ARTICLE NO. 0420 Adsorption Characteristics of Iron±Cyanide Complex on g-Al2O3

their slow decomposition kinetics under general soil condi-The adsorption behavior of ferrocyanide and ferricyanide to- tions (12). When these complexes are exposed to light, free ward aluminum oxide with a 0.01 M NaClO4 background electro- cyanide is released from the molecules by light irradiation lyte at 257C was investigated. Results obtained from different pH (13). Therefore, in this study, two complex ions, ferrocya-values demonstrated that the adsorption of these complex ions nide and ferricyanide, have been investigated with respectcould be described by a modi®ed Langmuir isotherm in the concen-to their adsorption on the g-Al2O3/water interface.tration range 0.5 1 1004 to 4 1 1004 M. This modi®ed Langmuir For the oxide/solution interface, the surface charge andisotherm developed here could accurately predict the equilibrium potential gradient decrease with increasing distance frompartition between solid and liquid phases while taking proton com-the interface to the solution phase. The concept of solutionpetition into account. Also, the apparent equilibrium constant coordination chemistry is generally applied in describing(K app) derived from the Langmuir equation for ferrocyanide or ferricyanide adsorption on aluminum oxide was compared with adsorption of ions at the oxide/solution interface. The triple-the intrinsic constant (K int) calculated by triple-layer model simu- layer model (TLM) developed by Hayes and Leckie (14) lation. This comparison revealed a strong correlation between the allows metal ions and anions to form an innersphere com-apparent equilibrium constant and the intrinsic constant. More- plexation at the surface layer (o-plane) or an outer-spher