CN115448271B - Purification method and purification system of wet-process phosphoric acid and preparation method of ferric phosphate - Google Patents
Purification method and purification system of wet-process phosphoric acid and preparation method of ferric phosphate Download PDFInfo
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- CN115448271B CN115448271B CN202211126187.0A CN202211126187A CN115448271B CN 115448271 B CN115448271 B CN 115448271B CN 202211126187 A CN202211126187 A CN 202211126187A CN 115448271 B CN115448271 B CN 115448271B
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- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 title claims abstract description 427
- 229910000147 aluminium phosphate Inorganic materials 0.000 title claims abstract description 215
- 238000000034 method Methods 0.000 title claims abstract description 115
- 238000000746 purification Methods 0.000 title claims abstract description 57
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 title claims abstract description 43
- 239000005955 Ferric phosphate Substances 0.000 title claims abstract description 34
- 229940032958 ferric phosphate Drugs 0.000 title claims abstract description 34
- 229910000399 iron(III) phosphate Inorganic materials 0.000 title claims abstract description 34
- 238000002360 preparation method Methods 0.000 title abstract description 11
- 239000012528 membrane Substances 0.000 claims abstract description 161
- 238000001728 nano-filtration Methods 0.000 claims abstract description 98
- 238000005341 cation exchange Methods 0.000 claims abstract description 95
- 238000001914 filtration Methods 0.000 claims abstract description 11
- 239000000243 solution Substances 0.000 claims description 52
- 239000011259 mixed solution Substances 0.000 claims description 31
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 29
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 claims description 27
- 229910000387 ammonium dihydrogen phosphate Inorganic materials 0.000 claims description 27
- 235000019837 monoammonium phosphate Nutrition 0.000 claims description 27
- 239000006012 monoammonium phosphate Substances 0.000 claims description 27
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 22
- 230000008569 process Effects 0.000 claims description 22
- 235000003891 ferrous sulphate Nutrition 0.000 claims description 20
- 239000011790 ferrous sulphate Substances 0.000 claims description 20
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 20
- 229910000359 iron(II) sulfate Inorganic materials 0.000 claims description 20
- 238000000502 dialysis Methods 0.000 claims description 16
- 238000002156 mixing Methods 0.000 claims description 11
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 9
- 229910000398 iron phosphate Inorganic materials 0.000 claims description 9
- 229920000642 polymer Polymers 0.000 claims description 9
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 8
- 239000012141 concentrate Substances 0.000 claims description 6
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 claims description 4
- 229910001448 ferrous ion Inorganic materials 0.000 claims description 4
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 239000012535 impurity Substances 0.000 abstract description 21
- 230000004907 flux Effects 0.000 abstract description 8
- 229910021645 metal ion Inorganic materials 0.000 abstract description 6
- 239000002253 acid Substances 0.000 description 30
- -1 hydrogen ions Chemical class 0.000 description 16
- 150000001768 cations Chemical class 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 13
- 150000002500 ions Chemical class 0.000 description 10
- 239000012466 permeate Substances 0.000 description 10
- 235000011114 ammonium hydroxide Nutrition 0.000 description 8
- 229910052739 hydrogen Inorganic materials 0.000 description 8
- 239000001257 hydrogen Substances 0.000 description 8
- 230000004048 modification Effects 0.000 description 7
- 238000012986 modification Methods 0.000 description 7
- 229920002873 Polyethylenimine Polymers 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000012467 final product Substances 0.000 description 5
- 239000003960 organic solvent Substances 0.000 description 5
- 239000002994 raw material Substances 0.000 description 4
- 238000000926 separation method Methods 0.000 description 4
- 238000000638 solvent extraction Methods 0.000 description 4
- 238000009388 chemical precipitation Methods 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 239000007772 electrode material Substances 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000003002 pH adjusting agent Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- LSNNMFCWUKXFEE-UHFFFAOYSA-M Bisulfite Chemical compound OS([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-M 0.000 description 2
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 2
- 229920001661 Chitosan Polymers 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 2
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 238000004873 anchoring Methods 0.000 description 2
- 229910001424 calcium ion Inorganic materials 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 229960004887 ferric hydroxide Drugs 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- IEECXTSVVFWGSE-UHFFFAOYSA-M iron(3+);oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Fe+3] IEECXTSVVFWGSE-UHFFFAOYSA-M 0.000 description 2
- 150000002642 lithium compounds Chemical class 0.000 description 2
- 229910001425 magnesium ion Inorganic materials 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 229920000128 polypyrrole Polymers 0.000 description 2
- 229910052708 sodium Inorganic materials 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 229910001415 sodium ion Inorganic materials 0.000 description 2
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000007334 copolymerization reaction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 229910001447 ferric ion Inorganic materials 0.000 description 1
- 239000003014 ion exchange membrane Substances 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- ILXAVRFGLBYNEJ-UHFFFAOYSA-K lithium;manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[O-]P([O-])([O-])=O ILXAVRFGLBYNEJ-UHFFFAOYSA-K 0.000 description 1
- 150000002697 manganese compounds Chemical class 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 239000002861 polymer material Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000012264 purified product Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- BDHFUVZGWQCTTF-UHFFFAOYSA-M sulfonate Chemical compound [O-]S(=O)=O BDHFUVZGWQCTTF-UHFFFAOYSA-M 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/18—Phosphoric acid
- C01B25/234—Purification; Stabilisation; Concentration
- C01B25/237—Selective elimination of impurities
- C01B25/238—Cationic impurities, e.g. arsenic compounds
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/37—Phosphates of heavy metals
- C01B25/375—Phosphates of heavy metals of iron
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The application relates to the technical field of batteries, and provides a purification method and a purification system of wet-process phosphoric acid. The purification method of the wet-process phosphoric acid comprises the following steps: dialyzing wet phosphoric acid by adopting a monovalent cation exchange membrane to obtain pre-purified phosphoric acid; and filtering the pre-purified phosphoric acid by adopting a nanofiltration membrane to obtain nanofiltration concentrated solution and purified phosphoric acid. The purification method of the wet-process phosphoric acid provided by the application adopts the monovalent cation exchange membrane and the nanofiltration membrane to carry out two-stage filtration to obtain the phosphoric acid, so that the impurity content is low, and the preparation requirement of the battery-grade ferric phosphate is met; meanwhile, most of divalent metal ions in the wet-process phosphoric acid are removed through the monovalent cation exchange membrane, so that the operation pressure of the nanofiltration membrane can be greatly reduced when the prepurified phosphoric acid enters the nanofiltration membrane for filtration, and the nanofiltration membrane is ensured to have higher flux.
