Process for producing sodium hydrogen phosphate or sodium dihydrogen phosphate from the residual acid and by-product sodium sulfate

Abstract

The method for preparing disodium hydrogen phosphate or sodium phosphate dibasic from raffinate acid of purified wet-process phosphoric acid and by-product sodium sulfate, the process steps are: (1) the raffinate acid is treated with precipitator to remove fluorine and get the raffinate acid without fluorine, then the raffinate acid without fluorine is extracted to get the extractant containing phosphoric acid and impurities and the raffinate phase; (2) the extractant containing phosphoric acid and impurities is washed with water to get the purified extractant containing phosphoric acid and washing liquid; (3) the raffinate phase is reacted with sodium hydroxide aqueous solution to get reaction liquid, when preparing disodium hydrogen phosphate, the pH of the reaction liquid is 9-12, when preparing sodium phosphate dibasic, the pH of the reaction liquid is 4-8; (4) the purified extractant containing phosphoric acid is neutralized with the reaction liquid, then the extractant is separated from the neutralized liquid; (5) the neutralized liquid is cooled to crystallize, then the crystal is separated from the mother liquor, the crystal is disodium hydrogen phosphate or sodium phosphate dibasic; (6) the mother liquor separated in step (5) is concentrated to crystallize when a small amount of crystal is separated out, the separated crystal is sodium sulfate.

Description

Technical Field

[0001] This invention belongs to the field of treatment and utilization of residual acid produced from the purification of wet-process phosphoric acid, and relates to a production method for preparing disodium hydrogen phosphate or sodium dihydrogen phosphate and sodium sulfate using residual acid from the purification of wet-process phosphoric acid as raw material. Background Technology

[0002] Phosphoric acid, as an important intermediate raw material in the chemical industry, is used not only in the production of fertilizers such as ammonium phosphate and superphosphate, but also in the production of various phosphates. Currently, phosphoric acid production is gradually shifting from the thermal process to the wet process. Among wet-process phosphoric acid, solvent extraction is the most widely used method. However, this process generates a large amount of raffinate, which is characterized by high levels of phosphorus pentoxide, sulfuric acid, and metallic impurities. Due to the widespread industrial application of solvent extraction technology for purifying wet-process phosphoric acid, a significant amount of raffinate is generated. Furthermore, as the grade of phosphate rock decreases, the impurity content of wet-process phosphoric acid will gradually increase, leading to a further increase in the amount of raffinate produced during solvent extraction. Treating this raffinate as waste not only increases the cost of wet-process phosphoric acid purification technology but also represents a significant waste of non-renewable phosphoric acid resources. Therefore, the treatment and utilization of raffinate is a key factor for the sustainable development of the wet-process phosphoric acid purification industry and an important pathway for the efficient utilization of phosphoric acid resources.

[0003] Disodium hydrogen phosphate is commonly used as a water softener, fabric weight enhancer, and fire retardant. It is also used in glazes, welding fluxes, pharmaceuticals, pigments, the food industry, and in the production of other phosphates for industrial water treatment, dyeing and printing detergents, quality improvers, neutralizing agents, antibiotic culture media, biochemical treatment agents, and food quality improvers. Currently, the preparation of disodium hydrogen phosphate mainly relies on wet-process phosphoric acid and sodium hydroxide synthesis. For example, CN105174239A provides a method for preparing disodium hydrogen phosphate using wet-process phosphoric acid. This method uses wet-process phosphoric acid as a raw material to prepare disodium hydrogen phosphate, which is then crystallized at a vacuum of 0.005 MPa and 90°C. However, this method suffers from drawbacks such as high raw material costs, complex operation, and high energy consumption.

[0004] Sodium dihydrogen phosphate is widely used in various fields such as food, medicine, chemical industry, printing and dyeing, metal corrosion protection, water treatment, chemical building materials, daily chemical products, and aquaculture. Currently, sodium dihydrogen phosphate is mainly produced using thermal phosphoric acid or wet purified phosphoric acid as raw materials, which also suffers from problems such as high energy consumption, high raw material costs, and low economic benefits. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing disodium hydrogen phosphate or sodium dihydrogen phosphate from the residual acid of purified wet-process phosphoric acid, with sodium sulfate as a byproduct, so as to broaden the utilization pathway of residual acid, reduce the cost of solvent extraction for refining phosphoric acid, and provide a new technical solution for the preparation of disodium hydrogen phosphate or sodium dihydrogen phosphate and sodium sulfate.

