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As already announced, the Arizona Meeting of the Institute is to be held from the 18th to the "25th of September. There will be a special train from New York City to Arizona and return, to take members and guests of the Institute to the meeting., The Committee in charge consists of Walter Douglas, Chairman, Cleveland E. Dodge, John C. Greenway, Arthur S. Dwight and Julius Kruttschnitt, Jr., and while the plans of this Committee are not complete, it may he announced that 'the train will be run with the requisite number of Pullman, dining and baggage cars to accommodate those who desire to go, which will accompany the party during the entire week of the Arizona Meeting as per the following program, including, of course, the visit to the Grand Canyon. It is especially desirable that the Committee should know, at as early a date as possible, the number of those who desire to make the trip; and those who desire special accommodations such as drawing rooms, state rooms, etc., are especially requested to communicate as soon as possible with the Secretary of the Institute, stating the number in their party.

Jan 6, 1916

By C. C. Herrick

The vapor pressure of indium has been measured by the torque-effusion technique, as a function of temperature between 1102o and 1422oK. For liquid indium, the vapor pressure (in atmospheres) can be represented by the equation -R In P = 5.782 x104/T - 25.29from 1000o to 1422oK. Extrapolation yields a calculated normal boiling point of 2329°K and a heat of vaporization at 298 oK of 58.09 kcal per mole by the third-law method and of 58.39 kcal per mole by the second-law method. Calculations indicate that the free-energy functions of Hultgren are to be preferred to those of Guruich. BECAUSE of the potential uses of liquid metals, it is important that convenient experimental methods be developed which will lead to a sufficient body of thermodynamic data so that reasonable estimates of properties of liquid metals can be made. Indium is particularly well-suited to investigation, since it remains liquid over a long temperature interval, it alloys readily, suitable containers for it are easily procured, and relatively few investigations of its thermodynamic properties in the region above 1000°K have been made. PREVIOUS RESEARCH The first determination of the vapor pressure of indium was made by Anderson,' using the Knudsen method and silica-lines stainless-steel cells. Kohlmeyer and spandau2 determined the normal boiling point, and a mass-spectroscopic investigation has been made by Lyubimov and Lyubitov.3 (Unfortunately, only an equation representing the data of the latter investigators has been available to us.) Hultgren et al.4 and Gurvich5 have published discordant tables of the free-energy functions for indium. EXPERIMENTAL METHOD The torsion-effusion principle has been described amply in the literature.8,7 With this method, one observes the angular deflection induced by effusion of vapor from a multihole effusion cell which is suspended from a filament producing a small rotational restoring force. The pressure within the effusion cell can be computed from the relation ziaifiai where k is the torsion constant of the filament, 6 is the observed angular deflection, and ai, fi, and qi are the area, force factor, and moment arm of the ith effusion orifice. The force factor f is analogous to the Clausing factor,' and corrects for the reduction in effusive force attributable to the finite geometry of the effusion orifice. Schultz and Searcy' have tabulated the force factors for various tube geometries. EXPERIMENTAL APPARATUS The physical arrangement employed in this study is shown in Fig. 1. The furnace elements are six Globar heat rods with 15-in. hot zones. Temperature is maintained to * 1°K by a Beck mechanism driving two 26-amp Powerstats in parallel. A Pt (Pt, Rh 10 pct) thermocouple serves as the sensing element. Four inner tubes act as vibration isolators; the air pressure required for maximum isolation was determined empirically, and is maintained by a solenoid valve. The tungsten fiber, 9 by 0.002 in., is joined to an 0.008-in. tungsten wire or graphite rod via a machined lightweight chuck.

Jan 1, 1964

For the seventh consecutive year, the value of nonfuel mineral raw ma¬terials produced in the US set a new record, reaching almost $20 billion-up 12.7% from the previous year, according to the US Bureau of Mines. The Bureau reported that this mineral production was the basis for about $200 billion worth of processed materials of mineral origin.

