand moulds. inverse technique

Jan 1, 2003

By Wei Luo, Yuanbo Zhang, Zhixiong You, Zijian Su, Guanghui Li, Tao Jiang

"In this study, the appropriate sintering process parameters for low-grade ferromanganese ores were investigated. The results showed that, under the condition of natural basicity (R=0.03), the optimal parameters were obtained as follows: moisture of mixture 9 .1 %, coke powder 9 .9% and sintering negative pressure 7 KPa. And the corresponding yield, ISO tumbling index and utilization coefficient reached at 80.18%, 61.27% and 1.515t·m-2·h-1, respectively. Under the optimal parameters, the emission of harmful gases, such as S02 and NOx, were reduced evidently with 30% of coke powder replaced by biomass charcoal. Moreover, it was found that the basicity had obvious effects on the quality of the sinters when it changed between 0.03 and 2.4. The ISO tumbling index gradually decreased from 61.27% to 55.47% with the basicity increasing from 0.03 to 1.2, then, it began to increase after the basicity further increased to 2.4.IntroductionManganese is mainly consumed by steel and battery industries, particularly in the steel plants and ferroalloy units. The consumption of metal manganese in the ferroalloy industry accounts for 85%-90% of the total Mn [1-2]. Therefore, ensuring sufficient manganese alloys is essential to meet the rapid development of steel industry. Recently, rich-manganese slag containing high grade Mn (>40%), low Fe (1%) and P (<0.03%) is considered as superior raw materials for manganese alloys. While the sinters made from manganese ores are major raw materials for producing rich-manganese slag with the increasing exhaustion of natural rich manganese lump ores [3-5]."

Jan 1, 2013

By J. W. Evans

Mathematical modeling has now become a standard technique in the development of new technology and the improvement of existing technology in the processing industries. Physical modeling has a longer history but a smaller following at present. The paper reviews some examples of the application of both types of modeling in non-ferrous metal extraction, particularly within the copper and aluminum industries. The objective is to show that well founded models can lead to results that have practical consequence in scaleup, design and operation.

Jan 1, 1993

An EAF dust generated in a Swedish steel mill has been leached in hydrochloric acid at The solution obtained has been subjected to purification by cementation followed by precipitation of zinc with sodium carbonate. The thermal decomposition of the precipitate was studied using thermal analysis and X-ray diffraction. The results show that during the calcination of the precipitate three different reactions occur. The decomposition of the solid phases Zn5(CO3) (OH)6, CaZn(CO3)2 and CaCO3 occur completely at 370°C, 560°C and 940°C respectively, yielding a final product containing 61.9% ZnO and 38.1% CaO. Methods to minimize calcium and manganese in the final product are discussed.

Jan 1, 2003

By Petrus Christiaan Pistorius, Farzin Fatollahi-Fard

The production of titanium oxycarbide – a consumable anode material used in molten-salt processes for electrowinning titanium – from heavy mineral concentrate, such as a high-titania leucoxene and natural rutile is described. The oxycarbide is prepared by carbothermic reduction of the oxide at elevated temperature. Particle size distribution (of the titanium oxide raw material) and temperature have large effects on the kinetics of the reaction, which seem to follow a “shrinking-core” model. It is anticipated that low porosity (in the anode pellets) would be advantageous during electrolysis. Particle size distribution, extent of reaction during carbothermic reduction, and sintering temperature are expected to affect pellet porosity after sintering, and are being tested experimentally.

Jan 1, 2015

By Yong Li, Tao Jiang, Xiangxin Xue, He Yang

"In this paper, we describe the current status and research progress on the utilization of typical industrial solid wastes in China. We propose a creative method called “eco-utilizing wastes” with an aim of both integration and increment but without second-time waste and pollution, in terms of the characteristics of typical industrial solid wastes, such as titanium-bearing blast furnace slag, high-silicon iron tailing and boron-enriched slag as well as oil shale.Situation of Typical Industrial Solid Wastes in ChinaThough mineral resources in China are abundant, most of these are low grade ores. Moreover, the distribution of mineral resources is asymmetric, which causes the increase of cost and decrease of the economic benefit. Over-exploitation of mineral resources results in a large number of solid wastes. The accumulation of solid wastes not only means the waste of valuable resources, but also causes environment deterioration. There exist some problems in the current practice of the disposal of industrial solid waste, such as only emphasizing the final results and causing new pollution and waste [1]. So the research and development of a high value-added method has a high practical relevance to our nation. Based on the present status and research progress of industrial solid wastes in China, a creative new idea and method for eco-utilization of solid wastes is proposed in this paper."

