A method for preparing battery-grade iron phosphate from phosphate rock and iron powder

Abstract

The present invention provides a method for preparing ferric phosphate from low-grade collophosphate ore and iron powder. The phosphate ore is acid-leached to obtain a mixed slurry of phosphoric acid and sulfuric acid. Iron powder is added to adjust the pH of the phosphate ore slurry. A flocculant is added to settle suspended solids. The iron-phosphorus mixed solution obtained after filtration is placed in a reactor. Iron phosphate dihydrate is obtained through oxidation reaction and crystallization reaction, and anhydrous iron phosphate is obtained through high-temperature calcination. The preparation of ferric phosphate by this process eliminates the steps of raw material impurity removal and concentrated extraction. The composite flocculation of polyferric sulfate and long-chain polyoxyethylene organic matter with terminal hydroxyl groups effectively removes impurity metal ions in the iron-phosphorus mixed solution, thereby improving product quality to a certain extent. In addition, the use of this process effectively saves raw material costs and has high economic value.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-ion battery positive electrode materials, and particularly relates to a method for preparing battery-grade iron phosphate from colloidal phosphate and iron powder. Background Art

[0002] With the rapid development of new energy vehicles, demand for power batteries in the domestic market has surged. The mainstream lithium iron phosphate batteries currently on the market have complex compositions and high production costs. The cathode material, lithium iron phosphate alone, accounts for 60% of the battery's total cost. Currently, the vast majority of manufacturers in the industry use soluble phosphates to react with ferrous sulfate, a byproduct of titanium dioxide, to produce battery-grade iron phosphate. Soluble phosphates are primarily produced through simple chemical reactions using phosphoric acid as an intermediate or final product of the wet-process phosphoric acid process. This production process requires large quantities of phosphoric acid and phosphate salts, which has led to a shortage of phosphate rock resources and increased the production burden on phosphorus chemical and fertilizer companies.

[0003] Phosphate rock has been designated a key strategic resource in my country. Despite its abundant reserves, my country's phosphate rock grade is generally poor, with an average P2O5 content of only 17%. Furthermore, my country's agricultural status has led to a growing demand for phosphate fertilizers. Currently, phosphate rock with a P2O5 content of 24-30% is used as the primary raw material for low-quality phosphate fertilizers. Phosphate rock with a P2O5 content of 15-24% must be enriched before it can be used as a raw material for high-grade compound fertilizers. Since phosphate rock in Hubei Province is primarily poor collophanite, with a P2O5 content of no more than 20%, its utilization is difficult. Furthermore, collophanite's high impurity content makes it difficult to grind, creating new challenges for flotation. Summary of the Invention

[0004] In view of the above problems faced by the utilization of collophanite and the dependence of lithium iron phosphate battery companies on phosphate products, a method for preparing iron phosphate using phosphate rock with a P2O5 content of 15-24% and iron powder as phosphorus source and iron source respectively is proposed. This method can promote the effective utilization of low-grade collophanite and reduce the production cost of iron phosphate. Iron powder serves as an iron source on the one hand and a pH regulator and impurity remover on the other hand. It can preliminarily remove heavy metal ions in phosphate rock; terminal hydroxyl long-chain alkyl polyoxyethylene is hydrolyzed under acidic conditions to generate multiple active hydroxyl functional groups, and the hydroxyl groups react with Fe in polyferric sulfate. 3+ The coordination complex fully utilizes the electrical neutralization ability of polyferric sulfate and the adsorption bridging performance of the organic polymer long chain, thereby improving the reaction flocculation and impurity removal effect. This method has good practical and economic value.

[0005] The present invention provides a method for preparing ferric phosphate from collophosphate and iron powder, comprising the following steps:

[0006] 1) Place the phosphate rock in a ball mill and use small-sized zirconium oxide microballs for dry grinding.

[0007] 2) placing the phosphate rock powder in step 1) in a reactor, adding concentrated sulfuric acid for acidification, adding iron powder to adjust the solution pH to 2.5-3.0, adding polyferric sulfate and stirring at high speed for 3-5 minutes, adding a long-chain polyoxyethylene organic compound with terminal hydroxyl groups and stirring at high speed for 3-5 minutes, letting it settle and filtering to collect the filtrate.

