Sorption of iron-cyanide complexes on goethite

Iron-cyanide complexes are present in soils on sites of former gas plants a nd coke ovens. We have studied the sorption of the complexes ferricyanide, [Fe(CN)(6)](3-), and ferrocyanide, [Fe(CN)(6)](4-), on goethite in batch ex periments, including the effects of concentration, time, ionic strength, pH , and the extent of reversibility. The sorption of ferricyanide showed feat ures of both outer-sphere and inner-sphere complexation: its extent decreas ed with increasing pH; it depended on ionic strength; it was quickly and co mpletely reversible; and it induced a change in surface electric potential. In contrast, sorption of ferrocyanide depended on pH to a lesser extent an d was not affected by ionic strength at different pHs. The desorption was s lower and incomplete. For ferrocyanide we conclude that sorption involves i nner-sphere complexation and precipitation of a Berlin-Blue-like phase on t he goethite surface.