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By Foster Fraas

Most commercial electrostatic separators utilize the electrical property of conductivity, but although based on the same principles, they are constructed in a variety of forms, a common one being the simple roll type. Some information obtained during an investigation of that type of separator, and which indirectly is applicable to other types, is presented here. In Fig. I material discharged from hopper 6 is fed onto grounded rotating roll 2. Electrode 3 is at a high electrical potential with respect to roll 2, and any conductive particle in contact with roll 2 therefore acquires an electrical charge of such polarity that, when present in the electrical field, the force on it is in the direction of electrode 3. A detailed description of the charging by conductance as utilized in electrostatic separators may be found in a previous publication.' As a result of this force, the path of the projected particle is changed in increasing amounts in the direction toward region C as the magnitude of the charge is increased. With the dividing edge 4 the projected particles may be divided into two fractions —those in region C designated as "deflected" or"deflectant"and those in region B designated as "residue." When material is passed over the roll only once, a complete separation is seldom obtained, therefore most commercial separators contain several roll-separator units in series, and some practical machines use as many as I2. In this paper a "pass" means the passage of material over a single-roll unit. The procedure is to repass either residue B with a low potential on electrode 3 or deflectant C with a high potential on 3. Most electrostatic separations follow a flowsheet of roughing and cleaning either the concentrate or the tailing, or both. In a specific instance, a dry, heated mixture of wet cleaned chromite and garnet from an

Jan 1, 1943

Charles R. Eeyes, Des Moines, Ia. (con~munication to the Secretary*):—It is not in a spirit of criticism that I offer a supplemental suggestion or two on the subjects covered by this valuable and highly instructive memoir. There are two points which, in my opinion, should have received greater emphasis in Mr. Emmons's excellent paper. One is the fundamental r6le played by the chlorides under certain conditions in ore-formation. The other is the possible establishment of geographic relationships among the four pheilomena of (1) excessive chlo-ridic content of mine-waters; (2) the abundance of chloridic compounds of the precious metals; (3) the presence of man-gancse oxides; and (4) the diminishing importance, in ore-genesis, of the metallic sulphates. Although Mr. Emmons's notes refer to gold alone, it may be pertinently asked whether the same principles do not hold good for silver and copper also, since these metals form, together with gold, a distinct and well-known chemical group. That the reactions involved apply equally well to the other two metals mentioned, is sbown by a number of recent observations and discussions. Chloridic ores of silver are, as I have lately endeavored to show, mainly worked in arid or desert regions only; and the great deposits of disseminated copper-ores are similarly characteristic of such regions, in which both classes doubtless owe their formation to the abundance of saline materials derived from desert dusts, and to the plentiful and almost universal presence of manganese oxide. Under these climatic conditions, silver is somewhat more abundantly deposited than copper and gold, because its chloride is so much less soluble. During volcanic emanations, the metallic chlorides perform at all times distinct functions; when these are

Jan 1, 1912

By Alexander Bowie

IN many places throughout the Western mountain plateau regions of the United States coal beds in place have been burned over very extensive, areas, the fire evidently originating on the nakedly exposed outcrop of the coal bed and gradually burning its way into the bed for considerable distances under very heavy cover. . The surface evidences of the burned-out coal beds are seen in the calcined and discolored rocks overlying the places of the outcrop. The greater the mass of the burned coal the higher the results of its combustion can be seen in the overlying strata. I have noted many instances of this condition in the States of South Dakota, Wyoming, Colorado, New Mexico, and Arizona. In the lignite fields of Dakota and Wyoming I noted stretches of level country many square miles in extent where the surface rocks were roasted and vitrified by the burning of a great bed of lignite lying nearly level and with a light cover; this is probably the most favorable natural condition for the burning out of a coal bed. The less the depth of the rock covering overlying the coal bed, the better the .chance for a continuous supply of air to the fire; but when the coal bed clips heavily into the ground, or even if level, if it, passes under a hill or mountain which gives the bed a heavy covering of strata, the fire has more chances of being extinguished from natural causes than in the first condition described. The distance which, a crop fire may extend into a coal field is very much influenced by the dip, the thickness of the coal bed, and the nature of the rock covering immediately overlying it.

