Synthesis of M(NpO4)2·nH2O (M = Mg, Ca, Sr, Ba) Using Н3ВО3 Solutions and Properties of These Salts

Abstract

Two procedures for preparing the compounds M(NpO₄)₂·nH₂O (M = Mg, Ca, Sr, Ba) using boric acid were suggested. In the first procedure, samples of freshly prepared salts M₃(NpO₅)₂·nH₂O (M = Ca, Sr, Ba) are treated with excess 0.5 M H₃BO₃ with vigorous stirring. In the process, the initially light green salts rapidly transform into black products of the general composition M(NpO₄)₂·nH₂O. In the second procedure, a measured volume of a Np(VII) solution with a known LiOH concentration was added to excess 0.5 M H3BO3 solution containing a calculated amount of Mg, Ca, Sr, or Ba nitrate. The reaction yields black precipitates of the same compounds as in the previous case. After washing with water and drying in an oxygen stream, the final products contain a small impurity of Np(VI). The IR spectra suggest that the compounds obtained are structurally related to the previously studied salts MNpO₄ (M = K–Cs), i.e., in their lattices there are neptunium–oxygen layers built of NpO₂³⁺ cations and bridging O atoms. New data on the properties of the compounds M₃(NpO₅)₂·nH₂O with M = Ca, Sr, and Ba were also obtained.