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By Xiaobing Yang, Animesh Jha, Greg Doughty

"Successful use of inert anodes should reduce the CO2 footprint in aluminum production. The search for a “holy grail” inert anode for metal electro-winning from constituent oxides using molten salt bath as an electrolytic medium is continuing. In this article we demonstrate the engineering approaches for the fabrication of intermetallic anodes, based on a quaternary Al-Ti-Cu-M (M:Ni, Fe) system for primary aluminium production. In particular, we examine the microstructural and electrochemical properties of alloys, based on the quaternary compositions. We explain the aspects of phase stability under anodic potential, which leads to the loss of anodic materials in the temperature range of 850-1050oC. The results are analysed in the context of oxidation reaction and formation of oxide layers which readily dissolve in the cryolite melt and prevent passivation. The paper also describes the conditions under which the reduction of aluminium at the graphite cathode occurs which also strongly depends on the molten salt chemistry for the nucleation of molten aluminium at the cathode.1. IntroductionOxygen-evolving inert anodes are an alternative to the conventional consumable carbon anodes for the production of primary aluminium. In this paper the materials selection criteria chosen for the engineering of anode is based on the understanding of the thermodynamic stabilities of aluminide intermetallic phases, some of which are formed and remained stable in fluoride melts. For example, the formation Al3Ti dispersed in aluminium metal via molten-fluoride flux reaction is well known in the context of aluminium casting and grain refining [1-3]. It is for this reason in our research we concentrated on the engineering of stable intermetallic phase mixture in the Al-Ti-Cu ternary system, shown in Figure 1 [4]. In this figure two compositions in the Al3-0.5zTi1-0.5zCuz family are shown with the substitution of 7 atomic % and 11 atomic % copper. However initial investigations showed that these two compositions were unsuitable due to the formation of low-temperature liquid (~540oC) and intermetallic phase, Al2Cu along the Al-Cu binary edge during solidification. The Al2Cu phase segregated along the boundaries of Al3Ti and Al5Ti2Cu, and dissolved away when electrolysis was carried out using these anodes above 800oC. The presence of consequential porosity in the anode material increased the corrosion of the alloy through local heating due to high current density at 0.8 A cm-2. The early tests were carried out with cryolite melts, shown in Figure 2, having 3 weight percent of Al2O3 in the bath at 850oC."

Jan 1, 2010

By Gerhard Meyer

A new instrument for the determination of iron., zinc, calcium, and other metals independently directly in the fumes emitted from steelmaking processes is described. Based on the well- accepted method of X-ray fluorescence, the instrument can detect numerous metals simultaneously in the fume as well as report their concentration on a mass per unit time basis real time to a control room computer. The instrument mounts on the wall of the fume duct and can., via a small opening, directly view the hot exhaust plum inside the duct. The concentration of metal in the fume over time has been shown to change dramatically depending on process variables. Variables such as oxygen flow rate, lance height and nozzle configuration., slag condition., and episodic scrap addition can affect the presence of metal particles and fume in the exhaust. An analysis response time of 6 seconds enables better control of the steelmaking process thereby conserving primary resources and reducing environmental impact.

Jan 1, 2001

By Thomas M. Harris

Cation exchange is not sufficiently selective to be used for the removal of heavy metal ions from a general industrial wastewater. However, if the metals can be converted to polyvalent anions through complexation, they may be removed both selectively and efficiently by anion exchange. This approach, referred to as chelation-assisted anion exchange (CAAE), has been examined using industrial wastewater samples contaminated with Ni2+ and Cr3+. For this particular application, the Ni2+ is complexed with 8-hydroxyquinoline-5-sulfonic acid, and the Cr3+ with sulfosalicylic acid. Removal efficiencies and adsorption isotherms for both the complexants and the complexes were determined in batch-mode tests.

Jan 1, 1994

By Gabriel Riveros

Fire refining of copper consists of two stages copper oxidation and copper reduction. Very frequently the capacity of the anode furnace is determined by the rate of copper reduction. The analysis of factors affecting the rate of the oxygen reduction from a liquid copper with solid carbon or injected hydrocarbons pointed out the role of the mass transfer in a liquid copper in final stage of the reduction. Experimental results of copper reduction with graphite and injected natural gas in laboratory- scale crucibles showed two stages of the reduction process with a sharp change of the controlling mechanism. The estimated dynamic surface area of gas bubbles based on the measured bubble frequency and the gas flowrate allowed for the detennination of the reaction constant as a degree of the partial pre-combustion of the air/natural gas mix. The variation of the used reductant as a function of the oxygen concentration and temperature has been evaluated based on the detennined kinetic model. The intensification of copper reduction in fire refining has been discusses on the basis of obtained kinetic data and analysis of various factors detennining the time of reduction.

