CN117342622A - Purification, refining and crystallization method of titanium dioxide byproduct ferrous sulfate - Google Patents
Purification, refining and crystallization method of titanium dioxide byproduct ferrous sulfate Download PDFInfo
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- sulfate heptahydrate
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- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 title claims abstract description 67
- 238000002425 crystallisation Methods 0.000 title claims abstract description 50
- 229910000359 iron(II) sulfate Inorganic materials 0.000 title claims abstract description 46
- 235000003891 ferrous sulphate Nutrition 0.000 title claims abstract description 45
- 239000011790 ferrous sulphate Substances 0.000 title claims abstract description 45
- 239000006227 byproduct Substances 0.000 title claims abstract description 44
- 239000004408 titanium dioxide Substances 0.000 title claims abstract description 29
- 238000007670 refining Methods 0.000 title claims abstract description 17
- 238000000746 purification Methods 0.000 title claims abstract description 11
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 title 1
- 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 claims abstract description 97
- 230000008025 crystallization Effects 0.000 claims abstract description 37
- 235000010215 titanium dioxide Nutrition 0.000 claims abstract description 37
- 239000007788 liquid Substances 0.000 claims abstract description 28
- 238000003756 stirring Methods 0.000 claims abstract description 28
- 238000001816 cooling Methods 0.000 claims abstract description 25
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 24
- 239000002994 raw material Substances 0.000 claims abstract description 18
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 13
- 239000011259 mixed solution Substances 0.000 claims abstract description 13
- 238000000926 separation method Methods 0.000 claims abstract description 13
- 239000012043 crude product Substances 0.000 claims abstract description 10
- 229940062993 ferrous oxalate Drugs 0.000 claims abstract description 7
- OWZIYWAUNZMLRT-UHFFFAOYSA-L iron(2+);oxalate Chemical compound [Fe+2].[O-]C(=O)C([O-])=O OWZIYWAUNZMLRT-UHFFFAOYSA-L 0.000 claims abstract description 7
- 230000009467 reduction Effects 0.000 claims abstract description 7
- 239000002253 acid Substances 0.000 claims abstract description 5
- 238000002360 preparation method Methods 0.000 claims abstract description 5
- 238000005189 flocculation Methods 0.000 claims abstract description 3
- 230000016615 flocculation Effects 0.000 claims abstract description 3
- 230000001105 regulatory effect Effects 0.000 claims abstract description 3
- 239000013078 crystal Substances 0.000 claims description 42
- 238000000034 method Methods 0.000 claims description 29
- 239000002245 particle Substances 0.000 claims description 24
- 239000011777 magnesium Substances 0.000 claims description 23
- 238000010025 steaming Methods 0.000 claims description 20
- 239000012452 mother liquor Substances 0.000 claims description 19
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 18
- 239000000243 solution Substances 0.000 claims description 18
- 239000012047 saturated solution Substances 0.000 claims description 13
- 238000001914 filtration Methods 0.000 claims description 10
- 238000005406 washing Methods 0.000 claims description 10
- 238000001035 drying Methods 0.000 claims description 8
- 239000000843 powder Substances 0.000 claims description 7
- 229920002401 polyacrylamide Polymers 0.000 claims description 6
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 3
- 229910052749 magnesium Inorganic materials 0.000 claims description 3
- 238000004064 recycling Methods 0.000 claims description 3
- 239000001038 titanium pigment Substances 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims description 2
- 238000011084 recovery Methods 0.000 claims description 2
- 238000002390 rotary evaporation Methods 0.000 claims description 2
- 238000001291 vacuum drying Methods 0.000 claims description 2
- 238000004090 dissolution Methods 0.000 claims 1
- 239000000047 product Substances 0.000 abstract description 58
- 239000008394 flocculating agent Substances 0.000 abstract 1
- 239000012535 impurity Substances 0.000 description 14
- 230000008569 process Effects 0.000 description 14
- 230000000052 comparative effect Effects 0.000 description 11
- 238000004581 coalescence Methods 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 7
- 230000005764 inhibitory process Effects 0.000 description 6
- 238000011160 research Methods 0.000 description 6
- 230000002776 aggregation Effects 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 230000003311 flocculating effect Effects 0.000 description 4
- 238000010899 nucleation Methods 0.000 description 4
- 230000006911 nucleation Effects 0.000 description 4
- 238000005054 agglomeration Methods 0.000 description 3
- 238000004140 cleaning Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 238000013341 scale-up Methods 0.000 description 3
