Method for separating magnesium and lithium in brine
By modifying nanofiltration membranes and combining nanofiltration with reverse osmosis, the problems of low magnesium-lithium separation efficiency and waste residue pollution in brine by traditional precipitation methods have been solved, achieving efficient and low-cost magnesium-lithium separation and lithium recovery, and improving the purity of lithium salts.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUNAN YUNENG RECYCLING TECHNOLOGY CO LTD
- Filing Date
- 2026-04-16
- Publication Date
- 2026-06-23
AI Technical Summary
Traditional chemical precipitation methods for separating magnesium and lithium in brine are inefficient, produce serious waste pollution, and are complex, making it difficult to meet the high purity requirements of battery-grade lithium salts.
Carboxylated MOF-modified nanofiltration membranes were used for brine pretreatment. Combined with nanofiltration and reverse osmosis technologies, magnesium and lithium were separated and lithium was recovered through primary nanofiltration, secondary nanofiltration and reverse osmosis concentration. A multi-level pore system was constructed using carboxylated ZiF-8 and carboxylated Uio-66 modified nanofiltration membranes to enhance the separation effect of Mg²+/Li+.
This improved lithium recovery rate, reduced production costs, decreased waste residue and waste liquid emissions, achieved a highly efficient and low-energy-consumption magnesium-lithium separation process, and improved the purity of lithium carbonate.
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Figure CN122010368B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of separation technology, and in particular to a method for separating magnesium and lithium in brine. Background Technology
[0002] Lithium, the lightest metal in nature, is widely used in lubricants, batteries, refrigerants, and pharmaceuticals. Globally, brine from salt lakes accounts for approximately 60% of lithium resources, while ore accounts for about 30%. Lithium extraction from ore is mainly used to produce battery-grade lithium carbonate and lithium hydroxide, while lithium extraction from salt lakes is primarily used to produce industrial-grade lithium carbonate. However, high-quality salt lakes are concentrated in the "Lithium Triangle" of South America, while lithium resources in countries like China are mainly composed of ores with a high magnesium-to-lithium ratio (such as spodumene containing 0.1%–0.5% MgO), requiring efficient separation of magnesium impurities to meet the purity requirements of battery-grade lithium salts (Mg < 20 ppm). The lithium sulfate solution formed after acid leaching of the ore contains Mg. 2+ Its ionic radius (0.72 Å) is similar to that of Li + With a value close to (0.76Å), traditional precipitation methods are difficult to separate efficiently and are prone to lithium loss.
[0003] Traditional chemical precipitation methods (such as lime for magnesium removal) have obvious drawbacks:
[0004] Low separation efficiency: Precipitation method has poor selectivity for solutions with Mg / Li>1;
[0005] The waste residue causes serious pollution and waste: magnesium hydroxide / magnesium carbonate waste residue is difficult to utilize, has high treatment costs, and pollutes the environment.
[0006] Complex process: multi-stage purification steps (such as ion exchange and solvent extraction), high investment cost, and poor process stability. Summary of the Invention
[0007] This application is made in view of the above-mentioned problems, and its purpose is to provide a method for separating magnesium and lithium in brine, which has a high lithium recovery rate.
[0008] Specifically, a method for separating magnesium and lithium in brine includes the following steps:
[0009] The brine is pretreated to obtain pretreated brine;
[0010] The pretreated brine is concentrated by primary nanofiltration, secondary nanofiltration, and reverse osmosis.
[0011] The nanofiltration membrane selected for the first-stage nanofiltration is a carboxylated MOF modified nanofiltration membrane;
[0012] The raw materials for preparing the carboxyl-modified nanofiltration membrane include:
[0013] Support, piperazine, carboxylated ZiF-8 and carboxylated Uio-66.
[0014] According to one of the technical solutions in this application, at least the following beneficial effects are achieved:
[0015] This application reduces the risk of brine fouling the nanofiltration membrane by pretreating the brine, and pumps the pretreated brine into the nanofiltration system to generate a magnesium and sulfate ion-rich retentate and a high-lithium permeate.
