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By G. Davis

Mineral properties and mineral firms often trade at a market value that is significantly greater than the value indicated by discounted cash flow (DCF) techniques. A possible explanation is that DCF analysis does not consider the value derived from managerial flexibility. Presumably, then, at least some of the difference between DCF value and market value is due to managerial flexibility. This paper surveys the recent attempts to empirically quantify the value of managerial flexibility using option pricing theory. The results indicate that managerial flexibility, at least as measured by the option pricing methodology, falls well short of explaining the gap between DCF value and market value.

Jan 1, 1995

By E. C. Truesdale

IN recent years various problems in connection with research work on the preparation and properties of zinc-base alloys have required reliable information concerning the constitution of the zinc-rich portion of the iron-zinc equilibrium diagram. On numerous occasions rather positive indications were obtained that, for example, the solubility of iron in zinc was incorrectly represented on the current equilibrium diagrams. A careful study of all the available literature relating to the iron-zinc system led to the conclusion that much of the early work was unsatisfactory as measured by present standards of experimental accuracy, and as a result it was decided to redetermine the location of the liquidus curve and of adjacent portions of the diagram. Part I of this paper comprises a description of the experimental methods and a summary of the results by means of which the zinc-rich end of the iron-zinc diagram has been revised in the following ways: 1. Measurements of the solubility of iron in liquid zinc by several different sampling methods, leading to a relocation of the liquidus curve. 2. Microscopic, conductivity, and X-ray studies of the solid solubility of iron in zinc, which, together with thermal analyses, have resulted in new values for the solid solubility and the eutectic temperature and composition. 3. Heating and cooling curves, obtained by a refined differential method, leading to new locations for the two peritectic horizontals. In Part II of the paper the attempt is made to review all of the pub-lished work having a bearing on the constitution of the iron-zinc system, and to correlate the present results, and some recently published data

Jan 1, 1935

By Filiz Sahin

This paper presents a synthesis of TiB2 via carbothermal reduction method using a mixture of TiO2, B4C and C prepared in molar ratio of 2:1:3. Reduction experiments were carried out in a high temperature graphite furnace in a graphite crucible under argon atmosphere at different time (0, 15, 30 and 60 min.) and temperatures (1400, 1500 and 1600 °C). The products obtained were investigated using XRD technique.

Jan 1, 2008

By Sedef Pinar Basag, Onuralp Yucel, Ahmet Turan

Niederschlag process is commonly used to produce metallic antimony. The process is a metallothermic process which is conducted in one step for metallic antimony production. Using this method Sb2S3 is mixed with coal and metallic iron and subjected to reduction. During heating, antimony sulfide is decomposed and sulphur combines with iron to form the matte phase. Metallic antimony is collected at the bottom of the crucible. In this study, evaluation of Sb2S3 concentrate, extracted and obtained from West Anatolian Region of Turkey was investigated by using Niederschlag process. The reductant stoichiometry, reduction temperature and duration were carried out in the experiments. Chemical analysis methods by using atomic absorption spectrometry (AAS) and X-ray diffraction spectrometry (XRD) techniques were used for the characterization of the concentrate, metallic nuggets and matte phases.

