Process for Removing Salts of Calcium, Magnesium, and other Metals from Aqueous Solutions.
Year: 1889

page_text: Date of Application, 28th May, 1889-Accepted, 21st Sept., 1889
CUDIT LEID SIMOITIATION.
Process for Removing Salts of Calcium, Magnesium, and other
Metals from Aqueous Solutions.
I, CHARLES AVERY DOREMUS, of Number 92 Lexington Avenue, in the City,
County, and State of New York, Professor of Chemistry, do hereby declare the
nature of this invention and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement:-
-
For household and technical use waters are classified as "hard" or "soft." Those
that are hard are sub-divided into those which retain their hardness when boiled,
and those that lose their hardness when boiled. The former have permanent
hardness" the latter "temporary hardness."
This classification is based chiefly upon the behaviour of waters to soap, hard
waters failing to give a lather.
"
"
The soap destroying power of the water depends generally on the presence of salts
of calcium (Ca.) and magnesium (Mg.) in the water. Temporary hardness is due
to calcium (Ca.) and magnesium (Mg.) carbonates held in solution by an excess of
carbon dioxide. When this is expelled by boiling, the calcium (Ca.) and the mag-
nesium (Mg.) carbonates precipitate, and the water becomes "soft." "Permanent
hardness is due to other salts of calcium (Ca.) and magnesium (Mg.). There are
also many waters possessing both permanent and temporary hardness. Strontium (Sr.)
and barium (Ba.) salts behave similarly.
وو
Where the application of heat is impracticable, waters of either character may be
treated with chemicals with the object of obviating the effect of any of the above
mentioned salts. For this purpose milk of lime, caustic alkali, carbonated alkali,
barium sulphide, and other chemicals have been, and are still employed with more or
less success.
When chemicals are used, the precipitate which they form is separated from
the water by some convenient mechanical means-such for instance as a suitable
filter.
Since hard waters, when used in steam boilers and like vessels, form an incrusta-
tion or scale, chemicals are frequently added, either to the water before it enters the
boiler, or in the boiler, with the object of preventing the formation of an adherent
scale.
In the manufacture of salt, it is desirable to remove as far as possible, all
impurities, and for this purpose numerous mechanical and chemical means have been
adopted.
In many other technical pursuits, as in woollen and silk manufactures, it is often
necessary to remove even small quantities of foreign substances from the water used
for washing, or the preparation of various solutions.
In the processes heretofore used, different substances have been employed, but there
are inherent objections to each.
Thus in the well known Clark's process the lime softens only waters having
temporary hardness, and removes only a portion of the magnesium (Mg.).
Caustic soda has also been used to remove magnesium and calcium. It has an
objection in the difficulties of handling. Though it acts on waters having both
temporary and permanent hardness, it does not remove all the magnesium and may
leave an objectionable residue in the water.
Ammonium chloride converts the calcium and magnesium into soluble forms, pre-
venting incrustation-but not precipitating calcium and magnesium, the waters can
not be employed for domestic or technical use.
"Soda ash" softens only permanently hard waters, and does not remove magnesium
entirely