[0016] The retentate is subjected to secondary nanofiltration to recover lithium, and the secondary retentate can be utilized as a resource. The permeate enters the reverse osmosis membrane to concentrate the lithium content, and the concentrated lithium solution enters the lithium precipitation process.
[0017] The nanofiltration process separates magnesium and lithium while simultaneously achieving lithium recovery through a purification process. This also reduces energy consumption for subsequent lithium precipitation, decreases sulfate content in the crude product, lowers purification costs, and ultimately reduces overall production costs.
[0018] Nanofiltration is highly effective for separating magnesium and lithium; it retains Mg as well as SO4 in the membrane. 2- The reason is that both are high-valence ions with strong repulsion and are easily trapped; when separating magnesium and lithium in the brine process, nanofiltration membrane is selected as the core magnesium removal technology, and the permeate is concentrated by reverse osmosis membrane treatment.
[0019] Mg 2+ As a counterion, it can accumulate in large quantities in the confined space near the membrane surface, competing with Li. + Water molecules within the hydration layer lead to weakly hydrated Li + Partial dehydration promotes Li + Through a negatively charged membrane. We call this phenomenon counter-ion competition, which can also be regarded as counter-ion promotion in ion-selective separation applications.
[0020] This application optimizes the magnesium-lithium separation process in brine by employing a separation method that primarily uses nanofiltration membranes to remove magnesium, supplemented by reverse osmosis membranes. Simultaneously, lithium in the retentate is recovered and reused. This achieves low emissions of waste materials and liquids and avoids resource waste, while realizing a low-energy-consumption and high-efficiency magnesium-lithium separation process.
[0021] This process combines magnesium and lithium separation in the nanofiltration stage with lithium recovery through a purification process. Furthermore, it reduces the sulfate content in the crude lithium carbonate after lithium precipitation, lowering subsequent purification costs and ultimately reducing overall production costs.
[0022] Carboxylated ZiF-8 and carboxylated Uio-66 exhibit hydrogen bonding with piperazine, thereby enhancing the interfacial bonding between the filler and the matrix and reducing non-selective interfacial porosity. Carboxylated ZiF-8 and carboxylated Uio-66 are immobilized by the rapidly formed polyamide network of piperazine, thus forming a nanofiltration membrane. In the final nanofiltration membrane, carboxylated ZiF-8 and carboxylated Uio-66 are dispersed as functional fillers within the polyamide matrix, constructing a multi-level pore system including micropores within MOFs, interfacial pores between MOFs and polyamide, and network pores within the polyamide itself. Simultaneously, the membrane surface and interior are rich in negatively charged carboxyl groups.
[0023] In this application, the nanofiltration membrane is modified with carboxylated ZiF-8 and carboxylated Uio-66. The blending of these two compounds can construct a hierarchical pore structure and a stronger negatively charged surface within the membrane, achieving the desired effect on Mg²⁺ filtration. + / Li + It achieves efficient separation through both size sieving and charge repulsion.
[0024] According to some embodiments of this application, the pretreatment includes filtration and pH adjustment to 5-7.
[0025] The charge state of the carboxyl group is affected by pH. Within this pH range, the -COOH groups on the membrane surface and within the MOF pores are partially ionized and negatively charged, efficiently repelling divalent ions (such as Mg²⁺) through electrostatic repulsion. + SO4² - ), while allowing Li + Pass through relatively freely.
[0026] According to some embodiments of this application, the primary nanofiltration collects the primary permeate and the primary intercepted liquid.
[0027] According to some embodiments of this application, the secondary nanofiltration process treats the primary effluent and collects the secondary permeate and the secondary effluent.
[0028] According to some embodiments of this application, the primary permeate and the secondary permeate are combined and then concentrated by reverse osmosis to obtain a concentrated solution.
[0029] According to some embodiments of this application, lithium carbonate is obtained by precipitating lithium from the concentrated liquid.
[0030] The high-concentration, low-magnesium, low-sulfate lithium solution obtained after reverse osmosis is reacted with sodium carbonate solution to form lithium carbonate precipitate. Since magnesium and sulfate have been deeply removed, the purity of lithium carbonate is improved.
[0031] According to some embodiments of this application, the lithium deposition temperature is 90°C to 95°C.
