A method for preparing lithium dihydrogen phosphate by extraction-CO2 stripping

Abstract

The application provides a method for preparing lithium dihydrogen phosphate by adopting extraction-CO2 stripping, and the method comprises the following steps: mixing calcium hydroxide and a lithium sodium solution, removing impurities by heating to obtain a decontaminated solution; adjusting the pH value of the decontaminated solution, and performing solid-liquid separation to obtain a refined lithium-containing solution; countercurrently extracting the refined lithium-containing solution to obtain a lithium-loaded organic phase and a raffinate aqueous phase; using carbon dioxide gas to extract a mixed solution of water and the lithium-loaded organic phase, and performing phase separation to obtain an aqueous phase and a regenerated organic phase; performing oil removal and precision filtration on the aqueous phase in sequence to obtain a lithium bicarbonate solution; mixing phosphoric acid and the lithium bicarbonate solution, and after the reaction is completed, performing concentration, cooling crystallization, solid-liquid separation and drying to obtain lithium dihydrogen phosphate. The application removes impurities by using calcium hydroxide in combination with extraction and CO2 stripping, and the operation is simple, no harmful waste water and waste gas are generated, and the regenerated organic phase can be recycled, so that the cost of preparing lithium dihydrogen phosphate is reduced.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology and relates to a method for preparing lithium dihydrogen phosphate by extraction-CO2 back-extraction. Background Technology

[0002] Lithium dihydrogen phosphate (LiH2PO4) is an important precursor for the preparation of lithium iron phosphate cathode materials for lithium-ion batteries. It can simultaneously provide lithium and phosphorus sources, effectively simplifying the lithium iron phosphate synthesis process, improving product tap density, and suppressing abnormal grain growth. It holds an irreplaceable position in the fields of new energy vehicles and energy storage. With the rapid development of the global new energy industry, the market demand for battery-grade lithium dihydrogen phosphate has exploded. Traditional methods for preparing lithium dihydrogen phosphate mainly include direct metathesis of lithium carbonate or lithium hydroxide and lithium phosphate conversion methods. Among them, the metathesis method, although simple in process, requires high purity of raw materials, and the reaction endpoint is difficult to control precisely. It is easy to generate byproducts such as lithium dihydrogen phosphate and lithium phosphate, resulting in reduced lithium yield and large fluctuations in product quality. The lithium phosphate conversion method has the problems of slow reaction rate and high equipment requirements. Moreover, all the above methods rely on high-purity lithium salt raw materials, resulting in high production costs and making it difficult to meet the needs of large-scale industrial production.

[0003] Solvent extraction has gradually become the mainstream technology for lithium dihydrogen phosphate (LiH2PO4) preparation due to its advantages such as high processing capacity, ability to handle low-concentration lithium-containing solutions, and good separation selectivity. Existing extraction methods for LiH2PO4 preparation (such as CN121493895A and CN121626946A) generally employ an extraction-phosphoric acid back-extraction process. This involves selectively extracting lithium ions through a co-extraction system, followed by direct back-extraction with a phosphoric acid solution to obtain a LiH2PO4 solution. However, phosphoric acid, being a strong acid, degrades both the extractant and co-extractant upon prolonged contact with the organic phase, significantly shortening the cycle life of the organic phase and increasing operating costs. The back-extraction process generates large amounts of acidic wastewater containing phosphoric acid, requiring significant amounts of alkali for neutralization, resulting in high environmental pressure and wastewater treatment costs. Furthermore, excess phosphoric acid in the back-extraction solution needs subsequent neutralization with alkaline lithium salts, which not only increases the consumption of expensive lithium salts but may also introduce new impurity ions, affecting product purity.

[0004] Furthermore, existing extraction methods generally suffer from inadequate pretreatment of raw materials. Most technologies remove impurities only through simple pH adjustment and calcium and magnesium removal resin treatment, without designing specific removal processes for difficult-to-remove impurities such as aluminum, silicon, and fluorine commonly found in lithium-sodium solutions. These impurities not only co-extract with lithium ions during the extraction process, reducing the purity of the back-extraction solution, but also gradually accumulate during the organic phase circulation, leading to emulsification of the extractant and difficulties in phase separation, severely affecting production continuity.

[0005] Therefore, developing a method for preparing lithium dihydrogen phosphate with mild back-extraction conditions, low extractant loss, thorough pretreatment, environmental friendliness, and low overall cost has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing lithium dihydrogen phosphate using extraction-CO2 back-extraction. This method combines calcium hydroxide impurity removal with extraction and CO2 back-extraction, is simple to operate, generates no harmful wastewater or waste gas, and allows the regenerated organic phase to be recycled, thereby reducing the cost of preparing lithium dihydrogen phosphate.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing lithium dihydrogen phosphate using extraction-CO2 back-extraction, the method comprising the following steps:

[0009] (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; adjust the pH of the impurity-removed solution to 9~11, and perform solid-liquid separation to obtain refined lithium-containing solution;

[0010] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0011] The extractant used in the countercurrent extraction includes benzoyltrifluoroacetone, trioctylphosphine oxide and sulfonated kerosene in a mass ratio of (15~25):(35~45):(35~45);

[0012] (3) The mixture of water and the lithium-loaded organic phase is extracted with carbon dioxide gas and separated to obtain an aqueous phase containing LiHCO3 and a regenerated organic phase; the aqueous phase containing LiHCO3 is then subjected to oil removal and precision filtration to obtain a lithium bicarbonate solution.

