A method for separating cations and weak anions from a solution

Abstract

The application discloses a method for separating cations and weak acid root ions from a solution. The method adds inorganic strong acid to the solution containing cations and weak acid root ions for sulfation treatment, so that the weak acid root is converted into a molecular state; subsequently, a hydrophilic organic solventing agent is added, and free water molecules in the solution are captured by virtue of the strong hydrophilicity of the solventing agent. The synergistic mechanism effectively inhibits the re-ionization of the molecular weak acid and completely blocks the coprecipitation path while greatly reducing the solubility of the sulfate to promote the crystallization and precipitation of the sulfate. Finally, through solid-liquid separation, crystal washing and filtrate separation, pure sulfate crystal is obtained, and bidirectional recovery of the weak acid and the solventing agent is realized. The application has the advantages of mild working condition, accurate separation and no secondary pollution, and is suitable for ore leaching solution, industrial waste liquid treatment and solid waste resource utilization.

Description

Technical Field

[0001] This invention relates to the field of resource recycling and element separation technology, specifically to a method for efficiently separating cations and weak acid radicals from a solution. It is applicable to scenarios such as ore leaching solutions, industrial wastewater treatment, solid waste resource utilization, and valuable metal recovery, and is particularly suitable for the component separation and resource utilization of phosphate rock leaching solutions, valuable metal organic acid complex leaching solutions, phosphorus-containing inorganic weak acid radicals, and metal salt wastewater containing organic acid radicals. Background Technology

[0002] In industrial production and solid waste resource utilization (such as phosphate rock treatment, waste lithium battery recycling, metallurgical slag recovery, and ammonia nitrogen-containing waste liquid treatment), a common type of solution system exists rich in target cations (metal ions and / or ammonium ions) and weak acid anions (such as phosphate and various organic acid anions). In these systems, cations (such as iron, magnesium, sodium, cobalt, nickel, lithium, ammonium, etc.) and weak acid anions often form stable complexes or insoluble salts with strong binding forces, making spontaneous separation difficult. Achieving efficient and green separation of target cations and weak acid anions has extremely high economic and environmental value for the purification and refining of valuable metals and ammonia nitrogen resources, as well as the recycling of weak acid resources.

[0003] For the aforementioned systems, traditional solution separation processes mainly include high-temperature calcination decomposition, chemical precipitation, and organic extraction. However, these processes generally suffer from insurmountable industrial drawbacks. High-temperature calcination consumes extremely high energy and easily causes equipment corrosion; weak acid anions are incompletely decomposed and cannot be recovered. Chemical precipitation is pH-sensitive, consumes a large amount of reagents, and easily produces co-precipitated sludge of various cations and weak acid anions, causing serious secondary pollution. Organic extraction faces problems such as expensive specialized extractants, easy emulsification and degradation, lengthy process flow, and high environmental risks. Therefore, seeking a mild, low-cost separation technology without secondary pollution has become an industry consensus.

[0004] In recent years, the solution-crystallization separation method has gradually attracted attention due to its mild operating conditions. For example, existing research literature (such as the report on the preparation of ferrous sulfate from NdFeB secondary waste in "Nonferrous Metals Science and Engineering") discloses the use of ethanol as a solvent in sulfuric acid leaching solutions to reduce solubility and recover metal ions in the solution as sulfates through crystallization. Meanwhile, related patent literature (such as CN104876194A) also discloses a process of adding methanol, ethanol, or acetone as precipitants to acidic sulfate-containing solutions for solid-liquid separation, combined with distillation to recover the solvent and acid. These existing technologies demonstrate that using organic solvents in acidic salt-containing systems can effectively reduce separation energy consumption.

[0005] Furthermore, for more complex systems containing weak acid anions, existing technologies have also explored the use of organic solvents for intervention. For example, in mixed systems containing weak phosphate anions (such as the crystallization process study on the calcium nitrate-phosphate-aqueous solution system in the *Journal of Chemical Engineering of Chinese Universities*), researchers used acetone or ethanol as solvents to induce the precipitation of specific cation salts in systems containing mixed strong and weak acids. This indicates that organic solvent crystallization processes have a certain theoretical basis and application exploration in complex waste liquid systems containing weak acid anions.

