Lithium salt crystallization method

Abstract

The invention discloses a lithium salt crystallization method, which adopts a lithium precipitation kettle with two layers of ultrasonic generators arranged at diagonal positions in a kettle body, and comprises the following steps: starting the ultrasonic generators, and adjusting the ultrasonic frequency to be 20-150KHz; adding sodium carbonate and a lithium sulfate solution into the lithium precipitation kettle by adopting an inverse addition method; continuously carrying out ultrasonic reaction for 2-4 hours, and turning off the ultrasonic generator; and carrying out solid-liquid separation to obtain lithium carbonate. According to the invention, the scaling phenomenon in the reaction kettle can be basically eliminated completely, and scale blocks do not need to be cleaned manually; the content of impurities in the lithium salt is reduced: the content of sulfate radicals is reduced to 0.07% or below from 0.08% in the prior art and can be reduced to 0.045%, and the content of sodium ions is reduced to 0.02% or below from 0.025% in the prior art and can be reduced to 0.01% or below; and the particle size of the lithium salt crystal particles is reduced from the average particle size of 25-40 microns in the existing process to 3-20 microns in the process disclosed by the invention, and the appearance of the particles is more uniform.

Description

Technical Field

[0001] This invention relates to the production process of lithium salt products, specifically to a method for lithium salt crystallization. Background Technology

[0002] Lithium carbonate is divided into industrial-grade lithium carbonate and battery-grade (EV-grade) lithium carbonate. The main difference between the two is the purity of lithium carbonate. Battery-grade lithium carbonate requires a purity of 99.5% or higher, while industrial-grade lithium carbonate has a relatively lower purity.

[0003] The existing process for producing lithium salts from solid lithium ores (such as spodumene, lepidolite, and lithium clay) using the "sulfuric acid process" or "sulfate process" includes a front-end and a back-end. The front-end, also known as the pyrometallurgical stage, is illustrated as follows: Lithium concentrate → feeder → preheater → rotary kiln system → grinding system → mixed acid system → acidification kiln system → ore slurry preparation → leaching → filtration system → purification → concentration. The front-end process yields a "purified lithium sulfate solution" from the lithium concentrate. Concentration controls the lithium concentration in the purified solution to the range of Li₂O≈40~55g / L, thus obtaining a concentrated lithium sulfate solution. The back-end, also known as the wet process, utilizes the concentrated lithium sulfate solution obtained in the front-end to produce lithium salts such as lithium carbonate or lithium phosphate. The process is illustrated as follows: concentration → lithium precipitation → separation → drying → pulverization → packaging, etc.

[0004] The reaction equation for producing lithium salts using lithium sulfate concentrate is as follows: sodium carbonate or sodium phosphate solution is added to lithium sulfate concentrate (temperature approximately 60–90°C), causing them to react in a reactor to form lithium carbonate (precipitate) or lithium phosphate precipitate, as shown in the following reaction:

[0005] Li2SO4+Na2CO3=Li2CO3↓+Na2SO4

[0006] 3Li2SO4+2Na3PO4=2Li3PO4↓+3Na2SO4

[0007] 2LiCL+Na2CO3=Li2CO3↓+2NaCL

[0008] 3LiCL+Na3PO4=Li3PO4↓+3NaCL

[0009] 2LiOH+Na2CO3=Li2CO3↓+2NaOH

[0010] 3LiOH+Na3PO4=Li3PO4↓+3NaOH

[0011] 2LiOH + CO2 = Li2CO3↓ + H2O

[0012] Lithium carbonate and lithium phosphate precipitate out as precipitates. However, lithium carbonate and lithium phosphate are slightly soluble in water, so the mother liquor still contains a small amount of soluble lithium salts. It also contains a small amount of unreacted sodium carbonate and a large amount of sodium sulfate. After acid-base neutralization, the mother liquor is evaporated and heated to obtain sodium sulfate (anhydrous sodium sulfate) as a byproduct, and the heated sodium sulfate mother liquor is separated. The heated sodium sulfate mother liquor mainly consists of a mixture of lithium sulfate, sodium sulfate, and a small amount of potassium sulfate and chloride salts. Lithium enrichment of the heated sodium sulfate mother liquor increases the Li₂O concentration (Li₂O ≈ 15-30 g / L). Adding sodium carbonate again to the heated sodium sulfate mother liquor for lithium precipitation further yields the lithium from the mother liquor. This process is called the secondary lithium precipitation process (e.g., ...). Figure 1 As shown in the figure, the lithium precipitation process before the secondary lithium precipitation process is called the primary lithium precipitation process. This process of combining two lithium precipitation processes is the conventional process for lithium carbonate production.