Jan 1, 2016

By V. Sheikhzadeh, M. Saghaeian, R. Hejazi, A. Abazarpoor

The research aimed to compare the chemical analysis (K, Na, Cl) of Iranian concentrate plants, which are the main source of materials corrosion in the pelletizing plants. Cl alongside alkaline elements (especially K) may cause corrosion and plug in the grate plates and other involved equipment. Therefore, it is tried in the processing plants to remove impurities from the concentrate to prevent potential problems in pelletizing and iron/steel making processes. Part of these impurities are existed in the nature of ores and others are sourced in the processing water. Various samples from the largest Iranian concentrate plants including Chadormalu, Gol-e-Gohar, Jalal-Abad and Sechahun were prepared to investigate the possibility of alkaline problems for each samples. The amount of Cl, K and Na of Chadormalu sample was obviously low and therefore no alkaline problem is expected. The Cl content of Gol-e-Gohar sample was high (980 ppm) while amount of K was less (0.008 Wt. %). Due to low content of K, most of Cl will release as Cl2 or HCl and so problems caused by KCl plugging would not be a problem. The amount of Cl in Sechahun case was nearly same as Jalal-Abad (400-600 ppm), higher than Chadormalu and less than Gol-e-Gohar samples. However, the K content was higher than all samples (0.04 Wt. %). Therefore, the amount of evaporated K would be 2-4 times more than other samples. Since the amount of Cl and K is simultaneously higher than usual iron ores, therefore alkaline problems may be a serious prevention factor for the continuous operation of this plant. In order to solve this problem some counter-measures is suggested and discussed including cleaning system, partial dust enriched with KCl removal and variation in the materials type of involved equipment.

Jan 1, 2018

By Achilles J. B. Dutra, Carlos M. Juarez

"The use of thiourea as a gold leaching reagent has been extensively studied by many researchers, and it has proved to be promising for some cases as refractory ores. Otherwise, the recovery of gold from these solutions did not receive so much attention. In this paper the electrowinning of gold in acidic thiourea solutions was studied by voltarnmetry and chronopotentiometry. An adsorption step was detected prior to Au(I) reduction and the diffusion coefficients at 25°C for Au-TU complex and FD were found to be 1.00 x 10.5 cm2 S-I and 1.98 x 10-5 cm2 S-I respectively. At -0.350 V (SCE) a passivation probably due to TU adsorption was observed. For higher overpotentials hydrogen evolution was the main reaction.IntroductionThe use of acidic thiourea solutions for the extraction of gold and silver has shown to be a promising alternative to the traditional process of cyanidation, specially for certain refractory ores (1-3) and electronic scrap (4). In some cases, the industrial scale was reached (1,5). The thiourea leaching of precious metals presents advantages over cyanidation, as faster kinetics, lower toxicity and lower sensibility to base metals; however the costs due to high thiourea consumption impairs its use.The majority of the publications on thiourea processing of gold is on leaching. Many are review papers (5-7). Recently, the adsorption and desorption of the gold-thiourea complex on activated carbon and ion exchange resins have been studied (8-11).Little research has been done on the electrowinning of gold from acidic thiourea solutions, most of it has been carried on the seventies and beginning of the eighties in the former USSR (12-17) and concerned the eletrolytic extraction of gold in tridimensional cathode cells.The present paper concerns the cathodic behavior of the gold-thiourea complex in the presence of formamidine disulfide in order to provide information on the electrowinning of gold from solutions obtained directly from leaching or from an elution process."

Jan 1, 1997

By S. Combrink, N. Naude

Hydrocyclones are widely used in wet mineral classification applications and can be notoriously prone to wear. The methods currently used for quantifying hydrocyclone wear profiles are mostly twodimensional. In this paper it was attempted to quantify and monitor wear in three-dimensions, using a micro-CT scanner (Nikon XTH 225 ST). Hydrocyclone wear and, more specifically, spigot wear was investigated on a Multotec HC250 (Dc 250 mm, barrel diameter) hydrocyclone. The hydrocyclone is lined by a vulcanised natural rubber compound within a metal shell, with a thermosetting polyurethane spigot and vortex finder. Tests were conducted on the hydrocyclone in a pilot-scale recirculating test setup. The wear rate of the spigot was quantified by measuring the volume change within the spigot over 122 days in operation, using the micro-CT scanner. After 122 days in operation (recirculating feed materials) the wear in the hydrocyclone led to only a 13.67% loss of spigot volume. The relatively low wear rate could be related to the fact that material recirculation led to particle smoothing and a reduction in size, thereby decreasing the wear rate. This also shows the enormous influence that particle shape and size have on wear. The research was conducted with the support of Multotec, NECSA and the University of Pretoria. Keywords: Wear, hydrocyclone, micro-CT

