Search Documents

By S. Goto, S. Yamashita, K. Hata

"The average consumption of zinc dust for purification of zinc leaching solution is more than 25 kg per tonne of electrolytic zinc. Authors proposed to remove impurities in zinc leaching solution by electrolysis instead of cementation by zinc dust. The effects of copper and arsenic on electrodeposition of cobalt in zinc sulfate solution were examined fundamentally using a potentiostat. It is observed that cobalt is easily deposited on a cathode at potentials under -480mV with arsenic. Mesh cathodes of stainless steel and lead anodes were used in a small electrolytic cell and the electrolyte was circulated through 'the electrodes during the electrolysis. The effect of electrolyte circulating rate , pH, cell temperature, current density, and concentration of copper and arsenious ions on removal of cobalt were studied. Removal of Cd and Ni are also examined.IntroductionCobalt is difficult to remove from a zinc leaching solution by a simple cementation reaction using zinc dust. However, it is easily precipitated by zinc dust with co-addition of arsenious or stibinous oxide and copper ion in practical operations(I), (2), (3). The consumption of zinc dust for purification is 16-152 kg per tonne of electrolytic zinc and 65% of this zinc dust consumption is used for cobalt purification. The average retention time for purification of cobalt is 4.5 hours (1). A more economical process for purification is desired instead of zinc dust. The mechanism of this acceleration effect of copper and arsenious oxide on removal of cobalt are explained by the authorsas follows; a galvanic cell is formed between zinc dust and copper which is precipitated firstly, and cobalt is reduced on copper as Co-As alloy by this galvanic current(2). This assumption was confirmed in experiments using a galvanic cell with a membrane( 4). The following galvanic reactions occur between zinc dust and copper precipitate; on copper cathode,2H+ + 2e -= Hz(g)2Coz+ + 2HAs02 + 6H ++ 10e -= 2CoAs + 4HzOand on zinc anode,Zn = Zn = 2+ 2e –This galvanic current becomes almost zero in a zinc sulfate solution which includes only cobalt and no arsenious oxide, and cobalt is weakly deposited on a copper cathode. Cobalt deposition requiers a high degree of cathodic polarization. However, the galvanic current flows almost constantly in an electrolyte, which includes arsenious oxide, and the cathode potential is kept at about -500mV. Cobalt is precipitated as Co-As on the cathode.The authors assumed that cobalt may be removed by electrolysis at a very low current density instead of zinc dust and the following experiments were carried out. In the first part of this paper, the fundamental experiments using a potentiostat on the behaviour of cobalt in zinc sulfate solution are described. In the second part, the results of the electrolysis are reported. Cobalt is removed by a new type of an electrolytic cell, which was desigoed to <Iccelerate the rate of deposition of cobalt. The removal of cadmium and nickel in a solution which includes cobalt and arsenic are also examined."

Jan 1, 1997

By B. Q. Li

A numerical study of the developing fluid flow and thermal aspects during the staning phase of aluminum continuous casting processes is presented. The deforming finite element method, coupled with a quasi-Lagrangian formulation, is used to represent the growth of an ingot and the dynamic fluid flow and thermal behavior that evolves in the growing ingot. The mathematical formulation of the problem and the numerical treatment are discussed. The algorithm solves the free moving nodes as part of total unknowns with an automatic time step control for time integration. This permits an optimal computing efficiency while still keeping the computational errors under control. A selection of the results obtained using the algorithm is presented. The results are concerned with the evolution of fluid flow, temperature and solidification phenomena during a DC round ingot casting process, as it evolves from the beginning of casting operation to a steady state. These results show that the time-varying, complex fluid flow and thermal phenomena during continuous casting processes can be very well represented by the computational algorithm. The results also illustrate that, during the casting process, ~e fluid flow and temperature fields change drastically at the initial stage but evolve slowly afterwards

Jan 1, 1993

By E G. Prado

We have confirmed on bench scale the removal of chlorides and alkalies (+95%) and over 2/3 of the zinc, lead and cadmium from EAF dusts. This has been achieved with arrononium acetate solutions alone, or with combinations of water wash, amonia-ammonium carbonate and ammonium acetate solutions. Also confirmed are the process routes for the recovery of the aforementioned elements into marketable products. The technology involves the complete recycling of the reagents. The FAF residue is returned to the electric furnace without risk of impurities buildup. Commercial scale testing with the recycled dust was satisfactory, including quality of the slag and its behavior during the melting stage. A cursory feasibility evaluation is presented.

