Calcium carbonate-based phosphorus removal agent as well as preparation method and phosphorus removal method thereof

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a calcium carbonate-based phosphorus removal agent and a preparation method and a phosphorus removal method thereof. Comprising the following steps: preparing a lanthanum layer on the surface of calcium carbonate by adopting a magnetron sputtering process to obtain a first material; spraying inorganic acid on the surface of the first material to form defects on the surface of the first material, and then cleaning the first material in water to remove residual inorganic acid so as to prepare a second material; terephthalic acid, absolute methanol and DMF are prepared into a solution, then the second material is placed in the solution, and La-O bonds are formed on the surface of the second material; and then adding a soluble metal salt ligand, and coordinating metal ions with terephthalic acid to prepare the calcium carbonate-based phosphorus removal agent. The calcium carbonate-based phosphorus removal agent provided by the invention can effectively remove phosphorus in a water body, and compared with a traditional chemical reagent, the removal effect is remarkably improved, the dosage of the reagent is favorably reduced, and further development of chemical phosphorus removal is favorably promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, and particularly relates to a calcium carbonate-based phosphorus remover, a preparation method thereof, and a phosphorus removal method. Background Art

[0002] Phosphorus is one of the widely used nutrient elements. However, the excessive use of phosphorus-containing products will inevitably cause water pollution and may lead to serious water eutrophication. Therefore, it is of great significance to study simple and efficient methods for removing phosphorus.

[0003] At present, the main methods for phosphorus removal from water bodies include biological phosphorus removal method, physical phosphorus removal method, and chemical phosphorus removal method. The physical phosphorus removal method includes precipitation method and filtration method. The precipitation method makes phosphorus-containing particles settle by gravity. The commonly used equipment is a sedimentation tank. It has simple operation and low cost, and is suitable for treating high-concentration phosphorus-containing wastewater. However, its removal effect on dissolved phosphorus is limited, and a large sedimentation tank is required, resulting in a large floor area. The filtration method uses materials such as sand filtration and activated carbon to intercept phosphorus particles. This method is suitable for treating low-concentration phosphorus-containing wastewater. The equipment is simple and easy to maintain. The disadvantage is that the filter material needs to be replaced or cleaned regularly, and it has poor effect on high-concentration phosphorus-containing wastewater. The biological phosphorus removal method uses polyphosphate-accumulating bacteria to absorb and release phosphorus under anaerobic-aerobic conditions and removes it by sludge discharge, which is suitable for sewage treatment plants. This method is environmentally friendly and has no chemical additives, and is suitable for large-scale sewage treatment plants. However, the operating conditions are strictly required (such as anaerobic-aerobic alternation), and the start-up and stable operation time are relatively long, which will affect the phosphorus removal effect and efficiency of the water body.

[0004] The chemical method is to add chemical reagents (such as lime, aluminum chloride, polyaluminum chloride, etc.) to make phosphorus form substances insoluble in water with the reagents, so as to separate phosphorus from sewage. Compared with the above-mentioned physical and biological treatment methods, the chemical precipitation method has the advantages of simple operation and good phosphorus removal effect, and is suitable for treating high-concentration phosphorus-containing wastewater. However, the chemical method requires the reagent to react fully with phosphorus in the water to ensure the removal effect. During this process, due to the influence of factors such as the water body environment, the pollutants in the water cannot react fully with the chemical reagent, which reduces the removal rate. In order to obtain a high removal effect, generally an excessive amount of chemical reagent needs to be added, which is likely to cause secondary pollution to the water body. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a calcium carbonate-based phosphorus remover, a preparation method thereof, and a phosphorus removal method. The present invention modifies calcium carbonate. The provided calcium carbonate-based phosphorus remover can effectively remove phosphorus in the water body. Compared with unmodified calcium carbonate, its ability to capture phosphorus in the water body is improved, and the phosphorus removal effect of the same mass of phosphorus remover is significantly improved. On the other hand, when achieving the same phosphorus removal effect, the required amount of phosphorus remover is reduced, which is conducive to promoting the further development of chemical phosphorus removal.

[0006] The present invention is achieved through the following technical solutions.

[0007] The first object of the present invention is to provide a preparation method of a calcium carbonate-based phosphorus removal agent, comprising the following steps: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering process to obtain a first material.

[0008] Spray inorganic acid on the surface of the first material to form defects on its surface, and then place it in water for cleaning to remove the residual inorganic acid, thus preparing a second material.

[0009] Prepare a first solution with terephthalic acid, anhydrous methanol and DMF, then place the second material in the first solution to form La-O bonds on the surface of the second material; then add a soluble metal salt ligand, and the metal ions coordinate with terephthalic acid to prepare the calcium carbonate-based phosphorus removal agent.

[0010] Preferably, the thickness of the lanthanum layer is 10nm - 50nm.

