A preparation method and application of ammonium phosphomolybdate-sodium alginate composite gel balls suitable for extraction of rubidium and cesium resources in seawater

Abstract

This invention relates to the field of adsorption material preparation technology, specifically providing a method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres and their application. The method includes: (1) preparing ammonium molybdate solution and potassium pyrophosphate solution respectively; (2) adding potassium pyrophosphate solution dropwise to ammonium molybdate solution to prepare ammonium phosphomolybdate powder; (3) mixing the obtained ammonium phosphomolybdate powder with sodium alginate solution evenly; (4) adding the mixed solution dropwise to a soluble calcium salt solution to obtain ammonium phosphomolybdate-sodium alginate composite gel spheres; (5) using the prepared gel spheres to adsorb rubidium ions and cesium ions in concentrated seawater. The ammonium phosphomolybdate-sodium alginate composite gel spheres prepared by this invention solve the problems of easy loss of powdered ammonium phosphomolybdate and difficulty in solid-liquid separation. After multiple adsorption-desorption cycles, the material still has good structural stability and reusability.

Description

Technical Field

[0001] This invention relates to the field of adsorption material preparation technology, specifically to a method for preparing a composite gel ball adsorbent with sodium alginate as the matrix and ammonium phosphomolybdate supported thereon, and its application. Background Technology

[0002] Rubidium (Rb) and cesium (Cs), as important rare alkali metal elements, are widely used in high-tech fields such as atomic clocks, special glasses, optoelectronic devices, energy materials, and aerospace due to their excellent photoelectric properties and unique physicochemical properties, possessing significant economic value and strategic importance. Currently, Rb and Cs resources are mainly found in ores and salt lake brines. However, Rb and Cs are often associated resources in natural mineral resources, leading to high extraction difficulty, complex processes, and relatively low environmental friendliness.

[0003] Although the concentrations of Rb and Cs ions in salt lake brines and seawater are generally low, salt lake brines, especially seawater, have large reserves, and both Rb and Cs resources exist in ionic form, making their extraction processes relatively milder and more environmentally friendly. If the Na+ concentration in brine or seawater could be reduced... + K + Ca 2+ Mg 2+ By mitigating interference from coexisting ions, efficient extraction of Rb and Cs ions can be achieved. Currently, methods for extracting Rb and Cs from brine and seawater mainly include chemical precipitation, solvent extraction, and adsorption. Among these, chemical precipitation is not suitable for low-concentration systems; solvent extraction suffers from organic solvent loss and potential environmental pollution; in contrast, adsorption is considered the most promising technical route for extracting low concentrations of Rb and Cs ions from water due to its simple operation, low cost, environmental friendliness, and recyclability.

[0004] In recent years, various adsorbent materials have been used for the separation and recovery of Rb and Cs, including Prussian blue and its analogues, aluminosilicate materials (such as zeolites and montmorillonite), heteropolyacid salts, and polyvalent metal phosphates. Among these, Prussian blue materials, while possessing high adsorption capacity, suffer from difficulties in desorption and poor regeneration performance. Ammonium phosphomolybdate (AMP) is a typical heteropolyacid salt ion exchanger with a specific Keggin structure and the chemical formula (NH4)3P(Mo3O2). 10 4. Can be transmitted via NH4 + With Rb + Cs +Ammonium phosphomolybdate exhibits excellent selectivity and high adsorption capacity through ion exchange, while also possessing good acid resistance and radiation stability. However, as a microcrystalline powder, it suffers from a small specific surface area, low mechanical strength, and is prone to loss during practical applications, leading to difficulties in solid-liquid separation, which severely limits its industrial application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres suitable for the extraction of rubidium and cesium resources from seawater, and their application. By loading ammonium phosphomolybdate into a sodium alginate gel system, effective immobilization and structural control of ammonium phosphomolybdate are achieved. This allows the resulting composite gel spheres to maintain the high selectivity and adsorption capacity of ammonium phosphomolybdate for rubidium and cesium ions, while significantly improving their mechanical strength and hydrodynamic properties. It also effectively solves the problems of easy loss of ammonium phosphomolybdate powder and difficulties in solid-liquid separation during application, thus facilitating its engineering application.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres, comprising the following steps:

