Method for removing potassium from monoammonium phosphate solution

Abstract

The invention discloses a method for removing potassium from a monoammonium phosphate solution, relates to the technical field of phosphate materials, and solves the problem that a method for removing potassium from a monoammonium phosphate solution in the prior art is difficult to achieve that the residual concentration of potassium ions is less than 10ppm. The method comprises the following steps: diluting a monoammonium phosphate solution to preset solid content, and filtering to remove suspended matters; adding a preset amount of fluosilicic acid into the monoammonium phosphate solution obtained in the step 100 in twice by taking the fluosilicic acid as a precipitator, and adjusting the pH and the reaction temperature to obtain a mixed solution containing K2SiF6 crystals; carrying out solid-liquid separation on the mixed solution containing the K2SiF6 crystals to obtain a monoammonium phosphate solution subjected to primary potassium removal; and carrying out deep potassium removal on the monoammonium phosphate solution subjected to primary potassium removal by utilizing resin adsorption to obtain the monoammonium phosphate solution with the potassium ion content of less than 10ppm. According to the method, the potassium ion concentration can be reduced to 10 ppm or below, the requirement of high-quality lithium iron phosphate is met, and meanwhile efficient, low-cost and continuous potassium removal can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of phosphate materials, and in particular to a method for depotassiumizing a monoammonium phosphate solution. Background Art

[0002] The presence of an appropriate amount of potassium ions in lithium iron phosphate positive electrode materials can alleviate the formation of non-conductive compounds deposited on the surface of metallic lithium, and prevent potassium ion transmission during battery charge and discharge, ultimately limiting the growth of lithium dendrites, thereby improving the battery's cycle performance. However, excessive potassium content will reduce the battery capacity retention rate and easily lead to instability in the lithium iron phosphate lattice, thereby shortening the battery life. Lithium iron phosphate positive electrode materials have high requirements for potassium ions. Usually, the potassium ion content in high-quality lithium iron phosphate positive electrode materials needs to be less than 10ppm.

[0003] In the related art, monoammonium phosphate is usually used as a raw material to synthesize lithium iron phosphate, and the traditional monoammonium phosphate depotassium process mainly includes solvent extraction or chemical precipitation.

[0004] The solvent extraction method mostly uses phosphate or amine extractants, and separates potassium ions through multi-stage countercurrent extraction-strip extraction operations. However, this method has the following defects: the dissolution loss rate of the extractant in the aqueous phase can reach 0.5-1.2%, and continuous addition of reagents is required to maintain the balance of the system; the potassium ion hydration layer is stable and the ion radius is large, and the single-stage extraction efficiency is usually less than 40%. To achieve a potassium ion removal rate of >80%, a 4-6-stage extraction device needs to be constructed, which significantly increases equipment investment and floor space; stable emulsions are easily formed during the stripping process, and demulsifiers or high-temperature treatment need to be introduced, resulting in increased energy consumption and degradation of the extractant.

[0005] The chemical precipitation method uses alkaline reagents such as sodium carbonate and sodium hydroxide to precipitate potassium ions. Although the operation route is simple, it has inherent defects that are difficult to overcome: coexisting cations such as Ca²⁺ and Mg²⁺ in the system will compete and consume the precipitant, resulting in an excessive dosage of the agent reaching 1.5 to 2 times the theoretical value, and a large amount of mixed sludge containing heavy metals is produced, and the subsequent dehydration and hazardous waste treatment costs are high; even under the optimal pH conditions (10.5 to 11.2), the potassium ion concentration at the end of the reaction is still maintained in the range of 120 to 180 ppm, which cannot meet the index requirements of high-end products; the particle size of the generated KOH·nH2O colloidal precipitate is less than 5μm, and it is difficult to effectively intercept it with conventional centrifugal or filter press equipment, resulting in the risk of secondary release of potassium ions in the filtrate.

