PH response hydrogel composite lithium adsorbent as well as preparation method and application thereof

Abstract

The invention provides a pH response hydrogel composite lithium adsorbent as well as a preparation method and application thereof. The method aims at solving the problems that an existing powder lithium adsorbent is poor in fluidity and difficult to recycle and reuse in practical application. The pH response hydrogel composite lithium adsorbent can expand under the alkaline adsorption condition required by a lithium ion sieve and shrink under the required acidic desorption environment, and the defect that the adsorption performance is reduced due to the fact that part of adsorption sites are covered when a traditional organic binder is formed is overcome. The preparation method of the pH response hydrogel composite lithium adsorbent comprises the following steps: dissolving acrylamide and acrylic acid in water, uniformly stirring, then adding a cross-linking agent and an initiator, dissolving and uniformly stirring, then adding lithium adsorbent powder, and ultrasonically dispersing uniformly to obtain a precursor solution; and adding a tetramethylethylenediamine accelerant into the precursor solution, quickly and uniformly stirring, sealing, standing and curing, washing with deionized water for multiple times, and drying to obtain the pH response hydrogel composite lithium adsorbent. The obtained adsorbent has the advantages of high mechanical strength, simple separation and recovery operation, good pH response cycle reversibility and the like. The hydrophilic three-dimensional network structure expands in an alkaline lithium-containing solution, so that lithium adsorbent particles are fully exposed, and the inherent high adsorption capacity of the powder lithium ion sieve is exerted.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium extraction materials, and specifically to a pH-responsive hydrogel composite lithium adsorbent and a preparation method and application thereof. Background Art

[0002] The advancement of global low-carbon transformation policies has accelerated the development of clean energy and new energy vehicles. Among the many lithium extraction technologies, adsorption has become one of the most promising lithium extraction technologies due to its simple process, high extraction efficiency, good selectivity, environmental protection and recyclability. Adsorbents are the core of adsorption technology. Among them, lithium ion sieve adsorbents have become a powerful tool for directly extracting lithium from liquid lithium resources due to their excellent adsorption capacity, selectivity and environmental friendliness, showing broad application potential. Lithium ion sieve adsorbents mainly include titanium-based adsorbents and manganese-based adsorbents. Both of them use the ion sieving effect of special memory channels to utilize Li in a stable crystal structure. + / H + Ion exchange enables the insertion and extraction of lithium ions, thus showing higher selectivity.

[0003] Traditional lithium ion sieve adsorbents are usually powdered materials, which face many challenges in practical applications, such as easy agglomeration, poor fluidity, and difficulty in recycling and reuse. In order to improve its operability and efficiency of use, it is usually necessary to use an effective molding carrier to make it appear in the form of granular balls, films, fibers or foams. The ideal carrier should have good pore structure, chemical stability, mechanical strength, surface affinity, economy and environmental friendliness. At present, a variety of binders are generally used to mold powder lithium ion sieves. For example, CN 116809013 A discloses a method for preparing spherical titanium-based lithium ion sieve particles, which is to disperse a titanium-based lithium ion sieve precursor powder modified by a coupling agent into an oil phase composed of a porogen, an organic monomer, a cross-linking agent and an initiator, and obtain spherical particles by suspension polymerization and post-treatment, and the lithium adsorption capacity is 15 mg / g. CN 112871127 A also discloses a method for preparing lithium ion sieve particles, which comprises grinding lithium ion sieve powder, mixing with an inorganic binder, spray drying, mixing with a template pore-forming agent, and then mixing with an aqueous resin emulsion for granulation, and heating and curing to obtain lithium ion sieve particles, wherein the saturated adsorption capacity of pure lithium ion sieve is 23.8 mg / g. However, the above two preparation methods for forming lithium ion sieve particles both have problems: the binder used will partially occupy or block the active sites of the adsorbent when forming the lithium ion sieve particles, limiting the mass transfer efficiency and reducing the original adsorption capacity of the adsorbent.

[0004] Therefore, how to achieve efficient molding and application while ensuring the inherent adsorption performance of powdered lithium ion sieve adsorbents is still a key issue that needs to be solved urgently. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a pH-responsive hydrogel composite lithium adsorbent. The present invention combines a pH-responsive hydrogel having a hydrophilic three-dimensional network structure with a lithium ion sieve adsorbent, innovatively utilizing the pH environmental changes required by the lithium ion sieve adsorbent during adsorption and desorption, and effectively dispersing and fixing the powder adsorbent material without affecting the inherent adsorption capacity of the lithium ion sieve.

