Modified calcium sulfate seed crystal material, preparation method and application
By preparing modified calcium sulfate seed crystals by loading calcium phosphate onto the surface of calcium sulfate, the problems of general fluoride removal performance and large amount of crystallizing agent required by existing seed crystal materials are solved, achieving efficient and stable removal of low-concentration fluorides and reducing the risk of secondary pollution.
Patent Information
- Application Number
- CN202511987409.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-26
- Publication Date
- 2026-02-10
AI Technical Summary
Existing seed crystal materials generally have poor defluorination performance and require large amounts of crystallizing agents. They are particularly inefficient in treating low-concentration fluorides and pose a risk of secondary pollution.
Modified calcium sulfate seed material was used to prepare modified calcium sulfate seed crystals coated with active calcium phosphate by loading highly reactive calcium phosphate on the surface of calcium sulfate. The specific surface area and pore volume of the seed crystals were increased by metathesis reaction, thereby enhancing their defluorination performance.
Without adding additional crystallizing agents, the fluoride concentration in groundwater can be reduced from 10 mg/L to below 1 mg/L within 30 minutes, significantly improving the defluorination efficiency, reducing the amount of seed crystals used and the concentration of residual calcium ions and phosphates, and the operation is simple and has good stability.
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Figure CN121493902A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of water treatment, in particular to a modified calcium sulfate seed material and a preparation method thereof. BACKGROUND
[0002] Fluoride pollution in groundwater has become a major problem in the global environmental field, especially in areas with high natural fluoride concentrations such as India, China and Africa. Long-term exposure to excessive fluoride can pose serious health risks, potentially causing dental fluorosis and skeletal fluorosis, and even affecting the nervous system; fluoride poisoning can cause symptoms such as excessive salivation, anxiety, stiffness, muscle contraction, respiratory and cardiac failure, and even affect the function of the kidneys, liver and neurons. Therefore, defluorination of fluoride-containing groundwater is necessary.
[0003] Current main defluorination technologies include adsorption, chemical precipitation, ion exchange and membrane separation, among which adsorption and chemical precipitation are the most widely used methods. Chemical precipitation is a mature technology with simple operation, but it generates a large amount of sludge, which can easily cause secondary pollution. Induced crystallization improves the shortcomings of the precipitation method, and by adding seed crystals to the water, low-concentration fluoride in groundwater can be efficiently removed.
[0004] For groundwater with low fluoride concentration (<10 mg / L), induced fluorapatite crystallization is generally used for defluorination, and the selection of seed crystal material has an important influence on the defluorination performance of induced crystallization. The most commonly used seed crystal material is a natural mineral seed containing fluorapatite (FAP) components, which has a single type of seed, low effective utilization rate, and general induced crystallization defluorination performance, and a large amount of calcium and phosphate is required as a crystallizing agent during the defluorination process. SUMMARY
[0005] The present application provides a modified calcium sulfate seed material, a preparation method and an application, which can solve the problems of general defluorination performance and large amount of crystallizing agent of the existing seed.
[0006] The present application discloses a preparation method of a modified calcium sulfate seed material, which comprises the following steps:
[0007] Step A1: under water bath conditions, calcium sulfate powder is added to deionized water, and stirring is performed to obtain a uniformly dispersed calcium sulfate solution;
[0008] Step A2: sodium phosphate solution is added dropwise to the calcium sulfate solution, and a complex reaction is performed to combine phosphate ions with calcium ions on the surface of calcium sulfate;
[0009] Step A3: the pH of the above system is adjusted to 12, and stirring is performed to load calcium phosphate on the surface of calcium sulfate;
[0010] Step A4: After the above reaction is completed, filter to obtain filter residue, wash the filter residue with ethanol, and dry and grind the filter residue to obtain modified calcium sulfate seed material with active calcium phosphate coated on the surface.
[0011] Optionally, in step A1, the temperature of the water bath is 20℃-25℃.
[0012] Optionally, in step A2, the concentration of the sodium phosphate solution is 0.1 mol / L to 0.25 mol / L.
[0013] Optionally, in step A3, the stirring time is 0.5h-2h.
[0014] Optionally, in step A1, the amount of deionized water and calcium sulfate used is 150 mL: 1 g.
