A method for preparing high-purity lithium carbonate based on lithium mica calcined clinker extraction

Abstract

This invention discloses a method for preparing high-purity lithium carbonate based on the extraction of calcined lepidolite clinker. First, the calcined lepidolite clinker is soaked in water and impurities are removed to obtain raffinate. Then, a lithium extractant is used to extract and separate the phases of the raffinate to obtain a lithium-containing organic phase. After washing the lithium-containing organic phase, it is back-extracted using a carbon dioxide back-extractant to obtain a lithium bicarbonate solution. Finally, polyethylene glycol is added to the lithium bicarbonate solution and stirred and mixed. The mixture is then spray-dried, pyrolyzed, and heat-treated to obtain lithium carbonate without lithium bicarbonate encapsulation. The lithium carbonate product prepared by this process can also achieve a main content purity of ≥99.9%, which is close to the liquid phase purity (≥99.9%) of lithium bicarbonate solution. This achieves complete conversion of lithium bicarbonate solution into lithium carbonate, meaning that there is no lithium bicarbonate entrainment in the lithium carbonate product. At the same time, the lithium carbonate product prepared by this process can achieve a particle size of D50=11-15μm and D100=20-27μm, avoiding the generation of fine powder particles that could adversely affect the downstream lithium iron phosphate or lithium manganese iron phosphate cathode material preparation process.

Description

Technical Field

[0001] This invention belongs to the field of lithium carbonate preparation technology, and particularly relates to a method for preparing high-purity lithium carbonate based on extraction from roasted lithium mica clinker. Background Technology

[0002] Lithium extraction from lepidolite is one of the important industrial methods for producing lithium carbonate (Li2CO3).

[0003] The currently used and relatively mature industrial method is to first leach the roasted clinker to obtain brine, then remove impurities, then concentrate it using MVR (Medium-Volume Reduction), and then add sodium carbonate for lithium precipitation. However, this method has economic drawbacks in actual production line applications, such as high energy consumption for MVR evaporation and concentration and high cost of sodium carbonate lithium precipitation.

[0004] Existing technologies also disclose preparation methods using carbonation or hydrocarbonation purification. The core logic of the carbonation method is to utilize the physicochemical property of the difference in solubility between lithium carbonate and lithium bicarbonate in water to achieve deep separation of impurities. The mechanism is as follows: The calcined clinker is mixed with water and slurried, then fed into a pressure-resistant reactor with stirring. At room temperature or slightly above room temperature, carbon dioxide is introduced into the slurry. The active lithium in the clinker first reacts with water and carbon dioxide to form slightly soluble lithium carbonate, and then, in the presence of excess carbon dioxide, rapidly transforms into highly soluble lithium bicarbonate, which enters the liquid phase. The deeply purified high-purity LiHCO3 solution is then fed into a pyrolysis reactor. Lithium bicarbonate is relatively stable at room temperature but extremely sensitive to heat. When the solution is heated to 85℃-95℃, LiHCO3 rapidly decomposes, precipitating high-purity Li2CO3 crystals, while simultaneously releasing CO2 gas.

[0005] In addition, with the continuous improvement of the process, lithium is also extracted by extraction and carbon dioxide back-extraction to obtain lithium bicarbonate, and then lithium carbonate is obtained by thermal decomposition of lithium bicarbonate.

[0006] Regardless of whether extraction or carbonation leaching is used, in practical applications, when testing the impurity content of high-purity lithium bicarbonate solutions to assess the purity of lithium carbonate, the purity values ​​found to differ by more than 0.5% from those obtained by directly testing the main content of solid lithium carbonate, significantly exceeding the error range of ±0.1%.

[0007] Based on this, we now study a method for preparing lithium carbonate by extraction from calcined lithium mica clinker, so as to achieve a purity of 99.9% for lithium carbonate with the same main content. Summary of the Invention

[0008] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for preparing lithium carbonate based on the extraction of calcined lithium mica, so as to achieve a main content purity of ≥99.9% for the lithium carbonate product.

