USES OF PYRITE AND SULPHUR
Pyrite and sulphur are closely related in their most essential uses, and one material can in many cases be substituted for the other. The largest and most important use of these minerals is in the manufacture of sulphuric acid, which is an essential material required for a very wide variety of purposes, including the production of acid phosphate for fertilizer, the manufacture of modern high-power explosives, the refining of petroleum, pickling of iron and steel, and for a vast number of chemical industries. The competition between pyrite and sulphur for this purpose has gone through several stages. With the large-scale development of Italian deposits sulphur was largely used for acid manufacture. As the prices of sulphur were increased it became cheaper to use pyrite, which in many localities then displaced sulphur, for this purpose. With the rapid expansion of the American production, and particularly with the tremendous increase in the capacity of sulphuric acid plants for war purposes, sulphur has again been very largely used for the manufacture of acid. The prospects since the close of the war are that, due to the tremendous capacity of the sulphur mines of the United States, sulphur may continue to compete with pyrite in this use.
Probably the second most important use of these materials is in the manufacture of sulphite wood pulp. In Europe pyrite is largely used for this purpose, while in the United States and Canada sulphur is the principal material used. For every ton of sulphite pulp manufactured, under the best practice, about 250 pounds of sulphur is required. In the United States and Canada about 175,000 tons of sulphur is used annually for this purpose, representing about 50 per cent. of the total sulphur consumption of these countries. There are also a number of other important purposes where sulphur is used rather than pyrite, the most important of which are in the manufacture of agricultural sprays and insecticides, and in the hardening of rubber. Sulphur is a primary ingredient of black powder, and considerable quantities are still used for that purpose. While most of the explosives used in modern warfare require the use of sulphuric acid in their manufacture, they do not use sulphur in its elemental form. There are many other minor chemical uses.
Substitutes for Sulphur and Pyrite.
—Because of the large deposits of sulphur now available, and of the extent and wide distribution of pyrite deposits, and of the cheapness of both these materials, there are no adequate commercial substitutes for them. The increase of by-product acid, from the copper and zinc smelters and possibly the nickel smelters of Sudbury, might be considered as the most important factors in replacing pyrite and sulphur. As a general thing, the factors of cost and transportation are the governing ones rather than any present or probable scarcity of materials.
GEOGRAPHICAL DISTRIBUTION OF PYRITE
While pyrite is a very widely distributed mineral, there are relatively few deposits which are of sufficient importance to enter into the world’s commerce. This is generally due to the relatively small value of its sulphur content per ton, usually from 40 to 45 per cent. of recoverable sulphur; which means that it takes almost 2¹⁄₂ tons of pyrite to be equivalent to the ton of sulphur which competes with it for many uses. Consequently pyrite seldom moves far, unless it is so situated as to take advantage of cheap ballast rates where little other freight is available for ships, or unless it carries important copper or gold values, which can be recovered after the sulphur content has been utilized. Many known deposits, such as those in Mexico and the Western United States, remain undeveloped because of their distance from market. In countries such as Russia, France, Italy, Germany, Sweden, Japan, and the Eastern United States production is absorbed by the local market. Spain and Portugal, the most important source of world supply, are favorably located to ship to near-by European countries or to secure cheap ballast rates to the United States, and in addition much of the ore carries several per cent. of copper.
Norway is second in export, with a high-grade pyrite carrying copper values, which is shipped to Sweden or across the Baltic to near-by countries. Canada ships considerable pyrite to the near-by markets of the United States, the Quebec product having copper values, while the product of Ontario takes advantage of boat shipments on the Great Lakes.
Spain and Portugal.
—The deposits of Spain and Portugal are the largest and most important in the world, furnishing approximately two-thirds of the world supply. The district is essentially a unit, and the principal deposits occur in a zone extending from Rio Tinto, Spain, to San Domingo, Portugal. The combined annual production of iron and copper pyrites for the two countries is normally almost 4 million metric tons, 90 per cent. of which is furnished by Spain and 10 per cent. by Portugal. About two-thirds of the total output carries copper values, which may be recovered before the pyrite is roasted for its sulphur value or after. When copper is to be recovered at the mine the ore is leached by spreading it out in beds exposed to the weather and frequently stirring it and wetting it down. The copper goes into solution and is precipitated on scrap iron, forming cement copper. The process takes about 3 years and the pyrite residue is shipped as washed ore. The ore is compact and finely crystalline and carries from 48 to 51 per cent. sulphur. Conservative estimates of ore reserves for the district give it from 300 to 400 million tons, or enough to last for one hundred years at the present rate of production. Consequently this district is destined to long remain the chief pyrite-producing center of the world.