A lithium dihydrogen phosphate production process

Abstract

This invention relates to the field of lithium iron phosphate (LFP) production technology for new energy batteries, and discloses a lithium dihydrogen phosphate (LDH) production process, including lithium solvent extraction, evaporation and concentration of lithium dihydrogen phosphate aqueous solution, and lithium dihydrogen phosphate refining. The lithium solvent extraction employs a co-extraction technology using β-diketone and neutral phosphorus extractants, and the lithium-containing wastewater can be chloride-free. The lithium content in the lithium-containing wastewater can be as low as 0.1 g / L, and the lithium concentration in the raffinate can be reduced to below 10 ppm. The lithium-loaded organic phase is back-extracted using a phosphoric acid aqueous solution to obtain an aqueous solution of lithium dihydrogen phosphate. The aqueous solution of lithium dihydrogen phosphate is then concentrated by evaporation, cooled and crystallized, and subjected to solid-liquid separation to obtain crude lithium dihydrogen phosphate. The crude lithium dihydrogen phosphate is then refined to obtain battery-grade lithium dihydrogen phosphate. This method can significantly reduce the production cost of lithium dihydrogen phosphate while reducing the generation of waste, resulting in significant economic and social benefits.

Description

[0001] This application is a divisional application of a patent application entitled "A process for producing lithium dihydrogen phosphate", the original application was filed on March 8, 2022, and the application number is 202210219083.8. Technical Field

[0002] This invention relates to the field of lithium iron phosphate production technology for new energy battery raw materials, and in particular to a lithium dihydrogen phosphate production process. Background Technology

[0003] Lithium iron phosphate (LFP) is widely used as the cathode material in batteries due to its excellent safety and low cost. Lithium dihydrogen phosphate (LiH2PO4) is a raw material for producing LFP and has promising market prospects.

[0004] Currently, the main production processes for lithium dihydrogen phosphate (LiH2PO4) are the lithium carbonate method and the lithium hydroxide monohydrate method. Both lithium carbonate and lithium hydroxide require lithium sulfate or lithium chloride as raw materials, and consume large amounts of sodium carbonate or sodium hydroxide, making the process complex. Therefore, the price of LiH2PO4 has remained high. To reduce the production cost of LiH2PO4 and simplify the production process, it is urgent to develop a new method for producing LiH2PO4. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a lithium dihydrogen phosphate production process.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A lithium dihydrogen phosphate production process includes lithium solvent extraction, concentration of lithium dihydrogen phosphate aqueous solution, and crystallization and purification of lithium dihydrogen phosphate. In the lithium solvent extraction process, lithium-containing wastewater is mixed with an organic phase containing a lithium extractant, and lithium is extracted into the organic phase to obtain a lithium-loaded organic phase. After washing and removing impurities, the lithium-loaded organic phase is back-extracted with phosphoric acid to obtain an aqueous solution of lithium dihydrogen phosphate. The lithium extractant is a mixture of β-diketone, tributyl phosphate, and trioctylphosphine oxide. The chemical structure of the extractant β-diketone is shown in formula (I).

[0008]

[0009] In formula (I), R1, R2, and R3 are F, H, or CH3, and R4 is H or a C1-C10 saturated alkyl group;

[0010] The β-diketone is a mixture obtained by combining β-diketones with different R1, R2, R3, and R4 structures;

[0011] The lithium extractant contains β-diketone to tributyl phosphate and trioctylphosphine oxide in a mass ratio of β-diketone:tributyl phosphate = 10:1 to 1:10 and β-diketone:trioctylphosphine oxide = 10:1 to 50:1. The extractant also contains C8-C12 saturated carboxylic acids, and the mass ratio of β-diketone to C8-C12 saturated carboxylic acids is 10:1 to 1:10.

[0012] The concentration of lithium extractant in the organic phase is 1-60% (V / V), the lithium concentration in the lithium-containing wastewater is 0.1-2 g / L, the extraction process includes 1-6 stages of extraction, and the extraction ratio O / A = 50:1-1:10;

[0013] The lithium dihydrogen phosphate aqueous solution is evaporated and concentrated, cooled and crystallized, and then separated into liquid and solid to obtain crude lithium dihydrogen phosphate. Phosphoric acid is added before evaporation and concentration to make the phosphoric acid concentration reach the concentration of back-extraction acid. The water recovered during the concentration and crystallization process is mixed with the crystallization mother liquor and used for lithium back-extraction.

