A method for preparing calcined seeds from titanium oxychloride solution by-product of chlorination process of titanium dioxide

Abstract

The application discloses a method for preparing calcined seeds by adopting titanium oxychloride solution by-produced in chlorination method of titanium white, and comprises the following steps: S1. pulp is obtained by taking the filter cake after alkali washing, titanium oxychloride solution is added, pH is adjusted to 3.5-5, and slurry II is obtained; S2. the slurry II is heated to 55-65 DEG C at a rate of 0.3-0.5 DEG C / min, then hydrochloric acid solution is added, heating is carried out to boiling at a rate of 0.3-0.5 DEG C / min, after keeping boiling for 2-4 h, water is added to dilute to the titanium dioxide content of 90-120 g / L in the material, and calcined seeds are obtained. The method can realize the recycling of hydrochloric acid and TiO2 in the titanium oxychloride, and reduces the cost of waste water treatment; the application is simple in operation, short in technological process, and easy to realize industrial production.

Description

Technical Field

[0001] This invention belongs to the field of titanium dioxide production technology, and specifically relates to a method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the chlorination process for titanium dioxide production. Background Technology

[0002] The chlorination process is one of the main methods for producing titanium dioxide. It has gained increasing attention due to its advanced technology, large capacity, simple process, low energy consumption, and superior product performance. During the chlorination process, the tail gas contains a certain amount of titanium tetrachloride. After being absorbed by hydrochloric acid spraying, it forms an acidic titanium oxychloride solution. This solution mainly consists of 25-35% hydrochloric acid and a titanium oxychloride concentration (based on TiO2 content) of 50-120 g / L. It also contains high levels of impurities such as Fe, V, and Si.

[0003] Most methods for treating titanium oxychloride involve neutralization followed by discharge. However, this method increases the cost of wastewater treatment and wastes both acid and titanium resources.

[0004] Some researchers have proposed using it in the coating process of titanium dioxide, but the high Fe and V content in this part of titanium oxychloride will affect the hue of the finished titanium dioxide product, thus affecting the product quality.

[0005] Patent CN109019680A, entitled "A Method for Producing Titanium Dioxide from Hydrochloric Acid Byproduct of Chlorination Process Titanium Dioxide," provides a method for recovering and utilizing hydrochloric acid, a byproduct of the chloride process titanium dioxide production. This method involves reacting the hydrochloric acid (containing TiOCl2) with titanium concentrate via acid hydrolysis. After separating and removing acid-insoluble substances such as silica, the acid-hydrolyzed titanium solution is hydrolyzed to obtain crude titanium dioxide. The crude titanium dioxide is then washed and post-treated to obtain the finished titanium dioxide product. This method is similar to the hydrochloric acid hydrolysis method; on the one hand, the process is long and complex; on the other hand, it requires sophisticated equipment, making it difficult to achieve industrial-scale production.

[0006] Patent CN110589884, "A Method for Recycling Waste Titanium Oxide Dichloride," provides a method for recycling waste titanium oxychloride dichloride. This method involves replacing sulfuric acid with an acidic environment during the metatitanic acid bleaching process, while simultaneously adding a certain amount of aluminum powder. The drawback of this method is that it cannot be determined whether the added aluminum powder has reacted completely. Since aluminum salts are inhibitors of rutile conversion, if the added aluminum powder does not react completely, it remains in the metatitanic acid, which increases the calcination temperature and worsens the particle size and particle size distribution of the product. This results in poor gloss and a tendency for the TiO2 coating to be washed away.

[0007] Special treatment methods can reduce the iron content in titanium oxychloride solution to below 1 ppm. While this solution does not affect the color of the product during the coating process, the high concentration of hydrochloric acid in titanium oxychloride increases the amount of alkali consumed during pH neutralization during coating, thus increasing the coating cost.

