MgO composite material as well as preparation method and application thereof

Abstract

The invention provides an MgO composite material as well as a preparation method and application thereof, and belongs to the field of wastewater treatment. The invention provides an MgO composite material. The MgO composite material comprises polyethyleneimine-sodium alginate gel balls and MgO loaded on the surfaces of the polyethyleneimine-sodium alginate gel balls in a complexing manner. Carboxyl and hydroxyl on an SA molecular chain can be effectively combined with cadmium ions, the ion exchange process is promoted by replacing H < + > and Na < + >, a three-dimensional gel network structure beneficial to MgO dispersion is formed by the SA molecular chain and the cadmium ions subjected to ion exchange, and the Cd adsorption performance of MgO can be maintained; the introduced PEI can strengthen the three-dimensional network skeleton structure of the SA gel and improve the adsorption and fixation capability of metal. The amino functional group on the PEI can also be complexed with Mg, so that the dispersing capacity of Mg is improved. SA + PEI can release H < + > into the solution in the deprotonation process, so that severe solution pH rise caused by MgO hydrolysis can be slowed down.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, specifically to an MgO composite material, its preparation method, and its application. Background Technology

[0002] Cadmium in water is highly toxic, exhibiting extreme toxicity even at low concentrations, making it the second most toxic heavy metal after mercury. Therefore, there is an urgent need to develop effective materials for removing cadmium from contaminated environments.

[0003] Nano-MgO is widely used due to its excellent adsorption properties for cadmium. The interaction between MgO and water causes hydrolysis, resulting in the formation of dissociated Mg(OH)₂. + Species and surface-bound Mg(OH)2, wherein Mg(OH) + Species participate in Cd 2+ Surface complexation reactions generate intermediate hydrolysis products (such as Cd(OH)). + ) and Mg 2+ It is released into the aqueous phase. Furthermore, intermediate hydrolysis products undergo further evolution under alkaline conditions, for example, Cd(OH)₂. + It readily undergoes further hydrolysis and precipitation to form Cd(OH)₂. This multi-step transformation pathway during cadmium adsorption by nano-MgO ensures that nano-MgO efficiently and irreversibly immobilizes cadmium ions from the aqueous phase through chemical precipitation and surface-mediated complexation. However, this process leads to the release of Mg and an increase in solution pH. Furthermore, due to the nanoscale size of MgO, its application in practical wastewater treatment can result in accumulation in the water, causing filter clogging and scaling.

[0004] Current research has introduced montmorillonite, biochar, and chitosan as supporting materials, utilizing their superior specific surface area and abundant pore structure to provide loading sites for MgO and address the problem of MgO's easy aggregation in water. Biochar, as a MgO supporting material, also mitigates the increase in solution pH at adsorption equilibrium. However, MgO alone exhibits a very high adsorption capacity for Cd (approximately 1000-2000 mg / g), and currently reported supporting materials have reduced the amount of Cd adsorbed by MgO. Therefore, supporting materials that can solve the MgO aggregation problem while maintaining MgO's superior adsorption capacity warrant further investigation. Summary of the Invention

[0005] This invention provides an MgO composite material, its preparation method, and its application. The MgO composite material of this invention exhibits good Cd... 2+ The adsorption capacity also improves the dispersibility of MgO.

[0006] The present invention provides a MgO composite material comprising polyethyleneimine-sodium alginate gel spheres and MgO complexed on the surface of the polyethyleneimine-sodium alginate gel spheres.

[0007] Preferably, the mass fraction of MgO in the MgO composite material is 30~40.51%.

[0008] This invention also provides a method for preparing the MgO composite material described in the above technical solution, comprising the following steps: MgO, polyethyleneimine, sodium alginate, and glutaraldehyde were first mixed and subjected to a first crosslinking reaction. Then, the system obtained from the first crosslinking reaction was mixed with CaCl2 solution and subjected to a second crosslinking reaction to obtain a wet gel. The wet gel was dried to obtain the MgO composite material; The ratio of polyethyleneimine, sodium alginate, and glutaraldehyde used is 0.2~0.5g: 0.1~0.3g: 0.3~0.6mL.

[0009] Preferably, the first mixing comprises: mixing MgO, polyethyleneimine and sodium alginate and then adding glutaraldehyde dropwise to the resulting mixture; The mass ratio of MgO to sodium alginate is 1:1~3.

[0010] Preferably, the second mixing comprises: adding the mixture obtained from the first mixing dropwise to a CaCl2 solution; The volume ratio of the CaCl2 solution to glutaraldehyde is 300-400:0.3; the mass fraction of CaCl2 in the CaCl2 solution is 2-3%.

[0011] Preferably, the temperature of the first crosslinking reaction is 20~25℃ and the time is 6~12h; The second crosslinking reaction is carried out at a temperature of 20-25°C for 8-12 hours.

[0012] Preferably, after the second crosslinking reaction, the process further includes: repeatedly filtering, washing, and immersing the obtained crosslinking reaction product in water and allowing it to stand; in the last repetition, the washed product is not immersed in water and allowed to stand. The drying process includes freeze drying, wherein the freeze drying temperature is -50 to -60°C and the time is 6 to 12 hours.

[0013] This invention also provides the application of the MgO composite material described in the above technical solution or the MgO composite material prepared by the preparation method described in the above technical solution as an adsorbent for adsorbing cadmium ions in wastewater.

