Chapter XI: Radium and Uranium

BY R. A. F. PENROSE, JR.

Radium is a metal and is a product of the disintegration in nature of the metal uranium. Both radium and uranium are elements. Radium has been isolated in its metallic state, but is not used in that form and is known better in the form of its salts, among the most important of which, so far as their uses are concerned, are the bromide, chloride and sulphate.

Wherever uranium occurs in nature, radium is associated with it in certain definable quantities. Uranium can contain, however, only a certain maximum amount of radium at a time, and when it has reached this stage, the radium and uranium ratio is said to be in equilibrium. In this condition the amount of radium per gram of uranium has been calculated by Rutherford to be 3.4 × 10⁻⁷ gram. This corresponds to 1 gram of radium element to about 3,000 kilograms of uranium element, or 1 part of radium element to about 3,000,000 parts of uranium element. Uranium minerals as mined are usually impure and carry only a small percentage of uranium elements, so that the ratio between radium and the crude uranium ore may be 1 to several or many times 3,000,000.

The production of radium from uranium is usually stated in milligrams or grams, and even in the richest ores there is usually only a small fraction of a gram to a ton, while in the ordinary lower-grade ore there are only a few milligrams to a ton, corresponding to a small fraction of a grain to a ton. Less than twenty years ago it was estimated that probably not one gram of radium element in the form of its refined salts had been extracted in the world. Today a great many times, perhaps a hundred times or more, this amount has been extracted and is in use. The annual production of radium today in the world is probably several grams. The annual production of uranium in the world is probably several hundred pounds.

The unique position of uranium as the source of radium in nature makes it necessary to discuss both materials together.

=Uses of Radium.=--Radium is a heavy white metal which is very unstable, and alters rapidly in the air. It is not used in its metallic stage but only in the form of its salts. A few years ago these salts were supposed to have a general beneficial effect in the treatment of cancer and other malignant growths, but more recent investigations seem to confine their influence to only certain forms of these afflictions. Their influence in other diseased conditions is often very marked, but the full extent of the field of usefulness of radium for medical purposes has not yet been very clearly defined.

In recent years radium has been applied to other important purposes, especially in luminous paint for watches, clocks, compasses and other instruments; and this use has so greatly increased in recent years, especially for military purposes, that it now consumes more radium than is used in medicine. Radium salts are more or less luminous when seen in a darkened room, and this quality is often increased by the admixture of certain other materials, notably zinc sulphide. Hence their value in luminous paints. Radium salts also cause certain minerals to fluoresce, notably the zinc minerals willemite and sphalerite. In Germany, where radium during the war became scarce on account of the shortage of the ores from which it is extracted, radium salts are said to have been preserved for medical purposes, and mesothorium and other radioactive substances used in making luminous paints.

=Uses of Uranium.=--Uranium is a heavy white metal, which slowly tarnishes on exposure to the air. The chief use of uranium today is as a source of radium. For many years before the discovery of radium, however, uranium compounds were used in a small way in coloring glass and porcelain, in photography, in reagents for chemical analysis, in mordants for dyeing and for other minor purposes. The use of uranium metal in small quantities in steel manufacture has been tried with some degree of success.

ORES OF RADIUM AND URANIUM

=General Statement.=--The principal uranium minerals at present known in nature, which are therefore the principal sources of both uranium and radium, are carnotite and uraninite, with the impure amorphous form of uraninite known as pitchblende. Torbernite, autunite and some of the rarer uranium minerals have produced a little radium and uranium.

Carnotite and uraninite or pitchblende as mined for ores are generally more or less mixed with other materials and are rarely found pure. The uranium in the ores is usually stated commercially, for convenience, in the form of the uranium oxides represented by the formula UO₂ + 2UO₃, briefly expressed as U₃O₈. Most carnotite ore varies from 1 per cent. to 3 per cent. of U₃O₈; a 5 to 10 per cent. ore is considered high grade; a 20 to 40 per cent. ore is remarkably rich. Uraninite and pitchblende ordinarily contain more uranium than carnotite contains, and even in the impure forms in which they are mined as ores, they often show this greater uranium content. The ordinary uraninite and pitchblende ores carry from 2 to 3 per cent. to 8 or 10 per cent. U₃O₈, and a 20 per cent. ore is very high grade, though some ore runs 60 or 70 per cent.

