Polymeric lanthanum titanium-based flocculant as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of material chemistry, and provides a polymerized lanthanum titanium-based flocculant as well as a preparation method and application thereof. The poly-lanthanum-titanium composite flocculant is prepared by adopting an electrochemical method, and the method has the advantages of simplicity and convenience in operation and controllable process. The composite flocculant shows a remarkable synergistic effect on pollutant removal efficiency, and has particularly outstanding removal rates on organic matters, phosphate and UV254 in a water body; the problem of high cost of a single lanthanum flocculant is reduced, and meanwhile, lanthanum provides strong phosphorus precipitation capacity, so that the problem of insufficient efficiency of titanium salt under a low-phosphorus condition is solved.

Description

Technical Field

[0001] This invention belongs to the field of materials chemistry technology, specifically relating to a polymeric lanthanum titanium-based flocculant and its applications. Background Technology

[0002] Lanthanum (La) is an abundant and inexpensive rare earth element with good biocompatibility and strong chemical reactivity. Lanthanum hydrolyzes rapidly with minimal temperature dependence. Furthermore, lanthanum has a large electron radius and its outer electrons are in an unfilled state, resulting in active coordination. Metallic lanthanum also exhibits a strong specific affinity for oxygen atoms in phosphate groups, readily forming insoluble lanthanide complexes, thus demonstrating excellent phosphorus removal performance. Its coagulation effect is less affected by water quality. However, using single lanthanum salt coagulants directly presents problems such as high cost, high residual lanthanum metal content, narrow pH application range, and large fluctuations in effluent pH, which can affect the stability of subsequent processes.

[0003] Studies have shown that titanium salts (such as TiCl4) hydrolyze during water treatment to form polynuclear hydroxy titanium complexes (such as Ti4(OH)8). 4+ This complex possesses the core characteristics of high charge density and rapid hydrolysis. It can adsorb the negative charge of colloidal particles in water through charge neutralization, and then encapsulate suspended impurities through a net-like sweeping action, thereby achieving efficient removal of turbidity and organic matter from water. Titanium salt coagulants have low hydrolysis residues, minimal impact on downstream treatment units, and exhibit rapid floc growth, large floc size, and fast settling during coagulation, significantly shortening the coagulation-sedimentation time. Furthermore, titanium salt coagulants possess other advantages, such as being non-toxic, producing flocs with excellent settling performance, and the chemical sludge generated after treatment can be recovered by calcination to prepare TiO2. Benefiting from these advantages, titanium salt coagulants have been extensively studied in drinking water treatment, wastewater treatment, sludge dewatering, and pre-membrane pretreatment. However, single titanium salt coagulants have limited removal efficiency for low-concentration phosphorus due to easy saturation of adsorption points, making it difficult to meet the requirements for deep phosphorus removal; secondly, the titanium salt hydrolysis process is easily affected by pH fluctuations, resulting in excessively low pH of the effluent after coagulation treatment, leading to insufficient stability in complex aquatic environments.

[0004] In summary, neither titanium salt nor lanthanum salt coagulants can simultaneously meet the requirements of efficient phosphorus removal, wide pH adaptability, rapid sedimentation, and the combined removal of turbidity and organic matter. Therefore, the invention of polylanthanum-titanium composite coagulants to achieve complementary advantages of both has become a necessary direction for solving phosphorus pollution in surface water. Summary of the Invention

[0005] In response to the increasing demand for wastewater treatment and the problem of phosphorus pollution in urban water, this invention provides an electrochemical preparation method for polylanthanum-titanium composite coagulants, and compares the coagulation effects to demonstrate the advantages of polylanthanum-titanium composite coagulants in high-efficiency phosphorus removal, wide pH adaptability, rapid sedimentation, and efficient turbidity and organic matter removal.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] An electrochemical method for preparing polymeric lanthanum-titanium coagulants includes the following steps: A mixture of titanium salt solution and lanthanum salt solution was used as the reaction solution for electrodialysis, allowing the anions OH- produced by the cathode electrolyte and anolyte to... - Obtained by reacting with a reaction solution through a semi-permeable membrane; The molar ratio of lanthanum ions to titanium ions in the reaction solution is (0.05-0.3):1, preferably 0.3:1.

