The filtration of diatomite filter aid is generally divided into two steps. Firstly, after mixing the filter aid with the clean filter slurry evenly, the filter aid forms a porous and loose filter cake on the filter medium, which is called "precoating" here. It can effectively prevent impurities from blocking the pores of the filter medium, prolong the filtration cycle and service life, and improve the filtration accuracy. The most important feature is that it is easy to remove the filter cake and clean the filter medium. After the pre coating is established, an appropriate amount of body feed is continuously added to the liquid to be filtered for filtration. With the progress of filtration, the filter aid is mixed with the suspended solid impurities in the stock solution and deposited on the precoat. In this way, new precoat is continuously formed. The fine filter aid particles have countless microchannels, which can block the suspended impurities, but will not block the passage of clean liquid.

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In the filtration process, when the filtrate passes through the precoating, the solid particles in the suspension form an aggregation state, and the size distribution changes. The impurities of large particles are captured and retained on the medium surface to form a layer with narrow size distribution, and they continue to block, capture the particle impurities close to their size, and gradually form a filter cake with certain pores. With the progress of filtration, impurities with small particle size gradually enter the porous diatomite filter aid medium and are intercepted. Because diatomite has a porosity of about 90% and a large specific surface area, as soon as the fine particles enter the inner pore and re pore of the filter aid, they are often intercepted due to adsorption and other reasons, which can reduce 0.5 μ The fine particles of M are removed, which has a good filtering effect.

In the precoating process, the key to the success or failure of additives is whether a uniform, stable, crack free and falling off diatomite precoating can be formed, which is more important and difficult in vertical blade filters. The main reasons are: the mesh of the filter medium used does not match the particle size of diatomite of the filtered slurry viscometer; The poor stiffness of filter medium support is the main cause of crack. In the filtration process, the pressure of the medium is small and there is no deformation, but with the growth of time, the filtration resistance becomes larger. When the support stiffness is not enough, it will deform and make the precoated diatom soil layer crack and crack.