A method of preparing a seawater extract and a food supplement

Abstract

The application discloses a method for preparing seawater extract and a food supplement, and relates to the technical field of seawater desalination and concentration. The first nanofiltration treatment makes calcium, magnesium and sodium ions in filtrate one be redistributed in the first desalination liquid and the first concentration liquid, so that the concentration of calcium and magnesium ions in the first desalination liquid is relatively low. Reverse osmosis treatment is performed on the first desalination liquid, which reduces the membrane flux reduction trend of the reverse osmosis membrane, so that the reverse osmosis membrane maintains a relatively high membrane flux recovery rate, thereby effectively reducing the fouling trend of the reverse osmosis membrane and the nanofiltration membrane. Compared with the filtrate one, the first nanofiltration treatment also preliminarily reduces the concentration ratio of sodium ions and main ions in the first concentration liquid. After the first concentration liquid and the second desalination liquid are mixed and then subjected to Dia nanofiltration treatment, the first concentration liquid is diluted, so that the calcium, magnesium and sodium ions in the first concentration liquid are redistributed in the nanofiltration process. Compared with the first concentration liquid, the concentration ratio of calcium and magnesium ions and main ions in the third concentration liquid is increased, and the concentration ratio of sodium ions and main ions is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of seawater desalination and concentration, and particularly relates to a method for preparing seawater extract and a food supplement. BACKGROUND

[0002] Deep seawater generally refers to unpolluted seawater below the depth of 200 meters from the sea level. Deep seawater contains various minerals beneficial to human body, such as magnesium, calcium, potassium, zinc, iodine and other trace elements, which play an important role in human health and physiological balance. Through desalination and concentration of deep seawater, a deep seawater mineral concentrate can be obtained for the health and beauty industry.

[0003] At present, the desalination and concentration technology of deep seawater mainly adopts a multi-stage combined technology of ultrafiltration, reverse osmosis and electrodialysis to obtain fresh water and a concentrated solution rich in minerals. However, this method has some disadvantages: 1) it is difficult to effectively remove multivalent ions such as magnesium ions and calcium ions in deep seawater before reverse osmosis, which can cause blockage and scaling on the surface of the reverse osmosis membrane, thereby shortening the service life of the reverse osmosis system; 2) reverse osmosis treatment can retain most of the monovalent and divalent ions in deep seawater, and under the condition of high recovery rate, the salinity of the reverse osmosis concentrated solution obtained is high, thus easily leading to the formation of fine suspended particles in the final seawater concentrated solution, resulting in poor water quality. SUMMARY

[0004] The main purpose of the present application is to provide a method for preparing seawater extract and a food supplement, aiming to solve the problems of scaling of reverse osmosis membrane and poor water quality of seawater extract in the prior art.

[0005] To achieve the above-mentioned purpose, the present application provides a method for preparing seawater extract, comprising the following steps:

[0006] S10, obtaining seawater with a depth of 200-1000 m; and subjecting the seawater to ultrafiltration treatment to obtain a filtrate I;

[0007] S20, subjecting the filtrate I to nanofiltration treatment to obtain a first desalination solution and a first concentrated solution;

[0008] S30, subjecting the first desalination solution to reverse osmosis treatment to obtain a second concentrated solution and a second desalination solution;

[0009] S40, mixing the first concentrated solution and the second desalination solution to obtain a mixed solution, and subjecting the mixed solution to Dia nanofiltration treatment to obtain a third desalination solution and a third concentrated solution;

[0010] S50, subjecting the third desalination solution to reverse osmosis treatment to obtain a fourth concentrated solution and a fourth desalination solution;

[0011] S60, the third concentrated liquid and part of the fourth dilute liquid are treated by electrodialysis to obtain a fifth dilute liquid and a fifth concentrated liquid;

[0012] S70, the fifth concentrated liquid and part of the fourth dilute liquid are treated by electrodialysis to obtain a sixth dilute liquid and a sixth concentrated liquid, and the sixth dilute liquid is the seawater extraction liquid.

[0013] In an embodiment, in step S20, the nanofiltration membrane comprises a polyamide composite nanofiltration membrane.

[0014] In an embodiment, in step S20, the pressure of the nanofiltration is 0.5-1.6 MPa.

[0015] In an embodiment, in step S20, the temperature of the nanofiltration is 20-40℃.

[0016] In an embodiment, in step S40, the volume ratio of the first concentrated liquid to the second dilute liquid is 4:(1-6).

[0017] In an embodiment, in step S40, the Dia nanofiltration membrane comprises a polyamide composite nanofiltration membrane.

[0018] In an embodiment, in step S40, the pressure of the Dia nanofiltration is 0.5-1.6 MPa.

[0019] In an embodiment, in step S40, the temperature of the Dia nanofiltration is 20-40℃.

[0020] In an embodiment, in steps S30 and S50: the reverse osmosis membrane comprises a polyamide composite membrane; and / or,

[0021] the pressure of the reverse osmosis is 3.5-4 MPa; and / or,

[0022] the temperature of the reverse osmosis is 20-40℃.

[0023] The application also provides a food supplement comprising the seawater extraction liquid prepared by the preparation method.

[0024] S10, obtaining seawater with a depth of 200-1000 m; and treating the seawater by ultrafiltration to obtain a filtrate I;

[0025] S20, treating the filtrate I by nanofiltration to obtain a first dilute liquid and a first concentrated liquid;

[0026] S30, treating the first dilute liquid by reverse osmosis to obtain a second concentrated liquid and a second dilute liquid;

[0027] S40, mixing the first concentrated liquid and the second diluted liquid to obtain a mixed liquid, and performing Dia nanofiltration on the mixed liquid to obtain a third diluted liquid and a third concentrated liquid;

[0028] S50, performing reverse osmosis treatment on the third diluted liquid to obtain a fourth concentrated liquid and a fourth diluted liquid;

[0029] S60, performing electrodialysis treatment on the third concentrated liquid and part of the fourth diluted liquid to obtain a fifth diluted liquid and a fifth concentrated liquid;

[0030] S70, performing electrodialysis treatment on the fifth concentrated liquid and part of the fourth diluted liquid to obtain a sixth diluted liquid and a sixth concentrated liquid, wherein the sixth diluted liquid is the seawater extraction liquid.

