A method for preparing low-sulfur and low-cost battery-grade iron phosphate

Abstract

The invention discloses a method for preparing low-sulfur and low-cost battery-grade iron phosphate, and relates to the technical field of iron phosphate preparation. The invention directly mixes ferrous sulfate heptahydrate removed from impurities by iron powder and wet-process phosphoric acid, adds a desulfurizer together, filters out insoluble matter, adjusts the pH value to further remove impurities, and finally oxidizes and crystallizes to obtain low-sulfur iron phosphate dihydrate, which is then calcined to further remove sulfur, fluorine and silicon impurities. Such a process avoids corrosion of calcination equipment by a large amount of sulfur oxides and fluorides, and assists in removing impurities in wet-process phosphoric acid, thereby improving phosphorus yield (phosphorus yield is above 98%) and product quality, and reducing processing costs (preparing one ton of anhydrous iron phosphate saves 2,000 yuan compared with traditional methods) and wastewater volume.

Description

Technical Field

[0001] The invention relates to the technical field of iron phosphate preparation, and in particular to a method for preparing low-sulfur and low-cost battery-grade iron phosphate. Background Art

[0002] There are impurity elements such as fluorine, aluminum, magnesium, manganese, potassium, and sodium in wet phosphoric acid. In particular, the fluorine impurity element has a great impact on the electrical performance of lithium iron phosphate. The chemical and thermodynamic instability of positive electrode materials containing fluorine, so wet phosphoric acid needs to be impurity-removed. At present, most manufacturers use the slurry method to remove impurities from wet phosphoric acid: ammonia is introduced for neutralization to form a monoammonium phosphate solution, but this treatment makes the phosphorus yield not high, and there is still no less than 1000ppm of fluorine. The cost has increased, and the quality of the prepared iron phosphate is not good. Further treatment of phosphorus impurities requires more costs. Usually, in order to further reduce costs, many manufacturers use cheap titanium dioxide byproduct ferrous sulfate heptahydrate as the iron source of iron phosphate, but the prepared dihydrate iron phosphate has a high sulfur content. When it is placed in a muffle furnace for calcination, the sulfur oxides produced corrode the equipment, and a lot of washing water is also used, which greatly increases the cost. Summary of the invention

[0003] In view of the above problems in the prior art, the present invention provides a method for preparing low-sulfur and low-cost battery-grade iron phosphate, which further solves many technical problems in the prior art, such as low phosphorus yield, high cost, poor product quality, severe equipment corrosion, and large amount of wastewater.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A method for preparing low-sulfur and low-cost battery-grade iron phosphate comprises the following steps:

[0006] (1) mixing ferrous sulfate heptahydrate, a titanium dioxide byproduct after impurities are removed by iron powder, and wet-process phosphoric acid in a molar ratio of 1.00:0.90-1.10, adding a desulfurizer, stirring and reacting at 30-80° C. for 10-30 minutes, filtering with suction to obtain a crude iron-phosphorus solution and a precipitate, and recovering the precipitate;

[0007] (2) adding ammonia water or ammonium phosphate to the crude iron-phosphorus solution to adjust the pH value to 2.5-3.2, stirring and reacting at 30-80° C. for 10-30 minutes, filtering with suction to obtain a refined iron-phosphorus solution and a precipitate, and recovering the precipitate;

[0008] (3) Add hydrogen peroxide to the refined iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80-100° C. to adjust the pH to 1.8-2.5, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter to obtain a filtrate and a filter cake, add ammonia water to the filtrate to adjust the pH to 7-10, stir and react at 30-80° C. for 10-30 minutes, filter to obtain an ammonium phosphate solution that can be used to replace part of the wet-process phosphoric acid in (1) or to adjust the pH in (2), and recover the precipitate; dry the filter cake at 80-120° C., crush it to obtain dihydrate iron phosphate, and calcine it at 600-650° C. in a muffle furnace for 1-2 hours to obtain battery-grade anhydrous iron phosphate.