Jan 1, 1994

By G. Lissens

In this work the electrochemical combustion of dissolved organic species in a single compartment cell containing a titanium mesh cathode and a boron doped diamond anode has been studied, The organic molecules involved were complexing agents such as EDTA (ethylenediaminetetraacetic acid) or NTA (nitrilotriacetic acid) used in metal plating shops and bright nickel plating bath additives, From batch experiments, it is shown that complete decomplexing of EDTA and NIA is feasible. Complete TOC (Total Organic Carbon) removal from solutions containing 0.01 M EDTA, 0.02 M NTA and bright nickel plating bath additives could also be achieved. Recycling experiments show that decomplexing of EDTA and NTA solutions can be obtained at an average electrical energy input of ~20kWh.kg-1 of complexing agent. Decomplexing rates of respectively 3.l3 mmol.Ah-1 for EDTA and NTA have been obtained, The Instantaneous Current Efficiency (ICE) was 71% for EDTA and 95% by NTA, Simultaneous recovery of Cu from a 0.01 M Cu-EDTA solution has also been evaluated. A solution (1.8 dm3) containing 0.01 M EDTA and 528 ppm of Cu was treated in a single compartment cell at a current density of 2 A.dm-2. 73% of the TOC could be removed and a final copper concentration of 8 ppm was obtained.

Jan 1, 2003

By Varuzan Kevorkijan

A new method for faster production of functionally graded metal-ceramic laminates is based on reactive pressureless counterflow infiltration/penetration of a ceramic substrate with two different metallic infiltrants. The porous or dense ceramic preform is pressurelessly infiltrated or penetrated from one side by the first metallic infiltrant to the desired cross section of the preform, producing the top layer made up of the solidified infiltrant and the underlayer consisting of reactive infiltrated preform. The partly infiltrated preform is then completely infiltrated starting from the other side by the second metallic infiltrant, in this way fabricating the internal layer, consisting of the ceramic preform infiltrated with the second infiltrant and the bottom layer formed by the solidified second infiltrant. Systems already investigated include carbide, nitride and boride ceramic performs infiltrated with aluminum and magnesium alloys.

Jan 1, 2003

By Kenneth C. Mills

Interfacial phenomena can have a dramatic effect on the separation of phases. Furthermore, since they involve surface-active materials, concentrations at ppm levels are enough to cause dramatic effects on separation processes. The effects of (i) emulsification, (ii) contact angle and wettability and (iii) Marangoni flows on phase separation are reviewed.

Jan 1, 1999

By Hiroshi Hashimoto

For the application of sodium carbonate slag treatment to product high purity copper on an industrial scale, the counter-flow batch process that reduces the amount of utilized slag is proposed from the viewpoint of the post-treatment of slag. Based on the distribution ratios of several impurities between the slag and molten copper determined previously, the effectiveness of this process is discussed using a mathematical model and confirmed experimentally. According to the model, the slag consumption to remove Sb to a required level in case of the counter-flow batch process with 3 reactors is calculated to be around 30 % of that in the case of an ordinary batch process, where pure sodium carbonate is used as a slag at every stage.

Jan 1, 2003

By Gus Van Weert

Hydrometallurgical oxidation of sulphides is capital and energy intensive, with autoclave and bio-technology competing for lowest overall cost status. The use of surface aerators instead of stirred tank reactors could provide lower costs for bio-oxidation of concentrates. With this in mind, the Delft Inclined Plate reactor was designed with inclined plates above a settler shaped reactor to continuously return slurry from the lowest point in the settler to the surface of the liquid. The multiplate superstructure overcomes the scale-up restriction of the standard circular surface aeration patterns. DIP aerator energy and volume requirements for oxygen transfer from air will be presented in terms of kg O2/kWh and kg O2/m3/h transferred as a function of wt % sand in the slurry and compared to stirred tank performance. Scale up from the 4 m3 pilot unit will be discussed.

Jan 1, 1996

By Varuzan Kevorkijan

A new method for faster production of functionally graded metal-ceramic laminates is based on reactive pressureless counterflow infiltration/penetration of a ceramic substrate with two different metallic infiltrants. The porous or dense ceramic preform is pressurelessly infiltrated or penetrated from one side by the first metallic infiltrant to the desired cross section of the preform, producing the top layer made up of the solidified infiltrant and the underlayer consisting of reactive infiltrated preform. The partly infiltrated perform is then completely infiltrated starting from the other side by the second metallic infiltrant, in this way fabricating the internal layer, consisting of the ceramic perform infiltrated with the second infiltrant and the bottom layer formed by the solidified second infiltrant. Systems already investigated include carbide, nitride and boride ceramic performs infiltrated with aluminum and magnesium alloys.

