A kinetic model for the adsorption of gold from I 2/I ^- solutions onto a porous polymer membrane

A model for the adsorption of gold from I ₂/I ^- aqueous solutions onto a cellulose acetate (CA)-polyaniline (PANI) porous membrane is presented. The adsorption of gold is represented by an ion-exchange overall reaction in which AuI ₂ ^- ions replace the Cl ^- ions at the active sites of the polyaniline matrix. The model incorporates the external mass transfer of AuI ₂ ^- from the bulk solution to the membrane surface, followed by the pore diffusion of AuI ₂ ^- to reach the active sites in the membrane. The overall ion-exchange reaction was assumed to achieve local instantaneous equilibrium. Verification of the kinetic model with the experimental data showed that the effective diffusivity of AuI ₂ ^- within the membrane is about 8.3 × 10 ^-6 cm ²/s. The potential applications of the present formulation are discussed.