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By Edouard Asselin, Guikuan Yue

"In the present study, electrochemical measurements, especially cathodic potentiodynamic polarization (CPC) and cyclic potentiodynamic polarization (CPP), have been employed to study the kinetics of ferric reduction on chalcopyrite in aqueous Fe( II )-Fe(III)-H2S04 solution at 25°C and 70 °C. Results from the calculation ofspeciation in the above solution reveal that, at both 25 °C and 70 °C, the real Fe3+/Fe2+ ratio is much lower than the nominal ratio, which leads to smaller values for the reversible potential of the ferric/ferrous couple based on the Nemst equation. Exchange current densities of the ferric/ferrous couple were obtained by extrapolating the cathodic linear Tafel line to the reversible potential and are on the order of 10-7·10-6 A/cm2 at 25°C and 10·6-10-5 A/cm2 at 70 °C, respectively. The transfer coefficients were about 0.35-0.38 at 25°C and 0.35-0.45 at 70 °C. Polarization plots of CPC and CPP under different nominal Fe3+/Fe2+ ratios are in good agreement at 25 ·c and at 70 °C. Based on the obtained exchange current densities, the rate constant k, was calculated and is on the order of 10-1 cm/s at 25 °C and 10 1 cm/s at 70 °C.IntroductionChalcopyrite is the most abundant copper mineral in nature, accounting for about 70% of copper reserves in the world [I]. In recent years, the metallurgical industry has been searching for a hydrometallurgical process as an alternative to pyrometallurgical treatment due to high emissions of S02 and capital costs associated with smelting. Activity in this area has increased recently due to some inherent advantages associated with hydrometallurgical processing, such as the possibility of treating low-grade ores (increasingly more abundant in the case of copper) and easier control of waste, with the attendant benefits to the environment [I]. Chalcopyrite is highly refractory under most hydrometallurgical conditions, owing to the formation of an anodic passivation layer on the chalcopyrite surface which renders the process kinetics very slow. Most of the currently proposed processes are based on sulfuric acid with ferric ions and/or dissolved oxygen as oxidants. Sulfuric acid is preferred over all other leaching reagents in terms of cost, environmental friendliness, and ease of its regeneration during electro-winning. Some of these processes have been piloted in attempts to implement these technologies on an industrial scale,"

Jan 1, 2012

By Jian Li, S. Penttilä, P. Liu, W. Zheng, C. Bibby

"The materials selection for Gen IV supercritical water reactor in-core components faces major challenges due to severe operating condition. The current Canadian pressure-tube supercritical water (SCW) concept design requires core outlet temperature of 650 °C at 25 MPa with peak cladding temperature reaching as high as 850 °C. Aside from oilier challenges, there is currently very limited data on candidate stainless steels' corrosion resistance under this operating condition. Austenite stainless steels that include 316L, 304H, AL6XN and 3 l0S that cover a wide range of Cr contents are promising candidates for either direct in core applications or as base coating materials. However, their corrosion resistance has not been tested systematically under this stringent condition. In this study, these types of stainless steels are tested, and their corrosion resistances are compared.IntroductionThe Canadian pressure-tube supercritical water (SCW) concept will operate at a core outlet temperature of 650 °C at a pressure of 25 MPa, with potential peak cladding temperature reaching as high as 850 °C. High-temperature corrosion resistance is one of the key design requirements for fuel cladding components. As summarized by Allen [1 ], most testing to date has been carried out at temperatures below 730 °C. To date, SCW corrosion data above 600 °C is very limited. Even at relatively low temperature exposure to SCW (e.g. 500 °C), F/M steels develop a thick oxide layer rapidly, while some austenitic stainless steels develop thinner surface oxide. Ni based alloys appear to form very thin surface oxide, however pitting was observed in the vicinity of intermetallic precipitates [2-5]. Dissolution of major alloying components from all of these alloys could also pose significant problems for downstream piping [6]. Kaneda et al. [7] suggested some modified stainless steels provide better SCW general corrosion resistance, with no sign of SCC under the slow-strain rate test.Cho [8] suggested that as the Cr content increase, general corrosion resistance improved at 510 °C and 25 MPa. However, similar to Cho's work, most of the SCW corrosion resistance assessments were based on weight change measurement. This can be unreliable due to potential exfoliation of thick oxide film. Besides, there have been no systematic SCW corrosion resistance tests for candidate stainless steels under higher temperatures. SCW corrosion rate increase dramatically for alloys tested at 600 °C [1]. It is also important to understand the role of major alloying elements under this stringent operating condition, not only for fuel cladding components' materials selection, but also for coating materials development."

