Fred D. DeVaney is a specialist in the field of grinding, iron ore concentration, and nonsulfide flotation. H e was born in Waubay, s. Dak.,in 1 9 0 1 . In 1 9 2 3 he graduated from the Minnesota School of Mines with an E.M. degree. H e held the Bureau of Mines Fellowship a t the University of Alabama in 1923-24, receiving his M.S. degree in 1 9 2 4 . DeVaney then started work for the U. s. Bureau of Mines at Tuscaloosa, Ala.; he remained there until 1927 and was then transferred to Rolla, M o . W h i l e with the bureau he studied ore concentration and published about thirty-five papers relating to problems in that field. Since 7942 DeVaney has been a research metallurgist, working on concentration of low-grade iron ores for Pickands M a t h e r & Company a t Hibbing, Minn. H e is a member of Sigma X i and of the Milling Methods Committee, American lnstitute of Mining Engineers.
FLOTATION Fred
D. DeVaney
URING the war the use of the flotation process has expanded greatly. Yot only have increased tonnages been treated in industry where its use had been common for years, but the process has been utilized in many novel separations. By far the greater part of our nonferrous metals was recovered from their ores by flotation. One of the first steps in the intricate processcs probably necessary for the production of the atomic bomb was the concentration of pitchblende from its gangue mineral at some mines by flotation, Although the tonnages of the sulfide ores of copper, lead, zinc, and minor metals far exceed those of nonsulfide ores separated by this method, many of the most interesting developments have been in the nonsulfide field. Some years ago when flotation was first adopted in the Florida phosphate district, the process was used to secure a small additional recovery from the washing plant wastes. Today in most of the plants the greater portion of the recovery comes from the flotation section, and the recovery from the washer proper is only incidental. Fine phosphatic sands are being concentrated economically that could not have been recovered by the older methods. The life of the district has accordingly been greatly lengthened. I n treating phosphate rock, the phosphate mineral is usually floated away from the quartz gangue by a tall oil and fuel oil in an alkaline circuit. At one Florida plant the concentrate grade has been improved by floating in the usual manner to reject the bulk of the silica and then giving the phosphate concentrate an acid wash to remove the fatty acid film. This concentrate is then re-treated by flotation, and the separation reversed by floating off in the froth the greater portion of the remaining quartz with an amine as collector. In the phosphate district the operators have developed a type of wet storage bin that has helped greatly in solving the troublesome problem of securing uniform feed to the flotation plant. These storage bins are upright cylindrical tanks from which the ore is either removed from the hopper-shaped bottom by a pipe, or is reclaimed by a diaphragm pump mounted on top of the bin. When the bottom discharge is used, the material at the bottom of the bin is kept fluid by a spray. Such bins are commonly built to supply the plant for a t least 8 hours. A t one mill the ore is sized into three bands before flotation; this step seems to give some additional selectivity since the reagent requirement can be better adjusted to suit the size treated. Swainson (16) described the operations in the Florida district in considerable detail. Fluorspar, particularly the chemical grade, has been in great demand during the war. This demand has come about largely through the need for large amounts of anhydrous hydrofluoric acid for the manufacture of high-octane
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gasoline. It has been supplied mainly through increased production from prewar flotation plants in the Illinois-Kentucky area and by the construction of new plants in this area as well as in the Rocky Mountain states. Since chemical grade fluorspar should contain a minimum of 98% calcium fluorideoand a maximum of 1% silica, precise separation is required. Several plants, after trying to replace oleic acid as a collector with cheaper fatty acids, have found it expedient to return to the use of distilled oleic acid. When calcite is present, quebracho is usually employed as depressant. Because of the high-grade concentrate required and the harmful effect of lime salts on the separation, this industry has found it essential to soften the mill water The zeolite method is usually employed, but one plant in the Rosiclaire district uses a lime-soda ash treatment. In World War I this country was shut off from its usual sources of potash and went to great lengths to recover small amounts from western saline lake deposits. Since that time American industry has developed the great potash beds in the Carlsbad, N.hiex., district to the point where no critical shortages developed during World War 11. This development was brought about by a farsighted exploration program and by the invention of successful concentration processcs. The adoption of the flotation process to the separation of two water-soluble minerals suspended in their own saturated- brine represented a