RU2389712C2 - Method for acid treatment of poor phosphorites - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to fertiliser industry, specifically to production of compound fertilisers through acid decomposition of natural phosphates. The method for acid treatment of phosphorites involves preliminary calcination of mineral raw material, acid decomposition, separation of phosphoric acid solution from insoluble residue with its subsequent processing into phosphorous compound fertiliser. After calcination the mineral material is crushed to 3.1-5 mm particles. The crushed material undergoes acid decomposition at 10 - 30°C using hydrochloric acid, nitric acid or a mixture of nitric acid and sulphuric acid. The crushed material undergoes acid decomposition using hydrochloric acid containing 10-20% hydrogen chloride, or nitric acid containing 45-55% nitric acid, or a mixture of nitric acid and sulphuric acid containing up to 25 wt % sulphuric acid. The phosphoric acid solution is separated from the insoluble residue through filtration at 50-60°C.

EFFECT: method increases output due to acceleration of filtration of insoluble residue, removal of iron and aluminium impurities from phosphoric acid, exclusion of steps for diluting and evaporating phosphoric acid solution.

3 cl, 8 tbl, 10 ex

Description

The invention relates to the field of fertilizer industry, in particular to the production of complex mineral fertilizers by acid decomposition of natural phosphates.

The present invention allows to engage in the production of qualified phosphate fertilizers low-quality mineral raw materials, characterized by a low content of phosphorus oxide V (P ₂ About ₅ ), contaminated with impurities of iron, aluminum and other transition metals, and also containing up to 20 wt.%, Insoluble in silicate rocks acid forming a hardly separable residue. An example of such raw materials is the phosphate rock of the Vyatka-Kama, Egorievsky, Polpinsky deposits.

A known method of producing complex fertilizers, protected by RF patent No. 2145316, CL. C05B 11/06, publ. 02/02/10. The method includes decomposition of apatite concentrate with nitric acid, precipitation of calcium nitrate by crystallization, neutralization of nitrogen-phosphate extract with ammonia, evaporation, mixing with a melt of ammonium nitrate and potassium salt, granulation and drying of the finished product. After separation of calcium nitrate, the nitrogen-phosphate extract is mixed with low-quality phosphate raw materials in the ratio of P ₂ O ₅ phosphorite to P ₂ O ₅ apatite as 0.05-0.8: 1 before or after ammonization or after evaporation.

The disadvantage of this method is the high content of impurities of iron and aluminum in the final product, which leads to losses of assimilable phosphorus in the final product. Also, the issue of separation of a hardly filtered insoluble silicate residue, which also passes into the final product and, being a ballast impurity, impairs its quality, is not considered. And finally, the described invention does not allow to process low-quality phosphate rock raw materials without the use of apatite concentrate.

A known method of processing the Vyatka-Kama phosphorite, protected by RF patent No. 2174969, Cl. C05B 11/06, publ. 2001.10.20.

The phosphate rock of Vyatka-Kama phosphorite before treatment with nitric acid is treated with stirring with an alkaline solution, preferably 3% sodium hydroxide solution at 95-100 ° C for 2-4 hours, separated from the alkaline solution by filtration, then treated with non-concentrated nitric acid, separated insoluble residue by filtration, the resulting solution is processed into fertilizer. The insoluble residue is washed with a spent alkaline solution, the resulting solution containing sodium nitrate and humate can be introduced into the fertilizer to increase its nutritional value. The method allows to process Vyatka-Kama phosphorites without preliminary calcining the raw material.

The disadvantages of this method are the need for preliminary alkaline processing of raw materials, which complicates the technological scheme of processing. The filtering performance of the acid insoluble residue remains low, which requires the use of complex and expensive equipment - filter presses. Despite the removal of humic acids, noticeable foaming persists. The separation of transition metal compounds is not considered.

Closest to the claimed technical essence and the achieved result, selected as a prototype, is a method protected by RF patent No. 2154045, Cl. C05B 11/06, publ. 08/08/10. The authors propose phosphorite raw materials, in particular poor phosphorites of the Vyatka-Kama deposit, to be calcined at a temperature of 850-1150 ° C, then decomposed calcined phosphorite with diluted nitric acid, diluted the resulting suspension with water in a ratio of 1-1.5: 1, removed by settling insoluble residue and evaporate the added water. Then the authors propose to separate calcium nitrate by freezing, ammonize the solution and process it into a fertilizer such as NP or NPK by evaporation, granulation and drying.

