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By C. O. Bounds

Management of emission control dust from electric? arc furnace (EAF) steelmaking as an RCRA-EPA listed hazardous waste places economic and environmental pressures on the steelmaking industry. Horsehead Resource Development Company, Inc. (HRD) serves the industry by recovering nonferrous metals from the dust in rotary kiln plants in Palmerton, PA and Chicago, IL, and has demonstrated the commercial viability of its patented coal-fired FLAME REACTOR Process. However, because of location and/or regulation, many steelmakers could be more economically served via on-site processing of its dust. Therefore, in 198-7, through a contract with the Gas Research Institute, HRD embarked on a program to develop a gas-fired reactor and test a prototype unit. The development program has successfully proven the environmental, technical and economic performance of the concept. Consistently high zinc, lead and cadmium recovery to an oxide concentrate as well as production of a nonhazardous, delistable slag have routinely been achieved. The gas-fired FLAME REACTOR field experiment results and the economic performance of on-site or smaller regional plants will be highlighted.

Jan 1, 1990

By Steven Wright

The reduction of a slag produced 6om the recycling of lead batteries was studied in a kilogram scale laboratory investigation by reacting with graphite at temperatures of 1180 and 1200°C. Simultaneous reduction of PbO, Fe203, Sb203 and As203 occurred with the Sb and As reporting to the metal while the lead content in the slag was above 2 wt%. The Sb and As distributions between metal and slag were strongly affected by temperature and slag oxidation state. The rates of reduction of PbO and Sb203 increased with increasing slag basicity and temperature and decreased as the PbO content in the slag decreased. The reduction rate of PbO from these slags was similar to other industrial lead slags at the same CaO/SiO2 ratio and temperature. The implications of the behavioural similarities of the antimonous slags during reduction with carbonaceous reductants and other lead slags are briefly discussed.

Jan 1, 1994

By A. R. Kiani-Rashid

In this paper, the effect of aluminum content on the formation mechanism, volume fraction, morphology and particle size distribution of graphite has been investigated. Addition of aluminum on ductile iron causes some fundamental changes in iron-carbon phase-diagram and as a result, improves the graphite formation during eutectic transformation. The results reveals that aluminum compounds have been formed in the core of graphite nodules, thus aluminum plays an important role in the formation of graphite nodules. Furthermore, it is indicated that an increase in the aluminum content also leads to an increase in the number of graphite nodules and a decrease in the nodules size. By using EPMA, the segregation of aluminum and silicon between graphite nodules has been studied

Jan 1, 2010

By R. Boussaa, Y. Fautrelle, K. Zaidat, O. Budenkova, B. Saadi, X-D. Wang, L. Hachani, H. Ben Hadid

"Comparison of experimental data obtained in a benchmark experiment of solidification of a Sn-3%wt.Pb ingot and numerical results of two-dimensional and three-dimensional simulations of the process is presented. The benchmark experiment consisted in solidifying a rectangular ingot of Sn-3%wt.Pb alloy using two heat exchangers. Conditions of solidification were thoroughly controlled due to six thermocouples embedded into each heat exchanger. Due to another array of thermocouples the evolution of the temperature field at a lateral wall of the crucible was registered during the whole experiment. A treatment of the temperature data provided an estimation of the velocity field in the experiment. Post-mortem analyses of the sample provided the pattern of macrostructure of the sample and qualitative segregations pattern. 2D and 3D numerical solidification models are developed to give the distribution of the solute in a solidified sample.IntroductionConvection, either natural or forced, plays a very important role during the solidification. Its intensity and flow pattern affect heat and mass transfer and, consequently, macrostructure and segregation in a solidified ingot [1-4]. The effect of buoyancy convection during solidification has been studied in many laboratory-scale experiments [5-6]. Due to these experiments a general comprehension of formation of various defects in the ingot has been achieved. However, mentioned studies were not consistent since alloys, solidification conditions and configurations were every time chosen arbitrary. That is why the role of each parameter characterizing solidification process remains unclear. Moreover, the question of reproducibility of defects under the same solidification conditions still exists. In addition, most of the experiments suffer from the insufficient knowledge of control parameters that makes difficult their use for validation of models for solidification. These parameters serve as boundary conditions for numerical modeling and their incomplete description leads unavoidably to the errors in simulations. This situation motivated us to develop a setup for benchmark solidification experiments and to perform a set of the solidification experiments which we reported in [7]. Here we presented a comparison between results obtained in a benchmark experiment of solidification of Sn-3%wtPb ingot and its numerical modeling, which was performed in two-dimensional and three-dimensional configurations."