[0008] (1) Prepare a 14.4% ammonium molybdate solution using deionized water to obtain solution I; dilute concentrated nitric acid with deionized water at a volume ratio of 1:7 to obtain a dilute nitric acid solution; use the dilute nitric acid solution as a solvent to prepare a 4.55% potassium pyrophosphate solution to obtain solution II;

[0009] (2) Under stirring conditions, solution II from step (1) was slowly added dropwise to solution I at a volume ratio of 1:1 at a dropping rate of 1.2 mL / min. After the addition was completed, the solution was allowed to stand for 24 h. The resulting precipitate was then subjected to 1 mol·L⁻¹ precipitate treatment. -1 The mixture was washed with nitric acid solution and deionized water and centrifuged until the washing solution was neutral. Then it was dried at 50°C to obtain ammonium phosphomolybdate powder.

[0010] (3) Dissolve sodium alginate in deionized water, add ammonium phosphomolybdate powder obtained in step (2), and stir evenly to obtain a homogeneous mixed solution.

[0011] (4) The mixed solution obtained in step (3) is transferred to a syringe and dripped into a soluble calcium salt solution with a mass concentration of 4% through a 1.2 mm needle. After solidification, the spherical particles are allowed to stand and washed to obtain ammonium phosphomolybdate-sodium alginate composite gel balls.

[0012] Preferably, in step (3), the sodium alginate has a mass-volume concentration of 1-2% in the solution; and the ammonium phosphomolybdate powder has a mass-volume concentration of 2%-6% in the sodium alginate solution.

[0013] Preferably, in step (4), the soluble calcium salt is calcium chloride.

[0014] Beneficial effects

[0015] The ammonium phosphomolybdate-sodium alginate composite gel spheres provided by this invention utilize sodium alginate and Ca... 2+ Cross-linking effectively immobilizes ammonium phosphomolybdate, overcoming the difficulties in solid-liquid separation and easy loss in its powder form, thus improving the stability of the adsorbent material. The composite gel spheres prepared in this invention, while maintaining the structural stability of the ammonium phosphomolybdate Keggin, exhibit high selectivity and adsorption capacity for rubidium and cesium ions, with theoretical maximum adsorption capacities reaching 127.9 mg / g and 159.7 mg / g, respectively. Furthermore, under elution conditions of 0.8 mol / L NH4Cl solution, the recovery rate remained above 80% after five adsorption-desorption cycles, indicating that the material possesses good structural stability and recyclability. Attached Figure Description

[0016] Figure 1 This is a photograph of the ammonium phosphomolybdate-sodium alginate composite gel spheres prepared in Example 1 of the present invention.

[0017] Figure 2 This is a SEM image of the ammonium phosphomolybdate powder prepared in Example 1 of the present invention;

[0018] Figure 3 This is a SEM image of the ammonium phosphomolybdate-sodium alginate composite gel spheres prepared in Example 1 of this invention;

[0019] Figure 4 The images show the XRD patterns of the ammonium phosphomolybdate-sodium alginate composite gel spheres and the synthesized ammonium phosphomolybdate powder prepared in Example 1 of this invention.

[0020] Figure 5 The images show the FTIR spectra of the ammonium phosphomolybdate-sodium alginate composite gel spheres and the synthesized ammonium phosphomolybdate powder prepared in Example 1 of this invention.

