Titanium dioxide clean production and by-product full recovery process

Abstract

The application discloses a clean production and full recovery process of titanium white powder, and belongs to the technical field of self-cleaning material preparation. First, titanium iron concentrate powder is mixed with concentrated hydrochloric acid, and HCl gas is introduced for gas phase heating leaching; after the leaching solution is reduced by adding iron powder, FeCl2*4H2O is recovered by freezing crystallization; FeCl3 mother liquor and high-purity iron powder are obtained by electrolysis of the crystallization mother liquor; the FeCl3 mother liquor is separated by extraction to obtain purified titanium liquid, and the extractant is recycled after back extraction; the purified titanium liquid is hydrolyzed by adding seed crystals, washed, dried, calcined to obtain high-purity titanium dioxide, and HCl is recovered synchronously; the hydrolysis mother liquor is recovered by extraction, precipitation and evaporation crystallization to obtain Sc, V, battery-grade MnO2, Al(OH)3, Mg(OH)2 and NaCl. The process realizes closed-circuit circulation in the whole process, has no three-waste emissions, has high resource utilization rate, can co-produce various high-value-added products, reduces environmental protection cost, and achieves zero-emission clean production.

Description

Technical Field

[0001] This application relates to the field of self-cleaning material preparation technology, specifically to a process for clean production of titanium dioxide and full recovery of by-products. Background Technology

[0002] Titanium dioxide (TiO2), as a high-performance inorganic functional material, possesses high refractive index, high whiteness, high chemical stability, and unique photocatalytic activity. It is not only a core white pigment in coatings, plastics, papermaking, and inks, but also a key component in self-cleaning materials due to its photocatalytic oxidation and decomposition of organic pollutants and its superhydrophilic properties. It has wide and important applications in self-cleaning coatings for building exteriors, glass curtain walls, photovoltaic panels, automotive surfaces, and municipal facilities. In self-cleaning material systems, titanium dioxide can generate electron-hole pairs through ultraviolet or visible light excitation, rapidly decomposing organic pollutants such as oil, dust, and microorganisms adhering to the surface. Simultaneously, its superhydrophilic properties allow water to form a film on the surface, carrying away the decomposed pollutants with the water flow, achieving a self-cleaning effect on the material surface, significantly reducing cleaning and maintenance costs, and improving the material's stain resistance and service life. With increasingly stringent environmental requirements and the development of high-end manufacturing industries, the self-cleaning materials market has placed higher demands on the purity, crystal form control, dispersibility, and photocatalytic activity of titanium dioxide, driving the titanium dioxide industry towards higher quality, cleaner production, and higher added value. Currently, the mainstream industrial production processes for titanium dioxide globally are the sulfuric acid process and the chloride process. The sulfuric acid process is the traditional process for titanium dioxide production. Its core advantage is its relatively low requirement for raw material grade, its ability to process low- to medium-grade ilmenite, and its wide range of raw material sources and strong adaptability. However, this process suffers from drawbacks such as large emissions of waste gas, wastewater, and solid waste, high environmental treatment costs, limited product quality, and the easy introduction of impurities such as iron and sulfur during production, resulting in poor whiteness, purity, and crystal uniformity of the product. The chloride process is currently the mainstream process for high-end titanium dioxide production. Its core advantages are a short production process, excellent product quality, and high whiteness, high purity, and controllable crystal form. However, this process has stringent requirements for raw materials, high raw material costs, demanding production conditions, and high safety risks. To address the shortcomings of the sulfuric acid and chlorination processes, academia and industry have increasingly focused on the hydrochloric acid process for titanium dioxide production. This process offers advantages such as strong raw material adaptability and controllable product quality, and also exhibits superior metal separation characteristics under chlorination systems. Chinese invention patent CN115974144B discloses a hydrochloric acid process for preparing titanium dioxide. This process includes sequentially subjecting titanium concentrate to acidolysis, solid-liquid separation of the acidolysis residue, titanium liquid reduction and crystallization, hydrolysis, solid-liquid separation of metatitanic acid, washing of the metatitanic acid filter cake, preparation of incineration mother liquor, incineration, HCl gas absorption, regenerated hydrochloric acid analysis and concentration, and acid preparation. The metatitanic acid obtained from the solid-liquid separation is then subjected to conventional treatment to obtain titanium dioxide. This process offers advantages such as no wastewater discharge, simplicity, and low cost.

[0003] However, the existing hydrochloric acid method for producing titanium dioxide has low raw material utilization and cannot effectively recover other components from the ore, resulting in low resource utilization. Therefore, there is an urgent need to develop a titanium dioxide production process that also considers the recovery of by-products. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the primary objective of this application is to provide a clean production process for titanium dioxide and a process for the complete recovery of byproducts. The process involves gas-phase heating leaching, utilizing the heat of dissolution of HCl gas to maintain the reaction temperature and enhance leaching. Then, ferric iron in the solution is reduced, followed by freeze crystallization to recover ferrous chloride crystals. Next, ferric titanium is oxidized to tetravalent titanium via electrolysis, simultaneously producing high-purity iron powder. The ferric iron is then separated using extraction to obtain pure titanium solution. Further hydrolysis yields titanium dioxide, and the remaining materials are recovered through extraction, precipitation, and evaporation crystallization.