[0009] Preferably, in step (1), the impurity removal process of the titanium dioxide by-product ferrous sulfate heptahydrate is as follows: add an appropriate amount of water to the ferrous sulfate to dissolve it, stir and heat it to 60-90° C., add iron powder, and when the pH value is 3.2-4.5, filter it by suction to obtain a ferrous sulfate solution.

[0010] Preferably, in step (1), the wet-process phosphoric acid is prepared by a hydrochloric acid method or a sulfuric acid method.

[0011] Preferably, in step (1), the amount of the desulfurizer added is 1.1-1.2 times the total amount of iron element.

[0012] Preferably, in step (1), the desulfurizing agent is one or more of calcium oxide, calcium hydroxide or calcium carbonate.

[0013] More preferably, the desulfurizing agent is calcium hydroxide.

[0014] Preferably, in steps (1), (2), and (3), the precipitate is recovered as gypsum.

[0015] Preferably, in step (2), the amount of hydrogen peroxide added is 0.5 to 0.6 times the total amount of iron element.

[0016] In summary, compared with the prior art, the present invention has the following advantages and beneficial effects:

[0017] 1. The present invention directly mixes ferrous sulfate heptahydrate and wet-process phosphoric acid after removing impurities with iron powder, then adds a desulfurizer, and adjusts with ammonia water. This not only removes sulfur impurities and avoids corrosion of calcination equipment by generated sulfur oxides, but also assists in removing impurities in wet-process phosphoric acid, improves phosphorus yield (phosphorus yield is above 98%), product quality, and reduces processing costs (preparing one ton of anhydrous iron phosphate saves 2,000 yuan compared with traditional methods) and wastewater volume;

[0018] 2. The battery-grade anhydrous iron phosphate prepared by the present invention has a sulfur content of less than 10 ppm;

[0019] 3. The precipitate obtained by adding the desulfurizer in the present invention is high-quality gypsum, and the by-product has high value. Secondly, the desulfurizer is cheap and can also achieve the effect of removing fluorine, silicon and other high-priced metal ions;

[0020] 4. The present invention realizes directional removal of impurities, and the phosphorus source and ammonium radical can be recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the process provided by the present invention;

[0022] Figure 2 is a SEM image of the anhydrous ferric phosphate obtained in Example 1;

[0023] Figure 3 This is the XRD pattern of the anhydrous iron phosphate obtained in Example 1. DETAILED DESCRIPTION

[0024] like Figure 1 As shown, it is a schematic diagram of the company process of the present invention, which specifically includes the following steps:

[0025] (1) mixing ferrous sulfate heptahydrate, a titanium dioxide byproduct after impurities are removed by iron powder, and wet-process phosphoric acid in a molar ratio of 1.00:0.90-1.10, adding a desulfurizer, stirring and reacting at 30-80° C. for 10-30 minutes, filtering with suction to obtain a crude iron-phosphorus solution and a precipitate, and recovering the precipitate;

[0026] (2) adding ammonia water or ammonium phosphate to the crude iron-phosphorus solution to adjust the pH value to 2.5-3.2, stirring and reacting at 30-80° C. for 10-30 minutes, filtering with suction to obtain a refined iron-phosphorus solution and a precipitate, and recovering the precipitate;

[0027] (3) Add hydrogen peroxide to the refined iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80-100° C. to adjust the pH to 1.8-2.5, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter to obtain a filtrate and a filter cake, add ammonia water to the filtrate to adjust the pH to 7-10, stir and react at 30-80° C. for 10-30 minutes, filter to obtain an ammonium phosphate solution that can be used to replace part of the wet-process phosphoric acid in (1) or to adjust the pH in (2), and recover the precipitate; dry the filter cake at 80-120° C., crush it to obtain dihydrate iron phosphate, and calcine it at 600-650° C. in a muffle furnace for 1-2 hours to obtain battery-grade anhydrous iron phosphate.

