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I HAVE striven to demonstrate to you as well as possible the method of bringing the metals of your ores to their ultimate perfection. But one cannot always do with gold that is found in the ores what is done with the other metals, for gold is not always accompanied by fine silver nor is it

Jan 1, 1942

By W. W. West

MACHINERY used for size reduction of materials may be divided into three classes-depending upon the manner in which the crushing force is applied. In the first class could be listed the primary crushing units, such as the jaw crusher and gyratory crusher-which crush to coarse sizes by applying pressure intermittently between converging surfaces. In the second class may be listed crushing units, such as the hammer mill, roller mill, and ball mill, which crush principally by grinding or attrition. In the third class is the impact mill which, as the name infers, crushes by impact. The second and third classes generally include machinery used as secondary units for intermediate or fine crushing and grinding. Theory of Crushing by Impact Throw a stone into the air and give it a severe blow while it is momentarily suspended, and it shatters into several pieces. The impact crusher uses this "batting" principle, but carries it one step further. As the material to be reduced enters the crushing chamber, it receives a severe free-air impact blow by hard-hitting beaters suspended from rotor discs. The shattered particles formed are then driven at high velocity against impact blocks, where a further reduction in particle size takes place. The rebounding particles from the impact blocks are again caught by the beaters, and the process repeated until the material is swept out of the open bottom of the crusher. Impact Crushing Versus Attrition Crushing Fig. 1 shows a Hammermill type of attrition crusher. This particular mill has central feed and is reversible. Because of the central feed, an impact section can be designed into it at the feed entrance for preliminary crushing, followed by the cage bar attrition area for final sizing. The material is caught and held in a crushing chamber enclosed by grate bars or perforated plate. It remains in this chamber until it is reduced to particle size small enough to pass through the openings between the bars or in the plate. In this manner the top particle size discharged from the mill is closely controlled. As the swinging hammers pass through the bed of material, the material is broken down by a scrubbing action between hammers and material, material and grate bars, and material against material. This attrition produces a rounded particle shape, accompanied by slivers and a comparatively high percentage of fines. The crusher is especially useful in industries where the material treated is not too abrasive, such as limestone, cement or coal plants. It can be readily understood that from the maintenance standpoint, it is not suitable for hard abrasive materials such as refractories and aluminum oxides. One common type of impactor is shown in Fig. 2. The bottom of this type crusher is entirely open and the passage of the material through the crushing chamber is almost instantaneous. Liberal clearances are maintained between the impact hammers and the anvil type breaker blocks. This eliminates practically all attrition. It is the elimination of attrition that makes the impactor particularly adaptable for reducing hard, abrasive materials. The impactor is also well suited for the reduction of wet or frozen materials, which clog an ordinary Hammermill. Particles broken by impact, when examined under the microscope, show a distinct tendency toward rough, cubical shape, with a minimum of fines. Another important factor in impact crushing is that crushing is accomplished along natural cleavage lines, thus freeing foreign ores or materials.

Jan 1, 1952

By Robert B. McCormick

World War II has developed a use for the nonmetal mineral quartz crystal that was unknown in World War I. During the interim period of peace, experimental work in the radio field with the piezoelectric properties of quartz crystal resulted in the almost universal adoption of quartz-crystal radio oscillator plates to control frequency in radio broadcasting, police, commercial and amateur communications equipment. Telephone resonators and filters made from quartz crystal also were developed, which vastly improved the frequency control of long distance telephone circuits. Expansion of the Industry The sudden war demands of the armed services for radio equipment using quartz crystal for frequency control led to an unprecedented expansion of the manufacturing industry. It is estimated that the 1940 peacetime volume amounted to approximately $1,500,000, while today a vast new quartz-crystal industry supplies more than $150,000,000 worth of quartz oscillator plates to the Army and Navy each year. This demand has caused an enormous expansion not only of American manufacturing facilities but also of Brazilian mining output, virtually our only source of raw quartz crystal. Actual figures of imports and consumption cannot be cited, for security reasons, but certain comparisons have been made, which indicate the transformation of quartz crystal from a minor to a major nonmetal. Lundl has shown that the value of quartz-crystal exports from Brazil is now about equal to that of phosphate rock produced domestically in 1941 and actually exceeds the combined value of crude feldspar, gypsum and fluorspar production in the United States in the same year. This great expansion under wartime pressure was not accomplished without some anxious moments, but all the demands of industry have been met and the Government has been able also to accumulate a substantial stock pile of material against future contingencies. Inspection and Grading of Quartz Crystal The swift growth of the quartz-oscillator industry necessitated the simultaneous evolution of methods and criteria for inspecting and grading quartz crystal. It has been found that, generally speaking, it is economically feasible to cut only crystals that are at least 30 per cent by volume free from major defects such as optical and electrical twinning, cracks and fractures. Blue needles, bubbles, "chuva" and other minor imperfections can be tolerated in the usable portion unless present in great excess. The present marketing system in use in both Brazil and the United States, as far as quality is concerned, depends solely on the "usability" of a crystal, which is defined in the Brazilian-American agreement2

