NOTE
Potentiostatically Enhanced Complexation Model for the Determination of Isopotential Equilibrium Curves in turn produce a charged surface and a double layer at the solid/liquid interface. The surface potential that is created (which is also the open circuit A potentiostatically enhanced complexation model for open syspotential) can be changed by manipulating the environmental conditions, i.e. tems has been developed that describes the adsorption of heavy pH and ionic concentrations, to strongly affect the adsorption equilibrium metal ions under different pH conditions and forcing electrostatic
between the ionic species and those adsorbed at the interface. The surface potentials. This model is based on the so-called complex formation potential can also be changed by establishing an overpotential in the matemodels, and it assumes adsorption of only free ionic species, exisrial, but in such a way as to avoid reduction of the electroactive species at tence of one type of adsorption site, and limited adsorption site the interface. In this way, with almost negligible faradaic redox reactions, availability. The results show that potentially enhanced adsorption changing the surface potential, e.g., using a potenstiostat, produces the same processes can be used for the adsorption of heavy metal ions at effect as that obtained by changing the pH. The advantages of using an pH conditions where adsorption is weak, yet potentials are small externally applied overpotential include the use of less chemicals and sim- enough to avoid reduction and plating, and also electrolysis of pler modes of operation which both manifest as lower capital and operating costs.
water. Moreover desorption can be achieved by turning off the
Many models have been offered to explain the adsorption behavior of applied potential or by reversing it, thereby avoiding the use of ionic species on various adsorbents (11-28). One of them that has received additional chemicals, e.g., a strong acid, to achieve regeneration.
considerable attention is the surface complexation model, which can be α§ 1998 Academic Press applied only to rather dilute solutions (0.001 M). The first ideas were Key Words: electrosorption; heavy metal ion adsorption; surface developed in the works of Hohl and Stumm (11) and Schindler et al. complexation model; aqueous solution; applied potential.
(12), who interpreted their results in terms of surface equilibrium reactions between free metal ionic species and amphoteric functional groups at the solid/aqueous interface of hydrous silica and alumina, respectively. Later, in a series of works, presented a more formal structure