Jan 1, 2003

By Bo Zhou

During secondary aluminum recovery, complex aluminum scraps are melted and refined often in a rotary melting furnace and the aluminum metal has to pass through a molten salt layer and melt down in a bottom aluminum bath. Previous experimental study and industrial observations have indicated that salt shell formation and re-melting on the metal solids in the early stage plays a critical role in the overall melting process of the scrap. In the present paper, mathematical models are developed to simulate the process of salt shell formation and its re-melting, as well as aluminum melting in the molten melt. Influence of the salt layer properties, the residence time of the metal particles in the salt layer, the particle size, the temperature of bulk melt were investigated. Reasonable agreement with the measurement data was reached. The developed melting model will be used to construct a population balance model of the scrap melting behavior for a rotary melting furnace, taking into account the distributed characteristics of the scrap. Finally, an overall process model based on Computational Fluid Dynamics (CFD) for the rotary furnace will be constructed, coupling with the population balance model for the scrap melting.

Jan 1, 2003

By Richard L. Werner

The petrographic microscope as a tool in determining impurities and grain size of limestones, clays, sand and coal ash for possible use as raw materials is discussed. Its use in the determination of the mineral composition of various size fractions of the raw mix, after fine grinding in ball mills, and of the waste dust from the rotary kiln. A description is given of the typical clinker crystals; alite, belite, tricalcium aluminate and ferrite. The process problems indicated by various changes in the crystal characteristics are listed with possible solutions. Finally the microscope as used in relation to field problems with concrete such as air void volume, percent hydration of the cement, cement aggregate bonding and the determination of solid additives, is presented.

Jan 1, 1982

By Markus A. Reuter

In this paper, the kinetics of phosphorous production in submerged-arc furnaces will be discussed as a function of temperature, as well as various ore and reductant types. Interesting positive synergetic effects on the rate of reaction could be observed when mixing different types of ores. The results will be discussed with reference to a kinetic model, microprobe analyses, etc. The effects these results have on the control of the furnace will also be discussed in detail, indicating how these could be incorporated into the electrode and metallurgical control systems for submerged arc-furnaces.

Jan 1, 2000

By B. J. Jody

This paper describes a one-step thennal-treatment process, developed at Argonne National Laboratory, to remove all organic contaminants from the glass-fiber waste that is generated during the glass-fonning process. The recovcred glass fibers can then be recycled into new glass fibers or new glass products without adversely impacting the operations of the glass industry or the quality of its products. Our process involves shredding the waste to a manageable size and then processing it at temperatures below its melting point to remove the polymeric-coating layer. The glass industry generates more than 60,000 tons of glass-manufacturing waste annually in the glass-forming process alone. Recycling of this waste stream can keep this non-biodegradable waste out of the landfills. In addition, use of recycled glass lowers energy costs, by an average of about $5 per ton as compared to using virgin raw materials to make virgin glass fibers. This process will also reduce the emission of C02 by 17,400 tons a year and it will also reduce the emission of nitrogen oxides. Economic analysis of our process shows a potential payback of less than 2 years.

Jan 1, 2003

By F. A. Steward

Copper is one of the trace minerals essential to life. It is added, usually in the form of copper sulfate, to virtually all formulated feedstuffs and to dietary supplements fed to animals on forage. Over the past five years, an improved inorganic copper source trademarked Micronutrients TBCC™, has been developed, tested and commercially introduced. TBCC is a crystalline form of basic copper chloride. Synthesis is accomplished in a continuous neutralization I crystallization process. In current commercial production, the primary sources of copper currently used as feedstocks are the etching solutions used to manufacture electronic printed wiring boards. These solutions have traditionally been managed as hazardous wastes, but their use to manufacture TBCC™ exempts them from regulation as wastes under the "Use/Reuse" provisions of RCRA. Research conducted over five years at multiple universities has shown that animals are healthier when fed this source of copper and that vitamin losses in feed are reduced by its use.

