Search Documents

By W. J. Carlson, S. M. Parmerter, I. Iwasaki

This article discusses the effect of physical and chemical modifications of starches on the anionic and cationic flotation of silica from oxidized iron ores and magnetite-taconite concentrates. It also deals with the results of the interaction of starch, pH, and calcium ions on the flocculation, clarification, and filtration of iron ore slimes and magnetite-taconite tailings. Starches, particularly when an-ionically modified, were found to be effective depressants in anionic silica flotation. British gums and dextrins were beneficial for oxidized iron ores, but none of the starches or starch derivatives appeared to have any effect on magnetite-taconite concentrates. The flocculation and filtration of iron ore slimes were affected most strongly by the level of starch, to a lesser degree by the pH, and virtually not at all by the level of calcium chloride. The clarification of iron ore slimes was complexly dependent on these three factors. The flocculation of magnetite-taconite tailings depended mainly on the level of starch, whereas their clarification depended on the level of lime. As previously reported in the literature, selective flocculation and partial upgrading of a semitaconite could be readily attained with starch and calcium chloride. A previous article discussed some of the parameters that are important when various corn starches are applied to the soap flotation of activated silica from iron ores and to the flocculation of iron ore slimes.' Methods of solubilizing the starches and the molecular size after mechanical and thermal treatments, as inferred from the viscosity measurements, were shown to influence the adsorption characteristics on iron ores, and the residual concentrations of both calcium ion and starch in the pulp liquor were in direct correlation with the flotation and flocculation behavior.2-4 The present article summarizes the results of more recent tests conducted to ascertain the role of starches and starch derivatives in various phases of iron ore beneficiation. The scope of this investigation has been extended to include not only anionic and cationic flotation, but also the flocculation and filtration of iron oxide slimes, the selective flocculation and partial upgrading of semitaconites, and the flocculation and clarification of magnetite-taconite tailings —all problems that are of vital importance to the iron ore industry of Minnesota. By combining a practical approach with adsorption studies and by using single-mineral systems5 in these research efforts, it is believed that the ultimate goal of developing a suitable modification of starch structure may be realized. The topics covered in this article are limited to the empirical aspects of the research program on the depressant activity of starches and products in the cationic and anionic flotation of silica and of their role in flocculation, water clarification and filtration. ANIONIC SILICA FLOTATION In the soap flotation of activated silica from iron

Jan 1, 1970

By R. P. King

The two-phase distributed-parameter kinetic model for flotation has been wed as the basis for a digital simulation of flotation plants of arbitrary configuration. Ores that contain any number of minerals can be handled. The effects of incomplete liberation and particle-size distribution are specifically allowed for. The simulator allows the investigation of variations in throughput and in the slurry density of the feed, and of variations in stage volumes and aeration rates. It can handle cell behavior even under conditions of hindered flotation. The requirements for data preparation are completely documented so that the computer program is suitable for general-purpose use. The program is written in Fortran. The output from the simulator consists of the complete material flows in the plant, as well as the grade, recovery, and particle-size distribution in each stream.

Jan 1, 1976

By Myron A. Pugacz, Frank S. McKenna, Clarence E. Jackson

The notched-bar impact test has proved worth while in certain applications as a test for control of the quality or the heat-treatment of steel. In view of the serious thought that even so simple a test as the tensile test has evoked during the past years, it is not surprising that the notched-bar impact test should have inspired much experimental work. The correlation of the great number of data has not been successful, although steady progress has been made toward a better understanding of this test. Progress has been made, especially, in the isolation of the effects of the many variables that control the results. The stress system imposed on a specimen with a notch is so complicated and unpredictable that no simple evaluation of the test has been possible. Because of this uncertainty, many engineers hesitate to use the notched-bar impact test, and this attitude may well continue until a better understanding of the effects of the variables in the test are available. Without doubt, any additional data that may be presented should be accompanied by as complete a description of the - details of test as possible, so that it may be added to the general fund of information that is to serve as the basis for the theory of the notched-bar impact test. The many factors that may control the test results have been pointed out repeatedly. The importance of the effect of the type and dimensions of the specimen has been recognized. Most of the work reported by American investigators has been limited to small-size (Charpy) specimens tested as a simple beam; two types of notches (Fig. I) have been commonly used. Considerable data have also been presented by many investigators using a small specimen tested as a cantilever beam; this commonly being called the Izod test. Here, however, a shear component of stress makes the stress system even more complex than that present in the simple beam type of test, hence a critical analysis is difficult. Much work has also been reported by investigators using the tension type of specimen. A second variable that must be controlled is the testing temperature. An indication that the tests were performed at room temperature is not sufficient, since in many steels a variation of a few degrees in the actual testing temperature may be sufficient to give an entirely different range of results. Other factors, such as the composition and condition of the material being tested and the speed of test, should also be considered. Many investigators have contributed data and theoretical discussions on the problems encountered in notched-bar test-

