Method for purifying titanium chloride white waste acid

Abstract

The present application relates to titanium white processing equipment technical field, specifically for chlorinated titanium white waste acid purification method, including using four-stage irreversible continuous purification process treatment containing hydrochloric acid, titanium oxychloride, silicic acid colloid, sulfate radical, trivalent iron impurity chlorinated titanium white chlorination section tail gas waste acid, whole process not neutralization system hydrochloric acid, steps as follows: S1, oxidation pretreatment; S2, barium chloride precipitation removes sulfate radical; S3, strong hydrochloric acid environment flocculation removes silicon; S4, titanium removal iron with phosphoric acid. The chlorinated titanium white waste acid purification method, solve the problem of low purity of titanium product caused by removing silicon and sulfate radical before titanium in the prior art. The present application adopts irreversible process arrangement of oxidation pretreatment, removing sulfate radical, removing silicon and titanium precipitation, removes silicic acid colloid and sulfate radical in advance, the generated titanium phosphate precipitate in the subsequent process is not wrapped with impurities, the purity of titanium slag is significantly improved, and there is no problem of large loss of extractant and silicon impurities.

Description

Technical Field

[0001] This invention relates to the field of titanium dioxide processing equipment technology, and more specifically, to a method for purifying waste acid from titanium dioxide chlorination. Background Technology

[0002] The tail gas from the chlorination process of titanium dioxide is absorbed by water or dilute hydrochloric acid, generating a large amount of waste acid containing 20%~30% hydrochloric acid, titanium chloride oxide, silica colloid, sulfate, and ferric iron. Direct discharge of this waste acid wastes hydrochloric acid resources and pollutes the environment. The impurities also easily cause pipe scaling, affecting waste acid reuse and the purification of valuable titanium slag. Existing representative technologies, such as patent CN112429780B, employ segmented extraction to recover valuable elements from the waste acid. This scheme first extracts titanium and then removes silicon and sulfate. Silica colloid and sulfate easily encapsulate titanium complexes, reducing product purity. Desiliconization requires neutralization with alkali, resulting in significant loss of hydrochloric acid. Furthermore, there is no pre-treatment with oxidation. The current process is prone to damaging the extractant and has poor system stability. Insufficient removal of sulfate ions can easily cause scaling on the equipment. Furthermore, there is a lack of automated closed-loop control equipment. At the same time, conventional lime precipitation, single flocculation, distillation, and neutralization processes in the industry also have problems such as introducing calcium scale, single impurity removal, high energy consumption, and complete loss of hydrochloric acid. Currently, there is still a lack of an irreversible four-stage synergistic purification process of "oxidation pretreatment → sulfate removal → strong acid desilication → phosphate titanium precipitation". It is difficult to simultaneously and deeply remove various impurities, retain high concentrations of hydrochloric acid throughout the process, and obtain high-purity titanium phosphate precipitate. There is also a gap in the availability of integrated automatic processing equipment adapted to this process. Summary of the Invention

[0003] The purpose of this invention is to provide a method for purifying waste acid from titanium dioxide, in order to solve the problems mentioned in the background art, such as the easy destruction of the extractant by the non-oxidative pretreatment process, poor system stability, insufficient sulfate removal depth causing equipment scaling, and lack of automated closed-loop control equipment. At the same time, conventional lime precipitation, single flocculation, distillation, and neutralization processes in the industry also have problems such as the introduction of calcium scale, single impurity removal, high energy consumption, and complete loss of hydrochloric acid.

[0004] To achieve the above objectives, this invention provides a method for purifying waste acid from titanium dioxide chlorination, comprising a four-stage irreversible continuous purification process to treat waste acid from the chlorination stage of titanium dioxide chlorination, which contains hydrochloric acid, titanium chloride oxide, silica colloid, sulfate, and ferric iron impurities. The hydrochloric acid in the system is not neutralized throughout the process. The steps are as follows:

[0005] S1. Oxidation pretreatment: Add 27.5%~30% hydrogen peroxide by mass to the waste acid at a dosage of 0.3~1.0 g / L, stir and react at 30~50℃ for 10~20 min to oxidize trace Fe²⁺ and sulfite reducing impurities to higher oxidation states;

[0006] S2. Barium chloride precipitation to remove sulfate: Add anhydrous barium chloride or barium chloride dihydrate solid in batches, control the molar ratio of Ba²⁺ to SO₄²⁻ to 1.0:1~1.2:1, stir and react at 30~50℃ for 30~60 min, and filter to separate the sulfate ions after they are converted into barium sulfate precipitate.