Description
Technical Field
The application belongs to the technical field of batteries, and particularly relates to a purification method and a purification system of wet-process phosphoric acid and a preparation method of ferric phosphate.
Background
The production method of phosphoric acid mainly comprises two methods: wet and thermal processes, wherein the wet process uses inorganic acids to decompose phosphate ore to produce phosphoric acid. The impurity content in the wet phosphoric acid is more, which is influenced by the raw materials and the process characteristics.
The prior wet-process phosphoric acid purification technology mainly comprises a chemical precipitation method and a solvent extraction method. Chemical precipitation is mainly carried out by adding precipitant into wet phosphoric acid, and removing impurities in the form of precipitate generated by reaction of impurities with precipitant. However, as wet phosphoric acid is a strong acid environment, most impurities cannot be completely precipitated, and the content of impurity ions in phosphoric acid prepared by a chemical precipitation method is still high, so that the requirement of preparing battery-grade ferric phosphate is not met. The solvent extraction method is based on that phosphoric acid is soluble in an organic solvent, and impurity ions are insoluble in the organic solvent, and phosphoric acid is obtained by extracting phosphoric acid into the organic solvent, back-extracting phosphoric acid from the organic solvent by using water, and evaporating and concentrating. Although the solvent extraction method can obtain phosphoric acid meeting the requirements for preparing battery-grade ferric phosphate, the solvent extraction method has long treatment flow, large investment and large environmental pollution caused by the use of organic solvents.
The membrane separation technology is considered as one of the most promising separation technologies, and has the characteristics of low energy consumption, good separation effect, simple equipment, environmental friendliness and the like. In the prior art, nanofiltration membranes are used for purifying wet-process phosphoric acid, however, the operation flux of the nanofiltration membranes is low in the purification process due to the existence of impurities in the wet-process phosphoric acid, and the working performance cannot be guaranteed.
Disclosure of Invention
The application aims to provide a purification method and a purification system of wet-process phosphoric acid and a preparation method of ferric phosphate, and aims to solve the problem of low operation flux of a nanofiltration membrane in the process of purifying the wet-process phosphoric acid.
In order to achieve the purposes of the application, the technical scheme adopted by the application is as follows:
in a first aspect, the present application provides a method for purifying wet-process phosphoric acid, comprising: dialyzing wet phosphoric acid by adopting a monovalent cation exchange membrane to obtain pre-purified phosphoric acid; and filtering the pre-purified phosphoric acid by adopting a nanofiltration membrane to obtain nanofiltration concentrated solution and purified phosphoric acid.
Alternatively, when the monovalent cation exchange membrane is used for dialysis of wet phosphoric acid, the feed side of the monovalent cation exchange membrane is the wet phosphoric acid, and the collection side of the monovalent cation exchange membrane is pure water.
Optionally, the flow rate of the wet phosphoric acid is greater than or equal to the flow rate of the pure water, the flow rate of the wet phosphoric acid is 30-60L/h, and the flow rate of the pure water is 30-60L/h.
Optionally, the nanofiltration concentrate is returned to the feed side of the monovalent cation exchange membrane and dialyzed again through the monovalent cation exchange membrane.
Optionally, the monovalent cation exchange membrane comprises a cation exchange membrane and a modifying layer attached to a surface of the cation exchange membrane.
Optionally, the modifying layer comprises an electropositive polymer.
In a second aspect, the present application provides a method for preparing iron phosphate, comprising: reacting purified phosphoric acid prepared by the wet-process phosphoric acid purification method provided by the first aspect of the application with ammonia water to obtain monoammonium phosphate solution; mixing the monoammonium phosphate solution with a ferrous sulfate solution to obtain a first mixed solution; adding hydrogen peroxide into the first mixed solution to obtain a second mixed solution; and reacting the second mixed solution at a first temperature for a first period of time to obtain ferric phosphate.
Optionally, the pH of the monoammonium phosphate solution is controlled to be 1.5-5.0.
Optionally, the first mixed solution further comprises a pH regulator, wherein the pH regulator is at least one of sulfuric acid and phosphoric acid, and the molar ratio of the pH regulator to ferrous sulfate is (0.1-0.4): 1.
Optionally, the molar ratio of the ferrous sulfate to the monoammonium phosphate in the first mixed solution is 1 (0.8-1.2).
Optionally, the mass fraction of ferrous ions in the second mixed solution is less than 0.01%.
Optionally, the first temperature is 50-100 ℃, and the first time period is 1-10 h.
