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By G. A. Vissac

The drying of fine coal involves special techniques, which are discussed and analyzed. Types of dryers employing these techniques are described. Calculations are presented for new methods of deal ing with the entrained dust that is always present in fine coal drying operations.

Jan 10, 1953

Fine Coal Evaluation by Gravity Methods

Sep 13, 2010

By M. C. Van Camp, J. D. Miller

Preliminary results are reported regarding the design and development of a pilot scale air sparged hydrocyclone for cleaning fine coal 590 pm (- 28 mesh) containing 24% ash and 1.6% sulfur. The principle of separation is the flotation of hydrophobic coal particles in the centnjugal field generated by the fluid flow in the air sparged hydrocyclone as discussed in another publication. This 152-mm (6-in.) hydrocyclone has a nominal capacity of 0.9 t/h (1 tph) and experimental results suggest that separations vastly superior to a water-only cyclone are possible. In addition the separation efficiency is as good, if not better, than that achieved with conventional flotation cells. For example, typical results indicate that 75% clean coal can be recovered at 15% ash leaving a tailing product of almost 50% ash. These experimental results coupled with the high capacity of the air sparged hydrocyclone (imagine a retention time for flotation of only two seconds compared to two minutes for conventional flotation) may represent a significant breakthrough, not only in coal preparation technology, but in the flotation of fine particles in general.

Jan 1, 1983

By J. D. Miller

Many factors -- political, environmental and technological -- will determine the extent to which the United States realizes the potential of its vast coal resources. Not the least of these factors is technogical development including mining, processing and transportation. With regard to processing technology, about 50% of the 800x106 tons of coal mined annually in the U.S. is processed in preparation plants. The purpose of the physical separations accomplished in these preparation plants is to remove ash (present as clays and other oxide minerals) and sulfur 'present mostly as pyrite). Coal flotation circuits for such separations are becoming more important in the processing of minus 28 mesh coal. (1,2,3) For example in the U.S. in 1960, 31 flotation plants processed 26,500 tpd; whereas in 1980, there were 80 flotation plants which processed 78,300 tpd. This corresponds to an annual growth in flotation plant capacity of 10 per year during the past two decades. Coal flotation is based on the natural or induced hydrophobicity of coal particles which are separated from hydrophilic ash and sulfur constituents by attachment to air bubbles. The coal particle/air bubble aggregates are collected in a froth phase which is created by the addition of a suitable frother such as MISC. Without exception, such separations are made in a conventional flotation cell, which, in essence, is a stirred tank reactor with a shrouded rotor to shear the air as it passes through a hollow shaft. The dispersed air bubbles (4.0 mm diameter) are stabilized by addition of the frother. Collision of the air bubbles with, and/or precipitation of the air bubbles on, the coal particles results in the formation of coal particle/air bubble aggregates which rise in the gravitational field and are collected in the froth phase developed at the top of the flotation cell. Restraints on successful separation by this conventional flotation technique are particle size and retention time. Generally it is found that effective flotation is only achieved for particle sizes between 10 and 1000 microns. Further, with respect to retention time, it is found that a nominal retention time of at least 2 minutes is required for successful separations. These facts limit the effectiveness of conventional coal flotation. Coal fines may be lost in the reject stream and disposal is frequently a problem. The retention time required for conventional flotation results in large floor space demands which limit the capacity of the plant.

Jan 1, 1981

By T. E. Durney

In the Fall of 1987 The Wellmore Coal division of The United Company installed a fines separation circuit in its #20 plant near Big Rock, Va. The addition of the fines circuit included a bank of classifying cyclones and two flotation units; one a conventional 4 cell, 34 m3 Wemco cell, the other an 2.4 meter diameter by 7.6 meter tall, 28.3 m3 column flotation cell. The new fine coal separation circuit is depicted in Figure 1. The column flotation cell is manufactured by the Deister Concentrator Company, Inc., under the trade name Flotaire. The Deister Flotaire column cell utilizes a counter current flow arrangement and a different means of generating air bubbles than that of conventional mechanical flotation cells found in coal processing plants. Other features include diffusers for additional air supply and a froth washer. This cell is one of the few commercial scale column cells processing coal.

