A lanthanum-containing phosphorus-locking agent, its preparation method and its application

Abstract

This invention discloses a lanthanum-containing phosphorus-locking agent, its preparation method, and its application, belonging to the technical field of black and odorous water body treatment. Its key technical points are: it is a mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel microsphere, characterized by a "core-shell" structure: the core structure is mesoporous lanthanum oxide, with mesopores of 3-6 nm forming inside; the shell structure is sodium alginate / chitosan gel; both the functional microorganism and the mesoporous lanthanum oxide are encapsulated within the shell structure; the surface of the shell structure also has through-pores with a pore size of 50-200 nm.

Description

Technical Field

[0001] This invention relates to the technical field of black and odorous water treatment, and more specifically, to a lanthanum-containing phosphorus-locking agent, its preparation method, and its application. Background Technology

[0002] Phosphorus is a significant pollutant in polluted and odorous water bodies. Due to the low dissolved oxygen concentration in these water bodies, phosphorus bound to iron oxides in sediments is released into the water, leading to an increase in phosphorus concentration. This phosphorus stimulates algae growth, and the decomposition of dying algae consumes large amounts of dissolved oxygen and forms black and odorous substances such as methane, hydrogen sulfide, and ammonia, further exacerbating the pollution. Therefore, phosphorus control is a crucial task in the treatment of polluted and odorous water bodies.

[0003] Adding phosphorus-locking agents is a widely accepted method for controlling phosphorus in water bodies in recent years. The Al in phosphorus-locking agents... 3+ Ca 2+ Or La 3+ Can be used with PO4 3- It can form precipitates or complexes, thereby effectively reducing the phosphorus concentration in water. At the same time, the phosphorus-locking agent can form a passivation layer at the sediment-water interface, preventing the release of phosphorus from the sediment into the overlying water.

[0004] Among various phosphorus-locking agents, lanthanum-containing phosphorus-locking agents have shown the most superior performance. In this class of phosphorus-locking agents, La... 3+ Can be used with PO4 3- It forms a very stable precipitate, and its effect is not affected by the external environment (pH and DO, etc.).

[0005] like:

[0006] Reference 1: AU8938198A, which developed Phoslock lanthanum-containing phosphorus-locking agent (LMB). Its phosphorus removal principle is to form an insoluble lanthanum-phosphate complex with free phosphate in water by lanthanum metal, thereby locking the phosphate in bentonite.

[0007] Reference 2: "Tian Liming. Preparation of Lanthanum-Loaded Phosphorus Locking Agent in Volcanic Ash and Its Inhibitory Effect on Phosphorus Release from Jiuli Lake Bottom Mud [D] China University of Mining and Technology, 2023" A NaOH-La modified volcanic ash phosphorus locking agent loaded with lanthanum was developed. Based on scanning electron microscopy (SEM) analysis, it was found that acidification treatment increased the surface roughness and pore number of the volcanic ash, increasing its specific surface area, and that lanthanum was loaded onto the modified volcanic ash surface and distributed relatively uniformly.

[0008] Reference 3: CN116177723A discloses a slow-release biological filter material for removing heavy metals / locking phosphorus, its preparation method and application. It is a clay mineral with montmorillonite as the main component. The cation in calcium-based bentonite is mainly calcium ion, which can also form calcium phosphate precipitate with phosphate ion. It also has a certain adsorption and slow-release effect on lanthanum chloride heptahydrate, thus prolonging the slow-release period of lanthanum chloride heptahydrate.

[0009] Reference 4: CN112237897B discloses a layered bimetallic lanthanum nanomaterial, its preparation method and application, which has a better phosphorus removal effect.

[0010] Therefore, the main research and development direction of existing lanthanum-containing phosphorus-locking agents is on how to improve phosphorus removal efficiency. However, when using lanthanum-containing phosphorus-locking agents to treat black and odorous water bodies, the following issues need to be considered:

[0011] (1) High concentrations of organic matter in black and odorous water bodies compete for effective adsorption sites on the surface of phosphorus-locking agents, resulting in a significant decrease in the phosphorus control performance of lanthanum-containing phosphorus-locking agents.

