A method for selectively separating lithium from impurities by multi-stage gradient carbon dioxide stripping

Abstract

The application provides a method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back extraction, comprising the following steps: subjecting a lithium-containing organic phase to N-stage carbon dioxide back extraction, wherein N>=2; in the N-stage carbon dioxide back extraction, the partial pressure of carbon dioxide is increased step by step; collecting lithium-containing back extraction liquid obtained by first-stage carbon dioxide back extraction; collecting impurity-containing back extraction liquid generated in stages other than the first-stage carbon dioxide back extraction, and subjecting the impurity-containing back extraction liquid to impurity removal treatment or recycling extraction and back extraction. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back extraction can directly obtain lithium bicarbonate solution with higher purity by designing gradient CO2 partial pressure in carbon dioxide back extraction, and most of the calcium, magnesium and other impurities are retained in subsequent stages, so that lithium bicarbonate solution with a purity of greater than or equal to 95% is obtained, and the amount of impurity removal agent can be greatly reduced when the impurity-containing back extraction liquid obtained subsequently is deeply removed.

Description

Technical Field

[0001] This invention belongs to the field of lithium extraction and impurity removal technology, and relates to a method for selectively separating lithium and impurities through multi-stage gradient carbon dioxide back-extraction. Background Technology

[0002] With the development of the new energy field, the use of lithium-ion batteries is gradually increasing, thus leading to a growing demand for lithium. Solvent extraction is a common method for extracting lithium from solutions such as ore brine, salt lake brine, oil and gas field brine, and lithium precipitation mother liquor in recent years. Specifically, it utilizes the unique extraction properties of organic solvents to achieve lithium extraction. However, during solvent extraction, metallic elements such as sodium and magnesium are still extracted along with the lithium. During back-extraction, these metallic elements still enter the back-extraction solution, making the subsequent preparation of high-purity lithium carbonate difficult. Furthermore, back-extraction mainly uses strongly acidic solutions such as hydrochloric acid or sulfuric acid, which is not only costly but also severely corrodes equipment made of stainless steel and other metal materials, posing safety hazards.

[0003] In existing technologies, a solution formed from carbon dioxide and water is used as the stripping agent to strip lithium-containing organic phases, yielding a stripping residue containing lithium bicarbonate. This avoids the corrosion of equipment caused by strong acid stripping. However, the stripping residue still contains a high level of impurities, which can easily co-precipitate during the subsequent pyrolysis of lithium bicarbonate to produce lithium carbonate, affecting product purity. Furthermore, to achieve high purity, a resin impurity removal or solvent washing process is required after stripping, increasing the number of process steps and costs.

[0004] Therefore, how to achieve selective separation of lithium ions and co-extracted metal impurity ions during carbon dioxide back-extraction, and how to directly obtain a higher purity lithium bicarbonate solution without adding an extra impurity removal process, are problems that need to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for selectively separating lithium and impurities through multi-stage gradient carbon dioxide back-extraction. The method designs a gradient CO2 partial pressure during carbon dioxide back-extraction. The first stage preferentially back-extracts lithium bicarbonate solution with a lithium purity ≥95%, while most impurities such as calcium and magnesium are retained in subsequent stages, thereby directly obtaining a higher purity lithium bicarbonate solution. When the subsequent back-extraction solution containing impurities is deeply purified, the amount of impurity removal agent can be significantly reduced.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a method for selectively separating lithium and impurities using multi-stage gradient carbon dioxide back-extraction, the method comprising the following steps:

[0008] The lithium-containing organic phase is subjected to N-stage carbon dioxide back-extraction, wherein N≥2, and the partial pressure of carbon dioxide increases step by step during the N-stage carbon dioxide back-extraction process. The lithium-containing back-extraction solution obtained from the first stage of carbon dioxide back-extraction is collected.

[0009] Collect the back-extraction liquid containing impurities generated in stages other than the first stage of carbon dioxide back-extraction, and perform impurity removal treatment or recycle it for extraction and back-extraction.