[0008] On the other hand, the main process flow for producing titanium dioxide using the sulfuric acid process is: acid hydrolysis → hydrolysis, first wash → bleaching, second wash → salt treatment → calcination → post-treatment. During the bleaching process, calcined seed crystals are generally added to promote the crystal transformation of calcined titanium dioxide and effectively control the grain size. The conventional preparation process of calcined seed crystals generally includes the following steps: alkali dissolution (reacting metatitanic acid after two washes with sodium hydroxide to generate sodium titanate and sodium metatitanic acid), alkali washing (washing the alkali-dissolved slurry with softened water to remove residual sodium hydroxide and sulfate ions, while sodium metatitanic acid reacts with water to generate sodium titanate, this process is called alkali washing), neutralization and acid adjustment (reacting sodium titanate with hydrochloric acid to generate sodium titanate), and acid dissolution (reacting sodium titanate with hydrochloric acid; the first step generates titanium oxychloride; the second step is the hydrolysis of titanium oxychloride to generate rutile titanium dioxide colloid, i.e., calcined seed crystals). The neutralization and acid adjustment stage requires a large amount of hydrochloric acid, which increases production costs. If titanium oxychloride is used instead of normal hydrochloric acid in the neutralization and acid adjustment stage of calcined seed crystals, it will not only not affect the quality of the calcined seed crystals, but also save production costs. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide process via the chloride method. This method applies titanium oxychloride solution to the preparation process of calcined seed crystals, thereby achieving high-value utilization of titanium oxychloride solution.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide production process via the chloride process, includes the following steps:

[0012] S1. After alkali washing, the filter cake is pulped to obtain slurry I. The concentration of slurry I, based on TiO2 content, is adjusted to 170-200 g / L. A titanium oxychloride solution, accounting for 0.1-0.3% of the TiO2 mass in slurry I, is added, and the pH is adjusted to 3.5-5 to obtain slurry II. The titanium oxychloride solution contains 25-35% hydrochloric acid by mass, and the titanium oxychloride concentration, based on TiO2 content, is ≥50 g / L.

[0013] S2. The slurry II is heated to 55-65°C at a rate of 0.3-0.5°C / min, and then a hydrochloric acid solution accounting for 0.2-0.5% of the TiO2 mass ratio in the slurry I is added. The amount of hydrochloric acid solution added is based on the mass of pure hydrochloric acid. The temperature is increased to boiling at a rate of 0.3-0.5°C / min and kept boiling for 2-4 hours. Then, water is added to dilute the material until the titanium dioxide content in the material is 90-120 g / L to obtain calcined seed crystals.

[0014] Preferably, the concentration of NaOH in the wash water after alkaline washing in step S1 is 3-5 g / L.

[0015] Preferably, the hydrochloric acid in the hydrochloric acid solution in step S2 has a mass fraction of ≥30%.

[0016] Preferably, the filter cake obtained after alkali washing in step S1 is prepared by the following steps:

[0017] (1) Alkali dissolution: The qualified metatitanic acid slurry after two washes is heated to 59.5-61.5℃ and then added to the alkaline solution heated to 110-115℃. After the initial reaction is completed, the solution is kept at 105-110℃ for 1-3 hours. The standard for the end of the initial reaction is that the material temperature no longer rises.

[0018] (2) Alkali washing: The alkali-dissolved material is washed with softened water to obtain the alkali-washed filter cake.

[0019] Preferably, the concentration of the qualified metatitanic acid slurry after the second washing is 250-300 g / L based on TiO2, and the iron content is ≤15 ppm based on titanium dioxide in the slurry.

[0020] Preferably, the mass fraction of the alkali solution is 45-52%, and the mass ratio of the alkali solution added to the TiO2 in the slurry, based on the mass of soda ash, is (1.45-1.9):1.

[0021] Preferably, the iron content in the titanium oxychloride solution is ≤1ppm.

