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By H. H. Wade, N. F. Schulz

The large quantities of iron-bearing materials, including taconite, semi-taconite,* and other low-grade ferruginous materials occurring in Minnesota and elsewhere, constitute an important potential source of iron. Satisfactory grade and recovery of iron ore concentrate cannot ordinarily be obtained from these ferruginous materials by simple methods of beneficiation. Iron is distinctive in that the free metal and two of its oxides [magnetite (Fe2O3) and maghemite (gamma-Fe2O3) ] are strongly ferromagnetic. The successful magnetic separation of natural magnetite from taconite has already been established on a commercial scale. The iron in semi-taconite, however, occurs largely as goethite (Fe2O3-H4O) and hematite (Fe2O3) which do not respond to ordinary magnetic separation methods. Magnetic roasting converts these iron oxides to magnetite, which can, after liberation, be magnetically concentrated. MAGNETIC ROASTING Hematite undergoes a stepwise reduction when exposed at moderately elevated temperatures to a reducing atmosphere containing hydrogen or carbon monoxide: Fe2O3? Fe3O4 ? FeO ? Fe Since the desirable product in magnetic roasting is Fe3O4, the conversion is halted after the first stage by controlling the reduction potential of the gas mixture with water vapor or carbon dioxide. The reducing gas mixture must be such that the oxygen partial pressure at the solid-gas reaction interface will be maintained intermediately between the oxygen partial pressures in equilibrium with Fe2O3 and Fe3O4 at the prevailing temperature. Because of the rapid increase in decomposition pressure of Fe3O4 with increase in temperature, the practical upper limit of useful reaction temperature is about 1400°F, above which over-reduction usually occurs in atmospheres containing hydrogen or carbon monoxide. On the other hand, useful reaction rates usually occur only above 800°F. Goethite reacts similarly except that the combined water probably has to be driven off thermally before the reduction to magnetite occurs. Iron carbonate must also be decomposed thermally to an oxide before conversion to magnetite. Iron silicates are apparently not amenable to magnetic roasting. The rate of penetration of the reaction toward the interior of a given ore fragment is dependent on the chemical composition and physical structure of the solid. Most ore fragments tested here reduced satisfactorily to 1/4-in. depth in less than 14 min at 1200°F. Some very dense fragments, however, were reduced to less than 1/32-in. depth under the same conditions. Determination of the optimum temperature, gas composition, ore fragment size, or time of exposure

Jan 1, 1961

By S. M. M. Safvi, A. Jowett

Small-scale continuous flotation tests are described in which the influence of 1) pulp density and 2) feed rate on the rate of flotation are investigated. The results provide further evidence of first-order kinetics for flotation and indicate that tests at different feed rates provide a particularly simple method of determining rate constants. Flotation kinetics are discussed in general terms. Over a period of many years numerous research workers have studied the rate of recovery of valuable materials from flotation pulps with a view to deter-mining the mechanism of the froth flotation process. Froth flo ation is fundamentally a collision process involviug at some stage collision and then mutual attachment between air bubbles and mineral particles. It is possible to draw analogies therefore between the flotation process involving mainly macroscopic particles and the ordinary processes of chemical reaction kinetics involving collisions between atoms, molecules and ions. By adopting this analogy we may postulate a general equation representing the kinetics of the flotation process: -dC/dt =K.CC ,Aa (1) The rate constant, K, will be a complex function involving reagent concentrations, particle and bubble sizes, induction times and no doubt flotation cell design. However, these are factors which can be kept constant in any series of experiments, permitting investigation of the exponents a and c, which determine the order of the reaction occurring in flotation. The various research investigations carried out so far have all aimed at evaluating a and c and in the majority of cases only since the concentration of air has usually been kept constant in a series of tests, so that a relationship of the following type has been investigated: -dC/dt = K1 Cc (2) The techniques of both batch testing and continuous testing have been used to investigate this relationship. The technique of continuous testing, in which steady-state conditions are established, permits direct investigation of the above equation. In the case of batch testing, C is decreasing continuously

