Sulfuric acid decolorization method

Abstract

The invention provides a sulfuric acid decoloring method, and belongs to the technical field of chemical separation and purification. The sulfuric acid decolorization method comprises the following steps: heating a colored sulfuric acid stock solution with the mass concentration of more than or equal to 80% to a preheating temperature according to a preset temperature rising speed or according to the preset temperature rising speed and a preset stirring speed, carrying out a heat preservation reaction, sealing, standing, and carrying out solid-liquid separation to obtain colorless and transparent sulfuric acid. According to the method, the micro-environment atmosphere of color developing chemical substances in the sulfuric acid stock solution is changed through heating or heating and stirring, the color developing chemical substances are separated out in a precipitation mode, finally colorless transparent sulfuric acid is obtained, the quality of the sulfuric acid is improved, and market application and economic values are improved; meanwhile, no other additional chemical reagents are added in the treatment process, the raw material purchasing, storing and adding cost is remarkably reduced, better economical efficiency is achieved, the operation process is simplified, the requirement for professional skills of personnel and the manual intervention intensity are reduced, and operation simplicity and wide adaptability of technological conditions are achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical separation and purification technology, and in particular to a method for sulfuric acid decolorization. Background Technology

[0002] Coke oven gas has a complex composition, containing impurities such as water vapor, coal tar gas, ammonia, benzene hydrocarbons, hydrogen sulfide, and other sulfides in addition to the target purified coke oven gas. It requires multiple purification processes, including gas cooling, naphthalene removal, tar removal, desulfurization, ammonia removal, benzene removal, and pressurized transportation, to obtain a qualified product. It is worth noting that sulfuric acid is a high-value-added chemical byproduct recovered during the coke oven gas purification process and has significant economic value. However, during the production process, when this sulfuric acid comes into contact with carbon steel equipment (such as storage tanks, pipelines, and valves), the liquid gradually turns purple or purplish-red. This abnormal discoloration directly leads to the deterioration of sulfuric acid product quality, seriously affecting its market application and economic value, becoming a key pain point for coking enterprises in the recycling and utilization of byproducts. Summary of the Invention

[0003] This invention addresses the issue of low market application and economic value of colored sulfuric acid by providing a sulfuric acid decolorization method. The method alters the microenvironment of the color-producing chemicals in the sulfuric acid stock solution through heating or a combination of heating and stirring, causing them to precipitate and ultimately yield colorless and transparent sulfuric acid. This improves the quality of the sulfuric acid and enhances its market application and economic value. Furthermore, the process requires no additional chemical reagents, significantly reducing raw material procurement, storage, and dosage costs, resulting in better economic efficiency. The simplified operation also reduces the demands on personnel skills and the intensity of manual intervention, achieving ease of operation and broad adaptability to various process conditions.

[0004] The technical solution adopted in this invention is:

[0005] A sulfuric acid decolorization method involves first heating a colored sulfuric acid stock solution with a mass concentration ≥80% to a preheating temperature according to a preset heating rate, maintaining the temperature for reaction, then sealing and allowing it to stand for solid-liquid separation to obtain colorless and transparent sulfuric acid. This technical solution is designed for colored sulfuric acid stock solutions with a mass concentration ≥80%, addressing the decolorization needs of core application scenarios. Through a standardized process of "heating-heating reaction-sealing and standing-solid-liquid separation," it achieves efficient separation of colored impurities from sulfuric acid, ultimately yielding colorless and transparent sulfuric acid. This completely improves the quality degradation problem caused by sulfuric acid discoloration, restoring its market application and economic value. The process involves no complex chemical reagents; decolorization is achieved solely through physicochemical reactions, avoiding the introduction of new impurities that contaminate the sulfuric acid, ensuring product purity, and meeting the quality requirements of high-value-added chemical by-products. The operation steps are simple and easy to understand, requiring no specially customized equipment, facilitating rapid implementation by coking enterprises and other similar businesses, and lowering the technology promotion threshold.

