Nine, the stability of titanium liquid and its impact on production
Stability, also known as stability, is the tendency of iron to precipitate white colloidal particles in the case of changing titanium dioxide in the case of changing conditions. The degree of strength of this tendency is called the stability of titanium liquid. The characteristic indicating the strength of this tendency is called the stability of the titanium liquid. The stability of the titanium liquid is expressed in milliliters of distilled water per milliliter of titanium solution diluted with distilled water at 25 ° C until the white turbidity appears.
Stability is an important indicator to measure the quality of titanium. Generally, the stability of the pigment-grade pressurized hydrolyzed titanium solution is controlled at K ≥ 350; the atmospheric pressure hydrolyzed titanium solution can be relaxed to K ≥ 300. If there is a poor stability of titanium liquid, it will have the following adverse effects on titanium dioxide production:
1 Titanium liquid is prone to early hydrolysis to form colloidal particles suspended in titanium liquid, causing difficulties in sedimentation and pressure filtration, so as to affect the increase in yield;
2 Titanium-containing colloidal particles produced by titanium solution are finally settled together with the residue and removed, so that the recovery rate of titanium is lowered;
3 Titanium liquid is a non-pigment grade titanium liquid, which can only produce low-grade enamel titanium dioxide, which has a lower price;
4 The meta-titanic acid produced by the late hydrolysis of titanium liquid has a small amount of particles, which is easy to cause the loss of water washing and filtering, and it is scattered from the chimney during calcination, so that the recovery rate is lowered;
5 This titanium liquid itself has been hydrolyzed early to form colloidal particles, which are easy to pass through the filter layer and exist in the titanium liquid. When it is hydrolyzed later, it becomes a bad crystal center, and the titanium obtained by hydrolysis is made. The size of the acid particles is not uniform, and it is easy to adsorb more impurities, which not only makes the washing time prolonged, but also affects the yield, and also causes the color of the product to affect the whiteness. At the same time, irregular small particles are more likely to cause sintering during calcination, which reduces the whiteness, color reduction and dispersion properties of the product, and affects the quality of the product.
X. Early hydrolysis of titanium liquid and factors affecting the stability of titanium liquid
In general, the titanium liquid should not contain two kinds of colloidal particles of metatitanic acid and orthotitanic acid from the time of acid hydrolysis to the stage of late formal hydrolysis, but sometimes during the leaching, reduction, transportation and storage of titanium liquid. The occurrence of the above two white colloidal substances in titanium liquid due to improper operation or changing conditions is called early hydrolysis of titanium liquid.
In order to understand the factors affecting the stability of titanium liquid, it is necessary to find the reason from the acid hydrolysis of ilmenite and the hydrolysis of titanium liquid.
1. From the reaction formula (1) and the reaction formula (2) of acid hydrolysis, it can be seen that under the same ilmenite, the reaction formula (1) is rich in acid, and the stable titanium sulfate is obtained, and the reaction formula (2) The use of less acid, the result is unstable titanium oxysulfate, indicating that the use of acid in the acid hydrolysis is beneficial to improve the stability of the molten iron. [next]
The main reaction formula of titanium liquid hydrolysis is as follows:
From the reaction formula (7), the reaction formula (8), and the reaction formula (9), it is known that all of the three hydrolysis reactions generate new sulfuric acid, indicating that the acid in the titanium solution is more reversible, and the occurrence of early hydrolysis can be suppressed. Therefore, when acid is used, more acid is used or more waste acid is added during leaching, so that the acid concentration in the titanium liquid is increased, which is beneficial to improving the stability of the titanium liquid.
It can be seen from the experiment that 1mL of concentrated titanium solution is used, and its stability is 400; if 1mL of the same concentrated titanium solution is taken, and 1 drop of concentrated sulfuric acid is added, the stability is determined to be 450, indicating the stability of the acid. Will improve.
2. From the hydrolysis reaction formula (7), reaction formula (8), and reaction formula (9), water is the reactant. According to the chemical reaction law, increasing the reactants will cause the reaction to proceed to the right, increasing the water, increasing The reactants are beneficial to the progress of the hydrolysis, and the titanium liquid is unstable, indicating that there is no benefit to the water.
From the comparison of the reaction formula (8) and the reaction formula (9), it is understood that in the case of the equivalent titanyl sulfate, the reaction formula (9) is added with a large amount of water, and the reaction formula (9) can be hydrolyzed under cold conditions. It can be seen that under the same conditions, the thinner the titanium liquid (the more water), the worse the stability.