[0021] Figure 6 The ammonium phosphomolybdate-sodium alginate composite gel spheres prepared in Example 1 of this invention are used to counteract Rb. + The adsorption isotherm fitting curve;

[0022] Figure 7 The ammonium phosphomolybdate-sodium alginate composite gel spheres prepared in Example 1 of this invention are Cs + The adsorption isotherm fitting curve. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] The main raw materials and reagents used in the embodiments and comparative examples of this invention are as follows:

[0025] Ammonium molybdate tetrahydrate (H 24 Mo7N6O 24 • 4H2O (≥99%), purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0026] Potassium pyrophosphate (K4P2O7, ≥97%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0027] Nitric acid (HNO3, ≥99.9%) was purchased from Tianjin Kemeo Chemical Reagent Co., Ltd.

[0028] Sodium alginate (SA, molecular weight 100K), purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0029] Anhydrous calcium chloride (CaCl2, ≥96%) was purchased from Shanghai E. En Chemical Technology Co., Ltd.

[0030] Deionized water, prepared in the laboratory (conductivity <2uS / cm).

[0031] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] Example 1:

[0033] (1) Prepare a 14.4% ammonium molybdate solution using deionized water to obtain solution I; dilute concentrated nitric acid with deionized water at a volume ratio of 1:7 to obtain a dilute nitric acid solution; use the dilute nitric acid solution as a solvent to prepare a 4.55% potassium pyrophosphate solution to obtain solution II.

[0034] (2) Under stirring conditions, solution II from the previous step was slowly added dropwise to solution I at a volume ratio of 1:1, at a dropping rate of 1.2 mL / min. After the addition was completed, the mixture was allowed to stand for 24 h. The resulting precipitate was then subjected to 1 mol·L⁻¹ precipitate treatment. -1 The mixture was washed with nitric acid solution and deionized water and centrifuged until the washing solution was neutral. Then it was dried at 50°C to obtain ammonium phosphomolybdate powder.

[0035] (3) Prepare a sodium alginate solution with a mass fraction of 2% using deionized water, and fully dissolve the sodium alginate under magnetic stirring to obtain a homogeneous solution; then prepare a sodium alginate solution with a mass fraction of 4.9%; continue stirring to uniformly disperse the ammonium phosphomolybdate to obtain a homogeneous mixed solution.

[0036] (4) Transfer the mixed solution obtained in step (3) into a syringe and add it dropwise into a 4% CaCl2 solution through a 1.2 mm needle. After the addition is complete, let the obtained gel balls stand in the cross-linking solution for 24 hours, collect the gel balls and wash them with deionized water. Finally, soak the obtained ammonium phosphomolybdate-sodium alginate composite gel balls in deionized water for storage.

[0037] Example 2

[0038] A method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres differs from Example 1 in that: in step (3), the amount of ammonium phosphomolybdate powder added accounts for 2.94% of the mass fraction of sodium alginate solution, while the other conditions remain unchanged.

[0039] Example 3

[0040] A method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres differs from Example 1 in that: in step (3), the amount of ammonium phosphomolybdate powder added accounts for 3.92% of the mass fraction of sodium alginate solution, while the other conditions remain unchanged.

[0041] Example 4

[0042] A method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres differs from Example 1 in that: in step (3), the amount of ammonium phosphomolybdate powder added accounts for 5.88% of the mass fraction of sodium alginate solution, while the other conditions remain unchanged.

[0043] Example 5

[0044] A method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres differs from Example 1 in that: in step (3), a sodium alginate solution with a mass fraction of 1% is prepared using deionized water, and the amount of ammonium phosphomolybdate powder added accounts for 4.95% of the mass fraction of the sodium alginate solution, while the other conditions remain unchanged.

[0045] Comparative Example 1:

[0046] A method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres differs from Example 1 in that: in step (2), ammonium phosphomolybdate is not added, while the other conditions remain unchanged.

[0047] Performance testing:

[0048] (1) Adsorption performance test

[0049] At room temperature, prepare 50 mL solutions of Rb with initial concentrations ranging from 0 to 1000 mg / L. + Cs + A solution was prepared by adding a predetermined mass of adsorbent. The conical flask was placed in a constant-temperature water bath shaker and shaken at 200 rpm for adsorption. After the predetermined reaction time, the supernatant was collected and filtered through a 0.45 μm microporous membrane. The remaining Rb in the filtrate was determined using a flame atomic absorption spectrophotometer. + Cs + The concentration.

