Preparation method of iron phosphate with controllable titanium content

Abstract

The application relates to a preparation method of iron phosphate with controllable titanium content, and the method comprises the following steps: dissolving titanium white by-product ferrous sulfate in water, then adding a phosphorus source, hydrogen peroxide and a saccharide flocculant for stirring, performing pressure filtration after the stirring, and obtaining an iron salt solution; mixing the iron salt solution and an oxidizing agent for an oxidation reaction, then adding a phosphorus salt for a precipitation reaction, and then performing a heat preservation reaction to obtain a precipitate; performing first washing and beating of the precipitate, then adding phosphoric acid for aging, taking the precipitate after the aging for second washing, drying and calcination. In the application, the impurity Ti content in the raw material ferrous sulfate by-product of titanium white is controlled, and then the titanium content in the finished product of iron phosphate is controlled; by introducing a soluble titanium salt, the titanium content of the finished product can be controlled between 50-5000 ppm, the specific capacity of the positive electrode material can be improved, and the compaction density of the positive electrode material can be ensured.

Description

Technical Field

[0001] This application relates to the field of ferric phosphate preparation technology, and in particular to a method for preparing ferric phosphate with controllable titanium content. Background Technology

[0002] The booming development of lithium-ion batteries for power applications has led to a rapid increase in the production of lithium iron phosphate (LFP) cathode materials. The precursor for LFP is iron phosphate, which is often prepared using ferrous sulfate or ferric sulfate, and ferric sulfate itself is also derived from ferrous sulfate. Ordinary ferrous sulfate, due to its low purity, cannot meet the requirements for preparing LFP. High-purity ferrous sulfate is obtained by reacting pure iron powder with sulfuric acid, causing LFP materials to compete with steel for resources, which is detrimental from a long-term development perspective.

[0003] my country is a major producer of titanium dioxide. When producing titanium dioxide using the sulfuric acid process, 3.5–4 tons of ferrous sulfate (FeSO4·7H2O) are generated as a byproduct for every ton of titanium dioxide produced. Aside from a small amount used as a polyferric sulfate water purifier, most of this byproduct is not fully utilized. This not only wastes sulfur and iron resources but also causes environmental pollution. However, the ferrous sulfate byproduct contains a relatively high amount of foreign matter and impurities, especially Ti, which is as high as 0.5%, failing to meet the raw material requirements for battery-grade ferric phosphate. Therefore, it is necessary to purify the insoluble matter and control the titanium content in the ferrous sulfate. Summary of the Invention

[0004] This application provides a method for preparing ferric phosphate with controllable titanium content, thereby providing a method for controlling the titanium content in ferrous sulfate.

[0005] This application provides a method for preparing iron phosphate with controllable titanium content, the method comprising:

[0006] Ferrous sulfate, a byproduct of titanium dioxide production, was dissolved in water. Then, a phosphorus source, hydrogen peroxide, and a sugar flocculant were added and stirred. After stirring, the mixture was filtered to obtain an iron salt solution.

[0007] The iron salt solution and oxidant are mixed for oxidation reaction, followed by the addition of phosphate salt for precipitation reaction, and then the reaction is carried out at a constant temperature to obtain the precipitate.

[0008] The precipitate was washed and pulped once, then phosphoric acid was added for aging. After aging, the precipitate was taken for a second washing, drying, and calcination.

[0009] Furthermore, the iron content in the iron salt solution is 65–75 g / L; and / or

[0010] The stirring time is 1 to 2 hours.

[0011] Furthermore, the mass ratio of phosphorus source to hydrogen peroxide in the iron salt is 1:(0.035~0.75), and the amount of sugar flocculant used is 2~5wt‰ of the solution mass.

[0012] Furthermore, the molar mass ratio of the iron salt solution, oxidant, and phosphate salt is 1:(0.6-0.7):(1.05-1.15).

