Method for separating boron from salt lake brine and application

Abstract

The invention discloses a method for separating boron from salt lake brine and application. The method comprises the following steps: pretreating the salt lake brine at least for removing organic matters and suspended matters to prepare purified brine; carrying out primary pH value regulation treatment on the purified brine, and then carrying out primary pressurized separation treatment by adopting a nanofiltration membrane separation system to prepare a lithium-boron-containing solution or a magnesium-boron-containing solution; and carrying out secondary pH value adjustment treatment on the lithium-boron-containing solution or the magnesium-boron-containing solution, and then carrying out secondary pressurized separation treatment by adopting a nanofiltration membrane separation system so as to separate boron, lithium and magnesium. According to the invention, the technology for extracting boron from the boron-containing salt lake brine is enriched, the process steps for separating boron, lithium and magnesium in the brine are reduced, and the energy consumption and cost of the whole separation process are reduced.

Description

Technical Field

[0001] This invention belongs to the field of separation technology, specifically relating to a method and application for separating boron from salt lake brine. Background Technology

[0002] Boron and its compounds have important applications in many fields. my country has abundant salt lake brine resources but scarce boron ore resources, making boron extraction from salt lake brine a key research focus. Existing extraction methods have several problems, such as the environmental damage and increased process complexity caused by the introduction of organic extractants, the complexity and pollution risks of co-extraction agents, the high cost of resin separation, and the low cost of flotation separation but the inability to achieve the desired boron separation and enrichment.

[0003] Boron and its compounds are widely used in many fields such as chemical industry, building materials, electronic equipment, and nuclear energy. Boron in nature usually exists in the form of solid borax (sodium borate), borate minerals, and ions in salt lake brine or seawater. my country is rich in boron resources, with total reserves (calculated as B2O3) of 39.02 million tons, accounting for approximately 8% of global reserves. Boron reserves in salt lake brine account for 33% of the country's total reserves. In recent years, my country's boron-magnesium ore reserves have decreased rapidly, and the grade has declined, leading to increasingly scarce boron ore resources. To meet market demand, efficient and green extraction of boron resources from salt lake brine has become a current research focus. However, efficient separation of boron from salt lake brine is a challenging problem. Current methods for extracting boron from salt lake brine include acidification extraction, adsorption, membrane separation, electrodialysis, and solvent extraction. However, these methods all have various shortcomings. For example, acidification precipitation in acidification extraction requires precise temperature control of the brine, and pH adjustment in acidification crystallization requires precise addition rate of concentrated hydrochloric acid (2.0-2.3 L / min). Adsorption and ion exchange methods offer high selectivity and adsorption efficiency for boron, but the large quantities of boron adsorbents or resins required for treating high-concentration boron-containing brine result in high extraction costs. While extraction can effectively extract boron, the addition of organic solvents pollutes the brine, potentially damaging the environment. Furthermore, the addition of organic solvents complicates the extraction of other ions. Moreover, these methods only extract boron and cannot selectively separate boron from lithium, magnesium, or potassium. Membrane separation methods, due to their unique ion-selective permeability and automated control, have been well-appointed for lithium extraction from salt lake brine. Magnesium-lithium separation technology based on nanofiltration and selective electrodialysis of monovalent and divalent ions demonstrates excellent separation performance for both monovalent and polyvalent ions. However, membrane separation technology alone can only separate or enrich boron from lithium, magnesium, and potassium, and cannot provide targeted separation or enrichment of boron in real time according to specific needs. Therefore, a method that can extract boron from boron-containing brine in salt lakes in real time and selectively separate boron from lithium, magnesium, and potassium in the brine is of great significance for supplementing boron extraction methods from salt lake brine, separating or enriching boron in brine, and removing boron impurities from lithium- and magnesium-containing target products.