[0006] Furthermore, the preset heating rate is 2℃ / min to 10℃ / min;

[0007] And / or, the preset temperature is 30℃~120℃;

[0008] And / or, the heat preservation reaction time is 5 min to 5 h;

[0009] And / or, the sealed standing time is 1h~72h;

[0010] And / or, the heating method is water bath heating, oil bath heating, forced air drying oven heating, vacuum drying oven heating, steam heat exchange or microwave heating;

[0011] And / or, the solid-liquid separation method is static sedimentation, centrifugation, or filtration. In the further optimized technical solution of this application, the preset heating rate is limited to 2℃ / min~10℃ / min, which ensures heating efficiency while avoiding uneven local reaction of sulfuric acid and incomplete separation of impurities due to excessively rapid heating, thus balancing the decolorization effect and operational efficiency. The preset temperature covers a wide range of 30℃~120℃, which can be flexibly adjusted according to the color depth and impurity content of the sulfuric acid stock solution to meet the treatment needs of colored sulfuric acid with different levels of pollution. The heat preservation reaction time (5min~5h) and the sealed standing time (1h~72h) provide multiple options. The time can be shortened to improve the treatment efficiency for slightly discolored sulfuric acid, while the time can be extended to ensure the decolorization effect for heavily discolored sulfuric acid, thus improving the flexibility of the method. It provides multiple heating methods such as water bath, oil bath, and forced-air drying oven, as well as multiple solid-liquid separation methods such as static sedimentation, centrifugation, and filtration. Enterprises can flexibly select according to their existing equipment conditions without additional large-scale equipment modification, thereby reducing production costs. The wide range of multi-dimensional parameters makes the method highly compatible with the production processes of coking enterprises of different sizes.

[0012] Furthermore, the preset heating rate is 5℃ / min~7℃ / min;

[0013] And / or, the preset temperature is 50℃~90℃;

[0014] And / or, the heat preservation reaction time is 10 min to 3 h;

[0015] And / or, the sealed standing time is 12h~24h;

[0016] And / or, the heating method is oil bath heating or forced-air drying oven heating;

[0017] And / or, the solid-liquid separation method is static sedimentation. In a further optimized technical solution of this application, the optimized heating rate (5℃ / min~7℃ / min) provides the optimal temperature gradient for the decolorization reaction, which can both promote the coagulation and separation of colored impurities (such as iron-based compounds) and avoid the impact of sudden temperature increases on the stability of sulfuric acid, thereby improving decolorization efficiency and effect stability; the preset temperature is focused on 50℃~90℃, which is the optimal temperature range for the separation of colored impurities (especially iron-induced color-changing products), ensuring thorough decolorization while reducing energy consumption (compared to high temperatures above 100℃), and improving process efficiency. The optimized range of heat preservation reaction time (10 min ~ 3 h) and sealed standing time (12 h ~ 24 h) significantly shortens the processing cycle and improves the turnover efficiency of sulfuric acid production while ensuring the decolorization effect, meeting the needs of continuous production in enterprises; oil bath heating or forced-air drying oven heating is preferred, which has stronger heating uniformity and higher temperature control accuracy, avoiding changes in sulfuric acid properties caused by local overheating, and further ensuring product quality; the preferred solid-liquid separation method is static sedimentation, which does not require additional power or centrifuge equipment, resulting in lower operating costs and a gentle separation process.

[0018] Furthermore, the sulfuric acid stock solution exhibits ferrochromic discoloration. The further optimized technical solution of this application specifically targets the ferrochromic sulfuric acid stock solution, precisely identifying the core cause of sulfuric acid discoloration in coking plants and other similar enterprises (iron compounds generated from the contact between sulfuric acid and carbon steel equipment). This targeted approach addresses key pain points, resulting in more targeted and reliable decolorization effects. It avoids redundant process parameters caused by blindly adapting to multiple discoloration types, simplifies the operation process, and allows enterprises to directly set optimal process parameters based on the ferrochromic characteristics, improving processing efficiency and effect stability. The targeted technical design reduces ineffective operations, lowers energy consumption and time costs, and further enhances the economic benefits of by-product recovery in coking plants and other similar enterprises.

