CN117580805A - Recycling method of waste lithium iron phosphate - Google Patents
Recycling method of waste lithium iron phosphate Download PDFInfo
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- CN117580805A CN117580805A CN202380011199.5A CN202380011199A CN117580805A CN 117580805 A CN117580805 A CN 117580805A CN 202380011199 A CN202380011199 A CN 202380011199A CN 117580805 A CN117580805 A CN 117580805A
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- filtrate
- leaching
- iron phosphate
- lithium iron
- waste lithium
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- 238000000034 method Methods 0.000 title claims abstract description 74
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 67
- 239000002699 waste material Substances 0.000 title claims abstract description 62
- 238000004064 recycling Methods 0.000 title claims abstract description 40
- 239000000706 filtrate Substances 0.000 claims abstract description 122
- 238000002386 leaching Methods 0.000 claims abstract description 99
- 239000012535 impurity Substances 0.000 claims abstract description 38
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 36
- 238000011282 treatment Methods 0.000 claims abstract description 35
- 239000012528 membrane Substances 0.000 claims abstract description 32
- 239000005955 Ferric phosphate Substances 0.000 claims abstract description 30
- 229940032958 ferric phosphate Drugs 0.000 claims abstract description 30
- 229910000399 iron(III) phosphate Inorganic materials 0.000 claims abstract description 30
- 229910003002 lithium salt Inorganic materials 0.000 claims abstract description 11
- 159000000002 lithium salts Chemical class 0.000 claims abstract description 11
- 239000000243 solution Substances 0.000 claims description 58
- 239000002893 slag Substances 0.000 claims description 53
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 46
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 44
- 238000001914 filtration Methods 0.000 claims description 41
- 239000012141 concentrate Substances 0.000 claims description 37
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 36
- 238000006243 chemical reaction Methods 0.000 claims description 32
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 29
- 239000007788 liquid Substances 0.000 claims description 25
- 238000001556 precipitation Methods 0.000 claims description 24
- 238000001223 reverse osmosis Methods 0.000 claims description 24
- 239000000654 additive Substances 0.000 claims description 23
- 230000000996 additive effect Effects 0.000 claims description 21
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 18
- 239000003638 chemical reducing agent Substances 0.000 claims description 17
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 16
- 238000000108 ultra-filtration Methods 0.000 claims description 16
- 239000002253 acid Substances 0.000 claims description 15
- 239000007800 oxidant agent Substances 0.000 claims description 15
- 230000001590 oxidative effect Effects 0.000 claims description 13
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 12
- 238000002156 mixing Methods 0.000 claims description 12
- 239000001301 oxygen Substances 0.000 claims description 12
- 229910052760 oxygen Inorganic materials 0.000 claims description 12
- 229910052742 iron Inorganic materials 0.000 claims description 11
- 230000001376 precipitating effect Effects 0.000 claims description 10
- LEAMSPPOALICQN-UHFFFAOYSA-H iron(2+);diphosphate;octahydrate Chemical compound O.O.O.O.O.O.O.O.[Fe+2].[Fe+2].[Fe+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O LEAMSPPOALICQN-UHFFFAOYSA-H 0.000 claims description 9
- 239000011259 mixed solution Substances 0.000 claims description 9
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 9
- 230000001105 regulatory effect Effects 0.000 claims description 8
- 239000004408 titanium dioxide Substances 0.000 claims description 8
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 claims description 6
- LHSCNAATFBJUDF-UHFFFAOYSA-J hydrogen phosphate titanium(4+) hydrate Chemical compound O.P(=O)(O)([O-])[O-].P(=O)(O)([O-])[O-].[Ti+4] LHSCNAATFBJUDF-UHFFFAOYSA-J 0.000 claims description 6
- 239000008213 purified water Substances 0.000 claims description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 4
- 239000012298 atmosphere Substances 0.000 claims description 4
- 238000001728 nano-filtration Methods 0.000 claims description 4
- ASTWEMOBIXQPPV-UHFFFAOYSA-K trisodium;phosphate;dodecahydrate Chemical compound O.O.O.O.O.O.O.O.O.O.O.O.[Na+].[Na+].[Na+].[O-]P([O-])([O-])=O ASTWEMOBIXQPPV-UHFFFAOYSA-K 0.000 claims description 3
- LCPVQAHEFVXVKT-UHFFFAOYSA-N 2-(2,4-difluorophenoxy)pyridin-3-amine Chemical compound NC1=CC=CN=C1OC1=CC=C(F)C=C1F LCPVQAHEFVXVKT-UHFFFAOYSA-N 0.000 claims description 2
- 239000007864 aqueous solution Substances 0.000 claims description 2
- CHQMHPLRPQMAMX-UHFFFAOYSA-L sodium persulfate Substances [Na+].[Na+].[O-]S(=O)(=O)OOS([O-])(=O)=O CHQMHPLRPQMAMX-UHFFFAOYSA-L 0.000 claims description 2
- 230000035484 reaction time Effects 0.000 claims 1
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 45
- 229910052744 lithium Inorganic materials 0.000 abstract description 45
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 21
- 238000011084 recovery Methods 0.000 abstract description 21
- 239000000047 product Substances 0.000 abstract description 20
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 19
- 239000000843 powder Substances 0.000 abstract description 13
- 239000000463 material Substances 0.000 abstract description 3
- 238000012958 reprocessing Methods 0.000 abstract description 3
- 239000002244 precipitate Substances 0.000 abstract description 2
- 230000000052 comparative effect Effects 0.000 description 27
- 239000000126 substance Substances 0.000 description 12
- 239000012299 nitrogen atmosphere Substances 0.000 description 10
- 239000007787 solid Substances 0.000 description 9
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 8
- 238000004090 dissolution Methods 0.000 description 8
- 230000002572 peristaltic effect Effects 0.000 description 8
- 229910052698 phosphorus Inorganic materials 0.000 description 8
- 239000011574 phosphorus Substances 0.000 description 8
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 7
- 239000000920 calcium hydroxide Substances 0.000 description 7
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 7
