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By E. C. Reed

Drilling operations in Nebraska during 1942 were reduced to approximately 50 per cent of the previous year's record. Forty- No new fields were discovered, but the Barada field was extended and developed. Deeper drilling in the Dawson field was disappointing in view of the high expectstions held for the Viola, but some small Viola production did result, the first from

Jan 1, 1943

By George C. Bravner

WITH the great expansion currently being made in the aluminum output of the United States, not only by the company that has heretofore been the sole producer but by a now organization in the field it is only natural to wonder to what degree the; ore reserves of the United States can contribute to the growing consumption. For the three-year period 1937-'39 the U.S. Bureau of Mine's figures indicate that the annual domestic production of bauxite averaged about 370,000 long tons, compared with average, annual import of about 194,000 long tons. About 85 per cent of the imports came from Surinam, nearly all of which went into aluminum manufacture. Not all of the or -kipped from mines in the United States is used to make alumimun however as Bureau figures indicate that in these three years an average of only 48 per cent of the domestic ore shipment were so used the abrasive chemical and other industries taking respectively 27, 21, and 4 per cent of the output. The recent increase in the demand for bauxite has been of course in it use for aluminum manufacture. This as is well known is largely attributable to the world race for supremacy in

Jan 1, 1941

By W. L. Honnold

(San Francisco Meeting, September, 1915) OWING to a unique labor situation and other unusual circumstances, the mining methods of the Rand are hardly comparable with practice elsewhere. They are' of considerable interest, however, and their impor-tance is increased by the magnitude of the industry with which they are identified, gold of $166,186,000 value, say 40 per cent. of the world's production, having been recovered from 25,701,954 tons of ore milled in 1914. In the sketchy remarks to follow, attention will first be drawn to some influential factors of general bearing, after which certain features at two mines of the writer's group will be referred to. It is hoped that engineers associated with similar or different conditions and practice will contribute to broaden the discussion. Before proceeding, recognition is due the generous assistance of C. E. Knecht and F. A. Unger. GENERAL OBSERVATIONS The principal mines are situated along the northern limit of an irregularly shaped geological basin, and extend in almost unbroken continuity over a distance of about 60 miles. As the boundaries are defined by vertical planes there are both "outcrop" and "deep-level" properties, all differing in size and in technical features. So much has been written in regard to the geology of the Rand that only a few pertinent features need here be recalled. Briefly, the ore deposits are profitably enriched portions of certain conglomerate beds or "reefs," rarely more than three, which are interposed between quartzite, or quartzite and slate, and lie so closely together that where more than one are mined they are dealt with as a work-ing unit, although they may lie stoped separately. Their collective extension is locally referred to as "the Reef."

Jan 8, 1915

By P. H. Dudley

I HAVE taken the liberty of calling the researches herein mentioned industrial, to distinguish them from those strictly scientific, where every known appliance is used to insure accuracy in determining principles. The industrial researches are made to ascertain wherein we have failed to embody, in practice, the principles which have been fully demonstrated by the more purely scientific investigations. So far the researches have been mostly confined to the conditions of combustion as used in locomotive furnaces, although we have examined, to some extent, furnaces under marine and stationary boilers. The products of complete combustion are gases, and, knowing what we should have, it is at once shown by analyzing the products whether the desired reactions are taking place. In spite of imperfect furnaces, lack of system in the arrangement of grate-bars and exhaust nozzles, the results are not altogether vitiated, because the analyses are not closer than one-tenth of one per cent., as under the present conditions it is hardly possible to collect gas exactly under the same conditions at different times. All of our industrial operations have developed in the past few years so rapidly, nearly all of them paying, that, until within the past three years, comparatively little attention has been given to their economy outside of the profession. Great corporations have not asked and considered the question in earnest, can we utilize our heat so as to produce the same effect at less cost? The applications of heat are so extensive, entering into every branch of industry, the principal power used to carry on metallurgical processes, to conduct transportation, that its economical generation becomes of universal importance; in fact, its economical generation and application is the leading industrial question of the day. It is stated by those who have given the subject much attention, that in our best steam-engines not over 10 per cent of the theoretical value of the fuel is utilized, and upon locomotives it is far less, probably not exceeding under the most favorable circumstances 5 or 6 per cent. In recent experiments made with the dynagraph, in drawing trains upon the Lake Shore and Michigan Southern Railway from Cleveland to Erie, 95i miles, we found the force required to draw a stock train of 709 tons to be 2,498,396,320 foot-pounds, exclusive of the force to move the locomotive itself. We

