CN111573722B - Method for realizing particle size normalization of titanium dioxide - Google Patents
Method for realizing particle size normalization of titanium dioxide Download PDFInfo
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Abstract
The invention relates to a method for realizing particle size normalization of titanium dioxide, which is characterized in that the particle size of primary metatitanic acid aggregate particles in metatitanic acid slurry is analyzed, and the temperature rise rate in the metatitanic acid calcination process is regulated and controlled according to the particle size of the primary metatitanic acid aggregate particles, so that the particle size normalization of the titanium dioxide is realized. Compared with the prior art, the method regulates and controls the heating rate of the titanium dioxide in different stages of calcination according to the size of the primary metatitanic acid aggregate, thereby changing the retention time of particles in different temperature stages and achieving the aim of regulating TiO2The crystal transformation rate and the crystal growth rate, realizes the regularization of the particle size of the titanium dioxide, and has guiding significance for the actual industrial production.
Description
Technical Field
The invention belongs to the technical field of titanium dioxide production, and particularly relates to a method for realizing particle size normalization of titanium dioxide.
Background
Titanium dioxide is commonly known as titanium dioxide. As a polycrystalline compound, the excellent optical performance of titanium dioxide comes from a specific crystal structure, and specific crystal forms include brookite form, anatase form and rutile form. The brookite crystal form belongs to an orthorhombic crystal system, is quite unstable, can be converted into a rutile crystal form at the temperature higher than 650 ℃, is usually only present in natural ores, and has low industrial value. The anatase crystal form is relatively stable at the temperature of less than 165 ℃, but when the temperature exceeds 730 ℃, the anatase crystal form begins to be rapidly converted into the rutile crystal form, and the anatase titanium dioxide has good photocatalysis effect and is widely applied to photocatalyst and air products. The rutile crystal form is the most stable crystal form of the three crystal forms, has excellent performance and is a pigment product with wide application. The anatase crystal form and the rutile crystal form belong to a tetragonal crystal system, but the respective crystal lattice arrangements are greatly different. Anatase crystals are generally approximately regular octahedra; while the rutile type is usually a twin crystal, and the crystal is slender and prismatic. The XRD spectrograms of anatase type and rutile type are different and are mainly reflected in different peak positions of main diffraction intensity. The main peak position of anatase diffraction is near the diffraction angle of 25.5 deg. and the main peak position of rutile diffraction is near the diffraction angle of 27.5 deg.. Anatase titanium dioxide and rutile titanium dioxide are formed at different temperatures during the calcination of metatitanic acid, respectively.
At present, the method for industrially producing titanium dioxide is mainly a sulfuric acid method. The production of titanium dioxide by sulfuric acid method mainly includes five steps of titanic iron ore acidolysis, titanyl sulfate solution hydrolysis, metatitanic acid rinsing, calcination and calcination post-treatment. The most important chemical reaction is shown as a formula (1-4).
The acidolysis process comprises: FeTiO3+3H2SO4→Ti(SO4)2+FeSO4+3H2O (1)
FeTiO3+2H2SO4→TiOSO4+FeSO4+2H2O (2)
And (3) hydrolysis process: TiOSO4+2H2O→H2TiO3↓+H2SO4 (3)
And (3) calcining: TiO 22·xSO3·yH2O→TiO2+xSO3↑+yH2O↑ (4)
In the sulfuric acid process, hydrolysis and calcination are two most important processes in titanium dioxide production.
The hydrolysis of the titanyl sulfate solution is to convert the titanium-containing component from a soluble state to an insoluble state, so as to realize the separation of the titanium dioxide component and soluble impurities in the titanium solution.
The hydrolysis process goes through three stages, namely a first stage, seed crystals added into the titanium liquid are dissolved in the titanium liquid to form crystal nuclei, the crystal nuclei have huge exposed surfaces, more crystal nucleus formation is induced in the titanium liquid through certain secondary nucleation theory (ECSN), and the grain diameter of the crystal nuclei is generally 4-8 nm. In the second stage, crystal nuclei can not exist independently but are connected with each other by crystal bridges in the suspension to form a firm structure which can bear the change of surface charge, namely, metatitanic acid primary agglomerate, and the particle diameter of metatitanic acid primary agglomerate is generally 60-100 nm. And in the third stage, the primary aggregates collide with each other to form micron-sized secondary aggregates through the action of chemical bonds such as sulfate radicals and the like, namely, the metatitanic acid secondary aggregates are finally obtained through hydrolysis, and the particle size of the metatitanic acid secondary aggregates is generally 1-2 mu m. The hydrolysis process is a complex process, and has a chemical reaction and a process of growing and agglomerating metatitanic acid particles. The formation of primary metatitanic acid particles and primary agglomerate particles is critical, and the primary agglomerate particles formed by primary particles with different particle sizes are different in size due to the difference of surface energy, so that the particle size and the distribution of the secondary agglomerate particles are influenced.
