PHOSPHATE ROCK INDUSTRY of the UNITED STATES. I WILLIAM H. WAGGAMAN 801 Hollingsworth Avenue. Lakeland, Florida
Part I of this @per discusses the chemical nature and probable geological origin of phosphate deposits. Data pertaining to the economic significance of the world phosphate industry and the relative part played by American phosphates are outlined. The important American phosphate deposits are described briejly.
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HERE are few, if any, more important minerals mined in the United States than phosphate rock. While we lead the world in the production of coal, sulfur, petroleum, and most of the metalliferous ores, none of these contribute, except indirectly, to our supplies of food and clothing. Phosphate rock, however, is one of the essential raw materials of agriculture, and one without which this fundamental industry (despite its present surpluses) could not long keep pace with population demands. In addition to its value as a fertilizer material, however, phosphate rock is the raw material from which elemental phosphorus and phosphoric acid are produced, and the latter compound is being used in everincreasing quantities in the arts and industries. By phosphate rock is meant a mineral consisting largely of phosphate of lime, usually expressed as tricalcium phosphate, Caa(P04)z,but the results of recent researches1indicate that in most deposits the phosphate compound is of a more complex nature. Nevertheless, the main constituents are Pz05and CaO combined with small percentages of fluorine, and forming a rock very resistant to weathering influences. ORIGIN OF PHOSPHATE ROCK
The original source of phosphate rock is apatite, a crystalline mineral widely distributed in igneous rocks but occurring chiefly in veins and intrusions and only under rather exceptional conditions readily and cheaply minable. Through countless ages these igneous rocks have been gradually disintegrated by natural forces and their phosphate content slowly dissolved by carbonated waters. Some of the phosphate became a constituent part of the soil and continues to he taken up by plants, which, in turn, are consumed by men and animals to build up bone and tissue. Much of this PzOs is returned to the soil after the decay of animal and vegetable life to take part again in Nature's well-ordered cycle. Vast
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' HENDEICKS, S. B..HILL, W. L , JACOB, K. D., AND SON, M. E., I d . Eng. Chem., 23, 1413 (1931).
JEWER-
quantities of P205in very dilute solutions, however, have found their way to the sea where the phosphoric acid has been taken up and concentrated by living organisms. The phosphoric acid has also reacted with other products of rock decomposition to form new and secondary phosphates which have been deposited as sedimentary strata on the ocean bottom. Subsequent geologic disturbances have caused these strata to be raised above the sea level, and in some cases to he actually exposed a t the surface of the ground. I t may be said, therefore, that the bulk of the workable deposits of phosphate now known are directly of marine origin, whether they take the form of unleached guano from birds feeding largely on fish, or sedimentary strata derived from lower forms of marine life and subsequently enriched and redeposited from aqueous media. No mineral is found a t a greater number of geologic horizons, occurs under a wider range of natural conditions, and varies more in its physical properties than phosphate rock. It is found in strata of Ordovician, Silurian, Devonian, Carboniferous, Jurassic, Cretaceous, and Tertiary age, and in even more recent strata. It occurs in massive seams which are mined or quarried like coal and limestone, as pebbles or nodules imbedded in a loose matrix, and even as a soft clay-like material resembling kaolin. It varies in color from almost jet black to rock of dazzling whiteness. Some of i t is hard and dense while other varieties are soft and porous and contain cavities filled with foreign material which must be removed by washing. Commercial grades vary in phosphate content from 26.5 to 39.0% PpOs [58.0 to 85.0% Ca3(P01)2]. The impurities with which it is associated are usually carbonate of lime, silica, iron and aluminum compounds, and small percentages of fluorine combined as a constituent part of the rock. PRODUCTION OF PHOSPHATE ROCK
Ever since the discovery of the Florida phosphate deposits, the United States has had a greater annual output of phosphate rock than any other single country. For years we not only supplied our own fertilizer needs, but furnished this fertilizer material to many of the European nations. Now, however, the combined output of the countries in northern Africa (Tunis, Algeria, Egypt, and Morocco) exceeds our production by fully thirty per cent. The phenomenal development of the Moroccan deposits which can he readily and cheaply mined has caused a serious curtailment in our exports of this mineral to Europe, and there is every indication
that the future expansion of this industry in the United States must depend largely upon the domestic demand. Soviet Russia is also becoming a factor in the phosphate industry and will probably soon be in a position not only to supply her own requirements but to furnish a surplus for export.= It is to the interest of American agriculture, however, to conserve our supplies of this important mineral, and though our reserves of phosphate rock are enormous, they are not inexhaustible and will be needed to meet the demands of future generations. Hence it is not greatly to be regretted that the Old World is no longer dependent on this country for its supplies of this basic fertilizer material. The world's production of phosphate rock according to the latest available statistics3is given in Table 1.
