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By Bruno Lebon, Koulis Pericleous, Georgi Djambazov, Mayur Patel

"High speed compressible jets are used in a number of steel-making applications. In the case of the BOF, a compressible oxygen jet reacts with a carbon-rich iron bath to reduce carbon levels and produce steel. The intensity of the process is governed by the speed of the jet and by the size and shape of the depression created in the metal and slag by the force of the jet, i.e. by the corresponding free surface. This is a difficult CFD problem, since there are compressible and incompressible regions in the flow domain, which need to be handled differently in a finite-volume (FV) pressure-correction scheme. Also, standard turbulence models do not account for compressibility, or the large difference in density between the cold oxygen jet and the hot reacting surroundings. Corrections are introduced to the k-E model to remedy this deficiency and the results are validated against experimental data. The compressible/incompressible boundary is handled through a transition region, based on Mach number.IntroductionThe deformation of a free surface by a compressible high speed jet is of paramount engineering interest, particularly for understanding the physical processes within a Basic Oxygen Furnace (BOF). In a BOF, a supersonic oxygen jet impinges on a molten iron surface, thereby creating a cavity. Oxygen penetrates the bath and removes carbon, resulting in low carbon steel [1].The challenges in modelling such a process lie in coupling a solution domain with distinct compressible and incompressible regions and in dealing with large density differences between the modelled gas and liquid. The modelling of compressibility within the jet is crucial, since the correct velocity profile in the jet is required to determine the cavity depth with accuracy."

Jan 1, 2012

By L. M. Lowe, D. B. Chambers, D. G. Feasby

"Potentially economic deposits of rare earth elements (REE) often contain elevated levels of naturally occurring radioactive materials (NORM), primarily thorium and uranium and their associated radioactive decay products. The concentrations of NORM usually exceed typical background levels of natural radioactivity, sometimes by factors of ten or more, and can be of concern relative to occupational radiation protection and the management and disposal of REE mineral processing and metallurgical wastes. This paper provides a summary of the radiological issues normally encountered in the REE concentrate production industry. In addition to an introduction to background radiation and radioactivity, including the thorium and uranium radioactive decay series, radiation levels expected to be encountered in REE concentrate production are outlined. The occupational, environmental and regulatory aspects of REE production related to NORM, including radiation dose limits, radioactive waste disposal guidelines, and threshold VALUES (for the application of transport regulations, are presented.INTRODUCTIONConcurrent with the increasing demand for new sources of rare earth elements (REE) to meet modern industrial needs, there is also an increasing awareness of the radioactivity associated with the REE ores and resources. This is an especially important consideration in addressing questions from the public and local communities who are often concerned about “radiation” and “radioactivity”. Public concern is heightened by reference to legacy issues that arose during times of less regulatory oversight; as well, the benefits of modern technologies, practices and regulation are overlooked. Such concerns are also often inflamed by unfounded claims by non-governmental organizations (NGO’s). Thus, it is important that all concerned have a full understanding of just what the potential risks from radiation associated with REE are, or are not. This paper provides an overview of the sources of radioactivity, the potential implications of radiation and radioactivity in the REE industry, and a brief discussion of established and reliable methods of managing exposure to radiation and radioactivity."

Jan 1, 2012

Early American history is filled with records of the search for and extraction of minerals-a Northwest passage to the treasures of the Indies-an overland route to the goldfields of California. Mining and its associated minerals industry have heralded advancing civilization throughout the ages. The two basic resources on which we all depend for our food, clothing, shelter, and other comforts are agriculture and minerals. Our endowment and how we use it; the spirit and industriousness of our people; our form of social organization all converge to make up our standard of living-our way of life.

Jan 1, 2012

By R. Butar-Butar, J. Mosher, G. Banini, J. Hollow, A. Villanueva

The effect of High Pressure Grinding Rolls (HPGR), as a preceding stage to a conventional ball mill circuit at PT Freeport Indonesia’s C1/C2 concentrators, has been studied in terms of downstream grinding efficiency and circuit performance. When milling the product from the HPGR, mill capacity increased by 21% for the same product grind size, when compared to processing similar ore from a conventional crushing circuit. This achievement is a result of several reasons, among them: reduction in feed size (F80), fines generation beyond the proportional reduction in F80, reduction in ore hardness induced by HPGR comminution mechanism, optimization of the recycle system of the HPGR and ball string optimization in the ball mill circuit given the new feed to the mill.