Since metatitanic acid has a large specific surface area, it also adsorbs a large amount of impurities along when it is precipitated from the titanyl sulfate solution. In industrial production, rinsing of metatitanic acid mainly refers to acid washing and water washing of metatitanic acid precipitate to remove impurities adsorbed by metatitanic acid precipitate, such as sulfuric acid, ferrous sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, manganese sulfate, metal oxides and the like.
The calcination process of metatitanic acid is a process for forming titanium dioxide, and the crystal form, particle size and distribution of calcined kiln waste directly influence the pigment performance of titanium dioxide finished products, and are very important titanium dioxide quality evaluation indexes. Control of calcination conditions on TiO2Growth of crystal grains, morphology of particles, granularity of particles and crystal form conversionAnd the pigment properties of the final product.
The calcination process of metatitanic acid is being studied.
Chinese patent CN110357153A discloses a method for preparing high-purity titanium dioxide by using industrial metatitanic acid hydrothermal method: filtering and drying metatitanic acid slurry subjected to hydrothermal washing, heating the metatitanic acid slurry from room temperature to 840-900 ℃ at the heating rate of 10-15 ℃/min, preserving the heat at 840-900 ℃ for 60-300 min, cooling to room temperature, crushing and grinding to obtain high-purity titanium dioxide with the particle size of 150nm-220nm and the rutile content of more than 99.8 percent, wherein the calcination process of the patent is heating to a specified temperature at a specific rate, and the calcination of the patent is described to be mainly used for removing impurities such as moisture, volatile components, ash, sulfate radicals and the like in a sample.
Chinese patent CN103183379B discloses a method for calcining metatitanic acid by flash drying: drying metatitanic acid by flash evaporation until the moisture content is 10-15%, introducing the metatitanic acid into a rotary kiln, calcining the material in three stages, wherein each stage accounts for one third of the whole length of the rotary kiln, the temperature of the first stage is controlled at 700 ℃ and the retention time is 1.5-2 hours, and the first stage mainly has the function of removing crystal water in metatitanic acid again; the temperature of the second stage is controlled at 700-; the temperature of the third stage is controlled at 850 ℃ and 950 ℃, the retention time is 2-2.5 hours, and the third stage mainly has the functions of crystal form conversion, grain size growth and outflow of the calcined qualified product from the lower end of the rotary kiln to a cooling roller. In the course of the invention of the present application, the inventors of the present application found that the following problems exist in the patent: 1. in the invention creation process of the application, the inventor of the application finds that hydrogen bond water removal and multilayer adsorption water removal of metatitanic acid are carried out simultaneously with desulfurization after removing free water. 3. The temperature of the third stage in the patent is controlled at 850-950 ℃, and the calcination temperature does not consider the difference of the correlation rules of the crystal form conversion rate of the crystal and the crystal growth rate and the temperature, so that the aims of controlling the crystal grain size and obtaining high rutile conversion rate cannot be achieved simultaneously.
Chinese patent CN108408770A discloses a sulfur removal process for metatitanic acid, which describes that the calcination process is: raising the temperature to 780 ℃ in 80min, and keeping the temperature at 780 ℃ for 1 h; raising the temperature to 910 ℃ for 15min, and preserving the heat at 910 ℃. In the course of the invention of the present application, the inventors of the present application found that the following problems exist in the patent: in the patent, the temperature rise rate in the process of rising from 780 ℃ to 910 ℃ is high and is more than 8K/min, and the calcination temperature does not consider the difference of the correlation rule between the crystal form conversion rate of the crystal and the crystal growth rate and the temperature, so that the crystal grows rapidly and TiO exists2The time for the conversion from the anatase form to the rutile form is insufficient.
Chinese patent CN110683577A discloses a method for improving whiteness of titanium dioxide by adjusting particle size, which is to dry a metatitanic acid filter cake obtained by filter pressing in front of a kiln at the temperature of 120-160 ℃ for 4-6h, then heat up to 600 ℃ according to 1h, and then calcine in a muffle furnace according to the temperature curve of heating up to 960 ℃ at 1 ℃/min, wherein the final particle size is within the range of 200-390 nm. The inventors of the present application found that the following problems exist in the patent: the temperature of the patent is too slow when the temperature is directly increased from 600 ℃ to 960 ℃, so that the retention time is prolonged, the grain growth is accelerated, and the difference of the grain size distribution is increased.
