Preparation of eight, rutile seed (titanium tetrachloride method)
The titanium tetrachloride seed crystal is prepared by dissolving a concentrated solution of titanium tetrachloride having a TiCl 4 concentration of 823 g/L and an effective acid concentration of 569 g/L in water to prepare a 475 g/L titanium tetrachloride solution. Further, sodium hydroxide was mixed into a 67 g/L lye. First, the calculated lye is placed in an enamel seed pot, and the newly prepared titanium tetrachloride solution is added under stirring to perform partial neutralization, and a part of excess hydrochloric acid is reserved for acid dissolution. The neutralization process keeps the temperature below 20 °C, the neutralization endpoint controls the acidity coefficient of HCl/Ti0 2 between 0.7-0.8, the Ti0 2 concentration is between 40-45 g/L, and then the temperature rises to 50 °C in the first 15 min. The temperature is controlled between 0. 25-0.45. Then, it was quenched to room temperature for use (the sol was further agglomerated with an alkali solution, and after washing off the chloride ions with ion-exchanged water, it was dispersed in ion-exchanged water to be used as a dispersion). Its relevant reaction formula is as follows:
When titanium tetrachloride is dissolved in water, a large amount of heat is released, and titanium tetrachloride must be slowly dissolved in water. The process of preparation releases a large amount of hydrogen chloride gas, which can be absorbed by water and discharged. When neutralizing, the titanium tetrachloride solution must be added to the lye. Only in this way can 100% rutile seed crystals be obtained. If the lye is added to the titanium tetrachloride solution, the mixture is prepared. Crystalline seed crystals, if cocurrently neutralized, produce amorphous seed crystals. Because of the high activity of titanium tetrachloride seed crystals, it is the most important and widely used one of rutile-type hydrolyzed seeds. In the past, there were many manufacturers in foreign countries, but the storage, transportation and dilution of titanium tetrachloride were very troublesome. Once leaked, a large amount of hydrogen chloride gas would overflow and pollute the environment, so it was rarely used in China.
9. Preparation of rutile calcined seeds
In the production of modern rutile titanium dioxide, it is not necessary to add rutile type seed crystals during hydrolysis, but instead use ordinary anatase type seed crystals to add calcined seeds to bleach or salt treatment. The method for preparing the calcined seed crystal is to wash the qualified metatitanic acid (the concentration of the slurry is about 250 g/L in terms of Ti0 2 ) and the sodium hydroxide solution having the concentration ≥ 42% according to NaOH: H 2 Ti0 3 = 2. The ratio of 3:1 was measured in a reaction vessel made of stainless steel under stirring, and the jacket was heated to boiling, and boiled under boiling for 4 hours to dissolve the metatitanic acid into sodium orthotitanate. During the boiling process, the slurry became very viscous at one time, so the strength of the stirring shaft and the power of the motor should be appropriately increased. After the alkali solution is finished, the mixture is cooled to 60 ° C with jacket cooling water, and the water is washed in a tank to wash off the free base and sodium sulfate to increase the seed crystal activity. During the water washing process, some sodium orthotitanate is hydrolyzed to form orthotitanic acid. After a single water wash, it was neutralized with a 1:2 hydrochloric acid to a pH of 3.5, and all of the sodium orthotitanate was precipitated with orthotitanic acid. It is then filtered and subjected to a second water wash to wash away chloride and sodium ions. Finally, acid-dissolve with hydrochloric acid, boil and keep boiling for 2 h, then quench to 40 ° C for use. Control F is between 0.45 and 0.55. The obtained calcined seed crystals have a TiO 2 concentration of 95-105 g/Lo rutile type conversion rate of 98%-100%, and the electron micrograph crystal seeds are in a well-dispersed willow-shaped particle. In the industry, calcined seeds are often added before bleaching, and bleaching and rinsing are used to remove soluble impurities such as iron , so that the whiteness of the product is not affected. The amount of the added calcined seed crystal is generally 2% to 5%. The reaction formula prepared is as follows: [next]
The preparation process of rutile type calcined seed crystal is shown in FIG. 3 .