[0019] A sulfuric acid decolorization method involves first heating a colored sulfuric acid stock solution with a mass concentration ≥80% to a preheated temperature using a preset heating and stirring speed, maintaining the temperature for reaction, then sealing and allowing it to stand for solid-liquid separation to obtain colorless and transparent sulfuric acid. This technical solution is designed for colored sulfuric acid stock solutions with a mass concentration ≥80%, addressing the decolorization needs of core application scenarios. Through a standardized process of "simultaneous stirring and heating - heat preservation reaction - sealing and standing - solid-liquid separation," it achieves efficient separation of colored impurities from sulfuric acid, ultimately yielding colorless and transparent sulfuric acid. This completely improves the quality degradation problem caused by sulfuric acid discoloration, restoring its market application and economic value. The process involves no complex chemical reagents, achieving decolorization solely through physicochemical processes, avoiding the introduction of new impurities to contaminate the sulfuric acid, ensuring product purity, and meeting the quality requirements of high-value-added chemical by-products. The operation steps are simple and easy to understand, requiring no specially customized equipment, facilitating rapid implementation by coking enterprises and other similar businesses, and lowering the technology promotion threshold.

[0020] Furthermore, the preset heating rate is 2℃ / min to 10℃ / min;

[0021] And / or, the preset stirring speed is 1 rpm to 1200 rpm;

[0022] And / or, the preset temperature is 30℃~120℃;

[0023] And / or, the heat preservation reaction time is 5 min to 5 h;

[0024] And / or, the sealed standing time is 1h~72h;

[0025] And / or, the heating method is water bath heating, oil bath heating, steam heat exchange or microwave heating;

[0026] And / or, the solid-liquid separation method is static sedimentation, centrifugation, or filtration. In the further optimized technical solution of this application, the preset heating rate is limited to 2℃ / min~10℃ / min, and the preset stirring speed is 1rpm~1200rpm. This ensures heating efficiency while avoiding uneven local reaction of sulfuric acid and incomplete impurity separation caused by excessively rapid heating, balancing the decolorization effect and operational efficiency, and combining the two synergistically over a wide range. The preset temperature covers a wide range of 30℃~120℃, which can be flexibly adjusted according to the color depth and impurity content of the sulfuric acid stock solution to meet the treatment needs of colored sulfuric acid with different levels of pollution. The heat preservation reaction time (5min~5h) and sealed static sedimentation... The process offers diverse options in terms of duration (1h~72h). For mildly discolored sulfuric acid, the processing time can be shortened to improve efficiency, while for severely discolored sulfuric acid, the processing time can be extended to ensure decolorization effect, thus enhancing the flexibility of the method. It provides multiple heating methods such as water bath heating, oil bath heating, steam heat exchange, or microwave heating, as well as multiple solid-liquid separation methods such as static sedimentation, centrifugation, and filtration. Enterprises can flexibly select the appropriate method based on their existing equipment conditions without the need for additional large-scale equipment modifications, thereby reducing production costs. The wide range of multi-dimensional parameters ensures strong process compatibility, making it suitable for the production processes of coking enterprises of different sizes.

[0027] Furthermore, the preset heating rate is 5℃ / min~7℃ / min;

[0028] And / or, the preset mixing speed is 1 rpm to 800 rpm;

[0029] And / or, the preset temperature is 50℃~90℃;

[0030] And / or, the heat preservation reaction time is 10 min to 3 h;

[0031] And / or, the sealed standing time is 12h~24h;

[0032] And / or, the heating method is oil bath heating;

[0033] And / or, the solid-liquid separation method is static sedimentation. In a further optimized technical solution of this application, the optimized heating rate (5℃ / min~7℃ / min) and stirring speed (1rpm~800rpm) synergistically provide the optimal temperature gradient for the decolorization reaction. This promotes the coagulation and separation of colored impurities (such as iron compounds) while avoiding the impact of sudden temperature increases on the stability of sulfuric acid, thus improving decolorization efficiency and stability. The preset temperature is focused on 50℃~90℃, which is the optimal temperature range for the separation of colored impurities (especially iron-induced color-changing products). This ensures thorough decolorization while reducing energy consumption (compared to 10...). High temperatures above 0℃ improve process economy; optimized reaction time (10min~3h) and sealed settling time (12h~24h) significantly shorten the processing cycle while ensuring decolorization effect, improve sulfuric acid production turnover efficiency, and meet the needs of continuous production; oil bath heating is preferred, which has stronger heating uniformity and higher temperature control accuracy, avoiding changes in sulfuric acid properties caused by local overheating, and further ensuring product quality; the preferred solid-liquid separation method is static sedimentation, which does not require additional power or centrifuge equipment, has lower operating costs, and the separation process is gentle.