As mentioned above, the prior art has been directed towards studying one of the hydrolysis processes and the other calcination process. However, the influence of the mass difference of metatitanic acid on the calcination process is not considered in the prior art, that is, the prior art has not studied the formation mechanism of metatitanic acid, has not recognized that the primary particles of metatitanic acid and the morphology size of the primary agglomerate particles formed by the primary particles are the key for determining the quality of metatitanic acid, has not studied the relationship between the particle size of the primary agglomerate particles of metatitanic acid and the temperature control in the subsequent calcination process of metatitanic acid, and has not studied the temperature control method for metatitanic acid calcination aiming at the particle size difference of the primary agglomerate particles of metatitanic acid.
Therefore, the particle size of titanium dioxide products in different batches is greatly fluctuated. This is because the factors that have a large influence on the hydrolysis of the titanium liquid mainly include two types: one is the index of the titanium liquid, which mainly comprises the stability of the titanium liquid, the content of various impurities and TiO2Concentration, Ti3+The content, iron-titanium ratio, F value, etc.; the other is the operation condition of hydrolysis, which mainly comprises the amount of bottom water, the heating rate, the hydrolysis temperature, the stirring speed, the activity and the addition amount of hydrolysis seed crystals, and the like. Thus, the hydrolysis process has a plurality of influencing factors and extremely high process control requirements. At present, an intermittent operation mode adopted by a hydrolysis process in the production of titanium dioxide by a sulfuric acid method is difficult to meet the requirement of accurate and stable production process control, and the particle shapes, sizes and distribution of different batches of hydrolyzed metatitanic acid have large fluctuation. Meanwhile, the difference of heat and mass transfer rates caused by the difference of residence time at each temperature in the calcining process affects the crystal form and the granularity of the titanium dioxide.
Therefore, the particle size and the distribution of the titanium dioxide of different batches have larger fluctuation, and the pigment performance of the product is influenced.
Disclosure of Invention
Based on the research of the prior art, the invention provides a method for realizing the particle size normalization of titanium dioxide. The invention combines the particle size of the primary metatitanic acid aggregate particles with the temperature control in the subsequent metatitanic acid calcining process, and achieves the purpose of regulating the particle size of titanium dioxide by representing the particle size of the primary metatitanic acid aggregate and regulating and controlling the temperature rise rate in the metatitanic acid calcining process according to the particle size change.
In the control of the metatitanic acid calcination process, the residence time of particles in different temperature sections is regulated and controlled by controlling the heating rate in the calcination process; the rate of chemical reaction, phase change and crystal growth in the process is regulated by regulating the amount of heat supplied to the calcination process. Thereby achieving the purposes of regulating the particle size of the titanium dioxide product, improving the performance of the pigment and increasing the high-quality product rate.
The purpose of the invention can be realized by the following technical scheme:
the invention provides a method for realizing particle size regularization of titanium dioxide, which is mainly used for analyzing the particle size of primary metatitanic acid aggregate particles in metatitanic acid slurry, and regulating and controlling the temperature rise rate of a metatitanic acid calcination process according to the particle size of the primary metatitanic acid aggregate particles so as to realize the particle size regularization of the titanium dioxide; when the particle size of the primary metatitanic acid agglomerate particles in the metatitanic acid slurry is small, the temperature rise speed is required to be faster in the calcining process, and when the particle size of the primary metatitanic acid agglomerate particles in the metatitanic acid slurry is large, the temperature rise speed is required to be slower in the calcining process.
In one embodiment of the present invention, when the particle size of the primary metatitanic acid agglomerate particle is 40 to 80nm, the method for controlling the temperature increase rate in the calcination process of metatitanic acid comprises: in the calcining step for preparing the titanium dioxide, a heating rate control sectional calcining mode is adopted, the calcining process is divided into three temperature sections for sectional calcining, the temperature of the first section is 25-800 ℃, the adopted heating rate is 5-10K/min, and the retention time is 155min-77 min; in the second stage, the temperature is increased at 800-950 ℃ at the heating rate of 0.5-1.5K/min and the retention time is 300-100 min; the third section is 950-1000 ℃, the adopted heating rate is 5-7K/min, and the retention time is 10-7 min.