[0006] The method for producing disodium hydrogen phosphate or sodium dihydrogen phosphate from the residual acid of purified wet-process phosphoric acid, with sodium sulfate as a byproduct, according to the present invention, comprises the following steps:

[0007] (1) The residual acid produced by the purification of wet phosphoric acid is defluorinated by a precipitant to obtain defluorinated residual acid. The defluorinated residual acid is then extracted. The ratio of extractant to defluorinated residual acid is 1 to 5:1. The extraction temperature is 30℃ to 70℃ and the extraction time is at least 10 min. After extraction, extractant and raffinate containing phosphoric acid and impurities are obtained and the two phases are separated.

[0008] (2) The extractant containing phosphoric acid and impurities separated in step (1) is washed with water. The ratio of extractant containing phosphoric acid and impurities to water is 8 to 12:1. The washing temperature is the same as the extraction temperature (30℃ to 70℃). The washing time is determined when the mass fraction of fluorine in the extractant is less than 0.05%. After washing, purified phosphoric acid extractant and washing liquid are obtained, and the two phases are separated.

[0009] (3) The raffinate separated in step (1) is reacted with sodium hydroxide aqueous solution to obtain a reaction solution, and the reaction time is at least 10 min; when preparing disodium hydrogen phosphate, the amount of sodium hydroxide aqueous solution added is limited to the pH of the reaction solution = 9 to 12; when preparing sodium dihydrogen phosphate, the amount of sodium hydroxide aqueous solution added is limited to the pH of the reaction solution = 4 to 8.

[0010] (4) Add all of the reaction solution with pH=9 to 12 or pH=4 to 8 obtained in step (3) to the purified phosphoric acid extractant obtained in step (2) and neutralize the phosphoric acid extractant. The neutralization temperature is the same as the extraction temperature (30℃ to 70℃) and the time is at least 30 minutes. After the neutralization treatment, separate the extractant from the sodium dihydrogen phosphate neutralization solution or sodium dihydrogen phosphate neutralization solution.

[0011] (5) Cool the neutralized solution of disodium hydrogen phosphate separated in step (4) at a constant rate of 10-30°C for 2-4 hours to complete the cooling crystallization. After cooling crystallization, separate the crystal and the mother liquor. The separated crystal is the disodium hydrogen phosphate product.

[0012] Alternatively, the sodium dihydrogen phosphate neutral solution separated in step (4) can be concentrated to remove half of the water, and then naturally cooled and crystallized. After cooling and crystallization, the crystals and mother liquor can be separated, and the separated crystals are the sodium dihydrogen phosphate product.

[0013] (6) Concentrate the mother liquor separated in step (5) until a small amount of crystals precipitate out, and then allow it to cool and crystallize naturally. The crystals separated after cooling and crystallization are sodium sulfate by-products.

[0014] In step (1) of the above method, the amount of precipitant used during defluorination is 150-300% of the theoretical amount required to remove fluoride from the residual acid produced during the purification of wet-process phosphoric acid. The precipitant is at least one of sodium carbonate, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0015] In step (1) of the above method, the defluorination process is as follows: the precipitant is added to the residual raffinate, and the reaction is carried out at the extraction temperature under stirring for at least 15 minutes. Then the residual raffinate is obtained by filtration.

[0016] In step (1) of the above method, the extractant used for extraction is composed of trioctyldecyl tertiary amine (N235), tributyl phosphate (TBP) and kerosene, and the volume ratio of N235, TBP and kerosene is 3-6:3-6:0.5-2.

[0017] In step (2) of the above method, the water used for washing is tap water or deionized water.

[0018] In step (3) of the above method, the sodium hydroxide aqueous solution is prepared from solid sodium hydroxide and tap water.