Jan 1, 2013

By Thomas J. O'Keefe, Pu Yu, George Houlachi, Xuewen Tang

"Impedance measurements were used to investigate the electrochemical characteristics of acidic zinc sulphate electrolytes containing Sb3+, gelatin and their mixtures. The data were correlated with cyclic voltammetry curves made using synthetic as well as industrial electrolytes. The cyclic voltammetry results were similar to those obtained in previous studies in that antimony caused a depolarizing effect while gelatin gave an increase in the potential for zinc nucleation on an aluminum substrate.The electrochemical impedance spectroscopy (ElS) evaluations were conducted on electrodeposited zinc at three overpotential values. The potentials were chosen to represent various current density regions in the zinc polarization curves. The antimony and gelatin gave characteristic impedance plots which correlated with expected behavior, particularly current efficiency. Both antimony and glue appear to modify the intermediate zinc reaction sequence, but in different ways. The data strongly suggest that film formation and stability are major factors in the zinc ion reduction mechanism.IntroductionThe zinc electrodeposition process is sensitive to the presence of a variety of organic and inorganic chemical species in the electrolyte [I]. Such components can produce either beneficial or harmful effects, depending on their relative concentrations and electrochemical behavior. Extensive investigations have been made to gain a better understanding of the changes occurring during zinc deposition in the presence of such additives. Techniques employed include microscopy, x-ray diffraction, dynamic voitammetry, current imd energy efficiency studies [2-5]. Ultimately, the objectives are to identify the factors which most affect the efficiency of the process and to provide a means to effectively control them.One of the most harmful impurities is antimony, which can be detrimental when present at concentrations as low as 10 to 20 parts per billion. Dramatic changes in zinc polarization behavior, deposition structure and current efficiency have been observed with antimony in the electrolyte. Antimony appears to lower the hydrogen overpotential by hydride formation or a similar catalytic mechanism, which allows an increase in localized corrosion and zinc dissolution [6-8]."

Jan 1, 1997

By S. S. Bogomolov

The relationship between the magnetic properties and micro- structures of Pr-Fe alloys rapidly quenched by melt-spinning and highly undercooled by containerless processing in the Cambridge drop-tube was studied. The maximum measured coercivity, Hc, of as-cast samples was 4450 Oe for Pr-2 wt.%Fe. However, rapid quenching or melt undercooling decreases coercivity for hypo- eutectic alloys (<10 wt.%Fe) and increases Hc for hyper-eutectic systems.

Jan 1, 1992

By M. Cross

Heap leaching presents a complex physico-chemical process to model and a significant challenge to develop a comprehensive model enabling reliable predictions of heap behavior over the long term. A computational modeling framework is described for the analysis of multi-phase flows in reactive porous media suitable for tracking metals recovery, for example, in heap leaching and environmental recovery processes. This modeling framework employs appropriately formulated, parameterized, and solution procedures to capture: 1) liquid and gas flow through heterogeneous porous media subject to variably saturated flow conditions, 2) the complex and dynamically changing nature of the porous media structure, 3) the transport of reactants and products of reaction, 4) the simultaneous mass and heat transfer, and 5) the role of bacteria as a catalyst for reactions. A second class of challenges to accurately model heap processes is to identify and then capture all the process data to characterize the reactivity of particular ores, the mine planning for the construction of the heap, leach schedules, meteorological data, etc. The objective of this paper is to outline these challenges and to describe a modeling framework that can cope with arbitrarily complex geometries and provide tools for rapid and accurate process assessment.

