Chapter XIII: Monazite, Thorium, and Mesothorium

BY R. B. MOORE

USES OF MONAZITE

Practically the only use of monazite has been as a source of thorium salts. In extracting these, by-products are recovered, such as cerium, lanthanum, and other rare earths. Thorium salts are used almost exclusively for the manufacture of Welsbach mantles, which consist of 99 per cent. thorium oxide and 1 per cent. cerium oxide. For this use there is no known substitute. The one other use of thorium salts is in ordinary chemical laboratories, but this use is very limited. The fluoride and other salts of cerium are used in connection with the flaming arc, their presence giving increased luminosity.

Mesothorium is a radio-active element always found in thorium minerals. Until quite recently it has been thrown away in the manufacture of thorium nitrate; but it is now being produced as a by-product, and is useful as a substitute for radium in luminous paints, and for therapeutic purposes.

GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION

The principal sources of monazite are Brazil and India, although it has been mined successfully in the United States in the Carolinas and in Idaho. It has been found in Swaziland, Africa, and in Australia, and also, to a limited extent, in native rock and in placers in Ekaterinburg, Russia.

Monazite is usually found in the gravels of small streams or bottom lands, although it is sometimes found in the soil of hillsides. In Brazil and India it occurs mainly in the beach sands of the sea coast. In places it is found in small crystals in gneiss, granite and pegmatite rocks. As these rocks become disintegrated, the crystals are washed into streams and with other heavy sands are deposited in the stream beds. On the coast of Brazil, the monazite grains from the crystalline rocks of the coastal mountains are concentrated by the waves of the sea.

=United States.=--The deposits of the Carolinas cover an area of several hundred square miles east of the Blue Ridge Mountains. In North Carolina, the counties of Cleveland, Burke, Alexander, Rutherford and Lincoln furnish the richest deposits. In South Carolina the only deposits of value are in the counties of Cherokee and Greenville. Practically all of the monazite mined in the Carolinas is derived from gravels in streams and bottom lands, the miners usually following the stream courses. The gravels vary greatly in thickness, and it is therefore difficult to make a true estimate of the average, but in general the monazite-bearing gravels are between 1¹⁄₂ and 2¹⁄₂ feet thick. The top soil in the bottom lands averages 3 to 6 feet thick and may be 7 feet or more.

The deposits in the State of Idaho are near Centerville and Idaho City. In the future, under more favorable conditions of price, transportation, etc., these deposits may possibly become a commercial source of monazite. Almost all of them contain small quantities of gold. The gravel beds are considerably thicker than those in the Carolinas, and with the gold content might be more profitable were it not for labor being higher priced.

Monazite has been found in Colorado, in the Newland Gulch district, 20 miles south of Denver, where it occurs in gravels that carry considerable gold.

=Brazil.=--There are three kinds of monazite sand deposits in Brazil; the deposits within the government lands along the coast; deposits lying behind the government coastal lands, which are private state possessions or belong to private parties; and inland deposits. The bulk of the monazite is derived from coast sands in the states of Espirito Santo and Bahia, the sand being washed by means of oscillating tables or sluice boxes. The coast lands are the property of the federal government for 33 meters inland, measuring from the point where the sea waves wash the beach at mean high tide. This uncertain method of marking property has of course given rise to disputes when boundaries are established.

At a few places along the coast strips of monazite-bearing sands lie directly behind the government land, and some of these might be worked profitably were it not for the fact that it has been difficult to prove to the federal government that these sands were not taken from the nearby government land. One French concern has exploited such lands in the State of Rio de Janeiro. Along the banks of the large rivers, such as Parahyba, there are great quantities of black sands with traces of monazite. Near Sapucaia such deposits have been worked by a French concern. Many of the inland deposits can not be exploited on account of the expense of transportation of the products, as the deposits are many miles from a railroad.

=India.=--India is the newest source of monazite sands, the deposits lying on the sea beach like those in Brazil. The deposits are in the Travancore district near the southwestern end of the Hindustan peninsula. Very little information is available concerning these deposits.

CHANGES IN TREATMENT PRACTICE

The general method of treatment employed until quite recently has involved leaching the concentrate with concentrated sulphuric acid, thus getting the thorium, cerium, and other rare earths in solution and separating them from the silica, zircon, ilmenite and other insoluble products. From this stage different companies used slight variations in practice, such variations being kept strictly secret, although they all involved the precipitation of the thorium as oxalate by means of oxalic acid.

