Molecular structure of the uranyl silicates—a Raman spectroscopic study

Abstract

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals including uranophane, sklodowskite, cuprosklodowskite, boltwoodite and kasolite. Raman spectra clearly show well resolved bands in the 750 to 800 cm -1 region and in the 950 to 1000 cm -1 region assigned to the ν 1 modes of the (UO 2 ) 2+ units and to the (SiO 4 ) 4-tetrahedra. Sets of Raman bands in the 200 to 300 cm -1 region are assigned to ν 2 δ (UO 2 ) 2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of ν 2 δ (UO 2 ) 2+ vibrations. The (SiO 4 ) 4-tetrahedral are characterized by bands in the 470 to 550 cm -1 and in the 390 to 420 cm -1 region. These bands are attributed to the ν 4 and ν 2 (SiO 4 ) 4-bending modes. The minerals show characteristic OH stretching bands in the 2900 to 3500 cm -1 and 3600 to 3700 cm -1 region ascribed to water stretching and SiOH stretching vibrations. The high wavenumber position of the δH 2 O bands indicate strong hydrogen bonding of water in these uranyl silicates. Bands in the 1400 to 1550 cm -1 region are attributed to δSiOH modes. The Raman spectroscopy of uranyl silicate minerals enabled separation of the bands attributed to distinct vibrational units. This enabled definitive assignment of the bands. The spectra are analysed in terms of the molecular structure of the minerals.

Thermal analysis of smithsonite and hydrozincite

“…Thus ZnO is unstable with respect to hydrozincite at partial pressures above 10 -5. 16 . If the partial pressure of CO 2 increases above 10 -1.41 smithsonite formation is favoured according to the reaction Zn 5 (CO 3 ) 2 (OH) 6 (s) + 3CO 2 (g) ↔ 5ZnCO 3 (s) +3 H 2 O (g).…”

“…Indeed Raman spectroscopy has proven most useful for the study of diagenetically related minerals such as carbonates and hydroxycarbonate [14][15][16][17][18]. Some previous studies have been undertaken by the authors using Raman spectroscopy to study complex secondary minerals formed by crystallisation from concentrated sulphate solutions [12][13][14][15][16][17][18][19][20][21].…”

Natural halotrichites—an EDX and Raman spectroscopic study

“…Indeed Raman spectroscopy has proven most useful for the study of diagenetically related minerals such as sulphates, alums and halotrichites [17][18][19][20][21] . Some previous studies have been undertaken by the authors using Raman spectroscopy to study complex secondary minerals formed by crystallisation from concentrated sulphate solutions [15][16][17][18][19][20][21][22][23][24] . In this work we extend this research by using Raman spectroscopy to study four natural halotrichites and compare the spectra with that of the natural minerals.…”

Raman spectroscopic study of the uranyl carbonate mineral voglite

“…[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Raman spectroscopy has proven most useful for the study of diagentically related minerals as often occurs with carbonate minerals. [30][31][32][34][35][36][37] No detailed Raman spectroscopic studies of the uranyl mineral voglite has been forth coming. Few Raman studies of any note are available.…”