Elemental Phosphorus and PhosPhoric Acid in Fertilizer Industry W. L. HILL Bureau of P l a n t I n d u s t r y , Soils, and Agricultural Engineering, U . S . D e p a r t m e n t of Agriculture, Beltsville, Md.
Phosphorus-containing compounds and materials are in short supply i n many parts of the world. In the United States the largest share of these materials move i n the fertilizer industry, where production depends on the use of sulfuric acid. Thus, in the face of the current sulfur shortage some adjustments are anticipated in the industry, i n order to meet a growing demand for phosphate fertilizers. In this article scattered data pertaining to production, handling, and use of elemental phosphorus and phosphoric acid are brought together and discussed with a view to showing current trends of interest to the fertilizer industry. In 1950 more than 9070 of the available phosphates produced was derived from sulfur-demanding processes, production of triple superphosphate was expanding marlredly, whereas ordinary superphosphate production had apparently leveled off, and more than 6570 of the wet-process phosphoric acid went to fertilizers.
P
HOSPHORUS, inclusive of all its useful forms and derivatives, is in short supply in many parts of the world-mainly
a consequence of recent rapid expansion of application and use. In the United States the largest share of phosphoruscontaining materials moves in the fertilizer industry, where the production of superphosphate (ordinary and triple), 955,200 short tons of available phosphorus pentoxide in 1941, more than doubled during the succeeding years through 1950. The manufacture of available phosphates for fertilizer use has always been dependent upon processes that require sulfuric acid-for example, of the 1950 production of available phosphates over 90% was derived from sulfuric acid use. Thus, the current temporary shortage of sulfur strikes the fertilizer industry a heavy blow. Adjustments will be necessary, and in anticipation of some possible changes it seems appropriate to discuss current trends in the manufacture, handling, and fertilizer use of elemental phosphorus and phosphoric acid. ELEMENTAL PHOSPHORUS
PRODUCTION. Phosphoric acid is now produced in a two-step process by heating a proportioned mixture of phosphate rock, silica, and coke in a n electric smelting furnace. The phosphate is thereby reduced t o phosphorus, which passes off as a gas and, after removal of dust from the gas stream, is recovered by condensation. The solid phosphorus of high purity (99.9%) is, with prior melting, converted t o phosphorus pentoxide by controlled combustion in dry air, or to phosphoric acid by the admission of water t o hydrate the phosphorus pentoxide. Formerly, some plants were designed to operate on a single-step basis, whereby the phosphorus vapor from the smelter furnace is converted to phosphoric acid without intervening condensation. Technical developments in furnace construction and operation are described in a recent bulletin (SZ),and the process, as embodied in a nen plant, w&s described early this year by Callaham (6). Nine companies, exclusive of successors, have participated in the development of the elemental phosphorus industry in the United States (Table I). Two of the companies discontinued
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operations years ago, whereas a third switched from the blastfurnace t o electric-furnace operation during the thirties. The electrothermal process now accounts for the entire production of furnace-process phosphoric a c i d The 5000-kv.-amp. furnace planned (7) by the newly organized Columbia Electro-Chemical Phosphate Co., Cascade Locks, Ore., has apparently not materialized. The growth of phosphorus making since 1914 is illustrated by the figures for annual capacity and production in Table I1 Between 1922 and 1949 the number of producers increased from 2 to 7. As late as 1934 only one furnace larger than 6000 kv.-amp. was in operation; by the end of 1950 there were 21. Since 1934 production capacity has increased to more than 6.5-fold that at the beginning of the period and production has kept close pace. With the completion of the current program of expansion, including Monsanto Chemical Co.'s expansion a t Monsanto, Tenn., and new plant at Soda Springs, Idaho (101, Victor Chemical Work's new plant at Silver Bow, Mont. (8, 18, 28), and enlargement of the plant of Westvaco a t Pocatello, Idaho (%?), the annual production capacity will, according to a recent estimate ( I S ) , be 201,000 short tons of phosphorus in comparison with an estimated 156,000 tons for 1950 (Table 11)
TABLEI. OPERATIOKSFOR PRODUCIXG PHOSPHORUS 0 eraiion Eegun 1896 1901n 1914; 1919 1929d
1934 1935 1938 1938' 1949
(PHOSPHORIC ACID)
Concern Location of Initial Plant Niagara Falls, N. Y . Oldbury Electro-Chemical Co. American Phosphorus Co. Near Harrisbur Piedmont Electro-Chemical Co. Mount Holly, Federal Phosphorus Co. Anniston, Ala. Victor Chemical Works (blast furnace) Nashville, Tenn. T e n n a s e e Valley Authority Wilson Dam, Ala. American Agricultural Chemical Co. South Amboy, N. J. Victor Chemical Works Mount Pleasant. T r n n Phosphate Mining Co. Nichols, Fla. Westvaco Chemical Div , Food filaohinery Carp. Pocatello, Idaho
A c'".
Carothers (6 because t h e power was needed for other uses. 0 Swann k r p . from 1932 to 1935, when it became Phosphate Divinion, Monsanto Chemical Co. (SO). d Discontinued in 19.19. e Virginia-Carolina Chemical Carp. sinre 1944.
PROPERTIES AND HANDLIXG. White (or yellow) phosphoms is a waxlike, semitransparent solid that burns spontaneously in air to form phosphorus pentoxide. It is normally stored, handled, and shipped under water, in which it is substantially insoluble. The solid has a density of 114 pounds per cubic foot and a vapor pressure of 0.025 mm. of mercury a t 68" F. (20' (3.). It melts at 114.4' F. (44.1' C.) to a liquid having a density of 109 pounds per cubic foot and a vapor pressure of about 0.19 mm. of mercury (14). The viscosity of molten phosphorus saturated with water is about tn-ice that of water a t 131" F. (55" (2.). Transfer within the plant and for shipping is accomplished by pumping the liquid phosphorus under water a t 130" F., or higher, through jacketed lines. When a container is filled, be it a storage tank or a
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 44, No. 7
Phosphorus and Phosphate TABLE11. GROWTHOF PHOSPHORUS (PHOSPHORICACID) PRODUCTION^ No. of Electric Furnaces Rated ~~~~~l ~~~~~l >I3000 Caparity. Productiunb,
