Method for preparing monoammonium phosphate from raffinate acid

Abstract

The invention relates to the technical field of phosphorus chemical industry, in particular to a method for preparing monoammonium phosphate from raffinate acid, which comprises the following steps: S1) uniformly mixing the raffinate acid with concentrated sulfuric acid, concentrating, and performing solid-liquid separation to obtain a concentrated solution; s2) dropwise adding a solvent into the concentrated solution for primary solvent purification; the solvent components are limited; s3) standing and splitting the light and heavy mixed phase obtained by purifying the primary solvent to obtain an acid-containing solvent phase; s4) mixing the acid-containing solvent phase with barium fluoride, carrying out a reaction, and carrying out solid-liquid separation to obtain a secondary purified acid-containing solvent and purified slag; s5) carrying out vacuum distillation on the secondary purified acid-containing solvent, and recovering the solvent to obtain a distillation kettle residual liquid which is purified acid; and S6) diluting the purified acid, then mixing the diluted purified acid with an ammonia-containing alkaline substance, carrying out a neutralization reaction, filtering after the reaction, and drying and granulating a filter cake to obtain the fire-fighting grade monoammonium phosphate product. The method provided by the invention has the advantages of high impurity removal rate, high phosphorus yield and high added value of the product, and can be used for preparing fire-fighting grade monoammonium phosphate.

Description

Technical Field

[0001] The invention relates to the technical field of phosphorus chemical industry, and in particular to a method for preparing monoammonium phosphate by utilizing raffinate acid. Background Art

[0002] Phosphoric acid is an important basic chemical raw material with a wide range of uses. It can be made into a series of other important products and plays a great role in the development of the national economy. At present, wet-process phosphoric acid is mainly obtained by decomposing phosphate rock with sulfuric acid and then separating it. This phosphoric acid has a relatively high impurity content, and its impurities are mainly calcium, magnesium, iron, aluminum, fluorine, silicon dioxide, sulfate, organic matter, etc. This wet-process phosphoric acid can be directly used to produce fertilizers, but it needs to be further purified and impurity-removed if it is used to produce high-purity industrial phosphoric acid or fine phosphate.

[0003] According to the characteristics of wet-process phosphoric acid impurities and the index requirements of fine products, researchers have developed many methods for purifying wet-process phosphoric acid, among which organic solvent extraction is the most widely used method for purifying phosphoric acid in industrial applications. In the process of purifying wet-process phosphoric acid by solvent extraction, the phosphoric acid purification rate is generally controlled at 50% to 60%. The process will inevitably produce raffinate acid (i.e., the acid remaining in the aqueous phase after extraction), which is mainly characterized by high P2O5 concentration and high impurity content (mainly metal cation impurities such as calcium, magnesium, iron, and aluminum). If the raffinate acid can be effectively utilized to prepare high value-added products, it will bring greater economic benefits to the enterprise.

[0004] For a long time, the recycling of raffinate has been a technical problem, mainly limited by factors such as high impurity ion content, difficulty in purification and high cost. Directly using raffinate instead of ordinary wet-process phosphoric acid in the production of monoammonium phosphate will result in low content of the main component of the product, high slurry viscosity, difficult reaction, low product yield, and easy scaling of process equipment pipelines. At present, the method of mixing raffinate with ordinary wet-process phosphoric acid to produce monoammonium phosphate is generally adopted. This method is to mix ordinary wet-process phosphoric acid with a P2O5 mass content of 25% with raffinate in a certain ratio to reduce the cation content, and then neutralize it with ammonia. The monoammonium phosphate produced by this method can only meet the quality standards of agricultural fertilizers, the product added value is low, and the raffinate needs to be mixed with ordinary wet-process phosphoric acid in a certain proportion, which cannot meet the process requirements of producing monoammonium phosphate with raffinate.

[0005] Some technical parties use solvent precipitation to purify and utilize the raffinate. For example, patent application document CN101704518B discloses "a method for purifying raffinate", which is to add alcohol to the raffinate with a P2O5 mass concentration of 40.9% to 47.0% and a magnesium mass concentration of 1.6% to 2.8% at room temperature to 75°C, and then add fluorosilicic acid and continue to react for 20 to 30 minutes; after cooling to room temperature to 35°C, vacuum filtration is performed to separate the precipitate to obtain a clear liquid; the clear liquid is vacuum distilled to recover the alcohol to obtain purified raffinate. This patent uses alcohol solvents and fluorosilicic acid in combination, and purifies the raffinate through solvent precipitation, separation, distillation and concentration, so that it can be reused to improve the utilization rate of phosphoric acid, the raw material of the solvent extraction method. At the same time, the purified raffinate has a low magnesium ion content, and the magnesium removal rate can reach up to 77.6%. It has good purification effect, simple process and low cost.

