A method for purifying sulfuric acid from mercury

Abstract

The application discloses a method for purifying mercury in sulfuric acid, which comprises the following steps: introducing waste sulfuric acid into a fully-sealed reaction device with a stirring mechanism, controlling the temperature of the waste sulfuric acid between 0-10 DEG C, starting the stirring mechanism, and feeding trace amount of dried hydrogen sulfide gas into the fully-sealed reaction device at a constant speed; using two-stage series absorption for tail gas generated by the reaction between the waste sulfuric acid and the hydrogen sulfide gas, wherein the first stage is a liquid absorption column filled with a mixed solution of sodium hydroxide and sodium thiosulfate, and the second stage is an activated carbon adsorption column; feeding the treated waste sulfuric acid into a ceramic membrane filter for filtration; and pumping the filtered waste sulfuric acid into a multi-stage sulfur-loaded activated carbon adsorption column for deep mercury removal. The application can significantly improve the mercury removal precision and material utilization rate.

Description

Technical Field

[0001] This invention relates to methods for treating pollutants in the field of environmental protection, specifically to a method for removing mercury by purifying sulfuric acid. Background Technology

[0002] Sulfuric acid, a key raw material in the chemical industry, is widely used in numerous sectors including fertilizer, metallurgy, and chemical raw material production. Driven by demand from industries such as fertilizer, titanium dioxide, and new energy, my country's sulfuric acid production and market size have continued to expand. Currently, the main raw materials for sulfuric acid production are sulfur, pyrite, and smelting flue gas. With the continuous expansion and technological upgrading of the metal smelting industry, strong environmental policies, and breakthroughs in process technology, sulfuric acid production from smelting flue gas has gradually become the mainstream route for sulfuric acid production. In 2023, sulfuric acid production from smelting flue gas accounted for over 40% of my country's total sulfuric acid production, with copper smelting flue gas accounting for over 70%, becoming the core source of sulfuric acid from smelting flue gas. However, due to factors such as flue gas characteristics and process conditions, the complex composition of the flue gas and severe interference from impurities lead to a decline in the quality of the produced sulfuric acid due to pollutants such as dust and heavy metals in the flue gas.

[0003] Currently, purification processes in sulfuric acid production primarily focus on the smelting flue gas stage. These processes aim to remove impurities such as dust, fluorine, chlorine, and heavy metals from the flue gas through pretreatment methods like washing, demisting, and drying, creating a clean environment for subsequent SO2 conversion and sulfuric acid production. While this flue gas purification-centric approach can reduce the amount of impurities entering the sulfuric acid system to some extent, trace amounts of heavy metals (such as mercury and lead), acid mist aerosols, and organic impurities still enter the acid production system and ultimately accumulate in the sulfuric acid product. For example, mercury, due to its high volatility, readily forms Hg... 0 Mercury in the form of Hg²⁺ can penetrate the flue gas purification device and dissolve in sulfuric acid to form soluble mercury compounds. Existing processes have limited direct purification methods for sulfuric acid products, resulting in some smelting flue gas producing sulfuric acid that fails to meet application requirements in terms of purity.

[0004] Because sulfuric acid is corrosive and has a high boiling point, it poses a severe challenge to direct purification processes. A few methods for direct purification of sulfuric acid include (1) adsorption, such as using modified silica gel or metal-organic frameworks (MOFs) to adsorb heavy metals, but the adsorption capacity is low (usually <50mg / g) and it is easy to deactivate in concentrated sulfuric acid, making regeneration difficult; (2) extraction, using specific extractants (such as tributyl phosphate) to separate impurities, but the extractants have high solubility in sulfuric acid, which can easily cause secondary pollution and is difficult to achieve continuous production; (3) electrochemical method: removing reducing impurities by electrolytic oxidation, but the energy consumption is high (electricity consumption per ton of sulfuric acid >100kWh) and it is ineffective for inert impurities such as mercury.

