A lithium-ion purification method, a lithium-ion purification apparatus, and its application.

Abstract

This invention relates to the field of ion purification and concentration, and discloses a lithium-ion purification method, a lithium-ion purification apparatus, and its applications. The lithium-ion purification method includes: contacting a portion of a lithium-ion-containing solution to be purified with a super-spreadable polypropylene fiber membrane to obtain a lithium-ion enrichment section on the super-spreadable polypropylene fiber membrane along the spreading direction of the lithium-ion-containing solution; contacting the lithium-ion enrichment section with a solvent, collecting the solution, and obtaining a purified lithium-ion-containing solution; optionally, circulating the obtained lithium-ion-containing solution for super-spreading, obtaining the lithium-ion enrichment section, and collecting the solution to obtain a further purified lithium-ion-containing solution. The lithium-ion purification method and apparatus of this invention can save a significant amount of energy, the super-spreadable polypropylene fiber membrane can be reused, and the cost is low. This method and apparatus can be used in fields such as lithium extraction from salt lakes, and have the characteristics of energy saving and high efficiency.

Description

Technical Field

[0001] This invention relates to the field of ion purification and concentration, and more specifically, to a lithium ion purification method, a lithium ion purification apparatus, and its applications. Background Technology

[0002] Due to the explosive growth in demand for lithium in various applications such as nuclear fusion, energy storage, and medicine, lithium is increasingly valued as a strategic resource. In 2018, global lithium demand reached 0.28 million tons (calculated as Li₂CO₃), and this demand is projected to increase to 1.4-1.7 million tons (calculated as Li₂CO₃) by 2030. Commercial lithium is mainly produced from terrestrial resources, such as spodumene, petalite, and lepidolite ores. However, these ores are limited in resources and unevenly distributed geographically, making mining very difficult. The lithium content in ocean and salt lake brines is approximately 5,000 times that of terrestrial resources, and lithium-bearing brines are readily available. Therefore, efficient lithium extraction from brines has become a current research hotspot.

[0003] Current methods for extracting lithium from brine face two main challenges: firstly, the lithium ion concentration in the brine is low (0.1-0.2 ppm); secondly, the brine contains numerous interfering ions, especially w% (Mg). 2+ ) / w%(Li + The magnesium-to-lithium ratio is too high. Currently, the main methods for extracting lithium from seawater / brine include electrodialysis, evaporation crystallization, solvent extraction, precipitation, and electrochemical methods. However, all of these methods require a large amount of energy to reduce the magnesium-to-lithium ratio, resulting in high costs. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a lithium-ion purification method, a lithium-ion purification apparatus, and its applications. The method and apparatus utilize a polypropylene membrane material with superspreading properties. This membrane material possesses excellent hydrophilicity and superspreading properties in water. Furthermore, due to the different saturated solubilities of different ions in water, different ions in the aqueous solution will precipitate at different times and locations during the spreading and drying process on the surface of the superspreading polypropylene fiber membrane, thereby achieving the separation of different ions. Simultaneously, the superspreading polypropylene fiber membrane of this invention has a large specific surface area and capillary action, enabling simultaneous dehydration and ion separation, thereby reducing the magnesium-to-lithium ratio and achieving lithium-ion concentration and purification. The lithium-ion purification method and apparatus of this invention can save a significant amount of energy, and the superspreading polypropylene fiber membrane is reusable, resulting in low cost. This method and apparatus can be used in fields such as lithium extraction from salt lakes, exhibiting energy-saving and high-efficiency characteristics.

[0005] The first aspect of the present invention is to provide a method for purifying lithium ions, comprising:

[0006] The lithium-ion-containing solution to be purified is brought into contact with a portion of the super-spreadable polypropylene fiber membrane. The lithium-ion-containing solution is super-spread on the super-spreadable polypropylene fiber membrane, and a lithium-ion enrichment section is obtained on the super-spreadable polypropylene fiber membrane along the spreading direction of the lithium-ion-containing solution.

[0007] The lithium-ion enrichment section is contacted with a solvent, and the solution is collected to obtain a purified lithium-ion-containing solution.

[0008] Optionally, the obtained purified lithium-ion-containing solution is recycled to perform the above steps: partial contact with a super-spreading polypropylene fiber membrane for super-spreading, obtaining a lithium-ion enrichment segment, contacting with a solvent and collecting the solution to obtain a further purified lithium-ion-containing solution.

[0009] The super-spreadable polypropylene fiber membrane comprises a polypropylene fiber membrane matrix and an amphiphilic polymer. Based on the mass of the super-spreadable polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spreadable polypropylene fiber membrane is 93%-99.99%; and the content of the amphiphilic polymer is 0.01%-7%.

[0010] According to the present invention, the lithium-ion-containing solution to be purified can be derived from a simple lithium-ion-containing solution or from a lithium-ion-containing solution contained in a mixture of insoluble substances.

[0011] According to the present invention, the super-spreadable polypropylene fiber membrane may or may not be dried before collecting the solution. Drying increases purification time but reduces lithium ion loss; while not drying improves efficiency, the super-spreadable polypropylene fiber membrane remains wet, causing lithium ions to migrate to other areas during collection (i.e., lithium ion loss). Whether or not to dry the super-spreadable polypropylene fiber membrane before collecting the solution can be determined based on specific operating conditions and cost requirements.

[0012] In this invention, "the lithium-ion-containing solution to be purified comes into contact with a portion of the super-spreadable polypropylene fiber membrane." "Partial contact" means that the contact could be with one end of the super-spreadable polypropylene fiber membrane or with the middle portion of the super-spreadable polypropylene fiber membrane contacting the lithium-ion-containing solution to be purified.

[0013] The method in this invention utilizes a polypropylene fiber membrane with superspreading properties to reduce the magnesium-lithium molar ratio in a lithium-containing solution to below 6:1. The concentrated lithium-containing solution can then be directly used for industrial precipitation and lithium extraction.

[0014] The lithium-ion purification method of this invention utilizes the different saturation solubilities of lithium ions and other ions in solution, such as magnesium ions. For example, when an aqueous solution containing lithium and magnesium ions is spread into a superspreadable polypropylene fiber membrane, each ion spreads with the solution. Due to the large specific surface area of ​​the superspreadable fiber membrane, the aqueous solution can evaporate relatively quickly. Magnesium ions, which have a higher concentration in the solution, reach saturation concentration first and precipitate, while lithium ions, with higher solubility, continue to spread with the solution. Therefore, in the superspreadable fiber membrane, along the spreading direction (i.e., away from the end of the superspreadable polypropylene fiber membrane that contacts the lithium-ion-containing solution), there is a phenomenon of continuously decreasing magnesium-to-lithium ratio. When a certain distance is reached from the point of contact between the solution and the superspreadable polypropylene fiber membrane, the magnesium-to-lithium ratio can be effectively reduced.

[0015] In the method of this invention, as an example, a purified lithium-ion-containing solution is obtained by the following method: a lithium-containing solution with a high magnesium-to-lithium ratio is spread in a superspreadable polypropylene fiber membrane. A portion of the spread fiber membrane (i.e., the lithium-ion enrichment section) has a lower magnesium-to-lithium ratio. This portion of the superspreadable fiber membrane is then contacted with deionized water, causing the ions in the low magnesium-to-lithium ratio portion to redissolve in the deionized water, thereby achieving the concentration and purification of lithium ions. One spreading and concentration process constitutes one spreading cycle, and multiple spreading cycles can be performed depending on the specific magnesium-to-lithium ratio.

[0016] Experiments revealed that using a product purchased from Yanshan Petrochemical, with a specification of 25g / m³, was effective. 2 A super-spreadable polypropylene fiber membrane, prepared from polypropylene meltblown nonwoven fabric with a fiber diameter of 0.5-8 micrometers according to the method of this invention, is obtained by immersing one end of the super-spreadable polypropylene fiber membrane in an aqueous solution. After continuous contact between the aqueous solution and the super-spreadable polypropylene fiber membrane, the maximum spreading distance of the aqueous solution can reach more than 15 cm after 12 hours. For example, when the super-spreadable polypropylene fiber membrane is placed vertically (with the aqueous solution below it), the maximum spreading distance is 15-20 cm. When the super-spreadable polypropylene fiber membrane is placed horizontally, the maximum spreading distance is even greater than when it is placed vertically. For example, when the spreading time is 30 minutes, the maximum spreading distance of the aqueous solution is 14-16 cm when placed horizontally and 13-15 cm when placed vertically. As can be seen from the above, the maximum spreading distance is obtained by balancing evaporation and spreading. The maximum spreading distance refers to the distance between the contact point between the aqueous solution and the super-spreadable polypropylene fiber membrane and the farthest point reached by the spreading of the aqueous solution.