[0008] 3) placing the filtrate in step 2) in a reaction kettle, adding an oxidant, adjusting the temperature and stirring speed of the reaction solution, and aging to obtain a reaction solution slurry.

[0009] 4) The reaction liquid slurry in step 3) is filtered and washed to obtain a filter cake, and then the filter cake is evenly mixed with deionized water, concentrated phosphoric acid is added to adjust the solution pH to 1.5-2.0, and high-temperature aging is performed to obtain iron phosphate slurry.

[0010] 5) The ferric phosphate slurry in step 4) is filtered and washed, and then spray-dried and calcined to obtain anhydrous ferric phosphate.

[0011] Preferably, in step 1), the ball mill rotation speed is 1600-2400 r / min, the ball milling time is 1-3 h, and the particle size of the phosphate rock powder is 50-250 μm.

[0012] Preferably, the concentration of concentrated sulfuric acid in step 2) is 40-80%, the mass ratio of phosphate rock powder, concentrated sulfuric acid and iron powder is 1-1.5:2-2.5:8-10, the reaction is in a boiling state, and the mass ratio of polyferric sulfate, organic matter with terminal hydroxyl long-chain polyoxyethylene and phosphate rock is 2-5‰:1-2‰:1.

[0013] Preferably, in the step 2), the mass ratio of the polyferric sulfate, the organic matter having terminal hydroxyl long-chain polyoxyethylene, and the phosphate rock is 2‰-5‰:1‰-2‰:1; wherein the organic matter having terminal hydroxyl long-chain polyoxyethylene is preferably one or more of 14-hydroxy-dodecylpolyoxyethylene, 16-hydroxy-tetradecylpolyoxyethylene, and 18-hydroxy-hexadecylpolyoxyethylene; and in the step 3), the oxidant is a mixture of one or more of H2O2, O2, and air; the stirring speed is 400-600 rpm, and the reaction is performed for 50-60 min.

[0014] Preferably, in step 4), the mass ratio of filter cake, deionized water and concentrated phosphoric acid is 10-15:20-25:1-1.3, the stirring speed is 400-600 rpm, and the reaction is carried out at 90-95° C. for 70-80 min.

[0015] Preferably, in step 5), the heating rate is 5-10° C. / min, the sintering temperature is 550-650° C., and the sintering time is controlled within 3-8 hours.

[0016] By optimizing the reaction system of iron powder and phosphate rock, the present invention has the following benefits:

[0017] 1) By using low-quality phosphate rock as a phosphorus source, the production cost of iron phosphate is reduced, and it has the advantages of a wide source of raw materials, simple processing, and low price.

[0018] 2) By hydrolyzing a long-chain polyoxyethylene organic compound with terminal hydroxyl groups under acidic conditions to generate multiple active hydroxyl functional groups, the hydroxyl groups react with Fe in the polyferric sulfate. 3+ Coordination forms an organic-inorganic composite flocculant, which gives full play to the electrical neutralization ability of polyferric sulfate and the adsorption and bridging performance of the organic polymer long chain, thereby improving the reaction flocculation and impurity removal effect.

[0019] 3) Iron powder participates in the synthesis of ferric phosphate as an iron source on the one hand, and on the other hand, acts as a pH regulator to promote the hydrolysis of impurity metal ions in the iron-phosphorus mixed solution. The composite flocculation effect of polyferric sulfate and long-chain polyoxyethylene organic matter with terminal hydroxyl groups is used to promote the agglomeration and bridging of colloidal suspended matter and hydrolyzed colloidal particles of calcium, magnesium, aluminum, etc. in low-grade phosphate ore, thereby achieving the flocculation and impurity removal effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a process flow chart for preparing ferric phosphate according to Example 1 of the present invention.

[0021] Figure 2 This is the XRD pattern of the iron phosphate prepared in Example 1 of the present invention.

[0022] Figure 3 These are SEM images of the iron phosphate prepared in Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, which does not limit the scope of protection thereof.

[0024] To avoid repetition, the materials involved in this specific embodiment are described as follows:

[0025] The low-quality phosphate rock is a type of collophosphate rock, which is a product obtained after mining and flotation, and its phosphorus content should be in the range of 15%-24%.

