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Патент USA US2114600

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April '19, 1938.
M. LARSSON
2,114,600
MANUFACTURE OF DICALCIUM PHOSPHATE AND ALKALI ,SALTS
,
Filed Dec. 18, 1934
PROCESS FOR THE MANUFACTURE OF
DICALCIUM PHOSPHATE AND ALKALI
SALTS
(IN MOLECULES)
3.6 CQO' P O
'
7.2 HNO (AS 50°/oSOL)
PHOSPHATE ROCK L
;
DISSOLVING OF 2.5 NonNO3
PHOSPHATE
AS 40 °/@ SOL.
INSOLUBLES
FILTRATION
s. Nora $iF6
.
3.6 CaINOgIg
2 H3PO4
2.5 NQNOa
REPULPING OF
025 010'
ECONDARY PRECIPITATE 75205
1.75 CaCO3
‘
_
.
+
"
4.5 NcxNO3
'
+AS 4o°/°so|_
PRIMARY
PRECIPITATION
2CaHPO4
-_-—--—
0.25 Ccx co 1;
'
co 2-<————
FILTRATION
*
3.6 (504N033) 2
21112835
SECONDARY
O.25Co:O"
_
PRECIPITATION P205
3.6 Ca: (N03) 2
2
C03
7 NQNOa
3.6 No‘2CO3____ PRECIPITATION
.
0F Ca e03
“
c
7‘2NoxNO3
. 35cc‘ co“
a
F||_TRAT|ON
l4 2N0; N01
3
__II\NEI\'TOR.
MARKUS LARSSON
BY.
ATTORNEY.
Zl 145%
Patented Apr. 19, 1938
UNITED STATES PATENT OFFICE.
2,114,600
MANUFACTURE OF DICALCIUM PHOSPHATE
AND ALKALI SALTS
Markus llarsson, Berlin, Germany, assignor to
Kunstdiinger Patent Verwertungs A. G., Glarus,
Switzerland
Application December 18, 1934, Serial No. 758,093
In Germany December 23, 1933
11 Claims.
This invention relates to the making of com
mercial fertilizers. More particularly it is con
cerned with producing phosphoric acid in a form
available for fertilizer purposes, (such as dical
5 cium phosphate) and alkali salts. Heretofore
the usual method of producing phosphoric acid
has been to treat phosphate rock with sulphuric
acid in order to liberate the phosphoric acid.
From this reaction calcium sulphate is obtained
10 which is a waste product or sometimes may be
used as a ?ller for superphosphate. This cal
cium sulphate has in most cases little or no value
and the sulphuric acid used in these processes is
consequently lost.
15
In contradistinction thereto this invention pro-l
poses to substitute for the sulphuric acid the use
of nitric acid. When nitric acid is used for re
acting with the phosphate rock, the solution ob
tained can be treated in different ways so that
2d the P205 is precipitated as discalcium phosphate
and a solution of calcium nitrate or a mixture of
calcium nitrate with alkali- or ammonium ni
trate is obtained. This method has the advan~
tage that the calcium nitrate may be converted.
25
by the addition of an alkali carbonate or bi-car
bonate into valuable alkali-nitrates and the by
product precipitate of calcium carbonate can be
partly reused in the process to precipitate the
(Cl. 23-102)
1y free from nitrate and with a minimum amount
of adherent moisture as otherwise the evapora
tion and drying costs will be so high that the proc
ess will be uneconomical.
However in carrying out such a nitric acid us
ing process difficulties are experienced caused by
the impurities, especially the ?uorine, usually
present in phosphate rocks. Most phosphate
rocks contain an amount of fluorine equal to
about 1%; of the amount of P205 present in the
rock and during the precipitation of the dical
cium phosphate this ?uorine is precipitated as
a very slimy calcium ?uoride extremely dimcult
to separate from-the nitrate solution.
