Preparation method of iron phosphate with high iron-phosphorus ratio

Abstract

The invention discloses a preparation method of iron phosphate with a high iron-phosphorus ratio. According to the method, a small amount of iron source is added in the process of dissolving and recrystallizing amorphous-state iron phosphate in the aging process, and the part of iron source enters crystalline-state iron phosphate, so that the utilization rate of a P element in a reaction system is increased, and meanwhile, the iron-phosphorus ratio of the prepared iron phosphate is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy material preparation, and specifically relates to a preparation method and application of iron phosphate with a high iron-to-phosphorus ratio. Background Art

[0002] With the increasingly prominent environmental problems brought about by the explosive growth of fuel vehicles and the gradual depletion of fossil energy, new energy vehicles have gradually begun to partially replace traditional fuel vehicles. Currently, the main cathode materials used in new energy vehicle batteries are ternary cathode materials and lithium iron phosphate materials. Compared with ternary cathode materials, the biggest features of lithium iron phosphate batteries are mainly low cost, good safety performance, good cycle performance, etc. With the increasing emphasis on the safety performance of current passenger cars, lithium iron phosphate has also received more and more attention, and its market share has gradually increased.

[0003] Lithium iron phosphate is mainly obtained by sanding, spraying, pulverizing, and sintering iron phosphate, a lithium source, and a carbon source. As the main raw material, iron phosphate has a great influence on the performance of lithium iron phosphate, and the iron-to-phosphorus ratio of iron phosphate is a key index to measure the performance of iron phosphate. Currently, the iron-to-phosphorus ratio of most iron phosphates on the market is in the range of 0.96 - 0.97. Although there is also iron phosphate with an iron-to-phosphorus ratio above 0.97, there are still some problems. In patents CN109205584A and CN109368610A, by adding polyethylene glycol to the reaction system, the solution distribution becomes more uniform, the existence of free iron ions is reduced, and the iron-to-phosphorus ratio of the prepared iron phosphate can reach above 0.98; although the iron-to-phosphorus ratio of iron phosphate can be adjusted by adding polyethylene glycol, the polyethylene glycol in the system will enter the wastewater system, increasing the difficulty and cost of wastewater treatment. In patent CN112479174A, by using inorganic strong acids such as hydrochloric acid and nitric acid to partially replace phosphoric acid as the acidifying solution, adjusting the feeding ratio of iron element to phosphorus element in the reaction process increases the concentration of iron ions in the system, improves the utilization rate of iron ions, and obtains iron phosphate with a high iron-to-phosphorus ratio; but in this process, impurity ions such as chloride ions and nitrate ions may be introduced. Summary of the Invention

[0004] In view of the above problems, the present invention provides a preparation method of iron phosphate with a high iron-to-phosphorus ratio, which improves the utilization rate of phosphorus element in the system and simultaneously increases the iron-to-phosphorus ratio of iron phosphate by adding a small amount of iron source when amorphous iron phosphate dissolves and recrystallizes during the aging process.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A preparation method of iron phosphate with a high iron-to-phosphorus ratio, the preparation method comprising the following steps:

[0007] (1) Add phosphoric acid solution to ferrous sulfate solution, let it stand and then filter to remove solid impurities to obtain refined ferrous sulfate solution;

[0008] (2) Prepare a phosphorus source solution, add hydrogen peroxide to it to obtain a mixed solution; add the mixed solution to the refined ferrous sulfate solution, stir and then add ammonia water, stir to obtain iron phosphate slurry A;

[0009] (3) Filter the obtained iron phosphate slurry and then wash it to remove impurity ions, control the washing conductivity below 200 μS / cm to obtain filter cake A;

[0010] (4) Slurry the obtained filter cake A with water and phosphoric acid to obtain iron phosphate slurry B, heat up and age the iron phosphate slurry B, and add iron source B after the slurry reaches the aging temperature t ± 3 min to obtain iron phosphate slurry;

[0011] (5) Filter and wash the obtained iron phosphate slurry to remove impurity ions, control the washing conductivity below 100 μS / cm to obtain filter cake B;

[0012] (6) Dry the filter cake B and calcine it to remove the bound water to obtain iron phosphate powder.

[0013] In a specific embodiment, the ferrous sulfate in step (1) is selected from by - product ferrous sulfate of titanium dioxide production; the ferrous sulfate solution is an aqueous solution of ferrous sulfate with a concentration of 30% - 40%; the phosphoric acid solution is an aqueous solution of phosphoric acid with a concentration of 60 - 85%.

