Salicylic acid anchored hydrotalcite-bentonite composite material based on salt lake bischofite as well as preparation method and application of salicylic acid anchored hydrotalcite-bentonite composite material

Abstract

The invention discloses a salicylic acid anchored hydrotalcite-bentonite composite material based on salt lake bischofite as well as a preparation method and application thereof, and belongs to the technical field of preparation and application of heavy metal adsorbents. According to the invention, salt lake bischofite is used as a magnesium source, is purified and then is mixed with aluminum chloride hexahydrate, salicylic acid, bentonite and an alkaline reagent, and the composite material is prepared through a heating and pressurizing reaction. According to the material, bentonite serves as a substrate, magnesium-aluminum hydrotalcite grows on the surface, carboxyl, phenolic hydroxyl and other functional groups are anchored through flocculation and electrostatic adsorption, and the complexing capacity on heavy metal ions is synergistically enhanced. Compared with traditional hydrotalcite, the composite material has higher specific surface area, larger adsorption capacity and regeneration stability, and can efficiently remove lead ion pollution in water. The method realizes high-value utilization of salt lake magnesium resources, provides a novel adsorption material for heavy metal treatment, and has environmental protection benefits and application values.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal adsorbents, and particularly relates to a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite, and a preparation method and application thereof. Background Art

[0002] The reserves of magnesium resources in the Chaerhan Salt Lake in Qinghai are huge. In the process of salt lake resource development, due to the long-term production of potassium, 10 tons of magnesium chloride with bischofite as the main existence mode will be attached for every ton of potassium chloride produced, and the utilization rate of this part of magnesium resources is only about 2%. The accumulation and discharge of a large amount of bischofite not only occupy land, causing serious waste of resources, but also lead to "magnesium harm" problems such as soil salinization and groundwater quality deterioration. Existing magnesium resource development focuses on refractory materials, but the development progress of high-end magnesium-based functional materials such as magnesium-based layered materials is slow. Although researchers have done a lot of research on the preparation and modification of magnesium-based layered materials such as magnesium-aluminum hydrotalcite, and have made more progress in the treatment of heavy metal pollutants, bischofite in salt lakes is rarely used to prepare high value-added materials such as magnesium-based adsorption materials, and is applied to lead (Pb) in water bodies. 2+ Among the many adsorbents, layered double hydroxides (LDHs) have shown significant advantages in the field of heavy metal adsorption due to their lamellar structure, unique memory effect, and adjustable interlayer ions. The chemical formula of the original hydrotalcite is Mg6Al2(OH) 16 CO₃·4H₂O has a layered structure, belonging to a layered double hydroxide, containing carbonate ions and water molecules between its layers. Due to its interlayer anion exchange capacity and the interaction of surface phenolic hydroxyl groups, it has a certain adsorption capacity for organic dyes and anionic and cationic pollutants such as phosphates, chromates, fluorides, and heavy metal ions. Furthermore, hydrotalcite has the advantages of readily available raw materials and low synthesis costs, showing promising practical application prospects. However, the limitations of pristine hydrotalcite, such as the single surface functional group and insufficient specific surface area, restrict its ability to remove heavy metal ions. Therefore, improving the adsorption properties of functionalized hydrotalcite materials has become a hot research topic.

[0003] The current research progress on the functionalization of hydrotalcite mainly includes: (1) Organic intercalation modification. This technology mostly uses nitrogen protection during the preparation process, replaces the interlayer carbonate ions with nitrates, and then further carries out organic anion exchange, calcination-hydration reconstruction and other processes to introduce organic anions into the interlayer of hydrotalcite. Although this method can significantly improve the adsorption capacity of heavy metal ions by the chelation effect of organic ligands, it is difficult to prepare and has a low yield. The interlayer organic anions are easily lost during the cycle, resulting in poor regeneration performance.

