A modified manganese oxide composite material for heavy metal adsorption and a preparation method thereof

Abstract

The present application belongs to the technical field of environmental pollution adsorption treatment, and particularly relates to a modified manganese oxide composite material for heavy metal adsorption and a preparation method thereof. The composition comprises the following raw materials: granular activated carbon, manganese source, reducing agent, silicate anchoring phase and carbonate buffer mineral. The present application uses granular activated carbon as a skeleton, forms a highly dispersed manganese oxide active phase through in-situ deposition, triggers silicate gelation through carbon dioxide, constructs an inorganic silicon network on the surface, firmly anchors the active components, enhances the mechanical strength, and reduces the shedding caused by hydraulic scouring. Meanwhile, the carbonate buffer mineral is embedded in the network, which can adjust the interface acidity, inhibit the dissolution of the active components, and broaden the pH application window. The composite material can still maintain stable adsorption performance and long-term operation reliability under fluctuating water quality, and overcomes the problems of traditional materials, such as easy powdering, easy deactivation, and narrow application conditions.

Description

Technical Field

[0001] This invention belongs to the field of environmental pollution adsorption treatment technology, specifically relating to a modified manganese oxide composite material for heavy metal adsorption and its preparation method. Background Technology

[0002] Heavy metal pollution in water bodies mainly originates from industrial wastewater discharges from mining, metallurgical electroplating, chemical and pharmaceutical industries, as well as seepage from mine runoff. Heavy metal ions such as cadmium, lead, chromium, and arsenic are bioaccumulative, persistently toxic, and difficult to degrade naturally. Once they enter water bodies, they not only disrupt the balance of aquatic ecosystems but also accumulate through the food chain, endangering human health. Therefore, the efficient treatment of heavy metal-polluted water bodies is a core research direction and engineering requirement in the field of water environment remediation.

[0003] Adsorption has become the mainstream technology for treating heavy metal-polluted water in practical engineering due to its simple operation, high treatment efficiency, controllable cost, and ease of heavy metal resource recovery. Granular activated carbon is one of the most commonly used adsorption carriers because of its well-developed pore structure, high mass transfer efficiency, good formability, and easy adaptation to engineering devices such as fixed beds and filter columns. However, its adsorption of heavy metal ions mainly relies on physical adsorption and weak surface complexation, and its specific adsorption capacity is weak. Under conditions of water acidity and alkalinity fluctuations and interference from coexisting ions, its adsorption selectivity and stability are poor, and it is difficult to meet the requirements of deep purification when used alone. Manganese oxide, due to its surface rich in active groups such as hydroxyl groups, can achieve efficient capture of heavy metal ions through multiple actions such as surface complexation, ion exchange, redox, and speciation regulation. Its adsorption specificity and capacity are significantly better than activated carbon. However, it is in powder form, has low mechanical strength, is prone to agglomeration, and is easily lost and causes secondary pollution when directly added. In addition, it is easily dissolved and deactivated in acidic water, so it cannot be used alone in practical engineering water treatment systems.

[0004] To balance the engineering adaptability of activated carbon with the high adsorption efficiency of manganese oxides, existing technologies often employ physical mixing and simple coating to load manganese oxides onto the surface of activated carbon to prepare composite adsorbent materials, which has become the main improvement approach in this field. However, such preparation processes have significant drawbacks: the active phase of manganese oxides has poor dispersion on the carrier surface, and the bond between it and activated carbon is only physical, resulting in weak binding force. Under actual water conditions such as hydraulic scouring, particle shearing friction, and repeated loading and operation, the active phase is prone to detachment and powdering, leading to rapid decline in the material's adsorption activity, secondary turbidity in the water, and poor long-term operational stability. Furthermore, existing composite materials lack an interfacial acidity control mechanism. Under actual water conditions of acid-base fluctuations or sudden acid shocks, manganese oxides are easily dissolved and deactivated, rapidly reducing adsorption sites and making it difficult to maintain stable adsorption performance over a wide pH range. In addition, some processes use strong acids and bases for curing and modification, which easily damages the pore structure of activated carbon, sacrificing mass transfer efficiency, and the preparation process poses environmental risks, hindering large-scale production. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a modified manganese oxide composite material for heavy metal adsorption and its preparation method. This solves the problems of existing adsorption materials, such as active component shedding, unstable adsorption performance, and insufficient adaptability to wide operating conditions, which are prone to occur under actual engineering conditions involving large acid-base fluctuations, strong shear erosion, and significant interference from coexisting ions.

