FIELD OF THE INVENTION
The present invention relates to manufacturing process for enriched SSP in granular form. Single super phosphate is typically an ideal phosphorus supplying fertilizer.
BACKGROUND OF THE INVENTION:
Super phosphates are generally manufactured to use as fertilizers. Super phosphates can be classified into three categories, first one being Single Super Phosphate simply called as SSP of available P205 content in the range of 16 to 18% based on the specifications prevailing in different countries and regions. For example in India, the specification for available P205 content in single super phosphate is 16% minimum with moisture content 12% maximum.
This grade of SSP is being manufactured without any difficulty with medium grade rocks containing P205 at 30-31 %.
It is appropriate to mention here the categorization of rock phosphates based on P205 content. Rocks containing more than 33% P205 are considered as high grade rocks. Whereas some sources of rocks contain this ievel of P205 as mined, some other sources are brought to this range P205 content by beneficiation process. This grade of rock is mainly used for manufacture of commercial Phosphoric acid.
Rocks containing P205 in the range of 30-33% are coming under medium grade category which are used for manufacture of commercial phosphoric acid and Super Phosphates.
Rock phosphates that are in the range of 26 to 30%P2O5 content are called as low grade rocks which are not suitable for manufacture of commercial phosphoric acid unless they are blended with high grade rocks. Even for Super phosphates manufacture also they cannot be used as single rock but can be used by blending with suitable grade of higher P205 content.
The second category of superphosphate is the Enriched grade super phosphate which contains available P205 i.e. CS P205 more than 20%. This grade of super phosphates are so far being manufactured with high grade rocks of appropriately

higher P205% or by using commercial grade phosphoric acid also along with sulphuric acid for acidulation of rock.
The third category of superphosphates is Triple super phosphate, some places it is called as double super phosphate or Concentrated super phosphate. It contains available P205 in the range of 44-48%. This is manufactured by acidulating the phosphate rocks with commercial grade Phosphoric acid containing about 46-50% P205. Processes are available to use weak phosphoric acid of around 30% P205 content but in this case the formed superphosphate slurry is dried at high temperature to evaporate the higher water content. Both these acids are considered to be costly because they are produced in wet process phosphoric acid plants which are meant for commercial phosphoric acid production and supplying to NP/NPK fertilizer plants.
Single Super Phosphates are generally manufactured, by acidulation of phosphate rock containing generally not less than 30% P205 with sulphuric acid. The Triple super phosphates or concentrated super phosphates as mentioned earlier are manufactured by acidulation of rock phosphate with commercial grade phosphoric acid and extensively used as a fertilizer. However, for several agronomical reasons, single super phosphate is used since it also provides the much-needed sulphur to the crops which Is one of the secondary nutrient that is required for the plants.
The advantages of SSP are
1. The process is simple, requiring little technical skill and small capital investment.
2. The economies of the scale are minor; thus small plants can be economical.
3. Since the process is not capital intensive, there is advantage of high percentage utilization of capacity.
4. The fertilizer effectiveness of SSP is unquestioned, infact, it is a standard for comparison of other phosphatic fertilizers.
Despite the impressive advantages, the disadvantages such as low analysis, i.e at around 16-18% available P205 and consequent high distribution costs have caused declining interest in its production and usage because the delivered cost at the farm

level is usually higher per unit of P205 than that of TSP and Ammonium Phosphates.
While using Single Super Phosphate as a fertilizer, farmers are forced to use higher quantity of SSP per acre when compared to other NP and NPK fertilizers such as DAP, MAP, TSP, 14-35-14, 28-28-0, 20-20-0 etc because of lesser available P205 content in SSP. This is leading to additional expenditure with respect to transportation and application part. To the manufacturers also it gives additional expenditure with respect to handling and transportation to the dealers shops.
In this aspect it is thought that higher P205 containing SSP would be more useful for them. For production of SSP containing higher P205 content, the processes available so far are one of the below
a. usage of high grade rocks (more than 33% P205 content) for acidulation with
sulphuric acid.
b. usage of some quantity of commercial grade Phosphoric acid along with
sulphuric acid for acidulating the rocks of medium grade
Both the above processes are costlier because of higher cost of high grade rocks and of commercial grade Phosphoric acid. Also the availability of high grade phosphate rock is diminishing day by day and most of the rocks of more than 33%P205 content are being used to produce commercial grade phosphoric acid, thereby the availability of phosphate rock of high grade is becoming scarce for producing enriched super phosphate.
Hence for producing Enriched SSP it is necessary to invent an innovative method that can avoid usage of high grade rocks or commercial grade phosphoric acid there by Enriched grade SSP would be available to the end user at a reasonable price.

