Vibrational spectroscopic study of the mineral penkvilksite Na ₂TiSi ₄O ₁₁·2H ₂O – a mineral used for the uptake of radionuclides

Abstract

We have used vibrational spectroscopy to study the formula and molecular structure of the mineral penkvilksite Na ₂TiSi ₄O ₁₁·2H ₂O. Penkvilksite is a mineral which may be used in the uptake of radioactive elements. Both Raman and infrared spectroscopies identify a band at ∼3638 cm⁻¹ attributed to an OH-stretching vibration of hydroxyl units. The inference is that OH units are involved in the structure of penkvilksite. The formula may be well written as Na ₂TiSi ₄O ₁₀(OH)₂·H ₂O. The mineral is characterised by a very intense Raman band at 1085 cm⁻¹ and a broad infrared band at 1080 cm⁻¹ assigned to SiO-stretching vibrations. Raman bands at 620, 667 and 711 cm⁻¹ are attributed to SiO and TiO chain bonds. Water-stretching vibrations are observed as Raman bands at 3197, 3265, 3425 and 3565 cm⁻¹. Vibrational spectroscopy enables aspects of the molecular structure of the mineral penkvilksite to be ascertained. Penkvilksite is a mineral which can incorporate actinides and lanthanides from radioactive waste.

Keywords:

• penkvilksite
• silicate
• radionuclide
• radioactive waste
• Raman spectroscopy
• infrared spectroscopy

Acknowledgements

The financial and infra-structure support of the Queensland University of Technology, School of Chemistry, Physics and Mechanical Engineering is gratefully acknowledged. The Australian Research Council (ARC) is thanked for funding the instrumentation.