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By Robert J. Hite, Samuel S. Adams

Potash, the generic term for a variety of potassium-bearing minerals, ores, and refined products (Table 1), owes its importance as an industrial mineral to the potassium requirement of growing plants. The term potash originally referred to potassium carbonate produced by the leaching of wood ashes. This process, for which the first US patent was issued in 1790, was the basis for the largest United States chemical industry in the early nineteenth century. The agricultural use of potash soon eclipsed the chemical applications following the German discovery in 1840 that potassium is essential to plant growth. The initial discoveries of large deposits of soluble potassium minerals, essential for agriculture applications, were made in 1857 in Germany and in 1914 in the United States. More than 90% of the 27.5 Mt K20 produced in the world in 1980 (Searls, 1981) was derived from marine evaporite deposits and approximately 90% was used in fertilizers. The potassium content of an ore, mineral, or product is customarily expressed as % K20, a unit of measure which is neither a natural nor synthetic compound of potassium (1.0% K is equivalent to 1.2046% K2O). Geology Potassium, the seventh most abundant element in the earth's crust, is present in silicate minerals in igneous, sedimentary and metamorphic rocks. Potassium is also a major constituent of many surface and subsurface brines (Table 2). Economic potash deposits are essentially restricted, however, to widespread, thick accumulations of marine chloride evaporite deposits. These deposits yield high grade, large tonnage ore bodies, many of which are amenable to low cost mining and beneficiation. The products from these deposits are, moreover, ideal for use in fertilizer because of the high relative solubility of the potassium chloride and sulfate evaporite minerals. World potash production and reserves for such deposits so vastly overshadow other sources of potassium that the following discussion will be limited largely to potash deposits in marine evaporites with brief reference to certain potash-rich brines. Approximately 85% of current domestic production is from bedded salt deposits and much of the balance is from brines. Marine evaporite deposits are accumulations of salt minerals deposited in structural sedimentary basins through the evaporation of seawater or mixtures of seawater and other brines. The salt minerals are precipitated in assemblages and sequences of assemblages as determined by the compositions of the brines and the solubility relations in the salt systems (D'Ans, 1933). The evaporation of seawater normally yields carbonate minerals as the first precipitates (Table 3). Further evaporation and concentration of the brine leads to the precipitation, in succession, of sulfate, chloride, and supersaline mineral assemblages including the salts of potassium and magnesium. The common minerals, ores, and products of potassium deposits are listed in Table 1. Many potash deposits contain accessory evaporite minerals together with a variety of detrital and authigenic silicates (Braitsch, 1971). The structural basins within which marine evaporites occur are of two main types: (a) cratonic basins formed by broad epirogenic movements (for example, the Michigan Basin of the midwestern United States and the Permian Zechstein Basin of eastern Europe), and (b) grabens, commonly related to continental

Jan 1, 1983

G. O. SMITH,* Washington, D. C.—This program is itself a demonstration of the widespread interest in the subject of more efficient development and operation of oil fields. The statements of fact already presented and the views expressed are sufficient evidence that the engineering and economic principles fundamental to the idea of unit operation are much more generally accepted than they were even one year ago. And real progress has been made in putting these principles to the test. No one realizes better than I that the fight against waste, whether physical or economic, must be waged in the front-line trenches: Washington at best is only an observation post. Yet viewed from this distance the advance made in the last few months has been notable and to a high degree encouraging. Five years ago the Federal Oil Conservation Board, in its first contacts with the industry, raised the question, "How can new pools be explored without exploitation until new production is warranted by the country's needs?" Three and one-half years ago the Board, in its first report to the President, paid largest attention, among what it listed as fundamental conservation measures, to "cooperative methods in sane development of new fields." A year ago, in its third report, the Board again endorsed as the essential factor in conserving the nation's reserves of oil, "full cooperation in unit control, whether by voluntary agreement or by state enforcement." The function of this federal agency has been purely fact-finding and educational. The Oil Conservation Board early declared that the major part of its task was to help the industry "formulate the broader by-laws in the sense of conservation." And now, after these five years of eventful history in the oil industry, may I size up the situation as I see it from the Washington point of view? First of all, and fundamental to a successful issue, I have observed in the industry a gradual acceptance of technical opinion as the guide to executive action; and this has at last led to some agreement as to what procedure offers most promise. Analyzed in more detail, this highly desirable progress has consisted in "self-restraint actuated by enlightened self-interest." We see emerging the general desire of oil producers for efficiency in operation, which means low costs and high recovery. As shown by facts presented at this meeting, competition in drilling is in direct opposition to efficiency in oil production, in that such competition increases costs and lowers recovery. The only route to conservation of this natural resource and also of the capital and labor involved in making it available is through unit control, which substitutes cooperative, well-planned action for competitive, unregulated activity, forced by the individualism of a small minority of landowners or perhaps by a single operator. Or, in terms of actual experience, development of an oil field and its subsequent operation under unit control means the substitution of majority rule for minority rule, yet the minority enjoys to the full the resulting economic benefits. So far as it affects the public interest, unit operation of oil properties deserves unqualified approval. It means more oil from the same area over a longer period

Jan 1, 1930

By Jeffrey L. Thompson, Kenneth A. Gutschick, Robert C. Freas, Robert S. Boynton

Lime, the "versatile chemical," is, generally speaking, a calcined or burned form of limestone commonly known as quicklime, calcium oxide or calcia, or, when water is added, calcium hydroxide or slaked lime. Almost 40 different lime products are available, a fact which has contributed to the rather loose use of the term lime as well as to much confusion and misunderstanding. The term is frequently, albeit erroneously, used to denote almost any kind of calcareous material or finely ground form of limestone or dolomite. Lime is usually made from high-calcium or high-magnesium limestone, generally having a minimum of 97% combined carbonate content. Normally, high-calcium limes contain less than 5% MgO. When the lime is produced from a high-magnesium limestone, the product is referred to as dolomitic lime. Calcination, or the production of lime, has its origins in the earliest days of alchemy, with the general reaction class having been identified in an Arabic text printed in 1000 A.D. It was much later, however, in the mid-1700s to the mid-1800s before this basic reaction became understood from a scientific perspective. The production of lime has been so basic and simple that its underlying scientific principles have over the years received only intermittent investigation. Rather, much of the thought and inquiry has been directed toward the development of kilns. Thus, it has only been in the last 15 to 20 years that lime has received any concentrated scientific investigation relative to the thermodynamics and kinetics of the calcination and hydration reactions. Calcination refers to a broad class of reactions, of which the lime/limestone reaction is just one, wherein a substance is heated to less than its melting point, resulting in a weight gain or weight loss. In the calcination of limestone to produce lime, the basic chemical reaction is as follows: [CaCO3 (limestone) + heat (1000° to 1300°C)= 100 CaO (quicklime) + CO2 T 5644 or CaCO3 • MgCO3 (limestone) 10084 + heat (900°C to 1200°C) CaO • MgO (quicklime) + 2CO2 T 56 4088] While there is nearly universal agreement about the equilibrium conditions related to the limestone/lime reaction above, there have been numerous and varied calcination models developed for the reaction. Recent investigations have resulted in the development of the model shown in Fig. 1. From this model it can be seen that calcination is a function of both temperature and CO2 pressure. It does not, however, provide any indication of the rate at which the reaction takes place. Calcination is strongly time variant with different limestones. In a very broad sense this relates to the fact that the calcination reaction starts on the exterior surface of the limestone and then proceeds toward the center. As the calcination reaction takes place, the CO2 released at the reaction interface must make its way through the lime to the exterior surface. Therefore, because calcination is limited by gas diffusion to the surface of the partially calcined limestone, natural impurities in the stone, differences in crystallinity, grain boundary chemistry, density variations, and imperfections in the atomic lattice all play a significant role in

