A method for high-concentration desalination of seawater resources and products

Abstract

The present application relates to the technical field of seawater comprehensive utilization, and particularly relates to a seawater resource high-concentration and salt separation method and product. The product is prepared by the method. The method comprises the following steps: after seawater raw water is filtered through a grid, the seawater is sequentially subjected to flocculation and precipitation treatment, multi-medium filtration treatment and ultrafiltration treatment to obtain purified seawater; the purified seawater is subjected to primary reverse osmosis treatment, the produced water is used as reclaimed water, and the concentrated water is subjected to first nanofiltration salt separation treatment; the produced water after the first nanofiltration salt separation treatment is subjected to main line treatment to obtain a main product; and the concentrated water after the first nanofiltration salt separation treatment is subjected to side line treatment to obtain a side product. The present application can truly realize the co-production of seawater "fresh water production" and "chemical raw material preparation".

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of seawater, and in particular to a method and product for high-concentration and salt separation of seawater resources. Background Technology

[0002] With the escalating global water crisis, seawater desalination has become a crucial means for coastal areas and water-scarce countries to obtain freshwater. Reverse osmosis (RO), as the mainstream seawater desalination technology, produces large quantities of freshwater but also generates concentrated seawater, which accounts for approximately 40% to 50% of the total intake. This concentrated seawater typically contains about 1.7 to 2 times the concentration of seawater in total dissolved solids (TDS). Direct discharge into the sea could cause negative impacts on the local marine ecosystem, including thermal, salinity, and chemical pollution. Therefore, the environmentally friendly treatment and resource utilization of this concentrated seawater is a key challenge for the sustainable development of the seawater desalination industry.

[0003] On the other hand, as a major producer of soda ash, my country's main production processes (such as the ammonia-soda process and the combined soda ash process) consume a huge amount of industrial raw salt (mainly composed of sodium chloride) annually. Traditional methods of obtaining industrial raw salt rely on seawater evaporation or rock salt mining, which suffer from problems such as large land area requirements, significant susceptibility to climate changes, and high resource consumption. Therefore, finding a new, stable, and economical method for obtaining industrial raw salt is of great significance for the green upgrading of the soda ash industry.

[0004] Currently, some studies have explored the use of concentrated seawater from seawater desalination, either directly or after preliminary concentration, in soda ash production. While this method of utilizing concentrated seawater from desalination achieves a certain degree of "waste-to-waste" treatment and resource recovery, it still has significant limitations: 1) Limited Concentration Ratio: Conventional reverse osmosis technology is difficult to stably concentrate brine to a TDS exceeding 100 g / L due to the influence of increased osmotic pressure and scaling tendency. To achieve higher concentration ratios (such as TDS > 150 g / L), serious technical bottlenecks need to be addressed, such as membrane scaling, excessive energy consumption, and unstable system operation.

[0005] 2) High transportation and processing costs: Conventional RO produces concentrated brine with low concentration (TDS approximately 60~70g / L) and a large volume. If it is transported over long distances to a soda ash plant, the logistics costs are high; if it is used directly within the soda ash plant, a large amount of energy is required for subsequent evaporation and concentration, which is not economical.

[0006] 3) Low level of technology integration: Existing concentrated seawater application solutions mostly focus on a single link, failing to deeply couple and optimize the water production benefits of seawater desalination with the high-value resource utilization benefits of concentrated water. There is room for further improvement in system energy efficiency and economic benefits.

[0007] Therefore, it is necessary to provide a high-concentration and salt separation method and product for seawater resource utilization to solve the problems of limited concentration ratio, high transportation and processing costs, and low technology integration of concentrated seawater produced after existing seawater desalination. Summary of the Invention

[0008] The purpose of this invention is to provide a method and product for high-concentration and salt separation of seawater resources. The specific technical solution is as follows: In a first aspect, the present invention provides a method for high-concentration and salt separation of seawater resources, comprising: Step S1: After filtering the raw seawater through a grid, it undergoes flocculation sedimentation, multi-media filtration, and ultrafiltration in sequence to obtain purified seawater. Step S2: The purified seawater is subjected to primary reverse osmosis treatment, the resulting permeate is reused as greywater, and the resulting concentrate is subjected to first nanofiltration desalination treatment. Step S3: The permeate after the first nanofiltration desalination treatment is processed in the main line to obtain the main product, soda ash raw salt solution; the concentrated water after the first nanofiltration desalination treatment is processed in the secondary line to obtain the by-products, calcium sulfate, magnesium hydroxide, calcium carbonate, and industrial sodium sulfate. The main process includes a first high-pressure concentration reverse osmosis process, a first high-concentration reverse osmosis process, a second high-concentration reverse osmosis process, a third high-concentration reverse osmosis process, a fourth high-concentration reverse osmosis process, and a first evaporation crystallization process, arranged sequentially. The secondary line treatment includes, in sequence, a second nanofiltration salt separation treatment, a first calcium precipitation treatment, a magnesium precipitation treatment, a second calcium precipitation treatment, a second high-pressure concentration reverse osmosis treatment, and a second evaporation crystallization treatment.