[0014] The washing process consists of two stages, each with 1 to 3 stages. The washing solution for the first stage is 0.01 to 1 mol / L hydrochloric acid or sodium hydroxide solution with a pH of 8-10, and the washing ratio O / A = 10:1 to 1:10. The washing solution for the second stage is purified water, and the washing water is combined with the lithium-containing wastewater after washing.

[0015] The back-extraction process consists of 1 to 4 stages connected in series, using a 0.1-0.5 mol / L phosphoric acid aqueous solution to back-extract lithium, yielding a lithium dihydrogen phosphate aqueous solution; the back-extraction ratio O / A = 10:1 to 1:10;

[0016] After lithium back-extraction is completed, the organic phase is washed with acid to remove metal impurities and obtain a regenerated organic phase, which is then returned to the extraction equipment for recycling.

[0017] The refining process of lithium dihydrogen phosphate involves refining and drying the crude lithium dihydrogen phosphate to obtain the finished lithium dihydrogen phosphate product.

[0018] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0019] 1. This technical solution features a green and environmentally friendly production process that generates virtually no waste, allowing lithium extraction from chloride-free wastewater. The production process mainly includes two material recycling processes: 1) Organic phase recycling, where the extractant is regenerated in the acid washing equipment and returned to the extraction equipment for reuse; 2) Crystallization mother liquor recycling, where the crystallization mother liquor is returned to the back-extraction equipment for lithium back-extraction, resulting in almost no loss of lithium and phosphoric acid. These measures in this solution reduce the production cost of lithium dihydrogen phosphate.

[0020] 2. This technical solution can achieve the separation of lithium from most metal ions. Besides sodium, potassium, calcium, magnesium, and lead, the metal impurities in the wastewater can also include transition metal ions such as cobalt, nickel, manganese, zinc, iron, and copper. It can utilize lithium-containing wastewater with a high magnesium chloride content, or lithium-containing wastewater from lithium battery recycling processes.

[0021] 3. This technical solution can treat wastewater with very low lithium content, thereby preventing the loss of lithium resources with the discharge of wastewater.

[0022] 4. This technical solution extracts lithium from lithium-containing wastewater and produces lithium dihydrogen phosphate, which has high economic value and social benefits. Furthermore, the production process simplifies the lithium dihydrogen phosphate production flow, making it easy to industrialize. The produced lithium dihydrogen phosphate product has stable quality and meets the requirements of the Chinese nonferrous metals industry standard YS / T967-2014. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flow chart of the lithium dihydrogen phosphate production process of the present invention.

[0025] Figure 2 This is a flowchart of the solvent extraction process in Example 1.

[0026] Figure 3 This is a flowchart of the solvent extraction process in Example 2.

[0027] Figure 4 This is a flowchart of the solvent extraction process in Example 3. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0030] The terms "first," "second," "third," and "fourth," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, including a series of steps, processes, methods, etc., is not limited to the steps listed, but may optionally include steps not listed, or may optionally include other steps inherent to these processes, methods, products, or devices.

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] The reference numerals in the accompanying drawings include: 1. Lithium solvent extraction; 2. Concentration of lithium dihydrogen phosphate aqueous solution and crystallization and purification of lithium dihydrogen phosphate; 3. Extraction equipment; 4. Washing equipment; 5. Back-extraction equipment; 6. Evaporation and concentration; 7. Cooling crystallization; 8. Solid-liquid separation; 9. Purification; 10. Drying; 11. Lithium-containing wastewater; 12. Raffinate; 13. Purified water; 14. Wash water; 15. Phosphoric acid; 16. Supersaturated solution; 17. Mother liquor; 18. Crude lithium dihydrogen phosphate; 19. Organic phase; 20. Acid washing equipment; 21. Hydrochloric acid aqueous solution; 23. Phosphoric acid aqueous solution.

