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By Z. Zak Fang, P. Fan, S. Middlemas

"Titanium dioxide (T1O2) has been widely used as pigment in paints, paper and cosmetic products, as well as high-tech applications such as PV Cells, semiconductors, biomedical devices and air purification. T1O2 pigment is primarily produced by the high temperature chloride process, resulting in considerable CO2 emissions. A novel hydrometallurgical process for making T1O2 pigment without direct CO2 emission is investigated. The new method promises to eliminate direct CO2 emissions, consume significantly less energy, and produce minimal environmental waste. The novel process involves molten salt roasting of titania slag, with subsequent washing, leaching, solution purification, hydrolysis, calcination and post-treatment stages, resulting in high-purity anatase or rutile pigments while realizing significantly reduced environmental impacts. Pigment whiteness is critically sensitive to trace amounts of discoloring impurities such as iron and chromium. Several methods for reducing the levels of these impurities are investigated. Energy consumption and emission models are also developed.IntroductionTitanium dioxide (T1O2) is one of the most commonly used minerals in the chemical manufacturing industry. It has been commercially processed since the early 1900's, and has a wide variety of applications. Pigment is used in paints [1], plastics and paper [2], sunscreen [3], cosmetics and even as a food additive [4]. T1O2 has also been used in photovoltaic cells [5], biomedical devices [6], and in air purification [7]. T1O2 pigment has a refractive index of 2.7, which imparts a high level of opacity (and hence whiteness) to whatever material it is added [8]."

Jan 1, 2012

By lndu S. Das

An analytical simulation of the material characteristics of Inconel 718 is developed and bounds for mechanical and microstructural stability are obtained for isothermal and temperature-dependent cases. Experimental flow stress data using hot compression tests are reported for a wide range of temperature and strain at various strain rates. A parametric study of strain rate sensitivity, dissipation and entropy are presented. A complete set of processing maps delineating the stable and unstable regions are developed to help define the most efficient means of manufacturing an Inconel product.

Jan 1, 1992

By H. Y. Sohn

A novel solvent extraction process in which the emulsion is generated by bottom gas injection rather than mechanical stirring has been developed. This process has a number of advantages over the mixer-settler unit or the spray column in terms of simple equipment configuration and the ease of cleaning and process control while providing a large interfacial area for mass transfer. The equipment consists of a horizontal cylindrical vessel in which the two immiscible liquids flow countercurrently. High-strength gas jets are injected from the bottom at certain intervals along the length of the vessel. The gas jet creates a plume zone consisting of an emulsion of the two liquids which contains a large interfacial area for rapid mass transfer. The two liquids then disengage and flow in the opposite directions before entering another plume zone. Thus, the process combines the simplicity of a cylindrical vessel, having no moving parts, with the contacting efficiency of a mixer-settler. The gas can be recycled in a closed loop, thus eliminating mist and other emission problems. These advantages would be especially significant for treating large-volume/low-value liquid streams which contain hazardous substances and/or suspended solid particulates.

Jan 1, 1996

By Sui Xue

A process has been developed from laboratory-scale experiments for the aqueous processing of various lead-bearing wastes. The process exploits the limited solubility of lead in sulfate-rich solutions to effectively separate lead from other metals. The lead sulfate is then completely converted to lead carbonate using sodium carbonate and ammonium carbonate. The effectiveness of this conversion was observed to be sensitive to the solution pH and carbonate concentration. The final stage of the process uses low temperature calcination of the lead carbonate to form PbO. Yellow lead oxide (massicot) is readily formed if calcination is conducted at a temperature at or iibove 50G°C, wlule red iead oxide (iitharge) is formed at temperatures near 450°?C. A complete economical analysis of the process will be discussed.

