Calcium-iron bimetallic modified pumice, and preparation method and application thereof

Abstract

The application discloses calcium-iron bimetal modified pumice, a preparation method and application thereof, and belongs to the field of environmental functional materials for sewage treatment. The preparation method is as follows: after mixing an aqueous solution of calcium chloride hexahydrate and ferric chloride trihydrate, the mixture is uniformly mixed with cleaned pumice to obtain a solid-liquid mixture; sodium hydroxide solution is added dropwise into the solid-liquid mixture, and the pH value of the solution is adjusted to 11-12; then, stirring is carried out under heating conditions to promote the loading of calcium and iron ions on the surface of the pumice; after the reaction is completed, the solid is separated from the mixed system, and the calcium-iron bimetal modified pumice is obtained after cleaning and drying. The prepared adsorption material has the advantages of not being easy to be lost and being simple to apply, and can reduce phosphorus pollution in water.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials for wastewater treatment, specifically relating to a calcium-iron bimetallic modified pumice, its preparation method, and its application. Background Technology

[0002] Nutrient loss during agricultural production is a major source of nutrient surplus in farmland, aquatic, and wetland ecosystems, and therefore a major cause of non-point source pollution. Agricultural non-point source pollution is complex in its causes, highly random, widespread in time and space, and has a long latency period, making its impact on the water environment increasingly prominent. Compared to physical and chemical methods, ecological control technologies play a crucial role in the removal of non-point source pollutants such as phosphorus. These technologies can fully utilize native ecosystems, have advantages such as low investment and operating costs, and are less likely to cause secondary pollution, making them suitable for small-scale wastewater treatment.

[0003] To enhance phosphorus removal efficiency, phosphorus removal modules filled with adsorption materials can be installed in ecological ditches, combining adsorption methods with ecological ditches. Currently, commonly used adsorption materials include solid waste, minerals, organic-inorganic composite materials, metal hydroxides, and carbon-based materials. Adsorption methods have gained significant attention in wastewater phosphorus removal and have been widely applied in the removal of phosphorus pollution from agricultural runoff due to their advantages such as simple process, ease of operation, low sludge production, wide applicable phosphorus concentration range, low energy consumption, small footprint, and regenerable adsorption materials.

[0004] Natural pumice is a porous volcanic rock, mainly composed of silicon dioxide. It is lighter than water, has good strength, and is corrosion-resistant. However, natural pumice has relatively few adsorption sites, so it is often modified with other materials. Studies have shown that iron modification can effectively enhance the adsorption performance of pumice, while calcium, with its environmental friendliness, wide availability, and natural occurrence, can synergistically enhance phosphorus removal through chemical precipitation. However, existing research mainly focuses on iron-modified systems, and exploration of calcium-iron bimetallic synergistic modification remains lacking. Furthermore, there is a lack of comparison regarding the differences in phosphorus removal performance of different carriers (pumice, expanded perlite, and lightweight ceramsite) under the same modification process. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies, specifically addressing the problems of low strength of existing adsorbents, their susceptibility to being washed away by water flow in actual farmland ditches, leading to material loss. This invention provides a calcium-iron bimetallic modified pumice, its preparation method, and its applications. This invention uses an alkaline co-precipitation method to synergistically load calcium and iron onto the surface of the pumice, which not only enhances the material's phosphorus adsorption capacity but also utilizes the inherent stability of the pumice, making it more suitable for phosphorus removal applications in aquatic environments.

[0006] The specific technical solution adopted in this invention is as follows: In a first aspect, the present invention provides a method for preparing calcium-iron bimetallic modified pumice, as detailed below: S1: Mix the aqueous solutions of calcium chloride hexahydrate and ferric chloride trihydrate, and then mix them evenly with the cleaned pumice to obtain a solid-liquid mixture; S2: Add sodium hydroxide solution dropwise to the solid-liquid mixture to adjust the pH of the solution to 11-12; then stir under heating conditions to promote the loading of calcium and iron ions on the surface of the pumice. S3: After S2 reaction is complete, the solid is separated from the mixture, washed and dried to obtain calcium-iron bimetallic modified pumice.

[0007] Preferably, in S1, the molar ratio of calcium ions to iron ions in the solid-liquid mixture is 2:1.

[0008] Preferably, in step S1, the cleaning method for the pumice is to rinse the surface of the natural pumice with deionized water until it is clean.

