Preparation method and application of polymeric lanthanum silicate efficient coagulant

Abstract

The invention discloses a preparation method and application of a polymeric lanthanum silicate efficient coagulant, and the preparation method comprises the following steps: adding an acid solution into an obtained sodium silicate solution, continuously stirring, controlling the pH value of a mixed solution in the reaction process, standing and curing to obtain a polysilicic acid solution; adding a lanthanum chloride solution into the obtained polysilicic acid solution, controlling the temperature and stirring at a high speed to obtain the high-efficiency polysilicate lanthanum coagulant. The invention provides a poly-lanthanum silicate coagulant system for algae control for the first time, La < 3 + > ions are introduced into a poly-silicic acid structure in a complexing form to form a composite coagulant meeting the requirement of efficient flocculation of algae, and the composite coagulant is different from a traditional single metal salt or polymer-based coagulant, can be applied to removal of high-concentration floating algae in a water body, and has the advantages of simple preparation process and low cost. The algae removal coagulant has the characteristics of low dosage, large generated floc, fast sedimentation and no dependence on additional coagulant aids or pH regulators, effectively solves the problem of large dosage of the existing algae removal coagulant, and aims to realize efficient removal of floating algae in water.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and particularly relates to a preparation method and application of a highly efficient lanthanum polysilicate coagulant. Background Art

[0002] Lake eutrophication refers to the phenomenon that due to excessive input of nutrients such as nitrogen and phosphorus, abnormal reproduction of algae and other plankton in water bodies occurs, often accompanied by water quality deterioration, dissolved oxygen decline, fish death and algotoxin release, seriously threatening the water ecosystem and human health. Therefore, controlling the growth of algae is crucial for ensuring water quality. Common algae removal technologies mainly include physical, chemical and biological methods. Among them, physical methods such as salvage, ultrasonic, air flotation, etc. are rapid but difficult to be thorough, biological methods are ecologically friendly but have a lagging effect, and chemical methods can quickly remove algae by adding chemicals, but may cause secondary pollution. The coagulation method is widely used because of its simple operation and high treatment efficiency. It destroys the charge balance on the surface of algal cells by adding coagulants, promotes the formation of flocs and settles them for removal, and has good applicability.

[0003] Polysilicate coagulants have attracted attention because of their three-dimensional network structure and high molecular weight, and show good bridging flocculation performance in algae removal. However, traditional polysilicate coagulants have poor stability, are easy to form colloids and inactivate, which limits their long-term storage and large-scale application; although introducing metal ions such as aluminum salts or iron salts can improve their performance, there are still side effects such as residual aluminum and chromaticity. Existing research has improved the stability of polysilicate coagulants through solidification processes, but the effect is still limited.

[0004] In recent years, the rare earth element lanthanum has attracted attention because of its high reactivity and specific complexing ability, and has been used to prepare a variety of highly efficient phosphorus removal materials. For example, the disclosure No. CN202210270158 discloses a coagulant composed of lanthanum chloride and an organic chelating agent. Although it shows excellent performance in removing phosphates, it has poor stability at high temperatures and may cause a significant change in the pH value of the water body. Another disclosure No. CN201610544745 discloses a highly efficient phosphorus removal coagulant with a composite structure of an outer layer of polyaluminum chloride and an inner layer of diatomite, and lanthanum chloride is loaded in the pores of diatomite. Although the phosphorus removal effect is significant, its preparation process is complex and difficult to promote. At present, there is no algae removal by combining lanthanum salts with polysilicic acid in the prior art. Summary of the Invention

[0005] The object of the present invention: Aiming at the problems existing in the prior art, the present invention provides a preparation method of a highly efficient lanthanum polysilicate coagulant. The highly efficient lanthanum polysilicate coagulant prepared by the present invention has the characteristics of low dosage, large flocs generated and fast sedimentation, effectively solving the problem of large dosage of existing algae removal coagulants, and aiming to achieve efficient removal of planktonic algae in water.

[0006] The present invention also provides the application of the lanthanum polysilicate high-efficiency coagulant.

[0007] Technical solution: To achieve the above object, a preparation method of a lanthanum polysilicate high-efficiency coagulant according to the present invention includes the following steps:

[0008] 1) Stir and mix sodium silicate and water to obtain a sodium silicate solution;

[0009] 2) Add an acid solution to the sodium silicate solution obtained in step 1), continuously stir, control the pH value of the mixed solution during the reaction, and let it stand for aging to obtain a polysilicic acid solution;

[0010] 3) Take an appropriate amount of lanthanum chloride heptahydrate, dissolve it in water to prepare a lanthanum chloride solution, and then add it to the polysilicic acid solution obtained in step 2), control the temperature and stir at a high speed to obtain a lanthanum polysilicate high-efficiency coagulant.

[0011] Among them, the volume ratio range of the sodium silicate and water in step 1) is 5:100 to 20:100.

[0012] Among them, the acid solution in step 2) is hydrochloric acid or sulfuric acid with a hydrogen ion molar concentration of 0.5 to 6.0 mol / L, the dropping rate of the acid solution is 0.5 to 3 mL / min, and the volume ratio of the acid solution to the sodium silicate solution is 5:100 to 70:100.

[0013] Among them, the stirring temperature in step 2) is 15 to 25 °C, the stirring speed is 200 to 500 r / min, and the stirring time is 1 to 3 h.

[0014] Among them, the pH value in step 2) is controlled at 2.0 to 4.0, and the standing aging time is 1 to 3 h.

[0015] Among them, the concentration of the lanthanum chloride solution in step 3) is 0.01 to 0.10 mol / L, and it is added to the polysilicic acid solution according to the La / Si molar ratio of 0.5 to 2.0.

[0016] Among them, the temperature in step 3) is controlled at 15 to 25 °C, the stirring speed is 600 to 900 r / min, and the stirring time is 10 to 60 min.