[0032] According to some embodiments of this application, the lithium deposition time is 1h to 3h.
[0033] According to some embodiments of this application, the final pH of the lithium precipitation is 10.5 to 11.5.
[0034] According to some embodiments of this application, the operating pressure of the first-stage nanofiltration is 0.6 MPa to 1.2 MPa.
[0035] According to some embodiments of this application, the temperature of the first-stage nanofiltration is 20°C to 35°C.
[0036] According to some embodiments of this application, the operating pressure of the secondary nanofiltration is 0.6 MPa to 1.2 MPa.
[0037] According to some embodiments of this application, the temperature of the secondary nanofiltration is 20°C to 35°C.
[0038] According to some embodiments of this application, the secondary nanofiltration membrane is the same as that of the primary nanofiltration membrane.
[0039] According to some embodiments of this application, the pressure of the reverse osmosis concentration is 4.0 MPa to 8.0 MPa.
[0040] According to some embodiments of this application, the temperature for reverse osmosis concentration is 15°C to 30°C.
[0041] According to some embodiments of this application, the support includes a polysulfone film, a polyethersulfone film, and a polyvinylidene fluoride film.
[0042] According to some embodiments of this application, the molecular weight cutoff of the support is 20kDa to 50kDa.
[0043] According to some embodiments of this application, the preparation method of the carboxylated MOF modified nanofiltration membrane includes the following steps:
[0044] The base film was prepared by immersing the support in a piperazine aqueous solution;
[0045] The base film was immersed in a dispersion of carboxylated ZiF-8 and carboxylated Uio-66 for interfacial polymerization.
[0046] Heat treatment is performed after polymerization.
[0047] According to some embodiments of this application, the piperazine aqueous solution has a mass percentage of 1% to 3%.
[0048] According to some embodiments of this application, the temperature of the heat treatment is 60°C to 80°C.
[0049] According to some embodiments of this application, the heat treatment time is 5 min to 10 min.
[0050] According to some embodiments of this application, the interface aggregation time is 0.5 min to 2 min.
[0051] According to some embodiments of this application, the preparation method of the carboxylated ZiF-8 and carboxylated Uio-66 dispersion includes the following steps:
[0052] The carboxylated ZiF-8, carboxylated Uio-66, and pyromellitic trimethylol chloride n-hexane solution were mixed and dispersed.
[0053] According to some embodiments of this application, the mass ratio of the carboxylated ZiF-8 to the carboxylated Uio-66 is 1:1~3.
[0054] According to some embodiments of this application, the mass percentage of the pyromellitic methyl chloride hexane solution is 0.1% to 0.3%.
[0055] According to some embodiments of this application, the method for preparing the carboxylated ZIF-8 includes the following steps:
[0056] S1. ZIF-8, concentrated ammonia, ethanol and water are mixed to prepare ZIF-8 dispersion;
[0057] S2. After mixing tetrabutyl silicate and ZIF-8 dispersion, react the mixture and collect the solid phase to obtain silica-modified ZIF-8.
[0058] S3. After mixing and reacting silica-modified ZIF-8, toluene, and γ-aminopropyltriethoxysilane, the solid phase was collected to obtain silane-modified ZIF-8.
[0059] S4. Silane-modified ZIF-8, DMF, and succinic anhydride are mixed and reacted to obtain carboxylated ZIF-8.
[0060] According to some embodiments of this application, the temperature of the reaction in step S2 is 20°C to 30°C.
[0061] According to some embodiments of this application, the reaction time in step S2 is 6h to 8h.
[0062] According to some embodiments of this application, the mass-to-volume ratio of ZIF-8 and tetrabutyl silicate is 1g:2mL~5mL.
[0063] According to some embodiments of this application, the mass-to-volume ratio of silica-modified ZIF-8 and γ-aminopropyltriethoxysilane is 1 g: 5 mL to 10 mL.
[0064] According to some embodiments of this application, the reaction temperature in step S3 is 70°C to 90°C.
[0065] According to some embodiments of this application, the reaction time in step S3 is 10h to 20h.