[0028] In order to better understand the present invention, the present invention is further specifically described below through the following embodiments and drawings, but it should not be understood as a limitation of the present invention. Some non-essential improvements and adjustments made by technicians in this field according to the above invention content are also considered to fall within the protection scope of the present invention.

[0029] Example 1

[0030] This embodiment provides a preparation process of battery-grade anhydrous ferric phosphate, comprising the following steps:

[0031] S1. Add appropriate amount of water to ferrous sulfate to dissolve, stir and heat to 80-90°C, then add iron powder, and when pH = 4.5, filter to obtain ferrous sulfate solution.

[0032] S2. Mix 5 mol of ferrous sulfate solution and 5 mol of wet-process phosphoric acid, add 5.5 mol of calcium hydroxide, stir and react at 30 to 40 ° C for 30 min, filter and obtain a crude iron-phosphorus solution and a precipitate, and recover the precipitate;

[0033] S3. Ammonia water was added to the crude iron-phosphorus solution to adjust the pH value to 2.5, the reaction was stirred at 30 ° C for 30 min, and the refined iron-phosphorus solution and precipitate were obtained by suction filtration, and the precipitate was recovered;

[0034] S4. Add hydrogen peroxide to the refined iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80°C to adjust the pH to 1.8, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter, dry at 80°C, and crush to obtain dihydrate iron phosphate, calcine at 600°C in a muffle furnace for 2 hours to obtain battery-grade anhydrous iron phosphate.

[0035] The SEM scanning electron microscope image (10000 times) of the anhydrous ferric phosphate prepared in this embodiment is as follows Figure 2 As shown by Figure 2 It can be seen that the anhydrous iron phosphate presents a flake structure.

[0036] The XRD pattern of the finished anhydrous ferric phosphate is as follows Figure 3 As shown by Figure 3 It can be concluded that the finished product is anhydrous ferric phosphate with a crystallinity of 86%.

[0037] Example 2

[0038] This embodiment provides a preparation process of battery-grade anhydrous ferric phosphate, comprising the following steps:

[0039] S1. Add appropriate amount of water to ferrous sulfate to dissolve, stir and heat to 80-90°C, then add iron powder, and when pH = 4.5, filter to obtain ferrous sulfate solution.

[0040] S2. Mix 5 mol of ferrous sulfate solution and 5 mol of wet-process phosphoric acid, add 5.5 mol of calcium carbonate, stir and react at 30 to 40 ° C for 30 min, filter and obtain a crude iron-phosphorus solution and a precipitate, and recover the precipitate;

[0041] S3. Ammonia water was added to the crude iron-phosphorus solution to adjust the pH value to 2.5, the reaction was stirred at 30 ° C for 30 min, and the refined iron-phosphorus solution and precipitate were obtained by suction filtration, and the precipitate was recovered;

[0042] S4. Add hydrogen peroxide to the refined iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80°C to adjust the pH to 1.8, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter, dry at 80°C, and crush to obtain dihydrate iron phosphate, calcine at 600°C in a muffle furnace for 2 hours to obtain battery-grade anhydrous iron phosphate.

[0043] Example 3

[0044] This embodiment provides a preparation process of battery-grade anhydrous ferric phosphate, comprising the following steps:

[0045] S1. Add appropriate amount of water to ferrous sulfate to dissolve, stir and heat to 80-90°C, then add iron powder, and when pH = 4.5, filter to obtain ferrous sulfate solution.

[0046] S2. Mix 5 mol of ferrous sulfate solution and 5 mol of wet-process phosphoric acid, add 5.5 mol of calcium hydroxide, stir and react at 30 to 40 ° C for 30 min, filter and obtain a crude iron-phosphorus solution and a precipitate, and recover the precipitate;

[0047] S3. Add ammonium phosphate to the crude iron-phosphorus solution to adjust the pH to 2.5, stir the reaction at 30 ° C for 30 min, filter and obtain a refined iron-phosphorus solution and a precipitate, and recover the precipitate;

[0048] S4. Add hydrogen peroxide to the refined iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80°C to adjust the pH to 1.8, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter, dry at 80°C, and crush to obtain dihydrate iron phosphate, calcine at 600°C in a muffle furnace for 2 hours to obtain battery-grade anhydrous iron phosphate.

