IL128837A - Fertilizing composition and process for its preparation - Google Patents

Abstract

A process for preparing a fertilizer composition comprising monopotassium phosphate and potassium sulphate which comprises obtaining from potassium bisulphate and calcium phosphate a solution of monopotassium phosphate and potassium sulphate and simultaneously crystallizing said salts from said solution, whereby to obtain a mixture of said salts in crystalline form and substantially uniform distribution, wherein the desired K2O/P2O5 weight ratio of the composition is attained by controlling the P2O5/SO4 weight ratio in the process and regulating the temperature of the crystallization.

Description

Ref:5038/98 128837/2 iri iT? i+?nm ιωτ ιοιπ FERTILIZING COMPOSmON AND PROCESS FOR ITS PREPARATION 5038/98 1- Novel Fertilizing Composition And Process for its Preparation Field of the Invention The present invention relates to a novel fertilizing composition, hereinafter M PS, comprising P2O5 and ¾0 moieties in a controlled weight ratio and to process for its preparation.

Background of the Invention The ratio between potassium and phosphorus in various fertilizers is determined by * the needs of the intended crop. Therefore, there is a wide array of fertilizers, which are tailored to the needs of the crop. One such fertilizer is known as " KP 0:39:39". This fertilizer composition contains no nitrogen and 39% by weight of potassium as K2O and phosphorus as P2O5 each. Hence, the weight ratio between K20 and P2O5 in the fertilizer is 1. In order to achieve such a ratio of 1 in a fertilizer composition comprising monopotassium phosphate (MKP), which has a K2O/P O5 ratio of 0.65, additional potassium, in the form of potassium sulphate, is mixed with MKP. Different weight ratios could in principle be achieved in the same way.

MKP can be prepared by a process described and claimed in USP 4,678,649 to Alexander Josef and Menachem Bar-On, which comprises reacting monopotassium sulfate with a calcium phosphate in the presence of phosphoric acid, separating out the formed calcium sulphate by filtration, neutralizing the filtrate with calcium hydroxide and or oxide and or carbonate, separating out the dicalcium phosphate (DCP) by filtration, and crystallizing monopotassium phosphate from the filtrate.

According to the current practice a fertilizer composition having a weight ratio Κ2θ/Ρ2θ5β1 is obtained by mechanically mixing MKP with potassium sulphate until the required ratio is achieved. The fertilizer composition obtained by this method is not homogenous: the concentration of the fertilizer components is not uniform throughout the composition. This is a drawback of the aforementioned method and of the product obtained from it, since non-uniform concentration of the fertilizer composition may impair its effectiveness and damage the crops. Further drawbacks of 128837/2 5038/98 -2- said method are the need for special equipment and a cumbersome handling of the fertilizer components.

It is therefore a purpose of the present invention to provide a method of producing a fully water soluble fertilizer composition having a controlled K2O P2OS weight ratio, e.g. of 1.

It is another purpose to provide such a method, which produces a fertilizer composition having a substantially uniform distribution of the fertilizer components throughout the mixture.

It is yet another purpose of the present invention to provide such a process for preparing a homogeneous fertilizer composition.

Other objects of the invention will become apparent as the description proceeds.

Summary of the Invention The present invention provides a process for preparing a fertilizer composition comprising monopotassium phosphate and potassium sulphate in such amounts that the 2O P OS weight ratio is as desired, preferably from 0.8 to 1.2 , hereinafter M PS, wherein the particles of the composition components are crystalline and the distribution of the particles of the components of the mixture is substantially uniform throughout The process of the present invention is a chemical process, which produces said composition via a series of selective chemical reactions, purification and crystallization.

Said process comprises the following steps: ~~ 1. Preparing a potassium bisulphate solution, hereinafter "bisulphate solution", by reacting potassium chloride with sulphuric acid according to reaction I.