[0013] Further, the phosphate salt is 10-18 wt% of ammonium monohydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, or sodium dihydrogen phosphate, and the pH of the phosphate salt is 5-9.

[0014] Furthermore, the process parameters for the oxidation reaction include:

[0015] The reaction time is 25–35 min, and / or

[0016] The process parameters for the precipitation reaction include: a reaction time of 45–60 min; and / or

[0017] The process parameters for the heat preservation reaction include: a reaction temperature of 50–70°C and a reaction time of 0.5–3 h.

[0018] Furthermore, the endpoint conductivity of the single wash is <5 mS / cm; and / or

[0019] The solid content of the pulping product is 10-15%; and / or

[0020] The aging process parameters include: pH 1.0–2.0, temperature 88–92°C, and time 0.5–3 h.

[0021] Furthermore, the final conductivity of the secondary washing is <5 mS / cm; and / or

[0022] The moisture content of the dried product is <2%.

[0023] Further, the calcination includes: calcining at 220-330℃ for 2.5-3.5 hours, then increasing the temperature at 4-6℃ / min to 550-600℃ for 3.5-4.5 hours, and then cooling to 45-55℃ for discharge.

[0024] The technical solutions provided in this application have the following advantages compared with the prior art:

[0025] This application controls the titanium content in the titanium dioxide byproduct ferrous sulfate by purifying and controlling the impurity Ti content, thereby controlling the titanium content in the finished iron phosphate product. By introducing soluble titanium salts, the titanium content of the finished product can be controlled between 50-5000 ppm, which can improve the specific capacity of the cathode material while ensuring the compaction density of the cathode material. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 SEM image of iron phosphate provided in Comparative Example 1 of this application;

[0029] Figure 2 SEM image of ferric phosphate dihydrate provided in Example 4 of this application;

[0030] Figure 3 SEM image of ferric phosphate dihydrate provided in Example 5 of this application;

[0031] Figure 4 The XRD pattern of anhydrous ferric phosphate provided in Comparative Example 1 of this application;

[0032] Figure 5 The XRD pattern of anhydrous ferric phosphate provided in Example 4 of this application;

[0033] Figure 6 The XRD pattern of anhydrous ferric phosphate provided in Example 5 of this application. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0035] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0037] This application provides a method for preparing iron phosphate with controllable titanium content, the method comprising:

[0038] Ferrous sulfate, a byproduct of titanium dioxide production, was dissolved in water. Then, a phosphorus source, hydrogen peroxide, and a sugar flocculant were added and stirred. After stirring, the mixture was filtered to obtain an iron salt solution.

[0039] The iron salt solution and oxidant are mixed for oxidation reaction, followed by the addition of phosphate salt for precipitation reaction, and then the reaction is carried out at a constant temperature to obtain the precipitate.

[0040] The precipitate was washed and pulped once, then phosphoric acid was added for aging. After aging, the precipitate was taken for a second washing, drying, and calcination.

[0041] In this application, the titanium content in the titanium dioxide byproduct ferrous sulfate is controlled through purification, thereby controlling the titanium content in the finished iron phosphate product. By avoiding the introduction of soluble titanium salts, the titanium content of the finished product can be controlled between 50-5000 ppm, which can improve the specific capacity of the cathode material while ensuring its compaction density. Phosphorus sources can be phosphoric acid, phosphate salts, etc., and oxidants can be hydrogen peroxide, oxygen, sodium hypochlorite, etc.

[0042] As one embodiment of the present invention, the iron content in the iron salt solution is 65-75 g / L; and / or

[0043] The stirring time is 1 to 2 hours.

[0044] In one embodiment of the present invention, the mass ratio of the phosphorus source to hydrogen peroxide is 1:(0.035-0.75), and the amount of the sugar flocculant is 2-5 wt‰ of the solution mass.