[0049] Comparative Example 1: No desulfurizer added

[0050] This comparative example prepares anhydrous ferric phosphate, comprising the following steps:

[0051] S1. Add appropriate amount of water to ferrous sulfate to dissolve, stir and heat to 80-90°C, then add iron powder, and when pH = 4.5, filter to obtain ferrous sulfate solution.

[0052] S2. Mix 5 mol of ferrous sulfate solution and 5 mol of wet-process phosphoric acid, stir and react at 30 to 40 ° C for 30 min, filter and obtain a crude iron-phosphorus solution and a precipitate, and recover the precipitate;

[0053] S3. Ammonia water was added to the crude iron-phosphorus solution to adjust the pH value to 2.5, the reaction was stirred at 30 ° C for 30 min, and the refined iron-phosphorus solution and precipitate were obtained by suction filtration, and the precipitate was recovered;

[0054] S4. Add hydrogen peroxide to the refined iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80°C to adjust the pH to 1.8, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter, dry at 80°C, and crush to obtain dihydrate iron phosphate, calcine at 600°C in a muffle furnace for 2 hours to obtain battery-grade anhydrous iron phosphate.

[0055] Comparative Example 2: No ammonia was added to adjust the pH value

[0056] This comparative example prepares anhydrous ferric phosphate, comprising the following steps:

[0057] S1. Add appropriate amount of water to ferrous sulfate to dissolve, stir and heat to 80-90°C, then add iron powder, and when pH = 4.5, filter to obtain ferrous sulfate solution.

[0058] S2. Mix 5 mol of ferrous sulfate solution and 5 mol of wet-process phosphoric acid, add 5.5 mol of calcium hydroxide, stir and react at 30 to 40 ° C for 30 min, filter and obtain a crude iron-phosphorus solution and a precipitate, and recover the precipitate;

[0059] S3. Add hydrogen peroxide to the crude iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80°C to adjust the pH to 1.8, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter, dry at 80°C, and crush to obtain dihydrate iron phosphate, calcine at 600°C in a muffle furnace for 2 hours to obtain battery-grade anhydrous iron phosphate.

[0060] Comparative Example 3

[0061] This comparative example prepares anhydrous ferric phosphate, comprising the following steps:

[0062] S1. Add appropriate amount of water to ferrous sulfate to dissolve, stir and heat to 80-90°C, then add iron powder, and when pH = 4.5, filter to obtain ferrous sulfate solution.

[0063] S2. Mix 5 mol of ferrous sulfate solution and 5 mol of wet-process phosphoric acid, add 5.5 mol of calcium chloride, stir and react at 30 to 40 ° C for 30 min, filter and obtain a crude iron-phosphorus solution and a precipitate, and recover the precipitate;

[0064] S3. Ammonia water was added to the crude iron-phosphorus solution to adjust the pH value to 2.5, the reaction was stirred at 30 ° C for 30 min, and the refined iron-phosphorus solution and precipitate were obtained by suction filtration, and the precipitate was recovered;

[0065] S4. Add hydrogen peroxide to the refined iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80°C to adjust the pH to 1.8, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter, dry at 80°C, and crush to obtain dihydrate iron phosphate, calcine at 600°C in a muffle furnace for 2 hours to obtain battery-grade anhydrous iron phosphate.

[0066] The impurity analysis of the ferric phosphate dihydrate and anhydrous ferric phosphate products obtained in the above examples and comparative examples is performed, and the results are shown in Tables 1 and 2.

