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By K. G. Wikle, J. G. Klein, W. W. Beaver

Consolidation of hydride process, electrolytic, calcium reduced, and comminuted thorium powder, as well as saw chips and lathe turnings, by vacuum hot pressing and by cold pressing-vacuum sintering was studied. The mechanical properties of the consolidated material in the extruded form are compared with those of wrought castings. AT present there little little industrial use for thorium metal, although it has some important though small scale applications in electronic equipment. Despite its high inelting point—about 1750°C —a low modulus of elasticity, 11.4xl0 si at 20°C;' relatively low mechanical properties coupled with a high density, 11.7 g per cu cm; and an unusually high chemical activity with normal atmospheres limit any structural applications. The metal is utilized as an alloying element principally in magnesium. Pure thorium finds utility as electrodes in gaseous discharge lamps such as the high intensity mercury lamp' because its low work function and high electron emissivity provide lower starting potentials and more uniform operating characteristics than other available materials. The metal is also found in photoelectric tubes used for the measurement of the ultraviolet spectrum." Thorium metal has been used in germicidal lamps of the cold cathode type as sputtered coatings on nickel in order to provide a low work function surface and a low starting voltage. Other applications have involved the radioactive properties of thorium for the production of ionized particles." The potential value of thorium is much greater than its present use pattern because of possible utility in the field of nuclear power. Th may be converted through nuclear reaction to a fissionable element U which should be capable of acting similarly to U in the g'eneration of atomic power. Thorium has been reported to be about three times as plentiful as uranium in the earth's crust, placing it in the order of abundance of lead and molybdenum." Thus, it is of interest in augmenting the potential supply of fissionable material for nuclear power. Because of its high melting point, thorium is usually produced as a powder through the calcium reduction of its oxide or thermal reduction of halides by sodium, magnesium, and calcium. It may also be produced in flake form by electrolysis of fused alkali or alkaline earth chloricles and fluorides. Therefore, powder metallurgy assumes importance in the fab- rication of thorium metal shapes. Furthermore, it is rather difficult to obtain pure thorium by melting, as the molten metal reacts readily with graphite as well as oxide, carbide, and nitride refractories. These contaminate the melt with oxides, carbides, and metallic impurities." The current investigation was undertaken to examine the fabrication of thorium by powder metallurgy methods which have been used for the commercial production of beryllium and other metals.' A sparcity of data concerning the comparative cold and hot compaction of thorium powders of different derivation existed. Therefore, all commercially available types were examined along with other experimentally produced thorium powders in order to round out the comparison of consolidated thorium powders with melted reguline metal. Review of the Literature By heating a mixture of ThC1, with potassium, Berzelius made the first thorium metal as an impure powder in 1828. Improvements in the basic process, increasing thorium assay to 99 pct, were made by several investigators including Arsem," Lely and Hamberger10 and Von Bolton." Calcium reduction of Tho, to make powders was investigated by Berger," Huppertz,'" Kroll," and Kuzel and Wedekind.'" A thorium powder produced by this method using a CaC1, fluxing agent assayed 99.7 pct, as reported by Marden and Rentschler.'" Compacted and sintered, this product was found to be ductile, and could be fabricated into wire and sheet. Improvements of the calcium reduction process were made later" wherein CaCl, was eliminated from the reaction, producing metal assaying 99.8 pct Th. Further work by Lilliendah118 howed that a coarser metal could be obtained by the substitution of ThC1, or ThOC1, for oxide with consequent advantage of stability to atmospheric reaction. Reports on the technology of thorium developed in Germany during World War II have been made by Espe."' Thorium powder of 99.5 pct Th was obtained by reduction of the oxide by calcium. Screening to —200 mesh, compacting with about 20 tsi, and sintering in vacuo at 1320" to 1360°C for 3 hr resulted in a porous sinter cake. The sinter cake was sufficiently ductile to be worked into bar, wire, and sheet which could be employed as electrode materials.

