Competitive adsorption of ferricyanide and ferrocyanide on gamma-Al2O3 surface

In the past 3 decades, research has proven the significance of competitive adsorption in the equilibrium of pollutants between solid and liquid phases . However, studies on the competitive adsorption of complex ions are very l imited in spite of its important role in transporting pollutants in the nat ural environment. The objective of this study is to derive the thermodynami c parameters of the competitive adsorption between ferricyanide and ferrocy anide from the modified Langmuir isotherm and the triple-layer model (TLM) to determine the location of adsorption. The effects of pH, temperature, an d ion concentration on competitive adsorption onto gamma-Al2O3 were investi gated. The results demonstrate that ferrocyanide is more competitive than f erricyanide. By comparing the derived K-app with K-int, we inferred that th e adsorption of ferricyanide and ferrocyanide onto gamma-Al2O3 was achieved through outer-sphere complexation. The negative Delta H-3 indicated that t he adsorption was exothermic, The positive entropy (Delta S degrees) was ca used by the replacement and release of a greater number of smaller surface ions by adsorbed ferricyanide and ferrocyanide ions of larger size. (C) 200 0 Academic Press.