27Al Pulsed Field Gradient, Diffusion-NMR Spectroscopy of Solvation Dynamics and Ion Pairing in Alkaline Aluminate Solutions

Pulsed field gradient nuclear magnetic resonance (PFG-NMR) measurements were successfully applied to the Al-27 (I = 5/2) nucleus in concentrated electrolytes to investigate the diffusion of aluminate ions [Al(OH)(4)(-)] in simulant high-level nuclear waste (3 M NaOH) between 25 and 85 degrees C. The temperature-dependent diffusion coefficients obtained from H-1, Na-23, and Al-27 PFG-NMR were well fit by a Vogel-Fulcher-Tammann model and a power law equation. Comparison of Al-27 diffusion coefficients of 0.1 M Al(OH)(4)(-) in similar to 3 M MOH (where M = Na+, K+, (CH3)(4)N+) at room temperature varied in agreement with the expected changes in solution viscosity via Stokes-Einstein relationship, confirming that the dominant Al species at these conditions are Al(OH)(4)(-) monomers. This Al-27 PFG-NMR study extends an established methodology to a previously unexplored nucleus enabling this experimental technique to be leverage for exploring ion transport, speciation, and solution structure in concentrated electrolytes.