Method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by hydrochloric acid process, as raw material

Abstract

The present invention relates to a method for preparing battery-grade iron phosphate using the by-product ferrous chloride mother liquor from titanium dioxide by the hydrochloric acid method, comprising the following steps: (1) filtering the by-product ferrous chloride mother liquor from titanium dioxide by the hydrochloric acid method, then adding deionized water for dilution, heating and reacting to obtain a turbid liquid, and continuing to filter to obtain a yellowish-green clear solution, which is the purified ferrous chloride solution; (2) adding a precipitant to the purified ferrous chloride solution under stirring, controlling the pH value to be 6.5-7.5, then adding H2O2 and stirring, washing and separating the obtained precipitate with a ferric chloride solution, and fully reacting with dilute phosphoric acid to obtain a purple transparent solution; (3) adjusting the pH value of the purple transparent solution to 1.5-2.0 with ammonia water to produce a white precipitate, filtering, washing and drying to obtain the battery-grade iron phosphate product. The present invention mainly uses the rutile mother liquor with a high manganese content to prepare the battery-grade FePO4 product with high added value, and has the characteristics of low preparation cost and easy large-scale synthesis, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of resource utilization of iron waste liquid and preparation of ferric phosphate, and relates to a method for preparing battery-grade ferric phosphate by using ferrous chloride mother liquor, a by-product of titanium dioxide produced by a hydrochloric acid process, as a raw material. Background Art

[0002] Titanium dioxide is an important white inorganic pigment, the main component of which is titanium dioxide (TiO2). It is non-toxic, has the best opacity, the best whiteness and brightness, and is considered to be the best white pigment in the world. It is widely used in coatings, papermaking, inks and other fields. The production process of titanium dioxide includes hydrochloric acid method, sulfuric acid method and chlorination method, which refers to the use of chemical processing methods to separate most of the iron elements in ilmenite to produce a titanium-rich raw material with the same composition and structural properties as natural rutile.

[0003] The acid method (hydrochloric acid or sulfuric acid) production process of titanium dioxide is to obtain artificial rutile after oxidation, reduction, acid leaching, filtration, washing and drying of ilmenite. The solution produced by the acid leaching process is rutile mother liquor, the main components of which are ferrous chloride (hydrochloric acid leaching) or ferrous sulfate (sulfuric acid leaching), and contain various impurities such as titanium, chromium, manganese, aluminum, vanadium, etc. Usually, a large amount of high-concentration acid mother liquor will be produced for every ton of artificial rutile produced (7 tons of mother liquor for hydrochloric acid method and 3.5 tons of mother liquor for sulfuric acid method).

[0004] Among the existing commercial secondary batteries, the positive electrode material of lithium-ion batteries is mainly lithium iron phosphate. Lithium iron phosphate batteries have excellent safety performance and can maintain a relatively stable structure even at high temperatures, making lithium iron phosphate batteries safe and reliable. Even when the battery is deformed and damaged, there will be no safety accidents such as smoke and fire. In terms of iron sources, some iron phosphate companies currently mainly produce ferrous sulfate by reacting iron sheets with sulfuric acid, such as Hunan Yacheng. The advantages are high product purity and few by-products, but the cost is high, and the reaction of iron sheets with sulfuric acid produces a large amount of hydrogen, which is more dangerous to operate. Some companies directly purchase ferrous sulfate produced as a by-product of sulfuric acid-based titanium dioxide companies. The advantage is low cost, but it requires a relatively reasonable transportation distance between the titanium dioxide companies and the impurities must be removed before it can be used.

