Absorption tendency

The term absorption must be considered in connection with the term adsorption. Both processes describe the accumulation of a foreign substance on an adsorbent or absorbent. However, the difference is as follows:

During absorption, molecules/atoms/ions penetrate into the interior of the absorbent and distribute themselves evenly there. During absorption, the entire volume of the absorbent is involved in the accumulation of the pollutants. A liquid or gas penetrates into the inner structure of the absorbent and can dissolve in it. Example: carbon dioxide is dissolved in water. This process is also reversible if the pressure of the liquid is reduced. A towel is also an absorbent when it is used to dry a surface.

The term sound absorption is used colloquially: the energy of the vibrating air (sound waves) is converted into frictional heat. This physical process is irreversible. However, many other absorption processes are reversible, regardless of whether they are chemical or physical absorption processes.

In adsorption, the molecules of the foreign substance are deposited on the surface of the adsorbent by molecular or interparticular binding forces. This process is used in filtration.

Adsorbing materials usually have a high specific surface/proportion and a high affinity for certain foreign substances. Examples include dehumidification with lithium hydroxide or silica gel or the accumulation of pollutants in activated carbon. Adsorption processes can be either irreversible or reversible, regardless of whether they are chemical or physical adsorption processes.

The two phenomena of absorption and adsorption are of great significance for the wetting of powders and agglomeration.

The reversal of absorption and adsorption occurs when moist powders are heated. The liquid phase evaporates. The drying process can be accelerated by applying a vacuum.