Monazite, thorium, and mesothorium

TN

948
M7K6

Kithil

Monazite, Thorium and
Meaotboriua

THE LIBRARY

OF

THE UNIVERSITY
OF CALIFORNIA

LOS ANGELES

The

DKI'AKIMI

UNIVERSITY

U)S ANGELES. CALIF .

1 U. C. L A. DUPLICATE

Technical Paper 110 Mineral Technology 8

DEPARTMENT OF THE INTERIOR
BU RE AU OF MINES

JOSEPH A. HOLMES, DIRBCTOR

MONAZITE, THORIUM, AND
MESOTHORIUM

BY

KARL L. KITHIL

WASHINGTON

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1915

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First edition. June, 1915.

Geology
Library

TN

M7KG
CONTENTS.

Page.

Introduction 5

Properties of monazite 5

Occurrence of monazite '. 6

Where monazite is mined 6

History of production of monazite 7

First German thorium convention 7

Second German thorium convention 8

Causes of reduced price of thorium 9

Consumption of monazite 9

Prospecting for monazite deposits 10

Use of spectroscope 10

Monazite deposits in North and South Carolina 10

North Carolina 11

South Carolina 12

Deposits in Idaho and Colorado '. . . . 12

Idaho 12

Colorado 13

Deposits in Brazil 13

Mining of monazite in the Carolinas , 14

Milling methods in the Carolinas 16

Electromagnetic equipment used J 6

By-product separation .' 17

Cost of mining and milling 17

Comments on electromagnetic process 18

Estimated monazite resources 19

Duty on monazite exported from United States and Brazil 20

United States 20

Brazil 20

Import duties on monazite 20

Examination and valuation of monazite deposits 20

Attempts to use by-products 22

Method for the determination of thorium in monazite 23

Treatment of monazite for the extraction of thorium 24

Separation of mesothorium on a commercial scale 25

Quantitative determination of mesothorium 2(5

Minerals in monazite sands 27

Flow sheet 2?

Selected bibliography 30

Publications on mineral technology 31

ILLUSTRATION.

FIGURE 1. Flow sheet, shdwlng steps in process of magnetic separation of

monazite sands

3

MONAZITE, THORIUM, AND MESOTHORIUM.

By KARL, L. KITHIL.

INTRODUCTION.

The monazite industry in the United States has been practically at
a standstill since 1906, principally for the reason that monazite could
he mined and obtained cheaper from Brazil, where large deposits are
found and exploited along the seacoast and in the interior. For-
merly part of the monazite mined in the States of North and South
Carolina was used for the manufacture of thorium nitrate in this
country and part of the production was sent to Germany. It seems
an opportune time to call attention to the monazite deposits in the
United States, as the imports of thorium nitrate are at present cur-
tailed. There is reason to believe that a more general manufacture of
thorium nitrate may be developed in this country. It may be many
years before supplies of the nitrate from Europe can be depended
upon.

There are deposits of monazite in several of our States, and with
the knowledge that a valuable product — mesothorium — can be made
as a by-product from the residues of thorium nitrate manufacture the
industry may be developed in this country and should pay well.
Mesothorium is used successfully in therapy in the same manner as
radium.

With these facts in view the following description of the occurrences
of monazite in the United States, the uses to which its products can
be put, and the methods of mining and treatment has been prepared
by the Bureau of Mines with the purpose of aiding more efficient
utilization of radioactive minerals.

PROPERTIES OF MONAZITE.

Monazite is an anhydrous phosphate of the rare earths, especially
cerium, lanthanum, neodymium, praseodymium, yttrium, and
erbium, and contains also a small percentage of thorium. So far its
content of thoria only gives the mineral its commercial importance,
although a market is being developed for some of the other rare
earths in special types of electrodes for arc lamps and in the flaming
arc. The content of thoria in monazite is small and varies from a
fraction of 1 per cent to about 12 per cent, although monazite con-
taining less than 3£ per cent of ThO2 can not be used successfully in

5

1019019

6 MONAZITE, THORIUM, AND MESOTHORIUM.

the manufacture of thorium nitrate, which is the important chemical
product necessary for the manufacture of incandescent gas mantles.
In this manufacture the thorium is mixed with 1 to 2 per cent of other
nitrates of the rare earths. References to the percentage of thoria in
"monazite" generally apply to a sand containing about 92 to 95 per
cent of true monazite; such sand is sold in the market on the basis of
its content of thoria at a fixed price per unit.

Monazite possesses radioactive properties strong enough to affect
a photographic plate and to be measured in the electroscope. The
activity of the sand is due to its content of mesothorium and radium.

The specific gravity of monazite varies from 4.9 to 5.3. It has a
hardness of 5, is somewhat brittle, and can be easily pulverized.

Nearly all of the monazite brought to the market is of a yellowish,
resinous color. The Brazilian monazite of the coast lands appears to
have a more uniform shade of color and size of grain than the mona-
zite from the interior. The region from which monazite from the
Carolinas has been mined can often be determined by its color alone.
Carolinian monazite ranges from yellowish to brownish, greenish and

grayish in color.

OCCURRENCE OF MONAZITE.

Monazite is usually found in the gravel of small streams or bottom
lands, but sometimes it is also found in the soil of hillsides. In Brazil
it occurs also in the beach sands of the coast. In places it is found in
small crystals in gneiss, granite, and pegmatite (crystalline) rocks.

As these rocks become disintegrated, the crystals are washed into
the creeks and streams _and, together with other heavy sands, are
deposited in the beds of such watercourses. They are thus concen-
trated in the gravel by the natural flow of the water; the lighter
clay and quartz sand being carried away. On the coast of Brazil the
monazite from the crystalline rocks of the coastal mountains is con-
centrated in strata by the waves of the sea. The mountain sides are
washed down by the strong waves at high tide and during storms.

In some places, especially Norway, monazite is imbedded in thin
layers of mica (biotite) in strata or, in places, in mica schists. Such
monazite is usually of high grade but, on account of the enormous
masses of rock material that have to be handled and crushed before
concentration, these deposits can not be considered of commercial
importance. The proportion of monazite in these rocks averages
perhaps 0.01 per cent.

WHERE MONAZITE IS MINED.

Monazite has thus far been mined successfully only in North and
South America — 'in North America, in the Carolinas and in Idaho,
and in South America in Brazil. The Brazil deposits occur along
the coast of the States of Bahia and Espirito Santo, and also less

HISTORY OF PRODUCTION OF MONAZITE. 7

abundantly on the Parahyba River in the States of Eio de Janeiro
and Minas Geraes. Other coastal lands in the State of Rio de
Janeiro have also been worked. Deposits of monazite sand have
been found, too, in Swaziland, Africa, as well as in Ceylon and in
Australia. In Jekaterinburg, Russia, it occurs in native rock and
placers. It has also been exported from Trovancore, India.

In the United States, occurrences of monazite are known in many
other States than the Carolinas, but it is probable that the deposits
in Idaho and the Carolinas alone are of importance commercially.

Brazil has furnished the bulk of monazite for commercial use.
Little has been mined elsewhere since the enormous price cut in the
earlier part of 1906, as the workings in the Carolinas have been
gradually abandoned. For some years past Brazil has furnished all
of the monazite for the gas-mantle industry for both Europe and the
United States.

HISTORY OF PRODUCTION OF MONAZITE.

Although generally known to interested persons, a short history
of the development of production and final overproduction of this
once rare mineral may be warranted.

The first monazite used in Europe for chemical purposes was
brought at great expense from Sweden and Norway.

About 27 years ago John Gordon, an American, found monazite
on the coast of Brazil, in the State of Bahia, and brought the mineral
in large quantities to Hamburg. The supply was sufficient to furnish
the thorium industry of the entire world with monazite at a com-
paratively low price. Mr. Gordon obtained a monopoly of the Bahian
monazite sands.

At that time the manufacture of thorium nitrate in Europe as a
specialty was confined to a few large chemical firms in Germany and
to the Welsbach Co. in Vienna. These were the only firms that
provided the European market with thorium nitrate. They also
sent large quantities of the nitrate to the United States. The
American Welsbach Co. early manufactured thorium nitrate from
sands mined in the Carolinas, a protective duty of 6 cents per pound
making this possible, as the mining of monazite in this country is
more expensive than in Brazil.

FIRST GERMAN THORIUM CONVENTION.

Late in 1902 Mr. Gordon entered into an agreement with the four
largest German manufacturers and with the Austrian manufacturer
by which he agreed to furnish monazite at a price of $150 per metric
ton and a percentage of the profits from the manufactured nitrates.
With this agreement a close combination was formed which prevented
other thorium manufacturers from acquiring any of the mineral

8 MONAZITE, THORIUM, AND MESOTHOBIUM.

mined by Mr. Gordon. The combination was known as the German
Thorium Convention, which, after the conclusion of the agreement
with Mr. Gordon, immediately raised the price of thorium nitrate
100 per cent.