[0015] Optionally, in step A2, the amount of sodium phosphate solution used is 50 mL.
[0016] Optionally, the dropping rate of the sodium phosphate solution is 1 mL / min.
[0017] Optionally, in step A3, a 0.5 mol / L to 1 mol / L NaOH solution is used to adjust the pH value of the system.
[0018] The present invention also discloses a modified calcium sulfate seed material, which is prepared by the above-described method for preparing modified calcium sulfate seed material.
[0019] The present invention also discloses an application of a modified calcium sulfate seed material, which is used for defluorination.
[0020] The beneficial effects of the modified calcium sulfate seed material, preparation method, and application provided in this invention are as follows: This invention uses calcium sulfate as the matrix material and modifies it through a metathesis reaction between sodium phosphate and calcium sulfate. Highly reactive calcium phosphate is loaded onto the surface of calcium sulfate, successfully preparing modified calcium sulfate seed crystals with surface-coated active calcium phosphate. Tricalcium phosphate is an existing seed material for induced crystallization and fluoride removal. Compared with tricalcium phosphate seed crystals, the modified calcium sulfate seed material of this invention has a significantly increased specific surface area and pore volume, a significantly reduced pore size, and significantly improved surface properties. Furthermore, the preparation method of this invention improves the reactivity of calcium phosphate on the seed crystal surface, enhancing the release efficiency of calcium ions and phosphates from the seed crystal, thereby further improving the fluoride removal performance of the seed crystal.
[0021] The modified calcium sulfate seed material prepared by the method of this invention possesses excellent surface properties and defluoridation performance, with a large specific surface area and strong inducing crystallization ability. It can reduce the F- concentration from 10 mg / L to below 1 mg / L within 30 minutes without adding calcium phosphate crystallizing agents, and can also reduce the F- concentration of actual fluoride-containing water below the standard limit. Furthermore, the modified calcium sulfate seed material of this invention exhibits good stability within a pH range of 4-10, and its defluoridation performance is unaffected. Compared with existing seed materials, the defluoridation process of the modified calcium sulfate seed material of this invention does not require the addition of additional crystallizing agents, reducing the amount of seed material needed to treat the same volume of fluoride-containing water. Simultaneously, the concentrations of residual calcium ions and phosphates in the water are further reduced after defluoridation, significantly improving the inducing crystallization defluoridation performance. Moreover, the preparation method of this invention is simple to operate, and the prepared modified calcium sulfate seed material has high surface activity, abundant inducing crystallization sites, good stability, and good performance in treating fluoride-containing groundwater, demonstrating significant application value. Attached Figure Description
[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. In the accompanying drawings:
[0023] Figure 1 X-ray diffraction patterns of the modified calcium sulfate seed materials prepared in Examples 1-4 provided for the embodiments of this application;
[0024] Figure 2 X-ray diffraction patterns of the modified calcium sulfate seed materials prepared in Examples 5-7 provided for the embodiments of this application. Detailed Implementation
[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[0026] This invention provides a method for preparing modified calcium sulfate seed material, the method comprising the following steps:
[0027] Step A1: Under water bath conditions, add calcium sulfate to deionized water and stir to obtain a uniformly dispersed calcium sulfate solution. The stirring speed is 450 rpm and the stirring time is 10 min.
[0028] Step A2: Use a peristaltic pump to slowly and uniformly drip sodium phosphate solution into calcium sulfate solution, so that phosphate ions combine with calcium ions on the surface of calcium sulfate through a metathesis reaction;
[0029] Step A3: Adjust the pH of the above system to 12 and stir to load calcium phosphate onto the surface of calcium sulfate;
[0030] Step A4: After the above reaction is completed, filter to obtain filter residue. Wash the filter residue with ethanol and place it in an oven to dry at 100°C for 12 hours. Grind the dried filter residue until there is no obvious particle feel to obtain modified calcium sulfate seed material with active calcium phosphate coated on the surface.
[0031] Specifically, in step A1, the temperature of the water bath is 20℃-25℃. The water bath temperature can be 20℃, 21℃, 22℃, 23℃, 24℃, or 25℃.