[0009] Technical solution: This invention relates to a method for preparing high-purity lithium carbonate by extraction from calcined lithium mica, comprising the following steps:

[0010] (1) After leaching and removing impurities from the calcined lithium mica, the raffinate is obtained;

[0011] (2) The raffinate was extracted and separated by lithium extractant to obtain a lithium-containing organic phase; the lithium-containing organic phase was washed and then back-extracted by carbon dioxide back-extractant to obtain a lithium bicarbonate solution.

[0012] (3) After adding polyethylene glycol to the lithium bicarbonate solution and stirring, the mixture is spray-dried, pyrolyzed, and heat-treated to obtain lithium carbonate without lithium bicarbonate encapsulation.

[0013] Furthermore, in step (3) of the preparation method, the amount of polyethylene glycol added is 0.2-1% of the theoretical lithium carbonate yield in the lithium bicarbonate solution.

[0014] Furthermore, in step (3) of the preparation method, the outlet temperature of the spray drying pyrolysis is 100-150℃ and the rotation speed is 15000-18000rpm.

[0015] Furthermore, in step (3) of the preparation method, the heat treatment temperature is 250-360℃ and the heat treatment time is 0.5-1h.

[0016] Furthermore, in step (2) of this preparation method, the lithium extractant is TBP and kerosene in a molar ratio of (0.1-0.6):1, with an O / A ratio of (1.5-2.5):1; the O / A ratio during back-extraction is (10-30):1. Preferably, the concentration of the lithium extractant is 0.5-3 mol / L, and the carbon dioxide injection rate is 1.1-1.2 times the theoretical mass of lithium carbonate produced.

[0017] Furthermore, in step (1) of the preparation method, the liquid-to-solid ratio of the water immersion is (1.5-2.5):1, and the water immersion time is 25-65 min.

[0018] Furthermore, in step (1) of the preparation method, the impurity removal step is as follows: after obtaining leaching brine by water leaching of calcined lithium mica, liquid alkali is added to adjust the pH to 12-13, and magnesium, iron and a small amount of calcium are removed by pressure filtration to obtain filtrate; and calcium is extracted from the filtrate using an extractant with a concentration of 1-5 mol / L and an O / A ratio of (0.2-0.8):1 to obtain raffinate.

[0019] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are:

[0020] (1) The lithium carbonate product prepared by this process can also reach a purity of ≥99.9%, which is close to the liquid phase purity (≥99.9%) of the lithium bicarbonate solution, so that the lithium bicarbonate solution can be completely converted into lithium carbonate, that is, there is no lithium bicarbonate entrainment in the lithium carbonate product.

[0021] (2) The lithium carbonate product prepared by this process can achieve a particle size of D50=11-15μm and D100=20-27μm, which avoids the generation of fine powder particles that may have an adverse effect on the downstream lithium iron phosphate or lithium manganese iron phosphate cathode material preparation process. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0023] The polyethylene glycol used in the following examples and comparative examples of the present invention has a molecular weight of 2000.

[0024] The main components of the lithium mica roasted clinker used in the following embodiments and comparative examples of the present invention are shown in Table 1 below.

[0025] Table 1. Main components of the lepidolite roasted clinker used in the examples and comparative examples.

[0026]

[0027] Example 1

[0028] This Example 1 describes a process for preparing high-purity lithium carbonate based on calcined lepidolite clinker, which includes the following steps:

[0029] (1) Leaching: Lithium mica roasted clinker was mixed with water at a liquid-to-solid ratio of 2.0 and leached for 40 minutes to obtain leaching brine;

[0030] (2) Impurity removal: Add liquid alkali to the leaching brine to adjust the pH to 12, remove magnesium, iron and a small amount of calcium, and obtain filtrate; extract calcium from the filtrate with 3 mol / L P204 extractant (O / A=0.5:1, room temperature) to obtain raffinate A, which is then introduced into the lithium extraction process.

