Method and system for preparing purified phosphoric acid by adopting centrifugal extraction technology

Abstract

The invention discloses a method and a system for preparing purified phosphoric acid by adopting a centrifugal extraction technology, and solves the problem that the existing purified phosphoric acid production technology cannot meet the requirements of high purity effect and low cost at the same time. The method comprises the following steps: S1, primary acid concentration: filtering to obtain concentrated crude acid; s2, desulfurizing the concentrated crude acid obtained in the step S1 by adopting a desulfurizing agent; s3, defluorinating the desulfurized crude acid obtained in the step S2 by adopting a defluorinating agent; s4, carrying out cationic complexing treatment on the defluorinated acid by adopting a mixture of a cationic complexing extraction agent 2-(2-ethylhexyl) phosphoric acid P204 and sulfonated kerosene; s5, carrying out centrifugal extraction by adopting an extraction agent; s6, centrifugal washing; s7, centrifugal reverse extraction; and S8, further separating acid and concentrating to obtain purified phosphoric acid. The method has the advantages of good phosphoric acid purification effect, low cost and the like.

Description

Technical Field

[0001] This invention relates to the field of phosphoric acid purification technology, specifically to a method and system for preparing purified phosphoric acid using centrifugal extraction technology. Background Technology

[0002] Currently, the mainstream purification technologies for phosphoric acid mainly include the following:

[0003] (1) Membrane separation technology

[0004] Membrane separation technology utilizes the selective permeation principle of semi-permeable membranes to separate substances through physical sieving, electrostatic repulsion, and solute diffusion. This technology is primarily used for preparing high-purity phosphoric acid (electronic / food grade). However, the membranes are expensive, and pretreatment of the original acid is required, necessitating high acid quality standards. This results in high costs and makes the technology unsuitable for large-scale application.

[0005] (2) Solvent extraction method

[0006] Solvent extraction separation technology mainly achieves separation through the partition law of the solvent or complexation reaction. The partition law of the solvent utilizes the difference in the partition coefficient of phosphate in the organic phase and the aqueous phase to achieve selective enrichment, thereby achieving separation and purification. The complexation reaction involves the formation of complexes between the extractant and impurity ions, thus achieving separation. Solvent extraction is low-cost and the extractant can be reused, but the extractant has a weak ability to remove anions, which can easily lead to excessive anion content.

[0007] (3) Dynamic crystallization control

[0008] Dynamic crystallization control primarily involves thermodynamic and kinetic coordination to induce premature crystallization of phosphate molecules, leaving impurities in the liquid and forming high-purity crystals. This technology produces high-purity products, but requires significant equipment investment, has high maintenance costs, minimal human intervention, and demands high stability of the upstream acid quality.

[0009] Therefore, existing purified phosphoric acid production technologies either fail to completely remove ions or have high production costs, creating an urgent need for a high-purity, low-cost method for preparing purified phosphoric acid. Summary of the Invention

[0010] The technical problem to be solved by this invention is that existing purified phosphoric acid production technology cannot simultaneously meet the requirements of high purity and low cost.

[0011] This invention is achieved through the following technical solution:

[0012] A method for preparing purified phosphoric acid using centrifugal extraction technology includes the following steps:

[0013] S1: Concentrate the initial acid to 40-45% P2O5, and filter to obtain concentrated crude acid;

[0014] S2: Desulfurized crude acid is obtained by desulfurizing the concentrated crude acid obtained from S1 using a desulfurizing agent;

[0015] S3: The crude acid obtained from S2 is defluorinated using a defluorinating agent, and then solid-liquid separation is performed to obtain extracted defluorinated acid and filter cake.

[0016] S4: The defluorinated acid was subjected to cationic complexation treatment using a mixture of cationic complexing extractant 2-(2-ethylhexyl)phosphoric acid (P204) and sulfonated kerosene to obtain the extractable original acid;

[0017] S5: After heating the extractant and the original extract acid separately, add them to a centrifuge for extraction to obtain the organic phase and the residual acid;

[0018] S6: The organic phase obtained in S5 is washed by countercurrent centrifugation using purified acid as washing acid to obtain washed organic phase and residual washing acid. The washed organic phase is directly fed into the back-extraction section, and the residual washing acid is returned to the extraction section for further extraction.

[0019] S7: Preheated desalinated water is used as the back-extraction carrier to back-extract the washed organic phase by countercurrent centrifugation to obtain back-extracted acid and back-extracted organic phase; the back-extracted acid enters the concentration section;

[0020] S8: The back-extracted acid obtained from S7 is sent to the overflow storage tank for further separation of the residual organic phase. The organic phase is returned to the back-extraction stage for further separation. The back-extracted acid after separation of the organic phase is sent to the concentration section for concentration to obtain purified phosphoric acid.

[0021] Preferably, it is concentrated to 85% phosphoric acid.

[0022] The primary acid is an acid produced by the wet-process phosphoric acid production process and is obtained directly from the production.