Mr. Gordon's supply came from the coast lands of Bahia, near
Prado, Brazil, and he exported the sands for a long period without
interference. Finally the Brazilian Government became acquainted
with the value of the resources and found an old law according to
which all of the Brazilian coast lands along the sea and navigable
rivers belong exclusively to the Federal Government for defensive
purposes. The Government concluded, therefore, that no private
individual or State government had the right to mine, sell, lease, or
remove any of this property without the consent of Federal authority.
In 1903 the Government of Brazil advertised that coast lands in the
State of Espirito Santo would be leased to the highest bidder for the
exploitation of the sands lying within its territory.

A business man living in Rio de Janeiro made a contract with the
Government, but for some reason allowed it to lapse. Finally an
engineer obtained the contract for the firm of A. C. de Freitas & Co.,
of Hamburg, Germany. By the contract the firm mentioned agreed
to pay to the Brazilian Government a rental of 50 per cent of the
selling price of monazite sand and to export at least 1 ,200 tons annu-
ally during the life of the contract.

SECOND GERMAN THORIUM CONVENTION.

To avoid interference, the German Thorium Convention arranged,
later on, that half of its supply should be furnished by Mr. Gordon
and half by the De Freitas Company; and a new convention was
formed by the four German chemical manufacturers with Mr. Gordon
and the De Freitas Company by which the latter two were to supply
the monazite to the four German manufacturers only and were to
receive therefor $150 per ton of monazite and a percentage of the
profits from the sale of the nitrates.

As a result of the convention other firms in various countries, which
had in the meantime begun to manufacture thorium nitrate, were
without a supply of raw material and had to depend upon the ashes
of spent mantles. Consequently, they made every effort to find and
develop new deposits of monazite in Brazil, the Carolinas, and else-
where. The whole world was searched for rare-earth minerals by
their engineers, with the interest and assistance of many governments.
The high price for thorium nitrate made it possible to mine monazite
hi the Carolinas and export it to Germany; thus one German manu-
facturer— an outsider — received his supply from North and South
Carolina. Later, American firms independent of the Welsbach com-

HISTORY OF PRODUCTION OF MONAZITE. 9

panies began to buy monazite in the Carolinas, and by the compe-
tition created for a brief period caused the price for lands and monazite
sand to rise to a point highly profitable to the farmers and landowners
of the Carolinas.

CAUSES OF REDUCED PRICE OF THORIUM.

On account of overproduction in thorium, the price for thorium
nitrate was suddenly dropped 50 per cent by the convention in the
year 1906. The mining of monazite consequently decreased in all
localities where the cost of the mining was high, as, for instance, in.
the Carolinas.

Since 1906 other difficulties have arisen between the Vienna and
English Welsbach companies and the German Thorium Convention;
and in 1910 the price was further lowered to a point that made the
mining of monazite absolutely unprofitable in the Carolinas, and also
in the interior of Brazil. The market was flooded with monazite
until the outbreak of the European war.

The German Incandescent Gas Light Co. of Berlin has succeeded
during the past few years in controlling the largest manufacturers of
thorium nitrate in Europe with the exception of those in France.
The German concern controls now both the English and Austrian
Welsbach companies, and consequently their thorium nitrate plant
in Austria. This combination is the strongest competitor of the so-
called Thorium Convention, and the latter has lost much of its power.

CONSUMPTION OF MONAZITE.

The world's consumption of monazite is now about 3,000 tons per
annum. The annual world consumption of incandescent gas mantles
is estimated at three hundred million. The United States alone, in
spite of the development and use of the electric metal-filament lamps,
has consumed in the past few years some eighty million incandescent
gas mantles as against forty million total before the year 1904.

In the manufacture of such gas mantles about 0.5 gram of ThO2,
equal to 1 gram of thorium nitrate, is used per mantle; hence, the
world consumption of thorium nitrate is 300,000 kilos, equal to
150,000 kilos of ThO2 per annum. If monazite is considered to
contain 5 per cent ThO2, with a 90 per cent recovery in the manufac-
ture, 1,000 kilos (1 metric ton) of monazite will yield 90 kilos of
thorium nitrate. The gas mantles are made of 99 per cent thorium
and 1 per cent cerium.

Perhaps the best work in regard to the manufacture of thorium
nitrate and incandescent gas mantles has been written by Bohrn.0

oBohm, Richard, Das Gasgluehlicht, Die Fabrication der Gluehkoerper fuer Oasgluehlicht, Leipsic
1905; Die Thorium Industrie: Chem. Ind., vol. 9, 1906, vol. 29, pp. 450-488.

93290°— 15 -2

10 MONAZITE, THORIUM, AND MESOTHORIUM.

PROSPECTING FOR MONAZITE DEPOSITS.

Prospecting for monazite is similar to a search for gold. The
mining pan of the batea is the most convenient apparatus in which
to wash the gravels of the streams and separate the heavier sands, from
among which monazite can be easily detected by its peculiar luster
and color. Sounding rods should be employed if quick estimates
are desirable and if the thickness and composition of the overlying
burden in the bottom lands must be established. The concentrated
material of the pannings is dried and sent to the chemical laboratory
for determination of the content of thoria and other rare earths.

USE OF SPECTROSCOPE.

It probably is not widely known that the presence of some of the
rare earths in monazite can be easily detected by the aid of a spec-
troscope, a pocket or hand spectroscope being sufficient. Peculiar
as it may seem, the presence of rare earths in the monazite samples
as taken from the pan can be at once determined by this method.
Determination is best accomplished by spreading some of the con-
centrated sand on a piece of paper or cloth and holding the spectro-
scope over the. sand at a convenient angle, the natural light falling
directly on the sand. A f airly broad dark line will appear between the
red and the yellow of the spectrum, and another but narrower line
will be seen in the green. These dark absorption bands seem to be
due principally to the presence of the rare-earth oxides of neodymium,
praseodymium, and erbium contained in the mineral. Such spec-
trum tests for monazite can be safely relied upon when observed by
the trained eye. The entire spectrum used is divided into a scale
of 63 mm., the first and broader dark line becoming visible between
the 13 and 15 mm. lines. The narrow dark line appears between 21
and 22 mm. of the scale.

The spectrum method of testing in the field is most helpful in fara-
way places where a laboratory is not available.

MONAZITE DEPOSITS IN NORTH AND SOUTH CAROLINA.

The monazite deposits in the Carolinas cover an area of several
hundred square miles east of the Blue Ridge Mountains and extend
in a southwest direction. In North Carolina the counties of Cleve-
land, 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 the gravels in the streams and bottom lands, the miner usually
following the old courses of the streams and creeks in the bottoms.
The gravels are of greatly varying thickness throughout, and it is,
therefore, difficult to arrive at a true estimate for an average value.

MONAZLTE DEPOSITS IN NORTH AND SOUTH CAROLINA. 11

From experience, however, it can be estimated that an average thick-
ness of the monazite-bearing gravels is between 1£ and 2£ feet. There
are deposits with a thickness of 3 feet and more, but they are of rare
occurrence. The top soil in the bottom lands varies on an average
from 3 to 6 feet, and on the outer seams of the bottom toward the
hillsides frequently increases to a thickness of 7 feet or more. The
top soil is barren and consists usually of sandy soil interlined with
clays, or is of clayey matter throughout. Hydraulic methods have
been tried on some of the richer soil deposits, but without much
success.

NORTH CAROLINA.

In North Carolina deposits of monazite sand are found in Burke
County in the Brindletown district. Here monazite is obtained from
the hydraulic washings of the gold placers. The content of monazite
in the concentrated black sands, however, is small compared with that
of the sluicing concentrates of other sections. The monazite in this
section after being purified seldom shows a higher content than 3.5 to
3.75 per cent ThO2. There is considerable magnetite in these sands,
and the bulk of the concentrates consists of ilmenite (titanif erous iron) .

McDowell County has a number of deposits in the vicinity of
Muddy Creek. The occurrence of monazite here is closely similar
to that of Brindletown, but perhaps contains less gold in the sand.

In Rutherford County, within a few miles of Rutherfordton, there
are a number of deposits that have been profitably worked for some
time for both gold and monazite. The gold has usually been extracted
by the miner and the residues further concentrated and shipped for
their content of monazite. This district is especially interesting on
account of the large area of the wide bottom lands where the gravel
bearing monazite and gold is found to a greater extent than in most
other sections. The percentage of monazite in the gravel, however, is
not large, and these lands have been worked profitably only on account
of their gold content, the monazite being obtained as a by-product.

