A method for preparing battery-grade iron phosphate from fertilizer-grade monoammonium phosphate

Abstract

The application belongs to the technical field of lithium battery materials, and particularly relates to a method for preparing battery-grade iron phosphate from fertilizer-grade monoammonium phosphate. The preparation method comprises the following steps: step 1, dissolving fertilizer-grade monoammonium phosphate in water at 95-110 DEG C, and performing solid-liquid separation to obtain a monoammonium phosphate solution; step 2, performing coprecipitation of the monoammonium phosphate solution obtained in step 1 with an iron salt, or performing oxidative coprecipitation of the monoammonium phosphate solution with a ferrous salt, performing solid-liquid separation, and purifying, to obtain battery-grade iron phosphate. The method can significantly reduce the production cost of battery-grade iron phosphate, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery materials, and particularly relates to a method for preparing battery-grade iron phosphate from fertilizer-grade monoammonium phosphate. BACKGROUND

[0002] Lithium iron phosphate positive electrode materials have increasing demand in the fields of electric vehicles and large-scale energy storage due to their high energy density, low cost and good stability. Iron phosphate is a key precursor for preparing lithium iron phosphate. Currently, battery-grade iron phosphate is mainly prepared by co-precipitation of monoammonium phosphate (or ammonium dihydrogen phosphate, or its clear solution or mother liquor) and iron salt (ferrous sulfate, etc.).

[0003] Currently, the main preparation processes of industrial monoammonium phosphate include hot-process phosphoric acid process and purified wet-process phosphoric acid route. The hot-process acid process first prepares phosphoric acid by burning yellow phosphorus and then neutralizes it with ammonia to prepare monoammonium phosphate, which has high energy consumption and causes serious pollution. The purified wet-process phosphoric acid route purifies wet-process phosphoric acid and then passes it into industrial monoammonium phosphate clear solution, which is crystallized to obtain industrial-grade monoammonium phosphate. However, this method has problems such as long process and large equipment investment. The production process of fertilizer-grade monoammonium phosphate first crushes phosphate ore by a crusher, further crushes it by adding water into a ball mill to obtain phosphate ore slurry; then, the slurry is preliminarily filtered, phosphoric acid is extracted by adding sulfuric acid, and the product is obtained after filtration; finally, the slurry is obtained by neutralization reaction with gaseous ammonia, concentrated, and granulated by spray granulation to obtain granular monoammonium phosphate, i.e., the product. This method has low production cost.

[0004] In order to ensure that the content of impurities in iron phosphate meets the requirements of battery-grade materials, the current monoammonium phosphate raw material used in the production process of battery-grade iron phosphate usually needs to use industrial monoammonium phosphate. However, due to the huge cost advantage of fertilizer-grade monoammonium phosphate, people still hope to realize the process of producing battery-grade iron phosphate from fertilizer-grade monoammonium phosphate.

[0005] Compared with industrial monoammonium phosphate, there are a large number of impurities in the fertilizer-grade monoammonium phosphate, such as ions of multiple elements of Ca, Mg, Al, Cu, Zu, Mn, Ti and Cr. If these impurities cannot be removed from the process, they will co-precipitate with the ferric phosphate product, seriously affecting the quality of the ferric phosphate product, so that it cannot reach the battery-grade standard. In order to solve this problem, the Chinese invention patent application "CN201710026629.7 A method for producing industrial first-grade and battery-grade monoammonium phosphate from fertilizer-grade monoammonium phosphate" removes the impurities in the fertilizer-grade monoammonium phosphate by adding a decolorizing agent, a precipitating agent, adjusting the pH, adding a decontaminating agent and filtering, and then produces industrial first-grade and battery-grade monoammonium phosphate. In addition, the Chinese invention patent application "CN201911364346.9 A preparation method of low-cost low-impurity ferric phosphate" discloses that in the process of preparing ferric phosphate by using compound fertilizer (containing potassium chloride, ammonium sulfate and monoammonium phosphate) as a phosphorus source, the adverse effects of excess ammonium ions on crystallization can be eliminated by adding nitrite, and the content of multiple impurity ions in the ferric phosphate product can be significantly reduced.