[0066] According to some embodiments of this application, the mass ratio of silane-modified ZIF-8 to succinic anhydride is 1:4~6.
[0067] According to some embodiments of this application, the reaction temperature in step S4 is 20°C to 30°C.
[0068] According to some embodiments of this application, the reaction time in step S4 is 10h to 30h.
[0069] According to some embodiments of this application, the preparation method of the carboxylated Uio-66 includes the following steps:
[0070] Zirconium salt, pyromellitic acid, 2,5-dicarboxylated terephthalic acid, and organic solvent were mixed and then subjected to a solvothermal reaction.
[0071] According to some embodiments of this application, the temperature of the solvothermal process is 110°C to 130°C.
[0072] According to some embodiments of this application, the solvothermal time is 12h to 24h.
[0073] According to some embodiments of this application, the molar ratio of the zirconium salt to pyromellitic acid is 1:0.4~0.6.
[0074] According to some embodiments of this application, the molar ratio of the zirconium salt to 2,5-dicarboxylated terephthalic acid is 1:0.4~0.6.
[0075] According to some embodiments of this application, the zirconium salt is zirconium chloride.
[0076] According to some embodiments of this application, the concentration of magnesium ions in the brine is 100 g / L or higher.
[0077] According to some embodiments of this application, the mass ratio of magnesium to lithium in the brine is 1:40~100. Attached Figure Description
[0078] To more clearly illustrate the technical solutions in the embodiments of this drawing 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 this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.
[0079] Figure 1 This is a process flow diagram for an example.
[0080] The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation
[0081] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.
[0082] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.
[0083] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.
[0084] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
[0085] In this embodiment, the support is a polyethersulfone ultrafiltration membrane with a molecular weight cutoff of 50 kDa.
[0086] The concentrations of the main ions in the brine in this application are as follows:
[0087] Mg 2+ 110g / L, Li + 2.5g / L, Na + 5.2g / L, K + 2.5g / L Ca 2+ 0.1g / L, SO4 2- 3.9g / L, Cl- 29.6 g / L.
[0088] Example 1
[0089] This embodiment describes a method for separating magnesium and lithium in brine, referring to... Figure 1 As shown, it consists of the following steps:
[0090] S1. After filtering the brine, collect the liquid phase, add water to the liquid phase until the volume is 5 times the original volume, and adjust the pH to 7 to obtain pretreated brine.
[0091] After pretreated brine is subjected to first-stage nanofiltration (operating pressure 1.2 MPa, temperature 25 °C), the first-stage permeate and first-stage effluent are collected.
[0092] The primary intercepted liquid is then subjected to secondary nanofiltration, and the secondary permeate and secondary intercepted liquid are collected.
[0093] The primary and secondary permeate were combined and then concentrated by reverse osmosis (pressure 5.0 MPa, temperature 25℃) to obtain the concentrate.
[0094] After adding a saturated sodium carbonate solution to the concentrate, lithium was precipitated at 95°C for 3 hours, with the final pH controlled at 11.5. After the addition was completed, the solution was aged at 95°C for 2 hours to obtain lithium carbonate.
[0095] The primary and secondary intercepting solutions were combined and used to prepare magnesium hydroxide.
[0096] The nanofiltration membranes used for primary and secondary nanofiltration are carboxylated MOF modified nanofiltration membranes;
[0097] The preparation method of carboxylated MOF modified nanofiltration membrane consists of the following steps:
[0098] The substrate (soaked in water for 2 hours) was immersed in a 1% piperazine aqueous solution for 5 minutes to obtain the base film;
[0099] The base film was immersed in a dispersion of carboxylated ZiF-8 and carboxylated Uio-66 for interfacial polymerization for 2 min;
[0100] After polymerization, heat-treat at 60℃ for 10 minutes.
[0101] The preparation method of the carboxylated ZiF-8 and carboxylated Uio-66 dispersions comprises the following steps:
[0102] The carboxylated ZiF-8, carboxylated Uio-66, and a 0.1% (w / w) solution of trimesoyl chloride in hexane were mixed and then ultrasonically dispersed for 30 min.
[0103] The mass ratio of carboxylated ZiF-8 to carboxylated Uio-66 is 1:2.
