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By Robert H. Weber

INCREASING acceptance of perlite products, chiefly in the fields of lightweight structural aggregates and thermal and acoustic insulation, has led to expanding market demands that have encouraged many new producers to enter the field. In some instances, however, the failure of these producers to anticipate the variable response of perlite to conventional processing methods has led to difficulty in establishing an economical flowsheet by which a predictable specification product could be obtained. It is not the writer's intent to provide a solution to these problems, but rather to summarize their nature. It is to be hoped that members of the industry who have hurdled some of these obstacles will document solutions arising from their experience. In this treatment the term perlite will not be restricted to the petrographic definition but will apply to all volcanic glasses. Expansible obsidians and pitchstones are accordingly included in this broader industrial classification. Chemical Properties: Although perlite has been reported to range in composition from that of rhyolite to that of andesite, it is probable that most of the glasses have the composition of rhyolite. When recalculated to an anhydrous basis, the five analyzed glasses from New Mexico, representing five distinct physical types from widely separated deposits, show an amazingly uniform oxide composition. Water content is the only major compositional variable; total water ranges from a low of 0.37 pct (non-expansible obsidian) to a high of 8.95 pct (expansible pitchstone). The wide range in expansion characteristics exhibited by these samples cannot be related to significant variations in the composition of the nonvolatile fraction and has been only partially correlated with variations in water content.

Jan 1, 1956

By John S. Crandall

THE mineral garnet, while ordinarily considered a semiprecious gem stone or a second-grade industrial gem, has also proved itself in the field of industrial abrasives. Its use is well known as a sandpaper grain, and as a sandblasting sand its qualities are rapidly becoming recognized in more and more industries. Production of garnet as an abrasive is confined chiefly to two areas in the United States, North Creek, N. Y., where the Barton Mines Corp. operates, and Emerald Creek, Benewah County, Idaho, where Occurrence: Garnets in the Emerald Creek area occur as disseminated crystals in beds of micaceous schists of the Belt Series, which in this section are estimated to be close to 4000 ft thick. The schists are high in alumina and silica with iron, manganese, and magnesium. Subjection of the original sediments to high temperatures and pressures caused metamorphism to take place with the resultant re-crystallization of high alumina-silica minerals such as garnet, mainly spessartite and almandite varieties, cyanite, sillimanite, chlorite, actinolite, tourmaline, biotite, and muscovite, with minor amounts of ilmenite and magnetite. Quartz is also present in considerable amounts. Fast erosion of the soft mica schists on exposure to weathering has created extensive alluvial deposits containing up to 10 pct garnet having a maximum grain size of 3/16 in. These alluvial sands and gravels are now being treated for the recovery of garnet sands. Treatment: Overburden of 1 to 4 ft must be stripped to expose the garnetiferous gravels. This operation and the subsequent feeding of the gravels to a trommel-screen washing plant are performed by a % yd dragline. The trommel-screen openings are 3/16 in., thus allowing a separation and concentration based on grain size, since over 95 pct of total free garnets are minus 3/16 in. All plus 3/16-in. material is wasted at this point. The minus 3/16-in. material is further concentrated in a sand-drag classifier, where the slimes and silts are washed out and wasted. The sand product from the classifier varies in garnet content from 20 to 60 pct according to the particular section of ground being worked. This sand product is trucked to a jig plant where two sized fractions are made in a trommel-screen. The minus 3/16-in. plus 10-mesh portion is fed to a Pan-American two cell 42-in. jig. The minus 10-mesh portion is treated in a Bendelari three cell 42-in. jig. The jig concentrates are combined to form a 98 pct garnet sand. The jig tailings contain 3 to 5 pct garnet which is mainly flat crystals and chips which will not settle into the jig hutch. Subsequent treatment of these tailings in a scavenger jig followed by drying and electromagnetic separation will, according to tests, reduce the garnet losses in the tailings to something around 1 pct. Jig treatment of this feed approaches ideal as the major portion of the garnet crystals are the natural dodecahedrons and so are, in general, close to spherical. The specific gravity of pure garnet is 4.2, while the next heaviest mineral in the feed is cyanite with a specific gravity of 3.6, then quartz with specific gravity of 2.6. The garnet concentrate is practically free of quartz. The predominant impurity is cyanite which amounts to about 1.5 pct. The rod-like crystals of cyanite appear to up-end in the jig and go into the hutch with the garnets. Some ilmenite and magnetite appear in the concentrate but in very minor amounts. Subsequent washing in a sand-drag classifier removes fine silts and iron oxides. The gravel feed to the washing plant will average 8 pct recoverable garnet content. Concentration ratio in this plant runs about 2.5 to 1. Washing-plant concentrate as fed to the jigs will average 45 pct garnet by weight. Concentration ratio of jigging runs about 2.2 to 1. The garnet concentrate is dried in a rotary oil-fired drier and then fed to vibrating screens in closed circuit with crushing rolls. Practically any grit from 10-mesh down to 150-mesh grain size may be graded to specifications in two 3-deck vibrating screens. The present production, however, is approximately 75 pct No. 36, 15 pct No. 60. and the balance No. 80 and No. 100. Metal-screen cloth is used for sizes down to 36 mesh. From 36 mesh and finer, silk-screen cloth is used since it has less tendency to blind. All garnet sand is bagged in 100 lb self-sealing, sleeve-type paper bags. Practically all shipments are made in carload lots. Car loading is convenient since the plant is in Fernwood on the tracks of a branch line of the Milwaukee railroad. Truck shipments can and are made occasionally.