[0009] Preferably, in S1, the solid-liquid ratio in the solid-liquid mixture is 20%.

[0010] Preferably, in step S2, the heating temperature is 85°C.

[0011] Preferably, in step S2, the stirring speed is 400-600 r / min and the stirring time is 4h.

[0012] Preferably, in S2, the concentration of the sodium hydroxide solution is 5 M.

[0013] Preferably, in step S3, ultrapure water is used for washing until the pH of the eluent is 7.0 ± 0.5.

[0014] In a second aspect, the present invention provides a calcium-iron bimetallic modified pumice obtained by any of the preparation methods described in the first aspect.

[0015] Thirdly, the present invention provides an application of calcium-iron bimetallic modified pumice as described in the second aspect in phosphorus removal from farmland ditch drainage.

[0016] Compared with the prior art, the present invention has the following advantages: This invention prepares calcium-iron bimetallic modified pumice by adding calcium and iron elements to the surface of natural pumice, effectively improving the material's phosphorus adsorption capacity and giving the material advantages such as low leaching and ease of application. The calcium-iron bimetallic modified pumice obtained by this invention removes phosphorus pollution through adsorption such as precipitation, and is suitable for treating phosphorus pollution in farmland ditch drainage. Attached Figure Description

[0017] Figure 1A comparison of the phosphorus adsorption performance of calcium-iron bimetallic modified pumice, calcium-iron bimetallic modified expanded perlite, and calcium-iron bimetallic modified lightweight ceramsite. Figure 2 The XRD pattern of calcium-iron bimetallic modified pumice; Figure 3 The microstructure and surface element distribution of calcium-iron bimetallic modified pumice; Figure 4 The effect of phosphorus removal from wastewater under different pH conditions; Figure 5 The phosphorus removal efficiency in wastewater under different time conditions; Figure 6 The effect of phosphorus removal from wastewater under different initial concentration conditions; Figure 7 The removal efficiency of different forms of phosphorus in wastewater. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the present invention can be combined accordingly without mutual conflict.

[0019] This invention provides a method for preparing calcium-iron bimetallic modified pumice. The resulting adsorbent material has advantages such as low leaching and ease of application, and can reduce phosphorus pollution in water bodies. The preparation method specifically includes the following steps: Step 1: Solution preparation: An aqueous solution of calcium chloride hexahydrate and ferric chloride trihydrate was mixed in a large beaker and then mixed evenly with cleaned pumice to obtain a solid-liquid mixture.

[0020] In a preferred embodiment of the present invention, the molar ratio of calcium ions to iron ions in the solid-liquid mixture is 2:1.

[0021] As a preferred embodiment of the present invention, the cleaning method of the pumice is: rinsing the surface of the natural pumice with deionized water until clean.

[0022] In a preferred embodiment of the present invention, the solid-liquid ratio in the solid-liquid mixture (i.e., the aqueous solution of pumice with calcium chloride hexahydrate and ferric chloride trihydrate) is 20%.

[0023] Step 2, Precipitation reaction: Slowly add sodium hydroxide solution dropwise to the solid-liquid mixture obtained in step one to adjust the pH of the solution to 11-12. Then, use a magnetic stirrer to heat and vigorously stir the mixture at the set temperature and speed to promote the loading of calcium and iron ions onto the surface of the pumice.

[0024] In a preferred embodiment of the present invention, the heating temperature is 85°C; the stirring speed is 400-600 r / min; and the stirring time is 4 h.

[0025] In a preferred embodiment of the present invention, the concentration of the sodium hydroxide solution is 5 M.

[0026] Step 3: Purification process: After the reaction in step two is complete, the solid is separated from the mixture, washed and dried to obtain calcium-iron bimetallic modified pumice.

[0027] As a preferred embodiment of the present invention, ultrapure water can be used for washing until the pH of the eluent is 7.0±0.5.

[0028] This invention prepares a calcium-iron bimetallic modified pumice material by loading calcium and iron elements onto the surface of natural pumice. This material exhibits excellent adsorption performance for phosphate ions through precipitation, significantly improving the material's phosphorus removal efficiency. The calcium-iron bimetallic modified pumice obtained by this invention has advantages such as low cost, good stability, and ease of operation, making it suitable for phosphorus pollution treatment in agricultural ditch drainage.

