Known and Potential Sulfur Resources of the World W. T. LUNDY Freeport Sulphur Company, New York 11, N. Y . tant source of sulfur, owing to ample suppliw and worldwide occurrences of deposits. Sulfur is produced aa a byproduct of numerous industries and the amount will undoubtedly increase in the future. In recent yean, plant. have been installed in the United States to recover sulfur in elemental form from sour gases. Natural sulfates are not an important source at present. The known and potential resources of sulfur of the world are sufficient to meet all requirements for many years.
T h e forms in which sulfur i s commonly found include native sulfur, sulfides of many metals, natural sulfates, and sulfide gases associated with natural gas and petroleum. Sulfur in some form has been recovered from all thene sources. At present the salt dome deposits of the gulf aoast region of Texas and Louisiana are the princibal sourae. Other native sulfur deposite include tho- of Italy and Sicily as well as the volcanic type found in many countries of the world. Pyrites have long been an impor-
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amounts is persistent in the cap rock of many domes, but deposits worthy of development have been found on only a small percentr age, and at depths not greater than 2500 feet. Sulfur occurs crystal aggregates in porous limestone and also in a semicrystalline and diaaeminated state. Thickness of the sulfur horizon i s seldom less than 25 feet and in some instances reaches 300 feet. It occurs in a pure state for a few feet, but the usual content of formations ranges from 20 to 40% (81). Geophysical methods of exploration have been factors of great importance for the past 25 years in locating salt domes. Their value and reliability were quickly demonstrated in search for peSALT DOME SULFUR DEPOSITS troleum, and the entire gulf coast area was surveed repeatedly and thoroughly (99). This intensive search justifies the present The development of the Frasch process early in this century assumption that few, if any, new domw will be found at depths was of outstanding importance in the sulfur industry, as evifavorable for sulfur. For this reason and in view of the amount of denced by the subsequent history of sulfur deposits of the salt drilling on known domes, the probabilities of discovering sulfur dome type in Texas and Louisiana (10). Their known reserves, deposits of considerable size in the land area of the Gulf Coast can productive capacity, low cost of ‘production, unparalleled purity be classed aa poor. of product as mined, proximity to deep water, and favorable fuel Salt domes of Texas and Louisiana produced 82,500,000tons of supplies are the principal factors which, in addition to availability sulfur to the beginning of this year. Five deposits have been of the Frasch process, have enabled these deposits to attain their mined and abandoned. Seven deposits now in operation prodominant and enviable position ($6). duced 4,745,000tons in 1949. For an estimate of reserves in the The area in which salt domes are found extends from the vicingulf coast area, a study of the mineral position of the United ity of the Rio Grande River on the west through Texas, Louisiana, States was made jointly by the U. S. Bureau of Mines and the U. S. and Mississippi, into Alabama on the east. Distances inland Geological Survey, based on information assembled in 1944 (6). from the Gulf of Mexico range from 75 to 300 miles. Within Reserves of sulfur, present and future, were placed at 80,000,OOO this area 194 salt domes occur in four salt basins which are classitons. I n the 6 years since that time 25,000,000tons have ,been fied separately because of differences in geology and geography. produced, and no discoveries of a substantial nature have been These areas are commonly known as the Gulf Coast Salt Basin, Interior Domes of Texas (84), Interior Domes of Louisiana (H), made. It is believed that the above estimate is on the conservative side and that ultimate production of gulf coast deposits will and Louisians-Mississippi Salt Basin. No sulfur has been proexceed government figures. duced from areas other than the Gulf Coast Salt Basin. As a In southern Mexico, on the gulf side of the Isthmus of Tehuanresult of geophysical surveys started in 1944, a number of salt tepec, a small, shallow, sedimentary basin contains 41 known and domes have been proved by drilling m open waters of the Gulf of inferred salt domes. Sulfur was reported in some of these domes Mexico off the coasts of Texas and Louisiana. Additional in cap rock similar to the domes of Texas and Louisiana. During domes will undoubtedly be found in this area, which is geologithe past few years prospecting for sulfur by more systematic cally an extension of the Gulf Coast Salt Basin. Depth of water drilling has been in progress, but production on a commercial ranges from 20 to 40 feet and the area in which domes have been basis has not been established. Because Tehuantepec domes ex-. located extends 40 miles beyond land. Assuming that one or hibit geological features that are favorable for sulfur, they cannot more of these domes contain substantial tonnages of sulfur, their be dismissed from consideration, but no estimate of possibilities economic value a t present is in serious question owing to great can be made. hazards and high costs of producing sulfur under such unfavorable There are known salt domes or similar structures in Colorado conditions. and Utah, as well as in Germany (39),Romania, Iran (IS), and Caprock formations overlying nearly all domes and consisting Russia (999).The absence of cap rock places many of them salt of limestone, gypsum, and anhydrite, differ materially in size, structures in a category unfavorable for sulfur. depth, thickness, and configuration (18). Sulfur in small
ULFUR is commonly found in several forms and is derived from many types of deposits widely distributed throughout the world. Sulfur and sulfur compounds were produced and consumed at greatly accelerated rates during the first half of this century. Apparent world consumption in 1900 was 1,250,000 long tons in comparison to 9,OOO,OOOlong tons in 1949 (6). A sevenfold increase in 50 years is evidence of the vital role now played in industry by this essential and irreplaceable commodity. These figures are also an indication of future needs from sources and by methods herein discussed.