[0005] The hydrochloric acid method of titanium dioxide is also an effective method commonly used by domestic titanium dioxide production enterprises. However, in recent years, with the decline in the grade of titanium dioxide raw materials (titanium concentrate), the manganese content in titanium concentrate is high, resulting in a relatively high content of manganese chloride in the by-product ferrous chloride. The ratio of ferrous chloride to manganese chloride in the rutile mother liquor is close to 4:1, and the mother liquor also contains a small amount of aluminum, calcium, titanium, magnesium and other impurities. The rutile mother liquor, a by-product of the hydrochloric acid method of titanium dioxide, is an iron-containing acidic solution, which is a hazardous waste solution and urgently needs to be recycled by effective methods. In recent years, with the sharp increase in the demand for lithium iron phosphate positive electrode materials, the demand for battery-grade iron phosphate as a raw material for lithium iron phosphate production has also increased significantly. If battery-grade iron phosphate can be prepared using high-manganese rutile mother liquor as a raw material, it can not only alleviate the supply problem of raw materials for lithium iron phosphate production in the energy field, but also solve the environmental treatment problem of the iron-containing acidic hazardous waste solution of the hydrochloric acid method of titanium dioxide, and at the same time improve the technical level of waste liquid resource utilization in my country. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a by-product of hydrochloric acid process titanium dioxide, as a raw material, so as to solve the problem of resource utilization of ferrous chloride, a by-product of hydrochloric acid process titanium dioxide, and at the same time obtain battery-grade ferric phosphate products.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by a hydrochloric acid process, as a raw material, comprising the following steps:

[0009] (1) filtering the ferrous chloride mother liquor, a byproduct of the hydrochloric acid process titanium dioxide, and then adding deionized water to dilute it, heating it for reaction, obtaining a turbid liquid, and continuing to filter it to obtain a yellow-green clear solution, which is the purified ferrous chloride solution;

[0010] (2) adding a precipitant to the purified ferrous chloride solution while stirring, controlling the pH value to 6.5-7.5, continuing to add H2O2 and stirring, and then washing and separating the obtained precipitate with ferric chloride solution, and fully reacting with dilute phosphoric acid to obtain a purple transparent solution;

[0011] (3) The pH value of the purple transparent solution is adjusted to between 1.5 and 2.0 with aqueous ammonia to produce a white precipitate, which is filtered, washed, and dried to obtain a battery-grade iron phosphate product.

[0012] Furthermore, in step (1), the amount of deionized water added satisfies: the dilution factor is 3.

[0013] Furthermore, in step (1), the heating reaction temperature is 115° C. and the time is 1 h.

[0014] Furthermore, in step (2), the precipitating agent is one or more of sodium hydroxide, sodium carbonate or sodium phosphate.

[0015] Furthermore, in step (2), the precipitant is added in the form of a solution with a concentration of 1 to 5 M, and the precipitant, H2O2 and the ferrous chloride in the purified ferrous chloride solution are added in a molar ratio of 1:1.2:1.

[0016] Furthermore, in step (2), the stirring time is 30 min, and the reaction is carried out at room temperature.

[0017] Furthermore, in step (2), the concentration of the ferric chloride solution is 1-2M.

[0018] Furthermore, in step (2), the concentration of the dilute phosphoric acid is 30-35%.

[0019] Furthermore, in step (2), the reaction is fully carried out at room temperature.

[0020] Furthermore, in step (2), when the precipitate is completely dissolved and the solution becomes purple and transparent, the addition of dilute phosphoric acid is stopped.

[0021] Furthermore, in step (3), the concentration of the ammonia water is 25-28%.

[0022] In recent years, due to the low grade of titanium concentrate and the high manganese content in titanium concentrate, the manganese content in the ferrous chloride mother liquor in the by-product of hydrochloric acid titanium dioxide is relatively high, which poses a challenge to the resource utilization of ferrous chloride mother liquor. The high manganese content ferrous chloride mother liquor is different from the low manganese content industrial ferrous chloride or ferrous sulfate. The manganese content (Mn% ≤ 0.02) in battery-grade ferric phosphate is relatively low. Therefore, it is technically difficult to prepare battery-grade ferric phosphate with high manganese content ferrous chloride mother liquor. Divalent iron ions begin to precipitate at pH 6.5, and the divalent iron ions are basically precipitated at pH 7.5; divalent manganese ions begin to precipitate at pH 7.8, and most of the divalent manganese ions can be precipitated at pH 8.8, and are basically precipitated at pH 10.4. Since the pH values ​​of divalent iron ions and divalent manganese ions are relatively close, it is necessary to strictly control the pH value of the solution to avoid the precipitation of divalent manganese ions while preventing the precipitation of divalent iron ions. Since a small amount of divalent manganese will also precipitate during the precipitation of divalent iron, the small amount of divalent manganese precipitate precipitated here can be washed and removed with a 1.0-2.0M ferric chloride solution, thereby effectively improving the quality of battery-grade iron phosphate. The main feature of the present invention is to use ferric chloride solution to remove the divalent manganese precipitate generated during the precipitation process, and there is no related technical report.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) Using high-manganese-content industrial ferrous chloride as raw material, by regulating the reaction conditions and parameters, a high-value-added battery-grade iron phosphate product is prepared, and the prepared battery-grade iron phosphate product has a white appearance;

