FIELD OF THE INVENTION
[0001] The present invention relates to a process for preparing a stable blend for slow release
of insoluble phosphate to soluble phosphate.
BACKGROUND OF THE PRIOR ART
[0002] Phosphorus (P) is an important nutrient required for plant growth and development,
making up 0.2% of plants on dry weight basis. Amongst a number of advantages, addition of
phosphorus creates deeper and more abundant plant roots. Conversely, a phosphorus
deficiency alters root architecture, which ultimately affects seed development and normal
crop maturity. Thus, the availability of adequate phosphorus is fundamental to stimulate early
plant growth and hasten maturity. However, phosphorus is among the least bio-available
nutrients for plants. Though phosphorus is abundantly present in soil, in both organic and
inorganic forms, but its availability to plants is restricted as it present mostly in insoluble
forms. Because most soil regimes are deficient in phosphorus, phosphatic fertilizer are
required to replenish the phosphorus demanded by crop plants.
[0003] Rock phosphate is the raw material used in the manufacture of most commercial
phosphate fertilizer. The processing of phosphate rock for use in fertilizer manufacturing
involves separation of phosphate rock from impurities and non-phosphate materials.
[0004] When processing rock phosphate, the chemical reaction produces an insoluble
precipitant that is known as phosphate sludge. Phosphate sludge is an undesirable waste byproduct
obtained as a result of acid treatment of rock phosphate. Phosphate sludge is
periodically discarded or continually removed via filter press or decanting and suck truck.
Phosphate sludge has no other real useful purpose though is contains some amount of
phosphorous in the form of phosphorous pentoxide.
[0005] There are many organic and inorganic phosphorus containing fertilizers available in
the market to satisfy phosphorous requirement of the soil. However, the problem with
inorganic phosphorous fertilizer is that large portions of soluble inorganic phosphate present
within the inorganic phosphorous fertilizer when applied to soil is readily consumed by
Ten DELHI 08-09-20!~ 17 ?~ .:·~··· --
2
microorganisms, present within the soil, becomes unavailable to plants thereby restricting
their normal growth and maturity.
[0006] Soil micro-organisms have the ability to solubilize inorganic and/or organic
Phosphorous from soil. Therefore, commercial hie-fertilizers has a mixture of microorganisms
along with fertilizers components such nitrogen, phosphorous, urea, etc. However, the
problem with such bio-fertilizers is their shorter shelf life because microorganisms of the hiefertilizers
deteriorate due to prolong storage. Additionally, these bio-fertilisers are also
sensitive to severe external condition during transportation such as high temperature, which
if present results in the micro-organisms becoming inactive.
[0007) The above noted prior attempts have tried addressing to the issues of phosphorous
nutrients requirement of plants. However, due to the reasons explained above such attempts
have failed to provide effective solutions to achieve plants phosphorous needs. Therefore, it
is highly desirable to develop phosphate solubilising fertilisers that addresses some of these
shortcomings yet resulting in good plant growth and yield.
OBJECTIVES OF THE INVENTION
[0008] An objective of the present invention is to develop a stable blend that slowly releases
soluble phosphate when contacted with the soil and has a higher shelf life.
[0009] Another objective ofthe present invention is to develop stable blend in a cost effective
manner.
SUMMARY OF THE INVENTION
[0010] Accordingly disclosed herein is an aspect of the present invention in which a process
for preparing a stable blend for slow release of insoluble phosphate to soluble phosphate
comprises the steps of mixing a source of insoluble phospha. te and a so. urce of sulphur to form
a mixture, and homogenizing the mixture in an agitator at an rpm of 400-1600 to a
temperature in the range of 80-85 d~gree Celsius to obtain a stable blend, wherein the stable
blend is capable of slowly releasing soluble phosphate when the stable blend contacts soil.
