Method for removing potassium from fertilizer-grade monoammonium phosphate and use of the product thereof

Abstract

The application provides a method for removing potassium from fertilizer-grade monoammonium phosphate and application of a product thereof. The method comprises the following steps: dissolving fertilizer-grade monoammonium phosphate in water to obtain a monoammonium phosphate solution; adding fluosilicic acid and / or a fluosilicate into the monoammonium phosphate solution, adjusting the pH value, and performing a reaction to obtain a mixed solution; performing solid-liquid separation on the mixed solution to retain a clear solution; and performing drying treatment on the clear solution to obtain purified monoammonium phosphate. The fluosilicic acid and / or the fluosilicate can react with potassium ions to generate potassium fluosilicate precipitate, and the potassium fluosilicate precipitate can be separated by a solid-liquid separation method to obtain monoammonium phosphate with a low potassium content. The product has high purity, the preparation method is reasonable and effective, and the method has strong operability and is suitable for industrial production.

Description

Technical Field

[0001] This application belongs to the field of phosphate materials technology, and more specifically, relates to a method for removing potassium from fertilizer-grade monoammonium phosphate and the application of its products. Background Technology

[0002] With the rapid development of lithium-ion batteries, the demand for lithium iron phosphate cathode materials in the new energy industry is constantly increasing, and monoammonium phosphate (MAP) is one of the most important phosphorus sources for synthesizing MAP. Because lithium-ion batteries have increasingly higher requirements for raw material purity, the content of various impurities is strictly limited. Fertilizer-grade MAP cannot meet the production requirements of cathode materials because it contains some potassium that is difficult to remove.

[0003] The presence of appropriate potassium ions in lithium iron phosphate cathode materials can alleviate the formation of non-conductive compounds deposited on the lithium metal surface and inhibit potassium ion transport during battery charging and discharging, ultimately limiting lithium dendrite growth and thus improving the cycle performance of potassium-ion batteries. However, excessive potassium content can reduce battery capacity retention and easily lead to instability in the lithium iron phosphate lattice, thereby shortening battery life. Therefore, potassium removal from fertilizer-grade monoammonium phosphate is essential.

[0004] Potassium ions have ionic radii and physical properties very similar to ammonium ions, making it challenging to remove potassium without losing ammonium from phosphate fertilizers. Consequently, there is limited research in the industry on potassium removal using monoammonium phosphate (MAP) in phosphate fertilizer systems. Currently, commonly used MAP methods for potassium removal include:

[0005] 1. Crystallization method: This is a low-energy, high-purity separation and purification method. After cooling the salt solution, seed crystals are added, and the crystals are allowed to precipitate and separate from the original solution, thus achieving purification. However, due to the similar properties of potassium ions and ammonium ions, the similar crystal lattice will coat the potassium ions during the crystallization process. Therefore, multiple crystallizations are often required to obtain high-purity monoammonium phosphate. Its time cost and efficiency are not suitable for large-scale industrial production.

[0006] 2. It seems feasible to use the selective reaction of complexing agents on potassium ions and then remove potassium chelates by electrodialysis. However, due to the small complexing constant of potassium ions and their instability, except for expensive crown ethers, other potassium chelates are prone to dissociation during electrodialysis. Summary of the Invention

[0007] Based on this, one objective of this application is to provide a method for removing potassium from fertilizer-grade monoammonium phosphate, in order to solve the technical problem that the existing methods for removing potassium from fertilizer-grade monoammonium phosphate are difficult and unsuitable for large-scale industrial applications.

[0008] Another objective of this application is to provide a method for removing potassium from fertilizer-grade monoammonium phosphate, and to apply the purified monoammonium phosphate obtained in the preparation of battery cathode materials, so as to reduce the production cost of cathode materials.

[0009] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0010] In one aspect, a method for removing potassium from fertilizer-grade monoammonium phosphate is provided, comprising the following steps:

[0011] Dissolve fertilizer-grade monoammonium phosphate in water to obtain a monoammonium phosphate solution;

[0012] Fluorosilicic acid and / or fluorosilicates are added to a monoammonium phosphate solution, the pH is adjusted, and the reaction is carried out to obtain a mixed solution.

[0013] The mixture is subjected to solid-liquid separation, and the clear liquid is retained;

[0014] The clarified liquid was dried to obtain purified monoammonium phosphate.

