JPS5827207B2 - Method for producing monocalcium phosphate and phosphoric acid - Google Patents

Description

Detailed Description of the Invention The present invention involves acidifying phosphorite using phosphoric acid in the presence of silica (hereinafter sometimes referred to as S i 02) and potassium ions (sometimes referred to as 20). The present invention relates to a method for producing monocalcium phosphate and phosphoric acid.

In the method of the present invention, fluorides in the burnt ash soil are converted to potassium silicofluoride, and calcium is converted to monocalcium phosphate, but it is also possible to generate potassium dihydrogen phosphate from this monocalcium phosphate. In this specification, silica, phosphoric acid, monocalcium phosphate, potassium dihydrogen phosphate, and compounds related to the reaction of the invention may be represented by chemical formulas).

The basic and well-known method of acidification of phosphoric acid used in currently operating phosphoric acid plants is to react phosphoric acid with sulfuric acid to form phosphoric acid, which is then reacted with, for example, ammonia to produce monoammonium phosphate. (MAP) and diammonium phosphate (DAP).

The phosphoric acid obtained by this method is called wet phosphoric acid.

In the above reaction, gypsum having the chemical formula CaSO4.2H20 is produced as a by-product.

The raw material phosphorite usually always contains about 3.0-4.0% fluoride, and gaseous fluorides are usually generated by the acidification reaction.

Due to the presence of fluorides in the feedstock, a major operational problem in wet phosphoric acid production plants is the need to treat the large amounts of fluorine compounds released as gaseous and aqueous effluents from such plants. This meant that an expensive method was needed.

Although research into the effects of fluorides in final products has only recently begun, the presence of these fluorides in fertilizers has long-term effects on soil productivity. It is almost clear that it will have a negative effect.

Therefore, the object of the present invention is to treat fluorides, iron, aluminum,
To produce relatively pure phosphoric acid and relatively pure monocalcium phosphate substantially free of magnesium and other impurities, without or significantly reducing the amount of K20 lost. , processing of insoluble fluorine compounds to retrievably concentrate the fluorine compounds so that they can be recovered and reused as fluorine and 20, and to minimize contamination of the environment and final products by fluorine compounds; and to produce the phosphoric acid and monocalcium phosphate.

The present invention provides a method for recovering and separating fluorinated compounds initially as 2SiF6 and finally as calcium fluoride, as well as a method for acidifying phosphoric acid and a method for producing phosphoric acid and monocalcium phosphate. The monocalcium phosphate can then be converted into potassium dihydrogen phosphate.

Basically, the process of the present invention is a method of acidifying phosphoric acid in the presence of silica and recycled phosphoric acid containing potassium ions, which simultaneously converts fluorides into insoluble potassium silicofluoride. The reaction is carried out to produce monocalcium phosphate in solution.

The resulting slurry is precipitated and concentrated to obtain a clear phosphoric acid solution of monocalcium phosphate and a concentrated suspension containing monocalcium phosphate in phosphoric acid.

This suspension contains marl and insoluble silicofluoride produced by the reaction.

As mentioned above, the concentrated suspension of silicofluoride also contains monocalcium phosphate and phosphoric acid, and this suspension is subjected to hydrolysis treatment to produce 20, which is used in the fluoride removal process performed during acidification of phosphorite. Recirculate.

The clear solution of monocalcium phosphate and phosphoric acid is then mixed with 2
Potassium dihydrogen phosphate and phosphoric acid can also be produced by reacting with SO4, KHSO3 or a mixture thereof.

Most of the solution of monocalcium phosphate and phosphoric acid may be reacted with sulfuric acid to precipitate a calcium sulfate hydrate and removed from the reaction system.

A portion of the phosphoric acid may be removed as a product, but the remainder is recycled to the acidification reactor after considering material balance.

Preferred embodiments of the present invention will be described below.

As mentioned above, the present invention is directed to a multi-step process for acidifying phosphorite to produce substantially fluoride-free products, preferably alkali metal phosphates and phosphoric acid.

The process of the present invention can be carried out substantially without fluorine contamination, the fluorides can be recovered in usable form, and the phosphoric acid can be regenerated for reuse in the reaction system or classified as a product. You can also.

As is known, most of the commercially important phosphate ores mined in the United States, particularly in the Florida region, contain 3-4% fluorine even after beneficiation.