[0006] However, considering the existing technologies, significant technical challenges remain in the complete separation of target cations and weak acid anions. Current techniques typically rely solely on the physical property of organic solvents reducing the solubility of inorganic salts, lacking precise control over the chemical behavior of weak acid molecules. In practice, weak acid molecules readily reionize in solution, leading to the co-precipitation of weak acid anions with cations (i.e., product entrainment or the formation of mixed salts), resulting in low purity of the target salt (metal or ammonium salt) and incomplete component separation. Furthermore, existing methods lack a holistic process design encompassing strong acid protonation, specific water molecule capture to suppress ionization, and closed-loop recovery of solvent and weak acid. This prevents the simultaneous and efficient stripping of high-purity target salts and high-yield recycling of weak acids with low energy consumption. Therefore, a novel separation method is urgently needed that fundamentally severs the binding pathway between cations and weak acid anions, achieving precise separation and maximizing resource utilization. Summary of the Invention

[0007] In addressing the deep-seated technical problems of existing technologies when processing complex solutions containing metal ions (and / or ammonium ions) and weak acid anions, which rely solely on differences in physical solubility, weak acid anions are prone to reionization and co-precipitation with cations, leading to incomplete component separation, low purity of metal salt extraction, and difficulty in closed-loop recovery of weak acid resources, the present invention aims to provide a method that is low in energy consumption, free of secondary pollution, and can achieve precise and efficient separation of metal ions (and / or ammonium ions) and weak acid anions.

[0008] To achieve the above objectives, the present invention employs the following technical solution: a method for separating cations and weak acid radicals from a solution, comprising the following steps: S1, sulfation reaction: adding an inorganic strong acid to a solution L1 containing cations M(a) and weak acid radicals for sulfation treatment, causing the weak acid radicals in the solution to convert into molecular-state weak acids, thereby obtaining a mixed solution L2 containing sulfates and molecular-state weak acids; S2, crystallization reaction: adding a hydrophilic organic solvent to the mixed solution L2 and stirring, wherein the hydrophilic organic solvent is miscible with water to capture free water molecules in the system and inhibit the ionization of molecular-state weak acids, thereby precipitating out the chemical formula M(a)2(SO4). aSulfate crystals of ·nH2O were obtained to form a solid-liquid mixture system; wherein, M(a) represents ammonium ion or metal element, a is the molar weighted average valence state corresponding to M, and 1≤a≤4, and n is the number of water molecules; S3, solid-liquid separation: the solid-liquid mixture system was subjected to solid-liquid separation to obtain sulfate crystals M(a)2(SO4). a • nH2O and a weak acid filtrate containing a molecular-state weak acid and a hydrophilic organic solvent are used to separate the cation M(a) from the weak acid anion; S4, Crystal washing: The sulfate crystals are washed with a washing solution to dissolve the weak acid solution trapped inside the crystals. The washing solution is collected and the weak acid is recovered. The washing solution is an aqueous solution containing a hydrophilic organic solvent; S5, Filtrate component separation: The weak acid filtrate is separated to recover the weak acid solution and the hydrophilic organic solvent. The cation M(a) is at least one of ammonium ion and a metal element in the periodic table. In a further technical solution, in solution L1, the cation M(a) is selected from ammonium ion (NH4+). + The concentration of M(a) is 0.1-8.0 mol / L, and / or at least one of sodium, potassium, lithium, iron, magnesium, cobalt, nickel, manganese, aluminum, copper, zinc, chromium, mercury, and cadmium ions. Preferably, the concentration of M(a) is 1.0-3.0 mol / L.

[0009] In a further technical solution, the weak acid anions contained in solution L1 are inorganic weak acid anions or organic acid anions other than chloride ions and nitrate ions; the inorganic weak acid anions are selected from H... x PO4 3-x H y PO3 1-y H z P2O7 4-z At least one of the following, wherein 0≤x≤3, 0≤y≤1, 0≤z≤4; the organic acid anion is selected from at least one of formate, acetate, oxalate, propionate, butyrate, citrate, malate, lactate, and tartrate.