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Two processes that have been suggested to explain the origin of cap rock on salt domea (2, 16) w u m e intrusive origin of salt structures. One theory is that anhydrite waa an original formation with salt beds and that it was lifted to its present position with the salt. The other theory aasumes that circulating waters dissolved vast quantities of salt during its upward movement, and that its anhydrite content waa concentrated and formed the dense cap rock which lies as a mantle on nearly all domes. Both theories assume that gypsum was formed by hydration of anhydrite (1,6,13,33).
SULFUR DEPOSITS OF ITALY Sulfur deposits of Sicily are outstanding, owing to their long history, past production, and future possibilities (87). The region of known sulfur deposition lies in the south central part of the island and is included in an area of approximately 500 square miles, although it is poseible that sulfur-bearing formations extend under an additional area of 1600 square miles. There are similar deposits on the mainland of Italy. Native sulfur in limestone and gypsum formations is found in these sedimentary basins of Miocene age. The presence of bituminous shales may be a clue to the origin of this sulfur (19). High-cost undergound mining methods are in general use, owing to the mode of occurrence of formations. The grade of ore as mined ranges from 12 to 50% with an estimated average of 26%. Methods used for beneficiation include the Calcaroni system and the Gill regenerative furnace, both of which employ the heat of combustion of sulfur to liquefy or vaporize the remaining sulfur, which is recovered by solidificationor condensation ($88). The Italian sulfur industry has experienced adversities of many kinds, as illustrated by production of 560,000 tons in 1900 in comparison to recent production of 170,000 tons annually (17). During their long life the Italian and Sicilian sulfur deposits have yielded 40,000,000 tons, 15,000,000of which were produced in the past 49 years. Accurate and reliable estimates on potential tonnage in these sulfur-bearing areas are not obtainable, but available information strongly indicates many years of production under favorable economic conditions. At this time costs are reported to be higher than world market prices for sulfur. A substantial increase in price is needed to place the Italian sulfur industry on a sound and profitable basis ( 3 6 ) .
VOLCANIC SULF'UR DEPOSITS Deposits of native sulfur which have their origin in volcanic activity are found in many countries. Surrounding formations are usually altered into masses of bleached porous rock by volcanic gases of a highly acid nature. Altered outcrops indicate presence of sulfur, which is formed at shallow depths hecause oxygen is necessary to effect deposition. The most important deposits from the standpoint of indicated tonnage are located in the Andes Mountains (14,37j in a zone about 3000 miles long paralleling the west coast of South America. Their remote location and high elevation, in aome cases about 18,000 feet, usually result in very high production costs. There are more than 100 deposits, and publications state that some contain large tonnages of high grade ores, the sulfur content of which may amount to 100,000,000 tons. These deposits must be classed as potential rather than available reserves because of their unfavorable location. Production of sulfur from 1900 to 1949, inclusive, ranged from 10,OOO to 60,000 long tons annually. In Japan sulfur is found in a chain of volcanoes extending through the main islands; at least 40 known deposits produced 3,400,000 long tons of sulfur from 1900 to 1949, inclusive. Re8erves of sulfur may range from 25,000,000 to 50,000,000 tons (34, 86). There are many deposits in European and Asiatic countries aa well as in mountain ranges bordering the Pacific Ocean. Many of these deposits of native sulfur cannot be classed as reserves under present conditions, but in the aggregate they have potential v&e for the future.