Jan 1, 1996

By Mark Kruzynski, Srinivas Garimella, James T. Wiswall

"A flue gas recirculation (FGR) system for a combustion fired aluminum melting furnace is experimentally investigated. The FGR system flows combustion air in a turbulent jet within the flue gas stream, and the turbulent jet flow is collected in a tube at a distance from the jet exit. Entrainment of the flue gases as well as heat transfer between the flue gases and the jet occurs over the length of the exposed jet. Heat transfer between the flue gases and the jet, and the amount of flue gas entrained into the jet (derived from temperature, flow rate and oxygen fraction measurements) were measured as a function of nozzle exit velocity and the distance between the nozzle exit and collection tube. In addition to flue gas entrainment, a fuel savings of up to 7%, due to heat transfer over the length of the jet, was projected from the measurements obtained.IntroductionFlue gas recirculation can be applied to aluminum melting furnaces to control combustion temperature. When coupled with a device to improve furnace efficiency by recovering heat from the furnace exhaust, flue gas recirculation provides a control technique that is integral to achieving the goals of reducing fuel consumption, increasing product yield, increasing the longevity of infrastructure, and reducing pollutant emissions. In particular, combustion temperature control can help reduce reactivity of the products of combustion with the molten metal surface and furnace refractory materials. Combustion temperature control can also help improve the life of heat exchangers used to recover energy lost to the environment in the flue gases, and reduce NOx formation in the combustion process. Flue gas recirculation can also dilute oxygen used in oxy-fuel combustion to reduce reactivity.Flue gas recirculation has been used since the 1970s to control flame temperatures in the automotive industry [1-3] and has successfully reduced NOx emissions. Many different flue gas recirculation approaches for high temperature melting such as melting aluminum and glass have been patented since the 1980s [4-12]. There has also been academic interest to determine the fundamental performance characteristics of flue gas recirculation in high temperature furnaces and in combustion [13-15]."

Jan 1, 2014

By Jian Wang, Hongyang Cao, Binxiu Wu, Junhong Li, Jimin Wang

"The enrichment and separation of scattered metal indium component in the pressure leaching solution with sulfuric acid from vacuum furnace germanium slag were studied by iron substitute and P204 extraction, which is supplied by shaoguan smelter. The experimental results show that the extracting power of P204 for indium from pressure leach solution is powerful. The optimal technological condition were the ratio of P204 and sulphonating serosene 3:7, phase ratio 1:3, solution pH 1.2, and extracting 5 minute. The enrichment indium solution of 21.7 g/L In at 95.2% recovery ratio was obtained by three-stage counter flow extraction and four- stage counter flow stripping.IntroductionScattered metals, such as Indium and germanium, were inriched as intermediate product or by-product during the metallurgy process of other non-ferrous metals, such as lead, zinc, copper and tin. For example, the indium and germanium were inriched in vacuum furnace germanium slag, which is the by-product of zinc vacuum distillation operation from hard zinc. It is difficult to recovery the indium from the vacuum furnace germanium slag, because the indium content is low, and the chemical composition and phase compositon were complex.Recovery indium from bearing indium zinc slag was researched extensively, such as pressure acid leaching, high temperature evaporation, solvent extraction method[l-7], acid leaching method has the advantages of high leaching rate, which can be separated hydrochloric acid, sulfuric acid and silicon fluoride acid systems. Solvent extraction method has the advantages of low production cost, fast reaction speed, high enrichment ratio, and simple operation."

Jan 1, 2013

By D. J. Chaiko

Certain radionuclide ions (e.g., TcO4) exhibit unusually strong Affinities toward the polymer-rich phase in aqueous biphase systems generated by combinations of salt solutions with polymers such as poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG). Thus, aqueous. polymer ,phases could potentially be used to selectively extract these ions during pretreatment of radioactive tank wastes at Hanford. To help develop a fundamental understanding of the interactions between various ions and polymers in aqueous solution, interaction enthalpies between sodium -perrhenate and a random copolymer of PEG and PPG (UCON-50) were measured by microcalorimetric titration. An entropy compensation effect was observed in this system in which changes in enthalpic interactions were balanced by entropy changes such that the interaction free energy remained constant and approximately equal to zero.

Jan 1, 1999

By Wantae Kim

In order to establish the optimized recovery process for heavy minerals from Korean beach sand, we investigated the several physical separation methods such as gravity and magnetic separation followed by mineralogical characterization. There was clear relationship between the particle size and heavy mineral content that heavy minerals were mostly concentrated in the particles below 100mesh. Gravity separation using the spiral and shaking table separators made it possible to concentrate heavy minerals by rejecting the light and coarse particles consist mainly of quartz and other non-valuable minerals. The high-intensity magnetic roll separator and subsequent induced magnetic separator were applied to fractionate magnetic particles according to their magnetic susceptibility. The content of TiO2 of high susceptible ilmenite-rich fraction was 43.98wt.% while those of ZrO2 of non-magnetic and magnetic residue were 6.78wt.% and 3.11wt.%, respectively.