[0014] This invention also provides a method for removing cadmium ions, comprising the following steps: The MgO composite material described in the above technical solution or the MgO composite material prepared by the above technical solution method is added to wastewater for adsorption.

[0015] Preferably, the pH value of the wastewater is 2 to 7; The wastewater also includes Na + K + Ca 2+ Mg 2+ and one or more of HA; Cd in the wastewater 2+ The concentration is 50~700 mg / L; The ratio of wastewater to MgO composite material is 100mL: 30~80mg; The adsorption temperature is 10~40℃ and the time is 5~8640min.

[0016] Sodium alginate (SA) has a high density of carboxyl (-COOH) and hydroxyl (-OH) functional groups on its molecular chain, which can effectively bind to cadmium ions and, through H+, form cadmium ions. + and Na + The substitution promotes the ion exchange process, forming a complex three-dimensional gel network structure with the cadmium ions after ion exchange. This three-dimensional network structure is beneficial for the dispersion of MgO and for maintaining the Cd adsorption performance of MgO. The introduced polyethyleneimine (PEI) strengthens the three-dimensional network framework structure of the SA gel, improving its mechanical properties and its ability to adsorb and fix metals. Simultaneously, the amino functional groups on PEI can also complex with Mg, improving the dispersion of Mg. Specifically, the carboxyl, hydroxyl, and amino functional groups on SA+PEI interact with Mg... 2+ The chelation effect reduces Mg 2+ Release into solution. Additionally, SA+PEI releases H+ into solution during deprotonation. + It can slow down the sharp increase in solution pH caused by MgO hydrolysis. Attached Figure Description

[0017] Figure 1 Cd in SA+PEI prepared from different raw materials 2+ Adsorption capacity; Figure 2 Cd-modified gel spheres of different MgO in a 300 mg / L Cd solution 2+ Adsorption capacity; Figure 3 SEM images of SA+PEI, SA+PEI+MgO and SA+PEI+MgO+Cd; Figure 4FTIR spectra of SA+PEI, SA+PEI+MgO and SA+PEI+MgO+Cd; Figure 5 XRD patterns of SA+PEI, SA+PEI+MgO and SA+PEI+MgO+Cd; Figure 6 XPS total spectra of SA, SA+PEI, SA+PEI+MgO and SA+PEI+MgO+Cd; Figure 7 XPS spectrum of Cd 3d for SA+PEI+MgO+Cd; Figure 8 High-resolution O1s spectra before and after Cd(II) adsorption in SA+PEI+MgO; Figure 9 The high-resolution N1s spectrum of SA+PEI+MgO; Figure 10 The high-resolution C1s spectrum of SA+PEI+MgO; Figure 11 The high-resolution Mg1s spectrum of SA+PEI+MgO; Figure 12 Cd-modified gel spheres of different MgO in a 500 mg / L Cd solution 2+ Adsorption capacity; Figure 13 Zeta potential diagrams of MgO-modified gel spheres at different pH values; Figure 14 Potential diagrams of MgO-Zeta at different pH values; Figure 15 The effect of pH on the experimental results of SA+PEI+MgO; Figure 16 The results are from the regeneration experiment of SA+PEI+MgO; Figure 17 The results of the competition experiment for SA+PEI+MgO; Figure 18 The solid-liquid ratio of SA+PEI+MgO affects the experimental results; Figure 19 The results are from the experiment on the removal rate of MgO-modified gel spheres. Figure 20 The results are from the adsorption kinetics experiments of SA+PEI+MgO. Detailed Implementation

[0018] The present invention provides a MgO composite material comprising polyethyleneimine-sodium alginate gel spheres and MgO loaded with complexes on the surface of the polyethyleneimine-sodium alginate gel spheres.

[0019] In this invention, the mass fraction of MgO in the MgO composite material is preferably 30~40.51%, and in specific embodiments of this invention it can be 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% or 40%.

[0020] This invention also provides a method for preparing the MgO composite material described in the above technical solution, comprising the following steps: MgO, polyethyleneimine, sodium alginate, and glutaraldehyde were first mixed and subjected to a first crosslinking reaction. Then, the system obtained from the first crosslinking reaction was mixed with CaCl2 solution and subjected to a second crosslinking reaction to obtain a wet gel. The wet gel was dried to obtain the MgO composite material.

[0021] In this invention, MgO, polyethyleneimine, sodium alginate, and glutaraldehyde are first mixed and subjected to a first crosslinking reaction. Then, the system obtained from the first crosslinking reaction is second mixed with CaCl2 solution and subjected to a second crosslinking reaction to obtain a wet gel.

[0022] In this invention, the first mixing preferably includes: mixing MgO, polyethyleneimine and sodium alginate and then adding glutaraldehyde dropwise to the resulting mixture.

[0023] In this invention, the ratio of polyethyleneimine, sodium alginate, and glutaraldehyde is 0.2~0.4g:0.1~0.3g:0.1~0.3mL, and in specific embodiments of this invention, it can be 0.4g:0.3g:0.3mL; the mass ratio of MgO to sodium alginate is 1:1~3, and in specific embodiments of this invention, it can be 1:1.5, 1:2, or 1:2.5.