Jan 1, 1944

By Frank S. McKenna, Myron A. Pugacz, Clarence E. Jackson

The notched-bar impact test has proved worth while in certain applications as a test for control of the quality or the heat-treatment of steel. In view of the serious thought that even so simple a test as the tensile test has evoked during the past years, it is not surprising that the notched-bar impact test should have inspired much experimental work. The correlation of the great number of data has not been successful, although steady progress has been made toward a better understanding of this test. Progress has been made, especially, in the isolation of the effects of the many variables that control the results. The stress system imposed on a specimen with a notch is so complicated and unpredictable that no simple evaluation of the test has been possible. Because of this uncertainty, many engineers hesitate to use the notched-bar impact test, and this attitude may well continue until a better understanding of the effects of the variables in the test are available. Without doubt, any additional data that may be presented should be accompanied by as complete a description of the - details of test as possible, so that it may be added to the general fund of information that is to serve as the basis for the theory of the notched-bar impact test. The many factors that may control the test results have been pointed out repeatedly. The importance of the effect of the type and dimensions of the specimen has been recognized. Most of the work reported by American investigators has been limited to small-size (Charpy) specimens tested as a simple beam; two types of notches (Fig. I) have been commonly used. Considerable data have also been presented by many investigators using a small specimen tested as a cantilever beam; this commonly being called the Izod test. Here, however, a shear component of stress makes the stress system even more complex than that present in the simple beam type of test, hence a critical analysis is difficult. Much work has also been reported by investigators using the tension type of specimen. A second variable that must be controlled is the testing temperature. An indication that the tests were performed at room temperature is not sufficient, since in many steels a variation of a few degrees in the actual testing temperature may be sufficient to give an entirely different range of results. Other factors, such as the composition and condition of the material being tested and the speed of test, should also be considered. Many investigators have contributed data and theoretical discussions on the problems encountered in notched-bar test-

Jan 1, 1944

By D. Weinstein, F. C. Holtz

AS a possible method of improving the elevated temperature strength properties of zirconium, an investigation was initiated on the feasibility of producing a dispersion-strengthened material. Because of the high reactivity of zirconium, its high solubility for oxygen, and the stability of the Zr-0 solid solution, the major problem in such a development is choice of a suitable dispersant. Thus, in the present investigation we were concerned primarily with the stability of various dispersants in the zirconium matrix. The experimental procedure consisted of blending powders of zirconium and a dispersant, followed by cold compaction and extrusion. The best available source of -325 mesh zirconium powder contained between 1500 and 3500 ppm Oz; to this material, powders of zirconium carbide (5 p max), vanadium carbide (5 p max), alumina (0.03 p average), lan-thana (0.8 to 2 p), ceria (0.8 to 2 p), yttria (0.8 to 2 p), calcia (44 p rnax), or thoria (0.6 to 0.8 p) were added in amounts of 7 vol pct and compacted at 65 tsi. A cylindrical compact having a density between 70 and 80 pct of theoretical and dimensions of 1 in. diam by 1-114 in. high was thus produced. After canning in copper, these billets could be extruded (5: 1) on a 54-ton capacity, slow-traverse hydraulic press with the billet temperature at 1550°F and the extrusion die at 900°F. However, lack of densifica-tion of some of the extruded billets necessitated ratios of at least 23 :1. Ultimately, all billets were successfully extruded at 1500°F to 0.190 in. diam (32 :I), fully dense rods using a 200-ton capacity press and a ram speed of 90 ipm. The microstructures of as-extruded Zr-7 vol pct LazOS and Zr-7 vol pct Y2Os are shown in Fig. l(a) and (c), respectively. These structures are similar to all the as-extruded materials and consist of an elongated, single-phase zirconium matrix dispersed with oxide or carbide particles. Very little porosity is observed, and the interface between matrix and particles appears satisfactory. The size and distribution of particles, however, are not ideally of the type desired for dispersion strengthening. Since the primary study was of particle stability with respect to zirconium, no attempt was made to overcome agglomeration during powder blending and fabrication. Some areas exhibit fine, well-distributed particles; undoubtedly, a small proportion is submicroscopic and has the

Jan 1, 1963

By R. J. Quigg, G. S. Doble

Commercial stress -relieved TD Nickel bar was shown to retain room- and elevated-temperature tensile strength after exposure up to 2501°F. Cold swaging increased both room -temperature and 2000°F tensile strength. After annealing at 2500°F the strengthening due to swaging was retained at 2000°F hilt eliminated at room temperature. Annealing produced changes in hardness and X-ray half peak width indicating the presence of recovery processes as 1071° as 1000°F but no recrystallization of swaged material was noted at any temperature. In contrast to swaging, rolling induced a recrystal-lized structure after annealing. The tensile strength of this recrystallized structure was comparable to the cold-worked condition. High-temperature tensile properties of as -received bar were highly anisotropic with the transverse tensile strength being one fifth the longitudinal value. The aniso-/ropy is affected by working direction and may he partially reversed by changing the direction of metal flow. The divergence in tensile strength, beginning above 550°F or- approximate one third the absolute melting point, is strain-rate dependent. T D Nickel is a commercial dispersion-hardened alloy containing 2 vol pct thoria. The dispersion, consisting of spherical particles 0.030 to 0.050 in diameter with an interparticle spacing of less than 1 is reported to maintain stable properties up to 2400°F.1 This stability of second phase results in maintenance of elevated-temperature strength at higher temperatures and longer times than normal nickel-base superalloys.2 The purpose of this paper is to describe the effect of various mechanical working operations on the strength and microstructural stability of TD Nickel bar. MATERIAL AND PROCEDURES All material used in this study was commercial TD Nickel bar. This material is produced by a chemical process which results in a nickel powder containing a dispersion of thoria particles. The powder is then pressed, sintered, extruded, and subsequently worked to bar stock. Three starting materials from three separate lots were used: as-extruded bar. 1-in.-diam stress-relieved bar, and 1/2-in.-diam stress-relieved bar. Since TD Nickel bar stock is cold-worked without a recrystalliza-tion anneal, the accumulated deformation or degree of cold work in these materials increases as the bar diameter decreases. Some of the 1/2-in.-diam bar was swaged to 1/4 in. diameter at room temperature in order to produce an as-worked condition for comparison with the stress-relieved stock. Tensile testing was performed on an Instron Tensile Tester at a constant crosshead speed of 0.020 in. per min. The 0.2 pct offset yield strength was measured from the load-crosshead movement plot. Specimen gage dimensions were 0.080 in. in diameter by 0.40 in. in length, producing a strain rate of approximately 0.050 min-1. Specimens were tested in air and heated within a resistance-wound furnace controlled to ±5°F. A 15-min soak at temperature was employed before testing. Samples were heat-treated in air and specimens machined after exposure with sufficient material removed to eliminate any surface contamination. X-ray line breadth was determined from a diffractometer scan of a transverse face of a bar using copper K, radiation. Metallographic preparation utilized standard mechanical polishing with Carapella's etch. Specimens for electron microscopy were electropolished in a 1:7 sulfuric/methaol solution and chromium-shadowed collodion replicas prepared. RESULTS AND DISCUSSION I) Effect of Elevated-Temperature Exposure on the properties of TD Nickel. The effect of various elevated-temperature exposures on the room-temperature tensile strength of TD Nickel is shown in Table I. In the unexposed condition the tensile strength, reduction in area, and hardness all increase with increasing accumulated deformation while the elongation decreases. After exposure at 2500°F the strength of all three materials decreases to about 65,000 psi and the elongations increase slightly. The apparent increase in strength of the 1-in. bar after a 2000°F treatment is probably experimental scatter. These results indicate that the room-temperature strengthening due to additional deformation is annealed out upon elevated-temperature exposure. In contrast to the room-temperature data, the 2000°F tensile strengths increase in order of increasing deformation even after exposure. Although some loss of strength occurs after exposure, much of the effect of working is still maintained at 2000°F. The room-temperature hardness after various