east of the Mississippi River. Practically all of the middle western states draw on these deposits for their supplies of phosphatic fertilizer. The Arkansas phosphates, while of rather low grade and as yet exploited to a very limited extent, are well situated to furnish fertilizers to the states just west of the Mississippi River and east of the Rocky Mountains. Finally, the vast deposits of phosphate rock in Utah, Idaho, Wyoming, and Montana serve California and the northwestern states, and even furnish a limited quantity of concentrated fertilizer materials (triple superphosphate and phosphoric acid) as far east as Illinois, Indiana, and Ohio. The limited use of fertilizers west of the Mississippi River, however, and the long haul to the established market, has held back the development of the western phosphates, but this vast : Rocr (1927-1931)
Algeria ............................ AngaurIPland ...................... A U S ~ ~ ........................ ~ I ~ ~ . . Belgium ........................... Canada ............................ China ............................. chrisfmas Island.. ................. Curacao Island ..................... ~ p y p............................. t
919.108 64.383 893 39,760 137d 12,000 118,553 108.881 279,389
India (British). ..................... 613 Indo-China ........................ 20,700 japan ............................. 75.386 Madaga-r ........................ 6,480 ~ ~ idand.. k ~ t ~ 135,666 ~ Morocco (French) 1,400,000 New Caledonia ..................... 9,000 Ocean and Nauru Islands.. 604,372 Philippine Islands.. ................. 705 poland ............................ 17,614 Rumania ................................ ~uesia 56,460 seyehelle~lolands.. ................. 11,511b Soain 4,202 Tunis ............................. 3,074,950 united States.. .................... 3.221.589 ~olol 10,403,771
...................
................... ..........
.............................
..............................
............................
Estimated. b Exports.
875.947 65,358 138 15,510 582d
......
113,687 104,194 20.563 6,859 219,200 Nil 818 19,629 58.776 8,450 136,306 1.337.100 7,000 509,971 1,550 20,311
......
121,711 15,655 7,897 2,789,000 3,557,604 10,209,816
upatite. d Apatite and phosphate rock.
DISTRIBUTION OF OUR PHOSPHATE DEPOSITS
IPZP
1931
747,035 65,494 71 40.330 1,07Sd
459,077
......
119.756 103,289 215,311 8.352 189.000 Nil 22 18,772 14.573 13,441 242,990 1,608,249 5,563 585,844 1,492 39.294 1,629 150,OOc-= 12,789b 7,626 2,511,000 3,821,217
......
121,858b 87.497 313,478 4,850 145.700 Nil 308 30.30 27,713 11,150 176,075 1,779,008'
......
512.265
...... 96 ...... Nil ...... ......
73,774 242,205
......
...... ...... ......
12,871
......
8.00 111,422 900,000
......
392,172
11,737.490 Marketed production.
agricultural area will eventually consume enormous tonnages of phosphate rock as the so-called "virgin lands" become depleted by constant cropping.
The deposits of phosphate rock in the United States are rather well distributed to supply our great agricultural centers. The Florida phosphates not only PRESENT RELATIVE IMPORTANCE O F T H E U N I T E D STATES PHOSPHATE DEPOSITS serve the South Atlantic states which draw their From the standpoint of development and convenience wealth chiefly from tobacoo, cotton, and fruit, but these deposits, being within a relatively short distance to the market, the phosphate deposits of the United of the coast, supply most of the factories along our States rank as follows in the order of their present ecoeastern seaboard which furnish fertilizer to vast areas nomic importance: the phosphates of Florida; the far removed from the coast. The Florida phosphate Tennessee phosphates; the western phosphates; the is shipped not only as far north as New England but deposits of South Carolina; and the phosphates of Kentucky and Arkansas. The best index of their relaalso to Canadian factories. The Tennessee phosphates are conveniently located tive commercial importance is the annual production to supply the inland southern states and those just of rock, given in Table Z,3 from these various fields. T H E FLORIDA PHOSPHATES ' H~nscn.A,, Chnn. & Met. Eng.. 39, 590-3 (1932); VOLFKOVICH, S . I., AND BERLIN,L. E., J . Ckem. Ind. (Moscow), 7, 86There are two commercially important types of 105 (1930); ZAPADINSKII, M.B., ibid.. 7, 964-71 (1930). phosphate rock in Florida, namely "hard rock" and a JACOB, K. D., Mimd Ind., 1932.
