SOLUTION OF PHOSPHATES BY NITRIC ACID

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP82-00039R000200020006-2
• Release Decision: RIPPUB
• Original Classification: R
• Document Page Count: 23
• Document Creation Date: December 22, 2016
• Document Release Date: May 15, 2012
• Sequence Number: 6
• Publication Date: April 29, 1952
• Content Type: REPORT

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SOLUTION OF PHOSPHATES BY NITRIC ACID
ux, 1+ky X~
S. I? Volffkovich
A. I. Loginova
A. M. Polyak
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STAT`
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SOLUTION OF PHOSPHATES BY NITRIC ACID
(Condensation of a paper read to the Conference on
Potash and Compound Fertilizers of the Chemical Group
of the Ussa Academy of Sciences 27~-29 June 1937)
A vast majority of USSR soils and agricultural crops re..
quire both phosphorus and nitrogen fertilizers. For this reason
the economically expedient combination of phosphate and nitre.
genus fertilizers production into a single technological process
Until recently' only anirnonia was used in the production of
pho spho~nitrogenous f eztili zer sd Nitric acid began to come into
\ d 4 e 7-J1
use for -solution of phosphate in the foreign fertilizer industry
only a few years ago, a result of large scale expansion of the
industrial amrnoni a synthesi s and o;dttion to nitric acids which
became considerably cheaper as a result.
The main advantage of the nitric acid process for di-s?? C ---,, s
so--v3ng..phosphates over the use of sulphuric and hydrochloric
acids for the same purpose lies in the virtually complete' com&?
plex utilization of the reacting masses, accompanied by utiliza-
tion of the energy of nitric acid to dissolve phosphorite, When
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and concentrated phosphate fertilizers are produced with
H3PO14 M o ~'
hophogypsum' which is utilized or, only slightly
H250)4, ,
p
when HC1 is used, Ca C12 i s formed, and t L`'
utilized, is produced;
0*
is also ~ ed, ? that is these processes o~1y utilt.ze the
-,ut.~liz ~
chemical energy of these acids, without their appearing in the
end products. When nitric acid s used instead for dissolution'
not only is its chemical energy utilized; it also appears in
... fertilize' -~ in the form of Ca(N03)2.
the product
The nitric acid process further allows the expedient use
of fluorine (according to work done by M. Dornish, M. Sladko?
vaya, A? Polyak and others); when Khibinsk apatite is processed
rare earths may also be used efficiently. These materials are
v~y necessary and valuable to the national ecorDflT.
In view of the vast scale of the f extilizer industry, the
p'
sso11:t4-Gn of phosphates by nitric acid would permit the assimp
nation of great quantities of HNO3.
Despite the great interest in the nitric acid method dis''
major foreign cartels and manufacturers these methods
played by ~
have still not been widely adopted. Oily three or four relatively
sma11 plants have been built in various countries during the
past few years (using various technological systems). This is
apparently dues on the one hand, to results of economic crisis
and depression in the capitalist countries, and on the other hand'
explained by the technical difficulties of mastering this
is ~'
technaloga.eal method. `
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In view of the lack of foreign literature throwing light
on the technology of phosphate dissolution by nitric acid
(except for the numerous patents) and in view of the number of
technical difficulties which arise when these methods are tried
out for checking purposes, the Scientific~Research Institute
for Fertilizers, Insecticides and Fungicides (NIUIF) has in
recent years been carrying on an extensive series of laboratory
experiments, and, to some extent, pilot plant operations with
various types of raw materials;: it has also made agronomic tests
and technical and economic computations as to the expediency of
this technological approach relative to others.
The following institutions have also worked in the same
field (starting earlier); The Institute of General and Inorganic
Chemistry of the Academy of Sciences USSR; the Ukrainian Affiliate
of. the NIUIF; the Belorussian Industrial Institute; the Central
Laboratory of the Chernoreka Plant, the GIPROAZOT, and others.