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 7
- 239000012047 saturated solution Substances 0.000 description 7
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 229910000398 iron phosphate Inorganic materials 0.000 description 6
- 239000000203 mixture Substances 0.000 description 5
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 4
- 229910021645 metal ion Inorganic materials 0.000 description 4
- 239000010936 titanium Substances 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- -1 aluminum ions Chemical class 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 238000001704 evaporation Methods 0.000 description 3
- 230000008020 evaporation Effects 0.000 description 3
- GQUJEMVIKWQAEH-UHFFFAOYSA-N titanium(III) oxide Chemical compound O=[Ti]O[Ti]=O GQUJEMVIKWQAEH-UHFFFAOYSA-N 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 235000011121 sodium hydroxide Nutrition 0.000 description 2
- 230000002195 synergetic effect Effects 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- REKWWOFUJAJBCL-UHFFFAOYSA-L dilithium;hydrogen phosphate Chemical compound [Li+].[Li+].OP([O-])([O-])=O REKWWOFUJAJBCL-UHFFFAOYSA-L 0.000 description 1
- 230000005518 electrochemistry Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 229910001448 ferrous ion Inorganic materials 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000005755 formation reaction Methods 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000010413 mother solution Substances 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- DPTATFGPDCLUTF-UHFFFAOYSA-N phosphanylidyneiron Chemical compound [Fe]#P DPTATFGPDCLUTF-UHFFFAOYSA-N 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Classifications
-
- 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
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/84—Recycling of batteries or fuel cells
Abstract
The invention discloses a recycling method of waste lithium iron phosphate, and belongs to the technical field of material recycling. The method is characterized in that the precipitate and the leaching solution obtained by separating and leaching the waste lithium iron phosphate powder are respectively subjected to specific reprocessing, the lithium ions in the leaching solution are highly enriched by adopting membrane concentration, the filtrate generated in the treatment process is fully utilized, the lithium salt and the ferric phosphate product can be finally and efficiently recovered and obtained, the lithium recovery rate of the whole method for the waste lithium iron phosphate can reach more than 95%, the impurity element concentration in the obtained ferric phosphate is not more than 5ppm at the highest, and the quality of the ferric phosphate product is higher.
Description
Technical Field
The invention relates to the technical field of material recovery, in particular to a method for recycling waste lithium iron phosphate.
Background
The lithium iron phosphate system lithium battery is a power battery with high electrochemistry and high safety, and in general, a special recovery system exists for recovering the positive pole piece containing the lithium iron phosphate in the battery after the positive pole piece is deactivated and scrapped. The current common method for recovering waste lithium iron phosphate is wet recovery, namely, metal ions (mainly lithium ions) in the lithium iron phosphate are totally leached, and then valuable metal ions are selectively recovered by adopting a mode of impurity removal and fractional precipitation. However, the recovery rate of the conventional wet recovery is low, and the main reason is that part of metal ions still exist in the waste residue or leaching solution obtained by precipitation in the treatment process and are not recovered, and if the recovery rate of the metal ions is to be improved, higher capital is required to upgrade recovery equipment such as an evaporation and concentration system (for example, to upgrade to an MVR system), or a part of products which can be recovered are required to be sacrificed, so that the low-cost and high-efficiency integrated full recovery of the waste lithium iron phosphate cannot be realized.
Disclosure of Invention
The method is characterized in that precipitation and leaching liquid obtained by separating and leaching waste lithium iron phosphate powder are respectively subjected to specific reprocessing, lithium ions in the leaching liquid are highly enriched by adopting membrane concentration, and filtrate generated in the treatment process is fully utilized, so that lithium salt and ferric phosphate products can be finally and efficiently recovered.
In order to achieve the above purpose, the technical scheme adopted herein is as follows:
a recycling method of waste lithium iron phosphate comprises the following steps:
placing the pole piece containing the waste lithium iron phosphate into an acid solution containing a first oxidant for leaching to obtain leaching liquid and leaching slag;
adjusting the pH value of the leaching solution to 8-9, precipitating impurities and filtering to obtain primary filtrate and primary filter residue;
concentrating the primary filtrate by a membrane system, and adding a precipitant to precipitate to obtain lithium salt and secondary filtrate;
reacting the leaching residue with an acid solution under inert atmosphere, adding a reducing agent and an additive for mixing reaction, filtering, adding a second oxidizing agent into the obtained mixed solution for reaction, and filtering to obtain ferric phosphate and a tertiary filtrate; the reducing agent is elemental iron, and the additive is at least one of ferric phosphate dihydrate, ferrous phosphate octahydrate, titanium hydrogen phosphate monohydrate, aluminum hydroxide, titanium dioxide and titanium dioxide; the mass ratio of the leaching slag to the reducing agent to the additive is 100: (20-65): (50-200);
mixing the secondary filtrate and the tertiary filtrate, regulating the pH to 9-10, filtering, regulating the pH to 4-6, and filtering again; the obtained filtrate is subjected to fine filtration, ultrafiltration and reverse osmosis treatment to obtain purified water and concentrate with pH of 2-4, wherein the concentrate is placed into primary filter residue and leached out, and the filtrate is filtered to obtain four times of filtrate, and is treated according to primary filtrate treatment steps.