[0006] The technical effects described in this invention are achieved through the following technical solution: a modified manganese oxide composite material for heavy metal adsorption, comprising the following raw materials: granular activated carbon, manganese source, reducing agent, silicate anchoring phase and carbonate buffer mineral;

[0007] Preferably, the particle size of the granular activated carbon is 1–1.6 mm;

[0008] Preferably, the manganese source is KMnO4;

[0009] Preferably, the reducing agent is either glucose or ascorbic acid;

[0010] Preferably, the silicate anchoring phase is a water glass solution; the water glass solution has a mass fraction of 2-5 wt%, calculated as SiO2;

[0011] Preferably, the carbonate buffer mineral is any one of CaCO3, dolomite powder, and shell powder; the particle size D of the carbonate buffer mineral is... 50 =1~10μm;

[0012] Preferably, another aspect of the present invention provides a method for preparing a modified manganese oxide composite material for heavy metal adsorption, which specifically includes the following steps:

[0013] S1: The granular activated carbon is washed in a deionized water circulation system, then washed with 0.05-0.1 mol / L NaHCO3 for 10-20 min, then washed with deionized water until neutral, and dried at 80-100℃ for 6-10 h to obtain pretreated activated carbon.

[0014] S2: Place the pretreated activated carbon from step S1 into a 0.04–0.08 mol / L manganese source solution and impregnate it at 25–35°C for 3–6 hours with stirring. Filter the filtrate without washing to obtain impregnated activated carbon.

[0015] S3: Add the impregnated activated carbon back into deionized water to form a slurry. Then, under stirring conditions at 40-65℃, slowly add 0.02-0.1 mol / L reducing agent solution dropwise over 30-60 minutes. After the addition is complete, continue the reaction for 1-2 hours. After the reaction, filter and wash with water until there is no obvious residual KMnO4 color to obtain in-situ deposited activated carbon.

[0016] S4: Place the activated carbon deposited in situ in step S3 into a silicate anchoring phase and impregnate it at room temperature for 60–90 min with stirring; after impregnation, drain the liquid for 2–5 min, then place it in a closed reactor, introduce CO2 at 0.1–0.5 L / min, control the temperature at 20–30 °C, and react for 10–30 min. The endpoint is controlled when the pH of the system gradually decreases from the initial strong alkalinity of water glass to pH 6.8–7.5; immediately add carbonate buffer minerals and stir to disperse evenly, let it stand and age at room temperature for 4–8 h, filter and wash until the pH of the effluent is neutral and the conductivity tends to stabilize, with a change rate ≤5% in two consecutive measurements; dry at 60–90 °C for 6–12 h, and then mature at 90–110 °C for 1–3 h to obtain the modified manganese oxide composite material;

[0017] Preferably, in step S2, the manganese source solution is prepared by adding a manganese source to deionized water;

[0018] Preferably, in step S2, the ratio of the amount of pretreated activated carbon to manganese source solution is 1g:10-15mL;

[0019] Preferably, in step S3, the ratio of impregnated activated carbon to deionized water is 1g:8-12mL;

[0020] Preferably, in step S3, the ratio of the amount of impregnated activated carbon to the reducing agent solution is 1g:5-12mL;

[0021] Preferably, in step S3, the stirring conditions are 150–250 rpm;

[0022] Preferably, in step S4, the ratio of the amount of in-situ deposited activated carbon to the silicate anchoring phase is 1g:8-12mL;

[0023] Preferably, in step S4, the mass ratio of the in-situ deposited activated carbon to the carbonate buffer mineral is 1g:0.02-0.03g.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention addresses common challenges in heavy metal-polluted water bodies, such as large pH fluctuations, strong shear erosion, and significant interference from coexisting ions. It employs a combination of material structure design and preparation processes to achieve a composite material that balances adsorption capacity, structural stability, and engineering applicability. The composite material uses granular activated carbon as a framework to ensure a good pore structure and mass transfer channels. A highly dispersed manganese oxide active phase is formed through in-situ deposition, allowing active sites to be stably distributed on the carrier surface and in the pore region. This provides a continuous and effective adsorption and fixation interface for heavy metal ions under different water quality conditions, avoiding the problems of uneven distribution, easy detachment, and easy deactivation of active components caused by relying solely on physical mixing or simple coating.

