Preparation method of boron adsorbent based on layered dihydroxide, obtained boron adsorbent and application of boron adsorbent

Abstract

The invention provides a preparation method of a boron adsorbent based on layered dihydroxide. The preparation method comprises the following steps: firstly, preparing layered dihydroxide LDHs from divalent metal salt M < 2 + > and trivalent metal salt M < 3 + >; then dispersing LDHs in a solvent to obtain slurry, adding a polyhydroxy organic matter into the slurry, and drying to obtain polyhydroxy organic matter intercalated hydrotalcite; the polyhydroxy organic matter is selected from meglumine, sodium gluconate, citric acid and / or tartaric acid, and finally calcining and grinding to obtain the boron adsorbent. According to the preparation method disclosed by the invention, the polyhydroxy organic matter is inserted, so that the obtained product has double effects of intercalation and surface functionalization, and active sites of reaction are increased while the interlayer spacing is increased, so that the adsorption capacity is greatly improved, and the adsorption capacity of the obtained product is remarkably higher than that of other adsorbents based on layered dihydroxide.

Description

Technical Field

[0001] The present invention relates to a boron adsorbent, in particular to a boron adsorbent based on layered double hydroxide, and also relates to a preparation method thereof and application of the adsorbent in water treatment. Background Art

[0002] With industrial development, the discharge of boron-containing wastewater has increased, leading to increasingly serious boron pollution of water resources. Mining or recovering boron from salt lakes, seawater, and other water bodies, as well as industrial and agricultural wastewater, is crucial for filling the gap in industrial and agricultural boron and its compounds and addressing boron pollution. Salt lake brines are particularly rich in boron, which exists in the form of boric acid or borates. Currently, adsorbents commonly used to absorb boric acid from water include boron-selective resins, fly ash, industrial scrap metals, natural adsorption materials, metal oxides and hydroxides, polymetallic hydroxides, and organometallic materials.

[0003] Among them, Chinese invention patent application CN 104874365 A discloses a carboxymethyl cellulose ion-intercalated hydrotalcite-like composite material and its preparation method. A mixed solution of soluble divalent metal salts and trivalent metal salts is mixed with a sodium hydroxide solution to obtain a layered double hydroxide material (LDH). This is then calcined to obtain a layered bimetallic composite oxide (LDO), which is redispersed in water and then mixed with a sodium carboxymethyl cellulose solution. After crystallization, the carboxymethyl cellulose-intercalated hydrotalcite-like composite material is obtained. This preparation method first calcines the layered double hydroxide material (LDH), converting the double hydroxide into a bimetallic oxide. Due to the reduced number of active sites in the bimetallic oxide, the insertion of carboxymethyl cellulose into the bimetallic oxide is a post-doping technique, resulting in a relatively low increase in adsorption capacity. Therefore, although the resulting material can be used to adsorb boron from water, the adsorption capacity achieved within 8 hours is approximately 8-9 mg / g, which fails to meet current technical requirements. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a boron adsorbent with a larger adsorption capacity, a simpler preparation process and an environmentally friendly process.

[0005] The idea of ​​the present invention is to increase the amount of organic functional groups loaded on the surface of the substrate. Layered double hydroxides (LDHs) are used as the substrate, and polyhydroxy compounds are intercalated to increase their adsorption capacity. The preparation process is optimized to optimize the adsorbent's specific surface area, pore size and other parameters, thereby solving problems such as the small applicability of the adsorbent in the boron removal process and difficulty in regeneration.

