Performance evaluation method of composite porous geopolymers for heavy metal adsorption

Abstract

The present invention provides a performance evaluation method for composite porous geopolymers for heavy metal adsorption. The method comprises: Step 1: preparing heavy metal solutions of varying concentrations; Step 2: establishing a calibration curve between the heavy metal solution concentration and the nuclear magnetic resonance (NMR) signal; Step 3: conducting adsorption experiments on multiple batches of composite porous geopolymer materials using NMR technology; and Step 4: monitoring and evaluating the adsorption performance of the composite porous geopolymer. The performance evaluation method for composite porous geopolymers for heavy metal adsorption disclosed herein can obtain concentration distribution information within the geopolymer material, characterize the adsorption process, and guide and optimize material preparation.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental pollution remediation and treatment, and in particular to a performance evaluation method for a composite porous geopolymer used for heavy metal adsorption. Background Art

[0002] With the continuous development of urbanization and industrialization, groundwater bodies are facing unprecedented pollution threats, among which heavy metal pollution is of particular concern. Heavy metal ions such as manganese, chromium, and cadmium are highly toxic, difficult to degrade, and easily absorbed by organisms, seriously affecting water quality, endangering human health, and damaging the ecological environment. Common methods for removing heavy metals from water bodies include chemical precipitation, ion exchange, material adsorption, and evaporation concentration. Adsorption is widely used due to its advantages such as high efficiency, environmental protection, relatively low cost, high recycling rate, and wide applicability. In recent years, geopolymers, as inorganic aluminosilicate gel materials with a three-dimensional molecular sieve network structure, have become a new research hotspot in adsorption materials.

[0003] Compared with adsorption materials such as activated carbon, chitosan, and diatomaceous earth, the preparation process of geopolymers is energy-saving and environmentally friendly, the raw materials are widely available, and they have excellent mechanical properties and stable chemical properties. They have demonstrated extremely high adsorption efficiency in the removal of heavy metals such as lead, chromium, and cobalt. In particular, porous geopolymers, the interconnected or closed pore spaces formed inside them make this type of material exhibit characteristics such as low density and high specific surface area, further broadening the application scenarios of geopolymers as adsorption materials. At present, geopolymer porous materials are mainly layered, spherical, and block structures, and are often prepared by direct foaming, solvent volatilization, porous filler addition, and suspension solidification. The internal pore structures formed based on different principles differ in terms of pore size distribution, connectivity characteristics, etc., which directly affect the adsorption performance and application areas of geopolymer porous materials.

[0004] In addition to improving the design ideas and synthesis processes of geopolymer porous materials themselves, the use of advanced heavy metal detection technology to characterize the adsorption process in real time is also an important step in guiding and optimizing material preparation. At present, the main methods for measuring heavy metal concentrations in water bodies include chromatography, spectroscopy, flow analysis detection, biochemical analysis, etc. Among them, the most commonly used is the combined detection technology of spectroscopy and mass spectrometry, including atomic absorption spectroscopy (AAS), inductively coupled plasma atomic emission spectroscopy (ICP-OES), atomic fluorescence spectroscopy (AFS), visible ultraviolet spectrophotometry (UV-Vis) and inductively coupled plasma mass spectrometry (ICP-MS).

[0005] Two major aspects need to be considered when evaluating the ability of different geopolymer materials to remove heavy metals from water bodies: one is the adsorption performance of the material itself. Generally, the larger the specific surface area, the higher the adsorption efficiency; the other is the difficulty of recovering the material from the water body, thereby achieving pollutant separation and material reuse.

[0006] In terms of adsorption performance, spherical geopolymer porous materials, due to the presence of interconnected pores on their surface and within their interiors, have a larger specific surface area and lower flow resistance than bulk porous materials, enabling more efficient adsorption and immobilization of heavy metals in water. However, such materials are difficult to rapidly collect and recover, particularly in the remediation of heavy metal contaminated groundwater, hindering long-term management of contaminated areas and the reuse of the materials. While bulk geopolymer porous materials facilitate uniform disposal, the connectivity and uniformity of their internal pore structure are difficult to control during the preparation process. Larger pore diameters facilitate interpenetration, allowing for full contact between contaminated water and the adsorbent material, but at the expense of a certain specific surface area. Smaller pore diameters can create a large number of closed, isolated pore spaces, preventing water from flowing through these areas and significantly reducing adsorption performance. Therefore, there is an urgent need for new geopolymer porous materials that balance adsorption performance and recovery efficiency to meet the application needs of efficient adsorption and separation of heavy metals in water.

[0007] For monitoring adsorption characteristics, combined detection techniques based on spectroscopy and mass spectrometry can only measure the heavy metal concentration of the entire solution or the outflow end, but cannot obtain information on the concentration distribution within the geopolymer material. Therefore, the detection data is difficult to use to analyze the dynamic characteristics and spatial differences of the adsorption process. However, this information is often an important parameter for exploring the effect of the pore structure of porous geopolymer materials on the adsorption behavior of heavy metals. It can not only comprehensively evaluate the adsorption performance of different materials, but also be used to improve the synthesis and preparation process of porous geopolymer materials, thereby obtaining porous geopolymers with better performance for the adsorption of heavy metals in water. Summary of the Invention

[0008] The purpose of the present invention is to at least partially overcome the defects of the prior art and provide a method for evaluating the performance of a composite porous geopolymer for heavy metal adsorption.

