Tannic acid modified magnetic fly ash-based tobermorite adsorbent as well as preparation method and application thereof

Abstract

The invention relates to a tannic acid modified magnetic fly ash-based tobermorite adsorbent as well as a preparation method and application thereof, the preparation method comprises the following steps: (1) mixing magnetic Fe3O4 and fly ash-based tobermorite, and then sequentially carrying out solid-liquid separation, washing and drying to obtain magnetic fly ash-based tobermorite; and (2) mixing the magnetic fly ash-based tobermorite obtained in the step (1) with tannic acid, carrying out a reaction, and then sequentially carrying out solid-liquid separation, washing and drying to obtain the tannic acid modified magnetic fly ash-based tobermorite adsorbent. The adsorbent provided by the invention can show a good adsorption effect on Pb (II), Cd (II) and Zn (II) in a single-metal system and a multi-metal system, not only can solve the problem of environmental pollution caused by fly ash, but also can effectively treat heavy metal pollution in a water environment.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorption materials, and particularly relates to a tannic acid-modified magnetic fly ash-based tobermorite adsorbent, a preparation method thereof, and uses thereof. Background Art

[0002] With the rapid development of urbanization and industrialization, heavy metals such as lead (Pb), cadmium (Cd), and zinc (Zn) discharged in excess enter groundwater, resulting in the pollution of drinking water sources and posing a serious threat to human life and health. In addition, the mixed pollutants containing multiple heavy metals discharged in industrial production are more harmful than single heavy metal pollution. Therefore, developing adsorbents with high adsorption capacity and capable of removing multiple heavy metal ions simultaneously has become an important research topic in current environmental governance.

[0003] Fly ash (FA) is a solid waste generated by the combustion of coal at high temperatures, with a global annual output of approximately 780 million tons. The large accumulation of fly ash not only occupies land resources but may also cause secondary pollution to soil, water bodies, and the atmosphere. Due to its unique physical and chemical properties, fly ash has been widely studied as an adsorbent for various heavy metal ions in recent years. The tobermorite (TFA) synthesized from FA has a high specific surface area and porosity and has a relatively high adsorption capacity for Pb(II), but its adsorption capacity for Cd(II) and Zn(II) is limited.

[0004] In addition, traditional powdered adsorbents are difficult to effectively separate from water bodies after adsorption due to their small particle size and poor dispersibility, resulting in difficult solid-liquid separation. Some adsorbents may remain in the water body, leading to secondary pollution. Therefore, the recovery problem of traditional powdered adsorbents has become a key factor restricting their wide application.

[0005] For example, CN103880113A discloses a method for recycling heavy metal ion wastewater using modified fly ash. In this method, fly ash is pre-mixed with alkali evenly, treated at 400 - 900 °C for 0.5 - 3 h, then activated by adding water at 90 - 100 °C, the liquid-solid ratio ranges from 3:1 to 10:1, the activation treatment time is 3 - 6 h, washed with water until neutral, and dried to obtain modified fly ash; the modified fly ash is added to heavy metal ion wastewater, and the addition amount of the modified fly ash is 0.1 - 5% of the heavy metal ion wastewater, stirred at room temperature for 1 - 3 h, precipitated, separated, and recycled. Although the modified fly ash obtained by this method has good adsorption effect in a single heavy metal ion wastewater system, its adsorption effect on heavy metal ion wastewater in a complex system is limited, and the separation and recovery process of the adsorbent is difficult.

[0006] Therefore, it is a technical problem to be solved in the present field to provide an adsorbent that uses fly ash as a raw material, has good adsorption effects on various heavy metal ions, and is easy to separate and recover. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a tannic acid-modified magnetic fly ash-based tobermorite adsorbent and its preparation method and use. Compared with the existing technology, the adsorbent provided by the present invention can show good adsorption effects on Pb(II), Cd(II) and Zn(II) in both single-metal systems and multi-metal systems, which can not only solve the environmental pollution problem of fly ash, but also effectively control the heavy metal pollution in the water environment.

[0008] To achieve the purpose of this invention, the following technical solutions are adopted in the present invention:

[0009] In the first aspect, the present invention provides a preparation method of a tannic acid-modified magnetic fly ash-based tobermorite adsorbent, and the preparation method includes the following steps:

[0010] (1) Mix magnetic Fe 3 O 4 and fly ash-based tobermorite, and then perform solid-liquid separation, washing and drying in sequence to obtain magnetic fly ash-based tobermorite;

[0011] (2) Mix the magnetic fly ash-based tobermorite obtained in step (1) and tannic acid and react, and then perform solid-liquid separation, washing and drying in sequence to obtain a tannic acid-modified magnetic fly ash-based tobermorite adsorbent.

