Structure of copper-potassium hexacyanoferrate (II) and sorption mechanisms of cesium

Abstract

A mixed potassium-copper hexacyanoferrate (II) K2CuFe(CN)6 was prepared by local growth on solid cupric sulfate in an aqueous solution of potassium hexacyanoferrate (II) and by growth in a gel. Powders having this composition and separable by filtration could not be obtained by normal precipitation from aqueous solution. This compound has a triclinic P-1 structure, described for the first time, and made up of non-linear –Fe–C–N–Cu-chains which form a puckered layered network. Sorption mechanisms for cesium have been studied in batch experiments including kinetics and isotherms, X-ray diffraction, infra-red spectroscopy and scanning electron microscopy. In neutral solutions the initial crystal structure is maintained and sorption proceeds through a K/Cs ion exchange. In acid solutions, even without addition of cesium, the initial structure is destroyed. The main phase formed in acidic media is Cu2Fe(CN)6. In the presence of cesium the structure is also destroyed and new solid phases are formed. All these processes have slow kinetics, the evolution of the solid being observed over a period of 6 months. This study confirms previous results, which have shown that the sorption mechanisms on hexacyanoferrates strongly depend on the composition and structure of the solid, together with the composition of the solution. Sorption mechanisms have considerable consequences on the use of these products for the decontamination of radioactive wastes.