- 238000010900 secondary nucleation Methods 0.000 description 3
- 239000002699 waste material Substances 0.000 description 3
- 230000007547 defect Effects 0.000 description 2
- 238000009776 industrial production 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
- 239000002904 solvent Substances 0.000 description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 230000003321 amplification Effects 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000003889 chemical engineering Methods 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 239000012847 fine chemical Substances 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000003199 nucleic acid amplification method Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000005192 partition Methods 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000009987 spinning Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium 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
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/41—Preparation of salts of carboxylic acids
- C07C51/412—Preparation of salts of carboxylic acids by conversion of the acids, their salts, esters or anhydrides with the same carboxylic acid part
-
- 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
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
Abstract
The invention discloses a purification, refining and crystallization method of titanium dioxide byproduct ferrous sulfate, which comprises the following steps: (1) Under the stirring condition, dissolving titanium dioxide raw materials containing by-product ferrous sulfate in a ferrous sulfate heptahydrate-water mixed solution at 60-80 ℃, then adding iron powder for reduction, adding acid for regulating the pH value to 1-3, and adding a flocculating agent for flocculation to obtain clear liquid; (2) Under the stirring condition, cooling and crystallizing the clear liquid obtained in the step (1) in three sections, and carrying out solid-liquid separation to obtain a primary crystallization crude product; (3) And (3) under the stirring condition, dissolving the primary crystallization crude product obtained in the step (2) in water at 60-80 ℃, and cooling and crystallizing in three sections to obtain the titanium white byproduct ferrous sulfate. The preparation process can continuously, stably, efficiently and massively prepare the ferrous sulfate heptahydrate product, so that the preparation process is used for preparing battery-grade ferrous oxalate.
Description
Technical Field
The invention belongs to the technical field of crystallization in chemical engineering industry, and particularly relates to a purification, refining and crystallization method of titanium dioxide byproduct ferrous sulfate.
Background
Ferrous sulfate heptahydrate (CAS: 7782-63-0), which is also called copperas, is an important byproduct in the production process of titanium dioxide, and widely exists in the fields of chemical industry, metallurgy and the like. Based on the calculation of about 3 tons of ferrous sulfate per 1 ton of titanium pigment produced, approximately 250 ten thousand tons of ferrous sulfate heptahydrate will be produced each year. In order to improve the resource utilization rate, the ferrous sulfate can also be used for preparing an iron source material of lithium iron phosphate serving as a positive electrode material of the lithium ion battery by a liquid phase method. However, the titanium white byproduct ferrous sulfate has high impurity content and low purity, and the direct use of the titanium white byproduct ferrous sulfate in preparing battery grade ferrous oxalate can greatly influence the performance of the subsequent lithium iron phosphate anode material. Therefore, the by-product ferrous sulfate needs to be purified before comprehensive utilization.
At present, the crystallization method is widely applied to the fields of food, pharmacy, fine chemical industry and the like as an important separation and purification method, but the systematic research on purifying the byproduct ferrous sulfate by the crystallization method is still very little. The crystallization method has the advantages of low cost, clean production, high separation efficiency and the like, and is particularly suitable for purifying ferrous sulfate. Therefore, the battery grade ferrous oxalate is prepared from the titanium white byproduct ferrous sulfate through treatment, so that the problem of serious stockpiling of the byproduct ferrous sulfate is solved, and the development requirement of the battery industry can be met.
At present, various researches are less in continuous research on the ferrous sulfate heptahydrate refining process, more researches focus on the removal rule, removal effect and the like of impurities (such as Ti, mg and Mn), but for industrial amplification experiments, the project goal can be reached only by continuously carrying out the whole process, and the research is conducted on key parameters and process optimization of ferrous sulfate heptahydrate continuous production.