Jan 2, 1914

By J. M. Hartman

ONE of the most important subjects to the blast-furnace engineer is a thorough knowledge of the conditions affecting the temperature in the different portions of the furnace. All efforts to decrease the consumption of fuel and improve the working of the furnace must be based upon it, and I may, therefore, be permitted to place before you the results of my observations, and detail the conclusions to which they have led me. Tracing the thermic conditions from below upwards we have at the bottom of a blast furnace making No. 3 iron a temperature of 2900' F., which increases slightly to a point a little below the tuyeres. In the immediate vicinity of the tuyeres the temperature is somewhat lower, owing to the entering blast; but a short distance above the tuyeres, where all the oxygen of the blast has been converted into carbonic acid, the highest temperature in the furnace must be attained. This carbonic acid is, however, almost as soon as formed, converted by the glowing coal into carbonic oxide, a process which absorb, heat, reduces the temperature, and provides the active agent for the reduction of the iron ores. In its ascent the hot carbonic oxide gradually parts with its heat, first melting the descending iron and earthy materials, which drop down to the hearth of the furnace. The limit of this zone of fusion is rather sharply defined, and the temperature above this zone suddenly decreases. In its further ascent the hot gas drives off the carbonic acid from the limestone, which causes a further absorption of heat, and finally the gas escapes at the top, at a ternperature of about 250' F. if the furnace is working well. These changes of temperature I have attempted to represent graphically,

Jan 1, 1880

By F. F. Aplan

INTRODUCTION The production of coal is a major part of the mining industry. In recent years the production of clean coal has exceeded 600 million tons per year and is reported to have reached 660 million tons in 1977. Some data on the magnitude and utilization for the year 1975 is given in Table I. In that year 648 million tons of soft coal were produced and of this 267 million tons or 41% approximately was produced by mechanical cleaning. Of the 374 million tons of raw coal sent to the preparation plant, 28.6% or 107 million tons was discarded as refuse. In the same year approximately 6 million tons of anthracite were produced and nearly all of this was cleaned. Table I also gives coal utilization statistics for 1975. Excluding the approximately 20% that goes to the coke ovens or to export, the vast bulk of our production is used for steam power generation and a lesser amount for captive production of industrial power and process steam. While much of the nation's coal (e.g. strip mined western, sub-bituminous coal) may be removed from the ground in relatively pure form by modest selective mining techniques, other coal requires preparation in order to remove ash and sulfur constituents and produce an acceptable steam or coking coal. Preparation is often a valuable adjunct to mining in that rather non-selective, low cost, bulk mining techniques may be used underground while the preparation plant is used to reject refuse at low cost above ground. The principal reason for the use of coal preparation is to convert raw coal into an acceptable commercial product by removing the high ash and high sulfur refuse material.

Jan 1, 1979

By Gordon S. Duncan

The U. S. Geological Survey, I believe, has almost completed a study of the Harney Peak quadrangle, preliminary to the publication of a report on that district. As I was engaged for some months on an investigation of the mode of occurrence of the ore-bearing formation in this area, it has seemed to me timely to make public the results of my study, as a contribution to the consideration of this subject. It seems scarcely necessary to describe the locality and general geology of the Black hills of South Dakota, for since 1846 many have contributed information concerning this region, some of the reports bearing such well-known names as those of Walter P. Jenney, Henry Newton, S. F. Emmons, and C. R. Van Hise, while me have only to glance at Bulletin No. 4 of the South Dakota School of Mines, in which Prof. C. C. O'Harra, of that institution, has given us a bibliography of contributions to the geography and geology of the section, to find that other well-known men have studied the district, and have given us the benefit of their researches. The U. S. Geological Survey has made geological maps of nearly the whole of the Black hills, the only quadrangle yet to be conlpleted being, as stated, the Harney Peak district. During the late summer and autumn of 1910, it was my lot to examine and report on a considerable area in this neighborhood, which once had been prospected, and in some cases exploited, for tin. This paper gives an account of certain geological phenomena, noted at that time, which greatly influenced my conclusions. The predominating formation of the district is pre-Cambrian, represented by a highly-cleaved mica-schist, usually very gar-netiferous, and sometimes hornblendic. Rising like an island from the surrounding schist is a large mass of granite, known as