[0005] To achieve the above objectives, this application provides the following technical solution:

[0006] This application provides a process for clean production of titanium dioxide and full recovery of by-products, including the following steps:

[0007] The ilmenite concentrate powder was mixed with concentrated hydrochloric acid in a reaction vessel, and then HCl gas was continuously introduced into the reaction vessel. After the reaction was completed, acidic leachate and slag were obtained.

[0008] In traditional hydrometallurgical leaching processes, reactors are typically heated via external steam jackets or internal coils. For hydrochloric acid systems, this approach suffers from two fatal flaws: firstly, severe scaling and corrosion occur on the heat exchanger surface; secondly, as the reaction proceeds, water generation and acid consumption cause changes in the solution's boiling point, and external heating cannot compensate for the rapidly decreasing chloride ion activity within the system. The proposed heating method using desorbed hydrogen chloride gas is a highly innovative thermodynamic coupling design. The dissolution of hydrogen chloride gas (HCl) in water is a strongly exothermic process, with a solubility enthalpy as high as -74.8 kJ / mol. Directly introducing high-temperature or room-temperature HCl gas into the leaching slurry effectively combines mass transfer and heat transfer. The enormous latent heat released by gas dissolution is directly converted into the sensible heat of the reaction system, rapidly raising the slurry temperature to the required 80–105°C range. More importantly, this heating method, while raising the temperature, not only avoids diluting the acid solution but also maintains or even increases the free acid concentration in the liquid phase by continuously replenishing HCl molecules. According to the principles of chemical reaction kinetics, the acidolysis rate of ilmenite is related to the proton concentration H. + and chloride ion concentration Cl -The product of these factors is positively correlated. In traditional processes, the water generated during the leaching reaction dilutes the acid solution, leading to a significant slowdown in reaction kinetics in the later stages and an increased risk of titanium hydrolysis. However, the gas-phase direct injection technology counteracts the dilution effect of water by supplementing HCl and utilizing exothermic reactions, ensuring that the reaction proceeds under high acidity and high activity conditions. This is crucial for ensuring a high leaching rate (>95%) and suppressing early titanium hydrolysis.

[0009] Iron powder was added to the acidic leachate to carry out a reduction reaction. After the reaction was completed, the solution was frozen and crystallized. The FeCl2·4H2O crystals and the mother liquor were obtained by centrifugation.

[0010] The leachate inevitably contains some ferric iron (Fe). 3+ The TiO2 is derived from hematite (Fe2O3) in the ore. FeCl3 has extremely high solubility in chloride systems and severely contaminates the TiO2 product during subsequent hydrolysis. Therefore, it is essential to remove Fe... 3+ Reduced to Fe 2+ Utilizing the characteristic that the solubility of FeCl2 in concentrated hydrochloric acid decreases sharply with decreasing temperature, FeCl2·4H2O crystals can be precipitated by freeze crystallization, which can remove approximately 70-80% of the iron impurities in the system, significantly reducing the load on subsequent membrane electrolysis and solvent extraction. Simultaneously, ferrous chloride tetrahydrate can be decomposed into high-purity iron oxide (Fe2O3) and HCl gas through high-temperature calcination; the latter is precisely the heat source and reagent required in step 1.

[0011] Electrolysis of the crystallization mother liquor yields FeCl3 mother liquor and high-purity iron powder after electrolysis.

[0012] In solvent extraction for iron removal, the commonly used extractant tributyl phosphate (TBP) can only efficiently extract ferric iron (Fe3+) complexes, but cannot effectively extract ferrous iron (Fe2+). Therefore, ferrous iron must be oxidized. Traditional processes generally use chlorine or hydrogen peroxide for oxidation. However, chlorine is toxic and difficult to control precisely, easily leading to over-oxidation; hydrogen peroxide is expensive and introduces water, disrupting the system's water balance. This application innovatively employs an electrolytic method to oxidize ferrous iron. Because Fe... 2+ / Fe 3+ The oxidation potential (0.77V) is significantly lower than the chlorine evolution potential (1.36V) and oxygen evolution potential (1.23V). Under appropriate current density and anode material (such as coated titanium anode), the current will be preferentially used for the oxidation of ferrous iron. That is, ferrous ions act as a "depolarizer", which greatly reduces the cell voltage and thus saves energy.

[0013] Extractant a is added to FeCl3 mother liquor. After multi-stage extraction and washing, aqueous purified titanium solution and iron-supported organic phase extractant are obtained. The organic phase extractant is then recycled by reverse extraction.

