Freundlich-Type Relations

Freundlich-Type Relations A binary Freundlich isotherm, obtained from the ideal adsorbed solution theory in loading-explicit closed form [Crittenden et al., Environ. Sti. TechnoL, 19,1037 (1985)], is 

---

As a typical example of an adsorption isotherm in aqueous phase, adsorption of propionic acid on activated carbon is shown in Hg. 3.16. At higher concentrations isotherms can be correlated by the Freundlich type equation, but at low coverage (q<0.l mmol/g), the slope of isotherms becomes steeper and seems to reach Henry s type relation. From isotherms at different temperatures, isosteric heat of adsorption was obtained as a function of the amount adsorbed as shown in Figs. 3.17 and 3.18. At higher coverage, measured isosteric heat of adsorption seems to decrease with increasing amount adsorbed. 

The above surface complexation models enable adsorption to be related to such parameters as the number of reactive sites available on the oxide surface, the intrinsic, ionization constants for each type of surface site (see Chap. 10), the capacitance and the binding constants for the adsorbed species. They, therefore, produce adsorption isotherms with a sounder physical basis than do empirical equations such as the Freundlich equation. However, owing to differences in the choice of adjustable... 

The extent of adsorption can have a profound effect on the rate of the surface reaction. Equilibrium isotherms of many kinds have been reported for adsorption from solution and have been classified by Giles et al. [24-27], The shapes of these adsorption curves often furnish qualitative information on the nature of the solute-surface interactions. Several of the types of isotherm observed in dilute solution are represented reasonably well by three simple and popular isotherm equations, those of Henry, Langmuir, and Freundlich. Their shapes are illustrated in Fig. 1. Each of these isotherms relates the surface concentrations cads (mol m"2) to the bulk equilibrium concentration c of the solute species in question. When few surface sites are occupied, Henry s law adsorption... 

The Freundlich adsorption isotherm is a special type of equilibrium relation of the general form ... 

An additional isotherm type is the Freundlich isotherm. For a pure gas (species /), the Freundlich isotherm has a power law relation... 

---