Freundlich Isotherm

A Freundlich isotherm is a mathematical expression for the adsorption equilibrium between a fluid (liquid or gas) and a solid material. The Freundlich equation is an empirical expression representing the isothermal variation of adsorption of a liquid or gas onto the surface of a solid material, derived by Freundlich (1909) as an empirical relation.

For adsorption of a gas as the adsorbate to a solid adsorbent, the following equation represents a Freundlich isotherm:

$$ \frac{x}{m}=k{P}^{\frac{1}{n}} $$

(1)

In this equation, x is the adsorbed quantity, m is the mass of the adsorbent, P is the partial pressure of the adsorbate in the gas, and k and n are empirical constants for each adsorbent-adsorbate pair at a given temperature.

For adsorption of a liquid, the relation between the adsorbed amount per gram of the solid at equilibrium Q (mg/g) and the concentration C in solution at the equilibrium (mg/l or μg/l) is given by the following equation:

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