RU2346916C1 - Method of obtaining one-way phosphoric fertiliser out of lean raw phosphate material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention concerns methods of obtaining one-way phosphoric fertilisers out of lean raw phosphate material. Method involves decomposition of part of raw phosphate material by sulfuric acid, neutralisation of obtained pulp by second part of raw phosphate material, and further processing of obtained pulp at high temperature. At the decomposition stage sulfuric acid of 25-35% concentration is fed in amount of 12.3-15.0 weight parts per unit of P₂O₅ of raw phosphate material. Raw material part involved at the decomposition stage comprises 48-70% of its total weight. Phosphoric acid can be fed at pulp neutralisation stage together with the rest of raw phosphate material in amount providing for ratio of P₂O₅ acid: P₂O₅ raw phosphate material=1:(0.5-1.6). Pulp obtained after neutralisation stage is processed either in granulation dryer or in rotating furnace.

EFFECT: obtaining fertilisers with required balance of nutrient elements (calcium and sulfur beside phosphor).

3 cl, 4 ex

Description

The invention relates to a method for producing unilateral phosphorus fertilizer from low-grade phosphate feedstock. A survey of the soils of agricultural lands of the Russian Federation in recent years has revealed a tendency to a decrease in the content of such elements important for plants as calcium and sulfur in soils. The proportion of land with insufficient content of these elements is 30-40% of the total agricultural land. Sulfur is part of some amino acids and proteins and is involved in the processes of photosynthesis, plant respiration, nitrogen and carbohydrate metabolism, the formation of chlorophyll and a number of vitamins. Calcium is necessary for plants to develop the root system of plants. Against the background of depletion of soils by these elements, the phosphorus content in soils remains at a sufficiently high level and tends to increase continuously.

The relevance of maintaining the balance of nutrients makes it necessary to involve poor phosphorite ores in the production of mineral fertilizers suitable for consideration as products containing not only the main nutrient component P ₂ O ₅ , but also a number of additional macroelements taken into account by agrochemists, such as sulfur and calcium. The development of such products will not only expand the range of mineral fertilizers, but will also save expensive apatite raw materials.

Currently, the most widely known methods for producing fertilizers from low-grade phosphate raw materials by decomposition of the latter with sulfuric acid. Thus, developments are known for producing simple superphosphate from low-quality phosphorites (for example, Florida, according to two schemes with two- and one-stage decomposition of raw materials)

According to option 1, in the first stage, phosphorite is decomposed with sulfuric acid, supplied in an amount of 70-80% of the stoichiometric norm. The reaction at this stage proceeds quickly, and the resulting semi-liquid pulp enters the chamber, where it turns into a porous mass. After 2 hours in the chamber, the mass is sent to the second stage of decomposition, another 10-30% of sulfuric acid is fed there. The resulting product is sent to the ripening warehouse. The matured superphosphate is granulated upon wetting with water, dried and classified.

In option 11, the decomposition of phosphorite by sulfuric acid (90-100% of stoichiometry) occurs in a continuous reactor and is accompanied by a strong evolution of gases. The maximum residence time of the mixture in the reactor is up to 3 seconds. The main decomposition occurs in the chamber, which is located under the reactor. The residence time of the mass in it is about 2 hours. The temperature of the reaction mass is quite high and sometimes reaches 180 ° C. After 2 hours in the chamber, the mass is unloaded mechanically, dampened with water (50 ° C) and sent to the warehouse for ripening.

The disadvantage of this method is the high moisture content in the product (8-12%), which will require significant energy consumption for its drying. (“Research on the development of phosphorus fertilizer technology using phosphorite raw materials of various deposits.” M., 1990, NIITEKHIM, Overview, p.16).