[0004] (2) Nanocomposite modification. Using a hydrothermal method, LDH is grown in situ on nanomaterials such as biochar (BC), graphene oxide (GO), and carbon titanium aluminum (Mxenes). Although this method can significantly increase the specific surface area of hydrotalcite by constructing a three-dimensional porous structure and reduce the stacking and agglomeration problem of hydrotalcite sheets, it cannot provide specific functional groups such as carboxyl and thiol groups, resulting in a low adsorption capacity.

[0005] In summary, the current organic ion intercalated hydrotalcite has poor regeneration performance in the cycle and lacks effective functional groups, and its adsorption performance needs to be further improved. Summary of the Invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite, as well as its preparation method and application. The salicylic acid-anchored hydrotalcite@bentonite composite material can effectively utilize the bischofite that causes "magnesium damage" due to excessive accumulation. At the same time, the prepared salicylic acid-anchored hydrotalcite@bentonite composite material can effectively and stably remove lead ion pollution in water bodies.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: The first object of the present invention is to provide a method for preparing a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite, comprising the following steps: S1, taking bischofite, a by-product of potassium extraction from salt lakes, and purifying it to obtain magnesium chloride hexahydrate; S2, mixing and dissolving magnesium chloride hexahydrate, aluminum chloride hexahydrate, salicylic acid, bentonite and an alkaline reagent, heating and pressurizing the mixture for reaction, washing and drying the precipitate to obtain a salicylic acid-anchored hydrotalcite@bentonite composite material.

[0008] Preferably, in step S1, bischofite, a by-product of potassium extraction from salt lakes, is first dissolved and filtered to obtain a filtrate, which is then crystallized at low temperature and dried to obtain magnesium chloride hexahydrate.

[0009] Preferably, in step S2, the molar ratio of aluminum chloride hexahydrate to magnesium chloride hexahydrate is 1:1.

[0010] Preferably, in step S2, the mass ratio of magnesium chloride hexahydrate to salicylic acid is 1:(0.9-1.6).

[0011] Preferably, in step S2, the reaction temperature of heating and pressurizing is 380-400K, and the reaction time of heating and pressurizing is 9-12h.

[0012] Preferably, in step S2, the alkaline substance is urea, and the pH value of the reaction system is adjusted to 12-13.

[0013] A second object of the present invention is to provide a salicylic acid-anchored hydrotalcite@bentonite composite material prepared by the above-mentioned preparation method, comprising a bentonite substrate on which magnesium-aluminum hydrotalcite is grown, and salicylic acid anions are connected to the positively charged hydrotalcite colloid through flocculation and electrostatic adsorption, and are fixed to the surface of the magnesium-aluminum hydrotalcite as they age.

[0014] Preferably, the anions on the magnesium aluminum hydrotalcite include one or more of carboxyl groups, phenolic hydroxyl groups and carbonate groups.