Jan 1, 1990

By M. E. Holuszko

A research program has been carried out at the Mining Department of the University of British Columbia to study the effect of wettability of coal on its handleability and bulk density. The effect of moisture content on the bulk density of coal was found to be more pronounced for hydrophilic coals than for hydrophopbic ones. Altering wettability of coal surface leads to different effects of moisture on bulk density. The samples were studied at different fine fractions content, and it was shown that there was no effect of increased content of fines on the bulk density for hydrophobic coals, while for hydrophilic coals this effect was very significant. It was shown that the moisture content at which the lowest bulk density was reached coincides with the critical moisture content for studied samples, as determined from handleability tests using Durham Cone method. This critical moisture is the moisture content at which a sudden deterioration of coal handleability occurs. Based on the bulk density and handleability tests, the flow theory of moist coal is proposed.

Jan 1, 2006

By Joseph L. Walker

INTRODUCTION In looking over the diversity of the papers that are being presented during this meeting on The Industrial Practice of Fine Coal Processing one cannot help but be impressed with the progress the industry has made in beneficiating fine raw coals, and in the number of innovations that are under study to increase recovery and to improve the quality of the finest size particles produced at a preparation plant. Those who are not in our industry, who look at the technical program, might be confused, when they see that the papers include such topics as cleaning to zero and heavy media cyclone cleaning 28M x 100M; application and performance of fine coal jigs, tables, hydrocyclones, spirals, and flotation; filtration, dewatering and thermal drying; and ancilliary aspects such as fines handling, instrumentation and process control plus screening and liberation. This is an observation and not a criticism of the diversity of papers being presented. The program fits within the parameters of fine coal preparation as the term "coal preparation" is defined, but perhaps not as the term "fine coal" is defined. Admittedly these definitions are sometimes loose. However, each should be made more definitive if a meaningful fine coal preparation overview is to be possible. COAL PREPARATION DEFINED In the opinion of the writer, the term "coal preparation" should be defined as including all work activities that are performed on all components of a run-of-mine coal from the time it leaves a surface reserve or an underground portal, until all components are either ready for shipment or are stowed on, or in the earth in an environmentally acceptable manner. This definition excludes the work that is performed to improve coal quality or handleability inside the mine or pit. This work is commonly called "face" or "pit" preparation. FINE COAL DEFINED The term "fine coal" means different things to different people. In the past, anthracite finer than No. 3 Buckwheat (3/16 in.) was considered fines which often were discarded from the breaker as an unsalable by product; and bituminous coals finer that about 1/4 in. (slack) were either discarded or sold at cost to prevent an accumulation of "no bills" which referred to a product having no immediate sale. Although a standard definition of "fine coal" is yet to be accepted by the industry, a designation of coals by particle-size range has evolved through the wide use of three-circuit flowsheets, wherein the optimum size range by washer type determines the size fractions: a coarse-coal circuit for the plus 3/8 in., a -11- coal circuit for the 3/8 in. x 28 Mesh, and a fine-coal circuit for the remaining 28 Mesh x 0. Logically, the term "fine coal" should refer to some resultant size fraction or some top size by zero. This definition should include a 28 Mesh x 0 feed to a flotation cell but should exclude a 28 x 100 Mesh size fraction fed to a heavy media cyclone. Failure to include the resultant sizes in the definition precludes accounting of the full range of particle sizes present in the feed to the plant. Since the 28 Mesh x 0 fraction is treated in the final circuit of the three discreet washing circuits, now almost always used in U.S. commercial applications, and since it contains all of its resultant sizes, in the writer's opinion, it should be designated "fine coal". FINE COAL CLEANING Cleaning coal fines, which in the past was at best marginally profitable, is now an essential part of coal preparation strategy for a number of reasons : 1. Raw coals now cost more to produce and

