The structure of synthetic andersonite, Na2Ca[UO2(CO3)3].xH2O (x≃5.6)

Thermal and infrared spectrum analyses of natural and synthetic andersonites

“…The reason for this was the fact that the losses of water and carbon dioxide (the start of decomposition of the anhydrous phase) are also overlapping processes. In the final Fourier map, there is no trace of one of the six water molecules in the formula of andersonite proposed earlier [1]. Five water molecules are coordinated to two sodium atoms and one calcium atom: the remaining approximately 0.6 H20 distributed in the structure channel is probably important for the stability of the entire crystal structure.…”

“…On the basis of our preliminary conclusions [2, 3], the formula Na2Ca[UO2(CO3)3]. _ 5.6H20 was proposed for synthetic andersonite [1], In this paper, attention is especially paid to the content of molecular water in natural andersonite and for comparison in synthetic andersonite, using combined TG and DTA and IR spectroscopy. A complex contribution to the crystal chemistry of andersonite will be published elsewhere [4].…”

“…According to the crystal structure of synthetic andersonite [1], only five water molecules in the formula were found in the final Fourier map. The possible statistical distribution of the remainder in a structure channel is presumed.…”

X-ray absorption spectroscopy identifies calcium-uranyl-carbonate complexes at environmental concentrations

“…On the basis of other Ca/Na-UO 2 -CO 3 systems, the approximate distances expected are 3.8-4.1 Å for U-Ca (Coda et al, 1981;Mereiter, 1982;Reeder et al, 2000;Bernhard et al, 2001;Rakovan et al, 2002;Kelly et al, 2003Kelly et al, , 2006) and 3.7-3.9 Å for U-Na (Coda et al, 1981;Ondrus et al, 2003). These paths were Table 2 Predicted uranium(VI) aqueous species distribution for the conditions of the EXAFS measurements at pH 6.9…”

“…1). Theoretical models were constructed with the program FEFF7 (Zabinsky et al, 1995) and the crystallographic atomic positions of liebigite (Mereiter, 1982) with calcium atoms coordinated to the uranyl-triscarbonate moiety and andersonite (Coda et al, 1981) with both sodium and calcium coordinated to the uranyl-triscarbonate moiety. Automatic overlapping of the muffin tin potentials was used in the FEFF7 calculation.…”