Method for preparing lithium phosphate from lithium-containing solution by using extraction-reverse extraction technology

Abstract

The invention relates to a method for preparing lithium phosphate from a lithium-containing solution by using an extraction-reverse extraction technology, an extraction agent adopted in the method comprises a main extraction agent, a synergistic extraction agent and a diluent, the pKa value of the main extraction agent is greater than 12.5, the synergistic extraction agent has a P = O group, a hydroxyl group or a cavity diameter of 0.12-0.15 nm, the water solubility of the synergistic extraction agent is less than or equal to 50 mg / L, the viscosity is less than or equal to 50 mpa.s, and the diluent is a diluent. The synergistic extraction factor R of the extraction agent is more than 100, R = Dmix / (D1 + D2), the Dmix is the extraction distribution ratio of the main extraction agent to lithium when the main extraction agent and the synergistic extraction agent are mixed according to the mass ratio of (1: 1)-(1: 2), the D1 is the extraction distribution ratio of the main extraction agent to lithium, the D2 is the extraction distribution ratio of the synergistic extraction agent to lithium, and the stripping agent is phosphoric acid. According to the method disclosed by the invention, by selecting the main extraction agent and the synergistic extraction agent, on one hand, lithium monohydrogen phosphate and lithium dihydrogen phosphate impurities cannot be generated by reaction when phosphoric acid is adopted for reverse extraction, and on the other hand, sodium and potassium can be separated at a higher degree during extraction, so that high-purity lithium phosphate can be efficiently prepared.

Description

Technical Field

[0001] This invention relates to the field of lithium salt preparation technology, and in particular to a method for preparing lithium phosphate from lithium-containing solutions using extraction-back-extraction technology. Background Technology

[0002] The preparation of lithium iron phosphate (LiFePO4) from lithium phosphate (Li3PO4) is a technically feasible and environmentally friendly process route. It simplifies the raw materials and improves the tap density of lithium iron phosphate. Currently, lithium phosphate can be prepared from lithium-containing solutions through steps such as impurity removal and precipitation, for example, by extracting lithium phosphate from lithium ore. However, the lithium phosphate prepared by this method has a high impurity content and needs to be purified before it can be used to prepare lithium iron phosphate. Summary of the Invention

[0003] Therefore, it is necessary to provide a method for preparing lithium phosphate from lithium-containing solutions using extraction-back-extraction technology to address the above problems. This method can efficiently prepare high-purity lithium phosphate, which can be directly used to prepare lithium iron phosphate.

[0004] A method for preparing lithium phosphate from a lithium-containing solution using an extraction-back-extraction technique, wherein the extractant comprises a main extractant, a co-extractant, and a diluent, wherein the main extractant has a pKa value greater than 12.5, the co-extractant has a P=O group, a hydroxyl group, or a cavity diameter of 0.12 nm-0.15 nm, and the water solubility of the co-extractant is ≤50 mg / L, the viscosity is ≤50 mPa·s, and the co-extraction factor R of the extractant is greater than 100, wherein R=D mix / (D1+D2)D mix The extraction distribution ratio of lithium when the main extractant and the co-extractant are mixed at a mass ratio of 1:1 to 1:2, where D1 is the extraction distribution ratio of lithium by the main extractant, D2 is the extraction distribution ratio of lithium by the co-extractant, and the back-extractant is phosphoric acid.

[0005] In one embodiment, the primary extractant is selected from at least one of 2,2,6,6-tetramethyl-3,5-heptadecane, 2,2,7,7-tetramethyl-3,5-octanedane, 2,2-dimethyl-6,6-diphenyl-3,5-hexanedione, 1-(1-adamantyl)-4,4-dimethyl-1,3-pentanedione, di(1-adamantyl)methane, (1-adamantyl)-tert-butyrylmethane, and 2-adamantyl-6,6-dimethyl-3,5-heptadecane.

[0006] In one embodiment, the co-extractant is selected from at least one of trialkylphosphine oxide, tributylphosphine oxide, triisobutylphosphine oxide, di(2-ethylhexyl) phosphate, tridecanoyl alcohol, isotriadecanoyl alcohol, octyldodecanoyl alcohol, isodecanol, trioctyl phosphate, tert-butylbenzo-12-crown-4 and its derivatives.

[0007] In one embodiment, the main extractant has a mass fraction of 10%-20% in the extractant, and the mass ratio of the main extractant to the co-extractant is 1:1-1:2.

