Europium structural role in silicate glasses: reduction kinetics at low oxygen fugacity.

This study is focused on the determination of the geochemical behaviour of europium (Eu) in a set of synthetic silicate glasses with composition relevant for the Earth Science and ranging from basaltic to granitic composition. The samples have been characterized through Eu L-III-edge by X-ray Absorption Spectroscopy (XAS) and the measurements have been performed in fluorescence mode at the ESRF (Grenoble, F). Eu L-III-edge XANES analysis allowed to obtain a semi-quantitative assessment of the Eu2+/(Eu2+ + Eu3+) redox ratio. Kinetics of europium reduction at low oxygen fugacity (IW buffer) has been studied on samples equilibrated at different times. Data obtained from kinetic experiments clearly show that glasses of basaltic composition reach equilibrium values of the Eu2+/(Eu2+ + Eu3+) ratio after 6 h at 1400 degrees C, whereas glasses of granitic composition reach equilibrium after 60 h at 1400 degrees C. Knowledge of Eu reduction kinetics is an absolute prerequisite for any study of Eu oxidation state at low oxygen fugacity.