=Carnotite.=--Carnotite is an amorphous, soft, powdery material, sometimes more or less coherent and of a talcose or waxy character, generally of a brilliant canary yellow color, though sometimes discolored by iron, organic matter and other substances. It is essentially a hydrous potassium uranium vanadate. Some authorities believe that carnotite is not a distinct mineral, but a mixture of different minerals.

=Uraninite and Pitchblende.=--The terms uraninite and pitchblende are often used synonymously to designate the same mineral, but more properly the term uraninite is a general name for all forms of the mineral and especially for the purer and distinctly crystalline variety, and the term pitchblende is applicable to the impure amorphous form. It is black or grayish black in color, opaque, and often has a submetallic glossy or pitchlike luster. Uraninite is often remarkably lacking in distinctive characteristics, so that its presence might frequently be overlooked. For this reason it seems possible that this mineral, now known in only comparatively small quantities, may some time in the future be found more abundantly.

Uraninite, like carnotite, has a somewhat indefinite formula, but is essentially a combination of the two uranium oxides UO₂ and UO₃, in which UO₂ seems to act as a base and UO₃ as an acid. A number of both the rarer and commoner elements are often associated with them. The relative amounts of the two oxides vary considerably in different specimens, especially in the impure form of pitchblende, and no definite formula can at present be given. In pitchblende a notable amount of water, perhaps sometimes in chemical combination, is often present. Several other minerals much rarer than uraninite or pitchblende are related to them in composition, among them being cleveite, bröggerite and nivenite.

=Other Ores.=--Though carnotite, uraninite and pitchblende are the most abundant of all the radium and uranium materials in nature, and produce almost all the radium and uranium of commerce, yet many other minerals contain both metals, and though as yet known only in such limited quantities as to be of small commercial value, may in the future be found in quantities of importance. Among them may be mentioned tyuyamunite, a hydrous calcium uranium vanadate often associated with the hydrous potassium uranium vanadate described above as carnotite; autunite, a hydrous calcium uranium phosphate; torbernite or chalcolite, a hydrous copper uranium phosphate.

GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION OF RADIUM AND URANIUM

The only regions of the world that have as yet produced any large amounts of radium and uranium minerals on a commercial scale are Colorado, Utah and Austria. Cornwall, Australia and Germany have produced a small quantity of these minerals. They are known in small quantities in France and Portugal, and have been reported in India and German East Africa, but in these regions they have not yet become commercially important. They occur sparingly, so far as yet known, and practically as only mineralogical curiosities, in Connecticut, North Carolina, Canada, Norway and many other regions, but may in the future be found in larger quantities.

Minute quantities of radium or its products of disintegration occur in almost all rocks and in the atmosphere, and in the waters of the sea and land, but in such small amounts as to be unavailable as a source of these substances. The source of all radium of commerce at the present time is in the certain few uranium minerals already mentioned. They are found in formations of various geologic ages, from recent superficial deposits to the older crystalline rocks, but show a tendency toward certain modes of occurrence, such as in southwestern Colorado and southeastern Utah as an impregnation in sandstone; in eastern Colorado, Cornwall, Austria and South Australia as one of the gangue minerals in veins of other ores; in North Carolina, Canada, Norway and West Australia in pegmatite or other feldspathic dikes.

RADIUM AND URANIUM RESOURCES OF THE UNITED STATES

=General Statement.=--The commercially important deposits of ores of radium and uranium in the United States are, so far as yet known, confined to the carnotite regions of southwestern Colorado and southeastern Utah, and the pitchblende deposits of Gilpin County, in eastern Colorado. In Connecticut, North Carolina and elsewhere, uraninite, pitchblende and other uranium minerals have been found; and near Mauch Chunk, in Pennsylvania, small quantities of carnotite have been discovered, but these occurrences are, so far as known, in quantities too small to be of commercial value.

=Colorado and Utah.=--The carnotite deposits of southwestern Colorado and southeastern Utah are the most important sources of radium and uranium in the world. In Colorado the largest quantities of ore have come from many mines in Montrose County, especially in Paradox Valley, while Mesa, San Miguel, Dolores, Rio Blanco, Routt and other counties have been producers. In southeastern Utah the ores are carnotite, as in southwestern Colorado, and occur especially in Grand, Emery and San Juan counties, but have not been worked to the same extent as in Colorado.

