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By S. C. Grand, T. J. Auping, K. Born

Process control, environmental monitoring, budgeting and accounting are based on process data. Without appropriate tools for data analysis, the process data could remain unused and wasted. This paper demonstrates how data reconciliation can be used as a tool to develop closed mass balances. Mass balances are the initial step in plant optimisation (technical, economical or environmental). From mass balances, fundamental process models can be developed. These balances link process parameters (e.g., feed materials) to process performance (e.g., recovery of valuable elements). Some of these models could find their way into simulators useful to plant operators. Classical regression methods regularly fail when they are applied to complex non-linear problems involving a large number of variables. Alternatively, multiparametrical regression analysis can be successfully applied with the aid of neural networks based on reconciled data. Both methods have been applied to plant data originating from the hydrometallurgical zinc plant at Ruhr-Zink, which in this paper serves as a case study. Very promising and useful results were obtained from this study.

Jan 1, 2000

By J. L. Delplancke

During copper electrowinning in sulphate electrolyte, intense oxygen evolution takes place at the anode. Lead alloy anodes are progressively replaced by dimensionally stable anodes in order to avoid the cathode contamination by dissolved lead. The electroactive coating of these anodes has to be as cheap as possible, adherent to the substrate, electrochemically stable and has to be efficient at high current density and high temperature. This requirement is even demanding in case of copper electrodeposition for the production of thin copper foils for the electronic industry. The production of thin (20 µm thick) copper foils for the printed circuit boards requires high purity copper electrodeposited at a current density as high as 7,000 A/m2. The choice of a long term coating composition is driven by economics. The purpose of this paper is mainly to review the anode compositions suitable for copper electrowinning and for copper electrodeposition at high current density. A short description of preliminary results obtained with a new anode coating on a titanium substrate is also presented.

Jan 1, 1999

By M. -L. Metsärinta, J. Nyberg, A. Roine

The Kokkola roasting plant uses more than 20 different zinc concentrates every year. During recent years there has been an increase in the variation in concentrate quality; in particular, the amount of fine-grained and low-grade concentrates has increased. Therefore, a great deal of development work has been carried out to improve the operational flexibility, online availability, production capacity and calcine quality of the roasting plant. This work consisted of a heat and material balance model of the roasting based on HSC Chemistry software, a new water admixture system for the concentrate feed, a new oxygen feed system for the process air line, improved cooling of the furnace and boiler and improved operational practices, dust removal and concentrate mixing. These new process control tools and other improvements, as well as some test results, will be described in this paper. The oxygen feed may be used to improve production capacity and to decrease the sulfide content of the calcine. The water feed may be used with fine concentrates to decrease both dust carry-over and the temperature in the top part of the furnace. Improved cooling of the furnace and boiler helps to increase production capacity.

Jan 1, 2000

By Gjergj Dodbiba, Toyohisa Fujita, Takahiro Kikuchi, I-Chen Wu

"In order to separate molybdenum (Mo) from the high-level radioactive liquid waste (HLLW), Pb-Fe based adsorbents were synthesized. The adsorbents were precipitated by adding sodium hydroxide in mixture of 1 mol/L lead nitrate and 1 mol/L ferric nitrate aqueous solutions. Each precipitate was then filtered, dried and ground to obtain a fine powder, which has been used as an adsorbent. Two main parameters were considered when synthesizing the adsorbents, i.e. the pH value at precipitation of adsorbent precursor and the calcination temperature of Pb-Fe based adsorbent. Moreover, the structures of the synthesized adsorbents were investigated by means of an X-ray diffractometer.The experimental results indicated that the calcination temperature of the Pb-Fe based adsorbent has a great influence on adsorption capacity of the adsorbent for Mo. It was found that when the Pb-Fe based adsorbent was calcinated at 500 oC, the sorbed concentration of Mo was the highest.1. IntroductionThe high-level radioactive liquid waste (HLLW), arising from the reprocessing of nuclear fuel are generally immobilized in an alkali borosilicate glass matrix. Broadly speaking, alkali borosilicate glasses are the matrix of choice for the immobilization of the HLLW, since they permit vitrification of waste stream of variable composition, [1]. Within this frame, the incorporation of molybdenum (Mo) is of particular interest in the vitrification of HLLW. Molybdenum is know to have a low solubility in borosilicate glass compositions and its presence in excess results in the phase separation of a complex yellow molten salt during vitrification, [1]. The formation of so-called “yellow phase” material during the vitrification process is undesirable since it leads to the accelerated corrosion of the inconel crucible liners. Furthermore, the “yellow phase”, which is reported to contain also other fission products, is soluble in aqueous solution providing a potential route for the leaching of radionuclides from the vitrified waste, should it come into contact with water, [1]."