[0050] Rb was calculated using formulas (1) and (2). + Cs + The adsorption efficiency AE (%) and desorption efficiency DE (%):

[0051]

[0052] In the formula, C0 (mg / L) and C e (mg / L) represent the Rb concentration in the solution. + Cs + The initial and equilibrium concentrations; C1 (mg / L) represents the Rb concentration in the eluent. + Cs + The concentration of V0 is the volume of the adsorption liquid; V1 is the volume of the elution liquid.

[0053] The adsorption behavior of the composite gel sphere adsorbent was determined using a pseudo-first-order kinetic model (Equation 3) and a pseudo-second-order kinetic model (Equation 4):

[0054] ln(q e -q t )=lnq e -k1t (3)

[0055]

[0056] In the formula, q e and q t (mg / g) represent the adsorption capacity at equilibrium time and time t, respectively; k1(min -1 ) and k2(g·mg -1 ·min -1 ) are the pseudo-first-order and pseudo-second-order rate constants, respectively.

[0057] The data were fitted using the Langmuir adsorption isotherm model (Equation 5) and the Freundlich adsorption isotherm model (Equation 6):

[0058]

[0059] In the formula, Ce (mg / L) represents Rb + Cs + equilibrium concentration, q e (mg / g) and q max (mg / g) represents the effect of Rb + Cs + The equilibrium adsorption and theoretical maximum adsorption capacity, K L (L / mg) is the Langmuir constant, 1 / n and K. F (mg / g) is the Freundlich constant, which is related to the adsorption strength and capacity, respectively.

[0060] Table 1 shows the effects of the composite gel spheres prepared in Example 1 on Rb at different adsorption times. + Cs + The adsorption effect (initial concentration was 3 mg / L).

[0061] Table 1. Effects of composite gel spheres on Rb at different adsorption times in Example 1. + Cs + adsorption effect

[0062]

[0063] As shown in Table 1, with the increase of adsorption time, the composite gel spheres' effect on Rb... + Cs + The adsorption capacity of Cs was significantly enhanced, with the first 30 minutes being a rapid adsorption phase, followed by a slow adsorption phase and gradually reaching equilibrium. + Equilibrium was reached in 120 minutes, while Rb + It reaches equilibrium in 180 minutes.

[0064] The above dynamic data were fitted using pseudo-first-order and pseudo-second-order dynamic models, and the results are shown in Table 2.

[0065] Table 2. Fitting results of the adsorption kinetics model

[0066]

[0067] As can be seen from Table 2, the linear correlation coefficient (R0) of the quasi-second-order dynamics model is... 2 The value is significantly higher than that of the pseudo-first-order dynamic model, where R... Rb 2 =0.99982; R Cs 2 =0.99995. This indicates that the quasi-second-order model can more accurately describe the effect of the composite gel spheres on Rb.+ and Cs + The adsorption process indicates that the adsorption process is mainly controlled by chemisorption.

[0068] Table 3 shows the results of Rb tests on the composite gel spheres prepared in Examples 1-5 and Comparative Example 1. + Cs + The adsorption effect (initial concentration was 3 mg / L).

[0069] Table 3 shows the effects of composite gel spheres prepared in Examples 1-5 and Comparative Example 1 on Rb. + Cs + adsorption effect

[0070]

[0071] As shown in Table 3, the adsorption performance of the ammonium phosphomolybdate-sodium alginate composite gel spheres is affected by the amount of ammonium phosphomolybdate. With increasing ammonium phosphomolybdate content, the overall adsorption efficiency increases. However, when the ammonium phosphomolybdate content is too high, the proportion of the sodium alginate cross-linking network decreases, leading to a decrease in the structural stability of the gel spheres. The ammonium phosphomolybdate component in the gel spheres may detach during oscillating adsorption, resulting in a decrease in adsorption efficiency. Furthermore, in Example 5, changing the sodium alginate content resulted in uneven coating of the ammonium phosphomolybdate, thereby reducing the adsorption performance. The pure sodium alginate gel spheres in Comparative Example 1 showed a lower adsorption performance for Rb. + Cs + The near absence of adsorption indicates that ammonium phosphomolybdate is the key active component for achieving efficient adsorption.