[0029] The embodiments of the present invention will be described in detail below. The following embodiments are implemented based on the technical solution of the present invention, and detailed implementation schemes and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0030] Example 1 This embodiment prepares a calcium-iron bimetallic modified pumice, the preparation method of which includes the following steps: Step 1: Solution preparation: Mix a solution of 0.4 M calcium chloride hexahydrate and 0.2 M ferric chloride trihydrate in a large beaker, ensuring a Ca / Fe molar ratio of 2:1. Add cleaned pumice until the solid-liquid ratio reaches 20%, and mix thoroughly to obtain a solid-liquid mixture.

[0031] Step 2, Precipitation reaction: Slowly add 5 M sodium hydroxide solution dropwise to the solid-liquid mixture obtained in step one to adjust the pH of the solution to 11. Heat and vigorously stir the mixture at 85°C and 500 r / min using a magnetic stirrer for 4 hours to load calcium and iron ions onto the surface of the pumice.

[0032] Step 3: Purification process: After the reaction was complete, the modified pumice was separated from the mixture. The modified pumice was washed with ultrapure water until the pH of the eluent was 7.0. After drying in an oven at 65°C, calcium-iron bimetallic modified pumice was obtained.

[0033] To systematically evaluate the advantages of pumice carrier in phosphorus adsorption performance of the modified material of this invention, it was compared in parallel with two other porous materials with buoyancy properties—expanded perlite and lightweight ceramsite. All three materials were modified using the calcium-iron bimetallic modification process described in Example 1 (calcium-iron molar ratio 2:1, co-precipitation at 85°C for 4 h, pH=11) to ensure consistent modification conditions and strong comparability.

[0034] The effects of the three modified materials were verified, as follows: 1) The initial phosphorus concentration (Cp,0) in the wastewater to be treated was set to 5.0 mg / L. -1 The three modified materials were added to wastewater at a dosage of 30 g / L. -1 The mixture was shaken at 25℃ and 120 rpm for 12 h. After adsorption, an appropriate amount of supernatant was placed in a colorimetric tube, and the concentration of phosphorus in the supernatant was determined by the molybdenum blue colorimetric method at a wavelength of 700 nm. The phosphorus removal rate of the material was calculated based on the concentration of the supernatant.

[0035] Experimental results are as follows Figure 1 As shown, under the same calcium-iron modification conditions and experimental parameters, the phosphorus removal capabilities of the three carriers differed significantly. The calcium-iron bimetallic modified pumice of this invention exhibited the highest removal rate, reaching approximately 77%, significantly higher than that of calcium-iron bimetallic modified expanded perlite (59.12%), while the modified lightweight ceramsite had the lowest removal rate, at only 22.28%. Therefore, the calcium-iron bimetallic modified pumice significantly outperforms expanded perlite and lightweight ceramsite in phosphorus adsorption performance, demonstrating a more efficient phosphorus removal capacity, giving it a clear advantage in practical water body phosphorus removal applications such as farmland ditches.

[0036] 2) X-ray diffraction (XRD) characterization The modified and adsorbed materials prepared in Example 1 were characterized by XRD, and the results are as follows: Figure 2 As shown. XRD characterization results confirmed that the main component of the natural pumice used in this invention is albite (NaAlSi3O2). The peak intensity of albite increased in the XRD spectrum after adsorption, which may indicate that some effective components of the calcium-iron bimetallic modified pumice were lost during the adsorption process. Comparison of the XRD spectra before and after adsorption revealed the presence of calcium silicate hydrate (Ca3(SiO3OH)2·2H2O) and calcium-iron-aluminum silicate (CaFe4Al2Si7O2). 22The structure of (OH)2 is consumed in the adsorption reaction, which indicates that calcium silicate hydrate and calcium iron aluminum silicate play an important role in the adsorption process and may be the active components for phosphorus removal.