f
PRIOR ARTS
Single Super Phosphate, also called normal or ordinary super phosphate has been the principal phosphatic fertilizer for more than ^century and being produced since 1955. Many prior arts are available for production of SSP through which the manufacturing process has been polished to the present level of Reactor and denning process. The basic chemical formula involved in the reaction is as below.
Ca3(P04)2 +2 H2S04 +H20 --»Ca(H2P04)2.H20+2 CaS04
The book "Superphosphate: Its history, Chemistry and manufacture", by US Dept of agriculture and Tennese Valley Authority delves into the history of superphosphates, current industry practices and how they came about, and the chemistry of manufacture. Much literature is available in this hook on manufacture of normal superphosphate and concentrated super phosphates. Normal superphosphate is the reaction product of rock phosphate acidulated with Sulphuric acid, whereas the concentrated superphosphate is the reaction product of rock phosphate acidulated with commercial grade Phosphoric acid.
Many books are available on superphosphates and concentrated super phosphates manufacturing process and equipments that have been developed. But all of them discussed on either single supper phosphate or Triple super phosphate which are not the subjects of present invention.
US patent 1475959 by Meyers Herbert H, filed on 21st Dec 1922 and published on 4th Dec 1923, with the title "Double super phosphate process" discusses on production of super phosphate of 40-50% P205 content by reacting phosphate rock with weak phosphoric acid and drying the slurry formed. The present invention of producing Enriched superphosphate is different from the above because the present invention does not aim to produce double super phosphate of 40-50% P205 content.
Patent US4452770 by Jay W Palmer and John C Gaynor filed on 14th Dec 1981 and published on 5th June 1984 with the title "Acidulation of phosphate rock with sulfuric acid and phosphoric acid" relates to the production of phosphoric acid and more particularly refers to an improved wet process for converting phosphate rock into a

concentrated phosphoric acid with concomitant production of an improved calcium sulfate. It is different from the present invention of production Enriched SSP.
Patent US 496687by Philip C Hoffmann filed on 15th March 1892 and published on 2™* May 1893 with the title "Process of treating Phosphates" focusses on production of phosphoric acid using phosphate rock from inland Florida deposits as first time. It is different from the present invention.
Patent US 1078887by MaxmillanMattheusHaff filed on 23rd June 1913 and published on 18th Nov 1913 with the title "Method of manufacturing double super phosphate" relates acidulatiqn of rock with pyro-phosphoric acid for production of double super phosphate. It is different from the present invention of Process for Enriched Single Super Phosphate.
Patent US 1351672 by Curtis C Maigs filed on 28th Oct 1919 and published on 31st Aug 1920 with the title "PROCESS OF PRODUCING DOUBLE SUPERPHOSPHATE" is related to usage of sodium sulphate to react with the Dicalcium phosphate formed by acidulation of phosphate rock with half the stoichiometric quantity of sulphuric acid. It is different from the present invention.
Patent US 1780620 by Barkley King William filed on 6* Jan 1930 and published on 4th Nov 1930 with the title "Double-superphosphate manufacture" is relating to a process where finely ground commercial phosphaterock is added to crude phosphoric acid solution, containing about 16% to 20% P2 05. As this process uses phosphoric acid for acidulation of rock it is different from the present invention.
Patent US 1851210 by Palazzo Francesco Carlo et al filed on 19th July1929 and published on 29th March 1932 with the title "Process for producing mixtures of mono-calcium and di-calclum phosphates7* Is relating to Process for the production of monocalcium phosphate, consisting in first preparing a concentrated aqueous extract of superphosphate containing free phosphoric acid, separating the undissolved residue therefrom, preparing a second aqueous extract of the said undissolved residue, treating the said second extract with milk of lime to precipitate the phosphoric content of free acid and monocalcium phosphate, as dicalcium phosphate and treating the first concentrated extract with the said precipitated