[0011] Preferably, the magnetron sputtering process parameters are: in an argon atmosphere, the working argon pressure is 0.5Pa - 3.0Pa, the power of the lanthanum metal target is 5W - 30W, the sputtering time is 5min - 10min, and during the sputtering process, the calcium carbonate is in a vibrating state.

[0012] Preferably, the inorganic acid is hydrochloric acid with a mass concentration of 0.1% - 0.5%.

[0013] Preferably, the residence time of the inorganic acid on the surface of the first material is 2min - 5min.

[0014] Preferably, the molar ratio of terephthalic acid, anhydrous methanol and DMF is 1:5 - 10:5 - 10.

[0015] Preferably, the metal in the metal salt solution is one of soluble iron salts, zirconium salts and cerium salts, and the molar ratio of terephthalic acid to the soluble metal salt ligand is 1:0.5 - 1.

[0016] Preferably, during coordination, the temperature is 100°C - 120°C.

[0017] The second object of the present invention is to provide a calcium carbonate-based phosphorus removal agent prepared by the above preparation method.

[0018] The third object of the present invention is to provide a phosphorus removal method, which uses the above calcium carbonate-based phosphorus remover for phosphorus removal, and includes the following steps: placing the calcium carbonate-based phosphorus remover in a water body containing phosphorus, and the dosage ratio of the calcium carbonate-based phosphorus remover to phosphorus is 0.01~0.05 g: 10 mol. Under room temperature conditions, stir for 1 min to 2 min first, then stand for reaction for 5 min to 10 min, stir again for 1 min to 2 min, and then stand for reaction for 5 min to 10 min. After the reaction is completed, solid-liquid separation can be carried out.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses calcium carbonate as a raw material, prepares a lanthanum layer on the surface of calcium carbonate, and then sprays an inorganic acid on the surface. The inorganic acid corrodes the lanthanum layer to form defects on the surface of the lanthanum layer and exposes the surface of the inner layer of calcium carbonate. Terephthalic acid is configured into a solution, and then the calcium carbonate with defects on the surface is placed in this solution. Terephthalic acid forms La-O bonds with the defect sites in the lanthanum layer, so that terephthalic acid is anchored on the surface of the lanthanum layer. Then, a soluble metal salt is added to the solution, and metal ions can undergo a coordination reaction with terephthalic acid to form a MOF material.

[0020] The calcium carbonate-based phosphorus remover prepared by the present invention has a core-shell structure, wherein calcium carbonate is the core, and a MOF material is distributed on the surface of calcium carbonate. This MOF material is the shell, and there is also a lanthanum layer intermediate layer between the core and the shell. At the initial stage of the reaction, the phosphorus elements in the water body are evenly distributed, so the phosphorus elements around the phosphorus remover are relatively less, which is not conducive to the rapid removal of phosphorus elements in the system. However, in the present invention, the MOF material on the outermost layer uses its three-dimensional porous structure to quickly adsorb and aggregate the phosphorus in the surrounding water body. The aggregated phosphorus can quickly react with calcium carbonate and be fixed by a chemical method. The MOF material plays a role in aggregating phosphorus elements, increasing the concentration of phosphorus around the phosphorus remover, that is, increasing the local reaction concentration of phosphorus elements, thereby increasing the amount of calcium phosphate generated per unit time and shortening the time for phosphorus removal. The rapid reaction of local phosphorus can further promote the diffusion and aggregation of phosphorus in the water body to the periphery of the phosphorus remover. As the phosphorus removal process progresses, the lanthanum in the intermediate layer can also be used to remove phosphorus in the water body to further generate lanthanum phosphate precipitates. As the lanthanum is consumed, the exposure degree of calcium carbonate gradually increases, and the precipitates fixed by the outer MOF material gradually undergo self-flocculation. The MOF material and the precipitates dissociate from the surface of calcium carbonate, enabling the remaining calcium carbonate and lanthanum to fully contact the remaining phosphorus elements in the water body to further remove the remaining phosphorus. The generated precipitates are further flocculated and removed by the precipitates that have already undergone self-flocculation in the water body.

[0021] The key point of the present invention is that in the initial stage of the reaction, the local phosphorus concentration is rapidly increased and then rapidly removed, forming a local phosphorus concentration difference. Due to this concentration difference, phosphorus in the water body is forced to rapidly accumulate around the phosphorus remover. Compared with unmodified calcium carbonate, the "spontaneous" rapid accumulation of phosphorus in the water body towards the phosphorus remover is achieved, improving the phosphorus removal efficiency. Moreover, the generated precipitate, under the action of the MOF material, flocculates rapidly, generating a large number of flocs, creating conditions for the flocculation of the subsequent precipitate. As the reaction proceeds, the remaining phosphorus in the water body is further removed under the action of calcium carbonate and lanthanum, and rapid flocculation occurs. Through the above process, the phosphorus removal effect and rate are improved. Compared with unmodified calcium carbonate, the phosphorus removal effect of the same mass of phosphorus remover is significantly improved. In other words, when achieving the same phosphorus removal effect, the required dosage of the phosphorus remover is reduced. Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the phosphorus removal principle of the calcium carbonate-based phosphorus remover of the present invention, where (a)-(f) are schematic diagrams of the phosphorus removal process after the phosphorus remover is added to the water body as time goes by.