This fluorine is contained as a component of fluoroapatite, which is usually expressed as Ca9(PO4)6・CaF2, and is a component of calcium silicofluoride (CaS).
iF6).

Silica is a component of phosphorite and is usually abundant in most ores used in the production of wet process phosphoric acid.

Normally, fluorine compounds in burnt ash soil react with sulfuric acid, and fluorine reacts with hydrofluoric acid (HF) and silicon tetrafluoride (SiF4) in steam.
), or other gases, etc., and in the phosphoric acid solution, it is present in the form of hydrosilicic acid (H2S IF6) and/or silicofluorides or other forms.

Acids originating from ores with low reactive silica content may also contain free hydrogen fluoride.

The problem of fluoride contamination is addressed by the present invention, which recovers virtually all fluorides in usable form while minimizing fluoride emissions and preventing contamination of the environment and desired products with said fluorides. This can be solved to a great extent by this method.

The present invention also provides a series of products that are more purified and useful than previous methods and a new method for obtaining these products without contamination.

The method of the present invention relates to a method for producing potassium phosphates and/or phosphoric acid; in a main embodiment of the invention, the potassium phosphate is potassium dihydrogen phosphate.

Preferred products are KH2PO4 and/or KH2PO4
and phosphoric acid, these compounds contain a high degree of plant nutrition and are of great value as fertilizers.

Yet another product is N a H2P 04,
Note that the method of the present invention is best carried out in a continuous manner.

In the first step of the process of the present invention, a phosphate earth of any type, but usually containing at least several fluorides, is used, using a phosphoric acid solution containing a potassium ion value, from room temperature to about 95°C, preferably about A reaction time of 1/2 to 4 hours, depending on the reaction temperature, is sufficient to substantially complete the acidification at a temperature of 70°C to 90°C, and to completely dissolve the calcium phosphate formed. Acidify using a sufficient amount of phosphoric acid solution.

A sufficient amount of potassium ions is present in the reaction mixture to mainly contain fluorides as 2 S t F6 and S +
02 and impurities.

Preferably, the potassium ion value is provided by KH2PO4 salts contained in the circulating phosphoric acid solution.

In carrying out the first step, the phosphoric acid solution is used in excess in order to substantially completely acidify and dissolve the calcium in the phosphate soil.

P2O in phosphoric acid solution. The content ranges from about 20-55% by weight, preferably about 2540% by weight.

Generally, phosphoric acid is used in excess, but preferably about 35-90 moles of phosphoric acid for each 6 moles of phosphate in the phosphate earth, or a molar ratio of P2O in the phosphoric acid to P2O5 in the phosphate earth. Phosphoric acid is used at a ratio of about 621-15:1.

In addition, in order to make K2O a little excessive, the formula Ca9(PO
4) About 1.0 to 10 moles, preferably 1 mole or more of 20 is present per 3 moles of phosphoric earth represented by 6.CaF2.

K2O or potassium ion is preferably KH2PO
Add as 4.

As mentioned above, the amount of phosphoric acid used is sufficient to dissolve calcium phosphate contained in the phosphoric acid soil.

In addition, a sufficient amount of 20-valent salt, such as KH2PO4 salt, is included in the phosphoric acid to precipitate any fluorides present as a dense crystalline solid that is easily recoverable.

Therefore, in the acidification step, the calcium phosphates are dissolved while the solid mixture is precipitated, from which the fluorides can be recovered.

This precipitate contains fluoride substantially as 2 S s Fa.

The phosphoric acid used as the treatment acid should be considered to be different from mineral acids stronger than phosphoric acid such as sulfuric acid, nitric acid, and hydrochloric acid.

As shown in many reference books, phosphoric acid has a smaller ionization constant than the above-mentioned strong mineral acids.

Phosphoric acid is an acid that ionizes less than 90% at a concentration of 0.1N and has an ionization constant of only 7.5×10 ″.

To carry out the first step of the reaction, phosphoric earth and phosphoric acid are reacted in the presence of reactive silica.

Also present in the reaction system is a circulating solution consisting of a solution of potassium dihydrogen phosphate and phosphoric acid.

Generally, sufficient potassium ions and reactive silica are present in this first reactor to convert the fluorides contained in the phosphate earth into potassium silicofluoride.