Jan 1, 1988

By Yuemin Zhao

Pre-combustion cleaning of coal plays a key role in the process of efficient and clean utilization of coal resources. Recently, wet beneficiation of coal is predominant around the world. Nevertheless, wet beneficiation processes are limited by the increasingly serious problem of worldwide shortage of water, especially in China. Thus, it is imperative to develop efficient dry coal beneficiation techniques. Currently, several technologies such as air dense medium fluidized bed, compound dry cleaning and air jigging have successfully achieved high-efficiency separation of 50~6 mm coal. However, in recent years, a large amount of fine coal is generated as the mechanized mining technology has been progressively deployed in coal sector. Thus, it is necessary to develop efficient dry beneficiation techniques for fine coal. In recent years, many countries including China, India, Canada, Germen, and Australia have carried out many research works on fine coal dry beneficiation techniques. China University of Mining and Technology has carried out systematic researches on the introduction the vibrated energy to traditional air dense medium fluidized bed for fine coal beneficiation. This paper studied air dense medium vibrated fluidized beds (ADMVFB) for fine coal dry beneficiation. The experimental results show that the coal of <6 mm size can be beneficiated in an ADMVFB efficiently with the E value of 0.065~0.085, the separating density can be adjusted in the range of 1.45~2.2 g/cm3, and the lower limit of beneficiation can reach to 0.5 mm. Keywords: fine coal, air dense medium vibrated fluidized bed, coal separation, dry separation

Sep 1, 2012

By S. K. Nicol

Flotation, water-washing cyclones (hydrocyclones) and spiral concentrators are the three process units most commonly utilised in fine coal preparation. The results of testwork conducted on these three units will be presented and their performance and separation characteristics examined in detail. In particular, the dependence of the separation characteristics of each unit on particle size and the constraint this places on product quality (ash and sulphur levels) will be discussed. This dependence will be shown to be a critical criterion in the selection of fine coal circuits.

Jan 1, 1986

By D. C. Hatch

At the MacIntyre Development of the Titanium Division of National Lead Company a magnetite-ilmenite ore together with gabbro-anorthosite waste is mined from an open pit by shovels and trucks. The ore from the pits is trucked to ore stockpiles for blending ahead of the crusher and to free the mine from crusher delivery schedules. The ore stockpiles are blended to yield a 16.5 to 17.0 % TiO, crusher feed. This requires mining on an assay cut-off rather than a visual grade cut-off. Highly mineralized ore runs from 20 plus % TiO2 and 30 plus % Fe to 15 % TiO2 and 40 plus % Fe as the ratio of ilmenite to magnetite changes. There are three major ore types in the present pit with magnetite ratios varying from about one to one up to three times as much magnetite as ilmenite. Ilmenite and magnetite together liberate from gangue down to about 10 mesh and this is the basis of the magnetic cobbing. Below 10 mesh the ilmenite and magnetite start to separate and ore cobbing pulleys will not hold the ilmenite.

Jan 1, 1968

By Graham Davey

High-speed stirred milling is a relatively new method of grinding in the metalliferous process industries. However, it has been widely used in the industrial mineral field for more than 30 years. Many existing metallurgical operations are looking to maximize economic return from existing deposits this requires new thinking and technologies. The operating experience of two copper operations is discussed here to show the effect of the introduction of the Metso Stirred Media Detritor (SMD), a new type of high speed stirred mill. Both operations have derived significant metallurgical benefits from this new technology. The benefits and process difficulties are explained. The initial drive in high speed stirred milling technology was toward ultra fine grinding where the mill product has an 80 percent passing size of 15 µm (937mesh) or less. More recently, a number of installations have occurred in a more conventional regrind setting. Few conventional copper concentrators require such fine grinding to attain satisfactory copper grades and recoveries. So other advantages must be considered here rather than just the ability to grind fine with good power efficiency.

Jan 1, 2004

By E. W. Davis

I . OPERATING TESTS 1. CHARACTER OF ORE UNDER INVESTIGATION On the eastern end of the Mesabi Range, in Northern Minnesota, is a large formation of siliceous rock which contains bands and fine grains of magnetite . The magnetite comprises about 35 per cent. of the rock. Fig.. 1 show&apos;s graphically that the tonnage of minus 200-mesh material produced varies directly with the tonnage fed to the mill. There is undoubtedly some limit to this relation, but there seems to be no indication of it at 18 T. per hr. Some of the conclusions drawn from this test are that: (a) The ball-mill is naturally a machine of very large capacity; (b) if it is not possible to deliver a large tonnage of original feed to the mill, a closed circuit should be provided so that the mill may crush its own oversize.

