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By C. Carrasco

"Over the last 30 years the average grade of mined ore bodies has significantly decreased while the proportion of waste removal has in many cases more than doubled. This has been identified as prime reason of a major increase in energy consumption and decrease in productivity across mining operation. Metal coarse preconcentration of ROM feed grades by size rejects low grade gangue/waste material in the size range of 10-100 mm prior to grinding, typically before primary crushing. This relies on propensity of metal to preferentially deport in the fine size fractions after breakage. Metal preconcentration by size has the potential to increase energy efficiency and therefore improve mining productivity on unit of metal basis. Results of an extensive belt cut sampling campaign conducted at a major Australian Au-Cu mine operation show that for some samples between 90% of Au and 80% of Cu is in 40% of the mass at -50 mm fraction. This indicates that low grade coarse material can be removed from the circuit, doubling feed grade at half of the tonnage and therefore improve energy efficiency per unit metal produced. This response, however presents significant variability in the same order as other processing attributes such as impact hardness and flotation recovery. This has led to development of geometallurgical laboratory tests using blast hole chips and drill core facilitating mapping and population of coarse metal preconcentration signatures in long term resources and short term production models. Preferential Cu deportment by size at drilling scale can be recognised, however scales up factors are required to transform laboratory results to production responses. At 50 % of mass the drilling products underestimate the belt cut responses by 20-30 %. Bulk sampling campaign with blast hole and drill core samples spatially related was also conducted to investigate in more detail the difference between production scale and drilling scale preconcentration responses."

Jan 1, 2014

By J. T. Liu

Packing in a flotation column is one way to increase separation efficiency and effective descending flotation-column height. In this paper, the difference between filling packing and sieve packing is described, and the flaws of filling packing in flotation columns in industrial application are pointed out. A change of flotation process and its effect on flotation results are reported. Based on sieve-plate filling, a high-efficiency mixed packing mode consisting of screen-plate packing and honeycomb-tube packing has been proposed, with the packing mode optimized in the cyclonic static microbubble flotation column in the separation zone. In the mixed packing mode, the honeycomb tubes are used to reduce the vortex effect at the base of the column and weaken the radial dispersion of jetting bubbles, and the sieve plates are used to comminute bubbles in the separation zone, to lengthen the bubble migration path, and to stabilize the foam layer. The superiority of honeycomb-tube packing is analyzed using bubble-particle collision theory, and the dynamic equations of collision probability are derived. The role of mixed packing in guaranteeing mineral recovery is analyzed by the axial dispersion method, and a dimensionless axial dispersion model is derived. When a high-turbulence flow is maintained, a static separation environment is formed in which secondary mineral processing is rendered more effective. In this way, a nonlinear separation environment is formed in the flotation column. Finally, mixed packing was applied in an industrial test. A large vortex developed at the base of the column. It was observed that the bubbles in the radial flow were homogeneously dispersed, the residence time of the pulp was prolonged, and the froth layer became thick and stable. Based on the test data, it was found that the sieve packing has the potential to yield a product of approximately 25.83% copper concentration with 91.78% recovery from a feed concentration of approximately 0.727%. If mixed packing were used, the product concentration could be further increased to 27.60% from a feed of approximately 0.739% concentration with 93.38% recovery.