dicalcium phosphate after drying the latter, whereby the free phosphoric acid content of the first extract is converted into monocalcium phosphate thus adding to that already contained in the first extract. This process uses the aqueous extract of superphosphate to prepare a mixture of Monocalcium phosphate and Dicalcium phosphate. It Is different from the present Invention of using the extracted solution from superphosphate for diluting the sulphuric acid that is to be used for acidulating the phosphate rock for production of Enriched super phosphate.
OBJECT OF THE INVENTION
SSP increases soil fertility. It softens the soil and hence improves the soil capability to absorb water. The phosphoric acid is also fully soluble. It speeds up the process of chJorophyM and improves the quality of the orop.
The main object of the invention is to manufacture enriched grade SSP with higher P205 content than of conventional SSP. The object is to disclose a manufacturing process by which the P205 content in the final product SSP is achieved more than that can be achieved by the conventional process of SSP manufacture. A manufacturing process which involves some modifications in the conventional process of SSP manufacture.
The second object of the invention is such Enriched SSP shall have available P205 content of more than 20%.
Another object of the invention is to manufacture Enriched SSP without using high grade rocks but by using only medium grade rocks of 30-31% P205 content. A process which specifies a lower ratio of Sulphuric acid to rock than that of the conventional process to balance the reaction has been disclosed in the patent.
A further object of Ihe invention is not to use commercial grade Phosphoric acid lhat is produced from the wet process phosphoric acid plants for this Enriched SSP production purpose. An innovative step which uses phosphate leach solution extracted from the conventional SSP by dissolution and filtration, for diluting the sulphuric acid instead of diluting with water which is a practice in conventional SSP manufacturing process.

One more object of the invention is to provide such Enriched SSP in granular form so that it would be comfortable to the end user for handling and transportation.
One important object of the invention is the Enriched SSP shall contain Sulphate Sulphur content in the range of 11-12%, because the Sulphuris an essential secondary nutrient to the plants. The invention discloses a process in which sulphuric acid is diluted for the reaction to an appropriately lower concentration which is different from the conventional process.
One another object of the invention is to achieve granulation of the powder SSP obtained by the above steps after curing.
Another object is to achieve a process which does not suggest usage of filler as the objective is to maintain tiigher P205 content in the product SSP.
The final object of the invention is to provide the Enriched SSP granules with a lower moisture content i.e. 2.5% moisture content that is far below compared the moisture content of conventional SSP which generally contains moisture upto 12%. Hence the object is to achieve drying of the granular SSP obtained above to reduce the moisture content to about 2.5%.
The last but not the least of the object is for a final product thus obtained which would be a granular Enriched SSP containing WS P205.CS P205 and Total P205 more than that the conventional SSP contains.
DESCRIPTION OF THE INVENTION
The SSP is a fertilizer, containing phosphorous, sulphur, calcium, magnesium and few other trace nutrients such as zinc and boron etc. thereby used typically for balanced growth of crops.
The novel feature of this invention is manufacture of Enriched single super phosphate in granular form containing >20% available P205 by acidulating the medium grade rocks of 30-31% P205 content with sulphuric acid diluted with phosphate leach solution extracted from conventional SSP, granulating the thus obtained Enriched SSP after curing and finally by drying the granular material to about 2.5% moisture. An additional important feature of this invention is that commercial phosphoric acid produced from the wet process which is costly either in

