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CN-122010368-A - Method for separating magnesium and lithium in brine

CN122010368ACN 122010368 ACN122010368 ACN 122010368ACN-122010368-A

Abstract

The application provides a method for separating magnesium and lithium in brine, which comprises the following steps of pretreating brine to obtain pretreated brine, carrying out primary nanofiltration, secondary nanofiltration and reverse osmosis concentration on the pretreated brine, wherein a nanofiltration membrane selected for the primary nanofiltration is a carboxylated MOF modified nanofiltration membrane, and the preparation raw materials of the carboxylated modified nanofiltration membrane comprise a support body, piperazine, carboxylation ZiF-8 and carboxylation Uio-66. The method reduces the risk of pollution of brine to nanofiltration membranes by pretreatment of brine, pumps pretreated brine into a nanofiltration system to generate trapped liquid enriched with magnesium and sulfate ions and high-lithium permeate liquid, carries out secondary nanofiltration on the trapped liquid to recover lithium, can carry out resource utilization on the secondary trapped liquid, and carries out a reverse osmosis membrane, concentration of lithium content and lithium precipitation process of concentrated lithium liquid, and the impurity removal process of lithium recovery is realized while separating magnesium and lithium in the nanofiltration process.

Inventors

  • FENG RONGFENG
  • LIU RAN
  • SHEN XIANGYANG

Assignees

  • 湖南裕能循环科技有限公司
  • 湖南裕能新能源电池材料股份有限公司

Dates

Publication Date
20260512
Application Date
20260416

Claims (10)

  1. 1. The method for separating magnesium and lithium in brine is characterized by comprising the following steps of: pretreating brine to obtain pretreated brine; carrying out primary nanofiltration, secondary nanofiltration and reverse osmosis concentration on the pretreated brine; the nanofiltration membrane adopted by the primary nanofiltration is a carboxylated MOF modified nanofiltration membrane; The preparation raw materials of the carboxylated modified nanofiltration membrane comprise: Support, piperazine, carboxylation ZiF-8 and carboxylation Uio-66.
  2. 2. The separation method according to claim 1, wherein the pretreatment comprises filtration and pH adjustment to 5-7.
  3. 3. The separation method according to claim 1, wherein the primary nanofiltration collects a primary permeate and a primary retentate; the secondary nanofiltration is used for treating the primary cut-off liquid, and the secondary permeate and the secondary cut-off liquid are collected; Combining the first-level permeate and the second-level permeate, and performing reverse osmosis concentration to obtain a concentrated solution; And precipitating lithium in the concentrated solution to obtain lithium carbonate.
  4. 4. The separation method according to claim 1, wherein the operation pressure of the primary nanofiltration is 0.6mpa to 1.2mpa; The temperature of the primary nanofiltration is 20-35 ℃; the operation pressure of the secondary nanofiltration is 0.6-1.2 MPa; the temperature of the secondary nanofiltration is 20-35 ℃; The pressure of the reverse osmosis concentration is 4.0 mpa-8.0 mpa; the temperature of the reverse osmosis concentration is 15-30 ℃.
  5. 5. The separation method according to claim 1, wherein the support comprises a polysulfone membrane, a polyethersulfone membrane, and a polyvinylidene fluoride membrane; the molecular weight cut-off of the support body is 20 kDa-50 kDa; The preparation method of the carboxylated MOF modified nanofiltration membrane comprises the following steps: immersing a support body into piperazine aqueous solution to prepare a base film; Immersing the base film into carboxylated ZiF-8 and carboxylated Uio-66 dispersion liquid for interfacial polymerization; heat treatment after polymerization is completed; the mass percentage of the piperazine aqueous solution is 1% -3%; the temperature of the heat treatment is 60-80 ℃; the heat treatment time is 5 min-10 min.
  6. 6. The method of claim 5, wherein the method of preparing carboxylated ZiF-8 and carboxylated Uio-66 dispersions comprises the steps of: Mixing carboxylated ZiF-8, carboxylated Uio-66 and trimesoyl chloride n-hexane solution, and dispersing; the mass ratio of carboxylation ZiF-8 to carboxylation Uio-66 is 1:1-3; the mass percentage of the trimesic acid chloride-hexane solution is 0.1% -0.3%.
  7. 7. The separation method according to claim 1, wherein the preparation method of carboxylated ZIF-8 comprises the steps of: s1, mixing ZIF-8, concentrated ammonia water, ethanol and water to prepare ZIF-8 dispersion; S2, mixing tetrabutyl orthosilicate and ZIF-8 dispersion liquid, reacting, and collecting a solid phase to prepare the silicon dioxide modified ZIF-8; s3, mixing silicon dioxide modified ZIF-8, toluene and gamma-aminopropyl triethoxysilane, reacting, and collecting a solid phase to prepare silane modified ZIF-8; s4, mixing and reacting the silane modified ZIF-8, DMF and succinic anhydride to obtain the carboxylated ZIF-8.
  8. 8. The separation method according to claim 7, wherein the mass-to-volume ratio of the ZIF-8 to the butyl tetrasilicate is 1g:2 mL-5 mL; The mass volume ratio of the silicon dioxide modified ZIF-8 to the gamma-aminopropyl triethoxysilane is 1g to 5mL to 10mL; the mass ratio of the silane modified ZIF-8 to the succinic anhydride is 1:4-6.
  9. 9. The method of claim 1, wherein the method of preparing carboxylated Uio-66 comprises the steps of: Mixing zirconium salt, trimesic acid, 2, 5-dicarboxyl terephthalic acid and an organic solvent, and performing solvothermal reaction; the temperature of the solvothermal is 110-130 ℃; The time of the solvothermal is 12-24 hours.
  10. 10. The separation method according to claim 9, wherein the molar ratio of the zirconium salt to the trimesic acid is 1:0.4-0.6; the molar ratio of the zirconium salt to the 2, 5-dicarboxylic terephthalic acid is 1:0.4-0.6.