The carnotite of Colorado and Utah occurs as an impregnation in sandstones and shaly sandstones, mostly in the McElmo and the La Plata formations, lying at the top of the Jurassic beds and below the Cretaceous sandstones and conglomerates of the region. The deposits seem to have been formed by the precipitation of carnotite from solution along certain strata of these formations, and the material occurs along bedding planes, in fissures and small cavities, in layers or irregular masses from a fraction of an inch to several inches in width, and sometimes as a general impregnation of the sandstone for several feet in thickness. It seems to be especially abundant in strata impregnated strongly with vegetable or animal matter, and is often in unusual quantities in lignitized or petrified trunks of trees. This phenomenon suggests the influence of organic matter in precipitating and segregating the carnotite.

The rocks carrying the carnotite lie horizontally or dip at low angles in most parts of the Colorado region; in Utah they lie often in the same way, but occasionally dip at steep angles. Where they appear on the surface, the carnotite sometimes impregnates certain strata for several hundred feet or more along the outcrops, but more generally it occurs in spots along them, with little or no carnotite in the intervening spaces. As these outcrops are followed into the hillsides, the ore appears to be even more irregular in its distribution than on the surface, and in many or most cases it becomes much scarcer the further it is explored underground, until within 10 to 40 or 50 feet from the surface it often mostly or entirely disappears. There are exceptions to this feature, but the gradual and often rapid decrease in quantity and grade of the carnotite ore as it is followed into a hill is generally recognized. This fact suggests that the carnotite may have been redissolved in the sandstone and carried to the surface by capillary action in this arid climate, forming rich, superficial efflorescences.

In many of the carnotite deposits, vanadium minerals occur independently of the vanadium in the carnotite, but this association is not always observed. They occur in sandstone and often give it a dark-gray or blackish color.

In eastern Colorado several mines near Central City, Gilpin County, have produced limited quantities of pitchblende. Among these are the Kirk, the Wood, the Belcher, the Alps, the German and the Calhoun mines. The pitchblende occurs as a subordinate constituent in the gold-bearing veins of that country. The veins intersect old metamorphic rocks intruded by igneous rocks. The mines of Gilpin County are today producing little if any pitchblende, and the total production has been small, amounting in all probably to only a few tons. Much more pitchblende, however, was let go to waste in former days when the mines were worked for other ores and the value of uranium was not recognized.

=Production.=--The United States is today by far the largest producer of radium and uranium ores in the world, and is also the largest producer of manufactured radium and uranium compounds. Before the war, England, France and Germany, especially Germany, imported large quantities of American ores and extracted the radium in a refined state as its different salts, much of which was returned to the United States for sale. Now, however, American ores are almost entirely treated in the United States, with the exception of a little shipped to England and possibly to France. The Standard Chemical Co., of Pittsburgh, was a pioneer in this work, and others quickly followed, among them the National Radium Institute, of Denver; the Schlesinger Radium Co., of Denver; the Chemical Products Co., of Denver; the Cummings Chemical Co., of Lansdowne, Pa.; the Radium Luminous Materials Corporation, of New York, and others.

Before the discovery of radium in 1898, but little attention was given to uranium ores in America, though some little pitchblende was shipped from the Central City, Colorado, region for use in making uranium compounds. Shortly after the discovery of radium, however, mining was begun on the carnotite of southwestern Colorado, and from 1900 to 1910 several companies were formed to work these ores both in Colorado and Utah. The pitchblende of Central City also began to attract renewed attention. For a few years active work was done in prospecting for it, but the quantities have so far proved to be small. A few tons probably represent the total amount derived from these mines since the search began. In the meantime, however, the production of carnotite increased rapidly until 1915, when it greatly decreased on account of the curtailment of shipments to Europe. In the latter part of 1916, however, the production increased again, on account of the increased consumption of ore in this country, and in 1918 the production was very active, largely on account of the increased use of radium not only in medicine but especially in luminous paints.