Much activity was shown years ago in the vicinity of Ellenboro,
extending to Oak Spring and Sandy Run Creek and up as far as
Duncan, which is about 18 miles from Ellenboro. The deposits in
this region are more or less alike and the monazite obtained is of good
grade and can still furnish considerable quantities of concentrates.
Near Ellenboro is a hillside deposit in which monazite is found in a
comparatively pure state in the sand of the hillside as well as in the
gravels of the bottom lands.

Cleveland County has a considerable area of riionazite-bea>ring
gravels which extends between Shelby and Mooresboro via Fallston
to a place called Zite near Carpenters Knob, a well-known peak in that
section. The deposits around Fallston and in the entire Carpenters
Knob region are of great importance and have furnished monazite

12 MONAZITE, THORIUM, AND MESOTHOBIUM.

concentrates of especially high thorium content. The rough concen-
trates obtained from many of the streams in that region contain less
black sand and garnets than those in most other sections.

There are also fair deposits in Lincoln County about 15 miles north-
west of Lincolnton. These deposits can also be reached from Shelby,
N.C.

Alexander County has furnished some monazite concentrates, and
there is no doubt but that other deposits can be found in that county.

There has been in former years considerable activity also near Hil-
debran, Burke County, where fair deposits of considerable extent have
been found.

SOUTH CAROLINA.

Nearly all the monazite-bearing gravel in South Carolina is found
north of Gaffney, Cherokee County, and Cowpens, Spartanburg
County, and in the vicinity of Greenville, Greenville County, south
of the Southern Railway.

There is a considerable area of monazite found in the gravels of
the creeks and bottoms in all of these sections, and although there
have been obtained considerable quantities of monazite concentrates
containing 30 to 40 per cent of monazite, the bulk of the crude con-
centrates coming from these South Carolina sections have been of
the "black-sand" variety containing considerable ilmenite.

Many of these deposits in both North and South Carolina have
been described by others, and the reader is referred to the bibli-
ography at the end of this report.

DEPOSITS IN IDAHO AND COLORADO.

The Idaho monazite deposits and the treatment of the gold-
monazite-bearing sands in that State have been well described by
Sterrett,0 also by Schrader,6 and the concentration methods for the
monazite sand used in Idaho are mentioned in the report of the
Idaho inspector of mines for 1910.

The monazite deposits near Centerville and Idaho City, Idaho,
seem to be of especial importance. There is no doubt but that con-
siderable monazite will be found in many places in the State and all the
gravels of the deposits contain a considerable amount of gold which
makes possible the working of such deposits for both gold and
monazite. The gravel beds are considerably thicker than those in
the Carolinas, and much monazite should be obtained from the
tailings from the old gold washings. It must be remembered, how-
ever, that the wages paid to the miners in Idaho are considerably
higher than those paid in the Carolinas.

« Sterrett, D. B., Monazite in Idaho: U. S. Geol. Survey Mineral Resources, 1909, pp. 898-903, 1910.
* Schrader, F. C., An occurrence of monazite in northern Idaho: IT. S. Geol. Survey Bull. 430, 1910, p. 184.

DEPOSITS IN BRAZIL. 13

COLORADO.

Monazite has been found in thg State of Colorado some 20 miles
south of Denver in the Newlands Gulch district, where the monazite
occurs in some of the gravels, which carry also considerable gold.
Monazite is also reported in the Platte Canyon.

DEPOSITS IN BRAZIL.

There are three kinds of deposits of monazitic sands found in
Brazil, as follows:

1. Deposits within the marinhas (Government lands).

2. Deposits lying behind the marinhas that are private State
possessions or belong to private parties.

3. Inland deposits.

The marinhas extend from points in the State of Rio de Janeiro
north through the State of Espirito Santo into the State of Bahia.

The bulk of the monazite is derived from these coast sands in the
States of Espirito Santo and Bahia. The monazite sand at some
places could in former years be taken off the beach by skimming the
surface after each tide, and was pure enough to be shipped.in the crude
state. In later years, however, the material has been of consider-
ably lower grade, so that oscillating tables have been employed, and
some of the sands have been washed in sluice boxes wherever enough
fresh water was obtainable. The sluice boxes used are larger and
of a different construction than in the Carolinas, and no perforated
plate is necessary, as there is no coarse gravel in the beach sands.
Electromagnetic separators have also been used direct. These
coast lands, called "marinhas," are the property of the Federal
Government for 33 meters inland, measured from the point where
the sea waters wash the beach at mean high tide. This method of
marking property is uncertain, and has, of course, given rise to dis-
putes when boundaries are established.

At a few places along the coast are strips of monazite-bearing sands,
lying directly behind or not far from the so-called marinhas, and some
of these could be worked profitably were it not for the difficulties
of proving to the Federal Government that these sands were not taken
from the near-by marinhas. One French concern is exploiting such
lands near Itabapoana, in the State of Rio de Janeiro, and has
exported several hundred tons of the mineral annually for some years.
There are several other deposits that could be worked, situated
between Gargahu and Itabapoana; but, owing to political influences,
no other concerns have thus far been able to obtain concessions.

In the interior of Brazil, monazite occurs in many places, but a
fuller description of the localities and deposits will not be given here.

The deposits of monazite in the interior of Brazil are of a formation
similar to those in the Carolinas, the small streams and bottom lands

14 MONAZITE, THORIUM, AND MESOTHORIUM. •

containing the only deposits of sands possessing commercial impor-
tance.

The contents of monazite in the gravels of the streams and bottom
lands averages about 0.25 to 0.3 per cent, a proportion about the
same as that in the monazite in the Carolinas. There are richer
deposits, however, in several sections.

Along the banks of larger rivers, as, for instance, the Parahyba,
great quantities of black sands with traces of monazite are found.
Near Sapucaia, opposite Benjamin Constant Station on the Central
Railway, such deposits have been worked by a French concern. They
finally had to stop work at this point and abandon also their openings
hi the mountainous part of this region.

Many of the inland deposits can not be exploited on account of the
expense of transportation of the product, the deposits being situated
many miles from the railroad and the roads and trails being in such
condition that it is often difficult to travel over them even with the
mule caraven (troupa). The soft clays in the thickets of the jungle-
like forests and the crossing of swamps make travel in many cases
almost impossible, especially with a heavy burden laden on the mule's
back. The rivers in most sections are not yet navigable. Frequent
floods, caused by heavy tropical rains, and the lack of proper labor
make difficult continuous operation in the interior of Brazil.

At the present prices of thorium nitrate such lands in the interior
can not be profitably exploited by any known method. When once
the large deposits along the coast are exhausted, however, and
the price for thorium rises, or if some other uses for the mineral and
its rare-earth contents are discovered, then these deposits may
become available.

MINING OF MONAZITE IN THE CAROLINAS.

Most of the mining for monazite in the Carolinas is carried out in
a primitive way, similar to the old methods of gold mining. The
gravel is washed in sluice boxes without riffles, the sands being stirred
with a square shovel, with an upward movement toward the head of
the sluice box, the sands of higher specific gravity being thus concen-
trated, whereas the lighter clay and some of the quartz sand are
washed away. The gravel dug from the pit is thrown on a perforated
plate, which is fastened over the head of the sluice box. The larger
stones are removed from the plate. A stream of water (about 18 to
20 gallons per minute) is fed through a spout to the gravel on the
screen, and the sand is washed through the holes, about one-eighth
of an inch in diameter, in the plate into the head of the box. Usu-
ally two men are employed to each sluice box, one digging and lifting
the gravel out of the pit to the screen and the other concentrating the
sand by stirring it in the box with the motion described above. With

MINING OP MONAZITE IN THE CAROLINAS. 15

this method much of the finer sand is lost, as the grains of sand vary
greatly in size, and the finer, heavier grains of monazite are carried
away by mechanical action with the lighter and coarser quartz. If
the sands are properly sized before being washed, a much better
result can be obtained, and practically all of the monazite contained
in the gravel or sand can thus be saved.

The sluice boxes are of such construction that easy transportation
is possible, a desirable feature, because, as the gravel is worked out
in one pit in one or two days' time, the boxes then have to be moved
higher up the stream or bottom. It has been found more practical
and cheaper to remove the box to the deposit than to bring the gravel
to the box. The sluice box is usually brought over the pit, which
has been worked out previous to the removal of the box, thereby
furnishing, to some extent, a dumping place for the tailings that flow
off the end of the sluice box. However, as the amount of tailings
washed out during one day is large, the so-called "tail-raise" must
be cleaned out with the shovel several times during the day, the tail-
ings so removed being thrown to one side of the bank of the tail-
raise. This is necessary in most instances, as the lands slope only
slightly, and in some sections the bottoms and stream beds are almost
level.