A serious drawback of this method is the need to dilute the suspension and subsequent evaporation of the phosphoric acid solution, which is associated with increased heat consumption, the introduction of an additional stage in the processing process, enhanced by corrosion of the equipment. In addition, the issues of contamination of the phosphoric acid solution with transition metal impurities, the possibility of separating the insoluble residue by filtration and other methods, the possibility of using other mineral acids other than nitric acid are not being addressed.

The objective of the present invention is to improve the method of acid processing of poor phosphorites with the possibility of obtaining qualified phosphoric and complex fertilizers that do not contain ballast impurities and are not digestible by plants phosphorus, based on poor phosphorite raw materials, in particular phosphate concentrate Vyatsko-Kamsky, Egoryevsky, Polpinsky deposits.

The technical result from the use of the invention is to increase productivity by accelerating the filtering of the insoluble residue, removing impurities of iron and aluminum from the phosphoric acid solution, eliminating the stages of dilution and evaporation of the phosphoric acid solution.

This result is achieved by the fact that in the method of acid processing of poor phosphorites, including preliminary calcination of mineral raw materials, acid decomposition, separation of the phosphoric acid solution from the insoluble residue, followed by its processing into phosphoric or complex fertilizer, after calcining the mineral raw materials, it is crushed to particles of size 3.1-5 mm, while the acid decomposition of the crushed raw materials is carried out at room temperature. The acid decomposition of crushed raw materials is carried out with hydrochloric or nitric acids or a mixture of nitric and sulfuric acids containing up to 25 wt.% Sulfuric acid. Phosphoric acid solution is separated from the insoluble residue by filtration at a temperature of 50-60 ° C.

Hydrochloric, nitric acids or a mixture of nitric and sulfuric acids are used for decomposition, decomposition is carried out at room temperature, after which the insoluble residue is separated by filtration at 50-60 ° C.

Thus, in order to achieve the indicated technical result, it is proposed to subject phosphate minerals after preliminary firing to dispersion, which allows changing the structure of the insoluble residue and improving the conditions of its separation. At the same time, due to the transformations occurring during the firing process and the selection of acid decomposition conditions, impurity compounds of iron, aluminum, and other transition metals are passivated. All this makes it possible to obtain phosphorus and complex mineral fertilizers that do not contain ballast impurities and indigestible phosphorus, using poor phosphorites of the Vyatka-Kama, Egorievsky, Polpinsky deposits as raw materials.

The method is as follows.

Phosphate raw materials, in particular the concentrate of poor phosphorites of the Vyatka-Kama, Egorievsky, Polpinsky deposits, are calcined at a temperature of 900-1100 ° C (preferably 950-1050 ° C). Lowering the firing temperature leads to a deterioration in the quality of the calcined intermediate, an increase can lead to melting of the charge and be accompanied by loss of phosphorus. The use of lumpy raw materials of 10-100 mm is preferable, however, it is possible to use larger (up to 50-70 cm) or small pieces (0.5-10 mm) and even phosphorite flour (particle size 50-200 microns). The duration of calcination depends on the particle size and is 10-120 minutes, preferably 20-60 minutes.

The calcined phosphate feed is ground and dispersed. The particle size of the natural phosphate sent for acid decomposition should be 3.1-5 mm, preferably 3.1-4.0 mm. Smaller particles worsen the conditions for separation of the insoluble residue (clogged filters, slowly precipitate upon settling), larger ones dissolve more slowly in acid.

