Magnetic rare earth composite oxide adsorbent and preparation method and application thereof

Abstract

The application belongs to the field of compound preparation and specifically relates to a magnetic rare earth composite oxide adsorbent and a preparation method and application thereof, and comprises the following steps: fully reacting a ferrous salt with sodium borohydride to obtain nanometer zero-valent iron, generating a large amount of ferrous ions and iron oxides after ultrasonic treatment, then reacting with a magnesium salt and a lanthanum salt, calcining, and then replacing magnesium ions to obtain the adsorbent. The adsorbent prepared by the application has excellent wide-pH phosphorus removal function, is easy to separate and has high recycling efficiency.

Description

Technical Field

[0001] This invention belongs to the field of compound preparation, specifically relating to a magnetic rare earth composite oxide adsorbent, its preparation method, and its application. Background Technology

[0002] Eutrophication is one of the main factors causing water pollution, and phosphorus is widely considered to be a key limiting factor in eutrophication. Once eutrophication occurs, water bodies emit a foul odor, their transparency and dissolved oxygen levels decrease, and various toxins are present, seriously endangering human health. Therefore, phosphorus removal from wastewater is of significant practical importance. Currently, the most commonly used phosphorus removal methods include chemical precipitation, biological methods, adsorption, and membrane separation. Adsorption phosphorus removal has been widely used due to its simple operation and low cost. In recent years, layered double hydroxides (LDHs) have been extensively studied as promising adsorbents for water purification. However, some problems remain when applying La-LDHs to phosphorus adsorption: 1) a narrow pH range of applicability; 2) difficulty in recycling. Therefore, a magnetic rare earth composite oxide was developed based on these issues. This adsorbent first prepares nano-zero-valent iron, which is then placed in deionized water to generate Fe. 2+ Various iron oxides (Fe3O4, FeOOH, γ-Fe2O3) are then co-precipitated on their surfaces to form iron oxide-MgFeLa-LDH. High-temperature calcination transforms all iron oxides into magnetic γ-Fe2O3, resulting in γ-Fe2O3-MgFeLa-LDO. Mg is then displaced by ethanol solution of LaCl3·7H2O. 2+ This process overcomes the problems of narrow pH adaptability and difficulty in recycling of LDH materials, while enhancing the absorption of phosphorus in wastewater and exhibiting good recycling performance, thus possessing broad research and application value. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a magnetic rare-earth composite oxide adsorbent with excellent phosphorus removal effect from wastewater and its preparation method. It has a wide range of applications and is easy to recycle. The technical solution is as follows:

[0004] A magnetic rare earth composite oxide adsorbent, which is a magnetic layered double hydroxide with a nanoscale flake morphology.

[0005] A method for preparing the above-mentioned magnetic rare earth composite oxide adsorbent includes the following steps:

[0006] a. In a nitrogen-protected atmosphere, ferrous salt is dissolved in water and then sodium borohydride is added. After the reaction is complete, the mixture is filtered, washed, and dried to obtain nano-zero valent iron.

[0007] b. Dissolve and mix the chlorides of lanthanum and magnesium in water to prepare solution A; dissolve sodium hydroxide and sodium carbonate in water to prepare solution B;

[0008] c. Place the above-mentioned nano-zero-valent iron in water and sonicate it to generate ferrous ions and iron oxides. Then add solution A and an equal volume of solution B to it, mix them evenly, adjust the pH of the system to alkaline, and wash and dry after the reaction is complete to obtain the iron oxide composite material.

[0009] d. The obtained iron oxide is calcined at high temperature, so that the iron oxide composite material is transformed into a magnetic magnesium-containing composite material;

[0010] e. Place the above magnesium-containing composite material in an ethanol solution of lanthanum chloride, mix thoroughly to displace magnesium ions, then filter and dry to obtain a magnetic rare earth composite oxide adsorbent.

[0011] Furthermore, the molar ratio of ferrous ions in the ferrous salt to borohydride ions in the sodium borohydride in step (a) is 1:(1-4).

