A rare earth compound flocculant, its preparation method and application

Abstract

The application discloses a rare earth compound flocculant and a preparation method and application thereof, and comprises a rare earth compound of gluconic acid, a rare earth compound of pyrithione and water, wherein the content of the rare earth compound of gluconic acid is 5-15 wt%, the rare earth compound of gluconic acid is prepared by reacting sodium gluconate and a first rare earth chloride salt in water; the content of the rare earth compound of pyrithione is 0.4-0.6 wt%, and the rare earth compound of pyrithione is prepared by reacting sodium pyrithione and a second rare earth chloride salt in water. The rare earth ions in the application have positive electricity, show extremely strong coordination ability and high coordination number. Meanwhile, the surface of Phaeodactylum tricornutum is negatively charged; therefore, when the rare earth ions contact with the Phaeodactylum tricornutum, the two can rapidly interact in electricity, cause the Phaeodactylum tricornutum to rapidly aggregate and form a mass, and then gradually precipitate.

Description

Technical Field

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

[0002] *Phaeodactylum tricornutum* is a single-celled marine diatom with high economic value. Due to its unique biological characteristics, it has been widely used in various fields such as food, pharmaceuticals, and biofuels. As a highly efficient oil producer, *Phaeodactylum tricornutum* has an extremely high oil content, typically between 30 wt% and 50 wt%, which gives it great potential in biodiesel production. Studies have shown that under specific culture conditions, the oil yield of *Phaeodactylum tricornutum* can reach 2.94 mg / L / d², indicating its significant advantages for large-scale industrial applications.

[0003] Besides its applications in the energy sector, *Phaeodactylum tricornutum* is also rich in fucoxanthin, a natural pigment with various potential pharmacological activities. Fucoxanthin possesses antioxidant, anti-inflammatory, and anti-tumor properties, and is therefore widely used in nutritional supplements, providing important protection for human health.

[0004] However, despite the numerous advantages of *Phaeodactylum tricornutum*, its harvesting and separation process remains a significant technical challenge. Currently, the main methods for harvesting *Phaeodactylum tricornutum* include centrifugation, filtration, and sedimentation. While centrifugation offers high separation efficiency, its high energy consumption and equipment requirements limit its application to laboratory-scale operations. Industrial production typically employs large filters, but this method suffers from low recovery rates, high costs, and can negatively impact the integrity of the algae. Furthermore, research specifically on the collection and flocculants for *Phaeodactylum tricornutum* is relatively limited, and related reports are extremely scarce.

[0005] Despite this, some patented technologies attempt to address this problem. For example, CN 1418825A discloses a highly efficient algal flocculant and its application method in controlling red tides and algal blooms. This method uses clay modified with natural polymers as a flocculant, achieving a flocculation rate of over 95 wt% after 8 hours of treatment at an input concentration of 0.005 g / L. This technology provides a possible solution for the industrial collection of *Phaeodactylum tricornutum*. Furthermore, Japanese patent JP57131119 proposes a method for treating clay with inorganic acids, while US patent US6071859 describes a method for mixing unsaturated fatty acids with clay. While these technologies improve flocculation effects to some extent, they still have many shortcomings. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a rare earth compound flocculant.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned rare earth compound flocculant.

[0008] Another object of the present invention is to provide the application of the above-mentioned rare earth compound flocculant.

[0009] The technical solution of the present invention is as follows:

[0010] A rare earth compound flocculant, comprising rare earth gluconate, rare earth pyridine thione, and water, wherein:

[0011] The content of rare earth gluconate is 5-15 wt%, which is prepared by reacting sodium gluconate with a first rare earth chloride salt in water.

[0012] The content of the rare earth compound pyridinethione is 0.4-0.6 wt%, which is prepared by reacting sodium pyridinethione with a second rare earth chloride salt in water.

[0013] In a preferred embodiment of the present invention, the first rare earth chloride salt is selected from lanthanum chloride, europium chloride, and gadolinium chloride.

[0014] More preferably, the second rare earth chloride salt is selected from samarium chloride, cerium chloride, and lanthanum chloride.