[0010] The method described in this invention employs a multi-stage series back-extraction process, using carbon dioxide and water as extractants. The partial pressure of carbon dioxide increases progressively in each stage, ensuring that the first stage is the preferred lithium back-extraction stage, yielding a lithium bicarbonate solution with a lithium purity ≥95%. Most impurities such as calcium and magnesium are retained in subsequent stages. Theoretically, no additional resin purification process is needed to directly obtain a high-purity lithium-rich solution. Pyrolysis of the lithium-containing back-extraction solution obtained in the first stage yields lithium carbonate with a product purity of 99.5%~99.9%, meeting battery-grade requirements, while also reducing the risk of impurity co-precipitation during subsequent pyrolysis. Since the lithium concentration in the impurity-containing back-extraction solution obtained in subsequent stages is significantly reduced, the resin usage and processing load can be significantly reduced during deep resin purification. Furthermore, the high-pressure carbon dioxide tail gas from the final stage of back-extraction can be recovered and reused in the preceding stages, improving overall carbon dioxide utilization efficiency. This invention also allows for flexible adjustment of the number of back-extraction stages and the partial pressure of carbon dioxide in each stage based on the composition of organic phase impurities in different raw materials.

[0011] In this invention, the organic phase exiting the final stage of the back-extraction process is a regenerated blank organic phase, which is returned to the extraction process for recycling.

[0012] The present invention states that N≥2, for example, can be 2, 3, 4, 5 or 6, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. Preferably, it is 2 to 5, and more preferably, it is 2 to 3.

[0013] Preferably, in the N-stage carbon dioxide back-extraction process, each stage is independently introduced with a back-extraction agent, which includes carbon dioxide and pure water.

[0014] In this invention, the aqueous phase used in each stage of back-extraction can be fresh pure water or the back-extraction solution from the later stage can be circulated back to achieve countercurrent operation.

[0015] Preferably, in the N-stage carbon dioxide back-extraction process, the carbon dioxide partial pressure used in the first stage of carbon dioxide back-extraction is 0.01MPa to 0.1MPa, for example, it can be 0.01MPa, 0.03MPa, 0.05MPa, 0.07MPa, 0.09MPa or 0.1MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.03MPa to 0.06MPa.

[0016] Preferably, in the N-stage carbon dioxide back-extraction process, the partial pressure of carbon dioxide used in the i-th stage of carbon dioxide back-extraction is 0.05MPa to 0.5MPa, for example, it can be 0.05MPa, 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa, where i=2 to N-1 (in this case, N>2).

[0017] Preferably, in the N-stage carbon dioxide back-extraction process, the partial pressure of carbon dioxide used in the Nth stage of carbon dioxide back-extraction is 0.1MPa to 1.0MPa, for example, it can be 0.1MPa, 0.3MPa, 0.5MPa, 0.7MPa, 0.8MPa or 1MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 0.2MPa to 0.8MPa.

[0018] Preferably, during the N-stage carbon dioxide back-extraction process, the back-extraction temperature increases progressively in each stage.

[0019] During the back-extraction process of this invention, the temperature of the back-extraction is gradually increased in stages in combination with the partial pressure of carbon dioxide, which can further improve the gradient extraction effect and increase the lithium purity in the lithium-containing back-extraction solution obtained in the first stage.

[0020] Preferably, when N=2, the partial pressure of carbon dioxide used in the first stage of carbon dioxide back-extraction is 0.03MPa~0.08MPa, for example, it can be 0.03MPa, 0.04MPa, 0.05MPa, 0.06MPa, 0.07MPa or 0.08MPa; the temperature is 15℃~35℃, for example, it can be 15℃, 20℃, 25℃, 30℃ or 35℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0021] Preferably, when N=2, the carbon dioxide partial pressure used in the second stage of carbon dioxide back-extraction is 0.2MPa~0.5MPa, for example, 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa; the temperature is 35℃~50℃, for example, 35℃, 40℃, 45℃ or 50℃, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0022] Preferably, when N=3, the partial pressure of carbon dioxide used in the first stage of carbon dioxide back-extraction is 0.01MPa~0.05MPa (0.05MPa when different from the partial pressure of carbon dioxide in the second stage), for example, it can be 0.01MPa, 0.02MPa, 0.03MPa, 0.04MPa or 0.05MPa; the temperature is 15℃~35℃ (35℃ when different from the temperature in the second stage), for example, it can be 15℃, 20℃, 25℃, 30℃ or 35℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0023] Preferably, when N=3, the carbon dioxide partial pressure used in the second stage of carbon dioxide back-extraction is 0.05MPa~0.15MPa, for example, it can be 0.05MPa, 0.07MPa, 0.09MPa, 0.10MPa, 0.12MPa, 0.14MPa or 0.15MPa; the temperature is 35℃~50℃, for example, it can be 35℃, 40℃, 45℃ or 50℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0024] Preferably, when N=3, the carbon dioxide partial pressure used in the third stage of carbon dioxide back-extraction is 0.4MPa~0.8MPa, for example, 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa or 0.8MPa; the temperature is 35℃~50℃, for example, 35℃, 40℃, 45℃ or 50℃, but not limited to the listed values, other unlisted values ​​within the range are also applicable.