Jan 1, 2006

By A. V. Tarasov, V. M. Paretsky

"Based on theoretical and experimental studies into the specific features of the mechanism, kinetics, aerodynamics and heat transfer parameters of the flame-type oxidation of metal sulfides in a stream of technical-grade oxygen, a three-dimensional deterministic mathematical model of an oxygen-flame smelting furnace has been developed on the basis of the zonal method for computation of heat exchange. The model is presented in the form of equations taking into consideration the radiation component of the selective radiation, the convection component of mass transfer between the space and surface zones, heating of charge particles due to heat conductivity, accretions formation on a multi-layer refractory lining with inserted cooling elements. The adaptation of the model for a full-scale furnace has demonstrated the possibility for its use for computation of main smelting process parameters. Multifactor model investigations were conducted and the results obtained were applied using statistical methods for development of a simplified computational regression model describing the interrelation of the main output parameters: temperatures of flame, lining, slag and off-gas; heat fluxes to the lining; thickness of accretions; heat removed by cooling elements; copper content of matte. On the basis of this model, a block diagram of the algorithm was developed for control of the thermal conditions of the furnace, as well as the control algorithm itself.IntroductionThis paper presents the results of an integrated modeling and development of principles for control of copper smelting process using as an example the oxygen-flame smelting process (KFP) for treatment of sulfide concentrates at the Kovoguty Krompahy copper smelter (Slovakia) with a capacity of 20,000 tpy of copper."

Jan 1, 2001

By Jiann-Yang Hwang, Ying Qin, Shu-Jing Zhu

Metallurgical Oil Sludge (MOS) is a byproduct created in the process of steelmaking. More than a million tons of MOS are generated each year throughout the world. The material contains hazardous components such as heavy metals and pathogenic organics, which can cause serious environmental problems and health issues. Landfill, combustion, and pyrolysis have been investigated for the disposal of MOS. However, these methods are unsatisfactory since they are unable to reach the clean environment goal. In this study, we investigate the possibility of using MOS as a reductant in a high temperature metallurgical process. The results are reported and discussed.

Jan 1, 2015

By John Demol

Monazite, a rare earth and thorium phosphate mineral, is one of the major minerals processed for extraction of rare earths. Industry practice for treating monazite concentrates is to use either a sulfuric acid bake or caustic conversion route. In the sulfuric acid bake, monazite concentrate is mixed with concentrated sulfuric acid and roasted. The rare earth phosphate mineral is converted to rare earth sulfate which dissolves in a subsequent water leach. As the bake temperature increases above 300 °C, thorium becomes less soluble. Although acid baking is practised in industry, the bake reactions are not well understood. A combination of chemical analysis, XRD and SEM-EDS was used to identify reaction processes occurring during sulfuric acid baking of a 93 wt% monazite concentrate between 200 °C and 800 °C. The effects of these reactions on the leachability of the rare earths, thorium and phosphate were also examined.

By Gustavo Díaz, Miguel A. García, Carlos Frías

"Under the auspices of the Commission of the European Union, a consortium composed of six European organi~ations has conducted a project to scale up the PLACID electrowinning cell to industrial size within the Placid process development. This paper is concerning the results and achievement of the industrial cell prototype after more than 1,000 hours operating time and about 10,000 Kg electrolytic lead production. In general, results have been very satisfactory, demonstrating the ability ofthe PLACID electrowinning cell to produce top quality electrolytic lead (> 99.99 %) with high current efficiency and low energy consumption.IntroductionThis paper is concerning the development of an industrial size PLACID electrowinning cell within the PLACID process development. This project began on January 1993 and was finished on April 1996.Lead metal production and manufacturing industries produce large amounts of dusts and also lead bearing slags. Spent lead-acid battery recycling also produces lead oxides from the battery pastes rather similar to those mentioned above. Those lead secondary materials are hazardous and difficult to handle by usual procedures.Existing processes to treat-lead oxides may inflict considerable damage on the environment, incur high operating costs and have limitations to produce top quality lead.The main aim of this project has been to develop a novel hydrometallurgical process able to deal with different lead bearing materials, mainly lead oxide secondaries: lead-acid battery pastes, lead fumes, furnace slags, oxide residues, etc., producing ""four nines"" pure lead in an efficient manner with a benign influence on the environment; it is called the PLACID process."

