Hydrotalcite-like adsorbent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of sewage treatment, and particularly discloses a hydrotalcite-like adsorbent as well as a preparation method and application thereof. According to the preparation method provided by the invention, the hydrotalcite-like compound is modified by utilizing ethylenediamine tetraacetic acid and dodecyl sulfonic acid through a two-step modification preparation method, the dodecyl sulfonic acid can inhibit competitive adsorption of calcium and magnesium ions, and is matched with the ethylenediamine tetraacetic acid to specifically chelate heavy metals such as chromium and mercury, so that the heavy metals such as chromium and mercury can be effectively removed; the prepared hydrotalcite-like adsorbent can still keep efficient removal of target heavy metals in desulfurization wastewater with high calcium and magnesium ion concentration. Meanwhile, the hydrotalcite-like compound prepared by the preparation method provided by the invention has relatively high electric charge quantity, and can adsorb heavy metal ions and negatively charged suspended matters at the same time through electrostatic interaction, so that the treatment effect of synchronous removal is realized.

Description

Technical Field

[0001] The invention relates to the technical field of sewage treatment, and specifically discloses a hydrotalcite-like adsorbent, a preparation method and application thereof. Background Art

[0002] During the operation of a wet flue gas desulfurization system in a coal-fired power plant, the slurry from the absorption tower continuously circulates within the tower. Simultaneously, overflow from the gypsum cyclone station and filtrate water also return to the absorption tower, forming an external loop. During this process, chloride ions, fluoride ions, and heavy metals such as mercury, selenium, arsenic, and chromium gradually accumulate in the slurry. To maintain stable system operation, guarantee gypsum product quality and desulfurization efficiency, and protect equipment and materials that come into contact with the slurry, the desulfurization equipment must discharge some desulfurization wastewater. This wastewater has a complex composition, containing not only high concentrations of calcium and magnesium ions, but also heavy metal ions such as chromium and mercury, as well as suspended solids. Effectively treating these heavy metals presents a significant challenge for power plant wastewater discharge.

[0003] In order to solve the above problems, the existing technology modifies layered double hydroxides, such as by calcination, intercalation, surface modification or synthesis of composite materials, and can use them as adsorbents to remove heavy metal ions from wastewater. However, in the actual treatment of desulfurization wastewater, the adsorbents in the existing technology are not effective in removing heavy metals due to the strong interference of high-concentration calcium and magnesium ions; and because the desulfurization wastewater has a complex composition and contains a large amount of suspended matter, it is difficult for existing adsorbents to achieve the simultaneous removal of heavy metals and suspended matter. Based on this, the development of an adsorbent that can resist the interference of calcium and magnesium ions and simultaneously remove heavy metals and suspended matter from desulfurization wastewater has important practical significance in the field of sewage treatment. Summary of the Invention

[0004] To address the problems of existing adsorbents lacking resistance to interference from calcium and magnesium ions and unable to simultaneously remove heavy metals and suspended solids from desulfurization wastewater, the present invention provides a hydrotalcite-like adsorbent, its preparation method, and its application. This preparation method sequentially modifies the hydrotalcite-like adsorbent with ethylenediaminetetraacetic acid and dodecylsulfonic acid, enhancing its selective adsorption capacity in complex water environments and effectively addressing the issue of existing adsorbents being susceptible to interference from calcium and magnesium ions.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A first aspect of the present invention provides a method for preparing a hydrotalcite-like adsorbent, characterized in that it comprises the following steps:

[0007] S1, dissolving a magnesium salt, an aluminum salt, and ethylenediaminetetraacetic acid in water to obtain a mixed solution; adjusting the pH of the mixed solution to alkaline, heating the mixed solution for a hydrothermal reaction, and obtaining an ethylenediaminetetraacetic acid-modified hydrotalcite-like material;

[0008] S2. Adding the ethylenediaminetetraacetic acid-modified hydrotalcite-like material and dodecylsulfonic acid into water, adjusting the pH to alkaline, and heating to perform a hydrothermal reaction to obtain a hydrotalcite-like adsorbent.