[0015] Optionally, the solid-liquid ratio of fertilizer-grade monoammonium phosphate to water is 1:3-1:5; and / or,

[0016] The potassium content of fertilizer-grade monoammonium phosphate is ≤5000 ppm; and / or,

[0017] The potassium content in the purified monoammonium phosphate is ≤50ppm.

[0018] Optionally, fluorosilicic acid and / or fluorosilicates are added to the monoammonium phosphate solution by slow dropwise addition at a rate of 8 mL / min–12 mL / min; and / or,

[0019] The amount of fluorosilicic acid and / or fluorosilicate added is 3%-9% of the mass of the fertilizer-grade monoammonium phosphate; and / or,

[0020] The steps for adjusting the pH value include: adding ammonia to adjust the pH value to be greater than or equal to 4; and / or,

[0021] Drying processes include spray drying.

[0022] Optionally, after adjusting the pH value, the following steps are also included:

[0023] An inducing agent is added to a monoammonium phosphate solution under heating conditions, followed by low-temperature treatment.

[0024] Optionally, the amount of inducer added is 0.02%-5% of the mass of fertilizer-grade monoammonium phosphate; and / or,

[0025] Inducing agents include at least one of polyacrylamide, ferric chloride, polyferric sulfate, small molecule alcohols, and hydrocarbon sulfonates; and / or,

[0026] The heating conditions are: temperature 40℃-50℃, heating time 30min-40min; and / or,

[0027] The low-temperature treatment temperature is 1℃-5℃, and the low-temperature treatment time is 3h-5h.

[0028] Following the low-temperature treatment step, the following steps are also included: adding a dispersant to the monoammonium phosphate solution and stirring;

[0029] Preferably, the amount of dispersant added is 0.05%-0.1% of the mass of fertilizer-grade monoammonium phosphate;

[0030] Preferably, the dispersant includes at least one of polyethylene glycol (PEG-200, PEG-600), Triton X-100, sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), tributyl phosphate (TBP), and fatty alcohol polyoxyethylene ether (AEO).

[0031] Optionally, after the low-temperature treatment step or after the step of adding the dispersant and stirring, the following steps are further included:

[0032] At room temperature, barium compounds and sulfates are added to a monoammonium phosphate solution to carry out a reaction.

[0033] Optionally, the amount of barium compound added is 1%-5% of the mass of fertilizer-grade monoammonium phosphate; and / or,

[0034] The molar ratio of barium compound to sulfate is 0.95-1.1:0.45-0.55; and / or,

[0035] Barium compounds include at least one of barium chloride, barium carbonate, and barium hydroxide; and / or,

[0036] Sulfates include ammonium sulfate and / or ammonium bisulfate.

[0037] Optionally, before adding the barium compound and sulfate, the step of adding the following steps is also included: adding a precipitation aid to the monoammonium phosphate solution and stirring until homogeneous;

[0038] Preferably, the amount of precipitation aid added is 0.06%-0.1% of the mass of fertilizer-grade monoammonium phosphate;

[0039] Preferably, the precipitation aid includes at least one of polyacrylic acid (PAA), acrylate, aminoethanol, tartaric acid (TA), dopamine (DOPA), and ethylenediaminetetraacetic acid (EDTA).

[0040] Secondly, the application of purified monoammonium phosphate obtained by the potassium removal method of the above-mentioned fertilizer-grade monoammonium phosphate in the preparation of battery cathode materials is provided.

[0041] The beneficial effects of this application are as follows:

[0042] The method for removing potassium from fertilizer-grade monoammonium phosphate provided in this application utilizes the fact that fluorosilicic acid and / or fluorosilicates can react with potassium ions in fertilizer-grade monoammonium phosphate to form potassium fluorosilicate precipitate, and then separates the potassium fluorosilicate precipitate by solid-liquid separation to obtain a monoammonium phosphate solution with low potassium content. Compared with the prior art, the method for removing potassium from fertilizer-grade monoammonium phosphate in this application utilizes the difference in chemical properties between potassium ions and ammonium ions. Potassium ions can react with fluorosilicic acid and / or fluorosilicates to form precipitate, while ammonium ions do not react with fluorosilicic acid and / or fluorosilicates. This method removes potassium from fertilizer-grade monoammonium phosphate, purifies the monoammonium phosphate, and results in minimal ammonium loss. The preparation method is reasonable and effective, highly operable, and suitable for industrial production.