[0012] In the adsorbent provided by the present invention, the fly ash-based tobermorite has a rich pore structure. Introducing magnetic Fe 3 O 4 into the fly ash-based tobermorite matrix can, on the one hand, achieve the rapid recovery of the adsorbent by applying an external magnetic field and avoid the agglomeration of Fe 3 O 4 nanoparticles. On the other hand, it can significantly enhance the adsorption of heavy metal ions by introducing strong chemical bond interactions (Fe-O) on the matrix. However, the adsorption effect of magnetic Fe 3 O 4 itself is insufficient, and its introduction will occupy some active sites of the adsorbent. Therefore, the adsorbent provided by the present invention is also modified with tannic acid. Tannic acid is composed of 10 gallic alcohol groups covalently linked to the central glucose nucleus. The Si-OH or Fe-OH contained on the matrix forms strong chemical bonds and strong hydrogen bond interactions with tannic acid, so that it is stably modified on the matrix. As a "multidentate" ligand, tannic acid can chelate with heavy metal ions through proton exchange, thereby further improving the adsorption effect on heavy metal ions.

[0013] In the present invention, the method for solid-liquid separation is not particularly limited and conventional methods in the art can be adopted. For example, it can be filtration.

[0014] Preferably, the preparation method of the fly ash-based tobermorite in step (1) includes: mixing fly ash and a calcium source and performing a hydrothermal reaction, and then successively performing solid-liquid separation, washing, and drying to obtain fly ash-based tobermorite.

[0015] Preferably, the calcium-silicon molar ratio of the calcium source to fly ash is (0.8 - 1.2):1. For example, it can be 0.8:1, 0.9:1, 1:1, 1.1:1, or 1.2:1, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0016] Preferably, the calcium source includes calcium hydroxide.

[0017] Preferably, the pH value of the hydrothermal reaction is 13 - 14. For example, it can be 13, 13.2, 13.4, 13.6, 13.8, or 14, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0018] Preferably, the temperature of the hydrothermal reaction is 160 - 220 °C. For example, it can be 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, or 220 °C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0019] Preferably, the time of the hydrothermal reaction is 4 - 8 h. For example, it can be 4 h, 5 h, 6 h, 7 h, or 8 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0020] Preferably, the liquid-solid ratio of the hydrothermal reaction is (10 - 30):1 mL / g. For example, it can be 10:1 mL / g, 15:1 mL / g, 20:1 mL / g, 25:1 mL / g, or 30:1 mL / g, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0021] Preferably, the solvent of the hydrothermal reaction includes sodium hydroxide solution.

[0022] In the present invention, the preparation method of the fly ash-based tobermorite specifically includes the following steps:

[0023] According to the calcium-silicon molar ratio of calcium hydroxide and fly ash being (0.8 - 1.2):1 and the liquid-solid ratio being (10 - 30):1 mL / g, mix fly ash, calcium hydroxide, and sodium hydroxide solution in a polytetrafluoroethylene liner, and carry out hydrothermal reaction in a homogeneous reactor for 4 - 8 h under the conditions of a rotation speed of 50 - 60 rpm, a temperature of 160 - 220 °C, and a pH of 13 - 14. Then cool the reaction product, separate the solid from the liquid, wash, and dry it to obtain fly ash-based tobermorite.

[0024] In the present invention, the source of the fly ash is not particularly limited. For example, fly ash generated from coal-fired boilers in industries such as thermal power plants, iron and steel, and cement can be used. Generally, in fly ash by mass percentage, it includes SiO 2 (40 - 60%), Al 2 O 3 (20 - 30%), Fe 2 O 3 (5 - 15%), CaO (1 - 15%) and other components (1 - 15%). Among them, the other components are mainly oxides of elements such as Al, K, and Mg.

[0025] Preferably, the specific surface area of the magnetic Fe 3 O 4 is 100 - 150 m 2 / g. For example, it can be 100 m 2 / g, 120 m 2 / g, 140 m 2 / g or 150 m 2 / g, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0026] Preferably, the particle size of the magnetic Fe 3 O 4 is 10 - 15 μm. For example, it can be 10 μm, 12 μm, 14 μm or 15 μm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0027] Preferably, the magnetic Fe 3 O 4 is prepared by the co-precipitation method.