Jan 1, 1876

By Alan Morris

IMPINGEMENT attack, as one of the types of corrosion suffered by condenser tubes, has been given a prominent place in corrosion literature of recent years. It has been reproduced and studied in carefully controlled laboratory tests. Much has been learned of its mechanism, and of the effects of variables such as temperature, amount of air, size of bubble and water velocity. Incidentally the technical public has been given comparisons between the behavior of some few metals under various conditions of impingement attack. The tests recorded here were undertaken in an effort to find at least some sort of qualitative answer to questions which arose occasionally as to the relative resistance of various alloys to impingement attack, and which could not be answered by reference to the literature. The final decision to start work on the problem was influenced in large measure by the nature of the water available in this particular place. The mill of the Bridgeport Brass Co. is located on the Pequonnock River at Bridgeport, Conn., within two miles of its mouth. The water is much like many other estuarine sources which are used in condensers, and which cause particularly severe corrosion. It seemed a most suitable water to use in such tests. As the work progressed an important seasonal variation was noted. The purpose of this note is to record this seasonal effect. The results of individual tests are given only incidentally.

Jan 1, 1931

By R. J. P. Lyon

It is usually assumed1,2 that ore deposition is relatively slow, taking place over tens of thousands of years. Yet many syntheses and phase changes can be completed in the laboratory in a matter of hours, under essentially the same pressure and temperature conditions to be expected in nature. Much has been written about geothermometry, and Ingerson's recent summary2 an hardly be surpassed. Rather than review the whole field, this article will deal specifically with diffusion rates in solid solutions* of the sulfide minerals. In the study and application of temperature-indicating phenomena to problems of ore genesis, the time factor has often been neglected. In the particular case of sulfide systems, the speed of unmixing and diffusion of the constituent phases in the solid solutions has seldom been considered when laboratory data are applied to the genesis of natural sulfide ores. Chalcopyrite and Bornite Intergrowths: Chal-copyrite and bornite are copper iron sulfides often found in association. In many ores the individual grains appear to have mutual boundaries, but bladed intergrowths are quite common. Early workers in the field, " deduced that while these patterns could have been formed by replacement, they could be experimentally reproduced from the unmixing of solid solutions of the two previously homogenized at 475°C. Much of the ore from Roan Antelope mine in the Rhodesian Copper Belt exhibits these bornite-chalcopyrite intergrowths, from which it has been deduced that the ores could have been subjected to a minimum temperature of 475°C. In several recent interpretations,' this temperature rise has been considered to result from a regional metamorphism of an original syngenetic copper-bearing sediment. The same temperature rise to 475 °C was suggested from similar intergrowths in the sulfide- • The general subject of solid solution in structurally similar minerels is treated in many texts'. :' ' and will not be further elucidated. bearing ore from the Happy Jack uranium mine8 on tile Colorado Plateau, although this temperature had a different origin. In 1931 SchwartzV etermined that 475°C represented the unmixing temperature of his bornite-chalcopyrite solid solutions but, more important, that the characteristic intergrowths of bornite and chalcopyrite could be preserved only if the solid solution were chilled quickly to room temperature. This significant corollary has been almost completely neglected by both Davis and Miller.7,8 By suitably decreasing the cooling rate, Schwartz found that the original pattern of the intergrowth was reformed (Fig. 1). The cooling rate was critical. In cooling from 475°C to room temperature in

Jan 1, 1960

By W. B. Potter

THERE is probably no more interesting group of mineral fuels to be found in any country than that occurring within the limits of the new State of Colorado. The supplies are so abundant, and the occurrence and distribution are so favorable for easy development and transportation to the future manufacturing centres of the State, that they are destined to play a very important part in the material growth and prosperity of the region, the more so because of the rich and varied stores of ores awaiting metallurgical treatment, and the comparative scarcity of timber for fuel. From a purely scientific point, also, these lignitic coals form an interesting and important series. An examination of their geological occurrence and relations opens up new and important questions regarding the comparative value of various kinds of geological evidence, while a study of the character and composition of this class of fuels, which forms a connecting link, as it were, between the lignites and the true bituminous coals, may lead to a more thorough and accurate classification of mineral fuels. The analyses here presented are from samples, of not less than fifty pounds each, obtained by myself during the summer of 1875, and may be regarded as representing very fairly the average run of