Jan 1, 2012

By G. Van Weert

Refractory gold ores and auriferous concentrates containing silver tend to form refractory silver jarosites during pressure oxidation. Earlier work with pure Ag2S has shown that the addition of iodine species to the autoclave feed yields cyanide soluble iodargyrite (Agl) instead. Near complete silver extractions from the autoclave product were obtained at a I-/Ag+ ratio of 5 or more. This paper reports on the pressure oxidation and cyanide leaching of two industrial refractory (arseno) pyritic silver-bearing concentrates: 1. from Peru (sulphosalts) and 2. from the USA (pyrite, with acanthite occlusions). While using a I-/Ag+ mol ratio of only 1 in the feed, it has been possible to obtain 98 and 97% Ag extraction from the two autoclave products by cyanide leaching, respectively. This compares to 11 and 54% Ag extraction from the as-received concentrates and 4 and 15% Ag extraction, respectively, after pressure oxidation without KI present. The results of the testwork are discussed in terms of concentrate mineralogy and pressure oxidation conditions.

Jan 1, 1994

By Zhijing Zhang

Sodium borosilicate is the basic composition of coating materials, Vycor and Pyrex glasses. In the present study, viscosities of Na2O-Si02-B2O3 ternary melts were measured under various compositions and temperatures. Experiments were carried out using rotary viscometer and graphite components. Our experimental results were compared with those in literature. Based on present experimental results, the previous structure based viscosity model was modified. The predicted viscosity results are in excellent agreement with the present experimental data in the temperature range with molten state samples. The fitting ranges of the model cover the composition of XB2O3 from 0.1 to 0.6 combined with xSio2 / xNa2O = 0.5, 1,2 and 5 respectively.

Jan 1, 1998

By Goran Vukovic

The use of gas purging plugs in the copper industry is a widely used practice. They provide substantial improvements especially in anode refining furnaces, where savings in process time and energy are obtained as well as refractory wear and buildups inside the furnace are minimized. The newly developed system, enables purging plugs to be implemented in both stationary and tilting furnaces, is in operation in vessels on three continents. An additional advantage in these furnaces above all other benefits is the significantly improved melting rate. This innovative and patented gas purging system consists of a purging plug cooling device and a slidable, cooled piping system. It provides compensation for any thermal expansion in the furnace lining and minimizes the risk of undesirable copper infiltration. User experiences and results of this widely used system are reported in this paper.

Jan 1, 2014

By Wayne Bell, Shivanand A. Borkar, Anish Upadhyaya, Matthew D. Andriese, Jiann-Yang Hwang, Zhiwei Peng