After the sands have been concentrated in the sluice box, the con-
centrates are often rewashed by an experienced hand and a further
amount of useless material removed. The concentrates are then
dried in the sun or in a form of drier — usually made of a piece of
sheet iron with turned-up edges — a wood fire being built underneath.

Many of the Carolina mines could not have been exploited had it
not been for the fact that the people worked out the mineral on their
own account from small deposits during times when no farm work
could be done. They seldom figured their time of work, mined out
what they could, and brought it to the separating plants, where they
were paid in cash at the rate of about 8 cents per pound of pure
monazite (machine-cleaned sand). Others were employed by some
of the corporations at about 80 cents to $1.25 per day at the richer
mines. It was not long, however, before new dealers arrived in the
Carolinas, greatly inspired by the high prices which were then paid
for the nitrate, who, knowing little of the trade, and with only crude
means of judging the content of monazite in the washed concentrates,
paid 12, 15, and often as high as 35 cents per pound, based on con-
centrates containing 92 per cent monazite. This development caused
unhealthy competition, which proved fatal to the farmers and small
operators, as they went to large expense to produce large quantities
of the sand, which they then held for higher prices, but could not sell
at all when finally the market for thorium nitrate broke. To-day
there is no mining of monazite in the Carolinas.

16 MONAZITE, THORIUM, AND MESOTHORIUM.

MILLING METHODS IN THE CAROLINAS

The deposits are too scattered and are not extensive enough to make
practical or profitable the use of sliming and oscillating tables. Other
concentrating apparatus of special design can be utilized, and with
proper sizing of the material excellent results can be obtained with
such machines and methods, as has often been demonstrated by prac-
tical tests.

The concentrates produced in the sluice boxes contain 20 to 60 per
cent of monazite. An average of about 35 per cent can be considered
a conservative estimate as a result of practical experience. The
concentrates have to be further refined, and are best treated by
electromagnetic separators, of which the Wetherill-Rowand type has
proved to be the most useful to the industry. The testing labora-
tories of Krupp now use a new type of electromagnetic separator of
the Ullrich type, which treats the material either "wet" or dry.. It
is reported to have a capacity of about 2 tons of material per hour,
which is considerably larger than that of any other type of magnetic
separator heretofore kno'wn. The Daggett separator has also been
used successfully for this kind of concentration.

ELECTROMAGNETIC EQUIPMENT USED.

In the separation of monazite from other minerals and its gangue
materials, electromagnetic methods0 were found to be most efficient.

Weakly magnetic bodies can be separated from each other by em-
ploying highly concentrated magnetic fields. Such separation is made
possible on account of the difference in the magnetic permeability of
different material. However, the magnetic permeability as a physical
property can be fixed only for absolutely pure material, entirely free
from any admixtures, as such admixtures of foreign matter influence
considerably the magnetic relativity of the material to be treated, and
it therefore can not be applied as a theory in the treatment of most
minerals, which always carry a certain amount of impurities. And
furthermore, it is impossible to bring different minerals, by known
methods of crushing, grinding, etc., to a uniform size and shape of
particles, as further factors, such as amount tested and whether the
charge is packed tight or loose, affect the results, and not even com-
paratively correct results can be obtained. Only practical tests,
therefore, will satisfactorily determine the best results for ores and
minerals, as on most of such electromagnetic separators the magnetic
power can be controlled to the finest points by means of a rheostat.
The intensity of the magnetic field must be adjusted for each specific
separation of minerals.

The large type of Wetherill separator has been used hi the United
States and in Brazil for the concentration of monazite. The separator

o See Gunther, C. G., Electromagnetic Ore Separation, 1909. See also "Bibliography on magnetic
concentration" in Richards, R. H., Ore dressing, 1909, vol. 2, pp. 832-837.

MILLING METHODS IN THE CAROLINAS. 17

has two magnets of different sizes, one being nearly twice the size of
the other. Each of these magnets has two pairs of poles, forming four
magnetic fields and permitting a separation of two products with each
magnet. (See fig. 1, p. 29.) The magnets are best adjusted so that
the first pole of the first magnet removes from the sand the highly
magnetic material, as, for instance, the magnetite and ilmenite; the
second pole of the first magnet extracts the garnets and also the finer
grams of ilmenite; the third magnet (being the first pole of the second
magnet) removes all of the coarser grains of monazite; and the last
pole extracts the finer grains of monazite. At the end turn of the
18-inch rubber belt of the machine the residues are then dropped into
a receptacle. This is best arranged in such manner that the residues
are dropped from the funnel of the receptacle into the feed box of a
small oscillating table, or other suitable means for the wet concentra-
tion of the gold and zircon, which are often present in small quantities.
Some fine monazite escaping with the nonmagnetic material may also
be recovered.

BY-PRODUCT SEPARATION.

Sometimes the by-products are found to be valuable enough for
market, and it is then of advantage to make a still finer separation,
which can be accomplished by employing a type of separator with
three magnets — giving six magnetic fields — of three different sizes
and strengths, the last magnet being the largest and strongest. In
this way the poles can be adjusted so that each magnetic field attracts
and removes practically the entire amount of one certain kind of
mineral contained in the sands, thereby giving six distinct products,
besides all of the nonmagnetic products, which are separated at the
end of the magnetic operation by running the residues over an oscil-
lating table.

COST OF MINING AND MILLING.

The deposits of monazite sands in the Carolinas are, as has been
previously stated, patchy, and not one single deposit is known to be
large enough to justify the erection of a large washing and concen-
trating plant at the mine itself. The 'magnetic separators are best
placed at a point on a railroad, and as nearly as possible in a district
central to many deposits.

The percentage of monazite in the gravel averages 0.25 per cent.
It will thus be seen that enormous quantities of crude material have
to be handled in order to obtain a ton of marketable material — about
400 tons of gravel furnishes 1 ton of monazite. In addition, the
quantities of barren overburden which must be removed have to
be added. The overburden often averages more than double the
amount of gravel to be moved. No monazite in the Carolinas can
be mined by present methods for less than 6 to 8 cents per pound of

18 MONAZITE, THORIUM, AND 'MESOTHORIUM.

monazite contained in the concentrated material as taken out of the
sluice box. This means that to the cost of the mining must be added
the cost of further concentration, sacking, interest on investment,
amortization on plant, management, freight, cartage, etc.

One man can dig and remove in nine hours (this being the usual
working shift in the Carolinas) about 9 cubic yards of material, includ-
ing top soil, barren sand and clay, and monazite-b earing gravel.

The wages paid are $1 to $1.25 a day. Therefore if we take for
a rough calculation an area of 3 square yards of ground and a depth
of soil and gravel of 9 feet, equal to 27 cubic yards, or about 80,000
pounds in weight, the cost would be as follows:

For digging and removing of barren material and dump, and digging
and removing to sluice box of the monazite-bearing gravel, 3 men
at $1.25, 1 day each, or $3.75; for rough washing of 9 cubic yards
of gravel in sluice box, 1 man 1 day, $1.25; final cleaning up in special
sluice box of rough concentrates, $0.50 — a total of $5.25.

As the content of monazite in gravel is 0.25 per cent, or about 68
pounds of pure monazite in washed concentrates, the cost is about
7f cents per pound of monazite contained in the washed concentrates.

The cost of transportation to the magnetic separator varies accord-
ing to the distance over which the material has to be hauled, and
averages about $4 per ton of monazite in concentrates, making a total
cost of $159 per ton of monazite in concentrates. To this has to be
added the cost of drying of the crude concentrates, and of electro-
magnetic separation. When the plant is running to its full capacity
(9-hour shift), turning out about 3 tons of pure monazite per shift,
$10 for treatment, depreciation, separation, and repairs can safely
be added to the above amount per ton of monazite. The entire cost
of 1 ton of machine-separated monazite, containing 92 to 95 per cent
monazite and about 4£ per cent ThO2 is, therefore, $169 at the con-
centrating plant. To this has to be added the cost of management,
commissions, tolls, if any, loading on cars, and freight to chemical
plant or port.

COMMENTS ON ELECTROMAGNETIC PROCESS.