Jan 1, 1965

By G. Britsianes, T. L. Joseph

THE reduction of a lump of iron ore is a complicated sequence of up to three reactions proceeding simultaneously in a gas-solid system. As the ore moves down the blast furnace into zones of higher temperature and higher reducing power, it is successively reduced through the three oxides of iron into metallic iron. The reduction process involves much more than chemical problems. Physical factors add to the complexity of the overall process. Under optimum conditions, reduction of the ore is completed at a level about one-half way down the blast furnace stock column. At this point, the ore undergoing reduction has attained a temperature of about 1000°C and has been in the furnace for about 6 hr. On the practical side, the behavior of the ore during smelting has been of great interest to operators. Unsatisfactory blast furnace operation on burdens containing magnetite ore or badly slagged sinter has often been attributed to poor re-ducibility. The question of reducibility has also been raised in formulating quality standards for agglomerates such as nodules, briquettes, and pellets. In the present investigation, the solid phases formed during reduction were studied as a step toward a better understanding of the overall process. Equilibrium Studies The iron-oxygen equilibrium diagram shown in Fig. 1 reveal; a number of facts pertinent to the gaseous reduction of iron ores. This diagram is from the work of Darken and Gurryl, 2 and represents a correlation of the best available data. Four solid phases may exist during the complete reduction of hematite to metallic iron. These are hematite (Fe2O3), magnetite (Fe3O4), wustite (FeO), and iron (Fe). The wustite phase is a solid solution which is not stable below 570°C. At this temperature the solid solution undergoes a eutectoid-type of decomposition into the phases, magnetite and iron. Thus above 570°C, the diagram dictates that a hematitic ore should pass through a four-phase sequence on reduction to metallic iron. Below 570°C, only hematite, magnetite, and iron should appear. Information on the iron-oxygen system has been derived largely from CO and H2 reduction equilibria. The Fe-C-0 relationships have been studied extensively by R. Schenck and his coworkers and well summarized by H. Schenck.3 More recent studies have been made by Darken and Gurry.1, 2 Data from these sources have been combined and plotted in Fig. 2. With respect to the Fe-H-O system, the works of Emmett and Schultz4 seem the most reliable, and these data have also been included in Fig. 2. Certain physical properties of the solid phases of the iron-oxygen system are summarized in Table I. The crystallographic information is of special interest as much of the present work has been concerned with the X-ray analysis of the products of reduction. Reduction with Hydrogen The reduction of ore with hydrogen is the net result of two or more gas-solid reactions. Above 570°C, the reaction sequence may be represented by stoichiometric stages as follows: 3Fe203+ H2e2Fe,O, + H20 [1] 2Fe3O, + 2H2 6FeOw + 2H2O [2] 6FeOw + 6H3 ^ 6Fe + 6H=O [3] Fe2O3 + 3H2 ^ 2Fe + 3H,O. [4] These reduction reactions follow the general form: A (solid) + B (gas) e C (solid) + D (gas). This type of gas-solid reaction has been investigated by Langmuirl' who has shown that such reactions can occur only at the boundary between the two solid phases. Furthermore, a nucleus of the second phase must initiate the reaction. Once such an interface exists, the reaction proceeds through a layer of the solid reaction product (C). The specific mechanisms involved will depend a great deal on the properties and condition of this particular layer. A number of heterogeneous reactions such as the dehydration of single crystals of copper penta-hydrate and the calcination of limestone follow this type of process. It should be noted that the inter-facial type of reaction also occurs even in dense polycrystalline material which simulates a mono-crystalline behavior.