[0010] In a further technical solution, in step S1, the inorganic strong acid is selected from at least one of hydrochloric acid, nitric acid, and sulfuric acid; in the mixed solution L2, SO4 2- The molar ratio of ions to cations M(a) is greater than 0.9a / 2. Preferably, SO42- 2- The molar ratio of ions to M(a) ranges from 0.5a to 0.6a.

[0011] In a further technical solution, in step S2, the hydrophilic organic solvent contains at least one functional group selected from hydroxyl, amino, carbonyl, cyano, sulfoxide, urea, and pyrrolidone; preferably, the hydrophilic organic solvent is selected from at least one of methanol, ethanol, n-propanol, isopropanol, acetone, methyl ethyl ketone, acetonitrile, dimethylformamide, dimethylacetamide, formamide, dimethyl sulfoxide, formic acid, acetic acid, propionic acid, lactic acid, ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, ethylenediamine, tetramethylurea, 1,4-butanediol, diethylene glycol, triethanolamine, N-methylpyrrolidone, methyl formate, acetylacetone, and monoethanolamine.

[0012] In a further technical solution, in step S2, the added mass of the hydrophilic organic solvent is not less than 0.8 times the water content of the mixed solution L2, and preferably the added mass is 1.0 to 3.0 times the water content of the mixed solution L2; the crystallization temperature in step S2 is 0 to 100°C, and preferably the crystallization temperature is 20 to 50°C.

[0013] In a further technical solution, in step S3, the solid-liquid separation method employs atmospheric pressure filtration, pressure filtration, or centrifugal separation. In step S4, the mass concentration of the hydrophilic organic solvent in the washing liquid is 40%~70%, the washing temperature is controlled at 10~80℃, and the washing method employs single washing, multiple washing, or countercurrent washing, with the number of washing cycles being 1~5 times.

[0014] In a further technical solution, in step S5, the weak acid filtrate is separated using a fractional distillation method: atmospheric or vacuum distillation is performed based on the difference in boiling points between the hydrophilic organic solvent and the weak acid, with a distillation temperature range of 50-150℃. When the boiling point of the hydrophilic organic solvent is less than 100℃, the distillation products are a hydrophilic organic solvent and a weak acid solution; when the boiling point of the hydrophilic organic solvent is greater than 100℃, the distillation products are pure water, the hydrophilic organic solvent, and a weak acid solution. Preferably, the purity of the recovered hydrophilic organic solvent is ≥95%, the overall yield is ≥90%, and the recovered hydrophilic organic solvent can be directly recycled for use in the crystallization and crystal washing processes.

[0015] In a further technical solution, in step S5, when the weak acid filtrate contains an inorganic weak acid, a precipitation-coupled separation method is used for separation: a precipitant is added to the weak acid filtrate, and combined with distillation and solid-liquid separation processes, a solid inorganic weak acid salt, a hydrophilic organic solvent that meets the requirements for crystallization reaction, and pure water are obtained; the precipitant is selected from at least one of NH3, NH3·H2O, (NH4)2CO3, NH4HCO3, NaOH, Na2CO3, NaHCO3, KOH, K2CO3, and KHCO3. Preferably, the solvent recovery rate is ≥90%.

[0016] The present invention also claims protection for the application of the method described above for separating metal elements and weak acid radicals from solution in wastewater treatment or solid waste resource utilization.

[0017] The working principle of this invention is as follows: This invention utilizes the interaction and solubility differences among the solvent, water molecules, sulfate, and weak acid to achieve elemental separation. The core principle lies in the fact that the added hydrophilic organic solvent is far more hydrophilic than the weak acid and sulfate, preferentially capturing and precipitating free water molecules in the solution. On one hand, this leads to changes in the polarity and dielectric constant of the solution system, significantly reducing the solubility of the sulfate and promoting its rapid crystallization. On the other hand, the reduction of free water molecules strongly inhibits the ionization of the weak acid, ensuring that the weak acid anion remains in the liquid phase as a neutral weak acid molecule, completely blocking its co-crystallization pathway with cations (metal ions or ammonium ions), ultimately achieving efficient and precise separation of cations and weak acid anions.