Jan 1, 1983

By S. R. Mitchell, M. Weissman, J. H. Brown

It has been demonstrated that for fine grinding operations, the energy input (E) and the product size modulus (k) are related by an equation of the form E = Ak1-n (1) where "A " and "n" are constants.(1) Also, it was suggested that "A" is determined by the comminuting device and that "n" depends primarily on the rock. It was the purpose of this investigation to study these constants by determining the form of an energy-size reduction relationship over an extreme range of energy inputs, and at the same time, to evaluate the minimum particle size produced during grinding. The comminution system consisted of a stainless steel laboratory ball mill in which quartz was ground at 60% solids for times ranging from 1 minute to 700 hours. The mill which measured 10" diameter by 12" long was loaded with about 60 pounds of balls ranging in diameter from 3/8" to 1-1/8" and was driven at 55 r.p.m. Quartz was selected for the tests because it is a brittle material for which size distribution data were expected to show a constant distribution coefficient regardless of product size.(1) This permitted specification of product size by a size modulus alone. The quantities measured were the time of grind (measure of energy input) and the specific surfaces of the products. Since no accurate method is available yet for determining particle size directly in the very fine size ranges specific surface data were used for this purpose. The relationship between these two quantities may be expressed as where Cis a constant which includes a shape factor, p is the specific gravity of the solid,_S is the specific surface and D is an equivalent particle diameter. For a material in which the distribution coefficient does not change with size the term (l/S) may be substituted for k in equation L if the proportionality constant "A" is changed correspondingly. This substitution was made in this work but in addition, screen analyses were made on several products to verify the equivalence of the two methods of size specification. EXPERIMENTAL DETAIL QUARTZ Quartz from two sources was tested. One series of tests was made on a clear, high purity crystalline quartz from Brazil and Arkansas, and another series was run on massive quartz fromNewHampshire. Grinding charges of the high purity material consisted of 2000 gram samples of -3-8 mesh particles, while the charges of the New Hampshire quartz were 500 gram samples of a -35+48 mesh screen fraction. The difference in the sizes of these two series of charges was not significant in view of the extreme size reduction accomplished, and the New Hampshire samples were smaller to permit ginding to finer sizes in shorter times than required for 2000 gram lots. SAMPLING AND ANALYSIS Separate charges were ground for all tests in which the grinding times were less than one hour and for all tests on New Hampshire quartz since these products were difficult to sample accurately without affecting the entire charge. During the long time grinding tests the mill was

Jan 1, 1961

By C. E. Lesher

COAL has been fighting a rear-guard action since the last World War. The battle against competitive fuels has been largely guerilla warfare with more sniping within the ranks than of organized opposition. Oil and natural gas are the fuels that over these twenty odd years have driven coal backward and out of many profitable markets. Now, somewhat timidly, the coal industry is trying a new weapon; namely, Research, or let us more properly say, Organized Research. Engineers have been designing this weapon for many years, supported by those interested in coal, including some coal producers. A part of this pioneer work has been Fundamental Research, the Ph.D. kind that is over the heads .of most of us. Another part has been aimed at immediate objectives and realizable profits, the practical, man-in-the-street sort. That is Industrial Research. Enough has been accomplished to make a fair exhibit, but whether this new weapon will have sufficient fire power to rout the opposition, whether the industry will really go into production and use it, the next few years will tell. NEED FOR COAL RESEARCH To utter "Research" is to use the modern magic word; to conjure up the miraculous-rubber from weeds; radar; magnesium from sea water; yes, even gasoline from coal. Research is a very general term. It means something different to every man. What is the coal industry seeking with its research; or what should it seek? And, specifically, how is it going about the job; and is it taking the best way? There are many who say that Coal has been asleep at the switch, while Oil and Gas have been taking the energy business. In an organized way this is true. Large-scale, privately financed research is just started in the Pennsylvania, anthracite industry, and it is still a dream for bituminous coal. What has been done so far collectively is purely defensive; as, for instance, to improve mechanical devices for burning coal so as to be able to recover markets for house-heating fuel long since abandoned to oil and gas. To appreciate just how seriously bituminous coal has slipped back in the national economy in the past 25 years, one has only to recall that, in the last war the Navy required for its operations all the high-grade, low-volatile coal that could be produced, and that anthracite was withdrawn from the middle and northwest markets to keep the eastern seaboard warm. All coal was "rationed" by zones, if not to individuals. Now the Navy, the Armed forces and the Merchant Marine are propelled by oil and gasoline. Gasoline and heating oil are rationed to individuals. Production of all coal in this country in 1918 reached the historic figure of 678,200, 000 tons, and in 1943, after 25 years, it is expected to reach a special wartime total of 660,000,000 tons. Meanwhile, production of crude oil this year may exceed 1,500,000,000 bbl., and like that of natural gas, reach four times the amount produced in 1918.

