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By V. Concha, M. Hashemzadeh

"The objective of this study was to gain a better insight into the kinetics of chalcocite leaching in an acidic ferric sulfate media. Chalcocite leaching in acidic media is known to occur in two sequential stages, with the first stage being much faster than the second. The leaching residue from the first stage is typically assumed to be a covellite type of material. This study hypothesized that the mineralogy after the first-stage leaching varies in response to different leaching conditions. We investigated the dependency of the mineralogy of the first-stage leaching residue on temperature and initial ferric concentration. The experimental results showed that chalcocite leaching behavior altered upon temperature and initial ferric concentration. A proposed combined reaction model was found to be able to describe the experimental data. The first stage was described very well by the shrinking core diffusion model while the second stage was described very well by the shrinking core chemical reaction model. This finding has important implications for mine operations to manipulate leaching conditions to create the desirable leaching kinetics.INTRODUCTION The kinetics of chalcocite leaching in sulfate media has been extensively studied (Cheng & Lawson, 1991; Fisher, 1994; Fisher, Flores, & Henderson, 1992; Niu, Ruan, Tan, Jia, & Sun, 2015). Sullivan (John D. Sullivan, 1930) proposed a two-stage process for chalcocite leaching in an acidified ferric sulphate solution. The two-stage leaching of chalcocite is presented as the following reactions:"

Jan 1, 2017

By F. Rashchi, A. Ghahreman, J. Moghaddam, S. Karimi

"In this work, the kinetics of ferric-ferrous redox reaction on a passivated sphalerite electrode is studied by the application of chronoamperometry method in 0.5 mol L-1 H2SO4 solution. The electrochemical behaviour of ferric and ferrous couple was investigated on two sphalerite minerals acquired from two different geological regions (Iran and Canada). The carbon paste electrode (CPE) of sphalerite was initially prepared and passivated in 0.5 mol L-1 H2SO4 solution and after reaching the steady-state condition, ferric and ferrous sulfate solution was added. The registered current density differences between the current density of the passivated electrode and that of the electrode in the iron salts added solution were interpreted for kinetics of ferric-ferrous reduction-oxidation reaction. The equilibrium potential for ferric-ferrous couple on sphalerites surface was about 500 mV vs. Ag/AgCl. The exchange current density (i0) for ferric-ferrous redox reactions on the sphalerite samples had the same magnitude of 10–6 A cm–2. The electrochemical impedance spectroscopy (EIS) measurements at 550 mV vs. Ag/AgCl illustrated that sphalerite oxidation was controlled by two charge transfer process in both of Fe-free and Fe-containing solutions. The charge transfer resistance remarkably decreased when Fe salts added to the 0.5 mol L-1 H2SO4 solution, owing to the ferric-ferrous redox reactions being the predominant reactions on sphalerite surface.INTRODUCTION Direct atmospheric leaching processes for sphalerite concentrates are performed by reduction of an oxidant (e.g. ferric ion and oxygen) and oxidation of sphalerite to zinc ions. Oxygen could be an oxidizing agent as well, but the concentration of oxygen is very low in the solution. The role of ferric ions is predominate in this oxidation (Babu, Sahu, & Pandey, 2002). The oxidation reaction for sphalerite in the presence of ferric in can be presented as follows (Lampinen, Laari, & Turunen, 2015):"

Jan 1, 2017

By R. K. Mishra, A. Kula, X. Jia, M. Niewczas

The mechanical properties of Mg-Gd and Mg-Y solid solutions have been studied under uniaxial tension and compression between 4K and 298K. The results reveal that Mg-Gd alloys exhibit higher strength and ductility under tension and compression attributed to the more effective solid solution strengthening effect and grain boundary strengthening. Profuse twinning has been observed under compression, resulting in a material texture with strong dominance of basal component parallel to compression axis. Under tension, twining is less active and the texture evolution is affected mostly by slip. The alloys exhibit pronounced yield stress asymmetry and significantly different work-hardening behaviour under tension and compression. Increasing of Gd and/or Y concentration leads to the reduction of the tension-compression asymmetry due to the weakening of the recrystallization texture and more balanced twinning and slip activity during plastic deformation. The results suggest that under compression of Mg-Y alloys slip is more active than twinning in comparison to Mg-Gd alloys.