[0012] (2) To remove organic pollutants and odorous substances from black and odorous water bodies, it is necessary to use microorganisms to biodegrade these substances. However, microbial agents are often lost due to water flow and also suffer from problems such as low viable bacterial count and poor bacterial stability, which affect the remediation effect of black and odorous water bodies. Therefore, how to fix microorganisms is also a technical problem. Summary of the Invention

[0013] The purpose of this application is to provide a lanthanum-containing phosphorus-locking agent to address the shortcomings of the prior art.

[0014] Another objective of this application is to provide a method for preparing a lanthanum-containing phosphorus-locking agent.

[0015] Another objective of this application is to provide an application of a lanthanum-containing phosphorus-locking agent in the treatment of black and odorous water bodies.

[0016] The technical solution of this application is as follows:

[0017] A lanthanum-containing phosphorus-locking agent is a mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel microsphere, the microsphere having a "core-shell" structure:

[0018] The core structure is mesoporous lanthanum oxide, and mesoporous lanthanum oxide has mesopores with a pore size of 3~6 nm inside;

[0019] The shell structure is sodium alginate / chitosan gel;

[0020] Both the functional microorganisms and the mesoporous lanthanum oxide are encapsulated within the shell structure.

[0021] The shell structure also has through holes on its surface, with the diameter of the through holes being 50~200 nm.

[0022] Furthermore, the sodium alginate / chitosan gel is a polymer network; the polymer network is formed by chitosan and sodium alginate under the action of CaCl2.

[0023] Furthermore, the diameter of the mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel microspheres is between 1 mm and 2 mm.

[0024] Furthermore, the functional microorganisms are located between the mesoporous lanthanum oxide and the sodium alginate / chitosan gel.

[0025] Furthermore, in a dry state, the specific surface area of ​​the lanthanum-containing phosphorus-locking agent is 100~200 m². 2 Between / g.

[0026] Furthermore, based on phosphorus element, the phosphorus adsorption capacity of the lanthanum-containing phosphorus-locking agent is 8~25 mg / g; the organic matter degradation capacity is characterized by the COD removal rate during water purification, and for water bodies with COD less than 100 mg / L, the COD removal rate can reach 60~85%.

[0027] A method for preparing a lanthanum-containing phosphorus-locking agent includes the following steps:

[0028] S100, preparation of mesoporous lanthanum oxide; S100 includes sub-steps S101~S103;

[0029] S101, use 1% (v / v) hydrochloric acid to prepare La solution with a concentration of 0.5~2 mol / L. 3+ An aqueous solution was prepared in which cetyltrimethylammonium bromide (CTAB) was dissolved as a template agent. The concentration of CTAB was close to its solubility, which was 13 g / L.

[0030] S102, using a 0.5–6 mol / L NaOH solution, KOH solution, or ammonia solution, titrate La at a rate of 0.1–0.5 mL / min. 3+ —CTAB solution was used to raise the pH of the mixture to 6-8, and stirring was continued for more than 4 hours.

[0031] S103, after centrifuging the mixture, the solid is transferred to a Soxhlet extractor and reacted with a 9:1 or 8:2 ethanol-water mixture (i.e., the ratio of ethanol to water is 9:1 or 8:2) for 4-8 hours to remove the template agent; then dried to obtain mesoporous lanthanum oxide.

[0032] S200, Preparation of mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel microspheres, which includes sub-steps S201~S203;

[0033] S201, prepare an aqueous solution of sodium alginate with a concentration of 2~20 g / L (i.e., 2~20 g of sodium alginate per liter of solution); add mesoporous lanthanum oxide obtained from S100 to it and mix, the mass concentration of mesoporous lanthanum oxide is 5~10 g of mesoporous lanthanum oxide per liter of solution; then, add functional bacterial solution, stir evenly, and obtain suspension A;

[0034] S202, prepare a chitosan solution with a mass concentration of 5~15 g / L (i.e., 5~15 g of chitosan per liter of solution), and add CaCl2 to make its concentration reach 2~20 g / L (i.e., 2~20 g of CaCl2 per liter of solution), forming solution B;

[0035] S203, while maintaining stirring, use a peristaltic pump to add suspension A dropwise to solution B at a rate of 0.5-1.5 mL / min; the volume ratio of solution A to solution B is 1:1.