[0008] The electrodialysis conditions were constant current electrodialysis at 0.02 A-0.05 A, with a dialysis time of 1-8 h. The electrodialysis time had little effect on the removal of organic matter by the coagulant. The preparation of flocculants using electrochemical methods is actually a pre-hydrolysis process, that is, under the impetus of an external DC power supply, OH... - It polymerizes with metal cations in the reaction chamber to form hydroxyl polymers. Increasing the electrodialysis time will naturally lead to more OH groups. - The generation of ions can reduce the zeta potential to a certain extent. The higher the zeta potential, the stronger the charge neutralization ability of the coagulant. However, the positive charge contained in the metal cations in the coagulant still plays a decisive role. Therefore, the electrodialysis time has little effect on the coagulation effect. Preferably, the dialysis time is 1-2 hours.

[0009] The titanium salt is selected from either titanium tetrachloride or titanium sulfate, and the lanthanum salt is selected from either lanthanum chloride, lanthanum nitrate, or lanthanum sulfate. The above salts contain titanium ions (Ti... 4+ ), lanthanum ion (La) 3+ The hydrolysis process and subsequent electrodialysis preparation process have the same effect.

[0010] The cation concentration in the reaction solution is 0.5-10 mol / L.

[0011] The cathode electrolyte is selected from sodium chloride or potassium chloride.

[0012] The anolyte is selected from sodium sulfate or potassium sulfate.

[0013] The concentrations of the cathode electrolyte and the anolyte are 0.1-1 mol / L; preferably 0.1-0.5 mol / L.

[0014] In the above method, in order to reduce concentration polarization and accelerate ion transfer in the room, the cathodic electrolyte and anodic electrolyte are stirred during the electrodialysis process.

[0015] Preferably, stirring continues after electrodialysis is stopped.

[0016] The present invention also provides a polymeric lanthanum-titanium coagulant prepared by the above method. This polymeric lanthanum-titanium coagulant can be used as a water treatment agent and for use in the flocculation process of water treatment.

[0017] A water treatment method includes the step of adding the above-mentioned polymeric lanthanum titanium coagulant and water treatment agent to the water to be treated.

[0018] The dosage is 2.5-50 mg-Ti / L; preferably 10-40 mg-Ti / L.

[0019] The mechanism of this invention is as follows: Lanthanum ions first combine with water molecules to form hydrated ions La(H₂O)₆ 3+ After the alkalizing agent is added, the OH in the system - As the concentration increases, the OH- in the system - Prefers lanthanum ions (La) 3+ This complexes with lanthanum ions, disrupting the original hydration layer structure and forming rare earth lanthanum complexes [La(OH)] with flocculation activity. m (H2O) n ] (3−m)+ Complex, OH - As a nucleophile, it attacks La(H2O)6 3+ The lanthanum ion, through a nucleophilic substitution reaction, first forms an initial La−O bond by replacing the water molecule with the lanthanum ion, which then attracts the lanthanum ion to bind with the Ti molecule. Since La has a lower electronegativity than Ti, the lanthanum ion will actively seek to bind with the Ti molecule. 4+ The complexed hydroxyl groups undergo competitive coordination reactions to form a Ti-O-La cross-linked structure, achieving cross-polymerization of lanthanum and titanium, exhibiting both electrostatic interactions (ionic bonding characteristics) and covalent interactions (electron sharing). Through cross-polymerization, they can form multinucleated, longer, and more stable molecular chains, achieving water purification through precipitation and trapping effects.

[0020] The present invention has the following advantages: The electrochemically produced polylanthanum-titanium composite flocculant provided by this invention has the advantages of simple operation and controllable process. Compared with single titanium-based flocculants, this product exhibits a significant synergistic effect in pollutant removal efficiency, effectively removing organic matter, phosphate, and UV pollutants from water. 254 The removal rate is particularly outstanding. The introduction of Ti reduces the amount of lanthanum used, alleviating the high cost of a single lanthanum flocculant. At the same time, lanthanum provides strong phosphorus precipitation ability, solving the problem of insufficient efficiency of titanium salts under low phosphorus conditions. The electrochemical method uses conditional current parameters to achieve controllable adjustment of the system pH, avoiding sudden changes in local pH. It is also simple to operate, facilitating automated and continuous preparation processes. It reduces the heterogeneous precipitation caused by uneven local hydrolysis in the dripping alkali method, while also helping to maintain the relative purity of the system composition. Attached Figure Description