Jan 1, 1877

T. Kirke Rose, London, Eng. (communication to the Secretary*) :—The authors have shown that, under certain conditions, the rate of dissolution of gold by chlorine and bromine is reduced by the addition of 10 per cent. of silver to the gold, and that the action is almost stopped when the silver amounts to 30 or 40 per cent. of the alloy. Even if full recognition is given to the practical way in which the work was done, however, it is to be regretted that Prof. Hofman and Mr. Magnusou did not determine the temperature at which the experiments were carried out. From the details given, it may be inferred that the temperature was raised by chemical action by about 20' C. when 21 g. of sulphuric acid was added, and that the mixture was then slowly cooled down during the experiment. When bromine or very weak chlorine solutions were used, there could not have been any perceptible heating-action. As the action of both chlorine and bromine is aided by heat, it follows that the stronger solutions of chlorine were given an unfair advantage over the weaker solutions, and over bromine. If the temperature had been the same in each case, I do not think that the conclusions deduced by Prof. Hofman and Mr. Magnuson' would have been found to be justified. (This is speaking generally. In barrel-treatment the conditions are similar to those in the experiments.) The superior speed of bromine as compared with chlorine at equivalent strengths is not yet disproved, and the differences noted between strong and weak solutions of chlorine may have been largely a function of the temperature. Moreover, the authors used somewhat-coarse particles of gold, and did not try how far time was a factor, although it is obvi-

Jan 1, 1906

By Theodore Simons

The rapid and comparatively recent development of flotation has opened so fascinating a field for study and research that the older processes of gravity concentration no longer receive the attention they deserve. The early work of Munroel and Richards12 and the more recent contributions by Clevenger and Coe,3 Laist and Wiggin,4 Ammon,5 Bardwell,6 Crowfoot,' and Hayden8 (to mention only some which have appeared in our own Transactions) and by Schu1z,9 have furnished so much data that to offer something new seems a difficult task. It is still possible, however, to present known facts from a different point of view, and, with this in mind, the writer has undertaken to express basic principles of gravity concentration in terms of simple mathematics and mechanics; the conclusions thus reached will be found to correspond, in general, with those obtained by experimental methods. Rittinger, in his classic Aufbereitungskunde (1867)) reached analogous conclusions by way of intricate higher mathematics, for which reason his interesting investigations have remained a sealed book to most of us. The writer hopes that a more elementary treatment of the subject, based in part on Rittinger's metheds, may arouse new interest in the study of basic principles.

Jan 1, 1923

By Theodore Simons

The rapid and comparatively recent development of flotation has opened so fascinating a field for study and research that the older processes of gravity concentration no longer receive the attention they deserve. The early work of Munroel and Richards12 and the more recent contributions by Clevenger and Coe,3 Laist and Wiggin,4 Ammon,5 Bardwell,6 Crowfoot,' and Hayden8 (to mention only some which have appeared in our own Transactions) and by Schu1z,9 have furnished so much data that to offer something new seems a difficult task. It is still possible, however, to present known facts from a different point of view, and, with this in mind, the writer has undertaken to express basic principles of gravity concentration in terms of simple mathematics and mechanics; the conclusions thus reached will be found to correspond, in general, with those obtained by experimental methods. Rittinger, in his classic Aufbereitungskunde (1867)) reached analogous conclusions by way of intricate higher mathematics, for which reason his interesting investigations have remained a sealed book to most of us. The writer hopes that a more elementary treatment of the subject, based in part on Rittinger's metheds, may arouse new interest in the study of basic principles.

Jan 1, 1923

By James P. Graham

In this paper the authors present the background information to preheating and its development and describe the facilities available at the British Carbonization Research Association. The results obtained at BCRA including those collected during commissioning of the new plant at BCRA are summarized and reference is made to the research work planned for the next stage. The enlarged test-plant facilities at the British Carbonization Research Association embrace both 10-t (4.2 m high) and 17-t (6.5 m high) test ovens and two types of preheater, the preheated coal being charged by either gravity or pipeline. During the commissioning of the new equipment, an extensive programme on preheating was initiated and the paper includes the results obtained so far. These cover tests on wet and preheated coals and commercial blends, the use of Rosin- and Cerchar-type preheaters and charging by both gravity and pipeline systems to the 10-t and 17-t ovens. Accordingly, for the first time a direct comparison is possible of both the performances of the plants and the qualities of the respective products. The paper also outlines the findings from a study of the carryover of solids during the charging of preheated coal and of the treatment of those solids.