Jan 1, 1951

By John S. Crandall

THE mineral garnet, while ordinarily considered a semiprecious gem stone or a second-grade industrial gem, has also proved itself in the field of industrial abrasives. Its use is well known as a sandpaper grain, and as a sandblasting sand its qualities are rapidly becoming recognized in more and more industries. Production of garnet as an abrasive is confined chiefly to two areas in the United States, North Creek, N. Y., where the Barton Mines Corp. operates, and Emerald Creek, Benewah County, Idaho, where Occurrence: Garnets in the Emerald Creek area occur as disseminated crystals in beds of micaceous schists of the Belt Series, which in this section are estimated to be close to 4000 ft thick. The schists are high in alumina and silica with iron, manganese, and magnesium. Subjection of the original sediments to high temperatures and pressures caused metamorphism to take place with the resultant re-crystallization of high alumina-silica minerals such as garnet, mainly spessartite and almandite varieties, cyanite, sillimanite, chlorite, actinolite, tourmaline, biotite, and muscovite, with minor amounts of ilmenite and magnetite. Quartz is also present in considerable amounts. Fast erosion of the soft mica schists on exposure to weathering has created extensive alluvial deposits containing up to 10 pct garnet having a maximum grain size of 3/16 in. These alluvial sands and gravels are now being treated for the recovery of garnet sands. Treatment: Overburden of 1 to 4 ft must be stripped to expose the garnetiferous gravels. This operation and the subsequent feeding of the gravels to a trommel-screen washing plant are performed by a % yd dragline. The trommel-screen openings are 3/16 in., thus allowing a separation and concentration based on grain size, since over 95 pct of total free garnets are minus 3/16 in. All plus 3/16-in. material is wasted at this point. The minus 3/16-in. material is further concentrated in a sand-drag classifier, where the slimes and silts are washed out and wasted. The sand product from the classifier varies in garnet content from 20 to 60 pct according to the particular section of ground being worked. This sand product is trucked to a jig plant where two sized fractions are made in a trommel-screen. The minus 3/16-in. plus 10-mesh portion is fed to a Pan-American two cell 42-in. jig. The minus 10-mesh portion is treated in a Bendelari three cell 42-in. jig. The jig concentrates are combined to form a 98 pct garnet sand. The jig tailings contain 3 to 5 pct garnet which is mainly flat crystals and chips which will not settle into the jig hutch. Subsequent treatment of these tailings in a scavenger jig followed by drying and electromagnetic separation will, according to tests, reduce the garnet losses in the tailings to something around 1 pct. Jig treatment of this feed approaches ideal as the major portion of the garnet crystals are the natural dodecahedrons and so are, in general, close to spherical. The specific gravity of pure garnet is 4.2, while the next heaviest mineral in the feed is cyanite with a specific gravity of 3.6, then quartz with specific gravity of 2.6. The garnet concentrate is practically free of quartz. The predominant impurity is cyanite which amounts to about 1.5 pct. The rod-like crystals of cyanite appear to up-end in the jig and go into the hutch with the garnets. Some ilmenite and magnetite appear in the concentrate but in very minor amounts. Subsequent washing in a sand-drag classifier removes fine silts and iron oxides. The gravel feed to the washing plant will average 8 pct recoverable garnet content. Concentration ratio in this plant runs about 2.5 to 1. Washing-plant concentrate as fed to the jigs will average 45 pct garnet by weight. Concentration ratio of jigging runs about 2.2 to 1. The garnet concentrate is dried in a rotary oil-fired drier and then fed to vibrating screens in closed circuit with crushing rolls. Practically any grit from 10-mesh down to 150-mesh grain size may be graded to specifications in two 3-deck vibrating screens. The present production, however, is approximately 75 pct No. 36, 15 pct No. 60. and the balance No. 80 and No. 100. Metal-screen cloth is used for sizes down to 36 mesh. From 36 mesh and finer, silk-screen cloth is used since it has less tendency to blind. All garnet sand is bagged in 100 lb self-sealing, sleeve-type paper bags. Practically all shipments are made in carload lots. Car loading is convenient since the plant is in Fernwood on the tracks of a branch line of the Milwaukee railroad. Truck shipments can and are made occasionally.

Jan 1, 1951

By J. J. Calaman, D. H. Fleming

DURING 1950 the jet-piercing process was used commercially in the piercing of primary blast-holes in magnetic taconite at the preliminary taconite plant of .the Erie Mining Co., Aurora, Minn. The Erie Mining Co. purchased a jet-piercing machine and associated equipment in 1949, and the machine has been in operation since its installation in the summer of that year. An overall view of the pit with the JPM-1 jet-piercing machine in operation is shown in Fig. 1. During three months of 1949 and continuously since February 1950, production piercing took place under all pit conditions. By the end of October 1950, a total of 15,000 linear ft of hole had been pierced in an open pit handling an average of 1200 to 1800 tons of crude a day in one 8-hr shift. While it is recognized that this output does not approach the millions of tons a year planned for the developing Minnesota taconite projects, the machine as a unit has been operating under conditions probably more adverse than those that eventually will be encountered in the large operations. This pilot operation has permitted evaluation of the piercing problem in the full-scale taconite plant. This paper describes jet-piercing process funda- mentals, important features of the latest jet-piercing burners and machine, actual piercing results obtained, and new developments that give promise of materially increasing overall process efficiency. To produce the blasthole, jet-piercing utilizes thermal energy, as contrasted with the application of mechanical energy in churn drills and jackham-mers. The heart of the process may be termed a tailored flame produced by a rocket-type burner, thermodynamically similar in every respect to that of the giant rockets being developed for military purposes. The heat release in the combustion chamber of the burner is about 50x10' Btu per cu ft per hr as compared with 5x10' for most modern steam generators.* Combustion of liquid petroleum fuels (kerosine, diesel oil, or No. 2 fuel oil) with gaseous oxygen in the burner chamber at pressures of 100 to 200 psi results in temperatures of about 4300°F. Expansion of the hot combustion gases through divergent nozzles produces high-temperature supersonic jets having measured velocities of about 6000 fps. Impinging the flame jets on rock causes a thin surface layer to expand and break away from the base as a result of the thermally induced stresses. This spalling action is aided further in chert and quartzite by the 0.82 pct volume change resulting from the 6 to p quartz inversion at 1066"F.t The dynamic action of the jets whisks the spalled rock