[0024] This invention does not impose any specific limitations on the mixing process; MgO, polyethyleneimine, and sodium alginate can be mixed until fully homogeneous. In a specific embodiment of this invention, the system is stirred at 300 rpm at 25°C until stable, and then stirred at 400 rpm for 24 hours.

[0025] The first crosslinking reaction is carried out at a temperature of 20-25°C for 6-12 hours. In specific embodiments of the present invention, the second crosslinking reaction can be carried out at a temperature of 21°C, 22°C, 23°C, or 24°C for 7 hours, 8 hours, 9 hours, 10 hours, or 11 hours. The first crosslinking reaction is preferably carried out under stirring conditions. The time of the first crosslinking reaction is preferably calculated from the time when the dropping ends.

[0026] In this invention, the second mixing includes adding the mixture obtained from the first mixing dropwise to a CaCl2 solution; the mass fraction of CaCl2 in the CaCl2 solution is preferably 3%; the volume ratio of the CaCl2 solution to glutaraldehyde is 300~400:0.3, and in specific embodiments of this invention, it can be 310:0.3, 320:0.3, 330:0.3, 340:0.3, 350:0.3, 360:0.3, 370:0.3, 350:0.3, or 390:0.3.

[0027] In this invention, the temperature of the second crosslinking reaction is preferably 20~25℃ and the time is preferably 8~12h. In specific embodiments of this invention, the temperature of the second crosslinking reaction can be 21℃, 22℃, 23℃ or 24℃ and the time can be 9h, 10h or 11h.

[0028] In this invention, after the second crosslinking reaction, it is preferable to further include: repeatedly filtering, washing, and immersing the obtained crosslinking reaction product in water and letting it stand; in the last repetition, the washed product is not immersed in water and left to stand.

[0029] In this invention, the repetition is preferably performed 3 times.

[0030] In this invention, the drying preferably includes freeze drying, the freeze drying temperature is preferably -50~-60℃, and the time is preferably 6~12h. In specific embodiments of this invention, it can be -55℃, 7h, 8h, 9h, 10h or 11h.

[0031] In this invention, the freeze-drying preferably includes a first freeze-drying and a second freeze-drying. The vacuum degree during the second freeze-drying is preferably 0~40 Pa, and in a specific embodiment of this invention, it can be 10 Pa, 20 Pa, or 30 Pa. The first freeze-drying causes the water in the gel spheres to freeze, and the second freeze-drying causes the ice in the gel spheres to directly sublimate into a gaseous state and be removed, thereby achieving the purpose of drying the gel spheres.

[0032] This invention also provides the application of the MgO composite material described in the above technical solution or the MgO composite material prepared by the preparation method described in the above technical solution as an adsorbent for adsorbing cadmium ions in wastewater.

[0033] This invention also provides a method for removing cadmium ions, comprising the following steps: The MgO composite material described in the above technical solution or the MgO composite material prepared by the above technical solution method is added to wastewater for adsorption.

[0034] In this invention, the pH value of the wastewater is preferably 2-7, and in specific embodiments of this invention it can be 3, 4, 5 or 6; the wastewater preferably also includes Na.+ K + Ca 2+ Mg 2+ and one or more of HA; Cd in the wastewater 2+ The concentration is preferably 50~700mg / L, and in specific embodiments of the present invention it can be 100mg / L, 200mg / L, 300mg / L, 400mg / L, 500mg / L or 600mg / L; the ratio of wastewater to MgO composite material is 100mL:30~80mg, and in specific embodiments of the present invention it can be 100mL:40mg, 100mL:50mg, 100mL:60mg or 100mL:70mg.

[0035] In this invention, the adsorption temperature is preferably 10~40℃, and the time is preferably 5~8640 min. In specific embodiments of this invention, the temperature can be 20℃ or 30℃, and the time can be 1h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, 110h, 120h, 130h, or 140h.

[0036] The MgO composite material of this invention has a negative Zeta potential, and the physical electrostatic adsorption between it and cadmium ions is one of the main adsorption mechanisms. In addition, the ion exchange of Mg(OH)2 and the complexation of amine and carboxyl groups can also adsorb cadmium ions.

[0037] The presence of dissolved CO2 promotes the formation of CdCO3. MgO + H₂O → Mg(OH)₂; MgO / Mg(OH)2+Cd 2+ →CdO / Cd(OH)2+Mg 2+ ; CO2 + H2O + Cd2+ → CdCO3 + 2H+ + ; Cd(OH)2+CO2→CdCO3+H2O.

[0038] The following detailed description of the MgO composite material, its preparation method, and its application provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0039] Cadmium nitrate (CdN2O6·4H2O, 99% purity, used to prepare Cd) 2+The following solutions were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.: sodium hydroxide (NaOH, 96% purity), anhydrous calcium chloride (CaCl2, 96% purity), magnesium oxide (MgO, 98% purity), and sodium chloride (NaCl, 99.5% purity). Sodium alginate ((C6H7NaO6)n, ultra-high viscosity type I, 1% viscosity: 5000 mPa·s) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; magnesium chloride (MgCl2·6H2O, analytical grade) was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd.; hydrochloric acid (HCl, analytical grade) was purchased from Chengdu Kelong Co., Ltd.; and anhydrous sodium acetate (CH3COONa, analytical grade) and potassium chloride (KCl, analytical grade) were purchased from Yunnan Jingrui Technology Co., Ltd.