[0009] Optionally, the parameters used in the primary reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 5.0~6.0MPa; the permeate recovery rate is 40%~53%; the permeate TDS is ≤500mg / L; and the concentrate TDS is 55,000~70,000mg / L.

[0010] Optionally, the parameters used in the first nanofiltration desalination treatment include: the membrane is a nanofiltration membrane with a sulfate rejection rate ≥98% and a sodium chloride rejection rate ≤20%; the operating pressure is 4.0~5.0 MPa; the permeate recovery rate is 60%~75%; the permeate TDS is 45,000~60,000 mg / L, of which sulfate ≤100 mg / L; and the concentrate TDS is 75,000~95,000 mg / L.

[0011] Optionally, the parameters used in the first high-pressure concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.0~8.0 MPa; the desalination rate is 97%~99.5%; the permeate recovery rate is 40%~50%; the permeate TDS is ≤1,000 mg / L; the concentrate TDS is 80,000~100,000 mg / L; the permeate after the first high-pressure concentration reverse osmosis treatment is reused as reclaimed water, while the concentrate flows into the first high-concentration reverse osmosis treatment.

[0012] Optionally, the parameters used in the first high-concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.5~9.0 MPa; the desalination rate is 35.0%~55.0%; the permeate recovery rate is 50%~60%; the permeate TDS is 40,000~55,000 mg / L; the concentrate TDS is 125,000~140,000 mg / L; the permeate after the first high-concentration reverse osmosis treatment is returned to the first high-pressure concentration reverse osmosis treatment, while the concentrate flows into the second high-concentration reverse osmosis treatment. The parameters used in the second high-concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.5~9.0 MPa; the desalination rate is 30.0%~50.0%; the permeate recovery rate is 35%~48%; the permeate TDS is 65,000~85,000 mg / L; and the concentrate TDS is 155,000~170,000 mg / L. The permeate after the second high-concentration reverse osmosis treatment is returned to the first high-concentration reverse osmosis treatment, while the concentrate flows into the third high-concentration reverse osmosis treatment. The parameters used in the third high-concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.5~9.0 MPa; the desalination rate is 25.0%~45.0%; the permeate recovery rate is 28%~40%; the permeate TDS is 90,000~110,000 mg / L; and the concentrate TDS is 175,000~185,000 mg / L. The permeate after the third high-concentration reverse osmosis treatment is returned to the second high-concentration reverse osmosis treatment, while the concentrate flows into the fourth high-concentration reverse osmosis treatment. The parameters used in the fourth high-concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.5~9.0 MPa; the desalination rate is 20.0%~40.0%; the permeate recovery rate is 20%~35%; the permeate TDS is 115,000~135,000 mg / L; and the concentrate TDS is 195,000~210,000 mg / L. The permeate after the fourth high-concentration reverse osmosis treatment is returned to the third high-concentration reverse osmosis treatment, while the concentrate flows into the first evaporation and crystallization treatment.

[0013] Optionally, the parameters used in the first evaporation crystallization process include: an evaporation temperature of 80~90℃; the condensate obtained from evaporation being reused as greywater, and the TDS of the condensate being ≤200mg / L; the TDS of the main product, soda ash raw salt solution, obtained from evaporation being 300,000~315,000mg / L; and the sodium chloride concentration in the soda ash raw salt solution being 300~315g / L.

[0014] Optionally, the parameters used in the second nanofiltration desalination treatment include: the membrane is a nanofiltration membrane; the operating pressure is 5.0~6.0 MPa; the permeate recovery rate is 25%~40%; the permeate TDS is 55,000~70,000 mg / L; the concentrate TDS is 85,000~105,000 mg / L; the permeate after the second nanofiltration desalination treatment is returned to the first nanofiltration desalination treatment, while the concentrate flows into the first calcium precipitation treatment.