[0009] Another object of the present invention is to provide a performance evaluation method for a composite porous geopolymer for heavy metal adsorption, which can obtain concentration distribution information inside the geopolymer material.

[0010] The present invention also aims to provide a performance evaluation method for composite porous geopolymers used for heavy metal adsorption, which can characterize the adsorption process and guide and optimize material preparation.

[0011] To achieve the above purpose or one of the purposes, the technical solutions of the present invention are as follows:

[0012] A performance evaluation method for a composite porous geopolymer for heavy metal adsorption, comprising:

[0013] Step 1: Prepare heavy metal solutions of different concentrations;

[0014] Step 2: Establish a line between the concentration of heavy metal solution and the NMR signal;

[0015] Step 3: Conduct adsorption experiments on multiple batches of composite porous geopolymer materials based on nuclear magnetic resonance technology;

[0016] Step 4: Monitor and evaluate the adsorption performance of the composite porous geopolymer.

[0017] According to a preferred embodiment of the present invention, step 1 includes:

[0018] Prepare 500 ml of a heavy metal solution with a concentration of 1000 ppm in a flask as a standard solution;

[0019] A certain amount of solution was gradually taken out into a 10 ml glass bottle using a pipette, and heavy metal solutions of different concentrations were prepared by adding different volumes of ultrapure water.

[0020] According to a preferred embodiment of the present invention, step 2 includes:

[0021] Use nuclear magnetic resonance pulse sequence to measure heavy metal standard solutions with different concentrations to obtain T2 values;

[0022] Establish the relationship between heavy metal ion concentration and nuclear magnetic signal [1 / T 2,i -1 / T 2,0 ], that is, to determine the marking line, where T 2,i is the measured transverse relaxation time, ms; T 2,0 is the transverse relaxation time of ultrapure water, ms.

[0023] According to a preferred embodiment of the present invention, step 2 includes:

[0024] Turn on the radio frequency switch of the low-field nuclear magnetic resonance instrument, use the oil sample to adjust the main frequency and sampling frequency, adjust the initial parameters, and in the SFG-MSCPMG pulse sequence, set the repeated sampling wait time to 6000ms, the echo time to 0.2ms, the number of echoes to 8000, the number of layers to 1, and the number of accumulations to 2;

[0025] Use this sequence to test heavy metal solution samples with different concentrations and obtain the corresponding T2 values. The correlation between the concentration of the heavy metal solution and T2 is shown in the following formula:

[0026]

[0027] Where C is the concentration of heavy metal solution, mM; R is the transverse relaxation rate, mM·s -1 ;T 2,i is the measured transverse relaxation time, ms; T 2,0 is the transverse relaxation time of ultrapure water, ms.

[0028] According to a preferred embodiment of the present invention, the transverse relaxation time T2 is measured using a SFG-MSCPMG pulse sequence based on a constant gradient encoding technique.

[0029] According to a preferred embodiment of the present invention, each time a predetermined number of samples are measured, an additional sample of ultrapure water is measured as a calibration.

[0030] According to a preferred embodiment of the present invention, step 3 includes: placing different forms of porous geopolymer samples in a nuclear magnetic resonance holder in sequence, first saturating them with ultrapure water, and then injecting heavy metal ion solutions of the same concentration at the same flow rate, and monitoring the concentration distribution characteristics and dynamic changes of the heavy metal solution inside the sample in real time based on nuclear magnetic resonance technology.

[0031] According to a preferred embodiment of the present invention, step 3 further includes: collecting the effluent at the outlet end of the holder, and performing a static measurement of the heavy metal concentration every time 2 ml is collected; combining with an established heavy metal ion concentration line, converting the nuclear magnetic resonance measurement data into the concentration of heavy metal ions in the effluent at different times, thereby quantifying and evaluating the adsorption behavior of different forms of porous geopolymer samples.

[0032] According to a preferred embodiment of the present invention, computed tomography and scanning electron microscopy are used to characterize the structure of porous geopolymer samples, analyze the porosity, pore size distribution, and connectivity, and establish a correlation between pore structure and adsorption performance.

[0033] According to a preferred embodiment of the present invention, in step 3, porous geopolymer samples of different forms are placed in a nuclear magnetic resonance holder in sequence to conduct displacement adsorption experiments to characterize the adsorption properties of different materials, including:

[0034] Use a pipette to remove 80 ml of the 1000 ppm standard solution and add 320 ml of ultrapure water to prepare a total volume of 400 ml of the 200 ppm standard solution for adsorption experiments;

[0035] Before each displacement adsorption experiment, ultrapure water was injected at a flow rate of 0.1 ml / min for 30 min to make the sample to be tested fully saturated;

[0036] Subsequently, a standard solution with a concentration of 200 ppm was continuously injected at a flow rate of 0.1 ml / min for 40 minutes, and then ultrapure water was injected at a flow rate of 0.1 ml / min. The total experimental time was 80 minutes; or a standard solution with a concentration of 200 ppm was continuously injected at a flow rate of 0.2 ml / min for 20 minutes, and then ultrapure water was injected at a flow rate of 0.1 ml / min. The total experimental time was 60 minutes.