[0033] Overview of the plan:

[0034] like Figure 1 As shown, a lithium dihydrogen phosphate production process includes the following steps:

[0035] Step I, Lithium Solvent Extraction 1: Lithium-containing wastewater 11 is mixed with an organic phase 19 containing lithium extractant in extraction equipment 3 to extract lithium into the organic phase, obtaining a lithium-loaded organic phase. Extraction equipment 3 includes 1 to 6 stages of extraction, with an extraction ratio O / A = 50:1 to 1:10. The lithium-loaded organic phase is then passed through washing equipment 4 to remove impurities. The washing equipment is divided into two sections, each with 1 to 3 stages. The washing solution in the first stage is hydrochloric acid with a concentration of 0.01-1 mol / L, and a washing ratio O / A = 10:1 to 1:10, mainly removing metal ions such as sodium and potassium. The washing solution in the second stage is purified water 13, mainly removing anions such as sulfate and chloride ions. The washing water 14 is then combined with the lithium-containing wastewater 11. The lithium back-extraction consists of 1 to 4 stages connected in series. In back-extraction device 5, a phosphoric acid aqueous solution 23 is used for back-extraction to obtain an aqueous solution of lithium dihydrogen phosphate. The organic phase is mixed with a hydrochloric acid aqueous solution 21 in an acid washing device 20 to regenerate the organic phase, which is then recycled back to extraction device 3. The phosphoric acid concentration for lithium back-extraction is 0.1-0.5 mol / L, and the O / A ratio for back-extraction is 10:1 to 1:10. The lithium extractant is a mixture of β-diketone, tributyl phosphate (TBP), and trioctylphosphine oxide; the volume concentration of the lithium extractant in the organic phase is 1-60%. C8-C12 saturated carboxylic acids can be added during extraction to improve the extraction effect. The chemical structure of the extractant β-diketone is shown in formula (I):

[0036]

[0037] In formula (I), R1, R2, and R3 are F, H, or CH3, R4 is H or a saturated alkyl group of C1-C10, and β-diketone is a mixture of two or more β-diketones with different structures of R1, R2, R3, and R4.

[0038] When used in combination, the lithium extractant is a mixture with the following mass ratios: β-diketone:tributyl phosphate = 10:1 to 1:10, β-diketone:trioctylphosphine oxide = 10:1 to 50:1, and β-diketone:C8-C12 saturated carboxylic acid = 10:1 to 1:10.

[0039] Step II, Lithium dihydrogen phosphate concentration and crystallization: After adding phosphoric acid to the aqueous solution of lithium dihydrogen phosphate, it undergoes evaporation and concentration (6), cooling crystallization (7), and liquid-solid separation (8) to obtain crude lithium dihydrogen phosphate (18). The lithium concentration in the aqueous solution of lithium dihydrogen phosphate entering the evaporation and concentration stage is between 10 and 25 g / L. The water recovered from evaporation and concentration is mixed with the crystallization mother liquor for lithium back-extraction and reused. The temperature during the cooling crystallization stage is 45-90℃.

[0040] Step III, Lithium dihydrogen phosphate refining: Crude lithium dihydrogen phosphate 18 is refined 9 and dried 10 to obtain finished lithium dihydrogen phosphate.

[0041] Example 1

[0042] In this embodiment, the extractant composition is a mixture of β-diketone, TBP, trioctylphosphine oxide, and neodecanoic acid, with a mass ratio of β-diketone:TBP = 2:1, β-diketone:trioctylphosphine oxide = 40:1, and β-diketone:neodecanic acid = 8:1. The β-diketone is a mixture of β-diketone A and β-diketone B, with a mass ratio of A:B = 2:1. The structure of β-diketone A is: R1, R2, R3 = F, R4 = CH3. The structure of β-diketone B is: R1, R2 = F, R3 = H, R4 = C5H. 11 .

[0043] The composition of lithium-containing wastewater is as follows:

[0044] Table 1

[0045] Element Li Na K Ca Fe Pb Mn Content (g / L) 0.71 8.60 10.50 0.08 0.11 0.08 4.30

[0046] Combination Figure 2 As shown, a lithium dihydrogen phosphate production process includes the following steps:

[0047] Step I, Solvent Extraction of Lithium: Take 15 ml of extractant and dilute it to 100 ml with hydrogenated kerosene. The extractant concentration in the organic phase is 15% (v / v). The organic phase is first saponified with 2.8 ml of 30% (w / w) sodium hydroxide, and then mixed with 100 ml of lithium-containing wastewater for 3 minutes. No solids precipitate during the mixing process. The extraction ratio O / A = 1:1, the extraction temperature is 20℃, and phase separation is completed within 60 seconds. The pH of the raffinate is 6.7. The lithium concentration in the raffinate is 8.9 ppm. The lithium extraction rate is 98.7%. The lithium-loaded organic phase is first mixed with 100 ml of pH 1.5 hydrochloric acid solution for 3 minutes, and then mixed with 100 ml of purified water for 3 minutes at 20℃. Then, it is back-extracted with 0.2 mol / L phosphoric acid aqueous solution at 60℃. The back-extraction ratio O / A is adjusted to control the back-extraction equilibrium pH at 3.0-3.5. After back-extraction, the organic phase is mixed with 0.5 mol / L hydrochloric acid for 5 minutes to remove impurities such as manganese, iron, lead, and calcium from the organic phase. The lithium extraction process is as follows... Figure 2 As shown.

