First, the purpose of hydrolysis of titanium liquid and seeding Neutralizing and hydrolyzing Ti(OH) 4 is peptized and heated and matured under mechanical stirring. The heating temperature is about 65 ° C and the temperature is kept for 20-30 min to make the colloidal particles crystallize to form Ti0 2+ with a certain charge. TiO 4+ adsorbs on the surface of metatitanic acid to make it positively charged and insoluble in dilute acid and enhance its activity. Neutralization, hydrolysis of Ti(0H) 3 during the peptization and ripening process, the acidity is not large enough, and is not enough to be dissolved. The peptization reaction formula of its orthotitanic acid is as follows: The seeded colloidal solution after heating and aging is used until it is cooled to room temperature or used. [next] The activity of this kind of seed crystal is relatively high, and it is relatively stable, but the pH value is strictly controlled during neutralization. It is very troublesome to wash the orthotitanic acid. If the sulfate is not washed, the mixed crystal seed crystal is obtained. It has rarely been adopted. The process flow of the parallel flow seed crystal preparation is shown in FIG. 1 . 7. Preparation of rutile-type hydrolyzed seed crystal (zinc oxide-type cocurrent method) The preparation of this hydrolyzed seed crystal is characterized by eliminating the water washing process in the preparation process. Since zinc oxide is used as a neutralizing agent to convert sulphate which inhibits rutile conversion in titanium liquid into zinc sulfate, and zinc salt is a promoter of rutile conversion, the water washing process can be omitted. The preparation method is as follows: the titanyl sulfate solution and the zinc oxide slurry are cocurrently neutralized to obtain orthotitanic acid, and the rutile type seed crystal is directly prepared by peptization with hydrochloric acid. Its reaction formula is as follows: [next] Modern titanium white production does not use much of this kind of seed crystal, but instead uses ordinary anatase type hydrolyzed seed crystal plus rutile type calcined seed crystal. The process flow of zinc oxide co-current seed crystal preparation is shown in FIG. 2 . Drawing Die,Monofilament Spinneret,Monofilament Yarn Spinneret,Multifilament Yarn Spinneret Changzhou Jier Precision Machinery Manufacturing Co., Ltd. , https://www.jier-spinneret.com
Because seed crystals are the key to determining the shape, size, and end product properties of the hydrolysate particles, they are the "guides" for inducing proper thermal hydrolysis. Therefore, it is necessary to add a seed crystal in the hydrolysis of the titanium liquid. Seeding has the following two effects.
1. It is ensured that the prepared particles are appropriately sized, uniform, and have a certain structure of hydrated titanium dioxide (i.e., metatitanic acid). In this way, before thermal hydrolysis, a certain number of crystal centers (seeds) with good structure should be cultured or added in the titanium solution to eliminate the influence of the randomly occurring crystal nuclei that may exist in order to induce The thermal hydrolysis reaction proceeds correctly. The hydrolyzate induced by the crystal center naturally formed by the titanium liquid itself has irregular particle and composition.
2. The hydrolysis rate is accelerated, the hydrolysis is carried out more completely, and a higher hydrolysis rate and a titanium dioxide which accelerates water washing and obtains excellent pigment properties are obtained.
2. Preparation of pigment-grade anatase hydrolyzed seeds by pressurized hydrolysis
Using a certain amount of crystallization was removed by freezing and ferrous sulfate was a plate and frame filter press had acceptable clarity addition of titanium was seeded pot open separation, Ti0 2 content is controlled to about 130g / L, and gradually added under stirring The caustic soda having a human NaOH content of about 100 g/L is neutralized, first fast and then slow until the pH is 2-3, F is 0. 25-0. 30, the effective acid content is 18-21 g/L, total titanium The content is 70-80g/L. The neutralization temperature is less than 45 °C, and the tetravalent titanium of the titanyl sulfate in the molten iron is neutralized to a certain acidity to be hydrolyzed to form a titanic acid precipitate, and the titanyl sulfate contained in the titanium liquid The trivalent titanium is 2-5 g/L, and is also hydrolyzed to form a blue titan hydroxide precipitate under such acidity, so that the entire slurry is a blue emulsion colloidal liquid. The reaction formula of neutralization and hydrolysis is as follows: 
3. Preparation of pigment-grade anatase hydrolyzed seeds by atmospheric pressure hydrolysis
The concentrated iron liquid is added to the open seed crystal pot, and the lye having a concentration of 10% is continuously added for neutralization under stirring, and the neutralization speed and the stirring speed can be fastened first and then slow to precipitate no hydroxide. Iron precipitation is prevailing (there is also the addition of lye and then the titanium solution to neutralize the lye, the first precipitated ferrous hydroxide will be dissolved by the acid in the titanium solution). The neutralization temperature is below 45 °C, and the composition is analyzed when the end point is close to the end point. If the effective acid is 14-16g/L and the Ti0 2 concentration is 50-55g/L, the temperature can be raised to 60°C in 10min and kept for 30min. Quenching to 40 ° C or less, you can stop stirring, spare.