Jan 1, 2015

By W. Dziurzynski, St. Wasilewski, T. Palka, A. Krach

"Air parameter monitoring systems, regardless of gasometrical protections, provide a significant number of measurement data. The obtained data broadens the knowledge on processes taking place in underground workings and shows the relationships and influence of machines and technological processes on the variability of ventilation parameters in the areas of longwalls. Nowadays, computer simulation methods are increasingly used to reproduce the flow of air and methane mixture in the area of longwalls equipped with shearers. The paper presents the results of a research experiment covering a long-term observation of a longwall area during mining with a shearer using sensors from the mine's monitoring system. Data from sensors for methane concentration, pressure and velocity were used and additional ventilation measurements were taken to determine the parameters characterising the air flow in the area. The influence of different machine cycles in the longwall on the changes of air parameters in the area of the longwall was shown. A numerical model of the ventilation area was developed and the computer program VentZroby was used for the calculations, which allows for the simulation of the process of ventilating the area of the active longwall during the extraction of coal with the use of a shearer and haulage of the run-of-mine. Computer simulation of the influence of the shearer's operation and the methane inflow associated with the distribution of the mixture of air and methane was carried out. The results of the simulation were compared with the data recorded by the monitoring system’s sensors during the measurement experiment. Comparison of the recorded methane concentration courses with the results of a computer simulation of the air and methane flow conditions in the mining area showed changes in the gassiness. INTRODUCTION Studies carried out in the Polish and global mining industry show that methane is an obvious factor in limiting mining production due to the loss of continuity in the operation of longwall complexes in hard coal mines under methane emission hazard (Schatzel et al., 2008). In addition, methane hazards have a significant impact on the safety of the operators of machinery in the longwall. The requirements of Polish regulations and the practice of safe operation of mining longwalls require correct determination of gas concentration, volume flow, as well as pressure and temperature of the flowing air. As part of the research undertaken in the Budryk (Wasilewski, 2010) and Bielszowice (Dziurzynski et al., 2009) mines to assess the methane hazard in the longwalls and workings in the vicinity of the longwall, research experiments were carried out, during which air parameters were recorded by the mine monitoring system and additional testing equipment in different cycles of shearer operation."

Jan 1, 2019

By S. Gregory

Many gold treatment plants have sulphides and coarse particle gangue components that contain gold in their tailings (cyanide leach residues and flotation tailings). Coarse and very fine liberated gold may also be present in some tailings streams. Two issues usually govern the economics of recovering additional gold from gold occluded in sulphide and gangue particles. The liberation characteristics of the gold in the sulphide and coarse gangue (gold liberation versus grind size) is the first and most important of the two. If fine grinding can liberate a reasonable amount of the gold, then the next important issue is how effectively these two constituents can be concentrated. Flotation will achieve high sulphide recovery but is usually costly. Selectivity is also an issue because of entrainment. Continuous centrifugal gravity concentration offers a viable solution to the recovery of both sulphides and coarse gangue however selectivity is also likely to be a problem. The possibility of improving concentrate grade by using a Falcon B separator was investigated. This paper describes a program of test work carried out on a gold leach tailings using a laboratory Falcon '13' separator. The program involved three different bowl angles: 10, 12 and 14 degrees and two bowl speeds (giving 250 and 350G accelerations). A number of tests were also performed on samples that had free gold present to ascertain the size-by-size recovery of gold in these samples.