[0004] For example, patent CN 103482640A discloses a method for separating boron using alcohols as extractants and aromatic hydrocarbons as diluents. This method involves mixing the extractant and diluent at a specific volume percentage concentration to obtain an extractable organic phase. This organic phase is then subjected to multi-stage extraction of boron-containing brine after pH adjustment to obtain a boron-containing organic phase. This boron-containing organic phase is then back-extracted using a back-extraction agent. The resulting aqueous phase is then evaporated, concentrated, and crystallized to obtain boric acid or borate, thus achieving the separation of boron from the boron-containing brine. This method boasts high separation efficiency, low organic phase loss, and a simple process. However, this method of using aromatic hydrocarbons as extractants and diluents introduces organic extractants into the brine, potentially damaging the local ecosystem. Furthermore, the addition of organic solvents increases the difficulty of subsequent separation processes for other ions. Patent CN 108342595A discloses a method for separating boron and lithium from the brine matrix by using a co-extractor loaded with Fe(III) to extract boron and lithium from the brine matrix after acidification and the addition of Fe(III) mixture. This method primarily employs acidic and alkaline solutions for back-extraction of lithium and boron in the organic phase. The lithium-containing back-extract is concentrated and cooled for crystallization to prepare lithium chloride or precipitated to prepare lithium carbonate. The boron-containing back-extract is directly concentrated and crystallized to prepare sodium borate or concentrated and crystallized after acidification to prepare boric acid. This method is simple, has high boron and lithium collection efficiency, and operates in a closed-loop cycle. However, the co-extractor in this method still contains phosphorus-containing organic matter, amines, diketones, etc., making the extractant complex, the extraction process cumbersome, and posing a risk of environmental pollution. Patent CN1042319A discloses a method for separating boron using resin. This method involves treating a free, basic, chelating, large-pore boron-selective ion exchange resin with dilute acid, converting it into a salt-type resin. Brine flows into the resin bed to adsorb boron, and the boron-loaded resin is regenerated with dilute acid and reused repeatedly to achieve boron separation and recovery. However, this method consumes a large amount of resin during repeated elution and regeneration, resulting in high industrial production costs. Patent CN107638960A discloses a method for separating boron by flotation using polyhydroxy compounds. This method involves adding polyhydroxy compounds (such as mannitol, D-sorbitol, D-fructose, xylitol, ribitol, etc.) to a boron-containing solution to form a boron-containing complex solution. A flotation agent (mainly anionic surfactants, cationic surfactants, or nonionic surfactants) solution is then added to the boron-containing complex solution for flotation, yielding a residual solution after boron separation. This method has multiple advantages, including simple process, low production cost, and wide applicability. However, this method also increases the difficulty of separating the remaining ions in the brine in the subsequent separation process due to the introduction of polyhydroxy compounds and flotation agents. In addition, this method cannot achieve the separation or enrichment of boron according to actual needs (it only achieves separation).Patent CN 109205635A discloses a method for separating boron from boron-containing brine using nanofiltration separation technology. The method mainly involves adjusting the pH of the boron-containing brine to 9.5-11, pumping the brine into a nanofiltration system, applying pressure to both sides of the nanofiltration membrane, and ultimately achieving boron enrichment on the high-pressure side while obtaining brine containing other ions on the low-pressure side. This method can remove boron from brine at low cost and high efficiency while improving lithium ion yield, achieving comprehensive utilization of boron resources. However, this method can only achieve boron enrichment and cannot achieve real-time boron separation on the high-pressure side of the nanofiltration membrane. Patent CN 116217011A discloses a method for separating boron from water. After adjusting the pH of the boron-containing aqueous solution to 8-13, reagents are added to obtain a solution containing boron complexes and / or boron chelates. The solution containing boron complexes and / or boron chelates is then subjected to membrane filtration to obtain permeate water. This invention focuses on combining reagents with membrane technology. Through the combined effects of the complexing or chelating action of the reagents and the selective retention of the filtration membrane, boron is separated from the aqueous solution, reducing the amount of reagents and membrane modules required. However, this method only achieves boron retention, not selective permeation and retention. Therefore, an efficient and rational technology for extracting boron from boron-containing brine is crucial for boron extraction from brine, reducing process costs, and minimizing energy consumption. Summary of the Invention

[0005] The main objective of this invention is to provide a method and application for separating boron from salt lake brine, in order to overcome the shortcomings of the prior art.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] This invention provides a method for separating boron from salt lake brine, comprising:

[0008] Pretreatment of salt lake brine is performed to remove organic matter and suspended solids, resulting in purified brine.

