Titanium dioxide with high covering power and preparation method thereof

Abstract

The preparation method comprises the following steps: taking a titanyl sulfate solution of which the concentration is 80-100g / L, the F value is 1.95-2.05 and the Fe / TiO2 ratio is 0.2-0.28, heating the titanyl sulfate solution to 40-55 DEG C, preheating alkali liquor to 30-40 DEG C, adding the preheated alkali liquor into the heated titanyl sulfate solution for 30-40 minutes, adding the preheated alkali liquor into the heated titanyl sulfate solution, heating the heated titanyl sulfate solution to 40-60 DEG C for 30-40 minutes, and cooling the heated titanyl sulfate solution to obtain the high-covering-power titanium dioxide. The final pH value is controlled to be 3.0-4.0, then the temperature is raised to 60 DEG C for curing, the curing time is 10-30 minutes, then the temperature is cooled to 25 DEG C or below, and the seed crystal with the uniform particle size is obtained through filtering; preparing wet-ground titanium dioxide slurry; and coating the wet-ground titanium dioxide slurry, curing, washing with water, drying, and grinding with steam to obtain the titanium dioxide powder. The covering power of the titanium dioxide is improved to be greater than 93% through the particle shape and size of the titanium dioxide and coating.

Description

Technical Field

[0001] The present invention relates to the field of titanium dioxide, in particular to high-hiding-power titanium dioxide and a preparation method thereof. Background Art

[0002] The most important role of titanium dioxide pigment in the industry is its ability to create a covering effect by creating an opaque effect when dispersed in a medium. A pigment's hiding power depends not only on its crystal structure, refractive index, and light-scattering ability, but also on its light absorption capacity. However, like other white pigments, titanium dioxide has a very low light absorption capacity. While light absorption does affect hiding power, it is not as significant as its scattering capacity. Therefore, its hiding power is primarily influenced by its scattering capacity.

[0003] The different shapes and sizes of titanium dioxide particles result in very different degrees of light scattering, which is a key factor affecting the hiding power of titanium dioxide.

[0004] Chinese patent publication number CN103880070B discloses a method for producing titanium dioxide particles. This method utilizes an existing sulfuric acid-processed titanium dioxide production line. By adjusting and improving process parameters and operating methods, including titanium liquid parameters, seed crystal preparation, atmospheric pressure hydrolysis, salt treatment, calcination, and post-treatment, and by adjusting detection and control accordingly, the method produces titanium dioxide with a particle size range of 400-1100 nm, accounting for over 60% of the particles and being completely rutile. The titanium dioxide particles produced by this method have excellent reflectivity for the near-infrared portion of sunlight, and products such as coatings and plastics made with them can achieve excellent cooling and energy-saving effects. However, the seed crystals produced by this method, with over 60% of the particles being in the 400-1100 nm range, are relatively large, and the particle size distribution is too wide, leaving room for improvement in the hiding power of the resulting titanium dioxide. Summary of the Invention

[0005] The present invention aims to provide a high-hiding power titanium dioxide and a preparation method thereof, which improves the light scattering degree of titanium dioxide particles through the interaction between the shape, size and coating of titanium dioxide particles, thereby improving the hiding power of titanium dioxide.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: A method for preparing high-hiding power titanium dioxide comprises the following steps: S1. Take a titanyl sulfate solution with a concentration of 80-200 g / L, an F value of 1.95-2.05, and an Fe / TiO2 ratio of 0.2-0.28, heat the titanyl sulfate solution to 40-55° C., preheat the alkali solution to 30-40° C., add the preheated alkali solution to the heated titanyl sulfate solution, add the preheated alkali solution for 30-40 minutes, control the endpoint pH value to 3.0-4.0, then heat to 60° C. for aging for 10-30 minutes, and then cool to below 25° C. to obtain a seed solution; S2, filtering the seed solution prepared in S1 to remove seed crystals with a particle size greater than 0.35 μm; S3, filtering the seed solution after S2 filtering to remove the seed crystals with a particle size less than 0.16 μm to obtain a filtered seed solution; S4, adding the filtered seed solution prepared in S3 to the titanium liquid, hydrolyzing, washing, bleaching, washing twice, salting, calcining, preparing rutile titanium dioxide powder, roller milling, and wet milling to obtain a wet-milled titanium dioxide slurry; S5. Coating, aging, water washing, drying and steam-powdering the titanium dioxide slurry wet-ground in S4 are performed.