[0037] 3) Characterization by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) SEM image of natural pumice used in Example 1 ( Figure 3 a) shows that its surface is covered with a large number of micropores, exhibiting a rich pore structure. The porosity is significant, with the pore volume accounting for more than 50% of the total volume. This porous structure provides a large specific surface area, which is beneficial for adsorbing pollutants. SEM image of the calcium-iron bimetallic modified pumice prepared in Example 1 ( Figure 3 b) indicates that a large number of pores remain on its surface, and discrete particulate matter was observed on the surface. Compared with the XRD characterization results, these particles were identified as calcium silicate hydrate (Ca3(SiO3OH)2·2H2O) and calcium iron aluminum silicate (CaFe4Al2Si7O). 22 (OH)₂) crystallization product. Uniformly dispersed particles significantly increased the number of adsorption sites in the modified pumice. The formation of calcium silicate not only improved the mechanical stability of the material but also introduced additional functional groups, further enhancing its adsorption capacity. Adsorption experiments further confirmed the effectiveness of the modified pumice. SEM images after adsorption (…) Figure 3 c) shows that a large number of pores are blocked by adsorbed particles, indicating that phosphorus has been successfully bound to the adsorption sites. This demonstrates that the modification process effectively enhances the material's ability to capture and retain phosphorus. Meanwhile, EDS images ( Figure 3 d) indicates that the modified pumice before adsorption already contains elements such as Ca and Fe, which is consistent with the XRD results, indicating that Ca and Fe have been successfully loaded onto the pumice.

[0038] 4) To verify the good adaptability of calcium-iron bimetallic modified pumice under different pH conditions, the following experiments were conducted: The initial phosphorus concentration (Cp,0) in the wastewater to be treated was set to 5.0 mg / L. -1 The solution pH gradient was 2-11. The calcium-iron bimetallic modified pumice prepared in Example 1 was added to the wastewater at a dosage of 30 g / L. -1 The mixture was shaken at 25℃ and 120 rpm for 12 h. After adsorption, an appropriate amount of supernatant was placed in a colorimetric tube, and the concentration of phosphorus in the supernatant was determined by the molybdenum blue colorimetric method at a wavelength of 700 nm. The phosphorus removal rate of the material was calculated based on the concentration of the supernatant.

[0039] Experimental results are as follows Figure 4As shown, the phosphorus removal rate of CFMP is about 77% at pH 7; when the pH exceeds 8, the removal rate decreases significantly, but it still maintains a high adsorption efficiency even in alkaline environments with pH greater than 8. This indicates that calcium-iron bimetallic modified pumice has good adaptability under different pH conditions.

[0040] 5) To investigate the adsorption mechanism of calcium-iron bimetallic modified pumice, the following experiments were conducted: The initial phosphorus concentration in the wastewater to be treated was 5 mg / L. -1 The amount of calcium-iron bimetallic modified pumice prepared in Example 1 was 30 g / L. -1 The oscillation time was set to 30, 60, 120, 240, 480, 720, 1080, 1440, and 2880 min, and the amount of calcium-iron bimetallic modified pumice added was 30 g / L. -1 The mixture was shaken at 25℃ and 120 rpm. After adsorption, an appropriate amount of supernatant was placed in a colorimetric tube, and the concentration of phosphorus in the supernatant was determined using the molybdenum blue colorimetric method at a wavelength of 700 nm. The phosphorus removal rate of the calcium-iron bimetallic modified pumice was calculated based on the measured concentration of the supernatant.

[0041] Experimental results are as follows Figure 5 As shown, the adsorption rate is relatively fast in the initial stage, and then tends to stabilize. Compared with the pseudo-first-order kinetic model, the pseudo-second-order kinetic model can more accurately describe the adsorption behavior of modified pumice on phosphate, indicating that the adsorption of phosphorus by the material prepared in this invention is mainly chemisorption. After adsorption equilibrium, the phosphorus adsorption capacity of the material reaches 204.56 mg / kg. -1 .

[0042] The initial phosphorus concentration in the wastewater to be treated was 5 mg / L. -1 The amount of calcium-iron bimetallic modified pumice added was 30 g / L. -1 The initial phosphorus concentrations were set to 1, 5, 10, 20, 35, 50, and 100 mg L. -1 The temperatures were 25℃, 35℃, and 45℃, and the amount of calcium-iron bimetallic modified pumice added was 30 g / L. -1 The mixture was shaken at 25℃, 120 rpm, and for 12 hours. After adsorption, an appropriate amount of the supernatant was placed in a colorimetric tube, and the concentration of phosphorus in the supernatant was determined using the molybdenum blue colorimetric method at a wavelength of 700 nm. The phosphorus removal rate of the calcium-iron bimetallic modified pumice was calculated based on the measured concentration of the supernatant.