[0006] In a first aspect, the present invention provides a method for preparing a pH-responsive hydrogel composite lithium adsorbent, comprising the following steps: Add acrylamide and acrylic acid into water and stir until they are completely dissolved to obtain a transparent mixed solution; Add the crosslinking agent and initiator to the above mixed solution, and stir evenly until they are completely dissolved; Adding powdered lithium ion sieve adsorbent to the above solution and dispersing it evenly by ultrasonication to obtain a precursor solution; Add tetramethylethylenediamine accelerator to the precursor solution, stir quickly and evenly, then seal and let stand to solidify; The hydrogel obtained above is immersed in deionized water, the unreacted monomers are washed for multiple times, and the pH-responsive hydrogel composite lithium adsorbent is obtained after low-temperature drying.

[0007] Preferably, in step 1), acrylic acid accounts for 1% to 80% of the total mass of acrylic acid and acrylamide monomers, and the total mass fraction of the mixed monomers in the mixed solution is 5% to 50%.

[0008] Preferably, in step 2), the crosslinking agent is N,N'-methylenebisacrylamide; the initiator is one or a combination of ammonium persulfate or potassium persulfate; the crosslinking agent accounts for 0.1% to 10% of the total monomer mass of acrylic acid and acrylamide, and the initiator accounts for 0.1 to 10 mol% of the total monomer mass of acrylic acid and acrylamide.

[0009] Preferably, in step 3), the powdered lithium ion sieve adsorbent is one or more of manganese lithium ion sieve or titanium lithium ion sieve powders, and the mixing ratio accounts for 10% to 80% of the total monomer mass of acrylic acid and acrylamide in the precursor solution.

[0010] Preferably, in step 4), the volume ratio of tetramethylethylenediamine accelerator to precursor solution is 1:20-1:100.

[0011] Preferably, in step 5), the hydrogel is washed in deionized water for at least 3 times, and then dried at a low temperature of 20-70° C. to obtain a pH-responsive hydrogel composite lithium adsorbent.

[0012] In a second aspect, the present invention provides a pH-responsive hydrogel composite lithium adsorbent obtained by the above-mentioned preparation method.

[0013] In a third aspect, the present invention provides the use of the pH-responsive hydrogel composite lithium adsorbent in lithium extraction. The pH-responsive hydrogel composite lithium adsorbent is suitable for adsorption under neutral or alkaline conditions and desorption under acidic conditions, and is suitable for various lithium-containing solutions, including but not limited to at least one lithium-containing solution in salt lake brine, geothermal water, seawater, oil and gas field produced water or lithium-containing wastewater.

[0014] Compared with the prior art, the present invention has the following beneficial effects: Acrylamide and acrylic acid monomers form a long-chain structure through copolymerization, which gives the hydrogel higher mechanical strength, elasticity and structural stability.

[0015] The carboxyl and amino groups on the hydrogel polymer chains interact with the hydroxyl groups rich in the surface of the lithium ion sieve through hydrogen bonds to form a stable composite material, ensuring the effective fixation of the lithium ion sieve particles.

[0016] When lithium ions are adsorbed under alkaline conditions, the swelling properties of the pH-responsive hydrogel help to expose more adsorption sites, promote the diffusion of lithium ions in the lithium-containing solution within the material, and thus improve the adsorption efficiency of lithium ions.

[0017] Under acidic conditions, the shrinkage properties of the hydrogel facilitate the smooth desorption process, further enhancing the reproducibility and recyclability of the adsorbent. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a physical picture of P(C1-M9)-20%HTO prepared in Example 1; Figure 2 The electron microscope images of the microscopic morphology of P(C1-M9)-20%HTO prepared in Example 1 after being treated in solutions of pH=1 and pH=12; Figure 3 The pH responsiveness cycle test results of P(C1-M9)-20%HTO prepared in Example 1; Figure 4 This is a comparison chart of the lithium adsorption performance of P(C1-M9)-20%HTO prepared in Example 1 in simulated lithium-containing solutions at pH = 9, 10, 11 and 12 and the adsorption effect of H2TiO3 powder adsorbent. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0020] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0021] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0022] Embodiment 1: This embodiment provides a method for preparing a pH-responsive hydrogel composite lithium adsorbent, comprising the following steps: Add 4.5 g acrylamide and 0.5 g acrylic acid into 20 mL water and stir until completely dissolved to obtain a transparent mixed solution; Add 15 mg of N,N'-methylenebisacrylamide crosslinker and 25 mg of ammonium persulfate initiator to the above mixture and stir until completely dissolved; Add 1 g of powdered titanium-based lithium ion sieve H2TiO3 (HTO) adsorbent to the mixed solution and disperse it evenly by ultrasonication to obtain a precursor solution; Add 0.6 mL of tetramethylethylenediamine accelerator to the precursor solution, stir quickly and evenly, then seal and let stand to solidify; The hydrogel obtained above was immersed in deionized water, and the unreacted monomers were washed 5 times, and then dried in an oven at 50°C to obtain a pH-responsive hydrogel composite lithium adsorbent, which was recorded as P(C1-M9)-20%HTO.