3. From the three hydrolysis reaction formulas of the reaction formula (7), the reaction formula (8), and the reaction formula (9), it is known that the hydrolysis of the titanium liquid is an endothermic reaction, so heating causes the reaction to proceed to the right, which promotes the occurrence of the titanium liquid. Early hydrolysis causes the titanium liquid to be unstable. It can be seen from the experiment that the same is 1 mL of titanium liquid, K=500 at 12 ° C; K=400 at 25 ° C; K=200 at 65 ° C; K=0 at 100 ° C. It can be seen that the temperature rises, the stability of the titanium liquid decreases, and the heating is unfavorable to the stability of the titanium liquid.
In summary, the main reason for the poor stability of titanium fluid is less acid, more water, and heating. Therefore, in order to improve the stability of the titanium liquid, it is necessary to analyze and control the three main factors of the acidity, concentration and temperature of the titanium liquid.
1. Acidity acidification acid can not only improve the stability of the titanium liquid, but also make the acid hydrolysis reaction more complete and improve the acid hydrolysis rate. However, if the acid is too much, it will increase the consumption of sulfuric acid and increase the production cost of titanium dioxide. Further, it will increase the difficulty of post-hydrolysis of the titanium liquid in the post-process, because it is known from the hydrolysis reaction formula that the acid is more reversible, the meta-titanic acid particles are difficult to grow, the hydrolysis rate is lowered, and the water-washing occurs due to the fine titanate particles. Loss through the filter through the loss. Therefore, we must weigh the pros and cons and optimize the optimal amount of acid that will stabilize the titanium solution without causing early hydrolysis and favoring later hydrolysis.
According to the calculation of the acid hydrolysis reaction formula, in order to obtain high stability titanium sulfate, it is required to react according to the reaction formula (1), so that the acid-mine ratio is 1.932:1, that is, 1 ton of ilmenite is used. The sulphuric acid sulphate sulphate; the sulphate ratio is 1.29:1, that is, the ton of ilmenite is 1.29 tons. Sulfuric acid. In addition to this, other compounds, especially iron oxides, also consume a certain amount of acid. In general, the larger the ratio of acid to mineral, the more acid is used, the more stable the titanium solution; the smaller the ratio of acid to mineral, the less acid is used, the more unstable the titanium solution. From the theoretical analysis and practical application, it is confirmed that the pressure hydrolysis process adopts the ratio of acid to mineral ratio (1.50-1.60):1 is the best ratio; the ratio of acid to mineral used in the atmospheric pressure hydrolysis process is (1.45-1.55):1 is the optimal ratio. . It depends on how much is used, depending on the quality of the ilmenite, the acidity required by the process, and whether or not the waste acid is added during the leaching and the amount of waste acid added. [next]
2. Concentration 1 Acid concentration The concentration of sulfuric acid and the concentration of sulfuric acid during the control reaction have a great influence on the stability of the molten iron. When the concentration of sulfuric acid is greater than 96%, the solid phase obtained by the acid hydrolysis reaction is hard, poor in porosity, and difficult to dissolve upon leaching, and the stability of the obtained titanium liquid is lowered, of course, the acid hydrolysis rate is also low; When the concentration is less than 92%, the solid phase after acid hydrolysis is not easy to be solidified, or even paste-like, the reaction is incomplete, the stability of the molten iron obtained by leaching is also poor, and the purification of sedimentation and the like is difficult, and the acid hydrolysis rate is not high. . The concentration of sulfuric acid generally used is preferably between 92% and 96%. Now many manufacturers have explored and mastered the law of concentrated acid reaction and directly used 98% sulfuric acid for acid hydrolysis.
When the concentration of sulfuric acid in the reaction is more than 90%, the reaction temperature is high, so that the early stage of the reaction has undergone early hydrolysis at the end of the reaction to make the titanium liquid unstable; the concentration of sulfuric acid in the reaction is less than 85%, and the obtained molten iron is leached. The stability is also poor, and the concentration of sulfuric acid in the general control reaction is between 85% and 90%. Practice has proved that the more concentrated sulfuric acid is used, the concentration of the dilution during the reaction should be lower; the use of the dilute sulfuric acid, the concentration of the dilution during the reaction should be too high. However, when dilute acid is used, since the acid hydrolysis adds less water, the heat generated by water and sulfuric acid is less, and it is often necessary to use steam to increase the heat of initiation to obtain a better acid hydrolysis effect.