Jan 1, 1948

By Robert B. McCormick

World War II has developed a use for the nonmetal mineral quartz crystal that was unknown in World War I. During the interim period of peace, experimental work in the radio field with the piezoelectric properties of quartz crystal resulted in the almost universal adoption of quartz-crystal radio oscillator plates to control frequency in radio broadcasting, police, commercial and amateur communications equipment. Telephone resonators and filters made from quartz crystal also were developed, which vastly improved the frequency control of long distance telephone circuits. Expansion of the Industry The sudden war demands of the armed services for radio equipment using quartz crystal for frequency control led to an unprecedented expansion of the manufacturing industry. It is estimated that the 1940 peacetime volume amounted to approximately $1,500,000, while today a vast new quartz-crystal industry supplies more than $150,000,000 worth of quartz oscillator plates to the Army and Navy each year. This demand has caused an enormous expansion not only of American manufacturing facilities but also of Brazilian mining output, virtually our only source of raw quartz crystal. Actual figures of imports and consumption cannot be cited, for security reasons, but certain comparisons have been made, which indicate the transformation of quartz crystal from a minor to a major nonmetal. Lundl has shown that the value of quartz-crystal exports from Brazil is now about equal to that of phosphate rock produced domestically in 1941 and actually exceeds the combined value of crude feldspar, gypsum and fluorspar production in the United States in the same year. This great expansion under wartime pressure was not accomplished without some anxious moments, but all the demands of industry have been met and the Government has been able also to accumulate a substantial stock pile of material against future contingencies. Inspection and Grading of Quartz Crystal The swift growth of the quartz-oscillator industry necessitated the simultaneous evolution of methods and criteria for inspecting and grading quartz crystal. It has been found that, generally speaking, it is economically feasible to cut only crystals that are at least 30 per cent by volume free from major defects such as optical and electrical twinning, cracks and fractures. Blue needles, bubbles, "chuva" and other minor imperfections can be tolerated in the usable portion unless present in great excess. The present marketing system in use in both Brazil and the United States, as far as quality is concerned, depends solely on the "usability" of a crystal, which is defined in the Brazilian-American agreement2

Jan 1, 1948

By Louis Moyd

In the preparation of illustrations to accompany reports of investigations concerning particle shapes of various natural and manufactured materials proposed for use as he aggretates in concrete structures, it was found that stereoscopic views of such materials presented the information much more effectively than the usual two-dimensional photographs. With the whole-hearted cooperation of the Photographic Section, a technique was developed in the petro-graphic laboratory of the Concrete Research Division, U.S. Corps of Engineers, at Clinton, Miss., for simple and rapid preparation of paired stereoscopic photographs and micrographs. The method requires only equipment which is usually part of the general stock of any laboratory, and it is adaptable for all purposes in which three-dimensional views would be found superior to ordinary photographs. Stereoscopic Photographs Where the subject or subjects to be photographed are small but not of microscopic size, an ordinary camera having a ground-glass focusing screen is set up vertically over the field. The material to be photographed is placed on a card, the surface of which is suitable as a background. The card is mounted so that it can be tilted about 5' above and below the horizontal plane, on an axis that coincides with the north-south diameter of the viewing screen. A simple way of achieving this is to mount the card on an object having a convex lower surface. In our laboratory, a watch-glass has been used, with plasticene as the mounting medium. The convex surface should be mounted on a support having a round opening on top and a flat bottom. A roll of tape, a petri dish, a beaker, or any other piece of equipment having the proper shape to give stability to the setup will be satisfactory. The arrangement of the required equipment is shown in Fig 1. For the best results, the subject to be photographed should be mounted in the plane of the axis of rotation. To achieve this effect, the depth of the mass of plasticene between the background and the watch-glass is varied so that when the watch-glass is tilted back and forth on the axis, the subject to be photographed does not appear to move back and forth across the viewing screen. A permanent piece of equipment, embodying an adjustable vertical screw, with lock-nuts, could be made for this purpose. The subject may be illuminated in any manner desired. It was found that the presence of shadows intensifies the effect of depth. In taking the photographs, the concave surface is mounted so that one side of the background card is about 5' below the horizontal, while the axis remains in the horizontal plane. The subject is focused carefully on the ground glass and a picture is taken. The card is then tilted so that the opposite side is about 5' below the horizontal, while the axis still remains in the horizontal plane. The subject is again put in focus and another picture is taken. After both pictures are developed and printed, they are placed side by side in the same orientation and examined with a stereoscopic viewer. If depressions appear where there ought