[0006] However, due to the high solubility of magnesium fluorosilicate, even if an excess of fluorosilicic acid is added within the concentration range of the raffinate acid, only a small amount of precipitation can be generated to separate the magnesium, resulting in the inability to further improve the magnesium removal rate. The remaining large amount of fluorosilicic acid needs to be treated with an alkali metal salt (such as sodium carbonate) to form a sparingly soluble fluorosilicate for separation, and sodium carbonate consumes phosphoric acid, resulting in increased phosphorus loss, and the fluorine removal is not thorough, which increases the risk of equipment corrosion and blockage during the subsequent raffinate acid concentration process. Summary of the invention

[0007] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing monoammonium phosphate using raffinate acid, which has high impurity removal rate, high phosphorus yield, and high product added value, and can produce fire-grade monoammonium phosphate.

[0008] The present invention provides a method for preparing monoammonium phosphate by utilizing raffinate acid, comprising the following steps:

[0009] S1) mixing the raffinate with concentrated sulfuric acid, concentrating, and separating the solid and liquid to obtain a concentrated solution;

[0010] S2) adding a solvent dropwise into the concentrated solution to perform primary solvent purification; the solvent comprises at least one of an alcohol solvent, a ketone solvent and an ether solvent;

[0011] S3) allowing the light and heavy mixed phase obtained by purifying the primary solvent to stand for phase separation, wherein the upper layer is the acid-containing solvent phase and the lower layer is the impurity-containing heavy phase;

[0012] S4) mixing the acid-containing solvent phase with barium fluoride to react, and after solid-liquid separation, obtaining a secondary purified acid-containing solvent and purified slag;

[0013] S5) subjecting the secondary purified acid-containing solvent to vacuum distillation to recover the solvent, and returning the obtained regenerated solvent to the primary solvent purification step for recycling, and the residual liquid in the distillation kettle is the purified acid;

[0014] S6) diluting the purified acid, and then mixing it with an ammonia-containing alkaline substance to carry out a neutralization reaction, filtering after the reaction, and drying and granulating the filter cake to obtain a fire-fighting grade monoammonium phosphate product.

[0015] Preferably, in step S1), concentrated sulfuric acid and raffinate are mixed according to SO4 2- Mix well with P2O5 in a mass ratio of 4.2 to 30:100.

[0016] Preferably, in step S1), the concentration method includes vacuum concentration, atmospheric pressure concentration, or one-stage atmospheric pressure and one-stage vacuum concentration;

[0017] The vacuum degree of the vacuum concentration is 80-90 KPa; after the concentration, the mass concentration of P2O5 in the solution is 23%-54%.

[0018] Preferably, in step S2), the volume ratio of the solvent to the concentrated solution is 1 to 3.5:1;

[0019] The time for adding the solvent dropwise is controlled within 30 to 90 minutes; the temperature for the primary solvent purification is 55 to 65° C.; and the time for the primary solvent purification after adding the solvent is 10 to 90 minutes.

[0020] Preferably, in step S3), the pH value of the acid-containing solvent phase is 0.8 to 1.2.

[0021] Preferably, in step S3), after obtaining the impurity-containing heavy phase, the process further comprises:

[0022] Superphosphate is prepared by using a heavy phase containing impurities, calcium carbonate and phosphogypsum; the phosphogypsum includes the precipitated phosphogypsum obtained in step S1);

[0023] The P2O5 in the impurity-containing heavy phase and the Ca in the calcium carbonate 2+ The mass ratio of phosphogypsum to P2O5 in the impurity-containing heavy phase is 4.8-5.2:1; the mass ratio of phosphogypsum to P2O5 in the impurity-containing heavy phase is 18-22:100.

[0024] Preferably, in step S4), the Mg in the acid-containing solvent phase 2+ and the F in the barium fluoride - The molar ratio is 1:2.

[0025] Preferably, in step S4), mixing the acid-containing solvent phase with barium fluoride comprises:

[0026] Add barium fluoride dropwise into the acid-containing solvent phase; the adding time is 30 to 120 minutes;

[0027] The reaction temperature is 55-65° C.; the reaction time after mixing is 10-60 min.

[0028] Preferably, in step S5), the temperature of the vacuum distillation is 60-80° C., and the vacuum degree is 80-90 KPa.

[0029] Preferably, in step S6), the dilution is performed by adding water; the mass ratio of the purified acid to water is 0.8-1.2:0.8-1.2;

[0030] The ammonia-containing alkaline substance includes ammonia water, ammonia gas, ammonium carbonate or ammonium bicarbonate;

[0031] When the ammonia-containing alkaline substance is aqueous ammonia, the mixing with the ammonia-containing alkaline substance comprises:

[0032] Adding ammonia water dropwise to the diluted purified acid until the pH value is 4.0 to 4.5; the adding time is 30 to 90 minutes;

[0033] The temperature of the neutralization reaction is 65-80° C.; after mixing with the ammonia-containing alkaline substance, the neutralization reaction time is 30-60 minutes.