[0017] The lanthanum polysilicate high-efficiency coagulant prepared by the preparation method of the lanthanum polysilicate high-efficiency coagulant according to the present invention.

[0018] The application of the lanthanum polysilicate high-efficiency coagulant prepared by the present invention in removing planktonic algae in water bodies.

[0019] Among them, the application includes the following steps:

[0020] 1) Add the highly efficient lanthanum polysilicate coagulant to the water body containing planktonic algae;

[0021] 2) Continuously stir the mixed solution, and then let it stand still to make the planktonic algae aggregate to form flocculent sediment;

[0022] 3) After the flocculent sediment completely settles to the bottom of the water, separate the supernatant from the sediment, and the obtained supernatant is the treated water after removing planktonic algae.

[0023] Among them, the planktonic algae described in step 1) include Microcystis aeruginosa, Chlorella vulgaris, Scenedesmus sp., Oscillatoria sp., etc., and the dosage of the highly efficient lanthanum polysilicate coagulant is 2 - 30 mg / L.

[0024] Among them, the continuous stirring described in step 2) is rapid stirring for 0.5 - 2 min, slow stirring for 10 - 35 min, the rotation speed range of rapid stirring is 100 - 300 rpm, the rotation speed range of slow stirring is 20 - 100 rpm, and the standing time is 15 - 30 min

[0025] The core of the present invention is the in-situ complexation mechanism of polysilicic acid and rare earth metal lanthanum ions. By slowly dropping the polysilicic acid solution into the lanthanum chloride solution, a stable –Si–O–La–O–Si– structure is formed under acidic conditions, realizing the uniform composite of polysilicic acid and lanthanum ions. This structure significantly improves the solution stability and structural integrity of the coagulant, overcoming the problems of easy gelling and difficult storage of traditional polysilicic acid products. The introduction of La 3+ not only enhances the spatial network configuration of polysilicic acid, but also realizes the synergistic optimization of coagulation performance and storage stability by controlling the La / Si molar ratio between 0.5 - 2.0. The coagulant prepared by the present invention forms large floc particles, dense structure, rapid sedimentation when treating high-concentration algae-containing water bodies, and has a low dosage requirement, with obvious performance advantages and practical application potential.

[0026] The present invention introduces La 3+ ions into the polysilicic acid structure in a complex form to prepare a composite inorganic polymer coagulant for the efficient flocculation of algae. La 3+ and polysilicic acid can form a stable –Si–O–La–O–Si– structure under suitable conditions, endowing the coagulant with a high charge density and three-dimensional bridging ability, significantly enhancing the flocculation and sedimentation performance while ensuring its stability. Compared with traditional single-component coagulants, this material has better structural stability, lower dosage, and denser flocs, and is especially suitable for the rapid treatment of high-concentration algae-containing water bodies. With the increasingly serious water pollution problem, how to improve the stability of coagulants and the synergy of action mechanisms has become the key. The present invention provides a new solution idea and technical support in the aspect of the synergistic mechanism of lanthanum polysilicate.

[0027] The core of the present invention is the in-situ composite mechanism of polysilicic acid and rare earth metal lanthanum ions. By introducing lanthanum salts during the formation of polysilicic acid, an inorganic polymer composite coagulant with stable structure, high flocculation efficiency and suitable for algae removal is prepared. The reaction mechanism is as follows: 1. Formation of the polysilicic acid network: Under acidic conditions, sodium silicate hydrolyzes to generate polysilicic acid anions, which form a –Si–O–Si– main chain structure through dehydration condensation, having good potential for flocculation bridging. 2. Electrostatic neutralization and complexation of lanthanum ions: La 3+ can combine with the hydroxyl groups or oxygen bridge bonds in polysilicic acid to form a –Si–O–La–O–Si– complex structure. This structure not only enhances the stability of polysilicic acid, but also improves its ability to capture and flocculate algae. 3. Triple synergistic coagulation mechanism: (1) Electrostatic neutralization: La 3+ as a strong cation neutralizes the negative charge on the surface of algal cells, destroying their stability; (2) Adsorption bridging: La 3+ and polysilicic acid jointly bridge multiple algal cells; (3) Enmeshment and sweeping: The three-dimensional network structure of polysilicic acid wraps and sediments algal cells, generating flocs that are denser and easier to sediment.

[0028] Compared with other conventional coagulants such as polyaluminum chloride and ferrous poly sulfate, the lanthanum polysilicate high-efficiency coagulant prepared by the present invention forms larger and denser flocs. It has a fast sedimentation rate, can significantly shorten the sedimentation time, improve the treatment efficiency, and can achieve the precipitation of algae within five minutes under the optimal working conditions. The dosage is low, and high-efficiency removal of algae can be achieved at a dosage of 4 mg / L. It does not rely on external coagulant aids or pH regulators and has strong adaptability.

[0029] The present invention introduces La 3+ ions into the polysilicic acid structure in a complex form to form a composite coagulant for efficient flocculation of algae, which is different from traditional single metal salt or polymer-based coagulants. The present invention first proposes a lanthanum polysilicate coagulant system for algae control: while in the prior art, most focus on phosphorus removal or heavy metals, and there is no polysilicic acid-rare earth composite coagulant dedicated to algae removal. The present invention forms a stable complex structure between La 3+ and polysilicic acid under certain conditions, making the coagulant have both high charge density and three-dimensional bridging ability.