Jan 1, 1944

By K. Barron

The glass insert stressmeter, or photoelastic stressmeter, is an instrument designed to determine stress changes occurring in rocks. It has several potential advantages over other such devices in that it is a biaxial device, it is simple and it is cheap to make. The object of this study was to assess the behaviour of the meter under biaxial loads and to examine some of the problems associated with measurement and interpretation of the fringe pattern. This assessment has been carried out by comparing theoretical and laboratory behaviour of the meter. It has been shown that: a) There are certain optimum measuring points in the meter at which measurements should be made for best accuracy. The position of the points depends on the ratio, n, of the biaxial stresses. b) The meter&apos;s sensitivity can be assumed to be independent of the rock modulus E provided that the rock modulus is < 2.5 x 106 psi and not, as previous workers have assumed, if E < 5 x 106 psi. c) There are several methods of separating the principal stresses; some of these are unsatisfactory. A new method is proposed and discussed. d) The meter sensitivity decreases as the ratio of the biaxial stresses approaches unity; the accuracy thus also decreases. e) The axes of symmetry of the fringe pattern give an excellent indication of applied stress direction. f) Laboratory calibrations are in good agreement with theory. The glass insert or photoelastic stressmeter is an instrument designed to determine stress changes occurring in rocks. It has several potential advantages over other such devices in that it is a biaxial device, it is simple and it is cheap to make. This stressmeter has been described in detail.l,2 Basically it is a hollow glass cylinder that has at one end a light source and filters producing circularly polarized light. The glass cylinder and source are grouted into a borehole in rock and the face of the cylinder is viewed through a quarter wave plate and an analyser. If, after installation, a stress change occurs in the rock, then a distinct colored isochro-matic fringe pattern is seen in the meter. The fringe order at any point in the meter can be determined by counting the fringes and measuring the fractional fringe orders by the Tardy compensation method. The relation between the fringe order at any point and the applied stress change can be determined either by calculation or by calibration. The object of this study was to assess the behavior of this stressmeter under biaxial loading conditions and to examine some of the problems of interpretation of the fringe pattern. THEORY Hiramatsu et a14 have determined the stress distribution in a hollow cylindrical inclusion in an elastic host material when subject to uniaxial stress. Using this solution, the biaxial case of stress p in the x direction and stress q in the y direction (Fig. 1) can be solved by superposition. This has been done in Appendix 1. It is shown that the principal stress difference (s1 -s2) at any point (r,?) in the cylinder is given by:

Jan 1, 1965

By S. F. Reiter, W. R. Hibbard

A survey of the effect of heat treatment on the room temperature hardness of Fe-Mo alloys has been made. Constant strain rate tensile tests were performed between room temperature and 1800°F. These data were analyzed to determine the effect of temperature and composition on the strain hardening coefficient and strain rate sensitivity. Constant load creep-rupture tests were made on these alloys and the results related to composition and structure. A relation between the high temperature strength of the precipitation hardened alloys and the volume of precipitate has been observed. IN view of the extensive use of ferritic materials at elevated temperatures, it is surprising to note the limited amount of information relating the variables of plastic deformation, i.e., composition, structure, temperature, stress, strain, and strain rate. Hollomon and Lubahn&apos; showed how the several variables of plastic flow might be treated analytically. No data were available on carbon-free iron and its alloys in a form suitable for this analysis. Several German investigations2-" constitute most of the experimental work relating high temperature properties to the constitution of these types of materials. In order to obtain new data, the iron-rich alloys of the Fe-Mo system were selected for detailed investigation for the following reasons: 1—Some of the important effects of molybdenum on the mechanical properties of iron have already been studied.&apos; , 821 2—By suitable heat treatment of selected alloys, it is possible to study strengthening effects of four types: AT -a transformation, B—substitutional, C—precipitation, and D—dispersion of hard inter-metallic compound. Materials and Treatment Four-pound ingots were vacuum cast, employing the same melting schedule previously used.? The raw materials were electrolytic iron and lamp-grade molybdenum. The ingots were forged to l/z in. sq. rod and one portion swaged to 0.350 in. diam rod for the production of 1 15/16 in. long button-head specimens. The button-head specimen blanks were solution treated for 16 hr at 2100°F in hydrogen of —70°C dewpoint and then water quenched. They were subsequently plunge ground to the standard 0.160 in. diam test bar. Micrographs of the solution treated alloys are given in Figs. la through Id. The higher molybdenum alloys contained large equiaxed ferrite crystals similar to those in Fig. Id. A portion of the % in. rod was hot rolled to 0.100 in., sandblasted, and cold rolled to 0.020 in. Strip tensile specimens having a 0.020x0.200 in. cross-section and a 2.25 in. gage length were machined from the sheet. The alloys containing molybdenum were subsequently annealed 1 hr at 1560°F. The iron strip was annealed 4 hr at 1300°F in wet hydrogen. The resultant structures are shown in Fig. 2a through h. The ASTM grain sizes were 1 to 3 as solution heat treated or 3 to 4 as annealed. The chemical analyses of the alloys are given in Table I. Carbon contents were obtained after the heat treatments in hydrogen. Alloy 15.9 pct Mo was tested as a cast alloy.&apos;

Jan 1, 1956

By E. E. Donath

THE coal hydrogenation process is well known as a means for the production of liquid fuels -from coal. In this paper the possibilities of the coal hydrogenation process as a source of chemical raw materials will be discussed. The recovery of chemicals from coal hydrogenation products necessitates some modifications and additions to the equipment used for the production of fuels. The conversion of coal into liquid fuels such as gasoline requires two steps: liquid phase and vapor phase hydrogenation. Intermediate oils obtained in the liquid phase contain oxygen and nitrogen compounds, especially aromatic compounds, since the coal itself is composed mainly of cyclic compounds. These oils are the raw material for the separation of high molecular weight aromatics and of tar acids and tar bases. The relative amounts of heavy and middle oil-boiling above and below, e.g., 325°C-can be influenced by temperature, residence time, and catalyst of the liquid phase hydrogenation. In the vapor phase hydrogenation a solid bed catalyst is used to convert the intermediate oil from the liquid phase operation into hydrocarbons of the gasoline boiling range. Essentially pure hydrocarbons with a low content of sulphur, oxygen, nitrogen, and olefines are obtained. Depending mainly on the catalyst, the high ring compound content of the liquid phase oil can be preserved and gasoline rich in aromatics obtained. However, with other catalysts, these ring compounds can be split into gasoline with a high content of isoparaffins.1 Again, depending on the operating conditions, products of varying boiling range can be obtained. Selection of catalyst and operating conditions therefore makes possible the production of different grades of motor fuel and also variations in the relative amounts of benzene, toluene, and xylene when aromatic hydrocarbons are produced. The schematic flowsheet, Fig. 1, shows the main steps of the coal hydrogenation process, and the product streams used for the recovery of chemicals are indicated. In the liquid phase hydrogenation stage, coal is made into a paste with recycle heavy oil. The coal paste is mixed with hydrogen and preheated at a pressure of 300 to 700 atm in heat exchangers and preheaters. The coal paste and hydro¬gen enter high pressure converters where the liquefaction of coal, conversion of the high boiling liquid materials initially obtained, into intermediate oils is performed at a temperature around 470°C. The reaction products enter the hot catchpot in which lower boiling oil vapors are separated from the residue containing unreacted coal, ash, and heavy oil. This residue, usually called H.O.L.D. (heavy oil let down), is processed to separate solid and liquid material. By thermal treatment of the residue, e.g., a coking process, distillate oil is obtained, which can be recycled as part of the pasting oil. This stream is rich in polynuclear aromatics and can be, and has been, used for the recovery of such material. The oil vapors and hydrogen from the hot catch-pot are cooled in heat exchangers and a cooler, and the condensed oil is separated from the recycle hy-