[0034] The invention provides a method for preparing monoammonium phosphate by using raffinate acid, comprising the following steps: S1) mixing raffinate acid with concentrated sulfuric acid, concentrating, and separating solid and liquid to obtain a concentrated solution; S2) adding a solvent dropwise into the concentrated solution to perform primary solvent purification; the solvent comprises at least one of an alcohol solvent, a ketone solvent and an ether solvent; S3) standing a light and heavy mixed phase obtained by the primary solvent purification for phase separation, wherein the upper layer is an acid-containing solvent phase and the lower layer is an impurity-containing heavy phase; S4) mixing the acid-containing solvent phase with barium fluoride, reacting, and after solid-liquid separation, obtaining a secondary purified acid-containing solvent and purified residue; S5) performing vacuum distillation on the secondary purified acid-containing solvent, recovering the solvent, and returning the obtained regenerated solvent to the primary solvent purification process for recycling, and the residual liquid in the distillation kettle is the purified acid; S6) diluting the purified acid, and then mixing it with an ammonia-containing alkaline substance to perform a neutralization reaction, filtering after the reaction, and drying and granulating the filter cake to obtain a fire-grade monoammonium phosphate product. The method provided by the invention has high impurity removal rate, high phosphorus yield and high product added value, and can produce fire-fighting grade monoammonium phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A process flow chart for preparing monoammonium phosphate using raffinate provided in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The present invention provides a method for preparing monoammonium phosphate by utilizing raffinate acid, comprising the following steps:

[0038] S1) mixing the raffinate with concentrated sulfuric acid, concentrating, and separating the solid and liquid to obtain a concentrated solution;

[0039] S2) adding a solvent dropwise into the concentrated solution to perform primary solvent purification; the solvent comprises at least one of an alcohol solvent, a ketone solvent and an ether solvent;

[0040] S3) allowing the light and heavy mixed phase obtained by purifying the primary solvent to stand for phase separation, wherein the upper layer is the acid-containing solvent phase and the lower layer is the impurity-containing heavy phase;

[0041] S4) mixing the acid-containing solvent phase with barium fluoride to react, and after solid-liquid separation, obtaining a secondary purified acid-containing solvent and purified slag;

[0042] S5) subjecting the secondary purified acid-containing solvent to vacuum distillation to recover the solvent, and returning the obtained regenerated solvent to the primary solvent purification step for recycling, and the residual liquid in the distillation kettle is the purified acid;

[0043] S6) diluting the purified acid, and then mixing it with an alkaline substance to carry out a neutralization reaction, filtering after the reaction, and drying and granulating the filter cake to obtain a fire-fighting grade monoammonium phosphate product.

[0044] Figure 1 A process flow chart for preparing monoammonium phosphate using raffinate provided in accordance with an embodiment of the present invention.

[0045] Regarding step S1):

[0046] The raffinate is mixed with concentrated sulfuric acid, concentrated, and then the solid and liquid are separated to obtain a concentrated solution.

[0047] In certain embodiments of the present invention, the mass content of P2O5 in the raffinate is 21% to 23%, and the mass content of Ca 2+ The mass content of Mg is 0.2% to 0.35%, 2+ The mass content of Fe is 0.8% to 1.2%, 3+ The mass content of Al is 0.2% to 0.3%, 3+ The mass content of is 0.2% to 0.3%, the mass content of SiO2 is 80 to 200ppm, and the mass content of SO4 is 0.2% to 0.3%. 2-The mass content is 200~400ppm, F - The mass content of Na is 700~1100ppm, + The mass content is 380~1000ppm, K + The mass content is 500~1000ppm, Cl - The mass content of Cr is 30-60ppm, 3+ The mass content of Ba is 20~55ppm, 2+ The mass content of P2O5 in the raffinate is 22.46%, and the mass content of Ca 2+ The mass content is 0.25%, Mg 2+ The mass content of Fe is 1.1%, 3+ The mass content of Al is 0.24%, 3+ The mass content of is 0.28%, the mass content of SiO2 is 94ppm, and the mass content of SO4 2- The mass content of F is 240ppm. - The mass content of Na is 1085ppm, + The mass content of K is 680ppm, + The mass content of Cl is 598ppm, - The mass content is 35ppm, Cr 3+ The mass content of Ba is 22ppm, 2+ The mass content is 5.5ppm.

[0048] In certain embodiments of the present invention, concentrated sulfuric acid and raffinate are reacted according to SO4 2- Mix evenly with P2O5 in a mass ratio of 4.2 to 30:100; for example, 5:100, 10:100, 15:100, 20:100 or 30:100.

[0049] The concentration can be vacuum concentration, but is not limited to vacuum concentration, and can also be atmospheric concentration or one-stage atmospheric pressure and one-stage vacuum concentration. The vacuum degree of the vacuum concentration is 80-90KPa, such as 85KPa. After the concentration, the mass concentration of P2O5 in the solution is 23%-54%.

[0050] The solid-liquid separation method is filtration. After solid-liquid separation, precipitated phosphogypsum and concentrated liquid are obtained.

