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By Meylin Terrel-Gutierrez

El presente texto muestra un modelo cuasianalítico para predecir la SD (Sechi) en cuerpos de agua claros y turbios. El enfoque está basado en el la relación inversamente lineal entre la SD y las concentraciones de OAS, donde la última ha sido reemplazada por su banda de reflectancia correspondiente o sus combinaciones propuestas por estudios previos de acuerdo con el tipo de cuerpo de agua.

Jan 1, 2014

By Biswadeep Saha, Meenakshisundaram Ramanathan, Chai Ren, Sivaraman Guruswamy

"Fe-Ga alloys have a large low-field magnetostriction and these alloys are attractive candidates in energy conversion and harvesting applications. Small additions of W also increase the magnetostriction of Fe. In this paper changes in magnetostriction by W substitution for Ga in various Fe-x at.% Ga alloys are presented. Fe-Ga-W single crystals were grown using vertical Bridgman Growth technique. [001]-orientated single crystal samples were prepared with faces within 1 degree off <100> orientation. The samples were annealed at 1150 °C in the alpha-phase region and water quenched. The magnetostriction coefficient (3/2)A-100 measurements were made on these Fe-Ga-W single crystals. The result on the effects of W substitution and annealing on the magnetostrictive behavior of these alloys are discussed.*Support of this work by NSF-DMR under the award DMR-0854166 is gratefully acknowledged.IntroductionMagnetostrictive materials changes their dimension exhibit reversible strains and changes in elastic properties in the presence of an applied magnetic field or the reciprocal effect of changes in the magnetic properties with the application of stress [IJ and are very important in sensor, actuator device, linear motor, magnetomechanical devices, microelectro- mechanical devices, active vibration dampening devices application areas. The discovery of an order of magnitude enhancement in the magnetostriction of Fe with Ga addition coupled with low saturation magnetic fields, and excellent mechanical properties opened up the possibility of obtaining larger magnetostriction values in other low-cost ductile a-Fe phase based alloys with alloying additives that are less expensive than rareearths such as Tb and Dy [2·4l_ The magnetostriction values observed in Fe-Ga single crystals are sensitive to thermal history and composition. The formation of second short range ordering phases and local defects inside crystal structure can also cause a dramatic change to this alloy's magnetostriction behavior [5-9l_"

Jan 1, 2012

By Italo Onederra, Miguel Araos

"Most of the current explosives for mining blasting activities are based on ammonium nitrate (ANFO, emulsions and watergels). AN-based explosives’ detonating properties were discovered in the 50’s and since then they have proven to be reliable, safe and cost effective. However, there is no current alternative raw material to replace AN. As part of a program of research initially funded by the Australian Coal Association Research Program (ACARP), Mining3 and the University of Queensland engaged in the search for potential oxidizing agent alternatives that could replace AN in the manufacture of mining explosives. Candidates included those that are produced in large quantities and that can be cost competitive with ammonium nitrate. The initial work identified hydrogen peroxide (HP), calcium ammonium nitrate (CAN) and sodium nitrate (SN). Explosives mixtures were prepared and sensitized using void sensitization techniques. The detonation properties results showed that explosives based onmixtures of HP/CN and HP/SN as the oxidizer were able to detonate in a range of 2000 – 5000 m/s, indiameters 50 and 102 mm, and densities in the range of 0.50 – 1.40 g/ml. Although more studies need to be conducted to fully understand these explosives, if successful, these explosives would be able to offer an alternative to the AN-based explosives in the mining industry."

