Crystal structures of some manganese (II) and cadmium hexacyanoferrates (II,III) and structural transformation related to the sorption of Cesium.

RICARDO MARTÍNEZ GARCÍA; E. REGUERA RUIZ; J. RODRIGUEZ; J. BALMASEDA; J. ROQUE

POWDER DIFFRACTION

J C P D S-INT CENTRE DIFFRACTION DATA

Año: 2004 vol. 19 p. 255 - 264

0885-7156

Mn21 and Cd21 form a family of isostructural hexacyanoferrates(II,III). Their crystal structures,including those of mixed compositions containing K1 and Cs1 as charge balance cations, wereresolved and refined from XRD powder patterns. The crystal structures of Fe3(Fe(CN)6)2?·xH2O and MCs2(Fe(CN)6) where M (Mn, Cd) were refined in the space group Fm3m. The mixed salts, MK2(Fe(CN)6)·2H2O, were found to be orthorhombic (space group Pmn21). The orthorhombic structure results from a local distortion due to monohydrated potassium ions located in interstitial sites. On ionic exchange in an aqueous solution containing Cs1, the orthorhombic distortion disappears and the cubic cell is obtained. Cs1 is a large ion, which practically fills the available interstitial voids stabilizing the cubic structure. In solutions of K1 and Cs1 the single salts, M2(Fe(CN)6)·8H2O (monoclinic P21 /n) also transform, in this case liberating M21 ions and forming the corresponding mixed salts. An analogous but slow structural transformation was also observed in the anhydrous forms of these single salts. These structural transformations could be relevant to the use of these compounds as ion exchangers and particularly for the sorption of 137Cs1 from radioactive waste solutions. The XRD data were complemented with structural information from infrared (IR), Mo¨ssbauer and water vapor adsorption techniques.