Vol. 42, No. 11
Mining methods for surface deposits consist of simple forms of open-pit, gophering, room and pillar, and open stope and pillar. One method of beneficiation is to melt sulfur ores in autoclaves; another is to distill sulfur in retorts heated externally (18).
ORIGIN OF NATIVE SULFUR Principal deposits of native sulfur-the salt dome type and those of Sicily-have several features in common, which may be indicative of their origin. In both regions sulfur is closely aasociated with limestone and gypsum; carbonaceous matter in the form of petroleum or bitumen is frequently present in sulfurbearing rock or associated formations; and hydrogen sulfide is present as a gas or in solution. These common features lead to a hypothesis that sulfur was formed through reduction of sulfates by carbonaceous matter (3). Another theory is based on the presence of certain species of anaerobic bacteria and their power to reduce mineral sulfates in presence of carbonaceous matter (11,30,40).Recent studies of natural variations in isotopic content of sulfur in a number of minerals may throw new light on this interesting subject. The origin of sulfur in volcanic deposits is not so obscure. Volcanic emanations frequently contain sulfur vapors, sulfur dioxide, and hydrogen sulfide. Many deposits that outcrop at the surface have evidently originated from one or more of these gases. .4t the seat of activities temperatures are excessive but at more remote locations, and during dying stages of volcanism, lower temperatures favor deposition. There are three methods by which sulfur may be deposited from solfataras: condensation of sulfur vapors, reaction between hydrogen sulfide and sulfur dioxide, and oxidation of hydrogen sulfide. Deposits may originate also by deposition from thermal springs containing hydrogen sulfide. PYRITES Pyrites, an inclusive term, is a general trade name for all of iron sulfide minerals containing from 25 to 50% sulfur. Pyrite is the most abundant in this classification. Principal deposits of this mineral are usually found in lenticular maases of great size, but it also occurs aa veins and in a disseminated state. It may be igneous, metamorphic, or sedimentary in origin (86). For a great many years pyrites has been the source of more than 50% of the world's sulfur requirements. From 1900 to 1948, inclusive, the apparent world sulfur consumption waa 214,000,000 tons, of which pyrites contributed 114,000,000 tons and native sulfur deposits 100,000,000 tons. Recent dislocations in Europe lowered the rate of production, but the trend is again upward. The principal use for pyrites as well as for native sulfur is in maqufacture of sulfuric acid, which accounts for at least 70% of all sulfur consumed (7,9, $8), Native sulfur enjoys a real advantage in low shipping costs due to its purity. On the other hand, pyrites usually haa an offsetting advantage in value of by-products such as iron and in some instances other metals. In addition to sulfuric acid, both elemental sulfur and liquid sulfur dioxide are made from pyrites by standard methods. Elemental sulfur is produced in Norway, Spain, and Portugal. One plant in the United States produces liquid sulfur dioxide and another is under construction. World reserves of pyrites are widely distributed, deposits being in operation in at least 30 countries. A large part of United States production, which was equivalent to 380,000 tons of sulfur in 1949, is obtained from the Ducktom region of Tennessee, but deposits are in operation in eight other states (8, g l ) . Government estimates (6) place present and future reserves of sulfur in pyrites deposits in this country at 76,000,000 tons. The largest reserve in the world, located in the southern part of Spain and in Portugal, is estimated at 500,000,000 tons, equivalent to more than 200,000,000 tons of recoverable sulfur ( 4 ) . Major deposita are also located on the island of Cyprus, and in Norway, Sweden, Finland, Japan, Italy, Russia, Germany, France, Greece, and
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Canada. The latest estimate of world reserves of pyrites908,000,000 tons-was made in 1926 by the 14th International Geological Congress a t Madrid. Because information was incomplete, particularly in regard to North and South America and Africa, total reserves may exceed this figure by 50% or more (800). Pyrites can be placed high on a list of major sulfur reserves of the world. The great tonnage in known deposits, their wide distribution, and flexibility of pyrites in supplying sulfur in any needed form, place this source of sulfur in a strong position.
