CN115676856A - Method and system for extracting lithium from salt lake - Google Patents
Method and system for extracting lithium from salt lake Download PDFInfo
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- CN115676856A CN115676856A CN202211364848.3A CN202211364848A CN115676856A CN 115676856 A CN115676856 A CN 115676856A CN 202211364848 A CN202211364848 A CN 202211364848A CN 115676856 A CN115676856 A CN 115676856A
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 100
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 99
- 238000000034 method Methods 0.000 title claims abstract description 73
- 238000001728 nano-filtration Methods 0.000 claims abstract description 408
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 291
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims abstract description 113
- 239000012267 brine Substances 0.000 claims abstract description 107
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims abstract description 96
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims abstract description 59
- 229910052796 boron Inorganic materials 0.000 claims abstract description 59
- 238000002425 crystallisation Methods 0.000 claims abstract description 55
- 230000008025 crystallization Effects 0.000 claims abstract description 55
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 53
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 53
- 229910052808 lithium carbonate Inorganic materials 0.000 claims abstract description 52
- 239000012452 mother liquor Substances 0.000 claims abstract description 51
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims abstract description 47
- 238000000502 dialysis Methods 0.000 claims abstract description 42
- 238000001179 sorption measurement Methods 0.000 claims abstract description 40
- 238000001704 evaporation Methods 0.000 claims abstract description 36
- 230000008569 process Effects 0.000 claims abstract description 35
- 230000008020 evaporation Effects 0.000 claims abstract description 32
- 239000002244 precipitate Substances 0.000 claims abstract description 20
- 238000002156 mixing Methods 0.000 claims abstract description 14
- 238000010992 reflux Methods 0.000 claims abstract description 13
- 238000001556 precipitation Methods 0.000 claims description 50
- 238000000926 separation method Methods 0.000 claims description 43
- 238000011084 recovery Methods 0.000 claims description 39
- 150000001450 anions Chemical class 0.000 claims description 30
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 29
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 25
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 22
- 239000011777 magnesium Substances 0.000 claims description 22
- 229910052749 magnesium Inorganic materials 0.000 claims description 22
- 238000001914 filtration Methods 0.000 claims description 19
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 18
- 239000011575 calcium Substances 0.000 claims description 18
- 229910052791 calcium Inorganic materials 0.000 claims description 17
- 239000000047 product Substances 0.000 claims description 17
- 150000003839 salts Chemical class 0.000 claims description 16
- 238000000605 extraction Methods 0.000 claims description 15
- 238000004519 manufacturing process Methods 0.000 claims description 15
- 229920005989 resin Polymers 0.000 claims description 14
- 239000011347 resin Substances 0.000 claims description 14
- 239000007787 solid Substances 0.000 claims description 13
- 239000012141 concentrate Substances 0.000 claims description 10
- 239000006228 supernatant Substances 0.000 claims description 9
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 claims description 8
- 239000003513 alkali Substances 0.000 claims description 8
- 239000000084 colloidal system Substances 0.000 claims description 6
- 238000002203 pretreatment Methods 0.000 claims description 3
- 239000010413 mother solution Substances 0.000 claims description 2
- 238000011045 prefiltration Methods 0.000 claims 1
- 239000012528 membrane Substances 0.000 description 25
- 150000001768 cations Chemical class 0.000 description 14
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 12
- GCICAPWZNUIIDV-UHFFFAOYSA-N lithium magnesium Chemical compound [Li].[Mg] GCICAPWZNUIIDV-UHFFFAOYSA-N 0.000 description 12
- 238000004064 recycling Methods 0.000 description 11
- 239000000243 solution Substances 0.000 description 9
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 8
- 239000007864 aqueous solution Substances 0.000 description 8
- 229910001414 potassium ion Inorganic materials 0.000 description 8
- 229910001415 sodium ion Inorganic materials 0.000 description 8
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical group [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 7
- 238000006243 chemical reaction Methods 0.000 description 7
- 238000000108 ultra-filtration Methods 0.000 description 7
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 6
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 description 6
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 6
- 229910001424 calcium ion Inorganic materials 0.000 description 6
- 150000003841 chloride salts Chemical class 0.000 description 6
- 238000004140 cleaning Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 239000012535 impurity Substances 0.000 description 6
- 239000007788 liquid Substances 0.000 description 6
- 229910001425 magnesium ion Inorganic materials 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 5
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 5
- 235000011941 Tilia x europaea Nutrition 0.000 description 5
- 150000002500 ions Chemical class 0.000 description 5
- 239000004571 lime Substances 0.000 description 5
- 238000001223 reverse osmosis Methods 0.000 description 5
- 239000007790 solid phase Substances 0.000 description 5
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 4
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- 229920001429 chelating resin Polymers 0.000 description 4
- 229910003002 lithium salt Inorganic materials 0.000 description 4
- 159000000002 lithium salts Chemical class 0.000 description 4
- 239000008267 milk Substances 0.000 description 4
- 210000004080 milk Anatomy 0.000 description 4
- 235000013336 milk Nutrition 0.000 description 4
- 239000011591 potassium Substances 0.000 description 4
- 239000011780 sodium chloride Substances 0.000 description 4
- 235000011121 sodium hydroxide Nutrition 0.000 description 4
- 229910000019 calcium carbonate Inorganic materials 0.000 description 3
- 239000013522 chelant Substances 0.000 description 3
- 238000005065 mining Methods 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 229910052700 potassium Inorganic materials 0.000 description 3
- 239000001103 potassium chloride Substances 0.000 description 3
- 235000011164 potassium chloride Nutrition 0.000 description 3
- 238000000746 purification Methods 0.000 description 3
- 239000011435 rock Substances 0.000 description 3
- 239000012266 salt solution Substances 0.000 description 3
- ODINCKMPIJJUCX-UHFFFAOYSA-N Calcium oxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 2
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 description 2
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical group [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 229910000029 sodium carbonate Inorganic materials 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910021653 sulphate ion Inorganic materials 0.000 description 2
- 238000005979 thermal decomposition reaction Methods 0.000 description 2
- 239000002918 waste heat Substances 0.000 description 2
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
- 239000000920 calcium hydroxide Substances 0.000 description 1
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 1
- USOPFYZPGZGBEB-UHFFFAOYSA-N calcium lithium Chemical compound [Li].[Ca] USOPFYZPGZGBEB-UHFFFAOYSA-N 0.000 description 1
- 239000000292 calcium oxide Substances 0.000 description 1
- 235000012255 calcium oxide Nutrition 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 239000006071 cream Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- GDVKFRBCXAPAQJ-UHFFFAOYSA-A dialuminum;hexamagnesium;carbonate;hexadecahydroxide Chemical compound [OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[OH-].[Mg+2].[Mg+2].[Mg+2].[Mg+2].[Mg+2].[Mg+2].[Al+3].[Al+3].[O-]C([O-])=O GDVKFRBCXAPAQJ-UHFFFAOYSA-A 0.000 description 1
- 238000007865 diluting Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000000909 electrodialysis Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000013505 freshwater Substances 0.000 description 1
- 229910052602 gypsum Inorganic materials 0.000 description 1
- 239000010440 gypsum Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000000887 hydrating effect Effects 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 229960001545 hydrotalcite Drugs 0.000 description 1
- 229910001701 hydrotalcite Inorganic materials 0.000 description 1
- 230000008676 import Effects 0.000 description 1
- 238000002386 leaching Methods 0.000 description 1
- VVNXEADCOVSAER-UHFFFAOYSA-N lithium sodium Chemical compound [Li].[Na] VVNXEADCOVSAER-UHFFFAOYSA-N 0.000 description 1
- INHCSSUBVCNVSK-UHFFFAOYSA-L lithium sulfate Inorganic materials [Li+].[Li+].[O-]S([O-])(=O)=O INHCSSUBVCNVSK-UHFFFAOYSA-L 0.000 description 1
- DHRRIBDTHFBPNG-UHFFFAOYSA-L magnesium dichloride hexahydrate Chemical compound O.O.O.O.O.O.[Mg+2].[Cl-].[Cl-] DHRRIBDTHFBPNG-UHFFFAOYSA-L 0.000 description 1
- 239000000347 magnesium hydroxide Substances 0.000 description 1
- 229910001862 magnesium hydroxide Inorganic materials 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
- 239000013618 particulate matter Substances 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000005185 salting out Methods 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 235000017557 sodium bicarbonate Nutrition 0.000 description 1
- 229910000030 sodium bicarbonate Inorganic materials 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- -1 target ions Chemical compound 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
- 210000003462 vein Anatomy 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Images
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention relates to a method and a system for extracting lithium from a salt lake, wherein the method for extracting lithium from the salt lake comprises the following steps: pretreating the raw brine; performing pre-nanofiltration on the pretreated raw brine, wherein the pre-nanofiltration comprises at least two nanofiltration processes; carrying out primary evaporation crystallization on the produced water subjected to pre-nanofiltration to obtain mother liquor containing lithium ions; carrying out multistage nanofiltration on the mother liquor, wherein the multistage nanofiltration comprises at least three nanofiltration processes, and carrying out secondary evaporation crystallization on produced water; performing secondary dialysis nanofiltration on part of concentrated water subjected to the multistage nanofiltration, and refluxing produced water to the multistage nanofiltration; carrying out first boron removal adsorption on the mother liquor subjected to secondary evaporation crystallization to obtain water for forming lithium carbonate precipitate; and mixing part of the concentrated water after the pre-nanofiltration with the concentrated water after the secondary dialysis and nanofiltration to recover and nanofiltration carbonate, refluxing the produced water to the pretreatment, and performing secondary boron removal adsorption on the concentrated water to mix the produced water after the secondary boron removal adsorption with the produced water after the primary boron removal adsorption to form lithium carbonate precipitate.
