SYNTHESIS METHOD FOR LAYERED BIMETAL-BASED NANO LANTHANUM MATERIAL CAPABLE OF SYNCHRONOUSLY LOCKING PHOSPHORUS, REMOVING ALGAE, AND REDUCING TURBIDITY, AND USE THEREOF

Abstract

The present invention discloses a synthesis method for a layered dimetal-based nano lanthanum material capable of synchronously locking phosphorus, removing algae, and reducing turbidity, and the use thereof, and belongs to the field of environmental functional materials. In the present invention, a synthesis method includes: synthesizing LDHs by means of a single-drop coprecipitation method; filtering out an obtained product, washing the product with distilled water and drying; then adding the product to an alcohol solution of a lanthanum salt at certain concentration, and stirring for reaction; precipitating lanthanum ions in situ by adjusting a pH value of the solution; filtering out the reaction precipitate, washing the precipitate with an alcohol, and drying the precipitate to obtain an LDH-based nano lanthanum material.

Claims

1. A method for preparing a layered dimetal-based nano lanthanum material capable of synchronously flocculating and locking phosphorus, comprising the following steps: 1) preparing a mixed solution of double metal salts as a solution A, and preparing a precipitant solution as a solution B; 2) taking certain amount of solution B, slowly pumping the solution A into the solution B to perform a coprecipitation reaction, continuously stirring the reaction system to mix evenly, and ending the reaction when observing that the pH reaches a specific value; 3) allowing a reaction product obtained in step 2) to stand in a water bath at certain temperature; 4) performing centrifugal separation on a product of step 3), washing the product with distilled water until the product is neutral, and freeze drying and grinding the product into powder to obtain the product LDHs; 5) adding the LDHs to an alcohol solution of a lanthanum salt at certain concentration and stirring for reaction; 6) adjusting the pH of the reaction system in step 5) to a specific value and continuing stirring for reaction; and 7) filtering out a product obtained in step 6), washing the product with alcohol until the product is neutral, and freeze drying the product to obtain the layered dimetal-based nano lanthanum material; wherein the mixed solution of the double metal salts in step 1) comprises a divalent metal salt and a trivalent metal salt, wherein the divalent metal salt is a magnesium salt, the magnesium salt is MgCl.sub.2 or Mg (NO.sub.3).sub.2; the trivalent metal salt is an iron salt, the iron salt is FeCl.sub.3 or Fe(NO.sub.3).sub.3; a molar ratio of the divalent salt to the trivalent salt in the double metal salts is 2:1 to 4:1; the total concentration of the double metal salts in the solution A is 1-4 mol.Math.L.sup.1; the solution B in step 1) is a NaOH solution with a concentration of 1-3 mol.Math.L.sup.1; or the solution B is a mixed solution of NaOH and Na.sub.2CO.sub.3, wherein a molar concentration ratio of the NaOH to the Na.sub.2CO.sub.3 is 12:1 to 8:1; and the layered dimetal-based nano lanthanum material is used for flocculating suspended solids in a water body, and also adsorbing phosphorus from the water body.

2. The preparation method according to claim 1, wherein the pH at the end of the reaction in step 2) is 9.0-11.0, and in step 3), the water bath temperature is 50 C.-80 C., and the water bath time is 12-24 h.

3. The preparation method according to claim 1, wherein the lanthanum salt in step 5) is LaCl.sub.3 or La(NO.sub.3).sub.3; the concentration of lanthanum ions in the alcohol solution of the lanthanum salt is 1-40 g.Math.L.sup.1; and the stirring for reaction in step 5) is performed at a solid-liquid ratio of 1:5 to 1:200 for a stirring time of 12-24 h, and the alcohol is methanol or ethanol.

4. The preparation method according to claim 1, wherein HCl/NaOH is used in step 6) to adjust the pH of the system, the concentration of the regulator is 0.1-5 mol.Math.L.sup.1, and the pH of the system is adjusted to 10.0-12.0.

5. A layered dimetal-based nano lanthanum material prepared by the preparation method according to claim 1, wherein the layered dimetal-based nano lanthanum material is an Mg/Fe-LDH-based nano lanthanum material, abbreviated as La-MF, the La-MF material is white powder, the La-MF material has a particle size of 1-10 m, and a lanthanum loading capacity in the La-MF material is 5-30%.

6. Use of the layered dimetal-based nano lanthanum material according to claim 5, wherein the layered dimetal-based nano lanthanum material prepared is used for flocculating suspended solids in a water body, and also adsorbing phosphorus from the water body.