[0032] Specifically, in step A2, the concentration of the sodium phosphate solution is 0.1 mol / L to 0.25 mol / L. The concentration of the sodium phosphate solution can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, or 0.25 mol / L.
[0033] Specifically, in step A3, the stirring time is 0.5s-2h. The stirring time can be 0.5h, 1h, 1.5h, or 2h.
[0034] Specifically, in step A1, the ratio of deionized water to calcium sulfate is 150 mL: 1 g, where the amount of deionized water can be 150 mL and the amount of calcium sulfate can be 1 g.
[0035] Specifically, in step A2, the amount of sodium phosphate solution used is 50 mL, and the dropping rate of the sodium phosphate solution is 1 mL / min.
[0036] Specifically, a NaOH solution with a concentration of 0.5 mol / L to 1 mol / L is used to adjust the pH value of the system. The concentration of NaOH can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1.0 mol / L.
[0037] This invention also provides a modified calcium sulfate seed material, which is prepared using the above-described method for preparing modified calcium sulfate seed materials.
[0038] This invention also provides an application of the modified calcium sulfate seed material, which is used for fluoride removal.
[0039] Example 1
[0040] Add 150 ml of deionized water to a beaker, control the water bath temperature at 25 °C, and stir at 450 rpm. Add 1 g of calcium sulfate to the water and stir for 10 min. Then, use a peristaltic pump to uniformly add 50 ml of 0.25 mol / L sodium phosphate solution to the calcium sulfate solution at a rate of 1 mL / min. After the addition is complete, adjust the pH of the mixed solution to 12 with 0.5 mol / L NaOH solution and continue stirring for 2 h. After the reaction is complete, filter the mixed solution and dry the filter residue in an oven at 100 °C to obtain modified calcium sulfate seed material.
[0041] Example 2
[0042] Add 150 ml of deionized water to a beaker, control the water bath temperature at 20 °C, and stir at 450 rpm. Add 1 g of calcium sulfate to the water and stir for 10 min. Then, use a peristaltic pump to uniformly add 50 ml of 0.25 mol / L sodium phosphate solution to the calcium sulfate solution at a rate of 1 mL / min. After the addition is complete, adjust the pH of the mixed solution to 12 with 0.6 mol / L NaOH solution and continue stirring for 2 h. After the reaction is complete, filter the mixed solution and dry the filter residue in a 100 °C oven to obtain modified calcium sulfate seed material.
[0043] Example 3
[0044] Add 150 ml of deionized water to a beaker, control the water bath temperature at 25 °C, and stir at 450 rpm. Add 1 g of calcium sulfate to the water and stir for 10 min. Then, use a peristaltic pump to uniformly add 50 ml of 0.25 mol / L sodium phosphate solution to the calcium sulfate solution at a rate of 1 mL / min. After the addition is complete, adjust the pH of the mixed solution to 12 with 0.7 mol / L NaOH solution and continue stirring for 30 min. After the reaction is complete, filter the mixed solution and dry the filter residue in an oven at 100 °C to obtain modified calcium sulfate seed material.
[0045] Example 4
[0046] Add 150 ml of deionized water to a beaker, control the water bath temperature at 25℃, and the stirring speed at 450 rpm. Add 1 g of calcium sulfate to the water and stir for 10 min. Then, use a peristaltic pump to uniformly add 50 ml of 0.25 mol / L sodium phosphate solution to the calcium sulfate solution at a rate of 1 mL / min. After the addition is complete, adjust the pH of the mixed solution to 12 with 0.8 mol / L NaOH solution and continue stirring for 1 h. After the reaction is complete, filter the mixed solution and dry the filter residue in a 100℃ oven to obtain modified calcium sulfate seed material.
[0047] Example 5
[0048] Add 150 ml of deionized water to a beaker, control the water bath temperature at 25 °C, and stir at 450 rpm. Add 1 g of calcium sulfate to the water and stir for 10 min. Then, use a peristaltic pump to uniformly add 50 ml of 0.2 mol / L sodium phosphate solution to the calcium sulfate solution at a rate of 1 mL / min. After the addition is complete, adjust the pH of the mixed solution to 12 with 0.9 mol / L NaOH solution and continue stirring for 2 h. After the reaction is complete, filter the mixed solution and dry the filter residue in an oven at 100 °C to obtain modified calcium sulfate seed material.