Jan 5, 1979

By W. R. Bull, J. R. Roos

A method is described whereby the true financial value of each constituent of each concentrate can be calculated. Each value is then compared with what this value would be in a perfect separation. The difference in each case represents the loss incurred by each aspect of an inefficient separation. The relative magnitudes of these losses indicate those avenues of plant investigation and research that offer the highest potential reward. The metallurgical efficiency of a concentration operation is difficult to express because there are two criteria of performance, namely, grade and recovery. Neither of these alone gives any indication of the effectiveness of an operation and, if they are combined in some formula, it must be empirical and unreliable because of many external factors. Since milling is an operation performed as one step in the most profitable overall method of producing a metal or other end product, the main objective of mill operation should be to make a maximum contribution to this maximum profit. When concentrates are sold to custom smelters, the income from the operation, and the costs, may be calculated. When concentrates are further processed by another division of the same company, and there is no formal financial relationship between, say, the milling and smelting divisions of the company, the mill superintendent's job is less well defined. But even so, if the mill superintendent works as though he were selling his concentrates, and uses reasonable, if fictitious, conditions of sale, then he can get a good indication of the effectiveness of his operation by calculating his "Economic Recovery". ECONOMIC RECOVERY This is a method used as a basis of operation by several mills and has been described in the literature. Very briefly, the "standard" of operation is taken as that of a mill separating the ore into perfectly pure concentrates with 100% recovery of each mineral in its respective concentrate. For example, a 4%Pb, 4% Zn ore (galena and sphalerite), would provide a lead concentrate weighing 4.62% of the feed and assaying 86.6% Pb and a zinc concentrate weighing 5.97% of the feed and assaying 67.1 % zinc. These perfect concentrates are (hypothetically) shipped to the appropriate smelters, freight and treatment charges and payments calculated, and the net return obtained. This is the optimum financial return for the operation of the mill and is used as the standard. Now the return for the actual, real-life, mill operation is calculated in the same way, and the ratio of the two is termed the Economic Recovery. Many additions and modifications may be made in any particular case. For example, if the zinc mineral is marmatite, the optimum grade of the zinc concentrate may be set lower than 67.1%. If silver is present, it will be recovered 100% in the lead concentrate in the perfect operation. Similarly, cadmium will be recovered 100% with the sphalerite. Mr. Weiss' paper' mentions a case where, because of extremely fine intergrowth between the valuable mineral, chalcocite, and pyrite, the optimum grade of copper concentrate was taken as 45% Cu instead of the theoretical 80%. Each operation will present its own possibilities in this way.

Jan 1, 1970

By Earl C. Herkenhoff

Publication of the article "The Flotation Behavior of Digested Asphalt Ridge Tar Sands" by R.J. Smith and J.D. Miller has confirmed and again spotlighted a most significant and important development in the field of tar sand and heavy oil mining. This is the ability to recover 95% of the bitumen in dry tar sands by a hot water process. The initial investigation by Miller and Sepulveda in early 1978. "Separation of Bitumen from Dry Tar Sands," was the first blockbuster. It is disappointing that there has been so little scientific and industry ackowledgement that the authors laid to rest the long entrenched belief that the sand grains had to be "water wetted" for a hot water process to be applicable. Dr. Miller and his researchers at the University of Utah used slightly different mineral dressing terminology in describing their process but it is essentially the old, established technique of high &lids attrition scrubbing at elevated temperatures with a conditioner or modifier, followed by dilution and froth flotation. Similar techniques were described in detail for other nonmetallic minerals in the mid-1940s by Stuart Falconer of American Cyanamid Co. The authors used a 15-minute "scrub" period (or in their terminology "digester step") at 73% solids and 95OC (203°F) in a 0.3 m solution of sodium carbonate-about 4 kg/t (8 lb per st) of tar sand. Flotation was at 10% solids. Obviously, the scrub is an expensive step with respect to energy input but the high recovery of bitumen appears to justify it. Two basic questions then arise: What are the effects of shorter scrubbing time, lower temperature, and less sodium carbonate? Would a two-stage approach be advantageous? That is, could you get the major proportion of the bitumen with a mild scrub and apply the high power and temperature only to the refractory portion? These variables should be evaluated. Apparently, all results were only for rougher flotation. What would the grade and recovery of bitumen be if multiple cleaner flotation steps were employed? We must concede that a 60.62% grade of bitumen leaves considerable room for upgrading. Finally, it should be noted by all executives who approve funds for heavy oil recovery schemes, most of which are variations of in-situ methods, that mining can yield a 95% recovery of bitumen. That is correct, 95%. Imagine what that does to the total barrels recovered from a heavy oil resource compared with the scrawny 30-35% maximum recovery we are getting now. The conclusion-let's mine heavy oil and tar sands.

