Calcium-iron composite material for treating phosphorus-fluorine wastewater, preparation method and application thereof

Abstract

The application discloses a calcium-iron composite material for treating phosphorus-fluorine wastewater and a preparation method and application thereof. The calcium-iron composite material comprises a core and a shell coated outside the core; wherein the core comprises the following components: (a) zero-valent iron; (b) divalent or trivalent iron oxide or divalent or trivalent iron salt; the shell comprises calcium oxide and / or calcium hydroxide; and the shell and the core are bonded by mechanical force. The calcium-iron composite material has the advantages of strong synergistic effect, fast reaction speed, wide concentration range, no need of pH adjustment, environmental friendliness and the like, can realize rapid and efficient purification of phosphorus and fluorine in 1-10 minutes under the pH value of the phosphorus-fluorine wastewater, makes the total phosphorus concentration of effluent lower than 0.2 mg / L, the total fluorine concentration of effluent lower than 1.0 mg / L, and is suitable for synchronous and deep removal of phosphorus and fluorine in surface water, underground water and slightly polluted wastewater.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus and fluoride pollution control technology, specifically relating to a calcium-iron composite material for treating phosphorus and fluoride wastewater, its preparation method, and its application. Background Technology

[0002] Phosphorus and fluoride are typical pollutants in water bodies. The "Surface Water Environmental Quality Standard" (GB 3838-2002) specifies the limits for phosphorus (as P) and fluoride (as F) in centralized drinking water surface water sources. - Strict limits were set for total phosphorus (e.g., ≤0.2 mg / L for total phosphorus and ≤1.0 mg / L for fluoride).

[0003] Currently, chemical precipitation is commonly used to treat high-concentration phosphorus / fluoride industrial wastewater. Phosphorus removal mainly relies on the addition of calcium salts (such as lime) to form insoluble precipitates like hydroxyapatite; fluoride removal mainly relies on aluminum or calcium salts to generate calcium fluoride precipitates or aluminum-fluoride complexes. While these methods are effective for high-concentration polluted wastewater, they face significant technical bottlenecks when dealing with the advanced treatment of low-concentration phosphorus and fluoride (e.g., total phosphorus concentration 0.3–10 mg / L, fluoride concentration 10–50 mg / L).

[0004] 1. Insufficient reaction kinetics and limited removal precision: According to the principle of chemical equilibrium, the precipitation method of sparingly soluble salts has an inherent solubility limit. When the concentration of pollutants drops to near or below their solubility product, the driving force of the reaction decreases sharply, and the precipitation reaction tends to stagnate. For example, the theoretical residual fluoride concentration of calcium fluoride is about 7.8 mg / L, and it is difficult to reach the stringent standard of below 1 mg / L by simply relying on calcium salt precipitation. Similarly, traditional calcium salt phosphorus removal is also difficult to stably break through the concentration barrier of 0.5 mg / L.

[0005] 2. Competition and Interference of Coexisting Ions: In phosphorus and fluoride coexisting systems, there are complex competition and inhibition effects between the two. On the one hand, phosphate and fluoride ions compete for a limited calcium source, forming fluorapatite with lower solubility. However, this process is kinetic and may lead to excessive calcium ion levels in the effluent. On the other hand, excessive calcium salt addition can cause the pH of the water to rise sharply to strong alkalinity (>11). This not only wastes reagents and generates a large amount of sludge, but also requires a large amount of acid to restore the effluent, increasing treatment costs and operational complexity.

[0006] 3. Conventional processes are lengthy and costly to operate: To achieve simultaneous and deep removal of low-concentration phosphorus and fluoride, existing technologies often require a lengthy combined process of "calcium precipitation + aluminum / magnesium salt flocculation + multi-stage adsorption". This multi-step treatment not only results in large infrastructure investments and a large land area, but its complex reagent dosing and sludge treatment systems also significantly increase the difficulty of operation management and cost control.

[0007] Therefore, developing a new type of treatment material and technology that can operate near neutral pH, has high synergistic removal efficiency and selectivity for low concentrations of phosphorus and fluoride, and requires no complex subsequent adjustments has become a major technical challenge to address the urgent needs of deep water purification and drinking water safety.

