WO2017151016A1

WO2017151016A1 - Solid phosphate salt and process for preparation thereof

Info

Publication number: WO2017151016A1
Application number: PCT/RU2017/000107
Authority: WO
Inventors: Alexander Vladimirovich TUGOLUKOV; Dmitry Vladimirovich VALYSHEV; Oleg Lvovich ELIN
Original assignee: Mineral And Chemical Company Eurochem, Joint Stock Company
Priority date: 2016-03-03
Filing date: 2017-03-01
Publication date: 2017-09-08
Also published as: EA030011B1; CN108473309A; RU2627403C1; EA201692454A1

Abstract

The present invention relates to a phosphate salt consisting of CaHPO₄ x n H₂O (dicalcium phosphate) and Ca₅(PO₄)₃F (fluorapatite), where n is 0 to 2, fluorapatite content in the phosphate salt is up to 99% and phosphorus content is 35% to 45%> in terms of P₂O₅ in the aforementioned salt, and also to a process for preparation thereof.

Description

SOLID PHOSPHATE SALT AND PROCESS FOR PREPARATION THEREOF

Description

The present invention relates to a solid phosphate salt being a mixture of fluorapatite of the formula Ca₅(P0₄)₃F and dicalcium phosphate of the formula CaHP0₄ x n ¾0, where n is 0 to 2, said mixture containing fluorapatite in the amount of 27 wt% to 99.0 wt% and phosphorus in the amount of 35 wt% to 45 wt% in terms of P₂0₅ in the aforementioned salt, and to a process for preparation thereof. This mixture may be used as a raw material for the preparation of complex mineral fertilizers, in particular, superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), NPK fertilizers, monocalcium phosphate, mono-dicalcium phosphate (MDCP), and phosphoric acid.

There are patents essentially disclosing the treatment of phosphate rock with hydrochloric acid, in particular, patents GB-1051521, SU-A-1470663, US-3304157 suggest the use of hydrochloric acid solutions with concentration of 20-30%. The use of this technology requires more expensive equipment due to the more intense corrosion caused by high concentration of acid and higher reaction temperature. In addition, zonal overheating may occur while arranging the fluid flow in the reactor due to high thermal effects per unit volume of the reaction mass. Also, there is an issue of higher production costs, since it is not possible to use low concentrations of acids obtained, for example, in the process of catching off-gases containing hydrochloric acid or in the process of decomposition of aqueous solutions of chlorides.

Furthermore, there is a known method of rock treatment with diluted hydrochloric acid. According to the method described in the patent application FR-A-21 15244, the treatment is performed in a counter current arrangement with different concentrations of hydrochloric acid in different stages, which results in increased capital costs and maintenance costs of the process.

Another known method comprises phosphate rock treatment with diluted hydrochloric acid for the purpose of its enrichment with subsequent processing in a manner similar to processing of the rocks with a high content of phosphorus. This acid is used to dissolve a substantial part of the calcium carbonate contained in the rock and also a minimal part of the phosphates to obtain a solid phase with high P₂0₅ content (Patent US-A-3.988.420).

The drawbacks of this method are: low P₂0₅ recovery from the rock, large amount of water introduced due to low concentration of hydrochloric acid, insufficient efficiency of rock decomposition stage as it is conducted at a low temperature.

Thus, the object of the invention is to obtain the above mixture having the specified purpose and to provide a process for preparation thereof with higher P₂0₅ recovery, eliminated use of large amounts of water, higher efficiency of decomposition stage due to conducting the process at the increased temperature and using a cascade of reactors, and using a process of solution of phosphates pre-neutralization.

The object is attained by providing the solid phosphate salt, which is a mixture of fluorapatite of the formula Ca₅(P0₄)₃F and dicalcium phosphate of the formula CaHP0₄ x n H₂0, where n is 0 to 2, said mixture containing fluorapatite in the amount of 27 wt% to 99.0 wt% and phosphorus in the amount of 35 wt% to 45 wt% in terms of P₂0₅ in the aforementioned salt.

The object in relation to the process for preparation is attained by providing a process for preparation of a solid phosphate salt from phosphate rock with P₂0₅ content of 20 wt% to 32 wt% and MgO content of 3.0 wt% to 4.5 wt% using one-stage direct flow process of phosphate rock decomposition by treatment with aqueous hydrochloric acid solution in a cascade of reactors to form a suspension, consisting of insoluble residue and an aqueous solution of phosphates, followed by separation of insoluble residue, neutralization of aqueous solution of phosphates with calcium carbonate suspension and filtration to yield phosphate salts in solid form and calcium chloride solution.