Jan 1, 1961

By S. A. Falconer

The benefication of non-sulfide or non-metallic minerals by froth flotation has been practiced commercially for at least 30 years. In the pioneer stages of development of this flotation art, most of the promoters investigated were fatty acids or soaps that had been found to float sulfide minerals. When commercial application of froth flotation started to assume importance in the late 1920' s and 1930's, a great deal of fundamental research work was done in the laboratory (11-14, 19, 22, 23, 26, 29, 32). Among other subjects, this work included studies of the relative effectiveness of the different fatty acids and their salts on the flotability of various non-sulfide and non-metallic minerals. The successful present-day use of fatty acid and petroleum sulfonate type promoters results from better understanding of the principles of non-sulfide flotation plus the developnent of effective selectivity modifying agents. Many investigators have contributed to a greater appreciation of the numerous interrelated factors involved in fatty acid and soap flotation of non-sulfide minerals. Of these, mention should be made of recent fundamental studies by Tagart and Arbiter (31); Wolstenholme and Schulman (35); Schulman and Smith (28); Wark and his co-workers(3,4) Du FIietz(l5); and J. Leja(24). According to J. Rogers, K. L. Sutherland and E. E. and I. W. Wark(27), "the basic requirements for a 'collector' in flotation are that it shall form a film over the surface of the mineral to be floated and that this film should be oriented so that hydrocarbon (non-polar) groups form the effective surface." When modified in that way, the mineral surface possesses some degree of air avidity. All investigators would agree with Taggart, Taylor and Ince (33)that such a film can be produced only if the collector compound contains an active (polar) group to be attracted to the mineral surface, as well as the non-polar group. The commonly used anionic-type promoters for non-sulfide, non-metallic and metallic oxide ores include: 1. Fatty acids, and their soaps and emulsions. 2. Fatty acids residues — "pitches" and "foots." 3. Sulfonated and sulfated fatty acids and so-called "petroleum sulfonates." 4. Paraffin chain salts — sulfonated and sulfated higher alcohols. 5. Cyclic organic acids or salts, such as naph-thenic acid and naphthenates. Certain fatty acids are more effective than others as promoters for particular minerals under certain specified conditions. Some of the more costly fatty acids or collectors of the paraffin chain salt type may give improved selectivity in some instances and are being used commercially in a limited number of operations. Local availability may dictate the choice of the fatty acid used — for example, the use of palmoil fatty acid for flotation of copper carbonate ores in the Belgian Congo. Coconut oil fatty acids have also found limited use.