[0049] Example 6
[0050] Add 150 ml of deionized water to a beaker, control the water bath temperature at 25 °C, and stir at 450 rpm. Add 1 g of calcium sulfate to the water and stir for 10 min. Then, use a peristaltic pump to uniformly add 50 ml of 0.15 mol / L sodium phosphate solution to the calcium sulfate solution at a rate of 1 mL / min. After the addition is complete, adjust the pH of the mixed solution to 12 with 1 mol / L NaOH solution and continue stirring for 2 h. After the reaction is complete, filter the mixed solution and dry the filter residue in a 100 °C oven to obtain modified calcium sulfate seed material.
[0051] Example 7
[0052] Add 150 ml of deionized water to a beaker, control the water bath temperature at 25 °C, and stir at 450 rpm. Add 1 g of calcium sulfate to the water and stir for 10 min. Then, use a peristaltic pump to uniformly add 50 ml of 0.1 mol / L sodium phosphate solution to the calcium sulfate solution at a rate of 1 mL / min. After the addition is complete, adjust the pH of the mixed solution to 12 with 0.5 mol / L NaOH solution and continue stirring for 2 h. After the reaction is complete, filter the mixed solution and dry the filter residue in an oven at 100 °C to obtain modified calcium sulfate seed material.
[0053] Figure 1 and Figure 2 These are X-ray diffraction patterns of the modified calcium sulfate seed materials prepared in Examples 1-7 of this invention. Figure 1 and Figure 2 It can be seen that the modified calcium sulfate seed materials all show diffraction peaks at 2θ = 25.4° corresponding to the standard card of calcium sulfate (PDF#70-0909), and at 2θ = 31.9° corresponding to the standard card of calcium phosphate (PDF#18-0303), confirming the successful preparation of the modified calcium sulfate seed materials.
[0054] Table 1 provides data on the specific surface area, pore volume, and average pore size of the modified calcium sulfate seed materials prepared in Examples 1-7 of this invention. As shown in Table 1, compared with the original calcium sulfate, the prepared modified calcium sulfate seed materials with surface-coated active calcium phosphate exhibit significantly increased specific surface area and pore volume, and a markedly reduced pore size.
[0055]
[0056] The modified calcium sulfate seed materials obtained in Examples 1-7 were used for defluorination, and a series of static induced crystallization defluorination experiments were conducted. The experimental steps are as follows: 50 ml of F... - A certain amount of seed crystals corresponding to Examples 1-7 were added to a sodium fluoride solution with a concentration of 9.5 mg / L. The mixture was stirred at 400 rpm for 2 min, followed by stirring for another 30 min. After the reaction was completed, the mixed solution was filtered, and the residual F in the filtrate was measured. - Ca 2+ And phosphate concentration; the results are shown in Table 2.
[0057] Comparative Example 1
[0058] The difference between Comparative Example 1 and Example 1 is that, in the defluorination application, a fluorapatite / calcite mixed seed material is used to replace the modified calcium sulfate seed material prepared in Example 1. The mass ratio of fluorapatite to calcite in the mixed seed material is 4:1, and the other defluorination conditions remain unchanged.
[0059] Comparative Example 2
[0060] The difference between Comparative Example 2 and Example 1 is that, in the defluorination application, tricalcium phosphate seed material was used to replace the modified calcium sulfate seed material prepared in Example 1, while the other defluorination conditions remained unchanged.
[0061] Comparative Example 3
[0062] The difference between Comparative Example 3 and Comparative Example 1 is that in the defluorination application, potassium dihydrogen phosphate solution and calcium chloride solution, which are crystallizing agents, were added.
[0063] The specific application for fluoride removal is as follows: Add 50ml of F - Add the same seed crystals as in Comparative Example 1 to a 9.5 mg / L sodium fluoride solution and stir at 400 rpm for 2 min. Add potassium dihydrogen phosphate solution as a crystallizing agent, followed by calcium chloride solution, and then stir at 400 rpm for 30 min. After the reaction is complete, filter the mixture and determine the residual F in the filtrate. - Ca 2+ And phosphate concentration; the results are shown in Table 2.
