Interaction of Europium and Nickel with calcite studied by Rutherford Backscattering Spectrometry and Time-Resolved Laser Fluorescence Spectroscopy

This study aims at elucidating the mechanisms regulating the interaction of Eu and Ni with calcite (CaCO3). Calcite powders or single crystals (some mm sized) have been put into contact with Eu or Ni enriched solutions. The concentrations ranged from 10−3 to 10−5 mol.L−1 for Eu and 10−3 mol.L−1 for Ni and the sorption durations ranged from one week to one month. In order to elucidate the retention mechanisms of these elements into calcite, Rutherford Backscattering Spectrometry (RBS) has been carried out. This technique is well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance). Moreover, using the fluorescence properties of Europium, the results have been compared to those obtained by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) on calcite powders. For the single crystals, complementary SEM observations of the mineral surfaces at low voltage have also been carried out. Results show that Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160 nm after 1 month of sorption. Ni was found to accumulate at the surface of calcite without incorporation.