[0006] The fluorosilicic acid precipitation method developed in recent years can achieve potassium ion immobilization by generating K2SiF6 crystals, and the theoretical potassium ion removal rate can reach more than 90%. However, practice has shown that this technology still has key defects: (1) The energy barrier for the formation of K2SiF6 crystal nuclei is high, and the supersaturation must be maintained at >150% to initiate the precipitation reaction, resulting in the actual reaction time being extended to 4-6 hours, which is much higher than the thermodynamic prediction value; (2) Unreacted SiF6 2 ⁻It is easy to hydrolyze under acidic conditions to generate HF and SiO2 colloid, causing equipment corrosion and pipeline blockage. At the same time, the fluoride ion concentration in the discharged wastewater exceeds the standard, and an additional deep treatment unit is required.

[0007] Therefore, providing an efficient method for removing potassium from monoammonium phosphate solution to meet the requirements of high-quality lithium iron phosphate is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0008] The invention discloses a method for depotassiumizing a monoammonium phosphate solution, so as to solve the technical problem that it is difficult to achieve a residual potassium ion concentration of less than 10 ppm in the method for depotassiumizing a monoammonium phosphate solution in the related art.

[0009] In order to solve the above problems, the present invention adopts the following technical solutions: The method for depotassiumizing a monoammonium phosphate solution of the present invention comprises the following steps: Step 100: diluting the monoammonium phosphate solution to a preset solid content, and filtering to remove suspended matter; Step 200: using fluorosilicic acid as a precipitant, adding a preset amount of fluorosilicic acid into the monoammonium phosphate solution obtained in step 100 twice, adjusting the pH and reaction temperature, and obtaining a mixed solution containing K2SiF6 crystals; Step 300: performing solid-liquid separation on the mixed solution containing K2SiF6 crystals to obtain a monoammonium phosphate solution after preliminary depotassium removal; Step 400: Deeply depotassiumizing the monoammonium phosphate solution after the initial depotassiumization by resin adsorption to obtain a monoammonium phosphate solution with a potassium ion content of less than 10 ppm.

[0010] According to an optional embodiment, in step 200, the amount of fluorosilicic acid added satisfies: the molar amount of potassium ions in the monoammonium phosphate solution: the molar amount of fluorosilicic acid = 2:1.

[0011] According to an optional embodiment, in step 200, the amount of fluorosilicic acid added for the first time is 40-60% of the preset amount, and the remaining fluorosilicic acid is added for the second time.

[0012] According to an optional embodiment, in step 200, after the first addition of fluorosilicic acid, the pH is adjusted to 3.0-3.5, the reaction temperature is controlled to 40-45° C., and the reaction is stirred for 10-20 minutes; After adding fluorosilicic acid for the second time, adjust the pH to 2.5-3.0, control the reaction temperature to 25-30°C, and mature for 20-40 minutes.

[0013] According to an alternative embodiment, the pH is adjusted using one or more of phosphoric acid, sulfuric acid and hydrochloric acid.

[0014] According to an optional embodiment, in step 400, the monoammonium phosphate solution after preliminary depotassium removal is subjected to deep depotassium removal, comprising the following steps: Passing the preliminarily depotassium-depleted monoammonium phosphate solution obtained after solid-liquid separation through a weak acid chelating resin column, and using the weak acid chelating resin column to adsorb calcium ions and magnesium ions in the preliminarily depotassium-depleted monoammonium phosphate solution; The monoammonium phosphate solution after the removal of calcium ions and magnesium ions is passed through a first strong acid cationic resin column and a second strong acid cationic resin column in sequence to perform deep depotassium removal on the monoammonium phosphate solution after the preliminary depotassium removal.

[0015] According to an optional embodiment, when a strong acid cationic resin column is used to deeply depotassiumize the monoammonium phosphate solution after preliminary depotassiumization, the first strong acid cationic resin column and the second strong acid cationic resin column are connected in series with each other, and when the potassium ion concentration at the outlet of the first strong acid cationic resin column is higher than 50 ppm, the monoammonium phosphate solution after the removal of calcium ions and magnesium ions is passed through a spare first strong acid cationic resin column and a spare second strong acid cationic resin column in sequence.