Jan 1, 1983

By C. S. Smith, L. W. Kempf, C. S. Taylor

The thermal conductivity of aluminum alloys is of considerable industrial importance. This is particularly true in such applications as internal-combustion engines where one of the principal reasons for the use of these alloys is their relatively higher thermal conductivity. In spite of this, relatively few data are available on this property of aluminum alloys. The reason is quite apparent to anyone concerned with the experimental determination of coefficients of thermal conductivity. This determination, in theory so simple, is extraordinarily difficult if any high degree of precision is desired. Fortunately, some .knowledge of the relationship between thermal and electrical conductivity has permitted the use of the latter physical property in deducing the relative approximate values of the thermal conductivities of metals. This fundamental relationship, first enunciated by Wiedemann and Franz' as applying to metallic elements and later shown by Lorenz2 to be applicable to alloys within a single metallic system, has been of service in the industrial application of metals. The electrical conductivity of metals is easily determined with a high degree of precision. It is, therefore, quite desirable that the relationship between electrical and thermal characteristics be determined with the greatest possible precision. This paper presents data on the electrical and thermal conductivities of a number of aluminum alloys of industrial importance. Literature on Thermal Conductivity of Aluminum Alloys Masumoto3 determined the electrical and thermal conductivities of 18 aluminum alloys. His results indicated a relatively constant relationship between thermal and electrical conductivity.

Jan 1, 1937

By John Birkinbine

A specimen of brown hematite, taken from an iron-ore mine near Anniston, Alabama, exhibits a metallic streak or thread running throngh it. This specimen having been sent to me, I have no personal knowledge of its occurrence; but Mr. Albert E. Noble

Jan 1, 1895

By Harmel A. Dawson, Robert A. Wilson

First the basic steps to determine the values present and the minerals involved which are the basis for the metallurgical testing are presented in this paper. Next, choosing the process or processes indicated for treating an ore are discussed. This is followed by the test procedures used, the results of which will indicate amenability to treatment. These test procedures have been developed, used and proven effective in laboratory evaluations relative to plant processing. Special, uncommon processing is beyond the scope of the paper. Evalutation of test results and incorporation into the preliminary and final flow sheet for plant design are discussed. The value of a flow sheet, with material and water balances, to plant design is shown.

Jan 1, 1978

By J. L. Huitt, B. B. McGlothlin, D. K. Lowe

Published correlations for the principal aspects of hydraulic fracturing were combined into a digital computer program to facilitate the study of interrelated variables. The computer program includes individual relationships for fracture width during pumping, fracture area generated, propping agent embedment, flow capacities of propped fractures and transport of propping agents in horizontal fractures. The effects of more than 20 treatment and formation parameters on the predicted results of hydraulic fracturing treatments were studied. The effects of these parameters were determined for (I) fracture width during injection, (2) fracture width after the overburden comes to rest on the propping agents, assumed not to be crushed, (3) generated and propped fracture area, (4) location and concentration of propping agents in the fracture when injection ceases, (5) flow capacities of the various propped sections of the fracture and (6) expected increase in the well productivity. The effects of propping agent, formation and fracturing fluid parameters on well productivity are discussed. The parameters that were found to have the most pronounced effects on hydraulic fracturing treat~nents are injection rate, treatment volume, fracturing fluid coefficient, size and amount of propping agent, spearhead volume, well drainage radius and formation capacity. INTRODUCTION Many correlations have been published for predicting effects of various parameters that are considered in the design of hydraulic fracturing treatments. The Carter equation' can be used to predict generated fracture radius as a function of fracture width, fracturing fluid leakoff and other parameters. Fracture width can be determined by use of the Perkins and Kern correlation' in which the fracture width is related to the fracture radius, fluid injection rate and certain formation and fracturing fluid parameters. Wahl and Lowe et aL4 have reported methods of predicting the location of propping agents in fractures when pumping ceases. The former study is applicable to the case where the ratio of propping agent diameter to fracture width is less than 0.1. The latter is applicable when this ratio is greater than 0.1. These studies showed that the propping agent placement in horizontal-radial fractures depends principally on how the individual particles are transported in the fracture by the carrying fluid. Particle transport in fractures is determined by local fluid velocity in the fracture, fluid and particle properties, and the size of the particle relative to the fracture width. The distribution of propping agents, effective overburden pressure and formation rock strength control the propped fracture width6 by controlling the extent to which the propping agent particles embed into the fracture faces. From the distribution of propping agents and the propped fracture width, fracture flow capacities can be calculated or the various regions of the fracture. The flow capacities and the radial extent of these regions can be combined with reservoir information to predict the productivity increases for fractured wells. In all these studies, the effects of certain treatment and/ or reservoir parameters on one facet of fracturing can be predicted only if other facets which the parameters affect are fixed. For instance, fracture width and radius are interrelated; that is, to calculate the value of one, the value of the other must be known. Also, some parameters influence more than one aspect of fracturing. For example, prop-pant transport is a function of both fracture width and fluid viscosity. but fracture width is itself a function of fluid viscosity. Since these calculations are complex and the parameters interrelated, it is not possible to write an equation with which the over-all effects of treatment parameters can be solved explicitly. For these reasons, the correlations for determining the effects of the parameters which are most significant in hydraulic fracturing treatments have been incorporated into a digital computer program. COMPUTER PROGRAM The program, which was written for an IBM 7094 computer, can be used to predict results of most of the combinations and values for the treatment parameters that are ordinarily considered for fracturing treatments. A spearhead of fracturing fluid and a propping agent-carrying fluid with different fluid properties can be taken into account. Also, the total volumes and relative amounts of the spearhead and carrying fluids can be varied. Two different propping agents (as used in tail-in operations) and a wide range of formation properties and injection rates are considered. The computer program (Fig. 12) consists of several sets of calculations. First, the final flooded fracture radius and average fracture width at the cessation of pumping are calculated. This is done by simultaneous solution of the Perkins and Kern fracture width equation and the Carter equation for flooded fracture radius (equations used in the computer program appear in the Appendix). The next step is to determine local fluid velocity in the fracture as a function of time and radius. Since it is not possible to write this function in closed form expression, a table of velocity values is generated by the program and stored for subsequent use. The time span from the beginning of