[0018] Compared with the prior art, the present invention has the following beneficial effects: First, this invention fundamentally solves the technical problem of co-precipitation caused by the easy reionization of weak acid anions in existing dissolution crystallization techniques, achieving precise separation of cations (metal ions or ammonium ions) and weak acid anions. Addressing the shortcomings of existing methods that rely solely on differences in physical solubility, easily resulting in mixed salts or product entrainment, this invention innovatively introduces a synergistic intervention mechanism of "strong acid displacement protonation" and "hydrophilic organic solvent." The added solvent not only significantly reduces the solubility of sulfate, but more importantly, it completely inhibits the re-dissociation of molecular-state weak acids by strongly capturing free water molecules in the solution. This mechanism effectively cuts off the pathway for the binding of weak acid anions and cations, thereby significantly improving the purity of the precipitated sulfate crystals and ensuring the complete stripping of the target component.

[0019] Secondly, this invention completely overcomes the inherent drawbacks of traditional high-temperature calcination, chemical precipitation, and organic extraction methods, such as high energy consumption, secondary pollution, and complex processes, providing a mild and environmentally friendly process route. Addressing the issues mentioned in the background art, such as the need for high-temperature pyrolysis at 800-1500℃, the consumption of large amounts of acid and alkali to adjust pH leading to mixed sludge, and the expensive extractants posing environmental risks, the overall process of this invention only needs to be carried out at 0-100℃, without the need for extreme reaction conditions or expensive specialized extractants. The entire process produces no toxic or harmful waste gas emissions or secondary solid waste, significantly reducing equipment investment and reagent consumption, greatly improving the economy and safety of large-scale industrial applications.

[0020] Finally, this invention fills the gap in the global process synergy design of existing separation methods, achieving efficient bidirectional recovery and closed-loop utilization of valuable metals and / or ammonium ions, weak acid resources, and solvents. Addressing the problem mentioned in the background art that existing purification processes easily lead to the complete loss of weak acids and the inability to recycle resources, this invention features interconnected solid-liquid separation, crystal washing, and fractional distillation / precipitation processes. This design not only simultaneously obtains pure sulfate and high-purity weak acid solutions, but also ensures a recovery purity of ≥95% and an overall yield of ≥90% for the hydrophilic organic solvent. The high-purity recovered solvent can be directly recycled an unlimited number of times for the preceding crystallization and washing processes, thereby completely transforming complex industrial wastewater into high-value-added resources with extremely low overall operating energy consumption. Attached Figure Description

[0021] Figure 1 This is a graph showing the trend of ferrous sulfate concentration as a function of the weight percentage of acetic acid in the ferrous sulfate-acetic acid-water ternary system in Example 1 of the present invention under saturated conditions at 25°C.

[0022] Figure 2 This is a graph showing the trend of ferric sulfate concentration as a function of the weight percentage of ethanol in the ferric sulfate-ethanol-water ternary system at 25°C under saturated conditions in Example 2 of the present invention.

[0023] Figure 3 This is a graph showing the trend of magnesium sulfate concentration as a function of the weight percentage of ethanol in the magnesium sulfate-ethanol-water ternary system at 25°C under saturated conditions in Example 3 of the present invention.

[0024] Figure 4 This is a graph showing the trend of ammonium sulfate concentration as a function of the weight percentage of ethanol in the ammonium sulfate-ethanol-water ternary system at 25°C under saturated conditions in Example 4 of the present invention.

[0025] Figure 5 This is a graph showing the trend of sodium sulfate concentration as a function of the weight percentage of ethanol in the sodium sulfate-ethanol-water ternary system at 25°C under saturated conditions in Example 5 of the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments. The present invention will be clearly explained in detail below. Any person skilled in the art, after understanding the embodiments of the present invention, can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0027] Example 1 Component of solution L1 to be treated: Fe 2+ The concentration of the weak acid anion acetate is 1.5 mol / L, and the concentration of acetate is 3.0 mol / L; acetic acid is selected as the solvent.