[0023] Figure 2 It is a data graph of the influence of the hydrochloric acid residence time on the removal rate. Detailed Embodiments

[0024] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings, but the specific embodiments cited do not limit the present invention. In the following embodiments, the experimental methods and detection methods are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified. The calcium carbonate used in the present invention has a particle size of 0.2 mm - 0.4 mm and is purchased.

[0025] The chemical phosphorus removal method is to use chemical reagents to react with phosphorus in the water body to generate precipitates, and then remove the precipitates from the water body to reduce the phosphorus content in the water body. However, after the chemical reagents are dispersed in the water body, due to the influence of the water body environment and concentration, the chemical reagents cannot effectively react with phosphorus. For example, when the concentration of the chemical reagent is low, it can only react with the surrounding phosphorus, and the phosphorus at a farther distance cannot react with the chemical reagent, so it cannot be effectively removed. In order to improve the removal rate, generally, the dosage of the chemical reagent is increased to increase the concentration of the chemical reagent in the water body, so that the phosphorus in the water body can react with the nearby chemical reagent as much as possible, thereby achieving the purpose of removing phosphorus in the water body. However, although this strategy can achieve good results, the amount of chemical reagent used is large. If excessive reagents are used, it is easy to cause secondary pollution of the water body. Therefore, while ensuring the removal effect, how to reduce the usage amount of chemical reagents is beneficial to the further industrial application of water body phosphorus removal.

[0026] To solve the above problems, the present invention proposes a solution strategy that can adsorb and aggregate phosphorus in water bodies, and then react to form precipitates, improving the ability of the phosphorus remover per unit mass to remove phosphorus in water bodies, thereby reducing the usage amount of the phosphorus remover. Specifically, the present invention provides a preparation method of a calcium carbonate-based phosphorus remover, comprising the following steps: Step 1: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering to obtain a first material; the function of the lanthanum layer is to form metal surface defects, and during phosphorus removal in water bodies, as the reaction proceeds, lanthanum ions can be released and react with phosphorus in the water body to produce precipitates, further removing phosphorus in the water body.

[0027] Step 2: Spray inorganic acid on the surface of the first material to form defects on the surface of the first material, and then place it in water for washing to remove the residual inorganic acid to prepare a second material.

[0028] Step 3: Prepare a solution of terephthalic acid, anhydrous methanol and DMF, and then place the second material in the solution to form La-O bonds at the defects on the surface of the second material; then add a soluble metal salt ligand, and the metal ions coordinate with terephthalic acid to prepare the calcium carbonate-based phosphorus remover.

[0029] The calcium carbonate-based phosphorus remover prepared by the above steps has a core-shell structure, wherein calcium carbonate is the core, and a MOF material is distributed on the surface of calcium carbonate. This MOF material is the shell, and there is an intermediate lanthanum layer containing defects between the two, as Figure 1As shown, at the initial stage of the reaction, the phosphorus element in the water body is evenly distributed. As shown in (a), therefore, the phosphorus element around the phosphorus remover is relatively less, which is not conducive to the rapid removal of phosphorus element in the system. In the present invention, the MOF material on the outermost side utilizes its three-dimensional porous structure to quickly adsorb and aggregate the phosphorus in the surrounding water body, increasing the local phosphorus concentration, as shown in (b). The aggregated phosphorus can quickly react with calcium carbonate and be fixed by chemical method, as shown in (c). The MOF material plays a role in aggregating the phosphorus element, increasing the phosphorus concentration around the phosphorus remover, that is, increasing the local reaction concentration of the phosphorus element, thereby increasing the amount of calcium phosphate generated per unit time and shortening the phosphorus removal time. The rapid reaction of local phosphorus can further promote the diffusion and aggregation of phosphorus in the water body towards the surrounding of the phosphorus remover, increasing the phosphorus content around the phosphorus remover, and more phosphorus is fixed around the phosphorus remover, as shown in (d). As the phosphorus removal process proceeds, the lanthanum in the middle layer can also be used to remove phosphorus in the water body, further generating lanthanum phosphate precipitate. As the lanthanum is consumed, the exposure degree of calcium carbonate gradually increases, and the precipitate fixed by the outer MOF material gradually undergoes self-flocculation, and the MOF material and the precipitate dissociate from the surface of calcium carbonate, as shown in (e), enabling the remaining calcium carbonate and lanthanum to fully contact the remaining phosphorus element in the water body, further removing the remaining phosphorus, and the generated precipitate is further flocculated and removed by the precipitate that has undergone self-flocculation in the water body, as shown in (f). The key point of the present invention is that at the initial stage of the reaction, the local phosphorus concentration is rapidly increased and then rapidly removed, forming a local phosphorus concentration difference. Through the concentration difference, the phosphorus in the water body is forced to rapidly aggregate towards the surrounding of the phosphorus remover. Compared with the unmodified calcium carbonate, the "spontaneous" rapid aggregation of phosphorus in the water body towards the phosphorus remover is realized, improving the phosphorus removal efficiency, and the generated precipitate is rapidly flocculated under the action of the MOF material, generating a large amount of flocs, creating conditions for the flocculation of the subsequent precipitate. As the reaction proceeds, the remaining phosphorus in the water body is further removed under the action of calcium carbonate and lanthanum, and rapid flocculation occurs. Through the above process, the phosphorus removal effect and rate are improved. Compared with the unmodified calcium carbonate, the phosphorus removal effect of the same mass of phosphorus remover is significantly improved. In other words, when achieving the same phosphorus removal effect, the required amount of phosphorus remover is reduced.