[0028] In the present invention, the magnetic Fe 3 O 4 is preferably prepared by the co-precipitation method, which specifically includes the following steps:

[0029] According to the molar ratio of Fe 2+ and Fe 3+ being (1 - 1.1):2, mix FeCl 3 ·6H2 O solution and FeSO 4 ·7H 2 O solution, under the conditions of 50 - 60 °C and a rotation speed of 180 - 200 rmp, magnetically stir for 10 - 30 min, and then quickly drop in NaOH solution while stirring to form black Fe 3 O 4 。The FeCl 3 ·6H 2 O solution, FeSO 4 ·7H 2 O solution, and NaOH solution have molar concentrations of 0.125 - 0.5 mol / L, 0.0625 - 0.25 mol / L, and 3.0 - 7.0 mol / L, respectively.

[0030] Preferably, the mass ratio of the magnetic Fe 3 O 4 and fly ash-based tobermorite is (0.2 - 0.6):1. For example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, or 0.6:1, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0031] Preferably, the temperature of the mixing in step (1) is 50 - 60 °C. For example, it can be 50 °C, 52 °C, 54 °C, 56 °C, 58 °C, or 60 °C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0032] Preferably, the time of the mixing in step (1) is 2 - 12 h. For example, it can be 2 h, 4 h, 6 h, 8 h, 10 h, or 12 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0033] Preferably, stirring is carried out during the mixing in step (1).

[0034] Preferably, the rotation speed of the stirring in step (1) is 180 - 200 rpm. For example, it can be 180 rpm, 185 rpm, 190 rpm, 195 rpm, or 200 rpm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0035] Preferably, the magnetic fly ash-based tobermorite and tannic acid are mixed in a solvent in step (2).

[0036] Preferably, the solvent includes deionized water.

[0037] Preferably, the mass ratio of tannic acid to magnetic fly ash-based tobermorite in step (2) is (0.0625 - 8):1. For example, it can be 1:16, 1:8, 1:4, 1:2, 1:1, 2:1, 4:1, and 8:1, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable. Preferably, it is (0.125 - 4):1, and more preferably (0.25 - 2):1.

[0038] In the present invention, by preferably controlling the mass ratio of tannic acid to magnetic fly ash-based tobermorite, the adsorption effect reaches the best. If the mass ratio is too small, the amount of grafted tannic acid is too little, and the provided active sites cannot meet the adsorption requirements. If the mass ratio is too large, the grafted tannic acid is too saturated, easily causing pore blockage and having a negative impact on the adsorption effect. Moreover, a large amount of tannic acid cannot be effectively utilized and dissolves in water, violating the principle of economy and high efficiency.

[0039] Preferably, the temperature of the reaction in step (2) is 21 - 25°C. For example, it can be 21°C, 22°C, 23°C, 24°C, or 25°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0040] Preferably, the reaction time is 0.5 - 12 h. For example, it can be 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, or 12 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0041] Preferably, stirring is carried out during the reaction process.

[0042] Preferably, the stirring speed during the reaction process is 180 - 200 rpm. For example, it can be 180 rpm, 185 rpm, 190 rpm, 195 rpm, or 200 rpm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0043] Preferably, the drying temperature in step (2) is 60 - 80°C. For example, it can be 60°C, 65°C, 70°C, 75°C, or 80°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0044] Preferably, the drying time is 8 - 24 h. For example, it can be 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, or 24 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0045] In the present invention, the washing in steps (1) and (2) is a conventional operation in the art. For example, in step (2), water and ethanol are used to wash three times respectively.

[0046] As a preferred technical solution of the first aspect of the present invention, the preparation method of the tannic acid-modified magnetic fly ash-based tobermorite adsorbent comprises the following steps:

[0047] (1) Mix magnetic Fe 3 O 4 and fly ash-based tobermorite at a mass ratio of (0.2 - 0.6):1 under the conditions of a temperature of 50 - 60 °C and a rotation speed of 180 - 200 rpm for 2 - 12 h. The specific surface area of the magnetic Fe 3 O 4 is 100 - 150 m 2 / g, and the particle size of the magnetic Fe 3 O 4 is 10 - 15 μm. Then, filter, wash, and dry in sequence to obtain magnetic fly ash-based tobermorite;

[0048] (2) Mix tannic acid and the magnetic fly ash-based tobermorite obtained in step (1) at a mass ratio of (0.0625 - 8):1 and react at a temperature of 21 - 25 °C and a rotation speed of 180 - 200 rpm for 0.5 - 12 h. Then, filter, wash, and dry at a temperature of 60 - 80 °C for 8 - 24 h to obtain the tannic acid-modified magnetic fly ash-based tobermorite adsorbent.