Jan 1, 1954

By Alfred Fisher

CONSERVATION of mine timber is becoming in-creasingly important, and the consumer is en-couraged to use treated wood to permit longer life of mine timbers, and attempts are also made to substitute other material for wood. The great diffi-culty in substituting metal and concrete props for wood is the inability of these to give yielding resistance to roof pressure as wood supports do. In Europe, where mine timber costs are somewhat more important than in America, many designs of steel props have been tried, but have been unsuccessful, chiefly on account of inability to give yielding resistances. A metal pit prop that gives the desired effect has been extensively used in European mines and has caused a considerable reduction in accidents from falls of roof. Where mining operations have been sus-pended on account of strikes, conditions were found to be much better where such props were used instead of wood props, and machinery, which would have been destroyed by roof falls had wood props been used, was protected by the use of these yielding metal props. As this prop is adjustable, all the work of adjusting and transferring long props through narrow ways is done away with. It can also be drawn with greater ease and safety than wooden props; when properly used it is practically indestructible. European users have reported savings as against wooden props as high as 80 per cent. It gives audible warning of its working because the sliding action takes place in minute jerks. As the prop yields gradually to pressure its force is taken up by friction between the H sections, and this movement progressively increases the resistance of the prop to the increasing roof pressure. In the early development of the prop, it was designed with two steel members a and b of standard H steel sec-tions of equal dimensions provided with guide claws a' and b', held in frictional contact against each other by two differential wedges, f and g, and a floating link, e. In setting up the prop its two members are drawn out to the required length, the loose wedge, g, is then fitted into the space between the left-hand roller of the link d and the lower member of the prop b, and tapped suf-ficiently tight to prevent any relative movement of the two members from taking place prematurely. The prop is then raised to its intended position and secured in the usual way.

Jan 8, 1927

By J. B. Newsom

During July and August, 1931, the Bloomington Limestone Co., at Bloomington, Ind., ran a single wire saw on ledge No. 2 at Maple Hill quarry. The ledge was hard rock, much harder than the average Indiana limestone. It was opened at two ends for a depth of about 20 ft., leaving a 130-ft. section between. During the tests 21 cuts were made in this ledge, to an average depth of 10.42 ft., for a total effective cutting area of 28,445 sq. ft. The actual area sawed was about 20 per cent higher, as we did not level down in the center, preferring to cut deeper on the ends. The various cuts were carefully logged, and the results plotted. A study of these results is interesting, as it enables a forecast of probable future costs to be made, and also because it points out the limitations of wire saws, and the lines development should logically take. Some of the inferences to be drawn are discussed below. Best Length of Cut.—No trouble was due to length of cut, except that we could not easily level down a long cut, and it is probable that longer cuts, say up to 200 ft., can be made. Obviously, longer cuts will result in a higher sawing rate in square feet per hour if they do not cause stoppages. Working Higher Ledges.—The cuts averaged 10.42 ft. high by 130 ft. long. A study of several logs indicated that during only about 15 per cent of the cutting time was the saw cutting to its full efficiency; that is, during about 85 per cent of the time the saw was bedding in at the ends and not cutting well in the center, or the ends were below the floor line and only part of the wire was doing effective cutting. This does not mean that the wire was cutting to only 15 per cent of its capacity, but it means that during about 85 per cent of the time part of the cutting was being wasted. If higher ledges had been worked, the wire would have cut to its full efficiency a large part of the time, as it would have had a greater distance to saw after it had bedded in to the ledge before the ends went down below the floor level. The exact saving to be expected cannot be calculated, but it would be large if really high cuts were made.

Jan 1, 1932

By Clarence Zener

The internal friction of nonferrous metals vibrating at low stress amplitudes has so far always been successfully interpreted in terms of inhomogeneities of one sort or another. Examples are the fluctuation of stress across a specimen vibrating transversely,1,2,3 the stress inhomogeneities due to the elastic anisotropy and partial random orientation of the individual crystallites, localized weak regions introduced by cold-working,6'7 grain boundaries and possibly twinning planes.8'9 Perfect single crystals are, by definition, homogeneous. Actual single crystals usually, perhaps always, contains some imperfections. The present investigation was undertaken to determine whether the internal friction of single crystals may likewise be attributed to inhomogeneities. This study was made possible through the gift of a large single crystal of 70-30 alpha brass by H. L. Burghoff, of the Chase Brass and Copper Co. The specimen, 3.i in. in diameter and 10 in. long, was similar to samples previously described by Mr. Burghoff. Experimental Method The experimental method used has previously been described in institute papers.5'6'9 The measure of internal friction adopted here, I/Q, is X the logarithmic decre- ment, a measure used by some writers, and is also X the specific damping capacity, a measure used by other writers. In all measurements the stress level was kept so low that the measurements were independent of stress level. In all measurements in which the temperature was varied, observations were made as the specimen slowly cooled from its highest temperature. The specimen was vibrated transversely. Observations were made at the fundamental frequency and at the first overtone, of about 620 and 1710 cycles per second, respectively. No attempt was made to avoid acoustical losses. Experimental Results The specimen was annealed for several hours at 450°C. The temperature dependence of the internal friction was then determined from room temperature to 400°C. As shown in Fig. I, the internal friction increased by only a factor of 2 from room temperature to 300°C., then by a factor of 100 during the next Ioo° interval. These measurements are consistent with the view that the observed internal friction is the superposition of two distinct parts. One, dominant at room temperature, is nearly independent of temperature. This part may be accounted for by acoustical losses and by transverse thermal currents. It was not further investigated. The second part, when plotted in the manner of Fig. I, lies upon a straight line. Therefore it has a heat of activation H; i.e., it varies with temperature as Internal friction e-H/RT [I]

