Lithium ion purification method, lithium ion purification device and application

Abstract

The invention relates to the field of ion purification and concentration, and discloses a lithium ion purification method, a lithium ion purification device and application. The lithium ion purification method comprises the following steps: enabling a solution containing lithium ions to be purified to be in contact with a part of an ultra-spreading polypropylene fiber membrane, and obtaining a lithium ion enrichment section on the ultra-spreading polypropylene fiber membrane along the spreading direction end of the solution containing lithium ions; contacting the lithium ion enrichment section with a solvent, and collecting a solution to obtain a purified solution containing lithium ions; optionally, the obtained solution containing the lithium ions is cyclically subjected to ultra-spreading, a lithium ion enrichment section is obtained, the solution is collected, and the further purified solution containing the lithium ions is obtained. According to the lithium ion purification method and device, a large amount of energy can be saved, the ultra-spread polypropylene fiber membrane can be repeatedly used, and the cost is low. The method and the device can be used in the fields of salt lake lithium extraction and the like, and have the characteristics of energy conservation and high efficiency.

Description

Technical Field

[0001] The present invention relates to the field of ion purification and concentration, and in particular to a lithium ion purification method, a lithium ion purification device and applications. Background Art

[0002] Lithium is increasingly valued as a strategic resource due to the explosive growth in demand for lithium in various applications such as nuclear fusion, energy storage and medicine. In 2018, global lithium demand reached 2,800 tons (in terms of Li2CO3), and it is expected that by 2030, this demand will increase to 1.4-1.7 million tons (in terms of Li2CO3). Commercial lithium is mainly produced from terrestrial resources, such as spodumene, petalite and lithium mica. However, these ore resources are limited and geographically unevenly distributed, making mining very difficult. The lithium content in marine and salt lake brines is about 5,000 times that of terrestrial resources, and lithium-containing brines are easy to obtain, so efficient lithium extraction from brines has become a current research hotspot.

[0003] The current method of extracting lithium from brine has two main problems. First, the lithium ion concentration of brine is low (0.1-0.2ppm). Second, there are many interfering ions in brine, especially w% (Mg 2+ ) / w%(Li + ) ratio is too high. At present, the methods for extracting lithium from seawater / brine mainly include electrodialysis, evaporation crystallization, solvent extraction, precipitation and electrochemical methods, but a large amount of energy is required to reduce the magnesium-to-lithium ratio during the extraction process, which has the problem of high cost. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a lithium ion purification method, a lithium ion purification device and applications. The method and device use a polypropylene membrane material with super-spreading properties. The membrane material has excellent hydrophilic properties and super-spreading properties of water. At the same time, due to the different saturated solubility of different ions in water, different ions in the aqueous solution will precipitate at different times, i.e., different positions, during the spreading and drying process on the surface of the super-spreading polypropylene fiber membrane, thereby achieving the separation of different ions. At the same time, the super-spreading polypropylene fiber membrane in the present invention has a large specific surface area and capillary action, which can achieve dehydration and ion separation at the same time, thereby reducing the magnesium-lithium ratio and achieving the concentration and purification of lithium ions. The lithium ion purification method and lithium ion purification device of the present invention can save a lot of energy, and the super-spreading polypropylene fiber membrane can be reused and has low cost. The method and device can be used in fields such as salt lake lithium extraction, and have the characteristics of energy saving and high efficiency.

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

[0006] The solution containing lithium ions to be purified is contacted with a portion of the super-spread polypropylene fiber membrane, the solution containing lithium ions is super-spread on the super-spread polypropylene fiber membrane, and a lithium ion-enriched section is obtained on the super-spread polypropylene fiber membrane along the spreading direction of the solution containing lithium ions;

[0007] contacting the lithium ion-enriched section with a solvent, collecting a solution, and obtaining a purified solution containing lithium ions;

[0008] Optionally, the obtained purified solution containing lithium ions is circulated to carry out the above steps: contacting with part of the super-spreading polypropylene fiber membrane to perform super-spreading, obtaining a lithium ion-enriched section, contacting with a solvent and collecting the solution to obtain a re-purified solution containing lithium ions;

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

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

[0011] According to the present invention, before collecting the solution, the super-spread polypropylene fiber membrane may be dried or not. Drying treatment will increase the purification time, but can reduce the loss of lithium ions; without drying treatment, work efficiency can be improved, but the super-spread polypropylene fiber membrane is in a wet state, and the collection process will cause lithium ions to migrate to other places (i.e., there is lithium ion loss). As for whether to dry the super-spread polypropylene fiber membrane before collecting the solution, it can be processed according to actual needs in combination with specific working conditions and costs.

[0012] In the present invention, "the solution containing lithium ions to be purified is in contact with part of the super-spread polypropylene fiber membrane", wherein partial contact means that it can be in contact with one end of the super-spread polypropylene fiber membrane, or the middle position of the super-spread polypropylene fiber membrane can be in contact with the solution containing lithium ions to be purified.

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

[0014] The lithium ion purification method of the present invention utilizes the different saturated solubility of lithium ions and other ions in the solution, such as magnesium ions, in the solution. For example, when the aqueous solution containing lithium ions and magnesium ions is spread into the super-spread polypropylene fiber membrane, each ion spreads with the solution. Since the super-spread fiber membrane has a large specific surface area, the aqueous solution can evaporate relatively quickly, and the magnesium ions with a higher content in the solution first reach the saturation concentration and precipitate, while the higher solubility of lithium ions will continue to spread with the solution. Therefore, in the super-spread fiber membrane, there will be a phenomenon that the magnesium-lithium ratio is continuously reduced along the spreading direction (i.e., away from the direction of the end where the super-spread polypropylene fiber membrane contacts the solution containing lithium ions), and the magnesium-lithium ratio can be effectively reduced when a certain distance is reached from the position where the solution contacts the super-spread polypropylene fiber membrane.

[0015] In the method of the present invention, as an example, the following method is used to obtain a purified solution containing lithium ions: a lithium-containing solution with a high magnesium-lithium ratio is spread in a super-spread polypropylene fiber membrane, and a portion of the fiber membrane after spreading (i.e., the lithium ion enrichment section) has a low magnesium-lithium ratio, and this portion of the super-spread fiber membrane is contacted with deionized water, so that the ions in the low magnesium-lithium ratio portion are redissolved in the deionized water, thereby achieving the concentration and purification of lithium ions. The process of spreading and concentrating once is a spreading cycle, and multiple spreading cycles can be performed according to the specific situation of the magnesium-lithium ratio.