[0045] In this application, the titanium content can be controlled by adjusting the ratio of hydrogen peroxide to phosphoric acid. This allows for the development of titanium-doped iron phosphate as needed, while maintaining the titanium content within a reasonable range. High-molecular-weight carbohydrate polymers enable rapid filtration and separation, improving production efficiency.

[0046] In one embodiment of the present invention, the mass ratio of the iron salt solution, oxidant, and phosphate salt is 1:(0.6-0.7):(1.05-1.15).

[0047] In one embodiment of the present invention, the phosphate salt is 10-18 wt% of ammonium monohydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, or sodium dihydrogen phosphate, and the pH of the phosphate salt is 5-9.

[0048] In this application, phosphate salts are used as the main material for preparing ferric phosphate. The pH of the reaction system can be controlled to provide the acidity or alkalinity for co-precipitation, while the primary particle size and secondary morphology of the ferric phosphate aggregates can be controlled.

[0049] As one embodiment of the present invention, the process parameters of the oxidation reaction include:

[0050] The reaction time is 25–35 min, and / or

[0051] The process parameters for the precipitation reaction include: a reaction time of 45–60 min; and / or

[0052] The process parameters for the heat preservation reaction include: a reaction temperature of 50–70°C and a reaction time of 0.5–3 h.

[0053] In this application, by controlling the process parameters of the oxidation reaction, complete oxidation can be ensured and the ferrous ion content can be controlled within 0.1%. Otherwise, the presence of ferrous phosphate phase is likely to occur, making crystal transformation difficult in the subsequent aging process.

[0054] As one embodiment of the present invention, the final conductivity of the single wash is <5 mS / cm; and / or

[0055] The solid content of the pulping product is 10-15%; and / or

[0056] The aging process parameters include: pH 1.0–2.0, temperature 88–92°C, and time 0.5–3 h.

[0057] In this application, the byproducts in the synthesized materials have high salt content and high content of metal ions Al, Mg, and Mn. Thorough washing can be ensured by controlling the endpoint of the first washing cycle. Pulping achieves slurry homogeneity, providing a well-dispersed slurry for the aging process. Controlling the pH value during the aging stage facilitates the adsorption of ferric phosphate crystals, resulting in low solubility. Controlling the aging time ensures high crystallinity and fewer impurity peaks, while simultaneously transforming mixed ferric phosphate crystals into single trigonal crystals.

[0058] As one embodiment of the present invention, the final conductivity of the secondary washing is <5 mS / cm; and / or

[0059] The moisture content of the dried product is <2%.

[0060] In this application, the aging system contains impurity elements released during the crystallization process, as well as excessive phosphorus source added to the aging system, which affect the impurity content of the finished product. Furthermore, the excessive phosphorus source affects the iron-to-phosphorus ratio of the finished product. The impurity content is controlled by controlling the endpoint of the secondary washing. In this application, the free water content can be controlled through flash evaporation, which can reduce the load on the calcination process, provide flowable powder for subsequent processes, provide granulation conditions for the conversion of hydrated ferric phosphate into single-crystal ferric phosphate, avoid over-burning of lumps, and control particle size uniformity.

[0061] As one embodiment of the present invention, the calcination includes: calcining at 220-330°C for 2.5-3.5 hours, then increasing the temperature at 4-6°C / min to 550-600°C for 3.5-4.5 hours, and then cooling to 55-45°C for discharge.

[0062] In this application, the calcination in the low-temperature stage is to fully remove the remaining free water, while avoiding the sulfur content that is trapped and difficult to volatilize due to instantaneous high temperature. At the same time, instantaneous high temperature can easily lead to uneven sintering of powder, easy agglomeration and wall formation, resulting in poor stability of the finished product.

