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HomeIndustry InformationProduction of titanium dioxide by sulfuric acid method--acid hydrolysis, leaching and reduction (3)

Production of titanium dioxide by sulfuric acid method--acid hydrolysis, leaching and reduction (3)

2019-11-14

13. Calculation of the amount of concentrated Sulfuric Acid and waste sulfuric acid added
The amount of concentrated sulfuric acid and waste sulfuric acid added during acid hydrolysis can be calculated by the following formula:

Where x-concentrated sulfuric acid is added, kg;
Y—waste sulfuric acid addition, L;
F-acid to mine ratio;
C1—concentrated sulfuric acid concentration, %;
C2—waste sulfuric acid concentration, %;
P—waste sulfuric acid density, kg/L;
C3—the concentration of sulfuric acid during the reaction, %;
G—mine powder feed amount.
[Example] Trial calculation, 3100kg of ore powder, acid-mine ratio of 1.55:1, concentrated sulfuric acid concentration of 95%, waste sulfuric acid concentration of 21%, waste sulfuric acid density of 1. lkg / L, reaction sulfuric acid concentration of 87. 5%, what is the amount of concentrated sulfuric acid and waste sulfuric acid?
Solution: It should be set to add concentrated sulfuric acid to xkg, and add waste sulfuric acid to yL.

14. Factors affecting leaching
1. Porosity of solid phase material If the solid phase material is porous, it will easily penetrate into the inside of the micropores when exposed to water, and the contact surface is large and easily dissolved. If the solid phase material is hard and hard, it is difficult to leach.
2. Temperature of the solid phase The high temperature of the solid phase is favorable for leaching. However, >80 ° C, easy to make the stability of titanium liquid deteriorate, and even early hydrolysis.
3. The concentration of leaching Titanium liquid is higher, the slower the leaching, but the concentration can not be too low, too low will cause early hydrolysis, will increase the concentration of work, even the structure of the hydrolysate metatitanic acid Have an adverse effect. [next]
4. Whether early hydrolysis occurs. Solid phase materials have different degrees of early hydrolysis. When leaching, there are a lot of dead blocks, which can not be dissolved and affect the leaching speed.
5. Speed of leaching water The speed of leaching water is adapted to the dissolution rate of the solid phase. In general, the equipment should be filled with water at a faster rate, and the equipment can be added at a slower rate.
Fifteen, solid phase leaching operation
According to the relationship between acid, water and heat which affect the stability of titanium liquid, after the acid solution of ferrite and sulfuric acid, when the solid phase is leached, the solution concentration is low, the acidity is small, the temperature is high, and early hydrolysis is easy to occur. That is, it is easy to produce colloids by its heat sensitivity. Or at the beginning of adding more water, the part that has just been added to the surface of the solid phase contains less titanium, and locally reaches the dilution to cause early hydrolysis. In order to prevent such defects, a large amount of recycled waste acid and a washing residue with a certain acidity and a light titanium solution of ferrous sulfate crystals should be added to increase the acidity and add a large amount of water. And increase the gas, speed up the leaching, if the rate of immersion and water intake is too slow, the amount is too small, the temperature at the initial stage of leaching is too high, the stability of the immersed titanium liquid will decrease, and early hydrolysis is also prone to occur. Therefore, it is necessary to strictly control the temperature, acidity and concentration during leaching, and try to avoid the early hydrolysis of the titanium liquid, so as not to affect the sedimentation, purification and post-hydrolysis of the titanium liquid. Washing, which in turn causes a decrease in the yield and quality of titanium dioxide.
Sixteen, the reduction of titanium liquid
Iron exists in ilmenite in two different states, divalent and trivalent. Therefore, in the leached titanium liquid, there are both ferrous sulfate (FeS0 4 ) and high-sulfur sulfate "Fe 2 (S0 4 ) 3 ]. Under certain conditions, these two kinds of iron salts will hydrolyze to form a precipitate, and the hydrolysis reaction formula is as follows:

Both of these reactions occur only when a certain pH is reached. Ferrous sulfate is stable in an acidic solution, and hydrolysis starts only when the pH is greater than 6.5. Therefore, in the hydrolysis process of titanium liquid, since the acidity of the titanium liquid is large, it remains in a dissolved state until the titanic acid is washed. Can be removed. The high-sulfur sulfate is more harmful in the solution because it begins to hydrolyze in an acidic solution with a pH of 1.5 to form a precipitate of high-iron hydroxide. In the case of washing with metatitanic acid, when the pH value reaches 1.5, the hydrolysis of high-iron hydroxide precipitates in the metatitanic acid, and when it is burned, the red-brown ferric oxide is mixed in the titanium dioxide. Affect the whiteness of the product. In order to prevent this from happening, the presence of ferric iron is not allowed in the titanium liquid, so it is necessary to reduce the ferric iron to divalent iron.
Iron filings or iron powder is an inexpensive reducing agent. The purpose of adding iron filings or iron powder is mainly to reduce the ferric iron in the titanium liquid to divalent iron. The reaction formula of the reduction reaction is as follows: [next]

