Search Documents

By Ozgul Dere Ozdemir, Muge Sari Yilmaz, Sabriye Piskin, Deren Sibel Kasap

"Galvanic sludge is generated at the end of the waste water treatment process of metal plating system. The waste sludge is one of the main hazardous solid wastes produced by metallurgical industries. It is caused the harm of human health and damage of the environment due to containing reasonable amounts of toxic metals (e.g., nickel, zinc, copper, chromium, iron, lead, cadmium, etc). The concentration of those toxic metals in the wastewater might reach 30% (w/w, dry weight) making their removal and recovery an interesting issue.In this study, synthesized titanium dioxide is used as adsorbent to remove nickel in leachate of galvanic sludge. The adsorption experiments were carried out isothermally at four different temperatures. The effects of pH, temperature, and contact time on nickel adsorption efficiency were investigated, and the optimum parameters were determined from the experimental studies. The experimental results indicated that pH, temperature, and contact time played a significant role on the adsorption capacity of nickel.IntroductionRapid industrialization has caused increasing the heavy metal concentration in biosphere with the industrial wastes. These wastes are generated in various industrial processes such as electroplating. Galvanic sludge is a hazardous waste that generates from metal plating industry by chemical precipitation of heavy metals from acidic or alkaline solutions during the waste water treatment process. Heavy metals are tend to bioaccumulate thus they are treated the living organism [1-2].Galvanic sludge is mainly disposed on landfills for these reason it is a big problem for environment. Galvanic sludge containing nickel (II) is common because nickel (II) is used in electroplating process [3]. In drinking water, nickel may cause health problems if found in amounts greater than the health standard set (MCLG: 0.1 mg/L) by the United States Environmental Protection Agency (EPA). The higher concentration of nickel (II) in ingested water may cause severe damage to lungs, kidneys, gastrointestinal distress, e.g., nausea, vomiting, diarrhea, pulmonary fibrosis, renal edema, and skin dermatitis [ 4]. For these reasons, it must be treated before disposed to landfill."

Jan 1, 2011

By D. Valic

In 1997, 9.2 million tonnes of mined, recoverable copper was produced, of which, 1.8 million tonnes or 19.4% was produced by leaching, solvent extraction and electrowinning. The amount of copper produced by this method grew faster than those attained from concentrate smelting, signifying the growing importance of this low-cost production method. Statistical experimental design, unlike traditional approaches, allows for proper distribution of experiments within the boundaries of factors being studied such that the number of experiments required to develop a sound relationship between the factors and a response is minimized. In the past, very little use has been made of statistical experimental design in copper electrowinning studies. Traditional one- variable-at-a-time approaches are widely employed for this purpose. The present study employs a factorial experimental design to relate current efficiency with current density (180 and 300 A/m2), copper concentration (25 and 65 gL), and temperature (40 and 60 °C). Pure synthetic electrolyte with a constant acid concentration of 180 g/L was used throughout the study. The designed study produced a linear relationship where the independent variables of current density, copper concentration, and temperature, and their interactions, were found statistically significant. It was shown that current efficiency could not solely be used as a predictor of copper cathode quality. The quality of the deposit is difficult to be incorporated into a model or relation. It was determined that other measures, such as cathode morphology and crystal structure should be considered. This was done through XRD and SEM analysis.

Jan 1, 1999

By Abhishek Asthana

The incineration of Municipal Solid Wastes (MSW) is an attractive process for reducing the volume of the wastes and recovering their energetic value, which, however, requires to be strictly controlled in order to limit its impact on the environment. In this context, we have undertaken the mathematical modeling of the different sections of a typical incineration plant. The combustion of the waste bed, usually carried out on a moving grate, is at the core of the process. This paper presents the 2-dimensional, steady-state model that we have developed for simulating the MSW combustion. The model describes gas flow through the porous waste particle bed, the gas-solid reactions, conductive and radiative heat transfers, drying of the feed, its pyrolysis and the emission of volatile species, combustion of the pyrolysis gases, the formation of char and its gasification by water vapor and carbon dioxide, and the consequent reduction of the bed volume. Pyrolysis kinetics distinguish between cellulosic and non-cellulosic materials and are experimentally derived from our laboratory measurements. The calculated results give a deep insight into the various involved phenomena, an example being the complete consumption of oxygen in a large zone of the bed and the related appearance of a char gasification zone. The influence of various operating parameters, like the temperature and flow rate of primary air, is presented and explained. Finally, the effect of stirring the waste bed on the moving grate is also analyzed.

