Why is the adsorption effect of coal-based activated carbon so good?

       Coal-based activated carbon is developed through a series of processes such as carbonisation → cooling → activation → washing. Its appearance is generally black cylindrical activated carbon, indeterminate coal granular activated carbon, also known as crushed carbon. Cylindrical activated carbon, also known as columnar carbon, is generally made from powdered raw materials and binders by mixing and kneading, extrusion moulding and then carbonisation, activation and other processes. It can also be extruded with powdered activated carbon and binder. It has developed pore structure, good adsorption performance, high mechanical strength, easy to regenerate repeatedly, low cost, etc. It is used in the purification of toxic gases, waste gas treatment, purification of industrial and domestic water, and solvent recovery.

 

       The adsorption of solute molecules in water by coal-based granular activated carbon is a complex process, which is the result of the combined action of several forces, including ionic attraction, van der Waals force, chemical heterogeneity and force. According to the double-rate diffusion theory of adsorption, adsorption is a double-rate process consisting of two phases of rapid diffusion and slow diffusion, and rapid diffusion is completed within a few hours, which plays a role in 60%~80% of the adsorption capacity of coal granular activated carbon. Rapid diffusion is the process of diffusion of solute molecules in the large pores with small resistance uniformly distributed along the radial direction in the carbon particles. These macropores create radial resistance to diffusion. When molecules diffuse further from the macropores into the micropores that are connected to the macropores, they do so very slowly due to the large resistance created by the narrow pore size. Micropores are also uniformly distributed within the carbon particles, but do not constitute a radial diffusion resistance. Factors affecting the adsorption of coal granular activated carbon relate to the polarity of solute molecules, molecular weight size, and spatial structure, which depend on the characteristics of the water source. Coal granular activated carbon has selective adsorption of different substance molecules.