Method for preparing manganese sulfate from low-grade pyrolusite based on sulfite circulation

Abstract

The invention provides a method for preparing manganese sulfate from low-grade pyrolusite based on sulfite circulation, a manganese-based material is prepared through the difference of the solubility of sulfite by utilizing the characteristic that the solubility of manganese sulfite is far smaller than that of calcium sulfite and magnesium sulfite, and manganese sulfate widely applied to the battery positive electrode industry is obtained. The by-product sulfur dioxide is used as a reducing agent to leach pyrolusite, the leaching cost is reduced, compared with a pyrite leaching method, the slag yield is reduced, recyclable ammonium sulfite is used as an intermediate manganese precipitation impurity removal agent, compared with an existing high-purity manganese sulfate preparation technology, the method is more efficient, the reagent cost is reduced, the quality of the prepared manganese sulfate is kept at the high-purity level, and the method is suitable for industrial production. The calcium and magnesium impurity removal effect is good, materials are simple, cost is low, recycling of main substances can be achieved, and environment friendliness is achieved.

Description

Technical Field

[0001] This application belongs to the field of manganese sulfate preparation, and specifically relates to a method for preparing manganese sulfate from low-grade pyrolusite based on the sulfite cycle. Background Art

[0002] Manganese sulfate is an important chemical raw material, widely used in new energy materials, metallurgy, fertilizers, feed additives and other fields. With the rapid development of the new energy field in recent years, the demand for manganese sulfate in electrode materials such as lithium manganate, lithium nickel manganate, and lithium iron manganese phosphate has gradually increased, and at the same time, the quality requirements for manganese sulfate have become higher and higher. The process for removing heavy metals in manganese sulfate is relatively mature, but the properties of divalent calcium and magnesium are similar to those of divalent manganese, so it is difficult to completely remove. The commonly used processes for removing calcium and magnesium in industrial-grade manganese sulfate mainly include evaporation crystallization method, ion exchange method, chemical precipitation method, etc. However, these methods have problems such as low removal rate of calcium and magnesium content, high cost, and complex process. Therefore, in the face of the bottleneck problem of high-purity manganese sulfate production, there is an urgent need to develop a new process for removing calcium and magnesium that is efficient, environmentally friendly and low-cost. Summary of the Invention

[0003] This application provides a method for preparing manganese sulfate from low-grade pyrolusite based on the sulfite cycle, aiming to solve the problem of low removal rate of calcium and magnesium content in industrial-grade manganese sulfate to a certain extent.

[0004] In the first aspect, this application provides a method for preparing manganese sulfate from low-grade pyrolusite based on the sulfite cycle, including the following steps:

[0005] S1. Mix pyrolusite with water to form a pyrolusite slurry, heat it up, stir and react, and then introduce SO 2 flue gas;

[0006] S2. Filter the pyrolusite slurry obtained in S1, and obtain a manganese sulfate mother liquor after preliminary impurity removal;

[0007] S3. Add an ammonium sulfite solution to the manganese sulfate mother liquor, react, and obtain a manganese sulfite filter residue and an ammonium sulfate filtrate after pressure filtration;

[0008] S4. Vacuum dry the manganese sulfite filter residue to obtain manganese sulfite;

[0009] S5. Mix the manganese sulfite with a dilute sulfuric acid solution, place it in a reaction kettle and heat it to react to obtain a manganese sulfate solution, evaporate and crystallize, filter and dry to obtain manganese sulfate, and the SO 2 flue gas generated by the reaction is blown into the mixed slurry in S1.

[0010] This solution utilizes the characteristic that the solubility of manganese sulfite is much smaller than that of calcium sulfite and magnesium sulfite, and prepares a manganese-based material through the difference in the solubility of sulfites, and obtains manganese sulfate widely used in the battery cathode industry.