Jan 1, 2005

By L. B. Smith

Introduction The property of Wright-Hargreaves Mines, Limited is situated at the northeastern end of Kirkland lake, Ontario. It lies immediately east of the Lake Shore mine, and about in the centre of the Kirkland Lake camp. The district is served by the Swastika-Rouyn branch of the Temiskaming & Northern Ontario railway, the town of Kirkland Lake being four miles northeast of Swastika, which is 63 miles north of Cobalt and 392 miles north of Toronto. The mine is developed by three shafts and has more than twenty-eight miles of underground workings. There are two main producing veins, which lie in a porphyry boss 1,350 feet wide. Milling started in May, 1921, and to-date (January, 1933) the mine has produced gold to the value of $21,770,183. Present production is at the rate of 800 tons of ore per day. For a description of the geology, reference may be made to the report by E. W. Todd on the Kirkland Lake Gold Area (1). Structure and Ore Deposits The two major productive veins on the Wright-Hargreaves property are known as the North vein and the South vein. In the vicinity of the shafts these veins are approximately 550 feet apart. A third vein, known as the Inclined vein, has been worked from its junction with the South vein at the 2,000-foot level to its intersection with the North vein at the 800-foot level. This inclined vein has to date been found only in the area east of the eastern major north-south fault. The main North vein and South vein have a general vertical dip, although local rolls and post-ore faults throw certain sections out of line. From the surface to 3,900 feet, the North vein is displaced south less than 200 feet, and the South vein at the same horizon is almost perpendicularly beneath the surface showings.

Jan 1, 1934

By Angus D. Campbell

Introduction Gowganda forms part of the general Cobalt area. Its rocks and ores are very similar to those of the other parts of the area. While its total production of silver is only 4 per cent of that of the famous Cobalt silver camp, its 1928 shipments contained 42 1/2 per cent as much silver as those of Cobalt for that year. During twenty years of production, 15,000,000 ounces of silver have been shipped from Gowganda. Of this, over 8,000,000 ounces have been shipped in the past five years. The area has thus made for several years a substantial contribution to the wealth of Ontario. Its future depends to a great extent on the priee of silver, which is now, unfortunately, at a record low price. This paper is a discussion of how the Gowganda ore-shoots occur, together with some notes on the milling of the ores at the Castle-Trethewey Mines. The first part is written in the hope of stimulating further study of the silver occurrences, which may lead to further discoveries. The second part, besides being a matter of record, may be of some use to operators of small mills. The drawings in the several Figures illustrating the text are by W. D. Stroud, mine superintendent of the Castle-Trethewey Mines, the benefit of whose opinions I have had in compiling these notes.

Jan 1, 1930

By Ainul Akhtar, Steve Cockcroft, Jixiang Xu, Daan Maijer, Lu Yao

"Nitrogen rich Ti-N inclusions are one of the more difficult inclusions to remove during liquid metal refining of titanium. If present in the final component, they can significantly decrease the mechanical performance of titanium and its alloys in applications involving cyclic loading. Understanding the kinetics of dissolution of Ti-N particles during consolidation/melting of titanium can help us better operate and design the melting processes to minimize their occurrence in Premium Quality Titanium production. A numerical model based on finite difference method has been developed to calculate the dissolution of a spherical Ti-N particles in molten titanium. Analytical solutions were used to verify the finite difference code for calculation of concentration profile and the dissolution of spherical solids. Taking into account the limitations in these approaches for the different cases examined, the invariant field approximation showed good agreement with the results from the numerical analysis. Evolution of the size of a spherical Ti-N particle during dissolution was predicted by the numerical model and the particle dissolves in 163 s.INTRODUCTION Properties like low density, high specific strength and excellent corrosion resistance make titanium attractive for a variety of applications. Key characteristics in the processing of titanium and its alloys include its high sensitivity to impurities, especially atmospheric oxygen and nitrogen and its high reactivity in the molten state. Nitrogen rich inclusions Ti-N, also known as Type ? or hard alpha defects, usually have substantially higher hardness and lower ductility than the surrounding material. Because they can act as fatigue initiation sites, Ti-N inclusions can significantly decrease the mechanical performance of titanium and its alloys in applications involving cyclic loading, even in minor amounts (tenth of a percent) (Lampman, 1990; Moiseyev, 2005; Lütjering & Williams, 2007). Ti-N encompasses as a broad range of nitrogen contents from a few wt% up to stoichiometric TiN. The liquidus temperature of Ti-N titanium increases substantially with increasing nitrogen content. Consequently, depending on the concentration of nitrogen, the melting point of Ti-N inclusions can be above bulk liquid metal temperatures during melt processing. Thus, removal of Ti-N defects hinges on dissolution and not melting."