In the recycling method of waste lithium iron phosphate, firstly, selectively extracting lithium from the waste lithium iron phosphate by using an oxidant and an acid solution to obtain a leaching solution containing lithium ions and leaching residues containing iron, phosphorus elements and other substances such as graphite of a pole piece, at the moment, firstly, adjusting the pH value of the leaching solution to enable some impurity ions such as iron and aluminum ions to precipitate out in the form of hydroxide or oxide, and then concentrating the obtained primary filtrate by using a membrane concentration process, wherein the process can prevent lithium salt in the filtrate from crystallizing compared with the existing MVR system component, and can further improve the purity of the obtained concentrated solution and reduce the energy consumption; concentrating, and adding precipitant to obtain high purity lithium salt. Meanwhile, iron powder is added into leaching slag containing iron and phosphorus elements as a reducing agent, and meanwhile, specific types of additives are introduced, so that a synergistic reaction can be carried out on the two substances, impurities such as titanium in the filter residue are induced to precipitate, the loss of the iron element is reduced, the impurity removal is efficiently realized, and the product after the impurity removal is oxidized to obtain the iron phosphate with higher purity. Finally, in order to realize high lithium ion recovery rate of the waste lithium iron phosphate, the technical scheme further recovers and converts the secondary filtrate and the tertiary filtrate generated in the process into a concentrate, the concentrate is in a liquid state and mainly contains lithium ions which are not recovered in the prior process, and meanwhile, the concentrate is acidic, so that the method can be used for leaching of primary filter residues, both lithium ions in the filter residues and lithium ions in the concentrate are enriched in the filtrate obtained by leaching, and then the lithium ions of the whole recovery product can be recovered by further carrying out process treatments such as membrane concentration and the like according to the treatment steps of the primary filtrate.
In an embodiment, the first oxidant is at least one of oxygen, hydrogen peroxide and sodium persulfate.
In one embodiment, the acid solution is an aqueous solution of at least one of sulfuric acid and hydrochloric acid.
In one embodiment, the pH of the leachate is adjusted to a pH of 8.5.
In the pH range, the leaching solution can fully precipitate impurity substances such as iron ions, ferrous ions, aluminum ions and the like, and meanwhile, lithium loss finally caused by partial lithium ion precipitation due to overhigh pH is avoided.
In one embodiment, the membrane system comprises a nanofiltration membrane system and a reverse osmosis membrane system in that order.
Compared with the traditional MVR system, the membrane system disclosed herein adopts a nanofiltration membrane system to separate metal impurity ions such as calcium, magnesium, aluminum and the like from primary filtrate, and then adopts a reverse osmosis membrane system to enrich lithium ions in the solution.
Further, the rate of the primary filtrate entering the membrane concentration system is 380-420L/h, the pH value is 2-4, and the pressure is 1-1.5 MPa.
Further, the concentration of lithium ions in the solution after the primary filtrate is concentrated by a membrane system is 20-25 g/L.
In one embodiment, the precipitant is at least one of sodium carbonate and sodium phosphate dodecahydrate, and the temperature during precipitation is 80-100 ℃ and the time is 2-4 h.
In one embodiment, the leaching residue reacts with the reducing agent and the additive for 3-6 hours.
The impurity removal rate of the leaching slag can reach more than 90% under the synergistic effect of the iron simple substance and the additive in the proportion, so that the purity of the prepared regenerated ferric phosphate is higher.
In an embodiment, the second oxidant is one of oxygen and hydrogen peroxide.
In one embodiment, the second oxidant is hydrogen peroxide, and the addition rate of the hydrogen peroxide is 0.7-1.1 mL/min.
Under the addition rate, the introduction of hydrogen peroxide can not cause the growth speed of precipitated grains to be too high or too low, and the finally obtained ferric phosphate has good crystal form and morphology.
In one embodiment, the second oxidant is oxygen, and the pressure of the introduced oxygen is 1.2-1.5 MPa.
Similar to hydrogen peroxide, the prepared ferric phosphate has better crystal form and morphology under the pressure of the introduced hydrogen peroxide.
In one embodiment, the temperature of the mixed solution and the second oxidant is equal to or higher than 80 ℃.
When the temperature of the ferric phosphate is controlled to be 80 ℃ or above during the formation reaction, the nucleation rate of crystal grains can be effectively controlled in a lower range, so that the particle size of the prepared ferric phosphate is maintained at a proper size.
In one embodiment, the unit dosage of the concentrate when leaching the filter residue once is 3-7 mL/g.
Further, the concentration of iron element in the concentrate is less than 0.001g/L, the concentration of phosphorus element is less than 0.001g/L, the concentration of copper element is less than 0.0001g/L, the concentration of aluminum element is less than 0.0001g/L, and the concentration of lithium element is 4-5 g/L.
Further, the secondary filtrate and the tertiary filtrate are mixed and the pH value is adjusted to 9-10, and then the mixture is filtered, and the mixture is filtered again after the pH value is adjusted to 4-6; sequentially passing the obtained filtrate through a microporous filter and a plate heat exchanger, and placing the filtrate in an ultrafiltration water producing tank after finishing fine filtration and ultrafiltration treatment by an ultrafiltration device; the water in the ultrafiltration water producing tank is subjected to primary reverse osmosis treatment, secondary reverse osmosis treatment and tertiary reverse osmosis treatment to obtain purified water, and the osmosis residual liquid phase after the primary reverse osmosis treatment is subjected to reverse osmosis treatment to obtain a concentrate.
The concentrate is used for leaching the filter residues once, so that lithium ions contained in the concentrate can be extracted together, lithium ions in the filter residues can be leached efficiently, and finally the overall lithium recovery rate is improved.
Compared with the prior art, the beneficial effects of the method are as follows:
the method is characterized in that precipitation and leaching liquid obtained by separating and leaching waste lithium iron phosphate powder are respectively subjected to specific reprocessing, membrane concentration is adopted to highly enrich lithium ions in the leaching liquid, filtrate generated in the treatment process is fully utilized, finally, lithium salt and ferric phosphate products can be simultaneously and efficiently recovered and obtained, the lithium recovery rate of the whole method for the waste lithium iron phosphate can reach more than 95%, the impurity element concentration in the obtained ferric phosphate is not more than 5ppm at the most, and the quality of the ferric phosphate products is higher.