[0023] Preferably, in S2, the specific method for desulfurization is as follows: dicalcium phosphate with a water content of less than 2% is slowly added at 75℃~85℃ according to a molar ratio of n(Ca):n(S) = 1.1~1.4:1, and stirred until fully reacted. Preferably, the reaction is carried out at 400-500 r / min for 1-6 h.

[0024] The moisture content of dicalcium phosphate is very important. If the moisture content is too high, the dicalcium phosphate will clump together, making it difficult to stir evenly after feeding, which will lead to poor desulfurization effect. The dicalcium phosphate is ground and passed through a 60-mesh sieve.

[0025] In addition, a temperature range of 75℃ to 85℃ and an excess of Ca can achieve deep desulfurization.

[0026] The chemical equation for the desulfurization process of this invention is as follows:

[0027] 2H + +SO42- +CaHPO4+2H2O=CaSO4•2H2O↓+H3PO4.

[0028] Preferably, in step S3, the specific method for defluorination is as follows: a NaOH solution with a solid content of 45%~50% is weighed according to a molar ratio of n(NaOH):n(F) = 3.5~5.5:1, and added dropwise at 75℃~85℃. After the addition is completed, the reaction is carried out for 3~4 hours. After the reaction is completed, the extractable original acid and filter cake are obtained by pressure filtration.

[0029] This temperature is chosen to better facilitate the release of fluorine products as gases; because the fluorine content is low and the concentration is small, this molar ratio allows for more thorough fluorine removal. Adding NaOH solution dropwise while providing the initial temperature to the acid results in a more vigorous reaction, and fluorine and its products are also more likely to escape as gases.

[0030] In addition, solid NaOH has poor defluorination effect. Low concentration NaOH will introduce too much water, and high concentration NaOH will react too violently and is difficult to control. NaOH with a concentration of about 50% is just right to be controlled and has a good defluorination effect.

[0031] Experiments revealed that fluorine removal was ineffective when the ratio of n(NaOH):n(F) was less than 3.5, and the Na concentration in the system needed to reach a certain level to achieve the desired removal effect.

[0032] The chemical equation for the defluorination process of this invention is as follows:

[0033] 2NaOH + H₂SiF = Na₂SiF↓ + 2H₂O

[0034] 2NaOH + HF = NaF + H₂O

[0035] After deep desulfurization, NaOH solution is used for defluorination to generate Na2SiF. After defluorination, impurities are removed by filtration based on the principle of impurity solubility.

[0036] Preferably, in step S4, the specific method of complexation treatment is as follows: 70% P204 by volume and 30% sulfonated kerosene, with a volume ratio of 5.0~8.0:1 to defluorinated acid, preheated to 45℃~50℃, and reacted in a complexation mixing reactor. After completion, the organic phase enters the complexing agent back-extraction section, and the aqueous phase enters the next stage of centrifugal extraction as the original acid.

[0037] Preferably, in step S5, the specific method of centrifugal extraction is as follows: the extractant and the extracting acid are fed in a volume ratio of V(extractant):V(extracting acid) = 4.0~7.0:1, the extractant and the extracting acid are preheated to 45℃~50℃ respectively, and at least three-stage countercurrent extraction is adopted. The extracted organic phase directly enters the extraction washing section, and the residual acid is treated and then enters the compound fertilizer section.

[0038] Preferably, in S5, the extractant is a mixture of methyl isobutyl ketone and sulfonated kerosene.

[0039] Methyl isobutyl ketone requires a high concentration of crude phosphoric acid and has a high viscosity, necessitating the use of a diluent. This invention employs a pretreatment process using a mixture of 2-(2-ethylhexyl)phosphoric acid (P204) and sulfonated kerosene. Under suitable viscosity conditions, the mixture of methyl isobutyl ketone and sulfonated kerosene achieves a high extraction rate.

[0040] Preferably, in step S6, the specific method for centrifugal washing is as follows: using a purification acid of 37%~40% P2O5 as the washing acid, preheating to 45℃~50℃, and performing at least three stages of countercurrent centrifugal washing according to a volume ratio of V (extracted organic phase):V (washing acid) = 3.0~5.0:1 to obtain a washed organic phase and residual washing acid. The washed organic phase is directly sent to the back-extraction section, and the residual washing acid is returned to the extraction section for further extraction.

[0041] The purification acid with P2O5 concentration of 37% to 40% refers to the back-extraction acid returned from the back-extraction process. Its P2O5 concentration is in the range of 37% to 40%, and it can be recycled and used directly. If the concentration of the washing acid is too low, it will lead to a large loss of phosphorus during the washing process. Its volume ratio with the extracted organic phase is also to reduce phosphorus loss. Preheating is to accelerate mass transfer and prevent high-concentration, high-impurity phosphoric acid from precipitating and clumping, which could clog the instrument.

[0042] It should be noted that when the total content of residual acid metal impurities in the washing process is ≥0.1% and the sulfate content is ≥0.2%, it will no longer be returned to the extraction section, but will be sent to be used as fertilizer.