The crushed feed is decomposed with mineral acids, preferably hydrochloric or nitric, or a mixture of nitric and sulfuric acids. The use of pure sulfuric acid is undesirable, since a viscous, thick pulp is formed, the release of phosphorus from which is difficult. The process is carried out with vigorous stirring of the reaction mass. The temperature of the process is 10-30 ° C, preferably 20-25 ° C (room). An increase leads to a transition to the solution of impurity compounds, primarily iron and aluminum, a decrease increases the viscosity of the system and decreases the yield of phosphorus in the solution. The preferred acid consumption is 400-600 g of 100% hydrochloric acid per 1 kg of non-calcined phosphorite (particularly preferably 1.8-2.1 mol of Hcl per 1 mol of Ca contained in the feed) or 950-1150 g of 100% nitric acid per 1 kg non-calcined phosphorite (particularly preferably 2.2-2.6 mol of HNO ₃ per 1 mol of Ca). It is possible to replace up to 25% nitric acid with sulfuric, in a molar ratio of 2: 1. The concentration of acids used is: 10-20% - hydrochloric, 45-55% - nitric, up to 60% - sulfuric. Increasing the concentration of acids increases the viscosity of the system, reducing the rate of decomposition of phosphate raw materials and making it difficult to separate the insoluble residue, lowering leads to excessive dilution of the solutions and increase the volume of equipment. The time of the process depends on the above factors (temperature, stoichiometry and acid concentration, particle size distribution of mineral raw materials) and is 60-150 min. Under these conditions, the degree of phosphorus release into the solution is 98-99%, and most of the impurities of iron and aluminum (70-90%) remain in the insoluble residue.

The separation of the insoluble residue is carried out using known procedures on standard equipment, for example, sedimentation, centrifugation, filtration on vacuum filters and filter presses. It is preferable to use vacuum filters of drum, belt types and the like. To facilitate these operations, it is possible to heat the pulp to 50-60 ° C to reduce viscosity. An increase in temperature above 60 ° C is undesirable, since it can lead to the release of transition metal impurities into a phosphoric acid solution. The insoluble residue is washed and discarded. In the future, it can be used as fillers or as a raw material for the isolation of valuable impurity compounds contained in it. Wash water is combined with a phosphoric acid solution.

The filtered phosphoric acid solution is neutralized. As a neutralizer, it is possible to use calcium carbonate (chalk or limestone), calcium oxide or hydroxide, ammonia and its aqueous solutions, hydroxides or carbonates of sodium or potassium. It is preferable to use chalk or calcium oxide to neutralize the hydrochloric acid solutions and ammonia, ammonia water, hydroxide or potassium carbonate to neutralize the nitric acid solutions. From calcium nitric acid solutions, excess calcium can be previously isolated by known methods (by freezing, evaporating and crystallizing from a supersaturated solution, precipitation with sulfatanions).

The invention can be illustrated by the following examples.

Example 1

Samples of natural phosphorites A, B and C were taken, the chemical composition of which is shown in Table 1. Mineral A was crushed phosphorite with a particle size of <100 μm, mineral B was lump phosphorite with a particle size of 10-400 mm, and mineral C was crushed phosphorite with a particle size <350 μm. Samples were calcined in a muffle furnace at a temperature of 900-1050 ° C for 15-60 minutes. The chemical composition of calcined phosphorites is given in table 1. As can be seen, under these conditions there is a complete burnout of organic and decomposition of carbonate-containing impurities, phosphorus loss is not observed. With an increase in the particle size of the mineral, an increase in the calcination time is required. The analysis of the components was carried out according to GOST (GOST 24596.1-81 - determination of fluorine, GOST 24596.3-81 - phosphorus, GOST 3594.13-93 - aluminum, GOST 2642.5-97 - iron, GOST 24596.5-81 - calcium).

Table 1 The chemical composition of the starting and calcined phoforites Phosphorite Calcination conditions Content, wt.% Temperature ° C Time min Sa P ₂ O ₅ F CO ₃ ^2- C org ^- Fe ₂ O ₃ Al ₂ O ₃ But* BUT - - 26,4 21.6 2,3 9.2 0.2 5.1 2.5 16.1 AT - - 26.1 20.5 2.1 12.6 0.25 5.9 3.2 23.8 FROM - - 31,4 27.5 2,4 0 0 4.4 2.0 15,5 A-1 900 thirty 28.3 23,2 2.5 0.1 0 5.5 2.7 17.3 A-2 1050 thirty 28.3 23,2 2.5 0 0 5.5 2.7 17.3 IN 1 1000 thirty 28.7 22.5 2,3 0.5 0 6.5 3,5 26.1 IN 2 1000 60 28.8 22.6 2,3 0 0 6.5 3,5 26.2 S-1 1000 fifteen 31,4 27.5 2,4 0 0 4.4 2.0 15,5 * - insoluble in acid residue

