RU2131404C1 - Method of preparing phosphoric fertilizers - Google Patents

Abstract

FIELD: agriculture. SUBSTANCE: method comprises decomposition of phosphate raw materials with mineral acid in the presence of monocalcium phosphate followed by granulation, drying and purification of off-gases. Monocalcium phosphate is added to mixture of phosphate raw materials and mineral acid in amount sufficient to maintain ratios (wt parts) of monocalcium phosphate to SO₃ ratio of (9.8-25):1, respectively. Mineral acid includes phosphoric and/or sulfuric acid, and phosphate raw materials include either apatite concentrate or dust- like fraction resulting from purification of off-gases in apatite concentrate production. Monocalcium phosphate constituent includes superphosphate pulp, coarse and fine fraction of final product, dust resulting from purification of gases. In order to use dust-like fraction of phosphate raw materials, dust is taken from cyclones and electric filters intended to purify apatite concentrate at 4:1 ratio, respectively. EFFECT: improved granulation and drying conditions of the phosphoric fertilizers and ecologically safe process. 4 cl, 6 ex

Description

 The invention relates to a method for producing phosphorus-containing mineral fertilizers widely used in agriculture.

 A known method of producing phosphorus-containing fertilizers by decomposing phosphate raw materials with phosphoric acid, followed by granulation and drying of the product (Double superphosphate. - M .: Chemistry, 1987, S. 134-140).

 The disadvantage of this method is the complexity of the technology by the long-term aging of the product in the warehouse, where fluoride compounds that cannot be neutralized are released.

Closest to the described by the technological essence and the achieved result is another known method for producing phosphate fertilizers, including the decomposition of phosphate raw materials with mineral acid in the presence of monocalcium phosphate, subsequent granulation, drying and purification of exhaust gases. According to this method, phosphorite is taken as a phosphate feedstock, and phosphoric acid as a mineral acid. Monocalcium phosphate (double superphosphate) is pre-mixed with phosphoric acid, and then the resulting mixture is fed into phosphorite. The ratio of monocalcium phosphate and SO ₃ ion present in phosphoric acid is (0.2 - 9.3) 5: 1, respectively. Upon preliminary mixing of phosphoric acid with monocalcium phosphate, the latter interacts with fluorine compounds to form mainly calcium fluoride and partially calcium silicofluoride. Part of the monocalcium phosphate interacts with SO ₃ ions contained in phosphoric acid to form calcium sulfate. As a result, a large amount of sediment is present in the resulting suspension, it is difficult to dose it, which causes technological difficulties. In addition, a significant part of monocalcium phosphate is lost, since it partially reacted with SO ₃ ions and fluorine compounds. During decomposition, significant amounts of dicalcium phosphate are formed, which leads to the formation of films of the latter on grains of phosphate raw materials and the degree of decomposition decreases.

 When using this method for the decomposition of apatite observation, the preparation of a finished product with a high content of free acid in it is obtained, since due to these reasons, the inhibition of the decomposition reaction occurs at the drying stage. (Auth. St. USSR N 1063798, C 05 B 1/04, 1983).

All these reasons lead to a product with a free acid content of 6-8% P ₂ O ₅ .

 We set the task to create a high-tech method for producing phosphate fertilizers with the production of products of various brands and improved properties.

The problem is solved in that in the method for producing phosphate fertilizers, including the decomposition of phosphate raw materials with mineral acid in the presence of monocalcium phosphate and subsequent granulation, drying and purification of exhaust gases, monocalcium phosphate is fed into the mixture of mineral acid and phosphate raw materials in an amount necessary to maintain the ratio of monocalcium phosphate: SO ion ₃ (in wt. Shares), equal to (9.8-25): 1, respectively. Either phosphoric and / or sulfuric acid is taken as a mineral acid, and apatite concentrate or apatite dust obtained after purification of exhaust gases during drying of apatite concentrate is taken as phosphate feedstock. This dust is captured in cyclones and electrostatic precipitators and it is supplied in the ratio of one part of the dust from electrostatic precipitators to 4 parts of dust after cyclones.

 A coarse and / or small fraction of the finished product, superphosphate pulp or dust of the product obtained after the stage of purification of the exhaust gases of the phosphorus fertilizer production process can be used as the monocalcium component. Phosphate raw materials or acids can be served both in one step, or in several, which is determined by the specific technological scheme.