[0006] In order to achieve the above object, the present invention provides a method for preparing a boron adsorbent based on a layered double hydroxide, the method comprising the following steps:

[0007] (1) With divalent metal salt M 2+ and trivalent metal salt M 3+ Preparation of layered double hydroxides (LDHs);

[0008] (2) dispersing layered double hydroxides (LDHs) in a solvent to obtain a slurry, adding a polyhydroxy organic compound to the slurry, maintaining the reaction system at 50° C.-70° C. and stirring thoroughly; then, filtering the mixture, washing the resulting filter cake with distilled water until the filtrate is neutral, and drying the resulting filter cake to obtain a polyhydroxy organic compound intercalated hydrotalcite; the polyhydroxy organic compound is selected from meglumine, sodium gluconate, citric acid and / or tartaric acid, and the amount of the polyhydroxy organic compound added is 1%-10% of the mass of the layered double hydroxides (LDHs);

[0009] (3) The polyhydroxy organic intercalated hydrotalcite is calcined and ground to obtain a boron adsorbent based on layered double hydroxide.

[0010] Layered double hydroxides (LDHs), commonly known as hydrotalcite, can usually be expressed by the following chemical formula: [M 2+ 1-x M 3+ x (OH)2] q+ (X n- ) q / n ·yH2O. The preparation of LDHs by metal salts belongs to the prior art.

[0011] In the present invention, the divalent metal salt M 2+ Selected from Mg 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ 、Mn 2+ or Cd 2+ ; Trivalent metal salt M 3+ Selected from Al 3+ 、Fe 3+ or Cr 3+ Layered double hydroxides (LDHs) can be prepared by coprecipitation using their sulfates, hydrochlorides or nitrates, such as magnesium sulfate, magnesium nitrate, magnesium chloride, nickel nitrate, nickel chloride, zinc nitrate and / or zinc chloride with aluminum sulfate, aluminum nitrate, anhydrous aluminum chloride, polyaluminum chloride, aluminum chloride hexahydrate, ferric nitrate, ferric chloride, chromium nitrate and / or chromium chloride.

[0012] For example, CN 117599743 A discloses a method for preparing a magnesium aluminum double hydroxide (MgAl-LDH) adsorbent, and CN 104874365 A also discloses a process for preparing a layered double hydroxide (LDH). Those skilled in the art can also refer to other prior art descriptions to prepare layered double hydroxides (LDHs).

[0013] When LDHs are prepared by coprecipitation, divalent metal salts M 2+ and trivalent metal salt M 3+ Prepare a mixed solution, then add an alkaline solution dropwise while stirring until the reaction system reaches an endpoint pH of 8-10. Raise the reaction temperature and maintain it at 40-90°C for 2-24 hours. Filter and wash with pure water until the supernatant reaches a pH of 8.5-9.5 to obtain a filter cake, which is layered double hydroxides (LDHs).

[0014] When this preparation method is adopted, the alkaline solution can be selected from 0.5-5 mol / L alkaline solution, such as sodium hydroxide, ammonia water, urea, potassium hydroxide or sodium carbonate solution.

[0015] As a preferred embodiment, in the present invention, the divalent metal salt M 2+ With trivalent metal salt M 3+ The molar ratio of M is 1.0 to 2.5:1.0 based on the metal element. 2+ / M 3+ It has a great influence on the stability of hydrotalcite. In the actual hydrotalcite layer structure, when M 2+ / M 3+ A stable hydrotalcite phase can be formed when the ratio is 1.0 to 2.5:1.0.

[0016] In the present invention, the solvent in step (2) is ethylene glycol, ethanol, isopropanol, or propylene glycol. A person skilled in the art can also select an appropriate solvent based on existing knowledge. The amount of solvent used is generally 2-4 times the volume of the layered double hydroxides (LDHs), as long as sufficient dispersion is achieved.

[0017] The calcination in step (3) is usually carried out at 300°C-600°C for 2-6 hours, and then ground and passed through a 100-mesh sieve to obtain a boron adsorbent with a D50 particle size of 0.1-50 μm, more preferably a D50 particle size of 0.1-30 μm.

[0018] Based on this, the present invention also provides a boron adsorbent prepared by the above preparation method.

[0019] The boron adsorbent prepared by the method of the present invention can be used for water purification, and is particularly used for adsorbing boron in water.

[0020] The present invention introduces polyhydroxy compounds into the interlayers of LDHs to optimize the physical and chemical properties of LDHs, effectively improve the exchangeability of interlayer anions, and provide more active sites to increase the boron adsorption rate and adsorption capacity of the material.