Disclosure of Invention
In order to overcome the defect that the content of Mg impurity in the existing titanium dioxide byproduct ferrous sulfate heptahydrate is too high to be used for preparing battery-grade ferrous oxalate, and meanwhile, for the theoretical defect of continuity of the technology in the production process, the invention provides a purification, refining and crystallization method of the titanium dioxide byproduct ferrous sulfate, the yield of the ferrous sulfate heptahydrate crystal prepared by the continuous crystallization method can reach more than 80%, the particle size is 150-250 microns, the ferrous sulfate heptahydrate crystal is not easy to agglomerate, the content of Mg impurity is lower than 500ppm, and the application of the ferrous sulfate heptahydrate crystal in preparing battery-grade ferrous oxalate is satisfied.
The technical scheme of the invention is as follows:
the invention aims to provide a purification, refining and crystallization method of titanium dioxide byproduct ferrous sulfate, wherein the flow of the purification, refining and crystallization is shown in a figure 1, and the method comprises the following steps:
(1) Under the condition of stirring, dissolving titanium dioxide raw materials containing by-product ferrous sulfate in water of 60-80 ℃ (for example 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃ and the like) to prepare ferrous sulfate heptahydrate-water mixed solution, then adding iron powder for reduction, adding acid for regulating the pH value to 1-3, adding flocculant for flocculation, and obtaining clear liquid;
(2) Under stirring, cooling the clear liquid obtained in the step (1) to 50-60 ℃ (such as 50 ℃, 55 ℃, 60 ℃ and the like) at one time, continuously adding seed crystals, cooling to 30-35 ℃ (such as 30 ℃, 32 ℃, 35 ℃ and the like) at the second time for 50-70min, cooling to 20-25 ℃ (such as 20 ℃, 22 ℃, 25 ℃ and the like) at the third time for 50-70min, and carrying out solid-liquid separation to obtain a primary crystallization crude product;
(3) Dissolving the primary crystallization crude product obtained in the step (2) in water of 60-80 ℃ (for example, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃ and the like) under the stirring condition, cooling to 50-60 ℃ (for example, 50 ℃, 55 ℃, 60 ℃ and the like) at the first time, continuously adding seed crystal, cooling to 30-35 ℃ (for example, 30 ℃, 32 ℃, 35 ℃ and the like) at the second time, maintaining for 50-70min, and cooling to 20-25 ℃ (for example, 20 ℃, 22 ℃, 25 ℃ and the like) at the third time, and maintaining for 50-70min to obtain the titanium dioxide byproduct ferrous sulfate.
In the invention, the ferrous sulfate heptahydrate has the characteristic of larger solubility change along with the increase of temperature, can be purified by adopting a cooling crystallization mode, and the conventional intermittent crystallization mode can not meet the demands of enterprises due to the huge yield of industrial byproduct ferrous sulfate in China, so that the continuous crystallization mode is considered to efficiently and stably purify the titanium dioxide byproduct on a large scale. Therefore, strict control of the entire crystallization process, including the temperature, residence time, feed rate, waste liquid treatment, etc., of each stage is required to maintain the stability of the entire process. Therefore, the ferrous sulfate heptahydrate-water solution with the temperature of 60-80 ℃ and the ferrous sulfate heptahydrate concentration of 1.3-2.0 g/m is continuously cooled and crystallized by a three-stage crystallizer (the temperature of each stage is 50-60 ℃ respectively, 30-35 ℃ and 20-25 ℃), the content of impurity Mg is successfully reduced to below 500ppm through the process of twice crystallization, and simultaneously, the yield of the whole process flow reaches more than 80 percent by adopting the method of carrying out rotary evaporation on primary crystallization mother liquor for 50-70 percent and recycling and dissolving titanium pigment byproduct raw materials through secondary crystallization mother liquor. The research determines the optimal process by changing the temperature and the residence time of each stage, and has great guiding significance on industrialized production due to the greatly improved yield of the excellent utilization of the mother liquor.
Preferably, in the step (1), the step (2) and the step (3), the stirring rate is 200 to 400rpm, for example 200rpm,300rpm,400rpm, etc.; in the invention, the particle size of the ferrous sulfate heptahydrate can be adjusted by changing the stirring rate and combining other process conditions, so that the average particle size of the product is controlled to be 150-250 mu m; if the stirring rate is outside the range defined in the present application, there may be caused a problem that the crystal size distribution is not uniform or there is burst nucleation, resulting in a large increase in the content of magnesium impurity in the product.