At the outbreak of the war the price of sulphuric acid went to four or five times the original cost, and the increased price of oxalic acid was practically prohibitive. Consequently the manufacturing companies had to change their entire procedure and to use chemicals that they could obtain at a reasonable price. In this difficult undertaking the companies were successful, and at least one company devised a process that was considerably more efficient than the old one.

At present mesothorium is being produced as a by-product by the Lindsay Light Co. and the Welsbach Co., the process used by the latter company having been originated by the Colorado Station of the United States Bureau of Mines. This process is cheap and extremely efficient, and will no doubt enable the Welsbach Co. to compete commercially with any other manufacturer of mesothorium. Of course as the process was developed by the Bureau of Mines it will ultimately be made available for anyone, but as mesothorium can only be made at a profit as a by-product of thorium nitrate, anyone who manufacturers mesothorium must first establish a thorium industry.

POLITICAL CONTROL

The important monazite resources of the world are controlled politically by three nations: the United States, Great Britain (India) and Brazil. The deposits of the United States, in normal times, probably can not be worked successfully in competition with the foreign deposits without the protection of a high tariff.

COMMERCIAL CONTROL

=United States.=--The widely scattered monazite deposits of the United States are of importance only during a period of abnormally high prices or during the restriction of imports from Brazil and India. The known reserves are small and the deposits will probably never be an important factor in the world monazite market. As far as the writer knows, all of the American deposits are controlled by American capital.

The manufacture of thorium nitrate in this country is closely controlled by two large companies, the Welsbach Co. and the Lindsay Light Co.; they own the only two commercial plants of any size in the United States.

All of the manufacturers of mantles in the United States, with one exception, must obtain their thorium nitrate from one of these two companies. As these companies supply practically all the thorium nitrate requirements of England and France, they control the thorium industry. The only other manufacturer of thorium nitrate in this country is the Block Co., of Chicago, which uses about 15 tons of monazite a year, making sufficient thorium nitrate for its own production of mantles. The Welsbach Co. uses about 1,200 tons of monazite annually and the Lindsay Light Co. about half that amount. The Welsbach Co. has contracts for the delivery of monazite, up to its requirements, from Brazil; the Lindsay Light Co. has obtained all of its monazite from India.

Most of the processes used, including those used by the Welsbach Co. and the Lindsay Light Co., are secret. As thorium can be extracted from monazite in more ways than one, a secret process does not necessarily mean commercial control unless such a process is in every way efficient and the company owning it is willing to get into a commercial war.

=Brazil.=--As the Brazilian deposits have for so many years been the chief source of the supply of monazite, the history of their commercial control is practically a history of the commercial control of the monazite industry. About 27 years ago, John Gordon, an American now residing in New York, found monazite on the coast of Brazil. He brought large quantities to Hamburg, Germany, and was able to obtain a monoply of the monazite sand.

At that time the manufacture of thorium nitrate, the principal product of the monazite sand, was confined in Europe to a few large chemical firms in Germany and the Welsbach Co. in Vienna. They not only supplied the European market with thorium nitrate, but also sent large quantities to the United States. The American Welsbach Co. early manufactured thorium nitrates from sands mined in the Carolinas, a protective duty of 6 per cent. making this possible.

In 1902 Mr. Gordon agreed to supply the four large German manufacturers and the Austrian manufacturers with monazite at a price of $150 a ton and a profit on the manufactured nitrates. A close combination thus formed, known as the German Thorium Convention, prevented other thorium manufacturers from acquiring any of the mineral mined by Mr. Gordon, and raised the price of thorium nitrate 100 per cent.

For a considerable period Mr. Gordon exported the sand from the coast lands of Bahia, near Prado, Brazil, without interference. Finally the Brazilian government became acquainted with the value of the resources and decided that no private individual or state government had the right to mine, sell, lease, or remove any monazite on so-called state lands without the consent of the federal authorities. In 1908 the government advertised that coast lands in the State of Espirito Santo would be leased to the highest bidder for the exploitation of the sands. A contract was thus obtained for the firm of A. C. de Freitas & Co., of Hamburg, Germany. By the contract the firm agreed to pay to the Brazilian government a rental equal to 50 per cent. of the selling price of the monazite sands and to export at least 1,200 tons annually.