Drawings
FIG. 1 is a schematic flow chart of a method for recycling waste lithium iron phosphate.
Detailed Description
For a better description of the objects, technical solutions and advantages herein, the following description will further explain the same in conjunction with the figures and specific embodiments.
The materials used in the examples and comparative examples are commercially available unless otherwise specified.
The pole pieces containing the waste lithium iron phosphate used in each example and comparative example are all positive pole pieces in commercial recovered lithium iron phosphate batteries, and the main components of the pole pieces are waste lithium iron phosphate, a conductive agent and a binder, and the content of lithium element, phosphorus element and iron element in the pole pieces is detected before the pole pieces are recycled.
The membrane concentration system is composed of a nanofiltration membrane system with the aperture of 1-10 nm and a reverse osmosis membrane system with the aperture of 0.4-0.6 nm, the rate of the primary filtrate entering the membrane concentration system is 400L/h, the pH value is 2-4, the pressure is 1-1.5 MPa, and the lithium ion concentration in the solution after the primary filtrate is concentrated by the membrane system is 20-25 g/L.
In the examples described herein, the secondary filtrate and the tertiary filtrate were adjusted to pH 9 to 10, filtered, then adjusted to pH 4 to 6 and filtered again; the obtained filtrate is treated by adopting a reclaimed water system, wherein the reclaimed water system comprises a fine filtration-ultrafiltration system and a reverse osmosis system, and the fine filtration-ultrafiltration system comprises a microporous precise filter, a plate heat exchanger, an ultrafiltration device and an ultrafiltration water producing tank connected with the ultrafiltration device; the reverse osmosis system comprises a first-stage reverse osmosis device, a second-stage reverse osmosis device, a third-stage reverse osmosis device and a corresponding connected water tank, which are sequentially connected, wherein the third-stage reverse osmosis device is connected with the terminal reverse osmosis device.
After the filtrate flows into a reclaimed water system, the filtrate sequentially passes through a microporous precise filter and a plate heat exchanger of a fine filtration-ultrafiltration system, the ultrafiltration device completes fine filtration and ultrafiltration treatment, water is accumulated in an ultrafiltration water production tank, purified water can be obtained after the water is subjected to reverse osmosis treatment by a primary reverse osmosis device, a secondary reverse osmosis device and a tertiary reverse osmosis device, the purified water is recycled, and liquid in a concentrated water tank of the primary reverse osmosis device is collected and passes through a terminal reverse osmosis device to obtain concentrate.
Example 1
An embodiment of the method for recycling waste lithium iron phosphate described herein, as shown in fig. 1, includes the following steps:
(1) 100g of pole piece powder containing waste lithium iron phosphate is placed into 1000mL of 1mol/L sulfuric acid solution, 30mL of 30% hydrogen peroxide is pumped into the solution by a peristaltic pump to leach for 4 hours, and leaching liquid and leaching slag are obtained after the step of selectively extracting lithium is completed;
(2) The leaching solution is subjected to precipitation reaction for 2 hours at the temperature of 50 ℃ by using a calcium hydroxide saturated solution, and after precipitation is filtered out, primary filtrate and primary filter residue are obtained, and the one-step impurity removal is completed;
(3) Concentrating the primary filtrate by a membrane system, adding 60g of precipitant sodium carbonate into the obtained high-concentration lithium liquid, and precipitating for 3 hours at 90 ℃ to obtain lithium salt lithium carbonate and secondary filtrate;
(4) Placing leaching slag obtained in the step (1) into a reaction kettle containing 500mL of 1mol/L sulfuric acid solution under a nitrogen atmosphere, reacting for 1h, then adding reducer simple substance iron powder and additive titanium dioxide in stages, mixing, reacting for 3h at 50 ℃ and filtering out insoluble slag, thereby realizing acid dissolution and impurity removal, transferring the obtained mixed solution into another reaction kettle, adding 1.2MPa of oxygen, reacting for 6h at 80 ℃, and filtering to obtain ferric phosphate and tertiary filtrate; the mass ratio of the leaching slag to the elemental iron powder to the titanium dioxide is 100:31: 65.
(5) Mixing the secondary filtrate and the tertiary filtrate, regulating the pH to 9-10 by using sodium hydroxide, regulating the pH to 4-6, filtering, and treating the mixture in a reclaimed water system to obtain concentrate with pH=3, wherein concentrated water of the concentrate is put into primary filter residues and leached, the liquid-solid ratio during leaching is 3mL/g, filtering is carried out, and four times of filtrate and mixed residues which finally cannot be used for further extracting lithium are obtained, and the four times of filtrate is treated according to the primary filtrate treatment step.
