Gas-phase conversion of U, Sr, and Mo compounds into water-soluble forms in a nitrating atmosphere

Abstract

Gas-phase conversion of uranyl molybdates UO₂MoO₄, UMo_1.7O_7.2, and UMo_0.4O_3.4, of strontium molybdate SrMoO₄, and of strontium uranate SrUO4 into water-soluble compounds in the NO_x–H₂O (vapor)–air or HNO₃ (vapor)–air atmosphere (hereinafter, nitrating atmosphere) was studied. The conversion of UO₂MoO₄, UMo_1.7O_7.2, and UMo_0.4O_3.4 in nitrating atmosphere results in formation of water-soluble uranium compounds and of the water-insoluble phase MoO₃·2H₂O. Rapid separation of the solution from the precipitate in reaction of UO₂MoO₄, UMo_1.7O_7.2, and UMo_0.4O_3.4 conversion products with water allows efficient transfer of U into the solution, with Mo remaining in the form of an insoluble precipitate. The conversion of SrMoO4 depends on the composition of the nitrating atmosphere. In the NO_x–H₂O (vapor)–air atmosphere, there is no SrMoO₄ conversion, whereas in the HNO₃ (vapor)–air atmosphere it is possible to reach ~85% conversion of SrMoO₄ into water-soluble Sr compounds. Complete conversion of SrUO₄ into water-soluble U and Sr compounds is reached when performing the gas-phase conversion at 130°С in both nitrating atmospheres. In the case of the HNO₃ (vapor)–air atmosphere, increasing the process temperature to 150°С leads to a decrease in the amount of water-soluble U(VI) phases.