Preparation method of novel high-hydrophilicity aluminum-based lithium adsorbent

Abstract

The invention discloses a preparation method of a high-hydrophilicity spherical aluminum-based lithium adsorbent, and belongs to the technical field of salt lake lithium extraction adsorbents. The method comprises the following steps: dispersing an aluminum-based lithium adsorption precursor in a turbid liquid containing sodium alginate and a hydrophilic organic adhesive, dropwise adding the turbid liquid into a calcium chloride solution, forming gel microspheres wrapping the precursor by utilizing cross-linking of the sodium alginate and calcium ions, and finally freeze-drying to obtain the porous spherical adsorbent. According to the method, a hydrophilic gel shell is constructed, a porous structure is maintained by freeze drying, and the problems of hole collapse and low performance caused by a traditional granulation process are solved. The obtained adsorbent has a core-shell structure, and the lithium adsorption capacity can reach 5.0 g / L or above. The method is simple to operate, excellent in adsorption performance and wide in application prospect.

Description

Technical Field

[0001] This invention belongs to the field of lithium adsorbent technology for salt lake extraction, specifically relating to a method for preparing a highly hydrophilic spherical aluminum-based lithium adsorbent and its application in lithium extraction from brine. Background Technology

[0002] Lithium, as a strategic and critical resource in modern technology and energy, is becoming increasingly important. With the rapid popularization of electric vehicles, portable electronic devices, and renewable energy storage systems, global demand for lithium-ion batteries is experiencing explosive growth, posing unprecedented challenges to lithium resource extraction technology. Currently, global lithium resources are mainly found in ores and brine in salt lakes, with brine accounting for over 60% of reserves. Compared to mature ore-based lithium extraction processes, brine extraction is becoming the mainstream direction for lithium resource development due to the limited availability of ore resources and high energy consumption and extraction costs.

[0003] Aluminum salt adsorbents have become an ideal choice for lithium extraction from salt lakes due to their low-pollution, green preparation process and operational stability. However, this technology faces a core bottleneck: its adsorption capacity is significantly lower than that of manganese-based and titanium-based adsorbents. For example, the capacity of current aluminum salt adsorbents is generally below 4 mg / g, which is insufficient to meet the needs of industrial upgrading. Therefore, overcoming the capacity limitation of aluminum salt adsorbents has become a current research focus in the field of lithium extraction from salt lakes.

[0004] Currently, the industrial granulation of aluminum-based adsorbents mainly relies on extrusion spheroidization, spray drying, and high-temperature sintering. These processes have serious performance limitations; for example, hydrophobic binders can cover 30% of the active sites, and high temperatures can cause the pore structure to collapse, resulting in a porosity of less than 50%. Summary of the Invention

[0005] In view of the shortcomings of existing technologies, this invention belongs to the field of lithium adsorbent technology for salt lake extraction, specifically relating to a method for preparing a highly hydrophilic spherical aluminum-based lithium adsorbent. This method utilizes the ionic cross-linking reaction between sodium alginate and calcium chloride to form a three-dimensional network structure of gel microspheres, thereby encapsulating the aluminum-based lithium adsorption precursor and a hydrophilic organic binder inside the gel microspheres. After freeze-drying, the porous structure of the gel microspheres is maintained while removing moisture, resulting in a porous spherical adsorbent. The obtained adsorbent has a core-shell structure, with the aluminum-based adsorbent as the core and the composite gel as the outer shell, significantly improving the hydrophilicity and specific surface area of ​​the adsorbent. To achieve the above-mentioned objectives, this invention adopts the following technical solution: A method for preparing a highly hydrophilic spherical aluminum-based lithium adsorbent includes the following steps: An aluminum-based lithium adsorption precursor was dispersed in a mixed solution containing sodium alginate and a hydrophilic organic binder to form a suspension. The suspension was added dropwise to a calcium chloride solution, and the sodium alginate reacted with the calcium chloride solution. 2+Ion cross-linking forms a three-dimensional network of gel microspheres, which encapsulate the aluminum-based lithium adsorption precursor; The gel microspheres were freeze-dried to obtain a porous spherical adsorbent.

[0006] The hydrophilic organic binder is at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, sodium carboxymethyl cellulose, or polyacrylic acid, accounting for 1-20 wt% of the dry weight of the mixed solution; the concentration of sodium alginate in the mixed solution is 1.0-4.0 wt%, the concentration of the hydrophilic organic binder is 0.5-5.0 wt%, the solid content of the aluminum-based precursor is 15-50 wt%; the concentration of the calcium chloride solution is 0.1-1.0 mol / L, and the crosslinking reaction time is 5-60 minutes.