[0030] In a preferred embodiment of the present invention, the thickness of the lanthanum layer is 10nm - 50nm. The lanthanum layer cannot be too thick, otherwise it is not easy to expose more surface of calcium carbonate, which is not conducive to the rapid chemical fixation of the aggregated phosphorus at the initial stage of the reaction. The lanthanum layer cannot be too thin either, as it is easily consumed by inorganic acid and cannot form a certain content of La - O bonds, reducing the formation amount of the subsequent MOF material and affecting the adsorption and aggregation of phosphorus in the initial stage of the reaction.

[0031] In a preferred embodiment of the present invention, the magnetron sputtering process parameters are as follows: in an argon atmosphere, the working argon pressure is 0.5 Pa to 3.0 Pa, the power of the lanthanum metal target is 5 W to 30 W, the sputtering time is 5 min to 10 min, and during the sputtering process, calcium carbonate is in a vibrating state.

[0032] In a preferred embodiment of the present invention, the inorganic acid is hydrochloric acid with a mass concentration of 0.1% to 0.5%, and the residence time of the inorganic acid on the surface of the first material is 2 min to 5 min. The inorganic acid is preferably an acid that can react quickly with lanthanum, and by controlling the reaction time, defects can be formed to expose the calcium carbonate core, and at the same time, lanthanum and calcium carbonate will not be consumed excessively.

[0033] In a preferred embodiment of the present invention, the molar ratio of terephthalic acid, anhydrous methanol, and DMF is 1:5 to 10:5 to 10. The role of using anhydrous methanol in the present invention is to regulate the balance between the nucleation and growth of the metal-organic framework. DMF decomposes into dimethylamine after heating, which can deprotonate the organic carboxylic acid ligand and promote the formation of La-O bonds.

[0034] In a preferred embodiment of the present invention, the metal in the metal salt solution is one of soluble iron salts, zirconium salts, and cerium salts, and the molar ratio of terephthalic acid to the soluble metal salt ligand is 1:0.5 to 1. Metal ions coordinate with terephthalic acid to form a MOF material.

[0035] In a preferred embodiment of the present invention, during coordination, the temperature is 100 °C to 120 °C.

[0036] The present invention provides a phosphorus removal method, which uses the above-mentioned calcium carbonate-based phosphorus remover for phosphorus removal, and includes the following steps: placing the calcium carbonate-based phosphorus remover in a water body containing phosphorus, and the dosage ratio of the calcium carbonate-based phosphorus remover to phosphorus is 0.01 g to 0.05 g: 10 mol. Under room temperature conditions, first stir for 1 min to 2 min, then stand for reaction for 5 min to 10 min, stir again for 1 min to 2 min, and then stand for reaction for 5 min to 10 min. After the reaction is completed, solid-liquid separation can be carried out, and the removal rate of phosphorus in the filtrate reaches 98.5%. It should be noted that when the phosphorus remover is first added, stir first to make the phosphorus remover evenly dispersed in the water body. At this time, as shown in (a) Figure 2 shown in, and then stand for treatment to facilitate the adsorption and aggregation of phosphorus around the MOF material in the phosphorus remover. At this time, a relatively stable environment needs to be provided by the water body to facilitate the aggregation and chemical fixation of phosphorus, promote the increase in the local phosphorus concentration in the water body and the formation of the spontaneous diffusion process of phosphorus. This process occurs Figure 1Processes (b) - (d). If stirring is not carried out during this process, phosphorus in the water body cannot be well aggregated around the phosphorus removal agent and will be dispersed in the water body under the action of external forces, which is not conducive to the "targeted" phosphorus removal operation of the phosphorus removal agent. After the above reaction, a large amount of insoluble substances are generated in the water body, which are rapidly flocculated under the action of the MOF material and gradually separated from the calcium carbonate core body. At this time, the calcium carbonate in the phosphorus removal agent is highly exposed. Stirring again releases the calcium carbonate. At this time, as shown in Figure 1 in (e), it is evenly dispersed into the water body again to further remove phosphorus in the water body. Under the action of the flocs that have formed in the water body, it rapidly precipitates out of the water body. At this time, as shown in Figure 1 in (f). Through the above phosphorus removal agent and the corresponding initial stirring, standing, re-stirring, and standing operations, the phosphorus removal agent can better react with phosphorus in the water body, improving the removal effect.

