What is the difference between absorption and adsorption?

What is the difference between absorption and adsorption?

Absorption and adsorption are homophonic terms but their meaning and application are different.

The word absorption is used in various fields and in each of them it has a specific connotation.

In physics, absorption occurs when a substance in a gaseous state, which is called “absorbate”, is incorporated into the volume occupied by another substance in a liquid state, which is called “absorbent”.

Adsorption is defined as the phenomenon that occurs when a substance, in a liquid or gaseous state, called an “adsorbate”, adheres to the wall of a solid, called an “adsorbent”.

What is absorption?

Absorption is a physical phenomenon involving the diffusion of mass in which one or more components of a gaseous mixture are dissolved in a liquid. It does not involve chemical changes, so it is reversible.

In industry, absorption is mainly used for gas purification, whether the gas is a product or a process residue. A typical application is the reduction of SO2 and CO2 in a gas stream in absorption columns.

What is adsorption?

Adsorption is a physical phenomenon, where a compound in a liquid or gaseous phase comes into contact with an adsorbing solid and adheres to its surface, by means of a physical force (London scattering force). This process does not involve an exchange of electrons, which makes it reversible.

Less frequently, chemisorption occurs, which involves changes in the chemical structure of the adsorbent and adsorbate, is irreversible.

Adsorption is widely used for the purification of gases and liquids. In industry it is common to find packed columns through which the treated liquid or gas is made to flow. Some examples are: the extraction of moisture from a gaseous stream, which is passed through a column with activated alumina that adsorbs the water molecule; another is the purification of water with activated carbon, which has the ability to absorb organic molecules such as pesticides, hydrocarbons, etc.

The most widely used adsorbent in industrial, commercial and domestic processes is activated carbon.


You can see in the following table, the comparison of each of these processes.

Table comparing adsorption and absorption:



Phenomenon in which atoms, ions or molecules of gases, liquids or solids are dissolved in another substance.
Phenomenon in which atoms, ions or molecules of gases, liquids or dissolved solids are retained on a surface of a solid or liquid substance.
It's a mass and volume phenomenon.
It's a superficial phenomenon.

Sorbent state of aggregation 


Solid and liquid.

Sorbtes state of aggregation


Liquid, gaseous.
Solid, liquid and gaseous.
Scheme of the phenomenon

Absorption and adsorption are although homophonic terms their meaning and application differ and therefore cannot be substituted or applied arbitrarily.

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