Method for regulating particle size and particle size distribution of titanium dioxide by adjusting oxygen content in calcination atmosphere

Abstract

The present invention relates to a method for regulating the particle size and particle size distribution of rutile titanium dioxide by adjusting the oxygen content in the calcination atmosphere in the process of preparing rutile titanium dioxide by the sulfuric acid method. Take the metatitanic acid filter cake after salt treatment and calcine it from room temperature to 1015 - 1020 °C. During this period, adjust the flow rate of the calcination atmosphere to 300 mL / min and the oxygen concentration to 5 - 16%, and at the same time control the rutile conversion rate of the titanium dioxide at the end of calcination to be above 98.5%. Compared with the prior art, the present invention can reduce the oxygen vacancies in the anatase TiO2 lattice and inhibit its phase transformation to rutile by adjusting the oxygen concentration in the calcination atmosphere within a certain concentration range, thereby affecting the growth rate of the rutile titanium dioxide crystal and realizing the optimization of the particle size and particle size distribution of the titanium dioxide base material product (the material under the calcination kiln). The process control method involved in the present invention is simple and direct. With the synergistic regulation of the calcination atmosphere and the salt treatment agent, it optimizes the particle size distribution of TiO2 and has guiding significance for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of titanium dioxide production by sulfuric acid process, and particularly to a method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere. Background Technique

[0002] Rutile titanium dioxide is widely used in fields such as coatings, plastics, papermaking, and inks due to its characteristics of high hiding power, high tinting strength, good weather resistance, and chemical stability.

[0003] The traditional sulfuric acid process for producing titanium dioxide includes the following steps:

[0004] (1) Acidolysis: Reacting titanium concentrate with sulfuric acid to obtain titanyl sulfate;

[0005] (2) Hydrolysis: Obtaining metatitanic acid slurry through hydrolysis reaction of titanyl sulfate;

[0006] (3) First water washing: Washing the hydrolyzed metatitanic acid slurry;

[0007] (4) Bleaching and second water washing: Adding calcination seeds to the metatitanic acid after the first water washing for bleaching and second water washing to obtain a qualified metatitanic acid slurry after water washing;

[0008] (5) Salt treatment: Performing salt treatment on the qualified metatitanic acid after water washing and pressure filtering to obtain a pre-kiln filter cake;

[0009] (6) Calcination: Feeding the pre-kiln filter cake into a rotary kiln for calcination to obtain titanium dioxide;

[0010] (7) Post-treatment: Performing processes such as organic / inorganic coating on the titanium dioxide to obtain the finished titanium dioxide product.

[0011] In the traditional sulfuric acid process for producing titanium dioxide, during the calcination process in step (6), metatitanic acid undergoes four stages: dehydration, desulfurization, crystal form transformation from anatase TiO2 to rutile TiO2, and growth of rutile TiO2 particles, forming the titanium dioxide base material (under-kiln product of the calcination kiln). In production practice, it is found that when the calcination raw material (particle size of the primary particles of metatitanic acid) changes, it will affect the particle morphology and particle size distribution of the calcined titanium dioxide, and further affect the pigment performance of the finished titanium dioxide product. In order to obtain an under-kiln product with regular morphology and uniform particle size, usually, the addition amount of calcination seeds, the addition amount of salt treatment agent, calcination time, and temperature are changed, etc. for optimizing the calcination process. However, due to many influencing factors and complex operations, the regulation difficulty is increased, and the production cost of the product is increased.

[0012] In order to further effectively control the morphology and particle size distribution of titanium dioxide base materials (under - calcined kiln materials) and improve the quality of titanium dioxide products, a method for controlling the particle size and particle size distribution of titanium dioxide base materials that is simple, convenient to operate, and more efficient is required.