[0043] Preferably, in step S7, the specific method for centrifugal back-extraction is as follows: using desalinated water preheated to 45°C~50°C as the back-extraction carrier, the ratio of washing organic phase to desalinated water feed is set at a volume ratio V(washed organic phase):V(desalinated water) = 7.0~12.0:1, and at least three stages of countercurrent centrifugal extraction are performed to obtain the back-extracted organic phase and back-extracted acid. The back-extracted acid enters the concentration section, and the back-extracted organic phase enters the extraction section as an extractant for recycling.

[0044] In this invention, the ratio of the washing organic phase to the deionized water is set relatively high, mainly to ensure that the resulting acid concentration is above 37% P2O5; it can be recycled and used directly. If the washing acid concentration is too low, it will lead to a large loss of phosphorus during the washing process, and it can also reduce the cost of subsequent concentration.

[0045] Preferably, in step S8, the back-extracted acid enters the overflow tank, and the production speed is controlled to be 1 / (m³) of the overflow tank storage volume ratio. 3 / h) / 24~48m 3 .

[0046] Preferably, the acid is back-extracted from the overflow tank and enters the concentration tank, where the vacuum degree is 0.08~0.10MPa and the temperature is 70℃~80℃, and it is concentrated to 61.2%-61.7% P2O5 to obtain 85% phosphoric acid.

[0047] This invention utilizes a centrifuge to provide centrifugal force, separating the light and heavy phases based on the magnitude of the centripetal force. Purified phosphoric acid is obtained through extraction, washing, and back-extraction processes. The multi-stage series separation ensures more thorough separation. Simultaneously, this method uses low-cost dicalcium phosphate as a highly efficient desulfurizing agent for deep desulfurization, increasing the concentration of orogenic acid (P2O5) and reducing subsequent concentration costs.

[0048] A system for preparing purified phosphoric acid using centrifugal extraction technology, used to implement the above-mentioned method for preparing purified phosphoric acid using centrifugal extraction technology, includes a first concentrator, a first pressure filter system, a desulfurization reactor, a defluorination reactor, a complexation mixing reactor, a second pressure filter system, a heat exchanger, an extraction centrifuge group, a washing centrifuge group, a back-extraction centrifuge group, and a second concentrator arranged sequentially.

[0049] Preferably, a settling tank is provided between the defluorination reactor and the second pressure filtration system, and an overflow storage tank is provided between the back-extraction centrifuge group and the second concentrator.

[0050] Preferably, a condenser heat exchanger is provided after the second concentrator to cool the phosphoric acid obtained in the second concentrator, and then transfer it to the finished product storage tank after cooling.

[0051] Preferably, the condensate washing water obtained from the heat exchanger is transported through the condensate washing water pipe to the first and second pressure filtration systems as pressure filtration washing water, thereby realizing the recycling of water.

[0052] The present invention has the following advantages and beneficial effects:

[0053] 1. This invention employs at least three-stage tandem centrifugal extraction technology to efficiently separate phosphoric acid from impurities. It uses undesulfurized primary phosphoric acid, dicalcium phosphate, sodium hydroxide, and demineralized water from the company's wet phosphoric acid production process as raw materials, resulting in lower costs. A complexing agent of 2-(2-ethylhexyl)phosphoric acid (P2O4) and sulfonated kerosene is used to efficiently remove metal cations. A complexing agent of methyl isobutyl ketone and sulfonated kerosene is used as the extractant, producing 85% phosphoric acid of high quality, meeting the requirements for industrial-grade products. Its byproduct, residual raffinate (P2O5), has a high content, which can be used to produce high-performance compound fertilizers, thus possessing good economic value.

[0054] 2. This invention concentrates the primary acid and uses calcium hydrogen phosphate for desulfurization. The desulfurizing agent itself contains phosphorus, which can remove sulfate ions and increase the phosphorus content; the desulfurization efficiency is higher after concentration.

[0055] 3. The present invention uses 2-(2-ethylhexyl)phosphoric acid (P204) and sulfonated kerosene as a complexing agent to efficiently remove metal cations; and 2-(2-ethylhexyl)phosphoric acid (P204) and sulfonated kerosene can be reused after washing with water.

[0056] 4. In this invention, the P2O5% of the back-extraction acid is about 37-40%, which can be directly used as the washing acid in the previous step to ensure the overall phosphorus yield.

[0057] 5. In this invention, the concentrated waste heat is fully utilized in the preheating and back-extraction desalination sections, realizing the recovery and utilization of materials and energy throughout the entire process. Attached Figure Description

[0058] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0059] Figure 1 This is a process flow diagram of the present invention;

[0060] Figure 2 This is a schematic diagram of the system structure of the present invention;

[0061] Figure 3 This is a schematic diagram of the complexation reactor of the present invention.