[0007] S3. Strong hydrochloric acid environment flocculation to remove silica: Heat the system to 60~80℃, add 10g / L industrial gelatin flocculant, the dosage is 1.0~2.0g / L; first stir rapidly at 150~200rpm for 5~15min, then stir slowly at 30~50rpm for 20~30min, let stand and settle for 30~60min, filter to remove the flocs formed by silica colloids and animal glue;

[0008] S4. Phosphoric acid precipitation to remove iron from titanium: Control the temperature at 60~80℃, maintain the pH of the system at 1.5~3.0, add 85% industrial phosphoric acid in batches, with a phosphoric acid to titanium molar ratio of 1.1:1~1.5:1, stir the reaction for 1~2 hours, titanium and trivalent iron will be converted into titanium phosphate and iron phosphate coprecipitates respectively and removed by filtration, finally obtaining purified waste acid with a hydrochloric acid concentration >18%.

[0009] This setup utilizes four irreversible processes—oxidative pretreatment, sulfate removal, strong acid desilication, and phosphate titanium precipitation—to work together without consuming hydrochloric acid. It simultaneously and deeply removes reducing impurities, sulfate, silica colloids, titanium, and ferric iron from waste acid. The purified hydrochloric acid concentration remains above 18%, allowing for direct reuse or export. At the same time, titanium and iron are simultaneously precipitated and separated, realizing the resource utilization of solid slag.

[0010] As a preferred embodiment of the present invention, the method is implemented using a complete set of purification equipment; the complete set of equipment consists of an oxidation pretreatment reactor, a sulfate removal precipitation reactor, a high-temperature flocculation and silica removal reactor, a phosphate titanium precipitation reactor, a multi-stage precision filter unit, and a purified acid product storage tank connected in series along the waste acid flow direction. Each reactor is equipped with a reagent dosing unit, a temperature control component, a stirring mechanism, and online monitoring instruments. The entire set of equipment is equipped with a PLC automatic control system, and the reactors are connected to a centrifugal pump via acid-resistant pipelines.

[0011] This setup, through the series connection of multiple process equipment and the automated control system, enables continuous automated treatment of waste acid. Each process is independently equipped with monitoring, dosing, stirring, and temperature control units, ensuring stable process connections, reducing manual intervention, and making it suitable for large-scale continuous industrial production.

[0012] As a preferred embodiment of the present invention, the oxidation pretreatment reactor is equipped with a hydrogen peroxide quantitative dosing unit and an online ferrous monitoring probe, and the stirring speed inside the reactor is 200~300rpm, which is suitable for the working condition where the primary Fe²⁺ content of waste acid is <0.1g / L.

[0013] This setting allows for precise quantitative addition of hydrogen peroxide, real-time monitoring of ferrous ion content, stable oxidation environment, and thorough oxidation of trace reducing impurities. It also prevents reducing substances from interfering with subsequent precipitation processes. The stirring speed is adapted to the mass transfer requirements of the oxidation reaction, ensuring a complete and thorough oxidation reaction.

[0014] As a preferred embodiment of the present invention, the sulfate removal precipitation vessel is equipped with a barium chloride batch feeding bin and an online EDTA sulfate titration analyzer. The analyzer signal is connected to a PLC for closed-loop control of the barium chloride feeding amount. A separate barium sulfate slag discharge port is set at the bottom of the vessel, and the sulfate removal rate is ≥95%.

[0015] This setup relies on online sulfate detection to achieve precise barium chloride dosing, avoiding waste from excessive reagents or insufficient dosing leading to substandard impurity removal. Batch dosing improves the barium sulfate precipitation effect, and a separate slag discharge port allows for the separate collection of barium sulfate slag, resulting in a high degree of sulfate removal.

[0016] As a preferred embodiment of the present invention, the high-temperature flocculation desiliconization kettle is equipped with a steam jacket heating system and inclined plate settling internals. It relies on the high hydrochloric acid environment of the waste acid itself to remove silicon, without the need for external alkali to adjust the pH, and the silicon removal rate is ≥90%.

[0017] This setup utilizes the existing highly acidic environment of waste acid to achieve animal glue flocculation and desilication, eliminating the need to add alkali solution to neutralize hydrochloric acid. The steam jacket provides stable temperature control, and the inclined plate sedimentation improves the sedimentation efficiency of silica flocs, ensuring thorough removal of silicon impurities without consuming hydrochloric acid resources.

[0018] As a preferred embodiment of the present invention, the phosphate titanium precipitation reactor is equipped with an online pH controller, and the phosphate is added in batches to strictly control the pH at the reaction endpoint to be greater than 1.5, thereby avoiding the precipitation of titanium phosphate by silica and sulfate ions and improving the purity of titanium slag.

