Multi-element doped synergistically modified ferrihydrite as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of wastewater treatment, and particularly relates to multi-element doped synergistically modified ferrihydrite as well as a preparation method and application thereof, and the ferrihydrite is doped with at least one rare earth element and at least one of an aluminum element and a silicon element; the doping amount of the rare earth elements in the ferrihydrite is 0.5-20wt%; the doping amount of the aluminum element in the ferrihydrite is 0-20wt%; the doping amount of the silicon element in the ferrihydrite is 0-20wt%. Compared with the prior art, the method solves the problems that in ferrihydrite single-element modification in the prior art, although stability is improved through Al / Si doping, element modification in the same period is limited in improvement of the adsorption capacity, and the specific recognition capacity on phosphate radicals cannot be improved; and the anti-interference performance of the rare earth doped in the complex water matrix still needs to be improved. According to the scheme, rare earth and Al / Si doping are combined, so that improvement of phosphorus adsorption stability, adsorption capacity, specific recognition capability and anti-interference performance of ferrihydrite is realized synergistically.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to ferrihydrite co-modified by multi-element doping, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its high specific surface area (200 - 400 m 2 / g) and environmentally friendly characteristics, ferrihydrite has been widely studied and applied in the field of water phosphorus pollution control. However, its actual engineering application is still limited by its inherent defects: (1) the theoretical phosphorus adsorption capacity is relatively low (2) poor selectivity for coexisting anions (such as Cl-, SO4 2 -); (3) the amorphous structure is prone to transform into a crystalline state (such as transforming into goethite or hematite), resulting in the attenuation of active sites.

[0003] In view of the above problems, researchers have explored the path of performance optimization through single-element doping modification. Recent studies have shown that rare earth elements (La 3+ , Ce 3+ etc.) can form stable coordination structures with phosphate groups, endowing the material with specific adsorption advantages, such as in the article "Lanthanum substitution enhances the intrinsic phosphate-adsorption capacity of hydrated ferric oxide via increasing Fe electron density" (Chemical Engineering Journal). In addition, doping with ions such as aluminum and silicon can effectively inhibit the phase transformation of ferrihydrite by inhibiting the Fe-O-Fe bridging effect, such as the silica-coated halloysite nanotube composite adsorbent and its preparation method and application disclosed in CN115739012A, and the application of aluminum-substituted ferrihydrite in the adsorption of heavy metals disclosed in CN109694114A. Based on this, researchers have successively developed new adsorbents such as lanthanum-modified zeolite, lanthanum hydroxide@magnetite composite material, and aluminum-modified ferrihydrite. However, the existing technology still has significant limitations: in the single-element modification strategy, although Al / Si doping improves the stability, the modification of such same-period elements has limited improvement in the adsorption capacity and cannot improve the specific recognition ability for phosphate groups; while the anti-interference performance of rare earth-doped materials in complex water matrices still needs to be improved.

[0004] So far, there has been no systematic research report on synchronously optimizing the adsorption capacity, selectivity, and structural stability of ferrihydrite through a multi-element co-doping strategy; that is, in the existing technology, there is a lack of a ferrihydrite adsorbent that simultaneously has good stability, high adsorption capacity, specific recognition ability for phosphate, and excellent anti-interference performance in complex water matrices to achieve phosphorus pollution control in complex water quality scenarios. Summary of the Invention

[0005] The purpose of the present invention is to provide a ferrihydrite co-modified by multi-element doping and its preparation method and application to solve at least one of the above problems. In the single-element modification strategy of ferrihydrite in the existing technology, although Al / Si doping improves stability, the modification of such same-period elements has limited improvement in adsorption capacity and cannot improve the specific recognition ability for phosphate; while the anti-interference performance of rare-earth doped materials in complex water matrices still needs to be improved. This solution combines rare-earth doping and Al / Si doping to synergistically improve the stability, adsorption capacity, specific recognition ability, and anti-interference performance of ferrihydrite for phosphorus adsorption.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The first aspect of the present invention discloses a ferrihydrite co-modified by multi-element doping, in which at least one rare-earth element is doped in the ferrihydrite, and at least one of aluminum element and silicon element is also doped in the ferrihydrite;

[0008] The doping amount of the rare-earth element in the ferrihydrite is 0.5-20 wt%;

[0009] The doping amount of the aluminum element in the ferrihydrite is 0-20 wt%;

[0010] The doping amount of the silicon element in the ferrihydrite is 0-20 wt%.