[0015] The third objective of the present invention is to disclose the application of the salicylic acid-anchored hydrotalcite@bentonite composite material in the field of heavy metal pollution control.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for efficiently utilizing bischofite, a magnesium resource in salt lakes. Bischofite, a byproduct of potassium extraction from the Qarhan Salt Lake, is used as a magnesium source. A salicylic acid-anchored hydrotalcite composite material SA-MgAl-LDH@Bentonite is prepared in one step using a hydrothermal method with bentonite as a growth substrate. The surface of the composite material has carboxyl groups, phenolic hydroxyl groups, etc., which can effectively complex Pb 2+ The hydrotalcite composite material prepared by the present invention has salicylic acid anions anchored to the surface of the magnesium-aluminum hydrotalcite through flocculation and electrostatic adsorption. Compared with existing hydrotalcite materials, the interlayer anions and the hydrotalcite lack interaction forces, resulting in a hydrotalcite with stronger regeneration performance. Furthermore, the salicylic acid-anchored hydrotalcite composite material grown on bentonite can achieve synergistic adsorption with the hydrotalcite, improving the poor recycling performance of anion-intercalated hydrotalcite and the lack of effective functional groups in nanomaterial composites, significantly improving the specific surface area, adsorption capacity, and regeneration performance of the composite material. In terms of lead ion adsorption performance, this material improves the adsorption and regeneration performance of hydrotalcite. This invention not only provides a high-performance adsorption material for heavy metal pollution control but also opens up a new path for the high-value utilization of bischofite, a byproduct of potassium extraction from salt lakes, and has important disciplinary value and research significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1(a) XRD pattern and (b) FT-IR spectrum of the sample of the present invention; Figure 2 SEM and mapping images of MgAl-LDH and SA-MgAl-LDH@Bentonite samples of the present invention, (a) (b) are SEM images of MgAl-LDH, (c) (d) are SEM images of SA-MgAl-LDH@Bentonite, (e) (f) are EDS-mapping images of SA-MgAl-LDH@Bentonite; Figure 3 (a) N2 adsorption / desorption isotherms and (b) pore size distribution of MgAl-LDH and SA-MgAl-LDH@Bentonite of the present invention; Figure 4 This is the adsorption performance diagram of SA-MgAl-LDH@Bentonite of the present invention at different solution pH; Figure 5 Graph showing the adsorption performance of lead ions by the hydrotalcite before and after modification at different times; Figure 6 This is the adsorption performance diagram of SA-MgAl-LDH@Bentonite of the present invention at different temperatures; Figure 7 This is the adsorption performance diagram of SA-MgAl-LDH@Bentonite of the present invention during 5 adsorption / desorption cycle regeneration; Figure 8 This is the adsorption mechanism diagram of SA-MgAl-LDH@Bentonite during the adsorption process of the present invention. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0019] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0020] This study used bischofite, a byproduct of potassium extraction from the Qarhan Salt Lake, as a magnesium source. A one-step process was used to prepare a composite material anchored to the surface of hydrotalcite, grown on a bentonite substrate: SA-MgAl-LDH@Bentonite. This composite not only addresses the poor regeneration performance of organic ion-intercalated hydrotalcite during recycling, but also overcomes the drawback of a lack of effective functional groups in nanocomposite modification.

[0021] The preparation method of SA-MgAl-LDH@Bentonite proposed in the present invention comprises the following steps: S1, taking bischofite, a by-product of potassium extraction from salt lakes, and purifying it to obtain magnesium chloride hexahydrate; S2, mixing and dissolving magnesium chloride hexahydrate, aluminum chloride hexahydrate, salicylic acid, bentonite and an alkaline reagent, heating and pressurizing the mixture for reaction, washing and drying the precipitate to obtain a salicylic acid-anchored hydrotalcite@bentonite composite material.

[0022] In the system of the present invention, MgCl2·6H2O is used to provide Mg 2+ ions, as a divalent metal source in hydrotalcite layered double hydroxide MgAl-LDH. AlCl3·6H2O provides Al 3+ ions, as a source of trivalent metals in hydrotalcite.

[0023] Existing anion-intercalated hydrotalcite adsorbents have poor recycling performance in heavy metal adsorption and anions are easily lost. This is mainly because the existing hydrotalcite anion intercalation directly enters the layer plate, or the hydration reconstruction method sandwiches the anions between the layers during the layer plate reorganization. This interaction without bond energy makes it easy to remove anions with heavy metal adsorption properties, affecting the adsorption and regeneration performance of the hydrotalcite, and easily leading to the lack of effective functional groups in the hydrotalcite composite material for complexing heavy metals in heavy metal adsorption.