[0012] Furthermore, the molar ratio of lanthanum to magnesium in step (b) is 1:(1-4); the molar ratio of sodium carbonate to sodium hydroxide in step (b) is 1:(1-3); and the molar ratio of total metal ions in solution A to sodium ions in solution B in step (b) is (1-3):(1-3).

[0013] Furthermore, the molar ratio of lanthanum in solution A to the nano-zero valent iron described in step (c) is 1:(2-4).

[0014] Furthermore, in step (c), the pH is adjusted to 9–12 using a dilute sodium hydroxide solution, the reaction temperature is 50–90°C, and the reaction time is 8–36 h.

[0015] Furthermore, the calcination temperature in step (d) is 200–600°C, and the reaction time is 1–5 h.

[0016] Furthermore, the replacement time in step (e) is 6–24 h; the mass ratio of lanthanum chloride in the magnesium-containing composite material and the lanthanum chloride ethanol solution in step (e) is 1:

[0017] (1-3).

[0018] A method for desorption and recovery of the above-mentioned magnetic rare earth composite oxide adsorbent is characterized by comprising the following steps: removing the adsorbent after adsorption using magnetic separation, drying the adsorbent after adsorption, and then calcining it at 200-400°C for 2-5 hours.

[0019] The application of the above-mentioned magnetic rare earth composite oxide adsorbent in phosphorus removal from waste is characterized in that the pH of the waste to which it is applied is 2 to 12.

[0020] By adopting the above scheme, the method of the present invention has the following advantages:

[0021] 1. The high anion exchange capacity of iron and rare earth metal lanthanum in the adsorbent of this invention, as well as the extremely high lanthanum content, give the material excellent wide pH phosphorus removal function, making it applicable to various complex aquatic environments.

[0022] 2. The high lanthanum content in the adsorbent of this invention has an excellent removal effect on phosphorus in wastewater.

[0023] 3. The adsorbent of the present invention has strong magnetism, which makes the separation of the adsorbent convenient and fast, and makes up for the problem that the adsorbent is difficult to recycle after adsorption, saving costs and avoiding secondary pollution caused by non-recyclability.

[0024] 4. During the phosphorus adsorption process, the material's structure transforms towards LDH due to the memory effect. After the reaction, it can be calcined in a muffle furnace to regenerate a magnetic rare earth composite oxide adsorbent. Moreover, the adsorption capacity loss is small after recycling, and it has excellent regeneration performance. Attached Figure Description

[0025] Figure 1 These are adsorption amount diagrams of embodiments and comparative examples of the present invention.

[0026] Figure 2 This is a graph showing the effect of the initial pH of the phosphorus-containing waste liquid on the adsorption capacity.

[0027] Figure 3 This is a comparison chart of the recycling performance of embodiments and comparative examples of the present invention.

[0028] Figure 4 This is the X-ray diffraction pattern of Embodiment 1 of the present invention.

[0029] Figure 5 This is a transmission electron microscope image of step (3) of Embodiment 1 of the present invention before calcination.

[0030] Figure 6 This is a transmission electron microscope image of the product after calcination in step (3) of Embodiment 1 of the present invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] (1) Under a nitrogen-protected atmosphere, add 100 ml of 200 mmol FeSO4 to a stirred three-necked flask, and then follow the steps outlined in BH4. - / Fe 2+ Add 100 ml of NaBH4 at a molar ratio of 2:1, and after sufficient reaction, filter, wash, and dry to obtain nano-zero valent iron.

[0034] (2) Take 1g of the above-mentioned nano-zero valent iron and place it in 100ml of distilled water for ultrasonic treatment for a period of time to generate a large amount of Fe. 2+ Iron oxides (Fe3O4, FeOOH, γ-Fe2O3) were added dropwise to a solution A prepared with 50 ml of 33.33 mmol MgCl2·6H2O and 16.67 mmol LaCl3·7H2O, and an equal volume of solution B prepared with 50 mmol NaOH and 25 mmol Na2CO3. The pH was controlled at 10, the mixture was stirred evenly, and then placed in a water bath at 65℃ for 24 h. After washing and drying, iron oxide-MgFeLa-LDH, i.e., iron oxide composite material, was generated.

