System and method for recovering lithium ions from a lithium sink solution

Abstract

This invention discloses a system and method for recovering lithium ions from lithium precipitation mother liquor. The system includes a primary nanofiltration unit, a secondary nanofiltration unit, a tertiary nanofiltration unit, and an extraction unit. The primary nanofiltration unit is used to nanofiltration the lithium precipitation mother liquor. The secondary inlet is connected to the outlet of the primary nanofiltration concentrate. The secondary nanofiltration unit is used to nanofiltration the primary nanofiltration concentrate. The tertiary inlet is connected to the outlets of the primary and secondary nanofiltration permeate. The tertiary nanofiltration unit is used to nanofiltration the primary and secondary nanofiltration permeate. The extraction unit is connected to the outlet of the tertiary nanofiltration permeate and is used to extract lithium ions from the tertiary nanofiltration permeate. This invention achieves the recovery of lithium ions from lithium precipitation mother liquor, avoiding the waste of lithium ions caused by directly discharging the mother liquor into salt fields. This is beneficial to the sustainable development and utilization of salt lake resources and can also reduce the production cost of lithium carbonate.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, and in particular to a system and method for recovering lithium ions from lithium precipitation mother liquor. Background Technology

[0002] Lithium carbonate is an important lithium salt. Currently, the lithium carbonate production process involves obtaining a lithium-rich solution through a salt lake extraction process, followed by impurity removal and precipitation with sodium carbonate. After washing and drying, the lithium carbonate product is obtained. The lithium-rich solution remaining after lithium carbonate precipitation is known as the lithium precipitation mother liquor. Due to the limited solubility of lithium carbonate, the lithium precipitation mother liquor produced in existing domestic lithium carbonate production processes contains approximately 20% lithium ions. Recovering this portion of lithium can effectively improve the lithium recovery rate.

[0003] However, due to limitations in current technology, existing technologies cannot effectively recover lithium ions from lithium precipitation mother liquor, resulting in most of the mother liquor being directly discharged into salt fields for storage, which wastes lithium ions and is detrimental to the sustainable development and utilization of salt lake resources. Summary of the Invention

[0004] This invention provides a system and method for recovering lithium ions from lithium precipitation mother liquor, thereby overcoming the deficiencies in the prior art, realizing the recovery of lithium ions from lithium precipitation mother liquor, and avoiding the waste of lithium ions caused by directly discharging lithium precipitation mother liquor into salt fields.

[0005] In a first aspect, the present invention provides a system for recovering lithium ions from lithium precipitation mother liquor, comprising: a primary nanofiltration device, a secondary nanofiltration device, a tertiary nanofiltration device, and an extraction device;

[0006] The primary nanofiltration unit includes a primary water inlet, a primary nanofiltration concentrate outlet, and a primary nanofiltration permeate outlet; the primary nanofiltration unit is used to perform nanofiltration on the lithium precipitation mother liquor; the primary nanofiltration concentrate outlet is used to discharge the primary nanofiltration concentrate; and the primary nanofiltration permeate outlet is used to discharge the primary nanofiltration permeate.

[0007] The secondary nanofiltration device includes a secondary inlet, a secondary nanofiltration concentrate outlet, and a secondary nanofiltration permeate outlet; the secondary inlet is connected to the primary nanofiltration concentrate outlet; the secondary nanofiltration device is used to perform nanofiltration on the primary nanofiltration concentrate; the secondary nanofiltration concentrate outlet is used to discharge the secondary nanofiltration concentrate; and the secondary nanofiltration permeate outlet is used to discharge the secondary nanofiltration permeate.

[0008] The three-stage nanofiltration device includes a three-stage inlet, a three-stage nanofiltration concentrate outlet, and a three-stage nanofiltration permeate outlet; the three-stage inlet is connected to the first-stage nanofiltration permeate outlet and the second-stage nanofiltration permeate outlet; the three-stage nanofiltration device is used to perform nanofiltration on the first-stage and second-stage nanofiltration permeates; the three-stage nanofiltration concentrate outlet is used to discharge the three-stage nanofiltration concentrate; the three-stage nanofiltration permeate outlet is used to discharge the three-stage nanofiltration permeate.

[0009] The extraction device is connected to the outlet of the three-stage nanofiltration permeate; the extraction device is used to extract lithium ions from the three-stage nanofiltration permeate.

[0010] Optionally, the outlet of the three-stage nanofiltration concentrate is connected to the inlet of the first-stage water.

[0011] Optionally, the lithium ion recovery system of the lithium precipitation mother liquor further includes: a first tank, the outlet of the first tank being connected to the primary inlet; the first tank is used to mix the initial lithium precipitation mother liquor of each production line evenly to obtain lithium precipitation mother liquor.

[0012] Optionally, the system for recovering lithium ions from lithium precipitation mother liquor further includes: a second tank and at least one heat exchanger;

[0013] The inlet of each heat exchanger is connected to the outlet of the first tank; the outlet of each heat exchanger is connected to the inlet of the second tank; the heat exchangers are used to cool the lithium precipitation mother liquor.

[0014] The outlet of the second tank is connected to the inlet of the first stage; the second tank is used to mix the cooled lithium mother liquor evenly.

[0015] Optionally, the system for recovering lithium ions from lithium precipitation mother liquor further includes: a third tank;

[0016] The inlet of the third tank is connected to the outlet of the first-stage nanofiltration permeate and the outlet of the second-stage nanofiltration permeate; the outlet of the third tank is connected to the tertiary inlet; the third tank is used to mix the first-stage nanofiltration permeate and the second-stage nanofiltration permeate evenly.

[0017] Optionally, the extraction device includes multiple extraction sub-devices connected in series; the inlet of the first-stage extraction sub-device is connected to the outlet of the third-stage nanofiltration permeate; in any two adjacent extraction sub-devices, the inlet of the latter extraction sub-device is connected to the outlet of the former extraction sub-device.