[0040] Example 1 Weigh x g of sodium alginate (SA) and y g of polyethyleneimine (PEI) into a 50 mL beaker. Stir at 300 rpm at 25 °C on a magnetic stirrer. After the stirring is stable, adjust the speed to 400 rpm and stir for 24 h. Then add z mL of glutaraldehyde (GLA, the values ​​of x, y and z are shown in Table 1). Adjust the speed to 500 rpm and continue stirring for 6.5 h. After stirring, use a 1 mL syringe to slowly drop the gel solution into 400 mL of prepared 3% (w / w) CaCl2 solution to form gel spheres and soak for 12 h. Then filter the gel spheres through a Buchner funnel, rinse several times with ultrapure water, transfer to 400 mL of ultrapure water and let stand for 10 min. Repeat 3 times. Finally, the washed gel beads were transferred to a weighing boat, covered with plastic wrap and punctured, and frozen at -50 to -60°C for 30 minutes. The frozen samples were then placed on the upper layer of a freeze dryer with a vacuum of 20 Pa and dried at -50 to -60°C for 12 hours to obtain gel beads with different proportions (denoted as SA+PEI). After drying, the samples were sealed and stored in centrifuge tubes.

[0041] After the gel spheres were prepared, a 300 mg / L solution of Cd was prepared. 2+ The solution was adjusted to pH 5 with 0.1M HCl or 0.1M NaOH. 50 mg of gel beads were weighed into 100 mL of Cd solution. 2+ In the solution, the mixture was shaken at 180 rpm and 25°C for 48 h in a constant-temperature shaking incubator. After adsorption was complete, the solution was filtered through a 0.45 μm aqueous filter membrane, and the Cd concentration was measured by ICP-OES. 2+ Concentration, results as follows Figure 1 As shown.

[0042] Table 1. Values ​​of x, y, and z

[0043] Figure 1 Cd in SA+PEI prepared from different raw materials 2+ Adsorption capacity.

[0044] Depend on Figure 1 It can be seen that when the ratio of SA, PEI and GLA is 0.3:0.4:0.3, the maximum adsorption capacity of the gel spheres for Cd is 186 mg / g. The experiment below uses this ratio.

[0045] In addition, during the preparation process, when x (x is 0.1, 0.2 or 0.3), y (y is 0.2, 0.3, 0.4 or 0.5) and z (z is 0.3, 0.4, 0.5 or 0.6) are combinations other than those in Table 1, the samples cannot form balls due to poor or high viscosity.

[0046] Weigh ag of MgO (a is 0.1, 0.2, 0.3, or 0.4), 0.3g of sodium alginate, and 0.4g of polyethyleneimine into a 50mL beaker. Stir at 300rpm on a magnetic stirrer at 25℃. After the stirring is stable, adjust the speed to 400rpm and stir for 24h. Then add 0.3mL of glutaraldehyde, and adjust the speed to 500rpm and continue stirring for 6.5h. After stirring, use a 1mL syringe to slowly drop the gel solution into 400mL of prepared 3% (w / w) CaCl2 solution to form gel spheres and soak them for 12h. Then filter the gel spheres through a Buchner funnel, rinse them several times with ultrapure water, transfer them to 400mL of ultrapure water and let them stand for 10min. Repeat this process 3 times. Finally, the washed gel spheres were transferred to a weighing boat, covered with plastic wrap and punctured, and frozen at 50 to -60°C for 30 minutes. The frozen samples were then placed on the upper layer of a freeze dryer with a vacuum of 20 Pa and dried at -50 to -60°C for 12 hours to obtain different MgO-modified gel spheres (denoted as SA+PEI+MgO). After drying, the samples were sealed and stored in centrifuge tubes.

[0047] After the gel spheres were prepared, a 300 mg / L solution of Cd was prepared. 2+ The solution was adjusted to pH 5 with 0.1M HCl and 0.1M NaOH. 50 mg of gel beads were weighed into 100 mL of Cd solution. 2+ In the solution, the mixture was shaken at 180 rpm and 25°C for 48 h in a constant-temperature shaking incubator. After adsorption was complete, the solution was filtered through a 0.45 μm aqueous filter membrane, and the Cd concentration was measured by ICP-OES. 2+ Concentration, results as follows Figure 2 As shown. Additionally, SA+PEI+MgO adsorbs Cd. 2+ The resulting gel spheres are denoted as SA+PEI+MgO+Cd.

[0048] Figure 2Cd-modified gel spheres of different MgO in a 300 mg / L Cd solution 2+ Adsorption capacity.

[0049] Depend on Figure 2 It can be seen that when the initial Cd concentration is 300 mg / L, the removal rate of Cd can reach 100% with a MgO loading of 0.1~0.4 g, proving the effectiveness of the adsorbent in Cd removal. However, the optimal composition ratio of the adsorbent is MgO:SA:PEI:GLA = 0.2 g:0.3 g:0.4 g:0.3 mL. Subsequent experiments were all conducted using the optimal adsorbent.

[0050] Figure 3 SEM images of SA+PEI, SA+PEI+MgO, and SA+PEI+MgO+Cd.

[0051] Figure 3 In the images a, b, and c, we see SEM images of SA+PEI: the gel spheres are flattened ellipses with abundant porous channels inside, the channel walls are thin layers, and some of them are broken.