[0035] (3) The obtained iron oxide composite material was calcined in a muffle furnace at 350°C for 3 hours to transform all iron oxides into magnetic γ-Fe2O3, thereby obtaining γ-Fe2O3-MgFeLa-LDO, i.e. magnesium-containing composite material. Figure 5 and Figure 6 The images show a comparison of transmission electron microscopy (TEM) images of the material before and after calcination. As can be seen from the images, the morphology of the material did not change significantly during the transformation from iron oxide-MgFeLa-LDH to γ-Fe2O3-MgFeLa-LDO, indicating that it has high stability.

[0036] (4) The magnesium-containing composite material was placed in an ethanol solution containing 1g LaCl3·7H2O, stirred, filtered, and dried to displace Mg. 2+ A magnetic rare-earth composite oxide adsorbent is generated. The XRD pattern of the product is shown below. Figure 4 As shown in the figure, the peak positions all match the diffraction data of the standard cards for γ-Fe₂O₃ and La₂O₂CO₃, indicating that the product contains γ-Fe₂O₃ and La₂O₂CO₃. Due to the substitution of LaCl₃·7H₂O, Mg... 2+ The content is extremely low, and no characteristic peaks of magnesium oxide were found in the figure, indicating that Mg 2+ It mainly plays a role in crystal form guidance, Fe 2+After calcination, it forms γ-Fe₂O₃ along with other iron oxides. Furthermore, a new La₂O₂CO₃ phase appears in the XRD, which is due to the presence of La. 3+ The larger radius leads to the formation of La on the MgFeLa-LDH layer. 3+ It is unstable and will release new rare earth oxides, La2O2CO3, after roasting.

[0037] Example 2:

[0038] (1) Under a nitrogen-protected atmosphere, add 100 ml of 200 mmol FeSO4 to a stirred three-necked flask, and then follow the steps outlined in BH4. - / Fe 2+ Add 100 ml of NaBH4 at a molar ratio of 2:1, and after sufficient reaction, filter, wash, and dry to obtain nano-zero valent iron.

[0039] (2) Take 1g of the above-mentioned nano-zero valent iron and place it in 100ml of distilled water for ultrasonic treatment for a period of time to generate a large amount of Fe. 2+ Iron oxides (Fe3O4, FeOOH, γ-Fe2O3) were added dropwise to a solution A prepared with 50 ml of 37.5 mmol MgCl2·6H2O and 12.5 mmol LaCl3·7H2O, and an equal volume of solution B prepared with 50 mmol NaOH and 25 mmol Na2CO3. The pH was controlled at 10, and the mixture was stirred evenly. After reacting in a water bath at 65℃ for 24 h, the mixture was washed and dried to produce iron oxide-MgFeLa-LDH, which is an iron oxide composite material.

[0040] (3) The obtained iron oxide composite material was calcined in a muffle furnace at 350°C for 3 hours to transform all iron oxides into magnetic γ-Fe2O3, thereby obtaining γ-Fe2O3-MgFeLa-LDO, which is a magnesium-containing composite material.

[0041] (4) The above magnesium-containing composite material was placed in an ethanol solution containing 1g LaCl3·7H2O, stirred, filtered, and dried to displace Mg. 2+ , thus generating magnetic rare earth composite oxide adsorbent.

[0042] Example 3:

[0043] (1) Under a nitrogen-protected atmosphere, add 100 ml of 200 mmol FeSO4 to a stirred three-necked flask, and then follow the steps outlined in BH4. - / Fe 2+ Add 100 ml of NaBH4 at a molar ratio of 2:1, and after sufficient reaction, filter, wash, and dry to obtain nano-zero valent iron.

[0044] (2) Take 1g of the above-mentioned nano-zero valent iron and place it in 100ml of distilled water for ultrasonic treatment for a period of time to generate a large amount of Fe. 2+ Iron oxides (Fe3O4, FeOOH, γ-Fe2O3) were added dropwise to a solution A prepared with 50 ml of 40 mmol MgCl2·6H2O and 10 mmol LaCl3·7H2O, and an equal volume of solution B prepared with 50 mmol NaOH and 25 mmol Na2CO3. The pH was controlled at 10, and the mixture was stirred evenly. The mixture was then placed in a water bath at 65℃ for 24 h and washed and dried to produce iron oxide-MgFeLa-LDH, which is an iron oxide composite material.

