Thermo-Raman spectroscopic study of the uranium mineral sabugalite

Abstract

The changes in the structure of sabugalite have been undertaken using thermo-Raman and infrared spectroscopy based upon the results of thermogravimetric analysis. Two Raman bands are observed at 835 and 830 cm-1 assigned to the (UO2)2+ stretching vibrations resulting from the non-equivalence of the uranyl bonds (UO2)2+. These bands give calculated U-O bond lengths of 1.773 and 1.7808 Å. A low intensity band is observed at 895 cm-1 assigned to the ν3 antisymmetric stretching vibration of (UO2)2+ units. Five bands are observed in the 950 to 1050 cm-1 region in the Raman spectrum of sabugalite and are assigned to the ν3 antisymmetric stretching vibration of (PO4)3- units. Changes in the Raman spectra reflect changes in the structure of sabugalite as dehydration occurs. No (PO4)3- symmetric stretching mode is observed. This result is attributed to the non-equivalence of the PO bonds in the PO4 units. The PO4 vibrations were not affected by dehydration. Thermo-Raman spectroscopy proved to be a very powerful technique for the study of the changes in the structure of sabugalite during dehydration.