Jan 1, 1913

IN CIRCLES where mining men are wont to fraternize, a statement often heard is: "Yes, I spent six (or two, or ten, or thirty) years down at 'Chuqui.' " This means Chuquicamata, the site in Chile of what in all probability is the world's largest deposit of copper ore. One hears similar remarks regarding Braden and Andes, and, in fact, regarding a score of other big mines in South America, Africa, and elsewhere, but Chuqui seems to lead the others as the locale of engineers who have done a stint in foreign countries. One reason probably is that it is the Anaconda Company's premier foreign operation. Because of its unusual size and the diversity of its operations a great many men are needed. It is a sort of training school for young engineers; but, also, Anaconda has sent down a great many mature members of its big organization for special assignments like metallurgical research or plant construction. Chuquicamata is about 150 miles northeast of Antofagasta, at an elevation of 9,500 ft. It is in an almost rainless desert country where the wind (it is alleged by some) blows most of the time. However, the copper mining entrepreneurs have done their best to make up for what nature has neglected to do in creating a pleasant environment for the people who operate the mines. These include about 160 "foreigners" of whom 86 are from the United States, most of them accompanied by their families. There are 165 Chileans on the staff. Comforts, conveniences, and many luxuries are provided to offset in some measure the disagreeable features of the climate. Nevertheless, as I have implied, engineers at Chuqui generally jump at the chance to become "alumni" when opportunity offers. At the same time, they appear to take pride in their alma mater.

Jan 1, 1957

By James Douglas

I had the good fortune to visit the Stockholm Exposition just before its close in October last, and to get a glimpse of the methods used in Sweden in making the wonderful steel and iron for which its furnaces are so famous. My time and opportunities for observation were limited, but some points which I noted may be worth bringing to the notice of the Institute. The Exposition itself was confined to the natural and artificial products of Scanclinavia, and therefore iron and steel held a very prominent place in it. There was a complete collection of the rocks and ores of the Peninsula made by the Geological Survey; and every iron-mine of note exhibited a glass model of its workings, as well as classified specimens, accompaniecl by thorough analyses of the ores. Another feature of interest was the display of models of the old mining-machinery, in the invention and introduction of which Sweden led the way, and of the old and new surveying-instruments and compasses devised for the exploration of the Swedish iron-ore bodies, all of which are more or less magnetic. The magnetometric collection and exhibit of methods of operation made by Prof. Nordestrijm were supremely instructive. The larger metallurgical works, such as those of the Kopparberg and Sandvik companies, exhibited their wares in separate pavilions, in which crude and manufactured objects were arranged most eflectively and tastefully; while the smaller companies erected in the Industrial Arts Building trophies, every one of which was an object of beauty. One was struck on all sides by the fine asthetic feeling exhibited in the ingenious installation of materials and objects not easily lending themselves to artistic treatment. Hammers, picks and drill-steel were grouped into mural designs which it was a delight to look at.

Jan 1, 1899

The notion prevails that writing is a knack, that the skilful use of the pen is a gift of nature. This is an error. Dogberry may be responsible for it; he said: "To be a well-informed man is the gift of fortune, but to write and read comes by nature". Because Dogberry said it, we may be sure that Shakespeare thought otherwise. Ability of any sort may be partly innate, but my own observation and experience lead me to conclude that most of the easy writers have become so by constant practice. As I recall the names of men successful with the pen, I remember that most of them have written a great deal and have taken particular pains to improve their style. The suggestion that proficiency in the difficult art is a happy accident provokes a sardonic smile. The larger part of the great writing in our literature is the result of persistent effort. An easy fluency has been the undoing of many; their flamboyant and fantastic scribbling has proved as perishable as froth. This criticism applies to technical writing also; in order that a technical description or discussion may hold the interest of the reader, at least long enough to cause him to read it to the end, the writing must be done carefully and systematically; otherwise it will fail in its purpose of conveying information. Clearness is absolutely essential. "It is not enough to use language that may be understood; it is necessary to use language that must be understood."* The purpose of writing, at least of that which is meant to be read by others, is not only to express ideas but to communicate them. Lack of perspicuity may prove as bad as