[0031] The present application provides a method for preparing a seawater extraction liquid and a food supplement. The first nanofiltration treatment re-distributes the calcium, magnesium and sodium ions in the filtrate one in the first diluted liquid and the first concentrated liquid, so that the concentration of calcium and magnesium ions in the first diluted liquid is relatively low. The reverse osmosis treatment using the first diluted liquid reduces the tendency of membrane flux reduction of the reverse osmosis membrane, so that the reverse osmosis membrane maintains a relatively high membrane flux recovery rate, thereby effectively reducing the tendency of fouling of the reverse osmosis membrane and the nanofiltration membrane. Compared with the filtrate one, the first nanofiltration treatment also preliminarily reduces the concentration ratio of sodium ions and main ions in the first concentrated liquid. After mixing the first concentrated liquid and the second diluted liquid and performing Dia nanofiltration treatment, the second diluted liquid dilutes the first concentrated liquid, which facilitates the re-distribution of calcium, magnesium and sodium ions in the first concentrated liquid in the nanofiltration process. Compared with the first concentrated liquid, the concentration ratio of calcium, magnesium and main ions in the third concentrated liquid is increased, and the concentration ratio of sodium ions and main ions in the third concentrated liquid is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative effort based on the drawings shown.

[0033] Figure 1 The seawater extraction liquid preparation process provided in Embodiment 1 of the present application.

[0034] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0035] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturers are adopted. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be purchased in the market are adopted. In addition, the meaning of "and / or" appearing in the entire text includes three parallel solutions. Taking "A and / or B" as an example, it includes the A solution, or the B solution, or the solution in which A and B are satisfied at the same time. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the premise that a person having ordinary skill in the art can realize it. When the combination of technical solutions appears to be contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application. Based on the embodiments in the present application, all other embodiments obtained by a person having ordinary skill in the art without creative labor belong to the protection scope of the present application.

[0036] Deep seawater generally refers to unpolluted seawater below the depth of 200 meters from the sea level, which is in a light-free, high-pressure and low-temperature environment all the year round, and the inorganic salt and mineral composition thereof is extremely stable, including various minerals beneficial to human health, such as magnesium, calcium, potassium, zinc, iodine and other trace elements, which have important effects on the human body. At the same time, the physical properties of deep seawater are similar to the liquid in human skin, and it has the characteristics of high purity, rich mineral content and easier absorption by the skin than ordinary water. Therefore, deep seawater can not only relieve the problem of dry skin, but also maintain an ion balance state similar to the human body. Compared with ordinary water, the moisture of deep seawater is increased by 17%.

[0037] The comprehensive utilization of deep seawater resources is not only the key material and technical basis for the development of marine resources, but also the core link of the marine industry value chain. The products based on deep seawater have practical benefits in maintaining human health and are widely used in postoperative rehabilitation, treatment of sinusitis and prevention of respiratory diseases, etc., and fully play the positive role of rich minerals and trace elements in deep seawater on human health. Among them, the deep seawater mineral concentrate and other products obtained by desalination and concentration of deep seawater can also be used in the health and beauty industries.

[0038] Deep seawater low-sodium mineral concentrate is a special product derived from deep seawater, which is refined from deep seawater through physical or chemical treatment process. The characteristic of this kind of concentrate is that it retains the rich natural mineral components such as magnesium and calcium in deep seawater, but the sodium element is reduced or adjusted to adapt to the population with the need for low sodium intake, whose daily sodium intake needs to be controlled at 1500-2000 mg.

[0039] Currently, the desalination and concentration technology of deep seawater mainly adopts the multi-stage combined technology of ultrafiltration, reverse osmosis and electrodialysis to obtain fresh water and concentrated liquid rich in minerals. However, this method has some shortcomings: 1) it is difficult to effectively remove multivalent ions such as magnesium ions and calcium ions in deep seawater before reverse osmosis, and on the concentration side of the reverse osmosis membrane, due to the osmotic pressure and local supersaturation effect, the originally dissolved divalent ions in the raw water may exceed their solubility limit in high-concentration brine, and calcium and magnesium ions combine with anions such as carbonate, sulfate or phosphate in water to precipitate as solid deposits, thereby depositing on the surface or inside of the reverse osmosis membrane, which is commonly known as "fouling", which can cause blockage and fouling on the surface of the reverse osmosis membrane, thereby shortening the service life of the reverse osmosis system; 2) reverse osmosis treatment will retain most of the monovalent and divalent ions in the deep seawater, and the salinity of the reverse osmosis concentrated liquid obtained under high recovery rate conditions is high, so it is easy to form fine suspended particles in the final seawater concentrated liquid, resulting in poor water quality.

[0040] The fouling phenomenon can be effectively alleviated by preparing anti-fouling reverse osmosis membrane materials or adding scale inhibitors. However, these two methods still have the following problems: 1) the production process of new membrane materials with anti-fouling properties is complex, special synthesis technology and surface modification treatment are required, the production cost and difficulty are high, the membrane maintenance is difficult, and at present it is only limited to theory, and its long-term stability and durability need to be verified. 2) The use of scale inhibitors increases the operating cost, and the scale inhibitors may not be compatible with the reverse osmosis membrane, and even cause harm to the membrane material, and may also decompose secondary products in water to affect the water quality.

[0041] Nanofiltration membranes can separate monovalent and divalent ions, but only one nanofiltration cannot effectively improve the reverse osmosis membrane fouling problem in the process of obtaining low-sodium seawater desalination liquid. Dia nanofiltration technology refers to adding desalinated fresh water to the nanofiltration concentrated liquid of the upper stage, and then performing nanofiltration separation to generate a solution with high concentration of Mg 2+ , Ca 2+ divalent ions and low concentration of sodium ions, which is used for drinking water mineral supplements. Therefore, the introduction of two-stage nanofiltration technology of ordinary nanofiltration and Dia nanofiltration can reduce the fouling of scale bodies such as calcium and magnesium on the surface of the reverse osmosis membrane in the process of preparing low-sodium seawater desalination liquid, and improve the efficiency of reverse osmosis and the service life of the membrane.