[0011] In the present invention, the chemical reaction involved in step S1 is as follows:

[0012] SO 2 +H 2 O==H 2 SO 3

[0013] MnO 2 +H 2 SO 3 ==MnSO 4 +H 2 O

[0014] The chemical reaction involved in step S3 is as follows:

[0015] Mn SO 4 +(NH 4 ) 2 SO 3 ==MnSO 3 +(NH 4 ) 2 SO 4

[0016] 3(NH 4 ) 2 SO 4 ==2(NH 4 ) 2 SO 3 +2SO 2 +6H 2 O+N 2

[0017] The chemical reaction involved in step S5 is as follows:

[0018] MnSO 3 +H 2 SO 4 ==Mn SO 4 +SO 2 +H 2 O

[0019] In some embodiments, the liquid-solid ratio of the pyrolusite slurry in step S1 is 3-6:1, and the conditions of the reaction are: rotation speed 300-400 r / min, temperature 40-60 °C, reaction time 90-120 min, and the molar ratio of the manganese content in the pyrolusite to the SO 2 flue gas input amount is 1:1.0-1.5.

[0020] In some embodiments, the conditions for preliminary impurity removal in step S2 are as follows: using a mixture of calcium carbonate and sodium dimethyldithiocarbamate as the impurity remover, under stirring conditions, with a rotation speed of 300 - 350 r / min, an impurity removal temperature of 70 - 80 °C, the mass ratio of calcium carbonate to pyrolusite being 0.1 - 0.3:1, and the mass ratio of sodium dimethyldithiocarbamate to pyrolusite being 0.006 - 0.01:1.

[0021] In some embodiments, in step S3, the concentration of the ammonium sulfite solution is 10 wt% - 50 wt%, the molar ratio of manganese sulfate to ammonium sulfite in the manganese sulfate mother liquor is 1:1.0 - 1.5, and the reaction conditions are: a rotation speed of 200 - 500 r / min, a temperature of 20 - 80 °C, and a time of 1 - 1.5 h.

[0022] In some embodiments, after evaporation crystallization and roasting of the ammonium sulfate filtrate in step S3, it is absorbed by water to obtain an ammonium sulfite solution, which is returned to S3 for reuse. The roasting temperature is 400 - 600 °C, and the amount of water used for the absorbing liquid is 5 - 10 times the mass of ammonium sulfate.

[0023] In some embodiments, the conditions for vacuum drying in step S4 are: a temperature of 90 - 120 °C and a drying time of 4 - 10 h.

[0024] In some embodiments, in step S5, the concentration of the dilute sulfuric acid solution is 0.5 - 2.0 mol / L, the molar ratio of ammonium sulfite to sulfuric acid is 1:1.0 - 1.5, the heating temperature in the reaction kettle is 80 - 100 °C, and the heating time is 30 - 90 min.

[0025] In some embodiments, in step S5, the evaporation crystallization is at 100 - 250 °C, the drying temperature is 100 - 120 °C, and the drying time is 4 - 10 h.

[0026] Compared with the prior art, the beneficial effects of the present application are as follows:

[0027] 1. The present invention uses the by - product sulfur dioxide as a reducing agent to leach pyrolusite, reducing the leaching cost and reducing the slag output compared with the pyrite leaching method.

[0028] 2. The present invention uses recyclable ammonium sulfite as an intermediate manganese - precipitation impurity remover, which is more efficient than the existing high - purity manganese sulfate preparation technology and reduces the reagent cost.

[0029] 3. The manganese sulfate prepared by the present invention maintains a high - purity level, has good calcium and magnesium impurity removal effects, simple raw materials, low cost, can realize the recycling of main substances, and is environmentally friendly. Description of the Drawings

[0030] To more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 is the process flow diagram for preparing high-purity manganese sulfate in the present invention. Detailed implementation manners

[0032] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application more clearly understood, the following further details the present application in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0033] In the present application, the term "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Among them, A and B can be singular or plural. The character " / " generally represents an "or" relationship between the front and rear associated objects.

[0034] In the present application, "at least one" means one or more, and "a plurality" means two or more. "At least one (item)" or its similar expression refers to any combination of these items, including any combination of single item (item) or plural items (items). For example, "at least one (item) of a, b, or c", or, "at least one (item) of a, b, and c" can both represent: a, b, c, a~b (that is, a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple respectively.