[0013] In lithium salt production, materials need to be heated and concentrated or crystallized to precipitate salt. In some processes, due to localized high temperatures (the surface temperature of components using steam reaches 90-170℃, and the temperature of components using hot oil to provide heat energy can reach 170-300℃) or enrichment, scale will form on the inner wall of the equipment, such as common MVR evaporators, jacketed reactors, and coil reactors. During operation, the material flows inside the reactor and the steam flows outside, mainly to heat the material. In this process, since the material cannot be a pure solution, insoluble or slightly soluble carbonates in the material gradually accumulate and deposit on the surface of the heated components to form scale, which eventually leads to blockage inside the tubes, reduced material circulation, increased steam consumption, increased production costs and reduced capacity.

[0014] Similar reaction processes, such as those described above, involve steam heating or intense exothermic reactions. As the reaction proceeds, precipitates adhere to the inner walls of the equipment, the surface of the agitator, or the outer walls of the coils, forming scale. This gradually reduces heating efficiency and increases production costs. Furthermore, during production, reducing or even stopping steam use before material discharge lowers the equipment temperature. The addition of new material also lowers the equipment temperature. Frequent alternations between high and low temperatures cause the scale to expand and partially detach. The scale contains a high amount of impurities, affecting the quality of lithium salt products and hindering quality control. Simultaneously, during product precipitation, impurities adhere to the product surface, even encapsulating impurity particles inside the product. While surface impurities can be washed away, impurities encapsulated inside the product cannot be removed. To mitigate this, the conventional lithium precipitation process requires manual cleaning once a week.

[0015] The lithium battery industry requires lithium salt crystals to be ultra-fine, narrowly distributed, and uniform (the particle size of lithium carbonate products is 3-13 micrometers), with the sulfate content of impurities controlled below 0.05%. This conventional lithium deposition process results in coarse, widely distributed, and unevenly distributed lithium carbonate particles (the particle size of lithium carbonate products is 1-45 micrometers). Furthermore, the lithium carbonate particles contain significant impurities (primarily sulfate, with a sulfate content exceeding 0.07%), compromising product quality. Summary of the Invention

[0016] To address the problems of uneven particle size distribution of lithium salts such as lithium carbonate, severe impurity inclusions in lithium salt product particles, and severe scaling in reaction vessels requiring frequent manual cleaning in existing technologies, this invention proposes a lithium salt crystallization method.

[0017] A lithium salt crystallization method employs a lithium precipitation reactor with two layers of ultrasonic generators positioned diagonally within the reactor body. The two layers of ultrasonic generators are an upper ultrasonic generator and a lower ultrasonic generator. The lower edge of the upper ultrasonic generator is located at the halfway point of the reactor body; the upper edge of the lower ultrasonic generator is located at the halfway point of the reactor body. One end of each ultrasonic generator is rotatably connected to an ultrasonic connecting pipe, allowing the upper and lower ultrasonic generators to rotate within the reactor body. The lithium salt crystallization method includes the following steps:

[0018] Turn on the ultrasonic generator and adjust the ultrasonic frequency to 20KHz~150KHz;

[0019] Sodium carbonate and lithium sulfate solutions were added to the lithium precipitation vessel using the "reverse addition" method, and the molar ratio of sodium carbonate to lithium sulfate was controlled so that the carbonate ion was 5% in excess of the lithium ion.

[0020] Continue the ultrasonic reaction until it ends, then turn off the ultrasonic generator.