[0009] The purified brine is subjected to a pH adjustment treatment to at least reduce boron content to B6O7(OH)6. 2- Or B(OH)4 - The solution exists in the form of lithium boron and is then subjected to a single pressurized separation process using a nanofiltration membrane separation system to obtain a lithium boron solution or a magnesium boron solution.

[0010] Furthermore, the lithium-boron-containing solution or the magnesium-boron-containing solution undergoes a secondary pH adjustment treatment, followed by a secondary pressurized separation treatment using a nanofiltration membrane separation system, thereby separating boron, lithium, and magnesium.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] (1) This invention adopts a method combining pH adjustment and nanofiltration membrane separation process, making full use of the characteristics of membrane separation technology and the differences in the form of boron in different pH solutions, to achieve effective separation of boron and lithium or effective separation of boron and magnesium in brine using salt lake brine as raw material, and to prepare boric acid or sodium borate according to the target product. At the same time, the lithium-rich solution can be used to prepare lithium carbonate or lithium hydroxide products.

[0013] (2) This invention enriches the technology for extracting boron from boron-containing salt lake brine, reduces the process steps for separating boron, lithium and magnesium in brine, and lowers the energy consumption and cost of the entire separation process. Attached Figure Description

[0014] 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 recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of a method for separating boron from salt lake brine in a typical embodiment of the present invention;

[0016] Figure 2 This is a schematic diagram of a method for separating boron from salt lake brine in a typical embodiment of the present invention. Detailed Implementation

[0017] In view of the deficiencies of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. This invention adopts a method combining pH adjustment and nanofiltration membrane separation and enrichment to ultimately achieve the purpose of extracting boron from salt lake brine as raw material, and then preparing sodium borate or boric acid. Furthermore, through the above process, the effective separation of boron and lithium in the brine is achieved, and the lithium-rich solution obtained can be used to prepare lithium carbonate or lithium hydroxide products.

[0018] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention innovatively employs a method combining pH adjustment and nanofiltration membrane processes to extract boron from salt lake brine, subsequently preparing sodium borate or boric acid. By precisely controlling the pH value of the brine and leveraging the unique separation characteristics of nanofiltration membranes, highly efficient extraction of boron from salt lake brine and effective separation from other ions are achieved. This innovative method not only improves the extraction efficiency and product purity of boron but also provides a completely new pathway for the comprehensive utilization of salt lake brine resources. Specific solutions include:

[0020] (1) pH adjustment of salt lake brine: First, the old brine of the salt lake is pretreated by adding an appropriate amount of fresh water to dilute it and reduce the concentration of salt solution in the brine. Then, the organic matter and suspended solids are removed through the brine pretreatment system to purify the brine. Next, according to the requirements of subsequent nanofiltration membrane separation, sodium hydroxide is added to the diluted brine to adjust the pH. When the pH is adjusted to 8-13, boron in the aqueous solution mainly exists as B6O7(OH)6. 2- Boron exists primarily as divalent anions; when the pH is adjusted to 2-5, boron mainly exists as B(OH)4. - It exists in the form of boron. This pH adjustment is based on the changes in the chemical form of boron under different acidity and alkalinity, which creates favorable conditions for subsequent nanofiltration membrane separation.

[0021] (2) Primary nanofiltration membrane separation or enrichment: The pH-adjusted brine from the salt lake is pumped into the nanofiltration membrane separation system. The pump creates a pressure difference across the nanofiltration membrane, driving ion separation or enrichment. Based on the principle of nanofiltration membranes' retention of divalent ions and permeation of monovalent ions, at pH values ​​of 2-5, the nanofiltration membrane allows water molecules and monovalent cations such as lithium ions to pass through, while boron also passes through as B(OH)4. - The lithium-boron ions permeate through the membrane to the freshwater side, while other divalent ions, such as magnesium ions, are retained on the concentrated water side according to their physicochemical properties, thus achieving preliminary separation between lithium-boron and magnesium. When the pH value is 8-13, boron mainly exists as B6O7(OH)6. 2- When boron exists in various forms, the retention capacity of the nanofiltration membrane changes. At this point, a solution containing magnesium and boron is obtained on the concentrate side, while a solution containing lithium is obtained on the desalination side, achieving separation between magnesium / boron and lithium. Through this single-stage nanofiltration membrane separation or enrichment operation, the separation degree can be adjusted in real time according to actual production needs, flexibly controlling the composition of the boron product.

