Method and device for removing sulfur-containing organic impurities in wet-process phosphoric acid

Abstract

The invention relates to the technical field of wet-process phosphoric acid purification production, in particular to a method and a device for removing sulfur-containing organic impurities in wet-process phosphoric acid. The method comprises the following steps: S1, reacting concentrated sulfuric acid with hydrogen peroxide on line to generate peroxymonosulfuric acid; s2, adding peroxymonosulfuric acid into wet-process crude phosphoric acid in proportion, and carrying out thermal activation oxidation reaction at 75-95 DEG C for 1-3 hours to generate sulfate free radicals (SO4 <->.) so as to deeply destroy an organic sulfur macromolecular structure; s3, activated carbon is added at the temperature of 70-90 DEG C, secondary catalytic activation and adsorption are carried out, the residual oxidizing agent is thoroughly decomposed, the degraded fragments are adsorbed, and the reaction is carried out for 15-40 minutes; s4, solid-liquid separation is performed to obtain purified phosphoric acid, efficient mineralization of humus-S, DBT and other stubborn sulfur-containing organic matter is achieved, soy sauce coloring of an extracting agent is eradicated from the source, the product chromaticity and the sulfate radical index stably reach the food-grade standard, and the method has the advantages of being continuous in process, low in cost and free of secondary pollution.

Description

Technical Field

[0001] This invention relates to the field of wet-process phosphoric acid purification production technology, specifically to a method and apparatus for removing sulfur-containing organic impurities from wet-process phosphoric acid. Background Technology

[0002] Wet-process phosphoric acid is an important basic chemical produced from phosphate rock through sulfuric acid decomposition. Its refined products are widely used in food, pharmaceutical, and electronics industries. However, wet-process phosphoric acid generally contains complex organic impurities originating from the phosphate rock itself and introduced during flotation and processing. These impurities are complex in composition, especially sulfur-containing organic compounds such as humic derivatives, Kerogen-S type macromolecules, bitumen-like colloidal aromatic sulfur-containing polymers, and dibenzothiophene (DBT) compounds. These compounds are structurally stable and highly aromatic, and are the root cause of the dark color (yellowish-brown to brownish-black) of crude phosphoric acid, high total sulfur content, and deterioration of subsequent processing performance. These substances readily accumulate in the organic phase during conventional solvent extraction, causing the extractant to rapidly turn a dark soy sauce color. This not only degrades the extractant's function but also contaminates the refined phosphoric acid through back-extraction, resulting in excessive sulfate (as a total sulfur content) in the final product, severely restricting the production of high-grade phosphoric acid, including food-grade.

[0003] Currently, commonly used industrial purification methods mainly revolve around physical adsorption and chemical oxidation, but both have significant limitations. Activated carbon adsorption is a common pretreatment method, but it is mainly effective for polar small-molecule pigments. Its adsorption capacity for neutral or weakly polar, sterically hindered sulfur-containing macromolecules and colloidal substances is extremely weak, and it cannot prevent the accumulation of such substances in the extractant. Furthermore, activated carbon requires frequent regeneration, its efficiency decreases, and it is classified as hazardous waste, resulting in high disposal costs. Chemical oxidation methods, such as using hydrogen peroxide (H2O2) to attempt to destroy chromophores and sulfur-containing structures, are prone to ineffective decomposition and quenching in high-concentration, high-impurity-loaded wet-process phosphoric acid systems, making it difficult to generate sufficient and effective hydroxyl radicals (·OH). Moreover, ·OH radicals have an extremely short lifetime (approximately 10). -9 -10 -6 In high-acid, high-impurity environments, the diffusion distance of s is limited, and the attack efficiency on stable structures such as humic substances-S, DBT and their oxidation products is very low, making it impossible to achieve deep decolorization and desulfurization.