[0036] S204, in 4 o Crosslinking at C for 24 hours forms a sodium alginate / chitosan gel with a semi-interpenetrating structure, encapsulating mesoporous lanthanum oxide and functional microorganisms within it.

[0037] Furthermore, the La used in S101 3+ The salt is any one or more of LaCl3 and LaNO3.

[0038] Furthermore, the S103 mesoporous lanthanum oxide product is dried by baking or freeze-drying, with the baking temperature being 45~65°C. o C.

[0039] Furthermore, suspension A and solution B during the titration process should be kept stirred, including mechanical stirring and magnetic stirring. The stirring rate should ensure that mesoporous lanthanum oxide does not precipitate, but it should not be too fast, which would affect the stability of the hydrogel particles in solution B and the immobilization of microorganisms. It should be controlled between 100 and 300 r / min.

[0040] Furthermore, the functional microbial solutions used are commercially available compound microbial solutions, specifically including, but not limited to, Bacillus, photosynthetic bacteria, lactic acid bacteria, and nitrifying bacteria. The functions of the encapsulated microorganisms include oxygen production, organic matter degradation, and ammonia nitrogen removal. The OD (dose distribution) of the compound microbial solutions was measured spectrophotometrically before use. 600 The cell concentration should be calculated based on the absorbance at λ=600nm, and should be greater than 1×10⁻⁶. 6cell / ml. When preparing suspension A, the amount of bacterial solution added is 0.5~10 g / L.

[0041] An application of the aforementioned lanthanum-containing phosphorus-locking agent in the treatment of black and odorous water bodies.

[0042] The beneficial effects of this application are as follows:

[0043] First, this application provides a lanthanum-containing phosphorus-locking agent that also has the function of degrading black and odorous substances. The mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel microspheres obtained in this application have a "core-shell" structure and are a lanthanum-containing phosphorus-locking agent that also has the function of degrading black and odorous substances.

[0044] Mesoporous lanthanum oxide is the "core" of this material. Under the action of the pore-forming agent CTAB, mesopores with a pore size of 3-6 nm are formed inside the lanthanum oxide. This pore size only allows phosphate ions (with an ion diameter of approximately 0.5 nm) to diffuse in, while organic matter such as humic substances and extracellular polymers of microorganisms in the water cannot enter. This ensures that the phosphorus-controlling sites on the "inner" surface of the lanthanum oxide particles are not occupied by organic matter in the water, thus maintaining its phosphorus-locking ability in black and odorous water environments with high organic matter content.

[0045] The sodium alginate / chitosan gel particles encapsulating functional microorganisms form the "shell" of this material. Microorganisms immobilized within the hydrogel can effectively remove black and odorous substances from the aquatic environment, reducing their adverse effects on the phosphorus control of mesoporous lanthanum oxide. The sodium alginate / chitosan hydrogel (i.e., the polymer network) has a semi-interpenetrating structure, making it relatively stable. The pore size of the "shell" layer is 50–200 nm, facilitating microbial attachment while not hindering phosphate from entering the mesoporous lanthanum oxide "core."

[0046] By organically combining lanthanum-containing phosphorus-locking agents with immobilized microbial technology to form a "core-shell" structure, the removal of organic pollutants from black and odorous water bodies was achieved, while minimizing their adverse effects on the function of the lanthanum-containing phosphorus-locking agents.

[0047] Secondly, the lanthanum-containing phosphorus-locking agent developed in this application has the following three effects when applied to the treatment of black and odorous water bodies:

[0048] (1) Good black and odor elimination ability: Black and odorous substances in water can be degraded by functional microorganisms immobilized in the sodium alginate / chitosan "shell";

[0049] (2) Super strong phosphorus fixation ability: Phosphate in water can diffuse freely through the sodium alginate / chitosan "shell" to the surface of lanthanum oxide, and then enter the interior of lanthanum oxide through mesopores to form lanthanum phosphate minerals with lanthanum atoms, permanently fixing phosphorus and eliminating the risk of algal blooms.

