RU2336250C2 - Method of obtaining complex fertiliser - Google Patents

Abstract

FIELD: chemistry, agriculture.

SUBSTANCE: method of obtaining complex fertiliser includes decomposition of apatite with nitric acid, cooling of nitric-acid extract with further separation of calcium nitrate sediment from mother liquor, separation of calcium phosphates sediment from nitrate-phosphate solution and processing the latter into complex NP or NPK fertilisers, ammoniating being performed in two stages, supporting on the first stage percentage of nitric acid 0.1÷1.0% wt, and on the second stage supporting pH 4.0÷5.5. Degree of calcium release is supported within 25-64% from the supplied to ammoniating. Time of ammoniated suspension stay at the second stage constitutes 30-60 minutes.

EFFECT: productivity of filtration of ammoniated suspension according to said method exceeds productivity of ammoniated suspension filtration according to prototype.

2 cl, 3 ex

Description

The invention relates to the chemical industry and can be used in the production of complex mineral fertilizers by the method of nitric acid processing of natural phosphates.

Currently, agriculture is in demand for complex fertilizers with different nutrient content.

A known method of producing nitrogen-phosphorus fertilizer (Pozin M.E. Technology of mineral salts. T.2, L .: "Chemistry", 1974, S. 1339-1346), including the nitric acid opening of natural calcium phosphate to obtain nitrogen acid extraction by crystallization of calcium nitrate upon cooling, followed by separation of the precipitate of calcium nitrate from the mother liquor by filtration or centrifugation, processing the mother liquor into fertilizer by known methods (granulation, prilling, preparation of fertilizer mixtures).

The disadvantage of this method is that the resulting fertilizer contains a low proportion of water-soluble phosphates (P ₂ About _{5v / p} ).

The closest in terms of the totality of existing signs and the achieved result to the proposed one is a method for producing a complex calcium-containing fertilizer with an adjustable Ca: P ₂ O ₅ ratio, including the decomposition of apatite with nitric acid, the separation of part of calcium from the nitric acid extract during cooling, followed by the separation of the precipitate of calcium nitrate from the mother liquor and ammonization of the mother liquor to pH 3 ÷ 7, separation of the precipitate of calcium phosphates from nitrate-phosphate solution and processing of the latter into complex NP and and NPK fertilizer known methods - granulation, prilling, the preparation of mixed fertilizers (RF patent №2261234, cells S05V 11/06, published 27.09.05, 2005 Bulletin №27...).

The disadvantage of this method is the low filterability of the precipitate of calcium phosphates during the separation of the ammoniated suspension, which complicates and increases the cost of the process.

The technical problem solved by the claimed method is to eliminate this drawback, i.e. an increase in the rate of filterability of the precipitate of calcium phosphates.

The stated technological problem is solved in that in the method for producing complex fertilizer, including the decomposition of apatite with nitric acid, the separation of calcium from the nitric acid extract during cooling, followed by separation of the precipitate of calcium nitrate from the mother liquor, ammonization of the mother liquor to pH no higher than 7, separation of the precipitate calcium phosphates from nitrate-phosphate solution and processing of the latter into complex NP or NPK fertilizers by known methods, in accordance with the invention, the ammonization is carried out in two stages, supporting -hand in the first step the content of free nitric acid 0.1 ÷ 1.0% wt., and in a second step maintaining the pH at 4.0 ÷ 5.5.

The degree of calcium excretion is maintained in the range of 25-65% of the incoming for ammonization. The residence time of the ammoniated suspension in the second stage is 30-60 minutes, the temperature during the ammonization process is maintained within 60-90 ° C.

The increase in filtering performance is due to the following factors. At the first stage of ammonization, the main part of free nitric acid is neutralized, however, its residue is maintained sufficient to prevent the formation of precipitation. Thus, the second stage ammonization is carried out under conditions that exclude the formation of solutions of a high degree of supersaturation with calcium phosphates. Since the precipitation of calcium phosphates occurs under conditions of a low degree of supersaturation, coarse crystalline precipitates are easily formed. The formation of coarse-grained precipitates is also promoted by an increase in the duration of the ammonization process.

The starting materials are natural raw materials apatite concentrate (GOST 22275-90) and industrial environments formed in the technology of nitric acid decomposition of apatite concentrate (Complex nitric acid processing of phosphate raw materials. / Ed. By A.L. Goldinova, B.A. Kopyleva L .: Chemistry, 1982, p. 122).

Example 1

With nitric acid decomposition of 1000 g of apatite concentrate, followed by cooling of the nitric acid extract to a temperature of + 4 degrees, separation and washing of crystals of calcium nitrate, 3092 g of a mother liquor containing 12.5% P ₂ O ₅ and 4.7% Ca are obtained. The degree of calcium excretion is 60%.

The mother liquor is ammoniated at a temperature of 80 ° C using gaseous ammonia in two stages: at the first stage, the content of free nitric acid is maintained at 0.5% by weight, and at the second, the pH is maintained at 4.7. 3379 g of an ammoniated suspension are obtained, which are separated on a vacuum filter. The filtering surface is 113 cm ² , the vacuum is 0.4 kg / cm ² , the filter cloth is polypropylene (Ref. 5650).