Lifeng of Zhuzhou Chemical Group Co., Ltd. uses alkaline titanium ratio NaOH/Ti0 2 = 2. 1, neutralization end point pH 3.5-4, HC1/TiO 2 =0.35-0.50, rapid cooling, and produces a higher activity calcined seed crystal . The use of such a highly active calcined seed crystal enables conversion to rutile at a lower temperature (about 100 ° C lower), which improves the coloring power of the product.
X. Preparation of high-activity seed crystals and treatment of abnormal conditions in seed crystals
The high-activity seed crystal is prepared by preheating the alkali liquid and the titanium liquid to a certain temperature, respectively, and thoroughly mixing the titanium liquid and the alkali liquid. After the violent reaction between the two, the aging reaction is performed, and the seed crystal performance index is quickly determined, and then the seed crystal performance index is quickly determined. Immediately, the qualified seed crystals are added to the hydrolyzed titanium liquid which has been preheated to a certain temperature. The key to this method is that the concentration of the lye used and the ratio between the lye and the titanium solution should be accurate. Highly active seed crystals should be formulated quickly and the entire operation should be completed within 30 minutes. After the seed crystals are prepared, the storage time must not exceed l0min.
A common anomaly in seed crystals is the excessive hydrolysis of the seed crystal, which produces a large amount of white precipitate, becomes cloudy, and becomes a bad species. 'The cause is because the preparation conditions are not well mastered or improperly stored. The treatment method can reduce the grade use, or 1 h after the hydrolysis of the titanium liquid, and the metamorphic crystal seeds are added to the hydrolysis pot for recovery. However, this metamorphic seed crystal can only be used in the production of low-grade titanium dioxide, and cannot be used to produce pigment-grade titanium dioxide.
XI. Calculation of the amount of hydrolyzed seeds added
The amount of seed added, the degree of hydrolysis, the degree of complete hydrolysis, the state of the hydrolysate metatitanic acid and the performance of the finished product have a greater impact, so it is necessary to control the amount of seed added. Through practice and exploration, the amount of seed crystals of various varieties is determined, calculated by the percentage of total Ti0 2 , and its calculation formula is as follows: [next]
   Twelve, the benefits of using tetravalent titanium to hydrolyze seeds
The tetravalent titanium seed crystal is obtained by first oxidizing the trivalent titanium in the titanium liquid with 30% hydrogen peroxide, and then neutralizing with a human alkali solution to form a tetravalent titanium hydroxide precipitate as a seed crystal. Crystal nucleus. This kind of seed crystal has good stability, and the titanium powder used for the preparation has better white powder and achromatic power. If you do not use hydrogen peroxide oxidation, but use liquid alkali, because the liquid alkali contains free oxidizing substances such as free chlorine and sodium hypochlorite, these strong oxidizing substances play the role of hydrogen peroxide, and soon the blue liquid in the titanium liquid The trivalent titanium is oxidized to a colorless tetravalent titanium. The seed crystals thus produced do not appear as yellow-green as the blue seed crystals normally produced with solid alkali. Tested with ammonium thiocyanate test solution, dark red has appeared, indicating that the liquid alkali contains more free chlorine and sodium hypochlorite, and has been oxidized excessively, so that a lot of ferrous sulfate is oxidized to trivalent iron sulfate. Then, when the seed crystal is seeded, the effective acid is controlled to be high, and the ferric iron is still a solution, and has not been hydrolyzed into iron hydroxide precipitate. When the seed crystal is added to the hydrolyzed titanium liquid, the ferric iron is trivalent titanium in the titanium liquid. It is reduced to ferrous iron, so it will not affect the product whiteness. At the same time, it also plays the role of tetravalent titanium seeds, which makes the whiteness and achromatic power of the products very good.
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