[0037] According to a preferred embodiment of the present invention, in step 3, a static adsorption experiment is performed to test the adsorption capacity of the granular porous material of the composite porous geopolymer, comprising:

[0038] The prepared 200 ppm standard solution was divided into two identical glass containers;

[0039] Then, 1g of each of the ground granular porous materials with mesh sizes of 25-30 and 12-14 was weighed and placed in a glass container, ensuring that the liquid level could submerge the sample and be at least 2cm higher;

[0040] The timing started immediately after the sample was placed in the container. Every 5 minutes, 2 ml of solution sample was taken out from the container with a pipette and injected into the chromatographic bottle for nuclear magnetic resonance measurement to monitor the adsorption behavior. The total experimental time was 60 minutes.

[0041] The performance evaluation method of the composite porous geopolymer for heavy metal adsorption of the present invention can obtain concentration distribution information inside the geopolymer material. The detection data can be used to analyze the dynamic characteristics and spatial differences of the adsorption process. It plays an important role in exploring the influence of the pore structure of the porous geopolymer material on the heavy metal adsorption behavior. It can not only comprehensively evaluate the adsorption performance of different materials, but also be used to improve the synthesis and preparation process of the porous geopolymer material, thereby obtaining a porous geopolymer with better performance for the adsorption of heavy metals in water bodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The production process and physical diagram of the composite geopolymer porous adsorption material according to an embodiment of the present invention;

[0043] Figure 2 The correlation between the concentration of Mn(II) solution and the NMR signal is shown;

[0044] Figure 3 The pore structure characterization of geopolymer porous materials is shown;

[0045] Figure 4 The heavy metal concentration distribution information inside the geopolymer porous material is shown;

[0046] Figure 5Shown is a comparison of the adsorption properties of granular porous filling materials with different mesh sizes. DETAILED DESCRIPTION

[0047] Below in conjunction with the accompanying drawings, exemplary embodiments of the present invention are described in detail, wherein the same or similar reference numerals represent the same or similar elements. In addition, in the detailed description below, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the disclosed embodiments. However, it is apparent that one or more embodiments may also be implemented without these specific details. In other cases, known structures and devices are embodied in a schematic manner to simplify the drawings.

[0048] The present invention belongs to the technical field of environmental pollution remediation and treatment, specifically involving the design and synthesis of composite geopolymer porous materials, and the comprehensive evaluation of their heavy metal adsorption performance based on nuclear magnetic resonance technology, thereby proposing an application technology that can achieve efficient adsorption and convenient separation of heavy metals in water bodies, which is suitable for wastewater treatment, groundwater pollution remediation and other fields.

[0049] This invention aims to establish an efficient, economical, and environmentally friendly integrated heavy metal adsorption and separation technology for water bodies. To address the removal of heavy metals from water, a composite geopolymer porous material has been designed and synthesized. This material not only leverages the inherent advantages of geopolymers as green, environmentally friendly, and low-cost adsorption materials, but also achieves the dual goals of efficient heavy metal adsorption and unified recovery through innovative porous material preparation and integration processes.

[0050] Geopolymers are inorganic polymers that undergo depolymerization and polycondensation of the silicon-oxygen and aluminum-oxygen bonds of aluminosilicates in natural minerals or solid wastes (metakaolin, kaolin, fly ash, etc.) under the conditions of alkali or acid activators, and then gel solidification to produce a three-dimensional network structure. This material is mainly composed of silicon tetrahedrons [Si(OH)4] and aluminum tetrahedrons [Al(OH)4 －] structural units and are connected by shared oxygen atoms. Due to its zeolite-like structure, it shows broad application prospects in the adsorption / stabilization of toxic heavy metal ions and other polluting impurities. The porous geopolymer is formed with a through or closed pore space inside by adding a foaming agent, a filler, etc. during the above-mentioned preparation process. These pores and the geopolymer skeleton form a new spatial structure, which further increases the specific surface area of ​​the material, thereby improving the adsorption performance. The present invention established an optimized geopolymer porous material preparation plan and process on the basis of systematic experimental comparative research, synthesized a cylindrical porous material with internal interconnected pore space, and then transformed its internal structure, and filled and encapsulated a spherical porous material, which greatly increased the total specific surface area of ​​the adsorption material. Thus, a composite geopolymer porous material is proposed, which can achieve efficient adsorption and unified separation of heavy metals in water bodies. With the idea of ​​preparing this composite geopolymer material for pollution remediation, different nuclear magnetic resonance test sequences have also been developed for accurate, rapid, and non-destructive measurement of heavy metal concentrations. This is to obtain spatiotemporal information on the distribution of heavy metal concentrations within the geopolymer, which can be used to guide and improve the preparation parameters and processes of the composite material, thereby determining the material synthesis scheme with the best adsorption performance.