Jan 1, 2008

By R. W. Lee

The first prototype plant using the Imperial Smelting Process commenced operation in 1950. It is timely therefore to review the developments that have occurred with the process over the past half-century. A major advantage claimed initially for the process was its ability simultaneously to recover zinc and lead from bulk concentrates. This has remained a fundamental advantage, but it has been extended by the increasing treatment of secondary materials containing zinc and lead. This has been facilitated by the development of hot briquetting and tuyere injection. These techniques and their impact on the technology of the operation will be described. The other major advantage claimed for the process was its potential to achieve new levels of productivity in the pyrometallurgical smelting of zinc. This has been realised with operating furnaces producing up to 400 t/d of zinc. The technical developments that have enabled this scale of operation will be reviewed.

Jan 1, 2000

By C. Allen

A series of zinc chloride electrowinning tests was carried out in a laboratory scale cell to evaluate the effect of temperature, current density, electrolyte composition, gas sparging and additives on the performance of the cell with respect to current efficiency, voltage, specific energy consumption and deposit morphology. The anode material was DSA for chlorine evolution and the cathode was made of aluminum. At 400 A/m2 current density, a current efficiency of 90.9%, a voltage of 3.4 V and an energy consumption of 2.78 kWh/kg were observed. Air sparging was found beneficial but was not pursued for health and safety reasons. Various additives in the same chemical family as tetrabutyl ammonium chloride (TBAC1) were tested. Both TBAC1 and tetrabutyl ammonium bromide were found to be equally effective. Attempts to carry out the electrolysis at 1200 A/m2 were not as successful.

Jan 1, 2000

By Takeshi Yoshikawa

For the development of low-cost silicon refining process for solar cells, the present authors have been studying the low temperature refining technique, ?solidification refining of Si with Si-Al melts at 1173 ? 1273K?. In the present work, we have investigated the B removal in that refining, utilizing the segregation effect and also the effect of Ti addition to the melt. Segregation ratio of B between solid Si and Si-Al melt was measured by the temperature gradient zone melting technique and it indicated the B removal fraction would be as much as 90%. Titanium addition to the melt was found to produce the TiB2 precipitation with soluble B in that melt and bring the effective B removal of refined Si to its content of 1ppma.

Jan 1, 2006

By Kamal Adham

Hydrochloric acid is used as lixiviant in such hydrometallurgy processes as synthetic rutile production and nickel extraction. The intermediary metal chloride is normally roasted to release gaseous HCl and a solid metal oxide. A large amount of fuel is required for this thermal regeneration, mainly to vaporize the water content of the feed solution. To conserve fuel, some energy recovery from the off-gas is currently achieved, but the fuel costs can further be reduced by process optimization and energy recovery from the gaseous, aqueous and solid products of the regenerator. Here, first the existing limitations to fuel efficiency in the industrial scale HCl regeneration roasters are described. Then, for the case of a dilute feed solution, options for pre-evaporation and fuel minimization are modeled and compared. Finally, energy recovery technologies including heat pumps, acid heat exchangers and solid waste heat boilers are described, and their potentials as the heat source for pre-evaporation of the feed are evaluated.