[0007] The freeze-drying steps include: a pre-freezing stage: freezing at -40°C to -80°C for 4-12 hours; and a sublimation stage: dehydration at 0.1-50 Pa pressure for 24-72 hours.

[0008] The mixed solution also contains lithium salt template ions, functional monomers for ion imprinting, and crosslinking agents; after the gel microspheres are formed, a polymerization reaction step is added to polymerize the functional monomers and crosslinking agents to form an ion-imprinted network on the gel shell; after polymerization is completed, the template ions are removed by an elution step.

[0009] The functional monomer used for ion imprinting is at least one of methacrylic acid, acrylic acid, or itaconic acid; the crosslinking agent is at least one of N,N-methylenebisacrylamide or ethylene glycol dimethacrylate; the polymerization reaction or copolymerization step is carried out in the presence of an initiator, at a reaction temperature of 50-70°C, and for a reaction time of 2-6 hours.

[0010] The mixed solution also contains functional monomers with sulfonic acid groups, which copolymerize with other monomers during the polymerization reaction step.

[0011] The functional monomer with sulfonic acid group is at least one of 2-acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, or vinylsulfonic acid; the initiator is ammonium persulfate, potassium persulfate, or azobisisobutyronitrile, and its amount accounts for 0.05-0.5 wt% of the aqueous solution.

[0012] The elution step involves soaking and washing with a 0.5-2.0 mol / L acid solution for 6-24 hours, preferably hydrochloric acid or nitric acid.

[0013] An aluminum-based adsorbent prepared by any one of the methods described herein.

[0014] The application of the aluminum-based adsorbent in the extraction of lithium from lithium-containing solutions.

[0015] The beneficial effects of this invention are: Sodium alginate (SA) is a linear polysaccharide composed of β-D-mannuronic acid (M segment) and α-L-guluronic acid (G segment), which ensures its strong hydrophilic properties. The adjacent carboxyl groups in its G segment can undergo specific "egg-box" crosslinking with Ca²⁺; specifically, each Ca²⁺ group... 2+ The four oxygen atoms in the two G segments coordinate to form a three-dimensional network gel. The reaction exhibits several properties, including instantaneous gelation at room temperature, tolerance over a wide pH range of 3.0 to 10.0, and good biocompatibility.

[0016] This invention employs a calcium alginate biogel granulation method, through SA-Ca at room temperature. 2+ Cross-linking forms hydrophilic gel microspheres. Simultaneously, directional freeze-drying technology maintains interconnected channels, achieving a porosity of 85% or higher, significantly exceeding the 45% of traditional processes. The hydrophilic gel shell constructs rapid water molecule channels, improving efficiency by 150% compared to traditional processes, and shortening the adsorption equilibrium time to 30 minutes. The freeze-drying process avoids high-temperature phase transitions, resulting in a specific surface area retention rate exceeding 90% (while traditional processes lose 60%), ultimately enabling a lithium adsorption capacity exceeding 5.0 g / L. A hydrogen bond network forms between the exposed carboxyl groups of sodium alginate and the amide groups of PVP, significantly improved compared to traditional processes, thus doubling the brine permeation efficiency.

[0017] By introducing ion-imprinted polymer technology, lithium ions are used as template ions for in-situ polymerization during the preparation of the gel shell. After polymerization, the template lithium ions are eluted, leaving a large number of recognition sites on the gel shell that are highly matched to lithium ions in terms of spatial configuration, size, and charge. When the adsorbent is added to the brine, these imprinted sites with memory effect preferentially capture lithium ions while repelling mismatched interfering ions, thereby achieving active recognition of lithium ions and significantly improving the Li / Mg selectivity coefficient.

[0018] By introducing monomers with strong sulfonic acid groups for copolymerization, the sulfonic acid groups remain completely dissociated within the pH range of the brine, resulting in a high-density, stable negative charge on the surface of the gel shell and the inner walls of the pores. This negatively charged layer generates a strong Donnan repulsion effect, which has a much greater repulsive force on divalent magnesium ions than on monovalent lithium ions. An electrostatic barrier is established on the outer layer of the adsorbent, passively repelling most of the high-valent magnesium ions. By combining the active recognition and passive repulsion mechanisms of ion imprinting, the adsorbent maintains high capacity and high hydrophilicity while improving Li / Mg selectivity. Attached Figure Description

[0020] Figure 1 The comparison chart of the adsorption capacity test results of the aluminum-based lithium adsorbent prepared in this invention shows that its adsorption capacity is significantly improved.