Jan 1, 1957

By J. P. BONARDI, William F. Boericke

BOULDER COUNTY, Colorado, ranked during the war years and until the end of 1918 as one of the foremost tungsten-producing districts of the world. In 1919 production fell off drastically, due to heavy importations of foreign ores from China, Burma and South America. So large were the imports that even after the enactment of a protective tariff in 1922 of 45c. per lb. on tungsten metal, equivalent to $7.14 per unit (201b.) of tungstic acid? (WO,), the stocks of metal in this country were extensive enough to supply the demands of industry, and prevent general resumption of mining by domestic producers. Even today there are only two producers in the Boulder district though at one time as many as twenty separate companies were in operation. About the same ratio holds for other tungsten-producing districts in the country, including California and Nevada. Total consumption of tungsten concentrate in terms of 60 per cent WO2 in the United States amounted to approximately 3790 tons in 1928, according to Frank L. Hess.' Of this amount, domestic mines contributed 1290 tons, and the rest, 2500 tons, was imported. Yet in 1917, with tungsten concentrate selling at $20 per unit, the Boulder district alone produced 2707 tons, indicating the effect of enhanced ore price upon production. It is believed by American tungsten miners that, given a sufficiently high tariff, all the demands of industry can be met by domestic production without placing a prohibitive burden on consumers. For instance, in steel manufacturing the percentage of tungsten entering into the manufacture is so small that, ?regardless of cost, it can constitute but a small fraction of the cost of steel to the buyer.

Jan 1, 1929

By AIME AIME

THE official opening at the 134th general meeting of the Institute was held on Oct. 6, but it was prefaced by two round table conferences on Oct. 5. The open-hearth group held the fourth of their semi-annual conferences at the William Penn Hotel, devoting the morning session to discussing a paper by R. L. Cain on the "Manufacture of Forging Steel by the Open-hearth Process," and the afternoon to discussing P. H. Shaeffer's paper on the open-hearth charge. At the Bureau of Mines, a round table conference on the combustibility of coke was held on Tuesday morning, and the afternoon was devoted to a similar conference on the testing of coke. The formal opening session of the meeting assembled in the Music Hall of Carnegie Institute at 10.30 a. m. Graham Bright, chairman of the Pittsburgh Section; called the meeting to order and presided. President Taylor welcomed the visiting members and guests to his home city and reviewed briefly the advancement of mining in the past half century during which, for ex- ample, the coal output had increased from 53,280,000 tons to 523,357,000 tons per year. He emphasized the important part Pennsylvania played in mining and brought out the principal changes that had taken place in methods. In part, his remarks were as follows: The centennial year, 1876, found the coal business of. this country, as a whole, producing 53,280,000 tons, of which amount the bituminous mines of this State yielded 24 per cent. In 1925, this country produced 523,357,000 tons of coal, of which Pennsylvania produced 24 per cent.

