Incorporation of rare earth elements into [formula omitted

Abstract

The structural effects of the incorporation of the rare earth elements (REE) La, Ce, Pr, Nd, Eu, Sm, Gd, Er, Tm, Yb and Y into a synthetic Ba–Ca carbonate have been investigated. We precipitated solutions with a composition Ba0.9Ca1.1(CO3)2 doped with REE-nitrates. The precipitate, with few exceptions, consisted of a crystalline solid, slightly depleted in Ba with respect to the expected composition, and an amorphous phase. On heating, the whole sample became crystalline and consisted of a Ba-enriched and a Ba-depleted phase. The phases are isostructural. The lattice parameters are strongly influenced by the incorporation of ≈ 6% REE. There is a linear dependence of the unit cell volume on the radius of the incorporated REE for those elements with a radius < 1.0 Å, i.e. Yb, Tm, Er, Y, Gd, Sm, Eu, Nd and Pr, while the unit cell volume of a sample doped with La (r(La) = 1.03 Å) and Ce (r(Ce) = 1.01 Å) is not well described by this dependency. Raman spectroscopy shows that the local environment of the CO3-groups does not differ substantially between the Ba-enriched and the Ba-depleted phase, but changes linearly as a function of the ionic radius of the REE. The present study clearly shows that substantial amounts of REE can be incorporated into the Ba–Ca-carbonate studied here, making it potentially useful as a matrix in nuclear waste treatments involving aqueous nitrate solutions of lanthanides and actinides.