[0015] The preparation method of the above-mentioned rare earth compound flocculant includes the following steps:

[0016] (1) Preparation of rare earth gluconate solution;

[0017] (2) Preparation of pyridinethione rare earth compound solution;

[0018] (3) Add the pyridine thione rare earth compound solution obtained in step (2) to the gluconic acid rare earth compound solution obtained in step (1) and stir thoroughly to obtain the rare earth compound flocculant.

[0019] In a preferred embodiment of the present invention, step (1) includes:

[0020] A. Add sodium gluconate to deionized water and stir to prepare a transparent solution;

[0021] B. Heat the transparent solution obtained in step A to 40°C and stir continuously to allow the sodium gluconate molecular chains to fully extend.

[0022] C. Dissolve the first rare earth chloride salt in deionized water by stirring to obtain a solution;

[0023] D. While stirring, slowly add the solution obtained in step C to the material obtained in step (2). After the addition is complete, continue the reaction at 40°C for 2 hours, and then cool to room temperature to obtain gadolinium gluconate solution.

[0024] In a preferred embodiment of the present invention, step (2) includes:

[0025] a. Add sodium pyrithione to deionized water and stir to mix evenly;

[0026] b. Dissolve the second rare earth chloride salt in deionized water by stirring to obtain a solution;

[0027] c. Add the solution obtained in step b to the material obtained in step a. After the addition is complete, react for 3 hours at room temperature and pressure to obtain a precipitate. After filtration and washing, obtain a lanthanum pyridinethione solution.

[0028] The application of the above-mentioned rare earth compound flocculants in the collection of seawater from *Phaeophyte Trigonella*.

[0029] In a preferred embodiment of the present invention, 20 kg of the rare earth compound flocculant is added per ton of seawater.

[0030] A method for collecting *Phaeophyte Triangularis* from seawater involves adding the aforementioned rare earth compound flocculant to seawater containing *Phaeophyte Triangularis*, stirring until homogeneous, and then collecting the precipitate.

[0031] In a preferred embodiment of the present invention, 20 kg of the rare earth compound flocculant is added per ton of seawater.

[0032] The beneficial effects of this invention are:

[0033] 1. The rare earth ions in this invention are positively charged, exhibiting extremely strong coordination ability and a high coordination number. At the same time, the surface of *Phaeodactylum tricornutum* is negatively charged; therefore, when rare earth ions come into contact with *Phaeodactylum tricornutum*, the two can rapidly interact with each other, causing *Phaeodactylum tricornutum* to quickly aggregate and form clumps, which then gradually precipitate.

[0034] 2. The pyrithione in this invention has the function of inhibiting the growth of bacteria and algae, and can provide antibacterial effect during the storage of rare earth gluconate, while promoting the release of rare earth ions and further enhancing the inhibitory effect on brown finger algae; therefore, the synergistic effect of pyrithione and rare earth gluconate can effectively promote the rapid flocculation of brown finger algae, and realize efficient, short-term and low-dose industrial application. Attached Figure Description

[0035] Figure 1 This is a flowchart illustrating the preparation process of the rare earth compound flocculant of the present invention. Detailed Implementation

[0036] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0037] The process flow of the following embodiments is as follows: Figure 1 As shown, and where:

[0038] Sodium gluconate is D-gluconate sodium, and its purity is food grade;

[0039] The purity of rare earth chloride salts is 99.99%;

[0040] Sodium pyrithione was a 40 wt% industrial-grade solution purchased from Guangzhou Lanfeng Chemical Co., Ltd., brand name SPT-40.

[0041] Example 1

[0042] The preparation method of rare earth gluconate in this embodiment includes the following steps:

[0043] (1) Add 0.1 mol of sodium gluconate (approximately 44.84 g) to 403.56 g of deionized water and stir for 10 min at 400 r / min to prepare a transparent solution with a concentration of 10 wt%.

[0044] (2) Heat the transparent solution obtained in step (1) to 40°C and stir continuously to allow the sodium gluconate molecular chains to fully extend. Stir for about 20 minutes.