[0050] (3) The elimination of black and odorous substances and the phosphorus fixation ability are coordinated: the sodium alginate / chitosan "shell" eliminates black and odorous substances and prevents them from competing for phosphorus fixation sites on the surface of lanthanum oxide, while not hindering the passage of phosphate; the mesoporous lanthanum oxide "core" can stably fix phosphorus, and the microorganisms and metabolites in the "shell" cannot enter the mesopore, so the two functions do not interfere with each other.

[0051] Third, the difficulty of the preparation method in this application lies in:

[0052] (1) How to ensure that mesoporous lanthanum oxide has mesopores with a pore size of 3-6 nm. First, pore-forming agent CTAB is added during the synthesis of lanthanum oxide. After synthesis, CTAB is eluted with ethanol using a Soxhlet extractor, and the vacancy of CTAB forms mesopores. Second, the concentration of CTAB is 13 g / L, which ensures that the pore size of the mesoporous lanthanum oxide is 3-6 nm.

[0053] (2) How to ensure that the surface of the shell structure also has through-pores with a diameter of 50~200 nm. The key influencing factor for this problem is the concentration of sodium alginate and chitosan solution: the lower the concentration, the looser the cross-linked network; conversely, the denser it is.

[0054] In addition, the CaCl2 concentration, crosslinking time, and crosslinking temperature were also taken into consideration to ensure that the pore size of the crosslinked network meets the requirements.

[0055] That is, "the concentration of sodium alginate is 2~20 g / L; the concentration of chitosan in the chitosan solution is 5~15 g / L", "the concentration of CaCl2 is 2~20 g / L", "the volume ratio of solution A to solution B is 1:1", "in 4 o Crosslinking at C for 24 hours forms sodium alginate / chitosan gel microspheres with a semi-interpenetrating structure, which is essentially the same as "the surface of the shell structure also has through-pores with a pore size of 50~200 nm". The above preparation method ensures that "the surface of the shell structure also has through-pores with a pore size of 50~200 nm". Attached Figure Description

[0056] The present invention will be further described in detail below with reference to the embodiments shown in the accompanying drawings, but this does not constitute any limitation on the present invention.

[0057] Figure 1 This is a process flow diagram of the lanthanum-containing phosphorus-locking agent of this application.

[0058] Figure 2 This is a picture of the actual product of the lanthanum-containing phosphorus-locking agent of this application. Detailed Implementation

[0059] The present invention will now be described in detail with reference to specific embodiments.

[0060] Example 1

[0061] (1) Material synthesis

[0062] First, mesoporous lanthanum oxide is produced.

[0063] Prepare a 1 mol / L LaCl3 aqueous solution and add CTAB to achieve a concentration of 13 g / L; titrate LaCl3 with 6 mol / L ammonia solution at a rate of 0.1 mL / min. 3+ The pH of the CTAB mixture was raised to 7.5 ± 0.5 and stirred for more than 4 hours. Then, the solid was centrifuged and transferred to a Soxhlet extractor. After reacting with a 9:1 ethanol-water mixture for 8 hours, the solid was dried to obtain mesoporous lanthanum oxide.

[0064] Then, mesoporous lanthanum oxide-functional bacteria-sodium alginate / chitosan hydrogel microspheres were fabricated.

[0065] Prepare a 10 g / L sodium alginate aqueous solution, add mesoporous lanthanum oxide to form a 10 g / L suspension, then add 5% (v / v) of Bacillus subtilis and photosynthetic bacteria functional bacterial solution, stir well to obtain suspension A; prepare a 5 g / L chitosan solution, and add CaCl2 to make the concentration 15 g / L to form solution B. Add suspension A dropwise to solution B at a rate of 1 mL / min, and at 4... o Crosslinking at C for 24 hours. The obtained mesoporous lanthanum oxide-functional bacteria-sodium alginate / chitosan hydrogel microspheres are approximately spherical with a particle size of 1~2 mm.