[0051] The specific technical methods of the present invention are as follows:

[0052] (1) Preparation of geopolymer porous materials with through pores

[0053] The preparation process for porous geopolymer materials involves mixing aluminosilicate raw materials with a liquid activator to form a uniform slurry, then adding a foaming agent and a foam stabilizer. After uniform mixing, the mixture is injected into a mold and compacted, followed by curing and curing under certain conditions. In addition to the selection of synthetic materials, key parameters in the preparation process include the activator modulus (i.e., the molar ratio of SiO2 to Na2O), the liquid-to-solid ratio (i.e., the mass ratio of water to solute in the uniform slurry), the molar ratio of the foaming agent to the foam stabilizer, and the curing temperature. These parameters collectively control the adsorption and mechanical properties of the resulting porous geopolymer material. Based on comparative optimization through systematic experimental testing, the present invention uses a mixed NaOH and Na2SiO3 as a composite alkaline activator solution with an activator modulus of 1.4; a mixture of fly ash and metakaolin in a mass ratio of 1:1 is used as the raw material, with a total liquid-to-solid ratio of 1.15; 3% hydrogen peroxide is used as the foaming agent, and sodium lauryl sulfate is used as the foam stabilizer, with a mixing ratio of the two of 1:1. The mold into which the slurry is injected is first placed in a microwave oven at 300W for 150 seconds to further promote the foaming effect and rapid curing, then removed and placed in a 40°C oven for heat curing for 18 hours. Finally, the mold is demolded, sealed, and stored at room temperature for 28 days. The mold is a cylindrical container with a diameter of 10 mm and a length of 60 mm, and both ends are polished to produce a cylindrical geopolymer porous material with a length of 50 mm.

[0054] (2) Synthetic composite geopolymer porous adsorption material

[0055] Cut the cylindrical geopolymer porous material into 50 mm lengths, use a 5 mm diameter hollow drill bit to remove the middle of the cylindrical porous material to obtain a 50 mm long circular porous material. Cut the removed part at both ends, leaving 5 mm on each side, and grind the rest to 25-30 mesh for filling. Figure 1 As shown, the ground geopolymer porous material is filled inside the annular geopolymer material, and the two ends are assembled and sealed with cut 5 mm thin sheets (cylindrical blocks), and finally a composite geopolymer porous adsorption material is obtained. Compared with porous materials with single columnar or spherical particles, this material combines the advantages of two structural types of materials. It not only has a large specific surface area, but also can more fully allow heavy metal-containing water to contact the adsorption material. In the process of flowing through the annular porous material and entering the porous material with internal granular filling, heavy metals are adsorbed, thereby purifying the water. In addition, the composite material can be easily and uniformly recycled for subsequent material replacement, regeneration and reuse.

[0056] (3) Establish heavy metal concentration benchmarks based on nuclear magnetic resonance technology

[0057] Low-field Nuclear Magnetic Resonance (NMR) can detect hydrogen protons in a solution non-destructively, accurately, and rapidly. If the solution contains paramagnetic heavy metal ions, the attenuation of the NMR signal will be accelerated, thereby establishing a correlation between the concentration of heavy metal ions and the NMR signal. Among them, the response of the NMR signal can be characterized by measuring the transverse relaxation time T2, which characterizes the time it takes for the atomic nuclei with a dipole magnetic moment to recover from the excited state to the equilibrium state through the spin-spin method after the application of the above-mentioned radio frequency wave is stopped. First, ultrapure water is used to prepare heavy metal ions into standard liquids of different concentrations, which are placed in glass bottles for later use; then a NMR pulse sequence is used to measure heavy metal standard solutions of different concentrations to obtain T2 values; finally, a correlation is established between the concentration of heavy metal ions in the solution and the NMR signal [1 / T 2,i -1 / T 2,0 ], the calibration line is determined for accurate and rapid measurement of heavy metal ion concentrations in subsequent adsorption experiments.

[0058] In addition to the effect of heavy metal concentration on T2 value, the pore structure of geopolymer porous materials also affects the NMR signal, as described in the following equation:

[0059]

[0060] Where ρ0 is the surface relaxation rate, S and V are the specific surface area and volume of the porous medium, respectively. Although the pore structure and heavy metal concentration jointly affect the NMR data T2, the two effects are independent of each other. For a specific heavy metal ion, its concentration is related to the NMR signal [1 / T 2,i -1 / T 2,0 ] does not change due to pore structure. Therefore, in porous geopolymer materials with fixed structures, changes in the NMR signal during adsorption depend on changes in heavy metal concentration. Based on this principle, acquired NMR T2 data can be converted into concentration distribution information and dynamic characteristics within the porous material, enabling non-destructive, real-time monitoring of heavy metal adsorption behavior within geopolymer materials.

[0061] The SFG-MSCPMG pulse sequence, based on constant gradient encoding technology, is used to measure T2 NMR data. This sequence not only measures heavy metal concentrations throughout the sample like a traditional CPMG sequence, but also generates distinct localization information under the influence of the gradient magnetic field generated by the gradient coils. Using mathematical transformation and decoding, the NMR signal is assigned to distinct spatial locations, thereby characterizing the distribution of heavy metal ions within the geopolymer. Constant gradient encoding technology applies selective radio frequency pulses, using a limited bandwidth to resonate only protons within the resonant frequency band. By applying a gradient in a specific direction, the layer-selective excitation pulse selectively excites protons outside the selected layer, which do not meet the resonance conditions and are therefore not excited, thus generating no NMR signal. By configuring the number of layers, it is possible to obtain both the overall NMR signal (one layer) and concentration data at specific locations (ten layers).

