A method and application for in-situ online detection of hydrolysis seed quality

Abstract

The present invention provides a method and application for in-situ online detection of hydrolysis seed quality. Specifically, for the preparation process of added seed crystals, the pH value of the reaction system is tested during the maturation of the hydrolysis seed crystals, and the stability of the hydrolysis seed crystals is determined by the pH value. Specifically, for the hydrolysis process of added seed crystals, the present invention provides a method for in-situ online detection of seed stability. Quantifying seed stability by pH value effectively avoids deviations in seed stability caused by manual judgment due to operator deviations in blue phase identification. This saves time and effort while ensuring consistency in seed quality across multiple batches under the same operating conditions, thereby obtaining metatitanic acid and a final titanium dioxide product of consistent quality.

Description

Technical Field

[0001] The invention belongs to the technical field of sulfuric acid process titanium dioxide, and in particular relates to a method and application for in-situ monitoring of hydrolysis seed crystal quality. Background Art

[0002] Titanium dioxide, scientifically known as titanium dioxide (TiO2), is the world's third-largest inorganic chemical and the highest-performing white pigment, widely used in various sectors of the national economy. Titanium dioxide production in my country primarily relies on the sulfuric acid process, which uses ilmenite or acid-soluble titanium slag as raw materials. After decomposition with sulfuric acid and water leaching, a titanyl sulfate solution is obtained. This solution is then hydrolyzed to produce metatitanic acid (hydrated titanium dioxide). After filtration and washing, the solution is calcined and post-processed to produce titanium dioxide. Hydrolysis is the core step of this process, encompassing three stages: the formation of crystallization centers, the growth of crystal nuclei, the precipitation and coagulation of metatitanic acid, and changes in the composition of the precipitate. The sulfuric acid process primarily involves two process pathways: external seeding and self-seeding. Compared to the self-seeded hydrolysis process, external seeding hydrolysis is adopted by most domestic titanium dioxide production companies due to its advantages: simple operation, stable seed quality, minimal batch-to-batch quality fluctuations, and low titanyl sulfate concentration requirements. The preparation of metatitanic acid by inducing the hydrolysis of titanyl sulfate with the addition of seed crystals is an epitaxial growth process, that is, the hydrolyzed metatitanic acid expands outward along the surface of the seed crystal. This is an interfacial process. Therefore, providing a sufficiently large seed crystal surface in the reaction system to consume the supersaturation can avoid spontaneous nucleation to produce finer particles. In addition, the surface characteristics of the hydrolyzed seed crystals (seed crystal activity) will also affect the final metatitanic acid morphology and growth habits as well as the growth rate of the primary metatitanic acid particles. It can be seen that the quality of the added seed crystals affects the quality of the final metatitanic acid, and ultimately affects the quality of titanium dioxide. The stability of the seed crystal is the only indicator for judging the quality of the seed crystals. The main method for judging the quality of the seed crystals is manual judgment: measure 10ml of seed crystals during the aging process, slowly add an appropriate amount of distilled water, and shake. If the liquid does not show a blue phase, continue to add distilled water until a blue phase appears. The total volume of the liquid at this time is used as the stability of the seed crystal. The disadvantage of this method is that it is greatly influenced by the subjective influence of the testers. Since the human eye has different ways of distinguishing the blue phase, the judgment of stability deviates greatly, and the activity of the seed crystals also deviates accordingly, resulting in large fluctuations in the hydrolysis products. The above-mentioned detection process usually takes 2 to 5 minutes to complete. During the detection, the seed crystal system in production is still undergoing maturation, which makes the quality of the hydrolysis seed crystals have a certain time lag.

[0003] Therefore, there is an urgent need in this field to provide a method for detecting the quality of titanium dioxide added seed crystals produced by the sulfuric acid process that is easy to operate, saves time and effort, and can accurately quantify the quality, so as to effectively solve the quantitative characterization and precise monitoring method of the seed crystal stability during the seed crystal preparation process. Summary of the Invention

[0004] The present invention provides an in-situ online quality monitoring method for hydrolysis seed crystals. This method monitors pH changes during the maturation process to determine the stability of the hydrolysis seed crystals. The added seed crystals are colloidal titanium hydroxide solutions prepared by incompletely neutralizing a titanyl sulfate solution. Therefore, as the maturation reaction proceeds, the pH of the reaction system changes accordingly.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for in-situ online detection of hydrolysis seed crystal quality is disclosed. Targeting the external seed crystal preparation process, the pH value of the reaction system is tested during the hydrolysis seed crystal ripening process, and the stability of the seed crystal is judged by the pH value.