Jan 1, 2014

By Brad Wells, Wayne Bull, Wayne Dickinson

"Antiscalants were evaluated for control of calcium carbonate (CaCO3) in gold processing applications. Under severely supersaturated conditions, 100 percent inhibition was achieved with 30 ppm antiscalant. Laboratory and field testing established that an antiscalant could both inhibit scale buildup and remove an estimated 0.5 kg/m2 per annum of pre-existing scale. A program was developed to control CaCO3 at a gold mill experiencing severe scale buildup. Annual accumulation of as much as 3 cm of scale in process piping was reduced to unmeasureable levels when 10 ppm antiscalant was applied. No scale-related upsets in mill operation occurred during a five-month trial period.INTRODUCTION Inorganic mineral scale is a crystalline deposit that forms when dissolved mineral constituents exceed the solubility of the respective mineral phase. Formation of mineral scale adversely affects a wide range of industries and is of particular interest in mining and metals processing. Scale affects numerous stages of metal extraction processes. Restricted flow in piping, nozzles, valves, screens, pumps and other components used to transport mineral slurries, metal concentrates, and tailings as well as scale in millwater and thickener overflow circuits are primary concerns (Alfano & Boffardi, 1994). Heap leaching, comminuation, flotation, vat leaching, carbon adsorption, and heat exchangers as well as oxidation steps used in processing sulfidic ores are among key unit operations that may be adversely affected (Simmons & Gathje, 2003). Antiscalant chemicals are designed to prevent formation and growth of mineral scales such as CaCO3. These chemicals, which include two primary classes – phosphonates and anionic carboxylate polymers and copolymers - are added to the gold processing stream at low parts-per-million (ppm) concentrations to interfere with nucleation and growth of scale forming crystals and to disperse fine particulate material. Application points may be located throughout the gold extraction process. Evaluation of the performance of antiscalants plays a critical role in determining the best product for a specific application. Performance evaluations include laboratory testing, pilot scale studies, in-plant trials, and ongoing performance monitoring during mill operation."

Jan 1, 2014

By William D. Swank, Prabhat K. Tripathy, Tedd E. Lister, Eric S. Peterson, Delon C. Haggerd

More than half of the primary neodymium, produced directly from ores, is being used to manufacture neo magnets. Neodymium, being a critical element in supply, has attracted considerable interest worldwide to recover this metal from a variety of waste streams. From among different recycling processes, hydriding-dehydriding can prove to be highly effective in recycling discarded neo magnets present in consumer electronics. In the present study, manually removed magnets from discarded Hard Disk Drives (HDDs) were subjected to the hydriding-dehydriding process in order to evaluate the resultant products for the re-fabrication of the magnets. The paper describes the effect of experimental parameters on both the hydriding and dehydriding processes as applied to different magnet chemistries.

Jan 1, 2014

By Kevin Phelps, Jason Baird

When dealing with high velocity projectiles, the ability for researchers to accurately and precisely measure the velocity of the projectile is of great value. This report will analyze three different methods of recording high velocity projectiles for: their ability to record velocity data, pros and cons for each method, and any possible bias or limitations that would result. Method 1 uses a Phantom V10 high-speed video camera and a velocity reference screen to record the projectile’s path and proprietary Phantom software to analyze the data and determine velocity. Method 2 utilizes two break screens. This method, consisting of strung copper wire as the break material, is one that has been used in the past by Missouri University of Science and Technology (MS&T) researchers in assisting in finding velocities of high-speed projectiles. Method 3 is a pair of make screens, similar to Method 2 in that two screens were used for each test but relies on a projectile making a circuit between two sheets of metal separated by an insulation layer, to find a velocity. All three methods will be used simultaneously in each shot to rule out any projectile differences in subsequent shots. Projectiles of three different relative velocities, low, medium, and high, will be fired and analyzed to determine strengths and weaknesses of each method.

Jan 1, 2014

By J. K. Afidenyo

Microbial pretreatment of a double refractory gold ore was investigated using a white rot fungus, Coriolus versicolor (ATTC 20869) to improve gold extraction. A series of preliminary tests were conducted to determine the amenability of the ore to fungus degradation. Pulp density, temperature, pH and retention times were the process variables considered. Both a single. Stage and two-step processes were studied to establish process conditions. During the single stage process, the ore was contacted with the fungus culture (biotic) for 3weeks at 30°C and pH 10.0. For the two-step process, the first step involves ore contact with the culture medium (abiotic) at 45°C and pH 10.0 followed by fungal contact (biotic) at 30°C. Results indicated that carbonaceous matter is not degraded but passivated by the fungus; as preg-robbing activities dropped significantly from 18.1% to below 1.0%. The single stage process resulted in higher gold recovery than the two-step process Gold ex-traction by cyanidation of the pretreated ore was 78.9% for the single stage compared with 15.0% for the untreated ore. In the two-step process, only 73.3% gold extraction was achieved. Application of the two step process conditions to a high grade flotation concentrate, resulted in 93.3% gold ex-traction as against untreated concentrate of 30.5%. The results show that the microbial pretreatment process degraded sulfide sulfur, passivated carbonaceous matter and enhanced gold extraction from double refractory gold ore and concentrate.