Jan 1, 2003

By Roberto Parra

The selective reduction smelting of Cu2O in Cu2O-FeOx-SiO2 melts has been studied at laboratory level, using as a feed a dead roasted calcine from a copper concentrate. The purpose of the study was to evaluate the kinetic and mechanisms of the indirect reduction with CO and the direct reduction with graphite from 1260°C to 1350°C. The reduction rate by CO was found to be 10-2 to 10-1 mole Cu2O m-2s-1. The graphite reduction macrokinetics for FeO and. Fe2O3 containing melts, was found to be a first order reaction with respect to the Cu2O concentration, with a kinetic constant of 104 to 10-3 s-1. The reduction rate was not sensitive to temperature nor to stirring, in the range studied. The measured reduction rate is almost one order of magnitude larger than the observed rate for the direct reduction of FeO.

Jan 1, 1999

By Isabel Lázaro

A detailed study has been undertaken into the electrochemistry of the leaching of chalcopyrite in acidic solutions containing ferric ions. Mixed potential measurements have shown that the maximum potential achievable on a chalcopyrite disk in a ferric sulfate medium lies within the so-called passive or prewave region in the anodic behavior of chalcopyrite. The very low current densities due to the anodic oxidation of chalcopyrite at potentials in the region of the mixed potential has made studies of the initial stages of dissolution difficult. However a careful rotating ring-disk electrode (RRDE) study has enabled data to be obtained for the stoichiometry of the initial dissolution reaction to be obtained. Thus, in addition to the detection of soluble iron and copper as products in this potential region, a soluble sulfur species has also been detected. A comparison of the experimental with the expected collection efficiencies of the products on the ring has revealed that this soluble sulfur species is likely to be thiosulfate. The characteristic transient anodic behaviour of chalcopyrite in this potential region has been interpreted in terms of a rate limiting solid-state diffusion process. Thus, extrapolated rates based on reported measured solid-state diffusion coefficients for the mineral at elevated temperatures have been shown to be consistent with the potentiostatic current-time transients. Furthermore, comparative studies of the anodic characteristics of the copper sulfide minerals covellite and bornite has confirmed their greater reactivity in this potential region. The results of this investigation have been combined with a parallel study of the non-oxidative behaviour of chalcopyrite in order to derive a model for the dissolution process which is consistent with other published studies of the electrochemistry and dissolution of the mineral.

Jan 1, 2003

By Fu-Shen Zhang, Mengjun Chen, Jianxin Zhu

"A novel approach for foam glass preparation, namely vacuum-aided powder sintering technique, was preliminarily investigated in the present communication. The key point of which was to prepare foam glass at a negative pressure. Compared to normal powder sintering process, the new approach could benefit the foaming process by shorting the holding time, reducing the amount of foaming agent and especially decreasing relative density of the product. Optimum conditions were 750 °C, 1000 Pa, 5 min and 1 wt.% foaming agent, respectively.IntroductionFoam glass represents a highly valuable solution for thermal and acoustic insulation, since it possesses a generally higher mechanical, chemical and thermal stability than other foams'1'. The first industrial processing for foam glass production, the direct introduction of gases (""blowing"") into the special molten glass, can be dated back to the end of 1930s'2'. At present, almost all foam glasses is prepared by powder sintering technique instead of blowing,3 since it reduces the temperature by several hundred degrees. Moreover, as fine glass powders or similar powders can be used to substitute corresponding glasses by this technique, considerable attention has been focused on the production of foam glass by considering fully recycled glasses, coal fly ash, or other solid wastes as raw materials,4 especially CRT glasses'3' 5', on the point of environmental protection.In a previous report'6', when discussing the lead removal and recovery from CRT funnel glass by a pyrovacuum process, we found that foam glass could be prepared at a negative pressure. Therefore, in this communication, the similarities and differences between the powder sintering process for foam glass at normal and negative pressure was preliminarily discussed."

