RU2373144C1 - Method of producing dicalcium phosphate feed - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing dicalcium phosphate feed involves a first stage, specifically treatment of calcined phosphogypsum with an alkaline carbonate-containing reagent to pH ranging from 9.15 to 10, a second stage, specifically mixing chalk pulp obtained at the first stage with purified phosphoric acid to pH ranging from 5.4 to 6 with subsequent filtration and drying the finished product. According to the invention, the first stage is carried out with initial ratio of liquid phase to solid phase equal to 4.7-5.5:1, after which the chalk pulp is thickened until attaining ratio of liquid phase to solid phase equal to 3-4:1, and the second stage is carried out until attaining ratio of liquid phase to solid phase equal to 4-4.7:1.

EFFECT: method allows for increasing output of P₂O₅ into the final product and so reducing loss of P₂O₅.

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Description

The present invention relates to a technology for processing extraction phosphoric acid into industrial phosphates, in particular feed fodder dicalcium phosphate using production waste.

A known method of producing feed dicalcium phosphate, including the treatment of phosphogypsum with phosphoric acid in the presence of calcium or sodium hydroxide at pH 7-11 and a concentration of P ₂ O _{5 of} 0.7-2.752 g / l to establish equilibrium (AS USSR No. 829559, C01 B 25/32, Berimzhanov B.A. et al. Op. 15.05.81. Bull. No. 18).

The disadvantages of this method are the use of dilute solutions of phosphoric acid, which complicates the process, the use of phosphogypsum containing a large amount of impurities, the use of expensive sodium hydroxide, a long process (until equilibrium is 8-15 hours) and low quality of the finished product - 32-41% P ₂ O ₅ and 0.45-0.5% F. Such a product cannot be used as a feed because of its high fluorine content.

Closest to the proposed method in technical essence is a method for producing dicalcium phosphate, which includes treating phosphogypsum with a phosphate solution, filtering and drying the finished product, in which the process is carried out in two stages: in the first stage, pre-calcined phosphogypsum is treated with an alkaline carbonate-containing reagent to pH 9.15-10 , in the second stage, the resulting chalk pulp is mixed with pre-purified phosphoric acid to a pH of 5.4-6 (RF Patent No. 2149828, СВВ 25/32. Op. 27.05.2000) (prototype).

The disadvantages of this method are the insufficiently high degree of transition of P ₂ O ₅ into the finished product and large losses of P ₂ O ₅ .

At the first stage of the process, the initial ratio of the liquid and solid phases (L: T) is 7.38-9: 1, the final L: T = 10-12.38: 1 This amount of the liquid phase enters the second stage, where phosphoric acid is supplied. In this case, the amount of the liquid phase increases to the ratio W: T = 9.9-12.2: 1. The amount of effluent solution of potassium sulfate (sodium) is 10 times the amount of precipitate. This results in a significant loss of P ₂ O ₅ with the sulfate effluent. The content of P ₂ O ₅ in the effluent solution is 1.23-2.1% P ₂ O ₅ . Losses of P ₂ O ₅ with the effluent are 21-34%. The output of P ₂ About ₅ in the finished product is 66-79%.

The task of the invention is to increase the yield of P ₂ O ₅ in the finished product.

The problem is achieved in that in the method for producing fodder dicalcium phosphate comprising the first stage, namely, the treatment of pre-calcined phosphogypsum with an alkaline carbonate-containing reagent to pH 9.15-10, the second stage, namely the mixing of the chalk pulp obtained in the first stage with pre-purified phosphoric acid to a pH of 5.4-6, followed by filtration and drying of the finished product, according to the invention, the first stage is carried out at the initial ratio of liquid and solid phases, comprising W: T = 4.7-5.5: 1, after which the Cretaceous the pulp was concentrated to a ratio of liquid and solid phases constituting L: S = 3.4: 1, and the second step is carried out to a ratio of liquid and solid phases constituting L: S = 4-4.7: 1.

Changing the process conditions is achieved by reducing the amount of the liquid phase in the first stage of producing chalk pulp, thickening the pulp and carrying out the process of precipitation of dicalcium phosphate in a thicker pulp, which leads to an increase in the yield of P ₂ O ₅ in the finished product.