When working according to the present in» 15
vention, however, the phosphate rock is dissolved
in the acid in the presenée of a fairly large
amount of silica and at the same time an alkali
salt, as e. g. alkali nitrate or -chloride is added
to the reaction ‘mixture. Thereupon the ?uo 20
rine reacts with the silica and the alkali salt giv
ing an insoluble, Well crystallized alkali silico
?uoride which can easily be separated from the
solution of nitrates and phosphoric acid. From
the remaining ?uorine-free solution, dicalcium
phosphate can then be precipitated by neutraliz- I
ing the acid solution.
In order to obtain a su?iciently good extraction
P205. A further advantage realized in this case ' of the phosphate ‘rock it is necessary to use so
much HNOa for the dissolving or reaction that 30
is that the acid used for converting the P205 into
available form is not lost but recovered as valu
able nitrates, which in large amounts can be
utilized for fertilizer purposes. A still further
advantage of the process of this invention is that
35 it oii‘ers an opportunity of obtaining a highly
available phosphate precipitate free of excess ca1~
the P205 is present in the solution practically as
free acid. The alkali silico?uoride is consequent
ly precipitated in a strongly acid solution and
must be separated from the solution before it is
neutralized as otherwise the silicoiiuoride will be 35
decomposed and converted into very slimy pre
cium carbonate while at the ‘same time essentially pcipitates of calcium ?uoride and hydrosilicic acid.
In order to obtain as complete a precipitation of
removing the P205 from the obtained nitrate solu
tion; That is, the phosphate precipitation can the silico?uoride as possible ‘it is necessary to
40 be carried out in two stages; in the primary of add a large excess preferably 5 to 15 times the 40
which there is used calcium carbonate in de? theoretical amount of alkali salt.
Phosphate rock however also contains other
ciency of the amount needed for complete precipi=
tation of the P205 in the solution as dicalcium impurities which play an important part in the
production of dicalcium phosphate. Such im
phosphate-resulting in a slightly acid end prod
45 uct solution and in the secondary stage there is purities include iron- and aluminum oxides which
effected a secondary precipitation using an ex > are dissolved by the treatment with nitric acid
and are then precipitated together with the di
cess of calcium carbonate precipitant which re
calcium phosphate. Precipitated under ordinary
sults in the formation of a phosphatic precipi
tate and a solution substantially free of P205. conditions the iron- and aluminum phospates
form a voluminous and slimy precipitate, but 50
50 This two stage operation of the phosphate pre
cipitation is commercially attractive because the when the precipitation takes place at a tempera
secondary precipitate can be redissolved in the ture above 70° C. an excellent precipitate is ob
tained, if the concentration of the solution is
acid solution being fed to the primary precipita
tionstage.
-
,
vIt is obvious that in such a “method the dical
55
cium phosphate must be produced in such a form.
that it can easily be separated from the nitrate
solution utilizing a minimum of- washwater so
that a fairly concentrated nitrate solution is ob
go tained and also a dicalcium phosphate practical~
not too low.
As it is thus desirable to carry out the precipi
55,
tation at‘ a temperature above 70° (2., the dical-,
cium phosphate obtained is in anhydrous form.
If the acid solution is neutralized directly with "
alkali- or alkali bicarbonate the dicalcium phos
phate will be obtained in too ?nely divided form 60
2
2,114,600
and as a result the separation of the precipitate
and the solution will be very di?icult and it will
be necessary to use such large amounts of wash
water that the nitrate solution will be highly
diluted and the dicalcium phosphate after the
washing will have a high content of adherent
moisture.
Accordingly by this invention, the precipitation
is carried out with calcium carbonate whereby
10 larger and more compact grains of dicalcium
phosphate are obtained. The size of the calcium
carbonate grains thus used determines or con
should be at least 95%. The remaining solution
still contains a small amount of P205 substan
tially all of which can be precipitated in‘ the
secondary precipitation stage by the addition
of excess calcium carbonate. This precipitate
is separated from the calcium- and sodium ni
trate solution by thickening and the thickened
sludge returned and'mixed with the acid solu
tion before the primary precipitation of CaHPO‘i.