[0026] This invention further constructs an inorganic silicon network on the surface of the carrier after in-situ deposition. This network firmly bonds the manganese oxide active phase to the activated carbon framework and provides reinforcement, thereby reducing the risk of active component detachment and powdering caused by water erosion and particle friction during use, and improving the mechanical stability and long-term operational reliability of the material. This inorganic silicon network is formed using carbon dioxide-triggered silicate precursor gelation, which provides mild preparation conditions and easy process control. It avoids damage to the pore structure or the introduction of unnecessary side reactions by strong acid and alkali treatments, which helps to maintain the material's pore openness and mass transfer efficiency while ensuring anchoring strength, thus improving the repeatability and scalability of the material in engineering applications.

[0027] Simultaneously, this invention introduces carbonate buffer minerals during the inorganic silicon network formation stage, dispersing them uniformly in particulate form and embedding them within the gel network. This buffer component can regulate local acidity changes near the material interface during water treatment, maintaining a more suitable chemical environment at the adsorption interface. This broadens the effective application range of the material and reduces the risk of manganese component dissolution or interfacial instability under acidic conditions. Under alternating acid-base conditions or sudden pH shocks, the buffer component and the anchoring network work together to help maintain the adhesion stability and site availability of the manganese oxide active phase, improving the stability and consistency of material performance.

[0028] In summary, this invention, through in-situ construction of manganese oxide active sites, anchoring and reinforcing inorganic silicon networks formed by carbon dioxide triggering, and embedded configuration of carbonate buffer components, enables the composite material to maintain stable adsorption and operation performance under complex water quality and fluctuating operating conditions. This overcomes the problems of traditional adsorption materials such as easy powdering, easy deactivation, and limited applicability under strong scouring, pH changes, and long-term operation conditions. Attached Figure Description

[0029] Figure 1 To test the pH stability of the composite materials of Example 1 and Comparative Examples 1-5, Pb was tested at different initial pH values. 2+ Removal rate results graph;

[0030] Figure 2 To test the pH stability of the composite materials of Example 1 and Comparative Examples 1-5, Cu was tested at different initial pH values. 2+ Removal rate results graph;

[0031] Figure 3 The pH stability of the composite materials in Example 1 and Comparative Examples 1-5 was tested under pH shock cycling to assess Pb. 2+ Removal retention rate;

[0032] Figure 4 The pH stability of the composite materials in Example 1 and Comparative Examples 1-5 was tested under pH shock cycling for Cu. 2+ Removal retention rate;

[0033] Figure 5 The graph shows the turbidity changes after scouring in the structural stability test of the composite materials of Example 1 and Comparative Examples 1-5.

[0034] Figure 6 The graph shows the results of Mn dissolution under acidic conditions in the structural stability test of the composite materials of Example 1 and Comparative Examples 1-5.

[0035] Figure 7 Cyclic erosion test of Pb for the composite materials of Example 1 and Comparative Examples 1-5 2+ Graph showing the changes in retention rate after removal;

[0036] Figure 8 Cyclic erosion test of the composite materials of Example 1 and Comparative Examples 1-5 Cu 2+ Graph showing the results of changes in retention rate after removal. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the raw materials involved in the present invention are all purchased through conventional commercial channels. Experimental methods without specific conditions are conventional methods and conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0038] Example 1: A modified manganese oxide composite material for heavy metal adsorption, comprising the following raw materials: granular activated carbon, manganese source, reducing agent, silicate anchoring phase and carbonate buffer mineral;

[0039] The preparation method of the modified manganese oxide composite material for heavy metal adsorption specifically includes the following steps:

[0040] S1: 100g of granular activated carbon with a particle size of 1.4mm was washed in deionized water circulation, then washed with 0.08mol / L NaHCO3 for 15min, then washed with deionized water until neutral, and dried at 90℃ for 8h to obtain pretreated activated carbon.

