Titanium dioxide hydrolysis method with added seeds

Abstract

The application discloses a titanium white powder seed-added hydrolysis method and belongs to the technical field of titanium white powder production. The application aims at the problems that stirring in the process of crystallization in the prior art easily leads to uneven sizes of crystalline particles, the particle size distribution is enlarged, and the hiding power is affected, but if no stirring is performed, the crystallization speed is slow, and the crystallization is insufficient, the stirring speed is reduced in the hydrolysis process, and continuous stirring is changed into intermittent stirring, the effect of uniformly distributing the seeds to all places of the titanium liquid and accelerating crystallization is achieved, the particle size distribution is not enlarged, the hydrolysis rate of the titanium liquid is improved by optimizing the alkali-titanium ratio of the hydrolysis seed preparation and optimizing the process of the hydrolysis section, the particle size distribution of the produced metatitanic acid is greatly improved, the subsequent metatitanic acid washing and impurity removal efficiency is improved, the particle size distribution of the titanium white powder is greatly improved, and the production cost of the titanium white powder is reduced.

Description

Technical Field

[0001] This invention belongs to the field of titanium dioxide production technology, specifically relating to a method for hydrolyzing titanium dioxide with added seed crystals. Background Technology

[0002] Titanium dioxide is an important industrial raw material with extensive applications in coatings, plastics, inks, and papermaking. Currently, the industrial production of pigment titanium dioxide both domestically and internationally mainly employs the sulfuric acid process and the chloride process, with the sulfuric acid process remaining dominant in China. However, most domestic sulfuric acid process titanium dioxide production utilizes an external seed crystal preparation process. The average hydrolysis rate of this process is 96%–96.5%, slightly higher than the 95%–96% rate of self-generated seed crystal hydrolysis, but there is still room for improvement.

[0003] For domestic titanium dioxide producers using the sulfuric acid process with an annual output of 100,000 tons, a 1% increase in the hydrolysis rate is equivalent to a 0.9% increase in the overall TiO2 yield, resulting in an annual output increase of 1,000 tons and a net income increase of 14 million yuan. Since the TiO2 yield in titanium dioxide production significantly impacts cost control and profits, a higher hydrolysis rate yields lower production costs and higher economic benefits for the same quantity of titanium dioxide. Therefore, improving the hydrolysis rate in the hydrolysis process to increase the overall TiO2 yield is of great significance for cost reduction and efficiency improvement for various enterprises.

[0004] During hydrolysis, the rotation speed affects the growth of hydrolyzed particles, as well as their size and distribution. Therefore, controlling the stirring speed is crucial. Stirring during crystallization can lead to uneven particle size and a larger particle size distribution, which in turn affects the covering power. However, without stirring, the crystallization speed will be slow, and there may be insufficient crystallization. Summary of the Invention

[0005] In the existing technology, stirring during the crystallization process can easily lead to uneven crystal particle size and an increased particle size distribution, which affects the covering power. However, if stirring is not performed, the crystallization speed will be slow and there may be insufficient crystallization. This invention provides a method for hydrolyzing titanium dioxide with added seed crystals.

[0006] The technical solution adopted in this invention is as follows:

[0007] The method for hydrolyzing titanium dioxide with added seed crystals includes the following steps:

[0008] S1. Take concentrated titanium solution and dilute alkali solution and preheat them to the same temperature. Take corresponding volumes of concentrated titanium solution and dilute alkali solution, mix them evenly and mature them to prepare hydrolytic seed crystals.

[0009] S2. Preheat the concentrated titanium liquid. Based on the amount of titanium dioxide in the concentrated titanium liquid, add the hydrolyzed seed crystals to the concentrated titanium liquid and continue to heat it until the hydrolyzed titanium liquid boils while stirring and mixing.

[0010] S3. After the hydrolyzed titanium solution boils, maintain a gentle boil. After the hydrolyzed titanium solution turns gray, stop heating, reduce the stirring speed, and change the continuous stirring to intermittent stirring to induce a period of time.

[0011] S4. Resume stirring speed, heat to boiling again, and maintain a gentle boil for a period of time before stopping heating;

[0012] S5. Maintain stirring speed, add dilution water, control the TiO2 concentration of the hydrolysate slurry, and the hydrolysis is complete.

