CN117361472A - Method for synthesizing low-impurity-content ferric phosphate by using titanium dioxide byproduct ferrous sulfate - Google Patents
Method for synthesizing low-impurity-content ferric phosphate by using titanium dioxide byproduct ferrous sulfate Download PDFInfo
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- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 title claims abstract description 94
- 239000005955 Ferric phosphate Substances 0.000 title claims abstract description 75
- 229940032958 ferric phosphate Drugs 0.000 title claims abstract description 75
- 229910000399 iron(III) phosphate Inorganic materials 0.000 title claims abstract description 75
- 239000011790 ferrous sulphate Substances 0.000 title claims abstract description 70
- 235000003891 ferrous sulphate Nutrition 0.000 title claims abstract description 70
- 229910000359 iron(II) sulfate Inorganic materials 0.000 title claims abstract description 70
- 238000000034 method Methods 0.000 title claims abstract description 63
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 title claims abstract description 59
- 239000006227 byproduct Substances 0.000 title claims abstract description 32
- 239000004408 titanium dioxide Substances 0.000 title claims abstract description 26
- 230000002194 synthesizing effect Effects 0.000 title claims abstract description 21
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 title claims abstract 19
- 239000012535 impurity Substances 0.000 claims abstract description 81
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims abstract description 76
- 239000000243 solution Substances 0.000 claims abstract description 71
- 239000002002 slurry Substances 0.000 claims abstract description 49
- 238000005406 washing Methods 0.000 claims abstract description 49
- 238000006243 chemical reaction Methods 0.000 claims abstract description 44
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims abstract description 38
- 239000000047 product Substances 0.000 claims abstract description 38
- 239000012065 filter cake Substances 0.000 claims abstract description 36
- 238000001914 filtration Methods 0.000 claims abstract description 31
- 150000003017 phosphorus Chemical class 0.000 claims abstract description 29
- 239000011259 mixed solution Substances 0.000 claims abstract description 24
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 18
- 230000032683 aging Effects 0.000 claims abstract description 13
- 239000013078 crystal Substances 0.000 claims abstract description 13
- 239000012266 salt solution Substances 0.000 claims abstract description 12
- 230000002378 acidificating effect Effects 0.000 claims abstract description 10
- 238000001035 drying Methods 0.000 claims abstract description 9
- 238000001354 calcination Methods 0.000 claims abstract description 8
- 238000002156 mixing Methods 0.000 claims abstract description 8
- 230000009466 transformation Effects 0.000 claims abstract description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 44
- 229910019142 PO4 Inorganic materials 0.000 claims description 23
- 239000010452 phosphate Substances 0.000 claims description 23
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims description 23
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 20
- 239000000725 suspension Substances 0.000 claims description 20
- 238000003756 stirring Methods 0.000 claims description 19
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 14
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 12
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 12
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 12
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 10
- 239000012047 saturated solution Substances 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 7
- 150000003839 salts Chemical class 0.000 claims description 7
- 239000012066 reaction slurry Substances 0.000 claims description 6
- 239000007787 solid Substances 0.000 claims description 6
- 230000035484 reaction time Effects 0.000 claims description 4
- ROFVEXUMMXZLPA-UHFFFAOYSA-N Bipyridyl Chemical compound N1=CC=CC=C1C1=CC=CC=N1 ROFVEXUMMXZLPA-UHFFFAOYSA-N 0.000 claims description 2
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 claims description 2
- 239000000920 calcium hydroxide Substances 0.000 claims description 2
- 229910001861 calcium hydroxide Inorganic materials 0.000 claims description 2
- 239000002352 surface water Substances 0.000 claims description 2
- 229910000398 iron phosphate Inorganic materials 0.000 abstract description 15
- 239000007788 liquid Substances 0.000 abstract description 11
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 abstract description 8
- 239000002243 precursor Substances 0.000 abstract description 3
- 239000010405 anode material Substances 0.000 abstract description 2
- SURQXAFEQWPFPV-UHFFFAOYSA-L iron(2+) sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Fe+2].[O-]S([O-])(=O)=O SURQXAFEQWPFPV-UHFFFAOYSA-L 0.000 description 52
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 32
- 235000010215 titanium dioxide Nutrition 0.000 description 20
- 230000008569 process Effects 0.000 description 18
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 17
- 239000002994 raw material Substances 0.000 description 11
- 229910052742 iron Inorganic materials 0.000 description 8
- 238000003825 pressing Methods 0.000 description 8
- 239000011572 manganese Substances 0.000 description 7
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 6
- 230000008901 benefit Effects 0.000 description 6
- 229910052748 manganese Inorganic materials 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 239000011574 phosphorus Substances 0.000 description 6
- 229910052698 phosphorus Inorganic materials 0.000 description 6
- 229910001448 ferrous ion Inorganic materials 0.000 description 5
- 239000010936 titanium Substances 0.000 description 5
- 229910001037 White iron Inorganic materials 0.000 description 4
