A method and system for purifying yellow phosphorus tail gas by pickling and recycling pickling liquid

Abstract

The application discloses a yellow phosphorus tail gas pickling purification and pickling liquid recycling and regenerating method and system, and aims at solving the technical problems that the oxidant consumption is large, the waste acid and waste water generation is large, and the phosphorus and sulfur elements in the yellow phosphorus tail gas are difficult to be effectively separated and utilized in the existing yellow phosphorus tail gas purification process. The method comprises the following steps: making the yellow phosphorus tail gas enter an acid washing tower; separating at least a part of the pickling liquid containing suspended elemental sulfur from the circulating pickling liquid of the acid washing tower, and performing first solid-liquid separation on the separated pickling liquid to separate the elemental sulfur, so as to obtain first filtrate; adding an iron source into the first filtrate, so that the iron source reacts with hydrogen ions in the first filtrate; performing oxidation treatment on the first filtrate containing divalent iron ions; performing second solid-liquid separation on the suspension liquid containing iron phosphate precipitates, so as to obtain iron phosphate solid and second filtrate; and sending at least a part of the second filtrate to the anode side of an electrolytic cell to perform electrolysis regeneration, so that peroxodisulfate and ammonium ions form ammonium peroxodisulfate.

Description

Technical Field

[0001] This invention relates to the field of yellow phosphorus tail gas purification technology, and in particular to a method and system for acid washing purification of yellow phosphorus tail gas and recycling of acid washing solution. Background Technology

[0002] During the production of yellow phosphorus, after the electric furnace gas is condensed, sprayed, or washed to recover yellow phosphorus, a certain amount of yellow phosphorus tail gas will still be generated. This yellow phosphorus tail gas usually has carbon monoxide as the main combustible component, and contains water vapor, hydrogen, and small amounts of impurities such as yellow phosphorus vapor, phosphine, and hydrogen sulfide. Because yellow phosphorus vapor, phosphine, and hydrogen sulfide are toxic, corrosive, or can easily have adverse effects on subsequent utilization equipment, the phosphorus- and sulfur-containing harmful components in the yellow phosphorus tail gas usually need to be purified before it can be used as industrial gas or as a source of effective components such as carbon monoxide and hydrogen.

[0003] like Figure 2 As shown, existing yellow phosphorus tail gas purification processes typically include two main treatment stages: multi-stage acid washing with concentrated sulfuric acid and lime slurry alkaline washing. Specifically, yellow phosphorus tail gas containing components such as carbon monoxide, yellow phosphorus vapor, phosphine, and hydrogen sulfide enters a multi-stage acid washing unit and contacts concentrated sulfuric acid to remove some phosphorus and sulfur-containing impurities through acid washing and oxidation. After multi-stage acid washing, the acid washing liquid is filtered to separate sulfur, which can be further recovered to produce sulfuric acid, while the liquid phase after filtration forms waste acid. The gas after multi-stage acid washing then enters the alkaline washing stage, where it contacts lime slurry to further remove acidic or sulfur-containing components; the alkaline washing liquid is filtered to form desulfurized gypsum solid waste, and the purified gas is discharged as industrial gas or used in subsequent utilization processes.

[0004] While the above-mentioned process can purify yellow phosphorus tail gas, it still has the following shortcomings. First, when using concentrated sulfuric acid as the pickling medium, the yellow phosphorus tail gas usually contains a certain amount of water vapor. After absorbing water, the concentrated sulfuric acid is diluted, reducing its oxidation and pickling capabilities, requiring continuous replenishment of concentrated sulfuric acid, resulting in a large consumption of pickling agents. Second, during the concentrated sulfuric acid pickling process, the phosphorus-containing components formed after the oxidation of phosphine and yellow phosphorus vapors easily enter the pickling solution and mix with the sulfuric acid system, forming phosphorus-containing waste acid that is difficult to directly utilize as a resource, making it difficult to separate and recover phosphorus in solid form. At the same time, the pickling solution still generates waste acid flow after pressure filtration, increasing the burden of subsequent waste acid disposal. Third, the tail gas after pickling still requires lime milk alkaline washing treatment. The alkaline washing process consumes lime milk and forms solid by-products such as desulfurization gypsum during subsequent pressure filtration, increasing the solid waste treatment volume, operating costs, and environmental pressure of the tail gas purification system. In addition, the pickling solution in the existing process mainly relies on the addition of concentrated sulfuric acid to maintain the pickling and oxidation capacity, and lacks an effective oxidant recycling mechanism; the phosphorus and sulfur elements absorbed by oxidation during the pickling process are also difficult to be separated and recovered in the same recycling system in a usable form, resulting in limited resource utilization of phosphorus and sulfur elements. Summary of the Invention

[0005] The purpose of this invention is to provide a method and system for acid washing purification of yellow phosphorus tail gas and recycling of acid washing solution, so as to solve the technical problems of large consumption of oxidant, large amount of waste acid and wastewater generated in the existing yellow phosphorus tail gas purification process, and difficulty in effectively separating and resource-utilizing phosphorus and sulfur elements in yellow phosphorus tail gas.