[0034] Furthermore, the sulfuric acid stock solution exhibits ferrochromic discoloration. The further optimized solution in this application specifically targets the ferrochromic sulfuric acid stock solution, precisely identifying the core cause of sulfuric acid discoloration in coking plants and other similar enterprises (iron compounds generated from the contact between sulfuric acid and carbon steel equipment). This targeted approach addresses key pain points, resulting in more targeted and reliable decolorization effects. It avoids redundant process parameters caused by blindly adapting to multiple discoloration types, simplifies the operation process, and allows enterprises to directly set optimal process parameters based on the ferrochromic characteristics, improving processing efficiency and effect stability. The targeted technical design reduces ineffective operations, lowers energy consumption and time costs, and further enhances the economic benefits of by-product recovery in coking plants and other similar enterprises.

[0035] The beneficial effects of this invention are:

[0036] This invention provides a sulfuric acid decolorization method that alters the microenvironment of color-developing chemicals in the sulfuric acid stock solution through heating or heating combined with stirring, causing them to precipitate out as a precipitate, ultimately yielding colorless and transparent sulfuric acid. This improves the quality of sulfuric acid and enhances its market application and economic value. Simultaneously, the process requires no additional chemical reagents, significantly reducing raw material procurement, storage, and addition costs, resulting in better economic efficiency. Furthermore, it simplifies the operation process, reduces the demands on personnel's professional skills and the intensity of manual intervention, achieving ease of operation and broad adaptability to process conditions. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 The appearance of the sulfuric acid stock solution in test groups 1-1# of Example 1 before / during / after treatment.

[0039] Figure 2 The appearance of the sulfuric acid stock solution in test groups 1-3# of Example 1 before / during / after treatment.

[0040] Figure 3 The appearance of the sulfuric acid stock solution in test group 2-1# of Example 2 before / during / after treatment.

[0041] Figure 4 The appearance of the sulfuric acid stock solution in test group 2-2# of Example 2 before / during / after treatment.

[0042] Figure 5 The appearance of the sulfuric acid stock solution in test groups 2-3# of Example 2 before / during / after treatment.

[0043] Figure 6 The appearance of the sulfuric acid stock solution in test groups 2-4# of Example 2 before / during / after treatment.

[0044] Figure 7 The appearance of the sulfuric acid stock solution in test groups 2-5# of Example 2 before / during / after treatment.

[0045] Figure 8 The appearance of the sulfuric acid stock solution in test groups 2-6# of Example 2 before / during / after treatment.

[0046] Figure 9 The appearance of the sulfuric acid stock solution in test groups 2-9# of Example 2 before / during / after treatment.

[0047] It should be noted that the "1h heat preservation reaction", "2h heat preservation reaction", and "24h standing" marked in the figure represent the observation time of the sulfuric acid stock solution during the treatment process. The actual final heat preservation reaction time and sealed standing time shall be based on the final statistics in the table. Detailed Implementation

[0048] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0049] The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, these are merely examples and are not intended to limit the present invention.

[0050] The embodiments of the invention will now be described in detail with reference to the accompanying drawings.

[0051] Example 1

[0052] Weigh 200 mL of sulfuric acid stock solution sample into beakers (determine the mass concentration using the acid-base titration method in GB / T534-2024), then place the beakers in an oil bath and heat to the preset temperature at the preset heating rate, maintaining the temperature for reaction. After the reaction is complete, remove the beakers, seal and allow them to stand (to isolate oxygen and prevent dust), and observe whether stratification occurs. If stratification occurs, take the supernatant to obtain sulfuric acid, and determine the final mass concentration of sulfuric acid using the same method. The experimental parameters and results for each group are shown in Table 1. Among them, the sulfuric acid stock solution used in experimental groups 1-1# to 1-6# was directly obtained from the concentrated sulfuric acid byproduct produced after desulfurization and purification of coke oven gas, while the sulfuric acid stock solution used in experimental groups 1-7# was obtained from the concentrated sulfuric acid byproduct produced after desulfurization and purification of coke oven gas and diluted to 80% with distilled water.