Jan 1, 1931

APRIL 10-Officially, spring comes to the Great Lakes on March 21 as it does elsewhere in the country but in the Superior district continued snow and freezing until late in March have caused citizens in Duluth to place their bets on April 15 for the first ore vessels if the ice breakup is left to Mother Nature. North and west of Duluth and near the eastern end of the Mesabilies the little town of Aurora, population 1100. As the little v-nosed snowplow, pride of the community, shuttled back and forth clearing Aurora's few sidewalks, the crowd in Bradich's Cafe were more interested in the impending high school state championship basketball tournament in Minneapolis than in the outcome of Erie Mining Company's petition for water rights for their proposed 10 million ton taconite concentrating plant. Such a plant would employ 4500 workmen, and at the prevailing ratio of 10 people for every mine worker in Minnesota, this would mean a 45,000 increase in population for Aurora and the vicinity in the next few years. Downstate fishermen are alarmed at the flurry of activity by the mining companies in pushing plans for large scale recovery of iron from taconite. Inconvenience to these gentlemen will be inconsequential when compared with the vast increase in payrolls for range communities. Oliver is pushing the construction of a fine ore agglomeration plant at Virginia which will give them valuable experience for projected taconite processing. Oglebay, Norton & Co. is ready to go at Beaver Bay, north of Duluth, as the right of way for a railroad from Babitt to Beaver Bay is secured as well as permission to dispose of tailing into Lake Superior at the site of the proposed concentrating plant. This company is also doing research in agglomeration at Ashland, Ky., in cooperation with other interests. The financing is yet to be worked out. Of the four possibilities for agglomerating taconite concentrate-sintering, pellitizing, nodulizing and briquetting-the prospects for pelletizing appear the most favorable., It seems likely that 60 cents per ton can be saved by this process over sintering because only 1 to 2 pct of coal is required as compared with 7 pct for sintering. One reason for the lower coal consumption is that the chemical transition of magnetite to hematite which transpires in the pelletizing process is exothermic.

Jan 5, 1950

By R. H. Swallow, George Hess

Aerial photography was once a crude, uncertain tool. Today it is a precision mapping instrument which saves important time and money for strip mining and other industry. Aerial photography began in the boxkite days of aviation. The Army first used it for rough reconnaissance photographs. Then, in the early Twenties, industry began to use aerial photographs of their plants and facilities for advertising or annual reports. The quality of these pictures was not very good by today's standards, but this work began the development of better cameras, better lenses, better photographic techniques.

Jan 1, 1949

By G. R. Fritterer

Investigators in the field of temperature measurement have long sought a thermoelectric couple fulfilling the following requirements: 1. It should be useful up to and including high industrial temperatures; i. e., 1000 to 1800 C. 2. Its thermoelectric variation with temperature should be linear and be maintained after heating to high temperatures for long periods of time. 3. It should be reproducible; i. e., different couples of the same elements should have similar calibration curves. 4. Its thermoelectric power should be large so as to allow the industrial use of rugged recording instruments. 5. Chemical reactions with, and physical changes within the elements of the couple should not alter its calibration. No thermocouple proposed to date exhibits simultaneously all of these characteristics, whereas the couple about to be described fulfills all requirements to a satisfactory degree. New Thermoelectric Materials A thorough survey of the literature on thermoelectricity revealed that present-day thermocouples could not meet the specifications mentioned above because their thermoelements are metallic. Metals have a marked tendency to deteriorate chemically and their melting points limit their use to low temperatures. Refractory substances, however, are usually resistant to chemical attack and are quite stable at high temperatures. Hence a survey of refractory substances having thermoelectric possibilities was made. One class of thermocouples considered was that in which carbon and a carbide of some metal or nonmetal were the thermoelements. Previous investigators neglected to study this field but certain recommendations were made by them for the use of couples in which carbon served as one element. These proposals are listed in Table 1. The couples suggested are unsatisfactory because of their low thermoelectric powers, the low melting points of their metallic elements, etc. The

