Method for preparing titanium phosphite from low-concentration titanium-containing waste acid

Abstract

The invention relates to the technical field of recycling of renewable resources, in particular to a method for preparing titanium phosphite from low-concentration titanium-containing waste acid. The method is characterized in that the titanium phosphite solution is directly prepared from the titanium white waste acid by adopting an extraction method, an intermediate is provided for further preparation of an electrode material and a catalyst, meanwhile, waste sulfuric acid is recycled, the process flow is simple, and the cost is relatively low.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling of renewable resources, and particularly relates to a method for preparing titanium phosphite from low-concentration titanium-containing waste acid. Background Art

[0002] Titanium dioxide is widely used in industries such as coatings, inks, papermaking, plastics, rubber, and ceramics. Its production processes mainly include the sulfuric acid method and the chloride method. Most industries in China use the sulfuric acid method for production. The sulfuric acid method uses ilmenite as the raw material, acidizes ilmenite FeTiO3 with concentrated sulfuric acid while introducing air for stirring. Ferric sulfate and titanium sulfate are leached out from the reactants. FeSO4·H2O is crystallized out, and the remaining solution is concentrated and precipitated to obtain hydrated titanium dioxide colloid. The precipitate is washed and filtered, and titanium dioxide is obtained after calcination. However, a large amount of waste residue, waste gas, and waste acid will be generated during the processing of minerals. The main components of the waste residue are acidolysis residues such as insoluble sulfates, silicates, and silicon dioxide. The waste gas mainly includes acidolysis waste gas and calcination waste gas. The waste acid contains 20% concentrated sulfuric acid, and the Ti content is about 4.9 - 5.4 g / L. Both of them can be recycled. Chinese Invention Patent (Patent No. CN202411533674.8, Patent Name: A Method for Recycling Titanium in Titanium White Waste Acid) discloses a method for recycling titanium in titanium white waste acid, which is characterized in that: S1. After heating the titanium white waste acid, Al(OH)3 and phosphoric acid are sequentially added under stirring, and after the reaction, it is allowed to stand, and the supernatant is removed to obtain titanium phosphate solid; S2. The titanium phosphate solid is bleached and washed with water to obtain titanium phosphate after impurity removal; S3. The titanium phosphate after impurity removal is added to the slurry before salt treatment of sulfuric acid method titanium white to recover titanium therein, and the finished product is obtained after salt treatment and calcination. Preferably, the titanium white waste acid includes sulfuric acid method titanium white waste acid and / or chloride method titanium white waste acid. Preferably, the TiO2 content in the titanium white waste acid is 4 - 9 g / L. Preferably, in step S1, the temperature after heating is 60 - 90 °C. Preferably, in step S1, the addition amount of Al(OH)3 is controlled according to the end point pH, and the pH of the liquid after adding Al(OH)3 is 1 - 3. Preferably, in step S1, after adding Al(OH), it is stirred and dispersed for 10 - 50 min and then phosphoric acid is added. Preferably, in step S1, the addition amount of phosphoric acid is measured according to the molar ratio H3PO4:TiO2 = 1.35 - 1.75. Preferably, in step S1, after adding phosphoric acid, the reaction time is 10 - 50 min. Preferably, in step S1, the standing time is 0.5 - 2 h. Preferably, in step S3, the addition amount of the titanium phosphate after impurity removal is controlled according to the Al2O3 content in the finished product, and the mass percentage of Al2O3 in the finished product is 0.2% - 0.3%.Before adding phosphoric acid in the method of the present invention, aluminum hydroxide is added first, which can effectively solve the problems that the particle size of titanium phosphate produced is too fine and the viscosity is too high, resulting in difficulty in filtration and water washing. Through bleaching and water washing, impurities in the titanium phosphate solid can be effectively removed. The titanium phosphate after water washing and impurity removal can be directly recycled to the salt treatment process of sulfuric acid process titanium dioxide production, effectively recovering titanium in the titanium white waste acid. And phosphate ions and aluminum ions can be recycled as salt treatment agents in production, without the need to add additional salt treatment agents during the salt treatment process, avoiding the introduction of other impurities, significantly reducing the dosage of salt treatment agents, and saving production costs. Chinese invention patent (patent number: CN202210940367.6, patent name: A method for preparing titanium phosphate from waste acid by-product in the production of titanium dioxide by chlorination method) discloses a method for preparing titanium phosphate from waste acid by-product in the production of titanium dioxide by chlorination method, which is characterized in that: (1) Dilute phosphoric acid is added to the heated titanium white waste acid, stirred, and naturally cooled to obtain a sol; (2) The sol is filtered and pickled to obtain a filter cake; (3) The filter cake is washed and bleached to obtain a colloid; (4) The colloid is washed and dried to obtain a filter residue; (5) The filter residue is calcined to obtain the finished product of titanium phosphate. Further, in step (1), the weight concentration of the dilute phosphoric acid is 6% - 10%, the temperature of the heated titanium white waste acid is 85 - 100 °C, and the molar ratio of the dilute phosphoric acid to the titanium salt in the titanium white waste acid is 1.1 - 1:1. Further, in step (2), the pickling is carried out with one or more of dilute hydrochloric acid, dilute phosphoric acid and dilute sulfuric acid. Further, the weight concentration of the acid used for pickling is 3% - 10%. Further, in step (3), the washing is carried out with demineralized water, and the bleaching is carried out with a bleaching agent. Further, the bleaching agent is a trivalent titanium salt solution. Further, in step (5), the calcination temperature is 600 - 1000 °C. The mechanism of the present invention is that the present invention selects phosphoric acid as the reactant to react with TiCl4 in the titanium white waste acid, and the phosphoric acid is slightly in excess. The main reaction process is as follows: 2TiCl4 + 2H3PO4 + H2O → 2TiO2·P2O5 + 8HCl. The formation rate of 2TiO2·P2O5 is fast, and it can be directly filtered. The preparation method is simple and convenient. The final product is washed and then calcined to obtain titanium phosphate with a better crystal form.

