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

A two-phase distributed-parameter model of the flotation process has been extended to allow consideration of the important process parameter, concentrate grade. A simple expression is presented for the grade of concentrate in terms of the zeroth and first moments of the concentrate distribution. An example is given for a binary ore containing two pure minerals each having nondistributed rate constants. For extend-ing the model to the distributed rate constant case, a cubic polynomial zoas utilized to simulate the feed distribution. One particular example is considered and grade-recovery curves are generated to show the dependence of such curves on the initial feed distribution. Operating flotation plant engineers have traditionally evaluated plant performance in terms of the recovery of valuable mineral and the grade of the concentrate. In both operation and research, grade-recovery relationships have been used as a guide for selecting flotation conditions. Weissl illustrated the use of grade-recovery curves in plant operation and considered the grade-recovery relationship to be a metallurgical one. The extensive experimental work of Chi" using standard batch flotation tests on iron ores shows that, even with extensive statistical correlation of data, little insight can be gained into the basic fundamentals of these relations. Such relations must depend on the kinetic behavior of the various mineral species in the flotation circuit. In his flotation text book, Gaudin3 considered the relationship of recovery and of product grade to flotation kinetic indices, but he did not extend his calculations to yield grade-recovery relations. Although Gaudin used a simplistic model for his analysis, he did recognize that variations in flotation rates must result from variations in locking, surface heterogeneity, particle size and shape, among other things. In a recent paper,' we presented a model of the flotation process that could be readily analyzed with an analog computer. This model combines the concept of a distributed set of rate constants"" with that of the two-phase flotation model,8" resulting in a model more powerful and flexible than previous ones. The purpose of the present paper is to show how this model can be used to generate grade-recovery curves and to determine the dependence of such curves on the various kinetic parameters. In this paper, the model will be limited to the semi-batch case, but extension to the continuous case is a straightforward step.

Jan 1, 1971

By R. E. Reed-Hill, W. H. Hartt

The "(3034) " twin lamellae in magnesium have been reexamined using electron microscope replicas. The double twinning sequence (1011)- (1012) for these lamellae has been reconfirmed. Evidence is presented showing that the irrational habit of these twins is probably the direct result of a need to accommodate the second-order twinning shear. This accommodation vesults in both an external shear in the matrix and an internal shear in the lamella. A model is presented which accounts for the experimental obseruations. HCP metals are generally characterized by strong textures in which the basal planes of the grains tend to be aligned parallel to the rolling direction in sheet or plate and to the axis of wires and rods. Since these directions are normally those in which finished products may be subjected to uniaxial tensile stress, these textures effectively place the crystals of magnesium objects in orientations unfavorable to both basal slip and {1012) twinning, the easily activated deformation systems of this metal. However, when magnesium crystals are deformed near room temperature by a tensile stress nearly parallel to the basal plane, another mode of deformation can occur.',2 This is _a double twin which forms first by twinning on {loll), followed by retwinning on (1012). The resulting twin lamellae are of considerable interest. First, they can be responsible for "brittle fracture''; when a tensile stress axis lies in the basal plane, because the reoriented crystal structure of a lamella is well-aligned for slip while the parent crystal is not. Extensive internal deformation may thus occur while the matrix is still almost undeformed. This deformation can produce a ductile rupture running the length of the twin.3 Complete failure of the specimen may then oc-cure by the spreading of cracks from one twin lamella to another, or by the movement of a crack into a grain boundary and then along grain boundaries. Since the the volume fraction of these doubly twinned elements is normally very small, the fracture may be classed as brittle, although the fracture mechanism is, of itself, essentially ductile. It is quite probable that the ductility transition, normally observed4 in magnesium at or slightly Obove room temperature, is closely associated with these second-order twins. The detailed relationship of these twins to fracture in single crystals will be the topic of another paper. The present paper is concerned with a second important aspect: the irrational habit of these double twins that falls close to {3034), or approximately 7 deg away from the primary (10il) twin habit. There is good reason to believe that this habit results directly