[0018] Optionally, the system for recovering lithium ions from lithium precipitation mother liquor further includes: a back-extraction device;

[0019] The lithium extractant outlet of the final stage extraction sub-device is connected to the back-extraction device.

[0020] Secondly, the present invention also provides a method for recovering lithium ions from lithium precipitation mother liquor, implemented based on the system for recovering lithium ions from lithium precipitation mother liquor described in any of the above claims, wherein the method for recovering lithium ions from lithium precipitation mother liquor includes:

[0021] The lithium precipitation mother liquor is pumped into a first-stage nanofiltration unit to obtain first-stage nanofiltration concentrate and first-stage nanofiltration permeate;

[0022] The primary nanofiltration concentrate and pure water are mixed in a preset ratio and then pumped into a secondary nanofiltration device to obtain secondary nanofiltration concentrate and secondary nanofiltration permeate.

[0023] The primary nanofiltration permeate and the secondary nanofiltration permeate are pumped into a tertiary nanofiltration unit to obtain tertiary nanofiltration concentrate and tertiary nanofiltration permeate.

[0024] Lithium ions in the three-stage nanofiltration permeate are extracted to obtain a lithium ion solution.

[0025] Optionally, the method for recovering lithium ions from lithium precipitation mother liquor further includes:

[0026] The three-stage nanofiltration concentrate is pumped into the first-stage nanofiltration unit to obtain the first-stage nanofiltration concentrate and the first-stage nanofiltration permeate.

[0027] Optionally, before pumping the lithium precipitation mother liquor into the primary nanofiltration unit to obtain the primary nanofiltration concentrate and primary nanofiltration permeate, the method further includes:

[0028] The initial mother liquor of lithium precipitation from each production line is recovered into the first tank to mix the initial mother liquor of lithium precipitation from each production line evenly, thereby obtaining the lithium precipitation mother liquor.

[0029] Optionally, before pumping the lithium precipitation mother liquor into the primary nanofiltration unit to obtain the primary nanofiltration concentrate and primary nanofiltration permeate, the method further includes:

[0030] The lithium precipitation mother liquor is cooled to reduce its temperature to below a preset temperature.

[0031] Optionally, the lithium precipitation mother liquor is cooled to a temperature below a preset temperature, including:

[0032] The lithium precipitated mother liquor is pumped into at least one heat exchanger to cool it down.

[0033] The cooled lithium precipitate mother liquor is pumped into the second tank to mix it evenly.

[0034] Optionally, before pumping the primary nanofiltration permeate and the secondary nanofiltration permeate into the tertiary nanofiltration unit to obtain the tertiary nanofiltration concentrate and the tertiary nanofiltration permeate, the method further includes:

[0035] The primary nanofiltration permeate and the secondary nanofiltration permeate are recycled to a third tank to ensure that the primary nanofiltration permeate and the secondary nanofiltration permeate are mixed evenly.

[0036] Optionally, lithium ions in the three-stage nanofiltration permeate are extracted to obtain a lithium ion solution, comprising:

[0037] The three-stage nanofiltration permeate is pumped into a multi-stage series extraction device for extraction to obtain the extraction residue and lithium extractant containing lithium ions.

[0038] The lithium extractant containing lithium ions is back-extracted using a back-extraction agent to obtain the lithium ion solution.

[0039] Optionally, the method for recovering lithium ions from lithium precipitation mother liquor further includes:

[0040] An adsorbent is used to adsorb the residual extract to remove the emulsified lithium extractant from the residual extract.

[0041] Optionally, after back-extracting the lithium extractant containing lithium ions using a back-extraction agent to obtain the lithium ion solution, the method further includes:

[0042] The lithium extractant after back-extraction is filtered through a ceramic membrane to recover the lithium extractant.

[0043] Optionally, the preset ratio is 1.

[0044] The technical solution of this invention connects the nanofiltration concentrate outlet of the primary nanofiltration unit to the secondary inlet, the primary and secondary nanofiltration permeate outlets to the tertiary inlet, and the tertiary nanofiltration permeate outlet to the extraction unit. This allows the primary nanofiltration unit to produce primary nanofiltration permeate and primary nanofiltration concentrate after nanofiltration of the lithium precipitation mother liquor. The primary nanofiltration concentrate outlet discharges the primary nanofiltration concentrate to the secondary nanofiltration unit for further nanofiltration, and the primary nanofiltration permeate outlet discharges the primary nanofiltration permeate to the tertiary nanofiltration unit for further nanofiltration. After the secondary nanofiltration unit nanofiltrations the primary nanofiltration concentrate, the secondary nanofiltration permeate outlet discharges the secondary nanofiltration permeate to the tertiary nanofiltration unit for further nanofiltration. The permeate is discharged to a three-stage nanofiltration unit for further nanofiltration. After the first-stage and second-stage nanofiltration permeates are filtered, the third-stage nanofiltration permeate is discharged to an extraction unit. This allows the lithium precipitation mother liquor to pass through three stages of nanofiltration to obtain a lithium and sodium ion solution free of carbonate ions. The resulting lithium and sodium ion solution is then extracted using an extraction unit to obtain a pure lithium ion solution. This process recovers lithium ions from the lithium precipitation mother liquor, avoiding the waste of lithium ions caused by directly discharging the mother liquor into the salt field. This is beneficial for the sustainable development and utilization of salt lake resources and can also reduce the production cost of lithium carbonate.

[0045] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of a system for recovering lithium ions from lithium precipitation mother liquor, provided in an embodiment of the present invention.