[0003] In the prior art 1, Al(OH)3 and phosphoric acid are added successively under stirring, and after the reaction, it is left standing. After removing the supernatant, titanium phosphate is obtained to recover titanium in the waste acid. Titanium is an element in Group ⅣB of the fourth period of the periodic table, and Ti 4+ The ionic radius is 60 pm, belonging to a high-charge, small-radius and high-field-strength cation, which has a strong polarization force on the coordinated ions. Therefore, all Ti(Ⅳ) compounds are covalent, and there is no Ti 4+ Free ions and solvated ions. At most, (-Ti-O-) exists in acidic solutions 2+Chain-like hydrated ions. Therefore, the structure of titanium sulfate in titanium white waste acid is TiOSO4 (titanium oxysulfate or titanium sulfate oxide). In the prior art 1, phosphate ions in phosphoric acid are used to displace sulfate ions in titanium oxysulfate. Substantially, it is to use a ligand anion PO4 3- to displace the ligand anion SO4 2- and form a coordination compound with Ti 4+ ions, that is, hydrated titanium phosphate solid. In the prior art 1, aluminum hydroxide is added before adding phosphoric acid. The purpose is to solve the problem that the particle size of the generated titanium phosphate is too fine and the viscosity is too high, resulting in difficulty in filtration and water washing. Then phosphoric acid is added to obtain TiPO4·xH2O hydrated aluminum phosphate solid. However, Al(OH)3 will form Al2(SO4)3·xH2O hydrated aluminum sulfate and AlPO3·xH2O hydrated aluminum phosphate solid in sulfuric acid and phosphoric acid solutions. That is, due to water molecules filling the gap between the central cation and the ligand anion of the above two, a stable coordination compound lattice is formed. Using the process of crystallization precipitation filtration, hydrated aluminum sulfate salt, hydrated aluminum phosphate and hydrated titanium phosphate as impurities are all solid crystalline precipitates and cannot be separated. Then, in the next step, to obtain titanium, the above impurities must be removed. The subsequent process of the prior art 1 is that "the titanium phosphate after water washing and impurity removal can be directly recycled to the salt treatment process of sulfuric acid process titanium white production". The hydrated aluminum sulfate salt, hydrated aluminum phosphate and hydrated titanium phosphate in the aqueous solution are all solid crystalline precipitates and cannot be separated. Obviously, the process steps of how to remove impurities by water washing are not disclosed; the prior art 2 recovers and prepares titanium phosphate from the waste acid by-product in the production of titanium dioxide by the chlorination method, and uses hydrochloric acid as the main raw material to participate in the reaction. The traditional chlorination process uses chlorine as the main raw material to produce TiCl4 products, and then refines TiCl4, and finally produces titanium white. Comparative document 2 does not disclose how to produce titanium white by the hydrochloric acid method and how to produce by-product waste acid in the production process. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing titanium phosphite from low-concentration titanium-containing waste acid, which is characterized in that: Step 1, the sulfuric acid method is a traditional method for producing titanium dioxide. Different process steps are adopted according to the changes in the raw material sources and the application fields of titanium dioxide products. Taking ilmenite as the raw material and producing pigment titanium dioxide as an example, it includes six major process steps: preparation of titanium solution, hydrolysis of titanium solution, purification of metatitanic acid, pretreatment and calcination of metatitanic acid, pulverization and post-treatment of titanium dioxide. Among them, the preparation of titanium solution includes acidolysis, leaching, reduction, sedimentation, freezing crystallization, filtration and separation of chlorovinyl, and pressure filtration and purification operation steps. Acidolysis is to use concentrated sulfuric acid to acidolyze ilmenite FeTiO3 to generate titanium sulfate, and other impurities in the ore such as Fe2O3, FeO, MgO, CaO, MnO, and Al2O3 also generate corresponding sulfates. The insoluble SiO2 and silicates in the ore form slag, and vanadium oxides exist as V2O5 in concentrated sulfuric acid. Leaching is to dissolve the acidolysis product with water under stirring of compressed air to convert titanium and soluble sulfates into a solution. Reduction is to add reducing agent iron powder to the leaching solution during the leaching process to reduce the high-valent impurity ions of Fe 3+ to low-valent states to create conditions for separating iron impurities later. Sedimentation is to flocculate and sediment and separate insoluble SiO2, silicates, and V2O5 hydrates by means of gravity. Freezing crystallization is that there are many soluble FeSO4 in the titanium solution, which crystallize out as FeSO4·7H2O chlorovinyl under freezing conditions. Pressure filtration and purification is to remove colloids such as hydrated vanadium pentoxide and fine solid particles such as SiO2 and silicates in the titanium solution by means of pressure filtration. The hydrolysis of the purified titanium solution into hydrated titanium dioxide is the key link in the production of titanium dioxide by the sulfuric acid method. After hydrolysis of titanyl sulfate, hydrated titanium dioxide precipitate and by-product sulfuric acid are generated. The by-product sulfuric acid is also called titanium dioxide waste acid, with a sulfuric acid concentration of 20%, containing Ti elements with a concentration of 4.9 - 5.4 g / L that can be recycled, and the impurities are Fe 2+ ions. Because Ti 3+ does not hydrolyze, the Ti element in the waste acid exists as Ti 3+ ions. Add H2O2 to oxidize Ti 3+ to Ti 4+ ions, and the addition amount is based on the reaction end point of oxidizing Ti 3+ to Ti 4+ ions as the measurement standard.