Jan 1, 2012

By Q. G. Reynolds

The dual-electrode DC arc furnace, an alternative design using an anode and cathode electrode instead of a hearth anode, was studied at small scale using computational modelling methods. Particular attention was paid to the effect of two key design variables, the arc length and the electrode separation, on the furnace behaviour. It was found that reducing the arc length to brush arc conditions was a valid means of overcoming several of the limitations of the dual-electrode design, namely high voltages and arc deflection.

Jan 1, 2012

By Andrew P. Schissler

The Citronen Zinc-Lead Project is one of the world?s largest undeveloped zinc-lead resources, containing more than 13 billion pounds of zinc and lead metal. The project is located in northern Greenland, a self-governed region of the Kingdom of Denmark (Figure 1). Citronen is the northern-most mine in the world, operating at a latitude of 83o 3? N. In excess of 67,000 meters of diamond drilling have been completed to delineate the resource. As of January 2012, the measured, indicated, and inferred reserves for the Citronen project totaled 70.8 million tonnes, consisting of 5.7% zinc + lead (3.5% zinc cut-off) (Ironbark, 2012). For the underground mine plan, room-and-pillar and long holestoping mining methods were selected. The beneficial application of structural fill was considered for increased recovery, efficient tailings disposal, and ground control. Three types of fill were compared - paste fill, cemented rock fill, and iced tailings. An environmental and economic feasibility study concluded that iced tailings was the preferred alternative provided it met the ground control requirements. The purpose of this paper is to explain the investigatory steps that led to the possibility for the use of iced tailings as structural fi

Jan 1, 2012

By Charlie Graham, Helen Shang, Ashley Scott, Andrew Hall

"Approaches to Energy Recovery• Upgrading for electricity generation - steam turbines• Direct extraction- process improvement or space heating- support medium for animal or plant growth– fish or microalgae• Heat pumps- space heating/coolingWater Energy Grades• High (150+ °C) - electricity Generation• Medium (26 to 121 °C) - direct extraction• Low (5 to 18 °Celsius)- use of heat pump is required• Temperatures between zones will depend on circumstances for best use."

Jan 1, 2012

By M. Vijayalakshmi, S. Saroja, C. Sudha, T. N. Prasanthi

"Ti-5Ta-2Nb alloy and 304L austenitic stainless steel were joined by explosive cladding process. Investigations on 'as received' explosive clad revealed high hardness very near the interface due to martensitic transformation of 304L steel base plate. To improve ductility, explosive clads were heat treated in the temperature range of 823 to 1073 K for 1 to 20 h. Consequent change in the microstructure and microchemistry of the clad interface was studied. No change in the interface microstructure was observed for heat treatment at 823 K. Increase in temperature lead to the formation of various reaction zones at the interface, their number and width increase with temperature and time of thermal exposure. Growth kinetics of the reaction zones was monitored and activation energy required for formation was calculated. From elemental redistribution profiles, effective inter-diffusivities of alloying elements were calculated as a function of concentration and activation energy required for inter-diffusion was evaluated.IntroductionFor engineering components exposed to highly oxidizing and corrosive environments, a titanium based alloy i.e Ti-5Ta-2Nb (Ti-Ta-Nb) is often chosen as a structural material [1,2]. For economic consideration, vessels and piping exposed to non-oxidizing conditions are fabricated from 304L austenitic stainless steel (304L SS). Hence, dissimilar joint of Ti-5Ta-2Nb alloy and austenitic stainless steel becomes unavoidable. Fusion welding processes are not suitable for joining Ti and Fe based alloys due to the propensity for the formation of intermetallic phases and subsequent reduction in the bond strength [3,4]. Hence, explosive cladding, a solid state welding technique, was used to achieve high integrity, corrosion resistant joints between the two alloys."

Jan 1, 2012

By E. Wolmarans

The selection of the main mineralised zone (MMZ) concentrator milling circuit has followed a comprehensive route over the preceding 10 years. Many knowledgeable parties have contributed and assisted in developing the milling circuit according to the best available information. The final selection of the flow sheet was completed after DRA conducted a techno-economic study on four possible comminution circuits ranging from conventional crushing and ball milling to fully autogenous (AG) milling. The results from all the above mentioned work indicated that it is possible to treat the MMZ ore at the desired throughputs to the desired grind sizes in a fully autogenous grinding circuit. The flow sheet was designed to treat the main mineralised zone (MMZ) arising?s from both underground and open cast operations and incorporates a fully autogenous grinding (AG) circuit. Commissioning of the 375ktpm concentrator at Nkomati Nickel began in August 2009 with the first ore reporting to the mill on the 15th of September 2009.

