Preparation method of magnesium iron mineral loaded amphoteric polymer heavy metal adsorbent

Abstract

The invention provides a preparation method of a modified ferruginous mineral loaded amphoteric polymer heavy metal adsorbent, which comprises the following steps: I, pretreating a mineral matrix, namely crushing, grinding and sieving ferruginous raw ore to obtain mineral powder, grinding and sieving biochar to obtain biochar powder, and calcining and activating the mineral powder and the biochar powder in a muffle furnace to obtain a modified ferruginous mineral loaded amphoteric polymer heavy metal adsorbent; naturally cooling to obtain a calcined modified mineral matrix; iI, preparing a precursor dispersion liquid, namely adding the calcined modified mineral matrix into an organic solvent, performing ultrasonic dispersion at room temperature for 20-40 minutes to obtain a uniform mineral dispersion liquid, sequentially adding an amino monomer, an acrylic monomer, a cross-linking agent and an initiator into the dispersion liquid, and uniformly stirring and mixing to obtain a polymerized precursor liquid; iII, in-situ polymerization reaction: continuously introducing nitrogen into the polymerization precursor liquid to remove air in the system, sealing, and carrying out in-situ free radical polymerization reaction in a constant-temperature environment to obtain a solid-phase product; and IV, post-treatment: sequentially washing the solid-phase product with methanol and deionized water for multiple times to remove unreacted monomer and oligomer impurities, and then drying, grinding and sieving to obtain the magnesium iron mineral loaded amphoteric polymer heavy metal adsorbent. The method can be flexibly applied according to actual wastewater pH characteristics, and the defect that a traditional adsorbent can only treat single type of heavy metal or needs to frequently adjust the pH is overcome.

Description

Technical Field

[0001] This invention relates to the field of water treatment functional adsorption material preparation technology, specifically to a method for preparing a mineral-supported polymer adsorbent that can be adapted to different pH environments and efficiently remove cationic or anionic heavy metals respectively. Background Technology

[0002] With the rapid development of industries such as mining, electroplating, metallurgy, and chemicals, heavy metal pollution in water has become increasingly prominent. Cationic heavy metals such as lead, cadmium, and copper, as well as anionic heavy metals such as chromium and arsenic, are highly toxic, bioaccumulative, and carcinogenic. They can accumulate through the food chain, seriously threatening aquatic ecosystems and human health. Adsorption methods, due to their simple operation, high treatment efficiency, and lack of secondary pollution, have become one of the mainstream technologies for treating heavy metal wastewater.

[0003] Existing heavy metal adsorbents are mainly divided into two major systems: inorganic mineral adsorbents and organic polymer adsorbents. Inorganic mineral adsorbents (such as olivine and magnetite) are characterized by large natural reserves, low raw material costs, and high mechanical strength, but they have drawbacks such as a small number of surface functional groups, low adsorption capacity, and poor selectivity for heavy metals. Organic polymer adsorbents can precisely control the type and density of functional groups through monomer molecule design, resulting in high adsorption capacity and good selectivity. However, pure polymer materials are prone to swelling and loss in water, and have poor mechanical stability and recyclability.

[0004] More importantly, existing amine-containing polymer adsorbents rely on the protonation of amine groups for the adsorption of anionic heavy metals, requiring acidic to neutral conditions (pH=4~7) for effective adsorption via electrostatic interactions. Conversely, carboxyl-containing polymers rely on the deprotonation of carboxyl groups for the adsorption of cationic heavy metals, requiring neutral to weakly alkaline conditions (pH=7~9) for effective adsorption via coordination interactions. Because the optimal operating pH ranges for these two types of functional groups differ, a single adsorbent cannot efficiently remove both anionic and cationic heavy metals simultaneously under the same pH conditions. In practical wastewater treatment, it is often necessary to select a suitable adsorbent type based on the wastewater's pH characteristics, or to adjust the pH and treat in stages, increasing process complexity and treatment costs.