Jan 1, 1997

By Keith E. Forrester

This paper presents results of laboratory and field optimization of a proprietary processes developed by FESI for the stabilization of heavy metal bearing wastes. The specific waste studies presented within the paper include foundry ash, aluminum sweat furnace ash and a heavy metal contaminated soil. The FESI process chemistry and engineered processes were found to be the most cost efficient demonstrated and available method of stabilizing heavy metals and highly successful in passing regulatory limits.

Jan 1, 1994

By G. Scavino

A 0.5 wt.% C, 22 wt.% Mn austenitic steel, recently proposed for fabricating automotive body structures by cold sheet forming, due to favorable overall strength and ductility, exhibits plastic localizations during uniaxial tensile tests, whereas no localization happens during biaxial Erichsen cupping tests. Full-thickness tensile and Erichsen specimens, cut from as-produced sheets, were polished and tested at different strain rates. During the tensile tests, the plastic localization phenomena consist first of macroscopic deformation bands traveling along the tensile axis, and then of series of stationary deformation bands, each adjacent to the preceding ones; both types of bands involve the full specimen width and yield macroscopically observable surface relief. No comparable surface relief was observed during the standard Erichsen tests. The stress state being known to influence plastic localization phenomena, reduced-width Erichsen tests were performed with 10 to 30 mm width polished specimens, in order to explore the transition from biaxial to uniaxial loading.

Jan 1, 2009

By Peter Hayes, Evgueni Jak, Ata Fallah Mehrjardi

Modern analytical tools, such as electron probe X-ray microanalysis (EPMA), are used in experimental characterization of phase equilibria and microstructures of complex slags. Integrated thermodynamic computer packages, such as FactSage, are used to provide more accurate descriptions of complex slag systems. These advanced methodologies have been applied to characterize dynamic steady state freeze linings in slag systems using submerged cold finger probes at controlled laboratory conditions, establishing the effects of bath chemistry, temperature, heat extraction rate and bulk fluid flow. It has been found that stationary freeze lining deposit interface temperatures at steady state conditions can be lower than the bulk slag liquidus temperature, and that stable operation below the liquidus is possible. A conceptual framework has been developed to explain the phenomenon and the range of interface temperatures that can be obtained in dynamic steady state conditions. These findings have important implications for the design of freeze linings and possible improvements to high-temperature metallurgical operations.

Jan 1, 2014

By Sung-Joo Lee, Gi-Chon Han, Nam-Il Um, Hee-Chan Cho

"In Korea, almost all of bottom ash produced by coal power plants is disposed of in ash ponds. Ash storage areas comprise more than 80% of most coal power plant sites. This disposal method is causing environmental problems and a managerial burden for plant operators. In this study, investigations to develop a beneficiation process for separating coal pond ash into various products were undertaken. To improve efficiency of the separation, coal ash was separated by sizes and each size fraction was subject to various beneficiation processes. The separation process used were flotation (-200 mesh size), hindered settling (16x200) and tabling (16x200 and 8x16 mesh). The results showed that various marketable products, such as lightweight aggregate, sand, high-carbon fuel, could be recovered from coal pond ash using simple physical separation techniques.IntroductionDue to the increased use of coals every year, about fifty million ton of coals were used in 2007 alone. As a result, about 6 million tons of coal ash were generated. In Korea, the coal bottom ash is classified as a general industrial waste and is usually disposed of in ash ponds. The costs for this disposal method continue to increase due to rising costs of site management and development and more strict environmental regulation. Therefore, utilities are constantly looking for ways to increase utilization of coal ash. In this study, various beneficiation processes were evaluated to examine the possibility of separating coal pond ash into various products which can be used as aggregates and high-carbon fuel."