milestone in the development of the flotation process. In separating sylvite (KC1) from halite (KaCl), two flotation processes are in use. I n one, sylvite is floated away from the halite by a cationic reagent of the amine type, by starch as a conditioning agent, and by a frother. The reverse separation, where halite is caused to collect in the froth and the sylvite passes into the underflow, is also practiced. Previously this separation was accomplished with coconut oil as collector, but this material seems t o have been displaced by naphthenic acid. -4 recent development in applying flotation to solids in saturated brines is the separation of lithium salts from the natural brine of Searles Lake, Calif. As a step in a complex refining operation, a lithium-sodium phosphate (LizNaPOd) is recovered. This concentrate is said to contain 19 to 21% LizO, which is considerably higher than that in the usual lithium ore concentrates. This process, first tried on a pilot plant basis in 1943, has been developed to the point where the potential capacity is greater than prewar world requirements ( 5 ) . Two plants, in which the lithium-bearing mineral spodumene was concentrated by froth flotation, were completed in 1943 Feldspar was a by-product at both plants (3). In our complex technical civilization, the need for one com-
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
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modity frequently has repercussions in industries seemingly not related. The tremendous demand for oil has resulted in a n increase in the number of wells drilled, many to a great depth. I n drilling deep holes, i t is necessary to use drilling muds of high density. These muds are customarily made up largely of ground barite which has the high density of 4.5. This has made for increased activity in the barite industry. Two large flotation plants in the Magnet Cove area of Arkansas are producing 25,000 tons monthly of flotation concentrates. Other mines at which flotation will be used are under development in Arizona, Nevada, and California. I n the flotation of barite ores, two general methods of treatment are in use. The barite can be floated with oleic acid, If the gangue minerals consist of silicates, cationic reagents such as amines can be used to float them and thus leave barite in the underflow. Where the latter method can be employed, it has some advantages in the preparation of the final concentrate. If fatty acids are used, the barite concentrate particles are covered with a film of fatty acid which mu burned off a t red heat to render the particles water disper If cationic reagents are used, no film forms and a simple drying operation suffices. The use of the flotation process in adjusting the lime-silicaalumina ratios in the raw materials used in making cement w a s increasing before the war. This increase was restricted during the war years, as the cement industry was one of the few that operated at reduced capacity due primarily to stoppage of road construction. However, a large modern plant was constructed for the Universal Atlas Cement Company at Northampton, Pa., which uses the flotation process. The cement industry in some areas faces the same problems that confront the metal industry?-namely, the utilization of lower grade materials. The use of the flotation process to concentrate lean available material rather than to mine higher grade material, if such high grade material requires more stripping or underground mining, will probably increase. The relatively small tonnage of coal being recovered by flotation from coal washery wastes is somewhat surprising in view of the clean-cut separations that can be made at low cost. Desliming of washery wastes for the rejection of claylike impurities, followed by the use of kerosene as a collector, is usually all that is required. The relatively low value of the product, together with the expense of dewatering and drying the final product, are believed to have been reasons why the process has not been more generally adopted. It is understood that recent tests in a high-speed continuous centrifuge have proved successful in cconomically dewatering fine coal fractions. One of the newest plants in which coal flotation is practiced is that of the Lehigh Navigation Coal Company a t Tamaqua, Pa., for the recovery of anthracite fines. Two more plants are contemplated (17). An earlier article gave considerable detail on the pilot plant results with this type of material (13). Much of the high-grade manganese ore produced in this country came from the flotation plants of the Anaconda Copper Company and the Domestic Manganese and Development Company in the Butte and Phillipsburg areas of Montana. The supplying of an unparalleled war demand for tungsten: after imports were cut off, was met by the construction and operation of B number of mills in the West. Improvements in the Rotation of the mineral scheelite contributed much to the success of these operations. A report on the operations of such a mill a t Mill City, Nev., by the Nevada-Massachusetts Company has recently been published (IO). The reagent combination is complex. The difficult separation of scheelite and calcite is accomplished by holding the p H a t 10.0 to 10.1 with soda ash, using a fatty acid mixture as collector and depressing the calcite with quebracho. Although there was much activity in the development of new methods t o treat low grade bauxite and other aluminumbearing materials, no flotation plants were put into operation. January, 1946