[0048] Step II, Concentration and Crystallization of Lithium Dihydrogen Phosphate Aqueous Solution: When the lithium concentration in the back-extraction solution reaches 22 g / L, phosphoric acid is added to bring the concentration to 0.2 mol / L, followed by evaporation and concentration, and then hot filtration at 60-70℃. The filter cake is crude lithium dihydrogen phosphate. The filtrate and distilled water obtained during the concentration process are mixed for the next lithium back-extraction.

[0049] Step III, Refining of primary lithium dihydrogen phosphate: The filter cake is washed with anhydrous ethanol and dried at 105°C for 4 hours to obtain battery-grade lithium dihydrogen phosphate.

[0050] Lithium dihydrogen phosphate metal impurities were determined by atomic absorption spectrometry, sulfate and chloride ions by ion chromatography, moisture by thermogravimetric analysis, and water-insoluble matter by precision filtration. The analytical results are as follows:

[0051] Table 2

[0052]

[0053] The quality of lithium dihydrogen phosphate meets the requirements of the Chinese nonferrous metals industry standard YS / T967-2014.

[0054] The analysis results of other components in the raffinate, excluding lithium, are as follows:

[0055] Table 3

[0056] Element Na K Ca Fe Pb Mn Content (g / L) 8.10 9.95 <0.2ppm <0.1ppm 0.1ppm 1.2ppm Extraction rate (%) 0.82 0.29 >99.75 >99.91 >99.88 99.97

[0057] Example 2

[0058] In this embodiment, the extractant composition is a mixture of β-diketone, TBP, trioctylphosphine oxide, and neodecanoic acid, with a mass ratio of β-diketone:TBP = 2:1, β-diketone:trioctylphosphine oxide = 40:1, and β-diketone:neodecanic acid = 8:1. The β-diketone is a mixture of β-diketone A and β-diketone B, with a mass ratio of A:B = 2:1. The structure of β-diketone A is: R1, R2, R3 = F, R4 = CH3. The structure of β-diketone B is: R1, R2, R3 = F, R4 = H.

[0059] The composition of lithium-containing wastewater is as follows:

[0060] Table 4

[0061] Element Li Na K Ca Fe Pb Mn Content (g / L) 0.13 12.50 17.60 0.05 0.07 0.08 9.30

[0062] Combination Figure 3 As shown, a lithium dihydrogen phosphate production process includes the following steps:

[0063] Step I, Solvent Extraction of Lithium: Take 25 ml of extractant and dilute it to 100 ml with hydrogenated kerosene. The extractant concentration in the organic phase is 25% (v / v). The organic phase is first saponified with 4.6 ml of 30% (w / w) sodium hydroxide, and then mixed with 100 ml of lithium-containing wastewater for 3 minutes. No solids precipitate during the mixing process. The extraction ratio O / A = 1:1, the extraction temperature is 20℃, and phase separation is completed within 60 seconds. The pH of the raffinate is 6.7. Raffinate 1 has a lithium concentration of 11 ppm and a lithium extraction rate of 91.5%. Raffinate 2 has a lithium concentration of 6.6 ppm and a lithium extraction rate of 94.8%. The lithium-loaded organic phase is first mixed with 100 ml of 0.06 mol / L hydrochloric acid for 3 minutes, and then mixed with 100 ml of purified water for 3 minutes at 20℃. Then, it is back-extracted with 0.1 mol / L phosphoric acid at 50℃. The back-extraction ratio O / A is adjusted to control the back-extraction equilibrium pH at 3.0-3.5. After back-extraction, the organic phase is mixed with 0.8 mol / L hydrochloric acid for 5 minutes to wash away impurities such as calcium, lead, iron, and manganese. The lithium extraction process is as follows... Figure 3 As shown.