[0008] In one embodiment, the following steps are included:

[0009] S1 provides a lithium-containing solution;

[0010] S2, the lithium-containing solution is extracted using an extractant to obtain a lithium-loaded organic phase and raffinate;

[0011] S3, the lithium-supported organic phase is back-extracted using phosphoric acid to obtain lithium phosphate precipitate, empty extractant, and lithium-containing back-extraction solution.

[0012] In one embodiment, the temperature during the extraction step using an extractant is 10°C-40°C.

[0013] In one embodiment, during the extraction step using an extractant, when the lithium content in the lithium-containing solution is 1 g / L, the amount of the main extractant used is 20 g to 65 g.

[0014] In one embodiment, the temperature for the back-extraction step using phosphoric acid is 10°C-40°C; and / or the back-extraction time is 4 min-15 min.

[0015] In one embodiment, during the back-extraction step using phosphoric acid, 12-17g of phosphoric acid is used per 1L of the lithium-supported organic phase.

[0016] In one embodiment, the unloaded extractant is recycled to step S2 for further extraction of the lithium-containing solution;

[0017] And / or, the lithium-containing back-extraction solution is used to prepare phosphoric acid for further back-extraction of the lithium-supported organic phase.

[0018] This invention utilizes extraction-back-extraction technology to prepare lithium phosphate from lithium-containing solutions. By selecting the main extractant and co-extractant, the co-extraction factor of the extractant reaches over 100. On the one hand, when using phosphoric acid for back-extraction, no lithium monohydrogen phosphate and lithium dihydrogen phosphate impurities are generated, and back-extraction is non-emulsified, allowing for rapid separation of the oil, water, and precipitate phases. On the other hand, higher separation of sodium and potassium can be achieved during extraction, thus enabling the efficient preparation of high-purity lithium phosphate, which can be directly used to prepare lithium iron phosphate. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a process flow diagram of the preparation of lithium phosphate from lithium-containing solutions using extraction-back-extraction technology according to the present invention. Detailed Implementation

[0021] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0023] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0024] With the continuous development of extraction-back-extraction technology, the applicant attempted to use extraction-back-extraction technology to directly prepare lithium phosphate from lithium-containing solutions. However, after long-term experiments, it was found that when preparing lithium phosphate from lithium-containing solutions using extraction-back-extraction technology, the lithium phosphate product would contain impurities such as lithium monohydrogen phosphate and lithium dihydrogen phosphate, and the content of impurities such as sodium and potassium was also high, which could not meet the purity requirements for preparing lithium iron phosphate.

[0025] In order to prepare high-purity lithium phosphate using extraction-back-extraction technology, the applicant conducted in-depth research on the back-extraction process using phosphoric acid and found that the generation of lithium phosphate, lithium monohydrogen phosphate, and lithium dihydrogen phosphate is related to the dissociation of phosphoric acid. Specifically, the dissociation process of phosphoric acid is as follows:

[0026] Process 1: H3PO4 → H + +H2PO4 - (pKa=2.12)

[0027] Process 2: H2PO4 - →H + +HPO4 2- (pKa=7.12)

[0028] Process 3: HPO4 2- →H + +PO4 3- (pKa=12.36)

[0029] Therefore, during the dissociation process of phosphoric acid, it first dissociates to form dihydrogen phosphate ions, then the dihydrogen phosphate ions further dissociate to form monohydrogen phosphate ions, and then the monohydrogen phosphate ions further dissociate to form phosphate ions. Therefore, when using phosphoric acid for back-extraction to prepare lithium phosphate, lithium dihydrogen phosphate and lithium monohydrogen phosphate will inevitably be formed first. In order to prepare high-purity lithium phosphate products, phosphoric acid must be completely dissociated into phosphate ions.

[0030] Since each dissociation stage of phosphoric acid corresponds to a dissociation constant pKa, which represents the degree of ionization of the acid, the smaller the pKa value, the higher the degree of dissociation and the stronger the acidity. Based on this, the present invention provides a method for preparing lithium phosphate from a lithium-containing solution using extraction-back-extraction technology. The extractant includes a main extractant, a co-extractant, and a diluent, and the back-extractant is phosphoric acid.