[0005] Therefore, developing a composite adsorbent with a wide pH adaptability range, selective and efficient removal of corresponding types of heavy metals based on environmental pH, and good mechanical stability has significant engineering application value. Summary of the Invention

[0006] The purpose of this invention is to address the technical problems of existing adsorbents' inability to simultaneously and efficiently remove both anionic and cationic heavy metals under the same pH conditions, and the poor mechanical stability of pure polymers. This invention provides a method for preparing a magnesium-iron-silicon mineral-supported amphoteric polymer heavy metal adsorbent. This adsorbent introduces both amine and carboxyl bifunctional groups into the same material and utilizes pH-responsive characteristics. In the acidic to neutral range (pH=4~7), it primarily adsorbs anionic heavy metals through protonated amine groups, while in the neutral to weakly alkaline range (pH=7~9), it primarily adsorbs cationic heavy metals through deprotonated carboxyl groups, thereby achieving adaptive removal of heavy metal pollution over a wide pH range.

[0007] The preparation method of the magnesium-iron mineral-supported amphoteric polymer heavy metal adsorbent of the present invention is carried out according to the following steps:

[0008] I. Pretreatment of mineral matrix: The magnesian ore is crushed, ground and sieved to obtain mineral powder. Biochar is ground and sieved to obtain biochar powder. The mineral powder is placed in a muffle furnace for calcination and activation. After natural cooling, the calcined modified mineral matrix is ​​obtained.

[0009] II. Preparation of precursor dispersion: The calcined modified mineral matrix is ​​added to an organic solvent and ultrasonically dispersed at room temperature for 20 min to 40 min to obtain a uniform mineral dispersion. Then, amine monomers, acrylic monomers, crosslinking agents, and initiators are added to the dispersion in sequence and stirred until uniform to obtain the polymerization precursor liquid.

[0010] III. In-situ polymerization reaction: Nitrogen gas is continuously introduced into the precursor liquid to remove air from the system. After sealing, the system is placed in a constant temperature environment to carry out in-situ free radical polymerization reaction to obtain a solid product.

[0011] IV. Post-processing: The solid product was washed repeatedly with methanol and deionized water to remove unreacted monomers and oligomer impurities. After drying, grinding and sieving, a magnesium-iron mineral-supported amphoteric polymer heavy metal adsorbent was obtained.

[0012] Preferably, the magnesian ore mentioned in step I is one or more of natural minerals such as pyroxene, olivine, and amphibole, and the mineral powder passes through a 50-100 mesh sieve. The biochar is one or more of rice husk powder, corn stalk, and wheat straw, and the biochar powder passes through a 100-200 mesh sieve.

[0013] Preferably, the calcination activation temperature in step I is 400℃~600℃, and the time is 2h~3h.

[0014] Preferably, the organic solvent in step II is one or a mixture of several of N,N-dimethylformamide, methanol, and ethanol, and the solid-liquid ratio of the calcined modified mineral matrix to the organic solvent is 1 g:(15~25) mL.

[0015] Preferably, the amino monomer in step II is one or more of 4-vinylbenzylamine and dimethylaminoethyl methacrylate; the acrylic monomer is one or more of acrylic acid and itaconic acid; and the molar ratio of the amino monomer to the acrylic monomer is (3~7):(7~3).

[0016] Preferably, the total amount of amine monomers and acrylic monomers mentioned in step II is in a mass ratio of (3~6) mmol:1g to the calcined modified mineral matrix.

[0017] Preferably, the crosslinking agent in step II is ethylene glycol dimethacrylate, and the ratio of the total amount of amino monomers and acrylic monomers to the amount of crosslinking agent is (8~12):1.

[0018] Preferably, the initiator in step II is azobisisobutyronitrile, and the mass ratio of the crosslinking agent to the initiator is 1 mmol:(60~80) mg.