[0007] A method for in-situ online detection of hydrolysis seed crystal quality specifically comprises the following steps:

[0008] (1) Determine the pH value when the hydrolysis seed reaction system reaches the required stability

[0009] Prepare hydrolysis seed crystals and mature the seed crystal reaction system. Take hydrolysis seed crystals at different time points during the hydrolysis seed crystal maturation process and test them by manual stability judgment. The stability index is the total liquid volume when the blue phase appears / the seed crystal volume. The stability index is 11-13. At the same time, record the pH value at the corresponding sampling time point.

[0010] (2) Repeat the above-mentioned hydrolysis seed crystal preparation process and carry out aging under the same reaction conditions. Use a pH meter to detect online. When the pH value reaches the value of the above-mentioned (1), the hydrolysis seed crystal with qualified stability is obtained.

[0011] The pH range is -0.25 to -0.15, and the corresponding hydrolysis seed crystals are the pH values ​​when the stability is qualified.

[0012] Furthermore, in the step (1), the hydrolysis seed crystal preparation process is: preheating the seed titanium liquid and the sodium hydroxide solution to 82-90° C. respectively, wherein the concentration of TiO2 in the seed titanium liquid is 160-200 g / L, and the mass concentration of the sodium hydroxide solution is 7-12 wt%; adding the preheated seed titanium liquid to the preheated sodium hydroxide solution, and heating it to 95-98° C. to obtain the hydrolysis seed crystal, wherein the sodium hydroxide solution is added according to the alkali-titanium ratio (the ratio of the mass of NaOH in the sodium hydroxide solution to the mass of TiO2 in the seed titanium liquid) of 1:8-1:12.

[0013] Furthermore, in step (1), the method of manually judging stability is to measure the seed crystals in the aging process, slowly add an appropriate amount of distilled water, and shake. If the liquid does not show a blue phase, continue to add distilled water until a blue phase appears. The total volume of liquid at this time is divided by the volume of seed crystals as the stability index of the hydrolyzed seed crystals. In order to avoid differences in the judgment of the blue phase by different operators, the stability judgment in this application is performed by the same person.

[0014] Furthermore, in the step (1), the pH value is tested during the aging of the hydrolysis seed crystals using a temperature-compensated pH meter.

[0015] The present invention also provides the use of hydrolysis seeds with qualified stability obtained by the method for online detection of hydrolysis seed quality in a hydrolysis reaction, comprising the following steps: adding hydrolysis seeds with qualified stability to a titanium liquid to be hydrolyzed that has been preheated to 95-100°C, stirring for 8-12 minutes, heating to boiling and heating to the graying point, stopping heating and stirring, and aging; after aging, resuming heating and stirring, heating to boiling again, maintaining a slight boil for 60-80 minutes, then adding water for dilution so that the final TiO2 concentration in the hydrolysis system is 150-170g / L, continuing boiling for 240 minutes, and completing hydrolysis; after the hydrolysis slurry is cooled to 60°C, filtering, adding dilute sulfuric acid and distilled water in sequence to wash the filter cake, and draining to obtain secondary titanate agglomerates.

[0016] The concentration of TiO2 in the titanium solution to be hydrolyzed is 160-200 g / L; the mass ratio of TiO2 in the hydrolysis seed with qualified stability to TiO2 in the titanium solution to be hydrolyzed is 0.02-0.05.

[0017] The aging time is 30 to 35 minutes.

[0018] The beneficial effect of the present invention is that the present invention provides a method for in-situ online detection of seed stability in the hydrolysis process of added seeds. Quantifying the seed stability by pH value can effectively avoid the deviation of seed stability caused by the operator's deviation in judging the blue phase during manual stability judgment, saving time and labor while ensuring the consistency of seed quality in multiple batches under the same operating conditions, thereby obtaining titanic acid and final titanium dioxide products with consistent quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 SEM images of metatitanic acid obtained by seed induction using different methods for judging stability in Example 2: (a) pH value judgment, (b) traditional method;

[0020] Figure 2 SEM images of metatitanic acid obtained by seed induction using different methods for judging stability in Example 3: (a) pH value judgment, (b) traditional method; DETAILED DESCRIPTION

[0021] Example 1

[0022] (1) Preheating titanium seed (195 g / L in terms of TiO2) and sodium hydroxide solution (mass concentration 10 wt%) to 85°C respectively; adding the preheated seed titanium liquid to the preheated sodium hydroxide solution, and heating to 96°C to obtain a hydrolyzed seed titanium liquid, wherein the sodium hydroxide solution is added according to an alkali-titanium ratio (ratio of the mass content of NaOH in the sodium hydroxide solution to the mass content of TiO2 in the seed titanium liquid) of 1:10; sampling at different aging times and measuring the seed stability simultaneously (taking the seed during the aging process, slowly adding an appropriate amount of distilled water and shaking; if the liquid does not show a blue phase, continue to add distilled water until a blue phase appears, and the total volume of the liquid / the volume of the seed is used as an index of the stability of the hydrolyzed seed); and measuring the pH value of the seed system at the same time. When the seed stability index is 12 (120 ml / 10 ml), the pH value measured is -0.25;

