[en] Radioactive iodine, present as alkali metal iodides or iodates in an aqueous solution, is incorporated into an inert solid material for long-term storage by adding to the solution a stoichiometric amount with respect to the formation of a sodalite (3M2O.3Al2O3. 6SiO2.2MX, where M alkali metal; X I^- or IO^3-) of an alkali metal, alumina and silica, stirring the solution to form a homogeneous mixture, drying the mixture to form a powder, compacting and sintering the compacted powder at 1073 to 1373 K (800⁰ to 1100⁰ C.) for a time sufficient to form sodalite