In concentrating monazite sands by the electromagnetic process,
it is essential that great care be taken throughout the entire operation
that the strength of the current is the same at all times, as the slightest
variation will cause imperfect separation. An impure product and
much loss of monazite will result unless this precaution is observed,
as the monazite will be taken up by the wrong poles. This contin-
gency is more fully illustrated below:

If the strength of current be too great, some of the monazite will be
mixed with the valueless ilmenite or garnets; or, if the amperage be
too low, ilmenite or garnets will be carried over to the next following
pole, and will then become mixed with the monazite, and, at the same

ESTIMATED MONAZITE RESOURCES. 19

time, too many of the liner grains of monazite will escape in the tail-
ings. The distance between pole magnets must be carefully adjusted,
and the number of amperes for each magnet regulated by rheostats
for each kind of sand, for every section of the country, or even when
from the same section different percentages of monazite and impuri-
ties are present.™

It may be stated that a better result is obtained when the sands
are slightly roasted before magnetic separation than if they are
simply sun-dried or air-dried. The difference is due to the fact that
roasting renders the material more magnetic. It has accordingly
been found that the proper adjustment of the amperage for magnetic
separation is quite different for sands that have been sun-dried than
for those dried over the fire.

Other electromagnetic separators have been used, operating on
similar principles, but did not give as high concentrates in one oper-
ation as the Wetherill type, although, perhaps, the new Krupp sepa-
rator may do so. However, some other concentrators have been used
with fair results.

By-products usually found in the residues that can be separated by
employing an oscillating table are zircon, rutile, gold, and sometimes
platinum. Some of the platinum is slightly magnetic, and may be
lost during this process of separation.

ESTIMATED MONAZITE RESOURCES.

It is difficult to give even a rough estimate of the quantities of
monazite obtainable in the various countries where it occurs. From
close calculations, however, it is estimated that the lands in the
marinhas along the sea coast of Brazil may yield from 15,000 to
20,000 tons of pure monazite. This does not include coast lands
where the deposits have been formed in comparatively short time.

In the interior of Brazil the writer knows of about 18,000,000 tons
of monazite-bearing gravel deposits which should yield monazite
containing 4^ per cent of thorium oxide; and it can be estimated that
these gravels contain 45,000 to 60,000 tons of monazite. No doubt
there will be found many other deposits of greater or less extent in
the interior of Brazil, but no single deposit in the interior, so far as
known, would warrant the erection of a large plant. In sections
where several large deposits are found together or near each other a
washing and concentrating plant might be profitably established,
provided that the price for the monazite obtained were higher than
at present (May, 1915), and especially if transportation facilities from
the interior to the coast became better..

The amount of purified monazite available in the Carolinas may be
conservatively estimated at about 15,000 to 20,000 tons (4£ per
cent ThO2).

a See table on page. 28.

20 - MONAZITE, THORIUM, AND MESOTHORIUM.

With better methods of mining and refining the moiiazite, perhaps
those deposits could be profitably exploited at the present prices for
monazite and thorium nitrate, especially if the mining of monazite
were carried on in connection with the manufacture of thorium nitrate
and inesothorium.

It is known that attempts have been made to extract the monazite
from the native rock, but this operation with even the richest rock
known — 0.1 to 0.2 per cent of monazite — has proved to be too expen-
sive, and such endeavors have been given up as hopeless.

DUTY ON MONAZITE EXPORTED FROM UNITED STATES AND
BRAZIL.

UNITED STATES.

There is no duty on monozite exported from the United States.

BRAZIL.

The duties on monazite exported from Brazil vary greatly, and
are as follows:

BRAZILIAN EXPORT DUTIES.

Federal Government. — Duty on monazite from the marinhas —
situated along the entire coast and navigable rivers of Brazil — is
charged at the rate of 50 per cent ad valorem, and is fixed at £30, or
about $150, per ton. Individual States have fixed duties, as follows:

Rio de Janeiro. — 651000 per metric ton (approximately $21).

Espirito Santo. — 80 per cent of selling value, established to be
£25 per ton. This duty is varying and is subject to reduction when
applied for.

Minas Geraes. — 12 per cent ad valorem, fixed at £25 per ton and
25 per cent ad valorem, fixed at £25 per ton, plus £2 specific duty.

IMPORT DUTIES ON MONAZITE.

The duty on monazite imported into the United States has been
6 cents per pound, but was reduced to 4 cents in 1910, and is now
25 per cent ad valorem.

The import duty on mantle ashes is $10 ad valorem.

The import duty on nitrates has been 25 per cent ad valorem.

EXAMINATION AND VALUATION OF MONAZITE DEPOSITS.

The following features should be ascertained in the investigation
of monazite deposits for exploitation:

1. Extent and depth of the monazite-bearing alluvial deposits,
sands, and gravels in river beds and bottoms.

2. Amount and character of barren overburden overlying the gravel
or sand deposit.

3. The percentage of monazite contained in the raw material to
be treated.

EXAMINATION AND VALUATION OF MONAZITE DEPOSITS. 21

4. Percentage of thorium oxide contained in the monazite.

5. Transportation facilities and cost of transportation.

6. Water conditions— rain-fall throughout the year and water
supply for concentrating purposes and for the boiler.

7. Timber obtainable on or near property for building use, fuel,
etc.

8. Depth and character of bedrock.

9. Occurrence and character of clays.

10. Power available.

11. Labor, also conditions for housing.

12. Mining laws.

13. Cost of supplies.

14. Import and export duties.

15. Best-suited methods for exploitation (concentration, etc.)

16. Quantities and value of by-products and methods of obtaining
same.

17. Dumping ground.

18. Inclination of surface of property.

These points having been thoroughly determined, and also
whether the existent volume of material, together with other condi-
tions, will warrant exploitation and the erection of a plant, it should
be concluded from the topographic features which methods of exploi-
tation of the material will be most suitable.

In determining the average extent and depth of such alluvial
deposits great care must be taken to ascertain the situation of the
old channels of the streams, as many of the deposits in bottom lands
are irregular, so that a true estimate of the amount of gravel or sand
contained can be given only after thorough testing by way of sound-
ings, and especially by opening test pits at short distances from
each other. As the percentage of the mineral contained in the
gravels is small and the thickness of the deposit is usually slight, it
will be realized that an enormous area of gravel and sand deposit
must be within easy reach to insure profitable exploitation. The
relation of volume to richness is therefore a most important con-
sideration.

Transportation is a feature that has to be well considered.

In sections in the Carolinas quickly rising streams and sudden
torrents have destroyed dams and carried away sluice boxes, imple-
ments, and other materials obtained by hard labor. Uncovered
deposits have been covered up again with the sands and mud brought
from the mountains duiing such torrents. Rich deposits have also
been purchased during favorable seasons, which could ordinarily
be worked during short periods only, on account of lack of water or,
in winter, hard frozen gravel, the thawing of which was too expensive.
Had the conditions been properly studied, much loss might have been
avoided.

22 MONAZITE, THORIUM, AND MESOTHORIUM.

Careful forethought regarding a dumping ground should be made
in all developments, for large quantities of bowlders, clay, and tail-
ings are produced. The deposits may become choked because the
refuse material is dumped in an undesirable place, causing further work
to be abandoned, as the removal of dump material is costly.

Clays give great trouble when present as an overburden or, as is
of frequent occurrence in the Carolinas, when mixed in large quanti-
ties with the gravel. The removal of the clayey overburden is much
more expensive than removal of sandy materials, and when the clay
is mixed with gravel washing consumes more tune and large volumes
of water.

When clay is mixed with gravel, particular care must be used
in removing it, as much monazite may adhere to it. The clays
seldom contain any of the mineral, but the mineral becomes embedded
in the outer parts of the clay while lying in the alluvium. The
practice of cutting up the clay is useless and wasteful, although this
method has been followed by some of the operators. It is sufficient
to wash the surface of such clays carefully and then remove them
to the dump.

ATTEMPTS TO USE BY-PRODUCTS.

Attempts have been made to utilize by-products from Carolina
monazite. Twenty tons or more of ilmenite has been shipped to
Europe, but could not bear transportation costs. Garnets derived
from the separators have been widely offered, but have been found
to be of no value as abrasives, the grains being rounded off by the
constant friction while rolling along with other sands in the stream
beds. The larger particles of garnets obtained by classification,
which could have been crushed, and thereby had their sharp edges
preserved, have been obtained in small quantities only from the
monazite sands.

In some sections gold is found in the concentrates. Although
the amount so obtained has been small, it has paid to put aside the
residues after treatment by electromagnetic methods, and then,
when sufficient quantities have been collected, to concentrate them
on an oscillating table or by some other suitable process. Although
the proportion of gold contained in such sands is not great, it has
been known to have a value of about $200 per 30 tons of monazite,
which is equal to about 1| cents per ton of gravel. This could be
considered almost clear profit, as the extraction of the gold from the
residues is inexpensive. Monazite sands purchased from gold-
mining sections, which have been treated for gold by the miners,
have, after the separation of the monazite, yielded a further small
amount of the precious metal.