The mixed Ca(N0a)2,NaN03-so1ution can be .
completely or partly converted to sodium nitrate
solution by precipitating the lime with Na2CO3,
trols the size of the produced dicalcium phos
phate grains and the preferable diameter of the
15 calcium carbonate grains is between 40-200/L.
and the produced CaCOs can then be used for
neutralizing the acid solution. In order to obtain
If the grains are larger than 200/1. the dissolution
of the carbonate will be too slow and incom
plete, and if the grains are smaller than ap
precipitation of CaHPOr and easy to separate
from the sodium nitrate solution the sodium car
bonate is dissolved in so large an amount of un
proximately 40,u the produced dicalcium phos
separated reaction products consisting of CaCOa
and approximately 40% NaNOa solution from a 20
previous operation of this step that the mixture
initially contains 2-4% NazCOa whereupon this
20 phate will be too ?ne for satisfactory ?ltering
and washing.
In order to obtain a complete precipitation of
substantially all the P205 in the solution, it would
be necessary to use an excess of calcium carbon
25 ate and the produced dicalcium phosphate would
then contain a fairly large amount of CaC03
which is undesirable. The precipitation of the
dicalcium phosphate is carried out most desir
ably in continuous operation in two precipitation
30 stages. In the primary stage precipitation is
effected in a slightly acid solution so that the
added CaCOa is completely dissolved. After the
dicalcium phosphate has been separated, the P205
in the remaining solution is completely precipi
35 tated in a secondary precipitation stage by add
ing an excess of calcium- or alkali-carbonate,
such reagent being referred to in the claims as
alkali carbonate and the precipitate after sepa
ration of the main part of the solution is then
40 mixed with the phosphoric acid containing solu
tion after the alkali silico?uoride separation.
Thus. the excess carbonate is decomposed but
only part of the dicalcium phosphate is dissolved
and when working in this stepwise Way the total
45 P205 is produced as carbonate-free dicalcium
phosphate.
The invention can be most advantageously uti
lized in the following process:
Phosphate rock is dissolved in or reacted with
50% nitric acid with addition of so much sodi
um nitrate solution (approximately 40% NaNO:
strength) that the produced solution contains
10 to 15% NaNOz. The precipitated NazSiFe
‘and the insoluble parts of the rock are then
55 ?ltered off. ' This ?ltration is facilitated, if the
phosphate rock has been freed from organic
products by calcination.. If a phosphate rock
high in silica as for instance Florida pebble is
this CaCOz-precipitate in a form suitable for the -
mixture and the Ca(NOa)2—-NaNO3 solution are
brought to react in continuous operation so that
the solution contains approximately 0.1% NazCOa
after the lime has been precipitated. The size
of the obtained CaCOs grains can be varied by
varying the amount of unseparated reaction
products used for dissolving‘the NazCOa and also
by varying the retention time in the precipita 30
tion agitator. A portion of the CaCOa corre
sponding approximately to the difference in cal
cium content between tri- and dicalcium car
bonate must be washed and removed from the
process and either sent to waste or otherwise
utilized. The bulk of the calcium carbonate is
recirculated for precipitation of the dicalcium
phosphate. The portion of the CaCO; used for
precipitating the CaHPO4 should not be sepa
rated from the sodium nitrate solution but be
utilized suspended therein in the form of a more 40
or less thickened sludge or slurry.
When working according to above description
it is possible to produce a washed dicalcium phos
phate with less than 25% adherent moisture and
a ?nal sodium nitrate solution of at least 40% 45
concentration.
‘It should be observed that when potassium ni
trate for instance is used instead of sodium ni
trate, the temperature at which CaHPOr is pre
cipitated must be considerably increased up to 50
90-100" C. as at lower temperature the precipi
tate becomes very slimy.
I
v The invention is not limited to the process
of producing alkali. nitrates and dicalcium phos
phate from nitric acid, phosphate rock and al 55
kali carbonate, but also refers to the production
of calcium nitrate and alkali nitrate, either sep
used, no extra silica is necessary, but otherwise
arately or as a mixture.
silica in the form of ?nely ground sand, quartz
or other silica containing material must be added.
method of dissolving phosphate rock in hydro
The clear solution is then in continuous opera
tion brought to react with 02.00;; at a tempera
ture of '75-80° C. so that a constant acidity of
65 0.2-0.3% P205 is kept in the produced solu
tion. If ground limestone is used, it should all
pass through a sieve with 1500 to 1600 mesh per
square centimeter. The CaCOs should be re
pulped in NaNOs solution before addition. The
produced CaHPO4 settles rapidly and can easily
be separated and washed free from adherent
solution.