- 238000004458 analytical method Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000000227 grinding Methods 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 238000000746 purification Methods 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- 239000011777 magnesium Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 238000004537 pulping Methods 0.000 description 3
- 229910052719 titanium Inorganic materials 0.000 description 3
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 2
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 239000011575 calcium Substances 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 239000000084 colloidal system Substances 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 229960004887 ferric hydroxide Drugs 0.000 description 2
- 229910001447 ferric ion Inorganic materials 0.000 description 2
- -1 iron ions Chemical class 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
- 239000007791 liquid phase Substances 0.000 description 2
- 229910001416 lithium ion Inorganic materials 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
- 238000010979 pH adjustment Methods 0.000 description 2
- DPTATFGPDCLUTF-UHFFFAOYSA-N phosphanylidyneiron Chemical compound [Fe]#P DPTATFGPDCLUTF-UHFFFAOYSA-N 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000001878 scanning electron micrograph Methods 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 239000011593 sulfur Substances 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 238000005660 chlorination reaction Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000000975 co-precipitation Methods 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000002001 electrolyte material Substances 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 239000008394 flocculating agent Substances 0.000 description 1
- 238000003837 high-temperature calcination Methods 0.000 description 1
- 229910010272 inorganic material Inorganic materials 0.000 description 1
- 239000011147 inorganic material Substances 0.000 description 1
- 150000002505 iron Chemical class 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910000403 monosodium phosphate Inorganic materials 0.000 description 1
- 235000019799 monosodium phosphate Nutrition 0.000 description 1
- 239000012452 mother liquor Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000003002 pH adjusting agent Substances 0.000 description 1
- 150000002978 peroxides Chemical class 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 239000011591 potassium Substances 0.000 description 1
- 229910052700 potassium Inorganic materials 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- AJPJDKMHJJGVTQ-UHFFFAOYSA-M sodium dihydrogen phosphate Chemical compound [Na+].OP(O)([O-])=O AJPJDKMHJJGVTQ-UHFFFAOYSA-M 0.000 description 1
- 239000001488 sodium phosphate Substances 0.000 description 1
- 229910000162 sodium phosphate Inorganic materials 0.000 description 1
- 235000011008 sodium phosphates Nutrition 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 230000001502 supplementing effect Effects 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 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
- C01B25/26—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
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/01—Particle morphology depicted by an image
- C01P2004/03—Particle morphology depicted by an image obtained by SEM
-
- 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)
- Compounds Of Iron (AREA)
Abstract
The invention discloses a method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct, which comprises the following steps: respectively adding alkaline and acidic impurity removing agents into the titanium dioxide byproduct ferrous sulfate solution in sequence, and filtering after two impurity removing reactions to obtain ferrous sulfate clear liquid A; preparing a phosphorus salt mixed solution B; adding the mixed solution B into the ferric salt solution A, filtering the slurry after the reaction, and washing to obtain a filter cake C; adding the filter cake C into a dilute phosphoric acid solution for size mixing, and performing high-temperature crystal transformation aging to obtain slurry D; filtering and washing the slurry D, and repeating the filtering and washing operations to obtain a filter cake E; drying, calcining at high temperature and crushing the filter cake E to obtain an anhydrous ferric phosphate product; the iron phosphate product prepared by the method has low impurity content and stable quality, and can be used as an ideal precursor anode material for preparing high-capacity lithium iron phosphate batteries.
Description
Technical Field
The invention relates to the field of inorganic materials, in particular to a method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct.
Background
With the benefit of the rapid development of new energy vehicles and energy storage industry in China in recent years, the lithium iron phosphate gradually exceeds ternary materials to obtain market acceptance by virtue of the advantages of high safety, long cycle life, low cost and the like, the demand of the lithium iron phosphate is continuously increased, the productivity is also increased from 18.12 ten thousand tons per year at the end of 2018 to 89.8 ten thousand tons per year at the end of 2021, the annual composite growth rate is 70.5%, and the 2021 annual comparably speed increase is more than 167.9%. The quality indexes such as impurity content, crystal structure, micro morphology and the like of the ferric phosphate serving as an important precursor for producing the lithium iron phosphate have extremely important influence on the electrochemical performance of a downstream lithium iron phosphate battery. At present, ferric phosphate is usually prepared by reacting an iron source with a phosphorus source, and most ferric phosphate manufacturers in industry generally adopt ferrous sulfate as a byproduct of titanium white as the iron source and phosphoric acid or phosphate as the phosphorus source to prepare the ferric phosphate for the battery in order to reduce the production cost.