[0072] Figure 1 The image shows the composite gel spheres prepared in Example 1. It can be seen that the composite gel spheres have a regular shape, uniform size, and a particle size of about 2 to 3 mm. Figure 2 The image shows a SEM image of ammonium phosphomolybdate powder. It can be seen that ammonium phosphomolybdate exhibits a regular and uniform polyhedral crystal morphology, demonstrating typical crystal structure characteristics. Figure 3 It is evident that the surface of the ammonium phosphomolybdate-sodium alginate composite gel spheres exhibits a relatively rough, wrinkled structure, and the ammonium phosphomolybdate particles are distributed within the calcium alginate matrix, with some particles exposed on the surface, indicating that they are mainly loaded through physical embedding and are not completely encapsulated.

[0073] Furthermore, Figure 4 The XRD patterns of the composite gel spheres and pure ammonium phosphomolybdate powder are shown. The results show that the characteristic diffraction peaks of the composite gel spheres are basically consistent with those of the ammonium phosphomolybdate powder, with no obvious peak shift or new diffraction peaks, indicating that the crystal structure of ammonium phosphomolybdate remains stable and does not undergo significant changes during the composite process. Figure 5 The FTIR spectra of gel spheres, ammonium phosphomolybdate, and sodium alginate are shown. The results indicate that at 1064, 967, 865, and 790 cm⁻¹...-1 The characteristic absorption peaks at these locations are respectively attributed to [PMo] 12 O 40 ] 3- PO in Keggin structure a Mo = O d Mo-O b -Mo and Mo-O c The stretching vibrations of the -Mo bonds indicate the integrity of its skeletal structure; 1409cm -1 The absorption peak at that location corresponds to NH4 + NH bending vibration; 1609cm -1 With 1118cm -1 The corresponding positions are -COO in the calcium alginate matrix. - Stretching vibration with CO; 3437cm -1 The broad peaks nearby are attributed to OH stretching vibrations, indicating the presence of water of crystallization in the material. Compared to pure ammonium phosphomolybdate and sodium alginate, the composite gel spheres retain the characteristic absorption peaks of both, and no new characteristic peaks were observed, further proving that ammonium phosphomolybdate did not undergo chemical structural changes during the composite process and was stably loaded into the calcium alginate matrix mainly through physical encapsulation.

[0074] Figure 6 , Figure 7 The ammonium phosphomolybdate-sodium alginate composite gel spheres prepared in Example 1 adsorb Rb + Cs + The effect of concentrations in the range of 0.5–1000 mg / L on adsorption performance. In the low concentration region, the equilibrium adsorption capacity (q...) e The adsorption capacity increases continuously with increasing initial concentration. This is attributed to the high concentration gradient providing the driving force for mass transfer, overcoming the mass transfer resistance at the solid-liquid interface. However, with further increases in concentration, the growth of adsorption capacity gradually slows down and tends to reach equilibrium in the high concentration region. This is because the number of specific active sites on the adsorbent surface is limited, gradually reaching saturation. + q max It is 127.9 mg / g; Cs + q max The value was 159.7 mg / g. Comparing the fitting results of the two models, Rb... + Cs + The correlation coefficients of the Langmuir model (0.9950, 0.9927) were significantly higher than those of the Freundlich model (0.8553, 0.8615), indicating that the composite gel spheres adsorbed Rb. + Cs + The adsorption behavior is more consistent with the Langmuir model. The results show that the adsorption process is mainly monolayer adsorption, occurring primarily on the adsorbent surface.

