Uranyl Selenite, UO₂SeO₃

Uranyl Selenite, UO₂SeO₃.2H₂O, is obtained as a lemon-yellow precipitate when sodium selenite is added to a solution of a uranyl salt. The anhydrous salt, UO₂SeO₃, is formed by heating the dihydrate with water and a little selenious acid in a sealed tube at 200° C. It yields microcrystalline needles, which are active towards polarised light. It decomposes on heating, leaving a residue of the green oxide.

A series of crystalline compounds, rich in selenious acid, have been prepared by decomposing uranyl salts in solution by means of selenious acid or an alkali selenite. The products are yellow in colour and insoluble in water. Compounds of the following composition have been prepared:

2UO₃.3SeO₂.7H₂O, 3UO₃.5SeO₂.7H₂O, or 9H₂O, UO₃.2SeO₂.H₂O.

By dissolving an alkali uranate in aqueous selenious acid, and allowing the solution to crystallise, the following compounds have been obtained:

K₂O.UO₃.2SeO₂, or K₂UO₂(SeO₃)₂;
(NH₄)₂O.UO₃.2SeO₂, or (NH₄)₂UO₂(SeO₃)₂.