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Патент USA US2126793

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2,126,793
Patented Aug. 16, 1938
UNITED STATES
7
PATENT OFFICE
2,126,793
REMOVING FLUORIDES FROM WATER.
Walter H. Maclntire, Knoxville, Tenn.
vNo Drawing. Application November 12, 1937,
Serial No. 174,203
.
(Cl. 210-23)
(Granted under the act of March a, 1883, as
amended April 30, 1928; 370 0. G. 757)
8 Claims.
The invention herein described may be manu
factured and used by or for the Government for
governmental purposes without the payment to
me of any royalty thereon.
.m
This invention relates to the art of water puri
?cation, particularly the removal of dissolved
?uorides from water.
One of the objects of this invention is to re
move ?uorides or to reduce the ?uorine content
10 of water containing the same in solution, to an
amount which is below the limit of toxicity for
the ?uorides in water. Another object of this
invention is to provide a convenient and rapid
method for removing or reducing the ?uorides
in water in order that it may be rendered potable.
Other objects of this invention include the prog
vision of a method for the economicalremoval
or reduction of ?uorides contained in water
solutions.
20
There are numerous areas in the United States
in which the water available for general con
sumption contains a considerable quantity of
dissolved ?uoride or ?uorides with the amount
of such dissolved ?uorides corresponding to 5
25 to 15 parts per million of ?uorine. It has been
found that water containing ?uoride correspond
ing to only 6 parts per million of ?uorine results
in the universal mottling of the enamel at the
time of acquiring permanent teeth which results
30 in premature tooth decay. It is now considered
that water containing ?uorides less than the
equivalent to 1 to 2 parts per million of ?uorine
is below the limit of toxicity as evidenced by this
particular type of malformation.
The generic invention and three speci?c adap
35
tations are described and claimed in my copend
ing application, Serial No. 164,139,,?1ed Septem
ber 16, 1937. Another adaptation is described
and claimed in this application.
40
I have discovered a process of removing dis
solved ?uorides from water by adding at least
30 p. p. m. of orthophosphoric acid to the wa
ter for each p. p. m. of ?uorine contained in
the water; by a ding calcium hydroxide to the
acidi?ed water in an amount to convert the
orthophosphoric acid to tricalcium orthophos
phate; and by maintaining the time of contact
between the product of the reactants and the
water such that the solute ?uoride content of
the water is reduced below the desired limit for
?uorine in the water.
One example of the operation of my process is
given for the treatment of water containing 6
p. p. m. of dissolved ?uorine and carrying 250
55 p. p. m. of suspended material. The water was
acidi?ed with 190 p. p. m. of orthophosphoric
acid. 271 p. p. m. of calcium hydroxide were
added to the uniform acidi?ed water and the
mixture maintained in an agitated condition for
a period of 15 minutes, which, under the condi- 5
tions, was sufficient to form tricalcium ortho
phosphate from the reactants and to reduce the
?uorine content of the water to 0.5 p. p. m.
It is evident that there are numerous factors
which will in?uence conditions for the most sat- l0
isfactory operation of my invention, the actual
limits'of which cannot be established except by
a detailed study of each set of raw materials
and the ?nish-ed product involved.
'
Water containing dissolved ?uorides may or 15
may not contain suspended matter. With the
amount of suspended matter of the order of 200
p. p. m. and upward, the time required for the
contact of the product of the reactants with the
water is of the order of 15 to 30 minutes. Where 20
no suspended matter is present, this time of
contact under otherwise identical conditions, and
as observed in a limited number of cases, is of
the order of 10 hours. This time, however, may
be materially reduced by the use of an amount 25
of reactants in considerable excess of that other
wise required. It is therefore, necessary, when
removing the solute ?uoride from water, which
is free of suspended matter, to add some sus
pended matter in order that the removal of the 30
?uorine content of the water may be expedited.
This may be accomplished by such means as the
addition of ?nely divided argillaceous material
to the water, or by adding to the water a rea
gent, or reagents, which produce ?nely divided 35
suspended matter in the water, either for the
sole purpose of providing the necessary suspend
ed matter, or for the purpose of ‘treating the
water to remove other undesirable constituents.
The use of aluminum sulfate with the subse- 40
quent product of a ?oc of aluminum hydroxide
is an example of suitable material for accom
plishing this result.
The orthophosphoric acid used may be of any
suitable commercial concentration. It is pref- 45
erable to use a commercial orthophosphoric acid
free from ?uorine. However, should the speci?c
circumstances require the use of an orthophos
phoric acid containing ?uorine, the amount of
?uorine which it contains must be taken into 50
account in addition to the amount of ?uorine in
the water, insofar as the requirements of ortho
phosphoric acid and calcium hydroxide are con
cerned, in calculating the amount of the respec
tive reactants required.
55
2
2,126,793
The amount of calcium hydroxide used is at
least equivalent to that required to form trical
cium orthophosphate from the orthophosphoric
acid used. Under these conditions the treated
5 water resulting will be at least neutral and gen
erally slightly alkaline.
-
The results of experimental work over a peri
01' several years has led me to believe that the
removal of soluble ?uorides from water is ac
.0 complished largely by the formation 0! ?uorapa
tite from the tricalcium crthophosphate and the
?uoride in the water. The ratio of ?uorine to
tricalcium orthophosphate required to form ?u
orapatite is 1:245. - In order to obtain e?ective
convert the orthophosphoric acid to tricalcium
orthophosphate; maintaining the time of contact
between the product of the reactants and the
water such that the solute ?uoride content 01' the
water is at least reduced below the limit of tox
icity for the ?uorides in the water; and sepa
rating the water from the residual solid material
with which it has been contacted.