2 The concentration of titanium liquid is less, the concentration of Ti0 2 in titanium liquid is higher, the solution is not easy to precipitate colloidal particles, and the stability is better; too much water, the concentration of leaching is too low, the titanium liquid is unstable, and early hydrolysis is easy to occur. At the same time, it will also have an adverse effect on the particle size and structure of the late hydrolysis product metatitanic acid, and will also increase the concentration work. For the purpose of water leaching, it must be strictly controlled. The relative density is generally controlled between 1. 5-1. 55, that is, the total Ti0 2 content should be ≥ 120g / Lo. In order to reduce the moisture, when the titanium liquid is crystallized, the removal is large. At the same time, part of the ferrous sulfate also takes away a large amount of crystallization water, so that the total Ti0 2 concentration of the titanium liquid is improved, which is beneficial to the stability of the titanium liquid. In order to reduce the moisture, the titanium liquid must also be concentrated to continue to remove a part of the water, so that the total TiO2 content reaches (200 ± 5) g / L (pressure hydrolysis) or 215-230 g / L (normal pressure hydrolysis), Titanium dioxide with superior pigment properties is produced when the concentration of Titanium solution is increased, stability is improved, and hydrolysis is obtained in the later stage.
Low acidity and low concentration (water) can cause poor stability of titanium liquid and prone to early hydrolysis. Therefore, washing residues, washing ferrous sulfate crystals, washing equipment water, try not to use a lot of tap water, and use a small amount of waste acid. water.
3. Temperature The temperature rises and the viscosity of the titanium liquid decreases, which is advantageous for the sedimentation of the impurity particles, but is not favorable for the stability of the titanium liquid. Since the temperature is too high, the stability of the titanium liquid is lowered, and early hydrolysis occurs. The reason why the titanium liquid should be concentrated by evaporation under vacuum is that the evaporation temperature of the atmospheric pressure is high, the stability of the titanium liquid is lowered, and early hydrolysis occurs soon. The critical temperature of hydrolysis of titanium liquid is 80 ° C, and the concentration can be reduced to below 80 ° C by vacuum concentration, which not only ensures a large amount of evaporation of water, but also ensures that early hydrolysis does not occur. It can be seen that the temperature rises, the stability of the titanium liquid decreases, and the temperature drop is favorable for the stability of the titanium liquid. Generally, the control temperature is less than 75 °C during leaching, and the control temperature is (60 ± 5) °C during purification. [next]
If the content of ferric iron in ilmenite is high, the stability of the titanium solution obtained by acid hydrolysis can be poor. One of the reasons is that the content of ferric iron is high, and the acid hydrolysis reaction emits more heat, the temperature is high, the reaction is severe, and sometimes there is a boiling pot phenomenon, which is prone to early hydrolysis and makes the titanium liquid unstable; the second reason is trivalent The iron content is high, the acid hydrolysis reaction itself needs to consume more sulfuric acid, and the titanium liquid produced requires a lot of iron filings (or iron powder) to reduce the ferric iron into divalent iron, and the consumption of iron scraps is more, and more Sulfuric acid is consumed, and these consumed sulfuric acids are ineffective acids. In the quantitative acid, there are more ineffective acids, and relatively less effective acid, that is, less free acid, so the stability of the titanium liquid will decrease.
The three factors affecting the stability of titanium fluid are: temperature > acidity > concentration. At lower temperatures and weaker acidity, the concentration is higher, the water content is less, the titanium solution is more stable; the concentration is lower, the water content is more, and the stability of the titanium liquid is poor. However, in the case of high temperature and high acidity, the concentration of titanium liquid affects the stability of titanium liquid. Below 80 ° C, the stability of the titanium liquid increases as the acidity increases. However, at a temperature higher than 80 ° C or higher, the titanium liquid with too large acidity is also unstable, and thermal hydrolysis can also be carried out to form metatitanic acid, but the acidity is large, the hydrolysis is inhibited to some extent, and even hydrolysis is difficult. The metatitanic acid particles obtained by hydrolysis are small, and the hydrolysis rate is also low. Of course, if the acidity is large, it is not a problem of inhibiting hydrolysis, but the reaction is reversible, and the generated metatitanic acid is dissolved.