[0035] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of the present application, the first XX can also be called the second XX. Similarly, the second XX can also be called the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features.

[0036] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms of "a", "the", and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0037] It should be understood that in various embodiments of the present application, the magnitude of the serial numbers of the various processes does not imply the order of execution, and some or all of the steps may be executed in parallel or sequentially. The execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application regulations.

[0038] The weights of the relevant components mentioned in the specification of the embodiments of the present application not only can refer to the specific contents of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the contents of the relevant components in the specification of the embodiments of the present application are enlarged or reduced in proportion, they are within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass described in the specification of the embodiments of the present application can be mass units well-known in the chemical industry such as μg, mg, g, kg, etc.

[0039] Unless otherwise defined, all the technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0040] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present application can be obtained through market purchases or can be prepared by existing methods.

[0041] The technical solutions of the present application will be described below through specific examples and comparative examples.

[0042] To enable those skilled in the art to clearly understand the above implementation details and operations of the present application, and to significantly reflect the advanced performance of the embodiments of the present application, the above technical solutions will be illustrated by multiple examples below.

[0043] Example 1:

[0044] A method for preparing manganese sulfate from low-grade pyrolusite based on the sulfite cycle:

[0045] Using rhodochrosite from a manganese ore producing area in Hunan as raw material, its main components are shown in Table 1.

[0046] S1. Take 10 kg of pyrolusite, add 50 L of water, heat up to 40 °C, rotate at 300 r / min, and the sulfur dioxide input amount is 10 L / min, and the reaction time is 90 min.

[0047] Table 1 Chemical composition of pyrolusite

[0048] Element Mn Ca Mg Fe K Zn Content 21.15 0.87 0.64 7.42 0.49 0.08

[0049] S2. After the leaching is completed, perform solid-liquid separation operation to obtain manganese sulfate solution. Add 1 kg of calcium carbonate powder and 100 g of sodium dimethyldithiocarbamate to the manganese sulfate solution, react for 2 h, keep the stirring speed at 300 r / min and the temperature at 60 °C during the impurity removal process. After the slurry is cooled, filter it under pressure to obtain 42 L of manganese sulfate mother liquor. Its main components are shown in Table 2, and the manganese leaching rate is 90.6%.

[0050] Table 2 Main components of manganese sulfate mother liquor in Example 1

[0051] Element <![CDATA[MnSO 4 > <![CDATA[Ca 2+ > <![CDATA[Mg 2+ > <![CDATA[Fe 3+ / 2+ > <![CDATA[K + > <![CDATA[Zn 2+ > Content 12.5％ 0.05％ 0.12％ 0.004％ 0.008％ 0.002％

[0052] S3. Configure an ammonium sulfite solution with a concentration of 10% according to the molar ratio of ammonium sulfite to manganese sulfate being 1.1:1. Input the ammonium sulfite solution into the manganese sulfate solution, and at the same time, react at 20 °C with a stirring rate of 200 r / min for 1 h. After the reaction, filter to obtain filter residue and filtrate. The filtrate is evaporated and crystallized and then calcined at 450 °C, and the water absorption obtains ammonium sulfite solution for recycling in S3;

[0053] S4. Vacuum dry the filter residue at 100 °C for 4 h to obtain high-purity manganese sulfite;

[0054] S5. Then dissolve the high-purity manganese sulfite in 0.5 mol / L dilute sulfuric acid, heat it in a water bath at 80 °C for 1 h to obtain high-purity manganese sulfate solution, and collect the generated gas for recycling in S1; Evaporate and crystallize the high-purity manganese sulfate at 200 °C, filter to obtain filter residue and filtrate, and dry the filter residue at 100 °C for 4 h to obtain high-purity manganese sulfate with very low impurity content. The element content of the obtained product is shown in Table 3.