Description
Technical Field
The invention relates to the technical field of lithium extraction from salt lake brine, in particular to a method and a system for extracting lithium from a salt lake.
Background
The global lithium resource distribution is concentrated, the domestic lithium reserves in salt lakes are abundant, and lithium is widely applied to rechargeable batteries in the fields of mobile phones, notebook computers, electric vehicles and the like as white petroleum in a new era. With the increasing importance of the society on the development of new energy fields, the strategic economic value of lithium resources is further improved.
From the aspect of resource morphology, the global lithium resource supply source mainly comprises hard rock ore (including pegmatite type, dolomitic type, quartz vein type and sedimentary mud type), salt lake brine, underground brine, geothermal brine and the like. The salt lake brine is mainly concentrated in Argentina, chilean, america and Qinghai-Tibet region of China, and the lithium extraction from the salt lake brine has more cost advantage than the lithium extraction from hard rock ore, so that the method is a main way for producing lithium products in the world.
The salt lake brine contains a large amount of sodium, potassium, boron, magnesium and other elements besides lithium, so impurity ions need to be separated and purified in the lithium extraction process, and the salt lake lithium extraction technology is different at home and abroad due to different salt compositions, wherein the separation of magnesium and lithium is the most difficult. Compared with the lithium extraction from hard rock ore, the lithium extraction from the salt lake brine has more cost advantage. The lithium extraction from salt lake is carried out by extracting residual brine after extracting potassium element, extracting lithium ion or lithium chloride solution from old brine after extracting potassium by natural evaporating or concentrating by evaporator, and then preparing lithium carbonate product by adding carbonate.
Compared with the foreign countries, most of the salt lakes in China are mainly concentrated in Qinghai and Tibet, wherein the Qinghai salt lake brine has large resource reserve and better mining environment, but has high magnesium-lithium ratio, high sodium-lithium ratio and high separation difficulty, so that the lithium loss rate in the lithium extraction process is high, the development cost is high and the comprehensive mining utilization degree is low. The Tibet salt lake belongs to carbonate type salt mine, has better quality and lower magnesium-lithium ratio, for example, although the magnesium-lithium ratio of the Zaubu salt lake is as low as 0.019, the Zaubu salt lake is positioned on a plateau with the elevation of 4400 meters, the natural environment condition is poorer, and the mining difficulty is higher.
CN103074502A discloses a salt lake brine treatment method for separating lithium from salt lake brine with high magnesium-lithium ratio, comprising the steps of: performing multi-stage salt pan evaporation on the salt lake brine to obtain first old brine; and (3) removing sulfur: adding lime milk into the first old brine to separate out gypsum to obtain second old brine; evaporating the second old brine in a salt pan, and separating out bischofite to obtain third old brine; diluting the third old brine, and sending the third old brine into a nanofiltration membrane device for nanofiltration treatment to obtain lithium-rich produced water and lithium-poor concentrated water; and (4) delivering the produced water in the last step into a reverse osmosis membrane device for reverse osmosis treatment to obtain reverse osmosis concentrated water and fresh water.
CN105177288A discloses a method for preparing lithium hydroxide by using salt lake brine with high magnesium-lithium ratio, which comprises the following steps: the method comprises the steps of taking salt lake brine with a high magnesium-lithium ratio as a raw material, adding a certain amount of soluble trivalent metal salt, synthesizing a magnesium-based layered functional material to reduce the magnesium-lithium ratio of the salt lake brine with the high magnesium-lithium ratio, separating magnesium and lithium in the salt lake brine with the high magnesium-lithium ratio, removing magnesium in the brine, and preparing lithium hydroxide by using lithium-rich hydrotalcite mother liquor.
CN101508450 discloses a method for extracting lithium salt from salt lake brine with low ratio of magnesium to lithium by calcium circulation solid phase conversion method, which comprises: brine concentration: evaporating and concentrating the salt lake brine with low magnesium-lithium ratio; demagging with lime cream: concentrating brine, mixing the concentrated mother liquor with lime milk, carrying out solid phase conversion reaction, and removing magnesium in the mother liquor in a magnesium hydroxide form through solid phase conversion from calcium hydroxide to magnesium hydroxide; calcium separation by lithium carbonate: mixing the calcium-lithium solution after magnesium removal with solid lithium carbonate, carrying out solid phase conversion reaction, and separating and removing calcium in the solution in a calcium carbonate form through solid phase conversion from the lithium carbonate to the calcium carbonate to obtain a purified lithium salt solution; lithium salt concentration, precipitation crystallization, lithium carbonate and calcium carbonate thermal decomposition and hydration: evaporating and concentrating the purified lithium salt solution obtained in the step of separating calcium from lithium carbonate; adding sodium carbonate to react with the lithium carbonate to precipitate and crystallize lithium carbonate; and (3) performing thermal decomposition on the calcium carbonate obtained in the calcium separation step of the lithium carbonate to obtain quick lime, hydrating to obtain lime milk, and returning to the magnesium removal step of the lime milk for magnesium removal.
A plurality of processes are developed aiming at the technology of extracting lithium from salt lake brine, and each process has advantages in the aspects of cost, operation process, selectivity, energy consumption, recovery rate and the like, but has no small limitation. For example, the precipitation method has long process flow, large material consumption and complex operation, and is only suitable for salt lakes with low magnesium-lithium ratio. In the adsorption method, most of the adsorbent is powder, which causes poor flowability and adsorption property and easily causes reduction of adsorption property. The nanofiltration membrane method is easy to generate membrane pollution phenomenon during separation, so that the separation efficiency is reduced, and most of aluminum membranes with excellent performance depend on import, so that the cost is extremely high. The electrodialysis membrane method is difficult to separate univalent cations, easy to pollute and high in cost. The extraction method has long process flow, is easy to cause equipment corrosion, and the extractant generally has water solubility, flammability, easy volatilization and other physical and chemical properties. The solar pond and carbonization method is easily limited by geographical condition factors, has low reproducibility, is difficult to popularize in a large area, and actually produces a lithium product with low taste. The calcining leaching method has complex flow, easy corrosion of equipment and high energy consumption.
Therefore, in order to solve at least one or more technical problems in the prior art, a process and a system for extracting lithium from salt lake brine are urgently needed to be provided, and particularly a method suitable for purifying lithium ions in salt lake brine in high altitude areas such as Tibet.
Furthermore, on the one hand, due to the differences in understanding to the person skilled in the art; on the other hand, since the applicant has studied a great deal of literature and patents when making the present invention, but the disclosure is not limited thereto and the details and contents thereof are not listed in detail, it is by no means the present invention has these prior art features, but the present invention has all the features of the prior art, and the applicant reserves the right to increase the related prior art in the background.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method and a system for extracting lithium from a salt lake, and aims to solve at least one or more technical problems in the prior art.
