The Difference between Adsorption and Absorption is that Adsorption is the attraction between the outer surface of a solid particle and a contaminant, whereas Absorption is the uptake of the contaminant into the physical structure of the solid.
Difference between Adsorption and Absorption

Adsorption Absorption
It is a surface phenomenon. It concerns with the whole mass of the absorbent.
In it, the substance is only retained on the surface and does not go into the bulk or interior of the solid or liquid. It implies that a substance is uniformly distributed, through the body of the solid or liquid.
In it the concentration of the adsorbed molecules is always greater at the free phase. In it the concentration is low.
It is rapid in the beginning and slows down near the equilibrium. It occurs at the uniform rate.
Examples : (i) Water vapours adsorbed by silica gel.
(ii) NH3 is adsorbed by charcoal.
Examples : (i) Water vapours absorbed by anhydrous CaCl2
(ii) NH3 is absorbed in water forming NH4OH

Absorption and adsorption are two natural occurring processes that are similar, but are not the same. Here is a basic breakdown of how they are different: absorption occurs when one materialís physical state is absorbed into another materialís physical state, while adsorption occurs when one material physically sticks to another material without changing itís physical state.
Absorption occurs when a gas turns into a liquid, or a liquid into a solid, etc. This is what separates it from adsorption, the physical state of the molecules have changed. For example if you were to drink a glass of milk, your body would absorb it into your digestive system and eventually into your bloodstream. The earth absorbs the suns rays and has converted its energy into the life sustaining planet we live on today. The roots of plants absorb water when it rains converting into the energy it needs to survive. All of these examples feature one materialís phase being turned into another.
Adsorption occurs when liquid or gas molecules stick to the side of surface, preserving their physical state. This is useful for separating certain molecules from one another. Adsorbents are most commonly found as carbon compounds or oxygen compounds.
Oxygen compound adsorbents are used to make products like silica gel which works to absorb moisture and reduce humidity levels or zeolites which can be tailored to specifically remove certain molecules from the air like carbon dioxide.
Carbon compound adsorbents like activated carbon can be effectively used to treat waste water and gas. Contaminates will get stuck to the pores that are found all over the surface area of activated carbon while the water filters through.