[0016] According to an optional embodiment, when the potassium ion concentration at the outlet of the first strong acid cation resin column or the first strong acid cation resin column is higher than 50 ppm, phosphoric acid solution is used for regeneration to obtain a phosphoric acid solution containing potassium ions.

[0017] According to an optional embodiment, a phosphoric acid solution containing potassium ions is added to step 200 to adjust the pH of the solution.

[0018] According to an optional embodiment, the monoammonium phosphate solution is diluted to a solid content of 10-18%.

[0019] The technical solution adopted by the present invention can achieve the following beneficial effects: The method for depotassiumizing a monoammonium phosphate solution of the present invention uses fluorosilicic acid as a precipitant to preliminarily remove potassium ions from the monoammonium phosphate solution, and then uses resin adsorption to deeply depotassiumize the monoammonium phosphate solution after the preliminarily depotassiumization. By coupling a fluorosilicic acid precipitation method with a resin adsorption method, the bottleneck of a single process can be broken through, and the potassium ion concentration can be reduced from more than 2000 ppm to less than 10 ppm, thereby meeting the requirements for high-quality lithium iron phosphate, and at the same time, efficient, low-cost and continuous depotassiumization can be achieved.

[0020] Further, the method for depotassiumizing monoammonium phosphate solution of the present invention is to add fluorosilicic acid twice during the initial depotassiumization of the monoammonium phosphate solution. After the first addition of fluorosilicic acid, the pH is adjusted and the reaction temperature is controlled to control the generation of micron-sized K2SiF6 seeds, providing uniform nucleation sites for subsequent crystal growth; after the second addition of fluorosilicic acid, the pH is adjusted and the reaction temperature is controlled, and the seeds can be used to induce crystallization to generate K2SiF6 crystals to avoid secondary nucleation. That is, the present invention adopts the step-by-step addition of fluorosilicic acid and the step-by-step control of pH and temperature, and uses self-generated K2SiF6 microcrystals as seeds to induce the generation of K2SiF6 crystals, which can not only shorten the aging time, but also improve the potassium removal effect of fluorosilicic acid, reduce potassium ion residues, and the K2SiF6 precipitation particle size can be increased to more than 5μm. During solid-liquid separation, the filter press efficiency can be increased by more than 30%, reducing the K2SiF6 crystals that penetrate into the solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 It is a process flow chart of the method for depotassiumization of monoammonium phosphate solution of the present application; Figure 2 This is a particle size distribution diagram of the crystals obtained after adding a fluorosilicic acid solution to a monoammonium phosphate solution in Example 1 of the present application; Figure 3 This is a particle size distribution diagram of the crystals obtained after adding fluorosilicic acid solution to monoammonium phosphate solution in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0023] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0024] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0025] The relevant technology uses the fluosilicic acid precipitation method to remove potassium, and the potassium ion is immobilized by generating K2SiF6 crystals. The theoretical removal rate of potassium ions can reach more than 90%. However, practice shows that this technology still has key defects: (1) The energy barrier for the formation of K2SiF6 crystal nuclei is high, and the supersaturation must be maintained at >150% to trigger the precipitation reaction, resulting in the actual reaction time being extended to 4-6 hours, which is much higher than the thermodynamic prediction value; (2) Unreacted SiF6 2 ⁻It is easy to hydrolyze under acidic conditions to generate HF and SiO2 colloid, causing equipment corrosion and pipeline blockage. At the same time, the fluoride ion concentration in the discharged wastewater exceeds the standard, and an additional deep treatment unit is required.

[0026] Although ion exchange resin has a high adsorption efficiency, when it is directly used to treat high potassium concentration solutions, the resin is easily poisoned and becomes ineffective, the regeneration frequency is high, and the operating cost increases.

