The factors that affect the filtering process are as follows:
1 Properties of the filtered slurry The concentration of the filtered slurry, the temperature, the particle size composition of the solid material in the slurry, and the flotation reagents contained therein all have an effect on the filtration process.
Within a certain range, increasing the concentration of the slurry can greatly increase the thickness of the filter cake, thereby increasing the productivity of the filter and simultaneously reducing the moisture of the filter cake. The pulp concentration is generally required to be greater than 40%.
As the temperature of the slurry increases, the viscosity of the slurry decreases, thereby increasing the filtration speed and increasing the thickness of the filter cake, thereby increasing productivity. However, the water content of the filter cake will not be greatly reduced. At present, for some fine and sticky pulps, in order to improve the filtration effect, measures for heating the slurry and filter cake using steam are being studied.
The effect of the particle size of the solid material in the slurry on the filtration is also significant. The coarse-grained material has large porosity due to the formation of the filter cake, and the filter cake has small resistance, which is favorable for the passage of the filtrate, the productivity of the filter is high, and the filter cake has low moisture; when the fine-grain slurry is filtered, it is easy to block the pores and cause filtration. Difficulties, reducing the productivity of the filter.
The particle size composition of the slurry has a great influence on the filtration efficiency. Generally speaking, the more the fine mud content, the worse the filterability. In order to improve the filtration effect of the material with a large amount of fine mud, an appropriate amount of coagulant and flocculant are often added to agglomerate the fine particles into larger particles, but at this time, the moisture of the filter cake is not significantly lowered because of adsorption in the agglomerates. The water still cannot be removed.
As for the presence of flotation agents, the filterability of the pulp is often lowered, but the filterability is also improved. Therefore, the impact of flotation agent on filtration should be analyzed according to the specific conditions.
2. Properties of the filter cake In the filtration operation, the porosity, resistance of the filter cake and cracking of the filter cake have a great influence on the filtration.
The higher the porosity of the filter cake, the lower the moisture. The filter cake porosity is related to the particle size and particle size composition of the filter material, so that the filter cake formed by the granular and narrow particle size range has less moisture.
The filtration rate is inversely proportional to the filter cake resistance. The resistance of the filter cake is determined by its thickness, porosity and viscosity of the filter. The thickness of each part of the filter cake layer should be consistent, and the unevenness of the thickness of each part of the filter cake may be caused by uneven thickness. In the thin place, the resistance is small, the filtrate is quickly extracted, and the â€œthousand-holeâ€ is quickly formed, so that the air enters, thereby reducing the vacuum degree of the filter chamber, reducing the pressure difference between the two sides of the filter medium, and the filtration speed is remarkably lowered. Cracking of the filter cake due to shrinkage also reduces the filtration rate. The solution is to speed up the filter, so that the resulting filter cake is thinner and the moisture is lower.
3. Pressure difference (vacuum degree) In general, the finer the particle size of the slurry, the greater the pressure required. However, the pressure difference will increase the damage of the filter medium and increase the power consumption. Sometimes, due to the pressure difference, the fine material is drilled into the filter hole, causing serious blockage, which will reduce the filtration speed. Therefore, it is preferable to use a small vacuum degree and a thin layer of filter cake for the filtration of the fine mud slurry, and the filtration time is appropriately extended.
4. Types and properties of filter media Filter media can generally be divided into three categories: the first type of granular media, such as fine sand, glass slag, etc.; the second type of fabric media, such as natural and man-made fiber fabrics; the third type of porous ceramics or plastic products.
Beneficiation plant medium used is a fabric medium, such as ordinary cotton cloth, artificial cloth or nylon nylon carpet. The cotton filter cloth has a short service life and the filter holes are easy to block; while the chemical fiber nylon cloth has a long service life and is easy to clean.
During the filtration process, the clogging of the filter cloth is mainly mechanical clogging, that is, clogging due to the entry of small particles into the filter holes. However, clogging due to precipitates formed by chemical reactions (usually carbonic acid compounds and sulfuric acid compounds) sometimes occurs. In order to ensure a certain filtration speed, the filter cloth must be cleaned after a period of time to eliminate the blockage. The cleaning is generally washed with high-pressure water, and the chemical precipitate may be washed with an acid solution, and is usually washed with a hydrochloric acid solution having a concentration of 1 to 2% to dissolve and remove the precipitate.
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