[0031] Among them, lithium-containing solutions are generally salt lake brine, lithium ore leaching solution, lithium battery waste leaching solution, lithium precipitation mother liquor, etc. The main impurities in the solution are sodium, potassium, chloride ions, sulfate ions, etc. Sodium and potassium are elements in the same group as lithium and have similar properties. Although extraction-back-extraction mainly serves to remove impurities, purify and concentrate, sodium and potassium will inevitably enter the lithium-loaded organic phase during the lithium extraction process. The content is related to the separation degree of sodium and potassium by the extractant, and then eventually enter the product during the back-extraction process.

[0032] In this invention, the pKa value of the main extractant is greater than 12.5, and it can be specifically selected from at least one of 2,2,6,6-tetramethyl-3,5-heptadecane, 2,2,7,7-tetramethyl-3,5-octanedione, 2,2-dimethyl-6,6-diphenyl-3,5-hexanedione, 1-(1-adamantyl)-4,4-dimethyl-1,3-pentanedione, di(1-adamantanoyl)methane, (1-adamantyl)-tert-butyrylmethane, and 2-adamantyl-6,6-dimethyl-3,5-heptadecane.

[0033] In this invention, the co-extractant has a P=O group; the strongly polar P=O group is a strongly coordinating atom, and the oxygen atom has a high electron cloud density, making it an excellent Li... + Ligand; or, the co-extractant has a hydroxyl (-OH) group, the oxygen atom in which carries a lone pair of electrons, and can act as a Lewis base, reacting with Li as a Lewis acid. + Coordination occurs, forming stable O-Li bonds; or, the cavity diameter of the co-extractant is 0.12 nm-0.15 nm, Li + The diameter is approximately 0.12 nm, Na + The diameter is approximately 0.20 nm, K + With a diameter of 0.27 nm, by controlling the cavity diameter of the co-extractor within the range of 0.12 nm to 0.15 nm, the co-extractor can react with Li. + It has a matching coordination space, achieving high selectivity and repelling Na. + K + Interfering ions.

[0034] Meanwhile, the water solubility of the co-extracting agent is ≤50mg / L and the viscosity is ≤50mpa·s. On the one hand, the co-extracting agent has extremely strong hydrophobicity, which can ensure that it and the lithium complex exist stably in the organic phase. On the other hand, it can reduce the frictional resistance inside the fluid and reduce the obstacles encountered by droplets when they approach and coalesce. This allows the oil, water and precipitate phases to be separated quickly during the back-extraction of phosphoric acid to prepare lithium phosphate, without emulsification, ensuring the continuous and normal operation of back-extraction.

[0035] Optionally, the co-extractant is selected from at least one of trialkylphosphine oxide, tributylphosphine oxide, triisobutylphosphine oxide, di(2-ethylhexyl) phosphate, tridecanoyl alcohol, isotridecanoyl alcohol, octyldodecanoyl alcohol, isodecanol, trioctyl phosphate, tert-butylbenzo-12-crown-4 and its derivatives.

[0036] In this invention, the co-extraction effect can be represented by the co-extraction factor R, where R = D. mix / (D1+D2)D mixThe extraction distribution ratio of lithium when the main extractant and the co-extractant are mixed at a mass ratio of 1:1 to 1:2 is defined as D1, where D1 is the extraction distribution ratio of lithium by the main extractant and D2 is the extraction distribution ratio of lithium by the co-extractant. By selecting the main extractant and the co-extractant, the present invention can make the co-extraction factor R reach more than 100.

[0037] Therefore, when using phosphoric acid for back-extraction, phosphoric acid dissociates in three steps. The final step involves the dissociation of the monohydrogen phosphate ion to generate phosphate and hydrogen ions. The pKa value of this step is 12.36, which is lower than the pKa values ​​of the first two steps, indicating the weakest acidity. However, the pKa value of the main extractant is greater than 12.5. This means that the hydrogen ions obtained from all three dissociation steps are more acidic than the main extractant, capable of displacing lithium from the lithium-supported organic phase and ultimately generating lithium phosphate. This allows the phosphoric acid dissociation to continue towards the third step. The back-extraction reaction formula is as follows:

[0038] H + +XH-Li + (Lithium-supported organic phase) = XH - H (unloaded extractant) + Li +

[0039] Furthermore, the dissociation constant pKa values ​​of all three steps are greater than those of the main extractant, indicating that they can all react with Li in the lithium-supported organic phase. + Reaction. When Li + When the hydrogen ions dissociated from phosphoric acid react completely, no monohydrogen phosphate or dihydrogen phosphate ions remain in the solution. Therefore, no lithium monohydrogen phosphate or lithium dihydrogen phosphate impurities are generated. Thus, the method of this invention can efficiently prepare high-purity lithium phosphate, specifically, with a purity reaching battery grade, which can be directly used to prepare lithium iron phosphate.