Jan 1, 1950

By AIME AIME

CHARLES WASHINGTON MERRILL, the second to be honored by the award of the James Douglas gold medal, throughout his entire professional career has been identified with the cyanide method of extracting gold from ore. To his efforts this branch of the metallurgical industry owes a large measure of its success in continuing to treat some gold ores profitably, in spite of economic adversities. Mr. Merrill was born at Concord, N. H., Dec. 21, 1869, and received the degree of B. S. from the School of Mines at the University of California in 1891. Among his first professional connections was the Standard Mining Co., at Bodie, Cal., followed by a short engagement at Harqua Hala, Ariz. From 1895 to 1899 he was connected with the Montana Mining Co., at Marysvale, Mont., and then followed his nine years of fruitful association with the Homestake Mining Co. In 1909, the Merrill Co. was formed, to exploit more than a score of patents granted to Mr. Merrill, covering various phases of the cyanide process and numerous pieces of equipment for its operation; among the most noteworthy of these innovations were the Merrill filter-press, and the use of zinc dust as a precipitant. The Merrill Co. has a long record of successful accomplishments in its chosen field, to mention only the plants at the Dome mines of Ontario and at the Sta. Gertrudis mines of Mexico as among the more recent. Mr. Merrill is president also of the Western Ore Purchasing Co.; and a director in two gold dredging companies of California.

Jan 1, 1924

By N. Brown

IT has been observed that a hexagonal-close-packed crystal will undergo the same macroscopic displacements as an isotropic material if the basal plane is perpendicular to the axis of twist.&apos; Other orientations may produce both bending and twisting, but this analysis will be confined to pure torsion of a right circular cylinder. The z axis, the axis of twist, and the specimen axis are coincident. The displacements are given by Uq = rz, Ur = Uz = 0 [1] where 4 is the angle of twist per unit length. This requires rotational slip, as discussed by Frank&apos; and Wilman, which may be observed readily. The relative rotation of adjoining slip planes is simply produced by a movement of a planar grid of screw dislocations."." The screw dislocations are of the same sign and they move radially inward. For hexagonal-close-packed metals, the grid is hexagonal and the screw dislocations lie in the < 2110 > directions. The displacement of a point is the resultant of two displacements produced by intersecting screws sweeping over the point. The dislocations must pass over the point (r, o) in such a manner that its resultant displacement corresponds to the observed macroscopic displacement. If 6&apos; is measured from the [1010] direction, then for 0 < ? < ~/3, only the [1210] and 121101 type screw dislocations are needed to produce the required displacement. If n1 screws of type [1210] and n2 of type [2110] pass over a point, then, in order that Ur = 0 n, sin ? - n2 sin (/3 — 6&apos;) = 0. [2] If the tangential displacement is to be independent of 0, then n1 cos ? + n2cos (/3 —?) = N [3] where N is independent of ? and thus depends only on r. Nb is the tangential displacement where b is the Burgers vector. Since U? is a linear function of r, then N must be a linear function of r. If a2 is the outer radius and a, is the inner radius to which the plastic deformation has extended, then N = Nm2 r-a1 [4] This function meets the conditions that at