weak form or in strong form is not used for acidulating the rock. One more important feature of this invention is non-usage of high grade rocks of more than 33% P205 content for acidulation with sulphuric acid which can give simply and without any difficulty the superphosphates containing >20% available P205.
Flow chart fig.1 Illustrates the process sequence and steps as per Invention.
An innovative thought is generated to produce higher grades of SSP i.e Enriched Super phosphate by the usage of phosphate leach solution that is extracted from the previously produced conventional SSP, to dilute the sulphuric acid instead of diluting it with water. In this way certain quantity of gypsum is separated from the SSP that is produced in the normal route and the phosphate leach solution extracted from conventional SSP will be utilized for production of Enriched SSP. Thus the overall consumption of the rock containing 30-31% P205 per ton of Enriched SSP would be higher than that per ton of conventional SSP.
30-31% P205 containing rocks are already being used for SSP manufacture but the technology is limited to produce SSP containing maximum 16-17% WS P205. This invention discloses a method to produce higher grades of SSP i.e SSP containing >18% WSP205 and >20% available P205, with the usage of same grade rock i.e rock containing 30-31% P205 content but higher quantity.
SSP being a mixture of Mono Calcium Phosphate and gypsum, and the gypsum content in the SSP being in the range of 47-52% which does not contribute to any form of P205 in the SSP, the final total P205 content in the SSP is limited to certain achievable value of around 18-19% out of which WS P205 woujd be only around 15-17%. In the manufacturing process of the conventional SSP, there is no step for separation of gypsum and hence the enrichment of grade to more than that can be obtained with a particular rock is not possible.
Typically and conventionally, preparation of conventional SSP involves using a mixer for mixing the Rock phosphate with sulphuric acid and then dumped into a Den. The den is an enclosed slow moving conveyor and the materials keep on reacting in the den. The mixed material which is free flowing slurry in the mixer becomes a semi solid in the den and becomes a cake at the exit end of the den. The reaction occurs

fast and is exothermic. The material discharged from den is heaped in the green SSP shade for curing. The reaction between the rock phosphate and the sulphuric acid is called acidulation and proceeds with emission of fluoride based gases. The homogenous mass is then granulated in a typical granulator drum.
Hence the present Invention Is to Incorporate some modifications and additional steps in the conventional SSP manufacturing process for production of enriched grade product. The conventional process typically involves size reduction of phosphate rock, acidulation in mixers, solidification of the reaction mass, curing process for hardening, de-lumping and then granulation.
The present innovation is to have an additional step that is separation of gypsum from a part of already produced SSP by dissolving it in water or dilute sulphuric acid and collecting the phosphate leach solution and using It for diluting the sulphuric acid instead of diluting with water. This can be considered as modification-1 to the conventional process
While using the phosphate leach solution for diluting the sulphuric acid, it is required to choose an appropriately reduced ratio of sulphuric acid to rock for acidulation process. The reduction shall be to an extent corresponding to the acidity of the phosphate leach solution that is being used for dilution of sulphuric acid. This can be considered as modlficatlon-2 to the conventional process.
The Third modification is that dilution of sulphuric acid to more extent than of SSP manufacture. The second additional step is to dry the resultant SSP to reduce the moisture content from 12% to 2.5% after granulation
Accordingly the above objectives are achieved by a process for the manufacture of Enriched grade single super phosphate from the same phosphate rock that is being used for conventional SSP, comprising the step of acidulating rock phosphate with sulphuric acid diluted with a phosphate leach solution leached from the conventional SSP to produce a final product comprising the super phosphate of Enriched grade.