Jan 1, 2012

By L. Filip

The roast-leach-electrowinning (RLE) process for zinc was modified to treat two typical complex concentrates containing zinc, lead, copper, gold and silver. Laboratory testwork results indicated that the optimum roasting temperature ranged from 700 to 800°C, in order to produce acceptable residual sulfur levels. The calcined concentrate was subjected to a three-stage leach sequence. The resulting leach solution was purified by hematitic precipitation and directed to the recovery of copper and zinc by solvent extraction and electrolysis. Alkaline smelting and subsequent electrolytic purification recovered the lead and precious metals from the leach residue. A flowsheet was developed based on the laboratory testwork results, and demonstrated in a large-scale pilot plant. The recoveries produced during the pilot plant operation ranged from 90 to 92% for zinc and copper, 85% for lead and 90% for gold and silver, respectively.

Jan 1, 1999

By David G. Dixon

A mathematical model is derived in dimensionless form which simulates the effluent concentration response of reagents from spent heaps under both fresh and recycled water rinsing. The model is based on dispersion from isochoric pathways distributed in length and cross-section, oriented normal to convection channels in ideal plug flow. The effects of heap height, rinsate flow, and initial reagent concentration are examined. It is shown that the rinsing cycle undergoes a distinct shift between fast and slow rinsing at a certain time depending on the amount of stagnant solution in the heap, and the distribution of dispersion pathways. Results of preliminary column rinsing tests on both agglomerated and unagglomerated ores are presented which partially validate the model.

Jan 1, 1994

By Frederico Muylaert Margem, Giulio Rodrigues Altoé, Glenio Daniel, Pedro Amoy Netto, Sergio Neves Monteiro, Maria Carolina Andrade Teles

The environmental concern is creating pressure for the substitution of high energy consumption materials for natural and sustainable ones. Compared to synthetic fibers, natural fibers have shown advantages in technical aspects such as flexibility and toughness. So there is a growing worldwide interest in the use of these fibers. Fique fiber extracted from fique plant, presents some significant characteristic, but until now only few studies on fique fiber were performed. This work aims to make the analysis of the tensile strength of polyester composites reinforced with fique fibers. The fibers were incorporated into the polyester matrix with volume fraction from 0 to 30%. After fracture the specimens were analyzed by a SEM (scanning electron microscope).

Jan 1, 2015

By L. Katgerman, H. J. Brinkman, J. Duszczyk

"The phase formation sequence in the in-situ synthesis ofTiB2 in A1 from elemental A1, Ti and B powders is identified with a combination of DSC and XRD. After the melting of A1, A1B2 and A13 Ti are formed at the contact areas between A1-B and A1-Ti. The influence of variations in starting composition on the reaction kinetics is explained in terms of there effect on the different processes in the formation sequence. Parameters in the starting composition that were investigated are; fraction ofTiB2 forming reactants, non stoichiometric Ti:2B ratio's, and addition of alloying element Cu.It was found that a liquid Al phase is necessary for the in-situ TiB2 forming reaction from the intermediate A1B2 and A13 Ti phases. If all Al is consumed by the formation of A1B2 and A13 Ti the TiB2 formation is halted until the decomposition of A1B2 and A13 Ti .Overstoichiometric amounts of B are needed for complete conversion of the Ti, present in A13Ti, into TiB2 This is explained by the fact that some of the stable A1B12 phase is formed after the decomposition of A1B2•The addition of Cu leads to an increasing reaction rate in the A1-Ti reaction. A possible explanation for this is that the A1-Cu liquid penetrates more easily between the Ti and its surface oxide than the unalloyed A1 liquid."

Jan 1, 1998

By Malti Goel

"Ferrous and Non-ferrous industry in India is undergoing a transition to meet the growing demand and a new thrust to Research & Development (R&D) is mounting. On one hand, to meet the target laid by the policy in the Iron and Steel sector of 110 million tones production by 2020; on the other, innovations taking place in light metal production technology; both have necessitated greater attention to development of industrial ecological framework. Industrial ecology provides a number of new challenges as well as opportunities for the industry. The development and growth in a particular industry should have a trend towards reduced energy consumption, reduced resource consumption, thereby reducing the cost of production. Technology management strategies will have a key role in achievement of these targets. The paper describes recent developments in technology management, importance of R&D and case studies on adoption of energy efficient & CO2 reduction technologies in metal industry in India. In the end suggestions for future are made.IntroductionInternational Energy Agency [1] has assessed that nearly one third of the World’s energy consumption and 36% of CO2 emissions are attributed to manufacturing industries. In case of ferrous and non-ferrous metals, the resource equality and product quality finally determine the energy share across the countries. In the overall, Iron & Steel industry accounts for about 19% of total industrial energy used. The saving potential for non-ferrous metals is estimated to be anywhere between 13 to 25 % of the energy consumed depending on the level of resource quality. The projections are that energy consumption worldwide in Industry sector would increase 1.8% per annum up to 2030 on average, and up to 2.5% in developing countries."

