Filtration is to use the medium (porous material) to intercept the solid in the suspension to form a filter cake, and the liquid is clarified through the medium, so as to achieve the purpose of liquid-solid separation. With the continuous development of industry, more and more materials need to be filtered. Especially when the content of fine particles in the filter material is high, a dense filter cake with fine pores is formed on the filter medium, or the pores of the filter medium are blocked, so that the filtration cannot be carried out. In addition, when the filter slurry contains viscous or gelling or highly compressible particles, the formed filter cake has great resistance to the filtrate, which is prone to problems such as compact filter cake, poor air permeability, reduced filtration speed, increased water content of filter cake and so on. In order to solve these problems, methods such as increasing the filtration area and increasing the filtration driving force can be adopted, but these methods generally involve changing the existing equipment and process flow, and the investment is relatively large. In contrast, the method of adding filter aid to the filter slurry has the advantages of rapidity, simplicity, saving investment and quick effect.

Another kind of solid particle with hard germplasm that can form loose filter residue is added to the filter slurry, or it is made into a paste with the filter slurry and supplemented on the filter medium to form a loose filter cake and make the filtrate flow smoothly. This kind of solid particle is called filter aid.

The function of filter aid is to reduce filtration resistance and improve filtration speed and clarity. The filter aid shall be chemically stable, insoluble, hard and irregularly shaped fine particles, which can form a loose and almost incompressible filter cake. Diatomite is a kind of irregular porous particles processed from diatom fossils. The main component is SiO2. It is highly inert and insoluble. It can form hard and incompressible filter cake. It is the most commonly used filter aid.