[0052] Figure 3 Images e, f, and g are SEM images of SA+PEI+MgO: The skeletal strength of the gel spheres is enhanced, and the gel spheres change from flat to spherical. The internal channels of the gel spheres change from thin layers to thicker layers. The thicker channel walls reduce wall breakage, and the porous channels also widen. These changes are all caused by the MgO strengthening of the skeleton.

[0053] Figure 3 h, i, and j are SEM images of SA+PEI+MgO+Cd: A large amount of adsorbed Cd, mainly in the form of Cd(OH)2, accumulates on the surface and internal channels of the MgO-gel spheres (refer to XRD results). Due to the large amount of adsorbed Cd, numerous plate-like Cd deposits appear on the surface of the gel spheres, and some internal channels are also blocked by adsorbed Cd. This phenomenon is due to the uniform doping of MgO on the surface and inside of the gel spheres, demonstrating the extremely effective adsorption of Cd by the MgO-gel spheres.

[0054] Figure 4 FTIR spectra of SA+PEI, SA+PEI+MgO, and SA+PEI+MgO+Cd.

[0055] Depend on Figure 4 It can be seen that in SA+PEI and SA+PEI+MgO, the material has a thickness of 3010–3710 cm⁻¹. -1 A broad absorption band appears within the range, with the highest absorption located at 3400 cm⁻¹. -1 At this location, the vibrations primarily correspond to the stretching vibrations of N–H and O–H. Furthermore, at 1630 cm⁻¹… -1 With 1420cm-1 The two absorption peaks can be attributed to the asymmetric stretching vibration of the carboxyl group (–COOH). The peak is located at 1029 cm⁻¹. -1 The peak corresponds to the C–O / C=O stretching vibration in the carboxyl group of alginate. FTIR analysis of SA+PEI+MgO+Cd showed a systematic shift in the structural vibrational peaks of the material after Cd adsorption: the stretching vibration peak attributed to NH and OH decreased from 3440.14 cm⁻¹. -1 Migrating to 3438.02 cm -1 Meanwhile, the asymmetric and symmetric stretching vibration peaks originating from the -COOH functional group are located at 1631.69 cm⁻¹. -1 With 1428.87 cm -1 Moved to 1629.57 cm -1 and 1422.53 cm -1 These changes are mainly due to the presence of lone pairs of electrons on N and O atoms, which enable them to act as coordination sites to form coordinate covalent bonds with Cd, thereby effectively adsorbing heavy metal ions. This result confirms that Cd successfully coordinates with O and N elements in the material.

[0056] Figure 5 XRD patterns for SA+PEI, SA+PEI+MgO, and SA+PEI+MgO+Cd.

[0057] Depend on Figure 5 It can be seen that no obvious peak was observed for SA+PEI. When MgO was incorporated, MgO (JCPDF:45-0946) appeared on the surface of the gel spheres, and no impurity peaks were observed, proving that the MgO crystalline phase introduced into the gel spheres was pure. After Cd adsorption, a peak for Cd(OH)2 appeared.

[0058] Figure 6 XPS spectra of SA, SA+PEI, SA+PEI+MgO and SA+PEI+MgO+Cd.

[0059] Depend on Figure 6 It can be seen that after adding PEI, the N content in SA+PEI and SA+PEI+MgO increased from 0.73% to 4.11% and 3.89%, respectively. The increase in N content is because PEI is a polyamine containing multiple amine groups; the introduction of PEI increases the N content in SA+PEI and SA+PEI+MgO, indicating that PEI has been successfully grafted onto SA. Furthermore, due to the introduction of MgO, a Mg signal peak appeared in SA+PEI+MgO. After SA+PEI+MgO reacts with Cd, the absorption peaks of C, O, N, and Mg in SA+PEI+MgO change significantly, with a Cd peak appearing, indicating that SA+PEI+MgO successfully adsorbs Cd through C, O, N, and Mg groups.

[0060] Figure 7 XPS spectrum of Cd 3d for SA+PEI+MgO+Cd.

[0061] Depend on Figure 7 It can be seen that the characteristic peaks of Cd 3d at 405.99 and 412.88 eV originate from Cd 3d. 5 / 2 and Cd3d 3 / 2 This indicates that the removal of Cd(II) by SA+PEI+MgO does not involve a reduction process. Furthermore, Cd 3d 5 / 2 The nearby spectral peaks indicate that Cd(OH)2 exists on the SA+PEI+MgO surface, suggesting that precipitation may be a reaction mechanism.

[0062] Figure 8 High-resolution O1s spectra of SA+PEI+MgO before and after adsorption of Cd(II). Figure 8 The image on the left shows the image before adsorption, and the image on the right shows the image after adsorption.

[0063] Depend on Figure 8 It can be seen that the peak values ​​of SA+PEI+MgO at 533.87, 532.59, and 531.24 eV before adsorption belong to the vibrations of COH, C=O, and COC / CO, respectively. After Cd(II) adsorption, the peak intensities of C=O and COC / CO decreased from 46.25% and 32.9% to 41.4% and 20.2%, respectively. This indicates that the carboxyl groups are involved in the adsorption process of Cd(II), and surface complexation may play a key role in the adsorption process.

[0064] Figure 9 The high-resolution N1s spectrum of SA+PEI+MgO is shown.