[0021] Figure 1 These are the infrared spectra of PLTC and PTC; Figure 2 It is PLTC and PTC phosphate (A), total organic carbon (B), UV 254 (C) Removal and effluent pH (D); Figure 3 The phosphate, total organic carbon, and UV content of PLTC prepared by different methods under different dosages are compared. 254 The removal effect. Detailed Implementation

[0022] The present invention will be further described below with reference to the embodiments and accompanying drawings, but the present invention is not limited to the following embodiments.

[0023] Example 1: Preparation of electrochemical polylanthanum-titanium composite coagulant (1) Add TiCl4 (purity ≥ 99%) dropwise to an ice water bath beaker containing ice water and stir continuously for 3 h to fully dissolve TiCl4 and prepare a TiCl4 solution with a volume fraction of 20% (c = 1.80 M). Take 9.28 g of LaCl3·7H2O and put it into a beaker. Add 0.1 mL of hydrochloric acid (c = 2.5 mol / L), stir until completely dissolved, cool to room temperature, transfer to a 50 mL volumetric flask and make up to volume to prepare a 0.5 M LaCl3 solution. The two solutions were mixed according to the lanthanum-titanium molar ratios of 0.30:1, 0.15:1, and 0.05:1, respectively, to obtain the reaction solution; Prepare a 0.5 M NaCl solution as the cathode electrolyte; Prepare a 0.5 M Na2SO4 solution as the anolyte; (2) An acrylic electrodialysis device is used, with a single chamber size of 40.0×80.0×80.0 mm and an effective volume of 50.0 mL. Anion exchange membranes are installed between the cathode chamber and the reaction chamber, and between the reaction chamber and the anode chamber. NaCl solution and Na2SO4 solution are added to the cathode chamber and the anode chamber, respectively, along with a magnetic stir bar. The reaction chamber is added with a reaction solution and a magnetic stir bar. (3) A graphite rod with a diameter of 6.0 mm × 100.0 mm was used as an electrode to connect the circuit. Then, a DC regulated power supply was connected and the current was adjusted to constant current (0.02A) mode. The reaction time was 1 h. During the reaction, the DC power supply was continuously connected and the stirring was continued for 2 h after the reaction was completed. The final product obtained in the reaction chamber was a polylanthanum titanium chloride flocculant (PLTC) solution.

[0024] Using the same method, an equal volume of the above 20% TiCl4 solution was added to the reaction chamber to obtain a polytitanium chloride flocculant (PTC) solution.

[0025] The polylanthanum-titanium flocculant prepared by the electrochemical method has an alkalinity of 0.25 when the molar ratio of lanthanum to titanium is 0.3:1, which is in a strongly acidic state with pH < 1.

[0026] Infrared spectra of PLTC and PTC as follows Figure 1 ; in 500-1000 cm -1 In the Ti-O / Ti-O-Ti vibration region, the peaks in the comparative example are sharper and have higher intensity, while the peaks in the embodiment are broadened, the intensity is reduced, and a weak new peak appears, which confirms the hypothesis that La has lower electronegativity than Ti and forms a Ti-O-La crosslinked structure. At the same time, the change in this region also indirectly supports the existence of La-O bonds.

[0027] Example 2: Treatment of simulated wastewater with polylanthanum-titanium-based composite flocculant The coagulation efficiency of flocculants was tested by preparing simulated wastewater using tap water.

[0028] Preparation of Humic Acid-Kaolin (HA-Kaolin) Simulated Water Samples: Simulated water samples were prepared using humic acid and kaolin as raw materials. The preparation steps are as follows: First, 10 mg of solid humic acid and 200 mg of solid kaolin were weighed and added to 35 mg / L sodium dihydrogen phosphate and a certain amount of tap water. The mixture was stirred in a magnetic stirrer for at least 30 minutes, then diluted to 1.0 L to obtain a 10 g / L humic acid-kaolin simulated water sample. All water samples were prepared and used immediately. The water quality characteristics are as follows: PO4 in the wastewater... 3- -P =35.0±1.0 mg / L, TOC =45.0± 1.0 mg / L, UV 254 =0.2±0.02 cm -1 pH=7.8±0.1.