[0022] The method described in this application can recover and utilize hydrochloric acid and TiO2 from titanium oxychloride, reducing the cost of wastewater treatment. This invention is simple to operate, has a short process flow, and is easy to implement for industrial production. Attached Figure Description

[0023] Figure 1 This is a scanning electron microscope image of the seed crystals obtained by neutralization and acid adjustment using the method of this application (Example 2);

[0024] Figure 2 This is a scanning electron microscope image of seed crystals (Comparative Example 1) obtained by neutralization and acid adjustment with conventional hydrochloric acid. Detailed Implementation

[0025] The method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide production process via the chloride method, provided by this invention, includes the following steps:

[0026] S1. Neutralization and Acid Adjustment: Take the alkaline-washed filter cake and slurry it to obtain slurry I. Adjust the concentration of slurry I, based on TiO2 content, to 170-200 g / L. Add a titanium oxychloride solution, accounting for 0.1-0.3% of the TiO2 mass ratio in slurry I, and adjust the pH to 3.5-5 to obtain slurry II. The titanium oxychloride solution contains 25-35% hydrochloric acid by mass, and the titanium oxychloride concentration, based on TiO2 content, is ≥50 g / L. The alkaline-washed filter cake refers to the filter cake after the second washing of metatitanic acid in the conventional calcined seed preparation process, which has undergone alkaline dissolution and alkaline washing.

[0027] S2. Acid dissolution: Heat slurry II to 55-65℃ at a rate of 0.3-0.5℃ / min, then add hydrochloric acid solution (hydrochloric acid mass fraction ≥30%) accounting for 0.2-0.5% of TiO2 in slurry I. The amount of hydrochloric acid solution added is based on the mass of pure hydrochloric acid. Heat to boiling at a rate of 0.3-0.5℃ / min and maintain boiling for 2-4 hours. Then add dilution water to control the titanium concentration of the material to 90-120 g / L to obtain calcined seed crystals. Test the conversion rate and activity of the prepared seed crystals. Filter the seed crystals and test the TiO2 content in the filtrate.

[0028] The following method can be used to evaluate the application of the prepared seed crystals: Take the metatitanic acid filter cake washed by conventional sulfuric acid method, and slurry it with softened water, controlling the TiO2 concentration in the slurry to be 280–340 g / L. Use conventional methods to apply the prepared seed crystals to the bleaching process, where: the sulfuric acid dosage is to ensure the free acid content in the slurry is ≥20 g / L, the R seed crystal dosage is 1.0% of the TiO2 mass in the slurry, and the trivalent titanium dosage is 0.35% of the TiO2 mass in the slurry. After bleaching, filter the material and then wash it with softened water at 40–60℃. The washed material is then subjected to salt treatment and calcination, where the elemental contents in the calcined material are: K2O% 0.15%, P2O5% 0.17%, and Al2O3% 0.09. Record the highest calcination temperature and time during the calcination process, and test the whiteness and CS / CSD of the calcined material.

[0029] In the conventional calcination seed crystal preparation process, hydrochloric acid is used as the reagent in the neutralization and acid adjustment stage. This process primarily involves the reaction of sodium titanate with hydrochloric acid to generate titanic acid, as shown in the reaction equation: Na₄TiO₄ + 4HCl = H₄TiO₄ + 4NaCl. However, using titanium oxychloride solution instead of hydrochloric acid offers several advantages. Firstly, the hydrochloric acid in titanium oxychloride can be utilized, reducing the consumption of hydrochloric acid. Secondly, with the addition of titanium oxychloride solution, the pH of the material gradually decreases, resulting in a neutralized mixture with a pH of 3.5–5. Titanium oxychloride hydrolyzes to form TiO₂ at pH greater than 2, as shown in the reaction equation: TiOCl₂ + nH₂O → TiO₂·(n+1)H₂O + HCl. The hydrolyzed titanium dioxide transforms into rutile titanium dioxide during the later acid dissolution process at high temperature and high acidity, without affecting the conversion rate or activity of the calcined seed crystals. In addition, after filtering the calcined seed crystals, the titanium dioxide content in the filtrate was <10ppm, which means that the added titanium dioxide dichloride was completely hydrolyzed during the neutralization process to form solid TiO2, which would not be carried away in liquid form with the wash water during the second washing process after bleaching.

[0030] Since titanium oxychloride solution contains more other components than conventional hydrochloric acid solution, and this application aims to fully recover titanium from titanium oxychloride solution in addition to utilizing hydrochloric acid in titanium oxychloride solution, the process parameters for neutralization, acid adjustment and acid dissolution stages need to be adjusted accordingly compared with conventional calcined seed crystals.