[0019] This setup allows for precise online pH control of the system. The addition of phosphoric acid in batches can slowly generate titanium phosphate precipitate. Since sulfate and silicon have already been removed in the pretreatment process, there will be no problem of colloidal encapsulation and precipitation, which greatly improves the purity of titanium phosphate solid slag and facilitates the recycling of titanium resources.

[0020] As a preferred embodiment of the present invention, the multi-stage precision filtration unit includes multiple plate and frame filter presses, which can respectively retain barium sulfate slag, silicon-animal flocculents, and titanium phosphate solid slag. Each type of waste residue is collected separately in separate compartments to achieve classified resource recycling.

[0021] This setup allows for the grading and filtration of sediments generated from different processes, with each type of solid residue collected and stored separately. Barium sulfate and titanium phosphate can be recycled as chemical raw materials, improving overall resource utilization and reducing hazardous waste disposal costs.

[0022] As a preferred embodiment of the present invention, all reactor bodies, pipelines, and stirring paddles in the entire device that come into contact with waste acid and reagents are made of enamel, PTFE-lined or Hastelloy-lined materials that are resistant to strong acids and corrosion. Buffer tanks are set between adjacent reactors to stabilize the feed flow rate.

[0023] This feature utilizes acid-resistant materials to adapt to highly corrosive conditions caused by high concentrations of hydrochloric acid, extending the equipment's service life. The buffer tank eliminates fluctuations in feed flow, ensuring stable reaction conditions in each process and consistently meeting impurity removal standards.

[0024] As a preferred embodiment of the present invention, both the barium chloride removal of sulfate and the phosphate precipitation of titanium reactions produce hydrogen chloride, and the process hydrochloric acid retention rate is ≥97%; the purified waste acid indicators meet the following requirements: SO4²⁻<0.5g / L, silicon<0.3g / L, titanium<0.5g / L, and total iron<0.1g / L, which can be directly concentrated and reused or sold externally.

[0025] This setup utilizes hydrogen chloride, a byproduct of the two-stage core precipitation reaction, to compensate for hydrochloric acid loss, resulting in a high hydrochloric acid retention rate. After purification, all impurity indicators are controlled at extremely low levels, ensuring stable purified acid quality. This allows for reuse and resale without additional deep treatment, reducing subsequent processing energy consumption and costs.

[0026] As a preferred embodiment of the present invention, the order of oxidation pretreatment, sulfate removal, silicon removal, and titanium removal cannot be changed; if it is changed to titanium removal first and then silicon and sulfate removal, defects will occur, such as titanium phosphate precipitate being encapsulated by silica colloid, increased consumption of barium chloride reagent, and a significant decrease in sulfate removal efficiency.

[0027] This setup limits the irreversible process layout, removes sulfate and silicon impurities in the pre-process to prevent them from interfering with titanium phosphate precipitation, reduces the ineffective consumption of barium chloride reagent, ensures the impurity removal efficiency and solid slag purity of each process, and avoids the inherent defects of traditional processes in terms of process sequence.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. This method for purifying waste acid from titanium dioxide chloride production solves the problem of low titanium product purity caused by prior titanium extraction followed by silicon and sulfate removal, as seen in the comparative patent. The invention employs an irreversible process arrangement of oxidation pretreatment → sulfate removal → silicon removal → titanium precipitation, pre-removing silicic acid colloids and sulfate ions. This ensures that the subsequently generated titanium phosphate precipitate is free of impurities, significantly improving the purity of the titanium slag. It also eliminates the problems of silicon impurities carried by the extractant and high reagent consumption.

[0030] 2. This method for purifying waste acid from titanium dioxide chloride production overcomes the shortcomings of existing technologies that require alkali neutralization for desilication and result in significant hydrochloric acid loss. This invention directly utilizes the waste acid's own high hydrochloric acid content (over 20%) to complete animal glue flocculation and desilication, eliminating the need for alkali addition. Furthermore, the barium chloride removal of sulfate and the phosphate precipitation of titanium both produce hydrogen chloride as a byproduct. The entire process maintains a hydrochloric acid retention rate of no less than 97%, and the purified waste acid salt concentration remains above 18%, saving additional energy consumption for concentration. The purified acid can be directly reused in titanium dioxide chloride production or exported.

[0031] 3. This method for purifying waste acid from titanium dioxide chloride overcomes the shortcomings of existing processes, such as the lack of oxidation pretreatment and poor system stability. Hydrogen peroxide oxidation pretreatment can completely eliminate trace amounts of reducing impurities such as ferrous sulfate and sulfite in the waste acid, preventing long-term accumulation of impurities that interfere with the precipitation reaction. The equipment operates stably under long-term continuous operation, without the continuous precipitation and scaling of sulfates, and without the need for frequent shutdowns for cleaning.