Jan 1, 2011

By L. Katgerman, H. J. Brinkman, J. Duszczyk

"The phase formation sequence in the in-situ synthesis ofTiB2 in A1 from elemental A1, Ti and B powders is identified with a combination of DSC and XRD. After the melting of A1, A1B2 and A13 Ti are formed at the contact areas between A1-B and A1-Ti. The influence of variations in starting composition on the reaction kinetics is explained in terms of there effect on the different processes in the formation sequence. Parameters in the starting composition that were investigated are; fraction ofTiB2 forming reactants, non stoichiometric Ti:2B ratio's, and addition of alloying element Cu.It was found that a liquid Al phase is necessary for the in-situ TiB2 forming reaction from the intermediate A1B2 and A13 Ti phases. If all Al is consumed by the formation of A1B2 and A13 Ti the TiB2 formation is halted until the decomposition of A1B2 and A13 Ti .Overstoichiometric amounts of B are needed for complete conversion of the Ti, present in A13Ti, into TiB2 This is explained by the fact that some of the stable A1B12 phase is formed after the decomposition of A1B2•The addition of Cu leads to an increasing reaction rate in the A1-Ti reaction. A possible explanation for this is that the A1-Cu liquid penetrates more easily between the Ti and its surface oxide than the unalloyed A1 liquid."

Jan 1, 1998

By R. C. Hubli

A panial equilibrium model? to simulate the dissolution of millerite (NiS) in aqueous solutions containing copper(II) chloride as the oxidizing species has been developed. The predominant copper(I) and copper(II) species are CuQ3 and CUO2 respectively. The model computes the initial concentrations of the species present in the aqueous phase under the specified input conditions, prior to the simulation of dissolution. During the dissolution of millerite, nickel enters the leach liquor as NiH and it has been found that the H+ decreases as a function of NiS dissolution. The simulation has been accomplished under conditions prevailing during actual dissolution, with only one mineral undergoing dissolution. The model can be applied for the simulation of co-dissolution of two or more sulfides. Under the given conditions, the precipitation of Cu1(OH»)O is negligible but loss of Cu(1l) could be significant if the initial H+ is lower than 0.03 M. The results of the simulation compare favorably with experimental observations.

Jan 1, 1996

By Takeshi Yoshikawa, Kazuki Morita, Kunitoshi Matsunaga

"In metallurgical grade silicon (MG-Si), most impurities mainly exist at the grain boundaries and distribute in silicon grains at extremely small contents. Grain boundary phases in MG-Si transform into liquid above the eutectic temperature, and migrate towards high temperature regions when heated under a temperature gradient. With the migration of all liquid phases in MG-Si to the surface, the impurity contents will be decreased less than their solubilities in principle.In the present work, the fundamental research was conducted to discuss the possibility for purification using the liquid phase migration technique. The purification limit was estimated by thermodynamic calculations, and metallic impurities were estimated to be effectively removed except for Fe and Al. The migration behavior of the liquid phase in the synthesized silicon substrate was investigated by unidirectional heating under infrared radiation at 1523-1548 K, and the proceeding of migration was confirmed. The migration velocity was 1.4--2.0xl0-7 mis, and found to be controlled by the liquid phase diffusion.IntroductionPhotovoltaic energy is one of promising energy resources in a sustainable society because of its inexhaustibility and cleanliness. Although the production and installation of solar cells have increased significantly during the last decade, the cost of solar cell installation is still high. To enable the widespread use of photovoltaics and for the photovoltaic electricity price to reach grid parity, a low-cost and abundant feedstock of solar grade silicon (SOG-Si) is essential. Recently, a modified Siemens process and a fluidized bed reactor process were developed to address the cost and energy issues associated with the conventional Siemens process. However, their cost reduction potential is limited because of the large energy consumption needed to convert silicon into gaseous compounds. Purification of silicon through metallurgical routes offers a promising way for producing SOG-Si from metallurgical grade silicon (MG-Si), because it enhances productivity and can also lower the process costs. Although several metallurgical processes such as directional solidification [l ], vacuum refining [2-4] and plasma oxidation [5-7], have been developed, processing times and refining efficiencies still have to be optimized."

Jan 1, 2013

By Shekhar Bhansali, Shyam Aravamudhan

"This paper reports on the design and simulation results of a silicon bulk-micromachined diaphragm-type piezoresistive pressure sensor capable of operating linearly over a wide dynamic range (0-1000 meters of water). The piezoresistor elements of the sensor are arranged in a wheat stone bridge configuration to achieve a higher output response. Simulation results (output voltage and sensitivity analysis) obtained using coupled MemPZR-MemMech module of the CoventorWare2003 Finite Element tool are presented. The effect of diaphragm size, diaphragm thickness and thickness of the piezos on output sensitivity were analyzed and optimized to get a linear response over the wide dynamic range.IntroductionThe physical and biological processes in the ocean are critically influenced by ocean parameters (pressure, salinity and temperature). Thus there is a need to develop inexpensive and reliable sensors to continuously measure large volumes of sea-space over long time spans. A key component in any such system will be a pressure/depth sensor. This sensor is routinely employed in marine applications such as wave and tide gauges, tsunami detection, platform leveling etc. More significantly, pressure measurement is needed for depth determination. Depth sensors are vital for remote operated vehicles (ROVs), profiling instruments and towed arrays.Several techniques have been routinely used in the past to measure pressure in the marine environment [1-3]. In general, the pressure sensor design is based on a flexible membrane as the spring element for the sensing pressure [4]. The deflection of the membrane, induced by the applied pressure, is converted into an electrical output through a component that is sensitive to diaphragm deflection (capacitive coupling) or associated stresses (piezoresistors, strain gauges). The temperature compensated pressure measurement can be readily converted to depth using"