Typically technical grade sulphuric acid that is 98.5% is preferred but spent sulphuric acid from other industries may be mixed to the technical grade sulphuric acid for manufacturing the enriched SSP as per the conventional process.
In conventional methods the sulphuric acid used In acidulating step Is diluted with water. According to the process of the present invention, while using the 30-31% P205 containing phosphate rock as starting material, the water used for diluting the sulphuric acid is replaced with phosphate leach solution extracted from the conventional SSP. In a continuous process, the phosphate leach solution extracted from conventional SSP is continuously added to the 30-31% P205 containing rock for acidulation purpose along with the sulphuric acid, which results in a final SSP product of Enriched P205 grade. This addition of phosphate leach solution extracted from conventional SSP offers advantage over the manufacturing processes known in the prior arts.
Moreover, the process according to the present invention does not use commercial grade phosphoric acid to enhance the phosphate value of the product and therefore, it is considerably economical. While it is known to the prior art that the P205 of super phosphate can be increased by addition of commercial grade phosphoric acid to the reactants, the present invention avoids the necessity to use commercial grade phosphoric acid, which Is very expensive and since the final product obtained by the process according to the present invention retains sulphur content at around 11-12%, which is another important nutrient to the plants and therefore superior than the triple super phosphate which does not contain Sulphur.
Thus the primary feature of the present invention is to provide a process for producing continuously Enriched grade SSP without using high grade rocks or commercial grade Phosphoric acid. Medium grade rock phosphate and sulphuric acid are the main raw materials. The manufacturing process out of this innovation can be adopted in the existing SSP plant with few modifications.
Another feature of the present invention is usage of the rock phosphate for the above process, of the same grade that is being used for manufacture of conventional SSP i.e rock phosphate containing 30-31% P205 content. It is essential to use dry rock phosphate for process as it is difficult to grind the wet Rock phosphates.

One more feature of the present invention is to utilise the phosphate leach solution that is extracted from the conventional SSP for production of Enriched grade SSP.
This invention provides a process for producing continuously Enriched grade super phosphate, that Is cost effective.
The advantageous, novelty and inventive features lie in many of the process steps and selection criteria which are summarized below :
The process is a novel process for the manufacture of Enriched Single Super Phosphate from medium grade rock phosphate, comprising the step of acidulating the rock phosphate with sulphuric acid diluted with a phosphate leach solution extracted from conventional SSP to ensure the final product i.e Enriched SSP contains the desired level of available P205%.
In another aspect the process is novel to the extent wherein the medium grade rock phosphate used as raw material will contain P205 content of 30-31%.
In another aspect the process is novel to the extent wherein the desired level of available P205% in the final granular product i.e in Enriched SSP would be >20%. The granulated SSP is effective and useful in long duration crops.
\r\ another aspect the process ts nGveJ to the -extent wherein the phosphate teach solution is extracted from conventional SSP by mixing the conventional super phosphate in a recycled wash solution with agitation followed by vacuum filtration.
In another aspect the process is novel to the extent wherein the specific gravity of phosphate leach solution is maintained around 1.15 and contains P205 at about 12-13%.
In another aspect the process is novel to the extent wherein the phosphate leach solution is produced In a 3 stage counter current leaching process from the conventional SSP using Water or dilute sulphuric acid of about 5% concentration as solvent.
In another aspect the process is novel to the extent wherein the sulphuric acid that is used for acidulation of rock is diluted with the phosphate leach solution that is obtained from the process as disclosed herein.

In another aspect the process is novel to the extent wherein the dilution of sulphuric acid is carried out to a calculated level of concentration which is about 60% for the rock of Israel source with 30-31% P205 content to achieve the desired level of available P205 at >20% in the final Enriched SSP granular product.
In another aspect the process Is novel to the extent wherein the usage of sulphuric acid for acidulating the rock phosphate is restricted to the sulphuric acid (100% basis) to rock ratio of a calculated figure for the source & grade of the rock chosen as raw material. For eg for Israel source rock of 30-31% P205% the ratio to be adopted is about 0.60 which is lower than the ratio adopted for the same source and same grade of rock in the conventional SSP manufacture.
In another aspect the process is novel to the extent wherein the acidulation of rock is carried out m a mixer cum reactor that is tfsed for any conventional SSP manufacture.
In another aspect the process is novel to the extent wherein the reaction mixture is passed through a den that is used for any conventional SSP manufacture and retained there for a period of 30 min to facilitate completion of reaction to the reasonable level and for evolution of gases.
In another aspect the process is novel to the extent wherein the green SSP from the den Is stored for curing for a reasonable period of 5-7 days before granulating.
In another aspect the oversize granules are ground and recycled with the undersize granules.
In another aspect the process is novel to the extent wherein the cured powder SSP is granulated and dried to obtain the free moisture content of 2.5% max.
In another aspect the process is novel to the extent wherein the filter cake obtained from the vacuum filtration step ts mostly of gypsum containing only about 0.5-1.0% P205 content. This gypsum can be sold as soil conditioner to the farmers.
In another aspect the process is novel to the extent wherein the conventional SSP to be used for extracting the phosphate leach solution would be about 230 kg per ton of Enriched SSP.