4. Process of removing dissolved ?uorides from
water, which comprises adding at least 30 p. p. m. 10
of orthophosphoric acid to the water for each
p. p. m. of ?uorine contained in the water; add
ing calcium hydroxide to the acidi?ed water in
an amount su?lcient to convert the orthophos
15 removal of ?uorine from water containing solute . phoric acid to tricalcium orthophosphate; main
?uorides, it is necessary to have present at least taining the time of contact between the product 15
double the amount of tricalcium orthophosphate of the reactants and the water such that the
theoretically required. Therefore, the minimum solute ?uoride content of the water is reduced
requirement for the amount of orthophosphoric below the desired limit for ?uorine in the water;
2o acid used is in vthe order of 30 to 40 p. p. m. for
and separating the water from the residual solid
' each p. p. m. of ?uorine contained in the water.
material with which it has been contacted.
In the treatment of considerable quantities of
5. Process of removing dissolved ?uorides from
water, it is more feasible to__carry out this treat
water, free from suspended matter, to render it
ment at the prevailing atmospheric temperature.
potable, which comprises forming at least 200
25 A number of experiments carried out over a
p. p. m. of suspended matter in the water; add
ing 30 to 40 p. p. m. of orthophosphoric acid to
period of several years has demonstrated the fact
that the removal of ?uorine from water contain
ing solute ?uorides is materially accelerated by
the use oi’ moderately elevated temperatures.
30
It will be seen, therefore, that this invention
actually may be carried out by the use of various
modi?cations and changes without departing
from its spirit and scope, with only such limita
tions placed thereon as are imposed by the prior
35 art.
'
I claim:
1. Process of removing dissolved ?uorides from
water, tree from suspended matter, to render it
potable, which comprises adding at least 200
40 p. p. m. 01’ suspended matter to the water; adding
30 to 40 p. p. m. of orthophosphoric acid to the
the water containing the suspended matter, for
each 1). p. m. of ?uorine contained in the water; '
adding calcium hydroxide to the acidi?ed water
in an amount su?icient to convert the ortho
phosphoric acid to tricalcium orthophosphate;
and maintaining the time of contact between the
product of the reactants and the water such that
30
the solute ?uoride content of the water is re
duced below the desired limit for ?uorine in the 35
water.
6. Process of removing dissolved ?uorides from
water to render it potable, which comprises add
ing 30 to 40 p. p. m. of orthophosphoric acid to
the water for each p. p. m. of ?uorine contained 40
in the water; adding calcium hydroxide to the
water containing the suspended matter, for each
acidi?ed water in an amount su?icient to con
p. p. m. of ?uorine contained in the water; add
vert the orthophosphoric acid to tricalcium or
thophosphate; and maintaining the time of con
tact between the product of the reactants and the
water such that the solute ?uoride content of the
water is at least reduced below the limit 01' tox
icity for the ?uorides in water.
'7. Process of removing dissolved ?uorides from
water to render it potable, which comprises add
ing at least 30 p. p. m. of orthophosphoric acid 50
ing calcium hydroxide to the acidi?ed water ‘n
an amount su?lcient to convert the orthophos
phoric acid to tricalcium orthophosphate; main
taining the time of contact between the product
of the reactants and the water such that the
solute ?uoride content of the water is at least re
50 duced below the limit of toxicity i'orthe ?uorides
in the water; and settling out the suspended mat
ter from the water.
,
2. Process of removing dissolved ?uorides from
water to render it potable, which comprises add
;5 ing 30 to 40 p. p. m. of orthophosphoric acid to
the water, for each p. p. m. of ?uorine contained
in the water; adding calcium hydroxide to the
acidi?ed water in an amount sui?cient to con
vert the orthophosphoric acid to tricalcium
a0 orthophosphate; maintaining the time of contact
between the product of the reactants and the
water such that the solute ?uoride content of the
water is at least reduced below the limit of tox
icity for the ?uorides in the water; and separat
65 ing the water from the residual solid material
with which it has been contacted.
'
3. Process of removing dissolved ?uorides from
water to render it potable, which comprises add
ing at least 30 p. p. m. of orthophosphoric acid
70 to the water for each p. p. m. or ?uorine con
tained in the water; adding calcium hydroxide
to the acidi?ed water in an amount su?icient to
to the water for each p. p. m. of ?uorinecon
tained in the water; adding calcium hydroxide
' to the acidi?ed water in an amount su?lcient to
convert the orthophosphoric acid to tricalcium 55
orthophosphate; and maintaining the time of
contact between the product of the reactants and
the water such that the solute ?uoride content
‘oi’ the water is at least reduced below the limit
of toxicity for the ?uorides in water.
8. Process of removing dissolved ?uorides from
water, which comprises adding at least 30 p. p. m.
01' orthophosphoric acid to the water for each
p. p. m. of ?uorine contained in the water; add
ing calcium hydroxide to the acidi?ed water in 65
an amount su?icient to convert the orthophos
phoric acid to tricalcium orthophosphate; and
maintaining the time of contact between the
product of the reactants and the water such that
the solute ?uoride content of the water is reduced
below the desired limit for ?uorine in the water.
WALTER H. MACINTIRE.
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