Jan 1, 1952

By C. E. Lesher

Coal has been fighting a rear-guard action since the last World War. The battle against competitive fuels has been largely guerilla warfare with more sniping within the ranks than of organized opposition. Oil and natural gas are the fuels that over these twenty odd years have driven coal backward and out of many profitable markets. Now, somewhat timidly, the coal industry is trying a new weapon; namely, Research, or let us more properly say, Organized Research. Engineers have been designing this weapon for many years, supported by those interested in coal, including some coal producers. A part of this pioneer work has been Fundamental Research, the Ph.D. kind that is over the heads of most of us. Another part has been aimed at immediate objectives and realizable profits, the practical, man-in-the-street sort. That is Industrial Research. Enough has been accomplished to make a fair exhibit, but whether this new weapon will have sufficient fire power to rout the opposition, whether the industry will really go into production and use it, the next few years will tell. Need foR Coal Research To utter "Research" is to use the modern magic word; to conjure up the miraculous—rubber from weeds; radar; magnesium from sea water; yes, even gasoline from coal. Research is a very general term. It means something different to every man. What is the coal industry seeking with its research; or what should it seek? And, specifically, how is it going about the job; and is it taking the best way? There are many who say that Coal has been asleep at the switch, while Oil and Gas have been taking the energy business. In an organized way this is true. Large-scale, privatelyfinanced research is just started in the Pennsylvania anthracite industry, and it is still a dream for bituminous coal. What has been done so far collectively is purely defensive; as, for instance, to improve mechanical devices for burning coal so as to be able to recover markets for house-heating fuel long since abandoned to oil and gas. To appreciate just how seriously bituminous coal has slipped back in the national economy in the past 2 5 years, one has only to recall that, in the last war the Navy required for its operations all the high-grade, low-volatile coal that could be produced, and that anthracite was withdrawn from the middle and northwest markets to keep the eastern seaboard warm. All coal was "rationed" by zones, if not to individuals. Now the Navy, the Armed forces and the Merchant Marine are propelled by oil and gasoline. Gasoline and heating oil are rationed to individuals. Production of all coal in this country in 1918 reached the historic figure of 678,200,-000 tons, and in 1943, after 25 years, it is expected to reach a special wartime total of 660,000,000 tons. Meanwhile, production of crude oil this year may exceed 1 ,500,000,000 bbl., and like that of natural gas, reach four times the amount produced in 1918.

Jan 1, 1944

By C. E. Lesher

Coal has been fighting a rear-guard action since the last World War. The battle against competitive fuels has been largely guerilla warfare with more sniping within the ranks than of organized opposition. Oil and natural gas are the fuels that over these twenty odd years have driven coal backward and out of many profitable markets. Now, somewhat timidly, the coal industry is trying a new weapon; namely, Research, or let us more properly say, Organized Research. Engineers have been designing this weapon for many years, supported by those interested in coal, including some coal producers. A part of this pioneer work has been Fundamental Research, the Ph.D. kind that is over the heads of most of us. Another part has been aimed at immediate objectives and realizable profits, the practical, man-in-the-street sort. That is Industrial Research. Enough has been accomplished to make a fair exhibit, but whether this new weapon will have sufficient fire power to rout the opposition, whether the industry will really go into production and use it, the next few years will tell. Need foR Coal Research To utter "Research" is to use the modern magic word; to conjure up the miraculous—rubber from weeds; radar; magnesium from sea water; yes, even gasoline from coal. Research is a very general term. It means something different to every man. What is the coal industry seeking with its research; or what should it seek? And, specifically, how is it going about the job; and is it taking the best way? There are many who say that Coal has been asleep at the switch, while Oil and Gas have been taking the energy business. In an organized way this is true. Large-scale, privatelyfinanced research is just started in the Pennsylvania anthracite industry, and it is still a dream for bituminous coal. What has been done so far collectively is purely defensive; as, for instance, to improve mechanical devices for burning coal so as to be able to recover markets for house-heating fuel long since abandoned to oil and gas. To appreciate just how seriously bituminous coal has slipped back in the national economy in the past 2 5 years, one has only to recall that, in the last war the Navy required for its operations all the high-grade, low-volatile coal that could be produced, and that anthracite was withdrawn from the middle and northwest markets to keep the eastern seaboard warm. All coal was "rationed" by zones, if not to individuals. Now the Navy, the Armed forces and the Merchant Marine are propelled by oil and gasoline. Gasoline and heating oil are rationed to individuals. Production of all coal in this country in 1918 reached the historic figure of 678,200,-000 tons, and in 1943, after 25 years, it is expected to reach a special wartime total of 660,000,000 tons. Meanwhile, production of crude oil this year may exceed 1 ,500,000,000 bbl., and like that of natural gas, reach four times the amount produced in 1918.

Jan 1, 1944

By Michael Bradbury

INTRODUCTION A major change in financing exports in recent years has been the decreased importance of subsidized export credits, following the commitment of the OECD countries to eliminate the subsidy element. Subsidized export credit rates are now often more expensive than market rates as the financing for exporters has decreased in volume and importance. The forfait market, in recognition of this decreasing importance, provides a rapidly expanding source of nonrecource finance for exporters. The following is a step by step guide to what it is, how it works, its benefits and problems. WHAT IS FORFAITING? Forfaiting is not new. It has been used in Europe for about 25 years to provide export finance for both capital goods and commodities without recourse to the exporter. Although long the preserve of exporters in Germany, and more lately Italy, forfaiting is now used increasingly by exporters in Great Britain, the United States, Canada and Scandinavia. It is a fairly simple operation with easy straight-forward documentation. The transaction involves the purchase by the forfaiting bank of a bill of exchange or a series of bills without recourse to the exporter. These bills will have been drawn by the exporter, accepted by the importer, and will usually bear the unconditional guarantee of the importer&apos;s bank. They are normally drawn payable at intervals during the credit period agreed between importer and exporter and are purchased at a discount by the forfaiter. The exporter thus obtains his cash payment and the importer receives his credit period. The forfaiter collects the amount of the bills as they mature directly from the importer. Credit periods vary, depending upon the type of goods and the country and commercial risk of the importer. The period is generally between one and five years with six monthly maturities. The usual forfait currencies are US dollars. Deutschmarks and Swiss francs and others, such as sterling, French francs, and the Scandinavian currencies are being used more frequently. CHOOSING FORFAITING Most types of financing require the continued involvement of the exporter in the financial side of the transaction during the credit period. Forfaiting has certain comparative advantages. In particular, it is possible to forfait 100 percent of the risk without recourse to the exporter, unlike government sponsored export finance schemes, where some retention of the risk by the exporter is required. In addition, exports from country sources do not present problems and forfaiting can also cover trade within the EEC. Other benefits for the exporter are: (a) The exporter&apos;s balance sheet is improved; debts are turned into cash thus improving the liquidity of the company and enhancing its cash flow. And there are no contingent liabilities for bills of exchange. (b) If the sales contract is in a foreign currency forfaiting removes the risk to the exporter of adverse movements in foreign exchange during the credit period. (c) Fluctuations in interest rates during the credit period can be ignored since in forfaiting the transaction is usually done on fixed interest rate terms on a discount basis. (d) The political and transfer risks are taken by the forfaiter. (e) The commercial risk is taken by the forfaiter. (f) The costs of administration and collection etc. during the credit period are removed.