The distinguishing feature of this process is that prior to the stage of separation of insoluble residue the solution of phosphates is pre-neutralized to pH value of 0.6 to 2.0, the concentration of hydrochloric acid solution used is 10% to 13% at the decomposition stage, and said decomposition is carried out at the temperature of 40° to 70°C with hydrochloric acid to calcium molar ratio of 1.6 to 2.2, the phosphate salt obtained after filtration is washed with water, said phosphate salt is dried to yield dihydrate or anhydride, calcium chloride solution is treated with sulfuric acid to give hydrochloric acid and gypsum dihydrate, and hydrochloric acid is returned to the decomposition stage.

Preferably, the pH regulator used at the rock decomposition stage is calcium carbonate suspension with a concentration of 25% to 35%, the resulting precipitate is washed with water to decrease content of chlorides in the phosphate salt, the insoluble residue is washed with water after filtration, and the resulting washing solution is returned to the solution of phosphates. Desirably, the resulting calcium chloride has a concentration of 18% to 22%.

Fig. 1 is a block diagram of the process for preparation of the phosphate salt according to the present invention.

Phosphate rock with phosphorus content of 25% to 30% in terms of phosphorus pentoxide (stream 1) is fed to the first reactor in the cascade, namely to rock decomposition reactor A, which also receives hydrochloric acid (stream 2) fed thereto with predetermined acid to rock ratio. From the reactor A reaction mixture is moved to maturing reactor B, where the rock decomposition reaction ends.

In the first embodiment of the process, the fluorine content in the solution of phosphates is regulated in the reactor C by regulating pH values of the solution of phosphates by means of dosing calcium carbonate suspension (stream 3) with concentration of 25 wt% to 35 wt% into the last reactor of the cascade of reactors of rock decomposition to attain the set pH values of 0.8 to 1.2. All reactors are equipped with mixing devices, the process is performed at a temperature of 40°C to 70°C.

After rock decomposition the flow of suspension (stream 4) containing an aqueous solution and precipitate is fed to filter in unit D, where it is separated into an aqueous solution of phosphates (stream 6), which is fed into unit E for neutralization, and sludge, which is a production waste (stream 5).

In unit E an aqueous solution of phosphates is neutralized to pH values of 2.8 to 3.2 using a weak base (stream 70), which leads to precipitation of insoluble form of the phosphate salt, and thereafter the suspension (stream 8) is fed to the filtration unit F. Upon filtration and after washing the product is formed, which is a wet precipitate of phosphate salt (stream 9) and an aqueous solution of chlorides. For proposes of imparting the commodity properties, phosphate salts are sent to drier, an aqueous solution of chlorides (stream 10) is fed to unit of decomposition of chlorides G, where said decomposition is performed using sulfuric acid (stream 13), and part of the solution of chlorides is removed from the process (stream 1 1). After filtration of suspension from unit G, which was obtained in the result of the process of decomposition of chlorides using sulfuric acid, wet gypsum (flow 12) is withdrawn from the process, and hydrochloric acid is returned to the stage of rock decomposition after adding the necessary amount of hydrochloric acid (stream 14) from outside the process.

Examples

Example 1

For the production of the phosphate salt the rock from eysik deposits (Kazakhstan) was used. The rock composition in terms of main components, content is provided in % by weight:

Phosphate rock is produced in the equipment under continuous operation conditions. To the first reactor of rock decomposition unit equipped with a stirrer, 1 1 t/h of rock crushed to a 1-2 mm fraction and 49.9 kg/h of 12% hydrochloric acid are fed, the reaction is carried out at the temperature of 55°C in a cascade of reactors connected by overflow. The result is slurry of phosphates containing 4.5% of phosphates in terms of phosphorus pentoxide, which is supplied to the filter. Filtration results in separation of the insoluble precipitate, said precipitate is washed to remove phosphates and the washing solution is returned to the system. After separation of the insoluble residue in the amount of 2.8 kg/h, the solution of phosphates in the amount of 57.8 kg/h is fed into neutralization unit, which is a cascade of reactors equipped with a stirrer, where the slurry of calcium carbonate in solution of chlorides is also fed in the amount of 3.5 kg/h in terms of 100% CaC0₃. The process is carried out at a temperature of 60°C. The increase in pH to 3.0 during neutralization results in obtaining slurry of phosphate salts containing 3.6% of phosphates in terms of phosphorus pentoxide, said slurry is divided in the process of filtration into solution of chlorides in the amount of 55.1 kg/h and wet phosphate salt, which, upon washing, is fed in the amount of 7.9 kg/h to the drier, while the washing water is returned to the system. Part of solution of chlorides is withdrawn from the system and 49.8 kg/h of the solution is fed to the unit of decomposition of chlorides, being a cascade of reactors with stirrer. 98% sulfuric acid in the amount of 7.2 kg/h is fed to the first reactor of the cascade. Decomposition of chlorides yields a slurry of gypsum dihydrate in hydrochloric acid. Gypsum is separated by filtration and upon washing to remove chlorides is removed from the process in the amount of 19.6 kg/h. Hydrochloric acid from unit of decomposition of chlorides in the amount of 45.9 kg/h is fed to rock decomposition unit, while the lacking hydrochloric acid in the amount of 4.0 kg/h is supplied from outside the process.