Jan 1, 1926

By Granville S. Borden

MANY complaints have been filed by mine prospectors, explorers and producers about inequities in mining taxation. They have insisted upon improvement, and in the past 35 years there has been some progress. Many of the best taxation provisions made to date are those contained in the Revenue Act of 1951. Mining economics presents special problems, a fact even recognized by many textbooks. Certain provisions have been made to take care of mining taxation rights, but these have been made by Congressional act and do not represent basic, constitutional, guarantees. Despite special provision, in the form of depletion allowances, there remain injustices. The industry faces the problem of gaining adequate income tax allowances for exploration and development expenditures, operating losses, and bonus and subsidy payments. Problems in mine taxation arose soon after the adoption of the 16th Amendment. This amendment gave Congress the power to impose income taxes. Supreme Court decisions against a number of mining companies held that Congress, under its power to tax income, could tax net operating revenue before depletion allowance was deducted. The court also ruled that the right to deduct depletion is a matter of Congressional permission. There is no statute provision permitting mining stockholders to recover their investment out of dividends while the mine is being operated. The Supreme Court did not recognize that part of mining proceeds are actually amortization of the cost of mineral rights. Both these omissions stem from failure to recognize that by its very nature mining consumes its mineral rights and therefore that a part of gross proceeds are not income but recovery of capital. Suppose a Congress unfriendly to mining interests repeals the provisions that allow deductions for depletion. Under such a situation assume that a corporation buys a mineral deposit for $300,000. They mine the deposit and earn an operating profit of $500,000. At the current rates they would pay a Federal Income tax of in excess of $250,000. This venture results in a loss of $50,000 as shown in the table below. For the example given the absence of depletion provisions in income tax law would turn ore into waste rock, because the word "ore" connotes commercially mineable rock. [ ] In retrospect the conclusion is clear: If the Supreme Court had recognized that a part of mining proceeds represent in reality sales proceeds of mineral rights, then profits derived from such sales would have been taxed at the favorable long-term capital rates, instead of being taxed at the high normal, surtax and excess profits rates. It is a question whether percentage depletion allowances offset this tax situation. History The history of depletion allowances has been one of general improvement. The original act did not include depletion, but an allowance at the rate of 5 pct of gross proceeds was provided in 1913. The Acts of 1916 and 1917 allowed depletion upon cost of property, and in 1918 the law was further changed to permit depletion upon cost, or market value as of date of discovery. In 1932 metal, coal and sulphur properties were permitted to elect depletion in percentages of gross income, limited to 50 pct of net income, in lieu of cost depletion. Shortly thereafter the rule was changed and percentage depletion is now allowable in any case where it is higher than cost depletion. Since 1942 percentage depletion allowances have been extended to cover many nonmetals, and in 1951 the rate for coal mines was increased from 5 to 10 pct of gross income. It is interesting to note that these allowances have been retained, and even

Jan 1, 1952

By Elizabeth L. Robinson

INTRODUCTION The financial structure of the mining industry has changed strikingly over the last thirty years. The changes that have taken place in the last ten years include both the acceleration of adverse trends in familiar balance sheet numbers and ratios, and the subtle but extensive increase in the complexity and diversity of funding sources, both on and off the balance sheet. The objectives of this paper are: 1. to briefly trace the evolution of trends in the mining industry's financial structure; 2. to focus in more detail on changes in the last decade; and 3. to analyze those trends both within the framework of capital structure theory, and in the context of changes in business and economic conditions. This survey focuses primarily on the mining companies listed on the major U.S. stock exchanges, since financial data for these firms are readily available. The producers of minerals are a diverse lot, however, and the quantitative data on "the mineral industry" as characterized in this survey fails to encompass the financial arrangements for the bulk of production worldwide, whether owned by governments or private-sector enterprises. Even large portions of the U.S. minerals industry - subsidiaries of still larger firms, medium-sized privately-held companies, and the small miners - were not included in the quantitative part of the analysis. THE EVOLUTION OF THE INDUSTRY'S FINANCIAL STRUCTURE In the aftermath of the business failures of the Great Depression, most borrowers and lenders considered minimal debt on the balance sheet the soundest policy. By the 1950's, however, a body of literature was developing which demonstrated that the use of leverage could improve the value of the firm, given a corporate tax structure which allows interest, but not dividends, to be deducted from income. Optimal Capital Structure The objective of undertaking a new project is to improve the wealth of the current owners of the firm. If internally-generated funds are insufficient to allow growth at the desired rate, the company can raise funds either by issuing new equity, or by incurring debt. The most attractive source is the one which will provide the funds for the lowest cost. Both stockholders and lenders expect to receive compensation for use of their funds at a rate which reflects two things: (1) the return they could earn in alternative investments, and (2) the riskiness of the projected return. Factors which increase business risk include the variability of demand, sales prices and input prices, and "operating leverage", or the proportion of fixed to variable costs. In addition, from the investors' point of view, the use of financial leverage concentrates risk onto the shareholders, because lenders enjoy a prior claim in the event of bankruptcy. So although financial leverage can increase a project's expected rate of return, and therefore, presumably, earnings per share, too much debt will be perceived as uncomfortably risky by equity investors, and have a negative effect on stock prices. In theory, then, there should be an optimal level of debt which the firm's managers should seek to obtain in its financial structure. The desirable proportion of debt should in general be lower for a firm with a higher inherent business risk. In addition to their own judgement, financial managers are sensitive to the attitudes of lenders, rating agencies, and investment bankers in setting financial targets (Scott and Johnson). In practice, financial structure will also depend upon the company's growth rate and level of profitability, and conditions in the capital markets at a given time.