Further, when the particle size of the primary metatitanic acid aggregate particles is 40-55nm, in the calcining step for preparing titanium dioxide, the temperature rise rate adopted by the second section is 800-950 ℃, and the temperature rise rate adopted by the third section is 1.0-1.5K/min, and the temperature rise rate adopted by the third section is 6-7K/min; when the particle size of the metatitanic acid primary aggregate particles is 65-80nm, the temperature rise rate adopted by the second section is 800-950 ℃, and the temperature rise rate adopted by the third section is 0.5-0.7K/min, and the temperature rise rate adopted by the third section is 5K/min at 950-1000 ℃; when the particle size of the metatitanic acid primary agglomerate particles is between 55 and 65nm, the temperature rise rate is between the particle size and the temperature rise rate.
In one embodiment of the present invention, a method for obtaining primary metatitanic acid agglomerate particles in a metatitanic acid slurry comprises: adding barium-containing inorganic substance into hydrolyzed metatitanic acid slurry, reacting to aggregate primary metatitanic acid agglomerate into sulfate radical of secondary agglomerate with BaSO4The secondary agglomerate of metatitanic acid is precipitated, thereby achieving the purpose of depolymerizing the secondary agglomerate of metatitanic acid into primary agglomerate of metatitanic acid.
In one embodiment of the present invention, after adding the barium-containing inorganic substance to the metatitanic acid slurry after hydrolysis, the molar ratio of sulfate groups to barium ions in the metatitanic acid slurry after hydrolysis is (3.8 to 12): (0.8-1.2).
In one embodiment of the present invention, the barium-containing inorganic substance is barium calcium chloride or barium nitrate.
In one embodiment of the present invention, the method for analyzing the particle size of primary metatitanic acid agglomerate particles in a metatitanic acid slurry comprises: and adding a barium-containing inorganic substance into the hydrolyzed metatitanic acid slurry, reacting, centrifuging, taking out an upper milky clear liquid, wherein the upper milky clear liquid is the primary metatitanic acid agglomerate particles, testing the particle size, and taking the light intensity average particle size as the average particle size of the primary metatitanic acid agglomerate particles.
Preferably, the primary agglomerate particle size is measured using a NICOMP 380 nm particle size analyzer.
In one embodiment of the invention, the calcination process is carried out in a muffle furnace.
In one embodiment of the present invention, the object of calcination is metatitanic acid after rinsing and drying a metatitanic acid slurry. The dried metatitanic acid is mainly metatitanic acid secondary agglomerate particles.
After the calcination, the mixture was cooled at room temperature and then subjected to XRD and SEM detection.
The rutile conversion rate of the titanium dioxide particles obtained after calcination is more than 98 percent.
The improvement of the invention mainly comprises the following aspects:
1. the invention regulates and controls the heating rate of titanium dioxide in different stages of calcination according to the size of the primary metatitanic acid aggregate, thereby changing the residence time of particles in different temperature stages and achieving the purpose of regulating TiO2The crystal transformation rate and the crystal growth rate of the titanium dioxide powder are achieved, and the particle size of the titanium dioxide powder is normalized.
When the particle size of the primary metatitanic acid agglomerate particles in the slurry is small (40 to 55nm), it means that the primary particles forming the primary metatitanic acid agglomerate particles are large, and therefore, the calcination process requires to be carried out while increasing the particle sizeThe temperature speed is faster, so that the growth of crystals in the calcining process is properly inhibited, the particle size of the final titanium dioxide is not too large, and when the particle size of primary metatitanic acid aggregate particles in metatitanic acid slurry is larger (65-80nm), the primary particles forming the primary metatitanic acid aggregate particles are smaller, so that the temperature rise speed is slower in the calcining process, so that the growth of crystals in the calcining process is promoted, and the particle size of the final titanium dioxide is not too small. Therefore, the invention achieves the purpose of adjusting TiO by characterizing the particle size of the primary metatitanic acid aggregate and regulating and controlling the temperature rise rate of the metatitanic acid calcination process according to the particle size2The crystal transformation rate and the crystal growth rate of the titanium dioxide powder are achieved, and the particle size of the titanium dioxide powder is normalized.
2. The present invention differs from the prior art in controlling the rate of temperature rise during calcination.
According to the research of the invention, the earlier stage of calcining the metatitanic acid is only the dehydration and desulfurization of the metatitanic acid, the conversion rate from amorphous to anatase is very low, and the particle size is almost unchanged, so that the dehydration and desulfurization are found to occur together through theoretical research and experimental demonstration and occur in the earlier stage of calcining, and the calcination is carried out at a higher temperature rise rate from 25-800 ℃, so that the metatitanic acid is dehydrated and desulfurized simultaneously; the invention has found that dehydration and desulfurization take place simultaneously at 300 ℃ to 700 ℃, wherein water is removed in the form of hydrogen bond water and multi-layer adsorbed water, and sulfur is removed in the form of Sulfur Oxide (SO)2、SO3) The morphology of (2) is removed.
