WO2014045301A2

WO2014045301A2 - A process for preparing phosphates from rock phosphate

Info

Publication number: WO2014045301A2
Application number: PCT/IN2013/000531
Authority: WO
Inventors: Prashant Micky PURI
Original assignee: Indo Gulf Fertilizers
Priority date: 2012-08-30
Filing date: 2013-08-30
Publication date: 2014-03-27
Also published as: WO2014045301A3

Abstract

The present disclosure provides a process for preparing phosphates from rock phosphate. Rock phosphate is powdered in a ball mill to fine powder with up to 75% of the powder having particle size less than 75 μm (microns) in diameter. Powdered rock phosphate is then reacted with an acidic reagent selected from the group consisting of sulfuric acid and phosphoric acid, under vigorous stirring maintained in the range of 1000 to 8000 rotations per minute to yield super phosphates variant such as single super phosphate or triple super phosphate. The reaction is carried out with the amount of acidic reagent to rock phosphate maintained in the range of 1 : 10 to 1 :50. The process of the present disclosure avoids the step of curing which leads to improved yield of super phosphates and decrease in the reaction time.

Description

A PROCESS FOR PREPARING PHOSPHATES FROM ROCK

PHOSPHATE

FIELD OF THE DISCLOSURE:

The present disclosure relates to phosphate fertilizers.

More particularly, the present disclosure relates to a process for preparing super phosphates from rock phosphate.

BACKGROUND:

Phosphates are generally manufactured from rock phosphates. Rock phosphate is a non-detrital sedimentary rock which contains high amounts of phosphate bearing minerals. The phosphate content of phosphorite is at least 15 to 20%, which is a large enrichment over the typical sedimentary rock content of less than 0.2%. The phosphate is present as fluorapatite Ca₅(P04)₃F(CFA) typically in cryptocrystalline masses. It is also present as hydroxyapatite Ca₅ (P0₄)₃OH, which is often dissolved from vertebrate bones and teeth, whereas fluorapatite can originate from hydrothermal veins.

Acidulation of rock phosphate yields super phosphates which are widely used as fertilizers. Super Phosphates (3CaH₄ (P0₄).7CaS0₄) obtained from rock phosphate are classified as single super phosphate and triple super phosphate. Super and triple super phosphates are extensively used as fertilizers since they also provide the much-needed sulphur to the crops. Single super phosphate is produced by the action of concentrated sulphuric acid on powdered rock phosphate and Triple super phosphate is produced by the action of concentrated phosphoric acid on powdered rock phosphate.

Another important phosphate obtained from rock phosphate is Ammonium phosphate (NH₄)₃P0₄, used as an ingredient in some fertilizers as a source of nitrogen.

DE 663253 discloses a reaction of in-situ generated phosphoric acid with rock phosphate in the presence of excess sulfuric acid for producing super phosphate.

US7374740 discloses a reaction of rock phosphate with phosphoric acid to produce monobasic calcium phosphate and further reaction of monobasic calcium phosphate with ammonium carbonate to produce ammonium phosphate. Dibasic calcium phosphate produced as a by-product is reacted with ammonium carbonate to produce phosphoric acid which is reused.

WO/2009/016641 discloses an acidulation of low grade phosphate containing a mixture of rock phosphate along with the previously manufactured single super phosphate to yield super phosphate.

WO/2011/055220 discloses reaction of lignite with ammonia and phosphoric acid to yield super phosphate.

In the prior art as disclosed above, the preparation of super phosphate involved grinding of rock phosphate in a ball mill and its subsequent acidulation with acid followed by solidification and curing of the resulting slurry. The curing took 10-15 days. During curing, the single super phosphate was reshuffled and aerated several times to aid the process of curing.

Thus, the processes as disclosed in the prior art are lengthy and time consuming, with reduced yield and poor quality of the super phosphate resulting there from. Additional equipment such as ID fans, multistage conventional scrubbers and venturi scrubbers are required to ensure effective removal of hydrogen fluoride generated during the process. This kind of post-milling processing adversely affects the overall economy of the conventional processes.

Thus, there is felt a need for providing a simple and economic process for preparing super phosphates which obviates the step of curing.

OBJECTS:

Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:

It is an object of the present disclosure to provide a simple and economic process for preparing high quality super phosphates from rock phosphate.

It is another object of the present disclosure to provide a process for preparing super phosphates in a single facility.

