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By Gi-Chun Han, Ki-Suk Han, Korea Energy Management Corp., Jin-Sang Cho, Hyung-Seok Kim, Jae-Hyun Oh

This study has been carried out to use the waste sludges generated at Pohang Iron & Steel Co. Ltd. (POSCO) as the raw materials of Ordinary Portland Cement (OPC). The burnability index of the raw mixture and the hydration characteristics and compressive strength of clinker have been examined. The waste sludges were mainly composed of CaO, SiO2, Al2O3, and Fe2O3, the main component of OPC. The Burnability index of mixture was improved, according to the replacement content of POSCO sludge increase. POSCO sludge can be used as a raw material for cement because the state of mineral development and property of clinker produced from POSCO sludge are similar to the plain. Therefore, POSCO sludges can be used as the source materials of iron and calcium oxide.

Jan 1, 2003

By Jochen Petersen, David G. Dixon

"Although heap leaching may be perceived as a somewhat low-tech route for the extraction of low-grade minerals, the underlying physical, chemical and biological processes are in fact extremely complex. There has been increased interest in heap leaching of sulphide minerals in recent years with the advent of controlled bio-heap leaching, and the need to mine more marginal ore deposits.A detailed investigation into the dynamics of heap leach processes has provided much insight into the underlying complexities, and has led to the development of a sophisticated modelling tool, HeapSim. Some of the sub-processes that are modelled include mineral kinetics, particle size effects, bacterial growth, oxidation and adsorption, gas adsorption, pore diffusion, bulk advection, gas balance and heat conservation. The interplay of these various sub-processes is illustrated in the paper.Two case studies are presented which illustrate specific features of the model for different applications and how these have helped to identify key areas of concern. The first is focussed on chalcocite heap bioleaching, which shows that by nature of the reaction the process is strongly dependent on the initial supply of acid to the mineral site. In heaps this acid supply can be severely limited by the rate of diffusion from channels of flowing solution into stagnant zones of the heap, whereas in narrow-bore laboratory columns this effect is not observed."

Jan 1, 2003

By A. I. A. Salama

In this paper, the problem of sedimentation and consolidation of poly-disperse suspensions is considered. The solid particles are assumed to be of different densities. If the sediment solids stresses are dropped out of the system equations and using the Richardson and Zaki hindered settling model, it has been found that in the limit, i.e., as time approaches infinity, the fluid is completely displaced to the top of the sediment zone. Furthermore, the species segregate completely with the heavier and coarser particles at the bottom of the sediment and the lighter and finer particles at the top of the sediment. Practical observations do not support these behaviors and physical-ly such behaviors do not exist; consequently, results of this kind in the literature are unrealistic. Here, a mathematical structure of the poly-disperse sedimentation and consolidation problem has been proposed. In this case the compaction zone species solids stresses are introduced in the momentum balance equations of the system. The species solid stresses in the sediment are constrained so that the system equations are consistent, i.e., sedimentation and consolidation of two or more identical species should behave as a mono-disperse system. Such a condition has not been recognized and imposed in some of the studies in the literature, which has led to unreliable results. Two practical forms of species stresses that satisfy the system consistency condition are here proposed. It should be noted that the study of sedimentation and consolidation of poly-disperse suspensions could result in more realistic suspension interfaces compared to mono-disperse suspensions, and could lead to more reliable engineering designs of tailings ponds. Predictions of sedimentation and consolidation in models of poly-disperse suspensions are demonstrated using published data.

Jan 1, 2014

By Máximo Pérez, Julio C. Videla, Rosa Dzioba

"This paper reports the hydrometallurgical treatment of gravity concentrates of gold samples and outcrops associated with graphite ores obtained from:• flotation tailings of crystalline graphite minerals• outcrop samples of graphitic rock associated with auriferous minerals and free gold located in the Villa Union district and surrounding areas - La Rioja Province - Argentina.Previous studies of the flotation potential of crystalline graphite minerals failed to consider the presence of noble metals.The samples represent a mineralized zone of crystalline graphite which is distributed in different formations with a NE - SW trend in Maz, Punta Colorada and Las Ramaditas hills, covering an area of about 300 square kilometers."

