A method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite.

Abstract

This invention discloses a method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite. Specifically, the method involves first calcining and leaching lepidolite sulfate to obtain a lithium sulfate-containing solution; then, extracting and washing the lithium sulfate-containing solution using a lithium extractant to obtain a lithium-loaded oil phase and an aqueous raffinate; back-extracting the lithium-loaded oil phase using ammonium dihydrogen phosphate and / or ammonium monohydrogen phosphate to separate an empty oil phase liquid, mother liquor, and crude lithium phosphate; adding pure water to the crude lithium phosphate and adjusting the pH using lithium hydroxide; and finally, filtering, washing, and drying to obtain rod-shaped high-purity lithium phosphate. This method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite not only effectively improves the lithium recovery rate but also effectively reduces the content of impurities such as potassium, sodium, and sulfate, thereby increasing the purity of the prepared lithium phosphate. Furthermore, this preparation method can obtain regular rod-shaped lithium phosphate, effectively solving the technical problem of irregular agglomeration morphology of lithium phosphate crystals prepared by existing processes. The process is simple and low-cost.

Description

Technical Field

[0001] This invention belongs to the technical field of lithium extraction from lepidolite to prepare lithium phosphate, and particularly relates to a method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite. Background Technology

[0002] Lithium mica contains various elements, and the current mainstream sulfate roasting process introduces impurities such as sodium, potassium, calcium, and sulfate ions. Therefore, multi-stage extraction and impurity removal are necessary to synthesize battery-grade lithium phosphate. The conventional approach involves extracting lithium from lepidolite, generating intermediate battery-grade lithium carbonate, and finally adding phosphoric acid and heating to produce qualified lithium phosphate. This method is relatively complex and requires multiple stages of evaporation during lithium extraction and phosphate preparation, resulting in high energy consumption and low production equipment continuity.

[0003] Meanwhile, using the above methods, it is difficult to control the morphology of lithium phosphate during the preparation process. Therefore, the prepared lithium phosphate crystals exhibit irregular agglomeration, which negatively impacts the electrochemical performance of subsequent lithium iron phosphate preparations. To improve the performance of irregularly agglomerated lithium phosphate, existing technologies typically employ ball milling dispersion, surface coating, or doping modification, but these methods do not inherently produce rod-shaped lithium phosphate. Therefore, if a rod-shaped structure is desired from irregularly agglomerated lithium phosphate, the only viable method is recrystallization to achieve directional control of the rod-shaped structure.

[0004] Therefore, a recycling process for preparing lithium phosphate based on lepidolite is being developed. This recycling process not only achieves excellent lithium back-extraction effect and high purity of lithium phosphate, but also improves the crystal structure of lithium phosphate to obtain lithium phosphate products with regular structure, thereby significantly improving the compaction density index of lithium iron phosphate and increasing its energy density. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing lithium phosphate based on lithium extraction from lepidolite, so as to achieve controllable crystal morphology of lithium phosphate and obtain lithium phosphate product with regular structure, based on the excellent back-extraction effect of lithium and high purity of lithium phosphate.

[0006] Technical solution: This invention relates to a method for preparing rod-shaped high-purity lithium phosphate by lithium extraction from lepidolite, comprising the following steps:

[0007] (1) Lithium mica sulfate was roasted and leached to obtain a solution containing lithium sulfate;

[0008] (2) The lithium sulfate-containing solution was extracted and washed using a lithium extractant to obtain a lithium-loaded oil phase and an aqueous raffinate.

[0009] (3) The lithium-loaded oil phase was back-extracted using ammonium phosphate to separate the empty oil phase liquid, mother liquor and crude lithium phosphate;

[0010] (4) Return the mother liquor to step (3) for recycling and back-extraction; add pure water to the crude lithium phosphate and adjust the pH to 10.5-11.5 with lithium hydroxide, and obtain rod-shaped high-purity lithium phosphate by filtration, washing and drying.

[0011] Furthermore, in step (3) of the preparation method, the ammonium phosphate used is ammonium dihydrogen phosphate and / or ammonium monohydrogen phosphate, and the concentration of the ammonium phosphate is 1-2 mol / L.

[0012] Furthermore, in step (1) of this preparation method, the calcination and leaching of lepidolite sulfate includes the following steps:

[0013] 1.1) Mix lepidolite, sulfate and calcium carbonate at a mass ratio of 100:40:(8-20), calcine at 700-950℃ for 1-3 hours, then leach with water at a solid-liquid ratio of (1-1.5):1 for 0.5-1 hours and separate to obtain leachate;

[0014] 1.2) Lime slurry is added to the leachate to adjust the pH to 11-12, and the purified solution is obtained. After further purification by carbonate and adsorption resin, a lithium sulfate-containing solution is obtained.