Jan 1, 2006

By B. J. Vorster

AngloGold South Africa region currently consists of 12 Gold Plants. These plants use a combined total of $20 million of cyanide per annum. Of this, the .major portion (60%) is consumed at two Ergo dump retreatment plants. Historically the primary motivation for cyanide control at Ergo has been one of leachlcost optimisation. However, more recently, with the increased public awareness of cyanide in the environment, a secondary but increasingly important motivation for control has been to ensure that only the minimum amount of cyanide is added to the process whilst not compromising leach performance. Following a brief overview of the Ergo process, the methodology in detennining the amount of cyanide to be added is described. The paper then traces the developments in cyanide control from very basic? manual systems to the current automated control system. In line with the increasingly sophisticated control systems, developments also took place in regards to the method of cyanide analysis. The development of these analysers is also discussed. Whilst cyanide is one of the major drivers, if not the major driver of gold dissolution, it cannot be viewed in. isolation particularly with respect to the relationship between cyanide and oxygen as ascertained from the Elsner's well known equation. Consequently, in order to control cyanide addition, knowledge of the relative cyanide/oxygen profiles is necessary. Various means investigated at Ergo for pulp oxygenation have therefore been included for the sake of completeness. Finally a comparison is made of the control achieved from the current system compared to the? original manual system. The knowledge and experience gained at Ergo is now being used to draw up guidelines for the installation and optimisation work at the other AngloGold plants. The net effect of this will be reduced cyanide consumption for the region, which also, apart from the obvious economic benefit, translates into a reduced environmental; risk.

Jan 1, 1998

By Roland Loewen

A review of the aqua regia method for the recovery of gold from jewelry shop wastes is given. Also outlined is a specialized procedure for the recovery of the silver that occurs in these wastes. A classic method for the recovery of platinum and palladium is, given. There is a brief review of other gold and silver refining methods. Environmental conditions are discussed and a few perhaps, new and useful processes ,are mentioned. References are by author or editor and are listed alphabetically. Suggestions for further information in the field of precious metals, are given in a final list.

Jan 1, 1989

By Mamoru Kuwahara, Tomohito Taki, Masamichi Sano

"Theoretical basis and experimental results on ultrasonic separation of dispersed inclusions from molten metal are outlined. Transitional formation of an ultrasonic standing ·wave field in a liquid bath is numerically predicted based .on the wave equations. Numerical solution of the equation of motion of a fine particle in a standing wave field indicates that the inertia term can be neglected during conventional ultrasonic separation of fine particles: Analytical solutions for the position at which particles are coagulated the minimum power for separation, and the ultrasonic separation time are derived to incorporate such key process parameters as the density difference and the acoustic energy density exerted. Cold model experiments have been carried out to observe ·transitional coagulation of polystyrene particles in an aqueous sugar solution with the incidence of standing ultrasonic plane wave. Experimental results agree well with the theoretical predictions.IntroductionDespite of recent progress of fundamental and applied researches in metallurgical systems, advanced materials· with less inclusions and better properties may demand more innovative processing in a: molten state. It may be realized by applying electromagnetic and/or ultrasonic external fields to the systems. The present authors1)·2) have been proposing : new methods of ultrasonic processing of materials based on such phenomena as acoustic streaming, acoustic radiation pressure on dispersed phase in a standing wave field, and the cavitation in liquid associated with use of high-intensity ultrasound and so on. Taking account of common physical natures between ultrasound and sound wave, we call such · a processing assisted by acoustic wave as ""sonoprocessing"". This report ·deals with some theoretical and technological aspects on the ultrasonic separation of fine particles from liquid, which could become an important operation to produce clean materials. Fundamental theory and ·supporting experimental results will be given below to give an insight into the liquid metal sonoprocessing."