In another aspect the process is novel to the extent wherein the required quantity of dilute sulphuric acid of 5% concentration as solvent for leaching process would be about 230 kg per ton of Enriched SSP.
\n another aspect the process is novel to the extent wherein the medium grade rock phosphate requirement on dry basis would be 600 kg/ton of enriched SSP.
In another aspect the process is novel to the extent wherein the overall medium grade rock consumption on dry basis would be 730 kg/ton of Enriched SSP, including the rock required for conventional SSP that is consumed.
In another aspect the process is novel to the extent wherein the overall sulphuric acid (on 100% purity basis) requirement would be 455 kg/ton of Enriched SSP including sulphuric acid required for conventional SSP that is consumed and the sulphuric acid required for preparing the solvent for leaching of conventional SSP and for preparing enriched SSP.
One more scope of application of this process is, this can be adopted for producing regular grade SSP of 14.5% WSP205 and 16% Available P205 by using low grade rocks of 28% P205 content by reacting with sulphuric acid diluted with Phosphate leach solution prepared from the regular grade SSP.
DESCRIPTION OF FIGURES 2 & 3
Legend for Fig 2( WS P205 Leaching from the Regular grade SSP)
A. Mixing tank-1 with agitator
B. Mixing tank-2 with agitator
C. Mixing tank-3 with agitator
D. Vacuum belt filter-1
E. Vacuum belt filter-2
F. Vacuum belt filter-3
G. Fresh SSP feed {Regular grade SSP) for leaching
H. Filter cake after 1st stage of leaching.
I. Filter cake after 1 * wash
J. Final Filter cake after 2nd wash
K. SSP slurry from Mixing tank-1
L. Lean SSP slurry from Mixing tank-2
M. Lean SSP slurry from Mixing tank-3
N. Fresh Water or Dilute Sulphuric acid of 5% concentration
O. Recycle filtrate liquid to Mixing tank-2

P. Recycle filtrate liquid to Mixing tank-1
Q. P205 leach solution (Target solution that is required for Enriched SSP Manufacturing process.)
Figure-2
Fig-2illustrates Water Soluble P205 Leaching process from regular grade SSP. A, B & C are the Mixing tanks with agitators. D,E & F are the Vacuum belt filters. "GM is regular grade SSP feed to the Mixing tank "A" for leaching of the Water soluble P205 from it. The leaching is done by serial number "P" which is the Lean P205 leach solution obtained from the Filter "E". The SSP feed "G" and the lean P205 leach solution "P" are mixed thoroughly in the Mixing Tank-UA" to leach the water soluble P205 from SSP into the solution. The resultant slurry" K" from the Mixing tank "A" goes to the Vacuum belt filter "D" where the P205 leach solution is separated from the filter cake "FT. This cake Is further leached In the Mixing tanks "B" and "C" and the leach solutions are separated by Vacuum belt filters "E" and "F" respectively. "L" and "M" are the slurries coming out from the Mixing tanks UB" & UC" respectively whereas "I" and "J" are the filter cakes coming out from the Vacuum belt filters "E" and "F" respectively. uNn is the fresh feed of the solvent entering into the system to leach the P205 from the filter cake "I". This solvent can be Pure water or Dilute sulphuric acid of 5% concentration. Dilute sulphuric acid of 5% concentration is found to be more effective to leach the P205 from the Filter Cake. The leach solution "O" obtained from the Filter "F" is used as solvent for leaching of the Filter cake "H" in the Mixing tank "B". Similarly, the leach solution "P" obtained from the Filter "F" is used as solvent "P" for leaching of the Fresh SSP in the Mixing tank "A".
Though the above process looks to be complicated due to recycling of the leach solutions, it is simple with two inputs into the process and two outputs from the process. The two inputs are G and N. G is the Regular grade SSP powder whereas N is the Dilute sulphuric acid of 5% concentration. The two outputs are Q and J. Q is the P205 leach solution which is required to be used for the process of Manufacturing Enriched SSP in the next process step which is explained in the Fig-3.
J is the final filter cake containing Gypsum and little P205 mostly in the form of Di-Calcium phosphate. This can be sold to the farmers, as it is a valuable fertilizer with