[0011] The second aspect of the present invention discloses a preparation method of the ferrihydrite co-modified by multi-element doping as described above, including the following steps:

[0012] Step 1, prepare a solution A dissolved with doping elements and trivalent iron elements;

[0013] Step 2, prepare a NaOH solution;

[0014] Step 3, drop the NaOH solution into solution A to react and form a precipitate, and then adjust the pH of the system;

[0015] Step 4, wash and dry the precipitate formed in Step 3 to obtain the ferrihydrite co-modified by multi-element doping.

[0016] Preferably, in Step 1,

[0017] The described Solution A is prepared by dissolving a ferric iron source, a rare earth metal source, and an aluminum source and / or a silicon source in water.

[0018] Preferably, it includes one or more of the following:

[0019] i) The ferric iron source is ferric chloride and / or ferric nitrate;

[0020] ii) The rare earth metal source is a chloride and / or nitrate of a rare earth element, and the rare earth element is one or more of lanthanum, cerium, and neodymium;

[0021] iii) The aluminum source is aluminum chloride and / or aluminum nitrate;

[0022] iv) The silicon source is inorganic silicate and / or organosilicon. The inorganic silicate includes sodium silicate and potassium silicate, and the organosilicon includes γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane.

[0023] Preferably, in Step 1,

[0024] The total concentration of the solute in Solution A is 0.1 - 0.5 mol / L.

[0025] Preferably, in Step 2,

[0026] The concentration of the NaOH solution is 1 - 4 mol / L.

[0027] Preferably, in Step 3,

[0028] The reaction time is 30 - 60 minutes.

[0029] Preferably, in Step 3,

[0030] The pH adjustment range for adjusting the pH of the system is 7 - 8.

[0031] Preferably, in Step 4, it includes one or two of the following:

[0032] i) The washing is until neutral;

[0033] ii) The drying temperature is 50 - 200 °C, and the drying time is 12 - 48 hours.

[0034] The third aspect of the present invention discloses an application of the goethite co-modified by multi-element doping as described above in the field of phosphorus adsorption.

[0035] The working principle of the present invention is:

[0036] This scheme reconfigures the iron electronic structure (reconfigures the iron electron cloud density) by introducing rare earth elements (such as lanthanum, cerium, and neodymium), forming specific phosphorus binding sites and enhancing the chemical affinity for phosphate; the doping of aluminum and / or silicon inhibits the reconstruction of the Fe-O-Fe network through strong covalent Al-O / Si-O bonds, constructs a stable crystal framework, and delays the phase transition process. The two synergistically manifest as rare earth-induced lattice expansion (such as La 3+ Ionic radius Significantly greater than Fe 3+ of ) complements the rigid substructure constructed by Al / Si, aluminum and / or silicon doping can reduce the lattice stress, while rare earth elements inhibit the migration of oxygen vacancies through grain boundary segregation.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The present invention provides a multi-element doped ferrihydrite with large adsorption capacity, good selectivity and superior dynamic performance, which can be widely used in phosphorus removal treatment of surface water and groundwater such as drinking water source water.

[0039] 1. Significantly enhanced adsorption capacity: The introduction of rare earth elements significantly improves the adsorption capacity of ferrihydrite by forming a stable rare earth-phosphate coordination structure, increasing the phosphorus adsorption capacity by 45-531% compared to pure ferrihydrite. In particular, the removal rate of low-concentration phosphorus (0.5 mg / L) is greater than 99%, meeting the needs of deep purification of drinking water.

