First, the cause of migraine titanate salt before calcination to be treated
The process of modifying the treatment of metatitanic acid with a small amount of chemical additives before calcination is called salt treatment, also known as pretreatment.
If the metatitanic acid is directly calcined without salt treatment, the obtained product particles tend to be very hard, the hue and other pigments are poor in performance, and the paint performance is inferior. Therefore, when producing pigment titanium dioxide, it is necessary to modify a small amount of chemicals in metatitanic acid according to the needs of different grades, and then calcined at a suitable temperature to make the product have good hue and luster. High achromatic power, hiding power, low oil absorption and proper grain size, shape and easy dispersibility in the paint medium. In some non-pigmented products, some chemicals are sometimes added to give the product a special property.
2. Additives commonly used in the salt treatment of anatase pigment titanium dioxide and their effects
When the salt production process anatase titanium dioxide pigment, the additives frequently used are phosphoric acid and potassium (or phosphate). Addition of additives, there are two main effects: â‘ make products with excellent pigment properties; â‘¡ that the anatase polymorph stabilizing effect, inhibition of rutile crystalline form, to prevent the product mixed with rutile. However, if the amount of additives is too large, the water-soluble salt content of titanium dioxide will increase significantly and the water dispersibility will decrease when water is selected. Only by strictly controlling the amount of addition, can the effect of the additive itself be exerted without affecting other properties of titanium dioxide. .
3. Reasons for adding potassium salt to the salt treatment of anatase pigment titanium dioxide and its addition amount
When the salt of the anatase pigment titanium dioxide is treated, a potassium salt such as potassium carbonate or potassium sulfate is added, and the effect is as follows: 1 can desulfurize the metatitanic acid at a lower temperature, thereby lowering the calcination temperature and making the material more Neutral at low temperatures, avoiding high temperature sintering and causing yellowing or ashing or discoloration of the product, resulting in poor paint performance and poor dispersion performance. The addition of potassium salt, even if calcined at a higher temperature, does not lose the excellent pigment properties of titanium dioxide, because the Ti0 2 particles are relatively dense when calcined at a higher temperature, which is beneficial to improve weather resistance and reduce oil absorption; It can promote the growth of anatase Ti0 2 microcrystals; 3 can improve the pigment properties, make the titanium dioxide particles soft, white and white, and improve the achromatic power. The amount of potassium salt added is generally from 0.4% to 2.0% of Ti0 2 , which corresponds to 0.25% to 1.40% of K 2 O.
4. Reasons for adding phosphoric acid when producing anatase pigment titanium dioxide
In the production of the electrode-grade titanium dioxide, the titanium dioxide has a high phosphorus content, and has a cold brittleness to the weld. Therefore, the phosphorus content of the titanium dioxide is not required to be greater than 0.05%, so that not only the phosphoric acid cannot be added in the production, but also It must be strictly controlled, especially in the mineral source, high phosphorus content is not allowed. However, in the production of anatase pigment titanium dioxide, not only does not have strict phosphorus requirements, but also phosphoric acid or its salt is added to improve the whiteness and weather resistance of titanium dioxide. However, the high phosphorus content of titanium ore is not good, because phosphorus is present in the form of phosphoric acid or dihydrogen phosphate after acid hydrolysis, and it is easy to combine with titanium to form a corresponding insoluble titanium salt. As the residue is removed, titanium recovery is caused. The rate is reduced.