[0064] Step II, Concentration and Crystallization of Lithium Dihydrogen Phosphate Aqueous Solution: When the lithium concentration in the back-extraction solution reaches 22 g / L, phosphoric acid is added to bring the concentration to 0.1 mol / L, followed by evaporation and concentration, and then hot filtration at 60-70℃. The filter cake is crude lithium dihydrogen phosphate. The filtrate and distilled water obtained during the concentration process are mixed and used for the next lithium back-extraction.

[0065] Step III, purification of primary lithium dihydrogen phosphate: The filter cake is washed with anhydrous ethanol and dried at 105°C for 4 hours. Battery-grade lithium dihydrogen phosphate is obtained.

[0066] Lithium dihydrogen phosphate metal impurities were determined by atomic absorption spectrometry, sulfate and chloride ions by ion chromatography, moisture by thermogravimetric analysis, and water-insoluble matter by precision filtration. The analytical results are as follows:

[0067] Table 5

[0068]

[0069] The quality of lithium dihydrogen phosphate meets the requirements of the Chinese nonferrous metals industry standard YS / T967-2014.

[0070] The analysis results of other components in the raffinate, excluding lithium, are as follows:

[0071] Table 6

[0072] Element Na K Ca Fe Pb Mn Content of raffinate 1 (g / L) 12.44 17.57 <0.2ppm <0.1ppm <0.1ppm 0.9ppm E1 extraction rate (%) 0.48 0.17 >99.60 >99.86 >99.88 99.99 Content of raffinate 2 (g / L) 12.14 17.19 <0.2ppm <0.1ppm <0.1ppm 1.9ppm E2 extraction rate (%) 1.20 0.68 >99.6o >99.86 >99.88 99.98

[0073] Example 3

[0074] The lithium extractant in this embodiment is a mixture of β-diketone, TBP, trioctylphosphine oxide, and neodecanoic acid, with a mass ratio of β-diketone:TBP = 2:1, β-diketone:trioctylphosphine oxide = 40:1, and β-diketone:neodecanic acid = 8:1. The β-diketone is a mixture of β-diketone A and β-diketone B, with a mass ratio of A:B = 1:3. The structure of β-diketone A is: R1, R2, R3 = F, R4 = CH3. The structure of β-diketone B is: R1, R2, R3 = CH3, R4 = C5H11.

[0075] The composition of lithium-containing wastewater is as follows:

[0076] Table 7

[0077] Element Li Na K Ca Fe Pb Mg c1 Content (g / L) 1.52 8.60 10.50 18.8 0.11 3.82 73.3 28o

[0078] Combination Figure 4 As shown, a lithium dihydrogen phosphate production process includes the following steps:

[0079] Step I, Solvent Extraction of Lithium: Take 50.0 ml of extractant and dilute it to 100 ml with hydrogenated kerosene. The extractant concentration in the organic phase is 50% (v / v). The organic phase is first mixed with a ferric chloride hydrochloric acid solution (containing 20 g / L Fe, 6 mol / L NaCl, and 2 mol / L HCl) for 3 minutes, and then mixed with 100 ml of lithium-containing wastewater for 3 minutes. The extraction ratio O / A = 1:1, the extraction temperature is 30℃, the pH of the raffinate is 1.2, and the lithium concentration in the raffinate is 128 ppm. The lithium extraction rate is 91.6%. The lithium-loaded organic phase is first mixed with 100 ml of pH 9 sodium hydroxide solution for 3 minutes, and then mixed with 100 ml of purified water for 3 minutes at 30℃. No solids precipitate during the mixing process, and phase separation is completed within 60 seconds. Then, back-extract with 0.3 mol / L phosphoric acid at 50℃, adjusting the back-extraction ratio O / A to control the back-extraction equilibrium pH at 3.0-3.5. After back-extraction, the organic phase is mixed with a sodium chloride hydrochloric acid solution (3 mol / L hydrochloric acid, 5 mol / L sodium chloride) for 5 min. The organic phase is reused. The lithium extraction process is as follows: Figure 4 As shown.

[0080] Step II, Concentration and Crystallization of Lithium Dihydrogen Phosphate Aqueous Solution: When the lithium concentration in the back-extraction solution reaches 22 g / L, phosphoric acid is added to bring the concentration to 0.3 mol / L, followed by evaporation and concentration, and then hot filtration at 60-70℃. The filter cake is crude lithium dihydrogen phosphate. The filtrate and distilled water obtained during the concentration process are mixed and used for the next lithium back-extraction.