Jan 1, 2008

By M. Rosales

Using the k-e turbulence model, a mathematical fluid dynamics simulation of the flow characteristics in a Teniente converter has been conducted. Two cases were studied: - Transversal sections in the smelting-converting zone; and - A three-dimensional simulation that includes the walls of the reactor The calculations give the velocities field, the gravity waves amplitude, the splashing behaviour, the phase distribution and the shear stress distribution. The latter helps to explain the pattern of refractory lining wear. The calculation includes the approximate shape and dimensions, and the eventual coalescence of bubbles.

Jan 1, 1999

By Xia Hong-ying, Peng Jin-hui, Zheng Zhao-qiang, Zhang Li-bo

"Preparation of activated carbon from the walnut shell by microwave assisted steam activation was studied. Influences of the three parameters, activation temperature, activation duration and steam flow rate on the adsorption capacity and yield of walnut shell activated carbon(WSAC) were investigated,optimization process was obtained by the Response Surface Methodology (RSM). The optimum preparation conditions were as follows: activation temperature of 980°C, activation duration of 41 min and steam flow rate of 1.66 ml/min. The optimum conditions resulted in an activation carbon with an iodine number of 1025 mg/g and a yield of 52.17%, while the BET surface area, total pore volume and average pore diameter of WSAC were 1328m2/g, 0.72ml/g and 2.2nm respectively. The study supported the potentiality of comprehensive utilization ofWalnut shell and the benefits of the microwave heating.IntroductionActivated carbons are one of the most important adsorbent materials in modern society because of its abundantly developed pore structure, strong adsorption ability, high surface area and thermo stability. They have extensive application in many industries fields which include gas purification [1], catalyst supports [2] and other pollutants [3]. However, in recent years, the industrial production of activated carbon is facing the problem of raw material scarcity and high cost, which limit to be widely used. Therefore, the selection of an appropriate precursor plays an important role and it has become hot sport to seek cheap raw material to lower preparation cost. As a kind of reproducible resource, the waste from agriculture and forestry is a high-grade raw material for preparing activated carbon due to is high carbon content, such as palm shell [4], rice hull [5], and coconut shell [6]. At present Walnut shell is widely accepted to be a renewable source of biomass. According to statistics, there is more than 1000,000 tonnes of walnut shells are produced in China annually [7]. As a good precursor for activated carbon production, Walnut shell is a major agricultural waste, to make better use of the cheap and abundant agricultural waste, it is proposed for activated carbon production."

Jan 1, 2014

By P. S. Dunn, A. D. Rollett, H. D. Lewis

"The results of preliminary work on the modeling and measurement of the heat transfer coefficients of metal/mold interfaces is reported. The system investigated is the casting of uranium in graphite molds. The motivation for the work is primarily to improve the accuracy of process modeling of prototype mold designs at the Los Alamos Foundry. The evolution in design of a suitable mold for unidirectional solidification is described, illustrating the value of simulating mold designs prior to use. Experiment indicated a heat transfer coefficient of 2 kW/m /K both with and without superheat. It was possible to distinguish between solidification due to the mold and that due to radiative heat loss. This permitted an experimental estimate of the emissivity, ~ = 0.2, of the solidified metal.IntroductionA feature that distinguishes casting processes from welding processes is the presence of an interface with a low heat transfer coefficient between the mold and the casting. Especially when chill casting, the interface delays the start of solidification and increases freezing times significantly. By comparison welds can be assumed to have a very high heat transfer coefficient. The heat transfer coefficient controls such phenomena as folds and laps on the surface of castings which can be crucial to the acceptability of a casting. The time delay for the start of solidification influences the occurrence of cold shut defects. The standard mold material for uranium casting is high quality graphite which is an excellent refractory when used in vacuum and coated with a refractory wash. Graphite is an effective chill material and has a thermal diffusivity approximately twice that of uranium. Experience has shown that practicable superheat without mold pre-heat is not sufficient for avoiding cold shut defects when casting in graphite molds.TheoryIt is possible to calculate the position of the freeze front s, as a function of time, t, the superheat and interface heat transfer coefficient, h, [1]. However, the value of h cannot be obtained explicitly. The Virtual Adjunct Method (VAM) [2] offers a method for extending the standard equation for an insulating mold where s is proportional to the square root of time. By considering the effect of the interface to be equivalent to finite thicknesses of mold and metal, the following quadratic equation is obtained,"