[0013] By adopting this technical solution, the stirring speed is reduced during the hydrolysis process, and the continuous stirring is changed to intermittent stirring, which achieves the effect of uniformly distributing the seed crystals throughout the titanium liquid, accelerating the crystallization, and does not lead to an increase in particle size distribution.

[0014] Preferably, step S3 specifically includes: heating the hydrolyzed titanium solution to boiling, maintaining a gentle boil, and observing the graying point of the hydrolyzed titanium solution. After graying, heating is stopped, and the stirring speed is reduced to 1-5 r / min. Stirring is performed for 1-2 minutes each time, with an interval of 3-5 minutes, and induction is performed for 30 minutes.

[0015] Preferably, in step S4, the stirring speed is 6-8 r / min, and the hydrolyzed titanium liquid is heated to a second boil within 15-20 min, maintained at a gentle boil for 150 min, and then the heating is stopped.

[0016] Preferably, in step S5, the stirring speed is 6-8 r / min, and dilution water at 70-80℃ is added within 30 min to control the TiO2 concentration of the hydrolysate slurry to 165-175 g / L, and the hydrolysis is completed.

[0017] Preferably, in step S1, the preheating temperature is 82-88℃, and the corresponding volume of concentrated titanium liquid and dilute alkali liquid are uniformly mixed and aged according to a titanium-alkali ratio of 5.7:1.

[0018] Preferably, step S1 specifically includes the following steps:

[0019] S1.1 Add concentrated titanium liquid to the titanium liquid preheating tank for preheating, and add dilute alkali solution to the alkali solution preheating tank for preheating. The dilute alkali solution is a sodium hydroxide solution with a concentration of 98-102 g / L. Preheat the dilute alkali solution to 82-88℃ within 15-20 min, and then put the dilute alkali solution into the seed crystal preparation tank for heat preservation.

[0020] S1.2 When the preheated temperature of the concentrated titanium solution reaches the same temperature as the alkaline solution, according to the titanium-alkali ratio of 5.7:1, the concentrated titanium solution is put into the seed preparation tank and mixed evenly with the dilute alkaline solution in 220-260s.

[0021] S1.3. Heat the seed crystals to 93-95℃ and test the initial stability of the seed crystals. The initial stability of the seed crystals should be within 170-200ml.

[0022] S1.4. The seed crystals are aged at 93-95℃, and a stability test is performed every 2 minutes. When the stability of the seed crystals drops to 100-140ml, the seed crystal preparation is complete.

[0023] Preferably, step S2 specifically includes the following steps:

[0024] S2.1 Add concentrated titanium liquid to the titanium liquid preheating tank for preheating. Preheat the titanium liquid to 94-98℃ within 60 minutes. Then place it in the hydrolysis tank for heat preservation and stir at a stirring speed of 18-25r / min.

[0025] S2.2. Based on the amount of titanium dioxide in the concentrated titanium solution, the hydrolyzed seed crystals are rapidly added to the concentrated titanium solution at a rate of 2.4-2.6%, and the addition time is controlled within 300 seconds.

[0026] S2.3 After adding the hydrolyzed seed crystals, turn on the direct heating steam to raise the temperature, so that the hydrolyzed titanium liquid boils in 15-25 minutes.

[0027] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0028] 1. This invention improves the hydrolysis rate of titanium liquid by optimizing the alkali-to-titanium ratio in the preparation of hydrolyzed seed crystals and optimizing the process of the hydrolysis stage. The particle size distribution of the produced hydrolyzed metatitanic acid is significantly improved, which not only improves the efficiency of subsequent metatitanic acid washing and impurity removal, but also significantly improves the particle size distribution of titanium dioxide and reduces the production cost of titanium dioxide.

[0029] 2. By reducing the stirring speed and changing continuous stirring to intermittent stirring during the hydrolysis process, the seed crystals are evenly distributed throughout the titanium liquid, accelerating crystallization without causing the particle size distribution to increase.