page_text: Where exact quantities of re-agent may be employed, either by weight or measure,
to given quantities of water, a preliminary test as to the quantity of fluoride to be
used will perhaps prove sufficient, and the testing of the water after treatment may
be omitted.
Since the character of the precipitate produced by a fluoride may be such that it
is difficult for a filter to separate it from the water, it may prove advisable to use with
the fluoride some chemical, capable of producing with the foreign substances in the
water a bulky precipitate, which shall act mechanically in removing any precipitate
of fluoride also produced. Since magnesium fluoride is precipitated in a more
flocculent form than calcium fluoride, waters containing much magnesium (Mg.) salts
may be treated effectually with the fluoride alone, unless for other reasons, hereafter
to be stated, it should be otherwise indicated. Since caustic soda (sodium hydrate)
causes a bulky precipitate when added to waters containing calcium (Ca.) salts, it
may be employed with a fluoride, for the above mentioned purpose.
In certain cases sodium carbonate will prove effective for the purpose above
suggested; in other cases sodium carbonate, sodium hydrate and a fluoride, such as
sodium fluoride, may be used in the treatment of the water.
I have found that the use of either or both of the above mentioned re-agents in
conjunction with a fluoride, has, in certain waters, enabled me to treat the waters in
a way which would prove more serviceable in practice than where a fluoride alone
was used. Highly carbonated water, especially, seemed to require the use of some
caustic alkali.
The chemical equivalent of sodium carbonate or hydrate may be taken, unless it is
incompatible with the fluoride employed.
That the quantity of each chemical may be properly adjusted, I either make a
compound, to be fed in calculated proportion, either in solid or liquid form, to the
water to be treated, or dissolve each chemical in a separate tank or vessel, and feed
each to the water, in such order and quantity as will produce the desired result,
namely, that of removing foreign substances from the water.
Where highly carbonated waters are to be fed after softening, to boilers, it is
frequently necessary, not only to remove all substances which might form a crust or
scale in the boiler, but to prevent foaming and frothing in the water so treated. For
this purpose I have found sodium hydrate effectual, when used in conjunction with a
fluoride, such as sodium fluoride. By its use some or all of the carbon dioxide may
be bound or fixed.
Where water is to be used in boilers, it is necessary to consider the character of the
precipitate which may form, either through the imperfection of the treatment, or of
the mechanical process resorted to in removing the precipitate from the water previous
to its entering the boiler.
As it is possible in some cases to add the precipitating compound directly to the
water in the boiler, additional caution must be used, either in the use of the fluoride
alone, or the fluoride with other chemicals, to prevent the formation of a precipitate
which will, by the action of the heat, become a compact, adherent scale. I have
learned from experience that a careful study of the characteristics of the water should
therefore precede the preparation of the compound to be used in its treatment on a
large scale.
:
Milk of lime has been used for many years for softening waters possessing tem-
porary hardness, the lime in solid form being held in suspension until mixed with the
water; fluoride may be used in a similar manner, bringing it partly in solution, partly
in solid form into contact with the water, or it may be employed in conjunction with
such other chemicals as before specified, or their chemical equivalents, for the purposes
mentioned.
When necessary, the application of fluoride to the water may either precede or
follow that of some other chemical. Thus, in waters of great temporary hardness, the
water may be first treated with milk of lime, and by it most of the calcium, magnesium
and carbon dioxide be removed, then any remaining calcium or magnesium may be

page_text: emoved by the use of fluoride alone, or combined with caustic or carbonated alkalı,
or both.
The relative cost of materials used to purify may determine the selection of the
modifications of the use of fluoride.
Since magnesium (Mg.) and other metals, have a tendency to form double salts,
and since the fluorides are frequently double in composition, it is not improbable that
the precipitate produced by the use of a fluoride will be composed of, or contain, such
double fluoride.
In brines, calcium and magnesium sulphates frequently exist, along with calcium
and magnesium chlorides; by the use of barium or strontium chloride these sulphates
may be converted into chlorides, the barium or strontium sulphate precipitating. The
magnesium, calcium, and any excess of barium or strontium may then be precipitated
by the use of sodium fluoride. A nearly pure solution of common salt, sodium
chloride, can thus be obtained. With care, the use of the foregoing re-agents may be
reversed.
Fluorides may be used alone where desired.
Where it is desirable to remove iron from the water, the iron may be precipitated
as a fluoride.
Since alum, and other salts of aluminium are employed in the treatment of the
water for potable purposes, any aluminium remaining in such water can be precipitated
therefrom by the use of a fluoride.
I have mentioned above some of the methods capable of being used in precipitating
compounds of fluorine, but since 1 believe I am the first to discover the practical
application of any compound of fluorine, to the removal of foreign substances from
waters, brines &c., 1 do not wish to he understood as limiting my invention to
the methods mentioned above, having given these for the purpose of illustration
merely.
I wish to be understood as claiming broadly the use of any fluorine compound, in
any way, for the removal of different foreign substances from waters, brines &c.
And in this connection I would say-by way of illustration-that I consider hydro-
fluoric acid, ammonium fluoride, "acid ammonium fluoride," potassium fluoride,
sodium fluoride, cryolite &c., as fluorine compounds.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
-
The herein described process for removing calcium, magnesium, and other like
substances from waters, brines etc., the same consisting in introducing into said
waters, brines etc., a fluorine compound, whereby the calcium, or other substance,
is converted into an insoluble fluorine compound, substantially as described.
Dated this 28th day of May 1889.
CARPMAEL & Co.,
Agents for the Applicant.