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By C. A. Heiland

THE Eötvös torsion balance permits the measurement of certain second derivatives of the gravity-potential, which are known as the gradients of gravity and the curvature values for an, equipotential plane of gravity. These quantities are influenced on level ground by the configuration of the masses underneath. Hence, the torsion balance has gained great importance for the location of geological structures and thus indirectly for the discovery of oil and other mineral deposits. If the ground is not level, however, the measurements become more difficult, because the superficial mass-irregularities also produce more or less considerable disturbances. It is necessary, therefore, to determine the shape of the surrounding topography by leveling as well as by consulting topographic maps and to compute its influence upon the torsion balance. The correction thus determined is called, in general, the topographic correction; it is composed of two constituents, the terrain correction and the cartographic correction. The terrain correction would be that part of the topographic correction as derived from the direct leveling of the area surrounding the station, whereas the data for the computation of the cartographic correction are obtained from a topographic map, usually beginning with a radius of 100 meters, as under most circumstances it is difficult to level along a larger concentric circle about the station.

Jan 1, 1928

By J. V. Richards

(Canal Zone Meeting, November, 1910,) THE Altar district, State of Sonora, Mexico, is for the most part a desert with but little rain-fall and few running streams. On account of this scarcity of water it is necessary for the natives to " dry-wash" the placer-gravel, and the object of the present paper is to describe some of the more common Mexican dry-washing devices. My observations were confined to a property known as Las Palomas placers, 15 miles from the Gulf of California and about 150 miles south of the United States border; a brief description of which property may be of interest as illustrating what is, perhaps, a typical Sonora dry placer. It is said that as long as a century ago the Yaqui Indians discovered rich cement-gravel, known as argo masa, at Las Palomas, and that there has been a more or less steady production of gold from the property ever since. The argo masa is a fairly-coarse gravel, the pebbles being quite firmly held together with a lime cement. Gold is scattered through this cement in particles ranging from fine specks to pieces several grams in weight, and occasional large nuggets are encountered. The contents vary so widely that it is difficult to estimate the average value, but returns of from $10 to $50 per cubic yard are common, and it is doubtful if the Indians considered anything less than from $4 to $5 a yard as "pay dirt." This argo masa occurs in channels varying in thickness from a few inches to several feet, and in width up to 300 ft.. These channels are continuous and are probably ancient stream-beds. They are for the most part covered with an over-burden of a more recent gravel, varying from 30 to 50 ft. thick, and the fact that this over-burden contains values as high as $1.50 per cubic yard, and yet was not worked by the Indians, shows that their idea of what constituted pay-ground was high.

Apr 1, 1911

By Herbert A. Stein, John B. Murdock

Perlite is a natural volcanic glass which expands into an insulation material upon the application of heat. This paper discusses the operating characteristics of eight different types of furnaces for the expansion of perlite. It also includes a section on the theory of perlite expansion which serves as the basis for the authors' analysis of the furnaces.

Jan 1, 1950

By Gordon I. Gould

The treatment of quicksilver ores to extract the metal, for centuries one of the fundamentally simpler metallurgical operations, has undergone few if any material changes during the past iew decades other than improvement and change of type of equipment used. Of almost universal application and as the seldom deviated from process, the roasting method is still considered superior to chemical metallurgy. Likewise, roasting of the crude ore without previous beneficiation continues to be standard practice, although some successful operations have employed concentration prior to roasting. The roasting process has been carried out in a variety of equipment, devised for different tonnage capacities, to treat "special" ores, and to satisfy an inventive notion of the particular builder, but during the past 25 years there has been one outstanding change in roasting equipment. This change, though neither originating in nor confined to the United States, has probably been developed and applied to a far greater extent in this country than in any other mercury-producing country of the world. The change from manually or gravity operated furnaces, mostly huge brickwork affairs justified largely by simplicity, lack of power and mechanical requirements, and occasionally by excellent metallurgical results, to mechanical furnaces, began actively during World War I under the stress of requirements for in- creased production, a shortage of labor, 2nd other factors to be brought out later. During the twenties the change to mechanical furnaces became nearly complete at American mines with the development of several types, the rotary furnace predominating. During the thirties, and the period of low prices in the early part of this period, few changes were made other than mechanical improvements and an almost complete acceptance of two types: the rotary furnace and the hearth or Wedge furnace. These two types have been developed to a high degree of metallurgical efficiency, have proved to be mechanically simple and have far greater flexibility and lower operating costs than pre-World War I furnaces. Of the two types the rotary is the more popular, about 30 rotaries having been in operation in the United States in 1943 as compared with about six hearth-type furnaces. The units of smaller capacity for roasting mercury ores have almost without exception been indirectly fired, such distinction being commonly accepted as the difference between retorts and furnaces, which are fired directly. The difference between indirect and direct firing obviously permits of quite different conditions surrounding the ore being roasted in relation to the chemical reaction to take place. In the indirect-fired unit the ore is contained within the body of the retort in a stagnant if not completely oxygen-impoverished atmosphere. In the direct-fired furnace the ore is in contact with the gases of combustion, which may easily (if not too easily) be supplied with an excess of