[0013] (4) Mix phosphoric acid with the lithium bicarbonate solution to make the pH of the reaction 4-5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

[0014] This method utilizes calcium hydroxide for deep impurity removal combined with pH adjustment to efficiently remove various impurities, followed by multi-stage countercurrent extraction for further purification; and employs a benzoyltrifluoroacetone, trioctylphosphine oxide, and sulfonated kerosene system for highly selective extraction of Li. + It is also compatible with CO2 back-extraction, which is convenient to operate and has a moderate cost. Replacing traditional strong acid back-extraction with CO2 back-extraction produces no harmful waste, and the regenerated organic phase can be directly recycled, which greatly reduces the consumption of extractant and production costs.

[0015] In some embodiments, calcium hydroxide may be provided by lime milk.

[0016] In some embodiments, the amount of calcium hydroxide used in step (1) is 1.2 to 2 times the theoretical amount.

[0017] The theoretical amount of calcium hydroxide refers to the amount of pure calcium hydroxide required for a completely reactive reaction, precisely calculated based on the molar concentration of the impurities to be removed and according to the stoichiometric ratio of the chemical reaction.

[0018] In some embodiments, the temperature for removing impurities in step (1) is 95°C to 100°C.

[0019] In some embodiments, the time for impurity removal in step (1) is 1.8h to 2.2h.

[0020] In some embodiments, step (1) of adjusting the pH of the impurity removal solution to 9-11 includes: using Na2CO3 to adjust the pH of the impurity removal solution to 9-11.

[0021] In some embodiments, the countercurrent extraction in step (2) has 6 to 8 stages.

[0022] In some embodiments, the O / A ratio of the countercurrent extraction in step (2) is 2:1 to 3:1.

[0023] In some embodiments, the temperature of the countercurrent extraction in step (2) is 25°C to 35°C.

[0024] In some embodiments, in the mixture described in step (3), the ratio of the loaded lithium organic phase to water (O / A) is 2:1 to 5:1.

[0025] In some embodiments, the amount of carbon dioxide gas used in step (3) satisfies that the volume ratio of the lithium-loaded organic phase, water and carbon dioxide gas is (2~5):1:(110~130).

[0026] In some embodiments, the absolute pressure of extraction in step (3) is 0.4 MPa to 0.6 MPa.

[0027] In some embodiments, the extraction temperature in step (3) is 25°C to 35°C.

[0028] In some embodiments, the residence time for extraction in step (3) is 15 min to 30 min.

[0029] In some embodiments, the mixing temperature in step (4) is 40°C to 60°C.

[0030] In some embodiments, the concentration method in step (4) includes vacuum evaporation with a vacuum degree ≤0.02MPa and a temperature of 60℃~70℃.

[0031] In some embodiments, the cooling crystallization temperature in step (4) is 3°C to 7°C, and the time is 1.8h to 2.2h.

[0032] In some embodiments, the drying in step (4) includes vacuum drying at a temperature of 75°C to 85°C, a vacuum degree of ≤0.01MPa, and a time of 3.5h to 4.5h.

[0033] As a preferred embodiment of the method provided by the present invention, the method includes:

[0034] (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; use Na2CO3 to adjust the pH of the impurity-removed solution to 9~11, and perform solid-liquid separation to obtain refined lithium-containing solution;

[0035] The amount of calcium hydroxide used is 1.2 to 2 times the theoretical amount;

[0036] The purification process is carried out at a temperature of 95℃~100℃ for 1.8h~2.2h.

[0037] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0038] The countercurrent extraction stage is 6 to 8 stages, the O / A ratio is 2:1 to 3:1, and the temperature is 25℃ to 35℃.

[0039] The extractant used in the countercurrent extraction includes benzoyltrifluoroacetone, trioctylphosphine oxide and sulfonated kerosene in a mass ratio of (15~25):(35~45):(35~45);

[0040] (3) The mixture of water and the lithium-loaded organic phase is extracted with carbon dioxide gas and separated to obtain an aqueous phase containing LiHCO3 and a regenerated organic phase; the aqueous phase containing LiHCO3 is subjected to oil removal and fine filtration in sequence to obtain a lithium bicarbonate solution; the regenerated organic phase is reused for countercurrent extraction in step (2);

[0041] The volume ratio of the lithium-loaded organic phase, water, and carbon dioxide gas is (2~5):1:(110~130);

[0042] The absolute pressure of the extraction is 0.4 MPa to 0.6 MPa, the temperature is 25°C to 35°C, and the residence time is 15 min to 30 min.

