Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
i~CI 6159L
GRANULATION OF POT~SH SALTS
This invention relates to the granulation of potash
salts. In a particular aspect this invention relates to
the granulation of potash salts by incorporation of a
binder prior to the granulation step.
Potash salts do not easily form large crystals or
particles, yet they are needed for use in mixed fertilizers
to prevent segregation. Also particles in the desired size
range must be strong enough to resist degradation during
handling and mixing steps. However, due to lack of plas-
ticity, potash salts resist granulation by conventional
rotary drum or pan granulators. Granules formed in these
devices lack degradation resistance when dried and the
yield of granules in the desired 6 x 14 mesh Tyler size
range is low, e.g. frequently in the 10% range. Conse
quently, recycle rates are very high resulting in exor-
bitant production costs.
Thus there is a need for a process for granulating
potash salts in high yield in the desired granulation
range which will have good structural stability during
storage, handling and use.
It is an object of this invention to provide a
process for the granulation of potash salts.
It is another object of this invention to provide
a process for the granulation of potash salts by incor-
porating therein a binder.
Yet another object is to provide a composition of
potash salt and binder in granulated form.
Other objects will be apparent to those skilled in
the art from the disclosure herein.
-2-
~ ~61S4
It is the discovery of this invention to provide a
process for the granulation of potash salts to produce
granules in high yield in the desired size range by the
step of mixing the potash salt with an inorganic phosphate
salt binder and water, and granulating the mixture and
drying it.
In the process of the present invention the potash
salt is mixed with the phosphate binder in a ratio of
about 30-300 lb (1.5 to 15~) preferably about 100-300 lb
(5 to 15% of binder per ton of crystals; the amount re-
quired is variable, depending on the binder selected and
the material to be granulated. Water is added, either
before or after mixing the potash salt with the binder,
in an amount of 150-400 lb per ton of mixture (7.5 to 20%),
the exact amount depending on the moisture content, the
type and particle size of the potash and binder being used
in the operation. The mixing is carried out in a conven-
tional drum or pan granulator and additional water can be
added as required to maximize the production of the pre-
ferred size granules. The preferred water content is fromabout 10 to about 15%. The mixture is then fed to a con-
ventional dryer.
The potash salts which can be granulated by the
process of this invention include but are not limited to
potassium chloride, potassium carbonate, potassium sulfate,
potassium nitrate, langbeinite, and mixtures thereof.
Suitakle binders include monoammonium phosphate,
diammonium phosphate, mono- or disodium phosphate, mono-
or dipotassium phosphate, or a mixture thereof. Also di-
basic magnesium phosphate is a suitable binder. All of
--3--
1~`615~
these compounds are known in the art and most of them arecommercially available. The usual commercial grades are
suitable for the practice of this invention.
A preferred binder is monoammonium phosphate which
can be suitably formed at the time of use. A particularly
preferred binder is a mixture of mono- and diammonium
phosphates obtained by reacting ammonia with phosphoric
acid in a mole ratio of about 1.1-1.5 to 1. Mono- or di-
ammonium phosphate, or mixture thereof, can be formed in
situ by premixing the potash salt with a suitable amount
of phosphoric acid, then ammoniating the mixture in an
ammoniator-granulator known in the art, e.y. a TVA rotary-
drum granulator as described by F . T . Nielsson, U.S.
Patents 2,729,554 and 2,741,545. A preferred source of
phosphoric acid is the grade known as wet-process acid
because it contains a minor amount of iron, aluminum and
other metallic impurities which improve the strength of
the potash granules. When the monoammonium phosphate is
formed in situ, water is preferably added to the potash
salt prior to introduction of the phosphoric acid. The
ammoniation step can be carried out preferably with
anhydrous ammonia, but aqua am~onia can also be used if
desired. ~n this case the amount of water added as aqua
ammonia should be taken into consideration when adding
additional water for the granulation step.
When magnesium phosphate is to be used as the
binder, it can also be conveniently formed in situ during
the granulation step. The magnesium is added to the
potash salt as the oxide, hydroxide or carbonate and phos-
phoric acid - preferably wet process phosphoric acid - is
111t~6~54
sparged into the mixture. me magnesium compound and phos-
phoric acid are used at a mole ratio, generally, of
between 0.5-1.5:1, preferably 1:1.
When langbeinite is to be granulated, it is prefer-
ably in a form wherein it contains at least 20% of minus
200 mesh Tyler size granules and a minimum amount of plus
30 mesh granules, preferably less than 5%.
Another embodiment of this invention is that gran-
ulation of other potash salts than langbèinite can be
enhanced by adding a small amount of pulverized langbeinite
or other suitable source of magnesium to the potash. Such
suitable sources of magnesium include, in addition to the
magnesium phosphate cited above, the oxide, the chloride,
the sulfate, the carbonate, the nitrate,~etc. Langbeinite
is used at a rate of 30-70 lb per ton of potash salt.
Other magnesium salts are used at a rate equivalent to 20-
40 lb of magnesium sulfate per ton of potash sal~.
The granulation step is carried out in the conven-
tional manner at the conventional temperatures, e.g. from
160 to 200~F. Similarly the drying step i9 carried out in
the conventional manner.