[0014] In a specific embodiment, the addition amount of phosphoric acid in the refining process of ferrous sulfate in step (1) is 2% - 5% of the molar amount of ferrous sulfate; the concentration of refined ferrous sulfate is 180 - 250 g / L, preferably 200 - 220 g / L.

[0015] In a specific embodiment, the phosphorus source in step (2) is one or more of ammonium phosphate, monoammonium phosphate, and diammonium phosphate.

[0016] In a specific embodiment, the molar ratio of the phosphorus source to the iron source substance in the refined ferrous sulfate solution in step (2) is 0.9 - 1.1:1, and the volume ratio of the phosphorus salt solution to the refined ferrous sulfate solution is 0.5 - 2:1.

[0017] In a specific embodiment, the amount of hydrogen peroxide in step (2) is more than 0.6 times the amount of ferrous sulfate in the refined ferrous sulfate solution.

[0018] In a specific embodiment, the addition amount of ammonia water in step (2) is 0.6 - 1 times the amount of ferrous sulfate.

[0019] In a specific embodiment, the stirring time before adding ammonia water in step (2) is 5 - 10 min; the stirring time after adding ammonia water is 10 - 30 min.

[0020] In a specific embodiment, the washing solvent in steps (3) and (5) is deionized water.

[0021] In a specific embodiment, the solid content of the iron phosphate slurry B in step (4) is 10% - 20%, and the addition amount of phosphoric acid is 8 - 15% of the amount of substance of the iron source in filter cake A.

[0022] In a specific embodiment, the time for adding iron source B in step (4) is after the slurry reaches the aging temperature t ± 3 min; where (T is the aging temperature of slurry B, and a is the ratio of the amount of substance of phosphoric acid added in slurry B to the amount of substance of iron in filter cake A).

[0023] In a specific embodiment, the aging temperature of the iron phosphate slurry B in step (4) is 85 - 95 °C, the aging time is 1.5 - 3.5 h, and the stirring speed is 200 - 600 rpm.

[0024] In a specific embodiment, the iron source B in step (4) is the refined ferrous sulfate solution obtained by refining phosphoric acid in step (1), and its amount of substance is 5 - 12% of the amount of substance of the iron source in the iron phosphate slurry B, and the iron source B is preheated to 70 - 80 °C in advance.

[0025] In a specific embodiment, in the calcination operation in step (6), the calcination temperature is 500 - 700 °C, and the calcination time is 2 - 4 h.

[0026] On the other hand, the present invention provides iron phosphate prepared by the above method, and the iron - phosphorus ratio of the iron phosphate is 0.97 - 0.985.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) By using phosphoric acid to refine titanium white by - product ferrous sulfate, the present invention can reduce the Mg and Mn impurities in the ferrous sulfate solution while removing Ti impurities; at the same time, the pH of the refined ferrous sulfate solution refined by phosphoric acid is relatively low, reducing the formation of Fe(OH)3 precipitation in the refined solution, and can be preheated before adding the aging slurry.

[0029] (2) In the present invention, ferrous sulfate refining solution is added to the second reactor in series during the aging process, that is, a small amount of iron source is added during the process of amorphous iron phosphate dissolving and recrystallizing. This part of the iron source enters the crystalline iron phosphate, improving the utilization rate of P element in the reaction system and the iron-phosphorus ratio of the prepared iron phosphate. Specific Embodiments

[0030] The technical solution of the present invention will be further described below in conjunction with specific embodiments. The embodiments give specific implementation manners and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0031] Raw materials and sources:

[0032] Raw materials Purity Raw materials Purity Ferrous sulfate By-product of titanium white Phosphoric acid Industrial grade, 85% Ammonium dihydrogen phosphate Industrial grade, >99% Ammonia water Industrial grade, 25 - 28% Hydrogen peroxide Industrial grade, 30% Iron(III) hydroxide Analytical reagent grade

[0033] Testing method: The Fe content of iron phosphate is obtained by titration with potassium dichromate method, the P content is obtained by titration with quinoline molybdate citrate method, and the iron-phosphorus ratio is obtained by conversion.

[0034] Example 1

[0035] (1) Prepare a titanium white by-product ferrous sulfate solution, add phosphoric acid equivalent to 2.5% of the molar amount of ferrous sulfate for refining, and after refining, prepare a ferrous sulfate solution with a concentration of 200 g / L.

