Abstract

The near infrared (NIR) spectra of the natural uranyl selenite minerals that include derriksite, demesmaekerite, guilleminite and haynesite are examined as a potential indicator of uranium occurring geologic materials at the earth's surface. NIR analysis, complimented with mid-IR studies, was used to investigate the co-ordination of UO₂²⁺ and Cu²⁺ in the uranyl selenites. Bands obtained from the infrared spectra of selenites are interpreted in terms of the stretching vibrations of uranyl, selenite units and OH groups and bending modes. NIR spectra of the uranyl selenite minerals exhibit distinctive characteristics of uranyl ion (UO₂)²⁺ absorptions over the range of 11,500–8000 cm⁻¹. The high- range NIR spectrum of Cu-bearing uranyl derriksite is resolved into two bands, UO₂²⁺ 8070 cm⁻¹ and Cu²⁺ 7175 cm⁻¹. The effect of lead in demesmaekerite leads to distortion of the spectrum and the NIR bands are observed for uranyl ion at 11,305 cm⁻¹ and 8475 cm⁻¹ and for Cu²⁺ at 7430 cm⁻¹. The δ U–OH bending vibrations are characterised by a strong absorption feature centred at 1015 cm⁻¹ in haynesite. A significant shift for UOH bending vibrations and the absence of ν₁ and ν₃ vibrations of UO₂²⁺ at the expense of Cu²⁺ are reflected in the spectrum of derriksite. The complexity of bands with shifts to low wavenumbers could take place due to the additional cations of Pb and Cu in the structure of demesmaekerite. NIR spectroscopy has proven to be a most useful tool for the identification of and distinction between different uranyl selenite minerals.

© 2008 IM Publications LLP

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