A good precipitate from this primary
It also refers to the
chloric acid (instead of in nitric acid) inpres
chloride, precipitating the lime with ammonium
carbonate in the ?nally obtained CaCl2—KCl
solution. The NH4Cl—KCl solution can then be
evaporated for producing a mixed fertilizer or 65
the salts can be separated in any known manner.
It is understood that in all cases where alkali
carbonate is recommended for use also alkali bi
carbonate can be used.
The invention is further explained in the fol 70
lowing diagram and example:
stage precipitation should not contain more than
(a) In an acid proof agitator calcined Florida
30%, preferably 20 to 25% adherent moisture
pebble phosphate containing 36% P205 and 51%
75 and the solubility in ammonium citrate solution
60
ence of alkali salts as for instance potassium
CaO is treated with nitric acid (50%) in pres
75
3
2,114,000
ence of sodium nitrate solution. The amounts
are as follows: 1000 grams rock, 2240 grams nitric
acid, 1300 grams sodium nitrate solution (40%)
21'
10
as produced by this method. Due to the reaction
heat the temperature oi the mixture rises to
I claim: '
'.
_
1. The method of producing dicalcium phos
phate and sodium nitrate from phosphate rock
which comprises reacting the phosphate rock
between 40 and 50° C. After two hours the re > with nitric acid; in a primary stage, adding to
the solution formed thereby calcium carbonate
action is ?nished and the solution containing cal
cium nitrate, phosphoric acid, and sodium nitrate v of controlled size suspended in alkali metal ni
is separated from the insolubles and the sodium trate solution both produced in the process, at an
elevated temperature, and in de?ciency of the 10
silico ?uoride precipitate.
(b) The ?ltrate with about 8% P205 is now
mixed with the so .called rest precipitate-ob
tained under d-consisting of a mixture oi’ di
calcium phosphate and calcium carbonate; it is
added in form of an unwashed ?lter cake.
15 Amounts: 1000 grams ?ltrate and '70 to 80 grams
?lter cake. The temperature is kept at 70° 0.,
whereby the calcium carbonate is completely dis
solved but the main part of the dicalcium phos
‘ A‘) phate remains undissolved.
(c), To this’ mixture calcium carbonate is added
in order to precipitate the P205 as Cal-IP04.
Before adding, the CaCOa is repulped and so
suspended in 40% NaNOa solution and the cor
responding amount of wash water. The re
25 action takes place between '75 and 80° C. The
amounts used are as follows: sludge or slurry
from b corresponding» to 1000 grams ?ltrate
a+'70-80 grams secondary precipitate, 111 grams
calcium carbonate ?lter cake (about 80 grams
30 CaCOa) sludged or suspended in '700 grams 30%
NaNOa solution. When working according to
these ?gures, the ?nal solution contains 0.2 to
0.3% free P205. After some hours the reaction
is completed and the dicalcium phosphate ob
35 tained is ?ltered, washed, and dried at 100° C.
The adherent moisture of the cake is about 26%.
The ?nal product has 47m 48% P205, of'which
95% is soluble in neutral ammonium nitrate
solution.
40
solution is used under a, c, d as already described.
(d) The ?ltrate from c is" mixed with the wash
water and the remaining P205 is completely pre
cipitated by further addition of 02.003. To 1000
grams ?ltrate. + wash water (speci?c gravity
about 1.35) 20-30 grams calcium carbonate cake
45 are added. The cake is obtained as described
under e and repulped in a few cubic centimeters
of sodium nitrate solution. The conditions are
the same as under 0. The precipitate is separated
from the mother liquor consisting of a mixture of
50 calcium nitrate and sodium nitrate by ?ltration.