Jan 1, 1943

By J. B. Newsom

DURING July and August, 1931, the Bloomington Limestone Co.,. at Bloomington, Ind., ran a single wire saw on ledge No. 2 at Maple Hill quarry. The ledge was hard rock, much harder than the average Indiana limestone. It was opened at two ends for a depth of about 20 ft., leaving a 130-ft. section between. During the tests 21 cuts were made in this ledge, to an average depth of 10.42 ft., for a total effective cutting area 028,445 sq. ft. The actual area sawed was about 20 per cent higher, as we did not level down in the center, preferring to cut deeper on the ends. The various cuts were carefully, logged, and the results plotted. A study of these results is interesting, as it enables a forecast of probable future costs to be made, and also because it points out the limitations of wire saws, and the lines development should logically take. Some of the inferences to be drawn are discussed below. Best Length of Cut.-No. trouble was due to length of cut, except that we could not easily level down a long cut, and it is probable that longer cuts, say up to 200 f t., can be made. Obviously, longer cuts will result in a higher sawing rate, in square feet per hour if- they do not cause stoppages. Working Higher Ledges.-The cuts averaged 10.42 ft. high by 130 ft. long. A study of several logs indicated that during only about 15 per cent of the cutting time was the saw cutting to its full efficiency; that is, during about 85 per cent of the time the saw was bedding in at the ends and not cutting well in the center, or the ends were below the floor line and only part of the wire was doing effective cutting. This does not mean that the wire was cutting to only 15 per cent of its capacity, but it means that during about 85 per cent of the time part of the cutting was being wasted. If higher ledges had been worked, the wire would have cut to its full efficiency a large part of the time, as it would have had a greater distance; to saw after it had bedded in to the ledge before the ends went down below the floor level. The exact saving to be expected cannot be calcu-lated, but it would be large, if really high cuts were made.

Jan 1, 1932

By Clarence Zener

The internal friction of nonferrous metals vibrating at low stress amplitudes has so far always been successfully interpreted in terms of inhomogeneities of one sort or another. Examples are the fluctuation of stress across a specimen vibrating transversely,1,2,3 the stress inhomogeneities due to the elastic anisotropy and partial random orientation of the individual crystallites, localized weak regions introduced by cold-working,6'7 grain boundaries and possibly twinning planes.8'9 Perfect single crystals are, by definition, homogeneous. Actual single crystals usually, perhaps always, contains some imperfections. The present investigation was undertaken to determine whether the internal friction of single crystals may likewise be attributed to inhomogeneities. This study was made possible through the gift of a large single crystal of 70-30 alpha brass by H. L. Burghoff, of the Chase Brass and Copper Co. The specimen, 3.i in. in diameter and 10 in. long, was similar to samples previously described by Mr. Burghoff. Experimental Method The experimental method used has previously been described in institute papers.5'6'9 The measure of internal friction adopted here, I/Q, is X the logarithmic decre- ment, a measure used by some writers, and is also X the specific damping capacity, a measure used by other writers. In all measurements the stress level was kept so low that the measurements were independent of stress level. In all measurements in which the temperature was varied, observations were made as the specimen slowly cooled from its highest temperature. The specimen was vibrated transversely. Observations were made at the fundamental frequency and at the first overtone, of about 620 and 1710 cycles per second, respectively. No attempt was made to avoid acoustical losses. Experimental Results The specimen was annealed for several hours at 450°C. The temperature dependence of the internal friction was then determined from room temperature to 400°C. As shown in Fig. I, the internal friction increased by only a factor of 2 from room temperature to 300°C., then by a factor of 100 during the next Ioo° interval. These measurements are consistent with the view that the observed internal friction is the superposition of two distinct parts. One, dominant at room temperature, is nearly independent of temperature. This part may be accounted for by acoustical losses and by transverse thermal currents. It was not further investigated. The second part, when plotted in the manner of Fig. I, lies upon a straight line. Therefore it has a heat of activation H; i.e., it varies with temperature as Internal friction e-H/RT [I]

Jan 1, 1943

THERE are, as I have heard, varying opinions among men experienced in minerals as to whether silver has its own mineral [i.e., occurs native] or not. Mineralogical reasons and the authority of the majority persuade me that it has, not only because I have seen the natural material separate but also because I know that in mines of gold, copper, lead, and other metals pieces of pure metal are found without admixture, and I have heard that pieces of silver, gold, and copper have been found that had been reduced to their ultimate purity by natural causes. This is also confirmed by a German, Georgius Agricola, who says* that in a mine in Saxony a piece of metallic silver was found so large that the Duke who was prince and patron of the place had a whole dining table of square German style made from it without its being enlarged or worked on by any human artifice except for the tripod legs, and he often boasted that in this he surpassed the greatness of the Emperor. In truth I have never seen any metal except copper that was brought out from the mine pure and without any mineral, but I think that such a thing is indeed possible, since I believe in the greatness and power of Nature, who strives toward no other goal than perfection and purity. Indeed most of the minerals that I have seen have not been without admixture, not only of their earth but also of other metals, and this is more true of that which I have heard called silver than of any of the others. I except the silver that is mined in Schio in the region of Vicenza. These doubts, therefore, are not born without some shadow of apparent reason. As I told you above I believe that silver may have and does have its own mineral, for every substance that is converted into metal can exist pure by itself in its own species, as it also exists separately even though it be mixed with others, since it is seen that in each ore its metal is generated in a single body. Therefore it happens many times that whoever speaks of the ore of silver in one breath, without distinction, speaks of that of all the other metals, because there are few ores that are not mixed. But because the most noble things always have the prerogative of including in their name that of the others, where there is gold or silver the ores are not called

