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By Preston C. Holloway

Transformational roasting involves the heating of a material along with specific additives to induce mineralogical changes in the starting material. By controlling the chemical composition, roasting atmosphere, temperature and time of reaction, the mineral transformations induced during roasting can be engineered to control the distribution of valuable, or harmful, metals and to produce new mineral assemblages that are more amenable to conventional methods of metals recovery or to environmentally safe disposal. To date, this type of process has only been applied to the recovery of a limited number of metals, but current research is looking to expand the application of these techniques to the recovery of metals from a wider range of materials. An introduction to these techniques is presented along with preliminary results from their application to metals recovery from zinc bearing wastes, such as zinc ferrite leach residues and carbon steel electric arc furnace dust.

Jan 1, 2006

By Yuanbo Zhang, Guanghui Li, Zhenyu Fan, Tao Jiang, Xiaohui Fan

"Iron ore sintering process is the main source of SO2 generated in the steel industry, of which the discharge amount of SO2 emission accounts for about 60% of the total. Aiming at the features of sintering flue gases and existing problems during the flue gas desulphurization, a technical route of flue gas circulation sintering (FGCS) for iron ores has been put forward. Under the simulated experimental conditions, effects of FGCS process on the main output and quality indexes and SO2 emission rule are researched using simulating flue gases. Compared the novel FGCS with conventional sintering process, SO2 in the final sintering flue gas is obviously enriched and the total exhaust gases can be reduced evidently. The decreasing of oxygen content in circulating gases has bad effect on the sintering indexes. Increasing the oxygen potential is beneficial to obtain high quality sinters. This investigation shows that the FGCS process is promising.IntroductionSteel is a kind of essential material for modern society, but steel-making process is characterized by high energy-consumption and emission as well as heavy environmental pollution. Chinese steel industry has developed rapidly in the last decade, and the environmental problem caused by ironmaking and steelmaking have also aroused the greatest concern, especially the atmospheric pollution caused by SO2, CO2, etc. Iron ore sintering process is the main source of SO2 generated in the steel industry, of which the discharge amount of SO2 emission accounts for about 60 % of the total. The development of the desulfurization process for sintering flue gases to reduce SO2 emission in sintering process is not only the requirements of sustainable development but also the most important environmental tasks for steel industry [1-5]."

Jan 1, 2011

By Yang Jian-guang, Deng Zi-xiang, Zhang Xu-liang, Li Jun-yuan

"Hyperaccumulator biomass harvested after heavy-metal phytoremediation must be considered as hazardous waste that should be contained or treated appropriately before disposal or reuse. As a potential method to detoxify the biomass and to convert this material to a suitable bio-energy resource, the hydrothermal upgrading process was applied to remove heavy metals and upgrading crude bio-oil from Pteris vittata stems and leaves harvest. Parameters such as material granularity, temperature, Liquid/Solid (L/S, ml/g), pressure, duration and catalysts were examined for their effect on the removal efficiency of heavy metals and upgrading efficiency of crude bio-oil. Maximum heavy metal removal efficiency of>99% and crude bio-oil upgrading efficiency of 83% were attained with an 200 mesh (75 µm) granularity, LIS 40:1and23 MPa at 380°C in the presence ofO.l mol L-1 K2C03 for 30 min. GC-MS analysis results show that the resulting bio-oil mainly consists of benzene 11 %, ketone 42%, alcohols 14%, alkene 15% and ester 11 %, etc., and the relative molecular weight distribution lies in 94-282, carbon number distribution lies in 6-18, calorific value is 32MJkg-1.IntroductionPhytoremediation of soil or water with hyperaccumulator has been extensively explored in recent years [1-4]. Living plants can clean up soils or waterways. This approach exploits the ability of various plant species to thrive in high metal environments where large amounts of toxic elements are accumulated, such as heavy metals, and is particularly appropriate when slow remediation of relatively low metal concentrations is acceptable. Advantages compared with existing remediation methods include the minimal site destruction and destabilization, low environmental impact, and favourable aesthetics; advantages compared with biosorption include continuous in situ regeneration of the biomass, and the ability of living plant cells to supplement passive sorption of metals with metabolic mechanisms of metal uptake and detoxification [5-8]."

