CN117534125A - Impurity removing method for titanium dioxide byproduct ferrous sulfate - Google Patents
Impurity removing method for titanium dioxide byproduct ferrous sulfate Download PDFInfo
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- CN117534125A CN117534125A CN202311599862.6A CN202311599862A CN117534125A CN 117534125 A CN117534125 A CN 117534125A CN 202311599862 A CN202311599862 A CN 202311599862A CN 117534125 A CN117534125 A CN 117534125A
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- ferrous sulfate
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- titanium dioxide
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- phosphoric acid
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- 239000012535 impurity Substances 0.000 title claims abstract description 99
- 239000011790 ferrous sulphate Substances 0.000 title claims abstract description 89
- 235000003891 ferrous sulphate Nutrition 0.000 title claims abstract description 89
- 229910000359 iron(II) sulfate Inorganic materials 0.000 title claims abstract description 89
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 title claims abstract description 64
- 238000000034 method Methods 0.000 title claims abstract description 51
- 239000004408 titanium dioxide Substances 0.000 title claims abstract description 32
- 239000006227 byproduct Substances 0.000 title claims abstract description 31
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 title claims 12
- 239000000243 solution Substances 0.000 claims abstract description 94
- 239000013078 crystal Substances 0.000 claims abstract description 62
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims abstract description 58
- 239000000706 filtrate Substances 0.000 claims abstract description 49
- 238000002425 crystallisation Methods 0.000 claims abstract description 45
- 230000008025 crystallization Effects 0.000 claims abstract description 45
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims abstract description 29
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 24
- 238000003756 stirring Methods 0.000 claims abstract description 22
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims abstract description 21
- 235000011114 ammonium hydroxide Nutrition 0.000 claims abstract description 21
- 239000005955 Ferric phosphate Substances 0.000 claims abstract description 19
- 229940032958 ferric phosphate Drugs 0.000 claims abstract description 19
- 229910000399 iron(III) phosphate Inorganic materials 0.000 claims abstract description 19
- 238000001914 filtration Methods 0.000 claims abstract description 18
- 238000001816 cooling Methods 0.000 claims abstract description 13
- 239000012452 mother liquor Substances 0.000 claims abstract description 13
- 238000001704 evaporation Methods 0.000 claims abstract description 11
- 239000012047 saturated solution Substances 0.000 claims abstract description 10
- 239000000126 substance Substances 0.000 claims abstract description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 32
- 229910052742 iron Inorganic materials 0.000 claims description 15
- 230000001105 regulatory effect Effects 0.000 claims description 9
- 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 abstract description 90
- 238000001953 recrystallisation Methods 0.000 abstract description 15
- 229910052751 metal Inorganic materials 0.000 abstract description 10
- 239000002184 metal Substances 0.000 abstract description 10
- 230000002194 synthesizing effect Effects 0.000 abstract description 3
- 238000004090 dissolution Methods 0.000 abstract description 2
- 239000007787 solid Substances 0.000 abstract description 2
- 238000004176 ammonification Methods 0.000 abstract 1
- 230000000694 effects Effects 0.000 description 20
- 239000007788 liquid Substances 0.000 description 14
- 239000000047 product Substances 0.000 description 13
- 238000000926 separation method Methods 0.000 description 13
- 238000011946 reduction process Methods 0.000 description 12
- 239000010936 titanium Substances 0.000 description 12
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 10
- 239000003795 chemical substances by application Substances 0.000 description 9
- 239000008367 deionised water Substances 0.000 description 9
- 229910021641 deionized water Inorganic materials 0.000 description 9
- 238000001514 detection method Methods 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 8
- 230000008020 evaporation Effects 0.000 description 7