Jan 1, 1985

By S. A. TAYLOR

THE aftermath of a world war brings up a number of economic problems for the consideration of all thinking and patriotic citizens. The solution of the problems which confront the country at this time cannot well be accomplished by reference to past experience, for such conditions as confront us today have not existed in the past. We must, therefore, in any attempt to solve the present problems, rely to a great extent upon a careful analysis of present conditions to determine what is wrong; and after this is determined, seek the remedy and apply it. It needs no argument to establish the fact that, in the effort to win the war, the cost of so doing, and the waste in connection with it were, to a large extent, lost sight of; and this situation caused high wages, high cost of all materials, and of food supplies.

Jan 1, 1921

By Freeman Bishop

Having obviously cleared the way for fast confirmation by the Senate Interior Committee, the Administration recently named Elburt F. Osborn, vice president of Penn State University, as director of the Bureau of Mines. Interior Committee Chairman Henry M. Jackson (D of Wash.) has moved hearings on the nomination right along, forecasting that they will end in a confirmation. Dr. Osborn not only made a good impression on the Committee, he also made it amply clear that he would be the boss of his job and have right-hand aides to help straighten out conflicts stemming from recently enacted health and safety regulations for miners. Mining engineers in the field hope this clarification can come soon. They are frankly fed up with local, state, regional and national overlapping of restrictions.

Jan 1, 1970

By Hans Lundberg

IN last year's report on the progress of geophysics, the airborne magnetometer was the featured new development. At that time only a relatively small number of surveys had been made. During 1947, the airborne magnetometer was used in making many surveys and is again one of the high lights of the year in geophysics. This report is mainly concerned with geophysics as applied to the search for minerals exclusive of petroleum. In 194,5 and 1946, the use of the magnetic method reached a peak, partly because of an active period of prospecting brought on by an active mining market, particularly in Canada.

Jan 1, 1948

By Hermann Bach, Walther Hänig, Willi Gehrhardt, Ernst Theurich, Walter Langner

With the construction of the Magdeburg zinc works, the Georg von Giesche's Erben Mining Co. of Breslau has to a certain extent completed the program of reconstruction which it set as its goal after the boundaries of Upper Silesia were drawn by the Treaty of Versailles. During its history, covering.more than two centuries, zinc and lead mining has been its chief activity. Through the new boundaries established, it lost to Poland all its mines and smelters, including five distillation smelters. Of its extensive properties, there remained only an apparently unimportant and unexplored portion of the old Bleischarley ore field which, however, happily made possible the resumption of its old business. In 1925 the Deutsch-Bleischarley shaft-only a few kilometers from the old Bleischarley shaft—was sunk and developed, and in May 1926 production of lead and zinc ore was resumed. As facilities for smelting were lacking, the ore was at first delivered to the neighboring smelters, which had now become Polish. Realization of the plan to build its own zinc works had to be postponed at first for lack of capital. In the meantime, however, plans for the new works were worked out in all details. After extensive experimentation in a semicommercial pilot plant it was decided, at the end of 1928 and the beginning of 1929, to use the electrolytic process and, for economic reasons, to place the works at Magdeburg. With zinc at the approximate price level that had ruled since the Deutsch-Bleischarley mine had begun working, it was hoped that the plan could be completed in 1930 with the company's own resources. However, falling metal prices, already noticeable in 1929, made this impossible, and further postponement for a time became necessary. Finally, at the end of July 1933, the funds for building the works became available, in the form of a loan granted under the first employment