[0037] The above content of the present invention will be specifically described below through the following examples and comparative examples.

[0038] Example 1 A preparation method of a calcium carbonate-based phosphorus removal agent includes the following steps: Step 1: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering process to obtain the first material. The magnetron sputtering process parameters are: in an argon atmosphere, the working argon pressure is 1.0 Pa, the power of the lanthanum metal target is 10 W, and the sputtering time is 7 min. The average thickness of the lanthanum layer is 20 nm. During the sputtering process, calcium carbonate is in a vibrating state.

[0039] Step 2: Spray hydrochloric acid with a mass concentration of 0.1% on the surface of the first material to form defects on its surface, and then place it in water for washing to remove the residual hydrochloric acid to prepare the second material. The residence time of hydrochloric acid on the surface of the first material is 2 min.

[0040] Step 3: Prepare a first solution by mixing terephthalic acid, anhydrous methanol, and DMF. The molar ratio of terephthalic acid, anhydrous methanol, and DMF is 1:5:5. Then place the second material in the first solution to form La - O bonds on the surface of the second material; then add FeCl 3 ligand, and Fe 3+ coordinates with terephthalic acid at a temperature of 120 °C for 1 h to prepare the calcium carbonate-based phosphorus removal agent. The molar ratio of terephthalic acid and Fe 3+ is 1:0.5.

[0041] Example 2 A preparation method of a calcium carbonate-based phosphorus removal agent includes the following steps: Step 1: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering to obtain the first material. The magnetron sputtering process parameters are as follows: in an argon atmosphere, the working argon pressure is 1.0 Pa, the power of the lanthanum metal target is 10 W, and the sputtering time is 7 min. The average thickness of the lanthanum layer is 20 nm. During the sputtering process, the calcium carbonate is in a vibrating state.

[0042] Step 2: Spray hydrochloric acid with a mass concentration of 0.1% on the surface of the first material to form defects on its surface, and then place it in water for cleaning to remove the residual hydrochloric acid, thus preparing the second material. The residence time of hydrochloric acid on the surface of the first material is 5 min.

[0043] Step 3: Prepare a first solution by mixing terephthalic acid, anhydrous methanol, and DMF. The molar ratio of terephthalic acid, anhydrous methanol, and DMF is 1:5:5. Then place the second material in the first solution to form La - O bonds on the surface of the second material; then add FeCl 3 ligand, and Fe 3+ coordinates with terephthalic acid at a temperature of 120 °C for 1 h to prepare the calcium carbonate-based phosphorus remover. The molar ratio of terephthalic acid and Fe 3+ is 1:0.5.

[0044] Example 3 A preparation method of a calcium carbonate-based phosphorus remover, comprising the following steps: Step 1: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering to obtain the first material. The magnetron sputtering process parameters are as follows: in an argon atmosphere, the working argon pressure is 3.0 Pa, the power of the lanthanum metal target is 30 W, and the sputtering time is 10 min. The thickness of the lanthanum layer is 45 nm. During the sputtering process, the calcium carbonate is in a vibrating state.

[0045] Step 2: Spray hydrochloric acid with a mass concentration of 0.1% on the surface of the first material to form defects on its surface, and then place it in water for cleaning to remove the residual hydrochloric acid, thus preparing the second material. The residence time of hydrochloric acid on the surface of the first material is 5 min.

[0046] Step 3: Prepare a first solution by mixing terephthalic acid, anhydrous methanol, and DMF. The molar ratio of terephthalic acid, anhydrous methanol, and DMF is 1:10:10. Then place the second material in the first solution to form La - O bonds on the surface of the second material; then add FeCl 3 ligand, and Fe 3+ coordinates with terephthalic acid at a temperature of 100 °C for 1 h to prepare the calcium carbonate-based phosphorus remover. The molar ratio of terephthalic acid and Fe 3+ is 1:1.

[0047] Example 4 A preparation method of a calcium carbonate-based phosphorus remover, comprising the following steps: Step 1: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering to obtain the first material. The magnetron sputtering process parameters are as follows: in an argon atmosphere, the working argon pressure is 0.5 Pa, the power of the lanthanum metal target is 5 W, and the sputtering time is 8 min. The thickness of the lanthanum layer is 30 nm. During the sputtering process, the calcium carbonate is in a vibrating state.

[0048] Step 2: Spray hydrochloric acid with a mass concentration of 0.2% on the surface of the first material to form defects on its surface, and then place it in water for cleaning to remove the residual hydrochloric acid, thus preparing the second material. The residence time of hydrochloric acid on the surface of the first material is 3 min.