A decrease in the amount of the liquid phase at the stage of chalk formation below 4.7: 1 will lead to thickening of the pulp due to the formation of calcium sulfate crystalline hydrates, with an increase in W: T above 5.5: 1, the losses of P ₂ O ₅ will increase. The decrease in W: T at the stage of thickening below 3: 1 will complicate the process due to the deterioration of mass transfer, an increase in pH above 4: 1 leads to an increase in losses of P ₂ O ₅ . A decrease in the amount of the liquid phase at the stage of dicalcium phosphate production is less than 4: 1 will reduce the yield of P ₂ O ₅ in the finished product. An increase in the amount of the liquid phase above 4.7: 1 will result in a loss of P ₂ O ₅ .

The essence of the process is illustrated by examples.

Example 1. 1000 kg of phosphogypsum calcined at 400 ° C (thermophosphogypsum (TFG)) having a basic composition of 38% CaO, 53.2% SO ₃ , 1.17% P ₂ O ₅ , treated with 1923 kg 47% potash solution and 3402 kg of water. The total amount of pulp is 6325 kg, W: T = 5.3: 1. The process proceeds for 1 hour at a temperature of 50 ° C to a pH of 9.15. Pulp in the amount of 6325 kg with a solid content of 735 kg and liquid 5590 kg has a ratio of W: T = 7.6: 1. The pulp is thickened to W: T = 3: 1 and in an amount of 2941 kg (2205.7 kg of the liquid phase and 735.3 kg of the solid phase) are sent to mix with 3143 kg of a phosphoric acid solution containing 19.8% P ₂ O ₅ , 2 , 66% CaO, 6.65% K ₂ O, 0.06% Fe ₂ O ₅ , 0.05% F, having a pH of 3. The total amount of pulp is 6084 kg, the amount of liquid phase is 5349 kg, solid - 735 kg W: T = 7.3: 1. The process of precipitation of dicalcium phosphate proceeds for 30 min at a temperature of 102 ° C to a pH of 5.8. Then the pulp in the amount of 6084 kg with W: T = 4.7: 1 is filtered, the precipitate is washed and dried. The amount of sediment is 1079 kg. The filtrate in an amount of 5005 kg, containing 2.1% P ₂ O ₅ , 6.5% K ₂ O, 0.68% CaO, 0.0047% Fe ₂ O ₃ , 0.003% F, is sent to the production of fertilizers. The finished product contains 49% P ₂ O ₅ , 38.65% CaO, 0.13% Fe ₂ O ₃ , 0.12% F. The amount of P ₂ O ₅ in the finished product is 528.7 kg. The ratio of P ₂ O ₅ ass. to R ₂ About ₅ total. equal to 99.9%. The output of P ₂ O ₅ in the finished product is 83.6%. The solution leaves 105.3 kg of P ₂ O ₅ , which is 16.4% of the loss.

Example 2. 1000 kg of phosphogypsum calcined at 400 ° C of the composition specified in example 1, treated with 720 kg of soda and 3980 kg of water. The amount of pulp is 5700 kg, W: T = 4.7: 1. The process proceeds for 1 hour at a temperature of 50 ° C to a pH of 9.15. Pulp in the amount of 5700 kg with a sediment content of 735 kg and a liquid phase of 4965 kg has W: T = 6.76: 1. The pulp is thickened to W: T = 3.5: 1 and in the amount of 3307.5 kg is sent to mix with 2679 kg of phosphoric acid solution containing 23% P ₂ O ₅ , 7% Na ₂ O, 0.08% Fe ₂ O ₃ 0.086% F having a pH of 3.5. The total amount of pulp is 5986.5 kg, W: T = 7.2: 1 The process of precipitation of dicalcium phosphate proceeds for 30 min at a temperature of 102 ° C to a pH of 5.8. Then the pulp in the amount of 5986.5 kg with W: T = 4: 1 is filtered, the precipitate is washed and dried. The amount of sediment is 1185 kg. The filtrate in the amount of 4801.9 kg, containing 1.33% P ₂ O ₅ , 6.5% Na ₂ O, 0.68% CaO, 0.008% Fe ₂ O ₃ , 0.003% F, is sent to the production of fertilizers. The finished product contains 48.1% P ₂ O ₅ , 37.9% CaO, 0.13% Fe ₂ O ₃ , 0.2% F. The ratio of P ₂ O ₅ assim. to P ₂ O ₅ total. equal to 99.8%. The yield of P ₂ O ₅ in the finished product is 89.9%. With the solution, 64 kg of P ₂ O _{5 are} consumed, which is 10.1% of the losses.

