Sulfuric acid method titanium dioxide production process

Abstract

The invention relates to the technical field of titanium dioxide production, and provides a sulfuric acid method titanium dioxide production process which comprises the following steps: respectively pumping a hydrolysis concentrated titanium solution and a seed crystal concentrated titanium solution into a preheating tank, respectively carrying out heat treatment on the hydrolysis concentrated titanium solution and the seed crystal concentrated titanium solution, and uniformly mixing the hydrolysis concentrated titanium solution and the seed crystal concentrated titanium solution to obtain a concentrated titanium solution; the method comprises the following steps: uniformly mixing alkali liquor with titanium dioxide, sulfuric acid and iron to obtain mixed liquor, then heating the mixed liquor, putting the seed crystal concentrated titaniferous solution into a seed crystal reaction tank for mixing after the temperature of the seed crystal concentrated titaniferous solution is raised to the same temperature as that of the mixed liquor, quickly raising the temperature after mixing, and obtaining seed crystals after the seed crystal concentrated titaniferous solution is stabilized; simultaneously discharging the seed crystal and the concentrated titaniferous solution at the same temperature into a premixer for fully mixing to obtain a premix; according to the preparation method, hydrolysis is carried out in a manner of adding seed crystals, so that the hydrolysis rate of the titanium dioxide is increased, the particle size and distribution uniformity of metatitanic acid of the titanium dioxide, the lightening power of a finished product and the like are improved, and the pigment properties such as whiteness, lightening power and the like of the titanium dioxide product are improved.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide production, and in particular to a sulfuric acid process for producing titanium dioxide. Background Art

[0002] Titanium dioxide is another name for titanium dioxide, an important inorganic chemical raw material, and is often used as a white pigment. At present, the production of titanium dioxide mainly adopts the sulfuric acid method and the chlorination method. The sulfuric acid method is a common process for producing titanium dioxide. There is a hydrolysis process of titanium liquid in the production process of sulfuric acid titanium dioxide. The hydrolysis of titanium liquid is an extremely important process in the production process of sulfuric acid titanium dioxide. The quality of hydrolysis not only affects the economic efficiency of industrial production, but also has a great impact on the quality of the final product. The hydrolysis of titanium liquid is to transform the titanium dioxide component from liquid titanium liquid to solid metatitanic acid, thereby separating it from the soluble impurities in the mother liquor to extract pure titanium dioxide.

[0003] There are two main hydrolysis processes at present, namely, self-seed hydrolysis and external seed hydrolysis according to the preparation method of hydrolysis seeds. The self-seed method is to add concentrated titanium liquid to boiling water to dilute it to produce crystal nuclei, and then hydrolyze it, but this method takes a long time to hydrolyze; the external seed method is to add pre-prepared seeds to the titanium liquid and then hydrolyze it. This method is simpler and easier to control, but the performance of the precipitated pigment is worse than that of the self-seed method. Therefore, it is particularly important to seek an effective hydrolysis method to improve the quality of the final product. Summary of the invention

[0004] The purpose of the present invention is to provide a sulfuric acid method titanium dioxide production process, which hydrolyzes by adding seed crystals, thereby improving the hydrolysis rate of titanium dioxide, the particle size, distribution uniformity and decolorizing power of titanium dioxide metatitanic acid, and improving the pigment properties of titanium dioxide products such as whiteness and decolorizing power.

[0005] The embodiments of the present invention are achieved through the following technical solutions:

[0006] A sulfuric acid process for producing titanium dioxide comprises the following steps:

[0007] (1) Material preparation: The hydrolyzed titanium concentrate liquid and the seeded titanium concentrate liquid obtained by the sulfuric acid process are pumped into a titanium concentrate liquid preheating tank and a seeded titanium concentrate liquid preheating tank respectively, and then the hydrolyzed titanium concentrate liquid and the seeded titanium concentrate liquid are heat treated respectively. After the heat treatment, the hydrolyzed titanium concentrate liquid and the seeded titanium concentrate liquid are stirred and mixed to obtain a titanium concentrate liquid. The indicators of the titanium concentrate liquid are tested, and the subsequent hydrolysis operation is performed after the indicators are qualified.