Jan 1, 1944

By Edward I. Salkovitz

RECENTLY a set of crystallographic angles for bismuth was calculated and a standard (111) projection was constructed. Since these calculations

Jan 1, 1957

By John R. Riede

Most beneficiation plants utilize automatic controls to varying degrees-some have the bare minimum of controls, others qualify as semi-auto- mated operations; a very few are nearing what may be termed "fully-automated" status. But for those plants that produce a filter cake product, the lack of suitable instrumentation for measuring and con- trolling the moisture of the filter cake has been a major stumbling block to fully-automated operations. Today in many cases, this bottle-neck can be removed because various moisture measuring devices are now available to permit automation of the filtering stage. What are these devices? . . . Where can they be used? To answer these questions, two types of operating plants-one, semi-automated and the other, almost fully automated-can be examined. Both plants employ disc filters from which is produced a magnetic concentrate for pelletizing. (The control schemes and equipment depicted in this article are similar to those usable in drum filter plants.)

Jan 3, 1967

By R. Y. Williams

IN the United States, fully 98 per cent. of the anthracite and bituminous coal tonnage obtained from underground operations is mined by the room-and-pillar system. Under this system, the total cost of the coal f. o. b. railroad cars contains as its greatest single item the money paid for "labor." Each labor dollar in an. average bituminous mine may be subdivided into 85 c. paid for work done inbye the gathering turnouts (including all work at the face), and 15 c. outbye that point (including all work in and under the tipple). In an average anthracite mine, the corresponding figures are 70 c. and 30 c., the larger breaker force accounting mainly for the difference between these and the bituminous figures. The next largest single item after "labor" is usually "supplies and power;" and a division of this item inbye and outbye the gathering turnouts shows somewhat the same relative proportions as has been noted under the case of "labor". During the past 10 years, the chief advances made in the coal industry have been to obtain economies through complete mechanization covering that portion of the work which lies outbye the gathering turnouts. These results have been accomplished by applying scientific principles to railroad yard layout, to cleaning and sizing machinery, to dumping facilities, to roller-bearing haulage equipment, and to heavy-rail, well-ballasted trackage. But these improvements, while gratifying in their resulting economies, apply only to 15 to 30 per cent. of the important cost items. Obviously, then, the big problem before the engineers of the coal industry today has to do with the methods of mining and the layout inbye the gathering turnouts. Four years ago, Weston Dodson & Co., Inc., determined to have an exhaustive study made of the conditions which must be met in order to gain complete face mechanization, and in order that such a mining layout would be based on, correct underlying principles. The result of that study, which was made by the writer, led to the adoption of a method of longwall mining wherein the. roof is worked on the caving system and is supported as an overhang along the face by steel jacks.

Jan 1, 1928

By Francis M. Walters

IN spite of the war and the preoccupation of many physical metallurgists with work on secret or confidential problems, definite progress was made during 1944 in our understanding of the behavior of steel and of the effect of alloying elements. During the first two years of the war there was much concern over the possible unavailability of certain alloying elements; this period saw the development of the N.E. (National Emergency) steels. However, the measures taken eased the alloy situation and currently, highly practical problems under study are the graphitization of low-carbon steel and weld-cracking, while investigations of more theoretical interest have concerned hardenability, isothermal reactions, the effect of hydrogen and the interpretation of the notched-bar impact test.

