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By David G. Dixon

From its first implementation for the recovery of gold from low-grade ores by cyanidation in the early 1970s, heap leaching has developed into a key hydrometallurgical technology, in conjunction with solvent extraction and electrowinning, for the recovery of base metals, including most notably copper from both oxides and secondary sulphides, and more recently, nickel and zinc. And, given recent advances in bioleaching with thermophilic microbes, the successful application of heap leaching technology to low-grade primary copper ores seems only a matter of time. However, with each new development, it becomes increasingly apparent that the successful application of heap leaching technology will ultimately depend on our having an ever more complete understanding of the fundamental processes underlying it. Much work has been done toward the development of this understanding, on many different fronts. In this paper, a critical overview of heap leach modeling work to date is presented in terms of the most important phenomena which occur during heap leaching, and potential directions for future work are discussed.

Jan 1, 2003

By Daniel Kim, Ari Rantala

Efficient on-line monitoring of electrolytic cell performance in copper electro-refining has been challenging due to the need for complex electrical measurement systems and the management of the enormous volume of data. Based on Kennecott Utah Copper's innovation Outotec has developed a novel and innovative electrolytic cell monitoring system called CellSense™ System. As the system is based on self-powering from bus bars, wireless communication, on-line adaptive modeling and easy to access information and alarming, traditional obstacles of electrolytic cell monitoring are eliminated. With cell voltage and electrolyte temperature measurements, CellSense System enables real-time cell performance discovery and early reaction to critical production or quality disturbances such as short-circuiting, flow blockages, cold cathodes or electrolyte temperature excursions. During the past few years the system has been delivered to over 3500 commercial cells. In this paper the largest CellSense™ System ever delivered and recently adapted by Kennecott Utah Copper with 1412 cells monitored on-line for high tankhouse performance, cathode quality and optimized operator work flow is presented. Early results and benefits are discussed.

Jan 1, 2012

By R. S. Celmer

The distributions of cobalt, molybdenum, copper, and selenium between nickel matte and silica-saturated iron silicate slag have been determined in the region of the metallic saturation boundary, at 1523 K. Results are given as a function of the composition of the coexisting Fe-Ni alloy and the activity of iron in the system. Under strongly reducing conditions, these minor elements display a marked preferential accumulation in the sulphide phase. It is shown that the dissolution of cobalt and molybdenum in slag follows an oxidative mechanism, and distribution equilibria are correlated with the oxygen potential. From these data, the thermodynamic properties of cobalt in nickel matte are computed. Further, comparisons of minor element partitions are made between the nickel and copper matte smelting cases under metal saturation conditions.

Jan 1, 1988

By L. J. Lutz

The U.S. Bureau of Mines has developed an electrorefining process to recover Ni, Co, Cr, and other metals from mixed and contaminated superalloy scrap. The superalloy scrap is cleaned then directly electrodeposited as a Ni -Co deposit. The process recovers approximately 90 pct of the Ni-Co available from the scrap as a 99t pct pure Ni-Co alloy. During electrorefining the electrolyte undergoes a purification process which results in Cr and other refractory metals reporting to the purification residue. Operating data is given for a 3-L compartmented electrolytic cell. Techniques for the removal of Fe, Cr, and trace impurities from the recycled electrolyte are outlined. The economics of a facility producing 15 mt/d of a Ni-Co alloy are also discussed.

Jan 1, 1993

By D. W. Hoey

Eight years use of the ISA Process is reviewed and current design and operations described. Nodern Technology used for impurity control and disposal as well as the use of mechanised electrode handling equipment, cell voltage monitoring, cell insulation and an efficient contact bar system are described. Improvements achieved in terms of energy usage and plant productivity are detailed.