[0024] The present invention uses bischofite, a byproduct of potassium extraction from the Qarhan Salt Lake, as a magnesium source. A hydrothermal method is used to prepare a composite material, SA-MgAl-LDH@Bentonite, anchored on the surface of hydrotalcite and grown on a bentonite substrate. The hydrotalcite is grown on a bentonite substrate with salicylic acid anchored thereon. The salicylic acid anions bind salicylic acid to the positively charged hydrotalcite colloid through electrostatic interactions and flocculation, becoming firmly fixed to the hydrotalcite surface as the hydrotalcite grows. This increases the stability and specific surface area of the composite adsorbent, significantly improving the heavy metal adsorption performance of the composite adsorbent, and addressing the agglomeration problem of hydrotalcite and the inhibitory effect of its small surface area on heavy metal ion adsorption. In the present invention, the anchoring of salicylic acid on the hydrotalcite plate layer and its growth on the bentonite are synergistic, significantly enhancing heavy metal adsorption performance and improving regeneration performance.

[0025] The typical chemical formula of hydrotalcite is Mg6Al2(OH) 16 CO3·4H2O, its chemical composition can be expressed as: , Among them, M 2+ and M 3+ Represent divalent and trivalent metal ions, respectively, generally Mg and Al are the most common, A n- The interlayers are generally composed mainly of carbonate ions, and zH2O represents the amount of crystalline water in the material.

[0026] Among them Mg 2+ With Al 3+ Together they form a laminate structure, and by adjusting the Mg / Al ratio, the material properties can be controlled.

[0027] Salicylic acid C7H6O3 (Salicylic Acid, SA) acts as an organic modifier and functional agent. The carboxyl group (-COOH) and phenolic hydroxyl group (-OH) of salicylic acid can serve as effective functional groups and do not occupy the interlayer CO3 2- position, which can effectively enhance the adsorption capacity of pollutants.

[0028] Bentonite, the carrier support material for the product system of this invention, exhibits a synergistic adsorption effect. Bentonite, primarily composed of montmorillonite, has a high specific surface area and cation exchange capacity. It provides physical support, preventing hydrotalcite particles from agglomerating. It forms a composite material with the hydrotalcite, combining their adsorption properties to enhance overall adsorption efficiency.

[0029] The mechanism of SA-MgAl-LDH@Bentonite during the adsorption process is as follows Figure 8 As shown: (1) Surface complexation. The surface complexation is attributed to the phenolic hydroxyl, carboxyl and Pb groups on the surface of SA-MgAl-LDH@Bentonite. 2+ The reaction between them can be described as chemical adsorption and electrostatic attraction.

[0030] (2) Ion exchange. Due to its unique interlayer structure, layered compounds are prone to ion exchange and isomorphous substitution. Mg on SA-MgAl-LDH@Bentonite layer in adsorption solution 2 + Can be used with Pb 2+ Isomorphous replacement occurs. After the reaction, Mg 2 + The concentration increased by 10.75 mg / L, further proving that Pb 2+ and Mg 2+ In addition, the cations between the bentonite layers have strong ion exchangeability, which can replace Pb 2+ Replacement between layers.

[0031] (3) Chemical precipitation. Pb 2+ It will chemically precipitate with the carbonate ions and hydroxide ions between the layers, thereby adsorbing heavy metal ions.

[0032] In some embodiments of the present invention, in step S1, bischofite, a by-product of potassium extraction from salt lakes, is first dissolved and filtered to obtain a filtrate, which is then crystallized at low temperature and dried to obtain magnesium chloride hexahydrate.

[0033] In some embodiments of the present invention, in step S2, the molar ratio of aluminum chloride hexahydrate to magnesium chloride hexahydrate is 1:1.

[0034] In some embodiments of the present invention, in step S2, the mass ratio of magnesium chloride hexahydrate to salicylic acid is 1:(0.9-1.6).

[0035] In some embodiments of the present invention, in S2, the reaction temperature of heating and pressurizing is 380-400 K, and the reaction time of heating and pressurizing is 9-12 h.

[0036] In some embodiments of the present invention, in step S2, the alkaline substance is urea, and the pH value of the reaction system is adjusted to 12-13.