[0023] (2) Re-prepare seed crystals, take seed crystals when the seed reaction system is -0.25 (its TiO2 accounts for 2wt% of the mass of TiO2 in the titanium solution to be hydrolyzed) and add them into the hydrolysis titanium solution preheated to 96°C (calculated on the basis of TiO2, the concentration is 195g / L), heat it to boiling and heat it to the graying point, stop heating and stirring, start aging, the aging time is 30min, after the aging is completed, resume heating and stirring, heat the system to boiling again, keep it slightly boiling for 60min, then add dilution water to make the final TiO2 concentration of the hydrolysis system at 160g / L, and the hydrolysis is completed after boiling for 240min; after the hydrolysis slurry is cooled to 60°C, filter it, add dilute sulfuric acid and distilled water in turn to wash the filter cake, and then drain it to obtain the corresponding titanic acid.

[0024] (3) The particle size and particle size distribution of titanic acid induced by hydrolysis seed induced by pH monitoring were tested. The D50 was 2.1 μm, the diameter distance was 1.50, and the hydrolysis rate was 94.8%, which were consistent with the particle size and hydrolysis rate of titanic acid obtained by manual stability judgment (seed stability was 12).

[0025] Example 2

[0026] (1) Preheating titanium seed (185 g / L in terms of TiO2) and sodium hydroxide solution (mass concentration 10 wt%) to 85°C respectively; adding the preheated seed titanium liquid to the preheated sodium hydroxide solution, and heating to 96°C to obtain a hydrolyzed seed titanium liquid, wherein the sodium hydroxide solution is added according to an alkali-titanium ratio (ratio of the mass content of NaOH in the sodium hydroxide solution to the mass content of TiO2 in the seed titanium liquid) of 1:10; sampling at different aging times and measuring the seed stability simultaneously (taking the seed during the aging process, slowly adding an appropriate amount of distilled water and shaking; if the liquid does not show a blue phase, continue to add distilled water until a blue phase appears, and the total volume of the liquid / the volume of the seed is used as an index of the stability of the hydrolyzed seed); and measuring the pH value of the seed system at the same time. When the seed stability index is 11 (110 ml / 10 ml), the pH value measured is -0.20;

[0027] (2) Re-prepare seed crystals, take seed crystals when the seed reaction system is -0.20 (its TiO2 accounts for 2wt% of the mass of TiO2 in the titanium solution to be hydrolyzed) and add them into the hydrolysis titanium solution preheated to 96°C (calculated on the basis of TiO2, the concentration is 195g / L), heat it to boiling and heat it to the graying point, stop heating and stirring, start aging, the aging time is 30min, after the aging is completed, resume heating and stirring, heat the system to boiling again, keep it slightly boiling for 60min, then add dilution water to make the final TiO2 concentration of the hydrolysis system at 160g / L, and the hydrolysis is completed after boiling for 240min; after the hydrolysis slurry is cooled to 60°C, filter it, add dilute sulfuric acid and distilled water in turn to wash the filter cake, and then drain it to obtain the corresponding titanic acid.

[0028] (3) The hydrolysis rate of the titanium solution induced by the hydrolysis seed induced by pH monitoring was 96.2%, and the SEM of the obtained metatitanic acid was as follows: Figure 1 As shown, the hydrolysis rate is consistent with that obtained by artificial stabilization (when the seed stability is 11), and the obtained metatitanic acid particle size is also consistent.

[0029] Example 3

[0030] (1) Preheating titanium seed (160 g / L in terms of TiO2) and sodium hydroxide solution (mass concentration 10 wt%) to 85°C respectively; adding the preheated seed titanium liquid to the preheated sodium hydroxide solution, and heating to 96°C to obtain a hydrolyzed seed titanium liquid, wherein the sodium hydroxide solution is added according to an alkali-titanium ratio (ratio of the mass content of NaOH in the sodium hydroxide solution to the mass content of TiO2 in the seed titanium liquid) of 1:8; sampling at different aging times and measuring the seed stability simultaneously (taking the seed during the aging process, slowly adding an appropriate amount of distilled water and shaking; if the liquid does not show a blue phase, continue to add distilled water until a blue phase appears, and the total volume of the liquid / the volume of the seed is used as an index of the stability of the hydrolyzed seed); and measuring the pH value of the seed system at the same time. When the seed stability index is 13 (130 ml / 10 ml), the pH value measured is -0.15;