[0041] S2: Place 100g of the pretreated activated carbon from step S1 into 1300mL of 0.06mol / L KMnO4 solution, stir and impregnate at 30℃ for 5h, filter the filtrate without washing, and obtain impregnated activated carbon.

[0042] S3: Add 100g of impregnated activated carbon back into 1000mL of deionized water to form a slurry. Then, under the conditions of stirring at 55℃ and 200rpm, slowly add 500mL of 0.05mol / L ascorbic acid solution over 45min. After the addition is complete, continue the reaction for 1.5h. After the reaction, filter and wash with water until there is no obvious residual color of KMnO4 to obtain in-situ deposited activated carbon.

[0043] S4: Place 100g of the in-situ deposited activated carbon from step S3 into 1000mL of 3wt% water glass solution and impregnate for 80min at room temperature with stirring; after impregnation, drain for 3min, then place in a closed reactor, introduce CO2 at 0.3L / min, control the temperature at 25℃, and react for 20min. The endpoint is controlled when the pH of the system gradually decreases from the initial strong alkalinity of the water glass to pH 7.2; immediately add particles with a diameter of D 50 2.5g of CaCO3 with a particle size of 5μm was stirred and dispersed evenly. The mixture was allowed to stand and age at room temperature for 6 hours. After filtration and washing until the pH of the effluent was neutral and the conductivity was stable, the mixture was dried at 75℃ for 10 hours and then aged at 100℃ for 2 hours to obtain the modified manganese oxide composite material.

[0044] Example 2: A modified manganese oxide composite material for heavy metal adsorption, comprising the following raw materials: granular activated carbon, manganese source, reducing agent, silicate anchoring phase and carbonate buffer mineral;

[0045] The preparation method of the modified manganese oxide composite material for heavy metal adsorption specifically includes the following steps:

[0046] S1: 100g of granular activated carbon with a particle size of 1.6mm was washed in deionized water circulation, then washed with 0.1mol / L NaHCO3 for 10min, then washed with deionized water until neutral, and dried at 100℃ for 6h to obtain pretreated activated carbon.

[0047] S2: Place 100g of the pretreated activated carbon from step S1 into 1000mL of 0.08mol / L KMnO4 solution, stir and impregnate at 35℃ for 3h, filter the filtrate without washing, and obtain impregnated activated carbon.

[0048] S3: Add 100g of impregnated activated carbon back into 1200mL of deionized water to form a slurry. Then, under the conditions of stirring at 65℃ and 250rpm, slowly add 1000mL of 0.02mol / L ascorbic acid solution over 30min. After the addition is complete, continue the reaction for 2h. After the reaction, filter and wash with water until there is no obvious residual color of KMnO4 to obtain in-situ deposited activated carbon.

[0049] S4: Place 100g of the in-situ deposited activated carbon from step S3 into 800mL of 5wt% water glass solution and impregnate for 90min at room temperature with stirring; after impregnation, drain for 5min, then place in a closed reactor, introduce CO2 at 0.5L / min, control the temperature at 30℃, and react for 10min. The endpoint is controlled when the pH of the system gradually decreases from the initial strong alkalinity of the water glass to pH 6.8; immediately add particles with a diameter of D 50 3g of dolomite powder with a particle size of 10μm was stirred and dispersed evenly. The mixture was allowed to stand and age at room temperature for 8 hours. After filtration and washing until the pH of the effluent was neutral and the conductivity was stable, the mixture was dried at 90℃ for 12 hours and then matured at 110℃ for 1 hour to obtain the modified manganese oxide composite material.

[0050] Example 3: A modified manganese oxide composite material for heavy metal adsorption, comprising the following raw materials: granular activated carbon, manganese source, reducing agent, silicate anchoring phase and carbonate buffer mineral;

[0051] The preparation method of the modified manganese oxide composite material for heavy metal adsorption specifically includes the following steps:

[0052] S1: 100g of granular activated carbon with a particle size of 1mm was washed in deionized water circulation, then washed with 0.05mol / L NaHCO3 for 20min, then washed with deionized water until neutral, and dried at 80℃ for 10h to obtain pretreated activated carbon.