Jan 1, 1937

By Sherwin F. Kelly

THE geophysical scene shifts and alters, the emphasis changes, and new possibilities loom, but the tendency is always towards widening the field and deepening the analytical penetration. Seismic methods have had their heyday, the torsion balance is being displaced by the gravimeter, electrical methods are showing deeper penetration, soil analysis is the newest tool, and gamma-ray logging appears on the horizon. One of the striking features of re- cent geophysical work in the oil fields has been the marked decrease in the number of seismic crews employed. Although the percentage of company crews is believed to have increased appreciably. the sum total has fallen sharply, as shown by the figures for the Gulf Coast area. About two years ago probably over 100 seismic parties were operating there, whereas now there are only about 35. This decrease may be partly due to the low prices of petroleum with a consequent reluctance to spend money to increase crude-oil re- serves but more probably to the fact that reflection and refraction shooting have been carried on so extensively that they have been applied to a large pro- portion of the areas in which they may reasonably be expected to succeed. Some of the earlier enthusiasm, particularly over reflection prospecting, may have erred on the side of over- optimism; some of the present curtailment may be due to over pessimism; but in the opinion of various observers seismic work at the present rate seems to be at it- optimum. It nevertheless remains pre-eminent as a technique for detailing structures in areas where good reflections can be obtained and is the only method that will give accurate depth to definite beds. Results may be poor in certain areas but many regions still remain wherein it can be applied, so that plenty of structural mapping remains to be done by the reflection seismic method.

Jan 1, 1940

By O. J. Hollister

Jan 1, 1888

By Lawrence P. Bonicatto

The steel industry's increased demand for higher grade pellets has caused the pellet producers to investigate methods of upgrading their product and the Hanna Mining Co.'s Groveland plant on the Upper Peninsula of Michigan is no exception. The low grade iron deposit is a complex mixture of magnetite and hematite with chert, quartz, jasper and various iron silicates.1 Beneficiation is by Humphrey spirals and anionic flotation of the iron minerals.2 Flotation of the spiral tailings makes up about 75% of the concentrate, while a minor amount of concentrate (less than 3%) is produced in magnetic circuits. The concentrate is pelletized at the rate of 1.6 million tpy. The initial concentrating facilities were constructed in 1958 and the concentrate was marketed as sinter feed until a pelletizing plant was added early in 1963. Grade improvement soon became a high priority research project, and several methods of concentration were investigated.

Jan 3, 1968

By F. J. Fayers, R. L. Perrine

For many years the problem of increasing ultimate recovery of oil from a reservoir has been a subject of interest to the oil industry. At present, a standard secondary recovery technique is to flood the reservoir with water once natural forces of the system are depleted. The permeability characteristics of the rock, together with interfacial forces which exist between the two fluids and the porous material. allow only part of the oil in the rock formation to be recovered by the water-flooding process. Laboratory experiments have shown that when detergents are added to the flooding water, the flow properties of oil in a porous rock arc improved. This improvement results in greater oil recovery. Even though higher recoveries are obtained using detergents, the extra cost associated with the method may make it economically unsatisfactory. To establish economic feasibility requires experimental laboratory measurement of fluid and rock properties together with a calculational procedure to predict field results. Pilot tests in the field may also be required. This paper presents a mathematical procedure for predicting detergent flood behavior. A number of reasonable simplifying assumptions are made to obtain a tractable system of equations. The resulting method may be regarded as a generalization of Buckley-Lev-crett' theory to solve simultaneously for water saturation and detergent concentration profiles. Consequently this type of calculation can be used in much the same manner as Buckley-Leverett theory is used to evaluate a water flood. The mathematical method employed is the so-called method of characteristics for solving hyperbolic partial differential equations. This application of the method is instructive because several other problems in reservoir analysis may be analyzed in a similar manner. FLUID FLOW EQUATIONS The flow behavior of oil and water without detergent through porous reservoir rock is usually expressed by Darcy's law and a continuity equation for each phase. If gravitational forces are neglected, vrg = kr (s)µr v p rg.........(1) vrg = kr (s)µr v p rg.........(1) ? pa va = F ?/?t (sd) where v is the volumetric flux, k represents permeability, S is saturation, and P the pressure. Fluid viscosity is denoted by 11, p is the density, 4 is porosity, and I the time. The subscripts w and o refer to water and oil. The capillary forces in the system lead to a difference in pressure between phases. This may be expressed by the relation: Pm -P0 =Pc(S).........(5) The capillary pressure? P,, is determined experimentally as a function of saturation. DETERGENT BALANCE EQUATION Addition of detergent to the water phase affects the flow properties of the system. Capillary pressure and relative permeability become functions of detergent concentration, c, as well as fluid saturation. That is: P--P (S,c) and k,,,.- - -- k,,,. At low oil saturation values, the presence of detergent reduces capillary pressure and reduces the relative permeability ratio. Detergents are surface-active and adsorb on rock surfaces. The quantity adsorbed, a, will depend on the concentration c of detergent solution and may also depend on the saturation; thus, a = a(S,c). In this analysis we have assumed that the detergents used are water soluble but not oil soluble, and their movement is therefore restricted to the water phase. The dispersion of detergent in water is neglected by comparison with transfer by flow within the system. Detergent movement is determined by the water flux and adsorption: ? cv m = -F ?/?t (cs + a) We will assume that the quantity of detergent in solution is too small to significantly change water density or viscosity. When the permeability and capillary pres-