[0009] The present invention utilizes a two-step modification method to modify a hydrotalcite-like adsorbent using ethylenediaminetetraacetic acid and dodecylsulfonic acid. The dodecylsulfonic acid inhibits competitive adsorption of calcium and magnesium ions, and, in combination with the ethylenediaminetetraacetic acid, specifically chelates heavy metals such as chromium and mercury. This allows the resulting hydrotalcite-like adsorbent to maintain efficient removal of target heavy metals even in desulfurization wastewater with high calcium and magnesium ion concentrations. Furthermore, the hydrotalcite-like adsorbent prepared by the present invention possesses a high charge, enabling it to simultaneously adsorb heavy metal ions and negatively charged suspended solids through electrostatic interaction, achieving simultaneous removal.

[0010] Preferably, in S1, the magnesium salt Mg 2+ and Al in aluminum salts 3+ The molar ratio is 1.5-2.5:1.

[0011] The present invention defines Mg 2+ With Al 3+ The molar ratio of 2.5 to 4.0 can ensure the stability of the layered structure of the prepared hydrotalcite-like particles and improve the charge density of the hydrotalcite-like particles.

[0012] Preferably, in S1, the aluminum salt Al 3+ The molar ratio of ethylenediaminetetraacetic acid is 1:0.3-0.7.

[0013] Preferably, in S1, the alkalinity refers to pH = 10.0-10.5.

[0014] Preferably, in S1, the mixed solution contains Mg 2+ The concentration is 0.01mol / L-0.2mol / L.

[0015] Further preferably, in S1, the pH of the mixed solution is adjusted to alkaline using a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is 0.5 mol / L-1.5 mol / L.

[0016] The present invention limits the pH of the mixed solution to alkaline and specifically limits the pH value, thereby ensuring that ethylenediaminetetraacetic acid can participate in the grafting reaction in an ionic form. At the same time, the present invention limits the concentration of sodium hydroxide to ensure that ethylenediaminetetraacetic acid is uniformly inserted into the interlayers of the hydrotalcite-like particles, thereby enhancing the chelating ability of the hydrotalcite-like particles for heavy metals.

[0017] Preferably, in S1, the temperature of the hydrothermal reaction is 100° C.-140° C., and the time is 12 h-36 h.

[0018] Further preferably, in S1, after adjusting the pH of the mixed solution to alkaline, the mixture is stirred at 50° C.-70° C. and 100 r / min-600 r / min for 20 min-40 min, and then the hydrothermal synthesis reaction is carried out.

[0019] The present invention ensures that the hydrotalcite-like crystallinity is good and the interlayer spacing is moderate by limiting the temperature and time of the hydrothermal synthesis reaction, which is conducive to the fixed intercalation modification of ethylenediaminetetraacetic acid. At the same time, the present invention improves the Mg content by pre-stirring before the hydrothermal synthesis reaction. 2+ ions and Al 3+ The uniformity of the mixing of ions and EDTA avoids defects in the structure of the prepared hydrotalcite-like material caused by poor uniformity.

[0020] Preferably, in S2, the usage ratio of the ethylenediaminetetraacetic acid modified hydrotalcite-like material and water is 1 g: (20-50) mL.

[0021] Preferably, in S2, the mass ratio of the ethylenediaminetetraacetic acid modified hydrotalcite-like material to dodecylsulfonic acid is 1:0.5-1.5.

[0022] Further preferably, in S2, the usage ratio of the ethylenediaminetetraacetic acid modified hydrotalcite-like material and water is 1 g: (20-50) mL.

[0023] Preferably, in S2, the temperature of the hydrothermal reaction is 50° C.-70° C., and the time is 5 h-7 h.