To what extent is it necessary to restore the ferric iron? In the high-valence state of titanium liquid, there are trivalent iron and tetravalent titanium. Since the reduction potential of ferric iron is greater than the reduction potential of tetravalent titanium, all the ferric iron must be reduced, and it is the turn to restore the tetravalent titanium. That is to say, when trivalent titanium appears in the titanium liquid, it means that there is no trivalent iron in the titanium liquid, and the trivalent iron has all been reduced to divalent iron. The reaction formula of the reduction of tetravalent titanium to trivalent titanium is as follows:

Another object is to increase the iron portion of the heavy metal ions are reduced to metal with removed debris.
Since the titanium liquid often encounters oxidizing conditions such as contact with air or stirring with compressed air during the production process, if trivalent titanium is not present, the ferrous iron is quickly oxidized to ferric iron. However, since the oxidation potential of trivalent titanium is greater than the oxidation potential of divalent iron, and there are oxidizing conditions, it is inevitable that all of the ferric iron is completely oxidized before the oxidation of the divalent iron is achieved. Therefore, a certain amount of trivalent titanium is maintained in the titanium liquid, which ensures that the ferrous iron is not oxidized, so that the titanium liquid is always kept free of trivalent iron. However, the presence of excessive trivalent titanium is unfavorable because, during hydrolysis, trivalent titanium does not undergo thermal hydrolysis to form metatitanic acid precipitate, and cold hydrolysis also requires hydrolysis at pH > 3, so it remains in the mother liquor. In the waste acid, if the waste acid is not recycled, it will cause loss of titanium.
17. Indicators for acid hydrolysis, leaching and reduction
1 sulfuric acid concentration > 92.5%.
2 quality requirements for ilmenite.
3MPa。 Steam pressure ≥ 0. 5MPa.
4air pressure ≥ 0. 3MPa.
5 acid ore ratio is (1.50-1.60): 1 (pressure hydrolysis method), or (1.45 ~ 1.55): 1 (normal pressure hydrolysis method).
6 The concentration of sulfuric acid during the reaction is 85%-90%.
7 preheating initiation temperature 80-120 ° C.
8 mature time 1-6h.
9 cooling time 10 - 30min o
10 leaching temperature <75 ° C.
8 reduction temperature <70 ° C.
The relative density of 10 titanium liquid is 1.5 to 1.55 (coating grade), or 1.48 to 1.52 (non-coating grade).
10 quality indicators of titanium work in this section (see table below). [next]
┌────────┬────────────┬──────┐
│Indicator name │Pigment level │Non-pigment level │
│ ├──────┬─────── │
│ │ Pressurized hydrolysis method │ Atmospheric pressure hydrolysis method │ │
├────────┼──────┼─────┼──────┤
│Total titanium content/(g/L)│120~135 │120~135 │120~130 │
│F value │1 . 8~2. 1 │1. 7~1.9│1 . 7~1.9│
│Trivalent titanium / (g / L) │ 2. 0 ~ 5 │ 1 . 5~3│ 2~3 │
│Stability │ ≥350 │ ≥300 │ ≥300 │
│ Acid solution rate /% │ ≥ 95. 5 │ ≥ 94. 5 │ ≥ 94 │
└────────┴──────┴─────┴──────┘
18. Reasons for the insoluble solid phase material during leaching and its treatment method
There are many reasons for the insoluble solid phase in leaching, and the following 10 aspects are summarized.
1 When the acid solution is blown, the compressed air is too humid, or too much condensed water in the acid solution is returned to the acid solution pot.
2 The acid concentration is too low, the amount of acid used is too small, the water is added less, and the hydration heat generated by the action of sulfuric acid is less; the heating temperature is too low, the main reaction time is long, the reaction is too gentle and incomplete, and the obtained The solid phase is not hard to be leached.
3 The concentration of sulfuric acid is too high, the acid hydrolysis adds more water, and the hydration heat is more; or the heating temperature is too high, the main reaction comes too early, the reaction temperature rises violently, not only easy to boil, but also the solid phase is hard and difficult to obtain. Dip. Pan Minggang Titanium Dioxide Factory He Mingchuan, Du Changshan, and Li Jianbin wrote that the temperature of the acid hydrolysis reaction of the plant is controlled between 80 and 90 °C, which can achieve the purpose of eliminating solid phase.
4 The cooling time is too short, and the temperature of the solid phase is too high to start leaching. As a result, a hard shell is formed, resulting in an insoluble titanium compound and a basic compound of iron.
5 improper mixing of the gas, or the pressure of the compressed air of the drummer is small, or the pressure pipe is small, especially during the curing, when the reactants will solidify, the air flow to the salary of the salary is not strong enough, resulting The solid phase is not loose and porous, even tight and solid, and the acidic water is difficult to invade, making the solid phase difficult to dissolve.
