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Oct. 29, 1946.
E. J. BRETON ET AL
2,410,043
PROCESS FOR MANUFACTURING CALCIUM FLUCRIDE
Filed Jan. 4, 1945
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INVENTORS
BWM'
ATTORNEY
Patented Oct. 29, 1946
>2,410,043
UNITED STATES PATENT OFFICE
2,410,043
l
PROCESS Fon MANUFACrURiNC CALCIUM
FLUORIDE
Ernest J. Breton, Arlington, and William H.
Waggaman, Alexandria, Va., assignors to the
United States of America, as represented by the
Secretary of the Interior
Application January 4, 1945, Serial No. 571,344
1 Claim. (Cl. 23-88)
w
(Granted under the act of March 3, 1883, as
.
amended April 30, 1928: 370 O. G. 757)
'
1
The invention described herein may be manu
factured and used by or for the Government of
the United States for governmental purposes
without the payment to us of any royalty thereon
in accordance with the provisions of the Act of
April 30, 1928 (Ch. 460, 45 Stat. L. 467).
The primary object of this process is to produce
droñuosilicic acid and precipitating gelatinous
silica as shown in Equation 3. 'I‘he acid solution
is then decanted off and treated with sodium
chloride to precipitate sodium fluosilicate as
shown in Equation 4.
relatively pure calcium fluoride from the gases
If it is desired to produce calcium iluosilicate,
evolved in certain. manufacturing processes. A
calcium chloride may be substituted for sodium
further object is to obtain a flux to be used in the 10 chloride.
basic open hearth furnace in lieu of fluorspar in
Calcium fluosilicate, however, is not as suitable
order to slag ofi' impurities and obtain steel of
for certain industrial uses as calcium fluoride.
certain desired quality. Still another object is
Therefore a simple process whereby the former
to recover in the form of marketable products,
can be converted into the latter compound with
fiuorine which is being lost or wasted in the
out loss of ñuorine is highly desirable.
manufacture- of fertilizers.
We have developed such a process for the pro
The known deposits of v.iiuorspar suitable for
duction of calcium fluoride from the gases
use as a iluxing agent in the manufacture of open
evolved in the decomposition of materials con
hearth steel are limited and hence di?liculty has
taining both iluorine and silica.
been encountered in obtaining adequate quanti 20 Briefly this process consists in ñrst producing
ties to take care of the demand. At the present
a solution of hydrofluosilicic acid, the concentra
time the specifications for metallurgical nuor
tion of which is built up by recirculating it in a
spar call for a product containing 85% of CaFz
scrubber into which the fiuorine gases are intro
and, while lower grade ores might be added di
duced. This acid solution after being filtered
rectly to the furnace charge, it is customary to 25 free of precipitated silica is discharged into a
beneficiate such ores as far as possible in order
chamber where it is heated to evolve both hydro
to avoid the necessity of adding further quan
iiuoric acid and silicon tetrañuoride. These gases
tities of limestone or other ñuxes which increases
are then led into a reaction chamber containing
the volume of slag to be handled and the quantity
lime
wherein relatively dry calcium flucsilicate is
of fuel required to ñux it.
30 formed according to Equation 5.
It is a well known fact that much fluorine is
evolved inthe >treatment of phosphate rock to
produce fertilizer and stock feed, but up to the
The calcium iluosilicate is then discharged into
present time only a small proportion has been
an electric or other suitable furnace and heated
collected and utilized. For instance, when phos 35 to at least 1300q C., resulting in the formation
phate rock is. calcined at high temperatures in
of molten calcium fluoride and the evolution of
the presence of water vapor, the bulk of the
silicon tetrafluoride. The former is tapped off,
iiuorine is evolved and the resultant de
cooled, and broken up to be marketed, while the
iluorinated product is suitable for use as either
latter is re-introduced intctthe system. This re
fertilizer or stock feed. Again, large quantities
40 action is shown in Equation 6:
of fluorine are annually lost in the manufacture
of superphosphate, a product which is the basis
of the fertilizer industry. While We do not wish to limit ourselves to a
When phosphate rock containing both ?luorine
specific assembly, the apparatus shown diagram
and silica is treated with sulphuric acid the re 45 matically in the accompanying drawing serves to
actions taking place (as far as the ?luorine com
illustrate the various steps of this process and a
pound is concerned) may î'ae represented by the
suitable
type of plant in which the process may
three following equations:
be carried out.