Jan 1, 1942

By Klaus Schwerdtfeger, Leo Zwell

The equilibrium between Ir-Fe or Rh-Fe alloys, iron oxide (wüstite or magnetite), and CO2-CO atmospheres has been determined at 1200°C. The data are used to derive the activities in these binary solid solutions. Both systems show negative deviations from Raoult's law. The lattice parameters are given for the investigated Ir-Fe and Rh-Fe alloys. IRIDIUM and iron form a continuous series of fcc solid solutions at elevated temperatures.' Rhodium-rich Rh- Fe alloys have fcc structure.' In the medium concentration range an ordered bcc phase is stable at temperatures up to about 1300°C. Phase relations in iron-rich alloys are not well-known. No thermody-namic data are available for these alloys. EXPERIMENTAL METHOD The experimental method used was to measure the equilibria between a gas phase of known CO2/C0 ratio, the alloy, and iron oxide (wüstite or magnetite). In one series of experiments the alloys of known composition were heated in CO 2-CO gas mixtures. After treatment (usually 1 day) the sample was quenched to room temperature and its surface examined visually to determine whether an oxide tarnish had formed. The procedure was repeated at slightly higher CO 2/CO ratios until the CO 2/CO ratio of incipient oxidation was found. Subsequently, the CO 2/C0 ratio was lowered again in small increments until the tarnish was reduced. In other experiments mixtures of alloy and iron oxide powders were pressed into pellets and equilibrated with the CO2-CO gas phase. In order to ensure that equilibrium was attained, two specimens with different starting iron content were heated side by side; in most cases, equilibrium was approached in one pellet by reduction of iron oxide and in the other pellet by oxidation of metallic iron. The sample was quenched to room temperature, and the composition of the equilibrated alloy was determined by X-ray measurements of lattice parameters and comparison of these values with calibration curves obtained from alloys of known composition. The oxides present in the specimens were identified by comparison of their diffraction patterns with those in the ASTM Card File. It may be expected from the noble character of iridium and rhodium that no appreciable amount of iridium or rhodium is dissolved in wiistite and magnetite under the present experimental conditions. The activity of iron in the alloy is then equal to that established in the iron oxide by the COrCO atmosphere. The activities of iron in wüstite and magnetite, as a function of oxygen pressure, were taken from the work of Darken and Gurry,

Jan 1, 1969

By Nathaniel Herz

(San Francisco Meeting, September, 1915) THE use of zinc dust for precipitating the precious metals from cyanide solutions is well established now in many places, and has many advantages over the shavings method of precipitation. Although much work has been clone on methods of testing zinc dust, as yet no absolutely positive test has been devised to determine the value of the material. Certain facts are known, but often it happens that results on a working scale are not as expected from the laboratory tests. The purpose of this paper is to record some observations made while testing. a large variety of zinc-dust samples in the laboratory. W. J. Sharwood1 has described standard analytical methods, which have been followed, with the changes noted. The regular determinations include zinc oxide, by solution in ammonia and ammonium chloride, lead, and precipitating efficiency. In some cases cadmium was determined by a method similar to that described by J. E. Clennell.2 I will discuss the precipitating-efficiency test in detail. The procedure is as follows: "A solution of potassium silver cyanide is prepared by dissolving 10 grams of silver cyanide (AgCN) and 5 grams of `99 0' potassium cyanide in a little water and diluting up to 1000 cc. It is then adjusted by addition of a little more KCN or AgCN until the solution indicates from 0.12% to 0.15% free KCN by titration with standard silver nitrate. The titration is best made by using a 10-cc. or 20-cc. sample, adding 1 cc. of 2 % potassium iodide, and a slight excess of ammonia, as the end point is then sharper. Or 15 grains of pure crystallized KAg(CN)2 may he dissolved in a liter of water and 1.5 grams KCN added. "Weigh out 0.5 grain zinc dust into a 300-cc. beaker. Add a few cubic centimeters of water and stir until, zinc is well mixed, then pour in 250 cc. of the prepared solution, stirring vigorously. See that all lumps are broken up, and continue stirring for fully five minutes. Stir occasionally (at least every 10 minutes) until the end of two hours from the addition of the solution. Then filter upon an 11-cm. filter, wash precipitate thoroughly, sprinkle with test lead, wrap it carefully in the paper, plaice in a scorifier with about 20 grams test lead, burn paper cautiously in muffle, scorify five minutes, cupel at low temperature and weigh silver. Milligrams silver obtained from 0.5 gram zinc X 0.0606 = percentage precipitating efficiency."'

Jan 8, 1915

By Clarence Zener

THE internal friction of nonferrous metals vibrating at low stress amplitudes has so far always been successfully interpreted in terms of inhomogeneities of one sort or another. Examples are the fluctuation of stress across a specimen vibrating transversely,1,2,3 the stress inhomogeneities due to the elastic anisotropy and partial random orientation of the individual crystallites,4,5 localized weak regions introduced by cold-working,6,7 grain boundaries and possibly twinning planes.8,9 Perfect single crystals are, by definition, homogeneous. Actual single crystals usually, perhaps always, contains some imperfections. The present investigation. was undertaken to determine whether the internal friction of single crystals may likewise be attributed to inhomogeneities. This study was made possible through the gift of a large single crystal of 70-30 alpha brass by H. L. Burghoff, of the Chase Brass and Copper Co. The specimen, ½ in. in diameter and 10 in. long, was similar to samples previously described by Mr. Burghoff.10 EXPERIMENTAL METHOD The experimental method used has previously been described in Institute papers.5,6,9 The measure of internal friction adopted here, 1/Q, is (1/p) X the logarithmic decrement, a measure used by some writers, and is also (1/2p) X the specific damping capacity, a measure used by other writers. In all measurements the stress level was kept so low that the measurements were independent of stress level. In all measurements in which the temperature was varied, observations were made as the specimen slowly cooled from its highest temperature. The specimen was vibrated transversely. Observations were made at the funda¬mental frequency and at the first overtone, of about 620 and 1710 cycles per second, respectively. No attempt was made to avoid acoustical losses. EXPERIMENTAL RESULTS The specimen was annealed for several hours at 450°C. The temperature dependence of the internal friction was then determined from room temperature to 400°C. As shown in Fig. 1, the internal friction increased by only a factor of 2 from room temperature to 300°C., then by a factor of l00 during the next 100° interval. These measurements are consistent with the view that the observed internal friction is the superposition of two distinct parts. One, dominant at room temperature, is nearly independent of temperature. This part may be accounted for by acoustical losses and by transverse thermal currents. It was not further investigated. The second part, when plotted in the manner of Fig. I, lies upon a straight line. Therefore it has a heat of activation H; i.e., it varies with temperature as Internal friction e~H/RT [I]