[0021] Lithium carbonate was obtained by solid-liquid separation.

[0022] Both the upper and lower ultrasonic generators are movably connected to the ultrasonic connecting tube, and rotate around the connection point with a rotation angle of 0 to 90°; the ultrasonic connecting tube is fixedly connected to the kettle lid and the upper end of the ultrasonic connecting tube penetrates through the kettle lid.

[0023] The precipitant in the lithium precipitation reactor is sodium carbonate, and the feed solution is a soluble lithium salt solution, namely lithium sulfate solution (lithium ion concentration measured in Li₂O, Li₂O = 40-55 g / L). The ultrasonic generator is turned off after the reaction is complete (reaction time is 2-4 hours). Preferably, the lithium sulfate solution has a lithium ion concentration measured in Li₂O, Li₂O = 45-50 g / L. Reverse addition method: First, the precipitant, such as sodium carbonate, is added to the reaction vessel, then the feed solution, such as concentrated lithium sulfate solution, is added, and then crystallization and precipitation occur.

[0024] Optionally, the ultrasonic frequency is 100–150 kHz. A higher ultrasonic frequency can result in finer and more uniform lithium carbonate crystal particles.

[0025] The molar ratio of sodium carbonate to lithium sulfate in the lithium precipitation vessel is controlled such that the carbonate ion is 5% in excess to the lithium ion, which will cause a large amount of lithium carbonate to precipitate.

[0026] Use 5-20m 3 In a lithium precipitation reactor, ultrasonic waves are used for 2–4 hours to indicate the reaction is complete. When a 12m... 3 When performing lithium precipitation in a lithium precipitation reactor, a continuous ultrasonic treatment time of 3 hours is sufficient to obtain lithium carbonate with a good particle size. When reducing or increasing the volume of the lithium precipitation reactor, the ultrasonic treatment time can be appropriately shortened or lengthened.

[0027] The lithium carbonate is added to deionized water at 95-100°C and stirred to separate the solid and liquid phases, thereby obtaining battery-grade lithium carbonate.

[0028] This invention utilizes the principle of "ultrasonic cavitation" and introduces an ultrasonic generator to modify the existing lithium salt crystallization process, resulting in smaller lithium salt crystal particles with a narrower and more uniform particle size distribution and more regular morphology; reducing impurity inclusions and improving product quality. It also solves the problem of scaling on the reaction vessel walls and agitator.

[0029] The battery-grade lithium salt crystallization method of this invention involves installing an ultrasonic generator in the reactor or a scaling-prone area during a similar production process. Utilizing the principle of "ultrasonic cavitation," it solves problems such as impurity encapsulation during precipitation and reactor scaling, while simultaneously achieving a one-time ultra-fine crystal particle size reduction effect. The ultrasonic equipment is configured in three dimensions to achieve this effect. Ultrasonication must be continuous throughout the entire crystallization process; otherwise, the uniform particle size distribution of the lithium salt cannot be guaranteed.

[0030] The ultrasonic frequency is generally controlled between 20 and 150 kHz. The appropriate frequency should be adjusted according to the actual working conditions in production. The specific control parameters should be based on meeting the actual needs of the working conditions and production.

[0031] With an ultrasonic generator positioned on one side, the lithium salt crystal particles have a wider size distribution (1–25 micrometers); with an ultrasonic generator positioned diagonally, the lithium salt crystal particles have a narrower and more concentrated size distribution (3–15 micrometers). Without an ultrasonic generator, the lithium salt crystal particles have a wide size distribution and large particle size (25–40 micrometers).

[0032] Compared with the prior art, the present invention has achieved at least the following beneficial effects:

[0033] The scaling inside the reactor has been almost completely eliminated, and manual cleaning of the scale is no longer required.

[0034] The lithium salt impurity content is reduced: the sulfate content is reduced from 0.08% in the original process to below 0.07%, and can be reduced to below 0.045%; the sodium ion content is reduced from 0.025% in the existing process to below 0.02%, and can be reduced to below 0.01%.