In order to achieve the aim, the invention provides a method for extracting lithium from a salt lake, which comprises the following steps:
performing pre-nanofiltration on the pretreated raw brine, wherein the pre-nanofiltration comprises at least two nanofiltration processes;
carrying out primary evaporation crystallization on the water produced by the pre-nanofiltration so as to obtain a mother solution containing lithium ions;
subjecting the mother liquor to a multistage nanofiltration comprising at least three nanofiltration processes;
carrying out secondary evaporation crystallization on the produced water after the multi-stage nanofiltration;
performing secondary dialysis and nanofiltration on part of concentrated water after the multi-stage nanofiltration, and refluxing produced water after the secondary dialysis and nanofiltration to the multi-stage nanofiltration;
carrying out first boron removal adsorption on the mother liquor subjected to secondary evaporation crystallization to obtain water for forming lithium carbonate precipitate;
mixing part of the concentrated water after the pre-nanofiltration with the concentrated water after the secondary dialysis and nanofiltration to carry out carbonate recovery nanofiltration, refluxing the produced water after the carbonate recovery nanofiltration to the pretreatment, and carrying out secondary boron removal adsorption on the concentrated water after the carbonate recovery nanofiltration, so that the produced water after the secondary boron removal adsorption is mixed with the produced water after the first boron removal adsorption to form lithium carbonate precipitate.
Preferably, the pre-nanofiltration of the raw brine extracted from the salt lake, comprising at least two nanofiltration processes, is preceded by:
pre-treating raw brine extracted from a salt lake, and the pre-treating comprises:
carrying out heat exchange treatment on the raw brine to raise the temperature of the raw brine to a preset temperature;
carrying out multistage filtration on the heated raw brine to remove colloids and suspended matters in the raw brine;
and performing resin adsorption on the raw brine after the multistage filtration to reduce the hardness of calcium and magnesium in the water.
In particular, since the temperature of the raw brine of the salt lake water concentrated in the preconcentrated salt field is low, which is inconvenient for separation and filtration, the raw brine needs to be subjected to a certain degree of temperature rise treatment. Furthermore, impurities such as colloids and suspended matters in water are filtered through a filter, ultrafiltration membrane equipment and the like, the water hardness is reduced through resin adsorption, the subsequent nanofiltration separation treatment of anions and cations in water is facilitated, and the grade of a lithium ion purification product in the later stage is improved.
Preferably, the pre-nanofiltration of the pre-treated raw brine comprising at least two nanofiltration processes comprises:
carrying out primary nanofiltration on the pretreated raw brine to carry out primary separation on chloride ions, carbonate and sulfate radicals in the raw brine, wherein concentrated water obtained by the primary nanofiltration reflows to a salt lake;
and carrying out secondary nanofiltration on the water produced by the primary nanofiltration to carry out secondary separation on chloride ions, carbonate and sulfate radicals, wherein the water produced by the secondary nanofiltration flows to primary evaporation crystallization, and the concentrated water flow obtained by the secondary nanofiltration flows to carbonate for recycling and nanofiltration. Particularly, the concentrated water of the first-stage nanofiltration has high content of carbonate and sulfate (relatively small amount of chloride ions), so that the concentrated water needs to be refluxed to a salt lake, and in the process, waste heat can be recovered through heat exchange equipment to improve the energy utilization rate. Furthermore, due to the nature of the nanofiltration membrane, the pH of the water produced by the first-stage nanofiltration is lower than that of the water produced by the first-stage nanofiltration, so that the water produced by the first-stage nanofiltration contains part of bicarbonate, and the bicarbonate can be converted into carbonate through alkali liquor such as sodium hydroxide and the like so as to improve the corresponding concentration or content, so that chloride ions and carbonate are further separated through the second-stage nanofiltration, and the separation ratio or effect is improved. On the other hand, based on the difference of melting boiling points among potassium ions, sodium ions and lithium ions in the secondary nanofiltration produced water, the potassium ions and the sodium ions in the water are firstly separated into sodium chloride and potassium chloride crystals through once evaporation crystallization so as to be removed, and the lithium ions which are not separated out are further concentrated.
Preferably, subjecting the mother liquor to a multistage nanofiltration comprising at least three nanofiltration processes comprises:
carrying out third-stage nanofiltration on the mother liquor subjected to the primary evaporation crystallization to carry out third-stage separation on chloride ions, carbonate radicals and sulfate radicals, wherein the concentrated water obtained by the third-stage nanofiltration flows to the second-stage dialysis nanofiltration;
fourth-stage nanofiltration is carried out on the water produced by the third-stage nanofiltration so as to carry out fourth separation on chloride ions, carbonate radicals and sulfate radicals, wherein concentrated water produced by the fourth-stage nanofiltration flows to the second-stage dialysis nanofiltration;
and (3) performing fifth-stage nanofiltration on the fourth-stage nanofiltration produced water to perform fifth separation on chloride ions, carbonate and sulfate radicals, wherein the concentrated water of the fifth-stage nanofiltration flows to the middle salt pan, and the water produced by the fifth-stage nanofiltration flows to secondary evaporation crystallization. Particularly, after primary evaporation and crystallization, the concentration of lithium ions is increased, and in order to ensure that lithium carbonate is not separated out from the produced water during five-stage nanofiltration, the concentration of carbonate in the produced water is greatly reduced through three-stage nanofiltration, bicarbonate radical in the four-stage nanofiltration water is converted into lithium carbonate, and chloride ions, lithium ions and carbonate radical in the water are separated for multiple times through three-stage nanofiltration, four-stage nanofiltration and five-stage nanofiltration, so that the separation degree of the lithium ions and the carbonate radical is improved.
Preferably, the second-stage dialysis and nanofiltration of part of the concentrated water after the multi-stage nanofiltration comprises:
mixing the concentrated water obtained by the third stage nanofiltration with the concentrated water obtained by the fourth stage nanofiltration, and sequentially carrying out primary dialysis nanofiltration and secondary dialysis nanofiltration on the mixed concentrated water flow so as to separate and recover lithium ions and carbonate ions,
wherein, the produced water after the second-stage dialysis nanofiltration is provided to the water inlet end of the fourth-stage nanofiltration. Particularly, the content of carbonate in the water produced by the three-stage nanofiltration and the concentrated water produced by the four-stage nanofiltration is relatively high, so that the water needs to be further separated by the two-stage dialysis nanofiltration, lithium ions in the water flow back to the water inlet end of the four-stage nanofiltration, and the purification concentration and the quality of the lithium ions in the later stage are improved. Particularly, part of lithium ions and carbonate in the concentrated water after the multi-stage nanofiltration are not separated, so that the lithium ions and the carbonate in the concentrated water need to be separated and recovered again through the secondary dialysis and nanofiltration.
Preferably, before the second stage nanofiltration of the water produced by the first stage nanofiltration, the method further comprises the following steps:
and adjusting the pH of the first-stage nanofiltration water production by using alkali liquor so as to convert bicarbonate radical in the first-stage nanofiltration water production into carbonate radical.
Preferably, before the fourth stage nanofiltration is carried out on the third stage nanofiltration water production:
and adjusting the pH value of the third-stage nanofiltration water production through alkali liquor so as to convert bicarbonate radical in the third-stage nanofiltration water production into carbonate radical.
Preferably, after mixing the water produced after the second boron removal adsorption with the water produced after the first boron removal adsorption to form a lithium carbonate precipitate, the method further comprises:
filtering the supernatant liquid after the lithium carbonate precipitate is formed to form lithium precipitation mother liquid;
carrying out lithium precipitation and nanofiltration on the lithium precipitation mother liquor so as to separate and recover lithium ions and carbonate in the lithium precipitation mother liquor;
refluxing the water produced by the lithium precipitation and nanofiltration until lithium carbonate precipitate is formed; and
and (3) recycling carbonate from the concentrated water flow after the lithium precipitation and nanofiltration.
Preferably, the refluxing of the produced water after nanofiltration for carbonate recovery to pretreatment comprises:
and refluxing the produced water after the carbonate recovery and nanofiltration to a water inlet end of the multistage filtration so as to be mixed with the heated raw brine for multistage filtration.