[0053] S2: Place 100g of the pretreated activated carbon from step S1 into 1500mL of 0.04mol / L KMnO4 solution, stir and impregnate at 25℃ for 6h, filter the filtrate without washing, and obtain impregnated activated carbon.

[0054] S3: Add 100g of impregnated activated carbon back into 800mL of deionized water to form a slurry. Then, under the conditions of stirring at 40℃ and 150rpm, slowly add 500mL of 0.1mol / L glucose solution over 60min. After the addition is complete, continue the reaction for 1h. After the reaction, filter and wash with water until there is no obvious KMnO4 residue to obtain in-situ deposited activated carbon.

[0055] S4: Place 100g of the in-situ deposited activated carbon from step S3 into 1200mL of 2wt% water glass solution and impregnate for 60min at room temperature with stirring; after impregnation, drain for 2min, then place in a closed reactor, introduce CO2 at 0.1L / min, control the temperature at 20℃, and react for 30min. The endpoint is controlled when the pH of the system gradually decreases from the initial strong alkalinity of the water glass to pH 7.5; immediately add particles with a diameter of D 50 2g of shell powder with a particle size of 1μm was stirred and dispersed evenly. The mixture was allowed to stand and age at room temperature for 4 hours. After filtration and washing, the pH of the effluent was neutral and the conductivity was stabilized. The mixture was dried at 60℃ for 12 hours and then aged at 90℃ for 3 hours to obtain the modified manganese oxide composite material.

[0056] Comparative Example 1: In Comparative Example 1, the reducing agent solution of the same concentration and total amount as in step S3 was added at once, and the parameters of the remaining steps were completely consistent with those of Example 1.

[0057] Comparative Example 2: Step S4 is omitted in Comparative Example 2, and the parameters of the remaining steps are completely consistent with those of Example 1.

[0058] Comparative Example 3: No carbonate buffer minerals were added in Comparative Example 3, and the remaining steps and parameters were completely consistent with those in Example 1.

[0059] Comparative Example 4: In Comparative Example 4, after in-situ deposition, carbonate buffer minerals were directly added for mixing, without water glass and CO2 gel anchoring. The remaining steps and parameters were completely consistent with those in Example 1.

[0060] Comparative Example 5: In Comparative Example 5, CO2 was not introduced, but citric acid was used to adjust the pH to the same endpoint range to gel the water glass. The remaining steps and parameters were completely consistent with those in Example 1.

[0061] Mechanical strength test: The compressive strength and wear rate of the composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 5 of this invention were tested using a universal testing machine in accordance with the standard GB / T 44750-2024. The test results are shown in Table 1 below.

[0062] Table 1. Mechanical strength test results of the composite materials in the examples and comparative examples

[0063]

[0064] Based on the results in Table 1, the composite material of the present invention is superior to the comparative examples in terms of compressive strength and wear resistance. In Comparative Example 2, the compressive strength decreased significantly and the wear rate increased significantly after S4 was removed, indicating that without the silicate gel anchoring network, the manganese oxide active phase and the activated carbon skeleton are not firmly bonded, making the particles more prone to structural damage and surface detachment during compression and friction. Although carbonate buffer minerals were added to Comparative Example 4, no water glass / CO2 gel anchoring was formed, and its compressive strength and wear resistance remained significantly lower, indicating that mineral mixing alone is insufficient to achieve effective reinforcement and anti-detachment. In Comparative Example 1, the wear rate increased significantly and the compressive strength decreased after the reducing agent was added all at once, indicating that the loss of dropwise control made it easier for external phase precipitation and weakly bonded fine powder to occur, leading to easier wear and detachment of the particle surface. In Comparative Example 3, while retaining the anchoring network, the compressive strength remained at a high level even after the carbonate buffer minerals were removed, but the wear rate increased compared to the examples, indicating that the embedding of buffer minerals has an auxiliary reinforcing effect on particle wear resistance and surface structure stability. Comparative Example 5, which uses citric acid-triggered gel instead of CO2 trigger, has lower overall performance than the Example and Comparative Example 3. This suggests that although acid triggering can achieve gelation and provide a certain anchoring effect, it is inferior to CO2 triggering in terms of pore structure maintenance, gel uniformity, or control of interfacial side effects, resulting in slightly inferior wear resistance and compressive strength compared to the CO2-triggered system.