[0040] 2. Excellent structural stability: Aluminum / silicon doping effectively inhibits the phase transition of ferrihydrite to a crystalline state. After accelerated aging at 60°C for 7 days, the adsorption capacity attenuation rate is less than 5%. After 5 cycles, the efficiency remains above 90%, and the material life is extended to 3 times that of traditional ferrihydrite.

[0041] 3. Highly selective anti-interference: in Cl-, SO4 2 -(100mg / L) and other competitive anions coexist, the phosphorus adsorption capacity only decreases by 8%-15%, which is significantly better than traditional materials (decreased by 30%-50%) and is suitable for complex water quality environments.

[0042] 4. Green and efficient regeneration: Using 5% NaOH can achieve more than 98% phosphorus desorption, combining the dual value of pollutant removal and phosphorus resource recovery, significantly reducing operating costs.

[0043] The multi-element doping synergistic modification strategy of the present invention successfully solves the bottleneck problems of low adsorption capacity, poor stability and weak anti-interference of ferrihydrite, and provides an efficient, economical and sustainable technical solution for the treatment and resource utilization of phosphorus pollution in water bodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1Adsorption isotherm of phosphate by the samples prepared in Example 1 and Comparative Example 1;

[0045] Figure 2 Performance of the sample prepared in Example 2 for adsorbing phosphate in 5 cycles. Detailed implementation manners

[0046] The present invention will be described in detail below with reference to the accompanying drawings and specific examples, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0047] In the following description, if not otherwise specified, the reagents used are conventional commercially available products, the methods used are well-known means in the art, and the matters not covered can be implemented by existing technologies.

[0048] A ferrihydrite co-modified by multi-element doping, in which at least one rare earth element is doped, and at least one of aluminum element and silicon element is also doped; wherein, the doping amount of the rare earth element in the ferrihydrite is 0.5-20 wt%; the doping amount of the aluminum element in the ferrihydrite is 0-20 wt%; the doping amount of the silicon element in the ferrihydrite is 0-20 wt%

[0049] The preparation method of the ferrihydrite is as follows:

[0050] Step 1, prepare solution A in which doping elements and trivalent iron elements are dissolved;

[0051] Step 2, prepare NaOH solution;

[0052] Step 3, add the NaOH solution dropwise to solution A to react and form a precipitate, and then adjust the pH of the system;

[0053] Step 4, wash and dry the precipitate formed in Step 3 to obtain the multi-element doped and co-modified ferrihydrite.

[0054] Among them,

[0055] In Step 1, solution A is prepared by dissolving a trivalent iron source, a rare earth metal source, and an aluminum source and / or a silicon source (determined according to the formula) in water, and the total concentration of the solutes is 0.1-0.5 mol / L; the trivalent iron source is ferric chloride and / or ferric nitrate; the rare earth metal source is a chloride and / or nitrate of a rare earth element, and the rare earth element is one or more of lanthanum, cerium, and neodymium; the aluminum source is aluminum chloride and / or aluminum nitrate; the silicon source is inorganic silicate and / or organic silicon, the inorganic silicate includes sodium silicate and potassium silicate, and the organic silicon includes γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane.

[0056] In Step 2, the concentration of the NaOH solution is 1-4 mol / L.

[0057] In Step 3, the reaction time is 30 - 60 minutes, and the pH adjustment range for adjusting the system pH is 7 - 8.

[0058] In Step 4, the washing is to wash the precipitate until it is neutral; the drying temperature is 50 - 200 °C, and the drying time is 12 - 48 hours.

[0059] This multi - element doped and synergistically modified ferrihydrite exhibits significantly improved phosphorus adsorption performance compared to ordinary ferrihydrite, and at the same time has better chemical stability. The phosphorus removal capacity increases by 45 - 531%, and the adsorption efficiency remains above 90% after 5 cycles of use. This material is applicable to the fields of wastewater treatment, agricultural non - point source pollution control, and phosphorus resource recovery, and has high efficiency, economy, and environmental friendliness, with broad application prospects.