Preferably, the present invention provides a salt lake lithium extracting system for implementing the salt lake lithium extracting method of the present invention, the system comprising:
the pretreatment unit is used for pretreating raw brine extracted from the salt lake;
a pre-nanofiltration unit for performing pre-nanofiltration of the pretreated raw brine including at least two nanofiltration processes;
the first evaporative crystallization device is used for carrying out primary evaporative crystallization on the produced water of the pre-nanofiltration so as to obtain mother liquor containing lithium ions;
a multi-stage nanofiltration unit for performing multi-stage nanofiltration on the mother liquor comprising at least three nanofiltration processes;
the second evaporation crystallization device is used for carrying out secondary evaporation crystallization on the produced water after the multi-stage nanofiltration;
the two-stage dialysis nanofiltration unit is used for carrying out two-stage dialysis nanofiltration on part of concentrated water subjected to the multi-stage nanofiltration and providing produced water to the multi-stage nanofiltration unit;
the first boron removal device is used for carrying out first boron removal adsorption on the mother liquor subjected to secondary evaporation crystallization to obtain water for forming lithium carbonate precipitate;
the recycling nanofiltration unit is used for carrying out carbonate concentration treatment on part of concentrated water provided by the pre-nanofiltration unit and concentrated water provided by the two-stage dialysis nanofiltration unit and providing produced water to flow back to the pretreatment unit;
and the second boron removing device is used for carrying out second boron removing adsorption on the concentrated water discharged by the recovery nanofiltration unit so as to provide water which is mixed with the water produced after the first boron removing adsorption to form lithium carbonate precipitate.
And the lithium precipitation nanofiltration unit is used for separating lithium ions and carbonate ions in the supernatant liquid provided by the lithium carbonate precipitation step and providing the produced water to flow back to the step of forming the lithium carbonate precipitation.
The beneficial technical effects of the invention comprise: firstly, carrying out temperature rise and impurity removal treatment on salt lake brine through pretreatment, then repeatedly separating monovalent anions and cations and divalent anions and cations in the brine through multi-stage nanofiltration for multiple times, firstly separating out a large amount of sodium ions and potassium ions through once evaporation crystallization in the multiple nanofiltration process, and then carrying out secondary evaporation crystallization on nanofiltration produced water to separate out and remove the remaining part of sodium ions and potassium ions so as to provide the produced water containing lithium ions with relatively high content. On the other hand, the concentrated water discharged from the whole multi-stage nanofiltration process contains carbonate ions with relatively high content. Specifically, the extraction of the lithium ions is realized by carrying out nanofiltration separation on carbonate ions and lithium ions in the brine for multiple times, respectively merging the flows, and finally mixing and reacting the carbonate ions and the lithium ions which are respectively separated to form lithium carbonate. For the salt lake brine with high magnesium-lithium ratio, the separation effect of anions and cations in the brine, particularly target ions, namely carbonate ions and lithium ions, is improved by performing nanofiltration separation for multiple times and performing circulating reflux on treatment products in part of process stages, so that the lithium ions in the brine can be recovered to the greatest extent, the waste of lithium resources is reduced, the quality of lithium products is improved, the pollution to the environment is reduced by recycling the reflux products, and the cost is greatly saved compared with the traditional membrane separation process.
Drawings
FIG. 1 is a process flow diagram of a method for extracting lithium from a salt lake according to a preferred embodiment of the invention.
List of reference numerals
1: a heat exchanger; 2: a multi-media filter; 3: a self-cleaning filter; 4: an ultrafiltration membrane device; 5: a chelating resin tower; 6: a first-stage nanofiltration device; 7: a secondary nanofiltration device; 8: middle salt pan; 9: a first evaporative crystallization device; 10: a three-stage nanofiltration device; 11: a four-stage nanofiltration device; 12: a five-stage nanofiltration device; 13: a second evaporative crystallization device; 14: a first boron removal device; 15: a two-stage dialysis nanofiltration unit; 16: a nanofiltration unit is recovered; 17: a second boron removal device; 18: a filtration device; 19: a lithium precipitation nanofiltration unit; 20: a lithium sinking workshop; 21: a salt lake; 100: raw brine; 200: producing water; 300: concentrated water; 400: mother liquor; 500: a chloride salt; 600: lithium carbonate; 700: supernatant fluid; 800: and (4) precipitating lithium mother liquor.
Detailed Description
The following detailed description is made with reference to the accompanying drawings.
The invention provides a method for extracting lithium from a salt lake, and figure 1 shows a process flow of the method for extracting lithium from the salt lake and a connection schematic diagram of a salt lake lithium extraction system corresponding to the method for extracting lithium from the salt lake. Particularly, the method for extracting lithium from the salt lake is particularly suitable for extracting lithium ions from salt lake brine in altitude areas such as Tibet and the like.
Specifically, as shown in fig. 1, the method for extracting lithium from a salt lake of the present invention may include: the raw brine 100 to be treated is provided from a salt lake 21. Further, the raw brine 100 enters a pretreatment unit for temperature rise and impurity removal pretreatment.
According to a preferred embodiment, the temperature of the raw brine 100 after the salt lake water is concentrated by the pre-concentrated salt pan is low (average-0.4 ℃), so that the temperature needs to be raised in advance for the subsequent process treatment. Specifically, the raw brine 100 is heated to about 30 ℃ by the heat exchanger 1. In particular, in the present invention, the heat exchanger 1 may be a plate heat exchanger. The heat exchanger 1 may for example be a plate heat exchanger of the PLP30 type.
According to a preferred embodiment, as shown in fig. 1, the raw brine 100 heated by the heat exchanger 1 flows through the multi-media filter 2, the self-cleaning filter 3 and the ultrafiltration membrane device 4 in sequence to filter out colloids and suspended particulate matters in the raw brine 100. In particular, the multimedia filter 2 may be, for example, a type LF-SYS500 multimedia filter. The self-cleaning filter 3 may be, for example, a JSY-AC20 type self-cleaning filter. The ultrafiltration membrane apparatus 4 may be, for example, a SUF-102NS type ultrafiltration membrane apparatus.
According to a preferred embodiment, as shown in fig. 1, the raw brine 100 from which the colloid and suspended particulate matter are filtered out is introduced into a chelating resin tower 5 to reduce the hardness of calcium and magnesium in the raw brine 100 by the replacement reaction of chelating resin with a part of metal ions in the raw brine 100. Further, the raw brine 100 enters a subsequent pre-nanofiltration unit for further filtration and separation treatment. The chelate resin column 5 may be, for example, an RTF type chelate resin column.
According to a preferred embodiment, the effluent after pretreatment is required to be, for example, mg 2+ The content is less than 20mg/L. SDI is less than 3. Turbidity was less than 0.1NTU. The discharge pressure is not less than 0.4MPaG.
According to a preferred embodiment, the requirements for the resin include, for example: the absolute value of the difference between the effective particle diameters of the resins is not more than 0.1mm. The wet true density difference of the resin is more than or equal to 0.15g/ml. The resin has temperature resistance of more than or equal to 75 ℃ and pressure resistance of more than or equal to 0.80MPa.
According to a preferred embodiment, as shown in fig. 1, the pre-nanofiltration unit according to the present invention may comprise a primary nanofiltration device 6 and a secondary nanofiltration device 7 connected in series. Specifically, the raw brine 100 enters the first-stage nanofiltration device 6, so that monovalent chloride ions, divalent carbonate and sulfate radicals in the raw brine 100 are separated by the first-stage nanofiltration device 6. Particularly, the rejection rate of the first-stage nanofiltration device 6 to sulfate radicals is about 97%, and the rejection rate of the first-stage nanofiltration device 6 to carbonate radicals is about 85%.
Further, as shown in fig. 1, the concentrated water 300 (containing a large amount of carbonate and sulfate) discharged after the raw brine 100 is filtered and separated by the primary nanofiltration device 6 is returned to the salt lake 21 after the waste heat is recovered by the heat exchange device (e.g. plate heat exchanger) so as to be mixed with the salt lake water in the salt lake 21, thereby recycling the pretreatment and the primary nanofiltration process.
On the other hand, the raw brine 100 is filtered and separated by the primary nanofiltration device 6, and the discharged produced water 200 enters the secondary nanofiltration device 7 for further filtering and separation treatment. Specifically, based on the nature of the nanofiltration membrane, the PH of the product water 200 discharged after the raw brine 100 is treated by the primary nanofiltration device 6 is lower than the previous value, i.e., the product water 200 contains a small amount of bicarbonate and carbonate. Before the second-stage nanofiltration influent water (the water 200 produced by the first-stage nanofiltration device 6) enters the second-stage nanofiltration device 7, the PH of the second-stage nanofiltration influent water is adjusted by liquid alkali (for example, 20% sodium hydroxide solution), that is, after bicarbonate is converted into carbonate, the second-stage nanofiltration influent water (the water 200 produced by the first-stage nanofiltration device 6) is conveyed to the second-stage nanofiltration device 7 for treatment.
According to a preferred embodiment, as shown in fig. 1, the produced water 200 of the first stage nanofiltration device 6 is subjected to PH adjustment by liquid caustic soda, and then enters the second stage nanofiltration device 7 for further filtration and separation treatment, so as to further separate monovalent chloride ions and divalent carbonate ions.