Jan 1, 2014

By Metehan Erdogan, Ishak Karakaya, Fuat Erden

"Mg-Ni system draws attention due to the promising hydrogen storage properties of Mg2Ni. The proposed method involves the use of NiO and MgCl2 in an electrochemical cell to from Mg-Ni intermetallics directly. The electrodeoxidation of NiO was followed by combination of Mg and Ni in molten salt electrolytes. The products were characterized by XRD analysis and SEM examinations. The quantitative results from Rigaku supported by Rietveld Refinement method conducted by Maud showed that more than 50 percent of the input Ni was converted to Mg-Ni intermetallics.INTRODUCTIONIt is well known that fossil fuels are the most common energy producing materials throughout the last century although, they are not renewable and their usage cause critical environmental problems [1, 2]. Hydrogen, on the other hand, is known as a clean, renewable energy carrier and instead of fossil fuels; usage of hydrogen for energy production will be the benefit of mankind. However, there are problems that hinder more common usage of hydrogen such as hydrogen storage [3]. Mg2Ni is known as Mg based hydrogen storage material with high hydrogen storage capacity [3-6]. Common Mg2Ni production methods are; mechanical alloying [8-11], vacuum induction melting [12, 13], vacuum arc melting [14], combustion synthesis [15], melt spinning [16], repetitive rolling [17] and isothermal evaporation casting [18] were also used. However, in all of these, pure Mg and Ni are required to be produced previously. Therefore, difficulties arise during handling, preparation and combination of Mg and Ni due to highly reactive nature of especially magnesium (i.e. oxidation of Mg) [11, 17, 19, 20]. Although hydrogen desorption dynamics can be significantly improved with usage of nanostructured Mg2Ni [7], it is difficult and it requires very long processing durations to produce nanostructured Mg2Ni by above processes."

Jan 1, 2014

By Luís Marcelo Tavares, Marko Hilden, Malcolm Powell, Grant Ballantyne, Lian Liu

The t10 relationship developed by Narayanan and Whiten has underpinned a number of the JKMRC models and the characterisation of ore competence through impact testing with the drop weight tester. This usefulness is based on a consistent relationship between the t10 value and the overall size distribution that was noted for brittle rocks. However, like all characterisation tests this should be used only when the controlling conditions apply, which in this case is single impact breakage between two metal platens and within the range of sizes in which fragment sizes are normalizable. For any other mode of breakage the relationship should be confirmed before being applied. Soft ores or bimodal ores with widely different competence between dominant components have non-typical breakage signatures. Breakage via single point impact abrasion, compressed-bed breakage, low-energy surface breakage and incremental breakage, to name some of the other breakage modes, do not obey the general t10 relationship, so their outcomes cannot be used to provide a direct comparison. Inappropriate use of the t10 parameter can result in misleading conclusions about efficiency of energy use. These issues and alternative comparison techniques are presented and discussed in terms of choosing appropriate measures of efficiency of breakage, ore competence and energy required for comminution.