[0037] Urea CO(NH2)2 acts as a pH regulator and structure-directing agent. Urea hydrolyzes at high temperature to generate NH3 and CO2, which slowly releases NH3 to increase the pH value of the solution, promoting the Mg 2+ and Al 3+ Co-precipitated as hydroxide.

[0038] The present invention also discloses a salicylic acid-anchored hydrotalcite@bentonite composite material prepared by the above preparation method, comprising growing magnesium-aluminum hydrotalcite on a bentonite substrate, and bonding salicylic acid anions to positively charged magnesium-aluminum hydrotalcite nuclei through flocculation and electrostatic adsorption.

[0039] In an embodiment of the present invention, the anions in the hydrotalcite include one or more of carboxylate, phenolic hydroxyl, and carbonate.

[0040] In addition, the present invention also discloses the application of the salicylic acid-anchored hydrotalcite@bentonite composite material in the field of heavy metal pollution control.

[0041] The present invention is described in further detail below with reference to the accompanying drawings: Purification of bischofite, a by-product of lithium extraction from salt lakes: The sediment-containing bischofite was dissolved in water and magnetically stirred at 318 K to obtain a supersaturated solution. The resulting mother liquor was filtered and the filtrate was refrigerated for 12 hours. After crystallization, it was filtered again and dried at 318 K for 16 hours to obtain high-purity magnesium chloride hexahydrate.

[0042] Example 1 Magnesium chloride hexahydrate (1.31 g), aluminum chloride hexahydrate (1.54 g), urea (6.00 g), salicylic acid (1.50 g) and bentonite (1.00 g) were dissolved in 65 mL of deionized water and ultrasonicated for 30 min. The mixture was then transferred to a high-pressure reactor. The reaction was carried out at 393 K for 10 h. After cooling to room temperature, the solid-liquid separation was carried out. The product was washed with distilled water three times and 80 o The sample was dried at 400 °C. The sample was labeled as SA-MgAl-LDH@Bentonite.

[0043] Example 2 Magnesium chloride hexahydrate (1.31 g), aluminum chloride hexahydrate (1.54 g), urea (6.00 g), salicylic acid (1.20 g), and bentonite (1.00 g) were dissolved in 65 mL of deionized water and ultrasonicated for 30 min. The mixture was then transferred to a high-pressure reactor. The reaction was carried out at 393 K for 10 h. After cooling to room temperature, the solid-liquid separation was performed. The product was washed three times with distilled water and 80 o The sample was dried at 400 °C. The sample was labeled as SA-MgAl-LDH@Bentonite.

[0044] Example 3 Magnesium chloride hexahydrate (1.31 g), aluminum chloride hexahydrate (1.54 g), urea (6.00 g), salicylic acid (2.00 g), and bentonite (1.00 g) were dissolved in 65 mL of deionized water and ultrasonicated for 30 min. The mixture was then transferred to a high-pressure reactor. The reaction was carried out at 393 K for 10 h. After cooling to room temperature, the solid-liquid separation was performed. The product was washed three times with distilled water and 80 o The sample was dried at 400 °C. The sample was labeled as SA-MgAl-LDH@Bentonite.

[0045] Example 4 Magnesium chloride hexahydrate (1.31 g), aluminum chloride hexahydrate (1.54 g), urea (6.00 g), salicylic acid (1.50 g) and bentonite (2.00 g) were dissolved in 65 mL of deionized water and ultrasonicated for 30 min. The mixture was then transferred to a high-pressure reactor. The reaction was carried out at 393 K for 10 h. After cooling to room temperature, the solid-liquid separation was carried out. The product was washed with distilled water three times and 80 o The sample was dried at 400 °C. The sample was labeled as SA-MgAl-LDH@Bentonite.

