A process for preparing nano-TiO2 from titanium-containing waste slag

Abstract

A process for preparing nano-TiO2 from titanium-containing waste belongs to the field of inorganic functional material preparation. This process prepares high-purity nano-TiO2 through pretreatment, selective leaching, continuous crystallization, washing, drying, and calcination. It employs a continuous micro-processing technology coupling a rotating microfilm reactor and a continuous tubular reactor to achieve efficient leaching of titanium components and uniform nucleation and growth of TiO2 crystals. Compared with traditional batch processes, this invention improves titanium resource utilization, reduces impurity introduction, and improves the particle size distribution, crystallinity, and specific surface area of ​​the product. The obtained TiO2 is predominantly anatase, characterized by uniform particle size, well-developed pore structure, and high specific surface area, and can be widely used in catalyst supports, photocatalysis, and adsorption materials. This invention provides a continuous, stable, and low-energy-consumption process, offering an efficient pathway for the high-value utilization of titanium-containing waste.

Description

Technical Field

[0001] This invention belongs to the fields of inorganic functional materials, resource recycling and continuous microchemical technology, and specifically relates to a continuous process for preparing nano-TiO2 from titanium-containing waste residue, and particularly to a resource utilization method for titanium-containing waste residue based on the coupling enhancement of a rotating micro-liquid membrane reactor and a continuous tubular reactor. Background Technology

[0002] The use of highly efficient heterogeneous Ziegler-Natta catalysts (ZN catalysts) and supported transition metal catalysts continues to grow, resulting in a large amount of titanium-containing waste. This type of waste not only contains more than 40% titanium resources by mass, but also contains high concentrations of chlorine, a MgCl2 support framework, heavy metal components, and a large amount of organic polymer residues, making it a typical solid waste with both environmental risks and resource recovery value.

[0003] For a long time, titanium-containing waste has been mainly treated using traditional methods such as landfilling or incineration. This not only easily leads to acid leaching of groundwater and secondary pollution from chlorinated organic compounds, but also results in a large waste of titanium resources. Therefore, achieving green and efficient resource utilization of titanium-containing waste has become an important issue that urgently needs to be addressed.

[0004] In recent years, extensive research has been conducted both domestically and internationally on the wet leaching of titanium resources from titanium-containing waste. While traditional inorganic strong acid leaching systems can dissolve titanium, they suffer from severe equipment corrosion, significant co-dissolution of impurities, and a heavy burden on acidic wastewater treatment. Therefore, research has gradually shifted towards selective complexation leaching routes centered on organic acids such as oxalic acid. For example, patent CN111333108B utilizes organic acids such as oxalic acid for selective leaching of titanium-containing industrial waste, causing titanium to form soluble complexes that enter the liquid phase, while impurities such as silicon and aluminum remain in the solid phase, thereby improving the separation efficiency of titanium.

[0005] However, most current processes still employ traditional batch stirred tank reactors. Due to the uneven flow field and shear distribution within the stirred tank, the solid-liquid two-phase mass transfer efficiency is low, resulting in leaching cycles that often last for several hours or even more than ten hours. As the leaching time extends, impurities such as aluminum, magnesium, and silicon undergo secondary dissolution, reducing the purity of the leachate and increasing the difficulty of subsequent separation. In the subsequent hydrolysis and crystallization stage, traditional batch reactors also face the problem of difficulty in precisely controlling the crystal phase, particle size, and pore structure. Patent CN103769406A discloses a method for treating titanium-containing waste residue from polyolefin catalysts, which also relies on conventional stirred tanks to complete the neutralization and precipitation process. However, due to the tendency for instantaneous high supersaturation environments and temperature gradients to form in localized areas, precursor particles are prone to random nucleation and agglomeration, ultimately resulting in titanium dioxide powder with mixed crystal forms, wide particle size distribution, and low specific surface area, making it difficult to meet the application requirements of high-end nano-anatase TiO2 materials.

[0006] To overcome the limitations of traditional stirred tank reactors in mass transfer, heat transfer, and mixing, microchemical technology has received widespread attention in recent years. For example, patent CN102633294A discloses a rotating liquid film reactor that forms a micron-sized liquid film through high-speed rotation, enhancing microscopic shearing and mass transfer processes, thereby significantly improving the mixing efficiency of reactants.

[0007] However, relying solely on rotating microfilms to enhance front-end leaching is insufficient to solve the subsequent crystallization control problem. Titanium-containing leachates require extremely high flow field stability and heat transfer uniformity during hydrolysis and crystallization. Savage T et al., in "Machinelearning-assisted discovery of flow reactor designs" (Nat. Chem. Eng., 2024, 1, 522–531), pointed out that a vortex structure with enhanced mixing can be formed inside a coil reactor, which helps improve plug flow performance and promotes the stable progress of the continuous crystallization process.