[0036] (2) Prepare an ammonium dihydrogen phosphate solution according to a raw material iron-phosphorus ratio of 1:1, add hydrogen peroxide equivalent to 0.65% of the amount of iron source substance to it to obtain a mixed solution; add the mixed solution to the ferrous sulfate refining solution, stir for 10 min, and then add ammonia water. The addition amount of ammonia water is 80% of the amount of ferrous sulfate substance, and stir for 10 min to obtain iron phosphate slurry A.

[0037] (3) Filter and wash the obtained iron phosphate slurry A to remove impurity ions, and control the washing conductivity below 200 μS / cm to obtain filter cake A.

[0038] (4) Slurry the obtained filter cake A with water and phosphoric acid to obtain iron phosphate slurry B. The solid content of slurry B is 10%, and the addition amount of phosphoric acid is 15% of the amount of iron source substance in filter cake A; Slurry B is aged at 90 °C for 2 h, and the refined ferrous sulfate refining solution preheated to 80 °C is added 32 min after the slurry temperature reaches 90 °C. The addition amount is 10% of the amount of iron source substance in slurry B.

[0039] (5) Filter and wash the obtained iron phosphate slurry to remove impurity ions, control the washing conductivity below 100 μS / cm, and dry at 90 °C for 6 h to remove free water.

[0040] (6) Calcinate the dried material at 600 °C for 3 h to remove bound water to obtain iron phosphate powder.

[0041] Example 2

[0042] (1) Prepare a titanium white by - product ferrous sulfate solution, add 3% phosphoric acid for purification, and the concentration of ferrous sulfate after purification is 250 g / L;

[0043] (2) Prepare an ammonium dihydrogen phosphate solution according to a raw material iron - phosphorus ratio of 1:1.1. The volume of the ammonium dihydrogen phosphate solution is 2 times the volume of the ferrous sulfate refined solution. Add hydrogen peroxide of 0.65% of the amount of iron source substance to it to obtain a mixed solution; add the mixed solution to the ferrous sulfate refined solution at a certain speed, stir for 5 min, then add ammonia water. The addition amount of ammonia water is 80% of the amount of ferrous sulfate in terms of the amount of substance, and stir for 30 min to obtain iron phosphate slurry A;

[0044] (3) Perform suction filtration and washing on the obtained iron phosphate slurry A to remove impurity ions, and control the washing conductivity below 200 μS / cm to obtain filter cake A;

[0045] (4) Add water and phosphoric acid to the obtained filter cake A for slurrying to obtain iron phosphate slurry B. The solid content of slurry B is 10%, and the addition amount of phosphoric acid is 8% of the amount of iron source substance in filter cake A; slurry B is aged at 90 °C for 2 h. Among them, when the temperature of the slurry reaches 90 °C for 45 min, add the ferrous sulfate refined solution refined by phosphoric acid pre - heated to 80 °C, and the addition amount is 5% of the amount of iron source substance in slurry B;

[0046] (5) Perform suction filtration and washing on the obtained iron phosphate slurry to remove impurity ions, control the washing conductivity below 100 μS / cm, and dry at 90 °C for 6 h to remove free water;

[0047] (6) Calcinate the dried material at 550 °C for 3 h to remove bound water to obtain iron phosphate powder.

[0048] Example 3

[0049] (1) Prepare a titanium white by - product ferrous sulfate solution, add 5% phosphoric acid for purification, and the concentration of ferrous sulfate after purification is 220 g / L;

[0050] (2) Prepare an ammonium dihydrogen phosphate solution according to a raw material iron - phosphorus ratio of 1:1. The volume of the ammonium dihydrogen phosphate solution is 1.5 times the volume of the ferrous sulfate refined solution. Add hydrogen peroxide of 0.65% of the amount of iron source substance to it to obtain a mixed solution; add the mixed solution to the ferrous sulfate refined solution at a certain speed, stir for 10 min, then add ammonia water. The addition amount of ammonia water is the same as the amount of ferrous sulfate in terms of the amount of substance, and stir for 20 min to obtain iron phosphate slurry A;

[0051] (3) Perform suction filtration and washing on the obtained iron phosphate slurry A to remove impurity ions, and control the washing conductivity below 200 μS / cm to obtain filter cake A;

[0052] (4) The obtained filter cake A is slurried with water and phosphoric acid to obtain iron phosphate slurry B. The solid content of slurry B is 10%, and the addition amount of phosphoric acid is 15% of the amount of iron source substance in filter cake A; Slurry B is aged at 85 °C for 3.5 h. Among them, when the slurry temperature reaches 80 °C for 55 min, a refined ferrous sulfate solution refined with phosphoric acid preheated to 80 °C is added, and the addition amount is 12% of the amount of iron source substance in slurry B;

[0053] (5) The obtained iron phosphate slurry is filtered and washed with deionized water to remove impurity ions, and the washing conductivity is controlled below 100 μS / cm, and dried at 90 °C for 6 h to remove free water;

[0054] (6) The dried material is calcined at 550 °C for 4 h to remove bound water to obtain iron phosphate powder.