In many sections "black sands" accompany monazite in large
quantities.

METHOD FOR THE DETERMINATION OF THORIUM IX MONAZITE. 23

In this paper methods of treatment in actual use have been de-
scribed. It is, however, more than probable that small dredges
would prove useful in the mining of monazite as they have in the
western field for gold.

METHOD FOB THE DETERMINATION OF THORIUM IN MONAZITE.

Many methods for determining thorium in monazite have been
described. Only the following well-known method is alone given
here.0

About 1 gram of the monazite is ground to an impalpable powder,
weighed into a platinum vessel, covered with 15 to 20 c.c. of con-
centrated sulphuric acid, and evaporated until fumes are no longer
driven off. More sulphuric acid is added and heated as before.
The operation is repeated several times until the conversion of the
phosphates into sulphates is complete. The mass resulting is added
in small quantities to about 700 c.c. of water at 0° C., with constant
stining, care being used not to allow the temperature to rise higher
than 2° C. The solution is allowed to stand 10 to 12 hours, when
it is filtered and washed. The filtrate is then nearly neutralized
with dilute ammonia, 50 c.c. of a cold saturated solution of oxalic
acid is added with constant stirring, and the solution is allowed
to stand for 12 hours. The solution is then filtered and the precipi-
tate washed well with water. The precipitated oxalates are then
washed into a beaker, and treated with a strong solution of caustic
potash, heated to boiling, diluted, and filtered.

The hydroxides are washed thoroughly with water and dissolved
off the filter with hot dilute hydrochloric acid (1-1). The solution
is evaporated to dryness to free it from acid, taken up with 75 to
100 c.c. of water, 15 c.c. of a saturated solution of sodium thiosul-
phate is added, and the solution is heated to boiling. It is then
filtered and the precipitate and the filter set aside for subsequent
filtration. An excess of ammonia is added to the filtrate, the pre-
cipitate is filtered off, washed, dissolved in hydrochloric acid, and
evaporated to dryness, the residue being taken up in water and
reprecipitated with thiosulphate as before. The solution is filtered
through the filter paper carrying the first precipitate, and the filtrate
is treated as before. The precipitations are continued as long as the
precipitate forms with the thiosulphate, three precipitations usually
being sufficient to completely extract the thorium. The combined
precipitates of thorium-thiosulphate are washed completely, dried,
and ignited. The ignited mass is fused for some time with potassium
bisulphate, taken up in water, and a few drops of hydrochloric acid
added, and precipitated with oxalic acid. The oxalates are converted

a. SeeMetzger, F. J., Anew separation of thorium from cerium, lanthanum, and didymium, and its appli-
cation to the analysis of monazite, Jour. Am. Them. Soc., vol. 24, 1902, p. 901: see also Levy, S. 1 ., The
rare earths, London, 1915, pp. 2 .5-290.

24 MONAZITE, THORIUM, AND MESOTHORIUM.

into the hydroxides, dissolved in hydrochloric acid, evaporated to
dryness, taken up in water, and reprecipitated with sodium thiosul-
phate, filtered, washed, dried, ignited, and weighed as ThO2.

TREATMENT OF MONAZITE FOB THE EXTRACTION OF THORIUM.

Soddy ° gives in a short form the technical treatment of the
monazite sand as it is carried on to-day in the industry.

In the first stage of the technical treatment of the monazite sand,
which is ground up very fine, it is heated with twice its weight of
sulphuric acid. The further procedure in the treatment is described
by Soddy 6 as follows :

The cold mass is dissolved in water and left to settle. The solution is then frac-
tionally precipitated with magnesia, the thorium being concentrated mainly in the
first fractions precipitated. The commonest and most useful reagent for precipitating
the rare earths from a solution containing common earths such as alumina, iron, etc.,
is oxalic acid. Now thorium oxalate is of all the rare-earth oxalates the least soluble
in acids, so that by working in fairly strong nitric acid solution thorium oxalate may
often be precipitated and separated at least partially from the other rare earths and
from calcium. The same is true of the rare-earth phosphates, that of thorium being
one of the most insoluble in dilute acids. On the same principle thorium is often
precipitated by weak bases, such as the substituted ammonias, for example, dimethyla-
mine, while zirconium, etc., remain dissolved. The potassium salt of hydrazoic
acid, KN3, precipitates thorium hydroxide only from mixtures of thorium and cerium
on boiling. The same separation may be effected by means of sodium thiosulphate
on boiling, thorium alone being separated, as hydroxide. This ready hydrolysis of
weak thorium is characteristic of the element. The oxalatos of thorium and zirconium
alone of the rare earths are soluble in ammonium oxalate, and on strongly acidifying
the solution the former alone is reprecipitated. The solution of the oxalate of tho-
rium and its conversion into soluble salts may be effected by means of concentrated
ammonium or sodium carbonate and precipitation of the concentrated solution as
thorium hydroxide with strong ammonium or sodium hydrate. Thorium is distin-
guished from the yttrium group of the rare earths by ite power of forming a double
sulphate with potassium sulphate, insoluble in excess of the latter reagent, and so
may be separated from a mixture of the sulphates by saturating the solution with
potassium sulphate. Alike in the old, now obsolete, as in the present, technical
methods of purifying thorium, the peculiar solubility relations of thorium sulphate
in water have been largely applied. The older method consisted in volatilizing the
excess of sulphuric acid from the material being treated, and in dissolving the
anhydrous sulphates in ice-cold water — a tedious operation — and in heating the
solution till the hydrated thorium sulphate was precipitated. The latter was then
dehydrated, at 300° to 400° and the process repeated. In present practice the sul-
phuric acid is always kept in great excess in the initial treatment of the mineral,
but the sulphate method may be employed at the final stage of manufacture as follows:

The thorium hydroxide is dissolved in hydrochloric acid, so that the solution
contains not more than 30 per cent ThO2, and sulphuric acid is added to the extent
of 0.5 per cent more than the equivalent quantity, the temperature being kept low,
and in any case below 40° as a maximum. , Under these conditions the hydrate
Th(SO4)28H2O is precipitated, departure from the conditions causing the separation

a Soddy, Frederick, The chemistry of the radio elements, 1911, pp. 64-69; see also, Bohm., Richard, Die
Darstellung der seltenen Erden, Leipzig, 1905, vol. 2, pp. 94-98; Levy, S. I., The rare earths, Lon-
don, 1915, pp. 276-285.

b Soddy, Frederick, loc cit.

SEPARATION OF MESOTHORIUM OX A COMMERCIAL SCALE. 25

of the tetrahydrate, which is in every way less easily manipulated. The precipitated
sulphate is reconverted into hydroxide, and the process repeated as often as necessary
to remove all impurities.

Thorium forms a curious compound with acetyl acetone, Th(C5H7O2)4, which is
soluble in chloroform and alcohol, and can be distilled in a vacuum, and so can
advantageously be employed for the purification and separation of the element.

It may be mentioned that in the fusion of refractory minerals, as with sodium
carbonate, the thorium, if present, is converted into the highly insoluble oxide,
Th02, and its presence is apt to be overlooked .

Thanks largely to the thorium industry, in which a product unusually pure Is
essential, there exist, therefore, a great variety of exceedingly good and sharp methods
for the separation and purification of thorium, and it muet be understood that ionium,
if present, and radio-thorium always remain unseparated from thorium in these
processes as far as they have been examined.

In the manufacture of- thorium nitrate from monazite a large amount
of residues of the cerium group of rare earths is ob tamed. Monazite con-
tains 60 to 70 per cent of the cerium group or other rare earths besides
thorium, and 3,000 tons, which is the annual consumption of mona-
zite, gives about 1,000 tons of cerium and about 1,200 tons of a mix-
ture of the rare earths, lanthanum, neodymium, and praesodymium
oxides. Considerable research work has been done in order to utilize
these waste materials, and experiments have been made with almost
every one of them. In order to obtain and separate the rare-earth
elements, thousands of crystallizations and fractionations are neces-
sary, although cerium itself is separated with comparative ease. The
untiring work carried on in the research laboratories of the industries
as well as by the scientists in both America and in Europe will, no
doubt, in time be crowned with successful technical applications of
the by-products.

SEPARATION OF MESOTHORIUM ON A COMMERCIAL SCALE.

Monazite sand is the main source of mesothorium and contains also
uranium and, consequently, radium. Mesothorium has properties
similar to radium, and the radium therefore is separated together with
the mesothorium. The methods employed in the extraction of meso-
thorium are well known and have been described by Haitinger and
Ulrich °, and have been used in the extraction of radium.6

Some manufacturers of mesothorium add a small quantity of barium
sulphate to the monazite sand during its treatment with sulphuric
acid, whereby the mesothorium is separated with the insoluble material
left after the treatment of the product with water.