Jan 1, 1961

By K. K. Landes

The north central and northeastern states supply over 50 pct of the chemical and metallurgical limestone produced annually in the United States, and Ontario is the leading source of this material in Canada. About three fourths of the chemical and metallurgical stone produced in this area comes from Michigan, Pennsylvania, Ohio, and Ontario. The specifications, physical and especially chemical, for chemical and metallurgical stone depend upon the end use, but in general the tolerance for impurities is so low as to rule out most limestones and dolomites. Both high calcium limestone and dolomite are used in the metallurgical and chemical industries. The principal metallurgical use is as a flux in iron ore blast furnaces and open hearth steel furnaces. The major chemical uses are in lime burning and soda-ash manufacture. Other important uses include glass manufacture, in making calcium carbide, and in sugar factories. All deposits of high quality carbonate rock are definitely finite. Invariably and inevitably they diminish in either thickness or quality laterally so as to become unworkable as chemical and metallurgical stone. The size of these high quality lenses ranges from a few thousands of tons to hundreds of millions of tons. The best hunting for new supplies is in the geologic formations known to contain premium quality deposits. However, because of high transportation costs, carbonate rocks, to be workable, must be close to market, dollarwise. Definitions: Chemical stone is limestone or dolomite used as a raw material by the chemical industry. The major chemical uses are in lime burning and soda-ash manufacture. Other important uses include glass manufacture, making calcium carbide, and in sugar factories. The specifications for chemical stone depend entirely upon the end product. Some uses require dolomite, some require high calcium limestone; in a few instances, notably in lime burning, either type of carbonate rock can be used as raw material. As a general rule, a fairly pure stone is necessary and for certain particular uses the tolerance for some elements such as sulfur, iron, and phosphorus may be extremely small. Metallurgical stone is used as a flux in furnace operations, especially in the blast furnace where iron ore is converted into pig iron and in the open hearth furnace where pig iron is made into steel. Either limestone or dolomite can be used in the blast furnace, but only high calcium stone is charged in the open hearth (except for rice-size dolomite used as a refractory). There are no rigid chemical specifications for blast furnace stone, but low silica, alumina, sulfur, and phosphorus are desirable. For open hearth use, in addition to low magnesia, a very low sulfur content is also specified by many furnace operators. For furnace use, fluxstone also must be sufficiently shatter resistant that it will remain in lump form during transport and charging into the furnace. Commercial stone is the term applied in the trade for crushed stone used for roadstone and in concrete aggregate. Many of our best chemical and metallurgical limestones are too soft to qualify in the Los Angeles abrasion test for use as commercial stone. However, some limestones, and a higher proportion of dolomites, do qualify for commercial stone and so can be sold to either market. Place Value: Even the highest grade limestone is still a bulk commodity with a relatively low value per ton. As a matter of fact there is very little difference in the average price per ton between high grade chemical and metallurgical stone and crushed limestone used commercially. Most high quality stone is produced in large operations with consequent low cost per ton whereas most commercial stone is produced in relatively small local quarries. As in the case of other bulk commodities most limestone buyers pay more for transporting the raw material than the cost of the stone at its source. For this reason steel furnaces and chemical plants

Jan 1, 1961

By N. A. Gokeen, M. Ohtani

EFFECT of elements on the solubility of carbon in liquid iron is useful in calculating and correlating a number of thermodynamic properties as shown elsewhere in detail.' Kitchener, Bockris, and spratt2, and later Turkdogan and Hancock3 have investigated the effect of sulfur on the solubility of carbon at various temperatures and concentrations. For any chosen sulfur concentration, the solubility of carbon reported by Kitchener et al. is considerably lower than that by Turkdogan and Hancock. It was therefore felt that a reinvestigation of this problem was necessary. EXPERIMENTAL METHOD An alloy of Fe-C-S .was prepared with electrolytic iron and ferrous sulfide melted by induction in a graphite crucible, 4 in. high 1 1/2 in. ID under a CO-atmosphere. The temperature, held at 1500" ± 5°C in all experiments, was measured with a Pt-Pt + 10 pct Rh thermocouple immersed into the melt. In order to assure saturation with carbon, the melt was stirred with a graphite rod. After approximately 1 hr at 1500 °C, a sample was obtained by sucking the melt into a silica tube, 4 mm ID. The sample was then analyzed for carbon and sulfur by usual methods. RESULTS The results are presented in Table I and plotted in Fig. 1 with the individual values of Turkdogan and Hancock.3 Scattering in the data is equivalent to 3 pct or less in carbon analysis. The broken line represents the empirical equation obtained by Kitchener et al. from their data. It is evident that the present data are in good agreement with those of the former investigators but in disagreement with the latter. The cause for this discrepancy cannot be readily offered since the experimental methods in the three investigations were nearly identical. Additional evidence corroborating the author's results may be presented in the following manner. The difference between the solubilities of carbon in the ternary Fe-C-X melt with a small concentration of any element X, and in the binary Fe-C melt is %?C = %CIII-%CII [1] where %?C is the change in solubility, and %CIII and %CII are the solubilities in the ternary and the binary systems respectively. The value of %Cii

Jan 1, 1961

By C. H. G. Bushell, G. Brown, C. J. Krauss

1N FLOTATION, copper sulphate is used universally for the activation of sphalerite and marmatite and, to some extent, for the activation of other minerals. The copper activated surface readily adsorbs standard collectors such as the xanthates and dialkyl dithiophosphates whereas untreated zir~ sulphide does not. With the host of reagents available, making a mineral float is seldom difficult. The problem is to achieve selective flotation. In zinc flotation, the great value of copper sulphate results from its ability to activate zinc sulphide preferentially to gangue minerals. At the Sullivan Concentrator of The Consolidated Mining and Smelting Company of Canada Limited, the most abundant gangue mineral in the lead-zinc ore is pyrrhotite, and the zinc mineral is marmatite of somewhat variable zinc to iron ratio. For this Cominco study, selectivity between marmatite and pyrrhotite was therefore the most interesting aspect of copper sulphate activation.