T g::;, n D E L H I 0 8 - 8 9 - 2 0 1 S: 1 •7
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(0011] According to some embodiments, the source of insoluble phosphate mixed with the
source of sulphur includes rock phosphate ore, sludge extracted from rock phosphate,
insoluble phosphate of soil, low grade minerals containing phosphate or the like materials
and compositions.
[0012] According to some embodiments, the source of sulphur mixed with the source of
insoluble phosphate includes elemental sulphur and all the sulphur compounds capable of
releasing sulphate through natural biochemical process.
[0013] According to some embodiments, the sulphur is in micronized form.
[0014] According to some embodiments, the process of preparing stable blend for slow
release of insoluble phosphate to soluble phosphate further comprising the steps of
processing the stable blend to obtain a micronized powder ofthe stable blend, adding suitable
additives to the micronized powder and treating the micronized powder to obtain granules.
[0015] According to some embodiments, the process of preparing stable blend for slow
release of insoluble phosphate to soluble phosphate further comprises the steps of adding
suitable additives such as MgS04, MnS04, Bentonite clay, Borax, CaN03, MOP, Sulphur, Neem
Cake, Urea, Organic Manure, Sea Weed Extract, Humic Acid and Zinc Sulphate to the mixture
of insoluble phosphate and sulphur.
[0016] According to some embodiments, the agitator is a high shear mixer having a pan which
is rotatable at a speed of 20-40 rpm for 5-15 minutes to obtain the stable blend.
BRIEF DESCRIPTION OF DRAWINGS
[0017] Figure 1 shows a flow chart illustrating process steps for preparing stable blend for
slow release of insoluble phosphate to soluble phosphate, according to an embodiment of
the present invention;
[0018] Figure 2 is a graph showing slow release pattern of phosphorous from stable blend of
Fig. 1 in soil as a function of amount of sulphur;
-n1-1=-1 -~-T- 4
[0019] Figure 3 is a graph showing slow release pattern of insoluble phosphate of Fig. 1 from
phosphorous sludge in solution as a function of pH and amount of sulphur; and
(0020] Figure 4 is a graph showing slow release pattern of insoluble phosphate of Fig. 1 from
phosphorous sludge in soil as a function ·of pH and amount of sulphur.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
[0021] FIG. 1 is a flow chart showing embodiments of the process of manufacturing of the
stable blend In accordance with the present invention. The first step ofthe process comprises
adding of mixing of raw materials, i.e. a source of sulphate and a source of insoluble
phosphate, to obtain a mixture. In a preferred embodiment of the invention, the source of
sulphate used is manganese sulphate, or magnesium sulphate or sulphur. However, in other
embodiments elemental sulphur and all the sulphur compounds capable of releasing sulphate
through natural biochemical process could also be used and considered to be within the scope
of the present invention.
[0022] In the embodiment in which the preferable source of sulphur is manganese sulphate,
or magnesium sulphate or sulphur, the preferred source of insoluble phosphate is phosphate
sludge. Utilizing phosphate sludge in preparing stable blend capable of providing
micronutrient to the plants is a cost effective way of recycling the phosphate sludge.
However, in some other embodiments of the present invention, the source of phosphorous
may be rock phosphate ore, sludge extracted from rock phosphate, insoluble phosphate of
soil, low grade minerals containing phosphate or the like materials and compositions. All
these embodiments or variations thereof are considered to be within the scope of the present
invention.
[0023] Referring to FOG. 2, in the second step, the mixture of source of sulphate and source
of phosphate· are subjected to an agitator, preferably a high shear mixer. To the mixture of.
source of sulphate and source of phosphate, other additives may also be added with an
objective of soil enrichment and to suffice plant nutrient deficiencies. Preferably, MgS04,
MnS04, Bentonite clay, Borax, CaN03, MOP, Sulphur, Neem Cake, Urea and Organic Manure
are added to the mixture of source of sulphate and the source of phosphate and then mixed
IPO DELHI 6~-09-28!5 17 ?~ 5
at a high speed within the high shear mixer. The raw materials can be pre-powdered prior to
combining in the high shear mixer in other embodiments of the present invention.