[0013] Chinese Patent CN108358238 A discloses a modifier for producing rutile using titanium - containing blast furnace slag, which relates to the field of metallurgical technology. It includes rutile - phase reserved substances. During the preparation of rutile, as the center of titanium enrichment, it enables titanium to be enriched into the rutile phase better and more quickly, forming rutile with a relatively concentrated particle size distribution and higher quality. First, the titanium - containing blast furnace slag is mixed with rutile - type titanium dioxide, and then oxygen - containing gas is introduced for oxidation at a temperature of 1500 - 1700 °C to convert low - valent titanium into tetravalent titanium. Then, the temperature is lowered to obtain rutile - phase coagulated slag with a concentrated particle size distribution. The coagulated slag is broken, ground, and screened to obtain artificial rutile.

[0014] The raw material of this patent CN108358238 A is high - titanium slag. Its preparation process is to melt the high - titanium slag into a liquid state at a high temperature (1500 - 1700 °C), and then oxidize melanotekite to rutile through oxygen (the oxygen content is 30 - 60%). Then, after cooling, the molten rutile solidifies into a solid phase, and the coagulated slag is re - selected after being broken and ground to obtain artificial rutile. In this preparation process, oxygen is a reactant, and its role is to oxidize low - valent titanium to high - valent titanium. Summary of the Invention

[0015] To solve the problems in the existing titanium dioxide preparation technology by the sulfuric acid method, such as the complex process for controlling the particle size and particle size distribution of titanium dioxide finished products and the relatively wide particle size distribution of products, the present invention provides a method for controlling the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere.

[0016] The present invention utilizes the change in the oxygen concentration in the calcination atmosphere to change the oxygen vacancies in the anatase TiO2 lattice, thereby controlling its phase transformation rate to rutile type, and further affecting the growth rate of rutile titanium dioxide crystals, so as to optimize the particle size and particle size distribution of titanium dioxide base materials (under - calcined kiln materials). The control method of the present invention is simple and can achieve the synergistic control effect of the calcination atmosphere and the salt treatment agent to efficiently optimize the particle size and its distribution of TiO2.

[0017] The object of the present invention can be achieved by the following technical solutions:

[0018] The present invention provides a method for controlling the particle size and particle size distribution of titanium dioxide by adjusting the calcination oxygen content. In the process of preparing rutile - type titanium dioxide by the sulfuric acid method, after taking the salt - treated metatitanic acid filter cake, it is calcined from room temperature to 1015 - 1020 °C, and the oxygen concentration in the calcination atmosphere is adjusted to be between 5% and 16%. The rutile conversion rate of the calcined titanium dioxide is above 98.5%.

[0019] In one embodiment of the present invention, preferably, in the early stage of calcination, the oxygen concentration in the calcination atmosphere is high, and in the later stage of calcination, the oxygen concentration in the calcination atmosphere is low.

[0020] In one embodiment of the present invention, the method for adjusting the oxygen concentration in the calcination atmosphere during the calcination process is: introducing nitrogen gas to adjust the content of oxygen.

[0021] In one embodiment of the present invention, during the calcination process, the heating rate is: heating it from room temperature to 900 °C, and then from 900 °C to 1015 - 1020 °C. Among them, it takes 90 min to heat from room temperature to 900 °C, and it takes another 110 min to heat from 900 °C to 1015 - 1020 °C.

[0022] Further preferably, during the calcination process, in the section from room temperature to 900 °C, the oxygen concentration in the calcination atmosphere is 10 - 16%; in the section from 900 °C to 1015 - 1020 °C, the oxygen concentration in the calcination atmosphere is 5 - 10%.

[0023] Even more preferably, during the calcination process, in the section from room temperature to 900 °C, the oxygen concentration in the calcination atmosphere is 15%; in the section from 900 °C to 1015 - 1020 °C, the oxygen concentration in the calcination atmosphere is 5%.

[0024] In one embodiment of the present invention, during the calcination process, the flow rate of the calcination atmosphere is 200 - 400 mL / min, preferably 300 mL / min.

[0025] In one embodiment of the present invention, the calcination is carried out in a tubular furnace.

[0026] In one embodiment of the present invention, the method for obtaining the metatitanic acid filter cake after salt treatment is as follows:

[0027] A. Take the filter cake qualified after bleaching and washing, make the filter cake into slurry with deionized water, and keep the TiO2 content in the slurry at 250 - 300 g / L;

[0028] B. Add a salt treatment agent to the slurry in step A, stir evenly, and perform suction filtration to obtain.

