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.