The silica added during the reaction of the present invention is amorphous silicon dioxide, and this silicon dioxide may be in any form as long as it does not adversely affect the reaction.

The silica is preferably obtained from a substance capable of bonding with phosphoric earth, such as slag or a product sold by Crafco under the trade name Dicalite J.

The product of the first stage reaction contains a relatively low concentration of solids (e.g. 3-15% by weight) suspended in a solution of monocalcium phosphate and phosphoric acid.

This mixture is preferably passed through a Shirafuna to separate the solids from the solution to obtain a clear solution of monocalcium phosphate.

This monocalcium phosphate can then be processed to produce phosphoric acid and/or potassium dihydrogen phosphate.

3CaF2 and/or 3CaF2 and Sin using calcium ions generated from phosphate earth.

An important feature of the present invention is that there is no need to supply an external source of calcium, such as limestone, as it can be removed as a mixture with calcium.

Although potassium ions are a critical component of this reaction system, they are not consumed but are merely recycled to perform the required fluoride removal function.

Therefore, the cost of 20 is not a significant factor in fluoride removal; it is simply necessary to replenish the amount lost.

Although it is within the scope of the present invention to optionally supply phosphoric acid and/or 2S i F6 externally in the first acidification reaction, in a preferred embodiment it is economically viable to recycle these materials. It is particularly preferable.

When Shirafuna is used, the underflow is a slurry of a solution of monocalcium phosphate and phosphoric acid, which usually contains fluorides as potassium silicofluoride and marl.

Another feature of the present invention is to hydrolyze this mixture by heating it to 100-115°C or reflux temperature to form potassium dihydrogen phosphate in phosphoric acid and convert the fluorides into calcium fluoride and silica. be.

This hydrolysis reaction proceeds as shown in the following formula.

In the above formula, R is a metal such as Fe or A1.

As understood from this formula, fluorides as K2SiF6 are a mixture of SiO3 and 3CaF2, and Al2
It becomes a solid by mixing with O3, Fe2O3, etc.

This solid content mixture (2KH2PO4+14H3PO4
) The useful fluorides can also be recovered from the solid fraction by separation from the solution.

The resulting solution is suitable for recycling to the reaction system and also provides at least a portion of the potassium ions needed to produce potassium silicofluoride as well as a source of phosphate.

Therefore, some of the SiO2 and 20 is not consumed in the reaction, but rather is recycled in a continuous process.

Of course, potassium ions and 5IO2 may be added to the acidification reactor from the outside when necessary for the reaction system.

Phosphoric acid can also be supplied externally. In one embodiment of the invention, a portion of the clear monocalcium phosphate and phosphoric acid solution is reacted with potassium sulfate, calcium bisulfate, or mixtures thereof to form KH2PO4 and H3PO4.
It is also possible to recover KH2PO4 as a fertilizer substance from this solution.

Phosphoric acid can also be produced in this embodiment, which can be recovered or recycled as make-up phosphoric acid.

The remaining monocalcium phosphate and phosphoric acid solution can be recovered as a calcium sulfate hydrate by reacting with sulfuric acid.

The phosphoric acid regenerated from this reaction may be recovered as product and/or recycled to the main reactor and used to acidify the phosphate feed.

A number of advantages result from the sequence of essential steps described above for the acidification reaction.

That is, by this method, useful hydrogen ions are regenerated as shown in the following formula.

Of these, SiO□, 2KH2PO4 and 14H3PO4 are recycled.

In this way, the phosphoric acid concentration is increased by 40% from 10 mol to 14 mol.
increase

More importantly, this 14 moles of free H3PO4 provides an additional supply of unreacted apatite.

In fact, the raw phosphoric earth can be acidified by an additional 10%, for example, as described below.

In the method of the present invention, unreacted phosphoric acid soil is removed from the acidification reaction system in a defluorination and hydrolysis system, and this phosphoric acid soil is subjected to stronger acidifying conditions to a) reduce the phosphoric acid concentration as described above. and b) the temperature can be further increased from 80-90°C.3 The process of the present invention utilizes a relatively small-scale defluorination and hydrolysis circulation system corresponding to 10% of the main circulation reaction system to achieve the above-mentioned It can have an increasing effect.