[0015] Preferably, the sulfate is selected from one or more of calcium sulfate, sodium sulfate, and potassium sulfate; the carbonate is selected from potassium carbonate or sodium carbonate.

[0016] Furthermore, in step (2) of this preparation method, the lithium sulfate-containing solution is extracted and washed using a lithium extractant, including the following steps:

[0017] 2.1) Add liquid alkali to the lithium sulfate solution to adjust the hydroxide concentration in the solution to 0.82-1 mol / L, and obtain the lithium sulfate solution after alkali adjustment;

[0018] 2.2) The lithium sulfate solution after alkali adjustment was subjected to multi-stage countercurrent extraction using lithium extractant to obtain an oil phase containing impurities loaded with lithium and an aqueous raffinate.

[0019] 2.3) The oil phase containing impurities loaded with lithium is subjected to multi-stage countercurrent washing with dilute sulfuric acid solution to remove potassium and sodium ions, resulting in a primary impurity-removed oil phase and washing solution. The washing solution is returned to step 2.2) for recycling extraction.

[0020] 2.4) The primary impurity-removed oil phase is washed in multiple countercurrent stages with pure water to remove sulfate ions and residual potassium and sodium ions, and the lithium-loaded oil phase and washing water are separated. The washing water is returned to step 2.3) to prepare dilute sulfuric acid.

[0021] Furthermore, in the process of extracting and removing impurities from a lithium sulfate-containing solution using a lithium extractant, the lithium extractant comprises a main extractant (10-40% by mass), a co-extractant (1-30% by mass), and the remainder being a diluent, with the diluent comprising more than 50% by mass of the lithium extractant; wherein:

[0022] The main extractant is selected from at least one of 1-phenyl-1,3-decanedione, 1-(3,5-bis(trifluoromethylphenyl)-1,3-butanedione, 1-heptyl-3-phenyl-1,3-propanedione, dodecylphenyl-methyl-β-dione, dioctyl phthalate, and butyl salicylate.

[0023] The co-extractant is selected from at least one of trioctylphosphine oxide, tributyl phosphate, di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphate mono-2-ethylhexyl ester, di(2,4,4-trimethylpentyl) phosphate, and di(n-octyl) phosphate.

[0024] The diluent is selected from 260# solvent oil and / or sulfonated kerosene.

[0025] Furthermore, the O / A ratio for extracting lithium sulfate-containing solutions using lithium extractant is (2-3):1, the O / A ratio for washing with dilute sulfuric acid solution is (8-15):1, and the O / A ratio for washing with pure water is (10-20):1. The O / A ratio for back-extracting lithium-loaded oil phases using ammonium phosphate is (1-15):1.

[0026] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are that the method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite can effectively reduce the content of impurities such as potassium, sodium, and sulfate, and improve the purity of the prepared lithium phosphate; and based on the excellent lithium back-extraction rate, the preparation method can obtain regular rod-shaped lithium phosphate, effectively solving the technical problem that the lithium phosphate crystals prepared by the existing process exhibit irregular agglomeration morphology. The process is simple and low-cost. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope (SEM) image of the lithium phosphate prepared in Example 1 of the present invention (magnification 10000x).

[0028] Figure 2 This is a scanning electron microscope (SEM) image of the lithium phosphate prepared in Example 1 of the present invention (magnification 40,000x).

[0029] Figure 3 This is a scanning electron microscope (SEM) image of the lithium phosphate prepared in Comparative Example 1 of the present invention (magnification 10000x).

[0030] Figure 4This is a scanning electron microscope (SEM) image of the lithium phosphate prepared in Comparative Example 1 of the present invention (magnification 40,000x).

[0031] Figure 5 Electron micrograph of lithium phosphate prepared in Example 2 of this invention (magnification 10000x).

[0032] Figure 6 The image shows the electron microscope (SEM) morphology of the lithium phosphate prepared in Example 2 of this invention (magnification 50,000). Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] It should be noted that the raw materials used in the extraction and back-extraction processes of this invention can be directly purchased from commercially available sources. The lithium extractant used in the examples and comparative examples consists of 30% by mass of the main extractant dodecylphenyl-methyl-β-dione, 10% by mass of the co-extractant tributyl phosphate, and 60% by mass of the diluent 260# solvent oil. Information on other main raw materials used is shown in Table 1. The composition of the lepidolite used in the examples and comparative examples is shown in Table 2.