[0048] Figure 2 This is a schematic diagram of another lithium ion recovery system provided in an embodiment of the present invention;

[0049] Figure 3 This is a schematic diagram of the structure of another lithium ion recovery system provided in an embodiment of the present invention;

[0050] Figure 4 This is a flowchart of a method for recovering lithium ions from lithium precipitation mother liquor, provided as an embodiment of the present invention. Detailed Implementation

[0051] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0052] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0053] Figure 1 This is a schematic diagram of a system for recovering lithium ions from lithium precipitation mother liquor, provided in an embodiment of the present invention. (Refer to...) Figure 1As shown in the embodiment of the present invention, the system for recovering lithium ions from lithium precipitation mother liquor includes: a primary nanofiltration device 1, a secondary nanofiltration device 2, a tertiary nanofiltration device 3, and an extraction device 4; the primary nanofiltration device 1 includes a primary inlet 11, a primary nanofiltration concentrate outlet 12, and a primary nanofiltration permeate outlet 13; the primary nanofiltration device 1 is used to perform nanofiltration on the lithium precipitation mother liquor; the primary nanofiltration concentrate outlet 12 is used to discharge the primary nanofiltration concentrate; the primary nanofiltration permeate outlet 13 is used to discharge the primary nanofiltration permeate; the secondary nanofiltration device 2 includes a secondary inlet 21, a secondary nanofiltration concentrate outlet 22, and a secondary nanofiltration permeate outlet 23; the secondary inlet 21 is connected to the primary nanofiltration concentrate outlet 12; the secondary nanofiltration device 2 is used to process the primary nanofiltration concentrate... The condensate is subjected to nanofiltration; the secondary nanofiltration concentrate outlet 22 is used to discharge the secondary nanofiltration concentrate; the secondary nanofiltration permeate outlet 23 is used to discharge the secondary nanofiltration permeate; the tertiary nanofiltration unit 3 includes a tertiary inlet 31, a tertiary nanofiltration concentrate outlet 32, and a tertiary nanofiltration permeate outlet 33; the tertiary inlet 31 is connected to the primary nanofiltration permeate outlet 13 and the secondary nanofiltration permeate outlet 23; the tertiary nanofiltration unit 3 is used to perform nanofiltration on the primary and secondary nanofiltration permeates; the tertiary nanofiltration concentrate outlet 32 ​​is used to discharge the tertiary nanofiltration concentrate; the tertiary nanofiltration permeate outlet 33 is used to discharge the tertiary nanofiltration permeate; the extraction unit 4 is connected to the tertiary nanofiltration permeate outlet 33; the extraction unit 4 is used to extract lithium ions from the tertiary nanofiltration permeate.

[0054] The lithium precipitation mother liquor is the mother liquor produced in the lithium carbonate production process, and its main components include carbonate ions, sodium ions, and lithium ions. Nanofiltration membrane modules are installed in the primary nanofiltration unit 1, the secondary nanofiltration unit 2, and the tertiary nanofiltration unit 3. Each nanofiltration module includes at least one nanofiltration membrane. Because the nanofiltration membrane allows low-valence ions to pass through while retaining high-valence ions, lithium ions and sodium ions can pass through the nanofiltration membrane, while carbonate ions cannot. It should be noted that the nanofiltration membrane modules in the primary nanofiltration unit 1, the secondary nanofiltration unit 2, and the tertiary nanofiltration unit 3 can be the same or different. This embodiment does not specifically limit this, as long as the inventive point of this embodiment can be achieved. The extraction device 4 contains a selective lithium extractant for extracting lithium ions. In an optional embodiment, the selective lithium extractant is a fluorodiketone.

[0055] It is understood that the primary nanofiltration unit is used to nanofiltration lithium precipitation mother liquor, which contains a high content of carbonate and lithium ions. Therefore, the operating pressure of the primary nanofiltration unit 1 can be higher than that of the secondary nanofiltration unit 2 and / or the tertiary nanofiltration unit 3 to improve nanofiltration efficiency. In one optional embodiment, the operating pressure range of the primary nanofiltration unit 1 is 2.0–4.0 MPa; in another optional embodiment, the operating pressure range of the secondary nanofiltration unit 2 is 2.5–4.0 MPa.

[0056] The first-stage nanofiltration concentrate is the solution retained by the first-stage nanofiltration unit 1, and the first-stage nanofiltration permeate is the solution permeated by the first-stage nanofiltration unit 1; the second-stage nanofiltration concentrate is the solution retained by the second-stage nanofiltration unit 2, and the second-stage nanofiltration permeate is the solution permeated by the second-stage nanofiltration unit 2; the third-stage nanofiltration concentrate is the solution retained by the third-stage nanofiltration unit 3, and the third-stage nanofiltration permeate is the solution permeated by the third-stage nanofiltration unit 3.

[0057] After the lithium precipitation mother liquor is nanofiltered by the primary nanofiltration unit 1, the resulting primary nanofiltration concentrate still contains a significant amount of lithium ions. Therefore, it can be pumped into the secondary nanofiltration unit 2 to further filter the primary nanofiltration concentrate, thereby improving the lithium ion recovery rate. After the primary nanofiltration concentrate is filtered by the secondary nanofiltration unit 2, i.e., after the lithium precipitation mother liquor undergoes two nanofiltrations, the resulting secondary nanofiltration concentrate contains only a small amount of lithium ions. At this point, considering the lithium ion recovery rate and recovery cost, further nanofiltration of the secondary nanofiltration concentrate is unnecessary. It should be noted that if a higher lithium ion recovery rate is required, the secondary nanofiltration concentrate can be pumped into other nanofiltration units for further nanofiltration to improve the lithium ion recovery rate. In an exemplary embodiment, the primary nanofiltration unit 1 can achieve a lithium ion recovery rate of greater than or equal to 60%, meaning that 60% of the lithium ions in the lithium precipitation mother liquor permeate through the primary nanofiltration unit 1 and dissolve in the primary nanofiltration permeate, and more than 90% of the carbonate ions are retained in the primary nanofiltration concentrate. In another exemplary embodiment, the secondary nanofiltration device 2 can achieve a lithium ion recovery rate of greater than or equal to 85%, and the concentration of carbonate ions in the secondary nanofiltration concentrate is as high as 50 g / L or more. Since the secondary nanofiltration concentrate contains a high concentration of carbonate ions, it can be used to prepare sodium carbonate solution, thereby reducing the amount of pure water and sodium carbonate raw materials required for preparing sodium carbonate in the lithium carbonate production process.