[0065] Depend on Figure 9 It can be seen that the peak values ​​of SA+PEI+MgO at 399.33 and 400.77 eV correspond to the -NH2 / -NH and -N= groups, respectively. After Cd(II) adsorption, the characteristic peaks -NH2 / -NH and -N= disappear, and the surface -NH2 / -NH groups can chemically bond with Cd. 2+ Strong complexation occurs, with a sharp peak at a binding energy of 405.98 eV, representing the formation of a Cd(II)-N covalent bond by nitrogen atoms sharing lone pairs of electrons.

[0066] Figure 10 The high-resolution C1s spectrum of SA+PEI+MgO is shown.

[0067] Depend on Figure 10It can be seen that the peak values ​​of SA+PEI+MgO at 284.8, 286.42, and 287.96 eV belong to the CC, CN, and OCO / OC=O groups, respectively. After SA+PEI+MgO adsorbs Cd(II), the peak position shifts slightly, indicating that these functional groups may provide active sites for Cd(II) binding and the formation of complex compounds during the adsorption process.

[0068] Figure 11 The high-resolution Mg1s spectrum of SA+PEI+MgO is shown.

[0069] Depend on Figure 11 It can be seen that the Mg 1s peak at 1303.93 eV is fitted to a single component and attributed to MgO. After Cd(II) adsorption, the Mg 1s peak shifts from 1303.93 eV to 1304.01 eV, the diffraction peak intensity weakens, and its average atomic concentration decreases from 7.92% to 5.99%. This is due to the Mg... 2 + with cd 2+ Ion exchange between them, Mg 2 + The release into the aqueous solution leads to a reduction in the Mg element on SA+PEI+MgO.

[0070] Cd adsorption experiment of MgO modified gel spheres Preparation of 500 mg / L Cd 2+ The solution was adjusted to pH 5 with 0.1M HCl or 0.1M NaOH. 50 mg of MgO-modified gel beads were weighed into 100 mL of Cd... 2+ In the solution, the mixture was shaken at 180 rpm and 25°C for 48 h in a constant-temperature shaking incubator. After adsorption was complete, the solution was filtered through a 0.45 μm aqueous filter membrane, and the Cd concentration was measured by ICP-OES. 2+ Concentration, results as follows Figure 12 As shown Figure 12 Cd-modified gel spheres of different MgO in a 500 mg / L Cd solution 2+ Adsorption capacity.

[0071] When the initial Cd concentration was increased to 500 mg / L and the MgO loading was 0.2 g, the adsorption capacity of MgO-gel beads for Cd was 731 mg / g. This result demonstrates that MgO significantly improved the adsorption capacity of the gel beads. Compared with the pH value of the solution after Cd adsorption by MgO alone, the pH value of the solution after Cd adsorption by the composite material of MgO coated with gel beads was only 7.9, indicating that the gel beads mitigated the pH increase caused by MgO. The advantages of MgO and gel beads complement each other.

[0072] pH effect experiment Figure 13Zeta potential diagrams of MgO-modified gel spheres at different pH values; Figure 14 This is a potential diagram of MgO-Zeta at different pH values.

[0073] Preparation of 500 mg / L Cd 2+ The solution was adjusted to pH 2, 3, 4, 5, 6, and 7 using 0.1M HCl and 0.1M NaOH, respectively. 30 mg of MgO-modified gel beads were weighed into 100 mL of Cd... 2+ In the solution, the mixture was shaken at 180 rpm and 25°C for 48 h in a constant-temperature shaking incubator. After adsorption was complete, the solution was filtered through a 0.45 μm aqueous filter membrane, and the Cd concentration was measured by ICP-OES. 2+ Concentration, results as follows Figure 15 As shown.

[0074] Figure 15 The experimental results show the effect of pH on SA+PEI+MgO.

[0075] Depend on Figure 15 It can be seen that the Cd adsorption capacity of MgO-gel beads increased from 683.3 mg / g to 830 mg / g with increasing pH. The reason for the increase in Cd adsorption capacity with pH is: 1) The surface of MgO-gel spheres carries a negative charge, which increases with the pH of the solution. This physical electrostatic interaction further promotes the growth of Cd. 2+ Adsorption; 2) An increase in OH content in the solution is more favorable for Cd. 2+ With OH - Cd(OH)₂ is formed. After Cd adsorption, the pH of the solution changes from 2 to 2.3, 3 to 7.5, 4 to 7.7, 5 to 7.8, 6 to 7.9, and 7 to 7.9. This is because the COOH on the surface of the gel spheres deprotonates, releasing H₂ into the solution. + This slows down the pH increase of the solution compared to when only MgO is present, keeping it neutral and slightly alkaline.

[0076] Regeneration Experiment Preparation of 100 mg / L Cd 2+ The solution was adjusted to pH 6 with 0.1M HCl or 0.1M NaOH. 30 mg of MgO-modified gel beads were weighed into 100 mL of Cd... 2+ In the solution, the mixture was shaken at 180 rpm and 25°C for 24 h in a constant-temperature shaking incubator. After adsorption, the filtered gel beads were transferred to 100 mL of 0.5 M CH3COONa solution and desorbed by shaking at 180 rpm and 25°C for 2 h in a constant-temperature shaking incubator. The gel beads were then rinsed thoroughly with deionized water until the aqueous solution was neutral. Then, 100 mL of Cd... 2+The adsorption experiment was repeated in the solution under the same conditions, and the adsorption-desorption process was repeated 4 times. The results are as follows. Figure 16 As shown.