[0032] 4. This method for purifying waste acid from titanium dioxide chloride production incorporates an integrated, automated control system, addressing the issues of traditional processes such as lack of closed-loop control, high manual labor intensity, and significant fluctuations in purification indicators. Each process, including reagent dosing, temperature, stirring, pH, and sulfate concentration, is monitored online and automatically adjusted via PLC, enabling continuous, large-scale waste acid treatment. Multi-stage filtration units collect barium sulfate slag, silica flocculent slag, and titanium phosphate slag separately, allowing for individual resource utilization of each type of solid slag, thus reducing hazardous waste disposal costs.

[0033] 5. This method for purifying waste acid from titanium dioxide produced by the chloride process overcomes the multiple drawbacks of conventional processes such as lime precipitation, single flocculation, distillation, and neutralization. This invention does not introduce calcium ions to form calcium scale, and can simultaneously and deeply remove multiple impurities such as sulfate, silicon, titanium, and iron. It eliminates the need for high-temperature distillation and energy-intensive equipment, and does not completely lose hydrochloric acid resources, resulting in lower overall treatment costs. It is suitable for industrial-scale continuous waste acid purification scenarios in the chloride process for titanium dioxide. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0035] Figure 2 This is a control framework diagram of the PLC automatic control system of the present invention;

[0036] Figure 3 This is a schematic diagram of the process framework in this invention;

[0037] The meanings of the labels in the diagram are as follows:

[0038] 1. Oxidation pretreatment reactor; 2. Sulfate removal precipitation reactor; 3. High-temperature flocculation and silica removal reactor; 4. Phosphate titanium precipitation reactor; 5. Multi-stage precision filtration unit; 6. Purified acid product storage tank; 7. PLC automatic control system. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] This invention provides a method for purifying waste acid from titanium dioxide, such as... Figures 1-3 As shown, this method employs a four-stage irreversible continuous purification process to treat the waste acid from the chlorination stage of titanium dioxide chlorination, which contains hydrochloric acid, titanium chloride oxide, silica colloid, sulfate, and ferric iron impurities. The hydrochloric acid in the system is not neutralized throughout the process. Specifically, it includes four steps:

[0041] S1 oxidation pretreatment: Add 27.5%~30% hydrogen peroxide by mass to the waste acid at a dosage of 0.3~1.0 g / L, stir and react at 30~50℃ for 10~20 min to oxidize trace Fe²⁺ and sulfite reducing impurities to higher oxidation states;

[0042] S2 Barium Chloride Precipitation to Remove Sulfate: Add anhydrous barium chloride or barium chloride dihydrate solid in batches, control the molar ratio of Ba²⁺ to SO₄²⁻ to be 1.0:1~1.2:1, stir and react at 30~50℃ for 30~60 min, and filter to separate the sulfate ions after they are converted into barium sulfate precipitate.

[0043] S3 Strong Hydrochloric Acid Environmental Flocculation for Silicon Removal: Heat the system to 60~80℃, add 10g / L industrial gelatin flocculant (dosage: 1.0~2.0g / L); first stir rapidly at 150~200rpm for 5~15min, then stir slowly at 30~50rpm for 20~30min, let stand and settle for 30~60min, and filter to remove flocs formed by silica colloids and animal glue;

[0044] S4 Phosphoric Acid Titanium Precipitation for Iron Removal: Control the temperature at 60~80℃, maintain the pH of the system at 1.5~3.0, add 85% industrial phosphoric acid in batches, with a phosphoric acid to titanium molar ratio of 1.1:1~1.5:1, stir the reaction for 1~2 hours, titanium and trivalent iron will be converted into titanium phosphate and iron phosphate coprecipitates respectively and removed by filtration, finally obtaining purified waste acid with a hydrochloric acid concentration >18%.

[0045] The four-stage process is irreversible. The pre-process removes sulfate and silica colloids to prevent impurities from coating titanium phosphate precipitates. Hydrogen chloride is produced as a byproduct throughout the process, and high-concentration hydrochloric acid is retained for easy reuse.