Jan 1, 1945

These pages may be used as order sheets. Mark the number desired opposite title of pamphlet wanted, add your name and address, tear out the sheets and mail them to us. Single orders 25 c. Pamphlets 10 c. each in lots of three or more. Pamphlets 5 c. each in lots of fifty or more. These prices prevail for orders for pamphlets of the same or different titles, when cash accompanies order. The pamphlets listed on the following sheets are advance copies printed to facilitate discussion at the meetings of the Institute. They are offered for sale at the reduced prices given above as long as-the supply lasts. This list is published in the Bulletin in order that members may have the first opportunity to secure pamphlets, which sometimes are in such great demand that the supply is exhausted before the wants of members can be supplied. The following list includes only a fraction of the pamphlets that have been published by the Institute. Any other paper published by the Institute may be obtained for the price of $1, except those published in Volume XXXI, which are rare. The Institute is still selling back volumes of Transactions at reduced prices, but some of these volumes are becoming rare and members who desire to complete their sets of these very important books on mining and metallurgy are advised to send in their orders as soon as convenient. (See Advertising page 15.) , The attention of members is also called to the bibliographical index of the science of ore, deposits contained in the Emmons Volume which is selling at $3 in paper and $4 in half morocco. The Posepny Volume is already exhausted and members who do not get in their orders for the Emmons Volume at the present reduced price may soon find themselves unable to obtain it on such favorable terms.

Jan 6, 1917

By E. W. Mehal, R. W. Haisty, D. W. Show

The next generation of integrated circuits will probably include circuits constructed in and of GaAs. The existence of both semi-insulating and semiconducting forms of GaAs is the fact which will bring this about. In this paper we discuss the uses and limitations of semi-insulating GaAs for integrated-circuit applications. The two main areas considered are the electrical isolation that can be achieved between components on a semi-insulating substrate and the characteristics of p-n junctions in contact with semi-insulating GclAs. A process basic to attaining integrated circuits in GaAs to fully utilize the insulating properties of the substrate is selective epitaxial deposition. This process involves the deposition of a SiO2 layer onto a The trend in integrated circuits is towards the use of high-resistivity substrates or regions to achieve component isolation. The use of SiO, layers in the oxide isolation methods and the use of sapphire substrates are examples of this idea. GaAs is also a polished surface of a GaAs substrate, etching out selected area of the SiO, film to expose a GaAs surface, and deposition only onto the exposed GaAs surface. By using this process , islands of semiconducting GaAs are deposited onto a semi-insulating GnAs substrate, the islands being electrically isolated from one another by the substrate. The deposition of both p- and n-type semiconducting GaAs can be carried out in this nzanner to form p-n junctions in the island areas. This process can also be used to produce a planav structure by deposition of GctAs through a SiO, mask into holes etched into the GaAs substrate. This Putterned Epitaxial Technology (PET) is described. very promising material for use in future integrated circuits because of the existence of both semi-in-sulating and semiconducting forms. Active devices can be fabricated in the semiconducting material, and these individual components can then be electrically isolated from one another by using semi-insulating GaAs as the substrate. Epitaxial semi-insulating GaAs can also be produced thus making three-dimensional monolithic integrated circuits feasible.' This paper describes the research aimed at developing the methods for producing both two- and three-dimensional integrated circuits in GaAs, and examines some of the properties of semi-insulating GaAs as they relate to these integrated circuits.

Jan 1, 1967

By Robert I. Kingman

SUFFICIENT testing has been performed with the Dutch State Mines Cyclone for thickening and desliming flotation feed at the concentrator of the National Lead Co., Tahawus, N. Y., to prove its application for this work. It is the purpose of this article to present some of the test results, operational details and advantages of cyclone thickening and classification. The metallurgy of the mill operation was described by Frank R. Milliken, assistant manager of the titanium division.l The present flowsheet for the recovery of ilmenite consists in grinding the crushing plant product in four open-end rod mills in closed circuit with mechanically vibrating screens to approximately -20 mesh. The screen undersize is treated in Crockett magnetic separators which produce three products: magnetic concentrate, nonmagnetic tailing containing ilmenite and gangue, and a Crockett slime overflow. The non- magnetic tailing is classified into eight sizer spigots products and a classifier overflow. The spigot sand products are tabled separately to produce a rough ilmenite concentrate, a middling product and a tailing. The table middlings are returned to Crockett feed. The table concentrate is dewatered and dried and further concentrated on Wetherill magnetic separators to produce the finished ilmenite concentrate.