[0040] Optionally, the diluent is selected from at least one of the following: n-hexane, n-dodecane, cyclohexane, D70 special solvent oil, D80 special solvent oil, No. 120 solvent oil, No. 160 solvent oil, No. 200 solvent oil, ordinary kerosene, aviation kerosene, sulfonated kerosene, light aromatic solvent oil, C9 / C10 aromatic solvent oil, and high-boiling-point aromatic solvent oil.

[0041] Optionally, the main extractant has a mass fraction of 10%-20% in the extractant, and the mass ratio of the main extractant to the co-extractant is 1:1-1:2. This not only allows the co-extraction factor to reach over 100, but also reduces process costs while ensuring extraction effect.

[0042] Specifically, such as Figure 1 As shown, the method for preparing lithium phosphate from a lithium-containing solution using extraction-back-extraction technology according to the present invention includes the following steps:

[0043] S1 provides a lithium-containing solution;

[0044] S2, the lithium-containing solution is extracted using an extractant to obtain a lithium-loaded organic phase and raffinate;

[0045] S3, the lithium-supported organic phase is back-extracted using phosphoric acid to obtain lithium phosphate precipitate, an empty extractant, and a lithium-containing back-extraction solution. Since lithium phosphate is slightly soluble in water, the lithium-containing back-extraction solution is a lithium phosphate solution.

[0046] It is understood that the extraction in step S2 and the back-extraction in step S3 of the present invention can be carried out in a continuous reaction mode or in a batch reaction mode, with the same result. For example, both can be carried out using a static mixer, or in a continuous mixing clarifier, extraction tower or centrifugal extractor for countercurrent back-extraction. The extraction and back-extraction can be carried out in multiple stages.

[0047] Optionally, in step S2, the extraction using an extractant is preferably carried out at a temperature of 10℃-40℃, more preferably 20℃-35℃, and the pressure is preferably atmospheric pressure, but can also be carried out under pressure. In the extraction step, when the lithium content in the lithium-containing solution is 1g / L, the amount of the main extractant used is preferably 15g-70g, more preferably 20g-65g. It can be understood that when the lithium content in the lithium-containing solution is 5g / L, the amount of the main extractant used is 75g-350g, more preferably 100g-325g.

[0048] Optionally, in the step of back-extraction with phosphoric acid, the temperature is preferably 10℃-40℃, more preferably 20℃-35℃, and the pressure is preferably atmospheric pressure, but it can also be carried out under pressure. In the step of back-extraction with phosphoric acid, 10g-20g of phosphoric acid is preferably used per 1L of the lithium-supported organic phase, more preferably 12g-17g of phosphoric acid.

[0049] Optionally, in step S3, where phosphoric acid is used for back-extraction, the back-extraction time is preferably 4 min-15 min, and more preferably 6 min-10 min.

[0050] Optionally, the unloaded extractant can be recycled to step S2 to continue extracting the lithium-containing solution.

[0051] Optionally, the lithium-containing back-extraction solution is used to prepare phosphoric acid for further back-extraction of the lithium-supported organic phase.

[0052] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.

[0053] The lithium-containing solution used in the following examples is a water sample after roasting and leaching of lepidolite ore to remove impurities, wherein the lithium content is 5 g / L, the sodium content is 30 g / L, the potassium content is 25 g / L, and the calcium content is 10 mg / L.

[0054] Example 1

[0055] In this embodiment, the extractant, by mass fraction, comprises 20% 2,2,6,6-tetramethyl-3,5-heptadecane (pKa 12.8), 40% tributylphosphine oxide (water-soluble 4 mg / L, viscosity 10 mPa·s), and 40% No. 200 solvent oil. The extraction partition ratio D1 of 2,2,6,6-tetramethyl-3,5-heptadecane for lithium is 0.15, and the extraction partition ratio D2 of tributylphosphine oxide for lithium is 0.16. When 2,2,6,6-tetramethyl-3,5-heptadecane and tributylphosphine oxide are mixed at a mass ratio of 1:2, the extraction partition ratio D2 for lithium is... mix The value is 42.4, from which the co-extraction factor R of the extraction system is calculated to be 151.4.