[0055] Example 4

[0056] (1) Prepare a by-product titanium white ferrous sulfate solution, add 2.5% phosphoric acid for refining, and the concentration of refined ferrous sulfate is 180 g / L;

[0057] (2) Prepare an ammonium dihydrogen phosphate solution according to the raw material iron-phosphorus ratio of 1:0.9. The volume of the ammonium dihydrogen phosphate solution is 0.5 times the volume of the refined ferrous sulfate solution. Add hydrogen peroxide of 0.7% of the amount of iron source substance to it to obtain a mixed solution; The mixed solution is added to the refined ferrous sulfate solution at a certain speed, stirred for 10 min, and then ammonia water is added. The addition amount of ammonia water is 60% of the amount of ferrous sulfate substance, and stirred for 20 min to obtain iron phosphate slurry A;

[0058] (3) The obtained iron phosphate slurry A is filtered and washed with deionized water to remove impurity ions, and the washing conductivity is controlled below 200 μS / cm to obtain filter cake A;

[0059] (4) The obtained filter cake A is slurried with water and phosphoric acid to obtain iron phosphate slurry B. The solid content of slurry B is 15%, and the addition amount of phosphoric acid is 10% of the amount of iron source substance in filter cake A; Slurry B is aged at 95 °C for 1.5 h. Among them, when the slurry temperature reaches 95 °C for 10 min, a refined ferrous sulfate solution refined with phosphoric acid preheated to 80 °C is added, and the addition amount is 8% of the amount of iron source substance in slurry B;

[0060] (5) The obtained iron phosphate slurry is filtered and washed with deionized water to remove impurity ions, and the washing conductivity is controlled below 100 μS / cm, and dried at 90 °C for 6 h to remove free water;

[0061] (6) The dried material is calcined at 650 °C for 3 h to remove bound water to obtain iron phosphate powder.

[0062] Example 5

[0063] (1) Prepare the by - product ferrous sulfate solution of titanium dioxide, add 2.5% phosphoric acid for refining, and the concentration of ferrous sulfate after refining is 220 g / L;

[0064] (2) Prepare the ammonium dihydrogen phosphate solution according to the raw material iron - phosphorus ratio of 1:1. The volume of the ammonium dihydrogen phosphate solution is the same as that of the refined ferrous sulfate solution. Add hydrogen peroxide accounting for 0.65% of the amount of substance of the iron source to it to obtain a mixed solution. Add the mixed solution to the refined ferrous sulfate solution at a certain speed, stir for 10 min, then add ammonia water. The addition amount of ammonia water is 70% of the amount of substance of ferrous sulfate, and stir for 20 min to obtain iron phosphate slurry A;

[0065] (3) Filter and wash the obtained iron phosphate slurry A to remove impurity ions, and control the washing conductivity below 200 μS / cm to obtain filter cake A;

[0066] (4) Add water and phosphoric acid to the obtained filter cake A for pulping to obtain iron phosphate slurry B. The solid content of slurry B is 10%, and the addition amount of phosphoric acid is 10% of the amount of substance of the iron source in filter cake A. Slurry B is aged at 85 °C for 2.5 h. Among them, when the temperature of the slurry reaches 85 °C for 44 min, add the refined ferrous sulfate solution refined by phosphoric acid pre - heated to 80 °C, and the addition amount is 12% of the amount of substance of the iron source in slurry B;

[0067] (5) Filter and wash the obtained iron phosphate slurry to remove impurity ions, control the washing conductivity below 100 μS / cm, and dry at 90 °C for 6 h to remove free water;

[0068] (6) Calcinate the dried material at 600 °C for 3 h to remove the bound water to obtain iron phosphate powder.

[0069] Comparative Example 1

[0070] The difference from the preparation method of Example 1 is that: in step (4), the refined ferrous sulfate solution refined by phosphoric acid is not added to the slurry during the aging process.

[0071] Comparative Example 2

[0072] The difference from the preparation method of Example 1 is only that: in step (4), when the temperature of the slurry reaches 90 °C for 1.5 h, add the refined ferrous sulfate solution refined by phosphoric acid pre - heated to 80 °C, and the addition amount is 10% of the amount of substance of the iron source in the slurry.