[0005] In summary, the current situation of sulfuric acid purification prioritizing flue gas over finished products stems from both the inertia of flue gas purification processes and limitations imposed by the technical difficulty of direct purification and insufficient market demand. With the increasing demand for high-purity sulfuric acid from industries such as new energy and electronics, and the tightening of environmental standards regarding heavy metal limits in products, developing efficient, stable, and low-cost direct sulfuric acid purification processes will become an important direction for future technological breakthroughs. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a method for purifying sulfuric acid and removing mercury. Specifically, it addresses waste sulfuric acid produced from flue gas in the non-ferrous metal smelting industry by reducing the content of pollutants, particularly mercury, in the sulfuric acid through methods such as coagulation sedimentation and adsorption filtration, thereby improving the quality of the sulfuric acid.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for purifying sulfuric acid to remove mercury includes the following steps: S1. Introduce waste sulfuric acid into a fully sealed reaction device with a stirring mechanism, and control the temperature of the waste sulfuric acid between 0-10℃. Turn on the stirring mechanism and introduce a small amount of dried hydrogen sulfide gas into the fully sealed reaction device at a constant speed. The tail gas generated by the reaction of waste sulfuric acid and hydrogen sulfide gas is absorbed by a two-stage series absorption. The first stage is a liquid absorption column containing a mixed solution of sodium hydroxide and sodium thiosulfate, and the second stage is an activated carbon adsorption column. S2. Pass the waste sulfuric acid treated in step S1 into a ceramic membrane filter for filtration. S3. Pump the waste sulfuric acid filtered in step S2 into a multi-stage sulfur-loaded activated carbon adsorption column for deep mercury removal.

[0008] Further, in step S1, the stirring mechanism is a magnetic stirring mechanism or a mechanical stirring mechanism, and the stirring speed is 200-300 rpm; the temperature of the waste sulfuric acid is controlled between 0-10℃ by a low-temperature circulating cooling system; the hydrogen sulfide gas introduction rate is ≤0.1L / min, the water content of the hydrogen sulfide gas is ≤0.1%, and the total molar amount of hydrogen sulfide gas introduced is controlled to be 1-3 times the theoretical reaction molar amount. The theoretical reaction molar amount of hydrogen sulfide gas is calculated according to the molar ratio of Hg²⁺ to H₂S of 1:1, and the total reaction time is 2-5h.

[0009] Further, in step S1, the mass concentration of sodium hydroxide in the mixed solution of sodium hydroxide and sodium thiosulfate is 20%-30%, and the mass concentration of sodium thiosulfate is 3%-5%; the activated carbon in the activated carbon adsorption column is columnar coal-based activated carbon with a particle size of 2-4 mm and a specific surface area ≥1000 m² / g, and the filling height of the activated carbon in the activated carbon adsorption column is 2 / 3 of the height of the activated carbon adsorption column; the material of the fully sealed reaction device is borosilicate glass or polytetrafluoroethylene, and the sealing element of the fully sealed reaction device is made of fluororubber.

[0010] Furthermore, in the ceramic membrane filter of step S2, the ceramic membrane is selected as a zirconia-based ceramic membrane with a pore size of 0.2-1μm, and the ceramic membrane adopts a multi-channel structure with ≥19 channels and an inner diameter of 3-5mm for each channel; the filtration temperature is maintained at 0-10℃, the operating pressure is 0.2-0.4MPa, and the crossflow velocity is 1.5-2.0m / s; during the filtration process, when the membrane flux drops to 60% of the initial flux, the ceramic membrane filter is cleaned and regenerated.

[0011] Furthermore, the ceramic filter cleaning and regeneration process is as follows: first, backwash with clean concentrated sulfuric acid at a temperature of 50-60℃ for 30 minutes, then purge with compressed air at 0.5MPa for 10 minutes to restore the membrane flux to more than 90% of the initial value.