[0022] (3) Secondary pH adjustment and nanofiltration membrane separation or enrichment: For the lithium- and boron-containing solution obtained after the first nanofiltration separation (pH 2-5), the pH is adjusted again to 8-13, and then pumped to the nanofiltration separation system for pressurized separation. During this process, due to the change in pH, the form of boron changes, and the separation performance of the nanofiltration membrane for boron and lithium also changes accordingly, resulting in a lithium-containing solution on the freshwater side and a boron-containing solution on the concentrated water side, thus achieving further separation between lithium and boron. At this point, the boron on the concentrated water side has been preliminarily enriched and can proceed to the next step of preparing sodium borate. For the boron- and magnesium-containing solution obtained after the first nanofiltration separation (pH 8-13), a secondary pH adjustment is also performed to 2-5, and then pumped to the nanofiltration separation system for pressurized separation, resulting in a boron-containing solution on the freshwater side and a magnesium-containing solution on the concentrated water side, achieving effective separation between boron and magnesium. At this point, the boron from the freshwater side can be used in the next step of boric acid preparation, while the magnesium from the concentrated water side can be returned to the salt field process for further treatment or recycling, thus achieving efficient separation and comprehensive utilization of various ions such as boron, lithium, magnesium, and potassium in the salt lake brine.

[0023] Specifically, as one aspect of the technical solution of this invention, a method for separating boron from salt lake brine includes:

[0024] Pretreatment of salt lake brine is performed to remove organic matter and suspended solids, resulting in purified brine.

[0025] The purified brine is subjected to a pH adjustment treatment to at least reduce boron content to B6O7(OH)6. 2- Or B(OH)4 - The solution exists in the form of lithium boron and is then subjected to a single pressurized separation process using a nanofiltration membrane separation system to obtain a lithium boron solution or a magnesium boron solution.

[0026] Furthermore, the lithium-boron-containing solution or the magnesium-boron-containing solution undergoes a secondary pH adjustment treatment, followed by a secondary pressurized separation treatment using a nanofiltration membrane separation system, thereby separating boron, lithium, and magnesium.

[0027] In some preferred embodiments, the method specifically includes: diluting the salt lake brine with fresh water, and then pretreating it with a brine pretreatment system to remove at least organic matter and suspended solids, thereby obtaining purified brine.

[0028] Furthermore, the volume ratio of the fresh water to the salt lake brine is 10 to 20:1.

[0029] Furthermore, the concentration of B2O3 in the solution obtained by diluting the salt lake brine is 230-250 mg / L, the concentration of Mg ions is 5500-5600 mg / L, the concentration of Li ions is 200-220 mg / L, and the pH value is 8.5-9.2.

[0030] In some preferred embodiments, the method specifically includes:

[0031] The pH of the purified brine is adjusted to 2-5, and then it is fed into a nanofiltration membrane separation system for a pressurized separation process. A lithium-boron-containing solution is obtained on the fresh water side, and a magnesium-containing solution is obtained on the concentrated water side, thereby achieving the separation between lithium-boron and magnesium.

[0032] The pH of the lithium-boron-containing solution is adjusted to 8-13, and then it is fed into a nanofiltration membrane separation system for secondary pressurized separation. A lithium-containing solution is obtained on the fresh water side and a boron-containing solution is obtained on the concentrated water side, thereby achieving the separation of lithium and boron.

[0033] Furthermore, the boron-containing solution is used to prepare boric acid or sodium borate, and the lithium-containing solution is used to prepare lithium carbonate or lithium hydroxide products.