Jan 1, 2017

By W. R. McDonald

The U.S. Department of the Interior, Bureau of Mines, conducted field tests on acidic copper tailing as part of its program to devise, improve, and demonstrate technology for stabilizing mining and mineral processing wastes. Results will be presented from successful 1/8-acre and 1-1/2-acre demonstration revegetation plots established in 1973 and 1974 on an abandoned copper tailing pond located on public land adjacent to Holden Village, Wash. The tailing was neutralized with treatments of either dolomitic lime or limerock and fertilized with processed sewage sludge and/or commercial fertilizer. Plant growth covering 60 percent of the surface was achieved on both test plots. Regar brome, Tegmar intermediate wheatgrass, and tall wheatgrass provided the best plant growth and surface coverage. In neutralizing the tailing, the target pH of 6.8 was not achieved; however, good plant growth occurred in areas where the pH ranged from 2.9 to 5.8.

Jan 1, 1979

By Rodney Hundermark, July Ndlovu, Lloyd Nelson, Phillimon Mukumbe, Paul van Manen, Whitey Seyanund, Bart Pieterse, Bertus de Villiers, Diale Mokwena

The 2003 redoubling in power to 68MW on the Polokwane Smelter furnace represented a significant intensification in platinum group metal (PGM) smelting. Combined with onerous ‘green’ PGM concentrate smelting requirements, this yielded conditions unusually corrosive to copper coolers and refractories. This presented unexpected operational and design challenges to reliable crucible operation and maintenance. Combined with specific operational control intervention, development of protective coatings has led to the life of water-cooled copper components improving from 9 to 40 months. The furnace matte endwall was extended in 2010 to address accelerated wear of refractories and the potential risk for contact of copper components by superheated matte. An 18 month planned endwall rebuild cycle has been demonstrated (versus catastrophic failure within 9 months). Finally, benefits including lower energy consumption, improved metal recoveries and higher productivity resulting from operational and in-house design developments will be described, that justify “Celebrating the Mega-scale” in PGM smelting.

Jan 1, 2014

By Youngsoo Song, Hyunjung Kim, Junhyun Choi, Siyoung Q. Choi, Gahee Kim

In this study, for the first time, to confirm the effect of bacterial growth phase on the malachite flotation were investigated in a well-controlled Hallimond tube system. The test results showed that the bacteria in the stationary phase exhibit two-fold greater floatability than those in mid-exponential phase. To understand the observed flotation behavior, complementary cell characterization tests and cell attachment tests were conducted. Interestingly, the bacteria at both phases exhibited similar surface properties as well as almost identical amount of cells attached onto the malachite, suggesting that the growth phasedependent flotation behavior cannot be attributed to the variation of cell surface properties and the extent of cell adsorption. On the other hand, cell detachment tests revealed that the amount of cells detached from the malachite surface is greater for the mid-exponential phase than the stationary phase due to the higher fluid drag applied to the cells at the mid-exponential phase, which was explained by the differences in the size and shape of attached bacteria onto the malachite surface. These morphological characteristics were found to cause the bacteria of mid-exponential phase to be separated highly sensitive and easy from malachite surface due to the fluid flow. Second, scale-up selective bioflotation tests were carried out in a 1 L Denver cell in malachite–silica binary mixture systems. Through the tests, we optimized the cell concentration and the malachite fraction in the feed. Overall, high malachite selectively was observed under optimized conditions (both recovery and grade showed more than 90%). The trend was in agreement with classical DLVO interaction energy profiles, which show the relative magnitudes of the adhesive forces between the mineral and the attached cell under equal hydrodynamic conditions.

Jan 1, 2016

By Charles George, Ronald Faul

The cementing process has been used in approximately 2.5 million oil and gas wells to seal, protect and isolate various downhole formations against communication. It has been adapted to other more specialized situations such as solution mining and sealing salt storage reservoirs. The technical literature contains very few papers specifically dealing with the cementing process for these applications, yet there have been many special projects in various parts of the world that are novel. These will be highlighted in this review. This paper also presents a comprehensive review of the various techniques used in cementing wells drilled for the recovery of soluble salts and brines. It also covers the application of cementing techniques to a large number of wells drilled for the storage of hydrocarbons in South Louisiana.