[0104] The mass ratio of carboxylated ZiF-8 to piperazine is 0.1:100.
[0105] The preparation method of carboxylated ZIF-8 consists of the following steps:
[0106] S1. ZIF-8 (CAS No.: 59061-53-9), 28% concentrated ammonia (volume ratio of ZIF-8: 1g: 10mL), ethanol (volume ratio of ZIF-8: 1g: 80mL), and water (volume ratio of ZIF-8: 4:1) were mixed and sonicated for 30 minutes to obtain a ZIF-8 dispersion.
[0107] S2. Tetrabutyl silicate (with a mass-to-volume ratio of 1 g to 3 mL for ZIF-8) was added dropwise to the ZIF-8 dispersion at a rate of 0.01 mL / min. After mixing, the mixture was reacted at 25 °C for 8 h. The solid phase was collected, washed, and silica-modified ZIF-8 was obtained.
[0108] S3. A mixture of silica-modified ZIF-8, toluene (in a mass-to-volume ratio of 1 g to 100 mL), and γ-aminopropyltriethoxysilane (in a mass-to-volume ratio of 1 g to 10 mL) was refluxed at 80 °C for 12 h. The solid phase was collected, washed, and silane-modified ZIF-8 was obtained.
[0109] S4. Silane-modified ZIF-8, DMF (mass-volume ratio of 1 g to 50 mL with silane-modified ZIF-8), and succinic anhydride (mass-volume ratio of 1:5 with silane-modified ZIF-8) were mixed and reacted at 20 °C for 24 h to obtain carboxylated ZIF-8.
[0110] The mass-to-volume ratio of ZIF-8 to tetrabutyl silicate is 1 g: 3 mL.
[0111] The mass-to-volume ratio of silica-modified ZIF-8 and γ-aminopropyltriethoxysilane is 1 g: 8 mL.
[0112] The mass ratio of silane-modified ZIF-8 to succinic anhydride is 1:5.
[0113] The preparation method of carboxylated Uio-66 consists of the following steps:
[0114] Zirconium salt (zirconium chloride), pyromellitic acid (molar ratio to zirconium 2:1), 2,5-dicarboxylic terephthalic acid (molar ratio to zirconium 2:1), acetic acid (volume ratio of acetic acid to organic solvent 1:10), and organic solvent (DMF, molar volume ratio to zirconium 1 mol:30 mL) were mixed and reacted solvothermally at 120 °C for 24 h. The solid phase was then collected after solid-liquid separation.
[0115] After mixing the solid phase and DMF, sonicate for 5 minutes to separate the solid and liquid phases, collect the solid phase, and repeat this step 3 times.
[0116] Mix the solid phase and methanol, sonicate for 5 minutes, separate the solid and liquid phases, collect the solid phase, and repeat this step 3 times.
[0117] After immersing the solid phase in methanol for 8 hours, the solid phase is collected, and this step is repeated 3 times.
[0118] The collected solid phase was dried to constant weight at 60°C.
[0119] Example 2
[0120] This embodiment is a method for separating magnesium and lithium in brine, which differs from Embodiment 1 in that:
[0121] The mass ratio of carboxylated ZiF-8 to carboxylated Uio-66 is 1:3.
[0122] The mass ratio of carboxylated ZiF-8 to piperazine is 0.05:100.
[0123] Example 3
[0124] This embodiment is a method for separating magnesium and lithium in brine, which differs from Embodiment 1 in that:
[0125] The mass ratio of carboxylated ZiF-8 to carboxylated Uio-66 is 1:1.
[0126] The mass ratio of carboxylated ZiF-8 to piperazine is 0.2:100.
[0127] Example 4
[0128] This embodiment is a method for separating magnesium and lithium in brine, which differs from Embodiment 1 in that:
[0129] The mass-to-volume ratio of ZIF-8 to tetrabutyl silicate is 1 g: 5 mL.
[0130] The mass-to-volume ratio of silica-modified ZIF-8 and γ-aminopropyltriethoxysilane is 1 g: 10 mL.
[0131] The mass ratio of silane-modified ZIF-8 to succinic anhydride is 1:4.