KC1+H2S04 → KHS04+HC1 (I) 5038/98 -3- It should be noted that potassium bisulphate may be represented as a mixture of potassium sulphate and sulphuric acid, hence, 2KHS04=K2S04 + H2SO4. Hereinafter the source for either K2S04 or H2S04 in the reactions of this process is from the potassium bisulphate solution, unless otherwise specifically mentioned. 2. This stage, hereinafter "the phosphate reaction", comprises two steps: a) Reacting crushed calcium phosphate or dicalcium phosphate or mixtures thereof with the solution obtained in stage 1, in the presence of additional sulphuric acid, to yield phosphoric acid and MKP, both in a solution, and calcium sulphate which precipitates from the reaction solution. The following reactions occur in this step: Ca3(P04)2+3H2SO4 →· 2H 3P04+3CaS04 J (II) Ca3(P04)2+4H3P04 → 3Ca(H 2P04)2 (ΙΠ) Ca(H2P04)2+K2S04 -→ 2KH 2P04+CaS04 † (TV) It should be noted that, as this takes place, dicalcium phosphate CaHP04 (DCP) reacts with H2SO4 and H3PO4 in a similar manner, as well as Qa^O^. b) Adding dicalcium phosphate (DCP) and additional bisulphate solution to the reaction mixture obtained in step (a), which contains phosphoric acid, MKP, K2S04 and calcium sulphate. The reaction between DCP, potassium sulphate and phosphoric acid yields additional MKP in solution and a precipitate of calcium sulphate, according to the following reaction: CaHP04+ H3P04 + 2S04 → 2KH2P04+CaS04 (V) The precipitate is removed and discarded. This stage is performed in four reactors with the use of various combinations of free acid values in the reactors and with purposeful, additional bisul&te solution feeding to the third reactor to give in 5038/98 -4- conjunction a possibility to regulate a P2O5/SO4 weight ratio in the resulting solution of this stage according to the desired K2O P2OJ ratio. 3. In this stage, hereinafter "DCP precipitation", dicalcium phosphate (DCP) is precipitated from the combined solutions of stage 2, which comprise phosphoric acid, K2SO4 and MKP. The precipitation occurs via reaction VI, by reacting said solution with lime. All the phosphoric acid reacts to yield DCP. The obtained mixture is enriched with a solution, hereinafter "mother liquor", which is taken from the evaporation-crystallization stage, as defined below, in such amount that the overall P2Os/S04 weight ratio in the resulting solution of this stage is determined according to the desired K2O P2O5 ratio. The DCP is filtered off and recycled to be used in stage 2 and the MKPS filtrate solution is used in stage 4.

H3P04 + Ca(OH)2 →· CaHP04 +2H20 (VI) 4. In this stage, hereinafter "evaporation-crystallization", the final MKPS product is obtained from the MKPS filtrate solution of stage 3 according to the following steps: a) The MKPS solution is concentrated by evaporation. b) The concentrated solution is cooled and MKPS crystalline precipitates. b) The solution precipitate is separated, leaving a solution herein called "mother liquor", which represents a saturated solution of MKP and K2SO4 at given conditions of crystallization. c) d) The MKPS precipitate is dried.

The ratio K20/P205 in said crystalline precipitate depends on the phase equilibrium and evaporation degree at the evaporation stage, and mainly on the crystallization temperature and on the ratio P2O5/SO4 produced by the maintaining of a definite combination of free acid values in the reactors of the phosphate reaction stage, by additional bisulfate solution feeding to the third reactor of the same stage and by the addition of mother liquor added in stage 3 to the combined solutions of stage 2. An increase in the crystallization temperature produces an increase of the ratio K2O/P2O5 and an increase in said ratio P20s S0 , produces a decrease of the ratio K2O P2OS . 5038/98 -5- Therefore a desired ratio K2O P2O5 can be produced by different combinations of said two parameters. By way of example, if such desired ratio is 1, it can be obtained by a P2O5/SO4 weight ratio of about 3.12 and a crystallization temperature of about 40°C. In general, K2O/P2O5 ratios from 0.8 to 1.2 can be obtained by combinations of P2O5/SO4 ratios from 2 to 4.5 and crystallization temperatures from 38 to 55°C. The combination of parameters used influences the yield of the process. For example, the combination of P2O5/SO4 ratio of about 3.12 and crystallization temperature of about 40°C is optimal for obtaining a K2O/P2O5 ratio of 1 and the corresponding yield is 55% calculated on P2O5.