The Bureau of Mines had an experimental plant in operation in Saline, Ark., during 1945,but information regarding its operation has not been released. Runke and O’Meara (14) reported the results of laboratory tests on bauxite ores. Flotation of magnesite has been put into successful operation at two mestern plants of Basic Magnesium a t Gobbs, Nev., and Chewellah, Wash. For several years a great deal of experimentation has been done to develop a successful method for concentrating iron ores by flotation. I n view of the need for concentrating low grade ores and the tonnages required annually, this field has great possibility, On the Mesabi Range of Minnesota three pilot plants were in operation during the 1945 season. American Cyanamid Company, Mineral Separation, and Pickands Mather & Company have all done test work, but details have not been released. Battelle Institute is also carrying out a research program which includes flotation testing for a group of iron and steel companies. Clemmer and associates (4) published the results of a n investigation made on the red ores of the Birmingham, Ala., district. They employed anionic reagents in a strongly alkaline pulp to float quartz and found sodium hexametaphosphate to be a strong depressant for hematite. A new flotation plant was put into operation during 1945 by Consolidated Feldspar Corporation at Kona, N. C. Feldspar is the chief product, with quartz and mica as by-products. The rock treated is a fin0 grained quartz-feldspar pegmatite known as alaskite. This mill is understood to be the first commercial plant using flotation as a method of concentrating feldspar. It had previously been separated by expensive and inefficient hand sorting (9). hlany plants have been constructed throughout the country t o concentrate sulfide ores. The newest of the large plants treating copper ores is that of the Cananea Consolidated Copper Company at Sonora, Mexico, which mills 12,000tons per day of ore containing about 1% copper ( l a ) . A feature of the flowsheet is the thickening of the primary and cleaner flotation Concentrates and the sending of these concentrates directly to ball mills for regrinding before treatment in the recleaner circuit. I n the cleaning, recleaning, and grinding circuits the lime content is held near the maximum to drop pyrite. Morenci increased its production to 60,000 tons per day by enlarging its mill in 1943. PhelpsDodge Corporation was scheduled to put into production, before the end of 1945, a new concentrator a t Warren, Ariz., to treat 400 tons of lead-zinc ore per day. A new 600-ton-per-day mill was put into operation in 1944 by the Missouri Cobalt Company to treat by selective flotation the complex lead-eopper-cobaltnickel ore of sdutheastern Missouri. Another new mill in the same area is the 300-ton plant of Park City Consolidated for treating lead ore. The flotation treatment of Cerro de Pasco complex ores was published recently (6). At this company’s four mills, four kinds of concentrates are produced: copper, lead, zinc, and pyrite, each containing values in gold, bismuth, and other metals. Much experimental work has been done by western operators in an effort to find more potent collectors and more selective reagents, and thus to reduce middling loads. Minerac hag been used successfully at several copper plants to achieve this purpose. The use of calcium lignin sulfonate as a slime dispersant, not only in copper but in other base metal plants, seems t o be increasing. The purpose of this addition agent is to disperse slimes and to give cleaner concentrates. In some plants using a high-lime flotation circuit, the .addition of small amounts of a phosphate, such as sodium septaphosphate, is helpful. This phosphate has the property of rendering harmless the ill effects of a lime buildup through the formation of a soluble complex lime phosphate. The flotation symposium of the American Institute of Mining and Metallurgical Engineers brought forth some excellent papers (f). Barr (2) discusses his experience in floating phosphate and potash ores. Pallanch (11) elaborates (Continued on page 96)
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FLOTATION CONTINUED FROM PAQE 21
on the idea that generalizations re ing flotation are dangerous. Fahrenwald (7) discusses the information that may be gained from batch frothers help or hinder flotati engineer (16)was revised an an up-to-date section on the theory and LITERATURE CITED
(1) Am. Inst. of Mining and Met. Mining Tech.. March, 1944. ( 2 ) Barr, J. A., Zbid., Sept., 1946.
s., Flotation Bymposium,
(3) Bowles, Oliver, Milting and Met., Feb., 1944, q6. (4) Clemmer, J. B., et at., U, 8. Bur. Mines, Rept. fnvestigation 3799, 42 (1945).
(5) Eng. Mining J., March, 1945,93 (“Searles Lake, Major Lithium
Source”).
(6) Ibid., Nov., 1945 (“Cerro de Pasco Entbrprise”) (7) Fahrenwald, A. W., Zbid., Jan., 1945, 74-6. (8)Zbtd., Oct., 1945, 94. (9) Mining Congr. J., “New Kona Feldspar Mine and Mill”, Oct., 1945, 81.