It is yet another object of the present disclosure to provide a process for preparing super phosphates without the need for expensive equipment.

It is yet another object of the present disclosure to provide a process for preparing super phosphates which obviates the method step of curing thereby shortening the reaction time.

These and other objects of the present disclosure are to a great extent dealt in the disclosure. SUMMARY OF THE DISCLOSURE

In accordance with the present disclosure there is provided a process for preparing phosphates from rock phosphate, said process comprising: reacting rock phosphate powder ,wherein up to 75% of said powder has a particle size less than 75 μηι in diameter, with an acidic reagent, wherein the ratio of acidic reagent to rock phosphate is in the range of 1 :10 to 1 :50 by weight, said acidic reagent selected from the group consisting of sulfuric acid and phosphoric acid, said reaction carried out under vigorous stirring maintained in the range of 1000 to 8000 rotations per minute, to obtain super phosphate; and neutralizing the super phosphate.

Typically, the rock phosphate powder is prepared by grinding rock phosphate in a ball mill.

In one embodiment of the process of the present disclosure, the acidic reagent is dilute sulphuric acid having concentration in the range of 50 to 85%.

In another embodiment of the process of the present disclosure, the acidic reagent is dilute phosphoric acid having concentration in the range of 30 to 50%.

Typically, the ratio of acidic reagent to rock phosphate is in the range of 1 :20 to 1 :40 by weight.

Typically, the stirring is increased intermittently from 1500 rpm to 5500 rpm during the reaction.

Typically, the stirring is carried out for a period of 10 to 200 minutes.

In a preferred embodiment of the present disclosure, the super phosphate is granulated to form granulated super phosphates. Typically, the granulation is carried out at a temperature in the range of 60 tolOO°C.

Typically, the granulation of the super phosphate is carried out in the presence of diluted acidic reagent selected from the group consisting of sulfuric acid and phosphoric acid, at least one additive selected from the group consisting of polyvinylchloride resins, cellulose, polyesters, polyanhydrides, polyamides, poly phosphates and esters of phosphoric acids lacquers, urea resin, gaur gum, collagen, albumin, casein, gelatin, lignosulphates, dextrose and alginate and at least one excipient selected from the group consisting of polyvinyl alcohol and lignosulphates.

Typically, the granulation is carried out in the presence of stoichiometric amount of diluted acidic reagent.

In a preferred embodiment of the present disclosure, the granulation of the super phosphate is carried out in the presence of ammonium salt to yield a mixture containing granulated super phosphate and ammonium phosphate.

Typically, the ammonium salt is selected from the group consisting of ammonia solution or ammonium sulphate, nitrate or chloride.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Fig la illustrates the X-Ray diffraction of sample 1 (15 min), Fig lb illustrates the X-Ray diffraction of sample 4 (105 min) , Fig lc illustrates the X-Ray diffraction of sample 2 (30 min) and Fig Id illustrates the X-Ray diffraction of sample 3 (60 min).

Fig 2a illustrates the thermo gravimetric analysis of sample 1 (15 min), Fig 2b and Fig 2e illustrates the thermo gravimetric analysis of sample 4 (105 min), Fig 2c illustrates the thermo .gravimetric analysis of sample 2 (30 min) and Fig 2d illustrates the thermo gravimetric analysis of sample 3 (60 min).

Fig. 3 illustrates the XRD analysis of - rock phosphate.

Fig 4 illustrates the XRD analysis of a sample acidulated for 45 minutes with 60% sulfuric acid, wherein, A=Anhydrite (CaS0₄); B=Bassanite (CaS0₄. 5H₂0); Quartz (Si0₂); and G=Gypsum (CaS0₄.2H₂0).

Fig 5 illustrates the XRD analysis of neutralized sample after acidulation reaction with 60%sulfuric acid, wherein, A=Anhydrite(CaS0₄); B=Bassanite (CaS0₄. 5H₂0); Quartz (Si0₂); and G=Gypsum (CaS0₄.2H₂0).

Fig 6 illustrates the XRD analysis of the neutralized super phosphate after washing.

Fig. 7 illustrates the formation of Triple super phosphate using phosphoric acid, wherein, CHPH= Calcium Hydrogen Phosphate Hydrate (Ca (H₂P0₄)₂(H₂0)), F= Fluorapatite (Ca₅ (P0₄)₃F); Q=Quartz (Si0₂); and A=Anhydrite (CaS0₄).