The ?lter cake is returned to the acid solution as
mentioned above.
amount needed for complete precipitation of _
the P205 in‘ the solution as dicalcium phosphate;
separating the so-produced dicalcium phosphate
from the solution; in a secondary stage, adding
to the separated solution calcium carbonate pro 15
duced in the process, in excess of the amount
needed to precipitate the ‘P205 therein as dical
cium phosphate; separating the so-produced
phosphatic precipitate from the solution and re
turning it to the primary stage of the process; 20
adding to said last-mentioned solution alkali
metal carbonate dissolved in unseparated reac
tion products from a previous operation of this
step, whereby a mixture is formed containing
alkali metal carbonate and alkali metal nitrate 25
from which a precipitate is formed comprising
calcium carbonate of controlled size suspended
in the ?nal solution of alkali metal nitrate;
separating therefrom the alkali nitrate solution
and calcium carbonate in excess of those amounts 30
needed in the previous steps of the process; and
returning the remaining slurry of calcium car
bonate in alkali nitrate to the primary and sec
ondary calcium phosphate precipitation stages
of the process in accordance with the steps out 35
lined.
'
1
2. The method of producing dicalcium phos
phate and sodium nitrate from phosphate rock
containing ?uorine which comprises reacting the
phosphate rock with nitric acid in the presence 40
of su?icient silica for precipitating as silico
?uoride substantially all of the fluorine present
in rock in the presence of an excess of alkali
metal nitrate produced in the process; separating
the so-produced silico?uoride from the obtained 45
solution; in a primary stage, adding to the solu
tion calcium carbonate of controlled size sus
pended in alkali metal nitrate solution both pro
duced in the process, at an elevated temperature,
and in de?ciency of the amount needed for com 50
plete precipitation of the P205 in the solution as
dicalcium phosphate; separating the so-produced
dicalcium phosphate from the solution; in a
(e) The ?ltrate from d contains 6 to 7% 021.0, ' secondary stage, adding to the separated solu-.
which is precipitated with calcined soda in a
55 series of agitators: In the ?rst agitator of the
series the soda is mixed with such an amount
of unseparated recirculated sludge or slurry that
a 3 to 4% solution is obtained.
tion calcium carbonate produced in the process,
in excess of the amount needed to precipitate
the P205 therein as dicalcium phosphate; sepa
rating the so-produced phosphatic precipitate
In the second ‘~ from the solution and returning it to the primary
agitator of the series the reaction with the cal
60 cium nitrate-sodium nitrate solution is carried
out at 50° C. The over?ow from the last agitator
stage of the process; adding to said last-men 80
tioned solution alkali metal carbonate dissolved
in unseparated reaction products froma previous
operation of this step whereby a mixture is
formed containing alkali metal carbonate and
liters sludge and this mixture is brought to ref alkali metal nitrate from which a precipitate 05
is formed comprising calcium carbonate of con
act continuously with 3400 grams calcium ni
trate-sodium nitrate solution (6.=—,'-;~ Z'aO). The trolled size suspended in the ?nal solution of val
?nished sodium nitrate ‘solution has an excess kali metal nitrate; separating therefrom alkali
of from 0.05 to 0.09% Na2COa. The calcium car- ' metal nitrate solution and calcium carbonate in
bonate is ?ltered oil and the unwashed ?lter cake excess of those amounts needed in theprevious 70
70 contains aboutv 73% CaCOa. The completely steps of the process; returning the remaining
slurry of calcium carbonate in alkali metal ni
washed dry cake has only 0.18% P205. The sodi
um nitrate solution produced contains 40% trate to the primary and secondary calcium phos
phate precipitation stages of the process in ac“
NaNOa and is practically free of P205.
The calcium carbonate and the sodium nitrate cordance with the steps outlined; and re "= ng a w
75
is recirculated as described. The amounts are
as follows: 420 grams soda are dissolved in 15
4-.
2,114,600
part oi.’ the alkali metal nitrate to the initial
phosphate rock-nitric acid reaction.