[0014] The mother liquor, after electrolytic oxidation, enters the extraction system. Because the system uses a high-concentration hydrochloric acid medium, Fe... 3+ It readily combines with TBP (tributyl phosphate) to form solvated complexes, and under these high acidity conditions, titanium (Ti) 4+ Iron and titanium mainly exist in the form of cationic or neutral complexes and are not easily extracted by TBP extractant, thus achieving efficient separation of iron and titanium. For back-extraction of the iron-loaded extractant, 1-2 mol / L dilute hydrochloric acid is used as the back-extraction agent. The volume ratio of the organic phase to the aqueous phase is 1:1, and a 2-3 stage countercurrent back-extraction process is performed at a temperature of 40-50℃. Each stage of extraction is mixed for 10 min, followed by clarification for 20 min. After back-extraction, the organic phase can be recovered after dehydration, and the aqueous phase can be used to prepare Fe-related products.

[0015] TiO2 seed crystals were added to the purified titanium solution, stirred evenly, and then heated for hydrolysis. HCl gas was recovered. After hydrolysis, the solution was centrifuged to obtain metatitanic acid filter cake and hydrolysis mother liquor. The metatitanic acid filter cake was washed, dried and calcined to obtain high-purity titanium dioxide.

[0016] The purified titanium solution is a high-purity titanium oxychloride solution. By heating and boiling, a hydrolysis reaction can occur, in which titanium oxychloride hydrolyzes to produce metatitanic acid and hydrogen chloride. The hydrogen chloride gas can be recovered and used in step 1.

[0017] After evaporating and concentrating the hydrolysis mother liquor, Sc and V are first extracted and recovered. Then, ozone is introduced to precipitate manganese and recover battery-grade MnO2. Then, the pH of the solution is adjusted with 30 wt.% sodium hydroxide solution to recover Al(OH)3 and Mg(OH)2. Finally, NaCl is recovered by evaporating and crystallizing the solution.

[0018] Scandium (Sc) is typically found in titanium dioxide waste acid at levels of only ppm, but it is extremely valuable. Scandium enrichment can be achieved by utilizing the ultra-high selectivity of P2O4 (di(2-ethylhexyl) phosphate) for Sc at a specific pH. Since the preceding steps have already deeply removed iron, eliminating the greatest interference of iron on scandium extraction, the scandium recovery efficiency in this process is far higher than that from direct extraction from the ore. Vanadium (V) is usually controlled by redox reactions after scandium extraction. 4+ Transform into V 5+ Subsequently, it is recovered using N235 (trioctyl tertiary amine) extractant. During the manganese precipitation process, the oxidation of divalent manganese ions to form manganese oxide precipitate by introducing ozone can more efficiently separate manganese and directly recover high-purity battery-grade MnO2. Compared with adjusting pH to precipitate Mn(OH)2, this process has higher separation efficiency and higher value of by-products.

[0019] Preferably, the recycling process further includes: calcining the FeCl2·4H2O crystals at high temperature to recover high-purity iron oxide and HCl gas.

[0020] Solid NaCl is obtained by evaporation and crystallization, which can be directly recovered as a byproduct and used as a raw material in the chlor-alkali industry.

[0021] Preferably, the process parameters for the reaction in the step of obtaining the acidic leachate and slag are as follows: reaction temperature 80~105℃, reaction pressure 0.1~0.11MPa, stirring speed 300~500rpm, reaction time 4~6h, free HCl concentration in the solution ≥8mol / L, and leachate discharge condition of TiO2 concentration ≥120g / L; the concentration of the concentrated hydrochloric acid is 28~32%; and the mass ratio of the ilmenite concentrate powder to the concentrated hydrochloric acid is 1:(3~4).

[0022] Preferably, the process parameters for the reduction reaction are: reaction temperature 40~50℃, stirring speed 200~300rpm, and reaction time 1~2h; the conditions for the freeze crystallization are to cool the reduced acidic leachate to -5~3℃ at a rate of 2~3℃ / h and continue the crystallization reaction for 6~8h; the mass ratio of the acidic leachate to iron powder is (400~500):1.

[0023] Preferably, the specific steps of the electrolysis are as follows: the mother liquor is fed into the anode and cathode chambers of the electrolytic cell, an ion exchange membrane is installed between the anode and cathode, the cell voltage is 1.5~2.5V, and the current density is 500~2000A / m. 2 The electrolysis temperature is 40~60℃ and the electrolysis time is 2~3h; the anode is an IrO2 coated titanium electrode, the cathode is a pure titanium plate, and the ion exchange membrane is a strongly basic anion exchange membrane.

[0024] The use of an anion exchange membrane (AEM) is crucial in this step. The AEM allows chloride ions (Cl-) to pass through the membrane. - The anode migrates from the cathode chamber to the anode chamber to balance the formation of Fe at the anode. 3+ The increased positive charge forms an extractable HFeCl4 complex in the anolyte, while simultaneously preventing iron ions from migrating and depositing at the cathode. This unit not only achieves precise control of chemical valence states but also realizes energy recovery and byproduct generation.

[0025] Preferably, the specific steps of the multi-stage extraction are as follows: FeCl3 mother liquor is fed into the extraction tower and mixed with extractant a at a volume ratio of (2~3):1. The mixing and stirring rate is 200~300 rpm and the time is 5~10 min. After the mixture is allowed to stand and separate into layers, the upper organic phase is countercurrently introduced into the next stage mixing chamber for extraction, and the lower aqueous phase is introduced into the next stage mixing chamber for further extraction. After 5 stages of extraction, the aqueous purified titanium liquid and the organic phase iron-supported extractant are obtained.