[0026] The iron powder is conventional reduced iron powder purchased on the market, and its iron content should be no less than 99%.

[0027] Example 1

[0028] A1: 1000 g of collophosphate after flotation was ball-milled in a jar to a particle size of 50-250 μm. A 40% concentrated sulfuric acid solution was added, maintaining a solid-to-liquid ratio of phosphate rock powder to concentrated sulfuric acid of 1:2.5. The solution was stirred and heated until boiling. After preliminary filtration through a filter cloth, iron powder was added to the boiling solution in a mass ratio of iron powder to concentrated sulfuric acid of 4:1. After the pH of the solution rose to 2.5, 2.0 g of polyferric sulfate was added, and the mixture was stirred at 700 rpm for 5 minutes. 1.0 g of 16-hydroxytetradecylpolyoxyethylene was added, and the mixture was stirred at 500 rpm for 5 minutes. The mixture was allowed to settle, and then filtered to obtain a filtrate.

[0029] A2: Place the filtrate in a reactor, start stirring and control the stirring speed to 300 rpm, add a 30% hydrogen peroxide solution, control the feed rate to 10 mL / min, and control the solution pH to 2.0. When the solution temperature rises rapidly, circulating water can be introduced for cooling to keep the reaction liquid slurry temperature at approximately 30°C.

[0030] A3: The reaction slurry in A2 was filtered and washed to obtain a filter cake. 3000 mL of deionized water and 100 g of concentrated phosphoric acid were added to the filter cake and mixed evenly. The temperature was raised to 95°C with a stirring speed of 500 rpm. After the reaction slurry turned white, the mixture was kept warm for 2 h. After cooling, the mixture was discharged and spray-dried to obtain ferric phosphate dihydrate.

[0031] A4: Wash the dihydrated ferric phosphate with pure water until the conductivity of the washed water is less than 0.3 mS / cm, dry it at 95°C, and calcine it at 600°C to obtain anhydrous ferric phosphate.

[0032] Examples 2-4

[0033] Compared with Example 1, Examples 2-4 only changed the type of organic compound with terminal hydroxyl long-chain polyoxyethylene in Step A1, and the other conditions remained the same as those in Example 1.

[0034] Example 2 is 14-hydroxy-dodecylpolyoxyethylene.

[0035] Example 3 is 18-hydroxy-hexadecylpolyoxyethylene.

[0036] Example 4 is a mixture of 14-hydroxy-dodecylpolyoxyethylene and 18-hydroxy-hexadecylpolyoxyethylene in a mass ratio of 1:1.

[0037] Example 5 is polyoxyethylene.

[0038] Examples 6-9

[0039] Compared with Example 1, Examples 6-9 only changed the amount of 16-hydroxy-tetradecylpolyoxyethylene added in Step A1, and the other conditions remained the same as in Example 1.

[0040] The amount of 16-hydroxy-tetradecylpolyoxyethylene in Example 6 is 0.5 g.

[0041] The amount of 16-hydroxy-tetradecylpolyoxyethylene in Example 7 is 1.5 g.

[0042] The amount of 16-hydroxy-tetradecylpolyoxyethylene in Example 8 is 2.0 g.

[0043] The amount of 16-hydroxy-tetradecylpolyoxyethylene in Example 9 is 2.5 g.

[0044] Examples 10-17

[0045] Examples 10-17 are examples in which only the mixing speed of polyferric sulfate and 16-hydroxy-tetradecylpolyoxyethylene is changed relative to Example 1, and the other conditions remain the same as Example 1. The flocculation effect of the flocculant is fed back in combination with the turbidity of the filtrate in A1.

[0046] Table 1 Example of mixing speed of polyferric sulfate and 16-hydroxy-tetradecylpolyoxyethylene

[0047]

[0048] Comparative Example 1

[0049] In Comparative Example 1, the addition of flocculant was omitted in step A1, and the pH of the phosphate rock and iron powder solution was adjusted to 2.5 by iron powder before direct filtration. The other conditions were the same as those in Example 1.

[0050] The performance characteristics of the anhydrous ferric phosphate prepared in the above example are shown in Table 2 below.

