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By P Townsend, F Russell

Palabora Mining Company operates an integrated open pit mine, concentrator, smelter and refinery complex located in the Northern Province of South Africa. The Palabora open pit went into production in 1966, mining 30 000 t/d to produce some 62 000 tpa of copper. With continuous modification and improvement, a mining rate of 82 000 t/d, producing up to 135 000 tpa of refined copper, has been achieved. While these improvements have also enabled the mine life to be nearly doubled, the open pit will reach the end of its economic life by 2003. The Palabora orebody is vertical and the reserve extends to a depth of 1800 m over an area of 700 m by 200 m. Studies to assess the economics of mining the orebody by underground means began in the mid-1980s. These studies indicated that block caving is the lowest cost underground mining method that would generate a suitable return. In March 1996, a decision was made to develop a 30 000 t/d block cave mine that will extend the life of the Palabora Mining Company by a further 20 years. In terms of the relatively high rock strength and the resultant coarse fragmentation that is expected at the drawpoint, the Palabora cave can be considered rather unique when compared to other block cave operations. This paper describes the project in broad terms and details the mining method, particularly with respect to the cavability of the orebody and the design features to deal with the coarse fragmentation. The project commenced in July 1996 and final development of the undercut and drawbells is scheduled for completion in November 2003. This paper describes the status of the project and planning as of April 2000.

Jan 1, 2000

By George J. Tamaro

The design and construction of foundations in the New York City area are usually dictated by the widely varying geologic conditions encountered in the five boroughs, particularly along the spine of Manhattan Island. Rock extends well above sea level at the northern reaches and falls to depths in excess of 250 m at the barrier islands at the southern extremities. These highly variable geologic conditions, significantly affected by glacial activity, dictate different design and construction approaches throughout the five boroughs of New York City. Extensive rock removal is required at the north while long piling is dictated in the south. Similar changes can occur within a project site on Manhattan Island. This paper will describe these conditions in general, will identify the various solutions used to solve these problems and will summarize various foundation types used in the New York City area.

Jan 1, 2000

By Kazusuke Sato, Takahiro Uno, Koji Hoshino

"A novel Ni coating technique of Ni(OH)2 powders was developed to improve the positive-electrode performance· of the Ni-MH batteries. It was found out that Ni(OH)2 powder was reduced by N2H4 without any catalysts in an alkaline - solution at high temperatures. In result of observation of pH and potential changes in the solution during the reaction, it was found that the reduced species was HNio2- ion dissociated from Ni(OH)2 in the alkaline solution. The molar fraction of reduced Ni of the Ni(OH)2 was increased in proportion to the amount of added N2H4. At the small Ni fraction, a porous Ni layer was formed on the surface of Ni(OH)2 powder. Open cell tests were carried out with the paste type electrodes made of either the Ni coated Ni(OH)2 powder or non-coat powder, and cell performances were compared. In result, it was found that the Ni coating technique is effective on improvement in the utilization of Ni(OH); as a positive-electrode active material under high current densities.IntroductionNi-MH rechargeable battery is generally used for the power source of portable machines and electric vehicles because of its good performance at high energy density and. long term cyclical life as well as cleanness and good safety. Cell component materials have been improved respectively, and as concerns ·the positive-electrode reducing 'the internal resistance is a principal problem to improve the discharging performance at higher current densities.In recent years, improved Ni(OH)2 powders coated with conductive materials as NI. or CoOOH have been developed for the· positive-electrode active materials in order to· reduce the internal resistance of the electrode1)· 2) The Ni coated Ni(OH)2, however, is costly because it is fabricated by .the -non-electrode plate technique which needs a expensive precious ·metal catalyst as PdC12We found that Ni(OH)2 powder was reduced by N2H4 without any cryatalysts in an alkaline solution at high temperatures. After the treatment, Ni(OH)2 powder become gray color like Ni powder from light-green color; and. turned into a magnetic. In this study, the mechanism of the -reducing reaction was investigated to apply the reactions .to a novel Ni coating technique of Ni(OH)2 powders, · and the performance of the Ni coated Ni(OH)2 powder obtained by the reducing process was evaluated as an -positive-electrode active material of Ni-MH batteries."