[0021] Figure 2 The comparison chart of contact angle test results of the aluminum-based lithium adsorbent prepared in this invention shows that its hydrophilicity is significantly improved.

[0022] Figure 3 The comparison chart of the specific surface area test results of the aluminum-based lithium adsorbent prepared in this invention shows that its specific surface area is significantly improved. Detailed Implementation

[0023] The test methods for the adsorbents prepared in the following examples are as follows: 1. Dynamic Adsorption Capacity Test: The prepared spherical adsorbent particles were packed into an adsorption column to form a fixed bed. Simulated high magnesium-to-lithium ratio brine (its composition can be referenced from Da Qaidam Salt Lake brine, where the initial Li⁺ concentration C0 is approximately 999 mg / L and the Mg²⁺ concentration is approximately 35,209 mg / L) was continuously passed through the adsorption column at a set flow rate. The Li⁺ concentration at the outlet was continuously monitored, and adsorption was stopped when the outlet Li⁺ concentration reached 5% of the inlet concentration. The dynamic adsorption capacity, expressed in g / L, was obtained by integrating the breakthrough curve or by material balance calculations to determine the mass (g) of lithium adsorbed per unit bulk volume (L) of adsorbent.

[0024] 2. Selectivity Test: A binary mixed solution containing both Li⁺ and Mg²⁺ was prepared, for example, with an initial concentration of 300 mg / L for both Li⁺ and Mg²⁺. Equal masses or volumes of adsorbent were placed in this solution, and static adsorption was performed under the same conditions. After equilibrium was reached, the concentration changes of Li⁺ and Mg²⁺ in the solution were detected by ICP or other methods. The adsorption capacities of the adsorbent for Li⁺ and Mg²⁺ were calculated separately, and the Li / Mg selectivity coefficient was calculated according to the formula. By comparing the selectivity coefficient values ​​of each embodiment, the effect of ion imprinting and sulfonic acid groups on improving selectivity was evaluated.

[0025] 3. Hydrophilicity test: Measured using a contact angle meter. Fix the dried adsorbent particles on a glass slide, and drop a drop of deionized water onto the particle surface using a microsyringe. Immediately photograph the shape of the water droplet on the particle surface, and measure the angle between the water droplet and the tangent to the particle surface using image analysis software; this is the contact angle.

[0026] Example 1 10.0 g of lithium aluminum layered double hydroxide (LiCl·2Al(OH)3, particle size D50 = 15 μm) was uniformly dispersed in 100 mL of 2.5 wt% sodium alginate solution and homogenized by ultrasonication (300 W, 30 min) to form a stable suspension. Using a stainless steel needle (0.7 mm inner diameter), the suspension was dropped into a 0.5 mol / L CaCl2 crosslinking bath at a rate of 0.5 mL / min, and reacted at room temperature for 10 min to form dense gel microspheres. The gel microspheres were removed, washed three times with deionized water to remove residual calcium ions, and then pre-frozen in a -60℃ blast freezer for 8 hours. They were then transferred to a freeze dryer (cold trap temperature -85℃, vacuum degree 5 Pa) for sublimation dehydration for 48 hours to obtain off-white spherical adsorbents with a diameter of 1.8 ± 0.2 mm and a specific surface area of ​​50.2 m². 2 / g, the contact angle measured by the contact angle meter is 8.5°, the static water absorption rate is 0.52mL / g·s; the dynamic adsorption capacity in the simulated Qinghai Chaka Salt Lake brine is 4.8g / L, and the capacity retention rate is 95.3% after 50 cycles.

[0027] Example 2 1.5 g of polyvinylpyrrolidone (PVP K30) was added to 100 mL of a 2.0 wt% sodium alginate solution. 12.0 g of the same aluminum-based precursor powder was added, and the mixture was dispersed into a homogeneous slurry using a high-speed homogenizer (8000 rpm, 15 min). The slurry was then injected into a 0.8 mol / L CaCl2 solution using a microfluidic dropper (1.2 mm needle diameter, 1.2 mL / min flow rate), and cross-linked and cured for 15 min to form elastic gel spheres. After pre-freezing at -80℃ for 12 hours, the spheres were freeze-dried under 0.1 Pa ultra-high vacuum for 72 hours to obtain spherical particles with a diameter of 2.5 ± 0.3 mm; the contact angle measured by a contact angle meter was 8.2°, and the specific surface area was 48.6 m². 2 / g, under the same brine conditions, the adsorption capacity is increased to 5.0g / L. Example 3