Jan 1, 2003

By Guo Xueyi

The reaction mechanism for the manganese dioxide reductive dissolution in acidic chloride media in the presence of ferrous/ferric ions are based on theoretical delineation and dual cell experiments. In terms of the Buttler-Volmer equation and chemical kinetic principles, a electrochemical kinetic equation was deduced, which successfully provided a theoretical basis for describing the role of Cl-, Fe2+, Fe3+ and H+ in solution, as well as their interrelationship in manganese dioxide reductive dissolution. Dual cell experimental studies indicate that the increases of Cl- and Fe2 in solution are helpful to accelerate the couple process; while, Fe3and Mn2+ hinder the coupled reaction to some degree. Higher acidity in solution is beneficial to the dissolution of MnO2. All the dual cell experimental results are consistent with the theoretical deduction. This study will be useful to understand the mechanism for the leaching of manganese nodules from the deep ocean, as well as the leaching of manganese dioxide ore from land.

Jan 1, 2003

By K. Th. Mavrommatis

Cleanness of steel is justified, measured and estimated in steelmaking process through different concepts which are mainly based on operational, empirical or semiempirical parameters and describe ?cleanness as a state?. In this work a theoretical concept is developed, considering ?cleanness as a process? and introducing a dynamic aspect into the quantification of cleanness of a steel melt, linking operational parameters with physicochemical variables, which are based on first principles. This concept and the here derived and developed variables and parameters are based on the earlier defined agglomeration index (AI) of a steel melt, the ratio of the mean inclusions diameter (MID) to the mean inter-particle distance (MIPD), which is shown to be a measure of the agglomeration tendency of the melt after deoxidation, and can serve both, to monitoring cleanness during steelmaking operation and to be useful as a basis for mathematical modelling of cleanness and of the metallurgical measures in plant, associated with production of clean steels.

Jan 1, 2006

By J. C. Riani

The release of heavy metals into the environment is increasing among others due to human activities such paint and pigment industries, tanneries, and metal finishing industries. Among metal releases, chromium is notable because this metal is carcinogenic. Thus, the aim of this work is to use an ion exchange system composed of one cationic resin column and one anionic resin column in order to adsorb the chromium (III, VI) from chromium electroplating effluents with the objective of recycling the water. The methodology consists of chromium adsorption tests using the ion exchange resins system with Purolite the 850 (polystyrene matrix, functional group quaternary amine) and Purolite C 150 (polystyrene matrix, functional group sulfonic acid). The contaminated solutions were passed through the columns with the assistance of peristaltic pump. Samples of the outgoing solution were taken in order to control the conductivity and pH and analyze the metals. The effects of the feeding outflow on the chromium adsorption were evaluated. The results show that the quality of the water collected at the end of the process is within the Brazilian standards about the discarding of toxic substances in the environment (CONAMA 357/05). This makes possible the recycling of water into the process and also its discharge in the rivers.

Jan 1, 2006

By Nicholas S. Lynn

"A new process has been developed to bioleach refractory gold ores to expose the precious metal values using Thiobacillus ferrooxidans bacteria.The ore is hosted in a limestone rock with secondary replacement of carbonaceous and pyritic minerals. Crushing, stacking, bioleaching, rinsing and neutralization have been completed in a 45-day total time cycle. The use of sulfuric acid operation, and concentrated Thiobacillus ferrooxidans population allows the short bioleaching cycle.The ore is then processed using conventional Carbon-In-Leach Cyanide recovery techniques.ABSTRACT ONLY"

Jan 1, 1997

By Peter G. Smith

Tri-calcium aluminate (TCA) is a dominant alkaline component of the red mud residue from the Bayer process. A method being considered for industrial implementation partially neutralizes the residue by contacting it with gaseous CO2. This paper outlines the chemistry of CO2neutralisation of TCA under conditions relevant to the treatment of Bayer residue. CO2 neutralisation of the liquor is fast. It results in the formation of amorphous aluminium hydroxide and dawsonite that agglomerate together. Neutralisation of solid TCA is slower and leads to the formation of calcite, dawsonite and amorphous aluminium hydroxide. The dissolution of TCA in partially neutralised slurries causes pH reversion. However the carbonated solutions contain a store of bicarbonate that can supply aqueous carbon dioxide to complete the transformation. The pH at which the carbonation is carried out will affect the degree of TCA transformation during the carbonation process. In particular, if the pH of the carbonation is too low (near 7.0), calcite precipitation is inhibited and the degree of transformation is low. Controlling the carbonation pH helps to optimise the neutralisation process.