The main difficulties and failings of the nitric acid
method (many of which have already been overcome) consist of
aggravated corrosion of plant equipment, considerable loss of
nitrogen in the dissolution of phosphorites of organic origin
(which losses it has proved possible to stop by elimination of
organic matter and oxidation of the ferrous compounds through
roasting the phosphorites); hygroscopicity of the end product by
reason of its Ca(N03)2 or NH) NO3 content (which can be reduced
by separation of the reaction products, by mixing with potassium
or other metal salts, by granulating them, or by other methods);
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 Ca3P2.O8 Rest + 6HN03 = 3Ca(NO3)2 2H3P04 + Rest (2)
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the difficulty of filtering and decanting the inta'mediate pro..
ducts when phosphorites of organic origin are processed (roast-
ing, elimination of fluorine and si~..ica by means of alkaline
salts, and other measures) have almost entirely eliminated this
difficulty.
There are a number of variations of mtr:d"phos~
Q, e c. p '1-i ? ' & --1 t/V '\-I 1 + i CC (n 1 ~l
phorite o?txt n: The one deserving the greatest attention -
-? tessed--ii the w~ iowL.ng technological eye: 3t- o 1 ' r a ,?e
(a) Ca3P208 Rest + L.HNO3 = CaH).(PO))2 + 20a(N03)2 + Rest, (1)
1. 1r .'
where Rest represents' bhe1constituents of the phosphate rock, in~
chiding the undissolved residues.
What we have in mind is a process not involving the
separation of the products of reaction.
As a result of this process, which recalls the production
of superphosphate, a heavy, comparatively low-grade product is
obtained, containing all the constituents of the original phos-
phate rock, P205 in water..soluble form, and nitrogen as Ca(N03 )2,
~ t-;
E, v " A'~1 G? t V to M
(b) ' z -iQn according to the equation
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e1 E1 Mr t; G - ; (1.
followed by separation decantation or filtration of the H3POJ
r
and Ca(N03)2 solution from the insoluble residue,
This operation is not essential if the insoluble residue
is very slight (as with flotation apatite). As a result of the
complete neutralization of the H3PO) by any base, either a corn.'
Alex nitrogen-rphosphorus fertilizer or separate phosphate and
nitrogenous fertilizers may be obtained in this variant,
Production of nitro$uperphosphate was accomplished a few
years ago on the pilot-plant scale in Switzat:'land (De..Lone),
but in view of a number of disadvantages, this method has not yet
been adopted elsewhere. At various times this process has been
studied in the NIUIF by different research workers .'p S. Vol'fko~
vich, M. Golitsina, L.. Berlin L. Gurevich, L. Goritskaya, and
R. Yakobson, An. advantage 'of this method is the simplicity of
the process, Since the product obtained, however, is low-grade
r'y v 1- "1 V. A~ t, C a~ '}G- "~ ?~
and very hygro sco is ( even when
of manufacture, or when the return product is chilled) and re-.
quires special storage conditions and special packing or mixture
with other fertilizers, the USSR is not contemplating production,
Many authors have proposed the d-s1ut4en, of phosphates
according to equation (2), with subsequent neutralization of the
acid solution by means of CaO or CaCO3,' NH3 or NH( C03), or
C ~ R rvirv S I, '{ g -"z,?,
c. `
ammoniates instead of 4=i-s-soi-ti ?on by H250), (NH )2SOJ~, Na230L.,
K2S0, NaN03, KN03, or other reagents (either singly or together).
A number of these schemes have been studied in the NIUIF,
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The advantage o1 these schemes is the production of a
higher-grade fertilizer than ritrosuperphowphate; their dis-
advantage is the great complexity of the technological processes
involved.
Study of the production of soMcalled ammonitrophos, which
is characterized by the processing of a nitric and phosphoric
Y
acid extract (without filtration of the undissolved residues from
the ammonia and carbonic acid) has not, up to the present, shown
any positive results. In this method, the calcium phosphates are
precipitated as residues (mostly in citrate-soluble form) together
with calcium carbonate and the undissolved residue, while ammonium
nitrate remains in solution. The product contains a dried and
ground mixture of all these salts. The difficulty of drying the
product, its high capacity for absorbing moisture, and primarily
the considerably lower availability for plant ass.miiation of the
P20S in ammonitrophos as compared with that in CaHPO have joined
to make these schemes of production ur.cceptable up to now. (See
papers by S. Vol ' fkovich, L. Antokhinaya, A. Bun A kovaya, I. Mirkin,
A. Loginovaya, A. Polk, L. Grinshpan, N. Blagoveshchenskaya,
S. Kaluginaya and other s. )
The production of CaHPOj~ and Ca(N03)2 based on the neutrali-
sation of the H3P04 in a mixture with Ca(N03 )2 is the simplest
method and the one that is most highly developed at present. It
is used in one foreign plant and is scheduled to be employed in
the USSR. Its basic disadvantage is its hygroscopicity and low
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concentration of ca(N03)2 in comparison with the method des..'
cribed below and the fact that the P205 it contains is in
citrate soluble (but not water-soluble) form.