Based on the production of anatase titanium dioxide, metatitanic acid after washing or bleaching, the pH value is still between 2-3, ferrous sulfate has not reached a pH of 6.5 hydrolysis, still divalent iron ion exist. Some manufacturers do not have a bleaching process. Some of the ferrous iron is oxidized by dissolved oxygen in the water to become ferric iron during washing. When the ferric iron is washed to a pH of 1.5, it is hydrolyzed to form iron hydroxide precipitate, which is intercalated with titanium. In acid. These divalent iron and ferric hydroxide impurities, if not treated, are sent directly to calcination, under the conditions of calcination, reddish brown iron oxide is formed, which greatly affects the whiteness of titanium dioxide. Therefore, it is necessary to carry out salt treatment before calcination, adding an appropriate amount of phosphoric acid or its salt in the salt treatment, reacting phosphoric acid with iron hydroxide to form a pale yellow stable iron phosphate; reacting phosphoric acid with ferrous iron to form white or A monobasic or dibasic salt of grayish white ferrous iron, which is also oxidized to a pale yellow iron phosphate under calcined conditions. Since the pale yellow iron phosphate is much lighter than the reddish brown iron oxide, the whiteness of the titanium dioxide is much less affected, so as to increase the whiteness of the titanium dioxide. The reaction formula of phosphoric acid and iron hydroxide is as follows:
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   Fifth, the disadvantage of adding too much or too little phosphoric acid
In the salt treatment, adding appropriate amount of phosphoric acid or its salt can improve the whiteness and weather resistance of titanium dioxide, and make the particles soft and easy to be pulverized, which can promote the conversion to anatase crystal form when producing anatase titanium dioxide. Prevent the formation of rutile crystal forms. However, if too much phosphoric acid is added, the acidity of the metatitanic acid in the kiln increases, and the desulfurization is difficult, so that the calcination temperature at which the maximum color reduction force is reached is shifted to a higher temperature, the calcination temperature is increased, and the material is at a higher temperature. Under calcination, sintering phenomenon sometimes occurs, which not only wastes fuel, but also makes the calcined particles hard and difficult to be pulverized, and the whiteness and the achromatic power of the titanium dioxide are lowered, and the oil absorption is increased.
If too little phosphoric acid is added, the amount of potassium carbonate is relatively increased, so that the acidity is lowered, which is favorable for desulfurization of the material at a lower temperature, softening of the calcined particles, whitening of the color, improvement of the color reduction power, and reduction of the oil absorption. Even because the amount of potassium carbonate is relatively increased, even if calcined at a higher temperature, the excellent pigment properties are not lost, because the particles of titanium dioxide are dense when calcined at a higher temperature, which is advantageous for improving the weather resistance of the product and reducing the oil absorption. However, the amount of phosphoric acid is too small to convert all the iron into yellowish iron phosphate, and the unconverted iron eventually appears as reddish brown iron oxide, which does not improve the whiteness of titanium dioxide.
6. Study on the amount of added phosphoric acid and the method of addition
According to calculations, if the iron-containing metatitanic acid contains 100*10 -6 , the phosphoric acid required for its action with iron is not much. If 0.1% of total titanium is added, the phosphoric acid required for its action with iron is only When 15.1% of the total amount of phosphoric acid was added, even if the iron content was 150*10 -6 , the phosphoric acid reacted with iron only accounted for 22.7% of the total amount of phosphoric acid added, and thus it was found that the added phosphoric acid was more than enough.
However, this is not the case. In the filtrate of the metatitanic acid after the salt treatment, there is no phosphate ion at all, indicating that the phosphoric acid has all been produced in the insoluble phosphate. Why do you add so much phosphoric acid than the calculated amount, and finally there is no phosphoric acid in the filtrate? The reason is that metatitanic acid contains a large amount of metal ions capable of forming insoluble phosphate with phosphate ions, and these metal ions need to react with phosphoric acid to form insoluble phosphate and consume phosphoric acid, so after salt treatment Phosphate ions were not detected in the filtrate.
In addition, from the filtrate after the salt treatment, it is also found to contain a lot of ferrous ions, indicating that there is soluble iron in the metatitanic acid, such iron can be burned to the rotary kiln, and eventually reddish brown Iron oxide affects the whiteness of titanium dioxide.
After all the added phosphoric acid and the iron are calculated, there should still be more phosphoric acid remaining, but in the end, not only the phosphoric acid remains in the filtrate, but even the iron does not work. The reason is as follows. 1 is because the metatitanic acid contains too much metal ions capable of forming insoluble phosphate with phosphate, and the concentration of these metal ions and the concentration of phosphate ions are much smaller than the concentration of divalent iron ions and phosphate ions. These metal ions first react with phosphate ions to form insoluble phosphates and consume all or most of the phosphoric acid, so that the whole system has no or very little phosphate and ferrous iron, so that there is still in the filtrate. More divalent iron. 2 The iron in the metatitanic acid is ferrous iron, and the ferrous iron is difficult to form a precipitate of insoluble ferrous phosphate at an acidity of pH 2-3, and it needs to be at a pH of 6 to be fully A ferrous phosphate precipitate is formed.