Description of the Drawings Fig. 1 is a Block diagram of the process; and Fig. 2 is an example of a diagram relating the K2O P2O5 ratio in crystals MKPS to the P2O5/SO4 ratio Detailed Description of a Preferred Embodiment of the Invention The following description is illustrative of a preferred embodiment of the invention, with reference to Fig. 1, which is a block diagram of the process. The following description is not to be construed as limiting, it being understood that the skilled person may carry out many obvious variations to the process.

Ratio indicated throughout is weight ratio, unless specifically noted otherwise.

According to a preferred embodiment of the invention a substantially homogenous fertilizer composition comprising monopotassium phosphate and potassium sulphate such that the K2O/P2O5 weight ratio is as desired, preferably from 0.8 to 1.2, is prepared via a process which comprises the following stages: 1. Preparation of a potassium bisulphate solution, as a source of potassium and of sulfate. 2. Phosphate reaction, 3. Dicalcium phosphate (DCP) precipitation, 4. Evaporation and crystallization. 5038/98 -6- 1. Preparation of a bisulphate solution (Fig.1 , block 1)- This is conducted by reacting potassium chloride with concentrated sulphuric acid at a temperature of about 130°C for about 1.5 hours, to yield a solution of potassium bisulphate and hydrochloric acid (reaction I, see hereinafter). The hydrogen chloride is separated from the bisulfate solution as concentrated hydrochloric acid and the bisulphate solution is used in the process. It is noteworthy that potassium bisulphate may be represented as a mixture of potassium sulphate and sulphuric acid, accordingly 2KHS04=K2S04 + H2SO4. The weight ratio H2SO4 K2SO4 in the potassium bisulphate is about 1.3 - 1.6. Hereinafter the source for either K2S04 or H2S04 in the reactions of this process is from the potassium bisulphate solution, unless otherwise specifically mentioned.

KC1+H2S04 — ► KHS04+HC1 (I) 2. Phosphate reaction: a) In this step (Fig.l, blocks 2 to 5) potassium bisulphate solution is reacted with a slurry of crushed calcium phosphate and additional sulphuric acid. The acid is added for completion of the reaction, which occurs in two reactors Rl and R2 (bocks 2 and 3) - in the first reactor Rl at a temperature of about 76°C for about 55 min, and in the second reactor R2 at a temperature of about 71°C for about 51 min The final products of reactions Π - IV (see hereinafter) are MKP, K2SO4, calcium sulphate (gypsum) and phosphoric acid. Most of the phosphoric acid is consumed by reacting with calcium phosphate, according to reaction ΠΙ, to yield monocalcium phosphate (MCP). Subsequently, the MCP is consumed by reacting with potassium sulphate, from the bisulphate solution, according to reaction IV, to yield MKP and calcium sulphate.

Ca3(P04)2+3H2S04 → 2HgP04+3CaS04| (Π) Ca3(P04)2+4H3P04 → 3Ca(H 2P04)2 (III) Ca(H2P04)2+K2S04 → 2KH2P04+CaS04 (TV) 5038/98 -7- b) The product mixture obtained from step (a) is reacted with a slurry of dicalcium phosphate (DCP), as a reactive neutralization agent for converting K2SO4 to MKP at low acidities, and bisulphate solution (Fig.l, blocks 4, Reactor R3, and 5, Reactor R4), and is maintained in reactor R3 at about 66°C for about 35 min. and in reactor R4 at a temperature of about 65°C for about 35 min. This step is carried out in order to complete the reaction (reaction V).