7. A layered dimetal-based nano lanthanum material prepared by the preparation method according to claim 2, wherein the layered dimetal-based nano lanthanum material is an Mg/Fe-LDH-based nano lanthanum material, abbreviated as La-MF, the La-MF material is white powder, the La-MF material has a particle size of 1-10 m, and a lanthanum loading capacity in the La-MF material is 5-30%.

8. A layered dimetal-based nano lanthanum material prepared by the preparation method according to claim 3, wherein the layered dimetal-based nano lanthanum material is an Mg/Fe-LDH-based nano lanthanum material, abbreviated as La-MF, the La-MF material is white powder, the La-MF material has a particle size of 1-10 m, and a lanthanum loading capacity in the La-MF material is 5-30%.

9. A layered dimetal-based nano lanthanum material prepared by the preparation method according to claim 4, wherein the layered dimetal-based nano lanthanum material is an Mg/Fe-LDH-based nano lanthanum material, abbreviated as La-MF, the La-MF material is white powder, the La-MF material has a particle size of 1-10 m, and a lanthanum loading capacity in the La-MF material is 5-30%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a process flowchart of a preparation method of the present invention.

[0029] FIG. 2a shows an SEM image of La-MF-1 prepared in Embodiment 1 of the present invention.

[0030] FIG. 2b shows a TEM image of La-MF-1 prepared in Embodiment 1 of the present invention.

[0031] FIG. 3 shows an XRD pattern of La-MF-1 and an Mg/Fe-LDH carrier prepared in Embodiment 1 of the present invention.

[0032] FIG. 4 shows an XRD pattern of La-MF-2 and an Mg/Fe-LDH carrier prepared in Embodiment 2 of the present invention.

[0033] FIG. 5 shows an XRD pattern of La-MF-3 and an Mg/Fe-LDH carrier prepared in Embodiment 2 of the present invention.

[0034] FIG. 6 shows removal ratios of La-MF-1 prepared in Embodiment 1 of the present invention for suspended solids and phosphates in a water body at different doses.

[0035] FIG. 7 shows schematic structural diagrams of La-MF prepared in Embodiment 1 of the present invention.

DETAILED DESCRIPTION

[0036] The present invention is further described below with reference to specific embodiments.

Embodiment 1

[0037] 1) A mixed solution of double metal salts MgCl.sub.2 (0.9 mol.Math.L.sup.1) and FeCl.sub.3 (0.3 mol.Math.L.sup.1) was prepared as a solution A, and a precipitant solution of NaOH (2 mol.Math.L.sup.1) and Na.sub.2CO.sub.3 (0.2 mol.Math.L.sup.1) was prepared as a solution B. [0038] 2) Certain amount of solution B was taken, the solution A was slowly pumped into the solution B to perform a coprecipitation reaction, the reaction system was continuously stirred to mix evenly, and the reaction was ended when observing that the pH reached 9.0. [0039] 3) A reaction product obtained in step 2) was allowed to stand in a water bath at 65 C. for 18 h to perform water bath heating crystallization. [0040] 4) Centrifugal separation was performed on a product of step 3), the product was washed with distilled water until the product was neutral, freeze dried, and ground into powder to obtain a product Mg/Fe-LDH. [0041] 5) The Mg/Fe-LDH powder material was added to an ethanol solution (0.375 g La.Math.L.sup.1) (1 g.Math.L.sup.1 LaCl.sub.3.Math.7H.sub.2O) and stirred for 12 h at a solid-liquid ratio of 1:50 for reaction. [0042] 6) The pH of the reaction system in step 5) was adjusted to 12.0 and stirring was continued for 12 h. [0043] 7) A precipitate reaction product obtained in step 6) was filtered out, washed with ethanol until the product was neutral, and freeze dried to obtain the layered dimetal-based nano lanthanum material (named La-MF-1).

[0044] The material prepared in the present embodiment is white powder, and the carrier Mg/Fe-LDH exhibits a sheet-like structure with a particle size of 1-10 m. The particle size of lanthanum nanoparticles is about 5-10 nm. After digestion, the lanthanum loading capacity is 13.12% as measured by ICP, it indicates successful loading of lanthanum. Lanthanum is distributed in the carrier in the form of nanoparticles, as shown in FIG. 2a and FIG. 2b. An XRD test was conducted on samples, and the results are shown in FIG. 3. The material retains the characteristic peaks of the carrier LDH, it indicates that the layered structure of the carrier material still exists. There are no obvious characteristic peaks related to lanthanum in the XRD pattern, it indicates that lanthanum is most likely to exist in the material in an amorphous or weakly crystalline state. A BET structure shows that the material has a specific surface area of 179.5 m.sup.2.Math.g.sup.1, with pores mostly being mesopores at 2-25 nm. The large specific surface area and rich pore structure are conducive to the adsorption of PO.sub.4.sup.3 by the material.