Jan 1, 1961

By R. A. Kearns

Biennially the Bureau of Mines issues a list of equipment that has been accepted as approved or permissible during the two calendar years immediately preceding the date of publication of the listing. By so doing the mining industry is kept informed of the availability of the latest equipment for safe use underground. This list supplements Bulletin 543, Permissible Mine Equipment Approved to January 1, 1953; Information Circular 7722, Permissible Mine Equipment Approved During the Calendar Years 1953-54; Information Circular 7840, Permissible Mine Equipment Approved During the Calendar Years 1955-56; and Information Circular 7957, Permissible Mine Equipment Approved During 1957-58. This list includes equipment meeting those standards that have been revised since Information Circular 7957 was .issued. Schedule 16E,4 a revision of Schedule 160, was approved May 19, 1960.

Jan 1, 1961

By Evan Just

?We are certain there is need for research in every phase of mining." This statement by R. M. Crump of the Jones and Laughlin Steel Company (047) paraphrases opinion widespread among mining people. It is undoubtedly true. In preparation for this presentation, 193 organizations were asked to describe their mining research efforts. 60% responded, The meaning of "research" was taken in several different ways. The continual efforts of progressive companies to improve themselves were reported as research. We will call this and any effort to solve specific and immediate problems "practical research". The continuing investigation of subjects of long range interest will be called "basic research".

Jan 1, 1961

By L. Adler

Two basic cases involved in the design of an opening in bedded rock are: 1) where the beds deflect from each other so as to be separated; and 2) where the beds deflect onto their lower neighbor, loading the latter while reducing their own load. Analysis of case 1 is relatively simple, while the interference of the original deflection curves in case 2 complicates analysis of the latter. Figures and formulae are presented for determination of interference loading in this situation. The design of an opening in bedded rock involves two basic alternatives.1'2 In one case the beds deflect away from each other, so as to be separated from their neighbors; in the other case the beds deflect onto their lower neighbor, loading it, while reducing their own load. This is shown in Fig. 1. The first case lends itself to a simple analysis, since the upper and lower boundaries of each beam remain a free surface. In the latter case, however, due to the interference of original deflection curves, the analysis is more complex. Earlier investigators of this interference problem solved it by making the tacit assumption that this type of loading was uniformly distributed along the beam's length. While there is no intuitive justification for this assumption, its use does lead to an approximate solution. Still, a more exact solution does not require this apparently unrealistic restriction. To achieve initial simplicity, the analysis will at first be limited to a two-bedded sequence, as in Fig. 2. Since both beams have identical end conditions and spans, the original deflections of their center lines are members of the same family of curves, as shown in Fig. 3. Therefore, if interference occurs at one point along their center lines, it will occur at every point. For convenience, the midspan point is that usually examined. Deflection at midspan for a uniformly loaded beam regardless of end conditions is: where c is a constant depending on end conditions; w is the body load and equals yh, lb per ft; y is the specific weight of rock, lb per ft'; L is the span, ft; E is Young's Modulus, lb per ft2; I is moment of inertia (for a rectangular section), I = bh3/12 = h3/12, (ft4); b is the width of beam and equals one; and h is the thickness of beam, ft; or 3U > yB an Substituting the appropriate values into Eq. lb, interference between the two beds can be predicted. Should it occur, the additional loads along the lower boundary of the upper bed and the upper boundary of the lower bed must be determined. From the principle of action and reaction, these added loads are known to be equal and opposite, as indicated in Fig. 4. Since the final deflection curves for both beds are identical (Fig. 3), their successive derivatives of y with respect tox must also be identical. That is:

Jan 1, 1961

By R. C. Neavel

One of the most important requirements to be met by any coal producer is delivery of size consists tailored to specific applications. Generally these specifications include a minimum as well as a maximum size limit. The customers of a major Indiana coal producer noticed that some shipments of sized coal contained a large proportion of undersize pieces. Also, in these shipments, the pieces which remained within the specified limits were cracked and, when handled, crumbled readily. The producer, certain that these shipments had been properly sized at the tipple, suspected that degradation had occurred in transit. The Indiana Geological Survey was requested to examine the coal from one of these shipments to attempt to determine the cause of breakage. Two basic facts about coal and coal seams led to the employment of petrographic techniques in this investigation. First, all coal seams consist of accumulations of diverse organic and inorganic constituents; and second, most coal breakage, either desirable or undesirable, can be attributed to the inherent weakness of some of these constituents or to poor adhesion between certain constituents. Analyses of degraded coal Sampling: Samples were secured from 2 stock piles of 2-by 4-inch coal in a dealer's yard. The coal in both piles had received the same treatment from mining to storage, although it had been mined and shipped on two different days. The size consist of one pile, however, appeared smaller than that of the other. The sample from the degraded pile is referred to as the slack sample, and the other is called the unslack sample. Size analyses: In order to determine the actual size consist, the samples were screened, with a minimum of rough handling, on square 2-inch, 1-inch, 1/2-inch, and 12-mesh screens. It is assumed that 100 percent of the 2-by 4-inch coal is retained on a 2-inch round screen at the tipple. Analyses of several loads at the tipple indicate that approximately 26 percent of the 2- by 4-inch coal, 100 percent of which was assumed held on a 2-inch round screen, passed through a 2-inch square screen. Twenty-six percent may be taken as the normal difference between round and square screens. Results of the analyses of stockpile coal are shown in Table 1. Cumulative percent versus size are plotted on a Rosin-Rammler chart as Figure 1. Both samples approximately follow normal size distribution; this indicates that breakage is not size preferential and also that the samples are representative of the stockpiles. Although both samples exhibit the same general size distribution, the median size of the slack sample is considerably smaller than that of the unslack sample. Fifty-five percent of the unslack sample was undersize (29 percent greater than the normal 26 percent difference), and 83 percent of the slack sample was undersize (57 percent greater than the normal 26 percent difference). Both piles contained a greater percentage than normal of undersize coal; this indicates that they were both affected by degradation, but to a different degree. Bedding-plane analyses: Coal, because of its laminated nature, will break preferentially along bedding planes, especially where adjacent constituents are poorly cemented to each other. Subsequent breakage perpendicular to the

Jan 1, 1961

By Marvin L. Whisman

Several parameters controlling the reproducibility of tritium determina¬tion in organic compounds by liquid scintillation counting were evaluated by the Federal Bureau of Mines. These included optimum volume of scintillator solution for maximum counting efficiency, reproducibility of counting a sealed commercial standard and comparison with duplicate counts on laboratory-prepared samples. The error introduced by using microliter pipets, optical differences in counting vials, reproducibility of counting organic samples where quenching is a factor, reproducibility of counting laboratory-prepared samples with an added internal standard, optimum ratio of internal standard activity to sample activity, effect of sample volume upon counting efficiency, count rate at which coincidence losses become apparent, and reproducibility of organic compound radioassay by the standard addition technique are outlined. From the evaluation of these parameters, a technique that can be applied routinely to organic compounds containing tritium has been established, and details are included in this report.