[0063] Example 1

[0064] A method for preparing iron phosphate with controllable titanium content, comprising:

[0065] (1) Dissolve ferrous sulfate (the impurity content of which is shown in Table 2), a byproduct of titanium dioxide, in water and control the iron content in the solution to be 70 g / L; add 10% of the iron molar mass of phosphoric acid and stir for 1 h; add 7.5% of the phosphoric acid molar mass of 27.5% hydrogen peroxide and 3 wt‰ of the solution mass of chitosan flocculant and stir for 30 min, then filter to obtain an iron salt solution;

[0066] (2) Take 28.9 kg of ferrous sulfate solution and add it to a double-layered glass reactor. Add 2.4 kg of 27.5% hydrogen peroxide using a peristaltic pump and oxidize for 30 min. Add 21.85 kg of prepared 16 wt% ammonium dihydrogen phosphate solution (pH 7) using a peristaltic pump for 50 min. Then keep the reactor at 60℃ for 1.5 h to obtain the precipitate.

[0067] (3) Wash the precipitate once with pure water, control the final conductivity to <5ms / cm, then pulp it according to the solid content of 12.5%, add phosphoric acid to adjust the pH to 1.2, and then age it for 1.5h.

[0068] (4) Take the precipitate from the aging reaction and wash it twice with pure water. Control the final conductivity to <0.5ms / cm. Flash evaporate the free water at 130℃ to remove the water content to <2%. Then calcine at 270℃ for 3 hours. Then calcine at 5℃ / min to 580℃ for 4 hours. Then cool naturally to 50℃ and package the material.

[0069] Example 2

[0070] A method for preparing iron phosphate with controllable titanium content, comprising:

[0071] (1) Dissolve ferrous sulfate (the impurity content of which is shown in Table 2), a byproduct of titanium dioxide, in water and control the iron content in the solution to be 65 g / L. Then add phosphoric acid with a molar iron content of 10% and stir for 30 min. Then add hydrogen peroxide with a concentration of 27.5% and a molar phosphoric acid content of 12.5% ​​and chitosan flocculant with a solution mass of 2 wt‰ and stir for 30 min. Then filter to obtain iron salt solution.

[0072] (2) Take 30.45 kg of iron salt solution and add it to a double-layer glass reactor. Add 2.2 kg of 27.5% hydrogen peroxide using a peristaltic pump. The oxidation reaction takes 30 min. Then add 24.98 kg of prepared 14 wt% ammonium dihydrogen phosphate solution (pH 5) using a peristaltic pump. The addition time is 45 min. Then keep the reaction at 50℃ for 2 h to obtain the precipitate.

[0073] (3) Wash the precipitate once with pure water, control the final conductivity to <5ms / cm, then pulp it according to the solid content of 10%, add phosphoric acid to adjust the pH to 1.5, and then age it for 3 hours.

[0074] (4) Take the precipitate from the aging reaction and wash it twice with pure water. Control the final conductivity to <0.5ms / cm. Flash evaporate the free water at 130℃ to remove the water content to <2%. Then calcine at 220℃ for 3.5h. Then raise the temperature to 550℃ at 4℃ / min and calcine for 4.5h. Then cool naturally to 45℃ and package the material.

[0075] Example 3

[0076] A method for preparing iron phosphate with controllable titanium content, comprising:

[0077] (1) Dissolve ferrous sulfate (the impurity content of which is shown in Table 2), a byproduct of titanium dioxide, in water, and control the iron content in the solution to be 75 g / L. Then add 10% of the iron molar mass of phosphoric acid and stir for 1 h. Then add 35% of the phosphoric acid molar mass of hydrogen peroxide with a concentration of 27.5% and 5 wt‰ of the solution mass of chitosan flocculant and stir for 1 h. Then filter to obtain an iron salt solution.

[0078] (2) Take 26.97 kg of iron salt solution and add it to a double-layer glass reactor. Add 2.6 kg of hydrogen peroxide using a peristaltic pump. The oxidation reaction is carried out for 30 min. Then, add 19.43 kg of prepared 18 wt% ammonium dihydrogen phosphate solution (pH 9) using a peristaltic pump. The precipitation reaction is carried out for 60 min. Then, keep the temperature at 70℃ for 1 h to obtain the precipitate.