[0043] The potassium removal method for fertilizer-grade monoammonium phosphate provided in this application results in purified monoammonium phosphate with low potassium content, which meets the production requirements for raw materials of lithium-ion battery materials and can be used to prepare battery cathode materials. Detailed Implementation

[0044] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following embodiments are provided to further illustrate this application in detail. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0045] The potassium removal method for fertilizer-grade monoammonium phosphate in this application includes the following steps:

[0046] S1: Provide fertilizer-grade monoammonium phosphate, dissolve the fertilizer-grade monoammonium phosphate in water to obtain a monoammonium phosphate solution.

[0047] Fertilizer-grade monoammonium phosphate is a solid raw material, which is prepared into a solution to prepare for subsequent reactions.

[0048] In some embodiments, the solid-liquid ratio of fertilizer-grade monoammonium phosphate to water is 1:3-1:5. This dissolution ratio yields a good solution concentration, which is beneficial for the subsequent reaction of potassium ions with fluorosilicic acid and / or fluorosilicates to form a precipitate. If the concentration of the monoammonium phosphate solution is too low, for example, the solid-liquid ratio of fertilizer-grade monoammonium phosphate to water is less than 1:5, the potassium ion content is low, the reaction rate is low, and it is not conducive to removing potassium to a large extent. If the concentration of the monoammonium phosphate solution is too high, for example, the solid-liquid ratio of fertilizer-grade monoammonium phosphate to water is greater than 1:3, the concentration of monoammonium phosphate is close to the saturation concentration, and monoammonium phosphate crystals may precipitate during the reaction, resulting in ammonium loss. Therefore, the solid-liquid ratio of fertilizer-grade monoammonium phosphate to water can be selected as 1:3-1:5.

[0049] The potassium content of fertilizer-grade monoammonium phosphate is ≤5000ppm. By treating fertilizer-grade monoammonium phosphate with the potassium removal method of this application, a very good potassium removal effect can be obtained.

[0050] S2: Add fluorosilicic acid and / or fluorosilicate to a monoammonium phosphate solution, adjust the pH value, and react to obtain a mixed solution.

[0051] Fluorosilicic acid and / or fluorosilicates react with potassium ions in monoammonium phosphate solution to form potassium fluorosilicate precipitate. Monoammonium phosphate does not react with fluorosilicic acid and / or fluorosilicates, so potassium can be separated and removed by solid-liquid separation.

[0052] In some embodiments, fluorosilicic acid and / or fluorosilicates are added to the monoammonium phosphate solution by slow dropwise addition. During the dropwise addition, the solution becomes noticeably turbid. The dropwise addition rate is 8 mL / min-12 mL / min. By controlling the dropwise addition rate, the concentration of fluorosilicic acid and / or fluorosilicates in the mixture and the reaction rate are controlled. This avoids the problem of excessively high local concentrations in the solution, which can lead to the formation of precipitates that encapsulate the monoammonium phosphate and cause loss of the monoammonium phosphate.

[0053] In some embodiments, the pH of the reaction solution is greater than or equal to 4, and by adjusting the pH of the solution, the potassium fluorosilicate precipitate can be maximized.

[0054] Generally, fertilizer-grade monoammonium phosphate is an acidic mixture. Therefore, in some embodiments, the pH of the solution can be adjusted by adding ammonia. Using ammonia as a regulator can adjust the pH of the solution while avoiding the addition of other impurities.

[0055] S3: Separate the mixture into solid and liquid components and retain the clear liquid.

[0056] Most of the potassium is contained in the potassium fluorosilicate precipitate, while monoammonium phosphate is in the clear liquid. The two can be separated by solid-liquid separation, thus achieving the purpose of purifying monoammonium phosphate.

[0057] In some embodiments, after the addition of fluorosilicic acid and / or fluorosilicate, a flocculent precipitate is formed, and the precipitate particles are small, which is not conducive to solid-liquid separation.

[0058] Therefore, in some embodiments, the following steps are included before solid-liquid separation of mixture A:

[0059] Under heating and stirring conditions, an inducing agent is added to the mixture to promote the precipitation of potassium fluorosilicate, followed by low-temperature treatment to obtain the mixture.