According to a preferred embodiment, the pre-nanofiltration unit discharge requires for example: the content of sulfate radicals is less than 0.05g/L, and the content of carbonate radicals is less than 0.3g/L. The lithium ion recovery rate is not less than 36%. The effluent pressure is not less than 0.4MpaG. The water yield at the outlet is not less than 456m < 3 >/h.
According to a preferred embodiment, as shown in fig. 1, the produced water 200 (containing only a small amount of divalent anions, such as sulfate and carbonate, and a large amount of monovalent cations, such as chloride) discharged from the secondary nanofiltration device 7 flows into the intermediate salt pan 8, and further enters the first crystallization evaporation device 9 for evaporation and crystallization. Specifically, the produced water 200 discharged from the secondary nanofiltration device 7 enters the first crystallization evaporation device 9 to be crystallized sequentially to separate out the chloride salt 500 (sodium chloride and potassium chloride). Further, when the chloride salt 500 is precipitated, lithium ions are not precipitated, and at this time, the produced water 200 is evaporated and crystallized to discharge the mother liquor 400 containing lithium ions. The mother liquor 400 after evaporation and crystallization at low temperature (about 8 ℃) enters a multi-stage nanofiltration system for further filtration and separation treatment. In particular, the mother liquor 400 is concentrated by lithium ions, sulfate and carbonate ions, and the like, after evaporation and crystallization.
On the other hand, as shown in fig. 1, the concentrated water 300 (containing carbonate) discharged from the secondary nanofiltration device 7 enters a recovery nanofiltration unit 16 for subsequent treatment. Specifically, as shown in fig. 1, the recovery nanofiltration unit 16 further concentrates carbonate in the concentrated water 300 discharged from the secondary nanofiltration device 7. Further, the produced water 200 discharged from the recovery nanofiltration unit 16 is returned to the pretreatment unit and, in particular, to the water inlet side of the multimedia filter 2.
Further, as shown in fig. 1, the multi-stage nanofiltration unit of the present invention may include a three-stage nanofiltration device 10, a four-stage nanofiltration device 11, and a five-stage nanofiltration device 12. Specifically, the mother liquor 400 discharged from the first crystallization evaporation device 9 is subjected to temperature rise treatment and then enters the third-stage nanofiltration device 10, so that monovalent chloride ions, divalent carbonate radicals and sulfate radicals in the incoming water (mother liquor 400) are filtered and separated by the third-stage nanofiltration device 10.
According to a preferred embodiment, as shown in fig. 1, the produced water 200 discharged from the three-stage nanofiltration device 10 enters a four-stage nanofiltration device 11 for further filtration and separation treatment. Specifically, before entering the fourth-stage nanofiltration device 11, the PH of the water from the fourth-stage nanofiltration (the water 200 discharged from the third-stage nanofiltration device 10) is adjusted by liquid alkali to convert bicarbonate therein into carbonate, i.e., convert sodium bicarbonate into sodium carbonate. Further, the water from the fourth-stage nanofiltration (the water 200 discharged from the third-stage nanofiltration device 10) enters a fourth-stage nanofiltration device 11 to further separate monovalent chloride ions and divalent carbonate ions.
According to a preferred embodiment, as shown in fig. 1, the water from the five-stage nanofiltration (the produced water 200 discharged from the four-stage nanofiltration device 11) enters the five-stage nanofiltration device 12 to further separate monovalent chloride ions and divalent carbonate radicals.
According to a preferred embodiment, as shown in fig. 1, the concentrate 300 discharged from the five-stage nanofiltration device 12 is returned to the intermediate salt pan 8. The produced water 200 discharged from the five-stage nanofiltration device 12 enters a second evaporative crystallization device 13, and then the chloride salt 500 (sodium chloride and potassium chloride) is crystallized and separated out. At this time, the produced water 200 is evaporated and crystallized by the second evaporation and crystallization device 13, and then the mother liquor 400 containing lithium ions is discharged. Further, the mother liquor 400 enters the first boron removal device 14 for further processing.
According to a preferred embodiment, the following table shows the elemental composition (in g/L) of the feed water to the multi-stage nanofiltration unit in an alternative embodiment.
In particular, since the lithium ion concentration is increased after the treatment of the first evaporative crystallization device 9 in the previous stage, and lithium carbonate is not precipitated when the five-stage nanofiltration product water passes through the second evaporative crystallization device 13, the mother liquor 400 needs to be treated by the third nanofiltration device 10 to reduce the carbonate concentration (carbonate content < 100 mg/L) in the nanofiltration product water entering the second evaporative crystallization device 13.
According to a preferred embodiment, the discharge requirements of the five-stage nanofiltration device 12 are, for example: and the catalyst does not contain bicarbonate and carbonate. The boron content is less than 20mg/L. The lithium ion recovery rate is not less than 95%. The pressure of the five-stage nanofiltration concentrated water, the five-stage nanofiltration water production and the second-stage dialysis nanofiltration concentrated water is not less than 0.4MPaG.
According to a preferred embodiment, as shown in FIG. 1, the mother liquor 400 discharged from the second evaporative crystallization device 13 enters the first boron removal device 14 to carry out boron removal resin adsorption on the mother liquor 400. In particular, the mother liquor 400 entering the first boron removal device 14 at this time contains a large amount of lithium ions after being subjected to multi-stage nanofiltration and multi-stage evaporative crystallization. Further, as shown in fig. 1, the mother liquor 400 treated by the first boron removing device 14 enters the lithium precipitation plant 20 for further treatment. Specifically, the mother liquor 400 (containing a large amount of lithium ions) forms a lithium carbonate precipitate after the lithium precipitation plant 20 is subjected to precipitation treatment.
According to a preferred embodiment, as shown in fig. 1, a supernatant 700 discharged from a lithium precipitation plant 20 after a lithium precipitation treatment is processed by a filtering device 18 to form a lithium precipitation mother liquor 800, and the lithium precipitation mother liquor 800 enters a lithium precipitation nanofiltration unit 19 for further processing.
Further, as shown in fig. 1, after the lithium precipitation mother liquor 800 is processed by the lithium precipitation nanofiltration unit 19, the discharged produced water 200 is returned to the lithium precipitation plant 20 for reaction to form lithium carbonate precipitate. On the other hand, concentrated water 300 discharged from lithium precipitation nanofiltration unit 19 enters recovery nanofiltration unit 16 to further concentrate carbonate ions in concentrated water 300 through recovery nanofiltration unit 16.
According to a preferred embodiment, as shown in fig. 1, the feed to the pre-nanofiltration unit comprises three streams, respectively concentrated water 300 of the primary nanofiltration device 6, produced water 200 of the recovery nanofiltration unit 16 and flash condensate discharged from the evaporative crystallization devices (9, 13). In particular, the following table shows the elemental composition (in g/L) of the feed water to the pre-nanofiltration unit in an alternative embodiment.
According to a preferred embodiment, as shown in fig. 1, recovery nanofiltration unit 16 is used to treat concentrated water 300 exiting secondary nanofiltration device 7, two-stage dialysis nanofiltration unit 15 and lithium precipitation nanofiltration unit 19. Specifically, the recovery nanofiltration unit 16 processes the three mixed concentrated water streams to perform carbonate concentration treatment. Further, the produced water 200 discharged from the recycling nanofiltration unit 16 is refluxed to the water inlet end of the multi-media filter 2, so that the part of the produced water 200 is recycled for the pretreatment, the multi-stage nanofiltration, the evaporative crystallization, the boron removal adsorption, the lithium precipitation nanofiltration treatment and the like. On the other hand, the concentrated water 300 discharged from the recovery nanofiltration unit 16 enters the second boron removal device 17 to be subjected to adsorption by the boron removal resin. Specifically, the concentrate 300 entering the second boron removal device 17 at this time is a mixed concentrate stream obtained by multiple nanofiltration separations in the previous stage, and contains a large amount of carbonate ions.
The following table shows, according to a preferred embodiment, the respective elemental compositions (in g/L) of the feed water of the recovery nanofiltration unit 16, in an alternative embodiment.
According to a preferred embodiment, the discharge requirements of the recovery nanofiltration unit 16 are, for example: and recycling nanofiltration produced water and recycling nanofiltration concentrated water without bicarbonate radical. The content of carbonate in the recovered nanofiltration produced water is less than 0.5g/L. The pressure of the recovered nanofiltration produced water and the recovered nanofiltration concentrated water is not less than 0.4MPaG.