Jan 1, 2003

By Maria de Campos

The pre-reduction behaviour of chromite particles in methane-argon and methane-hydrogen gas mixtures was investigated between 1050°C and 1250°C. Loose bed of chromite particles were reacted in a vertical tube furnace under a pre-set gas mixture predetermined time intervals. Metallization results were obtained for the Cr and Fe components by chemically analyzing the reaction products. SEM-EDAX techniques and X-ray diffraction were employed to elucidate the reduction mechanism. It was found that higher reduction kinetics and higher Cr:Fe ratios in the metal phase would be achieved when hydrocarbon gas was used in comparison to classical carbothermic reduction at a given temperature. The reduction rate was generally bulk gas mass transfer controlled to the reaction site for initial stages which then was followed by ionic diffusion rate control. It is proposed that methane did not partake directly in the reduction but cracked, presenting the reaction site with hydrogen gas and atomic carbon, which was able to immediately react at the immediate area of reduction regeneration CO and H2 and thus maintaining a low partial pressure of oxygen at the reaction site.

Jan 1, 2006

By Eustathios S. Kikkinides

This work presents an integrated approach for the optimal design and control of hydrogen storage beds. A detailed 2-D mathematical model is developed for metal hydride beds and validated against experimental and theoretical literature results. Based on recent advances in dynamic optimization, the model is used to find the optimal process design and operating strategy in order to minimize the storing time, while satisfying, a number of operating constraints (such as pressure drop limitations, cooling fluid availability and maximum tank temperature). Trade-offs between various objectives, alternative design options and optimal cooling control policies are revealed illustrating the potential of the approach. In a further step the model is used to exploit the benefits between material and process design. Systematic simulation and optimization studies are performed at two different length scales (tank and adsorbent pore level) for carbon based materials. The macroscopic approach determines the optimal values of the sorption parameters while, based on these results molecular simulation techniques are employed to determine the pore size distribution of the adsorbents.

Jan 1, 2006

By Gordon Holcomb, George R. St. Pierre, Robert A. Rapp

Carbon/Carbon composites offer promise as high-temperature structural materials. A primary limitation on their application is the need to provide protection against oxidation in hot oxidizing environments. Silicon carbide conversion coatings have been shown to provide extended protection at temperatures of 1600°C. SiC coated C/C components have been used in several aerospace applications. In the present paper, the preparation of carbon fibers and their treatment during subsequent processing into coated components are discussed with particular emphasis on the processing variables that can result in improved oxidation resistance. In particular, the influence of substrate inhibitors and selective sealants for cracks in coated C/C components are analysed.

Jan 1, 1988

By Viviane Tavares de Moraes, Denise Crocce Romano Espinosa, Jorge Alberto Soares Tenorio, Adriana Johanny Murcia Santanilla

"Increasing volumes of solid waste are generated worldwide, due to the continuous technological advances, the electronic scrap is part of these waste, requiring the study of recycling processes to stimulate this activity or the reuse of its components. The separation of nickel from sulphate leach solution, which also containing iron, zinc and aluminium was carried out using bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272) as extractant, in order to determinate the effects of pH and temperature. The number of stages required for extraction was also assessed. The results showed that the metal extraction increased with increasing pH. On the other hand, increasing temperature was not favorable for all metals. However, under conditions used in this paper the purification of solution containing nickel was possible.IntroductionIncrease in the demand of metals in the world for use in industry causes a great exploration of natural resources. One outcome of this is increased investigations for the recovery of metals from industrial wastes. Nickel is found in wastes, such as batteries and electric and electronic devices, this kind of waste becomes a significant source for metals recovery. Since nickel is also present in printed circuit boards, which are associated with electric and electronic equipment, it can be recovered from this kind of waste through different techniques. It is important to highlight that iron is generally associated with this scrap [1] and for its removal chemical precipitation is often used. On the other hand, the solvent extraction process is widely used for treatment of leach liquors, because it can be produce high purity solutions [2, 3]. This technique is based on the purification of solution using contact between a liquor leaching and the immiscible organic solution, which contains an extractant that promotes the desired metal transfer [4]."