Example 2
An embodiment of the method for recycling waste lithium iron phosphate described herein comprises the steps of:
(1) 200g of pole piece powder containing waste lithium iron phosphate is placed into 1000mL of 1mol/L sulfuric acid solution, 60mL of 30% hydrogen peroxide is pumped into the solution by a peristaltic pump to leach for 4 hours, and leaching liquid and leaching slag are obtained after the step of selectively extracting lithium is completed;
(2) The leaching solution is subjected to precipitation reaction for 2 hours at the temperature of 50 ℃ by using 30% liquid caustic soda solution, and after precipitation is filtered out, primary filtrate and primary filter residue are obtained, and the one-step impurity removal is completed;
(3) Concentrating the primary filtrate by a membrane system, adding 276g of precipitant sodium phosphate dodecahydrate into the obtained high-concentration lithium liquid, and precipitating for 3 hours at 90 ℃ to obtain lithium salt lithium phosphate and secondary filtrate;
(4) Placing leaching slag obtained in the step (1) into a reaction kettle containing 500mL of 1mol/L sulfuric acid solution under a nitrogen atmosphere, reacting for 2 hours, then adding reducer simple substance iron powder, additive titanium dioxide and titanium hydrogen phosphate monohydrate in stages, mixing, reacting for 5 hours at 80 ℃ and filtering out insoluble slag, thereby realizing acid dissolution and impurity removal, transferring the obtained mixed solution into another reaction kettle, adding 1.3MPa of oxygen to react for 6 hours at 80 ℃, and filtering to obtain ferric phosphate and tertiary filtrate; the mass ratio of the leaching slag to the elemental iron powder to the titanium dioxide to the titanium hydrogen phosphate monohydrate is 100:36:80:80;
(5) And (3) treating the secondary filtrate and the tertiary filtrate according to the same treatment method as in the embodiment 1 to obtain a concentrate, placing concentrated water of the concentrate into primary filter residues and leaching, wherein the liquid-solid ratio during leaching is 4mL/g, filtering to obtain four filtrates and mixed slag which finally cannot be used for further extracting lithium, and treating the four filtrates according to the primary filtrate treatment step.
Example 3
An embodiment of the method for recycling waste lithium iron phosphate described herein comprises the steps of:
(1) 200g of pole piece powder containing waste lithium iron phosphate is placed into 1000mL of 1mol/L sulfuric acid solution, 60mL of 30% hydrogen peroxide is pumped into the solution by a peristaltic pump to leach for 4 hours, and leaching liquid and leaching slag are obtained after the step of selectively extracting lithium is completed;
(2) The leaching solution is subjected to precipitation reaction for 2 hours at the temperature of 60 ℃ by using a calcium hydroxide saturated solution, and after precipitation is filtered out, primary filtrate and primary filter residue are obtained, and the one-step impurity removal is completed;
(3) Concentrating the primary filtrate by a membrane system, adding 84g of precipitant sodium carbonate into the obtained high-concentration lithium liquid, and precipitating for 3 hours at 90 ℃ to obtain lithium salt lithium carbonate and secondary filtrate;
(4) Placing leaching slag obtained in the step (1) into a reaction kettle containing 500mL of 1mol/L sulfuric acid solution under a nitrogen atmosphere, reacting for 3 hours, then adding a reducing agent simple substance iron powder and an additive titanium hydrogen phosphate monohydrate in stages, mixing, reacting for 6 hours at 50 ℃ and filtering out insoluble slag, thereby realizing acid dissolution and impurity removal, transferring the obtained mixed solution to another reaction kettle, adding 1.3MPa of oxygen to react for 6 hours at 80 ℃, and filtering to obtain ferric phosphate and a tertiary filtrate; the mass ratio of the leaching slag to the elemental iron powder to the titanium hydrogen phosphate monohydrate is 100:41:100;
(5) And (3) treating the secondary filtrate and the tertiary filtrate according to the same treatment method as in the embodiment 1 to obtain a concentrate, placing concentrated water of the concentrate into primary filter residues and leaching, wherein the liquid-solid ratio during leaching is 5mL/g, filtering to obtain four filtrates and mixed slag which finally cannot be used for further extracting lithium, and treating the four filtrates according to the primary filtrate treatment step.
Example 4
An embodiment of the method for recycling waste lithium iron phosphate described herein comprises the steps of:
(1) 200g of pole piece powder containing waste lithium iron phosphate is placed into 1000mL of 1mol/L sulfuric acid solution, 60mL of 30% hydrogen peroxide is pumped into the solution by a peristaltic pump to leach for 4 hours, and leaching liquid and leaching slag are obtained after the step of selectively extracting lithium is completed;
(2) The leaching solution is subjected to precipitation reaction for 2 hours at the temperature of 50 ℃ by using a calcium hydroxide saturated solution, and after precipitation is filtered out, primary filtrate and primary filter residue are obtained, and the one-step impurity removal is completed;
(3) Concentrating the primary filtrate by a membrane system, adding 96g of precipitant sodium carbonate into the obtained high-concentration lithium liquid, and precipitating for 3 hours at 90 ℃ to obtain lithium salt lithium carbonate and secondary filtrate;
(4) Placing the leached slag obtained in the step (1) into a reaction kettle containing 500mL of 1mol/L sulfuric acid solution under the nitrogen atmosphere, then adding a mixture of a reducing agent simple substance iron powder, an additive ferric phosphate dihydrate and titanium sesquioxide in stages, reacting for 2 hours, reacting for 5 hours at 50 ℃ and filtering out insoluble slag, thereby realizing acid dissolution and impurity removal, transferring the obtained mixed liquor into another reaction kettle, adding 1.5MPa oxygen to react for 6 hours at 80 ℃, and filtering to obtain ferric phosphate and tertiary filtrate; the mass ratio of the leaching slag to the mixture of the simple substance iron powder, the ferric phosphate dihydrate and the titanium sesquioxide is 100:32:85;
(5) And (3) treating the secondary filtrate and the tertiary filtrate according to the same treatment method as in the embodiment 1 to obtain a concentrate, placing concentrated water of the concentrate into primary filter residues and leaching, wherein the liquid-solid ratio during leaching is 7mL/g, filtering to obtain four filtrates and mixed slag which finally cannot be used for further extracting lithium, and treating the four filtrates according to the primary filtrate treatment step.