Jan 8, 1950

By R. Costantini

Long-distance transportation of solids by hydraulic pipelines holds promise of great economic benefits. In most mineral processing plants today, moving of solids in slurry-form by pipeline is commonplace. Yet in spite of this, the method is slow in being adopted on a broad scale for moving solids over distances of many miles. This is especially surprising in view of the successful realization of two daring ventures in long-distance solids pipelines in this nation within the last five years. One is the 72-mile long, 6-in. diam. pipeline of the American Gilsonite Co. which has been satisfactorily transporting 700 tpd of gilsonite from the mine at Bonanza, Utah, to the processing plant at Grand Junction, Colo., since April 1957. The other is the 108-mile long, 10-in. pipeline of the Pittsburgh Consolidation Coal Co., which has been transporting about 4000 tpd of finely crushed coal from the mine at Cadiz, Ohio, to the Eastlake Power Plant of the Cleveland Electric Illuminating Co. since January 1958.

Jan 8, 1961

By Walter Miller

A surprising development during the year was the continued high demand for petroleum products and the high level of crude oil charges to the stills. Generally speaking, the petroleum industry during 1946 succeeded in producing a greater quantity of crude oil and petroleum products than in any of the war years, and considerably exceeded the production of any prewar year. Daily crude still charges averaged between 4,700,000 and 4,800,000 bbl per day for 1946 and about equaled the 1945 record, although most pessimistic 1945 guesses, predictions, or fears ranged, for 1946, from only 3,900,000 to 4,400,000 bbl per day. In spite of the high crude charge to the stills, total stock of crude oil was higher at the end of the year by some 7,000,000 to 8,000,000 bbl. A similar story holds regarding stocks of the principal refined products. Gasoline on hand at year's end was two to three million barrels lower, and was considered low for the expected demand during the coming high consuming season, while stocks of light and heavy fuel oils, although some higher than a year previous, hardly reached a comfortable level. The trend in gasoline of high octane number, which has resulted in a marked rise in. the antiknock quality by the end of 1945 (five or six numbers higher than during the war and one number higher than the prewar quality of civilian motor gasoline of 1941) was abruptly arrested by an acute shortage of metallic lead for manufacturing tetraethyl lead. Government action in the form of lead price control, rationing, and the setting of octane ceiling specifications to conform to the reduced ethyl lead compound available were enforced until abrogated at the end of the year. It will be interesting to see how rapidly the octane levels will resume the rising trend, as more metallic lead slowly becomes available for making greater quantities of ethyl lead compound. As octane quality rises over present levels the disadvantage of the refiner without catalytic cracking equipment will increase. Gasoline made by catalytic cracking, without addition of ethyl lead, approximates 77 octane by the official ASTM Motor Method test, compared with 66 for gasoline generally similar in volatility made by the older thermal cracking operation. Catalytic gasoline shows an even greater improvement in the Research octane number, the comparison being roughly 86 Research versus 71 Research octane for the thermal cracked product. This higher differential in Research octane is credited by many, although not universally so, as contributing to better road performance, and consequently resulting in a more desirable product marketwise. In some parts of the country a premium of roughly one fourth cent per gallon is now being paid for gasoline with higher Research octane made possible by including catalytic cracked product in the final blends. If such price differentials in favor of catalytic gaso-