[0045] (3) Weigh 0.03 mol (approximately 7.35 g) of lanthanum chloride into a beaker, then add 4.90 g of deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt% for later use;

[0046] (4) While stirring, slowly add the solution obtained in step (3) to the material obtained in step (2). After the addition is complete, continue the reaction at 40°C for 2 hours, and then cool to room temperature to obtain lanthanum gluconate solution.

[0047] Furthermore, the preparation method of the rare earth compound flocculant in this embodiment includes the following steps:

[0048] (1) Add 0.1 mol (approximately 15.01 g) of sodium pyrithione to a beaker, add 45.03 g of deionized water, stir and mix evenly at a stirring rate of 600 r / min for 7 min.

[0049] (2) Weigh 0.03 mol (approximately 7.35 g) of samarium chloride into a beaker, then add deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt%.

[0050] (3) The solution obtained in step (2) is added dropwise to the material obtained in step (1). After the addition is completed, the reaction is carried out at room temperature and pressure for 3 hours to obtain a white powder precipitate. After filtration and washing, a samarium pyridinethione solution with a solid content of 32 wt% is obtained.

[0051] (4) Add 8.69g of the samarium pyridinethione solution obtained in step (3) to the above lanthanum gluconate solution, so that the concentration of samarium pyridinethione is 0.6wt% and the concentration of lanthanum gluconate is 10wt%. Stir continuously to obtain a transparent light yellow solution, which is the rare earth compound flocculant.

[0052] In seawater containing *Phaeolipoic trichomoniasis*, approximately 20 kg of the rare earth compound flocculant prepared in this example was added per ton of seawater and stirred until homogeneous. After 1 hour, *Phaeolipoic trichomoniasis* was observed to precipitate in the water, resulting in a collection rate of 94.2 wt% for *Phaeolipoic trichomoniasis*.

[0053] Example 2

[0054] The preparation method of rare earth gluconate in this embodiment includes the following steps:

[0055] (1) Add 0.1 mol of sodium gluconate (approximately 44.84 g) to 254.09 g of deionized water and stir for 10 min at 600 r / min to prepare a transparent solution with a concentration of 15 wt%.

[0056] (2) Heat the transparent solution obtained in step (1) to 40°C and stir continuously to allow the sodium gluconate molecular chains to fully extend. Stir for about 25 minutes.

[0057] (3) Weigh 0.03 mol (approximately 7.35 g) of europium chloride into a beaker, then add 4.90 g of deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt% for later use;

[0058] (4) While stirring, slowly add the solution obtained in step (3) to the material obtained in step (2). After the addition is complete, continue the reaction at 40°C for 2 hours, and then cool to room temperature to obtain europium gluconate solution.

[0059] Furthermore, the preparation method of the rare earth compound flocculant in this embodiment includes the following steps:

[0060] (1) Add 0.1 mol (approximately 15.01 g) of sodium pyrithione to a beaker, add 60.04 g of deionized water, stir and mix evenly at a stirring rate of 400 r / min for 10 min.

[0061] (2) Weigh 0.03 mol (about 7.35 g) of cerium chloride into a beaker, then add deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt%.

[0062] (3) The solution obtained in step (2) is added dropwise to the material obtained in step (1). After the addition is completed, the reaction is carried out at room temperature and pressure for 3 hours to obtain a white powder precipitate. After filtration and washing, a pyridinethione cerium solution with a solid content of 28 wt% is obtained.

[0063] (4) Add 4.46g of the cerium pyridinethione solution obtained in step (3) to the above europium gluconate solution, so that the concentration of cerium pyridinethione is 0.4wt% and the concentration of europium gluconate is 14.9wt%. Stir continuously to obtain a transparent light yellow solution, which is the rare earth compound flocculant.

[0064] (5) In seawater containing *Phaeolipoic trichomoniasis*, add approximately 20 kg of the rare earth compound flocculant prepared in this example per ton of seawater, stir and mix evenly. After 1 hour, *Phaeolipoic trichomoniasis* will be found to have precipitated in the water, and the collection rate of *Phaeolipoic trichomoniasis* will be 97.5 wt%.