CaHP04+ H3P04 +K2S04 ·→► 2Κ_¾ΡΟ4+0α8Ο4| (V) Upon completion of the reaction the resulting suspension is filtered. The calcium sulphate is discarded and the filtrate is fed downstream to the DCP reaction stage. The filtrate contains MKP, K2S04 and H3PO4. 3. Dicalcium phosphate (DCP) precipitation (Fig.l, block 6) - In this stage, remaining phosphoric acid in the filtrate from the former stage to which a mother liquor has been added, reacts with lime. The reaction is preferably conducted in three reactors which are connected in sequence. Thus, the phosphoric acid neutralization reaction with lime yields DCP (reaction VI). The reaction temperature is about 60°C.

H3P04 + Ca(OH)2 — ** CaHP04 +2H20 (VI) The resulting reaction mixture creates a suspension of DCP which is filtered. The DCP on the filter is rinsed and optionally recycled to make the DCP slurry which is fed to stages 4 and 5. The DCP created in the process is recycled to be used as a reactive neutalization agent for converting K2S04 to MKP at low acidity in the phosphate reaction stage. In order to obtain a final MKPS product of the desired composition, the filtrate from this stage has to have a P2O5/SO4 weight ratio of about 2.0 - 4.5. This is achieved by mamtaining a definite combination of free acid values in the reactors of the phosphate reaction stage, adding bisulphate solution to the third reactor (R3) of the same stage, and adding in the DCP formation stage an amount of mother liquor. This filtrate is the solution which contains MKP and K2S04 and from which the MKPS is crystallized. 5038/98 -8- 4. Evaporation and crystallization (Fig. 1, block 7)- The filtrate obtained from stage 3 is a solution which characteristically comprises K+, and (SC )2-. This solution is concentrated by evaporation, and MKPS is crystallized from the concentrated solution at a temperature of about 38-55°C, after cooling the solution from the evaporation temperature of about 80°C-90°C. The precipitate is a mixture of crystalline monopotassium phosphate and crystalline potassium sulphate. The mother liquor from the crystallizing step, containing MKP and potassium sulfate, is recycled to the second stage of the process (DCP precipitation). The crystalline mixture is separated via centrifugation and dried in an oven or a fluidized bed dryer by means of air that is at a temperature of about 80-130°C.

Examples Example 1: Preparation of bisulfate solution Raw potassium chloride is fed at a rate of 1.403 kg hr together with 0.768 kg/hr of water into a stirring tank for the preparation of a potassium chloride slurry. The potassium chloride comprises about 1.357 kg of potassium chloride and 0.046 kg of other by-products. The mixture is suspended and stirred for one hour. A slurry of saturated potassium chloride containing about 51.3% of solid having a density of about 1.43 g/cm3 and the temperature is about 10°C. The slurry is transferred to the bisulfate reactor which is a closed insolated stirred tank. The above-prepared slurry is fed to the reactor at a rate of about 2.171 kg/hr together with 98% concentrated sulfuric acid at a rate of about 3.170 kg/hr (which includes 3.108 kg. sulfuric acid and 0.062 kg. of water). Steam is fed to the reactor at a temperature of about 150°C at a rate of 0.971 kg/hr and water is added at a rate of about 0.058 kg/hr. The retention time in the reactor is about 1.5 hr. at a temperature of about 130°C. The reaction occurs creating a potassium bisulfate solution. The solution, at a temperature of about 130°C leaves the reactor at a rate of about 5.019 kg hr into the second reactor where the reaction is completed. The composition of the potassium bisulfate solution is: 2.215 kg H2S04 1.585 kg K2SO4 1.213 kg H20 0.0008 kg HC1 5038/98 -9- 0.00495 kg by-products The by-product of this reaction comprises gaseous HC1 and water vapours and is pumped by a vacuum system to an auxiliary system where it is absorbed by water with formation of concentrated hydrochloric acid as by-product. The composition of the HC1 stream is as follows: 0.323 kg HC1 0.647 kg H20 0. 0186 kg by-products The retention time in the second reactor is about 10 minutes. Upon completion of the reaction, in the second reactor, the potassium bisulfate solution is fed to another tank where it is diluted by adding water at a rate of about 4.981 kg/hr in order to create a solution at proper concentration for feeding to the reaction stage of the process.