Jan 1, 1947

By Walter Miller

A surprising development during the year was the continued high demand for petroleum products and the high level of crude oil charges to the stills. Generally speaking, the petroleum industry during 1946 succeeded in producing a greater quantity of crude oil and petroleum products than in any of the war years, and considerably exceeded the production of any prewar year. Daily crude still charges averaged between 4,700,000 and 4,800,000 bbl per day for 1946 and about equaled the 1945 record, although most pessimistic 1945 guesses, predictions, or fears ranged, for 1946, from only 3,900,000 to 4,400,000 bbl per day. In spite of the high crude charge to the stills, total stock of crude oil was higher at the end of the year by some 7,000,000 to 8,000,000 bbl. A similar story holds regarding stocks of the principal refined products. Gasoline on hand at year's end was two to three million barrels lower, and was considered low for the expected demand during the coming high consuming season, while stocks of light and heavy fuel oils, although some higher than a year previous, hardly reached a comfortable level. The trend in gasoline of high octane number, which has resulted in a marked rise in. the antiknock quality by the end of 1945 (five or six numbers higher than during the war and one number higher than the prewar quality of civilian motor gasoline of 1941) was abruptly arrested by an acute shortage of metallic lead for manufacturing tetraethyl lead. Government action in the form of lead price control, rationing, and the setting of octane ceiling specifications to conform to the reduced ethyl lead compound available were enforced until abrogated at the end of the year. It will be interesting to see how rapidly the octane levels will resume the rising trend, as more metallic lead slowly becomes available for making greater quantities of ethyl lead compound. As octane quality rises over present levels the disadvantage of the refiner without catalytic cracking equipment will increase. Gasoline made by catalytic cracking, without addition of ethyl lead, approximates 77 octane by the official ASTM Motor Method test, compared with 66 for gasoline generally similar in volatility made by the older thermal cracking operation. Catalytic gasoline shows an even greater improvement in the Research octane number, the comparison being roughly 86 Research versus 71 Research octane for the thermal cracked product. This higher differential in Research octane is credited by many, although not universally so, as contributing to better road performance, and consequently resulting in a more desirable product marketwise. In some parts of the country a premium of roughly one fourth cent per gallon is now being paid for gasoline with higher Research octane made possible by including catalytic cracked product in the final blends. If such price differentials in favor of catalytic gaso-

Jan 1, 1947

By Narendrakumar A. Chevli

Exploratory work was conducted in the fabrication of integrated circuitry, specifically linear amplifier circuits, by three general methods: 1) monolithic diffused silicon; 2) a combination of metal thin-film and monolithic diffused silicon; and 3) a hybrid of metal films and diffused silicon on an alunina substrate. In these linear amplifier integrated circuits the followzng conditions were desired: very high-frequency response, high voltage gain, and good thermal tracking stability of electrical characteristics. The resulting circuit designs imposed problems of isolation between elements, layout and smallness of size of active elements, and close tolerances on electrzcal characteristics of the passive elements. Interconnection problems for specific designs resulted from the small dimensions involved and the topography of the hybrid fabrication techniques. The desired integrated-circuit characteristics were achieved with the technologies of categories 2 and 3 above. Solutions to the problems imposed by these characteristics lay in the ability to isolate czrcuit elements of small size while providing a layout designed to minimize element-to-element variations. Sufficient freedom in the formation of passive elements was achieved by uniting the metal film and the monolithic silicon technologies. The most satisfactory designs were based on the beam-lead interconnection and isolation technique. SINCE the advent of integrated circuits, major emphasis has been on fabricating digital integrated circuits. Linear circuits require high performance, high voltage, and tighter tolerance components which are not always compatible with the capability of process technology available for fabrication of these circuits into integrated form. Fortunately the growth of newer and improved processes and materials for fabricating integrated circuits has been an accelerated one. This has now made possible the translation of stringent performance requirements of the linear circuits into microminiature integrated circuits of the same performance. In the exploratory work of fabricating high-performance Linear Integrated Circuits—LIC, the following objectives were formulated: i) fabrication of high-frequency transistors such as the type 2N918 isolated on a single silicon substrate; ii) fabrication of medium-frequency transistors having a very high gain at low collector currents such as the types 2N930/2N2484 isolated on a single substrate ; iii) fabrication of tight-tolerance, high-valued resistors having low temperature coefficients of resistance and stable thermal tracking characteristics, these resistors to be fabricated on an active or passive substrate; iv) simultaneous fabrication of complementary transistors—pn and pnp-on the same silicon substrate; v) fabrication of newer active elements such as MOS, FET transistors along with the conventional active and passive elements on the same silicon substrate. State-of-the-art assessment f all the available processes, materials, and technology to meet above objectives indicated that economic fabrication of LIC cannot be achieved by a single technology for all types of linear circuits. Where design and performance of a given linear circuit can be modified and tolerated to the extent of a particular technology, then alone is it possible to fabricate a LIC using a single process technology such as all diffused, planar technology. In order to evaluate this economic breakpoint with design and performance compromise in fabricating LIC, it is essential that a thorough understanding be obtained of techniques, potentials, and limitations of all the various process technology and materials