[0065] Example 3

[0066] The preparation method of rare earth gluconate in this embodiment includes the following steps:

[0067] (1) Add 0.1 mol of sodium gluconate (approximately 44.84 g) to 851.96 g of deionized water and stir for 10 min at 200 r / min to prepare a transparent solution with a concentration of 5 wt%.

[0068] (2) Heat the transparent solution obtained in step (1) to 40°C and stir continuously to allow the sodium gluconate molecular chains to fully extend. Stir for about 30 minutes.

[0069] (3) Weigh 0.03 mol (approximately 7.35 g) of gadolinium chloride into a beaker, then add 4.90 g of deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt% for later use;

[0070] (4) While stirring, slowly add the solution obtained in step (3) to the material obtained in step (2). After the addition is complete, continue the reaction at 40°C for 2 hours, and then cool to room temperature to obtain gadolinium gluconate solution.

[0071] Furthermore, the preparation method of the rare earth compound flocculant in this embodiment includes the following steps:

[0072] (1) Add 0.1 mol (approximately 15.01 g) of sodium pyrithione to a beaker, add 45.03 g of deionized water, stir and mix evenly at a stirring rate of 600 r / min for 7 min.

[0073] (2) Weigh 0.03 mol (about 7.35 g) of lanthanum chloride into a beaker, then add deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt%.

[0074] (3) The solution obtained in step (2) is added dropwise to the material obtained in step (1). After the addition is completed, the reaction is carried out at room temperature and pressure for 3 hours to obtain a white powder precipitate. After filtration and washing, a lanthanum pyridinethione solution with a solid content of 41 wt% is obtained.

[0075] (4) Add 11.97g of the lanthanum pyridinethione solution obtained in step (3) to the above gadolinium gluconate solution, so that the concentration of lanthanum pyridinethione is 0.5wt% and the concentration of gadolinium gluconate is 5wt%. Stir continuously to obtain a transparent light yellow solution, which is the rare earth compound flocculant.

[0076] In seawater containing *Phaeolipoic trichomoniasis*, approximately 20 kg of the rare earth compound flocculant prepared in this example was added directly per ton of seawater and stirred until homogeneous. After 1 hour, *Phaeolipoic trichomoniasis* was observed to precipitate in the water, resulting in a collection rate of 95.7 wt% for *Phaeolipoic trichomoniasis*.

[0077] Comparative Example 1

[0078] The preparation method of rare earth gluconate in this comparative example includes the following steps:

[0079] (1) Add 0.1 mol of sodium gluconate (approximately 44.84 g) to 2197.169 g of deionized water and stir for 10 min at 600 r / min to prepare a transparent solution with a concentration of 2 wt%.

[0080] (2) Heat the transparent solution obtained in step (1) to 40°C and stir continuously to allow the sodium gluconate molecular chains to fully extend. Stir for about 25 minutes.

[0081] (3) Weigh 0.03 mol (approximately 7.35 g) of europium chloride into a beaker, then add 4.90 g of deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt% for later use;

[0082] (4) While stirring, slowly add the solution obtained in step (3) to the material obtained in step (2). After the addition is complete, continue the reaction at 40°C for 2 hours, and then cool to room temperature to obtain europium gluconate solution.

[0083] Furthermore, the preparation method of the comparative flocculant in this comparative example includes the following steps:

[0084] (1) Add 0.1 mol (approximately 15.01 g) of sodium pyrithione to a beaker, add 60.04 g of deionized water, stir and mix evenly at a stirring rate of 400 r / min for 10 min.

[0085] (2) Weigh 0.03 mol (about 7.35 g) of cerium chloride into a beaker, then add deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt%.

[0086] (3) The solution obtained in step (2) is added dropwise to the material obtained in step (1). After the addition is completed, the reaction is carried out at room temperature and pressure for 3 hours to obtain a white powder precipitate. After filtration and washing, a pyridinethione cerium solution with a solid content of 28 wt% is obtained.

[0087] (4) Add 97.25g of the cerium pyridinethione solution obtained in step (3) to the above europium gluconate solution, so that the concentration of cerium pyridinethione is 1.2wt% and the concentration of europium gluconate is 2wt%. Stir continuously to obtain a transparent light yellow solution, which is the comparative flocculant.