The production method of the titanium dioxide mainly comprises a sulfuric acid method and a chlorination method, wherein the domestic titanium dioxide production enterprises mainly use the sulfuric acid method. In the process of producing iron white powder by a sulfuric acid method, 3.5 to 4.0 tons of ferrous sulfate heptahydrate can be produced as a byproduct for each 1 ton of titanium white powder product, and the yield of the 2021-year sulfuric acid method titanium white powder is estimated to be 300 ten thousand tons, and the byproduct ferrous sulfate is about 1000 to 1200 ten thousand tons. Because the content of metal impurity elements, especially Ti, mg, al and Mn in the titanium dioxide byproduct ferrous sulfate is high, the metal impurity elements are difficult to be directly used for synthesizing ferric phosphate, the metal impurity elements are required to be subjected to impurity removal and purification treatment by adopting a proper pretreatment process, and meanwhile, the impurity content control process in the synthesis process is a technical key for preparing high-purity low-impurity-content ferrous sulfate by adopting the titanium dioxide byproduct ferrous sulfate. The Chinese patent application No. CN106892415A discloses a method for preparing ferric phosphate by using ferrous sulfate as a titanium white byproduct, and specifically discloses a method for preparing ferric phosphate by heating, bubbling air, adding sulfuric acid to adjust pH value, adding a flocculating agent, adding sodium dihydrogen phosphate to filter to obtain a ferrous sulfate solution after impurity removal, and finally adding sodium phosphate and phosphoric acid to perform conversion reaction. The method has the advantages that the impurity removal reaction temperature of the ferrous sulfate is higher, after air is blown in, ferrous ions are easy to hydrolyze and precipitate in a large amount, the iron loss is large, the product yield is low, the impurity removal process in the process is complex, the impurity requirements on the raw material titanium dioxide byproduct ferrous sulfate are strict, meanwhile, the washing water amount in the process of preparing ferric phosphate is large, and the quality of ferric phosphate is difficult to control. Chinese patent application CN107857243a discloses a method for preparing battery grade superfine ferric phosphate from by-product ferrous sulfate, which comprises adding phosphoric acid and ferrous iron in solution to form ferric phosphate colloid adsorption part impurities, adding flocculant, settling, filtering, adding ammonia water, converting ferrous sulfate into ferric hydroxide, supplementing phosphoric acid, and converting into ferric phosphate. The colloid formed by adding phosphoric acid has good effect of removing Ti, but has poor effect of adsorbing Mn, al and Mn impurities; meanwhile, in the process of synthesizing the ferric phosphate, impurities are easily carried into ferric hydroxide by coprecipitation with iron due to the addition of ammonia water, and after the impurities are converted into ferric phosphate, impurity elements Mg, al and Mn in a finished product of the ferric phosphate are higher; in addition, the amount of phosphoric acid added in the process of the aging reaction of the transition crystal of the later-stage ferric phosphate can cause inaccurate metering of a phosphorus source due to the phosphoric acid brought in the impurity removal stage, fe/P is difficult to control, fluctuation of product quality stability and consistency is caused, and adverse effects are generated on the electrical performance of downstream products. Based on the above, a process for synthesizing high-purity, low-impurity-content and stable-quality ferric phosphate by using the titanium dioxide byproduct ferrous sulfate, which is simple to operate and high in controllability, needs to be further developed.
Disclosure of Invention
The invention aims to solve the problems that in the process of synthesizing ferric phosphate by adopting ferrous sulfate as a titanium white byproduct in the current industry, a large amount of ammonium sulfate mother liquor generated in the reaction process of ferric phosphate and raw material impurity introduction cause coating of a large amount of metal and sulfur impurities of products, and the fluctuation of pH of a reaction system causes incomplete ferric phosphate precipitation reaction and the generation of metal impurity salt, so that the impurity content of the products is high, the iron-phosphorus ratio is unstable, the quality stability among batches is poor, and the like, and provides an industrial preparation method of ferric phosphate for batteries with low impurity content and stable product quality among batches.
In order to achieve the above purpose, a method for synthesizing low impurity content ferric phosphate by using ferrous sulfate as a titanium white byproduct is to take ferrous sulfate subjected to deep impurity removal and purification treatment and industrial grade phosphate subjected to impurity removal and pH adjustment as raw materials, synthesize ferric phosphate intermediate slurry by adopting a liquid phase precipitation method, filter, wash and reslurry, age by high Wen Zhuaijing to obtain ferric phosphate dihydrate slurry, and finally filter, wash, dry, calcine at high temperature and crush to obtain anhydrous ferric phosphate product with stable quality and low impurity content, wherein the method mainly comprises the following steps:
s1, adding water into ferrous sulfate which is a byproduct of titanium dioxide to dissolve to obtain a saturated solution of ferrous sulfate, adding an alkaline impurity removing agent into the saturated solution of ferrous sulfate under a stirring state, controlling the pH value of the solution to be 4.0-6.0 for impurity removing reaction, filtering the obtained slurry to obtain a ferrous sulfate solution, adding an acidic impurity removing agent for secondary impurity removing reaction, controlling the pH value of the solution to be 2.0-3.0, filtering the obtained slurry to obtain a refined ferrous sulfate solution A, and adding water to dilute to Fe 2+ The concentration is 0.80 to 1.25mol/L for standby;
s2, dissolving industrial phosphate in water to prepare a phosphate solution with the concentration of 0.5-1.2 mol/L, adding a pH regulator to adjust the pH of the solution to 6.0-8.0 for impurity removal reaction, adding hydrogen peroxide with a certain excess coefficient into the filtered phosphate clear solution, stirring uniformly to obtain a phosphate mixed solution B, and controlling the pH value of the mixed solution to be 6.5-7.5;
s3, rapidly adding the phosphate solution B obtained in the step S2 into the ferrous sulfate solution A obtained in the step S1, heating to 45-60 ℃ for reaction, controlling the pH of synthetic reaction slurry to be 2.5+/-0.5, reacting for 20-30 min to obtain light yellow ferric phosphate intermediate slurry C, and detecting the existence of Fe in the slurry 2+ If there is, for exampleHydrogen peroxide is added to the slurry without Fe 2+ ；
S4, filtering the light yellow ferric phosphate intermediate suspension C obtained in the step S3, and repeatedly washing with pure water at 60-70 ℃ until the conductivity of the washing water is less than or equal to 5ms/cm, so as to obtain a filter cake D;
s5, fePO 4 ·2H 2 Adding a certain amount of dilute phosphoric acid solution into O according to the solid content of 10.0-15.0%, slurrying the filter cake D obtained in the step S3 to obtain suspension E, and adding H 3 PO 4 The concentration of the diluted phosphoric acid solution is 2.0-4.0%, and the ratio of the total P and the total Fe of the reaction system is controlled to be 1.05-1.30: 1, carrying out aging and crystal transformation reaction under the conditions of high temperature and stirring to obtain white ferric phosphate slurry F;
s6, filtering the ferric phosphate slurry F obtained in the step S5, repeatedly washing until the conductivity of washing water is less than or equal to 2500 mu S/cm, drying a filter cake obtained after washing to remove surface water, calcining at a high temperature to remove free water, crushing to obtain an anhydrous ferric phosphate product, and mixing washing water with conductivity less than or equal to 3500 in the washing process with concentrated phosphoric acid to prepare a dilute phosphoric acid solution required in the step S5.