secondary nutrients Ca and S and little P205 which are useful for the crops like Soyabean, Ground nut etc.
Legend for Fig-3( Enriched SSP Manufacturing process)
1. Mixing "T
2. Paddle mixer for SSP making
3. Rock Phosphate feed to Number 2
4. P205 leach solution to Number 1
5. Sulphuric acid feed to Number 1
6. Den
7. SSP heap for curing
8. SSP Granulator
9. Dryer
10. Enriched SSP with >20% available P205.
Figure-3:
Fig-3 illustrates Enriched SSP manufacturing process. Number 1 is mixing UT where the P205 leach solution (Number 4) and Sulphuric acid (Number 5) are fed for mixing and feeding into the Paddle mixer (Number 2). Rock Phosphate (Number 3) also is fed into the same for acidulation, reaction and mixing. Number Q from the Fig-2, which is P205 leach solution from the regular SSP, is used in this figure as Number 4 for diluting the sulphuric add as well as enriching the SSP that is formed in the Paddle mixer. The reaction product in the paddie mixer contains higher P2G5 content than the regular process SSP where water is used for diluting the sulphuric acid. The Reaction product goes to Den (Number 6) where the liberated gases are exhausted from the solid rnass by the exhaust system. The solid mass from the den falls on the ground as a heap (number 7). This is cured for about a week to 10 days for completion of the reaction and reduction of moisture content. After curing it Contains about 10-12% moisture, 18-19% Available P205. This SSP powder after curing is sent to the Granulator (Number 8) for making into round granules and then dried In the drier (number 9) to bring down the moisture content to 2.5%. At this stage the product SSP granules contain >20% Available P205 content hence it can be called as Enriched grade SSP.
WS P205 Recovery efficiency In the Leaching process (Fig-2)
Various experiments have been conducted for finding out the WS P205 recovery efficiency. 110 grams of Regular grade SSP has been taken as G in fig-2. From the

analysis results obtained, the recovery efficiency of the process shown In figure-2 can be calculated as below.
Analysis of Enriched SSP
The analysis of the Enriched SSP manufactured in the above process are as below.
P205 Recovery efficiency in the Enriched SSP Manufacturing process (Fig-3)
At various stages of Enriched SSP Manufacturing process, samples are analysed for WS P205 and CS P205. From the obtained results the Recovery efficiency is calculated below.

Granulated form of enriched SSP as prepared is an excellent fertilizer since it is more effective than the regular grade product for two reasons. It contains higher content of available P205 than the conventional SSP. The second reason is being in granulated form, the nutrients will get released slowly for a longer period. Nutrients will not get washed away and thus stays in the soil and enhances more benefit to the crop. Granulated enriched SSP can be extensively used in mechanized farming also.
The description has been provided for the purpose of understefsdrng the invention as required in the provisional specification and all of the details that can be understood by the skilled persons and are obvious to the skilled persons are well within the scope of the invention.

WE CLAIM
1. A method of preparing an enriched single super phosphate from conventional
SSP, comprising of:
a. acjd_ulati_og ejthej .medium grade rock phosphates containing .P205 In the
range 30-33% with diluted sulphuric acid, or acidulating low grade rock
phosphates containing P205 around 20.8% with diluted sulphuric acid, and
b. wherein the said sulphuric acid is diluted with phosphate leach SSP
solution and the said phosphate leach solution extracted by separating the
gypsum from a prepared conventional SSP, the said method characterized
in the combination of use of medium / low grade rock phosphates with
sulphuric acid diluted with phosphate leach solution for preparing enriched
SSP in granular form.
2. The method of manufacturing enriched single super phosphate as claimed in
claim 1, comprising of acidulating medium grade rock phosphates containing
P205 in the range 30 - 33% with diluted sulphuric acid, wherein the said
sulphuric acid is diluted with phosphate leach solution and the said phosphate
leach solution extracted by separating the gypsum from a prepared conventional
SSP,
the said method characterized in the combination of use of medium grade rock phosphates with sulphuric acid diluted with phosphate leach solution for preparing enriched SSP in granular form containing > 20% available CSP205 and containing 18% WS P205.
3. The said method as claimed in claim 2 comprising the steps of:
a. extracting and preparing phosphate leach solution from a prepared
conventional SSP having available P205 content in the range 16-18%
b. diluting sulphuric acid with the said phosphate leach solution,
c. acidulating medium grade rock phosphate <33% P205 content with said
diluted sulphuric acid to form enriched SSP, and