[0049] In the second aspect, the present invention provides a tannic acid-modified magnetic fly ash-based tobermorite adsorbent, which is obtained by using the preparation method of the tannic acid-modified magnetic fly ash-based tobermorite adsorbent described in the first aspect of the present invention.

[0050] The adsorbent provided by the present invention has strong adsorption performance for Pb(II), Cd(II), and Zn(II), and is easy to separate and recover.

[0051] In the third aspect, the present invention provides a use of the tannic acid-modified magnetic fly ash-based tobermorite adsorbent as described in the first aspect of the present invention, and the adsorbent is used for adsorbing heavy metal ions in wastewater.

[0052] The adsorbent provided by the present invention is used for adsorbing heavy metal ions in wastewater, including Pb(II), Cd(II), Zn(II), etc., and has strong adsorption performance. It can not only treat wastewater polluted by single-metal systems, but also has good adsorption ability for wastewater with multi-metal coexistence systems, and has broad application prospects.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] (1) In the preparation method provided by the present invention, through magnetic Fe 3 O4 The combined action of fly ash-based tobermorite and tannic acid is used to prepare an adsorbent with high adsorption performance by means of strong chemical bond action (Fe-O) and hydrogen bond action (Si-OH or Fe-OH and tannic acid). It has strong adsorption performance for Pb(II), Cd(II) and Zn(II), can not only treat the wastewater polluted by single-metal system, but also has good adsorption capacity for the wastewater in multi-metal coexistence system, and is easy to separate and recycle.

[0055] (2) Under the optimal conditions, for the adsorbent provided by the present invention in the single-metal system, the adsorption capacities for Pb(II), Cd(II) and Zn(II) can reach above 222.80 mg / g, above 48.08 mg / g and above 44.54 mg / g respectively, and can reach 337.5 mg / g, 80.28 mg / g and 79.8 mg / g respectively under more optimal conditions; in the multi-metal coexistence system, the adsorption capacities for Pb(II), Cd(II) and Zn(II) can reach above 113.33 mg / g, above 14.64 mg / g and above 21.00 mg / g respectively, and can reach 112.7 mg / g, 58.81 mg / g and 65.56 mg / g respectively under more optimal conditions.

[0056] (3) The preparation method of the adsorbent provided by the present invention uses raw materials that are cheap and easy to obtain, the preparation process is simple, the cost of instruments and equipment is low, the adsorption performance of the adsorbent is excellent, and the resource utilization of waste fly ash can be realized. Brief Description of the Drawings

[0057] Figure 1 is a simple structure diagram of the tannic acid-modified magnetic fly ash-based tobermorite adsorbent provided in Example 16 of the present invention;

[0058] Figure 2 is a structure diagram of tannic acid TA used in Example 16 of the present invention;

[0059] Figure 3 is a scanning electron microscope image: (a) is the SEM image and its partial enlarged image of TFA provided in Example 1 of the present invention; (b) is the SEM image and its partial enlarged image of TFA-Fe 3 O 4 of Example 2 of the present invention; (c) is the SEM image and its partial enlarged image of TFA-Fe 3 O 4 / TA of Example 16 of the present invention;

[0060] Figure 4 is TFA provided in Example 1 of the present invention and TFA-Fe provided in Example 2 of the present invention 3 O 4and Example 16 provides the XRD pattern of TFA-Fe 3 O 4 / TA;

[0061] Figure 5 are the TFA provided in Example 1 of the present invention, the TFA-Fe provided in Example 2 3 O 4 and the TFA-Fe provided in Example 16 3 O 4 / TA thermogravimetric plot;

[0062] Figure 6 are the nitrogen adsorption-desorption and pore size distribution test result graphs: (a) is the TFA provided in Example 1 of the present invention, the TFA-Fe provided in Example 2 3 O 4 and the TFA-Fe provided in Example 16 3 O 4 / TA nitrogen adsorption-desorption curve graph; (b) is the TFA provided in Example 1 of the present invention, the TFA-Fe provided in Example 2 3 O 4 and the TFA-Fe provided in Example 16 3 O 4 / TA pore size distribution result graph;