A. I. Loginovaya of the NIUIF ha; studied the production
or NHS (N03 ) 2 and NHi2PO baaed on the separation of H3POL and
Ca(N03)2 the calcium by means of (NHS) 250, followed by
neutralization of the solution with NHS and regeneration of the
phosphogypsum obtained by use of ammonium carbonate. A process
having a similar technological system is in use at one foreign
plant., Its advantage is the possibility of securing a highly
ammophos with ammonium nitrate
while its main disadvantages are the complexity and awkwardness
of the technological process.
Other variants of this process employing Na2SO, K2SO~,
K2C03, and other reagents have been tested, so far only for
Among the new variants the method proposed by A. Belopol'-
skiy for obtaining not CaHPO)~ but CaHi(P04)2 from the nitric.'.
phosphoric acid extract by neutralizing it with lime is deserving
of serious consideration. This proposal is the result of an
investigation into the physical chemistry of the equilibrium of
the system CaO w P2O5 w N205 H2O at 50 degrees and 25 degrees,
and is being studied at the present time.
Below we give short descriptions and characteristics of
two technological systems which have been most thoroughly studied
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and have the greatest practical interest from our
point of VOW.
METHOD OF DERIVING CaRPO AND Ca (NO3)2
This process was studj.ed in detail on flotation apatite
through an extensive laboratory research 'c
arr. ed out in
1935 by the NITIF, and the basic coefficients needed for the
formulation of plans for a plant were obtained
A
The process can be divided into three basic e .
lenients.
,,,
(a) dissolution off'' flotation apatite by means of nitric
(b) processing of the solutions obtained from that d1 s?
solution to precipitate out the phosphoric acid;
a
lc) evaporation or furtkier processing of the calcium
nitrate solutions.
This process is charactE j.~ed by the following basic
equatians;
F ~ 1OHNO3 -~ 5Ca ( NO3 ) 2 3 H3 PO f HF.
~
The hydrofluoric acid reacts with the silica which is
always assocd.ated in small quantitjes with it
otation apatlte9
according to the equation
6HF . Si02 -j H2S1F6 + 2H20.
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The project brought out the necessity of separating out
n to obtain a precipitate with satisfactory physical
the 5iF6
properties readily filtrable and washable). This separation
was accomplished by precipitating it out as Na25iF6 by means of
sodium nitrate according to the formula
H25iF6 + 2NaNO3 --+ 2HN03 + Na2SiF6.
coefficient of precipitation of the fluorine by this
The
method amounted to 80 to 8 percent.
This sy. 'licon fluoride precipitation yields as a by.product
The precipitation of the solutions after the nitric acid
precipitation by lime proceeds according to the equation
Ca(OH)2 + H3POL + Ca(N03)2 + aq --a CaHPO~ + Ca(N03)2 + aq.
The residual H2SiF6 and Na2SiF6 are hydrolyzed with the
(milk of lime) or limestone,
formation of colloidal forms of calcium fluoride and silica;
H2SiF6 + 30a(OH)2 --b' H2O + Si02 + 3CaF2 ?
The sesquioxides are precipitated as phosphates:
a salt that can be used as an insecticide.
dxssoluty. 'orl of the flotation apatite may be done with either lime
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3 (H03) 2 + 3H2Q + 2HP0
If the acid solution is precipitated by limestone (cafe m
carbonate) instead, the following reactions take place;
( 011 + '"(N03)2 Ca003 + aq CaHPO + Ca(N03)2 +aq +C021.
(1) H3P.
(2) CaCO3 ' + H2SIF6 -? CaSiF6 + H2O + c02.