Jan 1, 1961

By J. R. Lucas, R. L. Frantz

Mine sealing programs for the alleviation of acid mine drainage were begun by the Federal Government in the '30's. As part of an acid mine research project to The Ohio State University, a field test was undertaken to determine the effectiveness of mine seals for reducing mine acid. Details of the tests made at the McDaniels mine show the feasibility of air-sealing and flooding an acid-producing drift coal mine. Work by the University continues. The Federal Government undertook in the early thirties an extensive mine sealing program for the alleviation of acid mine drainage. In the states of West Virginia, Ohio, and Pennsylvania many general summaries have been made on this program but no critical evaluation with supporting data has been found on the effectiveness of mine seals for reducing mine acid. Because of this it was decided to undertake a field testing program as part of an acid mine research project of the Engineering Experiment Station, The Ohio State University. The objective of this phase of the project was to develop and install a field research laboratory for acid mine drainage studies. Specifications for such a mine laboratory were developed and resulted from the following considerations: 1) Size and preservation—the test mine shou1d be of limited size to permit frequent and detailed examinations; it should be in a reasonably sound condition to permit safe entry. 2) Isolation—the mine should be physically separated from all other mines. 3) Openings—a minimum number would be desirable to reduce the sealing problem. 4) Structure—the mine especially near the openings should be structurally sound. 5) Acid production—the mine should be producing significant quantities of acid. After considerable searching, the McDaniels mine was selected in the Hocking coal field in Vinton County just above Lake Hope State Park in southeastern Ohio. The small drift mine in the middle Kittaning coal consisted of two small rooms with one mine opening about 6 ft above a seasonal stream bed. Before it was finally decided to seal the mine, a short study was made of the acid drainage over several months. Fig. 1 shows a plot of acidity (milligrams per liter), flow (gallons per minute), and acid production (pounds per day) vs time over the sampling period. Because the coal was overlain with a porous sandstone, the mine drainage was consistent the year around even though the mine was

Jan 1, 1961

By F. H. Buchella, J. F. Buchanan

The San Manuel copper deposit is located about 45 miles northeast of Tucson. The concentrator, smelter, administration building, and other plant facilities are located about seven miles southeast of the ,nine area at the new town of Sari Manuel as shown on Figure 1 (Sketch).

Jan 1, 1961

By A. Boltax

Precipitation processes occurring during both furnace cooling and aging of copper-iron albys were studied by means of electrical and magnetic measurements. On furnace cooling, two distinct stages in the precipitation process were detected; one occurring above and the other below 850° C. The kinetics of precipitation from quenched alloys were studied between 200° and 700°C. The reaction appears to be consistent with the concept of tmcleation of precipitate particles at dislocation loops formed by the clustering of quenched-in vacancies. A study Of in copper-iron alloys is particularly interesting because the combination of magnetic and electrical properties in these allovs provides a quantitative means of following the course of the precipitation reaction. (The details of precip-

Jan 1, 1961

By D. R. Cook

This paper is a case history of an exploration venture for base metals, begun by the Rocky Mountain District of Bear Creek Mining Company in 1952 and completed in 1954. The project was based on the idea of W. S. Burbank, U. S. Geological Survey, that commercial deposits of base metals might occur in Paleozoic sediments beneath hydrothermally altered volcanic rocks in the Southern Bonanza mining district, Colorado. Here, an area of andesitic rocks, four square miles in extent, has been argillized, pyritized, chloritized and silicified. Geological, geophysical and geochemical studies were followed by the diamond drilling of three holes totalling 6,220 feet. Further alteration ang geochemical studies were made on the cores from these holes. A brief review of the alteration and geologic mapping, colored aerial photograph interpretation, geochemical soil and rock sampling, magnetic, gravity and radio-metric surveys are presented together with some conclusions regarding this work. This paper is a case history of an exploration venture for base metals, begun by the Rocky Mountain District of Bear Creek Mining Company in 1952 and completed in 1954. Important contributions were made to the project by personnel of the Rocky Mountain District and the Geophysics Division. Individual acknowledgements to these people are made at the end of the paper. BASIS FOR THE PROJECT The project was based on the idea of W. S. Burbank (1947, p. 444) that commercial deposits of base metals might occur in Paleozoic sediments beneath hydrothermally altered volcanic rocks in the Southern Bonanza mining district, Colorado. Paleozoic sedimentary rocks, including the favorable Leadville limestone, are exposed three miles south of the altered area, and reason exists to believe that they might underlie it within a reasonable depth. Alteration of pre-mineral volcanic rocks has been used successfully as a guide to concealed orebodies in the Main Tintic and East Tin tic mining districts, Utah (Bill-ingsley, 1933, p. 120-122; Lovering et al, 1949; Howd, 1957, p. 124-134; Cook, 1957, p. 73) and could be a useful guide here. GENERAL GEOLOGY AND STRUCTURE The Northern and Southern Bonanza mining districts are northwest of the San Luis Valley in southern Colorado, just within the northeastern edge of the San Juan volcanic province. The districts are1ocated on the southern extension of the Sawatch uplift, a prorninent northwest-trending structural high. The highly productive mining camp. of Leadville, Gilman and Aspen are on the northeastern and northwestern flanks of this uplift where Paleozoic limestones have