[0026] Preferably, the extractant a is any one of tributyl phosphate or a composite extractant, wherein the composite extractant is obtained by mixing tributyl phosphate and methyl isobutyl ketone in a volume ratio of 7:3.

[0027] Preferably, the stirring rate in the step of uniform stirring is 100~200 rpm; the hydrolysis temperature in the step of heating and hydrolysis is 95~100℃, and the hydrolysis time is 6~8h; deionized water is used as the washing liquid when washing the metatitanic acid filter cake, and the drying temperature is 120~150℃; the calcination temperature is 600~850℃, the calcination time is 1~2h, and the calcination atmosphere is air; the TiO2 seed crystals include any one of rutile or anatase; the mass ratio of the TiO2 seed crystals to the purified titanium liquid is (0.04~0.18):100.

[0028] Preferably, the specific steps for extracting and recovering Sc and V are as follows: Add 1 mol / L dilute hydrochloric acid to the concentrated hydrolysis mother liquor to adjust the pH to 1-2; add extractant b to the hydrolysis mother liquor, with a volume ratio of (4-5):1 between the hydrolysis mother liquor and extractant b; stir and mix for 10-15 min; then allow to stand and separate into layers to obtain an aqueous phase containing V and an organic phase carrying Sc; back-extract the organic phase carrying Sc to obtain Sc; introduce air into the aqueous phase containing V, stir at 150-200 rpm, react for 1-2 h; then add 1 mol / L dilute hydrochloric acid to adjust the pH to 0.5-1; add extractant c, with a volume ratio of (4-5):1 between the aqueous phase containing V and extractant c; stir and mix for 10 min; allow to stand and separate into layers to obtain an aqueous phase and an organic phase carrying V; back-extract the organic phase carrying V to obtain V; wherein extractant b is P2O4 and extractant c is N235.

[0029] In the process of obtaining Sc from an organically loaded Sc through back extraction, 2-3 mol / L hydrochloric acid is used as the back extraction agent, with a back extraction ratio of 1:1. The back extraction is carried out in 3-4 stages at 40-50℃, with a single-stage mixing time of 15 min and a clarification time of 30 min. After back extraction, the organic phase is recovered and recycled, while the aqueous phase can be used to produce Sc-related products. In the process of obtaining V from an organically loaded V through back extraction, 1-2 mol / L dilute sulfuric acid is used as the back extraction agent, with a back extraction ratio of 1:1. The back extraction is carried out in 2-3 stages at 25-35℃, with a single-stage mixing time of 10 min and a clarification time of 20 min. After back extraction, the organic phase is recovered and recycled, while the aqueous phase can be used to produce V-related products.

[0030] Preferably, the specific steps for recovering battery-grade MnO2 are as follows: ozone is introduced into the remaining aqueous phase after extraction, the pH is adjusted to 2-5, the reaction is carried out for 1-2 hours, and the battery-grade MnO2 and residual liquid are obtained by filtration; the pH of the residual liquid is adjusted to 4-5, and Al(OH)3 is obtained by filtration; the pH is adjusted to 10-11, and Mg(OH)2 is obtained by filtration; finally, the remaining solution is evaporated and crystallized to obtain NaCl.

[0031] The beneficial effects of this application are:

[0032] This application's process features a fully closed-loop circulation system. HCl gas is recycled for gas-phase heating leaching, and NaCl crystallization is recovered as a byproduct, resulting in no acidic wastewater or dilute acid waste liquid discharge. The extractant undergoes back-extraction regeneration and has a recycling rate of ≥90%, eliminating organic waste liquid pollution. Furthermore, it breaks away from the traditional titanium dioxide process that only extracts titanium while discharging other components as waste, achieving efficient recovery of all elements except oxygen. The main product is high-quality, high-purity titanium dioxide, along with co-productions of ferrous chloride tetrahydrate, high-purity iron powder, and high-value-added products such as scandium and vanadium enrichment solutions, battery-grade MnO2, aluminum hydroxide, and magnesium hydroxide. All metallic elements in ilmenite are recovered through resource utilization, eliminating waste stockpiling issues and achieving true zero-emission production, significantly reducing environmental treatment costs and environmental management risks for enterprises. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This application provides a process flow diagram for the clean production of titanium dioxide and the full recovery of by-products. Detailed Implementation

[0035] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0037] The following specific embodiments further illustrate this point:

[0038] Example 1

[0039] like Figure 1 As shown, this embodiment provides a clean production process for titanium dioxide and a process for full recovery of by-products, including the following steps:

[0040] 1. Mix 500 kg of ilmenite concentrate powder with 1500 kg of 31 wt.% concentrated hydrochloric acid, set the stirring speed to 300 rpm, and continuously introduce HCl gas into the mixture to maintain the free HCl concentration in the mixture ≥ 8 mol / L. The reaction pressure is 0.1 MPa, the reaction temperature is 80℃, and the reaction is continued for 4 h to obtain an acidic leachate.