Jan 1, 2012

By Takashi Nagai, Hideaki Sasaki, Masafumi Maeda

"The production of solar cells is increasing dramatically and the shortage of polycrystalline silicon for these cells has become a serious problem, making development of a low-cost production process for solar grade silicon essential. An electron beam melting technique is known to be effective for the removal of phosphorus from molten silicon. Although the phosphorus is removed by preferential evaporation in this process, the rate of removal is not sufficient, and its improvement requires thermodynamic information on phosphorus in the molten silicon. In this research, the vapor pressure of phosphorus in equilibrium with a siliconphosphorus alloy was measured by double Knudsen cell mass spectrometry with a system blowing gas into the Knudsen cell. The activity of phosphorus in silicon, the Gibbs energy change of the dissolution of phosphorus in silicon, and other factors were estimated from the results. Using these data, we provided guidelines on how this process can be improved.IntroductionSolar energy is in great demand since it is inexhaustible and cleaner than that from conventional energy resources. Silicon is the material most widely used to convert solar energy into electricity. Figure 1 shows the recent production of solar cells. High purity silicon for solar cells, namely solar grade silicon (SOG-Si), has been commercially supplied mainly from off-grade high purity silicon in the semiconductor industry. However, production of solar cells has increased rapidly in recent years, and the shortage of SOG-Si has become a serious problem, so that a new processes which can produce SOG-Si economically are required.Directional solidification was applied to remove transition metal elements such as Fe or Ti by segregating them from the remaining melt. However, such solidification is useless for phosphorus because the segregation coefficient of phosphorus is nearly unity. Numerous approaches have been made in an attempt to produce a resource of low cost SOG-Si from metallurgical-grade silicon (MG-Si). [1,2]"

Jan 1, 2012

By R. Ghisleni, R. E. G. Bohrer, L. Radtke, R. M. C. Santana

"The major source of environmental pollution in urban areas is the transport sector and its impact on human health and the greenhouse is preoccupying. In many works of literature is monitored the pollutants in urban cities, however in specific areas such as universities, they are scarce. Therefore, the aim of this work is to monitorate the gaseous pollutans in a bus terminal at Santa Cruz do Sul University-UNISC and to develop a control framework of the air quality. Six points were selected for monitoring, being one of them inside a bus. The monitoring of CO, HC and CO2 were carried out on arrival and departure of the bus. Preliminary results conducted in a day of spring showed that the most critical condition was during the night shift, where the concentration of CO (200 ppm) was the highest, caused by the vehicles increase, due to the larger number of students.IntroductionThe first major global assessment of climate change science in six years has concluded that changes in the atmosphere, the oceans and glaciers and ice caps show unequivocally that the world is warming. The report released on February 2, 2007, the first of four volumes to be released this year by the IPCC, also confirms that the marked increase in atmospheric concentrations of greenhouse gases is the result of human activities.The transport sector has become by far major source of environmental pollution in urban areas. The continual traffic growth has raised concerns over the impact of traffic emissions on human health and urban environmental quality, and has fuelled the demand for a coherent regulatory framework for the management of traffic, air quality and emission at urban level, as well as at regional and national scales.In Greater Metropolitan São Paulo, Brazil, fossil fuel combustion in the transportation system is a major cause of outdoor air pollution (Miraglia&El Kouri, 2007). In China several studies on gaseous emissions are being conducted by F. Costabile&Alegrini, (2007), developed a study on the pollutants in the city of Beijing suggesting methods for the control of pollution.The results obtained from the estimation of the atmospheric pollutants emitted monthly in Campo Grande/MS, Brazil, by buses and minibuses, which employ diesel, biodiesel or natural gas as fuels showed that the substitution of diesel by biodiesel would diminish the emissions of pollutants (Kozerski&Hess, 2006)."

Jan 1, 2008

By Linping Yu

A simplified ED process was developed for organic acids recovery from cyclohexanone waste in this paper. In this regard, the one-stage ED was investigated directly without pretreatment, such as ion-exchange or nanofiltration to removal of foulants. The current efficiency and the energy consumption in the ED process for the recovery of carboxylic acids from cyclohexanone waste is theoretically analyzed and experimentally tested. The concentration of recovered carboxylic acid is related to many parameters and still needs more work to be determined.

Jan 1, 2009