[0051] Table 2 Properties of anhydrous ferric phosphate prepared in some examples and comparative examples

[0052] serial number Fe content / % P content / % Al content / ppm <![CDATA[BET / m 3 ·cm -1 ]]> D50 / μm Example 1 36.22 20.62 38.94 9.8122 6.737 Example 2 36.16 20.65 39.43 9.6225 6.573 Example 3 36.27 20.78 34.73 9.9915 6.774 Example 4 36.14 20.68 28.39 8.4785 6.774 Example 5 35.98 20.90 98.27 8.9625 5.458 Example 6 35.89 20.84 68.43 8.7932 6.457 Example 7 36.12 20.83 55.27 8.4512 5.869 Example 8 36.23 20.74 41.43 9.6112 6.327 Example 9 36.31 20.92 69.18 9.2332 6.180 Example 10 36.02 20.87 82.54 9.4512 6.385 Example 17 36.05 20.93 91.23 8.9378 6.419 Comparative Example 1 35.46 20.78 153.68 9.4579 5.759

Claims

1. A method for preparing battery-grade iron phosphate from phosphate rock and iron powder, characterized in that: The method includes the following: S1. Place the phosphate rock in a ball mill and perform dry grinding using small-sized zirconium oxide microballs; S2, placing the phosphate rock powder in S1 into a reactor, adding concentrated sulfuric acid for acidification, adding iron powder to adjust the solution pH to 2.5-3.0, adding polyferric sulfate and rapidly stirring, then adding a long-chain polyoxyethylene organic compound with terminal hydroxyl groups and rapidly stirring, allowing to settle and filtering to collect the filtrate; S3, placing the filtrate in S2 into a reactor, adding an oxidant, adjusting the temperature and stirring speed of the reaction solution, and aging to obtain a reaction solution slurry; S4, filtering and washing the reaction liquid slurry in S3 to obtain a filter cake, then uniformly mixing the filter cake with deionized water, adding concentrated phosphoric acid to adjust the solution pH to 1.5-2.0, and aging at high temperature to obtain iron phosphate slurry; S5. Filter and wash the iron phosphate slurry in S4, and then spray-dry and calcine to obtain anhydrous iron phosphate.

2. The method for preparing battery-grade iron phosphate from phosphate rock and iron powder according to claim 1, characterized in that: In step S1, the ball mill rotation speed is 1600-2400 r / min, the ball milling time is 1-3 h, and the particle size of the phosphate rock powder is 50-250 μm.

3. The method for preparing battery-grade iron phosphate from phosphate rock and iron powder according to claim 1, characterized in that: In step S2, the concentration of concentrated sulfuric acid is 40-80%, the mass ratio of phosphate rock powder, concentrated sulfuric acid and iron powder is 1-1.5:2-2.5:8-10, and the reaction process is in a boiling state.

4. The method for preparing battery-grade iron phosphate from phosphate rock and iron powder according to claim 1, characterized in that: In step S2, the mass ratio of polyferric sulfate, organic matter with terminal hydroxyl long-chain polyoxyethylene, and phosphate rock is 2‰-5‰:1‰-2‰:1; wherein the organic matter with terminal hydroxyl long-chain polyoxyethylene is one or more of 14-hydroxy-dodecylpolyoxyethylene, 16-hydroxy-tetradecylpolyoxyethylene, and 18-hydroxy-hexadecylpolyoxyethylene.

5. The method for preparing battery-grade iron phosphate from phosphate rock and iron powder according to claim 1, characterized in that: In step S3, the oxidant is a mixture of one or more of H2O2, O2, and air; the stirring speed is 400-600 rpm, and the reaction is carried out for 50-60 min.

6. The method for preparing battery-grade iron phosphate from phosphate rock and iron powder according to claim 1, characterized in that: In step S4, the mass ratio of filter cake, deionized water and concentrated phosphoric acid is 10-15:20-25:1-1.3, the stirring speed is 400-600 rpm, and the reaction is carried out at 90-95° C. for 70-80 min.

7. The method for preparing battery-grade iron phosphate from phosphate rock and iron powder according to claim 1, characterized in that: During the calcination process in step S5, the heating rate is 5-10°C / min, the sintering temperature is 550-650°C, and the sintering time is controlled within 3-8 hours.

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