[0008] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0009] To address the aforementioned problems in the existing technology, this invention provides a calcium-iron composite material for treating phosphorus and fluoride wastewater, its preparation method, and its application. The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, the present invention provides a calcium-iron composite material for treating phosphorus and fluoride wastewater, comprising a core and a shell covering the outside of the core; The kernel contains the following components: (a) Zero-valent iron; (b) Iron oxides or iron salts with valence of divalent or trivalent valence; The outer shell contains calcium oxide and / or calcium hydroxide; The outer shell and the core are bonded by mechanochemical bonding.

[0010] In one embodiment of the present invention, the outer shell further comprises iron atoms; If the core contains iron oxide, then the iron atoms in the shell exist in the form of amorphous iron oxide; If the core contains iron salts, then the iron atoms in the outer shell exist in the form of doped iron.

[0011] In one embodiment of the present invention, the iron oxide includes one or more of FeO, Fe2O3, Fe3O4, FeO hydrate, Fe2O3 hydrate, and Fe3O4 hydrate; The iron salt includes one or more of FeSO4, FeCl2, Fe2(SO4)3, FeCl3, and Fe(NO3)3.

[0012] In one embodiment of the present invention, the particle size of the calcium-iron composite material is 2µm to 20µm; wherein the thickness of the outer shell is 50 nm to 500 nm.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned calcium-iron composite material for treating phosphorus and fluoride wastewater, comprising the following steps: S10. Obtain calcium source powder and iron source powder; S20. Mix calcium source powder and iron source powder according to the molar ratio of calcium to iron (0.5~5):1 to obtain mixed powder. S30. Under an inert atmosphere or an air atmosphere, the mixed powder is ball-milled at a speed of 300-600 rpm for 2-10 h, and the ball-to-powder ratio is (10-30):1, to obtain a calcium-iron composite material for treating phosphorus and fluoride wastewater.

[0014] In one embodiment of the present invention, the calcium source powder includes calcium oxide and / or calcium hydroxide; The iron source powder comprises the following components: (a) Zero-valent iron; (b) Iron oxides or iron salts with valence of divalent or trivalent valence; The iron oxide includes one or more of FeO, Fe2O3, Fe3O4, FeO hydrate, Fe2O3 hydrate, and Fe3O4 hydrate; the iron salt includes one or more of FeSO4, FeCl2, Fe2(SO4)3, FeCl3, and Fe(NO3)3.

[0015] Thirdly, the present invention provides an application of the above-mentioned calcium-iron composite material in the treatment of phosphorus and fluoride in wastewater. The calcium-iron composite material is added to the wastewater for reaction, and the precipitate is filtered off to obtain treated water. The ratio of the mass of the calcium-iron composite material to the mass of the total phosphorus in the wastewater is in the range of (10 to 100):1.

[0016] In one embodiment of the present invention, the initial total phosphorus concentration in the wastewater is 0.3 to 10 mg / L, and the initial total fluoride concentration is 10 to 50 mg / L.

[0017] In one embodiment of the present invention, the reaction time is 1 min to 10 min, and the reaction pH value is 6 to 8.

[0018] In one embodiment of the present invention, the total phosphorus concentration in the treated water is less than 0.2 mg / L and the total fluoride concentration in the treated water is less than 1 mg / L.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a calcium-iron composite material for treating phosphorus and fluoride wastewater. The calcium-iron composite material has a core containing calcium and / or iron and a shell. By adsorbing on the surface of the shell, trace pollutants are first enriched at the interface, transforming the low concentration problem of the wastewater environment into a high concentration reaction at the interface, thereby improving the treatment effect of low concentration phosphorus and fluoride.

[0020] 2. The calcium-iron composite material provided by the present invention generates a local high pH at the interface through micro-electrolysis of zero-valent iron, and the synergistic effect of calcium and iron coexistence makes the interface reach the thermodynamic conditions required for precipitation even in a neutral or slightly acidic pH environment of the overall solution.

[0021] 3. The method for preparing calcium-iron composite material provided by the present invention involves mixing calcium source powder and iron source powder and then performing high-energy ball milling (e.g., high-speed ball milling) to obtain a calcium-iron composite material with a core-shell structure. The core-shell structure is bonded by mechanochemical bonding. The preparation process is simple and easy to operate.