Furthermore, the method of the present invention allows recovery of very high concentrations of fluorite components and separation of 2S i F6 along with CaF2 in an unhydrolyzed manner.

In this case, chemical fluorite can be obtained by subsequent treatment with NH40H.

In the method of the present invention, after removing the high concentrations of CaF2 and 2SIF6, the R2O3 component is also removed, preferably to facilitate the separation (centrifugation) step and to
It is preferable to add pure gypsum to obtain a 0-0 normal superphosphate lime fertilizer.

If a temperature of 110-115°C is used for hydrolysis, R
The 2O3 components are aggregated to facilitate their separation.

The invention will now be described in conjunction with the drawings.

FIG. 1 shows a flow sheet of the main embodiment of the method of the invention.

In FIG. 1, phosphoric earth from line 1 and phosphoric acid from line 2 are reacted in acidification reactor 3. In FIG.

The reaction is carried out at a temperature of about 4095°C and is carried out using excess phosphoric acid.

This phosphoric acid contains potassium, which is usually added as KH2PO4, in an amount sufficient to react with the fluoride in the phosphoric acid soil to produce potassium silicofluoride.

Additionally, reactive silica is added through line 4 to react sufficiently with the potassium to form potassium silicofluoride.

This reactor 3 contains monocalcium phosphate produced and dissolved in phosphoric acid as a solution, and an insoluble precipitate containing mud ore and a portion of potassium fluorosilicate.

The amount of phosphoric acid is sufficient to dissolve the monocalcium phosphate.

Next, the reaction mixture is sent via line 5 directly to a membrane reactor or Shirafuna 6 to remove fluorides.

A membrane section thickener 6 removes the product or underflow, which is a slurry of potassium fluorosilicate, silica slime and other solids present in the phosphoric acid solution of monocalcium phosphate.

In the main embodiment of the invention, the potassium silicofluoride in this slurry is sent by line 7 to a hydrolysis unit 8.

Hydrolysis is carried out in a hydrolysis device 8 at a temperature of 100-115°C or at the reflux temperature of the reaction system, preferably by introducing steam from a line 9, and potassium silicofluoride is converted into silica and calcium fluoride using monocalcium phosphate. , and potassium dihydrogen phosphate and/or phosphoric acid.

The resulting mixture is sent through line 10 to separator 10,
Here, a portion of the calcium fluoride and silica is recovered from line 12.

In a preferred embodiment, the mixture from separator 11 is sent via line 13 to separator 15 after adding the appropriate amount of gypsum from tureen 14 .

The 0=20-0 fertilizer containing most of the R2O3 component or mud is then recovered from the separator 15 in line 16.

In this case, gypsum is added mainly to obtain a solid 0-20-0 (N-PK) product that can be used as a support and to facilitate separation of mud from the solution in the separator 15. It is.

The solutions of KH2PO4 and H3PO4 are then passed through line 17.
This solution may contain some 5i02.

Most of R2O3 has been removed at this stage, but R2
It is also conceivable that some of the O3 is removed along with other products.

Overflow or solution from the membrane device or Shirafuna 6 is recovered in line 18 as a phosphoric acid solution of monocalcium phosphate.

This product can be treated in a suitable manner to recover useful products such as monocalcium phosphate, phosphoric acid containing circulating H3P 04, and gypsum.

All of these products substantially contain fluoride.

By the method described above, the product obtained in the reaction of the invention is recovered from the membrane unit 6 via line 18.

The reaction product is a phosphoric acid solution of monocalcium phosphate, which is a valuable reaction product of high quality with little fluoride contamination.

This solution can be processed in a variety of ways to recover monocalcium phosphate and/or phosphoric acid, as well as other useful materials such as KH2PO4 and recycled phosphoric acid.

In the embodiment of FIG. 2, the monocalcium phosphate (MCP) and phosphoric acid solution products from line 18 may be sent to an intermediate storage tank 19 where the solution stream may be split into two streams for further processing.

At this point Ca (H2P 04 ) 2 and H3PO
The solution in step 4 can be divided in desired proportions, for example, about 40-60% by weight of the solution may be removed to recover KH2PO4 and H3PO4.

In this case, a portion of the solution stream is withdrawn from line 20 and fed to reactor 21 .