[0060] Example 1

[0061] A multi - element doped and synergistically modified ferrihydrite: The crystal phase is ferrihydrite, which is doped with lanthanum and aluminum, with the mass content of lanthanum being 10% and the mass content of aluminum being 5%.

[0062] The preparation method of this ferrihydrite includes the following steps:

[0063] In Step 1, dissolve the ferric source, lanthanum source, and aluminum source in water to obtain Solution A;

[0064] In Step 2, dissolve NaOH in water to obtain Solution B;

[0065] In Step 3, add Solution B dropwise to Solution A to obtain a metal precipitate, and adjust the system to maintain a certain pH value;

[0066] In Step 4, wash and dry the precipitate obtained in Step 3 to obtain multi - element doped hydrated iron oxide.

[0067] Among them, the total concentration of the ferric source, lanthanum source, and aluminum source in Step 1 is 0.1 mol / L; the ferric source is ferric nitrate; the lanthanum source is lanthanum nitrate; the aluminum source is aluminum nitrate; the concentration of NaOH is 1 mol / L; the equilibrium pH in Step 3 is 7.5; the reaction time in Step 3 is 30 minutes; the precipitate in Step 4 is washed until it is neutral; the drying temperature in Step 4 is 65 °C, and the drying time is 24 hours.

[0068] Comparative Example 1

[0069] Use unmodified ferrihydrite, which does not add lanthanum source and aluminum source compared to Example 1.

[0070] As Figure 1As shown, the adsorption tests for phosphates were carried out on the samples prepared in Example 1 and Comparative Example 1 (the same below): Under the condition of pH = 7.0 ± 0.2 (constant temperature at 25 °C), potassium dihydrogen phosphate solutions with initial concentrations of 5, 10, 25, 50, 80, 100, and 120 mg / L were respectively prepared, and batch adsorption experiments were carried out at a dosage of 0.5 g / L (shaken for 24 h until equilibrium). The adsorption isotherm was fitted by the Langmuir and Freundlich models and the theoretical maximum adsorption capacity was calculated; at the same time, an actual low-concentration phosphorus-containing water body was simulated, and the equilibrium adsorption behavior of a phosphate solution with an initial concentration of 0.5 mg / L was tested under the same pH and dosage conditions. It can be seen that the adsorption capacity of the above sample for phosphate is 78.7 mg P / g (about 19.8 mg P / g for pure goethite, an increase of 297% compared to pure goethite), and the removal rate of low-concentration phosphorus (0.5 mg P / L) is > 99%.

[0071] Example 2

[0072] A multi-element doped and synergistically modified goethite: The crystal phase is goethite, which is doped with lanthanum and silicon, and the mass content of lanthanum is 20% and the mass content of silicon is 1%;

[0073] The preparation method of this goethite includes the following steps:

[0074] Step 1, dissolve a trivalent iron source, a lanthanum source, and a silicon source in water to obtain solution A;

[0075] Step 2, dissolve NaOH in water to obtain solution B;

[0076] Step 3, add solution B dropwise to solution A to obtain a metal precipitate, and adjust the system to maintain a certain pH value;

[0077] Step 4, wash the precipitate obtained in Step 3 and then dry it to obtain multi-element doped hydrated iron oxide.

[0078] Among them, the total concentration of the trivalent iron source, lanthanum source, and silicon source in Step 1 is 0.2 mol / L; the trivalent iron source is ferric chloride; the lanthanum source is lanthanum nitrate; the silicon source is sodium silicate; the concentration of NaOH in Step 2 is 2 mol / L; the equilibrium pH range in Step 3 is 7.2; the reaction time in Step 3 is 60 minutes; the precipitate in Step 4 is washed to neutral; the drying temperature in Step 4 is 100 °C and the drying time is 12 hours.