[0028] Separation steps: S1, sulfation reaction: Solution L1 is acidified with concentrated sulfuric acid to convert acetate ions into acetic acid molecules, yielding solution L2; control n(SO4) 2- ) / (n(Fe 2+ The ratio of 1:1 is given; the corresponding reaction equation is: 2CH3COO - +H₂SO₄=2CH₃COOH+SO₄ 2- S2. Crystallization reaction: At a constant temperature of 40℃, add acetic acid with a water content 1.5 times that of L2, and stir until homogeneous. With the addition of acetic acid, the solubility of FeSO4 rapidly decreases to near zero. Figure 1 As shown, sulfate FeSO4·7H2O crystals precipitate out; S3. Solid-liquid separation: Filtration separates the mixed system to obtain ferrous sulfate crystals and acetic acid filtrate; completes the separation of iron and weak acid anions; S4. Crystal washing: Wash the crystals with a 50% acetic acid aqueous solution at 40℃, peel off the acetic acid solution wrapped around the crystals, and collect the washing liquid to recover the acetic acid. S5. Solvent recovery: The acetic acid filtrate is subjected to vacuum distillation at 80°C to recover acetic acid with a purity of 99.0%, and the acetic acid recovery rate is 95.2%. The recovered ethanol is directly recycled for the crystallization process.

[0029] Example 2 Component of solution L1 to be treated: Fe 3+ Concentration 1.7 mol / L, weak acid anion H2PO4 - Concentration 1.7 mol / L, SO4 2- Concentration 1.7 mol / L; ethanol was selected as the solvent.

[0030] Separation steps: S1. Sulphation reaction: Concentrated sulfuric acid is added dropwise to solution L1 for acidification treatment, and H2PO4 is removed. - The solution is converted to H3PO4 molecules to prepare sulfate solution L2; the concentration of SO42- in the solution is controlled. 2- ) / (n(Fe 3+ The ratio of reaction volume to total volume is 1.5:1; the corresponding reaction equation is: 2H2PO4 - +H₂SO₄=2H₃PO₄+SO₄ 2- S2. Crystallization reaction: At a constant temperature of 40℃, ethanol is added to solution L2. The amount of ethanol added is 1.5 times the water content of L2. After stirring evenly, as ethanol is added, the solubility of Fe2(SO4)3 rapidly decreases to near zero. Figure 2 As shown, sulfate Fe2(SO4)3·9H2O crystals precipitate out; S3. Solid-liquid separation: The mixed system is processed by centrifugation to separate ferric sulfate crystals and phosphoric acid filtrate, thus completing the separation of iron and weak acid ions. S4. Crystal washing: Under constant temperature of 40℃, the crude crystals are washed with a 50% ethanol aqueous solution to remove the phosphoric acid solution wrapped around the crystals, and the washing liquid is collected to recover the phosphoric acid. S5. Solvent recovery: The phosphoric acid filtrate is subjected to vacuum distillation at 80°C to recover phosphoric acid solution and ethanol with a purity of 98.2%, with an ethanol recovery rate of 95.5%. The recovered ethanol is directly recycled for the crystallization process.

[0031] Example 3 Component of solution L1 to be treated: Mg 2+ Concentration 1.6 mol / L, weak acid anion H2PO4 - Concentration 1.6 mol / L, Cl - Concentration 1.6 mol / L; ethylene glycol was selected as the solvent.

[0032] Separation steps: S1, sulfation reaction: Solution L1 is acidified with concentrated sulfuric acid to react with H2PO4. - The solution is converted to H3PO4 molecules to obtain solution L2; the concentration of SO42- is controlled. 2- ) / (n(Mg 2+ =1:1; S2, crystallization reaction: At a constant temperature of 40℃, ethylene glycol with a water content 1.5 times that of L2 is added. As ethylene glycol is added, the solubility of MgSO4 decreases rapidly to close to 0, and sulfate MgSO4·7H2O crystals are precipitated. S3. Solid-liquid separation: Centrifugation separates magnesium sulfate crystals and phosphoric acid filtrate, completing the separation of magnesium and weak acid ions; S4. Crystal washing: Wash the crystals with 50% ethylene glycol aqueous solution at 40℃ to remove the phosphoric acid solution wrapped around the crystals, and collect the washing liquid to recover the phosphoric acid. S5. Solvent Recovery: The phosphorus-containing filtrate is subjected to vacuum distillation at 120°C to separate high-concentration phosphoric acid and ethylene glycol with a purity of 98.6%, with a recovery rate of 96.8%, which can be recycled for crystallization and washing processes.