[0007] In S2, seed crystals with a particle size larger than 0.35 μm are removed, and seed crystals with a coarse particle size are removed.

[0008] In S3, the seed crystals with a particle size less than 0.16 μm are removed, and the seed crystals with a fine particle size are removed to obtain a filtered seed crystal solution.

[0009] The F value of titanyl sulfate solution, also known as the acidity coefficient, is the ratio of the effective acid to the total titanium mass concentration in the titanium solution. Its calculation formula is: The effective acid is the sum of the mass concentrations of the acid bound to titanium and the free acid. Fe / TiO2 is the mass of iron divided by the mass of TiO2 and is 0.2-0.28.

[0010] The present invention controls the particle size of hydrolyzed seed crystals and removes large and fine seed crystals through a secondary filtration method to produce seed crystals with a particle size of 0.16-0.35 μm. The appropriate seed crystal size facilitates subsequent water washing. If the particle size distribution is uneven, there will be more fine and coarse particles, which tend to aggregate firmly together, resulting in high viscosity of metatitanic acid and long water washing times. The seed crystals of the appropriate particle size are then provided to the titanium solution for hydrolysis. The prepared hydrolyzed metatitanic acid has a moderate particle size and a narrow distribution, ultimately producing titanium dioxide with high hiding power, as specifically described below: (1) Under the same conditions, when the particle size of titanium dioxide is 160-350nm, that is, the particle size is about 0.4-0.5 times the wavelength of visible light, it has a strong scattering ability for light, which will directly affect the hiding power of the coating during application.

[0011] High scattering power, and thus high hiding power, can only be achieved when the particle size is controlled within the range of 0.4 to 0.5 times the wavelength of visible light (0.4-0.7μm), that is, between 0.16 and 0.35μm. The main factors affecting the hiding power of titanium dioxide pigment after film formation are particle size and dispersibility. If the titanium dioxide particle size is very fine, with a large number of particles smaller than 0.16μm, the hiding power of titanium dioxide will be low. If the titanium dioxide particle size is very coarse, with a large number of particles larger than 0.35μm, the hiding power of titanium dioxide will also be low.

[0012] (2) The fine particle seeds are removed, and the overburning of fine particles is avoided during the calcination of titanic acid, thereby avoiding the influence of sintered particles on the hiding power.

[0013] In order to ensure that the seed solution with a particle size range of 0.16-0.35 μm is obtained, the present application adopts the following means to interact with each other: S1: The concentration of the titanyl sulfate solution is controlled to be 80-100 g / L. If the concentration of the titanium liquid is too low, the titanium liquid is at risk of early hydrolysis. If the concentration of the titanium liquid is too high, according to the reaction principle, the reactant TiO2 has more opportunities to collide with the alkali, and the particle size of the generated seed crystals will be extremely fine.

[0014] The F value is 1.95-2.05. If the F value is too low, the acidity is low and the titanium liquid has the risk of early hydrolysis. If the F value is too high, the acidity is high. + High ion concentration, H + There are more opportunities for collision with alkali, and more extremely fine particle seeds will be generated.

[0015] The titanium liquid is heated to 40-50°C, the reaction temperature is too low, the reaction speed is too slow, and the prepared seed crystals have too many uneven particle sizes. The formation of seed crystals is divided into the formation of crystal nuclei and the growth of crystal nuclei, which are carried out simultaneously and compete with each other. When the reaction speed is slow, the nucleation speed is slow, and the growth time is long, the particles that nucleate first are much larger than the seed crystal particles that nucleate later due to the long growth time. Overly coarse seed crystals will also indirectly affect the hiding power. The reaction temperature is too high, the reaction speed is too fast, and the prepared seed crystals have too many extremely fine particle sizes. Too many extremely fine seed crystal particles not only affect the yield of seed crystals with suitable particle sizes, but also affect subsequent filtration.

[0016] Preheat the alkali to 30-40°C to avoid lowering the temperature of the titanyl sulfate solution upon addition. This can cause a localized drop in the temperature of the solution and affect the rate of nucleation. If the alkali solution is not preheated and the cold solution is added directly to the titanium solution, the temperature at the point where the titanium solution is added will drop, and the seed crystals formed at this low temperature will have low activity.