[0035] The particle size of lithium salt crystals is reduced: the average particle size is reduced from 25-40 micrometers in the existing process to 3-20 micrometers in the process of this invention, and the particle appearance is more uniform. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of an ultrasonic generator installed in a lithium deposition reactor.

[0037] Figure 2 This is a schematic diagram of the external structure of the lithium deposition reactor.

[0038] Reference numerals: 1. Lid; 2. Body; 3. Motor; 4. Stirring paddle; 5. Upper ultrasonic generator; 6. Lower ultrasonic generator; 7. Ultrasonic connecting pipe. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0040] A lithium precipitation reactor is a type of reaction vessel, and its structure is as follows: Figure 1 , Figure 2 As shown, the reactor has a vessel body 1, which is equipped with a jacket or coil for temperature control of the reactants inside. A stirring paddle 4 is installed inside the vessel body 1. The vessel body 1 is sealed by a lid 2. A motor 3 is connected to the top of the shaft of the stirring paddle 4, and the motor 3 is mounted on the lid 2. Inside the vessel body 1 of the lithium deposition reactor, there are upper ultrasonic generators 5 and lower ultrasonic generators 6. The lower edge of the upper ultrasonic generator 5 is located at the halfway point of the vessel body; the upper edge of the lower ultrasonic generator 6 is located at the halfway point of the vessel body; the two ultrasonic generators are located diagonally within the vessel body. Both the upper and lower ultrasonic generators 5 and 6 are movably connected to an ultrasonic connecting pipe 7, allowing them to rotate around the connection point with the ultrasonic connecting pipe 7, with a rotation angle of 0–90°. The ultrasonic connecting pipe 7 is fixedly connected to the lid, and its upper end penetrates the lid. The ultrasonic connecting tube 7 is hollow inside, which can protect the cable of the ultrasonic generator through the ultrasonic connecting tube 7.

[0041] Each embodiment uses the lithium deposition reactor described above.

[0042] Example 1

[0043] 12m 3 An ultrasonic generator is installed diagonally inside the lithium precipitation reactor. The precipitant in the reactor is sodium carbonate, and the feed solution is a soluble lithium salt solution, namely lithium sulfate solution (Li₂O = 45 g / L). The molar ratio of sodium carbonate to lithium sulfate is 5% excess of carbonate over lithium ions. The sodium carbonate and lithium sulfate solution are added using the common "reverse addition" lithium precipitation method. Before adding the materials, the ultrasonic generator is turned on and the ultrasonic frequency is adjusted to 20 kHz. The ultrasonic generator is turned off after the reaction is completed (reaction time is 3 hours). Solid-liquid separation yields lithium carbonate. The lithium carbonate is then added to deionized water at 95–100 °C and washed with stirring, resulting in solid-liquid separation of lithium carbonate.

[0044] Lithium carbonate particle size and distribution were determined by laser particle size analysis, sodium impurity content was detected by inductively coupled plasma optical emission spectrometry (ICP-OES), and sulfate content was determined by barium sulfate turbidimetry. The obtained lithium carbonate had an average particle size of 20 micrometers, a sulfate content of 0.07%, and a sodium ion content of 0.02%.

[0045] Example 2

[0046] 12m 3 An ultrasonic generator was installed diagonally inside the lithium precipitation reactor. Sodium carbonate and lithium sulfate solutions were added using the common "reverse addition" lithium precipitation method. The ultrasonic generator was turned on before addition, and the ultrasonic frequency was adjusted to 50 kHz until the reaction was complete (reaction time was 3 hours). The ultrasonic generator was then turned off. Other procedures were the same as in Example 1. The resulting lithium carbonate had an average particle size of 16 micrometers, a sulfate content of 0.06%, and a sodium ion content of 0.015%.

[0047] Example 3

[0048] 12m 3 An ultrasonic generator was installed diagonally inside the lithium precipitation reactor. Sodium carbonate and lithium sulfate solutions were added using the common "reverse addition" lithium precipitation method. The ultrasonic generator was turned on before addition, and the ultrasonic frequency was adjusted to 80 kHz. The ultrasonic generator was turned off after the reaction was completed (reaction time was 3 hours). Other procedures were the same as in Example 1. The resulting lithium carbonate had an average particle size of 14 micrometers, a sulfate content of 0.06%, and a sodium ion content of 0.012%.