Jan 1, 1977

By E. O. Wagner, V. F. Parry, W. S. Landers

Following investigations by the Denver Bureau of Mines on drying fine coal in the entrained state, Texas Power & Light Co. employed the fluidized technique to upgrade Texas lignite for use in power plants. Because of the rapidly rising cost of natural gas in Texas the company agreed to cooperate with the Bureau of Mines in studying further the upgrading of lignite by low-temperature carbonization, since potential value of the tar would help off- set the cost of fuel. Considerable interest was aroused, therefore, when Aluminum Co. of America decided to use dried lignite in its 240,000-kw power plant at Rockdale, Texas, operated by Texas Power & Light. Carbonization of coal before burning in a power plant is not new. Plants in Germany have been operated for many years on carbonized brown coal and lignite briquets produced in large integrated plants. Large-scale experiments in carbonizing pulverized coal with hot flue gases were made 30 years ago at Milwaukee, and many inventors have proposed other processes. In the U. S., technical and economic problems have prevented successful operation of large plants on carbonized coal, but new techniques of handling solids in fluidized beds may overcome these difficulties, particularly if the higher volatile noncoking coals are used.

Jan 1, 1956

By Henry R. Piehler

Continuous seven- and nine teen -filament close-packed silver-steel filamentary composites mere tested in tension. For purposes of comparison, the tensile behavior of the composite was predicted from the measured properties of the individual com-ponents. It was assumed that the axial strain is the same in both components and that the contribution of each component to the composite flow stress is proportional to its volume fraction. Good agreetnent was obtained between the observed and predicted tensile behavior. However, the composite elongation at fracture was about twice that observed when the individual steel wires were tested alone. Composites in which the filaments were widely spaced failed by the consecutive fracture of the filaments. In composites with closely spaced filaments, a composite instability preceded frachcre. These effects are explained in terms of a lateral restraint to the necking of the filaments which develops in the deforming composite. TWO-COMPONENT or composite materials are increasingly being developed and used as structural materials. Of all the composite geometries used, the filamentary configuration has proved to be the most successful. Polymer-bonded fiber-glas, the most common of the filamentary composites, has been investigated most extensively to date. One explanation of the behavior of fiberglas1 suggests that the load transfer between the glass fibers and the polymer matrix occurs primarily through friction. Bond separation between the fibers and the matrix is presumed to occur at very low stresses. Subsequently, only frictional bonding can provide for the transfer of load from the matrix to the fibers. The force normal to the fiber-matrix interface which gives rise to this friction is assumed to arise from the matrix shrinkage which occurs during solidification. The behavior of metallic filamentary-composite materials would be expected to differ from that of fiberglas in several significant aspects. Residual stresses resulting from differences in thermal contraction can be kept to a minimum by proper heat treatment. A strong wetted bond is formed between the two phases. In brazed joints,2 for example, the interphase bond is sufficiently strong that the weaker material will fail before separation occurs at the interface. Most metal filaments can undergo appreciable amounts of plastic deformation before failure. Failure by plastic instability or necking frequently occurs in metallic filaments, but not in glass fibers tested at room temperature. Differences between the behavior of fiberglas-polymer and metallic filamentary composites have indeed been observed in composites containing various types of metallic filaments in a silver matrix.3,4 At strains of the order of 10-2 pct, all the deformation was accommodated by the silver matrix. Hence, the strength of the composite depended only on the fiber concentration and not on the nature of the fiber. At higher strains, the strength of the composite increased when filaments with higher work-hardening rates were used. Surface slip line observations on a silver-mild steel composite that had been stretched 4 pct showed that an appreciable amount of deformation occurred in the filaments. Work on tungsten-copper filamentary composites5 has shown that the ultimate tensile strength for varying filament fractions followed a linear mixture rule. Assuming that the axial strains in both filaments and the matrix are equal, this linear mixture rule can be expressed as: The subscripts c, f, and m refer to the composite, filaments, and matrix, respectively. A and V are the area and volume fractions of each component. sc and of are the ultimate tensile strengths of the composite and the filaments. sm is the flow stress of matrix at a strain equal to the elongation at failure of the filaments. However, the tungsten filaments can undergo only a limited elongation before they fracture without an appreciable reduction in area. A composite containing more ductile filaments might indeed deviate from this linear mixture rule for the ultimate tensile strength, since filament failure by necking might be arrested by the matrix. SPECIMEN PREPARATION Specimens were prepared from 0.8 pct carbon steel piano wires of 0.015 in. initial diameter. The wires were given a thin nickel flash and a silver plate varying in thickness from 0.015 to 0.007 in., depending on the filament fraction desired. In order