[0031] Specifically, in step S1, the NaOH concentration in the wash water after alkaline washing is controlled at 3-5 g / L (the conventional method is ≤3 g / L). After adding titanium oxychloride solution, the pH is adjusted to 3.5-5 (the conventional method is 2.8-3.2). When the NaOH content in the wash water after alkaline washing is high, it means that the washing is incomplete, the pH of the washed filter cake is also relatively high, and more titanium oxychloride needs to be consumed for neutralization. At this time, more titanium is recovered. However, the NaOH content in the wash water should not be too high. If it is too high, the NaCl produced during the neutralization process will also increase. On the one hand, this will result in a lower seed crystal conversion rate, and on the other hand, it will result in a lower titanium content in the seed crystals, affecting the seed crystal yield. If the neutralization pH is adjusted according to the conventional method, it will also lead to more titanium oxychloride consumption and an increase in NaCl produced during the neutralization process, resulting in the adverse consequences of a lower seed crystal conversion rate and a lower titanium content in the seed crystals. Therefore, the NaOH content in the wash water and the pH during the neutralization stage need to be adjusted appropriately to balance the consumption of hydrochloric acid and the recovery of titanium from titanium oxychloride, so as to ensure both the seed crystal conversion rate and the titanium content in the seed crystal.

[0032] In step S2, the heating rate is 0.3–0.5 °C / min (compared to approximately 1 °C / min in conventional methods), and boiling time is 2–4 h (compared to 1–1.5 h in conventional methods). This application reduces the heating rate, resulting in more uniform seed crystal size, better quality, and increased seed crystal activity. The increased boiling time allows for larger seed crystals obtained from titanium oxychloride hydrolysis, reducing filtration issues during later use. Evaluation of the calcined seed crystals prepared using titanium oxychloride during the neutralization process revealed that the rutile TiO2 formed after titanium oxychloride hydrolysis has a shorter formation time compared to conventional seed crystals, resulting in smaller particle size. For the same seed crystal mass, there are more rutile TiO2 crystals with higher activity. The activity of the calcined seed crystals was measured to be 100, with a conversion rate ≥99%. The calcination process slightly lowers the calcination temperature and shortens the calcination time, but has no impact on the quality of the final product.

[0033] Therefore, the method of this application can realize the recovery and utilization of hydrochloric acid and TiO2 in titanium oxychloride, reducing the cost of wastewater treatment; the present invention is simple to operate, has a short process flow, and is easy to realize industrial production.

[0034] Preferably, the filter cake after alkali washing is prepared by the following steps:

[0035] (1) Alkali dissolution: Add the qualified metatitanic acid slurry, which has been heated to 59.5-61.5℃, to the alkaline solution heated to 110-115℃. After the initial reaction is completed (metatitanic acid is acidic, and after being added to the alkaline solution, it will continue to release heat due to the neutralization reaction. When the temperature no longer rises, the initial reaction is complete), and then keep it at 105-110℃ for 1-3 hours.

[0036] (2) Alkali washing: The alkali-dissolved material is washed with softened water to obtain an alkali-washed filter cake.

[0037] Further preferred, the concentration of the qualified metatitanic acid slurry (calculated as TiO2) after the second washing is 250-300 g / L. At the same time, since the iron exists in the crystal lattice of the seed crystal after gelation and cannot be removed, the iron content in the qualified metatitanic acid after the second washing is required to be ≤15 ppm based on the titanium dioxide in the slurry.

[0038] More preferably, the mass fraction of the alkali solution is 45-52%, and the mass ratio of the alkali solution added to the TiO2 in the slurry is (1.45-1.9):1, based on the mass of soda ash; the alkali solution is preferably a sodium hydroxide or potassium hydroxide solution.

[0039] Preferably, in order to reduce the consumption of hydrochloric acid during the neutralization process while ensuring the recovery rate of titanium in titanium oxychloride, the concentration of NaOH in the wash water after alkaline washing is 3-5 g / L.