Jan 1, 2003

By Malcolm Mudge

"One of the oldest mining areas in the World exist in Africa and the Middle East. This area is being exploited by foreign and local mining entities. Several large plants, both foreign and local as well as small operators, conduct their mining business on a scale which would be could be prohibited in any other part of the world. Relatively recent European disaster with tailing disposal and breakout has highlighted the problem.More important to the author is that the presence of foreign entities in zones which have not remedied the situation but has heightened the concern due to those entities using similar outrageous methods in treatment of waste. The abject misuse of technology cannot be permitted to continue and the lack of any metallurgical knowledge in the treatment of gold ores is considered deplorable for the majority of third world countries.The destruction of cyanide is simple and straightforward and requires no special skills. In South America, we developed a system that is modular, compact and can be operated in batch mode to cater for several clients, as required. Larger installations would require a separate module, as treatmentwould be on a continuous basis."

Jan 1, 2003

By A. F. Raschenko, Y. A. Golodcov, V. V. Elshin

"The autoclave noble metal desorption in apparatuses with a dense stationary sorbent layer is perspective for the technology of sorption gold and silver extraction from solutions and pulps by carbon sorbents. The study of the mechanism and optimization of the autoclave desorption process involve some difficulties. To overcome them it is necessary to use mathematical and quantum-chemical modelling. The given paper deals with a mathematical model for the dynamics of gold and silver desorption from active carbons by alkali solutions based on the physical-chemical notions of the process. The kinetics and the mechanism of the process were investigated using the mathematical model for gold and silver desorption.The calculation of the efficient mass-transfer coefficient (ße) for various initial and intermediate noble metal concentrations in carbon (Cy) made it possible to find that the dependence of ße on Cy in case of gold desoprtion shows a clear extreme character. The value of the initial metal concentration in carbon therewith does not influence the character of the curve the inflection point of which is changed essentially at elevated process temperatures only. The revealed characteristic property, in the author's opinion can only be indicative of the change in the mechanism of gold desorption under autoclave desorption conditions. The assumed [Au(CN)(OH)]- type intermediate that has a higher diffusion coefficient in comparison with the adsorbed complex [Au(CN)2]- can be considered as an intermediate compound in the process of gold desorption."

Jan 1, 2003

By Stephen Gay, Dewetia Latti

"When improving a plant a mineral processing engineer would like to know the mineral composition distribution. In order to assess this distribution in particles, as compared to the corresponding distribution in particle sections, a procedure needs to be applied to the observed particle sections. Such a procedure is called a stereological correction. There exists many stereological correction procedures, but one group of such procedures is based on using those stereological equations that do not require making assumptions regarding particle shape or texture. These equations are called geometric probability equations.Davy derived a geometric probability equation to estimate the covariance of mineral composition distributions for particles from both particle sections and linear intercepts. This covariance can be used to measure the variance of the particle composition distribution of each mineral. The equation as presented by Davy requires textural information; however the equation was modified by Gay to be more directly applied to particle sections and linear intercepts. The variance obtained from applying this equation is fundamental to the binary stereological correction procedures developed by Gay and his colleagues; the covariance is fundamental to the multiphase stereological correction.Thus far, validation of both the binary and multiphase stereological correction has been achieved using numerical simulation. This paper shall present results comparing the covariance (and variance) estimates from Gay’s equation with actual three-dimensional information obtained from serially sectioning particles. This involved mounting a set of particles and continuously sectioning all particles uniformly so that the three dimensional structure of the particles could be obtained.The mineralogical data to which the equations described above were applied were derived from two individual size fractions from a hard-rock titanium deposit. The deposit contains a range of minerals and of mineral textures and the two size fractions selected were:"