[0019] In steps (5) and (6) of the above method, the natural cooling crystallization is to place the crystallization system at room temperature to complete the crystallization.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The method described in this invention uses the residual acid produced during the purification of wet-process phosphoric acid as raw material to prepare disodium hydrogen phosphate or sodium dihydrogen phosphate and sodium sulfate, providing a new way to utilize residual acid and contributing to the sustainable development of the wet-process phosphoric acid purification industry.

[0022] 2. Experiments show that, using the method described in this invention, the recovery rate of phosphorus pentoxide in the residual acid can reach about 66.2%, and the recovery rate of sulfuric acid can reach about 85.7% (see Example 1), thus improving the recovery and utilization rate of phosphorus resources and sulfuric acid.

[0023] 3. The method described in this invention provides a new technical solution for the preparation of disodium hydrogen phosphate or sodium dihydrogen phosphate and sodium sulfate, which can overcome the disadvantages of high cost and high energy consumption of traditional methods for producing disodium hydrogen phosphate or sodium dihydrogen phosphate.

[0024] 4. The method and equipment described in this invention are conventional equipment, easy to operate, low in production cost, and high in safety, thus making it easy to achieve industrial production. Detailed Implementation

[0025] The method for producing disodium hydrogen phosphate or sodium dihydrogen phosphate from the residual acid of purified wet-process phosphoric acid, with sodium sulfate as a byproduct, is further illustrated below through examples. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0026] In the following examples, the raw material used—the residual acid from the purification of wet-process phosphoric acid—contains 20% phosphorus pentoxide, 4% sulfuric acid, and 1% fluorine by mass.

[0027] Example 1

[0028] In this embodiment, disodium hydrogen phosphate is produced with sodium sulfate as a byproduct. The process steps are as follows:

[0029] (1) The residual acid is defluorinated by a precipitant, wherein the precipitant is disodium hydrogen phosphate. The specific operation is as follows: add 180% of the theoretical amount of disodium hydrogen phosphate required to remove fluoride from the residual acid to the residual acid, react at 60°C with stirring for 15 min, and then filter to obtain defluorinated residual acid.

[0030] The residual acid from defluorination was extracted using an extractant composed of N235, TBP, and kerosene in a volume ratio of N235:TBP:kerosene = 5:4:1. The ratio of extractant to residual acid from defluorination was 4:1. The extraction temperature was 60℃ and the extraction time was 40 min. The extracted phase contained phosphoric acid and impurities, and the extractant and raffinate phases were obtained and then separated.

[0031] (2) The extractant containing phosphoric acid and impurities separated in step (1) is washed with tap water. The ratio of extractant containing phosphoric acid and impurities to tap water is 10:1. The washing temperature is the same as the extraction temperature, which is 60°C. The washing time is 15 min (the mass fraction of fluorine in the extractant is 0.025%). After washing, purified phosphoric acid extractant and washing liquid are obtained, and the two phases are separated.

[0032] (3) The raffinate separated in step (1) is reacted with sodium hydroxide aqueous solution to obtain a reaction solution. The concentration of sodium hydroxide aqueous solution is 80 g / L, which is prepared by solid sodium hydroxide and tap water. The amount of sodium hydroxide aqueous solution added is such that the pH of the reaction solution is 10.6. The reaction time is 10 minutes.

[0033] (4) Add all of the reaction solution with pH=10.6 obtained in step (3) to the purified phosphoric acid extractant obtained in step (2) and neutralize the phosphoric acid extractant. The neutralization temperature is the same as the extraction temperature, which is 60°C, and the time is 45 min. After the neutralization treatment, separate the extractant from the disodium hydrogen phosphate neutralization solution.

[0034] (5) The neutralized solution of disodium hydrogen phosphate separated in step (4) is cooled to 23°C at a constant rate for 3 hours to complete the cooling crystallization. After cooling crystallization, the crystals and mother liquor are separated. The separated crystals are the disodium hydrogen phosphate (Na2HPO4·12H2O) product.

[0035] (6) Concentrate the mother liquor separated in step (5) until a small amount of crystals precipitate out, and then allow it to cool naturally under stirring to crystallize. After cooling to room temperature (about 20°C), separate the crystals. The obtained crystals are sodium sulfate by-products.