Jan 2, 1919

By Donald R. Rathburn

Screening during the production of high-grade lump ore for blast furnace burden, particularly from recently developed ore deposits in Australia, South America, and Africa, has resulted in large tonnages of fine iron ore. Certain owners have decided to stockpile these fines until some later date; however, others have either sold these fines "as is" for agglomeration at the steel plant or have established their own pelletizing plants to produce a premium quality agglomerate. Normally these fines consist of the higher oxides of iron and the hydrated oxides. Unfortunately, grinding these types of materials in a wet process produces a slurry that is difficult to filter to obtain the requisite moisture level for the subsequent balling and indurating operations. The purpose of this paper is to review recent developments in fine dry grinding of iron ore and to discuss the various design and operating parameters involved. Although dry grinding of raw feed and clinker has been practiced in the cement industry for many decades, its significant application to the iron ore industry has taken place within the past ten years. Even though the basic concept of dry grinding has been borrowed from the cement industry, the successful application to iron ore grinding has not taken place without some difficulties. Consequently, the application to iron ore has required the solution of several unique design and operating problems.

Jan 1, 1970

By J. D. Miller

Pilot-scale tests indicate that effec¬tive concentration of fine gold from Colorado River sands can be achieved by flotation with the air-sparged hydrocyclone. The fine sands (55% minus 400 mesh and 0.01 opt*) from gravity concen¬tration were processed with a 5-cm air-sparged hydrocyclone (capacity -1.0 tph dry solids). Concentrate grades as high as 5.0 opt were produced in a single stage at a recovery of 75.0%. The separation efficiency was significantly better than that achieved in conventional batch flotation experiments.

Jan 1, 1985

Fine Gravity Separation in the Reflux Classifier, Exploiting a High Shear Rate, Laminar Flow Mechanism The Reflux Classifier is used in the gravity separation of particles over a broad range of particle sizes. The device consists of a fluidised bed zone, with a system of parallel inclined channels above. The inclined channels provide a significant hydraulic advantage over conventional fluidised beds via the so-called Boycott Effect (Boycott, 1920). This paper describes a new advance in fine gravity separation based on the high shear rate and laminar flow profile that arises when closely spaced inclined channels are deployed. As reported recently (Galvin et al, 2009a), a powerful density based separation mechanism develops from this arrangement, suppressing the effects of particle size. In this paper we focus on two areas, firstly the application of the separator in the laboratory for batch fractionation of particles of varying size and density to determine the grade recovery curve and hence the liberation, and secondly the step change in separation performance achieved on a continuous steady state basis when closely spaced inclined channels are used. The variation in the separation density with particle size decreases significantly, and the Ecarte Probable Error (Ep) remains at low levels over a broad size range.

Sep 13, 2010

By Jan D. Miller

Under the name given to this column, I almost feel obliged to write about some aspect of grinding, but I have decided instead to comment on the future of chemical processing. In recent years, I have seen a tremendous interest in extractive metallurgy develop among undergraduate and graduate students at the University of Utah. For example, of the 12 graduating seniors this year, over half seem to prefer extractive metallurgy to physical metallurgy. In particular, they seem to be most interested in hydrometallurgy, or chemical processing, obtaining industrial exposure to the phenomena they study via part-time employment at the Kennecott Research Center and the USBM Metallurgical Center in Salt Lake City. The stimulus has been generated by society itself. Many students are dedicated to the proposition that new technology can circumvent the destruction of our environment, a concept which provides considerable motivation. At the governmental level, the recent concern for the quality of our environment has created action in the area of chemical processing both through imposition of stringent air and water quality standards, and through increased funding for technological research in this area. The National Academy of Sciences (NAS) gave impetus to this movement when it pointed up the need for development and support of such disciplines as extractive metallurgy, particularly chemical processing, in a recent report on Mineral Science and Technology. The recommendations in the NAS report have prompted governmental action on many fronts, including the Bureau of Mines, and have also given rise to direct legislation in the form of two bills -H. R. 3492 and S. 635- presently before Congress to a mineral engineering education. The report recommends that chemical processing technology (more generally extractive metallurgy) be developed by both new engineering techniques and unconventional chemical techniques such as application of the chemistry of nonaqueous liquids to mineral systems.