(3) 2P.(N03)3 + 2H3PO4 + 3CaC03 - 2RPO + 3Ca(N03)2 + 3002 + aq...
No hydrolysis of the residual Na2SiF6 takes place.
Comparison of the precipitations by lime and limestone
dictated preference be given the latter, since the precipitate
prepared from lime was considerably inferior in physical properties
(crystalline structure, filtrability) and chemical properties
(saluba.llty in citrate.mmoniacal solution) to that obtained by
limestone.
The coefficient of precipitation of P20~ by limestone of
the fineness of grind indicated reached a very high level
a9 to 98 percent. This fact shows to advantage the precipitation
,
of solutions obtained by flotation apatite dissolution with nitric
acid from that of sulfuric acid extracts of apatite, and is
apparently due to the buffer effect of Ca(N03)2?
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It has been demonstrated that it is possible to dry the
recipttate obtained with limestone to a total moisture content
P
of percent without loss of citrate solubility.
The conversion of calcium nitrate solutions to ammonium
nitrate by precipitation with ammonium carbonate has been tested
with the object of obtaining a fertilizer richer in nitrogen. The
equation is as follows;
ca(N03)2 + (4)
.0J3 + aq --? ca003 ' + 2NNL~N03 + aq.
The test bra elded wholly favorable results both as regards
the coefficient of conversion (which was 100 percent) and the
filtrability of the carbonate slurry.
Based on a large nurber of experiments' the industrial steps
for the process have been formulated as shown in Figure 1.
Flotation apatite is dissolved with percent nitric acid.
During the process a 17 percent solution of NaN03 is introduced
to precipitate out the H2SiF6 in the form of Na2SIF6. The soiw"
Lion is decanted to remove the undissolved residue of flotation
apatite mixed with the precipitated sodium silicofluorideg which
is washed free from the solution and either turned out as a
finished product containing up to L.2 percent Na2SiF6 (insecticide)
or further processed. Finely ground limestone is then added
is
to the solution to induce a twos-phase precipitation.
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During the first stage of precipitation before the main
precipitation occurs the rare earth phosphates separate out and
the liquid is decanted to remove theme
The main precipitation occurs during the second stage.
This precipitate consists of CaHPO, which is separated and
washed free of remaining calciwn nitrate solution by filtration
1 1~ n
through continuous?process drum filters, cried, and turned out
as finished fertilizer. The Ca(N03)2 solution is either evaporated
to obtain a fertilizer or is further processed by conversion to
ammonium nitrate through reaction with ammonium carbonate. Part
of the calcium carbonate formed in the latter case is returned
to the process for reruse in precipitation.
The consumption coefficients per 1x000 kilograms of
flotation apatite are as follows; S~ percent nitric acids 2,070
kilograms; sodium nitrate (in 17 percent solution), 777 kilograms;
limestone (or calcium carbonate), X95 kilograms; water, 112 kilo".
gams.
The yield per 1,000 kilograms flotation apatite is as
follows;
Insecticide containing up to L2 percent Na2SiF6 ?? 67 kilograms.
(The quality of this product is subject to check on a pilot-plant
scale.)
Precipitate containing GLi..S percent of assimilable P20 - 8L7
kilograms.
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Calcium nitrate (with admixture of L percent NaNO3) ~.? 1,950
kilograms.
Rare earth phosphates (with content of 25 percent T/R203)
20 kilograms.
formulation of a project for construction of the first industrial
have been completed. The method may now be used as a basis of
At present the laboratory and model tests of this method
plant.
TZl
METHOD OF DERIVING NH~NO3 AND NH4H2P0
This method was suggested in 1926 by S. T. Vol'fkovich and
abroad by G. Lilienrot.
ammonia and carbonic acid (or ammonium carbonate) to ammonium
phate. The calcium sulfate is then converted by treatment with
The method consists of treating with an ammonium sulfate
solution the solution obtained by dissolving phosphate rock with
nitric acid. After separation of the precipitated calciwn sulfate,
the solution is neutralized with arnmonia to form monoammonium phos-
sulfate.