Jan 1, 1968

By Don L. Kendall, Martin G. Buehler

A simple physical model has been developed to fit carrier-removal data in silicon irradiated near room temperature with reactor spectrum neutrons. Commonly observed donor and acceptor defect energy levels are assumed to be introduced linearly with neutron fluence. The donor levels (in ev) are Ev + 0.16, Ev + 0.27, and Ev + 0.31 and the acceptor levels are Ec - 0.55, Ec - 0.40, and Ec - 0.1 7, where Ev and Ec are the valence and conduction band energies, respectively. The introduction rates of each level are adjusted to fit literature initial carrier-removal rate data. When normalized with respect to the Ev +0.27 level, the relative values of introduction rates are 5.3, 1.0, 3.1, 1.0, 2.0, and 20.0, respectively for the six levels indicated above. To fit p-f (hole concentration vs neutron fluence) and n-f (electron concentration us neutron fluence) data, the introduction rates are multiplied by a factor which preserves the relative values given above. This factor depends upon irradiation temperature, reactor energy spectrum, neutron fluence calibration, and oxygen content of silicon. An extensive study of the effect of neutrons on carrier-removal in silicon irradiated with reactor spectrum neutrons (E > 10 kev) has been given by Stein and Gereth1 (SG) and Curtis, Bass, and Germano' (CBG). They measured initial carrier-removal rates for both p- and n-type silicon over an impurity range typical of silicon devices. In this work, we attempt to fit a simple theory to this data to establish a usable relationship between hole and electron concentration, p and n, respectively, and neutron fluence f. The p-f and n-f relations are needed to assist in the design of neutron tolerant silicon devices and are needed to clarify presently used empirical resistivity-fluence relationships.3 Neutron damage in silicon produces a variety of defects ranging from simple point defects to defect clusters. For the purpose of this treatment, we assume that simple point defects dominate carrier-removal effects. In contrast to this view, stein4 has proposed that defect clusters are responsible for a significant portion of carrier-removal effects. In the following section, it is shown that the carrier-removal effect in n-type silicon with an electron concentration less than 1015 cm-3 can be explained adequately by assuming that the divacancy is the dominant defect and that its introduction rate is independent of the electron concentration. For electron concentrations greater than 1015 cm-= an additional acceptor defect center is needed, and for simplicity the A-center (vacancy-oxygen pair) has been chosen. Although the E-center (vacancy-phosphorus pair) can account for some of the results, the A-center was chosen because the E-center requires a more involved treatment which the presently available data do not justify. In p-type silicon three radiation-induced donor levels are assumed, namely the divacancy and two other centers of unspecified nature located at Ev + 0.16 ev and Ev to 0.31 ev. The donor divacancy at Ev + 0.27 ev is assumed to be introduced at the same rate in p-type as in n-type. However, this rate is too low to fit p-type initial carrier-removal data. The dominant centers in p-type silicon are assumed to be the Ev + 0.16 ev and Ev + 0.31 ev levels where the latter is not the divacancy. The introduction rates are chosen to fit initial carrier-removal rate data. Assuming that the introduction rates are independent of Fermi level, the ratio between them is fixed for subsequent p-f and n-f calculations. Using the same ratios, the initial carrier-removal rate data1,2 as well as p-f and n-f data1,5 can be fit provided the absolute value of the introduction rates are adjusted to account for irradiation temperature, reactor energy spectrum, neutron fluence calculation, and the oxygen content of silicon. THEORETICAL ANALYSIS This analysis is basically the same as that used by Hi116 to analyze electron damage in silicon except we express the degree to which an impurity level is ionized not in terms of the Fermi level, but in terms of carrier concentration. Landis and pearson7 have used the latter approach to analyze y-damage in silicon. Neutron-induced defects responsible for carrier-removal at room temperature are assumed to be simple point defects with no interaction between defects so that they may be represented by discrete energy levels. It is also assumed that no constituent of a defect complex is used up and defects stabilize shortly after irradiation. Defects are assumed to be introduced linearly with fluence according to the product Rtf where Rt is the defect introduction rate and f the neutron fluence. Taking into account the ionization of defects according to Fermi statistics, and considering charge neutrality where minority carriers are neglected, the n-f relation is where no is the preirradiation electron concentration. The parameter Nt is the electron concentration at which the ionized defect concentration is one-half the total defect concentration (Rtf) or where Et is the defect energy level. For silicon at 300°K, ni = 1.45 X 1010 cm-3 and Ei = Ev+ 0.542 ev which was determined using Ec — Ev = 1.11 ev and me* = 1.07 mo and mh* = 0.558m0. The spin degeneracy factor, which usually appears as a number multiplying the Nt/n term of Eq. [1], is taken as unity. In effect, this factor has been incorporated into the defect en-