Jan 1, 2020

By Chen Xia, G. Deschenes, Wan-Tai Yen

"Ammonium thiosulphate is a potential replacement for the cyanide in gold leaching. However, the high reagent consumption hinders its practical applications. In order to reduce the thiosulphate consumption, chemical additives were used. The gold leaching tests were conducted on a sulphide copper-bearing gold ore with 0.3M thiosulphate, 0.03M copper sulphate and 3M ammonium hydroxide solution at 44% solids and pH 10.2. Sulphate, sulphite, amino acid and chelating agents were initially used as additives. It was found that chelating agents (EDTA and NTA) could reduce the thiosulphate consumption from 30 kg/t to 17.8 kg/t with some increase of gold extraction. The improvement from other additives was not significant. Other approaches were also attempted to reduce thiosulphate consumption with some success. The thiosulphate consumption could be reduced to about 17 kg/t by reducing copper sulphate concentration fiom 0.03M to 0.0015M; adding 0.04M of EDTA; replacing copper sulphate with 0.001M of nickel sulphate. The increase of pulp density fkom 44% to 60% solids could reduce the thiosulphate consumption to 17 kg/t as well. Limiting the dissolved oxygen content by sparging nitrogen reduced the thiosulphate consumption further to 10 kg/t. It could be concluded that the regulations of copper and oxygen supply in the lixiviant were the keys to reduce the reagent consumption.INTRODUCTIONCyanidation, as the predominant gold leaching method, has been used in mining industry for more than a century. The low reagent requirement and the high performance are the reasons for its great success. However, cyanidation cannot deal with ores containing large amount of copper, nickel, arsenic and zinc minerals. This type of ore may consume more reagents and result in a poor gold extraction. On the other hand, the carbonaceous materials may preg-rob the gold from pregnant solution and make cyanidation a problem leaching method. Further more, the high toxicity of cyanide represents another challenge to modern gold mines. In the beginning of the year 2000, an environmental disaster caused by an accidental spill in Yugoslavia was broadcasted world-widely (Gurevitch 2000). Gold mine operators are facing higher social pressures and increasing costs on environmental protections. The usage of cyanide in mining industry has been banned in some countries and locations such as Czech Republic, Japan, Turkey, California, Colorado, Wisconsin and Montana States. Thus, a non-cyanide lixiviant is required."

Jan 1, 2002

By F. Y. Kang

There are rich resources of natural graphite in China. It would be a good opportunity to upgrade national graphite industry if natural graphite with modification is used in lithium ion battery. Micro-crystalline graphite in high purity was coated with a carbon film on the surface. The initial cycle efficiency was improved to be 89.9% and cycle stability was remarkably improved. The experiments proved that microcrystalline graphite with carbon coating have excellent electrochemical performances at low cost as anode materials for lithium-ion battery. In addition, H2SO4-GIC technique was used to prepare the natural flake graphite powders with mild-exfoliation. Sub-micro and nano pores were found in the graphite samples. In correspondence the reversible capacity, rate capacity and cycle life were improved, which would meet the demand of high-power lithium-ion battery. Natural graphite is the most promising anode material for large-scale lithium-ion batteries. The demand of modified graphite grows up greatly in the market. Microcrystalline graphite with surface coating and flake graphite with mild-exfoliation are the promising commercial anode materials for the industry of lithium ion battery.

Jan 1, 2014

By M. S. Eygi

This study covers the investigations based on the electrokinetic and rheological properties to explain the interactions between kaolin minerals and commercially available polyelectrolyte in anionic character. Additional adsorption test were also conducted to support the interaction mechanism. Adsorption tests showed that adsorption densities decrease by increasing the solid content. In-creasing the solids contents from 1% to 30% by weight resulted in the decrease on adsorption from 2.14 mg/g to 1.85 mg/g. Because of its difficulty, the solids ratio at 70% was not studied. However, following to trend of the curve plotted adsorption density-solid ratio, an estimation was made and adsorption density at 70% solid content was extracted from the curve as 1.75~1.80 mg/g. The electrokinetic studies pointed out that the presence of polyelectrolyte increase the zeta potential of kaolin from 40 mV to 60 mV which is reasonable conditions to disperse and stabilize the kaolin slurry and lower the viscosity. When these result of the different tests are combined and considered together, 2 mg/g polyelectrolyte concentration was noted as optimal concentration where adsorption density, viscosity and zeta potential of the slurries give maxima and remain constant after this concentration.