[0079] The adsorption test for phosphates was carried out on the sample prepared in Example 2: The adsorption capacity of the above sample for phosphate is 125 mg P / g (an increase of 531% compared to pure goethite), and the adsorption efficiency remains above 98% after 5 cycles, as Figure 2 shown. The structure of pure goethite is poorly stable, and its efficiency drops by 40% after 3 cycles.

[0080] Comparative Example 2-1

[0081] Single La doping modification

[0082] A goethite co-modified by single element doping: the crystal phase is goethite, doped with lanthanum, and the mass content of lanthanum is 20%;

[0083] The preparation method of the goethite includes the following steps:

[0084] Step 1, dissolve ferric iron source and lanthanum source in water to obtain solution A;

[0085] Step 2, dissolve NaOH in water to obtain solution B;

[0086] Step 3, add solution B dropwise to solution A to obtain metal precipitate, and adjust the system to maintain a certain pH value;

[0087] Step 4, wash and dry the precipitate obtained in Step 3 to obtain single element doped iron hydroxide.

[0088] Among them, the total concentration of ferric iron source and lanthanum source in Step 1 is 0.2 mol / L; the ferric iron source is ferric chloride; the lanthanum source is lanthanum nitrate; the concentration of NaOH in Step 2 is 2 mol / L; the equilibrium pH range in Step 3 is 7.2; the reaction time in Step 3 is 60 minutes; the precipitate in Step 4 is washed to neutral; the drying temperature in Step 4 is 100 °C and the drying time is 12 hours.

[0089] Perform phosphate adsorption test on the sample prepared in Comparative Example 2-1: the adsorption capacity of the above sample for phosphate is 83 mg P / g (319% higher than that of pure goethite).

[0090] Comparative Example 2-2

[0091] Single Si doping modification

[0092] A goethite co-modified by single element doping: the crystal phase is goethite, doped with silicon, and the mass content of silicon is 1%;

[0093] The preparation method of the goethite includes the following steps:

[0094] Step 1, dissolve ferric iron source and silicon source in water to obtain solution A;

[0095] Step 2, dissolve NaOH in water to obtain solution B;

[0096] Step 3, add solution B dropwise to solution A to obtain metal precipitate, and adjust the system to maintain a certain pH value;

[0097] Step 4: Wash and dry the precipitate obtained in Step 3 to obtain single-element doped hydrated iron oxide.

[0098] Among them, the total concentration of the ferric iron source and the silicon source in Step 1 is 0.2 mol / L; the ferric iron source is ferric chloride; the silicon source is sodium silicate; the concentration of NaOH in Step 2 is 2 mol / L; the equilibrium pH range in Step 3 is 7.2; the reaction time in Step 3 is 60 minutes; the precipitate in Step 4 is washed until neutral; the drying temperature in Step 4 is 100 °C and the drying time is 12 hours.

[0099] Perform an adsorption test of phosphate on the sample prepared in Comparative Example 2-2: The adsorption capacity of the above sample for phosphate is 28 mg P / g (a 41.4% increase compared to ferrihydrite).

[0100] By adding the phosphate / root adsorption capacities of the single La doping modification of Comparative Example 2-1 and the single Si doping modification of Comparative Example 2-2 (111 mg P / g, equivalent to using them in combination), the adsorption capacity is still much lower than the phosphate adsorption capacity of 125 mg / g in Example 2, proving that there is a synergistic effect between lanthanum doping and silicon doping in the modified ferrihydrite of this scheme.