[0042] Therefore, the present application provides a method for preparing seawater extraction liquid, comprising the following steps:

[0043] S10, obtaining seawater with a depth of 200-1000 m; and performing ultrafiltration treatment on the seawater to obtain a filtrate I;

[0044] S20, performing nanofiltration treatment on the filtrate I to obtain a first desalination liquid and a first concentrated liquid;

[0045] S30, reverse osmosis treatment is performed on the first dilute liquid to obtain a second concentrated liquid and a second dilute liquid;

[0046] S40, the first concentrated liquid and the second dilute liquid are mixed to obtain a mixed liquid, and Dia nanofiltration treatment is performed on the mixed liquid to obtain a third dilute liquid and a third concentrated liquid;

[0047] S50, reverse osmosis treatment is performed on the third dilute liquid to obtain a fourth concentrated liquid and a fourth dilute liquid;

[0048] S60, electrodialysis treatment is performed on the third concentrated liquid and part of the fourth dilute liquid to obtain a fifth dilute liquid and a fifth concentrated liquid;

[0049] S70, electrodialysis treatment is performed on the fifth concentrated liquid and part of the fourth dilute liquid to obtain a sixth dilute liquid and a sixth concentrated liquid, and the sixth dilute liquid is the seawater extraction liquid.

[0050] In the technical scheme of the present application, the first nanofiltration treatment causes the calcium, magnesium and sodium ions in the filtrate one to be redistributed in the first dilute liquid and the first concentrated liquid, so that the concentration of calcium and magnesium ions in the first dilute liquid is relatively low, and the reverse osmosis treatment using the first dilute liquid reduces the tendency of membrane flux reduction of the reverse osmosis membrane, so that the reverse osmosis membrane maintains a relatively high membrane flux recovery rate, thereby effectively reducing the tendency of fouling of the reverse osmosis membrane and the nanofiltration membrane. Compared with the filtrate one, the first nanofiltration treatment also preliminarily reduces the concentration ratio of sodium ions and main ions in the first concentrated liquid. After mixing the first concentrated liquid and the second dilute liquid and performing Dia nanofiltration treatment, the addition of the second dilute liquid dilutes the first concentrated liquid, which facilitates the redistribution of calcium, magnesium and sodium ions in the first concentrated liquid in the nanofiltration process. Compared with the first concentrated liquid, the concentration ratio of calcium, magnesium and main ions in the third concentrated liquid is increased, and the concentration ratio of sodium ions and main ions in the third concentrated liquid is reduced. The two nanofiltrations achieve the separation of divalent ions and reduce the problem of fouling in the reverse osmosis process. Therefore, by coupling the membrane separation technologies such as ultrafiltration, nanofiltration, reverse osmosis and electrodialysis, the present application realizes the concentration of high-value-added calcium and magnesium ions and the reduction of sodium ions and sulfate ions, and retains part of the trace elements. No chemical reagent is added in the separation process, so that a deep seawater low-sodium mineral concentrate liquid with clean, rich nutrition and physiological activity is obtained. The dilute liquid in the preparation process can be treated by reverse osmosis to obtain desalted water, and the concentrated liquid byproduct can be used to prepare seawater crystal or salt products.

[0051] The ultrafiltration is used for pretreatment of deep sea water at a depth of 400 meters below sea level to remove suspended particles and macromolecular organic matter in the deep sea water, so as to obtain purified deep sea water. In any embodiment of the present application, in step S10, the ultrafiltration membrane comprises a polyether sulfone spiral membrane module. The polyether sulfone spiral membrane with a molecular weight cut-off of 8000 Da can effectively intercept particles, impurities and microorganisms, and realize efficient solid-liquid separation or solution clarification. Compared with other membranes, the polyether sulfone spiral membrane module has high chemical stability and thermal stability.

[0052] In any embodiment of the present application, in step S10, the pressure of the ultrafiltration is 0.1-0.3 MPa. The ultrafiltration pressure can be 0.1 MPa, 0.2 MPa or 0.3 MPa. The ultrafiltration pressure in the appropriate range can ensure that the polyether sulfone spiral membrane element will not be damaged due to excessive pressure, such as causing the membrane wire to break or the performance to decrease. Excessive ultrafiltration pressure will cause the membrane pore size to collapse, thereby damaging the membrane module; and low ultrafiltration pressure will reduce the separation efficiency.

[0053] The filtrate I obtained after ultrafiltration has a calcium ion concentration of 350-400 mg / L, a magnesium ion concentration of 1250-1350 mg / L, a sodium ion concentration of 9500-10500 mg / L, and a sulfate ion concentration of 2500-3000 mg / L. Among them, the proportion of sodium ions in the main ions is 68.9%-69.9%, and the calculation method is sodium ion concentration / (calcium ion concentration+ magnesium ion concentration+ sodium ion concentration+ sulfate ion concentration).

[0054] The filtrate I is separated by a nanofiltration system to remove part of the monovalent sodium ions, to obtain a first dilute liquid and a first concentrated liquid. In any embodiment of the present application, in step S20: the nanofiltration membrane comprises a polyamide composite nanofiltration membrane. The polyamide composite nanofiltration membrane is mainly prepared from polyamide high molecular materials by interface polymerization process, and the pore size is between ultrafiltration and reverse osmosis, i.e. between 0.1-2 nm, and the molecular weight cut-off is 200 Da. It has selective permeation effect on solutes with a molecular weight of less than 200 Da, i.e. it can effectively intercept divalent and above ions and part of small molecular organic matter, while allowing monovalent ions and most water molecules to pass through. Compared with other membranes, the polyamide composite nanofiltration membrane has the characteristics of high permeation flux and high salt rejection rate.

[0055] In any embodiment of the present application, in step S20, the pressure of the nanofiltration is 0.5-1.6 MPa, and the temperature of the nanofiltration is 20-40℃. The nanofiltration pressure can be 0.5 MPa, 0.9 MPa, 1.3 MPa or 1.6 MPa, which is in a suitable range to ensure effective separation of the nanofiltration membrane to the target substance, while not causing excessive operating energy consumption. The nanofiltration temperature can be 20℃, 30℃ or 40℃, which is in a suitable range to ensure relatively stable performance of the nanofiltration membrane, better permeation rate and rejection rate, while preventing changes in the physical and chemical properties of the membrane or damage due to excessively high temperature, and preventing the increase of the viscosity of the feed liquid due to excessively low temperature, thereby affecting the nanofiltration efficiency.