Example 2

To 100 parts of non-calcined phosphorite A from Example 1, 254 parts of 20% hydrochloric acid were added at 50 ° C. over 30 minutes with vigorous stirring. Then the suspension was kept at the same temperature for 60 minutes, while continuing stirring. The process was accompanied by intense foaming, the volume of the foam: the volume of the suspension was 10: 1. After the reaction, the mother liquor was separated from the precipitate by settling and filtering (filter cloth - polypropylene, vacuum - 0.5 atm) at the same temperature, the insoluble residue was washed on the filter. The sedimentation rate did not exceed 3 mm / h, the filtering capacity for the wet residue was <8 kg / m ² · h. The degree of extraction of phosphorus in the solution was 95.5%, iron and aluminum - 51% (hereinafter, the total amount of the component in the mother liquor and wash water is considered).

Example 3

To 100 parts of calcined phosphorites A-1, A-2 from Example 1, 242 parts of 20% hydrochloric acid were added at room temperature over 15 minutes with vigorous stirring. Then the suspension was kept at the same temperature for 60 minutes, while continuing stirring. No foaming was observed. After the reaction, the mother liquor was separated from the precipitate at 50 ° C, the insoluble residue was washed on the filter. The filtration performance and the outputs of phosphorus, iron and aluminum in the solution are shown in table 2.

table 2 Decomposition of calcined phosphorite A Phosphorite Filtration performance, kg / m ² · h The output in the solution, wt.% P ₂ O ₅ Fe Al A-1 one hundred 98.3 23.7 25,2 A-2 130 99.0 14.5 12.1

Example 4

To 100 parts of calcined phosphorites A-1, A-2 from Example 1, 226 parts of 52% nitric acid were added at room temperature over 15 minutes with vigorous stirring. Then the suspension was kept at the same temperature for 90 minutes, while continuing stirring. No foaming and emission of nitrogen oxides was observed. After the reaction, the mother liquor was separated from the precipitate at 60 ° C, the insoluble residue was washed on the filter. The filtration performance and the outputs of phosphorus, iron and aluminum in the solution are shown in table 3.

Table 3 Decomposition of calcined phosphorite A Phosphorite Filtration performance, kg / m ² · h The output in the solution, wt.% P ₂ O ₅ Fe A1 A-1 80 98.1 12.1 11.9 A-2 110 99,2 11.1 15.8

Example 5

Calcined phosphorites B-1, B-2 were crushed and dispersed using a set of sieves. Fractions with different particle sizes were treated with hydrochloric acid as described in Example 3, increasing the decomposition time from 60 minutes to 90 minutes. The insoluble residue was filtered at 50 ° C (see example 3). The filtering performance and the outputs of phosphorus, iron and aluminum in the solution are shown in table 4.

Table 4 Decomposition of calcined phosphorite B Phosphorite Granulometric composition, mm Filtering performance,
kg / m ² · h The output in the solution, wt.% P ₂ O ₅ Fe Al IN 1 3-5 170 95.3 25.6 21.5 IN 1 <3 90 97.7 28.0 26.2 IN 2 5-10 930 94.5 10.8 9.9 IN 2 4,5-5 890 97.0 11.6 10,2 IN 2 4-4.5 910 98.2 13.1 14,4 IN 2 3.1-4 940 98.9 14.6 12.7 IN 2 0.2-3.1 710 99.3 16.5 11,4 IN 2 <0.2 180 98.9 18.3 16,0

Example 6

Calcined phosphorites B-1, B-2 were crushed and dispersed using a set of sieves. Fractions with different particle sizes were treated with nitric acid as described in Example 4, increasing the decomposition time from 90 minutes to 105 minutes. The insoluble residue was filtered at 60 ° C (see example 4). The filtering performance and the outputs of phosphorus, iron and aluminum in the solution are shown in table 5.

Example 7

Calcined phosphorite C-1 was dispersed using a set of sieves. Fractions with different particle sizes were treated with hydrochloric acid as described in Example 3. The insoluble residue was filtered (see Example 3). The filtering performance and the outputs of phosphorus, iron and aluminum in the solution are shown in table 6.