[0006] To achieve the above objectives, the present invention provides a method for acid washing purification of yellow phosphorus tail gas and recycling and regenerating the acid washing solution, comprising: introducing yellow phosphorus tail gas into an acid washing tower, where it reacts with a circulating acid washing solution within the tower; the acid washing solution comprising ammonium bisulfate, ammonium dihydrogen phosphate, and ammonium persulfate, wherein the ammonium persulfate is the primary oxidant in the acid washing solution, the ammonium bisulfate provides bisulfate ions for electrolytic regeneration of the ammonium persulfate, and the ammonium dihydrogen phosphate is used to improve the conductivity of the acid washing solution; in the acid washing tower, the ammonium persulfate oxidizes phosphine and yellow phosphorus vapor in the yellow phosphorus tail gas into phosphoric acid or phosphate ions containing phosphorus components, and oxidizes hydrogen sulfide in the yellow phosphorus tail gas into elemental sulfur, so that the elemental sulfur exists in a suspended state in the acid washing solution; separating at least a portion of the acid washing solution containing suspended elemental sulfur from the circulating acid washing solution in the acid washing tower, and processing the separated acid washing solution... A first solid-liquid separation is performed to separate the elemental sulfur, yielding a first filtrate. An iron source is added to the first filtrate, causing it to react with hydrogen ions in the filtrate to form ferrous ions and consume some of the acidity. The first filtrate containing ferrous ions is then oxidized to convert at least some of the ferrous ions into ferric ions, and the acidity of the first filtrate is adjusted so that the ferric ions react with the phosphorus-containing components to form ferric phosphate precipitate. A second solid-liquid separation is performed on the suspension containing the ferric phosphate precipitate to obtain ferric phosphate solid and a second filtrate. At least a portion of the second filtrate is sent to the anode side of an electrolytic cell for electrolytic regeneration, causing the hydrogen sulfate ions in the second filtrate to oxidize at the anode side to form persulfate ions. The persulfate ions react with ammonium ions to form ammonium persulfate. The regenerated pickling solution is returned to the pickling tower for recycling.

[0007] Therefore, this invention uses ammonium persulfate as the main oxidant in the pickling solution to oxidize and purify phosphine, yellow phosphorus vapor, and hydrogen sulfide in the yellow phosphorus tail gas; the elemental sulfur generated by oxidizing hydrogen sulfide is separated from the pickling solution through the first solid-liquid separation; by adding an iron source, oxidation treatment, and acidity adjustment, the phosphorus-containing components formed by the oxidation of phosphine and yellow phosphorus vapor are further converted into iron phosphate precipitate and separated; by electrolytic regeneration of the second filtrate, the hydrogen sulfate ions are converted into persulfate ions, which then form ammonium persulfate with ammonium ions, thereby realizing the cyclic regeneration of the main oxidant in the pickling solution and the recycling of the pickling solution.

[0008] In some embodiments, the pickling solution comprises the following components in parts by weight: 15-20 parts ammonium bisulfate, 20-30 parts ammonium dihydrogen phosphate, and 1-5 parts ammonium persulfate. Furthermore, the pickling solution also includes free sulfuric acid and ammonium peroxydiphosphate oxidizing components. The free sulfuric acid is used to maintain the acidic environment of the pickling solution and to provide a source of bisulfate ions for electrolytic regeneration. The ammonium peroxydiphosphate oxidizing component acts as a synergistic oxidant, co-oxidizing with the ammonium persulfate in the oxidation of at least one component of phosphine, yellow phosphorus vapor, and hydrogen sulfide in the yellow phosphorus tail gas.

[0009] In this invention, the ammonium peroxydiphosphate oxidizing component refers to an ammonium diphosphate oxidizing component containing peroxy bonds formed by dihydrogen phosphate ions under anodic oxidation conditions, which may include ammonium peroxypyrophosphate. The ammonium peroxypyrophosphate can be understood as an ammonium pyrophosphate oxidizing component containing peroxy bonds, similar to ammonium persulfate, and can participate as a synergistic oxidant in the oxidation of low-valent phosphorus and low-valent sulfur components.

[0010] In some embodiments, a portion of the pickling solution is continuously or intermittently separated from the circulating pickling solution in the pickling tower for a first solid-liquid separation, in order to shorten the residence time of the elemental sulfur in the acidic oxidation system containing ammonium persulfate and reduce the proportion of elemental sulfur further oxidized. The first solid-liquid separation can be carried out using a first filter press. The separated pickling solution is fed into the first filter press via a first filter press feed pump. The first filter press is used to filter out the elemental sulfur suspended in the pickling solution, and the first filtrate obtained from the first filter press enters the iron melting tank.

[0011] In some embodiments, the iron source is iron powder, which reacts with hydrogen ions in the first filtrate under stirring in the iron-melting tank to generate ferrous ions and hydrogen gas. By controlling the amount of iron powder added, the pH of the liquid phase in the iron-melting tank can be controlled within the range of 0.5 to 1.8; the temperature of the liquid phase in the iron-melting tank can be controlled within the range of 60 to 90°C through the jacket of the iron-melting tank; and the hydrogen gas is discharged through the exhaust pipe at the top of the iron-melting tank.

[0012] In some embodiments, the first filtrate, after the addition of an iron source and the formation of ferrous ions, enters a filter to remove residual iron source and impurities; the filtered solution is cooled to below 50°C by a cooler before entering an oxidation tank; in the oxidation tank, hydrogen peroxide is added to the solution containing ferrous ions to oxidize the ferrous ions to ferric ions, and ammonia is added to adjust the pH to the range of 1.5 to 2.5; the liquid phase temperature in the oxidation tank is controlled within the range of 50°C to 60°C through the jacket of the oxidation tank; under the pH and temperature conditions, phosphate ions react with ferric ions to form ferric phosphate precipitate.

[0013] In some embodiments, the hydrogen peroxide is added in batches or continuously, and the amount of hydrogen peroxide added is controlled according to at least one of the redox potential, the concentration of ferrous ions, and the concentration of ferric ions; and / or, during the formation of ferric phosphate precipitate, at least one of the amount of iron source added, the amount of hydrogen peroxide added, and the amount of ammonia added is controlled according to the concentration of phosphate, the total iron concentration, and the pH in the solution, so that the reaction between ferric ions and phosphate ions proceeds in the direction of forming ferric phosphate precipitate.

[0014] In some embodiments, the second solid-liquid separation is carried out using a second filter press; the suspension containing ferric phosphate precipitate generated by the reaction is fed into the second filter press by a second filter press feed pump to separate the ferric phosphate from the solution; the second filtrate obtained by the second filter press is cooled to below 40°C by a second cooler, and part of it is directly returned to the acid washing tower for continued circulation, while the other part enters the anode chamber of the electrolytic cell from the inlet of the anode chamber for electrolytic regeneration.