11. Structure and acid hydrolysis operation of the acid solution pot
The structure of the acid solution pot is: the outer shell is a steel plate, the lead is first layered with lead , and then two layers of acid-resistant brick are built with acid-resistant cement; the chimney is lined with steel with two layers of acid-resistant bricks, or made of thick hard polyvinyl chloride plastic sheet. In order to be larger, the large amount of water vapor, S0 2 , S0 3 and other gases generated by the reaction can be discharged in time; the distribution plate of the cone bottom is made of lead or acid-resistant ceramic, and the angle of the opening is to ensure that the compressed air can be uniformly blown. Go to the periphery of the reaction pot without leaving a dead angle, so that the solid phase material is completely dissolved. The distribution plate of the large acid solution pot is often designed as a blister shape, which is favorable for uniform distribution of compressed air and prevents debris from clogging the hole; It is resistant to temperature and corrosion, and must be able to meet the functions of discharging, compressing air and steam. The volume used in China is 12-50m 3 , and abroad is generally 90m 3 . The volume of 3 sets imported from abroad is 130m. 3 , acid hydrolysis per pot is 27-30 tons. The height of the acid solution pot (including the bottom portion of the cone) is twice the diameter (the cylindrical portion). The angle a of the cone bottom is 60°. The structure of the acid solution pot is shown below.
Acid hydrolysis operation: In the technology introduced in China, raw material sulfuric acid pre-dilution and mineral acid pre-mixing are generally used before acid hydrolysis. The acid hydrolysis is carried out in an acidolytic pot. Under the strong stirring of the compressed air at the bottom of the cone, firstly, the sulfuric acid is injected according to the formula, then the mineral powder is injected, the mineral powder is mixed with the sulfuric acid, and the waste acid water for dilution is added, and the stirring is continued, due to the waste acid. The water in the water and sulphuric acid hydrate to generate a large amount of heat, so that the temperature of the material in the pot rises quickly. It is then heated directly with steam (if the heat of hydration is sufficient to initiate the main reaction, no external heating is required). When the temperature of the reactant in the pot rises to 80-120 ° C, the heating is stopped immediately, and after 10-20 min of dilution of the waste acid water is generally added, a violent reaction occurs. Since the reaction is an exothermic reaction, the temperature of the reactants rises sharply and reaches a maximum temperature (about 250 ° C) in a few minutes. In this stage, the reaction is very intense, the acidizing pot will have a perceptible vibration feeling, and at the same time, a large amount of SO 2 , SO 3 and water vapor are discharged, and the reaction gradually solidifies into a porous honeycomb solid phase through the viscous phase. After the main reaction is completed, the drummer is stopped to compress the air, allowing it to mature for a certain period of time, allowing the reaction to continue to be more complete, which is advantageous for increasing the acid hydrolysis rate. After the aging time, the compressed air is used for cooling, and when cooled to 90-120 ° C, the waste acid, light titanium solution and tap water are added for leaching. Then, iron scraps (or iron powder) are added for reduction to obtain a titanium liquid. Sometimes when the iron filings are reduced, the reaction is severe, and there is a bubble in the pan, which can be used to defoam a small amount of washing powder. [next]
The leaching of the domestic titanium dioxide factory is mostly done from the top of the pot, so that the leaching liquid penetrates the solid phase from top to bottom, and is blocked by the compressed air flow rising from the bottom for stirring. Slower, the acidity of the leachate located in the upper part of the solid phase can not be increased quickly, the amount of water added is large, the concentration of the solution is dilute, the acidity is small, and early hydrolysis occurs more or less, resulting in deterioration of the sedimentation effect.
In foreign countries, a small amount of waste acid is added to the slag water and the ferrous sulfate crystal is washed in a light titanium solution, and then added to the bottom of the acid solution pot, so that the air in the void of the solid phase is easily discharged, and As the acid water rises, the acidity gradually increases. When the acid water is filled with the solid phase, it is stirred with compressed air. At this time, the temperature of the upper part of the solid phase can reach 80 ° C, but no early hydrolysis occurs. The reason is that the high temperature leaching solution has a high acidity, and as the water continues to increase, the temperature quickly drops below 70 °C.
12. Acid solution rate and method for increasing acid hydrolysis rate
The total amount of soluble titanium in solution (in terms Ti0 2) accounting for the total amount of titanium administered (in terms Ti0 2) the percentage of the iron ore known as acid solutions contained:
The acid hydrolysis rate can be improved from the following eight aspects.
