Sorption Research Paper

Sorption is a separation process involving two phases between which certain components can become differentially distributed. There are three types of sorption classified according to the type of bonding involved: Physical sorption: it occurs as a result of nonspecific attraction between the solid and the adsorbate in several consecutive layers. Their origin lies in the attraction between the entire electron shell of the adsorbate and the adsorbent .this attraction are known as dispersion of Van-der Waals forces, and are similar in nature to those acting in any condensation process. In addition, the heat of adsorption, or activation energy, is low and therefore this type of adsorption is stable only at temperatures below about 150°C. [Adamson,

Chemical adsorption, or chemisorption, involves an exchange of electrons between specific surface sites and solute molecules which results in the formation of a chemical bond and it may be irreversible and slow. Chemisorption is typified by much stronger adsorption energy than physical adsorption. Such a bond is therefore more stable at higher temperature. These forces show characteristic stability, which reduces their action to a single adsorption layer [Gregg and Sing, 1967]. Electrostatic sorption (ion exchange). This is a term reserved for coulombic attractive forces between ions and charged functional groups and is more commonly classified as ion exchange. The electrostatic adsorption seems probably the most frequently type of adsorption from solution [Ross and Olivier, 1964].

In many systems the mechanism of adsorption cannot be characterized and several mechanisms may be involved simultaneously [Schulz et al., 1960]. Consequently it is difficult to assess the nature of adsorption forces even at macroconcentration of adsorbate. Nevertheless, it is well established that the mechanism of the adsorption of trace elements depends primarily on their state in solution [Ezz El-Din,

According to Freundlich sorption isotherm, the following equation is valid; log qe = log Kf + 1/n log Ce (3) Where qe is the amount adsorbed at equilibrium (mol/g), Ce is the equilibrium concentration of the adsorbate metal ions, Kf and n are Freundlich constants, Therefore, if the Freundlich isotherm is obeyed, a straight line relationship should be obtained between log qe and log