Jan 1, 1970

By C. E. Lesher

Low-TEMPERATURE carbonization needs no introduction to the literature on coal. This paper will attempt no review of that literature; it tells the story of the commercial development of one of the processes for carbonizing coal at so-called low temperatures, dealing with the technology and economics of the process rather than with the design of equipment. The process used is that covered by the patents of C. B. Wisner, with improvements and changes made by the Pittsburgh Coal Carbonization Co. The important and novel feature of the process is the phenomenon of making the product in ball form (Fig. 1). Melting coal dust into smokeless solid fuel in an apparatus as simple as a revolving cylinder of ordinary mild steel has been proved to be practical. Furthermore, it has been found that the process has a wide application, for by applying a knowledge of why and how this balling action is accomplished, the apparatus can be designed and adapted to treat any coal that has a certain minimum agglutinating property. The operating plant is 20 miles west of Pittsburgh, adjacent to the Champion preparation plant of the Pittsburgh Coal Co. The coal used is cleaned minus 3/8 -in- or finer sizes. The products are low-tem-perature coke, tar and tar products. Present capacity is 7000 tons per month of low-temperature coke and 140,000 gal, of tar. There is no surplus gas for sale, and none of the light oils are stripped from the gas. The coke is marketed in two sizes, 1 to 2 in. and 1 to 6 in., through retail coal dealers for domestic con-sumption in hand-fired furnaces, and for fireplace fuel. The smaller size is bagged by dealers. Crude tar and many distillates and road tars are sold.

Jan 1, 1940

By C. H. North, L. E. Lynd, W. W. Anderson, H. Sigurdson

CONSIDERABLE uncertainty is revealed in the literature regarding the nature of the titanium minerals which make up the bulk of the heavy, opaque fractions of numerous beach sand deposits of the world. An investigation was made, therefore, of beach sand concentrates of North Carolina, Florida, Brazil, and India. Magnetic concentration, X-ray, and microscope data were obtained which show that these concentrates consist essentially of ilmenite and its alteration products. The alteration, brought about by oxidation and leaching of iron values, has resulted in upgrading the ores to a range of 56 to 64 pct TiO2, as compared with 52.7 pct in ilmenite of theoretical composition. Conclusions drawn regarding the nature of the dominant titanium-bearing mineral in beach sand deposits have been based mainly on chemical composition, specific gravity, and petrography. This material has usually been referred to as ilmenite or weathered ilmenite. It has also been referred to as arizonite because in chemical composition it resembles an occurrence in Arizona which was described by Palmer1 in 1909.

Jan 8, 1954

By F. W. Maclennan

ORE production from the property of the Miami Copper Co. began early in 1911. Until 1925 this ore came from the so-called high-grade orebodies, which contained a little over 2 per cent. copper. This ore was mined by the following methods. 1. Top slicing after mining the peaks by square setting, which produced 4,524,347 tons, including ore from square setting. 2. Shrinkage stoping with sublevel caving of the pillars, which produced 2,230,577 tons. 3. Undercut caving with hand tramming, which, produced 15,427,672 tons. Estimating December tonnage, the total ore mined to the end of 1929 will amount to slightly more than 43,000,000 tons. The first method was described by E. G. Deane1 and the second by D. B. Scott,1 and the third, together with a general, description of the mine, by J. H. Hensley, Jr.1 The geology of the district has been worked out by. Dr. F. L. Ransome.2

Jan 1, 1930

By L. K. Smith, E. M. de Kock, J. van der Walt

A unique and systematic approach for analysing alternative methods of ventilating and cooling large hot mines is presented. The important factors that have a bearing on ventilation and cooling requirements and practices, such as air flow through the mine, geographical distribution of heat loads, micro ventilation considerations etc., are dealt with. Analysis of these leads to the definitive ventilation and cooling strategies, air and water process design, detail specifications and design of associated plant and equipment.

