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By F. H. Hueston, R. S. Barclay

"Depending on the application, zirconia, fused magnesia and graphite have been found to be the most suitable crucible materials for melting uranium metal and its alloys. Although graphite has been found to be satisfactory for uranium and uranium alloy castings with cross sections of 4 square inches or greater, ceramic-type molds are superior for small sections and those shaped castings which prohibit the economic use of machined graphite molds. Heating cycles, addition mechanisms and furnace conditions for melting are discussed."

Jan 1, 1967

By D. Sammut, F. Houllis, J-L. Huens, J. Moyes

The Intec Gold Process has been developed as a halide-based alternative for the recovery of gold from refractory sulphide deposits. The halide medium allows sulphide oxidation and gold extraction to be performed concurrently at moderate temperature and atmospheric pressure sourcing oxygen from direct air injection. The dissolved gold is loaded onto activated carbon and stripped in a conventional Zadra circuit. High gold extractions have been achieved from a range of refractory gold concentrates at laboratory scale, which has led to a continuous locked-cycle pilot plant program. The pilot plant operated at >99% availability, with a maximum of 96.5% gold extraction from a concentrate containing 58.6 g/t gold. >99% of the dissolved gold was loaded onto carbon at up to 1% w/w, with no loss of carbon activity detected over five loading/washing/elution cycles. This paper describes the process and presents both laboratory and pilot plant results as well as economic data from two costing studies.

Jan 1, 2005

Introduction A Hypothetical Scenario: Suppose that your company's research department has developed a new device which represents a significant innovation. You would like to begin selling it as soon as possible. The new device has not been publicly disclosed. You're not sure about what type of intellectual property protection you should be seeking, or when you should be seeking it. As discussed below, assuming that the costs are worth it, a patent application probably should be filed before any public disclosure is made. In general, if you do not file a patent application prior to a public disclosure, you will lose rights. Major Types of Intellectual Property In this paper, intellectual property protection is broadly discussed. Practical steps which can be taken to minimize the possibility of losing intellectual property rights (and maximizing the possibility of benefiting from your company's intellectual property) are outlined at the end of this paper. The issues discussed in this paper are somewhat complex, because a number of outcomes are possible, depending on the facts. It is strongly recommended that you seek legal advice in your jurisdiction in connection with any particular circumstances relating to intellectual property rights. "Intellectual property" refers to a number of different types of rights. The major types of intellectual property are: (i) patents; (ii) trademarks; and (iii) copyright. Trade secrets are also usually considered to be a type of intellectual property, and they are also discussed in this paper because of their importance. In general, each of these types of intellectual property protects different subject matter, although there can be some overlap. Intellectual property rights are generally territorial in nature. The scope of protection of a type of intellectual property in a country (e.g., patent protection) depends on whether the specific national requirements for protection have been met.

Feb 1, 2008

By M. J. Collins

The Advocate Mines Limited asbestos property is 6 km north of Baie Ve rte on the northeast coast of Newfoundland. Mining began in the early 1960s and was concluded in 1981. The chrysotile asbestos deposit lies at the north end of the Baie Verte Lineament, the interface between a closing ocean floor and continental margin. Asbestos occurs within ultramafic rocks of abducted ophiolite massifs that were thrust westward against Fleur-de-Lys Supergroup metasediments (continental rise sediments) in the Lower to Middle Ordovician. The asbestos-bearing ultramafics belong to the Central Ultrabasic Sequence of the Advocate Complex. Serpentinized peridotite of this sequence has a 'waste cap' core that grades outward to increasingly sheared rock. Asbestos is found mainly in a northtrending, basin-shaped zone surrounding the core, specifically within fractured serpentinized peridotite that abuts the sheared rock. Asbestos appears as stockworks of chrysotile cross fibre veins and is concentrated between brown, narrow brucitic dunite dykes and sills. Shear contacts commonly surround the ultrabasic body. Cross faults and complex Jointing also exist. The Advocate Mines Limited mill produced 65,000 tonnes of Group IV fibres and 1 l , 000 tonnes of Group VJ fibres annually. The bagged product enjoyed markets worldwide.