From 800 ℃ to 950 ℃, anatase TiO2Rutile type TiO2If the supplied heat is too large, the rapid growth of crystals can be promoted besides the transformation of crystal forms, so that the non-uniformity of grain growth is caused; 950 ℃ and 1000 ℃, which is a period of rapid crystal growth, if a slow temperature rise is adopted, the retention time is prolonged, the grain growth is accelerated, the difference of the grain size distribution is increased, and even the sintering phenomenon of particles may occur. Therefore, improper high-temperature calcination time can damage the product quality and also cause increase of production energy consumption.
The invention provides a calcination process of a metatitanic acid raw material with a specific particle size range based on the bulk phase characteristics of the calcined raw material and the associated reaction, phase change and crystal growth rules in the calcination process.
The research of the invention finds that the retention time can influence TiO at the temperature of 800-2Phase transition and crystal growth behavior of the particles. In the front temperature section of the range, under the slow temperature rise rate, the phase change process from anatase to rutile can occur in advance, the particle growth is slow, so that the conversion rate of rutile can be promoted, and TiO can promote the conversion rate of rutile2The particle size is not greatly changed; the opposite is true at fast ramp rates. In the later temperature range and at the slow heating rate, the growth rate of the crystal is accelerated, so that TiO with larger particle size is formed2And (4) crystals. Therefore, the invention divides the calcining process into three temperature sections for sectional calcining, the first section is 25-800 ℃, the adopted heating rate is 5-10K/min, and the retention time is 155-77 min; in the second stage, the temperature is increased at 800-950 ℃ at the heating rate of 0.5-1.5K/min and the retention time is 300-100 min; the third section is 950-1000 ℃, the adopted heating rate is 5-7K/min, and the retention time is 10-7 min.
The titanium dioxide with the particle size range of 245nm-260nm can be finally regulated and controlled by the method for regulating and controlling the calcining temperature. Can achieve the purpose of accurately regulating and controlling TiO2The particle size and the distribution thereof, and the purpose of stabilizing the quality of the product.
In addition, the research of the invention finds that the hydrolysis process is used as a front-stage process of the calcination process, and primary metatitanic acid agglomerate particles generated in the hydrolysis process are aligned with TiO2Grain growth, particle morphology and particle size, crystal form conversion and pigment properties of the final product have a direct impact. The invention adopts barium-containing inorganic substance treatment, depolymerizes the secondary agglomerated particles into primary agglomerated particles and establishes a preparation and test method of the primary agglomerated particles, and the final titanium dioxide particle size obtained based on the particle size of the obtained primary agglomerated particles can be further used for guiding the technological conditions of the hydrolysis process.
Compared with the prior art, the invention regulates and controls the heating rate of different stages of titanium dioxide calcination according to the size of the primary metatitanic acid aggregate, thereby changing the heating rate of the titanium dioxide calcinationThe residence time of the particles in different temperature sections is adjusted to adjust TiO2The crystal transformation rate and the crystal growth rate, realizes the regularization of the particle size of the titanium dioxide, and has guiding significance for the actual industrial production.
Drawings
FIG. 1 is an SEM photograph of metatitanic acid hydrolysis particles obtained at 2.5% seed addition; fig. 1 includes fig. 1-1 and fig. 1-2.
FIG. 2 is an SEM photograph of primary agglomerate of hydrolyzed metatitanic acid at 10% barium chloride loading; fig. 2 includes fig. 2-1 and fig. 2-2.
FIG. 3 is an XRD verification of the primary agglomerate of metatitanic acid.
Detailed Description
In the following examples, the analytical methods used were:
1. measurement of Primary agglomerate
The particle size of the primary agglomerate was measured using a NICOMP 380 nm particle size analyzer. Taking a proper amount of a primary agglomerate particle sample, dripping one to two drops of the primary agglomerate particle sample into a centrifugal tube with a seal, adding a proper amount of deionized water, covering a cover of the centrifugal tube, and shaking up. Washing the glass tube with deionized water, dropping the dispersed sample into the glass tube, rinsing the glass tube for three times, and loading into the tester. And closing the instrument shading cover. And (5) measuring the sample by the instrument.
2. Statistics of average particle diameter of titanium dioxide after calcination
The average particle size of the calcined titanium dioxide was obtained by statistically analyzing the particle sizes of about 600 particles in the SEM of the calcined titanium dioxide using smileview software.