[0036] Calculations show that the recovery rate of phosphorus pentoxide in this embodiment is 66.2%, and the recovery rate of sulfuric acid is 85.7%.

[0037] Example 2

[0038] In this embodiment, disodium hydrogen phosphate is produced with sodium sulfate as a byproduct. The process steps are as follows:

[0039] (1) The residual acid is defluorinated by a precipitant, wherein the precipitant is sodium carbonate. The specific operation is as follows: sodium carbonate is added to the residual acid at 220% of the theoretical amount required to remove fluoride from the residual acid, and the reaction is carried out at 50°C with stirring for 15 minutes. Then the defluorinated residual acid is obtained by filtration.

[0040] The residual acid from defluorination was extracted using an extractant composed of N235, TBP, and kerosene in a volume ratio of N235:TBP:kerosene = 5:4:1. The ratio of extractant to residual acid from defluorination was 3:1. The extraction temperature was 50℃ and the extraction time was 30 min. The extracted phase contained phosphoric acid and impurities, and the extractant and raffinate phases were obtained and separated.

[0041] (2) The extractant containing phosphoric acid and impurities separated in step (1) is washed with tap water. The ratio of extractant containing phosphoric acid and impurities to tap water is 8:1. The washing temperature is the same as the extraction temperature, which is 50°C. The washing time is 12 min (the mass fraction of fluorine in the extractant is 0.018%). After washing, purified phosphoric acid extractant and washing liquid are obtained, and the two phases are separated.

[0042] (3) The raffinate separated in step (1) is reacted with sodium hydroxide aqueous solution to obtain a reaction solution. The concentration of sodium hydroxide aqueous solution is 80 g / L, which is prepared by solid sodium hydroxide and tap water. The amount of sodium hydroxide aqueous solution added is such that the pH of the reaction solution is 9.8. The reaction time is 10 minutes.

[0043] (4) Add all of the reaction solution with pH=9.8 obtained in step (3) to the purified phosphoric acid extractant obtained in step (2) and neutralize the phosphoric acid extractant. The neutralization temperature is the same as the extraction temperature, which is 50°C, and the time is 40 min. After the neutralization treatment, separate the extractant from the disodium hydrogen phosphate neutralization solution.

[0044] (5) The neutralized solution of disodium hydrogen phosphate separated in step (4) is cooled to 25°C at a constant rate for 2.5 h to complete the cooling crystallization. After cooling crystallization, the crystals and mother liquor are separated. The separated crystals are the disodium hydrogen phosphate (Na2HPO4·12H2O) product.

[0045] (6) Concentrate the mother liquor separated in step (5) until a small amount of crystals precipitate out, and then allow it to cool naturally under stirring to crystallize. After cooling to room temperature (about 21°C), separate the crystals. The obtained crystals are sodium sulfate by-products.

[0046] Calculations show that the recovery rate of phosphorus pentoxide in this embodiment is 60.4%, and the recovery rate of sulfuric acid is 81.6%.

[0047] Example 3

[0048] In this embodiment, sodium dihydrogen phosphate is produced with sodium sulfate as a byproduct. The process steps are as follows:

[0049] (1) The residual acid is defluorinated by a precipitant, wherein the precipitant is sodium dihydrogen phosphate. The specific operation is as follows: sodium dihydrogen phosphate is added to the residual acid at 250% of the theoretical amount required to remove fluoride from the residual acid. The reaction is carried out at 50°C with stirring for 20 minutes. Then the defluorinated residual acid is obtained by filtration.

[0050] The residual acid from defluorination was extracted using an extractant composed of N235, TBP, and kerosene in a volume ratio of N235:TBP:kerosene = 6:3:1. The ratio of extractant to residual acid from defluorination was 4:1. The extraction temperature was 50℃ and the extraction time was 50 min. The extracted phase contained phosphoric acid and impurities, and the extractant and raffinate phases were obtained and then separated.