[0049] Example 5

[0050] 12m 3An ultrasonic generator was installed diagonally inside the lithium precipitation reactor. Sodium carbonate and lithium sulfate solutions were added using the common "reverse addition" lithium precipitation method. The ultrasonic generator was turned on before addition, and the ultrasonic frequency was adjusted to 110 kHz. The reaction continued until completion (reaction time was 3 hours), after which the ultrasonic generator was turned off. Other procedures were the same as in Example 1. The resulting lithium carbonate had an average particle size of 10 micrometers, a sulfate content of 0.05%, and a sodium ion content of 0.01%.

[0051] Example 5

[0052] 12m 3 An ultrasonic generator was installed diagonally inside the lithium precipitation reactor. Sodium carbonate and lithium sulfate solutions were added using the common "reverse addition" lithium precipitation method. The ultrasonic generator was turned on before addition, and the ultrasonic frequency was adjusted to 150 kHz until the reaction was complete (reaction time was 3 hours). The ultrasonic generator was then turned off. Other procedures were the same as in Example 1. The resulting lithium carbonate had an average particle size of 7 micrometers, a sulfate content of 0.045%, and a sodium ion content of 0.008%.

[0053] Comparative Example 1

[0054] The ultrasonic treatment was not activated; all other parameters were the same as in Example 1. The average particle size was 30 micrometers, the sulfate content was 0.08%, and the sodium ion content was 0.025%.

[0055] Although the invention has been described herein with reference to illustrative embodiments thereof, it should be understood that many other modifications and implementations can be devised by those skilled in the art, which will fall within the scope and spirit of the principles disclosed herein.

Claims

1. A method for crystallizing lithium salts, characterized in that, A lithium deposition reactor with two layers of ultrasonic generators arranged diagonally inside the reactor body includes the following steps: Turn on the ultrasonic generator and adjust the ultrasonic frequency to 20-150KHz. Sodium carbonate and lithium sulfate solutions were added to the lithium precipitation vessel using a "reverse addition method"; Continue the ultrasonic reaction until it ends, then turn off the ultrasonic generator. Lithium carbonate was obtained by solid-liquid separation.

2. The lithium salt crystallization method according to claim 1, characterized in that, The two ultrasonic generators are an upper ultrasonic generator and a lower ultrasonic generator. The lower edge of the upper ultrasonic generator is located at 1 / 2 of the reactor body; the upper edge of the lower ultrasonic generator is located at 1 / 2 of the reactor body.

3. The lithium salt crystallization method according to claim 1, characterized in that, The upper and lower ultrasonic generators can rotate inside the reactor, with a rotation angle of 0 to 90°.

4. The lithium salt crystallization method according to claim 3, characterized in that, Both the upper and lower ultrasonic generators are movably connected to the ultrasonic connecting pipe 7 and rotate around the connection point; the ultrasonic connecting pipe 7 is fixedly connected to the kettle lid and the upper end of the ultrasonic connecting pipe 7 penetrates through the kettle lid.

5. The lithium salt crystallization method according to claim 1, characterized in that, The lithium sulfate solution is measured by the lithium ion concentration in Li2O, where Li2O = 40–55 g / L.

6. The lithium salt crystallization method according to claim 5, characterized in that, The lithium sulfate solution is measured by the lithium ion concentration in Li2O, where Li2O = 45–50 g / L.

7. The lithium salt crystallization method according to claim 1, characterized in that, The ultrasonic frequency is 100-150 kHz.

8. The lithium salt crystallization method according to claim 1, characterized in that, The molar ratio of sodium carbonate to lithium sulfate in the lithium precipitation reactor is controlled such that the carbonate ion is 5% in excess of the lithium ion.

9. The lithium salt crystallization method according to claim 6, characterized in that, Use 5-20m 3 The ultrasonic treatment in the lithium deposition vessel lasts for 2 to 4 hours.

Images