[0079] (3) Wash the precipitate once with pure water, control the final conductivity to <5ms / cm, then pulp it according to the solid content of 15%, add phosphoric acid to adjust the pH to 1.7, and then age it for 0.5h.

[0080] (4) Take the precipitate from the aging reaction and wash it twice with pure water. Control the final conductivity to <0.5ms / cm. Flash evaporate the free water at 130℃ to remove the water content to <2%. Then calcine at 330℃ for 2.5h. Then calcine at 6℃ / min to 600℃ for 3.5h. Then cool naturally to 55℃ and package the material.

[0081] Example 4

[0082] A method for preparing iron phosphate with controllable titanium content, comprising:

[0083] (1) Dissolve ferrous sulfate (the impurity content of which is shown in Table 2), a byproduct of titanium dioxide, in water, and control the iron content in the solution to be 70 g / L. Then add 10% of the iron molar mass of phosphoric acid and stir for 1 h. Then add 45% of the phosphoric acid molar mass of 27.5% hydrogen peroxide and 3 wt‰ of the solution mass of chitosan flocculant and stir for 30 min. Then filter to obtain iron salt solution.

[0084] (2) Take 28.9 kg of iron salt solution and add it to a double-layer glass reactor. Add 2.4 kg of hydrogen peroxide using a peristaltic pump. The oxidation reaction is carried out for 30 min. Then, add 21.85 kg of prepared 16 wt% ammonium dihydrogen phosphate solution (pH 7) using a peristaltic pump. The precipitation reaction is carried out for 50 min. Then, keep the temperature at 60℃ for 1.5 h to obtain the precipitate.

[0085] (3) Wash the precipitate once with pure water, control the final conductivity to <5ms / cm, then pulp it according to the solid content of 12.5%, add phosphoric acid to adjust the pH to 1.6, and then age it for 1.5h.

[0086] (4) Take the precipitate from the aging reaction and wash it twice with pure water. Control the final conductivity to <0.5ms / cm. Flash evaporate the free water at 130℃ to remove the water content to <2%. Then calcine at 270℃ for 3 hours. Then calcine at 5℃ / min to 580℃ for 4 hours. Then cool naturally to 50℃ and package the material.

[0087] Example 5

[0088] A method for preparing iron phosphate with controllable titanium content, comprising:

[0089] (1) Dissolve ferrous sulfate (the impurity content of which is shown in Table 2), a byproduct of titanium dioxide, in water, and control the iron content in the solution to be 70 g / L. Then add 10% of the iron molar mass of phosphoric acid and stir for 1 h. Then add 75% of the phosphoric acid molar mass of hydrogen peroxide with a concentration of 27.5% and 3 wt‰ of the solution mass of chitosan flocculant and stir for 30 min. Then filter to obtain an iron salt solution.

[0090] (2) Take 28.9 kg of iron salt solution and add it to the reactor. Add 2.6 kg of hydrogen peroxide using a peristaltic pump. The oxidation reaction is carried out for 30 min. Then add 21.85 kg of prepared 16 wt% ammonium dihydrogen phosphate solution (pH 7) using a peristaltic pump. The precipitation reaction is carried out for 50 min. Then keep the temperature at 60℃ for 1.5 h to obtain the precipitate.

[0091] (3) Wash the precipitate once with pure water, control the final conductivity to <5ms / cm, then pulp it according to the solid content of 12.5%, add phosphoric acid to adjust the pH to 1.8, and then age it for 1.5h.

[0092] (4) Take the precipitate from the aging reaction and wash it twice with pure water. Control the final conductivity to <0.5ms / cm. Flash evaporate the free water at 130℃ to remove the water content to <2%. Then calcine at 270℃ for 3 hours. Then calcine at 5℃ / min to 580℃ for 4 hours. Then cool naturally to 50℃ and package the material.