[0043] (4) Mix phosphoric acid and the lithium bicarbonate solution at 40℃~60℃ to make the pH of the reaction 4~5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

[0044] The concentration method includes vacuum evaporation, with a vacuum degree ≤0.02MPa and a temperature of 60℃~70℃;

[0045] The cooling crystallization temperature is 3℃~7℃, and the time is 1.8h~2.2h;

[0046] The drying process includes vacuum drying at a temperature of 75℃~85℃, a vacuum degree of ≤0.01MPa, and a time of 3.5h~4.5h.

[0047] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] This method provides a lithium dihydrogen phosphate preparation process using extraction-CO2 back-extraction. It efficiently removes various impurities through deep purification with calcium hydroxide combined with pH adjustment, followed by multi-stage countercurrent extraction for further purification. A benzoyltrifluoroacetone, trioctylphosphine oxide, and sulfonated kerosene system is used for highly selective extraction of Li. + It is also compatible with CO2 back-extraction, which is convenient to operate and has a moderate cost. Replacing traditional strong acid back-extraction with CO2 back-extraction produces no harmful waste, and the regenerated organic phase can be directly recycled, which greatly reduces the consumption of extractant and production costs. Detailed Implementation

[0050] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0051] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0052] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0053] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0054] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0055] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0056] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0057] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0058] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0059] This invention provides a method for preparing lithium dihydrogen phosphate using extraction-CO2 back-extraction, the method comprising the following steps:

[0060] (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities (remove impurities such as aluminum, silicon, and fluorine by forming insoluble precipitates) to obtain a purified solution; adjust the pH of the purified solution to 9~11 (e.g., 9, 10, or 11), and perform solid-liquid separation to remove suspended solids and Ca. 2+ Mg 2+ with Fe 3+ Impurities are removed to obtain a refined lithium-containing liquid.

[0061] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0062] The extractant used in the countercurrent extraction includes benzoyltrifluoroacetone, trioctylphosphine oxide and sulfonated kerosene in a mass ratio of (15~25):(35~45):(35~45);

[0063] (3) The mixture of water and the lithium-loaded organic phase is extracted with carbon dioxide gas and separated to obtain an aqueous phase containing LiHCO3 and a regenerated organic phase; the aqueous phase containing LiHCO3 is then subjected to oil removal and precision filtration to obtain a lithium bicarbonate solution.

[0064] (4) Mix phosphoric acid with the lithium bicarbonate solution to make the pH of the reaction 4-5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

[0065] A pretreatment scheme combining calcium hydroxide heating for impurity removal and pH adjustment can effectively remove impurities such as aluminum, silicon, and fluorine from lithium-sodium solutions, yielding a refined lithium-containing solution and preventing impurities from interfering with the extraction process at the source. Countercurrent extraction using a specific ratio of benzoyltrifluoroacetone, trioctylphosphine oxide, and sulfonated kerosene provides high selectivity for lithium ions and yields a high-purity lithium-loaded organic phase. Carbon dioxide back-extraction of the lithium-loaded organic phase avoids direct contact between strong acid and the organic phase. The back-extraction solution, after oil removal and precision filtration, yields a high-purity lithium bicarbonate solution. This solution is then reacted with phosphoric acid at pH 4-5, a mild and easily controllable reaction condition. Subsequent processing allows for the direct preparation of a qualified lithium dihydrogen phosphate product.

[0066] In some embodiments, calcium hydroxide may be provided by lime milk.

[0067] In some embodiments, the amount of calcium hydroxide used in step (1) is 1.2 to 2 times the theoretical amount, for example, it can be 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times or 2 times, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0068] The theoretical amount of calcium hydroxide refers to the amount of pure calcium hydroxide required for a completely reactive reaction, precisely calculated based on the molar concentration of the impurities to be removed and according to the stoichiometric ratio of the chemical reaction.

[0069] In some embodiments, the purification temperature in step (1) is 95°C to 100°C, for example, it can be 95°C, 96°C, 97°C, 98°C, 99°C or 100°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] In some embodiments, the time for removing impurities in step (1) is 1.8h to 2.2h, for example, it can be 1.8h, 1.9h, 2h, 2.1h or 2.2h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0071] In some embodiments, step (1) of adjusting the pH of the impurity removal solution to 9-11 includes: using Na2CO3 to adjust the pH of the impurity removal solution to 9-11, for example, it can be 9, 10 or 11, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] In some embodiments, the countercurrent extraction in step (2) has 6 to 8 stages, for example, it can be 6, 7, or 8 stages.