[0030] The present invention controls the condensation degree and distribution of polysilicic acid: through optimization of pH regulation, dropping rate, temperature, etc., the polysilicic acid has high activity but does not gel. Combining the "post-addition method of polysilicic acid" with aging, the present invention first prepares a polysilicic acid solution and then slowly drops it into a pre-prepared lanthanum chloride solution, controlling the reaction temperature and stirring speed to make La 3+The ions and polysilicate segments are fully complexed under acidic conditions to avoid the formation of La(OH)3 precipitate at a relatively high pH. At the same time, the aging for 1 - 3 hours promotes the further stabilization of the polysilicate - lanthanum complex network structure, thereby improving the clarity and storage stability of the product. Optimization of the doping ratio (the La / Si molar ratio is controlled within 0.5 - 2.0): This ratio range can effectively balance the bridging performance of polysilicic acid and the charge - neutralizing ability of lanthanum ions, which can not only inhibit gelation precipitation but also ensure the coagulation activity and long - term storage performance.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0032] The gel - like lanthanum polysilicate high - efficiency coagulant of the present invention forms a stable complex by introducing lanthanum ions and polysilicic acid, effectively improving the colloidal stability and use reliability of the system, and avoiding the problems of easy gel precipitation and performance attenuation of traditional polysilicates during storage and use. This coagulant can achieve efficient flocculation of high - density algae - containing water at low dosage. The formed flocs have a compact structure and rapid sedimentation, showing excellent solid - liquid separation performance. At the same time, this product has strong adaptability to water quality conditions, little influence on pH, can achieve efficient algae removal without adding external additives, is easy to operate, and has strong application promotion potential and environmental compatibility. Description of the drawings

[0033] Figure 1 It is a bar chart showing the influence of the coagulant dosage in Example 1 on the removal effect of Microcystis aeruginosa in water by the lanthanum polysilicate high - efficiency coagulant. Among them Figure 1 the bar chart respectively represents the relationship between different coagulant dosages in Example 1 and the OD 680 (indicating the optical density absorption value of the algae - containing water at a wavelength of 680 nm) and the turbidity removal rate. Among them, Figure 1 in, the initial algae concentration = 2×10 6 cells / mL, the reaction temperature is 25 ± 5 °C, the volume of the reaction solution V = 500 mL, the La / Si molar ratio of the coagulant n(La / Si) = 1.0, the reaction time is 15 min, and the sedimentation time is 30 min.

[0034] Figure 2 It is a line chart showing the influence of the dosage of the lanthanum polysilicate high - efficiency coagulant in Example 1 on the removal effect of Microcystis aeruginosa within 5 minutes after coagulation. Among them Figure 2 the line chart respectively represents that the coagulant dosages in Example 1 are 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, and 5 mg / L. Among them, Figure 2 in, the initial algae concentration = 2×10 6cells / mL, the reaction temperature is 25 ± 5 °C, the volume of the reaction solution V = 500 mL, the dosage of the coagulant is 4 mg / L, and the reaction time is 15 min.

[0035] Figure 3 It is a bar chart showing the influence of the molar ratio of lanthanum to silicon in the coagulant on the removal effect of Microcystis aeruginosa in water by the highly efficient lanthanum silicate polymer coagulant in Example 2. Among them Figure 3 in the bar chart respectively represent the relationship between different molar ratios of lanthanum to silicon in the coagulant in Example 2 and the OD in the algae-containing water 680 and the turbidity removal rate. Among them, Figure 3 in, the initial concentration of algae = 2 × 10 6 cells / mL, the reaction temperature is 25 ± 5 °C, the volume of the reaction solution V = 500 mL, the dosage of the coagulant is 4 mg / L, the reaction time is 15 min, and the sedimentation time is 30 min.

[0036] Figure 4 It is a line chart showing the influence of the molar ratio of lanthanum to silicon on the removal effect of Microcystis aeruginosa within 5 minutes after coagulation by lanthanum silicate polymer in Example 2. Among them Figure 4 in the line chart respectively, the molar ratios of lanthanum to silicon in the coagulant in Example 2 are 0.2:1, 0.4:1, 0.6:1, 0.8:1, 1:1, 1.2:1. Among them, Figure 4 in, the initial concentration of algae = 2 × 10 6 cells / mL, the reaction temperature is 25 ± 5 °C, the volume of the reaction solution V = 500 mL, the dosage of the coagulant is 4 mg / L, and the reaction time is 15 min.

[0037] Figure 5 It is a bar chart showing the influence of different coagulants on the removal effect of Microcystis aeruginosa in water in Example 3. Among them Figure 5 in the bar chart respectively represent the relationship between different coagulants in Example 3 and the OD in the algae-containing water 680 and the turbidity removal rate. Among them, Figure 5 in, the initial concentration of algae = 2 × 10 6 cells / mL, the reaction temperature is 25 ± 5 °C, the volume of the reaction solution V = 500 mL, the molar ratio of lanthanum to silicon in the coagulant n(La / Si) = 1.0, the dosage of the coagulant is 4 mg / L, the reaction time is 15 min, and the sedimentation time is 30 min.

[0038] Figure 6 It is a line chart showing the influence of different coagulants on the removal effect of Microcystis aeruginosa within 5 minutes after coagulation in Example 3.

[0039] Among them Figure 6 in the line chart They respectively represent that in Example 3, the coagulants are lanthanum chloride heptahydrate, lanthanum polysilicate, polysilicic acid, polyaluminum chloride, and ferrous sulfate. Among them, Figure 6 in which, the initial algal concentration = 2×10 6 cells / mL, the reaction temperature is 25±5°C, the volume of the reaction solution V = 500 mL, the dosage of the coagulant is 4 mg / L, and the reaction time is 15 min.

[0040] Figure 7 It is the optical microscope observation result (magnification: 100×) after the coagulation treatment of Microcystis aeruginosa in water by lanthanum polysilicate and lanthanum chloride heptahydrate in Example 3.