In a third aspect, the present application provides a purification system for wet process phosphoric acid, comprising:
a dialysis unit comprising a monovalent cation exchange membrane for dialyzing wet phosphoric acid to obtain pre-purified phosphoric acid;
the nanofiltration unit comprises a nanofiltration membrane, and the nanofiltration membrane is used for filtering the pre-purified phosphoric acid to obtain nanofiltration concentrated solution and purified phosphoric acid.
Optionally, the monovalent cation exchange membrane comprises a cation exchange membrane and a modifying layer attached to a surface of the cation exchange membrane, the modifying layer comprising an electropositive polymer.
Optionally, the purification system of wet-process phosphoric acid further comprises a transfer pond, a first connecting pipeline and a second connecting pipeline, wherein the transfer pond is connected with the collecting side of the monovalent cation exchange membrane through the first connecting pipeline, and the transfer pond is connected with the feeding side of the nanofiltration membrane through the second connecting pipeline.
Optionally, the purification system of wet-process phosphoric acid further comprises a third connecting pipeline, wherein the third connecting pipeline is connected with the feeding side of the monovalent cation exchange membrane and the feeding side of the nanofiltration membrane.
The purification method of the wet-process phosphoric acid provided by the first aspect of the application firstly adopts a monovalent cation exchange membrane to dialyze the wet-process phosphoric acid, and the monovalent cation exchange membrane can selectively permeate monovalent cations such as hydrogen ions, sodium ions and the like, and entraps cations with more than two valences such as magnesium ions, calcium ions, iron ions, aluminum ions and the like. The radius of hydrogen ions in the monovalent cations is minimum, the hydrogen ions preferentially permeate the membrane, and due to the requirement of electric neutrality, the permeated hydrogen ions carry dihydrogen phosphate anions to permeate the monovalent cation exchange membrane together, namely phosphoric acid permeates the monovalent cation exchange membrane; since the selectivity of monovalent cation exchange membranes does not reach 100%, although most of the divalent or higher cations are trapped, a small fraction of the divalent or higher cations remain in the pre-purified phosphoric acid; further, the pre-purified phosphoric acid is filtered by a nanofiltration membrane, and cations with more than two valences are filtered again by the nanofiltration membrane, so that the purity of the finally obtained phosphoric acid meets the requirement of preparing battery-grade ferric phosphate. The purification method of the wet-process phosphoric acid provided by the first aspect of the application firstly adopts the monovalent cation exchange membrane to remove most of divalent metal ions in the phosphoric acid, so that the operation pressure of the nanofiltration membrane can be greatly reduced when the phosphoric acid enters the nanofiltration membrane for filtration, and the nanofiltration membrane is ensured to have higher flux.
The method for preparing the ferric phosphate provided by the second aspect of the application adopts the purified phosphoric acid prepared by the method for purifying the wet-process phosphoric acid provided by the first aspect of the application, and the content of phosphoric acid impurities is low, so that the purity of the ferric phosphate is ensured; further, phosphoric acid and ammonia water react to generate monoammonium phosphate, and then react with ferrous sulfate and hydrogen peroxide to generate ferric phosphate, so that the generation of ferric hydroxide in the reaction process can be effectively avoided, the conversion rate of raw materials is improved, impurities in the ferric phosphate are reduced, and the quality of the ferric phosphate is improved.
The purification system of the wet-process phosphoric acid provided by the third aspect of the application adopts a monovalent cation exchange membrane and a nanofiltration membrane to carry out two-stage membrane purification on the wet-process phosphoric acid, and the whole two-stage membrane purification process has no chemical reaction or phase change, thus the purification system of the wet-process phosphoric acid is a short-cut, low-cost and high-phosphoric acid yield purification system of the wet-process phosphoric acid.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for preparing iron phosphate provided by an embodiment of the present application;
fig. 2 is a schematic structural diagram of a purification system of wet phosphoric acid according to an embodiment of the present application.
Wherein, each reference sign in the figure:
1-a dialysis unit; 11-dialysis cell; 11 a-a first feed side; 11 b-a first collecting side; 12-monovalent cation exchange membranes;
a 2-nanofiltration unit; 21-nanofiltration tank; 21 a-a second feed side; 21 b-a second collection side; 22-nanofiltration membrane;
30-a transfer pool; 31-a first connection tube; 32-a first control valve; 33-a second connecting tube; 34-a second control valve; 35-a third connecting tube; 36-a third control valve.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
In the present application, the term "and/or" describes an association relationship of an association object, which means that three relationships may exist, for example, a and/or B may mean: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship.
In the present application, "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.
It should be understood that, in various embodiments of the present application, the sequence number of each process described above does not mean that the execution sequence of some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.
The terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The weights of the relevant components mentioned in the description of the embodiments of the present application may refer not only to the specific contents of the components, but also to the proportional relationship between the weights of the components, so long as the contents of the relevant components in the description of the embodiments of the present application are scaled up or down within the scope of the disclosure of the embodiments of the present application. Specifically, the mass described in the specification of the embodiment of the application can be mass units known in the chemical industry field such as mu g, mg, g, kg.
The terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated for distinguishing between objects such as substances from each other. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.
An embodiment of the present application provides a method for purifying wet-process phosphoric acid, including:
s11: dialyzing wet phosphoric acid by adopting a monovalent cation exchange membrane to obtain pre-purified phosphoric acid;
s12: and filtering the pre-purified phosphoric acid by adopting a nanofiltration membrane to obtain nanofiltration concentrated solution and purified phosphoric acid.