[0046] In this embodiment, a complete set of purification equipment can be used to implement the above-mentioned titanium dioxide waste acid purification method. The complete set of equipment is connected in series along the waste acid flow direction, including oxidation pretreatment reactor 1, sulfate removal precipitation reactor 2, high-temperature flocculation and silicon removal reactor 3, phosphate titanium precipitation reactor 4, multi-stage precision filter unit 5, and purified acid product storage tank 6. Each reactor is equipped with a reagent dosing unit, temperature control components, stirring mechanism and online monitoring instruments. The entire set of equipment is equipped with a PLC automatic control system 7, and the reactors are connected to a centrifugal pump through acid-resistant pipelines.

[0047] The entire set of equipment connects the reaction vessels in series according to the process sequence, and is equipped with multi-stage filtration to achieve staged solid-slag separation. The PLC automatic control system 7 realizes closed-loop automatic control of reagents, temperature, stirring, pH and sulfate concentration, and is matched with a four-stage continuous purification process to achieve automated industrial continuous processing.

[0048] Specifically, the oxidation pretreatment reactor 1 is equipped with a hydrogen peroxide quantitative dosing unit and an online ferrous monitoring probe. The stirring speed inside the reactor is 200~300rpm, which is suitable for the working conditions where the primary Fe²⁺ content of waste acid is <0.1g / L.

[0049] The oxidation pretreatment reactor 1 is equipped with an independent hydrogen peroxide quantitative dosing unit and an online ferrous ion monitoring probe, which can accurately control the amount of hydrogen peroxide added. Stirring at 200~300rpm improves the oxidation mass transfer efficiency, and real-time monitoring of ferrous ions ensures complete oxidation of trace reducing impurities, stabilizes the reaction system, and avoids interference with subsequent precipitation processes.

[0050] Furthermore, in addition to the sulfate precipitation vessel 2 being equipped with a barium chloride batch feeding bin and an online sulfate EDTA titration analyzer, the analyzer signal is connected to the PLC automatic control system 7 to control the barium chloride feeding amount in a closed loop. A separate barium sulfate slag discharge port is set at the bottom of the vessel, and the sulfate removal rate is ≥95%.

[0051] The sulfate removal precipitation vessel 2 adopts a batch feeding mode to add barium chloride solid. The feeding amount is automatically adjusted based on online sulfate detection data to accurately control the barium salt addition molar ratio. The independent slag discharge structure at the bottom of the vessel can collect barium sulfate precipitate separately. The sulfate removal depth is high and there is no excessive waste of reagents.

[0052] Furthermore, the high-temperature flocculation desiliconization kettle 3 is equipped with a steam jacket heating system and inclined plate settling internals. It relies on the high hydrochloric acid environment of the waste acid itself to remove silicon, without the need to add alkali to adjust the pH, and the silicon removal rate is ≥90%.

[0053] The high-temperature flocculation desiliconization kettle 3 relies on the steam jacket to stably maintain the reaction temperature of 60~80℃. The inclined plate sedimentation internals inside the kettle extend the sedimentation path of the silica flocs and improve the solid-liquid separation efficiency. The high acidity of the waste acid is directly used to complete the flocculation of animal glue, without the need to neutralize hydrochloric acid, which greatly reduces the cost of reagents and removes silicon impurities thoroughly.

[0054] Furthermore, the phosphate titanium precipitation reactor 4 is equipped with an online pH controller. Phosphoric acid is added in batches to strictly control the pH at the reaction endpoint to be greater than 1.5, thereby avoiding the precipitation of titanium phosphate by silica and sulfate ions and improving the purity of titanium slag.

[0055] The phosphate titanium precipitation reactor 4 uses an online pH controller to stably control the acidity of the system and slowly add industrial phosphoric acid in batches to avoid local high phosphoric acid concentrations that would produce fine, difficult-to-filter precipitates. Because the sulfate and silicon have been removed in the previous process, the phosphate titanium precipitate is free of colloidal coating, significantly improving the purity of the titanium slag and facilitating the recycling of titanium resources.

[0056] Furthermore, the multi-stage precision filtration unit 5 includes multiple plate and frame filter presses, which can separately trap barium sulfate residue, silicon-animal colloids, and titanium phosphate solid residue. Each type of waste residue is collected separately in different compartments, realizing classified resource recycling.

[0057] The multi-stage precision filtration unit is equipped with multiple independent plate and frame filter presses, corresponding to the sediments produced in each process. Different types of solid residues are filtered and stored separately. Barium sulfate residue and titanium phosphate residue can be utilized separately as resources, reducing the cost of disposing of mixed hazardous waste. The filtrate is clear and free of suspended solids, ensuring the quality of purified waste acid.

[0058] Furthermore, all reactor bodies, pipelines, and agitators in the entire system that come into contact with waste acid and reagents are made of enamel, PTFE-lined or Hastelloy-lined materials that are resistant to strong acids and corrosion. Buffer tanks are installed between adjacent reactors to stabilize the feed flow rate.