[0041] Figure 8 It is the bar chart showing the influence of the slow stirring time in Example 4 on the removal effect of the highly efficient coagulant of lanthanum polysilicate on Microcystis aeruginosa in water. Among them Figure 8 in the bar chart respectively represent the relationship between the slow stirring time in Example 4 and the removal rates of OD 680 and turbidity in the algae-containing water. Among them, Figure 8 in which, the initial algal concentration = 2×10 6 cells / mL, the reaction temperature is 25±5°C, the volume of the reaction solution V = 500 mL, the molar ratio of lanthanum to silicon in the coagulant n(La / Si) = 1.0, the dosage of the coagulant is 4 mg / L, and the sedimentation time is 30 min.

[0042] Figure 9 It is the line chart showing the influence of the slow stirring time in Example 4 on the removal effect of lanthanum polysilicate on Microcystis aeruginosa within 5 minutes after coagulation. Among them Figure 9 in the line chart respectively represent that the slow stirring times in Example 4 for coagulation are 10 min, 15 min, 20 min, 25 min, 30 min, and 35 min. Among them, Figure 9 in which, the initial algal concentration = 2×10 6 cells / mL, the reaction temperature is 25±5°C, the volume of the reaction solution V = 500 mL, the molar ratio of lanthanum to silicon in the coagulant n(La / Si) = 1.0, and the dosage of the coagulant is 4 mg / L.

[0043] Figure 10 It is the bar chart showing the influence of the initial pH of the solution in Example 5 on the removal effect of the highly efficient coagulant of lanthanum polysilicate on Microcystis aeruginosa in water. Among them Figure 10 in the bar chart respectively represent the relationship between the initial pH of the solution in Example 5 and the removal rates of OD 680 and turbidity in the algae-containing water. Among them, Figure 10 in which, the initial algal concentration = 2×10 6cells / mL, the reaction temperature was 25 ± 5 °C, the volume of the reaction solution V = 500 mL, the molar ratio of lanthanum to silicon in the coagulant n(La / Si) = 1.0, the dosage of the coagulant was 4 mg / L, the reaction time was 15 min, and the sedimentation time was 30 min.

[0044] Figure 11 It is a line graph showing the effect of the initial pH of the solution in Example 5 on the removal of Microcystis aeruginosa by lanthanum polysilicate within 5 minutes after coagulation. Among them Figure 11 in the line graph respectively represent that the initial pH of the solution in Example 5 was 2, 4, 6, 8, 10, and 12. Among them, Figure 11 in which, the initial concentration of algae = 2 × 10 6 cells / mL, the reaction temperature was 25 ± 5 °C, the volume of the reaction solution V = 500 mL, the molar ratio of lanthanum to silicon in the coagulant n(La / Si) = 1.0, the dosage of the coagulant was 4 mg / L, and the reaction time was 15 min.

[0045] Figure 12 It is a graph showing the change in the Zeta potential of the flocs formed after the coagulation and algae removal of the algae-containing water in Example 5. Among them Figure 12 in the line graph represents the relationship between the initial pH of the solution in Example 5 and the Zeta potential of the formed flocs. Among them, Figure 12 in which, the initial concentration of algae = 2 × 10 6 cells / mL, the reaction temperature was 25 ± 5 °C, the volume of the reaction solution V = 500 mL, the molar ratio of lanthanum to silicon in the coagulant n(La / Si) = 1.0, the dosage of the coagulant was 4 mg / L, and the sedimentation time was 30 min.

[0046] Figure 13 It is an X-ray diffraction pattern of lanthanum polysilicate-based high-efficiency coagulants with different lanthanum-to-silicon ratios and polysilicic acid in Example 2.

[0047] Among them Figure 13 in which ★ and ▲ respectively represent the diffraction peaks of NaCl and La3(Si2O7)Cl3. Detailed implementation mode

[0048] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0049] The materials, reagents, etc. used in the examples can be obtained from commercial channels without special instructions.

[0050] Urea was purchased from Sigma-Aldrich, USA, product number U1250-5KG.

[0051] Ru(bpy)3Cl2 is ruthenium (II) tris(2,2'-bipyridyl) dichloride hexahydrate, CAS number: 50525-27-4.

[0052] Example 1

[0053] Effect of Coagulant Dosage on the Removal Efficiency of Lanthanum Polysilicate High - efficiency Coagulant for Phytoplankton Algae in Water

[0054] A preparation method of a lanthanum polysilicate high - efficiency coagulant, which includes: After stirring and mixing 10 mL of sodium silicate solution with a mass fraction of 37.5% and 100 mL of ultrapure water and making up the volume, transfer it to a beaker to obtain a sodium silicate solution; Add 6.05 mL of 6 mol / L hydrochloric acid solution dropwise into the sodium silicate solution at a rate of 1 mL / min until pH = 3.0, continuously stir at 300 r / min at 25 °C for 1 h, and let it stand for aging for 1 h to obtain a polysilicate solution; Add 14.634 mL of the polysilicate solution to 100 mL of lanthanum chloride solution with a concentration of 0.054 mol / L, and continuously stir at 700 r / min at 25 °C for 30 min to obtain a lanthanum polysilicate high - efficiency coagulant with a lanthanum - silicon ratio of 1:1.

[0055] Add the lanthanum polysilicate high - efficiency coagulant (calculated by lanthanum mass) into 500 mL of water containing Microcystis aeruginosa at dosages of 1 mg / L, 2 mg / L, 3 mg / L, 4 mg / L, and 5 mg / L respectively. Use a six - blade stirrer to stir quickly at 200 rpm for 1 min, stir slowly at 40 rpm for 15 min, and after static precipitation for 30 min, take the supernatant 1.5 cm below the liquid surface for turbidity and absorbance (680 nm) detection.

[0056] In this example, the water containing Microcystis aeruginosa is prepared by centrifuging the algal solution cultured in a light incubator at 3000 rpm for 10 min, removing the supernatant, and then resuspending it in ultrapure water to obtain a water body containing Microcystis aeruginosa with an initial concentration of 2×10 6 cells / mL.

[0057] In this Example 1, the whole coagulation and algae - removal process is carried out at room temperature (25 °C).