TABLE 2 PRODUCrTON OF PBOSPBATE ROCK I N TBB UNITED SIATBS
1929
Florida Hard Roelr.. .. Florida Land Pebble?. Told, Florida.
.....
......... ...............
Tenner.eeh..
Idaho Montana ............ Wyoming Told, W . States.. .. South Carolina....... Kentuck,.
...........
...........
Tom Voluc 72,424 8267,218 9,633,856 3,015,874 $9,901,074 3,088.298 3,097,104 633,939 141,931 35,899 400 40 12,750 2,679 $155.000 38,618 No produdion since 1922 No production NO production since 1912 3,760,855 $13,193,259
1930
Tons 81,753 3,166,318 3,248,071 611,045 59,932 6,005 1.339 67,276
Vnluc 6517,229 10,273,076 810,790,305 2,938.525 234.543 27,451 6,000 5268,000
Tons 57,224 2,004,242 2,061,466 343,622 60.978 67,893 1.000 129,871
3,926.392
513,996,830
2,534,959
'Inelude. a nmall quantity of soft phosphate. b Brown and blue phosphate.
"pebble phosphate." A thud type, known as "soft phosphate," is also mined to a limited extent for local consumption, being applied directly to the soil without treatment with acid to render its P20bcontent soluble. Hard-rock phosphate, while the first to be discovered in the state and of the highest grade produced in this country, no longer ranks in importance with the Florida pebble phosphate. Practically all of the bard rock produced is either exported or used in this country for the manufacture of pure phosphate products. The hard-rock region lies toward the west side of the Florida peninsula, extending in a general.north and south direction from Suwanee and Columbia Counties to Citrus and Hernando Counties, a distance of over one hundred miles. Two railroads serve this region and all rock is shipped to a central drying plant at Fernandina, a port on the east coast, and from there by boat to Europe and our eastern seaboard. The rock belongs to the Oligocene epoch and occurs as nodules and bowlders imbedded in a matrix of sand, clay, and soft phosphate from which it must be separated by a washing process. The deposits are covered by an overburden of sand and clay ranging from a few inches to t h i i y feet or more in thickness, and the rock rests upon a relatively pure limestone. I t is generally conceded that these deposits are of secondary origin4 and are derived from formations which are now almost entirely lacking in the phosphate area, but are found in strata bordering these regions. The replacement of the original limestone by calcium phosphate, and the precipitation of phosphoric acid from solution were the important factors in the formation of these deposits. These deposits are quite irregular in their occurrence and require the most careful and detailed prospecting to determine their value and extent. I t is because of this irregularity, and the necessity of handling large tonnages of foreign material in order to extract a relatively small percentage of marketable product that the mining of hard rock is so much more costly than that of Florida pebble phosphate. The pebble phosphate deposits of Florida are the most extensively worked of any in the world, being approached only by those of Tunis. This type of phos-
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' SELLARBS,E. H., Fifth Annual Report, Fla. Geol. Survey
(1913);MATSON,C. G.,U. S. Geol. Survey Bull.604 (1915).
pbate supplies most of the phosphatic fertilizer requirements of the United States, and a large tonnage is still exported to European countries. The area at present productive comprises the eastern part of Hillsboro County, the southwestern part of Polk County, and the northwestern part of Desoto County. This region is served by two railroads and the mines are from twenty to fifty miles from Tampa and Port Tampa, from which most of the rock is shipped by boat to Europe and our eastern seaboard. These deposits are also of Tertiary age, but more recent than the hard-rock phosphate found to the north. The chief formation in which the pebble phosphate is found is locally known as the "Bone Valley gravel.'' It is believed that the pebble deposits are derived from the same source as the hard-rock phosphate but, whereas the latter are chemical precipitates or replacement deposits, the former are residual deposits from erosion of the parent f o r m a t i ~ n . ~ The pebble phosphate region is relatively level and the deposits much more uniform than those in the hardrock area. Not only is the average yield per acre greater, but the matrix contains as a rule a higher percentage of recoverable rock. Moreover, the relatively small size of the pebbles makes it possible to employ the hydraulic system of minmg which is both effective and cheap. Deposits of pebble phosphate range from a few feet to thirty feet or more in thickness, with an average thickness of about twelve feet. The pebbles vary in color from light cream to black, and in size from those as fine as sand to nodules as large as one's fist. The average quantity of phosphate recovered from the matrix by merely washing and screening is in the neighborhood of twenty per cent., but within the past few years the principles of flotation have been applied successfully to the separation of very fine phosphate granules from the silica sand with which they are intimately mixed, and this process bas made it possible to effect a considerably higher recovery of marketable phosphate. Pebble phosphate ranges in grade from 66 to 77% tricalcium phosphate, but the average is about 72%.