[0017] The alkali addition time is 30-40 minutes. If the alkali addition time is too short, the reaction between titanyl sulfate and the alkali solution will be too intense, resulting in a high degree of fine seed particles. If the alkali addition time is too long, the reaction between the titanyl sulfate solution and the alkali solution will be slow, leading to the risk of premature hydrolysis of the titanium solution. Preferably, the alkali addition time is 35-40 minutes.

[0018] The titanium solution in S4 is a colloidal solution containing liquid titanium and a large amount of impurities such as iron. The hydrolysis product is a suspension containing solid titanium and a large amount of impurities such as iron. The hydrolyzed hydrated titanium dioxide contains sulfuric acid and ions of iron, aluminum, manganese, copper, nickel, vanadium, and lead. These ions, after calcination, form corresponding oxides, exhibiting various colors and contaminating the product to varying degrees. Therefore, water washing is necessary to remove these ions. Hydrated titanium dioxide is insoluble in water, while sulfuric acid and ions of iron, aluminum, manganese, copper, nickel, vanadium, and lead are soluble in water. This is a prerequisite for water washing. The impurities are removed with water by exploiting the concentration difference between the washing water and the impurity ions in the hydrated titanium dioxide. After the first wash, the hydrated titanium dioxide still contains trivalent iron, which exists in the form of Fe(OH)3. Bleaching is required to convert the solid Fe(OH)3 into soluble Fe2(SO4)3, and a second wash is required to further remove impurities.

[0019] According to the embodiments of the present invention, the present invention can be further optimized. The following is the technical solution formed after optimization: in S1, alkaline solution is added to the titanyl sulfate solution, and the time for the pH to reach 2.0 is 18-20 minutes.

[0020] In one preferred embodiment, in S1, alkali solution is added to the titanyl sulfate solution, and the time for the pH to reach 2.5 from 2.0 is 5-8 minutes, the time for the pH to reach 3.0 from 2.5 is 3-6 minutes, the time for the pH to reach 3.5 from 3.0 is 2-5 minutes, and the time for the pH to reach 4.0 from 3.5 is 1-3 minutes.

[0021] Supersaturation significantly influences the formation of crystal nuclei and the growth rate of crystals. The speed of these two processes, in turn, affects the particle size and particle size distribution of the hydrolysis products. In the early stages of the reaction, the titanium concentration in the titanyl sulfate solution is relatively high. To ensure saturation in the solution, a large amount of alkali is required, so the alkali addition rate must be fast. However, this cannot be too fast. Otherwise, if the alkali is added too quickly, the local alkali concentration will be too high, and the concentrations of TiO2 and acid in the titanium solution will be limited, prompting the alkali to react with the iron in the titanyl sulfate to form ferrous precipitates, which are poor seed crystals. In the later stages of the reaction, the titanium concentration in the titanyl sulfate solution is low. To avoid oversaturation in the solution, a small amount of alkali is required, so the alkali addition rate must be slow.

[0022] The alkali solution in S1 is added to the titanyl sulfate solution through an axial flow pump.

[0023] In one preferred embodiment, in S1, an alkali solution is added to the titanyl sulfate solution, and the end point pH value is controlled to be 3.5-4.0.

[0024] The endpoint pH value is controlled to be 3.5-4.0. If the pH value is too low, the amount of seed crystals prepared will be small, and if the pH value is too high, it will easily cause early hydrolysis of the seed titanium liquid.

[0025] In a preferred embodiment, the concentration of the alkali solution in S1 is 60-80 g / L. The alkali solution includes one or two of LiOH, NaOH, and KOH. The concentration of the alkali solution is 60-80g / L. If the concentration of the alkali is too low, it will be added to the titanium liquid to reduce the concentration of the titanium liquid, thereby promoting the hydrolysis of the titanium liquid and the seed crystals during the reaction. If the concentration of the alkali is too high, the alkali solution and the titanium liquid will react too violently, which will cause the local temperature of the reactants to be too high and the local TiO2 to undergo early hydrolysis.

[0026] In one preferred embodiment, in S2, a Buchner funnel with filter cloth is used to filter out the coarse seed crystals.

[0027] Titanium dioxide concentration, iron-titanium ratio, F value, hydrolysis temperature, and hydrolysis time all affect the particle size and particle size distribution of hydrolyzed metatitanic acid. The particle size distribution of hydrolyzed metatitanic acid cannot be absolutely uniform; there will inevitably be some excessively fine particles. Further filtration is then used to remove coarse particles and fine particle seeds.