As a preferable technical scheme, the alkaline impurity removing agent in the step S1 is one of ammonia water, sodium hydroxide, potassium hydroxide or calcium hydroxide, and the acidic impurity removing agent is one of phosphoric acid and sulfuric acid.
As a further preferred aspect, the alkaline impurity removing agent in the step S1 is ammonia water, and the acidic impurity removing agent is phosphoric acid.
As a preferable technical scheme, the impurity removal reaction temperature is 50-60 ℃ and the reaction time is 30-90 min.
As a preferable technical scheme, the pH regulator in the step S2 is one of ammonia water, sodium hydroxide and potassium hydroxide.
As a further preferred aspect, the pH adjuster in step S2 is aqueous ammonia.
As a preferable technical scheme, the impurity removal reaction temperature is 40-50 ℃, the reaction time is 20-30 min, and the excess coefficient of hydrogen peroxide is 1.10-1.40.
As a preferable technical solution, in the step S3,the rapid charging time of the phosphorus salt mixed solution B is 5-15 min, and the presence or absence of Fe in the slurry is detected 2+ Is a bipyridine indicator.
As a preferable technical scheme, in the step S3, the adding amount of the phosphorus salt solution B is 0.85-0.95 according to the molar metering ratio of the phosphorus salt to the iron salt: 1.
Due to the adoption of the technical scheme, the method for synthesizing the low-impurity-content ferric phosphate by utilizing the titanium dioxide byproduct ferrous sulfate comprises the following steps of: (1) Respectively adding alkaline and acidic impurity removing agents into the titanium dioxide byproduct ferrous sulfate solution in sequence, performing impurity removing reaction twice, and filtering to obtain ferrous sulfate clear liquid A with lower impurity content; (2) Dissolving industrial-grade phosphate into phosphate solution by adding water, adding a pH regulator to adjust the pH of the solution to 6.0-8.0 for impurity removal reaction, removing main metal impurities affecting the quality of ferric phosphate products, adding hydrogen peroxide with a certain excess coefficient into the filtered phosphate mixed solution, and uniformly stirring to obtain a phosphate mixed solution B; (3) Rapidly adding the mixed solution B into the ferric salt solution A, reacting for a period of time, filtering the slurry, and washing to obtain a filter cake C; (4) Adding the filter cake C into a dilute phosphoric acid solution for size mixing, controlling the molar ratio of total P and total Fe of a reaction system to be 1.05-1.30, and performing high-temperature crystal transformation aging to obtain slurry D; (5) Filtering and washing the slurry D, repeating the filtering and washing operations until the conductivity of washing water is less than or equal to 2500 mu s/cm, obtaining a filter cake E, and taking washing water with the conductivity less than or equal to 3500 in the washing process for preparing dilute phosphoric acid solution for size mixing; (6) And drying, calcining at high temperature and crushing the filter cake E to obtain an anhydrous ferric phosphate product. The iron phosphate product prepared by the method has low impurity content and stable quality, and can be used as an ideal precursor anode material for preparing high-capacity lithium iron phosphate batteries.
The invention has the advantages that:
the invention provides an industrial preparation method of iron phosphate for batteries, which has low impurity content and stable product quality among batches. Firstly, ferrous sulfate subjected to impurity removal and purification treatment and phosphate subjected to impurity removal, purification and pH adjustment are used as raw materials, an iron phosphate intermediate slurry is synthesized by adopting a liquid phase precipitation method, diluted phosphoric acid is added after filtration and washing, then high-temperature crystal transformation aging is carried out to obtain a ferric phosphate dihydrate slurry, and finally, a product of anhydrous ferric phosphate with stable quality and low impurity content is obtained through filtration, washing, drying, high-temperature calcination and crushing.