[0024] The additives are selected according to the soil composition and act as micro nutrients
for soil enrichment. The additives greatly help in retaining carbon content of the soil and
contribute to the overall growth of the plants. When the mixture of source of sulphate and
source of phosphate alone are processed in high shear mixer wi.thout adding any additives,
the resultant granules are capable of only releasing phosphate and the plants may deprive of
other micro nutrients.
[0025] In the third step, the mixture is subjected to simultaneous homogenization and
micronization in the high shear mixer for around 5-15 minutes at 400-1600 rpm to obtain a
solid blend.
[0026] High shear mixing is caused by a velocity gradient within the material, where, when
two or more raw materials having different particle characteristics and size are subjected to
high shear mixing the particles break into primary particle size. Also, inter and intra particle
collision between different particles as well as the wall of the mixing device produces energy
which is transferred to the particles as kinetic energy. The kinetic energy helps in breaking
down the compounds and thereby homogenizes the mixture to give a uniform composition.
Further, the high shear mixing provides intense friction between the particles increasing
temperature on the surface ofthe particles. This increase in temperature results in: removal
of moisture and homogenization of the mixture.
[0027] The mixing device comprises: inclined rotating mixing pan, stationary bottom/wall
·scraper, and a fast-turning rotor positioned eccentrically at the centre of the pan. The pan of
the high shear mixer rotates in a clockwise direction at 20-40 rpm and rotor of the high shear
mixer rotates in an anti-clockwise direction at 400-1600 rpm. The opposite rotation of the
pan and the rotor facilitates fine unification (blending) of the mixture and reduces particle
size up to micron level. The mixing of the raw material is also enhanced by side and bottom
scrapper of the high shear IJiixer to ensure efficient mixing and homogenization of the solid
blend.
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[0028] The duration of mixing varies to the desired micronization and homogenization of all
ingredients. Typically 5 to 15 minutes is sufficient to achieve uniform dispersion and
micronization in to fine powder. The mixing operation in the high shear mixer raises the
temperature of the solid blend as high as 80 to 85 Deg C. The particle to particle temperature
of the solid blend could be higher.
[0029] Similarly, in the fourth step, liquid additives are mixed together in a separate container
in a desired quantity of water to obtain a liquid blend. The quantity of wat~r is dependent on
batch size. Approx. 4 to 10% of the total batch size may be required. Preferably, Sea weed
Extract, Urea, Humic acid and Zinc Sulphate are ·mixed together in the desired quantity of
water to obtain the liquid blend.
[0030] In the fifth step, the liquid blend thus obtained is poured over solid blend rotating in
the high shear mixer with 250-1600 rpm rotor speed to obtain a solid mass of stable blend. In
the sixth step, the granules are prepared from the solid mass of the stable blend in the pan
granulator and directly subjected to drying to get the granules of desired size and shape as
per product guidelines. The solid mass obtained as the mixture of solid blend and liquid blend
may also results in the form of pellets. The stable blend are typically dried to a moisture
content below 2% prior to packaging.
[0031] The granules retain its size and shape during handling and application to a desired
area. The granules thus obtained are inert in nature and due to absence of any biotic
component, they have longer shelf life.
[0032] The process of the present invention is a batch process, however the process can be
advanced as a continuous process. The stable blend from the mixing device can be received
in a fixed tunnel drier adapted to convey the granules on a perforated wire mesh to reduce
the moisture content between 1-2%. The dried, hardened granules can be passed through a
vibrating sieving device to separate the granules as per size. Additionally, the granules can be
further dried in a drum drier to reduce the moisture content to 0.2%.
[0033] The granules of the stable blend for slow release of insoluble phosphate to soluble
phosphate can be used by farmers interested to nourish plants with phosphorus which is a
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required nutrient for normal plant growth and maturity. Farmers can procure these granules
from the market and use it simply by way of dispersing the granules in the fields bearing crop
or it can also be dispersed in crop-less fields for the purpose of soil enrichment. Another way
of utilizing stable blend is to disperse them in water to form a solution and spray over soil.