Jan 1, 2006

By Joseph D. Lessard

A process simulation of the conversion of molybdenum disulfide concentrates into molybdenum dioxide via the Looping Sulfide Oxidation process has been performed using HSC 7.1 thermodynamic software. By decoupling molybdenite conversion and molybdenum oxidation, Looping Sulfide Oxidation changes the paradigm by turning molybdenite processing into an energy generator while producing a molybdenum dioxide, which has a lower vapor pressure and lower oxygen content than molybdenum trioxide. The Looping Sulfide Oxidation process selectively produces molybdenum dioxide over molybdenum trioxide. This process uses a stoichiometric mixture of oxygen and molybdenum trioxide as oxidants in the conversion of the molybdenum sulfide to the molybdenum oxide. The model simulates the two reactor scheme required by Looping Sulfide Oxidation and incorporates thermodynamic equilibrium simulations performed in FactSage 6.3.1 thermodynamic software. Energy capture is also maximized with heat exchanger systems to transfer heat released in reactions to preheat air.

Jan 1, 2014

By Michael P. Heisel

Solinox is a physical scrubbing process capable of removing a number of noxious materials from off-gasses, especially SO2, hydrocarbons, halogens, heavy metals such as dust, etc. As these materials are dissolved physically, (not chemically bound), the solvent is absolutely stable and no by-products are formed in the scrubbing cycle. The process has? been installed in three plants up to now, treating from approximately 30 MMSCFD to approximately 100 MMSCFD. These installations are in a non ferrous metal smelting operation, in a cellulose factory, and in a roasting process.

Jan 1, 1992

By B. Wan

The process of synthesizing silica nanopowder by the gas phase thermal oxidation of tetraethylorthosilicate (TEOS) in a diffusion flame reactor was simulated using a commercial computational fluid dynamic (CFD) code. The fuel combustion process and silica particle formation and growth in the flame are modeled. The temperature, velocity and particle size distribution (PSD) fields inside the reactor are computed. Chemical reaction rate and population balance model (PBM) were used to calculate the particle formation and growth and PSD.

Jan 1, 2006

By Rauf Hurman Eric

In this review paper the effect of composition and temperature on electrical conductivity and viscosity of the slags encountered in electric smelting of PGM-containing sulfide concentrates is described along with their liquidus temperatures. Optimization of slag composition is attempted on the basis of opposite trends of viscosity and electrical conductivity. Metal losses to slag, matte-slag separation and matte settling are also discussed in conjunction with interfacial and surface tension concepts. The electrode immersed in the slag phase is the main factor in the design and operation of the furnace. The most important electrode parameters are the size and the positioning in the slag phase which are determined by the slag resistivity, furnace resistance, cell constant and power input. The flow of heat generated by the electrode current determines the energy distribution and furnace dimensions creating viscosity profiles within the slag phase which in turn affects the flow conditions. Thus the flow of slag is discussed together with furnace geometry, stirring action, buoyancy and electromagnetic effects and the action of the electric furnace as a settler is emphasized. A discussion on the design d production capacity of the furnace is provided which are based on considerations derived mainly from slag properties.

Jan 1, 2006

By M. J. Perpich

Electrochemical and chemical leaching tests were carried out on chalcocite, covellite and chalcopyrite in acidified iron sulfate solutions sparged with a mixture of O2 - SO2. The gas mixture catalyzed the ferrous to ferric oxidation reaction in situ and, therefore, increased the redox potential and oxidizing strength of the solution. Anodic polarization curves in dilute sulfuric acid on copper sulfide electrodes showed that chalcopyrite passivates and dissolves at current densities orders of magnitude less than chalcocite and covellite. The addition of a depassivating agent (Ag+) increased the passive current density of chalcopyrite and caused breakdown near 0.625 V (SCE). The depassivating effect was also observed during the leaching of chalcopyrite particulate samples as small amounts of Ag+ added to acidified iron sulfate solutions in the presence of O2 - SO2 mixtures greatly increased the leaching rate and the total amount of Cu oxidized (> 90%). Passivation was prevented in the absence of Ag+ by decreasing the initial oxidizing power of the solution and by pretreating the sample in a reductive leach. Both of these methods resulted in transformation of the chalcopyrite surface from its characteristic greenish-gold into deep black. Increased concentrations of Fe+++ due to 02 - S02 sparging were then able to oxidize the transformation product.