The following is the composition of the final solution of this step: 2.215 kg H2S04 1.585 kg K2SO4 6.194 kg H20 0.0008 kg HC1 0.00495 kg bv-products 10.0 kg Total The weight % of the primary components of the bisulfate solution are about: 22.15% H2SO4 15.85% K2SO4 The weight ratio between H2SO4 and K2SO4 is about 1.4.

Example 2: Phosphate Reaction a. Preparing a phosphate slurry (5 kg of slurry containing about 35% solids') The phosphate used in this process is a rriixture of Ca3(P04>2 and by-products. The concentration of P2O5 in the phosphate is about 33-33.5%.

In a stirred tank about 1.750 kg crushed phosphate is stirred with 1.900 kg of water and about 1.350 kg. of "rinsing water" which represents the stream which has been used for rinsing the calcium sulfate (gypsum) of the phosphate reaction stage. 5038/98 -10- b. Preparation of DCP slurry containing about 28% solids In order to prepare 5 kg of DCP slurry from the recycled DCP, from the process, which contains 40% moisture, one needs to mix in a stirred tank 2.333 kg of the DCP and 2.667 kg of water which is recycled from the stage of rinsing the calcium sulfate (gypsum) of the phosphate reaction stage. c. Phosphate Reaction: The aforementioned phosphate slurry is fed at a rate of about 2.219 kg hr to a stirred and heated reactor. A solution of potassium bisulfate is fed at a rate of about 1.826 kg hr and sulfuric acid of a concentration of 98% is fed at a rate of 0.199S kg/hr. The temperature of the reactor is maintained at about 76 C. and the retention time is about 55 min. The reaction occurring creates a suspension with the following characteristics: P2O5 = 8.0% F.A. = 80% wherein F.A. (free acid) designates the percent of P2O5 in the form of phosphoric acid. The suspension from the reactor is fed to a second reactor which is also stirred and heated. The second reactor is fed with a phosphate slurry at a rate of 0.1993 kg/hr and a potassium bisulfate solution at a rate of about 0.3815 kg/hr. The temperature of the reactor is maintained at about 71°C and the retention time is about 51 minutes. The filtrate of the suspension from this reactor contains about 8.2% P2O5 and about 80% F.A. The third reactor which is also a stirred reactor which is heated, is charged with the suspension from the second reactor together with a slurry of DCP at a rate of 1.910 kg/hr and a bisulfate solution at a rate of about 0.673 kg/hr. The temperature in the reactor is maintained at about 66 °C and the retention time is about 35 minutes. The reaction is carried out until the following parameters are achieved: P20s=8.51% and F.A.=50%. The fourth reactor which is also a stirred reactor which is heated is charged with the overflow from the third reactor together with an additional portion of DCP slurry which is fed at a rate of about 0.908 kg/hr. The temperature in the reactor is maintained at about 65°C. and the retention time is about 35 minutes. The suspension from the fourth reactor containing about 23% solids is fed at a rate of about 8.04 kg/hr 5038/98 -11- to a collecting tank, and is filtered under vacuum. After the filtration is completed and the calcium sulfate is separated, the calcium sulfate on the filter is rinsed under vacuum with water, approximately 2.01 kg of water, and rinsing water is then transferred for the preparation of the DCP slurry and phosphate slurry of the former stage. At the end of this stage, approximately 2.97 kg of calcium sulfate are collected and discarded. The filtrate contains P205 =9.2%, F.A =30-35%, K20=5.15%, S04=2.1% (P205/S04=4.38), Cl-=0.07%, CaO=0.32% and the calcium sulfate (gypsum) contains P205 =1.8%, K20=1.3% and the moisture is about 26.5%.