"A refractory ore body located in Michigan’s Upper Peninsula contains high concentrations of nickel and copper chiefly occurring in the minerals pyrrhotite, chalcopyrite, and pentlandite. Refractory ore bodies are difficult to treat by conventional mineral processing methods so microwave pre-treatment of the ore is employed to increase metallic-particle/host rock liberation by making use the differential thermal expansion properties of the mineral phases that absorb microwave energy. The Curie temperature measurement of metallic-bearing particles is in agreement with the known value for pyrrhotite occurring at 325°C. A nickel-rich iron sulfide mineral is found to be in occurrence and also appears to be magnetic under BSE imaging. It is shown the ore particles heat rapidly when exposed to microwave radiation for short durations of time mainly due to the high concentration of ferromagnetic mineral phases. Rapid heating causes thermal expansion of constituent mineral phases that produce cracks within ore particles. SEM imaging shows fracture occurring along grain boundaries and throughout host rock matrix. Ball milling experiments show an increased grindability of the ore resulting in a decrease in work index values.IntroductionCrushing and grinding operations consume 50-70% amount of energy used in mineral processing operations [1]. All these processes involve high energy impact of surfaces to develop compressive stresses that produce cracks to initiate breakage of particles. Microwave pre-treatment of certain types of ore might provide an energy savings to these type grinding processes by taking advantage of the tensional forces produced by selectively heating microwave absorbing type mineral phases. The heating of ore particles produces cracking by thermal expansion of the constituent mineral phases. Conventional heating has been investigated and shown to positively aid in grinding processes but determined energy inefficient to be used commercially."

Jan 1, 2011

By Olga Karabelchtchikova

Keywords: Multipass grinding, Residual stress, Retained austenite, X-ray diffraction The study investigated residual stresses behaviors and their superposition effect in D2 dies for thread-rolling applications. A nested factorial experiment was applied to test hypotheses that the residual stresses profiles change due to combination of heat treatment and multipass grinding operations, and that certain patterns can be derived due to the memory relationship between pre-existing and final residual stresses distributions. The amount of the retained austenite along with residual stresses in variation with depth was measured using x-ray diffraction technique. Statistical analyses indicate that the proposed hypotheses hold. Residual stresses distributions as well as tensile peak location were found to be significantly influenced by the treatment parameters used. Unique characteristic patterns in the residual stresses profiles were observed due to multipass grinding technique across all experimental conditions. This finding suggested a plausible memory relationship between the cutting passes, and the causes of the foregoing results are further proposed and discussed.

Jan 1, 2005

By Teruo Bitoh, Shogo Izumi

"The effect of B203 flux melting on the structure and the soft magnetic properties of the (Feo.1sBo.20Sio.os)96Nb4 bulk metallic glasses prepared by casting has been investigated. The ringshaped bulk specimens were prepared by the B203 flux melting and copper mold casting. It was confirmed that the flux melting promotes the precipitation of the a-Fe(-Si) and Fe2B phases in the central region of the specimens. The ring-shaped bulk specimens show a flat hysteresis curve, indicating a good linear relationship between the magnetic induction and the applied magnetic field. These results show that it is possible to develop a new soft magnetic material that exhibits constant permeability, which is necessary for producing inductors and choke coils.IntroductionSince the success of forming Fe-based bulk metallic glasses (BMGs) with good soft magnetic properties, great attention has been developed to synthesis and properties of the BMGs [l, 2]. The BMGs have high glass-forming ability (GFA) and, therefore, they can be used to prepare bulk amorphous alloys with a thickness of the order of a few millimeters by casting. The soft magnetic properties of Fe-based BMGs are better than those of ordinary amorphous alloys; therefore, these BMGs have wider applications as soft magnetic materials [3-5]. It is often required for soft magnetic materials that the shape of the hysteresis curve is changed according to the demands of applications. For example, materials with ""flat hysteresis curves,"" which means the magnetic flux density (B) and the applied magnetic field (H) show a linear relationship up to rather high magnetic field, are necessary for producing inductors and choke coils. Flat hysteresis curves can be easily achieved by creating an air gap in the magnetic path. However, magnetic flux leakage generated in the air gap inhibits high-density packing of the electronic components. In order to achieve flat hysteresis curves without creating an air gap, Fe-based ordinary amorphous alloys are subjected to crystallization by annealing and transformed into thin surface layers of a-Fe; the crystallization results in the compression of the remained amorphous phase [6]. Another way to achieve flat hysteresis curves is the formation of secondary phase (such as Fe2B) that act as pinning site of magnetic domain wall displacements [7]."