- 238000010438 heat treatment Methods 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 230000001376 precipitating effect Effects 0.000 description 7
- 239000011777 magnesium Substances 0.000 description 6
- 229910052749 magnesium Inorganic materials 0.000 description 6
- 229910000398 iron phosphate Inorganic materials 0.000 description 5
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- LPXPTNMVRIOKMN-UHFFFAOYSA-M sodium nitrite Chemical compound [Na+].[O-]N=O LPXPTNMVRIOKMN-UHFFFAOYSA-M 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 230000007062 hydrolysis Effects 0.000 description 3
- 238000006460 hydrolysis reaction Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 238000004062 sedimentation Methods 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 3
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 2
- 229910021645 metal ion Inorganic materials 0.000 description 2
- 239000010413 mother solution Substances 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- 235000010288 sodium nitrite Nutrition 0.000 description 2
- 229910052979 sodium sulfide Inorganic materials 0.000 description 2
- GRVFOGOEDUUMBP-UHFFFAOYSA-N sodium sulfide (anhydrous) Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 2
- DDFHBQSCUXNBSA-UHFFFAOYSA-N 5-(5-carboxythiophen-2-yl)thiophene-2-carboxylic acid Chemical compound S1C(C(=O)O)=CC=C1C1=CC=C(C(O)=O)S1 DDFHBQSCUXNBSA-UHFFFAOYSA-N 0.000 description 1
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 1
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 229960004887 ferric hydroxide Drugs 0.000 description 1
- 229940116007 ferrous phosphate Drugs 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 1
- IEECXTSVVFWGSE-UHFFFAOYSA-M iron(3+);oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Fe+3] IEECXTSVVFWGSE-UHFFFAOYSA-M 0.000 description 1
- 229910000155 iron(II) phosphate Inorganic materials 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- SDEKDNPYZOERBP-UHFFFAOYSA-H iron(ii) phosphate Chemical compound [Fe+2].[Fe+2].[Fe+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O SDEKDNPYZOERBP-UHFFFAOYSA-H 0.000 description 1
- ORUIBWPALBXDOA-UHFFFAOYSA-L magnesium fluoride Chemical compound [F-].[F-].[Mg+2] ORUIBWPALBXDOA-UHFFFAOYSA-L 0.000 description 1
- 229910001635 magnesium fluoride Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- DPTATFGPDCLUTF-UHFFFAOYSA-N phosphanylidyneiron Chemical compound [Fe]#P DPTATFGPDCLUTF-UHFFFAOYSA-N 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 239000003755 preservative agent Substances 0.000 description 1
- 230000002335 preservative effect Effects 0.000 description 1
- 239000012629 purifying agent Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
- C01G49/00—Compounds of iron
- C01G49/14—Sulfates
-
- 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)
- Inorganic Compounds Of Heavy Metals (AREA)
Abstract
The invention discloses a method for removing impurities of titanium dioxide byproduct ferrous sulfate, which comprises the following steps: 1) Taking ferrous sulfate to prepare saturated solution; 2) Adding dilute phosphoric acid, stirring thoroughly, and filtering to remove insoluble substances; 3) Adding a proper amount of ammonia water into the obtained solution, filtering, and evaporating filtrate; 4) Cooling the rest solution under slow stirring until the temperature of the solution is reduced to 10 ℃, and centrifugally separating to obtain primary crystallization crystals and primary crystallization mother liquor; 5) Dissolving the primary crystallization crystal again to prepare a saturated solution, and repeating the steps 3) and 4) to obtain secondary crystallization crystal and secondary crystallization mother liquor; 6) The secondary crystallization crystal is dissolved to prepare ferrous sulfate solution, which can be directly used for preparing battery grade ferric phosphate; the method adopts a phosphoric acid method, an ammonification method and a recrystallization method to carry out multiple impurity removal on ferrous sulfate, and the ferrous sulfate heptahydrate after impurity removal has high solid purity and low metal impurity content, and can be directly used for synthesizing battery-grade ferric phosphate after dissolution.
Description
Technical Field
The invention relates to the technical field of chemical industry, in particular to a method for removing impurities from titanium dioxide byproduct ferrous sulfate.