[0066] (2) Effects of black and odorous water body treatment

[0067] This material was used to treat a polluted and odorous water body in Minhang District, Shanghai. Due to long-term agricultural non-point source pollution, the water quality had severely deteriorated, with dissolved oxygen at only 0.5 mg / L, black sediment, and COD, total phosphorus, and ammonia nitrogen concentrations of 41.6, 19.9, and 0.74 mg / L, respectively. -1 The water surface was covered with duckweed. (Based on 1 kg / m³) 2 After the materials were added, the dissolved oxygen concentration in the water continued to rise, remaining at 1.5 mg / L after 35 days. After 162 days, the concentrations of COD, total phosphorus, and ammonia nitrogen were 18.05, 0.15, and 0.24 mg / L, respectively. During this process, due to the significant decrease in phosphorus concentration in the lake water, the duckweed on the lake surface gradually turned yellow and died, the lake water changed from turbid to clear, and the odor basically disappeared.

[0068] Example 2

[0069] (1) Material synthesis

[0070] First, mesoporous lanthanum oxide is produced.

[0071] Prepare a 0.5 mol / L LaCl3 aqueous solution and add CTAB to achieve a concentration of 13 g / L; titrate LaCl3 with 2 mol / L NaOH at a rate of 0.1 mL / min. 3+ The pH of the CTAB mixture was raised to 6.5 ± 0.5 and stirred for more than 4 hours. After centrifugation, the solid was transferred to a Soxhlet extractor and reacted with an 8:2 ethanol-water mixture for 6 hours. The mixture was then dried to obtain mesoporous lanthanum oxide.

[0072] Then, mesoporous lanthanum oxide-functional bacteria-sodium alginate / chitosan hydrogel microspheres were fabricated.

[0073] Prepare a 10 g / L sodium alginate aqueous solution, add mesoporous lanthanum oxide to form an 8 g / L suspension, then add 5% (v / v) of nitrifying bacteria, photosynthetic bacteria, and lactic acid bacteria functional bacterial solution, stir well to obtain suspension A; prepare a 5 g / L chitosan solution, and add CaCl2 to make the concentration 15 g / L to form solution B. Add suspension A dropwise to solution B at a rate of 1 mL / min, and at 4... o Crosslinking at C for 24 h. The obtained mesoporous lanthanum oxide-functional bacteria-sodium alginate / chitosan hydrogel microspheres are approximately spherical with a particle size of 0.8~1.5 mm.

[0074] (2) Effects of black and odorous water body treatment

[0075] This material was used to treat a polluted and odorous water body in Xi'an City, Shaanxi Province. The water body was located in a slow-flowing section of a river. Due to long-term discharge of effluent from the city's sewage treatment plant and the burden from surrounding urban non-point source pollution, the water had become completely turbid, and benthic flora and fauna were completely extinct. The concentrations of COD, total phosphorus, and ammonia nitrogen in the water were 91.2, 3.95, and 7.84 mg·L⁻¹, respectively. -1 According to 2.5kg / m 2 After 52 days following the addition of the materials, the concentrations of COD, total phosphorus, and ammonia nitrogen were 13.05, 0.25, and 0.24 mg / L, respectively. Hydrilla verticillata, an aquatic plant, reappeared in the lake water, and the odor essentially disappeared. Continued monitoring for 208 days showed no further algae growth in the water, achieving long-term cleanliness after the treatment of the black and odorous water body.

[0076] The above-described embodiments are preferred embodiments of this application and are only used to facilitate the illustration of this application. They are not intended to limit this application in any way. Any person with ordinary knowledge in the art can make equivalent embodiments by making partial modifications or alterations to the technical content disclosed in this application without departing from the scope of the technical features of this application. Such equivalent embodiments are still within the scope of the technical features of this application.