The invention adopts ferrous sulfate as a byproduct of titanium white as a raw material, firstly adds an alkaline impurity removing agent to remove Al, zn, mn, mg impurity elements in the raw material, then adds an acidic impurity removing agent to remove Ti, mg and Mn in the raw material for the second time, obtains an iron source raw material with lower impurity content through twice impurity removal, and simultaneously adopts a mode of adding the alkaline impurity removing agent firstly and then adding the acidic impurity removing agent to properly callback the pH value of ferrous sulfate solution to prevent Fe under high pH condition 2+ Is formed into Fe (OH) 3 The stability of the ferrous raw material is ensured; the industrial phosphate is adopted to replace water-soluble phosphate and battery-grade phosphate with higher cost, and the use cost of the phosphorus source is reduced on the basis that the raw materials meet the impurity content requirement through impurity removal reaction; the method has the advantages that the method adopts the modes of improving the concentration of ferric salt and shortening the feeding time of the phosphate mixed solution, so that the number of ferric phosphate crystal nuclei is increased and crystals are quickly nucleated in the synthetic reaction process, the coating of impurity impurities in the process of growing crystal nuclei due to overlong feeding time is reduced, and the consumption of subsequent washing water is reduced; the characteristics of high phosphorus content and low impurity content of the secondary washing water of crystal transformation aging are fully utilized, the cyclic utilization of washing water and valuable phosphorus elements is realized, and the treatment load of a water system in the later stage is reduced; the method utilizes the characteristic that the dilute phosphoric acid solution is easier to disperse the filter cake obtained by the primary plate frame more uniformly in the reslurry process, and advances the adding point of phosphoric acid required by crystal transformation aging from the crystal transformation aging process to the reslurry process, thereby ensuring the uniformity of the aged ferric phosphate slurry.
According to the method, the problems of high impurity content, large process fluctuation, unstable iron-phosphorus ratio, poor quality stability among batches and the like of raw materials in the existing industry for synthesizing ferric phosphate by adopting the titanium dioxide byproduct ferrous sulfate are overcome by the innovative invention measures, and the ferric phosphate product with low impurity content and stable quality among batches is obtained.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is an SEM image of the iron phosphate prepared in example 1;
fig. 3 is an XRD pattern of the iron phosphate prepared in example 1.
Detailed Description
The invention provides a method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct.
The invention is further described in connection with the following embodiments in order to make the technical means, the creation features, the achievement of the purpose and the effect of the invention easy to understand.
Example 1:
(1) Dissolving ferrous sulfate in water to obtain saturated solution, adding 20% NH 3 ·H 2 Adjusting the pH of the ferrous solution to 5.5 by O, reacting for 90min at 50 ℃ to remove impurities, press-filtering the obtained slurry by a plate and frame to obtain a ferrous sulfate solution, and adding 15% phosphoric acid (in H) 3 PO 4 Calculated) reacts for 25min at 45 ℃, the obtained slurry is subjected to plate-frame filter pressing to obtain ferrous sulfate clear liquid, and water is added to dilute the ferrous sulfate clear liquid to Fe 2+ The concentration is 0.85mol/L for standby;
(2) Adding 20% NH into 0.65mol/L phosphorus salt solution 3 .H 2 O adjusts the pH of the solution to 6.8, reacts for 20min at 45 ℃ to obtain slurry, and the slurry is subjected to plate-frame filter pressing to obtain a phosphorus salt clear solution, wherein 27% hydrogen peroxide is added according to 1.20eq of the theoretical dosage of the ferrous ions completely oxidized into the ferric ions, and the mixed solution of the phosphorus salt is obtained after uniform stirring, and the pH of the mixed solution is 6.5;
(3) Taking the prepared ferrous sulfate solution, and stirring the phosphorus salt solution according to the mole ratio of phosphorus salt to ferric salt of 0.87:1 is added to a ferrous solution, the adding time of a phosphorus salt mixed solution is 10min, the temperature is raised to 52 ℃ after the adding is finished, the reaction is carried out, the pH of synthetic reaction slurry is controlled to be 2.2+/-0.2, and after the reaction is carried out for 25min, a yellow ferric phosphate intermediate suspension is obtained;
(4) Filtering the yellow ferric phosphate intermediate suspension, repeatedly washing with pure water with conductivity less than or equal to 100 mu s/cm at 65deg.C until the conductivity of the washing solution is less than or equal to 5ms/cm to obtain filter cake with solid content of 12.0% (FePO) 4 ·2H 2 O meter) add 3% of dilute phosphoric acid solution, and slurrying the washed filter cake to obtain a suspension;
(5) Adding phosphoric acid into the suspension E, and controlling the molar ratio of total P and total Fe of a reaction system to be 1.10:1, rapidly heating to 88 ℃ under the condition of stirring speed of 200r/min to perform high Wen Zhuaijing aging reaction, and preserving heat for 90min under the condition to obtain white ferric phosphate slurry;
(6) Filtering the obtained white iron phosphate slurry, washing the filter cake with washing water with the conductivity less than or equal to 100 mu s/cm until the conductivity of the washing water is 2500 mu s/cm to obtain a white filter cake, drying the filter cake at 105 ℃ for 3.5h, calcining at 580 ℃ for 4.5h at high temperature, crushing and grinding to obtain the anhydrous iron phosphate product.