[0016] After experiments, it was found that the material purchased from Yanshan Petrochemical, with a specification of 25g / m 2 , a super-spread polypropylene fiber membrane prepared by the method of the present invention according to the polypropylene melt-blown nonwoven fabric with a fiber diameter of 0.5-8 microns, one end of the super-spread polypropylene fiber membrane is immersed in an aqueous solution, and after the aqueous solution is in continuous contact with the super-spread polypropylene fiber membrane, the maximum spreading distance of the aqueous solution can reach more than 15cm after 12 hours, for example, when the super-spread polypropylene fiber membrane is placed vertically (the aqueous solution is below the super-spread polypropylene fiber membrane at this time), the maximum spreading distance of the aqueous solution is 15-20cm, and when the super-spread polypropylene fiber membrane is placed flat, the maximum spreading distance of the aqueous solution will be larger than the case of being placed vertically. For example, when the spreading time is 30 minutes, the maximum spreading distance of the aqueous solution when placed flat is 14-16cm, and when placed vertically, the maximum spreading distance of the aqueous solution is 13-15cm. As known from the above, the balance between evaporation and spreading is involved, and the maximum spreading distance will be obtained. The maximum spreading distance refers to the distance between the contact position between the aqueous solution and the super-spread polypropylene fiber membrane and the farthest position reached by the spreading of the aqueous solution.

[0017] The experiment also found that the use of Yanshan Petrochemical, specification 25g / m 2A super-spread polypropylene fiber membrane is prepared by the method of the present invention from a polypropylene melt-blown non-woven fabric with a fiber diameter of 0.5-8 μm. One end of the super-spread polypropylene fiber membrane is immersed in an aqueous solution. In a position where the super-spread polypropylene fiber membrane is spread more than 10 cm, the magnesium-lithium ratio is significantly reduced, and lithium ions are enriched in this section, i.e., a lithium ion enriched section.

[0018] In the present invention, the solution to be purified is a solution containing lithium ions, which may be a mixed solution containing insoluble substances such as mud, sediment, etc., or may be a simple solution containing lithium ions, and the present invention has no particular limitation on this.

[0019] The solvent in the solution containing lithium ions to be purified in the present invention includes but is not limited to water. In order to save costs, water is preferred.

[0020] Similarly, the solvent used when collecting the solution includes but is not limited to water. In order to save costs, water is preferred.

[0021] In the present invention, the solution containing lithium ions to be purified contains lithium ions and ions with different solubility from lithium ions; preferably, the solution containing lithium ions to be purified contains lithium ions and at least one of magnesium ions, potassium ions and calcium ions. The main problem in industry is that magnesium and lithium are not easy to separate. Therefore, more preferably, the solution containing lithium ions to be purified contains lithium ions and magnesium ions, and the molar ratio of magnesium to lithium is above 6, for example, it can be 6, 7, 8, 9, 10, 20, 30, 40, 50, 60... or more.

[0022] In the present invention, the purification method includes at least one super-spreading and enrichment process, preferably including multiple super-spreading and enrichment processes, i.e., multiple super-spreading cycles. The spreading cycle refers to the lithium-containing solution to be purified being spread after partial contact with the super-spreading polypropylene fiber membrane, and the impurities in the lithium-containing solution will gradually precipitate along the spreading direction, and the lithium ions will be enriched in one section. Due to the high solubility of lithium ions, they are generally enriched at the far end close to the maximum distance of super-spreading. Therefore, the lithium ion enrichment section is rinsed with deionized water near the far end of the solution spreading to obtain the first purified lithium-containing solution. After being treated by a spreading cycle process, the magnesium-lithium ratio in the lithium-containing solution will be reduced, that is, the lithium-magnesium ratio will be improved. The purified lithium-containing solution can be treated multiple times, such as the second, third, fourth, etc., and the specific number of times is selected according to demand.

[0023] Different spreading cycles are carried out on different super-spreading polypropylene fiber membranes, or on the same spreading membrane, but when carried out on the same spreading membrane, necessary treatments such as cleaning are required to eliminate the influence of the previous cycle process. In order to increase efficiency, it is preferred to carry out the treatments on different membranes.

[0024] After the super-spreading polypropylene membrane was used for spreading cycle treatment, after experimental analysis, in order to meet the requirements of industrial precipitation method for lithium extraction, the magnesium-lithium ratio needs to be below 6:1. When the magnesium-lithium ratio in the initial solution reaches 60:1, the magnesium-lithium ratio purchased from Yanshan Petrochemical with a specification of 25g / m 2 The super-spread polypropylene fiber membrane prepared by the method of the present invention from the polypropylene melt-blown non-woven fabric with a fiber diameter of 0.5-8 μm preferably needs to be spread for at least 5 cycles according to the method of Example 1 to achieve this requirement.

[0025] In order to illustrate the technical effect of the present invention, as an example, a 25g / m 2 , the super-spread polypropylene fiber membrane prepared by the method of the present invention from the polypropylene melt-blown nonwoven fabric with a fiber diameter of 0.5-8 microns, according to the method of Example 1, when the magnesium-lithium ratio in the initial solution reaches 60:1, after one spreading cycle of purification, the magnesium-lithium ratio can be reduced to 40-50:1; after two spreading cycles, the magnesium-lithium ratio can be further reduced to 30-40:1; after the third, fourth, and fifth spreading cycles, the magnesium-lithium ratio can be successively reduced to 20-30:1; 10-20:1; 5-10:1. More preferably, after the fifth spreading cycle, the magnesium-lithium ratio can be reduced to 5-6:1, which meets the requirements of industrial precipitation method for lithium extraction.

[0026] From the above, it can be seen that the present invention can separate and purify lithium ions in brine with an ultra-high magnesium-lithium ratio, meeting the requirements of industrial precipitation 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-spread polypropylene fiber membrane contains a polypropylene fiber membrane matrix and an amphiphilic polymer. Taking the mass of the super-spread polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spread polypropylene fiber membrane is 93%-99.99%; the content of the amphiphilic polymer is 0.01%-7%.

[0028] The so-called superspreading (superspreading, superdiffusion or superwetting) is a common term in this field. For example, the paper "Superspreading Phenomenon and Nature of Silicon Surfactants" in "Daily Chemicals Science" Issue 8, 2019, and the paper "Research Progress of Superspreading Characteristics of Fluids on Solid Surfaces" in "Chemical Industry Journal" Volume 65 Issue 3 (March 2014) all involve descriptions of superspreading. Generally, it means that a small volume of droplets (less than 2μl, excluding the influence of gravity) can quickly achieve a contact angle of 0° after contacting the surface of an object. For example, the superspreading polypropylene fiber membrane of the present invention reaches a static contact angle of 0 degrees for water in no more than 1 second, preferably in 0.005 seconds-1 second. Compared with traditional superhydrophilic materials (contact angle less than 5°), materials with superspreading properties have better hydrophilicity, can make liquids quickly transfer and flow in the material, and have high throughput, so they have significant advantages in separation, filtration and other fields. The superspreading polypropylene fiber membrane of the present invention refers to a water superspreading polypropylene fiber membrane.