[0028] In one preferred embodiment, ceramic membrane filtration is used in S3 to remove fine particle seeds, and filtration is performed through a water circulation pump.

[0029] In one preferred embodiment, the coating in S5 specifically includes the following steps: preparing a wet-ground titanium dioxide slurry of 300-500 g / L, heating it to 45-60°C, adding sodium silicate with a mass concentration of 4-5%, adding it for 20-40 minutes, adding an acidifier with a mass concentration of 5-10%, until the pH value of the slurry reaches 5.0-6.5, adding it for 40-60 minutes, aging it for 10-20 minutes, adding an aluminum sulfate solution with a mass concentration of 2-10%, and then adding a dilute alkali solution with a mass concentration of 5-10%, controlling the pH value of the slurry to 8-10, and adding it for 30-40 minutes.

[0030] The sodium silicate addition amount is 4-5%. Too little sodium silicate affects the dispersibility of titanium dioxide, thereby reducing its hiding power; too much sodium silicate affects its performance. The addition time is 20-40 minutes. Too short or too long a time will not allow the hydrated silica to coat the titanium dioxide particles. Add 5-10% dilute acid as an acidifier. The acidifier in S5 can be hydrochloric acid or sulfuric acid. Adjust the pH to 5.0-6.5 with acid. Too high a pH prevents the sodium silicate from fully forming silicic acid. Too low a pH will dissolve the formed silicic acid sol. Mature for 10-20 minutes. Add 2-3% aluminum sulfate solution and, concurrently, 5-10% dilute alkali solution, controlling the slurry's pH to 8-10. This allows the aluminum hydroxide to coat the TiO2 particles.

[0031] The coating temperature of the present invention is low, and the silicon coating method is loose silicon, which has the outstanding advantage of having ultra-high hiding power. The coating temperature of the Chinese patent with publication number CN103880070B is high, and the silicon coating method is dense silicon coating, which does not have ultra-high hiding power.

[0032] After adding dilute sulfuric acid to S5, sodium silicate generates silica gel.

[0033] Na2SiO3+ H2SO4= Na2SO4+ SiO2.nH2O Aluminum sulfate solution reacts with alkaline solution to form aluminum hydroxide.

[0034] Al2(SO4)3+6 NaOH = 3Na2SO4+2Al(OH)3 In one preferred embodiment, the aging time after adding the dilute alkali solution in S5 is 10-15 minutes.

[0035] Preferably, the pH value is adjusted to 3.5-4.0 after filtration in S3; and a dilute acid solution is added in S3 to adjust the pH value. Adding dilute acid water to control the pH value of the seed crystal solution is to ensure the activity of the seed crystals.

[0036] The invention also discloses high-hiding-power titanium dioxide prepared according to the preparation method.

[0037] Compared with the prior art, the present invention has the following beneficial effects: (1) The alkali solution is preheated and then added to the heated titanium liquid to avoid the decrease of the local reaction temperature of the titanium liquid and ensure the activity of the seed crystal.

[0038] (2) Controlling the pH value at the end point of seed crystal preparation can ensure the activity of the prepared seed crystals.

[0039] (3) The prepared seed solution is filtered to remove coarse and fine seed crystals, thereby obtaining seed crystals with uniform particle size. The seed crystals are added to the titanium solution for hydrolysis, and the resulting hydrolysis slurry has a more moderate particle size, a more uniform particle size distribution, a low viscosity, and a high water washing efficiency. Because if the particle size is uneven, large particles and small particles will agglomerate more seriously, resulting in a high viscosity slurry, which fundamentally solves the problem of high viscosity and low water washing efficiency of metatitanic acid. If the viscosity of the hydrolysis slurry is low, the filtration time of the hydrolysis slurry is short, and the water washing time is short, the iron content of the filter cake can be reduced to the production requirements. The salt-treated slurry has a low viscosity and the slurry is stirred more evenly. The surface of the TiO2 particles coated with the salt treatment agent is denser, and the calcined product particles are closer to spherical. The spherical particles scatter light more strongly and have higher covering power.

[0040] (4) The fine particle seeds are removed, and the phenomenon of over-burning of fine particles is avoided during the calcination of metatitanic acid. The influence of sintered particles on the hiding power is avoided.