[0049] Step 3: Prepare a first solution by mixing terephthalic acid, anhydrous methanol, and DMF. The molar ratio of terephthalic acid, anhydrous methanol, and DMF is 1:6:5. Then place the second material in the first solution to form La-O bonds on the surface of the second material; then add CeCl 3 , Ce 3+ to coordinate with terephthalic acid at a temperature of 100 °C for 1 h to prepare a calcium carbonate-based phosphorus remover. The molar ratio of terephthalic acid to Ce 3+ is 1:0.5.

[0050] Example 5 A preparation method of a calcium carbonate-based phosphorus remover, comprising the following steps: Step 1: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering to obtain the first material. The magnetron sputtering process parameters are as follows: in an argon atmosphere, the working argon pressure is 0.5 Pa, the power of the lanthanum metal target is 5 W, and the sputtering time is 5 min. The thickness of the lanthanum layer is 15 nm. During the sputtering process, the calcium carbonate is in a vibrating state.

[0051] Step 2: Spray hydrochloric acid with a mass concentration of 0.2% on the surface of the first material to form defects on its surface, and then place it in water for cleaning to remove the residual hydrochloric acid, thus preparing the second material. The residence time of hydrochloric acid on the surface of the first material is 4 min.

[0052] Step 3: Prepare a first solution by mixing terephthalic acid, anhydrous methanol, and DMF. The molar ratio of terephthalic acid, anhydrous methanol, and DMF is 1:5:5. Then place the second material in the first solution to form La-O bonds on the surface of the second material; then add CeCl 3 , Ce 3+ to coordinate with terephthalic acid at a temperature of 110 °C for 1 h to prepare a calcium carbonate-based phosphorus remover. The molar ratio of terephthalic acid to Ce 3+ is 1:1.

[0053] Example 6 A preparation method of a calcium carbonate-based phosphorus remover, comprising the following steps: Step 1: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering to obtain the first material. The parameters of the magnetron sputtering process are as follows: in an argon atmosphere, the working argon pressure is 1.5 Pa, the power of the lanthanum metal target is 20 W, the sputtering time is 5 min, and the thickness of the lanthanum layer is 15 nm. During the sputtering process, the calcium carbonate is in a vibrating state.

[0054] Step 2: Spray hydrochloric acid with a mass concentration of 0.4% on the surface of the first material to form defects on its surface, and then place it in water for cleaning to remove the residual hydrochloric acid to prepare the second material. The residence time of hydrochloric acid on the surface of the first material is 5 min.

[0055] Step 3: Prepare a first solution by mixing terephthalic acid, anhydrous methanol, and DMF. The molar ratio of terephthalic acid, anhydrous methanol, and DMF is 1:5:5. Then place the second material in the first solution to form La - O bonds on the surface of the second material; then add CeCl 3 , Ce 3+ to coordinate with terephthalic acid at a temperature of 100 °C for 1 h to prepare a calcium carbonate - based phosphorus remover. The molar ratio of terephthalic acid and Ce 3+ is 1:1.

[0056] The formation of the lanthanum layer in the middle of the present invention is crucial. On the one hand, it is the basis for the formation of the MOF material, and on the other hand, it needs to expose the inner - core calcium carbonate. Therefore, the etching degree is an important parameter. To verify the above - mentioned action mechanism of the lanthanum layer, the present invention conducts the following exploration. Compared with Example 1, the parameters are changed to prepare the phosphorus remover, and the parameter variables are shown in Table 1. Compared with Example 1, in Comparative Examples 1 - 5, only the residence time of hydrochloric acid is changed, and other steps are the same as those in Example 1.

[0057] Place the phosphorus removers prepared in each group in water containing phosphorus. The dosage ratio of the calcium carbonate - based phosphorus remover to phosphorus is 0.05 g:10 mol. Under room - temperature conditions, first stir for 2 min, then let it stand for reaction for 10 min, stir again for 2 min, and then let it stand for reaction for 5 min. After the reaction is completed, separate the solid and liquid, and measure the phosphorus content in the filtrate by ammonium molybdate spectrophotometry and calculate the removal rate. The removal rate is calculated as follows: Removal rate (%)=(C1 - C2) / C1, where C1 is the initial phosphorus concentration in the water body and C2 is the phosphorus concentration in the water body after treatment with the phosphorus remover.