[0041] 2. Add 1 kg of iron powder to every 400 kg of acidic leachate, maintain the reaction temperature at 40℃, stir at 200 rpm, and continue the reaction for 1 h. Then, cool the reduced acidic leachate to 3℃ at a rate of 2℃ / h and continue crystallizing for 6 h. Centrifuge to separate FeCl2·4H2O crystals and crystallization mother liquor.

[0042] 3. Place the crystallization mother liquor in the anode and cathode chambers of the electrolytic cell. A strongly alkaline anion exchange membrane is installed between the anode and cathode. The anode plate is an IrO2-coated titanium electrode, and the cathode plate is a pure titanium plate. Set the cell voltage to 1.5V and the current density to 500A / m. 2 The electrolysis temperature was 40℃, and the electrolysis time was 2h to obtain FeCl3 mother liquor and high-purity iron powder.

[0043] 4. The FeCl3 mother liquor was fed into the extraction tower and mixed with tributyl phosphate at a volume ratio of 2:1. The stirring speed was 200 rpm, and the mixture was stirred for 5 min. After standing until the solution separated into layers, the upper organic phase was countercurrently introduced into the next mixing chamber, and the lower aqueous phase was introduced into the next mixing chamber. The extraction steps were repeated. After 5 stages of extraction, the aqueous phase purified titanium solution and the organic phase iron-loaded extractant were obtained. Iron and extractant were recovered by reverse extraction of the organic phase.

[0044] 5. Add 0.1 kg of rutile TiO2 seed crystals to every 100 kg of purified titanium solution, stir evenly at 100 rpm, heat to 95°C, and hydrolyze for 6 hours, recovering HCl gas during the process. After hydrolysis, centrifuge to obtain metatitanic acid filter cake and hydrolysis mother liquor. Wash the metatitanic acid filter cake with deionized water until the filter cake contains Cl. - The content is ≤0.1%, then dried at 120℃ until the moisture content is less than 5%, and then calcined in air at 750℃ for 1 hour to obtain high-purity titanium dioxide;

[0045] 6. The hydrolysis mother liquor was evaporated and concentrated. 1 mol / L dilute hydrochloric acid was added to the concentrated mother liquor to adjust the pH to 1. P2O4 was added to the mother liquor at a volume ratio of 5:1 (mother liquor to P2O4). The mixture was stirred for 10 min, then allowed to stand and separate into layers, yielding a V-containing aqueous phase and a Sc-supported organic phase. The Sc-supported organic phase was back-extracted to obtain Sc. Air was introduced into the V-containing aqueous phase, and the reaction was carried out at a stirring rate of 150 rpm for 1 h. Then, 1 mol / L dilute hydrochloric acid was added dropwise to adjust the pH to 0.5. N235 was added. The V-containing aqueous phase and N235... The volume ratio was 4:1. The mixture was stirred for 10 min, allowed to stand and separate into an aqueous phase and a V-supported organic phase. The V-supported organic phase was back-extracted to obtain V. Ozone was introduced into the remaining aqueous phase after extraction, and 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH to 2. The reaction was carried out for 1 h, and the mixture was filtered to obtain battery-grade MnO2 and residual liquid. 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH of the residual liquid to 4, and the mixture was filtered to obtain Al(OH)3. 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH to 10, and the mixture was filtered to obtain Mg(OH)2. Finally, the remaining solution was evaporated and crystallized to obtain NaCl.

[0046] Example 2

[0047] like Figure 1 As shown, this embodiment provides a clean production process for titanium dioxide and a process for full recovery of by-products, including the following steps:

[0048] 1. Mix 500 kg of ilmenite concentrate powder with 1750 kg of 28 wt.% concentrated hydrochloric acid, set the stirring speed to 400 rpm, and continuously introduce HCl gas into the mixture to maintain the free HCl concentration in the mixture ≥ 8 mol / L. The reaction pressure is 0.105 MPa, the reaction temperature is 95℃, and the reaction is continued for 5 h to obtain an acidic leachate.

[0049] 2. Add 1 kg of iron powder to every 450 kg of acidic leachate, maintain the reaction temperature at 45℃, stir at 250 rpm, and continue the reaction for 1.5 h. Then, cool the reduced acidic leachate to 0℃ at a rate of 2.5℃ / h and continue crystallizing for 7 h. Centrifuge to obtain FeCl2·4H2O crystals and crystallization mother liquor.

[0050] 3. Place the crystallization mother liquor in the anode and cathode chambers of the electrolytic cell. A strongly alkaline anion exchange membrane is installed between the anode and cathode. The anode plate is an IrO2-coated titanium electrode, and the cathode plate is a pure titanium plate. Set the cell voltage to 2V and the current density to 1000A / m. 2 The electrolysis temperature was 50℃, and the electrolysis time was 2.5h to obtain FeCl3 mother liquor and high-purity iron powder.