[0015] Optionally, the parameters used in the first calcium precipitation treatment include: adding a calcium source to the concentrate after the second nanofiltration desalination treatment, and controlling the molar ratio of the amount of calcium source added to the amount of calcium to be removed in the concentrate to be 1.05:1~1.20:1; after mixing, adjusting the pH value to 7.0~8.5; after the calcium precipitation reaction for 30~60 minutes, the calcium ion removal rate is ≥95%, and gypsum slurry is obtained; subsequently, the gypsum slurry is sent to a forced circulation crystallizer for solid-liquid separation to obtain by-product calcium sulfate and the first calcium precipitation concentrate; the purity of the calcium sulfate is ≥94.0%; the calcium source includes lime milk with a mass concentration of 5%~15%; The parameters used in the magnesium precipitation treatment include: first, adjusting the pH of the first calcium precipitation concentrate to 10.5~12.0; after the magnesium precipitation reaction for 30~60 min, adding 2~10 mg / L of anionic polyacrylamide to aid coagulation; finally, through solid-liquid separation, obtaining magnesium hydroxide and magnesium precipitation concentrate as byproducts; the purity of the magnesium hydroxide is ≥93.0%; The parameters used in the second calcium precipitation treatment include: adding a carbon source to the magnesium precipitation concentrate, and controlling the molar ratio of the amount of carbon source added to the amount of calcium remaining in the magnesium precipitation concentrate to be 1.02:1~1.10:1. After mixing, after the calcium precipitation reaction is carried out for 20~45 minutes, solid-liquid separation is performed to obtain the by-product calcium carbonate and the second calcium precipitation concentrate; the purity of the calcium carbonate is ≥95.0%; the carbon source includes sodium carbonate or carbon dioxide.

[0016] Optionally, the parameters used in the second high-pressure concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane with a sodium sulfate rejection rate ≥98%; the operating pressure is 6.0~8.0MPa; the permeate recovery rate is 25%~40%; the permeate TDS is ≤3,000mg / L; the concentrate TDS is 140,000~170,000mg / L; the permeate after the second high-pressure concentration reverse osmosis treatment is reused as reclaimed water, while the concentrate flows into the second evaporation and crystallization treatment. The parameters used in the second evaporation crystallization process include: an evaporation temperature of 80~95℃; the condensate obtained from evaporation is reused as greywater, and the TDS of the condensate is ≤100mg / L; the byproduct obtained from evaporation is industrial sodium sulfate; and the purity of the industrial sodium sulfate is ≥97.0%.

[0017] In a second aspect, the present invention provides a main product and a by-product obtained by the high-concentration salt separation method for seawater resource utilization, wherein the main product is a soda ash raw salt solution; and the sodium chloride concentration in the soda ash raw salt solution is 300~315g / L. The byproducts include calcium sulfate, magnesium hydroxide, calcium carbonate, and industrial sodium sulfate. The purity of the calcium sulfate is ≥94.0%; The purity of the magnesium hydroxide is ≥93.0%; The purity of the calcium carbonate is ≥95.0%; The purity of the industrial sodium sulfate is ≥97.0%.

[0018] The application of the technical solution of the present invention has at least the following beneficial effects: (1) The present invention provides a high-concentration and salt separation method for seawater resource utilization. By combining the main process of step S3 with steps S1-S2, the concentration ratio can be increased, and the concentrated water from seawater desalination can be concentrated to a high concentration level close to saturated brine in an efficient and energy-saving manner. This significantly reduces the volume of the main product, soda ash raw salt solution, as well as the subsequent transportation and processing costs, making it economically feasible to replace traditional industrial raw salt. This truly realizes the co-production of seawater "freshwater production" and "chemical raw material preparation," promoting the development of a circular economy. In addition, by combining the secondary process of step S3 with steps S1-S2, the by-products calcium sulfate, magnesium hydroxide, calcium carbonate, and industrial sodium sulfate are gradually recovered, achieving high process integration, thorough resource utilization, and no hazardous waste generation. Therefore, the present invention achieves low energy consumption, full component resource utilization, and no hazardous waste generation of seawater desalination concentrated water through the synergy of steps S1-S3, namely, the synergy of "membrane concentration-nanofiltration salt separation-chemical recovery-separation crystallization." This invention is not only applicable to new seawater desalination projects, but also provides an efficient renovation solution for the concentrate treatment of existing facilities, and has broad application value.

[0019] (2) The mainline treatment adopted in step S3 of this invention achieves optimized design and coupling of material flow and energy flow through the organic integration of each stage of treatment, forming a highly efficient closed-loop circulation and cascade recovery system. It gradually concentrates the seawater desalination concentrate to an optimized TDS concentration range suitable for subsequent evaporation and crystallization, replacing part of the high-energy-consuming evaporation process with membrane high-concentration, thus significantly reducing the overall energy consumption of the system. In addition, in the mainline treatment, the first high-concentration reverse osmosis treatment to the fourth high-concentration reverse osmosis treatment achieves internal circulation of materials and energy through the tight coupling design of permeate reflux and concentrate progression, thereby maximizing the resource recovery rate.