Fig 8 illustrates the XRD analysis of monocalcium phosphate. DETAILED DESCRIPTION

The embodiments herein and the various features and advantageous details thereof , are explained with reference to the non-limiting embodiments in the following description^ Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The description herein after, of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

In accordance with the present disclosure there is provided a process for preparing super phosphates from rock phosphate. The rock phosphate is finely ground in a ball mill to fine powder with up to 75% of the powder having particle size less than 75 μηι (microns) in diameter. The finely ground rock phosphate powder is then filtered through a cyclone cum filter bag. Finely ground rock phosphate powder is then acidulated with an acidic reagent to provide super phosphate. The ratio of the amount of acidic reagent to rock phosphate is maintained between 1 :10 to 1 :50 by weight. The acidulation reaction is carried out in a mixer equipped with high speed motor for vigorous stirring. The diluted acid and ground rock phosphate powder are mixed thoroughly in a mixer at about 1500 rotations per min to 8000 rotations per min, for a period in the range of 10 to 200 minutes, to provide super phosphate, which is then neutralized washed and dried to obtain powdered super phosphate. Hydrogen fluoride liberated during the reaction is trapped in a solution ofNa₂Si0₃.

In one embodiment of the process of the present disclosure, the finely ground rock phosphate powder is acidulated with dilute sulfuric acid having concentration of 50 to 85% to provide single super phosphate. Dilute sulfuric acid is obtained by diluting 98% sulphuric acid with fresh or recycled water. The ratio of the amount of dilute sulphuric acid to rock phosphate is maintained between 1 :10 to 1 :50 by weight. The acidulation reaction is carried out in a mixer equipped with high speed motor for vigorous stirring. The diluted acid and ground rock phosphate are mixed thoroughly in a mixer at about 1500 rotations per min to 8000 rotations per min, for a period in the range of 10 to- 200 minutes, to provide single super phosphate (PSSP).

In another embodiment of the process of the present disclosure, the finely ground rock phosphate powder is acidulated with 30 to 50% dilute phosphoric acid to provide triple super phosphate. The ratio of the amount of dilute phosphoric acid to rock phosphate is maintained between 1 :10 to 1 :50 by weight. The acidulation reaction is carried out in a mixer equipped with equipped high speed motor for vigorous stirring. The diluted acid and ground rock phosphate are mixed thoroughly in a mixer at about 1500 rotations per min to 8000 rotations per min, for a period in the range of 10 to 200 minutes to provide triple super phosphate (PTSP).

The quantity of rock phosphate powder may further be increased in order to reduce the pH, without affecting mixing quality and conversion rate.

In another aspect of the present disclosure, the super phosphate is further granulated by reacting with stoichiometric amounts of an acidic reagent under vigorous stirring maintained at 1500 rotations per min to 8000 rotations per min, at a temperature between 60°C to 100°C for a time period ranging between 30 minutes and 180 minutes to obtain granulated super phosphate.

In yet another embodiment of the present disclosure, the granulation of super phosphate is carried out by mixing it with at least one additive selected from the group consisting of polyvinylchloride resins, cellulose, polyesters, polyanhydrides, polyamides, poly phosphates and esters of phosphoric acids lacquers, urea resin, gaur gum, collagen, albumin, casein, gelatin, lignosulphates, dextrose and alginate and at least one excipient selected from the group consisting of polyvinyl alcohol and lignosulphates.

In accordance with another aspect of the present disclosure there is provided a process for preparing ammonium phosphate. Ammonium salt is added to the reaction mixture containing rock phosphate and acidic reagent, particularly during granulation step, to yield a mixture of containing superphosphate and ammonium phosphate.

Further modification of the process can be carried out to form a range of fertilizer grade compounds such as Ammonium phosphate sulphate, Ammonium phosphate Sulphate Nitrate, Urea Ammonium Phosphate and or nitro phosphate, Ammonium Nitrate Phosphate or various NPK complexes with and without micro nutrients. The present disclosure is further described in light of the following non-limiting examples which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure.

EXAMPLES:

For the experimentation purpose following apparatus was used: RV 02 Mixer, star type rotor, speed controlled via V-Belt and 3 -stepped pulleys (No FI) , Maximum rotation (8000) per min, 1.8 Kw motor and pan speed 43 to 84 per minute.