[0051] 4. The FeCl3 mother liquor was fed into the extraction tower and mixed with the composite extractant at a volume ratio of 2.5:1. The stirring speed was 250 rpm, and the mixture was stirred for 7 min. After standing until the solution separated into layers, the upper organic phase was countercurrently introduced into the next mixing chamber, and the lower aqueous phase was introduced into the next mixing chamber. The extraction steps were repeated. After 5 stages of extraction, a purified titanium solution in aqueous phase and an iron-loaded extractant in organic phase were obtained. Iron and extractant were recovered by counter-extraction of the organic phase. The composite extractant was obtained by mixing tributyl phosphate and methyl isobutyl ketone at a volume ratio of 7:3.

[0052] 5. Add 0.04 kg of rutile TiO2 seed crystals to every 100 kg of purified titanium solution, stir evenly at 150 rpm, heat to 98°C, and hydrolyze for 7 hours, recovering HCl gas during the process. After hydrolysis, centrifuge to obtain metatitanic acid filter cake and hydrolysis mother liquor. Wash the metatitanic acid filter cake with deionized water until the filter cake contains Cl. - The content is ≤0.1%, then dried at 130℃ until the moisture content is less than 5%, and then calcined in air at 800℃ for 2 hours to obtain high-purity titanium dioxide;

[0053] 6. The hydrolysis mother liquor was evaporated and concentrated. 1 mol / L dilute hydrochloric acid was added to the concentrated mother liquor to adjust the pH to 1.5. P2O4 was added to the mother liquor at a volume ratio of 4:1 (mother liquor to P2O4). The mixture was stirred for 13 min, then allowed to stand and separate into layers, yielding a V-containing aqueous phase and a Sc-supported organic phase. The Sc-supported organic phase was back-extracted to obtain Sc. Air was introduced into the V-containing aqueous phase, and the reaction was carried out at 180 rpm for 1.5 h. Then, 1 mol / L dilute hydrochloric acid was added dropwise to adjust the pH to 0.8. N235 was added, with the volume ratio of the V-containing aqueous phase to N235 being... The ratio was 4.5:1. The mixture was stirred and mixed for 10 min, and allowed to stand to separate into an aqueous phase and a V-supported organic phase. The V-supported organic phase was back-extracted to obtain V. Ozone was introduced into the remaining aqueous phase after extraction, and 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH to 3. The reaction was carried out for 1.5 h, and the mixture was filtered to obtain battery-grade MnO2 and residual liquid. 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH of the residual liquid to 4.5, and the mixture was filtered to obtain Al(OH)3. 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH to 10.5, and the mixture was filtered to obtain Mg(OH)2. Finally, the remaining solution was evaporated and crystallized to obtain NaCl.

[0054] Example 3

[0055] like Figure 1 As shown, this embodiment provides a clean production process for titanium dioxide and a process for full recovery of by-products, including the following steps:

[0056] 1. Mix 500 kg of ilmenite concentrate powder with 2000 kg of 32 wt.% concentrated hydrochloric acid, set the stirring speed to 500 rpm, and continuously introduce HCl gas into the mixture to maintain the free HCl concentration in the mixture ≥ 8 mol / L. The reaction pressure is 0.11 MPa, the reaction temperature is 105℃, and the reaction is continued for 6 h to obtain an acidic leachate.

[0057] 2. Add 1 kg of iron powder to every 500 kg of acidic leachate, maintain the reaction temperature at 50℃, stir at 300 rpm, and continue the reaction for 2 h. Then, cool the reduced acidic leachate to -5℃ at a rate of 3℃ / h and continue crystallizing for 8 h. Centrifuge to separate FeCl2·4H2O crystals and crystallization mother liquor.

[0058] 3. Place the crystallization mother liquor in the anode and cathode chambers of the electrolytic cell. A strongly alkaline anion exchange membrane is installed between the anode and cathode. The anode plate is an IrO2-coated titanium electrode, and the cathode plate is a pure titanium plate. Set the cell voltage to 2.5V and the current density to 2000A / m. 2 The electrolysis temperature was 60℃, and the electrolysis time was 3h to obtain FeCl3 mother liquor and high-purity iron powder.

[0059] 4. The FeCl3 mother liquor was fed into the extraction tower and mixed with tributyl phosphate at a volume ratio of 3:1. The stirring speed was 300 rpm, and the mixture was mixed for 10 min. After standing until the solution separated into layers, the upper organic phase was countercurrently introduced into the next mixing chamber, and the lower aqueous phase was introduced into the next mixing chamber. The extraction steps were repeated. After 5 stages of extraction, the aqueous phase purified titanium solution and the organic phase iron-loaded extractant were obtained. Iron and extractant were recovered by reverse extraction of the organic phase.