 Carrying out the process by the described method avoids the disadvantages of the prototype method even when using apatite raw materials.

 The supply of monocalcium phosphate together with acid and apatite creates the conditions for better decomposition - the formation of films on phosphate grains in the form of calcium sulfate and dicalcium phosphate is excluded. The formation of dicalcium phosphate films is excluded due to the presence of monocalcium phosphate and the absence of calcium fluoride, which increases the area of formation of dicalcium phosphate. As a result, the degree of decomposition of apatite increases and the content of free acid in the pulp decreases, which significantly improves the granulation and drying conditions of the product.

 The method is illustrated by the following examples.

Example 1. Phosphate raw materials in the amount of 400 kg in the form of dust of apatite concentrate captured from the exhaust gases when it is dried in a cyclone and an electrostatic precipitator, taken in a ratio of 4: 1, respectively, and having a particle size distribution of +0.1 mm - 16%, -0.1 - 0.071 mm - 4.4%, -0.071 - 0.04 mm - 16.8%, -0.04 mm - 77.2%, mixed with monocalcium phosphate taken in the form of fine and coarse fractions of the finished product after screening with the addition of dust from cyclone in the amount of 1290.3 kg and pulp of double superphosphate in the amount of 1255 kg. The mixture is decomposed with phosphoric acid in an amount of 2778 kg in a stirred reactor. The ratio of monocalcium phosphate and SO ₃ acid ion is taken 25: 1. Then add another 600 kg of dust apatite concentrate and continue decomposition.

The pulp in the amount of 5068 kg is fed to granulation and drying. After drying, 3879 kg of dried product are obtained containing 80% of the commercial fraction. The finished product contains 47% P ₂ O ₅ assim. and 5% P ₂ O ₅ free.

 The gases after the dryer are cleaned from dust of double superphosphate and the dust is sent to the process. Post-treatment of gases from dust is carried out in absorbers. Absorption solutions are fed to the neutralization step with reuse of the purified solutions.

Example 2. Phosphate raw materials in the amount of 1000 kg in the form of apatite concentrate with fineness grinding +0.1 mm - 1.5%, -0.1 - 0.071 mm - 3%, -0.071 - 0.04 mm - 15.5% , 0.04 mm - 60%, monocalcium phosphate taken in the form of a fine fraction of the product after screening in the amount of 548 kg is mixed with phosphoric acid in the amount of 1700 kg and decomposed in the reactor without mixing devices. The ratio of monocalcium phosphate and SO ₃ acid ion is maintained at 9.8: 1.

The wet product in the amount of 3238 kg is fed to granulation. After drying the wet granules, 2944.3 kg of dried product are obtained containing 80% of the product fraction of the product. The finished product contains 46.5% P ₂ O ₅ assim. and 4.5% P ₂ O ₅ free.

 Gases after the drying apparatus are cleaned of dust in the cyclone, part of the dust is sent to the granulation stage. Gases are refined in absorbers. Absorption solutions are partially fed to granulation, the remaining solutions are sent to the neutralization stage in a closed cycle, since the purified solutions are reused in the process.

Example 3. Phosphate raw materials in an amount of 400 g in the form of apatite concentrate dust captured from the exhaust gases during drying of the concentrate in a cyclone and an electrostatic precipitator taken in a ratio of 4: 1, respectively (dust granulation in Example 1), monocalcium phosphate taken in the form of a fine product fraction after screening, cyclone dust in an amount of 752 kg, and phosphoric acid in an amount of 2963.0 kg are fed for decomposition into a stirred reactor. The ratio of monocalcium phosphate and SO ₃ acid ion is taken 17: 1. Then, at regular intervals, two more 300 kg dust portions are supplied and decomposition is continued.

The pulp in the amount of 4715 kg is served for granulation and drying. After drying, 2991 kg of dried product containing 85% of the commercial fraction is obtained. The finished product contains 46% P ₂ O ₅ assim. and 4.7% P ₂ O ₅

 After the dryer, the gases are cleaned of dust in the cyclone and sent to the process. Post-treatment of gases is carried out in the absorber. Absorption solutions are fed to the neutralization stage in a closed cycle.