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

[0030] According to the present invention, the super-spread polypropylene fiber membrane comprises a polypropylene fiber membrane matrix and an amphiphilic polymer, and based on the mass of the super-spread polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spread polypropylene fiber membrane is 93%-99.99%; the content of the amphiphilic polymer is 0.01%-7%; the static contact angle of the polypropylene fiber membrane with water can reach 0° within a time not exceeding 1 second. In a preferred embodiment of the present invention, based on the mass of the super-spread polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spread polypropylene fiber membrane is 95%-99.95%, for example, it can be 95%, 97%, 98.3%, 99%, 99.95%, and any two values ​​or any interval between any two values; the content of the amphiphilic polymer is 0.05%-5%, for example, 0.01%, 0.7%, 3%, 5%, and any two values ​​or any interval between 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-spread polypropylene fiber membrane can be detected by conventional detection methods in the art. Including but not limited to the following methods: take an unmodified polypropylene non-woven fabric and weigh its mass m1, treat it by the method listed in the embodiment and then dry it to obtain a treated polypropylene fiber membrane, weigh its mass m2, and calculate the percentage of (m2-m1) / m 2 ×100% is the mass content of the amphiphilic polymer.

[0033] According to the present invention, the content of the amphiphilic polymer per unit surface area of ​​the super-spread polypropylene fiber membrane can be selected in a wide range. In a preferred embodiment of the present invention, the content of the amphiphilic polymer per unit surface area of ​​the super-spread polypropylene fiber membrane is 0.005 g / m 2 -3g / m 2 , preferably 0.005g / m 2 -2g / m 2 , for example 0.005g / m 2 , 1g / m 2 , 2g / m 2 , and any two values ​​or any interval between any two values.

[0034] According to the present invention, the content of the amphiphilic polymer per unit surface area of ​​the super-spread polypropylene fiber membrane can be detected by conventional detection methods in the art. Including but not limited to the following methods: first, the sample to be tested is coated with gold on the surface, and then the coated sample is placed on the SEM detection table, and the 5μm×5μm area on the sample is scanned by SEM, and then the mass fraction of oxygen in the polypropylene non-woven fabric before modification and the polypropylene fiber membrane after hydrophilic modification is determined by EDS spectrum in this area, which are respectively recorded as w0 and w1, and calculated according to the following formula: W=(w1-w0) / (M O / M A )×M, where M O is the relative atomic mass of oxygen, M A is the molecular weight of a single chain segment of the amphiphilic polymer, M is the surface density of the polypropylene fiber membrane, and W is the content of the amphiphilic polymer per unit area of ​​the super-spread polypropylene fiber membrane.

[0035] According to the present invention, the polypropylene fiber membrane substrate has a wide range of options, and the fiber membrane substrate can be, for example, meltblown polypropylene nonwoven fabric, spunbonded polypropylene nonwoven fabric, or a multilayer composite fabric of meltblown polypropylene nonwoven fabric and spunbonded polypropylene nonwoven fabric.

[0036] According to the present invention, when the fiber diameter of the fiber membrane is within a certain range, capillary force can be generated between the fibers, thereby improving the hydrophilicity of the polypropylene fiber through the self-assembled amphiphilic polymer, so that water can spread at a very fast speed under the action of capillary force. In a preferred embodiment of the present invention, the fiber diameter in the super-spreading polypropylene fiber membrane is less than 20 microns, preferably less than 10 microns, and more preferably 0.1-10 microns.

[0037] The fiber diameter range of the polypropylene fiber membrane substrate in the present invention refers to the nominal fiber diameter range of commercially available polypropylene fiber membrane substrates in the art or the statistical value obtained by detection. As long as the nominal fiber diameter range or the statistical value obtained by detection is within the scope of the present invention, the situation that the diameter range of some (or several) fibers on the overall polypropylene fiber membrane substrate is not within the scope of the present invention also belongs to the protection scope of the present invention.

[0038] The above fiber diameter detection method can adopt conventional detection in the art, including but not limited to observing the fiber with a microscope, such as an electron microscope, an optical microscope, 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 the amphiphilic polymer on the surface of the polypropylene fiber through capillary self-assembly, thereby achieving super-hydrophilic and super-spreading effects. Experimental verification shows that non-amphiphilic polymers cannot improve the polypropylene fiber membrane.

[0040] According to the present invention, the water-soluble amphiphilic copolymer refers to a polymer containing both a hydrophilic segment and a lipophilic segment in the molecular chain, and such a polymer has a certain affinity for two phases (usually a water phase and an oil phase) with different properties. Preferably, the amphiphilic polymer is polyvinyl alcohol and / or a cross-linked polymer formed by polyvinyl alcohol and a cross-linking agent; more preferably, it is a cross-linked polymer formed by polyvinyl alcohol and a cross-linking agent.

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

[0042] According to the present invention, the cross-linking agent is preferably selected from at least one of a polyacid and a polyaldehyde, more preferably glutaraldehyde and / or boric acid.

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

[0044] The layered structure refers to the layering of the modified fiber membrane (or fiber cloth). Taking the fiber membrane modified with an amphiphilic polymer as an example, the fiber membrane modified with an amphiphilic polymer having a layered structure is a layer of amphiphilic polymer formed on the surface of the fiber membrane matrix, that is, the amphiphilic polymer layer, and the fiber membrane matrix is ​​lined on one side of the amphiphilic polymer layer. The prior art mainly has a modified fiber membrane with a layered structure, which will form a functional material layer (such as a polymer layer or an inorganic layer) on one side or both sides of the membrane matrix. This type of functional material layer is a layered structure that is relatively independent of the membrane matrix on a macroscopic level. The weight and thickness of a small amount of functional material that penetrates into the membrane matrix are negligible compared to the functional material in the functional material layer, which is different from the polymer without a layered structure in the present invention.

[0045] The super-spread 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 fiber surface in the polypropylene fiber membrane matrix, the lipophilic segments in the amphiphilic polymer are assembled on the polypropylene fiber surface, and the hydrophilic segments are distributed on the fiber surface after assembly, thereby improving the hydrophilicity of the polypropylene fiber membrane. Preferably, the super-spread polypropylene fiber membrane contains polypropylene fibers coated with amphiphilic polymers, which are observed under a transmission electron microscope after staining with metal ruthenium.