Jan 1, 2013

By Carlos A. Nunes

V-AI alloys have been used commercially to produce pure vanadium by Electron Beam Melting (EBM), as well as to obtain Ti-based alloys (ex. Ti-6AI-4V). The aluminothermic reduction of vanadium pentoxide (V205) is the primary method to obtain these alloys. Concerning the obtention of pure vanadium, earlier studies have indicated alloys presenting Al content between 10 and 15wt% as the most suitable alloys for direct EBM. In the present work we investigated the aluminothermic reduction of V205 in order to define process parameters for the obtention of V-AI alloys with composition in the previously mentioned range. It was studied basically the effect of excess AI, CaO addition and reaction atmosphere (air, argon) on the alloy composition (AI, 0, N). In addition, microstructural analysis of selected alloys by SEM (BSE images) and EPMA (WDX) were also performed.

Jan 1, 1996

By John E. Dutrizac, Tzong T. Chen

"Laboratory experiments were undertaken to ascertain the behaviour of various ""impurity"" species during the precipitation of hematite directly from ferric sulphate solutions at 225°C and in the presence of 40 or 50 g/L of hematite seed. Copper, nickel and zinc are not significantly incorporated in hematite precipitates. Although the nickel contents increase to 0.22% as the Ni concentration increases to 60 g/L, the solid solution Ni contents are low relative to the bulk Ni contents. Thus, part of the Ni may be present as tiny particles of poorly soluble NiS04.H20. Increasing germanium concentrations to 2,000 mg/L result in products containing up to 0.59% Ge. The Ge occurs either in solid solution in the hematite or is adsorbed on the nanometer-size hematite crystallites. Increasing As(V) concentrations to 10 g/L increase the AsO4 contents of the products up to 16%. However, the products consist of hematite together with As04-containing Fe(SO4)(OH) and an unknown Fe-AsO4 species. All the hematite products contain - 1% SO4 which appears to be adsorbed on the nanometer-size hematite crystallites.IntroductionDissolved iron is a common impurity in most hydrometallurgical processing circuits and, generally, the iron must be eliminated prior to the subsequent recovery of the sought after metals. Simple neutralization of iron-rich solutions yields slurries which are difficult to thicken and filter. To address these concerns, the jarosite, goethite and hematite processes have been developed, and these technologies are able to reject the dissolved iron in a readily filterable form [1]. Despite its higher cost, the hematite process offers several potential advantages. Because hematite is an iron-rich, high-density compound, its formation would reduce the mass of residue and the size of a residue storage pond. Hematite is the thermodynamically stable form of iron under ambient conditions, and this stability would facilitate the impoundment of hematite precipitates. Furthermore, hematite has some market potential for cement manufacture and even for iron making [2]. In all the commercial hematite processes, the dissolved ferric ions are first reduced to the ferrous state. Subsequently, the pH of the solution is adjusted and the solution is then oxidized. The ferric ions gradually generated during solution oxidation hydrolyze and precipitate mostly as hematite, although commercial hematite products also contain trace or minor amounts of jarosite-type compounds. However, there are potential advantages in precipitating hematite directly from ferric ion solutions, as the reduction and subsequent oxidation of the iron are not required. Although the precipitation of hematite directly from relatively concentrated ferric sulphate solutions (up to 0.5 M Fe(SO4)is) was recently demonstrated [3], the behaviour of impurity species during hematite precipitation is largely unknown. To address this issue, systematic laboratory experiments were undertaken to ascertain the behaviour of a number of ""impurity"" species during the precipitation of hematite directly from ferric sulphate solutions at 225°C, and the results are presented in this paper."

Jan 1, 2012

By W. D. Cho

The slag chemistry in steel processing plays an important role in terms of the removal of impurities including alumina particles. In the present study, the dissolution of solid aluimina particles in CaO-based fluxes at the temperatures between 1450 and 1550 °C has been investigated to determine dissolution kinetics and mechanism. Alumina particles were added directly in the slags and the size of alumina particles was measured as a function of time using optical and scanning electron microscopes. The dissolution rate has also been obtained as a function of Si02, CaF2, MgO and MnO contents in the slags. The diffusion boundary layer between alumina and bulk slag phase has been observed and analyzed using SEM and EDX. In addition, some experiments have been performed for the dissolution of alumina in BaO-based fluxes.