[0008] (2) Preparing seed crystals: adding an alkali solution into a seed crystal reaction tank, and then adding titanium dioxide, sulfuric acid and iron, while maintaining the pH of the system solution between 2 and 7, stirring evenly to obtain a mixed solution, and then heating the mixed solution until it reaches the same temperature as the seed crystal concentrated titanium liquid, and then placing the seed crystal concentrated titanium liquid into the seed crystal reaction tank for mixing, and rapidly heating the mixture after mixing, and obtaining seed crystals after stabilization;

[0009] When titanium dioxide is precipitated from a normal titanium sulfate solution, very fine particles are obtained, but these have only a slight nucleation effect; the inventors unexpectedly found that by keeping the system pH between 2-7, when titanium is precipitated from such a solution by hydrolysis (e.g., by heating), the precipitate unexpectedly has a high nucleation ability; it also has a high tinting strength and a good whiteness. More importantly, the seed crystals can maintain a high activity and maintain good stability. In the case of low acidity, HSO4 - Bridge to SO4 - bridge conversion, while SO4 - The bridge turns to OH-bridge, and at the same time, the polymer chain is extended; the acidity is further reduced, the polymerization is significantly enhanced, and SO4 - The bridge will basically be replaced by an OH-bridge with high hydration synthesis. When the titanium polymers containing OH-bridges are close to each other, a condensation reaction will occur, and water molecules will be lost, thereby showing higher activity and maintaining better stability.

[0010] (3) Premixing the seed crystals and the concentrated titanium liquid: feeding the seed crystals and the concentrated titanium liquid at the same temperature into the premixer at the same time, and controlling the feeding speed of the seed crystals and the concentrated titanium liquid so that the materials are fully mixed in the premixer to obtain a premix;

[0011] After the seed crystals are prepared, this method does not directly put them into the concentrated titanium liquid for mixing. Instead, the seed crystals and the concentrated titanium liquid are simultaneously put into a premixer for full mixing before entering the hydrolysis pot. This method solves the problem that the seed crystals will float on the surface of the titanium liquid after being directly added to the concentrated titanium liquid, that is, it solves the disadvantages that the two cannot be mixed evenly and the size of the metatitanic acid particles after hydrolysis is uneven. Because, if the stirring speed is too fast, the particle size of the metatitanic acid particles will become finer after hydrolysis, and its particle flocculation and growth will be affected, affecting the filtration and washing speed. Generally, the stirring speed is controlled to 8 to 15 r / min. Limited by the slow stirring speed, when the seed crystals are added to the titanium liquid, the two cannot be completely mixed evenly within 10 minutes. The seed crystals can only be mixed with the concentrated titanium liquid on the top, and the seed crystals are unevenly distributed, which cannot play a comprehensive hydrolysis induction role, affecting the size and uniform distribution of the metatitanic acid particles after hydrolysis.

[0012] Therefore, the seed crystal will float on the surface of the titanium liquid. At this time, the surface tension of the liquid limits its complete immersion in the liquid. In this case, gases (such as oxygen, hydrogen, etc.) will form inclusions between the contact surface of the seed crystal and the liquid, affecting the normal growth of the seed crystal. In addition, the floating seed crystal cannot be stably deposited at the bottom of the liquid, causing its growth to be affected by unstable liquid flow and temperature gradient. As a result, the temperature and composition distribution in the liquid are uneven, which will cause deviations in the growth rate and crystal shape of the crystal, and the quality and performance of downstream products will also be affected. Even if the seed crystal is mixed after floating on the surface of the titanium liquid, the problems of inclusions that have already been produced and particle size and distribution cannot be avoided.

[0013] The present invention adds a premixer, and the prepared seed crystals and concentrated titanium liquid are introduced into the premixer at the same time, and the feeding speed is controlled. After sufficient mixing, the seed crystals are evenly distributed in the concentrated titanium liquid, which provides good inducing conditions for subsequent hydrolysis, improves the size and distribution of primary particles and polymerized particles of titanate after hydrolysis, and improves the whiteness, decolorizing power and other pigment properties of titanium dioxide products in subsequent processes.