Embodiment 2

[0045] 1) A mixed solution of double metal salts MgCl.sub.2 (0.9 mol.Math.L.sup.1) and FeCl.sub.3 (0.3 mol.Math.L.sup.1) was prepared as a solution A, and a precipitant solution of NaOH (2 mol.Math.L.sup.1) and Na.sub.2CO.sub.3 (0.2 mol.Math.L.sup.1) was prepared as a solution B. [0046] 2) Certain amount of solution B was taken, the solution A was slowly pumped into the solution B to perform a coprecipitation reaction, the reaction system was continuously stirred to mix evenly, and the reaction was ended when observing that the pH reached 9.0. [0047] 3) A reaction product obtained in step 2) was allowed to stand in a water bath at 65 C. for 18 h to perform water bath heating crystallization. [0048] 4) Centrifugal separation was performed on a product of step 3), the product was washed with distilled water until the product was neutral, freeze dried, and ground into powder to obtain a product Mg/Fe-LDH. [0049] 5) The Mg/Fe-LDH powder material was added to an ethanol solution (0.375 g La.Math.L.sup.1) (1 g.Math.L.sup.1 LaCl.sub.3.Math.7H.sub.2O) and stirred for 12 h at a solid-liquid ratio of 1:50 for reaction. [0050] 6) A precipitate reaction product obtained in step 5) was filtered out, washed with ethanol until the product was neutral, and freeze dried to obtain the layered dimetal-based nano lanthanum material (named La-MF-2).

[0051] The material prepared in the present embodiment is white powder, and the carrier Mg/Fe-LDH exhibits a sheet-like structure with a particle size of 1-10 m. The particle size of lanthanum nanoparticles is about 5-10 nm. After digestion, the lanthanum loading capacity is 8.73% as measured by ICP, it indicates successful loading of lanthanum. An XRD test was conducted on samples, and the results are shown in FIG. 4. Because the material was not subjected to in-situ precipitation after lanthanum loading in the present embodiment, lanthanum mainly existed in a free state between the layers and on the surface, and the free state La could not be observed by XRD.

Embodiment 3

[0052] 1) A mixed solution of double metal salts MgCl.sub.2 (0.9 mol.Math.L.sup.1) and FeCl.sub.3 (0.3 mol.Math.L.sup.1) was prepared as a solution A, and a precipitant solution of NaOH (2 mol.Math.L.sup.1) and Na.sub.2CO.sub.3 (0.2 mol.Math.L.sup.1) was prepared as a solution B. [0053] 2) Certain amount of solution B was taken, the solution A was slowly pumped into the solution B to perform a coprecipitation reaction, the reaction system was continuously stirred to mix evenly, and the reaction was ended when observing that the pH reached 9.0. [0054] 3) A reaction product obtained in step 2) was allowed to stand in a water bath at 65 C. for 18 h to perform water bath heating crystallization. [0055] 4) Centrifugal separation was performed on a product of step 3), the product was washed with distilled water until the product was neutral, freeze dried, and ground into powder to obtain a product Mg/Fe-LDH. [0056] 5) The Mg/Fe-LDH powder material was added to an ethanol solution (0.375 g La.Math.L.sup.1) (1 g.Math.L.sup.1 LaCl.sub.3.Math.7H.sub.2O) and stirred for 12 h at a solid-liquid ratio of 1:50 for reaction. [0057] 6) A precipitate reaction product obtained in step 5) was filtered out, washed with ethanol until the product was neutral, and freeze dried. [0058] 7) A material obtained in step 6) was stirred in a 0.2 M NH.sub.4HCO.sub.3 solution for 12 h. [0059] 8) A reaction product obtained in step 7) was filtered out, washed with distilled water until the product was neutral, and freeze dried to obtain the layered dimetal-based nano lanthanum material (named La-MF-3).

[0060] The material prepared in the present embodiment is white powder, and the carrier Mg/Fe-LDH exhibits a sheet-like structure with a particle size of 1-10 m. The particle size of lanthanum nanoparticles is about 5-10 nm. After digestion, the lanthanum loading capacity is 8.23% as measured by ICP, it indicates successful loading of lanthanum. An XRD test was conducted on samples, and the results are shown in FIG. 5. Because the material was subjected to in-situ precipitation with the precipitant after lanthanum loading, a large amount of lanthanum was hydrolyzed and bound with carbonate radicals to form lanthanum carbonate crystals.