In accordance with the foregoing, it is an embodi-
ment of this invention to provide a composition adapted
for granulation comprising a potash salt and an inorganic
phosphate binder. More particularly, it is an embodiment
of this invention to provide a composition suitable for
granulation comprising a potash salt, an inorganic phos-
phate binder therefor in an a unt of about 30-300 lbs
per ton of potash salt and water in an amount of about
150-400 lb per ton of potash salt wherein the potash salt
~1~6~S4
is potassium chloride, potassium sulfate, potassium car-
bonate or langbeinite or mixtures thereof. Preferred
mixtures include those wherein langbeinite is a minor
component. The inorganic phosphate is supplied by mono-
or diammonium phosphate, mono- or disodium phosphate,
mono- or dipotassium phosphate or mono- or dibasic magne-
sium phosphate or mixtures thereof. It is also contem-
plated that another embodiment of this invention is to
provide granulated compositions of the foregoing materials
having a composition, d y basis, of from about 85-98.5%
potash salt and 15-1.5% binder, respectively. In addi-
tion, the granulated composition may contain residual
water of varying amounts, although usually the composition
will be substantially water-free.
The invention will be better understood by refer-
ring to the following examples. These examples are
intended merely to illustrate the invention and it is not
intended that the invention be limited thereby.
Example l
; Langbeinite fines were obtained from a dust collec-
tor and were used for granulation. It analyzed 5% plus
35 mesh and 26% minus 200 mesh. The granulator was run at
15 tons/hour, using 300 lbs of a mixture of mono- and di-
ammonium phosphate per ton of langbeinite. The ammonium
phosphate was formed in situ by introducing wet process
phosphoric acid in the appropriate proportions and ammon-
iating the mixture at a mole ratio of about 1.5 moles
anhydrous ammonia per mole of phosphoric acid.
-6-
61S4
Granulation was carried out in a TVA rotary-drum
ammoniator (F. T. Nielsson U.S. Patents 2,729,554 and
2,741,545). Water was added as necessary to provide good
granulation characteristics. The granulator drum was
operated at a temperature of 178-182F. The moisture
content of the granulated product as it exited from the
granulator was 14~. It was then sent to a drier having
an inlet temperature of 980 to 1020F. The temperature
of the exit gases was 200-225F and that of the dried
product was 110-120F.
Satisfactory granulation was obtained as shown by
the screen analysis in Table 1.
--7--
ll~`G~5~a
o ~r
o
~D
~D
o
o
o
o
In .
o
~ O a~ :
a ~ O~ -
~ .
,~ ~ ~ ~ o
E~ o
.
o ~ ~
- ~ ,` ,f,
a~
CO ~D ~
". CO
o ô
aJ
r~
U~ ~ ~
U~ ~o ~ o
o ~ o
,, ~ ,,
o ~ o
'd ~:: o ~: o
.
.
lS~
Degradation tests were performed and it was found
that 8.4% degradation occurred. This compares favorably
with the degradation rate of granular potassium sulfate
and diammonlum phosphate. The physical quality of the
product was acceptable.
Example 2
The experiment of Example 1 was repeated in all
essential details except that the mono- and diammonium
phosphate content was reduced to 100 lb/ton. Satisfactory
granulation was obtained as shown by the screen analysis
in Table 1. In degradation tests, there was a 7.4%
degradation of the granules. Physical quality was accept-
able.
Example 3
Potassium chloride, 1 ton, is mixed with mono-
ammonium phosphate, 100 lb, and water, 200 lb (10%), in a
pan granulator and granulated at 180~F as is known in the
art. The material exiting the granulator i9 dried, cooled
and delivered to storage. The physical quality is accept-
able.
;
Example 4
The experiment of Example 3 is repeated in all
essential details except that potassium carbonate is sub-
stituted for potassium chloride, diammonium phosphate is
substituted for monoammonium phosphate and 20~ water is
added. The physical quality of the granules is satisfactory.
.
_g_
1~6~L5~
Example 5
The experiment of Example 3 is repeated in all
essential details except that potassium sulfate is sub-
stituted for potassium chloride, monosodium phosphate, 30
lb/ton, is substituted for monoammonium phosphate and 7.5%
water is used. The physical quality of the granules is
acceptable.
Example 6
The experiment of Example 3 is repeated in all
essential details except that potassium nitrate is sub-
stituted for potassium chloride and monopotassium phos-
phate, 100 lb/ton, is substituted for monoammonium phos-
phate. The physical quality of the granules is acceptable.
Example 7
The experiment of Example 1 is repeated in all
- essential details except that disodium hydrogen phosphate
is substituted for ammonium phosphate. The physical
quality of the granules is acceptable.
Example 8
The experiment of Example 7 is repeated in all
essential details except that dipotassium hydrogen phos-
phate is substituted for disodium hydrogen phosphate.
The physical quality of the granules is acceptable.
.:
,~ -10-
LS~
Example 9
The experiment of Example 3 is repeated in all
essential details except that langbeinite is substituted
for ammonium phosphate. The physical quality of the
granules is acceptable.
Example 10
The experiment of Example 1 is repeated in all
essential details except that potassium chloride is sub-
stituted for langbeinite and magnesium oxide is substi-
tuted for ammonia in an amount to provide an equi-molar
ratio with the phosphoric acid. The physical quality of
the resulting granules is acceptable.