Jan 1, 1985

By W. J. West, W. W. Garvin, J. W. Sheldon

One of the most important problems of reservoir mechanics is the prediction of the behavior of a gas and oil producing reservoir for a variety of production programs. In the absence of a knowledge of the behavior of even idealized systems, it has been difficult, if not impossible, to determine which production program would yield maximum economic recovery. The problem was formulated mathematically many years ago, hilt a solution of the equations had never been obtained because of their extreme complexity. The solution of the problem became possible, however, with the advent of modern computing machines. This paper describes a digital method of solving the problem and discusses some of the results which have been obtained to date. The IBM Type 701 Electronic Data Processing Machines located at IBM&apos;s New York Scientific Computing Service were used successfully to perform the computations. The flow of gas and oil through a reservoir can be described mathematically by two second-order, nonlinear partial differential equations which must be solved simultaneously. All derivatives were replaced by finite differences to bring the equations into a form suitable for digital calculations. A number of finite ditference formulations were investigated and one form was found which resulted in stable, convergent solutions. This form was used to obtain .solutions for both radial and linear systems producing by solution gas drive. The results presented in this paper are: (a) saturation profile within the hypothetical reservoir vs. time, (b) pres.strre profile within the hypothetical reservoir vs. time. (c) gas-oil ratio vs. cumulative recovery, and (d) ultimate recovery. The saturation profile clearly shows the effect of critical gas saturation. The saturation near the well-bore drops quickly to the critical gas saturation and remains essentially at that value until the remainder of the reservoir also has dropped to the critical gas saturation. The pressure profile shows a smooth variation of pressure across the reservoir. The gas-oil ratio drops slightly during the early stage of production until the critical gas saturation is reached, rises rapidly from then on and eventually passes through a sharp maximum just before the economic limit of production is reached. For the radial example presented in this paper, the average oil .saturation of the reservoir at a time corresponding to the limit of economic production was 56.5 per cent and the ultimate recovery was 6.86 per cent. The difference between change in saturation and ultimate recovery is caused by .shrinkage of the oil phase. The solution time with the 701 Computer is sufficiently short to permit an economically feasible investigation of the effects of variation of the many parameters which describe an oil reservoir. In particular, the ultimate recovery for various systems can he determined as a function of rock and fluid properties, of well spacing. and of production rate. INTRODUCTION The effective planning for maximum economic depletion of oil reservoirs is one of the major problems confronting oil producers. The most important part of the planning is prediction of the response of the oil reservoir to a particular production program. The production program can be selected by imposing certain controls available to the operator. Some of these controls are: (a) well spacing, (b) production rate, (c) time

Jan 1, 1955

By Thomas P. Bispham

INTRODUCTION From the lender&apos;s point of view, the greatest period of risk in a project financing occurs during the construction phase. Therefore, most projects are supported during this phase by completion guarantees supplied by some credit-worthy entity; for example, the project sponsors in the case of a joint venture, such as that of W.R. Grace, Hanna Mining, and Liberty Capital; or by a strong contract with a utility or foreign importer/investor, such as the way North American Coal Corporation has structured many of its transactions. THE PROJECT LOAN REQUEST A project financing is a more complex form of term loan than one using an ongoing corporation&apos;s balance sheet as a credit base and, therefore, a potential lender will subject the loan request to a more rigorous analysis. To support this effort, the financial institution will require a more detailed information memorandum to evaluate the credit and technical risks of a project - especially since much of the necessary information is not otherwise available. (See also Gibbs and Sroka paper above in this Chapter) A well-prepared information memorandum will impress prospective lenders with the planning ability and general competence of management. Also, the process of preparing the memorandum will help management understand the true extent of the opportunities and limitations of its venture. Appendix A outlines the topics which comprise a complete information memorandum for a loan request. Of some interest to those seeking to sell a currently-operating mining venture, a similar information memorandum should be prepared i.e., covering the same topics discussed here, for the investment banker to use with potential purchasers. For that purpose, though, one might not want to prepare quite as much detail as for a lender. Appendix B outlines the elements of a reserve evaluation and feasibility study, often called the "Bankable Document." Usually, these studies are prepared by independent engineering consultants for use by potential borrowers and sellers. (Potential purchasers will often contract for a similar study for their use in evaluating an acquisition.) ELEMENTS OF A LOAN INFORMATION MEMORANDUM 1. Outline: The information memorandum should begin with a one-page outline covering such topics as: a. The borrower&apos;s name, address, and phone number. b. Principal contact at the borrower. c. Amount of the proposed financing. d. Desired pricing and structure of the proposed financing. This should include a description of the amount and source of equity in the proposed financing. e. Use of the proceeds and timing. 2. Summary: The most important information contained in the memorandum should be summarized in two pages. Note - If the borrower is a recently-formed single-purpose company, then elements 3, 4, and 5 will apply to the guarantors of completion and to the project sponsors. 3. The Borrower: This section is a brief biography of the borrower including such topics as date and state of incorporation, founder(s), lines of business, etc. 4. Capitalization: The borrower&apos;s current debt and equity position, including leases and trade debt, with amounts, terms, names, and addresses enumerated. Equity owners, and percentage ownership, should be identified. 5. Historical Financial Statements: If available, a minimum of five year&apos;s worth of complete historical financial statements