[0040] Preferably, to reduce the impact of iron content in titanium oxychloride on the iron content of the seed crystals, the titanium oxychloride solution needs to be de-ironized until the iron content is ≤1ppm. The method for iron removal can be referred to in patent "CN 112250117A, A Method for Improving the Quality of Waste Titanium Oxide".

[0041] Example 1

[0042] (1) Alkali dissolution: The qualified metatitanic acid slurry after two washes, heated to 59.5℃, is added to the alkaline solution heated to 110℃ within 30 minutes to carry out the alkaline dissolution reaction. The mass fraction of the alkaline solution is 45%, the mass ratio of the amount of alkaline solution to the mass of TiO2 in the metatitanic acid slurry is 1.9:1, the concentration of the qualified metatitanic acid slurry after two washes (calculated as TiO2) is 250g / L, the iron content is 15ppm, the reaction is completed, and the temperature is kept at 105℃ for 3h.

[0043] (2) Alkali washing: The material after alkali dissolution is washed with water, and the residual NaOH in the washing water is controlled to be 3.0 g / L;

[0044] (3) Neutralization and acid dissolution: After alkali washing, the filter cake was slurried and the material concentration (based on TiO2) was adjusted to 175 g / L. Titanium oxychloride solution was added to adjust the pH of the material to 3.5. The amount of titanium oxychloride solution added was 0.3% of the mass ratio of TiO2 in the slurry. The mass fraction of hydrochloric acid in titanium oxychloride was 25%, the TiO2 concentration was 55 g / L, and the iron content was 1 ppm. The acid-adjusted material was heated to 60°C at a rate of 0.4°C / min. Then, hydrochloric acid with a mass ratio of 0.25% of TiO2 in the slurry and a hydrochloric acid mass fraction of 30% was added. The temperature was raised to boiling at a rate of 0.4°C / min and kept boiling for 4 hours. Then, dilution water was added to control the TiO2 concentration of the material to 95 g / L. The conversion rate of the prepared seed crystals was tested to be 99.2% and the activity was 100. The seed crystals were filtered and the TiO2 content in the filtrate was tested to be 8 ppm.

[0045] Seed conversion rate test method: Take 50 mL of the prepared seed crystals and dry them in an oven at 105℃, then grind and press them into tablets, and analyze the content of rutile TiO2 by XRD.

[0046] Seed crystal activity test method: Measure 50 mL of R seed crystals and 50 mL of water, and mix thoroughly. Pour the mixture into a Buchner funnel lined with two layers of filter paper, and start the stopwatch. After 1 minute, if some of the mixed solution has not passed through, measure its volume using a measuring cup and record it as V. Activity = 100 - V.

[0047] (4) Evaluation of the application of R seed crystals:

[0048] A standard first-wash metatitanic acid filter cake was taken and pulped with softened water, controlling the TiO2 concentration in the slurry to be 280–340 g / L. Seed crystals were prepared and used in the bleaching process according to standard procedures, with the following additions: sulfuric acid to ensure a free acid content ≥20 g / L in the slurry, calcined seed crystals at 1.0%, and trivalent titanium at 0.35%. After bleaching, the material was filtered and then washed with softened water at 40–60 °C. The washed material was then subjected to salt treatment and calcination. The elemental contents of the calcined material were: K2O% 0.15%, P2O5% 0.17%, and Al2O3% 0.09%. The highest calcination temperature and total calcination time were recorded during the calcination process, and the whiteness and CS / CSD of the calcined material were tested.

[0049] The specific calcination operation is as follows: First, raise the temperature to 350℃ within 30 minutes, then raise it to 650℃ within 30 minutes, then raise it to 780℃ within 20 minutes and hold it for 1 hour, then raise it to 930℃ within 20 minutes and hold it for 2 hours, then raise it to 970℃ within 10 minutes. Take a sample every 30 minutes to test its rutile conversion rate. If the conversion rate is lower than 98.7%, raise the temperature by 10℃ and continue to hold it. Repeat the above operation until the conversion rate is between 98.7% and 99.2% (when the conversion rate is close to the target value, the detection frequency can be increased, and the temperature can be kept constant or increased slightly for the time being).