According to the above analysis, in order for the filtrate of metatitanic acid to have no iron ions and a slight amount of phosphate ions, the following measures must be taken.
1. Removal of heavy metal ions First, heavy metal ions which easily form insoluble phosphate with phosphate ions are removed, thereby reducing the consumption of phosphate during salt treatment. [next]
Generally, the ion concentration product of the heavy metal ion and the phosphate ion to form a phosphate is very small. Although the iron scrap has been added to reduce the ferric iron to divalent iron when leaching after acid hydrolysis, some heavy metal ions have been removed by iron reduction. However, there are still some heavy metals that have not been reduced. Among these heavy metals that have not been reduced, although some heavy metal ions and phosphate ions are insoluble phosphates, they are white, which affects the whiteness of titanium dioxide, but some are insoluble. Phosphate is colored and affects the whiteness of titanium dioxide. In addition, the concentration of ions of these heavy metal ions and hydroxide ions to form heavy metal hydroxides is also small, and when the acidity of the washing with metatitanic acid is large, it is possible to form precipitates of insoluble heavy metal hydroxides which are intercalated with metatitanic acid. In the end, heavy metal oxides are formed by satin burning, some of which are also colored, which affects the whiteness of titanium dioxide. Furthermore, the mixing of heavy metal impurities not only causes the color of the titanium dioxide to be colored due to the coloration of the heavy metal element itself, but ultimately affects the whiteness of the titanium dioxide. More importantly, the attraction of heavy metal ions makes the titanium dioxide lattice distorted or crystallized. The lattice deforms, the symmetry is lost and the color reaction occurs, so that the titanium dioxide is colored and not pure white. Therefore, heavy metals must be removed fundamentally. The method of removing heavy metals is to add a small amount of an inorganic substance to the titanium liquid obtained by acid desorption to make it react with heavy metal ions to form a heavy weight. The metal compound precipitates as the residue is removed. Since the heavy metal which easily forms insoluble phosphate with phosphate is removed at the time of leaching, the phosphoric acid or phosphate consumed in the salt treatment is reduced.
2. Increasing the amount of phosphoric acid to form insoluble phosphate. Although some metal ions are not heavy metal ions, their ion concentration products with phosphate ions are small, and it is easy to form insoluble phosphate precipitates. An example is the formation of insoluble titanium phosphate by titanium ions and phosphate ions. Although titanium phosphate is white, it does not interfere with the whiteness of titanium dioxide, but it consumes phosphate after all, and increases the amount of phosphoric acid or its salt.
Since the added phosphoric acid is insufficient, more phosphoric acid should be added to meet the requirement, that is, from the original 0.1% gradually increasing until there is no iron ion in the metatitanic acid filtrate and a little phosphate. But this is not desirable. Because the water-qualified metatitanic acid itself contains 8%-10% sulfuric acid, these sulfuric acid has been detrimental to the calcination and decomposition of metatitanic acid, and the addition of phosphoric acid to increase the acidity will increase the calcination desulfurization temperature. The whiteness and achromatic power of the product are reduced and the oil absorption is increased.
It is also possible to increase the amount of phosphoric acid and also increase the amount of potassium carbonate, and neutralize the excessive acidity with potassium carbonate. However, this method will increase the water-soluble salt of the product, and the water-soluble salt is too high. In addition to gelling and swelling the slurry, it is not conducive to the overall improvement and improvement of the quality of the titanium dioxide.
In order for phosphate and iron to form insoluble iron phosphate, thereby increasing the whiteness of titanium dioxide without affecting other quality indicators of titanium dioxide, the following three requirements must be met: 1 there is enough but not too much Phosphate ion; 2 the acidity of the whole system can not be too high, the pH should be controlled at 6; 3 water-soluble salt should meet the requirements of product quality indicators. To achieve these three requirements, the following methods should be used.