[0017] The experiment also found that using a product purchased from Yanshan Petrochemical, with a specification of 25g / m³, was effective. 2The super-spreadable polypropylene fiber membrane prepared by the method of the present invention is made of polypropylene meltblown nonwoven fabric with fiber diameter of 0.5-8 micrometers. When one end of the super-spreadable polypropylene fiber membrane is immersed in an aqueous solution, the magnesium-to-lithium ratio is significantly reduced in the position where the super-spreadable polypropylene fiber membrane is spread at a distance of more than 10cm, and lithium ions are enriched in this section, namely the lithium ion enrichment section.

[0018] In this invention, the solution to be purified is a lithium-ion-containing solution. This solution can be derived from a mixture containing insoluble substances such as mud, sediment, and precipitates, or it can be a simple lithium-ion-containing solution. This invention does not impose any particular restrictions on this.

[0019] The solvent in the lithium-ion-containing solution to be purified in this invention includes, but is not limited to, water. To save costs, water is preferred.

[0020] Similarly, the solvents used when collecting the solution include, but are not limited to, water; water is preferred to save costs.

[0021] In this invention, the lithium-ion-containing solution to be purified contains lithium ions and ions with different solubilities than lithium ions; preferably, the lithium-ion-containing solution to be purified contains lithium ions and at least one of magnesium ions, potassium ions, and calcium ions. A major industrial problem is the difficulty in separating magnesium and lithium; therefore, more preferably, the lithium-ion-containing solution to be purified contains both lithium ions and magnesium ions, and the magnesium-lithium molar ratio is 6 or higher, for example, it can be 6, 7, 8, 9, 10, 20, 30, 40, 50, 60… or higher.

[0022] In this invention, the purification method includes at least one superspreading and enrichment process, preferably multiple superspreading and enrichment processes, i.e., multiple superspreading cycles. The spreading cycle refers to the spreading of the lithium-containing solution to be purified after partial contact with the superspreading polypropylene fiber membrane. Along the spreading direction, impurities in the lithium-containing solution gradually precipitate, and lithium ions are enriched in one section. Due to the high solubility of lithium ions, they generally accumulate near the far end of the superspreading distance. Therefore, the lithium ion enrichment section is rinsed with deionized water near the far end of the solution spreading, yielding a initially purified lithium-containing solution. After one spreading cycle, the magnesium-to-lithium ratio in the lithium-containing solution decreases, i.e., the lithium-to-magnesium ratio increases. The purified lithium-containing solution can be processed a second, third, fourth, or subsequent time, the specific number of times selected according to requirements.

[0023] Different spreading cycles can be performed on different ultra-spreadable polypropylene fiber membranes, or on the same spreading membrane. However, when performing the same spreading cycle on the same membrane, necessary treatments, such as cleaning, must be performed to eliminate the influence of the previous cycle. To increase efficiency, it is preferable to perform the treatments on different membranes.

[0024] After spreading and circulating the super-spreadable polypropylene membrane, experimental analysis showed that, to meet the requirements of industrial precipitation for lithium extraction, the magnesium-to-lithium ratio needed to be below 6:1. When the magnesium-to-lithium ratio in the initial solution reached 60:1, a 25g / m³ membrane purchased from Yanshan Petrochemical was used. 2 The super-spreadable polypropylene fiber membrane prepared by the method of the present invention using polypropylene meltblown nonwoven fabric with fiber diameter of 0.5-8 micrometers, preferably requires at least 5 spreading cycles according to the method of Example 1 to achieve this requirement.

[0025] To illustrate the technical effects of this invention, as an example, a product purchased from Yanshan Petrochemical, with a specification of 25g / m³, was used. 2 The super-spreadable polypropylene fiber membrane, prepared from polypropylene meltblown nonwoven fabric with a fiber diameter of 0.5-8 micrometers according to the method of this invention, can be reduced to 40-50:1 after one spreading cycle of purification when the magnesium-to-lithium ratio in the initial solution reaches 60:1, according to the method of Example 1; after two spreading cycles, the magnesium-to-lithium ratio can be further reduced to 30-40:1; after the 3rd, 4th, and 5th spreading cycles, the magnesium-to-lithium ratio can be successively reduced to 20-30:1; 10-20:1; and 5-10:1. More preferably, after the 5th spreading cycle, the magnesium-to-lithium ratio can be reduced to 5-6:1, meeting the requirements for lithium extraction by industrial precipitation.

[0026] As can be seen from the above, the present invention can separate and purify lithium ions from brine with an extremely high magnesium-to-lithium ratio, meeting the requirements of industrial precipitation for lithium extraction. Compared with the purification methods in the prior art, the method of the present invention can save a lot of energy and has extremely high industrial application value.

[0027] According to the present invention, the super-spreadable polypropylene fiber membrane comprises a polypropylene fiber membrane matrix and an amphiphilic polymer. Based on the mass of the super-spreadable polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spreadable polypropylene fiber membrane is 93%-99.99%; and the content of the amphiphilic polymer is 0.01%-7%.

[0028] Superspreading (also known as superdiffusion or superwetting) is a common term in this field. For example, the paper "Superspreading Phenomenon and Essence of Silicon Surfactants" in the 8th issue of *Daily Chemicals Science* (2019) and the paper "Research Progress on the Superspreading Characteristics of Fluids on Solid Surfaces" in the 3rd issue of Volume 65 of *Journal of Chemical Industry and Engineering* (March 2014) both describe superspreading. Generally, it refers to the ability of small-volume droplets (below 2 μl, excluding the influence of gravity) to quickly achieve a contact angle of 0° upon contact with an object's surface. For instance, the superspreading polypropylene fiber membrane of this invention achieves a static contact angle of 0° for water within no more than 1 second, preferably within 0.005 seconds to 1 second. Materials with superspreading properties have better hydrophilicity than traditional superhydrophilic materials (contact angle less than 5°), allowing liquids to rapidly transfer and flow within the material, resulting in high throughput and significant advantages in separation, filtration, and other fields. The superspreading polypropylene fiber membrane of this invention refers to a water-superspreading polypropylene fiber membrane.

[0029] According to the present invention, the super-spreadable polypropylene fiber membrane has excellent hydrophilic properties, which can rapidly transfer water within the fiber membrane surface in a very short time, spread it in the fiber membrane, form a large specific surface area, and evaporate water more quickly. It is a key component of the present invention. The preferred embodiment of the super-spreadable polypropylene fiber membrane of the present invention is described in detail below.

[0030] According to the present invention, the super-spreadable polypropylene fiber membrane comprises a polypropylene fiber membrane matrix and an amphiphilic polymer. Based on the mass of the super-spreadable polypropylene fiber membrane, the content of the polypropylene fiber membrane matrix in the super-spreadable polypropylene fiber membrane is 93%-99.99%; the content of the amphiphilic polymer is 0.01%-7%; and the static contact angle between the polypropylene fiber membrane and water can reach 0° within no more than 1 second. In a preferred embodiment of the present invention, based on the mass of the super-spreadable polypropylene fiber membrane, the content of the polypropylene fiber membrane matrix in the super-spreadable polypropylene fiber membrane is 95%-99.95%, for example, 95%, 97%, 98.3%, 99%, 99.95%, or any two values ​​or any range of any two values; the content of the amphiphilic polymer is 0.05%-5%, for example, 0.01%, 0.7%, 3%, 5%, or any two values ​​or any range of any two values.

[0031] Preferably, the sum of the content of the polypropylene fiber membrane matrix and the content of the amphiphilic polymer is 100%.