[0014] (4) Hydrolysis of concentrated titanium solution:

[0015] ①. Open the feed valve and stirring system of the hydrolysis pot, feed the premix into the hydrolysis pot. After 20 to 22 minutes of feeding, turn on the steam to heat up the material, and bring the material to boiling within 30 to 40 minutes. After collecting the steam and observing the graying point, turn off the steam, stop stirring, and immediately take samples for testing: the hydrolysis rate at the graying point is 30 to 40%;

[0016] ②After sampling, close the observation hole and enter the 30-minute induction period. After the induction period, enter the secondary boiling, start stirring, start steam, raise the temperature to boiling within 10 minutes, reduce the steam, and keep boiling for 30 minutes;

[0017] ③. After the second boiling, collect small steam again to keep the material in a slightly boiling state for 2 hours. Calculate the amount of dilution water added (usually 7-9m 3 ), keep warm for 40 minutes, open the dilution water valve, add quantitative dilution water at 100L / min, about 70-90 minutes after the dilution water is added, the heat preservation ends, open the large steam valve, heat to three boilings, collect the small steam and keep warm for 50 minutes, then take samples and send them to the laboratory, and the hydrolysis ends;

[0018] (5) filtering the solution obtained after hydrolysis in step (4) to obtain a filter cake, washing and drying the filter cake, then mixing the seed crystals obtained in step (2) with the filter cake, and calcining them at 800 to 900° C. for 110 to 550 min. After the calcined product is cooled, grinding is performed to obtain titanium dioxide.

[0019] Furthermore, in step (1), the volume ratio of the hydrolysis concentrated titanium solution to the seed concentrated titanium solution is 40 to 50:1.

[0020] Furthermore, in step (1), when the hydrolyzed concentrated titanium liquid is heat treated, the temperature is raised to 90-100° C. within 90-120 minutes; when the seed concentrated titanium liquid is heat treated, the temperature is raised to 80-90° C. within 40-50 minutes.

[0021] Furthermore, in step (1), the indicators of the concentrated titanium solution are as follows: total titanium: 195-200 g / L, trivalent titanium: 0.5-1.3 g / L, F value: 1.84-1.90, iron-titanium ratio: 0.42-0.48, clarity: ≤20 mg / L, stability: ≥450.

[0022] Furthermore, in step (2), the alkali solution includes but is not limited to: sodium, carbonate, caustic soda lye, and ammonia solution.

[0023] Furthermore, in step (2), the concentration of the alkali solution is 88-92 g / L; and the temperature of the alkali solution is 80-90°C.

[0024] Furthermore, in step (2), when the mixed solution is heated, steam is turned on for heating, and the steam is turned off after the alkali solution is heated to 80-85°C.

[0025] Furthermore, in step (2), when the seed crystal concentrated titanium liquid is placed in the seed crystal reaction tank for mixing, the seed crystal concentrated titanium liquid needs to be placed in the reaction tank within 2.5 to 3 minutes.

[0026] Furthermore, in step (2), the seed crystal concentrated titanium liquid is placed in a seed crystal reaction tank and mixed, and then the temperature is quickly raised to above 95°C.

[0027] Furthermore, in step (3), the mass ratio of the seed crystal to the concentrated titanium liquid is 1:3-10.

[0028] Furthermore, in step (4), the first heating time to boiling is 30 to 40 minutes; the second heating time to boiling is 40 to 50 minutes; and the third heating time to boiling is 10 to 15 minutes.

[0029] Furthermore, in step (4.3), the material is kept at a slight boiling state for 1.5-2.5 hours, and is heated to boiling for the third time and then kept at this temperature for 0.5-1 hour.

[0030] Furthermore, in step (4.3), when water is added for dilution, the liquid-to-solid ratio of the dilution water to the material is 7 to 9:1m 3 / g.