Jan 1, 1985

By M. Misra

The removal of lead and other heavy metals present in an active US Army small arms firing range soil was evaluated in a pilot scale test program at Ft. Polk, Louisiana. Two different acid based extraction processes in conjunction with conventional physical separation methods were used. Physical separation processes consisting of screening and gravity operations removed most of the coarse lead particulates and slugs. Hydrochloric acid leaching followed by precipitation of lead as hydroxide recycled clean soil containing less than 500 mg/L. total lead and less than 5 mg/L TCLP lead. Lead extraction efficiency with hydrochloric acid was 96 percent. The results of lead removal by physical separation in conjunction with acetic acid leaching were not consistent over the whole test period and the total soil processed.

Jan 1, 1998

By R. A. Halet

"The Malartic Gold Fields mine is a good example of the association of ore deposits with a major fault zone. It also exemplifies the control exerted by the physical and chemical character of the host rocks on the localization of orebodies.The mine is in Fourniere and Dubuisson townships, Abitibi county. It is 6 miles east of the town of Malartic, 9n the main highway and railway from Noranda to Val d'Or.The discovery of the mine is due largely to the enterprise of the late J. P. Norrie, who organized the present Company in 1935. The ground is entirely covered by overburden, but Mr. Norrie believed that the extension of the Cadillac-Malartic 'break', the principal ore-bearing structure of the district, would be found on this group of claims. This belief was supported by the discovery of gold-bearing float in the area, and was confirmed by a dip-needle survey and a few pilot diamond drill holes that showed that the favourable Malartic greenstone band passes through the centre of the property.In this way the most favourable area for prospecting was narrowed to a zone 2 ½ miles long by ½ mile wide underlain' by greenstone. The remainder of the property is underlain by sedimentary rocks, which, from experience elsewhere in the camp, were not considered as promising. However, as the entire surface is covered by deep overburden, the location of orebodies even within this more or less restricted area could be accomplished only by a long campaign of diamond drilling. Systematic diamond drilling began in 1936.The contacts of the greenstone band were considered to be the most promising places to begin the work, and the early drilling was concentrated on the south contact, because the orebody of the East Malartic mine, 4 miles to the west, had been discovered on this structure and it was reasonable to hope for a repetition of these conditions. Although the south contact was very thoroughly explored, with a certain amount of encouragement, the work did not prove the existence of deposits of ore grade, and attention was shifted to the north contact zone of the greenstone band. In this locality much more promising results were obtained, and a number of good orebodies were outlined."