[0047] In a preferred embodiment of the present invention, the super-spread polypropylene fiber membrane contains polypropylene fibers coated with amphiphilic polymers. Preferably, the amphiphilic polymers are coated on the polypropylene fibers by capillary self-assembly. That is, self-assembly is achieved under the action of capillary force, the lipophilic segments in the water-soluble amphiphilic polymers are attached to the surface of the polypropylene fibers, and the hydrophilic segments are exposed to the outside, thereby forming a fiber surface with a hydrophilic structure. In application, the capillary structure of the fiber membrane itself is well retained, and coupled with the effect of the amphiphilic polymers, a hydrophilic / super-spreading effect is achieved under the action of capillary force. The amphiphilic polymers on the super-spread polypropylene fiber membrane of the present invention are different from the amphiphilic polymers cast or coated on the fiber membrane surface. The hydrophilicity distribution of the amphiphilic polymers of the present invention is more uniform, and the super-spread 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 spread polypropylene fiber membrane comprises:

[0049] The method comprises contacting a polypropylene fiber membrane substrate with a solution containing an amphiphilic polymer under the action of an external force, wherein the content of the amphiphilic polymer in the solution is not higher than 5wt%, and optionally subjecting the polypropylene fiber membrane obtained after the polypropylene fiber membrane substrate is contacted with the amphiphilic polymer to a cross-linking reaction in a solution containing a cross-linking agent to obtain the super-spread polypropylene fiber membrane.

[0050] As described above, the water-soluble amphiphilic polymer realizes self-assembly under the action of capillary force, the lipophilic segments in the water-soluble amphiphilic polymer are attached to the surface of the polypropylene fiber, and the hydrophilic segments are exposed to the outside, thereby forming a fiber surface with a hydrophilic structure (i.e., the amphiphilic polymer is wrapped on the fiber surface), and the hydrophilic / super-spreading effect is achieved under the action of capillary force. The amphiphilic polymer in the present invention is more evenly distributed and has a non-layered structure.

[0051] Preferably, the contacting is performed in a solution containing an amphiphilic polymer.

[0052] The contact utilizes intermolecular forces to cause the amphiphilic polymer to self-assemble on the surface of the polypropylene fiber membrane fiber, thereby obtaining a polypropylene fiber membrane coated with the amphiphilic polymer. That is, the water-soluble amphiphilic polymer (hydrophilic, lipophilic, and soluble in water) used in the present invention can disperse the water-soluble polymer molecular chain and load it on the surface of the polypropylene fiber by a self-assembly method, thereby forming a fiber membrane with a super-hydrophilic effect. The super-spreading polypropylene fiber membrane realizes the hydrophilic modification of the polypropylene fiber membrane by the amphiphilic polymer by a capillary force self-assembly method.

[0053] The present invention has found through experiments that, after induction by external force, a water-soluble polymer having a hydrophilic segment and a lipophilic segment can be assembled with a polypropylene fiber membrane through a self-assembly method. Since polypropylene is a lipophilic polymer, the lipophilic segment in the water-soluble polymer is assembled on the fiber surface in the polypropylene fiber membrane. The interaction force between the hydrophilic segment and the polypropylene fiber is weak, and the hydrophilic segment cannot be assembled on the fiber surface, thereby being exposed to the outside. Therefore, the polypropylene fiber has hydrophilic properties, and the polypropylene fiber membrane also has hydrophilic and lipophilic properties, and the spreading time is fast. At the same time, the fiber diameter of the polypropylene fiber membrane in the present invention is preferably less than 20 microns, preferably less than 10 microns, and more preferably 0.1-10 microns. A strong capillary action can occur, and water can be quickly transferred along the fiber under the action of capillary force, so that the polypropylene fiber membrane has excellent spreading performance. The maximum size of a droplet with a volume of 2 μL is not less than 7 mm in the spreading area after the fiber membrane is spread, the maximum size of a droplet with a volume of 5 μL is not less than 8 mm in the spreading area after the fiber membrane is spread, the maximum size of a droplet with a volume of 8 μL is not less than 12 mm in the spreading area after the fiber membrane is spread, and the maximum size of a droplet with a volume of 12 μL is not less than 15 mm in the spreading area after the fiber membrane is spread.

[0054] In a preferred embodiment of the present invention, the content of the amphiphilic polymer in the solution containing the amphiphilic polymer is 0.05-4.5wt%, preferably 0.1-4.5wt%. 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 to obtain 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 0.05-4.5wt%, preferably 0.1-4.5wt%, for example 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, and any two values ​​or any range between any two values, more preferably 0.3-3wt%.

[0056] In a more preferred embodiment of the present invention, the contacting is carried out in a solution containing an amphiphilic polymer, so that the super-spreading performance of the obtained polypropylene fiber membrane is more uniform.

[0057] According to the present invention, the contact between the fiber membrane and the amphiphilic polymer can be carried out in 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 drying step after the polypropylene fiber membrane substrate is contacted with the amphiphilic polymer; preferably, the contact temperature and the drying temperature each do not exceed the melting temperature of the fiber membrane substrate and the amphiphilic polymer, and more preferably 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 an external force; during the self-assembly process of the amphiphilic polymer on the surface of the polypropylene fiber, an external force can be used to induce its rapid assembly, and the external force is not limited to one or more of ultrasound, rolling, filtration, lamination, molding and the like.

[0060] According to the present invention, the range of conditions under which the external force acts is relatively wide, such as the treatment time, the number of treatments and the process conditions of the treatment method, and there is no specific limitation.

[0061] Preferably, the external force comprises a combination of one or more of ultrasound, rolling, filtration, lamination, and molding; more preferably,

[0062] The ultrasonic conditions include: the ultrasonic frequency is not less than 5kHz, preferably not less than 10kHz, such as 10kHz, 20kHz, 30kHz, 40kHz, 45kHz, 50kHz, 55kHz, 60kHz. The greater the ultrasonic power, the less the action time and the number of actions.

[0063] According to the present invention, the ultrasonic treatment equipment can be selected from conventional ultrasonic treatment equipment including but not limited to ultrasonic cleaning table, cell crusher, ultrasonic probe, industrial ultrasonic device, etc. The power of the specific ultrasonic treatment equipment is not particularly limited by the present invention. Preferably, the power is 50-750W, preferably 50-500W, and more preferably 150-350W.

[0064] According to the present invention, the selectable range of the time for ultrasonic treatment in the preparation step is relatively wide, and the ultrasonic time is related to the solution concentration, fiber diameter, and surface density. According to the process conditions of the embodiments of the present invention, preferably, the ultrasonic time is not less than 1 minute, 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, and the like.

[0065] In another preferred specific embodiment of the present invention, the conditions for suction filtration can be selected in a wide range, and as the vacuum degree increases, the processing time and the number of processing times can be reduced. In a preferred embodiment of the present invention, the conditions for suction filtration include: the vacuum degree is not less than 5Pa, preferably not less than 10Pa, and / or the suction filtration time is not shorter than 1 second, preferably not less than 5 seconds. Preferably, the infiltration state of the polypropylene fiber membrane substrate by the amphiphilic polymer solution is still maintained before stopping the suction filtration.