[0031] Furthermore, the indicators of the obtained titanium dioxide are as follows: TiO2 content: 165-175 g / L; soluble titanium content: ≤6 g / L; Ti 3+ Concentration: ≥0.3g / L; Hydrolysis rate: ≥96.0%; Particle size (d50): 1.8~2.3μm.

[0032] The technical solution of the embodiment of the present invention has at least the following advantages and beneficial effects:

[0033] The invention has high nucleation ability through self-made added seeds, and at the same time has very high tinting power and whiteness, shows high activity, and maintains good stability, which improves the hydrolysis rate of titanium dioxide, the particle size, distribution uniformity and finished product tinting power of titanium dioxide metatitanic acid, and improves the pigment properties of titanium dioxide products such as whiteness and tinting power. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 This is a particle size analysis report of the titanium dioxide prepared in Example 1 of the present invention;

[0036] Figure 2 This is a particle size analysis report of the titanium dioxide prepared in Example 1 of the present invention;

[0037] Figure 3 This is a particle size analysis report of the titanium dioxide prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0039] Example 1

[0040] A sulfuric acid process for producing titanium dioxide comprises the following steps:

[0041] (1) Material preparation: The hydrolyzed titanium concentrate and the seed titanium concentrate produced in the previous stage are pumped into the titanium concentrate preheating tank and the seed titanium concentrate preheating tank respectively. The volume of the hydrolyzed titanium concentrate is 70m3. 3 The volume of the seed titanium concentrate is 1.512m3 Then, the hydrolysis concentrated titanium liquid and the seed concentrated titanium liquid are heat-treated respectively. When the hydrolysis concentrated titanium liquid is heat-treated, the temperature is raised to 95°C within 100 minutes; when the seed concentrated titanium liquid is heat-treated, the temperature is raised to 85°C within 45 minutes; after the heat treatment, the hydrolysis concentrated titanium liquid and the seed concentrated titanium liquid are stirred and mixed evenly to obtain the concentrated titanium liquid, and the indicators of the concentrated titanium liquid are tested. The indicators of the concentrated titanium liquid are as follows: total titanium: 200g / L, trivalent titanium: 1g / L, F value is 1.87, iron-titanium ratio is 0.45, clarity: 10mg / L, stability: 480; the qualified concentrated titanium liquid enters the subsequent hydrolysis operation;

[0042] (2) Preparing seed crystals: Weigh 45 kg of caustic soda flakes and add them into a seed crystal reaction tank, then add process water, and after the caustic soda flakes are dissolved, a sodium hydroxide aqueous solution with a concentration of 90 g / L is prepared. The steam is turned on to heat the alkali solution to 85° C., then the steam is turned off, and a sample is taken to detect the sodium hydroxide concentration of 90%;

[0043] Then add 120g of titanium dioxide, 250g of sulfuric acid and 80g of iron, adjust the pH of the system solution to 2, stir evenly, and obtain a mixed solution. Then heat the mixed solution to the same temperature as the seed titanium solution, put the seed titanium solution into the seed reaction tank for mixing, quickly heat up after mixing, and obtain the seed crystal after stabilization;

[0044] (3) Premixing the seed crystals and the concentrated titanium liquid: The seed crystals and the concentrated titanium liquid at the same temperature are simultaneously discharged into the premixer, the mass ratio of the seed crystals to the concentrated titanium liquid is 1:6, and the discharge speed of the seed crystals and the concentrated titanium liquid is controlled so that the materials are fully mixed in the premixer to obtain a premix;

[0045] (4) Hydrolysis of concentrated titanium solution:

[0046] ①. Open the feed valve and stirring system of the hydrolysis pot, feed the premix into the hydrolysis pot. After 20 minutes of feeding, turn on the steam to heat up the material, and bring the material to boiling within 35 minutes. After collecting the steam and observing the graying point, turn off the steam, stop stirring, and immediately take samples for testing: the hydrolysis rate at the graying point is 35%;

[0047] ②After sampling, close the observation hole and enter the 30-minute induction period. After the induction period, enter the secondary boiling, start stirring, start steam, raise the temperature to boiling within 10 minutes, reduce the steam, and keep boiling for 30 minutes;