BY-PRODUCT SULFUR Sulfur has been recovered as a by-product of mining, metallurgical, and chemical operations for many years. Complete and accurate records for world production of by-product sulfur are not always available. Jt is also difficult to estimate future production because the rate will be determined by economics of and demand for materials other than sulfur. An important amount a t p m t is derived from smelters treating sulfide ores for the recovery of metals. In the United States, where statistics are available, the amount of by-product sulfur recovered by’ smelters is estimated at 170,000 tons for 1949, or about 5% of the 4,100,000 tons of sulfur conaumed in this country for the same period (6). This ia only a small pmt of sulfur so available. Unless there are radical changes in metallurgical practices, it seems safe to assume that stack gases will increase as an important source of sulfur. Growing need for fertilizers will accelerate recovery of sulfur from smeltera and power plants and the serious attention being given to atmospheric pollution is a factor of increasing importance. This trend R i evidenced by one new plant recently constructed and by enlargement of three others in the United States for recovery of by-product sulfur from smelter gasas. Recovery of sulfur in elemental form from hydrogen sulfide in natural gas and in refinery gasas is a development of recent years in this country (38). There are now six plants with a combined annual capacity of 270,000 tons. The recovery of sulfur from hydrogen sulfide in coke oven gases will probably be augmented. A fourth possible source of hydrogen sulfide may lie in conversion of coal to liquid hydrocarbons if this becomes an established practice. World sources of hydrogen sulfide now known are equivalent to 1,000,OOO tons of elemental sulfur annually. The amount of sulfur in coal, as coal brasses, is very great because of enormous reserves of coal in the world. It occura usually as marcasite in the form of lenses, nodules, and sheets, in both horizontal planes and vertical fissures in coal s e w . In addition, sulfur occurs in microscopic form, probably combined with organic matter. Coal brasses have been recovered and used as a source of sulfur in comparatively small amounts. A survey made about 1920 estimated that coal b r w e s meeting the usual specificationscould be made available at the rate of 1,456,000 tons a year (B). This figure has never been attained and there is little or no production at the present time. The small pyritea content of coal, ranging from 1 to 3%, results in high production costs and places this material at a disadvantage competitively. Sulfur may also be recovered from coke oven gaaes, gases from power plants burning coal, and underground gasification of coal. Noteworthy changes in metallurgical practices could have an important bearing on the amount of available by-product sulfur. One example is a recent tendency of steel plante to sinter or noduIke ores before charging to blast furnaces. A continuation of thia trend would result in an increased use of pyrites aa a source of iron ore and in production of by-product sulfur. SULFATES Natural sulfates are not important aa sources of sulfur at thia time. However, processes are available and planta in Europe are using sulfates for the production of sulfuric acid and ammonium sulfate. Natural sulfates can be described as almost inexhaustible in occurrence, yet high capital and operating cosb preclude their wideapread UBB in most countriesa a source of sulfur.
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Over the years to come inventions, research, and new methods could bring about profound changes and developments in the sulfur industry that cannot be visualized at present. The Fraach process for producing pure sulfur in one simple operation is an outstanding example of such an occurrence early in this century. Ftegardles.3 of unforeseen developments, the known and pcr tential resources of sulfur in the world will undoubtedly provide an abundance for all requirements, in any needed form, at very reasonable prices, and for an indefinitely great number of years.
LITERATURE CITED (1)Am. Assoc. Petroleum Geologists, numerous publications on
geology of saltrdome type of sulfur deposits.