Jan 1, 1987

By Yoshisada Michiura, Junko Umeda, Katsuyoshi Kondoh

Rice husks or straws, one of the main agricultural wastes in South-east Asia, have a large possibility to be employed as usefully renewable resources to produce energy and high-purity silica (SiO2), because they consist of about 70% organics such as cellulose or hemi-cellulose, and 20% amorphous SiO2. The former is utilized as bio-mass energy; for example, thermal or electric energy, and bio-mass ethanol. High-purity silica can be used as raw materials in the industrial uses. It would be possible to extract silica elements from rice husks and straws by burning them in air because their main contents are organics. In the previous studies, a strong acid leaching treatment on rice husks before burning was carried out by using H2SO4, HCl and HNO3 to prepare high-purity silica materials. This was available to accelerate the hydrolysis of celluloses and hemicelluloses contained in rice husks, and remove the above metallic impurities. A strong acid leaching treatment, however, is significantly hazardous to environment and human life, and causes an increase of the process cost. In this study, the environmentally benign, harmless to human and economically effective process to produce high-purity amorphous SiO2 materials from rice husks has been established without using strong acids. From a viewpoint of the harmless influence on human body, the carboxylic acids were used in the leaching treatment on rice husks. TG-DTA measurement and GCMS analysis indicated that the leaching was effective for the hydrolysis of celluloses and hemicelluloses contained in rice husks at 473K~873K, which produced the same results in using the conventional sulfuric acid. The metallic impurities could be also removed from the husks via a chelate reaction between carboxyl groups (-COOH) and the metal elements. In particular, it was clarified that cadmium (Cd) were completely removed from rice straws by this reaction. Concerning the burning conditions of rice husks after the acid leaching, it was necessary to supply a suitable amount of air to completely combust organics; for example it required air supplement of 50 ml/min. or more. The burning temperature should be less than 1273K to obtain amorphous structured silica. High-purity amorphous silica materials with 99% or more were prepared from rich husks by applying the citric acid leaching treatment and burning process at 1073K in air.

Jan 1, 2008

By Wu Liu

A modified falling ball technique for measuring the viscosity of liquids is described. It consists of recording the weight vs. time of a crucible holding the liquid of unknown viscosity, as a solid ball, or liquid drop, is let to fall through the liquid. This method does not require measurements at constant terminal velocity, as the conventional falling ball technique. Also, measurements do not depend on visual observation, which is not possible in opaque liquids or containers. The effect of process parameters on the utility of this method and its potential application to liquid systems of metallurgical interest were analyzed theoretically. The paper also com- pares the gravimetric method to the conventional falling ball technique for measuring viscosity.

Jan 1, 1992

By T. Asahina, M. Nakamura, M. Mabuchi, I. Shigematsu, M. Nakanishi, G. Yamauchi

"Commercial stainless steels (SUS304L and SUS430) were subjected to equal channel angular extrusion (ECAE) at room temperature to a total strain of 2.3 to 9.2. For each type of stainless steel, it was shown that the sample processed by ECAE showed higher room temperature strength than the as-quenched sample. This is probably due to the heavily worked structure. On the other hand, both strength and elongation of the ECAE processed SUS430 were increased by annealing at 773K. It is likely that higher strength is attributed to both the heavily worked structure and fine substructures. It is also likely that higher elongation is attributed to the fine substructures. It is concluded that ECAE is available for improving the room temperature strength of commercial stainless steels.INTRODUCTIONEqual channel angular extrusion ( ECAE ) is a technique that provides the repetitive deformation and allows to high intensity of deformation. With this procedure, a sample is pressed through a channel that has an equal cross section but bent at an angle of ?> [1-2]. Shear strain is introduced when a sample passes through the bending point of the channel. Repetitive processing is feasible because the cross-sectional dimension of a sample has no change during processing. To date, many reports have described that ECAE is available for the fabrication of fine-grained materials [3-14]. On the other hand, an ECAE processed sample can achieve high intensity of deformation through repetitive deformation. According to the equation given by Segal [ 2 ], a strain of about 1 is introduced in each pass through die if the angle ? is 90 deg.It is well known that high tensile strength can be achieved in metallic materials through work hardening [15]. It is also known that metallic materials with fine grain size show high strength [16]. Hence, it is expected that ECAE is available for strengthening method in metallic materials. In the present paper, we will report the mechanical properties of stainless steels processed by ECAE. As samples, SUS304L austenite stainless steel and SUS430 ferritic stainless steel were chosen. Each alloy has a single-phase structure (fee or bee) and shows no phase transformation, so that transformation strengthening cannot be applied. Hence, a heavy cold work such as ECAE may be effective for strengthening of this stainless steel. Annealing was conducted for the ECAE processed SUS430 to vary its microstructure. Then, the effect of annealing on the strength of the ECAE processed SUS430 was also investigated."