Background
The ferrous sulfate heptahydrate is a byproduct of preparing titanium dioxide by a sulfuric acid method, and 3 tons of ferrous sulfate heptahydrate are produced per 1 ton of titanium dioxide. Ferrous sulfate can be used as mordant, water purifying agent, preservative, etc. in early years, but the dosage is small, most of the ferrous sulfate is piled up as garbage, and is difficult to treat, so that the environmental pollution is caused, and the additional environmental protection treatment cost is increased. Ferrous sulfate has been increasingly used as a raw material for preparing iron phosphate in recent years, and iron phosphate can be used as a precursor for preparing a lithium iron phosphate positive electrode material, and along with the rapid development of lithium iron phosphate batteries, ferrous phosphate heptahydrate is also receiving a great deal of attention. However, ferrous sulfate heptahydrate is used as a byproduct of titanium dioxide, has high content of solid insoluble substances and metal impurities, and can be used as a raw material for synthesizing iron phosphate for batteries after impurity removal. Therefore, the research on the impurity removal method of ferrous sulfate has a strong practical application value, but the existing impurity removal modes of several ferrous sulfate can not realize the complete removal of impurity elements, especially the metal impurities such as Mg, mn and the like in the impurity elements, and almost can not realize a good removal effect by the conventional impurity removal means.
At present, more methods for removing impurities from titanium dioxide byproduct ferrous sulfate are reported, wherein more iron powder and ammonia water are used for removing impurities, the principles are similar, the pH value of ferrous sulfate solution is improved, hydroxide radicals and impurity metal ions in the solution are generated and precipitated, and then filtered, but precipitate particles generated in the impurity removing process are fine, so that the filtering time is long, the penetrating filtering phenomenon is serious, the impurity removing effect on Mg and Mn is poor, and the problem that the metal impurity content of a product is out of standard exists in the direct synthesis of ferric phosphate by using ferrous sulfate prepared by the impurity removing method.
In the patent CN112479174A, soluble alkali such as ammonia water, sodium hydroxide, potassium hydroxide and the like is adopted, experiments prove that the method is used for removing impurities from ferrous sulfate solution, has poor effect of removing impurities such as Mg and Mn, produces insoluble precipitate particles with small size and high viscosity, has high filtering difficulty, is easy to oxidize ferrous iron in alkaline environment and generates ferric hydroxide precipitate, and causes large iron content loss after filtering. The patent CN115432739a mentions a recrystallization method, which can effectively reduce the content of impurities such as Mg, mn and the like in ferrous sulfate solution after multiple recrystallization, but has poor effect of Ti removal, and a certain amount of impurity removing agent needs to be added for Ti removal. Patent CN107746082a discloses the technical content of titanium removal by phosphoric acid, by adding phosphoric acid to ferrous sulfate solution, the ferric iron to TiO is eliminated in advance 2+ The hydrolysis influence of the solution can stabilize the pH of the solution and inhibit the oxidation of ferrous iron, and the Ti removal rate can reach more than 99 percent, but only phosphoric acid is used as a impurity removing agent, so that the problem that the content of other impurities in the ferrous sulfate solution is high as a whole still exists.
In addition, the impurity removing agent can also select sodium sulfide, magnesium fluoride, sodium nitrite and the like, but impurity elements can be additionally introduced by using the sodium sulfide and the sodium nitrite, a certain safety risk exists in the production of hydrogen sulfide gas in the process, no obvious effect is caused on impurity removal, the removing capability of ammonium fluoride on Zn and Ti is poor, the impurity removing effect is inferior to that of phosphoric acid, and the experiment proves that the impurity removing agent has poor combining capability with metal impurity ions in solution, and can not achieve better impurity removing effect.
Aiming at the problems of poor impurity removing effect, difficult precipitation and separation after adding an impurity removing agent, low iron yield and the like in the existing ferrous sulfate impurity removing process, a titanium dioxide byproduct ferrous sulfate impurity removing method is urgently needed to solve the problems.
Disclosure of Invention
The invention provides a method for removing impurities from titanium dioxide byproduct ferrous sulfate.