In reactor 21, this solution stream is reacted with a potassium sulfate-based reactant, such as potassium sulfate, potassium hydrogen sulfate, or a mixture thereof, added via line 22.

The potassium sulfate reactant may be added as a solid or an aqueous solution, but is added in a sufficient stoichiometric amount to react with all monocalcium phosphate in the solution.

Water may be added via line 23 if necessary.

The reaction is carried out at a temperature of about 50-100°C with stirring.

In the reaction device 21, monocalcium phosphate and potassium sulfate react to produce potassium dihydrogen phosphate as a product together with gypsum and phosphoric acid.

The reaction when potassium sulfate is used as a reactant is represented by the following formula.

In the above formula, is Y a reaction system? ■Represents the amount of phosphoric acid.

The resulting reaction slurry is transferred via line 24 to a separator or filter 25, the KH2PO4 phosphoric acid solution is removed via line 26 and the gypsum is removed via line 27.

The furnace mass is washed with water from line 28, and this wash water may be recycled to reactor 21 via line 29.

The product recovered in line 26 contains potassium dihydrogen phosphate and has a fertilizer value of 0-24-6.

This solution is evaporated and precipitated with a water-soluble solvent such as methanol or extracted with a water-insoluble solvent such as butanol to obtain KH.
2PO4 can be recovered.

The remainder of the clear monocalcium phosphate and phosphoric acid solution divided in the intermediate storage tank 19 is sent through a line 31 to a crystallizer 31;
React with at least a stoichiometric amount of sulfuric acid from line 32.

This sulfuric acid contains Ca (H2P 04 ) 2 and H3PO
React with the solution of step 4 to obtain phosphoric acid and calcium sulfate hydrate.

This slurry is sent to Shirafuna 32 via line 33,
The slurry is now concentrated and the underflow slurry is sent via line 35 to filter 36.

Substantially pure solid calcium sulfate hydrate is present in line 3.
Recovered by T.

After removing the calcium sulfate hydrate, the phosphoric acid solution and solution are transferred via line 39 to an evaporator where water is optionally removed from the system via line 41.

The residual phosphoric acid may then be recovered as product via line 42 or combined via dotted line 42 with the overflow in line 38 from Shirafuna 34 to form the line necessary for the phosphate acidification reaction carried out in reactor 3. It may also be used as the second cyclic phosphoric acid.

Furthermore, a solution of monocalcium phosphate and phosphoric acid can be processed to recover solid monocalcium phosphate from phosphoric acid, and each product can be recovered or further processed.

That is, the clarified solution of monocalcium phosphate and phosphoric acid from the membrane unit 6 is charged into the crystallizer.

Up to this point, monocalcium phosphate and phosphoric acid solution
The solution is maintained at a temperature of 0-95°C.

In the crystallizer, this solution is evaporated and cooled to about 25 DEG-55 DEG C., preferably about 40 DEG C., to crystallize solid monocalcium phosphate from the phosphoric acid solution.

In this case, the mixture is preferably cooled to a temperature difference of 35-55°C.

The obtained slurry is transferred from the crystallizer to a separation device, where solid monocalcium phosphate and mother liquor C a (H2
P 04 ) 2 and the solution of H3PO4 are separated.

The solid monocalcium phosphate separated in the separator is then sent, for example, to the reactor 21, where it is converted into Ca (H2P
A solution of O4)2 and H3PO4 is reacted with a potassium sulfate reactant, such as potassium sulfate, potassium hydrogen sulfate, or a mixture thereof, as described above.

In the reaction device 21, monocalcium phosphate is reacted with 2SO4 and/or KH8O4 reactants to produce potassium dihydrogen phosphate and/or phosphoric acid as products together with gypsum.

The resulting mixture is then filtered to remove the gypsum from line 27.

The product recovered in line 26 is an aqueous solution of potassium dihydrogen phosphate and/or phosphoric acid.

These solutions can be further processed to obtain the desired compounds.

In this reaction, the reaction between monocalcium phosphate and potassium sulfate or potassium hydrogen sulfate is as follows.

In reaction (a) with K2SO4, the KH2PO4 fertilizer is a liquid 0-15-10 fertilizer and may be further concentrated.

In reaction (b) with KHSO3, KH2PO4 and H3
The PO4 product is a liquid 0-24-8 fertilizer.

