RU2217400C2 - Method for preparing complex fertilizers - Google Patents

Abstract

FIELD: fertilizers. SUBSTANCE: invention relates to methods for preparing complex fertilizers, in part, nitrogen- phosphorus-potassium fertilizers. Method for preparing complex fertilizers involves neutralization of phosphoric acid with potassium-containing alkaline reagent, mixing the prepared pulp with sulfate-containing reagents at pH = 3.8-5.3, granulation and drying the ready product. Phosphoric acid is neutralized preliminary with phosphoric acid slime in the ratio P₂O₅ of slime/P₂O₅ of acid = (0.02-0.4): 1. Sulfuric acid and ammonium sulfate are used as sulfate-containing reagent in the ratio = H₂SO₄ : (NH₄)₂SO₄ = (0.02-0.09):1. Method provides utilization of slimes obtained in treatment of phosphoric acid and rendering harmless of phosphate solutions and also ammonium sulfate that as by-side product in many chemical and petrochemical manufactures. EFFECT: improved preparing method, simplified method, reduced cost in preparing high-quality fertilizers. 3 cl, 1 tbl

Description

 The present invention relates to methods for producing complex fertilizers, in particular nitrogen-phosphorus-potassium fertilizers based on phosphoric and sulfuric acids, as well as potassium and nitrogen-containing reagents.

 A known method of producing complex fertilizers by mixing a mixture of phosphoric and sulfuric acids with potassium salts, followed by ammonization of the mixture to a pH of 4-4.5, its cooling and separation of the crystalline precipitate. To reduce caking, surfactants are added to the fertilizer (ed. Certificate. USSR 707901, C 05 G 3/06, op. 07.01.80). The disadvantages of this method are the complexity and duration of the process, the need for the introduction of surfactants, as well as the unbalanced composition of the fertilizer components.

 Closest to the claimed is a method of producing complex fertilizers by neutralizing phosphoric and sulfuric acids with a potassium alkaline reagent and ammonia, granulating and drying the finished product, in which neutralization is carried out in two stages: first, phosphoric acid is neutralized with an alkaline potassium reagent at pH 3.5-7, 2, and then sulfuric acid in the presence of potassium phosphates is neutralized with ammonia at pH 3.8-5.3 (RF patent 2107055, C 05 G 1/06, op. 20.03.98). The disadvantage of this method is the complexity of the process associated with the use of gaseous ammonia, as well as the high cost of fertilizer in connection with the use of expensive phosphoric and sulfuric acids.

 The objective of the invention is to simplify and reduce the cost of the fertilizer production process by involving solid and liquid wastes and intermediates containing phosphorus and nitrogen in the technology.

The inventive method for producing complex fertilizers consists in neutralizing phosphoric acid with a potassium alkaline reagent at pH 3.5-7.2, mixing the resulting pulp with sulfate-containing reagents at pH 3.8-5.3, granulating and drying the finished product, while phosphoric acid is preliminarily neutralize the phosphoric acid sludge in a mass ratio of P ₂ O ₅ sludge / P ₂ O ₅ acid = 0.02-0.4: 1, and sulfuric acid and ammonium sulfate are introduced into the pulp in a mass ratio of H ₂ SO4: (NH ₄ ) ₂ SO ₄ = 0.02-0.09: 1.

The use of a part of phosphorus in the process in the form of phosphoric acid sludge formed during the neutralization of phosphate solutions, with a mass fraction of P ₂ O ₅ from 0.1 to 5%, calcium-containing reagents, for example oxide, and / or calcium hydroxide and / or calcium carbonate to pH 6.0-9.0, or when purifying extraction phosphoric acid containing 20-35% P ₂ O ₅ , carbonates, and / or alkali metal hydroxides to pH 3.5-7.5, and replacing part of sulfuric acid with solid sulfate ammonia or its solutions, which are by-products of many chemical industries, leads to a significant reduction in the cost of the target fertilizer product, and the exclusion of the introduction of gaseous ammonia into the process leads to its substantial simplification. The dosage of phosphoric acid sludge to the stage of neutralization of phosphoric acid with an alkaline potassium reagent allows the fluorine contained in the acid and sludge to be converted into an unapproachable and safe form in the form of calcium fluoride and potassium fluorosilicate, which increases the environmental value of NPK fertilizers.

 The essence of technology is illustrated by examples.

 Example 1

100 kg of extraction phosphoric acid (23% P ₂ O ₅ ) neutralize 2 kg of sludge containing 23% P ₂ O ₅ , 8% F, 40% moisture, and then 71.5 kg of 47% potash solution (22.2 kg K ₂ O). The ratio of P ₂ O ₅ sludge / P ₂ O ₅ acid corresponds to 0.02: 1. The process is carried out at 80 ^o C for 20 minutes In this case, 10.4 kg of CO ₂ and 5 kg of water are released into the gas phase. The mass of neutralized phosphoric acid pulp is 15.8 kg, pulp pH 3.5. Then the pulp is sent for mixing with 3.1 kg of 70% sulfuric acid and solid ammonium sulfate in an amount of 109 kg at pH 3.8. The ratio of H ₂ SO ₄ : (NH ₄ ) ₂ SO ₄ = 0.02: 1. The amount of pulp is 280 kg. In this case, 10 kg of water goes into the gas phase. The neutralized pulp is sent to granulation and drying. The mass of the finished product is 181.5 kg. The fertilizer composition N is 13.4%, P ₂ O ₅ is 13.3%, K ₂ O is 12.9%. The amount of nutrients reaches 39.6%.