[0015] In some embodiments, during the electrolytic regeneration process, the hydrogen sulfate ions in the second filtrate are oxidized on the anode side of the electrolytic cell to generate persulfate ions, which then react with ammonium ions in the solution to form ammonium persulfate, thereby achieving the cyclic regeneration of the main oxidant in the pickling solution; at least a portion of the dihydrogen phosphate ions in the second filtrate are converted into peroxydiphosphate ions or their protonated form on the anode side of the electrolytic cell, forming ammonium peroxydiphosphate-based synergistic oxidants; the regenerated pickling solution flows out from the outlet of the anode chamber of the electrolytic cell and is pumped back to the pickling tower for circulation.

[0016] This invention also provides a system for acid washing and purification of yellow phosphorus tail gas and for recycling and regenerating the acid washing solution, comprising: an acid washing tower for contacting and reacting yellow phosphorus tail gas with an acid washing solution, wherein the acid washing solution comprises ammonium bisulfate, ammonium dihydrogen phosphate, and ammonium persulfate; an acid washing solution circulation pipeline connected to the acid washing tower for circulating the acid washing solution within the acid washing tower; a first solid-liquid separation device connected to the acid washing solution circulation pipeline for separating suspended elemental sulfur in the acid washing solution; an iron dissolving tank connected to the filtrate outlet of the first solid-liquid separation device for receiving the first filtrate and adding an iron source to form an acid solution containing ferrous ions; a filter connected to the iron dissolving tank for filtering out residual iron source and impurities; and a cooler. The filter is connected to a cooling tank to cool the filtered solution before feeding it into the oxidation tank. The oxidation tank, connected to the cooler, is used to add hydrogen peroxide and ammonia to convert ferrous ions into ferric ions, which then react with phosphate ions to form ferric phosphate precipitate. A second solid-liquid separation device, connected to the oxidation tank, separates the ferric phosphate precipitate and obtains a second filtrate. A second cooler, connected to the filtrate outlet of the second solid-liquid separation device, cools the second filtrate. An electrolytic cell has an anode chamber, the inlet of which is connected to the outlet of the second cooler, for receiving at least a portion of the second filtrate and performing electrolytic regeneration, causing bisulfate ions to generate persulfate ions on the anode side. The outlet of the anode chamber is connected to the pickling tower so that the electrolytically regenerated pickling solution returns to the pickling tower for circulation. The outlet of the second cooler is also connected to the pickling tower so that another portion of the second filtrate returns directly to the pickling tower without passing through the electrolytic cell for continued circulation.

[0017] In some embodiments, the pickling solution circulation pipeline is equipped with a flow regulating valve and a first filter press feed pump. The flow regulating valve is used to separate a portion of the pickling solution from the circulating pickling solution in the pickling tower, and the first filter press feed pump is used to send the separated pickling solution into a first solid-liquid separation device. The iron dissolving tank is equipped with a stirring device, an iron source addition device, a temperature regulating jacket, and a hydrogen exhaust pipe. The oxidation tank is equipped with a hydrogen peroxide inlet, an ammonia inlet, a temperature regulating jacket, and a stirring device. The anode of the electrolytic cell is a metal mesh coated with an inert coating, the inert coating including at least one of lead dioxide, platinum, and boron-doped diamond. The cathode of the electrolytic cell is a nickel mesh or a stainless steel mesh. The outlet of the anode chamber of the electrolytic cell is connected to the pickling tower through an anolyte pump to send the regenerated pickling solution back to the pickling tower for circulation.

[0018] The beneficial effects of the above-mentioned yellow phosphorus tail gas acid washing purification and acid washing liquid recycling method and system of the present invention include at least the following: First, the present invention uses ammonium persulfate as the main oxidant in the pickling solution, and converts hydrogen sulfate ions into persulfate ions through electrolytic regeneration, thereby forming ammonium persulfate, which can reduce the need for external oxidant replenishment.

[0019] Secondly, the present invention separates elemental sulfur generated by hydrogen sulfide oxidation from the pickling solution through a first solid-liquid separation, which helps to reduce further oxidation of elemental sulfur in the acidic oxidation system and realizes the separation and utilization of sulfur element.

[0020] Third, this invention uses iron source, oxidation treatment and acidity adjustment to form ferric phosphate precipitate and separate the phosphorus-containing components generated by the oxidation of phosphine and yellow phosphorus vapors, which is beneficial to the resource utilization of phosphorus in exhaust gas.

[0021] Fourth, the present invention divides the second filtrate into two paths: direct reflux and electrolytic regeneration. A portion of the second filtrate is directly returned to the pickling tower for continued circulation, while the other portion enters the electrolytic cell for main oxidant regeneration. This is beneficial for balancing the pickling solution circulation volume and oxidant regeneration requirements.

[0022] Fifth, the ammonium dihydrogen phosphate in this invention can improve the conductivity of the pickling solution, which is beneficial to the electrolytic regeneration process. In some embodiments, the dihydrogen phosphate ion can also form a peroxydiphosphate synergistic oxidant on the anode side, thereby further enhancing the oxidizing ability of the pickling solution to low-valent phosphorus and low-valent sulfur components.

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Additional aspects and advantages provided by the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of an embodiment of a yellow phosphorus tail gas acid washing purification and acid washing liquid recycling system.

[0025] Figure 2 This is a schematic diagram of the existing yellow phosphorus tail gas purification process.

[0026] The diagram is labeled as follows: 1-Acid washing tower, 2-Acid washing liquid circulation pipeline, 3-First filter press, 4-Iron melting tank, 5-Filter, 6-Cooler, 7-Oxidation tank, 8-Second filter press, 9-Second cooler, 10-Electrolytic cell. Detailed Implementation

[0027] The present invention will now be clearly and completely described in conjunction with the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that: The technical solutions and features provided in the various sections, including the following description, can be combined with each other without conflict. Furthermore, where possible, these technical solutions, features, and related combinations can be given specific technical subject matter and protected by relevant patents.

[0028] The embodiments of the present invention described below are generally only some embodiments and not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of patent protection.