[0048] ③. After the second boiling, collect the steam again to keep the material in a slightly boiling state for 2 hours. Calculate the amount of dilution water added according to the amount of concentrated titanium liquid hydrolyzed (control the liquid-to-solid ratio to 8m 3 : 1m 3 / g), keep warm for 40 minutes, open the dilution water valve, add quantitative dilution water at 100L / min, add dilution water for about 80 minutes, and then the heat preservation ends. Open the large steam valve, raise the temperature to three boilings, collect the small steam and keep warm for 50 minutes, then take samples and send them to the laboratory, and the hydrolysis ends;

[0049] (5) filtering the solution obtained after the hydrolysis in step (4) to obtain a filter cake, washing and drying the filter cake, then mixing the seed crystals obtained in step (2) with the filter cake, and calcining the mixture at 800 to 900° C. for 110 to 550 min, grinding the calcined product after cooling, and obtaining titanium dioxide; the obtained titanium dioxide has high whiteness and glossiness, and its indicators are as follows: TiO2 content: 175 g / L; soluble titanium content: 2 g / L; Ti 3+ Concentration: 2.3 g / L; hydrolysis rate: 98.6%; particle size (d50): 2.2 μm.

[0050] Example 2

[0051] The difference between this embodiment and embodiment 1 is that: in step (1), the volume ratio of the hydrolyzed concentrated titanium solution to the seed concentrated titanium solution is 50:1; the obtained titanium dioxide has high whiteness and glossiness, and its indicators are as follows: TiO2 content: 170g / L; soluble titanium content: 3g / L; Ti 3+ Concentration: 2.0g / L; hydrolysis rate: 98.3%; particle size (d50): 2.1μm.

[0052] Example 3

[0053] The difference between this embodiment and embodiment 1 is that: in step (1), when the concentrated titanium liquid is hydrolyzed and heat-treated, the temperature is raised to 100°C within 110 minutes; when the concentrated titanium liquid is seeded and heat-treated, the temperature is raised to 90°C within 40 minutes; the obtained titanium dioxide has high whiteness and glossiness, and its indicators are as follows: TiO2 content: 165g / L; soluble titanium content: 3.5g / L; Ti 3+ Concentration: 1.8 g / L; hydrolysis rate: 98.5%; particle size (d50): 2.1 μm.

[0054] Example 4

[0055] The difference between this embodiment and embodiment 1 is that: in step (2), the concentration of the alkali solution is 89 g / L; the temperature of the alkali solution is 90°C; the obtained titanium dioxide has high whiteness and glossiness, and its indicators are as follows: TiO2 content: 168 g / L; soluble titanium content: 4 g / L; Ti 3+ Concentration: 2.6 g / L; hydrolysis rate: 98.1%; particle size (d50): 2.1 μm.

[0056] Example 5

[0057] The difference between this embodiment and embodiment 1 is that in step (3), the mass ratio of the seed crystal to the concentrated titanium solution is 1:7; the obtained titanium dioxide has high whiteness and glossiness, and its indicators are as follows: TiO2 content: 166g / L; soluble titanium content: 2.4g / L; Ti 3+ Concentration: 2.1 g / L; hydrolysis rate: 98.4%; particle size (d50): 2.2 μm.

[0058] Example 6

[0059] The difference between this embodiment and embodiment 1 is that: in step (4), the first heating time to boiling is 30 minutes; the second heating time to boiling is 40 minutes; the third heating time to boiling is 10 minutes; the obtained titanium dioxide has high whiteness and glossiness, and its indicators are as follows: TiO2 content: 172g / L; soluble titanium content: 3.3g / L; Ti 3+ Concentration: 1.9 g / L; hydrolysis rate: 98.3%; particle size (d50): 2.1 μm.

[0060] Example 7

[0061] The difference between this embodiment and embodiment 1 is that: in step (4.3), when diluting with water, the liquid-solid ratio of the dilution water to the material is 7.5:1m 3 / g; the obtained titanium dioxide has high whiteness and glossiness, and its indicators are as follows: TiO2 content: 170g / L; soluble titanium content: 2.6g / L; Ti 3+ Concentration: 1.9 g / L; hydrolysis rate: 98.4%; particle size (d50): 2.2 μm.