[0081] Step III, purification of primary lithium dihydrogen phosphate: The filter cake is washed with anhydrous ethanol and dried at 105°C for 4 hours. Battery-grade lithium dihydrogen phosphate is obtained.

[0082] Lithium dihydrogen phosphate metal impurities were determined by atomic absorption spectrometry, sulfate and chloride ions by ion chromatography, moisture by thermogravimetric analysis, and water-insoluble matter by precision filtration. The analytical results are as follows:

[0083] Table 8

[0084]

[0085] The quality of lithium dihydrogen phosphate meets the requirements of the Chinese nonferrous metals industry standard YS / T967-2014.

[0086] The analysis results of other components in the raffinate, excluding lithium, are as follows:

[0087] Table 9

[0088] Element Na K Ca Fe Pb Mg Content (g / L) 8.08 9.93 17.76 0.01 3.60 69.2 Extraction rate (%) 1.16 0.48 0.56 90.43 0.78 0.62

[0089] Comparative Example 1

[0090] In this embodiment, the extractant composition is a mixture of β-diketone, TBP, and trioctylphosphine oxide, with a mass ratio of β-diketone:TBP = 2:1 and β-diketone:trioctylphosphine oxide = 70:1. The β-diketone is a single-structure β-diketone. R1, R2, R3 = F, R4 = H.

[0091] The composition of lithium-containing wastewater is as follows:

[0092] Table 10

[0093] Element Li Na K Ca Fe Pb Mn Content (g / L) 0.13 12.50 17.60 0.05 0.07 0.08 9.30

[0094] A process for producing lithium dihydrogen phosphate includes the following steps:

[0095] Step I, Lithium solvent extraction: Take 25 ml of extractant and dilute it to 100 ml with hydrogenated kerosene. The extractant concentration in the organic phase is 25% (v / v). The organic phase is first saponified with 4.6 ml of 30% (w / w) sodium hydroxide, and then mixed with 100 ml of lithium-containing wastewater for 3 minutes. During the mixing process of E1, solid precipitation occurs, affecting phase separation. The extraction ratio O / A = 1:1, the extraction temperature is 20℃, and phase separation is completed within 60 seconds. The pH of the raffinate is 6.7. The lithium concentration in raffinate 1 is 53 ppm, and the lithium extraction rate is 59.2%. The lithium concentration in raffinate 2 is 15 ppm, and the lithium extraction rate is 88.5%. The lithium-loaded organic phase is first mixed with 100 ml of 0.06 mol / L hydrochloric acid for 3 minutes, and then mixed with 100 ml of purified water for 3 minutes at 20℃. Then, it is back-extracted with 0.5 mol / L phosphoric acid at 50℃. The back-extraction ratio O / A is adjusted, and the back-extraction equilibrium pH is controlled between 0.5 and 1.0. After back-extraction, the organic phase is mixed with 0.8 mol / L hydrochloric acid for 5 minutes to wash away impurities such as calcium, lead, iron, and manganese. The lithium extraction process is as follows... Figure 3 As shown.

[0096] Step II, Concentration and Crystallization of Lithium Dihydrogen Phosphate Aqueous Solution: When the lithium concentration in the back-extraction solution reaches 22 g / L, it is evaporated and concentrated, then filtered while hot at 60-70℃. The filter cake is crude lithium dihydrogen phosphate. The filtrate and distilled water obtained from the concentration process are mixed and used for the next lithium back-extraction.

[0097] Step III, purification of primary lithium dihydrogen phosphate: The filter cake is washed with anhydrous ethanol and dried at 105°C for 4 hours. Battery-grade lithium dihydrogen phosphate is obtained.

[0098] Lithium dihydrogen phosphate metal impurities were determined by atomic absorption spectrometry, sulfate and chloride ions by ion chromatography, moisture by thermogravimetric analysis, and water-insoluble matter by precision filtration. The analytical results are as follows:

[0099] Table 11

[0100] Element <![CDATA[LiH2PO4]]> Na K Ca Fe Pb <![CDATA[SO4 2- ]]> <![CDATA[Cl - ]]> <![CDATA[H2O]]> Water-insoluble matter content(%) 96.35 0.008 0.001 0.012 0.015 0.184 0.008 0.005 0.937 0.005

[0101] In addition, the 2.47% water content is not listed in the table, therefore the quality of lithium dihydrogen phosphate does not meet the requirements of the Chinese nonferrous metals industry standard YS / T967-2014.