[0073] Comparative Example 3

[0074] The difference from the preparation method of Example 1 is that: in step (4), add the refined ferrous sulfate solution refined by phosphoric acid to the slurry B before the temperature of the slurry B rises, and the addition amount is 10% of the amount of substance of the iron source in the slurry.

[0075] The test results of the above examples and comparative examples are shown in the following table. The Fe / P of the examples is between 0.97 and 0.985, showing an obvious improvement.

[0076] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative example 1 Comparative example 2 Comparative example 3 Fe / P 0.974 0.971 0.977 0.985 0.979 0.965 0.964 0.967

Claims

1. A preparation method of iron phosphate with a high iron-to-phosphorus ratio, the preparation method comprising the following steps: (1) Add a phosphoric acid solution to a ferrous sulfate solution, let it stand and then filter to remove solid impurities to obtain a refined ferrous sulfate solution; (2) Prepare a phosphorus source solution, add hydrogen peroxide to it to obtain a mixed solution; add the mixed solution to the refined ferrous sulfate solution, stir and then add ammonia water, and stir to obtain iron phosphate slurry A; (3) Filter the obtained iron phosphate slurry and then wash it to remove impurity ions, control the washing conductivity below 200 μS / cm to obtain filter cake A; (4) Slurry the obtained filter cake A with water and phosphoric acid to obtain iron phosphate slurry B, heat up and age the iron phosphate slurry B, and add iron source B after the slurry reaches the aging temperature t ± 3 min to obtain iron phosphate slurry; (5) Filter and wash the obtained iron phosphate slurry to remove impurity ions, control the washing conductivity below 100 μS / cm to obtain filter cake B; (6) Dry the filter cake B and calcine it to remove the bound water to obtain iron phosphate powder; Among them T is the aging temperature of slurry B, and a is the molar ratio of phosphoric acid added in slurry B to iron in filter cake A.

2. The preparation method according to claim 1, wherein In the step (1), the ferrous sulfate is selected from by-product ferrous sulfate of titanium dioxide; the ferrous sulfate solution is an aqueous solution of ferrous sulfate with a concentration of 30% - 40%; the phosphoric acid solution is an aqueous solution of phosphoric acid with a concentration of 60 - 85%.

3. The preparation method according to claim 1 or 2, characterized in that, In the refined process of ferrous sulfate in the step (1), the addition amount of phosphoric acid is 2% - 5% of the molar amount of ferrous sulfate; the concentration of the refined ferrous sulfate is 180 - 250 g / L, preferably 200 - 220 g / L.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In the step (2), the phosphorus source is one or more of ammonium phosphate, monoammonium hydrogen phosphate, and diammonium hydrogen phosphate; and / or, the molar ratio of the phosphorus source to the iron source substance in the refined ferrous sulfate solution in the step (2) is 0.9 - 1.1:1, and the volume ratio of the phosphorus salt solution to the refined ferrous sulfate solution is 0.5 - 2:

1.

5. The preparation method according to any one of claims 1-4, characterized in that, In the step (2), the amount of hydrogen peroxide is more than 0.6 times the amount of ferrous sulfate in the refined ferrous sulfate solution; and / or, the addition amount of ammonia water in the step (2) is 0.6 - 1 times the amount of ferrous sulfate; and / or, the stirring time before adding ammonia water in the step (2) is 5 - 10 min; the stirring time after adding ammonia water is 10 - 30 min.

6. The preparation method according to any one of claims 1-5, characterized in that, In the step (4), the solid content of the iron phosphate slurry B is 10% - 20%, and the addition amount of phosphoric acid is 8% - 15% of the molar amount of the iron source in the filter cake A; and / or, the aging temperature of the iron phosphate slurry B in the step (4) is 85 - 95 °C, the aging time is 1.5 - 3.5 h, and the stirring speed is 200 - 600 rpm.

7. The preparation method according to any one of claims 1-6, characterized in that, In the step (4), the iron source B is the refined ferrous sulfate solution refined by phosphoric acid in the step (1), its amount of substance is 5% - 12% of the amount of the iron source in the iron phosphate slurry B, and the iron source B is preheated to 70 - 80 °C in advance.

8. The preparation method according to any one of claims 1-7, characterized in that, In the step (6), the calcination temperature in the calcination operation is 500 - 700 °C, and the calcination time is 2 - 4 h.

9. The preparation method according to any one of claims 1-8, characterized in that, The iron-to-phosphorus ratio of the iron phosphate is 0.97 - 0.985.

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