Jan 1, 2014

By S. Kelebek, E. Yalcin

"Two composite samples of a gold-bearing ore from North Western Quebec (Barry Township) were tested to assess their grindability, recovery by flotation and Knelson concentrator as well as extraction using cyanidation.Work index values (BWi) for two composites were found to be 10.4 and 11.0 kWh/tonne, respectively. Flotation tests involved feed samples for which the particle size ranged from a P80 value of 205 ?m to 53 ?m, which resulted in gold recoveries of 91.8% to 95.8% (at gold grades of 130 to 140 g/tonne). Cyanidation tests indicated gold extraction levels ranging from 94.2 to 97.5%. Higher, recoveries were obtained at finer grind sizes and higher cyanide strengths. However, the grind size had a bigger impact on gold leaching. Gold grade and recoveries obtained with the Knelson concentrator device were lower than those obtained by flotation. Mass recoveries to concentrate products strongly depended on the fluidization pressure used. High gold recoveries can be obtained generally at low water pressures of 3 to 4 psi. Higher water pressures produced more selectivity at the expense of higher gold losses.It can be concluded that the gold ore samples tested have good characteristics due to moderate levels of energy requirement, high gold recoveries and extraction rates attainable.INTRODUCTIONBench scale testing of ore samples is an important step in the long series of metallurgical and economic studies involved in bringing new ore bodies into production (Coleman, 1980). Through a laboratory testing program, the behaviour of an ore in a particular process on a larger scale can be established. In an exploratory manner, this testing can be helpful for classification of ores in terms of “good ore” or “problematic ore” by providing preliminary information on recoverability of target minerals. Potential problems if any can be assessed by further investigation of products (e.g., middlings) obtained as a result of testing. A detailed bench scale experimental program in the metallurgical laboratory can also provide the background work for flowsheet development. Depending on the simplicity or complexity of the ore to be tested and type of details required from a testing program, the amount of samples required in the mineral processing laboratory can vary from several kg to more than one hundred kg depending on how detailed the metallurgical testing program is."

Jan 1, 2008

JOHN W. BELL (communication to the Secretary*).-I have to thank Mr. Merrill not only for his very kind remarks, but for the weight of his implied opinion that the work accomplished probably has an important practical aspect. I think there is a distinct although unuttered impression among engineers, that it will be time enough for them to begin to take an interest in the law of crushing when it emerges from the cloud of violent and even vituperative controversy that has hovered over it during the last 6 or 7 years. I have a very confident feeling that as the result of the work done by Mr. Gates, by me and by Messrs. Mitchell, Baily and Cockfield, who so loyally helped me to obtain the necessary data, at least the practical law of crushing has emerged; that it is ready and available for use by our fellow engineers, and that it will help them to unravel a number of the many practical problems they are con¬stantly confronted with. In regard to Mr. Gates' discussion, I would indeed like to believe that McGill could claim, as a minor achievement, the credit which Mr. Gates so generously bestows of having established the "law" of crushing. I think that more work would be required to establish this claim in the, strict sense of the word, as there is a fairly large gap between the coarse and fine crushing results. I am not worried about that gap, because the reason for it is quite clear to me; at the same time I-think it will be well to bridge it by a series of tests, and I am bound to admit that the testing machine is the most promising machine right at hand to work with, although whether the minute amounts of power required to crush small quantities of rock can be so accurately integrated as to insure high accuracy in the final result is still a question in my mind. If we had an Amsler-Laffon machine I would certainly try it. Mr. Gates' remarks about choke crushing are extremely interesting. He compels me to wonder, too. It is a new and probably a very important factor to be considered in this connection. I am in perfect accord with Mr. Gates about the desirability of the determination of crushing constants, because when this is accomplished the efficiencies (not relative mechanical, but real efficiencies) of different types of rock-crushing plants in any part of the world will then be comparable. For this reason it would, seem desirable that the American Institute Committee should not only consider ways and means for accom-