According to the purification method of the wet-process phosphoric acid provided by the embodiment of the application, the wet-process phosphoric acid is dialyzed by adopting a monovalent cation exchange membrane, and the monovalent cation exchange membrane can selectively permeate monovalent cations such as hydrogen ions, sodium ions and the like, and entraps cations with more than two valences such as magnesium ions, calcium ions, iron ions, aluminum ions and the like. The radius of hydrogen ions in the monovalent cations is minimum, the hydrogen ions preferentially permeate the membrane, and due to the requirement of electric neutrality, the permeated hydrogen ions carry dihydrogen phosphate anions to permeate the monovalent cation exchange membrane together, namely phosphoric acid permeates the monovalent cation exchange membrane; since the selectivity of the monovalent cation exchange membrane cannot reach 100%, although most of the divalent or higher cations are trapped (the trapping rate is about 90%), a small amount of divalent or higher cations remain in the pre-purified phosphoric acid; further, the pre-purified phosphoric acid is filtered by a nanofiltration membrane, and cations with more than two valences are filtered again by the nanofiltration membrane, so that the purity of the finally obtained phosphoric acid meets the requirement of preparing battery-grade ferric phosphate. According to the purification method of the wet-process phosphoric acid, provided by the embodiment of the application, most of divalent metal ions in the wet-process phosphoric acid are removed by adopting the monovalent cation exchange membrane, so that the operation pressure of the nanofiltration membrane can be greatly reduced when the prepurified phosphoric acid enters the nanofiltration membrane for filtration, and the higher flux of the nanofiltration membrane is ensured.
In the prior art, in order to ensure the operation flux of the nanofiltration membrane, the wet process phosphoric acid before nanofiltration is usually pretreated to remove part of impurities or diluted. The purification method of the wet-process phosphoric acid provided by the first aspect of the application embodiment does not need complex pretreatment operation, reduces the cost, but adopts a monovalent cation exchange membrane for dialysis prepurification, and the process does not need pressure or electric field driving, so that the energy consumption is low and the blockage is not easy; and because the wet phosphoric acid is not diluted, the obtained purified phosphoric acid has high concentration, and after two-stage purification by an exchange membrane and a nanofiltration membrane, the removal rate of metal ions with more than two valences is more than 99 percent, and the quality and the concentration of the obtained purified phosphoric acid meet the preparation requirements of battery-grade ferric phosphate.
In some embodiments, in step S11 described above, when the wet phosphoric acid is dialyzed with a monovalent cation exchange membrane, the feed side of the monovalent cation exchange membrane is wet phosphoric acid and the collection side of the monovalent cation exchange membrane is pure water. The concentration difference is formed between the high-concentration wet-process phosphoric acid solution and the pure water, so that the phosphoric acid is accelerated to permeate through the monovalent cation exchange membrane from the feeding side to the collecting side. It will be appreciated that in other embodiments, the collection side of the monovalent cation exchange membrane may also be a dilute concentration phosphoric acid solution. The dilute concentration herein means that the phosphoric acid concentration is less than that in wet process phosphoric acid.
In some embodiments, in step S11 above, the flow rate of wet phosphoric acid on the feed side of the monovalent cation exchange membrane is greater than or equal to the flow rate of pure water on the collection side of the monovalent cation exchange membrane. The flow of the wet phosphoric acid and the flow of the pure water can influence the concentration of the final product, if the flow of the pure water is larger than the flow of the wet phosphoric acid, the content of phosphoric acid in the final product is not high, and by controlling the flow of the wet phosphoric acid not smaller than the flow of the pure water, the concentration of phosphoric acid in the final product is ensured to be higher. Alternatively, the flow rate of wet phosphoric acid is equal to the flow rate of pure water. Alternatively, the flow rate of the wet process phosphoric acid is 30L/h to 60L/h, for example 30L/h, 40L/h, 50L/h or 60L/h. Alternatively, the flow rate of the pure water is 30L/h to 60L/h, for example, 30L/h, 40L/h, 50L/h or 60L/h. The flow value can influence the purification efficiency of phosphoric acid and the concentration of the final product, and although the flow is smaller, the concentration of phosphoric acid in the purified product can be increased, the time cost can be increased, and the time cost can be considered while the higher concentration of phosphoric acid in the final product is ensured by controlling the flow value to be 30L/h-60L/h.
In some embodiments, in step S11 above, the monovalent cation exchange membrane operating conditions comprise: the operating pressure is normal pressure, and the operating temperature is normal temperature. The monovalent cation exchange membrane is operated at normal temperature and normal pressure, so that a large amount of equipment is not required to be invested, and the cost is reduced.
In some embodiments, in step S11 described above, the monovalent cation exchange membrane includes a cation exchange membrane and a modifying layer attached to a surface of the cation exchange membrane. The ion exchange membrane is a membrane made of a polymer material having selective permeability to ions. Cation exchange membranes are membranes that are selective for cations, typically of the sulfonic acid type, with an anchoring group and a dissociable ion, e.g., the sodium sulfonic acid type anchoring group is sulfonate and the dissociable ion is sodium. The preparation direction of the monovalent cation exchange membrane mainly comprises membrane matrix modification and membrane surface modification. Optionally, the monovalent cation exchange membrane is prepared by adopting a membrane surface modification mode, namely, a modification layer is attached to the surface of the cation exchange membrane, the membrane surface modification mode is simple to operate, and the modified effect is better than that of most of membrane matrix modification modes. The modified layer generally comprises an electropositive polymer which is coated on the surface of the cation exchange membrane to realize the effect of blocking the high valence ions by the membrane, wherein the effect mainly comes from the electrostatic force action of the modified layer on the ions, and the repulsive force of the high valence ions is far greater than that of the low valence ions due to the higher charge, so that the separation of the single multivalent cations is realized. Optionally, the electropositive polymer comprises Polyethylenimine (PEI), polypyrrole, or chitosan. Alternatively, the modifying layer is attached to the cation exchange membrane using electrostatic forces, for example, by immersing the cation exchange membrane in a solution containing polyethylenimine to produce a monovalent cation exchange membrane. Alternatively, the modifying layer may be chemically bonded to the cation exchange membrane by creating new bonds, for example, the electropositive polymer may be attached to the cation exchange membrane by graft copolymerization.