Jan 1, 2000

By Masahiro Yoshimura, Sergiy Korablov

"Hydi-othermal corrosion ofTiN, TlAlN and CrN PVD films (3 µm thick) deposited on SUS-304 substrate was studied in 100MPa water in 20-950°C temperature range up , to 750h. The beginning temperature of their reaction was determined as 200°c for TiN and TiAlN and 500°C for CrN films, which are quite low in comparison with that of air oxidation of those powders. Very thin oxide scales. of TinO; n-I homologous series phases were formed above 300°C. TiO2 anatare. is observed for TIN and TiAlN films at 400°C. The· feature of hydrothermal corrosion of CrN films seems to be CrNxOy phase formation.Distinguishable weight changes were observed at higher temperature than 700°C for TiN, 750°C for· TiAlN and 800°C for CrN respectively. Hydrothermal corrosion kinetics .was constructed to calculate the activation energy of hydrothermal corrosions. On the base of obtained data, hydrothermal corrosion resistance was as follows: TiN – TiAlN - CrN. Facetted oxide crystals were formed at higher temperature than 500°C for TiN, TiAlN and 850°C forCrN.IntroductionThe metallic nitride (TiN; TiAlN, CrN) PVD films have high hardness, strength and wear resistance. Therefore these films are widely used in industry for wear resistij.nce application such as cutting tools and die molds. Their performances depend on not only the mechanical properties but also corrosion resistance of coated films. High temperature oxidation of metalliq nitride and nitride films was well studied [1-5]. However there are no reliable data concerning the .corrosion resistance of coated nitride materials. In high-temperature and high-pressure water. There are a few reports on hydrothermal corrosion of nitride films [6,7]. The increase of corrosion resistance of CVD films was observed in following succession TiC - TiCNO - TiCN - TiN at 300-680°C temperature interval and I 00 MPa pressure water according to data of the first report. Kawana et al. [7] have reported about excellent corrosion resistance of CrN films under 290°C and 8, 6 MPa water during I 000 h in the circulating type experimental loop. The films thickness was about 7-10 µm in both cases. However it remains unclear the chemical state of the surface species and especially in-depth distribution, oxide scale thickness and its growth, and defects formation in the oxide film."

Jan 1, 2000

By Akita Ito, Sumio Kato, Mikio Sugai, Shinichi Nakata

"Spark Plasma Sintering (SPS) is a newly developed method for the sintering of metal and ceramic powders, and completes their densification at low temperature and in short period. The SiC powder was synthesized from diatomite and graphite or carbon black by heating at 1 450°C for 1 hr in an argon atmosphere. The synthesized SiC powder was heated at 1500-1800°C, 50 MPa for 15-18 min by SPS. The relative density of sintered SiC body increased with the rise in the temperature. The oxidation of the surface of the SiC particle and impurities in SiC from diatomite greatly influenced the sintering promotion of SPS.IntroductionThe SiC has high hardness because of the covalent bonding, and is also excellent in thermal and chemical stability. However, it is difficult to obtain a dense SiC sintered body by the combustion heating-method. Therefore, the dense SiC bodies have been made by the use of additives and I or the hot pressing (HP) method.In this study, the SiC powder was synthesized by using diatomite of natural products and graphite, and carbon black of reagent as raw materials, and the relationship between the properties of SiC powders prepared at various synthetic conditions and the density of sintered body by SPS was examined."

Jan 1, 2000

By Kazutaka Kunii

It is invariably certain that after punching for IC Leadframes, scrap metal were generated. These seraps were re-dissolved and in order to use as raw material for leadframes, it is necessary to remove the Ni plating. In this study a simple method was developed for the removal of Ni plating by surface oxidation of Ni plating. For this purpose a fundamental study was carried out on the oxidation behavior of Ni plating. Results showed that by controlling the oxidation condition, a considerably high rate of Ni could be removed.