Jan 1, 1986

By L. A. Barta

A new process for the leaching of chalcopyrite concentrates has been developed and tested in miniplant campaigns and locked cycle testwork carried out between 1996 and 1999. The process involves pressure leaching in a sulphuric acid solution, e.g. raffinate from copper solvent extraction. Iron in the feeds is precipitated predominantly as hematite in the autoclave, simultaneously with copper extraction. Gold and silver in the pressure leach residue are recoverable by conventional cyanidation, following flotation to remove elemental sulphur by-product. The results of recent miniplant tests and batch locked cycle tests are provided.

Jan 1, 1999

By Vinay Kumar, Jae-Chun Lee, Rakesh Kumar, Manis Kumar Jha, Archana Kumari, Pankaj Choubey

Present work is a part of developing novel recycling technique for waste printed circuit boards (PCBs) i.e. the liberation of metals from PCBs by organic swelling followed by the treatment of resin to remove/ recover hazardous soldering materials. In order to recover the hazardous metallic constituent lead from the liberated resin, initially the leaching studies were made using fresh solder containing 63.9% Pb and remaining tin. Experimental results obtained in different conditions viz. time, temperature and acidity showed -97.20% of lead dissolution with 6M HNO3 at solid to liquid (S:L) ratio 1:10 (g/mL) and temperature 90°C in 75 minutes. The result of the studies validated with crushed PCBs shows that almost total lead and tin was leached out with 6M HNO3 and 6M HC1 respectively at S:L ratio 1:10 (g/mL) and temperature 90°C within 50 minutes. The results will be useful for the treatment and safe disposal of PCBs resin.

Jan 1, 2011

By T. Maruyama

The Tamano Smelter of Hibi Kyodo Smelting CO. ,Ltd. went into operation in 1972. The Flash Smelting Furnace that was originally adapted was equipped with electrodes that were attached to the settler substitute of the slag cleaning furnace. Later the development of our own original coke combustion technology was promoted and a new Tamano Type Flash Smelting Furnace (T-FSF), without electrodes, was put into operation in 1988. The technology of coke combustion and combustion the burner have continued to improve. As a result the copper losses in the slag have been reduced as well as a stable operation has been achieved. Furthermore, this has been accomplished while increasing the concentration feed and the matte grade The current objective is to continue to strive for high matte grade operation and to raise production efficiency while paying attention to the important subject of copper losses in the slag. In this report, the data related to the copper loss in the slag reduction are presented along with the influence of the thickness, settling time and coke. The recent operation conditions of the T- FSF are also presented.

Jan 1, 2003

By Aiyuan Ma, Kun Yang, Weiheng Chen, Jinhui Peng, Shiwei Li, Feng Xie, Libo Zhang

In this thesis, a new process of recovering zinc sulfide ores was developed. The novel synthetic coordination leaching process mainly included two steps: microwave assisted phase reconstruction and compound coordination leaching. By applying various techniques, such as chemical composition analysis, X-ray diffractometry (XRD) and Raman spectroscopy, it could be concluded that sulfide phases would directly oxidized to zinc oxides under the 500 ºC microwave roasting and adding 30% Na2O2. What’s more, zinc leaching rate reached to 61.16% within 2 hours. Compared to the current technologies, this procedure had the advantage of avoiding SO2 emission, high leaching efficiency, simple process, manipulate easily, and low cost, which could be expected tremendous application potentials.

Jan 1, 2016