Jan 1, 2017

By Gerardo Fuentes

Arsenic extraction from Chilean copper concentrates up to nearly 99% was achieved, using hydrothermal reactions. Arsenic appears in nature in more than 200 mineral species, being arsenopyrite (FeAsS), enargite (Cu3AsS4), and tennantite (Cu12As4S13) the most common species. In addition, arsenic is present in a large amount of copper concentrates, produced in northern Chile. Medical statistics show that in northern Chile, the amount of cancer to the lung, skin and bladder are the highest in the country. The latter situation, demonstrates the importance of studying metallurgical processes that do not generate atmospheric pollution. The hydrometallurgical processes such as hydrothermal treatment in autoclave reactors, do not produce gaseous emissions. On the other hand, the arsenic remains in solution from where it can be transformed in scorodite by widely known methods. Previous works about hydrothermal treatment of enargite have shown the feasibility of transforming the enargite of the copper concentrates into chalcocite or mineral species of the chalcocite family such as djurleite, digenite and for this reason enrich the concentrate in copper and pass the arsenic to solution. For this research, two Chilean copper concentrates were used, concentrate 1 with 5.5% arsenic and concentrate 3 with 1.8% arsenic. These concentrates were subjected to a complete chemical and mineralogical characterization. Later these concentrates were carry out to batch tests of hydrothermal treatment. Also, these concentrates were subjected to grinding to have different particle sizes. For the hydrothermal tests, a liter capacity Autoclave Engineer reactor was used. Characteristic of this reactor was the maximum temperature 350°C, 5000 PSI pressure, and 900 rpm agitation speed. Kinetic tests were carried out with the two concentrates maintaining the same solid: liquid relationship, the same agitation velocity and the variables studied were treatment temperature, time of reaction, concentration of copper in the solution and grain size of the concentrates. The conclusions of the study indicated arsenic extraction of the order of 93.98% from the concentrate 1 and arsenic extraction of the order of 98.74% from concentrate 3. After the hydrothermal treatment, the solids and solutions were characterized chemically, by electron microscopy and X ray diffraction. Also the solids were characterized by grainsize through a particle size analyzer (MICROTRAC). Results of batch treatment shows that arsenic can be release almost completely from real copper concentrates using this hydrothermal process and the next stage will be a scale up process in order obtain results for pilot plant design. INTRODUCTION Arsenic is an impurity that appears associated with copper minerals forming enargite, tennantite, tetrahedrite, and that due to the pyrometallurgical treatment either in conversion or roasting furnaces, it goes into the atmosphere together with the sulfur dioxide. A great quantity of literature can be found to eliminate arsenic or try to separate arsenic from copper. The methods used are mainly leaching processes with or without pressure (Padilla, Jerez & Ruiz, 2015) with different reagents like chloride media (Herreros, Fuentes, Quiroz & Viñals, 2003) or chloride media with sulphuric acid (Riveros & Dutrizac, 2008) or sodium hypochlorite (Mihajlovic, Strbac, Zivkovic, Kovacevic & Stehernik, 2007). It is known too that Chile is the first copper producer in the world and a great quantity of its minerals are in the north of the country, in Antofagasta.

Jan 1, 2019

By X. -G. Chen, E. M. Elgallad

Direct chill (DC) cast ingot plates of 2xxx alloys have been increasingly used for large mold applications in the plastics and automotive industries. A novel heat treatment practice for Al-3%Cu-1%Mg DC cast ingot plates has been developed, involving solution treatment, furnace cooling to the desired aging temperature and holding for appropriate time at the aging temperature. The mechanical properties of the plates were studied for different combinations of aging temperature and time, using hardness measurements and tensile testing. The evolution of the strengthening precipitates was investigated under different cooling rates corresponding to cold water quenching, still-air cooling and furnace cooling, using electrical conductivity measurements. The results showed that by applying the novel heat treatment, the cast ingot plates could provide a wide range of combinations of strength and ductility satisfying the design specifications of large molds. This, in turn, offers a practical solution for the fabrication of extremely large DC cast plates combining between good mechanical properties and low levels of residual stress using the shortest possible heat treating cycle.