[0058] In an optional embodiment, when pumping the primary nanofiltration concentrate into the secondary nanofiltration unit 2, the nanofiltration concentrate and pure water can be mixed in a preset ratio to improve the nanofiltration efficiency of the secondary nanofiltration unit 2. The preset ratio can be determined based on the lithium-ion recovery rate and recovery cost. A higher preset ratio results in lower recovery costs and a lower lithium-ion recovery rate; conversely, a lower preset ratio results in higher lithium-ion recovery rates but also higher recovery costs. Optionally, the preset ratio can be 1.

[0059] The primary and secondary nanofiltration permeate mainly contains lithium and sodium ions, with a small amount of carbonate ions. Therefore, the primary and secondary nanofiltration permeate can be pumped into the tertiary nanofiltration unit 3 for further nanofiltration to improve the purity of the recovered lithium ions. In another exemplary embodiment, after the primary and secondary nanofiltration permeate are nanofiltered by the tertiary nanofiltration unit 3, the carbonate ion content in the resulting tertiary nanofiltration permeate is less than 500 ppm, thereby reducing impurities in the extracted lithium ions, improving the purity of the recovered lithium ions, and ensuring process stability.

[0060] Specifically, the lithium precipitation mother liquor is first pumped into the first-stage nanofiltration unit 1 through the first-stage inlet 11 to perform nanofiltration, producing first-stage nanofiltration concentrate and first-stage nanofiltration permeate. The first-stage nanofiltration concentrate is discharged through the first-stage nanofiltration concentrate outlet 12 and then pumped into the second-stage nanofiltration unit 2 through the second-stage inlet 21 to further nanofiltration the first-stage nanofiltration concentrate, producing second-stage nanofiltration concentrate and second-stage nanofiltration permeate. Then, the first-stage nanofiltration permeate and the second-stage nanofiltration permeate are discharged through the first-stage nanofiltration permeate outlet 13 and the second-stage nanofiltration permeate outlet 23, respectively, and then pumped into the third-stage nanofiltration unit 3 through the third-stage inlet 31 to further nanofiltration the first-stage and second-stage nanofiltration permeate, producing third-stage nanofiltration concentrate and third-stage nanofiltration permeate. Finally, the third-stage nanofiltration permeate is discharged through the third-stage nanofiltration permeate outlet 33 and then pumped into the extraction unit 4 to extract lithium ions from the third-stage nanofiltration permeate.

[0061] In this embodiment, by connecting the nanofiltration concentrate outlet of the primary nanofiltration unit to the secondary inlet, connecting the primary and secondary nanofiltration permeate outlets to the tertiary inlet, and connecting the tertiary nanofiltration permeate outlet to the extraction device, the primary nanofiltration unit produces primary nanofiltration permeate and primary nanofiltration concentrate after nanofiltration of the lithium precipitation mother liquor. The primary nanofiltration concentrate outlet discharges the primary nanofiltration concentrate to the secondary nanofiltration unit for further nanofiltration, and the primary nanofiltration permeate outlet discharges the primary nanofiltration permeate to the tertiary nanofiltration unit for further nanofiltration. After the secondary nanofiltration unit nanofiltrations the primary nanofiltration concentrate, the secondary nanofiltration permeate outlet discharges the secondary nanofiltration permeate. The permeate is discharged to a three-stage nanofiltration unit for further nanofiltration. After the first-stage and second-stage nanofiltration permeates are filtered, the third-stage nanofiltration permeate is discharged to an extraction unit. This allows the lithium precipitation mother liquor to pass through three stages of nanofiltration to obtain a lithium and sodium ion solution free of carbonate ions. The resulting lithium and sodium ion solution is then extracted using an extraction unit to obtain a pure lithium ion solution. This process recovers lithium ions from the lithium precipitation mother liquor, avoiding the waste of lithium ions caused by directly discharging the mother liquor into the salt field. This is beneficial for the sustainable development and utilization of salt lake resources and can also reduce the production cost of lithium carbonate.

[0062] Optional, continue to refer to Figure 1As shown, the tertiary nanofiltration concentrate outlet 32 ​​is connected to the primary inlet 11. Since the tertiary nanofiltration concentrate outlet 32 ​​is used to discharge the tertiary nanofiltration concentrate, which still contains a significant amount of lithium ions and carbonate ions, the tertiary nanofiltration concentrate is pumped into the primary nanofiltration unit 1 through the primary inlet 11 for nanofiltration, and then further pumped into the secondary nanofiltration unit 2 and the tertiary nanofiltration unit 3 for further nanofiltration, thereby further improving the recovery rate of lithium ions and, simultaneously, the recovery rate of carbonate ions.

[0063] Optional, Figure 2 This is a schematic diagram of another lithium-ion recovery system from lithium precipitation mother liquor provided in an embodiment of the present invention, with reference to... Figure 2 As shown, the lithium ion recovery system of lithium precipitation mother liquor also includes a first tank 5, the outlet 51 of the first tank is connected to the first-stage inlet 11; the first tank 5 is used to mix the initial lithium precipitation mother liquor of each production line evenly.

[0064] In the lithium carbonate production process, lithium carbonate can be produced through multiple production lines. Due to the differences in the processes of different production lines, the composition ratio of the initial mother liquor for lithium precipitation may vary from line to line. Therefore, the initial mother liquor for lithium precipitation produced by each production line can be recycled to the first tank 5 to ensure that the initial mother liquor for lithium precipitation from each production line is mixed evenly, thereby improving the nanofiltration effect of the nanofiltration device. By connecting the outlet 51 of the first tank to the primary inlet 11, the initial mother liquor for lithium precipitation can be pumped into the first nanofiltration device for nanofiltration.