 Example 2

100 kg of extraction phosphoric acid (23% P ₂ O ₅ ) neutralize 27 kg of sludge containing 17% P ₂ O ₅ , 6% F, 45% moisture and 84.3 kg of 47% potash solution (27 kg K ₂ O ) The ratio of P ₂ O ₅ sludge / P ₂ O ₅ acid corresponds to 0.2: 1. The process is carried out at 80 ^o C for 20 minutes In this case, 12.6 kg of CO ₂ and 5 kg of water go into the gas phase. The mass of neutralized phosphoric acid pulp (pH 6) is 193.7 kg. Then the pulp is mixed with 5.4 kg of 80% sulfuric acid and 204 kg of a 30% solution of ammonium sulfate at pH 4.5. The ratio of H ₂ SO ₄ : (NH ₄ ) ₂ SO ₄ = 0.07: 1. The amount of pulp is 392 kg. In this case, 11 kg of water goes into the gas phase. The neutralized pulp is sent to granulation and drying. The mass of the finished product is 120 kg. The fertilizer composition N is 10.8%, P ₂ O _{5 is} 23%, K ₂ O is 22.5%. Amount of nutrients: 56%.

 Example 3

100 kg of extraction phosphoric acid containing 23% P ₂ O ₅ neutralize 61.3 kg of sludge containing 15% P ₂ O ₅ , 4% F, 50% moisture, and 88.4 kg of 47% potash solution (28 , 3 kg K ₂ O). The ratio of P ₂ O ₅ sludge / P ₂ O ₅ acid is 0.4: 1. The process is carried out at 80 ^o C for 20 minutes In this case, 13.3 kg of CO ₂ and 5 kg of water go into the gas phase. The mass of neutralized phosphoric acid pulp is 170 kg, the pH of the pulp is 7.2. Then 7.3 kg of 93% sulfuric acid and 188.5 kg of a 40% solution of ammonium sulfate are introduced into the pulp at pH 5.3. The ratio of H ₂ SO ₄ : (NH ₄ ) ₂ SO ₄ = 0.09: 1. The amount of pulp is 406 kg. In this case, 10 kg of water goes into the gas phase. The neutralized pulp is sent to granulation and drying. The mass of the finished product is 183 kg. The fertilizer composition N is 8.7%, P ₂ O ₅ is 17.6%, K ₂ O is 16.4%. Amount of nutrients: 42.7%.

Reducing the amount of sludge below the ratio of P ₂ O ₅ sludge: P ₂ O ₅ acid = 0.02: 1 will not have a significant effect on saving phosphoric acid. An increase in the ratio of P ₂ O ₅ sludge: P ₂ O ₅ acid above 0.4: 1 leads to a significant reduction in the nutrient content of the fertilizer. A decrease in the ratio of H ₂ SO ₄ : (NH ₄ ) ₂ SO ₄ less than 0.02: 1 impairs the physical properties of the fertilizer. An increase in the ratio of sulfuric acid and ammonium sulfate above 0.09: 1 leads to a decrease in the pH of the finished product, which affects its agrochemical safety.

 The table shows the characteristics of the finished product obtained by the proposed and known methods.

 As can be seen from the table, the proposed method allows to produce high-quality fertilizers using sludges obtained during the purification of phosphoric acid and the neutralization of phosphate solutions, as well as ammonium sulfate, which is a by-product of chemical and petrochemical industries.

Claims (3)

1. The method of producing complex fertilizers, which consists in neutralizing phosphoric acid with a potassium alkaline reagent at pH 3.5-7.2, mixing the resulting pulp with sulfate-containing reagents at pH 3.8-5.3, granulating and drying the finished product, characterized in that phosphoric acid is pre-neutralized with phosphoric acid sludge in a mass ratio of P ₂ O ₅ sludge / P ₂ O ₅ acid = 0.02-0.4: 1, and a mixture of sulfuric acid with ammonium sulfate in a mass ratio H is introduced into the pulp as a sulfate-containing reagent ₂ SO ₄ : (NH ₄ ) ₂ SO ₄ = 0.02-0.09: 1. 2. The method according to claim 1, characterized in that they use phosphoric acid sludge generated during the neutralization of phosphate solutions, with a mass fraction of P ₂ O ₅ from 0.1 to 5%, calcium-containing reagents, for example, oxide, and / or hydroxide , and / or calcium carbonate to a pH of 6.0-9.0. 3. The method according to claim 1, characterized in that the use of phosphoric acid sludge generated during the purification of extraction phosphoric acid containing 20-35% P ₂ O ₅ , carbonates, and / or alkali metal hydroxides to a pH of 3.5-7 ,5.

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