RU2467988C1 - Method of producing dicalcium phosphate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to agriculture. The method of producing dicalcium phosphate, which involves mixing phosphoric acid with limestone, followed by ageing and drying the product, wherein phosphoric acid, purified from sulphate ions and fluorine, is mixed with limestone in recycle mode, and the product is dried at temperature ranging from plus 100°C to plus 105°C.

EFFECT: invention increases technological effectiveness of the method and quality of dicalcium phosphate.

3 cl, 3 tbl

Description

The invention relates to methods for producing mineral additives for animal feed, namely the production of dicalcium phosphate (feed precipitate).

Feed precipitate is a valuable calcium phosphate supplement for animals and birds. The products used in agriculture are subject to stringent requirements for the content of toxic impurities. The quality criterion for feed phosphate is its purity (the content of harmful impurities - fluorine, arsenic, heavy metals) and the content of P ₂ O ₅ soluble in a 0.4% hydrochloric acid solution corresponding to the acidity of the gastric juice of animals.

The quality indicators of the feed precipitate obtained from extraction phosphoric and thermal acids must satisfy the requirements presented in table 1.

Table 1 No. p / p The name of the quality indicator of feed precipitate Norms according to TU 2182-416-00209438-2007 Norms in accordance with GOST 23999 - 80 one. Mass fraction of total phosphorus soluble in 0.4% hydrochloric acid solution,%, in terms of P ₂ O ₅ 44 ± 1 46-47 in terms of P 19.2 ± 0.5 N.M. twenty 2. Mass fraction of calcium,%, not less 23 24 3. Mass fraction of water,%, no more - four four. Mass fraction of fluorine,%, no more 0.2 0.1 5. Mass fraction of ash insoluble in hydrochloric acid,%, no more - 10 6. Mass fraction of arsenic,%, no more 0.002 0.005 7. Mass fraction of lead,%, no more 0.002 0.002 8. Mass fraction of mercury,%, no more 0.00001 0.00001 9. Mass fraction of cadmium,%, no more 0.00004 0.00004 10. Coarseness residue on a sieve with holes with a diameter of 3 mm,%, no more 0 0 residue on a sieve with holes with a diameter of 2 mm,%, no more 5 5

The prototype of the claimed invention is a method for dicalcium phosphate / RF patent No. 2411222, publ. 02/10/2011, according to the application No. 2009109920 /, including mixing phosphoric acid with limestone at 60-80 ° C in a continuous mode, followed by ripening and drying of the product with flue gases at 120-145 ° C to a residual moisture content of 1.5-2.5 %, characterized in that the mixing is carried out in two series-connected twin-shaft mixers for 4-8 minutes with the addition of absorption liquid in an amount of 40-70% by weight of limestone.

The disadvantages of the prototype method are as follows. The method is not technologically advanced, because requires the addition of absorption liquid in a strictly defined amount - 40-70% by weight of limestone - to ensure optimal conditions for the progress of the decomposition of limestone, namely, to ensure the friable nature of the reaction mass exiting the mixer. The humidity of the reaction mass according to the prototype, however, is so high that it is dried after ripening by flue gases at a temperature of 120-145 ° C to a residual water content of 1.5-2.5%.

The prototype method, in addition, involves the use of concentrated 50% (in terms of P ₂ O ₅ ) extraction phosphoric acid (EPA) with a typical sulfate ion content of up to 2.5% (since extraction is carried out with sulfuric acid). Such a high content of sulfate ions, together with the use of an absorption liquid, makes it possible to obtain a friable reaction mass. But it also affects the quality of the obtained dicalcium phosphate, since sulfate ions form calcium sulfate with limestone, which dilutes the main product so that the content of sulfate ions in the amount of 2.5% leads to the formation of calcium sulfate in the amount of 4.25%.

In addition, the relatively high content of residual fluorine (0.9-1.0%) in concentrated extraction phosphoric acid obtained by the decomposition of Karatau phosphorites with sulfuric acid practically does not allow its use for the production of feed precipitate, since even according to TU 2182-416- 00209438-2007 (Table 1), the permissible mass fraction of fluorine in the feed precipitate is only 0.2%.