Jan 1, 1984

By D. G. Tisdale, W. Curlook, J. M. Toguri

"In this study, the vapour phase reduction of titanium tetrachloride conforms to the traditional Kroll chemistry, but employs argon as an inert carrier gas and requires a higher reaction temperature of 1150°C to 1250°C. A vapour phase reaction is advantageous because titanium is the only condensed phase present, and the metal can be collected free of magnesium or magnesium chloride, in marked contrast to the titanium sponge produced by the conventional Kroll process. The yield of metallic titanium from the reaction was determined as magnesium additions ranged from 36% to 168% of the stoichiometric requirement. Yields of over 99% were obtained when an excess of magnesium was present. Although the collection efficiency was low, metallic titanium was collected at the reaction site, where all other species were present as vapours. Magnesium and chlorine concentrations in the collected titanium were less than 0.3%.IntroductionA proposed method (Curlook, 1987) for titanium production has been investigated as an alternative to the conventional Kroll process (Kroll, 1940). The advantages of the new process include a simplified means of recovering the product metal, and a potential for lower overall energy consumption and greater product purity. A higher reaction temperature for the reduction of titanium tetrachloride results in a vapour phase reaction, rather than the conventional liquid phase reaction. This is the major conceptual difference between the proposed and the established (Kroll) processes.This study focussed on optimization of the process chemistry and briefly examined the issue of product deposition and collection. The reduction of titanium tetrachloride with magnesium, to produce metallic titanium and gaseous magnesium chloride:"

Jan 1, 1997

By L. W. Krahenbil

The programmable Logic Controller (PLC), at its present stage of evolution, is now considered as a mature control system. The PLC combines the solid-state reliability of hardwired logic and computer control systems with the simplicity of a relay ladder logic. Relay symbolic programming through a function-oriented keyboard provides a means which plant personnel can easily become accustomed to work with. In a large coal facility, it is shown that the control engineer can provide improved control flexibility with the advanced capabilities of the PLC.

Jan 1, 1979

By Haipeng Li, Jacob Masliyah, Barun Gorain, Jian Huang, Qingxia Liu, Zhenghe Xu, AuTec Innovative Extractive Solutions Ltd.

"Froth flotation is widely used to selectively separate one or more minerals from an ore over a wide range of particle sizes with high efficiency. Bubble–particle attachment is one of the most critical steps in flotation. The objective of this project is to demonstrate the need for an innovative dual bubble generator to improve flotation efficiency. This dual bubble generator was designed to generate two different sizes (micron size and typical flotation size) bubbles. The micron size bubbles generated on the crevices of particle surfaces in venturi type of cavitation tubes enhanced the attachment of fine particles to the bubbles in conventional flotation systems. They also acted as a secondary collector, which has the potential to reduce operation cost and improve flotation recovery. The dual bubble generator was evaluated for a double refractory gold ore with 3g/t Au, 1.5 wt% TCM (total carbonaceous matter) and 0.7 wt% sulfides. The results were compared with those obtained using a commercial bubble generator. Compared with the commercial bubble generator, the dual bubble generator showed not only a higher gold recovery, but also an improved separation efficiency, demonstrating the potential of dual bubble generator in fine particle flotation.INTRODUCTIONFroth flotation has been widely used in mineral processing and waste water treatment. However, flotation has been proven inefficient for fine particle recovery although it becomes increasingly inevitable to process fine particles with the depletion of easy processing ores. The critical problem of fine particle flotation is the low attachment of fine particles to flotation size bubbles due to their low collision rate. Based on a commonly acceptable flotation model given by R =F*[Pc*Pa*(1-Pd)], the probability of bubble–particle collision (Pc), attachment (Pa) and particles detachment from air bubbles (Pd) collectively determines fine particle recovery (R) (Yoon and Luttrell, 1986). Since Pc = (3Dp/Db) where Dp and Db are diameters of particles and bubbles, respectively, bubble size and particle size impact the bubble-particle collision in opposite directions. It is evident that the probability of bubble–particle collision decreases with decreasing the size of particles, leading to a low recovery of fine particles. In this case, reducing the bubble size and/or increasing the apparent size of particles by fine particle aggregation are clear means to improve fine particle recovery."