[0058] Table 1 Influence of changes in lanthanum layer preparation parameters on the removal rate From Table 1 and Figure 2It can be seen that taking Example 1 as an example, when the residence time of hydrochloric acid is changed, the final removal rate is affected. When the residence time is shortened, the removal rate decreases, and when the residence time is extended, the removal rate also decreases. Specifically analyzed, in Comparative Example 1, the residence time of hydrochloric acid is 0.5 min. Compared with the residence time of 2 min in Example 1, the removal rate is greatly reduced. This may be because the time is short, resulting in the lanthanum layer on the surface of calcium carbonate not being etched by hydrochloric acid, resulting in less exposed part of calcium carbonate. When used for phosphorus removal in water, in the initial stage of the reaction, more is due to the physical adsorption of the MOF material, and the chemical fixation effect is poor. In Comparative Example 2, the residence time of hydrochloric acid is extended compared with Comparative Example 1, and its removal efficiency is also improved compared with Comparative Example 1. This also shows that extending the residence time can increase the exposure degree of calcium carbonate, thereby improving the final removal rate. When the residence time is further extended to 2 - 5 min, it can not only ensure the exposure of calcium carbonate but also ensure the formation of the MOF material. Through the synergistic effect, the removal rate is improved. After further extending the residence time in Comparative Example 3 and Comparative Example 4, the removal rate decreases. This is because the extension of time leads to an increase in the etching degree of the lanthanum layer, and less MOF material is formed on the outside of calcium carbonate. In the initial stage of the reaction, due to the lack of sufficient MOF material to adsorb the surrounding phosphorus, no local phosphorus concentration increase is formed, resulting in a poor removal effect. This can also be verified by Comparative Example 5. When the residence time in Comparative Example 5 is further extended to 20 min, the removal rate decreases significantly at this time, probably because the lanthanum layer on the surface of calcium carbonate is etched and no MOF material is formed, only the chemical fixation of calcium carbonate. By changing the residence time of hydrochloric acid and obtaining the corresponding removal rate, it can be found that the etching degree of the lanthanum layer has an important impact on the removal rate, and the corresponding removal rate data also verify the role of the lanthanum layer in the present invention and the phosphorus removal mechanism of the phosphorus remover in the present invention.

[0059] In order to further verify the functions of each layer in the phosphorus remover prepared by the present invention and further verify the conclusions in Table 1, the present invention also sets the following comparative examples.

[0060] Comparative Example 6 Compared with Example 1, after forming a lanthanum layer on the surface of calcium carbonate, it is etched, but no MOF material is formed. The specific steps are as follows: Step 1: Prepare a lanthanum layer on the surface of calcium carbonate by magnetron sputtering process to obtain the first material. The magnetron sputtering process parameters are as follows: in an argon atmosphere, the working argon pressure is 1.0 Pa, the power of the lanthanum metal target is 10 W, and the sputtering time is 7 min. The average thickness of the lanthanum layer is 20 nm.

[0061] Step 2: Spray hydrochloric acid with a mass concentration of 0.1% on the surface of the first material to form defects on its surface, and then place it in water for cleaning to remove the residual hydrochloric acid to prepare the second material. The residence time of hydrochloric acid on the surface of the first material is 2 min.

[0062] Comparative Example 7 Without preparing the lanthanum layer, the specific steps are: Terephthalic acid, anhydrous methanol and DMF are prepared into a first solution, and the molar ratio of terephthalic acid, anhydrous methanol and DMF is 1:5:5. Calcium carbonate is then placed in the first solution; FeCl is then added 3 Ligand, Fe 3+ The calcium carbonate-based phosphorus removal agent was prepared by coordination with terephthalic acid at 120°C for 1 hour. 3+ The molar ratio is 1:0.5.

[0063] Comparative Example 8 Calcium carbonate.

[0064] The phosphorus remover was placed in a water body containing phosphorus. The ratio of calcium carbonate-based phosphorus remover to phosphorus was 0.05 g:10 mol. Under room temperature, it was first stirred for 2 minutes, then allowed to react for 10 minutes, stirred again for 2 minutes, and allowed to react for 5 minutes. After the reaction, the solid and liquid were separated. The phosphorus content in the filtrate was measured by ammonium molybdate spectrophotometry, and the removal rate was calculated. The calculation method was as described above. The results are shown in Table 2.

[0065] Table 2 Removal rate data of Example 1, Comparative Examples 6 to 8 As can be seen from Table 2, in Comparative Example 6, etching is performed after a lanthanum layer is formed on the surface of calcium carbonate, but no MOF material is formed, only a portion of the calcium carbonate is exposed, and there is no adsorption effect of the MOF material, so the removal rate is reduced. Comparative Example 7 is to place calcium carbonate in a MOF material formation system. Since there is no effect of the lanthanum layer, the MOF material formed is not anchored on the surface of calcium carbonate. When placed in water to remove phosphorus, the calcium carbonate and the MOF material do not have the synergistic removal effect of the present invention. Comparative Example 8 is calcium carbonate, which does not have the synergistic removal effect of the present invention, resulting in a lower removal rate than Example 1. The results of Comparative Examples 6 to 8 can also further verify that the phosphorus removal agent core, intermediate layer and outer layer MOF material prepared by the present invention have the effect of synergistically removing phosphorus.