In some embodiments, step S12 above further comprises returning the nanofiltration concentrate to the feed side of the monovalent cation exchange membrane and re-dialyzing through the monovalent cation exchange membrane. The nanofiltration concentrated solution is prepurified phosphoric acid residual acid which does not permeate through a nanofiltration membrane, the content of metal ions in the nanofiltration concentrated solution is far lower than the content of metal ions in wet phosphoric acid, the content of phosphoric acid in the nanofiltration concentrated solution is equivalent to the content of phosphoric acid in the wet phosphoric acid, and the nanofiltration concentrated solution is returned to the feed side of a monovalent cation exchange membrane and dialyzed again through the monovalent cation exchange membrane, so that the nanofiltration concentrated solution is recycled, the problem that the nanofiltration concentrated solution is difficult to treat is solved, and the yield of phosphoric acid is also improved. Alternatively, the nanofiltration concentrate is returned to the feed side of the monovalent cation exchange membrane and mixed with wet process phosphoric acid, and then together with it is again pre-purified through the monovalent cation exchange membrane. The nanofiltration concentrated solution is also obtained through dialysis of a monovalent cation exchange membrane, so that the content of impurities is low, the content of phosphoric acid is high, the nanofiltration concentrated solution is recycled, and the waste is reduced.
In some embodiments, in step S12 above, the nanofiltration membrane operating conditions include: the temperature is 10-60 ℃, the pressure is 1.5-6 MPa, and the concentration ratio is 1.5-6 times.
The phosphoric acid prepared by the purification method of the wet-process phosphoric acid provided by the embodiment of the application has the advantages of low impurity content, low cost and low cost, and meets the preparation requirements of battery-grade ferric phosphate.
A second aspect of the embodiment of the present application provides a method for preparing iron phosphate, including:
s21: reacting purified phosphoric acid prepared by the wet-process phosphoric acid purification method provided by the first aspect of the embodiment of the application with ammonia water to obtain monoammonium phosphate solution;
s22: mixing monoammonium phosphate solution with ferrous sulfate solution to obtain a first mixed solution;
s23: adding hydrogen peroxide into the first mixed solution to obtain a second mixed solution;
s24: and reacting the second mixed solution at a first temperature for a first period of time to obtain the ferric phosphate.
According to the method for preparing the ferric phosphate, the phosphoric acid prepared by the wet-process phosphoric acid purification method provided by the embodiment of the application has the advantages that the content of impurities in the phosphoric acid is low, so that the purity of the ferric phosphate is ensured; further, phosphoric acid and ammonia water react to generate monoammonium phosphate, and then react with ferrous sulfate and hydrogen peroxide to generate ferric phosphate, so that the generation of ferric hydroxide in the reaction process can be effectively avoided, the conversion rate of raw materials is improved, impurities in the ferric phosphate are reduced, and the quality of the ferric phosphate is improved.
In some embodiments, in the step S21, the pH of the monoammonium phosphate solution is controlled to be 1.5-5.0, i.e. at the end of the reaction between ammonia and phosphoric acid, the pH of the solution is controlled to be 1.5-5.0. Alternatively, the pH is 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5.0.
In some embodiments, in step S22 above, the first mixed solution further includes a pH adjuster, which is also mixed when the monoammonium phosphate solution is mixed with the ferrous sulfate solution. Optionally, the pH adjuster is at least one of sulfuric acid and phosphoric acid. By selecting sulfuric acid and/or phosphoric acid as pH adjusting agent, the introduction of new impurity types is avoided. Optionally, the molar ratio of the pH adjustor to the ferrous sulfate is (0.1-0.4): 1, e.g., 0.1:1, 0.2:1, 0.3:1, or 0.4:1, within which the pH of the first mixed solution can be adjusted to within a range of 1.0-3.0, thereby ensuring the formation of ferric phosphate.
In some embodiments, in step S22, the molar ratio of ferrous sulfate to monoammonium phosphate in the first mixed solution is 1 (0.8-1.2), such as 1:0.8, 1:0.9, 1:1.0, 1:1.1, or 1:1.2.
In some embodiments, in step S23, hydrogen peroxide is slowly added to the first mixed solution, and the ferrous ions are oxidized to ferric ions by hydrogen peroxide, so that the mass fraction of the ferrous ions in the second mixed solution is less than 0.01wt%, for example, 0.01wt%, 0.008wt%, 0.005wt%, 0.003wt%, or 0.001wt%.
In some embodiments, in step S24 above, the first temperature is 50 ℃ to 100 ℃, e.g., 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃, or 100 ℃; the first time period is 1h to 10h, for example 1h, 3h, 4h, 5h, 6h, 7h, 9h or 10h.
The iron phosphate prepared by the preparation method of the iron phosphate provided by the second aspect of the embodiment of the application is battery-grade iron phosphate, and the method reduces the impurity content in the iron phosphate by double control from the raw materials and the preparation process.