[0073] In some embodiments, the O / A ratio of the countercurrent extraction in step (2) is 2:1 to 3:1, for example, it can be 2:1, 2.1:1, 2.2:1, 2.4:1, 2.5:1, 2.7:1, 2.8:1 or 3:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0074] In some embodiments, the temperature of the countercurrent extraction in step (2) is 25°C to 35°C, for example, it can be 25°C, 27°C, 28°C, 30°C, 32°C, 33°C or 35°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0075] Through countercurrent extraction using the above process parameters, Li in the raffinate aqueous phase + It can be reduced to below 0.05g / L.

[0076] In some embodiments, in the mixture described in step (3), the ratio of the loaded lithium organic phase to water in the O / A ratio is 2:1 to 5:1, for example, it can be 2:1, 3:1, 4:1 or 5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0077] In some embodiments, the amount of carbon dioxide gas used in step (3) satisfies that the volume ratio of the lithium-loaded organic phase, water and carbon dioxide gas is (2~5):1:(110~130).

[0078] In some embodiments, the absolute pressure of extraction in step (3) is 0.4 MPa to 0.6 MPa, for example, it can be 0.4 MPa, 0.45 MPa, 0.5 MPa, 0.55 MPa or 0.6 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0079] In some embodiments, the extraction temperature in step (3) is 25°C to 35°C, for example, it can be 25°C, 27°C, 28°C, 30°C, 32°C, 33°C or 35°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0080] In some embodiments, the residence time for extraction in step (3) is 15 min to 30 min, for example, it can be 15 min, 16 min, 18 min, 20 min, 22 min, 24 min, 25 min, 28 min or 30 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0081] In some embodiments, the mixing temperature in step (4) is 40°C to 60°C, for example, it can be 40°C, 45°C, 50°C, 55°C or 60°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] In some embodiments, the concentration method in step (4) includes vacuum evaporation with a vacuum degree ≤0.02MPa and a temperature of 60℃~70℃.

[0083] In some embodiments, the cooling crystallization temperature in step (4) is 3°C to 7°C, and the time is 1.8h to 2.2h.

[0084] In some embodiments, the drying in step (4) includes vacuum drying at a temperature of 75°C to 85°C, a vacuum degree of ≤0.01MPa, and a time of 3.5h to 4.5h.

[0085] As a preferred embodiment of the method provided by the present invention, the method includes:

[0086] (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; use Na2CO3 to adjust the pH of the impurity-removed solution to 9~11, and perform solid-liquid separation to obtain refined lithium-containing solution;

[0087] The amount of calcium hydroxide used is 1.2 to 2 times the theoretical amount;

[0088] The purification process is carried out at a temperature of 95℃~100℃ for 1.8h~2.2h.

[0089] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0090] The countercurrent extraction stage is 6 to 8 stages, the O / A ratio is 2:1 to 3:1, and the temperature is 25℃ to 35℃.

[0091] The extractant used in the countercurrent extraction includes benzoyltrifluoroacetone, trioctylphosphine oxide and sulfonated kerosene in a mass ratio of (15~25):(35~45):(35~45);

[0092] (3) The mixture of water and the lithium-loaded organic phase is extracted with carbon dioxide gas and separated to obtain an aqueous phase containing LiHCO3 and a regenerated organic phase; the aqueous phase containing LiHCO3 is subjected to oil removal and fine filtration in sequence to obtain a lithium bicarbonate solution; the regenerated organic phase is reused for countercurrent extraction in step (2);

[0093] The volume ratio of the lithium-loaded organic phase, water, and carbon dioxide gas is (2~5):1:(110~130);

[0094] The absolute pressure of the extraction is 0.4 MPa to 0.6 MPa, the temperature is 25°C to 35°C, and the residence time is 15 min to 30 min.

[0095] (4) Mix phosphoric acid and the lithium bicarbonate solution at 40℃~60℃ to make the pH of the reaction 4~5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

[0096] The concentration method includes vacuum evaporation, with a vacuum degree ≤0.02MPa and a temperature of 60℃~70℃;

[0097] The cooling crystallization temperature is 3℃~7℃, and the time is 1.8h~2.2h;

[0098] The drying process includes vacuum drying at a temperature of 75℃~85℃, a vacuum degree of ≤0.01MPa, and a time of 3.5h~4.5h.

[0099] The main components of the lithium-sodium solution in this invention may be: Li +The content is 1g / L~3g / L, Na + The content is 10g / L~30g / L, SO4 2- It contains trace impurities of copper and nickel, with a content of 40g / L~100g / L, 50ppm~300ppm Al, 20ppm~200ppm Si, 30ppm~250ppm F, 10ppm~100ppm Fe, 50ppm~200ppm calcium and magnesium, and 1ppm~20ppm.

[0100] To clearly illustrate the technical solution of the present invention, the main components of the lithium-sodium solution in the following embodiments and comparative examples are: Li + The content is 2g / L, Na + The content is 24g / L, SO4 2- The content is 60 g / L, with 210 ppm Al, 100 ppm Si, 130 ppm F, 60 ppm Fe, 130 ppm calcium and magnesium, and 5 ppm copper and nickel trace impurities.