Jan 1, 1954

By E. Klar, A. B. Michael

Differences in the electrical conductivities of copper powder sintered under reducing, selectively oxidizing, and neutral atmospheres are related to impurities in solution or as precipitated oxides. The precipitation of impurities as oxides during sintering in nitrogen is proposed for maximizing the conductivity of sintered copper. Conductivity equations for two-phase systems are summarized. Selected equations are applied to porous sintered copper and composite structures. A recent review of the influence of impurities on the electrical conductivity of copper by Gregory et al.1 emphasized that an impurity in solid solution has a much more pronounced effect on reducing the electrical conductivity than when present partly or wholly as a second phase. When impurities in solid solution can be precipitated as oxides, the copper is purified with respect to these elements and the conductivity is increased. Cast and wrought copper, therefore, frequently contain an intentional residual oxygen concentration to oxidize and precipitate impurities less noble than copper. Copper powders generally also contain impurities which can contribute to a reduction in the electrical conductivity of the sintered material. The most deleterious impurities commonly found in commercial copper powders which markedly decrease the electrical conductivity when in solid solution but which can be precipitated as oxides include iron, tin, antimony, arsenic, cobalt, and nickel. In addition to impurities, porosity in sintered copper also contributes to a reduction in the electrical conductivity. The work reported herein discusses the influence of impurities, sintering atmospheres, and porosity on the electrical conductivity of sintered copper. These are important factors for controlling the electrical conductivity of materials such as sintered copper electrical contacts. Several publications on the electrical conductivity of sintered copper and composite materials with random pores or obstacles have incorrectly considered the conductivity to be proportional to the volume fraction of conducting material. However, analyses and equations have been proposed, the earliest of which is perhaps Lord Raleigh&apos;s of 1892,&apos; which more accurately describe the conductivity of two-phase systems. These equations which in many cases allow one to closely estimate the electrical conductivity of porous sintered materials and two-phase composites will be reviewed and related to the measured electrical conductivity of sintered copper, copper-graphite. and Ag-W composites. INFLUENCE OF IMPURITIES AND OXIDIZING, REDUCING, AND NEUTRAL ATMOSPHERES Zone-Melted and Leveled Copper. The electrical conductivities of an electrolytic copper and a lower-purity compacting grade of copper powder after consecutive treatments in reducing or selectively oxidizing atmospheres are compared in Fig. 1. The powder and drillings from the electrolytic copper ingot were melted and solidified in a graphite crucible under hydrogen. The vertical zone leveling technique of multiple passes in opposite directions was used to obtain a uniform distribution of impurities. The electrical conductivity was measured on machined specimens 3 by 0.10 in. diam of the zone-leveled material and after the same specimens were consecutively treated as follows: 1) heating in hydrogen at 1600°F for 3 hr; 2) heating in air in a sealed tube so that 0.04 pct 0 was introduced; heating was started at 1000°F for 1 hr and continued at 1800°F for 8 hr; the stepwise diffusion treatment was used to avoid loss of copper due to evaporation of copper oxide at higher temperatures; and 3) final heating in hydrogen at 1600°F for 3 hr. A L&N Kelvin Bridge, type 4306, and a test fixture with knife edges 2 in. apart were used to measure the room-temperature conductivity with an estimated accuracy of ±0.5 pct. In all cases the conductivity of the electrolytic copper was approximately 100 pct of IACS. The conductivity of the impure copper was 80 pct of IACS both in the cast state and after heating in hydrogen. However, after the heating in air, the conductivity of the impure material was 100 pct IACS. After again heating in hydrogen, the electrical conductivity decreased to 60 pct of IACS. This decrease is attributed both to the dissolution of impurities and observed intergranular cracks due to the phenomenon of hydrogen embrittle-ment in copper. These data show that the electrical conductivity of commercial copper as represented by a compacting type powder can be increased significantly by the precipitation of impurities as oxides through heat treatment in an oxidizing atmosphere. Sintered Copper Powder. A commercial compacting type of copper powder pressed to various densities was sintered either in nitrogen, dissociated ammonia, or dissociated ammonia followed by a selectively oxidizing atmosphere of air in sealed Vycor tubes so that 0.06 pct O was added to the material. The electrical conductivity was measured perpendicular to the pressing direction on as-sintered specimens of approximately 3 by 0.25 by 0.15 in. The fully dense material was obtained by zone melting and leveling

Jan 1, 1969

By Morris Cohen

This paper deals with the calculation of the composition of the infinitesimal trace of alloy that transfers from the liquid to the solid state at each temperature during the equilibrium solidification of a binary solid solution, and which thereby enables the compositions of the coexisting liquid and solid phases to follow along the liquidus and solidus lines respectively during the cooling. A general expression for the composition (d) of the liquid-to-solid transfer at each temperature has been derived: d = ZLXL(XL - P) + Zsxs(P- ZL(XL - P) + Zs(P - Xs) where ZL and Zs are the slopes of the liquidus and solidus lines at the given temperature, XL and xs are the composi-tions of the stable liquid and solid phases at the same temperature, and P is the composition of the alloy under considera-tion. The d equation is valid for the process of equilibrium heating as well as cooling, and may be applied to vapor-to-liquid, vapor-to-solid, liquid-to-liquid, and solid-to-solid transfers if the corresponding equilibrium diagrams are known. The d -versus-temperature curves for two alloys Pl and P2 are shown in Fig. I. In each case, the liquid-to-solid transfer has the same composition as the stable solid FIG. I.-GENERAL SOLID SOLUTION DIAGRAM SHOWING S CURVES FOR ALLOYS P1 AND P2. phase only at the temperature of the be-ginning of solidification, and has the same composition as the stable liquid phase only at the temperature of the completion of solidification. At each intermediate tem-perature, the composition of the liquid-to-solid transfer differs by a finite amount from those of the two coexisting phases. Therefore, during equilibrium cooling, the transfers must merge into the solid phase from the liquid without forming a transition phase; otherwise the condition of equilibrium would be violated. At any given temperature during solidification, the composition of the liquid-to-solid