[0029] The terms "comprising," "including," "having," and any variations thereof in this specification, the corresponding claims, and related parts are intended to cover non-exclusive inclusion. Unless otherwise expressly stated, the term "connection" in this invention can be a direct connection or an indirect connection achieved through pipelines, valves, pumps, heat exchangers, or other intermediate components; expressions such as "entering," "feeding," and "returning" can all be achieved through pipelines and corresponding conveying equipment. Other related terms and units can be reasonably interpreted based on the relevant content provided in this specification.

[0030] like Figure 1 As shown, this embodiment provides a system for acid washing purification of yellow phosphorus tail gas and recycling and regenerating the acid washing solution. The system mainly includes an acid washing tower 1, an acid washing solution circulation pipeline 2, a first filter press 3, an iron dissolving tank 4, a filter 5, a cooler 6, an oxidation tank 7, a second filter press 8, a second cooler 9, and an electrolytic cell 10. After the yellow phosphorus tail gas enters the acid washing tower 1, it comes into contact with the acid washing solution circulating within the tower. Phosphine, yellow phosphorus vapor, and hydrogen sulfide in the yellow phosphorus tail gas are oxidized and absorbed in the acid washing solution. Suspended elemental sulfur in the acid washing solution is separated by the first filter press 3. The phosphorus-containing components in the acid washing solution are precipitated as iron after dissolving, oxidation, and acidity adjustment, and then separated by the second filter press 8. Part of the second filtrate obtained from the second filter press 8 is directly returned to the acid washing tower 1 for continued circulation, while the other part enters the anode side of the electrolytic cell 10 for electrolytic regeneration, thereby regenerating the main oxidant in the acid washing solution.

[0031] In this embodiment, the pickling tower 1 is used to bring the yellow phosphorus tail gas into gas-liquid contact with the pickling solution. The yellow phosphorus tail gas can be the tail gas after yellow phosphorus has been recovered through condensation, spraying, or washing during the yellow phosphorus production process. Its main combustible components may include carbon monoxide and hydrogen, and may also contain water vapor, yellow phosphorus vapor, phosphine, hydrogen sulfide, and other components. The pickling tower 1 can be a packed tower, spray tower, plate tower, or other pickling equipment that can achieve sufficient gas-liquid contact. The pickling tower 1 can be equipped with a spray structure, a packing layer, or a gas-liquid distribution structure to ensure sufficient contact between the pickling solution and the yellow phosphorus tail gas, thereby improving the pickling oxidation efficiency.

[0032] In this embodiment, the pickling solution includes ammonium bisulfate, ammonium dihydrogen phosphate, and ammonium persulfate. Ammonium persulfate serves as the primary oxidant in the pickling solution, oxidizing phosphine, yellow phosphorus vapor, and hydrogen sulfide in the yellow phosphorus tail gas. Ammonium bisulfate provides bisulfate ions, enabling them to be oxidized on the anode side during subsequent electrolytic regeneration to generate persulfate ions, which further react with ammonium ions to form ammonium persulfate. Ammonium dihydrogen phosphate increases the conductivity of the pickling solution, allowing the electrolytic regeneration process to proceed under lower resistance conditions, thereby reducing energy consumption during electrolytic regeneration and improving the cycle stability of the pickling solution.

[0033] In one specific embodiment, the pickling solution comprises the following components in parts by weight: 15-20 parts ammonium bisulfate, 20-30 parts ammonium dihydrogen phosphate, and 1-5 parts ammonium persulfate. The pickling solution may also include free sulfuric acid and ammonium peroxydiphosphate oxidizing components. The ammonium peroxydiphosphate oxidizing components include ammonium peroxypyrophosphate, which refers to ammonium peroxydiphosphate oxidizing components containing peroxy bonds formed by dihydrogen phosphate ions under anodic oxidation conditions. Free sulfuric acid is used to maintain the acidic environment of the pickling solution and provides a source of bisulfate ions for electrolytic regeneration. The ammonium peroxydiphosphate oxidizing components can act as synergistic oxidants, participating together with ammonium persulfate in the oxidation of at least one component of phosphine, yellow phosphorus vapor, and hydrogen sulfide in the yellow phosphorus tail gas. It should be noted that the ammonium peroxydiphosphate oxidizing components can be components present during the preparation of the pickling solution, or oxidizing components generated in small quantities by dihydrogen phosphate ions on the anode side during electrolytic regeneration.

[0034] After the yellow phosphorus tail gas enters acid washing tower 1, the ammonium persulfate in the acid washing solution oxidizes the phosphine and yellow phosphorus vapor in the tail gas into phosphoric acid or phosphate-containing components, and oxidizes the sulfide to elemental sulfur. The elemental sulfur exists in suspension in the acid washing solution, while the phosphorus-containing components are dissolved or dispersed in the solution. For ease of understanding, the main reaction process can be represented as follows: phosphine reacts with ammonium persulfate to produce phosphoric acid and ammonium bisulfate; yellow phosphorus vapor reacts with ammonium persulfate to produce phosphoric acid and ammonium bisulfate; hydrogen sulfide reacts with ammonium persulfate to produce elemental sulfur and ammonium bisulfate.

[0035] In practical implementation, the above reaction may include the following main reaction pathway: PH3 + 4(NH4)2S2O8 + 4H2O → H3PO4 + 8NH4HSO4; P4 + 10(NH4)2S2O8 + 16H2O → 4H3PO4 + 20NH4HSO4; H2S + (NH4)2S2O8 → S↓ + 2NH4HSO4.

[0036] The reaction equations are used to illustrate the main material transformation relationships and do not indicate that the pickling solution contains only the above reactions. The pickling solution may also contain various ionic forms and their equilibrium relationships, such as phosphoric acid, dihydrogen phosphate, hydrogen sulfate, ammonium ions, and persulfate.