[0063] Figure 7 are the adsorption kinetics graphs: (a) is the adsorption kinetics graph of Pb(II) by TFA provided in Example 1 of the present invention and TFA-Fe provided in Example 16 3 O 4 / TA; (b) is the adsorption kinetics graph of Cd(II) by TFA provided in Example 1 of the present invention and TFA-Fe provided in Example 16 3 O 4 / TA; (c) is the adsorption kinetics graph of Zn(II) by TFA provided in Example 1 of the present invention and TFA-Fe provided in Example 16 3 O 4 / TA;

[0064] Figure 8 are the adsorption isotherm graphs: (a) is the adsorption isotherm graph of Pb(II) by TFA provided in Example 1 of the present invention and TFA-Fe provided in Example 16 3 O 4 / TA; (b) is the adsorption isotherm graph of Cd(II) by TFA provided in Example 1 of the present invention and TFA-Fe provided in Example 16 3 O 4 / TA; (c) is the adsorption isotherm graph of Zn(II) by TFA provided in Example 1 of the present invention and TFA-Fe provided in Example 16 3 O4 Adsorption isotherm diagram of Zn(II) adsorbed by / TA;

[0065] Figure 9 It is TFA-Fe provided in Example 16 of the present invention 3 O 4 Competition adsorption diagram of TFA-Fe / TA for mixed solutions of Pb(II), Cd(II) and Zn(II). Specific implementation manners

[0066] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0067] Example 1

[0068] This example provides a preparation method of a tannic acid-modified magnetic fly ash-based tobermorite adsorbent, and the preparation method includes the following steps:

[0069] (1) Mix 0.58 g of magnetic 0.58gFe 3 O 4 and 1 g of fly ash-based tobermorite for 2 h at a temperature of 55 °C and a rotation speed of 180 rpm, and then filter, wash and dry in sequence to obtain magnetic fly ash-based tobermorite, denoted as TFA-Fe 3 O 4 ;

[0070] (2) Mix 0.125 g of tannic acid and 0.5 g of the magnetic fly ash-based tobermorite obtained in step (1) in 40 mL of deionized water and react for 2 h at a temperature of 23 °C and a rotation speed of 180 rpm, and then filter, wash, and dry at a temperature of 70 °C for 16 h to obtain a tannic acid-modified magnetic fly ash-based tobermorite adsorbent, denoted as TFA-Fe 3 O 4 / TA.

[0071] In this example, the magnetic Fe 3 O 4 is obtained by the following preparation method:

[0072] Weigh 1.3525 g, 0.6950 g and 2.5 g of FeCl 3 ·6H 2 O, FeSO 4 ·7H 2 O and NaOH respectively, and then dissolve them in 20 mL, 20 mL and 10 mL of deionized water respectively. According to Fe 2+ and Fe3+ Mix FeCl 3 ·6H 2 O solution (0.25 mol / L) and FeSO 4 ·7H 2 O solution (0.125 mol / L) in a molar ratio of 1:2, magnetically stir for 10 min at 55 °C with a rotation speed of 200 rmp, and then quickly drop NaOH solution (6.25 mol / L) while stirring to form black Fe 3 O 4 , and the specific surface area of the magnetic Fe 3 O 4 is 125.83 m 2 / g, and the particle size of the magnetic Fe 3 O 4 is 14.43 μm.

[0073] In this example, the fly ash-based tobermorite is obtained by the following preparation method:

[0074] According to the calcium-silicon molar ratio of calcium hydroxide and fly ash being 0.85:1 and the liquid-solid ratio being 20:1 mL / g, mix 4 g of fly ash, 2.4427 g of calcium hydroxide, and 0.5 mol / L sodium hydroxide solution in a polytetrafluoroethylene inner lining, and conduct a hydrothermal reaction in a homogeneous reactor for 4 h under the conditions of a rotation speed of 50 rpm, a temperature of 200 °C, and a pH of 13.60. Then cool, filter, wash, and dry the reaction product to obtain fly ash-based tobermorite, denoted as TFA.