Jan 1, 2000

By A. T. Jakubick, A. MacG. Robertson

This paper reviews key issues related to the placement of dry (soil) covers on extremely weak, compressible fine tailings. The design and construction of soil covers on such tailings often presents a formidable challenge to the geotechnical as well as the environmental engineer due to the low shear strength, poor traffic ability, and high settlement of under consolidated tailings at the time of reclamation. The geotechnical issues to be considered include: (1) consolidation of near-surface tailings to achieve strength gains, improve traffic ability, and allow safe placement of initial cover layer; (2) stability of tailings slopes during dewatering of tailings ponds and/or cover placement; and (3) long-term settlement of tailings and its impact on cover integrity and final surface shaping. The environmental issues to be considered include: (1) management of contaminated (free) pond water; (2) management of contaminated pore water expelled during tailings consolidation; and (3) management of (uncontaminated) surface water on top of the cover. This paper summarizes recent experiences gained in a large uranium tailings reclamation project. It is concluded that a careful consideration of both geotechnical and environmental issues during the planning stages greatly reduces the costs and environmental risks associated with fine tailings reclamation.

Jan 1, 2000

By Y. Fukunaka, M. Niinae, E. Kusaka, T. Kuzuya, R. Ishii

"Samarium oxalattr particles was precipitated in oxalic acid aqueous solution from samarium-loaded D2EHPA solution emulsified with a conventional impeller. The calculated fractional precipitation of samarium oxalate was reasonably compared with the value determined by chemical analysis. Morphological variation of oxalate precipitate particles was then examined with H2C2O4 concentration in aqueous solution, Sm(III) and D2EHPA concentrations in organic phase. The needle-like precipitate was identified as Sm2(C2O4)3 10H2O by XRD. Precipitates obtained at higher H2C2O4· or Sm(III) concentration greatly decreased the length of major axis of precipitate, while those at higher D2EHPA concentration increased it. The oxalate was further precipitated under ultrasonic irradiation. However, the morphological variation caused by theses processing variables was not so evident under ultrasonic irradiation as in an impeller or shaking mixer.IntroductionThe materials processing of the rare earth elements must be reviewed from the scope of industrial ecology, since they have the potential applications of magnetic materials as well as secondary battery in developing programs of the electric vehicle. The technological trend to develop the electric vehicle may greatly influence the concept of materials processing, since the global· environmental problem must accommodate with the sustainable development for mankind. The recycle design must be a key issue in the materials science and engineering.Solvent extraction provides a unique separation technology -in this sense. Doyle (1)(2) reported the integrating solvent extraction with processing of advanced ceramic materials, whose chemical composition and microstructure must be precisely controlled. In her paper, the higher productivity inherent to the present process superior to hydrolyzing metal alkoxides was emphasized. Oxalic acid has been used as precipitant for rare earth purification process, since rare earth oxalate has a very small solubility in water and can be easily decomposed to oxide. It is thus suitable for precipitation stripping agent in cationic exchange type extracting system (i.e. D2EHPA, VA-10, PC-88A and so on)."

Jan 1, 2000

By Jean-Pierre Hamelin

Ground movements induced by underground excavation are always of critical concern, particularly in urban areas. Compensation grouting now appears as a safe means to control these movements. The paper presents new advanced systems developed by the specialist contractor to bring, at all stages of the project, an efficient control of operations and presents a case history taken from the project at Tren Urbano, Rio Piedras Section, constructed beneath an historic commercial section of San Juan de Puerto Rico.

Jan 1, 2000

By Launa Mallett

This paper introduces a method for teaching workers to communicate necessary information when giving or receiving emergency warning messages. Research has shown that when an emergency occurs, people may not get the information they need to take appropriate action. Interviews conducted with 48 underground coal miners who had escaped mine fires revealed that the warning information provided was inadequate. In some cases, sufficient information was not provided to the endangered miners. At other times, miners failed to ask for information they needed to plan and execute effective escapes. Researchers from the NIOSH Pittsburgh Research Laboratory have been studying the content of emergency warning messages and have developed an emergency communication protocol. A training intervention that presents the protocol and related mental cues is being evaluated for effectiveness in improving the content of emergency messages. In this paper the protocol is presented and the training package described. The evaluation procedures and a summary of the analyses conducted to-date are also provided. The training package was developed for use with underground coal miners, but could easily be modified for emergency communications training in other settings.