[0065] Optional, Figure 3 This is a schematic diagram of a system for recovering lithium ions from lithium precipitation mother liquor, provided in an embodiment of the present invention. (Refer to...) Figure 3 As shown, the lithium ion recovery system of lithium precipitation mother liquor also includes: a second tank 6 and at least one heat exchanger 7; the inlet 71 of each heat exchanger is connected to the outlet 51 of the first tank; the outlet 72 of each heat exchanger is connected to the inlet 61 of the second tank; the heat exchanger 7 is used to cool the lithium precipitation mother liquor; the outlet 62 of the second tank is connected to the primary inlet 11; the second tank 6 is used to mix the cooled lithium precipitation mother liquor evenly.

[0066] The heat exchanger 7 is used to cool the lithium precipitated mother liquor. In an optional embodiment, the heat exchanger 7 can be a plate heat exchanger, which can reduce the volume of the lithium ion recovery system from the lithium precipitated mother liquor. Furthermore, plate heat exchangers have high heat exchange efficiency, which is beneficial for rapidly cooling the lithium precipitated mother liquor. It should be noted that... Figure 3This example only illustrates the case where the lithium-ion recovery system from lithium-ion mother liquor includes two heat exchangers 7, and does not limit the number of heat exchangers 7. In this embodiment, the lithium-ion recovery system from lithium-ion mother liquor may also include one heat exchanger 7 or multiple heat exchangers 7. When the lithium-ion recovery system from lithium-ion mother liquor includes multiple heat exchangers 7, the inlet 71 of each heat exchanger is connected to the outlet of the first tank 5, and the outlet 72 of each heat exchanger is connected to the inlet 61 of the second tank.

[0067] Since higher temperatures decrease the solubility of lithium carbonate, which facilitates precipitation, lithium carbonate production requires higher solution temperatures, typically above 85 degrees Celsius. However, the nanofiltration unit needs to operate at lower temperatures when recovering lithium precipitate mother liquor. Therefore, at least one heat exchanger 7 can be used to cool the lithium precipitate mother liquor to a temperature below a preset temperature. In an optional embodiment, the preset temperature can be 30 degrees Celsius. By connecting the outlets 72 of each heat exchanger to the inlet 61 of the second tank, the cooled lithium precipitate mother liquor is pumped into the second tank 6 after cooling, ensuring uniform mixing and improving the nanofiltration efficiency of the first-stage nanofiltration unit 1.

[0068] Optional, continue to refer to Figure 3 As shown, the lithium ion recovery system of lithium precipitation mother liquor also includes a third tank 8; the inlet 81 of the third tank is connected to the outlet of the first-stage nanofiltration product and the outlet of the second-stage nanofiltration product; the outlet 82 of the third tank is connected to the tertiary inlet 31; the third tank 8 is used to mix the first-stage nanofiltration product and the second-stage nanofiltration product evenly to improve the nanofiltration effect of the tertiary nanofiltration device 3.

[0069] Optionally, the extraction device 4 includes multiple extraction sub-devices 41 connected in series; the inlet of the first-stage extraction sub-device 411 is connected to the outlet 33 of the third-stage nanofiltration permeate; in any two adjacent extraction sub-devices 41, the inlet of the latter extraction sub-device 41 is connected to the outlet of the former extraction sub-device 41, so that the third-stage nanofiltration permeate is extracted in multiple stages to obtain a lithium ion solution, thereby improving the lithium ion recovery rate.

[0070] Optional, continue to refer to Figure 3 As shown, the system for recovering lithium ions from lithium precipitation mother liquor also includes a back-extraction device 9; the lithium extractant outlet of the last stage extraction sub-device 412 is connected to the back-extraction device 9.

[0071] Each extraction sub-unit 41 contains a selective lithium extractant. After the three-stage nanofiltration permeate is extracted by each extraction sub-unit 41, the resulting extractant and lithium extractant containing lithium ions are obtained. The lithium extractant containing lithium ions is discharged from the lithium extractant outlet and enters the back-extraction unit 9 to back-extract the lithium extractant containing lithium ions to obtain a lithium ion solution.

[0072] In an optional embodiment, since the extraction residue contains a small amount of emulsified extractant, direct discharge into the salt field would damage the salt field's ecological environment. Therefore, an adsorbent can be used to adsorb the extraction residue to remove the emulsified lithium extractant, which is beneficial to protecting the ecological environment of the salt field.

[0073] In an optional embodiment, the lithium extractant after back-extraction and the extractant adsorbed by an adsorbent are filtered through a ceramic membrane to recover the lithium extractant, thereby enabling the lithium extractant to be reused repeatedly and saving costs.

[0074] Based on the same inventive concept, embodiments of the present invention also provide a method for recovering lithium ions from lithium precipitation mother liquor. Figure 4 A flowchart of a method for recovering lithium ions from lithium precipitation mother liquor provided in an embodiment of the present invention is shown below. Figure 4 As shown, the method for recovering lithium ions from the lithium precipitation mother liquor includes:

[0075] S110. Pump the lithium precipitation mother liquor into the first-stage nanofiltration unit to obtain the first-stage nanofiltration concentrate and the first-stage nanofiltration permeate.

[0076] The lithium precipitation mother liquor is the mother liquor produced in the lithium carbonate production process, and its main components include carbonate ions, sodium ions, and lithium ions. The first-stage nanofiltration unit is equipped with a nanofiltration membrane module, which includes at least one nanofiltration membrane. Since the nanofiltration membrane allows low-valence ions to pass through while retaining high-valence ions, lithium ions and sodium ions can pass through the nanofiltration membrane, while carbonate ions cannot.

[0077] The first-stage nanofiltration concentrate is the solution retained by the first-stage nanofiltration unit, while the first-stage nanofiltration permeate is the solution that permeates through the first-stage nanofiltration unit.