Claims

1. A lanthanum-containing phosphorus-locking agent, which is a mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel microsphere, characterized in that, The sphere has a core-shell structure: The core structure is mesoporous lanthanum oxide, and mesoporous lanthanum oxide has mesopores with a pore size of 3~6 nm inside; The shell structure is sodium alginate / chitosan gel; Both the functional microorganisms and the mesoporous lanthanum oxide are encapsulated within the shell structure. The shell structure also has through holes on its surface, with the diameter of the through holes being 50~200 nm.

2. The lanthanum-containing phosphorus-locking agent as described in claim 1, characterized in that, The sodium alginate / chitosan gel is a polymer network; the polymer network is formed by chitosan and sodium alginate under the action of CaCl2.

3. The lanthanum-containing phosphorus-locking agent as described in claim 1, characterized in that, The diameter of the mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel microspheres is between 1 mm and 2 mm.

4. The lanthanum-containing phosphorus-locking agent as described in claim 1, characterized in that, The functional microorganisms are located between the mesoporous lanthanum oxide and the sodium alginate / chitosan gel.

5. The lanthanum-containing phosphorus-locking agent as described in claim 1, characterized in that, In a dry state, the specific surface area of ​​the lanthanum-containing phosphorus-locking agent is 100~200 m². 2 Between / g.

6. The lanthanum-containing phosphorus-locking agent as described in claim 1, characterized in that, Based on phosphorus element, the phosphorus adsorption capacity of the lanthanum-containing phosphorus-locking agent is 8~25 mg / g; the organic matter degradation capacity is characterized by the COD removal rate during water purification, and for water bodies with COD less than 100 mg / L, the COD removal rate can reach 60~85%.

7. A method for preparing a lanthanum-containing phosphorus-locking agent, characterized in that, Includes the following steps: S100, preparation of mesoporous lanthanum oxide, which includes sub-steps S101~S103; S101, use 1% (v / v) hydrochloric acid to prepare La solution with a concentration of 0.5~2 mol / L. 3+ An aqueous solution in which CTAB is dissolved as a template agent, with a concentration of 13 g / L; S102: Using a NaOH solution, KOH solution, or ammonia solution with a concentration of 0.5~6 mol / L, titrate the solution obtained in step S101 at a rate of 0.1~0.5 mL / min until the pH of the mixture finally rises to 6~8, and continue stirring for more than 4 hours. S103: After centrifuging the mixture, the solid is transferred to a Soxhlet extractor and reacted with a 9:1 or 8:2 ethanol-water mixture for 4-8 hours to remove the template agent. The solid is then dried to obtain mesoporous lanthanum oxide. S200, Preparation of mesoporous lanthanum oxide-functional microorganism-sodium alginate / chitosan gel microspheres, which includes sub-steps S201~S203; S201, prepare an aqueous solution of sodium alginate with a concentration of 2-20 g / L; add mesoporous lanthanum oxide obtained from S100 and mix, with 5-10 g of mesoporous lanthanum oxide per liter of solution; then add functional bacterial solution and stir evenly to obtain suspension A; when preparing suspension A, the concentration of functional bacterial solution added is 0.5-10 g / L; S202, prepare a chitosan solution with a chitosan concentration of 5~15 g / L, and add CaCl2 with a CaCl2 concentration of 2~20 g / L to form solution B; S203, while maintaining stirring, use a peristaltic pump to add suspension A dropwise to solution B at a rate of 0.5-1.5 mL / min; the volume ratio of solution A to solution B is 1:

1. S204, in 4 o Crosslinking at C for 24 hours forms a sodium alginate / chitosan gel with a semi-interpenetrating structure, encapsulating mesoporous lanthanum oxide and functional microorganisms within it.

8. The method for preparing a lanthanum-containing phosphorus-locking agent as described in claim 7, characterized in that, The OD of the functional bacterial culture was measured by spectrophotometry before use. 600 The cell concentration should be calculated to be no less than 1 × 10⁻⁶. 6 cell / ml.

9. The method for preparing a lanthanum-containing phosphorus-locking agent as described in claim 8, characterized in that, La used in S101 3+ The salt is any one or more of LaCl3 and LaNO3.

10. An application of the lanthanum-containing phosphorus-locking agent as described in any one of claims 1 to 6 in the treatment of black and odorous water bodies.

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