[0035] Table 1 Raw Material Information Table

[0036]

[0037] Table 2 Main Components of Lithium Mica

[0038]

[0039] Example 1

[0040] This Example 1 describes a method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite, comprising the following steps:

[0041] (1) Lithium sulfate is roasted and leached to obtain a lithium sulfate solution. The specific steps are as follows:

[0042] 1.1) Lithium mica, sodium sulfate and calcium carbonate were mixed evenly at a mass ratio of 100:40:8, calcined at 900℃ for 1 hour, and then leached with water at a liquid-solid ratio of 1.2:1 for 30 minutes before separation to obtain the leachate.

[0043] 1.2) Add lime slurry to the leachate to adjust the pH to about 11.8, filter to obtain the purified liquid; add sodium carbonate to the purified liquid to remove calcium, filter to obtain the purified liquid; wherein, the amount of sodium carbonate added is 1.1 times the theoretical amount of calcium carbonate produced.

[0044] 1.3) After calcium removal and purification, the liquid is passed through an adsorption resin for deep removal of calcium and magnesium ions to obtain a lithium sulfate solution. The main components of the lithium sulfate solution are shown in Table 3. It can be seen that the potassium and sodium content in the lithium sulfate solution is relatively high, while the lithium content is relatively low.

[0045] (2) The lithium sulfate-containing solution was extracted and washed using a lithium extractant to obtain a lithium-loaded, purified oil phase. The specific steps are as follows:

[0046] 2.1) Add sodium hydroxide solution to the lithium sulfate solution to adjust the hydroxide ion concentration in the solution to about 0.91 mol / L, and obtain the adjusted lithium sulfate solution.

[0047] 2.2) The lithium sulfate solution after alkali adjustment was subjected to three-stage countercurrent extraction using lithium extractant, with an O / A ratio of 2.4:1, to obtain an oil phase containing impurities loaded with lithium and an aqueous raffinate.

[0048] 2.3) The oil phase containing impurities loaded with lithium was washed once with dilute sulfuric acid solution. Potassium and sodium ions were removed by a five-stage countercurrent washing method with an O / A ratio of 10:1. The resulting oil phase and washing solution were then removed once. The washing solution was returned to step 2.2) for cyclic extraction.

[0049] 2.4) The impurity-removed oil phase solution is washed twice with pure water. The sulfate ions and residual potassium and sodium ions in the first impurity-removed oil phase are removed by a two-stage countercurrent washing method. The washing O / A ratio is 15:1. The lithium-loaded oil phase and washing water are separated. The washing water is returned to step 2.3) to prepare dilute sulfuric acid.

[0050] (3) The lithium-loaded oil phase was back-extracted with ammonium dihydrogen phosphate to obtain crude lithium phosphate. The back-extraction O / A ratio was 10:1. The back-extraction process was carried out in a three-phase separation device to obtain an empty oil phase liquid, mother liquor and crude lithium phosphate.

[0051] (4) Add an appropriate amount of phosphoric acid to the mother liquor to obtain ammonium dihydrogen phosphate, and then return to step (3) for cyclic back-extraction.

[0052] (5) Add pure water to the crude lithium phosphate and adjust the pH to about 11 with lithium hydroxide. After filtration, washing with pure water, and drying, high-purity rod-shaped lithium phosphate is obtained. The morphology of the obtained lithium phosphate is as follows: Figure 1 and 2 As shown.

[0053] Table 3 Main components of lithium sulfate solution

[0054]

[0055] Comparative Example 1

[0056] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that in step (3), 1 mol / L phosphoric acid is used for back-extraction, and the O / A ratio is 10:1. The morphology of the obtained lithium phosphate is as follows. Figure 3 and 4 As shown.

[0057] Comparative Example 2

[0058] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that step 2.3 is omitted and only pure water is used for two-stage countercurrent washing in step 2.4).

[0059] Comparative Example 3

[0060] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that step 2.4 is omitted and only the dilute sulfuric acid in step 2.3) is used for five-stage countercurrent washing.

[0061] Example 2

[0062] The method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite in Example 2 is basically the same as that in Example 1, except that the ammonium phosphate salt used for back-extraction in step (3) is 2 mol / L ammonium hydrogen phosphate. The morphology of the obtained lithium phosphate is as follows. Figure 5 and 6 As shown.