[0043] Experimental results are as follows Figure 6As shown, compared to the Langmuir model, the Freundlich model can more accurately describe the adsorption isotherm equilibrium of phosphate by modified pumice, indicating that the adsorption behavior of phosphate by modified pumice is a complex multi-molecular adsorption. Modified pumice at 25℃ and 100 mg-PL... -1 Under the given conditions, the adsorption capacity reached 424.9 mg / kg. -1 This indicates that the material has good adsorption properties.

[0044] 6) To investigate the removal performance of calcium-iron bimetallic modified pumice under real-world conditions, the following experiments were conducted: The experiment used actual farmland ditch drainage samples, with a total phosphorus concentration of 0.30 mg / L. -1 The concentration of particulate phosphorus (PP, 450-1000 nm) was 0.22 mg / L. -1 The concentration of medium colloidal phosphorus (MCP, 220-450 nm) was 0.024 mg / L. -1 The concentration of fine colloidal phosphorus (FCP, 3 kDa - 220 nm) was 0.017 mg / L. -1 The concentration of truly soluble phosphorus (Truly DP, < 3 kDa) was 0.043 mg / L. -1 The amount of calcium-iron bimetallic modified pumice obtained in Example 1 was 30 g / L. -1 The mixture was shaken at 25℃, 120 rpm, and for 12 hours. After adsorption, an appropriate amount of the supernatant was placed in a colorimetric tube, and the concentration of phosphorus in the supernatant was determined using the molybdenum blue colorimetric method at a wavelength of 700 nm. The phosphorus removal rate of the calcium-iron bimetallic modified pumice was calculated based on the measured concentration of the supernatant.

[0045] Experimental results are as follows Figure 7 As shown, the average removal rates of total phosphorus, particulate phosphorus, medium colloidal phosphorus, fine colloidal phosphorus, and truly soluble phosphorus by calcium-iron bimetallic modified pumice were 92.85%, 85.84%, 83.51%, 83.82%, and 92.01%, respectively. Calcium-iron bimetallic modified pumice exhibited excellent phosphorus removal performance in actual farmland ditch drainage treatment. Truly soluble phosphorus was easily adsorbed directly by the active sites on the CFMP surface due to its free dissolution characteristics, while particulate and colloidal phosphorus were removed through a synergistic process of electrostatic attraction, physical interception, and chemical complexation.

[0046] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for preparing calcium-iron bimetallic modified pumice, characterized in that, Specifically as follows: S1: Mix the aqueous solutions of calcium chloride hexahydrate and ferric chloride trihydrate, and then mix them evenly with the cleaned pumice to obtain a solid-liquid mixture; S2: Add sodium hydroxide solution dropwise to the solid-liquid mixture to adjust the pH of the solution to 11-12; then stir under heating conditions to promote the loading of calcium and iron ions on the surface of the pumice. S3: After S2 reaction is complete, the solid is separated from the mixture, washed and dried to obtain calcium-iron bimetallic modified pumice.

2. The method for preparing calcium-iron bimetallic modified pumice according to claim 1, characterized in that, In S1, the molar ratio of calcium ions to iron ions in the solid-liquid mixture is 2:

1.

3. The method for preparing calcium-iron bimetallic modified pumice according to claim 1, characterized in that, In S1, the cleaning method for the pumice is to rinse the surface of the natural pumice with deionized water until it is clean.

4. The method for preparing calcium-iron bimetallic modified pumice according to claim 1, characterized in that, In S1, the solid-liquid ratio in the solid-liquid mixture is 20%.

5. The method for preparing calcium-iron bimetallic modified pumice according to claim 1, characterized in that, In step S2, the heating temperature is 85°C.

6. The method for preparing calcium-iron bimetallic modified pumice according to claim 1, characterized in that, In step S2, the stirring speed is 400-600 r / min and the stirring time is 4h.

7. The method for preparing calcium-iron bimetallic modified pumice according to claim 1, characterized in that, In S2, the concentration of sodium hydroxide solution is 5 M.

8. The method for preparing calcium-iron bimetallic modified pumice according to claim 1, characterized in that, In step S3, ultrapure water is used for washing until the pH of the eluent is 7.0 ± 0.

5.

9. A calcium-iron bimetallic modified pumice obtained by the preparation method according to any one of claims 1 to 8.

10. An application of the calcium-iron bimetallic modified pumice according to claim 9 in phosphorus removal from farmland ditch drainage.

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