[0060] The reaction involves adding fluorosilicic acid and / or fluorosilicates, which produces a precipitate. Then, under heating and stirring conditions, an inducing agent is added to the mixture to promote the precipitation of potassium fluorosilicate. After heating for a period of time, the reaction system is placed in a low-temperature environment to continue the reaction. Adding an appropriate amount of inducing agent can induce the formation of potassium fluorosilicate crystal nuclei, thereby promoting precipitation. Heating promotes complete reaction, while the low-temperature environment reduces the solubility of potassium fluorosilicate in solution, ensuring complete precipitation.

[0061] Understandably, the cryogenic treatment is carried out under conditions of constant stirring to avoid the agglomeration of the generated precipitate, and on the other hand, to prevent the precipitate from adhering to the bottom of the reactor and forming scale.

[0062] In some embodiments, the mass of the inducer is 0.02%-5% of the mass of fertilizer-grade monoammonium phosphate. If the mass of the inducer added is too small, for example less than 0.02% of the mass of fertilizer-grade monoammonium phosphate, the inducing effect of the inducer will be small and may not achieve the promoting effect. If the mass of the inducer added is too large, for example greater than 5% of the mass of fertilizer-grade monoammonium phosphate, the content of the inducer will be too large, which may affect the performance of the product or cause the monoammonium phosphate crystals to precipitate and be lost.

[0063] In some embodiments, the inducing agent includes at least one of polyacrylamide (PAM), ferric chloride, polyferric sulfate, small molecule alcohols, and hydrocarbon sulfonates. These inducing agents all have a good effect on promoting precipitation and do not react with monoammonium phosphate.

[0064] In some embodiments, after the cryogenic treatment step, the following step is further included:

[0065] Add a dispersant to the monoammonium phosphate solution and stir.

[0066] That is, after adding an inducing agent and reacting for a period of time under heating and stirring conditions, the temperature is lowered and the reaction continues. Then, a small amount of dispersant, i.e. surfactant, is added to the monoammonium phosphate solution. The dispersant increases the interfacial energy between potassium fluorosilicate and the solution, and between potassium fluorosilicate and the container, thereby reducing the surface adsorption of potassium fluorosilicate crystals, thus preventing the initial deposition of scale and preventing scale blockage in the solid-liquid separation system and transmission pipeline.

[0067] In some embodiments, the mass of the dispersant is 0.05%-0.1% of the mass of fertilizer-grade monoammonium phosphate.

[0068] In some embodiments, the dispersant includes at least one of polyethylene glycol (PEG-200, PEG-600), Triton X-100, sodium dodecyl sulfate (SDS), hexadecyltrimethylammonium bromide (CTAB), tributyl phosphate (TBP), and fatty alcohol polyoxyethylene ether (AEO).

[0069] In some embodiments, the heating conditions are at a temperature of 40°C-50°C and a heating time of 30-40 minutes, providing sufficient energy for the reaction of potassium ions with fluorosilicic acid and / or fluorosilicates to form a precipitate, thereby promoting the reaction to the maximum extent.

[0070] In some embodiments, the low-temperature treatment temperature is 1℃-5℃ and the low-temperature treatment time is 3h-5h. In this temperature range, the solubility of potassium fluorosilicate in solution is low, which is conducive to the complete precipitation of potassium fluorosilicate.

[0071] In some embodiments, after the low-temperature treatment step or after the step of adding the dispersant and stirring, the following step is further included:

[0072] At room temperature, barium compounds and sulfates are added to a monoammonium phosphate solution to carry out a reaction.

[0073] Before solid-liquid separation, an appropriate amount of barium compound and sulfate are added. The barium compound and sulfate react to form barium sulfate precipitate, which co-precipitates with suspended potassium fluorosilicate to form large-particle crystals, thereby increasing the filtration performance and separation effect of the precipitate. In addition, due to the dispersing and emulsifying effects of the dispersant, the particle size of potassium fluorosilicate becomes smaller, leading to increased filtration difficulty. Therefore, it is preferable to add the barium compound and sulfate to the monoammonium phosphate solution after the step of adding the dispersant and stirring.

[0074] In some embodiments, the mass of the barium compound is 1%-5% of the mass of fertilizer-grade monoammonium phosphate. By controlling the amount of barium compound added, the amount of barium sulfate precipitate generated is controlled, the co-precipitation effect of potassium fluorosilicate-barium sulfate is adjusted, and excessive barium sulfate precipitate generation is avoided, which would increase the workload of solid-liquid separation and reduce work efficiency.