Jan 1, 2014

By Ofra Damm, v du Preez, D. van Vuuren, L. Simpson, H. Chikwanda

"South Africa is the world?s second largest producer of titanium bearing minerals, but apart from producing titanium mineral concentrate to form TiO2 slag, little further value is added in South Africa to mined minerals. Various studies were undertaken by both government and the private sector in an un-coordinated manner until 2007 when the South African Department of Science and Technology (DST) planned and adopted a national strategy to establish a local titanium metal industry through the research and development of key technologies that would provide a competitive advantage to such a local industry. The strategy entailed a two-pronged approach in the development of this capability, viz. simultaneous investments in the development of high-level human capital and technology in the fields of titanium metal powder production and downstream titanium metal powder processing technologies. To date significant progress has been made to establish research and/or pilot scale facilities in the following technical areas: TiCl4 production technology, titanium powder production technology, high energy milling of titanium powder, metal injection moulding facilities, rapid production of large components using laser additive manufacturing technology, investment casting of titanium, resource efficient machining of titanium and friction stir welding of titanium. Supporting technologies are also at an advanced stage through investments in titanium powder spheroidization and direct rolling of titanium powder. The intent with investment in some of these areas is not to develop new technology per se, but rather to establish local capability that will position South Africa to collaborate with other organisations in the world so that technologies can be acquired and transferred when needed in the future."

Jan 1, 2014

By Robert B. Bittner

"AbstractLarge diameter tubular piles offer significant advantages in terms of design performance and economy for major marine structures. This is particularly true for foundations of major overwater bridges in regions of high seismicity such as the west coast of North America. The use of large diameter piles in the range of 2 to 3 m diameter means that fewer piles are required, and the size and mass of the pile caps can be significantly reduced, thereby greatly reducing lateral load demand during seismic events. Another advantage of using larger diameter piles is increased pile stiffness that allows the pile caps to be located at or near the waterline rather than being positioned at or below the mud line. This elevating of the pile cap offers significant cost savings by eliminating the need for deep cofferdams. However, relocation of the pile cap creates new problems and opportunities in regard to the means and methods used to construct the pile cap. With the pile cap at depth, conventional steel sheet pile cofferdams with thick tremie seals are typically used to isolated the cap location and allow dewatering for construction of the cap. However with pile caps positioned up off the bottom, conventional bottom founded cofferdams are no longer cost efficient. Float-in or lift-in cofferdams have been developed to address the need for a more cost efficient method for cap construction. This paper describes the key features of the concept and provides three case history examples of its successful implementation.Pier Construction Using Conventional Sheet-Pile CofferdamsCofferdams are temporary structures used in the construction of bridge piers and other marine structures. Their primary purpose is to hold out water and unstable soil from the construction area, and thereby, allow in-the-dry construction of the permanent structure below the water line and quite often below the mud line. Typically, cofferdams consist of long interlocking steel sheet piles driven through water into the bottom of the waterway. The sheet piles form temporary exterior walls which are typically braced internally with wales and struts. The bottom of the cofferdam is typically sealed with tremie concrete or an impervious clay layer if one exists. The depth at which this type of cofferdam can be used is typically limited by the length of steel sheet pile that can be transported and handled by conventional marine equipment."

Jan 1, 2014

By Y. S. Sun, P. Gao

Compared with conventional roasting and magnetic separation processes, higher reduction temperatures and stronger reducing atmospheres are used in reduction technologies to reduce iron oxides to metallic iron, which is often liberated during reduction and amenable to magnetic separation. Reduction and magnetic separation of an Australian refractory iron ore was therefore studied as a function of reduction temperature, time, coal addition, feed thickness and size of Australia iron ore. It was found that during reduction, the particle size of the reduced iron increased with reduction temperature and time. Subsequent magnetic separation tests were further conducted on the reduction products. A reduced iron powder with a Fe grade of 85.67% was obtained at a Fe recovery of 87.82% under optimum reduction conditions where a metallization rate of 85.82% was achieved. The mechanism involved in reduction is discussed based on XRD and SEM examinations. And the results indicated that theiron minerals such as hematite and limonite in the Australian iron ore were reduced as follows: Fe2O3?Fe3O4?FeO?Fe. Furthermore, the metallic iron particles produced by reduction increased in size with longer reduction times.