[0051] (2) The extractant containing phosphoric acid and impurities separated in step (1) is washed with tap water. The ratio of extractant containing phosphoric acid and impurities to tap water is 10:1. The washing temperature is the same as the extraction temperature, which is 50°C. The washing time is 15 min (the mass fraction of fluorine in the extractant is 0.018%). After washing, purified phosphoric acid extractant and washing liquid are obtained, and the two phases are separated.

[0052] (3) The raffinate separated in step (1) is reacted with sodium hydroxide aqueous solution to obtain a reaction solution. The concentration of sodium hydroxide aqueous solution is 80 g / L, which is prepared by solid sodium hydroxide and tap water. The amount of sodium hydroxide aqueous solution added is such that the pH of the reaction solution is 7.5, and the reaction time is 10 minutes.

[0053] (4) Add all of the reaction solution with pH=7.5 obtained in step (3) to the purified phosphoric acid extractant obtained in step (2) and neutralize the phosphoric acid extractant. The neutralization temperature is the same as the extraction temperature, which is 50°C, and the time is 45 min. After the neutralization treatment, separate the extractant from the sodium dihydrogen phosphate neutralization solution.

[0054] (5) After concentrating the sodium dihydrogen phosphate neutral solution separated in step (4) to remove half of the water, it is naturally cooled and crystallized under stirring. After cooling to room temperature (about 20°C), the crystals and mother liquor are separated. The separated crystals are sodium dihydrogen phosphate (NaH2PO4·2H2O) products.

[0055] (6) Concentrate the mother liquor separated in step (5) until a small amount of crystals precipitate out, and then allow it to cool naturally under stirring to crystallize. After cooling to room temperature (about 20°C), separate the crystals. The obtained crystals are sodium sulfate by-products.

[0056] Calculations show that the recovery rate of phosphorus pentoxide in this embodiment is 52.6%, and the recovery rate of sulfuric acid is 76.5%.

[0057] Example 4

[0058] In this embodiment, sodium dihydrogen phosphate is produced with sodium sulfate as a byproduct. The process steps are as follows:

[0059] (1) The residual acid is defluorinated by a precipitant, wherein the precipitant is sodium carbonate. The specific operation is as follows: sodium carbonate is added to the residual acid at 300% of the theoretical amount required to remove fluoride from the residual acid, and the reaction is carried out at 45°C with stirring for 20 minutes. Then the defluorinated residual acid is obtained by filtration.

[0060] The residual acid from defluorination was extracted using an extractant composed of N235, TBP, and kerosene in a volume ratio of N235:TBP:kerosene = 6:3:1. The ratio of extractant to residual acid from defluorination was 3:1. The extraction temperature was 45℃ and the extraction time was 40 min. The extracted phase contained phosphoric acid and impurities, and the extractant and raffinate phases were obtained and then separated.

[0061] (2) The extractant containing phosphoric acid and impurities separated in step (1) is washed with tap water. The ratio of extractant containing phosphoric acid and impurities to tap water is 8:1. The washing temperature is the same as the extraction temperature, which is 45°C. The washing time is 12 min (the mass fraction of fluorine in the extractant is 0.018%). After washing, purified phosphoric acid extractant and washing liquid are obtained, and the two phases are separated.

[0062] (3) The raffinate separated in step (1) is reacted with sodium hydroxide aqueous solution to obtain a reaction solution. The concentration of sodium hydroxide aqueous solution is 80 g / L, which is prepared by solid sodium hydroxide and tap water. The amount of sodium hydroxide aqueous solution added is such that the pH of the reaction solution is 6.4. The reaction time is 10 minutes.

[0063] (4) Add all of the reaction solution with pH=6.4 obtained in step (3) to the purified phosphoric acid extractant obtained in step (2) and neutralize the phosphoric acid extractant. The neutralization temperature is the same as the extraction temperature, which is 45°C, and the time is 40 min. After the neutralization treatment, separate the extractant from the sodium dihydrogen phosphate neutralization solution.

[0064] (5) After concentrating the sodium dihydrogen phosphate neutral solution separated in step (4) to remove half of the water, it is naturally cooled and crystallized under stirring. After cooling to room temperature (about 20°C), the crystals and mother liquor are separated. The separated crystals are sodium dihydrogen phosphate (NaH2PO4·2H2O) products.