6 The time of leaching during leaching is insufficient, or the air pressure of the drummer is too small, the stirring strength is not enough; or the iron filings (or iron powder) are added too early, the trivalent titanium meets the requirements too early and has to be prematurely discharged. Both make the solid phase dissolve incompletely. The stainless steel tube should be tested first, and the iron particles (or iron powder) should be added until the solid phase material is almost dissolved.
7 A small amount of solid phase material appears in the acid solution pot without clearing the pot, which affects the stirring of the next pot, and as a result, the solid phase material accumulates more.
8 ilmenite contains silicon and aluminum sand and mud. The acid hydrolysis produces more silicic acid and aluminate colloidal substances, and the solid phase of the rubber is hard to dissolve. Or the leached titanium solution has a large concentration of FeS0 4 and Ti0 2 , a large amount of free acid, and a total ion concentration of the titanium liquid is too large, so that the solid phase is difficult to dissolve.
9Using Dadou to mine, suddenly throwing the dumplings of the dumplings into the pot, it is difficult to disperse, it is difficult to stir evenly with compressed air, so that the mine and the acid are not fully contacted, especially after adding the mine. Dilution water, mineral and acid have not been fully stirred until they are evenly mixed, and a violent reaction occurs. The solid phase obtained is solid, and sometimes there is ilmenite powder, which is difficult to leaching. Disperse the ore, or allow it to stir until it is evenly mixed before adding dilution water. [next]
The ratio of the height and diameter of the 10 acid solution pot is not reasonable enough. Generally, the ratio of height to diameter increases, the angle a of the cone bottom decreases, the impulse of compressed air increases, the dead angle is small, and the solid phase is easily dissolved. On the contrary, the ratio of the height to the diameter is reduced, the angle a of the bottom of the acid solution pan is increased, the possibility that the solid phase produces a dead angle during acid hydrolysis increases, the momentum of the compressed air is weakened, the leaching is difficult, and the solid phase is increased.
Due to conditions or improper operation, some insoluble solid phase materials often occur unexpectedly. If the solid phase is discarded, the recovery rate will be affected. To do this, it must be treated. The treatment method is as follows: 1 If the solid phase is small, it can be taken out and chopped, then added to the next pot after acid hydrolysis, allowed to heat together, and then leached together with the next pot. 2 If the solid phase is more, add an appropriate amount of waste acid and water, and heat (to prevent low concentration, low acidity, easy to heat up early) and then add compressed air to dissolve it, then re-dip these The liquid is placed in a light titanium bath for recycling.
Nineteen, acid solution to save acid
1. Selection of good ore The titanium in the ilmenite has a low grade, contains less titanium, and contains more non-titanium impurities. In the acid hydrolysis, many sulfuric acids are consumed in combination with non-titanium impurities. For example, the unselected ore content of Ti0 2 is only 46.5%, the Ti0 2 content after selection is 48.5%, and the non-titanium impurity selected is 2%. According to the acid-slurry ratio of acidolysis is 1.6:1, per ton of titanium dioxide consumption of 2. 8 tons, per ton of titanium dioxide will consume more sulfuric acid 2.8X2%X1.6=0. 09 (at) (ie 90kg > 90kg of sulfuric acid is consumed by reaction with non-titanium impurities, is wasted, and is a waste acid. Since the total effective acid is basically controlled within a certain range, the effective acid is more, and the effective acid is relatively In order to ensure that the titanium liquid contains a certain amount of effective acid, it is necessary to use more acid. If the non-titanium impurity is less, the acid can be used less, thereby saving sulfuric acid and reducing the difficulty in removing impurities in production. To this end, some manufacturers will buy back the ore for magnetic separation before pulverization.
2. Use the premise of Fe 2 0 3 containing less iron in ilmenite ore and containing substantially the same total iron, which contains more Fe 2 0 3, which consume more sulfuric acid; in the scrap iron or iron powder The more rust (including Fe 2 0 3 ), the more acid it consumes. Its reaction formula is as follows:

It can be seen from the above reaction formula that 1 mol of Fe 2 O 3 (corresponding to 2 mol of Fe) requires 3 mol of sulfuric acid, and 1 mol of FeO or 1 mol of Fe only consumes 1 mol of sulfuric acid, indicating Fe 2 in ilmenite or iron filings. The O 3 content is high and the amount of sulfuric acid consumed is high. In addition, the action of Fe 2 O 3 and sulfuric acid produces trivalent iron sulfate, which is ultimately reduced to divalent ferrous sulfate by iron filings or iron powder. The more the reduction, the more sulfuric acid and iron scrap are consumed. Therefore, in order to save sulfuric acid and iron powder, ilmenite and iron filings containing less Fe 2 O 3 should be used in production.

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