[0004] In recent years, the generation of sulfate radicals (SO4) based on persulfates (such as permonosulfate, PMS) has been studied. - Advanced oxidation techniques, particularly those involving oxidation potentials (2.6–3.1 V) and free radical lifetimes (10⁻⁶ V), are highly effective due to their high oxidation potential (2.6–3.1 V) and long free radical lifetimes (10⁻⁶ V). -4 -10 -2 SO42 has attracted attention due to its specific electrophilic attack ability on electron-rich organic compounds (such as aromatics and sulfur-containing compounds). Theoretically, SO422...- This technology can more effectively penetrate into the interior of organic macromolecules, breaking stable CS bonds and completely oxidizing sulfur to sulfate, providing a potential approach to solving persistent organic sulfur impurities in wet-process phosphoric acid. However, directly applying this technology to industrial crude phosphoric acid environments faces severe challenges: First, industrial-grade persulfate exhibits poor long-term storage stability in highly corrosive concentrated phosphoric acid-sulfuric acid mixtures, leading to easy loss of active components; second, in such complex high-acid, high-ionic-strength media, single thermal activation or traditional catalytic activation methods are inefficient, resulting in slow free radical generation rates and insufficient concentrations, making it difficult to cope with high loads of organic impurities; third, simple addition methods cannot ensure efficient, targeted contact and reaction between free radicals and target impurities. Therefore, under the existing technological system, the removal of structurally stable sulfur-containing dark organic compounds from wet-process phosphoric acid has not been effectively solved. Developing a novel treatment technology that can adapt to the extremely acidic environment of wet-process phosphoric acid, achieve efficient in-situ generation and activation of oxidants, and synergistically enhance the reaction efficiency of free radicals with target impurities is of urgent and significant importance for overcoming current production bottlenecks and achieving stable production of high-quality wet-process phosphoric acid. Summary of the Invention

[0005] The purpose of this invention is to at least solve one of the technical problems existing in the prior art, and to provide a highly efficient and thorough method and apparatus for removing sulfur-containing organic impurities from wet-process phosphoric acid. This method achieves deep mineralization and decolorization of humic substances (S), colloidal sulfur-containing polymers, and DBT-like substances by generating a highly active oxidant online, combined with precise thermal activation and a synergistic catalytic adsorption mechanism with activated carbon. This eliminates the problem of extractant poisoning at the source and provides qualified pretreatment acid for the production of high-purity phosphoric acid.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for removing sulfur-containing organic impurities from wet-process phosphoric acid, comprising the following steps: S1. Generation of permonosulfuric acid: Concentrated sulfuric acid and hydrogen peroxide are added to a reactor to generate high-purity permonosulfuric acid (PMS). S2. Thermal activation oxidation with persulfate: The persulfate obtained in step S1 is added to wet-process crude phosphoric acid at 0.10-0.50 wt% of the crude acid mass, and stirred at 75-95℃ for 1-3 hours. Under these conditions, the persulfate undergoes thermal activation, mainly producing sulfate free radicals (SO42-), which have high oxidation potential and long lifetimes. - ·), supplemented by some hydroxyl radicals (·OH), these strong oxidizing free radicals can efficiently attack and break the stable structure of organosulfur macromolecules (such as CS bonds, aromatic rings). S3. Secondary Activation and Adsorption of Activated Carbon: After oxidation in step S2, an appropriate amount of activated carbon is added under hot conditions. Persulfate ions are rapidly catalyzed on the surface of the activated carbon to generate sulfate free radicals, which adsorb and degrade organic sulfur fragments and pigments after oxidation and breakage, and enable the catalytic decomposition of residual persulfate and high-valence metal oxides. The reaction includes: S2O2- 8→SO4 - • (Activated carbon surface catalysis); 2KMnO4 + 3C (reduction sites on activated carbon surface) → 2Mn 2+ +K + +3CO2↑; C+2S2O2- 8+2H2O→CO2↑+4SO2- 4+4H + ; In other words, the surface of activated carbon can not only adsorb small polar fragments and pigments produced by oxidation, but its surface catalytic sites (such as oxygen-containing functional groups and trace metals) can also further catalyze the residual persulfate ions (S2O2-) to produce SO4. - • (Secondary activation) and promote the reduction and decomposition of high-valence metal oxides, thereby ensuring that the oxidant is completely consumed and preventing residual oxidant from entering subsequent processes; S4. Solid-liquid separation: The crude acid treated with activated carbon is subjected to solid-liquid separation to remove the solid phase containing activated carbon, oxidation products and inorganic impurities, resulting in pretreated phosphoric acid with significantly reduced color, no residual oxidant and a substantial decrease in organic sulfur content.

[0007] Furthermore, the molar ratio of concentrated sulfuric acid to hydrogen peroxide is 1.8-2.8:1; wherein the concentration of the concentrated sulfuric acid is 96-98%; and the concentration of the hydrogen peroxide is 27-50%. This ratio and concentration range are beneficial for obtaining high-yield and high-stability mono-peroxide sulfuric acid.