[0021] On the other hand, the raw materials used in the preparation method of the present invention are cheap and readily available, the preparation method is simple, and suitable for large-scale application. The preparation method of the present invention does not produce harmful by-products during the process, is environmentally friendly, and is suitable for industrial wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic flow chart of the preparation method of the present invention;

[0023] Figure 2 The XRD patterns of the samples of Example 1 are shown in Figure 1, wherein curve (a) is that of Example 1 and curve (b) is that of reference sample 1 of Example 4;

[0024] Figure 3 This is a scanning electron microscope image of the sample obtained in Example 1. DETAILED DESCRIPTION

[0025] The following examples are used to illustrate the technical solutions of the present invention in a non-limiting manner.

[0026] In the present invention, unless otherwise specified, "%" used to explain concentration refers to percentage by weight, and ":" refers to ratio by weight.

[0027] Example 1 Preparation

[0028] Magnesium sulfate and aluminum chloride were weighed at a Mg / Al molar ratio of 2:1 and dissolved in deionized water to prepare a mixed solution. Under stirring at 40°C, 5M NaOH solution was slowly added dropwise until the reaction system reached a pH of 10. The reaction was allowed to proceed for 4 hours. The Mg-Al-LDHs wet cake was then obtained by conventional filtration and washing with pure water.

[0029] The resulting wet cake was thoroughly dispersed in ethylene glycol (twice the volume of the wet cake) to form a slurry. Meglumine (10% by weight of the Mg-Al-LDHs wet cake) was added. The mixture was thoroughly mixed in a three-necked flask and then stirred at 70°C for 8 hours. The mixture was then filtered and washed with boiling distilled water until the filtrate was neutral. The filter cake was then dried at 80°C, calcined at 400°C for 3 hours, and ground to a D50 particle size of 0.1-30 μm to obtain Sample 1.

[0030] Place sample 1 under an electron microscope for observation. Figure 3 As can be seen from the scanning electron microscope image, the adsorbent is composed of flakes and particles of irregular size (10μm to 100μm).

[0031] Example 2 Preparation

[0032] The same process as in Example 1 was performed, except that the amount of meglumine and Mg-Al-LDHs was 5%. The obtained product was Sample 2.

[0033] Example 3 Preparation

[0034] The same process as in Example 1 was performed, except that the Mg / Al molar ratio was 2.5:1 when preparing Mg-Al-LDHs. The obtained product was Sample 3.

[0035] Example 4 Performance Test

[0036] Preparation of reference substance 1

[0037] Magnesium sulfate and aluminum chloride were weighed at a Mg / Al molar ratio of 2 and dissolved in deionized water to prepare a mixed solution. A 5M NaOH solution was then slowly added dropwise with stirring at 40°C until the pH reached 10. The temperature was raised to 90°C and maintained constant for 3 hours. The final product was centrifuged and washed five times with distilled water. Finally, the product was dried (80°C for 20 hours), ground, and stored to yield Mg-Al-LDHs.

[0038] The XRD patterns of sample 1 (curve a) and reference product 1 (curve b) obtained in comparison with Example 1 are shown in FIG. Figure 2 shown.

[0039] The results show that the sample and the reference product of Example 1 have the typical characteristic structure of standard LDHs, and the characteristic diffraction peaks with larger diffraction intensity appear at 2θ of 11.11°, 22.39° and 34.42°, indicating that they all have a layered structure. Compared with the MgAl-LDH of curve b, the (003) peak in curve a shifts to a small angle, indicating that the interlayer spacing increases, and new characteristic diffraction peaks appear, which is consistent with the sample Mg-Al-LDHs. After intercalation treatment, the polyhydroxy organic matter enters the interlayer of LDHs, resulting in an increase in the interlayer spacing. This proves that the polyhydroxy organic matter of Example 1 is successfully intercalated.