[0078] S120. After mixing the primary nanofiltration concentrate and pure water in a preset ratio, pump the mixture into the secondary nanofiltration unit to obtain the secondary nanofiltration concentrate and the secondary nanofiltration permeate.

[0079] The preset ratio can be determined based on the lithium-ion recovery rate and recovery cost. The larger the preset ratio, the lower the recovery cost and the lower the lithium-ion recovery rate. Conversely, the smaller the preset ratio, the higher the lithium-ion recovery rate and the higher the recovery cost. Optionally, the preset ratio can be 1.

[0080] The secondary nanofiltration device is also equipped with a nanofiltration membrane module, which includes at least one nanofiltration membrane. Since the nanofiltration membrane allows low-valence ions to pass through while retaining high-valence ions, lithium ions and sodium ions can pass through the nanofiltration membrane, while carbonate ions cannot pass through the nanofiltration membrane.

[0081] Secondary nanofiltration concentrate is the solution retained by the secondary nanofiltration unit, while secondary nanofiltration permeate is the solution that permeates through the secondary nanofiltration unit.

[0082] S130. Pump the primary nanofiltration permeate and the secondary nanofiltration permeate into the tertiary nanofiltration unit to obtain tertiary nanofiltration concentrate and tertiary nanofiltration permeate.

[0083] The tertiary nanofiltration device also includes a nanofiltration membrane module, which comprises at least one nanofiltration membrane. Because the nanofiltration membrane allows low-valence ions to pass through while retaining high-valence ions, lithium ions and sodium ions can pass through the nanofiltration membrane, while carbonate ions cannot. It should be noted that the nanofiltration membrane modules in the primary, secondary, and tertiary nanofiltration devices can be the same or different. This embodiment does not specifically limit this, as long as the inventive points of this embodiment are achieved.

[0084] The tertiary nanofiltration concentrate is the solution retained by the tertiary nanofiltration unit, while the tertiary nanofiltration permeate is the solution that permeates through the tertiary nanofiltration unit.

[0085] Since the primary and secondary nanofiltration permeate mainly contains lithium and sodium ions, and a small amount of carbonate ions, it can be pumped into a tertiary nanofiltration unit for further nanofiltration to improve the purity of the recovered lithium ions. In another exemplary embodiment, after the primary and secondary nanofiltration permeate are filtered through the tertiary nanofiltration unit, the carbonate ion content in the resulting tertiary nanofiltration permeate is less than 500 ppm, thereby reducing impurities in the extracted lithium ions, improving the purity of the recovered lithium ions, and ensuring process stability.

[0086] S140. Extract lithium ions from the three-stage nanofiltration permeate to obtain a lithium ion solution.

[0087] Lithium ions in the tertiary nanofiltration permeate can be extracted using an extraction device. The extraction device contains a selective lithium extractant for extracting lithium ions; in an optional embodiment, the selective lithium extractant is a fluorodiketone.

[0088] Specifically, the lithium precipitation mother liquor is first pumped into a first-stage nanofiltration unit through a first-stage inlet to perform nanofiltration, producing a first-stage nanofiltration concentrate and a first-stage nanofiltration permeate. After the first-stage nanofiltration concentrate is discharged through the first-stage nanofiltration concentrate outlet, it is pumped into a second-stage nanofiltration unit through a second-stage inlet to further filter the first-stage nanofiltration concentrate, producing a second-stage nanofiltration concentrate and a second-stage nanofiltration permeate. Then, the first-stage and second-stage nanofiltration permeates are discharged through the first-stage and second-stage nanofiltration permeate outlets 23, respectively, and then pumped into a third-stage nanofiltration unit through a third-stage inlet to further filter the first-stage and second-stage nanofiltration permeates, producing a third-stage nanofiltration concentrate and a third-stage nanofiltration permeate. Finally, the third-stage nanofiltration permeate is discharged through the third-stage nanofiltration permeate outlet and then pumped into an extraction unit to extract lithium ions from the third-stage nanofiltration permeate.

[0089] Optionally, the method for recovering lithium ions from lithium precipitation mother liquor also includes pumping the tertiary nanofiltration concentrate into a primary nanofiltration unit to obtain primary nanofiltration concentrate and primary nanofiltration permeate.

[0090] Specifically, since the tertiary nanofiltration concentrate still contains a large amount of lithium ions and carbonate ions, the tertiary nanofiltration concentrate is pumped into the primary nanofiltration unit for nanofiltration, and then pumped into the secondary and tertiary nanofiltration units for further nanofiltration, in order to further improve the recovery rate of lithium ions and carbonate ions.

[0091] Optionally, before pumping the lithium precipitation mother liquor into the first-stage nanofiltration unit to obtain the first-stage nanofiltration concentrate and the first-stage nanofiltration permeate, the process also includes recovering the initial lithium precipitation mother liquor from each production line to the first tank to mix the initial lithium precipitation mother liquor from each production line evenly and obtain the lithium precipitation mother liquor.

[0092] In the lithium carbonate production process, lithium carbonate can be produced through multiple production lines. Due to the differences in the processes of different production lines, the composition ratio of the initial mother liquor for lithium precipitation may vary from line to line. Therefore, the initial mother liquor for lithium precipitation produced by each production line can be recycled to the first tank to ensure that the initial mother liquor for lithium precipitation from each production line is mixed evenly and thus obtain the initial mother liquor for lithium precipitation, thereby improving the nanofiltration effect of the nanofiltration device.

[0093] Optionally, before pumping the lithium precipitation mother liquor into the primary nanofiltration unit to obtain the primary nanofiltration concentrate and primary nanofiltration permeate, the method further includes: cooling the lithium precipitation mother liquor to make its temperature lower than a preset temperature.

[0094] In this process, a heat exchanger can be used to cool the lithium precipitated mother liquor. In an optional embodiment, the heat exchanger can be a plate heat exchanger, which can reduce the volume of the lithium ion recovery system from the lithium precipitated mother liquor. Moreover, the plate heat exchanger has high heat exchange efficiency, which is beneficial for rapidly cooling the lithium precipitated mother liquor.