[0050] Example 2

[0051] (1) Alkali dissolution: The qualified metatitanic acid slurry after two washes is heated to 60.5℃ and added to the alkaline solution heated to 112℃ within 30 min to carry out the alkaline dissolution reaction. The mass fraction of the alkaline solution is 52%, the mass ratio of the amount of alkaline solution to the mass of TiO2 in the metatitanic acid slurry is 1.7:1, the concentration of the qualified metatitanic acid slurry after two washes (calculated as TiO2) is 270 g / L, the iron content is 12 ppm, the reaction is completed, and the temperature is kept at 108℃ for 2 h.

[0052] (2) Alkali washing: The material after alkali dissolution is washed with water, and the residual NaOH in the washing water is 4.5g / L;

[0053] (3) Neutralization and acid dissolution: After alkali washing, the filter cake was slurried and the material concentration (based on TiO2) was adjusted to 185 g / L. Titanium oxychloride solution was added to adjust the pH of the material to 5. The amount of titanium oxychloride solution added was 0.1% of the mass of TiO2 in the slurry. The mass fraction of hydrochloric acid in titanium oxychloride was 32%, the TiO2 concentration was 75 g / L, and the iron content was 0.5 ppm. The acid-adjusted material was heated to 65°C at a rate of 0.5°C / min. Then, hydrochloric acid of 0.5% of the mass of TiO2 in the slurry was added. The hydrochloric acid mass fraction was 31%. The temperature was raised to boiling at a rate of 0.3°C / min. After boiling for 2 hours, dilution water was added to control the TiO2 concentration of the material to 105 g / L. The conversion rate of the prepared seed crystals was tested to be 99.5% and the activity was 100. The seed crystals were filtered and the TiO2 content in the filtrate was tested to be 5 ppm.

[0054] The methods for testing seed conversion rate and seed activity are the same as in Example 1.

[0055] (4) Evaluation of R seed crystal application: The method is the same as in Example 1.

[0056] The specific calcination operation is the same as in Example 1.

[0057] Example 3

[0058] (1) Alkali dissolution: The qualified metatitanic acid slurry after two washes was heated to 61℃ was added to the alkaline solution heated to 115℃ within 30 min to carry out the alkaline dissolution reaction. The mass fraction of the alkaline solution was 48%, and the mass ratio of the amount of alkaline solution added to the mass of titanium dioxide in the slurry was 1.45:1. The concentration of the qualified metatitanic acid slurry after two washes (calculated as TiO2) was 295 g / L, and the iron content was 10 ppm. After the reaction was completed, the temperature was kept at 110℃ for 1 h.

[0059] (2) Alkali washing: The material after alkali dissolution is washed with water, and the residual NaOH in the washing water is 5.0 g / L;

[0060] (3) Neutralization and acid dissolution: After alkali washing, the filter cake was slurried and the material concentration (based on TiO2) was adjusted to 198 g / L. Titanium oxychloride solution was added to adjust the pH of the material to 4. The amount of titanium oxychloride solution added was 0.25% of the mass of TiO2 in the slurry. The mass fraction of hydrochloric acid in titanium oxychloride was 29%, the TiO2 concentration was 98 g / L, and the iron content was 0.1 ppm. The acid-adjusted material was heated to 55°C at a rate of 0.3°C / min. Then, hydrochloric acid with a mass ratio of 0.4% of TiO2 in the slurry and a mass fraction of 32% was added. The temperature was increased to boiling at a rate of 0.5°C / min and kept boiling for 3 hours. Then, dilution water was added to control the titanium concentration of the material to 117 g / L. The conversion rate of the prepared seed crystals was tested to be 99.8% and the activity was 100. The seed crystals were filtered and the TiO2 content in the filtrate was tested to be 9 ppm.

[0061] The methods for testing seed conversion rate and seed activity are the same as in Example 1.

[0062] (4) Evaluation of R seed crystal application: The method is the same as in Example 1.

[0063] The specific calcination operation is the same as in Example 1.