[0027] The method for depotassiumizing a monoammonium phosphate solution of the present application uses fluorosilicic acid as a precipitant to preliminarily remove potassium ions from the monoammonium phosphate solution, and then uses resin adsorption to deeply depotassiumize the monoammonium phosphate solution after the preliminarily depotassiumization. By coupling the fluorosilicic acid precipitation method with the resin adsorption method, the bottleneck of a single process can be broken through, and the potassium ion concentration can be reduced from more than 2000 ppm to less than 10 ppm, meeting the requirements of high-quality lithium iron phosphate, and at the same time, efficient, low-cost, and continuous depotassiumization can be achieved.

[0028] The method for depotassiumizing the monoammonium phosphate solution provided in the present application is described in detail below.

[0029] Figure 1 The process flow chart of the method for removing potassium from monoammonium phosphate solution of the present application is shown. Figure 1 As shown, the method for depotassiumizing monoammonium phosphate solution of the present application comprises the following steps: Step 100: dilute the monoammonium phosphate solution to a preset solid content, and filter to remove suspended matter.

[0030] Preferably, the monoammonium phosphate solution is diluted to a solid content of 10-18%. Exemplarily, the monoammonium phosphate solution is diluted to a solid content of 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11% or 10%. Controlling the solid content of the monoammonium phosphate solution to 10-18% is conducive to the formation of seed crystals and the generation of crystals when fluorosilicic acid reacts with potassium ions, and can avoid the problem that the potassium ion concentration is too high, fluorosilicic acid and potassium ions directly form precipitation, and it is difficult to generate micron-sized K2SiF6 seed crystals.

[0031] Preferably, the diluted monoammonium phosphate solution is passed through a 200-mesh sieve to remove suspended matter. By removing the suspended matter, interference of the suspended matter with potassium ion precipitation, solid-liquid separation or adsorption process can be avoided.

[0032] Step 200: Using fluorosilicic acid as a precipitant, a preset amount of fluorosilicic acid is added twice to the monoammonium phosphate solution obtained in step 100, and after adjusting the pH and reaction temperature, a mixed solution containing K2SiF6 crystals is obtained.

[0033] Preferably, the amount of fluorosilicic acid added satisfies: the molar amount of potassium ions in the monoammonium phosphate solution: the molar amount of fluorosilicic acid = 2:1. With the method of the present application, only a theoretical amount of fluorosilicic acid needs to be added. The present application can achieve efficient removal of potassium ions without adding excessive fluorosilicic acid, which not only saves costs, but also avoids the problem of excessive fluorosilicic acid residue, the generation of HF and SiO2 colloids under acidic conditions, and the corrosion of equipment, pipeline blockage, and excessive fluoride ion concentration in discharged wastewater.

[0034] Preferably, the amount of fluorosilicic acid added for the first time is 40-60% of the preset amount, and the remaining fluorosilicic acid is added for the second time. Exemplarily, the amount of fluorosilicic acid added for the first time is 40% of the preset amount, and the remaining fluorosilicic acid is added for the second time, that is, 60% of the preset amount. Exemplarily, the amount of fluorosilicic acid added for the first time is 50% of the preset amount, and the remaining fluorosilicic acid is added for the second time, that is, 50% of the preset amount. Exemplarily, the amount of fluorosilicic acid added for the first time is 60% of the preset amount, and the remaining fluorosilicic acid is added for the second time, that is, 40% of the preset amount.

[0035] Preferably, after the first addition of fluorosilicic acid, the pH is adjusted to 3.0-3.5, the reaction temperature is controlled to 40-45°C, and the reaction is stirred for 10-20 minutes. Preferably, after the second addition of fluorosilicic acid, the pH is adjusted to 2.5-3.0, the reaction temperature is controlled to 25-30°C, and the reaction is aged for 20-40 minutes.

[0036] After the first addition of fluorosilicic acid, at 40-45°C and pH 3.0-3.5, high temperature is used to promote nucleation kinetics, accurately generate micron-sized K2SiF6 seeds, and provide uniform nucleation sites for subsequent crystal growth. Specifically, the particle size of the generated seeds is 1-5μm. After the second addition of fluorosilicic acid, in an acidic environment at 25-30°C and pH 2.5-3.0, secondary nucleation is inhibited by reducing supersaturation, and directional epitaxial growth is achieved by seed induction, which not only shortens the aging time, but also improves the potassium removal effect of fluorosilicic acid and reduces potassium ion residues. In addition, the particle size of K2SiF6 precipitation can be increased to more than 5μm. During solid-liquid separation, the filter press efficiency can be increased by more than 30%, reducing the number of K2SiF6 crystals that penetrate into the solution.