[0051] In step S1), adding concentrated sulfuric acid can increase the activity of hydrogen ions in the raffinate acid to increase the yield of phosphorus in the solvent extraction process. At the same time, adding concentrated sulfuric acid can remove calcium ions in the raffinate acid in advance, as shown in formula (1):

[0052] Ca 2+ +SO42- =CaSO4 formula (1).

[0053] Regarding step S2):

[0054] A solvent is added dropwise to the concentrated solution for primary solvent purification; the solvent includes at least one of an alcohol solvent, a ketone solvent and an ether solvent, preferably an alcohol solvent. The alcohol solvent is selected from C1 to C15 alcohol solvents, such as at least one of isopropanol, n-butanol, methanol and ethanol; preferably isopropanol and / or n-butanol. The ketone solvent may be acetone. The ether solvent may be methyl ether.

[0055] In certain embodiments of the present invention, the volume ratio of the solvent to the concentrated solution is 1 to 3.5:1, such as 2:1.

[0056] The time for adding the solvent dropwise is controlled to be 30 to 90 minutes, such as 60 minutes. The temperature of the first-level solvent purification is 55 to 65° C., such as 60° C.; the time for the first-level solvent purification after adding the solvent is 10 to 90 minutes, such as 50 minutes.

[0057] In step S2), a solvent, preferably a water-soluble solvent, is added to rob the "free water" in the residual acid system by utilizing the mutual solubility of the solvent and water, and most of the phosphoric acid and a small amount of cationic impurities follow into the mixed system of the solvent and water, and the remaining cationic impurities are transferred to the heavy phase. Through the primary solvent purification, the phosphorus yield can reach more than 92%.

[0058] Regarding step S3):

[0059] The light and heavy mixed phase obtained by purifying the primary solvent is allowed to stand for phase separation, wherein the upper layer is the acid-containing solvent phase and the lower layer is the impurity-containing heavy phase.

[0060] The pH value of the acid-containing solvent phase is 0.8-1.2.

[0061] The acid-containing solvent phase enters the next purification process.

[0062] After obtaining the impurity-containing heavy phase, it also includes:

[0063] Superphosphate is prepared by using a heavy phase containing impurities, calcium carbonate and phosphogypsum; the phosphogypsum includes the precipitated phosphogypsum obtained in step S1).

[0064] Specifically, the preparation method of superphosphate comprises the following steps:

[0065] a) adding calcium carbonate slurry to the heated impurity-containing heavy phase and mixing;

[0066] b) adding phosphogypsum to the slurry mixed in step a) and mixing;

[0067] c) drying, crushing and screening the slurry mixed in step b) to obtain a superphosphate product.

[0068] Regarding step a):

[0069] The temperature of the heated impurity-containing heavy phase is 90-100°C, such as 95°C.

[0070] The mass concentration of the calcium carbonate slurry is 55% to 65%, such as 60%. The solvent of the calcium carbonate slurry is water.

[0071] The P2O5 in the impurity-containing heavy phase and the Ca in the calcium carbonate 2+ The mass ratio is 4.8-5.2:1, for example 5:1.

[0072] The calcium carbonate slurry is added at a rate such that the foam does not overflow. The mixing is stirring and mixing.

[0073] Regarding step b):

[0074] The mass ratio of phosphogypsum to P2O5 in the impurity-containing heavy phase is 18-22:100, for example, 20:100. The phosphogypsum is firstly prepared from the precipitated phosphogypsum obtained in step S1), and the insufficient part is supplemented.

[0075] The mixing is stirring mixing.

[0076] Regarding step c):

[0077] The drying temperature is 90-105°C, for example 100°C.

[0078] Regarding step S4):

[0079] The acid-containing solvent phase is mixed with barium fluoride to react, and after solid-liquid separation, a secondary purified acid-containing solvent and purified slag are obtained.

[0080] In certain embodiments of the present invention, the barium fluoride is a precipitating agent for the purpose of removing Mg from the acid-containing solvent phase. 2+ and SO4 2- Mg in the acid-containing solvent phase 2+ and the F in the barium fluoride - The molar ratio is 1:2.

[0081] In certain embodiments of the present invention, mixing the acid-containing solvent phase with barium fluoride comprises:

[0082] The barium fluoride is added dropwise to the acid-containing solvent phase for a time of 30 to 120 minutes, such as 60 minutes.

[0083] The reaction temperature is 55-65° C., such as 60° C.; the reaction time after mixing is 10-60 min, such as 40 min.

[0084] The solid-liquid separation method is filtration.

[0085] In step S4), since barium fluoride is insoluble in water but easily soluble in alcohol solvents, the F - and Ba 2+ Mg 2+ and SO4 2- Combined to form insoluble precipitate, thus removing the introduced SO4 2- , and further purify the cationic impurities therein. The reaction formulas are shown in formula (2) and formula (3):

[0086] Ba 2+ +SO4 2- =BaSO4↓ Formula (2);

[0087] F - +Mg 2+ =MgF2↓Formula (3).