Jan 1, 2000

By Gökhan Demirci, Ishak Karakaya

"Energy consumption in electrolytic magnesium cells is well above the theoretical values. However, the mechanism of the back reaction, the main cause of the current losses, has not been fully understood yet. Magnesium dissolution into the melt is generally regarded as the limiting step for the back reaction. Accordingly, present cell designs are made with priority given to fast magnesium removal from the cell. However, experimental data and modeling results in this study indicate that the limiting step for the back reaction between magnesium and chlorine is the chlorine dissolution into the electrolyte when physical contact between electrolysis products was eliminated. Effects of chlorine bubbles on the current efficiency and the cell potential were investigated. Results show that the extent of back reaction is proportional to the chlorine surface area in contact with the electrolyte per unit time, and the cell potential increases with the amount of chlorine bubbles inside the electrolyte.1. IntroductionMagnesium is less dense than the electrolyte in electrolytic magnesium production. Therefore, both electrode products, magnesium and the chlorine gas, move upwards inside the molten salt electrolyte during electrolysis. The upward motion of electrode products promotes the most important current loss mechanism, the ""back reaction"". Separation of the highly reactive species; liquid magnesium and the chlorine gas in the cell, to prevent their recombination is one of the main concerns in cell designs. The employment of large inter-electrode distance or a separation wall in early cell designs; decreased the extent of recombination, but increased the cell voltage and energy consumption. Recent cell designs, on the other hand, make use of lifting action of chlorine gas [1,2] by utilizing smaller inter electrode distances to separate the magnesium and chlorine gas faster. Although energy consumption was reduced, but more physical interactions between electrode products make electrolytic magnesium cells still highly inefficient when energy consumptions are compared with the theoretical values. Today, the most efficient industrial cells utilizing high purity feed operate at 10.5-11.5 kWh kg-1 Mg [3-5] and it is considerably higher than the theoretically attainable value of about 6.0 kWh kg-1 [6]. This large gap demonstrates the necessity of more research on physics and chemistry of magnesium cell electrolysis."

Jan 1, 2011

By Wentao Guo, Xuefeng She, Qingguo Xue, Jingsong Wang

By the coke gasified reaction device and online measurement high-temperature compressive strength apparatus, the variation of pore structures of coke after gasified reaction with CO2 and H2O was investigated. Research illuminating the influences of solution loss rate, temperature, and carbon species on compressive strength of coke was also carried out. The results showed that the total compressive strength was higher than for the reaction with CO2. The high-temperature compressive strength of coke decreased with the increasing of solution loss ratio or temperature after reacting with CO2 and H2O. At the same solution loss ratio, the damage of pore structure to coke strength after gasified reaction with H2O was relatively smaller and the deformation resistance was stronger when compared with that in CO2.

Jan 1, 2016

By Michael Sheedy

Sulfuric acid is widely used as an electrolyte for the electrorefming and electrowinning or metals. Impurities in this electrolyte are controlled by continuously bleeding solution from the tank house. In addition to the contaminant these bleed streams contain high levels of sulfuric acid and the metal being recovered. Subsequent treatment of these bleed streams often requires neutralization which generates large volumes of solid waste. Absorption resin technology employing a novel ion exchange technique known as Recoflo® allows the separation of the mineral acid from dissolved metal salts. The recovered acid is suitable for recycle back to the electrolyte circuit. The metal salt and other contaminants leave the process free .of the sulfuric acid. In this process, known commercially as the APU®, ion exchange resin is used to sorb sulfuric acid while excluding the metal salts. The purified acid is then removed by washing the resin with water. The process has been extensively used for the recovery of waste pickling acids in the steel industry and anodizing solutions in the aluminum industry. In the mining and metallurgical industries the process has been successfully evaluated for the separation of excess sulfuric acid from copper electrolytes, the removal of magnesium and manganese contaminants from zinc electrolytes, and nickel and copper from copper electrolytes. A full scale installation on a copper refinery bleed stream at Palconbridge's Kidd Creek plant in Timmins, Ontario has now been operating successfully for more than 1 year while pilot field trials have been successfully completed on other applications.

Jan 1, 1997

By N. El-Kaddah, J. W. McKelliget

"A mathematical model for the analysis and design of hybrid plasma reactors for advanced materials synthesis is presented. The model is based upon a solution of the electromagnetic vector potential equation and is capable of predicting the two-dimensional velocity, temperature, and electromagnetic fields as well as the reaction kinetics inside the reactor for any axi-symmetric coil configuration. The model is used as a computer aided design tool for the design of hybrid plasma reactors consisting of a conventional DC torch augmented by an RF induction coil and it is demonstrated that the hybrid system possesses superior characteristics for materials synthesis over conventional DC or RF systems. The coupling between the RF and DC components is found to affect both the temperature field and the flow field and to have a significant effect on the reaction kinetics and on materials recovery. The model is used to study the thermal decomposition of silicon tetrachloride as a function of reactor design and operating parameters and it is demonstrated that through a CAD approach it is possible to significantly improve the operation of materials synthesis systems.IntroductionIn recent years there has been growing interest in the use of the inductively coupled plasma for chemical synthesis as a way of meeting the increasing demand for high quality, high performance materials for use in critical applications/l/. Although the basic feasibility of this approach has been demonstrated in the laboratory/2,3/ there still exists a number of operational problems that adversely affect system performance for some applications. In particular, the recirculation and back flow effects that arise from the electromagnetic forces in the plasma can result in the repulsion of the reactants from the hot plasma core and their subsequent deposition on the walls of the reactor. Another operational problem arises from the fact that the energy dissipated in the plasma has to compensate for the heat losses to the environment by conduction, convection, and radiation in order to maintain the ionization of the plasma and, hence, the stability of the plasma may be affected by the presence of the reactants and their products."