[0029] In one embodiment of the present invention, the addition amount of the salt treatment agent is such that the content of K2O in the titanium dioxide after calcination is 0.24 - 0.3%, the content of P2O5 is 0.16 - 0.22%, and the content of Al2O3 is 0.23 - 0.29%.

[0030] Preferably, the addition amount of the salt treatment agent is such that the content of K2O in the titanium dioxide after calcination is 0.27%, the content of P2O5 is 0.196%, and the content of Al2O3 is 0.260%.

[0031] In one embodiment of the present invention, the salt treatment agent is a soluble phosphate reagent with a mass fraction of 0.16 - 0.22% calculated as P2O5, a soluble potassium salt reagent with a mass fraction of 0.24 - 0.3% calculated as K2O, and a soluble aluminum salt reagent with a mass fraction of 0.23 - 0.29% calculated as Al2O3.

[0032] In addition, the present invention also relates to operations and methods for detecting the particle size and particle size distribution of titanium dioxide.

[0033] In order to more conveniently control the product quality stability and reduce the influence of metatitanic acid base material on the calcined titanium dioxide product, the present invention provides a method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen partial pressure in the calcination gas. The method of the present invention can simplify the operation steps, reduce costs and increase efficiency, and provide new ideas for titanium dioxide production.

[0034] Different from the patent solution of patent CN108358238 A in the background art, the present invention relates to a sulfuric acid process for preparing rutile titanium dioxide. During the calcination process, the calcination raw material metatitanic acid undergoes four stages: dehydration, desulfurization, crystal form transformation, and particle growth, and is transformed into rutile titanium dioxide. This is a solid-phase reaction and solid-phase crystallization process. During the preparation process, the valence of titanium does not change. By changing the way of the number of oxygen vacancies in the anatase TiO2 lattice through the change of oxygen concentration, the crystal form transformation and crystal grain growth of TiO2 are affected. In this application, oxygen is not a reactant, but an influencing factor for the crystal growth rate.

[0035] Currently, there is no report on the process of regulating the particle size and particle size distribution of titanium dioxide base material by adjusting oxygen concentration in rutile titanium dioxide production.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] 1. By adjusting the oxygen concentration in the calcination atmosphere at different temperature sections during the calcination process, the crystal form transformation and crystal growth rate of TiO2 are regulated, and the process operation is simple;

[0038] 2. The addition amount of the salt treatment agent and the addition amount of the calcination seed crystal can be appropriately reduced, saving production costs;

[0039] 3. The present invention adopts the synergistic regulation effect of the calcination atmosphere and the salt treatment agent, and has the characteristics of efficiently optimizing the particle size and its distribution of TiO2, which has guiding significance for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is the particle size distribution diagram of titanium dioxide in different calcination atmospheres in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0041] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] This example provides a method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere, including the following steps:

[0044] (1) Take the bleached and secondarily washed qualified metatitanic acid filter cake, add deionized water, pulp the filter cake, and adjust the TiO2 content to 280 g / L;

[0045] (2) Add soluble phosphates, potassium salts, and aluminum salts for salt treatment, and then filter by suction to ensure that the K2O content in the titanium dioxide after calcination is 0.270%, the P2O5 content is 0.196%, and the Al2O3 content is 0.260%;

[0046] (3) Place the filter cake in a tube furnace for calcination. The experimental calcination conditions are as follows: nitrogen gas is introduced (oxygen content is 0), and the gas flow rate is ensured to be 300 ml / min; heating rate: first raise the temperature to 900 °C in 90 min, and then raise the temperature to 1020 °C in 110 min to obtain titanium dioxide. Use XRD to detect the crystal form of the product and calculate the rutile conversion rate.

[0047] (4) Use a laser particle size analyzer to detect the particle size and particle size distribution of the titanium dioxide. The detection results are shown in Table 1, and the particle size distribution is shown in Figure 1 .