Jan 1, 2012

By P. J. Petit

Changing mining conditions, legislative issues, rising costs, and the constrained supply of skills and electricity in South Africa, have been some of the criteria forcing mine operators and engineers to review the traditional use of compressed air to power underground hand-held drilling operations in narrow-stope, hard-rock mines. In answering the question, 'What is the best way to power this mine?', they have resorted to trade-off studies with results of limited usefulness, because they are site-specific, and use only a few comparative parameters, based on a small data set. This paper aims to provide definitive, objective and quantitative decision-making approaches to evaluate alternative energy delivery systems for stoping in narrow-reef hard rock mines, based on primary and relevant criteria. These include quantifiable criteria such as capital expenditure, operating costs, resulting financial returns, energy and water usage, production performance, life-of-mine, etc. Other important criteria with qualitative aspects are integrated. These are safety, health and environmental concerns, legislative requirements, business risk, technology change, etc. The paper begins with a review of decision making processes available, and proposes the use of the analytical hierarchy process (AHP) method as a multiple-criteria decision making tool and the decision tree-based on milestone-driven uncertainties, to validate the selection of the energy delivery system. The results of a multiple-criteria questionnaire completed by a variety of industry experts and professionals, such as production and operation managers, consultants, suppliers and techno-financial analysts, are discussed. The evaluation indicates the potential for hydropower to be the best solution for narrow reef hard rock mines, based on current information, mine design layout and production.

Jan 1, 2012

By P. Gauvillé

The key driver for choosing a circulating fluidized bed (CFB) boiler is the ability to burn a wide range of fuels with highly efficient combustion while meeting low emission requirements. Reduced sorbent and water consumption compared with pulverized coal (PC) plants and the ability to deal with corrosive fuel constituents while still meeting local regulations make a CFB boiler-based power plant particularly attractive. CFB-based power generation is particularly relevant in coal mining areas. During mining, a portion of the roof and floor material may be extracted along with the coal seam in order to create adequate working height for the equipment and miners. Therefore, run-of-mine coal which comes directly from the mine contains impurities. The raw coal can undergo a washing or screening process in order to improve its quality by reducing the ash content in the fuel in order to sell it on the export market or to comply with domestic customer requirements. The coal discarded from the washing process usually has a high ash content and difficult mechanical properties resulting from the initial properties, the mining, and the coal cleaning processes. It can contain a large volume of stones or can be very fine as a result of the washing treatment. To create value from burning this discarded coal, the boiler supplier has to meet several technical challenges in developing the appropriate design. This paper highlights the performance achieved with Alstom's CFB boilers developed for power generation over the last two decades to extract value from discarded coals. Emile Huchet Power Plant is the first 125 MWe CFB unit developed for burning coal slurries (called schlamms in France). The Emile Huchet discarded coal fuel is a very fine high-ash residue with an average particle diameter by mass (d50) of around 80 µm as received from the washing plant. The paper describes the performances and the basic design of the CFB boiler to manage such a fine fuel. The performances of two other CFBs of approximately 300 MWe output in operation in the USA and PR China are also mentioned to demonstrate the capability of this technology to burn either low-volatile bituminous or anthracite waste coals. The significant issues experienced during commissioning are reported, and the conceptual choices for burning such fuels are mentioned.

Jan 1, 2012

By H. Dundar

An extensive testwork was performed around the HPGR plant at GoldFields Ghana Limited Tarkwa Gold Mine. The HPGR was used to prepare the feed for heap leaching. The circuit was configured in such a way that the edge material from the HPGR discharge was recycled for further crushing while the product from the centre reported to the heap leach section. The set-up of the Polysius HPGR provided an opportunity to study the effect of different design and operating variables. This paper will discuss the results from the tests performed to assess the effect of rolls? speed and applied pressure on the capacity and the grinding efficiency of the HPGR. Applying different pressure values appeared to have an influence on the amount of edge material recycled.

Jan 1, 2012

By M. Le Roux

Fine coal (-500 µm) is notoriously difficult to dewater. It is not uncommon for a dewatered product to have a moisture content as high as 30 per cent after vacuum filtration. This poses several handling and financial problems to such an extent that a lot of fine coal is discarded onto slurry waste ponds. A novel way of dewatering fine coal was developed at North-West University. It entails deliberately damaging the filter cake during dewatering to allow for an increased flow of air through the cake at the expense of the applied pressure differential. This method resulted in an average improvement in final cake moisture of between 3 per cent and 5 percent when executed in the laboratory under controlled conditions. A device was designed that could be fitted onto existing belt filters that would damage the filter cake as it passes by. This device was tested on a vacuum belt filter installation at a coal beneficiation operation in the Waterberg coal field in South Africa. The results showed a 3 per cent reduction in final moisture of the cake, proving the validity of the method at full industrial scale.