[0088] In seawater containing *Phaeolipoic trichomoniasis*, approximately 20 kg of the comparative flocculant prepared in this proportion was added directly per ton of seawater and stirred until homogeneous. After 1 hour, *Phaeolipoic trichomoniasis* was observed to precipitate in the water, resulting in a collection rate of 85.5 wt% for *Phaeolipoic trichomoniasis*.

[0089] Comparative Example 2

[0090] The preparation method of rare earth gluconate in this comparative example includes the following steps:

[0091] (1) Add 0.1 mol of sodium gluconate (approximately 44.84 g) to 134.52 g of deionized water and stir for 10 min at 600 r / min to prepare a transparent solution with a concentration of 25 wt%.

[0092] (2) Heat the transparent solution obtained in step (1) to 40°C and stir continuously to allow the sodium gluconate molecular chains to fully extend. Stir for about 25 minutes.

[0093] (3) Weigh 0.03 mol (approximately 7.35 g) of europium chloride into a beaker, then add 4.90 g of deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt% for later use;

[0094] (4) While stirring, slowly add the solution obtained in step (3) to the material obtained in step (2). After the addition is complete, continue the reaction at 40°C for 2 hours, and then cool to room temperature to obtain europium gluconate solution.

[0095] Furthermore, the preparation method of the comparative flocculant in this comparative example includes the following steps:

[0096] (1) Add 0.1 mol (approximately 15.01 g) of sodium pyrithione to a beaker, add 60.04 g of deionized water, stir and mix evenly at a stirring rate of 400 r / min for 10 min.

[0097] (2) Weigh 0.03 mol (about 7.35 g) of cerium chloride into a beaker, then add deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt%.

[0098] (3) The solution obtained in step (2) is added dropwise to the material obtained in step (1). After the addition is completed, the reaction is carried out at room temperature and pressure for 3 hours to obtain a white powder precipitate. After filtration and washing, a pyridinethione cerium solution with a solid content of 28 wt% is obtained.

[0099] (4) Add 1.58g of the cerium pyridinethione solution obtained in step (3) to the above europium gluconate solution, so that the concentration of cerium pyridinethione is 0.2wt% and the concentration of europium gluconate is 24.8wt%. Stir continuously to obtain a transparent light yellow solution, which is the comparative flocculant.

[0100] In seawater containing *Phaeolipoic trichomoniasis*, approximately 20 kg of the comparative flocculant prepared in this comparative proportion was added per ton of seawater and stirred until homogeneous. After 1 hour, *Phaeolipoic trichomoniasis* was observed to precipitate in the water, and the collection rate of *Phaeolipoic trichomoniasis* was 74.8 wt%.

[0101] Comparative Example 3

[0102] The preparation method of rare earth gluconate in this comparative example includes the following steps:

[0103] (1) Add 0.1 mol of sodium gluconate (approximately 44.84 g) to 254.09 g of deionized water and stir for 3 min at 600 r / min to prepare a transparent solution with a concentration of 15 wt%.

[0104] (2) Heat the transparent solution obtained in step (1) to 30°C and stir continuously to allow the sodium gluconate molecular chains to fully extend. Stir for about 25 minutes.

[0105] (3) Weigh 0.03 mol (approximately 7.35 g) of europium chloride into a beaker, then add 4.90 g of deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt% for later use;

[0106] (4) While stirring, slowly add the solution obtained in step (3) to the material obtained in step (2). After the addition is complete, cool to room temperature to obtain europium gluconate solution.

[0107] Furthermore, the preparation method of the comparative flocculant in this comparative example includes the following steps:

[0108] (1) Add 0.1 mol (approximately 15.01 g) of sodium pyrithione to a beaker, add 60.04 g of deionized water, stir and mix evenly at a stirring rate of 200 r / min for 10 min.

[0109] (2) Weigh 0.03 mol (about 7.35 g) of cerium chloride into a beaker, then add deionized water, stir until completely dissolved, and prepare a solution with a concentration of 60 wt%.