[0058] Figure 1 It is the removal efficiency diagram of the lanthanum polysilicate high - efficiency coagulant for Microcystis aeruginosa in water under different coagulant dosages in Example 1; As Figure 1 can be seen, with the increase of the coagulant dosage, the removal efficiency of the coagulant for turbidity and OD 680 rapidly increases in the initial stage. When the dosage reaches 4 mg / L, the removal rates of the coagulant for OD 680 and turbidity both exceed 90%, and then tend to be stable. When the dosage is 4 mg / L, the removal rates of OD 680 and turbidity reach the peak values of 98.41% and 94.30% respectively. Continuing to increase the dosage, the coagulant's removal rates for turbidity and OD 680Instead, the removal efficiency will decrease. It indicates that excessive dosage may cause the "re-stabilization" phenomenon (Zeta inversion), which is a typical electro-neutralization - re-stabilization turning point phenomenon, reflecting the "high efficiency and low dosage" characteristic of the dosage of this coagulant.

[0059] Figure 2 Figure showing the removal efficiency of lanthanum polysilicate on the turbidity of Microcystis aeruginosa water within 5 minutes after coagulation under different coagulant dosages in Example 1; Figure 2 It can be seen that with the increase of the coagulant dosage, the turbidity removal rate increases significantly, and a higher dosage can achieve a higher removal rate in a shorter time. When the dosage reaches 4 mg / L, the turbidity removal rate exceeds 90% within 2 minutes, reaching 90.32%; while a lower dosage requires a longer time to achieve a similar effect. Continuing to increase the dosage, the turbidity removal rate slows down. This is consistent with the trend that the flocs first increase and then decrease with the increase of the dosage in the experiment.

[0060] Example 2

[0061] Effect of the molar ratio of lanthanum to silicon in the coagulant on the removal effect of lanthanum polysilicate high-efficiency coagulant on planktonic algae in water

[0062] A preparation method of a lanthanum polysilicate high-efficiency coagulant, which includes: after stirring and mixing 10 mL of sodium silicate solution with a mass fraction of 37.5% and 100 mL of ultrapure water and making the volume constant, transferring it to a beaker to obtain a sodium silicate solution; adding 6.05 mL of 6 mol / L hydrochloric acid solution dropwise into the sodium silicate solution at a rate of 1 mL / min until pH = 3.0, continuously stirring at 300 r / min at 25 °C for 1 h, and standing for aging for 1 h to obtain a polysilicate solution; respectively adding 14.634 mL of the polysilicate solution into 100 mL of lanthanum chloride solutions with concentrations of 0.065 mol / L, 0.054 mol / L, 0.043 mol / L, 0.032 mol / L, 0.022 mol / L, and 0.011 mol / L in turn (the molar ratios of lanthanum to silicon are 1.2:1, 1:1, 0.8:1, 0.6:1, 0.4:1, 0.2:1), and continuously stirring at 700 r / min at 25 °C for 30 min to obtain lanthanum polysilicate high-efficiency coagulants with different lanthanum-silicon ratios.

[0063] Adding lanthanum polysilicate high-efficiency coagulants with different lanthanum-silicon molar ratios (by lanthanum mass, the molar ratios of lanthanum to silicon are 1.2:1, 1:1, 0.8:1, 0.6:1, 0.4:1, 0.2:1) into 500 mL of a solution with a concentration of 2×10 6In the water containing Microcystis aeruginosa at a concentration of cells / mL, use a six - blade stirrer to stir rapidly at 200 rpm for 1 min, stir slowly at 40 rpm for 15 min, let it stand and precipitate for 30 min, and then take the supernatant 1.5 cm below the liquid surface to detect the turbidity and absorbance (680 nm).

[0064] The entire coagulation and algae - removal process in this experiment was carried out at room temperature (25 °C).

[0065] Figure 3 It is the removal efficiency diagram of La - containing polysilicic acid with different La / Si molar ratios for Microcystis aeruginosa in water in Example 2; as can be seen from the appendix Figure 3 It can be seen that when the dosage is 4 mg / L, the La / Si molar ratio has little effect on the removal of Microcystis aeruginosa by the highly efficient coagulant of La - containing polysilicic acid. The removal rates of different La / Si molar ratio coagulants for OD 680 and turbidity both exceed 90%. When the La / Si molar ratio is 1:1, the removal rates of OD 680 and turbidity reach the peak values of 98.32% and 94.57% respectively. Judging only from the removal rate results, the difference in the algae - removal efficiency of different La / Si ratio coagulants is small. However, from the observation of the floc morphology, it can be seen that the flocs generated by the high La / Si ratio coagulant are denser and the sedimentation rate is faster, showing better flocculation performance. Combining with the subsequent XRD analysis results, it is found that La 3+ participates in the structural reconstruction of the polysilicic acid network and generates a new amorphous complex. This structural evolution may have a significant impact on the solution stability and service life of the coagulant. Therefore, although the La / Si molar ratio has limited contribution to the removal rate, it plays a key role in the structural regulation and performance maintenance of the composite system.

[0066] Figure 4 It is the removal efficiency diagram of La - containing polysilicic acid with different La / Si ratios for the turbidity of Microcystis aeruginosa water within 5 minutes after coagulation in Example 2; as can be seen from the appendix Figure 4 It can be seen that when the dosage is 4 mg / L, with the increase of the La / Si ratio, the turbidity removal rate increases significantly, and the high La / Si ratio can achieve a higher removal rate in a shorter time. When the La / Si ratio reaches 1:1, it reaches the peak value, and the turbidity removal rate can exceed 90% within 2 min; continuing to increase the La / Si ratio will instead lead to a decrease in the removal rate, probably because the excessive La ions disrupt the floc structure and reduce its stability and sedimentation performance.