According to a preferred embodiment, the first boron removing device 14 is used for performing boron removing adsorption treatment on the mother liquor 400 discharged from the second evaporative crystallization device 13. In particular, the mother liquor 500 entering the first boron removal device 14 contains a large amount of lithium ions. The second boron removing device 17 is used for carrying out boron removing adsorption treatment on the concentrated water 300 discharged from the recovery nanofiltration unit 16. Specifically, the concentrated water 300 entering the second boron removal device 17 contains a large amount of carbonate ions.
According to a preferred embodiment, the following table shows the elemental composition (in g/L) of the feed water to the first and second boron removal devices 14, 17 in an alternative embodiment.
According to a preferred embodiment, the discharge requirements of the first boron removal device 14 are for example: b in boron-removing produced water - The content is less than 10ppm. The lithium recovery rate is more than or equal to 98 percent. The water pressure of the boron-removing produced water is not less than 0.4MPaG. The discharge requirements of the second boron removal device 17 are, for example: boron-removing water B - The content is less than 10ppm. The water outlet pressure of the boron-removing water is not less than 0.4MpaG.
Further, after the produced water 200 discharged from each of the first boron removing device 14 and the second boron removing device 17 enters the lithium precipitation factory 20, the produced water is mixed according to a preset proportion to form lithium carbonate precipitation through reaction. As shown in fig. 1, the supernatant 700 after lithium precipitation enters a lithium precipitation nanofiltration unit 19 after being filtered. The produced water 200 discharged from the lithium precipitation nanofiltration unit 19 is returned to the lithium precipitation plant 20 to circulate the lithium carbonate precipitation reaction. Concentrated water 300 discharged from the lithium precipitation nanofiltration unit 19 enters a recovery nanofiltration unit 16 to recycle the carbonate concentration treatment.
According to a preferred embodiment, the following table shows the elemental composition (in g/L) of the feed water to the precipitated lithium nanofiltration unit 19 in an alternative embodiment.
According to a preferred embodiment, the discharge requirements of the lithium precipitation nanofiltration unit 19 are for example: lithium ions are kept on the water producing side as much as possible, and the recovery rate of lithium is more than or equal to 90 percent. The content of carbonate in the lithium precipitation nanofiltration produced water is less than 0.5g/L. The pressure of the lithium-precipitating nanofiltration produced water and the pressure of the lithium-precipitating nanofiltration concentrated water are not less than 0.4MPaG.
Specifically, in the present invention, multiple nanofiltration is performed to repeatedly separate monovalent anions and cations and divalent anions and cations, wherein the water 200 produced after nanofiltration generally contains relatively high contents of chloride ions, lithium ions, potassium ions, and sodium ions, and relatively low contents of carbonate ions, bicarbonate ions, and sulfate ions. The concentrated water 300 after nanofiltration generally contains relatively high contents of carbonate, bicarbonate and sulfate ions, and relatively low contents of chloride, lithium, potassium and sodium ions. Particularly, in the present invention, carbonate ions and lithium ions in the raw brine 100 are separated for a plurality of times, respectively, and merged, and finally the carbonate ions and lithium ions separated respectively are mixed and reacted to form lithium carbonate, thereby realizing extraction of lithium ions.
According to a preferred embodiment, as mentioned above, the process for extracting lithium from salt lake of the present invention involves a process of circulating reflux treatment of multiple concentrated water 300 and produced water 200, which specifically comprises: the concentrated water 300 discharged from the primary nanofiltration device 6 flows back to the salt lake 21 to be mixed with the raw brine 100, and then the pretreatment, the nanofiltration treatment and the like are circulated. The produced water 200 discharged after the recycling nanofiltration unit 16 carries out carbonate concentration treatment flows back to the water inlet unit of the multi-media filter 2. The concentrated water 300 discharged after the recycling nanofiltration unit 16 performs carbonate concentration treatment enters a second boron removal device 17 and is circulated for the lithium precipitation treatment. Preferably, the brine treated in each stage is circulated and refluxed, so that the recovery rate of the whole lithium ion purification process is improved.
According to a preferred embodiment, as shown in fig. 1, the present invention relates to a salt lake lithium extracting system, which may include:
and the pretreatment unit is used for heating the raw brine 100, filtering out impurity particles in the raw brine and reducing the hardness of calcium and magnesium.
A pre-nanofiltration unit comprising at least two nanofiltration for separating chloride and carbonate in the raw brine 100 provided by the pre-treatment unit and providing produced water 200 to the first evaporative crystallization device 9 and part of the concentrated water 300 to the recovery nanofiltration unit 16.
A first evaporative crystallization device 9 for extracting sodium ions and potassium ions in the produced water 200 provided from the pre-nanofiltration unit to convert them into chloride salts 500, and providing a mother liquor 400 containing lithium ions to the multi-stage nanofiltration unit.
And the multi-stage nanofiltration unit comprises at least three times of nanofiltration for separating chloride ions and carbonate ions in the produced water 200 provided by the first evaporative crystallization device 9, providing the produced water 200 to the second evaporative crystallization device 13 and providing part of the concentrated water 300 to the two-stage dialysis nanofiltration unit 15.
And a second evaporative crystallization device 13 for extracting sodium ions and potassium ions in the produced water 200 provided by the multi-stage nanofiltration unit to convert them into chloride salts 500, and providing a mother liquor 400 containing lithium ions to the first boron removal device 14.
A two-stage dialysis nanofiltration unit 15 for separating lithium ions and carbonate ions from a portion of the concentrate 300 provided by the multi-stage nanofiltration unit and providing a product water 200 back to the multi-stage nanofiltration unit and providing the concentrate 300 to the recovery nanofiltration unit 16.
The first boron removal device 14 is used for carrying out boron removal resin adsorption on the mother liquor 400 provided by the second evaporative crystallization device 13 and providing the produced water 200 to the lithium deposition factory 20.
And the recovery nanofiltration unit 16 is used for carrying out carbonate concentration treatment on the concentrated water 300 provided by the pre-nanofiltration unit and the two-stage dialysis nanofiltration unit 15, providing the produced water 200 to flow back to the pretreatment unit and providing the concentrated water 300 to the second boron removal device 17.
And the second boron removal device 17 is used for carrying out boron removal resin adsorption on the concentrated water 300 provided by the recovery nanofiltration unit 16 and providing the produced water 200 to the lithium precipitation plant 20.
And the lithium precipitation plant 20 is used for mixing the produced water provided by the first boron removal device 14 and the second boron removal device 17 according to a preset proportion to form lithium carbonate precipitate, and providing the supernatant 700 to the lithium precipitation nanofiltration unit 19.
And the lithium precipitation nanofiltration unit 19 is used for separating lithium ions and carbonate ions in the supernatant 700 provided by the lithium precipitation plant 20, providing produced water 200 to flow back to the lithium precipitation plant 20 and providing concentrated water 300 to flow back to the recovery nanofiltration unit 16.
According to a preferred embodiment, as shown in fig. 1, the pretreatment unit may include a heat exchanger 1, a multimedia filter 2, a self-cleaning filter 3, an ultrafiltration membrane apparatus 4, and a chelate resin column 5, which are connected in series. Specifically, the raw brine 100 is first heated by the heat exchanger 1. Further, the raw brine 100 flows through the multi-media filter 2, the self-cleaning filter 3 and the ultrafiltration membrane device 4 in sequence to filter out colloids and suspended particles in the raw brine 100. The raw brine 100 thereafter enters the chelating resin tower 5 for reducing the calcium and magnesium hardness in the water.
According to a preferred embodiment, as shown in fig. 1, the pre-nanofiltration unit may comprise a primary nanofiltration device 6 and a secondary nanofiltration device 7. Specifically, the raw brine 100 sequentially passes through the primary nanofiltration device 6 and the secondary nanofiltration device 7, so that monovalent chloride ions, secondary carbonate ions and sulfate ions in the raw brine 100 are separated in the primary nanofiltration device 6 and the secondary nanofiltration device 7 respectively. Further, the concentrated water 300 produced by the first-stage nanofiltration device 6 flows back to the salt lake 21. Concentrated water 300 produced by the secondary nanofiltration device 7 enters a recovery nanofiltration unit 16.
