FIXATION MECHANISMS OF CESIUM ON NICKEL AND ZINC FERROCYANIDES

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Abstract
The retention of cesium on rhomboedric M1 2Zn3/Fe(CN)6/2, xH2O, trigonal Zn2Fe(CN)6, 2H2O and cubic M1 2Ni-2, Fe(CN)4 ferrocyanides (M1 = H1, Na1, K) was studied. The influence of the ferrocyanide composition and structure, the retention kinetics and capacity and the changes in the solid phase at each step of the ion fixation were studied by several different methods i radioactive tracers, atomic absorption, infra-red spectroscopy, X-ray diffraction and potentiometric measurements. All the ferrocyanides examined can remove radioactive cesium from aqueous solutions with high efficiency. The main mechanism is the substitution of cations in the ferrocyanide by cesium leading to nixed cesium ferrocyanides. The kinetics are very fast on nixed ferrocyanides containing both alkali and divalent metal ions, but much slower (requiring several hours to reach equilibrium) on simple zinc ferrocyanide. In the first case, the fixation is the result of monovalent ion exchange with no structural change. In the second case, some zinc ions are released and the fixation is a complex phenomenon involving a structural change. A new preparation process (slow growth on solid alkaline ferrocyanide placed in a concentrated nickel or zinc solution) makes it possible to recommend these materials for the treatment of radioactive waste solutions using column chromatography.

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