Jan 1, 2016

By C. Tong, B. Hilscher

"Sensor based ore sorting is being rapidly adopted by the mining industry. The ability to boost mill feed grade by rejecting waste grade rocks early in the process has proven revolutionary for some operations.This paper briefly reviews the current position of ore sorting in the industry, as well as abridged results from specific operations such as Barrick, McEwen, New Gold, and two others. The paper also introduces the concept of “Profit Recovery™”, the measuring of recovery based on rock profitability rather than just metal content.IntroductionSensor based ore sorting is being rapidly adopted by the mining industry. The ability to increase mill feed grade by rejecting waste grade rocks early in the processing stage is proving to be revolutionary for some operations. These potential outcomes have been too invaluable to be overlooked by both producing operations and prospective projects, thus leading to a wide range of studies on ore sorting. In addition, the advent of ore sorting has also called for a new standard of recovery analysis. The answer to this is the creation of a new term and concept - Profit Recovery™.This paper evaluates the most recent results of ore sorting in the mining industry, and presents the results from five different mining operations. Additionally, this paper will discuss and evaluate the Profit Recovery™ of each of these operations. The goal of this paper is to address common concerns regarding ore sorting rejects and their actual impact on project economics.State Of The ArtOre Sorting is a sensor-based sorting and pre-concentration technology implemented before the processing stage that is used to reduce the amount of waste reporting to the mill feed. This technology can also be utilized to recover ore from previously uneconomic waste, as well as reduce the mill energy and reagent consumption (Tong, 2012). In greenfield projects, sensor-based sorting can further provide value by reducing processing capital costs. The decline of available high grade orebodies and decreasing head grades has further increased the attractiveness of pre-concentration, and subsequently ore sorting (Lessard et al., 2014).There are currently two notable types of sensor-based sorting: bulk and rock-by-rock. Bulk sorting consists of live, high tonnage sorting that can be installed on a scoop or on a conveyor belt with a diverter. Rock-by-rock is a selective sorting method that scans and sorts individual rocks on a conveyor belt, and rejects rocks using air jets or mechanical levers. Figure 1 shows a diagram for a typical air jet sorter."

Jan 1, 2018

By T. Boyd, K. McTaggart, J. Qiu

"Hudbay Minerals’ Flin Flon process plant produces a copper concentrate and zinc concentrate from the three ores it processes: 777, Reed and Lalor. Unlike many Cu-Zn ores, the average Zn: Cu ratio in feed is around 2:1, whereas, in many Cu-Zn separation plants the Zn: Cu feed grade is substantially higher than 2:1. The lower Zn: Cu in plant feed is a challenge for limiting Zn recovery to the Cu concentrate. While total recoveries of Cu and Zn at Flin Flon are very good; selectivity is the key challenge and small changes in ore or plant, can result in quite variable Zn recovery to Cu concentrate, and accordingly, Zn recovery to Zn concentrate. Magnetic conditioning has been shown to be selective between the two paramagnetic minerals chalcopyrite and sphalerite. Statistical testing of magnetic conditioning was undertaken at Flin Flon with the objective of increasing Cu recovery to Cu concentrate without increasing the Zn recovery to Cu concentrate - in effect increasing Cu-Zn selectivity. This has been achieved elsewhere with magnetic conditioning with the probable mechanism being an increase in fine chalcopyrite recovery, and a reduction in entrained, ultrafine, non-activated sphalerite to Cu concentrate. The results did indeed show an increase in Cu recovery to Cu concentrate of 0.8% to high confidence, but the decrease in Zn recovery to Cu concentrate was not to high confidence. This is effectively an increase in Cu: Zn selectivity in the Cu circuit – higher Cu recovery with no change in Zn recovery. However, while there was an increase of 1% in Zn recovery to Zn concentrate with magnetic conditioning, the variability in this parameter meant that this increase, though larger in magnitude than the Cu result, was not to high confidence."