Jan 1, 1985

THE paper on "Cross-cuts in Coal Mining," by J. J. Rutledge (published in MINING AND METAL-LURGY, February, 1927, p. 64) was brought up for discussion at the annual meeting, where the follow-ing comments were made T. D. Thomas (Lehigh Coal & Navigation Co., Lansford, Pa.) : This question has caused me a lot of worry, not in the particular district in which I am, but throughout other districts. There are always several angles to consider. If you are in a hurry to push development work, you might increase the distance between cross-cuts from 60 to 350 ft., but if you have a 40-ft. chain pillar every 60 ft. it will cut down your entry driving a whole lot. Looking at it from the ventilation angle, I agree that too many cross-cuts in entries are bad things. You have a tremendous amount of leakage, and I have seen currents starting out with 45,000 cu. ft., and after passing about 30 or 40 cross-cuts the current has dwindled down to about 18,000 or 15;000 cu. ft. The result is that the question of putting in auxiliary fans is raised. That involves several points into which I do not want to go too far, but I am in favor of not getting in too many cross-cuts, putting them in only where they are necessary: I think the state mining laws are wrong in a number of places on that, and that when you finish with a cross-cut it should be in the room. It should be well sealed on an entry. There are several ways of tightening up the cross-cuts so as not to have the great amount of leakage and wastage of: air that we now have. &apos;I prefer tile stopping; other people prefer cement or brick, but there is a big fac-tor to all mines, saving the mine. I checked up on the number of fans in the anthracite region and found there are 651. That was derived from the state report of 1921, and it enabled me to compute from the power the weight of the air. In the anthracite region of Pennsylvania we put in 9 tons of air to every ton of coal we get out. Tracing that back again and taking the Government&apos;s figures which they made some time ago, I found but 20 per cent of the air got to the faces where it was actually needed. That is a tremendous big loss and shows a possibility for saving, money for the various coal companies. Chairman Rice: I think what Mr. Thomas refers to was an investigation by R. Y. Williams, of the Bureau of Mines in Illinois, where a study was made of 100 typical mines, and, speaking off-hand, my recollection is that we found as little as 15 per cent of air reached the faces in one of the mines and another was as much as 50. That seems to be a reflection on the type of stoppings and general ventilation scheme.

Jan 3, 1927

By J. Murray Riddell

The method of treating hazards wherein value is decreased, is cited by R. D. Parks. Quite properly, the theory of probabilities is made use of when multiple hazards are under consideration. E. F. Fitzhugh, Jr. $ deals with the enhancement phase graphically and uses percentage of expectancy as derived by a study of conditions and the selection of a chance factor. It is believed that both of the authors referred to fully recognize the part which human judgment plays, and as coupled with experience, training, and the application of the theory of probabilities; in that respect the composer of this paper is in accord. Within the past year, the task of arriving at a mathematical method for handling the enhancement phase, and, additionally, coupling the negative and positive phases, was explored. In citing the hazard, or negative phase, reference is made to the text by Parks. Types of Items far Consideration On the hazard, or negative, side some of the common items to be considered are: 1. Subsidence and resulting damage. 2. Flo wage of water above that anticipated. 3. Geological. (a) Decline in quality of probable ore, and/or (b) Decline in quantity of probable ore. 4. Depressed economic conditions. 5. Litigation. Similarly, on the enhancement, or positive, side common items to be considered are: 1. Flo wage of water below that estimated. 2. Geological. (a) Increase in quality of probable ore, and/or (b) Increase in quantity of probable ore. 3. Elevated economic conditions. 4. Litigation. 5. Technological advance in the art. Tn all of the above items no consideration is given to placing a value on, or giving consideration to, possibilities. For example, referring to Table 1, the estimated normal present value (Vp) of a property, exclusive of risk consideration, is taken as $100,000. If subsidence affects the usefulness of the shaft, the present value of the property will decrease to $60,000, and it is judged that there is a 1 in 4 chance that the shaft will be impaired;, consequent.ly, if subsidence took place, the present value would be reduced ($100,000-$60,000) $40,000, but since the chance is 1 in 4, the allowable reduction would be only one-fourth of $40,000, or $10,000, or a discount of 10 pct (hazard factor) of the original value; the related safety factor is taken as unity minus 0.10, or 0.90. Thus, the original Vp, $100,000, multiplied by the safety factor ($100,000 X 0.90) gives $90,000, which is the adjusted present value of the property in this single instance. Additionally, there is a water hazard, which, if encountered, will reduce the present value to $85,000. The chance is 1 in 3. Following through with the same reasoning as shown above, the derived safety factor will be 0.95. To arrive at a single multiplying factor which will express the combined risks, the two safety factors are multiplied together, 0.90 X 0.95 = 0.855. That factor when multiplied by the origirial Vp will give the adjusted, and

Jan 1, 1950

Time as a Factor in the Making and Treating of Steel. By John Johnston. (Howe Lecture) (T.P. 1478) Influence of Chromium and Molybdenum on Structure, Hardness and Decarburization of 0.35 Per Cent Carbon Steel. By R. F. Miller and R. F. Campbell. (T.P. 1345) Mechanical Properties of Iron-manganese Alloys. By F, M. Walters, Jr., I. R. Kramer and B. M. Loring. (T.P. 1369) The Instability of Low-expansion Iron-nickel-cobalt Alloys. By I. R. Kramer and F. M. Walters, Jr. (T.P. 1370) The S-curve of a Chromium-nickel Steel. By B. M. Loring. (T.P. 1383) A Magnetic Determination of the A3 Transformation Point in Iron. By B. A. Rogers and K. 0. Stamm. (T.P. 1388) Rapid Tension Tests Using Two-load Method. By A. V. de Forest, C. W. MacGregor and A. R. Anderson. (T.P. 1393) Effects of Scrap in the Blast-furnace Burden. By C. L. T. Edwards. (T.P. 1270) Temperature Gradients through Composite Carbon Columns and their Application to Blastfurnace Linings. By F. J. Vosburgh and M. R. HatFIeld. (T.P. 1363) Correlations of Some Coke Properties with Blast-furnace Operation. By H. W. Johnson. (T.P. 1402) The Technical Cohesive Strength and Yield Strength of Metals. By D. J. McAdam, Jr. (T.P. 1414) Effects of Eight Complex Deoxidizers on Some 0.40 Per Cent Carbon Forging Steels. By George F. Comstock. (T.P. 1417) Significance of the Bessemer End Point. By H. T. Bowman. (T.P. 1428) Structural Diagrams of Nickel Irons and Steels. By J. T. EasE and N. B. Pilling. (T.P. 1432) Carbides in Low-chromium Steel. By Walter Crafts and C. M. OFFenhauer. (T.P. 1436) Hardenability Calculated from Chemical Composition. By M. A. Grossmann. (T.P. 1437) Recrystallization of Silicon Ferrite in Terms of Rate of Nucleation and Rate of Growth. By J. K. Stanley and R. F. Mehl. (T.P. 1438) The Solubility of Carbon as Graphite in Gamma Iron. By R. W. Gurry. (T.P. 1440) An Evaluation of the Factors Affecting Iron Oxide in the Open-hearth Bath. By J. E. Gould and H. J. Hand. (T.P. 1442) Precision in Creep Testing. By J. A. Fellows, Earnshaw Cook and Howard S. Avery. (T.P. 1443) Lattice Relationships in the Decomposition of Austenite to Pearlite, Bainite and Martensite. By G. V. Smith and R. F. Mehl. (T.P. 1459) Rate of Nucleation and Rate of Growth of Pearlite. By F. C. Hull, R. A. Colton and R. F. Mehl. (T.P. 1460) Weight Change as a Criterion of Extent of Decarburization or Carburization. By R. W. Gurry. (T.P. 1470) Observations in the Making and Use of Sulphite-treated Steels. By E. L, Ramsey and L. G. Graper. (T.P. 1476) Diffusion in Metal Accompanied by Phase Change. By L. S. Darken. (T.P. 1479) Engineering Properties of Heat-resistant Alloys. By Howard S. Avery, Earnshaw Cook and J. A. Fellows. (T.P. 1480) Distribution of Manganese and of Sulphur between Slag and Metal in the Open-hearth Furnace. By L. S. Darken and B. M. Larsen. (T.P. 1481)