[0048] Example 2

[0049] This example provides a method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the calcination oxygen content, including the following steps:

[0050] (1) Take the bleached and secondarily washed qualified metatitanic acid filter cake, add deionized water, pulp the filter cake, and adjust the TiO2 content to 280 g / L;

[0051] (2) Add soluble phosphates, potassium salts, and aluminum salts for salt treatment, and then filter by suction to ensure that the K2O content in the titanium dioxide after calcination is 0.270%, the P2O5 content is 0.196%, and the Al2O3 content is 0.260%;

[0052] (3) Place the filter cake in a tube furnace for calcination. The experimental calcination conditions are as follows: introduce a mixed gas of oxygen and nitrogen to ensure a gas flow rate of 300 ml / min; heating rate: first raise the temperature to 900 °C in 90 min, and then raise the temperature to 1015 °C in 110 min. In the temperature range from room temperature to 900 °C, the oxygen concentration is 5%; in the temperature range from 900 °C to 1015 °C, the oxygen concentration is 5%. Obtain titanium dioxide, detect the crystal form of the product by XRD, and calculate the conversion rate of rutile.

[0053] (4) Use a laser particle size analyzer to detect the particle size and particle size distribution of titanium dioxide. The detection results are shown in Table 1, and the particle size distribution is shown in Figure 1 .

[0054] Comparative Example

[0055] This comparative example provides a method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the calcination oxygen content, including the following steps:

[0056] (1) Take the bleached and secondarily washed qualified metatitanic acid filter cake, add deionized water, slurry the filter cake, and adjust the TiO2 content to 280 g / L;

[0057] (2) Add soluble phosphates, potassium salts, and aluminum salts for salt treatment, and then perform suction filtration to ensure that the K2O content in the calcined titanium dioxide is 0.270%, the P2O5 content is 0.196%, and the Al2O3 content is 0.260%;

[0058] (3) Place the filter cake in a tube furnace for calcination. The experimental calcination conditions are as follows: introduce a mixed gas of air + water vapor, in which the oxygen concentration is about 20%, ensure a gas flow rate of 300 ml / min; heating rate: first raise the temperature to 900 °C in 90 min, and then raise the temperature to 1015 °C in 110 min. Obtain titanium dioxide, detect the crystal form of the product by XRD, and calculate the conversion rate of rutile.

[0059] (4) Use a laser particle size analyzer to detect the particle size and particle size distribution of the titanium dioxide base material. The detection results are shown in Table 1, and the particle size distribution is shown in Figure 1 .

[0060] Example 3

[0061] Example 3 provides a method for preparing titanium dioxide, including the following steps:

[0062] (1) Take the bleached and washed qualified metatitanic acid filter cake, add deionized water, slurry the filter cake, and adjust the TiO2 content to 280 g / L;

[0063] (2) Add soluble phosphate, potassium salt and aluminum salt for salt treatment, and then perform suction filtration to ensure that the content of K2O in the titanium dioxide after calcination is 0.250%, the content of P2O5 is 0.186%, and the content of Al2O3 is 0.240%.

[0064] (3) Place the filter cake in a tube furnace for calcination. The experimental calcination conditions are as follows: introduce a mixed gas of oxygen and nitrogen to ensure a gas flow rate of 300 ml / min; heating rate: first raise the temperature to 900 °C in 90 min, and then raise the temperature to 1015 °C in 110 min. In the temperature range of room temperature to 900 °C, the oxygen concentration is 15%; in the temperature range of 900 °C to 1015 °C, the oxygen concentration is 5%. Obtain titanium dioxide, detect the crystal form of the product by XRD, and calculate the conversion rate of rutile.

[0065] Use a laser particle size analyzer to detect the particle size and particle size distribution of the titanium dioxide base material. The detection results are shown in Table 1, and the particle size distribution is shown in Figure 1 .

[0066] Table 1 Detection results of titanium dioxide indicators in examples and comparative examples

[0067]

[0068] In Table 1, the black paste B value is a measure of whiteness, indicating the ability to present white, and it is related to the particle size distribution.