[0037] The pickling solution circulates within pickling tower 1 via a pickling solution circulation pump. To promptly separate the generated elemental sulfur from the pickling solution, a flow regulating valve and a first filter press feed pump are installed on the pickling solution circulation pipeline 2. The flow regulating valve allows for the continuous or intermittent separation of a portion of the circulating pickling solution from pickling tower 1. This separated pickling solution is then fed into the first filter press 3 via the first filter press feed pump. The first filter press 3 filters out the suspended elemental sulfur from the pickling solution, yielding an elemental sulfur filter cake and a first filtrate. The elemental sulfur filter cake can be discharged as a sulfur-containing byproduct and utilized for resource recovery, such as for subsequent acid production or the preparation of other sulfur-containing products.

[0038] By continuously or intermittently separating a portion of the pickling solution and performing a first solid-liquid separation, the residence time of elemental sulfur in the acidic oxidation system containing ammonium persulfate can be shortened, reducing the proportion of elemental sulfur further oxidized to sulfate. This, in turn, helps to increase the proportion of sulfur elemental recovered in the form of elemental sulfur. This split-flow filtration process is not simply a solid-liquid separation step, but rather works in conjunction with the stability of elemental sulfur in the pickling oxidation system to remove it from the strongly oxidizing acidic environment as promptly as possible after its formation.

[0039] The first filtrate obtained from the first filter press 3 enters the iron-dissolving tank 4. The iron-dissolving tank 4 may be equipped with a stirring device, an iron source addition device, a temperature regulating jacket, and a hydrogen exhaust pipe. The iron source addition device is used to add an iron source into the iron-dissolving tank 4. The iron source is preferably iron powder, but other iron-containing materials capable of providing ferrous ions under acidic conditions can also be used. When iron powder is used, the iron powder reacts with hydrogen ions in the first filtrate under stirring to generate ferrous ions and hydrogen gas, consuming part of the acidity in the first filtrate. This process provides an iron ion source for the subsequent ferric phosphate precipitation process and utilizes the acidity of the first filtrate itself to dissolve iron and reduce acidity, reducing the need for significant neutralization using a simple alkaline regulator.

[0040] In practical implementation, the pH of the liquid phase in the iron melting tank 4 can be controlled within the range of 0.5 to 1.8, preferably within the range of 0.5 to 1.5, by controlling the amount of iron powder added. The temperature of the liquid phase in the iron melting tank 4 can be controlled within the range of 60℃ to 90℃ through the jacket. Hydrogen gas generated during the iron melting process is discharged through the exhaust pipe at the top of the iron melting tank 4. The hydrogen exhaust pipe can be connected to a safety venting, recovery, or tail gas treatment device to prevent hydrogen accumulation around the equipment. Since the iron melting tank 4 contains acidic liquid, iron powder, and generated hydrogen gas, flame arrestors, ventilation, hydrogen detection, or explosion-proof measures can be implemented in actual engineering according to safety requirements.

[0041] The acid solution from the reaction in the iron melting tank 4 enters the filter 5. The filter 5 is used to remove residual iron powder and impurities, preventing residual iron powder or solid impurities from entering the subsequent oxidation tank 7, which could adversely affect hydrogen peroxide consumption, ferric phosphate precipitation morphology, or product purity. The filter 5 can be a cartridge filter, bag filter, candle filter, or other solid-liquid filtration equipment suitable for acidic systems.

[0042] The filtered solution is cooled to below 50°C by cooler 6 before entering oxidation tank 7. This cooling step is used to adjust the solution temperature to a range suitable for subsequent hydrogen peroxide oxidation and ferric phosphate precipitation, avoiding excessively high temperatures that could lead to rapid decomposition of hydrogen peroxide or enhanced side reactions. Cooler 6 can be a shell-and-tube heat exchanger, plate heat exchanger, jacketed heat exchanger, or other acid-resistant heat exchange equipment.

[0043] Oxidation tank 7 is used to oxidize ferrous ions to ferric ions, and then react the ferric ions with phosphate ions to form ferric phosphate precipitate. Oxidation tank 7 may be equipped with a stirring device, a hydrogen peroxide inlet, an ammonia inlet, and a temperature control jacket. In oxidation tank 7, hydrogen peroxide is added to the solution containing ferrous ions to oxidize them to ferric ions; simultaneously, ammonia is added to adjust the pH of the solution, ensuring the system is within an acidic range conducive to the formation of ferric phosphate precipitate.

[0044] In one specific embodiment, hydrogen peroxide is added to the oxidation tank 7 to oxidize ferrous ions to ferric ions; ammonia is added to adjust the pH of the solution to the range of 1.5 to 2.5; and the liquid phase temperature in the oxidation tank 7 is controlled within the range of 50°C to 60°C through the jacket of the oxidation tank 7. Under the above pH and temperature conditions, phosphate ions react with ferric ions to form ferric phosphate precipitate. Since phosphate ions can exist in acidic solutions in the forms of phosphoric acid, dihydrogen phosphate, hydrogen phosphate, etc., the phosphate ions referred to in this embodiment can be understood as phosphate-containing components that can react with ferric ions to form ferric phosphate precipitate.

[0045] Hydrogen peroxide can be added in one go, in batches, or continuously dripped. To improve the controllability of the conversion of ferrous iron to ferric iron, hydrogen peroxide is preferably added in batches or continuously dripped, and the amount of hydrogen peroxide added can be controlled according to at least one of the redox potential, ferrous ion concentration, and ferric ion concentration. This method can reduce the rapid decomposition or non-target side reactions of hydrogen peroxide in acidic iron-containing systems and ensure a more complete conversion of ferrous iron to ferric iron.

[0046] During the formation of iron phosphate precipitate, at least one of the following amounts can be controlled based on the phosphate concentration, total iron concentration, and pH of the solution: the amount of iron source added, the amount of hydrogen peroxide added, and the amount of ammonia added. This ensures that the reaction between ferric ions and phosphate ions proceeds towards the formation of iron phosphate precipitate. Through this control, phosphorus-containing components generated from the oxidation of tail gas and enriched in the pickling solution can be precipitated and separated as iron phosphate, while avoiding the formation of excessive non-target iron precipitates due to excess iron ions. The iron phosphate precipitate can be further washed, dried, and purified to serve as a phosphorus-containing iron precursor for the preparation of lithium iron phosphate cathode materials, or as a resource for the utilization of other phosphorus-containing iron materials.