[0033] Example 4 Component L1 of the phosphorus-containing solution to be treated: NH4 + Concentration 2mol / L, Mg 2+ Concentration 1 mol / L, H2PO4 - Concentration 4 mol / L; ethanol was selected as the solvent.

[0034] Separation steps: S1, sulfation reaction: Solution L1 is acidified with concentrated sulfuric acid to react with H2PO4. - The solution is converted to H3PO4 molecules to obtain solution L2, and n(SO4) is controlled. 2- ) / (n(NH4 + +Mg 2+ =2:3; S2. Crystallization reaction: At a constant temperature of 40℃, add ethanol with a water content 1.5 times that of L2, and stir until homogeneous. With the addition of ethanol, the solubility of MgSO4 and (NH4)2SO4 rapidly decreases to near zero. Figure 3 , Figure 4 As shown, mixed salt crystals of sulfate MgSO4·7H2O and (NH4)2SO4 precipitate out; S3. Solid-liquid separation: Filtration separation yields mixed salt crystals and phosphoric acid filtrate, achieving the separation of ammonium, magnesium and weak acid ions; S4. Crystal washing: Wash the mixed crystals with 50% ethanol aqueous solution at 40℃ to remove the phosphoric acid solution wrapped around the crystals, and collect the washing liquid to recover the phosphoric acid. S5. Solvent Recovery: The phosphoric acid filtrate is subjected to vacuum distillation at 80°C to separate phosphoric acid solution and ethanol with a purity of 98.8%, with a recovery rate of 95.5%, which can be recycled for crystallization and washing processes.

[0035] Example 5 Component of solution L1 to be treated: Na + Concentration 4 mol / L, weak acid anion PO4 3- The concentration of acetate ions was 1 mol / L; ethanol was used as the solvent.

[0036] Separation steps: S1, sulfation reaction: Solution L1 is acidified with concentrated sulfuric acid to react with PO4. 3- The ions are converted to H3PO4 molecules, and the acetate ions are converted to acetic acid molecules, yielding solution L2; the concentration of n(SO4) is controlled. 2- ) / (n(Na + The ratio of reaction volume to volume is 1:2, and the reaction equation is: 2CH3COO - +H₂SO₄=2CH₃COOH+SO₄ 2- 2PO4 3- +3H₂SO₄=2H₃PO₄+3SO₄ 2- S2. Crystallization reaction: At a constant temperature of 40℃, add ethanol with a water content 1.5 times that of L2, and stir until homogeneous. With the addition of ethanol, the solubility of Na2SO4 rapidly decreases to near zero. Figure 5 As shown, sulfate Na2SO4·12H2O crystals precipitate out; S3. Solid-liquid separation: Centrifugation is used to separate sodium sulfate crystals and a weak acid filtrate. S4. Crystal washing: Wash the crystals with a 50% acetic acid aqueous solution at 40℃ to remove the acetic acid solution trapped inside, and collect the washing liquid to recover the acetic acid. S5. Solvent recovery: Add ammonia to the weak acid filtrate, filter to obtain phosphorus salt NH4H2PO4, place the filtrate at 80℃ for vacuum distillation, separate acetic acid solution and ethanol with a purity of 97.5%, with an ethanol recovery rate of 96.1%, which can be recycled for crystallization and washing processes.

