Method for recovering fluorine and phosphorus resources in dilute phosphoric acid defluorination residues by fractional precipitation method

Abstract

The invention discloses a method for recovering fluorine and phosphorus resources in dilute phosphoric acid defluorination residues by a fractional precipitation method. The method comprises the following steps: reacting the defluorination residues with sulfuric acid and process water to form slurry A; carrying out filter pressing and solid-liquid separation on the slurry A to obtain calcium sulfate and a solution containing phosphorus and fluorine; adding active silicon powder and sodium carbonate into the solution containing phosphorus and fluorine to react for 50-90 minutes, and precipitating fluorine element to form slurry B; carrying out filter pressing separation on the slurry B to obtain defluorinated phosphoric acid and a fluorine-containing precipitate; and re-pulping and recrystallizing the fluorine-containing precipitate, then centrifugally separating and washing to obtain a sodium fluosilicate semi-finished product, and drying to obtain a sodium fluosilicate product. According to the method, calcium is precipitated through sulfuric acid, fluorine is precipitated through active silicon and sodium carbonate, defluorinated slurry is re-pulped, and recrystallization is conducted in sequence, the process is simple, the cost is low, the method is environmentally friendly, calcium, fluorine and phosphorus are precipitated in sequence, high-value phosphorus and fluorine resources are efficiently recycled, the purity of sodium fluosilicate is larger than or equal to 99%, calcium hydrophosphate meets the feed-grade standard, and pollution of the fluorine resources to the environment is reduced.

Description

Technical Field

[0001] The present invention relates to the field of fluorine resource recovery and utilization in phosphorus chemical industry, and in particular to a method for recovering fluorine and phosphorus resources from defluorination slag by a step-by-step precipitation method. Background Art

[0002] The defluorination slag produced during wet-process phosphoric acid production contains complex salts such as phosphoric acid, calcium sulfate, sodium (potassium) fluorosilicate, and calcium fluoride. The fluorine content in dilute acid defluorination slag is 4-5 times that of phosphate rock, with a F content of 12%-15%. During wet-process phosphoric acid production, fluorine resources are often wasted in the form of defluorination slag or used at a low value as fertilizer (white fertilizer). Almost all of this fluorine is wasted and discharged into the soil, polluting the environment.

[0003] In the existing technology, although some technologies attempt to recover fluorine resources, such as patent number 202111591552.0, the invention name of which is a patent for a method for resource processing of white fertilizer, the calcination method is used to recover fluorine resources, but it has the disadvantages of high cost, complex process and low fluorine recovery rate. Summary of the Invention

[0004] The present invention aims to solve the deficiencies of the prior art and provides a method for simultaneously recovering and utilizing calcium, fluorine and phosphorus elements by means of a simple process flow and a stepwise precipitation and solid-liquid separation technology.

[0005] The technical solution adopted by the present invention is as follows: The method for recovering fluorine and phosphorus resources from dilute phosphoric acid defluorination residue by step-by-step precipitation comprises the following steps: (1) Precipitation of calcium: react defluorination slag with sulfuric acid and process water to form slurry A, so that calcium is converted into calcium sulfate precipitation, and phosphorus and fluorine elements enter the solution; (2) First press filter solid-liquid separation: press filter slurry A to separate the solid and liquid to obtain calcium sulfate and phosphorus and fluorine-containing solution, and separate the calcium sulfate solid and phosphorus and fluorine-containing filtrate; (3) Precipitation defluorination reaction: Add active silicon powder and soda ash to the phosphorus and fluorine solution and react for 50-90 minutes to precipitate fluorine to form slurry B; (4) Second filter press solid-liquid separation: slurry B is filtered to separate defluorinated phosphoric acid and fluorine-containing precipitate; (5) Second filter cake re-slurry and recrystallization reaction: re-slurry and recrystallization reaction of fluorine-containing precipitate; (6) Solid-liquid separation: The filter cake from the second filter press is re-pulped, the fluorine-containing sodium silicate slurry after the recrystallization reaction is centrifuged and washed to obtain fluorine to obtain a sodium silicate semi-finished product.

[0006] Furthermore, in step (1) of the present invention, the concentration of sulfuric acid is 30% to 50%, and the reaction temperature is 40° C. to 60° C. for 45 min to 60 min.

[0007] Furthermore, in step (3) of the present invention, the molar ratio of fluorine to silicon is 6:1, and the SiO2 content of the active silicon powder is ≥96%.

[0008] Furthermore, the recrystallization time in step (5) of the present invention is 30 min-60 min.