Preferably, the concentration of ferrous sulfate heptahydrate in the mixed solution of step (1) is 1.30-2.00 g/mL, such as 1.3g/mL, 1.4g/mL, 1.5g/mL, 1.6g/mL, 1.7g/mL,1.8g/mL,1.9g/mL,2.0g/mL, etc.; in the invention, when the concentration of the ferrous sulfate heptahydrate-water solution is too high, the content of Mg in the final product is too high; if the concentration is too low, the final yield is too low, which causes economic problems.
Preferably, the acid in the step (1) is dilute sulfuric acid, wherein the dilute sulfuric acid is obtained by mixing 98% concentrated sulfuric acid and water according to the volume ratio of (1-4) (9-6);
preferably, the iron in the step (1) is added in an amount of 1-3g based on 100g of the titanium white powder raw material containing the by-product ferrous sulfate.
Preferably, the flocculant of step (1) is a polyacrylamide;
preferably, the flocculant in the step (1) is added in an amount of 0.1-0.3g based on 100g of titanium dioxide raw material containing ferrous sulfate as a byproduct.
Preferably, the grain size of the seed crystal in the step (2) and the seed crystal in the step (3) is 100-200 mu m;
preferably, the addition amount of the seed crystal in the step (2) is 1/4-1/3 of the mass of the finally obtained ferrous sulfate heptahydrate.
Preferably, the liquid obtained by solid-liquid separation in the step (2) is recovered, wherein the recovery comprises rotary steaming the liquid, and spinning 50-70% of mother liquor for dissolving the titanium white raw material containing the byproduct ferrous sulfate in the step (1);
preferably, the temperature of the rotary steaming is 50-70 ℃, and the rotation number of the rotary steaming is 60-100rpm.
Preferably, the step (3) further comprises sequentially performing solid-liquid separation, cleaning and drying on the mixture obtained after the three times of cooling;
preferably, the solid-liquid separation mode is filtration;
preferably, the washing is 2-4 times with saturated ferrous sulfate heptahydrate solution;
preferably, the drying is vacuum drying, wherein the vacuum degree is 0.95bar drying temperature 40-50 ℃, and the drying time is 12-16h.
Preferably, the preparation method further comprises the steps of carrying out rotary steaming on the liquid obtained by the solid-liquid separation, and recycling 50-70% of mother liquor for dissolving the titanium white raw material containing the byproduct ferrous sulfate in the step (1);
preferably, the temperature of the rotary steaming is 50-70 ℃, and the rotation number of the rotary steaming is 60-100rpm.
And (3) in the rotary steaming process in the step (4), the solution after rotary steaming is reduced to 20-25 ℃ and filtered, so that a rotary steaming product is obtained. The product is then mixed with a new batch of starting material and the crystallization process is repeated twice.
The second purpose of the invention is to obtain the ferrous sulfate heptahydrate crystal by purifying, refining and crystallizing; preferably, the content of magnesium in the ferrous sulfate heptahydrate crystals is lower than 500ppm;
preferably, the particle size of the ferrous sulfate heptahydrate crystals is 150-250 μm.
The invention further aims at applying the ferrous sulfate heptahydrate crystal obtained in the second aim to the preparation of battery-grade ferrous oxalate.
The method has the following beneficial effects:
a) The ferrous sulfate heptahydrate product obtained by the method has uniform particle size, good inhibition of coalescence phenomena and successful inhibition of burst nucleation, so that the purity of the product is greatly improved.
b) The method efficiently and stably ensures continuity of the flow, can be used for guiding industrial scale-up production, and can be used for producing ferrous sulfate heptahydrate products with purity meeting the standard on a large scale.
c) The method effectively utilizes mother liquor in the primary crystallization and secondary crystallization processes, firstly, the yield of the process can be increased, the discharge of waste liquor can be reduced, and the economic problem of waste liquor treatment is reduced.
Drawings
FIG. 1 is a flow chart of primary crystallization of titanium dioxide byproduct ferrous sulfate;
FIG. 2 shows the limits of impurity removal (Mg content before washing) that can be achieved for primary and secondary crystallization at different feed concentrations;
FIG. 3 is a scanning electron micrograph (scale bar 500 μm) of the ferrous sulfate heptahydrate crystals prepared in example 1.