Jan 1, 1942

By C. S. Smith, K. K. Ikeuye

In an earlier paper1 one of the authors called attention to the significance of the relative free energies of grain boundaries and interphase boundaries in alloys in determining the shape and distribution of micro-constituents. The ratio of the interphase and inter-crystalline boundary energies (that is, —?12, where ?12 is the energy of the interface between a crystal of phase 1 and a crystal of phase 2, and ?11 is the energy of the boundary between two crystals of phase 1) will be denoted by F. It is this ratio that determines, by the simple triangle of forces relation, the dihedral angle, ?, of phase 2 where it adjoins a boundary between two grains of phase 1. On a metallographic sample various angles are actually obtained because of the random orientation of the plane of observation, but the statistically most frequent angle is the true one. These basic principles were discussed in detail in the earlier paper. The experiments described below show the effect of both composition and temperature on ? and T for some alloys containing a liquid phase, and provide data on the rate of approach to the equilibrium angles in both solid and liquid phases. All the alloys were melted in a graphite crucible and cast into ingots 3/4 by 11/8 in. cross-section. Some of the aluminum alloys consisted of two immiscible liquids from which uniform castings could not be obtained. The amount of liquid phase varied locally to a considerable extent and the analyses were meaningless. Nevertheless, the composition of the liquid would not differ from that in an alloy of the intended gross composition, and the synthetic composition of the alloys was therefore used in considering the surface energy results. The ingots were given initial deformation by cold-rolling to 50 pct reduction, annealed, and given a second 50 pct reduction prior to cutting into small samples for heat treatment at the times and temperatures subsequently reported. The resulting micro-samples were carefully prepared metallographically and examined at magnifications of 650, 1280, or 2500. The objectives used were 21X, 0.40 NA (dry); 41X, 0.65 NA (dry); and 80X, 1.40 NA (oil emulsion). The appropriate angles were measured by rotation of the stage of a Bausch and Lomb metallograph to align the appropriate boundaries successively with a cross-hair in a micrometer eyepiece. About 250 angles were measured on each phase. Though the angles were read to 1°, the accuracy is probably not above 3°, because of uncertainty in setting the cross-hair tangent to the sometimes curved boundary. The corners of very small particles, particularly in early stages of adjustment after cold-rolling, were difficult to measure and the results were slightly dependent on the magnification used (compare Fig 1-C and 1-D). With particles of larger size and more nearly equilibrium shape, magnification made no difference (vide Fig 1-F and 1-G). The measured angles were grouped in 10° intervals (5° if ? was less than 20°) and plotted in bar

Jan 1, 1950

Time as a Factor in the Making and Treating of Steel. By John Johnston. (Howe Lecture) (T.P. 1478) Influence of Chromium and Molybdenum on Structure, Hardness and Decarburization of 0.35 Per Cent Carbon Steel. By R. F. Miller and R. F. Campbell. (T.P. 1345) Mechanical Properties of Iron-manganese Alloys. By F, M. Walters, Jr., I. R. Kramer and B. M. Loring. (T.P. 1369) The Instability of Low-expansion Iron-nickel-cobalt Alloys. By I. R. Kramer and F. M. Walters, Jr. (T.P. 1370) The S-curve of a Chromium-nickel Steel. By B. M. Loring. (T.P. 1383) A Magnetic Determination of the A3 Transformation Point in Iron. By B. A. Rogers and K. 0. Stamm. (T.P. 1388) Rapid Tension Tests Using Two-load Method. By A. V. de Forest, C. W. MacGregor and A. R. Anderson. (T.P. 1393) Effects of Scrap in the Blast-furnace Burden. By C. L. T. Edwards. (T.P. 1270) Temperature Gradients through Composite Carbon Columns and their Application to Blastfurnace Linings. By F. J. Vosburgh and M. R. HatFIeld. (T.P. 1363) Correlations of Some Coke Properties with Blast-furnace Operation. By H. W. Johnson. (T.P. 1402) The Technical Cohesive Strength and Yield Strength of Metals. By D. J. McAdam, Jr. (T.P. 1414) Effects of Eight Complex Deoxidizers on Some 0.40 Per Cent Carbon Forging Steels. By George F. Comstock. (T.P. 1417) Significance of the Bessemer End Point. By H. T. Bowman. (T.P. 1428) Structural Diagrams of Nickel Irons and Steels. By J. T. EasE and N. B. Pilling. (T.P. 1432) Carbides in Low-chromium Steel. By Walter Crafts and C. M. OFFenhauer. (T.P. 1436) Hardenability Calculated from Chemical Composition. By M. A. Grossmann. (T.P. 1437) Recrystallization of Silicon Ferrite in Terms of Rate of Nucleation and Rate of Growth. By J. K. Stanley and R. F. Mehl. (T.P. 1438) The Solubility of Carbon as Graphite in Gamma Iron. By R. W. Gurry. (T.P. 1440) An Evaluation of the Factors Affecting Iron Oxide in the Open-hearth Bath. By J. E. Gould and H. J. Hand. (T.P. 1442) Precision in Creep Testing. By J. A. Fellows, Earnshaw Cook and Howard S. Avery. (T.P. 1443) Lattice Relationships in the Decomposition of Austenite to Pearlite, Bainite and Martensite. By G. V. Smith and R. F. Mehl. (T.P. 1459) Rate of Nucleation and Rate of Growth of Pearlite. By F. C. Hull, R. A. Colton and R. F. Mehl. (T.P. 1460) Weight Change as a Criterion of Extent of Decarburization or Carburization. By R. W. Gurry. (T.P. 1470) Observations in the Making and Use of Sulphite-treated Steels. By E. L, Ramsey and L. G. Graper. (T.P. 1476) Diffusion in Metal Accompanied by Phase Change. By L. S. Darken. (T.P. 1479) Engineering Properties of Heat-resistant Alloys. By Howard S. Avery, Earnshaw Cook and J. A. Fellows. (T.P. 1480) Distribution of Manganese and of Sulphur between Slag and Metal in the Open-hearth Furnace. By L. S. Darken and B. M. Larsen. (T.P. 1481)