[0037] The present application adds fluorosilicic acid in batches and adopts a gradient temperature control method of high-temperature nucleation-low-temperature growth and a staged pH control method, which can not only effectively shorten the crystal maturation time, but also improve the integrity of crystal growth, forming a high-purity, large-particle-size (>5μm) K2SiF6 precipitate, and avoiding grain refinement caused by explosive nucleation.

[0038] Preferably, one or more of phosphoric acid, sulfuric acid and hydrochloric acid are used to adjust the pH. Preferably, phosphoric acid is used to adjust the pH to avoid the introduction of additional ions, thereby improving product quality.

[0039] Preferably, the K2SiF6 precipitate generated by the reaction of fluorosilicic acid and potassium ions in the present application is washed three times with hot water at 80°C and then dried, with a purity of ≥99.5%, meeting the photovoltaic glass raw material standard (SiO2≤0.1%), and can be sold as a photovoltaic wheel additive, increasing the income of by-products by about 2,000 per ton.

[0040] Step 300: performing solid-liquid separation on the mixed solution containing K2SiF6 crystals to obtain a monoammonium phosphate solution after preliminary depotassium removal.

[0041] For example, the mixed solution is filtered in two stages by a centrifuge and a precision ceramic filter membrane filter press, and the pore size of the filter membrane is 1 to 5 microns. Compared with the traditional plate and frame filter press, this filtering direction can effectively improve the filtering efficiency and avoid the problem that small particles of K2SiF6 crystals are difficult to separate.

[0042] Step 400: Deeply depotassiumizing the monoammonium phosphate solution after the initial depotassiumization by resin adsorption to obtain a monoammonium phosphate solution with a potassium ion content of less than 10 ppm.

[0043] Preferably, in step 400, the monoammonium phosphate solution after preliminary depotassium removal is subjected to deep depotassium removal, comprising the following steps: The monoammonium phosphate solution after the preliminary depotassiumization obtained after solid-liquid separation is passed through a weak acid chelating resin column, and the calcium ions and magnesium ions in the monoammonium phosphate solution after the preliminary depotassiumization are adsorbed by the weak acid chelating resin column. Exemplarily, the weak acid chelating resin column is Amberlite IRC-86. By using the weak acid chelating resin column to adsorb the calcium ions and magnesium ions in the monoammonium phosphate solution after the preliminary depotassiumization, the calcium ions and magnesium ions can be prevented from entering the strong acid cation resin column, causing the problem of poisoning of the strong acid cation resin column.

[0044] The monoammonium phosphate solution after the removal of calcium ions and magnesium ions is sequentially passed through a first strong acid cation resin column and a second strong acid cation resin column to perform deep depotassium removal on the monoammonium phosphate solution after the preliminary depotassium removal. Exemplarily, the strong acid cation resin column is Amberlite IR-120.

[0045] After calcium fluoride precipitation, the potassium ion content in the monoammonium phosphate solution is greatly reduced, and then through two stages of strong acid cationic resin columns, the potassium ion content in the monoammonium phosphate solution can be reduced to below 10ppm.

[0046] Preferably, the flow rate of the monoammonium phosphate solution through the weak acid chelating resin column and the strong acid cation resin column is 5-8 BV / h.