Jan 1, 2014

By Xu Weihong

After being pre-treated, composite electro-deposits of semi-bright nickel/nano-SiO2 with bright nickel or with amorphous Ni-P alloy, and Composite electro-deposits of Zinc were prepared on Nd-Fe-B magnetic material. The effect of cathodic current density, nano-SiO2 concentration, stirring strength and surfactants on the corrosion resistance of electro-deposits were studied. In addition surface appearance and structure of the composite coatings were analyzed by SEM. The present investigation shows that the corrosion resistance of composite electro-deposits of semi-bright nickel/nano-SiO2 with amorphous Ni-P alloy was the best, the solution system of semi-bright nickel/nano-SiO2 with bright nickel was stable and its electro-deposits also had an excellent corrosion resistance, composite electro-deposits of Zinc not only had good corrosion resistance, but also low cost, thus making it an excellent electro-deposit for medium or low-class Nd-Fe-B magnetic material.

Jan 1, 2006

By John ?gren, Martin Schwind, Henrik Larsson

"A new model for internal oxidation, as well as similar processes, has been implemented on computer. It is based upon a combination of random walk and cellular automata and is capable of treating 3-dimensional cases. To model diffusion, it utilises quantised units of matter. All steps of the process are included: nucleation, growth and coarsening. The effect of grain boundaries on diffusion as well as nucleation is taken into account. Further possible development is briefly discussed; especially the treatment of nucleation needs further consideration. IntroductionComplex diffusion-controlled processes may now be simulated on a routine basis when concentration varies along one co-ordinate only. One-dimensional simulations capture much of the information of interest but not all. For the case at hand, especially the spatial and the size distribution of precipitates, as well as the impact of grain boundaries, would be interesting information not accessible from 1-D simulationsSolving the full Fick-Onsager law in three dimensions does not seem feasible with the computers of today. In the model described in this article, random walk by quantised units of matter are considered. The model should be useful for a number of cases involving dispersed systems. With further development, it would indeed seem possible to simulate most types of phase transformations.Previous workWe have previously published two articles [1,2] on the new approach discussed in this work. In those articles we described the basic idea and showed, among other things, that very good agreement with an experimental concentration profile can be obtained, in a single-phase system, using independently assessed thermodynamic and kinetic data. Also, Schwind used the same random walk based concept to model coarsening [3]."

Jan 1, 2001

By T. A. Venugopalan

The 'Hall-Heroult' Process of reduction of Alumina to Aluminium has remainded basically the same for over 100 years, but the technology has been undergoing drastic changes with respect to selection of materials for Cathode and Anode, and also energy consumption. The latest generation pots have a working life of about 1800-2000 days normally. After the failure of the pots, the Cathode Lining is dug out and disposed of on land. Since the lining contains objectional materials causing pollution, various processes have been tried for re-processing of this waste. However, most of the processes have been unsuccessful from the techno-economic point of view. At Hindalco a new chemical process for converting the fluorine values of the dug out material to Cryolite was developed in 1988 and a" one ton per day Cryolite production plant has been operating since 1989. This process is especially applicable where the integrated Alumina and Smelter Plants exist side by side. The experience in operating this Plant is discussed in detail in the paper.

Jan 1, 1992

By E. S. Peterson

The selective separations of trace metals- and organics from water are processes of importance to industry. The application of a new metals capture technology coupled with polymer membrane technology has proven to be one avenue to accomplish such selective separations. The polymers used in these studies are polyphosphazenes. Polyphosphazene polymers consist of an alternating backbone of nitrogen and phosphorus atoms. The polymers have high thermal and chemical stabilities. Experiments at the Idaho National Engineering Laboratory demonstrate that polyphosphazene membranes coupled with Chromato Chem,"Chelation Chromatography" process are capable of removing both chlorinated hydrocarbons and metal ions from process streams. These results point to a wide range of potential industrial and environmental applications for such systems. Data will be presented which show the efficiency and selectivity of separations, postulated separation mechanisms, and the initial designs of industrial demonstration units which are currently under construction. Parts of this work have been performed under a Cooperative Research and Development Agreement (CRADA) between ChromatoChem, Inc. and Idaho National Engineering Laboratory (INEL). The work at INEL was been sponsored by the United States Department of Energy's Office of Industrial Technologies

Jan 1, 1995

By Roland Kammel

In combination with various physical and chemical methods also electrochemical techniques are most frequently used to improve the recovery of metals from aqueous dilute process streams or effluents e.g. in electroplating, metal finishing, mining and metallurgical plants. To insure cathodic metal recoveries with favorable current efficiency and high throughputs per unit of cell volume seve¬ral types of electrolysis cells have been developed comprising extended electrode surface areas and/or intensive electrolyte. agitation. The practical experiences with these units indicate especially for the electrolytic recovery of metals whose values are high, that the treatment cost permits profitable operations with relativly short payback periods for the units. Anodic reactions can be utilized for the removal of undesired anion contents or buildups of impurities. Appropriate combinations of these recovery methods are used to improve the versatility and the overall economy. Industrial applications reveal their potentional as addidtive techniques for existing processes to reduce the metal content of effluents to values that meet the guide lines of environmental legislation whereas integrated in-operation recovery methods are nowadays increasingly introduced to approach nearly close-loop operations.