[0031] (3) Lithium extraction and back-extraction: A lithium-containing organic phase was obtained by three-stage extraction (the extractant was a mixture of 1.5 mol / L TBP and kerosene, the molar ratio of TBP and kerosene was 0.3:1, O / A=2:1, and the stirring speed was 500 rpm); the lithium-containing organic phase was washed in two stages (the amount of tap water was 1 / 3 of the volume of the extractant) and then back-extracted in two stages (the amount of CO2 introduced was 1.2 times the theoretical mass of lithium carbonate produced, CO2 dissolved in water to form a back-extraction solution, O / A=10:1) to obtain a lithium bicarbonate solution and raffinate B;

[0032] (4) Synthesis of lithium carbonate: After adding polyethylene glycol to the lithium bicarbonate solution and stirring, the mixture is spray-dried and pyrolyzed at an outlet temperature of 100°C and a rotation speed of 15000 rpm, and then heat-treated at 250°C for 0.5 h to obtain lithium carbonate; the amount of polyethylene glycol added is 0.2% of the theoretical lithium carbonate yield in the lithium bicarbonate solution.

[0033] Comparative Example 1

[0034] The basic steps are the same as in Example 1, except that the lithium bicarbonate solution is directly thermally decomposed. The specific steps are as follows:

[0035] (1) Leaching: Lithium mica roasted clinker was mixed with water at a liquid-to-solid ratio of 2.0 and leached for 40 minutes to obtain leaching brine;

[0036] (2) Impurity removal: Add liquid alkali to the leaching brine to adjust the pH to 12, remove magnesium, iron and a small amount of calcium, and obtain filtrate; extract calcium from the filtrate with 3 mol / L P204 extractant (O / A=0.5:1, room temperature) to obtain raffinate A, which is then introduced into the lithium extraction process.

[0037] (3) Lithium extraction and back-extraction: A lithium-containing organic phase was obtained by three-stage extraction (the extractant was a mixture of 1.5 mol / L TBP and kerosene, the molar ratio of TBP and kerosene was 0.3:1, O / A=2:1, and the stirring speed was 500 rpm); the lithium-containing organic phase was washed in two stages (the amount of tap water was 1 / 3 of the volume of the extractant) and then back-extracted in two stages (the amount of CO2 introduced was 1.2 times the theoretical mass of lithium carbonate produced, CO2 dissolved in water to form a back-extraction solution, O / A=10:1) to obtain a lithium bicarbonate solution and raffinate B;

[0038] (4) Synthesis of lithium carbonate: Lithium bicarbonate solution is directly heated to 90°C and reacted for 2 hours to obtain lithium carbonate.

[0039] Example 2

[0040] This Example 2 describes a process for preparing high-purity lithium carbonate from calcined lepidolite clinker, which includes the following steps:

[0041] (1) Leaching: Lithium mica roasted clinker was mixed with water at a liquid-to-solid ratio of 1.5 and leached for 40 minutes to obtain leaching brine;

[0042] (2) Impurity removal: Add liquid alkali to the leaching brine to adjust the pH to 12, remove magnesium, iron and a small amount of calcium, and obtain filtrate; extract calcium from the filtrate with 1 mol / L P204 extractant (O / A=0.2:1, room temperature) to obtain raffinate A, which is then introduced into the lithium extraction process.

[0043] (3) Lithium extraction and back-extraction: A lithium-containing organic phase was obtained by three-stage extraction (the extractant was a mixture of 0.5 mol / L TBP and kerosene, the molar ratio of TBP and kerosene was 0.1:1, O / A=1.5:1, and the stirring speed was 350 rpm); the lithium-containing organic phase was washed in two stages (the amount of tap water was 1 / 4 of the volume of the extractant) and then back-extracted in two stages (the amount of CO2 introduced was 1.1 times the theoretical amount of lithium carbonate produced, CO2 dissolved in water to form a back-extraction solution, O / A=10:1) to obtain a lithium bicarbonate solution and raffinate B;

[0044] (4) Synthesis of lithium carbonate: After adding polyethylene glycol to the lithium bicarbonate solution and stirring, the mixture is spray-dried and pyrolyzed at an outlet temperature of 100°C and a rotation speed of 15000 rpm, and then heat-treated at 250°C for 0.5 h to obtain lithium carbonate; the amount of polyethylene glycol added is 0.2% of the theoretical lithium carbonate yield in the lithium bicarbonate solution.