Jan 1, 1982

By K. Robert Dorman, F. Michael Jenkins

The occurrence of rock bursts in deep metal/nonmetal mines presents a major hazard to their safe and economical operation. As part of a Bureau of Mines program to reduce rock bursts in deep vein mining, a project was conducted in the Coeur d'Alene Mining District of Idaho to evaluate and demonstrate the mining of a destressed sill pillar using undercut-and-fill methods. A 50-ft sill pillar in a burst-prone area was preconditioned by drilling and blasting vertical holes in the ore. After raises were driven through the destressed pillar to the level above, it was mined by the undercut-and-fill method. The conclusion from this demonstration is that the combination of ore preconditioning and underhand mining resulted in greatly improved rock burst and ground control, allowing safe and efficient mining of a potentially hazardous, burst-prone pillar.

Jan 1, 1984

Jan 1, 1920

By John D. Morgan

THE tense international situation prevailing in the postwar period, and the outbreak of actual hostilities in Korea, directs attention to the status of United States reserves of strategic and critical materials for war. Geologists and mining and metallurgical engineers are particularly interested in this problem, since, with a few important exceptions, almost all of the materials on the official list of strategic and critical materials for stockpiling (see top of page) are metals and minerals.

Jan 3, 1951

By Milton E. Wadsworth, Daniel B. Brimhall

Column leach studies of a low-grade porphyry copper ore were made. The technique used involved alternating oxygen absorption and copper leach cycles. The leach solution was displayed from the column with oxygen. The volume of oxygen reacting with the ore was measured with a gas burette. The copper released as a result of exposure to oxygen was correlated with the oxygen uptake. The oxidation rate was found to be dependent on the pH of the solution wetting the particles and was markedly increased by increasing the temperature of the system. Decreasing the particle size of the sample increased the oxidation rate. A material balance on the system indicated 1 mole of oxygen yielded in excess of 1 mole of copper in solution. A discussion of the important parameters is presented and the results are related to dump leaching in general.

Jan 1, 1974

By N. A. DeCecco, H. M. Meyer

IN the early stages of a titanium brazing investigation, binary titanium systems partially or completely known and fundamental metallurgical data were surveyed to select the pure metal most likely to be satisfactory for producing a ductile high strength joint. The phase diagrams for the purpose of this survey were classified into two groups: 1—systems with large solubility in ß titanium, but negligible solubility in a titanium, and 2—systems with large solubility in a titanium. Those metals with melting points believed to be too high or too low for titanium brazing (Tim = 1730°C) were eliminated from consideration. The melting points of vanadium, tungsten, tantalum, hafnium, zirconium, and the platinum group are too high and those of zinc, lead, cadmium, and tin are too low. The remaining metals were grouped as follows: 1—large ß solubility: Cr,¹ Mn,² Fe;³ CO,4 Ni,5 Cu,6 Be,' Si." —large a solubility: Al.9

Jan 1, 1954

By D. J. McAdam, G. W. Geil, D. H. Woodard, W. D. Jenkins

INTRODUCTION IN a series of papers, the authors and their associates have shown that the resistance of a metal to fracture is a function of all three principal stresses. 10-18,20,21,23,[1] Consequently since a technical cohesion limit is defined as the technically determinable resistance to fracture, under a specific stress system, the technical cohesive strength comprises an infinite number of technical cohesion limits corresponding to the infinite number of possible combinations of the principal stresses. As shown in the previous papers, the technical cohesive strength increases with plastic deformation, with decrease in temperature, and with increase in the strain rate. The technical cohesion limit, therefore, is affected by the same factors that affect the flow stress,§ namely, the stress system, plastic deformation, temperature, and the strain rate. The effect of each of these factors on the fracture stress is qualitatively the same as its effect on the flow stress. The effect of any of the factors may be represented by a curve of cohesion limits, although only one point on the curve may represent actual fracture. Since the term "fracture stress" has come into general use with the same significance as technical cohesion limit; the authors are here using the' shorter term with the understanding that it, does not always refer to actual fracture. In the general investigation described. in the previously-mentioned papers,10-18,20,21,23 the influence of the stress 'system on the fracture stress was studied by means, of tension tests of notched specimens. When a circumferentially notched cylindrical' specimen is subjected to longitudinal ten-, sion, the minimum cross section is under " transverse radial tension. The mean radial stress increases with the depth and sharpness of the notch, but is always less than the longitudinal stress. The greatest principal stress (S,), therefore, is longitudinal, and since the radial stress is effectively equal to the circumferential stress, the transverse principal stresses are equiaxial in that plane (S2 = S3). By the use of notched specimens in tension tests it was shown that the fracture stress increases with increase in the radial stress ratio (S3/SI). The evidence is based not only on the results of tests to fracture at various constant temperatures, but also on. results of two-stage tests, in which each specimen was plastically deformed a predetermined