[0075] Examples 2 - 6

[0076] Examples 2 - 6 respectively provide a preparation method of a tannic acid-modified magnetic fly ash-based tobermorite adsorbent. The difference compared with Example 1 is only that the mixing time of magnetic Fe 3 O 4 and fly ash-based tobermorite in step (1) is 4 h, 6 h, 8 h, 10 h, and 12 h in sequence.

[0077] Examples 7 - 13

[0078] Examples 7 - 13 respectively provide a preparation method of a tannic acid-modified magnetic fly ash-based tobermorite adsorbent. The difference compared with Example 2 is only that the mixing time of tannic acid and magnetic fly ash-based tobermorite in step (2) is 0.5 h, 1 h, 4 h, 6 h, 8 h, 10 h, and 12 h in sequence.

[0079] Examples 14 - 20

[0080] Examples 14 - 20 respectively provide a preparation method of tannic acid modified magnetic fly ash based tobermorite adsorbent. The difference compared with Example 9 is only that the addition amounts of tannic acid in step (2) are 0.03125 g, 0.0625 g, 0.25 g, 0.5 g, 1 g, 2 g and 4 g in sequence, and the mass ratios of the two are 0.0625:1, 0.125:1, 0.5:1, 1:1, 2:1, 4:1 and 8:1 in sequence.

[0081] Performance test:

[0082] In the single metal system, the adsorbents provided in the above examples and comparative examples were used to adsorb heavy metal ions. The adsorption test conditions were as follows: the initial concentrations (C 0 ) of Pb(II), Cd(II) and Zn(II) were 400 mg / L, 100 mg / L and 100 mg / L respectively, and the pH values were adjusted to 4, 6 and 6 respectively. They were respectively shaken in a water bath environment at 25 °C for 10 h, 8 h and 8 h. The obtained adsorption capacities are shown in Table 1.

[0083] In the multi-metal coexistence system, the adsorbents provided in the above examples and comparative examples were used to adsorb heavy metal ions. The adsorption test conditions were as follows: the initial concentrations (C 0 ) of Pb(II), Cd(II) and Zn(II) were all set to 120 mg / L, the pH was adjusted to 4, and it was shaken in a water bath environment at 25 °C for 10 h. The obtained adsorption capacities are shown in Table 1.

[0084] Taking the fly ash based tobermorite TFA prepared in Example 1, the magnetic fly ash based tobermorite TFA-Fe 3 O 4 prepared in Example 2, and the tannic acid modified magnetic fly ash based tobermorite adsorbent TFA-Fe 3 O 4 / TA prepared in Example 16 as an example:

[0085] The simple structure diagram of the tannic acid modified magnetic fly ash based tobermorite adsorbent TFA-Fe 3 O 4 / TA is as shown in Figure 1 The structure diagram of tannic acid TA is as shown in Figure 2 As can be seen from Figure 1 and Figure 2 magnetic Fe 3 O 4 is introduced into the fly ash based tobermorite matrix. Tannic acid is covalently connected to the central glucose nucleus by 10 gallol groups, and the Si-OH or Fe-OH contained in the matrix forms strong chemical bonds and strong hydrogen bond interactions with tannic acid, so that it is stably modified on the matrix.

[0086] Detected by scanning electron microscopy, it can be seen from Figure 3 that TFA shows a spherical morphology, and smooth and slender nanofibers can be clearly observed; TFA-Fe 3 O 4 has an irregular morphology compared to TFA, and there are many irregular Fe 3 O 4 particles on the surface; TFA-Fe 3 O 4 / TA shows a morphology quite different from that of TFA-Fe 3 O 4 . It can be clearly seen that the surface becomes smooth, which is because the TA molecules are uniformly coated on the surface of TFA-Fe 3 O 4 .

[0087] Through X-ray diffraction analysis, it can be seen from Figure 4 that TFA shows the tobermorite phase and a partial CaCO 3 phase, and tobermorite is the dominant species; TFA-Fe 3 O 4 shows characteristic peaks attributed to Fe 3 O 4 . Both tobermorite and Fe 3 O 4 become the dominant species, indicating the successful synthesis of the composite material; after cross-linking with TA, some peaks of both tobermorite and Fe 3 O 4 weaken or disappear, which is due to the introduction of the amorphous component of TA, coating on the surface and reducing its crystallinity.