Example 3: DCP Precipitation 3 kg of lime slurry containing about 28% solid is prepared by mixing about 0.840 kg of lime and 2.160 kg. of water. The first reactor of this stage is a stirred reactor which is heated and charged with filtrates from the reaction stage at a rate of about 5.22 kg hr together with a lime slurry at a rate of 0.85 kg/hr. The temperature is maintained at 58°C. and the retention time is about 32 minutes. The pH in the reactor is maintained throughout at about 4, and this is regulated by controlling the feed rate of the lime slurry. The reaction occurring creates a suspension and the filtrate from this suspension contains P2Os =5.6%. The suspension from this reactor is fed to another reactor which is also a stirred and heated reactor. The second reactor is fed with a mother liqueur from the evaporation-crystallization stage at a rate of 1.37 kg hr. The mother liqueur comprises: P20s=14.5%. The temperature in the reactor is 61°C and the retention time about 31 minutes. The suspension from this reactor has a filtrate which comprises P2(¼ =7.1. The suspension is fed to a third reactor which is also a stirred and heated reactor, where the reaction is completed. The temperature in the reactor is 61°C and the retention time is 30 minutes. The suspension leaving the reactor at a rate of about 6.91 kg/hr contains about 8.4% solids. The suspension is collected and filtered under vacuum. Subsequent to the filtering and after separating the DCP, 5.41 kg/hr of filtrate is yielded. The DCP solid on the filter is rinsed under vacuum with water which is taken at an amount of 0.41 kg. (6% of 6.91 kg of suspension). Rinsing water is added to the filtrate. Subsequent to rinsing, DCP which has been rinsed is yielded at an amount of about 1.5 kg. containing: P20s=33% and K20=1.5%, moisture about 45%. The DCP is then transferred in order to prepare 5038/98 -12- DCP slurry which is used in the reaction step. The parameters of the filtrate after adding the rinsing water is as follows: P205=7.2%, K20=6.3%, S04=2.3% (weight ratio P205/S04=3.12). The filtrate is used for the evaporation-crystallization step.

Example 4: Evaporation-Crvstallization Step 12.5 kg of DCP filtrate are evaporated under reduced pressure. Subsequent to the evaporation, the suspension contains about 21.5% P2O5 which is about 4.19 kg and water at an amount of about 8.31 kg. The suspension at a temperature of about 85°C is transferred to a crystallizer, which is a stirred tank with a double jacket, where it is cooled to about 42°C for about 3.5 hr. Following crystallization, the suspension is fed to a centrifuge and the crystals are separated. The crystals are rinsed with about 0.25 kg of water from the condensate. Following rinsing of the crystals, they are transferred to a fluidized bed dryer and dried at a temperature of about 80°C. The yield of the crystallization is 55%. The following is a typical composition of the components of the crystallizing stage: Crystals Amount of wet crystals - 1.11 kg Moisture - 3% Amount of dry crystals - 1.08 kg.

SO =12.06%, K20=39%, P2O5=40.7%, Cd < lppm, AS < lppm, Heavy metals < 10 ppm Mother Liqueur Amount 2.97 kg.

P205=14.5%, K20 =10.7%, S04=4.1%.

Rinsing Water Amount 0.3 kg.

P20s=9.6%. 5038/98 -13- Example 5 Solubility Test of MKPS. MKP. K?.SQ4 and Mixtures MKP - K,SQ4 MKPS sample obtained according to this invention is tested f om the viewpoint of solubility in comparison with: 1 - Commercial MKP of "T" grade; 2 - Two samples of commercial K2S0 ("0-0-52" and "0-0-50"); 3 - Mixture of aforementioned MKP (75%) and K2S0 (25%) with composition of MKPS (K20/P205 = 1, K20 = 39%, P2Os = 39%).

Test results are represented in the following table: The table shows that solubility of MKPS is the same as one of MKP-T and significantly higher than solubility of each sample of K2S04 and of each mixture of MKP and K2S04.