[0020] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a high-concentration and salt separation method for seawater resource utilization in Example 1. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: See Figure 1 A method for high-concentration and salt separation of seawater resources, comprising: Step S1: After filtering the raw seawater through a screen, it undergoes flocculation sedimentation treatment (using polyaluminum chloride, abbreviated as PAC, as the flocculant, with a mass ratio of 1:10,000 to 1:5,000 between the flocculant and the raw seawater, specifically a mass ratio of 1:7,500), multi-media filtration treatment (specifically processed in a multi-media filter), and ultrafiltration treatment to obtain purified seawater; The total dissolved solids (TDS) of the raw seawater is approximately 35,000 mg / L, including 10,500 mg / L sodium ions, 19,000 mg / L chloride ions, 500 mg / L calcium ions, 1,200 mg / L magnesium ions, and 2,800 mg / L sulfate ions. The suspended solids are ≤10 mg / L, and the pH is 7.5. The suspended solids in the purified seawater are ≤1mg / L, the silt density index (SDI) is ≤3, and the total dissolved solids (TDS) is 35,000mg / L. Step S2: Pour the purified seawater at 17.0m 3 The system performs primary reverse osmosis treatment per hour, and the resulting permeate is reused as greywater. The resulting concentrate is then subjected to first nanofiltration desalination treatment. Step S3: The permeate after the first nanofiltration desalination treatment is processed in the main line to obtain the main product, soda ash raw salt solution; the concentrated water after the first nanofiltration desalination treatment is processed in the secondary line to obtain the by-products, calcium sulfate, magnesium hydroxide, calcium carbonate, and industrial sodium sulfate. The main process includes a first high-pressure concentration reverse osmosis process, a first high-concentration reverse osmosis process, a second high-concentration reverse osmosis process, a third high-concentration reverse osmosis process, a fourth high-concentration reverse osmosis process, and a first evaporation crystallization process, arranged sequentially. The secondary line treatment includes, in sequence, a second nanofiltration salt separation treatment, a first calcium precipitation treatment, a magnesium precipitation treatment, a second calcium precipitation treatment, a second high-pressure concentration reverse osmosis treatment, and a second evaporation crystallization treatment.

[0025] The parameters used in the primary reverse osmosis treatment include: reverse osmosis membrane; operating pressure of 5.5 MPa; and product water flow rate of 7.65 m³ / h. 3 / h (product water recovery rate 45%), TDS ≤ 300 mg / L; concentrate flow rate is 9.35 m³ / h. 3 The concentration of sodium ions in the concentrated water was 19,000 mg / L, chloride ions 34,500 mg / L, calcium ions 900 mg / L, magnesium ions 2,200 mg / L, and sulfate ions 5,100 mg / L.

[0026] The parameters used in the first nanofiltration desalination treatment include: a nanofiltration membrane (sulfate rejection ≥98%, sodium chloride rejection ≤20%); an operating pressure of 4.5 MPa; and a product water flow rate of 7.01 m³ / min. 3 The permeate flow rate is approximately 67.7% (product water recovery rate), with a TDS of 52,000 mg / L. The product water contains 17,500 mg / L sodium, 33,000 mg / L chloride, 8 mg / L calcium, 20 mg / L magnesium, and 50 mg / L sulfate. The concentrate flow rate is 3.343 m³ / h (product water recovery rate is approximately 67.7%). 3The concentration of sodium ions in the concentrated water was 23,760 mg / L, chloride ions 38,590 mg / L, calcium ions 2,500 mg / L, magnesium ions 6,110 mg / L, and sulfate ions 14,160 mg / L.

[0027] The parameters used in the first high-pressure concentration reverse osmosis treatment include: reverse osmosis membrane; operating pressure of 7.5 MPa; desalination rate of 98.5%; and permeate flow rate of 5.207 m³ / h. 3 / h (product water recovery rate approximately 44.7%), TDS 751 mg / L; concentrate flow rate 6.439 m³ / h. 3 / h, TDS is 90,000mg / L; the permeate after the first high-pressure concentration reverse osmosis treatment is reused as greywater, while the concentrate flows into the first high-concentration reverse osmosis treatment.