[0132] Example 5
[0133] This embodiment is a method for separating magnesium and lithium in brine, which differs from Embodiment 1 in that:
[0134] The mass-to-volume ratio of ZIF-8 to tetrabutyl silicate is 1 g: 2 mL.
[0135] The mass-to-volume ratio of silica-modified ZIF-8 and γ-aminopropyltriethoxysilane is 1 g: 5 mL.
[0136] The mass ratio of silane-modified ZIF-8 to succinic anhydride is 1:4.
[0137] Comparative Example 1
[0138] This comparative example is a method for separating magnesium and lithium in brine, which differs from Example 1 in that:
[0139] In this comparative example, the nanofiltration membrane was not modified with carboxylated MOF.
[0140] The preparation method of the nanofiltration membrane in this comparative example consists of the following steps:
[0141] The substrate (soaked in water for 2 hours) was immersed in a 1% piperazine aqueous solution for 5 minutes to obtain the base film;
[0142] The base film was immersed in a 0.1% (w / w) solution of pyromellitic chlorohexane for interfacial polymerization for 2 min.
[0143] After polymerization, heat-treat at 60℃ for 10 minutes.
[0144] Comparative Example 2
[0145] This comparative example presents a method for separating magnesium and lithium in brine, which differs from Example 4 in that:
[0146] In this comparative example, carboxylated ZIF-8 was replaced with ZIF-8.
[0147] Comparative Example 3
[0148] This comparative example presents a method for separating magnesium and lithium in brine, which differs from Example 4 in that:
[0149] In this comparative example, 2,5-dicarboxylated terephthalic acid was not added in the preparation method of carboxylated Uio-66.
[0150] That is, the molar ratio of pyromellitic acid to zirconium is 1:1.
[0151] Comparative Example 4
[0152] This comparative example presents a method for separating magnesium and lithium in brine, which differs from Example 4 in that:
[0153] In this comparative example, the carboxylated ZIF-8 was not modified with silica.
[0154] The preparation method of carboxylated ZIF-8 consists of the following steps:
[0155] S1. ZIF-8 (CAS No.: 59061-53-9), 28% concentrated ammonia (volume ratio of ZIF-8: 1g: 10mL), ethanol (volume ratio of ZIF-8: 1g: 80mL), and water (volume ratio of ZIF-8: 4:1) were mixed and sonicated for 30 minutes to obtain a ZIF-8 dispersion.
[0156] S2. The ZIF-8 dispersion, toluene (mass-volume ratio of ZIF-8 to ZIF-8 is 1g:100mL), and γ-aminopropyltriethoxysilane (mass-volume ratio of ZIF-8 to ZIF-8 is 1g:10mL) were mixed and refluxed at 80℃ for 12h. The solid phase was collected, washed, and silane-modified ZIF-8 was obtained.
[0157] S3. Silane-modified ZIF-8, DMF (mass-volume ratio of 1 g to 50 mL with silane-modified ZIF-8), and succinic anhydride (mass-volume ratio of 1:5 with silane-modified ZIF-8) were mixed and reacted at 20 °C for 24 h to obtain carboxylated ZIF-8.
[0158] The mass-to-volume ratio of ZIF-8 and γ-aminopropyltriethoxysilane is 1 g: 10 mL.
[0159] The mass ratio of ZIF-8 to succinic anhydride is 1:4.
[0160] Comparative Example 5
[0161] This comparative example presents a method for separating magnesium and lithium in brine, which differs from Comparative Example 3 in that:
[0162] In this comparative example, carboxylated ZIF-8 was replaced with ZIF-8.
[0163] In this comparative example, 2,5-dicarboxylated terephthalic acid was not added in the preparation method of carboxylated Uio-66.
[0164] That is, the molar ratio of pyromellitic acid to zirconium is 1:1.
[0165] Table 1 Performance test results of the examples and comparative examples
[0166]
[0167] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.