[0066] In another preferred specific embodiment of the present invention, the conditions for rolling include: the pressure is not less than 5 Pa, preferably not less than 10 Pa; and the number of rolling times is 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 substrate is placed in a solution containing an amphiphilic polymer and brought into contact with the solution containing an amphiphilic polymer under the action of an external force; the aqueous solution of the amphiphilic polymer is immersed in the polypropylene fiber membrane substrate; and the process is 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 the action of capillary force, the lipophilic segments in the water-soluble amphiphilic polymer are attached to the surface of the polypropylene fiber, and the hydrophilic segments are exposed to the outside, thereby forming a fiber surface with a hydrophilic structure. In application, the capillary structure of the fiber membrane itself is well retained, and coupled with the effect of the amphiphilic polymer, the hydrophilic / super-spreading effect is achieved under the action of capillary force.

[0070] The amphiphilic polymer on the super-spread polypropylene fiber membrane of the present invention is different from the amphiphilic polymer cast or coated on the fiber membrane surface. The hydrophilicity distribution of the amphiphilic polymer of the present invention is more uniform, and the super-spread polypropylene fiber membrane of the present invention does not have an obvious layered structure. In addition, the amphiphilic polymer of the present invention is wrapped on the surface of the fiber, rather than cast or coated on one side of the fiber membrane. In this way, the capillaries between the fibers of the fiber membrane of the present invention are well retained. In addition, the effect of the amphiphilic polymer enables water to achieve a hydrophilic / super-spreading effect under the action of capillary force in the application.

[0071] According to the present invention, there is no particular limitation on the molecular weight of the amphiphilic polymer, for example, the number average molecular weight may be 30000-300000. Taking the embodiments of the present invention as an example, polyvinyl alcohol with a degree of polymerization of 1700 may be selected.

[0072] According to the present invention, the polypropylene fiber film substrate has a wide range of options, for example, it can be meltblown polypropylene non-woven fabric, spunbond polypropylene non-woven fabric, meltblown and spunbond polypropylene composite non-woven fabric, spunlace polypropylene non-woven fabric, etc. According to the present invention, meltblown polypropylene non-woven fabric and meltblown and spunbond polypropylene composite non-woven fabric are preferred.

[0073] According to the present invention, preferably, the surface density of the polypropylene fiber membrane substrate is 10-60 g / m 2 , preferably 20-50g / m 2 , and / or, the fiber diameter is not greater than 20 microns, preferably less than 10 microns, more preferably 0.1-10 microns. In this preferred embodiment, the fiber diameter of the fiber membrane generates capillary force between the fibers, thereby improving the hydrophilicity of the polypropylene fiber through the self-assembled amphiphilic polymer, and after encountering water, the water can spread at a very fast speed under the action of capillary force.

[0074] The fiber diameter range of the polypropylene fiber membrane substrate in the present invention refers to the nominal fiber diameter range of the commercially available polypropylene fiber membrane substrate in the art or the statistical value obtained by detection. Among them, as long as the nominal fiber diameter range or the statistical value obtained by detection is within the scope of the present invention, the situation that the diameter range of some (or several) fibers on the overall polypropylene fiber membrane substrate is not within the scope of the present invention also belongs to the protection scope of the present invention. The above fiber diameter detection method can adopt conventional detection in the art, including but not limited to observing the fiber with a microscope, such as an electron microscope, an optical microscope, and measuring and statistically analyzing the fiber diameter.

[0075] The preparation method further comprises an optional cross-linking step, which can be performed optionally according to specific uses, and preferably comprises a cross-linking step.

[0076] When the cross-linking step is included, the polypropylene fiber membrane obtained by contacting the polypropylene fiber membrane substrate with the amphiphilic polymer is subjected to cross-linking reaction in a solution containing a cross-linking agent.

[0077] The cross-linked amphiphilic polymer forms a cross-linked structure, and the stability of the amphiphilic polymer in the fiber membrane is increased, thereby improving the hydrophilic stability.

[0078] The super-spreading performance stability refers to the degree of 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 cross-linking agent has a wide selection range. In a preferred embodiment of the present invention, the cross-linking agent is selected from at least one of a polyacid and a polyaldehyde, preferably at least one of glutaraldehyde and boric acid, more preferably glutaraldehyde; and / or,

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

[0081] The cross-linking 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 cross-linking agent is 4-7; the cross-linking 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 interval between any two values.

[0082] The present invention has no particular limitation on the raw materials for adjusting pH, and any conventional acid or alkali raw materials in the art may be used.

[0083] According to the present invention, the fiber membrane that has been cross-linked can be cleaned to remove residual cross-linking agents and other substances. The present invention has no particular restrictions on the cleaning method, including but not limited to rinsing with water. In order to improve the efficiency of cleaning, it is preferably cleaned under ultrasonic conditions. The ultrasonic conditions here are not particularly limited by the present invention. For example, the frequency of ultrasound is 20-80kHz. Preferably, the ultrasonic cleaning time is 1-30 minutes / time, preferably 15-25 minutes / time, and the number of cleaning times is selected from 1-5 times, preferably 2-4 times.

[0084] According to the present invention, if the super-spread polypropylene fiber membrane needs to be dried, the drying temperature is not higher than the glass transition temperature of the amphiphilic polymer. When the treatment temperature is higher than the glass transition temperature, the amphiphilic polymer undergoes molecular segment movement, which will destroy the structure formed by its self-assembly and affect the super-spreading performance.

[0085] The present invention described above is a super-spread polypropylene fiber membrane and a preferred preparation scheme of the present invention.

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

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

[0088] The method for detecting the maximum size of the droplet spreading area on the fiber membrane can be detected by conventional detection methods in the art. Including but not limited to the following methods: stick the fiber membrane sample flat on a glass slide, and pay attention to keep the sample flat in the horizontal direction during the pasting process, then place the glass slide on the sample stage of the contact angle meter and fix it, and control the volume of the droplet by adjusting the instrument, and the volume can be 2μL, 5μL, 8μL, 12μL. Drop a drop of water on the center of the sample, remove the glass slide after the contact angle becomes 0 degrees, and measure the size of the spreading area. The shape of the spreading area is approximately circular, and its diameter or diagonal can be taken as the maximum size.

[0089] According to the present invention, the super-spreading polypropylene fiber membrane can reach a static contact angle of 0 degrees with water within 1 second, and more preferably, can reach 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, and any two values ​​or any interval between any two values.

[0090] According to the present invention, the test of the time required for the static contact angle of the polypropylene fiber membrane to reach 0 degrees with water can be detected by conventional detection methods in the art. Including but not limited to the following methods: the fiber membrane sample is flat on a glass slide, and it is important to keep the sample flat in the horizontal direction during the pasting process, and then the glass slide is placed on the sample stage of the contact angle measuring instrument and fixed, and the instrument is adjusted to control the volume of water droplets below 2μL to the center of the sample, and the angle from the solid-liquid interface through the inside of the droplet to the vapor-liquid interface at the junction of the three phases is measured, which is the static contact angle (referred to as water contact angle). The time calculation starts from the droplet contacting the fiber membrane surface and adjusting the lift to leave the droplet, until the droplet is completely spread and the contact angle reaches 0 degrees. The volume is controlled to be below 2μL in order to eliminate the influence of gravity, and better illustrate that the polypropylene fiber membrane has good hydrophilicity and super spreading performance.