[0075] (2) Adsorption performance of rubidium and cesium in concentrated seawater

[0076] At room temperature, the composite gel spheres prepared in Example 1 were added to the prepared concentrated seawater at an adsorbent dosage of 120 g / L. The concentrations of the main ions and their concentrations are shown in Table 4. The solution was then placed in a constant temperature shaker and shaken for 180 min. The supernatant was filtered through a 0.45 μm microporous membrane, and the Rb content was measured using a flame atomic absorption spectrophotometer. + Cs + concentration.

[0077] Table 4. Major ions and their concentrations in concentrated seawater

[0078] Concentration (mg / L) 0.3 0.3 21600 760 820 2580 42900

[0079] Ammonium phosphomolybdate-sodium alginate composite gel spheres for the reaction of Rb in concentrated seawater + and Cs + Continuous adsorption-desorption experiments were conducted. The adsorbent dosage was set at 120 g / L, and the optimized 0.8 mol / L NH4Cl was used as the eluent. Five consecutive cycles were performed, and the results are shown in Table 5.

[0080] Table 5 Adsorption-Desorption Cycle Experiment

[0081]

[0082] As shown in Table 5, the ammonium phosphomolybdate-sodium alginate composite gel spheres prepared in Example 1 showed good performance against Rb in simulated concentrated seawater. + Cs + It has a high degree of selectivity. After 5 cycles, Rb + and Cs + The recovery rate remained above 80%. Although the adsorption capacity decreased slightly with increasing cycle number, it remained at a high level overall, indicating that the prepared ammonium phosphomolybdate-sodium alginate composite gel spheres have good structural stability and recycling performance, and are capable of long-term recovery of Rb from seawater. + and Cs + Its potential engineering application value.

[0083] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the above embodiments without departing from the spirit and substance of the present invention, and all such modifications or substitutions should fall within the scope of protection of the present invention.

Claims

1. A method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres, characterized in that, Includes the following steps: (1) Prepare a 14.4% ammonium molybdate solution using deionized water, denoted as solution I; dilute concentrated nitric acid with deionized water at a volume ratio of 1:7 to obtain a dilute nitric acid solution; use the dilute nitric acid solution as a solvent to prepare a 4.55% potassium pyrophosphate solution, denoted as solution II. (2) Under stirring conditions, solution II from step (1) was slowly added dropwise to solution I at a volume ratio of 1:1 at a dropping rate of 1.2 mL / min. After the addition was completed, the solution was allowed to stand for 24 h. The resulting precipitate was then subjected to 1 mol·L⁻¹ precipitate treatment. -1 The mixture was washed with nitric acid solution and deionized water and centrifuged until the washing solution was neutral. Then it was dried at 50°C to obtain ammonium phosphomolybdate powder. (3) Dissolve sodium alginate in deionized water, add ammonium phosphomolybdate powder obtained in step (2), and stir evenly to obtain a homogeneous mixed solution. (4) The mixed solution obtained in step (3) is transferred to a syringe and dripped into a soluble calcium salt solution with a mass concentration of 4% through a 1.2 mm needle. After solidification, the spherical particles are allowed to stand and washed to obtain ammonium phosphomolybdate-sodium alginate composite gel balls.

2. The method for preparing ammonium phosphomolybdate-sodium alginate composite gel spheres according to claim 1, characterized in that: In step (3), the mass fraction of the sodium alginate solution is 1% to 2%, and the amount of ammonium phosphomolybdate powder added is 2% to 6% of the mass of the sodium alginate solution.

3. Ammonium phosphomolybdate-sodium alginate composite gel spheres prepared by the preparation method according to any one of claims 1 to 2.

4. The ammonium phosphomolybdate-sodium alginate composite gel ball adsorbent according to claim 3 can be used to selectively extract rubidium ions and cesium ions from seawater, concentrated seawater or waste liquid containing rubidium and cesium.

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