[0088] Through thermogravimetric analysis, it can be seen from Figure 5 that the thermal loss of TFA-Fe 3 O 4 (14.39 wt%) from 25°C to 800°C is lower than that of TFA (21.16 wt%), indicating that the introduction of Fe 3 O 4 enhances the thermal stability; the thermal loss of TFA-Fe 3 O 4 / TA is the largest, reaching 42.93 wt%, indicating the successful grafting of TA, and the content is about 28.54 wt%; the highest pyrolysis temperatures of TFA, TFA-Fe 3 O 4 and TFA-Fe 3 O 4 / TA are 681.20°C, 684.59°C and 721.14°C respectively, which indicates that the Si-OH of TFA reacts with Fe 3 O 4 , TA and TFA-Fe3 O 4 forms a strong chemical bond with Fe.

[0089] Through nitrogen adsorption - desorption and pore size distribution detection, it can be seen from Figure 6 (a) that the isotherms of the three materials are of type IV with an H3 - type hysteresis loop, indicating the presence of mesopores (2 - 50 nm), and the pore size is mainly slit - shaped pores; it can be seen from Figure 6 (b) that compared with TFA, the pore structure of TFA - Fe 3 O 4 and TFA - Fe 3 O 4 / TA has not changed and is still a mesoporous adsorbent. Compared with TFA - Fe 3 O 4 , the pore volume (dV / dD) in TFA - Fe 3 O 4 / TA decreases, indicating a decrease in the number of mesopores, proving that the mesopores are blocked by TA.

[0090] Taking TFA and TFA - Fe 3 O 4 / TA for adsorption kinetics analysis, the adsorption kinetic diagrams of Pb(II), Cd(II) and Zn(II) are as shown in Figure 7 . It can be seen from Figure 7 that in the initial stage of adsorption, the adsorption rate of TFA - Fe 3 O 4 / TA is relatively faster than that of TFA. The adsorption efficiencies within the first 5 minutes reach 51.10%, 66.80% and 52.11% respectively. The adsorption of Pb(II), Cd(II) and Zn(II) by TFA and TFA - Fe 3 O 4 / TA reaches equilibrium at 10, 8 and 8 h respectively. The experimental equilibrium adsorption amounts q e (exp) of Pb(II), Cd(II) and Zn(II) reach 337.5 mg / g, 80.28 mg / g, 79.8 mg / g respectively, which are significantly higher than the q e (exp) of TFA, namely 284.3 mg / g, 62.99 mg / g, 50.92 mg / g.

[0091] Taking TFA and TFA - Fe 3 O 4 / TA for isothermal adsorption analysis, the adsorption isotherm diagrams of Pb(II), Cd(II) and Zn(II) are as shown in Figure 8 . It can be seen from Figure 8 that when the maximum initial concentrations (C 0When the concentrations are 500 mg / L, 300 mg / L, and 300 mg / L respectively, at 298, 308, and 318 K, the maximum experimental adsorption capacities (q 3 O 4 ) of TFA-Fe max / TA for Pb(II) are 348.4 mg / g, 362.1 mg / g, and 370.9 mg / g respectively; the q max values for Cd(II) are 109.6 mg / g, 121.2 mg / g, and 138.9 mg / g respectively; the q max values for Zn(II) are 101.1 mg / g, 114.4 mg / g, and 123.4 mg / g respectively. Compared with TFA, the q max values for Pb(II) are increased by 17.15%, 16.06%, and 14.02% respectively, those for Cd(II) are increased by 72.79%, 70.70%, and 63.55% respectively, and those for Zn(II) are increased by 76.59%, 60.67%, and 44.50% respectively.

[0092] The competitive adsorption analysis of the mixed solutions of Pb(II), Cd(II), and Zn(II) was carried out with TFA-Fe 3 O 4 / TA. As shown in Figure 9 , it can be seen from Figure 9 that compared with Cd(II) and Zn(II), TFA-Fe 3 O 4 / TA has higher adsorption capacity and removal rate for Pb(II), showing obvious selectivity. In the mixed system, the adsorption capacities of Pb(II), Cd(II), and Zn(II) reach 112.7 mg / g, 58.81 mg / g, and 65.56 mg / g respectively (the initial concentration of each ion is 120 mg / L). Compared with the single system, the adsorption capacity of each ion decreases. In addition, the adsorption capacity shows the trend of Pb(II)>Zn(II)>Cd(II), which is inconsistent with the result of Pb(II)>Cd(II)>Zn(II) in the single system, and this is attributed to competitive adsorption.