Jan 1, 2019

By H. R. Hammond, E. Sadar

Cominco is making substantial savings in secondary breaking by replacing dynamite with a new nitrate-based explosive. Compareo with dynamite. the new explosive, known locally as "Fine NCN," is significantly cheaper, more effective and safer to use. It also works better than prilled NCN, which is unsatisfactory for secondary blasting because of inadequate sensitivity, low strength and awkward handling properties. A simple apparatus has been devised for pulverizing prilled NCN to a fineness practical for effective secondary breaking. Blasting systems using cheap detonating cord for initiation have been developed.

Jan 1, 1966

By M. Sakata, H. Hata, K. Haiki

"Most of the secondary ZnO contains fluorine (F) in large quantities. Serious troubles at the zinc electrowinning are occurred by the cathode corrosion caused by F, therefore we developed iron compounds as F-adsorbents used in zinc sulfate solution. The iron compounds can be reused repeatedly as F-adsorbents because they can adsorb/desorb F alternatively depending on the pH. Moreover, if the adsorptive capacity decreases, we can dissolve and re-synthesize them easily. In this paper, results of the experimental process which consists of five steps (leaching, F removal, Cl removal, purification and electrowinning) to produce high purity electrolytic zinc from the secondary ZnO are reported. INTRODUCTIONThe recycle material for zinc, secondary ZnO, contains large amounts of fluorine (F) and chlorine (Cl) which are halogen elements, compared with calcine obtained by roasting of zinc sulfide concentrate. The halogen elements cause adverse effects in the zinc electrowinning process and particularly F causes corrosion of aluminum cathode plates and eventually sticking of electrodeposited zinc and therefore, F concentration in the electrolyte is controlled to less than approximately 20 mg/L. There are several methods to remove F from secondary ZnO, such as leaching with Na2CO3 or NaOH solution [1-2], vaporizing in a rotary kiln by roasting at 1000 to 1200 degrees C [3-4]. However, up to the moment, there has been no effective method for the removal of F from zinc electrolyte and it has been a big obstacle in treatment of secondary ZnO in electrowining of zinc.The authors, therefore, developed an iron compound used as an adsorbent of F in the zinc sulfate solution [5-8]. This iron compound is Akaganeite that has a crystalline structure of ß-FeOOH. Akaganeite is synthesized by neutralization of FeCl3 solution containing a small amount of SO4 2- with Na2CO3. When this iron compound is immersed into weak acidified zinc sulfate solution, F in the solution is adsorbed. F adsorbed in the iron compound is removed by immersing in weak alkaline solution and the iron compound can be reused as F adsorbent."

Jan 1, 2012

By G. Pouskouleli, T. A. Wheat

"The role and benefits of using statistical methodology in the development and optimization of materials and processes is examined. It is shown that considerable benefits accrue from the use of an appropriate design in which a number of factors (process parameters) are varied simultaneously while the system response such as percent recovery, degree of separation, purity, etc. is monitored and ultimately optimized.Compared with the commonly encountered one-factor-at-a time approach, this schema exploits reduced experimentation (thereby requiring reduced resources [staff, time, dollars, etc.]) yet yields quantitative information on the significance of each factor and their combinations on the measured response."