[0037] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for separating cations and weak acid anions from a solution, characterized in that, Includes the following steps: S1. Sulphation reaction: An inorganic strong acid is added to a solution L1 containing cation M(a) and weak acid anions to carry out sulfation treatment, causing the weak acid anions in the solution to be converted into molecular weak acids, thus obtaining a mixed solution L2 containing sulfate and molecular weak acids; the cation M(a) is at least one of ammonium ions and metal cations in the periodic table; the weak acid anions in solution L1 are inorganic weak acid anions or organic acid anions; the inorganic weak acid anions are selected from HxPO4. (3-x) HyPO3 (1-y) HzP2O7 (4-z) At least one of the following, wherein 0≤x≤3, 0≤y≤1, 0≤z≤4; the organic acid anion is selected from at least one of formate, acetate, oxalate, propionate, butyrate, citrate, malate, lactate, and tartrate. S2. Crystallization reaction: A hydrophilic organic solvent is added to the mixed solution L2 and stirred. The hydrophilic organic solvent is miscible with water to capture free water molecules in the system and inhibit the ionization of molecular weak acids, thereby precipitating out the chemical formula M(a)2(SO4). a Sulfate crystals of ·nH2O are used to obtain a solid-liquid mixed system; wherein, M(a) represents ammonium ion or metal ion, a is the molar weighted average valence state corresponding to M, and 1≤a≤4, n is the number of water molecules; the hydrophilic organic solvent is selected from at least one of methanol, ethanol, n-propanol, isopropanol, acetone, methyl ethyl ketone, acetonitrile, dimethylformamide, dimethylacetamide, formamide, dimethyl sulfoxide, formic acid, acetic acid, propionic acid, lactic acid, ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, ethylenediamine, tetramethylurea, 1,4-butanediol, diethylene glycol, triethanolamine, N-methylpyrrolidone, methyl formate, acetylacetone, and monoethanolamine; S3. Solid-liquid separation: The solid-liquid mixture is subjected to solid-liquid separation to obtain sulfate crystals M(a)2(SO4). a • nH2O and a weak acid filtrate containing a molecular weak acid and a hydrophilic organic solvent are used to separate cation M(a) from weak acid anions; S4. Crystal washing: The sulfate crystals are washed with a washing solution to dissolve the weak acid solution trapped inside the crystals. The washing solution is collected and the weak acid is recovered. The washing solution is an aqueous solution containing a hydrophilic organic solvent. S5. Separation of filtrate components: The weak acid filtrate is separated to recover the weak acid solution and the hydrophilic organic solvent.

2. The method according to claim 1, characterized in that: In the solution L1, the concentration of M(a) is 0.1~8.0 mol / L.

3. The method according to claim 1, characterized in that: In step S1, the mixed solution L2 contains SO4 2- The molar ratio of ions to cations M(a) is greater than 0.9a / 2.

4. The method according to claim 1, characterized in that: In step S2, the mass of the hydrophilic organic solvent added is not less than 0.8 times the water content of the mixed solution L2; the crystallization temperature in step S2 is 0~100℃.

5. The method according to claim 4, characterized in that: The mass of the hydrophilic organic solvent added is 1.0 to 3.0 times the water content of the mixed solution L2; the crystallization temperature in step S2 is 20 to 50°C.

6. The method according to claim 1, characterized in that: In step S3, the solid-liquid separation method is atmospheric pressure filtration, pressure filtration or centrifugation; in step S4, the mass concentration of the hydrophilic organic solvent in the washing liquid is 40%~70%, and the washing temperature is controlled at 10~80℃.

7. The method according to claim 1, characterized in that: The washing methods include single washing and multiple washing.

8. The method according to claim 1, characterized in that: The washing method uses counter-current washing.

9. The method according to claim 1, characterized in that: In step S5, the weak acid filtrate is separated using a fractional distillation method: distillation is performed based on the difference in boiling points between the hydrophilic organic solvent and the weak acid; when the boiling point of the hydrophilic organic solvent is less than 100°C, the distillation products are a hydrophilic organic solvent and a weak acid solution; when the boiling point of the hydrophilic organic solvent is greater than 100°C, the distillation products are pure water, a hydrophilic organic solvent, and a weak acid solution.

10. The method according to claim 1, characterized in that: In step S5, when the weak acid filtrate contains inorganic weak acid, a precipitation coupling separation method is used for separation: a precipitant is added to the weak acid filtrate, and a distillation and solid-liquid separation process is combined to obtain a solid inorganic weak acid salt, a hydrophilic organic solvent that meets the requirements of the crystallization reaction, and pure water; the precipitant is selected from at least one of NH3·H2O, (NH4)2CO3, NH3, NH4HCO3, NaOH, Na2CO3, NaHCO3, KOH, K2CO3, and KHCO3.

11. The application of a method for separating cations and weak acid radicals from a solution as described in any one of claims 1 to 10 in mineral leaching solutions, wastewater treatment, or solid waste resource utilization.

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