[0056] Extraction was carried out by mixing the extractant with 1L of lithium-containing solution, with the temperature controlled at 25℃ and the pressure at atmospheric pressure. The amount of main extractant used was 228g. After phase separation, lithium-supported organic phase and raffinate were obtained.

[0057] Phosphoric acid was mixed with 1 L of lithium-supported organic phase for back-extraction. The temperature was controlled at 25°C, the pressure at atmospheric pressure, and the back-extraction time was 6 min. The amount of phosphoric acid used was 16 g. After standing for 1 min to separate the phases, a clear oil phase, a clear aqueous phase, and a white precipitate were obtained. The white precipitate was centrifuged to obtain lithium phosphate product, the oil phase was the unloaded extractant, and the aqueous phase was the lithium phosphate solution. The unloaded extractant was recycled for extraction, and the lithium phosphate solution was used to prepare phosphoric acid for reuse in the back-extraction process.

[0058] Upon testing, the lithium phosphate obtained in this embodiment contained 0% lithium monohydrogen phosphate, 0% lithium dihydrogen phosphate, 0.0023% sodium, 0.0012% potassium, and 0.0018% calcium, with a purity of 99.85%.

[0059] Example 2

[0060] In this embodiment, the extractant, by mass fraction, comprises 20% 2,2,7,7-tetramethyl-3,5-octanedione (pKa 13.3), 30% tridecanoyl alcohol (water-soluble 2 mg / L, viscosity 45 mPa·s), and 70% sulfonated kerosene. The extraction partition ratio D1 of 2,2,7,7-tetramethyl-3,5-octanedione for lithium is 0.15, and the extraction partition ratio D2 of tridecanoyl alcohol for lithium is 0.09. When 2,2,7,7-tetramethyl-3,5-octanedione and tridecanoyl alcohol are mixed at a mass ratio of 1:1.5, the extraction partition ratio D2 for lithium is... mix The value is 36, thus the co-extraction factor R of the extraction system is calculated to be 150.

[0061] Extraction was carried out by mixing the extractant with 1L of lithium-containing solution, with the temperature controlled at 20℃ and the pressure at atmospheric pressure. The amount of main extractant used was 242g. After phase separation, lithium-supported organic phase and raffinate were obtained.

[0062] Phosphoric acid was mixed with 1 L of lithium-supported organic phase for back-extraction. The temperature was controlled at 20°C, the pressure at atmospheric pressure, the back-extraction time was 7 min, and the amount of extractant used was 15.1 g. After standing for 1.1 min to separate the phases, a clear oil phase, a clear aqueous phase, and a white precipitate were obtained. The white precipitate was centrifuged to obtain lithium phosphate product, the oil phase was the unloaded extractant, and the aqueous phase was the lithium phosphate solution. The unloaded extractant was recycled for extraction, and the lithium phosphate solution was used to prepare phosphoric acid for reuse in the back-extraction process.

[0063] Upon testing, the lithium phosphate obtained in this embodiment contained 0% lithium monohydrogen phosphate, 0.0025% lithium dihydrogen phosphate, 0.0014% potassium, and 0.0021% calcium, with a purity of 99.83%.

[0064] Example 3

[0065] By mass fraction, the extractant in this embodiment includes 10% 1-(1-adamantyl)-4,4-dimethyl-1,3-pentanedione (pKa 14.5), 15% di(2-ethylhexyl) phosphate (water-soluble 4 mg / L, viscosity 40 mPa·s), 40% n-dodecane, and 35% light aromatic solvent oil. The extraction partition ratio D1 of 1-(1-adamantyl)-4,4-dimethyl-1,3-pentanedione for lithium is 0.14, and the extraction partition ratio D2 of octyldodecaneol for lithium is 0.1. When 1-(1-adamantyl)-4,4-dimethyl-1,3-pentanedione and octyldodecaneol are mixed at a mass ratio of 1:1.5, the extraction partition ratio D2 for lithium is... mix The value is 35.5, from which the co-extraction factor R of the extraction system is calculated to be 147.9.

[0066] Extraction was carried out by mixing the extractant with 1L of lithium-containing solution, with the temperature controlled at 30℃ and the pressure at atmospheric pressure. The amount of main extractant used was 320g. After phase separation, lithium-supported organic phase and raffinate were obtained.