Jan 1, 1967

By John Ryan

SIR HUMPHREY DAVY'S epoch-making treatise delivered on Nov. 9, 1815, before the Philosophical Society of London, first announced and demon¬strated a flame safety lamp for detecting methane in mine air. Coal mining was known in England as early as 1180, more than 600 years before the advent of a safe lighting and gas-detecting appliance. Mining, no doubt, took place first in outcrop coal, and danger from gas did not become apparent until the workings became deeper and more extensive. Davy's lamp did much to increase the safety of miners, and a modified Davy lamp is still widely used for detecting the presence and approximate amount of combustible gas in mine air. No factor in coal mining has improved more rapidly during the past 15 years than safety measures. This progress came about not only as a result of the work-men's compensation laws now in force in most of the states of the Union, but because the research work of the U. S. Bureau of Mines has demonstrated some dan¬gers incident to coal mining which were not considered to be serious matters prior to that time. Electric power and explosives are necessary but 1-potential hazards in American coal mines. A general mechanization program is now under way, while the mines are growing deeper and more extensive. Conse-quently ventilation problems are more complex and a demand has been created for positive detecting devices for carbon monoxide as well as methane. Scientists and manufacturers, working hand in hand during the past 10 years, have invented and developed appliances which make systematic and effective examination of mine air possible. The object of this paper is to describe briefly the approved testing devices in use today, with the hope that they may lead to the saving of life. Dangerous coal mine gases may be placed in two groups: (1) those that are dangerous because of their explosive properties, and (2) those that are dangerous because of their toxic properties. Methane (CHI) is the important gas of the first group, and in so-called gaseous mines constantly exudes from the coal and rock; it may accumulate and form an explosive mixture.

Jan 2, 1927

By John I. Yellott

SINCE the days of Newcomen and Watt, when men first sought to turn the energy of fuels to useful purposes, coal-generated steam has supplied most of the power needed for both stationary and mobile applications. The low efficiency and large water requirements of the nineteenth century steam-power plant caused many engineers to turn their thoughts toward more direct means of converting heat into power. As far back as 1791, John Barber secured an English patent on a combination' which he might well have called a "gas turbine." He proposed to generate procducer gas from coal or charcoal, to burn it under pressure in air obtained from a reciprocating compressor, and to drive a turbine wheel with the resultant hot combustion products. With the optimism characteristic of the inventor, he hoped that the turbine would not only operate his compressor but also perform useful work. There is no record that Barber ever built his machine, but if he had done so he would have learned that useful power can result from such a combination only when both turbine and compressor are highly efficient and when the temperature of the gas entering the turbine is not far below 1000°F. Hot-air prime movers continued to attract attention, and both Stirling in England and Ericsson in America2 built reciprocating engines that operated with some success upon coal-heated air. The internal-combustion engine, burning liquid fuels, supplanted the hot-air type, and, for the first time, challenged the supremacy of both the steam cycle and its familiar fuel, coal. LIQUID FUELS COMPETE WITH COAL As the increasing use of the automobile multiplied the demand for gasoline, the supply of residual fuel increased rapidly, and heavy oil declined in price to the point where it became competitive with coal. First in the marine field and later in stationary plants in areas adjacent to refineries, oil began to be widely used. Oil's greater convenience and higher heating value per pound of weight or per cubic foot of bunker space have caused it to take over much of the marine field. The introduction of the highly efficient diesel engine, capable of burning a fuel that is cheaper than gasoline, again threatened the position of coal, for the operating costs of the diesel became directly competitive with those of coal- burning equipment. In isolated power plants and smaller marine installations, the diesel provided the medium by which oil again successfully invaded fields formerly dominated by coal. The diesel engine, provided with an

Jan 1, 1946

By H. W. Smith, A. K. Bjerring

A nonlinear dynamic model for a flotation cell is developed, using a number of simplifying assumptions, the most important of which is that of essentially complete liberation in the feed material. Using this model, a complete dynamic model for a flotation circuit is developed and calibrated against steady- state process data. The dynamic response of the circuit to disturbances in input feed rate and composition is simulated, as is the response of a linearized and simplified model on which control design might be more easily based. Preliminary results indicate the practicability of the modeling technique. However, difficulties in matching steady-state operating conditions in one process stream, and the apparent importance of recycle streams as indicators of process operation, indicate that inclusion of at least one species of middling particle in the model should be considered.