[0075] In some embodiments, the molar ratio of barium compound to sulfate is (0.95-1.1):(0.45-0.55). Based on the fact that the raw material contains 0.24%-0.25% sulfur impurities and the reaction characteristics of barium ions and sulfate, the molar ratio of barium to sulfate is 1:0.5. Therefore, it is preferable that the molar ratio of the reactants is about 1:0.5.

[0076] In some embodiments, the barium compound includes at least one of barium chloride, barium carbonate, and barium hydroxide.

[0077] In some embodiments, the sulfates include ammonium sulfate and / or ammonium bisulfate to reduce the introduction of other cations, and these sulfates are all capable of reacting with barium chloride, barium carbonate and barium hydroxide to produce barium sulfate precipitate.

[0078] In some embodiments, prior to the steps of adding the barium compound and sulfate, the following steps are also included:

[0079] Add a precipitation aid to the monoammonium phosphate solution and stir until homogeneous.

[0080] Barium sulfate precipitates often exhibit amorphous and easily aggregated characteristics during their formation. To rapidly form large, uniform precipitates of potassium fluorosilicate and barium sulfate, an appropriate amount of precipitation aid is added to the mixture to promote barium sulfate crystal growth, improve crystal morphology, and form uniform spherical large-particle precipitates in the system, thereby enhancing the separation effect.

[0081] In some embodiments, the mass of the precipitation aid is 0.06%-0.1% of the mass of fertilizer-grade monoammonium phosphate.

[0082] In some embodiments, the precipitation aid includes at least one of polyacrylic acid (PAA), acrylate, aminoethanol, tartaric acid (TA), dopamine (DOPA), and ethylenediaminetetraacetic acid (EDTA). These precipitation aids can promote the growth of barium sulfate crystals and can be removed during subsequent drying processes to avoid affecting the purity and properties of monoammonium phosphate.

[0083] Understandably, after solid-liquid separation, in addition to obtaining a clear liquid, a solid residue is also obtained. The solid residue contains potassium fluorosilicate, which can be recycled and reused in processes such as wood preservation and ceramic manufacturing. No solid waste is generated, and there are no environmental pollution problems.

[0084] S4: The clear liquid is dried to obtain purified monoammonium phosphate.

[0085] In some embodiments, the drying process includes spray drying, in which the filtered monoammonium phosphate solution is spray dried to obtain a solid product, while excess fluorosilicic acid in the solution is decomposed into hydrogen fluoride and silicon tetrafluoride gas under the high temperature conditions of spray drying and thus removed.

[0086] In some embodiments, after the mixture is subjected to solid-liquid separation treatment, the resulting solid residue can be washed with a small amount of cold water to collect the monoammonium phosphate remaining on the solid residue. The liquid obtained from the washing is retained and mixed with the clear liquid obtained from the solid-liquid separation treatment, and then dried together.

[0087] The method for removing potassium from fertilizer-grade monoammonium phosphate provided in this application embodiment utilizes the ability of fluorosilicic acid and / or fluorosilicates to react with potassium ions in fertilizer-grade monoammonium phosphate to generate potassium fluorosilicate precipitate, and then separates the potassium fluorosilicate precipitate by solid-liquid separation to obtain a monoammonium phosphate solution with low potassium content.

[0088] Compared with the prior art, the potassium removal method for fertilizer-grade monoammonium phosphate in this application utilizes the chemical difference between potassium ions and ammonium ions. Potassium ions can react with fluorosilicic acid and / or fluorosilicates to form precipitates, while ammonium ions do not react with fluorosilicic acid and / or fluorosilicates. This method removes potassium from fertilizer-grade monoammonium phosphate, purifies the monoammonium phosphate, and results in minimal ammonium loss. The preparation method is reasonable and effective, the process is simple and highly operable, and the amount of reagent used is small. It also exhibits high selectivity for potassium precipitation, lower overall cost, and ease of industrialization.

[0089] The potassium removal method for fertilizer-grade monoammonium phosphate provided in this application embodiment yields purified monoammonium phosphate with a potassium content of less than 50 ppm and a product purity of 99%. Under continuous feeding production conditions, the yield of monoammonium phosphate can reach over 99%, and the product performance is close to the raw material production requirements of lithium-ion battery materials. It can be applied to the preparation of positive electrode materials for batteries, such as positive electrode materials for phosphate-based batteries like lithium iron phosphate batteries, lithium manganese iron phosphate batteries, and lithium vanadium phosphate batteries.