[0062] Figure label:

[0063] 1-First concentrator; 2-Main pipeline; 3-First filter press system; 4-First filter residue outlet; 5-Desulfurization reactor; 6-Defluorination reactor; 7-Complexing mixing reactor; 8-Regenerated organic return pipe; 9-Complexing organic pipe; 10-Regenerated stirring tank; 11-Regenerated impurity pipe; 12-Purified water pipe; 13-Water purifier; 14-Wastewater discharge pipe; 15-Sedimentation tank; 16-Sedimentation slurry discharge outlet; 17-Second filter press system; 18-Second filter residue outlet; 19-Condensate washing water pipe; 20-Heat exchanger; 21-Extraction centrifuge unit; 22-Extraction acid discharge outlet; 23-Washing residual acid return pipe; 2 4-Washing acid discharge port; 25-Washing centrifuge group; 26-Back-extraction centrifuge group; 27-Heat exchange demineralized water pipe; 28-Overflow storage tank; 29-Second concentrator; 30-Condensing heat exchanger; 31-Finished product storage tank; 32-Steam pipe; 33-Reaction vessel body; 34-Stirring rod; 35-Propeller baffle; 36-Inorganic acid inlet; 37-Stirring rack; 38-Complexing agent inlet; 39-First stirring ring; 40-Complexing agent outlet; 41-Porous gas distributor; 42-First valve; 43-First check valve; 44-Acid outlet; 45-Second check valve; 46-Second stirring ring. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0065] Example 1

[0066] like Figure 1 As shown, a method for preparing purified phosphoric acid using centrifugal extraction technology is described, using 80% methyl isobutyl ketone + 20% sulfonated kerosene as the extractant and 70% P2O4 + 30% sulfonated kerosene as the cationic complexing agent. The steps are as follows:

[0067] S1: Initial acid concentration:

[0068] The initial acid is drawn into the first concentrator, the vacuum degree is set to 0.08~0.10MPa, the temperature is 75℃, the concentration time is 180min, and the concentration is carried out to 40%~42% P2O5. The concentrated crude acid is then obtained by filtration.

[0069] S2: Crude acid desulfurization:

[0070] Calcium hydrogen phosphate with a moisture content of less than 2% and sieved through an 80-mesh sieve was slowly added at 80℃ at a ratio of n(Ca):n(S) = 1.2:1, and reacted for 2 hours under stirring at 450 r / min. After the reaction was completed, desulfurized crude acid was obtained.

[0071] S3: Crude acid defluorination:

[0072] A NaOH solution with a solid content of 48% was weighed according to the ratio of n(NaOH):n(F) = 4.0:1. It was added dropwise to the desulfurized crude acid at 80℃ for 1 hour using a peristaltic pump. After the addition was completed, the reaction was carried out for 3 hours. After the reaction was completed, the defluorinated acid and filter cake were obtained by pressure filtration.

[0073] S4: Complexation reaction:

[0074] P204 (70% by volume) and sulfonated kerosene (30% by volume) are reacted with defluorinated acid at a volume ratio of 6.0:1, preheated to 48°C, in a complexing mixing reactor. The impure organic phase enters the complexing agent back-extraction section, where the demineralized water is preheated. The ratio of complexing agent to demineralized water is 6.0:1. After countercurrent three-stage extraction and centrifugation, the aqueous phase enters the wastewater treatment section, and the purified organic phase, i.e., the complexing agent, enters the next complexing reaction. The acid after complexation treatment enters the next stage of centrifugal extraction.

[0075] Before entering the centrifugal extraction, the complexed acid first enters the sedimentation tank for sedimentation and is filtered to obtain the extraction raw acid, i.e., the pretreated acid, and the filter residue obtained from the filtration enters the compound fertilizer production process.

[0076] S5: Centrifugal Extraction: The ratio of extractant to raw acid is V(extractant):V(raw acid) = 5.0:1. The extractant and raw acid are preheated to 45℃~50℃ respectively. Five-stage countercurrent extraction is adopted, and the centrifugal extractor speed is controlled at 2500r / min. The extracted organic phase directly enters the extraction washing section, and the residual acid is processed and then enters the compound fertilizer section.

[0077] S6: Centrifugal washing: Use 37%~40% P2O5 purified acid as washing acid, preheat to 45℃~50℃, and perform five-stage countercurrent centrifugal washing according to the ratio of V (extracting organic):V (washing acid) = 4.0:1. The speed of the centrifugal extractor is controlled at 2500r / min. The washing acid directly enters the back-extraction section, and the residual washing acid is returned to the extraction section for further extraction.

[0078] S7: Centrifugal back-extraction: Desalinated water preheated to 45℃~50℃ is used as the back-extraction carrier. The ratio of washing organic to desalinated water feed is V(washed organic):V(desalinated water) = 10.0:1 for five-stage countercurrent extraction. The speed of the centrifugal extractor is controlled at 2500r / min. The back-extraction acid enters the concentration section, and the back-extraction organic is recycled into the extraction section. Part of the back-extraction acid is used as washing acid in S6.

[0079] S8: The back-extraction acid obtained from S7 is sent to the overflow storage tank for further separation of the residual organic phase. The organic phase is returned to the back-extraction stage for further separation. The back-extraction acid after separation of the organic phase is sent to the concentration tank.

[0080] S9: Concentration of back-extracted acid: The back-extracted acid was concentrated under vacuum conditions of 0.08~0.10MPa and 75℃ to obtain 85% phosphoric acid by concentrating it to 61.2%-61.7% P2O5.

[0081] The test results of raw materials and materials at each stage are shown in Table 1 below.

