Nine, titanium factors influence the biasing effect of acid washing 5. Acidity of water washing As the washing process progresses, the acidity in the filter cake will gradually decrease and the pH value will increase accordingly. At the same time, part of Fe 2+ is oxidized to Fe 3+ due to oxygen dissolved in water. When the pH is higher than 1.5, Fe 3+ will hydrolyze to form water-insoluble ferric hydroxide or form basic iron sulfate which is insoluble in water; when the pH rises to above 6.5, ferrous sulfate is also Hydrolysis produces a water-insoluble precipitate of ferrous hydroxide. Therefore, the removal of iron as soon as possible in the higher acidity stage is the key to water washing. Increasing the acidity helps to inhibit the hydrolysis of iron salts, which is beneficial to water washing. If a small amount of sulfuric acid is added to the washing water to maintain the pH in the town 1.5, the hydrolysis of the iron salt can be prevented to maintain the soluble state of the iron salt, and the iron content of the metatitanic acid can be reduced to be comparable to bleaching after washing. Degree. Rod Coupling,Pump Rod Coupling,Sucker Rod Coupling,Api Sucker Rod Coupling PUYANG RENHE INDUSTRY CO.,LTD , https://www.rhsuckerrod.com
There are many factors affecting the vacuum filtration and water washing effect of metatitanic acid, which are also complicated and often cross together. Here, it is only a single factor.
1. Vacuum The pressure difference between the two sides of the filter medium is the degree of vacuum. Under the condition that the vacuum line is not leaking, the vacuum degree of filtration is determined by the resistance of the filter cake and the filter medium, except for the capacity of the vacuum pump. The filtration of metatitanic acid is generally 6.67*10 4 -8. 67*10 4 The vacuum of Pa is more suitable. When the degree of vacuum is too low, the washing time is long, and it is easy to cause a falling film accident; if the degree of vacuum is too high, cracks are easily generated on the surface of the filter cake, so that the washing water is short-circuited from the crack to reduce the washing efficiency.
2. Partial titanic acid particle size Filtration requires that the particle size of metatitanic acid should be even and moderate. The particles are coarse, the water flow is fast, and the washing is easy, but the particles are too thick, the water flow speed is too fast, the pipe resistance is increased, and the inside of the particles is not easy to be washed; the particles are too fine, the filtration and filtration are large, or the filter holes are blocked, which makes the washing difficult and affects the yield.
3. The water temperature of washing water removal process is mainly free sulfuric acid and ferrous sulfate. The solubility of ferrous sulfate in water increases with increasing temperature over a range of temperatures. Therefore, increasing the water temperature is beneficial to water washing, shortening the washing time, reducing the iron content of the filter cake, reducing the water consumption, and increasing the yield. At 60 ° C, the solubility of ferrous sulfate in water is the largest, but when the temperature exceeds 45 ° C, the plastic plate or plastic tube of the blade is easily deformed, so the general water temperature is controlled at 30-40 ° C. The temperature is low and the water is difficult to wash. When the temperature is too low, the ferrous sulfate is crystallized in the filter cake, and the washing is more difficult. In the production, the cooling water in the cooling tank and the condensed water in the concentration process can be used to increase the water temperature to save fuel.
4. Washing time When the titanic acid starts to be washed, the material has high acidity, large impurity concentration gradient and high washing efficiency. From the relationship between the washing time of the metatitanic acid and the iron content in the filter cake, it can be seen that when the water washing starts, the iron content in the metatitanic acid is rapidly decreased, and 80% or more can be removed in half an hour, and the water washing process continues, the impurities are continued. The concentration gradient between the filter cake and the filtrate gradually decreases, and the acidity also gradually decreases. At the same time, as the ion concentration decreases, the colloidal property of metatitanic acid gradually becomes obvious, and the washing efficiency decreases. After washing for 1h, the water washing gradually becomes gentle, indicating that it takes a longer washing time to further reduce the iron content. However, if the washing time is too long, the solid impurities suspended in the washing water will deposit on the surface of the filter cake, which will increase the impurities, and some tap water. The plant uses chlorinated high-iron or ferrous sulfate as a coagulant. The main solid impurity in water is iron hydroxide, which will affect the quality of the product. Therefore, the water washing process can only reduce the iron content to a certain extent, generally about 0.01%, and the residual iron needs to be further removed in the bleaching process. 
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6. Water quality and water intake method The water quality has a great influence on the washing effect, the water quality is poor, and the washing effect is also poor. The water mainly contains impurities such as calcium, magnesium and iron. Calcium and sulfuric acid form calcium sulfate precipitate mixed in metatitanic acid, affecting the quality of the product; iron remains on the surface of the filter cake into a brown layer (iron content is higher than l00*10 -6 ), which will increase the iron content of metatitanic acid Quantity also affects the quality of the product.
Add water to the washing tank, add water from the bottom, and wash water faster than adding water from the top.
7. Thickness of filter cake The filter cake is too thick, the surface cracks are many, and the washing time is long; the filter cake is too thin, although the washing time is short, but the yield is low. Generally controlled at 25-35mm.