[0065] pH stability test: Prepare 500 mL of solution containing 100 mg / L Pb 2+ and 100 mg / L Cu 2+ The simulated heavy metal contaminated water was thoroughly mixed and divided into three groups, which were then adjusted to acidic, neutral, and alkaline conditions, respectively (acidic conditions were adjusted to pH 3.0 with dilute hydrochloric acid, neutral conditions were left as is, and alkaline conditions were adjusted to pH 11.0 with dilute sodium hydroxide; after adjustment, the pH was allowed to stabilize for a short time). The corresponding sample material (0.5g of Example 1 and Comparative Examples 1-5, no material added to the blank group) was added to each container, and adsorption was performed at 200 rpm for 60 min under constant temperature conditions at room temperature. After adsorption, stirring was stopped, and the mixture was allowed to stand for 5 min. Then, 10 mL of sample was taken from approximately 2 cm below the liquid surface. After sampling, the sample was filtered through a 0.45 μm filter. The filtrate was used to determine the residual concentration of heavy metal ions in the solution. The same batch of material was recovered after one adsorption cycle, quickly rinsed with deionized water until the effluent was nearly neutral, and then transferred to freshly prepared Pb solution of the same concentration. 2+ / Cu 2+ In the mixed solution, three cycles of adsorption were performed in sequence, from pH 3.0 to pH 11.0 and then to pH 7.0. The same dosage, stirring speed, temperature, and contact time were maintained in each cycle. Samples were taken for Pb analysis. 2+ Cu 2+ Residual concentration, calculate removal retention rate (%) = removal rate in round n / removal rate in round 1 × 100%, test results are as follows Figure 1, Figure 2 , Figure 3 and Figure 4 As shown.

[0066] based on Figure 1-4 The results show that Example 1 exhibited high Pb levels under acidic, neutral, and alkaline conditions. 2+ With Cu 2+ The material exhibits the highest removal capacity and retention rate during pH shock cycles, enabling it to adapt to the wide pH fluctuations common in polluted water bodies. The manganese oxides on the material surface provide stable complexing / adsorption sites; the CO2-triggered silica gel anchoring layer firmly fixes the active phase onto the activated carbon framework, reducing detachment and deactivation under hydraulic disturbances; simultaneously, the embedded and locked carbonate buffer minerals can regulate the pH near the interface under acidic conditions, ensuring high availability of active sites even at low pH. Therefore, it maintains a high removal rate at pH=3 and exhibits better stability during cycling. In Comparative Example 2, the removal of S4 resulted in the absence of silicate anchoring and buffering microenvironment, leading to a decrease in removal capacity under acidic conditions and the most significant cycle decay. Comparative Example 4, although containing carbonate, lacked gel anchoring, making its buffering effect difficult to maintain long-term, and its erosion resistance was insufficient, resulting in a similarly poor cycle retention rate. Comparative Example 1, by adding the reducing agent all at once, resulted in an uncontrolled in-situ deposition process, easily forming external phase precipitation and weakly bound fine powder. This led to a slightly lower initial removal rate and a more significant decay during pH shock cycling, which corroborates the higher wear rate observed in its mechanical tests. Comparative Example 3, retaining silica anchoring but removing the carbonate buffer, maintained a high removal rate and good cycle retention under neutral and alkaline conditions. However, under acidic conditions, the lack of interfacial buffering resulted in a significant decrease in removal rate at pH=3, indicating that the buffer component's adaptability to acidity is crucial. Comparative Example 5, using citric acid triggering instead of CO2 triggering, achieved gelation and provided some anchoring effect, but its stability under cycling and acidic conditions was still slightly inferior to the CO2-triggered system.

[0067] Structural stability test: Take 500 mL of deionized water and adjust the pH of the solution to 7.0. Add 0.5 g of each sample material (Example 1 and Comparative Examples 1-5, blank control not added). Shake at 300 rpm for 60 min at room temperature to simulate water disturbance and scouring. After stirring, let stand for 10 min. Take the supernatant from about 2 cm below the liquid surface to measure the turbidity. Take 500 mL of deionized water and adjust the pH to 3.0 with dilute nitric acid. Add 0.5 g of each sample material (Example 1 and Comparative Examples 1-5, blank control not added). Shake at 200 rpm for 24 h at room temperature. After the reaction, let stand for 10 min. Take 10 mL of the supernatant, filter it through 0.45 μm, and use it to detect the Mn content in the filtrate. The test results are as follows. Figure 5 and Figure 6 As shown.