By G. Donald Emigh

Nothing is more important to life-plant and animal-than phosphate. Its compounds are essential to the energy functions of all living systems and for the formation of bones and teeth. Animals get their phosphate from eating plants and other animals, or domestically from feed supplements. Plants get their phosphate from the soil. Man's most important use of phosphate is for fertilizer; however, he is also a heavy user of many industrial phosphate chemicals. Phosphate occurs in all igneous and sedimentary rocks, and in all fresh and saltwater. The average content in rocks is 0.1 to 0.2% P2O5, as documented recently by McKelvey (1973). About 200 minerals contain more than 1 % P,O,. However, the important one in igneous rocks is fluorapatite, (Ca,(PO,) ,F) containing about 42% P,O, and 3.8% F,; in sedimentary rocks the one important mineral is francolite, a carbonate fluorapatite containing up to 2% molecular CO,. Both are in the apatite family of minerals. The mineralogy of phosphate minerals was reviewed recently by Altschuler (1973). Although phosphate occurs in nearly all rocks, economic recovery is limited to deposits where natural concentration of the phosphate mineral has occurred. Occasionally natural concentration is great enough that the material can be used as mined; generally, however, the ore is low grade and must be concentrated.

Jan 1, 1975

By Frederick C. Hull, Robert F. Mehl, Robert A. Colton

IT is known that pearlite forms from austenite by a process of nucleation and growth, and that the rate of formation of pearlite may be described by a rate of nucleation and a rate of growth 12 The manner in which these two quantities operate to produce the observed isothermal reaction curve has been analyzed in a paper published in 1939 3 Two types of process were described (I) that in which nucleation occurs at the grain boundaries of the parent phase, with the nodules growing toward the centers of the grains, initially as hemispheres and then after impingement as roughly radial-columnar structures, and (2) that in which nucleation occurs generally, with the nodules growing to full spheres until impingement with other growing nodules restricts growth Both cases are met in the formation of pearlite from austenite (Fig 1),2,3 the former, occurring near the knee of the S-curve has been named "grain-boundary transformation," and the latter, occurring at temperatures near AeI, has been named "group-nodule transformation " In developing our knowledge of the factors that determine the rate of formation of pearlite from austenite, it is important''' to obtain data on the rate of nucleation and the rate of growth of pearlite Such data, when obtained near the knee of the S-curve, will furnish information of use in understanding the actors that affect hardenability, when obtained at higher temperatures, such data will be useful in understanding the behavior of steels that during heat-treatment react to pearlite 2 It is the purpose of this paper to present data on the rate of nucleation and the rate of growth of pearlite in dependence upon composition, grain size, temperature,, and the degree of homogeneity of the parent austenite The studies are restricted chiefly to plain carbon commercial steels PREVIOUS DATA ON RAID OF NUCLEATION AND RATE OF GROWTH Data on the rate of nucleation and the rate of growth of pearlite have been published by Scheil and Lange-Weise,5 by Mirkin and Blanter,6,7 by Mehl,1 and by Dorn, De Garmo and Flanigan22 It is difficult to interpret the data, for in most cases too little information is given on austenitizing temperatures and times, the state of homogeneity of the austenite (presence or absence of carbide, etc ), austenite grain size, and mode of formation of pearlite at the temperatures given