Jan 1, 2003

By ?. ?. Zimin, B. A. Kutlin, X. Baddamsuren

"The ore features of Mongolian fluorspar deposits are shown in the paper. The possibilities of the technological of ore processing on the Bor-Undur combine scheme improvement are analyzed there. Some recommendations are done for scheme development: spare output technologies, the usage large-sized ore separation, flotation by columnar flotation cells, leaching and concentrate agglomeration.New evaluation and usage of mineral sources approach was developed for Mongolian fluoride ores. The conception allows using maximally available mineral resources for getting of metallurgical and acid fluoride concentrates while mining and technological processes: mining (as well as quarrying) -storing, blending-crushing, grinding-combined processing methods-metallurgical using preparation It has been established mining and processing technological schemes should include:• spare blasting technologies providing minimum effect on fluorite crystals which follows ore selective excavation;• large-sized ore separation methods resulted in maximum recovery for these operations in respect to metallurgical fluorite concentrates;• grinding and flotation regimes providing high-quality flotation concentrates getting for their usein chemical industry;• fluorite concentrates agglomeration technologies for providing ability of their use in metallurgical and cement industriesThe results of industrial usage of jugging machines, columnar and pneumomechanical flotation machines for fluospar dressing.The technological approaches implementation in “Bor-Undur” plant maintenance within 1993-2002 years leaded to:• change plant status from just flotation one to gravitational-flotation characterized by technological process stages which are traditional for metallurgical industry and plant capacity increase from 400 to 600 thousand tones of treatment ore as well as concentrate production increase from 120 to 150-170 thousand tones including 120-140 thousand tones of acid grade concentrates with 97% CaF2 ."

Jan 1, 2003

By John Ralston, Stephen Grano, Yongjun Peng, Daniel Fornasiero

"A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of rgrinding conditions on galena flotation and galena separation from pyrite. The various reactions occurring on the mineral surface were investigated by a range of techniques, including OH- addition to maintain the grinding pH, EDTA extraction, XPS and ToF-SIMS measurements.Galena flotation and galena separation from pyrite were strongly dependent on the metal oxidation species produced on galena and pyrite surfaces under different grinding conditions. Iron oxidation species depressed both galena and pyrite flotation, whilst lead oxidation species activated pyrite but had little effect on galena. Optimum galena flotation and galena selectivity against pyrite were achieved by selecting grinding conditions that enabled lead and iron oxidation production to be controlled."

Jan 1, 2003

By David Dreisinger

"The leaching of base and precious metal ores and concentrates continues to progress in both laboratory study and industrial application. These developments are being driven by the need to respond to difficult ores and concentrates that are not amenable to conventional treatment. In many cases alternatives are being developed to conventional treatment (e.g. Pyrometallurgy) for technical and economic reasons.In this paper, a brief general review of some new developments in leaching will be followed by a more detailed explanation of three process developments that have either been industrially applied or are expected to be applied in a short time frame. The three processes to be reviewed in detail are the Mt. Gordon Copper Process, the Anglo American Corporation/University of British Columbia Copper Process and the PLATSOL Process. These leaching processes operate at low (90°C), medium (150°C) and high (220°C) temperature and are successful in quickly and completely extracting metal values from ores and concentrates."

Jan 1, 2003

Compressive crushing is applied in crushing plants used in mineral, mining, and aggregate in-dustry for fragmentation of rock materials. From a global perspective, the total volume of crushed rock is massive and corresponds to several billion tons. All societies have to fulfil a daily need of rock material products and its derivatives such as metals and minerals. The business for metals and minerals is global while the aggregates production is mainly a local industry. This paper presents a broader overview of optimisation with respect to product yield, use of natural resources and energy consumption. High level plant optimisation of compressive crushing plants is covered as well as real-time optimisation and optimisation of single production units. Each of three optimisation areas are presented and a discussion around how these three areas will be able to communicate with each other is given. Several models, e.g. process performance behav-iour with respect to wear, as well as fitness functions can be common for all three areas. Well-defined and representative fitness functions are of the utmost importance in order to assure that the optimisation results reflect the production targets. It is concluded that great benefits can be achieved by linking together different areas of optimisa-tion. The future for compressing crushing lies, without a doubt, in tailored processes both with re-spect to machines optimised for each customer, plant parameters and operation routines as well as an on-line adjustment, which takes into account current information and control possibilities.