(2)Barton, D. C.,Bull. Am. Asaoc. Petroleum Geol., 17, 1025-33 (1933). (3)Bastin, E. S.,Ibid.. 10, No. 12,1270-99 (1926). (4) Bateman, A. M.,Econ. Qeol., 22,569-614 (1927). (5)Bureau of Mines, “Minerals Yearbook, Sulphur and Pyrites,” 1947. (6) DeGolyer, E.. J. Imt. Petroleum Technol., 17,331-3 (1931). (7) Duecker, W. W., and Eddy, E. W., Chem. I d . , 50, 174-82 (1 942). (8) Emmons, W. H., U. S. Geol. Survey, Profess. Paper 139 (1926). (9)Fairlie, A. M., “Sulfuric Acid Manufacture,” AM. CHEM. Soc., Monograph, New York, Reinhold Publishing Corp., 1936. (10) Frasch, H., J. IND. ENQ.CHEM.,4,132-40 (1912). (11) Ginter, R. L., “Sulphate Reduction in Deep Subsurface Waters,’’ in “Problems of Petroleum Geology.” pp. 907-25,Am. Assoc. Petroleum Geol., 1934. (12) Goldman, M. I., “Petrography of Salt Dome Caprocks,” in “Geolopu of Salt Dome Oil Fields,” . PP. . 50-86. Am. Assoc. Petroleum Geol., 1926, (13) Goldman, M. I., U. S. Geol. Survey, Profesa. Paper 175 (1932). (14) Griffith, 8. V., Mining Mag., 51, 15-20 (1934). (16) Hanna. M. A.. Bull. A m . Assoc. Petroleum Geol.. 18. 629-78 (1934). Harrison, J. V., J. Imt. Petroleum Technol., 17,252-8 (1931). Haynes, W.,“The Stone That Burns,’’ New York, D. Van Nostrand Co., 1942. Hazen, H. L., Mining J. (Nov. 15, 1929). Hunt, W. F., Econ. Geol., 10, 543-79 (1915). International GeologicalCongreea, 1926,“Les reserves mondiales en pyrites,” p p 210-13.
Lundy, W. T., Sulphur and Pyritea,” in “Industrial Minerals and Rocks,” 2nd ed., Chap. 47,Am. Inst. Mining and Metallurgical Engineers, New York, 1949. Mason, D. B.. IN?ENQ. CHEM.,30,740-6(1938). Mitchell, D. R., Recovery of Pyrite from Coal Mine Refuse,” T.P. 1744 (Class H,Ind. Min. No. 199) Am. Inst. Mining Met. Engrs., 1944. Powers, S., Interior Domesof Texas,” in“Geo1ogy of Salt Dome Oil Fields,” pp. 309-68,Am. Assoc. Petroleum Geol., 1926. Ridgway, R. H.,U.S. Bur. Mines, Inform. Circ. 6329 (19301. Ibid.,6523 (1931). Bagui, C., Econ. Geol., 18,278-87 (1923). Sagui, C., Inst. Mining Met., Bull. 229 (1923). Sanders, C. W.. Bull. Am. Aasoc. Petroleum Geol.. 23, 492-516
(1939). (30) Schneegans, D., VI1 Congr. Inet. Mines, Pari8 1,351-7(1935). (31) Spooner, W. C., “Interior Domes of Louisiana,” in “Geology of Salt Dome Oil Fields,” pp. 269-344, Am. Assoc. Petroleum Geol., l?p& (32) Stille, H., Upthrust Salt Masses of Germany,” in “Geology of Salt Dome Oil Fields,’’ p , 142,Am. Assoc. Petroleum Geol., 1926. (33) Taylor, R. E., La. Dept. Conservation and Geology, Bull. 11 (1938). (34) U. S. Supreme Commander for Allied Powers, Natural Re-
sources Section, Tokyo, “Descriptions of Japanese Sulphur Producing Areas and Mines’,’’ Suppl. to Rept. 66 (1947). (35) U. 9. Supreme Commander for Allied Powers, Natural Resources Section, Tokyo, “Sulphur Resourcesof Japan.” Rept. 66 (1946). (36) Vanutelli, C., “Sulphur, A Study of the Conditions of the World Market and of the Italian Production,” Milan, Industria Mineraria, 1931. (37)Vilaa, T., “Industria del Aeufre en Chile,” Departmento de Minas y Petroleo, Santiago de Chile, 1939. (38) Weber, G., Oil Gas J., 45, No. 44, (March 1947). (39)Wyckoff, R. D., ZW., 47, Nb. 28 (Nov. 11, 1948). (40) ZoBeU. C. E., “Marine Microbiologu.” Waltham, Mass.. Chronica Botanica Co.,1946. RECBIVED April 13, 1960.