The scheme of the invention is as follows:
a method for removing impurities of titanium dioxide byproduct ferrous sulfate comprises the following steps:
1) Taking ferrous sulfate as a byproduct of titanium dioxide, dissolving the ferrous sulfate at 50-90 ℃ and preparing saturated solution;
2) Adding dilute phosphoric acid, fully stirring, and filtering to remove insoluble substances to obtain a solution;
3) Adding a proper amount of ammonia water into the obtained solution, adjusting the pH value of the filtrate to be 2.5-3.5, then carrying out secondary filtration, evaporating the obtained filtrate, and reserving 60-80% of the solution;
4) Cooling at a fixed rate under the condition of slow and uniform stirring until the temperature of the solution is reduced to 10 ℃, and centrifugally separating to obtain primary crystal and primary crystallization mother liquor;
5) Re-dissolving the primary crystallization crystal obtained in the step 4) to prepare a saturated solution, and repeating the operations of the step 3) and the step 4) to obtain a secondary crystallization crystal and a secondary crystallization mother solution;
6) The secondary crystallization crystal is dissolved to prepare ferrous sulfate solution with iron content of 50-60 g/L, the pH value is regulated, and the regulated ferrous sulfate solution is directly used for preparing battery grade ferric phosphate.
As a preferable technical scheme, the addition amount of the dilute phosphoric acid in the 2) is 0.5-5% of the mass of the saturated solution, and the concentration of the dilute phosphoric acid is 10-30%.
As a preferable technical scheme, the filtrate obtained in the step 2) is added with ammonia water for adjustment, stirred for 30min and then subjected to secondary filtration.
As a preferable technical scheme, in the 4), when the temperature is reduced at a fixed rate, the fixed rate of temperature reduction is 0.2-0.5 ℃/min.
As a preferable embodiment, the ferrous sulfate solution ph=2.5 to 3.5 in the above 6).
As a preferable technical scheme, the slow and uniform stirring in the 4) is 30-80 rpm.
Due to the adoption of the technical scheme, the method for removing impurities of the titanium dioxide byproduct ferrous sulfate comprises the following steps of: 1) Taking ferrous sulfate as a byproduct of titanium dioxide, dissolving the ferrous sulfate at 50-90 ℃ and preparing saturated solution; 2) Adding dilute phosphoric acid, fully stirring, and filtering to remove insoluble substances to obtain a solution; 3) Adding a proper amount of ammonia water into the obtained solution, adjusting the pH value of the filtrate to be 2.5-3.5, then carrying out secondary filtration, evaporating the obtained filtrate, and reserving 60-80% of the solution; 4) Cooling at a fixed rate under the condition of slow and uniform stirring until the temperature of the solution is reduced to 10 ℃, and centrifugally separating to obtain primary crystal and primary crystallization mother liquor; 5) Re-dissolving the primary crystallization crystal obtained in the step 4) to prepare a saturated solution, and repeating the operations of the step 3) and the step 4) to obtain a secondary crystallization crystal and a secondary crystallization mother solution; 6) The secondary crystallization crystal is dissolved to prepare ferrous sulfate solution with iron content of 50-60 g/L, the pH value is regulated, and the regulated ferrous sulfate solution is directly used for preparing battery grade ferric phosphate.
The invention has the advantages that:
the invention firstly selects dilute phosphoric acid as a impurity removing agent, and enables TiO to be prepared by a hydrolysis method 2+ Hydrolysis to meta-titanic acid H 2 TiO 3 Filtering to remove metal impurity Ti in the solution, and adding ammonia water into the filtrate to adjust the pH to 2.5-3.5. Firstly, the pH value of the solution can be adjusted to be high, so that metal impurity ions generate precipitation in a high pH environment, and the metal impurity ions in the ferrous sulfate are further removed; secondly, NH is introduced 4 + Can consume the PO remained in the phosphoric acid impurity removal reaction 4 2- The problem of unstable iron-phosphorus ratio in the subsequent iron phosphate synthesis process is avoided. The filtrate obtained in the impurity removal step also contains a large amount of Mg, mn and other impurity elements which are not removed, and then the filtrate is heated, concentrated, cooled and crystallized by a recrystallization method to obtain ferrous sulfate crystals with low impurity content, and the obtained crystals are prepared into ferrous sulfate solution with certain iron concentration, so that the ferrous sulfate solution can be directly used for preparing ferric phosphate.