[0060] 5. Add 0.18 kg of anatase TiO2 seed crystals to every 100 kg of purified titanium solution, stir evenly at 200 rpm, heat to 100℃, and hydrolyze for 8 hours, recovering HCl gas during the process. After hydrolysis, centrifuge to obtain metatitanic acid filter cake and hydrolysis mother liquor. Wash the metatitanic acid filter cake with deionized water until the filter cake contains Cl. - The content is ≤0.1%, then dried at 150℃ until the moisture content is less than 5%, and then calcined in air at 600℃ for 1.5h to obtain high-purity titanium dioxide;

[0061] 6. The hydrolysis mother liquor was evaporated and concentrated. 1 mol / L dilute hydrochloric acid was added to the concentrated mother liquor to adjust the pH to 2. P2O4 was added to the mother liquor, with a volume ratio of mother liquor to P2O4 of 4.5:1. The mixture was stirred for 15 min, then allowed to stand and separate into layers, yielding a V-containing aqueous phase and a Sc-supported organic phase. The Sc-supported organic phase was back-extracted to obtain Sc. Air was introduced into the V-containing aqueous phase, and the reaction was carried out at a stirring rate of 200 rpm for 2 h. Then, 1 mol / L dilute hydrochloric acid was added dropwise to adjust the pH to 1. N235 was added. The V-containing aqueous phase and N235... The volume ratio was 5:1. The mixture was stirred for 10 min, allowed to stand and separate into an aqueous phase and a V-supported organic phase. The V-supported organic phase was back-extracted to obtain V. Ozone was introduced into the remaining aqueous phase after extraction, and 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH to 5. The reaction was carried out for 2 h, and the mixture was filtered to obtain battery-grade MnO2 and residual liquid. 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH of the residual liquid to 5, and the mixture was filtered to obtain Al(OH)3. 30 wt.% sodium hydroxide solution was added dropwise to adjust the pH to 11, and the mixture was filtered to obtain Mg(OH)2. Finally, the remaining solution was evaporated and crystallized to obtain NaCl.

[0062] Comparative Example 1

[0063] Comparative Example 1 provides a process for clean production of titanium dioxide and full recovery of by-products. The difference from Example 1 is that HCl gas is not introduced during the acid leaching of ilmenite concentrate powder with concentrated hydrochloric acid. The remaining steps are the same as in Example 1 and will not be repeated here.

[0064] Comparative Example 2

[0065] Comparative Example 2 provides a process for clean production of titanium dioxide and full recovery of by-products. The difference from Example 1 is that the step of electrolytic crystallization mother liquor is not performed. The remaining steps are the same as those in Example 1 and will not be repeated here.

[0066] To demonstrate the beneficial effects of this application, relevant performance tests were conducted on Examples 1-3 and Comparative Examples 1-2 to detect the final titanium dioxide yield and the residual content of various impurities in the processes of Examples 1-3 and Comparative Examples 1-2. The test results are shown in Table 1.

[0067] Table 1. Titanium dioxide yield and residual content of various impurities in each process of Examples 1-3 and Comparative Examples 1-2

[0068]

[0069] As shown in Table 1, the titanium dioxide yield in Examples 1-3 was significantly higher than that in Comparative Examples 1-2. This is because in Comparative Example 1, HCl gas was not continuously introduced during the leaching of titanium with concentrated hydrochloric acid, resulting in insufficient HCl concentration in the leachate. This prevented the complete extraction of titanium, leading to a decrease in the final titanium dioxide yield and an increase in impurity content. In Comparative Example 2, the electrolysis of the crystallization mother liquor was omitted. Electrolysis oxidizes trivalent titanium to tetravalent titanium, preventing titanium ions from being extracted by the extractant and thus avoiding titanium loss. The lack of this electrolysis step in Comparative Example 2 resulted in some titanium loss, ultimately leading to a decrease in titanium dioxide yield and an increase in impurity content. In conclusion, the titanium dioxide production process provided in this application not only effectively improves the leaching efficiency of titanium dioxide but also deeply removes impurities and recovers by-products, exhibiting excellent environmental benefits and economic advantages.

[0070] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the claims of this application.

Claims

1. A process for clean production of titanium dioxide and full recovery of by-products, characterized in that, Includes the following steps: The ilmenite concentrate powder was mixed with concentrated hydrochloric acid in a reaction vessel, and then HCl gas was continuously introduced into the reaction vessel. After the reaction was completed, acidic leachate and slag were obtained. Iron powder was added to the acidic leachate to carry out a reduction reaction. After the reaction was completed, the solution was frozen and crystallized. The FeCl2·4H2O crystals and the mother liquor were obtained by centrifugation. Electrolysis of the crystallization mother liquor yields FeCl3 mother liquor and high-purity iron powder after electrolysis. Extractant a was added to the FeCl3 mother liquor. After multi-stage extraction and washing, an aqueous purified titanium solution and an organic phase iron-supported extractant were obtained. The extractant was recovered by reverse extraction of the organic phase. TiO2 seed crystals were added to the purified titanium solution, stirred evenly, and then heated for hydrolysis. HCl gas was recovered. After hydrolysis, the solution was centrifuged to obtain metatitanic acid filter cake and hydrolysis mother liquor. The metatitanic acid filter cake was washed, dried and calcined to obtain high-purity titanium dioxide. After evaporating and concentrating the hydrolysis mother liquor, Sc and V are first extracted and recovered. Then, ozone is introduced to precipitate manganese and recover battery-grade MnO2. Next, the pH of the solution is adjusted to recover Al(OH)3 and Mg(OH)2. Finally, NaCl is recovered by evaporating and crystallizing the solution.

2. The process for clean production of titanium dioxide and full recovery of by-products according to claim 1, characterized in that, The recycling process further includes: calcining the FeCl2·4H2O crystals at high temperature to recover high-purity iron oxide and HCl gas.