[0019] Preferably, the nitrogen gas is introduced in step III for 10-15 minutes, and the temperature of the in-situ free radical polymerization reaction is 65-75°C for 12-18 hours.

[0020] Preferably, in step IV, the product is washed 3-5 times with methanol and deionized water, dried at 80℃-100℃, and sieved through a 200-mesh standard sieve.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention uses natural magnesium-iron minerals as a rigid matrix. After adding biochar and moderately calcining, the surface active sites are enriched. Then, an amphoteric polymer containing amine and carboxyl groups is grafted onto the mineral surface via in-situ free radical polymerization. The mineral matrix, acting as a rigid framework, effectively limits polymer swelling, solving the problem of easy loss of pure polymer adsorbents. Simultaneously, the polymer layer introduces a high density of amine and carboxyl groups, giving the material pH-responsive amphoteric characteristics.

[0023] The adsorbent of this invention exhibits predominantly amine protonation under acidic to neutral conditions (pH 4-7), enabling effective adsorption of anionic heavy metals such as Cr(VI) and As(V) through electrostatic attraction. Under neutral to weakly alkaline conditions (pH 7-9), predominantly carboxyl deprotonation allows for effective adsorption of cationic heavy metals such as Pb(II), Cd(II), and Cu(II) through coordination. Although the optimal adsorption pH ranges for the two types of heavy metals differ, preventing the simultaneous achievement of maximum efficiency at the same pH point, this invention broadens the effective pH adaptability range of a single material, allowing for flexible application based on the actual pH characteristics of wastewater. This avoids the limitations of traditional adsorbents that can only treat a single type of heavy metal or require frequent pH adjustments.

[0024] The preparation process of this invention is simple, the reaction conditions are mild, and the raw materials are widely available. The swelling rate of the prepared adsorbent in pure water is controlled within the range of 35% to 55%, which is much lower than that of polar or natural pure polymer adsorbents (commonly >300%). After 5 cycles of use, the adsorption capacity retention rate for heavy metals is >85%, and the mechanical stability and reusability are significantly better than those of polar or natural pure polymer materials. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the synthetic route for the modified magnesium-iron mineral-supported amphoteric polymer adsorbent prepared in this invention.

[0026] Figure 2 To obtain the full X-ray photoelectron spectroscopy (XPS) spectrum of the calcined mineral matrix;

[0027] Figure 3 The Fourier transform infrared (FTIR) spectra of the mineral matrix before and after calcination are shown.

[0028] Figure 4 X-ray powder diffraction (XRD) patterns of the mineral matrix before and after calcination;

[0029] Figure 5 This is a scanning electron microscope (SEM) image of the mineral matrix after calcination. Detailed Implementation

[0030] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0031] Example 1

[0032] The preparation method of the magnesium-iron-silicon mineral-supported amphoteric polymer heavy metal adsorbent of this embodiment is carried out according to the following steps:

[0033] I. Pretreatment of mineral matrix: The natural magnesian ore is crushed and ground, and passed through a 100-mesh standard sieve to obtain mineral powder. The biochar is ground and passed through a 200-mesh standard sieve to obtain biochar powder. The mineral powder and biochar powder are placed in a muffle furnace and calcined at 600℃ for 2.5h. After naturally cooling to room temperature, the calcined modified mineral matrix is ​​obtained.

[0034] II. Preparation of precursor dispersion: 1 g of calcined modified mineral matrix was added to 20 mL of anhydrous ethanol and ultrasonically dispersed at room temperature for 30 min to obtain a uniform mineral dispersion. Then, 2.5 mmol of 4-vinylbenzylamine, 2.5 mmol of acrylic acid, 0.5 mmol of ethylene glycol dimethacrylate and 40 mg of azobisisobutyronitrile were added to the dispersion in sequence and stirred at room temperature for 30 min to mix evenly to obtain the polymerization precursor liquid.