Jan 1, 1948

Jan 1, 1916

Jan 1, 1907

By Haydn H. Murray

The term clay is somewhat ambiguous unless specifically defined because it is used both as a rock term and as a particle size term. Actually most persons using the term clay realize that it has a double meaning and in most instances define it. As a rock term, clay is difficult to define because of the wide variety of materials that compose it so that the definition has to be general. Clay is a natural, earthy, fine-grained material composed largely of a limited group of crystalline minerals known as the clay minerals. Many definitions state that a clay has the property of plasticity when wet, but some clays are not plastic, i.e., halloysite and flint clay; however, most clay materials are plastic when wet. As a particle size term, clay is used for the category that includes the smallest particles. The maximum size particles in the clay size grade are defined differently on some grade scales. Soil investigators and mineralogists generally use 2 microns as the maximum size. The Wentworth scale' defines clay as material finer than approximately 4 microns. Grim' has found it convenient to use the term clay material for any fine-grained, natural, earthy, argillaceous material and in this way can include clays, shales, or argillites, and some soils if they are argillaceous. Even though no standard definition of the term clay is accepted by geologists, agronomists, engineers, and others, still the term is generally understood by all who use it. Clay is an abundant natural raw material and has an amazing variety of uses and properties which will be discussed in this chapter. In order to understand better the relationships between the clays and their uses, a brief discussion of the structure, chemical composition, and identification of the clay minerals is given. Mineralogical Composition of Clays Clays are composed of certain groups of hydrous aluminum, magnesium, and iron silicates that may contain calcium, potassium, and other ions, which are called the clay minerals, and other minerals of variable composition, which are nonclay minerals. Both clay minerals and nonclay minerals influence the properties of a clay material. In order to understand the relationship between clay minerals and the properties of a clay material, a short summary of the structure and composition of clay minerals is necessary. Any scheme of classification tends to impose a certain rigidity and as new and additional data become available it is necessary to revise classifications. Brindley3 has discussed the classification and structural mineralogy of clays in very lucid fashion and chose a classification based on structural features and chemical composition. Grim2 proposed a tentative classification which is based on the structural attributes of the various clay minerals. This classification is relatively simple and workable, and is shown as follows: I. Amorphous Allophane group II. Crystalline A. Two-layer types (sheet structures composed of units of one layer of silica tetrahedrons and one layer of alumina octahedrons). 1. Equidimensional Kaolin group kaolinite, dickite, nacrite 2. Elongate Halloysite group

Jan 1, 1960

By A. E. Gorum, I. Cornet

Fatigrle of ionic crystals has been studied primarily in magnesinm oxide. under cyclic stress dislocations move irrreversibly; they multiply; slip bands form and grow; cracks mucleate and propagnte, and failure occurs. The use of ionic crystals such as MgO is advantageorus in such investigations because they are optically transparent. Individual dislocation Intersections with {100} surfaces may be observed with a standard microscope, using etch-pit techniques. Slip, deformation, crack .formation, and fracture in MgO crystals under cyclic stress are compared with cotrresponditzg processes in metals. ThE effect of cyclic loading in metals has been studied for many years. The appearance of slip lines is readily observed and the ensuing fracture may also be seen. From these observations it is possible to predict the behavior of a material and make an educated guess as to what is happening internally, but the actual changes taking place within the structure are not readily apparent. If one could obtain a material in which the individual glide components could be observed, it would be invaluable in determining the actual slip distribution resulting from cyclic loading as well as the distribution of slip in the neighborhood of a growing crack. Such a material is magnesium oxide. Dislocation arrays may be observed by means of etch pits