In the impurity removal process, firstly, impurity Ti is removed after impurity removal reaction and filtration by controlling the concentration and the addition amount of phosphoric acid and the concentration and the temperature of ferrous sulfate solution, the sedimentation particles formed under the optimal condition are larger, the sedimentation effect is good, the filtration time is short, the pH value of the solution is regulated by adding ammonia water, the impurity removal pH value range can be widened, the removal rate of metal ions is improved, and the PO in the solution can be effectively reduced 4 2- The content is favorable for accurately regulating and controlling the content of iron and phosphorus in the subsequent iron phosphate synthesis process.
Different cooling rates in the subsequent recrystallization process directly influence the growth speed of the crystal, the crystal growth speed is high, impurities are easy to coat, and the impurity removal effect is poor; and the solution is kept to have certain fluidity by stirring in the cooling process, so that impurity cladding in the crystal growth process is avoided. Meanwhile, the evaporation capacity has a great influence on recrystallization impurity removal, the recrystallization yield is low due to the fact that the evaporation capacity is too small, and part of impurities are separated out along with a crystal product when the temperature is low due to the fact that the evaporation capacity is too large, so that the purity of ferrous sulfate is affected. Through the optimization, firstly, the yield of ferrous sulfate products in the recrystallization process is improved, and secondly, the wrapping of impurity elements in the crystallization process is avoided, so that high-purity ferrous sulfate crystals are obtained.
The treatment of the method can reduce the concentration of high-content impurities such as Ti, mg, mn, al, zn in the ferrous sulfate solution to a lower level, and the obtained ferrous sulfate can be directly used for synthesizing battery-grade ferric phosphate.
Compared with the prior art, the method has the advantages that the metal impurities in the ferrous sulfate solution are thoroughly removed, the process is simple, the impurity content of the obtained ferrous sulfate solution is low, and the method can be directly used for preparing battery-grade ferric phosphate.
Detailed Description
The invention provides a method for removing impurities from titanium dioxide byproduct ferrous sulfate
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:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃, stirred and fully dissolved, 13.5g of dilute phosphoric acid with 20% concentration is added into the solution, stirred at the constant temperature of 60 ℃ for 30min, and then filtered, and the filtrate is green.
Adding ammonia water into the filtrate to regulate the pH of the filtrate to 2.5, placing the filtrate in a program control constant temperature tank, heating to 70 ℃ to evaporate the solution, reducing the liquid level to about 80%, reducing the temperature at the rate of 0.2 ℃/min, keeping the stirring rotation speed at 80rpm in the temperature reduction process until the temperature of the solution is reduced to 10 ℃, slowly precipitating green ferrous sulfate crystals in the temperature reduction process, and carrying out centrifugal separation on a solid-liquid mixture to obtain primary crystal and primary crystallization mother liquor.
The obtained crystals are repeatedly dissolved, evaporated and cooled for crystallization, secondary crystallization crystals are obtained through separation, the secondary crystallization crystals are dissolved and prepared into ferrous sulfate solution with the iron content of 56g/L for standby, the ferrous sulfate solution is adjusted to pH value of 2.5, and then the ferrous sulfate solution is used for preparing battery grade ferric phosphate products, and filtrate is sent for ICP detection.
Example 2:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃, stirred and fully dissolved, 6.75g of dilute phosphoric acid with 40% concentration is added into the solution, stirred at the constant temperature of 60 ℃ for 30min, and then filtered, and the filtrate is green.
Adding ammonia water into the filtrate to regulate the pH of the filtrate to 3.5, placing the filtrate in a program-controlled constant temperature tank, heating to 70 ℃ to evaporate the solution, reducing the liquid level to 80%, cooling at the rate of 0.2 ℃/min, keeping the stirring rotation speed at 80rpm in the cooling process until the temperature of the solution is reduced to 10 ℃, slowly precipitating green ferrous sulfate crystals in the cooling process, and carrying out centrifugal separation on the solid-liquid mixture to obtain primary crystal and primary crystallization mother liquor.