[0102] Comparative Example 2

[0103] The lithium extractant in this embodiment is a mixture of β-diketone, TBP, and trioctylphosphine oxide, with a mass ratio of β-diketone:TBP = 2:1 and β-diketone:trioctylphosphine oxide = 70:1. The β-diketone is a single-structure β-diketone. R1, R2, R3 = F, R4 = CH3.

[0104] The composition of lithium-containing wastewater is as follows:

[0105] Table 12

[0106] Element Li Na K Ca Fe Pb Mg cl Content (g / L) 1.52 8.60 10.50 18.8 0.11 3.82 73.3 280

[0107] A process for producing lithium dihydrogen phosphate includes the following steps:

[0108] Solvent extraction of lithium: 50.0 ml of extractant was diluted to 100 ml with hydrogenated kerosene, resulting in an extractant concentration of 50% (v / v) in the organic phase. The organic phase was first mixed with a ferric chloride hydrochloric acid solution (containing 20 g / L Fe, 6 mol / L NaCl, and 2 mol / L HCl) for 3 minutes, then mixed with 100 ml of lithium-containing wastewater for 3 minutes. The extraction ratio was O / A = 1:1, the extraction temperature was 30℃, the raffinate pH was 1.2, and the lithium concentration in the raffinate was 128 ppm. The lithium extraction rate was 91.6%. The lithium-loaded organic phase was first mixed with 100 ml of pH 9 sodium hydroxide solution for 3 minutes, then with 100 ml of purified water for 3 minutes at 30℃. During this mixing process, a red solid precipitated, indicating significant losses of iron and extractant; therefore, the experiment was abandoned.

[0109] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0110] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A process for the production of lithium dihydrogen phosphate, characterized in that: The lithium solvent extraction process comprises mixing lithium-containing wastewater with an organic phase containing a lithium extractant, extracting lithium into the organic phase, and obtaining a lithium-loaded organic phase; The lithium-loaded organic phase is washed to remove impurities, back-extracted with phosphoric acid to obtain an aqueous lithium dihydrogen phosphate solution; the lithium extractant is a mixture of a β-diketone, tributyl phosphate and trioctylphosphine oxide; the chemical structure of the β-diketone is shown in formula (I): In formula (I), R1, R2 and R3 are F, H or CH3, and R4 is H or a saturated alkyl group with 1-10 carbon atoms; The β-diketone is a mixture obtained by combining β-diketones with different R1, R2, R3 and R4 structures; The mass ratio of the β-diketone to tributyl phosphate and trioctylphosphine oxide in the lithium extractant is β-diketone: tributyl phosphate = 10:1-1:10 and β-diketone: trioctylphosphine oxide = 10:1-50:1; the extractant further comprises a C8-C12 saturated carboxylic acid, and the mass ratio of the β-diketone to the C8-C12 saturated carboxylic acid is 10:1-1:10; The concentration of the lithium extractant in the organic phase is 1-60% (V / V), the lithium concentration in the lithium-containing wastewater is 0.1-2 g / L, the extraction process comprises 1-6 stages of extraction, and the phase ratio O / A = 50:1-1:10; The aqueous lithium dihydrogen phosphate solution is concentrated by evaporation, crystallized by cooling, and separated into a solid and a liquid, to obtain crude lithium dihydrogen phosphate; before evaporation and concentration, phosphoric acid is added to reach the back-extraction acid concentration; the recovered water in the concentration and crystallization process is mixed with the crystallization mother liquor and used for lithium back-extraction; The washing process comprises two stages of washing, each stage comprising 1-3 stages; the washing liquid in the first stage is 0.01-1 mol / L hydrochloric acid or a sodium hydroxide solution with a pH of 8-10, and the phase ratio O / A = 10:1-1:10; the washing liquid in the second stage is purified water, and the washing water is combined with the lithium-containing wastewater after washing; The back-extraction process comprises 1-4 stages connected in series, and 0.1-0.5 mol / L phosphoric acid is used to back-extract lithium to obtain an aqueous lithium dihydrogen phosphate solution; the phase ratio O / A = 10:1-1:10; After the back-extraction of lithium is completed, the organic phase is washed with acid to remove metal impurities in the organic phase to obtain a regenerated organic phase, which is recycled to the extraction equipment; The purification process of lithium dihydrogen phosphate comprises purifying and drying crude lithium dihydrogen phosphate to obtain finished lithium dihydrogen phosphate.

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