(1) After adding enough phosphoric acid, increase the potassium carbonate to neutralize its excessive acidity and lower the acidity until the ferrous iron and phosphate form insoluble ferrous phosphate. Although this method can be high in water-soluble salt, it can be added with some water in the meta-titanic acid during the salt treatment to make the slurry thinner. After the salt treatment, try to absorb the metatitanic acid to absorb more. Water soluble salt.
(2) Replace the phosphoric acid with an appropriate amount of soluble ammonium dihydrogen phosphate or potassium dihydrogen phosphate to ensure that there are enough phosphate ions or dihydrogen phosphate ions, and that the acidity and water-soluble salt of the product are not A big increase.
(3) In the metatitanic acid, the weaker the acidity (even alkaline), the more favorable the formation of the insoluble iron phosphite by the phosphate and the ferrous iron, and the more favorable the calcination and decomposition desulfurization of the metatitanic acid. Therefore, some foreign manufacturers use ammonia water to neutralize the sulfuric acid in metatitanic acid to a pH of 5-8, then wash away the sulfate, and then add phosphoric acid for salt treatment. With this method of reducing the overall acidity, promote ferrous and phosphoric acid. The combination of the roots and the easy decomposition of the metatitanic acid, thereby lowering the calcination temperature, softening the calcined material, and improving the whiteness and the achromatic power of the titanium dioxide.
Although iron can be made into yellowish iron phosphate by adding phosphoric acid or its salt, unlike the reddish-brown iron oxide, which has a large effect on the whiteness of titanium dioxide, iron phosphate is yellowish, not white. If the iron content is too high, more yellow iron phosphate is obtained. Moreover, the acidity of metatitanic acid often fails to reach a pH of 6, so that ferrous iron is difficult to form ferrous phosphate, and many ferrous iron is still present in the ionic state in metatitanic acid. These ferrous irons After the satin burning, the reddish brown iron oxide is still present. Due to the reddish brown color of the iron oxide and the light yellow color of the iron phosphate, the yellow phase of the titanium white powder appears, which has a great influence on the whiteness of the titanium dioxide. For this reason, it should be extended for some time during washing, and wash iron in some metatitanic acid as much as possible to make the iron content less than 90*10 -6 , because it is more than 90*10 -6 anatase pigment white powder white Degree is affected, but it is hoped that it is impossible to reduce the iron by water washing, because the acidity of the filter cake is getting lower and lower as the washing progresses. When the pH is ≥1.5, it is washed. The water-oxidized ferric ion is hydrolyzed to form a poorly soluble, insoluble iron hydroxide. [next]
It is because by the time water is difficult to extend the iron down very low, and therefore some manufacturers to increase the bleaching step, the addition of sulfuric acid to dissolve the ferric hydroxide, aluminum powder and then addition of trivalent iron is reduced to divalent ferrous sulfate Then, the ferrous sulfate is washed away by water washing, and finally the iron is reduced to 30*10 -6 or less (and vanadium , chromium , copper and the like can also be removed), so that the whiteness of the titanium white powder is greatly improved.
7. Operating procedures for the production of anatase titanium dioxide salt
The salt treatment for producing anatase pigment titanium dioxide is generally carried out in a cylindrical cone-shaped plastic or iron-lined soft-plastic salt treatment tank equipped with a stirrer. The rinsed qualified metatitanic acid is sent to the salt treatment tank, and the stirrer is stirred to homogenize the metatitanic acid, and the iron content is sampled and tested, and then the slurry concentration is measured twice (for the coating variety, the slurry concentration is controlled at 270-310 g/L). ). Then according to the iron content (generally controlled below 0.012%) and Ti0 2 concentration, calculate the amount of potassium carbonate and phosphoric acid required, first add human potassium carbonate, after stirring for 1h, then add phosphoric acid, continue to stir for 1h, then Open the discharge valve, put the treated slurry into the square trough, use the leaf filter to suck the blade through the vacuum suction filter, then lift the blade, continue to vacuum the residual liquid, and then put it on the trough. Shovel the titanic acid, start the squeeze pump and send it to the titanic acid storage tank for calcination.