Moreover, the quality of dicalcium phosphate obtained by the prototype method does not reach GOST standards not only in the content of toxic fluorine, but also in the mass fraction of calcium and phosphorus: according to the examples given in the description of the patent of the Russian Federation No. 2411222, the calcium content in the obtained dicalcium phosphate is 23% ; the content of P ₂ O ₅ soluble in 0.4% hydrochloric acid solution is 44%.

The problem to be solved and the expected technical result are to increase the manufacturability of the method of obtaining and the quality of dicalcium phosphate due to the use of phosphoric acid purified from sulfate ions and fluorine and to eliminate the use of absorption liquid, while maintaining the friable nature of the reaction mixture in the mixer and significantly lowering the drying temperature of the reaction mixture after it ripening. The resulting dicalcium phosphate content of calcium, phosphorus and fluorine meets the requirements of GOST and two times less wet than the prototype, despite the decrease in the drying temperature.

The problem is solved in that the method of producing dicalcium phosphate, including mixing phosphoric acid with limestone, followed by ripening and drying the product, differs in that the mixture purified from sulfate ions and fluorine phosphoric acid with limestone is carried out in reture mode, and the product is dried at a temperature from plus 100 ° C to plus 105 ° C. Use purified extraction phosphoric acid with a mass content of P ₂ O _{5 of} 50%, sulfate ions and fluorine, respectively, not more than 0.2-0.5% and 0.05-0.1%.

The retour mode of mixing purified phosphoric acid with limestone is provided by supplying the finished product - retur - to the first of two successively installed mixers with a flow rate of 1: 1 by weight to limestone.

Purified extraction phosphoric acid with a mass content of P ₂ O _{5 of} about 50%, sulfate ions and fluorine — respectively, not more than 0.2-0.5% and 0.05-0.1% —are obtained, for example, by feeding to extraction with tributyl phosphate of extraction phosphoric acid obtained from Karatau phosphorites with a concentration of 36-39% P ₂ O ₅ , 2.5-4% sulfate ions and 0.9-1.0% fluorine, with the number of extraction steps 4-5, followed by re-extraction of phosphoric acid from the organic phase and its evaporation under vacuum to a predetermined concentration of P ₂ About ₅ .

Purification by tributyl phosphate (TBP) of extraction phosphoric acid obtained from Karatau phosphorites with a concentration of, for example, 36% P ₂ O ₅ containing 3% sulfate ion and not more than 50 mg / l of solid inclusions is carried out in a five-stage extractor, each stage of which has a mixing chamber and slop chamber. The starting reagents enter the extractor from opposite ends, towards each other, with a volume ratio of organic and inorganic phases equal to 3: 1. The mixing time of the reagent flows in the mixing chamber is 1-2 minutes, the phase separation time in the settling chamber is 8-12 minutes, and the temperature is + 25 + 35 ° С.

The aqueous re-extraction of phosphoric acid from the organic phase with deionized water (approximately 20% of the sum of the above volumes of the organic and inorganic phases) with a temperature of + 60- + 70 ° С is carried out in a five-stage reextractor. The mixing process takes 2 minutes, the phase separation time is 8-12 minutes, the temperature is + 35- + 45 ° С.

The purified re-extract containing 25.6% P ₂ O ₅ , after separation of the captured organic phase from it in the sump, is pumped to the evaporator. Evaporation of the acid occurs under vacuum to a concentration of P ₂ O _{5 of} about 50% (the regenerated 100% TBP is returned to the head of the extraction process).

The result is a purified extraction phosphoric acid (OEFA) containing by weight (%): P ₂ O ₅ - 50.1; sulfate ions - 0.13; fluoride ions - 0.055%.

The inventive method for producing dicalcium phosphate consists of the following stages:

- preparation of raw materials;

- mixing heated to 80 ° C purified from sulfate ions and fluorine phosphoric acid heated to 60 ° C limestone and retur (ready dicalcium phosphate), possibly in two series installed mixers (to ensure complete neutralization);

- ripening of the reaction mass in the pre-heater at 50 ° C;

- drying the product with flue gases in a drying drum at a temperature of 100-105 ° C;

- grinding the finished dried product and sending it to the warehouse (part of the finished product is returned to the mixer as a retur).

Examples

For laboratory research, Turgayak limestone and purified with tributyl phosphate using extraction technology using the above technology, obtained from Karatau phosphorites, were used.