[0062] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A sulfuric acid process for producing titanium dioxide, characterized in that: The following steps are involved: (1) Material preparation: pumping the hydrolyzed titanium concentrate liquid and the seeded titanium concentrate liquid into a titanium concentrate liquid preheating tank and a seeded titanium concentrate liquid preheating tank respectively, and then heat treating the hydrolyzed titanium concentrate liquid and the seeded titanium concentrate liquid respectively, and after the heat treatment, stirring and mixing the hydrolyzed titanium concentrate liquid and the seeded titanium concentrate liquid to obtain a titanium concentrate liquid; (2) Preparing seed crystals: adding alkaline solution into a seed crystal reaction tank, and then adding titanium dioxide, sulfuric acid and iron, while maintaining the pH of the system solution between 2 and 7, stirring evenly to obtain a mixed solution, and then heating the mixed solution. When the seed crystal concentrated titanium solution rises to the same temperature as the mixed solution, the seed crystal concentrated titanium solution is placed in the seed crystal reaction tank for mixing, and the temperature is rapidly raised after mixing. After stabilization, the seed crystals are obtained; (3) Premixing the seed crystals and the concentrated titanium liquid: The seed crystals and the concentrated titanium liquid at the same temperature are simultaneously fed into the premixer so that the materials are fully mixed in the premixer to obtain a premix; (4) Hydrolysis of concentrated titanium solution: (4.1) The premix is ​​fed into a hydrolysis device, and then heated to boiling for the first time, and stirring is started. After the graying point is observed, the heating and stirring are stopped, and samples are taken for observation; (4.2) After sampling, enter the 30-min induction period. After the induction period, heat to boiling for the second time, start stirring, heat to boiling within 10 minutes, and keep boiling for a period of time; (4.3) The material is kept at a slight boiling state for a period of time, diluted with water, and then heated to boiling for a third time. After keeping the temperature for a period of time, it is filtered to obtain a filter cake, which is washed and dried. Then, the seed crystals obtained in step (2) are mixed with the filter cake, and after calcination, cooling and grinding, titanium dioxide is obtained.

2. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (1), the volume ratio of the hydrolyzed concentrated titanium solution to the seed concentrated titanium solution is 40 to 50:

1.

3. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (1), when the hydrolyzed concentrated titanium liquid is heat treated, the temperature is raised to 90-100° C. within 90-120 minutes; when the seed concentrated titanium liquid is heat treated, the temperature is raised to 80-90° C. within 40-50 minutes.

4. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (1), the indicators of the concentrated titanium solution are as follows: total titanium: 195-200 g / L, trivalent titanium: 0.5-1.3 g / L, F value: 1.84-1.90, iron-titanium ratio: 0.42-0.48, clarity: ≤20 mg / L, stability: ≥450.

5. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (2), the alkali solution is one or more of sodium, carbonate, caustic soda alkali solution, and ammonia solution; the concentration of the alkali solution is 88-92 g / L; and the temperature of the alkali solution is 80-90°C.

6. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (2), when the mixed solution is heated, steam is turned on for heating, and the steam is turned off after the alkali solution is heated to 80-85°C.

7. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (2), the concentrated titanium seed solution is placed in a seed reaction tank and mixed, and then the temperature is rapidly raised to above 95°C.

8. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (3), the mass ratio of the seed crystal to the concentrated titanium liquid is 1:3-10.

9. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (4), the first heating time to boiling is 30 to 40 minutes; the second heating time to boiling is 40 to 50 minutes; and the third heating time to boiling is 10 to 15 minutes.

10. The process for producing titanium dioxide by sulfuric acid method according to claim 1, characterized in that: In step (4.3), the material is kept at a slight boiling state for 1.5-2.5 hours, and the temperature is raised to boiling for the third time and then kept at this temperature for 0.5-1 hour.

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