Jan 1, 1940

By R. Stocker

Flotation recovery of molybdenite particles finer than 15 micrones sharpy decreases with decreasing size. A totally hydrophobic latex agglomerant (UBC-1), which was previously reported to be very efficient in agglomerating hydrophobic fine coal, has been found to agglomerate fine molybdenite particles. The agglomeration takes place only in the presence of MIBC which is commonly used as a frother in molybdenite flotation. Adsorption tests confirmed that MIBC is adsorbed onto molybdenite. The effect of the agglomeration on flotation has been studied by floating fine molybdenite from mixtures with quartz using the UBC-l agglomerant and the MIBC frother. A significant improvement in the flotation of fine molybdenite has been observed in the presence of the UBC-l agglomerant. The best results have been obtained around pH 5.5 which corresponds to the iso-electric-point of molybdenite.

Jan 1, 1997

The arbitration process, and its drawbacks: Any time you have taken part in a major arbitration, and the decision, when it comes out, is not what you thought it would be (which is bound to happen occasionally), the normal reaction is something like æthe arbitrator got it wrongÆ. Again normally, when you have cooled down a bit, and you look in more detail at the decision, you can see, probably, æwhere he got it wrongÆ (it is only male arbitrators who get it wrong). Ultimately, when reason prevails, and you reflect on it, you can see that what really happened was that you failed to get the arbitrator to see what you were getting at in the point or points concerned. This is doubly frustrating, when you consider what has been involved in getting to this point, having been through it all at least twice. An alternative to this process may be the dispute review board.

Jan 1, 1999

By J. F. Fitzpatrick

This paper examines the cost elements associated with changes to gold mining practice over the last decade that result from the changes in environmental regulation and the heightened governmental and public awareness of environmental issues. The main experience base is Pegasus Gold Corporation&apos;s flagship mine, Zortman/Landusky, located in the Little Rocky Mountains of Phillips County, Montana. This operation was among the first mines that were permitted under the 1974 Montana Metal Mining Reclamation Act. In 1974, the Montana Metal Mine Reclamation Act was enacted, creating a permit system for metal and industrial mineral mines for the state of Montana. The act established the content of mine permit applications and defined parameters for the reclamation of mining disturbances. The Act can be viewed as implementing legislation for Article 9, Section 2, of Montana&apos;s Constitution, which provides that "all lands disturbed by the taking of natural resources shall be reclaimed." Pegasus Gold Corporation&apos;s Zortman/Landusky mine was among the first mines permitted under the new Act. In 1978, the initial permit applications were submitted for Zortman and Landusky, and a full Environmental Impact Statement was prepared by the Montana Department of State Lands; permits were issued in 1979. When opened later that year, the anticipated mine life for the combined Landusky and Zortman operations was approximately 18 years, based upon a proven and probable ore reserve of 43.2 million tons. Zortman/Landusky was the first large-scale heap leach gold mine in the United States. Its distinguishing feature was, and remains, a remarkably low ore grade, now .016 oz/ton. The ore is economic because it requires neither crushing nor agglomerating to leach effectively. Approximately two years after the initiation of the state&apos;s regulatory process, the Federal Land Policy Management Act (FLPMA) was enacted, establishing a mine regulatory framework for lands under the administration of the Bureau of Land Management.