Example 3. 1000 kg of phosphogypsum calcined at 400 ° C of the composition indicated in example 1, treated with 2512 kg of 28% solution of ammonium carbonate and 3066 kg of water. The amount of pulp is 6578 kg, W: T = 5.5: 1. The process proceeds for 1 hour at a temperature of 50 ° C to a pH of 9.15. Pulp in the amount of 6578 kg with a sediment content of 735 kg and a liquid phase of 5843 kg has W: T = 7.95: 1. The pulp is thickened to W: T = 4: 1 and in the amount of 3675 kg is sent to mix with 2200 kg of a phosphoric acid solution containing 28% P ₂ O ₅ , 2.66% CaO, 3% NH ₃ , 0.07% Fe ₂ O ₃ , 0.12% F having a pH of 2.5. The total amount of pulp is 5875 kg, W: T = 7: 1. The process of precipitation of dicalcium phosphate proceeds for 30 min at a temperature of 102 ° C to a pH of 5.8. Then the pulp in the amount of 5875 kg with W: T = 4: 1 is filtered, the precipitate is washed and dried. The amount of sediment is 1174 kg. The filtrate in an amount of 4701 kg, containing 1.23% P ₂ O ₅ , 2.25 NH ₃ , 0.68% CaO, 0.005% Fe ₂ O ₃ , 0.005% F, is sent to the production of fertilizers. The finished product contains 48.5% P ₂ O ₅ , 38.25% CaO, 0.1% Fe ₂ O ₃ , 0.2% F. The ratio of P ₂ O ₅ assim. to P ₂ O ₅ total equal to 99.7%. The yield of P ₂ O ₅ in the finished product is 90.8%. With the solution leaves 58 kg of P ₂ O ₅ , which is 9.2% of the loss.

The table shows comparative indicators of the claimed and known methods.

As can be seen from the table, in the proposed method, the amount of the liquid phase decreases at all stages, which leads to an increase in the concentration of the sulfate effluent solution and an increase in the yield of P ₂ O ₅ in the finished product.

Thus, the inventive method allows to increase the yield of P ₂ O ₅ in the finished product and reduce the loss of P ₂ O ₅ in the second stage.

Table Indicators Proposed Famous (prototype) Example 1 Example 2 Example 3 1. Feedstock Phosphogypsum Is available Is available Is available Is available Calcination Is available Is available Is available Is available Phosphoric acid Is available Is available Is available Is available pH 2.5-3.5 2.5-3.5 2.5-3.5 2.5-3.5 Concentration % P ₂ O ₅ 19.6-28 19.6-28 19.6-28 19.6-28 Carbonates alkaline of metals Are available Are available Are available Are available 2. The stages of the process chalk deposition Is available Is available Is available Is available J: T ref. 5.3: 1 4.7: 1 5.5: 1 7.38-9: 1 J: T con. 7.3: 1 6.76: 1 7.95: 1 10-12.38: 1 Thickening Is available Is available Is available Absent W: T 3: 1 3.5: 1 4: 1 - DKF precipitation Is available Is available Is available Is available W: T 4.7: 1 4: 1 4: 1 9.9-12.2: 1 The composition of the finished product P ₂ O ₅ 49 48.1 48.5 48.1-49 CaO 38.65 37.9 38.25 37.9-38.25 Fe ₂ O ₃ 0.13 0.13 0.1 0.1-0.13 F 0.12 0.2 0.2 0.12-0.2 P ₂ O _{5 ass.} / R ₂ About _{5 total.,%} 99.9 99.8 99.7 99.7-99.9 The output of P ₂ O ₅ in the finished product 83.6 89.9 90.8 66-79

Claims (1)

A method for producing fodder dicalcium phosphate comprising the first stage, namely, treatment of pre-calcined phosphogypsum with an alkaline carbonate-containing reagent to pH 9.15-10, the second stage, namely, mixing the chalk pulp obtained in the first stage with pre-purified phosphoric acid to pH 5.4-6 followed by filtration and drying of the finished product, characterized in that the first stage is carried out at the initial ratio of liquid and solid phases, comprising W: T = 4.7-5.5: 1, after which the chalk pulp is concentrated to a liquid and solid ratio the first phase, component W: T = 3-4: 1, and the second stage is carried out to the ratio of liquid and solid phases, component W: T = 4-4.7: 1.