Jan 6, 1917

By M. L. Cunha

The lack of control of As and Sb compounds from copper smelters and converters has rendered some chalcopyrite containing arsenopyrite, stibnite and tetrahedrite minerals unusable for metal extraction. In the present investigation, we have studied the carbothennic reduction of Portuguese chalcopyrite mineral concentrate in the presence of lime/CaS04 and CaS04/Si02. Thermodynamic equilibrium calculations were performed to study the distribution of As and Sb between metal and the CaO-Si02-FeO slag phase. The phase equilibrium calculations also show the effect of oxygen partial pressure on the increase in the volume of the slag phase, which helps in lowering the copper metal formation temperature and facilitates a better separation between metal, matte and slag. The reduction reaction kinetics was studied between 850°C and 1100 °C, and the phases formed were identified by X-ray powder diffraction and scanning electron microscopy techniques. The importance of this research for using recycled matte, lean and rich minerals with As and Sb is also explained.

Jan 1, 2001

By A. Sadough vanini A. Kami

In this paper, effects of different ageing treatments on the mechanical properties, microstructure and formability of 7075 aluminum alloy have been studied. Forming limit diagrams of the alloy have been obtained for four ageing conditions including T6, OA1, OA2 and O. For this purpose, combination of uniaxial tensile tests and the Erichsen cupping tests with different sizes and shapes of sheet specimens have been performed after each ageing treatment. The highest formability and the lowest formability have been observed at samples with O and T6 ageing treatments, respectively. Also, investigation of precipitated microstructures showed that the size of precipitation particles has a significant effect on the formability of the alloy. Formability improves with coarsening of precipitation particles.

Oct 1, 2011

By Mohsen Amir-Rahmat

The ore of Sarcheshmeh copper deposit that has been located in the south ?east of Iran, contains four type of rock that they have their specific hardness and strength according to their alteration type and mineralization. Blasting of these various types of mine rocks prepares various types of size for the product of mine as the feed of concentration. Along the crushing of this feed a few factors effect on the efficiency of the crushing unit. The aim of this project has been the consideration of the effect of ore size on the efficiency of crushing unit. For this investigation along the year 2000 A.D., six sample from feed and six sample from product of crushing unit have been prepared. The results of the screen analyze of these samples has shown that the size of feed has been lesser than the primary plan and the size rate of the product has been bigger than the primary plan. Also in this research the effect of feed size on the quality of product size has been considered.

May 1, 2003

By Wang Zhi

High-Mg-content concentrates are usually treated in Jinchuan flash smelting Furnace. Because the viscosities of high-Mg-content slag is very high, the operation of flash smelting becomes very difficult. To solve this problem, the viscosities of the semi-synthesized FeO-MgO-Si02 slag of different compositions were measured. The results showed that when in the slag the weight percentage of MgO [m(Mgo)] is 6-10%, the ratio of the weight percentage of iron to that of Si02, m(Fe)/m(SiO2) is 1.1-1.4 and the temperatures are within 1473?1773K, the slag viscosities increased with the increase of m(Mgo) and m(Fe)/m(sio,). When m(Mgo)<6%, the smelting temperature should be controlled at I 300°C in order to to keep the smooth operation. When m(Mgo» 10%, the temperature should be kept above 1633K. When the content of MgO is higher, a lower viscosity slag ean be produced by decreasing the ratio of m(Fe)/m(sio,). The appropriate ratio of m(Fe)/m(sio,) for Jinchuan flash smelting furnace is about 1.2.