Example 1

Step 1 : Grinding

5000 gm of rock phosphate was charged into a ball mill and ground to a size until 75% of the rock phosphate powder had particle size less than 75 μιη (microns) in diameter. The fine particles of rock phosphate were filtered through a cyclone cum filter bag.

Step 2: Acidulation

[Ca₃(P0₄)₃CaF₂] + 7H₂S0₄ > 3CaH₄ (P0₄).7CaS0₄ + 2HF

Rock phosphate Single super phosphate

170 gm of 70% sulfuric acid was added to 5000 gm of powdered rock phosphate in a RV 02 Mixer under vigorous stirring maintained at 2500 rotations per minute (rpm). The rpm was increased to 3000 per minute and then to 5000 per minute to provide friction energy for accelerating the reaction. After addition, the stirring was continued and the reaction was observed to be exothermic. Hydrogen fluoride liberated during the reaction was trapped in a solution of Na₂Si0₃. The samples of the reaction mass were collected and analyzed for X-RD, DSC-TGA, and water solubility at a time interval of 15 min, 30 min, 60 min and 105 min. It was observed that phosphoric acid was released within first 15-20 .minutes of the reaction.

The results of the samples analyzed are shown in Table No. 1 :

Table No. 1

Initial mixing of Rock phosphate with Sulfuric acid .subsequently release phosphoric acid which further reacts with Rock phosphate to give desired water soluble phosphate product in the range of 14 to 16% .

Gypsum is a by-product formed during the conversion of rock phosphate to single super phosphate. Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaS0₄-2H₂0. When gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate, (bassanite) and, if heated further, to anhydrous calcium sulfate (anhydrite). Fig la illustrates the X-Ray diffraction of sample 1 (15 min) and Fig lb illustrates the X-Ray diffraction of sample 4 (105 min). XRD analysis shows that the reaction of formation of single super phosphate is very fast as indicated^' by the formation of gypsum and quartz.. The formation of gypsum by conventional process normally takes several days.

Fig 2a illustrates the thermo gravimetric analysis of sample 1 (15 min) and Fig 2b illustrates the thermo gravimetric analysis of sample 4 (105 min). Thermo gravimetric behavior of the sample 4 (105 min) is very similar to single super phosphate reported in literature indicating the formation of single super phosphate.

Water solubility test:

It is observed that the solubility of the sample increases as the reaction time period increases i.e., sample 4 (105 min) has more solubility than sample 1 (15 min). The rock phosphate is not soluble in water and single super phosphate has higher solubility in water. The increase in the solubility of the product confirms formation of super phosphate..

Example 2

170 gm of 60 % sulfuric acid was added to 5000 gm of powdered rock phosphate (with 75% of the rock phosphate powder having particle size less than 75 μπι in diameter), in a RV 02 Mixer under vigorous stirring maintained at 2500 rotations per minute (rpm). During the addition, the rpm was increased to 3000 per minute and then to 5000 per minute to provide friction energy for accelerating the reaction. After addition, the stirring was continued and the reaction was observed to be exothermic. Hydrogen fluoride liberated during the reaction was trapped in a solution of Na₂Si0₃. The sample of reaction mass was collected after 45 min and analyzed for X-RD (Fig. 4) which indicates the formation of gypsum and quartz. The reaction mass was then neutralized with ammonium hydroxide solution and analyzed for XRD (Fig. 5) which indicates the formation of single super phosphate. The neutralized reaction mass was washed with water and dried, again analyzed for XRD (Fig. 6).

Example 3 : Preparation of Triple Super Phosphate

Ca₃(P0₄)₂(5) + 4 H₃P0₄(acj) -> 3 Ca ²*(aq) + 6

-> 3 Ca(H₂P0₄)₂(oq)

180 gm of 45 % phosphoric acid was added to 5000 gm of powdered rock phosphate (with 75% of the rock phosphate powder having particle size less than 75 μηι in diameter) in a RV 02 Mixer and the mixture was stirred thoroughly at 2500 rotations per minute. The rpm was increased to 3000 per minute and then to 5000 per minute to provide friction energy for accelerating the reaction. The reaction was observed to be exothermic. Hydrogen fluoride liberated during the reaction was trapped in a solution of Na₂Si0₃. The sample of the reaction mass was collected and analyzed for X-RD (Fig 7).