[0006] However, the above processes all need to add additional decontaminating agents, set up additional process steps, and perform additional decontamination treatment on the fertilizer-grade monoammonium phosphate, which has an adverse effect on production efficiency and production cost. SUMMARY

[0007] In view of the defects of the prior art, the present application provides a method for preparing battery-grade ferric phosphate from fertilizer-grade monoammonium phosphate, which aims to prepare battery-grade ferric phosphate from fertilizer-grade monoammonium phosphate without any decontamination step, reduce the use of reagents, shorten the process flow, and maximize the cost advantage of fertilizer-grade monoammonium phosphate.

[0008] A method for preparing battery-grade ferric phosphate from fertilizer-grade monoammonium phosphate, comprising the following steps:

[0009] Step 1: dissolving the fertilizer-grade monoammonium phosphate in water not lower than 95°C, and solid-liquid separation to obtain a monoammonium phosphate solution;

[0010] Step 2: preparing battery-grade ferric phosphate from the monoammonium phosphate solution obtained in step 1 as a phosphorus source. As a preferred scheme, step 2 is specifically: co-precipitating the monoammonium phosphate solution obtained in step 1 with an iron salt, or oxidizing co-precipitating with a ferrous salt, solid-liquid separation, and purification to obtain the battery-grade ferric phosphate.

[0011] Preferably, in step 1, the fertilizer-grade monoammonium phosphate is dissolved in water of 95-100°C.

[0012] Preferably, in step 1, the mass fraction of the monoammonium phosphate solution is 13%-14%.

[0013] Preferably, step 2 specifically comprises the following steps:

[0014] Step 2.1, the ammonium phosphate solution obtained in step 1 and hydrogen peroxide are double-dropped into the ferrous sulfate solution to obtain a crude iron phosphate mother liquor;

[0015] Step 2.2, the crude iron phosphate mother liquor is washed to obtain a crude iron phosphate;

[0016] Step 2.3, the crude iron phosphate, water and phosphoric acid are mixed and aged to obtain an aging mother liquor;

[0017] Step 2.4, the aging mother liquor is subjected to solid-liquid separation, the solid is washed and dried to obtain a battery-grade iron phosphate.

[0018] Preferably, in step 2.1, the pH of the ferrous sulfate solution is adjusted to 1.6-1.8, the concentration of the ferrous sulfate is 4%-8% by mass, preferably 6.5%, the mass fraction of the hydrogen peroxide is 25%-30%, preferably 28%, and the amount ratio of the ammonium phosphate solution, hydrogen peroxide and ferrous sulfate solution is 1:0.05-0.2:0.96-1.02 by mole, preferably 1:0.14:0.98.

[0019] Preferably, the ferrous sulfate solution is prepared by using analytical pure ferrous sulfate.

[0020] Preferably, in step 2.3, the concentration of the phosphoric acid is 10%-30% by mass, preferably 20%, and the weight ratio of the crude iron phosphate, water and phosphoric acid is 1:10-3:0.1-0.2, preferably 1:5:0.12.

[0021] Preferably, the fertilizer-grade ammonium phosphate is ammonium phosphate that meets the national standard "GB 10206-88 First Grade Water Soluble Phosphorus (P2O5) 29%".

[0022] Preferably, the battery-grade iron phosphate is iron phosphate that meets the industry standard "HG / T 4701-2014".

[0023] The application also provides the battery-grade iron phosphate prepared by the above method.

[0024] In the application, the amount ratio of the solid raw material and the liquid raw material is a mass-volume ratio, and the unit is determined in the following manner: the numerical value of a mass-volume ratio of 1:1 is the same as that of a mass-volume ratio of 1g:1ml.

