Stability of europium(ii) in aqueous nitrate solutions

Abstract

In the lanthanide series, Eu³⁺ is most easily reduced to its divalent state. Reduction of Eu³⁺ has been studied extensively in aqueous media that are insensitive to reducing conditions. Recently, it has been reported that reduction of Eu³⁺ is also feasible in aqueous nitrate solutions and that Eu²⁺ remained sufficiently stable in these media to conduct separation experiments. However, additional fundamental research on the reduction efficiency of Eu³⁺ and stability of Eu²⁺ in these media has not been reported yet. In this paper, cyclic voltammetry, magnetic susceptibility measurements, UV-vis absorption spectroscopy and X-ray absorption near edge structure (XANES) spectroscopy were used to gain more insights into the reduction of Eu³⁺ in aqueous nitrate media. Within the parameters used in this work, near-quantitative reduction of Eu³⁺ could be achieved within 120 min in highly concentrated nitrate salt solutions, using both chemical and electrochemical reduction techniques. Moreover, Eu²⁺ was remarkably stable in these solutions, showing just a small percentage of back-oxidation after 5 h in a sealed measurement cell.