[0055] Table 3 Index parameters of high-purity manganese sulfate product

[0056] Element Mn <![CDATA[Ca 2+ > <![CDATA[Mg 2+ > <![CDATA[Fe 3+ / 2+ > <![CDATA[K + > <![CDATA[Zn 2+ > Content 32.13％ 0.0057％ 0.0034％ 0.002％ 0.006％ 0.002％

[0057] Example 2:

[0058] A method for preparing manganese sulfate from low-grade pyrolusite based on sulfite cycle:

[0059] The difference between this example and Example 1 is that: the leaching reducing agent sulfur dioxide and the precipitation impurity removal agent ammonium sulfite are mainly obtained from the recycling in Example 1.

[0060] S1. Use the same pyrolusite raw material as in Example 1. Take 10 Kg of pyrolusite, add 50 L of water, heat up to 40 °C, rotate at 300 r / min, and the sulfur dioxide input amount is 10 L / min. Use the by-product in Example 1 and make up the insufficient part externally. The reaction time is 90 min.

[0061] S2. After the leaching is completed, solid-liquid separation operation is carried out to obtain manganese sulfate solution. 1 kg of calcium carbonate powder and 100 g of sodium dimethyldithiocarbamate are added into the manganese sulfate solution, and the reaction is carried out for 2 h. During the impurity removal process, the stirring speed is maintained at 300 r / min and the temperature is 60 °C. After the slurry is cooled, it is pressure-filtered to obtain 43 L of manganese sulfate mother liquor. The main components are shown in Table 4, and the manganese leaching rate is 89.7%.

[0062] Table 4 Main components of manganese sulfate mother liquor in Example 2

[0063] Element <![CDATA[MnSO 4 > <![CDATA[Ca 2+ > <![CDATA[Mg 2+ > <![CDATA[Fe 3+ / 2+ > <![CDATA[K + > <![CDATA[Zn 2+ > Content 12.1％ 0.05％ 0.11％ 0.004％ 0.007％ 0.002％

[0064] S3. According to the molar ratio of ammonium sulfite to manganese sulfate being 1.1∶1, an ammonium sulfite solution with a concentration of 10% is prepared. The ammonium sulfite used is the product ammonium sulfite of Example 1, and the insufficient part is supplemented externally. The ammonium sulfite solution is input into the manganese sulfate solution, and at the same time, at 20 °C, the reaction is carried out for 1 h at a stirring rate of 200 r / min. After the reaction is completed, filtration is carried out to obtain filter residue and filtrate;

[0065] S4. The filter residue is vacuum dried at 100 °C for 4 h to obtain high-purity manganese sulfite;

[0066] S5. The high-purity manganese sulfite is dissolved in 0.5 mol / L dilute sulfuric acid, and water bath heating is carried out at 80 °C for 1 h to obtain high-purity manganese sulfate solution, and the generated gas is collected; the high-purity manganese sulfate is subjected to evaporation crystallization at 200 °C, and after filtration, filter residue and filtrate are obtained. The filter residue is dried at 100 °C for 4 h to obtain high-purity manganese sulfate. The element content of the obtained product is shown in Table 5.

[0067] Table 5 Index parameters of high-purity manganese sulfate product in Example 2

[0068] Element Mn <![CDATA[Ca 2+ > <![CDATA[Mg 2+ > <![CDATA[Fe 3+ / 2+ > <![CDATA[K + > <![CDATA[Zn 2+ > Content 32.04％ 0.0046％ 0.0042％ 0.003％ 0.006％ 0.002％

[0069] Example 3:

[0070] A method for preparing manganese sulfate from low-grade pyrolusite based on the sulfite cycle:

[0071] The difference between this example and Example 1 is that the molar ratio of ammonium sulfite to manganese sulfate is adjusted to 1.2

[0072] The method steps are as follows:

[0073] S1. Using the same pyrolusite raw material as in Example 1, 10 Kg of pyrolusite is taken, 50 L of water is added, the temperature is raised to 40 °C, the rotation speed is 300 r / min, the sulfur dioxide input amount is 10 L / min, and the reaction time is 90 min.