[0024] Further preferably, in S2, after the hydrothermal synthesis reaction is completed, the hydrothermal synthesis product is separated into solid and liquid, washed, dried, and ground to obtain a hydrotalcite-like adsorbent.

[0025] Further preferably, in S2, the solid-liquid separation is performed by centrifugal separation, and the centrifugal speed is 4000 r / min-6000 r / min and the time is 5 min-15 min.

[0026] Further preferably, in S2, the alkalinity refers to pH = 10.0-11.0.

[0027] By limiting the mass ratio of the EDTA-modified hydrotalcite-like material to dodecyl sulfonic acid, as well as the temperature and time of the hydrothermal synthesis reaction, the present invention avoids the problem of excessive dodecyl sulfonic acid blocking the adsorption sites of the hydrotalcite-like adsorbent, while also avoiding the problem of insufficient dodecyl sulfonic acid causing poor anti-interference ability. Furthermore, by limiting the post-treatment process of the hydrotalcite-like adsorbent, the present invention achieves a high specific surface area and high dispersibility.

[0028] A second aspect of the present invention provides a hydrotalcite-like adsorbent, which is prepared by the above-mentioned scheme.

[0029] A third aspect of the present invention provides an application of a hydrotalcite-like adsorbent in the treatment of desulfurization wastewater. The hydrotalcite-like adsorbent is prepared according to the above-mentioned solution.

[0030] In summary, the magnesium-aluminum hydrotalcite prepared by the preparation method provided herein is loaded with ethylenediaminetetraacetic acid and dodecylsulfonic acid. In the present invention, ethylenediaminetetraacetic acid has a good adsorption effect on chromium and mercury in desulfurization wastewater, and the sulfonic group in dodecylsulfonic acid has a good adsorption effect on the high concentrations of calcium and magnesium ions in desulfurization wastewater. Simultaneously, it can reduce the interference of calcium and magnesium ions with the hydrotalcite-like adsorbent, resulting in the hydrotalcite-like adsorbent having a good removal effect on typical heavy metals in desulfurization wastewater. Furthermore, the hydrotalcite-like adsorbent provided by the present invention has a high charge, which can achieve the simultaneous removal of heavy metals and suspended solids in desulfurization wastewater. DETAILED DESCRIPTION

[0031] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiment is only one embodiment of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] Example 1

[0033] The present invention provides a hydrotalcite-like adsorbent and its preparation method and application, which specifically include the following contents:

[0034] S1. Mg(NO3)2, Al2(NO3)3 and ethylenediaminetetraacetic acid were dissolved in water to obtain a mixed solution. The pH value was adjusted to 10 with 0.5 mol / L sodium hydroxide solution. The solution was stirred at 50°C and 100 r / min for 30 min. The solution was added into a hydrothermal synthesis reactor. The mixture was subjected to a hydrothermal synthesis reaction at 100°C for 12 h to obtain an ethylenediaminetetraacetic acid-modified hydrotalcite-like material. 2+ The concentration is 0.075mol / L, Al2(NO3)3 in the mixed solution 3+ The concentration is 0.05 mol / L, and the concentration of EDTA in the mixture is 0.015 mol / L;

[0035] S2. Add 0.1 g of ethylenediaminetetraacetic acid-modified hydrotalcite-like material to 2 mL of distilled water, disperse under 40 kHz ultrasonic conditions for 30 min, add 0.05 g of dodecyl sulfonic acid, adjust the pH of the solution to 10.0 with 0.5 mol / L sodium hydroxide solution, add to a hydrothermal synthesis reactor, carry out hydrothermal synthesis reaction at 50° C. for 5 h, cool to room temperature, centrifuge at 4000 r / min for 5 min, filter, and wash to obtain a hydrotalcite-like adsorbent.

