Materials and Mixtures

K. D. Jacob.

Our known resources of economically usable fertilizer raw materials--already sufficient to meet our domestic requirements for many years--are being augmented constantly by discovery of new supplies and by improvements in the techniques of processing them.

Each of the three great subdivisions of the earth the atmosphere, the lithosphere, and the hydrosphere is an economic source of one or more of the nutrient elements supplied in fertilizers. Thus, the atmosphere is the principal source of nitrogen. The lithosphere furnishes nearly all the phosphorus. The hydrosphere gives us potassium.

RESOURCES OF FERTILIZER NITROGEN in the United States comprise the atmosphere, deposits of mineral fuels (bituminous coal, lignite, and oil shale), and natural organic materials.

The atmosphere is a continually renewing, inexhaustible reservoir of nitrogen about 34,500 tons over each acre of the earth's surface. This nitrogen, present in the elemental form, cannot be utilized by plants, however, until it has been combined with other elements by chemical or biological means. Atmospheric nitrogen is the basis of the great chemical nitrogen-fixation industry, which accounted for about 90 percent of the Nation's production of some 2 million tons of commercial fertilizer nitrogen in 1955.

Huge quantities of atmospheric nitrogen also are made available annually for plant nutrition by the action of biological agencies such as the bacteria in root nodules of legumes.

The country's next most important source of fertilizer nitrogen is bituminous coal, from which ammonia is obtained as a byproduct, chiefly in the manufacture of coke. The nitrogen content of a ton of coal averages about 30 pounds, of which about 4 pounds are recoverable when the coal is processed in modern, byproduct coke ovens. This source annually supplies about 185,000 tons of nitrogen for fertilizer use.

Deposits of many billions of tons of lignite and oil shale, containing about 0.5 to 1.5 percent of nitrogen, occur in the western half of the United States.

These deposits, as yet virtually untapped, may supply substantial quantities of fertilizer nitrogen in the future.

Natural organic materials, such as plant residues, fish products, and animal tankages, accounted for about 90 percent of the Nation's consumption of commercial fertilizer nitrogen in 1900, but only 1.5 percent in 1955.

The proportion may decline still further. That is because production of the natural organic materials is geared to other processes and operations, so that it is not capable of independent expansion, and because many of the products are finding more profitable markets as animal feeds. Also, these materials generally have the disadvantage of low plant-nutrient content and high unit cost in comparison with chemical nitrogen fertilizers.

RESOURCES OF FERTILIZER PHOSPHORUS in the United States are almost entirely in the form of deposits of phosphate rock, which is composed chiefly of one or more complex fluorine-bearing calcium phosphates. Minor sources include bones and other natural organic materials and phosphatic iron ores. Utilization of the latter is confined to the area around Birmingham, Ala., where there is some production of low-analysis basic slag as a byproduct of steel manufacture.

Our phosphate rock resources are mainly in Idaho, Montana, Utah, Wyoming, Florida, and Tennessee. Minor deposits exist in Arkansas, Kentucky, South Carolina, and Virginia.

V. E. McKelvey and his coworkers in the Geological Survey have estimated that the reserves of phosphoric oxide (P₂O₅) in phosphate rock minable under 1956 conditions total 1,545 million long tons-56 percent in the Western States, 43 percent in Florida, and 1 percent in Tennessee.

An additional 12 thousand million long tons of phosphoric oxide are in inferred reserves of phosphate rock that are not minable under present conditions about 50 percent in the West, 40 percent in Florida, and 10 percent in Tennessee.

The United States in 1955 marketed 13,186,034 long tons of phosphate rock containing 4,179,532 long tons of phosphoric oxide, of which 73 percent of the rock and 76 percent of the phosphoric oxide came from the Florida deposits. The remainder was divided about equally between Tennessee and the Western States (Idaho, Montana, Utah, and Wyoming). Of the total quantity of rock, 83 percent was used within the country-61 percent for fertilizer and other agricultural purposes and 22 percent for industrial uses and 17 percent was exported.

Some sources of phosphate rock are such that preparation of the material for the market requires elaborate treatments to separate the phosphate from the accompanying impurities. The rock in other places is of commercial grade as it comes from the deposits.

Two notable technological advances have made possible the utilization of huge quantities of phosphate rock that formerly were wasted or were considered uneconomical to exploit.

One of the developments is the separation of phosphate particles from silica grains by flotation processes, which enable greatly increased recovery of phosphate from the Florida deposits and have brought many submarginal deposits into the economic reserve.