[0008] However, for titanium-containing waste residues in the petrochemical industry, characterized by heavy organic encapsulation, high chlorine content, and complex composition, there is still a lack of mature technological systems for achieving full-process synergistic coupling between pretreatment processes such as "calcination desorption—acid-base regulation and neutralization—ultrasonic slurry modulation" and microchemical enhancement units such as "rotating microfilm enhanced complexation leaching" and "continuous spiral coil push-flow hydrolysis crystallization." This invention, based on the concept of continuous microchemical processes and multi-unit synergistic directional crystallization regulation, proposes a novel process for the efficient preparation of nano-TiO2 from titanium-containing waste residues. Summary of the Invention

[0009] The purpose of this invention is to provide a continuous process for preparing nano-TiO2 from titanium-containing waste residue, so as to solve the problems of low titanium resource utilization, poor leaching selectivity, wide particle size distribution of nano-TiO2, and easy particle agglomeration in the prior art.

[0010] This invention employs a continuous microchemical technology that couples a rotating microfilm reactor with a continuous tubular reactor. Using titanium-containing waste as raw material, it achieves the continuous and stable preparation of nano-TiO2 through steps such as calcination pretreatment, neutralization adjustment, enhanced leaching, continuous crystallization, and calcination crystallization. By precisely controlling the fluid residence time distribution, micro-mixing behavior, and crystallization kinetics, the leaching efficiency of titanium components and the uniformity of the TiO2 crystal structure are effectively improved.

[0011] The technical solution of the present invention is as follows: First, the titanium-containing waste residue is placed in a roasting device for pretreatment. The roasting temperature is controlled within the range of 350–650℃, and the holding time is controlled within the range of 1–6 hours. The roasting process can remove organic residues, volatile impurities, and some carbon deposits from the waste residue, while promoting the loosening of the internal structure of the waste residue and improving the accessibility and leaching activity of the titanium components in the subsequent leaching reaction.

[0012] After calcination, a neutralizing agent is added to the system for acid-base adjustment. The neutralizing agent can be one or more of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, or sodium bicarbonate. The neutralization reaction temperature is controlled within the range of 30–80℃, the stirring speed within the range of 200–800 rpm, and the reaction time within the range of 0.5–4 h. Neutralization reduces the acidity of the system, decreases the leaching of impurity elements during subsequent leaching, and improves the rheological properties of the slurry.

[0013] The neutralized solid material is then pulverized and mixed with deionized water to form a slurry. The solid content of the slurry is controlled within the range of 10–30 wt%. To improve the stability and particle dispersibility of the slurry, a dispersant can be added to the system. The dispersant includes one or more of sodium hexametaphosphate, sodium polyacrylate, polyvinylpyrrolidone, or sodium citrate, and its addition amount is controlled within the range of 0.1–3 wt% of the total mass of the slurry.

[0014] The pretreated slurry and leaching agent are instantaneously premixed using a three-way mixing device, and then continuously pumped to a rotating microfilm reactor for leaching reaction. The leaching agent is one or more of oxalic acid, sulfuric acid, hydrochloric acid, or organic complex acids, with the concentration controlled in the range of 0.5–5 mol / L and the liquid-to-solid ratio controlled in the range of 5:1 ml / g–30:1 ml / g.

[0015] The rotational speed of the rotating microfilm reactor is controlled within the range of 2000–8000 r / min, the reaction temperature is controlled within the range of 60–120℃, and the material residence time is controlled within the range of 5–60 min. The high-speed rotation causes the reaction liquid to form a micron-scale ultrathin liquid film in the reactor, which can significantly improve the liquid-solid interface renewal rate and local shear strength, thereby enhancing the reaction mass transfer process and effectively narrowing the residence time distribution.

[0016] After the leaching reaction is completed, a titanium-containing leachate is obtained by centrifugation. An aluminum source and a precipitant are then added to the leachate. The aluminum source can be one or more of aluminum sulfate, aluminum nitrate, or aluminum chloride; the precipitant is one or more of urea, ammonia, or ammonium carbonate. After ultrasonic dispersion for 10–60 min, the system is continuously fed into a tubular reactor for continuous crystallization.