3. The process for clean production of titanium dioxide and full recovery of by-products according to claim 1, characterized in that, The process parameters for obtaining the acidic leachate and slag are as follows: reaction temperature 80~105℃, reaction pressure 0.1~0.11MPa, stirring speed 300~500rpm, reaction time 4~6h, free HCl concentration in the solution ≥8mol / L, and leachate discharge condition of TiO2 concentration ≥120g / L; the concentration of the concentrated hydrochloric acid is 28~32%; and the mass ratio of the ilmenite concentrate powder to the concentrated hydrochloric acid is 1:(3~4).

4. The process for clean production of titanium dioxide and full recovery of by-products according to claim 1, characterized in that, The process parameters for the reduction reaction are: reaction temperature 40~50℃, stirring speed 200~300rpm, and reaction time 1~2h; the conditions for the freeze crystallization are to cool the acidic leachate after reduction to -5~3℃ at a rate of 2~3℃ / h, and continue the crystallization reaction for 6~8h; the mass ratio of the acidic leachate to iron powder is (400~500):

1.

5. The process for clean production of titanium dioxide and full recovery of by-products according to claim 1, characterized in that, The specific steps of the electrolysis are as follows: the mother liquor is fed into the anode and cathode chambers of the electrolytic cell, an ion exchange membrane is installed between the anode and cathode, the cell voltage is 1.5~2.5V, and the current density is 500~2000A / m. 2 The electrolysis temperature is 40~60℃ and the electrolysis time is 2~3h; the anode is an IrO2 coated titanium electrode, the cathode is a pure titanium plate, and the ion exchange membrane is a strongly basic anion exchange membrane.

6. The process for clean production of titanium dioxide and full recovery of by-products according to claim 1, characterized in that, The specific steps of the multi-stage extraction are as follows: FeCl3 mother liquor is fed into the extraction tower and mixed with extractant a at a volume ratio of (2~3):

1. The mixing and stirring rate is 200~300 rpm and the time is 5~10 min. After the mixture is allowed to stand and separate into layers, the upper organic phase is countercurrently introduced into the next stage mixing chamber for extraction, and the lower aqueous phase is introduced into the next stage mixing chamber for further extraction. After 5 stages of extraction, the aqueous purified titanium liquid and the organic phase iron-supported extractant are obtained.

7. The process for clean production of titanium dioxide and full recovery of by-products according to claim 6, characterized in that, The extractant a is any one of tributyl phosphate or a composite extractant, wherein the composite extractant is obtained by mixing tributyl phosphate and methyl isobutyl ketone in a volume ratio of 7:

3.

8. The process for clean production of titanium dioxide and full recovery of by-products according to claim 1, characterized in that, The stirring rate in the step of uniform mixing is 100-200 rpm; the hydrolysis temperature in the step of heating and hydrolysis is 95-100℃, and the hydrolysis time is 6-8 h; deionized water is used as the washing liquid when washing the metatitanic acid filter cake, and the drying temperature is 120-150℃; the calcination temperature is 600-850℃, the calcination time is 1-2 h, and the calcination atmosphere is air; the TiO2 seed crystals include either rutile or anatase; the mass ratio of the TiO2 seed crystals to the purified titanium liquid is (0.04-0.18):

100.

9. The process for clean production of titanium dioxide and full recovery of by-products according to claim 1, characterized in that, The specific steps for extracting and recovering Sc and V are as follows: add 1 mol / L dilute hydrochloric acid to the concentrated hydrolysis mother liquor to adjust the pH to 1~2, add extractant b to the hydrolysis mother liquor, the volume ratio of hydrolysis mother liquor to extractant b is (4~5):1, stir and mix for 10~15 min, then let stand to separate the layers to obtain a V-containing aqueous phase and a Sc-loaded organic phase, and back extract the Sc-loaded organic phase to obtain Sc; Air is introduced into the aqueous phase containing V, and the stirring speed is 150~200 rpm. The reaction is carried out for 1~2 h. Then, 1 mol / L dilute hydrochloric acid is added dropwise to adjust the pH to 0.5~1. Extractant c is added, and the volume ratio of the aqueous phase containing V to extractant c is (4~5):

1. The mixture is stirred and mixed for 10 min. After standing and separating into layers, an aqueous phase and a V-supported organic phase are obtained. The V-supported organic phase is back-extracted to obtain V. The extractant b is P2O4 and the extractant c is N235.

10. The process for clean production of titanium dioxide and full recovery of by-products according to claim 1, characterized in that, The specific steps for recovering battery-grade MnO2 are as follows: ozone is introduced into the remaining aqueous phase after extraction, the pH is adjusted to 2-5, the reaction is carried out for 1-2 hours, and the battery-grade MnO2 and residual liquid are obtained by filtration; the pH of the residual liquid is adjusted to 4-5, Al(OH)3 is obtained by filtration, the pH is adjusted to 10-11, Mg(OH)2 is obtained by filtration, and finally the remaining solution is evaporated and crystallized to obtain NaCl.

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