Jan 1, 1942

By Howard H. Fields

Any mining engineer with a desire to operate independently, with some financial backing, and with no fear of heavy responsibility and long hours, should be able to make a comfortable living in Mexico. Barring a few inconveniences such as a lack of satisfactory liability or accident insurance, the difficulty of obtaining repair parts for vehicles, and the length of time required receive returns from shipments, the operation of a small mine is not at all difficult. It is, in fact, a little easier to find a good prospect in Mexico than in the U.S.

Jan 11, 1950

By J. A. Roberson, Robert A. Rapp

From the observation of platinum wire marker movement in the oxidation of columbium at high lemperatures and low oxygen pressures, predonzinant cation diffusion in CbO, has been demonstrated. The Cu,0 molecule was used as an oxidizing species to study the nature of the porous scale and the location of the reduction site in the oxidation of colum-bium. The Cb205 scale contains microporosity and forms by alternate ionic diffusional growth and fracture. The oxidation of columbium at high temperatures and very low po, results in a relatively compact and protective Cb205 layer. THE observation of marker movements during oxidation is one means for the identification of the mobile ionic species in an oxide lattice. Previous marker experiments in the oxidation of columbium have all resulted in the markers being found on the outside surface of the Cbz05 scale. The Cr203 powder markers of Klopp et a1.,' the gold film marker of Kofstad and ~jijllesdal,' and the platinum wire marker of Cathcart et a1 .3 were found at the oxide/gas interface for oxidation temperatures ranging from 450" to 120O0C. However, in all experiments relatively high oxygen pressures were used. As discussed by Mrowec, even the interpretation of marker experiments in simple scales containing only one compound is not without ambiguities. In brief, it can be said that a marker may be found almost anywhere in the scale layer if the metal oxidizes by cation diffusion through the scale; the position of the marker depends upon morphological happenings in the scale. When considering marker movement in a polyphase scale one must proceed with extreme caution. For example, in the past (and present) work markers have never been found at the columbium-scale interface, and one might infer that the oxygen ion is mobile in CbO and CbO,. However, only trace quantities of CbO and CbOz have been present on any of the specimens, so no firm statement is justified on this basis. Despite previous experimental work, considerable doubt still exists concerning the role of the oxides CbO and CbOz in the oxidation of columbium. The identification of the mobile ionic species in CbO and CbOz from the observation of platinum wire markers was one goal of the present investigation . The linear kinetics of columbium oxidation at high temperatures (T - 1000°C) suggests that the Cbz05 scales which form on columbium are porous. From mercury absorption measurements on a Cbz05 scale formed at 500"C, Aylmore et al.' reported a minimum volume fraction of connected voids equal to 0.15. While these scales often appear to be quite porous when viewed in metallographic cross section, they are so brittle that metallographic preparation is likely to exaggerate any porosity originally present. In this investigation, porosity developed during the oxidation of pure columbium and present at the high temperature was detected by oxidizing specimens in sealed evacuated capsules containing large compacts of mixed copper and CuzO powders. wooda has demonstrated that the CuzO, or (CuzO),, molecule is volatile and that oxygen is transferred by the CuzO molecule from a Cu/CuzO mixture to materials having a greater affinity for oxygen. For each molecule of CuzO that is reduced at a sink for oxygen, two atoms of copper are deposited. Quantitatively, essentially all of the oxidation carried out by a Cu-Cu20 compact results from a displacement reaction involving the CuzO molecule. When a metal which oxidizes to form a porous scale is exposed to the CuzO vapor, the CUZO molecules are reduced in the pores leaving a deposit of metallic copper to mark the site of the reduction. This technique has the rather unique advantage that any copper-coated pores found in the scale are unambiguously related to the reduction site in the growth of the scale under consideration. Pores or cracks which form in a msition*- external to the reduction site or which occur as a result of cooling or handling of the specimen will not exhibit the copper deposit. EXPERIMENTAL PROCEDURE Marker experiments were made on columbium metal, and on pellets of CbO which had been pressed and sintered. Platinum wire markers (0.001 and