The amount of radium and uranium ores produced in the United States, or in fact anywhere, during a given period, is difficult to determine, on account of the different bases on which reports are made, but it may be said that the tonnage is small compared with that of ores of commoner metals, a few thousand tons being a large amount of carnotite, and simply a few tons or pounds being a large amount of pitchblende. Though the mining of radium and uranium ores in the United States began about 1900 or shortly before, no very large quantities were produced until 1912, when about 1,100 tons were mined, consisting chiefly of Colorado carnotite. The production gradually increased to several thousand tons yearly, practically all of which is carnotite from Colorado and Utah.

RADIUM AND URANIUM RESOURCES OF EUROPE

=Austria.=--The most important radium and uranium ore in Europe at present is the uraninite or pitchblende found in the mines of Joachimsthal, in _Bohemia_. It occurs as a subordinate gangue mineral in certain silver veins of that region which intersect metamorphic and igneous rocks, and has been actively worked ever since the discovery of radium by M. and Mme. Curie in 1898. Before that time the mineral had a certain value as a source of uranium compounds.

These Austrian mines are second to those of the United States as a source of radium and uranium, but their production equals only a very small part of that of this country. Until the Great War this production was controlled largely, if not wholly, by the Austrian government, and as the production is said still to continue, it is probably still controlled in the same way.

=England.=--Next in importance in Europe to the uraninite or pitchblende ore of Joachimsthal as a source of radium and uranium, is the similar ore in some of the mines of _Cornwall_, England. It occurs as a subordinate mineral in the gangue of some of the old tin and copper mines, in veins intersecting metamorphic and igneous rocks, especially at St. Just, St. Ives, Grampound Road, St. Austell and elsewhere. The production and treatment of the ore has been under private or corporate auspices and the amount produced has not been large.

=Germany.=--In Germany the production of radium and uranium ores has always been insignificant. A small quantity of such ores has been produced at Schneeberg, Johanngeorgenstadt, Annaberg and elsewhere. Before the war, Germany was a large producer of manufactured radium and uranium compounds, but they were derived mostly from imported American ores.

=Other Localities.=--With the exception of Joachimsthal and Cornwall, Europe has produced but small quantities of radium and uranium minerals. A little uraninite or pitchblende has been found in other localities in Austria, such as Przibram and elsewhere, and sparingly in _Norway_. Autunite and other uranium minerals have been found in small quantities near Autun, _France_, and near Sabugal and Guarda, in _Portugal_, but no important quantities have been produced.

RADIUM AND URANIUM RESOURCES OF AUSTRALIA, INDIA AND AFRICA

=Australia.=--In _South Australia_ carnotite, autunite, torbernite and other rare uranium minerals occur in regions of metamorphic and igneous rocks at Radium Hill, near Olary, and at Mount Painter, in the Flinders range. A few hundred tons of ore containing these minerals have been mined by private or corporation interests. Most of this has been sent to Woolwich, near Sydney, _New South Wales_, or to England, for the extraction of the radium. Since the war started no very active mining operations in such ores have been carried on in the South Australian region.

At Cooglegong, in _Western Australia_, the uranium mineral fergusonite and to a less extent the uranium mineral euxenite occur in the surface detrital material of the region. At Wodgina the minerals mackintoshite, thorogummite and pilbarite, all hydrous silicates of uranium, thorium and lead, occur in an albite pegmatite dike. No important quantities of these Western Australia ores have yet been produced.

=India and Africa.=--Radium and uranium minerals have been reported in _India_ and _German East Africa_, but no important quantities have yet been produced.

PROSPECT OF FUTURE DISCOVERIES OF RADIUM AND URANIUM ORES

The prospect for increased discoveries of radium and uranium minerals at the present time seems best in the carnotite regions of Colorado and Utah. The workable deposits seem to be more or less superficial, and perhaps no large quantity of ore may be found in any one spot, yet the great extent of the region in which the formations carrying carnotite occur, will supply an immense aggregate amount of ore.

Increased discoveries of uraninite, pitchblende and other uranium minerals in Europe seem possible, even though that continent has already been well explored for them. Moreover, new discoveries of different radium and uranium minerals may very likely be made in still other parts of the United States than those mentioned, and in less explored parts of the world, especially certain regions of South America, Australia, Asia and Africa. Many of these minerals, especially pitchblende, have no very distinctive features when first observed, and might readily be overlooked many times before their true nature was discovered. Hence the possibilities of future discoveries.