Jan 1, 2000

By A. C. Stevenson

"There are many critical application issues that affect all AC drives, but there are several that are absolutely mandatory for pulse width modulated (PWM) AC drives. If these rules are not followed, the drive system will have insulation, bearing EMI or noise problems. Pulse Width Output VoltageFigure 1 shows the output current of a typical pulse width modulated (PWM) drive. This is, of course, not a clean sine wave thus will have a lot of very significant harmonics. In fact, the harmonic spectrum is directly related to multiples of the carrier switching frequency plus side bands related to the basic output frequency. A typical spectrum for a PWM source bridge switching at 5 kHz is shown in Figure 2. Notice that the spectrum has multiples of the 5 kHz switching frequency and the number of side bands gets larger as the harmonic number increases.IGBT Switching TransientsWhenever we have PWM inverter switching, voltage transients are formed that propagate (usually at about half the speed of light) down the power cables to the motor just like in a radio frequency transmission line. If we do not terminate these transmission lines (motor cables) properly, the voltage pulses will be reflected when they reach the motor end and will be transiently increased up to twice their original amplitude.This transient voltage rise, shown in Figure 3, is important for three reasons:1. Insulation Voltage Stress — Higher voltage stress in the motor connecting cables and motor insulation will lead to a shorter insulation lifetime. If any of the voltage transient peaks exceed the insulation corona discharge level (partial discharge level), the insulation will gradually degrade with each voltage pulse. When it has been sufficiently degraded, it will then fail.Most new “inverter rated” motors have triple layer insulation which has a 1600 to 2000 volt partial discharge level. This will make them suitable to withstand the double voltage peak transient from a 600 volt inverter. It is wise to make sure of this fact, since a “standard” induction motor will only withstand about 1200 volts. Use of a standard motor in this application would shorten its life drastically. This can sometimes be as little as a matter of hours."

Jan 1, 2000

By Jay. M. Khodadadi, Josef Štetina, František Kavicka

"With the aid of the proper original numerical model of solidification the instruction for preparation of input parameters for numerical simulation of technological processes, with change of the phase or structure, will be presented. A method of calculation analysis of influence of therrpophysical properties of materials entering the system of casting-mould-cores environment, and also of boundary conditions on the required simulation accuracy will be suggested. For the cast material, the influence of heat .conductivity, specific heat capacity, density and latent heat of phase transformation also has been analysed. For metallic or non-metallic moulding material"" the influence of the see main parameters has been analysed and, furthermore, their combination, influence of thermal conductivity, and of heat storage. The order of influence of all quoted parameters of a casting and moulding material was established. For example heat conductivity in the liquid state is on the last place. From the boundary conditions the -most important influence on the total solidification time and · on the mechanism of forming of temperature field has the ·boundary condition on the casting mould boundary, then follows the boundary condition on the level of a molten metal. The negligible influence has the boundary condition on the mould frame and on the bottom.IntroductionThe original and universal mathematical model of solidification, cooling and heating has been set up and checked, in order to be capable of analysing a one- to three-dimensional steady or unsteady temperature field of the casting-mould-environment system and, namely, of the system as a whole or its arbitrary parts, during any industrial technological process whose individual processes could be solidification, cooling, heating, refrigeration and others, in any sequence or singly. The model enables the simulation of traditional and also non-traditional technologies of casting in foundries, metallurgical plants, forging operations, heat treatment processes, etc. If solidification is not the matter, the metal part of the system need not be called the casting but a component, a block, a forging and the like."

Jan 1, 2000

By G. A. Irons, D. Colbert

Several electric arc furnace (EAF) shops have increased the zinc and lead grades of EAF dust by reinjecting it into their furnaces; however, the kinetics of this operation are poorly understood. To understand the kinetics, EAF dust was injected into 70 kg heats of iron or steel in an induction furnace. Supplemental additions of carbon and oxygen to overcome the heat load on the system were also investigated. In all cases, the dust was chemically transformed, and the zinc content increased from 16% Zn to 60 - 80% Zn. About 50% of the zinc in the EAF dust dissolved in the iron or steel. The zinc oxide in the dust is thought to be reduced by carbon and the zinc vapour subsequently dissolved in the iron. A kinetic model for the dissolution process is proposed, and the implications for EAF dust recycling are discussed.