Jan 1, 1965

By Theodore Simons

The rapid and comparatively recent development of flotation has opened so fascinating a field for study and research that the older processes of gravity concentration no longer receive the attention they deserve. The early work of Munroe1 and Richards,2 and the more recent contributions by Clevenger and Coe,3 Laist and Wiggin,4 Ammon,5 Bardwell,6 Crowfoot,7 and Hayden8 to mention only some which have appeared in our own Transactions-and by Schulz,9 have furnished so much data that to offer something new seems a difficult task. It is still possible, however, to present known facts from a different point of view, and, with this in mind, the writer has undertaken to express basic principles of gravity concentration in terms of simple mathematics and mechanics; the conclusions thus reached will be found to correspond, in general, with those obtained by experimental methods. Rittinger, in his classic Aufbereitungskunde (1867), reached analogous conclusions by way of intricate higher mathematics, for which reason his interesting investigations have remained a sealed book to most of us. The writer hopes that a more elementary treatment of the subject, based in part on Rittinger's methods, may, arouse new interest in the study of basic principles.

Jan 7, 1922

By Noel W. Kirshenbaum, George A. Pouska, James M. Link

Literally millions of words have been written on the subject of mineral slurry pipelining. The sheer bulk of literature on the subject should be enough to convince the interested observer that the method is both viable and widely applied. It is the intent of this paper to examine typical mineral slurry applications. This examination should reveal the reasons that the slurry system was selected over other transport modes and it should provide a framework for determining the applicability of the technique to new projects. Slurry transport involves the conveyance of solid particles by suspension in a moving liquid. Almost any combination of solids in liquids may be imagined, and the conduit may be an open channel or a closed pipe. Historically, the most numerous slurry transport applications consisted of mineral particles in water. However, current research investigations are emphasizing other liquid carriers, specifically those which have greater economic value. Among these are gaseous and liquid fuels and chemical feedstocks. Another area being investigated involves the use of the pipeline as a chemical reactor system. The long residence time and turbulent flow characteristics of the pipeline make it particularly attractive for certain chemical reactions. Because these new systems involve a valuable liquid as well as a valuable solid, there is increased attention to solid-liquid

Jan 1, 1980

By Elmer W. Pehrson

THE founding of the American Institute of Mining Engineers in 1871 came at an unusually significant moment in the life of our country. The industrial revolution, in which mineral production played a major role, was just getting underway. The iron industry, established several decades earlier, was reaching sizable proportions. In 1871 pig-iron production was approaching 2 million tons, and the industry had spread as far west as Missouri and Wisconsin. The chief sources of iron ore were Pennsylvania, New Jersey, New York, and Michigan. The age of steel was in its infancy; production had not yet reached 100,000 tons per annum. The gold rush to California two decades earlier and the discovery of other gold and silver bonanzas in the West paved the way for the transcontinental railways, which were then being built and which contributed much to the subsequent development of the great copper, lead, and zinc districts of the Rocky Mountain area. Regular production of copper in the Michigan peninsula and of lead in Missouri and the upper Mississippi region had been established for many years but on a scale dwarfed by the quantities later required as technical progress, invention and enterprise made possible the rapid expansion of industry. Discovery of oil in Pennsylvania in 1859, the growing recognition of the

Jan 1, 1947

The Office of Price Stabilization broke the copper price loggerhead between the U. S. and Chile when it permitted copper wire and brass mills to add to their ceiling prices 80 pct of the increase in cost of foreign copper above the 27 1/2 cents per pound specified in the agreement with Chile. Another step forward in the processing of taconite seems to have been made with the patenting of a process for the strengthening of taconite pellets. The patent was issued to Fred D. De Vaney and assigne to the Erie Mining Co., of Hibbing, Minn. Strength of the pellets is improved by adding from one to five pounds of starch or sodium silicate. A new iron ore deposit discovered on Vancouver Island will start producing soon, and is expected to yield 2 million tons of magnetite over its span of operation. A new mill will be built by the Argonaut Construction Co., of San Francisco, at the deposits of the Utah Construction Co., its parent organization. The Organization for European Economic Cooperation banned the use of nickel and nickel alloy in the manufacture of about 500 products in an attempt to conserve nonferrous metals in short supply. Some 18 members of the organization have already volunteered to restrict nickel consumption.

