Abstract: Process for the fine purification of fission molybdenum, dissolved in ionic form together with ions of the fission products of I, Sn, Ce, Ru and Zr in aqueous mineral acid solution, in which the fission molybdenum is fixed by a metal oxide in a sorption step and is then released in a desorption step, comprising: (a) passing the aqueous solution over an amphoteric oxide to sorb the ions of Mo, I, Ce, Ru, Sn and Zr, (b) drying the resulting charged oxide and thereafter heating the dried oxide to a temperature of about 1200.degree. C. to about 1300.degree. C. to sublimate the Mo, and at the same time passing a carrier stream containing water vapor and oxygen over the charged oxide to take up the Mo, and (c) desublimating Mo out of the carrier gas stream by cooling to a temperature below 600.degree. C., and followed by further cooling to room temperature, dissolving the resulting Mo residue in an aqueous solution of a strong alkali to form a molybdate solution.