Jan 1, 2000

By Tatsuro Ariyama, Michitaka Sato, Atsushi Sakai, Sumiyuki Kishimoto, Ryota Murai

"In order to achieve high pulverized coal injection operation in a blast furnace, optimization of the injection lance arrangement was carried out using an experimental furnace and mathematical models. To increase the injection rate of pulverized coal, it is required to raise the combustion efficiency of pulverized coal. It became clear that multi-point injection and the lance arrangement to avoid interference among the coal streams injected were so effective in increasing combustion efficiency. With these findings, the eccentric double lance arrangement has been newly developed.At NKK, Fukuyama No.4 Blast Furnace, after the improvement of the lance arrangement, the maximum injection rate reached up to 230 kg/thm and an average monthly record of 218 kg/thm was successfully achieved.IntroductionFrom the viewpoints of reducing the production cost of pig iron and prolonging coke oven life, high pulverized coal injection over 200 kglthm is actively pursued by ironmaking industries[1-2].Coal particles injected into the blast furnace are consumed by combustion in the raceway and also in-furnace reaction like solution-loss reaction (C + CO2 = 2CO). The amount of coal consumed by the latter process is determined by the carbon balance in the blast furnace and there is a limit. Therefore, to increase the injection rate, it is desirable to improve the combustion efficiency in the raceway. For these purposes, the optimization of the lance arrangement was examined by a hot model and mathematical models."

Jan 1, 1996

By Abhishek Lahiri, Animesh Jha

"A new technique for the selective separation of rare earths and impurities from lower grade titaniferous ores has been developed which will reduce the overall reduction in the energy costs, and therefore the CO2 generation by at least an order of magnitude during the chlorination and waste handling stages of TiO2 to TiCl4 reaction. The process includes roasting the ilmenite ore with alkali followed by water washing step, which removes nearly 80% of oxides of lanthanide and actinide elements present in lower grades of titaniferous minerals. In the context of preferential separation of rare- 3+ + earth and actinide oxides, we have examined the roles of Al and K ions on the lattice structures of ilmenite and complex titanate as the product layer forms during the roasting in air in the presence of potash. The composition of the mixtures of oxides derived from the separation process shows that the mixture of rare-earth oxides m ay be a high-value co-product of the overall beneficiation process.IntroductionWorldwide the production of synthetic rutile is carried out either by the sulphate or the slag-making followed by fluidised bed chlorination of TiO2 enriched slag granules. The chlorinated gas is then re-oxidized to make white pigment grade TiO2. The waste generated by the sulphate process is predominantly iron sulphate, which has limited use in the water treatment plant. The remaining wastes from the sulphate process undergo further treatment using filtration followed by evaporation and thermal decomposition after which it is disposed into deep sea. On the other hand the chloride waste is extremely hazardous and requires special case by neutralisation, followed by impoundment in a managed pond, where it is monitored for long-term for potential contamination to the soil and ground water. Rare-earth and prelanthanide wastes often end up in the pond where they are diluted and irretrievably lost for further use or recycle. Certain parts of the world the chloride process wastes are pumped via deep boreholes into porous geological strata. The present techniques of disposal are not only expensive but also pose continued threat groundwater and soil and marine life in case of sulphate waste [1, 2]."

Jan 1, 2009

By R. Rajiv Srivastava

Brine leaching of a TSL processed zinc-plant residue (ZPR), containing 83.3% anglesite, has been investigated for lead recovery. A prior treatment of ZPR in acid solution did not show any significant effect of acid concentration in zinc dissolution. The study reveals that the solubility limits of PbCl2 is as an important factor with respect to the brine concentration and pulp density in lixiviant. The dissociated sulfate ions hinder the formation of PbCl2 on prolong leaching (above 60 min), while exhibiting the reverse solubility of lead as PbSO4. A 3-step leaching process could yield >92% leaching efficiency when the parameters were maintained as: 10% pulp density in a 250 g/L NaCl solution, 80 °C temperature, and 60 min time. This leaves the insoluble ferrite, sulfides and oxy-sulfates of zinc and lead in the final residue as revealed by the XRD characterization.