[0032] According to the present invention, the mass content of the amphiphilic polymer in the super-spreadable polypropylene fiber membrane can be detected using conventional detection methods in the art. These methods include, but are not limited to, the following: weighing the unmodified polypropylene nonwoven fabric by mass m1, treating it according to the methods listed in the examples, and then drying it to obtain the treated polypropylene fiber membrane, weighing its mass as m2, and expressing the content as a percentage (m2-m1) / m 2 ×100% is the mass content of the amphiphilic polymer.

[0033] According to the present invention, the selectable range of amphiphilic polymer content per unit surface area of ​​the super-spreadable polypropylene fiber membrane is relatively wide. In a preferred embodiment of the present invention, the amphiphilic polymer content per unit surface area of ​​the super-spreadable polypropylene fiber membrane is 0.005 g / m². 2 -3g / m 2 The preferred value is 0.005 g / m 2 -2g / m 2 For example, 0.005g / m 2 1g / m 2 2g / m 2 , and any two values ​​or any interval of any two values.

[0034] According to the present invention, the content of amphiphilic polymer per unit surface area of ​​the super-spreadable polypropylene fiber membrane can be detected using conventional detection methods in the art. These methods include, but are not limited to, the following: First, the sample to be tested is coated with a gold coating on its surface. Then, the coated sample is placed on an SEM detection stage, and a 5μm × 5μm area on the sample is scanned using SEM. Then, the mass fraction of oxygen in this area is determined using EDS energy dispersive spectroscopy for the unmodified polypropylene nonwoven fabric and the hydrophilically modified polypropylene fiber membrane, denoted as w0 and w1 respectively. The oxygen content is then calculated using the following formula: W = (w1 - w0) / (M O / M A )×M, where M O M is the relative atomic mass of oxygen. A M is the molecular weight of a single unit of the amphiphilic polymer, M is the areal density of the polypropylene fiber membrane, and W is the content of the amphiphilic polymer per unit area of ​​the super-spreadable polypropylene fiber membrane.

[0035] According to the present invention, the polypropylene fiber membrane matrix can be selected from a wide range of options. For example, the fiber membrane matrix can be meltblown polypropylene nonwoven fabric, spunbond polypropylene nonwoven fabric, or a multilayer composite fabric of meltblown polypropylene nonwoven fabric and spunbond polypropylene nonwoven fabric.

[0036] According to the present invention, when the fiber diameter of the fiber membrane is within a certain range, capillary forces can be generated between the fibers, thereby improving the hydrophilicity of the polypropylene fibers through self-assembled amphiphilic polymers, allowing water to spread at an extremely rapid speed under the action of capillary forces. In a preferred embodiment of the present invention, the fiber diameter in the superspreadable polypropylene fiber membrane is less than 20 micrometers, preferably less than 10 micrometers, and more preferably 0.1-10 micrometers.

[0037] The fiber diameter range of the polypropylene fiber membrane matrix described in this invention refers to the nominal fiber diameter range or statistically obtained value of commercially available polypropylene fiber membrane matrices in the art. Where the nominal fiber diameter range or statistically obtained value is within the scope of this invention, even if some (or a few) fibers in the overall polypropylene fiber membrane matrix have diameter ranges outside the scope of this invention, they are still within the protection scope of this invention.

[0038] The above methods for detecting fiber diameter can employ conventional testing techniques in this field, including but not limited to observing fibers under microscopes such as electron microscopes and optical microscopes, and measuring and statistically analyzing the fiber diameter.

[0039] According to the present invention, only amphiphilic and water-soluble polymers can achieve capillary self-assembly. In a preferred embodiment of the present invention, the amphiphilic polymer is selected from polyvinyl alcohol. The present invention achieves the coating of amphiphilic polymers on the surface of polypropylene fibers through capillary self-assembly, thereby achieving superhydrophilic and superspreading effects. Experimental verification has shown that non-amphiphilic polymers cannot improve polypropylene fiber membranes.

[0040] According to the present invention, the water-soluble amphiphilic copolymer refers to a polymer whose molecular chain contains both hydrophilic and lipophilic segments. Such polymers exhibit a certain affinity for two phases with different properties (usually an aqueous phase and an oil phase). Preferably, the amphiphilic polymer is polyvinyl alcohol and / or a crosslinked polymer formed from polyvinyl alcohol and a crosslinking agent; more preferably, it is a crosslinked polymer formed from polyvinyl alcohol and a crosslinking agent.

[0041] According to the present invention, in order to ensure the long-term efficient operation of the purification and concentration device, the amphiphilic polymer needs to undergo a cross-linking reaction. The range of cross-linking agents is relatively wide. In a preferred embodiment of the present invention, the cross-linking agent is selected from at least one of polybasic acids and polybasic aldehydes, including but not limited to at least one of glutaraldehyde and boric acid.

[0042] According to the present invention, the crosslinking agent is preferably selected from at least one of polybasic acids and polybasic aldehydes, more preferably glutaraldehyde and / or boric acid.

[0043] According to the present invention, the super-spreadable polypropylene fiber membrane is a superhydrophilic polypropylene fiber membrane without a layered structure.

[0044] The layered structure refers to the layering of the modified fiber membrane (or fiber cloth). Taking an amphiphilic polymer-modified fiber membrane as an example, a layered amphiphilic polymer layer is formed on the surface of the fiber membrane substrate, with the fiber membrane substrate lining one side of the amphiphilic polymer layer. Existing technologies mainly involve modified fiber membranes with layered structures, forming functional material layers (e.g., polymer layers or inorganic layers) on one or both sides of the membrane substrate. These functional material layers are macroscopically independent layered structures from the membrane substrate. The small amount of functional material penetrating into the membrane substrate has negligible weight and thickness compared to the functional material in the functional material layer, unlike the non-layered polymer in this invention.

[0045] The super-spreadable polypropylene fiber membrane of the present invention is a super-hydrophilic polypropylene fiber membrane without a layered structure. The amphiphilic polymer in the present invention does not have the above-mentioned layering. Instead, the amphiphilic polymer is wrapped around the outside of each fiber of the polypropylene fiber membrane.

[0046] According to the present invention, preferably, the amphiphilic polymer can self-assemble on the surface of the polypropylene fiber membrane matrix, with the oleophilic segments of the amphiphilic polymer assembling on the surface of the polypropylene fibers and the hydrophilic segments distributed on the fiber surface after assembly, thereby improving the hydrophilicity of the polypropylene fiber membrane. Preferably, the superspreadable polypropylene fiber membrane contains polypropylene fibers coated with the amphiphilic polymer, which can be observed under a transmission electron microscope after staining with ruthenium.

[0047] In a preferred embodiment of the present invention, the superspreadable polypropylene fiber membrane contains polypropylene fibers coated with an amphiphilic polymer. Preferably, the amphiphilic polymer is coated onto the polypropylene fibers through capillary self-assembly. That is, self-assembly is achieved under the action of capillary force, with the oleophilic segments of the water-soluble amphiphilic polymer adhering to the surface of the polypropylene fibers, while the hydrophilic segments are exposed, thereby forming a fiber surface with a hydrophilic structure. In application, the capillary structure of the fiber membrane itself is well preserved, and with the effect of the amphiphilic polymer, a hydrophilic / superspreadable effect is achieved under the action of capillary force. The amphiphilic polymer on the superspreadable polypropylene fiber membrane of the present invention differs from amphiphilic polymers cast or coated on the surface of the fiber membrane. The hydrophilicity distribution of the amphiphilic polymer in the present invention is more uniform, and the superspreadable polypropylene fiber membrane of the present invention does not have an obvious layered structure.

[0048] In a preferred embodiment of the present invention, the method for preparing the super-spreadable polypropylene fiber membrane includes:

[0049] The method involves contacting a polypropylene fiber membrane matrix with a solution containing an amphiphilic polymer under external force, wherein the content of the amphiphilic polymer in the solution is not higher than 5 wt%. Optionally, the polypropylene fiber membrane obtained after contacting the polypropylene fiber membrane matrix with the amphiphilic polymer is subjected to a crosslinking reaction in a solution containing a crosslinking agent to obtain the super-spreadable polypropylene fiber membrane.