[0005] Step 2, select salicylhydroxamic acid as the extractant, which has high selectivity for Ti 4+ . Salicylhydroxamic acid has multiple donor atoms N and O. When forming a coordination bond with the extracted metal Ti 4+ ions, a stable six-membered ring structure can be formed. When forming the extractant complex, the phenolic hydroxyl group at one end of salicylhydroxamic acid releases H + , and the phenoxy anion forms a coordination bond with Ti 4+A coordination bond is formed, and the lone pair electrons of N in the oxime group at the other end form a coordination bond with Ti 4+ A coordination bond is formed, and the two ends form a six-membered ring structure. At the same time, an intramolecular hydrogen bond is also formed between -OH and the dissociated hydroxyl group in the oxime group, further increasing the stability of the chelate. The chelate is insoluble in water and soluble in organic solvents and easily enters the organic phase. Its reaction mechanism is as follows: .

[0006] In the organic phase, the extractant is 7% salicylhydroxamic acid, the diluent is kerosene, the ratio of the organic phase to the aqueous phase is O / A = 1.1 / 1, the temperature of the extraction system is room temperature, a 12-stage pulsed disc sieve plate extraction column is used, a sine wave pulse is used, the pulse frequency is 2 Hz, and the pulse amplitude is 2 cm. The raffinate waste acid is directly recycled to the acid hydrolysis step. The titanium-containing organic phase extracted is then back-extracted with a saturated phosphorous acid solution. The ratio of the organic phase to the aqueous phase is O / A = 1 / 10. Phosphorous acid is a dibasic acid. The H directly connected to the P atom in H3PO3 is very easy to react with H + in the aqueous solution, causing the above extraction reaction to proceed in the reverse direction. The cation H + in H3PO3 exchanges with the titanium salicylhydroxamate coordination compound Ti 4+ cation, thus disassembling the six-membered chelate ring structure. The organic phase and the aqueous phase are separated using a 14-stage pulsed disc sieve plate extraction column, a sine wave pulse is used, the pulse frequency is 2 Hz, and the pulse amplitude is 2 cm. The organic phase is recovered and recycled, and the aqueous phase is concentrated under the condition of isolating air to obtain a titanium phosphite solution with a concentration of 0.5 - 0.8%.