Jan 1, 2012

By Jr. Brown, A. Calderara, A. L. Antozzi

"The result of extensive research into fundamental mixed metal oxide catalyst morphology has produced a next generation all titanium Dimensionally Stable Anode (DSA ®). This new DSA ® anode, patent pending, is tailored for electrowinning of non-ferrous metals (copper, nickel, cobalt, zinc) by means of this new coating technology.These DSA ® anodes are characterized by a hanger bar with vertical distributor bars, having primary titanium mesh attached by weldments. The active mesh is provided with noble-metal electrocatalytic coatings, consisting of iridium and/or ruthenium oxides, obtained by thermal decomposition of precursor solutions applied to the titanium substrates. The catalytic activity of state-of-the-art DSA ® anodes is increased by controlling the crystallite size of the noble-metals without decreasing the decomposition temperature. It is known that below a certain value (typically 400°C) the stability of these oxides, and associated lifetime, is seriously compromised. A highly active DSA ® anode, consisting of a quasi-amorphous phase, is obtained at high temperature (above 450°C), therefore not compromising lifetime performance. Through optimization of these design parameters, the manufacture of these novel anodes was identified.DSA ® anode performance advantages include: lead-free ' green' all titanium anodes, true leadfree cathode quality, energy savings of 0.3 to 0.55 V can be realized depending on the EW application when compared to industry standard lead-alloy anodes, eliminate need for cobalt sulphate addition required for lead anodes, sustainability designed into long-life recoatable anode structures, increase plant cathode output through increased current density operations, improve plant on-stream production, no sludge generated or removed, and improve current distribution producing smooth high efficiency cathode.Introduction of ProductThere are many factors to consider when engineering a high performance DSA ® electrowinning anode. Half of the anode's performance is derived from the physical attributes of the electrocatalyst and methods employed when applying this catalyst to the titanium anode structure. The other half of the performance benefits relate to the proper structural design of the anode. In this paper, we will highlight the anode development program in which De Nora has invested to provide the Electrowinning marketplace with a high performance anode product."

Jan 1, 2012

By Yi Zheng

Under normal circumstances, methane released along a longwall face represents only 10%-20% of the total me- thane emitted from the entire longwall panel. However, there might be a sudden surge of methane at the face which may cause a potential problem because the friction from shearer cutting, support movement, and scraper conveyor dragging can be ready ignition sources. Therefore, to predict the distribution of methane will be critical to prevent possible explosions. In this paper, methane dispersion patterns along a lognwall face are simulated under normal and abnormal conditions. With the simulation of methane released from the face, around shearer drum, and from the broken coal on the conveyor, places with possible high methane content can be identified by different phases of working process and shearer positions. Local ventilation measures are evaluated so precautionary measures can be planned ahead.

Jan 1, 2012

By Ragnhild E. Aune, Mark William Kennedy, Shahid Akhtar, Jon Arne Bakken

"To determine the heating rate of billets using ‘short coils’, an appropriate correction factor must be applied to the theoretical relationship. In 1945, Vaughan and Williamson published a semi-empirically modified Nagaoka coefficient applicable for moderate frequency induction heating processes (10 kHz). Recently it was demonstrated that the method of Vaughan and Williamson gives <10% error in the estimated power when heating aluminum billets at 50 Hz.In the present study, experiments have been conducted on aluminum billets in order to verify an empirical frequency corrected ‘short coil’ equation. Measurements of electrical conductivity (<± 0.5%), current (± 1%), heat (± 1-3%), and magnetic flux density (± 1-2%) have been performed. The results are compared with 1D analytical calculations, and 2D axial symmetric FEM modeling using COMSOL 4.2®. The frequency corrected equation has proven to provide accurate predictions of power (<4% error) within the frequency range 50 Hz to 500 kHz.IntroductionInduction heating is commonly applied to the re-heating of billets before forging or extrusion processes. The resistive heating produced by eddy currents in the solid or semi-solid work piece during this procedure, is driven by the time varying magnetic flux density in the air-gap between the work piece and the coil. The flux in the air-gap is created by the current flowing in the induction coil, i.e. the magneto-motive force. In Figure 1 it can be seen that the currents present in the work piece are concentrated in the outer ‘shell’, or the first electromagnetic penetration depth (dw), and flow in a direction which opposes the magnetic field produced by the induction coil."