Jan 1, 1992

By M. Saghaeian, R. Hejazi, L. Hosseini, M. Zare

Difference between plant feed specifications in practice and design feed is a problem that most of processing plants face during operating and commissioning. This topic has led to inappropriate operating and necessitates repeating the basic tests on new feed. Gol-E-Gohar fourth concentrate line with a capacity of 2 MTPY, located in Kerman province, is the first iron concentrate plant in Iran in which High Pressure Grinding Roll (HPGR) technology has been applied. Plant&apos;s feed consists of 30% AG mills pebbles of lines 1-3 and 70% run of mine crushed ore whose Fe=51%, Fe/FeO=2.5, S=1.7% and work index=15 kWh/t. Desired concentrate has Fe>68% and S<0.7%. After the plant construction and operation commencement, providing design feed was not possible due to the crushing unit`s not being complete, therefore the plant was fed by AG mills pebbles. For predicting optimal conditions of the plant and investigating the possibility of improving the current concentrate specifications, sampling from the new feed and laboratory and pilot tests was performed again. Studies showed that new feed has Fe=41%, Fe/FeO=3.5, work index=17 kWh/t. Results of laboratory tests with Davis tube device and pilot tests run using magnetic separators with simulating the plant`s circuit showed that with current feed, achievable recovery in industrial scale would be 75.52% which compared to plant&apos;s recovery in studied period (75.94%) shows that plant operated in optimal conditions. To improve the current concentrate specifications (Fe=66%, S=1.03%, Ferec=75.94%) and for achieving desired concentrate, samples were reground to four fractions with k100= 300, 212, 100, 45 and Davis tube tests were performed on each of the samples separately. Results showed that the fraction whose k100=212 µm or k80=200 µm has respective Fe and S grades of 68.27% and 0.681% which are consistent with the desired concentrate.

Jan 1, 2014

By N. S. Dalal, X. Shi

It has been known for more than a decade that vanadium (V) stimulates the oxidation of NADH by plasma membranes (1) but the underlying mechanism is still not fully understood. This effect has been attributed to a membrane-associated NADH-dependent vanadium (V) oxidoreductase (1). Subsequent studies suggest that vanadium ( V) can accept an electron from fiavoprotein dehydrogenase that oxidizes NADH (2). The phenomenon ofNAD(P)H oxidation coupled to vanadium(V) reduction has also been demonstrated in other biological systems (3-6). A recent electron spin resonance (ESR) study from our laboratory reported on the accumulation of vanadium (IV) duringthe reduction ofvanadate (vanadium(V)) by the ftavoenzymes glutathione reductase (GSSG-R),4 lipoyl dehydrogenase, and ferredoxin-NADP+ oxidoreductase in the presence of NAD(P)H (7). It was concluded therein (7) that these ftavoenzymes function as NAD(P)H-dependent vanadium(V) reductases. More recently, however, Liochev and Fridovich (8) have argued that the ESR data (7) do not demonstrate that the investigated fiavoenzymes act as vanadate reductases. They suggest an alternative mechanism in which the fiavoenzyme simply serves as a generator ofsuperoxide (02) radical, which acts as a propagator of the radical chain reaction leading to NAD(P)H oxidation (9, 10), as summarized below:

Nov 1, 1995

By K Koskinen, S Ronkainen

The flow field induced in an Outokumpu TankCell and by an OK rotor-stator mixing device in a laboratory and a process size flotation cell was modelled numerically using computational fluid dynamics (CFD). The primary target was to discover and reproduce the various interactions between the flow field and the flotation cell by numerical means. As power consumption depends sensitively on flow field, it can be regarded as a top-level derived quantity (or measure/metric) indicating the validity of the numerically obtained flow field. Having properly validated numerical means to produce the flow field the influence of various design parameters can be captured with certain accuracy. In addition, separate gas and solid phase models for bubbles and solids, respectively, were implemented. The comparisons between velocities and turbulence quantities measured using the laser doppler velocimetry (LDV) technique and CFD modelling were performed. The grid generation was performed with the commercial Gambit 1.3 and the subsequent integration and solving of the resulting algebraic equations with the commercial CFD-code Fluent 6.22. The computationally economic multiple reference frame method was included to model the moving rotor blades. Gas and solid phase models were modified mixture models.