Detailed Description
Example 1:
as shown in fig. 1:
(1) Preparing a ferrous sulfate heptahydrate-water mixed solution with the concentration of 1.55g/ml at 70 ℃, stirring until titanium dioxide byproducts are completely dissolved in water, then adding Fe powder for reduction, adding dilute sulfuric acid to adjust the PH to be 1-3, and flocculating with a polyacrylamide flocculant;
(2) Cooling the solution to 50 ℃, and continuously stirring and adding a large amount of seed crystals (1/3 product); and then the temperature is instantaneously reduced to 32 ℃ and stirring is continued for a period of time, and then the temperature is instantaneously reduced to 20 ℃ and stirring is continued for a period of time, the product is obtained by filtering, and the primary crystallization crude product can be obtained by washing with ferrous sulfate heptahydrate saturated solution.
(3) Dissolving the product obtained in the step (2) at 70 ℃ to prepare a ferrous sulfate heptahydrate-water mixed solution with the ferrous sulfate heptahydrate concentration of 1.55g/mL, cooling to 50 ℃, and continuously stirring and adding a large amount of seed crystals (1/3 product); then the temperature is instantaneously reduced to 32 ℃ and continuously stirred for a period of time, and then the temperature is instantaneously reduced to 20 ℃ and continuously stirred for a period of time, the product is obtained by filtering, and the product is washed by ferrous sulfate heptahydrate saturated solution to obtain a secondary crystallization product;
(4) Recovering the mother liquor obtained in the step (2) in a rotary steaming mode, wherein the liquid quantity of the rotary steaming mother liquor is 65%, and the mother liquor obtained in the step (3) is used for dissolving the titanium dioxide byproduct raw material in the step (1) to keep the concentration of ferrous sulfate heptahydrate unchanged; the impurity Mg content of the product after twice crystallization is shown in figure 2 (corresponding to 55 ℃ saturated solution), and the required standard can be met, namely, the Mg content is 412ppm (after cleaning); as shown in figure 3, the prepared ferrous sulfate heptahydrate product has uniform particle size, well inhibition of coalescence phenomena and average particle size of about 200 microns.
Example 2:
(1) Preparing a ferrous sulfate heptahydrate-water mixed solution with the concentration of 1.75g/ml at 70 ℃, stirring until titanium dioxide byproducts are completely dissolved in water, then adding Fe powder for reduction, adding dilute sulfuric acid to adjust the PH to be 1-3, and flocculating with a polyacrylamide flocculant;
(2) Cooling the solution to 50 ℃, and continuously stirring and adding a large amount of seed crystals (1/3 product); and then the temperature is instantaneously reduced to 30 ℃ and continuously stirred for a period of time, then the temperature is instantaneously reduced to 22 ℃ and continuously stirred for a period of time, the product is obtained by filtering, and the primary crystallization crude product can be obtained by washing with a ferrous sulfate heptahydrate saturated solution.
(3) Dissolving the product obtained in the step (2) at 70 ℃ to prepare a ferrous sulfate heptahydrate-water mixed solution with the ferrous sulfate heptahydrate concentration of 1.55g/mL, cooling to 50 ℃, and continuously stirring and adding a large amount of seed crystals (1/3 product); then, the temperature is instantaneously reduced to 30 ℃ and continuously stirred for a period of time, then, the temperature is instantaneously reduced to 22 ℃ and continuously stirred for a period of time, the product is obtained by filtering, and the product is washed by ferrous sulfate heptahydrate saturated solution to obtain a secondary crystallization product;
(4) Recovering the mother liquor obtained in the step (2) in a rotary steaming mode, wherein the liquid quantity of the rotary steaming mother liquor is 50%, and the mother liquor obtained in the step (3) is used for dissolving the titanium dioxide byproduct raw material in the step (1) to keep the concentration of ferrous sulfate heptahydrate unchanged; the Mg content of the impurity after two crystallization of the product is shown in fig. 2 (corresponding to a saturated solution at 60 c), it can be seen that the desired standard, i.e. a Mg content of 488ppm (after washing), can be achieved.
The prepared ferrous sulfate heptahydrate product has uniform particle size, good inhibition of coalescence, and average particle size of about 220 microns.