[0077] Figure 16 The results are from the regeneration experiment of SA+PEI+MgO.

[0078] Depend on Figure 16 It can be seen that the removal rate of SA+PEI+MgO gradually decreases with the increase of the number of cycles in four consecutive adsorption-desorption cycles. The removal rate in the first cycle is close to the initial level, while a certain amount of adsorption performance is still retained after the fourth cycle, indicating that the material has good structural stability and regenerability.

[0079] Competition Experiment According to the molar ratio Cd: Na + / K + / Ca 2+ / Mg 2+ Binary mixed solutions were prepared with HA ratios of 1:1, 1:5, and 1:10 (where the Cd concentration was 100 mg / L). The pH was adjusted to 6 with 0.1 M HCl and 0.1 M NaOH. 30 mg of MgO-modified gel beads were weighed into 30 mL of the mixed solution, and the solution was shaken at 180 rpm and 25 °C for 24 h in a constant temperature shaking incubator. After adsorption was complete, the solution was filtered through a 0.45 μm aqueous filter membrane, and the Cd concentration was tested by ICP-OES. 2+ Concentration, results as follows Figure 17 As shown.

[0080] Figure 17 The results are from a competition experiment involving SA+PEI+MgO.

[0081] Depend on Figure 17 It can be seen that under the condition of multiple coexisting ions, the adsorption and removal rate of Cd(II) by SA+PEI+MgO did not decrease significantly, indicating that it can still maintain stable adsorption performance in complex water environments with different ions coexisting, and has high selectivity for Cd(II).

[0082] Experiment on the effect of solid-liquid ratio Preparation of 500 mg / L Cd 2+ The solution was adjusted to pH 5 with 0.1M HCl or 0.1M NaOH. 30, 40, 60, 70, and 80 mg of MgO-modified gel beads were weighed into 100 mL of Cd... 2+ In the solution, the mixture was shaken at 180 rpm and 25°C for 48 h in a constant-temperature shaking incubator. After adsorption was complete, the solution was filtered through a 0.45 μm aqueous filter membrane, and the Cd concentration was measured by ICP-OES. 2+ Concentration, results as follows Figure 18 As shown.

[0083] Figure 18 The solid-liquid ratio of SA+PEI+MgO affects the experimental results.

[0084] Depend on Figure 18 It can be seen that as the dosage decreased from 0.8 g / L to 0.3 g / L, the adsorption capacity of MgO-gel balls gradually increased from 649.5 mg / g to 860 mg / g. This is comparable to the previously reported adsorption capacity of MgO / biochar composites for cadmium ions (515.17 mg / g) and MgO and potassium citrate-modified biochar for cadmium ions (479.87 mg / g).

[0085] Removal rate experiment Prepare Cd solutions of 200, 300, 400, and 500 mg / L. 2+ The solution was adjusted to pH 6 with 0.1M HCl or 0.1M NaOH. 30 mg of MgO-modified gel beads were weighed into 30 mL of Cd... 2+ In the solution, the mixture was shaken at 180 rpm and 25°C for 144 h in a constant-temperature shaking incubator. After adsorption was complete, the solution was filtered through a 0.45 μm aqueous filter membrane, and the Cd concentration was measured by ICP-OES. 2+ concentration.

[0086] Figure 19 The results show the removal rate of MgO-modified gel spheres.

[0087] Depend on Figure 19 It can be seen that, under the condition of 1 g / L dosage, MgO-gel balls can achieve 100% removal capacity for Cd with initial concentrations of 200-500 mg / L, proving that MgO-gel balls can effectively achieve the removal capacity of high concentrations of Cd.

[0088] Adsorption kinetics experiment Preparation of 50 mg / L Cd 2+ The solution was adjusted to pH 6 with 0.1M HCl and 0.1M NaOH. 30 mg of MgO-modified gel beads were weighed into 100 mL of Cd... 2+ The solution was shaken at 180 rpm and 25°C for 48 h in a constant-temperature shaking incubator. The solution was then filtered through a 0.45 μm aqueous filter membrane at 5, 15, 30 min, 1, 2, 4, 8, 24, 36, and 48 h, and the Cd concentration was measured by ICP-OES. 2+ Concentration, results as follows Figure 20 As shown.

[0089] Preparation of 400 mg / L Cd 2+ The solution was adjusted to pH 6 with 0.1M HCl and 0.1M NaOH. 30 mg of MgO-modified gel beads were weighed into 100 mL of Cd...2+ The solution was shaken at 180 rpm and 25°C for 48 h in a constant temperature shaking incubator. The solution was then filtered through a 0.45 μm aqueous filter membrane at 5, 15, 30 min, 1, 2, 4, 8, 24, 36, 48, 72, 96, 120, and 144 h. The Cd concentration in the solution was then measured by ICP-OES. 2+ Concentration, results as follows Figure 20 As shown.

[0090] Figure 20 The results are from the adsorption kinetics experiments of SA+PEI+MgO.