[0046] Test Example 1 according to Figure 1 From the X-ray diffraction peak (a), we can see that at 2 θ = 11.712 o , 23.563 o 、35.001 o , 39.599 o , 47.180 o and 61.031 o The characteristic diffraction peaks appearing at , correspond to the (003), (006), (009), (015), (018) and (100) crystal planes of MgAl-LDH, respectively, which match the standard PDF card of MgAl-LDH (PDF # 89-0460), indicating that the product is a layered structure of MgAl-LDH. There are no other impurity diffraction peaks in the crystal structure, indicating that magnesium-aluminum hydrotalcite particles with high purity and excellent crystallinity were prepared by hydrothermal method. In the diffraction peaks of SA-Mg Al-LDH @ Bentonite crystals, the characteristic diffraction peaks of MgAl-LDH and bentonite are retained at the same time. It is worth noting that the (003) crystal plane of SA-MgAl-LDH@Bentonite shows obvious peak broadening and intensity reduction, indicating a decrease in crystallinity. Its (003) crystal plane spacing ( d =0.7548nm) and the original CO3 2- -MgAl-LDH ( d=0.7550 nm) remained basically unchanged, indicating that the salicylic acid anions did not occupy the LDH interlayer.

[0047] During the preparation process, Mg in the mixed solution 2+ and Al 3+ Under alkaline conditions, it immediately hydrolyzes, forming MgAl-LDH nuclei with carbonate ions as interlayer anions on the bentonite substrate. The salicylic acid anions are attracted to the positively charged MgAl-LDH nuclei through electrostatic attraction and macromolecular flocculation. Due to the large radius of SA, it can only bond to the MgAl-LDH surface in a surface-anchored manner, ultimately yielding the product SA-MgAl-LDH@Bentonite.

[0048] Depend on Figure 1 (b) shows that there is still CO3 in SA-Mg Al-LDH@Bentonite 2 - The characteristic peak (1360cm -1 ), proves that CO3 2 - Compared with MgAl-LDH and Bentonite, the FT-IR spectrum of SA-MgAl-LDH@Bentonite, i.e. Figure 1 In (b), at 1610 cm -1 , 1580 cm -1 and 1482 cm -1 The characteristic absorption peak of salicylate ion appeared at , corresponding to the asymmetric -COOH stretching vibration and aromatic ring CC stretching vibration, confirming that salicylic acid was successfully anchored on the MgAl-LDH surface.

[0049] Depend on Figure 2 It can be seen that after surface anchoring of salicylic acid and loading with bentonite, the morphology and size of LDHs undergo significant changes. SEM images of SA-MgAl-LDH@Bentonite show that the morphology of LDHs changes to a more uniform 3D structure with C-direction stacking, forming loose, flower-like aggregates of LDHs wrapped around the bentonite morphology. Furthermore, EDS analysis shows that while the composite material retains the characteristic elements of LDH, such as Mg, Al, and O, it also adds Si, K, Ca, and Na. The Si element originates from the layered structure of the bentonite, while the K, Ca, and Na elements are located between the bentonite layers.

[0050] according to Figure 3 From Table 1, it can be seen that after being anchored by salicylic acid and loaded with bentonite, the pore diameter and pore volume of the hydrotalcite increased, and the specific surface area also increased accordingly.

[0051] Table 1 Pore structure data of MgAl-LDH and SA-MgAl-LDH@Bentonite

[0052] Test Example 2 At natural pH, 0.05 g of SA-MgAl-LDH@Bentonite prepared in Example 1 was added to 50 mL of 300 mg / L Pb 2+ The solution was shaken at a constant temperature for 24 h at a speed of 150 rmp / min to reach adsorption equilibrium. The supernatant was prepared into the test solution and the residual lead ion concentration was detected by atomic absorption spectrophotometer (AAS). The adsorption of Pb by the composite material at 318 K was calculated. 2+ The maximum adsorption capacity is 317.00 mg / g.

[0053] Test Example 3 Pb 2+ The pH of the solution was adjusted to 3, 4, 5, 6, 7, 8, and the modified hydrotalcite was added to the Pb solution at each different pH value. 2+ The solution was oscillated at a constant temperature of 150 rmp / min for 24 h to reach adsorption equilibrium. The supernatant was taken to prepare the test solution, and the residual lead ion concentration was measured by AAS.