[0110] (3) The solution obtained in step (2) is added dropwise to the material obtained in step (1). After the addition is completed, the reaction is carried out at room temperature and pressure for 3 hours to obtain a white powder precipitate. After filtration and washing, a pyridinethione cerium solution with a solid content of 28 wt% is obtained.

[0111] (4) Add 4.46g of the cerium pyridinethione solution obtained in step (3) to the above europium gluconate solution, so that the concentration of cerium pyridinethione is 0.4wt% and the concentration of europium gluconate is 14.9wt%. Stir continuously to obtain a transparent light yellow solution, which is the comparative flocculant.

[0112] In seawater containing *Phaeolipoic trichomoniasis*, approximately 20 kg of the comparative flocculant prepared in this proportion was added directly per ton of seawater and stirred until homogeneous. After 1 hour, *Phaeolipoic trichomoniasis* was observed to precipitate in the water, and the collection rate of *Phaeolipoic trichomoniasis* was 81.6 wt%.

[0113] Table 2 Comparison of flocculation effects of flocculants in different embodiments

[0114] Serial Number name Flocculation rate / wt% 1 Example 1 94.2 2 Example 2 97.5 3 Example 3 95.7 4 Comparative Example 1 85.5 5 Comparative Example 2 74.8 6 Comparative Example 3 81.6

[0115] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A rare earth compound flocculant, characterized in that: It is composed of rare earth gluconate, rare earth pyridinethione, and water, wherein: The content of rare earth gluconate is 5-15 wt%, which is prepared by reacting sodium gluconate with a first rare earth chloride salt in water. The content of the pyridinethione rare earth compound is 0.4-0.6 wt%, which is prepared by reacting sodium pyridinethione with a second rare earth chloride salt in water.

2. The rare earth compound flocculant as described in claim 1, characterized in that: The first rare earth chloride salt is selected from lanthanum chloride, europium chloride, and gadolinium chloride.

3. The rare earth compound flocculant as described in claim 2, characterized in that: The second rare earth chloride is selected from samarium chloride, cerium chloride and lanthanum chloride.

4. A method for preparing a rare earth compound flocculant according to any one of claims 1 to 3, characterized in that: Includes the following steps: (1) Preparation of rare earth gluconate solution; (2) Preparation of pyridinethione rare earth compound solution; (3) Add the pyridine thione rare earth compound solution obtained in step (2) to the gluconic acid rare earth compound solution obtained in step (1) and stir thoroughly to obtain the rare earth compound flocculant.

5. The preparation method according to claim 4, characterized in that: Step (1) includes: A. Add sodium gluconate to deionized water and stir to prepare a transparent solution; B. Heat the transparent solution obtained in step A to 40°C and stir continuously to allow the sodium gluconate molecular chains to fully extend. C. Dissolve the first rare earth chloride salt in deionized water by stirring to obtain a solution; D. While stirring, slowly add the solution obtained in step C to the material obtained in step B. After the addition is complete, continue the reaction at 40°C for 2 hours, and then cool to room temperature to obtain a rare earth gluconate compound solution.

6. The preparation method according to claim 4, characterized in that: Step (2) includes: a. Add sodium pyrithione to deionized water and stir to mix evenly; b. Dissolve the second rare earth chloride salt in deionized water by stirring to obtain a solution; c. Add the solution obtained in step b to the material obtained in step a. After the addition is complete, react for 3 hours at room temperature and pressure to obtain a precipitate. After filtration and washing, obtain a pyridinethione rare earth compound solution.

7. The use of the rare earth compound flocculant according to any one of claims 1 to 3 in the collection of seawater from *Phaeophyte Trigonella*.

8. The application as described in claim 7, characterized in that: Add 20 kg of the rare earth compound flocculant per ton of seawater.

9. A method for collecting *Phaeophyte Triangularis* from seawater, characterized in that: include: Add the rare earth compound flocculant of any one of claims 1 to 3 to seawater containing *Phaeolipophyte triangularis*, stir until homogeneous, and then collect the precipitate.

10. The collection method as described in claim 9, characterized in that: Add 20 kg of the aforementioned rare earth compound flocculant per ton of seawater.

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