[0066] As mentioned above, the phosphorus removal agent in the present invention needs to be used in conjunction with corresponding stirring and standing steps to facilitate the controllable removal of phosphorus in the system. In order to verify this content, the phosphorus removal agent prepared in Example 1 is used as an experimental sample in the present invention, and the corresponding removal efficiency is obtained by coordinating different treatment methods. The specific operation steps are:

[0067] Put the phosphorus removal agent into the water body containing phosphorus. The dosage ratio of the calcium carbonate-based phosphorus removal agent to phosphorus is 0.05 g: 10 mol. Treatment method 1: Under room temperature conditions, continuously stir for 19 min. After the reaction ends, perform solid-liquid separation. Treatment method 2: Under room temperature conditions, first stir for 2 min, then let it stand and react for 10 min. After stirring again for 2 min, let it stand and react for 5 min. After the reaction ends, perform solid-liquid separation. By the ammonium molybdate spectrophotometric method, measure the phosphorus content in the filtrate respectively, and calculate the removal rate. The calculation method is as described in the previous text. The results are shown in Table 3.

[0068] Table 3 Effects of different water treatment methods on the removal rate It is found through experiments that during the water treatment process, if the water body is kept in a stirred state all the time, compared with the intermittent stirring in treatment method 2, the removal rate decreases. This shows that the phosphorus removal agent prepared by the present invention is not suitable for keeping the water body in a stirred state all the time when treating phosphorus in water. This is because the key of the phosphorus removal agent in the present invention is to form a local high phosphorus concentration difference in the water body, so that phosphorus spontaneously diffuses towards the phosphorus removal agent. At this time, the water body needs to be in a static state. If continuous stirring is carried out, the molecular dynamic behavior of this spontaneous diffusion will be destroyed, thereby reducing the removal rate.

[0069] Similarly, put the phosphorus removal agents prepared in Examples 3 to 6 into the water body containing phosphorus. The dosage ratio of the calcium carbonate-based phosphorus removal agent to phosphorus is 0.05 g: 10 mol. Under room temperature conditions, first stir for 2 min, then let it stand and react for 10 min. After stirring again for 2 min, let it stand and react for 5 min. After the reaction ends, perform solid-liquid separation, and then measure the removal rate. The removal effect is similar to that of Examples 1 and 2. See Table 4 for details.

[0070] Table 4 Phosphorus removal effects of the phosphorus removal agents in Examples 3 to 6 It can be seen from the above verification data of the present invention that after the modification of calcium carbonate by the present invention, the prepared phosphorus removal agent has a much higher removal effect than unmodified calcium carbonate. The phosphorus removal effect of the same mass of phosphorus removal agent is significantly improved. On the other hand, when achieving the same phosphorus removal effect, the required dosage of the phosphorus removal agent is reduced.

[0071] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, these changes and modifications are also intended to be included.

Claims

1. A method for preparing a calcium carbonate-based dephosphorizing agent, characterized in that: The following steps are involved: A lanthanum layer is prepared on the surface of calcium carbonate by a magnetron sputtering process to obtain a first material; Spraying inorganic acid on the surface of the first material to form defects on the surface of the first material, then washing it in water to remove residual inorganic acid, and preparing the second material; Terephthalic acid, anhydrous methanol and DMF are prepared into a solution, and then a second material is placed in the solution to form La-O bonds at defects on the surface of the second material; then a soluble metal salt ligand is added, and the metal ions are coordinated with the terephthalic acid to prepare a calcium carbonate-based phosphorus removal agent.

2. The preparation method according to claim 1, characterized in that: The thickness of the lanthanum layer is 10nm~50nm.

3. The preparation method according to claim 1, characterized in that: The process parameters of magnetron sputtering are as follows: under argon atmosphere, the working argon pressure is 0.5Pa~3.0Pa, the power of lanthanum metal target is 5W~30W, the sputtering time is 5min~10min, and during the sputtering process, calcium carbonate is in a vibrating state.

4. The preparation method according to claim 1, characterized in that: The inorganic acid is hydrochloric acid with a mass concentration of 0.1% to 0.5%.

5. The preparation method according to claim 1, characterized in that: The inorganic acid stays on the surface of the first material for 2 minutes to 5 minutes.

6. The preparation method according to claim 1, characterized in that: The molar ratio of terephthalic acid, anhydrous methanol and DMF is 1:5~10:5~10.

7. The preparation method according to claim 1, characterized in that: The metal in the metal salt solution is one of soluble iron salt, zirconium salt and cerium salt, and the molar ratio of terephthalic acid to the soluble metal salt ligand is 1:0.5~1.

8. The preparation method according to claim 1, characterized in that: During coordination, the temperature is 100℃~120℃.

9. A calcium carbonate-based phosphorus removal agent prepared according to the preparation method according to any one of claims 1 to 8.

10. A phosphorus removal method, characterized in that: The method of removing phosphorus using the calcium carbonate-based phosphorus removal agent according to claim 9 comprises the following steps: placing the calcium carbonate-based phosphorus removal agent in a water body containing phosphorus, wherein the ratio of the calcium carbonate-based phosphorus removal agent to phosphorus is 0.01 to 0.05 g: 10 mol, stirring for 1 to 2 minutes at room temperature, and then standing to react for 5 to 10 minutes, stirring again for 1 to 2 minutes, and then standing to react for 5 to 10 minutes. After the reaction is completed, solid-liquid separation is performed.

Images