There is also known a method for producing granular neutralized superphosphate from poor phosphate feedstock, in which a suspension of a portion of the phosphate feedstock is sent to decomposition with sulfuric acid at a concentration of 93%, taken in an amount of 2.5-8.7 wt.h. per unit of P ₂ O ₅ phosphate raw materials. Next, the remainder of the suspension of phosphate feed is fed to the pulp. Then, neutralization with ammonia and ammophos pulp is carried out (RF patent No. 2156754, class С05В 1/06, publ. September 27, 2000).

Using this method, a fertilizer containing phosphorus and nitrogen is obtained, and Ca is contained therein only in the form of CaSO _{4 of a} practically insoluble compound in water and not digestible by plants. This is because the final neutralization is carried out by ammonia. The process is “hard” and translates all Ca ions into CaSO ₄ .

Closest to the described by the technical nature and the achieved result is another well-known method for producing one-way fertilizer, namely the production of granular superphosphate from poor raw materials, protected by author. testimonial. USSR No. 1682355, class С05В 1/02, publ. 10/07/91, the Method includes the decomposition of part of the phosphate feedstock with sulfuric acid, the neutralization of the obtained pulp by the second part of the phosphate feedstock and the subsequent processing of the obtained pulp at elevated temperature. Sulfuric acid with a concentration of 75%, taken in an amount of 1.6-2.5 parts by weight, is fed to the decomposition step by this method. per unit of phosphate feedstock and 42-69% of the total amount of phosphate feedstock (depending on the grade of phosphate feedstock). The decomposition temperature is 100-105 ° C, the time is 1-2 hours. The process is conducted in the presence of a large number of absorption effluents. Then, the resulting pulp is fed into a granulator-dryer, where the rest of the phosphate feed and retur are simultaneously introduced. Drying is carried out by flue gases with an inlet temperature of 900 ° C, at the outlet - 155 ° C. The disadvantage of this method is that when processing phosphate raw materials containing less than 24% P ₂ O ₅ , such as phosphate raw materials of the Yegoryevsky and Vyatka-Kama deposits, its decomposition will not be sufficient and will make it unprofitable to use. In addition, the calcium and sulfur in the product are in insoluble form, only in the form of CaSO ₄ .

Our task was to develop a method for producing unilateral phosphorus fertilizer from poor phosphate raw materials, which will have the necessary balance of nutrients (except for phosphorus - calcium and sulfur).

The problem is solved in the proposed method, including the decomposition of a portion of the phosphate feedstock with sulfuric acid, the neutralization of the obtained pulp with the second part of the phosphate feedstock and the subsequent processing of the obtained pulp at elevated temperature. According to this method, sulfuric acid with a concentration of 25-35% in an amount of (1.23-13.2) parts by weight is fed to the decomposition stage. per unit of P ₂ About ₅ .

At the stage of decomposition serves part of the feedstock in an amount of 48-70% of its total mass. It is possible at the stage of neutralization to increase the content of P ₂ O ₅ in the finished product into the pulp of decomposition simultaneously with the remaining part of the phosphate feedstock to introduce phosphoric acid in an amount that provides a ratio of P ₂ O _{5 to-you:} P ₂ O _{5 f.s.} = 1: (0.5-1.6).

The pulp obtained after the neutralization step is sent either to a granulator dryer or to a rotary kiln.

The essence of the method is as follows.

The main in the proposed method is the concentration and amount of sulfuric acid supplied to the decomposition stage. The kinetics of the decomposition of phosphate feedstock by sulfuric acid depends on the quality of the phosphate feedstock. Our studies have shown that the maximum decomposition rate of poor phosphorites is achieved at acid concentrations of 25-35% and its amount of 12.3-15 wt.h. for 1 h. P ₂ O ₅ phosphate raw materials. In the first stage (decomposition stage), with such an amount of sulfuric acid, the completely sulfuric acid decomposition of the raw material takes place. The result is pulp, phosphogypsum and small impurities of undecomposed phosphate feed. Reducing the acid concentration below 25% will lead to unjustified “thinning” of the mass, which will significantly complicate the process both at the stage of decomposition and at the stage of drying of the product. An increase in the concentration of sulfuric acid above 35% slows down the decomposition of poor phosphate raw materials.