[0101] Example 1

[0102] This embodiment provides a method for preparing lithium dihydrogen phosphate using extraction-CO2 back-extraction, including the following steps:

[0103] (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; use Na2CO3 to adjust the pH of the impurity-removed solution to 10, and perform solid-liquid separation to obtain refined lithium-containing solution;

[0104] The amount of calcium hydroxide used is 1.5 times the theoretical amount;

[0105] The purification process is carried out at a temperature of 98°C for 2 hours.

[0106] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0107] The countercurrent extraction process consists of 7 stages, with an O / A ratio of 2.5:1 and a temperature of 30°C.

[0108] The countercurrent extraction uses an extractant comprising benzoyltrifluoroacetone, trioctylphosphine oxide, and sulfonated kerosene in a mass ratio of 20:40:40.

[0109] (3) In the pressurized gas-liquid mixing reactor, carbon dioxide gas is used to extract the mixture of water and the lithium-loaded organic phase, and the phases are separated to obtain a LiHCO3-containing aqueous phase and a regenerated organic phase; the LiHCO3-containing aqueous phase is subjected to oil removal and precision filtration through a polytetrafluoroethylene ultrafiltration membrane to obtain a lithium bicarbonate solution; the regenerated organic phase is reused for countercurrent extraction in step (2);

[0110] The volume ratio of the lithium-loaded organic phase, water, and carbon dioxide gas is 4:1:120.

[0111] The extraction was performed at an absolute pressure of 0.5 MPa, a temperature of 30°C, and a residence time of 25 min.

[0112] (4) Mix phosphoric acid (85 wt%) with the lithium bicarbonate solution at 50 °C to make the pH of the reaction 4.5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

[0113] The concentration method includes vacuum evaporation until the solution density is 1.35 g / cm³. 3 The vacuum degree is 0.02 MPa and the temperature is 65℃; the cooling crystallization temperature is 5±2℃ and the time is 2h; solid-liquid separation is performed using a centrifuge, and the filter cake is washed twice with anhydrous ethanol; the drying includes vacuum drying at 80℃, vacuum degree is 0.01 MPa, and time is 4h.

[0114] Example 2

[0115] This embodiment provides a method for preparing lithium dihydrogen phosphate using extraction-CO2 back-extraction, including the following steps:

[0116] (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; use Na2CO3 to adjust the pH of the impurity-removed solution to 9, and perform solid-liquid separation to obtain refined lithium-containing solution;

[0117] The amount of calcium hydroxide used is 1.2 times the theoretical amount;

[0118] The impurity removal temperature is 95℃, and the time is 2.2 hours;

[0119] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0120] The countercurrent extraction process consists of 6 stages, with an O / A ratio of 2:1 and a temperature of 25°C.

[0121] The countercurrent extraction uses an extractant comprising benzoyltrifluoroacetone, trioctylphosphine oxide, and sulfonated kerosene in a mass ratio of 15:35:45.

[0122] (3) In the pressurized gas-liquid mixing reactor, carbon dioxide gas is used to extract the mixture of water and the lithium-loaded organic phase, and the phases are separated to obtain a LiHCO3-containing aqueous phase and a regenerated organic phase; the LiHCO3-containing aqueous phase is subjected to oil removal and precision filtration through a polytetrafluoroethylene ultrafiltration membrane to obtain a lithium bicarbonate solution; the regenerated organic phase is reused for countercurrent extraction in step (2);

[0123] The volume ratio of the lithium-loaded organic phase, water, and carbon dioxide gas is 2:1:130.

[0124] The extraction was performed at an absolute pressure of 0.4 MPa, a temperature of 25°C, and a residence time of 30 min.

[0125] (4) Mix phosphoric acid (85 wt%) with the lithium bicarbonate solution at 40 °C to make the pH of the reaction 4. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

[0126] The concentration method includes vacuum evaporation until the solution density is 1.35 g / cm³. 3 The vacuum degree is 0.02 MPa and the temperature is 60℃; the cooling crystallization temperature is 5±2℃ and the time is 2h; solid-liquid separation is performed using a centrifuge, and the filter cake is washed twice with anhydrous ethanol; the drying includes vacuum drying at a temperature of 75℃, a vacuum degree of 0.01 MPa, and a time of 4.5h.

[0127] Example 3

[0128] This embodiment provides a method for preparing lithium dihydrogen phosphate using extraction-CO2 back-extraction, including the following steps:

[0129] (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; use Na2CO3 to adjust the pH of the impurity-removed solution to 11, and perform solid-liquid separation to obtain refined lithium-containing solution;

[0130] The amount of calcium hydroxide used is twice the theoretical amount;

[0131] The purification process is carried out at a temperature of 100°C for 1.8 hours.