Jan 1, 1992

"These standards were developed by the CIM for use with the value or worth of a Mineral Property as opposed to “evaluation” where the key objective is an economic assessment or determination of the economic merit of a propertyP1 .0 BACKGROUNDPl.1 There are at present no comprehensive standards for valuation of Mineral Properties in the Canadian mining industry. The Mining Standards Task Force (MSTF) of the Toronto Stock Exchange and the Ontario Securities Commission in its Final Report (January 1999) specifically recommended that the Canadian Institute of Mining, Metallurgy and Petroleum (CIM) form a committee of valuation practitioners to review and advise on approaches to valuation of Mineral Properties.Pl.2 On May 5, 1999 at the Calgary Annual General Meeting, CIM Council approved the formation of a Special Committee on Valuation of Mineral Properties (CIMV al) to be co-chaired by Keith Spence (Chairman of the CIM Mineral Economics Society) and Dr. William Roscoe (Roscoe Postle Associates Inc.).Pl.3 The mandate of CIMVal is to recommend Standards and Guidelines for Valuation of Mineral Properties to be used by the mining industry in general and to be adopted by Canadian securities regulators and Canadian stock exchanges.Pl.4 The members of CIMVal represent of a mix of professional disciplines and experience in the field of Mineral Property valuation:Keith N. Spence (Co-chair), Alliance Pacific Resources Inc., TorontoWilliam E. Roscoe (Co-chair), Roscoe Postle Associates Inc., TorontoMichael J. Bourassa (Secretary), Aird & Berlis LLP, TorontoChristopher R. Lattanzi, Micon International Limited, TorontoRoss D. Lawrence, Watts, Griffis and McOuat Limited, TorontoPaul E. Lunney, Noranda Inc., TorontoCraig A. Roberts, Pacific International Securities, VancouverDavid A. Scott, CIBC World Markets, TorontoIan S. Thompson, Derry, Michener, Booth & Wahl Consultants Ltd., VancouverWilloughby A. Trythall, retired Placer Dome executive and consultant, Vancouver"

Jan 1, 2003

By M. Somppi, D. Weirmeir, Z. Yamak

"Milling operations commonly employ activated carbon to capture complexed gold from lixiviants in leaching processes. As the carbon moves through pipes, pumps, vessels, kilns and other processes in the gold leaching circuit, this consumable may experience losses by various mechanisms like attrition, breakage, and rupturing. Whenever possible, capturing the fine gold-bearing carbon portion of this stream could provide value to milling operations at low capital cost and manageable financial risk. Identifying, testing, and validating the successful payback of a low-tech flocculant system is described. However, the work more closely explores a Monte Carlo risk-based methodology for understanding the potential payback of this project at various confidence levels – an approach that many improvement projects can follow where some level of uncertainty exists.INTRODUCTION Gold milling operations commonly employ activated carbon to adsorb gold from solutions. Normal handling causes the carbon particles from this material to abrade, break, rupture to a size that becomes too small for further use in the process. Operations often concentrate on capturing the fine particles because gold is associated with the carbon and this metal content can be a valuable revenue stream for toll processing. However, the small particle sizes become difficult to separate from the process and can ultimately leave the facility in the waste stream. Hence, operations often place a great deal of care in capturing as much fine carbon as possible by a variety of methods including using screens, settling tanks, and chemical methods. Retrofitting a circuit to capture more carbon fines is common but can expose the operation to financial risk. Approaching this potential improvement by leveraging a Monte Carlo methodology can be effective in understanding the risk and the associated payback of a project at various confidence levels. This method provides a strong framework for capital go-no-go decisions and the structure to validate the potential project success before implementation."

Jan 1, 2019

By B. MohammadSadeghi, S. Bakhshivash, M. Haghshenas, F. Rahimi

"Constrained groove pressing (CGP), as a severe plastic deformation (SPD) technique, is one of the applicable methods for sheet metal forming capable of producing ultra-fine grained materials (UFGMs). In CGP, processing and die design parameters can significantly affect the deformation response of sheet metal specimen. Having said this, in the present research the effects of die design variables and processing parameters (i.e. shear angle and friction) on the deformation behaviour of an Al-Mg-Si Alloy are studied thoroughly. Finite element analysis (FEA), was used to evaluate the effectiveness of mentioned parameters on the deformation homogeneity, strain distribution and pressing load variations. Also, mechanical properties of the deformed sample in term of micro-hardness was analyzed. It is observed that with increasing the shear angle, effective stress, strain and pressing load are enhanced. Moreover, by increasing the coefficient of friction, pressing load enhances. The color coded micro-hardness measurement showed a good agreement with the strain distribution obtained from FEA (higher hardness for the zones associated with higher shear plastic strain values).INTRODUCTIONWork hardening results in enhanced mechanical properties upon cycles of deformation (Hosford & Caddell, 2007). However, the formability of the processed products are affected by work hardening reducing the possibility of processing in subsequent deformation cycles. Therefore, many industrial processes cannot be performed on sheet metals to produce products with desired mechanical and physical properties (Valiev, Islamgaliev, & Alexandrov, 2000). Severe plastic deformation (SPD) is an effective grain refining technique which can impose large plastic strains through cold working on a metallic specimen (Bisadi, Rastgou, Payganeh, Zeynali, & Ghahremani, 2010). SPD techniques are mainly categorized into three types; sheet, bulk and tube forming. Among SPD sheet forming methods, Constrained Groove Pressing (CGP) (Shin, Park, Kim, & Park, 2002), Accumulative Roll Bonding (ARB) (Saito, Tsuji, Utsunomiya, Sakai, & Hong, 1998) and Repetitive Corrugation and Straightening (RCS) (Zhu, Lowe, Jiang, & Huang, 2001) possess potential applications in manufacturing industries."