Jan 1, 1961

By B. M. Larsen, T. E. Brower, J. W. Bain

A mass of circumstantial evidence is presented to indicate that the main source of alloy losses in open-hearth tapping is oxidation by air, with the steel apparently reacting with an amount of oxygen equivalent to about 30 times its own volume of air. The effect is erratic from heat to heat, depending largely on turbulence and distance of free fall of the stream of liquid metal. THIS paper reports another phase in a general study of oxidation in the open-hearth, various aspects of which have already been discussed in previous papers.1,2,3 It is based on experiments conducted on commercial, basic open-hearth furnaces at various times when opportunity offered, beginning about 1938, in an attempt to determine the mechanism and measure the amount of air oxidation during the flow of the tapping stream through the air into a ladle. This effect is closely connected, not only with alloy losses and control of chemical analysis, but possibly with various questions regarding inclusion content and steel quality and with a true picture of the deoxidation of steel in general. Thus it is believed that discussion of a large part of the results to date may be of assistance to others who are studying problems related to deoxidation or to steel cleanliness and quality. The literature reveals that strangely little attention has been devoted specifically to the effect of pouring steel through open air. Bardenheuer and Henke4 in 1939, in a paper devoted largely to overall losses of manganese in the basic open-hearth, reported that for a number of heats tapped into a tilted ladle held just beneath the runner so that the maximum distance of drop of the stream through the air was held to less than about 30 in., there was in most cases almost no loss of manganese from furnace to ladle. Hultgren,5 in 1945, showed that in high-carbon basic electric steel deoxidized in the furnace and containing no large inclusions as it left the furnace, large silicate inclusions, often rich in manganese oxide, were present in samples dipped from the pool in the ladle; also that the rise in content of large inclusions (above 0.01 mm dim) was greater when the metal stream was made to spray or flow in a turbulent manner. Our interest in this phase of oxidation in the open-hearth was first aroused by a study of alloy efficiencies on ladle additions. The frequency curves of manganese efficiency (net recovery of metal added in ladle) given in fig. 1 are of interest in this connection. Lowest, and also most variable (47 to 95 pct), recovery was in low-carbon heats having no coal additions to the ladle, progressing upward to a maximum average and least variable (82 to 97 pct) recovery in high-carbon heats killed with aluminum and silicon. Both coal additions and higher carbon contents in the tap stream, as well as additions of silicon and aluminum, help to lower the amount of manganese loss. But the most interesting point is the amount of manganese oxidized in many heats tapped at 0.50 to 1.06 pct carbon. It has been shown in a previous paper3 that the amount of oxygen in the tap stream in such heats is very small, usually below 0.01 pct, too small to oxidize any appreciable amount of manganese. Also, the fact that manganese should be oxidized at all in a metal solution containing such more stable oxide-forming elements as aluminum and silicon is an indication of some rather intense oxidizing effect such as could be caused by reaction with the air during ladle filling. Oxygen Balances from Tap Stream to Teeming Stream: Data in the form of alloy efficiencies, such as those shown in fig. 1, are not a proper measure of such a general oxidation effect. Having available

Jan 1, 1951

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 Richard E. McElvain, I. Cave

The selection of centrifugal pumps for mill discharge duty should be based on the total circuit concept. The practice of operating the mill circuit based on limitation of the pump can result in losses in one day which would offset the pump cost. Operating data from 25 grinding circuits have been reviewed and comparative results on added mill capacity have established advantages far beyond the less significant maintenance costs with increased circulating load and better cyclone operation. Mill discharge pumps should be selected on the following basis: i) Best available design for wear performance ii) Size to provide best economic life iii) Liner material best suited to circuit conditions Pump efficiency is a secondary consideration because power consumed by pumps is small compared to mill power input. Energy dissipated in mill pumps is contributing to comminution of ore.

Jan 1, 1982