[0088] In the alcohol solvent purification process, Mg 2+ and a small amount of Fe 3+ 、Al 3+ All of them are dissolved in the solvent in the form of sulfate. Therefore, in the acid-containing solvent phase, Mg 2+ and SO4 2- The molar ratio is 1:1.06, and barium fluoride can be used for purification and removal with low residual fluorine and barium. Through secondary precipitation purification, Mg 2+ The removal rate is as high as 95% or more, SO4 2- The removal rate is over 98%.

[0089] Regarding step S5):

[0090] The secondary purified acid-containing solvent is subjected to vacuum distillation to recover the solvent, and the obtained regenerated solvent is returned to the primary solvent purification process for recycling, and the residual liquid in the distillation kettle is the purified acid.

[0091] In certain embodiments of the present invention, the temperature of the vacuum distillation is 60-80° C., such as 70° C.; the vacuum degree is 80-90 KPa, such as 85 KPa.

[0092] Regarding step S6):

[0093] The purified acid is diluted and then mixed with an ammonia-containing alkaline substance to carry out a neutralization reaction. After the reaction, the purified acid is filtered and the filter cake is dried and granulated to obtain a fire-fighting grade monoammonium phosphate product.

[0094] In some embodiments of the present invention, the dilution may be performed by adding water. The mass ratio of the purified acid to water is 0.8-1.2:0.8-1.2, such as 1:1.

[0095] The ammonia-containing alkaline substance includes ammonia water, ammonia gas, ammonium carbonate or ammonium bicarbonate.

[0096] When the ammonia-containing alkaline substance is aqueous ammonia, the mixing with the ammonia-containing alkaline substance comprises:

[0097] Ammonia water is added dropwise to the diluted purified acid until the pH value reaches 4.0 to 4.5. The adding time is 30 to 90 minutes.

[0098] The temperature of the neutralization reaction is 65-80° C., such as 70° C.; after mixing with the ammonia-containing alkaline substance, the neutralization reaction time is 30-60 minutes, such as 40 minutes.

[0099] The mother liquor obtained by filtration is returned to dilute the purified acid or used to prepare the calcium carbonate slurry in step a).

[0100] The present invention adds concentrated sulfuric acid before concentration, which can increase the hydrogen ion activity of the raffinate acid, so that more phosphoric acid enters the solvent during the solvent purification process, thereby increasing the phosphorus yield; and can remove calcium in advance during the concentration process, so that the calcium exists in the form of calcium sulfate, thereby reducing the phosphorus loss during the solvent purification process. By adopting the technical solution of the present invention, the final phosphorus yield can reach more than 92%.

[0101] The present invention adopts barium fluoride as a precipitant for the first time, and utilizes the property that barium fluoride is easily soluble in alcohol solvents to precipitate Mg in the acid-containing solvent. 2+ and SO4 2- Remove at the same time, and the remaining F - and Ba 2+ In addition, it also avoids the step-by-step addition of agents for desulfurization and removal of metal cations at the back end, simplifying the process steps. 2+ The removal rate of SO4 is above 95%. 2- The removal rate is above 98%, and the obtained purified acid can be used to prepare fire-grade monoammonium phosphate, and the product meets the standard requirements of fire-grade monoammonium phosphate.

[0102] The present invention combines primary solvent purification with secondary precipitation purification. The primary solvent purification removes about 70% of impurities. The introduction of barium fluoride is used as an innovation point, taking into account both magnesium removal and desulfurization. The secondary precipitation purification finally makes the impurity removal rate above 95%. The present invention combines solvent purification with precipitation impurity removal technology, has high impurity removal rate and phosphorus yield, and obtains a fire-fighting grade monoammonium phosphate product with high value.

[0103] The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

[0104] In order to further illustrate the present invention, a method for preparing monoammonium phosphate using raffinate provided by the present invention is described in detail below in conjunction with examples, but it should not be construed as limiting the scope of protection of the present invention.

[0105] In the embodiment, the mass content of P2O5 in the raffinate is 22.46%, and the mass content of Ca 2+ The mass content is 0.25%, Mg 2+ The mass content of Fe is 1.1%, 3+ The mass content of Al is 0.24%, 3+ The mass content of is 0.28%, the mass content of SiO2 is 94ppm, and the mass content of SO4 2- The mass content of F is 240ppm. - The mass content of Na is 1085ppm, + The mass content of K is 680ppm, + The mass content of Cl is 598ppm, - The mass content is 35ppm, Cr 3+ The mass content of Ba is 22ppm, 2+ The mass content is 5.5ppm.

[0106] Embodiments 1 to 5

[0107] Method for preparing monoammonium phosphate using the raffinate acid:

[0108] 1) Raffinate concentration and activation: according to SO4 2- The mass ratio of SO4 to P2O5 is R (see Table 1), concentrated sulfuric acid is added to the raffinate, stirred evenly, and then vacuum concentrated at 70°C and 85KPa vacuum degree until the mass concentration of P2O5 in the solution is as shown in Table 1, filtered, and precipitated phosphogypsum and concentrated solution are obtained. 2- The mass ratio (R) to P2O5 and the indicators of the obtained concentrated solution are shown in Table 1.