[0009] The present invention mainly relates to the following chemical reaction process: H2SO4+Ca(H2PO4)2.H20+H20=CaSO4.2H20+2H3PO4 (1) H2SO4+CaHPO4.2H20=CaSO4.2H20+H3PO4 (2) H2SO4+CaF=CaSO4.2H20+HF (3) 6HF+SiO2=H2SiF6+2H2O (4) H2SiF6+Na2CO3=Na2SiF6+H2O+CO2 (5) Ca(OH)2+H3PO4=CaHPO4.2H2 (6) Beneficial effects of the present invention: The process of the invention is simple, low in cost, and environmentally friendly. Calcium, fluorine, and phosphorus are precipitated in sequence, and phosphorus and fluorine resources are efficiently recovered. The purity of sodium fluorosilicate is ≥99%, and calcium hydrogen phosphate meets the feed grade standard, thereby reducing the pollution of fluorine resources to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0011] The following description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed, but rather merely represents selected embodiments of the invention. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0012] The defluorination residue, raw material content and dosage used in the following Examples 1 to 3 are shown in Table 1: Table 1 Defluorination slag, raw material content and dosage used in Examples 1 to 3 Example 1

[0013] like Figure 1 As shown, the method for recovering fluorine and phosphorus resources from dilute phosphoric acid defluorination slag by step-by-step precipitation method comprises the following steps: (1) Precipitation of calcium: The defluorination slag shown in Table 1 was fully reacted with 40% sulfuric acid and process water in a precipitation reaction tank. The temperature of the reaction tank was controlled at 40°C and the reaction time was maintained for 45 min. The defluorination slag and sulfuric acid were fully reacted, and the calcium element was converted into calcium sulfate precipitation. Phosphorus and fluorine elements entered the solution and reacted to form slurry A. (2) First filter press solid-liquid separation: Filter press the slurry A to separate the solid and liquid to obtain the calcium sulfate gypsum product and the phosphorus and fluorine-containing solution; (3) Precipitation defluorination reaction: Add active silicon powder (the molar ratio of fluorine to silicon in the solution is 6:1) to the phosphorus and fluorine solution and send it into the precipitation defluorination tank to fully react with the soda ash solution from the alkali dissolution tank for 50 minutes to precipitate fluorine to form slurry B; (4) Second filter press solid-liquid separation: Slurry B is filtered and separated to obtain defluorinated phosphoric acid, which is sent to the subsequent workshop to produce feed-grade calcium hydrogen phosphate products and fluorine-containing precipitates. The calcium hydrogen phosphate product contains 17.1% P, 21.2% Ca, and 0.15% F.

[0014] (5) Re-slurrying and recrystallization of the second filter cake: re-slurrying and recrystallizing the fluorine-containing precipitate (the second filter cake) for 30 minutes to obtain a fluorine-containing sodium silicate slurry; (6) Solid-liquid separation: The slurry after the recrystallization reaction of sodium fluoride silicate is sent to a centrifuge for centrifugal solid-liquid separation and washing. 1 / 3 of the recrystallization slurry is used as a seed crystal to return to the defluorination precipitation tank to participate in the reaction, and 2 / 3 is sent to a centrifuge for centrifugal separation. During the centrifugal separation process, 1 / 2 of the mass of water is used for washing, and the centrifuge liquid and washing liquid are sent to a soda ash dissolving tank to prepare a soda ash solution. After centrifugal washing, a sodium fluoride semi-finished product with a purity of 99% is obtained and sent to the fluoride salt workshop to produce the finished product, wherein the sodium fluoride product contains 0.32% insoluble matter; Example 2

[0015] like Figure 1 As shown, the method for recovering fluorine resources from defluorination slag by step-by-step precipitation method comprises the following steps: (1) Precipitation of calcium: The defluorination slag shown in Table 1 was fully reacted with 30% sulfuric acid and process water in a precipitation reaction tank. The temperature of the reaction tank was controlled at 50°C and the reaction time was maintained for 50 min. The defluorination slag and sulfuric acid were fully reacted, and the calcium element was converted into calcium sulfate precipitation. Phosphorus and fluorine elements entered the solution and reacted to form slurry A. (2) First filter press solid-liquid separation: Filter press the slurry A to separate the solid and liquid to obtain the calcium sulfate gypsum product and the phosphorus and fluorine-containing solution; (3) Precipitation defluorination reaction: Add active silicon powder (the molar ratio of fluorine to silicon in the solution is 6:1) to the phosphorus and fluorine solution and send it into the precipitation defluorination tank to fully react with the soda ash solution from the alkali dissolution tank for 70 minutes to precipitate fluorine to form slurry B; (4) Second filter press solid-liquid separation: Slurry B is filtered and separated to obtain defluorinated phosphoric acid, which is sent to the subsequent workshop to produce feed-grade calcium hydrogen phosphate products and fluorine-containing precipitates. The calcium hydrogen phosphate product contains 17.3% P, 21.5% Ca, and 0.12% F.