[0012] Further, in step S3, 4-6 stages of sulfur-loaded activated carbon adsorption columns are set up in series. The ratio of the filling height of the sulfur-loaded activated carbon in a single sulfur-loaded activated carbon adsorption column to the diameter of the column is 3-5:1. The residence time of waste sulfuric acid in a single sulfur-loaded activated carbon adsorption column is 30-60 min. The inlet and outlet pressure difference of the sulfur-loaded activated carbon adsorption column is controlled at 0.1-0.2 MPa. When the amount of mercury adsorbed in a sulfur-loaded activated carbon adsorption column drops to 50% of the initial adsorption amount, the sulfur-loaded activated carbon in that column is replaced, and the replaced sulfur-loaded activated carbon is regenerated.

[0013] Further, in step S3, the preparation process of sulfur-loaded activated carbon in the sulfur-loaded activated carbon adsorption column is as follows: columnar coal-based activated carbon with a particle size of 2-4 mm and an iodine value ≥800 mg / g is first soaked in dilute sulfuric acid with a mass concentration of 8%-15% at a liquid-to-solid ratio of L / kg=3:1 for 2 hours to remove surface impurities and ash. Then, it is rinsed with deionized water until the pH of the filtrate is 5-6. Then, it is placed in a sodium sulfide solution with a mass concentration of 10%-15% and impregnated at 60-70℃ for 8-12 hours. Subsequently, it is dried at 105℃ for 4 hours to obtain sulfur-loaded activated carbon.

[0014] Furthermore, in step S3, the regeneration process of the sulfur-loaded activated carbon is as follows: the sulfur-loaded activated carbon to be regenerated is placed in a tube furnace and heated at 300-350°C for 2 hours under nitrogen protection. The desorbed mercury vapor is recovered by condensation. After regeneration, the activated carbon is reloaded with sulfur, and the sulfur loading is restored to more than 90% of the initial value.

[0015] The beneficial effects of this invention are as follows: This invention utilizes a three-stage synergistic process of "chemical precipitation + precision filtration + deep adsorption" to purify and remove mercury from waste sulfuric acid, thereby improving the removal efficiency and deep purification capacity of mercury in waste sulfuric acid, realizing the resource reuse of waste sulfuric acid, saving the comprehensive cost of hazardous waste treatment and new acid procurement, and significantly improving the mercury removal accuracy and material utilization rate through low-temperature rate-controlled reaction, multi-stage adsorption and activated carbon regeneration technology. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method in Embodiments 1-2 of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0018] Example 1

[0019] A copper smelting company collected mercury-containing waste sulfuric acid with a sulfuric acid concentration of 93% and a mercury content of 0.035%.

[0020] This embodiment provides a method for purifying and removing mercury from sulfuric acid to treat the aforementioned mercury-containing waste sulfuric acid, such as... Figure 1 As shown, it includes the following steps: (1) 10L of mercury-containing waste sulfuric acid was pumped into a polytetrafluoroethylene fully sealed reaction apparatus using a metering pump. The low-temperature circulating cooling system was turned on to lower the temperature of the waste sulfuric acid to 5℃ and maintain a constant temperature. The stirring mechanism was turned on and the stirring speed was adjusted to 250rpm. The valve of the hydrogen sulfide cylinder was opened. After the hydrogen sulfide gas was dried by the dryer, it was introduced into the fully sealed reaction apparatus through the gas distributor, and the introduction rate was controlled to be 0.08L / min. Based on the mercury content in the waste sulfuric acid, the actual total molar amount of hydrogen sulfide gas introduced was about 3 times the theoretical molar amount (based on a 1:1 molar ratio of Hg²⁺ to H₂S). The introduction process lasted for 2.5h to ensure that the mercury ions reacted fully to form mercury sulfide precipitate. The exhaust gas (containing unreacted hydrogen sulfide) generated during the reaction enters the exhaust gas treatment system through the outlet interface. It is first passed into the first-stage liquid absorption column (the absorbent is a mixed solution of 25% sodium hydroxide and 4% sodium thiosulfate, with a liquid-to-gas ratio of 10L / m³). The remaining trace amount of hydrogen sulfide is adsorbed by the second-stage activated carbon adsorption column. The activated carbon is columnar coal-based activated carbon with a particle size of 2–4 mm and a specific surface area ≥1000 m² / g. The filling height is 2 / 3 of the height of the activated carbon adsorption column to ensure that the exhaust gas emission concentration meets the "Integrated Emission Standard of Air Pollutants" (GB 16297-1996).