[0065] (6) Concentrate the mother liquor separated in step (5) until a small amount of crystals precipitate out, and then allow it to cool naturally under stirring to crystallize. After cooling to room temperature (about 20°C), separate the crystals. The obtained crystals are sodium sulfate by-products.

[0066] Calculations show that the recovery rate of phosphorus pentoxide in this embodiment is 50.3%, and the recovery rate of sulfuric acid is 71.6%.

Claims

1. A method for producing disodium hydrogen phosphate or sodium dihydrogen phosphate from the residual acid of purified wet-process phosphoric acid, with sodium sulfate as a byproduct, characterized in that... The process steps are as follows: (1) The residual acid produced by the purification of wet phosphoric acid is defluorinated by a precipitant to obtain defluorinated residual acid. The defluorinated residual acid is then extracted. The extractant consists of trioctyldecyl tertiary amine, tributyl phosphate and kerosene. The volume ratio of trioctyldecyl tertiary amine, tributyl phosphate and kerosene is 3~6:3~6:0.5~2. The ratio of extractant to defluorinated residual acid during extraction is 1~5:

1. The extraction temperature is 30℃~70℃ and the extraction time is at least 10min. After extraction, extractant and raffinate containing phosphoric acid and impurities are obtained and the two phases are separated. (2) The extractant containing phosphoric acid and impurities separated in step (1) is washed with water. The ratio of extractant containing phosphoric acid and impurities to water is 8~12:

1. The washing temperature is the same as the extraction temperature. The washing time is determined when the mass fraction of fluorine in the extractant is less than 0.05%. After washing, purified phosphoric acid extractant and washing liquid are obtained, and the two phases are separated. (3) The raffinate separated in step (1) is reacted with sodium hydroxide aqueous solution to obtain a reaction solution. The reaction time is at least 10 min. When preparing disodium hydrogen phosphate, the amount of sodium hydroxide aqueous solution added is limited to pH 9~12 of the reaction solution. When preparing sodium dihydrogen phosphate, the amount of sodium hydroxide aqueous solution added is limited to pH 4~8 of the reaction solution. (4) Add all of the reaction solution with pH=9~12 or pH=4~8 obtained in step (3) to the purified phosphoric acid extractant obtained in step (2) and neutralize the phosphoric acid extractant. The neutralization temperature is the same as the extraction temperature and the time is at least 30 minutes. After the neutralization treatment, separate the extractant from the sodium dihydrogen phosphate neutralization solution or sodium dihydrogen phosphate neutralization solution. (5) Cool the neutralized solution of disodium hydrogen phosphate separated in step (4) to 10-30℃ at a constant rate for 2-4 hours to complete the cooling crystallization. After cooling crystallization, separate the crystals and the mother liquor. The separated crystals are the disodium hydrogen phosphate product. Alternatively, the sodium dihydrogen phosphate neutral solution separated in step (4) can be concentrated to remove half of the water, and then naturally cooled and crystallized. After cooling and crystallization, the crystals and mother liquor can be separated, and the separated crystals are the sodium dihydrogen phosphate product. (6) Concentrate the mother liquor separated in step (5) until a small amount of crystals precipitate out, and then allow it to cool and crystallize naturally. The crystals separated after cooling and crystallization are sodium sulfate by-products.

2. The method for producing disodium hydrogen phosphate or sodium dihydrogen phosphate from the residual acid of purified wet-process phosphoric acid, with sodium sulfate as a byproduct, according to claim 1, is characterized in that... In step (1), the amount of precipitant used during defluorination is 150-300% of the theoretical amount required to remove fluoride from the residual acid; the precipitant is at least one of sodium carbonate, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

3. The method for producing disodium hydrogen phosphate or sodium dihydrogen phosphate from the residual acid of purified wet-process phosphoric acid, with sodium sulfate as a byproduct, as described in claim 1 or 2, is characterized in that... In step (1), the defluorination process is as follows: the precipitant is added to the residual raffinate, and the reaction is carried out at the extraction temperature under stirring for at least 15 minutes. Then the residual raffinate is obtained by filtration.