The battery grade ferric phosphate prepared by the preparation method of the ferric phosphate provided by the second aspect of the embodiment of the application is used for preparing the electrode material, for example, lithium iron phosphate is synthesized by the battery grade ferric phosphate and a lithium compound, or lithium manganese phosphate is synthesized by the battery grade ferric phosphate, the lithium compound and a manganese compound, the purity of the electrode material is higher, and the safety of a battery adopting the electrode material is ensured.
Referring to fig. 1, a third aspect of the embodiment of the present application provides a purification system for wet phosphoric acid, including: a dialysis unit 1, the dialysis unit 1 comprising a monovalent cation exchange membrane 12, the monovalent cation exchange membrane 12 being used for dialysis of wet process phosphoric acid to obtain pre-purified phosphoric acid; nanofiltration unit 2 comprises nanofiltration membrane 22, nanofiltration membrane 22 being used to filter the pre-purified phosphoric acid to obtain nanofiltration concentrate and purified phosphoric acid.
The wet-process phosphoric acid purification system provided by the third aspect of the embodiment of the application adopts a monovalent cation exchange membrane and a nanofiltration membrane to carry out two-stage membrane purification on the wet-process phosphoric acid, has no chemical reaction and no phase change in the whole two-stage membrane purification process, and is a short-cut, low-cost and high-phosphoric acid yield wet-process phosphoric acid purification system.
In some embodiments, the monovalent cation exchange membrane comprises a cation exchange membrane and a modifying layer attached to the surface of the cation exchange membrane, the modifying coating comprising an electropositive polymer applied to the surface of the cation exchange membrane to effect the barrier of the membrane to higher valency ions. Optionally, the electropositive polymer comprises Polyethylenimine (PEI), polypyrrole, or chitosan.
In some embodiments, the dialysis unit 1 comprises a dialysis cell 11, the dialysis cell 11 referring to a site for wet phosphoric acid to be dialyzed, a monovalent cation exchange membrane 12 being provided within the dialysis cell 11, the monovalent cation exchange membrane 12 dividing the dialysis cell 11 into a first feed side 11a and a first collection side 11b; wherein the first feed side 11a is the side corresponding to the feed side of the monovalent cation exchange membrane 12 and the first collection side 11b is the side corresponding to the collection side of the monovalent cation exchange membrane 12. The nanofiltration unit 2 comprises a nanofiltration tank 21, wherein the nanofiltration tank 21 refers to a place for nanofiltration of purified phosphoric acid, a nanofiltration membrane 22 is arranged in the nanofiltration tank 21, and the nanofiltration membrane 22 divides the nanofiltration tank 21 into a second feeding side 21a and a second collecting side 21b; wherein the second feed side 21a is the side corresponding to the feed side of the nanofiltration membrane 22 and the second collection side 21b is the side corresponding to the collection side of the nanofiltration membrane 22.
In some embodiments, the purification system of wet-process phosphoric acid further comprises a transfer tank 30, a first connection pipe 31 and a second connection pipe 33, the transfer tank 30 being connected to the collecting side, i.e. the first collecting side 11b, of the monovalent cation exchange membrane 12 by the first connection pipe 31, and the transfer tank 30 being connected to the feeding side, i.e. the second feeding side 21a, of the nanofiltration membrane by the second connection pipe 33. The transfer tank 30 is used for transferring and temporarily storing the pre-purified phosphoric acid, the pre-purified phosphoric acid obtained after the wet phosphoric acid in the dialysis tank 11 is dialyzed flows into the transfer tank 30 for temporary storage through the first connecting pipeline 31, and the pre-purified phosphoric acid temporarily stored in the transfer tank 30 continues to flow into the nanofiltration tank 21 for nanofiltration through the second connecting pipeline 33. Optionally, the first connection pipe 31 is provided with a first control valve 32 for controlling the on-off of the first connection pipe 31. Optionally, a second control valve 34 for controlling the on-off of the second connecting pipeline 33 is arranged on the second connecting pipeline 33.
In some embodiments, the purification system of wet process phosphoric acid further comprises a third connecting line 35, the third connecting line 35 connecting the feed side of the monovalent cation exchange membrane, i.e. the first feed side 11a, and the feed side of the nanofiltration membrane, i.e. the second feed side 21a. Thus, the nanofiltration concentrate of the second feed side 21a may be returned to the first feed side 11a through the third connection line 35 and mixed with the wet phosphoric acid of the first feed side 11a and dialyzed again. Optionally, the third connecting pipeline 35 is further provided with a third control valve 36 for controlling the on-off of the third connecting pipeline 35.
The following description is made with reference to specific embodiments.
Example 1
S1, mixing 80L of wet-process phosphoric acid and 25L of nanofiltration concentrated residual acid to obtain mixed acid, taking the mixed acid as a feed acid, taking 100L of pure water as a receiving solution, respectively adding the mixed acid and the pure water into the feed side and the receiving side of a monovalent cation exchange membrane, and dialyzing to obtain 100L of prepurified phosphoric acid under the conditions of normal temperature and normal pressure, wherein the flow rate of the mixed acid and the pure water is 45L/h.
S2, adding 100L of prepurified phosphoric acid into nanofiltration small test equipment, controlling the operation temperature to 33 ℃, the operation pressure to 3.2MPa, and the concentration multiple to 4 times to obtain 75L of purified phosphoric acid and 25L of nanofiltration concentrated residual acid. And (3) returning 25L of nanofiltration concentrated residual acid to the front end, mixing with wet phosphoric acid, and pre-purifying again. The phosphoric acid yield was 81.3%.