Example 3:
(1) Preparing a ferrous sulfate heptahydrate-water mixed solution with the concentration of 1.4g/ml at 70 ℃, stirring until titanium dioxide byproducts are completely dissolved in water, then adding Fe powder for reduction, adding dilute sulfuric acid to adjust the PH to be 1-3, and flocculating with a polyacrylamide flocculant;
(2) Cooling the solution to 55 ℃, and continuously stirring and adding a large amount of seed crystals (1/4 product); then the temperature is instantaneously reduced to 35 ℃ and continuously stirred for a period of time, and then the temperature is instantaneously reduced to 25 ℃ and continuously stirred for a period of time, the product is obtained by filtering, and the primary crystallization crude product can be obtained by washing with saturated solution of ferrous sulfate heptahydrate.
(3) Dissolving the product obtained in the step (2) at 70 ℃ to prepare a ferrous sulfate heptahydrate-water mixed solution with the ferrous sulfate heptahydrate concentration of 1.4g/mL, cooling to 55 ℃, and continuously stirring and adding a large amount of seed crystals (1/4 product); then the temperature is instantaneously reduced to 35 ℃ and continuously stirred for a period of time, and then the temperature is instantaneously reduced to 25 ℃ and continuously stirred for a period of time, the product is obtained by filtering, and the product is washed by ferrous sulfate heptahydrate saturated solution to obtain a secondary crystallization product;
(4) Recovering the mother liquor obtained in the step (2) in a rotary steaming mode, wherein the liquid quantity of the rotary steaming mother liquor is 55%, and the mother liquor obtained in the step (3) is used for dissolving the titanium dioxide byproduct raw material in the step (1) to keep the concentration of ferrous sulfate heptahydrate unchanged; the impurity Mg content of the product after two crystallization is shown in FIG. 2 (corresponding to a saturated solution at 52 ℃ C.), and it can be seen that the required standard, i.e. the Mg content is 400ppm (after washing), can be achieved.
The prepared ferrous sulfate heptahydrate product has uniform particle size, good inhibition of coalescence, and the average particle size of the product is about 190 microns.
Example 4:
(1) Preparing a ferrous sulfate heptahydrate-water mixed solution with the concentration of 1.55g/ml at 70 ℃, stirring until titanium dioxide byproducts are completely dissolved in water, then adding Fe powder for reduction, adding dilute sulfuric acid to adjust the PH to be 1-3, and flocculating with a polyacrylamide flocculant;
(2) Cooling the solution to 60 ℃, and continuously stirring and adding a large amount of seed crystals (1/4 product); and then the temperature is instantaneously reduced to 30 ℃ and continuously stirred for a period of time, then the temperature is instantaneously reduced to 22 ℃ and continuously stirred for a period of time, the product is obtained by filtering, and the primary crystallization crude product can be obtained by washing with a ferrous sulfate heptahydrate saturated solution.
(3) Dissolving the product obtained in the step (2) at 70 ℃ to obtain a ferrous sulfate heptahydrate-water mixed solution with the ferrous sulfate heptahydrate concentration of 1.55g/mL, cooling to 60 ℃, and continuously stirring and adding a large amount of seed crystals (1/4 product); then, the temperature is instantaneously reduced to 30 ℃ and continuously stirred for a period of time, then, the temperature is instantaneously reduced to 22 ℃ and continuously stirred for a period of time, the product is obtained by filtering, and the product is washed by ferrous sulfate heptahydrate saturated solution to obtain a secondary crystallization product;
(4) Recovering the mother liquor obtained in the step (2) in a rotary steaming mode, wherein the liquid quantity of the rotary steaming mother liquor is 50%, and the mother liquor obtained in the step (3) is used for dissolving the titanium dioxide byproduct raw material in the step (1) to keep the concentration of ferrous sulfate heptahydrate unchanged; the impurity Mg content of the product after two crystallization is shown in FIG. 2 (corresponding to 55 ℃ C. Saturated solution), and it can be seen that the required standard, namely, the Mg content is 450ppm (after cleaning), can be achieved.
The prepared ferrous sulfate heptahydrate product has uniform particle size, good inhibition of coalescence, and the average particle size of the product is about 240 microns.
Comparative example 1:
the only difference from example 1 is that the initial concentration of the solution is 2.5mg/ml.