[0016] (5) Re-slurry and recrystallization of the second filter cake: re-slurry and recrystallize the fluorine-containing precipitate (the second filter cake) for 45 minutes to obtain a slurry of the fluorine-containing sodium silicate product; (6) The third solid-liquid separation: The slurry after the recrystallization reaction of sodium fluoride silicate is sent to a centrifuge for centrifugal solid-liquid separation and washing. 1 / 3 of the recrystallization slurry is used as a seed crystal to return to the defluorination precipitation tank to participate in the reaction, and 2 / 3 is sent to a centrifuge for centrifugal separation. During the centrifugal separation process, 1 / 2 of the mass of water is used for washing, and the centrifuge liquid and washing liquid are sent to a soda ash dissolving tank to prepare a soda ash solution. After centrifugal washing, 99.2% of the sodium fluoride semi-finished product is obtained and sent to the fluoride salt workshop to produce the finished product, of which the insoluble matter in the sodium fluoride product is 0.28%; Example 3

[0017] like Figure 1 As shown, the method for recovering fluorine resources from defluorination slag by step-by-step precipitation method comprises the following steps: (1) Precipitation of calcium element: The defluorination slag shown in Table 1 is fully reacted with 50% sulfuric acid and process water in a precipitation reaction tank. The temperature of the reaction tank is controlled at 60°C and the reaction time is maintained for 60 min. The defluorination slag and sulfuric acid are fully reacted, and the calcium element is converted into calcium sulfate precipitation, while phosphorus and fluorine elements enter the solution and react to form slurry A. (2) First filter press solid-liquid separation: Filter press the slurry A to separate the solid and liquid to obtain the calcium sulfate gypsum product and the phosphorus and fluorine-containing solution; (3) Precipitation defluorination reaction: Add active silicon powder (the molar ratio of fluorine to silicon in the solution is 6:1) to the phosphorus and fluorine solution and send it into the precipitation defluorination tank to fully react with the soda ash solution from the alkali dissolution tank for 90 minutes to precipitate fluorine to form slurry B; (4) Second filter press solid-liquid separation: Slurry B is filtered and separated to obtain defluorinated phosphoric acid, which is sent to the subsequent workshop to produce feed-grade calcium hydrogen phosphate products and fluorine-containing precipitates. The calcium hydrogen phosphate product contains 17.2% P, 21.8% Ca, and 0.11% F.

[0018] (5) Re-slurrying and recrystallization of the second filter cake: re-slurrying and recrystallizing the fluorine-containing precipitate (the second filter cake) for 60 minutes to obtain a slurry of the fluorine-containing sodium silicate product; (6) The third solid-liquid separation: The slurry after the recrystallization reaction of sodium fluoride silicate is sent to a centrifuge for centrifugal solid-liquid separation and washing. 1 / 3 of the recrystallization slurry is used as a seed crystal to return to the defluorination precipitation tank to participate in the reaction, and 2 / 3 is sent to a centrifuge for centrifugal separation. During the centrifugal separation process, 1 / 2 of the mass of water is used for washing, and the centrifuge liquid and washing liquid are sent to a soda ash dissolving tank to prepare a soda ash solution. After centrifugal washing, 99.1% of the sodium fluoride silicate semi-finished product is obtained and sent to the fluoride salt workshop to produce the finished product, of which the insoluble matter in the sodium fluoride silicate product is 0.24%; The method of the present invention is used to treat wet-process phosphoric acid dilute acid defluorination residue, so as to recover high-value phosphorus and fluorine elements. The recovered sodium fluorosilicate product meets the quality requirements of industrial-grade superior products; the recovered phosphorus element meets the quality requirements of feed-grade phosphoric acid products, and has high economic benefits.

[0019] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for recovering fluorine and phosphorus resources from dilute phosphoric acid defluorination residue by a step-by-step precipitation method, characterized in that: The following steps are involved: (1) Precipitation of calcium element: reacting defluorination slag with sulfuric acid and process water to form slurry A; (2) First filter press solid-liquid separation: Filter press the slurry A to separate the solid and liquid to obtain calcium sulfate and phosphorus and fluorine-containing solution; (3) Precipitation defluorination reaction: Add active silicon powder and soda ash to the phosphorus and fluorine solution and react for 50-90 minutes to precipitate fluorine to form slurry B; (4) Second filter press solid-liquid separation: slurry B is filtered to separate defluorinated phosphoric acid and fluorine-containing precipitate; (5) Second filter cake re-slurry and recrystallization reaction: re-slurry and recrystallization reaction of fluorine-containing precipitate; (6) Solid-liquid separation: The filter cake from the second filter press is re-pulped, and the fluorine-containing sodium silicate slurry after the recrystallization reaction is centrifuged and washed to obtain a sodium silicate semi-finished product.

2. The method according to claim 1, wherein: The concentration of sulfuric acid in step (1) is 30% to 50%, and the reaction temperature is 40°C to 60°C for 45 minutes to 60 minutes.

3. The method according to claim 1, wherein: In step (3), the molar ratio of fluorine to silicon is 6:1, and the SiO2 content of the active silicon powder is ≥96%.

4. The method according to claim 1, wherein: The recrystallization time in step (5) is 30 min-60 min.

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