[0090] The lithium iron phosphate cathode material made using the above-mentioned monoammonium phosphate has fewer impurities from the monoammonium phosphate and a suitable potassium content, which improves the lattice stability of the lithium iron phosphate cathode material and the cycle performance of lithium-ion batteries.

[0091] The following examples illustrate this point.

[0092] Example 1

[0093] The potassium removal method for fertilizer-grade monoammonium phosphate in this embodiment includes the following steps:

[0094] S1: Dissolve 15g of fertilizer-grade monoammonium phosphate completely in deionized water at a solid-liquid ratio of 1:3 to obtain a monoammonium phosphate solution.

[0095] S2: Slowly add 3% fluorosilicic acid and ammonium fluorosilicate to a monoammonium phosphate solution at a dropping rate of 10 mL / min. While stirring, adjust the pH of the reaction solution to 4.0 with ammonia water to form potassium fluorosilicate precipitate, and obtain mixture A.

[0096] S3: Add 0.02% DNSK to mixture A, stir at 50°C for 30 min, cool the reaction solution at 1°C for 3 h to precipitate, then add 0.05% AEO and stir to obtain mixture B.

[0097] S4: Add 0.06% PAA to mixture B, stir well, then add 5% barium hydroxide and 0.5 times the molar mass of sulfate, and react at room temperature for 2 hours to obtain mixture C.

[0098] S5: Filter the C mixture to separate it, rinse the filter cake with a small amount of cold water to obtain a clear liquid.

[0099] S6: After spray drying the clear liquid, purified monoammonium phosphate solid is obtained.

[0100] The component analysis of fertilizer-grade monoammonium phosphate raw material and purified monoammonium phosphate product in this embodiment is shown in Table 1.

[0101] Table 1

[0102]

[0103] Example 2

[0104] The potassium removal method for fertilizer-grade monoammonium phosphate in this embodiment includes the following steps:

[0105] S1: Dissolve 15g of fertilizer-grade monoammonium phosphate completely in deionized water at a solid-liquid ratio of 1:3 to obtain a monoammonium phosphate solution.

[0106] S2: Slowly add 3% fluorosilicic acid / ammonium fluorosilicate dropwise into monoammonium phosphate solution at a rate of 10 mL / min. While stirring, adjust the pH of the reaction solution to 4.0 with ammonia water to form potassium fluorosilicate precipitate, thus obtaining mixture A.

[0107] S3: Add 5% ethanol to mixture A, stir at 50°C for 10 min, cool the reaction solution at 5°C for 5 h to precipitate, then add 0.05% Triton X-100, stir evenly to obtain mixture B.

[0108] S4: Add 0.06% EDTA to mixture B, stir well, then add 3% barium carbonate and 0.5 times the molar mass of sulfate, and react at room temperature for 2 hours to obtain mixture C.

[0109] S5: Filter the C mixture to separate it, rinse the filter cake with a small amount of cold water to obtain a clear liquid.

[0110] S6: After spray drying the clear liquid, purified monoammonium phosphate solid is obtained.

[0111] The component analysis of fertilizer-grade monoammonium phosphate raw material and purified monoammonium phosphate product in this embodiment is shown in Table 2.

[0112] Table 2

[0113]

[0114] Example 3

[0115] The potassium removal method for fertilizer-grade monoammonium phosphate in this embodiment includes the following steps:

[0116] S1: Dissolve 15g of fertilizer-grade monoammonium phosphate completely in deionized water at a solid-liquid ratio of 1:4 to obtain a monoammonium phosphate solution.

[0117] S2: Add 5% ammonium fluorosilicate to a monoammonium phosphate solution. After the solid dissolves, adjust the pH of the reaction solution to 4.0 with ammonia while stirring to generate potassium fluorosilicate precipitate, thus obtaining mixture A.

[0118] S3: Add 5% ethanol to mixture A, stir at 50°C for 30 min, cool the reaction solution at 1°C for 3 h to precipitate, then add 0.075% SDS and stir to obtain mixture B.

[0119] S4: Add 0.06% PAA to mixture B, stir well, then add 5% barium hydroxide and 0.5 times the molar mass of sulfate, and react at room temperature for 2 hours to obtain mixture C.