Nowadays, the technology introduced by the big factory is to use the vacuum drum filter to drain the slurry after the salt treatment, and use the screw pump to send the material to the rotary kiln. By doing so, the water content of the metatitanic acid is greatly reduced, and the calcination energy consumption is also greatly reduced. There is also a salt treatment agent after beating and dewatering, so that the salt treatment agent has high utilization rate and the amount of addition is stable.
Eight, the reason why the concentration of metatitanic acid slurry should be controlled within a certain range
The salt treatment additive added in a certain proportion must be fully adsorbed on the surface of the metatitanic acid particles or entrained in the gap to exert the best salt treatment effect during calcination. If the concentration of the metatitanic acid slurry is too low, most of the soluble additives are carried away when the suction pad is dried, so that the amount of actual adsorption by metatitanic acid is reduced, which affects the salt treatment effect; if the titanic acid slurry If the concentration is too high, the additive cannot be uniformly dispersed in the slurry, and the salt treatment effect is also affected. For this reason, it is preferred to control the metatitanic acid slurry to have a TiO 2 content of 270-310 g/L.
IX. Method for determining the concentration of metatitanic acid slurry
After the beryric acid is evenly beaten, a certain slurry is taken out, the content of Ti0 2 per unit volume is measured, and the relative density of the slurry is measured, and then the result is obtained according to the approximate equation:
Ti0 2 content (g / L) = (d - 1) * 1190
Where d is the relative density of the slurry; 1190 is the experimental constant.
It is also plotted as a relationship between the relative density and concentration of the metatitanic acid paste, which is easy to find during production.
The relationship between the relative density and concentration of the metatitanic acid paste during production is shown in the figure below. The slurry concentration can be determined using an asphalt pycnometer or a mud pycnometer or a round thin wall plastic weighing bottle. The volume of these pycnometers is corrected in advance, and the upper cover has a small hole. After the slurry is evenly stirred, a part of the slurry is taken out into the weighing bottle, and the cover is tightly closed. The excess slurry is small. The hole overflows, and then the overflowed slurry is wiped off with a dry filter paper, and the slurry concentration can be determined from the graph, or the slurry concentration can be calculated by an equation. [next]
   X. The reason why the concentration of the salt treatment agent should be controlled within a certain range
In order to allow the salt treating agent to be sufficiently mixed with the metatitanic acid, the salt treating agent used in the production is made into a soluble salt as much as possible, and it is formulated into a solution. The concentration of the solution prepared by the salt treatment agent should not be too rich or too thin. When the concentration is too rich, the mixing is not easy to be uniform. When the temperature is too thin, the vacuum filtration loss is relatively increased. Generally, the potassium carbonate concentration can be formulated into (400 ± 5) g / L; phosphoric acid can be formulated into 100-140 g / L (based on P 2 0 5 ).
11. Reasons why potassium carbonate and phosphoric acid cannot be added at the same time.
In order for phosphoric acid to function as a concealed impurity element iron, it is necessary to ensure that the added phosphoric acid reacts sufficiently with the iron hydroxide in the metatitanic acid. Potassium carbonate is a basic substance, and phosphoric acid is an acidic substance. If phosphoric acid and potassium carbonate are added simultaneously, the two salt treating agents will mutually neutralize the acid-base reaction, greatly weakening the action of phosphoric acid and iron hydroxide. Therefore, the role of phosphoric acid to conceal the impurity element iron is not achieved. Therefore, potassium carbonate and phosphoric acid cannot be added at the same time, but potassium carbonate should be added first, and it is fully stirred to completely react with sulfuric acid in metatitanic acid, and then phosphoric acid is added. Of course, there is no side effect on the salt treatment at the same time, but the amount added must be properly adjusted to receive the desired effect.
A modern and improved method, various salt treatment additives can be pre-formulated into a mixture and then added in one portion. This can reduce the mixing equipment of the additive and shorten the mixing time of the slurry.