[0007] Step 3: The pulse injector consists of a mixing chamber, a reflux pipe, a gas distribution plate, a diffuser pipe, and a nozzle, forming the structure of a spouted bed. Compressed gas is injected into the diffuser pipe through the nozzle, and the pressure energy is converted into kinetic energy, thus creating a negative pressure in the diffuser pipe. The negative pressure drives the liquid to flow through the reflux pipe into the diffuser pipe to mix with the compressed gas, and then it is ejected through the gas distribution plate and diffused into the pulsed disk sieve plate extraction column through the mixing chamber. The gas-liquid mixture in the mixing chamber is mixed with the compressed gas under the drive of negative pressure through the reflux pipe. After multiple cycles, the compressed gas forms tiny bubbles with a very large specific surface area during the process of diffusing into the liquid flow multiple times. During the adsorption process between the bubbles and the liquid flow, the bubbles serve as carriers with a very large specific surface area for the interfacial contact and mass transfer exchange between the organic phase and the aqueous phase in the liquid flow. The compressed gas used for the pulse is nitrogen. The organic phase flows upstream from the organic phase inlet and makes interfacial contact with the original aqueous phase feed liquid input in the middle section of the pulsed disk sieve plate extraction column. Each extraction column stage is designed with a disk group. The disk group is composed of two disk rings paired in parallel. The disk ring structure is simple and not prone to fouling deposition. When the liquid flow passes through the disk group, part of the liquid flow passes through the central through-hole and sieve holes, i.e., axial flow, and part of the liquid flow diffuses from the disk ring to the periphery and passes through, i.e., radial flow. The axial flow and the radial flow intersect to obtain a better mixing effect. The organic phase gradually accumulates upward and is output from the organic phase outlet, while the aqueous phase gradually flows downward and is output from the aqueous phase outlet.

[0008] Compared with the prior art, the present invention has at least the following advantages: First, the method of extraction is adopted to directly prepare titanium phosphite solution from titanium white waste acid, providing an intermediate for further preparation of electrode materials and catalysts, and at the same time realizing the recycling of waste sulfuric acid. The process flow is simple and the cost is relatively low. Second, the pulsed disk sieve plate extraction column forms tiny bubbles with a very large specific surface area. During the adsorption process between the bubbles and the liquid flow, the bubbles serve as carriers with a very large specific surface area for the interfacial contact and mass transfer exchange between the organic phase and the aqueous phase in the liquid flow, improving the column efficiency, enhancing the loading capacity of the organic phase, and reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a front view structural schematic diagram of a method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to the present invention.

[0010] Figure 2 It is an A-A sectional view structural schematic diagram of a method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to the present invention.

[0011] Figure 3 It is a B-B sectional view structural schematic diagram of a method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to the present invention.

[0012] Figure 4 It is a large sample C structural schematic diagram of a method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to the present invention.

[0013] Figure 5Schematic diagram of the D large sample structure of the method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to the present invention.

[0014] 1 - Gas outlet 2 - Organic phase outlet 3 - Extraction column stage 4 - Disk group 5 - Pulse injector 6 - Organic phase inlet 7 - Aqueous phase outlet 8 - Mixing chamber 9 - Return pipe 10 - Gas distribution plate 11 - Diffusion pipe 12 - Nozzle. Detailed implementation manner