[0109] Table 1R and the concentrated liquid index (mass concentration, %)

[0110] R <![CDATA[P2O5 / %]]> Ca / % Mg / % Fe / % Al / ％ <![CDATA[SO4 2- / %]]> Example 1 5％ 40.96 0.09 1.28 0.35 0.26 2.21 Example 2 10％ 40.14 0.05 1.29 0.39 0.29 3.00 Example 3 15％ 40.98 0.04 1.31 0.40 0.30 4.70 Example 4 20％ 39.11 0.04 1.27 0.38 0.29 5.60 Example 5 30％ 40.68 0.03 1.22 0.35 0.25 6.92

[0111] 2) Add isopropanol dropwise to the concentrated solution (time controlled within 60 minutes), the volume ratio of isopropanol to the concentrated solution is 2:1, after adding isopropanol, react at 60°C for 50 minutes to complete the primary solvent purification. After the primary solvent purification, most of the phosphoric acid and a small amount of cationic impurities follow into the mixed system of isopropanol and water (containing acid solvent), and the remaining cationic impurities are transferred to the heavy phase. The distribution of each component in the acid-containing solvent and the heavy phase is shown in Table 2; due to the existence of detection errors, the sum of ion or component distribution cannot reach an absolute 100%, and generally the sum of 90% to 110% is considered to be within the acceptable range.

[0112] Through primary solvent purification, the phosphorus yield of Example 1 can reach 75.44%, the phosphorus yield of Example 2 can reach 84.31%, the phosphorus yield of Example 3 can reach 87.81%, the phosphorus yield of Example 4 can reach 92.95%, and the phosphorus yield of Example 5 can reach 93.23%.

[0113] Table 2 Distribution of components in acid-containing solvent and heavy phase

[0114]

[0115] 3) The light and heavy mixed phase obtained by the primary solvent purification is allowed to stand for phase separation, the upper layer is the acid-containing solvent phase, and the lower layer is the impurity-containing heavy phase. The acid-containing solvent phase enters the next purification process. Superphosphate is prepared using the impurity-containing heavy phase, calcium carbonate and phosphogypsum:

[0116] a) heating the impurity-containing heavy phase to 95°C;

[0117] According to the P2O5 in the impurity-containing heavy phase and the Ca in calcium carbonate 2+ Weigh calcium carbonate at a mass ratio of 5:1, and add water to prepare a calcium carbonate slurry with a mass concentration of 60%;

[0118] Add the calcium carbonate slurry to the impurity-containing heavy phase at a rate that does not allow the foam to overflow, and stir to mix;

[0119] b) weighing phosphogypsum and adding it to the slurry mixed in step a) at a mass ratio of phosphogypsum to P2O5 in the impurity-containing heavy phase of 20:100, and stirring and mixing; the phosphogypsum is firstly the precipitated phosphogypsum obtained in step 1), and the insufficient part is additionally added;

[0120] c) drying the slurry mixed in step b) at 100° C., crushing and screening to obtain a superphosphate product.

[0121] The indicators of the acid-containing solvent phase are shown in Table 3 ("%" in Table 3 represents mass concentration).

[0122] Table 3 Indicators of acid-containing solvent phase

[0123] <![CDATA[P2O5 / %]]> <![CDATA[Ca 2+ / ppm]]> <![CDATA[Mg 2+ / %]]> <![CDATA[Fe 3+ / %]]> <![CDATA[Al 3+ / %]]> <![CDATA[SO4 2- / %]]> Example 1 17.87 154 0.16 0.06 0.05 0.22 Example 2 19.95 62 0.21 0.10 0.06 0.68 Example 3 20.44 58 0.26 0.12 0.08 1.02 Example 4 19.95 64 0.29 0.12 0.08 1.2 Example 5 20.94 55 0.30 0.13 0.08 1.29

[0124] 4) adding barium fluoride dropwise to the acid-containing solvent phase (addition time is 60 min), and the Mg in the acid-containing solvent phase 2+ and the F in the barium fluoride - The molar ratio of Mg is 1:2; after reacting at 60°C for 40 minutes, filtering is performed to obtain a secondary purified acid-containing solvent and purified residue. 2+ The removal rate of SO4 is 95.4%. 2- The removal rate was 96.5%. In Example 2, Mg 2+ The removal rate of SO4 is 95.4%. 2- The removal rate was 98.6%. In Example 3, Mg 2+ The removal rate of SO4 is 95.6%. 2- The removal rate was 98.9%. In Example 4, Mg 2+ The removal rate of SO4 is 95.8%, 2- The removal rate was 98.8%; in Example 5, Mg 2+ The removal rate of SO4 is 95.4%. 2- The removal rate was 98.5%.