[0034] In some preferred embodiments, the method for separating boron from the salt lake brine is illustrated as follows: Figure 1 As shown.

[0035] In some preferred embodiments, the method specifically includes:

[0036] The pH of the purified brine is adjusted to 8-13, and then it is fed into a nanofiltration membrane separation system for a pressurized separation process. A lithium-containing solution is obtained on the fresh water side, and a magnesium-boron-containing solution is obtained on the concentrated water side, thereby achieving the separation between lithium and magnesium-boron.

[0037] The pH of the magnesium-boron-containing solution is adjusted to 2-5, and then it is fed into a nanofiltration membrane separation system for secondary pressurized separation. A boron-containing solution is obtained on the fresh water side and a magnesium-containing solution is obtained on the concentrated water side, thereby achieving the separation between magnesium and boron.

[0038] Furthermore, the boron-containing solution is used to prepare boric acid or sodium borate, and the lithium-containing solution is used to prepare lithium carbonate or lithium hydroxide products.

[0039] In some preferred embodiments, the method for separating boron from the salt lake brine is illustrated as follows: Figure 2 As shown.

[0040] In some preferred embodiments, the salt lake brine includes old salt lake brine, which is old brine after potassium extraction.

[0041] In some preferred embodiments, the metallic elements in the salt lake brine include boron, lithium, and magnesium.

[0042] In some preferred embodiments, the reagents used in the primary pH adjustment treatment and the secondary pH adjustment treatment include sodium hydroxide or hydrochloric acid.

[0043] In some preferred embodiments, the nanofiltration membrane of the nanofiltration membrane separation system has the effect of retaining divalent ions and allowing monovalent ions to pass through.

[0044] In some preferred embodiments, the nanofiltration membrane separation system operates at a pressure of 1–4 MPa.

[0045] In some preferred embodiments, the nanofiltration membrane separation system operates at room temperature.

[0046] In some preferred embodiments, the feed flow rate is between 1 L / min and 5 L / min.

[0047] This invention utilizes a pH adjustment-nanofiltration membrane process to ultimately extract boron from salt lake brine, thereby preparing sodium borate or boric acid. Furthermore, the process effectively separates boron from lithium or magnesium in the brine, resulting in a lithium-rich solution that can be used to prepare lithium carbonate or lithium hydroxide products. The main steps of this technical solution are as follows:

[0048] (1) pH adjustment of salt lake brine

[0049] After diluting the old brine in the salt lake with a certain amount of fresh water, the brine pretreatment system removes organic matter and suspended solids. At this point, sodium hydroxide or hydrochloric acid needs to be added to the diluted brine to adjust the pH to 8-13 or 2-5. When the pH value is 8-13, boron exists mainly in the aqueous solution as B6O7(OH)6. 2- Boron exists primarily in aqueous solution as B(OH)4 when the pH value is 2-5, with divalent anions being the main component. - It exists in the form of.

[0050] (2) Primary nanofiltration membrane separation or enrichment

[0051] The pH-adjusted brine from the salt lake is pumped into a nanofiltration membrane separation system, where ions are separated or enriched by applying pressure to both sides of the nanofiltration membrane.

[0052] Based on the retention of divalent ions, permeation of monovalent ions, and sieving effect of nanofiltration membranes, boron in the feed solution after pH adjustment can be separated or enriched in real time during nanofiltration membrane separation according to actual needs. Specifically, when the pH of the feed solution is 2-5, a lithium- and boron-containing solution is obtained on the desalination side of nanofiltration separation, and a magnesium-containing solution is obtained on the concentrate side, thus achieving separation between lithium and boron and magnesium. When the pH of the feed solution is 8-13, a lithium-containing solution is obtained on the desalination side, and a magnesium- and boron-containing solution is obtained on the concentrate side, thus achieving separation between magnesium and boron and lithium. The resulting desalination and concentrate are then passed to the next process for separation or enrichment.

