Brief introduction

Diatomite is the sediment of ancient single celled diatom remains. Its features: light weight, porous, high strength, wear resistance, insulation, heat insulation, adsorption and filling. It has good chemical stability. It is an important industrial material for heat insulation, grinding, filtration, adsorption, anticoagulation, demoulding, filling, carrier and so on. It can be widely used in metallurgy, chemical industry, electric power, agriculture, chemical fertilizer, building materials, thermal insulation products and other industries. It can also be used as industrial functional fillers such as plastics, rubber, ceramics and papermaking.

classification

Diatomite filter aids can be divided into dry products, calcined products and flux calcined products according to different production processes.

① Dried product

The silicon dry soil raw materials purified, pre dried and crushed are dried at a temperature of 600 ~ 800 ° C and then crushed. This product has fine particle size and is suitable for precision filtration. It is often used in combination with other filter aids. Most of the dried products are light yellow, milky white and light gray.

② Calcined product

The purified, dried and crushed diatomite raw material is fed into a rotary kiln, calcined at a temperature of 800 ~ 1200 ° C, then crushed and graded to obtain the calcined product. Compared with dry products, the permeability of calcined products is more than three times higher. Calcined products are mostly light red.

③ Flux calcined product

After purification, drying and crushing, the diatomite raw material is added with a small amount of melting aids such as sodium carbonate and sodium chloride, calcined at 900 ~ 1200 ° C, and the flux calcined product is obtained after crushing and particle size grading ratio. The permeability of flux calcined products is significantly improved, which is more than 20 times that of dry products. Flux calcined products are mostly white, and light pink when Fe2O3 content is high or flux dosage is small.

Filtration

The filtering effect of diatomite filter aid is mainly carried out through the following three functions:

Screening action

This is a kind of surface filtration. When the fluid flows through diatomite, the pore of diatomite is smaller than the particle size of impurity particles, so that impurity particles cannot pass through and be intercepted. This effect is called screening. In fact, the surface of the filter cake can be regarded as a screen surface with equivalent average pore size. When the diameter of solid particles is not less than (or slightly less than) the pore diameter of diatomite, the solid particles will be "screened" out of the suspension to play the role of surface filtration.

Depth effect

Depth effect is the retention effect of deep filtration. During deep filtration, the separation process only occurs in the "interior" of the medium. Some of the relatively small impurity particles passing through the surface of the filter cake are blocked by the tortuous microporous channels in the diatomite and the finer pores in the filter cake. These particles are often smaller than the micropores in the diatomite. When the particles hit the wall of the channel, they may leave the liquid flow, However, whether it can achieve this depends on the balance of inertial force and resistance of particles. This interception and screening action are similar in nature and belong to mechanical action. The ability to filter solid particles is basically only related to the relative size and shape of solid particles and pores.

Adsorption

Adsorption is quite different from the above two filtration mechanisms. In fact, this effect can also be regarded as electrokinetic attraction, which mainly depends on the surface properties of solid particles and diatomite itself. When the particles with small pores in diatomite collide with the internal surface of porous diatomite, they are attracted by opposite charges, or the particles attract each other to form chains and adhere to diatomite, which belong to adsorption. Adsorption is more complex than the first two. It is generally believed that the reason why solid particles smaller than pore diameter are intercepted is mainly due to:

(1) Intermolecular forces (also known as van der Waals attraction), including permanent dipole action, induced dipole action and instantaneous dipole action;

(2) The existence of zeta potential;

(3) Ion exchange process.