Jan 1, 1956

By Vincent P. Gianella

Barite deposits are of widespread occurrence in Nevada but there are few producing properties; most of the latter are in northern Nevada. The production of the state is small at present-in the neighborhood of 15,000 tons annually-but is steadily increasing. The barite occurs in veins and also as replacement deposits in limestone. The bulk of the production has come from the replacement deposits. It is thought that the barite was deposited from rising hot waters similar to-and probably contemporaneous with-those responsible for some of the metallic ores of the state. This paper discusses only the deposits in northern Nevada. THE commercial mining of barite did not begin in Nevada until 1916 but although the production has been small there has been a rapid increase in tonnage during the past several years. Barite is widely distributed in the state and production comes from at least nine of the seventeen counties. Apparently this is not generally known, as only two counties are mentioned in a recent publication6 dealing with barite. The increase in output is due largely to recently discovered barite deposits in northern Nevada. The principal production has come from the northern portions of Lander and Eureka counties; smaller amounts from Elko County. The discussion in this paper is confined largely to the deposits in these counties. Most of the producing area is tributary to the Western Pacific and Southern Pacific Railroads, whose tracks lie along the Humboldt River. Barite is known from other northern counties but so far the production has been small. The output has come entirely from veins and replacement deposits, the latter largely in sedimentary rocks. In general, the barite from veins is white; that from the replacement deposits usually is dark gray to black, although some is light gray or white. Most of the veins contain sulphides and many barite-bearing veins have been worked for their content of base or precious metals. PRODUCTION The recorded production in Nevada to the end of 1938, according to the U. S. Bureau of Mines,3 is 66,424 short tons, of which 57,157 tons

Jan 1, 1940

Jan 1, 1906

By R. D. Reiswig, D. J. Mack

THE use of pyrophoric alloys in ignition devices dates back more than fifty years to a German patent granted to Carl Auer von Welsbach in 1903.&apos; This patent named a composition essentially the same as that used in most present-day cigarette lighter "flints:" 70 pct mischmetal, 30 pct Fe, referred to here as "Auer alloy." Among the few current exceptions to this composition are those "flints" based on titanium or zirconium. The rare-earth metals of which mischmetal is composed are so similar chemically and physically remarkable similarity in their alloying behaviors would be expected. Comparison of the binary phase diagrams2 of these elements with nonrare-earth metals shows that this is true to a striking degree, so much so, in fact, that it appears that a mixture of these elements may be treated as a single component of alloys without fear of serious error. In considering alloys containing mischmetal, therefore, the mixture of rare-earth elements will be referred to merely as "cerium," the predominant element in mischmetal. In polishing cerium alloys for metallographic examination, it was soon discovered that aqueous polishing media were highly corrosive. Free cerium in the alloys acts similarly to calcium (though not quite so rapidly) in evolving bubbles of hydrogen at the metal-water interface; thus, special metallographic techniques are required. The simplest polishing technique found to be satisfactory consisted of slow hand grinding on dry emery papers through

Jan 1, 1956

By John A. Hosking

The recent activity of numerous foreign mining companies in the once flourishing tin fields in Cornwall, England has resulted in renewed interest in the evaluation of hypothermal tin deposits. These deposits are mainly narrow tabular bodies and are usually steeply dipping. They exhibit thermal zoning the mineralization changing from lead/zinc through copper to tin with depth. The tin zone virtually never exceeds 1,000&apos; in depth and the ore shoots within this zone tend to be erratic and localized. The grade which is presently considered to be economic is about 0.7% Sn. , this means a concentration of about l% cassiterite (the only economic mineral) which, being twice as heavy as the gange, represents only. 5% of the lode volumetrically. Within the lode, only one third may reach this economic grade and values within the shoots can range from 100% cassiterite to zero over a few inches. The enormity of the problem of evaluating such a deposit has not been fully appreciated by the companies involved whose experience has, for the main part, been in larger and more predictable ore bodies. This paper attempts to put these problems into perspective and out- lines the useful applicatations of statistical and computer techniques. It also stresses the need for enlightened interpretation of data by men familiar with the problem and that even in this day and age, educated, intuitive deduction should not yet be relegated to the limbo of alchemy and witchcraft.

Jan 1, 1969

HENRY FAY, Cambridge, Mass. (written discussion *).-Mr. Rawdon has made a distinct contribution to our knowledge of wrought iron, and .perhaps of steel. It will undoubtedly lead to more careful scrutiny of high-phosphorus steels, with perhaps important results. In view of his results, it would seem to be unprofitable to push further any propaganda on the use of higher-phosphorus low-carbon steels until further information is available. As is well known, and as Mr. Rawdon clearly shows, the process of solidification is a selective one, and there is abundant opportunity for those portions of the melt last to solidify to become rich in phosphorus, and the diffusion of this phosphorus-rich area is slow. Hot work does not help the situation appreciably and only serves to concentrate the low-melting material. It is undoubtedly true, as some writers have recently claimed, that the specifications for steels as they. now exist eliminate some perfectly good material. Higher phosphorus in steel may be perfectly safe provided all of the phosphide is completely and uniformly, diffused in the solid solution. If, on the contrary, it is not evenly diffused, and there is a reasonable chance for it not to be, it makes the steel unsafe. Until our knowledge: of the rate of diffusion of phosphorus in steel, and the effect of other elements upon the rate, is more complete, it seems to me unwise, in view of Mr. Rawdon&apos;s experiments, to listen to the recommendations for the use of higher-phosphorus steels.

Jan 1, 1918

By Anne Nicholson Hird, H. A. Schwartz

Of the outstanding investigators of the system iron-carbon-silicon Gontermann,1 Charpy and Cornu-Thenard,= and Honda,3 only the first touched on the chemical composition of the solid and liquid phases in equilibrium with one another. He concluded that his data did not permit a decision as to which of an indefinitely large number of pairs of compositions of liquid and solid would be found in any given case. If through the three dimensional equilibrium diagram of the iron-carbon-silicon system an isothermal plane is passed in the region of partial solidification, two lines of intersection with the liquidus and solidus, respectively, are obtained, also a point marking the alloys&apos; composition. If, in this plane, a straight line is drawn through the point, and intersecting both the liquidus and solidus isothermals, the two intersections mark a liquid and a solid alloy that may be chemically in equilibrium at the chosen temperature. From thermal data alone, Gontermann could not assign any particular direction to the line and, hence, could not determine which pair of conjugate points to choose, A separation of the liquid and solid for analysis, obviously, presents grave experimental difficulties. During the solidification of white cast iron, austenite of progressively higher carbon will separate as the temperature falls and cementite will appear suddenly at the freezing point of the eutectic. This cementite will be accompanied by a corresponding amount of austenite which, for our purpose, will be chemically inseparable from the primary austenite. We have attempted to decide on the conditions at the end of the freezing by a chemical separation applied to the solid metal.

Jan 1, 1925

By John V. Beall

If there is one thing that makes a fellow feel like the years are catching up with him, it is to go through a second cycle in which the adequacy of mineral resources is being "viewed with alarm." The first time we experienced such a flap was in 1951. At that time, the United Nations convened a meeting at Lake Success to study ways and means of averting a crisis in minerals. Presently there is some sentiment being expressed about the mineral scarcities that will occur in the decades ahead, in view of world population trends and increasing per capita consumption of metals. To be greatly concerned about the adequacy of metal supplies is to be highly pessimistic about the capabilities of technology. As in the past, shortages will be of temporary duration for as far ahead as the most ambitious prognosticators are projecting. The study of mineral economics is a fascinating and surprising subject. The law of supply and demand is but a starting point. The iron ore market for the steel industry is an example which comes to mind because of our receipt this week of the United Nations report "Survey of World Iron Ore Resources."

Jan 1, 1970

By G. A. Burrell

A gasoline recovery plant at a refinery is usually considered such a profitable investment, and performs so well apparently, even under conditions of low efficiency, that frequently but little attention is given it to make it perform at top efficiency. Further, there are so many other units in a refinery that demand most of the available attention that the recovery plant is left to shift for itself. "It seems to be doing pretty well so why bother with it," is sometimes the attitude toward it. On the other hand, there is no reason why it should not be placed on the same high plane of efficiency as that of many natural gasoline plants. The two problems, gasoline recovery from natural gas and gasoline recovery from refinery gases, have much in common. At some refineries the gasoline recovery plant produces too much gasoline, because too low a pressure is carried on the gathering lines and the condenser boxes are robbed of gasoline that they can and should take care of, and as a consequence the refiner fools himself into believing that his recovery plant is an extraordinarily fine unit, when on the contrary it may be working at low efficiency insofar as doing its rightful job is concerned.