Jan 1, 2000

This chapter focuses on smoke as it relates to escape from underground mine fires. Among the topics discussed are the measurement of visibility in smoke; smoke-related hazards such as the production of CO, hydrochloric acid (HCI), or other byproducts of combustion; and miners' personal experiences while escaping through smoke. Smoke Measurement and Visibility In general, smoke consists of hundreds of thousands of very small particles. These particles have some "size," usually expressed in terms of their diameters, and they have some concentrations, usually expressed either in the number of these particles per unit volume or the total mass of the particles per unit volume. Humans cannot see individual smoke particles because they are too small. Similarly, "umber concentrations" and "mass concentrations" of smoke particles do not have much meaning to people unless they are trained technically. Still, individuals know that they can see smoke, independent of all the technical jargon used to describe it. Also, they know that when the smoke level gets too high, it is no longer visible. In fact, nothing is visible because the smoke absorbs all of the light in its surroundings. The eye is only sensitive to light in the wavelength region from about 400 nm to about 700 nm. The maximum sensitivity of the human eye is to light that has a wavelength of about 555 nm. It is important to know how the eye responds to light because if its response is known, it is possible to use a light detector that has almost the same response as the eye. Such a detector can then be used to quantify the visible characteristics of smoke because it responds in the same manner as the human eye. Smoke is visible because it either scatters or attenuates (diminishes) light. In some instances, smoke is visible because the smoke particles reflect light which is then detected by the eye. The eye actually "sees" an intensity of light that has been reflected from a cloud of smoke particles. Imagine shining a flashlight into a cloud of smoke. Someone off to the side can actually "see" the beam of light as it traverses the smoke cloud. This is called scattering. Smoke is also visible be¬cause it attenuates light. Imagine having someone shine a flashlight into your eyes. As smoke begins to build up along the beam of the flashlight, the light begins to dim. The smoke is visible because it is now reducing the intensity of light that falls upon the eye. As the smoke level increases, it is said to obscure our visibility. When the beam is no longer visible, the smoke obscuration is said to be 100%. In other words, none of the light energy from the flashlight makes its way through the cloud of smoke. Another way of saying that the obscuration is 100% is to say that the transmission of light through the cloud is zero.

Jan 1, 2000

By Masanori Abe, Yoshitaka Kitamoto, Kazuhiro Nishimura

"Ferrite plating is a chemical processing which utilizes Fe2+ - Fe3+ oxidation to synthesizing polycrystalline films of ferromagnetic spinels (MFe20 4, M = Fe, Co, Ni, Zn, Al, Cr, TI, etc:) directly from an aqueous solution at 24 - 100°C. This low temperature process allows us to fabricate new ferrite film devices on · substrates of such non-heat-resistant materials as plastics, GaAs integrated circuits, and biomaterials. Synthesized from an aqueous solution the ferrite plated ·films are highly biocompatible. Thus various magnetic device and biomedical applications have been proposed and realized using ferrite-plated films. Ferrite-encapsulated polymer microspheres are applied to antibody carries for enzyme immunoassay, and also to toners/carriers for photocopying. Perpendicular magnetic recording media utilizing plated CoNi ferrite films are proposed. The low-temperature synthesized films of NiZn and Co ferrites are potentially used as soft-magnetic and/or insulating layers, respectively at high/microwave frequencies.IntroductionFerrite plating is a processing which facilitates the formation of crystalline spinel ferrite films with various compositions, (Fe, M)30 4 (M = Fe, Co, Ni, Zn, Al, Cr, TI, etc.), directly from an aqueous solution at 60 - 100°C [1]. This opened the door to fabricating novel ferrite-film devices using substrates of such non-heat-resistant materials as plastics and GaAs integrated circuits [2-4]; conventional ferrite film preparation techniques such as sputtering, vacuum evaporation, MBE, LPE, etc., require high temperatures(> -600°C) for crystallization of ferrites, which deteriorates the non-heat-resistant substrates. Recently we extended ferrite plating to be preformed at room temperature [5, 6]. This enables us to use as substrates such organic materials as biomaterials (e.g. enzymes) having very low heat-resistance."