[0047] Preferably, when the monoammonium phosphate solution after preliminary potassium removal is deeply depotassiumized by using a strong acid cation resin column, the first strong acid cation resin column and the second strong acid cation resin column are connected in series to form a two-stage adsorption column. Exemplarily, the system is provided with two groups of two-stage strong acid cation resin columns, and the two groups of two-stage strong acid cation resin columns are connected in parallel to each other, wherein one group of two-stage strong acid cation resin columns is used for deep potassium removal, and the other group is used as a standby. When one group of two-stage strong acid cation resin columns needs to be regenerated, the standby group is enabled; at the same time, the two-stage strong acid cation resin columns of the regeneration group need to be regenerated and used as the standby group; so circulate to ensure the continuity of the potassium removal process. Exemplarily, when the potassium ion concentration at the outlet of the first strong acid cation resin column is higher than 50ppm, the monoammonium phosphate solution after removing calcium ions and magnesium ions is sequentially passed through the standby first strong acid cation resin column and the standby second strong acid cation resin column.

[0048] Preferably, when the first strong-acid cation resin column or the first strong-acid cation resin column outlet potassium ion concentration is higher than 50ppm, phosphoric acid solution is adopted to regenerate, and the phosphoric acid solution containing potassium ions is obtained. Not limited to this, hydrochloric acid solution can also be adopted to regenerate. By regenerating the strong-acid cation resin column, the adsorption capacity of the strong-acid cation resin column can be guaranteed.

[0049] Preferably, a phosphoric acid solution containing potassium ions is added to step 200 to adjust the pH of the solution. The use of the phosphoric acid solution containing potassium ions to adjust the pH value of the solution in step 200 can reduce the acid consumption for adjusting the pH value and further reduce the cost. The phosphoric acid solution used for regeneration contains less potassium ions, most of which can be removed in the fluosilicic acid precipitation stage, and will not affect the removal efficiency of potassium.

[0050] The method for depotassiumizing a monoammonium phosphate solution provided in the present application is described in detail below through specific embodiments and their application scenarios.

[0051] Example 1 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0052] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to the molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.2 with phosphoric acid, and stir at 40°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.7 with phosphoric acid, and mature at 25°C for 30 minutes.

[0053] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 122 ppm.

[0054] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 8 ppm.

[0055] This example also tests the particle size distribution of the crystals obtained after adding 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution for the first time. Specifically, the particle size distribution of the crystals was tested using a Malvern 3000 laser particle size analyzer. The results are as follows: Figure 2 shown.

[0056] from Figure 2 It can be seen that the crystal size distribution obtained by this method is concentrated, D 50 4.95 μm, D 95The result shows that adding fluorosilicic acid to the monoammonium phosphate solution twice can generate micron-sized K2SiF6 seed crystals, providing uniform nucleation sites for subsequent crystal growth.

[0057] Example 2 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0058] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to a molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 50% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.2 with phosphoric acid, and stir at 40°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.7 with phosphoric acid, and mature at 25°C for 30 minutes.

[0059] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 113 ppm.

[0060] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 9 ppm.

[0061] Example 3 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0062] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to a molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 60% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.2 with phosphoric acid, and stir at 40°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.7 with phosphoric acid, and mature at 25°C for 30 minutes.

[0063] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 101 ppm.

[0064] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 8 ppm.

[0065] Example 4 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0066] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to a molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the pH of the solution to 3.5 with phosphoric acid, and stir at 40°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the pH of the solution to 3.0 with phosphoric acid, and mature at 25°C for 30 minutes.

[0067] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 109 ppm.

[0068] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 7 ppm.

[0069] Example 5 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0070] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to a molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.0 with phosphoric acid, and stir at 40°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.5 with phosphoric acid, and mature at 25°C for 30 minutes.

[0071] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 128 ppm.

[0072] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 8 ppm.

[0073] Example 6 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0074] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to the molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.2 with phosphoric acid, and stir at 42°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.7 with phosphoric acid, and mature at 28°C for 30 minutes.

[0075] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 125 ppm.

[0076] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 8 ppm.

[0077] Example 7 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0078] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to a molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.2 with phosphoric acid, and stir at 45°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.7 with phosphoric acid, and mature at 30°C for 30 minutes.

[0079] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 131 ppm.

[0080] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 9 ppm.

[0081] Example 8 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0082] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to the molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.2 with phosphoric acid, and stir at 40°C for 10 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.7 with phosphoric acid, and mature at 25°C for 20 minutes.