Jan 1, 1992

By I. J. Moon

The reduction behavior of hematite by H2 and H2-CO gas mixtures was investigated to elucidate the reduction mechanism at 800-950 °C. The hematite compacts were made by Cold Isostatic Pressing to produce compacts of uniform shape and size. The compacts were sintered at 1000° C for 30min, and showed a contraction of 29%. Mercury pressure porosimeter was used for measuring the total porosity, pore size distribution and pore surface area of the compacts. Reduction was measured by means of weight-loss technique using Cahn Balance (Model : TG-171, capacity log, accuracy f 10pg). Microscopic examination and X-ray analysis were used to correlate the structure of reduced compacts with the mechanisms of reduction. Neither chemical reaction control nor diffusion control is adequate in describing the complete course of reduction of the hematite compact. The reduction of hematite compacts was initially controlled by the chemical reaction at oxidelmetal interface. The reaction goes through a transition phase .where it is undergoing a mixed control, followed by the diffusion control towards the end of the reduction. The values of apparent activation energies for chemical reaction control were 3.48-8.43 kcal/mol depending on the gas compositions.

Jan 1, 1997

By Shadia J. Ikhmayies

"Cadmium telluride (CdTe) is a very interesting material that has many applications. Thin films of p-type CdTe can be used as the absorber layer in the heterojunction CdS/CdTe thin film solar cells in which n-type cadmium sulfide (CdS) works as the window layer. A review of the photoluminescence (PL) spectra ofp-type CdTe thin films prepared by different techniques was performed. The presence of defects and impurities such as oxygen and chlorine influence the PL spectrum. Copper and other dopants change the PL spectra and enhance the defects band. Chemical-heat treatment especially with CdCh is known to improve the quality of CdTe thin films because it decreases the Cd vacancies and quenches deep traps, so it enhances the PL signal. A discussion of chemical-heat treatment especially with CdCh, the effect of the ambient atmosphere, and that of the measuring temperature is performed.IntroductionCadmium telluride (CdTe) is a II-VI compound semiconductor that has a cubic zincblende (sphalerite) structure with a lattice constant of 0 A4~11]. Other than all of II -VI semiconductors, CdTe can be made both n- and p-type. But due to self compensation it is not easy to get p-type CdTe films [2]. Polycrystalline CdTe thin films are interesting because they have a lot of applications. Most of the problems associated with the use of these films are attributed to inhomogeneity, self-compensation, and the difficulty of forming a stable and lowresistivity ohmic contact [3]. CdTe technology has been established for a large number of applications, including solar cells, optical and nuclear detectors, and thermal- and radiationimaging devices [3]. At present, the highest demonstrated conversion efficiency for a CdTe based heterojunction (ID), with CdS as a window layer, is 16.5% [4, 5]. CdTe thin films can be prepared by different experimental techniques, such as thermal evaporation [l], electrochemical deposition (ED) [3], close-spaced sublimation (CSS) [3, 4, 6], physical vapor deposition (PVD) [3], chemical molecular beam deposition (CMBD) [7], and close space vapor transport (CSVT) [8].The objective of this paper is to make a review of the photoluminescence (PL) spectra ofp-type CdTe thin films prepared by different techniques and discuss the factors that influence the PL spectra. The composition of the film is very interesting in determining its PL spectrum. Different kinds of defects, impurities and dopants have their finger prints in the PL spectrum. Deposition techniques and deposition parameters such as the deposition temperature and ambient atmosphere also have their influence. Heat and chemical treatments which are known to improve crystallization and reduce the defects change the PL spectrum."