4. Preparation of Pigmented Anatase Type Autogenous Seeds by Atmospheric Pressure Hydrolysis
First add a certain amount of water at a temperature of 90-100 ° C in an atmospheric pressure hydrolysis pot, then add Ti0 2 concentration of 240-260 g / L, F is 1.75 ~ 1.95, and preheated to 90-100 ° C with 2% Seeded titanium solution. The stirring was started, and within a period of 20 minutes, the titanium liquid was added to the hydrolysis pot according to the volume ratio of the titanium liquid to the boiling water of 100 (20-30). When titanium liquid was added to water, the initial 1 min, white turbidity due to dilution, indicating that colloidal Ti0 2 has been formed. Continue to add titanium solution, turbidity disappears. This is because, under agitation, it is uniformly dispersed in the continuously added titanium liquid, which is indistinguishable to the naked eye. At this time, the temperature can be appropriately increased to about 103 ° C, and after about 10 minutes, the turbidity reappears, indicating that a large amount of colloidal Ti 2 2 has been formed. When the colloidal suspension emits opalescence without precipitation, the colloidal TiO 2 content reaches the highest value and its activity is also the highest. However, at this time, the colloidal Ti0 2 is the most unstable, and the precipitate is easily precipitated, and the main titanium liquid to be hydrolyzed must be added immediately.
V. Conditions for preparing anatase type seed crystals
1. Neutralization speed and neutralization temperature neutralization is an exothermic reaction. Neutralization and addition of human caustic soda will cause the temperature of the material to be too high to cause thermal hydrolysis of titanyl sulfate, resulting in metatitanic acid. Instead of orthotitanic acid, this will reduce the activity of the seed crystals, and at the same time add the caustic soda too quickly, so that the local NaOH is too concentrated, the pH value is too large, and the acidity of the hydrolysis of ferrous sulfate is reached to hydrolyze to form ferrous hydroxide. Precipitation, the occurrence of this side reaction will affect the quality of the seed crystal. In order to control the neutralization temperature, the reaction temperature is maintained at 40-50 ° C, and the neutralization speed can be accelerated only when the neutralization temperature is ensured. Excessive temperature and extended neutralization time (such as more than 1h> will reduce the activity of the seed crystal. However, the low neutralization temperature will also affect the dispersion of the lye, which will easily cause excessive neutralization and the quantity and quality of the crystallization center will be affected. influences.
2. Neutralization degree Neutralization degree is the degree of neutralization of the effective acid in the titanium liquid at the neutralization end point. The degree of neutralization is an important factor determining the number of crystal centers and the stability and activity of the crystal colloidal solution. If the degree of neutralization is not sufficient, that is, if the amount of alkali added is too small, the center of crystallization is small, and the hydrolysis rate is slow, the hydrolysis rate is low, and the obtained metatitanic acid particles are too fine, resulting in difficulty in washing, or a suspension which does not precipitate. The water wash through filter is lost. If the neutralization is excessive, that is, an excessive amount of alkali is added, it is easy to cause excessive hydrolysis of the seed crystal, which greatly reduces the activity of the seed crystal, and even a large amount of precipitated ferrous hydroxide contaminates the seed crystal.
3. The ripening temperature and the ripening time are neutralized at a low temperature. The obtained orthotitanic acid dispersion is an amorphous colloidal particle which has a tendency to be dissolved by the free acid in the titanium liquid or aged during storage to change its structure. danger. After being heated and peptized, the crystal nucleus after aging is determined to be anatase-type microcrystals, so that it is insoluble in dilute acid. The seed crystal has a curing temperature of 60 ° C and is kept for half an hour. The concentration and acidity of the seed crystal are lower than that of the titanium liquid. Excessive curing temperature and excessive holding time will cause excessive hydrolysis of the seed crystal, resulting in insufficient number of crystal centers and deterioration of quality. The two should work together, that is, when the temperature is selected high, the holding time should be shorter.
4. Concentration of seed crystal The concentration of seed crystal refers to the Ti0 2 concentration of the seed solution. As far as the stability of the seed solution is concerned, as the concentration of the seed crystal increases, the stability also increases. When the concentration is lower than 40 g/L, the stability of the seed crystal is poor, and at the same time, the volume of the seed crystal is increased, which lowers the Ti0 2 concentration of the titanium liquid during hydrolysis.
5. Neutralization mode and stirring speed [next]
Anatase type crystals are mostly made by adding lye to human titanium solution. One is to ensure the anatase crystal form; the other is to reduce the iron into the microcrystals. The stirring speed should be fast and slow first.
Six preparation, rutile seed hydrolysis (chloride type parallel-flow method)
The ortho-titanic acid chlorinated type hydrolysis seed crystal, also known as cocurrent seed crystal. The preparation method comprises the steps of: cocurrently neutralizing the metered titanium oxysulfate solution and the alkali solution (Na 2 CO 3 or NaOH) to obtain an orthotitanic acid precipitate, removing the sulfate ion by washing with water, and then heating the acid solution with hydrochloric acid to make the ortho titanium The acid is converted to peptization. When the solution became transparent and turbid and opalescence occurred, the heating was stopped and quenched, and a rutile-type hydrolyzed seed crystal was obtained. Its reaction formula is as follows: