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By G. S. Rice

Some form of longwall mining is generally used in Continental Europe; also in Great Britain where the coal is weak and friable, or the coal bed provides material for pack walls and filling, or where the bottom is soft and squeezes up easily, or the roof is pliable, or the bed is thin and brushing provides building material, or the thick multiple seams are mined in layers, such as the 24-ft.seam at Weymss, Scotland, or the 10-yd. pitching bed near Coventry, England. Pillar methods have been retained in British fields where the coal beds are from 5 to 9 ft. (1.5 to 2.7 m.) thick, and free from thick partings or binders or without draw slate, which would provide waste rock for pack walls, or where the roof is hard and requires shooting to bring down, and also the bottom or floor is comparatively hard. The room-and-pillar system, by which probably 95 per cent. of the coal of the United States is produced, is now found in only a few mines in Wales, where it is known as the pillar and (single) stall method. The American room-and-pillar system is not equivalent to the bord-and-pillar or stoop-and-room system. The essential difference between the bord-and-pillar and the average American room-and-pillar system is probably due to natural conditions. The majority of the coal mines in the United States have a depth of less than 700 ft. (213 m.). The bulk of the coal mined in Europe comes from a depth of more than 1200 ft., while the deepest mines in Great Britain, Belgium, and France reach 3500 to 4000 ft. In deep workings wide spans are impracticable, even with the use of abundant timber; accordingly, as the mines in the United States become deeper the rooms will become narrower and the pillars thicker, and the bulk of the coal will be extracted on the retreat. It is generally conceded, without reference to the cost of production, that the larger the pillars left on the first mining, the more thoroughly can the coal be extracted. In Europe complete extraction is generally compelled either by the lessors or by the governments; whereas in this country it has been more largely a question of competitive cost of production, or the support of the surface in the flat farming districts of the

Jan 1, 1922

By G. D. Arsdale

This paper describes a series of experiments leading to the development. of a method for leaching the mixed ores of the Inspiration Consolidated Copper Co., containing chalcocite and silicates of copper, by the use of solutions acidified with sulfuric acid and carrying ferric sulfate. Iron is added to the solutions and ferric iron is regenerated electrolytically to a percentage high enough to act as an efficient solvent. The decreased yield is partly compensated for by a higher current density. AN IMPORTANT problem in modern copper metallurgy, particularly in the Southwest, has been to obtain good recoveries from what are commonly known as mixed ores; that is ores in which the copper occurs partly as oxide and partly as sulfide compounds. The dividing line between mixed ores and ores commonly accepted as concentrating is not definite. In other words, much ore now being concentrated carries considerable copper in non-sulfide form, on which recoveries are hot so good as on ores carrying less of these constituents. While treatment by concentration may be commercially profitable, on ores carrying oxide copper within certain limits, there are large deposits for which the application of con-centration could not be considered, and yet which have not been considered amenable to leaching because they carried too much sulfide. The Inspiration Consolidated Copper Co. has large amounts of such mixed ores, and this paper is an account of the experimental work by which a method was developed for their treatment, and for which a large plant is now being erected by the Inspiration Co. It is not claimed that the method is a general solution of the problem of mixed-ore treatment but it is apparently well adapted for leaching the ores of the Inspiration Co., for which it was designed. The work done has covered preliminary laboratory and test-plant investigation, and .a pilot-plant run, extending from March to the middle of December, 1923. Thoroughly consistent and satisfactory results, were obtained continuously for more, than six months in the pilot plant; and it is believed that the results; and probable costs that can be had on a large scale have been definitely, proved. The method, however, was designed for local conditions; and while the basic principles are general, there are ores on which it will not work and other ores for which considerable modification may be required.

Jan 10, 1925

By Hallan N. Marsh

The subject of mud sounds so simple, uninteresting and unimportant that it has failed to receive the attention that it deserves, at least as applied to the drilling of oil wells. As a matter of fact, it is one of the most complicated, technical, important and interesting subjects in connection with rotary drilling. In 1923, R. E. Colloml said "It should be possible to establish certain physical standards for mud fluid," but while considerable work has probably been done on the subject before and since that time, and numerous articles have been written, the progress of general knowledge of the subject and the application of better practices have not kept pace with other developments in rotary drilling, and physical standards cannot be considered as established. Mud is apt to be thought of as an accessible and cheap material, but its cost is likely to be an important factor in the total cost of drilling a well. Some wells "make" most of their own mud out of the formations drilled, but in most cases a great deal of mud-making material has to be supplied from more or less distant sources. Expenditures for mud materials by one California company totaled practically one-quarter million dollars during 1929 and averaged about $13 per rig per drilling day, or about $2000 per well. Under unfavorable conditions, mud cost may reach many times this figure. Parker2 says that in the Hobbs, N. M., field "as much as $75,000 has been spent on one well alone for mud and mud-weighting compounds."' Presumably this is an exceptional case. Unit cost of mud fluid will range from 10 c. per barrel, where suitable material is close at hand, to $1 where crude material is available at moderate price but must be hauled long distances, and on up to as much as $11 per barrel where high gas pressure requires the use of special processed weighting material. The cost of mud pales into insignificance, however, when the results of using improper mud are considered. Blow-outs and lost circulation are obviously the result of inadequate mud. Stuck drill pipe, whether or not twisted off, in many if not most cases probably is caused by cuttings settling out of the mud or the mud itself precipitating. Recent experi-

Jan 1, 1931

By James K. Stanley

PREFERRED orientation, particularly in irons and low-carbon steel, is a phenomenon that is both of considerable importance and theoretical interest. At times it is a liability and at other times an asset. In deep-drawing operations, preferred orientation is extremely undesirable because it necessitates trimming operations and increases scrap loss. Furthermore, oriented metals are likely to crack more easily than randomly oriented material because the forming of symmetrical and unsymmetrical shapes out of preferentially oriented metals and alloys increases the probability of rupture in regions of high stress, owing to differential ductility.1 In the electrical industry, on the other hand, preferentially oriented silicon irons are in demand for transformer application because of the improved magnetic permeabilities in the rolling direction.2 This phenomenon of preferred orientation in soft magnetic materials has been responsible for the tremendous improvement in transformer design and construction in recent years. Directional properties in metals have received a great deal of attention in the metallurgical literature,3-9 in which much of the information reported about orientation has been obtained by conventional methods, mechanical properties and X-rays. A wealth of data has been obtained and often at a great expenditure of time. The recent introduction of the magnetic torque measurements on ferromagnetic materials provides a very simple and rapid method of evaluating orientation. The judicious use of the method can supply important in- formation, but it should be borne in mind that such studies must be supplemented by X-rays, optical methods,10 and etch and pressure figures" to get a rational under- standing of the orientation phenomena. No claims are made that the magnetic torque of evaluating orientation will reveal the behavior of the metal in deep drawing. For this purpose the accepted tests for deep-drawing quality must be used. For a good drawing 'stock, which must have low impurities, desirable grain size, ductility, strength, hardness, good surface, random orientation, and good recrystallization behavior, it cannot be expected that any simple test will be satisfactory for appraising all the factors. The only factor on which the magnetic method can be used is orientation, which is, of course, of considerable importance. When directionality can cause a 10 to 15 per cent change in tensile strength and a IOO to 300 per cent change in tear length,12 it goes without saying that a reliable as well as rapid method for detecting these changes would be desirable. There are certain inherent advantages in testing orientation by the torque method: The method is rapid with the proper type of equipment; no elaborate preparation of specimens is required-it is only necessary punch or machine a disk of the sheet material and insert it into the testing device.

Jan 1, 1943

By T. A. Klinefelter

Lightweight concrete aggregates are materials weighing less than the usual aggregates of sand, gravel, and crushed rock. Concretes made with sand and gravel or crushed rock weigh 145 to 150 lb per cu ft, compared with 50 to 90 lb per cu ft for concretes made with lightweight aggregate. The ultra-lightweight concretes weigh much less than 50 lb per cu ft. Lightweight aggregates may be natural or manufactured materials, or byproducts from other commercial operations. Natural materials include pumice and pumicite, tuffs, breccia, scoria, diatomite, and vegetable products, such as peat, straw, and sawdust. Manufactured materials include expanded perlite, vermiculite, slag, clay, shale, and slate. Byproducts include cinders, aircooled slags, and coke breeze. Concretes made with lightweight aggregate were used first in construction of commercial buildings, later in homes. Present usage is general in multistory and other building construction, such as bridge decks, barges, jet-plane runways, piers and other structures. The industry has grown remarkably in the last decade. General Considerations The particular use to which the concrete may be put determines the importance of the various properties of the aggregates employed. Any given type of aggregate, however, should be reasonably uniform in composition and properties. It should be suitably graded and maintain proper weights, insulation values, and adequate strength to prevent breakdowns in mixing. It should bond properly with the cement, be inert to chemical reactions with cement and steel, and resist weathering, moisture, insects, and fungi. Some properties of any given type of lightweight aggregate from different suppliers may vary considerably because of differences in the source of raw material and the method of treatment. This statement applies particularly to expanded clays, shales and slates. All lightweight concretes have higher absorption of moisture and lower thermal conductivity, lower compressive strength, as well as lower unit weight as compared with standard concretes made with sand, gravel or crushed rock. Excepting cinders, the cost of lightweight aggregates is usually higher. Grading and unit weight requirements are given in ASTM standards: C 330-53T, Lightweight Aggregates for Structural Concrete; C 331-53T, Lightweight Aggregates for Concrete Masonry Units; C 332-54T, Lightweight Aggregates for Insulating Concrete. The production of masonry units shows the growth of the use and types of lightweight aggregates. In 1947 the total number of lightweight block was 460,000,000 units in 8 by 8 by 16-in. equivalents. By 1954 this had increased to 950,000,000 units. Of the 1954 production, 27 pct was of manufactured types, 43 pct of cinders, and 30 pct of remaining types. Raw Materials Used as Lightweight Aggregates It was stated above that a variety of products both natural and manufactured are used as lightweight aggregates. It is easy to understand that a bulky material of low unit value cannot be transported far and still remain a low cost product. Hence the product used in a particular market depends upon the availability of the possible raw materials. Thus it is

Jan 1, 1960

By Kenneth K. Humphreys, R. M. Quinlan, Stan Venkatesan

INTRODUCTION 1 * The coal industry in the United States has undergone significant economic changes in recent years. For example, the price of coal remained relatively constant from 1950 to 1969 (see Figs. 5-1 and 5-2) but steam coal prices tripled and metallurgical coal prices doubled from 1969 to 1974. This price structure has created a new economic environment for coal preparation. Contributing factors to these price trends include: 1) Coal Mine Health and Safety Act of 1969. 2) Mid-East oil embargo of 1973.

Jan 1, 1979

By D. M. S. Bhatia, Richard D. Hagni

Five sulfide minerals from the Magmont mine, southeast Missouri were sampled for 31 trace elements in over 300 samples by laser microprobe spectrographic analysis of polished sections. The concentration of several trace elements shows a pattern of progressive variation with depth (space) and variation with different paragenetic stages (time) of each mineral. Factor analysis of the geochemical data shows sympathetic correlation both in space and in time of Bi, Cd, Ge, and Sn in galena and sphalerite, and Ni and Co in sphalerite and marcasite.

Jan 1, 1981

By I. N. Zavarine

THE observations presented in this paper were recorded during a study of the spheroidizing process. Spheroidization of cementite in steel is either brought about to develop a set of desirable mechanical properties or is an incidental result of mechanical and heat-treating manipulations. Physical properties of steel are materially influenced by the state of the cementite. Conversion of cementite from the lamellar to the spheroidal state is usually accom-panied by a decrease of hardness and of strength and by an increase in ductility. The spheroidized structure is usually considered as an ultimate step in the process of the softening of steel. The unorthodox hardening of a 3.5 per cent Ni steel (SAE No. 2330) after a heat-treatment that previously proved entirely suitable for a complete spheroidization of cementite in carbon steels led to the observa-tions that constitute the subject of the present paper.

Jan 1, 1939

By H. S. McQueen

THE insoluble residue method for the examination and correlation of limestones and dolomites, or other sedimentary rocks containing calcium and magnesium carbonates, originated and was developed in the laboratory of the Missouri Geological Survey. The numerous and ever-increasing problems in the field of applied geology, and the need for a tool or aid in the solution of them, led to experimental work with samples collected from deep wells, in the early part of 1924. The success attained, almost at the outset, with this method was so great that the method has now been developed from the state of the experimental to the realm of large-scale, every-day routine. In a previous paper the writer' described the procedure in detail and the characteristics of the residues obtained from certain Paleozoic forma-tions in Missouri. The purpose of the present paper is to discuss the economic application of the insoluble residue method.

Jan 1, 1936

By I. Stapf

Systematic investigations on silver-rare earth metal systems have been extended on the Ag-Ce system in order to clarify the discrepancies reported in literature. The phase diagram has been reinvestigated on the base of thermal analyses and of microstructure examination on cast and annealed specimen. All intermetallic phases Ag4Ce, Ag3Ce, Ag2Ce and AgCe show no extended range of homogeneity, they melt congruently fm), or decompose peritectically (d) at 815 °C (d), 1030 °C (m), 855 °C (d) and 855 °C (m), respectively. The system shows eutectics at 793 °C/10 at.%, 780 °C/42 at.%, and about 505 °C/81 at.% Ce. d-Ce dissolves up to 2 at .% Ag and decomposes metatectically at 710 °C. Furthermore, the phase transformation of the intermetallics would be clarified. The phases Ag5Ce and Ag51Ce14 reported in literature could not be verified.

Jan 1, 1984

By Milton E. Wadsworth, W. Martin Fassell, William H. Dresher

A study of the rate of dissolution of molybdenite (MoS2) in alkaline solution was carried out under carefully controlled conditions. Effects of temperature, oxygen over-pressure, and KOH concentration were evaluated. Studies were made in the temperature range 100°C to 175°C and in the pressure range 0 to 700 psia of oxygen. Under these conditions molybdenite was found to leach according to a linear mechanism. Both oxygen over-pressure and KOH concentration were found to control the rate of leaching. The mechanism has been explained in terms of adsorption of oxygen at the molybdenite surface followed by configurational rearrangement of the adsorbed molecules. The hydroxyl ion dependency is believed to be diffusion-controlled. Laboratory batch studies have shown that molybdenite can be readily dissolved in alkaline solutions under moderate conditions of temperature and pressure. Commercial application of this process to the production of ferro-molybdenum and molybdenum chemicals is promising in view of the ease of dissolution of molybdenite and the relatively noncorrosive conditions involved in the process.

Jul 1, 1956

By Jan D. Miller

The application of computers to the control and study of mineral processing operations such as grinding, classification and flotation has created an interest in simulation studies of these operations with mathematical models. Evidence of this interest is confirmed by papers presented at the 1969 International Computer Application Symposium held concurrently with the Fall Meeting of the Society of Mining Engineers in Salt Lake City, September 17-19, 1969. Proceedings of this symposium, entitled A Decade of Digital Computing in the Mineral Industry. were edited by Alfred Weiss and published by SME. Two sections of this book are devoted to computer application and simulation of mineral processing operations. In the area of comminution, several papers were presented at the International Computer Symposium. The size-discretized batch grinding model was described, and its application to the simulation of batch grinding, locked-cycle grinding and closed circuit grinding were discussed1. Freeh, Horst and Kellner2 approached simulation using a steepest ascent parameter-fitting technique, while Schoner3 considered the dependence of the elements of the mill matrix and classifier matrix on operating conditions, especially the feed rate.

Jan 1, 1970

By Henry G. Granger

A residence of 14 Sears in the Republic of Colombia, spent . in almost continuous traveling and prospecting-trips, has given me an intimate knowledge of the resources of that wonderful country. The man who best knows Colombia is unquestionably General Rafael Reyes, President of the Republic for the past three years, and with seven years more to serve in his present term. Such is the strength of his personality and the wisdom of his policies that his term of office will no doubt endure as long as he is milling to serve. The vastly improved economic situation and the brilliant outlook for Colombia are so directly due to the influence of President Reyes that a few lines concerning him will not be amiss, if they serve towards a better understanding of his personality. Born of a distinguished ancestry in the mountain~ of Boyaca, he is now 57 years old, just the age of his friend Porfirio Diaz when he began the work which has placed Mexico in the rank of great modern nations. It was Reyes who came to Washington to protest against the action of the government of the United States of America in

Jan 1, 1909

By William Hurst

THE content of this paper is a presentation of the diffusivity theory for the calculation of the water drive on an oil reservoir in which b the history of reservoir pressure with time are the essential parameters for the determination of the rate and cumulative water encroachment into a field. The paper is divided into two parts-the main portion and appendix. The main body is essentially the application of the principles underlined here to actual field data. It consists of the work plots of the radial-flow case, and includes a discussion of an illustrated problem for which the water-drive calculations are treated in conjunction with the volumetric-balance equation. The appendix is a mathematical treatment of the linear, radial, and spherical cases of water influx into a reservoir.

Jan 1, 1942

By H. J. Beattie, G. C. Gould

J. B. Seabrook' recently published properties of a low-alloy Ni-A1 age-hardening steel known commercially as "Nitralloy-N". He mentioned three possible mechanisms of age hardening, viz. order-disorder in the matrix, order -disorder in a precipitate, and a precipitate that goes in and out of solution reversibly without losing coherency. The following results indicate that the last - mentioned of these mechanisms is the cause of age hardening in Nitralloy-N. The reversibility of the age hardening with a sub-critical solution temperature was demonstrated strikingly by Seabrook, whose results are reproduced in Fig. 1. Aging for 22 hr at 975°F (525°C) can reharden the fully-tempered martensite to its original as-quenched hardness of R, 45. A Nitralloy steel was obtained from Seabrook' with the following analysis:

Jan 1, 1962

By Peter G. Chamberlain

Many mining engineers considering in place leaching for the first time are uncertain as to how to evaluate ore bodies for potential leachability. Evidence presented in this report emphasizes the critical role of permeability in such evaluations. Whether an engineer is considering leaching "tight" formations typified by the porphyry copper deposits of the southwest or the permeable uraniferous sandstones of Texas and Wyoming, permeability measurements are the keystone of any testing program. Permeability tests range from cheap and easy to highly expensive and sophisticated operations. Constant head, variable head, and pumping tests all have application in evaluating ore bodies for in-place leaching. Costs of these tests will not unduly deflate the pocketbooks of most mining companies. The basic procedures for selecting and running these field tests--including preparing suitable wells--are reviewed for the benefit of newcomers to in-place leaching.

Jan 1, 1979

By F. W. Rols-Hausen, F. W. Jessen

It is the purpose of this paper to present data on brines occurring in the Frio formation of the Texas Gulf Coast, and to show how their composition varies, (1) with depth below the surface, (2) with depth below the top of the formation, and (3) along the approximate strike. The brines vary in chloride content from 3,180 to 73,000 p.p.m., though the average salinity of the salt waters is shown to vary with total depth; the concentration being 35,000 to 40,000 p.p.m. at 3500 to 5500 ft., slightly less than 50,000 p.p.m. chloride at 5500 to 6500 ft. and average 38,000 to 40,000 below 6500 feet. From the analyses available, it appears that the highest concentration of salts occurs in the upper 300 ft. of the formation, while lower salinity is found with increasing depth below this point. The salt waters from wells in Starr County show less concentration of dissolved salts than in any other group of wells farther north along the strike. In all, 116 analyses from 63 fields and 14 wildcats, from depths ranging from 1300 to 11,400 ft. below the surface and from z to 3240 ft. below the top of the Frio, are recorded. Introduction Brines have been studied for many Years in an attempt to solve some of the geologic and production problems associated with the production of oil and gas. One practical application of study of . water analyses is the correlation of waters occurring above, in, or below the producing sand in the same field or throughout the same formation. The Frio formation, the series of sands and shales occurring below the Marginulina zone and above the Vicksburg, is one of the major oil and gas-producing formations in the Texas Gulf Coast. Fossils are rare or absent in the upper Frio throughout most of the area. When available, cuttings and cores, and electric logs were used to determine the top of the Frio. A change in lithology was used to determine this point in most of the wells, and fossils were used in some of the deep wells. It is realized that a change in lithology is not perfect for correlation purposes over long distances and some of the trends may be influenced by the inability to differentiate between the nonfossiliferous Marginulina zone and the Frio. It underlies virtually all the area shown on the accompanying map (Fig. I). Although it is not productive in the updip facies, it has been explored to a limited degree below I2,000 ft. Further more, toward the coast line future drilling to deeper depths should encounter this formation. Although thousands of wells have penetrated or drilled entirely through the formation, very few water samples have been secured from the many sands occurring in this formation and analyzed. Previous Investigation No previous published study has been made of the chemical composition and concentration of waters from the Frio formation. However, one water analysis

Jan 1, 1944

By Michael J. Messel

The critical shortage of asbestos fiber in the world today brings to the foreground the question of locating and developing new deposits. The object of this paper is to discuss some of the more important factors which should be considered in the examination and valuation of a new asbestos enterprise. Some of the more important uses of asbestos fiber are for textiles, heat insulators, building materials, filters and a series of other uses. The properties of this mineral, such as fibrous structure, color, strength, silkiness and flexibility, coupled with resistance to fire, certain chemical action and decay make its application unique for certain industrial uses which consume over 500,000 tons annually. These same unique properties which make this mineral so valuable also make a deposit one of the most difficult to appraise accurately, because of the many undeterminable and varying factors which must be considered before a deposit can properly be termed commercial. The majority of the asbestos fiber today, having the above mentioned properties, is sold by grades which are based on fiber length. Present day fiber prices vary over a wide range from $800 to $225 for crude fibers and $300 to $20.00 per ton for milled grades. For valuation purposes a careful study should be made of existing fiber prices and markets. Examination of Deposits In carrying out prospecting and examination of a deposit, considerable caution is required to get the necessary information in the form that will have the most value for the final determination. There are two main classes of asbestos fibers, chrysotile and the amphiboles, the chrysotile being, by far, the most important both in abundance and uses. This paper will stress mainly chrysotile deposits, however, the amphiboles have many important uses, especially amosite and crocidalite. Their valuation presents special problems as other factors may be involved, especially as they are not graded according to any well defined and adopted standard but usually according to the use for which they are being supplied. Most chrysotile deposits occur in two main types of rock, (I) mainly in basic igneous, such as dunite and peridotite, (2) to a lesser extent in sedimentary rocks, such as dolomite and limestone. All of these require a certain degree of metamorphism to be favorable to asbestos formation. Approximately 90 pct of the asbestos deposits are derived from serpentinization of dunite or peridotite, whereby the magnesium-silicate olivine was altered to hydrous magnesium-silicate serpentine. Under certain favorable geological conditions, this serpentine takes a fibrous form having a definite crystal structure, probably due to molecular rearrangement, and is known as chrysotile. The fiber veins are usually ir-

Jan 1, 1948

By H. C. H. Darley

Particles of montmorillonite-type clays consist of plate-like clay crystals stacked face to face. Under certain conditions in a suspension, these particles disperse to individual platelets with the formation of diffuse double layers round each platelet. This action has a profound influence on the rheo-logical and other properties of the suspension. This paper describes a test for degree of dispersion and uses this test to correlate changes in dispersion with changes in viscosity and gel strength. The test is of practical value in determining and controlling dispersion in drilling muds. INTRODUCTION It has long been recognized that the hydration and dispersion of clays, particularly those of the montmoril-loilite type, strongly influences the rheological and other properties of drilling muds, but little has been done to measure either of these phenomena under conditions that exist in drilling muds. The hydration of clays as such has been extensively studied by those interested in clay mineralogy, but in drilling muds it is to be expected that dispersion is at least as important a factor as hydration because of the much higher water-to-clay ratios and the very high degree of mechanical agitation. The term dispersion as generally applied to colloidal systems means the subdivision of large particles to small. Particles of montmorillonitic clays, however, consist of plate-like particles stacked face to face. Dispersion of these aggregates to individual platelets may be expected to have an unusually large influence on the properties of the suspension because of the shape factor, the enormous increase in specific surface, and the pronounced surface phenomena exhibited by the crystal surfaces. It is this form of dispersion that is particularly considered in this paper, -and the term degree of dispersion is used to imply the number of platelets per particle. The term aggregation is used to denote the opposite of dispersion, the association of individual platelets face to face to form stacks. It is important, as Garrison' has pointed out, to distinguish between the deflocculation-flocculation phenomenon and the dispersion-aggregation phenomenon. Flocculation of clay suspensions is characterized by the formation of voluminous sediments that are stable under quite high centrifugal fields. This indicates an edge to plate association of particles to form an open network type of structure, which obviously will have quite a different influence on the properties of the suspension than aggregation of the platelets face to face. The work described in this paper was primarily concerned with developing a test for degree of dispersion in clay suspensions and by means of this test to follow changes of dispersion brought about by addition of electrolytes and to show the influence of dispersion on the rheological properties. The Clay-Volume Test This test is based on the assumption that the greater the number of particles per unit weight of clay in a suspension the greater will be the volume of sediment when it is flocculated under standard conditions and centrifuged. After considerable experimentation the following procedure was established: 1 cc of the test mud vigorously shaken with 100 cc of 1-N NaCl in an ASTM oil centrifuge tube and centrifuged for five minutes in an International No. 2 centrifuge at 2,000 rpm. When drilling fluids of different solids content are being compared, the clay volume is expressed in cc per gram of clay solids, but generally changes in dispersion in a given mud are being compared and it is more convenient to report as cc of sediment. The test is strictly a comparative test, so that it is not necessary to adhere to the conditions specified above, e.g., with field muds a stronger flocculant such as Al2(SO4)3 may be preferable to NaCl.

Jan 1, 1958

By O. E. Palasvirta

Close examination of most so-called n.eu processes in mineral dressing reveals that they were conceived and developed a long time ago. High-intensity magnetic separation is no exception. Although its application in iron ore beneficiation seems new, in Germany the process has been commercially successful for almost two decades. High-intensity separators have long been standard equipment in the glass sand industry; they have also been used in concentrating some of the more unusual para-magnetic minerals. The basic features of an induced-rotor, high-intensity magnetic separator were described by Desire Korda in Paris in 1905,' and many patents have since been issued for improvements on the original design. Fig. 1 shows the basic design of an induced-rotor separator. Several U. S. manufacturers have been supplying induced-rotor separators for many years, but these are all devices of relatively low capacity, not suitable for treating such low-cost commodities as iron ore. On the other hand, two German manufacturers are offering induced-rotor separators of high capacity, both proven in the field. The present investigation was prompted by the apparent success of the German installations and by the discovery of iron ores on this continent which may be amenable to high-intensity separation. The objective was to gain better insight into the underlying principles of separation in a high-intensity field and to use this knowledge in selecting or designing an optimum separator. THEORETICAL CONSIDERATIONS he well known low-intensity magnetic separators are. without exception, of the the magnet type with more or less similar field shapes. It is therefore permissible to speak of their comparative strengths in terms of field intensity alone. However, proper understanding of the high-intensity magnetic separation process requires somewhat deeper analysis of the relationship between the magnetic field and the attractive force. Contrary to a widely held belief, a magnetic field of parallel lines of flux exerts no attractive force on a magnetically susceptible particle, but merely aligns its poles parallel to the lines of flux. On the other hand, a non-uniform field attracts a magnetically susceptible particle in the direction of the converging lines of flux. Thus the force of magnetic attraction varies as the product of the field intensity and the field gradient: dH ds As the induced-rotor magnetic separator is primarily intended for separating feebly magnetic materials, it is important that maximum attraction be attained. For the designer, then, the relationship between the magnetic field and the attractive force has the following implications: 1) Insofar as possible, the separation gap must be saturated with flux. 2) The rotor surface must be shaped to insure maximum convergence of lines of flux toward the rotor. 3) The primary pole face (opposite the rotor, on the other side of the separation gap) must be shaped so that the lines of flux do not diverge from it at any location in the effective separation zone. The actual attractive force of the rotor, and its critical speed, can be calculated as shown by Runo-linna, provided that the true flux density, the field gradient, and the magnetic susceptibility of the mineral can be measured with sufficient accuracy. The irregular shape of the rotor surface makes flux measurements difficult, but it can be done if a suitable gaussmeter is available (see Fig. 2). Calculations by the author, and comparisons with the centrifugal force exerted by the rotor, indicate that the force pinning a hematite particle to the rotor is of the same order of magnitude as the force holding a

Jan 1, 1960