By Roshan B. Bhappu

This is the Centennial year of AIME and many of us reading this issue of ' will be getting ready to attend the Centennial Celebration in New York from February 26 through March 4. The officers of the Division sincerely hope that a large number of our members will attend the fine technical sessions and social functions arranged for this really big meeting. The year 1971 will be a crucial one for MBD. This SME Division is a working group organized "to furnish a medium of cooperation among those interested in the basic unit processes and unit operations of minerals beneficiation; and to promote the advancement of this branch of mineral technology through meetings for professional intercourse, and to stimulate the preparation, reading discussion and circulation of papers connected therewith." No one can deny the worthiness of these objectives or minimize the efforts that Division officers and members have made to attain them. Much has been done over the past several years to achieve a smooth-running and effective MBD organization. However, there is still room for improvement and much more needs to be done in order to provide the best possible services for the membership and the profession.

Jan 1, 1971

By Owen W. Ellis, Telfer E. Norman

The use of cadmium as a base for bearing metals is one of the most interesting recent developments in this field. It has caused a strong demand for cadmium and a marked rise in its price. It appeared to the authors, therefore, that the situation might be relieved for users if acceptable substitutes could be developed. A preliminary investigation has revealed that to some extent mercury may be substituted for cadmium. Whether its use is justified cannot be stated at this time. Most of the authors' work has indicated that the addition of mercury to alloys of cadmium and nickel detracts from their desirable physical properties; but this work has not been extended to cover service tests, which might reveal that the addition of low percentages of mercury to the cadmium-base alloys would improve their performance. The results of tests made by the authors are therefore briefly summarized for this paper. Table 1 gives the proportions of the metals used in preparing the alloys. After preparation of these alloys, th composition was checked by chemical analysis. Particular care taken to ensure that the nickel content did not vary appreciably from 1 per cent.

Jan 1, 1938

By Owen W. Ellis, Telfer E. Norman

The use of cadmium as a base for bearing metals is one of the most interesting recent developments in this field. It has caused a strong demand for cadmium and a marked rise in its price. It appeared to the authors, therefore, that the situation might be relieved for users if acceptable substitutes could be developed. A preliminary investigation has revealed that to some extent mercury may be substituted for cadmium. Whether its use is justified cannot be stated at this time. Most of the authors' work has indicated that the addition of mercury to alloys of cadmium and nickel detracts from their desirable physical properties; but this work has not been extended to cover service tests, which might reveal that the addition of low percentages of mercury to the cadmium-base alloys would improve their performance. The results of tests made by the authors are therefore briefly summarized for this paper. Table 1 gives the proportions of the metals used in preparing the alloys. After preparation of these alloys, th composition was checked by chemical analysis. Particular care taken to ensure that the nickel content did not vary appreciably from 1 per cent.