Jan 1, 1988

By Xi Yun Yang

Ultrafine (0.1µm) spherical magnetite powder was prepared successfully by hydrothermal reaction of ferrous sulfate and sodium hydroxide with activated pyrite as reducing agent in the temperature range 120-140?. XRD and XPS analyses indicate that pH value and pyrite amount have a direct influence on the composition of the product. Stoichiometric Fe3O4 can be obtained only when pH value is 12 and the molar ratio of pyrite/ferrous sulfate is 1:1.8. The hysteresis loop of Fe3O4 shows a ferromagnetic behavior with a saturation magnetization of 75.2 emu/g and a coercivity of 152Oe.

Jan 1, 2006

By L. L. Ludwig, S. E. James, B. L. Motycka

Significant modifications to the electrolytic zinc plant operated by Big River Zinc Corporation were made at the end of the 1990's resulting in increased capacity and improved efficiencies. A new cell room, with the innovative use of acid-resistant concrete cells and a modern ventilation system, was installed to raise the capacity from 80,000 tonne/y to 106,000 tonne/y of finished zinc. Improvements to the leaching section include the conversion from a single to a two-step process, with associated equipment changes, to improve the quality of the residues produced. Another key change is the construction of a facility to allow the use of zinc oxides from secondary sources as a feed to the plant. This paper describes these improvements and the current operations.

Jan 1, 2000

By D. N. Collins

A sampling program was conducted in which both spoon and isokinetic sampling techniques were used to collect samples from the reaction shaft. The samples were then characterised by chemical, XRD and mineralogical analysis. Further information was acquired by measuring the oxygen potential and temperature at the bottom of the shaft using disposable probes. Comparison of the results of the two sampling methods showed that the spoon samples were devoid of material less than 25 m. Sulfur analyses on the samples provided information on the extent of reaction, plume shape and recirculation patterns. Disposable probe measurements showed the measurable particle temperatures ranged from 1150 to 1700 °C and that the material falling into the bath had a normalised oxygen potential similar to the slag. These latter measurements combined with the sulphur elimination and mineralogical analyses provided further information on the extent of reaction and enabled the reaction sequence to be ascertained.

Jan 1, 1999

By F. F. Aplan

Though over 100 minerals are known to contain the rare earth (RE) or lanthanide elements, only a few provide the bulk of the world's source of these elements. The principal RE-containing mineral, monazite [(Ce,La,Th,Y)PO4], is recovered by gravity, magnetic, electrostatic and flotation concentration methods, while the other important source mineral, bastnasite [CeFC03], is concentrated by flotation. The processing of the lesser important source minerals is discussed, as is the recovery of the lanthanides from apatite [Ca5(P04)3(F,OH)] where the rare earth elements are present from trace amounts to over 10% as the mixed oxides.

Jan 1, 1989

By Patrick R. Taylor

The synthesis of high-purity ultra-fine barium strontium titanate powders (BST: BaO6Sro.4TiO3) has been performed in a non-transferred are D.C. thermal plasma reactor. Slurries of aqueous solutions of dissolved barium and strontium nitrates and solid titanium dioxide powders were used as precursors. Oxygen and argon were used as carrier gases, and pure argon and combinations of argon and nitrogen were used as plasma gases. The plasma torch power was varied, as well as the oxygen flow rate and the total molar concentration of the precursors. A graphite plate was designed to protect the torch electrode and lower the level of impurities in the product. A thermochemical analysis of the Ba(NO3)2-Sr(NO3)2-TiO2-H2O-O2 system was performed to predict the conditions for the formation of BST and the feasibility of the reaction, The powders collected from the different sections of the reactor were characterized using Transmission and Scanning Electron Microscopy, X-Ray Diffraction, and ICP chemical analysis. The powders produced showed high conversion to BST, ultra-fine particle size (< 30 rim) and high purity, which makes this a potential process to produce ceramic materials for electronic devices.

Jan 1, 2003

By Jonathan M. Berkoe

Design engineers and metallurgists have long recognized the need for better methods to calculate a wide range of fluid dynamic effects in smelters and hydro- metallurgical facilities. Examples can range from the capture of fume in the secondary hoods of a copper converter, to controlling the thermal effects of heat transfer resulting from metal and slag flows within a furnace. With the advent of relatively low-cost, high- speed computers and user-friendly, commercially available computerized fluid dynamic (CFD) programs, these calculations can now be made. Use of CFD increased the understanding of both hot gas and molten flows in smelter facilities and has already led to design improvements in converter fume control hoods as well as improved management of heat transfer in electric furnaces. This paper will present two representative CFD applications to metals industry facilities. To date, Bechtel has implemented CFD results on four continents.