[0059] All components of the entire unit that come into contact with corrosive media are made of strong acid-resistant and corrosion-resistant materials, which are suitable for long-term continuous operation of 20%~30% high-concentration hydrochloric acid to prevent equipment corrosion and leakage; the inter-reactor buffer tank buffers the fluctuation of feed flow rate to ensure stable reaction conditions in each process and that the impurity removal index continues to meet the standards.

[0060] Furthermore, the PLC automatic control system 7 has a built-in four-stage process timing interlock program, which automatically adjusts the dosage of reagents, stirring speed and heating steam supply based on online data of temperature, sulfate concentration, pH and ferrous content.

[0061] The PLC automatic control system 7 enables the entire device to operate automatically with time-interlocking. Various online monitoring data are fed back in real time and the equipment operating parameters are adjusted in a closed loop. No continuous on-site manual operation is required, eliminating index fluctuations caused by manual adjustment and ensuring stable and consistent waste acid purification effect.

[0062] Furthermore, the reactions of barium chloride to remove sulfate and phosphate to precipitate titanium both produce hydrogen chloride, and the process hydrochloric acid retention rate is ≥97%. The purified waste acid meets the following specifications: SO4²⁻<0.5g / L, silicon<0.3g / L, titanium<0.5g / L, and total iron<0.1g / L, and can be directly concentrated and reused or sold externally.

[0063] The two precipitation processes generate hydrogen chloride simultaneously, compensating for the small amount of hydrochloric acid lost during the process. After purification, the acid concentration of the waste acid salt is stably greater than 18%, and all impurity indicators are controlled at extremely low levels. It can be reused in the titanium dioxide chlorination process or sold externally without secondary deep treatment, reducing subsequent concentration energy consumption and processing costs.

[0064] Furthermore, the order of oxidation pretreatment, sulfate removal, silicon removal, and titanium removal cannot be changed; if it is changed to titanium removal first, followed by silicon removal and sulfate removal, defects will occur, such as titanium phosphate precipitate being encapsulated by silica colloid, increased consumption of barium chloride reagent, and a significant decrease in sulfate removal efficiency.

[0065] The four irreversible process steps are the core technological features of this invention. Pre-removal of sulfate and silica colloids can prevent impurities from encapsulating titanium phosphate precipitates at the source, reduce the ineffective consumption of barium chloride reagent, and ensure simultaneous and deep removal of sulfate, silicon, and titanium. This overcomes the inherent defects of high reagent consumption, low precipitation purity, and poor impurity removal effect caused by the traditional process sequence.

[0066] When using this complete set of titanium dioxide waste acid purification equipment, the first step is to install and deploy the equipment: Position the oxidation pretreatment reactor 1, sulfate removal precipitation reactor 2, high-temperature flocculation and silica removal reactor 3, and phosphate titanium precipitation reactor 4 sequentially according to the material flow direction. Connect each reactor in series with an acid-resistant centrifugal pump using PTFE-lined pipelines. Connect the corresponding plate and frame filter press in the multi-stage precision filter unit 5 at the discharge end of each reactor. Connect the filtrate outlet of the filter unit to the purified acid finished product storage tank 6. Connect the hydrogen peroxide quantitative dosing unit, barium chloride batch feeding silo, phosphate batch dosing device, various online monitoring instruments, stirring motor, and steam heating pipeline to the PLC automatic control system 7 to complete the hardware installation and wiring of the entire set of equipment.

[0067] After the equipment is installed, start the PLC automatic control system 7 to carry out whole machine debugging: fill each reagent dosing unit with 27.5%~30% hydrogen peroxide, anhydrous barium chloride or barium chloride dihydrate solid, 10g / L industrial gelatin solution, and 85% industrial phosphoric acid respectively. Turn on the stirring mechanism, steam jacket heating system, and online monitoring instruments of each reactor. The PLC automatic control system 7 self-checks the signals of each instrument, the reagent dosing actuator, and the operating status of the filter unit. Set the temperature, stirring speed, reagent molar ratio, and pH control threshold of each process. Debug the interlock start and stop logic of each process. After confirming that there are no abnormalities in the signal transmission and action execution of all equipment, enter the material waiting operation state.