[0045] Comparative Example 2

[0046] The basic steps are the same as in Example 2, except that the lithium bicarbonate solution is directly thermally decomposed. The specific steps are as follows:

[0047] (1) Leaching: Lithium mica roasted clinker was mixed with water at a liquid-to-solid ratio of 1.5 and leached for 40 minutes to obtain leaching brine;

[0048] (2) Impurity removal: Add liquid alkali to the leaching brine to adjust the pH to 12, remove magnesium, iron and a small amount of calcium, and obtain filtrate; extract calcium from the filtrate with 1 mol / L P204 extractant (O / A=0.2:1, room temperature) to obtain raffinate A, which is then introduced into the lithium extraction process.

[0049] (3) Lithium extraction and back-extraction: A lithium-containing organic phase was obtained by three-stage extraction (the extractant was a mixture of 0.5 mol / L TBP and kerosene, the molar ratio of TBP and kerosene was 0.1:1, O / A=1.5:1, and the stirring speed was 350 rpm); the lithium-containing organic phase was washed in two stages (the amount of tap water was 1 / 4 of the volume of the extractant) and then back-extracted in two stages (the amount of CO2 introduced was 1.1 times the theoretical amount of lithium carbonate produced, CO2 dissolved in water to form a back-extraction solution, O / A=10:1) to obtain a lithium bicarbonate solution and raffinate B;

[0050] (4) Synthesis of lithium carbonate: Lithium bicarbonate solution is directly heated to 90°C and reacted for 2 hours to obtain lithium carbonate.

[0051] Example 3

[0052] This Example 3 describes a process for preparing high-purity lithium carbonate from calcined lepidolite clinker, which includes the following steps:

[0053] (1) Leaching: Lithium mica roasted clinker was mixed with water at a liquid-to-solid ratio of 2.5 and leached for 40 minutes to obtain leaching brine;

[0054] (2) Impurity removal: Add liquid alkali to the leaching brine to adjust the pH to 13, remove magnesium, iron and a small amount of calcium, and obtain filtrate; extract calcium from the filtrate with 5 mol / L P204 extractant (O / A=0.8:1, room temperature) to obtain raffinate A, which is then introduced into the lithium extraction process.

[0055] (3) Lithium extraction and back-extraction: A lithium-containing organic phase was obtained by three-stage extraction (the extractant was a mixture of 3 mol / L TBP and kerosene, the molar ratio of TBP and kerosene was 0.6:1, O / A=2.5:1, and the stirring speed was 600 rpm); the lithium-containing organic phase was washed in two stages (the amount of tap water was 1 / 2 of the volume of the extractant) and then back-extracted in two stages (the amount of CO2 introduced was 1.2 times the theoretical amount of lithium carbonate produced, CO2 dissolved in water to form a back-extraction solution, O / A=15:1) to obtain a lithium bicarbonate solution and raffinate B;

[0056] (4) Synthesis of lithium carbonate: After adding polyethylene glycol to the lithium bicarbonate solution and stirring, the mixture is spray-dried and pyrolyzed at an outlet temperature of 100°C and a rotation speed of 15000 rpm, and then heat-treated at 250°C for 0.5 h to obtain lithium carbonate; the amount of polyethylene glycol added is 0.2% of the theoretical lithium carbonate yield in the lithium bicarbonate solution.

[0057] Performance Test 1

[0058] The purity of the lithium bicarbonate solutions obtained from Examples 1 to 3, Comparative Example 1, and Comparative Example 2 were tested, and the results are shown in Table 2 below. The main purity of the lithium carbonate prepared from Examples 1 to 3, Comparative Example 1, and Comparative Example 2 was tested, and the results are shown in Table 3 below.