Jan 1, 1969

By Jose A. Ruiz

INTRODUCTION For heterogeneous non-catalytic solid-gas reactions carried out in fluidized bed reactors, nominal bed temperature is an average value between gas and solid. For highly exothermic reactions, actual particle temperature can be up to hundred degrees above termocouple temperature, since heat dissipate at slower rate than heat generation during some steps of transformation. These micro instabilities at particle level can displace thermodynamic equilibrium from the desired phase to others. This effect is important when relatively narrow range of phase stability exists, like in sulphation roasting of sulphides, where bed discharge contains, in addition to the desired sulphate others metastable phases such as basic sulphate and ferrite. For example, for copper-iron sulphide concentration roasted below 680°C, no cupric ferrite is formed, as shown by Jakob et al., therefore the separate Kellogg's stability phase diagrams Cu-S-O represent the roasting (Fig.l). At temperature above this one, like 760°C for example, phase stability changes from CuSO4 to the basic sulphate Cu0•CuSO4. Solid state reaction between Cu0•CuSO4 and Fe203 also occurs to form cupric ferrite, Cu0•Fe2O3, therefore the Cu-Fe-S-O Kellogg's phase diagram of Fig. 1 (continuous line) represents this condition of roasting. Although both Cu0•CuSO4 and Cu0•Fe2O3 are metastable phases under normal operating conditions of sulphation roasting(1-10% SO2, 1-10% 02 and 680°C, points A and B,Fig. 1) sulphation of these species and particularly ferrite are slow and limited due to diffusional control. This explain why reactors discharge contains several phases: CuSO4, Cu0•CuSO4, CuO•Fe203 plus small amounts of CuS and FeS due to the baclonixed conditions of fluidized bed reactors. The presence of cuprous ferrite due to reducing conditions inside individual particles also occurs, but in very limited extent at the reaction interface, as it is demonstrated by the low soluble iron levels of calcines. On the other hand, the presence of cupric ferrites can be explained only due to the higher temperature achieved by particles, since below 680°C cupric ferrite formation does not take place. [ ] This phenomena also occurs for others non-ferrous metal sulphides concentrates roasted under sulphation conditions, such as 7n, Co and Ni. Therefore the prediction of discharge composition of fluidized beds is not possible based only on kinetics and mechanistics models alone or purely thermodynamical considerations, since all factors should be integrated to describe the overall phenomena. SINGLE PARTICLE TRANSFORMATION Assuming a first order reaction with respect to the gas and zero for solid, such as

Jan 1, 1984

By George Smith

TWELVE years ago, the Director of the United States Geological Survey addressed to the Secretary of the Interior a letter calling attention to the government's need for liquid fuel for naval use and pointing out that the rate of increase in demand was more rapid than the increase in production.1 This letter, in a way, inaugurated the policy of public oil-land withdrawals, which was well founded in its primary purpose of protecting the oil industry and highly desirable in its immediate effect of checking the over-development of that day in California. Unfortunately, however, through delays in legislation, this policy may be regarded now as having outlived both its intent and its usefulness. In 1908, the country's production of oil was 178,500,000 bbl., and there was a surplus above consumption of more than 20,000,000 bbl. available to go into storage.: In 1918, 10 years later, the oil wells of the United States yielded 356,000,000 bbl.-nearly twice the yield of 1908-but to meet the demands of the increased consumption more than 24,000,000 bbl. had to be drawn from storage. Nor is this all of the brief comparison. In 1918, our excess of imports over exports of crude petroleum was nearly 33,000,000 bbl. whereas in 1908 we exported 3,500,000 bbl., which was net, as we had not begun to import Mexican oil. In this period, the annual fuel-oil consumption of the railroads alone has increased from 16,871,000 to 36,714,000. bbl.; the annual gasoline production from 540,000,000 gal. to 3,500,000,000 gal. This record may be taken not only as justifying the earlier appeal for Federal action, but as warranting deliberate attention to the oil problem of today.

Jan 1, 1920