[0082] Example 2

[0083] The difference between this embodiment and Embodiment 1 is that a four-stage centrifugal extraction is performed in S5;

[0084] Comparative Example 1

[0085] The difference between this comparative example and Example 1 is that the initial acid is not concentrated, and subsequent processes such as desulfurization are carried out directly.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 1 is that the desulfurization process is set after the back-extraction acid concentration.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 1 is that the type of desulfurizing agent is changed to CaCO3.

[0090] Comparative Examples 4-6

[0091] The differences between these three comparative claims and Example 1 are as follows:

[0092] Comparative Example 4 used only two-stage extraction;

[0093] Comparative Example 5 used only 3-stage extraction;

[0094] Comparative Example 6

[0095] The difference between this comparative example and Example 1 is that defluorination is performed first, followed by desulfurization after extraction.

[0096] Comparative Example 7

[0097] The difference between this comparative example and Example 1 is that the complexation reaction step is omitted, and the extractant is still a mixture of 80% methyl isobutyl ketone and 20% sulfonated kerosene. The specific steps are as follows:

[0098] S1: Initial acid concentration: The initial acid is drawn into the first concentrator, the vacuum degree is set to 0.08~0.10MPa, the temperature is 75℃, the concentration time is 180min, and the concentration is carried out to 40%~42% P2O5. The concentrated crude acid is obtained by filtration.

[0099] S2: Crude acid desulfurization: Dicalcium phosphate with a moisture content of less than 2% and sieved through 80 mesh is slowly added at 80℃ at a ratio of n(Ca):n(S) = 1.2:1, and reacted for 2 hours under stirring at 450 r / min;

[0100] S3: Crude acid defluorination: Weigh out a NaOH solution with a solid content of 45%~50% according to n(NaOH):n(F) = 4:1, add it dropwise at 80℃ using a peristaltic pump for 1 hour, and react for 3~4 hours after the addition is complete; after the reaction is complete, filter under pressure to obtain the extractable raw acid and filter cake;

[0101] S4: Centrifugal Extraction: The ratio of extractant to raw acid is V(extractant):V(raw acid) = 5.0:1. The extractant and raw acid are preheated to 48℃ respectively. Five-stage countercurrent extraction is used. The centrifugal extractor speed is controlled at 2500r / min. The extracted organic phase directly enters the extraction washing section, and the residual acid is processed and then enters the compound fertilizer section.

[0102] S5: Centrifugal washing: Use 37%~40% P2O5 purified acid as washing acid, preheat to 45℃~50℃, and perform five-stage countercurrent centrifugal washing according to the ratio of V (extracted organic):V (washing acid) = 4:1. The speed of the centrifugal extractor is controlled at 2500r / min. The washing acid directly enters the back-extraction section, and the residual washing acid is returned to the extraction section for further extraction.

[0103] S6: Centrifugal back-extraction: Desalinated water preheated to 45℃~50℃ is used as the back-extraction carrier. The ratio of washing organic to desalinated water feed is V(washed organic):V(desalinated water)=10.0:1 for five-stage countercurrent extraction. The speed of the centrifugal extractor is controlled at 2500r / min. The back-extracted acid enters the concentration section, and the back-extracted organic enters the extraction section for recycling.

[0104] S7: The back-extracted acid obtained from S6 is sent to the overflow storage tank for further separation of the residual organic phase. The organic phase is returned to the back-extraction stage for further separation. The back-extracted acid after separation of the organic phase is sent to the concentration tank.

[0105] S8: Concentration of back-extracted acid: The back-extracted acid was concentrated under vacuum conditions of 0.08~0.10MPa and 75℃ to obtain 85% phosphoric acid by concentrating it to 61.2%-61.7% P2O5.

[0106] Comparative Example 8

[0107] The difference between this comparative example and Example 1 is that the complexation reaction step is omitted. The extractant used is a mixture of 40% methyl isobutyl ketone, 20% 2-(2-ethylhexyl)phosphoric acid (P204), and 40% sulfonated kerosene. The steps are as follows:

[0108] S1: Initial acid concentration: The initial acid is drawn into the first concentrator, the vacuum degree is set to 0.08~0.10MPa, the temperature is 75℃, the concentration time is 180min, and the concentration is carried out to 40%~42% of P2O5. The crude acid is released, cooled to room temperature, and filtered to obtain concentrated crude acid.

[0109] S2: Crude acid desulfurization: Dicalcium phosphate with a moisture content of less than 2% and sieved through 80 mesh is slowly added at 80℃ at a ratio of n(Ca):n(S) = 1.2:1, and reacted for 2 hours under stirring at 450 r / min;

[0110] S3: Crude acid defluorination: Weigh out a NaOH solution with a solid content of 45%~50% according to n(NaOH):n(F) = 4.0:1, add it dropwise at 80℃ using a peristaltic pump for 1 hour, and react for 3~4 hours after the addition is complete; after the reaction is complete, filter to obtain the extractable raw acid and filter cake.