To avoid trouble the German Thorium Convention arranged later that half of its supply should be furnished by Mr. Gordon and half by the de Freitas company. A new convention was formed by the four German chemical manufacturers with Mr. Gordon and the de Freitas company, preventing firms in other countries that had started to manufacture thorium nitrate from getting raw material. Consequently great efforts were made to find and develop new deposits of monazite. The high price for thorium nitrate made possible the mining of monazite in the Carolinas and its export to Germany, especially to one German manufacturer who was not in the German Thorium Convention.

Ultimately there was an overproduction of thorium and in 1906 the price dropped 50 per cent. Monazite mining declined in all localities where the cost of mining was high, and production in the Carolinas and the interior of Brazil practically stopped.

During the four or five years antedating the war the German Incandescent Gas Light Co., of Berlin, succeeded in controlling the largest manufacturers of thorium nitrate in Europe, except those in France. It controlled both the English and Australian companies and became the active competitor of the so-called Thorium Convention, which at that time had lost much of its power. Mr. Gordon still has extensive interests in Brazil, but he does not have a monoply. The exportation rights from Brazil are in the hands of Luis de Rezende & Co. (Rio de Janiero), Mr. Gordon, and others. Luis de Rezende & Co. is mainly a French concern, but has Brazilian and Portuguese stockholders. The company controls the French company, Société Minière, associated with the Welsbach Co.

As noted above, one French company has exploited monazite deposits in the territory immediately behind the government lands in the State of Rio de Janeiro. Another French company has worked the black sands along the Parahyba River, near Sapucaica, which contain traces of monazite.

=India.=--Before the war, the German manufacturers of thorium nitrate exercised as close control over the monazite deposits of Travancore, India, as over those of Brazil. Only a limited quantity of the sand was sold to gas-mantle manufacturers and other consumers in the United Kingdom, and then at a price nine times the price paid by the German consumers. Such a monoply of the supplies of raw material made the German monoply of the thorium nitrate industry almost complete.

According to S. J. Johnstone, in an address at the annual meeting of the Society of Chemical Industry in July, 1916, the Germans obtained practical control of the Travancore monazite deposits in the following manner: A lease for working these deposits was granted some years ago by the Travancore Durbar, with the approval of the Government of India, to the London Cosmopolitan Tin Mining Co., which contracted to sell the whole of its output to a German firm. Soon after the outbreak of war it was found that the whole of the preference shares and 11,000 of the ordinary shares of the Travancore Minerals Co. were held in trust for the Auer company, of Berlin.

The India Office decided that in the future all directors of the company working the concession must be British-born and that the company, must be ready at all times to sell monazite sand direct, and at a fair price, to British firms. German contracts were canceled. A second company, Thorium, Ltd., obtained a 20-year lease to work 150 acres in Travancore for monazite sand, and is exporting the sand and manufacturing thorium nitrate from it at works in England. A great deal of Travancore monazite has been imported by American companies.

POSITION OF THE UNITED STATES

As outlined above, it can be readily seen that the United States is dependent upon Brazil and India for its raw materials, as domestic deposits are not large enough to furnish the required supply and cannot be worked in competition with the more cheaply mined foreign deposits.

The average concentrate obtained in the Carolinas runs about 3¹⁄₂ to 4 per cent. thorium oxide; that obtained in Brazil averages somewhat over 8 per cent. Under such conditions it is difficult for the Carolina monazite to compete with that from Brazil or from India. In addition, a very considerable amount of the Carolina monazite available has been removed. The old workings are more or less covered up and the whole industry has become completely disorganized.

Whilst these deposits were being mined and operated farmers were in the habit of making their own concentrate in crude sluice boxes. The product thus obtained averaged about 35 per cent. monazite. The concentrates were then sold to a refinery, where it was best treated by electromagnetic separators, such as the Wetherill machine. The final product obtained from these machines was ready for chemical treatment for the extraction of the thorium.

Practically the same treatment is given to the monazite from Brazil and India. As the concentrate obtained is of much higher grade, the additional charges for freight and duty, which are not borne by the Carolinas product, are more than offset. Undoubtedly, unless a very high tariff is placed on the monazite from Brazil and India, our future supplies will come from these two sources, at least for some time. It is very doubtful whether with a high tariff the Carolina deposits could furnish the monazite required in this country, even for a few years, and under the most favorable conditions it would take some time, possibly six months to a year, to revive the industry.

The Allies and practically the whole world are dependent upon the United States for the manufactured products, thorium nitrate and gas mantles. Whether this monoply will continue is doubtful, as there is a movement in England to encourage both the thorium nitrate and the gas-mantle industry.