[0053] (3) Secondary pH adjustment and nanofiltration membrane separation or enrichment

[0054] The lithium and boron-containing solution obtained by nanofiltration separation of the above raw material solution with pH 2-5 is adjusted to pH 8-13 and pumped to nanofiltration separation system. After pressure separation, lithium-containing solution is obtained on the fresh water side and boron-containing solution is obtained on the concentrated water side, thus achieving the separation between lithium and boron. At this time, the boron on the concentrated water side can enter the process of preparing sodium borate, and the lithium on the fresh water side can enter the process of preparing lithium carbonate or lithium hydroxide.

[0055] Similarly, the solution containing boron and magnesium obtained by nanofiltration separation of the above-mentioned raw material solution with pH of 8-13 is adjusted to pH 2-5 and pumped to nanofiltration separation system. After pressure separation, boron-containing solution is obtained on the fresh water side and magnesium-containing solution is obtained on the concentrated water side, thus achieving the separation between boron and magnesium. At this time, the boron on the fresh water side can enter the next process of preparing boric acid, and the magnesium on the concentrated water side can be returned to the salt field process.

[0056] Another aspect of the present invention provides the application of the aforementioned method for separating boron from salt lake brine in the separation and / or enrichment of boron, lithium, and magnesium.

[0057] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0058] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0059] Example

[0060] The raw material used in this embodiment comes from the old brine after potassium extraction from a salt lake. After dilution, the pH of the raw material solution is adjusted to 9±0.1, 7±0.1, 5±0.1, and 3±0.1 using 1mol / L NaOH or 1mol / L HCl. At this time, the composition of the raw material solution is B2O3 content of 230.1 mg / L, magnesium ion content of 5579.4 mg / L, and lithium ion content of 207.2 mg / L.

[0061] Solutions with different pH values ​​were fed into a primary nanofiltration membrane separation system. The nanofiltration membrane separation system used a traditional spiral wound nanofiltration membrane and operated at a pressure of 3 MPa. This resulted in the separation of permeate or concentrate from the feed solutions with different pH values. The composition of the permeate and concentrate is shown in the table below.

[0062] Table 1 shows the ion content in the permeate and concentrate of different feed solutions after a single nanofiltration separation in the examples.

[0063]

[0064] Note: Permeation flux is expressed as the volume of permeate per unit time and unit membrane area. The rejection rate is the percentage of the difference in ion concentration between the feed solution and the product water relative to the ion concentration in the feed solution. (R = 1 - Cp / Cf)

[0065] After one nanofiltration step, the rejection ratio shows that for a solution with pH=9, the concentrate mainly consists of B6O7(OH)6. 2- The product water mainly contains Li, and for a solution with pH=3, the concentrate mainly contains Mg, while the product water mainly contains B(OH)4. - And Li.

[0066] a) The concentrated water (pH=9.01) obtained after separating the pH=9 solution was adjusted to pH 9±0.1, 7±0.1, 5±0.1, and 3±0.1 with 1 mol / L HCl. At this time, the raw material composition was 220.94 mg / L of B2O3, 5322.40 mg / L of magnesium ions, and 207.01 mg / L of lithium ions.

[0067] Similarly, solutions with different pH values ​​were fed into a secondary nanofiltration membrane separation system at an operating pressure of 3 MPa to obtain permeate or concentrate after separation of feed solutions with different pH values. The permeate and rejection rates are shown in the table below:

[0068] Table 2 shows the ion content in the permeate and concentrate of different feed solutions after secondary nanofiltration in the examples.

[0069]

[0070] b) Further, the product water (pH=3.01) obtained after the pH=3 solution was separated by nano-separation was adjusted to pH 9±0.1, 7±0.1, 5±0.1, and 3±0.1 with 1 mol / L NaOH. At this time, the composition of the raw material solution was B2O3 content of 223.52 mg / L, magnesium ion content of 127.58 mg / L, and lithium ion content of 288.24 mg / L.

[0071] Solutions with different pH values ​​were fed into a secondary nanofiltration membrane separation system at an operating pressure of 3 MPa to obtain permeate or concentrate with different pH values. The permeate and rejection rates are shown in the table below.

[0072] Table 3 shows the ion content in the permeate and concentrate of different feed solutions after secondary nanofiltration in the examples.