[0056] The calcium ion concentration in the first concentrated liquid obtained after the nanofiltration is 700-800 mg / L, the magnesium ion concentration is 2700-2950 mg / L, the sodium ion concentration is 9500-10000 mg / L, and the sulfate ion concentration is 4500-4700 mg / L. Among the main ions, the proportion of sodium ions is 54.2%-54.6%, i.e. the concentration ratio of sodium ions to main ions is 54.2%-54.6%, and the calculation method is sodium ion concentration / (calcium ion concentration+magnesium ion concentration+sodium ion concentration+sulfate ion concentration), wherein the sodium ion concentration is the mass concentration of sodium ions in the first concentrated liquid. Compared with the filtrate, the proportion of sodium ions in the main ions in the first concentrated liquid is reduced by 14.7%-15.3%. This is because water is separated together with ions during the nanofiltration process, and the concentrations of the main ions in the first concentrated liquid are all increased. Among them, the concentrations of the divalent ions calcium ions, magnesium ions and sulfate ions are all increased by about 2 times, while the increase of the sodium ion concentration is relatively low, indicating that a part of the sodium ions is removed in the nanofiltration process.

[0057] The calcium ion concentration in the first concentrated liquid obtained after the nanofiltration is 700-800 mg / L, the magnesium ion concentration is 2700-2950 mg / L, the sodium ion concentration is 9500-10000 mg / L, and the sulfate ion concentration is 4500-4700 mg / L. Among the main ions, the proportion of sodium ions is 54.2%-54.6%, i.e. the concentration ratio of sodium ions to main ions is 54.2%-54.6%, and the calculation method is sodium ion concentration / (calcium ion concentration+magnesium ion concentration+sodium ion concentration+sulfate ion concentration), wherein the sodium ion concentration is the mass concentration of sodium ions in the first concentrated liquid. Compared with the filtrate, the proportion of sodium ions in the main ions in the first concentrated liquid is reduced by 14.7%-15.3%. This is because water is separated together with ions during the nanofiltration process, and the concentrations of the main ions in the first concentrated liquid are all increased. Among them, the concentrations of the divalent ions calcium ions, magnesium ions and sulfate ions are all increased by about 2 times, while the increase of the sodium ion concentration is relatively low, indicating that a part of the sodium ions is removed in the nanofiltration process.

[0057] The calcium ion concentration in the first concentrated liquid obtained after the nanofiltration is 700-800 mg / L, the magnesium ion concentration is 2700-2950 mg / L, the sodium ion concentration is 9500-10000 mg / L, and the sulfate ion concentration is 4500-4700 mg / L. Among the main ions, the proportion of sodium ions is 54.2%-54.6%, i.e. the concentration ratio of sodium ions to main ions is 54.2%-54.6%, and the calculation method is sodium ion concentration / (calcium ion concentration+magnesium ion concentration+sodium ion concentration+sulfate ion concentration), wherein the sodium ion concentration is the mass concentration of sodium ions in the first concentrated liquid. Compared with the filtrate, the proportion of sodium ions in the main ions in the first concentrated liquid is reduced by 14.7%-15.3%. This is because water is separated together with ions during the nanofiltration process, and the concentrations of the main ions in the first concentrated liquid are all increased. Among them, the concentrations of the divalent ions calcium ions, magnesium ions and sulfate ions are all increased by about 2 times, while the increase of the sodium ion concentration is relatively low, indicating that a part of the sodium ions is removed in the nanofiltration process.

[0058] In any embodiment of the present application, in step S30, the pressure of the reverse osmosis is 3.5-4 MPa, and the temperature of the reverse osmosis is 20-40℃. The pressure of the reverse osmosis can be 3.5 MPa, 3.5 MPa or 3.5 MPa. The pressure of the reverse osmosis in the appropriate range can ensure that almost all ions in the first dilution liquid are removed, so that only a small amount of monovalent ions remain in the second dilution liquid. The temperature of the reverse osmosis can be 20℃, 30℃ or 40℃. The temperature of the reverse osmosis in the appropriate range can ensure that the performance of the reverse osmosis membrane is relatively stable, and can maintain a high water flux and a high desalination rate. When the temperature is lower than the range, the viscosity of the water will increase, resulting in a decrease in the amount of water passing through the membrane, i.e. a decrease in the water flux. When the temperature is higher than the range, the water flux can be improved, but a too high temperature can cause changes in the chemical structure and surface pore size of the membrane material, resulting in a decrease in the separation performance of the membrane.

[0059] The second concentrated liquid obtained after the reverse osmosis has a calcium ion concentration of 220-250 mg / L, a magnesium ion concentration of 250-300 mg / L, a sodium ion concentration of 18500-19500 mg / L, and a sulfate ion concentration of 360-450 mg / L.

[0060] The second dilution liquid obtained after the reverse osmosis has a calcium ion concentration of 0.8-1.2 mg / L, a magnesium ion concentration of 0.5-1.5 mg / L, a sodium ion concentration of 300-380 mg / L, and a sulfate ion concentration of 5-10 mg / L. Compared with the first dilution liquid, the second dilution liquid has a lower concentration of monovalent and divalent ions.

[0061] The first concentrated liquid produced by the nanofiltration process and the second dilution liquid obtained by the reverse osmosis process are mixed to perform a second nanofiltration. The second nanofiltration uses Dia nanofiltration technology to obtain a third concentrated liquid and a third dilution liquid. The membrane material and operating pressure, temperature and other conditions used in the Dia nanofiltration process are consistent with those of the first nanofiltration process. That is, in any embodiment of the present application, in step S40, the Dia nanofiltration membrane comprises a polyamide composite nanofiltration membrane, the pressure of the Dia nanofiltration is 0.5-1.6 MPa, and the temperature of the Dia nanofiltration is 20-40℃.

[0062] In any embodiment of the present application, in step S40, the volume ratio of the first concentrated solution and the second dilute solution is 4:(1-6). The volume ratio of the first concentrated solution and the second dilute solution can be 4:1, 4:3 or 4:6. Too high volume ratio leads to too high concentration of sodium ions in the seawater extract; too low volume ratio, i.e. increased dilution multiple of the first concentrated solution, leads to low concentration of high value ions such as calcium and magnesium ions in the seawater extract. The second nanofiltration process is different from the first nanofiltration in that a certain proportion of the second dilute solution is added to the first concentrated solution, which can dilute the first concentrated solution and help to further remove monovalent sodium ions in the first concentrated solution, thereby effectively reducing the tendency of scaling. Therefore, the second nanofiltration aims to further remove monovalent sodium ions and increase the concentration of divalent calcium and magnesium ions.