[0101] Example 3

[0102] A multi-element doped and synergistically modified ferrihydrite: The crystal phase is ferrihydrite, which is doped with rare earth element cerium, as well as aluminum and silicon elements, and the mass content of the rare earth element is 5%, the mass content of aluminum is 20%, and the mass content of silicon is 1%;

[0103] The preparation method of this ferrihydrite includes the following steps:

[0104] Step 1: Dissolve the ferric iron source, cerium source, aluminum source and silicon source in water to obtain Solution A;

[0105] Step 2: Dissolve NaOH in water to obtain Solution B;

[0106] Step 3: Drop Solution B into Solution A to obtain a metal precipitate, and adjust the system to maintain a certain pH value;

[0107] Step 4: Wash and dry the precipitate obtained in Step 3 to obtain multi-element doped hydrated iron oxide.

[0108] Among them, the total concentration of the ferric source, cerium source, aluminum source and silicon source in Step 1 is 0.5 mol / L; the ferric source is ferric nitrate; the cerium source is cerium nitrate; the aluminum source is aluminum nitrate; the silicon source is γ-aminopropyltriethoxysilane; the concentration range of NaOH in Step 2 is 4 mol / L; the equilibrium pH in Step 3 is 8; the reaction time in Step 3 is 60 minutes; the precipitate in Step 4 is washed until neutral; the drying temperature in Step 4 is 150 °C and the drying time is 36 hours.

[0109] The adsorption test of phosphate was carried out on the sample prepared in Example 3: the adsorption capacity of the above sample for phosphate was 54.5 mg P / g (175% higher than that of pure goethite), and the amorphous structure was still maintained after the accelerated aging experiment (60 °C / 7 days), and the attenuation rate of the phosphorus adsorption capacity was <5%. Compared with the traditional goethite (the sample in Comparative Example 1), the material life can be extended to 3 times.

[0110] Example 4

[0111] A goethite co-modified by multi-element doping: the crystal phase is goethite, which is doped with rare earth element neodymium and silicon element, and the mass content of neodymium is 0.5%, and the mass content of silicon is 0.5%;

[0112] The preparation method of the goethite includes the following steps:

[0113] Step 1, dissolve the ferric source, neodymium source and silicon source in water to obtain solution A;

[0114] Step 2, dissolve NaOH in water to obtain solution B;

[0115] Step 3, drop solution B into solution A to obtain a metal precipitate, and adjust the system to maintain a certain pH value;

[0116] Step 4, wash and dry the precipitate obtained in Step 3 to obtain multi-element doped iron hydroxide.

[0117] Among them, the total concentration of the ferric source, neodymium source and silicon source in Step 1 is 0.1 mol / L; the ferric source is ferric nitrate; the neodymium source is neodymium nitrate; the silicon source is sodium silicate; the concentration of NaOH is 1 mol / L; the equilibrium pH in Step 3 is 7.5; the reaction time in Step 3 is 40 minutes; the precipitate in Step 4 is washed until neutral; the drying temperature in Step 4 is 65 °C and the drying time is 16 hours.

[0118] The adsorption test of phosphate was carried out on the sample prepared in Example 4: the adsorption capacity of the above sample for phosphate was 28.7 mg P / g (45% higher than that of pure goethite), and the adsorption efficiency remained above 95% after 5 cycles.

[0119] Example 5

[0120] A ferrihydrite co-modified by multi-element doping: The crystal phase is ferrihydrite, which is doped with rare earth element cerium and aluminum element, and the mass content of rare earth element is 2% and the mass content of aluminum element is 1%;

[0121] The preparation method of the ferrihydrite includes the following steps:

[0122] Step 1, dissolve ferric source, cerium source and aluminum source in water to obtain solution A;

[0123] Step 2, dissolve NaOH in water to obtain solution B;

[0124] Step 3, drop solution B into solution A to obtain metal precipitate, and adjust the system to maintain a certain pH value;

[0125] Step 4, wash and dry the precipitate obtained in Step 3 to obtain multi-element doped hydrated iron oxide.