[0036] Example 2

[0037] The present invention provides a hydrotalcite-like adsorbent and its preparation method and application, which specifically include the following contents:

[0038] S1. Mg(NO3)2, Al2(NO3)3 and ethylenediaminetetraacetic acid were dissolved in water to obtain a mixed solution. The pH value was adjusted to 10.5 with 1.5 mol / L sodium hydroxide solution. The solution was stirred at 70°C and 600 r / min for 30 min. The solution was added to a hydrothermal synthesis reactor. The mixture was subjected to a hydrothermal synthesis reaction at 140°C for 36 h to obtain an ethylenediaminetetraacetic acid-modified hydrotalcite-like material. 2+ The concentration is 0.125mol / L, Al2(NO3)3 in the mixed solution 3+ The concentration is 0.05 mol / L, and the concentration of EDTA in the mixture is 0.035 mol / L;

[0039] S2. Add 0.1 g of ethylenediaminetetraacetic acid-modified hydrotalcite-like material to 5 mL of distilled water, disperse under 40 kHz ultrasonic conditions for 30 min, add 0.15 g of dodecyl sulfonic acid, adjust the pH of the solution to 11.0 with 1.5 mol / L sodium hydroxide solution, add to a hydrothermal synthesis reactor, carry out hydrothermal synthesis reaction at 70 ° C for 7 h, cool to room temperature, centrifuge at 6000 r / min for 15 min, filter, and wash to obtain a hydrotalcite-like adsorbent.

[0040] Example 3

[0041] The present invention provides a hydrotalcite-like adsorbent and its preparation method and application, which specifically include the following contents:

[0042] S1. Dissolve Mg(NO3)2, Al2(NO3)3 and ethylenediaminetetraacetic acid in water to obtain a mixed solution, adjust the pH to 10.2 with 1.0 mol / L sodium hydroxide solution, stir at 60°C, 300 r / min for 30 min, add the solution into a hydrothermal synthesis reactor, and perform hydrothermal synthesis at 120°C for 24 h to obtain an ethylenediaminetetraacetic acid-modified hydrotalcite-like material, wherein the Mg(NO3)2 in the mixed solution is Mg 2+ The concentration is 0.10mol / L, Al2(NO3)3 in the mixed solution 3+ The concentration is 0.05 mol / L, and the concentration of EDTA in the mixture is 0.025 mol / L;

[0043] S2. Add 0.1 g of ethylenediaminetetraacetic acid-modified hydrotalcite-like material to 3 mL of distilled water, disperse under 40 kHz ultrasonic conditions for 30 min, add 0.1 g of dodecyl sulfonic acid, adjust the pH of the solution to 10.5 with 1.0 mol / L sodium hydroxide solution, add to a hydrothermal synthesis reactor, carry out hydrothermal synthesis reaction at 60 ° C for 6 h, cool to room temperature, centrifuge at 5000 r / min for 10 min, filter, and wash to obtain a hydrotalcite-like adsorbent.

[0044] Comparative Example 1

[0045] This comparative example provides an adsorbent and its preparation method and application, which specifically include the following contents:

[0046] 100 mL of a mixed solution of Mg(NO3)2 and Al2(NO3)3 was mixed with 100 mL of ethylenediaminetetraacetic acid solution, and the pH was adjusted to 10.5. After stirring at 70°C and 600 r / min for 30 min, the mixture was added to a hydrothermal synthesis reactor, and the hydrothermal synthesis reaction was carried out at 140°C for 36 h. The mixture was washed and filtered to obtain an ethylenediaminetetraacetic acid-modified hydrotalcite-like material. 2+ The concentration is 0.15mol / L, Al in Al2(NO3)3 3+ The concentration is 0.05 mol / L, the concentration of EDTA in the EDTA solution is 0.035 mol / L, and the concentration of sodium hydroxide is 1.25 mol / L.