Jan 1, 2003

By Huimin Lu, Shi Zhou, Lisha Yang

"The Zeolitic imidazolate frameworks (ZIFs) were successfully synthesized by applying a combination of ionothermal synthesis and microwave energies for rapid synthesis. The synthesis was proceeded under various conditions including different raw materials, reaction temperature as well as microwave irradiation time. Zeolitic imidazolate frameworks (ZIFs), also known as coordination polymers, are new type of porous materials formed by inerratic polyhedral in three-dimensional. They are the ideal crystalline substances for gas separation and storage. The assynthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and C02 adsorption test. Results illustrated that the synthesized samples had stable structure, high thermal stability (up to 530 °C) and C02 adsorption capacity (10.2 cm3/g at 0°C under ambient pressure). This novel method also showed great advantage with high energy efficiency, safe synthesis conditions, and rapid crystallization time (60 minutes).IntroductionNowadays, carbon dioxide capture has become imperative due to the global warming caused by the increase of C02 in the atmosphere, especially produced by the concentrated sources such as power plants [1]. Zeolitic imidazolate frameworks (ZIFs), also known as coordination polymers, are ideal crystalline substances for gas separation and storage due to their structure diversity, high thermal and chemical stability [2-5]. They are formed by inerratic polyhedra in threedimensional with large cages and small apertures. Traditionally, ZIFs are synthesized by solvothermal method in a sealed autoclave under autogenous pressure [6-9]. However, in order to generate the products, the solvothermal temperature should not be lower than 100°C according to the sovlothermal mechanism. Moreover, at such a temperature, molecules with a low boiling point (such as water) may generate high pressure in reactor which might cause danger [9]. Thus the synthesis requires the equipment to possess resistance to autogenous pressure and corrosion. Further, conventional solvothermal methods need a long time to prepare products, usually a few days, which is a large energy consumption and inefficiency. So it is interesting to synthesis ZIFs through other ways under mild reaction condition with high energy efficiency."

Jan 1, 2012

By Roderick I. L. Guthrie, Donghui Li, Mihaiela Isac, Luis Calzado

The HSBC is an ideal process for the production of BMG strips. The purpose of the present work was to investigate the casting of Ca-based, bulk amorphous strips. The possibility of casting three Ca-based alloys (60Ca-20Mg-20Al, 60Ca-15Mg-10Al-15Zn and 55Ca-15Mg-10Al-15Zn- 5Cu (at.%).) was investigated, using the HSBC simulator. Numerical simulation and mathematical modeling were used to predict temperature variations and cooling rates, under different interfacial gaseous atmospheres (helium and air) near the meniscus region. Given the critical cooling rates and glass temperatures needed to be reached for the vitrification of the respective alloys, this leads to predictions of the critical thicknesses possible with this novel casting process. To validate our predictions, these alloys were then prepared and cast onto the sand-blasted, solid copper substrate mould of the HSBC simulator. The possibility of producing Ca-based metallic glassy strips via the HSBC processes was confirmed, using optical microscopy, X-ray diffraction and Scanning Electron Microscopy, to characterize the glassy properties of the cast strips. It was found that the HSBC process would be able to provide sufficient cooling to form amorphous strips for the 60CA-15Mg-10Al-15Zn and 55Ca-15Mg- 10Al-15Zn-5Cu alloys, but not the 60Ca-20Mg-20Al alloy.