The obtained crystals are repeatedly dissolved, evaporated and cooled for crystallization, secondary crystallization crystals are obtained through separation, the secondary crystallization crystals are dissolved and prepared into ferrous sulfate solution with the iron content of 56g/L for standby, the ferrous sulfate solution is adjusted to pH 3.5, and then the ferrous sulfate solution is used for preparing battery grade ferric phosphate products, and filtrate is sent for ICP detection.
Example 3:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃, stirred and fully dissolved, 13.5g of dilute phosphoric acid with 20% concentration is added into the solution, stirred at the constant temperature of 60 ℃ for 30min, and then filtered, and the filtrate is green.
Adding ammonia water into the filtrate to regulate the pH value of the filtrate to 3.0, placing the filtrate in a program-controlled constant temperature tank, heating to 70 ℃ to evaporate the solution, reducing the liquid level to about 80%, reducing the temperature at the rate of 0.5 ℃/min, keeping the stirring rotation speed at 80rpm in the temperature reduction process until the temperature of the solution is reduced to 10 ℃, slowly precipitating green ferrous sulfate crystals in the temperature reduction process, and carrying out centrifugal separation on a solid-liquid mixture to obtain primary crystal and primary crystallization mother liquor.
The obtained crystals are repeatedly dissolved, evaporated and cooled for crystallization, secondary crystallization crystals are obtained through separation, the secondary crystallization crystals are dissolved and prepared into ferrous sulfate solution with the iron content of 56g/L for standby, the ferrous sulfate solution is adjusted to pH 3.0, and then the ferrous sulfate solution is used for preparing battery grade ferric phosphate products, and filtrate is sent for ICP detection.
Example 4:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃, stirred and fully dissolved, 13.5g of dilute phosphoric acid with 20% concentration is added into the solution, stirred at the constant temperature of 60 ℃ for 30min, and then filtered, and the filtrate is green.
Adding ammonia water into the filtrate to regulate the pH of the filtrate to 2.5, placing the filtrate in a program control constant temperature tank, heating to 70 ℃ to evaporate the solution, reducing the liquid level to about 80%, reducing the temperature at the rate of 0.2 ℃/min, keeping the stirring rotation speed at 30rpm in the temperature reduction process until the temperature of the solution is reduced to 10 ℃, slowly precipitating green ferrous sulfate crystals in the temperature reduction process, and carrying out centrifugal separation on a solid-liquid mixture to obtain primary crystal and primary crystallization mother liquor.
The obtained crystals are repeatedly dissolved, evaporated and cooled for crystallization, secondary crystallization crystals are obtained through separation, the secondary crystallization crystals are dissolved and prepared into ferrous sulfate solution with the iron content of 56g/L for standby, the ferrous sulfate solution is adjusted to pH 3.5, and then the ferrous sulfate solution is used for preparing battery grade ferric phosphate products, and filtrate is sent for ICP detection.
Example 5:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃, stirred and fully dissolved, 13.5g of dilute phosphoric acid with 20% concentration is added into the solution, stirred at the constant temperature of 60 ℃ for 30min, and then filtered, and the filtrate is green.
Adding ammonia water into the filtrate to regulate the pH of the filtrate to 3.5, placing the filtrate in a program control constant temperature tank, heating to 70 ℃ to evaporate the solution, reducing the liquid level to about 60%, reducing the temperature at the rate of 0.2 ℃/min, keeping the stirring rotation speed at 80rpm in the temperature reduction process until the temperature of the solution is reduced to 10 ℃, slowly precipitating green ferrous sulfate crystals in the temperature reduction process, and carrying out centrifugal separation on a solid-liquid mixture to obtain primary crystal and primary crystallization mother liquor.