Jan 1, 1952

By W. B. Potter

There is probably no more interesting group of mineral fuels to be found in any country than that occurring within the limits of the new State of Colorado. The supplies are so abundant, and the occurrence and distribution are so favorable for easy development and transportation to the future manufacturing centres of the State, that they are destined to play a very important part in the material growth and prosperity of the region, the more so because of the rich and varied stores of ores awaiting metallurgical treatment, and the comparative scarcity of timber for fuel. From a purely scientific point, also, these lignitic coals form an interesting and important series. An examination of their geological occurrence and relations opens up new and important questions regarding the comparative value of various kinds of geological evidence, while a study of the character and composition of this class of fuels, which forms a connecting link, as it were, between the lignites and the true bituminous coals, may lead to a more thorough and accurate classification of mineral fuels. The analyses here presented are from samples, of not less than fifty pounds each, obtained by myself during the summer of 1875, and may be regarded as representing very fairly the average run of

By C. A. Zapffe

BOTH the foundryman and the theoretical metallurgist are now generally agreed that the anomalous "rising" or "bleeding" of certain ferrous castings of killed metal is primarily attributable to hydrogen. How and why the phenomenon occurs, however, have not been made clear. The following discussion is intended to harmonize foundry experience with metallurgical theory so that the foundryman may possibly improve his ability to prognosticate whether a certain casting may bleed or not. BLEEDING, RISING, AND PIPING The "rising" to be discussed here is not to be confused with the action in rimming ingots as a result of the carbon-oxygen reaction, although a conclusion will be drawn that may apply to the art of controlling the rimming action. Only killed metal is considered, which includes both steels and irons. In Fig. I, three killed, chill-cast ingots are shown: a porous ingot whose evolution of gas during late stages of solidification has ejected metal through the top; an ingot in which moderate gas evolution during solidification has lifted the mushy central metal, i.e., it has "risen"; and, third, a sound ingot with good piping characteristics. The first type is referred to as "bleeding," and generally infers that a solid skin had first formed through which the liquid metal later erupted. There is no fundamental distinction between bleeding and rising in reference to killed metal.* POROSITY Hydrogen appears as a cause of bleeding because the gas evolution simultaneously leaves a porosity of a type traceable to hydrogen. Twenty years ago, Melmoth1 noted that killed steel that rose unexpectedly in the mold, if returned while liquid to the furnace and heated further under a reducing lime slag, would again rise in the mold; but that if the ingot were allowed to solidify and was then remelted no rising occurred. A critical quantity of the responsible gas is therefore removed by the rising action. Melmoth associated rising with high silicon (0.7 to 0.9 per cent) and concluded that silicon increased gas absorption. Because silicon is a strong deoxidizer, oxygen must, therefore, be eliminated from consideration of the three common gases in steel-oxygen, nitrogen, and hydrogen. Butterworth2 later decided that pinhole porosity was caused by gases dissolved in the metal and that hydrogen was obtained from steam in the mold. Allen's classical work on copper castings,3 soon followed by

Jan 1, 1942

By F. C. Schora, H. P. Meissner

Iron ore from Cerro Bolivar, Segre', and Sierre Grande was reduced in fluid beds at about SOOT, using gas analyzing 20.5 pct CO, 41 pct Hz, and 38.5 pct N2. Except in the early stages of reduction, the rate of oxygen loss from the bed was directly proportional to the oxygen concentration in the bed, independent of gas composition as long as the gas was reducing, and little affected by temperature. The percentage reduction of the bed solids at any time was independent of particle size. I HE reduction of spheres or cubes of dense iron ore in a slowly moving stream of either pure H, or pure CO has been found to take place at distinct interfaces between well defined layers of iron and the iron oxides.'y4 These interfaces generally penetrate the ore lump in topochemical fashion, remaining parallel to the original contours of the specimen. Thus in the earlier stages of reducing hematite, the specimen's core is Fe,O, surrounded by successive shells of the lower oxides, and finally by an exterior shell of iron. McKewan5 assumed that the rate limiting step occurred at the Fe-FeO interface, with reducing gas penetrating up to this interface through the external porous iron shell, and reduction of the higher oxides within the ore lump occurring by diffusion of iron through the dense FeO shell. He developed an analytical expression based on this model relating the amount of oxygen removed from

Jan 1, 1962