[0022] 4. The calcium-iron composite material provided by this invention has a significant synergistic effect. The calcium component (calcium oxide / calcium hydroxide) can directly react with phosphate and fluoride ions in water to generate insoluble precipitates such as hydroxyapatite (Ca5(PO4)3OH), fluorapatite (Ca5(PO4)3F), and calcium fluoride (CaF2), achieving chemical precipitation removal. The iron component (zero-valent iron, iron oxides, or iron salt hydrolysis products) further captures phosphorus and fluoride ions through surface adsorption, complexation, co-precipitation, and in-situ generation of iron (hydride) oxide loading, promoting the aggregation and separation of precipitate particles. The calcium-iron composite structure not only provides dual active sites chemically but also physically enhances the specific surface area and the exposure of reactive sites, significantly improving the reaction kinetics and removal capacity under low concentration conditions.

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0024] Figure 1 These are schematic diagrams of the morphology of the calcium-iron composite material for treating phosphorus and fluoride wastewater provided in Examples 1-4 of the present invention. Figure 2 This is a TEM characterization image of the calcium-iron composite material for treating phosphorus and fluoride wastewater provided in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the water sample test results after application examples 1-3 of the present invention; Figure 4 This is a schematic diagram comparing the test results of water samples after treatment in Application Example 4 and Comparative Example 1 of the present invention. Detailed Implementation

[0025] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following, in conjunction with the accompanying drawings and specific embodiments, provides a detailed description of a calcium-iron composite material for treating phosphorus and fluoride wastewater according to the present invention, its preparation method, and its application.

[0026] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0027] It should be noted that, in this document, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0028] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0030] Example 1 A method for preparing a calcium-iron composite material for treating phosphorus and fluoride wastewater includes the following steps: Raw materials obtained: 5.6 g calcium oxide, 7.3 g micron zero-valent iron powder, and 10.6 g ferrous sulfate (FeSO4).

[0031] The three raw materials were weighed according to a molar ratio of calcium to total iron (zero-valent iron and ferrous sulfate) of 0.5:1 and placed in a ball mill jar. Under argon protection, the mixture was ball-milled for 4 hours at a ball-to-material ratio of 20:1 and a speed of 500 rpm. (See [reference needed]). Figure 1 A black powdery calcium-iron composite material was obtained. The calcium-iron composite material prepared in Example 1 is defined as calcium-iron composite material 1. See [link to example]. Figure 2 The figure shows the TEM (transmission electron microscopy) characterization of calcium-iron composite material 1. It can be seen from the figure that the calcium-iron composite material has a core-shell structure.

[0032] Example 2 A method for preparing a calcium-iron composite material for treating phosphorus and fluoride wastewater includes the following steps: Raw materials: 7.4 g calcium hydroxide, 2.8 g micronized zero-valent iron powder, 8.1 g ferric chloride (FeCl3).

[0033] The three components were weighed according to a 1:1 molar ratio of calcium to total iron (zero-valent iron and ferric chloride) and placed in a ball mill jar. Under air atmosphere, the mixture was ball-milled at a ball-to-material ratio of 15:1 and a speed of 400 rpm for 6 hours. (See [reference needed]). Figure 1 A black powdery calcium-iron composite material was obtained. The calcium-iron composite material prepared in Example 2 is defined as calcium-iron composite material 2.

[0034] Example 3 A method for preparing a calcium-iron composite material for treating phosphorus and fluoride wastewater includes the following steps: Raw materials obtained: 8.4 g calcium oxide, 1.7 g micronized zero-valent iron powder, 7.2 g ferric oxide (Fe2O3); The three components were weighed at a molar ratio of calcium to total iron (zero-valent iron and ferric oxide) of 2:1 and placed in a ball mill jar. Under argon protection, the mixture was ball-milled for 8 hours at a ball-to-material ratio of 25:1 and a speed of 350 rpm. (See [reference needed]). Figure 1 A black powdery calcium-iron composite material was obtained. The calcium-iron composite material prepared in Example 3 is defined as calcium-iron composite material 3.