12. Reasons for the salt treatment of rutile titanium dioxide production by sulfuric acid method
The rutile titanium dioxide has a large absorption in the ultraviolet region, and the reflectance in the visible region is higher than that of the anatase titanium dioxide. Therefore, the photochemical stability and gloss of the rutile titanium dioxide are higher than that of the anatase titanium dioxide, which is more practical. value. The metatitanic acid obtained by hydrolysis with titanium sulfate solution is amorphous (except for rutile type seed crystals), and calcination at high temperature (below 1050 ° C) for a long time can convert all products into rutile crystal form, but crystallize The process will produce severe sintering, many lattice defects, too large and hard grains, and very poor pigment properties. In addition, high temperatures often deoxidize the crystal lattice, making the product gray. Therefore, in production, it is necessary to add some rhodamine promoters and crystal modifiers to the metatitanic acid to make Ti0 2 grow at a reasonable speed, and to produce complete conversion and size at a lower calcination temperature. Medium-sized, regular-shaped pigment particles.
Thirteen, the role of rutile accelerators and their addition
Most of the metal oxides have the functions of induction, promotion and positive catalyst in the anatase-type rutile conversion process of titanium dioxide. It is generally believed that the smaller the ionic radius of the cation, the stronger the effect of promoting the golden pebbles. However, it is of practical use to those metal compounds which produce white oxides. Commonly used accelerators include oxides and salts of elements such as zinc , magnesium , strontium , tin , antimony , and titania sol. [next]
Zinc salt is a strong and most widely used gold-red petrochemical accelerator, commonly used zinc sulfate, zinc chloride and zinc oxide. The use of zinc salts can accelerate the conversion of crystal form, increase the conversion rate, lower the temperature to reach the highest conversion rate, and improve the weather resistance and powder resistance of the product. However, if the zinc salt is added alone, the particles grow too fast, which tends to cause sintering to lower the pigment properties of the product, redden the bottom phase, harden the particles, lower the dispersibility, increase the viscosity of the resulting coating, and lower the storage stability. If a titanium dioxide gel or an aluminum salt is added at the same time, the particle shape can be improved and the sintering can be reduced. Therefore, the zinc salt is mostly used in combination with a potassium salt, a phosphoric acid, an aluminum salt, a ferric oxide sol or the like. Generally, the amount of zinc salt added is from 0.2% to 1.2% (based on Zn0) of TiO 2 .
Magnesium salt is a weak rutile type conversion agent, which has a significant effect on accelerating the pH of the calcined product to a neutral value, and is generally used in an amount of 0.2% to 0.5% of TiO 2 .
TiO 2 sol, commonly known as calcined seed crystal, emulsified seed crystal or metatitanic acid plus seed crystal, has a strong promotion effect, can improve product color reduction, reduce conversion temperature, improve the shape of calcined particles, make it more round and regular, Make the product loose and easy to smash. It is often used in combination with zinc salts and aluminum salts. The amount added is from 2% to 5% of TiO 2 . The amount of seed crystal is too high, the induction period of rutile type is shortened, the transformation speed is accelerated, and the rutile crystal grains are reduced.
Ti0 2 sol can be used as a calcined seed crystal added in metatitanic acid, and can also be used as a hydrolysis seed crystal to promote rutile conversion. Method is often used industrially double seed, i.e., two different methods, methods such as titanates and titanium tetrachloride into the legal Ti0 2 sol. One of them is used as a hydrolysis seed crystal (usually made of titanium tetrachloride), and the modern anatase type seed crystal is often used in modern times; the other is used as a calcined seed crystal (usually made by the titanate method) to obtain more pigment properties. Excellent product.
14. The role of rutile grain conditioner and its addition
In order to make the rutile titanium dioxide conversion speed not too fast during calcination, and to form smooth and regular pigment particles with excellent performance, and to meet the special requirements of various grades of titanium dioxide, it is necessary to add some adjusting agent to the metatitanic acid ( Also known as crystal stabilizers). Commonly used modifiers are potassium salts, aluminum salts, phosphorus salts, ammonium salts and barium salts. Most of these modifiers are rutile-type negative catalysts.