[0063] After the second nanofiltration, the third concentrated solution obtained has a calcium ion concentration of 800-900 mg / L, a magnesium ion concentration of 3300-3500 mg / L, a sodium ion concentration of 5500-6000 mg / L, and a sulfate ion concentration of 6500-6900 mg / L. Among the main ions, the proportion of sodium ions is 34.2%-34.7%, and the calculation method is sodium ion concentration / (calcium ion concentration+ magnesium ion concentration+ sodium ion concentration+ sulfate ion concentration). Compared with the first concentrated solution, the proportion of sodium ions in the third concentrated solution is reduced by about half.

[0064] The third dilute solution obtained after Dia nanofiltration is further desalted by second reverse osmosis to obtain a fourth concentrated solution and a fourth dilute solution. The membrane material and operating conditions used in the second reverse osmosis are consistent with those of the first reverse osmosis, i.e. in any embodiment of the present application, in step S50: the reverse osmosis membrane includes a polyamide composite membrane; the reverse osmosis pressure is 3.5-4 MPa; and the reverse osmosis temperature is 20-40°C.

[0065] After the second reverse osmosis, the fourth dilute solution obtained has a calcium ion concentration of 0.5-0.7 mg / L, a magnesium ion concentration of 0.4-0.6 mg / L, a sodium ion concentration of 100-150 mg / L, and a sulfate ion concentration of 4-8 mg / L. Compared with the second dilute solution, the concentrations of various ions in the fourth dilute solution are further reduced.

[0066] In any embodiment of the present application, step S60 includes: adding part of the fourth dilute solution to a concentrated pool of electrodialysis, adding the third concentrated solution to a desalination pool of electrodialysis, and performing first electrodialysis separation to obtain a fifth concentrated solution and a fifth dilute solution. The first electrodialysis aims to reduce the concentration of sulfate ions which are prone to cause scaling in the third concentrated solution, and to increase the concentration of high value ions such as sodium ions, magnesium ions and calcium ions.

[0067] In any embodiment of the present application, in step S60: the first electrodialysis membrane comprises a monovalent anion selective exchange membrane and a conventional cation exchange membrane; the electrodialysis temperature is 20-35℃. The monovalent anion selective exchange membrane allows monovalent anions in the aqueous solution to pass through preferentially, while excluding / making no allowance for multivalent anions such as sulfate ions to pass through the membrane, so it can effectively separate monovalent and multivalent anions. In the first electrodialysis process, monovalent and divalent anions are separated and cations are directed into the concentration cell through the monovalent anion selective exchange membrane, the conventional cation exchange membrane and the electric field, thereby obtaining the fifth concentrated solution and the fifth dilution solution. The first electrodialysis temperature is 20-35℃, and the first electrodialysis temperature in the appropriate range can ensure that the structure stability, service life and separation efficiency of the electrodialysis membrane are good.

[0068] The fifth concentrated solution obtained after the first electrodialysis treatment has a calcium ion concentration of 2900-3200 mg / L, a magnesium ion concentration of 9200-9800 mg / L, a sodium ion concentration of 15800-16000 mg / L, and a sulfate ion concentration of 300-450 mg / L. Compared with the third concentrated solution, the concentrations of sodium ions, calcium ions and magnesium ions in the fifth concentrated solution are significantly increased, and the concentration of sulfate ions is significantly reduced. Among the main ions, the proportion of sodium ions is 54.3%-56%, and the calculation method is sodium ion concentration / (calcium ion concentration+ magnesium ion concentration+ sodium ion concentration+ sulfate ion concentration).

[0069] In any embodiment of the present application, step S70 comprises: adding part of the fourth dilution solution to the concentration cell of the electrodialysis, adding the fifth concentrated solution to the desalination cell of the electrodialysis, performing second electrodialysis treatment on the fifth concentrated solution to obtain the sixth concentrated solution and the sixth dilution solution, and the sixth dilution solution is the seawater extraction solution. The second electrodialysis is used to further remove part of the sodium ions in the fifth concentrated solution.

[0070] In any embodiment of the present application, the second electrodialysis membrane comprises a monovalent cation selective exchange membrane and a conventional anion exchange membrane; the second electrodialysis temperature is 20-35℃. The monovalent cation selective exchange membrane allows monovalent cations such as sodium ions to pass through preferentially, while not allowing other high-valence cations such as calcium ions and magnesium ions or anions such as sulfate ions to pass through, so it is more effective for sodium ions in the treatment solution in the electrodialysis system. In the second electrodialysis process, the sodium ions in the fifth concentrated solution are allowed to enter the fourth dilution solution through the monovalent cation selective exchange membrane and the conventional anion exchange membrane, thereby obtaining the sixth concentrated solution and the seawater extraction solution. The second electrodialysis temperature is 20-35℃, and the second electrodialysis temperature in the appropriate range can ensure that the structure stability, service life and separation efficiency of the electrodialysis membrane are good.

[0071] The concentration of calcium ions in the seawater extract obtained after the second electrodialysis is 2500-3000 mg / L, the concentration of magnesium ions is 9000-9500 mg / L, the concentration of sodium ions is 1000-1500 mg / L, and the concentration of sulfate ions is 300-450 mg / L. Among the main ions, the proportion of sodium ions is 7.8%-10.4%, and the calculation method is the concentration of sodium ions / (the concentration of calcium ions + the concentration of magnesium ions + the concentration of sodium ions + the concentration of sulfate ions).

[0072] During the whole process, the back-adding and use of desalinated freshwater can ensure that the solution and solute of the prepared low-sodium concentrated solution are all from the same deep seawater, and the functionality of the product is ensured. The main ions in the whole process are sodium ions, magnesium ions, calcium ions and sulfate ions, and the concentration is the mass concentration of ions in the solution.

[0073] The deep seawater low-sodium mineral concentrated solution can be used to make low-sodium beverages, food supplement additives or as raw materials for skin care products, which can not only provide necessary mineral supplements but also reduce sodium intake, and is suitable for hypertensive patients or consumers who need to control sodium intake. At the same time, in the field of beauty, the low-sodium deep sea mineral concentrated solution can also be used for product development in aspects of water replenishment and moisturizing, repair of skin barrier and promotion of skin health. The application also provides a food supplement, which comprises the seawater extract prepared by the method for preparing seawater extract. The food supplement has all the technical solutions of the method for preparing seawater extract, and therefore also has all the beneficial effects brought by the above technical solutions, which will not be repeated here. The food supplement can be applied to special application scenarios including but not limited to food, health products, medicines or laboratories.

[0074] The technical solutions of the application will be further described in detail in combination with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the application and do not limit the application.