[0074] S2. After the leaching is completed, perform solid-liquid separation operation to obtain a manganese sulfate solution. Add 1 kg of calcium carbonate powder and 100 g of sodium dimethyldithiocarbamate to the manganese sulfate solution, react for 2 h, maintain the stirring speed at 300 r / min and the temperature at 60 °C during the impurity removal process, filter under pressure after the slurry is cooled, and obtain 44 L of manganese sulfate mother liquor. Its main components are shown in Table 6, and the manganese leaching rate is 89.3%.

[0075] Table 6 Main components of the manganese sulfate mother liquor in Example 3

[0076] Element <![CDATA[MnSO 4 > <![CDATA[Ca 2+ > <![CDATA[Mg 2+ > <![CDATA[Fe 3+ / 2+ > <![CDATA[K + > <![CDATA[Zn 2+ > Content 11.8％ 0.04％ 0.11％ 0.003％ 0.006％ 0.002％

[0077] S3. Prepare an ammonium sulfite solution with a concentration of 10% according to the molar ratio of ammonium sulfite to manganese sulfate being 1.2:1, input the ammonium sulfite solution into the manganese sulfate solution, and at the same time react at 20 °C with a stirring rate of 200 r / min for 1 h. After the reaction is completed, filter to obtain filter residue and filtrate;

[0078] S4. Vacuum dry the filter residue at 100 °C for 4 h to obtain high-purity manganese sulfite;

[0079] S5. Dissolve the high-purity manganese sulfite in 0.5 mol / L dilute sulfuric acid, heat it in a water bath at 80 °C for 1 h to obtain a high-purity manganese sulfate solution, and collect the generated gas; evaporate and crystallize the high-purity manganese sulfate at 200 °C, filter to obtain filter residue and filtrate, and dry the filter residue at 100 °C for 4 h to obtain high-purity manganese sulfate. The element content of the obtained product is shown in Table 7.

[0080] Table 7 Index parameters of the high-purity manganese sulfate product

[0081] Element Mn <![CDATA[Ca 2+ > <![CDATA[Mg 2+ > <![CDATA[Fe 3+ / 2+ > <![CDATA[K + > <![CDATA[Zn 2+ > Content 31.96％ 0.0076％ 0.0063％ 0.003％ 0.007％ 0.002％

[0082] In summary, from the results obtained through the examples, it can be seen that the reuse of by-products does not affect the product purity, and high-purity manganese sulfate can also be prepared by changing some experimental conditions within the parameter range.

[0083] Comparative example:

[0084] A method for preparing manganese sulfate from low-grade pyrolusite based on the sulfite cycle:

[0085] Different from the example: The product manganese sulfate is prepared by evaporating and crystallizing the manganese sulfate mother liquor

[0086] (1) Soft manganese ore leaching process

[0087] Using rhodochrosite from a manganese ore producing area in Hunan as raw material, its main components are shown in Table 1. Take 10 Kg of soft manganese ore, add 50 L of water, heat up to 40 °C, the rotation speed is 300 r / min, the sulfur dioxide input amount is 10 L / min, and the reaction time is 90 min.

[0088] After the leaching is completed, solid-liquid separation is carried out to obtain a manganese sulfate solution. 1 kg of calcium carbonate powder and 100 g of sodium dimethyldithiocarbamate are added to the manganese sulfate solution, and the reaction is carried out for 2 h. During the impurity removal process, the stirring speed is maintained at 300 r / min and the temperature is 60 °C. After the slurry is cooled, it is pressure-filtered to obtain 41 L of manganese sulfate mother liquor. The main components are shown in Table 8, and the manganese leaching rate is 90.1%.

[0089] Table 8 Main components of manganese sulfate mother liquor

[0090] Element <![CDATA[MnSO 4 > <![CDATA[Ca 2+ > <![CDATA[Mg 2+ > <![CDATA[Fe 3+ / 2+ > <![CDATA[K + > <![CDATA[Zn 2+ > Content 12.8％ 0.06％ 0.17％ 0.004％ 0.009％ 0.002％

[0091] (2) Preparation of manganese sulfate

[0092] The 41 L of manganese sulfate mother liquor is directly subjected to evaporation crystallization at 120 °C, and after filtration and drying, manganese sulfate powder is obtained.