[0067] Phosphoric acid was mixed with 1 L of lithium-supported organic phase for back-extraction. The temperature was controlled at 30℃, the pressure at atmospheric pressure, the back-extraction time was 8 min, and the amount of extractant was 11.4 g. After standing for 1.1 min to separate the phases, a clear oil phase, a clear aqueous phase, and a white precipitate were obtained. The white precipitate was centrifuged to obtain lithium phosphate product, the oil phase was the unloaded extractant, and the aqueous phase was the lithium phosphate solution. The unloaded extractant was recycled for extraction, and the lithium phosphate solution was used to prepare phosphoric acid for reuse in the back-extraction process.

[0068] Upon testing, the lithium phosphate obtained in this embodiment contained 0% lithium monohydrogen phosphate, 0% lithium dihydrogen phosphate, 0.0029% sodium, 0.0016% potassium, and 0.0022% calcium, with a purity of 99.83%.

[0069] Example 4

[0070] In this embodiment, the extractant, by mass fraction, comprises 15% 2,2-dimethyl-6,6-diphenyl-3,5-hexanedione (pKa 13.2), 15% trioctyl phosphate (water-soluble 2 mg / L, viscosity 45 mPa·s), and 70% light aromatic solvent oil. The extraction partition ratio D1 of 2,2-dimethyl-6,6-diphenyl-3,5-hexanedione for lithium is 0.15, and the extraction partition ratio D2 of trioctyl phosphate for lithium is 0.11. When 2,2-dimethyl-6,6-diphenyl-3,5-hexanedione and trioctyl phosphate are mixed at a mass ratio of 1:1, the extraction partition ratio D2 for lithium is... mix The value is 36.7, from which the co-extraction factor R of the extraction system is calculated to be 141.1.

[0071] Extraction was carried out by mixing the extractant with 1L of lithium-containing solution, with the temperature controlled at 35℃ and the pressure at atmospheric pressure. The amount of main extractant used was 285g. After phase separation, lithium-supported organic phase and raffinate were obtained.

[0072] Phosphoric acid was mixed with 1 L of lithium-supported organic phase for back-extraction. The temperature was controlled at 35℃, the pressure at atmospheric pressure, the back-extraction time was 9 min, and the amount of extractant was 12.8 g. After standing for 1.2 min to separate the phases, a clear oil phase, a clear aqueous phase, and a white precipitate were obtained. The white precipitate was centrifuged to obtain lithium phosphate product, the oil phase was the unloaded extractant, and the aqueous phase was the lithium phosphate solution. The unloaded extractant was recycled for extraction, and the lithium phosphate solution was used to prepare phosphoric acid for reuse in the back-extraction process.

[0073] Upon testing, the lithium phosphate obtained in this embodiment contained 0% lithium monohydrogen phosphate, 0% lithium dihydrogen phosphate, 0.0032% sodium, 0.0019% potassium, and 0.0023% calcium, with a purity of 99.81%.

[0074] Example 5

[0075] By mass fraction, the extractant in this embodiment comprises 10% 2,2,6,6-tetramethyl-3,5-heptadecane (pKa = 12.8), 5% 1-(1-adamantyl)-4,4-dimethyl-1,3-pentanedione (pKa = 14.4), 15% tert-butylbenzo-12-crown-4 (water-soluble 20 mg / L, viscosity 2 mPa·s), and 70% light aromatic solvent oil, wherein 2,2,6,6-tetramethyl-3,5-heptadecane (pKa = 12.8) is the most abundant component. The extraction partition ratio (D1) of lithium for 1,2,6,6-tetramethyl-3,5-heptadecane (pKa 14.4) was 0.15, and the extraction partition ratio (D2) of lithium for tert-butylbenzo-12-crown-4 was 0.51. The extraction partition ratio (D2) of lithium for 2,2,6,6-tetramethyl-3,5-heptadecane (pKa 12.8) mixed with 1,2,6,6-tetramethyl-4,4,4-dimethyl-1,3-pentanedione and tert-butylbenzo-12-crown-4 in a 1:1 mass ratio was also [not specified]. mix The value is 91, thus the co-extraction factor R of the extraction system is calculated to be 137.8.

[0076] Extraction was carried out by mixing the extractant with 1L of lithium-containing solution, with the temperature controlled at 35℃ and the pressure at atmospheric pressure. The amount of main extractant used was 296g. After phase separation, lithium-supported organic phase and raffinate were obtained.