[0053] Table 1. Experimental parameters and results for each group in Example 1.

[0054]

[0055] Figure 1 and Figure 2 The table shows the appearance of the sulfuric acid stock solution in test groups 1-1# and 1-3# of Example 1 before, during, and after treatment. (See Table 1 and...) Figures 1-2 As can be seen, the purple sulfuric acid stock solution is initially purple (due to the presence of iron), then gradually turns into a white suspension after heating, and finally forms distinct layers: the upper layer is a colorless and transparent clear liquid, and the lower layer is a white precipitate (the composition was detected as Fe2(SO4)3).

[0056] The concentration of concentrated sulfuric acid produced from the desulfurization and ammonia removal purification of coke oven gas is generally around 98%. Due to its strong corrosiveness, concentrated sulfuric acid cannot be directly analyzed for complex components. Considering that this concentrated sulfuric acid will come into contact with carbon steel equipment (such as storage tanks, pipelines, valves, etc.) during the production process, storage, or transportation, it is inferred that the purple or purplish-red color of concentrated sulfuric acid indicates the presence of iron. Based on the following literature: "Study on the Color of Ferric Hexahydrate (III) Ions" (Zhang Zuyu, Article No.: 1009-8135(2005)03-0114-02), "Experimental Demonstration of the Purple Color of Ferric Hexahydrate (III)" (Wu Guoying and Zhou Bing, Article No.: 1002-2201(2024)02-0045-02), and "Theoretical Analysis and Experimental Verification of the Light Purple Color of Ferric Hexahydrate Ions" (Bao Zimin and Wang Jun, Chemical Education, 2012, Issue 1), it can be concluded that the purple or purplish-red color of concentrated sulfuric acid indicates the presence of ferric hexahydrate (Fe6+). 3+ The central ion binds to six water molecules via coordinate bonds, forming an octahedral geometry. In this embodiment, precise temperature control alters the Fe... 3+ The aqueous microenvironment utilizes the energy provided by the ambient temperature to attack the coordination bonds, ultimately achieving the removal of ligand water molecules. Furthermore, due to the competitive mechanism, SO42-... 2- with Fe 3+ An amorphous white precipitate is formed, achieving the purpose of removing purple or purplish-red chemical substances from the sulfuric acid solution (i.e., decolorization).

[0057] Example 2

[0058] Weigh 200 mL of sulfuric acid stock solution sample into beakers (determine the mass concentration using the acid-base titration method as described in GB / T534-2024), then place the beakers in an oil bath and heat to the preset temperature simultaneously with stirring at the preset heating and stirring speeds, maintaining the temperature for the reaction. After the reaction is complete, remove the beakers, seal them, and allow them to stand to observe whether they separate into layers. If separation occurs, take the supernatant to obtain sulfuric acid, and determine the final mass concentration of sulfuric acid using the same method; if no separation occurs, determine the mass concentration of sulfuric acid using the same method. The experimental parameters and results for each group are shown in Table 2. Among them, the sulfuric acid stock solution used in experimental groups 2-1# to 2-9# was obtained from concentrated sulfuric acid byproducts produced after desulfurization and purification of coke oven gas, and then diluted with distilled water (simulating samples where the concentration gradually increases at different stages during the sulfuric acid generation process).

[0059] Table 2. Experimental parameters and results for each group in Example 2.

[0060]

[0061] Figures 3-9Table 2 shows the appearance of the sulfuric acid stock solution in test groups 2-1# to 2-6# and 2-9# in Example 2 before, during, and after treatment. (From Table 2 and...) Figures 2-7 As can be seen, the sulfuric acid stock solution with a mass concentration greater than 80% gradually turned into a white suspension after stirring and simultaneous heating, and finally clearly separated into two layers: the upper layer was a colorless and transparent clear liquid, and the lower layer was a white precipitate (analyzed as Fe2(SO4)3). In this embodiment, by precisely controlling the temperature in conjunction with mechanical stirring, the Fe2(SO4)3 concentration was changed. 3+ The aqueous microenvironment utilizes the energy provided by the ambient temperature to attack the coordination bonds, ultimately achieving the removal of ligand water molecules. Furthermore, due to the competitive mechanism, SO42-... 2- with Fe 3+ An amorphous white precipitate is formed, achieving the purpose of removing purple or purplish-red chemical substances from the sulfuric acid solution (i.e., decolorization).