[0050] As described above, the water-soluble amphiphilic polymer achieves self-assembly under capillary action. The lipophilic segments of the water-soluble amphiphilic polymer adhere to the surface of the polypropylene fiber, while the hydrophilic segments are exposed, thereby forming a fiber surface with a hydrophilic structure (i.e., the amphiphilic polymer is wrapped around the fiber surface), achieving a hydrophilic / superspreading effect under capillary action. The amphiphilic polymer in this invention has a more uniform distribution and does not have a layered structure.

[0051] Preferably, the contact is carried out in a solution containing an amphiphilic polymer.

[0052] The contact process utilizes intermolecular forces to enable the amphiphilic polymer to self-assemble on the surface of the polypropylene fiber membrane, resulting in a polypropylene fiber membrane coated with the amphiphilic polymer. Specifically, the water-soluble amphiphilic polymer (hydrophilic, oleophilic, and soluble in water) used in this invention allows the water-soluble polymer molecular chains to be dispersed in water and loaded onto the surface of the polypropylene fibers through self-assembly, thereby forming a fiber membrane with superhydrophilic properties. The superspreadable polypropylene fiber membrane achieves hydrophilic modification of the polypropylene fiber membrane by the amphiphilic polymer through capillary self-assembly.

[0053] This invention, through experiments, reveals that, through external force induction, water-soluble polymers with both hydrophilic and oleophilic segments can be self-assembled with polypropylene fiber membranes. Since polypropylene is an oleophilic polymer, the oleophilic segments of the water-soluble polymer assemble onto the fiber surface of the polypropylene fiber membrane. The hydrophilic segments, however, have weaker interactions with the polypropylene fibers and cannot assemble onto the fiber surface, thus remaining exposed. This process endows the polypropylene fibers with hydrophilic properties, and consequently, the polypropylene fiber membrane possesses both hydrophilic and oleophilic properties, with a rapid spreading time. Meanwhile, the fiber diameter in the polypropylene fiber membrane of the present invention is preferably less than 20 micrometers, preferably less than 10 micrometers, and more preferably 0.1-10 micrometers, which can generate strong capillary action. Water can be rapidly transferred along the fiber under the action of capillary force, thereby giving the polypropylene fiber membrane excellent spreading performance. The maximum size of the spreading area after the 2μL droplet is spread in the fiber membrane is not less than 7mm, the maximum size of the spreading area after the 5μL droplet is spread in the fiber membrane is not less than 8mm, the maximum size of the spreading area after the 8μL droplet is spread in the fiber membrane is not less than 12mm, and the maximum size of the spreading area after the 12μL droplet is spread in the fiber membrane is not less than 15mm.

[0054] In a preferred embodiment of the present invention, the content of the amphiphilic polymer in the solution is 0.05-4.5 wt%, preferably 0.1-4.5 wt%. Under the above-mentioned amphiphilic polymer concentration conditions and the action of external force, the contact utilizes intermolecular forces to cause the amphiphilic polymer to self-assemble on the surface of the polypropylene fiber membrane, thereby obtaining a polypropylene fiber membrane coated with the amphiphilic polymer.

[0055] As described above, the content of the amphiphilic polymer in the solution containing the amphiphilic polymer is 0.05-4.5 wt%, preferably 0.1-4.5 wt%, for example 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, and any two values ​​or any range of any two values, more preferably 0.3-3 wt%.

[0056] In a more preferred embodiment of the present invention, the contact is carried out in a solution containing an amphiphilic polymer, thereby resulting in a more uniform superspreading property of the obtained polypropylene fiber membrane.

[0057] According to the present invention, the contact between the fiber membrane and the amphiphilic polymer can be carried out over a wide temperature range, preferably not exceeding the melting temperature of polypropylene and the amphiphilic polymer, and more preferably not exceeding the glass transition temperature of the amphiphilic polymer.

[0058] In a preferred embodiment of the present invention, the preparation method further includes a step of drying the polypropylene fiber membrane matrix after it comes into contact with the amphiphilic polymer; preferably, the contact temperature and the drying temperature do not exceed the melting temperature of the fiber membrane matrix and the amphiphilic polymer, more preferably they do not exceed the glass transition temperature of the amphiphilic polymer.

[0059] According to the present invention, preferably, the contact is carried out under the action of external force; during the self-assembly of the amphiphilic polymer on the surface of polypropylene fiber, external force can be used to induce it to quickly achieve assembly, and the external force includes, but is not limited to, one or more of the following methods: ultrasound, rolling, filtration, lamination, molding, etc.

[0060] According to the present invention, the conditions for the application of external force are wide-ranging, such as the processing time, the number of processing times, and the process conditions of the processing method, without specific limitations.

[0061] Preferably, the external force is applied in a manner that includes one or more of the following: ultrasonication, rolling, filtration, lamination, and molding; more preferably,

[0062] The conditions for ultrasound include: the frequency of the ultrasound is not less than 5 kHz, preferably not less than 10 kHz, such as 10 kHz, 20 kHz, 30 kHz, 40 kHz, 45 kHz, 50 kHz, 55 kHz, and 60 kHz. The higher the ultrasonic power, the fewer the intervals and number of treatments.

[0063] According to the present invention, the ultrasonic processing equipment can be selected from conventional ultrasonic processing equipment, including but not limited to ultrasonic cleaning tables, cell disruptors, ultrasonic probes, industrial ultrasonic devices, etc. The present invention does not particularly limit the power of the specific ultrasonic processing equipment; preferably, the power is 50-750W, more preferably 50-500W, and even more preferably 150-350W.

[0064] According to the present invention, the ultrasonic treatment time in the preparation step can be selected within a wide range. The ultrasonic time is related to the solution concentration, fiber diameter, and areal density. According to the process conditions of the embodiments of the present invention, preferably, the ultrasonic time is not less than 1 minute, more preferably not less than 5 minutes, and more preferably 10-120 minutes, for example, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 60 minutes, 100 minutes, 120 minutes, etc.

[0065] In another preferred embodiment of the present invention, the filtration conditions can be selected over a wide range, and the processing time and number of processes can be reduced as the vacuum level increases. In a preferred embodiment of the present invention, the filtration conditions include: a vacuum level of not less than 5 Pa, preferably not less than 10 Pa, and / or a filtration time of not less than 1 second, preferably not less than 5 seconds. Preferably, the amphiphilic polymer solution remains wetted in the polypropylene fiber membrane matrix until filtration is stopped.

[0066] In another preferred embodiment of the present invention, the conditions for roller pressing include: pressure not less than 5 Pa, preferably not less than 10 Pa; and roller pressing times not less than 1 time.

[0067] In a more preferred embodiment of the present invention, the preparation method may include the following steps:

[0068] The polypropylene fiber membrane matrix is ​​brought into contact with a solution containing an amphiphilic polymer under external force; an aqueous solution of the amphiphilic polymer is then immersed in the polypropylene fiber membrane matrix; and the membrane is then dried.

[0069] As described above, in a preferred embodiment of the present invention, the amphiphilic polymer is selected from polyvinyl alcohol. That is, self-assembly is achieved under capillary action, with the lipophilic segments of the water-soluble amphiphilic polymer adhering to the surface of the polypropylene fiber, while the hydrophilic segments are exposed, thereby forming a fiber surface with a hydrophilic structure. In application, the capillary structure of the fiber membrane itself is well preserved, and with the added effect of the amphiphilic polymer, a hydrophilic / superspreading effect is achieved under capillary action.

[0070] The amphiphilic polymer on the superspreadable polypropylene fiber membrane of this invention differs from amphiphilic polymers cast or coated onto the surface of the fiber membrane. The amphiphilic polymer of this invention exhibits a more uniform hydrophilic distribution, and the superspreadable polypropylene fiber membrane of this invention does not have a significant layered structure. Furthermore, the amphiphilic polymer of this invention coats the surface of the fibers, rather than being cast or coated onto one side of the fiber membrane. This ensures excellent retention of capillary action between the fibers in this invention. Combined with the effect of the amphiphilic polymer, this allows water to achieve a hydrophilic / superspreading effect under capillary force during application.