[0093] Comparative Example 1

[0094] The amount of hydrogen peroxide used in step (1) of Example 1 was changed to 3.4%, and the rest was the same as in Example 1.

[0095] Table 1. Test results of ferric phosphate obtained from the examples and comparative examples. As can be seen from the data in Examples 1-5 and Comparative Example 1 in Table 1, as the titanium content in the finished product increases, the iron-to-phosphorus ratio in the finished product decreases, and the sulfur content stabilizes, which solves the problem of sulfur content reaching 300 ppm in conventional processes. At the same time, as the titanium content increases, the specific surface area of ​​the finished product increases, indicating that titanium doping can refine the primary particles.

[0096] From the data of Examples 4 and 5 and Comparative Example 1 in Table 1, and... Figures 1-3 It can be seen that as the titanium content in the finished product increases, the primary particles become thinner and the regularity decreases, which leads to the inference that the specific surface area increases, consistent with the actual test results. Therefore, the titanium content needs to be controlled at <3000ppm.

[0097] from Figures 4-6 It can be seen that the crystal form of iron phosphate obtained in Examples 4 and 5 and Comparative Example 1 did not change, indicating that the doping of titanium did not change the crystal phase of iron phosphate.

[0098] Table 2. Impurity content in ferrous sulfate by-product of titanium dioxide production. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing iron phosphate with controllable titanium content, characterized in that, The method includes: Ferrous sulfate, a byproduct of titanium dioxide production, is dissolved in water, and then phosphoric acid, hydrogen peroxide, and a sugar flocculant are added and stirred. After stirring, the mixture is filtered to obtain an iron salt solution. The titanium content is controlled by adjusting the ratio of hydrogen peroxide to phosphoric acid. The molar mass ratio of phosphoric acid to hydrogen peroxide in the iron salt is 1:(0.035~0.45), and the amount of sugar flocculant used is 2~5wt‰ of the solution mass. The iron salt solution and oxidant are mixed for oxidation reaction, followed by the addition of phosphate salt for precipitation reaction, and then the reaction is carried out at a constant temperature to obtain the precipitate. The precipitate was washed and pulped once, then phosphoric acid was added for aging. After aging, the precipitate was taken for a second washing, drying, and calcination.

2. The preparation method according to claim 1, characterized in that: The iron salt solution contains 65-75 g / L of iron; and / or The stirring time is 1-2 hours.

3. The preparation method according to claim 1, characterized in that: The molar mass ratio of the iron salt solution, oxidant, and phosphate salt is 1:(0.6~0.7):(1.05~1.15).

4. The preparation method according to claim 1, characterized in that: The phosphate salt is 10-18 wt% of ammonium monohydrogen phosphate, sodium monohydrogen phosphate, ammonium dihydrogen phosphate, or sodium dihydrogen phosphate, and the pH of the phosphate salt is 5-9.

5. The preparation method according to claim 1, characterized in that, The process parameters for the oxidation reaction include: The reaction time is 25-35 min, and / or The process parameters for the precipitation reaction include: a reaction time of 45-60 min; and / or The process parameters for the heat preservation reaction include: a reaction temperature of 50~70℃ and a reaction time of 0.5~3h.

6. The preparation method according to claim 1, characterized in that, The final conductivity of the single wash is <5 mS / cm; and / or The solid content of the pulping product is 10-15%; and / or The aging process parameters include: pH 1.0~2.0, temperature 88~92℃, and time 0.5~3h.

7. The preparation method according to claim 1, characterized in that, The final conductivity of the secondary washing is <5 mS / cm; and / or The moisture content of the dried product is <2%.

8. The preparation method according to claim 1, characterized in that, The calcination process includes: calcining at 220~330℃ for 2.5~3.5h, then increasing the temperature at 4~6℃ / min to 550~600℃ for 3.5~4.5h, and then cooling to 45~55℃ before discharging.

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