[0093] Table 9 Index parameters of manganese sulfate product

[0094] Element Mn <![CDATA[Ca 2+ > <![CDATA[Mg 2+ > <![CDATA[Fe 3+ / 2+ > <![CDATA[K + > <![CDATA[Zn 2+ > Content 30.03％ 0.20％ 0.12％ 0.020％ 0.031％ 0.014％

[0095] By comparison, it can be seen that the present invention uses manganese sulfite as an intermediate product, and the prepared manganese sulfate has lower impurity content.

[0096] In the above embodiments, the descriptions of each embodiment have their own emphases. For the parts not detailed or recorded in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0097] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of each embodiment of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for preparing manganese sulfate from low-grade pyrolusite based on sulfite circulation, characterized in that: The following steps are involved: S1, mixing pyrolusite with water to form pyrolusite slurry, heating, stirring and reacting, and then introducing SO2 flue gas; S2, filtering the pyrolusite slurry obtained in S1, and obtaining manganese sulfate mother liquor after preliminary impurity removal; S3, adding ammonium sulfite solution to the manganese sulfate mother liquor, reacting, and obtaining manganese sulfite filter residue and ammonium sulfate filtrate after filter pressing; S4, vacuum drying the manganese sulfite filter residue to obtain manganese sulfite; S5, mixing the manganese sulfite with a dilute sulfuric acid solution, placing the mixture in a reactor and heating the mixture to obtain a manganese sulfate solution, evaporating and crystallizing the mixture, filtering and drying the mixture to obtain manganese sulfate, and blowing the SO2 flue gas generated by the reaction into the mixed slurry in S1.

2. The method according to claim 1, characterized in that The liquid-to-solid ratio of the pyrolusite slurry in step S1 is 3-6:1, the reaction conditions are: rotation speed 300-400r / min, temperature 40-60°C, reaction time 90-120min, and the molar ratio of manganese content in pyrolusite to SO2 flue gas introduction amount is 1:1.0-1.

5.

3. The method according to claim 1, characterized in that The conditions for preliminary impurity removal in step S2 are: using a mixture of calcium carbonate and sodium furam as an impurity remover, carrying out under stirring conditions, a rotation speed of 300-350 r / min, an impurity removal temperature of 70-80° C., a mass ratio of the calcium carbonate to pyrolusite of 0.1-0.3:1, and a mass ratio of the sodium furam to pyrolusite of 0.006-0.01:

1.

4. The method according to claim 1, characterized in that: The concentration of the ammonium sulfite solution in step S3 is 10wt% to 50wt%, the molar ratio of manganese sulfate to ammonium sulfite in the manganese sulfate mother liquor is 1:1.0 to 1.5, and the reaction conditions are: rotation speed of 200 to 500 r / min, temperature of 20 to 80°C, and time of 1 to 1.5h.

5. The method according to claim 1, characterized in that: In step S3, the ammonium sulfate filtrate is evaporated and crystallized, then roasted and absorbed by water to obtain an ammonium sulfite solution which is returned to S3 for repeated use. The roasting temperature is 400-600° C., and the amount of the absorption liquid water is 5-10 times the mass of the ammonium sulfate.

6. The method according to claim 1, characterized in that The vacuum drying conditions in step S4 are: temperature of 90-120° C., and drying time of 4-10 hours.

7. The method according to claim 1, characterized in that The concentration of the dilute sulfuric acid solution in step S5 is 0.5-2.0 mol / L, the molar ratio of ammonium sulfite to sulfuric acid is 1:1.0-1.5, the heating temperature in the reactor is 80-100° C., and the heating time is 30-90 min.

8. The method according to claim 1, characterized in that In step S5, the evaporation crystallization is at 100-250° C., the drying temperature is 100-120° C., and the drying time is 4-10 hours.

Images