Application Example 1

[0061] This application example used the La-MF-1 as a material to test flocculation of suspended solids and synchronous phosphorus removal: a mixed solution containing 2 mg P.Math.L.sup.1, kaolin (30 mg.Math.L.sup.1), HA (Humic Acid) (10 mg.Math.L.sup.1), and M. aeruginosa (having an absorbance of 0.2 at 680 nm) was prepared as a target water body to be treated, and doses of the material were 0.05 g.Math.L.sup.1, 0.1 g.Math.L.sup.1, 0.2 g.Math.L.sup.1, 0.3 g.Math.L.sup.1, 0.4 g.Math.L.sup.1, and 0.5 g.Math.L.sup.1, respectively. Coagulation experiment operations were simulated at an initial pH of 8.0. A mixture was stirred at 600 rpm for 2 min and then at 120 rpm for 15 min, and allowed to stand for 1 h. The supernatant was taken to measure turbidity, chlorophyll-a concentration, absorbance at 254 nm, and PO.sub.4.sup.3 concentration.

[0062] As shown in FIG. 6, when the dose of the La-MF-1 is 0.3 g.Math.L.sup.1, the turbidity removal ratio is 97.98%, the chlorophyll a removal ratio is 97.86%, the HA (ABS, 254 nm) removal ratio is 91.44%, and the PO.sub.4.sup.3 removal ratio is 99.87%. The results indicate that the material has good flocculation and phosphorus removal effects at the dose of 0.3 g.Math.L.sup.1. As shown in FIG. 7a, lanthanum exists in the material in a weak crystalline state and a small amount in a free state. When the material is added to the water body, some of lanthanum may be hydrolyzed to generate a large number of positive charges, and is complexed with hydroxyl groups on the surface of the LDH to form a chain structure of [La(OH).sub.m(H.sub.2O).sub.n].sup.(3m)+, to exert the functions of adsorption and charge neutralization, sweep flocculation of precipitate, and the like, to rapidly reduce the turbidity and settle algae suspended solids in the water body. Moreover, the specific binding between the La.sup.3+ and the PO.sub.4.sup.3 enables the material to exhibit an excellent long-term phosphorus locking ability.

[0063] Under the same initial conditions, the La-MF-2 material maintains good removal ratios for turbidity, chlorophyll a and HA, but has a poor phosphorus removal effect, with only a 40% phosphorus removal ratio at a dose of 0.5 g/L. As shown in FIG. 7b, lanthanum exists in the material in a free state, and thus is hydrolyzed to generate a large amount of positive charges, to remove suspended solids via adsorption and charge neutralization and sweep flocculation of precipitate, but also binds and competes with phosphorus for adsorption sites, resulting in a significant decrease in phosphorus removal effect.

Application Example 2

[0064] This application example used the La-MF-3 as a material to test the basic performance of phosphorus removal and flocculation: a solution containing 50 mg P.Math.L.sup.1 was prepared to test the phosphorus adsorption capacity; and a solution containing kaolin (30 mg.Math.L.sup.1), HA (10 mg.Math.L.sup.1), and M. aeruginosa (having an absorbance of 0.2 at 680 nm) was prepared to test the flocculation performance, and the dose of the material was 0.5 g.Math.L.sup.1. At an initial pH of 8.0, the adsorption capacity was measured by reacting at 180 rpm for 72 h. Coagulation experiment operations were simulated. The mixture was stirred at 600 rpm for 2 min and then at 120 rpm for 15 min, and allowed to stand for 1 h. The supernatant was taken to measure turbidity, chlorophyll-a concentration, and absorbance at 254 nm.

[0065] The La-MF-3 has an adsorption capacity of 37.88 mgP/g, which is excellent in performance, but performs poorly in flocculation performance, with almost a removal ratio of 0 for chlorophyll a, a removal ratio of 9.02% for turbidity, and a removal ratio of 27.42% for HA. As shown in FIG. 7c, lanthanum exists between the layers and on the surface of the material as stable lanthanum carbonate, and thus the material performs well in phosphorus removal. However, due to the inability to hydrolyze and generate positive charges and a chain-like structure, the material performs poorly in flocculation.

[0066] The embodiments described above are only some embodiments of the present invention, and the implementations of the present invention are not limited by the embodiments. Various forms of combinations of the solutions in the embodiments, as well as any other changes, modifications, substitutions, or combinations that do not deviate from the spirit and principles of the present invention, should be equivalent replacements and are within the scope of protection of the present invention.