[0028] 1.5 g of polyvinylpyrrolidone (PVP K30) was added to 100 mL of a 2.0 wt% sodium alginate solution. Subsequently, 1.0 g of methacrylic acid (MAA) as a functional monomer, 0.3 g of N,N-methylenebisacrylamide (MBA) as a crosslinking agent, and 0.8 g of LiCl as a template ion were added. After complete dissolution, 12.0 g of the same aluminum-based precursor powder was added, and the mixture was dispersed in a high-speed homogenizer (8000 rpm, 15 min) to form a homogeneous slurry. The slurry was injected into a 0.8 mol / L CaCl2 solution using a microfluidic dropper (1.2 mm needle diameter, 1.2 mL / min flow rate), and crosslinked and cured for 15 min to form elastic gel spheres. The gel spheres were then removed and transferred to an aqueous solution under nitrogen protection containing 0.1 wt% ammonium persulfate (APS) initiator, and reacted at 60 °C for 4 hours to polymerize MAA and MBA, forming an ion-imprinted network on the gel shell. After polymerization, the microspheres were immersed and washed in 1.0 mol / L hydrochloric acid solution for 12 hours to fully elute the template ions Li⁺, followed by washing with deionized water until neutral. After pre-freezing at -80℃ for 12 hours, the microspheres were freeze-dried under 0.1 Pa ultra-high vacuum for 72 hours to obtain spherical particles with ion-imprinted recognition sites. The specific surface area was 53.4 m². 2 / g, the contact angle measured by the contact angle meter is 8.2°, under the same brine conditions, its lithium adsorption capacity is 5.1 g / L, and the adsorption interference of Mg²⁺ is significantly reduced, and the selectivity coefficient (Li / Mg) is 3 times higher than that of Example 2. Example 4

[0029] 1.5 g of polyvinylpyrrolidone (PVP K30) and 1.0 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) were added to 100 mL of a 2.0 wt% sodium alginate solution. AMPS was introduced as a functional monomer with a strong sulfonic acid group. Subsequently, 1.0 g of methacrylic acid (MAA) as a functional monomer, 0.3 g of N,N-methylenebisacrylamide (MBA) as a crosslinking agent, and 0.8 g of LiCl as a template ion were added. After complete dissolution, 12.0 g of the same aluminum-based precursor powder was added, and the mixture was dispersed in a high-speed homogenizer (8000 rpm, 15 min) to form a uniform composite functional slurry. The slurry was injected into a 0.8 mol / L CaCl2 solution using a microfluidic dropper (needle diameter 1.2 mm, flow rate 1.2 mL / min), and crosslinked and cured for 15 min to form elastic gel spheres. The gel spheres were retrieved and transferred to an aqueous solution under nitrogen protection containing 0.1 wt% ammonium persulfate (APS) initiator. The reaction was carried out at 60°C for 4 hours to copolymerize MAA, AMPS, and MBA, simultaneously forming an ion-imprinted network and a sulfonic acid functional layer on the gel shell. After polymerization, the microspheres were immersed and washed with 1.0 mol / L hydrochloric acid solution for 12 hours to fully elute the template ions Li⁺, followed by washing with deionized water until neutral. After pre-freezing at -80°C for 12 hours, the microspheres were freeze-dried under 0.1 Pa ultra-high vacuum for 72 hours to obtain a composite functional adsorbent exhibiting both ion-imprinted selectivity and Donnan repulsion. Specific surface area: 52.7 m². 2 / g, the contact angle measured by the contact angle meter is 8.1°. Under the same brine conditions, its lithium adsorption capacity is stable at 5.2 g / L, and it exhibits extremely strong repulsion to Mg²⁺. The selectivity coefficient (Li / Mg) is more than 8 times higher than that of Example 2.

[0030] Comparative Example 1 10.0 g of the same aluminum-based precursor powder was mixed with 2.0 g of polyvinyl alcohol (PVA-124, degree of hydrolysis 99%), and 20 mL of deionized water was added to knead into a plastic paste. The paste was then shaped using a twin-screw extruder (die diameter 1.8 mm, extrusion pressure 15 MPa), granulated, and dried in a 120℃ hot air circulating oven for 6 hours. The resulting cylindrical particles (length-to-diameter ratio 1.2:1) had a contact angle of 32° and a specific surface area of ​​30.2 m². 2 / g; In the same dynamic adsorption test, the adsorption capacity was only 3.2g / L.