Jan 1, 2014

By Z. Y. Ma, H. Y. Yang

The process of microwave-ultrasound assisted leaching of valuable metals from copper anode slime was proposed in this paper. Design of experiments has been used to study the effect of the main leaching parameters, such as microwave power, ultrasound power and reaction time. The central composite design (CCD) was used to predict the maximum leaching efficiency of copper, tellurium and selenium. The experimental data obtained were fitted to a second-order polynomial equation, and they also were analyzed by analysis of variance (ANOVA). The 3-D response surface plots and the contour plots were applied to determine the optimal conditions. The optimum conditions of microwave-ultrasound assisted leaching process were: microwave power 834W, ultrasonic power 638W and reaction time 403s. Under these conditions, the experimental leaching efficiency of copper, tellurium and selenium were 98.88±0.56% 98.96±0.78% and 98.57±0.67%, respectively, which agreed well with the predicted values.

Jan 1, 2014

By Carlos Lam, Joram M. Amir, Erez I. Amir

"Abstract The modulus of elasticity of pile material (E) is an important parameter for the interpretation of both static and dynamic loading tests on piles. This value is commonly assumed to be constant with depth though it may not be true for deep bored piles due to the chosen casting method and/or selfweight consolidation. To provide evidence to support this proposition, the results of compressive strength tests on core samples taken from four different studies have been presented. The results show a marked increase in the strength and stiffness values with depth. The results of crosshole ultrasonic tests conducted at another site also confirm the same pattern. It is therefore recommended that before load testing a pile the distribution of the E values along the pile axis should be investigated. This will ensure the use of a realistic elastic modulus value and hence the correct interpretation of thedistribution between the shaft and end resistances.IntroductionThe modulus of elasticity of pile material (E) is an important parameter for the interpretation of both static and dynamic load tests on piles. Multiplying E by the strain measured by either strain gauges (e.g. ASTM D4945) or tell-tales (e.g. Geffen and Amir, 1971) gives the stresses acting at a given pile section. Typically, in the absence of better information, the value of E is derived from laboratory tests on concrete cubes or cylinder specimens taken on site and is assumed to be constant along the pile. While this may be correct for pre-fabricated concrete piles that are cast in horizontal molds, it may not be true for cast-in-place piles that are produced in the vertical position.There are at least two factors that may contribute to the change in concrete properties with depth in a bored pile. First, the casting methods may be by free fall in dry holes (e.g. Kiefer and Baker, 1994) or by using a tremie tube if support fluids are used. In the former case, the earlier batches reach the bottom of the pile bore at a higher velocity and are thus compacted under higher energy. Second, regardless of the casting method, the fresh concrete in the pile bore will always consolidate at least partially under its own self weight. The materials in the lower parts of the pile will therefore experience a higher consolidating pressure. This can reduce the pore volume and the water content in the wet concrete, thus changing the properties of the hardened concrete. Recent research by Justs et al. (2011) has shown that even a relatively small pressure can have a significant positive effect on concrete properties such as compressive strength and stiffness. However, the possible change of concrete properties with depth is commonly ignored by foundation engineers in the current design practice."

Jan 1, 2014

By Cathy Aimone-Martin, Robert Brentar, Brent Meins, James Lauer

Vibration measurements of multi-story structures in an urban environment began 3 years ago in New York City during close-in blasting to adopt correct measurement procedures and recommend revised ground vibration limits that best characterize cracking potential in mid- to high-rise structures. Two broad categories of structures included non-engineered 4- to 6-story multi-family unreinforced brick masonry buildings, built from the late 1800s to around 1930, and post-WWII, high-rise structures of reinforced concrete and steel rising 12 to 40 stories. In-ground vibration limits similar to those recommended by the U.S. Bureau of Mines safe criteria, developed for 1- and 2-story residential structures, are imposed by the New York City Fire Code. However, these limits are often lowered by project engineers or New York Department of Buildings when blasting is planned near buildings designated Landmark or historic and classified as fragile or vibration-sensitive. Seismograph measurements to determine compliance with in-ground velocity limits currently employ geophones mounted to basement walls and on concrete slabs overlying rock. These measurements cannot be correlated with upper structure cracking potential and are often exceeded, resulting in excessive and costly downtime to allow post-blast damage investigations.