Jan 1, 1928

By J. R. Finlay

THE other day, I fell into conversation with two gentlemen who desired to improve the condition of the people; so that the talk was semi-political. They seemed to agree that I was inclined to be "con-servative," "reactionary," perhaps an "evolutionist," looking upon "reform" with suspicion. Finally I rejoined somewhat in this manner: "You attach to me phrases that I have heard all my life but which convey no meaning to me. It is quite true that I do not make a fetish of terms like reform, liberty, democracy and so forth; neither do I worship the idea that `things are good enough as they are,&apos; `leave well enough. alone&apos; and so forth. There is more satisfaction in building something up than in tearing something down, or in just maintaining something that is already built. Progress is a popular word; but what is progress? In my opinion it is comprised, so far as public welfare is concerned, of two elements: Improvements in production of goods and knowledge; improvements in keeping order." This substitute for politics, economics, reform, pro-gress, conservatism, radicalism, democracy, socialism, monarchism and all the phrases of public welfare may seem over-simple; perhaps it is, but at least it defines something. It seems to me to be at least worth attention.

Jan 4, 1922

By Richard McCaffery

THIS paper considers certain aspects of the acid Bessemer process, particularly in its relations to the duplex process-that combination in which the pig iron is first desiliconized and decarburized in acid Bessemer converters and then dephosphorized in basic open-hearth furnaces. The acid Bessemer process employs an acid-lined converter and produces an acid slag. The blow is usually thought to eliminate the silicon and manganese as oxides and then to burn off the carbon as carbon monoxide. On account, however, of the relatively large amount of metallic iron present in the converter, compared with the relatively small amount of the impurities it is desired to oxidize, the first reaction in the converter probably is the formation of iron oxide, which dissolves in the bath and acts as an oxygen carrier for the silicon and carbon. As soon as iron oxide is dissolved throughout the bath, the oxidation of silicon commences; but in the early stages of the blow the mass law would indicate that iron oxide must form first, and this oxide probably increases up to some saturation point. The molten metal in the converter from the early stages of the blow right through to its completion remains basic, while the slag produced is siliceous. This fact is shown by the corrosion of the acid bottom and the tuyeres, which is greatest at the tuyere orifice where oxidation is most active and where there is the most iron oxide. Why does this acid bottom corrode? Because it is attacked by a base. The thought, therefore, suggests itself, why not make the bottoms of basic or neutral material?1 As the converter slag is acid, those parts of the converter coming in contact with the slag should be acid; but those parts of the converter that are in contact with the molten metal saturated with metallic oxides should be basic or neutral. Bessemer operators have for some time tacitly admitted this condition, for the blast pressures have steadily increased with the object of keeping the metal in suspension, and so preventing bottom corrosion; if the molten metal were not basic, it would not attack an acid bottom. In addition, the tuyeres are bunched together at the middle of the bottom and a clear space is left around the outside of the bottom; if tuyeres are placed too near the side walls the

Jan 8, 1920

By W. F. McDermott

This is the dawning of the computer age in process control. As 1968 drew to a close, many plants had computer installations which were being used for logging, monitoring and reporting. Today, computer usage is given serious consideration before the construction of any major minerals processing plant. Unitized automatic control of individual processes is abundant. Many plants are considering closing these control loops, i.e., allowing the computer to direct the operation of the controllers (Digital Analog Control-DAC). The next step is to make the computer itself the controller (Direct Digital Control-DDC)1 Perhaps the most important future use of computers will be in controlling interrelated operations and control units. Progress along these lines depends on the steadily improving capabilities in the field of mathematical modeling.