According to a preferred embodiment, as shown in fig. 1, the multi-stage nanofiltration unit may include a three-stage nanofiltration device 10, a four-stage nanofiltration device 11, and a five-stage nanofiltration device 12. Specifically, the produced water discharged from the secondary nanofiltration device 7 in the nanofiltration unit is first subjected to evaporative crystallization treatment by the first crystallization evaporation device 9 to discharge a mother liquor 400 containing lithium ions. Further, the mother liquor 400 sequentially passes through the third nanofiltration device 10, the fourth nanofiltration device 11 and the fifth nanofiltration device 12 to filter monovalent chloride ions, divalent carbonate ions and sulfate ions in the mother liquor 400 through each stage of nanofiltration for multiple times.
In particular, the concentrated water 300 discharged from the three-stage nanofiltration device 10 and the four-stage nanofiltration device 11 is mixed and enters the two-stage dialysis nanofiltration unit 15 for recovering or separating monovalent lithium ions and divalent carbonate in the incoming water. Specifically, the two-stage dialysis nanofiltration unit 15 may include a first-stage dialysis nanofiltration device and a second-stage dialysis nanofiltration device connected in sequence, and the concentrated water 300 sequentially enters the first-stage dialysis nanofiltration device and the second-stage dialysis nanofiltration device to perform separation treatment of target ions. Further, the produced water 200 (containing more lithium ions) of the two-stage dialysis nanofiltration unit 15 flows back to the water inlet end of the four-stage nanofiltration device 11. The concentrated water 300 (containing more carbonate ions) discharged from the two-stage dialysis nanofiltration unit 15 enters a recovery nanofiltration unit 16.
On the other hand, the concentrated water 300 discharged through the five-stage nanofiltration device 12 in the multi-stage nanofiltration unit is refluxed to the middle salt pan 8 downstream of the two-stage nanofiltration device 7.
According to a preferred embodiment, although a large amount of calcium and magnesium is removed by the pretreatment process before the nanofiltration separation of the brine containing calcium and magnesium impurities, it is not guaranteed that the raw brine 100 entering the nanofiltration stage does not contain any calcium and magnesium ions, even if its content is reduced to a negligible level. If the content of calcium and magnesium in the lithium-containing product finally extracted is high, the quality of the lithium carbonate product is affected, and especially for the industrial-grade lithium carbonate product, the requirement is stricter. These technical grade lithium carbonate products are generally used as raw materials of battery grade lithium carbonate, and when the content of calcium and magnesium is too high, the use of the battery grade lithium carbonate has higher risk and the performance of the battery grade lithium carbonate is obviously reduced. Therefore, the contents of calcium ions and magnesium ions also need to be strictly controlled in the nanofiltration separation stage so as to reduce the influence on the quality of lithium carbonate.
According to a preferred embodiment, the nanofiltration separation is used for anion and cation separation of brine based on the selective permeability of nanofiltration membranes to ions of different valence states. Generally, nanofiltration membranes are more prone to reject divalent ions. In most cases, the selective rejection of divalent anions (including sulfate, carbonate) by nanofiltration membranes may be better than divalent cations (including calcium, magnesium). Therefore, when the raw brine 100 is subjected to anion-cation separation by each nanofiltration device (6, 7,10,11, 12), more divalent anions (including sulfate, carbonate) may be more easily filtered out than divalent cations (including calcium, magnesium). In particular, the separation rejection effect for divalent cations may be worse after the concentration of divalent anions in the incoming water is continuously decreased.
According to a preferred embodiment, the separation rejection of the nanofiltration membrane against dianions (e.g. sulphate, carbonate) will generate electrostatic adsorption when the concentration of the dianions (e.g. sulphate, carbonate) in the incoming water is a certain percentage higher than the Total Dissolved Solids (TDS), e.g. calcium, magnesium. The electrostatic adsorption can improve the separation and repulsion action of the nanofiltration membrane on divalent cations (including calcium ions and magnesium ions), especially under the condition that the divalent cations in the residual produced water are low. In particular, the concentration percentage of divalent anions (e.g., sulfate, carbonate) compared to Total Dissolved Solids (TDS) can be determined by the designer through a limited number of experimental analyses.
According to a preferred embodiment, the concentration of divalent anions (e.g., sulfate, carbonate) is generally higher in the raw brine 100 than the concentration of Total Dissolved Solids (TDS). When the raw brine 100 is subjected to nanofiltration separation by, for example, the primary nanofiltration device 6, the content of divalent anions in the produced water 200 of the primary nanofiltration device 6 is reduced, and the hardness is reduced. However, when the produced water 200 of the primary nanofiltration device 6 enters the secondary nanofiltration device 7, the hardness of the produced water 200 of the secondary nanofiltration device 7 may not be significantly reduced, and a desired softening degree may not be achieved. The reason is that the raw brine 100 has been filtered to remove a large amount of divalent anions (including sulfate and carbonate) by the primary nanofiltration device 6, and the concentration difference between the divalent anions and the Total Dissolved Solids (TDS) in the incoming water (the produced water 200 of the primary nanofiltration device 6) of the secondary nanofiltration device 7 is smaller than that of the incoming water of the primary nanofiltration device 6, so that no obvious electrostatic adsorption is generated, and the separation and rejection effects of the nanofiltration membrane on calcium ions and magnesium ions are remarkably reduced.
According to a preferred embodiment, in order to increase the filtering effect of the downstream nanofiltration device on calcium ions and magnesium ions in the incoming water, an aqueous solution containing divalent anions (including sulfate and carbonate) with a preset concentration can be mixed into the produced water of the upper nanofiltration device before the produced water of the upper nanofiltration device enters the lower nanofiltration device. Specifically, according to the concentration value of Total Dissolved Solids (TDS) in the produced water of the upper-stage nanofiltration device, the concentrated value of the aqueous solution containing divalent anions (including sulfate and carbonate) and the concentration value of the current Total Dissolved Solids (TDS) are kept in a preset concentration ratio interval and mixed into the produced water of the upper-stage nanofiltration device. For example, the concentration of the divalent anion (including sulfate, carbonate) containing aqueous solution mixed into the production water of the upper nanofiltration device may be 0.7 to 0.9 times or more the concentration of Total Dissolved Solids (TDS) therein. Preferably, when the concentration of the divalent anions (including sulfate and carbonate) and the concentration of the Total Dissolved Solids (TDS) in the water are kept in a preset concentration ratio range, the divalent anions (including sulfate and carbonate) and the Total Dissolved Solids (TDS) have no larger concentration difference. Further, when the filtering for the divalent anions (including sulfate and carbonate) is provided by the nanofiltration membrane, the nanofiltration membrane generates electrostatic adsorption for the separation rejection of the divalent anions (including sulfate and carbonate), and the electrostatic adsorption promotes the separation rejection of the nanofiltration membrane for soluble total solids (including calcium ions and magnesium ions), so that the water hardness of upstream produced water or downstream water is obviously improved.
According to a preferred embodiment, in particular, the aqueous solution containing divalent anions (including sulfate, carbonate) can come partly from the nanofiltration concentrate water of each stage. Preferably, the aqueous solution containing divalent anions (including sulfate and carbonate) can be obtained from the concentrated water of the first-stage nanofiltration, and the content of the sulfate and the carbonate in the concentrated water of the first-stage nanofiltration is relatively high. Preferably, the molar concentration of divalent anions (including sulfate and carbonate) in the concentrated water of the first-stage nanofiltration can be adjusted through solution configuration. Mixing part of water solution containing divalent anions (including sulfate radicals and carbonate radicals) in the original brine 100 into the incoming water of the next-stage nanofiltration device, not only can be used for remarkably reducing the hardness of the produced water of the next-stage nanofiltration device, but also can realize the recycling of substances and reduce the input consumption of resources outside the system.
Preferably, the present invention comprises a multistage nanofiltration process. Before any stage of nanofiltration water production enters a next stage nanofiltration device, the hardness of the water production after multi-stage nanofiltration is obviously reduced by mixing an aqueous solution containing divalent anions (including sulfate and carbonate) and keeping the concentration value of the aqueous solution and the concentration value of dissolved total solids (TDS) in the aqueous solution within a preset concentration ratio range.
According to a preferred embodiment, the salt lake lithium extraction system of the present invention may further comprise a pure water reverse osmosis unit (not shown in the figure). The pure water reverse osmosis unit is used for preparing a pure water solvent for providing a prepared alkali solution (a sodium hydroxide solution) and a prepared salt solution (a sodium chloride solution).
It should be noted that the above-mentioned embodiments are exemplary, and that those skilled in the art, having benefit of the present disclosure, may devise various arrangements that are within the scope of the present disclosure and that fall within the scope of the invention. It should be understood by those skilled in the art that the present specification and figures are illustrative only and are not limiting upon the claims. The scope of the invention is defined by the claims and their equivalents. The present description contains several inventive concepts, such as "preferably", "according to a preferred embodiment" or "optionally", each indicating that the respective paragraph discloses a separate concept, the applicant reserves the right to submit divisional applications according to each inventive concept.