Jan 1, 2015

By M. Turek

Cost management in the conditions of increasing competition and unforeseen market turbulence constitutes one of the key areas of the enterprise?s activity. In the last two years the demand for hard coal on the domestic and global market of non-renewable resources has increased significantly. Polish hard coal mining industry, as an industry in the stage of decline, received a chance for rejuvenation. However, one of the most significant conditions of seizing this opportunity is the rationalization of mining costs and improvement of production effectiveness. Due to the significance of this issue, the main objective of the paper is to identify the possibilities of improving the production effectiveness in the hard coal mining industry. In order to meet such an objective, in the first part of the paper we measured effectiveness in the Polish hard coal mines in years 2006- 2011. The research encompassed three out of five mining enterprises operating in the country. Then based on the received results, guidelines concerning the improvement of effectiveness of production were created, taking into consideration infrastructural, technical, economic and organizational determinants. Furthermore, opportunities and threats for improving the production effectiveness, stemming from the external conditions have also been indicated.

Aug 1, 2013

By O. Hungr, V. Gischig, G. Preisig

Deep-seated landslides are characterized by slow time-dependent movements induced by constant gravitational creep, and periods of acceleration associated with stress changes within the rock and the preexisting fracture network. Natural stress changes are typically caused by seasonal variations in surface temperatures and groundwater pressures, but also by rare and more violent events such as earthquakes. These processes are responsible for cyclic loading and unloading that leads to rock mass damage, fatigue and progressive failure with time, and may explain sudden, unexpected rock slope acceleration phases. In this work, we present a set of distinct-element models to investigate and compare the role of hydromechanical fatigue and seismic fatigue in the history of a deep-seated landslide. Hydromechanical fatigue arises from the fluctuation of pore pressure in fractures accompanying periods of significant groundwater recharge. In alpine areas, there are usually one or two cycles per year associated with snow melt and intense rainfall periods. In the presence of a deep confined aquifer within the rock slope, the amplitude of pressure fluctuations may reach values of 0.25-0.5 MPa. Hydromechanical models considering such pressure changes are able to reproduce observed slope accelerations-decelerations phases. Substantial accelerations may occur even in the absence of a cycle of exceptional amplitude, depending on the current state of fatigue. At a given time, one or more fractures may be critically-stressed, and a small change in applied stress is enough to cause local failure and induce a crisis of enhanced slope acceleration. This is augmented if the rock slope contains planes of weakness associated with its tectonic history, glacial debuttressing, etc. The corresponding behaviour is analogous to laboratory experiments on rock and metal fatigue. Similar fatigue effects have also been proposed for repeated earthquake events in seismically active regions. Unlike hydromechanical stress changes that occur in a more localized portion of the rock slope, those induced by passing seismic waves involve the entire rock mass. Moreover, the frequency and amplitude of stress perturbations due to earthquakes are different than those induced by pore pressure variations, although both likely contribute in combination to the degradation and progressive failure of large deep-seated landslides when both are present. The results presented illustrate that: (1) assessment of slope stability near critical infrastructure (e.g., hydroelectric reservoirs) should not only consider static stability, but also failure mechanisms related to fatigue that evolve over time and may result in an apparently stable slope progressing towards a critical state due to relatively small but repetitive stress changes; and that (2) characterization of fatigue processes affecting a deep-seated landslide requires multiparametric continuous monitoring at different observation points.

Jan 1, 2015

By T. Billotte, G. Tirand, J. Zollinger, V. Robin, B. Rouat, D. Daloz

The grain structure prediction of metallic alloys during a welding process is often an issue. In addition to the welding parameters and the alloy nominal composition and properties, the base metal grain structure and chemical homogeneity also play an important role in the formation of the final microstructure. In this paper intensive characterisation of solidification structure in gas tungsten arc welding of Ni base alloy 600 are described. It is shown that in transverse section of the weld, while the grain structure shows some texture following constrained solidification growth, grain density in the weld is similar or greater than grain density in the heat affected zone. This suggests that simulation of the welding structure needs, in order to be predictive, to take into account : epitaxial growth, secondary nucleation events and 3D growth inside the weld pool.