[0059] Table 2. Purity of lithium bicarbonate solutions in the examples and comparative examples

[0060]

[0061] Table 3. Main purity of lithium carbonate in the examples and comparative examples

[0062]

[0063] Comparative Example 3

[0064] Comparative Example 3 is essentially the same as Example 1, except that it involves direct spray drying for decomposition. Specifically, it includes the following steps:

[0065] (1) Leaching: Lithium mica roasted clinker was mixed with water at a liquid-to-solid ratio of 2.0 and leached for 40 minutes to obtain leaching brine;

[0066] (2) Impurity removal: Add liquid alkali to the leaching brine to adjust the pH to 12, remove magnesium, iron and a small amount of calcium, and obtain filtrate; extract calcium from the filtrate with 3 mol / L P204 extractant (compared to O / A=0.5:1, room temperature) to obtain raffinate A, which is then introduced into the lithium extraction process.

[0067] (3) Lithium extraction and back-extraction: A lithium-containing organic phase was obtained by three-stage extraction (the extractant was a mixture of 1.5 mol / L TBP and kerosene, the molar ratio of TBP and kerosene was 0.3:1, O / A=2:1, and the stirring speed was 500 rpm); the lithium-containing organic phase was washed in two stages (the amount of tap water was 1 / 3 of the volume of the extractant) and then back-extracted in two stages (the amount of CO2 introduced was 1.2 times the theoretical amount of lithium carbonate produced, CO2 dissolved in water to form a back-extraction solution, O / A=10:1) to obtain a lithium bicarbonate solution and raffinate B;

[0068] (4) Synthesis of lithium carbonate: The lithium bicarbonate solution was spray-dried and pyrolyzed at an outlet temperature of 100°C and a rotation speed of 15000 rpm to obtain lithium carbonate without lithium bicarbonate encapsulation.

[0069] Comparative Example 4

[0070] Comparative Example 4 is essentially the same as Example 1, except that after adding polyethylene glycol and spray drying, a water washing process is used directly without heat treatment. Specifically, the steps are as follows:

[0071] (1) Leaching: Lithium mica roasted clinker was mixed with water at a liquid-to-solid ratio of 2.0 and leached for 40 minutes to obtain leaching brine;

[0072] (2) Impurity removal: Add liquid alkali to the leaching brine to adjust the pH to 12, remove magnesium, iron and a small amount of calcium, and obtain filtrate; extract calcium from the filtrate with 3 mol / L P204 extractant (O / A=0.5:1, room temperature) to obtain raffinate A, which is then introduced into the lithium extraction process.

[0073] (3) Lithium extraction and back-extraction: A lithium-containing organic phase was obtained by three-stage extraction (the extractant was a mixture of 1.5 mol / L TBP and kerosene, the molar ratio of TBP and kerosene was 0.3:1, O / A=2:1, and the stirring speed was 500 rpm); the lithium-containing organic phase was washed in two stages (the amount of tap water was 1 / 3 of the volume of the extractant) and then back-extracted in two stages (the amount of CO2 introduced was 1.2 times the theoretical amount of lithium carbonate produced, CO2 dissolved in water to form a back-extraction solution, O / A=10:1) to obtain a lithium bicarbonate solution and raffinate B;

[0074] (4) Synthesis of lithium carbonate: After adding polyethylene glycol to the lithium bicarbonate solution and stirring, the solution is spray-dried and pyrolyzed at an outlet temperature of 100°C and a rotation speed of 15000 rpm to obtain lithium carbonate, which is then washed multiple times with deionized water. The amount of polyethylene glycol added is 0.2% of the theoretical lithium carbonate yield in the lithium bicarbonate solution.

[0075] Performance Test 2

[0076] The main purity of lithium carbonate obtained from Examples 1 and Comparative Examples 3 to 4 was tested, and the results are shown in Table 4 below. Meanwhile, the particle size of lithium carbonate prepared from Examples 1 to 3 and Comparative Examples 3 to 4 was tested, and the results are shown in Table 5 below.

[0077] Table 4. Main purity of lithium carbonate in Example 1 and Comparative Examples 3 to 4

[0078]

[0079] Table 5. Particle size distribution of lithium carbonate in the examples and comparative examples.