[0008] Furthermore, the crude phosphoric acid contains 40-55% P2O5 and 70-85% H3PO4. This concentration range of crude acid is representative, and the method can still operate efficiently at this acidity.

[0009] Furthermore, the amount of activated carbon added is 0.3-0.5 wt% of the crude acid mass.

[0010] Furthermore, the reaction temperature in step S3 is 70-90℃; the reaction time is 15-40 min.

[0011] An apparatus for removing sulfur-containing organic impurities from wet-process phosphoric acid, employing the aforementioned method for removing sulfur-containing organic impurities from wet-process phosphoric acid, includes an online supersulfuric acid generation unit, which includes a first metering pump, a second metering pump, and a mixer (such as a tubular static mixer or a microchannel reactor) connected to the outlets of both; this unit enables the oxidant to be produced and used immediately, avoiding storage failure. The thermal oxidation co-reactor is equipped with a wet phosphoric acid inlet and a separate supersulfuric acid injection port at the top, and an activated carbon dosing port on its side wall or top; the supersulfuric acid injection port is directly connected to the outlet of the mixer through a first acid-resistant conveying pipeline. The solid-liquid separation unit has its inlet connected to the bottom outlet of the thermal oxidation co-reactor via a second acid-resistant delivery pipeline. A temperature control system, comprising a heater and a temperature sensor located within the thermal oxidation co-reactor, is used to control the material temperature within the reactor at 75-95°C. The activated carbon inlet is located in the upper middle part of the thermal oxidation co-reactor. Its position ensures that activated carbon can be conveniently and safely added only after the material level in the reactor has reached a certain height (such as more than 70% of the total volume) and the oxidation stage of step S2 has been completed, thereby achieving the process requirements of step-by-step and sequential operation.

[0012] Furthermore, the mixer in the online sulfuric acid generation unit is a tubular static mixer or a microchannel reactor, with a cooling jacket on the outside; the first metering pump is used to deliver concentrated sulfuric acid with a concentration of 96-98%, the second metering pump is used to deliver hydrogen peroxide with a concentration of 27-50%, and the volume design of the mixer allows the material residence time to be 60-120 minutes.

[0013] Furthermore, the thermal oxidation co-reactor is a steel reactor, graphite reactor, or high-silicon cast iron reaction vessel with a polytetrafluoroethylene liner, and its effective volume is 300-500 m³; the reactor is equipped with an axial flow or turbine impeller.

[0014] Furthermore, the solid-liquid separation unit can be a plate and frame filter press, a horizontal screw centrifuge, or a ceramic membrane filtration system.

[0015] Compared with the prior art, the technical solution of this application has the following beneficial effects: 1. Achieved deep mineralization of stubborn sulfur-containing organic matter: This invention, through online generation of per-monosulfuric acid combined with precise thermal activation, can generate high concentrations and long-lived sulfate radicals (SO4) in high-acid systems. -This free radical possesses extremely strong oxidizing power and electrophilic properties, effectively attacking and completely destroying stable structures such as humic-S, Kerogen-S type macromolecules, DBT-type aromatic sulfides, and bitumen-like colloids that are difficult to handle by traditional methods. It efficiently converts the organic sulfur in these molecules into inorganic sulfate ions, achieving a fundamental breakthrough from "difficult to adsorb" to "complete oxidation".

[0016] 2. Addressing the root cause of extractant poisoning: After pretreatment using this invention, the core component in wet-process crude phosphoric acid that causes excessive color and sulfur content—recalcitrant sulfur-containing macromolecules—is pre-decomposed. Therefore, in the subsequent solvent extraction stage, the organic phase almost no longer accumulates these dark-colored substances, thus maintaining a healthy light yellow or light green state for a long time. This fundamentally eliminates the "soy sauce discoloration" phenomenon, significantly extends the lifespan and regeneration cycle of the extractant, and ensures the stability of continuous production.

[0017] 3. Significantly improves the quality of the final product, easily meeting food-grade standards: Because organic sulfur impurities are deeply oxidized and removed during the pretreatment stage, rather than being transferred to the extractant, they are avoided from being carried back into the refined acid during the back-extraction process. This allows the total sulfur content (calculated as sulfate) of the finished phosphoric acid to be stably controlled within the stringent range required by food-grade standards, solving the pain point of fluctuating sulfate index and easy exceeding of standards in traditional processes.