[0045] (3) The obtained iron oxide composite material was calcined in a muffle furnace at 350°C for 3 hours to transform all iron oxides into magnetic γ-Fe2O3, thereby obtaining γ-Fe2O3-MgFeLa-LDO, which is a magnesium-containing composite material.

[0046] (4) The above magnesium-containing composite material was placed in an ethanol solution containing 1g LaCl3·7H2O, stirred, filtered, and dried to displace Mg. 2+ , thus generating magnetic rare earth composite oxide adsorbent.

[0047] Comparative Example 1:

[0048] Solution A, prepared by 50 ml of 33.33 mmol MgCl2·6H2O and 16.67 mmol LaCl3·7H2O, was mixed with an equal volume of solution B, prepared by 50 mmol NaOH and 25 mmol Na2CO3. The pH was controlled at 10, and the mixture was stirred evenly. The mixture was then placed in a water bath at 65℃ for 24 h and washed and dried to generate MgLa-LDH adsorbent.

[0049] Comparative Example 2:

[0050] Solution A, prepared by mixing 50 ml of 37.5 mmol MgCl2·6H2O and 12.5 mmol LaCl3·7H2O, was mixed with an equal volume of solution B, prepared by mixing 50 mmol NaOH and 25 mmol Na2CO3. The pH was controlled at 10, and the mixture was stirred evenly. The mixture was then placed in a water bath at 65℃ for 24 h and washed and dried to generate MgLa-LDH adsorbent.

[0051] Desorption Example:

[0052] The adsorbent after adsorption was removed by magnetic separation, dried, and then placed in a muffle furnace at 300°C for 3 hours.

[0053] Example and comparative performance tests:

[0054] Phosphorus removal tests were conducted on the phosphate solutions. Phosphate solutions with pH values ​​of 2, 4, 6, 8, 10, and 12 were prepared at 20 mg / L. 0.2 g / L of the adsorbent from each example and comparative example was added to the phosphate solutions at each pH. Adsorption experiments were conducted in a constant-temperature shaker at 25°C and 200 rpm. Supernatants were collected at 0, 10, 20, 50, 90, 120, 150, 180, 240, 270, and 300 min, filtered through a 0.45 μm filter membrane, and the phosphate concentration in the solution after adsorption was determined by UV absorption. The adsorption capacity was then calculated.

[0055] like Figure 1 As shown, the adsorption capacity of each embodiment of the present invention is higher than that of the comparative examples throughout the entire time period, and reaches more than 83 mg / g at 90 min, while the comparative examples are all below 80 mg / g. The adsorption efficiency of the adsorbent in each embodiment of the present invention is significantly higher than that in the comparative examples.

[0056] like Figure 2 As shown, the adsorbents of the various embodiments of the present invention exhibit adsorption capacities exceeding 90 mg / g in a pH range of 2–12, while the comparative examples only show phosphorus removal effects approaching those of the embodiments of the present invention in a pH range of 4–8. At pH values ​​below 4, the adsorption capacity of the comparative examples is only half that of the embodiments of the present invention. At pH = 10, the adsorption capacity of the comparative examples is approximately 80 mg / g, and at pH = 12, the adsorption capacity is approximately 70 mg / g, both significantly lower than those of the embodiments of the present invention. This demonstrates that the adsorbents of the present invention maintain good phosphorus removal capabilities even under more extreme acidity and alkalinity conditions.

[0057] After adsorption for 300 min in a 20 mg / L phosphate solution at pH 6, all examples and comparative examples were subjected to desorption according to the desorption examples. The adsorption and desorption processes were then repeated using a fresh phosphate solution to obtain... Figure 3 The graph shows a comparison of the regeneration performance of the adsorbent.