Jan 1, 1952

By Norman Ketzlach

ANGANESE today overshadows all strategic materials in our planning for national se-curity," according to a report issued recently by the American Manganese Producers Association. By far the greater part of the manganese ore used in the United States is imported. "We have enough manganese ore in the United States to last from one hundred to three hundred years and longer, but most of the deposits are undeveloped. As in the case of copper, lead, and zinc, manganese ore, both foreign and domestic are low grade. Manganese ores have to be concentrated and processed. After being processed, domestic ores are higher grade than foreign." Most of the manganese ore found in this country, however, is not amenable to concentration by ore-dressing methods. Manganese Products, Inc. has developed a sulphurous-sulphuric acid leaching process for the recovery of manganese from low-grade, intermediate manganese ores. By the term "intermediate manganese ores" is meant those ores in which the manganese in the form of manganese oxides is found to have two different valences, usually two and four, as is probable in Mn,O, or the ore may be a mixture of manganous and manganic oxides. "Intermediate" manganese siliceous ores are ores in which the silica is a constituent of the ore and is loosely linked to the manganese by water of crystallization. This process has been carried out with the type of manganese ore found in the Olympic Peninsula of western Washington; Clough, N. C.; and Lava Hot Springs, Idaho, as well as just recently with manganese ore from Las Vegas, Nev. As far as the manganese leaching process is concerned, these ores differ primarily in the form in which the manganese oxides occur. The tetravalent manganese, the manganese existing in the dioxide form, is soluble in a sulphurous acid solution. To dissolve the divalent manganese, sulphuric acid is required. To dissolve the type of ore found in Washington and North Carolina, a mixture of both sulphurous and sulphuric acid is used. Whereas to dissolve the type of manganese ore found in Idaho and also in Montana, sulphurous acid alone is sufficient. The Nevada manganese ore is of the same type as that found in Idaho as far as the leaching process is concerned. It has long been known that manganese ores, with the exception of rhodonite, which is a true manganese silicate ore, can be dissolved readily in sulphurous and sulphuric acids.' The removal of the impurities such as silica, iron, and alumina from the resulting solution is the step that has been difficult. The process worked out by Manganese Products has been carried through pilot-plant equipment. This process has also been extended to the production of ammonium sulphate. Leaching of Ore: The manganese ore, ground to —-65 mesh is leached with sulphurous acid and sul-

Jan 1, 1951

By Norman Ketzlach

ANGANESE today overshadows all strategic materials in our planning for national se-curity," according to a report issued recently by the American Manganese Producers Association. By far the greater part of the manganese ore used in the United States is imported. "We have enough manganese ore in the United States to last from one hundred to three hundred years and longer, but most of the deposits are undeveloped. As in the case of copper, lead, and zinc, manganese ore, both foreign and domestic are low grade. Manganese ores have to be concentrated and processed. After being processed, domestic ores are higher grade than foreign." Most of the manganese ore found in this country, however, is not amenable to concentration by ore-dressing methods. Manganese Products, Inc. has developed a sulphurous-sulphuric acid leaching process for the recovery of manganese from low-grade, intermediate manganese ores. By the term "intermediate manganese ores" is meant those ores in which the manganese in the form of manganese oxides is found to have two different valences, usually two and four, as is probable in Mn,O, or the ore may be a mixture of manganous and manganic oxides. "Intermediate" manganese siliceous ores are ores in which the silica is a constituent of the ore and is loosely linked to the manganese by water of crystallization. This process has been carried out with the type of manganese ore found in the Olympic Peninsula of western Washington; Clough, N. C.; and Lava Hot Springs, Idaho, as well as just recently with manganese ore from Las Vegas, Nev. As far as the manganese leaching process is concerned, these ores differ primarily in the form in which the manganese oxides occur. The tetravalent manganese, the manganese existing in the dioxide form, is soluble in a sulphurous acid solution. To dissolve the divalent manganese, sulphuric acid is required. To dissolve the type of ore found in Washington and North Carolina, a mixture of both sulphurous and sulphuric acid is used. Whereas to dissolve the type of manganese ore found in Idaho and also in Montana, sulphurous acid alone is sufficient. The Nevada manganese ore is of the same type as that found in Idaho as far as the leaching process is concerned. It has long been known that manganese ores, with the exception of rhodonite, which is a true manganese silicate ore, can be dissolved readily in sulphurous and sulphuric acids.' The removal of the impurities such as silica, iron, and alumina from the resulting solution is the step that has been difficult. The process worked out by Manganese Products has been carried through pilot-plant equipment. This process has also been extended to the production of ammonium sulphate. Leaching of Ore: The manganese ore, ground to —-65 mesh is leached with sulphurous acid and sul-

Jan 1, 1951

By M. M. Fine

THE problem of producing a uniform, medium-fine sand for glass-furnace feed has been of interest to the glass-container industry for many years. In the present investigation of the problem, conducted by the Bureau of Mines in cooperation with the Owens-Illinois Glass Co., Alton, Ill., a satisfactory method of producing such sand was developed. The investigation involved continuous-grinding studies of glass sand with flint and porcelain pebbles, steel balls and rods, and a simultaneous study of classification. The most satisfactory procedure consisted of grinding in a pebble or ball mill followed by a double classification: hydraulic classification to separate the oversize for return to the grinding unit and mechanical classification to remove fines and impurities from the ground sand. The proper application of this flowsheet usually yielded a graded sand containing less iron than the feed even when grinding was done in a steel-lined ball mill. The amount of sand ground into the so-called "dusting" sizes was, in all cases, less than 10 pct. Experiments were made which showed that this very fine sand could be beneficiated to a usable material. Background The advantages in utilizing a uniform, medium-fine sand as a feed for glass furnaces has motivated a considerable amount of research on the ,problem of producing such sand by glass producers and others. For the glass producer, the faster melting rate of such a graded sand offers the possibilities of reduced fuel costs and increased furnace capacity. In addition, there is the likelihood of improving the quality of the melt and thereby reducing the number of seeds (air bubbles) and stones (unrnelted grains) in the finished ware. Although the melting rate of a glass batch depends on other factors in addition to the grain size of the sand, there is experimental evidence to show that grain size influences the melting rate considerably. Potts, Brookover, and Burch' found that when the raw materials (sand, soda ash, and limestone) were always matched in- size, there was a great decrease in the melting time as the grain size of the materials was decreased. They found, too, that when the grain sizes of the soda ash and Limestone were held constant at 40 to 60 mesh, the minimum melting time occurred when 40 to 60 mesh sand was used. The increase in melting time with decrease in grain size beyond 40 to 60 mesh was due, they postulated, to accelerated demixing or separation of batch during melting as the grain size of the sand decreased in relation to the grain size of the other materials. An earlier investigatora found that the highest rate of melting and purifying ordinary glass was obtained when medium-size sand (0.385 to 0.120 mm, correspondingly roughly to 40 to 120 mesh) was used. Although batches containing smaller-size sand were found to fuse more rapidly, the time required to remove air bubbles from such melts actually increased the total duration of the process. Coarsegrained sand, it was stated, increased greatly the times of both melting and purifying. Although the laboratory data are difficult to confirm on a plant scale, observations by the Owens-Illinois Glass Co. indicate a higher furnace capacity of better-quality ware when a medium-fine sand is used in the batch. During the recent war, the glass producer was inclined to overlook a considerable variation in raw materials in the interest of higher production. For instance, table I shows the wide range in the amounts of various screen fractions in sand supplied by one producer to the Terre Haute plant of Owens-Illinois. The sand, from the northern Illinois St. Peter sandstone, represented material used by that plant over a period of a few years during the war. Since the war, the glass industry has insisted on