Jan 1, 2014

By David Dreisinger

"The leaching of base and precious metal ores and concentrates continues to progress in both laboratory study and industrial application. These developments are being driven by the need to respond to difficult ores and concentrates that are not amenable to conventional treatment. In many cases alternatives are being developed to conventional treatment (e.g. Pyrometallurgy) for technical and economic reasons.In this paper, a brief general review of some new developments in leaching will be followed by a more detailed explanation of three process developments that have either been industrially applied or are expected to be applied in a short time frame. The three processes to be reviewed in detail are the Mt. Gordon Copper Process, the Anglo American Corporation/University of British Columbia Copper Process and the PLATSOL Process. These leaching processes operate at low (90°C), medium (150°C) and high (220°C) temperature and are successful in quickly and completely extracting metal values from ores and concentrates.INTRODUCTIONThe process of leaching is widely used in hydrometallurgy to selectively recover a metal of interest from an ore or a concentrate. Leaching and by extension hydrometallurgy is well established in the recovery of copper (copper heap leach ? SX-EW), nickel (Moa Bay and Caron process), zinc (roast ? leach ? electrowin and zinc pressure leach), gold (cyanidation) and uranium (acid sulfate leach). Of course this success extends to many of the metals found in nature. Recently, the importance of hydrometallurgy appears to be increasing with hydrometallurgy viewed as an attractive alternative to both traditional mineral processing and conventional smelting/converting/refining. This increasing interest has led to intensive study and increasing application. Selected developments include:Copper ? the Mt. Gordon process and new concentrate processes such as INTEC, Activox, CESL, Dynatec, Total Pressure Oxidation, MIM Albion, BioCop, and the AAC/UBC Process.Nickel ? Voisey Bay process for hydrometallurgical treatment of Voisey Bay concentrate, HPAL processing of laterites at Murrin Murrin, Bulong and Cawse, atmospheric leaching of laterites, heap bioleaching of nickel sulfides by Titan Resources (Australia).Zinc ? establishment of zinc leach, solvent extraction and electrowinning technology for treatment of the Skorpion deposit in Namibia, new developments in atmospheric and pressure leaching, the Hydrozinc process.Gold ? development of a number of thiosulfate leaching processes for recovery of gold from refractory carbonaceous ores or concentrates."

Jan 1, 2003

By Benoit Clermont, Jan Lux

"Magotteaux and Anglo Platinum started a co-operation program with the main aim of establishing the optimum milling configuration measured in terms of throughput, fineness and energy consumption.For this purpose, a fully instrumented pilot milling plant, supplied by Magotteaux (Pty) Ltd, and equipped with a 0.9 x 1.0 m ball mill, was erected at Frank concentrator (Merensky Pt ore). The primary ball mills at Frank concentrator were surveyed in order to set the conditions for the base case. This data was then replicated in the pilot mill under the same configuration. Thereafter, a series of different parameters were varied in order to attempt to optimize the milling system.Only grate versus overflow discharge and open versus closed circuit will be discussed in this paper.It should be noted that this paper does not attempt to give a universal solution as to what milling configuration is optimum in all cases. The conclusions apply for this particular case and probably most others, but it would be advisable to consider each case on its own.CONCLUSION• Overflow versus grate dischargeAn overflow mill has a “pool” of slurry around the toe of the ball charge, which creates a counter lever to the ball charge. This will reduce the absorbed power in the range of 10-15% (depending on the case) and will consequently result in a coarser grind. The tests found a 4% gain in grinding efficiency (Wio) with an overflow mill but this is probably not significant.This lower absorbed power and coarser grind can be counteracted by increasing the ball charge (if below maximum) and/or by increasing the mill volume when removing the grate discharge (a typical grate takes up about 300mm of the mill length).• Open versus closed circuit"