Filtration performance (Wf) was calculated by the formula:

where MS is the mass of the suspension taken for filtration, t;

S is the filter area, m ² ;

τ is the filtration time, hours.

In this case, 2574 g of a solution (filtrate) containing 14.2% nitrogen, 7.2% P ₂ O ₅ and 0.03% Ca, and 805 g of a wet precipitate of calcium phosphates containing 7.3% nitrogen, 24.8 are obtained. % P ₂ O ₅ and 18.0% Ca. Suspension filtration performance (excluding auxiliary operations) is 10.3 t / m ² hour.

The calcium phosphate precipitate is washed on a filter and dried. In this case, 983 g of wash water containing 4.9% nitrogen and 2.5% P ₂ O ₅ and 440 g of dry product containing 2.2% nitrogen, 39.8% P ₂ O ₅ and 33.0% are obtained Ca, 6% F.

The calculated composition of the precipitate, wt.%: CaHPO ₄ - 46, Ca ₃ (PO ₄ ) g - 35, CaF ₂ - 12, NH ₄ NO ₃ - 6, Н ₂ О - 1.

The analysis of the obtained products was carried out according to the methods given in the regulatory documentation for fertilizers:

- mass fraction of calcium - according to GOST 24596.4 complexometric method;

- mass fraction of phosphates in terms of phosphorus oxide - GOST 2085.2-75 “Mineral fertilizers. Analysis Methods ”by differential photometric method for the formation of a yellow-colored phosphorovanadium-molybdenum complex;

- mass fraction of water - according to GOST 20851.4, section 1;

- mass fraction of ammonium nitrogen - according to GOST 30181.1-94;

- mass fraction of nitrate nitrogen - by the calculation method according to the difference between the total mass fraction of ammonium and nitrate nitrogen in the fertilizer, determined according to GOST 30181.1-94;

- mass fraction of free nitric acid - by the calculation method for the difference in titrations of the sum of free acids and phosphoric acid (GOST 20851.2-75). The mass fraction of phosphoric acid was determined calculated by the content of water-soluble phosphates in the sample;

- mass fraction of fluoride ion - according to GOST 24596.7-81.

Example 2

A series of similar experiments is carried out in which the content of free nitric acid in the first stage of ammonization is changed and the pH in the second stage. Table 1 shows the results of the experiments, including the experience of example 1 (p. 1) and the experience of the prototype (p. 2).

Table 1 No. p / p The content of HNO _3svob in the first stage of ammonization, wt.% PH values in the second stage of ammonization Suspension filtration performance, t / m ² hour one 0.5 4.7 10.3 2 prototype experience out 4,5 0.9 3 1,1 5,0 4.7 four 0.6 6.0 3.8 5 0.3 4.0 9,4 6 0.5 3.8 4,5 7 0.5 7.0 2,8 8 0.6 7.2 2.0

From the presented data it follows that the inventive method of ammonization in two stages with a content of free nitric acid in the first stage of 0.1 ÷ 1.0 wt.%, And a pH in the second stage of 4.0 ÷ 5.5 provides a high performance filtering precipitate of calcium phosphates . The filtering performance of the ammoniated suspension by the proposed method is more than 10 times higher than the filtering performance of the ammoniated suspension obtained in the prototype experiment.

Example 3

A series of experiments similar to Example 1 was carried out, in which the degree of calcium evolution, the residence time of the ammoniated suspension in the second stage, and the temperature of ammonization were changed. The results are shown in table 2.

table 2 No. p / p The degree of calcium excretion,% The residence time of the suspension in the second stage, min Ammonization temperature, ° С Suspension filtration performance, t / m ² hour 6 60 45 80 10,2 7 twenty 40 70 6.2 8 68 45 80 8.4 9 53 25 65 5.8 10 57 70 90 10,2 eleven 58 45 55 5.3 12 55 fifty 93 9.8

When the degree of calcium release is below 25% and above 65%, the filterability of the suspension decreases (experiments 7, 8). When the residence time of the suspension in the second stage of ammonization is less than 30 minutes, the filterability decreases. An increase in the residence time of the suspension for more than 60 minutes does not lead to an additional positive effect (experiments 9, 10). At an ammonization temperature of less than 60 ° C, filterability decreases, an increase in temperature above 90 ° C complicates the process.

Claims (2)

1. A method of producing a complex fertilizer, including the decomposition of apatite with nitric acid, cooling the nitric acid extract, followed by separating the precipitate of calcium nitrate from the mother liquor, ammonizing the mother liquor, separating the precipitate of calcium phosphates from the nitrate-phosphate solution and processing the latter into complex NP-or NPK -fertilizers, characterized in that the ammonization is carried out in two stages, maintaining in the first stage the content of free nitric acid 0.1 ÷ 1.0 wt.%, and in the second stage maintaining a pH of 4.0 ÷ 5.5. 2. The method according to claim 1, characterized in that the residence time of the ammoniated suspension in the second stage is maintained within 30 ÷ 60 minutes