Jan 1, 2000

By J. Pesl, U. Kemey, F. Sauert

"The CONTOP® smelting cyclone is a water-cooled, upright, high-intensity smelting reactor. The technology for the reactor was initially developed and brought into industrial-scale operation in the area of non-ferrous metallurgy. The two largest smelting cyclones were built with a capacity of 32 tons per hour of copper concentrate mix.The newest industrial CONTOP® plant treats up to five tons per hour of zinc-bearing residues including EAF dust. The highly concentrated zinc-lead oxide produced is sold to the zinc industry. The slag fulfills the leaching criteria and is used in waterway construction. The heat transferred to the cyclone cooling system and the off-gas boiler produces steam from which power is generated in a turbine.V AI has erected a new CONTOP® demonstration plant at MEFOS, Lulea, Sweden. A zinc volatilization rate of 90% was achieved during hot commissioning with Swedish EAF dust.Treatment costs in the range of 85 to 100 EUR per ton were estimated in a feasibility study on the treatment of 73,000 and 57 ,000 tons EAF dust for a group of steelmaking mills in Southern Europe."

Jan 1, 2000

By D. C. Foguel, J. L. R. Bravo

For several years, Caraiba Metais S.A. (CMSA) had to stock the arsenic sludge generated from the electrolyte purification process of its tankhouse. The amount stocked · reached approximately 3,500 tonnes, as the effects of its recycling during the smelting process and consequently in the sulfuric acid plant were unknown. Besides, it had as limiting factors the high content of arsenic in the copper concentrates supplied by foreign countries as well as the reduced capacity of the tankhouse's purification plant. The choice for selling the mentioned residue, which generally contains more than 50% of Cu, was attractive, but the environmental policies and regulations had not allowed this option. Other alternatives, such as the production of bicupric arsenic by means of a solvent extraction process or arsenic trioxide, were considered but the economic feasibility was not attractive due to the absence of a domestic market and a poor international market. After a study of the arsenic partition in the metallurgical process, it was verified that the residue could be recycled without causing any operational problems or damage to the environment. To make this possible, the capacity of the purification plant was increased and the way of removing the arsenic sludge from the cells was modified from manual to mechanical, therefore avoiding the direct contact of the workers with this poisonous substance. Moreover, procedures for recycling in the smelter were established and tolerance limits were set for both the smelter and the sulfuric acid plant. The main amount of arsenic to be recycled is released with the smelting furnace off-gas, which is washed during the purification stage of the sulfuric acid plant. The acid water, rich in arsenic, is then treated in the waste plant and the arsenic, in its stabilized condition, is confined in an appropriate area.

Jan 1, 2000

By J. F. Stenebråten, W. P. Johnson

Carbonaceous material (CM) from the Barrick Goldstrike Mines, NV, was characterized with respect to its gold sorption (preg-robbing) and gold recovery behavior. The breadth of graphite peaks measured by X-ray diffraction were used to calculate crystallite dimensions (002) of the CM. The (002) dimension was found to vary inversely with preg-robbing activity and directly with gold-recovery behavior, indicating that the degree of graphitization (maturation) experienced by the carbonaceous material is correlated with gold-loss during ore processing. The inverse correlation of preg-robbing activity was improved when percent preg-robbing was regressed against (002) crystallite size and carbon content. The (101) crystallite dimensions of all samples were calculated from laser Raman analysis, and were not found to correlate with preg-robbing behavior of the CM. BET surface area and micropore size distribution results were affected by grinding history, negating comparison of these characteristics between samples.

Jan 1, 2000

At Bulong, the mineralised (>0.8 per cent nickel) ore exists within numerous lithologies, which can and do occur coincidently. It is very important to discriminate between the different host units for estimation purposes, stockpiling and scheduling. This allocation of host unit has relied upon visual interpretation by the geologist recording the information, which can be very subjective by its nature. By using quantified constraints, such as assayed magnesium oxide and iron, the subjectivity of describing the host material of nickel laterite ore is reduced. The constraints permit consistent identification of the various host units, which improves the confidence in the overall estimation and scheduling of the ore.

Jan 1, 2000

By Brad Bjornson, Geoff Stevens, Mike Ashar, Cliff Britch

"LocationThe facilities are located 30 km north of Fort McMurray, Alberta (or 470 km northeast of Edmonton, Alberta).Brief Description of OperationThe operation includes the mining of oil sands, extraction of bitumen from the oil sands, and upgrading of the hydrocarbon fraction prior to shipment via pipelines to refineries.HistorySuncor was initially called Great Canadian Oil Sands. It was started by Sun Oil of Philadelphia. Construction began in 1965, with the first production coming on September 1967.Details of Present Milling Practice (Plant 3)Plant 3 recovers bitumen from the oil sand using the Clark hot water process. The basic steps in the process are conditioning, primary recovery, secondary recovery and tailings oil recovery.Oil Sand Feed SystemThe oil sand feed from the mine is transferred to the feed bin in extraction by two conveyor systems. Oil sand analyzers on each conveyor system measure the amount of bitumen and fines in the ore. Cones at the bottom of the feed bin distribute the oil sand to five process lines. Feed flow from each cone is regulated by an apron feeder which transfers the oil sand to conveyors that discharge into the conditioning drums. Weightometers on each of these five conveyors measure the rate at which the oil sand is delivered into the drums. The oil sand feed rate to each drum can be adjusted by varying the speed of the apron feeders."