[0071] According to the present invention, there are no particular limitations on the molecular weight of the amphiphilic polymer; for example, the number average molecular weight can be 30,000-300,000. Taking the embodiments described later as examples, polyvinyl alcohol with a degree of polymerization of 1700 can be selected.

[0072] According to the present invention, the polypropylene fiber membrane matrix can be selected from a wide range of materials, such as meltblown polypropylene nonwoven fabric, spunbond polypropylene nonwoven fabric, meltblown and spunbond polypropylene composite nonwoven fabric, spunlace polypropylene nonwoven fabric, etc. According to the present invention, meltblown polypropylene nonwoven fabric and meltblown and spunbond polypropylene composite nonwoven fabric are preferred.

[0073] According to the present invention, preferably, the areal density of the polypropylene fiber membrane matrix is ​​10-60 g / m³. 2 Preferably 20-50g / m 2 And / or, the fiber diameter is not greater than 20 micrometers, preferably less than 10 micrometers, and more preferably 0.1-10 micrometers. In this preferred embodiment, the fiber diameter of the fiber membrane generates capillary forces between the fibers, thereby improving the hydrophilicity of the polypropylene fibers through self-assembled amphiphilic polymers. Upon contact with water, water can spread out at an extremely rapid speed under the action of capillary forces.

[0074] The fiber diameter range of the polypropylene fiber membrane matrix described in this invention refers to the nominal fiber diameter range or statistically obtained value of commercially available polypropylene fiber membrane matrices in the art. Where the nominal fiber diameter range or statistically obtained value is within the scope of this invention, even if some (or a few) fibers in the overall polypropylene fiber membrane matrix have diameter ranges outside the scope of this invention, they are still within the protection scope of this invention. The fiber diameter detection method can employ conventional methods in the art, including but not limited to observing the fibers under a microscope, such as an electron microscope or an optical microscope, and measuring and statistically analyzing the fiber diameter.

[0075] The preparation method further includes an optional crosslinking step, which can be optionally performed according to the specific application, and preferably includes a crosslinking step.

[0076] In the crosslinking step, the polypropylene fiber membrane obtained by contacting the polypropylene fiber membrane matrix with the amphiphilic polymer is crosslinked in a solution containing a crosslinking agent.

[0077] The cross-linked amphiphilic polymers form a cross-linked structure, which increases the stability of the amphiphilic polymers in the fiber membrane and enhances the hydrophilic stability.

[0078] The aforementioned superspreading stability refers to the change in contact angle after the hydrophilic fiber membrane is completely immersed in deionized water and treated under ultrasonic cleaning conditions for 5 minutes, repeated 3 times. The smaller the change in contact angle, the better its hydrophilic stability.

[0079] According to the present invention, the crosslinking agent can be selected from a wide range. In a preferred embodiment of the present invention, the crosslinking agent is selected from at least one of polybasic acids and polybasic aldehydes, preferably at least one of glutaraldehyde and boric acid, and more preferably glutaraldehyde; and / or,

[0080] The crosslinking agent content in the solution is 0.005-0.8 wt%, preferably 0.01-0.5 wt%; and / or, the crosslinking temperature conditions include:

[0081] The crosslinking temperature does not exceed the glass transition temperature of the amphiphilic polymer, preferably 30-70°C; and / or the pH of the solution containing the crosslinking agent is 4-7; the crosslinking reaction time is 1 min-120 min, preferably 1 min-90 min, for example, it can be 1 min, 3 min, 5 min, 10 min, 20 min, 50 min, 70 min, 90 min, and any two values ​​or any range of any two values.

[0082] The present invention does not have any particular limitations on the raw materials used to adjust the pH; any conventional acid or base raw materials in the art can be used.

[0083] According to the present invention, the cross-linked fiber membrane can be cleaned to remove residual cross-linking agents and other substances. The present invention does not particularly limit the cleaning method, including but not limited to rinsing with water. To improve cleaning efficiency, ultrasonic cleaning is preferred. The ultrasonic conditions are not particularly limited here. For example, the ultrasonic frequency is 20-80 kHz. Preferably, the ultrasonic cleaning time is 1-30 minutes per cycle, more preferably 15-25 minutes per cycle, and the number of cleaning cycles is selected from 1-5 times, preferably 2-4 times.

[0084] According to the present invention, if the superspreadable polypropylene fiber membrane needs to be dried, the drying temperature shall not exceed the glass transition temperature of the amphiphilic polymer. When the processing temperature exceeds the glass transition temperature, the amphiphilic polymer undergoes molecular chain segment movement, which will destroy its self-assembled structure and affect the superspreading performance.

[0085] The above describes the super-spreadable polypropylene fiber membrane of the present invention and its preferred preparation method.

[0086] In a preferred embodiment of the present invention, the super-spreadable polypropylene fiber membrane has at least one of the following characteristics:

[0087] The maximum size of the spreading area after a 2μL droplet is spread on the superspreadable polypropylene fiber membrane is not less than 7mm, the maximum size of the spreading area after a 5μL droplet is spread on the superspreadable polypropylene fiber membrane is not less than 8mm, the maximum size of the spreading area after an 8μL droplet is spread on the superspreadable polypropylene fiber membrane is not less than 12mm, and the maximum size of the spreading area after a 12μL droplet is spread on the superspreadable polypropylene fiber membrane is not less than 15mm.

[0088] The method for detecting the maximum size of the droplet spreading area on the fiber membrane can be performed using conventional detection methods in the art. These methods include, but are not limited to, the following: The fiber membrane sample is flatly attached to a glass slide, ensuring the sample remains horizontal during attachment. The slide is then fixed on the sample stage of a contact angle measuring instrument. The droplet volume is controlled by adjusting the instrument; the volume can be 2 μL, 5 μL, 8 μL, or 12 μL. A droplet is placed in the center of the sample. After the contact angle reaches 0 degrees, the glass slide is removed, and the size of the spreading area is measured. The spreading area is approximately circular; its diameter or diagonal can be taken as the maximum size.

[0089] According to the present invention, the super-spreadable polypropylene fiber membrane can achieve a static contact angle of 0 degrees with water within 1 second; more preferably, it can achieve a static contact angle of 0 degrees with water within 0.005 seconds to 1 second. For example, it can be 0.005 seconds, 0.01 seconds, 0.05 seconds, 0.1 seconds, 0.5 seconds, 0.9 seconds, 1 second, or any two values ​​or any interval between any two values.

[0090] According to the present invention, the time required for the static contact angle between the polypropylene fiber membrane and water to reach 0 degrees can be tested using conventional testing methods in the art. These methods include, but are not limited to, the following: The fiber membrane sample is flatly attached to a glass slide, ensuring the sample remains horizontal during attachment. The slide is then fixed on the sample stage of a contact angle measuring instrument. A water droplet with a volume of less than 2 μL is dropped into the center of the sample. The angle between the solid-liquid interface, through the interior of the droplet, and the vapor-liquid interface at the three-phase interface is measured; this is the static contact angle (referred to as the water contact angle). The time is calculated from the moment the droplet contacts the fiber membrane surface and is lifted off the surface, until the droplet is fully spread and the contact angle reaches 0 degrees. Controlling the volume to less than 2 μL eliminates the influence of gravity, better demonstrating the excellent hydrophilicity and superspreading properties of the polypropylene fiber membrane.

[0091] A second aspect of the present invention is to provide a lithium-ion purification apparatus suitable for the method described in the first aspect, comprising:

[0092] Purification components, including ultra-spreadable polypropylene fiber membranes;

[0093] The liquid inlet assembly is used to bring a portion of the lithium-ion-containing solution to be purified into contact with the super-spreadable polypropylene fiber membrane.

[0094] Collection component, used to collect purified lithium-ion-containing solutions.

[0095] According to the present invention, the water inlet assembly contains a lithium-ion-containing solution to be purified, and this solution can be transported to the purification assembly using any method available in the prior art. The techniques include, but are not limited to, spraying, dripping, and immersion. The water inlet assembly can be connected via pipes or other means, or one end of the spreading membrane in the purification assembly can be directly immersed in the lithium-containing solution.