Jan 1, 2003

By N. Raeis Hosseiny, S. H. Bassir

"Chador-Malu iron ore is one of the most important iron mines of Iran.About 98 percent of Fe in the ore is in shape of Magnetite, Hematite, Martite, aqua oxide of Iron and the other irons are with ferrous silicates, actinolite, cholorite and ferrous dolomites. 1% of Fe has replaced in pyrite. The phosphor distribution in the ore is non-hemogenous and its average in the whole of the deposit is 94%. It is in shape of Apatite.This mine contains considerable phosphor, which makes it useless for metallurgical uses. At this mine the phosphor is reduced in the iron ore at two steps. At the first step, magnetic part of the ore is separated from the gangues and phosphors by magnetic separator. At the second step, the ore is enriched by the flotation methods. Experimental flotation methods to obtain the optimum conditions are as follows:• Effect of Starch as Hematite depressant with ATRAC as Apatite collector• Effect of Sodium silicate as Hematite depressant with ATRAC as Apatite collector• Effect of ASAM as Apatite collector with Sodium silicate as Hematite depressant• Effect of ATRAC (BEROL) as Apatite collector with Sodium silicate as Hematite depressant• Effect of ASAM & ATRAC mixture as Apatite collector with Sodium silicate as Hematite depressant• Effect of Kcarbonate as pH-modifier• Final test to Optimize pH, Collector, DepressantAt this research we have found the optimum circumstance of the flotation of Chador-Malu iron ore in order to decreasing phosphors of iron oxide and floating of Apatite to make pure Hematite.To reach the optimum conditions, some tests were done with different amounts of pH, collector and depressant. The results are as follows:"

Jan 1, 2003

By G. Onal, E. Gock, H. Dincer

"During the conventional chromite dissolution process; chromite ore concentrates were ground to at least <90 µm using the ball mill and after adding Na2CO3 and leaning material (instead of CaCO3 also residues from the leaching process) at a ratio of e.g. 1:0.75:1.2, depending on the specific formulation, follows the digestion e.g. in a rotary kiln, heated in countercurrent. The reaction time is 3 to 8 h. The calcine is comminuted and leached with water or a thin chromate solution. Depending on the type of ore used, the yield is 75-85 %. The disadvantage of the above-described process is that it is impossible, using current technology, to achieve a complete digestion of the chromite ores and that the chromium-containing residues have to be disposed of as special waste, involving a large financial effort.The subject of this study was the investigation of the effect of vibratory milling on chromite dissolution. The impact stress in the vibratory mill causes the mechanical activation of chromite, which is characterised by lattice defects. The degree of mechanical activation can be quantified by measuring the relative X-ray diffraction intensities at the parent lattice planes of chromite. Each relative X-ray diffraction ratio correlates with a certain degree of digestion. As opposed to vibratory milling, a complete digestion of chromite using a ball mill is impossible, even at extremely long grinding times.In this investigation a chromite concentrate from Pulpinar/Kayseri with content of 44 % Cr2O3 and the Eccentric Vibratory Mill was used. In order to verify the effect of the vibrating grinding on chromite dissolution, reaction kinetic investigations on digestion and leaching were carried out."