[0029] Flocculant was added to the simulated wastewater at a concentration of 0-50 mg-Ti / L. The results are as follows: Figure 2 As shown: Figure 2 A represents the effect of different flocculants on phosphate (PO4) in simulated wastewater. 3-The removal efficiency of phosphate (LaPO4) was assessed. The phosphate removal rates of all four reagents increased with increasing dosage. The lanthanum-titanium molar ratio of 0.3:1 showed the best phosphorus removal performance, exhibiting a significant advantage in the low dosage range of 0-10 mg-Ti / L. At a medium dosage of 30 mg-Ti / L, its removal rate reached 94%, significantly higher than PTC's 83%. In the high dosage range of 30-50 mg-Ti / L, the removal rates of all reagents tended to plateau, but the lanthanum-titanium ratio of 0.30:1 approached complete removal, demonstrating both high efficiency and economy. This difference stems from the synergistic effect of the specific coordination of lanthanum ions with phosphate (forming a stable LaPO4 precipitate) and the adsorption bridging effect of titanium-based hydrolysis products. This result not only verifies the superior phosphorus removal performance of the lanthanum-titanium composite coagulant compared to PTC alone, but also provides optimized reagent ratios and application guidelines for phosphorus-containing wastewater treatment, offering important reference value for the synergistic design of functional materials for water treatment.

[0030] Figure 2 B represents the TOC removal efficiency of different flocculants in simulated wastewater. Compared with PTC, the lanthanum-titanium composite coagulant has a higher TOC removal efficiency, and the composite coagulant with a lanthanum-titanium molar ratio of 0.15:1 has the best TOC removal rate. At a dosage of 50 mg-Ti / L, the lanthanum-titanium ratio of 0.15:1 can achieve a TOC removal rate of 70%, significantly higher than the 61% of PTC.

[0031] Figure 2 C represents the effect of different flocculants on UV in simulated wastewater. 254 The removal effect. Compared with PTC, lanthanum-titanium composite coagulant has a better effect on UV removal. 254 The removal efficiency is higher, and the composite coagulant with a lanthanum-titanium molar ratio of 0.3:1 has a higher overall UV removal efficiency. 254 The highest removal rate was observed at a dosage of 50 mg-Ti / L for UV removal. 254 The removal rate can reach 80%, which is significantly higher than PTC's 65%.

[0032] Figure 2 D represents the effluent pH of simulated wastewater treated with different flocculants. The pH of all groups decreased with increasing dosage (due to the consumption of hydroxide ions by coagulant hydrolysis). However, the pH decrease of the lanthanum-titanium composite flocculant was significantly less than that of PTC. At a medium dosage (30 mg-Ti / L), it remained around 6.5, and at a high dosage (50 mg-Ti / L), it remained stable above 6.0. This highlights the difference in hydrolysis characteristics between the polylanthanum-titanium composite flocculant and PTC alone; the latter causes a gentler disturbance to the pH of the water body and is more conducive to maintaining pH stability.

[0033] Comparative Example 1: Preparation of polylanthanum-titanium composite coagulant by slow-drop alkali method (lanthanum-titanium molar ratio of 0.3:1) Polylanthanum titanium coagulant was prepared according to the following slow-drop alkali method: (1) Take 12.5 ml of 20% TiCl4 solution and add it to a 100 mL beaker. Add 0.5 mol / L LaCl3 solution at a lanthanum-titanium molar ratio of 0.3:1 at 200 rpm to obtain a mixed solution. (2) 7.4 mL of 1 M NaOH solution was added dropwise to the mixture. White flocculent material was produced during the dropwise addition. Each drop of NaOH solution was added after the white flocculent material disappeared. After the dropwise addition was completed, the mixture was stirred stably for 3 hours and then refrigerated for 24 hours to obtain a polymeric lanthanum-titanium composite coagulant solution with an alkalinity of 0.25 and a pH < 1.