After cake drying solid phosphate salt is obtained from the neutralization unit, said salt being essentially a fluorapatite with main substance content of 99%.

Example 2

Phosphate rock similar to the rock in Example 1 is produced in the equipment under continuous operation conditions. To the first reactor of rock decomposition unit equipped with a stirrer, 1 1 t/h of rock crushed to a 1-2 mm fraction and 50.7 kg/h of 12% hydrochloric acid are fed, the reaction is carried out at the temperature of 55°C in a cascade of reactors connected by overflow. Calcium carbonate slurry in the amount of 1.3 kg h in terms of 100% CaC0₃, is fed to the last reactor of decomposition cascade to obtain a medium with pH = 0.8 in the final reactor. The result is slurry of phosphates containing 4.9% of phosphates in terms of phosphorus pentoxide, which is supplied to the filter. Filtration results in separation of the insoluble precipitate, said precipitate is washed to remove phosphates and the washing solution is returned to the system. After separation of the insoluble residue in the amount of 3.2 kg/h, the solution of phosphates in the amount of 64 kg/h is fed into neutralization unit, which is a cascade of reactors equipped with a stirrer, where the slurry of calcium carbonate in solution of chlorides is also fed in the amount of 2.2 kg/h in terms of 100% CaC0₃. The process is carried out at a temperature of 60°C. The increase in pH to 3.0 during neutralization results in obtaining slurry of phosphate salts containing 4.1% of phosphates in terms of phosphorus pentoxide, said slurry is divided in the process of filtration into solution of chlorides in the amount of 59.8 kg/h and wet phosphate salt, which, upon washing, is fed in the amount of 7.9 kg/h to the drier, while the washing water is returned to the system. Part of solution of chlorides is withdrawn from the system and 39.6 kg h of the solution is fed to the unit of decomposition of chlorides, being a cascade of reactors with stirrer. 98% sulfuric acid in the amount of 4.6 kg/h is fed to the first reactor of the cascade. Decomposition of chlorides yields a slurry of gypsum dihydrate in hydrochloric acid. Gypsum is separated by filtration and upon washing to remove chlorides is removed from the process in the amount of 9.9 kg/h. Hydrochloric acid from unit of decomposition of chlorides in the amount of 39.3 kg/h is fed to rock decomposition unit, while the lacking hydrochloric acid in the amount of 1 1.3 kg/h is supplied from outside the process.

After drying cake the solid phosphate salt is obtained from the neutralization unit, said salt being essentially a fluorapatite with main substance content of 27% with rest of the salt being dicalcium phosphate in the form of hydrate and anhydride mixture, and calcium phosphate.

Claims

1. A solid phosphate salt, which is a mixture of fluorapatite of the formula Ca₅(P0₄)₃F and dicalcium phosphate of the formula CaHP0₄ x n H 0, where n is 0 to 2, said mixture containing fluorapatite in the amount of 27 wt% to 99.0 wt% and phosphorus in the amount of 35 wt% to 45 wt% in terms of P₂0₅ in the aforementioned salt.

2. A process for preparation of a solid phosphate salt of claim 1 from phosphate rock with P₂0₅ content of 20 wt% to 32 wt% and MgO content of 1.5 wt% to 4.5 wt% using one- stage direct flow process of phosphate rock decomposition by treatment with aqueous hydrochloric acid solution in a cascade of reactors to form a suspension, consisting of insoluble residue and aqueous solution of phosphates, followed by separation of insoluble residue, neutralization of aqueous solution of phosphates with suspension of calcium carbonate and filtration to yield phosphate salts in solid form and solution of calcium chloride, characterized in that prior to the stage of separation of insoluble residue the solution of phosphates is pre-neutralized to pH value of 0.6 to 2.0, the concentration of hydrochloric acid solution used is 10% to 13% at the decomposition stage, and said decomposition stage is carried out at the temperature of 40° to 70°C with hydrochloric acid to calcium molar ratio of 1.6 to 2.2, the phosphate salt obtained after filtration is washed with water, said phosphate salt is dried to yield dihydrate or anhydride or a mixture thereof, and solution of calcium chloride is treated with sulfuric acid to give hydrochloric acid and gypsum dihydrate, and hydrochloric acid is returned to the decomposition stage.

3. The process of claim 2, characterized in that the pH regulator used at the rock decomposition stage is suspension of calcium carbonate with a concentration of 25% to 35%.

4. The process of claim 2, characterized in that the resulting precipitate is washed with water to decrease content of chlorides in the phosphate salt.

5. The process of claim 2, characterized in that the insoluble residue is washed with water after filtration, and the resulting washing solution is returned to the solution of phosphates.

6. The process of claim 2, characterized in that resulting calcium chloride has a concentration of 18% to 22%.