Meanwhile, monocalcium phosphate and phosphoric acid from the separator are sent to a calcium sulfate hydrate crystallizer where they are reacted with sulfuric acid to form a phosphoric acid product and/or circulating mother liquor and calcium sulfate hydrate as described in the method of Figure 2. generate things.

This cyclic reaction is shown by the following formula.

In the above formula, "128H3PO4" represents phosphoric acid available for circulation.

Therefore, useful fertilizer products and recyclable phosphoric acid can also be obtained by this process.

The present invention will be explained by the following examples, but the present invention is not limited to these examples.

In the examples and the text of this specification, parts refer to parts by weight unless otherwise specified.

Example ■ 1.278g (9 moles) of P2O5 in phosphate soil at 35%
10.224 g (72 moles) of P2O5 as circulating phosphoric acid
and P2O5 (acid)/P2O5 (phosphoric earth) at a weight ratio of 8/1.

There is a sufficient excess of phosphoric acid in the reaction mixture to dissolve substantially all of the calcium in the phosphate earth as monocalcium phosphate, and the P2O5/CaO weight ratio is 6.7571.

The acidification reaction is carried out at 80-90°C, and the reaction system contains a minimum of 1 mole of reactive silica (20), which is supplied from the outside.
SiO2) and removes substantially all of the fluoride as insoluble potassium silicofluoride.

Sand, some R2O3 slimes and unreacted phosphate earths also do not dissolve.

Add a small amount (3-4 liters) of Na1calite flocculant to precipitate the solids from this reaction.
ppm) is effective.

The temperature of this low concentration reaction slurry is 90° C., and it is separated via a decanter and a shirafuna (a separatory funnel can also be used in the laboratory).

In this case, approximately 10% Ca(H2PO4)2 and H3
A solution of PO4 remains along with the underflow insolubles.

The slurry thus thickened is placed in a hydrolysis sector where the temperature is increased to 11O-1 using low pressure steam, for example.
Raise to 15°C.

Under these conditions hydrolysis is substantially complete in 1-2 hours.

This slurry contains dense crystalline fluorite (CaF2), which is composed of unreacted but somewhat agglomerated R2O3 and P2O5 components, such as hydraclone. ) or can be easily separated by suitable gravity separation means.

Sufficiently pure gypsum is then left with finely dispersed R2O3
and P2O6 to obtain a 0-20-O fertilizer similar to N5P (ordinary lime superphosphate).

For this purpose, collect F20. Approximately 3 per unit weight of mud ore
．． 649 of CaSO4 is required.

P2O3 and F20. Both components were significantly agglomerated or agglomerated during hydrolysis at 110-115°C.

However, the advantage of using pure gypsum is that it serves as a support and separation does not involve any troublesome difficulties.

The products can be easily separated via suitable means, such as centrifuges or precoat filters.

After separation of the solids, the residual solution containing 2KH2PO4+14H3PO4 and a small amount of silica is recycled to the acidification reactor as regenerated phosphoric acid containing potassium ions.

EXAMPLE 1 The clear overflow of monocalcium phosphate and phosphoric acid from Shirafuna of 2 SiF6 is fed to a crystallizer where the temperature is lowered to 40° C. to crystallize the monocalcium phosphate.

Solid monocalcium phosphate and residual Ca (H2PO4)
The 2 and H3PO4 solutions are separated using a filter, centrifuge or other separation device.

The solid monocalcium phosphate can also be removed and then optionally reacted with a stoichiometric amount of potassium hydrogen sulfate at 90° C. in an aqueous medium.

Through this reaction, monocalcium phosphate becomes KH2PO4+
It becomes H3PO4 and gypsum.

The gypsum is removed and the KH2PO4+H3PO4 liquid is separated and recovered as a 0-24-8 fertilizer solution.

The phosphoric acid solution from the separator still containing monocalcium phosphate is reacted with a stoichiometric amount of sulfuric acid at 85° C. to crystallize calcium sulfate hydrate.

This solid content is filtered and removed from the reaction system.

The phosphoric acid obtained can be recycled to the acidification reactor.

Application Examples In yet another reaction, it is also possible to react solid monocalcium phosphate with potassium sulfate to obtain primarily KH2PO4.

In this case, H3PO4 is hardly produced.