[0062] (4) Evaluation of the adsorption performance of composite geopolymer porous materials

[0063] Based on the established method for monitoring the dynamic behavior of heavy metal ion concentration, adsorption experiments were conducted on composite and unmodified cylindrical geopolymer porous materials to quantitatively compare their adsorption performance. The two geopolymer porous materials were placed in the holder of the nuclear magnetic resonance equipment in turn, first saturated with ultrapure water, and then injected with heavy metal ion solutions of the same concentration at the same flow rate. The concentration distribution characteristics and dynamic changes of the heavy metal solution inside the sample were monitored in real time based on nuclear magnetic resonance technology. At the same time, the effluent was collected at the outlet of the holder, and a static measurement of the heavy metal concentration was performed every 2 ml collected. Combined with the established heavy metal ion concentration line, the nuclear magnetic resonance measurement data was converted into the concentration of heavy metal ions in the effluent at different times, so as to quantify and evaluate the overall adsorption behavior of different materials. In addition, computed tomography (CT) and scanning electron microscopy (SEM) were used to characterize the structure of the prepared composite geopolymer porous material, and its pore structure parameters related to adsorption behavior, such as porosity, pore size distribution, and connectivity, were analyzed to establish a correlation between pore structure and adsorption performance.

[0064] The following describes the specific experimental steps using the adsorption of heavy metal manganese (Mn(II)) by composite geopolymer porous materials as an example:

[0065] S1: Raw materials and equipment for preparing composite geopolymer materials

[0066] To prepare the alkaline activator, add granular sodium hydroxide to sodium water glass (an alkali metal silicate formed by combining alkali metal oxides and silicon dioxide) with an initial modulus of 2.3. Adjust the modulus to 1.4, stir thoroughly to completely dissolve the added sodium hydroxide, and let it stand at room temperature for at least 24 hours. Once the activator liquid turns transparent from the initial turbidity, it can be used in subsequent geopolymer preparation. 3% hydrogen peroxide is used as a foaming agent, and sodium lauryl sulfate is used as a foam stabilizer. Mix the two in a 1:1 molar ratio, stir thoroughly, and set aside.

[0067] A certain amount of fly ash and metakaolin was first dried in an oven at 80°C for 12 hours. 50g of each fly ash and metakaolin were then weighed on a scale and mixed for later use. The fly ash and metakaolin used in this study had particle sizes of 5μm and 3.75μm, respectively. The main chemical compositions and contents, measured using X-ray fluorescence spectrometry, are shown in Tables 1 and 2. Due to differences in the chemical composition of raw materials obtained from different sources, the optimal raw material ratio may vary.

[0068] Table 1 Main chemical composition and content of fly ash

[0069]

[0070] Table 2 Main chemical components and contents of metakaolin

[0071]

[0072] The tests and analyses used a Meso MR23-060H low-field nuclear magnetic resonance imaging analyzer from Suzhou Newmai Analytical Instruments, an LH-XRFII X-ray fluorescence spectrometer from Tianjin Luhai Petroleum Equipment System Engineering Co., Ltd., and an Xradia 510Versa computed tomography scanner from Carl Zeiss, Germany. The mixing of the various materials during geopolymer preparation was performed using a cement slurry mixer, model NJ-160B, from the Shangyu Binxin Instrument Factory in Shaoxing.

[0073] S2: Preparation and curing of composite geopolymer porous materials

[0074] First, gradually add the fly ash and metakaolin mixture as raw materials to a composite alkaline activator solution with a modulus of 1.4. After thorough mixing, pour it into a cement slurry mixer. Place the pot on the mixer pot base, raise it to the stirring position, start the mixer, and stir at low speed until it mixes evenly. This process lasts for 10 minutes. After stopping the machine, add the prepared foaming agent and foam stabilizer mixture and ultrapure water to a liquid-to-solid ratio of 1.15. After thorough mixing, turn on the cement slurry mixer and stir at low speed for 5 minutes. Then scrape the slurry from the blades and the pot wall into the center of the pot. Pour the stirred slurry into four identical cylindrical special molds with a diameter of 10 mm and a length of 60 mm. Shake, compact, and seal. The curing process adopts a dual mode of microwave heating and oven heating. First, the mold injected with the slurry is placed in a microwave oven, set to 300W and microwave for 150 seconds, then taken out and placed in an oven at 40°C for heat curing for 18 hours. After taking out and demolding, the four sides are sealed with a sealing mold and cured at room temperature for 28 days.

[0075] This yielded four identical cylindrical geopolymer porous samples. Two were cut into 50 mm lengths and reserved for future use, while the remaining two were used to prepare composite geopolymer porous materials. First, a 5 mm diameter hollow drill was used to remove the center of the cylindrical porous material. The ends were then cut, leaving a 5 mm thick slice for subsequent composite sample packaging. The remaining portion was ground to a 25-30 mesh size for filling the inner ring. After filling the cylindrical material with the ground porous material, two 5 mm slices were placed on each end and sealed to the ring sample using epoxy resin glue. This resulted in two composite geopolymer porous materials.