[0067] Example 3

[0068] The influence of different coagulants on the removal effect of planktonic algae in water

[0069] A preparation method of a highly efficient lanthanum polysilicate coagulant, the method comprising: after stirring and mixing 10 mL of a sodium silicate solution with a mass fraction of 37.5% and 100 mL of ultrapure water and making up the volume, transferring it to a beaker to obtain a sodium silicate solution; adding 6.05 mL of a 6 mol / L hydrochloric acid solution dropwise to the sodium silicate solution at a rate of 1 mL / min until the pH = 3.0, continuously stirring at 300 r / min at 25 °C for 1 h, and standing and aging for 1 h to obtain a polysilicic acid solution; adding 14.634 mL of the polysilicic acid solution to a 0.054 mol / L lanthanum chloride solution, and continuously stirring at 700 r / min at 25 °C for 30 min to obtain a highly efficient lanthanum polysilicate coagulant.

[0070] Adding the highly efficient lanthanum polysilicate coagulant (calculated by lanthanum mass) at a dosage of 4 mg / L into 500 mL of a water body containing Microcystis aeruginosa with a concentration of 2×10 6 cells / mL, using a six-blade stirrer to stir quickly at 200 rpm for 1 min, stir slowly at 40 rpm for 15 min, and after static precipitation for 30 min, take the supernatant liquid 1.5 cm below the liquid surface for turbidity and absorbance (680 nm) detection.

[0071] In this Example 3, the entire coagulation and algae removal process was carried out at room temperature (25 °C).

[0072] Comparative Example 1: The difference from Example 3 is that during the process of using the highly efficient lanthanum polysilicate coagulant for coagulation and algae removal, the added lanthanum polysilicate coagulant was replaced with an equal amount of lanthanum chloride heptahydrate (calculated by lanthanum mass).

[0073] Comparative Example 2: The difference from Example 3 is that during the process of using the highly efficient lanthanum polysilicate coagulant for coagulation and algae removal, the added lanthanum polysilicate coagulant was replaced with an equal amount of the polysilicic acid prepared in Example 3 (calculated by silicon dioxide mass).

[0074] Comparative Example 3: The difference from Example 3 is that during the process of using the highly efficient lanthanum polysilicate coagulant for coagulation and algae removal, the added lanthanum polysilicate coagulant was replaced with an equal amount of polyaluminum chloride.

[0075] Comparative Example 4: The difference from Example 3 is that during the process of using the highly efficient lanthanum polysilicate coagulant for coagulation and algae removal, the added lanthanum polysilicate coagulant was replaced with an equal amount of ferrous sulfate.

[0076] Figure 5 It is a comparison chart of the coagulation and algae removal performance of the highly efficient lanthanum polysilicate coagulant in Example 3 and Comparative Examples 1, 2, 3, and 4; from Figure 5It can be seen that at a dosage of 4 mg / L, polyaluminium chloride and lanthanum chloride heptahydrate have better removal effects on Microcystis aeruginosa and turbidity. Ferrous sulfate and polysilicic acid have unsatisfactory removal effects on Microcystis aeruginosa and turbidity. Polylanthanum silicate high-efficiency coagulant has the best treatment effect and has a good effect on OD 680 The removal rates of turbidity and turbidity reached 98.05% and 94.57% respectively. Compared with the use of polysilicic acid or lanthanum chloride alone, polylanthanum silicate can remove turbidity and turbidity through La 3+ The synergistic coupling of electrical neutralization and polysilicate bridging effect effectively improves the formation efficiency and mechanical strength of flocs, enhances the overall performance of the coagulation system from the mechanism level, and demonstrates clear synergistic enhancement characteristics.

[0077] Figure 6 The figure is a diagram showing the removal efficiency of different coagulants on the turbidity of Microcystis aeruginosa water within 5 minutes after coagulation in Example 3; Figure 6 It can be seen that compared with other coagulants, lanthanum polysilicate has a more significant improvement in turbidity removal efficiency, and can achieve a removal rate of 90% within 2 minutes. Its performance is better than that of lanthanum chloride heptahydrate and polysilicic acid used alone, indicating that the lanthanum polysilicate formed by the combination of the two has a synergistic enhanced coagulation effect. At the same time, compared with traditional coagulants such as polyaluminium chloride and ferrous sulfate, lanthanum polysilicate also shows better turbidity removal effect.

[0078] Figure 7 The optical microscope observation results of the coagulation treatment of Microcystis aeruginosa in water by polylanthanum silicate and lanthanum chloride heptahydrate in Example 3. In the microscopic image of polylanthanum silicate, the coagulated flocs are large, dense and uniformly distributed, indicating that polylanthanum silicate can effectively promote the formation of flocs during the coagulation process and enhance their mechanical strength and sedimentation ability. This phenomenon is consistent with the coagulation treatment of polylanthanum silicate by La 3+ The mechanism of improving floc formation efficiency by the synergistic effect of electrical neutralization and polysilicate bridging effect is consistent. The microscopic image of lanthanum chloride heptahydrate shows that the flocs formed are small and uneven, indicating that its coagulation effect is relatively poor and it is difficult to form stable flocs, resulting in poor sedimentation performance. In addition, the flocs formed by low lanthanum-silicon ratios are looser. These results further verify the superiority of polysilicate lanthanum as a coagulant, which can significantly improve the removal of Microcystis aeruginosa and turbidity in water.

[0079] Example 4

[0080] Effect of slow stirring time on the removal of fluoride from water by lanthanum polysilicate coagulant

[0081] A preparation method of a highly efficient lanthanum polysilicate coagulant, the method comprising: after stirring and mixing 10 mL of a sodium silicate solution with a mass fraction of 37.5% and 100 mL of ultrapure water to make up the volume, transferring it to a beaker to obtain a sodium silicate solution; adding 6.05 mL of a 6 mol / L hydrochloric acid solution dropwise to the sodium silicate solution at a rate of 1 mL / min until the pH = 3.0, continuously stirring at 300 r / min at 25 °C for 1 h, standing and aging for 1 h to obtain a polysilicate solution; adding 14.634 mL of the polysilicate solution to a 0.054 mol / L lanthanum chloride solution, continuously stirring at 700 r / min at 25 °C for 30 min to obtain a highly efficient lanthanum polysilicate coagulant.

