Abstract: Process for recovering molybdenum-99 from a matrix which has been irradiated with neutrons and contains fissionable materials and fission products, wherein the matrix is decomposed in an aqueous alkali hydroxide solution and the molybdenum-99 and part of the fission products are dissolved, the solution containing the molybdenum-99 is separated from a residue of particles containing at least actinides and lanthanides and is treated with thiocyanate ions to form a molybdenum complex. In the process, the alkali solution containing molybdenum in the form of molybdate (MoO.sub.4.sup.--) is conditioned with an iodine reduction agent. Mineral acid is added to the alkali solution. The molybdenum contained in the acidified solution is reduced to form three-valent molybdenum Mo(III) and the Mo(III) is complexed with SCN.sup.- ions to form [Mo (SCN).sub.6 ].sup.3- ions. The acid solution which contains [Mo (SCN).sub.6 ].sup.