[0076] S3: Prepare heavy metal Mn(II) solutions of different concentrations

[0077] The Mn(II) standard solution was diluted with ultrapure water. First, 500 mL of a 1000 ppm Mn(II) solution was prepared in a flask. Subsequently, varying amounts of this solution were pipetted into 10 mL glass vials for dilution. Different concentrations of Mn(II) solutions were prepared by adding varying volumes of ultrapure water for the calibration assay. Twenty Mn(II) solution samples were obtained, with concentrations of 0.025, 0.05, 0.5, 0.8, 1, 2, 5, 8, 10, 30, 50, 60, 80, 100, 200, 400, 600, 800, 900, and 1000 ppm, respectively.

[0078] S4: Establishing a line between Mn(II) solution concentration and NMR signal

[0079] Turn on the radio frequency switch of the low-field NMR instrument and use an oil sample to adjust the main frequency and sampling frequency. Adjust the initial parameters. In the SFG-MSCPMG pulse sequence, set the repetitive sampling wait time (TW) to 6000ms, the echo time (TE) to 0.2ms, the number of echoes to 8000, the number of layers to 1, and the number of accumulations to 2. Use this sequence to test 20 Mn(II) solution samples with different concentrations and obtain the corresponding T2 values. The correlation between Mn(II) concentration and T2 is shown in the formula:

[0080]

[0081] Where C is the concentration of Mn(II) solution, mM; R is the transverse relaxation rate, mM·s -1 ;T 2,i is the measured transverse relaxation time, ms; T 2,0 is the transverse relaxation time of ultrapure water, in ms. During the test, every 10 samples were measured, an additional ultrapure water sample was measured as a correction (the T2 value of ultrapure water is ≈ 2800ms). The final calibration line is as follows Figure 2 As shown, according to formula 2, the concentration of Mn(II) can be related to [1 / T 2,i -1 / T 2,0 ] was fitted to obtain the nuclear magnetic relaxation rate R of Mn(II) ion as 9.45 mM·s -1 The goodness of fit is 0.9998. Since the effects of pore structure and heavy metal concentration on the NMR signal are independent of each other, the NMR relaxation rate of Mn(II) ions does not change within the porous geopolymer material with a fixed structure, and the measured calibration line remains applicable.

[0082] S5: Conduct adsorption experiments on multiple batches of composite geopolymer materials

[0083] The two unmodified cylindrical geopolymer porous samples prepared in S2 and the two modified composite geopolymer porous samples were placed in the nuclear magnetic resonance holder in succession for displacement experiments to characterize the adsorption properties of different materials. First, 80 ml of the 1000 ppm Mn (II) standard solution prepared in step S3 was taken out using a pipette, and then 320 ml of ultrapure water was added to prepare a total volume of 400 ml of 200 ppm Mn (II) standard solution for adsorption experiments. Before the start of each displacement experiment, ultrapure water was injected at a flow rate of 0.1 ml / min for 30 minutes to make the sample to be tested fully saturated. Subsequently, Mn (II) with a concentration of 200 ppm was continuously injected at a flow rate of 0.1 ml / min for 40 minutes, and then ultrapure water was injected at a flow rate of 0.1 ml / min. The total experimental time was 80 minutes. Alternatively, Mn(II) with a concentration of 200 ppm was continuously injected at a flow rate of 0.2 ml / min for 20 minutes, and then ultrapure water was injected at a flow rate of 0.1 ml / min. The total experimental time was 60 minutes to ensure that the heavy metal expulsion rate was consistent with that of another batch of experiments, focusing on comparing the effect of the injection flow rate of the heavy metal solution on the adsorption behavior of the porous material.

[0084] In addition to the displacement adsorption experiment, a static adsorption experiment was also carried out to test the adsorption capacity of the granular porous material filled inside the composite material. First, the prepared 200ppm Mn(II) standard solution was divided into two identical glass containers, and then 1g of the ground granular porous material with a mesh size of 25-30 and 12-14 was weighed and placed in the glass container to ensure that the liquid level could submerge the sample and was more than 2 cm higher. The adsorption experiment started after the sample was placed, and the timing started immediately. Every 5 minutes, 2ml of solution sample was taken out from the container with a pipette and injected into the chromatographic bottle for nuclear magnetic resonance measurement to monitor the adsorption behavior. The total duration of the experiment was 60 minutes.

[0085] S6: Monitoring and evaluating the adsorption performance of composite geopolymer materials

[0086] Displacement adsorption experiments were conducted in real time using a nuclear magnetic resonance (SFG-MSCPMG) pulse sequence to characterize the distribution of heavy metal ions within the porous material. First, the radio frequency unit of the low-field nuclear magnetic resonance instrument was turned on and the parameters were adjusted using the same steps as in S4. The SFG-MSCPMG pulse sequence (number of layers: 10) was used, and the remaining parameters were set as described in S4. Tests were conducted every 10 minutes. The Mn(II) solution concentration curve established in S4 was used to calculate the solution concentrations for different experimental groups and at different times to characterize the dynamic adsorption process.