By John J. J. Chen, Barry J. Welch

"The production of primary aluminium can potentially lead to metal that, with minimum treatment, meets a high purity standard. Smelters that can achieve a significant proportion of their production in this manner have a competitive edge which is of growing importance as the use grows for such items as compact discs and the like. Superimposed on the desire to produce high quality metal are stringent environmental requirements that the industry must adhere to. The environmental legislation focuses on fluoride emissions and the approach adopted is towards a zero waste management philosophy. The fluoride recycling process does, however, result in volatile impurities being captured and recycled to the cell. Aluminium has an extremely high reduction potential and this results in a significant proportion of the recycled impurities being reduced at the electrolyte metal interface and thus contaminating the metal. This paper reviews sources of impurities and the impact of the operating procedures adopted on metal treatment.IntroductionSeveral factors have contributed to the immense growth in the aluminium smelting industry. Initially the ready availability of hydro electricity provided a primary reduction energy source for the production of the light-weight metal. Because of its unique properties and innovation in the industry there has been a continued exploitation of its unique properties, especially at the high purity end of the metal. The industry has shown considerably versatility and innovation in adapting to the ever increasing demands of quality and purity. It is however a competitive industry and the ability to produce high purity grade metal (>99.9% pure) gives a competitive edge. Emerging markets such as for CD ROM disc production etc, will keep the quality demand stringent.While the industry has met the continuing demands for metal quality, it has also had to respond to stringent environmental requirements for emissions from the production plant. Like all extractive metallurgical processes carbon dioxide is an inevitable reaction byproduct. However, the volatilization and hydrolysis of the solvent electrolyte leads to fluoride emissions that are potentially harmful. Accordingly, the industry has adopted essentially a zero non-process waste management approach. All cell emissions, including reducible impurities, are recycled back to the cell. This has had a significant influence on the metal treatment processes."

Jan 1, 1996

By T. Gunawansa, T. L. Alford, Zhao Zhao, A. R. Lanz, N. David Theodore

Many sustainability issues arise during the manufacturing processes that are currently used for solar cells. Solar energy is a renewable energy source that is independent of the earth’s resources, and it is therefore important for the development of more sustainable technologies. Microwave annealing (MW) has been proposed as a technically feasible fabrication scheme for large area silicon solar cells. Apart from that, microwave annealing has been demonstrated to be a promising alternative for repairing damage and electrically activating dopants in ion-implanted semiconductors for integrated circuit manufacturing. A microwave oven is cheaper than conventional furnace systems. In addition, microwave heating is much more efficient than conventional furnace heating, as heating is directly produced inside the material. This minimizes the loss of energy due to heating of the ambient. There is a need for more efficient processing techniques. In this study, microwave annealing is used as an alternative to the current postimplantation processing. Arsenic-doped silicon was microwave annealed (with an aluminacoated silicon carbide susceptor) to activate dopant atoms and to repair damage that was caused by ion implantation. Sheet resistance and Hall effect measurements were used to assess the extent of dopant activation. Rutherford backscattering spectrometry (RBS) with ion channeling was conducted to determine the extent of recrystallization. The dopant activation and recrystallization resulting from microwave annealing is compared with that resulting from conventional rapid thermal annealing (RTA) with the same heating profile. The results show that when compared to RTA, susceptor-assisted microwave annealing results in better dopant activation for shorter anneal times under the same heating conditions.

Jan 1, 2015

By Varadarajan Seshadri

The performance of mould fluxes in satisfying its quality requirements can have a significant effect on the efficiency of the continuous casting process and on the surface quality of the products. This performance is affected by various parameters including the characteristics of the mould fluxes, the quality of the steel being cast and the operational conditions of the caster. The extremely complex relationships involving the parameters mentioned above make it very difficult to have simple criteria for selecting mould fluxes for casting a certain grade of steel in a continuous casting machine. These difficulties led steelmakers and mould flux suppliers to select mould fluxes based mainly on plant trials. In the present work, a software to help in the analysis and development of mould fluxes for continuous casting was developed. This software includes several models for prediction of mould flux viscosity and consumption. A mathematical model was also used to predict the heat flux through the mould flux. The proposed methodology was applied to continuous casting of crack sensitive steels. Some of the results given by this software are presented, discussed and compared to plant data.

Jan 1, 2003

By Aureo D. V. Machado

An experimental study to obtain zirconia powders (ZrOz) from carboxylate zirconium solutions followed by hydrogen peroxide stripping and precipitation, has been carried out. Zirconium carboxylate was prepared by solvent extraction from a chloride aqueous phase using magnesium carboxylate as organic phase. The variables examined in the precipitation reaction were: Temperature: 25 - 90 ?C ? H202= concentration: 0.3 - 5% wt/wt - pH: 1 ? 9 Organic/Aqueous ratio (1/1) and reaction time (30 minutes) were maintained at constant levels. The optimum results (98% precipitation) were achieved at 25 °C, 5 % wt/wt H202=, and pH = 5. The precipitates were composed of large amorphous aggregates (<I00 micrometers). After calcination for 1 hour at 1000 OC, monoclinic ZrO2 with a large variation in particle size (1 -100 micrometers) was obtained.