Jan 1, 2014

By H. Hahn, B. H. Kear, K. Kan, S. C. Danforth, G. Skandan, W. Chang

"A new chemical synthetic process for the production of non-agglomeratednano structured ceramic (n-ceramic) powders, starting from metalorganic precursors, is described. The process combines rapid thermal decomposition of a precursor/carrier gas stream in a hot tubular reactor with rapid condensation of the product particle species on a cold substrate. Critical to the success of this Chemical Vapor Condensation (CVC) process are (1) a low concentration of precursor compound in the carrier gas, (2) rapid expansion of the gas stream through an uniformly heated tubular reactor under a reduced inert gas pressure of 1-35 mbar, and (3) rapid quenching of the gas phase nucleated clusters or nanoparticles as they exit from the reactor tube. A wide variety of metal organic precursors is available commercially, all of which can be utilized in the CVC process to produce n-ceramic powders, including single phase, multiphase and multicomponent systems.The CVC process has been used to synthesize non-agglomerated n-SiCxNy and n-ZrOxCy powders, with controlled particle size in the range 2-20 nm. Heat treatment of the assynthesized n-powders in various high purity gas streams causes compositional and structural modifications, including particle purification and crystallization, as well as transformation to a whisker-like morphology. Thus, as-synthesized amorphous n-SiCxNy particles transform to (1) cubic n-SiC particles, when heated in flowing argon at temperatures> 1350 °C, (2) hexagonal n-Si3N4 whiskers, when heated in flowing NH3IH2 at 1400 °C, and (3) cubic nSiC whiskers, when heated in flowing H2 at 1400 °C.Non-agglomerated n-ceramic powders form uniformly dense powder compacts by cold pressing, which can be sintered to theoretical density at temperatures as low as 0.5 Tm' For example, full densification ofn-Zr02 powder compacts under free sintering conditions can be achieved at 1125 °C."

Jan 1, 1994

By Leonard J. Friedman

Modern smelting systems using continuous, flash and/or oxygen smelting processes have a significant effect on the choice of sulfur dioxide control processes and system arrangements. Based on gases from an enriched air or oxygen smelting furnace and copper converters the paper reviews and analyzes alternate processes and system arrangements for recovery of sulfur dioxide. The work indicates the choice system to include a conventional sulfuric acid plant for converter gas and a liquid SO2 plant to handle the high strength smelting fur¬nace gas. The liquid SO2 plant would be used as a fly-wheel to damper the flow and SO2 concentration variations of the con-verter acid plant. Potential energy recovery alternates and product flexibility are also reviewed.

Jan 1, 1983

By Ricardo A. Valls

The Sechol Nickel-Cobalt Laterite Project is located in East-Central Guatemala, 140 km northeast from Guatemala City. In-situ resources in the immediate Sechol area, including those on other mining concessions contain 133 million tonnes of mineralization, grading 1.5 1% nickel. Considering the ever-increasing market for these metals, and the potential quick return on the initial investment, Jaguar Nickel Inc. is confident that by late 2006, it will be producing the first nickeltcobalt hydroxides from Guatemala. The path from now until the production stage passes through a pre-feasibility study, scheduled for completion by mid 2004, and bankable feasibility by mid 2005. Jaguar's objective, however, is not only to have a producing nickel-cobalt mine by late 2006, but also to continue with the exploration work in order to make Guatemala one of the world's leading nickel-cobalt producers. The Sechol group of deposits is conformed of several lateritic pockets, delimited by tectonic faults, and hosted by ultramafic rocks of the Sierra de Santa CW. ophiolitic belt that intruded the Maya Continental Block during the Early Tertiary age. The intrusive is mainly represented by a layered sequence of dunites, peridotites, and pyroxenites, usually strongly serpentinized. Existing data indicate that these rocks underwent fractional crystallization, and probably some degree of magma mixing and contamination previous to their main tectonic event. The most complete profiles are usually present over weathered dunites and serpentinites, while on top of the less altered pyroxenites, there is usually the formation of only a limonitic zone. The relative complexity of the ophiolitic belt explains the variety of mineral resources in the area, which include Ni-Co-Fe laterite, chromite, bauxite, magnesia, and also has the potential for gold, PGMs, and precious and semi-precious stones such as jade, nephrite, and chrysoprase. Metal recovery from the Sechol deposit will be based on an atmospheric chloride process, followed by solution purification, production of an intermediate nickellcobalt hydroxide suitable for sale, and finally acid and magnesia recovery by standard spray roasting technology. The chloride process will allow exploitation of the whole lateritic profile to produce 20,000 Mt of nickel hydroxide and 800 Mt of cobalt hydroxide per year. The exploration work completed to date has concentrated mostly on the Sechol group of deposits, representing less than 5% of the current land position of Jaguar in Guatemala. Within Sechol, the company has identified a large pocket of more than 5 Mt of laterites grading 2.1% nickel and 0.08 % cobalt as a startup pit "El Inicio". Including the work previously completed Keywords: Laterite deposits, Ophiolitic Belts, Central Guatemala, Nickel, Cobalt