[0132] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0133] The countercurrent extraction process has 8 stages, an O / A ratio of 3:1, and a temperature of 35°C.

[0134] The extractant used in the countercurrent extraction includes benzoyltrifluoroacetone, trioctylphosphine oxide and sulfonated kerosene in a mass ratio of 25:45:35.

[0135] (3) In the pressurized gas-liquid mixing reactor, carbon dioxide gas is used to extract the mixture of water and the lithium-loaded organic phase, and the phases are separated to obtain a LiHCO3-containing aqueous phase and a regenerated organic phase; the LiHCO3-containing aqueous phase is subjected to oil removal and precision filtration through a polytetrafluoroethylene ultrafiltration membrane to obtain a lithium bicarbonate solution; the regenerated organic phase is reused for countercurrent extraction in step (2);

[0136] The volume ratio of the lithium-loaded organic phase, water, and carbon dioxide gas is 5:1:110.

[0137] The extraction was performed at an absolute pressure of 0.6 MPa, a temperature of 35°C, and a residence time of 15 min.

[0138] (4) Mix phosphoric acid (85 wt%) with the lithium bicarbonate solution at 60 °C to make the pH of the reaction 5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

[0139] The concentration method includes vacuum evaporation until the solution density is 1.35 g / cm³. 3 The vacuum degree is 0.02 MPa and the temperature is 70℃; the cooling crystallization temperature is 5±2℃ and the time is 2h; solid-liquid separation is performed using a centrifuge, and the filter cake is washed twice with anhydrous ethanol; the drying includes vacuum drying at a temperature of 85℃, a vacuum degree of 0.01 MPa, and a time of 3.5h.

[0140] Example 4

[0141] This embodiment provides a method for preparing lithium dihydrogen phosphate by extraction-CO2 back-extraction. Except for the absolute pressure of extraction in step (3) being 0.2 MPa, the rest is the same as in Example 1.

[0142] Example 5

[0143] This embodiment provides a method for preparing lithium dihydrogen phosphate by extraction-CO2 back-extraction. Except for the absolute pressure of extraction in step (3) being 0.7 MPa, the rest is the same as in Example 1.

[0144] Comparative Example 1

[0145] This comparative example provides a method for preparing lithium dihydrogen phosphate, which is the same as in Example 1 except that calcium hydroxide is not added for impurity removal, and includes the following steps:

[0146] (1) The pH of the lithium sodium solution was adjusted to 10 using Na2CO3, and solid-liquid separation was performed to obtain a refined lithium-containing solution;

[0147] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0148] The countercurrent extraction process consists of 7 stages, with an O / A ratio of 2.5:1 and a temperature of 30°C.

[0149] The countercurrent extraction uses an extractant comprising benzoyltrifluoroacetone, trioctylphosphine oxide, and sulfonated kerosene in a mass ratio of 20:40:40.

[0150] (3) In the pressurized gas-liquid mixing reactor, carbon dioxide gas is used to extract the mixture of water and the lithium-loaded organic phase, and the phases are separated to obtain a LiHCO3-containing aqueous phase and a regenerated organic phase; the LiHCO3-containing aqueous phase is subjected to oil removal and precision filtration through a polytetrafluoroethylene ultrafiltration membrane to obtain a lithium bicarbonate solution; the regenerated organic phase is reused for countercurrent extraction in step (2);

[0151] The volume ratio of the lithium-loaded organic phase, water, and carbon dioxide gas is 4:1:120.

[0152] The extraction was performed at an absolute pressure of 0.5 MPa, a temperature of 30°C, and a residence time of 25 min.

[0153] (4) Mix phosphoric acid (85 wt%) with the lithium bicarbonate solution at 50 °C to make the pH of the reaction 4.5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

[0154] The concentration method includes vacuum evaporation until the solution density is 1.35 g / cm³. 3 The vacuum degree is 0.02 MPa and the temperature is 65℃; the cooling crystallization temperature is 5±2℃ and the time is 2h; solid-liquid separation is performed using a centrifuge, and the filter cake is washed twice with anhydrous ethanol; the drying includes vacuum drying at 80℃, vacuum degree is 0.01 MPa, and time is 4h.

[0155] Comparative Example 2

[0156] This comparative example provides a method for preparing lithium dihydrogen phosphate, which is the same as in Example 1 except that carbon dioxide gas back-extraction is replaced by phosphoric acid back-extraction, and includes the following steps:

[0157] (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; use Na2CO3 to adjust the pH of the impurity-removed solution to 10, and perform solid-liquid separation to obtain refined lithium-containing solution;

[0158] The amount of calcium hydroxide used is 1.5 times the theoretical amount;

[0159] The purification process is carried out at a temperature of 98°C for 2 hours.

[0160] (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase;

[0161] The countercurrent extraction process consists of 7 stages, with an O / A ratio of 2.5:1 and a temperature of 30°C.