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SELLARDS. E. H.. Seventh Annual R e o o r t . FLa. Geol. Survey
(1915)
TENNESSEE PHOSPHATES
There are three distinct types of phosphate in Tennessee, namely, the brown rock, the blue rock, and the white phosphate. The last-named, however, is so pockety in nature that its exploitation has proved unprofitable and only the blue and the brown are now being mined. These deposits occur in what is known as the Central Basin of Tennessee and in the valleys of the western part of the Highland Rim surrounding this Basin. The area covers approximately 7000 square miles of gently undulating country, but the phosphate deposits have been developed only in the western part of this area. Mining operations are conducted in Lewis, Maury, Hickman, and Giles Counties, and the region is served by two railroads which afford excellent transportation facilities to the southern and middle western states. The brown rock phosphate is of Ordovician age.6 This type of rock is derived from phosphatic limestone by the leaching out of the more soluble carbonate of lime, the removal of which was attended by a diminution in thickness and a settling of the phosphate strata. Some secondary deposition has also taken place in the pores of the leached mother rock. Brown rock varies in color from gray to a deep chocolate brown, and in texture from a porous rock disintegrating into a phosphatic sand to a hard, close-grained rock quite resistant to weathering influences. The beds range in thickness from a few inches to twenty feet or more, with an average thickness of six to eight feet. The overburden also varies considerably from place to place, but is of such character that it can usually be readily removed by steam shovel, drag line, or by hydraulic means. The average grade of the marketed product is from 72 to 75% tricalcium phosphate, but certain deposits yield rock running as high as 78%. Tennessee blue rock phosphate belongs to the Devonian period6 and a t present is mined only in Lewis County near the little town of Gordonsburg. This type of rock occurs as a conglomerate deposit, derived in part from the underlying Ordovician limestone, and in part from the remains of marine life which were more highly phosphatic than those of the Ordovician period and hence required little or no subsequent leaching to render them of economic value. Blue rock occurs as distinct strata, varying in color from gray to bluish black, and in texture from a hard, massive, close-grained rock to coarsely oolitic material which is rather easily disintegrated. The thickness of the beds varies from a few inches to four feet, with an average thickness of about two and one-half feet. No bed less than eighteen inches thick is considered worth mining. The rock is overlain by a massive blue-black shale, three feet or more in thickness, and hence it is usually necessary to employ underground methods of mining. 'HAYES AND ULRICA, U. S. Geol. Survey ColumKa Folio 95 (1903); HOOK, J. S., Resources of Tenn., 4, 514 (1914).
The average grade of this type of phosphate is about 72% tricalcium phosphate, though individual deposits will sometimes run over 75%. WESTERN PHOSPHATES
The most extensive deposits of phosphate rock in the United States, and probably in the world, occur in southeastern Idaho, western Wyoming, northern Utah, and western Montana. These fields have also been traced into Canada. Most of the development work in this vast area, however, has been done in southeastern Idaho and on the Idaho-Wyoming border. The phosphate region is served by two railroads, though some of the rich deposits are too far removed from transportation facilities to waxrant their commercial development a t the present time. The western phosphates are generally regarded as original sedimentary deposits laid down when that portion of the earth's surface was submerged in water. They are of Carboniferous age and occur in both Permian and Mississippian rocks, but the deposits in the former formation have so far proved of the greater commercial importance.' The topography of much of this area is extremely rugged, the phosphate strata being folded, faulted, and submitted to intense erosion. As Mansfield states, however, the phosphate owes its exposures to these disturbing erosive forces, as otherwise they would be buried too deep to render their commercial exploitation ~ossible.~ These deposits resemble somewhat the blue phosphate rock of Tennessee, but the beds are usually much thicker. The richer strata are from two to six feet in thickness and contain from 65 to 75% tricalcium phosphate, and less than 3% of iron and aluminum oxides. The beds of phosphate are interstratified with limestone and shale, which a t present are regarded as of little commercial importance though many of these strata are highly phosphatic. Most of the development work in this area is being done by a large copper company in Montana, which utilizes the rock to market its surplus sulfuric acid, producing thereby both triple superphosphate and phosphoric acid. SOUTH CAROLINA PHOSPHATE
The phosphate area of South Carolina lies along the coast in a belt about twenty miles in width, extending from the Wando River in Charleston County to the Broad River in Beaufort County. This rock belongs to the Tertiary period and according to Rogersgis derived from the Edisto Marl which is believed to be of Miocene age. The rock occurs as bowlders, nodules, and small pebbles in a matrix of sand and clay somewhat similar to that found in the
' MANSFIELD, G. R., Am. 3. SSci., 46, 591-8 (1918).