Jan 1, 1933

By H. C. Fiedler

Heats of high purity iron containing 3.1 pct Si and be -tween 0.0003 and 0.0295 pct N were prepared by vacuum melting ad then pouring while in a nitrogen atmosphere with the pressure between 0 and 90 psi. Strip from a heat with 0.0184 pct N underwent complete secondary recrystallization during the final anneal. Heats with less nitrogen had too few Si3N4 particles to restrain normal grain growth, and the heat with higher nitrogen had too many particles to allow complete secondary recrystallization. In the hot-rolled structure, Si3N4 precipitates only at the grain boundaries, with the consequence that annealing after hot-rolling diminishes the ability to subsequently undergo secondary recrystallization. In contrast to this behavior, ALNprecipitates uniformly in the hot-rolled structure. Under 1 atm of nitrogen, Si3N, in 3.1 pct Si-Fe dissociates between 900" and 950°C; the solubility of nitrogen increases from 0.0010 pct at 900" to 0.0030 pct at 1200°C. The solubility of nitrogen in Si-Fe has been the subject of many investigations. Corney and Turkdogan1 heated a 2.83 pct Si alloy in nitrogen and found the solubility, under 1 atrn of nitrogen, to be 0.0019 pct at 900°C. They claimed that Si3N4 did not form in the alloy above 705°C in 1 atrn of nitrogen. Fryxell et al.2 heated samples of 3.25 pct Si-Fe containing 0.0025 pct N over a range of temperatures and then analyzed for total nitrogen by vacuum fusion and for nitrogen in solution by a modified Kjeldahl technique. At 900°C, they reported the solubility of nitrogen in equilibrium with Si3N4 to be 0.0011 pct. pearce9 found the solubility of nitrogen at 900°C under 0.95 atrn of nitrogen to be 0.0017 pct in a 3.06 pct Si alloy. He reported that Si3N4 does not form above 770°C in 1 atrn of nitrogen. Although internal friction measurements have given somewhat higher values for the solubility,4-6 if the solubility of nitrogen is as low as has been reported by most investigators, and if Si3N4 is stable up to at least 945°C at 1 atrn pressure of nitrogen as reported by Seybolt,7 a small amount of nitrogen in properly processed Si-Fe should be effective in promoting secondary recrystallization. The requirement is that in the final heat treatment there be enough small, well-dispersed particles of Si3N4 to restrain normal grain growth. Fast8 has obtained secondary recrystallization by nitriding high-purity 3 pct Si-Fe after hot-rolling to a thickness of 0.118 in., followed by processing to 0.012 in., and annealing. A large amount of nitrogen, 0.076 pct. was introduced during the nitriding heat treatment, but he has since reported9 that "a few hundredths of a percent" is sufficient. Small amounts of aluminum10 or vanadium" nitride are capable of promoting secondary recrystallization. Heats containing as little as 0.010 pct A1 or 0.042 pct V and from 0.006 to 0.009 pct N underwent complete secondary recrystallization at final gage, whereas heats with lesser amounts of aluminum or vanadium did not.l2 To be reported is the behavior of nitrogen in high-purity 3.1 pct Si-Fe, and the relation of this behavior to the ability to undergo secondary recrystallization. PROCEDURE Ingots weighing 1 lb were made by vacuum melting high-purity electrolytic iron (A104, Glidden Co.) and high-purity silicon (Monsanto Co.). The latter was used in preference to ferrosilicon to insure a low aluminum content. The design of the melting furnace permitted pouring with the furnace atmosphere either below or above atmospheric pressure. Accordingly, at the completion of melting, nitrogen was admitted to the desired pressure and the heat then immediately poured. The ingots were sound, with no indication of porosity. In Table I are listed the heats investigated, the nitrogen pressure at pour, and the nitrogen and oxygen contents as determined by vacuum fusion with a platinum bath at 1850°C, a procedure which insures measurement of the total nitrogen.13 In addition, all heats contained 3.1 pct Si and not more than 0.002 pct C, 0.003 pct S or 0.005 pct Al. It was subsequently found that the quantity of nitrogen contained in the heats in Table I does not necessarily represent that obtained under equilibrium conditions. For example, the ingot poured immediately after 1 atrn of nitrogen was admitted to the chamber contained 0.0093 pct N, whereas an ingot poured 3 min after the nitrogen was admitted contained 0.021 pct N and another poured after a 6-min delay contained 0.029 pct N. While some bleeding of the hot top occurred in the latter instance, the ingot when examined in cross section appeared sound. The ingots were heated to 1325°C in hydrogen and rapidly rolled to 0.080 in. in 3 passes. The roll speed of the final pass was reduced so as to increase the quenching effect of the rolls. The hot-rolled pieces were processed both as-hot-rolled and after heating for 3 min at 900°C in hydrogen. After cold-rolling to 0.026 in., the strips were heated for 2 min at 900°C in hydrogen, then cold-rolled to the final gage of 0.012 in. The loss of nitrogen in going from the ingot to cold-rolled strip was no more than 10 pct. The final heat treatment, which was for the purpose of develop-