Table 6 Decomposition of calcined phosphorite C-1 Grand composition, microns Filtration performance, kg / m ² · h The output in the solution, wt.% P ₂ O ₅ Fe Al 200-350 250 99,2 15,5 14.9 50-200 110 98.6 14.3 14.0 <50 fifty 99.0 19.8 21.1

Example 8

158 parts of 52% nitric and 27 parts of sulfuric acid diluted to a concentration of 40-98% were added to 100 parts of calcined B-2 phosphate of the 3.1-5 mm fraction. The conditions for the decomposition and separation of the insoluble residue are the same as in Example 4. The filtration performance of the suspension is shown in Table 7. When using phosphorite B-2 with a particle size of less than 1 mm, the filtration performance was reduced to 200-250 kg / m ² · h even when using diluted acid.

Table 7 Decomposition of phosphorite B-2 with a mixture of sulfuric and nitric acids The concentration of H ₂ SO ₄ , wt.% Filtration performance, kg / m ² · h 40 670 60 550 80 40 98 <1

Example 9

158 parts of 52% nitric and 40-60 parts of 60% sulfuric acid were added to 100 parts of calcined B-2 phosphate of the 3.1-5 mm fraction. The conditions for decomposition and separation of the insoluble residue are the same as in example 4. The filtering performance of the suspension are shown in table 8.

Table 8 Decomposition of phosphorite B-2 with a mixture of sulfuric and nitric acids The amount of H ₂ SO ₄ , parts by weight Filtration performance, kg / m ² · h 40 505 fifty 440 60 210

Example 10

Calcined phosphorite B-2 was crushed and dispersed using sieves. 1000 parts of the 3.1-4 mm fraction were mixed with 2600 parts of nitric acid at a concentration of 54% and kept at room temperature for 105 minutes with vigorous stirring. The resulting pulp was filtered on a vacuum filter at 60 ° C. Received 600 wet sediment and 3000 parts of nitric phosphate solution (AFR), the filtering capacity was 550 kg / m ² · h The precipitate was washed on the filter with 1100 parts of recycle precipitate washing water, 450 parts of the precipitate and 1250 parts of washing water were obtained. AFR was cooled to -5 ° C, while Ca (NO ₃ ) ₂ · 4H ₂ O crystallized in an amount of 1000 parts. Chilled AFR in an amount of 2000 parts was mixed with wash water (1250 parts), gaseous ammonia was passed through the solution. Ammonized AFR (AAFR) was filtered, a precipitate of 1000 parts was washed with 1000 parts of water. Wash water in an amount of 1150 parts was used to wash the insoluble residue of acid decomposition. After drying the washed precipitate residue, 370 parts of a powder containing 40.3 wt.% P ₂ O ₅ , all phosphorus in citrate-soluble form, were obtained. After evaporation of the AAFR filtrate, 740 parts of a complex NP fertilizer were obtained containing 17.5% P ₂ O ₅ , 19% N, all phosphorus in a water-soluble form.

Thus, the proposed method allows to obtain qualified phosphorus and complex fertilizers that do not contain ballast impurities and phosphorus that is not digestible by plants, based on poor phosphorite raw materials, in particular, phosphate concentrate of the Vyatsko-Kamsky, Yegoryevsky, Polpinsky deposits.

This increases the productivity of the process by accelerating the filtering of the insoluble residue, removing impurities of iron and aluminum from the phosphoric acid solution, eliminating the stages of dilution and evaporation of the phosphoric acid solution.

Claims (3)

1. The method of acid processing of poor phosphorites, including preliminary calcination of mineral raw materials, acid decomposition, separation of the phosphoric acid solution from the insoluble residue, followed by its processing into phosphoric or complex fertilizer, characterized in that after calcining the mineral raw materials they are crushed to particles of size 3 , 1-5 mm, while the acid decomposition of the crushed raw materials is carried out at a temperature of 10-30 ° C with hydrochloric acid or nitric acid or a mixture of nitric and sulfuric acids. 2. The method according to claim 1, characterized in that the acid decomposition of the crushed material is carried out with hydrochloric acid containing 10-20% hydrogen chloride, or nitric acid containing 45-55% nitric acid, or a mixture of nitric and sulfuric acids containing up to 25% massive sulfuric acid. 3. The method according to claim 1, characterized in that the phosphoric acid solution is separated from the insoluble residue by filtration at a temperature of 50-60 ° C.