[0028] The parameters used in the first high-concentration reverse osmosis treatment include: reverse osmosis membrane; operating pressure of 8 MPa; desalination rate of 45.0%; and permeate flow rate of 4.636 m³ / h. 3 / h (product water recovery rate approximately 53.3%), TDS 47,204 mg / L; concentrate flow rate 4.060 m³ / h. 3 / h, TDS is 130,000mg / L; the permeate after the first high-concentration reverse osmosis treatment is returned to the first high-pressure concentration reverse osmosis treatment, while the concentrate flows into the second high-concentration reverse osmosis treatment; The parameters used in the second high-concentration reverse osmosis treatment include: reverse osmosis membrane; operating pressure of 8 MPa; desalination rate of 40.0%; and permeate flow rate of 2.257 m³ / h. 3 / h (product water recovery rate approximately 42.9%), TDS 73,880 mg / L; concentrate flow rate 3.006 m³ / h. 3 / h, TDS is 160,000mg / L; the permeate after the second high-concentration reverse osmosis treatment is returned to the first high-concentration reverse osmosis treatment, while the concentrate flows into the third high-concentration reverse osmosis treatment; The parameters used in the third high-concentration reverse osmosis treatment include: reverse osmosis membrane; operating pressure of 8 MPa; desalination rate of 35.0%; and permeate flow rate of 1.203 m³ / h. 3 / h (product water recovery rate approximately 32.7%), TDS 100,000 mg / L; concentrate flow rate 2.471 m³ / h. 3 / h, TDS is 180,000mg / L; the permeate after the third high-concentration reverse osmosis treatment is returned to the second high-concentration reverse osmosis treatment, while the concentrate flows into the fourth high-concentration reverse osmosis treatment; The parameters used in the fourth high-concentration reverse osmosis treatment include: reverse osmosis membrane; operating pressure of 8 MPa; desalination rate of 30.0%; and permeate flow rate of 0.668 m³ / h. 3 The permeate flow rate was 1.803 m³ / h (permeate recovery rate approximately 27%), with a TDS of 126,000 mg / L; the concentrate flow rate was 1.803 m³ / h. 3 / h, TDS is 200,000mg / L; the permeate after the fourth high-concentration reverse osmosis treatment is returned to the third high-concentration reverse osmosis treatment, while the concentrate flows into the first evaporation and crystallization treatment.

[0029] The first evaporation crystallization process uses an MVR forced circulation evaporator with the following parameters: evaporation temperature of 85~90℃; the condensate obtained from evaporation is reused as greywater, and the condensate flow rate is 0.621m³ / h. 3 / h, TDS≤100mg / L; the flow rate of the main product, soda ash raw salt solution, obtained by evaporation is 1.182m. 3 / h, TDS is 305,000 mg / L; the sodium chloride concentration in the raw soda ash salt solution is 305 g / L (near saturation), and the raw soda ash salt solution can be directly supplied to downstream soda ash production enterprises.

[0030] The parameters used in the second nanofiltration desalination treatment include: nanofiltration membrane; operating pressure of 5.5 MPa; and permeate flow rate of 1.003 m³ / h. 3 The permeate flow rate is approximately 30% (permeate recovery rate), with a TDS of 62,000 mg / L; the concentrate flow rate is 2.34 m³ / h. 3 The concentration of sodium ions in the concentrate is 37,460 mg / L, chloride ions 17,000 mg / L, calcium ions 6,990 mg / L, magnesium ions 13,980 mg / L, and sulfate ions 19,570 mg / L. The permeate from the second nanofiltration desalination treatment is returned to the first nanofiltration desalination treatment, while the concentrate flows into the first calcium precipitation treatment.

[0031] The parameters used in the first calcium precipitation treatment include: adding a calcium source to the concentrate after the second nanofiltration desalination treatment, and controlling the molar ratio of the amount of calcium source added to the amount of calcium to be removed in the concentrate to be 1.1:1. After mixing, the pH value is adjusted to 7.5~8.0. After the calcium precipitation reaction for 45 minutes (the calcium ion concentration in the concentrate after the calcium precipitation reaction decreases from 6,990 mg / L to 80 mg / L, with a removal rate of approximately 98.9%; the sulfate ion concentration decreases from 19,570 mg / L to 12,000 mg / L, with a consumption of approximately 7,570 mg / L), gypsum slurry is obtained. Subsequently, the gypsum slurry is sent to a forced circulation crystallizer for solid-liquid separation to obtain calcium sulfate as a byproduct and the first calcium precipitation concentrate, and the calcium sulfate production rate is 14.6 kg / h; the purity of the calcium sulfate is 96.5%; the calcium source includes lime milk with a mass concentration of 10%; The parameters used in the magnesium precipitation treatment include: first, adjusting the pH of the first calcium precipitation concentrate to 11.0~11.5; after the magnesium precipitation reaction for 40 min (the magnesium ion concentration after the magnesium precipitation reaction drops from 13,980 mg / L after the first nanofiltration desalination treatment to below 20 mg / L, with a removal rate of approximately 99.9%), adding 5 mg / L of anionic polyacrylamide to aid coagulation; finally, after solid-liquid separation, magnesium hydroxide and magnesium precipitation concentrate are obtained as byproducts, and the production rate of magnesium hydroxide is 13.3 kg / h; the purity of the magnesium hydroxide is 95.8%. The parameters used in the second calcium precipitation treatment include: adding a carbon source to the magnesium precipitation concentrate, and controlling the molar ratio of the added carbon source to the remaining calcium in the magnesium precipitation concentrate to be 1.05:1. After mixing, after the calcium precipitation reaction for 30 minutes (the calcium ion concentration after the calcium precipitation reaction drops from 80 mg / L after the first calcium precipitation treatment to below 5 mg / L), solid-liquid separation is performed to obtain the byproduct calcium carbonate and the second calcium precipitation concentrate, and the calcium carbonate production rate is 0.23 kg / h; the purity of the calcium carbonate is 97.2%; the carbon source includes sodium carbonate or carbon dioxide, specifically carbon dioxide is selected.