[0120] S5: Filter the C mixture to separate it, rinse the filter cake with a small amount of cold water to obtain a clear liquid.

[0121] S6: After spray drying the clear liquid, purified monoammonium phosphate solid is obtained.

[0122] The component analysis of fertilizer-grade monoammonium phosphate raw material and purified monoammonium phosphate product in this embodiment is shown in Table 3.

[0123] Table 3

[0124]

[0125] Example 4

[0126] The potassium removal method for fertilizer-grade monoammonium phosphate in this embodiment includes the following steps:

[0127] S1: Dissolve 15g of fertilizer-grade monoammonium phosphate completely in deionized water at a solid-liquid ratio of 1:3 to obtain a monoammonium phosphate solution.

[0128] S2: Slowly add 3% fluorosilicic acid dropwise into monoammonium phosphate solution at a rate of 10 mL / min, while stirring and adjusting the pH of the reaction solution to 4.0 with ammonia water to form potassium fluorosilicate precipitate, thus obtaining mixture A.

[0129] S3: Add 0.02% naphthalenesulfonic acid to mixture A, stir at 50°C for 10 min, cool the reaction solution at 5°C for 5 h to precipitate, then add 0.05% Triton X-100, stir evenly to obtain mixture B.

[0130] S4: Add 0.06% EDTA to mixture B, stir well, then add 3% barium carbonate and 0.5 times the molar mass of sulfate, and react at room temperature for 2 hours to obtain mixture C.

[0131] S5: Filter the C mixture to separate it, rinse the filter cake with a small amount of cold water to obtain a clear liquid.

[0132] S6: After spray drying the clear liquid, purified monoammonium phosphate solid is obtained.

[0133] The component analysis of fertilizer-grade monoammonium phosphate raw material and purified monoammonium phosphate product in this embodiment is shown in Table 4.

[0134] Table 4

[0135]

[0136] Comparative Example 1

[0137] The potassium removal method for fertilizer-grade monoammonium phosphate in this comparative example includes the following steps:

[0138] S1: Dissolve 15g of fertilizer-grade monoammonium phosphate completely in deionized water at a solid-liquid ratio of 1:3 to obtain a monoammonium phosphate solution.

[0139] S2: Take 1% fluorosilicic acid / ammonium fluorosilicate and slowly add it dropwise to the monoammonium phosphate solution. While stirring, use ammonia water to adjust the pH of the reaction solution to 4.0 to generate potassium fluorosilicate precipitate, and obtain mixture A.

[0140] S3: Add 5% ethanol to the above solution, stir at 50℃ for 10 min, cool the reaction solution at 1℃ for 5 h to precipitate, add 0.05% Triton X-100, stir evenly to obtain mixture B.

[0141] S4: Add 0.06% EDTA to mixture B, stir well, then add 3% barium carbonate and 0.5 times the molar mass of sulfate, and react at room temperature for 2 hours to obtain mixture C.

[0142] S5: Filter the C mixture to separate it, rinse the filter cake with a small amount of cold water to obtain a clear liquid.

[0143] S6: After spray drying the clear liquid, purified monoammonium phosphate solid is obtained.

[0144] The component analysis of the monoammonium phosphate raw material and the purified monoammonium phosphate product in Comparative Example 1 is shown in Table 5.

[0145] Table 5

[0146]

[0147] As shown in Tables 1-4, by utilizing the technical solution of this application to remove potassium impurities from fertilizer-grade monoammonium phosphate in Examples 1-4, the potassium content of the purified monoammonium phosphate is consistently below 50 ppm, significantly reducing the potassium impurity content. The purified monoammonium phosphate exhibits high purity, meeting the requirements for use as a raw material in battery cathode materials. Furthermore, small amounts of calcium and magnesium impurities in the raw material are removed by reacting with hydrogen fluoride produced from the decomposition of fluorosilicic acid / ammonium fluorosilicate to form precipitates, and small amounts of sulfur impurities are removed by forming barium sulfate precipitates with soluble barium salts, further improving the purity of the purified monoammonium phosphate.

[0148] As can be seen from the data in Table 5, compared with Example 2, this comparative example kept the liquid-solid ratio and reaction temperature unchanged. After reducing the precipitant fluorosilicic acid / ammonium fluorosilicate to less than 1% of the mass of monoammonium phosphate raw material, the potassium precipitation reaction was not fully carried out, the purification degree was reduced, and the residual potassium content was relatively high, which did not meet the raw material production requirements of battery cathode materials.