[0096] In this invention, the purification method includes at least one superspreading and enrichment process, preferably multiple superspreading and enrichment processes, i.e., multiple spreading cycles. For example... Figure 2As shown, the spreading cycle refers to the spreading of the lithium-containing solution to be purified after partial contact with the superspreadable polypropylene fiber membrane. Along the spreading direction, impurities in the lithium-containing solution gradually precipitate, while lithium ions are enriched in one section. Due to the high solubility of lithium ions, they generally accumulate near the far end of the superspreading distance. Therefore, the lithium-ion enrichment section is rinsed with deionized water near the far end of the solution spreading, resulting in a initially purified lithium-containing solution. After one spreading cycle, the magnesium-to-lithium ratio in the lithium-containing solution decreases, i.e., the lithium-to-magnesium ratio increases. The purified lithium-containing solution can be processed a second, third, fourth, or subsequent times, the specific number of times selected according to requirements, ultimately obtaining a concentrated and purified lithium-containing solution that meets the requirements, such as a magnesium-to-lithium ratio (i.e., magnesium-to-lithium molar ratio) of less than 6.

[0097] To meet the application requirements of multiple cyclic spreading, according to the present invention, the lithium-ion purification apparatus of the method preferably includes multiple cyclic spreading enrichment units, each cyclic spreading enrichment unit comprising:

[0098] Purification components, including ultra-spreadable polypropylene fiber membranes;

[0099] The liquid inlet assembly is used to bring a portion of the lithium-ion-containing solution to be purified into contact with the super-spreadable polypropylene fiber membrane.

[0100] Collection component for collecting purified lithium-ion-containing solutions;

[0101] In this way, multiple circulating spreading enrichment units are connected in series. The purified lithium-ion-containing solution collected by the collection component of the previous unit is transported to the liquid inlet component of the next unit, and so on, until the target lithium-ion solution with the required purity is obtained in the collection component of the last unit.

[0102] To facilitate understanding of the lithium-ion purification apparatus of the present invention, the following is combined with... Figure 1 The structural schematic diagram of one embodiment of the lithium-ion purification apparatus of the present invention is shown below for explanation. Figure 1 As shown, the lithium-ion purification device includes a circulating spreading enrichment unit, which includes a liquid inlet component 1, a purification component 2, and a collection component 3. If multiple circulating spreading enrichment units are included, it is preferable that these multiple circulating spreading enrichment units are connected in series, that is, the purified lithium-ion-containing solution collected by the collection component of the previous unit is transported to the liquid inlet component of the next unit, and the lithium-ion solution with the required purity is obtained by the collection component of the last unit.

[0103] After spreading and cycling the polypropylene membrane, experimental analysis showed that in order to meet the requirements of industrial precipitation extraction of lithium, the magnesium-to-lithium ratio needs to be below 6:1, and preferably, at least 5 spreading cycles are required to achieve this requirement.

[0104] According to the present invention, the lithium-ion purification device of the method comprises a plurality of circulating spreading enrichment units, which may be one or more, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10... preferably 2-5.

[0105] A third aspect of the present invention provides an application of a lithium-ion concentration and purification method or apparatus in the field of lithium purification.

[0106] The lithium-ion concentration and purification method and apparatus described in this invention can be applied to lithium extraction from salt lakes and seawater, and preferably to lithium extraction through solution extraction, which has advantages such as low energy consumption and low cost.

[0107] Compared with the prior art, the present invention has the following advantages:

[0108] The lithium ion concentration and purification device of this invention utilizes the excellent spreading performance of ultra-spreadable polypropylene fiber membrane (preferably ultra-spreadable non-woven fabric), and takes advantage of the different saturation concentrations and spreading speeds of different ions in water to achieve the goal of lithium ion concentration and purification. Compared with the prior art, it can save a lot of energy.

[0109] The super-spreadable fiber membrane (also known as a super-spreadable polypropylene fiber membrane) of this invention uses polypropylene, which has good corrosion resistance, as the matrix. The preparation process is simple, and it exhibits excellent corrosion resistance, making it suitable for various lithium-containing aqueous solutions. Furthermore, the device is easy to operate, consumes little energy, and is readily applicable for widespread implementation.

[0110] The polypropylene fiber membrane (also called polypropylene fiber membrane) of this invention possesses the above-mentioned properties through the inventors' research, which unexpectedly revealed that when the fiber diameter of the polypropylene fiber membrane is less than a certain size, capillary action occurs on the surface and inside of the fiber membrane. During contact or impregnation with an amphiphilic polymer aqueous solution, the solution comes into contact with the polypropylene fiber surface through capillary force or with the assistance of external force. When the content of the amphiphilic polymer in the solution is not higher than 5 wt%, the amphiphilic polymer molecular chains in the aqueous solution are uniformly dispersed. The lipophilic segments (segments without hydroxyl groups) exhibit good compatibility with the equally lipophilic polypropylene and undergo self-assembly upon contact with the polypropylene fiber membrane matrix. In this process, the amphiphilic polymer separates the hydrophilic and lipophilic segments, i.e., the lipophilic segments coat the polypropylene fiber surface, while the hydrophilic segments are exposed on the polypropylene fiber surface after self-assembly, thus giving the polypropylene fiber membrane hydrophilic properties. By controlling process conditions (e.g., external force, concentration of the amphiphilic polymer, etc.), thin-layer self-assembly of the amphiphilic polymer on the polypropylene fiber surface can be achieved. Through the combined effects of capillary force and self-assembly, the polypropylene fiber membrane contains polypropylene fibers coated with amphiphilic polymers, giving it superspreading properties. This process can occur more effectively under external forces, such as ultrasound. The amphiphilic polymer solution can rapidly penetrate between the fibers, promoting contact between the oleophilic segments and the polypropylene fiber surface, thereby accelerating the speed and efficiency of self-assembly.

[0111] In the prior art, the preparation of superspreadable materials with capillary action requires methods such as chemical etching, which results in high raw material and process costs, or complex process implementation. The polypropylene fiber membrane used in this invention has the characteristics of low cost and corrosion resistance, and has the advantage of being easier to industrialize than the prior art. Attached Figure Description

[0112] Figure 1 This is a schematic diagram of one embodiment of the lithium-ion purification device of the present invention.

[0113] 1. Liquid inlet assembly; 2. Purification assembly; 3. Collection assembly.

[0114] Figure 2 This is a schematic diagram of the lithium-ion concentration and purification process. Detailed Implementation

[0115] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0116] The experimental data in the examples were measured using the following instruments and methods:

[0117] The water contact angle and spreading time (spreading time is the time required for the water contact angle to reach 0°) obtained in the example were measured using the German EASYDROP contact angle tester: The fiber membrane was cut into a sample of 1cm×1cm size, and then the sample was flatly attached to a glass slide. During the attachment process, care was taken to keep the sample flat in the horizontal direction. Then the glass slide was placed on the sample stage of the EASYDROP contact angle measuring instrument and fixed. The instrument was adjusted to control the volume of 2μL water droplet to the center of the sample. After 10 seconds, the angle between the solid-liquid interface, through the interior of the droplet, and the vapor-liquid interface at the three-phase interface was measured, which is the static contact angle (abbreviated as water contact angle).

[0118] Water spread area test method: Cut the fiber membrane into 3cm×3cm samples, place the samples flat on a flat glass surface, and then use a Masterflex 78018-10 peristaltic pump to draw different volumes of deionized water droplets onto the surface of the fiber membrane. After the water has spread completely, measure the maximum dimension at both ends of the spread area as the spread dimension.

[0119] Liquid content of hydrophilic polypropylene fiber membrane: Take a dried hydrophilic polypropylene fiber membrane and weigh it. Then rinse the sample with deionized water until there is no foam, and suspend it at 25°C and 30% humidity. After no water droplets fall for 1 minute, weigh it again. The difference between the two weighings divided by the mass after drying is the liquid content of the sample, expressed in multiples.

[0120] The mass content of amphiphilic polymer in the polypropylene fiber membrane obtained in the example: Weigh the unmodified polypropylene nonwoven fabric (m1), process it according to the method listed in the example, and then dry it to obtain the processed polypropylene fiber membrane. Weigh the membrane (m2). The mass content of amphiphilic polymer is (m2-m1) / m2×100%.