Jan 1, 1942

By Clarence Zener

THE internal friction of nonferrous metals vibrating at low stress amplitudes has so far always been successfully interpreted in terms of inhomogeneities of one sort or another. Examples are the fluctuation of stress across a specimen vibrating transversely,1,2,3 the stress inhomogeneities due to the elastic anisotropy and partial random orientation of the individual crystallites,4,5 localized weak regions introduced by cold-working,6,7 grain boundaries and possibly twinning planes.8.9 Perfect single crystals are, by definition, homogeneous. Actual single crystals usually, perhaps always, contains some imperfections. The present investigation was undertaken to determine whether the internal friction of single crystals may likewise be attributed to inhomogeneities. This study was made possible through the gift of a large single crystal of 70-30 alpha brass by H. L. Burghoff, of the Chase Brass and Copper Co. The specimen, 3-s in. in diameter and 10 in. long, was similar to samples previously described by Mr. Burghoff.10 EXPERIMENTAL METHOD The experimental method used has previously been described in Institute papers.5,6.9 The measure of internal friction adopted here, I/Q, is (p) X the logarithmic decrement, a measure used by some writers, and is also (I/2p) X the specific damping capacity, a measure used by other writers. In all measurements the stress level was kept so low that the measurements were independent of stress level. In all measurements in which the temperature was varied, observations were made as the specimen slowly cooled from its highest temperature. The specimen was vibrated transversely. Observations were made at the fundamental frequency and at the first overtone, of about 620 and 1710 cycles per second, respectively. No attempt was made to avoid acoustical losses. EXPERIMENTAL RESULTS The specimen was annealed for several hours at 450°C. The temperature dependence of the internal friction was then determined from room temperature to 400°°C. As shown in Fig. i, the internal friction increased by only a factor of 2 from room temperature to 300°°C., then by a factor of 100 during the next :too' interval. These measurements are consistent with the view that the observed internal friction is the superposition of two distinct parts. One, dominant at room temperature, is nearly independent of temperature. This part may be accounted for by acoustical losses and by transverse thermal currents. It was not further investigated. The second part, when plotted in the manner of Fig. I, lies upon a straight line. Therefore it has a heat of activation H; i.e., it varies with temperature as Internal friction ~ e-HI/RT [I]

Jan 1, 1942

By D. W. Fuerstenau, P. C. Kapur

The kinetics of green pelletization in a laboratory balling drum have been studied, using pulverized limestone as a model system. The growth characteristics of green pellets were found to be extremely sensitive to the moisture content of the material. Empirical kinetic equations, which incorporate a function of specific surface of the pellets as the criterion for growth potential, have been found to describe growth in a nucleation region and in a ball growth region. The rate constants in the kinetic equations are strongly dependent on the moisture content of the material being pelletized. Size distributions of the balls at different stages of pelletiz-ing are also discussed. In many industrial chemical processes, particulate matter can only be utilized if it is in an agglomerated form, such as pellets. Pelletizing is now widely used in iron ore technology1, and it has also been applied to a number of diverse fields such as the production of cement-kiln feed2, fertilizers3, and fluorspar4. Recently, it has been proposed to pelletize dispersion-type ceramic nuclear fuel elements5. In iron ore technology, for example, the production of agglomerates by pelletizing involves two major steps: 1) the preparation of green balls by rolling particles in a suitable balling device and 2) the firing of the green balls to form compact, strong bodies upon sintering. The critical step in a successful iron ore pelletizing operation is generally considered to be the balling operation1. In this paper, which is not concerned with the sintering of green pellets, the words green pelletizing and balling will be used interchangeably. Green pelletizing, or balling, will be defined as the process of forming larger bodies by rolling fine particles on a surface without the application of direct pressure. Two recent literature surveys6" indicate that in spite of the considerable amount of industrial pelletizing, very little is known about the fundamental principles of balling and its kinetics. The first reported research on the kinetics of pelletizing is the work of Newitt and Conway-Jones8. Using silica sands of different sizes in a batch laboratory balling drum, they found that the average green pellet diameter increased linearly with time at constant drum speed, and qualitatively the growth rate increased with moisture content. Generalized conclusions cannot be drawn from their research since the materials which they pelletized were sand and sand-silt mixtures rather than comminuted materials. Moreover, Newitt and Conway-Jones used testing sieves to estimate the size distribution of the green pellets, and this technique limited the range over which they could study the growth kinetics of the pellets. Bhrany and co-workers9 investigated the kinetics of balling iron ore fines on disk pelletizers ranging in diam from 1 to 18 ft. In their investigation, balling was carried out as a continuous operation, and growth kinetics were studied in terms of retention time of the material on the disk. Although the feed material in their study was quite coarse (the maximum size being about 1/2 in.), they also found qualitative relationships between pellet growth and water content, and feed size. In the present investigation, a number of innovations were introduced that refined the experimental measurements and established the reproducibility of balling experimentation. This enabled extension of the range of measurements to include study of agglomerate nucleation phenomena in the fractional mm size. This paper presents a detailed analysis of the nucleation and growth of green pellets in a laboratory balling drum. MATERIALS AND METHOD Pulverized limestone of specific gravity 2.72 was used as a model system in these studies. It has already been established that the balling characteristics of limestone and silica are similar to those of iron ore concentrates 2,8,10, depending on physical, rather than chemical, properties of the particles. The size distribution of the limestone was determined by a wet-dry sieving technique in the sieve range and by a sedimentation balance in the sub-sieve range. Fig. 1 presents the size distribution of the limestone used in this research. This figure shows that the material is finer than 200p (65 mesh) and that 25% of it is finer than 12. The specific surface area of this powder, as measured by BET gas adsorption methods,