Jan 1, 2016

By M. M. Williams

ALBERTA has been generously endowed with oil, natural gas, coal and water power, thus giving power producers a wide choice in the type of plant and fuel which can be used. Therefore, with such a variety of energy sources to choose from, why was coal selected as the primary fuel at Calgary Power's Wabamun steam plant? This part of the paper will cover the circumstances that led the Company to decide in favour of coal. The second part, to be presented by C. F. Doerr, will describe how the Wabamun coal mine has been developed to supply the large fuel requirements of the power plant. Before considering the Wabamun plant, we require a general under-standing of? the Company's electric system and load. Power is fed into a 5,100-mile high-voltage transmission grid from eleven hydroelectric plants and from the Wabamun steam electric plant. These plants have a combined generating capacity of 820,000 horse-power. Of this total, the hydro

Jan 1, 1963

By Micheal Mayhew

"This presentation will provide information and facts on the drilling and blasting within a frozen shaft using a full face methodology. The Author will briefly discuss the history of the sinking of a frozen shaft in Saskatchewan, the challenges faced, and the solutions delivered. The case study will include a discussion describing the series of events that led to the decision to adopt a full face blasting methodology. The case study will describe key elements such as the drilling pattern, hole size and depth, explosive products and blast vibration monitoring systems. INTRODUCTION During the shaft sinking process at a project in Saskatchewan, it was recommended that a drill & blast benching method be utilized. Following an evaluation of the site, the geological conditions proved amenable to a ground freezing system that would stabilize the rock formations and prevent inflows of water into the shaft (Table 1).The shaft sinking process required that the ground surrounding the proposed shaft be frozen by drilling several near vertical freeze holes radially at a specified distance from the edge of the proposed shaft excavation. This would allow for the circulation of a chilled brine solution down the freeze holes. The circulation is achieved by means of stainless steel pipes encased within each other to provide a delivery and return conduit for the brine (Figure 1). As a result of this periphery freezing, the ground within the shaft excavation is also predominately frozen.The finished internal diameter of the shaft was 5.5 meters with varying overall excavation diameters to facilitate different liner designs used for various rock formations. For the most part, the fully unsupported/unfinished excavated diameter of the shaft varied from 6.9 meters to 8.5 meters depending on the zone excavated. The challenge was that the proposed drill and blast excavation method posed a significant risk due to the potential to damage the freeze wall and pipes during blasting. The decision was made to commence the excavation through mechanical excavation (i.e. chip and cut) methods then change to a drill and blast method utilizing a split benching design. Through this process, the team encountered five main challenges: 1. Sub-horizontal geological structures and slips that affected blasting performance and sometimes resulted in a sloping surface to the top of the bench; 2. Confined working area for the crews and equipment due to a limited work area as a result of utilizing the split (half) bench drill and blast methodology; 3. Mechanical chipping and cutting of the one-meter buffer zone to the final shaft diameter; 4. Crews working on extremely slippery uneven frozen rock and ice surfaces, which affected safety and efficiency; 5. Establishing a blast vibration monitoring system to determine if the drilling and blasting of the full shaft excavation diameter were acceptable."