Jan 1, 2015

By G. Azimi, C. A. Ang, F. Zhang

"Nickel recovery from laterite ores generates large amounts of solid and liquid wastes. This is primarily due to the low concentration of Ni (about 1.4 wt%) in the feed ore to the High-Pressure-Acid-Leaching (HPAL) process. It is known that the HPAL residue contains a high concentration of hematite, a commercially important source of iron in the steelmaking industry. However, the balance is natroalunite, containing sulfur, which is a detrimental element in the steelmaking process. Hence, to make the HPAL residue a suitable feed for steelmaking, natroalunite must be removed. The current work is focused on: 1) a thorough characterization of the HPAL residue obtained from Vale, and 2) a systematic investigation of an alkaline leach process to remove natroalunite. The characterization results indicated that there are about 83 and 12 wt% hematite and natroalunite in the HPAL residue, respectively. The leaching results indicate that sodium hydroxide is the best leaching agent, which results in 55 wt% reduction in the sulfur content. The results of this work enable the conversion of an otherwise waste product into a useful feedstock for steelmaking. Furthermore, this project could potentially have significant environmental benefits by reducing the amount of residue produced during the HPAL process.INTRODUCTION Conventionally, crude steel has been obtained by reducing iron ore containing oxides such as hematite (Fe2O3), magnetite (Fe3O4), and wüstite (FeO) in a blast furnace with coke. The product is then refined in a basic oxygen furnace to produce steel with useful properties (McGannon, 1969; Turkdogan, 1978). Steel has been sought for its desirable properties and its application is widespread throughout modern civilizations. Surpassing the growth rate of other materials, the annual demand of steel has increased at a compound growth rate of 5% over the last 20 years (Baddoo, 2008). The global demand for steel was reported to be 1501 Mt in 2016 and demand is expected to double by 2050 (Cullen, Allwood, & Bambach, 2012; World Steel Association, 2016). In recent years, to meet the rapid growth of demand, secondary resources for iron have been identified as strategic sources of iron (Das, Kumar, & Ramachandrarao, 2000; Li, Sun, Bai, & Li, 2010; Matschullat et al., 2000). The residue produced from high-pressure acid leaching (HPAL) of laterite ore has been identified as one of the important secondary sources of iron (McDonald & Whittington, 2008). Laterite ore represents 60% of the world’s nickel resources and accounts for approximately 40-50% of the world annual nickel production (U.S. Geological Survey, 2016). Therefore, the amount of iron residue produced by the process is substantial and its utilization will produce both economic and environmental benefits."

Jan 1, 2017

By L. Chunpongtong

ABSTRACT Oil sands production occurs on a massive scale, making orebody estimation a challenge. In rainy conditions, operators can have difficulty accessing ore at the mapped location. Without enough inventory as a buffer, the high-cost stockpile is depleted quickly, necessitating the removal of significant amounts of overburden and interburden to meet plant feed requirements. The inventory curve—a plot of ore inventory on a period-by-period basis—plays an important role in selecting an appropriate scheduling scenario. This paper presents a programmable method for creating an inventory definition by using a pit optimization tool.