[0063] Performance Test 1: Purity and Morphology of Finished Lithium Phosphate

[0064] The lithium phosphate content of the products prepared in Example 1 and Comparative Examples 1-3 is shown in Table 4. The main content and impurities of lithium phosphate meet the requirements of Li3PO4-1 in industry standard YS / T 637-2022. The morphologies of the lithium phosphate products prepared in Example 1 and Comparative Example 1 are shown in Table 4. Figure 1 and Figure 2 , Figure 3 and Figure 4 As shown; the morphologies of the lithium phosphate products prepared in the examples are as follows. Figure 5 and Figure 6 As shown.

[0065] Table 4 Test Results of Lithium Phosphate Products

[0066]

[0067] As shown in Table 4, the lithium phosphate product prepared in Example 1 of this invention has a purity greater than 99.9%, meeting the requirements of Li3PO4-1 in industry standard YS / T 637-2022. Combining Example 1 with Comparative Examples 2 and 3, it can be seen that adding a five-stage countercurrent washing process with dilute sulfuric acid can significantly reduce the potassium and sodium content in the solution; followed by a two-stage countercurrent washing process with pure water removes residual sulfate ions. However, the data from Comparative Examples 2 and 3 show that the lithium phosphate prepared using only a single washing method cannot meet the requirements of Li3PO4-1 in YS / T 637-2022.

[0068] Furthermore, based on the morphological electron micrographs of Examples 1, 2, and Comparative Example 1, it can be seen that the preparation process of the present invention can yield a lithium phosphate product with a regular rod-shaped structure. In contrast, Comparative Example 1 directly used phosphoric acid for back-extraction, and although its purity was similar to that of the examples, it only yielded a lithium phosphate product with an irregular aggregate structure. Combining the effectiveness of this technology, further mechanistic analysis reveals that the present invention uses ammonium dihydrogen phosphate and / or ammonium monohydrogen phosphate for back-extraction. During the back-extraction process, the hydrogen ions of ammonium dihydrogen phosphate and / or ammonium monohydrogen phosphate can combine with lithium, forming a slow back-extraction. The ammonium ions also have a complexing effect, which can reduce the crystallization rate of lithium phosphate. The lithium phosphate solid formed during the extraction process acts as a crystal nucleus guide, ultimately resulting in a lithium phosphate product with a regular rod-shaped structure. In contrast, in Comparative Example 1, only phosphoric acid was used for back-extraction, and the lithium phosphate crystallization process was not orderly guided and constrained, resulting in irregular aggregates of lithium phosphate.

[0069] Performance Test 2: Extraction Efficacy

[0070] After back-extraction of the oil phases of Examples 1 to 2 and Comparative Examples 1 to 3, the residual lithium content in the empty oil phase liquid was determined, as shown in Table 5.

[0071] Table 5 Residual lithium content in the empty oil phase after back-extraction

[0072]

[0073] Combining the data in Table 5 and Table 3, it can be seen that Comparative Example 1, using phosphoric acid back-extraction, achieved a better back-extraction effect. However, Examples 1, 2, and 3, using ammonium dihydrogen phosphate back-extraction, showed residual lithium in the extractant around 0.05 g / L, with equally excellent back-extraction effects. Example 2, using ammonium monohydrogen phosphate solution for back-extraction, had a relatively high residual lithium, but it was still within a reasonable extraction residue range. This demonstrates that during back-extraction, both ammonium dihydrogen phosphate and / or ammonium monohydrogen phosphate of this invention can achieve excellent back-extraction and obtain rod-shaped high-purity lithium phosphate. Ammonium dihydrogen phosphate is preferred.

[0074] In addition to the above embodiments, it should be noted that the technical effects claimed by this invention can be achieved by using the preparation process and the defined parameter range of this invention, and therefore, no further examples will be provided. For instance, in the extraction of lithium, the main extractant may be at least one of 1-phenyl-1,3-decanedione, 1-(3,5-bis(trifluoromethylphenyl)-1,3-butanedione, 1-heptyl-3-phenyl-1,3-propanedione, dodecylphenyl-methyl-β-dione, dioctyl phthalate, and butyl salicylate; the co-extractant may be at least one of trioctylphosphine oxide, tributyl phosphate, di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphate mono-2-ethylhexyl ester, di(2,4,4-trimethylpentyl) phosphate, and di(n-octyl) phosphate; and the diluent may be at least one of 260# solvent oil and sulfonated kerosene. The mass ratio of the three components must satisfy the following: main extractant 10-40%, co-extractant 1-30%, and balance diluent, with the diluent accounting for more than 50% of the lithium extractant by mass. The O / A ratio for the lithium extractant to extract lithium sulfate solution can be (2-3):1.