[0047] The suspension containing ferric phosphate precipitate generated in oxidation tank 7 is fed into second filter press 8 via a feed pump. Second filter press 8 serves as a second solid-liquid separation device to separate ferric phosphate from the solution, yielding ferric phosphate solid and a second filtrate. Second filter press 8 can be a plate and frame filter press, a diaphragm filter press, or other solid-liquid separation equipment suitable for separating ferric phosphate precipitate. The obtained ferric phosphate solid can be further washed, dried, and purified to reduce the content of entrained ammonium salts, sulfates, or free acid.

[0048] The second filtrate obtained from the second filter press 8 is cooled to below 40°C by the second cooler 9 and then split for further processing. A portion of the second filtrate is directly returned to the pickling tower 1 for continued circulation, while the other portion enters the anode chamber of the electrolytic cell 10 through the inlet for electrolytic regeneration. By dividing the second filtrate into direct reflux and electrolytic regeneration paths, the portion of the pickling solution requiring regeneration can be electrolyzed while maintaining the circulating volume of the pickling tower 1, thus replenishing the main oxidant, ammonium persulfate. The direct reflux ratio and the electrolytic regeneration ratio can be adjusted according to the operating load of the pickling tower 1, the concentration of ammonium persulfate in the pickling solution, the oxidizing capacity of the pickling solution, the concentration of harmful components in the tail gas, or the system's processing capacity.

[0049] Electrolytic cell 10 is used to electrolytically regenerate the second filtrate entering the anode chamber. Electrolytic cell 10 may include an anode chamber and a cathode-side reaction zone. The anode chamber is equipped with an anode, and the cathode-side reaction zone is equipped with a cathode. The inlet of the anode chamber is connected to the outlet of the second cooler 9 to receive at least a portion of the second filtrate; the outlet of the anode chamber is connected to the pickling tower 1 to return the electrolytically regenerated pickling solution to the pickling tower 1 for circulation. In a specific implementation, the outlet of the anode chamber can be connected to the pickling tower 1 via an anolyte pump to stably return the regenerated pickling solution to the pickling tower 1.

[0050] On the anode side of electrolytic cell 10, hydrogen sulfate ions in the second filtrate are oxidized to persulfate ions under the action of direct current. This can be represented by the following electrode reaction: .

[0051] The generated persulfate ions react with ammonium ions in the solution to form ammonium persulfate, thereby achieving the cyclic regeneration of the main oxidant in the pickling solution. The regenerated pickling solution flows out from the outlet of the anode chamber of electrolytic cell 10 and is pumped back to pickling tower 1 for circulation via the anolyte pump. Through this electrolytic regeneration process, the bisulfate ions generated in the pickling solution due to the oxidation of phosphine, yellow phosphorus vapor, and hydrogen sulfide can be reconstituted into persulfate ions with strong oxidizing power, and then form ammonium persulfate, reducing the amount of external oxidant required.

[0052] On the anode side, in addition to the main reaction of bisulfate ions forming persulfate ions, there may also be a side reaction in which water is oxidized to produce oxygen. In actual operation, the selectivity of bisulfate ion conversion to persulfate ions can be improved and the proportion of oxygen evolution side reactions can be reduced by selecting anode materials, controlling current density, controlling electrolysis temperature, controlling anolyte acidity and residence time.

[0053] On the cathode side of electrolytic cell 10, hydrogen ions or water molecules in the solution can accept electrons and undergo a reduction reaction to generate hydrogen gas. The main reaction on the cathode side can be represented as follows: ; Alternatively, in localized areas with low hydrogen ion concentrations, a reaction can occur to reduce water to hydrogen. The hydrogen produced on the cathode side can be discharged through the cathode-side exhaust port and enter a safe venting, recovery, or tail gas treatment device. Since hydrogen may be generated on the cathode side, the electrolyzer 10 and its surrounding pipelines can be equipped with explosion-proof, ventilation, flame-retardant, hydrogen detection, or safety interlocking measures as needed for the project.

[0054] In one embodiment, the electrolytic cell 10 may be provided with an anode chamber and a cathode chamber, which can be separated by a diaphragm, ion exchange membrane, porous partition, or other partitioning structure. This partitioning structure reduces the likelihood of persulfate ions generated on the anode side migrating to the cathode side and being reduced and consumed, while allowing necessary ion migration to maintain the electrolytic circuit. It should be noted that the partitioning structure can be selected based on the type of electrolytic cell 10, the composition of the pickling solution, current efficiency requirements, and equipment cost; not all embodiments must use the same type of partitioning structure.

[0055] The anode of the electrolytic cell 10 can be a metal mesh coated with an inert coating. The inert coating may include at least one of lead dioxide, platinum, and boron-doped diamond. These anode materials are advantageous in acidic systems as they can withstand higher anode potentials and promote the oxidation of bisulfate ions to persulfate ions. The cathode of the electrolytic cell 10 can be a nickel mesh or a stainless steel mesh. Nickel mesh or stainless steel mesh has good conductivity and corrosion resistance, making it suitable as a cathode material in acidic ammonium-containing systems. In practical applications, the anode and cathode can be mesh-like, plate-like, tubular, or other forms suitable for the structure of the electrolytic cell 10.

[0056] Because the pickling solution contains ammonium dihydrogen phosphate, the dihydrogen phosphate ions in the ammonium dihydrogen phosphate may at least partially generate peroxydiphosphate ions or their protonated form on the anode side, forming a peroxydiphosphate synergistic oxidant with ammonium ions. This oxidizing component can be returned to pickling tower 1 with the regenerated pickling solution and participate in the oxidation of at least one component among phosphine, yellow phosphorus vapor, and hydrogen sulfide together with ammonium persulfate. This process can be considered the preferred synergistic oxidation mechanism of the present invention without affecting the establishment of ammonium persulfate as the main oxidant and the electrolytic regeneration main line.