Jan 1, 2003

By József Faitli, Barnabás Csoke, Károly Solymár, Zoltán Hatvani, Dimitri Papanastassiou

In most cases, the sizing of dry or wet mills for ore processing is primarily based on the determination of the Bond grindability index, using the Bond-Kjos-Rowland relations. In several cases, grinding takes place under conditions different from these and the grinding conditions have a great influence on the postgrinding process. This is particularly true for the grinding of bauxites where grinding takes place in alkali, often in higher temperature in alkali Liquor. So it is necessary to develop a testing method providing a reliable grindability index even under these special circumstances and allowing a more precise mill sizing. Therefore we surrounded the grinding crucible of the Hardgrove mill with a crucible furnace to heat it. The new heated mill is suitable to determine the grindability index under temperature-controlled circumstances, in liquids (water and alkali) with different temperatures. The required heating power is 2000 W. In the implemented equipment we installed four 230V/500W electric heating wires made from heat-resistant alloyed material and surrounded by ceramic insulators. The temperature and temperature-gradient are measured by four PT100 platinum thermal resistors. The data acquisition and control program written in the C language in the Lab Windows CVI program environment measures the voltage proportional to the temperature. Determining the grindability indices of hungarian and greek bauxites experimentally, first dry grinding tests were carried out under standard conditions. During wet and alkaline grinding, to 50 g of dry bauxite 85.5 g of industrial alkali with a concentration of about 200 g/l was added. As grinding aid 2 g of CaO (4 % of dry bauxite) was dosed. From the data it can be concluded: - The tested bauxites show a similar behaviour against temperature change. However, the extent of grindability change is different for different bauxites. - Soft Hungarian boehmitic bauxite can be ground in a high-temperature alkaline medium better than hard Greek one. The increase of grindability according to the high-temperature Hardgrove indices: (kHT = Dry o HT,alkaline H /H ): for hard Greek and soft Hungarian boehmitic bauxites: kHT = 1.7 and 2.4 respectively; according to estimated Bond indices (kB,HT =Wi,dry/Wi,HT, alkaline ): kB,HT = 1.6 and 2.1. - The increase of grindability is the most important factor the reaction of kaolinite with caustic liquor and lime and the loosing of the textural structure at 80 ºC and especially at 100 ºC.

Jan 1, 2003

By T. Tsurata

The accumulation of thorium and/or uranium by various microorganisms from a solution containing thorium and/or uranium at pH 3.5 was examined. Among the species tested, a high accumulation ability for thorium was exhibited by strains of gram-positive bacteria, such as Bacillus megaterium, B. subtilis, Micrococcus luteus, Rhodococcus erythropolis, and actinomycetes, such as Streptomyces levoris. On the other hand, though uranium was accumulated in small amounts from the solution containing both elements by all these microorganisms, actinomycetes, such as S. flavoviridis and S. levoris had relatively high uranium accumulation abilities. In these high performance thorium- and uranium- accumulating microorganisms, S.levoris, which accumulated the largest amount of uranium from the solution containing only uranium at pH 3.5, could accumulate about 300 µmol thorium and 133 µmol uranium per gram dry wt. of microbial cells from a solution containing both thorium and uranium at pH 3.5. After this screening, uranium accumulation using microorganisms isolated from uranium mines, among which some strains of bacteria were found to possess an extremely high uranium accumulating ability. The microbial biomass may thus be considered for use as an accumulating agent for the removal and recovery of uranium that may be present in metallurgical effluents, mine tailings, seawater and other sources. Recently, hundreds of micro-organisms existing in uranium deposits located in North America, Australia, and Japan for their ability to accumulate large amounts of uranium, and found some new strains which accumulated large amounts of uranium, such as Lactobacillus and Bacillus sp. from Japanese and Arthrobacter and Bacillus sp. from the United States uranium deposits. These bacterial strains can accumulate about 2500 µmol uranium per gram dry wt. of microbial cells within one hour. These microbial cells can remove uranium from the uranium refining wastewater with a high efficiency. The accumulation of uranium from a solution (pH 5.8) by microorganisms contained Arthrobacter nicotianee, which is a similar strain mentioned above Arthrobacter sp., was examined. Among the 76 strains of 69 species tested (23 bacteria, 20 actinomycetes, 18 fungi, and 15 yeasts), high uranium accumulation ability was exhibited by strains of the bacteria, A. nicotianae, B. subtilis, and M. luteus. A. nicotianae cells, which showed the best performance, could accumulate about 698 mg uranium (2.58 mmol) per gram dry wt. of microbial cells.