[0121] The content of amphiphilic polymer per unit surface area of ​​the polypropylene fiber membrane is determined as follows: First, the sample to be tested is coated with gold. Then, the coated sample is placed on an SEM stage, and a 5μm × 5μm area on the sample is scanned using SEM. Then, the mass fraction of oxygen in the unmodified and hydrophilically modified polypropylene fiber membranes in this area is determined using EDS energy dispersive spectroscopy, denoted as w0 and w1 respectively. The oxygen content is calculated using the following formula: W = (w1 - w0) / (M O / M A )×M, where M O M is the relative atomic mass of oxygen. A M is the molecular weight of a single unit of the amphiphilic polymer, M is the areal density of the polypropylene nonwoven fabric, and W is the content of the amphiphilic polymer per unit area of ​​the polypropylene fiber membrane.

[0122] Test method for specific surface area of ​​super-spreadable polypropylene fiber membrane: Use mercury porosimeter to test, weigh a certain mass of sample, transfer it into a dilatometer, then seal and weigh it; put the weighed dilatometer into a low-pressure chamber, and then conduct a high-pressure test, and calculate the specific surface area result through software.

[0123] Magnesium-lithium ratio test method: The test solution was diluted 50 times with deionized water and the magnesium and lithium ion contents were measured using an inductively coupled plasma mass spectrometer (iCAPQ, Thermo Fisher Scientific, USA) to calculate the magnesium-lithium ratio.

[0124] In the following examples, polyvinyl alcohol, PVA-1799, has a degree of polymerization of 1700 and a degree of alcoholysis of 99%.

[0125] Preparation Example 1

[0126] Take polypropylene meltblown nonwoven fabric (purchased from Yanshan Petrochemical, specification 25g / m²) 2 Polypropylene (PP) fibers (0.5-8 μm in diameter) were immersed in a 0.3 wt% aqueous solution of polyvinyl alcohol (PVA-1799, glass transition temperature 72℃) at 25℃ and ultrasonically treated at 50 kHz for 30 minutes under a 250W ultrasonic probe. The treated PP meltblown fibers were then crosslinked in a 0.5 wt% glutaraldehyde crosslinking solution (pH 6) at 60℃ for 1 hour. After crosslinking, the PP meltblown fibers were cleaned three times in a 100W ultrasonic water bath at 50 kHz for 20 minutes each time, followed by drying (at 60℃ for 1 hour) to obtain an ultra-spreadable polypropylene fiber membrane.

[0127] The obtained polypropylene fiber membrane was tested for water contact angle, specific surface area, and spreading time. The specific test data are shown in Table 1.

[0128] Preparation Example 2

[0129] A three-layer composite fiber membrane consisting of polypropylene spunbond nonwoven fabric and polypropylene meltblown fabric (purchased from Yanshan Petrochemical, model SMS, specification 50g / m³) was prepared. 2 (The fiber diameter is 0.5-45 micrometers). Except for changing the ultrasonic treatment time when soaking in polyvinyl alcohol aqueous solution to 50 minutes, everything else is the same as in Example 1, and an ultra-spreadable polypropylene fiber membrane is obtained. The specific test data are shown in Table 1.

[0130] Preparation Example 3

[0131] The polypropylene meltblown nonwoven fabric from Preparation Example 1 was immersed in a 0.1 wt% polyvinyl alcohol (from Aladdin, PVA-1799) aqueous solution at 25°C and ultrasonically treated at a frequency of 50 kHz for 30 minutes under a 250 W ultrasonic probe. The treated polypropylene meltblown fabric was then crosslinked in a 0.5 wt% glutaraldehyde crosslinking solution (pH 6) in an 80°C oven for 1 hour. After crosslinking, the polypropylene meltblown fabric was cleaned three times in a 100 W ultrasonic water bath at a frequency of 50 kHz, each time for 20 minutes, and then dried (at 85°C for 1 hour). The glass transition temperature of PVA-1799 is 72°C. Specific test data are shown in Table 1, yielding a modified polypropylene fiber membrane.

[0132] Preparation Example 4

[0133] A 0.8 wt% aqueous solution was prepared using PVA1750 (purchased from Shandong Jiaying Chemical Technology Co., Ltd.) and deionized water at 90℃. 500 ml of the PVA solution was weighed and mixed with 600 ml of the crosslinking solution to obtain a mixed solution. The crosslinking solution contained 45 ml of glutaraldehyde aqueous solution (50 wt%), as well as acetic acid aqueous solution (10 vol%), methanol aqueous solution (10 vol%), and sulfuric acid aqueous solution (10 vol%), with a volume ratio of 3:2:1. Polypropylene meltblown nonwoven fabric (Sinopec Yanshan Petrochemical, surface density 25 g / m²) was used. 2 The mixture was placed in a mixed solution and vibrated at 150 rpm for 60 minutes at 50°C in a shaking incubator. It was then placed in deionized water for 1 hour to remove residual crosslinking agent and PVA, and finally dried in a 50°C oven for 1 hour to obtain the modified polypropylene fiber membrane. Specific test results are shown in Table 1.

[0134] Preparation Example 5

[0135] The concentration of PVA aqueous solution was changed to 0.1 wt%, the crosslinking agent was changed to boric acid with a mass fraction of 0.5 wt%, and the crosslinking time was 90 minutes. All other operations were the same as in Preparation Example 1. Specific test data are shown in Table 1.

[0136] Example 1

[0137] Weigh out a certain amount of deionized water, lithium chloride, and magnesium chloride to prepare 50 ml of an aqueous solution with a magnesium-to-lithium ratio of 60:1. Pour the aqueous solution into the water tank of the inlet assembly. The purification assembly includes the super-spreadable polypropylene fiber membrane of Preparation Example 1, with dimensions of 20 cm x 3 cm.

[0138] One end of the super-spreadable polypropylene fiber membrane from Preparation Example 1 was placed 4 cm below the surface of the liquid in a water tank, while the remaining portion of the membrane was above the surface but not in contact with it. The aqueous solution spread within the membrane. After standing for 30 minutes, the spread polypropylene membrane was completely wetted. The membrane was then removed and dried at 50°C for 30 minutes. The outermost 5 cm x 3 cm section was cut off and immersed in 50 ml of deionized water for 10 minutes, then removed. The resulting concentrated solution was sampled and tested for the magnesium-lithium ratio. A second spreading cycle was then performed using the same method with a new super-spreadable polypropylene fiber membrane from Preparation Example 1. The solution was sampled after each cycle, and the spreading cycle was repeated 5 times. The concentrated solutions obtained from the 5 spreading cycles were placed in the water tank of the collection module and analyzed.

[0139] Table 2 shows the magnesium-to-lithium ratio in solutions after different cycles of spreading and final concentration and purification.

[0140] Comparative Example 1

[0141] Unmodified polypropylene meltblown nonwoven fabric was used instead of the superspreadable polypropylene fiber membrane in Example 1, with no other changes. Unmodified polypropylene meltblown nonwoven fabric lacks hydrophilic properties, preventing aqueous solutions from spreading in the membrane and hindering concentration and purification.

[0142] Comparative Example 2

[0143] The polypropylene membrane from Preparation Example 3 was used instead of the superspreadable polypropylene fiber membrane from Example 1. The polypropylene membrane from Preparation Example 3 lacks hydrophilic properties, preventing water from spreading and thus hindering concentration and purification.

[0144] Comparative Example 3

[0145] The polypropylene membrane from Preparation Example 4 was used instead of the superspreadable polypropylene fiber membrane from Example 1. The polypropylene membrane in Preparation Example 4 is hydrophilic, but it cannot spread in aqueous solutions; only the edges of the membrane below the water surface are wetted, making concentration and purification impossible.

[0146] Comparative Example 4

[0147] When Xuan paper was used to replace the super-spreadable polypropylene fiber membrane in Example 1, the Xuan paper broke due to insufficient strength after water was spread during the spreading cycle, making it impossible to complete the spreading cycle.