The quality analysis results of the anhydrous phosphoric acid product in the embodiment are shown in table 1, and from table 1, it can be seen that the Fe/P of the iron phosphate product synthesized by the method is 0.964, and meets the requirements of 0.965+/-0.05 of the main stream market product; d50 (D50)<The particle size distribution is uniform and is 4 mu m, which meets the requirement of the particle size of the product; the BET (specific surface area) distribution range of the product is narrow and is 8-9 m 2 Between/g; tap density of 0.95g/m 3 Far greater than 0.60g/m required by the iron phosphate standard for HG/T4701-2004 batteries 3 The impurity elements of the product are far lower than those of the iron phosphate product obtained by the traditional process. As shown in the SEM images and XRD images of the anhydrous ferric phosphate products respectively as shown in the figures 2 and 3, the ferric phosphate particles synthesized by the method have uniform size and a porous structure, the lithium iron phosphate product synthesized by the ferric phosphate with the microcosmic appearance has high specific surface area, increases the contact area of electrolyte and positive electrode materials, is beneficial to the diffusion of lithium ions, overcomes the defect of poor conductivity and ploidy of micron-sized lithium iron phosphate particles, simultaneously retains higher compaction density, increases the discharge capacity of a battery, reduces internal resistance, reduces polarization loss, and achieves the purposes of prolonging the cycle life of the battery and improving the utilization rate of the lithium ion battery. As can be seen from XRD patterns of the product, all diffraction peak positions and intensities of the ferric phosphate synthesized by the method correspond to those of standard card PDF#84-0876, no impurity peak exists in the diffraction patterns, and the purity of the product is high.
Table 1 results of physicochemical analysis and ICP contrast analysis of the products
Example 2:
(1) Dissolving ferrous sulfate in water to obtain saturated solution, adding 20% NH 3 ·H 2 Adjusting the pH of the ferrous solution to 6.0 by O, reacting at 55 ℃ for 70min for impurity removal, press-filtering the obtained slurry by a plate and frame to obtain a ferrous sulfate solution, and adding 15% phosphoric acid (in H) 3 PO 4 Calculated) reacts for 30min at 45 ℃, the obtained slurry is subjected to plate-frame filter pressing to obtain ferrous sulfate clear liquid, and water is added to dilute the ferrous sulfate clear liquid to Fe 2+ The concentration is 0.90mol/L for standby;
(2) Adding 20% NH into 0.60mol/L phosphorus salt solution 3 .H 2 O adjusts the pH of the solution to 7.2, reacts for 30min at 48 ℃, and obtains a phosphorus salt clear solution by plate-and-frame filter pressing of slurry, and 27% hydrogen peroxide is added according to 1.18eq of the theoretical dosage of the ferrous ions to be completely oxidized into iron ions, and the mixed solution of the phosphorus salt is obtained by uniformly stirring, wherein the pH of the mixed solution is 6.8;
(3) Taking the prepared ferrous sulfate solution, and stirring the phosphorus salt solution according to the mole ratio of phosphorus salt to ferric salt of 0.90:1 is added to a ferrous solution, the adding time of a phosphorus salt mixed solution is 15min, the temperature is raised to 52 ℃ after the adding is finished, the reaction is carried out, the pH of synthetic reaction slurry is controlled to be 2.3+/-0.2, and after the reaction is carried out for 25min, a yellow ferric phosphate intermediate suspension is obtained;
(4) Filtering the yellow ferric phosphate intermediate suspension, repeatedly washing with pure water with conductivity less than or equal to 100 μs/cm at 60deg.C until the conductivity of the washing solution reaches 4500 μs/cm to obtain filter cake, and mixing with FePO solution with solid content of 11.0% 4 ·2H 2 O meter) adding 2.5% dilute phosphoric acid solution, and pulping the washed filter cake to obtain suspension;
(5) Adding phosphoric acid into the suspension E, and controlling the molar ratio of total P and total Fe of a reaction system to be 1.12:1, rapidly heating to 90 ℃ under stirring to perform high Wen Zhuaijing aging reaction, and preserving heat for 70min under the condition to obtain white ferric phosphate slurry;
(6) Filtering the obtained white iron phosphate slurry, washing the filter cake with washing water with the conductivity less than or equal to 100 mu s/cm until the conductivity of the washing water is 1800 mu s/cm to obtain a white filter cake, drying the filter cake at 105 ℃ for 4.5 hours, calcining the filter cake at 600 ℃ for 4.0 hours at high temperature, and crushing and grinding to obtain the anhydrous iron phosphate product.