[0162] The countercurrent extraction uses an extractant comprising benzoyltrifluoroacetone, trioctylphosphine oxide, and sulfonated kerosene in a mass ratio of 20:40:40.

[0163] (3) The mixture of lithium-loaded organic phases was subjected to three-stage extraction (O / A ratio of 3:1) using 50wt% phosphoric acid solution to separate the phases and obtain lithium dihydrogen phosphate back-extraction solution and regenerated organic phase; the regenerated organic phase was reused for countercurrent extraction in step (2);

[0164] The extraction was performed at an absolute pressure of 0.5 MPa, a temperature of 30°C, and a residence time of 25 min.

[0165] (4) The lithium dihydrogen phosphate back-extraction solution is concentrated, cooled and crystallized, separated from solid and dried to obtain lithium dihydrogen phosphate;

[0166] The concentration method includes vacuum evaporation until the solution density is 1.35 g / cm³. 3 The vacuum degree is 0.02 MPa and the temperature is 65℃; the cooling crystallization temperature is 5±2℃ and the time is 2h; solid-liquid separation is performed using a centrifuge, and the filter cake is washed twice with anhydrous ethanol; the drying includes vacuum drying at 80℃, vacuum degree is 0.01 MPa, and time is 4h.

[0167] Performance Characterization

[0168] In the methods provided in the above embodiments and comparative examples, the recovery rate of lithium and the purity of the obtained lithium dihydrogen phosphate were measured, and the results are shown in Table 1. The lithium recovery rate was calculated based on the percentage of lithium in the lithium dihydrogen phosphate relative to the lithium in the sodium lithium solution.

[0169] Table 1

[0170]

[0171] As can be seen from Examples 1 to 3 in Table 1, the method for preparing lithium dihydrogen phosphate by extraction-CO2 back-extraction provided by the present invention can stably achieve a high lithium recovery rate and high product purity. The lithium recovery rate can reach more than 90.9%, and the purity of the obtained lithium dihydrogen phosphate is stable at more than 99.89 wt%.

[0172] A comparison of Examples 4 and 5 with Examples 1 to 3 shows that when the back-extraction pressure is below 0.4 MPa, the solubility of CO2 in the aqueous phase is insufficient, resulting in incomplete lithium back-extraction. The lithium recovery rate drops significantly to 77.5%, and the product purity also drops to 99.18 wt%. When the back-extraction pressure is above 0.6 MPa, the back-extraction effect is not significantly improved, and the lithium recovery rate is only 84.9%. Instead, it increases the energy consumption of equipment operation and the pressure resistance cost of equipment, causing unnecessary waste of resources.

[0173] As can be seen from the comparison between Comparative Example 1 and Examples 1 to 3, when the high-temperature purification process of lime milk is omitted and only sodium carbonate is used to adjust the pH for purification, it is impossible to deeply remove impurities such as aluminum, silicon, and fluorine in the solution. These impurities will cause organic phase emulsification during the subsequent extraction process, resulting in increased lithium entrainment loss and a lithium recovery rate of 80.7%. At the same time, impurities will enter the product, causing the purity of lithium dihydrogen phosphate to decrease to 98.35 wt%.

[0174] A comparison of Comparative Example 2 with Examples 1-3 shows that CO2 back-extraction has significant technical advantages over traditional strong acid back-extraction. When phosphoric acid is used for back-extraction, the strong acid destroys the molecular structure of the extractant, causing the extractant's performance to decline rapidly, the lithium recovery rate drops to 82.8%, and the product purity is only 99.06 wt%. At the same time, phosphoric acid back-extraction generates a large amount of acidic wastewater containing hydrochloric acid, which is costly to treat and pollutes the environment. In contrast, the CO2 back-extraction of this invention does not generate any harmful waste, and the regenerated organic phase can be directly recycled, significantly reducing extractant consumption and production costs.

[0175] In summary, the method provided here for preparing lithium dihydrogen phosphate using extraction-CO2 back-extraction efficiently removes various impurities through deep purification with calcium hydroxide combined with pH adjustment, and further purifies the phosphate by multi-stage countercurrent extraction. A benzoyltrifluoroacetone, trioctylphosphine oxide, and sulfonated kerosene system is used for highly selective extraction of Li. + It is also compatible with CO2 back-extraction, which is convenient to operate and has a moderate cost. Replacing traditional strong acid back-extraction with CO2 back-extraction produces no harmful waste, and the regenerated organic phase can be directly recycled, which greatly reduces the consumption of extractant and production costs.