H3PO + Ca(NO3)2 + (NH4,)2S0h? + 2H20 .4, CaSO4 . 2H20 + 2NH4NO + H3P0j'
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The following are the basic equations for this process;;
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CaSO)4. 2H20 + 2NB3 + CO2 - (N;)
50)4. * c c03 4 + H2O.
The conditions of separation of the rare earth from apatite
were investigated in this paper. The latter may be separated as
phosphates by neutralizing the solution of rdtric and phosphoric
acids with lime, ammonia or other alkali. With the separation of
the rare earth the crystallization of the calcium sulfate improves
and then forms compact agglomerates
The H3P04 + NH)NO3 process solution is saturated with
annnonia at 80 degrees, while the pH is slowly increased with
rigid uniformity; this makes separation of the admixtures in
the form of a crystalline precipitate possible.
The main reactions which take pace while the solution is
being saturated with ammonia up to pH = H follow:
H3PO4 + NHZ.NO3 3 + H20 -p NH4H2P0 + NH~N03, (3)
R(NO3)3 + 2H3POj + 4NH3 + aq - RNHL 2(PO ) 2 - + 3N4H N0
3 (~)
Ca(N03)2 + H3P0j + 2NH!OH?
CaHP04 + 2NH)NO3 + 2H20. (5)
H2Si'6 + 8NH3 + L Ca(NO3)2 + 3H20 - , CaF2 + CaSiO + 8NH NO . (6
3 ~. 3 )
When the Ca0 content in the liquid phase is in excess relative
to 'the F and Si02, and all other conditions are unchanged the
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crystallization of CaF2, and especially of CasiO3, is improved.
This may be explained by the passage of all the 8i02 over into
the molecular?disperse state under such conditions. Similarly
favorable conditions are created if, as the reader has already
been reninded, the greater part of the F and Si'O2 (70 percent)
is separated from the solution in the form of Na2SiF6.
By evaporating the pulp (containing principally NHbNO3
and NH H2PO) a fertilizer containing 15.E percent P205 and
26.6 percent of N may be obtained. This fertilizer is in a
state of disbalance in the ratio between its P20~ and N contents
(P2O5; N = 0.6;x), and it suffers from considerable hygroscopicity.
Therefore, it is more expedient to produce a separation
of the mixture into NH)NO3 and NH) H2PO~.
Such a separation is based on a reduction in the mono-
ammonium phosphate solubility as the N}I)NO3 concentration increases.
At a concentration of 60 to 62 percent for the latter, and temper-
ature of 20 degrees, 92 to 94 percent of the monoammonium phos-
phate is precipitated out. One method of separating out this
mixture is by salting out the ammonium phosphate by means of the
returning ammonium nitrate.
The corresponding equilibrium system has been studied in
the NIUIF by A. I. Loginovaya and in the IONKh of the Academy of
Sciences by Professor A. G. Bergman.
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A mixture of ammonium phosphate and ammonium nitrate with
any desired content o: the latter may be obtained by a regular
system of filtration.
Another method of improving the physica1 properties of the
product and at the same time obtaining a triple fertilizer could
be the fusion of a mixture of ammonium tti.trate and ammonium pho s?
p hate with potassium chloride, which yields a nitropho$l ferti"
liter with any desired ratio between nitrogen, phosphorus, and
potassium. This process has been studied by A. M. Dubovitslciy
?
on the laboratory and pilot-plant scale in the NIUIF.
Numerous experiments have made possible the formulation of
the production steps for the process (Cf Figi.re 2, page 10$).
Flotation apatite is dissolved in ~6 percent nitric acid.
During the process of dissolution a 17-percent solution of
sodium nitrate is introduced to precipitate the hydrofluosilicic
acid in the form of Na2SiF6o The undissolved residue of the
apatite mixed with the Na2SiF6 is separated from the solution by
decantation, washed, and' either turned out as a finished product
insecticide - or returned for further processing.
To precipitate out the rare earths the solution is neutra-
lized by ammonia to a pH of 2 to 2.~. The precipitate of the
phosphates of the rare earths the ttcancentrate"
by decantation from the solution.
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The washed precipitate then goes for fuxthex processing to
obtain fluorides. of the rare earths.