The obtained crystals are repeatedly dissolved, evaporated and cooled for crystallization, secondary crystallization crystals are obtained through separation, the secondary crystallization crystals are dissolved and prepared into ferrous sulfate solution with the iron content of 56g/L for standby, the ferrous sulfate solution is adjusted to pH value of 2.5, and then the ferrous sulfate solution is used for preparing battery grade ferric phosphate products, and filtrate is sent for ICP detection.
Comparative example 1:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃ and stirred to be fully dissolved, and insoluble impurities are filtered.
Heating the filtrate to 70 ℃ in a program-controlled constant temperature tank to evaporate the solution, reducing the liquid level to about 80%, reducing the temperature at a rate of 0.2 ℃/min, keeping the stirring rotation speed at 80rpm in the temperature reduction process until the temperature of the solution is reduced to 10 ℃, slowly precipitating green ferrous sulfate crystals in the temperature reduction process, and carrying out centrifugal separation on the solid-liquid mixture to obtain primary crystal and primary crystal mother liquor.
The obtained crystals are repeatedly dissolved, evaporated and cooled for crystallization, secondary crystallization crystals are obtained through separation, the secondary crystallization crystals are dissolved and prepared into ferrous sulfate solution with the iron content of 56g/L for standby, the ferrous sulfate solution is subsequently used for preparing battery grade ferric phosphate products, and filtrate is sent for ICP detection.
Comparative example 2:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃ and stirred to be fully dissolved, and insoluble impurities are filtered.
Adding ammonia water into the filtrate to regulate the pH of the filtrate to 3.0, placing the filtrate in a program-controlled constant temperature tank, heating to 70 ℃ to evaporate the solution, reducing the liquid level to about 80%, reducing the temperature at the rate of 0.2 ℃/min, maintaining the stirring rotation speed at 80rpm in the temperature reduction process until the temperature of the solution is reduced to 10 ℃, slowly precipitating green ferrous sulfate crystals in the temperature reduction process, and centrifuging the solid-liquid mixture to obtain crystal crystals and mother liquor.
And dissolving the crystal to prepare ferrous sulfate solution with the iron content of 56g/L for later use, adjusting the pH value of the ferrous sulfate solution to 3.0, and subsequently preparing a battery grade ferric phosphate product, and sending a filtrate sample for ICP detection.
Comparative example 3:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃, and is stirred to be fully dissolved, 13.5g of dilute phosphoric acid with 20% concentration is added into the solution, and is stirred for 30min at the constant temperature of 60 ℃ and then is filtered, the filtrate is green, and is subsequently used for preparing battery grade ferric phosphate products, and the filtrate is sent to be subjected to ICP detection.
Comparative example 4:
700g of titanium dioxide byproduct ferrous sulfate heptahydrate is added into 2L of deionized water at 60 ℃, stirring is carried out for full dissolution, 25% ammonia water is added into the solution to adjust the pH value of the solution to be=5.0, the solution is stirred at 30 ℃ for 30min at constant temperature and then filtered, the filtrate is green, the pH value is 4.52, 98% sulfuric acid is added to adjust the pH value of the solution back to be=3.0 for later use, the battery grade ferric phosphate product is prepared, and the filtrate is sent to be used for ICP detection.
The major metal impurity contents of the ferrous sulfate filtrate in the above examples are shown in the following table:
examples 1 to 5 compare the influences of different solution pH values, phosphoric acid concentrations, cooling rates, stirring speeds and evaporation amounts on the impurity removal process, and experimental data show that the relationship between the impurity removal effect and Fe loss is balanced when ammonia water is added to adjust the pH value of the impurity removal solution, and the optimal condition is the pH value of 2.5; the phosphoric acid with the concentration of 20 percent can achieve better impurity removal effect after being added into ferrous sulfate solution, and the formed precipitate particles are larger, the sedimentation effect is good, and the filtering time can be effectively shortened. The cooling rate in the recrystallization process has a larger influence on the impurity removal effect, different cooling rates directly influence the growth speed of the crystal, the crystal growth speed is high, impurities are easy to be coated, and the impurity removal effect is poor; the impurity removing effect of different stirring speeds in the cooling process is also different, certain fluidity is required to be maintained, and impurity coating in the crystal growth process is avoided. The evaporation capacity has a larger influence on recrystallization impurity removal, the recrystallization yield is low due to the fact that the evaporation capacity is too small, and part of impurities are separated out along with products when the temperature is low due to the fact that the evaporation capacity is too large, so that the purity of ferrous sulfate is influenced.