[0064] Comparative Example 4
[0065] The difference between Comparative Example 4 and Comparative Example 2 is that potassium dihydrogen phosphate crystallizer and calcium chloride solution were added in the defluorination application.
[0066] The specific application for fluoride removal is as follows: Add 50ml of F - Add the same seed crystals as in Comparative Example 2 to a 9.5 mg / L sodium fluoride solution and stir at 400 rpm for 2 min. Add potassium dihydrogen phosphate solution as a crystallizing agent, followed by calcium chloride solution, and then stir at 400 rpm for 30 min. After the reaction is complete, filter the mixture and determine the residual F in the filtrate. - Ca 2+ And phosphate concentration; the results are shown in Table 2.
[0067]
[0068] As shown in Table 2, compared with the fluorapatite / calcite mixed seed crystals of Comparative Example 1 and the tricalcium phosphate seed crystals of Comparative Example 2, when treating the same volume of fluoride-containing water, the modified calcium sulfate seed crystals prepared in Examples 1 to 4 do not require the addition of additional calcium phosphate crystallizing agent when the seed crystal dosage is consistent. - The concentration decreased from 9.5 mg / L to below 1 mg / L, meeting emission standards. Furthermore, under the same defluorination effect (reducing F... - (The concentration was reduced from 9.5 mg / L to below 1 mg / L). Compared with Comparative Examples 3 and 4, the modified calcium sulfate seeds prepared in Examples 1 to 7 did not require the addition of calcium phosphate crystallizing agent. In addition to not requiring the addition of calcium phosphate crystallizing agent, the modified calcium sulfate seeds prepared in Examples 5 to 7 had a lower seed quantity and less residual phosphate in the solution after defluorination. This indicates that the modified calcium sulfate has better defluorination performance.
[0069] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Those skilled in the art can modify the technical solutions described in the above embodiments, or make equivalent substitutions for some of the technical features; and all such modifications and substitutions should fall within the protection scope of the appended claims of the present invention.
Claims
1. A method for preparing a modified calcium sulfate seed material, characterized in that, The method includes the following steps: Step A1: Under water bath conditions, add calcium sulfate powder to deionized water and stir to obtain a uniformly dispersed calcium sulfate solution; Step A2: Add sodium phosphate solution dropwise to the calcium sulfate solution, so that phosphate ions combine with calcium ions on the surface of calcium sulfate through a metathesis reaction; Step A3: Adjust the pH of the above system to 12 and stir to load calcium phosphate onto the surface of calcium sulfate; Step A4: After the above reaction is completed, filter to obtain filter residue, wash the filter residue with ethanol, and dry and grind the filter residue to obtain modified calcium sulfate seed material with active calcium phosphate coated on the surface.
2. The method for preparing the modified calcium sulfate seed material according to claim 1, characterized in that, In step A1, the temperature of the water bath is 20℃-25℃.
3. The method for preparing the modified calcium sulfate seed material according to claim 1, characterized in that, In step A2, the concentration of the sodium phosphate solution is 0.1 mol / L to 0.25 mol / L.
4. The method for preparing the modified calcium sulfate seed material according to claim 1, characterized in that, In step A3, the stirring time is 0.5h-2h.
5. The method for preparing the modified calcium sulfate seed material according to claim 1, characterized in that, In step A1, the ratio of deionized water to calcium sulfate is 150 mL: 1 g.
6. The method for preparing the modified calcium sulfate seed material according to claim 1, characterized in that, In step A2, the amount of sodium phosphate solution used is 50 mL.
7. The method for preparing the modified calcium sulfate seed material according to claim 1, characterized in that, In step A2, the dropping rate of the sodium phosphate solution is 1 mL / min.
8. As described in claim 1, characterized in that, In step A3, a 0.5 mol / L to 1 mol / L NaOH solution is used to adjust the pH value of the system.
9. A modified calcium sulfate seed material, characterized in that, The modified calcium sulfate seed material is prepared by the method described in any one of claims 1 to 8.
10. An application of a modified calcium sulfate seed material, characterized in that, The modified calcium sulfate seed material of claim 9 is used for fluoride removal.