Jan 1, 2008

By N. Shi, T. C. Lowe, S. J. Zhou, M. L. Lovato, Y. T. Zhu, J. A. Valdez, W. R. Blumenthal, M. G. Stout

"A major problem of short-fiber composites is that the interfaces between the fiber and matrix become a limiting factor in improving mechanical properties such as strength. For a short fiber, a strong interface is desired to effectively transfer load from matrix to fiber, thus reducing the ineffective fiber length. However, a strong interface will make it difficult to relieve fiber stress concentration in front of an approaching crack. Stress concentrations result in fiber breakage. We report in this paper an innovative approach to overcome this problem: reinforcement morphology design. Short-fibers with enlarged ends are processed and used to reinforce a polyester matrix. The initial results show that the bone-shaped short-fibers produce a composite with significantly higher strength than can be attained with conventional short, straight fibers.IntroductionThese interfaces between the fiber and the matrix in short-fiber composites play a critical role and, in many cases, become a limiting factor in improving such mechanical properties as strength and toughness of the composites (1-4). For a short fiber, a strong interface is desired to effectively transfer load from matrix to fiber. A stronger interface can reduce the ineffective length at both ends of the fiber and, therefore, can increase the effective length that carries load (5-9). However, with a strong interface it is difficult to relieve fiber stress concentration -in front of an approaching crack; and such stress concentration can result in fiber breakage (10, 11). This effect is particularly severe for ceramic matrix composites, because of their low matrix toughness and lack of plasticity. Even for a composite with a highly ductile matrix, such as plastics, too strong an interface may still cause successive adjacent fiber breakage and subsequently reduce composite toughness (1, 11). On the other hand, a weak interface significantly decreases the fiber load-carrying length due to ineffective load transfer and complete fiber interfacial debonding and pullout during loading. A compromise in the interfacial bond strength will also compromise the load-carrying potential of short fibers."

Jan 1, 1998

By Florian Aurelian, Mihai Popescu

"It will be tested four types of “geochemical barriers”. All those mixtures were contacted with mine waters containing uranium, radium and heavy metals. The loading capacity was determined. The optimum mixture was determined and its efficiency was tested within an uranium areal, where the activity was stopped. It was determined the possibility to recover the radioactive elements and the heavy metals from the investigated barriers.IntroductionThe paper presents the results concerning the performances of some “geochemical barriers” used for the decontamination of mine waters from uranium mining sites, which were tested in lab and in situ.ExperimentalThe research activity was carried out in lab and on the site.In the lab a module was constructed in order to follow up the uptake capacity of the “permeable reactive geochemical barriers” used to remove the radiolelements from the contaminated waters originated from the uranium mining industry. The barriers, which were used, are made of cheap natural materials, which can be easily got (wood chips, peat coal, sawdust, iron span, steel and zeolitic tuff). The following types of barriers were tested:•, 1st barrier: peat coal, sawdust, zeolite on weight ratio of 1/1/1;•, 2nd barrier: bentonite, sand, wood chips, peat coal on weight ratio of 1/1/1/1;•, 3rd barrier: iron span, steel, sawdust, peat coal on weight ratio of 2/1/1;•, 4th barrier: iron span, steel, sand, firry wood chips on weight ratio of 1/1/1.Lab researches concerning the uranium uptake capacity of the above described “reactive barriers” pointed out that the 3rd mixture (iron span, steel, sawdust, peat coal on a ratio of 2/1/1) didn’t reach the maximum uranium uptake capacity not even after eleven contact stages (the uptake capacity being of 70.6 mg U/ kg of mixture) and the mixture of peat coal, sawdust and zeolite has an uranium uptake capacity of 26.6 mg U/kg of mixture and becomes saturated after four contact stages.Each one of the components involved in physical-chemical processes of sorption, reduction and precipitation, will determine the diminution of uranium and other metals contents upstream the permeable reactive barrier."

Jan 1, 2008