[0031] (2) Re-prepare seed crystals, take seed crystals when the seed reaction system is -0.15 (its TiO2 accounts for 2wt% of the mass of TiO2 in the titanium solution to be hydrolyzed) and add them into the hydrolysis titanium solution preheated to 96°C (calculated on the basis of TiO2, the concentration is 195g / L), heat it to boiling and heat it to the graying point, stop heating and stirring, start aging, the aging time is 30min, after the aging is completed, resume heating and stirring, heat the system to boiling again, keep it slightly boiling for 60min, then add dilution water to make the final TiO2 concentration of the hydrolysis system at 160g / L, and boil it for 240min before the hydrolysis is completed; after the hydrolysis slurry is cooled to 60°C, filter it, add dilute sulfuric acid and distilled water in turn to wash the filter cake, and then dry it to obtain the corresponding titanic acid.

[0032] (3) Test the SEM of titanic acid induced by hydrolysis seed induced by pH monitoring. Figure 2 As shown, the particle size of the titanate is consistent with that obtained by artificial stabilization (when the seed stability is 13).

Claims

1. A method for in-situ online detection of hydrolysis seed quality, characterized in that: For the preparation process of the added seed crystals, the pH value of the reaction system is tested during the maturation of the hydrolysis seed crystals to determine the stability of the hydrolysis seed crystals. The process specifically includes the following steps: (1) Determine the pH value when the hydrolysis seed reaction system reaches the required stability Prepare hydrolysis seed crystals and mature the hydrolysis seed crystal reaction system. Take hydrolysis seed crystals at different time points during the hydrolysis seed crystal maturation process and test them by manual stability judgment. The stability index is the total liquid volume when the blue phase appears / the seed crystal volume. The stability index is 11-13. At the same time, record the pH value at the corresponding sampling time point. (2) Repeat the above-mentioned hydrolysis seed crystal preparation process and carry out aging under the same reaction conditions. Use a pH meter to detect online. When the pH value reaches the value of the above-mentioned (1), the hydrolysis seed crystal with qualified stability is obtained.

2. The method for in-situ online detection of hydrolysis seed quality according to claim 1, wherein: In the step (1), the hydrolysis seed crystal preparation process is: preheating the seed titanium liquid and the sodium hydroxide solution to 82-90°C respectively, wherein the concentration of TiO2 in the seed titanium liquid is 160-200 g / L, and the mass concentration of the sodium hydroxide solution is 7-12wt%; adding the preheated seed titanium liquid to the preheated sodium hydroxide solution, and heating it to 95-98°C to obtain the hydrolysis seed crystal, wherein the sodium hydroxide solution is added according to the alkali-titanium ratio (the ratio of the mass of NaOH in the sodium hydroxide solution to the mass of TiO2 in the seed titanium liquid) of 1:8-1:

12.

3. The method for in-situ online detection of hydrolysis seed quality according to claim 1, wherein: In the step (1), the method of manually judging stability is to measure the seed crystals in the aging process, slowly add distilled water, and shake. If the liquid does not show a blue phase, continue to add distilled water until a blue phase appears.

4. Use of hydrolysis seed crystals with qualified stability obtained by the method for in-situ online detection of hydrolysis seed crystal quality according to claim 1 in a hydrolysis reaction, characterized in that: The method comprises the following steps: adding hydrolysis seed crystals with qualified stability to a titanium liquid to be hydrolyzed which is preheated to 95-100° C., stirring for 8-12 minutes, heating to boiling and heating to a graying point, stopping heating and stirring, and aging; after aging, resuming heating and stirring, heating to boiling again, maintaining a slight boil for 60-80 minutes, and then adding water for dilution so that the final TiO2 concentration in the hydrolysis system is 150-170 g / L, continuing boiling for 240 minutes, and completing the hydrolysis; After the hydrolysis slurry is cooled to 60 o C and then filtered, dilute sulfuric acid and distilled water were added in sequence to wash the filter cake, and the secondary agglomerates of metatitanic acid were obtained after drying.

5. Use of the hydrolysis seed crystals with qualified stability according to claim 4 in a hydrolysis reaction, characterized in that: The concentration of TiO2 in the titanium solution to be hydrolyzed is 160-200 g / L; the mass ratio of TiO2 in the hydrolysis seed crystals with qualified stability to TiO2 in the titanium solution to be hydrolyzed is 0.02-0.05.

Images