[0040] Preparation of reference substance 2

[0041] 2 g of chlorine balls (containing 11 mmol of chloromethyl) and 10.79 g of meglumine (55 mmol, 5 times the chloromethyl equivalent) were completely dissolved in 40 ml of a mixed solvent of distilled water / 40 ml of DMF and placed together in a 100 ml three-necked flask. 2.226 g of triethylamine (22 mmol, 2 times the chloromethyl equivalent) was added as a catalyst and acid binding agent. The mixture was stirred and refluxed at 50° C. for 12 h, and the resin particles were collected. The resin was sequentially eluted with ethanol and distilled water for 24 h, and finally dried in vacuo at 50° C. for 12 h to obtain the final resin product PS-NMDG, which was used as reference product 2.

[0042] Configure simulated brine:

[0043]

[0044] Accurately weigh 1g of each of Samples 1-3 and the reference into 100mL of simulated brine solution. The solution was placed on a shaker for adsorption at room temperature for 2 hours. After the reaction, the adsorbed liquid was centrifuged and sampled. The boron ion concentration in the adsorbed solution was measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The saturated adsorption capacity of each adsorbent sample was calculated by comparing it with the simulated brine solution before adsorption.

[0045] The test results are as follows:

[0046]

[0047] These results demonstrate that the boron adsorbent based on layered double hydroxides prepared using the present invention exhibits significantly higher adsorption capacity than other layered double hydroxide-based adsorbents. This is likely due to the insertion of polyhydroxy organic compounds after the layered double hydroxides are synthesized while the material is still in a wet filter cake state. This results in the product having both intercalation and surface functionalization effects, increasing the interlayer spacing and the number of reactive sites, thus significantly boosting the adsorption capacity.

Claims

1. A method for preparing a boron adsorbent based on a layered double hydroxide, the method comprising the following steps: (1) With divalent metal salt M 2+ and trivalent metal salt M 3+ Preparation of layered double hydroxides (LDHs); (2) dispersing layered double hydroxides (LDHs) in a solvent to obtain a slurry, adding a polyhydroxy organic compound to the slurry, maintaining the reaction system at 50° C. to 70° C. and stirring thoroughly; then, filtering the mixture, washing the resulting filter cake with distilled water until the filtrate is neutral, and drying the resulting filter cake to obtain a polyhydroxy organic compound intercalated hydrotalcite; the polyhydroxy organic compound is selected from meglumine, sodium gluconate, citric acid and / or tartaric acid, and the amount of the polyhydroxy organic compound added is 1% to 10% by mass of the layered double hydroxides (LDHs); (3) The polyhydroxy organic intercalated hydrotalcite is calcined and ground to obtain a boron adsorbent based on layered double hydroxide.

2. The preparation method according to claim 1, wherein The divalent metal salt M 2+ Selected from Mg 2+ 、Co 2+ 、Ni 2+ 、Zn 2+ 、Mn 2+ or Cd 2+ Sulfate, hydrochloride or nitrate of trivalent metal salt M 3+ Selected from Al 3+ 、Fe 3+ or Cr 3+ sulfate, hydrochloride or nitrate.

3. The preparation method according to claim 1, wherein With divalent metal salt M 2+ and trivalent metal salt M 3+ Layered double hydroxides (LDHs) were prepared by coprecipitation.

4. The preparation method according to claim 1, characterized in that Divalent metal salt M 2+ With trivalent metal salt M 3+ The molar ratio is 1.0 to 2.5:1.0 based on the metal element.

5. The preparation method according to claim 1, characterized in that The solvent in step (2) is ethylene glycol, ethanol, isopropanol or propylene glycol.

6. The preparation method according to claim 1, characterized in that The calcination in step (3) is carried out at 300° C.-600° C. for 2-6 hours, and then ground and passed through a 100-mesh sieve to obtain a boron adsorbent with a D50 particle size of 0.1-50 μm.

7. The boron adsorbent prepared according to the preparation method according to any one of claims 1 to 6.

8. Use of the boron adsorbent prepared by the preparation method according to any one of claims 1 to 6 in water purification.

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