Claims (10)
1. A method for extracting lithium from a salt lake is characterized by comprising the following steps:
subjecting raw brine (100) extracted from a salt lake (21) to pre-nanofiltration comprising at least two nanofiltration processes;
carrying out primary evaporative crystallization on the produced water (200) of the pre-nanofiltration so as to obtain a mother solution (400) containing lithium ions;
subjecting the mother liquor (400) to a multistage nanofiltration comprising at least three nanofiltration processes;
carrying out secondary evaporation crystallization on the produced water (200) after the multistage nanofiltration;
performing secondary dialysis and nanofiltration on part of the concentrated water (300) subjected to the multi-stage nanofiltration, and refluxing the produced water (200) subjected to the secondary dialysis and nanofiltration to the multi-stage nanofiltration;
carrying out first boron removal adsorption on the mother liquor (400) after the secondary evaporation and crystallization to obtain water (200) for forming lithium carbonate precipitate;
mixing part of the concentrated water (300) after the pre-filtration with the concentrated water (300) after the secondary dialysis and nanofiltration to perform carbonate recovery and nanofiltration, refluxing the produced water (200) after the carbonate recovery and nanofiltration to the pre-treatment, and performing second boron removal adsorption on the concentrated water (300) after the carbonate recovery and nanofiltration, so that the produced water (200) after the second boron removal adsorption is mixed with the produced water (200) after the first boron removal adsorption to form lithium carbonate precipitate.
2. The method according to claim 1, wherein prior to the pre-nanofiltration of the raw brine (100) extracted from the salt lake (21) comprising at least two nanofiltration processes further comprises:
pre-treating raw brine (100) extracted from a salt lake (21), and the pre-treatment comprises:
carrying out heat exchange treatment on the raw brine (100) to raise the temperature of the raw brine to a preset temperature;
carrying out multistage filtration on the heated raw brine (100) to remove colloids and suspended matters in the raw brine;
and (3) performing resin adsorption on the raw brine (100) after the multistage filtration to reduce the hardness of calcium and magnesium in the water.
3. The method according to claim 1 or 2, wherein said subjecting the pre-treated raw brine (100) to pre-nanofiltration comprising at least two nanofiltration processes comprises:
carrying out primary nanofiltration on the pretreated raw brine (100) to carry out primary separation on chloride ions, carbonate and sulfate radicals in the raw brine (100), wherein concentrated water (300) obtained by the primary nanofiltration reflows to a salt lake (21);
and carrying out secondary nanofiltration on the water (200) produced by the primary nanofiltration so as to carry out secondary separation on the chloride ions, carbonate and sulfate radicals, wherein the water (200) produced by the secondary nanofiltration flows to the primary evaporation crystallization, and the concentrated water (300) produced by the secondary nanofiltration flows to the carbonate recovery nanofiltration.
4. The method according to any one of claims 1-3, wherein said subjecting the mother liquor (400) to a multistage nanofiltration comprising at least three nanofiltration processes comprises:
carrying out third-stage nanofiltration on the mother liquor (400) subjected to the primary evaporation crystallization so as to carry out third-stage separation on the chloride ions, carbonate radicals and sulfate radicals, wherein concentrated water (300) of the third-stage nanofiltration flows to the secondary dialysis nanofiltration;
performing fourth-stage nanofiltration on the third-stage nanofiltration produced water (200) to perform fourth separation on the chloride ions, carbonate and sulfate, wherein the concentrated water (300) of the fourth-stage nanofiltration flows to the second-stage dialysis nanofiltration;
and (3) performing fifth-stage nanofiltration on the fourth-stage nanofiltration produced water (200) so as to perform fifth separation on the chloride ions, carbonate and sulfate, wherein the concentrated water (300) of the fifth-stage nanofiltration flows to an intermediate salt pan (8), and the fifth-stage nanofiltration produced water (200) flows to the secondary evaporative crystallization.
5. The method according to any one of claims 1 to 4, wherein the performing of the secondary dialysis nanofiltration on the part of the concentrated water (300) after the multi-stage nanofiltration comprises:
mixing the concentrated water (300) obtained by the third-stage nanofiltration with the concentrated water (300) obtained by the fourth-stage nanofiltration, and sequentially carrying out first-stage dialysis nanofiltration and second-stage dialysis nanofiltration on the mixed concentrated water flow so as to separate and recover lithium ions and carbonate in the concentrated water,
wherein the water (200) produced after the secondary dialysis nanofiltration is provided to the water inlet end of the fourth stage nanofiltration.
6. The method according to any one of claims 1-5, further comprising, prior to subjecting the first stage nanofiltration water production (200) to a second stage nanofiltration:
and adjusting the pH of the first-stage nanofiltration water production (200) by alkali liquor so as to convert bicarbonate in the first-stage nanofiltration water production (200) into carbonate.
7. The method according to any one of claims 1 to 6, further comprising, prior to the fourth stage nanofiltration of the third stage nanofiltration water product (200):
and adjusting the pH value of the third-stage nanofiltration water production (200) by alkali liquor so as to convert bicarbonate radicals in the third-stage nanofiltration water production (200) into carbonate radicals.
8. The method according to any one of claims 1 to 7, wherein the step of mixing the water produced after the second boron removal adsorption (200) with the water produced after the first boron removal adsorption (200) to form a lithium carbonate precipitate further comprises the following steps:
filtering the supernatant (700) after the lithium carbonate precipitate is formed to form a lithium precipitation mother liquor (800);
carrying out lithium precipitation nanofiltration on the lithium precipitation mother liquor (800) so as to separate and recover lithium ions and carbonate in the lithium precipitation mother liquor;
refluxing said lithium precipitation nanofiltration water (200) to form said lithium carbonate precipitate; and
and enabling the concentrated water (300) after lithium precipitation and nanofiltration to flow to the carbonate recovery and nanofiltration.
9. The method according to any one of claims 1 to 8, characterized in that the water (200) produced by an upper nanofiltration device is mixed into the water (200) produced by the upper nanofiltration device in such a way that the concentration value of the water containing divalent anions is maintained within a predetermined concentration ratio interval with the concentration value of the total soluble solids in the water (200) produced by the upper nanofiltration device, wherein the water containing divalent anions originates at least partially from the concentrated water (300) of the upper nanofiltration device, before the water (200) produced by the upper nanofiltration device enters the lower nanofiltration device.
10. A salt lake lithium extraction system is characterized by comprising:
a pretreatment unit for pretreating raw brine (100) extracted from a salt lake (21);
a pre-nanofiltration unit for pre-nanofiltration of the pre-treated raw brine (100) comprising at least two nanofiltration processes;
a first evaporative crystallization device (9) for carrying out primary evaporative crystallization on the water (200) produced by the pre-nanofiltration so as to obtain a mother liquor (400) containing lithium ions;
a multi-stage nanofiltration unit for subjecting the mother liquor (400) to a multi-stage nanofiltration comprising at least three nanofiltration processes;
the second evaporation crystallization device (13) is used for carrying out secondary evaporation crystallization on the produced water (200) after the multi-stage nanofiltration;
a two-stage dialysis nanofiltration unit (15) for performing a second-stage dialysis nanofiltration on a part of the concentrated water (300) subjected to the multi-stage nanofiltration and providing produced water (200) to the multi-stage nanofiltration unit;
a first boron removal device (14) for carrying out first boron removal adsorption on the mother liquor (400) after the secondary evaporation and crystallization to obtain water (200) for forming lithium carbonate precipitate;
a recovery nanofiltration unit (16) for performing carbonate concentration treatment on part of the concentrate (300) provided by the pre-nanofiltration unit and the concentrate (300) provided by the two-stage dialysis nanofiltration unit (15), and providing produced water (200) to be refluxed to the pretreatment unit;
and the second boron removal device (17) is used for carrying out second boron removal adsorption on the concentrated water (300) discharged by the recovery nano-filtration unit (16) so as to provide water (200) for mixing with the water (200) produced after the first boron removal adsorption to form lithium carbonate precipitate.
A lithium precipitation nanofiltration unit (19) for separating lithium ions and carbonate ions in the supernatant (700) provided by the lithium carbonate precipitation step and providing a water of production (200) back to the step of forming the lithium carbonate precipitate.
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