S3, taking 3L of purified phosphoric acid, slowly adding 260mL of 25% ammonia water, adjusting the pH to 3.6, and then adding pure water to dilute to 3.32L to obtain 3.32L of monoammonium phosphate solution.
S4, mixing the monoammonium phosphate solution obtained in the step 3 with 4L of ferrous sulfate solution with the concentration of 2.73 mol/L; the molar ratio of ferrous sulfate to monoammonium phosphate solution in the mixed solution is 1:1, and then 0.18mol of S2 is added to obtain purified phosphoric acid.
S5, 680mL of 30% hydrogen peroxide is slowly added into the mixed solution in the step 4, the temperature is raised, the reaction temperature is controlled to be 90 ℃, and the reaction is carried out for 3 hours, so that the battery grade ferric phosphate is obtained.
TABLE 1 example 1 purification of phosphoric acid by wet method before and after impurity and phosphoric acid content
Example 2
S1, mixing 33L of wet-process phosphoric acid and 67L of nanofiltration concentrated residual acid to obtain mixed acid, taking the mixed acid as a feed acid, taking 100L of pure water as a receiving solution, respectively adding the mixed acid and the pure water into the feed side and the receiving side of a monovalent cation exchange membrane, and dialyzing to obtain 100L of prepurified phosphoric acid under the conditions of normal temperature and normal pressure, wherein the flow rate of the mixed acid and the pure water is 60L/h.
S2, adding 100L of chemically pretreated phosphoric acid into nanofiltration small test equipment, controlling the temperature at 10 ℃, controlling the operating pressure at 6MPa, and concentrating the phosphoric acid by 1.5 times to obtain 33L of purified phosphoric acid and 67L of nanofiltration concentrated residual acid. 67L of nanofiltration concentrated residual acid is returned to the front end to be mixed with wet phosphoric acid, and pre-purification is carried out again. The phosphoric acid yield was 71.4%.
S3, taking 3L of purified phosphoric acid, slowly adding 30mL of 25% ammonia water, adjusting the pH to 1.5, and then adding pure water to dilute to 3.25L to obtain 3.25L of monoammonium phosphate solution.
S4, mixing the monoammonium phosphate solution obtained in the step 3 with 4L of ferrous sulfate solution with the concentration of 3.02 mol/L; the molar ratio of ferrous sulfate to monoammonium phosphate solution in the mixed solution is 1:0.8, and then 0.60mol of S2 is added to obtain purified phosphoric acid.
And S5, slowly adding 750mL of 30% hydrogen peroxide into the mixed solution obtained in the step 4, heating, controlling the reaction temperature to be 50 ℃, and reacting for 1h to obtain the battery-grade ferric phosphate.
TABLE 2 example 2 purification of wet phosphoric acid before and after impurity and phosphoric acid content
Example 3
S1, mixing 83L of wet-process phosphoric acid and 17L of nanofiltration concentrated residual acid to obtain mixed acid, taking the mixed acid as a feed acid, taking 100L of pure water as a receiving solution, respectively adding the mixed acid and the pure water into the feed side and the receiving side of a monovalent cation exchange membrane, and dialyzing to obtain 100L of prepurified phosphoric acid under the conditions of normal temperature and normal pressure, wherein the flow rate of the mixed acid and the pure water is 30L/h.
S2, adding 100L of chemically pretreated phosphoric acid into nanofiltration small test equipment, controlling the temperature at 60 ℃, controlling the operating pressure at 1.5MPa, and concentrating the phosphoric acid by 6 times to obtain 83L of purified phosphoric acid and 17L of nanofiltration concentrated residual acid. 17L of nanofiltration concentrated residual acid is returned to the front end to be mixed with wet phosphoric acid, and the pre-purification is carried out again. The yield of phosphoric acid was 85.7%.
S3, taking 2.5L of purified phosphoric acid, slowly adding 680mL of 25% ammonia water, adjusting the pH to 5.0, and then adding pure water to dilute to 3.5L to obtain 3.5L of monoammonium phosphate solution.
S4, mixing the monoammonium phosphate solution obtained in the step 3 with 4L of ferrous sulfate solution with the concentration of 2.02 mol/L; the molar ratio of ferrous sulfate to monoammonium phosphate solution in the mixed solution is 1:1.2, and then 1.6mol of S2 is added to obtain purified phosphoric acid.
S5, slowly adding 500mL of 30% hydrogen peroxide into the mixed solution obtained in the step 4, heating, controlling the reaction temperature to be 100 ℃, and reacting for 10 hours to obtain the battery grade ferric phosphate.
TABLE 3 example 3 purification of wet phosphoric acid before and after impurity and phosphoric acid content
Comparative example
S1, filtering 100L of wet phosphoric acid, adding the filtered phosphoric acid into nanofiltration small test equipment, controlling the temperature at 45 ℃, controlling the operating pressure at 5MPa, and controlling the concentration multiple to 2 times to obtain 50L of purified phosphoric acid and 50L of nanofiltration concentrated residual acid. The 50L nanofiltration concentrated residual acid is discarded, and the yield of phosphoric acid is 43 percent
S2, taking 2.8L of purified phosphoric acid, slowly adding 310mL of 25% ammonia water, adjusting the pH to 3.7, and then adding pure water to dilute to 3.4L to obtain 3.4L of monoammonium phosphate solution.
S3, mixing the monoammonium phosphate solution obtained in the step 2 with 4L of ferrous sulfate solution with the concentration of 2.46 mol/L; the molar ratio of ferrous sulfate to monoammonium phosphate solution in the mixed solution is 1:1.1, and then 0.5mol of purified phosphoric acid obtained in the step 1 is added.