[0111] S4: Centrifugal Extraction: The ratio of extractant to raw acid is V(extractant):V(raw acid) = 5.0:1. The extractant and raw acid are preheated to 48℃ respectively. Five-stage countercurrent extraction is used. The centrifugal extractor speed is controlled at 2500r / min. The extracted organic phase directly enters the extraction washing section, and the residual acid is processed and then enters the compound fertilizer section.

[0112] S5: Centrifugal washing: Use 37%~40% P2O5 purified acid as washing acid, preheat to 45℃~50℃, and perform five-stage countercurrent centrifugal washing according to the ratio of V (extracted organic):V (washing acid) = 4.0:1. The speed of the centrifugal extractor is controlled at 2500 / min. The washing acid directly enters the back-extraction section, and the residual washing acid is returned to the extraction section for further extraction.

[0113] S6: Centrifugal back-extraction: Desalinated water preheated to 45℃~50℃ is used as the back-extraction carrier. The ratio of washing organic to desalinated water feed is V(washed organic):V(desalinated water)=10.0:1 for five-stage countercurrent extraction. The speed of the centrifugal extractor is controlled at 2500r / min. The back-extracted acid enters the concentration section, and the back-extracted organic enters the extraction section for recycling.

[0114] S7: The back-extracted acid obtained from S6 is sent to the overflow storage tank for further separation of the residual organic phase. The organic phase is returned to the back-extraction stage for further separation. The back-extracted acid after separation of the organic phase is sent to the concentration tank.

[0115] S8: Concentration of back-extracted acid: The back-extracted acid was concentrated under vacuum conditions of 0.08~0.10MPa and 75℃ to obtain 85% phosphoric acid by concentrating it to 61.2%-61.7% P2O5.

[0116] The results of testing different embodiments and comparative examples are shown in Table 1 below.

[0117] Table 1. Detection results of different embodiments and comparative examples

[0118]

[0119] Note: In Table 1 above, data containing % indicates percentage content, while data without % indicates ppm.

[0120] By analyzing the data in Table 1 above, the following conclusions can be drawn:

[0121] 1. As can be seen from Examples 1, 2, 4 and 5, under the premise that other conditions remain unchanged, the extraction rate gradually increases with the increase of the number of extraction stages. When performing five-stage extraction, the extraction rate can reach more than 88%.

[0122] 2. The results of Example 1, Comparative Example 2 and Comparative Example 6 show that setting the desulfurization process in the later stage will result in a significant increase in sulfate ions and a certain degree of decrease in the extraction rate. The main reason is that if sulfate is not removed in the early stage, it will occupy some extraction sites.

[0123] In Comparative Example 3, after replacing the desulfurizing agent from dicalcium phosphate to calcium carbonate, the sulfate removal effect decreased compared to Example 1, and the extraction rate also decreased slightly. This may be due to sulfate occupying the extraction rate sites. At the same time, since calcium carbonate does not contain phosphorus, it will affect the subsequent phosphorus content, thus demonstrating the beneficial contribution of the selection of dicalcium phosphate in this process.

[0124] 3. A comparison of the results from Examples 1, 7, and 8 shows that when no complexation treatment is performed and the extractant remains unchanged (Comparative Example 7), the content of metal impurities is higher and the extraction rate is reduced. However, Comparative Example 8 shows that when no complexation treatment is performed alone, but a complexing agent is added to the extractant for treatment, the content of metal impurities is higher than that in Example 1 but lower than that in Comparative Example 7 which is completely without a complexing agent. However, the extraction rate is lower. This is mainly because although the addition of the complexing agent is beneficial to the removal of metal impurities, the amount of extractant used is reduced after the addition of the cationic complexing agent, and the extraction capacity decreases, thus resulting in a lower extraction rate.

[0125] Example 4

[0126] like Figure 2 As shown, a system for preparing purified phosphoric acid using centrifugal extraction technology is used to implement the method for preparing purified phosphoric acid using centrifugal extraction technology in the above embodiments. It includes a first concentrator 1, a first pressure filter system 3, a desulfurization reactor 5, a defluorination reactor 6, a complexation mixing reactor 7, a second pressure filter system 17, a heat exchanger 20, an extraction centrifuge group 21, a washing centrifuge group 25, a back-extraction centrifuge group 26, and a second concentrator 29 connected in sequence. The main equipment is connected by a main pipeline 2.

[0127] The first filter press system 3 is provided with a first filter residue discharge port 4; the second filter press system 17 is provided with a second filter residue discharge port 18.

[0128] A settling tank 15 is provided between the complexing mixing reactor 7 and the second pressure filtration system 17, and an overflow storage tank 28 is provided between the back-extraction centrifuge group 26 and the second concentrator 29. The settling tank 15 is provided with a settling slurry discharge port 16.

[0129] The extraction centrifuge unit 21 is provided with an extraction acid discharge port 22; the washing centrifuge unit 25 is provided with a washing acid discharge port 24;

[0130] A condenser heat exchanger 30 is also provided after the second concentrator 29 to cool the phosphoric acid obtained in the second concentrator 29, and then transfer it to the finished product storage tank 31 after cooling.

[0131] The steam discharged from the second concentrator 29 is sent to the heat exchanger 20 through the steam pipe 32 for heat utilization.