[0064] Comparative Example 1

[0065] Calcined seed crystals were prepared using conventional methods, with steps S1 and S4 being the same as in Example 2;

[0066] (2) Alkali washing: The material after alkali dissolution is washed with water, and the residual NaOH in the washing water is 2.5g / L;

[0067] (3) Neutralization and acid dissolution: After washing with alkali, the filter cake was slurried and the material concentration (based on TiO2) was adjusted to 185 g / L. A hydrochloric acid solution with a mass fraction of 32% was added to adjust the pH of the material to 2.9. The acid-adjusted material was heated to 65°C at a rate of 1°C / min. Then, hydrochloric acid with a mass fraction of 31% and a mass fraction of 0.5% of TiO2 in the slurry was added. The temperature was increased to boiling at a rate of 1°C / min and kept boiling for 1.5 h. Then, dilution water was added to control the TiO2 concentration of the material to 105 g / L. The conversion rate of the prepared seed crystals was tested to be 99.4% and the activity was 100.

[0068] Comparative Example 2

[0069] Calcined seed crystals were prepared using conventional methods, with steps S1 and S4 being the same as in Example 3;

[0070] (2) Alkali washing: The material after alkali dissolution is washed with water, and the residual NaOH in the washing water is 1.0 g / L;

[0071] (3) Neutralization and acid dissolution: After washing with alkali, the filter cake was slurried and the material concentration (based on TiO2) was adjusted to 198 g / L. A hydrochloric acid solution with a mass fraction of 29% was added to adjust the pH of the material to 3.15. The acid-adjusted material was heated to 55°C at a rate of 1°C / min. Then, hydrochloric acid with a mass fraction of 32% and a TiO2 mass ratio of 0.4% was added to the slurry. The temperature was increased to boiling at a rate of 1°C / min and kept boiling for 1 hour. Then, dilution water was added to control the titanium concentration of the material to 117 g / L. The conversion rate of the prepared seed crystals was tested to be 99.6% and the activity was 100.

[0072] Table 1 shows a comparison of the main parameters and calcined product indexes of the method of this invention with those of Comparative Examples 1 and 2:

[0073] Table 1

[0074]

[0075] To better understand the role of calcined seed crystals prepared using titanium oxychloride in the neutralization stage and during the calcination stage, the morphology of calcined seed crystals prepared by the two methods is compared with that of Example 2 and Comparative Example 1 (see Appendix). Figure 1 and attached Figure 2 The BET (specific surface area) and average particle size were analyzed.

[0076] Table 2

[0077] Sample number <![CDATA[BET specific surface area (m 2 / g)]]> Average particle size (nm) Example 2 96 85 Comparative Example 1 77 100

[0078] By comparing scanning electron microscopy images and specific surface areas, it can be seen that using titanium oxychloride in the neutralization stage to prepare calcined seed crystals results in slightly smaller seed crystals with larger specific surface areas. Under the same seed crystal mass, there are more seed crystals, which will exhibit higher activity during the calcination process, leading to a decrease in calcination temperature and / or a shortening of calcination time, thereby achieving the goal of reducing calcination energy consumption.

[0079] The data comparison above shows that after using titanium oxychloride solution to prepare calcined seed crystals, the conversion rate and activity of the calcined seed crystals meet the requirements. Filtering the calcined seed crystals revealed that the titanium dioxide content in the filtrate was less than 10 ppm, indicating that the titanium in the titanium oxychloride solution was fully recovered and utilized. Because the seed crystals have a short formation time, small particle size, and large specific surface area, a greater quantity and higher activity are achieved for the same seed crystal mass. With consistent conversion rates in the kiln-feed products, the calcination temperature and / or calcination time can be reduced, thereby lowering calcination energy consumption. Simultaneously, at the same conversion rate, there is no impact on the quality of the kiln-feed products, including blue light whiteness, crystal size, and crystal size distribution. The method of this invention is simple, low-cost, and has good industrialization prospects.