The invention is described in detail below with reference to the figures and specific embodiments.
Example 1
Adding amount of barium-containing inorganic substance required for preparing metatitanic acid hydrolyzed primary agglomerate
Table 1 shows the average particle diameters of the primary agglomerate of seed hydrolyzed metatitanic acid neutralized by a high concentration of alkali added in amounts of 1.5%, 2.0% and 2.5% when the addition ratio of barium chloride (in terms of the ratio of sulfate radical to titanium dioxide) was 10% and 20%, respectively. It can be seen that the average particle diameters of the high concentration alkali neutralized seed hydrolyzed metatitanic acid secondary agglomerate of 1.5%, 2.0% and 2.5% added amounts were depolymerized from the original 1.722 μm, 1.688 μm and 1.837 μm to 54.5nm, 50.4nm and 49.65nm primary agglomerates, respectively, when the ratio of the added barium chloride solution was increased to 20%, no significant white precipitate was observed in the primary agglomerate solution, and the average particle diameters of the primary agglomerates were not significantly changed from those of 10%, and the distribution curves of the hydrolyzed primary agglomerates of the same seed crystal addition amount were almost completely overlapped with each other at different barium chloride addition ratios, indicating that the average particle diameter and distribution of the primary agglomerates were hardly changed. This indicates that the main force between the crystals contained in the primary agglomerate particle is derived from the crystal bond bridge, thereby enabling the formation of a highly strong agglomerate. And the secondary agglomerate is adsorbed on the surface and connected with sulfate inside, so that the acting force is weak and the secondary agglomerate can be damaged or eliminated. It is considered that when the barium chloride is added in a proportion of 10%, primary agglomerate can be prepared.
FIG. 1 is an SEM photograph of metatitanic acid hydrolyzate particles obtained with a seed addition of 2.5%. FIG. 2 is an SEM photograph showing primary agglomerates of hydrolyzed particles of metatitanic acid obtained at a seed addition of 2.5% by hydrolysis at a barium chloride addition ratio of 10%.
TABLE 1 average particle diameter of primary agglomerate at various barium chloride solution addition ratios
In order to confirm that the particles in the supernatant obtained after the barium chloride treatment were primary agglomerated particles, the supernatant obtained after the barium chloride treatment was dried and subjected to XRD analysis, as shown in fig. 3. And comparing the diffraction pattern of the metatitanic acid secondary agglomerate with that of metatitanic acid secondary agglomerate, and finding that the metatitanic acid secondary agglomerate and the metatitanic acid secondary agglomerate both have anatase characteristic peaks. It was thus confirmed that the particles in the supernatant obtained after the treatment with barium chloride were primary agglomerated particles, and the method was used for preparing and testing the primary agglomerated particles.
In this embodiment, the strong binding action of barium ions to sulfate ions is utilized to deprive sulfate radicals adsorbed in the secondary agglomerate particles to form a stable barium sulfate precipitate, so that after the metatitanic acid is treated by barium salt, the internal acting force of the secondary agglomerate particles, that is, the interaction force between the primary agglomerate particles is eliminated, thereby obtaining the primary agglomerate particles.
Example 2
The embodiment provides a method for realizing particle size normalization of titanium dioxide.
In this embodiment, the particle size of the primary metatitanic acid aggregate particles is combined with the temperature control in the subsequent metatitanic acid calcining process, and the purpose of regulating the particle size of titanium dioxide is achieved by characterizing the particle size of the primary metatitanic acid aggregate and regulating and controlling the temperature rise rate in the metatitanic acid calcining process according to the change of the particle size.
Hydrolysis slurry (metatitanic acid slurry) in the traditional sulfuric acid method titanium dioxide production process is used as a raw material, and a plurality of metatitanic acid slurries after hydrolysis are taken for analysis.
Wherein the measurement of the primary agglomerate of metatitanic acid and the statistics of the average particle diameter of the titanium dioxide after calcination are carried out according to the methods disclosed in the embodiments.
The analysis method comprises the following steps: taking out a certain amount of metatitanic acid slurry with enough analysis dosage after hydrolysis, adding barium chloride, wherein the adding proportion of barium chloride (calculated by sulfate radical and titanium dioxide) is 10%, reacting to make sulfate radical combined with metatitanic acid primary agglomerate to form secondary agglomerate with BaSO4The form of (2) is precipitated, thereby achieving the purpose of depolymerizing the metatitanic acid secondary agglomerate into metatitanic acid primary agglomerate, and then determining the particle size of the metatitanic acid primary agglomerate.