Example 3:
(1) Dissolving ferrous sulfate in water to obtain saturated solution, adding 25% NH3.H2O to adjust the pH of the ferrous solution to 5.7, reacting at 58 deg.C for 60min to remove impurities, press-filtering the slurry to obtain ferrous sulfate solution, and adding 20% phosphoric acid (as H) 3 PO 4 Calculated) reacts for 20min at 45 ℃, the obtained slurry is subjected to plate-frame filter pressing to obtain ferrous sulfate clear liquid, and water is added to dilute the ferrous sulfate clear liquid to Fe 2+ The concentration is 0.94mol/L for standby;
(2) Adding 20% NH into 0.71mol/L phosphorus salt solution 3 .H 2 O adjusts the pH of the solution to 7.0, reacts for 25min at 45 ℃ to obtain slurry, and the slurry is subjected to plate-frame filter pressing to obtain a phosphorus salt clear solution, wherein 27% hydrogen peroxide is added according to 1.25eq of the theoretical dosage of the ferrous ions completely oxidized into the ferric ions, and the mixed solution of the phosphorus salt is obtained after uniform stirring, and the pH of the mixed solution is 6.7;
(3) Taking the prepared ferrous sulfate solution, and stirring the phosphorus salt solution according to the mole ratio of phosphorus salt to ferric salt of 0.88:1 is added into ferrous solution, the adding time of the mixed solution of the phosphate and the ferrous solution is 10min, the temperature is raised to 58 ℃ after the adding is finished, the low-temperature reaction is carried out, the pH value of the synthesized reaction slurry is controlled to be 2.3+/-0.2, and the yellow ferric phosphate intermediate suspension is obtained after the reaction is carried out for 30 min;
(4) Filtering the yellow ferric phosphate intermediate suspension, repeatedly washing with pure water with conductivity less than or equal to 100 μs/cm at 68deg.C until the conductivity of the washing solution is 3200 μs/cm to obtain filter cake, and mixing with FePO solution with solid content of 13.0% 4 ·2H 2 O meter) add 2.Pulping the washed filter cake with 0% dilute phosphoric acid solution to obtain suspension;
(5) Adding phosphoric acid into the suspension E, and controlling the molar ratio of total P and total Fe of a reaction system to be 1.17:1, rapidly heating to 87 ℃ under stirring to perform high Wen Zhuaijing aging reaction, and preserving heat for 120min under the condition to obtain white ferric phosphate slurry;
(6) Filtering the obtained white iron phosphate slurry, washing the filter cake with washing water with the conductivity less than or equal to 100 mu s/cm until the conductivity of the washing water is 1900 mu s/cm to obtain a white filter cake, drying the filter cake at 105 ℃ for 4.0h, calcining at 620 ℃ for 3.5h at high temperature, crushing and grinding to obtain the anhydrous iron phosphate product.
Example 4:
(1) Dissolving ferrous sulfate in water to obtain saturated solution, adding 22% NH3.H2O to adjust the pH of ferrous solution to 5.4, reacting at 60deg.C for 45min to remove impurities, press-filtering the slurry with plate and frame to obtain ferrous sulfate solution, and adding 15% phosphoric acid (as H) 3 PO 4 Calculated) reacts for 20min at 48 ℃, the obtained slurry is subjected to plate-frame filter pressing to obtain ferrous sulfate clear liquid, and water is added to dilute the ferrous sulfate clear liquid to Fe 2+ The concentration is 1.04mol/L for standby;
(2) Adding 20% NH into 0.90mol/L phosphorus salt solution 3 .H 2 O adjusts the pH of the solution to 7.2, reacts for 20min at 50 ℃, and obtains a phosphorus salt clear solution by plate-and-frame filter pressing of slurry, and 27% hydrogen peroxide is added according to 1.30eq of the theoretical dosage of the ferrous ions to be completely oxidized into iron ions, and the mixed solution of the phosphorus salt is obtained by uniformly stirring, wherein the pH of the mixed solution is 6.8;
(3) Taking the prepared ferrous sulfate solution, and under the condition of stirring speed of 300r/min, mixing the phosphorus salt solution according to the mole ratio of phosphorus salt to ferric salt of 0.92:1 is added into ferrous solution, the adding time of the mixed solution of the phosphate and the ferrous solution is 7min, the temperature is raised to 52 ℃ after the adding is finished, the low-temperature reaction is carried out, the pH value of the synthesized reaction slurry is controlled to be 2.4+/-0.1, and the yellow ferric phosphate intermediate suspension is obtained after the reaction is carried out for 25 min;
(4) Filtering the yellow ferric phosphate intermediate suspension, repeatedly washing with pure water with conductivity less than or equal to 100 μs/cm at 60deg.C to conductivity 1500 μs of the washing liquids/cm to give a filter cake with a solids content of 14.0% (as FePO) 4 .2H 2 O meter) adding 3.2% dilute phosphoric acid solution, and pulping the washed filter cake to obtain suspension;
(5) Adding phosphoric acid into the suspension E, and controlling the molar ratio of total P and total Fe of a reaction system to be 1.15:1, rapidly heating to 92 ℃ under the condition of stirring speed of 200r/min to perform high Wen Zhuaijing aging reaction, and preserving heat for 60min under the condition to obtain white ferric phosphate slurry;
(6) Filtering the obtained white iron phosphate slurry, washing the filter cake with washing water with the conductivity less than or equal to 100 mu s/cm until the conductivity of the washing water reaches 2100 mu s/cm to obtain a white filter cake, drying the filter cake at 105 ℃ for 4.5h, calcining at 570 ℃ for 4.5h at high temperature, crushing and grinding to obtain the anhydrous iron phosphate product.
As can be seen from Table 2, the iron phosphate produced by the invention in the industrial device has good consistency of the products among batches, the Fe/P deviation of the products among batches is +/-0.001, and the indexes such as D50, a comparison table, tap density and the like are stable. The impurity content is obviously lower than that of the traditional process, wherein, sodium (Na) is less than or equal to 5ppm, potassium (K) is less than or equal to 5ppm, calcium (Ca) is less than or equal to 10ppm, copper (Cu) is less than or equal to 5ppm, zn is less than or equal to 20ppm, chromium (Cr) is less than or equal to 10ppm, cobalt (Co) is less than or equal to 5ppm, lead (Pb) is less than or equal to 10ppm, nickel (Ni) is less than or equal to 5ppm, manganese (Mn) is less than or equal to 50ppm, titanium (Ti) is less than or equal to 10ppm, magnesium (Mg) is less than or equal to 50ppm, aluminum (Al) is less than or equal to 20ppm, and sulfur (S) is less than or equal to 50ppm.