[0054] exist Figure 4 It can be seen that the SA-MgAl-LDH@Bentonite adsorbent prepared in Example 1 has a strong adsorption capacity for Pb in lead ion solutions with pH = 4, 5, 6, and 7. 2+ The adsorption capacity remains at a high value.

[0055] Test Example 4 At natural pH, 0.05 g of SA-MgAl-LDH@Bentonite prepared in Example 1 was added to 50 mL of 300 mg / L Pb 2+ The solution was shaken at a constant temperature for 24 h at a speed of 150 rmp / min to achieve adsorption equilibrium. The supernatant was taken to prepare the test solution and the residual lead ion concentration was measured by AAS. Figure 5 It can be seen that the composite material has a strong 2+ The maximum adsorption capacity of LDH was 235.00 mg / g, which was several times higher than that of the original LDH (37.00 mg / g).

[0056] Test Example 5 from Figure 6 The SA-MgAl-LDH@Bentonite prepared in Example 3 was subjected to adsorption tests at different temperatures, and it was found that the maximum adsorption performance of the composite material for lead ions reached 317.50 mg / g at 318K.

[0057] Test Example 6 from Figure 7 It can be seen that SA-MgAl-LDH@Bentonite adsorbent has strong stability and good adsorption / desorption cycle performance. After 5 adsorption / desorption cycles, the adsorption capacity of lead ions is still 84.8% of the initial adsorption capacity.

[0058] The above content is only for explaining the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite, characterized in that: The following steps are involved: S1, taking bischofite, a by-product of potassium extraction from a salt lake, and purifying it to obtain magnesium chloride hexahydrate; S2, mixing and dissolving magnesium chloride hexahydrate, aluminum chloride hexahydrate, salicylic acid, bentonite and an alkaline reagent, heating and pressurizing the mixture for reaction, washing and drying the precipitate to obtain a salicylic acid-anchored hydrotalcite@bentonite composite material.

2. The method for preparing a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite according to claim 1, characterized in that: In the step S1, bischofite, a by-product of potassium extraction from a salt lake, is first dissolved and filtered to obtain a filtrate, which is then crystallized at low temperature and dried to obtain magnesium chloride hexahydrate.

3. The method for preparing a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite according to claim 1, characterized in that: In step S2, the molar ratio of aluminum chloride hexahydrate to magnesium chloride hexahydrate is 1:

1.

4. The method for preparing a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite according to claim 1, characterized in that: In step S2, the mass ratio of magnesium chloride hexahydrate to salicylic acid is 1:(0.9-1.6).

5. The method for preparing a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite according to claim 1, characterized in that: In step S2, the reaction temperature of heating and pressurizing is 380-400K.

6. The method for preparing a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite according to claim 1, characterized in that: In step S2, the reaction time of heating and pressurizing is 9 to 12 hours.

7. The method for preparing a salicylic acid-anchored hydrotalcite@bentonite composite material based on salt lake bischofite according to claim 1, characterized in that: In step S2, the alkaline substance is urea, and the pH value of the reaction system is adjusted to 12-13.

8. A salicylic acid-anchored hydrotalcite@bentonite composite material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The method comprises a bentonite substrate, on which magnesium-aluminum hydrotalcite grows; salicylic acid anions are connected with the positively charged hydrotalcite colloid through flocculation and electrostatic adsorption, and are fixed on the surface of the magnesium-aluminum hydrotalcite as aging occurs.

9. The salicylic acid-anchored hydrotalcite@bentonite composite material according to claim 8, characterized in that: The anions on the magnesium aluminum hydrotalcite include one or more of carboxyl, phenolic hydroxyl and carbonate.

10. Use of the salicylic acid-anchored hydrotalcite@bentonite composite material according to claim 8 or claim 9 in the field of heavy metal pollution control.

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