Jan 1, 2014

By G. T. Lapidus, A. Garcés, O. J. Restrepo

"Colombian nickel laterites have historically been processed by pyrometallurgy. However, due to the depletion in ore grades, alternative processes are required. Hydrometallurgical processes, such as pressure acid leaching, have been proposed as alternatives to extract nickel from deposits with suitable characteristics. Such a leaching process requires high concentrations of acid to achieve acceptable extractions, and is not selective. In this study, an alternative aqueous alkaline glycine system has been employed to evaluate the leaching behaviour of a Colombian nickel laterite which contains 1.15% Ni, 0.12% Co and 41.1% Fe. Additionally, the effect of the addition of chloride ions, the use of a reducing agent and the application of a pre-treatment to improve the extraction of nickel were evaluated. Extractions of 4.63% Ni, 42.16% Co and 0.33% Fe were obtained using a 1M solution of glycine at pH 9. In addition, an increase in nickel extraction from 4.63% to 25.68% was achieved by applying a pre-treatment to the sample. The results show that even though nickel dissolution was much slower than in acid leaching, it was selective over other metals such as iron, proving the proposed method to have potential as a process for the extraction of nickel from Colombian laterites.INTRODUCTION Before 2010, most of the industrial operations used pyrometallurgical processes for the extraction of nickel, mainly in saprolitic regions of deposits, with greater contents of the metal. Nevertheless, due to the gradual depletion of such deposits, different hydrometallurgical processes have been studied as alternatives to process those nickel laterites with low grade and those which present problems of refractoriness due to the presence of acid consuming materials (McDonald & Whittington, 2008; Oxley & Barcza, 2013; Wang et al., 2012). However, such leaching processes require high concentrations of acid to achieve acceptable extractions and they are not selective. Facing lateritic nickel ore deposits containing high levels of acid consuming materials, an alkaline leaching medium becomes an advantageous alternative over acidic media, due to the increase in selectivity and decreased corrosiveness and reagent consumption (Tanda, Eksteen, & Oraby, 2017). Unlike conventional acidic reagents used for metal recovery, alkaline reagents can selectively dissolve the desired metal, leaving in the solid residue other elements such as iron, magnesium and aluminum, which are problematic in subsequent stages of metals separation and recovery. Furthermore, there are no serious corrosion problems associated with alkaline leaching, even at higher reagent concentrations, or at elevated temperature and pressure (Ntumba Malenga, Mulaba-Bafubiandi, & Nheta, 2015)."

Jan 1, 2017

By H. Nejati

Experimentally, the Semi-Circular Bending Moment (SCB) fracture toughness test results of Basalt Specimens Under Illumination (BSUI) have shown reduction in fracture toughness and failure force as a result of micro-cracking. The fractographic investigation of BSUI confirms initiation and extension of micro-cracks. Determination of a relation between strength reduction (herein fracture toughness reduction) and density, location and orientation of thermo-mechanical induced cracks due to microwave radiation is critically important. Numerical modeling can bridge strength reduction and the density of thermal microcracks generated due to microwave radiation. Discrete Element Modeling (DEM) is a power tool for simulation of micro-crack initiation, coalescence into macroscopic fractures and failure mechanisms in brittle rock specimens under different stress regimes (herein combination of pure tensile stress due to SCB testing, and thermal stress due to microwave radiation). For this purpose, a DEM modeling of SCB testing of basalt using EDEM (i.e., a DEM based software). DEM models are calibrated according to results of experimental SCB testing as reported in previous papers. This paper first reviews some background data on SCB fracture toughness, and experimental results of fracture toughness of microwave treated SCBs. Then it proposes a new methodology for simulation and validation of rock samples exposed to microwave illumination with regard to experimental results, and discusses the correlation between fracture toughness of BSUIs and density of micro-cracks, which is attributed to applied microwave power and duration of illumination.

Aug 1, 2013

By D. C. Crothers

"What is new in air compressors? A good deal - the designers have been keeping pace with technical developments in related fields and also contributing new techniques of their own. Plant reliability no longer requires bulky slow-speed machines. Even the reciprocating machines, which still provide the most efficient method of compressing air, have been greatly reduced in size and installation cost for a given capacity rating. New materials and fabrication techniques are being used, by most manufacturers, to produce less costly plants in total. Many packaged plants are available, which generally means a more complete assembly for shipment. This type of construction offers savings in handling and erection costs at the site. A warning is in order, however - the extent of packaging in any given plant should be investigated carefully to determine what is included and just what field costs can be realized. A suggested specification has been offered for consideration when studying comparative costs. Rotating machines intrigue many because of their potential as regard fewer wearing parts, higher speeds and hence smaller units, utilizing less expensive drivers, and lack of contamination of the compressed air by lubricants. The inherent shortcomings of these machines - lower •efficiency and capacity control - have been much improved lately, and this type of plant is now becoming quite popular. Noise control, of much concern to everyone, is another development that has received considerable attention.Systems for efficient capacity control and continuous monitoring of compressor operation offer additional reliability and low-cost operation of the modern compressed air plant. Accessory equipment and its effect on over-all plant operation is also considered."