[0032] The parameters used in the second high-pressure concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane (sodium sulfate rejection rate ≥98%); the operating pressure is 6.5~7.0 MPa; and the feed water flow rate is 2.32 m³ / h. 3 The influent TDS is 112,000 mg / L; the product flow rate is 0.696 m³ / h. 3 The permeate TDS was 2,240 mg / L; the concentrate flow rate was 1.624 m³ / h. 3 / h, the concentrated water TDS is 159,000 mg / L; the permeate after the second high-pressure concentration reverse osmosis treatment is reused as reclaimed water, while the concentrated water flows into the second evaporation crystallization treatment; The second evaporation crystallization process uses an MVR forced circulation evaporator with the following parameters: evaporation temperature of 85~90℃; the condensate obtained from evaporation is reused as greywater, and the condensate flow rate is 1.62m³ / h. 3 / h, TDS≤80mg / L; Evaporation yields industrial sodium sulfate as a byproduct, with a production rate of 41.6kg / h; The purity of the industrial sodium sulfate is 97.6%.

[0033] As shown in Example 1: Regarding water recycling and product output (based on 17.0m³ of purified seawater) 3 / h flow meter): In step S2, the permeate flow rate after primary reverse osmosis treatment is 7.65 m³ / h. 3 / h; The permeate flow rate after the first high-pressure concentration reverse osmosis treatment in step S3 main line processing is 5.207m³ / h. 3 The condensate flow rate after the first evaporation and crystallization treatment is 0.621 m³ / h. 3 / h; the permeate flow rate of the second high-pressure concentration reverse osmosis treatment in step S3 is 0.696m³ / h. 3 The flow rate of condensate after the second evaporation and crystallization treatment is 1.62 m³ / h. 3 / h. Therefore, the total recycled water consumption is approximately 15.794m³. 3 / h, TDS≤600mg / L, the overall water recovery rate is still >90%, specifically reaching 92.9%, and the rest is produced in the form of resources, with no solid waste generated.

[0034] Soda ash original salt solution: 1.182m 3 / h, which is equivalent to about 360.6 kg / h of sodium chloride (8000 hours of operation per year, with an annual output of about 2885 tons).

[0035] Calcium sulfate: 14.6 kg / h (8000 hours of operation per year, annual production of approximately 116.8 tons).

[0036] Magnesium hydroxide: 13.3 kg / h (8000 hours of operation per year, annual production of approximately 106.4 tons).

[0037] Calcium carbonate: 0.23 kg / h (8000 hours of operation per year, annual production of approximately 1.84 tons).

[0038] Industrial sodium sulfate: 14.2 kg / h (8000 hours of operation per year, annual production of approximately 113.6 tons).

[0039] Energy consumption: The overall system power consumption is 14.8 kWh / m³. 3 Seawater, compared to traditional total evaporation processes (approximately 30.1 kWh / m³), 3 Seawater can save approximately 51% of energy, resulting in annual electricity savings of approximately 2.08 million kWh.

[0040] Economic benefits (8000 hours of operation per year): The total annual revenue is approximately RMB 2.25 million (including the value of recycled water, product sales revenue, and savings in raw salt procurement and disposal costs).

[0041] The annual operating cost is approximately 1.85 million yuan.

[0042] Annual net income is approximately 400,000 yuan, achieving positive profitability.

[0043] In summary, this embodiment 1 first obtains purified seawater through step S1, and then achieves source separation of monovalent and divalent salts through primary reverse osmosis treatment in step S2 and first nanofiltration salt separation treatment. The main line concentrates sodium chloride to near saturation through high-pressure concentration followed by reverse osmosis treatment, and then through one and multiple stages of high-concentration reverse osmosis treatment with staged reflux (total product water reflux), directly producing a raw soda ash salt solution for use in soda ash production. The secondary line achieves the full resource utilization of magnesium, calcium, and sulfate ions through directional stepwise precipitation of "calcium removal → magnesium removal → deep calcium removal". This embodiment 1 saves approximately 51% energy compared to traditional processes, has a water recovery rate of >90%, no waste liquid discharge, and no impurity salt generation, making it economically feasible for independent commercial operation.