[0035] III. In-situ polymerization reaction: The precursor liquid was transferred into a stoppered reaction flask, and nitrogen gas was continuously introduced for 10 minutes to remove the air in the system. After removing the vent tube, the reaction flask was quickly sealed and placed in a constant temperature oven. The polymerization reaction was carried out at 70°C for 16 hours to obtain a solid product.

[0036] IV. Post-processing: The solid product was washed four times each with methanol and deionized water to remove unreacted monomers and oligomer impurities. It was then dried in an 80°C oven to constant weight, ground, and passed through a 200-mesh standard sieve to obtain a magnesium-iron-silicon mineral-supported amphoteric polymer heavy metal adsorbent.

[0037] Swelling rate test: Take 0.5g of dry adsorbent, immerse it in 100mL of deionized water, filter and weigh after 24h, and calculate the swelling rate as 42%.

[0038] Adsorption performance test: In a Cr(VI) solution with an initial concentration of 100 mg / L, under pH=5.0 conditions, and with shaking adsorption at 25℃ for 24 h, the equilibrium adsorption capacity for Cr(VI) was 68.5 mg / g, and the removal rate was 65.2%.

[0039] In a Pb(II) solution with an initial concentration of 100 mg / L, under pH 8.0 conditions, the adsorption was carried out at 25 °C with shaking for 24 h. The equilibrium adsorption capacity for Pb(II) was 85.3 mg / g, and the removal rate was 89.2%.

[0040] pH adaptability test: In the pH range of 4 to 9, the adsorption capacity of this adsorbent for Cr(VI) reaches its peak (>60 mg / g) at pH 4.5 to 5.5, and the adsorption capacity for Pb(II) reaches its peak (>80 mg / g) at pH 6.5 to 7.5, demonstrating the selective adsorption characteristics of pH response.

[0041] Cyclic stability test: Five adsorption-desorption cycles were performed using 0.1 mol / L NaOH solution (for Pb(II) desorption) and 0.1 mol / L HCl solution (for Cr(VI) desorption). After the fifth cycle, the adsorption capacities for Pb(II) and Cr(VI) were 87.3% and 85.6% of the initial capacities, respectively, showing good cyclic stability.

[0042] Example 2

[0043] The difference between this embodiment and Example 1 is that the calcination activation temperature in step one is 500°C and the time is 3 hours. Other steps and parameters are the same as in Example 1.

[0044] The adsorbent prepared in this embodiment has a slightly lower specific surface area, and its adsorption capacities for Pb(II) and Cr(VI) are 78.6 mg / g and 58.3 mg / g, respectively, with a swelling rate of 38%.

[0045] Example 3

[0046] The difference between this embodiment and Example 1 is that in step two, the amino monomer is dimethylaminoethyl methacrylate, and the acrylic monomer is itaconic acid, with a molar ratio of 4:6. Other steps and parameters are the same as in Example 1.

[0047] The adsorbent prepared in this embodiment has enhanced coordination ability for cationic heavy metals due to the presence of two carboxyl groups in itaconic acid. The adsorption capacity for Pb(II) is increased to 92.4 mg / g, but the adsorption capacity for Cr(VI) is reduced to 52.1 mg / g.

[0048] Example 4

[0049] The difference between this embodiment and Example 1 is that the organic solvent in step two is N,N-dimethylformamide, the polymerization reaction temperature is 75°C, and the reaction time is 14 hours. Other steps and parameters are the same as in Example 1.

[0050] Comparative Example 1

[0051] This comparative example uses a purely modified mineral matrix, without subsequent steps, and other pretreatment parameters are the same as in Example 1. Tests showed that its adsorption capacity for Pb(II) was only 12.3 mg / g at pH=8.0 and its adsorption capacity for Cr(VI) was only 8.7 mg / g at pH=5.0, demonstrating the limited adsorption capacity of the pure mineral matrix.