[0025] (2) Using ferric chloride solution to remove the divalent manganese precipitate remaining in the divalent iron precipitation process. This technical method is simple, effective, and has very low cost. The prepared battery-grade iron phosphate product has high purity and uniform morphology;

[0026] (3) The method of the present invention is applicable to the preparation of battery-grade iron phosphate products from most iron-containing waste liquids, especially the treatment of rutile mother liquor with high manganese content. The iron phosphate preparation technology and manganese removal method used are universal and have the advantages of low equipment requirements, low production cost, low energy consumption and easy large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a process flow chart of the present invention;

[0028] Figure 2 This is an optical photograph of ferrous chloride solution, a byproduct of titanium dioxide produced by the hydrochloric acid process;

[0029] Figure 3 This is an optical photograph of the battery-grade iron phosphate product prepared in the present invention. DETAILED DESCRIPTION

[0030] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0031] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercial products or conventional processing techniques in the art.

[0032] like Figure 1 As shown, the present invention provides a preparation process flow chart for preparing battery-grade ferric phosphate from ferrous chloride solution, a byproduct of titanium dioxide produced by the hydrochloric acid process. The method of the present invention uses ferrous chloride solution, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material. First, the tiny particle impurities in the ferrous chloride mother liquor are removed by filtering, and then the ferrous chloride mother liquor is diluted with deionized water. The ferrous chloride mother liquor is then heated and filtered to obtain a purified ferrous chloride solution. A precipitant is added to the purified ferrous chloride solution, and hydrogen peroxide is added for oxidation treatment. The precipitate is then washed once with the ferric chloride solution and then reacted with dilute phosphoric acid. The pH value of the solution is then adjusted with ammonia water, and the obtained white product is filtered, washed and dried to finally obtain a battery-grade FePO4 product.

[0033] The present invention will be described in more detail below in conjunction with more specific embodiments.

[0034] Embodiment 1:

[0035] Optical photo of ferrous chloride mother liquor (i.e. rutile mother liquor), a byproduct of hydrochloric acid process titanium dioxide Figure 2 The solution composition analysis is shown in Table 1. As can be seen from Table 1, the Fe content in the solution is 78428.396 mg / L, while the Mn element reaches 19504.159 mg / L, and the ratio of Fe to Mn in the ferrous chloride mother liquor is about 4:1, indicating that the ferrous chloride mother liquor, a by-product of hydrochloric acid titanium dioxide, is an acid leaching solution with a high manganese content.

[0036] In this embodiment, 100 mL of ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, is measured, two layers of filter paper are added to a Buchner funnel, and then 100 mL of ferrous chloride mother liquor is poured into the Buchner funnel. After suction filtration, the tiny particle impurities in the ferrous chloride mother liquor are intercepted, and then the filtered ferrous chloride mother liquor is diluted 3 times, and then the solution is placed in a glass beaker, heated to 115° C. in an oil bath, and stirred with magnetic stirring for 1 hour. The turbid liquid obtained after the ferrous chloride mother liquor is heat-treated at 115° C. for 1 hour is filtered through a Buchner funnel to obtain a yellow-green clear solution, which is the purified ferrous chloride solution.

[0037] Prepare a 1.0M NaOH solution, slowly add the NaOH solution to the purified ferrous chloride solution, continue stirring, and control the pH value of the solution at 6.5. The resulting precipitate is ferrous hydroxide. Add excess H2O2 to the precipitate solution, stir for 30 minutes, and then wash the precipitate once with a 1.0M ferric chloride solution. Then react the precipitate with an excess of 30% dilute phosphoric acid and stir thoroughly. After the reaction is sufficient, the precipitate is completely dissolved, stop adding dilute phosphoric acid, and obtain a purple transparent solution. Then adjust the pH value of the solution to 1.5 with 25% ammonia water. At this time, a large amount of white precipitate is produced in the solution. After filtering, washing and drying the white precipitate, a battery-grade iron phosphate FePO4 product ( Figure 3 ).