Jan 1, 2004

By Junzo Hino

Most of the waste that contains a small portion of copper is landfilled. The recycling process of copper from the waste, such as shredder residue, should be developed in order to save mineral resources and prevent environmental pollution. Shredder residue, generated from disposed automobiles and electric appliances, consists of many types of plastics, glasses and metals. The combustion heat of plastics is efficiently used for smelting in the recycling process that consists of melting and reduction. Because the waste contains numerous components the knowledge of the distribution behaviors of the main components is necessary to develop the recycling process. The distribution behaviors in the recycling process are evaluated by using the thermodynamic calculation program, HSC Chemistry. The calculation results are compared with the practical operation data of the recycling process and discussed.

Jan 1, 2003

A study was undertaken to remove the Se from waste solutions using a raw form of the biomass called Iota Chips derived from the seaweed, Eucheuma spinosum. Removal of Se from solutions was investigated as a function of time, pH, conc. of Se in solution (0.1 to 100 ppm) and lota Chips to liquid ratios of 10-2 to 10-5. For solutions containing initial conc. of 0.1 ppm Se, with the addition of Iota Chips at a solid to liquid ratio of 10-3, the Se conc. decreased to 0.03 ppm in about 3 hours. Iota Chips absorption capacity to the Se and its application to the treatment of the metallurgical processing effluents are discussed.

Jan 1, 1992

By S. Eckert, G. Gerbeth, K. Timmel, B. Willers, T. Wondrak, N. Shevchenko, M. Röder

The quality of the produced steel in the continuous casting process is significantly governed by the melt flow in the mold. However, direct flow measurements in liquid metals are still rather scarce. In order to investigate these flow phenomena, three experimental facilities operating with low melting liquid metals were installed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The melt flow in the models is measured by the Ultrasonic Doppler Velocimetry (UDV) or the Contactless Inductive Flow Tomography (CIFT), multi-phase flows can be visualized by X-ray imaging. The obtained measurement results are primarily used for validation of numerical models. In this paper we will investigate the fluid flow in the mold and the behavior of the surface of the liquid metal using flow measurements by UDV and surface profile measurement by a laser scanner, respectively. Strong fluctuations and deviations of the free surface were observed in case of a static magnetic field

Jan 1, 2016

By W. Song, C. Richards, B. Q. Li

"This paper presents a two-phase flow numerical model for spouting gas-particle flow reactors used in chemical vapor deposition processes for manufacturing heart valves and other biomedical implants. The model is developed based on the Eulerian-Eulerian formulation of gas-particle flows, with the k-e engineering model modified with the presence of particles for the description of turbulent gas flows. In parallel with the numerical model development, physical models are set up, where the particle image velocimetry is used for visualizing the particle flows and spout shapes and heights and optical probes are used to measure the particle velocities. The numerical model predictions are compared reasonably well with the experimental measurements.IntroductionVarious biomedical implant components, such as bone joints, dental components and heart valves, are coated with bio-compatible thin films by chemical vapor deposition in particle-laden chemical reactors [l-5]. In these reactors fine particles are used as packing and supporting media. During the coating operation, these packed particles are fluidized by an upward gas jet from the nozzle, reach a certain height and fall back on the top of an annulus region. These recirculating particles are mainly for levitating the implant components (usually one or two in a reactor at one time) so that every portion of them is equally exposed to the gaseous atmosphere. An equal exposure is critical for forming a uniform, mechanically strong and corrosion-resistant coating on implants. Plant experience shows that the quality of the coating is directly related to a stream of operating parameters such as temperature, particle size and loading, and gas flow rates [6]. Optimization of these operating parameters for improved reactor performance depends crucially upon our fundamental understanding of the physics governing the gas-particle flow, heat, and mass transfer phenomena taking place in these reactors."

Jan 1, 2004