Jan 1, 2014

By Susanna G. de Jager, Francis W. Petersen

"To enable the prediction of reagents suitable for fine coal flotation, it is necessary to develop a methodology applicable to different South African coal types. Statistical confirmation of the applicability of this methodology is important to avoid recommendation of reagents on a trial and error basis.The study included 5 coal samples from different collieries and included Highveld seam 3 and 4 coal (as one sample), Waterberg coal (zone 10 -11), Highveld seam 5 upper coal and Witbank seam 2 and seam 4 coal. Seam 3 and 4 (mixture) coal, Waterberg and the seam 5 upper coal were all found to be vitrinite rich coals. The coal characterisation study included petrographic analysis, proximate analysis, float-sink analysis, oxygen-containing functional groups, surface extraction, flotation release analysis and contact angle measurements. Flotation tests were used to validate expectations from the characterisation of the coal samples.RESULTSThe flotation data indicated that all of the coal samples were amendable to froth flotation. The best results were obtained with the Witbank seam 2 coal and the poorest flotation with Syferfontein seam 5 coal. The flotation tests showed that the best reagents to float all of the coal samples studied were iso-decanol and dodecene. These reagents produced flotation products that were near to the release curve, which are the optimum flotation results (obtained when using iso-paraffin as collector). Dodecene resulted in low ash products and iso-decanol in high yield products."

Jan 1, 2003

By C. A. Acuña

Extensive literature exists on the motion of single bubbles and the behaviour of swarms of bubbles. This contribution describes work to track and reveal the motion of individual bubbles in a swarm. The technique is based on high speed cinematography and tracking of multiple moving objects. Image processing algorithms were implemented in Matlab to isolate and measure geometric proper-ties of the bubbles in image sequences recorded at 2 ms interval; and these properties were compiled into a data structure. To track a bubble, the geometric properties and a matching criterion were applied on consecutive pictures to identify the bubble. The bubble trajectory was reconstructed from the data structure for the matched objects. The methodology is briefly described. The new technique was tested for bubbles produced at slot-type spargers (i.e., approximately 2-D swarms) in the presence of two frother types (&apos;strong&apos; and &apos;weak&apos;). Two observations are discussed: a) that bubble motion in a swarm describes a velocity-size relationship dictated by the dominant bubble size class; and b) that surfactant type influences bubble rise velocity for bubbles in the range 0.1 mm to 4 mm. The latter suggests surface viscosity rather than surface immobilization determines bubble rise velocity.

Jan 1, 2014

By Hermann Wotruba, Lars Weitkämper

"Dry coal dressing was popular during the 1950’s and 60’s in many parts of the world. The devices mainly used were air jigs and air tables.The increase in ash and moisture content of run-of-mine coals due to the wide advanced mechanisation of mining methods during and after this period led to that pneumatic devices being unable to treat run-of mine coals with the desired efficiency. Since the 1960’s almost all new coal preparation plants have been based on wet processes that are highly efficient in terms of coal recovery and their ability to handle damp and sticky run-of-mine coals. (Frankland, 1995)However, water is becoming increasingly costly and the disposal of fine products, containing most of the water, is an environmental concern. There would be significant cost savings and a lower total energy consumption if coal could be cleaned dry. Efficient dry coal treatment would be an interesting solution in desert, arid or cold areas.In Germany one dry coal dressing plant is in operation. This is the last operating dry coal dressing plant existing in Europe. The actual technical standard of dry coal dressing has been analysed during test-work and sampling in this plant (Saar Region in Germany). The process and the advantages and disadvantages are presented. The plants problems are low efficiency in the fine fraction –6 mm and the coarse fraction +30 mm and a low overall throughput as well as the lack of an automatic process control system. The separation results in the medium size fractions between +6 and -30 mm are excellent"

Jan 1, 2003