Example 4

Granulation of Single Super Phosphate

Stoichiometric amount of diluted sulfuric acid was added to the super phosphate (as prepared in the above examples) in a high speed mixer under vigorous stirring at 2500 rotations per minute, over a period of 10 to 30 minutes and the stirring was continued for a period of 180 minutes, at a temperature maintained between 80 C to 100°C. During the process a mixture of polyvinyl alcohol and lignosulphates was added, and stirring was intermittently increased from 2500 rpm to 6000 rpm to give variants of granulated single superphosphate.

Example 5

Granulation of Triple Super Phosphate

Stoichiometric amount of diluted phosphoric acid was added to the super phosphate (as prepared in the above examples) in a high speed mixer under vigorous stirring 'at 2500 rotations per minute, over a period of 10 to 30 minutes and the stirring was continued for a period of 100 minutes at a temperature maintained between 70 °C to 100°C. During the process, a mixture of polyvinyl alcohol and lignosulphates was added and stirring was intermittently increased from 2500 rpm to 6000 rpm. Excess acid was then neutralized with an ammonium salt to yield a mixture containing granulated triple super phosphate and ammonium phosphate.

TECHNICAL ADVANCEMENT AND ECONOMIC SIGNIFICANCE

The process of the present disclosure has following advantages:

- the process employed is very simple and requires less capital expenditure, - the rate of conversion of rock phosphate to single super phosphate or triple super phosphate is rapid and hence require much less time as compared to existing processes,- and

- the process of the present disclosure obviates the need for post milling processing such as curing and solidification whereas the existing technology involves several steps after milling.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results.

Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.

While considerable emphasis has been placed herein on the specific embodiments - of the preferred process, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiments of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.

Claims

Claims:

L A process for preparing phosphates from rock phosphate, said process comprising: reacting rock phosphate powder ,wherein up to 75% of said powder has a particle size less than 75 μιη in diameter, with an acidic reagent, wherein the ratio of acidic reagent to rock phosphate is in the range of 1 :10 to 1:50 by weight, said acidic reagent selected from the group consisting of sulfuric acid and phosphoric acid, said reaction carried out under vigorous stirring maintained in the range of 1000 to 8000 rotations per minute, to obtain super phosphate; and neutralizing the super phosphate.

2. The process as claimed in claim 1, wherein said powder is prepared by grinding rock phosphate in a ball mill.

3. The process as claimed in claim 1, wherein the acidic reagent is dilute sulphuric acid having concentration in the range of 50 to 85%.

4. The process as claimed in claim 1, wherein the acidic reagent is dilute phosphoric acid having concentration in the range of 30 to 50%.

5. The process as claimed in claim 1, wherein the acidic reagent is a diluted mixture of sulphuric acid and phosphoric acid.

6. The process as claimed in claim 1, wherein the ratio of acidic reagent to rock phosphate is in the range of 1 :20 to 1 :40 by weight.

7. The process as claimed in claim 1, wherein the stirring is increased intermittently from 1500 rpm to 5500 rpm during the reaction.

8. , The process as claimed in claim 1, wherein the stirring is carried out for a period of 10 to 200 minutes.

9. The process as claimed in any one of the claim 1, wherein the super phosphate is single super phosphate.

10. The process as claimed in any one of the claim 1, wherein the super phosphate is triple super phosphate.

11. The process as claimed in claim 1, wherein the neutralized super phosphate is washed with water and dried to obtain super phosphate powder.

12: The process as claimed in claim 1, wherein the process further includes granulating super phosphate in the presence of diluted acidic reagent selected from the group consisting of sulfuric acid and phosphoric acid, at least one additive selected from the group consisting of polyvinylchloride resins, cellulose, polyesters, polyanhydrides, polyamides, poly phosphates and esters of phosphoric acids lacquers, urea resin, gaur gum, collagen, albumin, casein, gelatin, lignosulphates, dextrose and alginate and at least one excipient selected from the group consisting of polyvinyl alcohol and lignosulphates, at a temperature in the range of 60 tol00°C, under vigorous stirring maintained in the range of 1000 to 8000 rotations per minute, for a period of 10 to 200 minutes, to obtain granulated super phosphates.

13. The process as claimed in claim 12, wherein the granulation is carried out using stoichiometric amount of the diluted acidic reagent.

14. The process as claimed in claim 12, wherein ammonium salt is added during granulation step to form a mixture of superphosphate and ammonium phosphate.

15. The process as claimed in claim 12, wherein ammonium salt is selected from the group consisting of ammonia solution or ammonium sulphate, nitrate or chloride.