Jan 1, 2014

By J. E. Gebhardt, D. McBride, M. Cross

Heap leach processes can encounter diverse flow conditions, such as infiltration into dry ore material, drainage, perched water tables and heterogeneous materials, leading to large variations in permeability and the creation of preferential flow pathways. Climate and meteorological conditions, such as precipitation, evaporation, and temperature, can also have a significant effect on the hydrodynamics of the heap. Nonuniform and adverse flow behavior within the heap contributes to reducing the leaching efficiency of the heap leading to lower metal recoveries. The variability of flow within the heap can result in solute transport problems, which limit the leach reaction kinetics. Therefore, understanding the flow and transport phenomena within the heap is critical in its design and optimization. A comprehensive heap leach model, developed within a computational fluid dynamics (CFD) framework, employs robust algorithms to solve diverse variably saturated flow conditions. The model allows for a wide array of complex thermo-fluid physics to be represented and captures suites of very complex reactions that are closely coupled with thermal conditions and key microbial populations. Employing a three-dimensional heterogeneous ‘test’ heap, a number of flow conditions are investigated and the sensitivity of metal recovery is discussed.

Jan 1, 2014

By Sangseom Jeong, Moonkyung Chung, Junyoung Ko

"Abstract The plugging effect of open-ended piles in sandy soil is analyzed by full-scale field test and plugging measurement. PLR (plug length ratio) measurement data from 144 field cases are analyzed with pile diameter. Based on the plugging measurements, PLR of open-ended piles which have above 1000mm diameter is predicted to be above 0.9. Through plugging measurements, a new empirical method is suggested for quantifying the plugging effect of open-ended piles. The proposed PLR equation is possible to predict the behavior of soil plug in the preliminary design stage. In addition, in order to investigate the behavior of the soil plug of open-ended pile, field load tests are performed on instrumented three piles driven into sand. It is obtained that the resistance components of open-ended pile are separated by double-walled pile system. It is found that inner shaft capacity is developed nearby pile tip. However, upper soil plug did not influence the inner shaft capacity. Also, it is found that all test piles are floating piles and unplugged condition because the sum of inner shaft capacity and outer shaft capacity is calculated about 58 to 76% of the ultimate bearing capacity.INTRODUCTIONIn Korea, a number of huge construction projects such as harbor terminals, offshore grand bridges, and lifeline systems are progress in urban and costal area. In these areas, steel pipe piles are frequently used to support high-rise buildings and heavy weight structures for ensuring structural safety rather than serviceability limit capacity. Also, steel pipe piles are frequently used in civil engineering structures because they have many advantages such as high-load bearing capacity, light weight and outstanding workability. The mega foundations of grand bridges and high-rise buildings are required in geotechnical engineering. Large diameter driven piles are frequently used in several projects.Many specifications such as API, FHWA and AASHTO have been reported as a design guideline of plugging effect, however , the current design method for plugging effect of steel pipe piles are mainly based on the our knowledge derived from observation of the model test or the small diameter pile load test. Therefore, these specifications have limitation to apply the large diameter steel pipe piles.Much work has been done to study the plugging effect by many researchers. Yamahara (1964) reported that soil plug has been modeled as a thin disk element as shown in Figure 1, since the increment of radial strain of the soil plug can be neglected due to high rigidity of the pile compared to that of the soil plug. Klos and Tejchman (1977) reported that the end bearing capacity of open-ended piles was almost equal to that of a closed-ended pile when penetration depth of pile was above 15times the pile diameters by model tests. Paikowsky and Whitman(1990) reported fundamental studies on mechanism of plugging effect in sand. Paik et al. (2003) reported that empirical relations for plug load capacity, annulus load capacity, and shaft load capacity of open-ended piles are proposed based on the model pile tests. As discussed above, much work has been done in the area of plugging effect. But little work has been done to study the plugging effect by full scale field tests."