[0041] (5) The loose silicon coated with TiO2 has a honeycomb shape and has a high hiding power after coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is the particle size of the hydrolyzed metatitanic acid obtained in Example 1 of the present invention.

[0043] Figure 2 is the particle size of the hydrolyzed metatitanic acid obtained in Example 2 of the present invention.

[0044] Figure 3 is the particle size of the hydrolyzed metatitanic acid obtained in Example 3 of the present invention.

[0045] Figure 4 It is the particle size of the hydrolyzed metatitanic acid obtained in Comparative Example 1 of the present invention.

[0046] Figure 5 It is the particle size of the hydrolyzed metatitanic acid obtained in Comparative Example 2 of the present invention.

[0047] Figure 6 It is the particle size of the hydrolyzed metatitanic acid obtained in Comparative Example 3 of the present invention.

[0048] Figure 7 is the particle size of the titanium dioxide product obtained in Example 1 of the present invention.

[0049] Figure 8 is the particle size of the titanium dioxide product obtained in Example 2 of the present invention.

[0050] Figure 9 is the particle size of the titanium dioxide product obtained in Example 3 of the present invention.

[0051] Figure 10It is the particle size of the titanium dioxide finished product obtained in Comparative Example 1 of the present invention.

[0052] Figure 11 It is the particle size of the titanium dioxide product obtained in Comparative Example 2 of the present invention.

[0053] Figure 12 It is the particle size of the titanium dioxide finished product obtained in Comparative Example 3 of the present invention.

[0054] The blue line represents the cumulative distribution of particle size, and the red line represents the interval distribution of particle size. DETAILED DESCRIPTION

[0055] The present invention will be described in detail below with reference to the embodiments. It should be noted that the embodiments and features of the embodiments of the present invention can be combined with each other without conflict.

[0056] Example 1 1. Seed crystal preparation: Titanium liquid index: TiO2: 200g / L, F value: 1.95, Fe / TiO2: 0.28, stability 500mL.

[0057] (1) Place 200 mL of titanyl sulfate solution in a 1000 mL glass beaker, start stirring, and add 200 mL of deionized water to adjust the concentration of the titanyl sulfate solution to 100 g / L. Then heat it to 45 °C. At the same time, place a 60 g / L NaOH solution in a glass beaker and preheat it to 30 °C.

[0058] Use an axial flow pump to add 60g / L NaOH solution. The alkali addition time is 39'18", and the end pH value is controlled to 4.0. Raise the temperature to 60℃ and mature for 30 minutes. Cool to 25℃ with ice water and set aside.

[0059] Table 1 Time of adding NaOH solution in Example 1 (2) The prepared seed crystals are filtered through a secondary filter to remove coarse particles and fine particles in batches, and the obtained seed crystals have a uniform particle size and the pH value is adjusted to 4.0.

[0060] (3) Adding seed crystals to titanium liquid for hydrolysis, primary washing, bleaching, secondary washing, salt treatment, calcination to prepare crude rutile titanium dioxide, roller milling, and wet milling.

[0061] (4) Coating: Prepare a 500g / L titanium dioxide slurry from the wet-ground titanium dioxide. Heat the mixture to 45°C and add 20% by weight (as SiO2) and 4.0% sodium silicate for 20 minutes. Use an axial flow pump to pump in 5% sulfuric acid, controlling the flow rate and adding it for 40 minutes. Keep the pH at 5.0. Mature for another 10 minutes. Add 10% by weight aluminum sulfate (as Al2O3) and 5% sodium hydroxide solution in parallel, with the amount of aluminum sulfate added being 2.0%. Keep the pH at 10. Add them for 40 minutes and mature for 10 minutes. Wash, dry, and steam powder.

[0062] Example 2 Seed crystal preparation: Titanium liquid indicators: TiO2200g / L, F value: 2.05, Fe / TiO2: 0.2, stability 500mL.

[0063] (1) Place 200 mL of titanyl sulfate solution in a 1000 mL glass beaker, start stirring, and add 300 mL of deionized water to adjust the concentration of titanyl sulfate solution to 80 g / L. Then heat it to 55 °C. At the same time, place 80 g / L NaOH solution in a glass beaker and preheat it to 40 °C.