[0058] The embodiments of the present invention maintained an adsorption capacity of over 90 mg / g after 8 cycles, while the comparative examples showed a significant decrease in adsorption capacity during cycling. Comparative Example 2, in particular, only achieved an adsorption capacity of over 70 mg / g after 8 cycles, far lower than the embodiments. This demonstrates that the adsorbent of the present invention exhibits good cyclic stability and retains good adsorption capacity even after multiple cycles.

[0059] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A method for producing a magnetic rare earth complex oxide adsorbent, characterized by comprising the steps of: The magnetic rare earth composite oxide adsorbent is a layered double hydroxide with magnetism, and has a morphology of nanoscale flake; and comprises the following steps: ​ a. Dissolving ferrous salt in water under N2 protection, then adding sodium borohydride, filtering, washing and drying after sufficient reaction to obtain nanoscale zero-valent iron; b. Dissolving and mixing chloride of lanthanum and magnesium in water to prepare solution A; dissolving sodium hydroxide and sodium carbonate in water to prepare solution B; c. Placing the nanoscale zero-valent iron in water for ultrasonic treatment to generate ferrous ions and iron oxides, then adding solution A and the same volume of solution B dropwise, mixing uniformly and adjusting the pH of the system to be alkaline, washing and drying after sufficient reaction to obtain iron oxide composite material; d. High-temperature calcining the obtained iron oxide composite material at 200-600°C to convert the iron oxide composite material into a magnesium-containing composite material with magnetism; e. Placing the above magnesium-containing composite material in an ethanol solution of lanthanum chloride, mixing sufficiently to replace magnesium ions, then filtering and drying to obtain the magnetic rare earth composite oxide adsorbent.

2. The method of producing a magnetic rare earth complex oxide adsorbent according to claim 1, characterized by, The molar ratio of iron ions in the ferrous salt to borohydride ions in sodium borohydride in step (a) is 1:(1-4).

3. The preparation method of the magnetic rare earth composite oxide adsorbent according to claim 1, characterized in that, The molar ratio of lanthanum to magnesium in step (b) is 1:(1-4); the molar ratio of sodium carbonate to sodium hydroxide in step (b) is 1:(1-3); and the molar ratio of total metal ions in solution A to sodium ions in solution B in step (b) is (1-3):(1-3).

4. The method of claim 1, wherein the magnetic rare earth complex oxide adsorbent is prepared by the steps of: preparing a mixed oxide of a rare earth element and a transition metal element; and adding a metal element to the mixed oxide of the rare earth element and the transition metal element. The molar ratio of lanthanum in solution A to nanoscale zero-valent iron in step (c) is 1:(2-4).

5. The method of claim 1, wherein the magnetic rare earth complex oxide adsorbent is prepared by the steps of: preparing a mixed oxide of a rare earth element and a transition metal element; and adding a metal element to the mixed oxide of the rare earth element and the transition metal element. The pH in step (c) is adjusted to 9-12 using a dilute sodium hydroxide solution, the reaction temperature is 50-90°C, and the reaction time is 8-36h.

6. The method of claim 1, wherein the magnetic rare earth complex oxide adsorbent is prepared by the steps of: preparing a mixed oxide of a rare earth element and a transition metal element; and adding a metal element to the mixed oxide of the rare earth element and the transition metal element. The reaction time of the calcination in step (d) is 1-5h.

7. The method of claim 1, wherein the magnetic rare earth complex oxide adsorbent is prepared by the steps of: preparing a mixed oxide of a rare earth element and a transition metal element; and adding a metal element to the mixed oxide of the rare earth element and the transition metal element. The replacement time in step (e) is 6-24h; and the mass ratio of the magnesium-containing composite material to lanthanum chloride in the ethanol solution of lanthanum chloride in step (e) is 1:(1-3).

8. A method for desorbing and recovering the magnetic rare earth complex oxide adsorbent produced by the method of claim 1, characterized by, The following steps are included: Using magnetic separation to take out the adsorbed adsorbent, drying the adsorbed adsorbent, and then calcining at 200-400°C for 2-5h.

9. Use of the magnetic rare earth complex oxide adsorbent produced by the method of claim 1 in the dephosphorization of waste, characterized by, The pH of the applied waste is 2-12.

Images