Jan 1, 1942

By R. L. Schmidt, J. D. Verhoeven

The diffusion coefficients and electrotralzsport mobilities of aluminum, gallium, and arsenic have been determined in molten germanium with the capillary reservoir technique. The diffusion coefficients are slightly higher than those determined by the solidification technique of Brirton et a1.1 It was found that aluminium and gallium migrate to the cathode in molten germanium) whereas arsenic migrates to the anode under an electric field. A possible technique for producing p-n junctions by means of electric field freezing is discussed in view of the experimental data. In the past decade or so the literature has abounded with articles concerning the solid-state properties of the semiconducting elements germanium and silicon. It is surprising by comparison how little has been published concerning the liquid-state properties of these materials. In the production of doped germanium or silicon the diffusion coefficient of the dopant in liquid germanium or silicon is an important quantity. Yet, to the best of our knowledge, no one has ever made a direct measurement of the diffusion coefficient of solutes in either molten germanium or silicon. A number of authors&apos;-4 have determined some diffusion coefficients by the indirect technique developed by Burton et al.1 This technique appears to give numbers of the correct order of magnitude but it does depend upon a number of assumptions in the analysis and also requires prior knowledge of the viscosity of the melt. In the present work a more direct measure of the diffusion coefficients of arsenic, gallium: and aluminum in molten germanium has been made. It has been shown independently by two groups of authors5, 6 that, when an electric current is passed through the interface of a solidifying metal containing an impurity, the resulting electrotransport in the liquid boundary layer at the interface offers a mechanism for control over the redistribution of the impurity accompanying the solidification. These authors show that the degree of control is proportional to the mobility, U of the impurity atoms in the liquid boundary layer, where the mobility is defined as the drift velocity relative to the solvent per unit electric field. In principle the results apply to the solidification of a doped semiconductor and offer an interesting technique for control of the doping of a semiconductor. In the present work the mobilities of aluminum, gallium, and arsenic were determined in molten germanium in order to evaluate the potential usefulness of electro-transport as a technique for solute control when applied to the solidification of doped germanium. EXPERIMENTAL PROCEDURE Both the diffusion coefficients and the mobilities were measured using high-purity alumina capillaries and a resistivity technique for analysis. A schematic diagram of the electrotransport apparatus is shown in Fig. 1 and the details of the cell design are shown in Fig. 2. For the mobility experiments electrical contact with the bottom of the capillary was made with graphite, as shown in Fig. 2. In order to prevent electrical contact with the melt the graphite was coated with a thin layer of alumina using a plasma spray torch. The cell assembly, a graphite electrode, and another assembly containing two blank capillaries were fastened to the lavite disk shown in Fig. 1. To make a run the system was evacuated and the doped germanium was outgassed at the operating temperature of 1030°C. The cell and blank capillaries were then submerged beneath the melt and a slightly positive pressure of helium was introduced to fill them. After passing current through the cell for a given time the cell and blank capillaries were raised from the melt and the furnace was shut off. The temperature of the cells dropped below the freezing point of germanium within 1 to 2 min after the furnace was shut off.

Jan 1, 1968

By E. C. Tveter, L. A. Roe

The authors present a general outline of the theory and development of heavy-liquid application to mineral processing. Patent literature and processes are reviewed with special emphasis on liquid recovery systems which have been employed or proposed. Advantages and disadvantages of the process are discussed together with the recent developments which have revived interest in this old concentration method. The most important single factor in this resurgence of interest is concluded to be the narrowing gulf between chemical engineering and mineral dressing which has opened the field for new concepts of mineral plant design. A partial summary of patents on heavy liquid separations is included. In spite of the fact that heavy-liquid separation with organic liquids has been used in the laboratory for over 50 years, this process has never graduated to large scale commercial use for any extended period. However, a variation of this process, the sink-float or heavy-media separation process has found wide acceptance and is used to separate minerals from diamonds to gravel. Materials used to increase the specific gravity of the pulps used as heavy media include sand, clay, barite, magnetite, galena, hematite, atomized lead and ferrosilicon. Because of the greater ease of recovery, the magnetic materials, magnetite and ferrosilicon, are the preferred media today. In the U. S. alone, heavy-media iron ore plants with a capacity of over 10 million tons of concentrate per year are in existence. Heavy-media separation involving use of solid, inorganic particles suspended in water rapidly found a wide range of commercial use with the introduction of magnetic media. The minerals engineer is experienced in working with suspensions and quickly learned to develop and control such media at a cost compatible to the type of separation desired. The natural superiority of a heavy liquid with uniform chemical and physical properties has never been questioned since its first use in laboratory mineral separatory procedures. It offers the only method for gravity separation of fine particles of relatively close specific gravity. The most important early attempt to make heavy liquid separations commercial were made by the DuPont Co. which began experimental work on Virginia limonite in 1904. The appended "Partial Summary of Patents" compiled by W.L. O&apos;Connell of The Dow Chemical Co. demonstrates the quantity and sequence of this work. Both inorganic and organic parting liquids were investigated and numerous patents were issued on the use and recovery of these liquids. The work culminated in the heavy liquid plant of the Weston Coal Co. at Shenandoah, Pa. Chemical engineering design of this plant was the responsibility of Francis I. and Hubert I. DuPont. Heavy-liquid separation of coal almost achieved commercial status at this plant which actually processed over 20,000 tons of coal. The liquids used were tetrabromethane, pentachloroethane and trichlo-roethylene, with liquid losses ranging from 8.9 to 12.4 oz per ton of cleaned coal. The reasons for failure of this plant are not clear but probably involved toxicity problems as well as other problems in chemical engineering. Excellent economics were reported. A more recent pilot plant was built in 1954-55 by Norris Goodwin for the Inerto Co. to treat hectorite clay. This plant employed carbon tetrachloride in jigs with liquid recovery by evaporation. Although good separation was achieved, incomplete removal of the CCl, from the clay prevented commercial operation. The only present operations known to the authors employing heavy liquids for gravity separations are limited to the use of calcium chloride in certain coal washers and bromochloromethane in a small batch operation (one ton solids per day) for the separation of beryllium metal particles from slag materials. This is not strictly a minerals beneficiation problem but it has demonstrated the feasibility of such separations. PROBLEMS Critics of early attempts to commercialize heavy-liquid separation of minerals summarize the draw-

Jan 1, 1963