The other development is the manufacture of elemental phosphorus directly from lower grade phosphate rock by the electric-furnace process and by the blast-furnace process. The latter has experienced only limited commercial operation. The processes require substantial quantities of silica, and it is often more economical to use directly the lower analysis siliceous phosphate than to smelt high-grade rock with added silica. Thus certain phosphate deposits, especially in Tennessee and the West, that are unsuited for beneficiation to the grades of rock required for acid-treatment processes have been raised to the level of economic reserves.

Further improvements and developments in methods and techniques of mining, beneficiating, and processing undoubtedly will enable the utilization of additional large resources of phosphate rock.

RESOURCES OF FERTILIZER POTASSIUM in the United States include water-soluble minerals, lake and subterranean brines, insoluble minerals and rocks, and natural organic materials.

Sea water contains an average of about 0.04 percent of potassium and constitutes a potentially inexhaustible source of potassium. The technical feasibility of recovering potassium salts from the ocean has been demonstrated in Europe, but the cost is not yet competitive with customary sources.

The Nation's proved reserve of potassium economically recoverable under present conditions is mostly in the Carlsbad, N. Mex., deposits of readily soluble minerals (sylvite and langbeinite) and in the brines of Searles Lake in California and Salduro Marsh in Utah. The reserve in these three sources is estimated to be equivalent to more than 200 million tons of potash (K₂O). An additional large reserve, of unknown extent, resides in the undeveloped deposits of soluble minerals in Utah, Texas, and New Mexico.

Many millions of tons of potassium are present in the deposits of insoluble minerals and rocks including alunite, greensand, leucite, and certain shales and feldspars that are widely distributed over the country. The cost of mining and processing these materials, which commonly contain no more than 6 to 10 percent of potash, is such, however, that they generally cannot compete with the brines and soluble minerals as sources of fertilizer potassium.

Tobacco waste, plant ash, dried animal manures, Steffens waste from the beet-sugar industry, and cement-kiln dust are among the minor sources of potassium for fertilizer.

In 1955 the United States produced potassium materials containing 2,064,808 tons of potash, of which 91 percent came from the New Mexico deposits. Exports totaled 130,226 tons of potash, as compared with imports of 177,052 tons, chiefly from Germany.

RESOURCES OF SECONDARY NUTRIENT elements are abundant and widely distributed in the United States.

Calcium resources are chiefly in the form of limestone, large deposits of which occur in practically every State. Other important resources include deposits of marl, shells, calcium sulfate (gypsum and anhydrite), and phosphate rock.

Magnesium supplies for agricultural use reside largely in deposits of high-magnesium limestone and dolomite, particularly in the eastern half of the country. Additional resources include deposits of magnesite (magnesium carbonate), silicate minerals (olivine and serpentine), soluble salts, and lake and well brines. Magnesium compounds are recovered from sea water on the Pacific, gulf, and Atlantic coasts.

The world's most extensively developed deposits of native sulfur occur in the coastal areas of Louisiana and Texas. Minor deposits are known elsewhere in the country. Additional resources of sulfur, widely distributed among the States, include deposits of iron pyrites and other metallic sulfides,calcium and alkali sulfates, and natural and oil-refinery gases.

The Nation's total known reserve of the materials economically usable as sources of elemental sulfur or sulfuric acid in 1951 was equivalent to nearly 100 million long tons of the element about half in the form of native sulfur and the remainder mostly in pyrites. The production of elemental sulfur in 1955 was about 6,145,000 long tons.

Vast reserves of potentially usable sulfur reside in the country's deposits of calcium sulfate. Processes for the manufacture of sulfuric acid and cement from calcium sulfate, as well as for its conversion into ammonium sulfate by treatment with ammonia and carbon dioxide, have been developed in several foreign countries.

RESOURCES OF TRACE NUTRIENT elements include more than 14 million tons of boron probably the world's largest reserve of this element in deposits and brines in California. The domestic production of boron compounds in 1955 was equivalent to about 91 thousand tons of the element, mostly in the form of sodium borates. The consumption as a plant nutrient probably did not exceed 2.5 thousand tons of boron.

The country's resources of copper, manganese, molybdenum, and zinc are mostly in deposits of sulfide, oxide, carbonate, and silicate ores, from which they are recovered principally by the metallurgical industry. The domestic productions of copper, manganese, and zinc are supplemented by imports, but our productive capacity for molybdenum chiefly from the Climax, Colo., deposits exceeds the peacetime world requirements. It is estimated that about 4,500 tons of copper, 3,600 tons of manganese, and 2,000 tons of zinc were consumed for plant nutrient purposes in 1952, for example.