[0021] (2) The waste sulfuric acid containing mercuric sulfide precipitate after the reaction is fed into a zirconia-based ceramic membrane filter through a feed pump. The ceramic membrane has a pore size of 0.5 μm, adopts a multi-channel structure, has 19 channels, and a single channel inner diameter of 4 mm. The constant temperature circulation system is turned on to maintain the filtration temperature at 5℃. The cross-flow pump speed is adjusted to control the cross-flow rate at 1.8 m / s. The operating pressure is slowly increased to 0.3 MPa to start filtration. The sulfuric acid obtained after filtration is temporarily stored in an intermediate storage tank for further deep processing.

[0022] During the filtration process, when the membrane flux drops to 60% of the initial flux, the ceramic membrane filter is cleaned and regenerated: first, it is backwashed with clean concentrated sulfuric acid at 50℃ for 30 minutes, and then purged with compressed air at 0.5MPa for 10 minutes to restore the membrane flux to more than 90% of the initial value.

[0023] (3) Take 5 kg of columnar coal-based activated carbon with a particle size of 2-4 mm and an iodine value of 1000 mg / g, put it into an acid-resistant container with a stirrer, add 15 L of 12% dilute sulfuric acid and soak for 2 hours, stirring once every 30 minutes during the soaking period to fully remove the ash, metal impurities and soluble organic matter attached to the surface of the activated carbon; after soaking, rinse the activated carbon with deionized water in a reverse direction, take a sample to test the pH value of the rinsing solution, and drain the surface water of the activated carbon until the pH value stabilizes at 5-6. Transfer the cleaned activated carbon to a sealed impregnation tank with a heating jacket, add 12 L of 12% sodium sulfide solution, turn on the jacket heating system, raise the temperature of the impregnation solution to 65℃, and impregnate for 8 hours; after impregnation, take the activated carbon out of the sodium sulfide solution and transfer it to a hot air drying oven, set the drying temperature to 105℃, and dry at normal pressure for 4 hours, turning the activated carbon once every 1 hour during the period to ensure uniform drying; after drying, take out the activated carbon, cool it to room temperature, seal and store it for later use.

[0024] (4) The prepared sulfur-loaded activated carbon was loaded into four adsorption columns connected in series. The ratio of the height of the sulfur-loaded activated carbon in a single adsorption column to the diameter of the adsorption column was 3:1, and the loading amount of each column was 1 kg. During loading, the column wall was tapped in layers to avoid the formation of voids between the activated carbon particles. At the same time, two layers of polytetrafluoroethylene filter screens with a pore size of 0.1 mm were laid at the top and bottom of each column to prevent the activated carbon particles from flowing out with sulfuric acid. The sulfuric acid in the intermediate storage tank was pumped into the top of the first-stage sulfur-loaded activated carbon adsorption column through a metering pump. The flow rate of the metering pump was adjusted so that the residence time of the waste sulfuric acid in each stage of the sulfur-loaded activated carbon adsorption column was 30 min. The pressure difference between the inlet and outlet of the sulfur-loaded activated carbon adsorption column was controlled at 0.12 MPa. During the adsorption process, a sample was taken from the outlet of the fourth-stage adsorption column every 10 min, and the mercury content in the sulfuric acid was detected to be 0.000041%.