Jan 1, 1999

By G. K. Ruhlandt, C. W. Kim

"A 3-D Finite Element Method program called ""SOLCAST"" has been developed to simulate the casting solidification process. Using the temperature recovery method to evaluate the latent heat of fusion and applying a new combination of the time integration scheme, SOLCAST reduces the computational time significantly compared to an existing commercial FEM program, and produces accurate results comparable to experimental casting results. Prediction of casting shrinkage porosity for A390 aluminum alloy will also be discussed. To make this FEM program useful for foundry engineers, this program was connected to a commercial pre- and post-processor.IntroductionBecause of recently increased competition, foundrymen must produce high quality castings more economically. Therefore, casting solidification analysis prior to casting production is an attractive way to reduce costs and development time.Although the actual casting solidification process is a very complicated phenomena, foundrymen could predict where shrinkage defects would occur based on a transient conduction heat transfer analysis that includes the liberation of latent heat. A numerical analysis is generally required to solve the heat diffusion equation with the latent heat diffusion term, because casting shapes are very complicated and pure materials are rarely used.Different numerical methods have been applied to the casting solidification analysis 1. Among them, a finite difference method 2 and a finite element method (FEM)3 are most commonly used.Each simulation method has one or more basic difficulties which are different for each method. These difficulties are:(1) Modeling casting shapes on a computer.(2) Time consuming computation.(3) Uncertain material properties."

Jan 1, 1986

By Seung-Chul Lee

Transparent conducting tin(1V) oxide thin films have been studies and developed for the electrode materials of solar cell substrate. Fabrication of tin oxide thin films by sol-gel method is process development of lower cost photovoltaic solar cell system. The research is focused on the establishment of process condition and development of precursor. The precursor solution was made of tin isopropoxide dissolved in isopropyl alcohol. The hydrolysis rate was controlled by addition of triethanolamine. Dip and spin coating technique were applied to coat tin oxide on borosilicate glass. The resistivity of the thin film was lower than 0.18-cm and the transmittance is higher than 90% in a visible range.

Jan 1, 1999

By Elsa Agante

Recycling of solid wastes, a common practice nowadays, requires the separation of the different materials in order to increase the products added value. The separation of one plastic from mixtures of different types of plastics is not easy due to their similar physical properties, but different techniques are available, from automatic sorting systems based on optical sensors to techniques adapted from mineral processing, namely gravity, froth flotation and electrostatic processes. In the last decade, many researchers have addressed the separation?s problem of different polymers, like Polyethylene Terephthalate (PET) and Polyvinyl Chloride (PVC), two polymers commonly used in packaging which have similar density. One proposed technique is the classical froth flotation performed in agitated cells. Froth flotation is a versatile and relatively cheap process widely used in mineral separation. It is based on the different behaviour of particles in the presence of an inter-phase air-water, which depends on the materials surfaces properties. Froth flotation can be affected by some variables such as impeller speed and air flow rate. Agitated cells, when used with low density materials, like plastics, can produce overstated turbulence that prevents the adhesion and collection of particles in the froths. In this case, separation is favoured by column flotation smoother hydrodynamics. This paper proposes the separation of PET from PVC by column flotation. The experimental work was carried out in a column of 9cm diameter and 1m high. The effects of some operating conditions, such as depressor and frother concentration, air flow rate and feed grain size on products grade and recovery were evaluated and the best flotation conditions for the separation of these plastics were established.

Jan 1, 2006

By Khosrow Nikkhah

Increasingly ion exchange systems are being included in design of hydrometallurgical plants for metal extraction or impurity removal. Because such systems operate sequentially and are based on resins that exchange one ion for another, store it temporarily and release it to a regenerating solution, the usual steady state heat and mass balancing tools and spreadsheets cannot be used to design them successfully. This paper outlines the role of dynamic simulation in design of ion exchange systems. Examples are given for use of dynamic simulation in design and investigation of equipment based on consideration of the effect of input criteria such as expected ion loading and elution profiles. The methodology for dynamic modeling using IDEAS in design of multi column ion exchange trains operating in parallel is presented. Results shown include the non-steady state distribution of extracted metal and limitations imposed on operating conditions. These conditions include proposed sequencing of columns for loading and elution cycles, loading, elution and recycle flow rates as well as size and choice of related ion exchange plant equipment.

Jan 1, 2003