[0038] The ICP analysis of the above-synthesized battery-grade iron phosphate FePO4 product is shown in Table 2. As can be seen from Table 2, the manganese content in the iron phosphate FePO4 product is relatively low (Mn% = 0.0025), which is less than the manganese content required in battery-grade iron phosphate (Mn% ≤ 0.02), and the contents of other impurity elements are also within the standard range of battery-grade iron phosphate. Therefore, the battery-grade iron phosphate prepared by the present invention using the ferrous chloride mother liquor, a byproduct of the hydrochloric acid process titanium dioxide, has a high quality and has important application prospects in the field of treating ferrous chloride, a byproduct of the acid process titanium dioxide with high manganese content.

[0039] Comparative Example 1:

[0040] Measure 100mL of ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, and after filtering through a Buchner funnel (2 layers of filter paper), dilute the ferrous chloride mother liquor by 3 times, then heat and stir in a 115°C oil bath for 1h, then filter through a Buchner funnel, and then adjust the pH value to 6.5 with a 1.0M NaOH solution. Add excessive H2O2 to the resulting precipitate, and after stirring for 30min, the precipitate is not washed with ferric chloride solution, and the precipitate is directly reacted with excessive 30% dilute phosphoric acid. When the precipitate is completely dissolved, stop adding dilute phosphoric acid to obtain a purple transparent solution, and then adjust the solution pH value to 1.5 with ammonia water with a concentration of 25%. At this time, a large amount of white precipitate is produced in the solution. After filtering, washing and drying, the white precipitate obtains an iron phosphate FePO4 product, and the ICP analysis results of the product are shown in Table 3. As can be seen from Table 3, the iron and phosphorus contents are not greatly affected, but the impurity contents are increased, especially manganese, whose content reaches 0.1028 (Mn%), indicating that the present invention is very effective in removing impurities by washing the precipitate with ferric chloride solution.

[0041] Comparative Example 2:

[0042] Measure 100mL of ferrous chloride mother liquor, a byproduct of hydrochloric acid titanium dioxide, and after filtering through a Buchner funnel (2 layers of filter paper), dilute the ferrous chloride mother liquor 3 times, then heat and stir in a 115°C oil bath for 1h, then filter through a Buchner funnel, and then adjust the pH value to 8.0 with a 1.0M NaOH solution. Add excessive H2O2 to the resulting precipitate, stir for 30min, and wash the resulting precipitate once with a ferric chloride solution, then filter and react the precipitate with excessive 30% dilute phosphoric acid, wait for the precipitate to completely dissolve, stop adding dilute phosphoric acid, obtain a purple transparent solution, and then adjust the solution pH to 1.5 with a 25% ammonia solution. At this time, a large amount of white precipitate is produced in the solution. After filtering, washing and drying, the white precipitate obtains an iron phosphate FePO4 product, and the ICP analysis results of the product are shown in Table 4. It can be seen from Table 4 that when the reaction pH is adjusted to 8.0, the manganese content in the prepared ferric phosphate product is 0.0476 (wt%), which is higher than the manganese content of battery-grade ferrous phosphate of 0.02 (Mn% ≤ 0.02, wt%). Therefore, it is important to control the pH value between 6.5 and 7.5 during the reaction.

[0043] Embodiment 2:

[0044] 100mL of ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, was measured and filtered through a Buchner funnel (2 layers of filter paper), and the ferrous chloride mother liquor was diluted 3 times, and then heated and stirred in a 115°C oil bath for 1h, and then filtered through a Buchner funnel, and then the pH value was adjusted to 7.5 with a 1.0M NaOH solution, and the resulting precipitate was added with excess H2O2, stirred for 30min, and the resulting precipitate was washed once with a ferric chloride solution, and then filtered and the precipitate was reacted with an excess of 30% dilute phosphoric acid, and when the precipitate was completely dissolved, the addition of dilute phosphoric acid was stopped to obtain a purple transparent solution, and then the pH value of the solution was adjusted to 1.5 with ammonia water with a concentration of 25%. At this time, a large amount of white precipitate was produced in the solution. After filtering, washing and drying the white precipitate, an iron phosphate FePO4 product was obtained, and the ICP analysis results of the product are shown in Table 5. As can be seen from Table 5, the impurity content in the prepared iron phosphate product is relatively low, and the manganese content is 0.0021 (wt%), which meets the requirements of battery-grade iron phosphate.