[0095] Since the higher the temperature, the lower the solubility of lithium carbonate, which is more conducive to the precipitation of lithium carbonate, the production of lithium carbonate requires a high solution temperature, generally above 85 degrees Celsius. However, when recovering lithium precipitation mother liquor, the nanofiltration device needs to operate at a lower temperature. Therefore, the lithium precipitation mother liquor can be cooled by at least one heat exchanger to make the temperature of the lithium precipitation mother liquor lower than a preset temperature. In an optional embodiment, the preset temperature can be 30 degrees Celsius.

[0096] Optionally, the lithium precipitation mother liquor is cooled to a temperature lower than a preset temperature, including: pumping the lithium precipitation mother liquor into at least one heat exchanger to cool it down; and pumping the cooled lithium precipitation mother liquor into a second tank to mix it evenly.

[0097] In this system, at least one heat exchanger can be used, or multiple heat exchangers can be used. When the lithium-ion recovery system from lithium-ion precipitation mother liquor includes multiple heat exchangers, the inlet of each heat exchanger is connected to the outlet of the first tank, and the outlet of each heat exchanger is connected to the inlet of the second tank. After cooling the lithium-ion precipitation mother liquor, the cooled mother liquor is pumped into the second tank to mix it evenly, thereby improving the nanofiltration effect of the first-stage nanofiltration unit.

[0098] Optionally, before pumping the primary and secondary nanofiltration permeate into the tertiary nanofiltration unit to obtain the tertiary nanofiltration concentrate and the tertiary nanofiltration permeate, the method further includes: recovering the primary and secondary nanofiltration permeate to a third tank to ensure that the primary and secondary nanofiltration permeate are mixed evenly, thereby improving the nanofiltration effect of the tertiary nanofiltration unit.

[0099] Optionally, lithium ions in the three-stage nanofiltration permeate are extracted to obtain a lithium ion solution, including: pumping the three-stage nanofiltration permeate into a multi-stage series extraction device for extraction to obtain extraction residue and lithium extractant containing lithium ions; and using a back-extraction agent to back-extract the lithium extractant containing lithium ions to obtain a lithium ion solution.

[0100] Each extraction sub-unit contains a selective lithium extractant. The three-stage nanofiltration permeate is pumped into a multi-stage series extraction unit for extraction to improve lithium ion recovery. After extraction by each extraction sub-unit, the three-stage nanofiltration permeate yields extract residue and lithium extractant containing lithium ions. The lithium extractant containing lithium ions is discharged from the lithium extractant outlet and then enters a back-extraction unit to back-extract the lithium extractant containing lithium ions, obtaining a lithium ion solution.

[0101] Optionally, the method for recovering lithium ions from lithium precipitation mother liquor further includes: using an adsorbent to adsorb the extraction residue to remove the emulsified lithium extractant in the extraction residue.

[0102] Since the residual extract contains a small amount of emulsified extractant, direct discharge into the salt field would damage the salt field's ecological environment. Therefore, an adsorbent can be used to adsorb the residual extract to remove the emulsified lithium extractant, which is beneficial to protecting the ecological environment of the salt field.

[0103] Optionally, after using a back-extraction agent to back-extract the lithium extractant containing lithium ions to obtain a lithium ion solution, the method further includes: filtering the back-extracted lithium extractant through a ceramic membrane to recover the lithium extractant, thereby enabling the lithium extractant to be reused repeatedly to save costs.

[0104] The method for recovering lithium ions from lithium precipitation mother liquor is implemented using the lithium precipitation mother liquor recovery system provided in any embodiment of the present invention, and can achieve the beneficial effects of the lithium precipitation mother liquor recovery system provided in the embodiments of the present invention. The similarities can be referred to the above description.

[0105] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A system for recovering lithium ions from lithium precipitation mother liquor, characterized in that, include: Primary nanofiltration unit, secondary nanofiltration unit, tertiary nanofiltration unit, and extraction unit; The primary nanofiltration unit includes a primary water inlet, a primary nanofiltration concentrate outlet, and a primary nanofiltration permeate outlet; the primary nanofiltration unit is used to perform nanofiltration on the lithium precipitation mother liquor; the primary nanofiltration concentrate outlet is used to discharge the primary nanofiltration concentrate; and the primary nanofiltration permeate outlet is used to discharge the primary nanofiltration permeate. The secondary nanofiltration device includes a secondary inlet, a secondary nanofiltration concentrate outlet, and a secondary nanofiltration permeate outlet; the secondary inlet is connected to the primary nanofiltration concentrate outlet; the secondary nanofiltration device is used to perform nanofiltration on the primary nanofiltration concentrate; the secondary nanofiltration concentrate outlet is used to discharge the secondary nanofiltration concentrate; and the secondary nanofiltration permeate outlet is used to discharge the secondary nanofiltration permeate. The three-stage nanofiltration device includes a three-stage inlet, a three-stage nanofiltration concentrate outlet, and a three-stage nanofiltration permeate outlet. The three-stage inlet is connected to the first-stage nanofiltration permeate outlet and the second-stage nanofiltration permeate outlet. The three-stage nanofiltration device is used to nanofiltration the first-stage and second-stage nanofiltration permeates, mixing them evenly to improve the nanofiltration effect. The three-stage nanofiltration concentrate outlet is used to discharge the three-stage nanofiltration concentrate, and the three-stage nanofiltration permeate outlet is used to discharge the three-stage nanofiltration permeate. The extraction device is connected to the outlet of the three-stage nanofiltration permeate. The outlet of the three-stage nanofiltration permeate discharges the three-stage nanofiltration permeate to the extraction device. The lithium precipitation mother liquor is passed through the three-stage nanofiltration to obtain a lithium ion and sodium ion solution without carbonate. The extraction device is used to extract lithium ions from the three-stage nanofiltration permeate. The outlet of the third-stage nanofiltration concentrate is connected to the inlet of the first-stage water.