Jan 1, 1951

By M. M. Fine

THE problem of producing a uniform, medium-fine sand for glass-furnace feed has been of interest to the glass-container industry for many years. In the present investigation of the problem, conducted by the Bureau of Mines in cooperation with the Owens-Illinois Glass Co., Alton, Ill., a satisfactory method of producing such sand was developed. The investigation involved continuous-grinding studies of glass sand with flint and porcelain pebbles, steel balls and rods, and a simultaneous study of classification. The most satisfactory procedure consisted of grinding in a pebble or ball mill followed by a double classification: hydraulic classification to separate the oversize for return to the grinding unit and mechanical classification to remove fines and impurities from the ground sand. The proper application of this flowsheet usually yielded a graded sand containing less iron than the feed even when grinding was done in a steel-lined ball mill. The amount of sand ground into the so-called "dusting" sizes was, in all cases, less than 10 pct. Experiments were made which showed that this very fine sand could be beneficiated to a usable material. Background The advantages in utilizing a uniform, medium-fine sand as a feed for glass furnaces has motivated a considerable amount of research on the ,problem of producing such sand by glass producers and others. For the glass producer, the faster melting rate of such a graded sand offers the possibilities of reduced fuel costs and increased furnace capacity. In addition, there is the likelihood of improving the quality of the melt and thereby reducing the number of seeds (air bubbles) and stones (unrnelted grains) in the finished ware. Although the melting rate of a glass batch depends on other factors in addition to the grain size of the sand, there is experimental evidence to show that grain size influences the melting rate considerably. Potts, Brookover, and Burch' found that when the raw materials (sand, soda ash, and limestone) were always matched in- size, there was a great decrease in the melting time as the grain size of the materials was decreased. They found, too, that when the grain sizes of the soda ash and Limestone were held constant at 40 to 60 mesh, the minimum melting time occurred when 40 to 60 mesh sand was used. The increase in melting time with decrease in grain size beyond 40 to 60 mesh was due, they postulated, to accelerated demixing or separation of batch during melting as the grain size of the sand decreased in relation to the grain size of the other materials. An earlier investigatora found that the highest rate of melting and purifying ordinary glass was obtained when medium-size sand (0.385 to 0.120 mm, correspondingly roughly to 40 to 120 mesh) was used. Although batches containing smaller-size sand were found to fuse more rapidly, the time required to remove air bubbles from such melts actually increased the total duration of the process. Coarsegrained sand, it was stated, increased greatly the times of both melting and purifying. Although the laboratory data are difficult to confirm on a plant scale, observations by the Owens-Illinois Glass Co. indicate a higher furnace capacity of better-quality ware when a medium-fine sand is used in the batch. During the recent war, the glass producer was inclined to overlook a considerable variation in raw materials in the interest of higher production. For instance, table I shows the wide range in the amounts of various screen fractions in sand supplied by one producer to the Terre Haute plant of Owens-Illinois. The sand, from the northern Illinois St. Peter sandstone, represented material used by that plant over a period of a few years during the war. Since the war, the glass industry has insisted on

Jan 1, 1951

By Oliver Bowles

EACH year the broad diversified field of industrial minerals offers a panorama of new and interesting developments that not only concern the welfare of the industries themselves but have a more or less direct influence on the lives of citizens at large. Thus, the home life of multirudes may be affected by new building units that transmit light through walls instead of windows, by illuminated processed marble lighting fixtures and decorations, by the vast impetus given to thermal insulation Ly .mineral wool, expanded vermiculite, and related products, and, more remotely, by fireproof rugs and drap-

Jan 1, 1937

By Fred H. Klaer

Water supplies dependent upon induced infiltration can be developed by vertical wells, by infiltration galleries, or by horizontal water collectors. Each method is described and the advantages of water obtained by induced infiltration with respect to cost, chemical quality, and temperature are shown by specific water supplies. THE subject of ground water in industry is assuming increasing importance as new processes and new industries are developed. Industrial specifications of chemical quality and temperature for process water and for cooling purposes are becoming more rigid, and water must now have many properties to meet these requirements. As ground water is usually more constant in quality and temperature, many industries are turning to ground-water supplies to satisfy their growing need. As many published articles have stated during the past several years, the ever increasing demands have caused shortages of water supply in many localities throughout the United States. Although such shortages are generally of a local nature, they have given rise to many attendant problems, such as increased pumping costs, salt water encroachment, and rising ground-water temperatures. One partial solution to the problems of overdevelopment of the ground-water reservoirs in many areas can be accomplished by developing ground-water supplies that are dependent upon induced infiltration and by planning the use of underground reservoirs. These reservoirs can be filled during periods of excess precipitation and stream flow and can be emptied during periods of drought, in a manner similar to the use of surface reservoirs. In this way water that otherwise would be wasted into the oceans is salvaged during periods of excess. The development of water supplies dependent on induced infiltration is a relatively new concept and should be defined. When a well is pumped, the water level around the well is lowered in the shape of an inverted cone or cone of depression. As pumping is continued, the cone of depression will continue to expand, horizontally and vertically, until the quantity of water crossing the perimeter of the cone plus the recharge within the area of the cone is equal to the quantity of water being pumped.