The norm of sulfuric acid is strictly regulated in the range of 12.3-15 wt.h. 1 unit of P ₂ O ₅ phosphate raw materials, since a decrease in it reduces the degree of decomposition of the raw material, and an increase leads to the content of free sulfuric acid in the decomposition pulp and, as a result, sulfation upon addition of the second part of the phosphate raw material.

Carrying out the process under the proposed conditions allows us to separate two sequentially occurring reactions (sulfuric acid and phosphoric acid decomposition). Separation of these processes is convenient when creating a “flexible” technological scheme, representing the possibility of varying the type and ratio of raw materials in order to obtain a wide range of products with different contents of nutrient components. With this process management, calcium in the finished product is not only in the form of CaSO ₄ , but also in the form of citrate-soluble salts such as CaHPO ₄ and Ca (H ₂ PO ₄ ) ₂ . The need to separate the processes of sulfuric acid and phosphoric acid decomposition also determines the rate of phosphate feed to the first stage. The technology involves the introduction of phosphoric acid in the second stage. The amount of acid in each case is selected based on, on the one hand, from obtaining the required grade of fertilizer (according to the content of P ₂ O ₅ ), and on the other hand, from the necessary degree of decomposition of the raw material. A decrease in the acid norm will lead to a decrease in the degree of decomposition, and an increase will acidify the finished product, since free acid will remain in it.

Using the proposed method will allow to process poor phosphate raw materials of various deposits and to obtain a complex product containing, in addition to phosphorus, calcium and sulfur. Calcium and sulfur in it are in a form assimilated by plants.

The method is illustrated by the following examples.

Example 1. 1000 kg of Egorievsky phosphorite - 70% of the total amount, is decomposed in the reactor with sulfuric acid at a concentration of 30%, taken in an amount of 3000 kg (15 parts by weight per unit of P ₂ O ₅ phosphate feed). Decomposition is carried out at a temperature of 90 ° C until a decomposition temperature of 95% is reached. The resulting decomposition of 4000 kg of pulp is fed into the second reactor, where the remaining Egorievsky phosphorite in the amount of 438 kg is fed. The ratio of the amount of pulp and the second part of the phosphate feedstock is 1: 0.11. After the decomposition of an additional amount of phosphate feedstock in the second reactor at a temperature of 90 ° С, the pulp is fed into a BHS type apparatus, where it is dried and granulated. Drying is carried out by flue gases. There retur is supplied in the amount of 4400 kg, which provides a ratio of retur: pulp 1: 1. At the exit of the apparatus receive a product containing P ₂ O ₅ total. 12.3%, P ₂ O ₅ assim. 11.1%, SO ₃ aq. 22.3%, CaO aq. 13.6%.

Example 2

1000 kg of Chilisay phosphorite - 68% of the total amount, is decomposed in the reactor with sulfuric acid at a concentration of 30%, taken in an amount of 3170 kg (13.2 parts by weight per unit of P ₂ O ₅ raw materials). Decomposition is carried out at a temperature of 85 ° C until a degree of decomposition of 93% is achieved. The resulting decomposition of 4200 kg of pulp is fed into the second reactor, where 143 kg of extraction phosphoric acid with a concentration of 30% P ₂ O ₅ and the remaining Chilisai phosphorite in the amount of 460 kg are fed. The ratio of P ₂ O ₅ EPA: P ₂ O ₅ phosphorite is 1: 0.5. The ratio of the amount of pulp and the second part of the phosphate feedstock is 1: 0.11. After the decomposition of an additional amount of phosphate feedstock in the second reactor at a temperature of 85 ° C, the pulp is fed into a rotary kiln, where it is heat treated. Heat treatment is carried out by flue gases with an outlet temperature of at least 250 ° C. Retur in the amount of 2900 kg is fed there, which ensures a retur: pulp ratio of 0.6: 1. At the exit of the apparatus receive a product containing P ₂ About ₅ total. 16.3%, P ₂ O ₅ ass. 15.0%, SO ₃ water. 19.8%, CaO aq. 16.5%.