Jan 1, 2014

By H. Utsunomiya, J. Su, K. S. Tamimi, S. Yue, M. Sanjari, L. Kestens, Hara, A. S. Kabir, R. Petrov

Manufacturing of thin sheet is difficult in industries. Some approaches, such as small-draft multi-pass rolling, intermediate annealing, isothermal rolling and high-speed rolling were proposed to overcome the deformability. In this study, different rolling speeds from 15 to 1000 m/min were employed to twin rolled cast AZ31B magnesium alloy to different reductions. The results show thatAZ31B sheets rolled at 15 m/min and 100 °C has fractured for reductions of more than 30% per pass. However, by increasing the rolling speed to 1000 m/min the rollability was improved significantly and the material can be rolled to reductions of more than 70% per pass. The high speed and heavily deformed materials are fully recrystallized even at 100 °C.

Jan 1, 2014

By T. Ouellet, F. Chiesa, J. Carignan, D. Levasseur

Common practice for the preparation of permanent mold for aluminum casting is to coat the mold with a ceramic suspension to obtain a chemically stable interface with the aluminum melt. This practice serves two purposes: first, it helps the thermal regulation of the mold and second, it prolongs its life. The possibility of increasing the coating durability by applying it by thermal spray is appealing. Plasma spray of zirconium oxide based coatings was performed on H13 tool steel to study the coating’s thermal fatigue resistance. A unique dip test setup was used to characterize the thermal fatigue resistance of the coatings and of bare H13 steel. Observations of the failure mechanism bring an insight on the requirements of the coating to maximize its durability.

Jan 1, 2014

Most of the Indian coking coals are medium coking and of very high ash content. Beneficiation of these coals is a must for their utilisation in coke making. During washing while the ash content of the coal is reduced, the same is expected to affect the reactive-inert ratio and the proportion of various petrographic constituents in the clean coal. This will affect the coking behaviour, including the expansion characteristics, of such coal. An increase in expansion behaviour of coal increases the wall pressure and may damage the battery wall. Therefore, close monitoring of coking properties along with drop in ash is necessary for smooth use of the coal in coke ovens. An effort is, therefore, essential to understand the impact of washing on its coking properties. The studies were carried out with captive coals of Tata Steel, India. Three medium coking coal samples namely, VII A, VI A and XI SEB seam coals of West Bokaro Colliery were used for the study. The coal samples after washing to different ash levels were subjected to the following analysis: proximate, crucible swelling number (CSN), LT GK test, dilatometer and plastometer tests and petrography. The experimental data were then analysed to assess the relationship of various coking properties of the coal with its ash content. The studies clearly show that there is a strong impact of beneficiation of the coal on its coking behaviour. The impacts are more at lower level of ash in the clean coal. In general, the coking properties increase with a decrease in ash. This is primarily due to an enrichment of vitrinte materials in the clean coal and an increase in the reactive-inert ratio in the coals. However, the most important impact of the lowering ash is on the increase in the swelling nature of the coal. The coals with lower ash become highly expanding in nature. This may be very critical from operations of coke ovens point of view, especially stamp charged coke ovens. Necessary precaution should be taken in selecting the other coal blend constituents when these coals are beneficiated to a very low level of ash content.

Jan 1, 2014

By J. Jung, W. Keller, N. Rohn

In hydrometallurgical minerals processing slurries are often processed at very small grind sizes and high solids concentrations. This normally results in flow anomalies of such slurries. Due to flow limits or yield stress the slurry tends to stagnate close to the vessel bottom, the walls and at any internals. The main mixing task therefore generally is not suspending of the solids but the homogeneous blending of the entire vessel volume. If not considered during the agitator design only a fraction of the vessel contents will be mixed. Therefore the knowledge of the slurry rheology as well as the variations in process parameters is vital to design e.g. storage or surge tanks. The integral mixing solution considers the motor power, the choice of the impeller type and number, the impeller diameter as well as the design of the baffles and feed and discharge positions.

Jan 1, 2014