Jan 1, 1961

Recent literature is reviewed with emphasis on the design and scale up of mixers. Most important aspects of mixing have resulted from the study of Newtonian fluids and only a minor attempt has been made to extend the work to non-Newtonian materials.The rheology of non-Newtonian materials is outlined and the typical behaviour of mineral slurries is indicated.The importance of flow velocity, flow pattern, and fluid turbulence is discussed with relation to suspension of solids and rate of reaction.Data on experimental leaching of ore from Mary Kathleen, Queensland, show the effect of different mixing impellers.In conclusion, factors involved in the selection of a mixer are presented with emphasis on economic appraisal after pilot experimentation.INTRODUCTIONThe subject of mixing has attracted considerable attention during recent years, but relatively little work has been undertaken for the study of non-Newtonian materials. Most work has been restricted to Newtonian fluids because there are less inconsistencies in such study.Mixing, by definition, implies blending or combining, and ranges from gentle mixing which blends the contents of a large tank in 24 hours to violent mixing which completely homogenises the contents of a tank within seconds. Metzner and Otto (1957) have pointed out the present lack of knowledge on the degree (or quality) of mixing. Apart from this fact the design of mixers for Newtonian materials would seem to be reasonably certain.Both capital and operating costs rise rapidly with increasing mixer size. Therefore the design, or selection, of a mixer is a matter for economic consideration in the overall aspect of plant design and operation.

Jan 1, 1961

By E. G. King

In continuation of the study of thermodynamic properties of the common interoxidic compounds of ferroalloy elements, this report gives the results of low-termperature heat-capacity measurements and entropy evaluations of the monotungstates of sodium, magnesium, and calcium. Previous reports4 5/ of this laboratory dealt with low-temperature heat capacities, entropies, and heats of formation of the sodium vanadates. Heat-capacity measurements of the monotungstates of sodium, magnesium, and calcium (Na2W04, MgW04, and CaW04) were conducted throughout the temperature range 51° to 298° K. The entropies at 298° K. were evaluated and then combined with entropy data for the elements and oxides to obtain entropies of formation. This information is an essential part of the data needed for thermodynamic appraisals of chemical reactions of these substances. No similar data for any tungstate are to be found in the literature.