[0044] The above description is only a preferred embodiment of the present invention and does not limit the scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the protection scope of the present invention.

Claims

1. A method for high-concentration and salt separation of seawater resources, characterized in that, include: Step S1: After filtering the raw seawater through a grid, it undergoes flocculation sedimentation, multi-media filtration, and ultrafiltration in sequence to obtain purified seawater. Step S2: The purified seawater is subjected to primary reverse osmosis treatment, the resulting permeate is reused as greywater, and the resulting concentrate is subjected to first nanofiltration desalination treatment. Step S3: The permeate after the first nanofiltration desalination treatment is processed in the main line to obtain the main product, soda ash raw salt solution; the concentrated water after the first nanofiltration desalination treatment is processed in the secondary line to obtain the by-products, calcium sulfate, magnesium hydroxide, calcium carbonate, and industrial sodium sulfate. The main process includes a first high-pressure concentration reverse osmosis process, a first high-concentration reverse osmosis process, a second high-concentration reverse osmosis process, a third high-concentration reverse osmosis process, a fourth high-concentration reverse osmosis process, and a first evaporation crystallization process, arranged sequentially. The secondary line treatment includes, in sequence, a second nanofiltration salt separation treatment, a first calcium precipitation treatment, a magnesium precipitation treatment, a second calcium precipitation treatment, a second high-pressure concentration reverse osmosis treatment, and a second evaporation crystallization treatment.

2. The method for high-concentration and salt separation of seawater resources as described in claim 1, characterized in that, The parameters used in the primary reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 5.0~6.0MPa; the permeate recovery rate is 40%~53%; the permeate TDS is ≤500mg / L; and the concentrate TDS is 55,000~70,000mg / L.

3. The high-concentration and salt separation method for seawater resource utilization as described in claim 1, characterized in that, The parameters used in the first nanofiltration desalination treatment include: the membrane is a nanofiltration membrane with a sulfate rejection rate ≥98% and a sodium chloride rejection rate ≤20%; the operating pressure is 4.0~5.0 MPa; the permeate recovery rate is 60%~75%; the permeate TDS is 45,000~60,000 mg / L, of which sulfate ≤100 mg / L; and the concentrate TDS is 75,000~95,000 mg / L.

4. The method for high-concentration and salt separation of seawater resources as described in claim 1, characterized in that, The parameters used in the first high-pressure concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.0~8.0MPa; the desalination rate is 97%~99.5%; the permeate recovery rate is 40%~50%; the permeate TDS is ≤1,000mg / L; the concentrate TDS is 80,000~100,000mg / L; the permeate after the first high-pressure concentration reverse osmosis treatment is reused as reclaimed water, while the concentrate flows into the first high-concentration reverse osmosis treatment.

5. The method for high-concentration and salt separation of seawater resources as described in claim 4, characterized in that, The parameters used in the first high-concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.5~9.0 MPa; the desalination rate is 35.0%~55.0%; the permeate recovery rate is 50%~60%; the permeate TDS is 40,000~55,000 mg / L; the concentrate TDS is 125,000~140,000 mg / L; the permeate after the first high-concentration reverse osmosis treatment is returned to the first high-pressure concentration reverse osmosis treatment, while the concentrate flows into the second high-concentration reverse osmosis treatment. The parameters used in the second high-concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.5~9.0 MPa; the desalination rate is 30.0%~50.0%; the permeate recovery rate is 35%~48%; the permeate TDS is 65,000~85,000 mg / L; and the concentrate TDS is 155,000~170,000 mg / L. The permeate after the second high-concentration reverse osmosis treatment is returned to the first high-concentration reverse osmosis treatment, while the concentrate flows into the third high-concentration reverse osmosis treatment. The parameters used in the third high-concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.5~9.0 MPa; the desalination rate is 25.0%~45.0%; the permeate recovery rate is 28%~40%; the permeate TDS is 90,000~110,000 mg / L; and the concentrate TDS is 175,000~185,000 mg / L. The permeate after the third high-concentration reverse osmosis treatment is returned to the second high-concentration reverse osmosis treatment, while the concentrate flows into the fourth high-concentration reverse osmosis treatment. The parameters used in the fourth high-concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane; the operating pressure is 7.5~9.0 MPa; the desalination rate is 20.0%~40.0%; the permeate recovery rate is 20%~35%; the permeate TDS is 115,000~135,000 mg / L; and the concentrate TDS is 195,000~210,000 mg / L. The permeate after the fourth high-concentration reverse osmosis treatment is returned to the third high-concentration reverse osmosis treatment, while the concentrate flows into the first evaporation and crystallization treatment.