»
Referring to Figure l, finely ground phosphate
50 rock and sulphuric acid are mixed in a mixer I
of conventional design to produce ordinary super
phosphate. 'I‘he iluorine gases evolved from this
The usual method of recovering the iiuorine
mixer I are drawn through the ñue 2 by means
evolved in this process is to absorb the gases in
of the fan 5 into the absorption chamber 3 which
Water, thus producing a dilute solution of hy 55 is fed with a. recirculated solution of hydro
2,410,04s
`
A
4
3
iluosllio'ic acid. Any gaseous iiuorlne compounds
not absorbed in this chamber pass into a second
.
tained at a temperature of at least 1300’ C. where
it is converted into molten calcium fluoride which
is drawn on periodically through the tap hole `
absorption -chamber 4 of similar design where
they are removed before' discharging the spent
I1.
The gases evolved from this furnace consist
gases to the atmosphere through the vent 6.
In order to compensate for the water lost through
ing largely of`silicon tetrafluoride are conducted
through tlie ilue I8 and reintroduced> into the
silica rejection and evaporation in the primary
absorption chamber 3 by means of the fan I9. '
absorption" system, a portion of the solution in
It will be apparent that we have provided a
the secondary absorption chamber 4 is constantly
injected into absorption chamber 5 by means of 10 practical way to. make calcium iluoride from
sources oi' iluorine which are now completely
the pump 20. An equivalent volume of water is
wasted. However, various changes may be made
added- to chamber 4 through the valve 2| to
in the invention as described without departing
maintain the efllciency of Ythis secondary absorp
tion unit and keep the system in balance.
from the spirit and scope thereof.
The solution of hydroiluosilicic acid, contain 15 We claim:
A cyclic process for producing calcium iiuòride
ing silica in suspension, flows from the absorp
consisting in'absorbing gases containing silicon
tion chamber 3 into the continuous filter or cen
trifuge 1 where the silica is separated. 'I'he clear
tetrailuoride in water to produce hydroiluosiliclc
acid and silica; separating the acid solution from
acid solution then flows into the evaporator 8
heated by means of the stem coils .9 and ,20 silica; continuously evolving gaseous iluorine
compounds from said solution by means of heat
the liquid eilluent is continuously recirculated
and evaporation; recirculating the solution thus
through the absorption chamber 3 by means of
partially freed from ñuorine in order to absorb
the pump I0.
‘ .
additional quantities of silicon tetrafluoride;
The gases Aevolved in the evaporator 8 are.
drawn by means of the fan II into the reaction 25 contacting the gases evolved from the heated
chamber I2 similar to the well known Herres
solution with lime to form calcium ñuosilicate:
decomposing said calcium fluosilicate at elevated
hofl’ multiple hearth furnace, and fitted with
evolving arms which rake the lime introduced . temperatures to produce molten calcium ñuoride
and silicon tetraiiuoride; and reintroducing the
-by means of the conveyor I3 from the hopper I 4
exposing said lime to the action of the iiuorine 80 evolved silicon tetrailuoride'into the absorption
stage to produce further quantities of calcium
gases flowing counter-current thereto. The
spent gases, i’ree from ilu'orine are discharged
fluoride.- through the vent IB.
‘
The calcium iluosilicate formed ln. the reaction
chamber is discharged into the furnace I6 main 35
WILLIAM H. WAGGAMAN.
ERNEST J_. BRETON. »
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