Jan 1, 1972

By M. Amsden

"Since the computer program is far from complete this must be only a brief progress report on the computerization of flotation metallurgy at the Ecstall concentrator at Timmins.Ecstall is currently treating about 10,000 tons per day of two different ore types. One is a low sulphide copper-zinc ore, the other is a high sulphide lead-zinc-silver ore. The concentrator is divided into three individual grinding and flotation circuits. In effect there are three mills under one roof. Normally there are two circuits on copper-zinc ore and oneone lead-zinc-silver ore. At this point in time one of the copper-zinc circuits is under computerized metallurgy control.The first step in this control is the use of an ARL on-stream x-ray analyzer, coupled with a Honeywell 21 computer which types out assays and recoveries for each individual circuit. Our approach to a computer program was to keep it simple. The program was written to coincide as closely as possible to what an operator would do in the performance of his duties based on the in-formation he was getting from the x-ray analyser read-out. Initially, computer control was put on just the copper circuit of the ""A"" Division, controlling the collector addition at three points in the circuit; primary, secondary, and scavengers. The control was based on recoveries and the grade of the copper concentrate. Targets like 95% recovery and 24% copper concentrate grades that it was felt the circuit could achieve were set to start with. It quickly became apparent that this alone was not enough because if on a certain ore the best recovery that could be made was only 94.9% the computer kept calling for more reagents until the circuit was completely out of control. On another ore it might have been quite possible to get 96% recovery but when the set point of 95% was reached the computer stopped trying for any more. To overcome this problem a very simple optimum seeking program was devised by one of the Ecstall staff and it has worked very satisfactorily since being put into use in July 1970.In the copper float only the two collectors R-208 and the xanthate R-317 are under computer control. The addition of frother and depressant is left to the operator. The flotation cells have automatic level controls which can be adjusted by the operator. pH is controlled automatically through a lime loop-sensor arrangement."

Jan 1, 1971

By J. Sliwinski, H. Kikutani, J. Atwood, D. Larimer, J. Pyecha

"The Pogo mine start-up milling targets of 2005 are vastly different than the targets of today. Improvements have been driven by unintentional design oversight, continual circuit optimization or optimization due to changing mineralogy. The more significant process improvements to date have occurred in the gravity, flotation and leach/CIP unit operations. Details of the significant improvements are presented along with the impacts to the process.INTRODUCTION Deposit Overview Pogo mine is located along the Goodpaster River, southeast of Fairbanks, Alaska. This deposit sits in the center of the Tintina Gold Province (Figure 1), a region of similar Intrusion Related Gold deposits in Interior Alaska, the Yukon and British Columbia Canada (McCoy et al., 1997). The Pogo deposit is hosted in a rock sequence of amphibolite-grade gneisses intruded by mid-Cretaceous granitic plutons and dikes, which in turn, were cut by and host the auriferous quartz veins of the Pogo deposit.The Pogo deposit is comprised of three distinct zones of auriferous quartz veins spatially adjacent to each other. These are the Liese Zone, North Zone, and the East Deep Zone. The Liese Zone consists of three stacked, massive quartz veins, designated the L1, L2, and L3. Vein thickness averages 3.0 m, with variations from 0.3–18 m thick. The North Zone mineralization is comprised of four veins with more consistent thickness, between 1 and 1.5 m. The East Deep deposit lies northeast of the Liese Zone ore body. It is separated by a post mineralization, quartz diorite pluton. The East Deep Zone is comprised of two stacked massive quartz veins with similar orientation as the Liese Zone."

Jan 1, 2017