The obtained product has serious agglomeration condition, nonuniform particle size, wide CSD distribution and 1500ppm of Mg content after secondary crystallization.
Comparative example 2:
the only difference from example 1 is that the residence time per stage is 30min.
Too little residence time results in insufficient time for crystal growth, the average particle size of the product particles is smaller, 150 microns, a great amount of nucleation occurs in the excessive supersaturation, the aggregation phenomenon is obvious, and the Mg content after secondary crystallization is 1200ppm.
Comparative example 3:
the only difference from example 1 is that the temperature of the intermediate one of the three-stage crystallizers is 28 ℃.
The obtained product has serious agglomeration condition, nonuniform particle size, wide CSD distribution and 850ppm of Mg content after secondary crystallization. .
Comparative example 4:
the only difference from example 1 is that the amount of seed added is 1/5 of the product.
The supersaturation degree generated by the solution remains after the growth of the crystals, resulting in secondary nucleation of the solution, which leads to coalescence, and the Mg content of the secondary crystallized product is 900ppm.
Comparative example 5:
the only difference from example 1 is that the seed amount added had a particle size of 100 microns.
Too small particle size affects the solubility of the crystals, deviates from the thermodynamics originally measured, and is partially dissolved after the addition of seed crystals, resulting in subsequent supersaturation being consumed after crystal growth and remaining, resulting in secondary nucleation of the solution, resulting in coalescence, the Mg content of the secondary crystallized product being 760ppm
Comparative example 6:
the only difference from example 1 is that the end temperature of the tertiary crystallizer is 10 ℃.
The purity of the product can meet the requirement, but for industrial production, the temperature of 10 ℃ is relatively low, a large amount of steam is consumed for reducing the temperature to such low temperature in the process of scale-up production, and meanwhile, the scaling problem is easy to occur, so that the temperature of the last set of the three-stage crystallizer is set to be more than 20 ℃ in view of heat exchange and economy.
As is apparent from comparison of example 1 and comparative example 1, when the initial concentration of the solution is lower than the limit range of the present invention, since the partition coefficient of the solvent is constant, a certain amount of the solvent cannot handle a larger amount of Mg impurities, so Mg is more present in the product, and thus the amount of feed cannot be increased in order to pursue an excessively high yield.
From a comparison of example 1 and comparative example 2, it is understood that when the residence time of the solution in each stage of the crystallizer is not within the limit of the present invention, the crystal grain size is caused to be small, resulting in supersaturation for nucleation rather than growth or unnecessary residence time to increase the process cost.
As is evident from example 1 and comparative example 3, when the temperature of each stage of the crystallizer is not within the limit of the present invention, the agglomeration of the product is serious, the particle size is not uniform, the CSD distribution is wide, and the impurity content of the product is high.
As is apparent from comparison of example 1 and comparative examples 4 and 5, when the amount of seed crystals added or the particle diameter of seed crystals is out of the limit of the present invention, supersaturation caused by the solution is consumed for crystal growth and remains, resulting in secondary nucleation of the solution, thereby causing coalescence, and thus high impurity content of the product.
As is clear from a comparison of example 1 and comparative example 6, the temperature of 10℃is relatively too low for industrial production, a large amount of steam is consumed for lowering the temperature to such low temperature during the scale-up production, and the problem of scaling is liable to occur, so that the temperature of the last set of the three-stage crystallizer is set to 20℃or more for heat exchange and economic consideration.
The invention discloses and provides a novel technology for purifying, refining and crystallizing titanium dioxide byproduct ferrous sulfate, which can be realized by appropriately changing links such as initial concentration, residence time of each stage of crystallizer, temperature of each crystallizer, stirring rate, rotary steaming percentage, seed crystal adding amount, particle size and the like by referring to the content of the technical proposal. While the method of the present invention has been described in terms of preferred embodiments, it will be apparent to those skilled in the relevant art that variations and combinations of the methods and products described herein can be made to practice the present technology without departing from the spirit or scope of the invention. It is expressly noted that all such similar substitutes and modifications apparent to those skilled in the art are deemed to be included within the spirit, scope and content of the invention.