Jan 1, 1938

By L. R. Plitt, E. O. Lilge

Tests carried out with both kaolin and silica slurries show that flocculants of the polyacrylamide type can be used to improve the thickening performance of hydrocyclones. This thickening improvement demonstrates that contrary to previously held theories, flocs can be formed which are capable of resisting the shear forces in a hydrocyclone. For the 1.25-in.-diam cyclone used, optimum thickening occurs when the flocculant solution is injected into the slurry stream at or near the feed inlet. Hydrocyclones offer many distinct advantages over gravity thickeners. These advantages include simplicity, low initial and operating costs, small space requirements, and flexibility of operation. In spite of these advantages hydrocyclones have not been widely used as thickeners. The main reason for their lack of application is that hydrocyclones are unable to efficiently remove semicolloidal particles (less than 5 microns) from the suspending solution. In gravity thickeners, the fine particles can be induced to form particle aggregates, or flocs, which have the settling characteristics of large particles. In the hydrocyclone, however, it was always assumed that the existence of shear would prevent the formation of flocs.1-3 Thus, if no floc structure is retained, the thickening hydrocyclone must be designed so that its separation size is below the size of the smallest particle to be recovered. To obtain a very small separation size requires the formation of very high centrifugal forces, which necessitates the use of small-diameter cyclones. Small hydrocyclones have, in turn, very low throughput capacities which render them impractical for many industrial thickening applications. Thus, if the effects of flocculation cannot be utilized, the usefulness of hydrocyclones as thickeners remains limited to pulps which contain no very fine particles. It is well established that most substances acquire a surface electric charge when brought into contact with an aqueous medium. The repulsive interactions between similarly charged particles act to prevent flocculation. One method of flocculating a dispersion is to neutralize the repulsive surface charges by the addition of an electrolyte. The reduction of the electrostatic surface charge (Zeta potential) then permits the universal van der Waals attractive forces to operate between the atoms of the various particles and form particle aggregates. The lime additions used by thickener operators promotes flocculation by this mechanism. A second method of flocculating a dispersion is by the addition of long-chain macromolecules. In this case flocculation is brought about by a bridging mechanism in which the molecules are adsorbed with part of their length on two or more particles, thus forming a molecular bridge between the particles.4,5 The molecules also form bridges between themselves when a single particle is bonded to several polymer molecules. The type of bonding between the flocculant molecule and the particle may be hydrogen bonding, chemical bonding, or electrolytic attraction.6 The flour and glue which are used as thickener additives are believed to promote flocculation in this manner. In the past decade synthetic long-chain polymers with extremely high flocculating capabilities have been developed. The flocs formed by these new polymeric flocculants are larger and more shear-resistant than those formed by the presence of electrolytes.7 The advent of these flocculants raises the question: Are the flocs formed by these synthetic polymers stable enough to resist the liquid shearing forces in a hydrocyclone? The investigations reported in this paper were carried out in order to provide some answers to this question. EXPERIMENTAL WORK For the bulk of the test work a 5% slurry of commercially available kaolin with an average particle size of 5 microns was used. An initial evaluation of the available flocculants was carried out to determine which flocculant formed the most shear-resistant flocs. A combination of the techniques used by Healy7 and Booth8 was used for this purpose. This initial study revealed that the neutral high-molecular weight polyacrylamides produced the most shear-resistant flocs. One of these flocculants, Separan MGL*, was selected and then used for all the hydrocyclone tests. The flocculant was dissolved in water and added to the hydrocyclone as a dilute solution.