Jan 1, 1970

By L. S. Kolbert, C. H. Baab

Introduction In June 1981, the Electric Power Research Institute (EPRI) issued a report titled "Control Systems in Coal Preparation Plants" to determine the status of instrumentation and automation systems in the coal preparation industry. EPRI concluded that the control systems presently being employed in the US coal preparation plants "are relatively primitive compared with those in other mineral processing industries; and analytical instrumentation is virtually non-existent." With tighter specifications on the quality of steam coal, interest is increasing in more sophisticated control systems. One type of device that is currently assisting the preparation plant operator optimize and control the coal cleaning process is nuclear based instrumentation. Nuclear instrumentation includes methods for measuring weight, level, and density as well as for performing elemental analysis on coal. Major Features and Benefits of Nuclear Measurement and Analysis Systems There are many features and benefits of nuclear instrumentation. The major benefit is that nuclear instrumentation is non-contacting. The measuring heads do not contact the process materials. This enables measurements of corrosive, abrasive, or high temperature materials with no loss of performance, reliability, or useful life. Also, there are no moving parts to wear or be fouled by dust or corrosion. Installation is simple and inexpensive. For instance, density gauges are simply clamped onto existing pipe runs. Weigh scales and level switches usually require nothing more than welding brackets to customers&apos; equipment. Once installed, routine maintenance can be performed without interrupting the process. Thus, nuclear instrumentation is highly reliable and easily installed and maintained. The operating life of the instrumentation is virtually unlimited. Principle of Operation Nuclear belt weigh scales, point level switches and density gauges all operate on the gamma-ray transmission principle. A beam of gamma radiation from a radioisotopic source is projected through the process material either on a belt, in a vessel, or in a pipe. Opposite the source is a radiation detector whose electrical output is proportional to the intensity of the radiation it absorbs. Gamma radiation is part of the same electromagnetic spectrum that encompasses light, infrared, and x-rays. In many respects, gamma radiation behaves much like light. However, it is far more penetrating and can be transmitted through considerable thickness of materials that are opaque to visible light, e.g., several inches of steel. Types of Nuclear Instrumentation in Coal Preparation Plants There are four types of nuclear instrumentation presently being employed in coal preparation plants. They are: •Belt Weigh Scales •Point Level Switches •Density Gauges •Coal Analysis Equipment. Each type of instrumentation has a number of potential applications within the plant. What follows is a discussion of three different types of devices and their applications. Weigh Scales In coal preparation plants, weighing instruments are used for measuring material throughput, totalized weight, and batch weight on conveyor belts and other transport equipment. They are also used on drag chain conveyors, vibrating conveyors, and screw conveyors. Weighing is important for receiving the run-of-mine coal, controlling mass flow, scheduling production, and loading and shipping the washed coal to market. There are two basic types of weighing instruments: gravimetric and nongravimetric devices. Gravimetric devices are units which measure the pull of gravity on the material being weighed. Nongravimetric devices are not dependent on the force of gravity on the sample. Nuclear weigh scales are the most prevalent nongravimetric devices used. The nuclear weigh scale works on the same basic principle as other nuclear gauges. The greater the quantity of material placed in the path of a radiation beam, the more radiation will be absorbed by the material. In weigh scales, Cesium 137 source is generally placed above the moving stream of material so that the radiation is directed through the material. An ion chamber radiation detector is on the opposite side of the material. The radiation passing to the detector generates a signal which is inversely proportional to the weight of the material present. This signal is amplified and integrated with the speed of the process flow yielding the weight. The weight is indicated and can be totalized for throughput, batch control, etc. In conclusion, radiation weighing methods have become well established in the coal preparation industry throughout the world. As mentioned before, this device finds its most

Jan 1, 1985

By Robert R. French

Beneficiation of low-grade nonmetalliferous mineral deposits by electronic color sorting is currently undergoing a period of rapid development. For those deposits in which the specific gravity, strength, soundness, and electric and magnetic properties of the ore and gangue are similar, the possibility of separation by color, reflectivity, or fluorescence offers hope for the utilization of much poorer quality ore than previously thought possible. For those ores in which consistency of color is required or for which a dry process is preferred, the electronic color sorter is particularly adaptable. Tests performed late in 1966 and reported herein are the result of the continued interest in the dry beneficiation of gypsum and the development of higher capacity color sorting machines. The ore used was a discarded fraction that consisted of – 1 ¼ -in, to + 3/8 -in. ore containing 63.1 to 71.4% (average 67.7%) gypsum. This material was contaminated by various amounts of both carbonate rock and shale, but no pretreatment was performed other than screening to closer size limits before electronic color sorting.

Jan 4, 1969