[0068] Entering the formal waste acid purification treatment stage, the waste acid absorbed by the tail gas of the titanium dioxide chlorination section is sent into the oxidation pretreatment reactor 1 through the feed pipeline to start the first purification process: the hydrogen peroxide quantitative dosing unit adds hydrogen peroxide at a dosage of 0.3~1.0g / L, the stirring mechanism in the reactor maintains stirring at 200~300rpm, the temperature control system stabilizes at 30~50℃, the reaction is carried out for 10~20min, the online ferrous monitoring probe detects the reducing impurities in the system in real time, and oxidizes trace amounts of Fe²⁺ and sulfite to higher oxidation states. After oxidation is completed, the waste acid is transported to the sulfate removal precipitation reactor 2.

[0069] After the waste acid enters the sulfate removal precipitation tank 2, barium chloride solid is added in batches from the barium chloride batch feeding hopper. The PLC adjusts the feeding amount according to the detection results of the sulfate EDTA online titration analyzer, controlling the molar ratio of Ba²⁺ to SO₄²⁻ to 1.0:1~1.2:1. The system is maintained at 30~50℃ and stirred for 30~60 minutes. Sulfate ions are converted into barium sulfate precipitate. The slag discharge port at the bottom of the tank is used in conjunction with the corresponding plate and frame filter press to intercept the barium sulfate slag. The filtrate is sent to the high-temperature flocculation desiliconization tank 3.

[0070] The high-temperature flocculation desiliconization reactor 3 is heated to 60~80℃ through a steam jacket, and 10g / L of industrial gelatin flocculant is added. The dosage is controlled at 1.0~2.0g / L. The stirring mechanism first stirs rapidly at 150~200rpm for 5~15min, and then switches to 30~50rpm for 20~30min. The material is allowed to settle in the inclined plate settling internals of the reactor for 30~60min. The silica colloid and animal glue form flocs. The matching plate and frame filter press separates the silica flocs. The desiliconized waste acid is transported to the phosphate titanium precipitation reactor 4.

[0071] The temperature of the phosphate titanium precipitation reactor 4 is controlled at 60~80℃, and the pH of the system is maintained at 1.5~3.0 by an online pH controller. 85% industrial phosphoric acid is added in batches, and the molar ratio of phosphoric acid to titanium is controlled at 1.1:1~1.5:1. The reaction is stirred for 1~2 hours. Titanium and trivalent iron in the waste acid are converted into titanium phosphate and iron phosphate co-precipitates, respectively. The titanium phosphate solid residue is intercepted by the plate and frame filter press at the end. After filtration, the clarified and purified waste acid flows into the purified acid product storage tank 6 for storage. The entire process is monitored in real time by a PLC automatic control system 7. The barium chloride removes sulfate and the phosphate titanium precipitation reaction simultaneously generate hydrogen chloride. The acid concentration of the purified waste acid is maintained at greater than 18%, and the impurity indicators meet the requirements of SO4²⁻<0.5g / L, silicon<0.3g / L, titanium<0.5g / L, and total iron<0.1g / L.

[0072] After all batches of waste acid have been processed, the reagent dosing units, heating steam, and stirring motors of each reactor are shut down in sequence, and the PLC automatic control system 7 stops the timing interlock program. The plate and frame filter presses of the multi-stage precision filter unit 5 are turned on in sequence, and the barium sulfate slag, silicon-animal flocculents, and titanium phosphate solids are unloaded and collected and stored in separate compartments. The qualified purified waste acid in the purified acid finished product storage tank 6 is emptied and transported to the titanium dioxide production concentration and reuse system or the external sales storage tank. The operating lines of each online monitoring instrument, dosing equipment and PLC automatic control system 7 are disconnected. The entire set of equipment, including the reactor, pipelines and filter units, is flushed and cleaned. All equipment is then organized and stored, and the entire equipment operation process is completed.

[0073] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for purifying waste acid from titanium dioxide chloride, characterized in that: A four-stage irreversible continuous purification process is used to treat the waste acid from the chlorination section of titanium dioxide chlorination, which contains hydrochloric acid, titanium chloride oxide, silica colloid, sulfate, and ferric ions. The hydrochloric acid in the system is not neutralized throughout the process. The steps are as follows: S1. Oxidation pretreatment: Add 27.5%~30% hydrogen peroxide by mass to the waste acid at a dosage of 0.3~1.0 g / L, stir and react at 30~50℃ for 10~20 min to oxidize trace Fe²⁺ and sulfite reducing impurities to higher oxidation states; S2. Barium chloride precipitation to remove sulfate: Add anhydrous barium chloride or barium chloride dihydrate solid in batches, control the molar ratio of Ba²⁺ to SO₄²⁻ to 1.0:1~1.2:1, stir and react at 30~50℃ for 30~60 min, and filter to separate the sulfate ions after they are converted into barium sulfate precipitate. S3. Strong hydrochloric acid environment flocculation to remove silica: Heat the system to 60~80℃, add 10g / L industrial gelatin flocculant, the dosage is 1.0~2.0g / L; first stir rapidly at 150~200rpm for 5~15min, then stir slowly at 30~50rpm for 20~30min, let stand and settle for 30~60min, filter to remove the flocs formed by silica colloids and animal glue; S4. Phosphoric acid precipitation to remove iron from titanium: Control the temperature at 60~80℃, maintain the pH of the system at 1.5~3.0, add 85% industrial phosphoric acid in batches, with a phosphoric acid to titanium molar ratio of 1.1:1~1.5:1, stir the reaction for 1~2 hours, titanium and trivalent iron will be converted into titanium phosphate and iron phosphate coprecipitates respectively and removed by filtration, finally obtaining purified waste acid with a hydrochloric acid concentration >18%.