[0132] Example 5

[0133] The difference between this embodiment and embodiment 4 is the recycling of materials. Specifically, a washing residual acid return pipe 23 is provided between the extraction centrifuge group 21 and the washing centrifuge group 25 to return the washing residual acid generated after the washing centrifuge group 25 to the extraction centrifuge group 21. A back-extraction acid return pipe is also provided between the washing centrifuge group 25 and the back-extraction centrifuge group 26 to use the back-extraction acid generated after the back-extraction centrifuge group 26 as washing acid for the washing centrifuge group 25.

[0134] The back-extraction centrifugal unit 26 is connected to the condenser heat exchanger 30 through the heat exchange demineralized water pipe 27, and is used to use the heat in the condenser heat exchanger 30 to heat the demineralized water for back-extraction.

[0135] The condensed washing water obtained from the heat exchanger 20 is transported through the condensed washing water pipe 19 to the first filter press system 3 and the second filter press system 17 as filter press washing water, thereby realizing the recycling of water.

[0136] Example 6

[0137] The complexing mixing reactor 7 is also connected to a regeneration stirring reactor 10 via a complexing organic pipe 9. The regeneration stirring reactor 10 is connected to a water purifier 13. A regeneration impurity pipe 11 and a purified water pipe 12 are provided between the regeneration stirring reactor 10 and the purifier. The purifier is also provided with a sewage discharge pipe. The regenerated complexing agent is returned to the complexing mixing reactor 7 for reuse via the regeneration organic return pipe 8. The impurity discharged from the regeneration stirring reactor 10 is transported to the water purifier 13 for purification via the regeneration impurity pipe 11. The purified water produced by purification is returned to the regeneration stirring reactor 10 via the purified water pipe 12. The sewage is discharged from the system via the sewage discharge pipe 14.

[0138] Example 7

[0139] like Figure 3 As shown, the complexation mixing reactor 7 described in this embodiment includes a reactor body 33, a stirring assembly and a feeding / discharging assembly located inside the reactor body 33. The inner wall of the reactor body 33 is provided with propulsion baffles 35 at intervals to block water and increase longitudinal mass transfer.

[0140] The stirring assembly includes a mechanical stirring assembly and a gas stirring assembly. The mechanical stirring assembly includes a stirring rod 34 and a stirring ring disposed on the stirring rod 34. One end of the stirring rod 34 passes through the reactor body 33 and is connected to an external driving device. The gas stirring assembly includes a porous gas distributor 41 disposed at the lower part of the reactor body 33.

[0141] The feed and discharge assembly includes an inorganic acid inlet 36, a complexing agent inlet 38, a complexing agent outlet 40, and an acid outlet 44, wherein the inorganic acid inlet 36 is located at the top of the reactor body 33, and the complexing agent inlet 38 is located at the lower part of the side wall of the reactor body 33.

[0142] The bottom of the reactor body 33 is cone-shaped, the porous gas distributor 41 is located inside the cone-shaped space, the complexing agent outlet 40 is located on the side wall of the cone-shaped space, and the acid outlet 44 is located at the bottom of the cone-shaped space.

[0143] The bottom of the conical space is provided with an extension that communicates with the reactor body 33. A first valve 42 and a first check valve 43 are sequentially provided on the extension. The first valve 42 and the first check valve 43 are used to control the opening and closing of the compressed air inlet. When gas stirring is required, the single valve 42 and the first check valve 43 are opened to allow compressed air to enter and be stirred through the porous gas distributor 41. A second check valve 45 is also provided on the side wall of the extension to control the acid to be discharged from the acid outlet 44.

[0144] Example 8

[0145] The difference between this embodiment and embodiment 7 is that the stirring ring includes a first stirring ring 39 and a second stirring ring 46. The first stirring ring 39 is located below the second stirring ring 46. A stirring blade is connected between the first stirring ring 39 and the stirring rod 34. The second stirring ring 46 is connected to the stirring rod 34 through a stirring rack 37. The teeth of the stirring rack 37 face the top of the reactor body 33. The setting of the stirring rack 37 is beneficial to increase longitudinal mass transfer and improve the efficiency of complexation reaction.

[0146] The second stirring ring 46 can be configured as multiple layers; in this embodiment, it is three layers.

[0147] Between each layer of the second stirring ring 46 and the stirring rod 34, there are three stirring racks 37 spaced apart, and the stirring racks 37 of each layer of the second stirring ring 46 are arranged in an axially staggered manner.