Jan 1, 2003

By Wang Zhi

High-Mg-content concentrates are usually treated in Jinchuan flash smelting Furnace. Because the viscosities of high-Mg-content slag is very high, the operation of flash smelting becomes very difficult. To solve this problem, the viscosities of the semi-synthesized FeO-MgO-SiO2 slag of different compositions were measured. The results showed that when in the slag the weight percentage of MgO [w(MgO)] is 6-10%, the ratio of the weight percentage of iron to that of Si02, w(Fe)/w(Si02) is 1.1-1.4 and the temperatures are within 1473-1773K, the slag viscosities increased with the increase of W(MgO) and w(Fe)/w(SiO,). When w(Mgo)<6%, the smelting temperature should be controlled at I 300°C in order to to keep the smooth operation. When w(MgO)>10%, the temperature should be kept above I 633K. When the content of MgO is higher, a lower viscosity slag can be produced by decreasing the ratio of w(Fe)/w(SiO,). The appropriate ratio of w(Fe)/w(SiO,) for Jinchuan flash smelting furnace is about 1.2.

Jan 1, 2003

By E. Stiakakis

The paper presents a geotechnical simulation of the "Mavropigi" open pit mine (Western Macedonia Lignite Center, Greece), using the finite element method. The simulation was based on the initial planning of the pit using Mohr-Coulomb and Soil Hardening models. Results indicate high stability factors as well as the magnitude of the expected horizontal displacements and floor heaving. However, these deformations do not influence decisively the overall stability unless locally adverse tectonics are encountered. Results can be used in the ongoing update of mine planning and stability evaluation.

Jan 1, 2006

By S. C. Chelgani

The Thor lake deposit is a world class resource of rare earth (REE) metals and minerals in Canada. Development work to optimize a REE mineral recovery process flow sheet is underway, however, given the ore mineralogy; the developed reagent scheme is relatively complex. As part of a research project, micro flotation tests were conducted on a feed sample in order to examine factors affecting stream partitioning. SEM-EDX was performed to evaluate variability in grain composition between streams (concentrate and tails) and TOF-SIMS surface analysis was used to determine statistically significant differences in surface species particularly related to potential activation (or depression) of the examined mineral phases. SEM-EDX analysis reveal that the concentrate has a significantly higher proportion of REE bearing grains (carbonates and phosphates) relative to the tail (almost none were identified). Spectral fingerprinting by TOF-SIMS has allowed for the identification of all reagent species investigated. Reagent signal intensity discrimination on test stream mineral surfaces was observed by the TOF-SIMS analysis using reagents at plant concentration levels. TOF-SIMS analysis confirmed that REE bearing grains reporting to the concentrate are doing so in response to collector attachment whereas grains reporting to the tail are doing so in response to a lack of collector and/or in combination with the presence of the depressant. The surface analysis of gangue phases reveal a similar reagent discrimination; the signal intensity of collector species was significantly higher on the concentrate samples relative to the tails while depressant species were significantly enriched on the surface of the gangue phases in the tail samples. A detailed evaluation of the surface species representing the various reagents used in flotation scheme revealed a distinct competitive relationship between two of the reagents. The surface analysis identified that when used in concurrently, there appears to be a negative feedback resulting in a significant reduction in loading for several of the collectors on grains reporting to the concentrate. An evaluation of the effect of reagents on REE mineral in pilot plant is currently under way. Key words: Rare earth minerals, Flotation, Surface chemistry, TOF-SIMS, SEM-EDX

Feb 27, 2013

By L. Lehasa

The purpose of the project was to investigate the challenges faced by Khutala Colliery pertaining to underground road construction and maintenance. Furthermore the influence of these challenges on productivity and safety requirements were taken into consideration. The operating standards required for the construction and maintenance of the 2 seam road transport infrastructure was investigated, together with reasons why the standards of operating procedure are not met. The Code of Practice put in place by Khutala Colliery was used to view the standard operating procedures. Leading practices on underground road construction were researched. The project aims to discover the gaps that Khutala Colliery must bridge to implement enhanced practices with regards to underground road construction. During the period of study, observations were carried out to determine whether the road construction standards of operating procedure were being adhered to at all times for both road construction and road maintenance. Khutala Colliery has put in place a traffic management plan, which includes safety practices and work policies that must be adhered to while travelling on underground transport roads.

Jan 1, 2012