[0126] Among them, the total concentration of ferric source, cerium source and aluminum source in Step 1 is 0.5 mol / L; the ferric source is ferric nitrate; the cerium source is cerium nitrate; the aluminum source is aluminum chloride; the concentration range of NaOH in Step 2 is 4 mol / L; the equilibrium pH in Step 3 is 8; the reaction time in Step 3 is 60 minutes; the precipitate in Step 4 is washed to neutral; the drying temperature in Step 4 is 150 °C and the drying time is 36 hours.

[0127] Performance test on the deep phosphorus removal performance of the sample prepared in Example 5: Taking the secondary effluent of a certain urban sewage treatment plant in Shanghai as the treatment object (initial total phosphorus concentration 0.52 ± 0.06 mg P / L), continuously running in a dynamic fixed-bed reactor at an empty bed flow rate of 2 m / h. Experimental data shows that when the treatment load reaches 2800 bed volumes (BV), the total phosphorus concentration in the effluent is stably maintained at 0.043 ± 0.012 mg P / L, and the removal rate reaches more than 91.8%. The iron dissolution amount in the packing layer during the breakthrough stage is < 0.08 mg / L, and the material structure integrity remains good.

[0128] Performance test

[0129] The performance differences between multi-element doped ferrihydrite (the material prepared in Example 5) and pure-phase materials were evaluated through comparative experiments: the adsorption amount of pollutants under the interference of co-existing ions was measured in a simulated high-salt environment (100 mg / L NaCl / Na2SO4), and the environmental adaptability of the materials was quantified by combining the adsorption kinetic curves under different pH conditions (2 - 10); the structural stability was analyzed by cyclic adsorption-desorption experiments (3 - 5 times), and the changes in specific surface area, crystal phase composition, and surface chemical state during the cyclic process were traced by XRD, BET, and XPS; regarding the problem of crystal phase transformation, the goethite formation ratio of the materials before and after doping was compared after accelerated aging at 60 °C for 7 days. The experimental data showed that the adsorption amount of the doped sample only decreased by 8 - 15% in the high-salt environment (30 - 50% for the pure phase), the adsorption efficiency remained above 75% of the initial value in the pH range of 3 - 9 (the pure phase decreased by 50 - 80% when pH < 4 or > 7), the performance attenuation was < 8% after 3 cycles (20 - 40% for the pure phase), and no characteristic peaks of goethite were detected by XRD (the proportion of goethite in the pure phase after aging was > 40%).

[0130] In summary, this solution successfully breaks through the performance bottleneck of traditional ferrihydrite materials through innovative material design, providing a systematic solution for water body phosphorus pollution control and resource recovery. Aiming at the core pain points of traditional ferrihydrite materials, such as low adsorption capacity (benchmark value is about 19.8 mg P / g), poor structural stability (the efficiency decreased by 20 - 40% after 3 cycles), and weak anti-interference ability (the adsorption amount decreased by 30 - 50% due to co-existing ions), the research team pioneered the use of a rare earth-aluminum / silicon multi-element co-doping strategy. Specific phosphorus binding sites were formed by reconstructing the iron electron cloud density with rare earth elements (lanthanum, cerium, neodymium), and a stable crystal framework was constructed by combining aluminum / silicon doping, achieving a comprehensive improvement in adsorption performance while maintaining the economy of the materials. The new material has made significant breakthroughs in key performance indicators: the phosphorus adsorption capacity can be increased to 28.7 - 125 mg P / g, a 45 - 531% increase compared with traditional materials; the adsorption capacity attenuation rate is < 5% after accelerated aging at 60 °C for 7 days, and the efficiency remains above 90% after 5 cycles of use; in a high-salt environment (Cl-, SO4 2 - concentration of 100 mg / L), the adsorption efficiency can still be maintained above 85%, effectively solving the technical problem that it is difficult to synergistically optimize the "high efficiency - stability - economy" of existing phosphorus removal materials.