[0083] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 132 ppm.

[0084] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 9 ppm.

[0085] Example 9 The method for depotassiumizing a monoammonium phosphate solution in this embodiment comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0086] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to a molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.2 with phosphoric acid, and stir at 40°C for 20 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.7 with phosphoric acid, and mature at 25°C for 40 minutes.

[0087] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 107 ppm.

[0088] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 8 ppm.

[0089] Comparative Example 1 The method for depotassiumizing monoammonium phosphate solution in this comparative example comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0090] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution at a molar ratio of potassium ions to H2SiF6 of 2:1, add the fluorosilicic acid solution to the monoammonium phosphate solution at once, adjust the pH of the solution to 3.2 with phosphoric acid, and stir the reaction at 40°C for 45 minutes.

[0091] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 594 ppm.

[0092] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h, and the potassium ion concentration of the outlet solution is 241 ppm.

[0093] This comparative example also tests the particle size distribution of the crystals obtained after adding the fluorosilicic acid solution to the monoammonium phosphate solution. Specifically, the particle size distribution of the crystals was tested using a Malvern 3000 laser particle size analyzer. The results are as follows: Figure 3 shown.

[0094] from Figure 3 It can be seen that when fluorosilicic acid is added to the monoammonium phosphate solution at one time, the resulting crystals are of different sizes, with a large proportion of small particles and an uneven particle size distribution. 50 1.30 μm, D 95 It is 21.23 microns.

[0095] It can be seen that the method of adding fluorosilicic acid to the monoammonium phosphate solution at one time not only leaves more potassium ions in the solution, but also the particle sizes of the obtained K2SiF6 vary. During filtration, the smaller particle sizes of K2SiF6 easily pass through the filter membrane and enter the solution, while the strong acid resin column only adsorbs the potassium ions remaining in the solution and cannot adsorb the K2SiF6 crystals. The residual K2SiF6 in the solution not only affects the adsorption efficiency of the strong acid resin column, but also affects the potassium removal effect of the monoammonium phosphate solution.

[0096] Comparative Example 2 The method for depotassiumizing monoammonium phosphate solution in this comparative example comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0097] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to a molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 4.0 with phosphoric acid, and stir at 40°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 3.0 with phosphoric acid, and mature at 25°C for 30 minutes.

[0098] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 465 ppm.

[0099] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 86 ppm.

[0100] Comparative Example 3 The method for depotassiumizing monoammonium phosphate solution in this comparative example comprises the following steps: Step 100: Take 1 ml of monoammonium phosphate solution containing a potassium ion concentration of 2011 ppm 3 , dilute to a solid content of 18%, pass through a 200-mesh sieve to remove suspended matter.

[0101] Step 200: Prepare a 40% fluorosilicic acid solution. Take a fluorosilicic acid solution according to the molar ratio of potassium ions to H2SiF6 of 2:1, and add the fluorosilicic acid solution to the monoammonium phosphate solution twice. The first time, add 40% (weight) fluorosilicic acid solution to the monoammonium phosphate solution obtained in step 100, adjust the solution pH to 3.2 with phosphoric acid, and stir at 50°C for 15 minutes; the second time, add the remaining fluorosilicic acid solution to the solution, adjust the solution pH to 2.7 with phosphoric acid, and mature at 35°C for 30 minutes.

[0102] Step 300: The mixed solution obtained in step 200 is subjected to solid-liquid separation by centrifuge and precision ceramic filter membrane filtration, wherein the pore size of the filter membrane is 1 micron. The K⁺ concentration in the obtained filtrate is reduced to 531 ppm.

[0103] Step 400: The filtrate obtained in step 300 is passed through a chelating resin column (removing 98% of calcium ions) and a double-series strong acid resin column in sequence, with a flow rate of 8 BV / h and an outlet solution potassium ion concentration of 122 ppm.

[0104] In each embodiment and comparative example, the potassium ion concentration was detected using an ICP detector.