[0064] Use an axial flow pump to add 80g / L NaOH solution. The alkali addition time is 33 minutes and 33 seconds. The end pH value is controlled at 3.5. The temperature is raised to 60°C and the aging time is 10 minutes. Cool to 25°C with ice water and set aside.

[0065] Table 2 Time of adding NaOH solution in Example 2 (2) The prepared seed crystals are filtered through a secondary filter to remove coarse particles and fine particles in batches, and the obtained seed crystals have a uniform particle size and the pH value is adjusted to 4.0.

[0066] (3) Adding seed crystals to titanium liquid for hydrolysis, primary washing, bleaching, secondary washing, salt treatment, calcination to prepare crude rutile titanium dioxide, roller milling, and wet milling.

[0067] (4) Coating: Prepare a 400 g / L titanium dioxide slurry from the wet-ground titanium dioxide. Heat the mixture to 60°C and add 5.0% sodium silicate at a weight percentage concentration of 20% (calculated as SiO2) for 40 minutes. Pump in 5% sulfuric acid using an axial flow pump, controlling the flow rate and adding it for 50 minutes. The pH value is controlled at 6.5. Mature for another 20 minutes. Add 10% aluminum sulfate (calculated as Al2O3) and 5% sodium hydroxide solution in parallel, with the amount of aluminum sulfate added being 3.0%. Control the pH value at 8.0. Add for 30 minutes and mature for 15 minutes. Wash, dry, and steam-powder.

[0068] Example 3 Seed crystal preparation: Titanium liquid indicators: TiO2: 200g / L, F value: 2.0, Fe / TiO2: 0.25, stability 500mL.

[0069] (1) Place 200 mL of titanyl sulfate solution in a 1000 mL glass beaker, start stirring, add 244.4 mL of deionized water to adjust the concentration of titanyl sulfate solution to 90 g / L, and heat to 50 °C. At the same time, place a 60 g / L NaOH solution in a glass beaker and preheat to 35 °C.

[0070] Use an axial flow pump to add 70g / L NaOH solution. The alkali addition time is 34 minutes and 53 seconds. The end pH value is controlled at 3.8. The temperature is raised to 60℃ and the aging time is 20 minutes. Cool to 25℃ with ice water and set aside.

[0071] Table 3 Time of adding NaOH solution in Example 3 (2) The prepared seed crystals are filtered through a secondary filter to remove coarse particles and fine particles in batches, and the obtained seed crystals have a uniform particle size and the pH value is adjusted to 4.0.

[0072] (3) Adding seed crystals to titanium liquid for hydrolysis, primary washing, bleaching, secondary washing, salt treatment, calcination to prepare crude rutile titanium dioxide, roller milling, and wet milling.

[0073] (4) Coating: Prepare a 300g / L titanium dioxide slurry from the wet-ground titanium dioxide. Heat the mixture to 50°C and add 4.5% sodium silicate at a weight percentage concentration of 20% (as SiO2) for 30 minutes. Pump in 5% sulfuric acid using an axial flow pump, controlling the flow rate and adding it for 60 minutes. Keep the pH at 6.0. Mature for another 15 minutes. Add 10% aluminum sulfate (as Al2O3) and 5% sodium hydroxide solution in parallel, with the amount of aluminum sulfate added being 2.5%. Keep the pH at 9.0. Add for 35 minutes and mature for 15 minutes. Wash, dry, and steam-powder.

[0074] Comparative Example 1 Seed crystal preparation: Titanium liquid indicators: TiO2: 200g / L, F value: 1.95, Fe / TiO2: 0.28, stability 500mL.

[0075] Conventional method for preparing seed crystals (1) Measure 50 mL of sodium hydroxide with a concentration of 100 g / L into a beaker. According to the seed crystal preparation requirement of a titanium-alkali ratio of 6.4:1, measure 162 mL of titanium liquid with a TiO2 concentration of 198 g / L. Heat the titanium liquid and the alkali to 80 °C respectively. Pour the titanium liquid into the alkali cup in about 3 minutes to prepare orthotitanic acid crystal nuclei. Take 10 mL of seed crystals and test its initial stability, which is 165 mL. Continue to heat to 95 °C for maturation. After 6 minutes, test the seed crystal stability, which is 110 mL. (2) Adding seed crystals to titanium liquid for hydrolysis, primary washing, bleaching, secondary washing, salt treatment, calcination to prepare crude rutile titanium dioxide, roller milling, and wet milling.