While embodiments of the invention have been described by way of illustration, it will be apparent that the invention may be carried out with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims. 5033/98 128837/2 -14-

Claims (18)

1. .1. A process for preparing a fertilizer composition comprising monopotassium phosphate and potassium sulphate which comprises obtaining from potassium bisulphate and calcium phosphate a solution of monopotassium phosphate and potassium sulphate and simultaneously crystallizing said salts from said solution, whereby to obtain a mixture of said salts in crystalline form and substantially uniform distribution, wherein the desired K2O P2O5 weight ratio of the composition is attained by controlling the P2O5 SO4 weight ratio in the process and regulating the temperature of the crystallization .

2. A process according to claim 1, comprising the following stages: I. Preparing a potassium bisulphate solution; Π. a) Reacting calcium phosphate with said potassium bisulphate solution and with sulphuric acid; b) Reacting DCP and additional potassium bisulphate solution with the product of (a); c) Filtration of gypsum (calcium sulfate) ; III. Precipitating DCP from the solution obtained from stage Π by reacting said solution with lime slurry and filtering out the DCP; IV. Evaporating and crystallizing the solution obtained from stage ΠΙ.

3. A process according to claim 2 wherein the stages of the process are carried out as follows: — I) obtaining a potassium bisulphate solution by reacting potassium chloride with sulphuric acid according to reaction I, wherein the obtained solution represents a rnixture of H2SO4 and K2SO4: CI+H2S04 → KHS04+HC1 H) 128837/2 5038/98 -15- a) Reacting crushed calcium phosphate with the solution of stage 1 in the presence of additional sulphuric acid to produce phosphoric acid and MKF, both in solution, and a calcium sulphate precipitate according to the following reactions: 0¾(ΡΟ4)2+3¾8Ο4— *- 2¾P04+3CaSO^ (II) C¾(P04¼+4¾P04→ 3Ca(¾P04¾ (III) Ca(¾P04)2+K2S04→ 2K¾P04+CaS

4. A process according to claim 3 -wherein, the reaction of step 1 takes place at a temperature of about 130°C.

5. A process according to claim 2, wherein the reactions of step 2 are carried out in four reactors with the use of various combinations of free acid values in the reactors and with purposeful additional bisulphate solution feeding to the third reactor to give in conjunction a possibility to regulate P2OJ/SO4 weight ratio of this stage according to the desired K2O/P2O5 ratio.

6. A process according to claim 2 wherein, the reactions of step 2 are carried out at * temperatures of about 71°C to 76 °C.

7. A process according to claim 2 wherein, the dicalcium phosphate (DCP) created in the process is recycled to be used as a reactive neutralization agent for converting K2SO4 to KP.

8. A process according to claim 2 wherein DCP is precipitated by reacting phosphoric acid with lime.

9. A process according to claim 2, wherein the potassium bisulphate solution has a H2SO4 K2SO4 weight ratio of about 1. 3-1.6.

10. A process according to claim 1, wherein the P2O5/SO4 weight ratio is about 2.0-4.5.

11. A process according to claim 10, wherein the P2O5/SO4 weight ratio is about 3.12.

12. A process according to claim 2, wherein the filtrate from stage 3 has a P2O5/SO4 weight ratio of about 2.0-4.5. 128837/2 5038/98 -17-

13. A process according to claim 11, wherein the filtrate from stage 3 has a P2O5/SO4 weight ratio of about 3.12.

14. A process according to claim 1, wherein the K2O/P2O5 weight ratio of the composition is about 0.8-1.2.

15. A process according to claim 14, wherein the 2O/P2OS weight ratio of the composition is about I.

16. A process according to claim 2 wherein, the crystallization is carried out at a temperature of about 38-55°C.

17. A process according to claims 1 and 2, wherein the P2O5/SO4 weight ratio is about 3.12, the crystallization temperature is about 40°C and the K2O/P2O5 weight ratio of the composition obtained is about 1.

18. A process according to any of claim 1-16, as illustrated and exemplified, with particular reference to the Examples. LUZZATTO & LUZ2ATT0