A IOwp erc eflt solution of ammor i-trn sulfate is mixed with
the solution and CaO separated out as CaSOJ~.2H2O. The calcium
sulfate as separated by decantation from the solution and after
washing goes into reaction with ammonium carbonate.
After separation of the calcium sulfate the solution is
neutralized with ammonia and forms monoammonium phosphate. The
return ammonium nitrate is then introduced into the hot sass
pension. The precipitated monoammonium phosphate is separated
by decantation, faltered' and, without washing, mixed with
potassiwn chloride and the mixture is ground.
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Na2SiF6*
Apatite
t
e
i
Fiuorides of
the Rare
Earths 6 kj
3000 kg
(N1 L) 25~01~
Saying Out
Decantation
Filtration
KOL
27$ kg
Granulation
1263 kg
Nitrophoska
P2O 27.8%
N 13.9%
Figure 2. La?p=Out of production Routing for "Azophaska" Production
b Treatment of Apatite with Nitric Acid.
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11 Saturation
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The solution of ammonium nitrate with 6 percent salts con.
tent is evaporated and part of it put out as a finished product
wh5.le part of it is returned for use in salting out the annmo'rtl.um
phospbaten
The following are the coefficients of conswmption in k.1o-
grams per 1,000 kilograms of apatite:
8.?percent nitric acid
17~percernt solution of NaNO3
Ammonia gas
1~0-percent solution of ammonium
sulfat e
Potassium chloride
The yield in kilograms per 1,000 ka.lograans of
apatite is as follows;
Insecticide containing about L2 percent Na2SiF6
(The quality of this product is subject to
check on a pilot-plant scale.)
Rare earths concentrate (content 25 percent)
Azophoska, containing about 28 percent P20,
14 percent N and 14 percent of K20
Ammonium nitrate, containing about 32.6 per-
cent N
1,998
777
101
3,000
2"l8
2
126
1,290
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At the present time laboratory studies on the above.
described process with flotation apatite and Vyatka phosphorite
have been completed. In 1937.1938 experiments with model
apparatus involving the utilization of fluorine and the rare
earths will be conducted. In spite of the interest oi this
method, we do not recommend immediate transition to industrial'
scale production in view of the complexity of the process, which
requires the elaboration of all details on a model or pilot"
plant scale of equipment, as well as a number of technical and
economic conditions.
Thanes to the fact that in nitric acid dissolution of
low-grade phosphorites containing large quantities of sequioxides
the latter pass into solution to a relatively small extent, this
method is of interest not only for flotation apatite but for most
of ow' phosphorites as well. Even after roasting most of our low..
grade phosphorites yield slimy slurries on dissolution by nitric
acid ?slurries which are very hard to separate from the solution
and to wash free of. For this reason the extraction and separation
of the phases had to be done by way of decantation and counterflow
rinsing to relatively weak dilutions of HNO3 which would involve
extremely great difficulties and increased expense in the subs
sequent evaporation of the Ca(N03)2 solution, and might also cause
loss of nitrogen0 . Future research on nitric acid dissolution of
low-'grade phosphorites, a considerable number of which have already
Declassified in Part - Sanitized Copy Approved for Release 2012/05/15 : CIA-RDP82-00039R000200020006-2
 Declassified in Part - Sanitized Copy Approved for Release 2012/05/15 : CIA-RDP82-00039R000200020006-2
been subjected to preliminary tests by the NEUIF and other re..
search institutl.ons~ should be directed principally towards the
elin?nation of these difficulties,
A number of technical and economic computations made by
the NIUIF and GIPROAZOT showed that nitric acid dissolution of.
phosphorites was, on the average, not less than 1Op1 percent
cheaper' and for some types up to 3O4.O percent cheaper, than
sulfuric acid methods of malting concentrated fertilizers?
In the future' besides the earliest"-possible initiation
of experiments with model or pilot-plant equipment for the
preparation of dicalcium phosphate and calcium nitrate, it is
also desirable to make a detailed study of A. P. Belopolskiy's
suggestion for the preparation of CaH~P2O8, a study of new
variants for preparation of non-hygroscopic itrosuperphospbate,
and a number of technological details of the above-described
production processes.
Declassified in Part - Sanitized Copy Approved for Release 2012/05/15 : CIA-RDP82-00039R000200020006-2