[0080]

[0081] As shown in Tables 2 to 4, the purity of the lithium bicarbonate solution and the main purity of the lithium carbonate product are not significantly different using the purification and preparation process of this invention, and are within the error range. This verifies that the combination of polyethylene glycol + spray drying pyrolysis + heat treatment can achieve truly high purity of lithium carbonate product, effectively avoiding incomplete decomposition of lithium bicarbonate and the situation of entrainment (undecomposed lithium bicarbonate entering lithium carbonate crystals).

[0082] As can be seen from Examples 1 and 3, the formation of small particles with a large specific surface area does not theoretically indicate a complete pyrolysis reaction, thus naturally leading to the formation of high-purity lithium carbonate. On the contrary, simply using spray drying to decompose the particles into small particles and then fully pyrolyze them (Comparative Example 3) did not significantly improve the purity compared to Comparative Examples 1 and 2 (99.47%, 99.27%, 99.31%). In fact, the formation of small particles can constrain the downstream cathode material preparation process. Specifically, the small particles will be suspended on the surface of the slurry during preparation, resulting in insufficient mixing.

[0083] Only through the combined action of polyethylene glycol + spray drying pyrolysis, and simultaneously a heat treatment process (Comparative Example 4), can the final effect of improving the purity of the lithium carbonate main phase be achieved. Furthermore, it can promote the fusion of fine particles to achieve a conventional particle size, avoiding the formation of fine particles that could adversely affect the preparation of downstream cathode materials. In addition, it can improve the conductivity of the prepared lithium carbonate product, thus playing a supporting role in enhancing the electrochemical performance of downstream cathode materials.

[0084] In addition to the above embodiments, the preparation process steps and parameters of the present invention can achieve the technical effects claimed above, and therefore no further testing is required to verify them.

Claims

1. A method for preparing high-purity lithium carbonate based on extraction from calcined lithium mica clinker, characterized in that, Includes the following steps: (1) After leaching and removing impurities from the calcined lithium mica, the raffinate is obtained; (2) The raffinate was extracted and separated by lithium extractant to obtain a lithium-containing organic phase; the lithium-containing organic phase was washed and then back-extracted by carbon dioxide back-extractant to obtain a lithium bicarbonate solution. (3) After adding polyethylene glycol to the lithium bicarbonate solution and stirring, the mixture is spray-dried, pyrolyzed, and heat-treated to obtain lithium carbonate without lithium bicarbonate encapsulation.

2. The method for preparing high-purity lithium carbonate based on extraction from calcined lithium mica clinker according to claim 1, characterized in that, In step (3), the amount of polyethylene glycol added is 0.2-1% of the theoretical lithium carbonate yield in the lithium bicarbonate solution.

3. The method for preparing high-purity lithium carbonate based on extraction from roasted lithium mica clinker according to claim 1, characterized in that, In step (3), the outlet temperature of the spray drying pyrolysis is 100-150℃ and the rotation speed is 15000-18000rpm.

4. The method for preparing high-purity lithium carbonate based on extraction from calcined lithium mica clinker according to claim 1, characterized in that, In step (3), the heat treatment temperature is 250-360℃ and the heat treatment time is 0.5-1h.

5. The method for preparing high-purity lithium carbonate based on extraction from calcined lithium mica clinker according to claim 1, characterized in that, In step (2), the lithium extractant is TBP and kerosene with a molar ratio of (0.1-0.6):1 and an O / A ratio of (1.5-2.5):1; the O / A ratio of the back-extractant during back-extraction is (10-30):

1.

6. The method for preparing high-purity lithium carbonate based on extraction from calcined lithium mica clinker according to claim 1, characterized in that, In step (1), the liquid-to-solid ratio of the water immersion is (1.5-2.5):1, and the immersion time is 25-65 min.

7. The method for preparing high-purity lithium carbonate based on extraction from calcined lithium mica clinker according to claim 1, characterized in that, In step (1), the impurity removal step is as follows: after obtaining leaching brine by water leaching of calcined lithium mica, liquid alkali is added to adjust the pH to 12-13, and magnesium, iron and a small amount of calcium are removed by pressure filtration to obtain filtrate; and calcium is extracted from the filtrate using an extractant with a concentration of 1-5 mol / L and an O / A ratio of (0.2-0.8):1 to obtain raffinate.

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