[0025] When N=3, the first stage of carbon dioxide back-extraction preferentially back-extracts Li. + The Li back-extraction rate reaches 40-70%. During the second stage of carbon dioxide back-extraction, the residual Li continues to be back-extracted. + and some Na + K + During the third stage of carbon dioxide back-extraction, Ca is back-extracted. 2+ Mg 2+ and residual impurities.

[0026] Preferably, in the N-stage carbon dioxide back-extraction process, the contact time of each back-extraction stage is 5 min to 60 min, for example, it can be 5 min, 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably 10 min to 30 min.

[0027] Preferably, in the N-stage carbon dioxide back-extraction process, the O / A ratio of each back-extraction stage is (1~20):1, for example, it can be 1:1, 5:1, 10:1, 15:1 or 20:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable, preferably (3~10):1.

[0028] Preferably, in the N-stage carbon dioxide back-extraction process, carbon dioxide is introduced into the back-extraction system in the form of microbubble aeration.

[0029] The carbon dioxide described in this invention is introduced into the back-extraction system in the form of microbubble aeration, which can enhance the gas-liquid-liquid three-phase mass transfer efficiency. Each section of the back-extractor can be equipped with an independent temperature control system and pressure regulating valve.

[0030] Preferably, the lithium concentration in the lithium-containing organic phase is 0.5 g / L to 3 g / L, for example, it can be 0.5 g / L, 1 g / L, 2 g / L or 3 g / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The lithium-containing organic phase described in this invention is a lithium-loaded organic phase obtained through an extraction process, and also contains co-extracted impurity metal ions.

[0032] Preferably, the lithium-containing organic phase includes lithium ions and impurity ions, wherein the impurity ions include Na+. + K + Ca 2+ or Mg 2+ Any one or at least two of them.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) Significantly improved lithium selectivity: Through gradient CO2 partial pressure design, the first stage preferentially back-extracts lithium bicarbonate solution with lithium purity ≥95%, and most of the impurities such as calcium and magnesium are retained in the subsequent stages, eliminating the need for additional resin impurity removal process.

[0035] (2) Improved purity of final lithium carbonate product: Lithium carbonate is prepared by pyrolysis of the first stage lithium-rich liquid, and the product purity can reach 99.5%~99.9%, which meets the battery grade requirements and reduces the risk of impurity co-precipitation during subsequent pyrolysis.

[0036] (3) Reduce resin impurity removal load: The lithium concentration in the back-extraction solution containing impurities obtained in the subsequent stages has been greatly reduced. If deep resin impurity removal is required, the amount of resin and the processing load can be reduced by 40-70%.

[0037] (4) High carbon dioxide utilization rate: The high-pressure CO2 tail gas at the end can be recovered to the front for supplementary use, thus improving the overall CO2 utilization efficiency.

[0038] (5) Flexible operation and strong adaptability: The number of back-extraction sections and the partial pressure of CO2 in each section can be flexibly adjusted according to the composition of organic phase impurities in different raw materials. Detailed Implementation

[0039] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0040] Example 1

[0041] This embodiment provides a method for selectively separating lithium and impurities using multi-stage gradient carbon dioxide back-extraction, the method comprising the following steps:

[0042] (1) Provide a lithium-containing organic phase, wherein the lithium element concentration is 2 g / L (calculated as Li), and also contains Na. + K + Ca 2+ and Mg 2+ ;

[0043] (2) The lithium-containing organic phase described in step (1) is sequentially passed through N series back-extraction sections, where N is 3, including the first carbon dioxide back-extraction, the second carbon dioxide back-extraction and the third carbon dioxide back-extraction performed sequentially. Each back-extraction section is independently introduced with CO2 (in the form of microbubble aeration) and pure water. The contact time of each back-extraction section is 20 min, and the O / A ratio (organic phase / water phase volume ratio) is 7:1.

[0044] The first stage of carbon dioxide back-extraction uses a carbon dioxide partial pressure of 0.03 MPa and a temperature of 35°C.

[0045] The second stage of carbon dioxide back-extraction uses a carbon dioxide partial pressure of 0.12 MPa and a temperature of 40°C.

[0046] The third stage of carbon dioxide back-extraction uses a carbon dioxide partial pressure of 0.6 MPa and a temperature of 50°C.

[0047] The organic phase at the final outlet is a regenerated blank organic phase, which is returned to the extraction process for recycling; the high CO2 partial pressure tail gas generated in the final stage can be recovered and used to supplement the CO2 supply in the preceding stage.