[0018] 4. Significant Color Improvement: During the treatment process, the appearance of crude phosphoric acid undergoes a fundamental transformation, changing from dark brown or brownish-black. After oxidation, it may briefly turn purplish-black (intermediate state due to macromolecular breakage), and finally, after adsorption by activated carbon, it appears as a light blue or light yellowish-green transparent liquid. This significant color improvement not only enhances the product's appearance grade but also facilitates purity monitoring and operation in subsequent processes.

[0019] 5. The process is green and economical, and easy to integrate into industrial applications: The entire process consumes only concentrated sulfuric acid, hydrogen peroxide, and a small amount of activated carbon, and the raw materials are inexpensive and readily available. The final products of the reaction are sulfate, carbon dioxide, and water, without introducing any heavy metal ions or harmful byproducts, fully meeting the cleanliness requirements of food-grade products. The device can be directly integrated into existing wet-process phosphoric acid production processes, requiring only the addition of a pretreatment step before extraction. The modification cost is low, the operation is simple, and it is very suitable for large-scale continuous production. Attached Figure Description

[0020] Figure 1 This is a flowchart of a preferred embodiment of the method for removing sulfur-containing organic impurities from wet-process phosphoric acid. Figure 2 This is a schematic diagram of the structure of the apparatus for removing sulfur-containing organic impurities from wet-process phosphoric acid in a preferred embodiment of the present invention.

[0021] Reference numerals: 1. Online generation unit of supersulfuric acid; 11. First metering pump; 12. Second metering pump; 13. Mixer; 14. Cooling jacket; 2. Thermal oxidation co-reactor; 21. Wet phosphoric acid feed inlet; 22. Supersulfuric acid injection port; 23. Activated carbon dosing port; 24. Stirring paddle; 3. First acid-resistant conveying pipeline; 4. Second acid-resistant conveying pipeline; 5. Solid-liquid separation unit. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] Unlike traditional wet-process phosphoric acid decolorization and desulfurization methods that use high-temperature H2O2 to generate hydroxyl radicals, the existing technology, although ·OH has an extremely high oxidation potential, has a very short half-life (typically 10) in crude wet-process phosphoric acid with a high heterophosphate ratio and high acidity. -9 -10 -6 The limited diffusion distance of sulfuric acid free SO₄²⁻ (s) significantly reduces its effective utilization rate. In contrast, the online preparation and thermal activation of sulfuric acid free SO₄²⁻ in this invention has the following key advantages: 1. Longer free radical lifetime: SO4 - • Lifespan can reach 10 years -4 -10 -2 Its lifespan is on the order of s, and it is further stabilized in concentrated sulfuric acid-phosphoric acid mixed acid systems. Its lifespan is several orders of magnitude longer than that of ·OH, giving it sufficient diffusion pathways to penetrate deep into the interior of humic colloids, organosulfur polymers, and macromolecular structures such as DBT / DBTO / DBTO2, completing deep oxidative cleavage.

[0024] 2. Oxidation potential higher than or equivalent to ·OH: In highly acidic systems, SO42- - The effective oxidation potential of · can reach 2.6-3.1V, which is significantly higher than that of ·OH under the same environment (which usually decreases to 1.8-2.0V due to acid quenching). Therefore, even highly aromatic and sterically shielded sulfur-containing structures such as sulfides (RSR), sulfoxides / sulfones (RS(O)-R, R-SO2-R), stable thiophene aryl sulfides, and humic acids-S can still undergo continuous oxidation ring opening, chain scission, and complete oxidation of sulfur to sulfate under SO4· attack.

[0025] 3. It has extremely strong electrophilic properties and can target electron-rich sulfur-containing groups: SO4 -Due to its stronger electrophilicity than ·OH, it has a greater affinity for sites rich in π electron clouds in aromatic sulfoxide rings (thiophene), aromatic sulfoxides, and sulfur-containing humic polymers. It can directly initiate electron migration, free radical addition, or single electron transfer (SET) reactions at the α-position of aromatic rings or sulfoxides, rapidly destroying the original conjugated structure, causing its color to disappear, and promoting the complete conversion of sulfur to the +6 oxidation state.

[0026] Therefore, the core of the process of this invention is "strong acid environment + on-site preparation of high-purity PMS + thermal activation → high-density SO-4·free radicals → cracking of stubborn sulfur-containing dark organic compounds".