[0025] When the amount of mercury adsorbed by the sulfur-loaded activated carbon adsorption column drops to 50% of the initial adsorption capacity, the sulfur-loaded activated carbon in the adsorption column is replaced. The replaced sulfur-loaded activated carbon is then regenerated: the sulfur-loaded activated carbon to be regenerated is placed in a tubular furnace and heated at 300°C for 2 hours under nitrogen protection. The desorbed mercury vapor is condensed and recovered. After regeneration, the activated carbon is reloaded with sulfur, and the sulfur loading is restored to more than 90% of the initial value.

[0026] Example 2

[0027] A lead-zinc smelting enterprise produced mercury-containing waste sulfuric acid with a sulfuric acid concentration of 93% and a mercury content of 0.028%.

[0028] This embodiment provides a method for purifying and removing mercury from sulfuric acid to treat the aforementioned mercury-containing waste sulfuric acid, such as... Figure 1 As shown, it includes the following steps: (1) 15L of the above-mentioned mercury-containing waste sulfuric acid was transported to the fully sealed polytetrafluoroethylene reaction device through an acid-resistant metering pump. The low-temperature circulating cooling system was started to lower the temperature of the waste sulfuric acid to 8℃ and maintain a constant temperature. The mechanical stirring device was turned on and the stirring speed was adjusted to 220rpm to make the waste sulfuric acid form a stable turbulent state. The hydrogen sulfide cylinder was opened. The hydrogen sulfide gas was first dried by an anhydrous calcium chloride dryer (moisture content controlled ≤0.1%) and then uniformly introduced into the reaction device through a porous titanium alloy gas distributor, with the introduction rate controlled at 0.06L / min. The theoretical reaction amount was calculated based on the mercury content in the waste sulfuric acid. The actual total molar amount introduced was 2.4 times the theoretical reaction molar amount. The gas was continuously introduced for 2h to ensure that the mercury ions and hydrogen sulfide reacted fully to form mercury sulfide precipitate. The tail gas generated during the reaction is discharged through the tail gas port at the top of the device and first enters the first-stage liquid absorption column (the absorbent is a mixed solution of 20% sodium hydroxide and 3% sodium thiosulfate, with a liquid-to-gas ratio of 8L / m³). After preliminary absorption, the remaining tail gas enters the second-stage columnar coal-based activated carbon adsorption column (activated carbon particle size 2-4mm, specific surface area 1100m² / g, and filling height is 2 / 3 of the height of the activated carbon adsorption column). The final tail gas emission concentration meets the requirements of the "Integrated Emission Standard of Air Pollutants" (GB 16297-1996).

[0029] (2) After the reaction is completed, the waste sulfuric acid containing mercury sulfide precipitate is fed into a zirconia-based ceramic membrane filter through a variable frequency feed pump. The ceramic membrane has a pore size of 0.5 μm, adopts a multi-channel structure with 19 channels, and the inner diameter of each channel is 4 mm. The filter constant temperature control system is started to maintain the filtration temperature at 8℃. The cross-flow pump speed is adjusted to stabilize the cross-flow rate at 1.5 m / s. The operating pressure is slowly increased to 0.25 MPa before filtration begins. The preliminarily purified sulfuric acid obtained after filtration is collected in an acid-resistant intermediate storage tank for subsequent deep mercury removal treatment.

[0030] During the filtration process, when the membrane flux drops to 60% of the initial flux, the ceramic membrane filter is cleaned and regenerated: first, it is backwashed with clean concentrated sulfuric acid at 60℃ for 30 minutes, and then purged with compressed air at 0.5MPa for 10 minutes to restore the membrane flux to more than 90% of the initial value.