1. Potassium Salts Potassium carbonate, potassium sulfate and potassium hydrogen sulfate (one of the negative catalysts) are commonly used. The addition of potassium salt has great advantages in improving the pigment properties of the product, which can loosen the particles, improve the whiteness and the achromatic power, and can make the titanium dioxide calcined at a higher temperature without losing the excellent pigment property because at a higher Titanium dioxide particles are relatively dense when calcined at a temperature, which is beneficial to improve weather resistance and reduce oil absorption. The amount added is generally from 0.25% to 0.70% (in terms of K 2 0) of Ti0 2 .
2. Aluminum salt At present, the use of aluminum salt additives is increasing abroad, and aluminum sulfate is generally used and formulated into a solution of human titanic acid. The addition of aluminum salt prevents the sintering of titanium dioxide, avoids excessive growth of the particles, and the product is relatively soft. Even when calcined at 1000-1100 ° C, the whiteness of the product is still very good. Due to the addition of aluminum salt, it can be calcined at a higher temperature, and the product particles are denser, and the light resistance and weather resistance are good. However, the aluminum salt is a negative catalyst and must be used in combination with other positive catalysts (such as TiO 2 sol) to achieve higher conversion and achromatic power. When the amount added is from 0.8% to 1.0% (as Al 2 O 3 ) of TiO 2 , the product hiding power is the highest.
3. Phosphoric acid or phosphate (also a negative catalyst)
It can improve the whiteness and weather resistance of the product, and the particles are soft and easy to be crushed. The amount added is generally 0.1% of Ti0 2 (calculated as P 2 O 5 ). If the zinc salt is added at the same time, the amount of phosphoric acid can be appropriately increased, and a small amount of phosphoric acid does not hinder the rutile formation, and the negative influence can be overcome by appropriately increasing the amount of the seed crystal, but the achromatic power is slightly lowered and maximized. The calcining temperature of the achromatic force is increased. If the amount of heavy metals such as soluble titanium and rare earth in the titanic acid slurry increases, more phosphoric acid is added because a part of the phosphoric acid is first consumed in combination with heavy metal elements such as titanium and rare earth. [next]
4. Ammonia or ammonium brine washing qualified metatitanic acid contains about 8%-10% sulfuric acid, and is neutralized with ammonia to a pH of 5-8. The product is easy to grind, but it will reduce the rutile ability, such as in ammonia. After neutralization, the ammonium sulfate is washed away, and 1% of zinc oxide is added, and the color reduction of the obtained product can be relatively improved. In general, the addition of ammonia makes the product loose and soft, with improved whiteness and achromatic power, but higher oil absorption. The addition of ammonia to the rutile will reduce the ability to form rutile and will therefore be used in conjunction with the rutile type accelerator.
5. 锑 salt in the anatase titanium dioxide powder added bismuth salt, can form iron bismuth citrate with iron in the material, has the effect of shielding iron, can make the product slightly blue phase, can improve product gloss, improve weather resistance Sexuality, more importantly, can prevent the phenomenon of light-color interconversion, but the dosage can not be large, otherwise it will affect the dispersion, generally only 0.05%-0.15%.
15. Salt treatment agent for producing enamel, ceramics and capacitor titanium dioxide
When producing enamel and ceramic titanium dioxide, 0.10%-0.15% magnesium chloride and 0.05%-0.10% acetic acid drill are added. Magnesium oxide is a rutile type accelerator, which keeps the rutile crystal form in the product at a certain ratio (80%-83%), and improves the use effect. The acetic acid drill makes the enamel and ceramics have high gloss, making the product bright and bright. When the capacitor titanium dioxide is produced, the addition of 0.3%-0.4% magnesium carbonate can improve the electrical insulation and the product has a certain degree of rutile. The divalent magnesium ion can prevent the reduction of tetravalent titanium to trivalent titanium because the presence of trivalent titanium greatly reduces electrical properties.