3. The method of producing dicalcium phos
phate and sodium nitrate from phosphate rock
which comprises reacting the phosphate rock with
nitric acid; in a primary stage, adding to the
solution formed thereby calcium carbonate of
' controlled size suspended in alkali metal nitrate
solution both produced in the process, at an ele
10 vated temperature, and in de?ciency of the
amount needed for complete precipitation of the
P205 in the solution as dicalcium phosphate;
separating the so-produced dicalcium phosphate
from the solution; in a secondary stage, adding
15 to the separated solution a suitable alkali car
bonate in excess of the amount needed to precip
itate the P205 therein as dicalcium phosphate;
separating the so-produced phosphatic precip
itate from the solution and returning it to the
20 primary stage of the process; adding to said last
mentioned solution alkali metal carbonate dis
solved in unseparated reaction products from a
previous operation of this step whereby a mixture
is formed containing alkali metal carbonate and
25 alkali metalm'trate from which a precipitate is
formed comprising calcium carbonate of con
trolled size suspended in the ?nal solution of
alkali metal nitrate; separating therefrom the
alkali metal nitrate solution and calcium car~
bonate in excess of those amounts needed in the
previous steps of the process; and returning the
remaining slurry of calcium carbonate in alkali
metal nitrate to the primary and secondary cal
cium phosphate precipitation stages of the proc
ess in accordance with the steps outlined.
4. The method of producing dicalcium phos
phate and sodium nitrate from phosphate rock
containing ?uorine which comprises reacting the
phosphate rock with nitric acid in the presence
of sufficient silica for precipitating as silico?uoride
substantially all of the ?uorine present in the rock
in the presence of an excess of alkali metal
nitrate produced in the process; separating the
so-produced silico?uoride from the obtained ‘solu
tion; in a primary stage, adding to the solution
calcium carbonate of controlled size suspended in
alkali metal nitrate solution both produced in the
process, at an elevated temperature, and in de?
ciency of- the amount needed for complete precip
50 itation of the P205 in the solution as dicalcium
phosphate; separating the so-produced dicalcium
phosphate from the solution; in a secondary
stage, adding to the separated solution a suitable
alkali carbonate in excess ‘of the amount needed
:3 Li
to precipitate the P205 therein as dicalcium phos
phate; separating the so-produced phosphatic
precipitate from the solution and returning it to
the primary stage of the process; adding to said
last-mentioned solution alkali metal carbonate
60 dissolved in unseparated reaction products from
a previous operation of this step whereby a mix
ture is formed containing alkali metal carbonate
and alkali metal nitrate from which a precip
itate is formed comprising calcium carbonate of
65 controlled size suspended in the ?nal solution of
alkali metal nitrate; separating ‘therefrom the
alkali metal nitrate solution and calcium car
bonate in excess of those amounts needed in the
previous steps of the process; returning the re
maining slurry of calcium carbonate in alkali
metal nitrate to the primary and secondary cal
cium phosphate precipitation stages of the proc
ess in accordance with the steps outlined; and
returning a part of the alkali metal nitrate to the
initial phosphate rock-nitric acid. reaction.
5. The method of producing dicalcium phos
phate and sodium nitrate from phosphate rock
containing ?uorine which comprises reacting the
phosphate rock with nitric acid in the‘ presence
of su?icient silica for precipitating as silico?uo
ride substantially all of the ?uorine present in the
rock in the presence of an excess of around 10%
to 15% of alkali metal nitrate produced in the
process; separating the so-produced silico?uoride
from the obtained solution; in a primary stage, 10
adding to the solution calcium carbonate of con
trolled size suspended in alkali metal nitrate solu
tion both produced in the process, at an elevated
temperature, and in de?ciency of the amount
needed for complete precipitation of the P205 in
the solution as dicalcium phosphate; separating
the so-produced dicalcium phosphate from the
solution; in a secondary stage, adding to the
separatedsolution calcium carbonate produced in
the process, in excess of the amount needed to
precipitate the P205 therein as dicalcium phos
phate; separating the so-produced phosphatic
precipitate from the solution and returning it to
the primary stage of the process; adding to said
last-mentioned solution alkali metal carbonate
dissolved in unseparated reaction products from
a previous operation of this step whereby a mix
ture is formed containing alkali metal carbonate
and alkali nitrate from which a precipitate is
formed comprising calcium carbonate of con
trolled size in the ?nal solution of alkali metal
nitrate; ‘separating therefrom the alkali metal
nitrate solution and calcium carbonate in excess
of those amounts needed in the previous steps of
the process; returning the remaining slurry of
calcium carbonate in alkali metal nitrate to the
primary and secondary calcium phosphate precip
itation stages of the process as needed; and re
turning a part of the alkali metal nitrate to the
initial phosphate rock-nitric acid reaction.