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

[0092] a purification component including an ultra-spread polypropylene fiber membrane;

[0093] A liquid inlet assembly, used for providing a solution containing lithium ions to be purified to contact the portion of the super-spread polypropylene fiber membrane;

[0094] A collecting component is used to collect the purified solution containing lithium ions.

[0095] According to the present invention, the water inlet assembly contains a solution containing lithium ions to be purified, and the solution can be transported to the purification assembly by any method in the prior art. The technology includes but is not limited to spraying, dripping, dipping, etc. The water inlet assembly can be connected by a pipeline or the like, or one end of the spreading membrane in the purification assembly can be directly immersed in the lithium-containing solution.

[0096] In the present invention, the purification method comprises at least one super-spreading and enrichment process, preferably comprises multiple super-spreading and enrichment processes, i.e., multiple spreading cycles. Figure 2As shown, the spreading cycle refers to the spreading of the lithium-containing solution to be purified after partial contact with the super-spread polypropylene fiber membrane, and the impurities in the lithium-containing solution will gradually precipitate along the spreading direction, and the lithium ions will be enriched in one section. Due to the high solubility of lithium ions, they are generally enriched at the far end close to the maximum distance of super spreading. Therefore, the lithium ion enrichment section is rinsed with deionized water near the far end of the solution spreading to obtain the first purified lithium-containing solution. After a spreading cycle process, the magnesium-lithium ratio in the lithium-containing solution will decrease, that is, the lithium-magnesium ratio will increase. The purified lithium-containing solution can be treated multiple times, such as the second, third, fourth, etc., and the specific number of times is selected according to the needs, and finally a concentrated and purified lithium-containing solution that meets the requirements is obtained, such as a magnesium-lithium ratio (i.e., a magnesium-lithium molar ratio) of less than 6.

[0097] In order to meet the application requirements of multiple cyclic spreading, according to the present invention, the lithium ion purification device of the method described above preferably includes multiple cyclic spreading enrichment units, each of which includes:

[0098] a purification component including an ultra-spread polypropylene fiber membrane;

[0099] A liquid inlet assembly, used for providing a solution containing lithium ions to be purified to contact the portion of the super-spread polypropylene fiber membrane;

[0100] A collecting component, used for collecting the purified solution containing lithium ions;

[0101] In this way, multiple circulating spreading enrichment units are connected in series, and 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, and the target lithium ion solution with purity meeting the requirements is obtained in the collection component of the last unit.

[0102] In order to facilitate the understanding of the lithium ion purification device of the present invention, the following Figure 1 The schematic diagram of the structure of one embodiment of the lithium ion purification device of the present invention is shown to explain. 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 preferred that the multiple circulating spreading enrichment units are connected in series, that is, the purified solution containing lithium ions 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 purity meeting the requirements is obtained in the collection component of the last unit.

[0103] After spreading cycle treatment with super-spread polypropylene membrane, experimental analysis showed that in order to meet the requirements of industrial precipitation method for lithium extraction, the magnesium-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 described comprises a plurality of cyclic spreading enrichment units, which may be one or more, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ... preferably 2-5.

[0105] A third aspect of the present invention provides a method or device for concentrating and purifying lithium ions and its application in the field of lithium purification.

[0106] The lithium ion concentration and purification method and device described in the present invention can be applied to the fields of lithium extraction from salt lakes and seawater, preferably by solution lithium extraction, which has the advantages of 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 in the present invention utilizes the excellent spreading performance of the super-spread polypropylene fiber membrane (preferably super-spread non-woven fabric) and 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 existing technology, a large amount of energy can be saved.

[0109] The super-spread fiber membrane (also called super-spread polypropylene fiber membrane) of the present invention uses polypropylene with good corrosion resistance as the matrix, has a simple preparation process, and has excellent corrosion resistance, and can be applied to different environments containing lithium aqueous solutions. The device has the characteristics of simple operation and low energy consumption, and is easy to promote and implement.

[0110] The polypropylene fiber membrane (also called polypropylene fiber membrane) of the present invention has the above properties because the inventors unexpectedly discovered through their research that when the fiber diameter of the polypropylene fiber membrane is less than a certain size, capillary phenomena occur on the surface and inside of the fiber membrane, and the solution contacts the surface of the polypropylene fiber through the action of capillary force or with the help of external force during the contact or impregnation process with the aqueous solution of the amphiphilic polymer. When the content of the amphiphilic polymer in the solution of the amphiphilic polymer is not higher than 5wt%, the molecular chains of the amphiphilic polymer in the aqueous solution are uniformly dispersed, and the lipophilic segments (segments without hydroxyl groups) thereof show good compatibility with the equally lipophilic polypropylene, and self-assemble and combine after contacting with the polypropylene fiber membrane matrix. In this process, the amphiphilic polymer arranges the hydrophilic segments and the lipophilic segments separately, that is, the lipophilic segments are coated on the surface of the polypropylene fiber, and the hydrophilic segments are exposed on the surface of the polypropylene fiber after self-assembly, so that the polypropylene fiber membrane has hydrophilic properties. By controlling the process conditions (such as external force, concentration of the amphiphilic polymer, etc.), the thin layer self-assembly of the amphiphilic polymer on the surface of the polypropylene fiber can be achieved. Through the combined action of capillary force and self-assembly, the polypropylene fiber membrane contains polypropylene fibers coated with amphiphilic polymers, and the polypropylene fiber membrane has super-spreading properties. This process can be better achieved under the action of external forces. For example, under the action of ultrasound, the amphiphilic polymer solution can quickly enter between the fiber membrane fibers, promoting the contact between the lipophilic segments and the surface of the polypropylene fibers, thereby accelerating the speed and efficiency of self-assembly.

[0111] In the prior art, the preparation of super-spreading materials with capillary action requires methods such as chemical etching, which has high raw material and process costs, or complex process implementation. The polypropylene fiber membrane used in the present invention has the characteristics of low cost and corrosion resistance, and has the advantage of being easier to industrialize than the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Figure 1 It is a structural schematic diagram of one implementation scheme of a lithium ion purification device in the present invention.

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

[0114] Figure 2 This is a schematic diagram of the lithium ion concentration and purification process. DETAILED DESCRIPTION

[0115] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0116] The experimental data in the examples were measured using the following instruments and measurement 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 embodiment are measured using the German EASYDROP contact angle tester: the fiber membrane is cut into samples of 1 cm×1 cm in size, and then the sample is flatly attached to a glass slide. During the pasting process, care should be taken to keep the sample flat in the horizontal direction. The glass slide is then placed and fixed on the sample stage of the EASYDROP contact angle meter. The instrument is adjusted to control the volume to 2 μL and a water droplet is dropped into the center of the sample. After 10 seconds, the angle at the three-phase junction from the solid-liquid interface through the inside of the droplet to the vapor-liquid interface is measured, which is the static contact angle (referred to as the water contact angle).

