Filter medium filtration is an operation in which a certain porous substance is used as a medium to treat the suspension. Under the action of external force, the liquid in the suspension passes through the pores of the medium and the solid particles are intercepted, thereby achieving solid-liquid separation. According to the different places where the solid particles are trapped in the filter medium, the filtration method is divided into deep filtration and surface filtration.
Deep filtration. The solid particles in the suspension enter the internal pores of the filter medium and adhere to the inside of the medium. This method is suitable for removing solid particles in very dilute suspensions, such as the purification of drinking water.
Surface filtration: accumulate the solid particles in the suspension on the surface of the medium to form a filter cake, also known as filter cake filtration. It is usually used to treat suspensions with high solid concentration (volume concentration greater than 1%). In this way, the filtrate can be obtained. This method is widely used in the chemical industry, food, metallurgy, etc.
For filtration operations, choosing the right filter media is a very important issue. The basic requirements for filter media in industry are porosity, low resistance, corrosion resistance, heat resistance, and sufficient mechanical strength. There are many types of filter media used in production, including the following:
- The fabric medium is a filter cloth woven with cotton, linen, silk, wool, synthetic fiber, metal wire, etc., which is the most widely used.
- The granular medium includes the accumulation layer of fine sand, gravel, glass slag, charcoal, bone charcoal and acid clay, etc., which is mainly used to filter the suspension with very little filter residue.
- Porous solid media, such as porous ceramics, porous plastics, porous metals, etc., are commonly used in intermittent filtration equipment for suspensions containing a small amount of particles.