[0017] The temperature of the continuous tubular reactor is controlled within the range of 70 to 120°C, the material flow rate is controlled within the range of 0.05 to 1.0 ml / s, and the residence time is controlled within the range of 1 to 6 h. The continuous flow conditions can effectively suppress the phenomenon of local supersaturation, so that the Ti precursor can be uniformly nucleated and grown in a stable environment, thereby obtaining nano-TiO2 materials with uniform particle size and high crystallinity.

[0018] After crystallization, the resulting slurry was continuously filtered and repeatedly washed with deionized water until no obvious impurity ions were found in the filtrate. The filter cake was then dried at 80–150°C for 4–24 h and calcined at 400–700°C for 1–6 h to finally obtain nano-TiO2 material.

[0019] Compared with the prior art, the present invention has the following technical advantages: First, the present invention uses a rotating microfilm reactor to enhance the leaching process. Compared with the traditional stirred tank reactor, the liquid film thickness is significantly reduced and the liquid-solid interface area is significantly increased, which can effectively enhance the heat and mass transfer behavior of titanium components during the leaching process and improve the leaching rate and resource utilization efficiency.

[0020] Secondly, the present invention achieves precise control of residence time distribution through a continuous flow system, which can effectively avoid side reactions and particle agglomeration problems caused by local concentration fluctuations in traditional batch systems, thereby improving the uniformity of product structure.

[0021] Third, the present invention utilizes a continuous tubular reactor to achieve uniform nucleation and stable growth of Ti precursors, which can significantly narrow the particle size distribution range of TiO2 particles, reduce the tendency of particle agglomeration, and improve the specific surface area and pore structure uniformity of the material.

[0022] Fourth, the process of this invention adopts a continuous flow, which can realize continuous raw material transportation, continuous reaction and continuous separation, and has the advantages of stable process and high degree of automation. Compared with traditional batch process, it can significantly reduce energy consumption and labor costs.

[0023] Fifth, the TiO2 material obtained by this invention mainly exhibits anatase crystal form, with high specific surface area, uniform pore structure and excellent surface activity, and can be widely used in catalyst support, photocatalytic degradation, energy storage materials and functional adsorption materials. Attached Figure Description

[0024] Figure 1 Cl content of materials calcined at different temperatures Figure 2 Impurity removal effect at different pH levels Figure 3 Effect of dispersants on sedimentation stability Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Example 1

[0026] Titanium-containing waste residue was placed in a muffle furnace and roasted at 500°C for 3 hours. After roasting, it was naturally cooled to room temperature.

[0027] Subsequently, sodium hydroxide solution was added to the calcined waste residue for neutralization and adjustment, and the pH of the system was controlled to be 4.5. The reaction was carried out at 50°C and stirred at 400 rpm for 2 h.

[0028] After neutralization, solid-liquid separation was carried out. The resulting solid was initially crushed and deionized water was added to prepare a slurry. The solid content of the slurry was controlled at 15 wt%. Sodium hexametaphosphate with a final concentration of 0.5 wt% was added to the slurry as a dispersant. The mixture was then stirred for 30 min and allowed to stand for 30 min.

[0029] The slurry and oxalic acid leachate were then instantaneously premixed using a three-way mixer, with an oxalic acid concentration of 3 mol / L and a liquid-to-solid ratio of 20:1 ml / g.

[0030] The mixture is continuously pumped into a rotating microfilm reactor via a peristaltic pump. The reactor speed is set to 4000 r / min, the reaction temperature is set to 85℃, and the material residence time is controlled to 30 min.

[0031] After leaching, the titanium-containing leachate was obtained by centrifugation.

[0032] Aluminum sulfate solution was then added to the leachate, and the Al / Ti molar ratio was controlled at 1:14. After ultrasonic dispersion for 20 min, urea was added as a precipitant, and the molar ratio of metal ions to urea was controlled at 1:20.

[0033] The mixture is continuously fed into a tubular reactor for continuous crystallization. The reaction temperature is set at 95℃, the material flow rate is set at 0.3 m / s, and the residence time is controlled at 3 h.

[0034] After the reaction is complete, the resulting slurry is continuously filtered and repeatedly washed with deionized water until no impurity ions are detected in the filtrate.

[0035] The filter cake was then dried in an oven at 120°C for 12 hours, and then calcined at 550°C for 3 hours to finally obtain nano-TiO2 material.

[0036] XRD analysis showed that the obtained product mainly exhibited anatase crystal form; SEM results indicated that the particles were uniformly dispersed with no obvious agglomeration; BET test results showed that the material had a high specific surface area and a uniform mesoporous structure. Example 2

[0037] Titanium-containing waste residue was placed in a muffle furnace and roasted at 550°C for 4 hours. After roasting, it was naturally cooled to room temperature.