Jan 1, 1970

By W. W. Beddow

TWENTY years or so ago I wrote an article on management which consisted mostly of a chart similar to thousands of others of that day showing line functions, staff functions, and the chain of command in a typical mining organization. Since hen we have been "bossing" from the faces to the swivel chair and we have made many errors of no little expense to our companies. We have kept the chart in mind but many times we have changed the functions to fit the people we have had to work with. Good management after all is getting results with the people, the equipment, the supplies, and the natural conditions of the coal seam or seams and adjacent strata present. We have made, with little effort, a good showing with average people and equipment in good natural conditions. We have made a miserable showing (although expending every personal effort) with better than aver- age people and equipment in bad natural conditions. In the latter case many of our stockholders felt that better management would have found some way to save their investment. Perhaps they were right.

Jan 1, 1944

By Charles A. Ashburner

The petroleum industry of western Pennsylvania and southwestern New York lias been one of phenomenal development. Greater and more sudden flucuations hare occurred in the price* of crude oil, and in all the collateral interests dependent upon its production, than in the case of any other mineral product which has been extensively exploited in the United States. This was more particularly so from the commencement of drilling for oil in 1859 down to the end of 1877. The experience gained during these early years has enabled the oil men to operate more intelligently since; the business is not now attended with the hazardous risks with which it is generally credited. The most important questions connected with the oil industry are those of (a) the oil-supply, and (6) the possible ultimate exhaustion of the field. Since 1876 my attention has been directed to the study of the statistics of the product of the oil regions. In January, 1880, in order to slow some interesting points connected with these questions, I prepared a graphic chart which was used to illustrate a lecture on petroleum delivered before the Franklin Institute. This chart was afterwards reconstructed in two distinct forms for publication in the census report. on Petroleum and its Products. These latter I have redrawn in a condensed form, and have extended them to include the statistics up to 1885, for publication in the Transac tions of the Institute, in conjuction with a map of the oil-re&'~IOIIS prepared by Mr. John F. CarII and myself. It is hoped that these illustrations will be found interesting to the members of the Institute, and of practical utility to oil-men, without any extended discussion, since it is my desire to make only such brief references to them and give such additional detailed facts as may serve to make the prominent features understood.

Jan 1, 1886

By T. B. Counselman

The importance of concentration of iron ores too low in grade to be smelted direct is shown by Table I, showing 1940 ship- ments from the Lake Superior district. Canadian ores are omitted. Only in Minnesota is concentrating, other than crushing and screening, prac- ticed at present. Tonnage produced by various methods of concentration is shown in Table 2. The curves in Fig.. I show the gradual increase in tonnage of concentrated ores shipped, compared with total shipments from Minnesota. Most of the concentration work is performed on the Mesabi Range. This range is about 100 miles long, and not over 3 miles wide from the line at which the formation tapers out to a feather edge on the north to the place on the south at which, some 600 ft. thick, it is overlain with slates. Classes OF Ore The Mesabi Range contains three classes of iron ore. First is the unaltered taconite, or banded iron-bearing chert. It is estimated that there are some 60 billion tons of this material, which contains, roughly, 25 to 30 per cent iron. This material is virtually untouched, since no commercially successful method has yet been found for concentrating it to a grade suitable for the blast furnace. Intensive exgerimental work is in progress, and the problem is gradually being solved. In 1922 the Mesabi Iron Co. spent several million dollars erecting a large-scale pilot plant for concentrating and sintering the magnetic taconites on the east end of the range. An important tonnage of high-gade sinter was shipped to lower lake furnaces, proving that the taconite can be concentrated to a satisfactory grade. The costs, with equipment and methods then in use, were too high for