[0015] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0016] As Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 shown, a method for preparing titanium phosphite from low-concentration titanium-containing waste acid, characterized in that: Step 1, the sulfuric acid method is a traditional method for producing titanium dioxide, and different process steps are adopted according to the change of the raw material source and the application field of the titanium dioxide product. Taking ilmenite as the raw material and producing pigment titanium dioxide as an example, it includes six major process steps: preparation of titanium liquid, hydrolysis of titanium liquid, purification of metatitanic acid, pretreatment and calcination of metatitanic acid, pulverization and post-treatment of titanium dioxide. Among them, the preparation of titanium liquid includes acidolysis, leaching, reduction, sedimentation, freeze crystallization, filtration and separation of chlorvanadite, and pressure filtration and purification operation steps. Acidolysis is to acidolyze ilmenite FeTiO3 with concentrated sulfuric acid to generate titanium sulfate, and other impurities in the ore such as Fe2O3, FeO, MgO, CaO, MnO, and Al2O3 also generate corresponding sulfates. The insoluble SiO2 and silicates in the ore form slag, and vanadium oxides exist as V2O5 in concentrated sulfuric acid. Leaching is a process of dissolving the acidolysis product with water under the stirring of compressed air to convert titanium and soluble sulfates into a solution. Reduction is to add a reducing agent iron powder to the leaching solution during the leaching process to reduce the 3+ high-valent impurity ions to a low-valent state to create conditions for separating iron impurities later. Sedimentation is to flocculate and sediment and separate insoluble SiO2, silicates, and V2O5 hydrates by gravity. Freeze crystallization is that there are many soluble FeSO4 in the titanium liquid, which crystallize out as FeSO4·7H2O chlorvanadite under freezing conditions. Pressure filtration and purification is to remove colloids such as vanadium pentoxide hydrate and fine solid particles such as SiO2 and silicates in the titanium liquid by pressure filtration. The hydrolysis of the purified titanium liquid into hydrated titanium dioxide is the key link in the production of titanium white by the sulfuric acid method. After hydrolysis of titanyl sulfate, hydrated titanium dioxide precipitate and by-product sulfuric acid are generated. The by-product sulfuric acid is also called titanium white waste acid, with a sulfuric acid concentration of 20%, containing 4.9 - 5.4 g / L of Ti element that can be recovered, and the impurity is Fe 2+ ions, because Ti 3+ does not hydrolyze, and the Ti element in the waste acid exists as Ti3+ ions are present, add H2O2 to oxidize Ti 3+ to Ti 4+ ions. The addition amount is based on the reaction endpoint of oxidizing Ti 3+ to Ti 4+ ions as the stoichiometric standard.

[0017] Step 2: Select salicylhydroxamic acid as the extractant, which has high selectivity for Ti 4+ Salicylhydroxamic acid has multiple donor atoms N and O. When forming a coordination bond with the extracted metal Ti 4+ ions, a stable six-membered ring structure can be formed. When generating the extract, the phenolic hydroxyl group at one end of salicylhydroxamic acid releases H + , the phenoxy anion forms a coordination bond with Ti 4+ ions, and the lone pair electrons of N in the oxime group at the other end form a coordination bond with Ti 4+ ions. The two ends form a six-membered ring structure. At the same time, an intramolecular hydrogen bond is also formed between -OH and the dissociated hydroxyl group in the oxime group, further increasing the stability of the chelate. The chelate is insoluble in water and soluble in organic solvents and easily enters the organic phase. Its reaction mechanism is as follows: .

[0018] The extractant in the organic phase is 7% salicylhydroxamic acid, and the diluent is kerosene. The ratio of the organic phase to the aqueous phase is O / A = 1.1 / 1. The temperature of the extraction system is room temperature. A 12-stage pulsed disc sieve plate extraction column is used, with a sine wave pulse, a pulse frequency of 2 Hz, and a pulse amplitude of 2 cm. The residual waste acid is directly recycled to the acid hydrolysis section. The titanium-containing organic phase extracted is then back-extracted with a saturated phosphorous acid solution. The ratio of the organic phase to the aqueous phase is O / A = 1 / 10. Phosphorous acid is a dibasic acid. The H directly connected to the P atom in H3PO3 is very easy to exchange with H + in the aqueous solution, making the above extraction reaction proceed in the reverse direction. The cation H + in H3PO3 exchanges with the titanium salicylhydroxamate coordination compound Ti 4+ cation, thus disassembling the six-membered chelate ring structure. The organic phase and the aqueous phase are separated using a 14-stage pulsed disc sieve plate extraction column, with a sine wave pulse, a pulse frequency of 2 Hz, and a pulse amplitude of 2 cm. The organic phase is recovered and recycled, and the aqueous phase is concentrated under air-insulated conditions to obtain a titanium phosphite solution with a concentration of 0.5 - 0.8%.