[0038] Subsequently, a mixture of ammonia and sodium carbonate was added to the roasted waste residue for neutralization and adjustment, and the pH of the system was controlled to be 5.0. The reaction was carried out at 60°C and stirred at 500 rpm for 2 h.

[0039] After neutralization, solid-liquid separation was performed. The resulting solid was pulverized and deionized water was added to prepare a slurry with a solid content of 20 wt%. Sodium polyacrylate with a final concentration of 1 wt% was added to the slurry as a dispersant. The mixture was then stirred for 40 min and allowed to stand for 20 min.

[0040] The slurry was then instantaneously premixed with the oxalic acid-sulfuric acid composite leachate using a three-way mixer, wherein the oxalic acid concentration was 2 mol / L, the sulfuric acid concentration was 1 mol / L, and the liquid-solid ratio was 15:1 ml / g.

[0041] The mixture is continuously pumped into a rotating microfilm reactor via a peristaltic pump. The reactor speed is set to 6000 r / min, the reaction temperature is set to 90℃, and the material residence time is controlled to 20 min.

[0042] After leaching, the titanium-containing leachate was obtained by centrifugation.

[0043] Aluminum nitrate solution was then added to the leachate, and the Al / Ti molar ratio was controlled at 1:12. After ultrasonic dispersion for 30 min, urea was added as a precipitant, and the molar ratio of metal ions to urea was controlled at 1:25.

[0044] The mixture is continuously fed into a tubular reactor for continuous crystallization. The reaction temperature is set at 100℃, the material flow rate is set at 0.5 ml / s, and the residence time is controlled at 2 h.

[0045] After the reaction is complete, the resulting slurry is continuously filtered and repeatedly washed with deionized water.

[0046] The filter cake was then dried in an oven at 110°C for 10 h, and then calcined at 500°C for 4 h to finally obtain nano-TiO2 material.

[0047] Test results show that the TiO2 particle size obtained in this embodiment is further reduced compared with that in Example 1, the particle uniformity is significantly improved, and the material pore structure is more developed. Example 3

[0048] Titanium-containing waste residue was placed in a muffle furnace and roasted at 450°C for 2 hours. After roasting, it was naturally cooled to room temperature.

[0049] Subsequently, potassium hydroxide solution was added to the calcined waste residue for neutralization and adjustment, and the pH of the system was controlled at 4.8. The reaction was carried out at 45°C and stirred at 350 rpm for 1.5 h.

[0050] After neutralization, solid-liquid separation was performed. The resulting solid was crushed and deionized water was added to prepare a slurry with a solid content of 25 wt%. Sodium hexametaphosphate with a final concentration of 0.8 wt% was added as a dispersant. The mixture was then stirred for 30 min and allowed to stand for 20 min.

[0051] The slurry and oxalic acid leachate were then instantaneously premixed using a three-way mixer, with an oxalic acid concentration of 4 mol / L and a liquid-to-solid ratio of 25:1 ml / g.

[0052] The mixture is continuously pumped into a rotating microfilm reactor via a peristaltic pump. The reactor speed is set to 3500 r / min, the reaction temperature is set to 80℃, and the material residence time is controlled to 40 min.

[0053] After leaching, the titanium-containing leachate was obtained by centrifugation.

[0054] Aluminum chloride solution was then added to the leachate, and the Al / Ti molar ratio was controlled at 1:16. After ultrasonic dispersion for 25 min, ammonium carbonate was added as a precipitant, and the molar ratio of metal ions to precipitant was controlled at 1:18.

[0055] The mixture is continuously fed into a tubular reactor for continuous crystallization. The reaction temperature is set at 90℃, the material flow rate is set at 0.2 ml / s, and the residence time is controlled at 4 h.

[0056] After the reaction is complete, the resulting slurry is continuously filtered and repeatedly washed with deionized water.

[0057] The filter cake was then dried in an oven at 130°C for 14 hours, and then calcined at 650°C for 2 hours to finally obtain nano-TiO2 material.

[0058] The results show that the TiO2 obtained in this embodiment has high crystallinity and good thermal stability, and still maintains a good mesoporous structure under high temperature conditions. Comparative Example 1

[0059] The traditional batch stirred tank process was used for leaching titanium-containing waste residue and preparing TiO2.

[0060] First, titanium-containing waste residue is placed in a muffle furnace and roasted at 500°C for 3 hours.

[0061] Subsequently, sodium hydroxide solution was added to the calcined waste residue for neutralization and adjustment, and the pH of the system was controlled to be 4.5. The reaction was carried out at 50°C and stirred at 400 rpm for 2 h.