Example 5
An embodiment of the method for recycling waste lithium iron phosphate described herein comprises the steps of:
(1) 200g of pole piece powder containing waste lithium iron phosphate is placed into 1000mL of 1mol/L sulfuric acid solution, 60mL of 30% hydrogen peroxide is pumped into the solution by a peristaltic pump to leach for 4 hours, and leaching liquid and leaching slag are obtained after the step of selectively extracting lithium is completed;
(2) The leaching solution is subjected to precipitation reaction for 2 hours at the temperature of 50 ℃ by using a calcium hydroxide saturated solution, and after precipitation is filtered out, primary filtrate and primary filter residue are obtained, and the one-step impurity removal is completed;
(3) Concentrating the primary filtrate by a membrane system, adding 75g of precipitant sodium carbonate into the obtained high-concentration lithium liquid, and precipitating for 3 hours at 90 ℃ to obtain lithium salt lithium carbonate and secondary filtrate;
(4) Placing leaching slag obtained in the step (1) into a reaction kettle containing 500mL of 1mol/L sulfuric acid solution under a nitrogen atmosphere, reacting for 2 hours, then adding a reducing agent elemental iron powder and an additive ferrous phosphate octahydrate in stages, mixing, reacting for 5 hours at 50 ℃ and filtering out insoluble slag, thereby realizing acid dissolution and impurity removal, transferring the obtained mixed liquor into another reaction kettle, adding hydrogen peroxide with the concentration of 30% continuously at the rate of 0.7mL/min, reacting for 6 hours at 80 ℃, and filtering to obtain ferric phosphate and tertiary filtrate; the mass ratio of the leaching slag to the elemental iron powder to the ferrous phosphate octahydrate is 100:52:100;
(5) And (3) treating the secondary filtrate and the tertiary filtrate according to the same treatment method as in the embodiment 1 to obtain a concentrate, placing concentrated water of the concentrate into primary filter residues and leaching, wherein the liquid-solid ratio during leaching is 6mL/g, filtering to obtain four filtrates and mixed slag which finally cannot be used for further extracting lithium, and treating the four filtrates according to the primary filtrate treatment step.
Example 6
An embodiment of the method for recycling waste lithium iron phosphate described herein comprises the steps of:
(1) 200g of pole piece powder containing waste lithium iron phosphate is placed into 1000mL of 1mol/L sulfuric acid solution, 60mL of 30% hydrogen peroxide is pumped into the solution by a peristaltic pump to leach for 4 hours, and leaching liquid and leaching slag are obtained after the step of selectively extracting lithium is completed;
(2) The leaching solution is subjected to precipitation reaction for 2 hours at the temperature of 50 ℃ by using a calcium hydroxide saturated solution, and after precipitation is filtered out, primary filtrate and primary filter residue are obtained, and the one-step impurity removal is completed;
(3) Concentrating the primary filtrate by a membrane system, adding 75g of precipitant sodium carbonate into the obtained high-concentration lithium liquid, and precipitating for 3 hours at 90 ℃ to obtain lithium salt lithium carbonate and secondary filtrate;
(4) Placing leaching slag obtained in the step (1) into a reaction kettle containing 500mL of 1mol/L sulfuric acid solution under a nitrogen atmosphere, reacting for 2 hours, then adding reducer simple substance iron powder and additive ferric phosphate dihydrate in stages, mixing, reacting for 5 hours at 50 ℃ and filtering out insoluble slag, thereby realizing acid dissolution and impurity removal, transferring the obtained mixed liquor into another reaction kettle, adding hydrogen peroxide with the concentration of 30% continuously at the rate of 1.1mL/min, reacting for 6 hours at 80 ℃, and filtering to obtain ferric phosphate and tertiary filtrate; the mass ratio of the leaching slag to the elemental iron powder to the ferric phosphate dihydrate is 100:40:90;
(5) And (3) treating the secondary filtrate and the tertiary filtrate according to the same treatment method as in the embodiment 1 to obtain a concentrate, placing concentrated water of the concentrate into primary filter residues and leaching, wherein the liquid-solid ratio during leaching is 6mL/g, filtering to obtain four filtrates and mixed slag which finally cannot be used for further extracting lithium, and treating the four filtrates according to the primary filtrate treatment step.
Example 7
An embodiment of the method for recycling waste lithium iron phosphate described herein comprises the steps of:
(1) 200g of pole piece powder containing waste lithium iron phosphate is placed into 1000mL of 1mol/L sulfuric acid solution, 60mL of 30% hydrogen peroxide is pumped into the solution by a peristaltic pump to leach for 4 hours, and leaching liquid and leaching slag are obtained after the step of selectively extracting lithium is completed;
(2) The leaching solution is subjected to precipitation reaction for 2 hours at the temperature of 50 ℃ by using a calcium hydroxide saturated solution, and after precipitation is filtered out, primary filtrate and primary filter residue are obtained, and the one-step impurity removal is completed;
(3) Concentrating the primary filtrate by a membrane system, adding 75g of precipitant sodium carbonate into the obtained high-concentration lithium liquid, and precipitating for 3 hours at 90 ℃ to obtain lithium salt lithium carbonate and secondary filtrate;
(4) Placing leaching slag obtained in the step (1) into a reaction kettle containing 500mL of 1mol/L sulfuric acid solution under a nitrogen atmosphere, reacting for 2 hours, then adding reducer simple substance iron powder and additive aluminum hydroxide in stages, mixing, reacting at 50 ℃ for 5 hours, filtering out insoluble slag, thereby realizing acid dissolution and impurity removal, transferring the obtained mixed solution into another reaction kettle, adding hydrogen peroxide with concentration of 30% continuously at the rate of 0.8mL/min, reacting at 80 ℃ for 6 hours, and filtering to obtain ferric phosphate and tertiary filtrate; the mass ratio of the leaching slag to the elemental iron powder to the aluminum hydroxide is 100:62:80;
(5) And (3) treating the secondary filtrate and the tertiary filtrate according to the same treatment method as in the embodiment 1 to obtain a concentrate, placing concentrated water of the concentrate into primary filter residues and leaching, wherein the liquid-solid ratio during leaching is 6mL/g, filtering to obtain four filtrates and mixed slag which finally cannot be used for further extracting lithium, and treating the four filtrates according to the primary filtrate treatment step.
