Working principle of Diatomite Filter Aid
The function of filter aids is to change the aggregation state of particles, thereby altering the size distribution of particles in the filtrate. Diatomite Filter Aidare mainly composed of chemically stable SiO2, with abundant internal micropores, forming various hard frameworks. During the filtration process, diatomaceous earth first forms a porous filter aid medium (pre coating) on the filter plate. When the filtrate passes through the filter aid, the solid particles in the suspension form an aggregated state, and the size distribution changes. The impurities of large particles are captured and retained on the surface of the medium, forming a narrow size distribution layer. They continue to block and capture particles with similar sizes, gradually forming a filter cake with certain pores. As the filtration progresses, impurities with smaller particle sizes gradually enter the porous diatomaceous earth filter aid medium and are intercepted. Because diatomaceous earth has a porosity of about 90% and a large specific surface area, when small particles and bacteria enter the inner and outer pores of the filter aid, they are often intercepted due to adsorption and other reasons, which can reduce 0.1 μ The removal of fine particles and bacteria from m has achieved a good filtering effect. The dosage of filter aid is generally 1-10% of the solid mass intercepted. If the dosage is too high, it will actually affect the improvement of filtration speed.
Filtering effect
The filtration effect of Diatomite Filter Aid is mainly achieved through the following three actions:
1. Screening effect
This is a surface filtration effect, where when the fluid flows through diatomaceous earth, the pores of the diatomaceous earth are smaller than the particle size of the impurity particles, so the impurity particles cannot pass through and are intercepted. This effect is called sieving. 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 solid particles is not less than (or slightly less than) the pore diameter of diatomaceous earth, the solid particles will be "screened" out of the suspension, playing a role in surface filtration.
2. Depth effect
The depth effect is the retention effect of deep filtration. In deep filtration, the separation process only occurs inside the medium. Some of the smaller impurity particles that pass through the surface of the filter cake are obstructed by the winding microporous channels inside the diatomaceous earth and the smaller pores inside the filter cake. These particles are often smaller than the micropores in the diatomaceous earth. When the particles collide with the wall of the channel, it is possible to detach from the liquid flow. However, whether they can achieve this depends on the balance between the inertial force and resistance of the particles. This interception and screening action are similar in nature and 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.
3. Adsorption effect
The adsorption effect is completely different from the two filtering mechanisms mentioned above, and this effect can actually be seen as electrokinetic attraction, which mainly depends on the surface properties of solid particles and diatomaceous earth itself. When particles with small internal pores collide with the surface of porous diatomaceous earth, they are attracted by opposite charges or form chain clusters through mutual attraction between particles and adhere to the diatomaceous earth, all of which belong to adsorption. The adsorption effect is more complex than the first two, and it is generally believed that the reason why solid particles with smaller pore diameters are intercepted is mainly due to:
(1) Intermolecular forces (also known as van der Waals attraction), including permanent dipole interactions, induced dipole interactions, and instantaneous dipole interactions;
(2) The existence of Zeta potential;
(3) Ion exchange process.
Post time: Apr-01-2024