Jan 1, 2000

By K. Biswas, F. C. Felipe

Paste backfill, because of its colloidal or water-holding properties, does not produce run-off water when placed underground. Paste backfill is generally, prepared from relatively low water content, full mill tailings with a certain proportion of ultra-fine particles and mixed with cement, thus producing early and better strength. Mill plant discharge tailings and other materials available at or near the mine site such as sand, aggregates or waste rock are used as blending materials in the mix design. This study investigates the influence of the above-mentioned blending materials on the mechanical characteristics of paste backfill, as well as the grading, shape, specific surface area, mineralogy and workability of the different mix design.

Jan 1, 2000

By Hideharu Fukunaga, Jin Pan

"The recognition of Metal Matrix Composites (MMCs) as a means of providing high specific strength, high specific stiffness, excellent wear resistance, low thermal expansion and improved high temperature properties has led to a number of new processing, not previously used for plastic and ceramic matrix composites. As a primary fabricating process, the liquid methods are the major ones, which are reviewed briefly from the view of processing terminology. One of them, squeeze casting process is the most traditional and well-developed, because it is rapid, versatile and near-net shape production of materials. Two of new squeeze casting processes are presented to offer the hardness· controlled MMC and the· functionally graded MMCs as well as a newly developed whisker preform.I .IntroductionA large number of liquid processes and techniques including semi-solid liquid process are proposed. The most primitive process is ''pressure infiltration casting” of liquid metal into the fiber preform. It is called as follows depending on pressure and its source squeeze casting (1-4) by hydraulic ram, gas pressure infiltration casting (5, 6), vacuum infiltration, centrifugal casting (7), Lorentz-force-driven infiltration (8). The pressurizing on the liquid metal requests a large and stiff equipment, so pressureless infiltration technique has been developed using K2ZrF6 flux (9,10) while the mechanical properties are not high enough, and using H2 gas with Mg alloying element called pressureless infiltration casting (11-13), spontaneous infiltration process (14) and PRIMEX (15). In those processes, no severe reaction occurred between the reinforcement and matrix molten metal. In early l 990's, the reactive processing with pressure or without pressure, in which one material is totally transformed into another of the required shape, eq. assisted oxidation, has been developed, called reaction squeeze casting (16,17), DIMOX (18) reactive infiltration casting (19,20), and in-situ process (21,22). Die casting of SiCp/Al alloy (23,24) and thixocasting of SiCp/Mg alloy (25) are also applied to produce the machine component of MMCs."

Jan 1, 2000

By M. Furuta, M. Hasimoto, Y. Komoda, K. Haiki

"Tamano Smelter & Refinery started its operation in 1972 with high current density electrolysis (350Nm2 of maximum) applying PRC technology. After the start up, four times of expansion have been done, the cathode production capacity has increased from- 84,000 t/y to 191,000 t/y. However, recent refining technology with permanent stainless steel cathode enabled to increase current density up to 300 Nm2 or more without PRC method. In order to increase current density more than 350 A/m2 , experimental work using commercial size cell has been carried out at several conditions, such as current density, PRC conditions, electrolyte composition and electrode condition. As a result, it was found that high quality (LME A grade) cathode can be produced at such a high current density as 405 A/m2•IntroductionWhen considering the production increase of electrolytic copper, what becomes important is the improvement of productivity per unit of production facility. Conventionally, production had been expanded by increasing the number of cells but a huge investment required for this had a influence to the business profitability. Because of this, increase of current density, which is one of the methods to improve unit productivity, 'was expected and this method at the same time has another advantage of shortening the retention time of copper and other precious metals in the cells. At present, the average current density at Tamano during full capacity production is around 350 A/m2 and this used to be the limit throughout the world (1)."

Jan 1, 2000