Example 8
An embodiment of the method for recycling waste lithium iron phosphate described herein comprises the steps of:
(1) 200g of pole piece powder containing waste lithium iron phosphate is placed into 1000mL of 1mol/L sulfuric acid solution, 60mL of 30% hydrogen peroxide is pumped into the solution by a peristaltic pump to leach for 4 hours, and leaching liquid and leaching slag are obtained after the step of selectively extracting lithium is completed;
(2) The leaching solution is subjected to precipitation reaction for 2 hours at the temperature of 50 ℃ by using a calcium hydroxide saturated solution, and after precipitation is filtered out, primary filtrate and primary filter residue are obtained, and the one-step impurity removal is completed;
(3) Concentrating the primary filtrate by a membrane system, adding 75g of precipitant sodium carbonate into the obtained high-concentration lithium liquid, and precipitating for 3 hours at 90 ℃ to obtain lithium salt lithium carbonate and secondary filtrate;
(4) Placing leaching slag obtained in the step (1) into a reaction kettle containing 500mL of 1mol/L sulfuric acid solution under nitrogen atmosphere, reacting for 1h, then adding a reducing agent elemental iron powder, an additive of titanium sesquioxide and ferrous phosphate octahydrate in stages, mixing, reacting for 4h at 50 ℃ and filtering out insoluble slag, thereby realizing acid dissolution and impurity removal, transferring the obtained mixed solution into another reaction kettle, adding hydrogen peroxide with the concentration of 30% continuously at the rate of 1.5mL/min, reacting for 6h at 80 ℃, and filtering to obtain ferric phosphate and tertiary filtrate; the mass ratio of the leaching slag to the elemental iron powder to the ferrous phosphate octahydrate is 100:62:80:80;
(5) And (3) treating the secondary filtrate and the tertiary filtrate according to the same treatment method as in the embodiment 1 to obtain a concentrate, placing concentrated water of the concentrate into primary filter residues and leaching, wherein the liquid-solid ratio during leaching is 6mL/g, filtering to obtain four filtrates and mixed slag which finally cannot be used for further extracting lithium, and treating the four filtrates according to the primary filtrate treatment step.
Comparative example 1
The recycling method of waste lithium iron phosphate is different from the method in the embodiment 3 only in that the primary filter residue in the step (5) is directly leached by pure water, the liquid-solid ratio during leaching is 5mL/g, four times of filtrate and mixed slag are obtained by filtering, and the four times of filtrate is treated according to a primary filtrate treatment step.
Comparative example 2
The recycling method of waste lithium iron phosphate is different from the embodiment 3 only in that the nitrogen atmosphere in the step (4) is changed into an air atmosphere.
Comparative example 3
The recycling method of waste lithium iron phosphate is different from the embodiment 3 only in that no additive is added in the step (4).
Comparative example 4
The recycling method of waste lithium iron phosphate is different from the embodiment 7 only in that the mass ratio of the leaching slag to the elemental iron powder to the aluminum hydroxide is 100:62:300.
comparative example 5
The recycling method of waste lithium iron phosphate is different from the embodiment 5 only in that the mass ratio of the leaching slag to the elemental iron powder to the ferrous phosphate octahydrate is 100:52:400.
comparative example 6
The recycling method of waste lithium iron phosphate is different from the embodiment 5 only in that the mass ratio of the leaching slag to the elemental iron powder to the ferrous phosphate octahydrate is 100:52:20.
comparative example 7
The recycling method of waste lithium iron phosphate is different from the embodiment 4 only in that the primary filtrate in the step (3) is concentrated by adopting a commercially available MVR evaporation system.
Comparative example 8
The recycling method of waste lithium iron phosphate is different from the embodiment 8 only in that the pH of the solution in the step (2) is 3 after the pH of the leaching solution is regulated.
Comparative example 9
The method for recycling the waste lithium iron phosphate is different from the embodiment 8 only in that the pH of the solution in the step (2) is 12 after the pH of the leaching solution is regulated.
Comparative example 10
The method for recycling waste lithium iron phosphate differs from example 8 only in that the concentrate in step (5) has a ph=1.
Comparative example 11
The method for recycling waste lithium iron phosphate differs from example 8 only in that the concentrate in step (5) has a ph=6.
Comparative example 12
The recycling method of waste lithium iron phosphate is different from the embodiment 8 only in that the concentrate in the step (5) is not subjected to fine filtration and ultrafiltration treatment in the process of obtaining the concentrate, and the total concentration of impurity elements except lithium elements is 0.08g/L.
Effect example 1
In order to verify the high efficiency of the recycling method of the waste lithium iron phosphate, the impurity content of the iron phosphate, the iron content of the iron phosphate product, the phosphorus content of the iron phosphate product and the molar content ratio of the iron and phosphorus elements, and the specific surface area of the iron phosphate product prepared in the methods of the examples and the comparative examples are detected and counted, and finally the lithium recovery rate of the method is counted, wherein the calculation method of the lithium recovery rate is 100-m (lithium in mixed slag)/m (lithium in lithium iron phosphate pole piece powder); if no reclaimed water recycling system exists, only pure water is used for washing the lithium-containing mixed slag, the recovery rate of lithium is calculated to be 100-m (lithium in the mixed slag, lithium in the ferrophosphorus slag and lithium in the precipitated lithium mother solution)/m (lithium in the lithium iron phosphate pole piece powder), and finally purity detection is carried out on the prepared lithium salt.