Jan 1, 2012

By H. Singh, Anupam Agrawal, H. S. Grewal

"Erosion in industrial appliances causes huge loss of valuable resources especially when solid particles are present in the working medium. A number of erosion models that are available in the literature claimed to predict the erosion response. In this work, five erosion models have been evaluated using computational fluid dynamics (CFD) methodology. Three most commonly used experimental test rigs (solid particle and unsubmerged slurry jet type and pot type) have been simulated and comparisons with the experimental results have been performed. The study helps in understanding the effect of fluid medium and flow pattern on the erosion process. The knowledge acquired shows that phenomenological based erosion models give better results considering the wide range of operating parameters. The in-depth study of the flow field shows the possibility that erosion mechanism, being parameter dependent, could change with location on the same specimen.1.0 IntroductionErosion is a surface degradation phenomenon which causes the removal of material due to impacts either of solid particles and/or bubbles or gas entrained in a fluid medium. Erosion has various categories depending upon the erosion medium such as, solid particles erosion (solid particles entrained in gaseous medium), slurry erosion (solid particles entrained in liquid medium) or cavitation erosion (erosion caused by exploding gas or vapor bubbles). Humphrey [1] has listed 21 different factors that decide the erosion response of the components under a given working condition. The number of factors involved in the erosion process gives us an idea about its complex nature."

Jan 1, 2012

By Tex M. Kubacki

In 2007, the University of Utah Seismograph Stations (UUSS) temporarily expanded its seismic monitoring network in Emery County, Utah, in response to the August 6 Crandall Canyon mine collapse that trapped six workers. In spite of this additional coverage, no seismic events were located in the area during a six-day period (gap) from August 8 to August 13. The Mine Safety and Health Administration (MSHA) ?Command Center Log Books? however, contain references to 16 instances of underground ?bumping? and ?bouncing? that occurred during the gap. When ground truth information provided by the log books is compared to the raw seismic data recorded by the UUSS network, the correlation offers insight into the chronology of mininginduced seismicity (MIS) in the aftermath of the collapse. The new research focuses on identifying and locating seismic events that occurred during the six-day gap using double-difference relocation techniques and correlating them with log book ground truth. Ten seismic events were identified in the vicinity of the mine during the six-day gap, ranging in magnitude from coda magnitude (MC) 0.5 to 1.4. Three of these events were amenable to location by double-difference techniques. The location of one of these events is directly confirmed by ground truth information from the log books. As a result of this new research, the accuracy of Crandall Canyon double-difference locations has been improved, and the number of events correlated with ground truth information has increased. The seismic events occurring in and around the collapsed area appear in two distinct sections of the mine?east and west of the center of collapse. It was originally reported that the post-collapse events occurred in episodic clusters. The first two episodes occurred to the east, followed in time by a cluster on the west, and then by a third episode on the east. With the addition of new events to the data set, this pattern is no longer as clear, although the events still occur in clusters. Only one MIS cluster was found to occur within the bounds of the minimum estimated collapse area (Pechmann et al., 2008).

Jan 1, 2012

By M. Maleki-Moghaddam

At the concentration plant of the Gol-E-Gohar Iron Ore Company (Iran) three 9 m × 2.05 m AG mills (fixed speed) are used in parallel in a dry operation. The performance of AG mills has been lower than the target value indicated by an increase in the product size (P80) from 450 µm (target) to 515 µm and low power draw (50% of nominal). By simulation it was found that increasing the liner lifter face angle from 7 to 30o while keeping the original lifter height (i.e., 22.5 cm) could provide an appropriate charge trajectory. When the proposed liners installed in one of the AG mills, the throughput increased by 27%; when 5% (v/v) balls were added the throughput increased by 40%. The product size also decreased from 515 to 501 µm.

Jan 1, 2012

By Christopher Mark

Severe dynamic multiple seam interactions can occur when active mine workings are subsided by underlying mining activity. The most dramatic events are usually caused by longwall mining or pillar recovery beneath open, overlying entries. But pillars in abandoned workings can also fail and cause subsidence and damage an overlying mine. This paper describes a case history in which an apparent ?pillar squeeze? in the abandoned workings of a lower seam was initiated during retreat mining in an upper seam. The event subsequently extended more than 1,500 ft and ultimately closed the upper seam mine. Analysis indicated that the pillars in the lower mine were adequately sized for the lower seam mining and were not affected by the initial development above them. When retreat mining in the upper seam had progressed several hundred feet, however, the pillars located directly beneath the pillar line were overloaded, and an extensive squeeze initiated in the underlying workings. The squeeze, in turn, subsided the overlying workings, causing widespread rib falls and roof instability. Previous examples of dynamic multiple seam interactions resulting from delayed subsidence of underlying workings have been reported in the literature. This is, apparently, the first recorded incident in which pillar recovery in an active mine triggered pillar failure in an underlying mine, which then triggered a dynamic interaction that impacted the active overlying seam.

Jan 1, 2012