[0087] Static adsorption experiments were conducted in real time using the SFG-MSCPMG NMR pulse sequence, with the layer selection set to 1. The overall concentration signal of the heavy metal ion solution was measured, and the remaining parameters were set as described in S4. The radio frequency unit of the low-field NMR instrument was turned on, and the parameters were adjusted using the same adjustment steps as in S4. The concentration of Mn(II) solution samples collected at the outflow end at different time points was measured. The chromatographic vial containing the sample was placed in the test coil of the low-field NMR instrument, and the concentration was measured using the SFG-MSCPMG pulse sequence.

[0088] Pore ​​structure characterization of a spare sample of cylindrical geopolymer porous material was performed. Images revealed dense pore development within the geopolymer porous material, with a total porosity of 56.2%. The largest pore diameter was approximately 1.34 mm, while the smallest pore diameter was concentrated around 0.635 mm. Overall pore connectivity was good, with a connected porosity of 50.2%. The granular porous material within the composite geopolymer porous material had a particle size of 0.6-0.71 mm (25-30 mesh), allowing it to be effectively filled within the prepared annular porous material without leakage.

[0089] Different heavy metal solution injection flow rates were set in the displacement adsorption test to compare the adsorption performance differences between cylindrical and composite geopolymer porous materials. The test method based on the nuclear magnetic resonance SFG-MSCPMG pulse sequence can obtain the heavy metal concentration distribution information inside the geopolymer porous material in real time and non-destructively. The relevant results are as follows Figure 4 shown. Figure 4 (a)-(b) are experiments in which heavy metal solution was injected at a flow rate of 0.1 ml / min. Figure 4 (a) is the concentration distribution inside the porous material at 20 minutes of experiment. Figure 4 (b) shows the heavy metal concentration at the outflow end at different times. Compared with the unmodified cylindrical porous geopolymer, the composite geopolymer material can quickly adsorb heavy metal ions in the system near the injection end, and no heavy metal ions are detected at the outflow end (e.g. Figure 4 (b)). Although the unmodified cylindrical porous geopolymer was able to remove heavy metals in the system at the beginning of the experiment, as more heavy metal ions were injected, a small amount of heavy metal ions could still be detected flowing out of the solution at the outflow end.

[0090] Figure 4 (c)-(d) are experiments in which heavy metal solution was injected at a flow rate of 0.2 ml / min. Figure 4 (c) is the concentration distribution inside the porous material at 10 minutes of the experiment. Figure 4(d) shows the heavy metal concentration at the outflow end at different times. Under faster injection conditions, the difference in adsorption performance between the two materials becomes more pronounced. Compared to slow flow rates, the composite porous material consistently and completely adsorbs the injected heavy metal ions, requiring a relatively large amount of adsorbent material. However, the cylindrical porous polymer's adsorption rate struggles to match the injection rate of the heavy metal ions, resulting in a limited amount of heavy metal outflow being detected at the outflow end.

[0091] The static adsorption experiment compared the adsorption rate and adsorption capacity of granular porous fillers with different mesh sizes. Figure 5 As shown, porous materials with larger mesh sizes (25-30), or finer particles, can more quickly and fully adsorb heavy metal ions from water due to their greater specific surface area. After 20 minutes of adsorption, the smaller porous material had a 71.1% higher adsorption capacity than the larger particle size. At the end of the experiment, the total adsorption capacity of the smaller particles was 46.4% higher than that of the larger particle size. These results demonstrate that using smaller porous materials as fillers within composite porous geopolymers can significantly improve the material's overall adsorption performance. Furthermore, removing the material after the experiment allows for the rapid separation of heavy metal pollutants from the water.

[0092] Compared with the prior art, the present invention has the following beneficial effects:

[0093] (1) The designed composite geopolymer porous material can significantly increase the specific surface area of ​​the block porous material, thereby greatly increasing the adsorption rate of heavy metals in water by the geopolymer.

[0094] (2) The designed composite geopolymer porous material helps the fluid flow into the interior of the material, allowing heavy metal ions to fully contact the internal granular porous material, significantly improving the adsorption capacity of the same mass material.

[0095] (3) The designed composite geopolymer porous material can achieve efficient removal of heavy metal ions even when the polluted water flows through it at a faster rate.

[0096] (4) The designed composite geopolymer porous material can achieve centralized and convenient separation from the water body while ensuring adsorption performance. It is particularly suitable for groundwater pollution remediation and treatment, can facilitate the long-term and effective operation of the remediation device, and can realize the recovery, regeneration and reuse of the adsorption material.

[0097] The performance evaluation method of the composite porous geopolymer for heavy metal adsorption of the present invention can obtain concentration distribution information inside the geopolymer material. The detection data can be used to analyze the dynamic characteristics and spatial differences of the adsorption process. It plays an important role in exploring the influence of the pore structure of the porous geopolymer material on the heavy metal adsorption behavior. It can not only comprehensively evaluate the adsorption performance of different materials, but also be used to improve the synthesis and preparation process of the porous geopolymer material, thereby obtaining a porous geopolymer with better performance for the adsorption of heavy metals in water bodies.

[0098] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes can be made to these embodiments without departing from the principles and spirit of the invention. The scope of application of the present invention is defined by the following claims and their equivalents.