[0025] The application mainly provides a process for preparing battery-grade iron phosphate by adopting fertilizer-grade monoammonium phosphate as a phosphorus source and ferrous sulfate as an iron source through a coprecipitation method. The fertilizer-grade monoammonium phosphate contains a large amount of impurity ions. In the existing preparation process, the fertilizer-grade monoammonium phosphate raw material is dissolved in water at 60-90 DEG C, and then various impurity ions are removed by adding various impurity removal reagents. The solubility of most inorganic salts in water generally increases with the increase of temperature. However, the inventors of the application accidentally found that the impurity ion dissolution amount of the fertilizer-grade monoammonium phosphate is very low at a high temperature of not less than 95 DEG C, which makes the monoammonium phosphate obtained under this condition not need to be removed and can be further used for preparing battery-grade iron phosphate. Thus, the fertilizer-grade monoammonium phosphate is subjected to simple solution filtration treatment and then reacts with ferrous sulfate to prepare iron phosphate, the purification and impurity removal of the traditional monoammonium phosphate and the precipitation and washing of iron phosphate are coupled, industrial-grade ammonium phosphate is not needed to be used, or the fertilizer-grade ammonium phosphate clear solution (or mother liquor) is not needed to be purified, the production cost of the battery-grade iron phosphate can be reduced, and the application has a good application prospect.

[0026] Obviously, according to the above content of the application, according to the ordinary technical knowledge and common means in the art, other various forms of modifications, replacements or changes can be made without departing from the above basic technical idea of the application.

[0027] The above content of the application will be further explained in detail through the following embodiment. However, it should not be understood that the above subject matter of the application is limited to the following examples. All the technologies realized based on the above content of the application belong to the scope of the application. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The figure is a flowchart of the embodiment 1 of the application. DETAILED DESCRIPTION

[0029] In the following examples, the reagents or materials not specifically explained are commercially available.

[0030] Example 1

[0031] The process of the embodiment is shown in Figure 1 and specifically includes the following steps:

[0032] (1) The fertilizer-grade monoammonium phosphate powder (Yunnan Hongtai Biochemical Co., Ltd., monoammonium phosphate first-grade product) is dissolved in water at 100 DEG C, the obtained product system is subjected to solid-liquid separation, and monoammonium phosphate solution is obtained; the mass fraction of the monoammonium phosphate solution is 13.5%;

[0033] (2) using an analytical pure ferrous sulfate solution (mass fraction 6.5%) as a base solution, adjusting the pH value of the obtained system to 1.6-1.8 by using 98% sulfuric acid, and adding the ammonium dihydrogen phosphate solution and hydrogen peroxide (mass fraction 28%) dropwise into the base solution to perform oxidation and synthesis reaction, thereby obtaining a crude iron phosphate mother liquor; the dosage ratio of the ammonium dihydrogen phosphate solution, the hydrogen peroxide and the ferrous sulfate solution is 1:0.14:0.98 in mole ratio;

[0034] (3) washing the crude iron phosphate mother liquor by using hot water, mixing the obtained crude iron phosphate after washing with water and phosphoric acid to perform aging, thereby obtaining an aging mother liquor; the concentration of the phosphoric acid is 20% in mass fraction, and the weight ratio of the crude iron phosphate, the water and the phosphoric acid is 1:5:0.12;

[0035] (4) performing solid-liquid separation on the aging mother liquor, washing the obtained solid material by using hot water, and then drying to obtain the battery-grade iron phosphate.

[0036] In order to further illustrate the technical scheme of the present application, the beneficial effects of the present application are further illustrated by experiments as follows.

[0037] Experimental Example 1: Influence of dissolution temperature of fertilizer-grade ammonium phosphate on the process

[0038] I. Experimental method

[0039] In this experimental example, the process of Example 1 is used to prepare iron phosphate, and the water temperature for dissolving the fertilizer-grade ammonium phosphate powder is changed in the range of 40-100°C.

[0040] The content of impurity elements in the ammonium phosphate solution and the iron phosphate product is detected by ICP method.

[0041] The iron-phosphorus ratio in the iron phosphate product is detected by chemical titration method.

[0042] The yield of iron phosphate is calculated based on the ammonium phosphate raw material.