[0035] Example 4 A method for preparing a calcium-iron composite material for treating phosphorus and fluoride wastewater includes the following steps: Raw materials obtained: 14.8 g calcium hydroxide, 0.6 g micronized zero-valent iron powder, 7.0 g iron(III) oxide (Fe3O4); The three raw materials were weighed according to a molar ratio of calcium to total iron (zero-valent iron and iron(III) oxide) of 5:1 and placed in a ball mill jar. The mixture was ball-milled for 2 hours at a ball-to-material ratio of 10:1 under air atmosphere at a speed of 300 rpm. (See [reference needed]). Figure 1 A black powdery calcium-iron composite material was obtained. The calcium-iron composite material prepared in Example 4 is defined as calcium-iron composite material 4.

[0036] The core of the calcium-iron composite material prepared in the embodiments of the present invention comprises zero-valent iron + divalent / trivalent iron oxides or divalent / trivalent iron salts. The zero-valent iron (Fe) in the core... 0 It can serve as a micro-electrolysis engine, providing a continuous supply of reduction electrons (Fe). 0 → Fe 2+ + 2e This drives the cathode hydrogen evolution or oxygen reduction reaction, generating a local high OH concentration at the interface. -And a strong reducing environment. Zero-valent iron slowly dissolves Fe. 2+ Fe in divalent / trivalent iron oxides or divalent / trivalent iron salts 2+ or Fe 3+ It can diffuse into the shell and participate in subsequent reactions.

[0037] The outer shell of the calcium-iron composite material comprises calcium oxide and / or calcium hydroxide (CaO / Ca(OH)2), and amorphous iron oxide or doped iron. The calcium oxide and / or calcium hydroxide in the shell provide a significant amount of Ca. 2+ , with PO4 3- and F - The reaction directly produces stable precipitates such as Ca5(PO4)3OH and CaF2. The iron salts / oxides in the outer shell can act as adsorbents and bridges; on the one hand, after hydrolysis, the iron salts / oxides form positively charged sites (≡FeOH2). + ), which strongly captures phosphate (PO4) ions in water through electrostatic attraction and specific inner-layer complexation. 3- ) and fluoride ions (F - On the other hand, during ball milling, iron undergoes mechanochemical bonding with CaO, forming a strong Ca-O-Fe bond. This allows the iron sites that adsorb pollutants to connect with the iron-providing CaO sites. 2+ The calcium sites are closely adjacent, and the reaction pathway is extremely short.

[0038] Traditional precipitation methods require the compounds used to remove phosphorus and fluoride to collide and combine with the pollutants, but this probability is extremely low at low concentrations. The calcium-iron composite material provided by this invention first enriches trace pollutants at the interface through surface adsorption, transforming the low-concentration problem of the wastewater environment into a high-concentration reaction at the interface. This solves the problem of "reactants not being able to reach each other," improving the treatment effect for low-concentration phosphorus and fluoride. Simultaneously, the calcium-iron composite material provided by this invention generates a localized high pH at the interface through zero-valent iron micro-electrolysis, and the synergistic effect of calcium and iron coexistence allows the interface to reach the thermodynamic conditions required for precipitation even in a neutral pH environment of the overall solution. This overcomes the limitation of traditional lime methods, which require adjusting the pH of the entire water body to above 11 for effective removal of phosphorus and fluoride.

[0039] Application Example 1 An application of a calcium-iron composite material in the deep treatment of low concentrations of phosphorus and fluoride in water includes the following steps: Water sample 1: Low-concentration phosphorus and fluoride simulated wastewater, total phosphorus (as PO4) 3- (calculated) 10 mg / L, total fluoride (as F) - (Calculated) 50 mg / L, pH=6.8; Using the calcium-iron composite material 1 prepared in Example 1, calcium-iron composite material 1 was added to water sample 1 at a mass ratio of calcium-iron composite material 1:phosphorus = 30:1. At room temperature, the stirring speed was 200 rpm, and the reaction time was 5 min. After filtration to remove the precipitate, the water sample was collected for measurement. The phosphorus concentration was measured according to "HJ671-2013 Determination of Total Phosphorus in Water - Flow Injection-Ammonium Molybdate Spectrophotometric Method", and the fluoride concentration was detected according to "GB / T7484-1987 Determination of Fluoride in Water - Ion Selective Electrode Method". The test results are as follows: Figure 3 As shown.

[0040] Test results: The total phosphorus concentration in the effluent was 0.15 mg / L, and the total fluoride concentration was 0.8 mg / L, meeting the requirements of GB 3838. 2002 Class III water quality standard.