Sixteen, the operation of salt treatment
1. Stirring should be evenly distributed into the solution of the salt [K 2 C0 3 , H 3 P0 4 , Al 2 (S0 4 ) 3 ], must be formulated into a certain concentration of the solution before use, can not be formulated into the salt of the solution The treatment agent (ZnO, MgO) is added to the water after being adjusted into a slurry. After adding people, stir at room temperature for 1 to 2 hours.
2. The concentration of metatitanic acid slurry should not be too low or too high. The concentration of Ti0 2 is low and the reaction is relatively uniform. However, some soluble salt treatment agents will affect the salt treatment effect when the filtrate is removed with the filtrate; the slurry concentration is too high. Although the filtration loss is small, the material viscosity is large, it is not easy to disperse evenly, and the salt treatment effect is also affected. Usually the slurry concentration is controlled at 270-300 g/L in terms of Ti0 2 . If the problem of stirring and dispersion of thick slurry can be solved, the slurry concentration should be higher. Some plants in foreign countries use spiral conveying and stirring, and the slurry concentration is increased to 300-400g/L, which can also reduce rotary kiln forging. Energy consumption for dehydration during burning.
3. The amount of salt treatment agent added and the order of addition should pay attention to the combination of positive and negative catalysts and the order of addition when considering the formulation. It is necessary to consider reducing the calcination temperature, promoting the transformation of crystal form, and considering that it cannot be converted too fast. In order to avoid excessive particle size or sintering, it is also necessary to consider the influence of pigment properties such as achromatic power, whiteness, weather resistance and softness. Usually, the amount of addition should be determined by experiment. Adding too much amount will not only reduce the purity of the product, but also increase the water-soluble salt and reduce the dispersibility. Generally, the amount of people added (according to Ti0 2 ) and the order of addition are as follows.
(1) anatase type 1K 2 C0 3 , 0.5% to 1.0%;
2H 3 P0 4 , 0.20% to 0.35%. [next]
(2) rutile type 1 calcined seed crystal (Ti0 2 sol), 2% - 5%;
2ZnO, 0.2%-1.5%;
3MgO, 0.2%-0.5%;
4K 2 C0 3 , 0. 5%-1.0%;
5H 3 PO 4 , 0.01%-0.02%.
Seventeen, the use of various salt treatment agents
In the production of pigment titanium dioxide, the following three functions must be mastered in order to achieve complete pigment properties.
1. Damage The added salt treatment agent, although it can improve a certain performance of the product, often damages the performance of the other pigment. If adding phosphoric acid or its salt, although it can improve the whiteness of titanium dioxide, it will increase the oil absorption. Increasing the potassium salt and phosphoric acid will make the particles soft and easy to be crushed, but the water-soluble salt content will increase, which will affect the subsequent water selection. Dispersibility.
2. Addition and cooperation When adding the Golden Red Petrochemical Accelerator, adding two or more accelerators at the same time will increase the cooperation. That is, the conversion rate of the golden pebbles is increased at the same calcination temperature, or the conversion temperature can be lowered. For example, adding 6.0% TiCl 4 sol, adding 1.85% zinc sulfate, the conversion temperature is reduced by about 100 ° C.
3. Complementary effect If zinc salt is added alone, the product's color reduction is not high. If potassium salt is added at the same time, the achromatic power is significantly improved. At the same time, the aluminum salt is added separately, and the color reduction is not high. The color force is compensated and significantly improved. In the production process of rutile titanium dioxide, 0.2% zinc oxide of Ti0 2 , 0.2% magnesium oxide, 0.5% potassium carbonate and 2% Ti0 2 sol are added to the ferric acid, calcined at 800 ° C, rutile type The conversion rate is 98%, and the color reduction power can reach more than 90% of Japan R-930 titanium dioxide.
However, the amount of the salt treating agent to be added should be as small as possible in the case of ensuring the quality of the pigment, since most of the additives are water-soluble, and an excessive amount causes an increase in water-soluble salt and a decrease in water dispersibility in water selection. It is also said that the salt treatment agent is increased, and the oil absorption and water absorption are also increased.
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