[0131] The new material also demonstrates multi-scenario adaptability. It can not only meet the requirements of upgrading and transformation of municipal sewage treatment, reducing the total phosphorus concentration in the effluent from 0.5 mg P / L to below 0.05 mg P / L, but also effectively treat agricultural non-point source polluted water bodies with a pH value in the range of 6 - 9. With a single treatment, the phosphorus concentration in paddy field return water and aquaculture wastewater can be reduced from 5 mg P / L to 0.1 mg P / L. In the field of phosphorus resource recovery, based on the process chain of "adsorption - desorption - crystallization", a 98% phosphorus desorption efficiency can be achieved by using 5% NaOH solution. Combined with the crystallization process, high-purity phosphate products can be produced, thus closing the technical loop from pollution treatment to resource regeneration. The material is prepared using bulk raw materials such as ferric chloride and lanthanum nitrate, and the comprehensive cost can be controlled below 15 yuan / kg. Moreover, the low-temperature drying process at 50 - 200°C is highly compatible with the existing production line. It can be directly integrated into the existing flocculation - precipitation process section in the conventional sewage treatment pH environment (7 - 8). Combining with a service life 3 - 5 times that of traditional materials and a 98% alkali solution regeneration efficiency, the full-life-cycle dynamic operation cost is significantly lower than that of commercially available phosphorus removal resins.

[0132] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. Obviously, those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention as disclosed should be within the protection scope of the present invention.

Claims

1. An ferrihydrite co-modified by multi-element doping, characterized in that, The goethite doped with at least one rare earth element, and the goethite is also doped with at least one of aluminum element and silicon element; The doping amount of the rare earth element in the goethite is 0.5-20 wt%; The doping amount of the aluminum element in the goethite is 0-20 wt%; The doping amount of the silicon element in the goethite is 0-20 wt%.

2. A preparation method of goethite co-modified by multi-element doping as described in claim 1, characterized in that, Comprising the following steps: Step 1, prepare solution A dissolved with doping elements and ferric elements; Step 2, prepare NaOH solution; Step 3, drop the NaOH solution into solution A to react and form a precipitate, and then adjust the pH of the system; Step 4, wash and dry the precipitate formed in step 3 to obtain the multi-element doped and synergistically modified goethite.

3. The preparation method of the ferrihydrite co-modified by multi-element doping according to claim 2, characterized in that, In step 1, The solution A is prepared by dissolving a ferric source, a rare earth metal source, and an aluminum source and / or a silicon source in water.

4. The preparation method of ferrihydrite with multi-element doping and synergistic modification according to claim 3, characterized in that, Including one or more of the following: i) The ferric source is ferric chloride and / or ferric nitrate; ii) The rare earth metal source is a chloride and / or nitrate of a rare earth element, and the rare earth element is one or more of lanthanum, cerium, and neodymium; iii) The aluminum source is aluminum chloride and / or aluminum nitrate; iv) The silicon source is inorganic silicate and / or organosilicon, the inorganic silicate includes sodium silicate and potassium silicate, and the organosilicon includes γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane.

5. The preparation method of ferrihydrite co-modified by multi-element doping according to claim 2, wherein In step 1, The total concentration of the solute in the solution A is 0.1-0.5 mol / L.

6. The preparation method of ferrihydrite co-modified by multi-element doping according to claim 2, characterized in that, In step 2, The concentration of the NaOH solution is 1-4 mol / L.

7. The preparation method of goethite with multi-element doping synergistic modification according to claim 2, characterized in that, In step 3, The reaction time is 30-60 minutes.

8. The preparation method of ferrihydrite with multi-element doping and synergistic modification according to claim 2, characterized in that, In step 3, The pH adjustment range for adjusting the pH of the system is 7-8.

9. The preparation method of ferrihydrite co-modified by multi-element doping according to claim 2, characterized in that, In step 4, including one or two of the following: i) The washing is to wash until neutral; ii) The drying temperature is 50-200 °C, and the drying time is 12-48 hours.

10. Application of the multi-element doped and synergistically modified goethite as described in claim 1 in the field of phosphorus adsorption.

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