Jan 1, 1943

By T. B. Counselman

The importance of concentration of iron ores too low in grade to be smelted direct is shown by Table I, showing 1940 ship- ments from the Lake Superior district. Canadian ores are omitted. Only in Minnesota is concentrating, other than crushing and screening, prac- ticed at present. Tonnage produced by various methods of concentration is shown in Table 2. The curves in Fig.. I show the gradual increase in tonnage of concentrated ores shipped, compared with total shipments from Minnesota. Most of the concentration work is performed on the Mesabi Range. This range is about 100 miles long, and not over 3 miles wide from the line at which the formation tapers out to a feather edge on the north to the place on the south at which, some 600 ft. thick, it is overlain with slates. Classes OF Ore The Mesabi Range contains three classes of iron ore. First is the unaltered taconite, or banded iron-bearing chert. It is estimated that there are some 60 billion tons of this material, which contains, roughly, 25 to 30 per cent iron. This material is virtually untouched, since no commercially successful method has yet been found for concentrating it to a grade suitable for the blast furnace. Intensive exgerimental work is in progress, and the problem is gradually being solved. In 1922 the Mesabi Iron Co. spent several million dollars erecting a large-scale pilot plant for concentrating and sintering the magnetic taconites on the east end of the range. An important tonnage of high-gade sinter was shipped to lower lake furnaces, proving that the taconite can be concentrated to a satisfactory grade. The costs, with equipment and methods then in use, were too high for

Jan 1, 1943

By Harry M. Conger

It is a pleasure for me to keynote this first Western Regional Minerals and Coal Conference here in the Black Hills of South Dakota. It is pleasing for two main reasons. First, Homestake Mining Company has been associated with the Black Hills since 1875 when gold was discovered following Custer's trek through the Hills during 1874. Second, the future mineral development of the Black Hills will depend, to a great extent, on minerals and metals covered in this conference. The metals and minerals that are featured in this conference have unique similarities--and important differences--and therefore, will be of great interest to all who are involved in our industry in this area of the country. Precious metals have always been, and likely will always be, subject to political influence; they are only partially affected by the demands of our industrial economy. Energy minerals, while more directly affected by industrial stimulus, are also politically sensitive. In this regard, the need for a minerals policy affecting the energy sphere has been made very clear to us in the last five years. More importantly, the lack of a national policy and purpose relating to our total future energy needs has severely affected the overall economy and security of this country. Very briefly today, I would like to outline for you my thoughts on the future of these most important minerals. I will start by a discussion of precious metals, primarily my favorite precious metal, gold. A brief history of gold will be helpful in setting a perspective for forecasting its future although it is difficult to give a brief description of a metal that has been prized by man for over 6,000 years. Until recently, as you know, gold was held by the Federal government as a metal to be owned by the government only and

Jan 1, 1983

By Reich G. Gaertner

Almost every mining engineer who has had charge of extensive underground workings will have observed how often directions as to course and levels, deduced from careful theodolite measurements, have been slighted or disregarded by mine-foremen and shift-bosses, and how often these tedious measurements had to be repeated, even for minor works, such as ventilation-drifts or winzes, in order to carry them on with the required or desirable regularity. Besides the time and care absorbed by theodolite surveys, there is still another inconvenience, namely, the interruption of transportation during the time of observation, and, in heavily producing mines, the loss consequent upon such interruption. In proposing a subsidiary instrument to the theodolite, it is my purpose not to present a new one, but simply to recommend to the consideration of American mining engineers one which has been in use in nearly all the prominent mines of Europe for many decades, and has there fulfilled its purpose admirably. I refer to the mining or hanging compass (Fig. 1). At my urgent request, the firm of Keuffel & Esser, of New York, have lately constructed this instrument in a form which adapts it better to use in this country. By the addition of the trigonometer, the banging compass becomes at once an instrument which will prove of value even in the hands of foremen and practical miners, who have little or no knowledge of trigonometrical calculations. Probably many will say that me have no use for needle-instruments ; that our modern theodolites are of such perfect description, and leave so little to be desired, that the introduction of a compass would look like a step backwards compared to the fine results obtained by angle-instruments. I concede all that, and do not pre-