Example 3

1000 kg of Vyatka-Kama phosphorite - 54% of the total amount, decomposed in the reactor with sulfuric acid at a concentration of 35%, taken in the amount of 2860 kg (12.4 parts by weight per unit of P ₂ O ₅ raw material). Decomposition is carried out at a temperature of 95 ° C until a degree of decomposition of 90% is achieved. The resulting decomposition of 3860 kg of pulp is fed into the second reactor, where 760 kg of extraction phosphoric acid with a concentration of 33% P ₂ O ₅ and the remaining Vyatka-Kama phosphorite in the amount of 856 kg are fed. The ratio of P ₂ O ₅ EPA: P ₂ O ₅ phosphorite is 1: 1.5. The ratio of the amount of pulp and the second part of phosphate raw materials 1: 0.22. After the decomposition of an additional amount of phosphate feedstock in the second reactor at a temperature of 95 ° C, the pulp is fed into a BHS type apparatus, where it is dried and granulated. Drying is carried out by flue gases. Retur in the amount of 6020 kg is fed there, which ensures a retur: pulp ratio of 1.1: 1. At the exit of the apparatus, a product is obtained containing P ₂ O ₅ total 21.8%, P ₂ O ₅ assim. 19.9%, SO ₃ aq. 16.4%, CaO aq. 14.2%.

Example 4

1000 kg of Kingisepp phosphorite - 48% of the total amount, is decomposed in the reactor with sulfuric acid at a concentration of 25%, taken in an amount of 3440 kg (12.3 parts by weight per unit of P ₂ O ₅ phosphate feed). Decomposition is carried out at a temperature of 97 ° C until a degree of decomposition of 98% is achieved. The resulting decomposition of 4440 kg of pulp is fed into the second reactor, where 1350 kg of extraction phosphoric acid with a concentration of 37% P ₂ O ₅ and the remaining Kingisepp phosphorite in the amount of 1090 kg are fed. The ratio of P ₂ O ₅ EPA: P ₂ O ₅ phosphorite is 1: 0.25. After the decomposition of an additional amount of phosphate feedstock in the second reactor at a temperature of 91 ° C, the pulp is fed to an AG-type apparatus, where it is mixed with reture and granulated. Retur is supplied in an amount of 13800 kg, which provides a ratio of retur: pulp 2: 1. After granulation, the obtained granules are dried. The output is a product containing P ₂ O ₅ total. 31.5%, P ₂ O ₅ assim. 29.6%, SO ₃ aq. 13.2%, CaO water. 17.6%.

Claims (3)

1. A method of producing one-sided phosphorus fertilizer from poor phosphate feedstock, comprising decomposing a portion of the phosphate feedstock with sulfuric acid, neutralizing the obtained pulp with a second portion of phosphate feedstock and subsequent processing of the obtained pulp at an elevated temperature, characterized in that sulfuric acid with a concentration of 25- is fed to the decomposition step 35% in the amount of 12.3-15.0 parts by weight per unit of P ₂ O ₅ phosphate feed. 2. The method according to claim 1, characterized in that at the stage of decomposition serves part of the feedstock in an amount of 48-70% of its total mass, and phosphoric acid in an amount providing a ratio of P ₂ is introduced into the pulp neutralization step simultaneously with the remaining part of the phosphate feedstock. O ₅ acid: P ₂ O ₅ phosphate feed, equal to 1: (0.5-1.6). 3. The method according to claim 1, characterized in that the processing of the pulp obtained after the neutralization step is carried out either in a granulator-dryer or in a rotary kiln.