Jan 1, 1954

By H. Leslie Bullock

From aluminum to zirconium, the quantitative preponderance of quartz as a gangue material is well recognized. lf this material is to be efficiently removed, its variations must be understood. Variations with temperature are especially important. Too little attention has been given to the thermal polarization of quartz. Under closely controlled conditions, electrostatic upgrading is very reliable. For efficient separation, contact charges must be fostered and charges due to radiation, surface coatings, or thermal polarization avoided. This paper lists thermal transition points of quartz and shows their effect on actual separations. Simple separation tests with all factors except temperature held constant are recommended for determining transition points. With silica making up more than 27% of the earth's crust, its oxides comprising more than 59% of all igneous rocks, and quartz accounting for most of the main free oxides, the mining engineer is in constant contact with quartz, which may occur as a valuable mineral to be purified or, far more frequently, as a gangue material to be removed as completely and economically as possible. As a means of effecting such purification or removal, dry beneficiation is becoming more and more desirable owing to local water scarcities, wet waste disposal problems, or freezing conditions. One method that has been gaining particularly rapid acceptance is electrostatic beneficiation, or the separation of dry free-flowing materials by means of opposite surface charges, differences in potential, or differences in conductivity. Electrostatic beneficiation dates back to the 1870's, but only in recent years have newly developed methods and apparatus and a growing knowledge of solid-state physics widened the field for its economical application. Because the term "electrostatic beneficiation" has been rather loosely used in the literature, it has come to include both electrostatic and electrodynamic procedures. Attracting type separators, however, in which oper- ation is based on differences of surface charge or potential, are truly electrostatic, because the separation occurs in a substantially static field set up between oppositely charged surfaces. Separations with this type of equipment may occur at potentials as low as 1000 v and seldom require potentials as high as 30,000 v. In the new contact charge dielectric separators1 the variation in charge is produced by continuous contact and separation of the particles in the moving feed stream and these charges are fostered by the use of non-conducting support and feed surfaces and by handling the feed in the form of streams of appreciable depth. This favors uniformity of feed and allows higher production rates. The distinctive surface charge differences are set up on the separation of the particles according to Coehn's Law,2 which states that equal and opposite charges are generated on the separation of any two materials in contact and that the substance having the highest dielectric constant will be positively charged. The basic contact charge concept is reliable, but all electrical charges are transient and modified by the electrical conditions of the surroundings. Pyro-electric, photoelectric and radiant effects may modify or totally destroy the contact charges necessary for efficient separation, or contact with conducting surfaces may neutralize them. Such hostile conditions must be carefully guarded against, since they have led to many costly failures in the past. The most consistent difference in surface charges to insure good separation is produced by repeated uniform contact and separation of particles in the moving stream. The thickness of the feed stream possible with this method reduces the effect of contact with the supporting surfaces, but as some contact is inevitable, the best results may be assured by having the dielectric constants of the supporting surfaces between the dielectric constants of the substances to be separated. In general, the hard smooth surface of quartz makes it an ideal substance for electrostatic separation from most minerals. For instance, with calcite, starting with a feed containing 1.9% acid insolubles, one can produce a concentrate containing 0.30% acid insolubles with a tailings containing 21.7% acid insolubles and a yield of 92.8%. The color can be held at 92 or above and the tint at 1.7 or lower. Working with specularite iron ore, laboratory work has given a concentrate of 68.8% Fe., with an iron unit recovery of 96.7%. Excellent results are also in pros-

Jan 1, 1969

By J. C. Holm

ALTHOUGH the main constituents of Portland cement are the oxides of calcium, silicon, aluminum, and iron, characteristics of the cement are seriously affected by such contaminants in the raw materials as magnesium, phosphorus, sodium, potassium, sulfur, and others of lesser importance. Sources of cement raw materials comprise a long list of minerals occurring in nature in various degrees of purity. The calcareous raw materials are generally limestone of purity varying from calcite to cement rock (a low-grade limestone of natural, almost correct chemical composition), chalk, marl, seashells, coral, and coral sand. The argillaceous raw materials supplying silicon, aluminum, and iron are mainly various forms of clay and shale, to which may be added silicious sand, iron ore, bauxite, or kaolin for minor adjustment of the chemical composition. The quality of Portland cement in this country, as in most parts of the world, is controlled by rigid specifications limiting both its chemical and physical characteristics, and cement manufacturers must comply with these specifications to market their products. Brandon Raw Materials: An unusual deposit of marl, limestone, and clay occurs 12 miles east of Jackson, Miss., near the village of Brandon. The deposit is of sedimentary origin and of relatively young geological age. Layers of marl vary from putty-like consistency to such hardness that it can be cut with a knife. Interspersed between the layers of marl are bands of limestone varying from very soft to hard. the compressive strength of the hardest layers exceeding 15,000 lb per sq in. The layers of marl range in thickness from a few inches to about 25 ft. The limestone bands seldom exceed 2 to 3 ft but often occur in thinner veins in the quarry face. Above the top layer of the deposit, which may be marl or limestone, a layer of clay ranges in thickness from a few inches to more than 20 ft. Part of this clay is harvested with the raw material to supply part of the argillaceous components, but most of it is stripped as overburden and wasted. A highly silicious clay of extreme fineness, harvested from the bottom of the quarry below the marl and limestone bands, is to correct the silica content. Fig. 1 shows typical examples of the interrelation of the various materials, based on drill logs obtained during exploration of the deposit. The marls vary in moisture content in the bank from 15 to 30 pct and contain up to 70 pct -200 mesh particles and up to 40 pct —10 p particles. A large percentage of the fine fraction is within the colloidal range, making the marl extremely sticky. The limestone beds range in hardness from that of the hardest marl to a medium hard limestone and in moisture content from 2 pct to approximately 14 pct. The line of demarcation is often difficult to draw and the moisture content is possibly the best means of classification. The ratio of soft to hard material is not constant throughout the deposit, but the average is approximately 70 pct soft to 30 pct hard material. Through the years this deposit had been repeatedly explored by cement companies and rejected as unsuitable for cement manufacture, mainly because of physical characteristics. In 1950, after careful exploration of the deposit and comprehensive laboratory and pilot plant tests of the raw materials, officials of Marquette Cement Mfg. Co. of Chicago were convinced that a practical and economical method of processing the raw materials had been devised and authorized construction of a new plant that began production in December 1951. Marl and limestone, common raw materials for Portland cement, usually occur in such a manner that they can be worked separately. Their harvesting and processing normally have presented no difficult problems, as standard equipment and methods are available for handling either sticky or hard materials. No other cement plant utilizes a deposit of the nature of that at Brandon, however, and for this reason no prior art was available for design. When properly blended, the raw materials produced an excellent cement without additives. Basic problems to be solved in designing the cement plant were:

Jan 1, 1957

By H. R. Deeth, C. J. Koenig

About ten years ago nepheline syenite was introduced to the ceramic industry and the material has now found application in the various branches of the industry, namely, as a vitrifying agent in white-wares and as a source of alumina and alkalies in glasses, glazes, and porcelain enamels. Spencel described the early mining and processing developments regarding this material. Since the time of his article many research papers have appeared relating to the usage of nepheline syenite but little has been published relative to subsequent mining and processing methods. A complete indexed review of the literature was issued recently by Ohio State University.2 Since "Lakefield" nepheline syenite from Blue Mountain, Ontario (Fig I); is the only commercial ceramic-grade nepheline syenite now being marketed on this continent, discussion is limited to this operation carried on by American Nepheline Limited, Lakefield, Ont., and its subsidiary in the United States, American Nepheline Cory. at Rochester, N. Y. The Deposit Blue Mountain is a long ridge rising to an elevation of about 350 ft at its highest point above the surrounding country and extending for about six miles in a northeasterly direction across Methuen township, Peterborough County. The rock of the Blue Mountain central alkaline intrusive is fine grained, light colored and of even granitic texture. The solidified mass consists predominately of the minerals albite, nepheline and microcline in order of abundance. The average mineralogical composition for the deposit obtained by a study of 112 samples taken regularly over the whole formation is as follows:3 Volumetric Mineral Per Cent Albite.................... 54 Microcline................ 20 Nepheline................ 22 Muscovite................ 2 Mafics.................... 2 (Biotite, hastingsite, magnetite) Total................... loo The mineral nepheline (or nephelite) belongs to the feldspathoid group but is lower in silica content than are the feldspars. It is a silicate of soda, potash, and alumina (NaKAl2O32SiO2). Its presence with albite (Na2oA12O3 6SiO2) and microcline (K2O A12O3 6SiO2) gives the Blue Mountain deposit an alkali content of 15 pct and an alumina content of approximately 24 pct. While this huge alkaline mass is somewhat variable mineralogically, it has a uniform chemical composition. When the iron, mostly in the form of magnetite, is removed during processing, a remarkably uniform finished product is obtained. Geological surveying has disclosed many million tons of nepheline syenite in the Blue Mountain deposit. Diamond drilling in the area where mining is now being carried out indicates a block of about one million tons.

Jan 1, 1949

By John E. Conley, John A. Ruppert

LIGHTWEIGHT aggregates have been in use for many years in the United States but are now receiving more and more attention by manufacturers and users of concrete shapes. These shapes comprise building blocks, special forms, such as door sills, lintels, floor slabs, and beams. Lightweight aggregate also is adapted for monolithic construction. The increased building activity since termination of the war, together with the widespread shortage of cinders resulting from a general trend toward the use of oil and pulverized-coal fuels, has aggravated the situation. In some localities? new producers of lightweight aggregates have been stimulated to increased efforts to supply the demand. In addition, various estab- lishments of the United States Government have recently given attention to this problem. The National Bureau of Standards, in the Commerce Department, and the Bureau of Reclamation, in the Interior Department, have completed a series of tests on concretes made from some of the available commercial aggregates in order to evaluate their qualities. The tests have been made to focus attention on the desirable properties of good aggregates. This work was done at the request of the Technical Office of the National Housing Agency and Housing and Home Finance Agency. Some time previously, the former office had conducted a survey of the locations where lightweight aggregates are produced.' A study of this information discloses that the producing centers are widespread and that certain areas, notably the region east of the Mississippi River and especially the southeastern states in the sections along the Atlantic Coast, have only a limited number of such plants. The situation has been alleviated to some extent with new plants having been erected near Richmond, Va., and Lansford, Pa. Experiment Stations of the Federal Bureau of Mines at Tuscaloosa, Ala., Norris, Tenn., and College Park, Md., have investigated types and sources of potential raw materials such as clays, shales, and slates, as well as methods and procedures for utilizing these materials for their conversion into aggregates, and have published the data as a Bureau of Mines report.' Structural Uses of Lightweight Aggregates: Production of masonry blocks in the United States has averaged close to a billion units a year for the past three years, and of these it is estimated that more than 40 pct consisted of the lightweight type. It is anticipated that the future will witness an increase in this percentage in view of the superior insulating properties, decrease in dead weight, and ease of handling, transporting, and laying units of this type. Lightweight aggregates are used extensively in multistoried buildings in which the weight of the walls and floors is carried by a structural steel framework. The substitution of a lightweight concrete for normal concrete in a building of this type has brought about in many instances some or all of the following advantages:

Jan 1, 1951

By John A. Ruppert, John E. Conley

LIGHTWEIGHT aggregates have been in use for many years in the United States but are now receiving more and more attention by manufacturers and users of concrete shapes. These shapes comprise building blocks, special forms, such as door sills, lintels, floor slabs, and beams. Lightweight aggregate also is adapted for monolithic construction. The increased building activity since termination of the war, together with the widespread shortage of cinders resulting from a general trend toward the use of oil and pulverized-coal fuels, has aggravated the situation. In some localities? new producers of lightweight aggregates have been stimulated to increased efforts to supply the demand. In addition, various estab- lishments of the United States Government have recently given attention to this problem. The National Bureau of Standards, in the Commerce Department, and the Bureau of Reclamation, in the Interior Department, have completed a series of tests on concretes made from some of the available commercial aggregates in order to evaluate their qualities. The tests have been made to focus attention on the desirable properties of good aggregates. This work was done at the request of the Technical Office of the National Housing Agency and Housing and Home Finance Agency. Some time previously, the former office had conducted a survey of the locations where lightweight aggregates are produced.' A study of this information discloses that the producing centers are widespread and that certain areas, notably the region east of the Mississippi River and especially the southeastern states in the sections along the Atlantic Coast, have only a limited number of such plants. The situation has been alleviated to some extent with new plants having been erected near Richmond, Va., and Lansford, Pa. Experiment Stations of the Federal Bureau of Mines at Tuscaloosa, Ala., Norris, Tenn., and College Park, Md., have investigated types and sources of potential raw materials such as clays, shales, and slates, as well as methods and procedures for utilizing these materials for their conversion into aggregates, and have published the data as a Bureau of Mines report.' Structural Uses of Lightweight Aggregates: Production of masonry blocks in the United States has averaged close to a billion units a year for the past three years, and of these it is estimated that more than 40 pct consisted of the lightweight type. It is anticipated that the future will witness an increase in this percentage in view of the superior insulating properties, decrease in dead weight, and ease of handling, transporting, and laying units of this type. Lightweight aggregates are used extensively in multistoried buildings in which the weight of the walls and floors is carried by a structural steel framework. The substitution of a lightweight concrete for normal concrete in a building of this type has brought about in many instances some or all of the following advantages:

Jan 1, 1951

By John E. Conley, John A. Ruppert

W. B. Mather—A minor recommendation that may be offered to improve the paper is the inclusion of a map of Oregon showing the general location of the various deposits. This is of especial importance to persons like myself who are not familiar with the various areas and counties mentioned. N. S. Wagner and R. S. Mason (authors' reply)—We agree that an index map of Oregon showing the location of the various nonmetallic deposits would add to the paper (fig. 1).

Jan 1, 1951

By John A. Ruppert, John E. Conley

W. B. Mather—A minor recommendation that may be offered to improve the paper is the inclusion of a map of Oregon showing the general location of the various deposits. This is of especial importance to persons like myself who are not familiar with the various areas and counties mentioned. N. S. Wagner and R. S. Mason (authors' reply)—We agree that an index map of Oregon showing the location of the various nonmetallic deposits would add to the paper (fig. 1).

Jan 1, 1951

By Michael J. Messel

OF the various minerals that occur in fibrous form known as asbestos, chryso-tile is the variety most in demand for commercial uses, and, last year, over 683,000 tons of the various grades were produced in Canada and United States, exclusive of African and Russian production, which figures are uncertain. Production has not been able to keep up with the increased demand, and an acute shortage exists. Canada, Russia, and Africa are still the most important producers. However, Russia consumes most of its production at home and exports very little. The United States consumes over 60 pct of the total production and produces only about 4 pct of the total from deposits in Vermont and small quantities from Arizona. This paper will review mainly, some of the more recent developments concerned with the extraction and processing of this fibrous mineral for various industrial uses, such as textiles, insulation, building materials and brake linings. Four of the more important factors that have influenced recent developments are: 1. The lack of discovering and developing new deposits of any important size to supply the increased demand. 2. Rapid postwar expansion of industrial uses, especially in asbestos cement products, together with in-rreased manufacturing facilities. Euro-peal) countries are again back on the market with their demand. 3. The ability of manufacturers to develop their technique of blending fibers and obtaining more utility value out of each ton of fiber, together with the utilization of shorter grades of fiber to obtain equally as good products. In the past, many manufacturers were wasteful in their use of fibers. 4. The struggle for reduced operating costs, in face of increased wages and prices of supplies, together with the necessity, at some mines, to change the method of mining from open quarry to underground. Most of the recent capital invested in the asbestos mining industry has gone into more efficient extraction of the fibers from the existing ore, especially in the recovery of the shorter grades. There has been very little new plant expansion. Progress in the utilization of shorter fibers has been so far reaching that some of the mining companies are retreating present tailings as they leave the mill, and others are considering retreating of the old tailing dumps for recovery of fibers that, until recently, were not saleable and were discarded as part of the tailing. Many of these dumps contain much valuable fiber from days when milling was very inefficient. It might be appropriate to mention here that the present known asbestos reserves of proved commercial value (excluding Russia) are being depleted at an alarmingly rapid rate, about 10,000,000 tons of ore is being mined annually. No new deposits have come into production during the last 15 years, with the exception of certain deposits in Africa, which are the most promising, and minor developments in Canada, Venezuela, Cyprus, Australia, and Brazil. The African deposits are the only ones that hold promise of developing large reserves. Unless new deposits are developed, in twenty years or maybe sooner, the supply picture will not be a very bright one. Stimulated by the acute shortage, increasing fiber prices and technical developments, many new areas are being prospected in Canada, United States, New Zealand, Newfoundland, South America, Europe, Africa, and China. From information now available, it appears that no real progress has been made in duplicating this rare development of nature by producing synthetic asbestos. The most promising experiments were carried out at the University of Leipzig, but they seem far from practical. There has been marked progress in fiber glass manufacture, but so far, it has replaced asbestos only in very few instances for minor uses. Asbestos ore and the fiber it yields are different in some respect at each mine and vary usually in the following: 1. Percentage of fiber content by weight to the gangue. 2. Variations in proportions of long and short fibers, some deposits being predominantly long fiber and others short fiber. 3. The hardness of the rock in which the fiber occurs. 4. The nature of the fiber, as to