[0023] Example 2: This example is basically the same as Example 1, except that 4.5 g acrylamide and 0.5 g acrylic acid are replaced by 4 g acrylamide and 1 g acrylic acid to obtain P(C2-M8)-20%HTO.

[0024] Example 3: This example is basically the same as Example 1, except that 4.5 g acrylamide and 0.5 g acrylic acid are replaced with 3.5 g acrylamide and 1.5 g acrylic acid to obtain P(C3-M7)-20%HTO.

[0025] Example 4: This example is basically the same as Example 1, except that: adding 1 g of powdered titanium-based lithium ion sieve H2TiO3 adsorbent to the mixed solution is replaced by adding 1.5 g of powdered titanium-based lithium ion sieve H2TiO3 to obtain P(C1-M9)-30%HTO.

[0026] Comparative Example 1: This comparative example is basically the same as Example 1, except that the addition of acrylic acid is eliminated to obtain PM-20% HTO hydrogel.

[0027] Performance Testing: 1) pH responsiveness test of pH responsive hydrogel composite lithium adsorbent Weigh the mass m 0 (g) of low-temperature dried P(C1-M9)-20%HTO was immersed in a certain volume of lithium hydroxide solution with a pH of 12. After 12 hours, it was taken out and the excess water on the surface was absorbed with filter paper. The weight was weighed and recorded as m 1 (g). After that, the P(C1-M9)-20%HTO expanded in the alkaline solution was transferred to a certain volume of dilute hydrochloric acid solution with a pH of 1, and was also left to soak for 12 hours before being taken out. The excess water on the surface was absorbed with filter paper, and the weight was recorded as m 2 (g). The pH response cycle reversibility test is to repeat the above experimental steps under the same conditions. The swelling degree calculation formula of the hydrogel composite lithium adsorbent is: Swelling degree = ( m 1或2 - m 0) / m 0 (g / g).

[0028] Figure 1 The actual picture of P(C1-M9)-20%HTO. The hydrogel after low temperature drying has good flexibility and mechanical strength. Its shape can also be prepared by using molds of different shapes and specifications according to needs. The above P(C1-M9)-20%HTO was treated in pH=1 and pH=12 solutions, and its microscopic morphology was characterized after freeze drying. Figure 2 As shown in the figure, the dried gel presents a dense particle stacking state with small pores. When immersed in an acid solution, the hydrogel absorbs water and swells, and the pores partially swell. After being treated in an alkaline solution, the carboxyl groups on the polymer chains of the composite hydrogel are ionized and generate electrostatic repulsion, which causes the hydrogel network to expand further, increase the specific surface area, and enlarge the pores, thereby more fully exposing the loaded H2TiO3 particles. In the 10 pH-responsive swelling-shrinkage reversible cycle tests, the results are as follows: Figure 3 As shown in the figure, P(C1-M9)-20%HTO has excellent pH response reversibility. After 12 hours of swelling in an alkaline environment, the swelling degree of the composite hydrogel adsorbent is about 65 g / g, while in an acidic environment, the swelling degree of the hydrogel can shrink to about 15 g / g after 12 hours, which is attributed to the reversible ionization behavior of the composite hydrogel adsorbent. In an alkaline environment, the carboxyl group is deprotonated to -COO ⁻ , the electrostatic repulsion is enhanced, and the hydrogel expands; in an acidic environment, the carboxyl groups are protonated, and the electrostatic repulsion in the hydrogel structure is weakened, causing the hydrogel to shrink. Acrylamide, as the main monomer of the polymer, forms a long-chain structure through copolymerization, giving the hydrogel higher mechanical strength, elasticity and structural stability, ensuring the stability of the network skeleton in the reversible pH responsiveness test.