[0069] In Table 1, the grain size is determined by Malvern 2000.

[0070] In Table 1, the grain size distribution is measured by CSD, and the grain size distribution is characterized by (D90 - D10) / D50.

[0071] Among them, the conversion rate of rutile is calculated by the method of XRD measurement, which is a conventional technical means in the art.

[0072] The particle size of the titanium dioxide obtained by the method of the present invention is 0.318 - 0.349 μm, and the particle size distribution of the obtained titanium dioxide is more concentrated. Especially in the solution of Example 3, that is, during calcination, in the section from room temperature to 900 °C, the oxygen concentration is 15%; in the section from 900 °C to 1015 °C, the oxygen concentration is 5%. In the first stage of calcination (from room temperature to 900 °C), a relatively high oxygen concentration of 15% is adopted to reduce the oxygen vacancies in the anatase TiO2 lattice and inhibit its phase transformation to rutile type, so as to ensure the orderly progress of the crystal transformation; while in the second stage of calcination (900 - 1015 °C), the oxygen concentration is reduced to 5% to ensure the full completion of the crystal transformation of TiO2 to rutile type, and at the same time, the growth rate of rutile TiO2 crystals is also reduced, avoiding the sintering between particles caused by the rapid growth of crystals. Therefore, the grain size of the titanium dioxide as-produced in the kiln is concentrated and the particle size distribution is better. Under such calcination conditions, the rutile conversion rate of the product is 98.97%, which is the highest conversion rate in the examples.

[0073] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention as disclosed should be within the protection scope of the present invention.

Claims

1. A method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere, characterized in that, In the process of preparing rutile titanium dioxide by the sulfuric acid process, take the metatitanic acid filter cake after salt treatment and calcine it from room temperature to 1015 - 1020 °C. During the calcination process, the heating rate is as follows: heat it from room temperature to 900 °C, and then from 900 °C to 1015 - 1020 °C. Among them, it takes 90 min to heat from room temperature to 900 °C, and it takes another 110 min to heat from 900 °C to 1015 - 1020 °C. During the calcination process, in the range of room temperature to 900 °C, the oxygen concentration in the calcination atmosphere is 10 - 16%; in the range of 900 °C to 1015 - 1020 °C, the oxygen concentration in the calcination atmosphere is 5 - 10%. Calcinate according to the set temperature and time, and the rutile conversion rate of titanium dioxide at the end of calcination is above 98.5%.

2. The method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere according to claim 1, characterized in that, The method for adjusting the oxygen concentration in the calcination atmosphere during the calcination process is: introduce nitrogen to adjust the oxygen content in the calcination atmosphere.

3. The method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere according to claim 1, characterized in that, During the calcination process, in the range of room temperature to 900 °C, the oxygen concentration in the calcination atmosphere is 15%; in the range of 900 °C to 1015 - 1020 °C, the oxygen concentration in the calcination atmosphere is 5%.

4. The method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere according to claim 1, characterized in that, During the calcination process, the flow rate of the calcination atmosphere is 200 - 400 mL / min.

5. The method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere according to claim 4, characterized in that, During the calcination process, the flow rate of the calcination atmosphere is 300 mL / min.

6. The method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere according to claim 1, characterized in that, The said calcination is carried out in a tubular furnace.

7. The method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere according to claim 1, characterized in that, The method for obtaining the metatitanic acid filter cake after salt treatment is as follows: A. Take the filter cake qualified after bleaching and washing, make the filter cake into slurry with deionized water, and keep the TiO2 content in the slurry at 250 - 300 g / L; B. Add a salt treatment agent to the slurry in step A, stir evenly, and obtain it after suction filtration and drying.

8. The method for regulating the particle size and particle size distribution of titanium dioxide by adjusting the oxygen content in the calcination atmosphere according to claim 7, characterized in that, The addition amount of the said salt treatment agent is such that the K2O content in titanium dioxide after calcination is 0.24 - 0.3%, the P2O5 content is 0.16 - 0.22%, and the Al2O3 content is 0.23 - 0.29%.

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