Description

Method for separating magnesium and lithium in brine Technical Field The application relates to the technical field of separation, in particular to a method for separating magnesium and lithium in brine. Background Lithium is the lightest metal in nature and is widely used in the fields of lubricating grease, batteries, refrigerants, medicines and the like. In the global lithium resource, the salt lake brine accounts for about 60 percent and the ore accounts for about 30 percent. The ore lithium extraction is mainly applied to the production of battery-grade lithium carbonate and lithium hydroxide, and the salt lake lithium extraction is mainly applied to the production of industrial-grade lithium carbonate. However, high-quality salt lakes are concentrated in 'lithium triangle' in south america, while lithium resources in China and other countries are mainly ores with high magnesium-lithium ratio (such as spodumene contains 0.1-0.5% of MgO), and magnesium impurities need to be separated efficiently to meet the purity of battery-grade lithium salts (Mg <20 ppm). The lithium sulfate solution formed after acid leaching of the ore contains Mg 2+, the ionic radius (0.72A) of which is similar to that of Li + (0.76A), and the traditional precipitation method is difficult to separate efficiently, thus easily causing lithium loss. The defects of the traditional chemical precipitation method (such as lime magnesium removal) are obvious: The separation efficiency is low, the solution selectivity of the precipitation method to Mg/Li >1 is poor; The waste residue is seriously polluted, the magnesium hydroxide/magnesium carbonate waste residue is difficult to use, the treatment cost is high, and the environment is polluted; The process is complex, the multistage purification steps (such as ion exchange and solvent extraction) are high in investment cost and poor in process stability. Disclosure of Invention The present application has been made in view of the above problems, and an object thereof is to provide a method for separating magnesium from lithium in brine, which has a high lithium recovery rate. The method for separating magnesium and lithium in brine comprises the following steps: pretreating brine to obtain pretreated brine; carrying out primary nanofiltration, secondary nanofiltration and reverse osmosis concentration on the pretreated brine; the nanofiltration membrane adopted by the primary nanofiltration is a carboxylated MOF modified nanofiltration membrane; The preparation raw materials of the carboxylated modified nanofiltration membrane comprise: Support, piperazine, carboxylation ZiF-8 and carboxylation Uio-66. According to one of the technical schemes of the application, the application has at least the following beneficial effects: According to the application, brine is pretreated, so that the pollution risk of brine to nanofiltration membranes is reduced, and pretreated brine is pumped into a nanofiltration system to generate trapped liquid enriched with magnesium and sulfate ions and high-lithium permeate; the trapped fluid is subjected to secondary nanofiltration to recover lithium, the secondary trapped fluid can be recycled, the permeate fluid enters a reverse osmosis membrane, the lithium content is concentrated, and the concentrated lithium fluid enters a lithium precipitation process. The nano-filtration process is separated from magnesium and lithium, and meanwhile, the impurity removal process for lithium recovery is realized, the subsequent lithium precipitation energy consumption is reduced, the sulfate radical content in the crude product is also reduced, the impurity removal cost is reduced, and the production cost is generally reduced. The nanofiltration has remarkable magnesium-lithium separation effect, and can intercept SO 42- while intercepting Mg element in the membrane, because the magnesium element and the SO 42- are strong in rejection as high-valence ions and easy to intercept, and when the magnesium-lithium separation is carried out on a brine process, the nanofiltration membrane is selected as a core magnesium removal technology, and permeate is concentrated through reverse osmosis membrane treatment. Mg 2+, as a counter ion, can be largely enriched in the confined space near the membrane surface, competing for water molecules within the Li + hydration layer, resulting in partial dehydration of weakly hydrated Li +, promoting Li + permeation through the negatively charged membrane. We refer to this phenomenon as counterion competition, which can also be considered as counterion promotion in ion selective separation applications. According to the application, the magnesium-lithium separation process of brine is optimized, the separation method mainly comprising magnesium removal by using nanofiltration membranes and assisted by using reverse osmosis membranes is adopted, meanwhile, lithium in trapped liquid is recycled, and the magnesium-lithium separation process with low