MANSPIBLD, G. R.,Second Pan-American Scientific Can-
gress (1917).p. 23.
' ROGERS.G. S.. U. S. Geol.Survey B d . 580 (1914)
Florida pebble regions. The nodules are much pitted and these pits are filled with clay and foreign material which must be washed out before the product is marketable. The South Carolina phosphate beds have an average thickness of only one foot and hence mining is considerably more costly than in the Florida pebble regions where the beds are twelve feet and more in thickness. The rock is also of a much lower grade, averaging about 60% tricalcium phosphate, and containing a rather high percentage of carbonate of lime. While the South Carolina phosphate deposits are by no means exhausted, and are excellently located in regard to transportation facilities and proximity to the fertilizer market, the higher grade and more cheaply mined deposits of rock in Florida have gradually caused a curtailment in the output and in 1925 mining operations were suspended. PHOSPHATES OF KENTUCKY
The phosphate deposits of Kentucky so far developed have proved to be of such limited extent that they are no longer a factor in the industry. The more readily accessible deposits have been mined out and in 1926 operations were suspended. Prospecting for phosphate has been carried on intermittently a t various places in Jessamine, Scott, Woodford, and Franklin Counties, but only in Woodford County, a t Midway and Wallace Stations, close to the Louisville and Nashville Railroad, has any quantity of the mineral been mined. The Kentucky phosphate region forms part of the great Cincinnati agricultural line, extending from Nashville, Tennessee, in a generally northeasterly direction throuzh Lexington County almost to Cincinnati. South of that city i t divides into two broad domes, one culminating near Nashville and the other in Jessamine County, Kentucky. The phosphate strata are of the same age (Ordovician) and closely resemble the brown rock phosphate of Tennessee.'" Much of the rock is so disintegrated and mixed with foreign material that it must be washed in order to obtain a product suitable for the manufacture of superphosphate. The material which has been sold for this purpose has had an average grade of 72% tricalcium phosphate. In addition to that manufactured into superphosphate, an appreciable tonnage has been sold as finely ground raw rock for direct application to the field. ARKANSAS PHOSPHATE
The phosphates of northern Arkansas, while well situated to supply the areas west of the Mississippi River, have so far proved of little economic importance due to their relatively low grade as compared to the Tennessee deposits. The workable beds have been developed in the northwestern part of Independence County along Lafferty Creek, north and west of the l o PEALEN, W. C.,"Phosphate Rocks in Central Kentucky," Ky. Geol. Survey, 1915, 80 pp.
White River and about ten miles from Batesville on the Missouri Pacific Railroad. This rock was formerly shipped to Little Rock, Arkansas, and manufactured into superphosphate, but in 1912 mining operations were suspended as it was found more economical to supply this fertilizer factory with phosphate rock from the Tennessee fields. While formerly considered of Devonian age, more recent investigations indicate that the Arkansas phosphate belongs to an older period. It is closely associated with manganese ore which may insure their future devel~pment.'~ The phosphate occurs in two strata, one directly overlying the other. The first, or upper, layer is from three and one-half to six feet in thickness and consists of a hard, massive rock made up of the rounded fragments of organic debris, closely cemented together. I t varies in color from light gray to brownish black. This bed averages from 55 to 60% tricalcium phosphate, but is rather high in iron oxide. Directly under this stratum is another bed of phosphate from two to four feet in thickness, closely resembling the upper stratum, but containing only from 30 to 40% tricalcium phosphate. This lower layer was thrown away in mining operations. WAGGAMAN. W. H.. Bureau of Soils Bdl. 81 (1912). pp 30-6. (Part II will appear in the August issue.)