[0125] 5) The secondary purified acid-containing solvent is subjected to vacuum distillation at 70°C and 85KPa vacuum to recover the solvent, and the obtained regenerated solvent is returned to the primary solvent purification process for recycling, and the residual liquid in the distillation kettle is the purified acid. The index of the purified acid is shown in Table 4 (the "%" in Table 4 represents the mass concentration).

[0126] Table 4 Index of purified acid

[0127] <![CDATA[P2O5 / %]]> <![CDATA[Ca 2+ / ppm]]> <![CDATA[Mg 2+ / ppm]]> <![CDATA[Fe 3+ / ppm]]> <![CDATA[Al 3+ / ppm]]> <![CDATA[SO4 2- / ppm]]> <![CDATA[F - / ppm]]> <![CDATA[Ba 2+ / ppm]]> Example 1 50.23 25 390 184 655 124 155 273 Example 2 50.19 21 540 200 800 220 142 245 Example 3 49.53 24 640 210 820 263 166 249 Example 4 50.05 24 620 202 800 327 176 275 Example 5 50.45 18 650 221 863 339 156 236

[0128] 6) dilute the purified acid with water (the mass ratio of the purified acid to water is 1:1), add ammonia water to the diluted purified acid until the pH value is 4.0-4.5, and the dropping time is 60 minutes; then, react at 70°C for 40 minutes, filter, dry and granulate the filter cake to obtain a fire-grade monoammonium phosphate product. The mother liquor obtained by filtration is used to dilute the purified acid or to prepare the calcium carbonate slurry in step a). The indicators of the fire-grade monoammonium phosphate product are shown in Table 5.

[0129] Table 5 Specifications of fire-fighting grade monoammonium phosphate products

[0130] <![CDATA[NH4H2PO4 / wt%]]> Moisture / wt% <![CDATA[Bulk density / (g / cm 3 )]]> Moisture absorption rate / % Example 1 95.9 0.91 0.82 2.5 Example 2 95.5 0.91 0.78 2.5 Example 3 95.7 0.89 0.71 2.2 Example 4 94.9 0.89 0.73 2.4 Example 5 94.4 0.86 0.71 3.1 Quality Standards for Fire-Fighting Grade Monoammonium Phosphate ≥90.0 ≤1.0 ≥0.65 ≤4.0

[0131] Example 6

[0132] The difference from Example 3 is:

[0133] The isopropanol in step 2) was replaced with n-butanol. In step 2), the phosphorus yield was 88.24% through primary solvent purification; in step 4), the Mg was purified through secondary precipitation. 2+ The removal rate of SO4 is 84.3%. 2- The removal rate was 85.5%.

[0134] Example 7

[0135] The difference from Example 3 is:

[0136] The isopropanol in step 2) was replaced with ethanol. In step 2), the phosphorus yield was 82.2% through primary solvent purification; in step 4), the Mg was purified through secondary precipitation. 2+ The removal rate of SO4 is 95.5%. 2- The removal rate was 96.8%.

[0137] Example 8

[0138] The difference from Example 3 is:

[0139] The isopropanol in step 2) was replaced with methanol. In step 2), the phosphorus yield was 92.2% through primary solvent purification; in step 4), the Mg was purified through secondary precipitation. 2+ The removal rate of SO4 is 92.8%, 2- The removal rate was 92.5%.

[0140] Example 9

[0141] The difference from Example 3 is:

[0142] The aqueous ammonia in step 6) is replaced with ammonium carbonate.

[0143] Example 10

[0144] The difference from Example 3 is:

[0145] The aqueous ammonia in step 6) was replaced with ammonium bicarbonate.

[0146] Embodiment 11

[0147] The difference from Example 4 is:

[0148] The isopropanol in step 2) was replaced with methyl ether. In step 2), the phosphorus yield was 78.2% by primary solvent purification; in step 4), the Mg was purified by secondary precipitation. 2+ The removal rate of SO4 is 92.7%. 2- The removal rate was 95.5%.

[0149] Example 12

[0150] The difference from Example 4 is:

[0151] The isopropanol in step 2) was replaced with acetone. In step 2), the phosphorus yield was 88.5% through primary solvent purification; in step 4), the Mg was purified through secondary precipitation. 2+ The removal rate of SO4 is 94.3%. 2- The removal rate was 96.9%.

[0152] Comparative Example 1

[0153] The difference from Example 4 is:

[0154] The barium fluoride in step 4) is replaced with calcium fluoride. In step 4), Mg is purified by secondary precipitation. 2+ The removal rate of SO4 is 33.1%. 2- The removal rate was 45%.

[0155] Comparative Example 2

[0156] The difference from Example 4 is:

[0157] When the aqueous ammonia in step 6) is replaced with ammonium sulfate, ammonium nitrate or ammonium chloride, no monoammonium phosphate product can be obtained.

[0158] The indicators of the monoammonium phosphate products obtained in Examples 6 to 12 and Comparative Examples 1 to 4 are shown in Table 6.