Jan 1, 2019

By Ivor da Cunha

Ontario Mining Association (OMA) represents 57 members that are engaged in exploring, producing & processing mineral resources in an environmentally responsible manner. Conservation Bureau at the Ontario Power Authority (OPA) develops, coordinates and stimulates commitment to electricity conservation and demand management programs ? OMA selected compressed air optimization for high impact cost savings and energy efficiency potential ? Ontario Power Authority (OPA) provided $218k funding for $532k project ? Commenced summer 2006, Final Report June 2007 ? Three representative sites participating: ? Williams, CVRD Inco & FNX McCreedy ? Different levels of energy management ? Small, medium and large mining operations ? Different corporate practices and culture

May 1, 2007

By B. Yamamoto, D. Post, J. De Leon, A. Meike

"This paper describes the theory, design, building, and testing of the passive magnetic bearing stabilizing system which is the core of the passive magnetic bearing system. The stabilizing system is made up of two large magnetic disks opposing themselves with a stabilizing disk in the center which allows the system to self-locate in a null position without the need for external power sources or sensors. When outside forces act upon the stabilizer, the magnetic fields interact with the stabilizing plate to return the system to its null position. Collaboration between two industry leaders has allowed an actual prototype to be built and tested providing real data to prove out the theory.INTRODUCTIONMagnetic bearing/stabilizer systems have many advantages over conventional mechanical bearing systems. These include near-zero drag losses and no need for lubrication since the rotating elements make no mechanical contact with the stationary elements of the bearing system. However all magnetic bearing systems must contend with a constraint known as Earnshaw’s Theorem in the early 1800’s, this theorem asserts the impossibility of constructing a stable, non-contacting, electrostatic or magnetostatic levitation system using only fixed charges or fixed magnetic poles, such as those produced by permanent magnets. Because of the constraint imposed by Earnshaw’s Theorem virtually all present-day commercial magnetic bearing systems are of the “active” type. That is, they employ electromagnets that are powered by amplifiers the inputs to which come from sensors embedded in the bearing system. These sensors are a part of a feedback loop that operates to keep the levitated rotating parts of the bearing stable and centered. The resulting complexity means that active magnetic bearings are expensive, require periodic maintenance, and continuously consume electrical power to energize their amplifiers and their electromagnets.Passive magnetic bearings are, of course, also subject to the constraints imposed by Earnshaw’s Theorem but they solve this problem in a straightforward and simple way, with only “passive” elements that take advantage of a loophole implicit in the derivation of Earnshaw’s Theorem. This loophole is that Earnshaw’s Theorem as derived applies only to static systems, i.e. an assembly of stationary permanent magnets arranged so as to levitate an object containing other permanent magnets. The theorem can be overcome if dynamic effects are taken into account. In active magnetic bearings the “dynamic effects” involve the afore-mentioned sensors, amplifiers, and electromagnets."

Jan 1, 2012

By L. Tong

"The oxidation of Quebracho was evaluated by acid-butanol assay, which indicates depolymerization of Quebracho. Anthocyanidin, an oxidation product of Quebracho, is stable at 95?C for up to 2 h. The ionization, complexation, and oxidation properties of Quebracho were discussed. Complexation of metal-Quebracho occurs at ambient temperature. The formation of complex precipitates is influenced by the acidity of the solution. Temperature is another important parameter that influences the oxidation and the complexation of Quebracho. Quebracho-ferric complex precipitate forms at 90?C, 0.1 mol/L H2SO4. The formation of Quebracho-metal complex in the leach solution is a possible reason for the consumption of Quebracho. Quebracho molecules adsorption on the mineral surface is reduced by consumption of Quebracho, resulting in poor sulfur dispersing effect in the leaching process. INTRODUCTIONQuebracho is used as a sulfur dispersing agent (SDA) in the pressure leaching of zinc concentrate as stated in U.S. Patent No. 3,867,268 (1975). It prevents the zinc sulfide particles from being coated with molten sulfur, thus preventing the inhibition of the zinc leaching reaction. Recently, the sulfur dispersing effect of Quebracho was investigated in the oxygen pressure leaching of nickel concentrate. The oxygen pressure leaching of pentlandite can be represented by reactions 1-3."

Jan 1, 2012