[0080] In addition, this application also attempted to directly prepare calcined seed crystals using titanium oxychloride solution. However, it was found that titanium oxychloride is not easily hydrolyzed, requiring the addition of additional seed crystals for hydrolysis, resulting in harsh production conditions unsuitable for large-scale production. Alternatively, an alkali neutralization followed by acid dissolution method was used to prepare calcined seed crystals. However, due to the high hydrochloric acid content in titanium oxychloride, a large amount of alkali was required for neutralization, leading to a lower titanium content in the seed crystals. With the same amount of seed crystals (based on TiO2 content), a larger volume of seed crystals would be needed, resulting in the generation of large amounts of chloride-containing wastewater during bleaching, putting pressure on water treatment. Therefore, this method is also unsuitable. In contrast, the method described in this application, combined with the alkali-washed filter cake from conventional seed crystal preparation, yields calcined seed crystals with higher activity and conversion rate and smaller particle size under milder conditions. This reduces the subsequent calcination temperature and time, enabling successful recycling of the titanium oxychloride solution.

[0081] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide production process via the chloride process, characterized in that, Includes the following steps: S1. Take the alkaline-washed filter cake and slurry it to obtain slurry I. The NaOH concentration in the alkaline-washed water is 3-5 g / L. Adjust the concentration of slurry I, based on TiO2 content, to 170-200 g / L. Add a titanium oxychloride solution, accounting for 0.1-0.3% of the TiO2 mass in slurry I, and adjust the pH to 3.5-5. This allows the hydrochloric acid in the titanium oxychloride solution to react with the sodium titanate in the alkaline-washed filter cake to generate titanic acid. Simultaneously, the titanium oxychloride in the titanium oxychloride solution undergoes hydrolysis to generate titanium dioxide, resulting in slurry II. The hydrochloric acid mass percentage in the titanium oxychloride solution is 25-35%, and the titanium oxychloride concentration, based on TiO2 content, is ≥50 g / L. S2. The slurry II is heated to 55-65°C at a rate of 0.3-0.5°C / min, and then a hydrochloric acid solution accounting for 0.2-0.5% of the TiO2 mass ratio in the slurry I is added. The amount of hydrochloric acid solution added is based on the mass of pure hydrochloric acid. The temperature is increased to boiling at a rate of 0.3-0.5°C / min and kept boiling for 2-4 hours. The orthotitanic acid reacts with the hydrochloric acid to generate rutile titanium dioxide colloid, and the titanium dioxide generated by the hydrolysis of titanium oxychloride is converted into rutile titanium dioxide. Then, water is added to dilute the material to a titanium dioxide content of 90-120 g / L to obtain calcined seed crystals.

2. The method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide process via chloride production, as described in claim 1, is characterized in that... The hydrochloric acid solution in step S2 has a mass fraction of ≥30% hydrochloric acid.

3. The method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide process via the chloride method, as described in claim 1, is characterized in that... The alkaline-washed filter cake described in step S1 is prepared through the following steps: (1) Alkali dissolution: The qualified metatitanic acid slurry after two washes is heated to 59.5-61.5℃ and then added to the alkaline solution heated to 110-115℃. After the initial reaction is completed, the solution is kept at 105-110℃ for 1-3 hours. The standard for the end of the initial reaction is that the material temperature no longer rises. (2) Alkali washing: The alkali-dissolved material is washed with softened water to obtain the alkali-washed filter cake.

4. The method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide production process via the chloride method, as described in claim 3, is characterized in that... The concentration of the qualified metatitanic acid slurry after the second washing is 250-300 g / L (based on TiO2), and the iron content is ≤15 ppm (based on titanium dioxide in the slurry).

5. The method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide process via the chloride method, as described in claim 3, is characterized in that... The alkali solution has a mass fraction of 45-52%, and the amount of alkali solution added is calculated based on the mass of soda ash and the mass ratio of TiO2 in the slurry as (1.45-1.9):

1.

6. The method for preparing calcined seed crystals using titanium oxychloride solution, a byproduct of the titanium dioxide process via the chloride method, as described in claim 1, is characterized in that... The iron content in the titanium oxychloride solution is ≤1ppm.

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