d. curing and granulating the said enriched SSP granules wherein the said prepared enriched SSP is in dry granular form containing > 20% available CSP205.
4. The said method as claimed in claim 2&3 wherein the prepared enriched SSP also contains > 18% WS P205.
5. The said method as claimed in claim 2-4 wherein the prepared enriched SSP also contains 11 -12% sulphur.
6. The said method as claimed in claim 2-5 wherein the prepared enriched SSP has moisture content of around 2.5%. o
7. The said method as claimed in claim 2&3 wherein the said medium grade rock Is medium grade rock of 30 - 31°/p P205 content preferably.
8. The said method as claimed in claim 2&3, wherein the specific gravity of phosphate leach solution is around 1.15 and contains P2G5 around 12-13%.
9. The said method as claimed in claim 2&3, wherein the said diluted sulphuric acid with phosphate leach solution has around 5% concentration.
tO.The said method as claimed In claim 2&3 wherein the extraction of phosphate leach solution from conventional SSP is by dissolution and filtration.
11. The said method as claimed in claim 10 wherein dissolution includes mixing conventional SSP in a recycled wash solution with agitation and the filtration is preferably vacuum filtration.
12. The said method as claimed in claim 2&3 wherein the acidulating may be carried out in a conventional mixer cum reactor used in conventional SSP preparation.
13. The said method as claimed in claim 2, 3 & 12 wherein the duration of acidulating may include 30 minutes retention period in the den.

14. The said method as claimed in claim 2&3 wherein the duration of curing period is preferably in the range 5-7 days.
15. The said method as claimed in claim 10, wherein the filter cake formed by filtration is gypsum cake which is soH conditioner containing 0.5 - 1% P205 content.
16. The said method as claimed in claim 2&3 wherein around 230 Kg of conventional SSP is used for extracting phosphate leach solution for every ton of prepared enriched SSP.
17. The said method as claimed in claim 2&3 wherein around 230 Kg of diluted sulphuric acid of 5% concentration is used as solvent for leaching, for every ton of prepared enriched SSP.
18. The saidmethod as claimed in claim 2&3 wherein around 600 Kg of medium grade rock phosphates is acidulated for every ton of prepared enriched SSP.
19. The said method as claimed in claim 2&3 wherein the conventional SSP is prepared with medium grade rock phosphates.
20. The said method as claimed in claim 2, 3&19 wherein 730 Kg of medium grade rock phosphate is combinedly used for preparing conventional SSP and for acidulation for every ton of prepared enriched SSP.
21. The said method as claimed in claim 2, 3 & 19 wherein around 455 Kg of sulphuric acid (on 100% purity basis) is combinedly used for preparing conventional SSP, for preparing solvent for leaching the prepared conventional SSP and for preparing Enriched SSP.
22. A fertilizer containing enriched SSP granules produced by the process according to claims 1 - 6.
23. The said method as claimed in claim 1, comprising of acidulating low grade P205 around 28% with diluted sulphuric acid, wherein the said sulphuric acid is diluted

with phosphate leach solution and the said phosphate teach solution extracted by separating the gypsum from a prepared conventional SSP,
the said method characterized in the combination of use of low grade rock phosphates with sulphuric acid diluted with phosphate leach solution for preparing enriched SSP in granular form containing 16% available CS P205 and containing 14.5% WS P205.
Dated on this the 18th day of April, 2016
For COROMANOEL INTERNATIONAL LIMITED,
By its attorney,