[0034] Application Example 1: Treatment of Urban Wastewater with Polylanthus Titanium Composite Coagulants Prepared by Different Methods Urban wastewater was treated using polylanthanum-titanium composite coagulant (E-PLTC) prepared by the electrochemical method in Example 1, with a lanthanum-titanium molar ratio of 0.3:1, and polylanthanum-titanium composite coagulant (S-PLTC) prepared by the slow drip alkali method in Comparative Example 1.

[0035] The urban wastewater sample was taken from the effluent of the secondary sedimentation tank at the Jinan University wastewater treatment plant. The water quality characteristics are as follows: PO4 3- -P = 2.29± 0.22 mg / L, TOC = 36.10 ± 0.23 mg / L, UV 254 = 0.13 ± 0.01 mg / L, pH = 6.5 ±0.1.

[0036] The pollutant removal efficiency and other indicators of electrochemical and slow-drop alkali methods using polylanthanum titanium flocculants (E-PLTC and S-PLTC), such as... Figure 3 As shown.

[0037] Overall, E-PLTC performed better than S-PLTC. The highest TOC removal rate of E-PLTC reached 82.61% at a dosage of 40 mg-Ti / L, while the highest TOC removal rate of S-PLTC was only 77.31%, 5.3% lower than E-PLTC; Regarding PO4... 3- Both flocculants showed excellent performance in removing -P, but E-PLTC achieved a removal rate of 99.29% at a dosage of only 10 mg-Ti / L, while S-PLTC's removal rate was only 73.86%, 25.43% lower than E-PLTC; similarly, in UV... 254 In terms of UV removal, E-PLTC also demonstrated significant advantages, achieving a maximum removal rate of 59.68% at a dosage of 40 mg-Ti / L. At this dosage, S-PLTC showed better removal of UV radiation. 254The removal rate was 37.78%, 21.9% lower than E-PLTC. S-PLTC has a lower UV removal rate than E-PLTC. 254 The removal rate was the highest at 41.48%, which was still 18.2% lower than that of E-PLTC.

[0038] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for preparing polymeric lanthanum-titanium coagulant by electrochemical means, characterized in that, Includes the following steps: A mixture of titanium salt solution and lanthanum salt solution was used as the reaction solution for electrodialysis, allowing the anions OH- produced by the cathode electrolyte and anolyte to... - Obtained by reacting with a reaction solution through a semi-permeable membrane; The molar ratio of lanthanum ions to titanium ions in the reaction solution is (0.05-0.3):

1.

2. The method according to claim 1, characterized in that, The electrodialysis conditions are constant current electrodialysis at 0.02 A-0.05 A and dialysis time of 1-8 h.

3. The method according to claim 1, characterized in that, The concentration of cations in the reaction solution is 0.5-10 mol / L; the concentration of the cathode electrolyte or anolyte is 0.1-1 mol / L.

4. The method according to claim 1, characterized in that, The molar ratio of lanthanum ions to titanium ions in the reaction solution is 0.3:1; the electrodialysis time is 1-2 h; and the concentration of the cathode electrolyte or anolyte is 0.1-0.5 mol / L.

5. The method according to claim 1, characterized in that, The titanium salt is selected from either titanium tetrachloride or titanium sulfate; the lanthanum salt is selected from either lanthanum chloride, lanthanum nitrate, or lanthanum sulfate. The cathode electrolyte is selected from sodium chloride or potassium chloride; the anolyte is selected from sodium sulfate or potassium sulfate.

6. The method according to claim 1, characterized in that, The cathode electrolyte and anolyte are stirred during the electrodialysis process.

7. A polymeric lanthanum titanium coagulant prepared by the method according to any one of claims 1-6, and a water treatment agent prepared therefrom.

8. The application of the polymeric lanthanum titanium coagulant or water treatment agent as described in claim 7 in water treatment.

9. A water treatment method, characterized in that, This includes the step of adding the polymeric lanthanum-titanium coagulant or water treatment agent as described in claim 7 to the water to be treated.

10. The water treatment method according to claim 9, characterized in that, The dosage is 2.5-50 mg-Ti / L; preferably 10-40 mg-Ti / L.

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