Adsorption kinetics of dicyanoaurate and dicyanoargentate ions in activated carbon

A kinetic model describing the adsorption of dicyanoaurate and dicyanoargentate ions in activated carbon has been derived assuming that the dicyanoions adsorbed onto the external surface are in equilibrium with those in solution. This equilibrium may be described by a modified Langmuir-Hinselwood equation as is usual in heterogeneous catalysis systems. Once adsorbed onto the outer surface, the dicyanoions can diffuse toward the inner surface of the particle through the pores of the carbon, or they can be desorbed back to the liquid phase. The two exit stages are fast enough to maintain the outer surface in a pseudostationary state in normal experimental conditions. Finally, the kinetic parameters for the process are determined. The fitting of the model with experimental data is satisfactory and the range of applications is wide. M. SEGARRA and M. FERNáNDEZ, former Graduate Students, and F. ESPIELL