[0075] During back-extraction, the back-extraction O / A ratio for back-extracting the lithium-loaded oil phase with ammonium phosphate can be (1-15):1.

Claims

1. A method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite, characterized in that, Includes the following steps: (1) Lithium mica sulfate was roasted and leached to obtain a solution containing lithium sulfate; (2) The lithium sulfate-containing solution was extracted and washed with lithium extractant to obtain a lithium-loaded oil phase and an aqueous raffinate. (3) The lithium-loaded oil phase was back-extracted using ammonium phosphate to separate the empty oil phase liquid, mother liquor and crude lithium phosphate; (4) Return the mother liquor to step (3) for recycling and back-extraction; add pure water to the crude lithium phosphate and adjust the pH to 10.5-11.5 with lithium hydroxide, and obtain rod-shaped high-purity lithium phosphate by filtration, washing and drying.

2. The method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite according to claim 1, characterized in that, In step (3), the ammonium phosphate salt is ammonium dihydrogen phosphate and / or ammonium monohydrogen phosphate, and the concentration of the ammonium phosphate salt is 1-2 mol / L.

3. The method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite according to claim 1, characterized in that, In step (1), the calcination and leaching of the lithium mica sulfate includes the following steps: 1.1) Mix lepidolite, sulfate and calcium carbonate at a mass ratio of 100:40:(8-20), calcine at 700-950℃ for 1-3 hours, then leach with water at a liquid-solid ratio of (1-1.5):1 for 0.5-1 hours and separate to obtain leachate; 1.2) Lime slurry is added to the leachate to adjust the pH to 11-12, and the purified solution is obtained. After further purification by carbonate and adsorption resin, a lithium sulfate-containing solution is obtained.

4. The method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite according to claim 3, characterized in that, The sulfate is selected from one or more of calcium sulfate, sodium sulfate, and potassium sulfate; the carbonate is selected from potassium carbonate or sodium carbonate.

5. The method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite according to claim 1, characterized in that, In step (2), the extraction and washing of the lithium sulfate-containing solution using a lithium extractant includes the following steps: 2.1) Add liquid alkali to the lithium sulfate solution to adjust the hydroxide concentration in the solution to 0.82-1 mol / L, and obtain the lithium sulfate solution after alkali adjustment; 2.2) The lithium sulfate solution after alkali adjustment was subjected to multi-stage countercurrent extraction using lithium extractant to obtain an oil phase containing impurities loaded with lithium and an aqueous raffinate. 2.3) The oil phase containing impurities loaded with lithium is subjected to multi-stage countercurrent washing with dilute sulfuric acid solution to remove potassium and sodium ions, resulting in a primary impurity-removed oil phase and washing solution. The washing solution is returned to step 2.2) for recycling extraction. 2.4) The primary impurity-removed oil phase is washed in multiple countercurrent stages with pure water to remove sulfate ions and residual potassium and sodium ions, and the lithium-loaded oil phase and washing water are separated. The washing water is returned to step 2.3) to prepare dilute sulfuric acid.

6. The method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite according to claim 1 or 5, characterized in that, The lithium extractant comprises a main extractant (10-40% by mass), a co-extractant (1-30% by mass), and the remainder being a diluent, wherein the diluent constitutes more than 50% by mass of the lithium extractant; wherein: The main extractant is selected from at least one of 1-phenyl-1,3-decanedione, 1-(3,5-bis(trifluoromethylphenyl)-1,3-butanedione, 1-heptyl-3-phenyl-1,3-propanedione, dodecylphenyl-methyl-β-dione, dioctyl phthalate, and butyl salicylate. The co-extractant is selected from at least one of trioctylphosphine oxide, tributyl phosphate, di(2-ethylhexyl) phosphate, 2-ethylhexyl phosphate mono-2-ethylhexyl ester, di(2,4,4-trimethylpentyl) phosphate, and di(n-octyl) phosphate. The diluent is selected from 260# solvent oil and / or sulfonated kerosene.

7. The method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite according to claim 1, characterized in that, The O / A ratio for the lithium extractant to extract the lithium sulfate solution is (2-3):1, and the O / A ratio for the ammonium phosphate salt to back-extract the lithium-loaded oil phase is (1-15):

1.

8. The method for preparing rod-shaped high-purity lithium phosphate based on lithium extraction from lepidolite according to claim 5, characterized in that, The O / A ratio for washing with the dilute sulfuric acid solution is (8-15):1, and the O / A ratio for washing with pure water is (10-20):1.

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