Jan 1, 1964

By Roy C. Kirkman

Dear Editor: It is with great pleasure that I read Mr. Howard M. Wells article in the December 1978 issue of MINING ENGINEERING entitled: "Optimization of Mining Engineering Design in Mineral Valuation." Mr. Wells very adequately presents the case and point that there are a great number of variables which must be analyzed during an economic evaluation of an FUND RESOURCE, such as copper or uranium. I wish to take this opportunity to suggest that, given today's economic climate, decision making takes place under conditions of uncertainty and that this uncertainty justifies our need to examine each one of the parameters entered into the evaluation model. It is my contention that the influence of the tonnages and grades as well as their distributions, have the most profound effect upon the results of an evaluation. Everyone concerned with the evaluation of FUND RESOURCES realizes that as metal prices decline or stagnate with sharply rising direct operating costs, cutoff grades (Gc) must increase according to the equation below which Mr. Wells uses: Gc = Total Operating Cost/(Market Price X 20 X Recovery) However, historically, we have seen cutoffs move dramatically lower in both the copper and uranium industries for the past decade. Henceforth, this established the metals industry most important argument for processing greater tonnages of lower grade materials from disseminated deposits (refer to paper by Kirkman, Roy C.). These disseminated deposits, created by either concentration processes (uranium) or dispersion processes (copper, gold, molybdenum), have log-normal grade distributions (Fig 1). Gross profits are rising, but unit profits are falling. The industry has created longevity through economy of scale, i.e., mining vast tonnages of low grade. In order to develop the great tonnages necessary to prove economic viability, we must examine alternatives at the low-end of the tonnage grade relationship. Notice from [Fig. 2] that as we move further to the right away from line A-B drawn tangential to the average grade curve at 45°, total profits will increase (given fixed annual production capacity) and unit profits decrease. The theoretical optimum operating point is where: [ ] At this point my observation is that slight shifts in production capacity bring about greater changes in profitability due to greater grade changes. Therefore, the best financial risk evaluation is obtained by totally revising the mining engineers methods and fixing the financial parameters such as discount and interest rates. A 10% shift in either of these two parameters will not cause near the same variance in economic viability as will a change on the GRADE-TONNAGE curve [(Fig. 2)].

Jan 1, 1980

By Nathaniel Herz

The use of zinc dust for precipitating the pecious metals from cyanide solutions is well established now in many places, and has many advantages over the shavings method of precipitation. Although much work has been done o,n methods of testing zinc dust, as yet. no absolutely positive test has been devised to determine the value of the material. Certain facts are known, but often it happens that results on a working scale are not as expected from the laboratory tests. The purpose of this paper is to record some obscrvations made while testing a large variety of zinc-dust samples in the laboratory. W. J. Sharwoodl has described standard analytical methods, which have been followed, with the changes noted. The regular determinations include zinc oxide, by solution in ammonia and ammonium chloride, lead, and precipitating efficiency. In some cases cadmium was determined by a method similar to that described by J E Clennell.2 I will discuss the precipitating-efficiency test in detail. The procedure is as follows: "A solution of potassium silver cyanide is prepared by dissolving 10 grams of silver cyanide (AgCN) and 5 grams of 99 %' potassium cyanide in a little water and diluting up to 1000 cc. It is then adjusted by addition of a little more XCN or AgCN until the solution indicates from 0.12% to 0.15% free KCN by titration with standard silver nitrate. The titration is best made by using a 10-cc. or 20-cc. sample, adding 1 CC. of 2 % potassium iodide, and a slight excess of ammonia, as the end point is then sharper. Or 15 grams of pure crystallized XAg(CN)2 may be dissolved in a liter of water and 1.5 grams XCN added. " Weigh out 0.5 gram zinc dust into a 300-cc. beaker. Add a few cubic centimeters of watcr and stir until zinc is well mixed, then pour in 250 cc. of the prepared solution, stirring vigorously. See that all lumps are broken up, and continue stirring for fully five minutes. Stir occasionally (at least every 10 minutes) until the end of two hours from the addition of the solution. Then filter upon an 11-cm. filter, wash precipitate thoroughly, sprinkle with test lead, wrap it carefully in the paper, place in a scarifier with about 20 grams test lead, burn paper cautiously in muffle, scorify five minutes, cupel at low temperature and weigh silver. Milligrams silver obtained from 0.5 gram zinc X 0.0606 = percentage precipitating efflciency."³

Jan 1, 1916