[0043] II. Experimental results

[0044] Under different dissolution temperatures, the content (ppm) of impurity elements in the ammonium phosphate solution is shown in the following table:

[0045] Temperature / °C Ca Mg Al Cu Zn Mn Ti Cr 40 999.43 1119.63 1645.04 0.48 28.79 264.45 14.54 7.76 60 1033.78 1143.52 1667.76 0.49 30.49 270.84 11.95 7.45 80 101.21 1149.74 1629.05 0.59 30.11 265.40 12.68 7.82 95 7.96 0.90 30.36 0.00 2.39 54.94 4.18 2.39

[0046] From the data in the above table, it can be seen that when the water temperature is in the range of 40-80°C, a large amount of impurities will be dissolved at the same time as the fertilizer-grade ammonium phosphate is dissolved. When the water temperature for dissolution reaches 95°C, the dissolution amount of impurities including Ca, Mg, Al, Cu, Zn, Mn, Ti and Cr is significantly reduced. This is very beneficial to improving the quality of the iron phosphate product.

[0047] The indicators of the iron phosphate products obtained by dissolving the fertilizer-grade monoammonium phosphate at water temperatures of 60 DEG C and 95 DEG C are as follows:

[0048]

[0049] As can be seen from the data in the above table, the iron phosphate product obtained by dissolving the fertilizer-grade monoammonium phosphate at 60 DEG C has an iron-phosphorus ratio significantly lower than 1 and a relatively high content of various impurity elements. The iron phosphate product obtained by dissolving the fertilizer-grade monoammonium phosphate at 95 DEG C has an iron-phosphorus ratio close to 1 and a low content of impurity elements, which meets the standard of battery-grade iron phosphate

HG / T 4701-2014

[0050] As can be seen from the above examples and experimental examples, the present application improves the production process of iron phosphate and achieves the purpose of producing battery-grade iron phosphate by using fertilizer-grade monoammonium phosphate. The present application can significantly reduce the production cost of battery-grade iron phosphate and has a good application prospect.

Claims

1. A method for preparing battery-grade iron phosphate using fertilizer-grade monoammonium phosphate, characterized in that, Includes the following steps: Step 1: Dissolve fertilizer-grade monoammonium phosphate in water at 95-100 °C, and perform solid-liquid separation to obtain a monoammonium phosphate solution; the mass fraction of the monoammonium phosphate solution is 13%-14%. Step 2: Use the monoammonium phosphate solution obtained in Step 1 as a phosphorus source to prepare battery-grade iron phosphate; Step 2 specifically includes the following steps: Step 2.1: Add the monoammonium phosphate solution and hydrogen peroxide obtained in Step 1 dropwise to the ferrous sulfate solution to obtain crude ferric phosphate mother liquor; Step 2.2: Wash the mother liquor of the crude ferric phosphate to obtain crude ferric phosphate; Step 2.3: Mix the crude ferric phosphate, water, and phosphoric acid, and age the mixture to obtain an aging mother liquor; Step 2.4: Separate the aged mother liquor into solid and liquid components, wash and dry the solid to obtain battery-grade iron phosphate.

2. The method according to claim 1, characterized in that: In step 2.1, the pH of the ferrous sulfate solution is adjusted to 1.6-1.8, the concentration of the ferrous sulfate is 4%-8% by mass, the mass fraction of the hydrogen peroxide is 25%-30%, and the molar ratio of the monoammonium phosphate solution, hydrogen peroxide, and ferrous sulfate solution is 1:0.05-0.2:0.96-1.

02.

3. The method according to claim 1 or 2, characterized in that: The ferrous sulfate solution is prepared using industrial-grade ferrous sulfate.

4. The method according to claim 1, characterized in that: In step 2.3, the concentration of phosphoric acid is 10%-30% by mass, and the weight ratio of crude iron phosphate, water and phosphoric acid is 1:10-3:0.1-0.

2.

5. The method according to claim 1, characterized in that: The fertilizer-grade monoammonium phosphate is monoammonium phosphate that meets the national standard "GB10206-88 First-class water-soluble phosphorus (P2O5) 29%".

6. The method according to claim 1, characterized in that: The battery-grade iron phosphate is iron phosphate that conforms to the industry standard "HG / T4701-2014".

7. Battery-grade iron phosphate prepared according to any one of claims 1-6.

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