The test results are shown in tables 1, 2 and 3.
TABLE 1
TABLE 2
TABLE 3 Table 3
As is apparent from tables 1 and 2, after the recovery method of the waste lithium iron phosphate is implemented, the recovery rate of lithium can reach more than 96%, the purity of the prepared ferric phosphate product is high, the main impurity concentration is not more than 5ppm at most, the specific surface area is moderate, and the phosphorus-iron ratio corresponds to that of a standard substance. In contrast, in the method described in comparative example 1, the secondary filtrate and the tertiary filtrate are not recovered and the primary filter residue is leached, so that lithium ions in the waste lithium iron phosphate cannot be fully recovered, and the lithium recovery rate is low; the conversion process of leaching residues in the method described in comparative example 2 is not carried out under nitrogen atmosphere, and partial iron and phosphorus loss can be caused when the leaching residues are dissolved in air atmosphere, so that the iron and phosphorus element content of the prepared product is low, and the specific surface area of the prepared product is low; the product of comparative example 3 does not introduce additives for synergism during conversion of leaching residues, so that good impurity removal and precipitation effects cannot be realized, the titanium impurity concentration is high, the titanium content of the finally prepared product is relatively high, and meanwhile, the yield of the ferric phosphate product is low; however, the content of the additive aluminum hydroxide introduced into the product of comparative example 4 is too high, so that the aluminum element of the final product is too high, which means that the additive addition amount cannot be too large in the method, and similarly, the addition amount of the ferrous phosphate octahydrate in the product of comparative example 5 is too large, and the iron phosphate and the quality and the specific surface area are not ideal; the additive of comparative example 6 was excessively small in addition amount, and similarly to comparative example 3, titanium impurities were not effectively removed. Comparative example 7 uses a relatively conventional MVR evaporation system to perform evaporative concentration on the primary filtrate, and the method is easy to cause lithium ion loss compared with a membrane concentration process; comparative example 8 and comparative example 9 were too high or too low in performing the pH adjustment of the leachate, resulting in too high impurity concentration or too low lithium recovery of the prepared lithium salt product. In contrast, in comparative examples 10 and 11, the recovery rate of lithium ions in the process was low or the impurity content of the obtained lithium salt was high due to too high or too low pH of the concentrate when leaching the primary filter residue. The impurity content of the concentrate itself in comparative example 12 was too high, thus resulting in a higher impurity content of the final lithium salt.
Finally, it should be noted that the above embodiments are only intended to illustrate the technical solutions herein and not to limit the scope of protection herein, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made to the technical solutions herein without departing from the spirit and scope of the technical solutions herein.
Claims (10)
1. The method for recycling the waste lithium iron phosphate is characterized by comprising the following steps of:
placing the pole piece containing the waste lithium iron phosphate into an acid solution containing a first oxidant for leaching to obtain leaching liquid and leaching slag;
adjusting the pH value of the leaching solution to 8-9, precipitating impurities and filtering to obtain primary filtrate and primary filter residue;
concentrating the primary filtrate by a membrane system, and adding a precipitant to precipitate to obtain lithium salt and secondary filtrate;
reacting the leaching residue with an acid solution under inert atmosphere, adding a reducing agent and an additive for mixing reaction, filtering, adding a second oxidizing agent into the obtained mixed solution for reaction, and filtering to obtain ferric phosphate and a tertiary filtrate; the reducing agent is elemental iron, and the additive is at least one of ferric phosphate dihydrate, ferrous phosphate octahydrate, titanium hydrogen phosphate monohydrate, aluminum hydroxide, titanium dioxide and titanium dioxide; the mass ratio of the leaching slag to the reducing agent to the additive is 100: (20-65): (50-200);
mixing the secondary filtrate and the tertiary filtrate, regulating the pH to 9-10, filtering, regulating the pH to 4-6, and filtering again; the obtained filtrate is subjected to fine filtration, ultrafiltration and reverse osmosis treatment to obtain purified water and concentrate with pH of 2-4, wherein the concentrate is placed into primary filter residue and leached out, and the filtrate is filtered to obtain four times of filtrate, and is treated according to primary filtrate treatment steps.
2. The method for recycling the waste lithium iron phosphate according to claim 1, wherein the first oxidant is at least one of oxygen, hydrogen peroxide and sodium persulfate; the acid solution is an aqueous solution of at least one of sulfuric acid and hydrochloric acid.
3. The method for recycling the waste lithium iron phosphate according to claim 1, wherein the membrane system comprises a nanofiltration membrane system and a reverse osmosis membrane system in sequence.
4. The method for recycling waste lithium iron phosphate according to claim 1, wherein the precipitant is at least one of sodium carbonate and sodium phosphate dodecahydrate, and the temperature during precipitation is 80-100 ℃ and the time is 2-4 h.
5. The method for recycling the waste lithium iron phosphate according to claim 1, wherein the reaction time of the leaching residue with the reducing agent and the additive is 3-6 hours.
6. The method for recycling waste lithium iron phosphate according to claim 1, wherein the second oxidant is one of oxygen and hydrogen peroxide.
7. The method for recycling waste lithium iron phosphate according to claim 6, wherein when the second oxidant is hydrogen peroxide, the adding rate of the hydrogen peroxide is 0.7-1.1 mL/min.
8. The method for recycling waste lithium iron phosphate according to claim 6, wherein when the second oxidant is oxygen, the pressure of the introduced oxygen is 1.2-1.5 MPa.
9. The method for recycling waste lithium iron phosphate according to claim 1, wherein the temperature of the mixed solution and the second oxidant in the reaction is not less than 80 ℃.
10. The method for recycling waste lithium iron phosphate according to claim 1, wherein the unit dosage of the concentrate when leaching the filter residue once is 3-7 mL/g.
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