Jan 1, 1996

By Weizhi Zeng, Michael L. Free, Sayan Sarkar, Prashant K. Sarswat

Black Phosphorus was recently discovered as a 2D material and it exemplified huge prospects for application in electronics, optoelectronics, photonics and catalysis. It is a direct band semiconductor with tunable band gap varying from 0.35 eV (bulk) to 2 eV (single layer). But the layer dependent band gap of black phosphorus restricts it to make use of the full spectra of sunlight for absorption. First principle calculations were performed using ‘Quantum Wise Atomistic Toolkit’ package with Perdew-Burke-Ernzerhof (PBE) exchange-correlation for black phosphorus doped with non-metallic dopants of B, S and Se and metallic dopants of Ti, Mg and In. It has been found that doping with non-metallic impurities result in a small diminution of the band edges (0.96–0.57 eV), whereas doping with metallic impurities decrease the band edge drastically (0.85–0.025 eV). Moreover, it was also observed that dopants with an even number of valence electrons incorporated a metallic nature of black phosphorus, whereas dopants with odd number of valence electrons further attributed to its semiconducting features. Thus in a holistic discernment, black phosphorus with the incorporation of some dopants in appropriate amounts can absorb more visible range of the optical spectra, making it ideal for use in photovoltaics.

Mar 1, 2017

By R. Gampala

The consolidation of mom matrix composite monotapes occurs by the plastic (time independant) and creep deformation of monotape asperities. Past models of the process used seperate micromechanical analyses of the contact deformation by (rate independent) plasticity and power law creep (i.e steady state creep). These models are now used to simulate consolidation and to optimize/control consolidation process cycles so that the composite's microstructure is "steered" to, a user defined goal state. However, the models do not incorporate the sometimes dominant transient creep process and the instantaneous response of the plasticity mechanism causes finite discontinuities in the microstructure state vector field and therefore eliminates the possibility of using the powerful array of trajectory optimization schemes that all require continuous vector field for optimization and control. To overcome this problem, a inified creep/plasticity constitutive model that results in a continuous state vector field is used to rederive the contact deformation response during monotape consolidation. The contact blunting of a laterally constrained hemispherical asperity is first analyzed and its response represented by two coefficients; one relating the contact area to the blunting strain (C), the second, the mean contact pressure to the blunting rate (F).The C and F coefficients for this unified blunting problem are then obtained by finite element analysis, and detailed results presented for two composite matri-ces of topical interest (Ti-24A1-11Nb and Ti-6Al-4V).

Jan 1, 1996

By Martin Reyes, Juan Hernández, Julio Cesar Juárez, Isauro Rivera, Ma. de los Ángeles Hernández, Francisco Patiño

The dissolution of Ag contained in metallurgical tailings was studied by adding ions Cu2+ and Zn2+ in S2O3 2- medium. Chemical analysis of mine tailings by cupellation revealed a Ag concentration of 71 g/ton. The XRF and XRD analysis confirmed the preponderance of SiO2 in the mineral matrix. The experimental dissolution process was conducted in alkaline solution using six concentrations of NaOH and five of S2O3 2-, at different temperatures, also using five concentrations of Cu2+ and Zn2+ as a catalyst. The results showed similar values for both systems (96.8% and 97.13%). The ion Cu2+ and Zn2+ increases the dissolution of Ag, and decrease the reaction time of dissolution. Under the conditions used, pH and stirring rate did not affect the dissolution of Ag.

Jan 1, 2015

By Yuanbo Zhang, Zhixiong You, Daoxian Duan, Guanghui Li, Tao Jiang, Xiaohui Fan

"Presently, high-grade manganese oxide ores are usually utilized by a coal-based reduction roasting process. However, there were some obvious drawbacks, including serious environmental pollution, high energy consumption, etc. The reduction temperature is relatively high (850-900 °C). In this study, a kind of biomass, pine black charcoal, was used as a reductant to reduce low-grade manganese oxide ores. Under the optimal conditions of reduction temperature of 600~650 °C, roasting time of 30~45 min and ratio of ore to reductant 5:1, the leaching efficiency of manganese reached more than 98%. Compared with the traditional coal-based reduction process, the reduction temperature is reduced by 250-300 °C.IntroductionManganese plays a very important strategic role in the national economy, and it is widely used not only in the metallurgical industry, but also in the light industry, chemical industry, medicine, agriculture, etc [1]. The average grade of manganese ores in China is evenly about 21%, which belongs to typical low-grade manganese ores [2]. Therefore, large quantity of high-grade manganese ores is required to import in order to meet the rapid development of Chinese manganese industry. As reported, the conventional treatment of reduction roasting has been widely applied for processing manganese oxide ores, in which coals or reducing gases (CO, H2 or CHi) were usually used as reducers [3]. However, there were some insuperable problems, such as high energy consumption, poor operating conditions, serious environmental pollution, etc [ 4-9]."