[0057] In this embodiment, the outlet side of the second cooler 9 is also connected to the pickling tower 1, so that another portion of the second filtrate can be directly returned to the pickling tower 1 for continued circulation without passing through the electrolytic cell 10. That is, after being cooled by the second cooler 9, the second filtrate is divided into two paths: one path flows directly back to the pickling tower 1 to continue participating in pickling as circulating pickling liquid; the other path enters the anode chamber of the electrolytic cell 10 for electrolytic regeneration, generating a regenerated pickling liquid containing ammonium persulfate, which is then returned to the pickling tower 1. This diversion method can balance the circulating liquid volume requirements and oxidant regeneration requirements of the pickling tower 1, avoiding excessive equipment load caused by all circulating liquid entering the electrolytic cell 10, and also avoiding insufficient oxidizing capacity of the pickling liquid due to an excessively high proportion of unregenerated circulating liquid.

[0058] In this embodiment, the pickling solution circulation pipeline 2, the first filter press 3, the iron melting tank 4, the filter 5, the cooler 6, the oxidation tank 7, the second filter press 8, the second cooler 9, and the electrolytic cell 10 together form a pickling solution treatment and regeneration cycle. Hydrogen sulfide in the yellow phosphorus tail gas is mainly separated from the first filter press 3 as elemental sulfur after pickling and oxidation; phosphine and yellow phosphorus vapor in the yellow phosphorus tail gas form phosphorus-containing components after pickling and oxidation, and are further separated from the second filter press 8 as ferric phosphate; the second filtrate is returned to the pickling tower 1 after direct reflux and electrolytic regeneration, thus realizing the recycling of the pickling solution.

[0059] Compared with existing multi-stage acid washing with concentrated sulfuric acid and lime milk alkaline washing processes, this embodiment combines ammonium persulfate acid washing oxidation, electrolytic regeneration, elemental sulfur separation, and ferric phosphate precipitation separation. This allows the phosphorus and sulfur elements in the yellow phosphorus tail gas to be converted into easily recyclable solid products in the acid washing solution circulation system. Furthermore, the main oxidant in the acid washing solution can be regenerated through electrolysis. This helps to reduce the consumption of concentrated sulfuric acid and alkaline washing agents, reduce the amount of waste acid and solid by-products generated, and improve the resource utilization level of the yellow phosphorus tail gas purification process.

[0060] The foregoing has described the relevant content of the present invention. Those skilled in the art will be able to implement the present invention based on these descriptions. All other embodiments obtained by those skilled in the art based on the foregoing content of this specification without inventive effort should fall within the scope of the present invention.

Claims

1. A method for acid washing and purification of yellow phosphorus tail gas and recycling of acid washing solution, characterized in that: include: The yellow phosphorus tail gas is introduced into the pickling tower and reacts with the pickling solution circulating in the pickling tower. The pickling solution includes ammonium bisulfate, ammonium dihydrogen phosphate, and ammonium persulfate. The ammonium persulfate is the main oxidant in the pickling solution, the ammonium bisulfate provides bisulfate ions for electrolytic regeneration of ammonium persulfate, and the ammonium dihydrogen phosphate is used to improve the conductivity of the pickling solution. In the pickling tower, the ammonium persulfate oxidizes the phosphine and yellow phosphorus vapor in the yellow phosphorus tail gas into phosphoric acid or phosphate in the form of phosphoric acid or phosphate, and oxidizes the sulfide in the yellow phosphorus tail gas into elemental sulfur, so that the elemental sulfur exists in the pickling solution in a suspended state. At least a portion of the pickling liquid containing suspended elemental sulfur is separated from the circulating pickling liquid in the pickling tower, and the separated pickling liquid is subjected to a first solid-liquid separation to separate the elemental sulfur and obtain a first filtrate. An iron source is added to the first filtrate, causing the iron source to react with hydrogen ions in the first filtrate to form ferrous ions and consume part of the acidity in the first filtrate. The first filtrate containing ferrous ions is oxidized to convert at least some of the ferrous ions into ferric ions, and the acidity of the first filtrate is adjusted so that the ferric ions react with the phosphorus-containing components to form ferric phosphate precipitate. A second solid-liquid separation is performed on the suspension containing the ferric phosphate precipitate to obtain ferric phosphate solid and a second filtrate; At least a portion of the second filtrate is fed into the anode side of the electrolytic cell for electrolytic regeneration, so that the hydrogen sulfate ions in the second filtrate are oxidized on the anode side to generate persulfate ions. The persulfate ions react with ammonium ions to form ammonium persulfate. The regenerated pickling solution is returned to the pickling tower for recycling.

2. The method according to claim 1, characterized in that: The pickling solution comprises the following components in parts by weight: 15 to 20 parts of ammonium bisulfate, 20 to 30 parts of ammonium dihydrogen phosphate, and 1 to 5 parts of ammonium persulfate. Furthermore, the pickling solution also includes free sulfuric acid and ammonium peroxydiphosphate oxidizing components, wherein the ammonium peroxydiphosphate oxidizing components include ammonium peroxypyrophosphate. The free sulfuric acid is used to maintain the acidic environment of the pickling solution and to provide a source of bisulfate ions for electrolytic regeneration; the ammonium peroxydiphosphate oxidizing component is used as a synergistic oxidant to participate in the oxidation of at least one component of phosphine, yellow phosphorus vapor and hydrogen sulfide in the yellow phosphorus tail gas together with the ammonium peroxydisulfate.

3. The method according to claim 1, characterized in that: A portion of the pickling liquid is continuously or intermittently separated from the circulating pickling liquid in the pickling tower for the first solid-liquid separation, so as to shorten the residence time of the elemental sulfur in the acidic oxidation system containing ammonium persulfate and reduce the proportion of the elemental sulfur that is further oxidized. The first solid-liquid separation is carried out using a first filter press. The separated pickling liquid is fed into the first filter press via a first filter press feed pump. The first filter press is used to filter out elemental sulfur suspended in the pickling liquid. The first filtrate obtained from the first filter press enters the iron melting tank.