[0048] (3) Collect the lithium-containing back-extraction solution obtained from the first stage of carbon dioxide back-extraction as a lithium-rich lithium bicarbonate solution;

[0049] Collect the back-extraction liquid containing impurities obtained from carbon dioxide back-extraction in stages other than the first stage, and perform resin purification to obtain the purified liquid from the other stages.

[0050] Example 2

[0051] This embodiment provides a method for selectively separating lithium and impurities using multi-stage gradient carbon dioxide back-extraction, the method comprising the following steps:

[0052] (1) Provide a lithium-containing organic phase, wherein the lithium element concentration is 3 g / L (calculated as Li), and also contains Na. + K + Ca 2+ and Mg 2+ ;

[0053] (2) The lithium-containing organic phase described in step (1) is sequentially passed through N series back-extraction sections, where N is 3, including the first carbon dioxide back-extraction, the second carbon dioxide back-extraction and the third carbon dioxide back-extraction performed sequentially. Each back-extraction section is independently introduced with CO2 (in the form of microbubble aeration) and pure water. The contact time of each back-extraction section is 30 min, and the O / A ratio (organic phase / water phase volume ratio) is 10:1.

[0054] The first stage of carbon dioxide back-extraction uses a carbon dioxide partial pressure of 0.05 MPa and a temperature of 15°C.

[0055] The second stage of carbon dioxide back-extraction uses a carbon dioxide partial pressure of 0.15 MPa and a temperature of 35°C.

[0056] The third stage of carbon dioxide back-extraction uses a carbon dioxide partial pressure of 0.5 MPa and a temperature of 50°C.

[0057] The organic phase at the final outlet is a regenerated blank organic phase, which is returned to the extraction process for recycling; the high CO2 partial pressure tail gas generated in the final stage can be recovered and used to supplement the CO2 supply in the preceding stage.

[0058] (3) Collect the lithium-containing back-extraction solution obtained from the first stage of carbon dioxide back-extraction as a lithium-rich lithium bicarbonate solution;

[0059] Collect the back-extraction liquid containing impurities obtained from carbon dioxide back-extraction in stages other than the first stage, and perform resin purification to obtain the purified liquid from the other stages.

[0060] Example 3

[0061] This embodiment provides a method for selectively separating lithium and impurities using multi-stage gradient carbon dioxide back-extraction. Except for step (2) where N=2, the method includes a first stage of carbon dioxide back-extraction and a second stage of carbon dioxide back-extraction performed sequentially. The carbon dioxide partial pressure used in the first stage of carbon dioxide back-extraction is 0.05 MPa and the temperature is 25°C. The carbon dioxide partial pressure used in the second stage of carbon dioxide back-extraction is 0.35 MPa and the temperature is 50°C. All other aspects are the same as in Example 1.

[0062] Example 4

[0063] This embodiment provides a method for selectively separating lithium and impurities using multi-stage gradient carbon dioxide back-extraction. Except for step (2) where N=2, the method includes a first stage of carbon dioxide back-extraction and a second stage of carbon dioxide back-extraction performed sequentially. The carbon dioxide partial pressure used in the first stage of carbon dioxide back-extraction is 0.03 MPa and the temperature is 25°C. The carbon dioxide partial pressure used in the second stage of carbon dioxide back-extraction is 0.5 MPa and the temperature is 50°C. All other aspects are the same as in Example 1.

[0064] Example 5

[0065] This embodiment provides a method for selectively separating lithium and impurities using multi-stage gradient carbon dioxide back-extraction. Except for step (2), in which the partial pressure of carbon dioxide used in the first stage of carbon dioxide back-extraction is 0.1 MPa, the method is the same as in embodiment 1.

[0066] Example 6

[0067] This embodiment provides a method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction. Except for step (2), where the temperature of the first stage carbon dioxide back-extraction, the second stage carbon dioxide back-extraction, and the third stage carbon dioxide back-extraction is 40°C, the method is the same as in embodiment 1.

[0068] Comparative Example 1

[0069] This comparative example provides a method for selectively separating lithium and impurities by carbon dioxide back-extraction. Except for step (2), in which the partial pressure of carbon dioxide used in the first, second and third stages of carbon dioxide back-extraction is the same and the partial pressure of carbon dioxide is 0.15 MPa, the rest of the method is the same as in Example 1.