[0030] 3. This invention optimizes the titanium-alkali ratio of concentrated titanium solution and dilute alkali solution in seed preparation, and obtains hydrolyzed seed crystals with seed stability of 100-140 ml after mixing and aging. The prepared seed crystals have uniform particle size and high hydrolysis activity, which can effectively improve the hydrolysis rate of titanium solution, improve the utilization rate of titanium resources, and increase the yield of titanium dioxide. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0032] Example 1

[0033] The method for hydrolyzing titanium dioxide with added seed crystals includes the following steps:

[0034] S1. Preheat concentrated titanium solution and dilute alkaline solution to 85°C respectively. Mix corresponding volumes of concentrated titanium solution and dilute alkaline solution at a titanium-alkali ratio of 5.7:1 and allow to mature to prepare hydrolyzed seed crystals. Specifically, this includes the following steps:

[0035] S1.1 Add concentrated titanium liquid to the titanium liquid preheating tank for preheating, and add dilute alkali solution to the alkali solution preheating tank for preheating. The dilute alkali solution is a sodium hydroxide solution with a concentration of 100g / L. Preheat the dilute alkali solution to 85℃ within 15min, and then put the dilute alkali solution into the seed crystal preparation tank for heat preservation.

[0036] S1.2 When the preheating temperature of the concentrated titanium liquid reaches 85℃, according to the titanium-alkali ratio of 5.7:1, the concentrated titanium liquid is put into the seed preparation tank and mixed evenly with the dilute alkali solution in 240s.

[0037] S1.3. Heat the seed crystals to 95℃ and test the initial stability of the seed crystals. The initial stability of the seed crystals should be within 170-200ml.

[0038] S1.4. The seed crystals are kept at 95℃ for maturation, and a stability test is performed every 2 minutes. When the stability of the seed crystals drops to 100-140ml, the seed crystal preparation is complete.

[0039] S2. Preheat the concentrated titanium solution to 96°C. Based on the amount of titanium dioxide in the concentrated titanium solution, add the hydrolyzed seed crystals at a dosage of 2.5%. Continue heating until the hydrolyzed titanium solution boils while stirring and mixing. Specifically, this includes the following steps:

[0040] S2.1 Add concentrated titanium liquid to the titanium liquid preheating tank for preheating. Preheat the titanium liquid to 96°C within 60 minutes. Then place it in the hydrolysis tank for heat preservation and stir at a stirring speed of 20 r / min.

[0041] S2.2. Based on the amount of titanium dioxide in the concentrated titanium solution, add the hydrolyzed seed crystals rapidly at a rate of 2.5% to the concentrated titanium solution, and control the addition time within 300 seconds.

[0042] S2.3 After adding the hydrolyzed seed crystals, turn on the direct heating steam to raise the temperature, so that the hydrolyzed titanium liquid reaches boiling point in 20 minutes.

[0043] S3. After heating the hydrolyzed titanium solution to boiling, maintain a gentle boil while observing the graying point of the hydrolyzed titanium solution. After graying, stop heating and reduce the stirring speed to 2 r / min. Stir for 1 min each time, with an interval of 5 min, and induce for 30 min.

[0044] S4. Restore the stirring speed, raise the temperature to boiling again, and maintain a gentle boil for a period of time before stopping heating. Specifically, restore the stirring speed to 8 r / min, heat the hydrolyzed titanium solution to a second boil within 20 min, maintain a gentle boil for 150 min, and then stop heating.

[0045] S5. Increase the stirring speed, add dilution water at 75℃, and control the TiO2 concentration of the hydrolysate slurry to 165-175 g / L. Hydrolysis is then complete. Specifically, maintain the stirring speed at 8 r / min, add dilution water at 75℃ within 30 minutes, and control the TiO2 concentration of the hydrolysate slurry at 165-175 g / L. Hydrolysis is then complete.

[0046] In this embodiment, the method for controlling the amount of hydrolyzed seed crystals and dilute alkali solution is as follows:

[0047] Hydrolysis seed crystal addition (g) = Hydrolysis titanium liquid volume (L) × Total titanium (g / L) × Seed crystal addition %, where the hydrolysis titanium liquid volume and total titanium are the volume of concentrated titanium liquid and titanium dioxide content in step S2.

[0048] The amount of alkali added (g) = the amount of seed crystal added (g) / the titanium-alkali ratio.

[0049] Since the volumes of titanium liquid and alkaline solution are different, the preheating time is also different. Therefore, those skilled in the art can reasonably control the start time of the process so that the titanium liquid in the hydrolysis process reaches the preheating temperature when the seed preparation is completed in the seed preparation process, thereby improving production efficiency.