Jan 1, 1968

By N. F. Dyson, T. R. Scott, M. R. Thornber, W. E. Ewers, M. Bussell

Leach liquors derived from the processing of nickel ores are generally highly contaminated and contain appreciable free acid. Methods are described for obtaining a commercial grade of concentrate from such solutions using pyrrhotite as the seed material to abstract nick- el, cobalt, etc. from solution. At temperatures in excess of 160° C., recoveries of 99% can be obtained from contaminated solutions where the free acidity is as high as 0.5 M in sulphuric acid. At lower temperatures down to 80° C., high recoveries can also be obtained either by adding H2S to the system with appropriate adjustment of the free acidity or by using "activated" pyrrhotite or artificial FeS in the system without prior addition of H2S. The methods are applicable to liquors derived from either oxide or sulphide ores, and the products are suitable for smelting or other known processes used to obtain pure metals. The mechanism of the reaction appears to vary with the operating temperature, and the results ye therefore discussed in the light of electron probe and optical microscopic studies.

Jan 1, 1973

By N. A. Zeigler

GRaphitization phenomena occurring in solid cast iron have principally been studied from the angle of the reactions taking place during annealing of white castings in the manufacturing of malleable iron. The selected bibliography at the end of this paper presents the high spots of the published information in this field. Graph-itization of gray iron upon reheating has received much less attention, primarily because only on rare occasions is this material subjected to any kind of industrial heat-treating. Moreovcr, articles made from gray iron are seldom used commercially at temperatures when any graphitization can take place. When used in such conditions, it is assumed that the articles can be replaced at frequent intervals, which can be afforded because of the low cost of gray iron. However, there is at least one commercial process in which articles made from gray iron, during their manufacturing processing, are subjectcd to rather high temperatures; that is, manufacturing of cast-iron enamelware, which is glazed at about 1600° to 1700°F. (870' to 930°C.) From practical experience, it has been found that one of the convenient and economical compositions of gray iron suitable for enameling is, in round figures, as follows: Si, 2.50 per cent; Mn, 0.35; S, 0.07; P, 0.80; T.C., 3.35; C.C., 0.70. Since this iron usually is cast into thin-walled sections, the percentage of com- bined carbon in it is relatively high. Upon heating in the enameling furnaces, this combined carbon graphitizes, which causes permanent dimensional changes of the articles. Obviously, from practical considerations, it is desirable to maintain these dimensional changes as constant as possible. In the course of experimentation with this iron, two series of experimental heats were prepared in which the manganese to sulphur ratio of the standard cupola metal was offset by ladle additions of: (I) progressively larger amounts of sulphur, and (2) progressively larger amounts of manganese. Each one of these ladle charges was cast into experimental plates 8 by 4 in. and about 5/16 in. thick. All told, 13 ladle charges were thus treated. All of them are listed in Table I, together with their chemical analyses. It may be noted that the manganese to sulphur ratio in these samples ranges between 1.2 and 30.2. Every one of these compositions was subjected to thermal allalysis, using an automatic, self-recording differential dila-tometer. The specimens used in this instrument are 50 mm. long and 4 mm. in diameter. During the dilatometer cycle they are kept under a vacuum of about 3 microns. Each one of them was subjected to a thermal cycle by heating it to I830°F. (1000°C.) in 3 hr. and cooling to room temperaturc in 5 hr. Figs. I, 2 and 3 present three automatically recorded dilatometer curves for irons: Serial No. I (normal composition), Serial No. 6 (high sulphur), and Serial No. 13 (high manganese). All three of these figures are