[0045] Embodiment 3:

[0046] 100mL of ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, was measured and filtered through a Buchner funnel (2 layers of filter paper), and the ferrous chloride mother liquor was diluted 3 times, and then heated and stirred in a 115°C oil bath for 1h, and then filtered through a Buchner funnel, and then the pH value was adjusted to 7.5 with a 1.0M NaOH solution, and the resulting precipitate was added with excess H2O2, stirred for 30min, and the resulting precipitate was washed once with a ferric chloride solution, and then filtered and the precipitate was reacted with an excess of 30% dilute phosphoric acid, and when the precipitate was completely dissolved, the addition of dilute phosphoric acid was stopped to obtain a purple transparent solution, and then the pH value of the solution was adjusted to 2.0 with ammonia water with a concentration of 25%. At this time, a large amount of white precipitate was produced in the solution. After filtering, washing and drying, the white precipitate was obtained to obtain an iron phosphate FePO4 product, and the ICP analysis results of the product are shown in Table 6. As can be seen from Table 6, the impurity content in the prepared iron phosphate product is relatively low, and the manganese content is 0.0032 (wt%), which meets the requirements of battery-grade iron phosphate.

[0047] Table 1

[0048]

[0049] Table 2

[0050]

[0051]

[0052] Table 3

[0053]

[0054] Table 4

[0055]

[0056] Table 5

[0057]

[0058] Table 6

[0059]

[0060]

[0061] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material, characterized in that: The following steps are involved: (1) Filter the ferrous chloride mother liquor, a by-product of the hydrochloric acid process titanium dioxide, and then add deionized water to dilute it. Heat the reaction to obtain a turbid liquid, and continue filtering to obtain a yellow-green clear solution, which is the purified ferrous chloride solution; (2) Add a precipitant to the purified ferrous chloride solution while stirring, control the pH value to 6.5-7.5, then add H2O2 and stir. The resulting precipitate is then washed and separated with a ferric chloride solution and fully reacted with dilute phosphoric acid to obtain a purple transparent solution. (3) The purple transparent solution is adjusted to a pH value between 1.5 and 2.0 with aqueous ammonia to produce a white precipitate, which is then filtered, washed, and dried to obtain a battery-grade iron phosphate product; In step (2), the concentration of the ferric chloride solution is 1-2M.

2. The method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material according to claim 1, characterized in that: In step (1), the amount of deionized water added satisfies: the dilution factor is 3; The heating reaction temperature was 115°C and the time was 1 h.

3. The method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material according to claim 1, characterized in that: In step (2), the precipitating agent is one or more of sodium hydroxide, sodium carbonate or sodium phosphate.

4. The method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material according to claim 1, characterized in that: In step (2), the precipitant is added in the form of a solution with a concentration of 1 to 5 M. The precipitant, H2O2 and the ferrous chloride in the purified ferrous chloride solution are added in a molar ratio of 1:1.2:

1.

5. The method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material according to claim 1, characterized in that: In step (2), the stirring time is 30 min and the temperature is room temperature.

6. The method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material according to claim 1, characterized in that: In step (2), the concentration of the dilute phosphoric acid is 30-35%.

7. The method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material according to claim 1, characterized in that: In step (2), the temperature for sufficient reaction is room temperature.

8. The method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material according to claim 1, characterized in that: In step (2), the amount of dilute phosphoric acid added is such that when the precipitate is completely dissolved and the solution becomes purple and transparent, the addition of dilute phosphoric acid is stopped.

9. The method for preparing battery-grade ferric phosphate using ferrous chloride mother liquor, a byproduct of titanium dioxide produced by the hydrochloric acid process, as a raw material according to claim 1, characterized in that: In step (3), the concentration of the ammonia water is 25-28%.

Images