[0093] Table 1

[0094]

[0095]

[0096] It can be seen from the data in Table 1 as follows:

[0097] (1) As can be seen from Examples 1-6, magnetic Fe 3 O 4The mixing time with TFA has little effect on the adsorption efficiency of heavy metal ions. Among them, when the mixing time is 4 h (i.e., Example 2), the overall adsorption efficiency is close to the best.

[0098] (2) As can be seen from Examples 7 - 13, when the mixing time of TA and TFA-Fe 3 O 4 is in the range of 0.5 - 12 h, the adsorption capacity of TFA-Fe 3 O 4 / TA for heavy metal ions shows a trend of first increasing and then stabilizing. Among them, when the mixing time is 4 h (i.e., Example 9), the overall adsorption efficiency is close to the best.

[0099] (3) As can be seen from Examples 14 - 20, as the mass ratio of TA to TFA-Fe 3 O 4 increases, the adsorption capacity for heavy metal ions shows a trend of first increasing and then decreasing. When the mass ratio is 0.5:1 (i.e., Example 16), the overall adsorption efficiency is close to the best.

[0100] In summary, the adsorbent provided by the present invention can exhibit good adsorption efficiency for Pb(II), Cd(II) and Zn(II) in both single-metal and multi-metal systems, which can not only solve the environmental pollution problem of fly ash, but also effectively control the heavy metal pollution in water environment.

[0101] The applicant declares that the above description is only the specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing a tannic acid modified magnetic fly ash-based tobermorite adsorbent, characterized in that: The preparation method comprises the following steps: (1) mixing magnetic Fe3O4 and fly ash-based thoberylite, and then sequentially performing solid-liquid separation, washing and drying to obtain magnetic fly ash-based thoberylite; (2) The magnetic fly ash-based tobermorite and tannic acid obtained in step (1) are mixed and reacted, and then solid-liquid separation, washing and drying are performed in sequence to obtain a tannic acid-modified magnetic fly ash-based tobermorite adsorbent.

2. The preparation method according to claim 1, characterized in that: The method for preparing fly ash-based thobermorite in step (1) comprises: mixing fly ash and a calcium source and performing a hydrothermal reaction, and then sequentially performing solid-liquid separation, washing and drying to obtain fly ash-based thobermorite; Preferably, the calcium-silicon molar ratio of the calcium source and fly ash is (0.8-1.2):1; Preferably, the calcium source comprises calcium hydroxide; Preferably, the temperature of the hydrothermal reaction is 160-220°C; Preferably, the hydrothermal reaction time is 4-8h; Preferably, the liquid-to-solid ratio of the hydrothermal reaction is (10-30): 1 mL / g.

3. The preparation method according to claim 1 or 2, characterized in that: The specific surface area of ​​the magnetic Fe3O4 in step (1) is 100-150m 2 / g; Preferably, the particle size of the magnetic Fe3O4 is 10-15 μm; Preferably, the magnetic Fe3O4 is prepared by co-precipitation; Preferably, the mass ratio of the magnetic Fe3O4 and the fly ash-based tobermorite is (0.2-0.6):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that The mixing temperature in step (1) is 50-60° C. Preferably, the mixing time in step (1) is 2-12 hours; Preferably, stirring is performed during the mixing process in step (1); Preferably, the stirring speed in step (1) is 180-200 rpm.

5. The preparation method according to any one of claims 1 to 4, characterized in that: Step (2) the magnetic fly ash-based tobermorite and tannic acid are mixed in a solvent; Preferably, the solvent comprises deionized water.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The mass ratio of tannic acid to magnetic fly ash-based tobermorite in step (2) is (0.0625-8):1, preferably (0.125-4):1, and further preferably (0.25-2):

1.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The reaction temperature in step (2) is 21-25°C; Preferably, the reaction time is 0.5-12h; Preferably, stirring is performed during the reaction; Preferably, the stirring speed during the reaction is 180-200 rpm.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The drying temperature in step (2) is 60-80° C. Preferably, the drying time is 8-24 hours.

9. A tannic acid modified magnetic fly ash-based tobermorite adsorbent, characterized in that: The adsorbent is obtained by the preparation method of the tannic acid modified magnetic fly ash-based tobermorite adsorbent according to any one of claims 1 to 8.

10. A use of the tannic acid modified magnetic fly ash-based tobermorite adsorbent as claimed in claim 9, characterized in that: The adsorbent is used for adsorbing heavy metal ions in wastewater.

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