The half-value period or period of half life (the time required in
which one-half of any given quantity of radioactive matter disinte-
grates — becomes transformed — is called half-value period or period of

o Haitinger, Ludwig, and Ulrich, Karl, Bericht iiber die BearbeitiniK der Pechblendo
Her. K. Akad. Wiss., vol. 117, 1908, p. 619.

6 Moore, R. B., and Kithil, K. L., A preliminary report on uranium, radium, and vanadium: Bull. 70,
Bureau of Mines, 1914, p. 79.

26 MONAZITE, THORIUM, AND MESOTHORIUM.

half life) of meso thorium is 5.5 years, whereas that of radium is ahout
2,000 years.

The manufacture of mesothorium alone from monazite is not prof-
itable, as the value of the mesothorium extracted would not pay for
the cost of the monazite. As a by-product from thorium nitrate man-
ufacture such manufacture should be of importance.

QUANTITATIVE DETERMINATION OF MESOTHORIUM.

The quantitative determination of mesothorium is carried on in
the same manner as for radium.0

The content of mesothorium in preparations, all of which carry
about 25 per cent of radium, is expressed in terms of the gamma ray
activity of radium in equilibrium. For example, 5 milligrams of
mesothorium on this standard indicates that the gamma ray activity
of the mesothorium plus the radium contained in it one month after
separation gives a gamma ray activity equal to that of 5 milligrams
of pure radium bromide.

If both the radium and the mesothorium are to be determined then
radium plus mesothorium is determined by means of the gamma ray
method, and afterwards, by the emanation method, the radium alone
is determined.

By the gamma ray method alone can be determined the ratio of
radium to mesothorium by measuring the gamma rays before and
after boiling the solutions. The content of mesothorium plus radium
is found before the solution is boiled ; after it has been boiled, the con-
tent of mesothorium alone is given, as the radium emanation is re-
moved by boiling, and radium Ct, which emits the gamma rays, is, for
all practical purposes, disintegrated after three hours' time.

In regard to the method of measuring mesothorium and radium by
the gamma ray method, reference is made to the work of Ebler,b and of
Meyer and Hess.c

The quantities of mesothorium that can be extracted from monazite
are, of course, very small. One hundred metric tons of monazite with
a content of 5 per cent ThO2 contains approximately 4.3 tons of tho-
rium metal. According to Rutherford, d one metric ton of thorium
metal contains 0.42 milligram of mesothorium. We have, therefore,
0.42 milligram of mesothorium per weight of 10~6 grams of tho-
rium, or 4.3 times 0.42, equals 1.8 milligrams of mesothorium by
weight. The activity due to mesothorium is three times as great as

o Soddy, Frederick, The chemistry of the radio elements, 1911, pp. 46-49; Rutherford, E., Radioactive
substances and their radiations, 1913, p. 550.

6 Ebler, Erich, Chemiker Kalender for 1914, vol. 2, pp. 371-372.

c Meyer, Stefan, and Hess, V. F., Gamma Strahlenmessung von Meso-thorpriiparaten: Mitt. Inst. Ra-
diumforschung, Vienna, July 2, 1914, pp. 1443-1458.

d Rutherford, E., Radioactive substances and their radiations, 1913, p. 552.

MONAZITE SANDS.

27

that due to radium when compared weight with weight. The meso-
thorium obtained from one ton of monazite, therefore, would be cal-
culated as 5.4 milligrams. Lorenzen,0 however, states that tech-
nically 2.5 milligrams of mesothorium can be obtained from 1 metric
ton of monazite, or 100 tons of monazite would yield 250 milligrams
of mesothorium. It seems, therefore, that technically a recovery of
about 50 per cent is made. Mesothorium is sold on the basis of its
activity compared with radium bromide of highest purity (determined
by the gamma ray method), and has been sold with increasing de-
mand at $45 to $60 per milligram. The separation of mesothorium
has been widely discussed in scientific and technical papers and is
outlined on page 25.

The manufacture of thorium nitrate from monazite is well known
and has been described extensively. This manufacture, however, is
briefly described on pages 24-25. The manufacture of the thorium
nitrate is so highly developed that a recovery of 90 to 95 per cent of
the thorium contained in the monazite has been made by many indus-
trial concerns.

Although in former years monazite and thorium nitrate were
imported into this country, lately, since the manufacture of meso-
thorium from the thorium residues has been begun, Europe prefers
to export the ash of the broken incandescent mantles, which are high
in ThO2, and keeps the monazite in order to obtain the mesothorium
from the residues. The import duty on the ash brought into the
United States is only 10 per cent ad valorem, whereas thorium nitrate
pays 25 per cent duty. The thoria ash has been sold for 25 marks
($6) per kilogram in Europe.

MINERALS IN MONAZITE SANDS.

The minerals contained in monazite sands, arranged according to
their specific gravity, are shown in the tabulation following:

Minerals contained in monazite sands, arranged according to specific gravity.

Letter

Letter

showing

showing

Mineral.

Specific
gravity.

relative
quantita-
tive oc-

Mineral.

Specific
gravity.

relative
nuantita-
tive oc-

currence.!)

currence^

2 05

Rutile

42 to 4 25

|

Feldspar

2.5 to 2.7

Zircon

4.5 to 4. 7

i

Tourmaline

3.0 to 3. 2

Ilmenite

4.5 to5

6

Apatite

Epidote

3.2 to 3. 25
3.2 to 3. 5

9

Monazite
Magnetite

4.8 to5.3
5. 16 to 5. 18

t

Ouvine

33 to 3. 6

Gold

15 to 19

k

Garnet

3.8 to 4. 3

c

a- Private information received from Juliu.s Lorenzen, Tegel-Berlin, on Chemical Manufacture of Meso-
thorium.
6 The order varies according to localities.

28

MONAZITE, THORIUM, AND MESOTHOEIUM.

The conglomerate must be freed from the larger gravels and from
the clays.

Proper sizing is important before concentration; in sizing the
remaining clay and mica particles should be removed by a sliming
process.

Four or five sizes should be made through sieves of 20, 50, 80, and
100 mesh.

Such properly sized material when treated on the large type of
Wetherill electromagnetic separator, having two magnets and 18-inch
belt, gives the following results :
Results of action of Wetherill electromagnetic separator on properly sized monazite sands.

Mineral."

|

Point in separator at which mineral separated.

Current.

Magnetite '

Ilmenite 1

Hematite i

Platinum (if any)

Epidote
Apatite

Second pole, first magnet; distance between poles, about

peres.

Olivine ."
Tourmaline

Monazite (92 to 95 per cent)
and traces of zircon and
rutile.
Platinum, etc. (if any)

First and second pole of second magnet; distance, first pole,
6 mm.; second pole, 2 to 3 mm.

12 to 15 am-
peres.

1

« Residues off belt were quartz, feldspar, gold, zircon, rutile, etc.

Data showing fluctuation of prices for thorium nitrate for use in incandescent gas
mantles.0

Europe
(per kilo).

United
States (per
pound).*

1894 . .

Marks.
2,000
900
500
300
150
96
60
40
30
28
36
43
43
43
43
27
32
32
32
27
19
17
22
22
21
21
22
22

Dollars.

1895 July

1895, November . . .

1896, early part
1896 later part

1897

1898

1899

1900

1902

5.86
5.86
6.10
6.53
3.78
3.93
4.65
4.70
3.87
3.20
3.00
3.00
3.00
2.85
2.60
2.71
3.25

1904, later part

1006

1907, early part....

1907 later part

1908* . .

1909

1910 later part

Will
1912

1913, later part

1914, early part
1914, later part

Price of thorium
nitrate.

"Import duty on thorium nitrate brought into the United States, 25 per cent ad valorem.
6I)ata furnished by Dr. Hugo Liebcr, 25 Madison Avenue, New York, N. Y.

MINERALS IX MONAZITE SANDS.
FLOW SHEET.

A flow sheet of the separation process is shown in figure 1.

29

I

Zircon and rutile

Quartz and f eld-
spar

Slime and lighter
materials

FIGURE 1. — Flow sheet, showing steps in process of magnetic separation of monazite sands.

SELECTED BIBLIOGRAPHY.

BOHM, RICHARD. Die Darstellung der seltenen Erden, 2 vole., Leipzig, 1905.

- Die Venvendung der seltenen Erden, Leipzig, 1913.

- Monazite sand: Eng. and Min. Jour., vol. 81, May 5, 1906, p. 842.