[0019] Step 3: The pulse ejector 5 is composed of a mixing chamber 8, a reflux pipe 9, a gas distribution plate 10, a diffuser pipe 11, and a nozzle 12, forming the structure of a spouted bed. Compressed gas is ejected into the diffuser pipe 11 through the nozzle 12, and the pressure energy is converted into kinetic energy, thereby forming a negative pressure in the diffuser pipe 11. The negative pressure drives the liquid flow to enter the diffuser pipe 11 through the reflux pipe 9 to be mixed with the compressed gas, and then is ejected through the gas distribution plate 10 and diffused into the pulsed disk sieve plate extraction column through the mixing chamber 8. The gas-liquid mixture in the mixing chamber 8 is mixed with the compressed gas under the drive of the negative pressure through the reflux pipe 9. After multiple cycles, the compressed gas forms tiny bubbles with a very large specific surface area during the process of diffusing into the liquid flow multiple times. During the adsorption process of the bubbles and the liquid flow, the bubbles serve as carriers with a very large specific surface area for the interfacial contact and mass transfer exchange between the organic phase and the aqueous phase in the liquid flow. The compressed gas used for the pulse is nitrogen. The organic phase flows upstream from the organic phase inlet 6 and makes interfacial contact with the original aqueous phase feed liquid input in the middle section of the pulsed disk sieve plate extraction column. Each extraction column stage 3 is designed with a disk group 4. The disk group 4 is composed of two disk rings paired in parallel. The disk ring structure is simple and not prone to fouling deposition. When the liquid flow passes through the disk group 4, a part of the liquid flow passes through the central through hole and the sieve holes, i.e., axial flow, and a part of the liquid flow diffuses from the disk ring to the periphery and passes through, i.e., radial flow. The axial flow and the radial flow intersect to obtain a better mixing effect. The organic phase gradually accumulates upward and is output from the organic phase outlet 2, and the aqueous phase gradually flows downward and is output from the aqueous phase outlet 7.

Claims

1. A method for preparing titanium phosphite from low-concentration titanium-containing waste acid, characterized in that: Step 1: The sulfuric acid method is a traditional method for producing titanium dioxide. Different process steps are adopted according to the changes in the source of raw materials and the application fields of titanium dioxide products. Taking ilmenite as raw material and the production of pigment titanium dioxide as an example, there are six major process steps: preparation of titanium liquid, hydrolysis of titanium liquid, purification of titanic acid, pretreatment and calcination of titanic acid, and crushing and post-treatment of titanium dioxide. The preparation of titanium liquid includes the steps of acidolysis, leaching, reduction, sedimentation, freezing crystallization, filtration separation of chlorinated alum, and filter pressing purification; in step 2, the extractant in the organic phase is 7% salicyl hydroxamic acid, the diluent is kerosene, the organic phase is O / A=1.1 / 1 with respect to the water phase, the temperature of the extraction system is room temperature, a 12-level pulse disc sieve plate extraction column is used, a sine wave pulse is used, the pulse frequency is 2Hz, the pulse amplitude is 2cm, the residual waste acid is directly recycled to the acidolysis stage, the extracted titanium-containing organic phase is then stripped with a saturated phosphorous acid solution, the organic phase is O / A=1 / 10 with respect to the water phase, and the organic phase and the water phase are stripped with a 14-level pulse The disc sieve plate extraction column is used for separation, and a sinusoidal wave pulse is used with a pulse frequency of 2 Hz and a pulse amplitude of 2 cm. The organic phase is recycled and reused, and the aqueous phase is concentrated under air-tight conditions to obtain a titanium phosphite solution with a concentration of 0.5-0.8%; Step three, the pulse ejector is composed of a mixing chamber, a reflux pipe, an air distribution plate, a diffusion pipe, and a nozzle to form a spouted bed structure. The organic phase flows upstream from the organic phase inlet and contacts with the original aqueous phase liquid input from the middle section of the pulse disc sieve plate extraction column. Each extraction column stage is designed with a disc group. The organic phase is gradually enriched upward and output from the organic phase outlet, and the aqueous phase is gradually output downward from the aqueous phase outlet.