Jan 1, 1886

By J. Szekely, P. Tarassoff, N. J. Themelis

In a copper converter air enters the bath in the form of turbulent jets. The interaction of these jets with the molten matte is fundamental to the converting process. In the present study, an equation is derived to describe the trajectory of a gas jet in a liquid. Calculated and experimental results for air jets injected into water are in good agreement. The trajectories of air jets in copper matte are predicted. THE air injected through the tuyeres of a Peirce-Smith copper converter emerges into the bath of molten matte in the form of a highly turbulent jet. The air jets affect a number of chemical and physical processes occurring in the converter: i) Converting Rate. It is generally recognized that the production capacity of a converter is limited by the flow of air which can be injected through the tuyeres and by the oxygen efficiency. In turn, the air flow is limited by pressure drop considerations or by the amount of splashing within the converter. ii) Oxygen Efficiency. This depends on the dispersion of the air jet in the liquid bath, and its trajectory through the bath. iii) Mixing. The jets act as mixing devices by transferring momentum energy to the bath; in this way the heat generated by the converting reactions occurring in the jets is distributed through the bath. iv) Refractory Wear. The proximity of the jets, which are centers of heat generation, to the refractories in the tuyere zone may have an important effect on refractory life. Mixing conditions in the bath will also influence refractory erosion. v) Splashing, and Accretion Build-Up. The energy of the jets is not dissipated entirely in mixing the bath. particles of liquid are carried out kith the gas above the surface of the bath in the form of liquid spouts and droplets. These result in the undesirable build-up of accretions on the converter mouth, and dust losses in the flue gas. Despite the importance of the interaction of the air jets and the matte in a converter, very few studies of the fluid dynamics of converting have been reported in the literature. Metallurgists in the USSR appear to have been more concerned with the subject than their Western counterparts. Deev et al.1 studied the interaction of an air jet with aqueous solutions in a converter model and qualitatively determined the tuyere air velocity and tuyere inclination which produced the most favorable results with respect to good mixing in the bath, and minimum splashing. Shalygin and Meyer-ovich2 also examined the air-matte physical interaction both in models and in industrial converters; they concluded that in conventional converting practice, there was no significant penetration of the air jets into the matte layer, and consequently the converting reactions occurred mainly in a zone adjacent to the tuyeres. The behavior of air jets in a converter bath, and the aerodynamic characteristics of tuyeres are discussed at length in a monograph on converting by Shalygin.3 However, the description of the phenomena occurring in the converter bath is largely qualitative. The side-blown Bessemer converter for steelmak-ing is very similar to the Peirce-Smith copper converter. Among the few investigations of the behavior of air jets in the bath of a Bessemer converter are those of Kootz and Gille4 who studied splashing in the course of an investigation on the effect of blowing conditions and converter shape on nitrogen pick-up in Bessemer steel. They found that during blowing standing waves were formed on the surface of the bath; the amplitude of the waves increased with the depth and angle of tuyere immersion until the whole bath moved backwards and forwards causing heavy splashing. Kazanstev5 used a model of a Bessemer converter to obtain correlations between the axial velocity of a gas jet and distance from the tuyere orifice and the Froude number of the jet. shalygin3 used these results to calculate the horizontal penetration of an air jet in a copper converter; the penetration was defined as the distance in which the axial jet velocity decreased to 10 pct of its initial value. However, the rising trajectory of the jet was not taken into account. In the absence of quantitative information on the fluid dynamics of converting, the design of copper converters has been based mainly on operating experience. Such experience tends to vary widely from smelter to smelter., This is reflected in Table I which is based on data compiled by Lathe and Hodnett.6 Aside from a rough, and perhaps obvious correlation between the total air flow and converter volume, Fig. 1, no pattern emerges from the data. For example, tuyere throat air velocities vary from 215 to 465 ft per sec in converters of the same size, for little apparent reason. The air jet energy input per cubic foot of converter volume, which may be taken as a measure of the amount of mixing in the converter bath, also varies greatly. A recent analysis of converter data by Milliken and Hofinger7 has also revealed unexplained variations in operating parameters. It is believed that by gaining a better understanding of the fluid dynamics of converting a more rational basis may be provided for the design of converters. In particular, it is proposed that if one takes into account the desirable criteria of a high converting rate, high oxygen efficiency and long refractory life, there should be an optimum configuration of tuyere air flow for a converter of a given diameter. The present investigation is concerned with the form and trajectory of an air jet in a converter bath. The general theory of turbulent jets has been expounded by Schlichting8 and Abramovich.9 However, most experi-

Jan 1, 1970