[0159] Table 6 Index of monoammonium phosphate products

[0160] NH4H2PO4 / wt% Moisture / wt% <![CDATA[Bulk density / (g / cm 3 )]]> Moisture absorption rate / % Example 6 89.9 1.00 0.86 3.9 Example 7 94.5 0.89 0.77 2.5 Example 8 91.4 0.78 0.80 3.1 Example 9 93.7 0.95 0.88 3.6 Example 10 93.9 0.91 0.84 3.6 Embodiment 11 91.4 0.79 0.76 3.0 Example 12 92.6 0.76 0.73 3.1 Comparative Example 1 84.9 1.32 0.89 4.5 Quality Standards for Fire-Fighting Grade Monoammonium Phosphate ≥90.0 ≤1.0 ≥0.65 ≤4.0

[0161] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing monoammonium phosphate using raffinate acid, comprising the following steps: S1) mixing the raffinate with concentrated sulfuric acid, concentrating, and separating the solid and liquid to obtain a concentrated solution; S2) adding a solvent dropwise into the concentrated solution to perform primary solvent purification; the solvent comprises at least one of an alcohol solvent, a ketone solvent and an ether solvent; S3) allowing the light and heavy mixed phase obtained by purifying the primary solvent to stand for phase separation, wherein the upper layer is the acid-containing solvent phase and the lower layer is the impurity-containing heavy phase; S4) mixing the acid-containing solvent phase with barium fluoride to react, and after solid-liquid separation, obtaining a secondary purified acid-containing solvent and purified slag; S5) subjecting the secondary purified acid-containing solvent to vacuum distillation to recover the solvent, and returning the obtained regenerated solvent to the primary solvent purification step for recycling, and the residual liquid in the distillation kettle is the purified acid; S6) diluting the purified acid, and then mixing it with an ammonia-containing alkaline substance to carry out a neutralization reaction, filtering after the reaction, and drying and granulating the filter cake to obtain a fire-fighting grade monoammonium phosphate product.

2. The method according to claim 1, characterized in that In step S1), concentrated sulfuric acid and raffinate are mixed according to SO4 2- Mix well with P2O5 in a mass ratio of 4.2 to 30:

100.

3. The method according to claim 1, characterized in that: In step S1), the concentration method includes vacuum concentration, atmospheric pressure concentration, or one-stage atmospheric pressure and one-stage vacuum concentration; The vacuum degree of the vacuum concentration is 80-90 KPa; after the concentration, the mass concentration of P2O5 in the solution is 23%-54%.

4. The method according to claim 1, characterized in that In step S2), the volume ratio of the solvent to the concentrated solution is 1 to 3.5:1; The time for adding the solvent dropwise is controlled within 30 to 90 minutes; the temperature for the primary solvent purification is 55 to 65° C.; and the time for the primary solvent purification after adding the solvent is 10 to 90 minutes.

5. The method according to claim 1, characterized in that In step S3), the pH value of the acid-containing solvent phase is 0.8-1.

2.

6. The method according to claim 1, characterized in that In step S3), after obtaining the impurity-containing heavy phase, the process further comprises: Superphosphate is prepared by using a heavy phase containing impurities, calcium carbonate and phosphogypsum; the phosphogypsum includes the precipitated phosphogypsum obtained in step S1); The P2O5 in the impurity-containing heavy phase and the Ca in the calcium carbonate 2+ The mass ratio of phosphogypsum to P2O5 in the impurity-containing heavy phase is 4.8-5.2:1; the mass ratio of phosphogypsum to P2O5 in the impurity-containing heavy phase is 18-22:

100.

7. The method according to claim 1, characterized in that In step S4), the Mg in the acid-containing solvent phase 2+ and the F in the barium fluoride - The molar ratio is 1:

2.

8. The method according to claim 1, characterized in that In step S4), mixing the acid-containing solvent phase with barium fluoride comprises: Add barium fluoride dropwise into the acid-containing solvent phase; the adding time is 30 to 120 minutes; The reaction temperature is 55-65° C.; the reaction time after mixing is 10-60 min.

9. The method according to claim 1, characterized in that: In step S5), the temperature of the vacuum distillation is 60-80° C., and the vacuum degree is 80-90 KPa.

10. The method according to claim 1, characterized in that In step S6), the dilution is performed by adding water; the mass ratio of the purified acid to water is 0.8-1.2:0.8-1.2; The ammonia-containing alkaline substance includes ammonia water, ammonia gas, ammonium carbonate or ammonium bicarbonate; When the ammonia-containing alkaline substance is aqueous ammonia, the mixing with the ammonia-containing alkaline substance comprises: Adding ammonia water dropwise to the diluted purified acid until the pH value is 4.0 to 4.5; the adding time is 30 to 90 minutes; The temperature of the neutralization reaction is 65-80° C.; after mixing with the ammonia-containing alkaline substance, the neutralization reaction time is 30-60 minutes.

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