In comparative example 1, phosphoric acid was not used as a impurity removing agent, and impurities were removed only by recrystallization, and the analyzed data showed that the content of Ti was greatly affected, so that it was concluded that the content of Ti in the ferrous sulfate filtrate could be significantly reduced after the addition of dilute phosphoric acid.
In comparative example 2, phosphoric acid was not used as a impurity removing agent, aqueous ammonia was added to adjust the pH of the solution to a certain concentration, and then the solution was subjected to primary recrystallization, and the impurity content of the obtained ferrous sulfate crystals was higher than that of the whole of example 1, thereby obtaining secondary recrystallization to further remove impurities in the solution.
In comparative example 3, phosphoric acid was used as the impurity removing agent, and recrystallization was not used for removing impurities, and as can be seen from the analysis data, the use of phosphoric acid can achieve a good impurity removing effect on Ti, but the contents of other impurities such as Mg, mn and the like are all at a high level.
In comparative example 4, ammonia water is used for removing impurities, the iron loss of the method is large, the impurity removing effect is not great from the impurity removing effect of ferric phosphate, but Al and Ti can be completely removed by an ammonia water method.
The method for removing impurities by comparison has thousands of times, but under the condition that the impurity content is taken as a judgment standard, the example 1 can reduce the impurity in the titanium dioxide byproduct ferrous sulfate to the minimum level.
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 (6)
1. The method for removing impurities of the titanium dioxide byproduct ferrous sulfate is characterized by comprising the following steps of:
1) Taking ferrous sulfate as a byproduct of titanium dioxide, dissolving the ferrous sulfate at 50-90 ℃ and preparing saturated solution;
2) Adding dilute phosphoric acid, fully stirring, and filtering to remove insoluble substances to obtain a solution;
3) Adding a proper amount of ammonia water into the obtained solution, adjusting the pH value of the filtrate to be 2.5-3.5, then carrying out secondary filtration, evaporating and concentrating the obtained filtrate, and reserving 60-80% of the solution;
4) Cooling at a fixed rate under the condition of slow and uniform stirring until the temperature of the solution is reduced to 10 ℃, and centrifugally separating to obtain primary crystal and primary crystallization mother liquor;
5) Re-dissolving the primary crystallization crystal obtained in the step 4) to prepare a saturated solution, and repeating the operations of the steps 3) and 4) on the obtained solution to obtain secondary crystallization crystal and secondary crystallization mother liquor;
6) The secondary crystallization crystal is dissolved to prepare ferrous sulfate solution with iron content of 50-60 g/L, the pH value is regulated, and the regulated ferrous sulfate solution is directly used for preparing battery grade ferric phosphate.
2. The method for removing impurities of the titanium dioxide byproduct ferrous sulfate, which is characterized in that: the addition amount of the dilute phosphoric acid in the step 2) is 0.5-5% of the mass of the saturated solution, and the concentration of the dilute phosphoric acid is 10-30%.
3. The method for removing impurities of the titanium dioxide byproduct ferrous sulfate, which is characterized in that: adding ammonia water into the filtrate obtained in the step 2), regulating, stirring for 30min, and performing secondary filtration.
4. The method for removing impurities of the titanium dioxide byproduct ferrous sulfate, which is characterized in that: and 4) when the temperature is reduced at a fixed rate, the fixed rate of temperature reduction is 0.2-0.5 ℃/min.
5. The method for removing impurities from titanium dioxide byproduct ferrous sulfate as claimed in claim 1, which is characterized in that: the ferrous sulfate solution ph=2.5 to 3.5 in the 6) 。
6. The method for removing impurities of the titanium dioxide byproduct ferrous sulfate, which is characterized in that: the slow and uniform stirring in the step 4) is 30-80 rpm.
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