[0047] Comparative Example 2

[0048] This comparative example provides an adsorbent and its preparation method and application, which specifically include the following contents:

[0049] S1. After mixing 100 mL of a mixed solution of Mg(NO3)2 and Al2(NO3)3 with 100 mL of ethylenediaminetetraacetic acid solution, the pH was adjusted to 10.5, stirred at 70°C and 600 r / min for 30 min, and then added to a hydrothermal synthesis reactor. After hydrothermal synthesis reaction at 140°C for 36 h, an ethylenediaminetetraacetic acid-modified hydrotalcite-like material was obtained, wherein the Mg in the Mg(NO3)2 in the mixed solution was 1.174 mmol / l. 2+ The concentration is 0.20mol / L, Al in Al2(NO3)3 3+ The concentration is 0.05 mol / L, the concentration of EDTA in the EDTA solution is 0.035 mol / L, and the concentration of sodium hydroxide is 1.25 mol / L;

[0050] S2. Add 0.1 g of ethylenediaminetetraacetic acid-modified hydrotalcite-like material to 5 mL of distilled water, disperse it under 40 kHz ultrasonic conditions for 30 min, add 0.15 g of dodecyl sulfonic acid, adjust the pH of the solution to 11.0, add it to a hydrothermal synthesis reactor, carry out hydrothermal synthesis reaction at 70 ° C for 7 h, cool to room temperature, centrifuge at 6000 r / min for 15 min, filter, and wash to obtain an adsorbent.

[0051] Comparative Example 3

[0052] This comparative example provides an adsorbent and its preparation method and application, which specifically include the following contents:

[0053] S1. After mixing 100 mL of a mixed solution of Mg(NO3)2 and Al2(NO3)3 with 100 mL of EDTA solution, the pH value was adjusted to 10.2, and the mixture was stirred at 60°C and 300 r / min for 30 min. The mixture was added to a hydrothermal synthesis reactor, and the mixture was subjected to a hydrothermal synthesis reaction at 120°C for 24 h to obtain an EDTA-modified hydrotalcite-like material, wherein the Mg in the Mg(NO3)2 in the mixed solution was 1.174 mmol / l. 2+ The concentration is 0.10mol / L, Al in Al2(NO3)3 3+ The concentration is 0.05 mol / L, the concentration of EDTA in the EDTA solution is 0.025 mol / L, and the concentration of sodium hydroxide is 1.0 mol / L;

[0054] S2. Add 0.1 g of ethylenediaminetetraacetic acid-modified hydrotalcite-like material to 3 mL of distilled water, disperse it under 40 kHz ultrasonic conditions for 30 min, add 0.2 g of dodecyl sulfonic acid, adjust the pH of the solution to 10.5, add it to a hydrothermal synthesis reactor, carry out hydrothermal synthesis reaction at 60 ° C for 6 h, cool to room temperature, centrifuge at 5000 r / min for 10 min, filter, and wash to obtain an adsorbent.

[0055] The mercury removal rate, hexavalent chromium removal rate and average suspended solids removal rate of the hydrotalcite-like adsorbents in Examples 1-3 and the adsorbents in Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0056] The detection method of mercury removal rate and suspended solids removal rate is as follows: 0.1g adsorbent, 0.1g polyaluminium chloride and 50mL mixed solution are mixed, pH is adjusted to 6, stirred in a blender for 2h, filtered, and then the filtrate is poured out. The filtrate is analyzed by ICP-MS and water quality analyzer to obtain mercury removal rate and suspended solids removal rate. Among them, Hg 2+ The concentration is 50mg / L, Ca 2+ The concentration is 500mg / L, Mg 2+ The concentration of 500 mg / L and the concentration of 200 mesh clay was 200 mg / L.