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

[0119] Liquid content of hydrophilic polypropylene fiber membrane: Take a dry hydrophilic polypropylene fiber membrane and weigh it. Then rinse the sample with deionized water until there is no foam, hang it under the conditions of 25℃ and 30% humidity, and weigh it again after no water drops for 1 minute. The difference between the two weighings divided by the mass after drying is the liquid content of the sample, expressed in times.

[0120] The mass content of the amphiphilic polymer in the polypropylene fiber membrane obtained in the example: take an unmodified polypropylene non-woven fabric and weigh its mass m1. Treat it by the method listed in the example and then dry it to obtain a treated polypropylene fiber membrane, and weigh its mass m2. (m2-m1) / m2×100% is the mass content of the amphiphilic polymer.

[0121] The content of the amphiphilic polymer per unit surface area of ​​the polypropylene fiber membrane is as follows: first, the sample to be tested is coated with gold on the surface, and then the coated sample is placed on the SEM detection table, and a 5 μm×5 μm area on the sample is scanned by SEM, and then the mass fraction of oxygen in the polypropylene fiber membrane before modification and the polypropylene fiber membrane after hydrophilic modification is determined by EDS energy spectrum in the area, which are respectively denoted as w0 and w1, and calculated according to the following formula: W=(w1-w0) / (M O / M A )×M, where M O is the relative atomic mass of oxygen, M A is the molecular weight of a single chain segment of the amphiphilic polymer, M is the surface density of the polypropylene non-woven fabric, and W is the content of the amphiphilic polymer per unit area of ​​the polypropylene fiber membrane.

[0122] The test method for the specific surface area of ​​super-spread polypropylene fiber membrane is as follows: Use a mercury intrusion instrument to test, weigh a certain mass of sample, transfer it into a dilatometer, and then seal and weigh it; put the weighed dilatometer into a low-pressure chamber, and then perform 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 then the magnesium ion and lithium ion contents were measured using an inductively coupled plasma mass spectrometer (model 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 / m 2 , fiber diameter 0.5-8 microns) was immersed in a 0.3wt% polyvinyl alcohol (PVA-1799 from Sinopharm, glass transition temperature 72°C) aqueous solution at 25°C, and ultrasonically treated at a frequency of 50kHz for 30 minutes under a 250W ultrasonic probe. The treated polypropylene melt-blown was placed in a 0.5wt% glutaraldehyde cross-linking solution (pH 6) and cross-linked in a 60°C oven for 1 hour. The cross-linked polypropylene melt-blown was cleaned three times in a 100W ultrasonic water bath at a frequency of 50kHz, each time for 20 minutes, and then dried (at 60°C for 1 hour) to obtain an ultra-spread polypropylene fiber membrane.

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

[0128] Preparation Example 2

[0129] Take a three-layer composite fiber membrane of polypropylene spunbond nonwoven fabric and polypropylene meltblown fabric (purchased from Yanshan Petrochemical, model SMS, specification 50g / m 2 , fiber diameter 0.5-45 μm). Except that the ultrasonic treatment time during immersion in the polyvinyl alcohol aqueous solution was changed to 50 minutes, the rest was the same as in Example 1 to obtain an ultra-spread polypropylene fiber membrane. The specific test data are shown in Table 1.

[0130] Preparation Example 3

[0131] Take the polypropylene melt-blown nonwoven fabric in Preparation Example 1 and soak it in a 0.1wt% polyvinyl alcohol (from Aladdin, PVA-1799) aqueous solution at 25°C, and ultrasonically treat it at a frequency of 50kHz for 30 minutes under a 250W ultrasonic probe. The treated polypropylene melt-blown is arranged in a 0.5wt% glutaraldehyde cross-linking solution (pH is 6) and cross-linked in an 80°C oven for 1h. The cross-linked polypropylene melt-blown is arranged in a 100W ultrasonic water bath and cleaned three times at a frequency of 50kHz, each time for 20 minutes, and then dried (at 85°C for 1h). The glass transition temperature of PVA-1799 is 72°C. Specific test data are shown in Table 1 to obtain a modified polypropylene fiber membrane.

[0132] Preparation Example 4

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

[0134] Preparation Example 5

[0135] The concentration of the PVA aqueous solution was changed to 0.1 wt %, the cross-linking agent was changed to boric acid, the mass fraction of the cross-linking agent was 0.5 wt %, the cross-linking time was 90 minutes, and the remaining operations were the same as those in Preparation Example 1. The specific test data are shown in Table 1.

[0136] Example 1

[0137] Weigh a certain amount of deionized water, lithium chloride and magnesium chloride to prepare 50 ml of an aqueous solution with a magnesium-lithium ratio of 60:1. Fill the aqueous solution into the water tank of the water inlet component. The purification component includes the ultra-spread polypropylene fiber membrane of Preparation Example 1, with a size of 20 cmx3 cm.

[0138] One end of the super-spread polypropylene fiber membrane in Preparation Example 1 is placed 4 cm below the liquid surface in a water tank, and the rest of the super-spread polypropylene fiber membrane is located above the liquid surface and does not contact the liquid surface, and the aqueous solution is spread in the super-spread membrane. After standing for 30 minutes, the polypropylene membrane is completely soaked after spreading. After removing the polypropylene membrane, dry it at 50°C for 30 minutes, cut off the farthest 5cmx3cm part and soak it in 50ml deionized water for 10 minutes, and then take it out. After sampling the obtained concentrated solution to test the magnesium-lithium ratio, the super-spread polypropylene fiber membrane in the new Preparation Example 1 is used to carry out a second spreading cycle in the same manner as above, and the solution is sampled after each cycle, and the cyclic spreading is carried out 5 times. The concentrated solutions obtained from the 5 spreading cycles are placed in the water tank of the collection component and tested and analyzed.

[0139] Table 2 shows the magnesium-lithium ratio in different cycle spreading and final concentrated and purified solutions.

[0140] Comparative Example 1

[0141] Unmodified polypropylene melt-blown nonwoven fabric was used to replace the super-spread polypropylene fiber membrane in Example 1, and other changes were unchanged. Unmodified polypropylene melt-blown nonwoven fabric has no hydrophilic properties, and the aqueous solution cannot be spread in the membrane, and cannot be concentrated and purified.

[0142] Comparative Example 2

[0143] The polypropylene membrane in Preparation Example 3 was used to replace the super-spread polypropylene fiber membrane in Example 1. The polypropylene membrane in Preparation Example 3 did not have hydrophilic properties, and water could not spread therein, and could not be concentrated and purified.