Jan 1, 2005

By S. Parent, J. -F. Lepage, S. Glover

"Goldcorp – Eleonore’s 7 000 tonnes per day gold mill was started up in October 2014 and achieved commercial production in April 2015. During the first year, operation has faced challenges from grinding, flotation, sulfide cyanidation and tailing filtration to achieve targeted throughput, availability and recovery.The optimization of non-sulfide tails filter cloth lifetime and filter press availability had the most significant impact on ramp-up of both mill throughput and availability. A change in steel ball addition size to the grinding circuit was made to meet the targeted p80 of 65 µm. Various optimization efforts were conducted on the flotation circuit, intended to recover all sulfide-bearing minerals. The goal is to attain the environmental target of 0.12% sulfur in flotation tails (to eliminate acid mine drainage or AMD), while an average of 0.31% sulfur was obtained over the first months of 2015. Collectors, frothers, activators and hydrodynamic parameters were tested to improve the circuit desulfurization efficiency. High sulfide reactivity in pre-oxidation and cyanidation severely impacted dissolved oxygen levels and cyanide consumption. Studies were undertaken to understand the effects of mineralogy, grind size and leach conditions on gold dissolution kinetics and cyanide consumption. Efforts were focused on pre-oxidation to restore dissolved oxygen levels as well as optimizing both lead nitrate addition and pre-oxidation time.INTRODUCTIONGoldcorp Eleonore’s mill commissioning started in September 2014. It was considered to operate the mill at 3 500 tpd during design, as the mine was planning to operate at this throughput for the first year. However, with the stockpile of ore and a higher throughput from the mine, the mill was able to run at higher tonnage than initially anticipated.While increasing tonnage, a few bottlenecks were discovered and overcome in areas such as filtration and cyanide destruction. There were also recovery issues which were addressed in areas such as grind and sulfide leach. This paper focusses on the first complete year of operation ending September 30th 2015. A process description and the flowsheet are presented below and it will then go into detail about operational, metallurgical, mechanical and design issues experienced during the year."

Jan 1, 2016

By I. D. Reznik

On blowing nickel matte in a converter without quartz, first the oxidation of metallic iron and a part of FeS occurs without evolving sulfur dioxide, the formed FeO dissolves in a sulphide smelt and form a homogeneous oxysulphide smelt. On further increasing the FeO content, the oxysulphide separates into 2 layers. Based on the laboratory investigation of FeO-(FeS+Fe°) - (Ni3S2+Ni°) ternary phase diagram we have identified the separation region at 1250°C. The boundaries of the separation region have the form of an arc and the composition of the separated oxysulphide layers is defined by the canodes. In the nickel or copper-nickel matte - silicacalcium oxide slag system at 1250°C three layers, namely sulphide, oxysulphide, and slag may be formed. A high slag basicity due to the presence of CaO can serve to enhance the activity of FeO; a low nickel content in the matte corresponds to a high concentration of FeS therein; FeO from slag and FeS from the matte form a homogeneous FeO-FeS solution, i.e. an oxysulphide layer. The investigation on the "Camebaks" apparatus and by the nuclear gamma-ray resonance spectroscopy method of the phase composition in a slowly cooled oxysulphide layer has shown the presence of four phases: wustite, troilite, ferronickel grains, and calcium oxide-silica inclusions. Knowledge of regularities in the oxysulphides formation makes it possible to use them in pyrometallurgy of nickel and cobalt or preventing their formation.

Jan 1, 1997

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