TABLE 2 analysis and detection results of iron phosphate products
Although the invention has been described herein with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope and spirit of the principles of this disclosure. More specifically, various variations and modifications may be made to the component parts or arrangements of the subject combination arrangement within the scope of the disclosure, drawings and claims of this application. In addition to variations and modifications in the component parts or arrangements, other uses will be apparent to those skilled in the art.
The foregoing has shown and described the basic principles, main features and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made without departing from the spirit and scope of the invention, which is defined in the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (9)
1. The method for synthesizing the low-impurity-content ferric phosphate by using the titanium dioxide byproduct ferrous sulfate is characterized by comprising the following steps of:
s1, adding water into ferrous sulfate which is a byproduct of titanium dioxide to dissolve to obtain a saturated solution of ferrous sulfate, adding an alkaline impurity removing agent into the saturated solution of ferrous sulfate under a stirring state, controlling the pH value of the solution to be 4.0-6.0 for impurity removing reaction, filtering the obtained slurry to obtain a ferrous sulfate solution, adding an acidic impurity removing agent for secondary impurity removing reaction, controlling the pH value of the solution to be 2.0-3.0, filtering the obtained slurry to obtain a refined ferrous sulfate solution A, and adding water to dilute to Fe 2+ The concentration is 0.80 to 1.25mol/L for standby;
s2, dissolving industrial phosphate in water to prepare a phosphate solution with the concentration of 0.5-1.2 mol/L, adding a pH regulator to adjust the pH of the solution to 6.0-8.0 for impurity removal reaction, adding hydrogen peroxide with a certain excess coefficient into the filtered phosphate clear solution, stirring uniformly to obtain a phosphate mixed solution B, and controlling the pH value of the mixed solution to be 6.5-7.5;
s3, rapidly adding the phosphate solution B obtained in the step S2 into the ferrous sulfate solution A obtained in the step S1, heating to 45-60 ℃ for reaction, controlling the pH of the synthetic reaction slurry to be 2.5+/-0.5, reacting for 20-30 min,obtaining yellowish ferric phosphate intermediate slurry C, and simultaneously detecting the existence of Fe in the slurry 2+ If so, adding hydrogen peroxide to the slurry without Fe 2+ ；
S4, filtering the light yellow ferric phosphate intermediate suspension C obtained in the step S3, and repeatedly washing with pure water at 60-70 ℃ until the conductivity of the washing water is less than or equal to 5ms/cm, so as to obtain a filter cake D;
s5, fePO 4 ·2H 2 Adding a certain amount of dilute phosphoric acid solution into O according to the solid content of 10.0-15.0%, slurrying the filter cake D obtained in the step S3 to obtain suspension E, and adding H 3 PO 4 The concentration of the diluted phosphoric acid solution is 2.0-4.0%, and the ratio of the total P and the total Fe of the reaction system is controlled to be 1.05-1.30: 1, carrying out aging and crystal transformation reaction under the conditions of high temperature and stirring to obtain white ferric phosphate slurry F;
s6, filtering the ferric phosphate slurry F obtained in the step S5, repeatedly washing until the conductivity of washing water is less than or equal to 2500 mu S/cm, drying a filter cake obtained after washing to remove surface water, calcining at a high temperature to remove free water, crushing to obtain an anhydrous ferric phosphate product, and mixing washing water with conductivity less than or equal to 3500 in the washing process with concentrated phosphoric acid to prepare a dilute phosphoric acid solution required in the step S5.
2. The method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct according to claim 1, wherein the method comprises the following steps: in the step S1, the alkaline impurity removing agent is one of ammonia water, sodium hydroxide, potassium hydroxide or calcium hydroxide, and the acidic impurity removing agent is one of phosphoric acid and sulfuric acid.
3. The method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct according to claim 2, wherein the method comprises the following steps: in the step S1, the alkaline impurity removing agent is ammonia water, and the acidic impurity removing agent is phosphoric acid.
4. The method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct according to claim 1, wherein the method comprises the following steps: the impurity removal reaction temperature is 50-60 ℃, and the reaction time is 30-90 min.
5. The method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct according to claim 1, wherein the method comprises the following steps: the pH regulator in the step S2 is one of ammonia water, sodium hydroxide and potassium hydroxide.
6. The method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct according to claim 5, wherein the method comprises the following steps: and the pH regulator in the step S2 is ammonia water.
7. The method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct according to claim 1, wherein the method comprises the following steps: the impurity removal reaction temperature is 40-50 ℃, the reaction time is 20-30 min, and the excess coefficient of hydrogen peroxide is 1.10-1.40.
8. The method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct according to claim 1, wherein the method comprises the following steps: in the step S3, the rapid feeding time of the phosphorus salt mixed solution B is 5-15 min, and the presence or absence of Fe in the slurry is detected 2+ Is a bipyridine indicator.
9. The method for synthesizing low-impurity-content ferric phosphate by using ferrous sulfate as a titanium dioxide byproduct according to claim 1, wherein the method comprises the following steps: in the step S3, the adding amount of the phosphorus salt solution B is 0.85-0.95 according to the mole metering ratio of phosphorus salt to ferric salt: 1.
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