A Raman and infrared spectroscopic study of the uranyl silicates - weeksite, soddyite and haiweeite: Part 2

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals including weeksite K-2[(UO2)(2)(Si5O13)]center dot H2O, soddyite [(UO2)(2)SiO4 center dot 2H(2)O] and haiweeite Ca[(UO2)(2)(Si5O](2)(OH)(2)/(H2O)(3) with UO22+/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm(-1) region and in the 950-1000 cm(-1) region assigned to the v, modes of the (UO2)(2+) units and to the (SiO4)(4-) tetrahedra. Soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm(-1), 909.6 and 898.0 cm(-1). and 268.2, 257.8 and 246.9 cm(-1), attributed to the v(1), v(3), and v(2) (delta) (UO2)(2+), respectively. Coincidences of the v(1) (UO2)(2+) and the v, (SiO4)(4-) is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm(-1) are attributed to the v(3) (SiO4)(4-). Sets of Raman bands in the 200-300 cm(-1) region are assitgned to v(2) (delta) (UO2)(2+) and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of v(2) (delta) (UO2)(2+) vibrations. The (SiO4)(4-) tetrahedral are characterized by bands in the 470-550 cm(-1) and in the 390-420 cm(-1) region. These bands are attributed to the v(4) and v(2) (SiO4)(4-) bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 and 3600-3700 cm(-1). (c) 2005 Elsevier B.V All rights reserved.