Claims (10)
1. The purification, refining and crystallization method of the titanium dioxide byproduct ferrous sulfate is characterized by comprising the following steps of:
(1) Under the stirring condition, dissolving titanium dioxide raw materials containing by-product ferrous sulfate in water at 60-80 ℃ to prepare ferrous sulfate heptahydrate-water mixed solution, then adding iron powder for reduction, adding acid for regulating pH to 1-3, and adding flocculant for flocculation to obtain clear liquid;
(2) Under the stirring condition, cooling the clear liquid obtained in the step (1) to 50-60 ℃ for one time, continuously adding a large amount of seed crystals, cooling to 30-35 ℃ for 50-70min for the second time, cooling to 20-25 ℃ for 50-70min for the third time, and carrying out solid-liquid separation to obtain a primary crystallization crude product;
(3) Under the stirring condition, dissolving the primary crystallization crude product obtained in the step (2) in water at 60-80 ℃, cooling to 50-60 ℃ for the first time, continuously adding a large amount of seed crystals, cooling to 30-35 ℃ for 50-70min for the second time, and cooling to 20-25 ℃ for 50-70min for the third time, thus obtaining the titanium dioxide byproduct ferrous sulfate.
2. The method for purifying and refining crystallization according to claim 1, wherein in the step (1), the step (2) and the step (3), the stirring rate is 200 to 400rpm;
preferably, the concentration of ferrous sulfate heptahydrate in the mixed solution in the step (1) is 1.30-2.00 g/mL.
3. The method for purifying, refining and crystallizing according to claim 1, wherein the acid in the step (1) is diluted sulfuric acid, wherein the diluted sulfuric acid is obtained by mixing 98% concentrated sulfuric acid with water in a volume ratio of (1-4): 9-6;
preferably, the iron in the step (1) is added in an amount of 1-3g based on 100g of the titanium white powder raw material containing the by-product ferrous sulfate.
4. The method for purifying and refining crystals according to claim 1, wherein the flocculant in the step (1) is polyacrylamide;
preferably, the flocculant in the step (1) is added in an amount of 0.1-0.3g based on 100g of titanium dioxide raw material containing ferrous sulfate as a byproduct.
5. The method for purifying and refining crystallization according to claim 1, wherein the seed crystals in step (2) and step (3) have a particle diameter of 100 to 200 μm;
preferably, the addition amount of the seed crystal in the step (2) is 1/4-1/3 of the mass of the finally obtained ferrous sulfate heptahydrate.
6. The purification, refining and crystallization method according to claim 1, characterized in that the liquid obtained by solid-liquid separation in the step (2) is recovered, the recovery comprises rotary evaporation of the liquid, and 50-70% of mother liquor is taken out for dissolving titanium pigment raw material containing by-product ferrous sulfate in the step (1);
preferably, the temperature of the rotary steaming is 50-70 ℃, and the rotation number of the rotary steaming is 60-100rpm.
7. The method for purifying, refining and crystallizing according to claim 1, wherein the step (3) further comprises sequentially subjecting the mixture obtained after the three times of cooling to solid-liquid separation, washing and drying;
preferably, the solid-liquid separation mode is filtration;
preferably, the washing is carried out for 2-4 times by using saturated ferrous sulfate heptahydrate saturated solution;
preferably, the drying is vacuum drying, wherein the vacuum degree is 0.95bar, the drying temperature is 40-50 ℃, and the drying time is 12-16h.
8. The purification, refinement and crystallization method according to claim 1, wherein the preparation method further comprises recycling the liquid obtained by the solid-liquid separation in the step (3) for dissolution of the titanium white powder byproduct raw material in the step (1);
preferably, the concentration of the ferrous sulfate heptahydrate in the solution after the titanium dioxide byproduct raw material is dissolved is kept consistent with the concentration of the ferrous sulfate heptahydrate in the solution after the titanium dioxide byproduct raw material is dissolved.
9. The purified and refined crystals according to any one of claims 1 to 8, to obtain a ferrous sulfate heptahydrate crystal;
preferably, the content of magnesium in the ferrous sulfate heptahydrate crystals is lower than 500ppm;
preferably, the particle size of the ferrous sulfate heptahydrate crystals is 150-250 μm.
10. The use of the ferrous sulfate heptahydrate crystal according to claim 9 for preparing battery grade ferrous oxalate.
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