Jan 1, 1999

By S. H. Castro

In 1997 Chile was the world's largest copper mine producer with around 3.4 million metric tomes of copper. Conventional technology (conminution-flotation- smelting-converting-electrorefining) for copper sulfide ores was used. For copper oxidized ores hydrometallurgical processes (heap leaching-solvent extraction- electrowinning) were employed. Consequently, the most important waste effluents include flotation tailings, gaseous emissions, smelter slags, acidic and alkaline wastewater, electrolytic sludges, solid residues from leaching, etc. The introduction of stricter environmental regulations are forcing the Chilean industry to minimise the generation of waste and promote cleaner production. Gas emissions such as SO2 and arsenic from smelters and process wastewater are the major problems at this stage. The environmental impact assessment of gas emissions in all six largest smelters namely Chuquicamata, Caletones, Potrenllos, Ventanas, Paipote and Chagres led to design a "decontamination plan." The implementation of this plan resulted in (i) the installation of sulfuric acid plants for SO2 abatement and (ii) the installation of electrostatic precipitators to remove arsenic oxides condensed from cooling gases. The aim of this paper is (i) to describe the type of waste associated to the various stages of the metallurgical processes and (ii) review the main abatement technologies used in medium and large size companies.

Jan 1, 1999

By O. Morfín

The most probable source of Pb contamination in the perennial reach of Aravaipa Creek, Arizona, has been determined using Pb isotope ratios and total metals analyses of samples collected from the ephemeral and perennial reaches and mine wastes located in the Aravaipa Mining District . Previously, elevated levels of Pb, Cd and As in fish in the perennial reach of Aravaipa Creek, a protected wilderness area,, were assumed to be due to off-site transport from abandoned flotation tailings piles located at Klondyke, Arizona upstream of the wilderness area.Our work replaces this inference with isotopic data that allows us to confirm this hypothesis. The Pb/Zn deposits of the district were mined between the late 1890s and the late1960s, with the most significant ore production coming from one deposit in a rhyolite dike swarm on the Western front of the Santa Teresa Mountains, a granitic pluton of Cretaceous-Tertiary age (~65 ma). Mineralogy has been well constrained across the length of the lode system: Pb and Zn sulfides predominate in the NW sector, and a mixed suite of hypogene/supergene Pb sulfide and Pb oxide minerals comprises the majority of its SE corner. Total metals analyses and comparison of metals ratios serve to constrain the source and transport of certain metals within different parts of the system. Pb isotope ratios in samples, obtained by ICP-MS analysis, define two distinct contributors. The first end-member (208Pb/204Pb = 38.513 to 38.721 and 207Pb/204Pb= 15.550 to 15.598) is characteristic of the mixed, oxide/sulfide ores at the SE end of the deposit. A second end-member (208Pb/204Pb = 38.855 to 38.946 and 207Pb/204Pb = 15.610 to 15.625) characterizes samples taken from the NW, purely Pb sulfide end of the lode. Pb isotope ratios from perennial reach sediments are closely correlated with ratios given by samples from the Klondyke tailings site and by Pb sulfide samples from the NW sector, the primary source of ores processed at Klondyke.

Jan 1, 2003

By Ovidiu Pasca

Several improvements in converter equipment and operation at BHP Copper have reduced the converter cycle time as necessitated by an increase in flash furnace output. The resulting higher intensity performance of the Peirce-Smith Converters has had a major impact on the dust handling and off-gas cleaning systems. This paper describes work carried out on the design of a new converter hood with particular reference to the thermal analysis and hood performance aspects. Changes in converter cycle time and campaign life as result of the process and equipment improvements are discussed in a separate paper.