- Die Thorium Industrie: Chem. Ind., vol. 29, 1906, pp. 450-488.

DAY, D. T., and RICHARDS, R. H. Useful minerals in the black sands of the Pacific
Slope: TJ. S. Geol. Survey, Mineral Resources for 1905, 1906, pp. 1175-1258.

GUNTHER, G. G. Electromagnetic ore separation, 1909, 193 pp.

JOURNAL OF THE FRANKLIN INSTITUTE. Report on Welsbach light, by Committee on
Science and Arts. Vol. 150, December, 1900, pp. 406-415.

JOHNSTONE, S. J. Monazite from some new localities: Jour. Soc. Chem. Ind., vol.
33, January 31, 1914, pp. 55-59.

LANEY, F. B., and WOOD, K. H. Bibliography of North Carolina geology, miner-
alogy, and geography: N. C. Geol. and Econ. Survey Bull. IS, 1909. Gives a
comprehensive bibliography concerning monazite deposits in North Carolina.

LEVY, S. I. The rare earths, their occurrence, chemistry, and technology. London,
1915, 345 pp.

LINDGREN, WAI.DEMAR. Mining district of Idaho Basin and Boise Ridge: U. ,S. Geol.
Survey, Eighteenth Annual Report, pt. 3, 1898, pp. 617-744; The monazite sands,
pp. 677-679.

METZGER, F. J., and ZONS, F. W. A volumetric method for the determination of
thorium in the presence of other rare earths. The analysis of monazite sand:
Chem. News, vol. 107, March 7, 1913, pp. 112-113.

MINING REPORTER. The industrial position of thorium. Vol. 53, February 22, 1906,
p. 190.

NITZE, H. B. C. Monazite, U. S. Geol. Survey, Sixteenth Annual Report, pt. 4, 1896,
pp. 667-693.

- Monazite and monazite deposits in North Carolina: N. C. Geol. Survey Bull.
9, 1895, p. 47.

PRATT, J. H. Monazite: U. S. Geol. Survey, Mineral Resources, 1901-1905.
PRATT, J. H., and STERRETT, D. B. Monazite and monazite mining in the Carolinaa:

Trans. Am. Inst. Min. Eng., vol. 40, 1910, pp. 315-340.
RICHARDS, R. H. Ore dressing. 1909, vol. 2, pp.832-837. Contains bibliography

of magnetic ore concentration.
SCHRADER, F. C. An occurrence of monazite in northern Idaho: U. S. Geol. Survey

Bull. 430, 1910, pp. 184-191.
SLOAN, EARLE. Catalogue of mineral localities in South Carolina: S. C. Geol. Survey

Bull. 2, 1908, pp. 129-142.
STERRETT, D. B. Monazite: U. S. Geol. Survey, Mineral Resources, 1906-1910.

- Monazite deposits of the Carolinas: U. S. Geol. Survey Bull. 340, 1908, pp.
272-285.

TRUCHOT, P. Occurrences and extraction of thorite, monazite, and zircon: Chem.
News, vol. 77, pp. 134-135, 145-147, 1898.
30

PUBLICATIONS ON MINERAL TECHNOLOGY.

A limited supply of the following publications of the Bureau of
Mines is temporarily available for free distribution. Requests for
all publications can not be granted, and to insure equitable distribu-
tion applicants are requested to limit their selection to publications
that may be of especial interest to them. Requests for publications
should be addressed to the Director, Bureau of Mines.

'BULLETIN 3. The coke industry of the United States as related to the foundry, by

Richard ^1enke- 191°- 32PP-

BULLETIN, " n Apparatus and methods for the sampling and analysis of furnace gases,
by J C. W. j :azer and E. J. Hoffman. 1911. 22 pp., 6 figs.

BULLETI! •*>• The uses of peat for fuel and other purposes, by C. A. Davis. 1911.

214pp.. I*'1-' !"*«•

-gT^LETiN 42. The sampling and examination of mine gases and natural gas, by G.
Burrell and F. M. Seibert. 1913. 116 pp., 2 pis., 23 figs.

BULLETIN 45. Sand available for filling mine workings in the northern anthracite
coal basin of Pennsylvania, by N. H. Darton. 1913. 33 pp., 8 pis., 5 figs.

BULLETIN 47. Notes on mineral wastes, by C. L. Parsons. 1912. 44 pp.

BULLETIN 53. Mining and treatment of feldspar and koalin in the southern Appa-
lachian region, by A. S. Watts. 1913. 170 pp., 16 pis., 12 figs.

BULLETIN 64. The titaniferous iron ores of the United States, their composition and
economic value, by J. T. Singewald, jr.. 1913. 145 pp., 16 pis., 3 figs.

BULLETIN 70. A preliminary report on uranium, radium, and vanadium, by R. B.
Moore and K. L. Kithil. 1913. 101 pp., 4 pis., 2 figs.

BULLETIN 71. Fuller's earth, by C. L. Parsons. 1913. 38 pp.

BULLETIN 81. The smelting of copper ores in the electric furnace, by D. A. Lyon
and R. M. Keeney. 1914. 80 pp., 6 figs.

BULLETIN 84. Metallurgical smoke, by C. H. Fulton. 1914. 94 pp., 6 pis., 15 figs.

BULLETIN 85. Analyses of mine and car samples of coal collected in the fiscal years
1911 to 1913, by A. C. Fieldner, H. I. Smith, A. H. Fay, and Samuel Sanford. 1914.
444pp., 2 figs.

TECHNICAL PAPER 3. Specifications for the purchase of fuel oil for the Government.
with directions for sampling oil and natural gas, by I. C. Allen. 1911. 13 pp.

TECHNICAL PAPER 8. Methods of analyzing coal and coke, by F. M. Stanton and
A. C. Fieldner. 1913. 42 pp., 12 figs.

TECHNICAL PAPER 14. Apparatus for gas-analysis laboratories at coal mines, by
G. A. Burrell and F.M. Seibert. 1913. 24 pp., 7 figs.

TECHNICAL PAPER 38. Wastes in the production and utilization of natural gas, and
means for their prevention, by Ralph Arnold and F. G. Clapp. 1913. 29 pp.

TECHNICAL PAPER 39. The inflammable gases in mine air," by G. A. Burrell and
F. M. Seibert. 24 pp., 2 figs.

TECHNICAL PAPER 41. Mining and treatment of lead and zinc ores in the Joplin
district, Missouri; a preliminary report, by C. A. Wright. 1913. 43 pp., 5 figs.

TECHNICAL PAPER 43. The influence of inert gases on inflammable gaseous mixtures,
by J. K. Clement. 1913. 24 pp., 1 pi., 8 figs.

TECHNICAL PAPER 50. Metallurgical coke, by A, W. Belden. 1913. 48 pp., 1 pi.,
23 figs.

31

32 MONAZITE, THORIUM, AND MESOTHORIUM.

TECHNICAL PAPER 60. The approximate melting points of some commercial copper
alloys, by H. W. Gillett and A. B. Norton. 1913. 10 pp., 1 fig.

TECHNICAL PAPER 66. Mud-laden fluid applied to well drilling, by J. A. Pollard and
A. G. Heggem. 1914. 21 pp., 12 figs.

TECHNICAL PAPER 70. Methods of oil recovery in California, by Ralph Arnold and
V. R. Garfias. 1914. 57 pp., 7 figs.

TECHNICAL PAPER 76. Notes on the sampling and analysis of coal, by A. C. Fieldner.

1914. 59 pp., 6 figs.

TECHNICAL PAPER 81. The vapor pressure of arsenic trioxide, by L. H. Duschak.

1915. 22 pp., 2 figs.

TECHNICAL PAPER 88. The radium-uranium ratio in carnotites. by S. 0. Lind :uid
.C. F. Whittemore. 1915. 29 pp., 1 pi., 4 figs.

TECHNICAL PAPER 89. Coal-tar products, and the possibility of their successful
manufacture in the United States, by H. C. Porter, with a chapter on coal-tar prod-
ucts used in explosives, by C. G. Storm. 1915. 21 pp.

TECHNICAL PAPER 90. Metallurgical treatment of the low-grade am) (.n,,.j,iex on,s
of Utah; a preliminary report, by D. A. Lyon, R. H. Bradford, S. S- J^entz Q <•
Ralston, and C. L. Larson. 1915. 40 pp.

TECHNICAL PAPER 95. Mining and milling of lead and zinc ores in tru
district, Wisconsin, by C. A. Wright. 1915. 39 pp., 2 pis., 5 figs.

TECHNICAL PAPER 99. Probable effect of the war in Europe on the ceramic' iml.,
tries of the United States, by A. S. Watte. 1915. 15 pp.

o

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