[0076] (3) Coating: Prepare a 400 g / L titanium dioxide slurry from the wet-ground titanium dioxide. Heat the mixture to 50°C and add 20% by weight (as SiO2) and 4.5% sodium silicate for 30 minutes. Use an axial flow pump to pump in 5% sulfuric acid, controlling the flow rate until the pH reaches 6.0. Add for 35 minutes. Mature for 15 minutes. Add 10% by weight aluminum sulfate (as Al2O3) and 5% sodium hydroxide solution in parallel. The amount of aluminum sulfate added is 2.5%. The pH value is controlled at 9.0. Add for 30 minutes and mature for 15 minutes. Wash, dry, and steam powder.

[0077] Comparative Example 2 The second step (2) of Example 1 is modified as follows: the prepared seed crystals are passed through a Buchner funnel to remove coarse particles, thereby obtaining seed crystals with coarse particles removed.

[0078] Comparative Example 3 The second step (2) of Example 1 is modified as follows: (2) the prepared seed crystals are filtered through a ceramic membrane to remove fine particle seed crystals, thereby preparing seed crystals with fine particle removal.

[0079] In Examples 1-3, the prepared hydrolyzed seed crystals were treated to remove coarse and fine particle sizes. The resulting seed crystals had a uniform particle size distribution and a moderate size. The hydrolyzed metatitanic acid had a narrow and uniform particle size distribution and a small pitch ratio. As a result, the final titanium dioxide product had a uniform particle size, strong light scattering ability, and high hiding power.

[0080] Titanium dioxide hiding power test method: After titanium dioxide is prepared into a slurry, it is prepared into a coating on a transparent polyester film. After the coating is dried, the whiteness value of the coating on a blackboard and a whiteboard is tested using a whiteness meter. The ratio of the blackboard to the whiteboard is used to characterize the hiding power of the coating.

[0081] Take 300 mL of the hydrolysis slurry and filter it with water using a Buchner funnel with a diameter of 11 cm.

[0082] Table 4 Washing time and iron content of hydrolyzed metatitanic acid prepared in Examples 1-3 and Comparative Examples When seeds with uniform particle size are added to titanium liquid for hydrolysis, the resulting hydrolysis slurry has a more moderate particle size, a more uniform particle size distribution, a low viscosity of the hydrolysis slurry, a high water washing efficiency, a short water washing time, and a low iron content.

[0083] Table 5 Hiding power of titanium dioxide obtained in Examples 1-3 and Comparative Examples and a foreign sample In the embodiment, the seed crystals are subjected to step 2 to remove coarse particles and fine particles, thereby obtaining seed crystals with uniform particle size. The uniform particle size of the seed crystals leads to uniform particle size of the hydrolyzed metatitanic acid, and the hydrolyzed metatitanic acid has good filtration performance.

[0084] The hydrolyzed seeds prepared in Comparative Example 1 were untreated, and the seed particles were uneven in size. The hydrolyzed metatitanic acid particles varied in size, with a wide distribution of material sizes. The coarse particles and fine particles were tightly bound together, resulting in a filter cake with few pores and few water flow channels. It took a long time for the water washing to remove the impurities mainly composed of iron. On the other hand, the seeds with fine particle sizes produced a hydrolyzed metatitanic acid with a fine particle size and were easily sintered after calcination, which reduced the light scattering ability and the covering power of titanium dioxide. The seeds with coarse particle size produced a hydrolyzed metatitanic acid with a coarse particle size, which reduced the light scattering ability and ultimately reduced the covering power of the titanium dioxide product.

[0085] The seeds prepared in Comparative Example 2 removed coarse particles, and the seeds with fine particle size were mostly fine, and the hydrolyzed metatitanic acid particles were mostly fine. The hydrolyzed metatitanic acid washing time was long, and long-term washing would easily oxidize the divalent iron ions in the hydrolyzed metatitanic acid to trivalent iron ions. The trivalent iron ions easily formed Fe(OH)3 precipitation, which could not be removed by washing. Instead, the iron content of the hydrolyzed metatitanic acid was high. After the hydrolyzed metatitanic acid was treated, the calcined fine particles were easily sintered, and a lot of energy was required to open the aggregated particles. On the other hand, the number of fine particles increased, and the fine particles of the titanium dioxide finished product increased. The fine particles would reduce the hiding power of the final product.