[0062] Based on the unified working principle of this invention—"decolorizing by disrupting the coordination structure of Fe³⁺ and water molecules through temperature control and utilizing SO₄²⁻ to form a precipitate through competitive coordination"—its core technology lies in the targeted removal of purple / purple-red Fe³⁺ coordination compound impurities generated by the contact between sulfuric acid and iron. This core logic is not limited to sulfuric acid from a specific source. Therefore, those skilled in the art can clearly foresee that all sulfuric acid decolorization methods disclosed in this invention can not only accurately adapt to the decolorization treatment of high-value-added by-product sulfuric acid produced after desulfurization and purification of coke oven gas in coking enterprises, but also have equal applicability and stable decolorization effect for various types of purple / purple-red sulfuric acid that are induced to change color by contact with iron equipment in other industrial scenarios (such as sulfuric acid production, long-distance transportation, and storage tanks).

Claims

1. A method for sulfuric acid decolorization, characterized in that, First, heat the colored sulfuric acid stock solution with a mass concentration ≥80% to the preheating temperature according to the preset heating rate, maintain the temperature for reaction, then seal and let it stand to separate the solid and liquid, and obtain colorless and transparent sulfuric acid.

2. The sulfuric acid decolorization method according to claim 1, characterized in that, The preset heating rate is 2℃ / min to 10℃ / min; And / or, the preset temperature is 30℃~120℃; And / or, the heat preservation reaction time is 5 min to 5 h; And / or, the sealed standing time is 1h~72h; And / or, the heating method is water bath heating, oil bath heating, forced air drying oven heating, vacuum drying oven heating, steam heat exchange or microwave heating; And / or, the solid-liquid separation method is static sedimentation, centrifugation, or filtration.

3. The sulfuric acid decolorization method according to claim 1 or 2, characterized in that, The preset heating rate is 5℃ / min to 7℃ / min; And / or, the preset temperature is 50℃~90℃; And / or, the heat preservation reaction time is 10 min to 3 h; And / or, the sealed standing time is 12h~24h; And / or, the heating method is oil bath heating or forced-air drying oven heating; And / or, the solid-liquid separation method is static sedimentation.

4. The sulfuric acid decolorization method according to claim 1, characterized in that, The color of the sulfuric acid stock solution is due to iron-induced discoloration.

5. A method for sulfuric acid decolorization, characterized in that, First, the colored sulfuric acid stock solution with a mass concentration ≥80% is stirred and heated to the preheating temperature according to the preset heating rate and preset stirring rate. The reaction is maintained at the temperature, and then sealed and allowed to stand. Solid-liquid separation is performed to obtain colorless and transparent sulfuric acid.

6. The sulfuric acid decolorization method according to claim 5, characterized in that, The preset heating rate is 2℃ / min to 10℃ / min; And / or, the preset stirring speed is 1 rpm to 1200 rpm; And / or, the preset temperature is 30℃~120℃; And / or, the heat preservation reaction time is 5 min to 5 h; And / or, the sealed standing time is 1h~72h; And / or, the heating method is water bath heating, oil bath heating, steam heat exchange or microwave heating; And / or, the solid-liquid separation method is static sedimentation, centrifugation, or filtration.

7. The sulfuric acid decolorization method according to claim 5, characterized in that, The preset heating rate is 5℃ / min to 7℃ / min; And / or, the preset mixing speed is 1 rpm to 800 rpm; And / or, the preset temperature is 50℃~90℃; And / or, the heat preservation reaction time is 10 min to 3 h; And / or, the sealed standing time is 12h~24h; And / or, the heating method is oil bath heating; And / or, the solid-liquid separation method is static sedimentation.

8. The sulfuric acid decolorization method according to claim 5, characterized in that, The color of the sulfuric acid stock solution is due to iron-induced discoloration.

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