[0075] Embodiment 1

[0076] A method for preparing seawater extract, comprising the following steps:

[0077] S10, 10 L of deep seawater at about 400 m below sea level is taken, and the main ion concentration thereof is detected, and the results are as follows: the concentration of calcium ions in the deep seawater is 392 mg / L, the concentration of magnesium ions is 1291 mg / L, the concentration of sodium ions is 10778 mg / L, and the concentration of sulfate ions is 2529 mg / L.

[0078] Ultrafiltration pretreatment: the deep sea water is pretreated by an ultrafiltration system to remove suspended particles and macromolecular organic matters in the deep sea water, so as to obtain purified deep sea water. The ultrafiltration membrane used in the ultrafiltration process is a polyether sulfone roll membrane with a molecular weight cut-off of 8000 Da, and the operating pressure is 0.2 MPa;

[0079] S20, nanofiltration separation: the deep sea water after the ultrafiltration pretreatment is subjected to nanofiltration to separate divalent ions, to obtain 4 L of a first concentrated solution and 6 L of a first dilution solution. The nanofiltration membrane material used in the nanofiltration process is a polyamide composite nanofiltration membrane with a molecular weight cut-off of 200 Da, the nanofiltration process pressure is 1.5 MPa, and the temperature is 25°C.

[0080] The calcium ion concentration in the obtained first concentrated solution is 750 mg / L, the magnesium ion concentration is 2600 mg / L, the sodium ion concentration is 9850 mg / L, and the sulfate ion concentration is 4600 mg / L.

[0081] S30, first reverse osmosis treatment: the first dilution solution obtained by the nanofiltration process is subjected to desalination treatment by a reverse osmosis membrane to obtain 3 L of a second concentrated solution and 3 L of a second dilution solution. The reverse osmosis membrane material is a polyamide composite membrane, the reverse osmosis treatment pressure is 4 MPa, and the temperature is 25°C.

[0082] The calcium ion concentration in the obtained reverse osmosis desalination water is 1.2 mg / L, the magnesium ion concentration is 1.5 mg / L, the sodium ion concentration is 380 mg / L, the chloride ion concentration is 450 mg / L, and the sulfate ion concentration is 7.2 mg / L.

[0083] S40, second nanofiltration separation: 4 L of the first concentrated solution and 3 L of the second dilution solution obtained by the first reverse osmosis process are mixed to obtain 7 L of a mixed solution, which is subjected to second nanofiltration to obtain 2.8 L of a third concentrated solution and 4.2 L of a third dilution solution. The membrane material and operating conditions used in the second nanofiltration process are consistent with those used in the nanofiltration process.

[0084] The calcium ion concentration in the obtained third concentrated solution is 900 mg / L, the magnesium ion concentration is 3500 mg / L, the sodium ion concentration is 5930 mg / L, and the sulfate ion concentration is 6820 mg / L.

[0085] S50, second reverse osmosis desalination: the 4.2 L of the third dilution solution obtained after the second nanofiltration is subjected to second reverse osmosis treatment for further desalination to obtain 2.1 L of a fourth concentrated solution and 2.1 L of a fourth dilution solution. The reverse osmosis membrane material used in the second reverse osmosis treatment is a polyamide composite membrane, the reverse osmosis treatment pressure is 4 MPa, and the temperature is 25°C.

[0086] The calcium ion concentration in the obtained fourth dilute solution was 0.55 mg / L, the magnesium ion concentration was 0.45 mg / L, the sodium ion concentration was 130 mg / L, the chloride ion concentration was 210 mg / L, and the sulfate ion concentration was 5.1 mg / L.

[0087] S60, first electrodialysis separation: 2.8 L of the third concentrated solution obtained in the second nanofiltration process was subjected to second electrodialysis treatment to remove sulfate ions which are prone to cause scaling and concentrate high-value ions, to obtain 0.8 L of a fifth concentrated solution and 2.5 L of a fifth dilute solution. 0.5 L of the fourth dilute solution was added to the electrodialysis concentration cell, and 2.8 L of the third concentrated solution was added to the electrodialysis desalination cell. In the first electrodialysis separation process, a conventional anode membrane was used as the anode membrane, and a monovalent selective cathode membrane was used as the cathode membrane, and the temperature was 25°C.

[0088] The calcium ion concentration in the obtained fifth concentrated solution was 3200 mg / L, the magnesium ion concentration was 9800 mg / L, the sodium ion concentration was 16000 mg / L, and the sulfate ion concentration was 440 mg / L.

[0089] S70, second electrodialysis separation: 0.8 L of the fifth concentrated solution obtained in the first electrodialysis process was subjected to second electrodialysis treatment to further remove part of the sodium ions. 1.6 L of the fourth dilute solution was added to the electrodialysis concentration cell, and 0.8 L of the fifth concentrated solution was added to the electrodialysis desalination cell, to obtain 1.4 L of a sixth concentrated solution and 1 L of a seawater extraction solution. In the second electrodialysis treatment process, a monovalent selective anode membrane was used as the anode membrane, and a conventional cathode membrane was used as the cathode membrane, and the temperature was 25°C.

[0090] The calcium ion concentration in the obtained seawater extraction solution was 3000 mg / L, the magnesium ion concentration was 9400 mg / L, the sodium ion concentration was 1500 mg / L, and the sulfate ion concentration was 425 mg / L.

[0091] Example 2

[0092] Except that the mixing ratio of the first concentrated solution: the second dilute solution in the second nanofiltration was 4:1, the nanofiltration pressure was 0.5 MPa, the nanofiltration temperature was 20°C, the reverse osmosis pressure was 3.5 MPa, and the reverse osmosis temperature was 20°C, the others were the same as in Example 1.

[0093] Example 3

[0094] Except that the mixing ratio of the first concentrated solution: the second dilute solution in the second nanofiltration was 4:6, the nanofiltration pressure was 1.6 MPa, the nanofiltration temperature was 40°C, the reverse osmosis pressure was 4 MPa, and the reverse osmosis temperature was 40°C, the others were the same as in Example 1.

[0095] Comparative Example 1

[0096] Comparative Example 1 is the same as Example 1 except that steps S20, S40 and S50 are not performed.

[0097] Since steps S20, S40 and S50 are not performed in Comparative Example 1, the reverse osmosis membrane surface of Comparative Example 1 is scaled, resulting in low membrane performance.

[0098] Comparative Example 2

[0099] Comparative Example 2 is the same as Example 1 except that step S20 is not performed.

