Activated carbon filter material is a commonly used filter media in water treatment. There are usually: coconut shell activated carbon, shell activated carbon, coal particle activated carbon, coal columnar activated carbon, etc. Activated carbon is a kind of carbon that has been specially processed by heating organic materials (such as shells, coal, wood, etc.) in the absence of air to reduce non-carbon components (this process is called carbonization), and then react with gas to erode the surface and produce a structure with developed micropores (this process is called activation).
Since the activation process is a microscopic process, that is, a large number of molecular carbonaceous surfaces are eroded in point-like erosion, so the surface of activated carbon has countless small pores.
The micro-pore diameter of activated carbon surface is mostly between 2-50 nanometers. Even with a small amount of activated carbon, there is a huge surface area, and the surface area of each gram of activated carbon is 500-1500 square meters. High-quality activated carbon is prepared by thermolysis and activation processing of carbon-containing raw materials such as wood, coal, and petroleum coke. It has a developed pore structure, a larger specific surface area, and rich surface functional groups. It is a general term for carbon materials with strong specific adsorption capacity.
The specific surface area, ash content, and pH value of the suspended water in activated carbon all increase with the increase of activation temperature. The higher the activation temperature, the more completely the residual volatile substances are volatilized, and the more developed the microporous structure, the larger the specific surface area and adsorption activity.
The composition and content of ash in activated carbon have a great influence on the adsorption activity of carbon. The ash content is related to the raw materials used to make activated carbon, and the ash content in the carbon increases with the removal of volatiles.
Granular activated carbon filter material has cylindrical, spherical, hollow cylindrical, hollow spherical, and irregular shape broken charcoal, etc. With the development of modern industry and scientific and technological progress, many new varieties of activated carbon have emerged, such as molecular sieve carbon, microsphere carbon, activated carbon nanotubes, activated carbon fibers, etc.
The micropore specific surface area in activated carbon accounts for more than 95% of the specific surface area of activated carbon, which largely determines the adsorption capacity of activated carbon. The specific surface area of large pores generally does not exceed 0.5m2/g, it is only the channel for adsorbate molecules to reach micropores and mesopores, and it has little effect on the adsorption process.
The adsorption performance of activated carbon depends not only on the physical (porous) structure of activated carbon, but also on the chemical structure of the activated carbon surface.
Activated carbon adsorption refers to the adsorption of one or more substances in water on the solid surface of activated carbon to achieve the purpose of purifying water quality. The adsorption capacity of activated carbon is related to the size and structure of the pores in activated carbon. Generally speaking, the smaller the particles, the faster the diffusion rate of the pores and the stronger the adsorption capacity of activated carbon filter material.
The adsorption capacity and adsorption rate are the main indicators of the adsorption process. The size of the adsorption capacity is measured by the adsorption amount, and the adsorption rate refers to the amount of adsorbent absorbed by unit weight of adsorbent per unit time. In water treatment, the adsorption rate determines the contact time between the adsorbent and the sewage.