Example 4. Phosphate raw materials in the form of apatite concentrate (with granular composition according to example 2) in the amount of 1000 kg, monocalcium phosphate supplied in the form of dust from a cyclone, a fine fraction of the product and superphosphate pulp in the amount of 950 kg and 1517 kg, respectively, phosphoric acid in the amount of 1296 kg and part of sulfuric acid in the amount of 81.5 kg is fed for decomposition into the reactor. The ratio of monocalcium phosphate and SO ₃ acids is maintained at 10: 1. Then another 532 kg of sulfuric acid is fed and decomposition is continued. Sulfuric acid is fed 30 minutes after the first feed.

The pulp in the amount of 4657.5 kg is served for granulation and drying. After drying, 3189 kg of dried product are obtained with a content of a commercial fraction of 75% of a commercial fraction. Product with a content of 32% P ₂ O ₅ and 3% P ₂ O ₅ free. Further, as in example 2.

Example 5. Phosphate raw materials in the form of 1000 kg of dust of apatite concentrate captured in the cyclone from the exhaust gases during its drying, having a particle size: +0.1 mm - 2%, -0.1 - 0.071 mm - 5.0%, -0.071 - 0 , 04 mm - 20% and -0.04 mm - 73%, monocalcium phosphate supplied in the form of a fine fraction of superphosphate, dust from a cyclone in an amount of 1480 kg and superphosphate pulp in an amount of 1960 kg, part of sulfuric acid in an amount of 109 kg is fed for decomposition into the reactor. The ratio of monocalcium phosphate and SO ₃ ion is maintained at 9.8: 1. Then, sulfuric acid in an amount of 815 kg and 1578 kg of dilution solutions is supplied and decomposition is continued.

The pulp in the amount of 4908 kg is served for granulation and drying. After drying, 2387.8 kg of dried product are obtained with a content of 75% of the commercial fraction. After neutralization, the finished product contains 19.0% P ₂ O ₅ assim. and 3% P ₂ O ₅ free.

 After the dryer, the gases are cleaned of dust in the cyclone and the dust is sent to the reactor. Post-treatment of gases is carried out in absorbers. Absorption solutions are fed to the reactor.

Example 6. Phosphate raw materials in the form of dust of apatite concentrate captured from the exhaust gases when it is dried in a cyclone and an electrostatic precipitator, taken in a ratio of 4: 1, respectively (with granular composition in Example 1) in the amount of 1000 kg, monocalcium phosphate supplied in the form of dust from a cyclone and a fine fraction of the product in the amount of 1290.3 kg, phosphoric acid in the amount of 1700 kg is fed for decomposition into the reactor without stirring. The ratio of monocalcium phosphate and SO ₃ acid ion is maintained at 10: 1. After decomposition, 3169 kg of wet product are obtained, which are mixed with absorption solutions in a stirred reactor. The resulting pulp in the amount of 4520 kg is fed to granulation and drying.

After drying, 2832 kg of dried product with a content of 85% of the commercial fraction are obtained. The finished product contains 46.5% P ₂ O ₅ assim. and 4% P ₂ O ₅

 The gases from the dryer are cleaned of dust in the cyclone and sent to the reactor. Post-treatment of gases is carried out in absorbers. Absorption solutions are fed into the reactor for mixing with a wet product.

 The introduction of the proposed technology for the production of phosphate fertilizers will allow to obtain phosphate fertilizers using apatite concentrate and its dust trapped from the exhaust gases after drying the concentrate in an environmentally friendly way.

Claims (4)

1. A method of producing phosphate fertilizers, including the decomposition of phosphate raw materials with mineral acid in the presence of monocalcium phosphate, subsequent granulation, drying and purification of exhaust gases, characterized in that monocalcium phosphate is fed into the mixture of phosphate raw material and mineral acid in an amount necessary to maintain the ratio in the mixture (wt. fractions) monocalcium phosphate: SO ₃ ion, equal to (9.8 - 25): 1, respectively.  2. The method according to claim 1, characterized in that phosphoric and / or sulfuric are taken as a mineral acid, and the phosphate feed is supplied either as an apatite concentrate or as a dust fraction obtained after purification of exhaust gases from the production of apatite concentrate.  3. The method according to claims 1 and 2, characterized in that as the monocalcium phosphate component use superphosphate pulp, a large and / or small fraction of the finished product, dust obtained after the gas purification stage.  4. The method according to PP. 1 - 3, characterized in that when using a pulverized fraction as a phosphate feed, dust is taken from cyclones and electrostatic precipitators for purification of apatite concentrate at a ratio of 4: 1, respectively.