Jan 1, 1971

By J. M. Karpinski

The need for standard test methods in the minerals beneficiation industry is growing with the increasing complexity of our processes and the more stringent requirements imposed on the quality and uniformity of our products. Although solutions of our problems have never been easy, they will become increasingly difficult to achieve unless we can develop a reliable and reproducible set of test methods. Historically speaking, our need was greatest for methods of chemical analysis. As these methods developed, they improved our ability to determine the grade of ore and measure the effect of our beneficiation attempts. The entire concept of grade and recovery is only as old as chemical analysis. Then came physical measurements. Each new concept in minerals beneficiation was related to certain properties and required corresponding test methods: specific density for jigging, magnetic susceptibility for magnetic separation, and tumbler strength for pellets. And associated with each process was the need for size determination. Size measurement is probably the first physical test ever conceived, and yet we are still improving on it. Dry sieving was quite acceptable for direct-shipping ores, but we had to go to wet sieving to control pelletizing and flotation. Subsieve analyzers have extended our routine measurements to the subsieve sizes, hut not below a few microns. As we all know, the solution of slimes- beneficiation and pollution-abatement problems is hampered by the lack of reliable and reproducible test methods in the fine-particle size range.

Jan 1, 1971

By E. J. Duggan

CLIMAX ore is an altered and highly silicified granite, about half of the gangue being quartz. Molybdenite is the only mineral recovered and most of it is intimately associated with the quartz in fine veinlets. Other minerals are molybdite, pyrite, and chalcopyrite. Although the molybdite may be readily extracted by hydrometallurgical methods, its content is too low to make this profitable. The pyrite ranges from 2 to 5 per cent and the chalcopyrite from 0.03 to 0.05 per cent. There is not enough copper to make its recovery attractive and one of the problems is its elimination, and that of pyrite iron, from the final product. On account of the high degree of dissemination of the molybdenite and the necessity of eliminating the iron and copper, fine-grinding followed by flotation is the only known feasible method of concentration. Two factors, peculiar to Climax ore, have a predominating influence on the metallurgical attack: (1) Molybdenite is one of the most easily floated minerals. High recoveries may be made with pine oil alone if the

Jan 1, 1946

By Graham Davey

"Low speed stirred milling has been employed for many years in the metalliferous and industrial minerals industries. High speed stirred milling is a relatively new method of grinding in the metalliferous process industries. However it has been it has been in wide spread use in the industrial mineral field for over 30 years for various minerals. Many existing metallurgical operations are looking to maximize economic return from existing deposits, requiring new thinking and technologies. By combining low speed and high-speed milling fine and ultrafine grinding efficiency and operating costs can be improved.The correct selection of different fine grinding technologies is covered, when each mill is applicable and when a combination of the VERTIMILL® Grinding Mill and SMD provides the best economic solution.INTRODUCTIONUltra-fine grinding of minerals has been in wide spread use in the industrial mineral field for over 30 years. Within the last 10 years the metalliferous industry has shown interest in the ability to produce ultrafine particles, as chemical, physio-chemical and physical separation processes have advanced to be able to treat ultrafine metalliferous particles. Also as the primary mineral deposits, around the world are depleted, new more difficult deposits must be mined. Existing operations are also looking to maximize economic return from existing deposits, requiring new thinking and technologies.The traditional approach for gold containing refractory material has been to liberate the locked gold by chemically destroying the pyrite through oxidation. Roasting, pressure oxidation, and bacterial oxidation all employ various degrees of temperature, pressure and catalysis to react the pyrite with oxygen to produce iron oxide and sulfur by-products. However all of these methods are economically impacted due to specific operational added requirements and emissions controls. Pressure and bacterial oxidation have very high capital and operating costs."

Jan 1, 2006

By Fred T. Towne

Recent developments in fine grinding by the means of mechanical impaction are the result of continuing improvements in modern machine construction. This is especially true when related to the bearings and mechanically operated parts of impact mills. These improvements allow manufacturers to increase the speeds of the impacting members Most of the more common forms of size reductions, such as percussion, pressure, friction and sectioning, or cutting were at one time accomplished by human hands. These actions were transferred to machinery. Originally of limited application, their use widened as industrial materials and construction became more sophisticated.

Jan 1, 1965