8. Cracks and voids Excessive cracks and voids can cause short-circuiting of water flow, large water consumption, long washing time, and even the phenomenon that the test cake is qualified and the iron content of the filter cake is still high. A small amount of polyacrylamide can be added to the water or blocked with a filter cloth.
9. Filter media When the slurry is filtered, the separation substance separating the solid and the liquid is called a filter medium. The filter cloth on the blade is the filter medium. The pore size of the filter cloth has a direct influence on the washing efficiency. If the cloth hole is too thin, it is easily blocked by the material, and the water washing becomes slow, which will affect the yield; if the cloth hole is too large, the material will be filtered and lost.
10. Trivalent titanium of the mother liquid Since the oxidation potential of the trivalent titanium is larger than the oxidation potential of the ferrous iron, when the oxygen in the air or water is oxidized, the trivalent titanium is first oxidized. This inhibits the oxidation of ferrous iron in the material to ferric iron, thereby ensuring the quality of the product. Therefore, maintaining an appropriate amount of trivalent titanium is advantageous for water washing. 5å…‹/å·¦å³å·¦å³ã€‚ After the hydrolysis of the trivalent titanium in the slurry was 0. 5g / L or so.
Ten, the choice of filter cloth
Due to the high acidity of the slurry, the filter cloth must be selected from acid-resistant materials. Currently widely used are 240 # and 758 # two grades of acid-resistant polyester fabric. 240 # is a long-fiber polyester fabric with a small hole size. It is not easy to fall off during operation, but it is easy to block. It should be brushed frequently when used. 758 # is a short-fiber polyester fabric with a fast filtering speed, but sometimes it can be filtered or dropped. Especially after changing the new cloth, it is easier to drop. To do this, a flocculant is needed to remedy it. When using a new cloth, it is necessary to soak for 1 to 2 days in advance to reduce the pore size to avoid excessive filtration loss.
11. Reasons for adding flocculant sometimes when washing
Since the operating conditions are not well controlled during hydrolysis, some colloidal small particles of metatitanic acid appear to increase the sedimentation rate. These small particles are lost through the filtration and the recovery rate is lowered, or the filter holes are blocked to make the washing difficult. In order to flocculate these small particles of metatitanic acid into loose agglomerates, thereby reducing the colloidal particles due to their shape being easily changed by pressure to cause clogging of the pores or permeation, it is necessary to add a flocculant. A commonly used flocculant in the industry is an aminomethyl modified polypropylene decylamine. It can floculate metatitanic acid into agglomerates which are easy to be filtered and washed in an acidic medium, thereby shortening the washing time and improving the washing efficiency. If the sedimentation rate of the slurry after hydrolysis is ≥ 440, it is not necessary to add a flocculant. But now each pot (2.6m 3 ) slurry is cooled to about 50 ° C in the cooling pot, adding 1. 35kg 1% flocculant (for 0.5% use). On this basis, if the sedimentation rate is still greater than 470, then more flocculant should be added. In addition, when the filter cake and the perforation of the washed cake are too much, a proper amount of flocculant should be added to the washing tank to replace the new filter cloth. Also, apply a flocculant to the surface. [next]
However, the flocculant is not added as much as possible. Because the flocculant forms agglomerates with the metatombotic colloidal particles, it will adsorb some ferrous ions and cause difficulty in washing, or too much flocculant will make the metatitanic acid slippery. It causes difficulty in suction and drops after the suction. Therefore, there is no benefit in adding too much flocculant.
12. Benefits of using pulp to aid filtration and its operating procedures
By atmospheric hydrolysis, the meta-titanic acid which produces fine particles is more hydrolyzed than the pressurized one, so that the metatitanic acid which is filtered and washed through the filtrate to the recovery tank is more. In this way, the amount of the settling agent is increased, and the trouble of recovering the metatitanic acid is greatly increased.
In order to solve these contradictions, you can take the method of pulp filtration: first buy the thick white paper from the paper company, then add the water and paper to the pot in a pot, according to the ratio of 1 ton of water plus 10 kg of paper. The person directly cooks the steam into a uniform pulp, and then puts it into a very thin pulp slurry and puts it into the suction filter box. Under the square box, the compressed air is used to make the air evenly stirred, and then rinsed with a high-pressure water gun. The suction filter blade is immersed in the square box, and vacuum vacuum suction filtration is started for 1-2 minutes, so that a thin layer of loose paper is adsorbed on the filter cloth of the suction filter blade, and the whole set of suction filter blades are taken out, and then released. The titanic acid is filtered by suction into a square box of titanic acid.
Through this pulp assisted filtration, small particles of metatitanic acid are difficult to pass through, so that the recovery pool has less metatitanic acid, the trouble of recovering metatitanic acid is reduced, and the amount of sedimentation agent is reduced or even eliminated. The washing speed is increased and the recovery rate is also increased.
The paper adhered to metatitanic acid, at a high temperature of calcination, generates gaseous oxides of carbon and hydrogen that escape through the chimney, and has no adverse effect on quality indicators such as whiteness of the product. It is calculated that only 0.3-0.4 kg of white paper is used per ton of titanium dioxide.
XIII. Reasons for improper washing and measures taken (see Table 3-7) [next]