2. The method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to claim 1, characterized in that: Acid hydrolysis is the use of concentrated sulfuric acid to hydrolyze ilmenite FeTiO3 to generate titanium sulfate. Other impurities in the ore, Fe2O3, FeO, MgO, CaO, MnO, Al2O3, also generate corresponding sulfates. Insoluble SiO2 and silicates in the ore form slag. Vanadium oxide exists as V2O5 in concentrated sulfuric acid. Leaching is the process of dissolving the acid hydrolysis product with water under compressed air stirring to convert titanium and soluble sulfate into solution. Reduction is the process of adding reducing agent iron powder to the leaching solution to convert Fe 3+ The high-valent impurity ions are reduced to a low-valent state, creating conditions for the subsequent separation of iron impurities. Sedimentation is the flocculation and sedimentation of insoluble SiO2, silicates, and V2O5 hydrates by gravity. Frozen crystallization is the crystallization of FeSO4·7H2O chloroaluminate in the titanium liquid under freezing conditions. Press filtration purification is the removal of colloids such as hydrated vanadium pentoxide, fine solid particles such as SiO2 and silicates in the titanium liquid by press filtration.

3. The method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to claim 1, characterized in that: The key step of producing titanium dioxide by sulfuric acid method is to hydrolyze titanium liquid after purification to hydrated titanium dioxide. Titanium sulfate is hydrolyzed to generate hydrated titanium dioxide precipitation and byproduct sulfuric acid. The byproduct sulfuric acid is also called titanium dioxide waste acid. The concentration of sulfuric acid is 20%, and the concentration of Ti element is 4.9-5.4g / L, which can be recovered. The impurity is Fe. 2+ ions, because Ti 3+ Without hydrolysis, the Ti element in the waste acid is Ti 3+ ions exist, adding H2O2 will 3+ Oxidized to Ti 4+ ions, added in Ti 3+ Oxidized to Ti 4+ The reaction endpoint of the ion is used as the measurement standard.

4. The method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to claim 1, characterized in that: Salicylic acid was selected as the extractant to extract Ti 4+ It has high selectivity. Salicylic acid has multiple donor atoms N and O, which react with the extracted metal Ti. 4+ When the ions form coordination bonds, they can form a stable six-membered ring structure.

5. The method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to claim 1, characterized in that: When the extractant is formed, the phenolic hydroxyl group at one end of salicyl hydroxamic acid releases H + , phenoxy anion and Ti 4+ The lone pair of electrons of N in the oxime group at the other end forms a coordination bond with Ti 4+ A coordination bond is formed, and the two ends are bonded to form a six-membered ring structure. At the same time, an internal hydrogen bond is formed between the -OH in the oxime group and the dissociated hydroxyl group, which further increases the stability of the chelate. The chelate is insoluble in water but soluble in organic solvents and can easily enter the organic phase. The reaction mechanism is: 。 6. The method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to claim 1, characterized in that: Phosphorous acid is a dibasic acid. The H atoms directly connected to the P atoms in H3PO3 can easily react with H + The exchange allows the above extraction reaction to proceed in reverse, and the cation H in H3PO3 + Titanium salicylate hydroxamate coordination compound Ti 4+ The cations are exchanged, thereby breaking up the six-membered chelate ring structure.

7. The method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to claim 1, characterized in that: The compressed gas is sprayed into the diffusion tube through the nozzle, and the pressure energy is converted into kinetic energy, thereby forming a negative pressure in the diffusion tube. The negative pressure drives the liquid to flow through the reflux pipe into the diffusion tube and mix with the compressed gas, and then is sprayed out through the gas distribution plate and diffused into the pulse disc sieve plate extraction column through the mixing chamber. The gas-liquid mixture in the mixing chamber is mixed with the compressed gas under the drive of negative pressure through the reflux pipe. After multiple cycles, the compressed gas forms tiny bubbles with a large specific surface area in the process of multiple diffusions into the liquid flow.

8. The method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to claim 1, characterized in that: During the adsorption process of bubbles and liquid flow, the bubbles act as carriers with a large specific surface area to provide interphase contact and mass transfer exchange between the organic phase and the aqueous phase in the liquid flow, and the compressed gas used for the pulse is nitrogen.

9. The method for preparing titanium phosphite from low-concentration titanium-containing waste acid according to claim 1, characterized in that: The disc group consists of two disc rings paired in parallel. The disc rings have a simple structure and are not easy to deposit dirt. When the liquid flows in the disc group, part of the liquid flows through the central through hole and the sieve hole, that is, axial flow, and part of the liquid flows from the disc ring to the periphery, that is, radial flow. The axial flow and the radial flow intersect to obtain a better mixing effect.

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