And S5, slowly adding 600mL of 30% hydrogen peroxide into the mixed solution obtained in the step 3, heating, controlling the reaction temperature to 80 ℃, and reacting for 2 hours to obtain the battery-grade ferric phosphate.
TABLE 4 comparative examples impurity and phosphoric acid content before and after purification of wet phosphoric acid
Compared with example 1, the comparative example is not prepurified, and nanofiltration purification is directly carried out, so that the operation load of nanofiltration membranes is greatly increased, the temperature is increased from 33 ℃ to 45 ℃, the pressure is increased from 3.2MPa to 5MPa, the operation flux can still only reach 70% of that of example 1, and the quality of the obtained purified phosphoric acid is poor. Thus, more nanofiltration membrane equipment is required to be invested, the service life of the membrane is reduced, and the replacement cost is increased; the nanofiltration concentration residual acid is not recycled, the yield of phosphoric acid is only 43%, which is far lower than 81.3% of that of the embodiment 1, and the concentration residual acid is difficult to dispose, and additional investment is required.
Compared with the existing membrane purification process, the wet-process phosphoric acid purification method provided by the embodiment of the application does not need chemical pretreatment or dilution of the wet-process phosphoric acid, and simultaneously solves the problem of low operation flux of nanofiltration membranes, is a short-distance, low-cost and high-phosphoric acid yield wet-process phosphoric acid purification method, and the purified phosphoric acid can meet the technical requirements for preparing battery-grade ferric phosphate.
The foregoing description of the preferred embodiments of the application is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the application.
Claims (9)
1. A method for purifying phosphoric acid by wet process, comprising: dialyzing wet phosphoric acid by adopting a monovalent cation exchange membrane to obtain pre-purified phosphoric acid; filtering the pre-purified phosphoric acid by adopting a nanofiltration membrane to obtain nanofiltration concentrated solution and purified phosphoric acid; when the monovalent cation exchange membrane is adopted to dialyze the wet-process phosphoric acid, the feeding side of the monovalent cation exchange membrane is the wet-process phosphoric acid, and the collecting side of the monovalent cation exchange membrane is pure water or phosphoric acid solution with the concentration of phosphoric acid being less than that of the wet-process phosphoric acid.
2. The method for purifying wet process phosphoric acid according to claim 1, wherein when pure water is on the collecting side of the monovalent cation exchange membrane, the flow rate of the wet process phosphoric acid is greater than or equal to the flow rate of the pure water, the flow rate of the wet process phosphoric acid is 30 to 60L/h, and the flow rate of the pure water is 30 to 60L/h.
3. The method of wet phosphoric acid purification according to claim 1, wherein the nanofiltration concentrate is returned to the feed side of the monovalent cation exchange membrane and dialyzed again through the monovalent cation exchange membrane.
4. The method for purifying wet-process phosphoric acid according to claim 1, wherein the monovalent cation exchange membrane comprises a cation exchange membrane and a modifying layer attached to the surface of the cation exchange membrane.
5. The method of purifying wet process phosphoric acid according to claim 4, wherein the modifying layer comprises an electropositive polymer.
6. A method for preparing iron phosphate, comprising: reacting the purified phosphoric acid produced by the purification method of wet-process phosphoric acid according to any one of claims 1 to 5 with aqueous ammonia to obtain monoammonium phosphate solution; mixing the monoammonium phosphate solution with a ferrous sulfate solution to obtain a first mixed solution; adding hydrogen peroxide into the first mixed solution to obtain a second mixed solution; and reacting the second mixed solution at a first temperature for a first period of time to obtain ferric phosphate.
7. The method for producing iron phosphate according to claim 6, wherein the pH of the monoammonium phosphate solution is controlled to be 1.5 to 5.0;
and/or the first mixed solution further comprises a pH regulator, wherein the pH regulator is at least one of sulfuric acid and phosphoric acid, and the molar ratio of the pH regulator to ferrous sulfate is (0.1-0.4): 1;
and/or the molar ratio of the ferrous sulfate to the monoammonium phosphate in the first mixed solution is 1 (0.8-1.2);
and/or the mass fraction of ferrous ions in the second mixed solution is less than 0.01%;
and/or the first temperature is 50-100 ℃, and the first time period is 1-10 h.
8. A wet process phosphoric acid purification system, comprising:
a dialysis unit comprising a monovalent cation exchange membrane for dialyzing wet phosphoric acid to obtain pre-purified phosphoric acid;
the nanofiltration unit comprises a nanofiltration membrane, and the nanofiltration membrane is used for filtering the pre-purified phosphoric acid to obtain nanofiltration concentrated solution and purified phosphoric acid.
9. The purification system of wet process phosphoric acid according to claim 8, wherein the monovalent cation exchange membrane comprises a cation exchange membrane and a modifying layer attached to a surface of the cation exchange membrane, the modifying layer comprising an electropositive polymer;
and/or the purification system of the wet-process phosphoric acid further comprises a transfer pond, a first connecting pipeline and a second connecting pipeline, wherein the transfer pond is connected with the collecting side of the monovalent cation exchange membrane through the first connecting pipeline, and the transfer pond is connected with the feeding side of the nanofiltration membrane through the second connecting pipeline;
and/or, the purification system of wet-process phosphoric acid further comprises a third connecting pipeline, wherein the third connecting pipeline is connected with the feeding side of the monovalent cation exchange membrane and the feeding side of the nanofiltration membrane.
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