Jan 1, 1999

At the present time, cyanide is the most widely used reagent to extract gold from its ores and concentrates. However, its use in mining has become the focus of intense attack by various groups throughout the world; as a consequence, a renewed effort has been launched to find suitable alternative lixiviants to recover gold. Chlorination was the most popular process to extract gold, before it was rendered obsolete with the advent of the cyanidation process at the turn of the last century, not least because it required the use of potentially hazardous and costly chlorine to oxidize/complex the gold. The PLASTOL® process, originally designed to recover the platinum group metals (PGM?s) from their ores and concentrates, provides an alternative to cyanide for gold ores. The process generates oxidizing conditions in the autoclave capable of forming the AuIII ion, and gold chloro-complexes result from the addition of small quantities (~5-10 g/L) of sodium chloride to the autoclave. The principles of the PLASTOL® process are briefly described, and several applications of the process to gold concentrates are presented. Various options available to recover gold from PLASTOL® leach solutions are also discussed.

Jan 1, 2003

By William Bourcier

Geothermal Brines are a significant potential source of valuable minerals and metals. These brines are water that is heated by the natural heat flow from the depths of the earth. Hotter brines, typically with temperatures greater than 120°C, are used to generate electricity. Lower temperature brines are directly used to supply thermal energy to applications such as agriculture, aquaculture and process/domestic heat. The geothermal waters have had intimate and lengthy contact with the layers of the earth?s crust that they flow through, resulting in dissolution of minerals and metals from the rocks, and solution into the hot water. These aqueous solutions can be processed to recover minerals and metals. Some potential products include silica, zinc and lithium, along with other materials. Recovery of minerals and metals from geothermal brines can be viewed as ?solution mining by nature?, followed by application of known or new hydrometallurgical techniques for isolation and purification. This paper discusses the opportunities, the processes, the challenges, the current status, the economics and the potential for recovery of minerals and metals from geothermal brines.

Jan 1, 2006

By T. L. Baum

External oxidation during in-line heat treatment of TRIP steels can cause problems for the subsequent coating process. This research aims to elucidate the kinetic rates of internal oxidation, external oxidation and decarburization and their interdependence under different gas atmospheres and temperatures. A rolled steel sample chemistry of 0.14 wt.% C, 1.8 wt% Mn, 0.6 wt.% Si and 1 wt.% Al is used as a case study. Thermogravimetric techniques are used to examine the net mass change in a sample during heat treatment and the results show an initial mass decrease and later an increase for particular partial pressures of H2O. SEM-EDS, optical microscopy and glancing-angle x-ray are used to quantify the microstructure. The cross-section of the samples have 4 distinct zones: (i) an external scale, rich in fayalite, (ii) an internally oxidized region with Al, Si and Mn oxides in an Fe matrix, (iii) a decarburized steel region, characterized by large ferrite grains and low carbon content, and (iv) a relatively unaffected steel core with a structure similar to the starting material.

Jan 1, 2006

By Takamasa Ishigaki, Gervais Soucy, Mohamed Rahmane

"The induction plasma jets employed for the in-flight nitridation of molybdenum disilicide (MoSi2) powders were investigated in terms of their flow characteristics. The present study shows the effect of the operating parameters of the plasma torch, as used for this process, on the plasma jet properties. The enthalpy probe techniques, along with mass spectrometry, were employed for the measurement of the jet temperature, velocity and concentration fields. The measured values were compared to the results of a numerical simulation performed on the plasma flowing inside the torch-reactor system. The process operating conditions studied were the plasma plate power, chamber pressure and sheath gas composition. The optimal conditions for effecting the nitridation process using thermal plasma are obtained at moderate plasma plate power, at around atmospheric pressure and by using a mixture of argon and nitrogen as the plasma torch sheath gas.IntroductionMolybdenum disilicide (MoSi2) based composites are considered to be one of the most promising candidates for high temperature structural material applications [!], especially because of their high melting points, good oxidation resistance and relatively low cost. However, the wide application of these composite materials is still limited by some factors such as their brittleness at room temperature and lower strength at high temperature (> 1500 K). To overcome such limitations, a number of researchers [2-4] have earlier studied various kinds of reinforcements for MoSi2, e.g. oxides, silicides and nitrides. More recently, Fan and coworkers [5-9] have demonstrated the possibility of in-flight nitridation and carburization of MoSi2, using a thermal plasma process. This work has confirmed the plasma synthesis route as one of the most promising methods for creating an in-situ second phase structure. Properties of the plasma flow, such as its temperature, flow velocity and composition, are of crucial importance for the nitridation of MoSi2 powders during their flight in the plasma. Therefore, the optimization of such a process involving plasma· generated reactive species necessitates a thorough understanding of the plasma flow characteristics."

Jan 1, 2000