4. The method according to claim 1, characterized in that: The iron source is iron powder, which reacts with hydrogen ions in the first filtrate under stirring in the iron melting tank to generate ferrous ions and hydrogen gas. By controlling the amount of iron powder added, the pH of the liquid phase in the iron melting tank is controlled within the range of 0.5 to 1.8; The liquid phase temperature inside the iron melting tank is controlled within the range of 60 to 90°C by means of the jacket of the iron melting tank. The hydrogen gas is discharged through the exhaust pipe at the top of the melting iron tank.

5. The method according to claim 1, characterized in that: The first filtrate enters the filter after an iron source is added and ferrous ions are formed, in order to remove residual iron source and impurities; The filtered solution is cooled to below 50°C by a cooler before entering the oxidation tank. In the oxidation tank, hydrogen peroxide is added to the solution containing ferrous ions to oxidize the ferrous ions to ferric ions, and ammonia is added to adjust the pH to the range of 1.5 to 2.

5. The liquid phase temperature inside the oxidation tank is controlled within the range of 50℃ to 60℃ by means of the jacket of the oxidation tank. Under the specified pH and temperature conditions, phosphate ions react with ferric ions to form ferric phosphate precipitate.

6. The method according to claim 1, characterized in that: The hydrogen peroxide is added in batches or continuously, and the amount of hydrogen peroxide added is controlled according to at least one of the redox potential, the concentration of ferrous ions, and the concentration of ferric ions. And / or, during the formation of ferric phosphate precipitate, at least one of the following is controlled according to the concentration of phosphate, the total iron concentration and the pH in the solution: the amount of iron source added, the amount of hydrogen peroxide added and the amount of ammonia added, so that the reaction between ferric ions and phosphate ions proceeds in the direction of forming ferric phosphate precipitate.

7. The method according to claim 1, characterized in that: The second solid-liquid separation is carried out using a second filter press; The suspension containing ferric phosphate precipitate generated by the reaction is fed into the second filter press by the second filter press feed pump to separate the ferric phosphate from the solution; After the second filtrate obtained from the second filter press is cooled to below 40°C by the second cooler, part of it is directly returned to the acid washing tower for continued circulation, and the other part enters the anode chamber of the electrolytic cell from the inlet of the anode chamber for electrolytic regeneration.

8. The method according to claim 1, characterized in that: During the electrolytic regeneration process, the hydrogen sulfate ions in the second filtrate are oxidized on the anode side of the electrolytic cell to generate persulfate ions. The persulfate ions react with ammonium ions in the solution to form ammonium persulfate, thereby achieving the cyclic regeneration of the main oxidant in the pickling solution. At least a portion of the dihydrogen phosphate ions in the second filtrate are converted into diphosphate ions or their protonated form containing peroxy bonds on the anode side of the electrolytic cell, and form ammonium peroxy diphosphate synergistic oxidants with ammonium ions, wherein the ammonium peroxy diphosphate synergistic oxidants include ammonium peroxy pyrophosphate. The regenerated pickling solution flows out from the outlet of the anode chamber of the electrolytic cell and is pumped back to the pickling tower for circulation.

9. A system for acid washing and purification of yellow phosphorus tail gas and recycling and regenerating acid washing solution, characterized in that, include: A pickling tower is used to react yellow phosphorus tail gas with a pickling solution, wherein the pickling solution includes ammonium hydrogen sulfate, ammonium dihydrogen phosphate and ammonium persulfate. A pickling solution circulation pipeline is connected to the pickling tower to circulate the pickling solution within the pickling tower. The first solid-liquid separation device is connected to the pickling solution circulation pipeline and is used to separate elemental sulfur suspended in the pickling solution; The iron melting tank is connected to the filtrate outlet of the first solid-liquid separation device and is used to receive the first filtrate and add an iron source to form an acid solution containing ferrous ions. A filter, connected to the iron melting tank, is used to filter out residual iron sources and impurities; A cooler, connected to the filter, is used to cool the filtered solution before sending it into the oxidation tank; An oxidation tank, connected to the cooler, is used to add hydrogen peroxide and ammonia to convert ferrous ions into ferric ions and react with phosphate ions to form ferric phosphate precipitate. The second solid-liquid separation device is connected to the oxidation tank and is used to separate the ferric phosphate precipitate and obtain the second filtrate. The second cooler is connected to the filtrate outlet of the second solid-liquid separation device and is used to cool the second filtrate. An electrolytic cell has an anode chamber, the inlet of which is connected to the outlet side of the second cooler for receiving at least a portion of the second filtrate and performing electrolytic regeneration, so that hydrogen sulfate ions are converted into persulfate ions on the anode side; The outlet of the anode chamber is connected to the pickling tower so that the pickling liquid after electrolytic regeneration can be returned to the pickling tower for circulation; the outlet of the second cooler is also connected to the pickling tower so that another part of the second filtrate can be returned directly to the pickling tower for continued circulation without passing through the electrolytic cell.

10. The system according to claim 9, characterized in that: The pickling solution circulation pipeline is equipped with a flow regulating valve and a first filter press feed pump. The flow regulating valve is used to separate a portion of the pickling solution from the circulating pickling solution in the pickling tower, and the first filter press feed pump is used to send the separated pickling solution into the first solid-liquid separation device. The iron melting tank is equipped with a stirring device, an iron source addition device, a temperature regulating jacket, and a hydrogen exhaust pipe. The oxidation tank is equipped with a hydrogen peroxide inlet, an ammonia inlet, a temperature regulating jacket, and a stirring device. The anode of the electrolytic cell is a metal mesh coated with an inert coating, the inert coating comprising at least one of lead dioxide, platinum, and boron-doped diamond. The cathode of the electrolytic cell is a nickel mesh or a stainless steel mesh. The outlet of the anode chamber of the electrolytic cell is connected to the pickling tower via an anolyte pump to send the regenerated pickling solution back to the pickling tower for circulation.

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