The diatomite filter aid mainly uses the following three functions to keep the impurity particles suspended in the liquid on the surface of the medium, so as to achieve solid-liquid separation:
1. Depth effect The depth effect is the retention effect of deep filtration. In deep filtration, the separation process only occurs in the “inside” of the medium. Part of the relatively small impurity particles that penetrate the surface of the filter cake are blocked by the tortuous microporous channels inside the diatomaceous earth and the smaller pores inside the filter cake. This kind of particles are often smaller than the micropores of diatomaceous earth. When the particles hit the wall of the channel, they may leave the liquid flow. However, whether it can reach this point depends on the inertial force and resistance of the particles. Balance, this kind of interception and screening are similar in nature, both belong to mechanical action. The ability to filter out solid particles is basically only related to the relative size and shape of the solid particles and pores.
2. Screening effect This is a surface filtering effect. When the fluid flows through the diatomaceous earth, the pores of the diatomaceous earth are smaller than the particle size of the impurity particles, so that the impurity particles cannot pass through and are intercepted. This effect is called For the screening effect. In fact, the surface of the filter cake can be regarded as a sieve surface with an equivalent average pore size. When the diameter of the solid particles is not less than (or slightly less than) the diameter of the pores of the diatomite, the solid particles will be “sifted from the suspension”. Separate out, play the role of surface filtration.
3. Adsorption The adsorption is completely different from the above two filtration mechanisms. In fact, this effect can also be regarded as an electrokinetic attraction, which mainly depends on the surface properties of the solid particles and the diatomaceous earth itself.
Diatomaceous earth merchants use loose granular diatomaceous earth filter aid as the filter medium in the net pressure filtration process of the suspension. From the above three functions, the main purpose is to provide as much as possible for the filter medium layer, namely the filter cake. The multiple pores and the formed pore spacing layer allow the suspension to pass through the small pores of the barrier layer, and trap the solid impurity particles suspended in the liquid on the surface and channel of the medium, thereby making the solid-liquid To achieve the purpose of separation.