[0068] based on Figure 5 The results show that in Example 1, the supernatant had the lowest turbidity after strong disturbance rinsing under neutral conditions, indicating minimal particle shedding and surface detachment, and the best structural stability. In Comparative Example 2, the highest turbidity was observed after removing S4, indicating insufficient bonding between the active phase and the carrier when the silica anchoring network is missing, making particles more prone to debris and suspended fine powder under disturbance. Comparative Example 4, although carbonate was added, was only physically mixed, lacking an anchoring structure, resulting in significantly higher turbidity, further demonstrating that buffer minerals cannot replace the anchoring reinforcement effect. In Comparative Example 1, the uncontrolled deposition process due to the one-time addition of the reducing agent led to more easily formed external phase precipitation and weakly bound fine powder, resulting in a significant increase in turbidity after rinsing, consistent with its higher mechanical wear rate and faster decrease in pH shock cycle retention rate. In Comparative Example 3, retaining the anchoring but removing the carbonate buffer resulted in only a slight increase in turbidity, indicating that the anchoring network still maintained good anti-powdering ability, while the carbonate embedding had an auxiliary reinforcing effect on wear resistance and surface stability. Comparative Example 5, which used citric acid-triggered gel instead of CO2-triggered gel, showed slightly higher turbidity than Example 1. This indicates that although acid triggering can achieve gelation, the uniformity of gel formation or the control of interfacial side effects are not as good as the CO2-triggered system, resulting in a slight decrease in erosion resistance.

[0069] based on Figure 6 The results showed that under acidic conditions, Example 1 exhibited the lowest Mn dissolution. The synergistic effect of the silica anchoring network and the carbonate buffer microenvironment reduced the risk of active phase dissolution and migration under acid shock: the anchoring network reduced active phase shedding, while the buffer component improved pH stability near the interface, thereby inhibiting the acid dissolution behavior of manganese oxides. Comparative Example 3 lacked carbonate buffering, making it difficult to effectively regulate the acidic interface, thus resulting in a significant increase in Mn dissolution. Comparative Examples 2 and 4 lacked effective anchoring, leading to even higher Mn dissolution under acidic conditions, reflecting the risk of secondary release due to insufficient structural binding. Although Comparative Example 5 possessed gel anchoring, its Mn dissolution was still higher than that of the CO2-triggered system due to the difference in triggering mechanism.

[0070] Circulation flushing test: Prepare 500 mL of solution containing 100 mg / L Pb 2+ and 100 mg / L Cu 2+ Mixed simulated heavy metal contaminated water was prepared, and the pH of the solution was adjusted to 7.0. 0.5 g of each sample material (Example 1 and Comparative Examples 1-5, blank control was not added) was added, and the mixture was stirred at 300 rpm for 60 min at room temperature for adsorption. After adsorption, the mixture was allowed to stand for 5 min, and 10 mL of the supernatant was collected and filtered through a 0.45 μm filter to determine Pb. 2+ Cu 2+The residual concentration was used to obtain the first round of adsorption effect; subsequently, the material was recovered (by filtration) and gently regenerated as follows: the recovered material was placed in 500 mL of 0.05 mol / L NaHCO3 solution and shaken at 200 rpm for 30 min at room temperature; then washed with deionized water until the pH of the effluent was near neutral and drained. The regenerated material was then transferred to a freshly prepared Pb solution of the same concentration. 2+ / Cu 2+ In the mixed solution, the above adsorption steps were repeated for 10 cycles, and the test results are as follows. Figure 7 and Figure 8 As shown.