[0077] Phosphoric acid was mixed with 1 L of lithium-supported organic phase for back-extraction at a controlled temperature of 35°C and atmospheric pressure for 10 min. The amount of phosphoric acid used was 12.34 g. After standing for 1 min to separate the phases, a clear oil phase, a clear aqueous phase, and a white precipitate were obtained. The white precipitate was centrifuged to obtain lithium phosphate product, the oil phase was the unloaded extractant, and the aqueous phase was the lithium phosphate solution. The unloaded extractant was recycled for extraction, and the lithium phosphate solution was used to prepare phosphoric acid for reuse in the back-extraction process.

[0078] Upon testing, the lithium phosphate obtained in this embodiment contained 0% lithium monohydrogen phosphate, 0% lithium dihydrogen phosphate, 0.0036% sodium, 0.0022% potassium, and 0.0025% calcium, with a purity of 99.80%.

[0079] Comparative Example 1

[0080] The only difference between Comparative Example 1 and Example 1 is that the main extractant is selected from 1-phenyl-3-methyl-5-pyrazolone (pKa is 4), the extraction partition ratio D1 of 1-phenyl-3-methyl-5-pyrazolone for lithium is 0.21, and the extraction partition ratio D1 of lithium when 1-phenyl-3-methyl-5-pyrazolone and tributylphosphine oxide are mixed at a mass ratio of 1:2 is [missing information]. mix The value is 47.4, from which the co-extraction factor R of the extraction system is calculated to be 143.6.

[0081] Testing revealed that the product obtained in this comparative example is lithium dihydrogen phosphate, with a lithium monohydrogen phosphate content of 0%, a lithium phosphate content of 0%, a sodium content of 0.0031%, a potassium content of 0.0017%, a calcium content of 0.0025%, and a purity of 99.85%.

[0082] Comparative Example 2

[0083] The only difference between Comparative Example 2 and Example 1 is that the main extractant is selected from 1-phenyl-1,3-pentanedione (pKa is 9.0), the extraction partition ratio D1 of 1-phenyl-1,3-pentanedione for lithium is 0.18, and the extraction partition ratio D1 of 1-phenyl-1,3-pentanedione and tributylphosphine oxide at a mass ratio of 1:2 for lithium is [not specified]. mix The value is 44.1, from which the co-extraction factor R of the extraction system is calculated to be 147.

[0084] Testing revealed that the product obtained in this comparative example contained 0% lithium phosphate, 65.45% lithium monohydrogen phosphate, and 34.55% lithium dihydrogen phosphate.

[0085] Comparative Example 3

[0086] The only difference between Comparative Example 3 and Example 1 is that the co-extractant is tributyl phosphate, which has a water solubility of 280 mg / L, a viscosity of 3.5 mPa·s, and an extraction partition ratio (D2) of 0.25 for lithium. The extraction partition ratio (D2) for lithium is also different when 2,2,6,6-tetramethyl-3,5-heptadecyl dione and tributyl phosphate are mixed at a mass ratio of 1:2. mix The value is 25.2, from which the co-extraction factor R of the extraction system is calculated to be 61.4.

[0087] The lithium phosphate obtained in this comparative example contained 1.08% sodium, 0.88% potassium, and 0.11% calcium, with a purity of 97.71%.

[0088] Comparative Example 4

[0089] The only difference between Comparative Example 4 and Example 1 is that the co-extractant is selected from methyl isobutyl ketone, which has a water solubility of 16000 mg / L, a viscosity of 0.6 mPa·s, and an extraction partition ratio D2 of 0.02 for lithium. When 2,2,6,6-tetramethyl-3,5-heptadecane and methyl isobutyl ketone are mixed at a mass ratio of 1:2, the extraction partition ratio Dmix of lithium is 0.18. Based on this, the co-extraction factor R of the extraction system is calculated to be 1.

[0090] The lithium phosphate obtained in this comparative example contained 4.01% sodium, 2.21% potassium, and 0.40% calcium, with a purity of 93.12%.

[0091] Comparative Example 5

[0092] The only difference between Comparative Example 5 and Example 1 is that the co-extractant is selected from bis(2,4,4-trimethylpentyl)phosphonic acid, with a water solubility of 5 mg / L, a viscosity of 150 mPa·s, and an extraction partition ratio D2 of 0.12 for lithium. The extraction partition ratio D2 for lithium is also different when benzoyltrifluoroacetone and methyl isobutyl ketone are mixed at a mass ratio of 1:2. mix The value is 39, thus the co-extraction factor R of the extraction system is calculated to be 139.2.