Jan 1, 1991

By Patrick R. Taylor

Iron phosphate glasses are promising host matrices for vitrifying actinide rich nuclear wastes materials because of their high solubility of actinide oxides, high chemical durability, and relatively low melting temperatures. An iron phosphate waste form was developed at the University of Missouri-Rolla. The structure and property of the waste form were well characterized by materials techniques. However, to scale the process and advance it to commercial viability, it is necessary to understand the processing parameters, such as the partitioning of waste elements and the viscosity as a function of temperature. Viscosity of 40 Fe203 - 60 P205 mole % iron phosphate melts (prepared with phosphorous pentoxide and ferric oxide) at 1000-1200 C was measured by the rotating-spindle method. It was discovered that this fluid has non-Newtonian behavior. Experiments were performed to study flow properties following the Standard Test methods for Rheological Properties of Non-Newtonian Materials by Rotational (Brookfield) Viscometer (ASTM D 2196-86). Samples prepared using ammonium phosphate and ferric oxide showed Newtonian behavior and the temperature dependence of the viscosity was studied over the range of 1000 to 1200 degrees C. The difference in flow behavior between the two fluids was analyzed in terms of preparation conditions and variation in the final composition and phases. The partitioning behavior of waste elements in the iron phosphate glass was studied by melting in a high temperature furnace and JCP analysis. The experimental results show that the solubility of Ce and Sr in phosphate glasses is significantly higher than the solubility associated with borosilicate glasses. This strengthens the conclusion that iron phosphate may be a viable alternative to borosilicate glass for immobilization of high heavy-metal-content wastes and actinide rich wastes.

Jan 1, 2002

By K. H. Bech, S. T. Johansen

"The mass transfer at fluid-fluid interfaces due to turbulent agitation is investigated theoretically. In particular a theory is derived for interface stresses due to interface energy and surface renewal. This theory indicates that surface renewal may take place if the geometry is sufficiently large and if surface tension is sufficiently low.By using a model for a typical turbulent structure we compute the interface mass transfer for a stressless interface and a fully interface. Results for the general situation is not presently available. The computed results are used to derive analytical expressions for the mass transfer based on turbulent kinetic energy and free stream turbulent length scales.One important application of the theory is the mass transfer at the electrolyte side of the bath-metal interface in the Hall-Heroult process. For this process we show that mass transfer should be expected to be of the rigid surface type."

Jan 1, 1999

By F. J. Tavera

Recently Jameson cell technology has gained acceptance in both mineral and non-mineral applications, mainly because of the high degree of contact between the involved phases in the downcomer, fact that leads to an efficient collection performance. The key for an acceptable performance of the downcomer operation depends on the stability of the jet zone, the mixing zone, and the plug flow zone. in this work the behaviour of the downcomer of a laboratory Jameson cell is reported, as a function of gas hold-up, superficial gas velocity, superficial liquid (or slurry) velocity, and length of the operating zones. The presence of carbon is evaluated in terms of its effect on the gas hold-up and bubble surface area flux. The influence of the downcomer operating conditions on the gas-liquid disengaging cell is presented. Keywords: Jameson cell, downcomer, gas hold-up, mixing, plug flow, conductivity.

Jan 1, 2003

By W. Kasprzak

Press-fit systems are widely used to seal oil lines in the automotive engine components. In the case studied a ball plug made from the 7075 A1 alloy was inserted into a 319 Al alloy cast component. The oil lines were subjected to the required component service pressure. This paper addresses the analysis of the ball plug/casting hole press-fit performance. The tools used to investigate the plug system included: the SEMIEDS technique for the assessment of the plug and the casting hole wall surface integrity; image analysis methods for the characterization of the ball plug/casting hole interface; matrix microhardness measurements of the plug and casting components; laboratory ball plug insertion, speed and force correlation; as well as the ball shearing mechanism analysis. Laboratory tests indicated that optimization of the aluminum matrix hardness in the 319 A1 alloy cast components resulted in considerable improvement of the press-fit system sealing properties.

Jan 1, 2002