[0034) Following the application, the granules ofthe stable blend rapidly disperses on contact
with moisture from the treated area itself, from irrigation or from natural precipitation or
absorption of moisture from the soil. The dispersion ofthe granules allows rapid oxidation of
the sulphur particles mto plant available sulphate. In the J.He::,errLe uf soil, the sulph~te thus
obtained facilitates release of phosphate from source of phosphorous and is readily taken up
by the plants to fulfil its phosphorus requirement.
[0035] For the purpose of mixing the source of sulphate and the source of phosphate, high
shear mixer is used for better homogenization. Alternatively, various other equipment meant
for simultaneous mixing and blending operation can be used.
Elution Study to ascertain slow release characteristic of insoluble phosphate to soluble
phosphate
[0036] Elution study was performed to determine release pattern of phosphorous and
sulphur from the granules obtained from the stable blend. Accordingly, granules were
dispersed in soil. The sample of soil with dispersed granules was taken out and washed with
desired quantity of water. The concentration of phosphorous pentoxide-a·nd sulphur wast hen
determined in the washed sample. The study (Table 1) revealed that granules continued
releasing phosphorous pentoxide in the presence of micronized sulphur even after 10 washes.
The study confirms the slow release characteristic of granules obtained from the stable blend.
TDn DELHI 88-89-28!~ !7?: 26 .. r-· 8
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Table 1
Elution study of soil sample treated with granules
pH EC (mS) P20s (ppm) S (ppm)
wash-1 7.80 22.28 26.49 1525
wash-2 7.80 16.69 21.29 1492
wash-3 7.80 12.13 19.31 1475
'
wash-4 7.80 7.82 14.81 1450
wash-5 7.90 5.05 14.38 1390
wash-6 8.00 4.26 17.16 1003
wash-7 8.10 3.85 17.16 823
wash-8 8.10 3.45 14.38 775
wash-9 8.04 3.19 8.00 635
wash-10 8.08 2.94 6.60 481
wash-11 8.41 2.90 Nil 342
wash-12 8.02 2.79 Nil 325
Remarks Elution has been stopped after 12 washing
[0037) Fig. 2, illustrates the average release of phosphorous pentoxide from phosphate
source in the presence of micronized sulphur. It has been observed that as the concentration
of sulphur in soil increases from 0 to 0.5 gm, the amount of phosphorous pentoxide also
increases. The increased concentration of phosphorous pentoxide confirms the effective
conversion of phosphate in the presence of micronized sulphur. The maximum concentration
of phosphorous pentoxide is obtained in solution in 50 days which confirms slow release of
phosphate in the form of phosphorous pentoxide.
EXAMPLE 1
[0038] The effect of addition of micronized sulphur to the phosphate sludge was studied
wherein phosphate sludge is dissolved in the water to obtain a solution. Aim of this study was
to ascertain the fact that the phosphate release from the source of phosphorous (Phosphate
Sludge in this example) increases in the presence of micronized sulphur over the period of
.time. Fig. 3 illustrates the .results wherein phosphate sludge is dissolved in water and
DELHI 8 :8 - 8 g - 2 8 1 ~· 9
micronized sulphur is added to the solution over the period of time. As the concentration of
sulphur increased from 0.00 gm to 0.5 gm, the pH of the solution decreased. This confirms
the conversion of micronized sulphur to sulphate. Therefore, increasing the concentration of
sulphur results into more acidic pH which further facilitates release of phosphate from
phosphorous sludge. The addition of micronized sulphur over the period of 50 days have
shown decrease in the pH of the solution confirming slow release of phosphate from the
phosphorous sludge and after that there observed a slight increase in the pH. This shows that
the saturation point has achieved and most of the sulphur gets converted to sulphate that
lead to conversion of phosphate from phosphorous sludge.