[0041] Application Example 2 An application of a calcium-iron composite material in the deep treatment of low concentrations of phosphorus and fluoride in water includes the following steps: Water sample 2: Urban landscape water body, total phosphorus (as PO4) 3- Total fluoride (as F) 3.8 mg / L - (Calculated) 35 mg / L, pH=7.2; Using the calcium-iron composite material 2 prepared in Example 2, calcium-iron composite material 2 was added to water sample 2 at a mass ratio of calcium-iron composite material 2:phosphorus = 50:1. After standing for 10 min at room temperature, the precipitate was filtered off and the water sample was collected for measurement. The phosphorus concentration was measured by the flow injection-ammonium molybdate spectrophotometric method (HJ671-2013), and the fluoride concentration was detected by the ion-selective electrode method (GB / T7484-1987). The test results are as follows. Figure 3 As shown.

[0042] Test results: The total phosphorus concentration in the effluent was 0.12 mg / L, and the total fluoride concentration was 0.6 mg / L, meeting the requirements of GB 3838. 2002 Class III water quality standard.

[0043] Application Example 3 An application of a calcium-iron composite material in the deep treatment of low concentrations of phosphorus and fluoride in water includes the following steps: Water sample 3: Phosphorus and fluoride contaminated groundwater, total phosphorus (as PO4) 3- Total fluoride (as F) 1.0 mg / L - (Calculated) 20 mg / L, pH=7.5; Using the calcium-iron composite material 3 prepared in Example 3, calcium-iron composite material 3 was added to water sample 3 at a mass ratio of calcium-iron composite material 3:phosphorus = 80:1. At room temperature, the stirring speed was 100 rpm, and the reaction time was 8 min. After filtration to remove the precipitate, the water sample was collected for measurement. The phosphorus concentration was measured according to "HJ671-2013 Determination of Total Phosphorus in Water - Flow Injection-Ammonium Molybdate Spectrophotometric Method", and the fluoride concentration was detected according to "GB / T7484-1987 Determination of Fluoride in Water - Ion Selective Electrode Method". The experimental results are as follows: Figure 3 As shown.

[0044] Test results: The total phosphorus concentration in the effluent was 0.10 mg / L, and the total fluoride concentration was 0.5 mg / L, meeting the requirements of GB 3838. 2002 Class III water quality standard.

[0045] Application Example 4 An application of a calcium-iron composite material in the deep treatment of low concentrations of phosphorus and fluoride in water includes the following steps: Water sample 4: Total phosphorus (as PO4) 3- Total fluoride (as F) 0.3 mg / L - (Calculated) 10 mg / L, pH=7.0.

[0046] Using the calcium-iron composite material 4 prepared in Example 4, calcium-iron composite material 4 was added to water sample 4 at a mass ratio of calcium-iron composite material 4:phosphorus = 20:1. After standing for 5 minutes at room temperature, the precipitate was filtered off and the water sample was collected for measurement. The phosphorus concentration was measured by the flow injection-ammonium molybdate spectrophotometric method (HJ671-2013), and the fluoride concentration was detected by the ion-selective electrode method (GB / T7484-1987). The test results are as follows. Figure 4 As shown.

[0047] Test results: The total phosphorus concentration in the effluent was 0.03 mg / L, and the total fluoride concentration was 0.1 mg / L, meeting the requirements of GB 3838. 2002 Class III water quality standard.

[0048] Comparative Example 1 Water sample 4: Total phosphorus (as PO4) 3- Total fluoride (as F) 0.3 mg / L - (Calculated) 10 mg / L, pH=7.0.

[0049] Lime was added to water sample 4 until the pH reached 11. After reacting for 30 minutes, samples were taken for measurement. Phosphorus concentration was measured using the "HJ671-2013 Determination of Total Phosphorus in Water - Flow Injection-Ammonium Molybdate Spectrophotometric Method", and fluoride concentration was detected using the "GB / T7484-1987 Determination of Fluoride in Water - Ion Selective Electrode Method". The test results are as follows: Figure 4 As shown.

[0050] Test results: The total phosphorus concentration in the effluent was 0.6 mg / L, and the total fluoride concentration was 5.4 mg / L, both failing to meet GB 3838 standards. 2002 Class III water quality standard.