Jan 1, 2013

By H. Soto, J. Jara, F. Nava

A method has been developed to recover cyanide and copper from solutions containing copper complexes and thiocyanate. Copper is precipitated as copper thiocyanate or as copper cyanide depending on pH and the concentrations of thiocyanate and cyanide in the effluent. The copper precipitate assays over 50% copper and presents good dewatering characteristics. After settling it can be separated from the effluent by filtration. The solution containing the bulk of the cyanide is then oxidized with ozone to transform the remaining thiocyanate into cyanide. This results in a regenerated solution rich in free cyanide that can be recycled to the cyanidation process. Careful control of the pH of the solution is required. First, pH of the effluent is lowered to optimize the precipitation and oxidation stages, then the pH is restored to an alkaline value to regenerate the cyanide solution. Recoveries of over 96% copper and cyanide were obtained in laboratory tests using industrial solutions. With this procedure, cyanocidic gold/copper ores could be treated economically by heap leaching, since the cyanide consumed by the copper impurities could be regenerated at very low cost (most of the cost of cyanide regeneration would be compensated by the copper credits). In order to achieve this, a bleed of the barren solution could be treated by the proposed method, and then recycled to the leaching step. The volume of solution to be treated should be large enough to keep a cyanide/copper molar ratio higher than 3:1. This would assure that copper does not cause undue interferences in the leaching or the carbon adsorption stages. If the thiocyanate content is low, the oxidation stage can be avoided, and the solution can be recycled to the leaching stage directly after the solid-liquid separation stage.

Jan 1, 1997

The oxidation of ferrous ions by oxygen in sulphate solutions is a very slow process, but it tills long been known that the addition of sulphur dioxide increases the rate of reaction very significantly. The kinetics and mechanism of the process were investigated in the laboratory and the results confirmed the advantage of adding small amounts of sulphur dioxide to the oxygen stream for the removal of iron from solutions. The effect of various parameters on the overall rate of iron oxidation and precipitation was studied. In particular, temperature, acidity and composition of the gas mixture were considered and the optimum conditions for the precipitation of goethite were determined.

Jan 1, 1991

By V. E. Antonov

Hydrides of iron and iron-based alloys are thermodynamically stable only at hydrogen pressures in the gigapascal range and rapidly loose hydrogen under ambient conditions. At low temperatures, however, these hydrides can be retained in a metastable state at atmospheric pressure after being cooled under the high pressure to liquid nitrogen temperature. This review will discuss the current state of studies on phase transformations in the Fe-H and related systems and also on the composition, crystal structure and physical properties of the hydrides, both under high hydrogen pressures and in the "quenched" metastable state at ambient pressure. The studies at ambient pressure include magnetization measurements, X-ray and neutron diffraction, Mossbauer spectroscopy and inelastic neutron scattering. In the sections on Mossbauer and structural investigations of hydrides of Fe-Cr and Ni-Fe alloys new experimental results will be presented.

Jan 1, 2002

By Russell James Hewertson

Since 1989 Air Products and Chemicals, Inc. has converted over 40 air fuel fired furnaces to oxy-fuel and air-oxy-fuel. Advances in burner design, flow control technology and operating experience have lead to improved performance with quicker melt times and lower costs. Metal recoveries are improved by faster melting and better furnace atmosphere control, allowing lower grade materials to be processed economically. The presentation will discuss the improvements made in recent years and review data from state of the art installations.

Jan 1, 2000

By Chikabumi Yamauchi

The comprehensive scientific development of conventional industrial technologies stimulates the creation of new ones in the next generation. Prof. Akira Yazawa has just accomplished such an important work in the non-ferrous pyrometallurgical field. The results of his successful research are immortal. The research group of the author has conducted since 1985 fundamental studies on the application of sodium carbonate slag to copper fire refining. In the present paper, a calculation method for the distribution ratios of impurity elements between sodium carbonate slag and molten copper will be shown. The specific treatment by sodium carbonate slag will also be presented as an effective way for reducing each impurity content in the molten copper to 0.1 mass ppm, which is the level required for the production of high purity copper. The thinking-out of this evaluation method gets a hint from the Equation (2) in the text which was proposed by Prof. Akira Yazawa.