Jan 1, 1968

By Charles V. Jenkins

The structure of steel, when rendered coarse by over-heating, is made fine by re-heating to a certain temperature, the determination of which has received much attention from eminent metallurgical authorities. Among these, I may particularly mention Prof. D. Tschernoff' [Chernoff], who, about thirty years ago, studied this question in connection with his investigations on the structure of steel in genera1. † Some years later, Mr. J. A. Brinell took up the inquiry, and arrived at many important conclusions, stated in his well-known rules on the treatment of steel. ‡ These two gentlemen, however, based their reasoning chiefly upon the aspect of fractures—a method which, though it affords valuable information, does not readily reveal the different steps by which a change in structure takes place. For further light on the subject, we owe much to more recent microscopic investigations, which have made us better acquainted with the internal structure of metals. Such an investigation, closely connected with the present subject, and made by Mr. John E. Stead a few years ago, was first published in 1898.6

Jan 1, 1903

Jan 1, 1883

By Louis A. Panek

INTRODUCTION AND SUMMARY With respect to the geomechanics aspects, the primary technical objectives in mining by an undercut-cave method are to achieve a controlled, sustained caving of the mineral body and to remove the fragmented ore with a minimum of dilution from surrounding unmineralized rock, while maintaining stability or control of the rock structure around the access openings. The structurally ideal ore body probably does not exist. If the rock mass is so weak as to cave on a short span, it may tend to be too sticky for easy drawing and handling, or create special problems in regard to support of the access openings. If the ore is strong, caving may be difficult and the caved fragments may be of such a large size as to require special equipment for transferring the ore from the caved zone. Given enough time and money to generate data and conduct trials, engineering and ingenuity can devise an appropriate combination of mine layout, sequence of extraction, and mechanical equipment to achieve a technically successful caving extraction operation to meet the foregoing requirements in many types of deposits. The large capital investment involved, however, reduces the freedom to make major changes once the mine development is well under- way, and the penalties for failure to accurately anticipate operating conditions militate against selecting any but the most obvious candidates for mining by an undercut-cave method. The demonstrated capability to extract large, deep, economically marginal deposits by this low-cost, high-volume method of mining provides an incentive to develop a rationale for predicting the cavability and stability characteristics of a deposit prior to mining, so that the undercut-cave method may be extended to a much wider range of mineral deposit characteristics. The ultimate goal is to establish as explicitly as possible the quantitative interrelationships between the measured rock-mass characteristics, the caving span, the size distribution of caved ore fragments, and the sizes and locations of stable access openings. Lacking an understanding of these relation- ships, a designer may readily change some factor in the wrong direction (e.g., excessively reduce the distance between the extraction level and the undercut to increase the convenience of operations for the undercutting crew, increasing the frequency of repairs to the extraction-level support system) or create unnecessary problems elsewhere in the system by introducing a design change that can achieve only minimal improvement in the factor of direct interest (e.g., unnecessarily complicate the ore-transfer system by changing the orientations of the openings, with- out succeeding in the objective of improving the ground support conditions). Although successful predesign is the prime objective, subsequent modifications in mine lay- out and sequence of extraction operations are inevitable. In developing the modified solution, systematic experimentation based on an understanding of the underlying structural relationships, coupled with monitoring measurements of selected diagnostic structural-behavior parameters, can achieve an acceptable solution in a minimum number of steps, which is far superior to the typical operational trial-and-error approach, in view of the cost of implementing each successive change. Since a drill-core sample of ore rock from a successful undercut-cave operation may exhibit a uniaxial crushing strength in excess of 100 MPa, the caving of such a rock mass is now commonly believed to be ascribable to the presence of discontinuities such as joints or fractures throughout the ore body. An essential part of the present investigation was therefore to characterize the natural discontinuities at each of the test sites by measuring their attitudes and spacings. The term "fracture" is used herein in a general sense to include any planar discontinuity without implication as to its suggested mode of origin. Most, but not all, of the fractures are properly termed joints. As a point of departure we may consider the possibility that the rock mass is transected by three families of joints, each family possessing a distinct orientation, such that parallelepipeds of intact rock are delineated by the jointing. Even if cementation is absent between adjoining parallelepipeds, the undercutting of the rock mass will not necessarily initiate sustained caving--owing to the all-around confinement, an arch may tend to stabilize over the undercut unless prevented from doing so by the failures of key blocks of intact rock. Thus, although the jointing can be assumed to weaken the rock mass, creating preferred directions of

Jan 1, 1981