[0051] Application Examples 1-4 above demonstrate that the calcium-iron composite material provided by this invention achieves a 99.0% removal rate of low-concentration phosphorus and fluoride (e.g., P = 0.3 mg / L, F = 10 mg / L in Application Example 4) in wastewater within 5 minutes. Under higher pollution loads (e.g., P = 10 mg / L, F = 50 mg / L in Application Example 1), the phosphorus removal rate can still reach 98.5% and the fluoride removal rate can reach 98.4% within 5 minutes. The total phosphorus in the treated effluent is consistently below 0.2 mg / L, and the total fluoride is below 1 mg / L, all within the natural pH range (6). 8) The reaction is completed internally, without the need for acid-base adjustment. Compared with single calcium oxide agents, the calcium-iron composite material provided by this invention shows significant advantages in removal efficiency, reaction rate, and pH stability.

[0052] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A calcium-iron composite material for treating phosphorus and fluoride wastewater, characterized in that, Includes a core and a shell covering the outside of the core; The kernel contains the following components: (a) Zero-valent iron; (b) Iron oxides or iron salts with valence of divalent or trivalent valence; The outer shell contains calcium oxide and / or calcium hydroxide; The outer shell and the core are bonded by mechanochemical bonding.

2. The calcium-iron composite material for treating phosphorus and fluoride wastewater according to claim 1, characterized in that, The outer shell also contains iron atoms; If the core contains iron oxide, then the iron atoms in the shell exist in the form of amorphous iron oxide; If the core contains iron salts, then the iron atoms in the outer shell exist in the form of doped iron.

3. The calcium-iron composite material for treating phosphorus and fluoride wastewater according to claim 2, characterized in that, The iron oxide includes one or more of FeO, Fe2O3, Fe3O4, FeO hydrate, Fe2O3 hydrate, and Fe3O4 hydrate; The iron salt includes one or more of FeSO4, FeCl2, Fe2(SO4)3, FeCl3, and Fe(NO3)3.

4. The calcium-iron composite material for treating phosphorus and fluoride wastewater according to any one of claims 1-3, characterized in that, The particle size of the calcium-iron composite material is 2µm to 20µm; wherein the thickness of the outer shell is 50 nm to 500 nm.

5. A method for preparing a calcium-iron composite material for treating phosphorus and fluoride wastewater as described in any one of claims 1-4, characterized in that, Includes the following steps: S10. Obtain calcium source powder and iron source powder; S20. Mix calcium source powder and iron source powder according to the molar ratio of calcium to iron (0.5~5):1 to obtain mixed powder. S30. Under an inert atmosphere or an air atmosphere, the mixed powder is ball-milled at a speed of 300-600 rpm for 2-10 h, and the ball-to-powder ratio is (10-30):1, to obtain a calcium-iron composite material for treating phosphorus and fluoride wastewater.

6. The method for preparing the calcium-iron composite material for treating phosphorus and fluoride wastewater according to claim 5, characterized in that, The calcium source powder includes calcium oxide and / or calcium hydroxide; The iron source powder comprises the following components: (a) Zero-valent iron; (b) Iron oxides or iron salts with valence of divalent or trivalent valence; The iron oxide includes one or more of FeO, Fe2O3, Fe3O4, FeO hydrate, Fe2O3 hydrate, and Fe3O4 hydrate; the iron salt includes one or more of FeSO4, FeCl2, Fe2(SO4)3, FeCl3, and Fe(NO3)3.

7. The application of the calcium-iron composite material according to any one of claims 1-4 in the treatment of phosphorus and fluoride wastewater, characterized in that, The calcium-iron composite material is added to the wastewater for reaction, and the precipitate is filtered off to obtain treated water; wherein the mass ratio of the calcium-iron composite material to the total phosphorus in the wastewater is in the range of (10~100):

1.

8. The application according to claim 7, characterized in that, The initial total phosphorus concentration in the wastewater is 0.3–10 mg / L, and the initial total fluoride concentration is 10–50 mg / L.

9. The application according to claim 8, characterized in that, The reaction time is 1 min to 10 min.

10. The application according to claim 7, characterized in that, The treated water has a total phosphorus concentration of less than 0.2 mg / L and a total fluoride concentration of less than 1 mg / L.

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