[0149] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for removing potassium from fertilizer-grade monoammonium phosphate, characterized in that: Includes the following steps: Dissolve fertilizer-grade monoammonium phosphate in water to obtain a monoammonium phosphate solution; Fluorosilicic acid and / or ammonium fluorosilicate are added to the monoammonium phosphate solution, the pH value is adjusted, and the reaction is carried out to obtain a mixed solution; the amount of fluorosilicic acid and / or ammonium fluorosilicate added is 3%-9% of the mass of the fertilizer-grade monoammonium phosphate. The mixture is subjected to solid-liquid separation, and the clear liquid is retained; The clarified liquid was dried to obtain purified monoammonium phosphate; Following the step of adjusting the pH value, the method further includes the following steps: adding an inducing agent to the monoammonium phosphate solution under heating conditions, followed by low-temperature treatment; the inducing agent includes at least one of polyacrylamide, ferric chloride, polyferric sulfate, small molecule alcohols, and hydrocarbon sulfonates; the heating conditions are at a temperature of 40℃-50℃; the low-temperature treatment is at a temperature of 1℃-5℃. Following the low-temperature treatment step, the method further includes the following step: adding a dispersant to the monoammonium phosphate solution and stirring; After the low-temperature treatment step or after the step of adding the dispersant and stirring, the following steps are also included: At room temperature, a barium compound and a sulfate were added to the monoammonium phosphate solution to carry out a reaction; Prior to the steps of adding barium compounds and sulfates, the method further includes the following step: adding a precipitation aid to the monoammonium phosphate solution and stirring until homogeneous.

2. The method for potassium removal from fertilizer-grade monoammonium phosphate as described in claim 1, characterized in that: The solid-liquid ratio of the fertilizer-grade monoammonium phosphate to water is 1:3-1:5; and / or, The potassium content in the fertilizer-grade monoammonium phosphate is ≤5000ppm; and / or, The potassium content in the purified monoammonium phosphate is ≤50ppm.

3. The method for potassium removal from fertilizer-grade monoammonium phosphate as described in claim 1, characterized in that: The fluorosilicic acid and / or ammonium fluorosilicate are added to the monoammonium phosphate solution by slow dropwise addition at a rate of 8 mL / min to 12 mL / min; and / or, The step of adjusting the pH value includes: adding ammonia water to adjust the pH value to be greater than or equal to 4; and / or, The drying process includes spray drying.

4. The method for potassium removal from fertilizer-grade monoammonium phosphate as described in claim 1, characterized in that: The amount of the inducer added is 0.02%-5% of the mass of the fertilizer-grade monoammonium phosphate; and / or, The heating time is 30-40 minutes; and / or, The low-temperature treatment time is 3-5 hours.

5. The method for potassium removal from fertilizer-grade monoammonium phosphate as described in claim 1, characterized in that: The amount of dispersant added is 0.05%-0.1% of the mass of the fertilizer-grade monoammonium phosphate; The dispersant includes at least one of polyethylene glycol, Triton X-100, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide, tributyl phosphate, and fatty alcohol polyoxyethylene ether.

6. The method for potassium removal from fertilizer-grade monoammonium phosphate as described in claim 1, characterized in that: The amount of barium compound added is 1%-5% of the mass of the fertilizer-grade monoammonium phosphate; and / or, The molar ratio of the barium compound to the sulfate is (0.95-1.1):(0.45-0.55); and / or, The barium compound includes at least one of barium chloride, barium carbonate, and barium hydroxide; and / or, The sulfates include ammonium sulfate and / or ammonium bisulfate.

7. The method for potassium removal from fertilizer-grade monoammonium phosphate as described in claim 1, characterized in that: The amount of the precipitation aid added is 0.06%-0.1% of the mass of the fertilizer-grade monoammonium phosphate; The precipitation aid includes at least one of polyacrylic acid, acrylate, aminoethanol, tartaric acid, dopamine, and ethylenediaminetetraacetic acid.

8. The application of purified monoammonium phosphate obtained by the potassium removal method of fertilizer-grade monoammonium phosphate as described in any one of claims 1-7 in the preparation of battery cathode materials.

Images