[0100] Since step S20 is not performed in Comparative Example 2, the permeation flux of the reverse osmosis membrane of Comparative Example 2 is low.

[0101] Comparative Example 3

[0102] Comparative Example 3 is the same as Example 1 except that steps S40 and S50 are not performed.

[0103] Since steps S40 and S50 are not performed in Comparative Example 3, the concentration of calcium and magnesium ions in the first concentrated solution after nanofiltration treatment of Comparative Example 3 is low, and the content of sodium ions is high.

[0104] Comparative Example 4

[0105] Comparative Example 4 is the same as Example 1 except that no second diluting solution is added in step S40.

[0106] Since no second diluting solution is added in step S40 of Comparative Example 4, the permeation flux of the second nanofiltration membrane in Comparative Example 4 is low, and the content of sodium ions in the third concentrated solution is high.

[0107] Performance test

[0108] The methods for preparing seawater extract solutions in Examples 1-3 and Comparative Examples 1-4 were used, and steps S10, S20, S30, S40 and S50 therein were performed, which include the processes of ultrafiltration, first nanofiltration, first reverse osmosis, Dia nanofiltration and second reverse osmosis. Each method was run by sequentially passing three batches of seawater, each batch was run for 4 h, a total of 12 h, and the flux of two nanofiltration membranes and two reverse osmosis membranes was recorded during each run. The first nanofiltration membrane is referred to as the first nanofiltration membrane, and the Dia nanofiltration membrane is referred to as the second nanofiltration membrane. The first reverse osmosis membrane is referred to as the first reverse osmosis membrane, and the second reverse osmosis membrane is referred to as the second reverse osmosis membrane. The first batch of seawater is referred to as the first round, the second batch of seawater is referred to as the second round, and the third batch of seawater is referred to as the third round.

[0109] The detection method of membrane flux is as follows: after 0.5 h of flushing with 2000 mL of pure water, the volume of the permeate is observed or calculated, which is the pure water flux, and the process is repeated three times.

[0110] The scaling conditions of the nanofiltration membrane and the reverse osmosis membrane are characterized by determining the reduction rate and the recovery rate of the membrane flux, and the specific calculation formula is as follows:

[0111] The membrane flux F is calculated by the following formula:

[0112]

[0113] Wherein V is the water volume per unit time through the effective area of the membrane, A is the effective area of the membrane, and t is the time, whose unit is Lm -2 h -1 .

[0114] The reduction rate of the membrane flux is calculated by the following formula:

[0115]

[0116] Wherein, F d is the reduction rate of the flux, F0 is the initial flux during the scaling operation, and F t is the flux after t hours of the scaling operation. The detection results are shown in Tables 1 and 2.

[0117] The recovery rate of the membrane flux FRR is calculated by the following formula:

[0118]

[0119] Wherein F w0 is the initial pure water flux of the nanofiltration membrane or the reverse osmosis membrane, and F wt is the pure water flux of the nanofiltration membrane or the reverse osmosis membrane after filtering the deep sea water for 12 h. The detection results are shown in Tables 3 and 4.

[0120] The inductively coupled plasma emission spectrometer analyzer and the method of HJ 776-2015 are used to determine the contents of calcium ions, magnesium ions and sodium ions in the filtrate I, the first dilution liquid, the first concentrated liquid, the second dilution liquid, the second concentrated liquid, the third dilution liquid, the third concentrated liquid, the fourth dilution liquid and the fourth concentrated liquid. The ion chromatograph and the method of HJ 84-2016 are used to determine the sulfate ions in the filtrate I, the first dilution liquid, the first concentrated liquid, the second dilution liquid, the second concentrated liquid, the third dilution liquid, the third concentrated liquid, the fourth dilution liquid and the fourth concentrated liquid. The results are shown in Table 5.

[0121] Table 1 Reduction rate of the membrane flux of the nanofiltration membrane in Examples 1-3 and Comparative Examples 1-4 (%)

[0122]

[0123] From Table 1, compared with Examples 1-3, the membrane flux of the nanofiltration membrane in Comparative Example 4 is reduced more, which is because the Dia nanofiltration process in Examples 1-3 adds the second dilute liquid, and the second dilute liquid plays a role of diluting the ions in the solution, thereby reducing the fouling tendency of the nanofiltration membrane.

[0124] Table 2 Membrane flux reduction rate (%) of reverse osmosis membranes in Examples 1-3 and Comparative Examples 1-4

[0125]

[0126] From Table 2, compared with Comparative Examples 1-2, the membrane flux of the first reverse osmosis membrane in Examples 1-3 is reduced less, which is because the reverse osmosis membrane in Examples 1-3 processes the nanofiltration dilute liquid, and the main component in the dilute liquid is monovalent ions, and the content of multivalent ions such as calcium, magnesium and sulfate which are prone to fouling is less. In Comparative Examples 1-2, the first reverse osmosis membrane directly contacts the seawater concentrate containing a large amount of fouling-prone ions.

[0127] Table 3 Membrane flux recovery rate (%) of nanofiltration membranes in Examples 1-3 and Comparative Examples 1-4

[0128]

[0129] From Table 3, in Examples and Comparative Examples, the nanofiltration membranes all have good flux recovery rates; among them, compared with the second nanofiltration membrane in Comparative Example 4, the second nanofiltration membrane in Examples 1-3 has a higher recovery rate, which is because the nanofiltration process in which the second nanofiltration membrane is located in the Examples adds the second dilute liquid to dilute the first concentrate, so that the concentration of ions prone to fouling in the first concentrate is also reduced accordingly; while in Comparative Example 4, the second nanofiltration process does not add fresh water to process the first concentrate after nanofiltration, and the concentration of fouling-prone ions gradually increases, resulting in fouling on the surface of the second nanofiltration membrane.

[0130] Table 4 Membrane flux recovery rate (%) of reverse osmosis membranes in Examples 1-3 and Comparative Examples 1-4

[0131]

[0132] From Table 4, compared with Comparative Examples 1-2, the first reverse osmosis membrane in Examples 1-3 has a higher recovery rate, showing excellent anti-fouling property, because in the examples, the reverse osmosis membrane is used to treat the dilute liquid of the nanofiltration process, and the main component in the dilute liquid is monovalent ion, and the multivalent easy-fouling ions such as calcium, magnesium and sulfate are less, and there is almost no fouling trend on the membrane surface, so the flux recovery rate is high. In Comparative Examples 1-2, the reverse osmosis membrane directly contacts the seawater concentrate, and there are a large number of easy-fouling ions, which are easy to foul on the membrane surface, and it is difficult to remove the scale by simple flushing, so the flux recovery rate is relatively low.

