Characteristics and precautions of filter aid for diatomite filter

Natural diatomite is not a good filter aid. It must be chemically treated, burned at high temperature, crushed, washed, dried, ground and screened to remove organic matter and other impurities, and improve particle size, porosity and surface characteristics, so as to obtain good filter function.

Diatomite is a kind of biochemical sedimentary rock composed of cell walls of aquatic plants called diatomite thousands of years ago. It has numerous small holes and complex holes. Its powder particle size is very small. About 90% of it is permeable and free, and the main component SiO2 accounts for 85% – 90%. It has good chemical stability, high temperature resistance, insoluble and non-toxic. This porous particle provides great filtration capacity, can remove particles less than 1-0.1 microns (including microorganisms and bacteria) and contain fission products.

The function is not disordered and the adaptability is good. Because the diatomite filter aid is mainly composed of silica, the chemical property is not disordered. It can also be used in hot and cold acid solutions with different concentrations without affecting the basic properties of its stock solution.
High filtration rate and ideal clarity can be obtained. Due to its uneven size, hard skeleton, rich relationship between single and multiple pores and various shapes, the filter layer can not agglomerate tightly, and has large surface area and porosity, so as to achieve high filtration rate and ideal clarity.
Diatomite has the effect of removing bacteria, with fine particles. It forms a biological protective film on the diaphragm and can remove most pathogens.

  1. In the pre coating process, the key to the success or failure of the filter aid is whether an average, undisturbed, crack free and desolvated diatom pre coating can be formed. The main reasons are: the number of filter media used should match the viscosity of the filtered slurry and diatomite, and the poor stiffness of the support of the filter media is also the main reason for the cracks. The pressure of the filter media is small, No deformation. When the time is prolonged, the resistance increases, and when the support stiffness is not enough, it will deform, resulting in cracks and cracks in the pre coated diatomite soil layer. If diatomite is used only and the particles are too fine, sometimes cracks will occur. At this time, diatomite can be mixed with a certain number of asbestos fibers, which can be avoided. (however, asbestos fiber is not added in practice, which is very good).
  2. In the pre coating process, diatomite forms 2mm thick on the filter cloth, which is not disordered on average, and there is no crack and falling off soil layer. In this way, the thickness value is a common scale and is obtained based on experience. When precoating, the flow rate is too slow, and the established precoating powder is scattered and wet, which is not disordered, or the fast flow rate will increase the precoating pressure, and the pressure is also high when it is transferred to liquid filtration, which narrows the working pressure range, shortens the filtration time, and affects the production capacity. Therefore, it is more appropriate to adjust the pressure to 0.5-1.5kg/cm2 during and after precoating.
  3. If the production process needs to be suspended, first close the outlet valve, then close the inlet valve, and then stop the pump. In this way, the pressure in the chamber increases. When starting work again, start the pump first, open the inlet valve, and then the outlet valve. Why maintain the pressure in the filter? It keeps the diatom attached to the filter cloth from falling off the soil layer. On the contrary, the liquid and pressure in the machine will not be maintained. When working for the second time, due to the fast flow rate and large impact force of the pump, the soil layer glue solution is available on the filter cloth, so that the liquid through the filter is opaque and clear. It is necessary to restart the work according to the first use process, so as not to affect the normal productivity.