40
6. The method of producing dicalcium phos
phate and sodium nitrate from phosphate rock
which comprises reacting the phosphate rock
with nitric acid; in a primary stage, adding to the,
solution formed thereby calcium carbonate of 45
controlled size suspended in alkali metal nitrate
solution both produced in the process, at a tem
perature between 70° C. and the boiling point of
the solution, and in de?ciency of the amount
needed for complete precipitation of the P205 in 50
the solution as dicalcium phosphate; separating
the so-produced dicalcium phosphate from the
solution; in a secondary stage, adding to the sepa
rated solution calcium carbonate produced in the
process, in excess of the amount needed to precip 55
itate the. P205 therein as dicalcium phosphate;
separating the so-produced phosphatic precip
itate from the solution and returning it to the
primary stage of the process; adding to said last
mentioned solution alkali metal carbonate dis 60
solved in unseparated reaction products from a
previous operation of this step whereby a mixture
is formed containing alkali metal carbonate and
alkali metal nitrate from which a precipitate is
formed comprising calcium carbonate of con 65
trolled size suspended in the ?nal solution of
alkali metal nitrate; separating therefrom the
alkali metal nitrate solution and calcium car
bonate in excess of those amounts needed in the
previous steps of the process; and returning the 70
remaining slurry of calcium carbonate in alkali
metal nitrate to the primary and secondary cal
cium phosphate precipitation stages of the proc
ess as needed.
7. The method of producing dicalcium phos~ 75
5
9,114,600
phate and sodium nitrate i'rom phosphate rock
containing ?uorine which comprises reacting the
phosphate rock with nitric acid in the presence of
su?icient silica for precipitating as silico?uoride
substantially all or the ?uorine present in the
rock in the presence of an excess of alkali metal
nitrate produced in the process; separating the
so-produced silico?uoride from the obtained so
lution; in a primary stage, adding to the solution
10 calcium carbonate of controlled size suspended in
alkali metal nitrate solution both produced in the
process, at a temperature between 70° (Land the
9. The method of producing dicalcium phos
phate and sodium nitrate from phosphate rock
containing ?uorine which comprises reacting the
phosphate rock with nitric acid in the presence
of sufficient silica forprecipitating as silico?uo
ride substantially all of the ?uorine present in the
rock in the presence of an excess of alkali metal
nitrate produced in the process; separating the
so-produced silico?uoride from the obtained so
lution; in a primary stage adding to the solution 10
calcium carbonate of, controlled size suspended in
alkali metal nitrate solution both produced in
boiling point of the solution, and in de?ciency oi the process, at a temperature between 70° C. and
the amount needed for complete precipitation of » ,. the boiling point of the solution, and in de?ciency
the P205 in the solution as dicalcium phosphate; of the amount needed for complete precipitation 15
separating the so-produced dicalciumphos'phate
from thelsolution; in a secondary stage, adding
to the separated solution calcium carbonate pro~
duced in the process, in excess of the amount
20 needed to precipitate the P205 therein as dical
cium phosphate; separating the so-produced
phosphatic precipitate from the solution and re
turning it to the primary stage of the process;
adding to said last-mentioned solution alkali
25 metal carbonate dissolved in unseparated reac
tion products from a previous operation of this»
step whereby a mixture is formed containing al
kali metal carbonate and alkali metal nitrate
of the P205 in the solution as dicalcium phos
phate; separating the so-produced dicalcium
phosphate from the solution; in a secondary
stage, adding to the separated solution a suitable
alkali carbonate in excess of the amount needed 20
to precipitate the P205 therein as dicalcium phos
phate; separating the‘ so-produced phosphatic
precipitate from the solution and returning it to
the primary stage of the process; adding to said
last-mentioned solution alkali metal carbonate 25
dissolved in unseparated reaction products from
a previous operation of this step whereby a mix
ture is formed containing alkali metal carbonate
from which a precipitate is formed comprising , and alkali metal nitrate from which a precipitate
80 calcium carbonate'of controlled size suspended in is formed comprising calcium carbonate of con 30
trolled size suspended in the ?nal solution of al
the ?nal solution of alkali metal nitrate; separat
ing therefrom the alkali metal nitrate solution kali metal nitrate, separating therefrom the al
and calcium carbonate in excess of_ those amounts kali metal‘ nitrate solution and calcium carbonate
in excess of those amounts needed in the previous
needed in the previous steps of the process; re
steps of the process; returning the remaining 35
turning the remaining slurry of calcium carbo
nate in alkali metal nitrate to the primary and slurry of calcium carbonate in alkali metal nitrate
secondary calcium phosphate precipitation stages
of the process as needed; and returning a part of
the alkali metal nitrate to the initial phosphate
rock-nitric acid reaction.