Table 2
Phosphorous sludge treated with micronized sulphur in
solution
Time 11 Days 35 Days 50 Days
Amount of Sulphur
Blank 7.86 7.86 7.93
0.05 gm S 7.76 7.81 7.94
0.1 gm S 7.73 7.79 7.99
0.2 gm S 7.8 7.68 7.83
0.3 gm S 7.58 7.61 7.82
0.4 gm S 7.65 7.6 7.83
0.5 gm S 7.67 7.56 7.78
EXAMPLE 2
[0039] The effect of addition of micronized sulphur to the phosphate sludge was studied
wherein phosphate sludge is dispersed in the soil and the sample was then studied. Fig. 4
illustrates the results wherein phosphate sludge is dispersed in soil and micronized sulphur is
added to the soil over the period of time. As the concentration of sulphur increased from
0.00 gm to 0.5 gm, the pH of the soil decreased. This confirms the conversion of micronized
sulphur to sulphate. Therefore, increasing the concentration of sulphur results into more
acidic pH which further facilitates release of phosphate from phosphorous sludge dispersed
in the soil. The addition of micronized sulphur over the period of 50 days have shown decrease
in the pH of the soil confirming slow release of phosphate from the phosphorous sludge and
after that there observed a slight increase in the pH. This shows that the saturation point has
achieved and most of the sulphur gets converted to sulphate that lead to conversion of
phosphate from phosphorous sludge.
TPn DELHI og-89-2815 17 ?~ 10
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Table 3
Phosphorous sludge treated with micronized sulphur in soil
Time 11 Days 35 Days 50 Days
Amount of Sulphur
0.00 gm S 8.09 8.1 8.22
0.05 gm S 7.98 8.13 8.2
0.1 gm S 7.97 7.86 8.1
0.2 gm S 7.78 7.72 8
0.3 gm S 7.67 7.65 7.9
0.4 gm S 7.6 7.55 7.8
0.5 gm S 7.59 7.49 7.8
[0040] It will be apparent to those skilled in the art that various modifications and variations
can be made to the present invention without departing from the spirit and scope of the
invention. Thus it is intended that the present invention cover the modifications and
variations of this invention provided they come within the scope of the appended claims and ·
their equivalents.

We Claim:
1. A process for preparing a stable blend for slow release of insoluble phosphate to soluble
phosphate comprising the steps of:
mixing a source of insoluble phosphate and a source of sulphur to. form a mixture; and
homogenizing the mixture in an agitator at an rpm of 400-1600 to a temperature in
the range of 80-85 degree Celsius to obtain a stable blend,
wherein the stable blend is capable of slowly releasing soluble phosphate when the
stable blend contacts soil.
2. The process according to claim 1, wherein the source of insoluble phosphate mixed with
the source of sulphur includes rock phosphate ore, sludge extracted from rock phosphate,
insoluble phosphate of soil, low grade minerals containing phosphate or the like materials
and compositions.
3. The process according to claim 1, wherein the source of sulphur mixed with the source of
insoluble phosphate includes elemental sulphur and all the sulphur compounds capable of
releasing sulphate through natural biochemical process.
4. The process according to claim 3, wherein the sulphur is in micronized form.
5. The process according to claim 3, wherein the sulphur is in molten form.
6. The process according to claim 1, further comprising:
processing the stable blend to obtain a micronized powder of the stable blend;
adding suitable additives to the micronized powder; and
treating the micronized powder to obtain granules.
7. The process according to claim 1, further comprising adding suitable additives such as
MgS04, MnS04, Bentonite clay, Borax, CaN03, MOP, Sulphur, Neem Cake, Urea, Organic
Manure, Sea Weed Extract, Humic Acid and Zinc Sulphate to the mixture of ihsoluble
phosphate and sulphur.

8. The process according to claim 1, wherein the agitator is a high shear mixer having a pan
which is rotatable at a speed of 20-40 rpm for 5-15 minutes to obtain the stable blend.