Conditioning of minor actinides in lanthanum monazite ceramics: A surrogate study with Europium

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• The La-Eu monazite solid solution series was synthesized hydrothermally at 200 °C.
• Ceramic pellets were prepared by pressing and sintering at 1400 °C.
• Dissolution kinetics were studied at 90 °C in c(HCl) = 0.01 mol/L.
• Steady state dissolution rates indicate a stabilizing effect of Eu XEuPO4 < 0.2.
• At higher Eu mole fractions, the dissolution rate increases.

A solid solution series of La-Eu monazite was synthesized hydrothermally at 200 °C. Ceramic pellets were prepared by pressing and sintering at 1400 °C. Results from XRD and electron microscopy indicate the synthesis of pure monazite. The linear change of the lattice parameters with increasing Eu-content suggests that the La-Eu monazite solid solution follows Vegard's law. Dynamic dissolution experiments were carried out at 90 °C and C(HCl) = 0.01 M. A well-defined powder was obtained via crushing of pellets and sieving to the fraction 100–180 μm. The La and Eu based steady state dissolution rates are congruent and range between 5 × 10−5 g m−2 d−1 and 1.7 × 10−3 g m−2 d−1, depending on the Eu-content. The lowest rates are in a similar order of magnitude as described in literature for natural Monazite. A minimum of the dissolution rate is observed at XEuPO4 = 0.2. At higher EuPO4 mole fractions, the dissolution rate increases until the dissolution rate of pure EuPO4 is reached.