[0029] 2) Lithium ion adsorption performance test of pH-responsive hydrogel composite lithium adsorbent In this experiment, powdered H2TiO3 was used as a control. The static adsorption experiment of P(C1-M9)-20%HTO on Li + The static adsorption experiment was carried out in a constant temperature shaker, and the ion concentration was determined by ICP-OES. + The adsorption amount is calculated according to the formula: In the formula, q e The effect of HTO on Li + Equilibrium adsorption capacity (mg / L); c 0 and c e are the initial concentration of lithium ions in the solution and the concentration at adsorption equilibrium (mg / L); V is the volume of lithium-containing solution (L); m is the mass of lithium ion sieve adsorbent (g).

[0030] Lithium adsorption test results are as follows Figure 4 As shown, H2TiO3 in the composite hydrogel adsorbent can exert a lithium adsorption capacity comparable to that of the powder adsorbent H2TiO3 in the pH=11 and 12 environments. The adsorption capacity of lithium ions by powdered H2TiO3 in a lithium-containing solution at pH=12 is 38 mg / g, while the adsorption capacity of pure H2TiO3 in P(C1-M9)-20%HTO after molding can reach 42 mg / g. This shows that after H2TiO3 is molded in this way, there is no problem of a large amount of adsorption sites being covered, resulting in a decrease in adsorption capacity. At the same time, the hydrophilic three-dimensional network structure can not only evenly distribute the adsorbent particles, but also expand significantly in an alkaline environment, effectively avoiding the agglomeration of particles of the powder adsorbent during use, thereby maximizing the inherent lithium adsorption capacity of the lithium ion sieve H2TiO3.

Claims

1. A pH-responsive hydrogel composite lithium adsorbent, characterized in that: The hydrogel composite lithium adsorbent is pH-responsive and has a hydrophilic three-dimensional network structure that can swell under alkaline conditions and shrink under acidic conditions. It effectively combines the properties of lithium ion sieve adsorbent adsorption under alkaline conditions and desorption under acidic conditions, thereby promoting the adsorption and desorption process of lithium ions by lithium adsorbent particles.

2. A method for preparing a pH-responsive hydrogel composite lithium adsorbent, characterized in that: The following steps are involved: Add acrylamide and acrylic acid into water and stir until they are completely dissolved to obtain a transparent mixed solution; Add the crosslinking agent and initiator to the above mixed solution, and stir evenly until they are completely dissolved; Adding powdered lithium ion sieve adsorbent to the above solution and dispersing it evenly by ultrasonication to obtain a precursor solution; Add tetramethylethylenediamine accelerator to the precursor solution, stir quickly until uniform, seal and let stand to solidify; The hydrogel obtained above is soaked in deionized water, the unreacted monomers are washed for multiple times, and the pH-responsive hydrogel composite lithium adsorbent is obtained after low-temperature drying.

3. The preparation method according to claim 2, characterized in that: In step (1), the acrylic acid accounts for 1% to 80% of the total mass of acrylic acid and acrylamide monomers, and the total mass fraction of the mixed monomers in the mixed solution is 5% to 50%.

4. The preparation method according to claim 2, characterized in that: In step (2), the cross-linking agent is N,N'-methylenebisacrylamide, and the initiator is one or a combination of ammonium persulfate or potassium persulfate; the cross-linking agent accounts for 0.1% to 10% of the total monomer mass, and the initiator accounts for 0.1 to 10 mol% of the total monomers of acrylic acid and acrylamide.

5. The preparation method according to claim 2, characterized in that: In step (3), the powdered lithium ion sieve adsorbent is one or more of manganese lithium ion sieve or titanium lithium ion sieve powders, and the mixing ratio accounts for 10% to 80% of the total mass of acrylic acid and acrylamide monomers in the precursor solution.

6. The preparation method according to claim 2, characterized in that: The volume ratio of the tetramethylethylenediamine accelerator to the precursor solution in step (4) is 1:20 to 1:100, and the mold can be of any shape and specification.

7. The preparation method according to claim 2, characterized in that: The hydrogel described in step (5) is washed with deionized water for at least 3 times and then dried at a low temperature of 20-70° C. to obtain a pH-responsive hydrogel composite lithium adsorbent.

8. An application of a pH-responsive hydrogel composite lithium adsorbent prepared by the preparation method according to any one of claims 1 to 7, characterized in that The pH-responsive hydrogel composite lithium adsorbent is used as a lithium adsorbent for lithium extraction in at least one lithium-containing solution of salt lake brine, geothermal water, seawater, oil and gas field produced water or lithium-containing wastewater.

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