Claims

1. A method for evaluating the performance of a composite porous geopolymer for heavy metal adsorption, characterized in that: The performance evaluation method includes: Step 1: Prepare heavy metal solutions of different concentrations; Step 2: Establish a line between the concentration of heavy metal solution and the NMR signal; Step 3: Conduct adsorption experiments on multiple batches of composite porous geopolymer materials based on nuclear magnetic resonance technology; Step 4: Monitor and evaluate the adsorption performance of the composite porous geopolymer; The step 1 comprises: Prepare 500 ml of a heavy metal solution with a concentration of 1000 ppm in a flask as a standard solution; A certain amount of solution was gradually taken out into a 10 ml glass bottle using a pipette, and heavy metal solutions of different concentrations were prepared by adding different volumes of ultrapure water; The step 2 includes: Use nuclear magnetic resonance pulse sequence to measure heavy metal standard solutions with different concentrations to obtain T2 values; Establish the relationship between heavy metal ion concentration and nuclear magnetic signal [1 / T 2,i -1 / T 2,0 ], that is, to determine the marking line, where T 2,i is the measured transverse relaxation time, ms; T 2,0 is the transverse relaxation time of ultrapure water, ms; The step 3 comprises: placing porous geopolymer samples of different forms in a nuclear magnetic resonance holder in sequence, first saturating them with ultrapure water, then injecting heavy metal ion solutions of the same concentration at the same flow rate, and monitoring the concentration distribution characteristics and dynamic changes of the heavy metal solution inside the sample in real time based on nuclear magnetic resonance technology.

2. The performance evaluation method for composite porous geopolymer for heavy metal adsorption according to claim 1, characterized in that: The step 2 includes: Turn on the radio frequency switch of the low-field nuclear magnetic resonance instrument, use the oil sample to adjust the main frequency and sampling frequency, adjust the initial parameters, and in the SFG-MSCPMG pulse sequence, set the repeated sampling wait time to 6000ms, the echo time to 0.2ms, the number of echoes to 8000, the number of layers to 1, and the number of accumulations to 2; Use this sequence to test heavy metal solution samples with different concentrations and obtain the corresponding T2 values. The correlation between the concentration of the heavy metal solution and T2 is shown in the following formula: Where C is the concentration of heavy metal solution, mM; R is the transverse relaxation rate, mM·s -1 ;T 2,i is the measured transverse relaxation time, ms; T 2,0 is the transverse relaxation time of ultrapure water, ms.

3. The method for evaluating the performance of a composite porous geopolymer for heavy metal adsorption according to claim 1, wherein: The transverse relaxation time T2 was measured using the SFG-MSCPMG pulse sequence based on the constant gradient encoding technique.

4. The method for evaluating the performance of a composite porous geopolymer for heavy metal adsorption according to claim 3, wherein: The step 3 further includes: collecting the effluent at the outlet of the holder, and performing a static measurement of the heavy metal concentration every time 2 milliliters are collected; and converting the nuclear magnetic resonance measurement data into the concentration of heavy metal ions in the effluent at different times in combination with the established heavy metal ion concentration line, thereby quantifying and evaluating the adsorption behavior of different forms of porous geopolymer samples.

5. The method for evaluating the performance of a composite porous geopolymer for heavy metal adsorption according to claim 4, wherein: Computed tomography and scanning electron microscopy were used to characterize the structure of porous geopolymer samples, analyze the porosity, pore size distribution, and connectivity, and establish the correlation between pore structure and adsorption performance.

6. The method for evaluating the performance of a composite porous geopolymer for heavy metal adsorption according to claim 5, wherein: In step 3, different types of porous geopolymer samples were placed in the NMR holder to conduct displacement adsorption experiments to characterize the adsorption properties of different materials, including: Use a pipette to remove 80 ml of the 1000 ppm standard solution and add 320 ml of ultrapure water to prepare a total volume of 400 ml of the 200 ppm standard solution for adsorption experiments; Before each displacement adsorption experiment, ultrapure water was injected at a flow rate of 0.1 ml / min for 30 min to make the sample to be tested fully saturated; Subsequently, a standard solution with a concentration of 200 ppm was continuously injected at a flow rate of 0.1 ml / min for 40 minutes, and then ultrapure water was injected at a flow rate of 0.1 ml / min. The total experimental time was 80 minutes; or a standard solution with a concentration of 200 ppm was continuously injected at a flow rate of 0.2 ml / min for 20 minutes, and then ultrapure water was injected at a flow rate of 0.1 ml / min. The total experimental time was 60 minutes.

7. The performance evaluation method for a composite porous geopolymer for heavy metal adsorption according to claim 5, characterized in that: In step 3, a static adsorption experiment is performed to test the adsorption capacity of the granular porous material of the composite porous geopolymer, including: The prepared 200 ppm standard solution was divided into two identical glass containers; Then, 1g of each of the ground granular porous materials with mesh sizes of 25-30 and 12-14 was weighed and placed in a glass container, ensuring that the liquid level could submerge the sample and be at least 2cm higher; The timing started immediately after the sample was placed in the container. Every 5 minutes, 2 ml of solution sample was taken out from the container with a pipette and injected into the chromatographic bottle for nuclear magnetic resonance measurement to monitor the adsorption behavior. The total experimental time was 60 minutes.

Images