[0067] Table 1 Content of ferric phosphate dihydrate (unit: ppm)

[0068]

[0069]

[0070] Table 2 Anhydrous iron phosphate content (unit: ppm)

[0071] example Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 S 2.45 9.30 5.31 320.35 220.32 132.10 F Not detected Not detected Not detected Not detected Not detected Not detected Si 0.32 0.12 0.41 0.43 0.39 0.56 Zn 21.54 19.84 16.37 20.04 27.82 55.28 Pb 5.63 10.04 10.34 5.80 7.50 4.43 Co 0.27 0.07 0.05 0.30 1.48 0.02 Ni 0.32 0.37 0.26 1.23 1.56 0.47 Mn 2.43 0.91 0.93 2.56 2.05 1.62 Mg 10.29 13.17 13.42 10.96 26.70 37.97 Cr 4.92 12.57 12.10 9.63 9.89 7.37 Ti 2.04 4.18 4.38 1.96 2.48 3.86 Ca 0.43 0.29 0.26 0.23 1.08 0.40 Al 35.78 32.87 35.32 1320.13 865.83 50.01 Na 15.34 8.54 8.37 10.95 12.31 55.38 K 2.34 4.10 3.68 2.35 3.43 5.60

[0072] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A method for preparing low-sulfur and low-cost battery-grade iron phosphate, characterized in that: The steps include: (1) mixing ferrous sulfate heptahydrate, a titanium dioxide byproduct after impurities are removed by iron powder, and wet-process phosphoric acid in a molar ratio of 1.00:0.90-1.10, adding a desulfurizing agent, stirring and reacting at 30-80° C. for 10-30 min, filtering to obtain a crude iron-phosphorus solution and a precipitate, and recovering the precipitate, wherein the desulfurizing agent is one or more of calcium oxide, calcium hydroxide or calcium carbonate; (2) Adding ammonia water or ammonium phosphate to the crude iron-phosphorus solution to adjust the pH value to 2.5-3.2, stirring and reacting at 30-80°C for 10-30 minutes, filtering to obtain a refined iron-phosphorus solution and a precipitate, and recovering the precipitate; (3) Add hydrogen peroxide to the refined iron-phosphorus solution until the divalent iron is completely oxidized, add phosphoric acid at 80-100°C to adjust the pH to 1.8-2.5, wait until the precipitate turns pink, continue to keep warm for 90 minutes, wash and filter to obtain a filtrate and a filter cake, add ammonia water to the filtrate to adjust the pH to 7-10, stir and react at 30-80°C for 10-30 minutes, filter to obtain an ammonium phosphate solution that can be used to replace part of the wet phosphoric acid in (1) or to adjust the pH in (2), and recover the precipitate; dry the filter cake at 80-120°C, crush it to obtain dihydrate iron phosphate, and calcine it at 600-650°C in a muffle furnace for 1-2 hours to obtain battery-grade anhydrous iron phosphate. In step (1), the amount of the desulfurizing agent added is 1.1-1.2 times the total amount of iron element; In step (3), the amount of hydrogen peroxide added is 0.5 to 0.6 times the total amount of iron.

2. The method for preparing a low-sulfur and low-cost battery-grade iron phosphate according to claim 1, characterized in that: In step (1), the impurity removal process of the titanium dioxide by-product ferrous sulfate heptahydrate is as follows: add an appropriate amount of water to the ferrous sulfate to dissolve it, stir and heat it to 60-90° C., add iron powder, and when the pH value is 3.2-4.5, filter it by suction to obtain a ferrous sulfate solution.

3. The method for preparing a low-sulfur and low-cost battery-grade iron phosphate according to claim 1, characterized in that: In step (1), the wet-process phosphoric acid is prepared by a hydrochloric acid method or a sulfuric acid method.

4. The method for preparing a low-sulfur and low-cost battery-grade iron phosphate according to claim 1, characterized in that: The desulfurizing agent is calcium hydroxide.

5. The method for preparing a low-sulfur and low-cost battery-grade iron phosphate according to claim 1, characterized in that: In steps (1), (2) and (3), the precipitate is recovered as gypsum.

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