[0148] Example 2

[0149] The fiber membrane in Example 1 was replaced with the fiber membrane prepared in Example 2, and no other changes were made.

[0150] Example 3

[0151] The fiber membrane in Example 1 was replaced with the fiber membrane of Preparation Example 5, and no other changes were made.

[0152] Table 1

[0153]

[0154] Table 2

[0155]

[0156] As can be seen from the above embodiments, the lithium-ion purification method and apparatus of the present invention can purify lithium ions in solutions with a high magnesium-to-lithium ratio, thereby reducing the magnesium-to-lithium ratio and saving energy. Furthermore, the apparatus of the present invention is simple, low-cost, and easy to promote and apply.

[0157] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for purifying lithium ions, comprising: The lithium-ion-containing solution to be purified is brought into contact with a portion of the super-spreadable polypropylene fiber membrane. The lithium-ion-containing solution is super-spread on the super-spreadable polypropylene fiber membrane, and a lithium-ion enrichment section is obtained on the super-spreadable polypropylene fiber membrane along the spreading direction of the lithium-ion-containing solution. The lithium-ion enrichment section is contacted with a solvent, and the solution is collected to obtain a purified lithium-ion-containing solution. Optionally, the obtained purified lithium-ion-containing solution is recycled to perform the above steps: partial contact with a super-spreading polypropylene fiber membrane for super-spreading, obtaining a lithium-ion enrichment segment, contacting with a solvent and collecting the solution to obtain a further purified lithium-ion-containing solution. The super-spreadable polypropylene fiber membrane comprises a polypropylene fiber membrane matrix and an amphiphilic polymer. Based on the mass of the super-spreadable polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spreadable polypropylene fiber membrane is 93%-99.99%; and the content of the amphiphilic polymer is 0.01%-7%.

2. The method according to claim 1, characterized in that: The lithium-ion-containing solution spreads at a maximum distance of 15 cm or more on the superspreadable polypropylene fiber membrane; and / or, The lithium-ion enrichment segment was obtained at a super-spreading depth of more than 10 cm.

3. The method according to claim 1, characterized in that: The solvent in the lithium-ion-containing solution to be purified is water; and / or, The solvent used to collect the solution is water; and / or, The lithium-ion-containing solution to be purified contains lithium ions and ions with different solubilities than lithium ions.

4. The method according to claim 1, characterized in that: The lithium-ion-containing solution to be purified contains lithium ions, as well as at least one of magnesium ions, potassium ions, and calcium ions.

5. The method according to claim 1, characterized in that: The lithium-ion-containing solution to be purified contains both lithium and magnesium ions, and the magnesium-to-lithium molar ratio is greater than 6.

6. The method according to any one of claims 1-5, characterized in that: Based on the mass of the super-spreadable polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spreadable polypropylene fiber membrane is 95%-99.95%; the content of the amphiphilic polymer is 0.05%-5%; and / or, The super-spreadable polypropylene fiber membrane is a non-layered, superhydrophilic polypropylene fiber membrane; and / or The content of amphiphilic polymer per unit surface area of ​​the super-spreadable polypropylene fiber membrane is 0.005 g / m². 2 -3g / m 2 .

7. The method according to any one of claims 1-5, characterized in that: The content of amphiphilic polymer per unit surface area of ​​the super-spreadable polypropylene fiber membrane is 0.005 g / m². 2 -2g / m 2 .

8. The method according to any one of claims 1-5, characterized in that: The fiber diameter in the super-spreadable polypropylene fiber membrane is less than 20 micrometers; and / or, The amphiphilic polymer is selected from polyvinyl alcohol and / or cross-linked polymers formed by polyvinyl alcohol and a cross-linking agent; and / or, The super-spreadable polypropylene fiber membrane contains polypropylene fibers coated with an amphiphilic polymer.

9. The method according to any one of claims 1-5, characterized in that: The fiber diameter in the super-spreadable polypropylene fiber membrane is less than 10 micrometers; and / or, The amphiphilic polymer is selected from polyvinyl alcohol and / or a crosslinked polymer formed from polyvinyl alcohol and a crosslinking agent; the crosslinking agent is selected from at least one of polybasic acids and polybasic aldehydes; and / or... The super-spreadable polypropylene fiber membrane contains polypropylene fibers coated with an amphiphilic polymer, which is self-assembled onto the polypropylene fibers by capillary force.

10. The method according to any one of claims 1-5, characterized in that: The fiber diameter in the super-spreadable polypropylene fiber membrane is 0.1-10 micrometers; and / or, The amphiphilic polymer is selected from polyvinyl alcohol and / or cross-linked polymers formed by polyvinyl alcohol and a cross-linking agent; the cross-linking agent is glutaraldehyde and / or boric acid.

11. The method according to any one of claims 1-5, characterized in that: The method for preparing the super-spreadable polypropylene fiber membrane includes contacting a polypropylene fiber membrane substrate with a solution containing an amphiphilic polymer under external force, wherein the content of the amphiphilic polymer in the solution is not higher than 5 wt%, and optionally, the polypropylene fiber membrane obtained after contacting the polypropylene fiber membrane substrate with the amphiphilic polymer is subjected to a crosslinking reaction in a solution containing a crosslinking agent to obtain the super-spreadable polypropylene fiber membrane.

12. The method according to claim 11, characterized in that: The contact is carried out in a solution containing an amphiphilic polymer; and / or, The contact utilizes intermolecular forces to enable the amphiphilic polymer to self-assemble on the surface of the polypropylene fiber membrane, resulting in a polypropylene fiber membrane coated with the amphiphilic polymer.

13. The method according to claim 11, characterized in that: The content of amphiphilic polymers in the solution is 0.05-4.5 wt%.

14. The method according to claim 11, characterized in that: The amphiphilic polymer content in the solution is 0.1-4.5 wt%.

15. The method according to claim 11, characterized in that: The preparation method further includes a step of drying the polypropylene fiber membrane matrix after it comes into contact with the amphiphilic polymer.

16. The method according to claim 15, characterized in that: The contact temperature and the drying temperature do not exceed the melting temperatures of the fiber membrane matrix and the amphiphilic polymer, respectively.

17. The method according to claim 15, characterized in that: The contact temperature and the drying temperature each do not exceed the glass transition temperature of the amphiphilic polymer.

18. The method according to any one of claims 1-5, characterized in that: The super-spreadable polypropylene fiber membrane has at least one of the following characteristics: The maximum size of the spreading area after a 2 μL droplet spreads on the superspreadable polypropylene fiber membrane is not less than 7 mm; the maximum size of the spreading area after a 5 μL droplet spreads on the superspreadable polypropylene fiber membrane is not less than 8 mm; the maximum size of the spreading area after an 8 μL droplet spreads on the superspreadable polypropylene fiber membrane is not less than 12 mm; and the maximum size of the spreading area after a 12 μL droplet spreads on the superspreadable polypropylene fiber membrane is not less than 15 mm; and / or, The super-spreadable polypropylene fiber membrane has a specific surface area greater than 0.3 m² / g; and / or, The super-spreadable polypropylene fiber membrane achieves a static contact angle of 0 degrees with water within 1 second.

19. The method according to any one of claims 1-5, characterized in that: The super-spreadable polypropylene fiber membrane has at least one of the following characteristics: The super-spreadable polypropylene fiber membrane has a specific surface area greater than 0.7 m² / g; and / or, The super-spreadable polypropylene fiber membrane achieves a static contact angle of 0 degrees with water within 0.005 seconds to 1 second.

20. A lithium-ion purification apparatus suitable for the method according to any one of claims 1-19, comprising: Purification components, including ultra-spreadable polypropylene fiber membranes; The liquid inlet assembly is used to bring a portion of the lithium-ion-containing solution to be purified into contact with the super-spreadable polypropylene fiber membrane. Collection component, used to collect purified lithium-ion-containing solutions.

21. The application of the method according to any one of claims 1-19 or the lithium-ion purification apparatus according to claim 20 in the field of lithium purification.

22. The application according to claim 21, characterized in that: The lithium purification fields mentioned are lithium extraction from salt lakes and lithium extraction from seawater.

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