In this embodiment, the total number of the selected metatitanic acid slurries is 8, and after the metatitanic acid secondary agglomerate is depolymerized into metatitanic acid primary agglomerate due to differences in the preceding hydrolysis processes and the like, the particle size of the metatitanic acid primary agglomerate is different, the overall particle size is 40-80nm, and specifically, the particle sizes of the metatitanic acid primary agglomerate corresponding to the 8 metatitanic acid slurries are 80, 55, 65, 47, 75, 58, 64 and 40nm, respectively.
After the particle size of the primary metatitanic acid agglomerate particles is determined by analysis, the metatitanic acid slurry is rinsed and dried to obtain a metatitanic acid sample which can be directly calcined.
The method for rinsing and drying the metatitanic acid slurry comprises the following steps: respectively carrying out suction filtration on metatitanic acid slurry corresponding to the metatitanic acid hydrolyzed primary agglomerate, washing with deionized water at 60 ℃ for the first time, and filtering; according to metatitanic acid slurry TiO2Adding deionized water with the concentration of 300g/L for pulping, and stirring in a constant-temperature water bath at 70 ℃ for 30 min; then adding the following components in turn: adding 98% concentrated sulfuric acid according to the concentration of 100g/L of slurry, and washing industrial Ti with the concentration of 1.3g/L in the slurry3+The Ti content in the solution, the calcined crystal seed and the slurry is TiO24.0 percent of calcined seed crystal is calculated, and the seed crystal needs to be stirred for 30min after each feeding; then, the slurry is filtered, and is subjected to secondary washing by using deionized water at 60 ℃ and is filtered; and putting the filter cake into an oven, and drying for 6 hours at the temperature of 120 ℃ to obtain calcined experimental raw material metatitanic acid.
Then, calcining the dried metatitanic acid in stages by controlling the heating rate, dividing the calcining process into three temperature stages for stage calcining, wherein the first stage is 25-800 ℃, the adopted heating rate is 5-10K/min, and the retention time is 155-77 min; in the second stage, the temperature is increased at 800-950 ℃ at the heating rate of 0.5-1.5K/min and the retention time is 300-100 min; the third section is 950-1000 ℃, the adopted heating rate is 5-7K/min, and the retention time is 10-7 min. And (4) taking out the calcined product after the calcination is finished, cooling to room temperature, grinding by using a grinder, and then carrying out SEM and XRD detection.
However, during the calcination, the temperature increase rate of each stage is adjusted according to the particle size of the metatitanic acid primary agglomerates, and the adjustment direction is as follows: when the particle size of the metatitanic acid primary agglomerate particle is small (40-55nm), the temperature rise speed is required to be faster in the calcination process to properly inhibit the growth of crystals in the calcination process, and when the particle size of the metatitanic acid primary agglomerate particle is large (65-80nm), the temperature rise speed is required to be slower in the calcination process to promote the growth of crystals in the calcination process. The calcination experiment raw material metatitanic acid corresponding to 8 different metatitanic acid slurries is in a specific calcination processThe rate of temperature rise is referenced in table 2. After different calcination processes, the rutile conversion rate and TiO of metatitanic acid slurry corresponding to different primary aggregate particles2The average particle diameters are shown in Table 2.
TABLE 2 Effect of different temperature ramp rates on rutile conversion and average particle size
When the particle size of the metatitanic acid primary aggregate particles is small (40-55nm), the temperature rise rate adopted by the second section is 800-950 ℃, the temperature rise rate adopted by the third section is 1.0-1.5K/min, and the temperature rise rate adopted by the third section is 950-1000 ℃, is 6-7K/min. When the particle size of the metatitanic acid primary aggregate particles is larger (65-80nm), the temperature rise rate adopted by the second section is 800-950 ℃, the temperature rise rate adopted is 0.5-0.7K/min, and the temperature rise rate adopted by the third section is 950-1000 ℃, is 5K/min. When the particle size of the metatitanic acid primary agglomerate particle is between 55 and 65nm, the temperature rise rate is between the two. While the temperature rise rate corresponding to the particle size of different primary metatitanic acid aggregate particles does not have obvious difference at the first calcining stage of 25-800 ℃.
In the above embodiment, the temperature rise rates of the titanium dioxide at different stages of calcination are regulated and controlled according to the size of the primary metatitanic acid aggregate, so that the residence time of particles at different temperature stages is changed, and the purpose of regulating TiO is achieved2Although the sizes of primary metatitanic acid aggregate particles corresponding to 8 different metatitanic acid slurries are different, the particle size of the largest particle is 80nm and even is twice the particle size of the smallest particle, the particle size of the finally obtained titanium dioxide is 245-258 nm by regulating and controlling the heating rate of different stages of titanium dioxide calcination, and the rutile conversion rate is over 98.3 percent, so that the particle size of the titanium dioxide is normalized, and the method has guiding significance for practical industrial production.