[0105] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0106] In addition, it should be noted that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in a reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0107] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for depotassiumizing a monoammonium phosphate solution, characterized in that: The steps include: Step 100: diluting the monoammonium phosphate solution to a preset solid content, and filtering to remove suspended matter; Step 200: using fluorosilicic acid as a precipitant, adding a preset amount of fluorosilicic acid into the monoammonium phosphate solution obtained in step 100 twice, adjusting the pH and reaction temperature, and obtaining a mixed solution containing K2SiF6 crystals; Step 300: performing solid-liquid separation on the mixed solution containing K2SiF6 crystals to obtain a monoammonium phosphate solution after preliminary depotassium removal; Step 400: Deeply depotassiumizing the monoammonium phosphate solution after the initial depotassiumization by resin adsorption to obtain a monoammonium phosphate solution with a potassium ion content of less than 10 ppm.

2. The method for depotassiumizing a monoammonium phosphate solution according to claim 1, characterized in that: In step 200, the amount of fluorosilicic acid added satisfies: the molar amount of potassium ions in the monoammonium phosphate solution: the molar amount of fluorosilicic acid = 2:

1.

3. The method for depotassiumizing a monoammonium phosphate solution according to claim 1 or 2, characterized in that: In step 200, the amount of fluorosilicic acid added for the first time is 40-60% of the preset amount, and the remaining fluorosilicic acid is added for the second time.

4. The method for depotassiumizing a monoammonium phosphate solution according to claim 1 or 2, characterized in that: In step 200, after the first addition of fluorosilicic acid, the pH is adjusted to 3.0-3.5, the reaction temperature is controlled to 40-45°C, and the reaction is stirred for 10-20 minutes; After adding fluorosilicic acid for the second time, adjust the pH to 2.5-3.0, control the reaction temperature to 25-30°C, and mature for 20-40 minutes.

5. The method for depotassiumizing a monoammonium phosphate solution according to claim 4, characterized in that: The pH is adjusted using one or more of phosphoric acid, sulfuric acid and hydrochloric acid.

6. The method for depotassiumizing a monoammonium phosphate solution according to claim 1, characterized in that: In step 400, the monoammonium phosphate solution after the initial depotassium removal is subjected to deep depotassium removal, comprising the following steps: Passing the preliminarily depotassium-depleted monoammonium phosphate solution obtained after solid-liquid separation through a weak acid chelating resin column, and using the weak acid chelating resin column to adsorb calcium ions and magnesium ions in the preliminarily depotassium-depleted monoammonium phosphate solution; The monoammonium phosphate solution after the removal of calcium ions and magnesium ions is passed through a first strong acid cationic resin column and a second strong acid cationic resin column in sequence to perform deep depotassium removal on the monoammonium phosphate solution after the preliminary depotassium removal.

7. The method for depotassiumizing a monoammonium phosphate solution according to claim 6, characterized in that: When the monoammonium phosphate solution after preliminary depotassium removal is deeply depotassiumized using a strong acid cation resin column, the first strong acid cation resin column and the second strong acid cation resin column are connected in series with each other, and when the potassium ion concentration at the outlet of the first strong acid cation resin column is higher than 50 ppm, the monoammonium phosphate solution after the removal of calcium ions and magnesium ions is passed through the spare first strong acid cation resin column and the spare second strong acid cation resin column in sequence.

8. The method for depotassiumizing a monoammonium phosphate solution according to claim 7, characterized in that: When the first strong acid cation resin column or the potassium ion concentration at the outlet of the first strong acid cation resin column is higher than 50 ppm, phosphoric acid solution is used for regeneration to obtain a phosphoric acid solution containing potassium ions.

9. The method for depotassiumizing a monoammonium phosphate solution according to claim 8, characterized in that: A phosphoric acid solution containing potassium ions is added to step 200 to adjust the pH of the solution.

10. The method for depotassiumizing a monoammonium phosphate solution according to claim 1, characterized in that: Dilute the monoammonium phosphate solution to a solid content of 10-18%.

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