[0091] Table 2. Effects of SA+PEI+MgO on Cd 2+ Fitting parameters of the first and second kinetic models

[0092] Table 3. Effects of SA+PEI+MgO on Cd 2+ Elovich dynamic model fitting parameters

[0093] Depend on Figure 20 It was found that the adsorption equilibrium for 50 mg / L Cd by MgO-gel balls was reached at 24 h, but rapidly reached 75% of the adsorption equilibrium at 8 h. For a higher concentration of Cd solution (400 mg / L), the MgO-gel balls reached 642.2 mg / g at 24 h, which is 60% of the adsorption equilibrium amount, and approached adsorption equilibrium (941.1 mg / g) at 72 h. The adsorption rate of MgO-gel balls for 50 mg / L Cd (2.4 × 10⁻⁶) was... -3 The adsorption rate is faster than that for 400 mg / L Cd (6.97 × 10⁻⁶). -4 In the initial stage of adsorption, the surface of the gel spheres has sufficient adsorption sites. As Cd gradually occupies these sites, the adsorption rate gradually decreases. The correlation coefficient of the pseudo-second-order kinetic model is only slightly higher than that of the pseudo-first-order kinetic model, indicating that the adsorption of Cd on MgO-gel spheres is dominated by chemisorption.

[0094] Adsorption isotherm experiment Prepare Cd solutions of 50, 150, 350, 550, and 700 mg / L. 2+ The solution was adjusted to pH 6 with 0.1M HCl or 0.1M NaOH. 30 mg of MgO-modified gel beads were weighed into 100 mL of Cd... 2+ In the solution, the mixture was shaken at 180 rpm for 144 h at 10, 25, and 40 °C in a constant-temperature shaking incubator. After adsorption was complete, the solution was filtered through a 0.45 μm aqueous filter membrane, and the Cd concentration was measured by ICP-OES.2+ concentration.

[0095] The isothermal adsorption model fitting results show that when the initial Cd concentration of the solution is in the range of 50–150 mg / L, the adsorption capacity of MgO-gel balls ranges from 195.6 to 461.2 mg / L, with minimal effect from temperature. As the initial Cd concentration increases to 300–700 mg / L, the Cd adsorption capacity of MgO-gel balls increases significantly with increasing temperature. Notably, at 10℃ and 25℃, the Cd adsorption capacity of MgO-gel balls increases with increasing initial Cd concentration. At an adsorption temperature of 40℃, the MgO-gel balls reach their maximum adsorption capacity of 1250.5 mg / L at an initial concentration of 400 mg / L. With further increases in concentration, the Cd adsorption capacity of MgO-gel balls remains almost constant, indicating that temperature promotes Cd adsorption on the MgO-gel balls.

[0096] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A MgO composite material, characterized in that, It includes polyethyleneimine-sodium alginate gel spheres and MgO complexed on the surface of the polyethyleneimine-sodium alginate gel spheres.

2. The MgO composite material according to claim 1, characterized in that, The MgO composite material has a MgO mass fraction of 30~40.51%.

3. The method for preparing the MgO composite material according to claim 1 or 2, characterized in that, Includes the following steps: MgO, polyethyleneimine, sodium alginate, and glutaraldehyde were first mixed and subjected to a first crosslinking reaction. Then, the system obtained from the first crosslinking reaction was mixed with CaCl2 solution and subjected to a second crosslinking reaction to obtain a wet gel. The wet gel was dried to obtain the MgO composite material.

4. The preparation method according to claim 3, characterized in that, The first mixing process includes: mixing MgO, polyethyleneimine, and sodium alginate, and then adding glutaraldehyde dropwise to the resulting mixture; The ratio of polyethyleneimine, sodium alginate, and glutaraldehyde used is 0.2~0.5g: 0.1~0.3g: 0.3~0.6mL; The mass ratio of MgO to sodium alginate is 1:1~3.

5. The preparation method according to claim 3, characterized in that, The second mixing includes: adding the mixture obtained from the first mixing dropwise to a CaCl2 solution; The volume ratio of the CaCl2 solution to glutaraldehyde is 300-400:0.3; the mass fraction of CaCl2 in the CaCl2 solution is 2-3%.

6. The preparation method according to claim 3, characterized in that, The temperature of the first crosslinking reaction is 20~25℃, and the time is 6~12h; The second crosslinking reaction is carried out at a temperature of 20-25°C for 8-12 hours.

7. The preparation method according to claim 3, characterized in that, After the second crosslinking reaction, the process further includes: repeatedly filtering, washing, and immersing the obtained crosslinking reaction product in water and allowing it to stand; in the last repetition, the washed product is not immersed in water and allowed to stand. The drying process includes freeze drying, wherein the freeze drying temperature is -50 to -60°C and the time is 6 to 12 hours.

8. The application of the MgO composite material according to claim 1 or 2 or the MgO composite material prepared by any one of the preparation methods according to claims 3 to 7 as an adsorbent for adsorbing cadmium ions in wastewater.

9. A method for removing cadmium ions, characterized in that, Includes the following steps: The MgO composite material according to claim 1 or 2, or the MgO composite material prepared by any one of the preparation methods according to claims 3 to 7, is added to wastewater for adsorption.

10. The removal method according to claim 9, characterized in that, The pH value of the wastewater is 2-7; The wastewater also includes Na + K + Ca 2+ Mg 2+ and one or more of HA; Cd in the wastewater 2+ The concentration is 50~700 mg / L; The ratio of wastewater to MgO composite material is 100mL: 30~80mg; The adsorption temperature is 10~40℃ and the time is 5~8640min.

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