[0148] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing purified phosphoric acid using centrifugal extraction technology, characterized in that, Includes the following steps: S1: Concentrate the initial acid to 40-45% P2O5, and filter to obtain concentrated crude acid; S2: Desulfurized crude acid is obtained by desulfurizing the concentrated crude acid obtained from S1 using a desulfurizing agent; S3: The crude acid obtained from S2 is defluorinated using a defluorinating agent, and then solid-liquid separation is performed to obtain extracted defluorinated acid and filter cake. S4: A mixture of cationic complexing extractant 2-(2-ethylhexyl)phosphoric acid P204 and sulfonated kerosene was subjected to cationic complexation treatment with defluorinated acid, and the extractable original acid was obtained after separation; S5: After heating the extractant and the original extract acid separately, add them to a centrifuge for centrifugal extraction to obtain the organic phase and residual acid; S6: The organic phase obtained in S5 is washed by countercurrent centrifugation using purified acid as washing acid to obtain washed organic phase and residual washing acid. The washed organic phase is directly fed into the back-extraction section, and the residual washing acid is returned to the extraction section for further extraction. S7: Using preheated desalinated water as the back-extraction carrier, the washed organic phase is back-extracted by countercurrent centrifugation to obtain back-extracted acid and back-extracted organic phase; S8: The back-extracted acid obtained from S7 is further separated to separate the residual organic phase, and the organic phase is returned to the back-extraction stage for further separation; the back-extracted acid after separation of the organic phase enters the concentration section for concentration to obtain purified phosphoric acid.

2. The method for preparing purified phosphoric acid using centrifugal extraction technology according to claim 1, characterized in that, In S2, the specific method for desulfurization is as follows: dicalcium phosphate is slowly added at a molar ratio of n(Ca):n(S) = 1.1~1.4:1 under conditions of 75℃~85℃, and the reaction is carried out under stirring conditions.

3. A method for preparing purified phosphoric acid using centrifugal extraction technology according to claim 1 or 2, characterized in that, In S3, the specific method for defluorination is as follows: a NaOH solution with a solid content of 45%~50% is weighed according to a molar ratio of n(NaOH):n(F) = 3.5~5.5:1, and added dropwise at 75℃~85℃. After the addition is completed, the reaction is carried out for 3~4 hours. After the reaction is completed, the extractable original acid and filter cake are obtained by pressure filtration.

4. A method for preparing purified phosphoric acid using centrifugal extraction technology according to claim 1 or 2, characterized in that, In S4, the specific method of complexation treatment is as follows: 70% P204 by volume and 30% sulfonated kerosene, with a volume ratio of 5.0~8.0:1 to defluorinated acid, preheated to 45℃~50℃, and reacted in a complexation mixing reactor. After completion, the organic phase enters the complexing agent back-extraction section, and the aqueous phase enters the next stage of centrifugal extraction as the original acid.

5. A method for preparing purified phosphoric acid using centrifugal extraction technology according to claim 1 or 2, characterized in that, In S5, the specific method of centrifugal extraction is as follows: the extractant and the extracting acid are fed in a volume ratio of V(extractant):V(extracting acid) = 4.0~7.0:

1. The extractant and the extracting acid are preheated to 45℃~50℃ respectively. At least three-stage countercurrent extraction is adopted. The extracted organic phase directly enters the extraction washing section, and the residual acid is treated and then enters the compound fertilizer section.

6. The method for preparing purified phosphoric acid using centrifugal extraction technology according to claim 5, characterized in that, In S5, the extractant is a combination of methyl isobutyl ketone and sulfonated kerosene.

7. A method for preparing purified phosphoric acid using centrifugal extraction technology according to claim 1 or 2, characterized in that, In step S6, the specific method for centrifugal washing is as follows: using a purification acid of 37%~40% P2O5 as the washing acid, preheating to 45℃~50℃, and performing at least three stages of countercurrent centrifugal washing according to a volume ratio of V (extracted organic phase):V (washing acid) = 3.0~5.0:1 to obtain the washed organic phase and residual washing acid. The washed organic phase is directly sent to the back-extraction section, and the residual washing acid is returned to the extraction section for further extraction.

8. A method for preparing purified phosphoric acid using centrifugal extraction technology according to claim 1 or 2, characterized in that, In S7, the specific method of centrifugal back-extraction is as follows: using demineralized water preheated to 45℃~50℃ as the back-extraction carrier, the ratio of washing organic phase to demineralized water feed is set at a volume ratio of V (washed organic phase):V (demineralized water) = 7.0~12.0:1, and at least three stages of countercurrent centrifugal extraction are carried out to obtain back-extracted organic phase and back-extracted acid. The back-extracted acid enters the concentration section, and the back-extracted organic phase enters the extraction section for recycling.

9. A method for preparing purified phosphoric acid using centrifugal extraction technology according to claim 1 or 2, characterized in that, In step S8, the organic phase is further separated in the overflow tank. The back-extracted acid from the overflow tank enters the concentration tank, where the vacuum degree is 0.08~0.10MPa and the temperature is 70℃~80℃, and it is concentrated to 61.2%~61.7% P2O5 to obtain 85% phosphoric acid.

10. A system for preparing purified phosphoric acid using centrifugal extraction technology, characterized in that: The method for preparing purified phosphoric acid using centrifugal extraction technology according to any one of claims 1-9 comprises, in sequence, a first concentrator (1), a first pressure filtration system (3), a desulfurization reactor (5), a defluorination reactor (6), a complexation mixing reactor (7), a second pressure filtration system (17), a heat exchanger (20), an extraction centrifuge group (21), a washing centrifuge group (25), a back-extraction centrifuge group (26), and a second concentrator (29).

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