,
'
'
'
i
to the primaryand secondary calcium phosphate
precipitation stages of the process as needed; and
returning a part of the alkali metal nitrate to the
40
initial phosphate rock-nitric acid reaction.
10. In a process for the production of dicalcium
phosphate wherein the dissolved P205 is precipi
8. The method of producing dicalcium phos
phate and sodium nitrate from phosphate rock
which comprises reacting the phosphate rock tated ‘ as substantially dicalcium phosphate by
with nitric acid; in a primary stage, adding to , the addition of calcium carbonate to a phosphate
the solution formed thereby calcium carbonate of solution, the step of reacting with a substantially 45
controlled size suspended in alkali metal nitrate phosphate-free solution of calcium nitrate formed
solution both produced in the process, at a tem
perature between 70° C. and the boiling point of
the solution, and in de?ciency of the amount
needed for complete'precipitationof the P205 in
the solution as dicalcium phosphate; separating
the so-produced dicalcium phosphate from the
solution; in a secondary stage, adding to the sep
arated solution a suitable alkali carbonate in ex
55 cess of the amount needed to precipitate the
P205 therein as dicalcium phosphate; separating
the so-produced phosphatic precipitate from the
solution and returning it to the primary stage of
the process; adding to said last-mentioned solu
tion alkali metal carbonate dissolved in unsep
arated reaction products from a previous opera
tion of this step whereby a mixture is formed
‘containing alkali metal carbonate and alkali
metal nitrate from which a precipitate is formed
comprising calcium carbonate of controlled size
suspended in the ?nal solution of, alkali metal
nitrate; separating therefrom the alkali metal
nitrate solution and calcium carbonate in excess ‘
of those amounts needed in the previous steps 01'
70 the process; returning the remaining slurry of
calcium carbonate in alkali metal nitrate to the
primary and secondary calcium phosphate pre
cipitation stages of the process as needed.
in the process, an alkali metal carbonate mixed
with unseparated reaction products consisting of
calcium carbonate and an alkali metal nitrate so
lution wherein the solution contains alkali metal 50
carbonate and alkali metal nitrate, and returning
part of the so-formed calcium carbonate for the
precipitation of the dicalcium phosphate.‘
11. In a process for the production of dicalcium phosphate wherein the dissolved P205 is 55
precipitated as substantially dicalcium phosphate
by the addition oi calcium carbonate'to a phos
phate solution, the‘step of reacting with a sub
stantially phosphate-free solution of calcium ni
trate formed in the process, an alkali metal car
bonate mixed with unseparated reaction products
consisting of calcium carbonate and an alkali
metal nitrate solution wherein the solution con
tains alkali metal carbonate and alkali metal
nitrate and the/salt solution after the precipita 65
tion has taken place contains an excess'of sub
stantially 0.1% of dissolved alkali metal carbon
ate, and returning part of the so-formed calcium
carbonate for the precipitation of dicalcium phos- '
phate. '
v
,
,I
_ MARKUS LARSSON.
70
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