[0031] (3) Take 6 kg of columnar coal-based activated carbon with a particle size of 2-4 mm and an iodine value of 800 mg / g, put it into a polypropylene acid-resistant container with a stirrer, add 18 L of 8% dilute sulfuric acid (liquid-solid ratio 3:1), soak for 2 h, stirring once every 30 min during the soaking period to fully remove ash, metallic impurities and soluble organic matter from the surface of the activated carbon. After soaking, rinse the activated carbon with deionized water in a counter-current manner, taking a sample every 30 min to test the pH value of the rinsing solution until the pH stabilizes at 5-6, and drain the water from the surface of the activated carbon. Transfer the cleaned activated carbon to a stainless steel sealed impregnation tank with a heating jacket, add 15 L of 15% sodium sulfide solution, turn on the jacket heating system, raise the temperature of the impregnation solution to 70℃, and keep it at a constant temperature for 12 h. After impregnation, the activated carbon is removed from the sodium sulfide solution and transferred to a hot air drying oven. The drying temperature is set to 105℃ and the carbon is dried at normal pressure for 4 hours. During this period, the carbon is turned over once every hour to ensure uniform drying. After cooling to room temperature, the carbon is sealed and stored for later use.

[0032] (4) The prepared sulfur-loaded activated carbon was loaded into five adsorption columns connected in series. The ratio of the height of the sulfur-loaded activated carbon in a single adsorption column to the diameter of the adsorption column was 5:1, and the loading amount per column was 1.2 kg. During loading, the column wall was tapped in layers to avoid the formation of voids between the activated carbon particles. At the same time, two layers of polytetrafluoroethylene filter screens with a pore size of 0.1 mm were laid at the top and bottom of each column to prevent the activated carbon from flowing out with the sulfuric acid. The pre-purified sulfuric acid in the intermediate storage tank was pumped into the top of the first-stage sulfur-loaded activated carbon adsorption column by a metering pump. The flow rate of the metering pump was adjusted so that the residence time of the waste sulfuric acid in each adsorption column was 60 min. The pressure difference between the inlet and outlet of the sulfur-loaded activated carbon adsorption column was controlled at 0.18 MPa. During the adsorption process, a sample was taken from the outlet of the fifth-stage adsorption column every 15 min. The mercury content in the sulfuric acid was detected by atomic fluorescence spectrometry. The final detection result was 0.000035%.

[0033] When the amount of mercury adsorbed by the sulfur-loaded activated carbon adsorption column drops to 50% of the initial adsorption capacity, the sulfur-loaded activated carbon in the adsorption column is replaced. The replaced sulfur-loaded activated carbon is then regenerated: the sulfur-loaded activated carbon to be regenerated is placed in a tubular furnace and heated at 350°C for 2 hours under nitrogen protection. The desorbed mercury vapor is condensed and recovered. After regeneration, the activated carbon is reloaded with sulfur, and the sulfur loading is restored to more than 90% of the initial value.

[0034] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for purifying sulfuric acid to remove mercury, characterized in that, The steps include the following: S1. Introduce waste sulfuric acid into a fully sealed reaction device with a stirring mechanism, and control the temperature of the waste sulfuric acid between 0-10℃. Turn on the stirring mechanism and introduce a small amount of dried hydrogen sulfide gas into the fully sealed reaction device at a constant speed. The tail gas generated by the reaction of waste sulfuric acid and hydrogen sulfide gas is absorbed by a two-stage series absorption. The first stage is a liquid absorption column containing a mixed solution of sodium hydroxide and sodium thiosulfate, and the second stage is an activated carbon adsorption column. S2. Pass the waste sulfuric acid treated in step S1 into a ceramic membrane filter for filtration. S3. Pump the waste sulfuric acid filtered in step S2 into a multi-stage sulfur-loaded activated carbon adsorption column for deep mercury removal.