[0082] Adding the highly efficient lanthanum polysilicate coagulant (calculated by lanthanum mass) into 500 mL of a water body containing Microcystis aeruginosa at a concentration of 2×10 6 cells / mL at a dosage of 4 mg / L, using a six-stirrer to quickly stir at a speed of 200 rpm for 1 min, adjusting the slow stirring time to 10 - 35 min at a speed of 40 rpm, and taking the supernatant 1.5 cm below the liquid surface after static precipitation for 30 min to detect the turbidity and absorbance (680 nm).

[0083] In this Example 4, the entire coagulation and algae removal process was carried out at room temperature (25 °C).

[0084] Figure 8 It is a graph of the removal efficiency of the highly efficient lanthanum polysilicate coagulant on Microcystis aeruginosa in water at different slow stirring times in Example 4; from Figure 8 it can be seen that the slow stirring time has little effect on the removal of Microcystis aeruginosa by the highly efficient lanthanum polysilicate coagulant. When the slow stirring time is 15 min, the removal rate of OD 680 reaches a peak of 97.44%. When the slow stirring time is 25 min, the removal rate of OD 680 reaches a peak of 95.66%.

[0085] Figure 9 It is a graph of the removal efficiency of the turbidity of Microcystis aeruginosa water within 5 minutes after coagulation with lanthanum polysilicate at different slow stirring times in Example 4; from the appendix Figure 9 it can be seen that with the extension of the slow stirring time, the turbidity removal rate increases significantly. When the stirring time is 15 min, the turbidity removal rate can reach 90% within 2 min. Further extending the stirring time can increase the removal rate in the initial stage, but the time required to reach 90% changes little. Considering the comprehensive cost and engineering adaptability, it is recommended to use 15 min as the optimized slow stirring time.

[0086] Example 5

[0087] Effect of Initial pH Value of Solution on Removal Efficiency of Planktonic Algae in Water by Lanthanum Polysilicate High-Efficiency Coagulant

[0088] A preparation method of a lanthanum polysilicate high-efficiency coagulant, which includes: after stirring and mixing 10 mL of sodium silicate solution with a mass fraction of 37.5% and 100 mL of ultrapure water and making up the volume, transfer it to a beaker to obtain a sodium silicate solution; add 6.05 mL of 6 mol / L hydrochloric acid solution dropwise into the sodium silicate solution at a rate of 1 mL / min until pH = 3.0, continuously stir at 300 r / min at 25 °C for 1 h, and let it stand and age for 1 h to obtain a polysilicate solution; add 14.634 mL of the polysilicate solution to a 0.054 mol / L lanthanum chloride solution, and continuously stir at 700 r / min at 25 °C for 30 min to obtain a lanthanum polysilicate high-efficiency coagulant.

[0089] Add the lanthanum polysilicate high-efficiency coagulant (calculated by lanthanum mass) into 500 mL of water containing Microcystis aeruginosa at a concentration of 2×10 6 cells / mL at a dosage of 4 mg / L respectively, and use 1 mol / L HCl and NaOH solutions to adjust the initial pH of the mixed solution to 2 - 12. Use a six-blade stirrer to stir quickly at 200 rpm for 1 min, stir slowly at 40 rpm for 15 min, and after standing and sedimenting for 30 min, take the supernatant 1.5 cm below the liquid surface for turbidity and absorbance (680 nm) detection.

[0090] In this Example 5, the entire coagulation and algae removal process is carried out at room temperature (25 °C).

[0091] Figure 10 It is the removal efficiency diagram of the lanthanum polysilicate high-efficiency coagulant on Microcystis aeruginosa in water at different pH values in Example 5; as can be seen from the attachment Figure 10 It can be seen that at a dosage of 4 mg / L, as the initial pH value of the solution increases, the removal rates of the coagulant for OD 680 and turbidity first increase and then decrease. When the initial pH of the solution is 10.0, the removal rate of the coagulant for OD 680 reaches a peak value of 92.31%. When the initial pH of the solution is 8.0, the removal rate of the coagulant for turbidity reaches a peak value of 90.92%.

[0092] Figure 11 It is the removal efficiency diagram of the turbidity of Microcystis aeruginosa water within 5 minutes after coagulation with lanthanum polysilicate at different initial pH values in Example 5; as can be seen from the attachment Figure 11 It can be seen that as the initial pH increases, the turbidity removal rate increases significantly; when the initial pH is 8, the turbidity removal rate can reach 90% within 5 min. Further increasing the pH value, the turbidity removal rate decreases, probably because the stability of the flocs decreases or the surface charge of the algal cells increases under over-alkaline conditions, affecting the coagulation effect.

[0093] Figure 12 It is the change diagram of the Zeta potential of the flocs generated after the coagulation and algae removal of the algae-containing water in Example 5; the change of the Zeta potential value is considered an effective tool for exploring the coagulation mechanism, which is usually explained by electro-neutralization and sweep flocculation. Negatively charged algal cells and algal organic matter can undergo electro-neutralization reactions with the hydrolyzed products of positively charged coagulants. When the algal solution is at the isoelectric point (Zeta = 0), there is no repulsive force between particles, and it is most likely to be destabilized, promoting the aggregation and sedimentation of algal cells. In the original high-algal water before coagulation, the Zeta potential corresponding to the algal cells in the stationary phase was -34.55 Mv. As can be seen from the appendix Figure 12 it can be seen that the Zeta potential of the flocs generated by the lanthanum polysilicate high-efficiency coagulant gradually changes from negative to positive with the decrease of the initial pH of the solution. The charge in the coagulation system undergoes inversion and the "re-stabilization" phenomenon occurs, and the algal cell removal rate decreases instead, which is the same as the result of Figure 9 ; and the lower the pH, the higher the Zeta potential value, which shows that the coagulation mechanism of the lanthanum polysilicate high-efficiency coagulant changes with the change of pH. When pH = 10.0, the Zeta value of the flocs is closest to zero, and under this condition, the coagulation effect is the best. The potential of the lanthanum polysilicate high-efficiency coagulant coagulation system is 0.126 mV, indicating that electro-neutralization plays a major role.