Jan 1, 2003

By Chenhui Liu, Ka-ma Huang, Hong-ying Xia, Bingguo Liu, Hua Chen, Jinhui Peng, Libo Zhang

"The rising popularity of microwave heating in mineral processing has fuelled the need for knowledge concerning dielectric properties of minerals. Dielectric property and microwave absorption property of anthracite were measured over a temperature range of 20-100°C at 2.45GHz by using an open-ended coaxial sensor measurement system. The results show that the dielectric constant, loss factor and loss tangent increase with temperature rising at 2.45GHz. Microwave absorption properties of anthracite are highly dependent on temperature and frequency. At frequency of 2.45GHz frequency used in microwave metallurgy, anthracite is suitable for reducing agent to achieve fast elevation of temperature then returning to original state. The research will be helpful in explaining the thermal running of microwave dielectric heating the anthracite.IntroductionThe application of microwave heating in minerals processing and treatment has recently attracted great interest from the metallurgical industry. Compared with conventional heating methods, the advantages of microwave heating include rapid and selective heating, uniform distribution, high efficiency, fast on and off switching as well as flexible and modular design[l-3]. As a result of these advantages, microwave heating has been applied in a variety of mineral processing and extractive metallurgy, such as microwave-assisted ore grinding, microwave heating for carbothermic reduction and acid leaching of ilmenite ore, microwave drying, microwave-assisted roasting and smelting of sulfide concentrate, microwave-assisted spent carbon regeneration and microwave-assisted waste management [ 4-6]. Though the application of microwave heating in the metallurgical industry is promising, further studies on the interaction between microwave radiation and minerals and its effects are highly desired to develop innovative techniques for minerals processing and ore treatment using microwave heating [7]."

Jan 1, 2013

By Napisporn Memongkol

Syntheses of Al-TiC-Al2O3 and Al-SiC-Al2O3 composites were obtained in situ by carbothermal reduction of mixtures of Al powder, TiO2 powder and activated carbon powders and Al powder, SiO2 powder and activated carbon powders. The reductions were carried out in a horizontal tube furnace under flow of inert gas. The standard Gibbs energy minimization method was used to calculate the equilibrium composition of the reacting species. The synthesized products were mixtures of aluminum reinforce with titanium carbide and alumina and aluminum reinforce with silicon carbide and alumina. The effect of the reaction temperature (1000 o C ? 1200 o C) and condition of precursors on the Al powder, TiO2 powder and activated carbon powders and Al powder, SiO2 powder and activated carbon powders were investigated using XRD and SEM method. The synthesized products showed those composites with aluminum matrix and titanium carbide and alumina as reinforced phases and aluminum matrix and silicon carbide and alumina as a reinforced phase was formed.

Jan 1, 2006

By Claudia Gasparrini

Uranium occurs in a variety of minerals, the more common primary ones of which are uraninite-pitchblende, coffinite and a group known as the complex multiple oxides. Identification and description of the uranium-bearing and associated minerals in ore samples may give a preliminary indication of the potential economic importance of the deposit and may also suggest initial approaches to metal extraction. The present paper reviews the common uranium minerals, describes their manner of occurrence and compares the types of deposits with which they are associated. Methods and techniques for their identification are described and their leaching characteristics discussed.

Jan 1, 1981

The kinetics of the oxidation of cyanide by manganese dioxide was studied using a rotation disc electrode system. The rate? of the half-cell reaction of cyanide oxidation is increased at higher hydroxide concentrations. An addition of copper up to 0.001 mole/l was found to enhance the diffusion current, especially at a high hydroxide concentration (0. 1M). A similar enhancement of the reaction rate is also achieved with nickel added at levels up to 0.01 mole/l. Manganese dioxide however requires a i:ow pH to achieve reasonable reduction rates. Leaching studies indicated that the initial reaction rate is strongly dependent on pH, initial concentration of cyanide. Using manganese dioxide cyanide could be oxidized at neutral pH's and ambient temperatures.

Jan 1, 1989

By Alan James Parker

Chalcopyrite can be converted to pure copper by the following five steps. An exothermic sulfation roast of chalcopyrite; leaching of cupric sulfate from the calcine with dilute acid; precipitation of Chevreul's salt and or other copper sulfites with ammonium sulfite or precipitation of crude copper by autoclaving ammonium sulfite and cupric sulfate at 150°C; dissolution of Chevreul's salt, or the crude copper, as cuprous sulfate, using acidic cupric sulfate in an acetonitrile-water solution as oxidant; precipitation of pure copper by thermal disproportionation of the cuprous sulfate solution. Acetonitrile and acidic cupric sulfate solution recycle. Advantages over conventional processes include lower cost, lower energy consumption as waste heat, sulfur removal as ammonium sulfate or gypsum, rather than as sulfur dioxide and rapid throughput. The net reaction is: 2 CuFeS2 + 4H20 + 15/2 02 + 8 NH3?2Cu + 4 (NR4)2 SO4 + Fe2O3

Jan 1, 1976