[0062] After neutralization, the resulting solid is crushed and deionized water is added to prepare a slurry. The solid content of the slurry is controlled at 15 wt%, and sodium hexametaphosphate with a final concentration of 0.5 wt% is added as a dispersant.

[0063] The slurry and oxalic acid leachate were then directly added to a conventional stirred tank for leaching reaction. The oxalic acid concentration was 3 mol / L, the liquid-to-solid ratio was 20:1 ml / g, the reaction temperature was set at 85℃, the stirring speed was set at 500 rpm, and the reaction time was set at 3 h.

[0064] After leaching, the titanium-containing leachate was obtained by allowing it to settle.

[0065] Subsequently, aluminum sulfate solution and urea were added to the leachate, and an intermittent crystallization reaction was carried out in a conventional stirred tank. The reaction temperature was set at 95°C and the reaction time was set at 4 h.

[0066] After the reaction was completed, the slurry was filtered, washed and dried, and then calcined at 550℃ for 3 h to finally obtain TiO2 material.

[0067] Test results show that the TiO2 particles obtained in the comparative example have a wider particle size distribution and obvious agglomeration. Their specific surface area is lower than that of the samples obtained in Examples 1-3, and the batch stability of the material is poor. Compared with the continuous microchemical process of this invention, the traditional batch process, due to the lack of enhanced mass transfer and precise control of residence time, results in large local concentration fluctuations, easily leading to excessive particle growth and non-uniform nucleation, thus resulting in significantly lower material performance.

Claims

1. A process for preparing nano-TiO2 from titanium-containing waste residue, characterized in that... Includes the following steps: A. The titanium-containing waste residue is pretreated by roasting at a temperature of 350–650℃ for 1–6 hours to remove organic residues and volatile impurities. B. Add a neutralizing agent to the calcined titanium-containing waste residue for acid-base adjustment. The reaction temperature is 30-80℃ and the reaction time is 0.5-4 h. After stirring and reacting, solid-liquid separation is carried out, and the obtained solid is crushed and mixed with deionized water to prepare a slurry. C. The pretreated slurry obtained in step B is instantaneously premixed with the leaching agent through a mixing device and then pumped into a rotating microfilm reactor for continuous leaching reaction. The reaction temperature is 60-120℃ and the material residence time is 5-60 min. After the reaction is completed, titanium-containing leachate is obtained by solid-liquid separation. D. Add aluminum source and precipitant to the titanium-containing leachate obtained in step C, and after ultrasonic dispersion for 10-60 min, pump it into a continuous tubular reactor for continuous crystallization reaction. The reactor temperature is 70-120℃ and the material residence time is 1-6 h. E. The reaction solution obtained in step D is subjected to filtration, washing with water, drying and calcination. The drying temperature is 80-150℃ and the drying time is 4-24 h. The calcination temperature is 400-700℃ and the calcination time is 1-6 h, finally obtaining nano-TiO2 material.

2. The process according to claim 1, characterized in that, The neutralizing agent mentioned in step B is one or more of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, or sodium bicarbonate.

3. The process according to claim 1, characterized in that, In step B, the solid content of the slurry is controlled at 10-30 wt%, and a dispersant is added to improve the stability of the slurry.

4. The process according to claim 3, characterized in that, The dispersant is one or more of sodium hexametaphosphate, polyvinylpyrrolidone, sodium polyacrylate, or sodium citrate, and its addition amount is controlled within the range of 0.1 to 3 wt% of the total mass of the slurry.

5. The process according to claim 1, characterized in that, The leaching agent mentioned in step C is one or more of oxalic acid, sulfuric acid, hydrochloric acid, and organic complex acid, and the concentration of the leaching agent is 0.5 to 5 mol / L.

6. The process according to claim 1, characterized in that, In step C, the liquid-to-solid ratio of the material pumped into the rotating microfilm reactor for continuous leaching reaction is controlled within the range of 5:1 ml / g to 30:1 ml / g.

7. The process according to claim 1, characterized in that, In step C, the rotational speed of the rotating microliquid membrane reactor is 2000–8000 r / min.

8. The process according to claim 1, characterized in that, The aluminum source mentioned in step D is one or more of aluminum sulfate, aluminum nitrate, or aluminum chloride.

9. The process according to claim 1, characterized in that, The precipitant mentioned in step D is one or more of urea, ammonia, or ammonium carbonate.

10. The process according to claim 1, characterized in that, In step D, the material flow rate is 0.05–1.0 ml / s.

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