[0031] Comparative Example 2 The raw material formulation and granulation process were basically the same as in Example 1, but the freeze-drying process was changed to hot air drying at 60°C for 12 hours. The resulting particles were severely shrunken and deformed. Micro-CT scanning showed that the internal porosity was only 48.7%, the specific surface area decreased to 28.2 m² / g, and the contact angle reached 8.4°. In the brine dynamic adsorption experiment, the equilibrium adsorption capacity after 24 hours was 3.8 g / L, which was lower than that of the freeze-dried sample. After 20 cycles, the gel shell cracked and fell off, proving that the hot drying caused irreversible structural collapse.

[0032] By comparing Examples 1-2 with Comparative Example 1, it is evident that the adsorbent prepared by the sodium alginate gel granulation combined with freeze-drying method used in this invention exhibits significantly better hydrophilicity and adsorption capacity than the traditional extrusion-thermal drying method. Secondly, comparing Example 1 with Comparative Example 2, both used sodium alginate gel granulation, but Example 1 employed freeze-drying while Comparative Example 2 used hot air drying. The results showed that hot air drying led to particle shrinkage, pore structure collapse, and a significant reduction in specific surface area and capacity, demonstrating that freeze-drying is a key step in maintaining high specific surface area and high adsorption capacity. Example 3 introduced ion imprinting technology, which improved the Li / Mg selectivity coefficient by 3 times compared to Example 2. Example 4 introduced sulfonic acid groups, which improved the selectivity coefficient by more than 8 times, achieving high selectivity.

Claims

1. A process for the preparation of a high hydrophilicity spherical aluminum-based lithium sorbent, characterized in that The method comprises the following steps: dispersing an aluminum-based lithium adsorption precursor in a mixed solution containing sodium alginate and a hydrophilic organic binder to form a suspension; The suspension is dropped into a calcium chloride solution, and a three-dimensional network gel microsphere is formed by ionic cross-linking of the sodium alginate and Ca 2+ encapsulating the aluminum-based lithium adsorption precursor. freeze-drying the gel microspheres to obtain a porous spherical adsorbent.

2. The method of claim 1, wherein, The hydrophilic organic binder is at least one of polyvinyl alcohol, polyethylene glycol, polyvinylpyrrolidone, sodium carboxymethyl cellulose or polyacrylic acid, and accounts for 1-20 wt% of the dry weight of the mixed solution; the concentration of sodium alginate in the mixed solution is 1.0-4.0 wt%, the concentration of the hydrophilic organic binder is 0.5-5.0 wt%, and the solid content of the aluminum-based precursor is 15-50 wt%; the concentration of the calcium chloride solution is 0.1-1.0 mol / L, and the crosslinking reaction time is 5-60 minutes.

3. The method of claim 1, wherein, The freeze-drying step comprises a pre-freezing stage of 4-12 hours at-40℃ to-80℃ and a sublimation stage of 24-72 hours at a pressure of 0.1-50 Pa.

4. The method of claim 1, wherein: The mixed solution further contains a lithium salt template ion, a functional monomer for ion imprinting and a crosslinking agent; after the gel microspheres are formed, a polymerization step is added to make the functional monomer and the crosslinking agent polymerize to form an ion imprinting network on the gel shell; After the polymerization is completed, the template ion is removed by an elution step.

5. The method of claim 4, wherein, The functional monomer for ion imprinting is at least one of methacrylic acid, acrylic acid or itaconic acid; the crosslinking agent is at least one of N,N-methylene bisacrylamide or ethylene glycol dimethacrylate; and the polymerization or copolymerization step is carried out in the presence of an initiator at a reaction temperature of 50-70℃ and a reaction time of 2-6 hours.

6. The method of claim 4, wherein, The mixed solution further contains a functional monomer with a sulfonic acid group, which is copolymerized with other monomers in the polymerization step.

7. The method of claim 6, wherein, The functional monomer with a sulfonic acid group is at least one of 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid or vinyl sulfonic acid; and the initiator is ammonium persulfate, potassium persulfate or azobisisobutyronitrile, and the amount is 0.05-0.5 wt% of the mass of the aqueous solution.

8. The method according to claim 6 or 8, characterized in that, The elution step uses an acid solution of 0.5-2.0 mol / L for soaking and washing for 6-24 hours, and the acid solution is preferably hydrochloric acid or nitric acid.

9. An aluminum-based adsorbent prepared by the method of any one of claims 1-8.

10. Use of the aluminum-based adsorbent of claim 9 for extracting lithium from a lithium-containing solution.

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