[0094] Figure 13 It is the X-ray diffraction pattern of the lanthanum polysilicate high-efficiency coagulant with different lanthanum-silicon ratios and polysilicic acid in Example 2; the self-made polysilicic acid and lanthanum polysilicate coagulant powder were measured by XRD and analyzed with Jade software. Crystalline materials usually show sharp diffraction peaks in the X-ray diffraction pattern, and the positions and intensities of these diffraction peaks can provide information about the crystal structure in the sample, while amorphous materials usually show a flat baseline in the X-ray diffraction pattern without obvious diffraction peaks. By analyzing Figure 13 it can be found that these coagulants have diffraction peaks at diffraction angles of 27°, 32°, 46°, 57°, 67°, and 77°. After comparing with the standard crystal library (PDF#01-088-2300), the crystals corresponding to these diffraction peaks may be the NaCl crystal structure. In addition, when the lanthanum-silicon ratio of the lanthanum polysilicate coagulant exceeds 0.6:1, a diffraction peak appears at a diffraction angle of 33°. Further comparison with the standard crystal database (PDF#97-008-2386) shows that this diffraction peak may be attributed to the La3(Si2O7)Cl3 crystal structure. At other diffraction angles, it shows a flat baseline of amorphous materials, indicating that an amorphous polymerization product is formed between polysilicic acid and metal ions in the newly prepared lanthanum polysilicate coagulant, where Na in the NaCl crystal diffraction peak + mainly comes from sodium silicate, and Cl -It mainly comes from lanthanum chloride heptahydrate and hydrochloric acid, which combine to form NaCl crystals during the polymerization process. Diffraction peaks of LaCl3, HCl, Na2SiO3, etc. were not found in the XRD pattern, while the appearance of diffraction peaks that may be attributed to La3(Si2O7)Cl3 indicates that a series of reactions occurred after the introduction of lanthanum ions, resulting in the generation of new substances. Therefore, we can infer that complex chemical reactions occurred among materials such as lanthanum chloride heptahydrate, hydrochloric acid, and sodium silicate, producing various more complex compounds, and then forming an amorphous new inorganic polymer coagulant without characteristic diffraction peaks.

Claims

1. A preparation method of a highly efficient lanthanum polysilicate coagulant, characterized in that, It includes the following steps: 1) Stir and mix sodium silicate and water to obtain a sodium silicate solution; 2) Add an acid solution to the sodium silicate solution obtained in step 1), continuously stir, control the pH value of the mixed solution during the reaction, and let it stand for ripening to obtain a polysilicic acid solution; 3) Dissolve lanthanum chloride heptahydrate in water to prepare a lanthanum chloride solution, and then add it to the polysilicic acid solution obtained in step 2), control the temperature and stir at a high speed to obtain a highly efficient coagulant of lanthanum polysilicate.

2. The preparation method of the lanthanum polysilicate high-efficiency coagulant according to claim 1, characterized in that, In step 1), the volume ratio range of the sodium silicate to water is 5:100 to 20:

100.

3. The preparation method of the highly efficient lanthanum silicate polymer coagulant according to claim 1, characterized in that, In step 2), the acid solution is hydrochloric acid or sulfuric acid with a hydrogen ion molar concentration of 0.5 - 6.0 mol / L. The dropping rate of the acid solution is 0.5 - 3 mL / min, and the volume ratio of the acid solution to the sodium silicate solution is 5:100 to 70:

100.

4. The preparation method of the highly efficient lanthanum silicate polymer coagulant according to claim 1, characterized in that, In step 2), the stirring temperature is 15 - 25 °C, the stirring speed is 200 - 500 r / min, and the stirring time is 1 - 3 h.

5. The preparation method of the highly efficient lanthanum polysilicate coagulant according to claim 1, characterized in that, In step 2), the pH value is controlled at 2.0 - 4.0, and the standing ripening time is 1 - 3 h.

6. The preparation method of the lanthanum polysilicate high-efficiency coagulant according to claim 1, characterized in that, In step 3), the concentration of the lanthanum chloride solution is 0.01 - 0.10 mol / L, and it is preferably added to the polysilicic acid solution according to the La / Si molar ratio of 0.5 - 2.

0.

7. The preparation method of the highly efficient lanthanum silicate polymer coagulant according to claim 1, characterized in that In step 3), the temperature is controlled at 15 - 25 °C, the stirring speed is 600 - 900 r / min, and the stirring time is 10 - 60 min.

8. A highly efficient coagulant of lanthanum polysilicate prepared by the preparation method of the highly efficient coagulant of lanthanum polysilicate described in claim 1.

9. An application of the highly efficient coagulant of lanthanum polysilicate prepared in claim 8 in removing planktonic algae in water bodies.

10. The application according to claim 9, wherein The said application includes the following steps: 1) Add the highly efficient coagulant of lanthanum polysilicate to the water body containing planktonic algae; 2) Continuously stir the mixed solution, and then let it stand to make the planktonic algae coagulate to form flocculent sediment; 3) After the flocculent sediment completely settles to the bottom of the water, separate the supernatant from the sediment, and the obtained supernatant is the treated water after removing planktonic algae.

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