2. The method according to claim 1, characterized in that, In step S1, the stirring mechanism is a magnetic stirring mechanism or a mechanical stirring mechanism, and the stirring speed is 200-300 rpm; the temperature of waste sulfuric acid is controlled between 0-10℃ through a low-temperature circulating cooling system; the hydrogen sulfide gas introduction rate is ≤0.1L / min, the water content of hydrogen sulfide gas is ≤0.1%, and the total molar amount of hydrogen sulfide gas introduced is controlled to be 1-3 times the theoretical reaction molar amount. The theoretical reaction molar amount of hydrogen sulfide gas is calculated based on the molar ratio of Hg²⁺ to H₂S of 1:1, and the total reaction time is 2-5h.

3. The method according to claim 1, characterized in that, In step S1, the mass concentration of sodium hydroxide in the mixed solution of sodium hydroxide and sodium thiosulfate is 20%-30%, and the mass concentration of sodium thiosulfate is 3%-5%. The activated carbon in the activated carbon adsorption column is columnar coal-based activated carbon with a particle size of 2-4 mm and a specific surface area ≥1000 m² / g. The filling height of the activated carbon in the activated carbon adsorption column is 2 / 3 of the column height. The material of the fully sealed reaction device is borosilicate glass or polytetrafluoroethylene, and the sealing element of the fully sealed reaction device is made of fluororubber.

4. The method according to claim 1, characterized in that, In the ceramic membrane filter of step S2, the ceramic membrane is a zirconia-based ceramic membrane with a pore size of 0.2-1 μm and a multi-channel structure with ≥19 channels and an inner diameter of 3-5 mm for each channel. The filtration temperature is maintained at 0-10℃, the operating pressure is 0.2-0.4 MPa, and the crossflow velocity is 1.5-2.0 m / s. During the filtration process, when the membrane flux drops to 60% of the initial flux, the ceramic membrane filter is cleaned and regenerated.

5. The method according to claim 4, characterized in that, The process of cleaning and regenerating ceramic filters is as follows: first, backwash with clean concentrated sulfuric acid at a temperature of 50-60℃ for 30 minutes, then purge with compressed air at 0.5MPa for 10 minutes to restore the membrane flux to more than 90% of the initial value.

6. The method according to claim 1, characterized in that, In step S3, 4-6 stages of sulfur-loaded activated carbon adsorption columns are set up in series. The ratio of the filling height of the sulfur-loaded activated carbon in a single sulfur-loaded activated carbon adsorption column to the diameter of the column is 3-5:

1. The residence time of waste sulfuric acid in a single sulfur-loaded activated carbon adsorption column is 30-60 min. The inlet and outlet pressure difference of the sulfur-loaded activated carbon adsorption column is controlled at 0.1-0.2 MPa. When the amount of mercury adsorbed in a sulfur-loaded activated carbon adsorption column drops to 50% of the initial adsorption amount, the sulfur-loaded activated carbon in that column is replaced, and the replaced sulfur-loaded activated carbon is regenerated.

7. The method according to claim 1, characterized in that, In step S3, the preparation process of sulfur-loaded activated carbon in the sulfur-loaded activated carbon adsorption column is as follows: columnar coal-based activated carbon with a particle size of 2-4 mm and an iodine value ≥800 mg / g is first soaked in dilute sulfuric acid with a mass concentration of 8%-15% at a liquid-to-solid ratio of L / kg=3:1 for 2 hours to remove surface impurities and ash. Then, it is rinsed with deionized water until the pH of the filtrate is 5-6. Then, it is placed in a sodium sulfide solution with a mass concentration of 10%-15% and impregnated at 60-70℃ for 8-12 hours. Subsequently, it is dried at 105℃ for 4 hours to obtain sulfur-loaded activated carbon.

8. The method according to claim 6, characterized in that, In step S3, the regeneration process of sulfur-loaded activated carbon is as follows: the sulfur-loaded activated carbon to be regenerated is placed in a tube furnace and heated at 300-350℃ for 2 hours under nitrogen protection. The desorbed mercury vapor is condensed and recovered. After regeneration, the activated carbon is reloaded with sulfur, and the sulfur loading is restored to more than 90% of the initial value.

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