[0027] Thermal activation mechanism of persulfate: In a strong acid system at 75-95℃, persulfate undergoes thermal decomposition, generating highly reactive sulfuric acid free radicals SO4. - ·; SO4 - • Attack mechanism of sulfur-containing organic compounds: Sulfate radicals have extremely strong oxidation potentials (E°≈2.5-3.1V), which can break sulfoxide / sulfone (S(IV) / S(VI) are further oxidized and broken), thiophene rings (ring opening and further oxidation to carboxylic acids or sulfates), Kerogen-S (breaking CSC networks), Bitumen-like colloids (breaking the connecting chains of aromatic systems), and aromatic sulfides (breaking CS bonds and oxidizing to S). 6+ Ultimately, most of the sulfur is converted into SO2-4 or stable colorless small molecules.

[0028] The synergistic mechanism of activated carbon: Catalytic activation of residual PMS: HSO5 - +C→SO4 - · + CO2 + H2O; Adsorption oxidation products include carboxylic acid, sulfonic acid, or polar aromatic oxidation fragments; Adsorbed metal complex chromophores (Fe 3+ Mn 3+ This step significantly reduces the color of the final phosphoric acid. Example 1

[0029] Reference Figure 1 The apparatus in this embodiment includes an online sulfuric acid generation unit 1, a thermal oxidation co-reactor 2, a solid-liquid separation unit 5, and a safety and interlock control unit.

[0030] Online generation unit 10: The first metering pump 11 pumps 98% concentrated sulfuric acid and the second metering pump 12 pumps 50% hydrogen peroxide (H2O2) at a molar ratio of 2:1 into a tubular static mixer 13 with a cooling jacket 14. The materials stay for about 90 minutes and react to generate permonosulfuric acid (PMS) solution. The temperature is controlled below 40°C.

[0031] Thermal oxidation co-reactor 2: This is a stirred reactor with an effective volume of 400 m³ and a PTFE liner, equipped with a turbine-type agitator 24 and a coil-type heater. It has a phosphoric acid inlet 21 and a PMS injection port 22 at the top, and an activated carbon dosing port 23 in the upper middle section. The PMS injection port 22 is directly connected to the outlet of the mixer 13 via a first acid-resistant delivery pipeline.

[0032] Solid-liquid separation unit 5: A plate and frame filter press is selected, and its inlet is connected to the bottom outlet of the thermal oxidation co-reactor through the second acid-resistant conveying pipeline 4.

[0033] The temperature control system includes a heater and a temperature sensor installed inside the thermal oxidation co-reactor, used to control the material temperature inside the reactor at 75-95℃. To ensure the long-term, stable, and safe operation of this industrial plant, a conventional safety monitoring and interlocking control system can be configured. This system typically includes the following components: Process parameter monitoring: An online sulfuric acid concentration monitor is installed on the first acid-resistant pipeline 3, which transports sulfuric acid, to monitor the concentration and stability of the oxidant in real time.

[0034] Temperature safety protection: Connected to the temperature control system, a temperature alarm module is provided. When the material temperature inside reactor 2 deviates from the set range of 75-95℃, the system will trigger an audible and visual alarm to prompt the operator to intervene.

[0035] Pressure interlock protection: A pressure sensor is installed on reactor 2 and electrically interlocked with the metering pumps (11, 12) of the supersulfuric acid online generation unit 1 and the reactor stirring motor. When the internal pressure of the reactor is detected to rise abnormally to the set safety threshold, the interlock device will automatically execute the safety procedure: immediately cut off the feed of oxidant, while keeping the stirring motor running continuously to ensure uniform heat distribution and safe pressure relief of the reaction system.

[0036] It should be noted that the specific instruments, interlocking logic, and execution methods used in the aforementioned safety control unit are all well-known technologies and conventional designs in the field of chemical process control. Their purpose is to provide the necessary safe operating environment for the core process of this invention, and they are not, in themselves, the innovative aspects of this invention.

[0037] like Figure 2 As shown, the steps of the method for treating wet-process crude phosphoric acid using the above-mentioned apparatus are as follows: S1. Online preparation and thermal activation of persulfate.

[0038] PMS preparation: Concentrated sulfuric acid (98-99%) and hydrogen peroxide (50wt%) are mixed at a molar ratio of 1:1.05 and precisely metered into an acid-resistant mixer using dual metering pumps to immediately generate permonosulfuric acid (PMS). PMS does not require storage and flows directly into a thermally activated reactor to ensure activity and safety.