Jan 1, 1961

By R. E. Hudrlik, G. W. Preckshot

The diffusion coefficients of silver from solid silver in molten lead were measured to within ± 0.8 pet in a columnar type diffusion cell ower, the temperature range of 326° to 530°C. Fick's law describes the process up to 530°C where the laminar mechanism appareltly breaks down. These is negligible resistance at the interface as shown by mathematical analyses. The diffusion coefficients are found concentration independent. IT would seem that diffusion in liquid metals would be free of such effects as molecular structure, dissociation. polarization. and compound formation. This view was taken by Gorman and preckshot in their study of diffusion of copper from solid copper into molten lead. They reported diffusion coefficients which were independent of the concentration over the range of 478° to 750°C. They found that the Stokes-Einstein equation with constant radius of the diffusing specie represented the diffusion data better than Eyring's rate theory equation and Sheibel's correlation. The radius of diffusion was found to be that of the doubly charged copper. There appeared to be no resistance across the solid-liquid boundary. In the present work the diffusion coefficients for silver in liquid lead were measured over a range of temperatures of 350° to 505°C. The solubility of silver in lead over the range of 303° to 630°C was also obtained. These results are compared with calculated or correlated values or with data in the literature. EXPERIMENTAL Procedure—The experimental equipment techniques and procedures were those reported in detail by Gorman and preckshot9 and will not be repeated here. Measured values of WT, Co, A. L were obtained for various diffusion times and the diffusion coefficient was computed for the case of no resistance at the interface9, 11 by: WT/CoAL = 1- 8/p2 n=1 1/(2n - 1)2 exp[-(2n - 1)2p2 Dt/4L2] [1] or where there was resistance at the interface by: WT = 1- ?n=1 2h2/ap2L [sxp [-Dan2t]/[(h2 + an2) L + h] The roots an are those of the transcendental equation3 tan (an L) = Iz/cun. The diffusion coefficient is that defined by Hartley and Crank.7 The total silver in the lead cylinder and equilibrium slug was determined by a cupellation technique' with proper correction for losses. Analysis of known samples showed that this method is surprisingly accurate. The amount of silver in the lead adhering to the silver cylinder was obtained in the same fashion as shown by Gorman and preckshot.9 The small errors involved in this determination are not critical since the silver in this adhering lead layer is only 3 to 15 pet of the total diffused. Materials—Electrolytic silver containing 99.9+ pet Ag obtained from General Refineries of Minneapolis, Minn. was used for all but runs 7 and 8. For the balance of the runs this silver was reduced with hydrogen at 1100°C and its oxygen content was found to be about 0.017 pet. For the runs. 7 and 8, phosphorous-reduced silver of the same purity was obtained from Handy and Harman Co. of Chicago, Ill. The densities of the phosphorus-reduced silver and the hydrogen-reduced electrolytic silver were 10.484 and 10.487 g per cm3, respectively. These values agree with those reported for pure silver. Silver which was reduced at 900 C had an average density of 9.998 g per cm3, indicating porosity. This silver was used for a number of runs which were not tabulated in Table I. These are indicated by crosses on Fig. 2. The 99.999 pet Pb was obtained from the National Lead Co. Research Laboratory of Brooklyn, New York. DISCUSSION OF RESULTS The diffusion and solubility results are reported in Table I for eleven runs using either phosphorus-reduced electrolytic silver or hydrogen-reduced silver at 1100° C. The solubility data shown in Fig. 1 show the excellent agreement with that reported by Heycock and Neville.8 The data of Friedrichs5 apparently are in error. The experimental solubility data of this work are reported to 0.3 pet. The experimental diffusion coefficients computed from Eq. [1] are reported within 1.2 pet of the mean and are plotted in Fig. 2. These are expressed within +0.8 pet of the experimental values over the entire temperature range by: D= 8.26 x 10 -5 e-1925/RT . [3] There appears to be little difference due to the

Jan 1, 1961

By R. W. Baldwin

On page 309, column 1, the second equation should read: Ma-M1 = dlog_Pa M2-M1 d log P2

Jan 1, 1961

A general outline of the significant features in the quality and manufacture of the more common refractories is given. Where possible, linkage between quality development and control and service applicationhas been shown and explained. INTRODUCTIONThe refractory industry is no stranger to change. New processes and revision of old processes in other industries are the harbinger of new and revised products in refractories.Few of the changes are dramatic; generally they are evolutionary rather than revolutionary. New developments are additional to, and inclusive of, established practice.Therefore in this paper it is necessary to repeat much of what is already known in order to show the development taking place.FIRECLAY REFRACTORIESGeneral technology Fireclay refractories are the most common, the most varied and the most versatile of all refractories. Virtually any composition of silica and alumina up to the composition of kaolin is possible. For purposes of comparison they may be classified in the Continental fashion in accordance with chemical composition or in the American way according to "duty". That the two methods are equivalent is shown by an inspection of the alumina-silica diagram of Bbwen and Greig (1924). 'Fireclay refractories are composed of a glassy and a crystalline component derived from the chemical and physical nature of the raw materials used in their manufacture.

Jan 1, 1961