[0057] The detection method of hexavalent chromium removal rate and suspended solids removal rate is as follows: 0.1g adsorbent, 0.1g polyaluminium chloride and 50mL mixed solution are mixed, pH is adjusted to 6, stirred in a blender for 2h, filtered, and then the filtrate is poured out. The filtrate is analyzed by ICP-MS and water quality analyzer to obtain the hexavalent chromium removal rate and suspended solids removal rate. Among them, Cr2O4 in the mixed solution is 2- The concentration is 50mg / L, Ca 2+ The concentration is 500mg / L, Mg 2+ The concentration of 500 mg / L and the concentration of 200 mesh clay was 200 mg / L.

[0058] Table 1 Mercury removal rate, hexavalent chromium removal rate and suspended solids removal rate test table

[0059] project Mercury removal rate (%) Hexavalent chromium removal rate (%) Average suspended solids removal rate (%) Example 1 99.26 99.96 78.47 Example 2 97.26 96.61 78.35 Example 3 98.39 99.97 82.61 Comparative Example 1 61.27 43.71 66.44 Comparative Example 2 83.84 88.54 77.43 Comparative Example 3 82.74 80.61 67.19

[0060] As shown in Table 1, the hydrotalcite-like adsorbents provided in Examples 1-3 of the present invention are capable of adsorbing and removing mercury, hexavalent chromium, and suspended solids in environments with high calcium and magnesium ion concentrations, while the adsorbents in Comparative Examples 1-3 exhibit poor adsorption and removal of mercury, hexavalent chromium, and suspended solids. This demonstrates that the preparation method of the hydrotalcite-like adsorbent provided by the present invention achieves efficient and simultaneous removal of heavy metals and suspended solids from desulfurization wastewater.

[0061] The above are all preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a hydrotalcite-like adsorbent, characterized in that: The steps include: S1, dissolving a magnesium salt, an aluminum salt, and ethylenediaminetetraacetic acid in water to obtain a mixed solution; adjusting the pH of the mixed solution to alkaline, heating the mixed solution for a hydrothermal reaction, and obtaining an ethylenediaminetetraacetic acid-modified hydrotalcite-like material; S2. Adding the ethylenediaminetetraacetic acid-modified hydrotalcite-like material and dodecylsulfonic acid into water, adjusting the pH to alkaline, and heating to perform a hydrothermal reaction to obtain a hydrotalcite-like adsorbent.

2. The method for preparing a hydrotalcite-like adsorbent according to claim 1, wherein: In S1, the magnesium salt Mg 2+ and Al in aluminum salts 3+ The molar ratio is 1.5-2.5:1; and / or In S1, the aluminum salt Al 3+ The molar ratio of ethylenediaminetetraacetic acid is 1:0.3-0.

7.

3. The method for preparing a hydrotalcite-like adsorbent according to claim 1, wherein: In S1, the alkaline refers to pH = 10.0-10.

5.

4. The method for preparing a hydrotalcite-like adsorbent according to claim 1, wherein: In S1, the temperature of the hydrothermal reaction is 100° C.-140° C., and the time is 12 h-36 h.

5. The method for preparing a hydrotalcite-like adsorbent according to claim 1, wherein: In S1, Mg in the mixed solution 2+ The concentration is 0.01mol / L-0.2mol / L.

6. The method for preparing a hydrotalcite-like adsorbent according to claim 1, wherein: In S2, the usage ratio of the ethylenediaminetetraacetic acid modified hydrotalcite-like material and water is 1 g: (20-50) mL.

7. The method for preparing a hydrotalcite-like adsorbent according to claim 1, wherein: In S2, the temperature of the hydrothermal reaction is 50°C-70°C, and the time is 5h-7h.

8. The method for preparing a hydrotalcite-like adsorbent according to claim 7, wherein: In S2, the mass ratio of the ethylenediaminetetraacetic acid modified hydrotalcite-like material to dodecylsulfonic acid is 1:0.5-1.

5.

9. A hydrotalcite-like adsorbent, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the hydrotalcite-like adsorbent prepared according to the preparation method according to any one of claims 1 to 8 or the hydrotalcite-like adsorbent according to claim 9 in the treatment of desulfurization wastewater.