Conversely, if part of the (uncrystallized) MCP and H3P04 liquid is reacted with potassium sulfate, the resulting KH2PO4/
The H3PO4 solution will have a plant food value of 0-24-6.

A portion of any K20 product can be recycled to the acidifier to replace the K20 lost in the hydrolysis sector.

As described above, in the present invention, a fertilizer composition containing monocalcium phosphate, phosphoric acid and/or potassium phosphate is obtained by a method including a step of acidifying phosphoric acid soil with phosphoric acid in the presence of silica and potassium ions.

By this method, the fluorides contained in the phosphoric acid soil can be reduced to 2
It becomes SiF6, and upon acidification, monocalcium phosphate is produced in a form dissolved in phosphoric acid.

An important feature of the present invention is to separate and hydrolyze K2SiF6 to recycle 20 from 2S t F6 into KH2P.
It is to be regenerated as a solution of O4 and H3PO4 and further reacted with the fluoride contained in the new phosphate mineral.

The monocalcium phosphate crystallized with part of the Ca(H2PO4)2 and H3P04 solution is reacted with potassium sulfate, potassium hydrogen sulfate, or a mixture thereof to form KH2PO4.
Alternatively, solutions of KH2PO4 and H3PO4 and gypsum are obtained.

Further remaining Ca (H2P 04 ) and H3PO
The solution of No. 4 is reacted with sulfuric acid to obtain the phosphoric acid product and/or the circulating phosphoric acid needed in the phosphate acidification process.

[Brief explanation of the drawing]

The drawings show flow sheets illustrating embodiments of the process of the invention, with Figure 1 showing the main aspects of the process and Figure 2 showing further processing of the monocalcium phosphate and phosphoric acid products. This figure shows an embodiment in which this is the case. Explanation of symbols of main parts, 3... Acidification reaction device, 6... Membrane unit device or Shirafuna, 8...
... Hydrolysis device, 11 ... Separator, 15.
... Separator, 19 ... Intermediate storage tank, 22.
...Reactor, 25...Filter, 31
...Crystallizer, 32...Shirafuna, 36
... Filter, 40 ... Evaporator.

Claims (1)

[Claims] 1. Acidifying phosphorite with excess phosphoric acid in the presence of silica and potassium ions to produce a first slurry containing insoluble potassium silicofluoride in a phosphoric acid solution of monocalcium phosphate, and separating this mixture. to obtain a clear phosphoric acid solution of monocalcium phosphate and a second slurry containing monocalcium phosphate dissolved in phosphoric acid and insoluble potassium silicofluoride, and subjecting the second slurry to hydrolysis at a high temperature. KH2PO4 and H3
Production of monocalcium phosphate and phosphoric acid consisting of regenerating a PO4 solution and producing calcium fluoride and silica, then recovering the calcium fluoride and silica and recycling the KH2PO4 and H3P04 solution to an acidification reaction step. Method. 2. A process as claimed in claim 1, characterized in that the acidification of the phosphorite is carried out at a temperature of about 20-95°C. 3. Separating the mixture recovered from the acidification reaction step with a decanter and a sirafuna to obtain a clear overflow consisting of a phosphoric acid solution of monocalcium phosphate and an underflow slurry containing 2SiF6 in a solution of monocalcium phosphate and phosphoric acid. The method according to claim 2. 4. Hydrolyzing the K2 S t F6 by heating the bottom stream at a temperature within the range of about 95° C. to the reflux temperature of the reaction system to convert K2 S t F6 into calcium fluoride and silica. the method of. 5 Calcium fluoride is first separated from the hydrolysis reaction product and gypsum is added to the remaining mixture to form a solid 0-20-0
A process according to claim 1, comprising removing the fertilizer and recycling the remaining solution to the acidification reaction step. 6. The method of claim 2, comprising having about 1.0-10 moles of potassium ions per 3 moles of phosphorite present in the acidification reactor. 7. A method according to claim 6, comprising adding potassium ions as KH2PO4. 8. Cooling the clear phosphoric acid solution of monocalcium phosphate to precipitate at least a portion of the monocalcium phosphate as a solid product and separating the residual solution of monocalcium phosphate and phosphoric acid. A method for producing monocalcium phosphate and phosphoric acid as described in section.