[0086] The seed crystals prepared in Comparative Example 3 removed fine particles, resulting in a coarse seed particle size. The hydrolyzed metatitanic acid particles were also coarse. The water flow rate was too fast, and the washing time for the hydrolyzed metatitanic acid was too short. The iron in the hydrolyzed metatitanic acid was not easily washed away, and the iron content in the washed metatitanic acid was increased. The coarse particle size of the hydrolyzed metatitanic acid resulted in a coarse particle size in the calcined product. Excessively coarse particles reduced the product's hiding power.

[0087] The contents described in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications to the embodiments made by those skilled in the art fall within the scope defined by the claims attached to the present invention.

Claims

1. A method for preparing high hiding power titanium dioxide, characterized in that: The following steps are involved: S1. Take a titanyl sulfate solution with a concentration of 80-100 g / L, an F value of 1.95-2.05, and an Fe / TiO2 ratio of 0.2-0.28, heat the titanyl sulfate solution to 40-55° C., preheat the alkali solution to 30-40° C., add the preheated alkali solution to the heated titanyl sulfate solution, add the preheated alkali solution for 30-40 minutes, control the endpoint pH value to 3.0-4.0, then heat to 60° C. for aging for 10-30 minutes, and then cool to below 25° C. to obtain a seed solution; S2, filtering the seed solution prepared in S1 to remove seed crystals with a particle size greater than 0.35 μm; S3, filtering the seed solution after S2 filtering to remove the seed crystals with a particle size less than 0.16 μm to obtain a filtered seed solution; S4, adding the filtered seed solution prepared in S3 to the titanium liquid, hydrolyzing, washing, bleaching, washing twice, salting, calcining, preparing rutile titanium dioxide powder, roller milling, and wet milling to obtain a wet-milled titanium dioxide slurry; S5. Coating, aging, water washing, drying and steam-powdering the titanium dioxide slurry wet-ground in S4 are performed.

2. The method for preparing high hiding power titanium dioxide according to claim 1, wherein: In S1, alkali solution is added to the titanyl sulfate solution, and the time required for the pH to reach 2.0 is 18-20 minutes.

3. The method for preparing high hiding power titanium dioxide according to claim 2, wherein: In S1, alkali solution is added to the titanyl sulfate solution, and the time for pH to reach 2.5 from 2.0 is 5-8 minutes, the time for pH to reach 3.0 from 2.5 is 3-6 minutes, the time for pH to reach 3.5 from 3.0 is 2-5 minutes, and the time for pH to reach 4.0 from 3.5 is 1-3 minutes.

4. The method for preparing high hiding power titanium dioxide according to claim 1, wherein: In S1, alkali solution is added to the titanyl sulfate solution, and the end point pH value is controlled to be 3.5-4.

0.

5. The method for preparing high hiding power titanium dioxide according to claim 1, wherein: The concentration of alkali solution in S1 is 60-80g / L.

6. The method for preparing high hiding power titanium dioxide according to any one of claims 1 to 5, characterized in that: In S2, a Buchner funnel with filter cloth was used to filter out coarse seed crystals.

7. The method for preparing high hiding power titanium dioxide according to any one of claims 1 to 5, characterized in that: In S3, ceramic membrane filtration is used to remove fine particle seeds, and filtration is performed through a water circulation pump.

8. The method for preparing high hiding power titanium dioxide according to any one of claims 1 to 5, characterized in that: The coating in S5 specifically includes the following steps: preparing a wet-ground titanium dioxide slurry of 300-500g / L, heating it to 45-60°C, adding sodium silicate with a mass concentration of 4-5% for 20-40 minutes, adding an acidifier with a mass concentration of 5-10% until the pH value of the slurry reaches 5.0-6.5 for 40-60 minutes, aging for 10-20 minutes, adding an aluminum sulfate solution with a mass concentration of 2-10%, and then adding a dilute alkali solution with a mass concentration of 5-10% to control the pH value of the slurry to 8-10, and adding it for 30-40 minutes.

9. The method for preparing high hiding power titanium dioxide according to any one of claims 1 to 5, characterized in that: The aging time after adding the dilute alkali solution in S5 is 10-15 minutes.

10. A high hiding power titanium dioxide prepared according to the preparation method according to any one of claims 1 to 9.

Images