1. Prolong the ripening time After the acid hydrolysis reaction, the aging is carried out, the purpose of which is to gradually cool the solid phase. During this cooling process, a part of the unacidified mineral powder continues to interact with the free acid present to enhance the acid. Solution rate. The ripening time is long, the acid hydrolysis rate is improved, but the solid phase temperature is low, the leaching speed is slow, the aging time is short, the solid phase temperature is high, the leaching time is short, but the acid solution rate is low. Generally, according to the size of the acid solution pot, the amount of the ore, the temperature of the room temperature is controlled at 1-6h, the amount of mineralization is large, the curing time is long, the amount of mineralization is small, and the curing time is short. The author has done such a test, in the 12m 3 acid solution pot, the curing time was shortened from 3h to 1h, and the acid hydrolysis rate did not decrease. In this regard, the author believes that in the stage of intense acid hydrolysis, the concentration of sulfuric acid is high, the reaction temperature is high, and the mines that can react should react. After the reaction, especially after further curing for 1 h, the acidity and temperature were greatly reduced. Thus, it is difficult to increase the acidification rate by prolonging the ripening time. Prolonging the curing time can only prolong the acid hydrolysis cycle and affect the yield increase.
2. Properly increase the concentration of sulfuric acid in reaction Sulfuric acid is a kind of active and strong acid. It can be dissolved in water in any proportion, and a large amount of heat is released. The concentration of sulfuric acid has a great influence on the acid hydrolysis reaction. When the acid to mineral ratio is constant, the concentration of sulfuric acid in the reaction is appropriately increased. It is beneficial to speed up the acid hydrolysis rate and increase the acid hydrolysis rate. More than 96% of sulfuric acid reacts more sharply than 92.5% of sulfuric acid, not only because of the amount of heat released when it is diluted to the process requirements, but also because H + ions and S0 2 - 4 ions infiltrate ferrotitanium due to increased concentration The probability of cracks in the surface of the mineral increases, and the dipole action of the H + -SO 2 - 4 ion pair and the in-situ action of the solid surface are enhanced to accelerate the decomposition of the ilmenite. [next]
3. Appropriately increase the ratio of acid to mineral The higher the ratio of acid to mineral, the more complete the reaction and the higher the acid hydrolysis rate. However, the excessive acid-mine ratio increases the unit consumption of sulfuric acid, but the acid hydrolysis rate is not significant.
4. Properly increase the acid hydrolysis temperature The decomposition reaction of ilmenite powder and sulfuric acid itself will release a lot of heat, and the reaction formula is as follows:
Under normal circumstances, the material needs to be properly heated at the beginning to initiate the acid hydrolysis reaction. This kind of heat is often caused by the action of water and concentrated sulfuric acid when adding diluted acid to the human, if it is produced. If these heats have not yet reached the requirements for heat generation, steam heating is required; if these heats are sufficient to meet the heat generation requirements, it is not necessary to heat them.
In general, the higher the temperature, the more intense the reaction, the more complete, the higher the acid hydrolysis rate, but the acid hydrolysis reaction is an exothermic reaction, and when the initiation of the reaction starts, a large amount of heat is released, so that the reaction temperature rises rapidly and is short. It reaches 200 °C or more in time. If the estimation is insufficient in advance, if the heating is too much and the temperature of the material is too high, for example, >130 °C, the main reaction will be too early, which will not only make the reaction too violent, but also cause the phenomenon of boiling or early hydrolysis, and also reduce the acid hydrolysis rate. Even the solid phase formed is difficult to be leached; if the heating is too low, for example, >60 ° C, the main reaction takes a long time, the reaction is not severe, and a poorly soluble solid phase is easily formed, and the acid hydrolysis rate is also low. At the end of the main reaction, immediately stop the blowing and continue to maintain high temperature, which is conducive to increasing the acid hydrolysis rate.
5. The particle size of the ore powder is small and the particle size of the uniform ore is larger, the reaction is slower, and even some coarse particles do not react, so the acid hydrolysis rate is lowered; the particle size of the ore powder is uneven, coarse and fine, in the reaction, fine particles first After the reaction, the concentration of sulfuric acid is lowered, the reaction of coarse particles is incomplete, and the acid hydrolysis rate is also low.
6. Stirring should be uniform. Stirring before the reaction is uneven. There are undistributed ore particles, which will affect the acid hydrolysis rate. Stir too much, the material splashed too much on the wall of the pot, unable to react, and will reduce the acid hydrolysis rate.
7. A good selection of acid soluble mineral good choice ore, titanium dissolution rate, high rate of acid hydrolysis; as rutile ore is decomposed sulfate extremely difficult, and therefore must use less component rutile ore, in order to improve the rate of acidolysis .
8. Avoid early hydrolysis and insoluble solids. Because these phenomena will reduce the acid hydrolysis rate.
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