[0050] Examples 2-4 and Comparative Examples 1-4 are based on the same principles as Example 1, with the differences and performance test results shown in Table 1:

[0051] Table 1. Parameters and performance test results of different embodiments and comparative examples.

[0052]

[0053] As can be seen from the above embodiments and comparative examples, by reasonably controlling the stirring speed at each stage and combining it with intermittent stirring, the particle size distribution of titanium dioxide can be made more uniform, thereby improving the particle size distribution of titanium dioxide and reducing the production cost of titanium dioxide.

[0054] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A method for hydrolyzing titanium dioxide with added seed crystals, characterized in that: Includes the following steps: S1. Take concentrated titanium solution and dilute alkali solution and preheat them to the same temperature. Take the corresponding volume of concentrated titanium solution and dilute alkali solution, mix them evenly and mature them to prepare hydrolytic seed crystals. The stability of the hydrolytic seed crystals is 100-140 ml. S2. Preheat the concentrated titanium liquid. Based on the amount of titanium dioxide in the concentrated titanium liquid, add the hydrolyzed seed crystals to the concentrated titanium liquid and continue to heat it until the hydrolyzed titanium liquid boils while stirring and mixing. S3. After the hydrolyzed titanium solution boils, maintain a gentle boil. After the hydrolyzed titanium solution turns gray, stop heating, reduce the stirring speed, and change the continuous stirring to intermittent stirring to induce a period of time. S4. Resume stirring speed, reheat to boiling, and maintain a gentle boil for a period of time before stopping heating; S5. Maintain stirring speed, add dilution water, control the TiO2 concentration of the hydrolysis slurry, and the hydrolysis is complete; Step S1 specifically includes the following steps: S1.1 Add concentrated titanium liquid to the titanium liquid preheating tank for preheating, and add dilute alkali solution to the alkali solution preheating tank for preheating. The dilute alkali solution is a sodium hydroxide solution with a concentration of 98-102 g / L. Preheat the dilute alkali solution to 82-88℃ within 15-20 min, and then put the dilute alkali solution into the seed crystal preparation tank for heat preservation. S1.2 When the preheated temperature of the concentrated titanium solution reaches the same temperature as the alkaline solution, according to the titanium-alkali ratio of 5.7:1, the concentrated titanium solution is put into the seed preparation tank and mixed evenly with the dilute alkaline solution in 220-260s. S1.

3. Heat the seed crystals to 93-95℃ and test the initial stability of the seed crystals. The initial stability of the seed crystals should be within 170-200ml. S1.

4. The seed crystals are aged at 93-95℃, and a stability test is performed every 2 minutes. When the stability of the seed crystals drops to 100-140ml, the seed crystal preparation is complete. Step S2 specifically includes the following steps: S2.1 Add concentrated titanium liquid to the titanium liquid preheating tank for preheating. Preheat the titanium liquid to 94-98℃ within 60 minutes. Then place it in the hydrolysis tank for heat preservation and stir at a stirring speed of 18-25r / min. S2.

2. Based on the amount of titanium dioxide in the concentrated titanium solution, the hydrolyzed seed crystals are rapidly added to the concentrated titanium solution at a rate of 2.4-2.6%, and the addition time is controlled within 300 seconds. S2.3 After adding the hydrolyzed seed crystals, turn on the direct heating steam to raise the temperature and heat the hydrolyzed titanium liquid to boiling in 15-25 minutes. Step S3 specifically includes: heating the hydrolyzed titanium solution to boiling, maintaining a gentle boil, and observing the graying point of the hydrolyzed titanium solution. After graying, stop heating, reduce the stirring speed to 1-5 r / min, stir for 1-2 minutes each time, with an interval of 3-5 minutes, and induce for 30 minutes. In step S4, the stirring speed is 6-10 r / min, and the hydrolyzed titanium liquid is heated to a second boil within 15-20 min. After maintaining a gentle boil for 150 min, the heating is stopped.

2. The method for hydrolyzing titanium dioxide with added seed crystals according to claim 1, characterized in that: In step S5, the stirring speed is 6-10 r / min, and dilution water at 70-80℃ is added within 30 min to control the TiO2 concentration of the hydrolysis slurry to 165-175 g / L. Hydrolysis is then completed.

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