[0073]

[0074] Through the examples, the effective separation of boron and lithium or boron and magnesium in salt lake brine is achieved. The boron retention rate is above 80% at pH=9 and below 3% at pH=3. Based on the difference in retention rate, boron can be specifically retained and permeated, and boric acid or sodium borate can be prepared according to the target product.

[0075] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0076] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A method for separating boron from salt lake brine, characterized in that, include: Pretreatment of salt lake brine is performed to remove organic matter and suspended solids, resulting in purified brine. The purified brine is subjected to a pH adjustment treatment to at least reduce boron content to B6O7(OH)6. 2- Or B(OH)4 - The solution exists in the form of lithium boron and is then subjected to a single pressurized separation process using a nanofiltration membrane separation system to obtain a lithium boron solution or a magnesium boron solution. Furthermore, the lithium-boron-containing solution or the magnesium-boron-containing solution undergoes a secondary pH adjustment treatment, followed by a secondary pressurized separation treatment using a nanofiltration membrane separation system, thereby separating boron, lithium, and magnesium.

2. The method according to claim 1, characterized in that, Specifically, it includes: The salt lake brine is diluted with fresh water and then pretreated using a brine pretreatment system to remove organic matter and suspended solids, thereby obtaining purified brine. Preferably, the volume ratio of fresh water to salt lake brine is 10-20:1; Preferably, the concentration of B2O3 in the solution obtained by diluting the salt lake brine is 230-250 mg / L, the concentration of Mg ions is 5500-5600 mg / L, the concentration of Li ions is 200-220 mg / L, and the pH value is 8.5-9.

2.

3. The method according to claim 1, characterized in that, Specifically, it includes: The pH of the purified brine is adjusted to 2-5, and then it is fed into a nanofiltration membrane separation system for a pressurized separation process. A lithium-boron-containing solution is obtained on the fresh water side, and a magnesium-containing solution is obtained on the concentrated water side, thereby achieving the separation between lithium-boron and magnesium. The pH of the lithium-boron-containing solution is adjusted to 8-13, and then it is fed into a nanofiltration membrane separation system for secondary pressurized separation. A lithium-containing solution is obtained on the fresh water side and a boron-containing solution is obtained on the concentrated water side, thereby achieving the separation of lithium and boron. Furthermore, the boron-containing solution is used to prepare boric acid or sodium borate, and the lithium-containing solution is used to prepare lithium carbonate or lithium hydroxide products.

4. The method according to claim 1, characterized in that, Specifically, it includes: The pH of the purified brine is adjusted to 8-13, and then it is fed into a nanofiltration membrane separation system for a pressurized separation process. A lithium-containing solution is obtained on the fresh water side, and a magnesium-boron-containing solution is obtained on the concentrated water side, thereby achieving the separation between lithium and magnesium-boron. The pH of the magnesium-boron-containing solution is adjusted to 2-5, and then it is fed into a nanofiltration membrane separation system for secondary pressurized separation. A boron-containing solution is obtained on the fresh water side and a magnesium-containing solution is obtained on the concentrated water side, thereby achieving the separation between magnesium and boron. Furthermore, the boron-containing solution is used to prepare boric acid or sodium borate, and the lithium-containing solution is used to prepare lithium carbonate or lithium hydroxide products.

5. The method according to claim 1, characterized in that: The salt lake brine includes old salt lake brine, which is old brine after potassium extraction.

6. The method according to claim 1, characterized in that: The metallic elements in the salt lake brine include boron, lithium, and magnesium.

7. The method according to claim 1, characterized in that: The reagents used in the primary and secondary pH adjustment treatments include sodium hydroxide or hydrochloric acid.

8. The method according to claim 1, characterized in that: The nanofiltration membrane in the nanofiltration membrane separation system has the effect of retaining divalent ions and allowing monovalent ions to pass through.

9. The method according to claim 1, characterized in that: The nanofiltration membrane separation system operates at a pressure of 1–4 MPa.

10. The method for separating boron from salt lake brine according to any one of claims 1-9, and its application in the separation and / or enrichment of boron, lithium, and magnesium.

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