[0039] Thermal activation conditions: The temperature is controlled at 80℃, and the reaction is ensured to be uniform through the tube heating section and temperature control sensor; the residence time is 2 hours, which can be adjusted to 1-3 hours according to the organic load; during the reaction, the color of phosphoric acid gradually changes from yellowish brown to bright purple-black, indicating that most of the organic sulfur has been oxidized.

[0040] Oxidation mechanism monitoring: GC-MS, FT-IR, and TOC analysis confirmed that humic sulfur and bitumen-like colloids were cleaved and ring-opened during the thermal activation phase; aromatic sulfides such as DBT were oxidized to sulfates or polar intermediates; the oxidation rate of high molecular weight organic sulfur reached 85-90%, and the total color decreased, but residual PMS kept the solution purplish-black. S2, synergistic oxidation and adsorption of activated carbon.

[0041] Adding activated carbon: Add 0.03-0.05 wt% powdered activated carbon to the thermally activated phosphoric acid, and maintain the temperature at 50-80℃; stir for 20-40 minutes to ensure that the activated carbon and phosphoric acid are in full contact.

[0042] Synergistic mechanism: Hydrophobic molecules such as DBT are adsorbed first; the surface of activated carbon provides electron transfer channels, and the residual PMS is locally activated to generate SO4. - · The generated SO4 - • It is more stable on the AC surface and further oxidizes incompletely degraded organic matter; activated carbon reduces the purplish-black color of high-valence metal oxides, turning the solution from purplish-black to light green to blue-green.

[0043] Effect evaluation: The ratio of sulfate to total sulfur content (converted to sulfate) increased from 60%-70% to 96-98%, while the proportion of organic sulfur was greatly reduced. Example 2

[0044] Applications in industrial continuous production.

[0045] Continuous process layout: PMS online preparation section → thermally activated tube reaction section → activated carbon addition section → filtration and collection section; flow rate, residence time and temperature are precisely controlled by pumps and valves to achieve continuous and efficient reaction and avoid safety hazards caused by PMS storage.

[0046] Operating conditions: Temperature of the thermal activation section is 80℃, residence time is 1.5-2.5 hours; temperature of the activated carbon section is 50-80℃, residence time is 20-40 minutes, dosage is 0.03-0.05wt%; filtration is carried out using an acid-resistant high specific surface area filter or a continuous centrifuge to collect activated carbon and adsorbents.

[0047] Industrial effects: 1. High oxidation efficiency: The synergistic effect of thermally activated PMS and activated carbon can realize the chain scission of macromolecular organic sulfur, the ring opening of aromatic ring and sulfur oxidation, with a total oxidation rate of 95%.

[0048] 2. The ratio of sulfate to total sulfur has increased significantly: the ratio of sulfate to total sulfur content (converted to sulfate) has increased from 60%-70% to 96-98%, while the proportion of organic sulfur has decreased significantly.

[0049] 3. Strong feasibility for continuous industrial production: PMS online generation avoids storage risks; the thermal activation section and the activated carbon synergy section can be continuously connected in series to achieve efficient, stable and controllable production.

[0050] 4. Balancing safety and economy: Avoids safety hazards associated with PMS storage and large-dose operation; uses less activated carbon, with high adsorption and synergistic activation efficiency, reducing operating costs; the process can be monitored in real time, and reaction conditions can be controlled through online color and total sulfur analysis.

[0051] Comparative experiment Traditional H2O2 oxidation: limited reduction in color (approximately 20-30%), total sulfur content remains high; Ordinary activated carbon adsorption: low adsorption efficiency for high molecular weight organic sulfur and poor decolorization effect; The process of this invention combines the synergistic effect of thermally activated PMS and activated carbon, resulting in a color reduction of >90% and a total sulfur reduction of 40-70%, which is significantly better than traditional methods.

[0052] Without causing conflict, those skilled in the art can freely combine and use the above-mentioned additional technical features.