2. The method for purifying waste acid from titanium dioxide chloride according to claim 1, characterized in that: The method is implemented using a complete set of purification equipment; the complete set of equipment consists of an oxidation pretreatment reactor (1), a sulfate removal precipitation reactor (2), a high-temperature flocculation and silicon removal reactor (3), a phosphate titanium precipitation reactor (4), a multi-stage precision filter unit (5), and a purified acid product storage tank (6) connected in series along the waste acid flow direction. Each reactor is equipped with a reagent dosing unit, temperature control components, stirring mechanism and online monitoring instruments. The entire set of equipment is equipped with a PLC automatic control system (7), and the reactors are connected to a centrifugal pump via acid-resistant pipelines.

3. The method for purifying waste acid from titanium dioxide according to claim 2, characterized in that: The oxidation pretreatment reactor (1) is equipped with a hydrogen peroxide quantitative dosing unit and an online ferrous monitoring probe. The stirring speed inside the reactor is 200~300rpm, which is suitable for the working condition where the original Fe²⁺ content of waste acid is <0.1g / L.

4. The method for purifying waste acid from titanium dioxide according to claim 3, characterized in that: The sulfate removal precipitation vessel (2) is equipped with a barium chloride batch feeding bin and an online sulfate EDTA titration analyzer. The analyzer signal is connected to the PLC for closed-loop control of the barium chloride feeding amount. A separate barium sulfate slag discharge port is set at the bottom of the vessel. The sulfate removal rate is ≥95%.

5. The method for purifying waste acid from titanium dioxide according to claim 1, characterized in that: The high-temperature flocculation desiliconization kettle (3) is equipped with a steam jacket heating system and inclined plate settling internals. It relies on the high hydrochloric acid environment of the waste acid itself to remove silicon without the need for external alkali to adjust the pH. The silicon removal rate is ≥90%.

6. The method for purifying waste acid from titanium dioxide according to claim 1, characterized in that: The phosphate titanium precipitation reactor (4) is equipped with an online pH controller. Phosphoric acid is added in batches to strictly control the pH at the reaction endpoint to be greater than 1.5, thereby avoiding the precipitation of titanium phosphate by silica and sulfate ions and improving the purity of titanium slag.

7. The method for purifying waste acid from titanium dioxide chloride according to claim 1, characterized in that: The multi-stage precision filter unit (5) includes multiple plate and frame filter presses, which can respectively intercept barium sulfate residue, silicon-animal colloids, and titanium phosphate solid residue. Various waste residues are collected separately in separate compartments to achieve classified resource recycling.

8. The method for purifying waste acid from titanium dioxide according to claim 1, characterized in that: All reactor bodies, pipelines, and agitators in contact with waste acid and reagents in the entire set of equipment are made of enamel, PTFE-lined or Hastelloy alloy resistant materials that are resistant to strong acids and corrosion. Buffer tanks are set between adjacent reactors to stabilize the feed flow rate.

9. The method for purifying waste acid from titanium dioxide chloride according to claim 1, characterized in that: The process of removing sulfate with barium chloride and precipitating titanium with phosphate both produce hydrogen chloride, and the process retains ≥97% of hydrochloric acid. The purified waste acid meets the following specifications: SO4²⁻<0.5g / L, silicon<0.3g / L, titanium<0.5g / L, and total iron<0.1g / L. It can be directly concentrated and reused or sold externally.

10. The method for purifying waste acid from titanium dioxide chloride according to claim 1, characterized in that: The order of oxidation pretreatment, sulfate removal, silicon removal, and titanium removal cannot be changed; if it is changed to titanium removal first, followed by silicon removal and sulfate removal, defects will occur, such as titanium phosphate precipitate being encapsulated by silica colloid, increased consumption of barium chloride reagent, and a significant decrease in sulfate removal efficiency.

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