[0093] After 6 minutes of back-extraction mixing, the oil and water emulsified, making it impossible to quickly separate the phases to obtain a clear oil phase, a clear water phase, and a white precipitate, thus preventing continuous extraction and back-extraction processes.

[0094] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing lithium phosphate from a lithium-containing solution using an extraction-back-extraction technique, characterized in that, The extractant comprises a primary extractant, a co-extractant, and a diluent. The primary extractant has a pKa value greater than 12.

5. The co-extractant has a P=O group, a hydroxyl group, or a cavity diameter of 0.12 nm-0.15 nm. Furthermore, the co-extractant has a water solubility ≤50 mg / L and a viscosity ≤50 mPa·s, resulting in a co-extraction factor R of the extractant greater than 100, wherein R = D. mix / (D1+D2)D mix The extraction distribution ratio of lithium when the main extractant and the co-extractant are mixed at a mass ratio of 1:1 to 1:2, where D1 is the extraction distribution ratio of lithium by the main extractant, D2 is the extraction distribution ratio of lithium by the co-extractant, and the back-extractant is phosphoric acid.

2. The method for preparing lithium phosphate from a lithium-containing solution using extraction-back-extraction technology according to claim 1, characterized in that, The main extractant is selected from at least one of 2,2,6,6-tetramethyl-3,5-heptadecane, 2,2,7,7-tetramethyl-3,5-octanedane, 2,2-dimethyl-6,6-diphenyl-3,5-hexanedione, 1-(1-adamantyl)-4,4-dimethyl-1,3-pentanedione, di(1-adamantyl)methane, (1-adamantyl)-tert-butyrylmethane, and 2-adamantyl-6,6-dimethyl-3,5-heptadecane.

3. The method for preparing lithium phosphate from a lithium-containing solution using extraction-back-extraction technology according to claim 1, characterized in that, The co-extractant is selected from at least one of trialkylphosphine oxide, tributylphosphine oxide, triisobutylphosphine oxide, di(2-ethylhexyl) phosphate, tridecanoyl alcohol, isotridecanoyl alcohol, octyldodecanoyl alcohol, isodecanol, trioctyl phosphate, tert-butylbenzo-12-crown-4 and its derivatives.

4. The method for preparing lithium phosphate from a lithium-containing solution using extraction-back-extraction technology according to claim 1, characterized in that, The main extractant has a mass fraction of 10%-20% in the extractant, and the mass ratio of the main extractant to the co-extractant is 1:1-1:

2.

5. The method for preparing lithium phosphate from a lithium-containing solution using extraction-back-extraction technology according to any one of claims 1-4, characterized in that, Includes the following steps: S1 provides a lithium-containing solution; S2, the lithium-containing solution is extracted with an extractant to obtain a lithium-supported organic phase and raffinate; S3, the lithium-supported organic phase is back-extracted using phosphoric acid to obtain lithium phosphate precipitate, empty extractant, and lithium-containing back-extraction solution.

6. The method for preparing lithium phosphate from a lithium-containing solution according to claim 5, characterized in that, In the extraction step using an extractant, the temperature is 10℃-40℃.

7. The method for preparing lithium phosphate from a lithium-containing solution according to claim 5, characterized in that, In the extraction step using an extractant, when the lithium content in the lithium-containing solution is 1 g / L, the amount of the main extractant used is 20 g to 65 g.

8. The method for preparing lithium phosphate from a lithium-containing solution according to claim 5, characterized in that, In the step of back-extraction using phosphoric acid, the temperature is 10℃-40℃; and / or the back-extraction time is 4min-15min.

9. The method for preparing lithium phosphate from a lithium-containing solution according to claim 5, characterized in that, In the step of back-extraction using phosphoric acid, 12-17g of phosphoric acid is used per 1L of the lithium-supported organic phase.

10. The method for preparing lithium phosphate from a lithium-containing solution according to claim 5, characterized in that, The unloaded extractant is recycled to step S2 to continue extracting the lithium-containing solution; And / or, the lithium-containing back-extraction solution is used to prepare phosphoric acid for further back-extraction of the lithium-supported organic phase.

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