The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.
Claims (9)
1. A method for realizing particle size regularization of titanium dioxide is characterized in that the particle size of primary metatitanic acid aggregate particles in metatitanic acid slurry is analyzed, and the temperature rise rate of a metatitanic acid calcination process is regulated according to the particle size of the primary metatitanic acid aggregate particles, so that the particle size regularization of the titanium dioxide is realized; when the particle size of the primary metatitanic acid aggregate particles in the metatitanic acid slurry is small, the temperature rise speed is required to be faster in the calcining process, and when the particle size of the primary metatitanic acid aggregate particles in the metatitanic acid slurry is large, the temperature rise speed is required to be slower in the calcining process;
when the particle size of the primary metatitanic acid agglomerate particles is 40-80nm, the method for regulating and controlling the temperature rise rate in the metatitanic acid calcination process comprises the following steps:
in the calcining step for preparing the titanium dioxide, a heating rate control sectional calcining mode is adopted, the calcining process is divided into three temperature sections for sectional calcining, the temperature of the first section is 25-800 ℃, the adopted heating rate is 5-10K/min, and the retention time is 155min-77 min; in the second stage, the temperature is increased at 800-950 ℃ at the heating rate of 0.5-1.5K/min and the retention time is 300-100 min; the third section is 950-1000 ℃, the adopted heating rate is 5-7K/min, and the retention time is 10-7 min.
2. The method for realizing the particle size normalization of titanium dioxide according to claim 1, wherein when the particle size of the primary aggregate particles of metatitanic acid is 40-55nm, in the calcining step for preparing titanium dioxide, the temperature rise rate adopted in the second stage is 1.0-1.5K/min at 800-950 ℃, and the temperature rise rate adopted in the third stage is 6-7K/min at 950-1000 ℃; when the particle size of the metatitanic acid primary aggregate particles is 65-80nm, the temperature rise rate adopted by the second section is 800-950 ℃, and the temperature rise rate adopted by the third section is 0.5-0.7K/min, and the temperature rise rate adopted by the third section is 5K/min at 950-1000 ℃; when the particle size of the metatitanic acid primary agglomerate particles is between 55 and 65nm, the temperature rise rate is between the particle size and the temperature rise rate.
3. The method for realizing the particle size normalization of titanium dioxide according to claim 1, wherein the method for obtaining the primary metatitanic acid agglomerate particles in the metatitanic acid slurry comprises the following steps:
adding barium-containing inorganic substance into hydrolyzed metatitanic acid slurry, reacting to aggregate primary metatitanic acid agglomerate into sulfate radical of secondary agglomerate with BaSO4The secondary agglomerate of metatitanic acid is precipitated, thereby achieving the purpose of depolymerizing the secondary agglomerate of metatitanic acid into primary agglomerate of metatitanic acid.
4. The method for realizing the particle size normalization of titanium dioxide according to claim 3, wherein after the barium-containing inorganic substance is added into the metatitanic acid slurry after hydrolysis, the molar ratio of sulfate radicals to barium ions in the metatitanic acid slurry after hydrolysis is (3.8-12): (0.8-1.2).
5. The method for realizing the particle size normalization of titanium dioxide according to claim 3, wherein the barium-containing inorganic substance is barium chloride or barium nitrate.
6. The method for realizing the particle size normalization of titanium dioxide according to claim 1, wherein the method for analyzing the particle size of the primary metatitanic acid agglomerate particles in the metatitanic acid slurry comprises the following steps:
and adding a barium-containing inorganic substance into the hydrolyzed metatitanic acid slurry, reacting, centrifuging, taking out an upper milky clear liquid, wherein the upper milky clear liquid is the primary metatitanic acid agglomerate particles, testing the particle size, and taking the light intensity average particle size as the average particle size of the primary metatitanic acid agglomerate particles.
7. The method for realizing the particle size normalization of the titanium dioxide according to claim 1, wherein the calcination process is carried out in a muffle furnace.
8. The method for realizing the particle size normalization of titanium dioxide according to claim 1, wherein the object of calcination is metatitanic acid obtained by rinsing and drying metatitanic acid slurry.
9. The method for realizing the particle size normalization of titanium dioxide according to claim 1, wherein the rutile conversion rate of the titanium dioxide particles obtained after calcination is greater than 98%.
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