Turgayak limestone had by mass,%:

Ca = 39.38; Mg = 0.22; Fe = 0.064; Al = 0.015; insoluble residue = 0.48; H ₂ O = 0.05; F = 0.023; Cd = 0.000013; Pb = 0.00018; Hg = 0.000021.

The granulometric composition of limestone had fractions,%: more than 0.1 mm - 5.15; from 0.071 to 0.1 mm - 4.29; less than 0.071 mm - 90.56.

(It is recommended to use limestone with a particle size of up to 0.071 mm of at least 80%).

Purified extraction phosphoric acid (OEFK) from Karatau phosphorites in one of the series of experiments had a density of d = 1.496 g / cm ³ and contained by weight,%: P ₂ O ₅ = 49.98; SO ₃ = 0.22; F = 0.069; Ca = 0.077; Mg = 0.14; Fe = 0.004; Al = 0.069.

(In other series of experiments, in order to justify the preferred degree of purification of OEFC “the mass content of P ₂ O _{5 is} 50%, sulfate ions and fluorine — respectively, not more than 0.2-0.5% and 0.05-0.1%” - was used OEFK with somewhat excellent levels of P ₂ O ₅ , sulfate ions and fluorine).

The preparation of dicalcium phosphate was carried out in a porcelain beaker used as a mixer and a heater, heated with a water bath, the temperature of which was set by the experimental conditions.

Limestone preheated to 60 ° C was loaded into a porcelain cup and purified phosphoric acid heated to 80 ° C was added dropwise over 3-6 minutes at a given calculated CaO / P ₂ O ₅ ratio. The neutralization was carried out with continuous stirring for 5 minutes at a temperature of the reaction mass of 60 ° C. The neutralization of phosphoric acid by limestone is complicated by the abundant release of carbon dioxide with the formation of very small crystals of dicalcium phosphate in the foam layer; therefore, a slow dosing of phosphoric acid to limestone is an important condition for obtaining coarse-grained dicalcium phosphate.

To prevent sticking to the walls of the mixer and improve the physical properties of the reaction mass, retur (a crushed fraction of the finished product) was fed into the mixer.

The reaction mass was ripened with periodic stirring for 60 min at a temperature of 50 ° C. At the end of the mixing and ripening processes, an analytical control of the reaction mass was carried out.

The experimental conditions for obtaining dicalcium phosphate are presented in table 2.

Drying of the product after ripening was carried out in an oven with aeration at a temperature of no higher than 105 ° C with periodic stirring for 1.5-3.0 hours to a residual moisture content of 0.9-1.2% in the product. At temperatures below 100 ° C, residual moisture in the finished product may increase by 0.1%. (In practice, at the outlet of the drying drum, the product temperature will be from 90 ° C to 100 ° C; waste flue gases from 95 ° C to 110 ° C).

The dry finished product was weighed and analyzed. The results of the analyzes are presented in table 3.

It can be seen (Table 2) that in order to prevent sticking to the walls of the mixer and improve the physical properties of the reaction mass, a retur (crushed fraction of the finished product) should be fed into the mixer, optimally in an amount of 1: 1 by weight to limestone.

The proposed retour method for producing dicalcium phosphate using phosphoric acid purified from sulfate ions and fluorine is more technologically advanced, since it does not require the use of absorption liquid, and a much lower temperature is sufficient to dry the reaction mass after its maturation; while the obtained dicalcium phosphate in terms of calcium, phosphorus and fluorine content meets the requirements of GOST (Table 3) and is half as wet as in the prototype, despite the decrease in the drying temperature.

Claims (3)

1. A method of producing dicalcium phosphate, comprising mixing phosphoric acid with limestone, followed by ripening and drying the product, characterized in that the mixture purified from sulfate ions and fluorine phosphoric acid with limestone is carried out in reture mode, and the product is dried at a temperature of from 100 to 105 ° C. 2. The method according to claim 1, characterized in that use purified extraction phosphoric acid with a mass content of P ₂ O ₅ 50%, sulfate ions and fluorine - respectively, not more than 0.2-0.5 and 0.05-0, one%. 3. The method according to claim 1, characterized in that the reture mode of mixing purified phosphoric acid with limestone provides the supply of the finished product - reture to the first of two successively installed mixers with a flow rate of 1: 1 by weight to limestone.