Jan 1, 1945

By Edward A. Vitunac

The emerging importance of pneumatic conveying systems for bulk materials is largely due to the economic advantages such systems frequently exhibit when compared to alternate methods. Included in these advantages are relative simplicity, ease of installation, flexibility, ease of maintenance, cleanliness, safety and ease of automation to the degree desired. In general, installed costs favor a pneumatic system when compared to competing mechanical systems if the transporting distances are long or to and from many points. In addition, supplemental use such as cooling, heating, or drying may supply the incremental value required to justify its selection.1 The main disadvantages of a pneumatic system are the greater horsepower required per unit weight of material conveyed, material limits in abrasiveness, and density. In addition, material breakage tends to increase at changes of direction and at any obstruction such as that caused by the imperfect butting of two pipe sections in the conveying line. Classification of the material at the discharge may also cause problems in dusting and segregation. Materials weighing less than 4 lb per cu ft tend to cause feeding and collecting problems although they can be conveyed easily. Material between 4 lb and 20 lb per cu ft can be handled with fewer problems, but flow rate is hard to predict. The 20-60 lb per cu ft range offers best results, whereas materials of over 60 Ib per cu ft tend to drop out of the air stream and settle in the pipeline unless careful pro- visions are made to prevent this.2

Jan 5, 1968

By K. L. Woodruff

The first step in processing municipal solid waste (MSW), principally household waste, for resource recovery is usually shredding. A trommel has been investigated as a step to precede shredding. This way abrasive inorganic materials, such as stones and metals, would be removed prior to shredding, thus lowering the amount of feed and hence maintenance on the shredder. In addition, friable materials such as glass would be removed in large pieces, rather than pulverized too mall to process for recovery. The utility of a trommel for these purposes was investigated on a pilot scale using a unit 9 ft diam by 10 ft long with 4-in. square clear openings. Experimental results indicate that up to approximately half of the MSW may be removed as -4-in. material prior to shredding. The -4-in. fraction contains approximately 70% of the metals and 95% of the glass present in the MSW feed to the unit. Scale-up and cost information necessary for the design of a 60 to 70 tph unit is developed.

Jan 1, 1977

By C. BARING HORIVOOD

(Chattanooga Meeting, October, 1908.) THIS paper is intended, in the light of recent investigations, to call attention to some of the essential features of good practice in sampling and mine-valuation. Mine-sampling may be divided broadly into two classes : (1) development-sampling and computation of ore-reserves; and, (2) stope-sampling and estimation of stope-values. DEVELOPMENT-SAMPLING. It is with development-sampling only that this paper deals-the term development being taken to mean the opening-up of a mine by cross-cuts, drives, connections, etc., preparatory to actual extraction of the ore for milling. In development-sampling the work of the sampler and the consequent estimation of the probable value of the mine or portions of the mine, as the case may be, cannot be verified until a later period, when the ground thus sampled has been exploited; hence, extreme care and accuracy are essential. Moreover, the development-sampler has to foresee and allow for contingencies which may arise when stoping is started. It follows that the sampling, in development-work, demands familiarity with the conditions likely to be encountered later in actual mining. In stopes, on the other hand, sampling is clone under actual working-conditions, and the sampler's valuations are immediately checked by the gold-output, or in some cases by a second sampling of the broken ore. A stope-sampler therefore need not be an experienced miner, though he should possess sound technical training and work accurately. Should he be somewhat inexperienced, be soon has his errors discovered for him, and learns to avoid them. Taking these facts into account, it is obvious that a mining company employing two or more samplers should

Jan 1, 1909

By J. A. Herbst, A. L. Mular

Digital simulation is defined and simulation techniques are re- viewed. Typical methodology involves the selection of models, the adjustment of raw data, the selection of a fitting strategy, the assessment of model accuracy in a statistical sense, and the development of an executive simulation structure. Simulations serve as aids for process engineers in evaluating the feasibility of a proposed flowsheet and the effect of a modification to an existing flowsheet. In addition, simulation plays an important role in off-line optimization and in the evaluation of alternative circuit control strategies. Several examples are presented to illustrate these uses for simulation including applications in crushing circuits, grinding circuits, and flotation circuits. It is the opinion of the authors that, within the next decade, mineral processing plants will be studied routinely via digital simulation during the preliminary design stage. Simulation will constitute an important component of the design decision making process.

Jan 1, 1978

By James Hyslop

MECHANIZATION of American coal mining continues to make rapid progress. Economic pressure will compel abandonment of manual methods wherever possible and will also provide the incentive needed for the improvement of machines and mining systems. However, rapid progress may be made along strictly technological lines and at the same time much slower progress in approaching maximum productivly and efficiency. One can well ask, just how efficient are mechanized mines, and to what extent is productivity affected by the mental attitude of management and workers?

Jan 1, 1946