(10) Nevada-Massachusetts Go., Eng. Mincng J.. July, (11) Pallanoh, R. A,, Mining and Met., 26, 167-70 (19 (12) Ramaey, R.33..8 % Mining ~. J., Dec., 1944,74-88; Sept., 1945, 78-8.
(13) Rubert, C . D., and Parton, W. J., Deco Trefozl, June, 1944. (14) Runke, S. M., and O’Meara, R . G., Trans. Am. f n s t . &fin& Met. h’ngrs., 159, 218-26 (1944). (15) Swainson, 8. J., Eng. M i n i n g J., Oct., 1944,469-74. (IS) Taggart, A. F., “Handbook of Mineral Dressing”, New York, John Wiley & Sons, 1945. (17) Wright, F. C., Jr., Mining Conur. J., Feb., 1945,78.
DRYING C O N T I N U ~ DFROM PAGE
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effect of the variables on capacity. Some performance data for this type of equipment are available on t sludges (1,79,80). Although some information is presented on the operation of kilns ( 2 2 , 17,18,30,47,60, 76,83,84,loa), no data are available which would allow ready design of such units. Bayard (91) recorrelated the data of Sullivan, Maier, an present expressions for estimatirlg the time o kiln under different operating conditions. The d y i n g of inks has received some attention (19, 90). Bead (90)found that tlie rate of drying is affected by the pH of the coating on the paper. The only articles on rotary dryers describe the operation of the Roto-Louvre type (9,.@), M in the field of rotary drying, GENERALDBYING.Farmer ( views available drying methods and discusses the relative merits of steam, gRS, electricity, and direct fiting. The importanbe of dewatering mechanically in SO far as possible, of providing adequate insulation, and of preventing leaks is stressed. A nontechnical review of dryers, principally for (86‘). An introductory art principles of drying solids s for drying, the types of by Marshdl (71)discusses moisture mdvement in a selection of dryers. A lengthy paper by of convection drying and illustrates t h e calculations involved in January, 1946
designing a convection-type dryer. Dryer design is based on moisture pickup of the air rather than on drying rates. The author stresses the importance of the proper amount of air recirculation to steam economies. I n another paper (107) the author g,oes into more detail regarding the optimum amount of air recirculation. He concludes that, with drying temperaturea in excess of 260” F., the drying rate when removing unbound moisture will actually increase with an increased amount of recirculation. This is open to some question. RELATEDSTUDIES,A few papers not directly involving drying are worthy of mention. The drying characteristics of materials are sometimes related to their vapor transmission characteristics. The latter property was measured for a number of different insulating materials by Rowley and Lund (92). Waddams (109) describes a method for easily determining the thermal conductivity of granular solids. The water retention characteristics of a solid are of importance in understanding the basic phenomena relevant to drying. Wadsworth (110) interprets the moisture-vapor pressure curves for some soils and concludes that the sigmoidal shape of the curve is thc result of two independent processes. At low vapor pressures the moisture retention is caused by unimolecular adsorption which follows the Williams-Henry law. A t high vapor pressures the moisture retention is caused primarily by capillary condensation. These two phenomena have been separated for a few soils, Nutting (76) develops a thermodynamic relation between the amount of fluid retained by a solid at any temperature and pressure and the energy required to transfer it to the vapor phase. He indicates that the heat required to liberate the last traces of moisture from a solid is considerably in excess of the heat of vaporization of the water. Experimental data on the moisture retention of minerals are presented and interpreted in the light of the thermodynamic theory. The mass transfer in the of gases through granular solids at low Reynolds numbers studied by Wilke and Hougen (111). This work supplements that of Gamson, Thodos, and Hougen (46) and of Hurt (64,and places the study of drying by through circulation on a firm fundamental basis. The evaporation of water from a free water surface was studied by Hickox (62),and many of the data from meteorologiof mass transfer to the cal sources are correlated b process of’heat transfer. M data are in line with the correlation proposed by Shepherd, Hadlock, and Brewer (96‘) for drying during the constant-rate period. The effect of pan length on the rate of evaporation is discussed. Similar experiments on the evaporation of water from cloth surfaces arc reported by Rees (91). He found that the rate of evaporation from waterproofed fabrics was considerably less than that For nonwater-repellent fabrics, Osburn and I h t z (78) studied the effect of structure as a variable in the application of diffusion theory to extraction. Most of the results and conclusions obtained can be directly adapted