6. The method for high-concentration and salt separation of seawater resources as described in claim 5, characterized in that, The parameters used in the first evaporation crystallization process include: an evaporation temperature of 80~90℃; the condensate obtained from evaporation is reused as greywater, and the TDS of the condensate is ≤200mg / L; the TDS of the main product, soda ash raw salt solution, obtained from evaporation is 300,000~315,000mg / L; and the sodium chloride concentration in the soda ash raw salt solution is 300~315g / L.

7. The method for high-concentration and salt separation of seawater resources as described in claim 1, characterized in that, The parameters used in the second nanofiltration desalination treatment include: the membrane is a nanofiltration membrane; the operating pressure is 5.0~6.0 MPa; the permeate recovery rate is 25%~40%; the permeate TDS is 55,000~70,000 mg / L; the concentrate TDS is 85,000~105,000 mg / L; the permeate after the second nanofiltration desalination treatment is returned to the first nanofiltration desalination treatment, while the concentrate flows into the first calcium precipitation treatment.

8. The method for high-concentration and salt separation of seawater resources as described in claim 7, characterized in that, The parameters used in the first calcium precipitation treatment include: adding a calcium source to the concentrate after the second nanofiltration desalination treatment, and controlling the molar ratio of the amount of calcium source added to the amount of calcium to be removed in the concentrate to be 1.05:1~1.20:

1. After mixing, the pH value is adjusted to 7.0~8.

5. After the calcium precipitation reaction is carried out for 30~60 minutes, the calcium ion removal rate is ≥95%, and gypsum slurry is obtained. Subsequently, the gypsum slurry is sent to a forced circulation crystallizer for solid-liquid separation to obtain calcium sulfate by-product and the first calcium precipitation concentrate. The purity of the calcium sulfate is ≥94.0%. The calcium source includes lime milk with a mass concentration of 5%~15%. The parameters used in the magnesium precipitation treatment include: first, adjusting the pH of the first calcium precipitation concentrate to 10.5~12.0; after the magnesium precipitation reaction for 30~60 min, adding 2~10 mg / L of anionic polyacrylamide to aid coagulation; finally, through solid-liquid separation, obtaining magnesium hydroxide and magnesium precipitation concentrate as byproducts; the purity of the magnesium hydroxide is ≥93.0%; The parameters used in the second calcium precipitation treatment include: adding a carbon source to the magnesium precipitation concentrate, and controlling the molar ratio of the amount of carbon source added to the amount of calcium remaining in the magnesium precipitation concentrate to be 1.02:1~1.10:

1. After mixing, after the calcium precipitation reaction is carried out for 20~45 minutes, solid-liquid separation is performed to obtain the by-product calcium carbonate and the second calcium precipitation concentrate; the purity of the calcium carbonate is ≥95.0%; the carbon source includes sodium carbonate or carbon dioxide.

9. The method for high-concentration and salt separation of seawater resources as described in claim 8, characterized in that, The parameters used in the second high-pressure concentration reverse osmosis treatment include: the membrane is a reverse osmosis membrane with a sodium sulfate rejection rate ≥98%; the operating pressure is 6.0~8.0MPa; the permeate recovery rate is 25%~40%; the permeate TDS is ≤3,000mg / L; the concentrate TDS is 140,000~170,000mg / L; the permeate after the second high-pressure concentration reverse osmosis treatment is reused as reclaimed water, while the concentrate flows into the second evaporation and crystallization treatment. The parameters used in the second evaporation crystallization process include: an evaporation temperature of 80~95℃; the condensate obtained from evaporation is reused as greywater, and the TDS of the condensate is ≤100mg / L; the byproduct obtained from evaporation is industrial sodium sulfate; and the purity of the industrial sodium sulfate is ≥97.0%.

10. A method for separating the main product and by-product obtained by high-concentration and salt separation of seawater resources as described in any one of claims 1 to 9, characterized in that, The main product is a raw soda ash solution; the sodium chloride concentration in the raw soda ash solution is 300~315g / L. The byproducts include calcium sulfate, magnesium hydroxide, calcium carbonate, and industrial sodium sulfate. The purity of the calcium sulfate is ≥94.0%; The purity of the magnesium hydroxide is ≥93.0%; The purity of the calcium carbonate is ≥95.0%; The purity of the industrial sodium sulfate is ≥97.0%.

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