[0176] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing lithium dihydrogen phosphate using extraction-CO2 back-extraction, characterized in that, The method includes the following steps: (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; adjust the pH of the impurity-removed solution to 9~11, and perform solid-liquid separation to obtain refined lithium-containing solution; (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase; The extractant used in the countercurrent extraction includes benzoyltrifluoroacetone, trioctylphosphine oxide and sulfonated kerosene in a mass ratio of (15~25):(35~45):(35~45); (3) The mixture of water and the lithium-loaded organic phase is extracted with carbon dioxide gas and separated to obtain an aqueous phase containing LiHCO3 and a regenerated organic phase; the aqueous phase containing LiHCO3 is then subjected to oil removal and precision filtration to obtain a lithium bicarbonate solution. (4) Mix phosphoric acid with the lithium bicarbonate solution to make the pH of the reaction 4-5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate.

2. The method according to claim 1, characterized in that, The amount of calcium hydroxide used in step (1) is 1.2 to 2 times the theoretical amount.

3. The method according to claim 1 or 2, characterized in that, The temperature for impurity removal in step (1) is 95℃~100℃; And / or, the time for impurity removal in step (1) is 1.8h~2.2h.

4. The method according to any one of claims 1 to 3, characterized in that, Step (1) involves adjusting the pH of the impurity removal solution to 9-11, which includes using Na2CO3 to adjust the pH of the impurity removal solution to 9-11.

5. The method according to any one of claims 1 to 4, characterized in that, The countercurrent extraction in step (2) has 6 to 8 stages; And / or, the O / A ratio of the countercurrent extraction in step (2) is 2:1 to 3:1; And / or, the temperature of the countercurrent extraction in step (2) is 25℃~35℃.

6. The method according to any one of claims 1 to 5, characterized in that, In the mixture described in step (3), the ratio of the lithium-loaded organic phase to the water's O / A ratio is 2:1 to 5:1; And / or, the amount of carbon dioxide gas used in step (3) satisfies that the volume ratio of the lithium-loaded organic phase, water and carbon dioxide gas is (2~5):1:(110~130).

7. The method according to any one of claims 1 to 6, characterized in that, The absolute pressure of the extraction in step (3) is 0.4 MPa to 0.6 MPa; And / or, the extraction temperature in step (3) is 25°C to 35°C; And / or, the residence time for extraction in step (3) is 15 min to 30 min.

8. The method according to any one of claims 1 to 7, characterized in that, The mixing temperature in step (4) is 40℃~60℃.

9. The method according to any one of claims 1 to 8, characterized in that, The concentration method described in step (4) includes vacuum evaporation, with a vacuum degree ≤0.02MPa and a temperature of 60℃~70℃; And / or, the cooling crystallization temperature in step (4) is 3℃~7℃, and the time is 1.8h~2.2h; And / or, the drying in step (4) includes vacuum drying at a temperature of 75℃~85℃, a vacuum degree of ≤0.01MPa, and a time of 3.5h~4.5h.

10. The method according to claim 1, characterized in that, The method includes: (1) Mix calcium hydroxide and sodium lithium solution, heat to remove impurities, and obtain impurity-removed solution; use Na2CO3 to adjust the pH of the impurity-removed solution to 9~11, and perform solid-liquid separation to obtain refined lithium-containing solution; The amount of calcium hydroxide used is 1.2 to 2 times the theoretical amount; The purification process is carried out at a temperature of 95℃~100℃ for 1.8h~2.2h. (2) The refined lithium-containing liquid was countercurrently extracted to obtain a lithium-loaded organic phase and a raffinate aqueous phase; The countercurrent extraction stage is 6 to 8 stages, the O / A ratio is 2:1 to 3:1, and the temperature is 25℃ to 35℃. The extractant used in the countercurrent extraction includes benzoyltrifluoroacetone, trioctylphosphine oxide and sulfonated kerosene in a mass ratio of (15~25):(35~45):(35~45); (3) Extract the mixture of water and the lithium-loaded organic phase using carbon dioxide gas, and separate the phases to obtain an aqueous phase containing LiHCO3 and a regenerated organic phase; the aqueous phase containing LiHCO3 is subjected to oil removal and precision filtration in sequence to obtain a lithium bicarbonate solution; the regenerated organic phase is reused for countercurrent extraction in step (2); The volume ratio of the lithium-loaded organic phase, water, and carbon dioxide gas is (2~5):1:(110~130); The absolute pressure of the extraction is 0.4 MPa to 0.6 MPa, the temperature is 25°C to 35°C, and the residence time is 15 min to 30 min. (4) Mix phosphoric acid and the lithium bicarbonate solution at 40℃~60℃ to make the pH of the reaction 4~5. After the reaction is completed, concentrate, cool and crystallize, separate solid and liquid and dry to obtain lithium dihydrogen phosphate. The concentration method includes vacuum evaporation, with a vacuum degree ≤0.02MPa and a temperature of 60℃~70℃; The cooling crystallization temperature is 3℃~7℃, and the time is 1.8h~2.2h; The drying process includes vacuum drying at a temperature of 75℃~85℃, a vacuum degree of ≤0.01MPa, and a time of 3.5h~4.5h.

Images