Jan 1, 2004

By María Cristina Ruiz

Hematite precipitation is a convenient alternative for the removal of iron from leaching circuits because of its chemical stability, high density and high iron content. The precipitation of hematite from ferrous sulfate solutions was studied in a batch reactor. The precipitation occurs by two sequential steps: oxidation of the ferrous to ferric ions followed by hydrolysis of the ferric to hematite. The main objective of this study was to determine the effect of the main operating variables on the rate of two steps of hematite precipitation. The variables studied included: stirring speed (100 to 600 rpm), temperature (160 to 200 ºC), concentration of sulfuric acid (1 to 10 g/L), initial iron concentration (1 to 15 g/L), and partial pressure of oxygen (1 to 6 atm). The sulfur content and the particle size of the solids that precipitated under various conditions were also determined. The results showed that at low temperature and high acid concentration the rate of Fe3+ hydrolysis is the step that controls the overall process. The variable that affects most the rate of Fe2+ to Fe3+ oxidation and the rate of hematite precipitation is the temperature.

Jan 1, 2008

By Nagahiro Saito, Takahiro Ishizaki, Mituhito Hirota, Akio Fuwa

"Owing to their extremely high toxicity in the environment, the dioxins have been attracting social, technical and scientific attention in recent years. The authors theoretically had predicted the thermodynamic properties of all the dioxins via quantum chemistry and statistical thermodynamics and elucidated the generation-decomposition behavior of dioxins in the equilibrium calculation· of C-H-0-Cl system. In actual combustion processes, it is said that metallic compounds have much influences on the dioxins behavior. The aim of this study is to reveal the roles of metallic compounds the generation-decomposition behavior of dioxins is revealed from the viewpoints of quantum chemistry. Especially, the catalytic effect of copper has been investigated for the reaction, 2HCl(g)--H2(g}+Cl2(g) and for the etherification reaction from precursors, which is Phenol(g) here, to dioxins. The catalytic role of Cu is shown to have much influence on the generation -decomposition of dioxins.1. IntroductionIt is well known that dioxins are very harmful not only for our health but also for that of our children and grandchildren because they are very stable substance and their reaction rates of decomposition are considerably low. On the other hands, it is not well know how dioxins are generated and decomposed; the generation-decomposition conditions and paths as well as the catalysts to decompose them'1l. The authors believe that the thermodynamic and kinetic study of dioxins is useful to find a solution to these issuers. The authors have been investigating the following problems to reveal the generation-decomposition behavior of dioxins; (a) the prediction of the thermodynamic parameters of dioxins (2), (3), (b) the generation -decomposition behavior of non-chlorinated dioxins by the thermodynamic equilibrium calculations in C-H-O system(4) and (c) the generation-decomposition behavior of dioxins by the thermodynamic equilibrium calculations in C-H-O-CI system(5). Summaries of these thermodynamic researches are as follows.(I) The thermodynamic parameters for dioxins, which had been unknown and/or inaccurate'6 l, could be predicted and are available within the scientific accuracy."

Jan 1, 2000