[0133] Table 5: Calcium ion concentration (mg / L) in Examples 1-3 and Comparative Examples 1-4

[0134]

[0135]

[0136] From Table 5, compared with Comparative Examples 1-2, the calcium ion concentration of the second dilute liquid and the second concentrate in Examples 1-3 is lower, reducing the fouling trend on the surface of the reverse osmosis membrane. Compared with Comparative Example 4, the calcium ion concentration of the third dilute liquid and the third concentrate in Examples 1-3 is lower, reducing the fouling trend on the surface of the nanofiltration membrane.

[0137] Table 6: Magnesium ion concentration (mg / L) in Examples 1-3 and Comparative Examples 1-4

[0138]

[0139] From Table 6, compared with Comparative Examples 1-2, the magnesium ion concentration of the second dilute liquid and the second concentrate in Examples 1-3 is lower, reducing the fouling trend on the surface of the reverse osmosis membrane. In Comparative Example 4, no second dilute liquid is added for Dia nanofiltration, and white suspended particles appear in the third concentrate, indicating that the concentration of the easy-fouling divalent ion is too high to form a precipitate. Compared with Comparative Example 4, the magnesium ion concentration of the third dilute liquid and the third concentrate in Examples 1-3 is lower, reducing the fouling trend on the surface of the nanofiltration membrane.

[0140] Table 7: Sodium ion concentration (mg / L) in Examples 1-3 and Comparative Examples 1-4

[0141]

[0142] From Table 7, compared with Comparative Examples 1-2, the sodium ion concentration in the first and third dilute solutions in Examples 1-3 is only slightly lower than that of the second and fourth concentrated solutions, which indicates that the nanofiltration membrane has a good separation effect on divalent cations, and divalent ions are retained on the concentrated solution side, while monovalent ions mostly permeate through the membrane into the dilute solution side. Compared with Comparative Example 4, the sodium ion concentration in the third dilute solution and the third concentrated solution in Examples 1-3 is lower, which indicates that adding the second dilute solution in the Dia nanofiltration process can reduce the sodium ion concentration.

[0143] Table 8: Sulfate ion concentration (mg / L) in Examples 1-3 and Comparative Examples 1-4

[0144]

[0145]

[0146] From Table 8, compared with Comparative Examples 1-2, the sulfate ion concentration in the second dilute solution and the second concentrated solution in Examples 1-3 is lower, which reduces the fouling trend on the surface of the reverse osmosis membrane. Compared with Comparative Example 4, the sulfate ion concentration in the third dilute solution and the third concentrated solution in Examples 1-3 is lower, which reduces the fouling trend on the surface of the nanofiltration membrane.

[0147] In summary, the method for preparing a seawater extract provided by the present application first removes part of the divalent ions in seawater using a nanofiltration process before the first reverse osmosis, and uses the first dilute solution for reverse osmosis treatment, which reduces the membrane flux reduction trend of the first nanofiltration membrane and the first reverse osmosis membrane, and maintains a high membrane flux recovery rate, thereby effectively reducing the fouling trend of the first reverse osmosis membrane and the first nanofiltration membrane. Before the second reverse osmosis, the Dia nanofiltration process is used to remove part of the divalent ions in seawater, and the third dilute solution is used for reverse osmosis treatment, which reduces the membrane flux reduction trend of the second nanofiltration membrane and the second reverse osmosis membrane. Finally, a seawater extract with high value-added ion content and low sodium content is obtained through the electrodialysis process.

[0148] The above is only an exemplary embodiment of the present application, and does not limit the patent scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made under the technical concept of the present application shall be included in the patent protection scope of the present application.

Claims

1. A method for preparing seawater extract, characterized in that, Includes the following steps: S10. Obtain seawater at a depth of 200~1000m; treat the seawater by ultrafiltration to obtain filtrate one; S20. The filtrate is subjected to nanofiltration to obtain a first desalinated solution and a first concentrated solution. S30. The first desalination solution is subjected to reverse osmosis treatment to obtain a second concentrate and a second desalination solution; S40. Mix the first concentrate and the second desalination solution to obtain a mixture, and then perform nanofiltration on the mixture to obtain a third desalination solution and a third concentrate. S50. The third desalination solution is subjected to reverse osmosis treatment to obtain a fourth concentrate and a fourth desalination solution; S60. Electrodialysis is performed on the third concentrate and part of the fourth desalination solution to obtain the fifth desalination solution and the fifth concentrate. S70. The fifth concentrate and part of the fourth desalination solution are electrodialyzed to obtain the sixth desalination solution and the sixth concentrate, wherein the sixth desalination solution is the seawater extract.

2. The method for preparing seawater extract as described in claim 1, characterized in that, In step S20, the nanofiltration membrane used for nanofiltration treatment includes a polyamide composite nanofiltration membrane.

3. The method for preparing seawater extract as described in claim 1, characterized in that, In step S20, the pressure of the nanofiltration process is 0.5~1.6 MPa.

4. The method for preparing seawater extract as described in claim 1, characterized in that, In step S20, the temperature of the nanofiltration process is 20~40℃.

5. The method for preparing seawater extract as described in claim 1, characterized in that, In step S40, the volume ratio of the first concentrate to the second desalination solution is 4:(1~6).

6. The method for preparing seawater extract as described in claim 1, characterized in that, In step S40, the Dia nanofiltration membrane used in the Dia nanofiltration process comprises a polyamide composite nanofiltration membrane.

7. The method for preparing seawater extract as described in claim 1, characterized in that, In step S40, the pressure of the Dia nanofiltration process is 0.5~1.6 MPa.

8. The method for preparing seawater extract as described in claim 1, characterized in that, In step S40, the temperature of the Dia nanofiltration process is 20~40℃.

9. The method for preparing seawater extract as described in claim 1, characterized in that, In steps S30 and S50: the reverse osmosis membrane used in the reverse osmosis treatment comprises a polyamide composite membrane; and / or, The reverse osmosis treatment pressure is 3.5~4 MPa; and / or, The temperature for the reverse osmosis treatment is 20~40℃.

10. A food supplement, characterized in that, The seawater extract prepared by the method for preparing seawater extract as described in any one of claims 1 to 9.

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