[0071] based on Figure 7-8 The results show that, under neutral conditions, after 10 cycles of cyclic scouring tests, Example 1 showed that Pb 2+ With Cu 2+ All three examples exhibited optimal cyclic stability: high removal rate in the first round, minimal decline with increasing cycle count, and maintained a high removal level even in the 10th round. Comparative Example 2 showed the most significant cyclic decline after removing S4, indicating that the lack of silica anchoring and buffer microenvironment resulted in insufficient binding between the active phase and the carrier. Under the combined effects of 300rpm rinsing and multiple regenerations, it was more prone to powder shedding, activity loss, and a reduction in adsorption sites, leading to a rapid performance decline. Comparative Example 4, although it added carbonate, only involved physical mixing and lacked gel anchoring, also showing significant decline during cycling, indicating that buffer minerals cannot replace the crucial role of the anchoring network in resisting erosion and detachment. Comparative Example 1, by adding the reducing agent all at once, resulted in uneven in-situ deposition and more weakly bound fine powder, with a significantly greater cyclic decline than Example 1. This corroborates its trend of higher rinsing turbidity and greater wear rate. In Comparative Example 3, without the addition of carbonate buffer minerals, the initial removal rate was higher and the cycle decay was moderate due to the retention of CO2-triggered silica gel anchoring. However, overall, it was still inferior to Example 1, indicating that the embedding of buffer minerals has an auxiliary enhancing effect on maintaining particle surface stability and slowing down long-term wear and deactivation. In Comparative Example 5, after replacing CO2 triggering with citric acid-triggered gel, the cycle stability was lower than that of Example 1 and Comparative Example 3, but still better than Comparative Examples 2 and 4, which did not construct a silicate gel anchoring network. This shows that although acid triggering can achieve gelation and provide a certain anchoring effect, it is inferior to the CO2-triggered system in terms of gel formation uniformity and control of interfacial side effects, resulting in a slight decrease in long-term cycle stability.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A modified manganese oxide composite material for heavy metal adsorption, characterized in that, Its composition includes the following raw materials: granular activated carbon, manganese source, reducing agent, silicate anchoring phase and carbonate buffer mineral; The particle size of the granular activated carbon is 1–1.6 mm; The manganese source is KMnO4; The reducing agent is either glucose or ascorbic acid; The silicate anchoring phase is a water glass solution; the mass fraction of the water glass solution is 2-5 wt%. The carbonate buffer mineral is any one of CaCO3, dolomite powder, and shell powder; the particle size D of the carbonate buffer mineral is... 50 =1~10μm; The modified manganese oxide composite material for heavy metal adsorption is prepared by the following steps: S1: The granular activated carbon is washed in a deionized water circulation system, then washed with NaHCO3, and then washed with deionized water until neutral. After drying, pretreated activated carbon is obtained. S2: Place the pretreated activated carbon from step S1 into a manganese source solution, stir and impregnate, filter the filtrate without washing, and obtain impregnated activated carbon. S3: Add the impregnated activated carbon back into deionized water to form a slurry, and then slowly add the reducing agent solution under stirring conditions. After the addition is complete, continue the reaction. After the reaction, filter and wash with water to obtain in-situ deposited activated carbon. S4: Place the activated carbon deposited in situ in step S3 into a silicate anchoring phase and impregnate it at room temperature with stirring; after impregnation, drain the liquid and then place it in a closed reactor, introduce CO2, control the temperature, and react; immediately after the reaction is completed, add carbonate buffer minerals and stir to disperse evenly, let it stand and age at room temperature, filter and wash until the pH of the effluent is neutral and the conductivity tends to stabilize; dry and then ripen to obtain the modified manganese oxide composite material.

2. The modified manganese oxide composite material for heavy metal adsorption according to claim 1, characterized in that, In step S2, the ratio of the amount of pretreated activated carbon to manganese source solution is 1g:10-15mL.

3. The modified manganese oxide composite material for heavy metal adsorption according to claim 1, characterized in that, In step S3, the ratio of impregnated activated carbon to deionized water is 1g:8-12mL; the ratio of impregnated activated carbon to reducing agent solution is 1g:5-12mL.

4. The modified manganese oxide composite material for heavy metal adsorption according to claim 1, characterized in that, In step S3, the stirring conditions are 150–250 rpm.

5. The modified manganese oxide composite material for heavy metal adsorption according to claim 1, characterized in that, In step S4, the ratio of the amount of in-situ deposited activated carbon to silicate anchoring phase is 1g:8-12mL; the ratio of the mass of the in-situ deposited activated carbon to carbonate buffer mineral is 1g:0.02-0.03g.

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