Jan 1, 1950

By Michael J. Messel

W. P. MOULD*—Has consideration been given to the problem of retreating the 4,000,000 ton tailings pile to recover the very considerable amount of asbestos fiber that was lost over the years due to insufficient operation and poor recoveries? Also, what was known about the possible content of chromite and the sulphides of nickel and cobalt? M. J. MESSEL (author's reply)—Consideration was given to the problem but nothing concrete has been done up to this time. W. P. MOULD—I am certain the tail- ings contain a very considerable quantity of fiber, not all of which is in the shortest lengths, because in the milling of talc rock from a neighboring location having a common origin with the asbestos bearing serpentine source of the tailings pile, a concentrate carrying 15 pct Ni and Co in complex sulphides and constituting about 4/10 of 1 pct of the talc rock was recovered. In the belief that the tailings also contained an appreciable content of chromite (then in demand, 1937) it was suggested to the management of the asbestos company that a truck load of the current tailings be sent to the flotation plant of the talc company where it would be put over the concentrating tables in an effort to discover the presence and roughly the percentages of chromite, nickel, and cobalt. Preparations for the test were woefully inadequate and the test was completely snarled up by the surprisingly large quantity of asbestos fiber from 1 in. long down to very short fiber, all of which matted up and plugged launders and pumps with disastrous effects and practically the total loss of the sample. If anything was indicaded by the test, it was that a wet process for milling asbestos was worthy of very serious consideration. M. J. MESSEL—A wet milling process for tailings retreatment only, is at present under study at our plant. One asbestos mining company in Canada has constructed a fairly large test plant for this purpose, but as yet no definite results have been obtained other than in a small test unit plant which were in some respects quite encouraging.

Jan 1, 1950

By M. L. Brashears

IN the last 15 years industrial use of ground water has more than doubled, and in 1951 amounted to 5 billion gallons per day. A similar sharp increase in the utilization of ground water for irrigation and public-water supply occurred in the same period. In many areas rapid increase in withdrawal from wells has taken place almost entirely unhampered by regulatory control and with little or no integration of effort. As might be expected, the chief interest in many regions has been maximum production rather than sustained perennial yield. As a result, widespread depletion of underground reservoirs and deterioration of the quality of the water stored in them has taken place in many areas, even though total pumpage in the United States is far below ultimate potential. Of even more concern is the fact that excessive withdrawal has drawn salt water into the reservoirs beneath many heavily populated centers along the Atlantic, Gulf, and Pacific coasts, causing costly abandonment of pumping plants.' Many hydrologists expect that consumption of water will rise rapidly in the near future, and some predict that industrial requirements will more than double in the next decade.2,3 Thus it appears likely that the draft on many already heavily pumped underground reservoirs will be greatly increased and the search for additional sources of usable ground water intensified in years to come. In view of this, industry as a whole will be forced more and more to recognize the potentialities and limitations of ground-water reservoirs and to utilize them more effectively to prevent costly water shortages and disruption of production. Through painful experience, some industries are already well aware of the need for effective water utilization, and have managed individually or through joint effort to check trends threatening to deplete underground reservoirs completely or to impair the quality of the water. Various remedial measures have been used to bring about successful management of local or regional ground-water resources. Of these, replen-ishment of aquifers by recharge wells or basins has played an important role in overcoming some ground water problems. Artificial recharge of underground reservoirs by water spreading has been practiced successfully in the United States for many years. In the West it has become an important method of salvaging flood run-off for irrigation of crops and maintenance of public water-supply reserves, and it is used to some extent in parts of the East. Artificial recharge by means of wells, on the other hand, is a relatively new development. Until recently it was employed in only a few areas, principally along the East coast. For the last few years, in the ever increasing search for additional water supplies, industry has had greater recourse to this method. Utilization of recharge wells to control the temperature and quality of underground water supplies is also being considered seriously. Operation of recharge wells, like water spreading, is governed largely by local conditions. It requires water relatively low in turbidity, whereas in some areas water spreading has been used successfully with water of high turbidity and silt content. However, water spreading must be employed in large areas and can be carried on effectively only where aquifers crop out at the surface. Recharge wells can be used in limited space. Recharge wells are similar to production wells except that the water flows in the opposite direction. Thus any water-bearing bed that will yield water to wells may be recharged by wells. Often, however, the water available for recharge is of a different character and temperature from that existing in the ground-water reservoir and if transmitted directly underground from a recharge well to a production well might require expensive or difficult treatment before it could be used. Fortunately the physical characteristics of reservoir beds, which control the movement and behavior of ground water, are generally not homogeneous. Moreover, the movement of ground water is very slow because of the frictional resistance of the reservoir beds. By taking full advantage of hydrologic and geologic conditions, it is therefore possible in many instances to bring about favorable changes of temperature and dilution as the water moves from the recharge wells underground to the production wells. Furthermore, if the natural quality or temperature of ground water is unfavorable for industrial purposes, recharge wells may be used to introduce water of more favorable quality or temperature into the ground-water reservoir. When water is discharged into a recharge well, the head in the well is increased. Because of this, a cone of elevation is produced on the water table or the artesian pressure surface in the area surrounding the well. The cone of elevation is similar to the cone of depression produced around a pumping well except that the apex of the cone is above the water table or artesian pressure surface. Thus if a recharge well and a production well tapping the same water-bearing bed are close together, as would be the case at many industrial plants, some of the water discharged from the recharge well would be drawn into the production well within a short time. Under such conditions it is apparent that water of unfavorable temperature and chemical characteristics should not be used for recharging. The more important ground-water reservoirs in the United States often consist of alternating layers of impermeable beds and porous material that will yield water readily to wells. Physical characteristics of individual beds in a ground-water reservoir may not persist over great distances, the impermeable layers grading into beds that will yield large quantities of water. Thus the water-yielding material in underground reservoirs, whether large or small,

Jan 1, 1954