[0144] Comparative Example 3

[0145] The polypropylene membrane in Preparation Example 4 was used to replace the super-spread polypropylene fiber membrane in Example 1. The polypropylene membrane in Preparation Example 4 has hydrophilic properties, but the aqueous solution cannot spread in it, and only the edge of the part immersed below the water surface is wetted, and it cannot be concentrated and purified.

[0146] Comparative Example 4

[0147] When the super-spread polypropylene fiber membrane in Example 1 was replaced with rice paper, during the spreading cycle, the rice paper was insufficiently strong and broke after water spreading, resulting in the inability to complete the spreading cycle.

[0148] Example 2

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

[0150] Example 3

[0151] The fiber membrane of Preparation Example 5 was used to replace the fiber membrane in Example 1, and there were no other changes.

[0152] Table 1

[0153]

[0154] Table 2

[0155]

[0156] It can be seen from the above embodiments that the lithium ion purification method and device of the present invention can purify lithium ions in a solution with a high magnesium-lithium ratio, reduce the magnesium-lithium ratio, and have the advantage of saving energy. In addition, the device 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 used to explain the present invention and do not constitute any limitation to 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 words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for purifying lithium ions, comprising: The solution containing lithium ions to be purified is contacted with a portion of the super-spread polypropylene fiber membrane, the solution containing lithium ions is super-spread on the super-spread polypropylene fiber membrane, and a lithium ion-enriched section is obtained on the super-spread polypropylene fiber membrane along the spreading direction of the solution containing lithium ions; contacting the lithium ion-enriched section with a solvent, collecting a solution, and obtaining a purified solution containing lithium ions; Optionally, the obtained purified solution containing lithium ions is circulated to carry out the above steps: contacting with part of the super-spreading polypropylene fiber membrane to perform super-spreading, obtaining a lithium ion-enriched section, contacting with a solvent and collecting the solution to obtain a re-purified solution containing lithium ions; The super-spread polypropylene fiber membrane contains a polypropylene fiber membrane matrix and an amphiphilic polymer. Taking the mass of the super-spread polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spread polypropylene fiber membrane is 93%-99.99%; the content of the amphiphilic polymer is 0.01%-7%.

2. The method according to claim 1, characterized in that: The maximum spreading distance of the solution containing lithium ions on the super-spread polypropylene fiber membrane is more than 15 cm; and / or, The lithium ion-enriched section is obtained above the super-spreading of 10 cm.

3. The method according to claim 1, characterized in that: The solvent in the solution containing lithium ions to be purified is water; and / or, The solvent used in collecting the solution is water; and / or, The lithium ion-containing solution to be purified contains lithium ions and ions having different solubility from lithium ions; preferably, The solution containing lithium ions to be purified contains lithium ions and at least one of magnesium ions, potassium ions, and calcium ions; more preferably, the solution containing lithium ions to be purified contains lithium ions and magnesium ions, and the molar ratio of magnesium to lithium is greater than 6.

4. The method according to any one of claims 1 to 3, characterized in that: Taking the mass of the super-spread polypropylene fiber membrane as 100%, the content of the polypropylene fiber membrane matrix in the super-spread polypropylene fiber membrane is 95%-99.95%; the content of the amphiphilic polymer is 0.05%-5%; and / or, The super-spread polypropylene fiber membrane is a super-hydrophilic polypropylene fiber membrane without a layered structure; and / or, The content of the amphiphilic polymer per unit surface area of ​​the super-spread polypropylene fiber membrane is 0.005 g / m 2 -3g / m 2 , preferably 0.005g / m 2 -2g / m 2 .

5. The method according to any one of claims 1 to 3, characterized in that: The fiber diameter of the super spread polypropylene fiber membrane is below 20 microns, preferably below 10 microns, more preferably 0.1-10 microns; and / or, The amphiphilic polymer is selected from polyvinyl alcohol and / or a cross-linked polymer formed by polyvinyl alcohol and a cross-linking agent; the cross-linking agent is preferably selected from at least one of a polyacid and a polyaldehyde, more preferably glutaraldehyde and / or boric acid; and / or, The super-spread polypropylene fiber membrane contains polypropylene fibers coated with an amphiphilic polymer. Preferably, the amphiphilic polymer is self-assembled and coated on the polypropylene fibers through capillary force.

6. The method according to any one of claims 1 to 3, characterized in that: The method for preparing the super-spread polypropylene fiber membrane comprises contacting a polypropylene fiber membrane substrate with a solution containing an amphiphilic polymer under the action of an external force, wherein the content of the amphiphilic polymer in the solution containing the amphiphilic polymer is not higher than 5wt%, and optionally subjecting the polypropylene fiber membrane obtained after the polypropylene fiber membrane substrate is contacted with the amphiphilic polymer to a cross-linking reaction in a solution containing a cross-linking agent to obtain the super-spread polypropylene fiber membrane; preferably, The contacting is carried out in a solution containing an amphiphilic polymer; and / or, 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.

7. The method according to claim 6, characterized in that: 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 %; and / or, The preparation method further comprises a step of drying the polypropylene fiber membrane matrix after contacting the amphiphilic polymer; preferably, The contacting temperature and the drying temperature each do not exceed the melting temperature of the fiber membrane matrix and the amphiphilic polymer, and more preferably do not exceed the glass transition temperature of the amphiphilic polymer.

8. The method according to any one of claims 1 to 3, characterized in that: The super-spread polypropylene fiber membrane has at least one of the following characteristics: The maximum size of the spreading area after a droplet with a volume of 2 μL is spread on the super-spread polypropylene fiber membrane is not less than 7 mm, the maximum size of the spreading area after a droplet with a volume of 5 μL is spread on the super-spread polypropylene fiber membrane is not less than 8 mm, the maximum size of the spreading area after a droplet with a volume of 8 μL is spread on the super-spread polypropylene fiber membrane is not less than 12 mm, and the maximum size of the spreading area after a droplet with a volume of 12 μL is spread on the super-spread polypropylene fiber membrane is not less than 15 mm; and / or, The specific surface area of ​​the super spread polypropylene fiber membrane is greater than 0.3 m2 / g, preferably greater than 0.7 m2 / g; and / or, The super-spreading polypropylene fiber membrane has a static contact angle of water reaching 0 degrees within no more than 1 second, preferably within 0.005 seconds to 1 second.

9. A lithium ion purification device suitable for the method described in claims 1 to 8, comprising: a purification component including an ultra-spread polypropylene fiber membrane; A liquid inlet assembly, used for providing a solution containing lithium ions to be purified to contact the portion of the super-spread polypropylene fiber membrane; A collecting component is used to collect the purified solution containing lithium ions.

10. Use of the method according to any one of claims 1 to 8 or the lithium ion purification device according to claim 9 in the field of lithium purification, preferably in extracting lithium from salt lakes or seawater.

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