[0070] In the above examples and comparative examples, the lithium back-extraction rate in the first stage of carbon dioxide back-extraction and the total calcium and magnesium back-extraction rate in other back-extraction stages are shown in Table 1:

[0071] Table 1

[0072]

[0073] As can be seen from Table 1 above:

[0074] As can be seen from Examples 1-4 and Comparative Example 1, the present invention employs a gradient carbon dioxide partial pressure design during multi-stage carbon dioxide back-extraction, which can improve the back-extraction rates of lithium and impurities respectively. As can be seen from Examples 1 and 5, the carbon dioxide partial pressure used in the first stage of carbon dioxide back-extraction in the present invention will affect the back-extraction rate of the lithium-containing back-extraction solution, preferably within a specific range. As can be seen from Examples 1 and 6, the present invention preferably increases the back-extraction temperature step by step, which can further improve the gradient back-extraction effect and increase the purity of the final solution.

[0075] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for selectively separating lithium and impurities using multi-stage gradient carbon dioxide back-extraction, characterized in that, The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction includes the following steps: The lithium-containing organic phase is subjected to N-stage carbon dioxide back-extraction, wherein N≥2, and the partial pressure of carbon dioxide increases step by step during the N-stage carbon dioxide back-extraction process. The lithium-containing back-extraction solution obtained from the first stage of carbon dioxide back-extraction is collected. Collect the back-extraction liquid containing impurities generated in stages other than the first stage of carbon dioxide back-extraction, and perform impurity removal treatment or recycle it for extraction and back-extraction.

2. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction according to claim 1, characterized in that, The value of N is 2 to 5; Preferably, in the N-stage carbon dioxide back-extraction process, each stage is independently introduced with a back-extraction agent, which includes carbon dioxide and pure water.

3. The method for selectively separating lithium and impurities using multi-stage gradient carbon dioxide back-extraction according to claim 1 or 2, characterized in that, In the N-stage carbon dioxide back-extraction process, the carbon dioxide partial pressure used in the first stage of carbon dioxide back-extraction is 0.01MPa~0.1MPa, preferably 0.03MPa~0.06MPa; Preferably, in the N-stage carbon dioxide back-extraction process, the partial pressure of carbon dioxide used in the i-th stage of carbon dioxide back-extraction is 0.05MPa~0.5MPa, where i=2 to N-1, and N is greater than 2. Preferably, in the N-stage carbon dioxide back-extraction process, the partial pressure of carbon dioxide used in the N-stage carbon dioxide back-extraction is 0.1 MPa to 1.0 MPa, more preferably 0.2 MPa to 0.8 MPa.

4. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction according to claim 1 or 2, characterized in that, During the N-stage carbon dioxide back-extraction process, the back-extraction temperature increases progressively in each stage.

5. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction according to claim 1 or 2, characterized in that, When N=2, the carbon dioxide partial pressure used in the first stage of carbon dioxide back-extraction is 0.03MPa~0.08MPa, and the temperature is 15℃~35℃. Preferably, when N=2, the carbon dioxide partial pressure used in the second stage of carbon dioxide back-extraction is 0.2MPa~0.5MPa, and the temperature is 35℃~50℃.

6. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction according to claim 1 or 2, characterized in that, When N=3, the carbon dioxide partial pressure used in the first stage of carbon dioxide back-extraction is 0.01MPa~0.05MPa, and the temperature is 15℃~35℃. Preferably, when N=3, the carbon dioxide partial pressure used in the second stage of carbon dioxide back-extraction is 0.05MPa~0.15MPa, and the temperature is 35℃~50℃; Preferably, when N=3, the carbon dioxide partial pressure used in the third stage of carbon dioxide back-extraction is 0.4MPa~0.8MPa, and the temperature is 35℃~50℃.

7. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction according to claim 1 or 2, characterized in that, During the N-stage carbon dioxide back-extraction process, the contact time for each stage of back-extraction is 5 min to 60 min, preferably 10 min to 30 min; Preferably, in the N-stage carbon dioxide back-extraction process, the O / A ratio of each back-extraction stage is (1~20):1, more preferably (3~10):

1.

8. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction according to claim 1 or 2, characterized in that, In the N-stage carbon dioxide back-extraction process, carbon dioxide is introduced into the back-extraction system in the form of microbubble aeration.

9. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction according to claim 1 or 2, characterized in that, The lithium-containing organic phase has a lithium concentration of 0.5 g / L to 3 g / L.

10. The method for selectively separating lithium and impurities by multi-stage gradient carbon dioxide back-extraction according to claim 1 or 2, characterized in that, The lithium-containing organic phase includes lithium ions and impurity ions, wherein the impurity ions include Na. + K + Ca 2+ or Mg 2+ Any one or at least two of them.

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