[0052] Comparative Example 2

[0053] This comparative example uses a pure amphoteric polymer without the addition of a modified mineral matrix, and the monomer ratio is the same as in Example 1. Testing showed that its swelling rate in water reached 285%, and its adsorption capacity decreased by 62.4% after 5 cycles of reuse. Its mechanical stability and reusability are far lower than the composite adsorbent prepared in Example 1, demonstrating the crucial role of the mineral matrix in improving material stability.

[0054] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a modified magnesium-iron mineral-supported amphoteric polymer heavy metal adsorbent, characterized in that... This method is performed in the following steps: I. Pretreatment of mineral matrix: The magnesian ore is crushed, ground and sieved to obtain mineral powder. Biochar is ground and sieved to obtain biochar powder. The mineral powder and biochar powder are placed in a muffle furnace for calcination and activation. After natural cooling, the calcined modified mineral matrix is ​​obtained. II. Preparation of precursor dispersion: The calcined modified mineral matrix is ​​added to an organic solvent and ultrasonically dispersed at room temperature for 20 min to 40 min to obtain a uniform mineral dispersion. Then, amine monomers, acrylic monomers, crosslinking agents, and initiators are added to the dispersion in sequence and stirred until uniform to obtain the polymerization precursor liquid. III. In-situ polymerization reaction: Nitrogen gas is continuously introduced into the precursor liquid to remove air from the system. After sealing, the system is placed in a constant temperature environment to carry out in-situ free radical polymerization reaction to obtain a solid product. IV. Post-processing: The solid product was washed repeatedly with methanol and deionized water to remove unreacted monomers and oligomer impurities. After drying, grinding and sieving, a magnesium-iron mineral-supported amphoteric polymer heavy metal adsorbent was obtained.

2. The preparation method according to claim 1, characterized in that, The magnesium-iron ore mentioned in step I is one or more of the natural minerals such as pyroxene, olivine, and amphibole, and the mineral powder passes through a 50-100 mesh sieve. The biochar is one or more of rice husk powder, corn stalk, and wheat straw, and the biochar powder passes through a 100-200 mesh sieve.

3. The preparation method according to claim 1, characterized in that, The calcination activation temperature in step I is 400℃~600℃, and the time is 2h~3h.

4. The preparation method according to claim 1, characterized in that, The organic solvent mentioned in step II is one or a mixture of several of N,N-dimethylformamide, methanol, and ethanol, and the solid-liquid ratio of the calcined modified mineral matrix to the organic solvent is 1 g:(15~25) mL.

5. The preparation method according to claim 1, characterized in that, The amino monomer mentioned in step II is one or more of 4-vinylbenzylamine and dimethylaminoethyl methacrylate, and the acrylic monomer is one or more of acrylic acid and itaconic acid. The molar ratio of the amino monomer to the acrylic monomer is (3~7):(7~3).

6. The preparation method according to claim 1, characterized in that, The total amount of amine monomers and acrylic monomers mentioned in step II is in a mass ratio of (3~6) mmol:1g to the calcined modified mineral matrix.

7. The preparation method according to claim 1, characterized in that, The crosslinking agent mentioned in step II is ethylene glycol dimethacrylate, and the ratio of the total amount of amino monomers and acrylic monomers to the amount of crosslinking agent is (8~12):

1.

8. The preparation method according to claim 1, characterized in that, The initiator mentioned in step II is azobisisobutyronitrile, and the mass ratio of the crosslinking agent to the initiator is 1 mmol:(60~80) mg.

9. The preparation method according to claim 1, characterized in that, In step III, nitrogen gas is introduced for 10-15 minutes, and the temperature of the in-situ free radical polymerization reaction is 65℃-75℃, and the time is 12-18 hours.

10. The preparation method according to claim 1, characterized in that, In step IV, wash with methanol and deionized water 3 to 5 times each, dry at 80℃ to 100℃, and pass through a 100-mesh standard sieve.

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