Jan 1, 2013

By Jiann-Yang Hwang

A study on microwave assisted chalcocite leaching was carried out with a microwave hydrothermal reactor. The leaching was conducted with thick mineral slurries (50-100 g/l). The leaching media is a mixed solution of CuCL2 and NaCL The investigation included the effect of leaching temperature, quantities of the minerals per unit slurry volume as well as the initial concentration of cupric ions were investigated. The results were discussed and compared with that using conventional leaching method.

Jan 1, 2003

By Ademar B. Lugão, Sandra R. Scagliusi, Elizabeth C. L. Cardoso

When butyl rubbers are subjected to high energy radiation, they form easy free radicals that initiate various chemical reactions. These reactions alter the molecular distribution of irradiated rubbers by crosslinking or scission affect their physical and mechanical properties. This work aims to the analysis of effect induced by γ-exposure on the crosslinking density in butyl rubbers by swelling measurements accomplished before and after irradiation at 25, 50, 100 and 200 kGy, with further evaluation of crosslinking density accomplished by Flory-Rehner equation; this is a proper procedure for the qualification of radiation resistance. It can be noticed that changes in material structure was due to build-up of new three-dimensional network in studied rubbers. Changes in crosslinking density of butyl rubber compounds emphasize that degradation mechanism is strongly influenced by gamma-radiation doses higher than 50 kGy, since chain scission process predominates over crosslinking reaction.

Mar 1, 2017

By S. Tandon

Equilibria studies of selenium distribution for sodium-borate slags were initiated at 1473k under reducing condition as a function of slag composition and alloy composition. The Se distribution coefficient (% Se in slag/% Se in metal) increased from 0.4 to 2.9 with increase in basicity (0.53 to 0.86) for Cu-0.446% Se alloy. However, the results are not very useful from industrial application viewpoint. Therefore, in order to improve the distribution of Se, CaO (10% to 50%) was added to the sodium-borate slag of basicity 0.864. On addition of 502 CaO, the distribution coefficient increased roughly by 100% for slag composition - 44.5% Borax, 22.2% Na2C03, 33.3% CaO and Cu-0.44677 Se alloy. Further, the value of this distribution coefficient has been found to increase by an additional 80% on addition of 20% CaF2 to the above slag for all Cu-Se alloy compositions. Also with increase in initial concentration of Se, the distribution coefficient has been noted to increase.

Jan 1, 1992

By Kazuhiro Asai

Hitachi Refinery of Nippon Mining & Metals Co., Ltd. installed a reverberatory type recycling fumace in 1978 in order to treat the industrial wastes which contain metal elements such as copper, gold and silver. Pyrite and industrial waste materials such as galvanizing sludge, hydroxide slime and dust are smelted. Sulfidized copper, iron and precious metals are transformed into matte and other metallic elements are oxidized into slag This copper matte is transported to Saganoseki smelter and copper and precious metals in the matte are recovered. Recently it is difficult to obtain pyrite economically because of the decrease of pyrite production. Therefore, a new treating process of the liquid waste has been investigated at Hitachi Refinery. In this process, the sulfide or sulfate from the liquid waste are smelted as a source of sulfur.

Jan 1, 1997

By M. Kawakami

In relation to the designing of a new-type blast furnace, the reaction of carbonaceous materials with CO2 is expected to occur at as low temperature as possible. In order to get a highly reaetive carbonaceous material at low temperature, the reaction kinetics was investigated by measuring such quantities as the reaction rate from weight loss, the amount of CO adsorption and specific surface area by BET method. The reaction rates were large in the order of the Bintyo char, metallurgical coke, graphite and glassy carbon. If the rate was converted to the rate per unit area, however, those of the Bintyo char was smaller than that of graphite. Thus, it is suggested that the rate of the Bintyo char is influenced by the pore diffusion of CO2. The rate had a positive relation with the amount of CO adsorption, showing that the rate determining step would be the desorption of CO from the active side on the surface. The rate independent of surface area was derived, combining all the obtained data.

Jan 1, 2003