[0053] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for removing sulfur-containing organic impurities from wet-process phosphoric acid, characterized in that: Includes the following steps: S1. Generation of peroxymonosulfuric acid: Concentrated sulfuric acid and hydrogen peroxide are added to a reactor to generate high-purity peroxymonosulfuric acid; S2. Thermal activation oxidation with persulfate: The persulfate obtained in step S1 is added to wet-process crude phosphoric acid at 0.10-0.50 wt% of the crude acid mass. The mixture is stirred at 75-95°C for 1-3 hours to thermally activate the persulfate and generate sulfuric acid free radicals SO4. - ·, hydroxyl radical ·OH; S3. Secondary Activation and Adsorption of Activated Carbon: After oxidation in step S2, an appropriate amount of activated carbon is added under hot conditions. Persulfate ions are rapidly catalyzed on the surface of the activated carbon to generate sulfate free radicals, which adsorb and degrade organic sulfur fragments and pigments after oxidation and breakage, and enable the catalytic decomposition of residual persulfate and high-valence metal oxides. The reaction includes: S2O2- 8→SO4 - • (Activated carbon surface catalysis); 2KMnO4 + 3C (reduction sites on activated carbon surface) → 2Mn 2+ +K + +3CO2↑; C+2S2O2- 8+2H2O→CO2↑+4SO2- 4+4H + ; S4. Solid-liquid separation: The crude acid treated with activated carbon is subjected to solid-liquid separation to obtain pretreated phosphoric acid that is significantly decolorized and free of oxidants.

2. The method for removing sulfur-containing organic impurities from wet-process phosphoric acid according to claim 1, characterized in that: The molar ratio of concentrated sulfuric acid to hydrogen peroxide is 1.8-2.8:1; wherein the concentration of concentrated sulfuric acid is 96-98%; and the concentration of hydrogen peroxide is 27-50%.

3. The method for removing sulfur-containing organic impurities from wet-process phosphoric acid according to claim 1, characterized in that: The crude phosphoric acid contains 40-55% P2O5 and 70-85% H3PO4.

4. The method for removing sulfur-containing organic impurities from wet-process phosphoric acid according to claim 1, characterized in that: The amount of activated carbon added is 0.3-0.5 wt% of the crude acid mass.

5. The method for removing sulfur-containing organic impurities from wet-process phosphoric acid according to claim 1, characterized in that: The reaction temperature in step S3 is 70-90℃; the reaction time is 15-40 min.

6. A device for removing sulfur-containing organic impurities from wet-process phosphoric acid, characterized in that: The method for removing sulfur-containing organic impurities from wet-process phosphoric acid according to any one of claims 1-5 includes an online supersulfuric acid generation unit, which includes a first metering pump, a second metering pump, and a mixer connected to the outlets of both. The thermal oxidation co-reactor is equipped with a wet phosphoric acid inlet and a separate supersulfuric acid injection port at the top, and an activated carbon dosing port on its side wall or top; the supersulfuric acid injection port is directly connected to the outlet of the mixer through a first acid-resistant conveying pipeline. The solid-liquid separation unit has its inlet connected to the bottom outlet of the thermal oxidation co-reactor via a second acid-resistant delivery pipeline. A temperature control system, comprising a heater and a temperature sensor located within the thermal oxidation co-reactor, is used to control the material temperature within the reactor at 75-95°C. The activated carbon inlet is located in the upper middle part of the thermal oxidation co-reactor. Its position is configured such that activated carbon can only be added through this inlet after the material liquid level in the reactor reaches more than 70% of its total volume and the predetermined oxidation stage is completed.

7. The apparatus for removing sulfur-containing organic impurities from wet-process phosphoric acid according to claim 6, characterized in that: The mixer in the online sulfuric acid generation unit is a tubular static mixer or a microchannel reactor, with an external cooling jacket; the first metering pump is used to deliver concentrated sulfuric acid with a concentration of 96-98%, the second metering pump is used to deliver hydrogen peroxide with a concentration of 27-50%, and the volume design of the mixer allows the material residence time to be 60-120 minutes.

8. The apparatus for removing sulfur-containing organic impurities from wet-process phosphoric acid according to claim 6, characterized in that: The thermal oxidation co-reactor is a steel reactor, graphite reactor, or high-silicon cast iron reaction vessel with a polytetrafluoroethylene liner, and its effective volume is 300-500 m³; the reactor is equipped with an axial flow or turbine impeller.

9. The apparatus for removing sulfur-containing organic impurities from wet-process phosphoric acid according to claim 6, characterized in that: The solid-liquid separation unit is a plate and frame filter press, a horizontal screw centrifuge, or a ceramic membrane filtration system.

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