2. The system for recovering lithium ions from lithium precipitation mother liquor according to claim 1, characterized in that, Also includes: The first tank has its outlet connected to the primary inlet; the first tank is used to mix the initial mother liquor of lithium precipitation from each production line evenly to obtain lithium precipitation mother liquor.

3. The system for recovering lithium ions from lithium precipitation mother liquor according to claim 2, characterized in that, Also includes: A second tank and at least one heat exchanger; The inlet of each heat exchanger is connected to the outlet of the first tank; the outlet of each heat exchanger is connected to the inlet of the second tank; the heat exchangers are used to cool the lithium precipitation mother liquor. The outlet of the second tank is connected to the inlet of the first stage; the second tank is used to mix the cooled lithium mother liquor evenly.

4. The system for recovering lithium ions from lithium precipitation mother liquor according to claim 1, characterized in that, Also includes: The third tank; The inlet of the third tank is connected to the outlet of the first-stage nanofiltration permeate and the outlet of the second-stage nanofiltration permeate; the outlet of the third tank is connected to the tertiary inlet; the third tank is used to mix the first-stage nanofiltration permeate and the second-stage nanofiltration permeate evenly.

5. The system for recovering lithium ions from lithium precipitation mother liquor according to claim 1, characterized in that, The extraction device includes multiple extraction sub-devices connected in series; the inlet of the first-stage extraction sub-device is connected to the outlet of the third-stage nanofiltration permeate; in any two adjacent extraction sub-devices, the inlet of the later-stage extraction sub-device is connected to the outlet of the earlier-stage extraction sub-device.

6. The system for recovering lithium ions from lithium precipitation mother liquor according to claim 5, characterized in that, Also includes: Back-extraction device; The lithium extractant outlet of the final stage extraction sub-device is connected to the back-extraction device.

7. A method for recovering lithium ions from lithium precipitation mother liquor, characterized in that, Based on the system implementation for recovering lithium ions from lithium precipitation mother liquor according to any one of claims 1-6, the method for recovering lithium ions from lithium precipitation mother liquor includes: The lithium precipitation mother liquor is pumped into a first-stage nanofiltration unit to obtain first-stage nanofiltration concentrate and first-stage nanofiltration permeate; The primary nanofiltration concentrate and pure water are mixed in a preset ratio and then pumped into a secondary nanofiltration device to obtain secondary nanofiltration concentrate and secondary nanofiltration permeate. The first-stage nanofiltration permeate and the second-stage nanofiltration permeate are pumped into a third-stage nanofiltration unit to mix them evenly, thereby improving the nanofiltration effect of the third-stage nanofiltration unit and obtaining a third-stage nanofiltration concentrate and a third-stage nanofiltration permeate. Lithium ions in the three-stage nanofiltration permeate are extracted to obtain a lithium ion solution; The three-stage nanofiltration concentrate is pumped into the first-stage nanofiltration unit to obtain the first-stage nanofiltration concentrate and the first-stage nanofiltration permeate.

8. The method for recovering lithium ions from lithium precipitation mother liquor according to claim 7, characterized in that, Before pumping the lithium precipitation mother liquor into the primary nanofiltration unit to obtain the primary nanofiltration concentrate and primary nanofiltration permeate, the process further includes: The initial mother liquor of lithium precipitation from each production line is recovered into the first tank to mix the initial mother liquor of lithium precipitation from each production line evenly, thereby obtaining the lithium precipitation mother liquor.

9. The method for recovering lithium ions from lithium precipitation mother liquor according to claim 7, characterized in that, Before pumping the lithium precipitation mother liquor into the primary nanofiltration unit to obtain the primary nanofiltration concentrate and primary nanofiltration permeate, the process further includes: The lithium precipitation mother liquor is cooled to reduce its temperature to below a preset temperature.

10. The method for recovering lithium ions from lithium precipitation mother liquor according to claim 9, characterized in that, Cooling the lithium precipitation mother liquor to reduce its temperature below a preset temperature includes: The lithium precipitated mother liquor is pumped into at least one heat exchanger to cool it down. The cooled lithium precipitate mother liquor is pumped into the second tank to mix it evenly.

11. The method for recovering lithium ions from lithium precipitation mother liquor according to claim 7, characterized in that, Before pumping the primary nanofiltration permeate and the secondary nanofiltration permeate into the tertiary nanofiltration unit to obtain the tertiary nanofiltration concentrate and the tertiary nanofiltration permeate, the process further includes: The primary nanofiltration permeate and the secondary nanofiltration permeate are recycled to a third tank to ensure that the primary nanofiltration permeate and the secondary nanofiltration permeate are mixed evenly.

12. The method for recovering lithium ions from lithium precipitation mother liquor according to claim 7, characterized in that, Lithium ions in the three-stage nanofiltration permeate are extracted to obtain a lithium ion solution, comprising: The three-stage nanofiltration permeate is pumped into a multi-stage series extraction device for extraction to obtain the extraction residue and lithium extractant containing lithium ions. The lithium extractant containing lithium ions is back-extracted using a back-extraction agent to obtain the lithium ion solution.

13. The method for recovering lithium ions from lithium precipitation mother liquor according to claim 12, characterized in that, Also includes: An adsorbent is used to adsorb the residual extract to remove the emulsified lithium extractant from the residual extract.

14. The method for recovering lithium ions from lithium precipitation mother liquor according to claim 12, characterized in that, After back-extracting the lithium extractant containing lithium ions using a back-extraction agent to obtain the lithium ion solution, the process further includes: The lithium extractant after back-extraction is filtered through a ceramic membrane to recover the lithium extractant.

15. The method for recovering lithium ions from lithium precipitation mother liquor according to claim 7, characterized in that, The preset ratio is 1.

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