Claims
1. A method for separating magnesium and lithium in brine, characterized in that, Includes the following steps: The brine is pretreated to obtain pretreated brine; The pretreated brine is concentrated by primary nanofiltration, secondary nanofiltration, and reverse osmosis. The nanofiltration membrane selected for the first-stage nanofiltration is a carboxylated MOF modified nanofiltration membrane; The raw materials for preparing the carboxylated MOF modified nanofiltration membrane include: Support, piperazine, carboxylated ZIF-8 and carboxylated Uio-66; The method for preparing the carboxylated MOF-modified nanofiltration membrane includes the following steps: The base film was prepared by immersing the support in a piperazine aqueous solution; The base film was immersed in a dispersion of carboxylated ZIF-8 and carboxylated Uio-66 for interfacial polymerization. Heat treatment is performed after polymerization. The method for preparing the carboxylated ZIF-8 includes the following steps: S1. ZIF-8, concentrated ammonia, ethanol and water are mixed to prepare ZIF-8 dispersion; S2. After mixing tetrabutyl silicate and ZIF-8 dispersion, react the mixture and collect the solid phase to obtain silica-modified ZIF-8. S3. After mixing and reacting silica-modified ZIF-8, toluene, and γ-aminopropyltriethoxysilane, the solid phase was collected to obtain silane-modified ZIF-8. S4. The silane-modified ZIF-8, DMF and succinic anhydride were mixed and reacted to obtain carboxylated ZIF-8; The preparation method of the carboxylated Uio-66 includes the following steps: Zirconium salt, pyromellitic acid, 2,5-dicarboxylated terephthalic acid and organic solvent were mixed and then subjected to a solvothermal reaction. The temperature of the solvothermal process is 110℃~130℃; The solvothermal time is 12h~24h.
2. The separation method according to claim 1, characterized in that, The pretreatment includes filtration and pH adjustment to 5-7.
3. The separation method according to claim 1, characterized in that, The first-stage nanofiltration collects the first-stage permeate and the first-stage retentate; The secondary nanofiltration process treats the primary retentate and collects the secondary permeate and the secondary retentate. The primary and secondary permeates are combined and then concentrated by reverse osmosis to obtain a concentrate. Lithium carbonate was obtained by precipitating lithium from the concentrated solution.
4. The separation method according to claim 1, characterized in that, The operating pressure of the first-stage nanofiltration unit is 0.6 MPa to 1.2 MPa; The temperature of the first-stage nanofiltration is 20℃~35℃; The operating pressure of the secondary nanofiltration unit is 0.6 MPa to 1.2 MPa; The temperature of the secondary nanofiltration is 20℃~35℃; The pressure for reverse osmosis concentration is 4.0 MPa to 8.0 MPa; The temperature for reverse osmosis concentration is 15℃~30℃.
5. The separation method according to claim 1, characterized in that, The support includes a polysulfone membrane, a polyethersulfone membrane, and a polyvinylidene fluoride membrane; The molecular weight cutoff of the support is 20kDa~50kDa; The piperazine aqueous solution has a mass percentage of 1% to 3%; The heat treatment temperature is 60℃~80℃; The heat treatment time is 5 min to 10 min.
6. The separation method according to claim 5, characterized in that, The preparation method of the carboxylated ZIF-8 and carboxylated Uio-66 dispersions includes the following steps: The carboxylated ZIF-8, carboxylated Uio-66, and pyromellitic trimethylol chloride n-hexane solution were mixed and then dispersed. The mass ratio of carboxylated ZIF-8 to carboxylated Uio-66 is 1:1~3; The mass percentage of the pyromellitic methyl chloride n-hexane solution is 0.1% to 0.3%.
7. The separation method according to claim 1, characterized in that, The mass-to-volume ratio of ZIF-8 to tetrabutyl silicate is 1g:2mL~5mL; The mass-to-volume ratio of silica-modified ZIF-8 and γ-aminopropyltriethoxysilane is 1g:5mL~10mL; The mass ratio of silane-modified ZIF-8 to succinic anhydride is 1:4~6.
8. The separation method according to claim 1, characterized in that, The molar ratio of zirconium salt to pyromellitic acid is 1:0.4~0.6; The molar ratio of the zirconium salt to 2,5-dicarboxylated terephthalic acid is 1:0.4~0.6.